Amino acids are the building blocks of the molecular structure of the important and very complex class of compounds known as proteins. The proteins on hydrolysis yield mixtures of the component amino acids. Therefore, to understand the structure and chemistry of proteins, we have to first undertake the study of amino acids.
Amino Acids are compounds that contain at least one carboxyl group (-COOH) and one amino group ( NH2). In α-amino acids, the amino group is located on the alpha (α) carbon (the carbon next to the carboxyl group). Their general Formula is:
Where R may be H, alkyl group, or may be quite complex containing other functional groups.
Properties of amino acids.
- Amino acids are colourless, crystalline substances having sweet taste. They melt with decomposition at high temperature.
- They are soluble in polar solvents like water and insoluble in organic solvents such as petroleum ether, ethanol and benzene.
- Excepting glycine, all α-amino acids possess an asymmetric carbon atom and are optically active.
- Their water solutions are neutral to litmus owing to the formation of their internal salt or Zwitterion.
- From Natural Proteins. Natural proteins are polymers of different amino acid units joined to each other by amide linkages. Thus proteins when boiled with dilute hydrochloric acid yield mixtures of amino acids. The mixture of amino acid is esterified and the individual esters separated by fractional distillation. They are then hydrolysed to get the free amino acids. Physical techniques such as fractional precipitation, chromatography, and electrophoresis are now widely used for the recovery of amino acids.
Amino acids give reactions characteristic of both carboxylic acids amines. α-Amino acids give the following reactions:
REACTION OF THE CARBOXYL GROUP.
(2) Reduction With LiAlH4.
It is so named because of its sweet taste (Greek, glycys = sweet).
Preparation of glycine.
Glycine may be readily obtained in the laboratory by treating chloroacetic acid with concentrated ammonium hydroxide solution.
A sample of pure glycine can also be prepared by Gabriel Phthalimide Synthesis.
Properties of glycine.
Glycine is white crystalline substance, mp 235°C with decomposition. It is very soluble in water but insoluble in ethanol and ether. Its aqueous solutions are neutral owing to the formation of Zwitterion.
It gives all the general reactions of α-amino acids already discussed.
Glycine is used:
- In medicine for certain muscular disorders.
- For the manufacture of resins and varnishes.