Vitamin B12

 Vitamin B12

Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. It is one of eight B vitamins. It is a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. It is important in the normal functioning of the nervous system via its role in the synthesis of myelin,and in the maturation of red blood cells in 

the bone marrow

Cobalt appears centrally in the periodic table, and with its neighbours, iron, manganese, 

nickel and copper, has a central rôle in a number of biochemical metalloenzyme reactions.However cobalt's vital status was not proved until after World War II, in 1948, when the 'anti-pernicious anæmia factor', which became called Vitamin B12, was finally purified and isolated as crystals by Folkers and his co-workers at Merck Laboratories, and by Smith and Parker at Glaxo 

Laboratories. Small red crystals of Vitamin B12 were then grown by Lester Smith and given to Dorothy Hodgkin for crystal structure analysis. empirical formula was C61-64H84-90N14O13-14PCo.

Vitamin B12 and Diet 

We only need minute traces of Vitamin B12 in our diet, as little as 1µ gram per day, If the 

stomach does not secrete hydrochloric acid properly, and the intestine thus not absorb the vitamin,then pernicious anæmia results.

Structural Details

Vitamin B12 Vitamin B12 is the only known biomolecule with a stable carbon-metal bond 

- it is an organometallic compound. The core of the molecule is a corrin ring with various attached sidegroups. The ring consists of 4 pyrrole subunits, joined on opposite sides by a C-CH3 methylene link, on one side by a C-H methylene link, and with the two of the pyrroles joined directly. It is thus like a porphyrin, but with one of the bridging methylene groups removed. The nitrogen of each pyrolle is coordinated to the central cobalt atom. 

The sixth ligand below the ring is a nitrogen of 5,6-dimethylbenzimidazole. The other nitrogen is linked to a five-carbon sugar, which in turn connects to a phosphate group, and thence back onto the corrin ring via one of the seven amide groups attached to the periphery of the corrin ring. 

The base ligand thus forms a 'strap' back onto the corrin ring.An important aspect of the corrin ring, when compared to the porphyrin, is the relative flexibility of the corrin system, the corrin ring is also less flat when viewed from the side than is a porphyrin ring.

 This adds up to some considerable differences between the chemistry of a cobalt porphyrin and a cobalt corrin.