tag:blogger.com,1999:blog-328327292024-03-13T11:02:24.367+07:00Fesaphile Blog"Bila kau ingin memahami wanginya mawar,atau kekuatan pohon jati,jika kau tak pernah puas sampai kau tahu rahasia bagaimana perpaduan sinar mentari dan udara
menghasilkan wanginya mawar dan kuatnya jati, bila kau ingin tahu ilmu yang mendasari luasnya khasanah pengetahuan yang dimiliki manusia, dan bila kau ingin mengetahui materi dari tingkat atomik sampai tingkat makro,maka belajarlah <b>KIMIA</b>" (nasehat C. A. Coulson, kimiawan dan ahli dalam Ikatan Kimia).salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.comBlogger16125tag:blogger.com,1999:blog-32832729.post-8250982766309076062007-05-13T10:35:00.001+07:002010-10-08T01:42:21.479+07:00What is an LD50 and LC50<!--[if !mso]> <style> v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} </style> <![endif]--><!--[if gte mso 9]><xml> <w:worddocument> <w:view>Normal</w:View> <w:zoom>0</w:Zoom> <w:trackmoves/> <w:trackformatting/> <w:punctuationkerning/> <w:validateagainstschemas/> <w:saveifxmlinvalid>false</w:SaveIfXMLInvalid> <w:ignoremixedcontent>false</w:IgnoreMixedContent> <w:alwaysshowplaceholdertext>false</w:AlwaysShowPlaceholderText> <w:donotpromoteqf/> <w:lidthemeother>EN-US</w:LidThemeOther> <w:lidthemeasian>X-NONE</w:LidThemeAsian> <w:lidthemecomplexscript>X-NONE</w:LidThemeComplexScript> <w:compatibility> 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10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} </style> <![endif]--> <h2>What is an LD50 and LC50 </h2> <p class="MsoNormal" style="margin-bottom: 12pt;"><b>What does LD50 mean?</b><br /><br />LD stands for "Lethal Dose". LD50 is the amount of a material, given all at once, which causes the death of 50% (one half) of a group of test animals. The LD50 is one way to measure the short-term poisoning potential (acute toxicity) of a material.<br /><br />Toxicologists can use many kinds of animals but most often testing is done with rats and mice. It is usually expressed as the amount of chemical administered (e.g., milligrams) per 100 grams (for smaller animals) or per kilogram (for bigger test subjects) of the body weight of the test animal. The LD50 can be found for any route of entry or administration but dermal (applied to the skin) and oral (given by mouth) administration methods are the most common.<br /><br /><b>What does LC50 mean?</b><br /><br />LC stands for "Lethal Concentration". LC values usually refer to the concentration of a chemical in air but in environmental studies it can also mean the concentration of a chemical in water.<br /><br />For inhalation experiments, the concentration of the chemical in air that kills 50% of the test animals in a given time (usually four hours) is the LC50 value.<br /><br /><b>Why study LD50's?</b><br /><br />Chemicals can have a wide range of effects on our health. Depending on how the chemical will be used, many kinds of toxicity tests may be required.<br /><br />Since different chemicals cause different toxic effects, comparing the toxicity of one with another is hard. We could measure the amount of a chemical that causes kidney damage, for example, but not all chemicals will damage the kidney. We could say that nerve damage is observed when 10 grams of chemical A is administered, and kidney damage is observed when 10 grams of chemical B is administered. However, this information does not tell us if A or B is more toxic because we do not know which damage is more critical or harmful.<br /><br />Therefore, to compare the toxic potency or intensity of different chemicals, researchers must measure the same effect. One way is to carry out lethality testing (the LD50 tests) by measuring how much of a chemical is required to cause death. This type of test is also referred to as a "quantal" test because it is measures an effect that "occurs" or "does not occur".<br /><br /><b>Who invented the idea of an LD50?</b><br /><br />In 1927, J.W. Trevan attempted to find a way to estimate the relative poisoning potency of drugs and medicines used at that time. He developed the LD50 test because the use of death as a "target" allows for comparisons between chemicals that poison the body in very different ways. Since Trevan's early work, other scientists have developed different approaches for more direct, faster methods of obtaining the LD50.<br /><br /><b>What are some other toxicity dose terms in common usage?</b><br /><br />LD01 Lethal dose for 1% of the animal test population<br /><br />LD100 Lethal dose for 100% of the animal test population<br /><br />LDLO The lowest dose causing lethality<br /><br />TDLO The lowest dose causing a toxic effect<br /><br /><b>Why are LD50 and LC50 values a measure of acute toxicity?</b><br /><br />Acute toxicity is the ability of a chemical to cause ill effects relatively soon after one oral administration or a 4-hour exposure to a chemical in air. "Relatively soon" is usually defined as a period of minutes, hours (up to 24) or days (up to about 2 weeks) but rarely longer.<br /><br /><b>How are LD/LC50 tests done?</b><br /><br />In nearly all cases, LD50 tests are performed using a pure form of the chemical. Mixtures are rarely studied.<br /><br />The chemical may be given to the animals by mouth (oral); by applying on the skin (dermal); by injection at sites such as the blood veins (i.v.- intravenous), muscles (i.m. - intramuscular) or into the abdominal cavity (i.p. - intraperitoneal).<br /><br />The LD50 value obtained at the end of the experiment is identified as the LD50 (oral), LD50 (skin), LD50 (i.v.), etc., as appropriate. Researchers can do the test with any animal species but they use rats or mice most often. Other species include dogs, hamsters, cats, guinea-pigs, rabbits, and monkeys. In each case, the LD50 value is expressed as the weight of chemical administered per kilogram body weight of the animal and it states the test animal used and route of exposure or administration; e.g., LD50 (oral, rat) - 5 mg/kg, LD50 (skin, rabbit) - 5 g/kg. So, the example "LD50 (oral, rat) 5 mg/kg" means that 5 milligrams of that chemical for every 1 kilogram body weight of the rat, when administered in one dose by mouth, causes the death of 50% of the test group.<br /><br />If the lethal effects from breathing a compound are to be tested, the chemical (usually a gas or vapour) is first mixed in a known concentration in a special air chamber where the test animals will be placed. This concentration is usually quoted as parts per million (ppm) or milligrams per cubic metre (mg/m3). In these experiments, the concentration that kills 50% of the animals is called an LC50 (Lethal Concentration 50) rather than an LD50. When an LC50 value is reported, it should also state the kind of test animal studied and the duration of the exposure, e.g., LC50 (rat) - 1000 ppm/ 4 hr or LC50 (mouse) - 5mg/m3/ 2hr.<br /><b><br />Which LD50 information is the most important for occupational health and safety purposes?</b><br /><br />Inhalation and skin absorption are the most common routes by which workplace chemicals enter the body. Thus, the most relevant from the occupational exposure viewpoint are the inhalation and skin application tests. Despite this fact, the most frequently performed lethality study is the oral LD50. This difference occurs because giving chemicals to animals by mouth is much easier and less expensive than other techniques. However, the results of oral studies are important for drugs, food poisonings, and accidental domestic poisonings. Oral occupational poisonings might occur by contamination of food or cigarettes from unwashed hands, and by accidental swallowing.<br /><br /><b>How do I compare one LD50 value to another and what does it mean to humans?</b><br /><br />In general, the smaller the LD50 value, the more toxic the chemical is. The opposite is also true: the larger the LD50 value, the lower the toxicity.<br /><br />The LD50 gives a measure of the immediate or acute toxicity of a chemical in the strain, ***, and age group of a particular animal species being tested. Changing any of these variables (e.g., type animal or age) could result in finding a different LD50 value. The LD50 test was neither designed nor intended to give information on long-term exposure effects of a chemical.<br /><br />Once you have an LD50 value, it can be compared to other values by using a toxicity scale. Confusion sometimes occurs because several different toxicity scales are in use. The two most common scales used are the "Hodge and Sterner Scale" and the "Gosselin, Smith and Hodge Scale". These tables differ in both the numerical rating given to each class and the terms used to describe each class. For example, a chemical with an oral LD50 value of 2 mg/kg, would be rated as "1" and "highly toxic" according to the Hodge and Sterner Scale (see Table 1) but rated as "6" and "super toxic" according to the Gosselin, Smith and Hodge Scale (see Table 2). It is important to reference the scale you used when classifying a compound.<br /><br />It is also important to know that the actual LD50 value may be different for a given chemical depending on the route of exposure (e.g., oral, dermal, inhalation). For example, some LD50s for dichlorvos, an insecticide commonly used in household pesticide strips, are listed below:<br /><br /><br />* Oral LD50 (rat): 56 mg/kg<br />* Dermal LD50 (rat): 75 mg/kg<br />* Intraperitoneal LD50: (rat) 15 mg/kg<br />* Inhalation LC50 (rat): 1.7 ppm (15 mg/m3); 4-hour exposure<br />* Oral LD50 (rabbit) 10 mg/kg<br />* Oral LD50 (pigeon): 23.7 mg/kg<br />* Oral LD50 (rat): 56 mg/kg<br />* Oral (mouse): 61 mg/kg<br />* Oral (dog): 100 mg/kg<br />* Oral (pig): 157 mg/kg<br /><br />Differences in the LD50 toxicity ratings reflect the different routes of exposure. The toxicity rating can be different for different animals. The data above show that dichlorvos is much less toxic by ingestion in pigs or dogs than in rats. Using Table 1, dichlorvos is moderately toxic when swallowed (oral LD50) and extremely toxic when breathed (inhalation LC50) in the rat. Using Table 2, dichlorvos is considered very toxic when swallowed (oral LD50) by a rat. </p> <p class="MsoNormal" style="text-align: center;" align="center"> </p> <div align="center"> <table class="MsoNormalTable" style="width: 480pt;" border="0" cellpadding="0" width="640"> <tbody><tr style=""> <td style="padding: 0.75pt; width: 15pt;" width="20"> <p class="MsoNormal"><img src="file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtmlclip1/01/clip_image001.gif" alt="Resigzed Image" height="16" width="16" /></p> </td> <td style="padding: 0.75pt;"> <p class="MsoNormal">Click this bar to view the full image.</p> </td> </tr> </tbody></table> </div> <p class="MsoNormal" style="margin-bottom: 12pt; text-align: center;" align="center"><img src="file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtmlclip1/01/clip_image003.jpg" height="441" width="640" /></p> <div align="center"> <table class="MsoNormalTable" style="width: 480pt;" border="0" cellpadding="0" width="640"> <tbody><tr style=""> <td style="padding: 0.75pt; width: 15pt;" width="20"> <p class="MsoNormal"><img src="file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtmlclip1/01/clip_image001.gif" alt="Resigzed Image" height="16" width="16" /></p> </td> <td style="padding: 0.75pt;"> <p class="MsoNormal">Click this bar to view the full image.</p> </td> </tr> </tbody></table> </div> <p class="MsoNormal" style="text-align: center;" align="center"><img src="file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtmlclip1/01/clip_image005.jpg" height="286" width="640" /></p> <p class="MsoNormal"><b><br />Can animal LD50 data be applied to man?</b><br /><br />In general, if the immediate toxicity is similar in all of the different animals tested, the degree of immediate toxicity will probably be similar for humans. When the LD50 values are different for various animal species, one has to make approximations and assumptions when estimating the probable lethal dose for man. Tables 1 and 2 have a column for estimated lethal doses in man. Special calculations are used when translating animal LD50 values to possible lethal dose values for humans. Safety factors of 10,000 or 1000 are usually included in such calculations to allow for the variability between individuals and how they react to a chemical, and for the uncertainties of experiment test results.<br /><br /><b>How should an LD50 value be used?</b><br /><br />The LD50 can be used:<br /><br />* As an aid in developing emergency procedures in case of a major spill or accident.<br />* To help develop guidelines for the use of appropriate safety clothing and equipment. For example, if the dermal LD50 value for a chemical is rated as extremely toxic, it is important to protect the skin with clothing, gloves (etc.) made of the right chemical-resistant material before handling. Alternatively, if a chemical has an inhalation LC50 value which indicates that it is relatively harmless, respiratory protective equipment may not be necessary (as long as the oxygen concentration in the air is in the normal range - around 18%).<br />* For the development of transportation regulations.<br />* As an aid in establishing occupational exposure limits.<br />* As a part of the information in Material Safety Data Sheets. Remember, the LD50 is only a ball park figure so that lethal toxicity can be compared. It says nothing about levels at which other acute toxic, but non-lethal, effects might occur.<br /><br />The LD50 is only one source of toxicity information. For a more thorough picture of the immediate or acute toxicity of a chemical, additional information should be considered such as the lowest dose that causes a toxic effect (TDLO), the rate of recovery from a toxic effect, and the possibility that exposure to some mixtures may result in increasing the toxic effect of an individual chemical.<br /><br /><b>Where can I find LD50 and LC50 values?</b><br /><br />The largest, single collection of LD50 and LC50 values is in the database <a href="http://www.chem4all.vn/forums/redirector.php?url=http%3A%2F%2Fwww.ccohs.ca%2Fproducts%2Fcdrom%2Fc2.html" target="_blank">Registry of Toxic Effects of Chemical Substances (RTECS)</a> that is available by subscription on CD-ROM and on the Internet. Two other databases available from CCOHS, CHEMINFO and the Hazardous Substances Data BankÆ (HSDB). Both of these are on the <a href="http://www.chem4all.vn/forums/redirector.php?url=http%3A%2F%2Fwww.ccohs.ca%2Fproducts%2Fcdrom%2Fa2.html" target="_blank">CHEMpendium CD-ROM</a>; <a href="http://www.chem4all.vn/forums/redirector.php?url=http%3A%2F%2Fwww.ccohs.ca%2Fproducts%2Fdatabases%2Fcheminfo.html" target="_blank">CHEMINFO</a> is also accessible on the Internet. </p> <p class="MsoNormal"> </p>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-9839640524639825662007-05-13T10:34:00.002+07:002010-10-08T01:09:28.798+07:00Windows Vista (indonesia language) Coming Soon<span id="result_box" class="long_text" lang="en"><span style="" title="">After several times through resignation, Microsoft has finally officially launched Windows Vista, Microsoft Office and Exchange Server 2007 to customers in Indonesia.<br /><br /></span><span style="" title="">Located at the Plenary Hall of Jakarta Convention Center, today (04/11/2007) Microsoft made a very lively launch event by inviting dozens of partners and clients.