CHEMISTRY OF LIPIDS

LIPID CHEMISTRY

Definition Classification

Biological importance

Organic substances relatively insoluble in water but soluble in organic solvents

like chloroform, ether and benzene

LIPID CHEMISTRY

Definition

• Fats and Oils (triglyceride) • Waxes• Steroids• Fat- soluble vitamins• Phospholipid• Mono- di glycerides

Lipid compounds including:

CLASSIFICATION OF LIPIDS

Simple lipid

Complex lipid

Derived lipids

SIMPLE LIPIDS

They are esters of FA with various alcohols

The type of alcohols these are subclassified as

Neutral fats or oils

Alcohol is GLYCEROL

Waxes

Alcohol is other than

glycerol

NEUTRAL FATS OR OILS

Fats and oils are

also called triglycerides.

esters of glycerol+ 3 FA

WAXES

EXAMPLES Beeswa

x

When hydrolysis of waxes gives : one fatty acid + alcohol

Result of hydrolysis gives FA with alcohol and containing additional[prosthetic] groups.

Subclassified according to the type of prosthetic group

Phospholipids Glycolipids Lipoproteins

COMPLEX LIPIDS

FA + ALCOHOL + PHOSPHORIC ACID

PHOSPHOLIPIDS

They frequently

have nitrogen

containing bases

Phospholipids may be classified on the basis of the type of alcohol present

PHOSPHOLIPIDS

A. Glycerophospholipids B. Spingophospholipids

ALCOHOL IS GLYCEROL ALCOHOL IS SPINGOSINE

Examples PlasmalogensCardiolipins

ExamplesSpingomyelins

FA + ALCOHOL[SPINGOSINE] +CARBOHYDRATE WITH NITROGEN BASE

They do not contain phosphate group

Example Cerebrosides Gangliosides

GLYCOLIPIDS

Chylomicrons Very low density lipoprotein (VLDL)Low density lipoprotein (LDL)High density lipoprotein (HDL)

LIPOPROTEINS

Lipid with prosthetic group PROTEIN

Derived from lipids (simple or complex)or precursors of lipids

Example

Fatty acids Steroids Cholesterol Vitamin A and D

DERIVED LIPIDS

FUNCTIONS OF LIPIDS

Storage form of energy

Structural component of

cell membrane.

Precursor of many steroid hormones, vitamin D

Protection of internal organs

Fatty acids are

long-chain carboxylic acids.

typically 12-18 carbon atoms.

insoluble in water.

saturated or unsaturated.

Fatty acids aresaturated with all single C–C bonds.

unsaturated with one or more double C=C bonds.

are solids at room temperature

are liquids at room temperature.

1. Solubility in polar and nonpolar solvent2. Emulsification 3. Oxidation of unsaturation FA4. Qualitative analysis of detection in natural products ( salkowski reaction)

Chemical tests for:

Precursor of many steroid hormones, vitamin D

1. Solubility in polar and nonpolar solvent• Reagents • Olive oil (vegetable oil), butter (animal fat), • stearic acid (saturated fatty acid), oleic acid (unsaturated fatty acid), • Solvents: dilute acid and alkali solutions, cold alcohol, hot alcohol,

benzene, chloroform, ether and carbon tetrachloride.

Procedure1. 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.

Reagents

• Neutral olive oil, 0.5 % Na2C03, Rancid olive oil

Procedure1. 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 percent 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.

2- Emulsification

• An emulsion is a mixture of two or more liquids that are normally immiscible (no 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.

2- Emulsification

A. Two immiscible liquids, not yet emulsifiedB. An emulsion of Phase II dispersed in Phase IC. The unstable emulsion progressively separatesD. The surfactant stabilizing the emulsion

• Into test tube place one drop of oil and 3 ml of Na2CO3

• Warm it slightly and drop solution KMnO4 .after each drop the violet color

disappear

• The end of the reaction recognized by ppt brown solid MnO2

1. Oxidation of unsaturation FA

4-Qualitative analysis of detection in natural products ( salkowski reaction)

27

R C OH

O

Carboxylic Acid Alcohol Ester

R OH R C O R

O