B12 vitamin

Cobalt compounds have been in use for centuries, notably as pigments ( cobalt blue ) in glass and porcelain (a double silicate of cobalt and potassium) the metal itself has been produced on an industrial scale only during the twentieth century. Cobalt is relatively uncommon but widely distributed it occurs biologically in vitamin B12 (a complex of cobalt(III) in which the cobalt is bonded octahedrally to nitrogen atoms and the carbon atom of a CN group). In its ores, it is usually in combination with sulphur or arsenic, and other metals, notably copper and silver, are often present. Extraction is carried out by a process essentially similar to that used for iron, but is complicate because of the need to remove arsenic and other metals. 

Firefly lucifenn is an example of an azole that contains a benzene ring fused to the five membered ring Such structures are fairly common Another example is benzimidazole present as a structural unit m vitamin B12 Some compounds related to benzimidazole include purine and its ammo substituted derivative adenine one of the so called het erocychc bases found m DNA and RNA (Chapter 28)... 

Naturally occurring compounds with carbon-metal bonds are very rare The best example of such an organometallic compound is coenzyme Bi2 which has a carbon-cobalt ct bond (Figure 14 4) Pernicious anemia results from a coenzyme B12 deficiency and can be treated by adding sources of cobalt to the diet One source of cobalt IS vitamin B12 a compound structurally related to but not identical with coen zyme B12... 

The vitamin B12 content of a multivitamin tablet is determined by dissolving ten tablets in water. The dissolved tablets are transferred to a 100-mL volumetric flask and diluted to volume. A 50.00-mL portion is removed and treated with 0.500 mg of radioactive vitamin B12 having an activity of 572 cpm. After homogenization, the vitamin B12 in the sample is isolated and purified, producing 18.6 mg with an activity of 361 cpm. Calculate the average concentration of vitamin B12 in the tablet (in milligrams per tablet). 

Equations 1-10 illustrate some mild methods that can be used to cleave amides. Equations 1 and 2 indicate the conditions that were used by Woodward and Eschenmoser, respectively, in their synthesis of vitamin B12. Butyl nitrite, nitrosyl chloride, and nitrosonium tetrafluoroborate (NO BF4 ) have also been used to cleave amides. Since only tertiary amides are cleaved by potassium -butoxide (eq. 3), this method can be used to effect selective cleavage of tertiary amides in the presence of primary or secondary amides.(Esters, however, are cleaved by similar conditions.) Photolytic cleavage of nitro amides (eq. 4) is discussed in a review. 

The structure of the diamagnetic, cherry-red vitamin B12 is shown in Fig. 26.6 and it can be seen that the coordination sphere of the cobalt has many similarities with that of iron in haem (see Fig. 25.7). In both cases the metal is coordinated to 4 nitrogen atoms of an unsaturated macrocycle (in this case part of a corrin ring which is less symmetrical and not so unsaturated as the porphyrin in haem) with an imidazole nitrogen in the fifth position. A major... 

Figure 26.6 Vitamin B12 (a) a corrin ring showing a square-planar set of N atoms and a replaceable H, and (b) simplified stmcture of B12. In view of the H displaced from the corrin ring, the Co-C bond, and the charge on the ribose phosphate, the cobalt is formally in the - -3 oxidation state. This and related molecules are conveniently represented as r...

Hydroxy- and 8-nitro-4-chloroquinazolines have been incorporated into the nucleotide of vitamin B12. These quinazoline-containing vitamin analogs stimulated the growth of cobalamine requiring cultures. ... 

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