<br /><br /></span><span style="" title="">Ari Kunwidodo, Microsot Indonesian vice president, said this newest product is already available in 70 countries with 18 different languages, and is planned to be available in 99 types of languages at the end of this year. </span><span style="" title="">"Special Vista, we will provide the Indonesian version in June," he said, during a press conference.<br /><br /></span><span style="" title="">Ari explained further, it is done the company to further increase the local market because it has been given the ease in communication.<br /><br /></span><span style="" title="">Compared to previous products, Vista is claimed to have increased capacity in some parts. </span><span style="" title="">In addition to security factors, changes in a more dynamic and live in Vista is considered as something unique.<br /><br /></span><span style="" title="">As for Office 2007, the functions that were previously closed are rarely used by users are now trying to further brought out by Microsoft in the form of ribbons. </span><span style="" title="">The goal, according to Ari, to change the habits of the user to optimize the feature. </span><span title="">"The function does not ogled the eye and do not try," he said.<br /><br /></span><span style="" title="">For the price, as was reported earlier Vista will be priced manufacturer of the software giant is the same as the price of their products before, XP.<br /><br /></span><span style="" title="">Although Microsoft just released Vista and Office 2007 in Indonesia today. </span><span style="" title="">However, pirated software of those products have adorned the various shopping malls in Jakarta since the beginning of the year.</span></span>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-75360147989427928342007-05-13T10:32:00.001+07:002010-10-08T01:46:52.697+07:00Theory of Drug Design<!--[if !mso]> <style> v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} </style> <![endif]--><!--[if gte mso 9]><xml> <w:worddocument> <w:view>Normal</w:View> <w:zoom>0</w:Zoom> <w:trackmoves/> <w:trackformatting/> <w:punctuationkerning/> <w:validateagainstschemas/> <w:saveifxmlinvalid>false</w:SaveIfXMLInvalid> <w:ignoremixedcontent>false</w:IgnoreMixedContent> <w:alwaysshowplaceholdertext>false</w:AlwaysShowPlaceholderText> <w:donotpromoteqf/> <w:lidthemeother>EN-US</w:LidThemeOther> <w:lidthemeasian>X-NONE</w:LidThemeAsian> <w:lidthemecomplexscript>X-NONE</w:LidThemeComplexScript> <w:compatibility> <w:breakwrappedtables/> <w:snaptogridincell/> <w:wraptextwithpunct/> 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semihidden="false" unhidewhenused="false" name="Colorful Grid Accent 6"> <w:lsdexception locked="false" priority="19" semihidden="false" unhidewhenused="false" qformat="true" name="Subtle Emphasis"> <w:lsdexception locked="false" priority="21" semihidden="false" unhidewhenused="false" qformat="true" name="Intense Emphasis"> <w:lsdexception locked="false" priority="31" semihidden="false" unhidewhenused="false" qformat="true" name="Subtle Reference"> <w:lsdexception locked="false" priority="32" semihidden="false" unhidewhenused="false" qformat="true" name="Intense Reference"> <w:lsdexception locked="false" priority="33" semihidden="false" unhidewhenused="false" qformat="true" name="Book Title"> <w:lsdexception locked="false" priority="37" name="Bibliography"> <w:lsdexception locked="false" priority="39" qformat="true" name="TOC Heading"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} </style> <![endif]--> <h2>Theory of Drug Design </h2> <p class="MsoNormal" style="text-align: center;" align="center"><b><span style="font-size: 18pt; color: red;">What are drugs?</span></b></p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />The vast majority of drugs are small molecules designed to bind, interact, and modulate the activity of specific biological receptors. Receptors are proteins that bind and interact with other molecules to perform the numerous functions required for the maintenance of life. They include an immense array of cell-surface receptors (hormone receptors, cell-signaling receptors, neurotransmitter receptors, etc.), enzymes, and other functional proteins. Due to genetic abnormalities, physiologic stressors, or some combination thereof, the function of specific receptors and enzymes may become altered to the point that our well-being is diminished. These alterations may manifest as minor physical symptoms, as in the case of a runny nose due to allergies, or as life threatening and debilitating events, such as sepsis or depression. The role of drugs is to correct the functioning of these receptors to remedy the resulting medical condition.<br /><br />As an example, the highest grossing drug in 2000 was Prilosec, which earned $4.102 billion in sales. Prilosec is used to treat stomach ulcers and acid reflux disease. Prilosec targets a specific enzyme, the proton pump, which is located in the acid producing cells lining the stomach wall. This enzyme is responsible for the production of stomach acid. Due to genetic reasons, such as deficient enzymes that regulate acid secretion, or physiologic causes, such as stress, too much acid may be produced. This leads to ulceration of the stomach lining or acid reflux disease and heartburn. Prilosec binds to the proton pump and shuts it down, thereby diminishing the production of stomach acid and its associated symptoms.</p> <p class="MsoNormal" style="text-align: center;" align="center"><b><span style="font-size: 18pt; color: red;">The biochemistry of drugs</span></b></p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />Enzymes are a subset of receptor-like proteins that are directly responsible for catalyzing the biochemical reactions that sustain life. For example, digestive enzymes act to break down the nutrients of our diet. DNA polymerase and related enzymes are crucial for cell division and replication. Enzymes are genetically programmed to be absolutely specific for their appropriate molecular targets. Any errors could have grave consequences. One can imagine the end result should blood clotting enzymes start activating throughout the body. Or consider the problems that arise when our immune system attacks our own tissues. Enzymes ensure the specificity of their targets by forming a molecular environment that excludes interactions with inappropriate molecules. The analogy most often mentioned is that of a lock and key. The enzyme is a molecular lock, which contains a keyhole that exhibits a very specific and consistent size and shape. This molecular keyhole is termed the active site of the enzyme and allows interaction with only the appropriate molecular targets. Just as a typical lock is much bigger than the keyhole, the receptor is usually much larger than the active site. The receptor, as specified by our DNA, is a folded protein whose major purpose is to form and maintain the size and shape of the active site. This is illustrated in Figure 1 using the structure of the HIV-1 protease.</p> <p class="MsoNormal" style="text-align: center;" align="center"><img src="file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtmlclip1/01/clip_image001.jpg" height="270" width="360" /></p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />The most important concept in drug design is to understand the methods by which the active site of a receptor selectively restricts the binding of inappropriate structures. Any potential molecule that can bind to a receptor is called a ligand. In order for a ligand to bind, it must contain a specific combination of atoms that presents the correct size, shape, and charge composition in order to bind and interact with the receptor. In essence, the ligand must possess the molecular key that binds the receptor lock. Figure 2 schematically shows a typical ligand-receptor binding interaction.</p> <p class="MsoNormal" style="text-align: center;" align="center"><img src="file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtmlclip1/01/clip_image002.gif" height="178" width="409" /><br /><b>Figure 2. Enzyme substrate complementary interactions.</b></p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />We see here that a putative ligand-receptor interaction must have complementary size and shape. This is termed steric complementarity. As is the case with an actual key, if a different molecule varies by even a single atom in the wrong place, it may not fit properly, and will most likely not interact with the receptor. However, the more closely the fit between the ligand and receptor, the more tightly the interaction becomes. Again, keep in mind that this is only a two-dimensional schematic. Both ligand and active site are volumes with complex three-dimensional shape.<br /><br />In addition to steric complementarity, electrostatic interactions influence ligand binding. Charged receptor atoms often surround the active site, imparting a localized charge is specific regions of the active site. From physics, we know that opposite charges attract while similar charges repel. Electrostatic complementarity further restricts the binding of inappropriate molecules since the ligand must contain correctly placed complementary charged atoms for interaction to occur.<br /><br />The main driving force for ligand and receptor binding is hydrophobic interaction. Nearly two-thirds of the body is water, and this aqueous milieu surrounds all our cells. In order for ligand and receptor to interact, there must be a driving force that compels the ligand to leave the water and bind to the receptor. The hydrophobicity of a ligand is what causes this. Hydrophobicity stands for 'water fearing' and is a measure of how 'greasy' a compound is. It can be roughly approximated by the percentage of hydrogen and carbon in the molecule. This force is easily demonstrated by placing a few drops of oil in a cup of water. The oil is composed of hydrocarbon chains and is highly hydrophobic. The oil droplets will instantly coalesce into a single globule in order to avoid the water, which is highly polar. As shown in Figure 2, the active site may contain a mixture of hydrophobic pockets and regions that are more polar. Since the hydrophobic portions of the ligand and receptor prefer to be juxtaposed, the arrangement of hydrophobic surfaces provides yet another way that receptors can limit the binding of inappropriate targets.</p> <p class="MsoNormal" style="text-align: center;" align="center"><img src="file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtmlclip1/01/clip_image003.gif" height="338" width="487" /></p> <p class="MsoNormal"><br />As discussed above, there are numerous potential interactions between ligand and receptor. Depending upon the size of the active site, there may be a myriad steric, electrostatic, and hydrophobic contacts. However, some are more important than others. The specific interactions that are crucial for ligand recognition and binding by the receptor are termed the pharmacophore. Usually, these are the interactions that directly factor into the structural integrity of a receptor or are involved in the mechanism of its action. Using our lock and key analogy from above, we can imagine a lock having numerous tumblers. There may be many keys that can sterically complement the lock and fit within the keyhole. However, all but the correct key will displace the wrong tumblers, leading to a sub-optimal interaction with the lock. Only the correct key, which presents the pharmacophore to the receptor, contacts the appropriate tumblers and properly interacts with the lock to open it. This is crucial to the design of pharmaceuticals since any successful drug must incorporate the appropriate chemical structures and present the pharmacophore to the receptor.<br /><br />This is shown in Figure 3 above. In the upper left frame of this figure, we see our native ligand bound within the active site. Assume that through biochemical investigation, we determine that the phenyl ring (blue) and the carboxylic acid group (green) are vital to receptor interaction. Thus, we deduce that these two groups must be the pharmacophore that a ligand must present to the receptor for binding. In future drugs that we develop to mimic the native ligand, we must include these two pharmacophoric elements for successful binding to occur. This is shown in the upper right derivative compound where a bicyclic group has been substituted. Because it maintains the pharmacophore and retains its complementary size and shape, it has a reasonable chance of successfully binding. However, any drug that we develop which lacks a complete pharmacophore may not interact with the receptor target. </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p class="MsoNormal" style="text-align: center;" align="center"><b><span style="font-size: 18pt; color: red;">The challenge of drug design</span></b></p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />Given our introduction to the biochemistry of ligand receptor binding, we can begin to appreciate the difficulties in designing drugs towards specific target receptors. Table 1 lists the major tasks and concerns in this endeavor.<br /><br />Table 1. Major tasks and concerns in drug development.<br /><br />1. Characterize medical condition and determine receptor targets.<br /><br />2. Achieve active site complementarity: steric, electrostatic, and hydrophobic.<br /><br />3. Consider biochemical mechanism of receptor.<br /><br />4. Adhere to laws of chemistry.<br /><br />5. Synthetic feasibility.<br /><br />6. Biological considerations.<br /><br />7. Patent considerations.<br /><br />When a medical condition exists where a drug could be beneficial, extensive scientific study must first be done in order to determine the biological and biochemical problems that underlie the disease process. This often takes years of study in order to characterize the targets for a potential drug. The reason is that nearly all biological processes in the human body are tightly interconnected. Altering the behavior of select receptors or enzymes may have detrimental effects with other systems. These are the side effects that occur with nearly all drugs. Furthermore, the human body is a homeostatic machine, and always attempts to achieve equilibrium. As a result, the body will attempt to counteract any pharmacotherapeutic intervention.<br /><br />Once a receptor target has been established and well characterized, the process of ligand design begins. Obviously, the first consideration is that the designed ligand must complement the active site of the receptor target. Steric, electrostatic, and hydrophobic complementarity must be established as we discussed above. The pharmacophore must be presented to the receptor in order for recognition and binding to occur. Otherwise, the designed ligand will have no chance of interacting with the receptor.</p> <p class="MsoNormal" style="text-align: center;" align="center"><img src="file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtmlclip1/01/clip_image004.gif" height="193" width="330" /><br /><b>Figure 4. Designing ligands to offset enzyme mechanism.