Lipids

Lipids Definition: Lipids: are a group of naturally occurring substances consisting of the higher fatty acids, their naturally occurring compounds and substances with different structures. Organic substances relatively insoluble in water but soluble in organic solvents like: chloroform, ether and benzene (like dissolve like).

Functions of lipids Storage form of energy. Structural component of cell membrane. Precursor of many steroid hormones as: estrogen, vitamin D. Protection of internal organs.

Types of lipids Lipids with fatty acids: Waxes. Fats and oils (tri-glycerides). Phospholipids. Sphingolipids. Lipids without fatty acids: Steroids.

Classification of Lipids Simple Lipids: fatty acids with alcohol (glycerol or alcohol other than glycerol) attached to each other by ester bonds. If alcohol is glycerol Fats and Oils. Oils: Triglycerides rich in unsaturated fatty acids are generally liquid at room temperature. Fats: Triglycerides rich in saturated fatty acids are generally semisolids or solids at room temperature. If alcohol is other than glycerol Waxes.

Fatty acid + Alcohol + Phosphoric acid. Conjugated Lipids (polar lipids): if hydrolysis: gives fatty acids with alcohol and containing additional [prosthetic] groups. Phospholipids : contain a phosphoric acid molecule and a fat molecule. Fatty acid + Alcohol + Phosphoric acid. Glycolipid : contain a carbohydrate and a fat molecule. Fatty acid + Alcohol + Carbohydrate. Sulfolipids : contain a sulfate radical and a fat molecule. Fatty acid + Alcohol + sulfate. Lipoprotein : contain a Protein and a fat molecule. Fatty acid + Alcohol + protein.

Qualitative chemical tests for lipids Solubility in polar and non-polar solvent. Emulsification test. Oxidation of unsaturated fatty acids. Qualitative analysis of detection in natural products (salkawski reaction).

Solubility in polar and non-polar solvent ( like dissolve like ) Note : the solubility depend on polarity. Reagents : Lipids: Olive oil (vegetable oil) and butter (animal fat). Solvents: (Ethanol, Chloroform, Ether and Water).

Procedure Add a 2 drops of the liquid fat or 0.1 g of the solid fat in labeled test tubes. To each test tube add a 1 ml of solvent and write down your observations. Repeat the experiment with a different solvent and make your observations.

Emulsification An emulsion: is a mixture of two or more liquids that are normally immiscible (not mixable). Bile Salts: synthesized from cholesterol and stored in the gallbladder. when you eat fat, the bile salts act as soap and help emulsify the large globules of fat.

Emulsification types: Two immiscible liquids, not yet emulsified. B. An emulsion of Phase II dispersed in Phase I. C. The unstable emulsion progressively separates. D. The surfactant (outline around particles) positions itself on the interfaces between Phase II and Phase I, stabilizing the emulsion. Emulsification types: Permanently : very viscous and stable, they don’t separate. Temporary: formed by shaking the tubes, and they separate on standing “unstable”.

Emulsification Reagents : 0.5 % Na2C03. Neutral olive oil: (partially oxidation), produce few of free fatty acids. Rancid olive oil: (complete oxidation), produce many of free fatty acids. Rancidity : is the development of unpleasant smells in fats and oils, which are often accompanied by changes in their texture and appearance. Oliec acid يعمل على فساد الزيت

Procedure Shake up a drop of neutral olive oil with a little water in a test tube, the fat becomes finally divided forming an emulsion, upon standing fat separates and rises to the top. To 5 ml water in a test tube add 2 to 3 drops of 0.5 % Na2CO3. Introduce a drop of neutral olive oil and shake, the emulsion is not permanent and is not so transitory. Repeat step 2 using rancid olive oil. In this case the alkali combines with the free fatty acids to form soap and the soap being an emulsifying agent, it emulsifies the fat.

Oxidation of un saturated Fatty Acids Unsaturated fatty acids have one or more double bonds. Oleic acid is unsaturated fatty acid. Stearic acid is saturated fatty acid. They can undergo oxidation using an oxidizing agent as KMnO4.

procedure Into test tube place one drop of oleic oil and 3 ml of Na2CO3. Add the solution of KMnO4 (oxidizing agent), After each drop of KMnO4 the violet color disappear. The end of the reaction recognized by brown ppt. (solid MnO2)

Qualitative analysis of cholesterol detection in natural products (salkawski reaction) Concentrated sulfuric acid is highly hygroscopic, and it removes two molecules of water from two molecules of cholesterol. It causes a connection at position (3) forming bi-cholestadien . Simulatineously ,the sulfuric acid sulfonates the molecule of bi-cholestadien at position (7,7) of aromatic ring and as a final product bi-sulfonic acid of bi-cholestadien is formed (red color).

B) Bi-sulfonic acid of bi-cholestadien

Salkawski reaction Reagents: Chloroform. 2% pure cholesterol and olive oil. Chloroform. (Inhalation of high concentrations may cause central nervous system effects characterized by nausea, headache, dizziness, unconsciousness and coma). Conc. sulfuric acid.

Procedure Into the dry test tubes (the reaction is very sensitive for even traces of water) add 1ml of chloroform solution of 2% of pure cholestrol. Add carefully concentrated sulfuric acid keeping the tube under 45 angle don’t mix. In the presence of cholesterol, the upper chloroform layer turns red.

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