LIPIDS

The Lipids are a large and Diverse group of naturally occuring compounds that are related by their solubility in non-polar organic solvents(e.g; Ether, Choloform, acetone & benzene) and General Insolubility in water.

Lipids include Fats, waxes, Sterols, Fat-soluble Vitamins (Such as  Vitamin-A,D,E and K), monoglycerides, diglycerides, triglycerides, Phospholipids, and others. The main  biological functions of lipids includeenergy storage,signalling and acting as structural components of cell membranes. 

Lipids have found applications in cosmetics and food industries as well as in nanotechnology.

Fats, Oils, Waxes & Phospholipids

1. Fatty Acids

The common features of these lipids is that they are all esters of moderate to long chain fatty acids. Acid  or base-catalysed hydrolysis yields the component fatty acid, some examples of which are given in the following table, together with the alcohol components of the lipid. These long-chain carboxylic acids are generally referred to by their common names, which in most cases reflect their sources.

Natural Fatty Acids may be saturated or unsaturated and as following data indicate, the saturated acids have higher melting points than unsaturated acids or corresponding size. The double bonds in the unsaturated compounds listed on the right are all cis(or Z).

The higher melting points of the saturated fatty acids reflect the uniform rod-like shape of their molecules. the Cis-double bond(s) in the unsaturated fatty Acids introduce a kink in their Shape, which makes it more difficult to pack their molecules together in a stable repeating array or crystalline lattice.

The Trans-double bond isomer of oleic acid known as Elaidic Acid, has a linear shape and a melting point of 45°C(32 ° higher than its cis isomer)
Two polyunsaturated fatty acids, linoleic and linolenic, are designed " essential" because their absence in the human diet has been associated with health issues, such as scaly skin, stunted growth and increased dehydration.
These acids are also precursors to the prostagladins, a family of physiologically potent lipids present in minute amounts in most body tissues.
Because of their enhanced acidity, Carboxylic acids react with base to form ionic salts, as shown in the following equations. In the case of alkali metal hydroxides and simple amines(or ammonia) the resulting salts have pronounced ionic character and are usually soluble in water.

Heavy metals such as silver, mercury, and lead form salts having more covalent character (3rd example), and the water solubility is reduced, especially for acids composed of four or more carbon atoms.

RCO2H + NaHCO3 ----------> RCO2(-) Na(+) + CO2 + H2O

RCO2H + (CH3)3N: ----------> RCO2(-) (CH3)3NH(+)

RCO2H + AgOH      -----------> RCO2δ(-)Ag(+) + H2O