</b></p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />In addition to adequately binding the receptor, the biochemical mechanism of the receptor target must be taken into consideration. This is shown in Figure 4. In this figure we schematically represent the biochemical mechanism of a protease. A protease is an enzyme that cleaves proteins and peptides. In the top part of the figure, we see that a protease recognizes a specific group of atoms, colored in red and blue, called a peptide bond. If the peptide bond is present at a specific position in the active site when the ligand binds, it is cleaved by the protease with the addition of water (H2O) to form two separate fragments. If our goal is to inactivate this protease, any designed ligand cannot possess this peptide bond at the same position. Otherwise, it will simply be cleaved by the protease, and the protease will continue to function unperturbed. However, the ligand can be modified so that the peptide bond is no longer present as shown in the bottom portion of the figure. If this ligand is then bound by the enzyme, the enzyme will not be able to cleave it. As such, the enzyme would be inactivated, as the ligand remains lodged in the active site.<br /><br />Having characterized the active site region and the mechanism of action of the target receptor, the challenge then becomes one of designing a suitable ligand. This is, by far, the most daunting task of the entire drug design process. The optimal combination of atoms and functional groups to complement the receptor is often the natural ligand of the receptor. Unfortunately, this is usually an unacceptable candidate for a drug. This is because the natural ligand either fails to inactivate the receptor, as described above, or it is a natural substance that cannot be patented. Patent considerations are often paramount, as legal protection for the developed drug affords the opportunity to recoup the financial costs of development. Therefore, alternate combinations of chemical structures must be devised.<br /><br />The design of novel ligands is often restricted by what chemists are physically able to synthesize. It is of no use to design the ultimate drug if it cannot be manufactured. The laws of chemistry dictate that each atom type has a specific size, charge, and geometry with respect to the number and types of neighboring atoms that it can be joined to. The entire field of chemistry is predicated on the establishment of synthetic rules for the construction and manipulation of various combinations of atoms and functional groups. It is the expertise in these chemical rules that govern the ability of the synthetic chemist to design and synthesize postulated ligand candidates. Within these rules, the drug developer must creatively propose suitable chemical structures that satisfy the requirements discussed above.<br /><br />Finally, there are biological considerations to the development of new drugs. The liver is the major organ of detoxification in the human body. Any drug that is taken undergoes a number of chemical reactions in the liver as the body attempts to neutralize foreign substances. This set of reactions is well characterized, and a great deal of knowledge exists as to how drugs are modified as the body eliminates them. More importantly, various chemical structures are highly toxic to biological systems, and these are also well characterized. These constraints must also be taken under consideration as novel drugs are developed.</p> <p class="MsoNormal" style="text-align: center;" align="center"><b><span style="font-size: 18pt; color: red;">The drug discovery pipeline</span></b></p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />As discussed above, the development of any potential drug begins with years of scientific study to determine the biochemistry behind a medical problem for which pharmaceutical intervention is possible. The result is the determination of specific receptor targets that must be modulated to alter their activity in some way. Once these targets have been identified, the goal is then to find compounds that will interact with the receptors in some fashion. At this initial stage of drug development, it does not matter what effect the compounds have on the targets. We simply wish to find anything that binds to the receptor in any fashion.<br /><br />The modern day drug discovery pipeline is outlined in Figure 5. The first step is to determine an assay for the receptor. An assay is a chemical or biological test that turns positive when a suitable binding agent interacts with the receptor. Usually, this test is some form of colorimetric assay, in which an indicator turns a specific color when complementary ligands are present. This assay is then used in mass screening, which is a technique whereby hundreds of thousands of compounds can be tested in a matter of days to weeks. A pharmaceutical company will first screen their entire corporate database of known compounds. The reason is that if a successful match is found, the database compound is usually very well characterized. Furthermore, synthetic methods will be known for this compound, and patent protection is often present. This enables the company to rapidly prototype a candidate ligand whose chemistry is well known and within the intellectual property of the company.</p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />If a successful match is found, the initial hit is called a lead compound. The lead compound is usually a weakly binding ligand with minimal receptor activity. The binding of this structure to the receptor is then studied to determine the interactions that foster the ligand-receptor association. If the receptor is water soluble, there is a chance that x-ray crystallographic analysis can be employed to determine the three-dimensional structure of the ligand bound to the receptor at the atomic level. This is a very powerful tool for it allows scientists to directly visualize a snapshot of the individual atoms of the ligand as they reside within the receptor. This snapshot is referred to as a crystal structure of the ligand-receptor complex. Unfortunately, not all complexes can be analyzed in this manner. However, if a crystal structure can be determined, a strategy can then be developed based upon this characterization to improve and optimize the binding of the lead compound. From this point onward, a cycle of iterative chemical refinement and testing continues until a drug is developed that undergoes clinical trials. The techniques most often used to refine drugs are combinatorial chemistry and structure based design.</p>Combinatorial chemistry is a very powerful technique that chemists can employ to aid in the refinement of the lead compound. Combinatorial chemistry is a synthetic tool that enables chemists to rapidly generate thousands of lead compound derivatives for testing. As shown above in Figure 6, a scaffold is employed that contains a portion of the ligand that remains constant. Subsite groups (shown in red, green, and blue) are potential sites for derivatization. These subsites are then reacted with combinatorial libraries to generate a multitude of derivative structures, each with different substituent groups. One can see how a vast number of compounds can be generated as a result of the combinatorial process. If a scaffold contains three derivatization sites and the library contains ten groups per site, theoretically 1000 different combinations are possible. By carefully selecting libraries based upon the study of the active site, we can target the derivatization process towards optimizing ligand receptor interaction. <p class="MsoNormal"><br />Structure based design, often called rational drug design, is much more focused than combinatorial chemistry. As shown above in Figure 7, it involves using the biochemical laws of ligand-receptor association discussed above to postulate ligand refinements to improve binding. For example, we discussed that steric complementarity is vital to tight receptor binding. Using the crystal structure of the complex, we can target regions of the ligand that fit poorly within the active site and postulate chemical changes to improve complementarity with the receptor. In a similar fashion, functional groups on the ligand can be changed in order to augment electrostatic complementarity with the receptor. However, the danger in altering any portion of the ligand is the effect on the remaining ligand structures. Modifying even a single atom in the middle of the ligand can drastically change the shape of the overall structure. Even though complementarity in one portion of the ligand might be improved by the chemical revision, the overall binding might be severely compromised. This is the difficulty in any ligand refinement procedure.</p> <p class="MsoNormal"> </p> <p class="MsoNormal"><br /></p> <p class="MsoNormal" style="text-align: center;" align="center"><b><span style="font-size: 18pt; color: red;">Use of computers in drug design</span></b></p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />In the early 1990’s there was a great deal of optimism that computer aided drug design would revolutionize the way in which drugs could be developed. The enduring exponential increase in computing power had progressed to the point that rudimentary estimations of ligand receptor complementarity could be performed. Furthermore, computer graphics technology had achieved the ability to generate vector models of chemical structures and manipulate them in real-time. This offered, for the first time, the ability to interactively study computer models of ligand structures and their binding interactions with a receptor.<br /><br />Concomitant with the development of this technology was the emergence of the AIDS epidemic. During the late 1980s, scientists had isolated the causative agent of AIDS, the HIV-1 virus. Considerable characterization of the viral life cycle provided numerous potential targets for pharmaceutical intervention. Among them was the HIV-1 protease. This aspartyl protease was an enzyme that was unique to HIV, and absolutely required for the processing and maturation of HIV proteins. Thus, if a drug could be developed to inactivate this protease, the virus would be unable to generate mature infectious particles to sustain the infection. Numerous groups around the world rapidly solved the crystal structure of this enzyme (see Figure 1). The mechanism of this enzyme was determined, and the layout of the active site was carefully mapped.<br /><br />It was known that humans possess similar classes of proteases. Renin is an enzyme secreted by the kidneys that is responsible for initiating a cascade of reactions that regulate blood pressure. It too is an aspartic protease, and ligands that inhibited its function were known. With the wealth of data from the study of the HIV-1 protease, the hope was that this target could be exploited by computer-aided rational drug design to rapidly generate novel AIDS drugs. Computational chemists believed they could circumvent much of the time and effort required for drug synthesis and testing by simply generating novel compounds using the computer. Testing would be replaced by merely calculating the ligand-receptor binding affinity using the physical laws of chemistry. The concept of generating virtual lead compounds entirely through computer simulation was termed denovo design.</p> <p class="MsoNormal" style="text-align: center;" align="center"><b><span style="font-size: 18pt; color: red;">Difficulties implementing denovo design</span></b></p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />Many of the worlds largest pharmaceutical firms spent millions of dollars on hardware and software in their endeavor to make denovo design a reality. Unfortunately, successes were rare. Except for a few exceptions, denovo design was an utter failure, and did not prove to be an effective method to discover lead compounds. The main reasons were limitations in computing power and the lack of useful software functionality. In scientific computing, accuracy and processing time are always a tradeoff. Thus, in order to make the calculations run in a finite period of time, a plethora of assumptions, significant approximations, and numerous algorithmic shortcuts had to be utilized. This, in turn, greatly diminished the calculated accuracy of any ligand receptor interaction. As such, chemists could postulate numerous chemical structures that could potentially complement the active site; however, the calculated binding had no correlation with reality.<br /><br />This remains the most significant challenge in denovo design to this day. Although computers have become exponentially faster, the sheer number of calculations needed to accurately predict the binding of a denovo generated ligand to its receptor in a useful timeframe still requires significant approximations. In denovo design, we are attempting to generate a whole ligand from scratch and dock it within the receptor. As stated above, the difficulty lies in predicting how the chemical structure will behave in real life. A ligand is an inherently flexible structure, and can assume a plethora of different conformations and orientations. The big question remains whether the predicted binding structure will mirror the calculated one. Failure in this endeavor has undermined the utility of denovo structure generating software. We will discuss these shortcomings and the technological advances of RACHEL, which attempt to circumvent these deficiencies, in detail below.<br /><br />The second most significant problem in computer aided denovo design is the generation of undesired chemical structures. There are a nearly infinite number of potential combinations of atoms. However, the vast majority of these structures are of no use. As discussed above, undesired structures are rejected due to toxicity, chemical instability, or synthetic difficulty. Nearly all denovo design software packages are plagued by this problem, especially with respect to synthetic feasibility. Thus, although such software can postulate potential complementary ligands, the vast majority of them are worthless. We will discuss in great detail below how RACHEL attempts to circumvent this problem with newly developed technology.<br /><br />The end result of these shortcomings was that computer aided denovo design soon fell out of favor as a means of generating viable lead compounds. By the mid 1990’s there had been a tremendous number of denovo software packages released; however, they all suffered these same problems. Gradually, such programs were shelved and investigators looked to other technologies to aid in their drug development efforts.</p> <p class="MsoNormal" style="text-align: center;" align="center"><b><span style="font-size: 18pt; color: red;">Rebirth of computer-aided drug refinement</span></b></p> <p class="MsoNormal"><br />It was at this time that the techniques of mass screening and combinatorial chemistry began to gain widespread acceptance and use. The use of mass screening and combinatorial chemistry allowed researchers to discover lead compounds in a rapid and efficient manner. As such, denovo design tools and their associated problems were no longer needed to generate lead structures. One would surmise that computer-aided drug design technology would have soon ceased to exist. On the contrary, it soon became apparent that computational tools were needed that could optimize these lead compounds into potent drugs.