PRACTICAL I: Physical Properties of biomolecules.
In this practical the polarity, solubility in water, of different biomolecules was tested. A 1% solution of each compound was prepared and their solubility was tested in ; heptane, acetone, and distilled water. Compounds were classified as soluble, insoluble or partially soluble in each of the solvent solutions. The following table of results was obtained;
It can be observed that cholesterol, which is a lipid, is partially soluble in water. By looking at its molecular structure it could be assumed that it is hydrophobic, however is an amphiphilic compound possessing both hydrophilic and lipophilic properties. This explains the way cholesterol is transported in the blood stream within lipoproteins which are molecules with a water soluble outward face and a lipid soluble inward face. Cholesterol resulted to be insoluble in heptane, this is due again to the amphiphilic nature of the cholesterol molecule, heptane is a long chain of hydrocarbons whereas acetone a carbonyl group with a negatively charged oxygen and a short chain of hydrocarbons, this makes it a more suitable substance to act as a dissolvent for an amphiphilic compound. On the other hand it can be seen in the table of results that cholesterol ester is insoluble in water, but still soluble in acetone. However, it could be supposed by looking at its structure that it is partially soluble in water like cholesterol because of the presence of an extra hydroxyl group, and amide group and a sulfonyl group.
Palmitic acid and taurodeoxycholic acid are also amphiphilic both having a long chain of hydrocarbons and a hydrophilic tail.
Valproic acid, D+Glucose and caffeine are clearly hydrophilic. Leo-Trp dipeptide is soluble in water because proteins have all their polar groups to the outside being thus able to form hydrogen bonds with water.
Finally, the dye mix is clearly hydrophobic being soluble only in the organic compounds.
Overall the more polar groups a molecule has the more soluble it is, and the more non polar the less soluble it is. It is the overall ratio of polar to unpolar groups which is determinant of solubility.
Very nice summary of results with the table and good concluding lines on the principles of the ID.
ReplyDeleteI have a few comments re. the cholesterol story - cholesterol is generally considered to be insoluble in water, as the small hydrophilic OH group cannot overcome the overall non-polar nature of the other 27 carbons. That said, when cholesterol is leaving a cell and moving to a e.g. a lipoprotein, it does appear to move through the water in between them. However, the reason that it goes from one to the other is that its not favourable for it to be present in the water; hydrophobic compunds prefer the company of other hydrophobic compounds. With regards to t5he cholesteryl ester I think you may have mixed up the structures - CE is much *less* soluble than cholesterol as the OH group 'disappears' when the cholesterol is esterified to a fatty acid (check out the structure of an ester bond).
Lastly the dye mixture was just that - a mix of a water soluble blue dye and a lipid soluble red dye. When you add the different solvents it changes colour as only one compound at a time is dissolving in the solvent.
/Steve
Kindly upload about the lipid estimation by zlatkis method and DPA and orcinol for DNA and RNA respectively.
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