410 



VITAMIN Bi2 



Bi2, has been isolated. ^^ An unidentified organism isolated from bovine 

 rumen contents when grown under anaerobic conditions has been found to 

 produce a mixture of cobalt-containing pigments belonging to the vitamin 

 Bi2 group. ^^ From this mixture, two compounds have been isolated in crys- 

 talline form. Their microbiological growth activity, measured by L. lei- 

 chmannii and L. lactis Dorner, is about the same as that of vitamin B12. 

 In the chick and the rat, however, they are inactive. One of these, pseudo- 

 vitamin B12, appears to differ from vitamin B12 in containing adenine in- 

 stead of 5 , 6-dimethylbenzimidazole in the nucleotide part of the molecule. ^^ 

 Acid hydrolysis of pseudovitamin B12 produced Dg-l-amino-2-propanol, 

 phosphate, ammonia, adenine, and hypoxanthine. The hypoxanthine ap- 

 parently results from hydrolytic deamination of adenine. 



Various ideas as to the more exact structure of the cobalt coordination 

 complex in vitamin B12 have been expressed as a result of structure work 

 thus far completed. A generalized expression for the vitamin B12 molecule 

 as a cyanocobalt coordination complex has been represented as follows:'*^ 



R 



Co^ 



CN- 







The cyano group contributes one negative charge and satisfies one coordi- 

 nation position; the two minus signs and the ciphers represent another group 

 or groups which furnish two negative charges and three electron pairs, re- 

 spectively, to satisfy the remaining five coordination bonds. In the case of 

 hydroxocobalamin, the following equilibrium has been suggested to exist: 



R 



Co^ 



OH- 







H2O 



R 



Co^ 







HoO 



OH- 



The vitamin Bi2-Bi2a eciuilibrium has been represented by the equation 

 below : 



(H^O)" 



Co+++ 

 



+ CN- 



CN^ 



Co+++ 

 



+ H20 



Polarographic examination of this equilibrium failed to demonstrate de- 

 tectable amounts of cyanide ion, which indicates that the equilibrium con- 

 stant K must be very large. ^° 



In more general form the equilibrium becomes: 



" J. J. Pfiffner, D. G. Calkins, R. C. Peterson, O. D. Bird, V. McGlohon, and R. W. 

 Stipek. Ahstr. 120th Meeting Am. Chem. Soc. p. 22C (1951); H. W. Dion, D. G. 

 Calkins, and J. J. Pfiffner, /. Am. Chem. Soc. 74, 1108 (1952). 