<br /><br />The concept of drug optimization versus denovo design is an important one. The difficulty with denovo ligand generation is that an entire structure is being created from scratch. The confidence one has of accurately predicting how this structure will interact and bind within a target receptor is shaky at best. In drug optimization, we begin with a lead compound whose bound structure within the receptor has been characterized, most likely through x-ray crystallography. Subtle modifications are then performed to generate derivative compounds using structure based drug design to improve binding affinity. Because we are making much smaller changes, our faith in the validity of the resulting structures is far greater. These derivatives then undergo testing to determine which modifications improve binding. The structures of the best ligands can then be elucidated to verify the accuracy of the modifications. This refinement process continues iteratively until optimal binding ligands are produced.<br /><br />Since subtle modifications are being made to a common structure, the predictive ability of ligand refinement software is much higher. This is because the effect of a single chemical modification on ligand-receptor binding is far easier to quantitate than an extreme change. No longer are we trying to determine the binding affinities of drastically different structures. Instead, we are simply determining the rank order of a list of derivative compounds. This greatly increases the confidence that proposed structures will bind in a manner consistent with our understanding.<br /><br />In addition, the act of generating chemical derivatives is highly amenable to computerized automation. Consider the application of targeted structure based combinatorial chemistry as discussed above. Libraries of derivative components are assembled based upon the analysis of the active site. Because of the combinatorial nature of this method, an extremely large number of candidate structures may be possible. A computer can rapidly generate and predict the binding of all potential derivatives, creating a list of the best potential candidates. In essence, the computer filters all weak-binding compounds, allowing the chemist to focus, synthesize, and test only the most promising ligands. Thus, utilizing computer aided drug design software to aid in the refinement of weak binding lead compounds is the most effective manner in which these tools can be employed. The use of computer modeling to refine structures has become standard practice in modern drug design.</p><br /><p class="MsoNormal" style="text-align: center;" align="center"><b><span style="font-size: 18pt; color: red;">Hybrids</span></b></p> <p class="MsoNormal" style="margin-bottom: 12pt;"><br />The primary utility of a hybrid program is in denovo ligand generation. Figure 11 depicts how these programs work. In the upper left hand corner of this figure, we see an active site with three distinct regions colored in blue, green, and red. The goal of a hybrid program is to generate a complete ligand that complements the active site region. To do so, these programs employ a combination of scanner and builder algorithms in divide and conquer approach. These programs first utilize scanner technology to find components that will complement individual subsites within the active site volume. This is depicted by the components in the blue, green, and red boxes. These individual components are then docked into their respective regions within the active site as shown in the upper right. Splicing fragments, shown in purple, are then used to join these components into a single complete ligand. It is important to note that numerous possible fragments may exist that complement the various active site regions. Thus, a potentially large number of ligands may be generated by combinatorially linking the various components.</p> <p class="MsoNormal">As stated above, hybrid-type programs are mainly used for denovo generation of lead compounds. The strength of these programs is in their ability to generate a large number of diverse potential hits. However, they suffer the same shortcomings as all denovo design packages described above. The difficulties in accurately calculating ligand receptor binding affinity are significant. In addition, the combinatorial nature of the algorithm often leads to the generation of chemical structures that are undesirable, unstable, or synthetically difficult. Finally, the developer of the software may bias the generation of compounds. For example, many of these programs place components within the active site using a pre-determined binding algorithm based upon the functional groups that are presented by the receptor. Additionally, the algorithms used to splice the components together greatly affect the generated ligands.</p>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-88973826416267640642007-05-13T10:29:00.001+07:002010-10-08T01:48:03.210+07:00new catalyst that generates hydrogen from sea water<!--[if !mso]> <style> v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} </style> <![endif]--><!--[if gte mso 9]><xml> <w:worddocument> <w:view>Normal</w:View> <w:zoom>0</w:Zoom> <w:trackmoves/> <w:trackformatting/> <w:punctuationkerning/> <w:validateagainstschemas/> <w:saveifxmlinvalid>false</w:SaveIfXMLInvalid> <w:ignoremixedcontent>false</w:IgnoreMixedContent> <w:alwaysshowplaceholdertext>false</w:AlwaysShowPlaceholderText> <w:donotpromoteqf/> <w:lidthemeother>EN-US</w:LidThemeOther> <w:lidthemeasian>X-NONE</w:LidThemeAsian> 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priority="39" qformat="true" name="TOC Heading"> </w:LatentStyles> </xml><![endif]--><!--[if !mso]><object classid="clsid:38481807-CA0E-42D2-BF39-B33AF135CC4D" id="ieooui"></object> <style> st1\:*{behavior:url(#ieooui) } </style> <![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} </style> <![endif]--> <p class="MsoNormal">A new catalyst that generates hydrogen from sea water has been developed by scientists in the US. This new metal-oxo complex displays high catalytic activity and stability, whilst being low cost, the researchers say.<br /><br />Hydrogen is very attractive as a clean source of power. Currently, it is produced by natural gas reforming - where steam is reacted with methane in the presence of a nickel catalyst to form hydrogen - but this method produces the greenhouse gas carbon dioxide.<br /><br />Jeffrey Long and colleagues from the University of California, Berkeley, prepared a simple molybdenum-oxo complex that can serve as an electrocatalyst, reducing the energy required to generate hydrogen from water on a mercury electrode. As an abundant metal, molybdenum is much cheaper than precious metal catalysts where the costs associated with large scale hydrogen production would be high.<br /><br />Long explains that the stability of the catalyst is due to a ligand that bonds to the molybdenum in five places (pentadentate) making it a very strong complex. 'The molecule is very robust and is stable in aqueous conditions for long periods of time so we don't see degradation of the catalytic activity over three days of running the reaction,' he says.<br /><br />Significantly, Long's catalyst is also stable in the presence of impurities that can be found in the ocean, meaning that sea water can be used without pre-treatment. The team used a sample of California sea water in the system and found the results to be similar to the results obtained for water at neutral pH. In addition, no other electrolyte is necessary when using sea water, which helps reduce costs and removes any need for organic acids or solvents that could degrade the catalyst.<br /><br />'The work clearly demonstrates that the molybdenum-oxo complex explored shows good catalytic activity, with at least an order of magnitude higher turnover frequency [the speed at which a catalytic cycle is completed] than alternative catalysts quoted,' says Bruce Ewan, an expert in hydrogen production and renewable energy at the University of Sheffield, UK. 'This new catalyst also opens up new possibilities as a catalytic agent in other proton reducing scenarios,' he adds.<br /><br />Long and his team hope to develop this system so that 'in the future a catalyst like this could be used in conjunction with a solar cell to produce hydrogen,' he explains. The team is now working on modifying the catalyst to reduce the potential at which the electrochemical reaction proceeds and make the system more efficient.<br /><br /><b>Reference:</b></p> <p class="MsoNormal">Code:</p> <pre>H I Karunadasa, C J Chang and J R Long, Nature, 2010, DOI: 10.1038/nature08969</pre> <p class="MsoNormal"> </p>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-1169285255989923562007-01-20T16:24:00.001+07:002010-10-08T01:24:24.523+07:00Fireworks!<div align="center">Have you ever been to an aerial fireworks show at an amusement park, baseball game, Fourth of July celebration, or on New Year's Eve and wondered about how all the impressive colors and sounds are produced? People everywhere enjoy the fantastic explosions and the brilliant light displays of fireworks. However, these spectacles are much more than just a form of entertainment. Each firework launched into the sky is a precisely formed assembly of chemicals and fuel, carefully calibrated to produce a particular effect – a red chrysanthemum spray accompanied by a powerful explosion, or a blue strobe, for example. Understanding how the contents of a firework produce the impressive variety of colors, forms, and sound intensities requires only a simple understanding of chemical reactions.<br /><br /><br />Fireworks generate three very noticeable forms of energy: a tremendous release of sound, bright light, and heat. The tremendous booms heard at ground level are the result of the rapid release of energy into the air, causing the air to expand faster than the speed of sound. This produces a shock wave, a sonic boom.<br /><br />The colors are produced by heating metal salts, such as calcium chloride or sodium nitrate, that emit characteristic colors. The atoms of each element absorb energy and release it as light of specific colors. The energy absorbed by an atom rearranges its electrons from their lowest-energy state, called the ground state, up to a higher-energy state, called an excited state. The excess energy of the excited state is emitted as light, as the electrons descend to lower-energy states, and ultimately, the ground state. The amount of energy emitted is characteristic of the element, and the amount of energy determines the color of the light emitted. For example, when sodium nitrate is heated, the electrons of the sodium atoms absorb heat energy and become excited. This high-energy excited state does not last for long, and the excited electrons of the sodium atom quickly release their energy, about 200 kJ/mol, which is the energy of yellow light.<br /><br /><br />The amount of energy released, which varies from element to element, is characterized by a particular wavelength of light. Higher energies correspond to shorter wavelength light, whose characteristic colors are located in the violet/blue region of the visible spectrum. Lower energies correspond to longer wavelength light, at the orange/red end of the spectrum.<br /><br /><img src="http://scifun.chem.wisc.edu/CHEMWEEK/fireworks/images/spectrum.gif" alt="" border="0" /><br /><br />In making fireworks, the metal salts are put into stars, small clay or dough-like lumps or cubes 3 to 4 cm in diameter. Stars consist of a blend of oxidizing agent, reducing agent, coloring agent (metal salt), and binders. When ignited, the stars produce both sound and light effects. The appearance of a firework is determined by its stars, which are made by hand and carefully packed into cardboard compartments within the firework shell, where they await ignition by a time-delay fuse.<br /><br />From lift-off to color release, a carefully choreographed sequence of events takes place, producing the desired effect. The power needed to lift each firework into the air is provided by the highly exothermic combustion of black powder, a slow-burning combination of 75% potassium nitrate, 15% charcoal, and 10% sulfur. Said to have first been used in China about 1000 years ago, the recipe for black (or coal) powder has undergone little change since then. This formulation explodes at a rate of about 3 meters per second, classifying it as a low explosive. In fact, when it burns in the open air, black powder’s heat and gas dissipate quickly. The key to fireworks’ success is to trap the heat and gas in the bottom of the shell, which is positioned in a launch tube or mortar, until the trapped gas pressure builds to such a force that, when it escapes, it hurls the firework high into the air.<br /><br />A firework is ignited by lighting the main fuse. That simultaneously starts both the fast action fuse, which quickly carries the flame down to the lift charge, and the time delay fuse, which continues to burn upward toward the cardboard compartments containing the stars, even as the firework is hurtling skyward.<br /><br /><br /><br />Fireworks are classified as both a low and a high explosive. The initial lift charge that sends the firework into the sky is a low explosive. The burning charge undergoes rapid decomposition, but not detonation. The firework can be thought of as flying through the air powered by a fast burning wick. Where the wick ends, it meets the high explosive components of the firework. In this second stage there is an instantaneous detonation producing both a loud explosion and a bright flash of color.<br /><br /> <img src="http://cache.daylife.com/imageserve/030icme6BJ7uw/610x.jpg" alt="" border="0" /><br /><br />The black powder lift-charge is calculated to exhaust itself precisely when the slow-burning, time-delay fuse reaches the first compartment packed with light-producing stars and black powder. This happens when the firework is at the very apex of its upward flight. Simultaneously the fuse sets off sound-producing explosives and detonates the stars, initiating color emission. If the timing of the fuses is off, however, the firework may detonate early, too close to the ground, or late, when the firework is falling back to earth.<br /><br /><table id="ncode_imageresizer_warning_1" class="ncode_imageresizer_warning" width="640"><tbody><tr><td class="td1" width="20"><img alt="Resigzed Image" src="http://www.chem4all.vn/forums/images/statusicon/wol_error.gif" border="0" height="16" width="16" /></td><td class="td2">Click this bar to view the full image.</td></tr></tbody></table><img id="ncode_imageresizer_container_1" src="http://www.garden-mowers.co.uk/images/fireworks/fireworks.jpg" alt="" border="0" height="512" width="640" /><br /><br />When an aerial firework explodes, its component stars fly off in all directions. However, when viewed from a distance, these aerial fireworks seem flat, as though they were displayed on a screen. We do not easily perceive that some parts are coming toward us, while others are moving away. We have a hard time seeing this, because we don't perceive the normal clues that tell us the direction in which something is moving. Normally, when an object moves toward us, it appears to grow larger, and when it moves away, it appears to grow smaller. However, the stars in fireworks are so bright against a dark background, that we can't get an accurate impression of what size they are; their intensity saturates our retinas. We can't tell if they are getting larger or smaller, so we judge them not to be moving either away from us or toward us. Therefore, they look flat. If, however, we could see them from directly below, we would observe that the stars move in all directions away from the central explosion.