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.

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

Types of lipids Lipids with fatty acids Waxes Fats and oils (trigycerides) Phospholipids Sphingolipids Lipids without fatty acids Steroids .

Classification of Lipids 1. Simple Lipids : fatty acid with alcohol (Glycerol or other than Glycerol) If alcohol is glycerol …….Fats (triglyceride) and Oils Oils: Triglycerides rich in unsaturated fatty acids are generally liquid at room. Fats: Triglycerides rich in saturated fatty acids are generally semisolids or solids at room temperature. If alcohol other than glycerol …….. Waxes Conjugated Lipids (polar lipids): Result of hydrolysis gives FA with alcohol and containing additional[prosthetic] groups. Phospholipids: contain a phosphoric acid molecule and a fat molecule. FA + ALCOHOL + PHOSPHORIC ACID Glycolipid: contain a carbohydrate and a fat molecule. FA + ALCOHOL[SPINGOSINE] +CARBOHYDRATE WITH NITROGEN BASE Sulfolipids: contain a sulfate radical. Lipoprotein: (Lipid with prosthetic group Protein)

Chemical tests for lipids Solubility in polar and nonpolar solvent Emulsification Oxidation of unsaturated FA Qualitative analysis of detection in natural products ( salkowski reaction)

Solubility in polar and non-polar solvent (like dissolve like ) The solubility depend on polarity Reagents : Lipids: Olive oil (vegetable oil), butter (animal fat), stearic acid (saturated fatty acid), oleic acid (unsaturated fatty acid). Solvents: dilute acid and alkali solutions, acetone, cold alcohol, hot alcohol, benzene, chloroform, ether and carbon tetrachloride.

Procedure 1. Add a 2drops of the liquid fat or 0.1 g of the solid fat in labeled test tubes. 2. To each test tube add a 1 ml of solvent and write down your observations. 3. 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: A. 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: Temporary and permanently Permanently vey viscous and stable, they don’t separate. Temporary formed by shaking and they separate on standing “unstable”

Emulsification Reagents Neutral olive oil(partially oxidation, produce few fatty acids), 0.5 % Na2C03 (emulsifying agent), Rancid olive oil(complete oxidation many of free fatty acids) Prepare neutral olive oil: shaking ordinary oil with 10% solution of sodium bicarbonate this mixture should then be extracted with ether and the ether should be removed by evaporation Rancid olive oil: to prepare add 5 drops of oleic acid to 10 ml of olive oil and mix well Oliec acid يعمل على فساد الزيت

Rancidity: is the development of unpleasant smells in fats and oils, which are often accompanied by changes in their texture and appearance.

Procedure 1. 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. 2. 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. 3. 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 saturation FA unsaturated fatty acids have one or more double bonds They can undergo oxidation using an oxidizing agent.

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

Qualitative analysis of cholesterol detection in natural products salkowski 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, red color bi sulfonic acid of bicholestadien is formed

B) Bisulfonic acid of bi-cholestadiene

Salkowski reaction Reagents: Chloroform 2% pure cholesterol, extract of yellow hen egg, lecithin and 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 an extract of yellow hen egg Add carfully concentrated sulfuric acid keeping the tube under 45 angle don’t mix In the presence of cholesterol, the upper chloroform layer turns red whereas a lower acidic become yellow green

Thanks