Chemistry 305 Lab 7 Isolation of Phosphatidyl Choline Due at the beginning of th

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Chemistry 305 Lab 7 Isolation of Phosphatidyl Choline Due at the beginning of this lab period Name ent, phosphatidyl choline will be extracted from animal cells, specifically [SiO (H2O)n] In this experime from chicken egg yolks. Duri ng the separation procedure, column chromatography using alumina (A1:O) as the stationary phase and thin-layer chromatography (TLC) using silica gel as the stationary phase will be employed. Alumina is a nonstoichiometric compound. Normally, some of the lattice sites are pied by hydroxide ions (OH), making the alumina quite alkaline - an aqueous slurry is typicail about pH 10. (Al+ is a strong Lewis acid.) Alumina is also commercially available as ac washed" products, either with aqueous slurry pH of about 7 or about 4. Alumina is acid- also available in a variety of mesh sizes, with a typical separation grade chromatographic product having a mesh size of about 200. Another variable is the moisture content of the alumina the higher the moisture content, the less the chromatographic activity of the material. Choosing the correct "alumina" for a specific chromatographic separation is a matter of some theoretical knowledge, some experience and some luck! Silica gel, thinly coated on either a metal sheet, glass plate, or flexible plastic plate, is a reliable adsorbant medium for a variety of substances. The particle size is typically very small 300 mesh or greater); thus, separations can be quite good, even with small distances of travel, small sample sizes, and small amounts of adsorbant present. Silica gel plates are typically "acti- vated" before use by heating at 100°C for a few minutes to drive off surface moisture from the particles. The experimental procedure can be briefly summarized as follows Egg yolks are first extracted with cold acetone to remove lipids less polar than phospho- lipids and most pigment molecules. The residue remaining after acetone treatment is then with CHCl/CH,OH (1:1) solvent to dissolve the polar phospholipids. The extract containing the these phospholipids (the "crude" phosphatidyl choline) is then passed through a chromatography column of alumina to separate PC from monoacyl phosphatidyl choline and other phosphoglycer- ides. Solvents of different polarity are used to elute fractions of the crude PC from the column. The fractions from the alumina chromatography are silica gel plates, and the fraction containing the most PC is evaporated to recover purified PC. Purified PC is hydrolyzed by phospholipase Az, releasing the fatty acids. The fatty acids are extracted into hexane and recovered by evaporation. Note: In the experimental procedure which follows, procedural notes are given frequently following this format. You should read each of these notes carefully before actually doing the procedure Note: A flow chart summary of the experimental procedure is provided on a separate page so that you can more easily keep track of the steps in this procedure.

Explanation / Answer

In alumina chromatography, alumina is a polar adsorbent. It is used for separation of weakly or moderately polar components from more polar components. The more polar components are elute at last from the collumn.

In this experiment, the monoacyl phosphatidyl choline is the polar head group while PC is the less polar component. THe non polar component is due to hydrocarbon chain while the polar component has positively charged Nitrogen, presence of Phosphorous and negatively charged oxygen.

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