<br /><br />When watching fireworks, we see them much sooner than we hear them. That happens because light travels about a million times as fast as sound. The speed of light is 300,000,000 meters per second, but the speed of sound is only about 340 meters per second. If you are watching fireworks that are about a kilometer (1000 meters) away, the light takes only 3 millionths of a second to reach you. The sound takes about 3 seconds. You can tell how many kilometers away fireworks are exploding by starting to count seconds as soon as you see an explosion. Stop counting when you hear the explosion and divide the count by 3. This gives the distance away in kilometers.<br /><br /> <img src="http://www.pbs.org/wgbh/nova/fireworks/images/anat_2tdfuse.gif" alt="" border="0" /><br /><br /><br /><br /><b>Chemistry of Fireworks</b><br /><br /> <br /><br />The sights and sounds of each explosion are the result of several chemical reactions – oxidations and reductions – taking place within the firework as it ascends into the sky. Oxidizers produce the oxygen gas required to burn the mixture of reducing agents and to excite the atoms of the light-emitting compounds. Various oxidizers are used in both the black powder and the stars. The most commonly used oxidizers are nitrates, chlorates, and perchlorates. The reducing agents, sulfur and carbon, combine with the oxygen from the oxidizers to produce the energy of the explosion.<br /><br />The most commonly used oxidizers are nitrates, the major component of black powder. Nitrates are composed of nitrate ions (NO3-) with metal ions. The most common oxidizer is potassium nitrate, which decomposes to potassium oxide, nitrogen gas, and oxygen gas.<br /><br /><br /><img src="http://scifun.chem.wisc.edu/CHEMWEEK/fireworks/images/eq1.gif" alt="" border="0" /><br /><br /><br />When reacting, nitrates release two of their three oxygen atoms. Because the oxidation does not result in the release of all available oxygen, the reaction is not as vigorous as that of other oxidizers and is more controlled. This is why nitrates are used as the major component of black powder. In fireworks their main purpose is to provide the initial thrust to power the package into the sky and to ignite each bundle of stars. Nitrates are usually not used in star explosions, because reactions of nitrates do not produce a temperature high enough to energize many of the more colorful metal salts.<br /><br /><br /><br />In the 1830s Italian fireworks makers found a group of more explosive oxidizers, which produced temperatures of 1700 to 2000°C and made possible the creation of much more intense colors. These oxidizers are the chlorates, which contain the chlorate ion (ClO3-), and they give up all their oxygen upon reaction.<br /><br /> <img src="http://scifun.chem.wisc.edu/CHEMWEEK/fireworks/images/eq2.gif" alt="" border="0" /><br /><br />This results in a much more intense and spectacular reaction.<br /><br /><br /><br />These chlorates have the disadvantage of being less stable mechanically than nitrates, and therefore more dangerous to handle. Chlorate compounds sometimes can be detonated just by dropping them on the ground! This instability results from the fact that although the chlorine atom has the potential to bond with four oxygen atoms, in chlorates it bonds with only three, leaving the chlorine atom unsaturated and reactive. The complete release of its oxygen atoms makes chlorate a better oxidizing agent than nitrate. Unlike nitrate-containing compounds that produce a relatively slow burning rate, the oxidation by chlorates produces a much faster detonation – an explosion. In recent years, fewer fireworks manufacturers are using chlorates. Instead, perchlorates are now more commonly used because of their increased stability and oxygen release.<br /><br />Perchlorates contain the perchlorate ion (ClO4-), in which each chlorine atom is bonded to four oxygen atoms. The chlorine is bonded to its maximum number of oxygen atoms, and so perchlorates are more stable than chlorates. Yet, perchlorate is able to release all four of its oxygen atoms.<br /><br /> <img src="http://scifun.chem.wisc.edu/CHEMWEEK/fireworks/images/eq3.gif" alt="" border="0" /><br /><br />So, perchlorates are not only more stable, but more oxygen-rich than chlorates. They, like chlorates, produce more vigorous reactions than nitrates.<br /><br />The oxygen released by nitrates, chlorates, and perchlorates in the star compartments immediately combines with the reducing agents to produce hot, rapidly expanding gasses. The most common reducing agents are sulfur and carbon (charcoal) –standard components of black powder – which react with oxygen to produce sulfur dioxide and carbon dioxide respectively:<br /><br /><img src="http://scifun.chem.wisc.edu/CHEMWEEK/fireworks/images/eq4.gif" alt="" border="0" /><br /><br /><br /><b>Combustion of sulfur and carbon</b><br /><br /><br />The reactions that produce these gases also release a great deal of heat energy, so no only are the gases produced rapidly, they are hot and rapidly expanding gases. This adds to the explosive force of the reaction.<br /><br /><br /><br /><b>Firework Safety</b><br /><br /><br />Fireworks are used so frequently today in celebrations that it is easy to forget that they are dangerous explosives. Every year more than 8,000 people in the U.S. suffer injuries caused by the personal use of fireworks. Nearly half of the victims are children. A third of the injuries are caused by illegally obtained fireworks, and burns account for half the injuries. (An ordinary sparkler burns at a temperature of more than 1000°C!)<br /><br /><br /><br />The National Fire Protection Association (<a href="http://www.chem4all.vn/forums/redirector.php?url=http%3A%2F%2Fwww.nfpa.org" target="_blank" rel="nofollow">www.nfpa.org</a>) enforces stringent safety regulations for large fireworks displays. Spectators must be kept at least 840 feet from the launch area (that's based on the height and burst diameter of the largest shells). Shells may not be launched if winds are stronger than 20 miles per hour, because they could be blown off course. Nevertheless, many accidents occur with unregulated, informal neighborhood displays, when spectators attracted to the activities stand dangerously close to the launch area.<br /><br /><br /><br />Fireworks manufacturers also go to great lengths to ensure safety, but even so, more than 20 workers were killed in firework plants in the U.S. between 1970 and 1995. Safety regulations require that buildings be separated by concrete blast walls and that roofs be weakened to ensure that any explosion travels upwards rather than outwards. In addition, most fireworks are still made by hand because metal machinery could produce sparks or static electricity which would ignite the explosives.<br /><br /><br /><br />Many animals are frightened by the noise of fireworks and people are urged to leave their pets at home when they go to fireworks displays. Sadly, there are reports of dogs running away and some were lost.<br /><br /><br /><br /><b>Origins of Black Powder</b><br /><br /><br />Gunpowder or black powder was invented in China by alchemists experimenting with a naturally-occurring salt, potassium nitrate, also known as saltpeter. Ironically, they were looking for an elixir of immortality. But in handling and heating the sensitive substance they inevitably discovered its explosive properties. The first known account of the use of gunpowder as a weapon dates to 1046 in China, describing a catapult-launched grenade, an incendiary bomb, and a smoke bomb. The Song Dynasty Emperor in 1067 banned the sale of saltpeter and sulfur to foreigners and nationalized the production of gunpowder.<br /><br /><br />Marco Polo is sometimes given credit for bringing gunpowder to Europe but that is unlikely. When Europeans invaded the Middle East during the Crusades, they encountered gunpowder weapons used by Moslem forces. Despite government control and attempts to keep the formula secret, gunpowder probably traveled the Silk Road from China to the Moslem world far earlier than Marco Polo's trip in the late 1200s. English philosopher Roger Bacon (1217-1292) is believed to the first Westerner to describe gunpowder and fireworks. By the mid-1300s, European armies were using crude cannons and other gunpowder weapons.<br /><br /><br /><br /><b>Environmentally Friendly Fireworks</b><br /><br />Chemists continue to explore ways to make new pyrotechnic compounds and mixtures that are environmentally friendly. Two recent reports describe pyrotechnics made from high-nitrogen compounds that produce less smoke and particulate matter, and also replace perchlorates as oxidizers.</div>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-1169284640886895102007-01-20T16:16:00.001+07:002010-10-08T01:17:33.782+07:00Comparison between valence bond theory and molecular orbital theory<div align="center"><span><span><span><i><span i=""><div align="left"><span id="result_box" class="long_text" lang="en"><span style="" title="">In some areas, valence bond theory is better than the molecular orbital theory. </span><span style="" title="">When applied to the two-electron molecule, H2, valence bond theory, even with Heitler-London approach to the most simple, to provide energy approach closer ties and a more accurate representation of the behavior of electrons when chemical bonds are formed and broken. </span><span style="" title="">In contrast, molecular orbital theory predicts that the hydrogen molecules will dissociate into a linear superposition of the hydrogen atom and hydrogen ions positive and negative. </span><span style="" title="">This prediction does not match the physical description. </span><span style="" title="">This in part explains why the total energy curve of the distance between atoms on the valence bond method is above the curve using the molecular orbital method. </span><span style="" title="">This situation occurs in all diatomic molecules homonuklir and appears clearly in F2 when the minimum energy curve using molecular orbital theory is still higher than the two atomic energy F.<br /><br /></span><span style="" title="">The concept of hybridization is very useful and variability in bonding in most organic compounds are very low, leading to this theory is still an integral part of organic chemistry. </span><span style="" title="">However, the work of Friedrich Hund, Robert Mulliken, and Gerhard Herzbergmenunjukkan that molecular orbital theory provides a more precise description of spektrokopi, ionization, and magnetic properties of molecules. </span><span style="" title="">Lack of valence bond theory become clearer in the berhipervalensi molecules (eg, PF5) when the molecule is described without the use of d orbitals is very crucial in the bonding hybridization proposed by Pauling. </span><span style="" title="">Metal complexes and compounds yangkurang electrons (such as diborana) is described very well by molecular orbital theory, although the explanation that using valence bond theory has also been made.<br /><br /></span><span style="" title="">In 1930, two competing methods to realize that both are only an approximation to the theory better. </span><span style="" title="">If we take the simple valence bond structure and incorporate all covalent and ionic structures are possible on a group of atomic orbitals, we get what is called full configuration interaction wave function. </span><span style="" title="">If we take the simple molecular orbital description of the ground state and to combine these functions with the functions that describe the whole possibility of excited states using unfilled orbitals from the same set of atomic orbitals, we also get a full configuration interaction wave functions. </span><span style="" title="">Seen that the simple molecular orbital approach is too focused on the structure of the ion, whereas the valence bond theory is simple too little emphasis on ion structure. </span><span style="" title="">Can we say that the molecular orbital approach too delocalized, whereas the valence bond approach in too much of localization.<br /><br /></span><span style="" title="">Now the two approaches considered to meet each other, each giving his own views on issues on chemical bonds. </span><span style="" title="">Modern calculations in quantum chemistry usually starts from (but in the end away) molecular orbital approach than the valence bond approach. </span><span style="" title="">This is not because the molecular orbital approach is more accurate than the approach of valence bond theory, but because the molecular orbital approach makes it easier to convert into numerical calculations. </span><span title="">But program-program a better bond valence is also available.</span></span></div></span></i></span></span></span></div>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-1160983452910158392006-10-16T14:21:00.001+07:002010-10-08T01:49:23.435+07:00How to install GROMACS on windows vista 641. Download cygwin from http://www.cygwin.com/<br /> a. click on the link to "install from internet" and run the installer<br /> b. when you get the dialog that asks you what packages to install expand and select "gdn" "gdb" and "make"<br /> c. follow the rest of the installation instructions<br /><br />EDIT: this website has a pictorial guide to install the packages with cygwin. I forgot to mention they are all under Developer, so expand that first.<br /><br />EDIT: also install the tcsh package<br /><br />http://www.eecg.utoronto.ca/~aamodt/ece242/cygwin.html<br /><br />2. Next you are going to need the GROMACS source code. You can get it <a href="http://www.gromacs.org/index.php?option=com_content&task=view&id=79&Itemid=98">here</a>.<br />a. download and save the file someplace handy<br /><br />3. Next you need <a href="http://www.fftw.org/">FFTW</a>. There are pre-compiled dlls for Windows, but I would recommend not using them unless you know how to set the path variables. The easiest way is to grab <a href="http://www.fftw.org/fftw-3.2.1.tar.gz">fftw-3.2.1.tar.gz</a> . Again, save this someplace handy.<br /><br />4. create a folder someplace (C:\FFTW) and extract FFTW to it.<br /><br />5. start cygwin and change the directory to your FFTW folder: cd c:\fftw<br /><br />6. type: ./configure --enable-threads --enable-sse --enable-float<br /><br />7. then: make<br /><br />8. then: make install<br /><br />9. now create a folder for gromacs (C:\gromacs) and extract the distribution there. There should be a few folders like admin, src, etc.