Molecular test tube

Place a mixture of 0-5 g. of finely powdered thiourea, 0-5 g. of the alkyl halide and 5 ml. of alcohol in a test-tube or small flask equipped with a reflux condenser. Reflux the mixture for a j)eriod depending upon the nature of the halide primary alkyl bromides and iodides, 10-20 minutes (according to the molecular weight) secondary alkyl bromides or iodides, 2-3 hours alkyl chlorides, 3-5 hours polymethy lene dibromides or di-iodides, 20-50 minutes. Then add 0 5 g. of picric acid, boil until a clear solution is obtained, and cool. If no precipitate is obtained, add a few drops of water. RecrystaUise the resulting S-alkyl-iso-thiuronium picrate from alcohol. 

Reflux gently in a test-tube under a short air condenser 1 g. of the base with 2 5 mols or 3 0 g. (3 0 ml.) if the molecular weight is unknown of redistilled acetic anhydride for 10-15 minutes. Cool the reaction mixture and pour it into 20 ml. of cold water (CAUl ION). Boil to decompose the excess of acetic anhydride. When cold, filter the residual insoluble acetyl derivative and wash it with a little cold water. Recrystal-/ise from water or from dilute alcohol. 

Use a thermometer and collect the distillate in a test-tube. Note the boiling-point, and observe if it fluctuates oi remains constant and if any solid residue remains. A low boiling - point generally denotes a low molecular weight. A portion distilling in the neighboui-hood of ioo may indicate the presence of water. 

While this may in fact be the case for natural product mixtures, it is rarely the case when dealing with synthesized mixtures. Despite our attempts to create real molecular diversity in the test tube, our efforts have not even begun to anticipate the true diversity of atomic connectivity within "drug space" (estimated to be of the order of 1063 unique compounds, theory, famously in this case, greatly outpacing the amount of matter in the universe). Thus, combinatorial chemistry was never practically able to produce true chemical diversity and compounds produced in such library format ended up looking very much like one another, with the attendant similarities in biological activity profiles. 

As the field of molecular genetics grew, the DNA molecule became the focus of many research efforts. Francis Crick and George Gamov developed the sequence hypothesis to explain how DNA makes protein. They stated that the DNA sequence specifies the amino acid sequence of a protein and postulated the central dogma of molecular genetics the flow of genetic information is a one-way road, it always takes the direction from DNA to RNA to protein [16]. In the same year, 1957, Mathew Meselson and Frank Stahl demonstrated the replication mechanism of DNA [17]. In 1958, DNA polymerase became the first enzyme used to make DNA in a test tube. 

A technique that has revolutionized the field of molecular biology during the last decade is the polymerase chain reaction (PCR). This method, conceived by Kary B. Mullis (1944—) in 1983, involves making multiple copies of fragments of DNA in a short time. Mullis received the 1993 Nobel Prize in chemistry for his work. PCR mimics DNA s natural ability to replicate itself It involves three basic steps conducted at different temperatures. In the first step, a mixture of DNA and other basic PCR ingredients is heated in a test tube to approximately 90°C. At this temperature, the DNA strands unwind. The second step involves lowering the temperature to around 55°C, which allows special enzymes called... 

Reaction of a Metal with Water. 1. Fill a test tube with water up to its edges. Close its mouth with your thumb, invert it in a bath with water and fasten it in this position in the clamp of a stand. Wrap up several pieces of metallic calcium in cheese-cloth and rapidly place the metal under the tube with pincers. Determine what gas is evolved. Write the molecular and electron equations of the reaction. 

Pour 5 ml of a 1 W hydrochloric acid solution into a test tube and throw a small piece of zinc into it. When the evolution of hydrogen becomes quite vigorous, add 1-2 g of sodium acetate. Explain the change in the rate of hydrogen evolution. Write the molecular and net ionic equations of the chemical reaction of hydrochloric acid with sodium acetate. Does the activity of acetic acid decrease when dry sodium acetate is added to its solution ... 

Precipitation of Sparingly Soluble Salts. Pom 2-3 ml of barium chloride, strontium chloride, and calcium chloride solutions into three test tubes. Add a sodium sulphate solution to the first tube, a saturated calcium sulphate solution to the second one, and a saturated strontium sulphate solution to the third one. Write the equations of the chemical reactions in the molecular and net ionic forms. 

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