<br /><br />10. in the cygwin console, change your directory to the gromacs folder: cd c:\gromacs<br /><br />11. type: ./configure --enable-shared LDFLAGS='-L/usr/local/lib'<br /><br />12. then: make (this took a couple of hours to run through)<br /><br />13. then: make install<br /><br />14. make links<br /><br />15. make clean<br /><br />when you get your prompt back in cygwin (or from a fresh session change your directory to c:\gromacs) type: luck<br /><br />to test if you have access to gromacs. You should get something like:<br /><br />gcq#93: "Pretend That You're Hercule Poirot" (TeX)<br /><br />Also note I really haven't tested anything else yet, so this could all end up to be bogus. However if you're not really a computer guy, all bringing your ibook to dinner "in case you need to compile something" like me, then you may find this a good start. I'll update as necessary.salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-1157609362553693322006-09-07T13:01:00.002+07:002010-10-08T02:23:24.466+07:00BipyridyldiolNice, I just noticed that <a href="http://dx.doi.org/10.1021/jp9032172">my Master's thesis article</a> is already available online [1]. Well, you can take a look at it if you are interested in excited state proton transfer or if you want to know what I did for my Master's thesis. I'll put some additional things here that did not make it there. This is basically what happens:<br /><br /><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQsyQmQHR1YGeLfrvMko9-6KrUU1tbgQ5GjN1ctIS77jaEInaPhMO5wO3A_qzBlZ0IFFgX0MEUxuDNvQxkQ5_-wrxphS_CiRLKd7X6WDOUidpKB_G1qNv2BsgZYawZjGAxk6AI/s1600-h/scheme_new_11.JPG"><img style="margin: 0px auto 10px; display: block; text-align: center; cursor: pointer; width: 400px; height: 128px;" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQsyQmQHR1YGeLfrvMko9-6KrUU1tbgQ5GjN1ctIS77jaEInaPhMO5wO3A_qzBlZ0IFFgX0MEUxuDNvQxkQ5_-wrxphS_CiRLKd7X6WDOUidpKB_G1qNv2BsgZYawZjGAxk6AI/s400/scheme_new_11.JPG" alt="" id="BLOGGER_PHOTO_ID_5357259464555932530" border="0" /></a><br />Bipyridyl-diol has two intramolecular hydrogen bonds. You excite it with UV light wait a few femtoseconds and the protons get transferred. It was understood that the double-transfer product DK is finally formed. The main question was wether there were sequential and/or concerted transfers. The general idea was that there would be a branched reaction path: An ultrafast (100 fs) first step that was either a single or double proton transfer and a "very fast" (10 ps) step from MK to DK. According to us it looks more like there is no branched reaction but rather a dynamical equilibrium between MK and DK that cools toward DK. Well I hope some experimental groups are still interested enough in this system to test for this hypothesis.<br /><br />This is one trajectory, a simulation of the molecule for 300 fs after UV excitation.[2] You can see a very quick initial transfer and then some more transfers.<br /><br /> <a href="rtsp://v5.cache6.googlevideo.com/ChoLENy73wIaEQnL9jIyLrDw-hMYDSANFEgDDA==/0/0/0/video.3gp" type="video/3gpp"><img alt="video" src="http://video.google.com/ThumbnailServer2?app=blogger&contentid=faf0b02e3232f6cb&offsetms=5000&itag=w160&sigh=Jp_Lu0BBhykxr_faa13WVQyg2Bc" class="BLOG_mobile_video_class" id="BLOG_mobile_video-faf0b02e3232f6cb" height="266" width="320" /></a><br /><br />Actually I wanted also to show the development of the normal modes in the video. To compare them with the results of <a href="http://dx.doi.org/10.1016/j.chemphys.2008.03.007">Stock et al.</a>'s experiment. But this does not seem to work out here because the videos need to have a fixed 4:3 format. So I'll just show a figure. The important thing is that there is strong participation of the totally symmetric modes (blue, red) even if the process does not conserve the symmetry. Another very interesting thing is that activation of the non-totally symmetric (black) mode is a violation of the Franck-Condon rules. A way to explain this is that the Franck-Condon rules work only under ideal assumptions and not with a strongly anharmonic reactive potential.<br /><br /><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgpP749ekwJbxVioJMLDboocZCwUGvN3zEz5kMEHOpeQhqbkGEqBPT1sxLh34wMXkE0Kqe8J7SLdNvpEWpbnyT5xdZHhhFqPKj0IWHaX7PLh55bw2jVkWVNIQfG6VcWpDaV9hes/s1600-h/im_0000.png"><img style="margin: 0px auto 10px; display: block; text-align: center; cursor: pointer; width: 400px; height: 300px;" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgpP749ekwJbxVioJMLDboocZCwUGvN3zEz5kMEHOpeQhqbkGEqBPT1sxLh34wMXkE0Kqe8J7SLdNvpEWpbnyT5xdZHhhFqPKj0IWHaX7PLh55bw2jVkWVNIQfG6VcWpDaV9hes/s400/im_0000.png" alt="" id="BLOGGER_PHOTO_ID_5357526520359520082" border="0" /></a>Here is another trajectory for comparison. In this case the second proton transfer occured only a little bit later.<br /><br /> <a href="rtsp://v6.cache7.googlevideo.com/ChoLENy73wIaEQkNJRjOLUWt3xMYDSANFEgDDA==/0/0/0/video.3gp" type="video/3gpp"><img alt="video" src="http://video.google.com/ThumbnailServer2?app=blogger&contentid=dfad452dce18250d&offsetms=5000&itag=w160&sigh=j1aVohGKG6RWy6KV-BKxQDw2Wmk" class="BLOG_mobile_video_class" id="BLOG_mobile_video-dfad452dce18250d" height="266" width="320" /></a><br /><br /><br />Actually another nice figure would be this one. What I am doing is projecting the trajectories onto a normal mode. And then I can average for every time step over the 36 trajectories that we ran. This time-dependent average should represent the coherent motions. Here I am showing 17a<sub>g</sub>, an aromatic breathing vibration, which is the classical case for a coherent Franck-Condon excitation (in the context of proton transfer the lower frequency skeletal modes were of more interest). In the harmonic vibrational analysis that we did at the DK equilibrium geometry, the mode has a wavenumber of 682/cm. This corresponds to a period of about 49 fs. Well and there really is a coherent oscillation with just that frequency. So we see that the harmonic vibrational analysis at the minimum and the dynamics nicely work together. If I compute the standard deviation over time of this time-dependent average then I get only one number per normal mode. These numbers are what we are showing in Fig. 10. And by the way: The tools to do this are in the new <a href="http://www.univie.ac.at/newtonx/">Newton-X</a> version (aside from many other nice things ...).<br /><br /><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEheCtnA51VJJ3Ts7P4E_HkalRmgSRQ7S5MMuJcHLpwlcbqeCDBlcy_1A3Kx3hzbtEf_-F71jKsjZKwQSaDlVMFhpbbU_Bzf9q6ytf7yve_UVSsPAKULhMysbQBLl_LJivRIHsFf/s1600-h/mode_027.png"><img style="margin: 0px auto 10px; display: block; text-align: center; cursor: pointer; width: 400px; height: 300px;" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEheCtnA51VJJ3Ts7P4E_HkalRmgSRQ7S5MMuJcHLpwlcbqeCDBlcy_1A3Kx3hzbtEf_-F71jKsjZKwQSaDlVMFhpbbU_Bzf9q6ytf7yve_UVSsPAKULhMysbQBLl_LJivRIHsFf/s400/mode_027.png" alt="" id="BLOGGER_PHOTO_ID_5357276701057273586" border="0" /></a><br /><hr />[1] And interestingly there is a direct link to facebook which of course I had to click.<br /><br />[2] One of these 300 fs RI-CC2/SVP-SV trajectories takes about a month on one processor.<br /><br /><br />Source : http://chemical-quantum-images.blogspot.com/2009/07/bipyridyldiol.htmlsalman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-1156154912331798212006-08-21T17:03:00.001+07:002010-10-08T01:14:39.433+07:00How to Clean Laboratory Glassware<span style="font-size:100%;"><i><span style="color:Blue;">My Prof. said that If I can't clean Laboratory glasswares well, I won't become a good chemist. I think it's true. </span></i><br /><br />By Anne Marie Helmenstine, Ph.D., About.com<br />Cleaning laboratory glassware isn't as simple as washing the dishes. Here's how to wash your glassware so that you won't ruin your chemical solution or laboratory experiment.<br /><br /><span style="color:Red;"><b>Cleaning Basics</b></span><br /><br />It's generally easier to clean glassware if you do it right away. When detergent is used, it's usually one designed for lab glassware, such as Liquinox or Alconox. These detergents are preferable to any dishwashing detergent you might use on dishes at home.<br /><br />Much of the time, detergent and tap water are neither required nor desirable. You can rinse the glassware with the proper solvent, then finish up with a couple of rinses with distilled water, followed by final rinses with deionized water.<br /><br /><span style="color:Red;"><b>How to Wash Out Common Lab Chemicals</b></span><br /><br /><span style="color:Red;"> * Water Soluble Solutions</span><br /> (e.g., sodium chloride or sucrose solutions) Rinse 3-4 times with deionized water then put the glassware away.<br /><br /><span style="color:Red;"> * Water Insoluble Solutions</span><br />(e.g., solutions in hexane or chloroform) Rinse 2-3 times with ethanol or acetone, rinse 3-4 times with deionized water, then put the glassware away. In some situations other solvents need to be used for the initial rinse.<br /><br /><span style="color:Red;"> * Strong Acids</span><br />(e.g., concentrated HCl or H2SO4) Under the fume hood, carefully rinse the glassware with copious volumes of tap water. Rinse 3-4 times with deionized water, then put the glassware away.<br /><br /><span style="color:Red;"> * Strong Bases</span><br />(e.g., 6M NaOH or concentrated NH4OH) Under the fume hood, carefully rinse the glassware with copious volumes of tap water. Rinse 3-4 times with deionized water, then put the glassware away.<br /><br /><span style="color:Red;"> * Weak Acids</span><br />(e.g., acetic acid solutions or dilutions of strong acids such as 0.1M or 1M HCl or H2SO4) Rinse 3-4 times with deionized water before putting the glassware away.<br /><br /><span style="color:Red;"> * Weak Bases</span><br />(e.g., 0.1M and 1M NaOH and NH4OH) Rinse thoroughly with tap water to remove the base, then rinse 3-4 times with deionized water before putting the glassware away.<br /><br /><span style="color:Red;"><b>Washing Special Glassware</b></span><br /><br /><span style="color:Red;"> * Glassware Used for Organic Chemistry</span><br />Rinse the glassware with the appropriate solvent. Use deionized water for water-soluble contents. Use ethanol for ethanol-soluble contents, followed by rinses in deionized water. Rinse with other solvents as needed, followed by ethanol and finally deionized water. If the glassware requires scrubbing, scrub with a brush using hot soapy water, rinse thoroughly with tap water, followed by rinses with deionized water.<br /><br /><span style="color:Red;"> * Burets</span><br />Wash with hot soapy water, rinse thoroughly with tap water, then rinse 3-4 times with deionized water. Be sure the final rinses sheet off of the glass. Burets need to be thoroughly clean to be used for quantitative labwork.<br /><br /><span style="color:Red;"> * Pipets and Volumetric Flasks</span><br />In some cases, you may need to soak the glassware overnight in soapy water. Clean pipets and volumetric flasks using warm soapy water. The glassware may require scrubbing with a brush. Rinse with tap water followed by 3-4 rinses with deionized water.<br /><br /><span style="color:Red;"><b>Drying or Not Drying Glassware</b></span><br /><br /><span style="color:Red;"> * Not Drying</span><br />It is inadvisable to dry glassware with a paper towel or forced air since this can introduce fibers or impurities that can contaminate the solution. Normally you can allow glassware to air dry on the shelf. Otherwise, if you are adding water to the glassware, it is fine to leave it wet (unless it will affect the concentration of the final solution). If the solvent will be ether, you can rinse the glassware with ethanol or acetone to remove the water, then rinse with the final solution to remove the alcohol or acetone.<br /><br /><span style="color:Red;"> * Rinsing with Reagent</span><br /> If water will affect the concentration of the final solution, triple rinse the glassware with the solution.<br /><br /><span style="color:Red;"> * Drying Glassware</span><br />If glassware is to be used immediately after washing and must be dry, rinse it 2-3 times with acetone. This will remove any water and will evaporate quickly. While it's not a great idea to blow air into glassware to dry it, sometimes you can apply a vacuum to evaporate the solvent.<br /><br /><span style="color:Red;"><i><b>Additional Notes</b></i></span><br /><br /><span style="color:Blue;"> * Remove stoppers and stopcocks when they are not in use. Otherwise they may 'freeze' in place.<br />* You can degrease ground glass joints by wiping them with a lint-free towel soaked with ether or acetone. Wear gloves and avoid breathing the fumes.<br />* The deionized water rinse should form a smooth sheet when poured through clean glassware. If this sheeting action is not seen, more aggressive cleaning methods may be needed.</span></span>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-1156151431794944322006-08-21T15:58:00.001+07:002010-10-08T01:10:53.138+07:00Relationship Between Science (Chemistry) and Technology<span id="result_box" class="long_text" lang="en"><span style="" title="">Relationship Between Science (Chemistry) and Technology<br /></span><span style="" title="">by: salman<br /><br /></span><span style="" title="">Technology is the application of science that is concerned with practical uses in industry. </span><span style="" title="">Therefore, science (chemistry) and technology need each other, because "science (chemistry) without a technology like a fruitless tree, while the technology without science is like a tree without roots" (science (chemistry) is fruitless without technology, without science technology </span><span style="" title="">(chemistry) is Rootless). </span><span style="" title="">With support resources manusis quality and natural resources sufficient and adequate, there was rapid progress in science and technology, whose products will equip people with various (1) The material is good (such as construction of buildings, various types of foods and beverages, </span><span style="" title="">various types of information or communication and transportation, the various devices that can generate great energy and improve the working efficiency of the machines, thus speeding / improving production, various types of medicines, clothing, soap and detergents, cosmetics, plastics, </span><span style="" title="">polymers, fibers, dyes, and various other items), and (2) Services / Services 9meliputi waiter: transport, telkomunikasi, hotel / lodging, security and safety for individuals or communities), so terwujudlah welfare. </span><span style="" title="">From the above brief description terliat that chemistry is very important to be learned and in apliksikan in life.</span></span>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com1tag:blogger.com,1999:blog-32832729.post-1155913851432991962006-08-18T21:53:00.001+07:002010-10-08T01:33:13.781+07:00ChemLab v 2.0Model ChemLab originated from academic work in computer simulation and software design at McMaster University. It has continued to be developed with extensive input from educators interested in the possible application of computer simulations for classroom and distance learning.<br /><br />Model ChemLab is a unique product incorporating both an interactive simulation and a lab notebook workspace with separate areas for theory, procedures and student observations. Commonly used lab equipment and procedures are used to simulate the steps involved in performing an experiment. Users step-through the actual lab procedure while interacting with animated equipment in a way that is similar to the real lab experience.<br /><br />ChemLab comes with a range of pre-designed lab experiments for general chemistry at the high school and college level. Users can expand upon the original lab set using ChemLab's LabWizard development tools, thus allowing for curriculum specific lab simulation development by educators. These user designed simulations combine both text based instructions and the simulation into a single distributable file.<br /><br /><table id="ncode_imageresizer_warning_1" class="ncode_imageresizer_warning" width="640"><tbody><tr><td class="td1" width="20"><img alt="Resigzed Image" src="http://www.chem4all.vn/forums/images/statusicon/wol_error.gif" border="0" height="16" width="16" /></td><td class="td2">.</td></tr></tbody></table><img id="ncode_imageresizer_container_1" src="http://modelscience.com/Pro.gif" alt="" border="0" height="492" width="640" />salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-1155912319679432022006-08-18T21:27:00.001+07:002010-10-08T01:13:51.426+07:00Chemistry Laboratory Safety Rules<span style="font-size:100%;"><span style="color:Blue;"><b><i>Better Safe than Sorry</i></b></span><br />By Anne Marie Helmenstine, Ph.D., About.com<br />Some rules are NOT made to be broken. That is true of the rules used in a chemistry lab. They are really, truly for your safety and not your humiliation.<br /><br /><b><span style="color:Red;"> * Do Not Pipette By Mouth - Ever</span></b><br />You say, "But it's only water." Even if it is, how clean do you think that glassware really is? Using disposable pipettes? I know lots of people who rinse them and put them back! Learn to use the pipette bulb or automated pipetter. Don't pipette by mouth at home either. Gasoline and kerosene should be obvious, but people get hospitalized or die every year, right? I know someone who used his mouth to start the suction on a waterbed to drain it. Do you know what they put in some waterbed additives? Carbon-14. Mmmm...radiation. He couldn't retch fast enough! The lesson is that even seemingly harmless substances may be dangerous!<br /><br /><span style="color:Red;"><b> * Read the Chemical Safety Information</b></span><br />A Material Safety Data Sheet (MSDS) should be available for every chemical you use in lab. Read these and follow the recommendations for safe use and disposal of the material.<br /><br /><span style="color:Red;"><b> * Dress Appropriately (for chemistry lab, not fashion or the weather)</b></span><br />No sandals, no clothes you love more than life, no contact lenses, and long pants are preferable to shorts or short skirts. Tie long hair back. Wear safety goggles and a lab coat. Even if you aren't clumsy, someone else in the lab probably is. If you take even a few chemistry courses you will probably see people set themselves on fire, spill acid on themselves, others, or notes, splash themselves in the eye, etc. Don't be the bad example to others, remembered for all time for something stupid!<br /><br /><span style="color:Red;"><b> * Identify the Safety Equipment</b></span><br />And know how to use it! Given that some people (possibly you) will need them, know the locations of the fire blanket, extinguishers, eyewash, and shower. Ask for demonstrations! If the eyewash hasn't been used in a while the discoloration of the water is usually sufficient to inspire use of safety glasses.<br /><br /><b><span style="color:Red;"> * Don't Taste or Sniff Chemicals</span></b><br />For many chemicals, if you can smell them then you are exposing yourself to a dose that can harm you! If the safety information says that a chemical should only be used inside a fume hood, then don't use it anywhere else. This isn't cooking class - don't taste your experiments!<br /><br /><span style="color:Red;"><b> * Don't Casually Dispose of Chemicals Down the Drain</b></span><br />Some chemicals can be washed down the drain, while others require a different method of disposal. If a chemical can go in the sink, be sure to wash it away rather than risk an unexpected reaction between chemical 'leftovers' later.<br /><br /><b><span style="color:Red;"> * Don't Eat or Drink in Lab</span></b><br /> It's tempting, but oh so dangerous... just don't do it!<br /><br /><span style="color:Red;"><b> * Don't Play Mad Scientist</b></span><br />Don't haphazardly mix chemicals! Pay attention to the order in which chemicals are to be added to each other and do not deviate from the instructions. Even chemicals that mix to produce seemingly safe products should be handled carefully. For example, hydrochloric acid and sodium hydroxide will give you salt water, but the reaction could break your glassware or splash the reactants onto you if you aren't careful!<br /><br /><span style="color:Red;"><b> * Take Data During Lab</b></span><br />Not after lab, on the assumption that it will be neater. Put data directly in your lab book rather than transcribing from another source (e.g., notebook or lab partner). There are lots of reasons for this, but the practical one is that it is much harder for the data to get lost in your lab book. For some experiments, it may be helpful to take data beforelab. No, I'm not telling you to dry-lab or cheat, but being able to project likely data will help you catch bad lab procedure before you are three hours or so into a project. Know what to expect. You should always read the experiment in advance. </span><span style="font-style: italic;font-family:courier new;" ></span>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-1155742987537701382006-08-16T22:42:00.001+07:002010-10-08T01:12:00.781+07:00Man and Love<span id="result_box" class="long_text" lang="en"><span title="">Love is a gift of God, he is inside every human being, so he is universal. </span><span title="">He is associated with the deepest aspects of human beings, because we sense it will never be able to understand nature in other words, love only to be felt not to think about. </span><span title="">Also difficult to deny that love is one of the needs of human life is quite fundamental.<br /></span><span title="">Love can be happy at once miserable. </span><span title="">Kekuatanya can make people laugh, sad, whimpering or even crying. </span><span title="">But make no mistake cry in sex was common. </span><span title="">In love with no complaints and complaining, because no other lover goal is the goal of the lover. </span><span title="">Moaned and groan clearly contrary to the willingness, for lovers of all deeds are always willing lover. </span><span title="">In a hadith, the Prophet once said: "Three things come from good pembendaharaan; hide charity, hide and conceal complaints disaster."<br /></span><span title="">Love is one of the most interesting themes to be discussed, written, or filmed disyairkan. </span><span title="">Hundreds of the definition of love has been put forward by the scholars, psychologists and philosophers. </span><span title="">Thousands of strands of beautiful poems have been woven by the poets of the world, all trying to define and a portrait of the nature of love. </span><span title="">Tetapih love remains a mystery and the biggest puzzle for humans.<br /></span><span title="">A Sufi divide love into two categories; Divine Love And Human Love. </span><span title="">Love divine grace is essential is delegated to humans. </span><span title="">He is the incarnation of His nature; ar-rahman ar-uterine and the impossible can be calculated with an estimated human, as it is impossible to calculate favors which has given him.<br /></span><span title="">In our every breath, every cell in our blood, in each of the elements contained in soil, there is a divine love that we often do not realize. </span><span title="">With his rahmaniyah God has revealed the beauty of the rainbow through the mediation of both our eyes, and make itself merdunya water splashing through His gift of a pair of ears. </span><span title="">With his rahmaniyah God has given sweet taste of sugar through through our tongues. </span><span title="">Unfortunately we often forget about giving yourself to Him. </span><span title="">Clever-clever we are grateful, still not adequate as an expression of gratitude is too large due to the grace of God.<br /></span><span title="">Second is human love. </span><span title="">This love comes from first love. </span><span title="">Love between men and women is a portion of divine love. </span><span title="">Apapaun we feel about love, in the manner and extent of any small part of the love god. </span><span title="">Tetapih sometimes lover becomes a veil between love and reality of true love. </span><span title="">One day the veil will be lifted where purposes and a true lover will appear in all the greatness of god.<br /></span><span title="">The theme of love is not be exhausted to talk. </span><span title="">He belongs to everyone and everyone is entitled to speak about love.<br /><br /><br /><br /></span><span title="">1. </span><span title="">Meaning of Love<br /></span><span title="">Love is a matter of heart problems, he relates to the deepest feelings in man. </span><span title="">It is not surprising that it has a sense of love and planting a diverse, depending on who and what is perceived by a person and how he mengeskpresikan gust love it.<br /></span><span title="">In a simple love can be said as an alloy of sympathy between the two creatures. </span><span title="">Sympathy is not only growing among men and women, will tetapih could also between man to man or woman to woman. </span><span title="">Examples are easy to understand for this we can see in a loving relationship between a father with his son, or between a mother with her daughter.<br /></span><span title="">Love is very closely adrift with human life. </span><span title="">selintas never any people think that love is not important. </span><span title="">They are hungry for love. </span><span title="">Many people do not stop watching movies about love stories, both ended with a happy and vice versa. </span><span title="">Many people like to hear dozens of songs about love that pattern. </span><span title="">Nevertheless, almost every people never think about what and how to love it. </span><span title="">In fact, love can be described as an art as any other art form, it requires knowledge and practice to be mengapainya.<br /><br /></span><span title="">2. </span><span title="">Motif-motif is Driving The emergence of Love.<br /></span><span title="">The motive of love is a feeling, followed by the desire and tendency to love something one's heart. </span><span title="">He also could mean something that is inside of a person who causes he loved. </span><span title="">Thus, it is the motive is a combination of both, the properties of a person who encourages others to love him, and feelings of love that is in the lover. </span><span title="">Besides the existence of harmony and compatibility, as the force that will build and bind their love.<br /></span><span title="">Thus, there are several motives that drive the emergence of a sense of love, that is something that is inside of her lover, especially the beauty and the beauty, the feeling of love the lover and the conformity and harmony among them. </span><span title="">The stronger and is also perfect love caused by it. </span><span title="">Vice versa.<br /></span><span title="">When the loved one being in the top of the charm of her beauty, coupled with sempurnannya harmony and harmony that binds the two souls, will be created lasting love and eternal.<br /></span><span title="">Sometimes, the lover levels of beauty it mediocre, tetapih seen so perfect in the eyes of lovers, her love will be perfect. </span><span title="">So that beauty is relative, depending on how much love is felt by someone that, because "your love for something can make you blind and deaf."<br /></span><span title="">No doubt that one lover is one of the most beautiful in the eyes of the lover of all things and beyond. </span><span title="">It could be the perfect beauty of a woman, but can not be fully enjoyed by a man, so that his love be mediocre ..<br /><br /></span><span title="">3. </span><span title="">Affection<br /></span><span title="">According to the Indonesian general dictionary writing WJS </span><span title="">Purwodarminto, compassion is defined by feelings of affection, feelings of love or feelings of love to someone.<br /></span><span title="">In married life affection is the key to happiness. </span><span title="">Compassion is a growth of love. </span><span title="">When youth romance ended with marriage, then married a young family in that no longer make love-love, but it is shed each other's love to love or affection.<br /></span><span title="">If one element of love lost, for example elements of responsibility, then the integrity retaklah household. </span><span title="">Compassion is not accompanied by honesty will terancamlah happiness that household.<br /><br /><br /></span><span title="">4. </span><span title="">Intimacy<br /></span><span title="">Intimacy comes from the intimate meaning of intimate feelings of sympathy. </span><span title="">Intimacy is a good intimate relationship between men and women who are intoxicated by romance or already married.<br /></span><span title="">Yose Ortega Y. </span><span title="">Gasset in his novel "On Love" say "in his soul a lover feels himself united with the object of unconditional love. </span><span title="">Unity is the fundamental unity and involve the whole existence ".<br /></span><span title="">Intimacy can lead to the power of human creativity. </span><span title="">with the intimacy of people to create various art forms in accordance with ability and talent.<br /><br /></span><span title="">5. </span><span title="">True love<br /></span><span title="">Love is based on the motives and purposes may not be lasting. </span><span title="">So it is with love that is based on material owned by her lover, because with the loss or change something, it will disappear also love earlier. </span><span title="">But when love is based on motifs derived from the lover's inner ssendiri and nature, her love would be eternal while there are no obstacles that cause love is lost. </span><span title="">Barriers could include changes in circumstances (mental), the condition of the suffering lover or arising by her lover because of this suffering could weaken or even eliminate the feeling of love at all.<br /></span><span title="">Therefore, the lovers are divided in two groups. </span><span title="">The first group said that it was not true love if he could cut off by suffering or disturbance. </span><span title="">Indications that true love is not love because of reduced levels keberpalingan lover, he also could not remove only because of the suffering endured by the lover, even he will enjoy whatever treatment her lover against him;<br /></span><span title="">'My love blossomed, no matter who you are<br /></span><span title="">how are you, past or present<br /></span><span title="">you do not care (in my situation), so I will<br /></span><span title="">you're acting like the behavior of my enemies<br /></span><span title="">then I will love them<br /></span><span title="">judgment against you<br /></span><span title="">same as in their judgment<br /></span><span title="">kuperoleh enjoyment if people insult me<br /></span><span title="">I felt the reproach in the love<br /></span><span title="">as a delicacy<br /></span><span title="">love has been imprinted, then let them picking on me<br /></span><span title="">this is called true love, which grows from a strong harmony. </span><span title="">He hinakan himself because sanag melecehkanya lover, he loved his enemies because they like the lover who often hurt.<br /></span><span title="">This is a consequence of a feeling of perfect love, despite sincere heart and soul not accept it.<br /></span><span title="">The second group is different from the first, they thought it could relieve the suffering of love, because nature and human nature is naturally going to hate people who hurt him, as where he would like people who do good to him.<br /><br /></span><span title="">6. </span><span title="">The emergence of Cause For Love<br /></span><span title="">The cause of the emergence of a sense of love that there are three kinds. </span><span title="">First sight, be it through the eye and vision care. </span><span title="">Both assessments are good, if the outlook was not accompanied by assessments and the assumption that good, then it is unlikely that love will appear. </span><span title="">Third, think about what he had seen and what is dancing her heart. </span><span title="">If someone is preoccupied by matters more important (according to him) than what he had seen, then there will emerge a sense of love, although interest in it can not be eliminated. </span><span title="">Because it is said that love is the movement of an empty soul. </span><span title="">If the view. </span><span title="">Assessment and thought had occurred to the heart that is empty, will emerge feeling of love.<br /><br /><br /></span><span title="">7. </span><span title="">Signs of Love<br /></span><span title="">There are some signs that the supporters love love it:<br /></span><span title="">1. </span><span title="">Concentration in the lover's eyes<br /></span><span title="">The eyes are the heart door, he pushed all the secrets contained in the liver. </span><span title="">The eyes convey more honest than of the tongue, because the indications look more real, spontaneous, without any artificial or cultivated, while the tongue indication lafadz, who follow what the intended meaning of the speech. </span><span title="">Eyes of someone who is in love will always be drawn to people who loved, wherever she goes.<br /></span><span title="">2. </span><span title="">Bowed shame if in view by her lover<br /></span><span title="">The lovers could only close his eyes, lowered his face and looked away when looking at her lover. </span><span title="">This is all driven by a sense of shame because of the greatness and majesty of his beloved his heart.<br /></span><span title="">3. </span><span title="">Always remember and mention the name of her lover<br /></span><span title="">The name of a lover will not be forgotten at all in the heart of the lover, because his name has stuck deep inside his heart. </span><span title="">But because keterbatasanya place in my heart, the lover can terkandang melupakannaya, because something was missing interrupt, ingatanya will return.<br /><br /></span><span title="">4. </span><span title="">Can not wait as far away from lover<br /></span><span title="">A lover would feel uneasy when he had to be away from her lover, but he will be very patient, as for the patience of a lover for far and away with her lover is apparent patience, patience is not true.<br /><br /></span><span title="">5. </span><span title="">Anything like that favored by her lover<br /><br /></span><span title="">6. </span><span title="">The road to the house lover was actually much closer though<br /></span><span title="">7. </span><span title="">Embarrassed when being together with her lover<br /></span><span title="">8. </span><span title="">Something fun like all the lover.<br /></span><span title="">9. </span><span title="">Jealous lover<br /></span><span title="">Jealousy someone will emerge if the lover have been wronged or dihianati.<br /></span><span title="">10. </span><span title="">Like tandem<br /></span><span title="">Nothing is more beautiful felt by people who are in love than be alone with a lover.<br /></span><span title="">11. </span><span title="">The existence of harmony between the two of them<br /></span><span title="">harmony between the two lovers will terbina if there is a match between two of them dalamberbagai thing, many of them are sick because of her illness her lover, while he was not aware of a lover to say something, and at the same time her boyfriend also said something similar and exactly the same.<br /><br /><br /></span><span title="">8. </span><span title="">Meaning of Worship<br /></span><span title="">Adoration is the embodiment of human love to God. </span><span title="">because God is love only for humans, while the lovers love and the love of neighbor is a blessing that God put in the human heart.<br /></span><span title="">Love that there are three kinds: love God, love for God and love with God. </span><span title="">Loving God is the perfection of love and tuntunanya. </span><span title="">Love for God requires that to love what is loved by Him and love anything that can help her love, menghantarkanya in proximity to His good pleasure. </span><span title="">While love with God is the love that smell of shirk, like love people to shirk their god.<br /><br /><br /></span><span title="">9. </span><span title="">Mercy<br /></span><span title="">Love this fellow is given the term "Twelve Pity" to distinguish between the love of god, love to parents, male-female love, love the nation and homeland.<br /></span><span title="">In the letter Al-Pen paragraph 4 of the human being merciful to others, because compassion is the act of a virtuous person, while the righteous man is praised by Allah SWT.<br /></span><span title="">In the essay "On Love" is the understanding that love is a feeling of unity without conditions. </span><span title="">That means in a sense of pity belasa not contain elements of self-interest. </span><span title="">Pity that we really shed from a sincere heart.<br /><br /><br /></span><span style="" title="">Source: Shaykh ibn al-Qayyim al-Jawzi, 2004. </span><span title="">Why no love. </span><span style="" title="">Abla Publisher. </span><span style="" title="">Jakarta.</span></span>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com1tag:blogger.com,1999:blog-32832729.post-1155742836953425642006-08-16T22:39:00.001+07:002010-10-08T01:09:02.212+07:00How to Write a Lab ReportLab reports are an essential part of all laboratory courses and usually a significant part of your grade. If your instructor gives you an outline for how to write a lab report, use that. Here's a format for a lab report you can use if you aren't sure what to write or need an explanation of what to include in the different parts of the report. A lab report is how you explain what you did in experiment, what you learned, and what the results meant. Here is a standard format:<br /><br /> 1. Title Page<br /> Not all lab reports have title pages, but if your instructor wants one, it would be a single page that states:<br /> * The title of the experiment.<br /> * Your name and the names of any lab partners.<br /> * Your instructor's name.<br /> * The date the lab was performed or the date the report was submitted.<br /><br /> 2. Title<br />The title says what you did. It should be brief (aim for ten words or less) and describe the main point of the experiment or investigation. An example of a title would be: "Effects of Ultraviolet Light on Borax Crystal Growth Rate". If you can, begin your title using a keyword rather than an article like 'The' or 'A'.<br /><br /> 3. Introduction / Purpose<br />Usually the Introduction is one paragraph that explains the objectives or purpose of the lab. In one sentence, state the hypothesis. Sometimes an introduction may contain background information, briefly summarize how the experiment was performed, state the findings of the experiment, and list the conclusions of the investigation. Even if you don't write a whole introduction, you need to state the purpose of the experiment, or why you did it. This would be where you state your hypothesis.<br /><br /> 4. Materials<br /> List everything needed to complete your experiment.<br /><br /> 5. Methods<br />Describe the steps you completed during your investigation. This is your procedure. Be sufficiently detailed that anyone could read this section and duplicate your experiment. Write it as if you were giving direction for someone else to do the lab. It may be helpful to provide a Figure to diagram your experimental setup.<br /><br /> 6. Data<br />Numerical data obtained from your procedure usually is presented as a table. Data encompasses what you recorded when you conducted the experiment. It's just the facts, not any interpretation of what they mean.<br /><br /> 7. Results<br />Describe in words what the data means. Sometimes the Results section is combined with the Discussion (Results & Discussion).<br /><br /> 8. Discussion or Analysis<br />The Data section contains numbers. The Analysis section contains any calculations you made based on those numbers. This is where you interpret the data and determine whether or not a hypothesis was accepted. This is also where you would discuss any mistakes you might have made while conducting the investigation. You may wish to describe ways the study might have been improved.<br /><br /> 9. Conclusions<br />Most of the time the conclusion is a single paragraph that sums up what happened in the experiment, whether your hypothesis was accepted or rejected, and what this means.<br /><br /> 10. Figures & Graphs<br />Graphs and figures must both be labeled with a descriptive title. Label the axes on a graph, being sure to include units of measurement. The independent variable is on the X-axis. The dependent variable (the one you are measuring) is on the Y-axis. Be sure to refer to figures and graphs in the text of your report. The first figure is Figure 1, the second figure is Figure 2, etc.<br /><br /> 11. References<br />If your research was based on someone else's work or if you cited facts that require documentation, then you should list these references.<br /><br />( Source : <a href="http://www.chem4all.vn/forums/redirector.php?url=http%3A%2F%2Fchemistry.about.com" target="_blank" rel="nofollow">http://chemistry.about.com</a> )salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-1155739141925951602006-08-16T21:35:00.001+07:002010-10-08T00:55:18.642+07:00Khalil Gibran<div style="text-align: center;"><span id="result_box" class="long_text" lang="en"><span title="">When love calls you, follow him, despite the steep winding road.<br /></span><span title="">And when his wings merangkummu, pasrahlah and surrender,<br /></span><span title="">though the sword hidden in between the wing was hurt.<br /></span><span title="">And if she talks to you, believe me, even though his words interrupted dream,<br /></span><span title="">like a north wind rifling through landscaping.<br /></span><span title="">For as love memahkotaimu, demikuan did he crucify you.<br /></span><span title="">For the sake of your growth, as well as also for the sake of pemangkasanmu.<br /></span><span title="">As he was rising, kissed the tops of ketinggianmu,<br /></span><span title="">tenderly caressing the softest twigs which tremble in the sunlight,<br /></span><span title="">so did he menghunjam to the bottom akarmu,<br /></span><span title="">ikatanmu shake of the ground.<br /><br /></span><span title="">Like a grain of wheat you reach, you get plain nude ditumbuknya,<br /></span><span title="">diketamnya you, for free from your skin, rubbed, so that becomes pure white,<br /></span><span title="">squeezed, squeezed into a limp material is formed,<br /></span><span title="">and finally delivered to the sacred fire,<br /></span><span title="">like holy bread which is dedicated to the feast of the Holy God.<br /><br /></span><span title="">Thus the character of self-love of man, so you understand the secret of the heart,<br /></span><span title="">and this awareness of life make you a piece of liver.<br /><br /></span><span style="" title="">But if the anxiety, selfhood only love and joy you seek,<br /></span><span style="" title="">it is more okay for you to cover your body, then withdrew from the board forging,<br /></span><span style="" title="">enter the world without seasons, where you can laugh, but not entirely,<br /></span><span title="">where you can cry, but not after tears.<br /><br /></span><span style="" title="">Love does not give anything, except the whole himself, fully intact.<br /></span><span title="">Did not take anything, except from himself.<br /></span><span style="" title="">Love does not have or even possessed, for love is sufficient for love.<br /><br /></span><span title="">If you love, do not you say "God is in my heart,"<br /></span><span title="">but should you feel, "I was in the Lord."<br /><br /></span><span title="">Love no desire other than to realize its meaning,<br /></span><span title="">but if you're in love with a variety of desires,<br /></span><span title="">Make it happen his way.<br /><br /></span><span title="">Melt away, flows like time,<br /></span><span title="">who sings the song offerings of the night,<br /></span><span style="" title="">recognize the hurt caused by his own understanding of love,<br /></span><span title="">and the blood shed by voluntary as well as joy.<br /><br /></span><span title="">Wake up at dawn at dawn with a heart as light as clouds,<br /></span><span title="">grateful for a new day full of light love,<br /></span><span title="">istirah in the hot afternoon peak-peak vibration contemplate love,<br /></span><span style="" title="">home in times of dusk with full gratitude in the chest cavity,<br /></span><span title="">then fall asleep with a prayer for the beloved in the heart,<br /></span><span title="">and a song of praise smile tugging at his lips.<br /><br /></span><span style="" title="">Quotations about Love, from the book The Prophet, by Kahlil Gibran.</span></span><div id="gt-res-tools" class="g-section" style=""><div style="display: none;" class="gt-icon-c" tabindex="0" id="gt-res-listen"><span class="gt-icon gt-icon-listen-off"></span><span class="gt-icon-text">Simak</span></div><div class="gt-icon-c" tabindex="0" style="display: none;" id="gt-res-roman"><span class="gt-icon gt-icon-roman-off"></span><span class="gt-icon-text">Baca secara fonetik</span></div><br /></div></div>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0tag:blogger.com,1999:blog-32832729.post-1155735438789266102006-08-16T20:35:00.001+07:002010-10-08T00:53:39.120+07:00sage advice<span id="result_box" class="" lang="en"><span style="" title="">make time to read<br /></span><span style="" title="">because it is the source of wisdom<br /></span><span style="" title="">make time to laugh<br /></span><span style="" title="">therefore his musical soul<br /></span><span style="" title="">provide time to think<br /></span><span style="" title="">because it is fundamental progress<br /></span><span title="">make time for fun<br /></span><span style="" title="">because it makes young always<br /></span><span style="" title="">provide time for the faithful<br /></span><span style="" title="">because it is the mother of all peace and quiet</span></span>salman Shttp://www.blogger.com/profile/11111529501012666878noreply@blogger.com0