II. CHEMISTRY 409 



from the fact that differentiation was based on preHminary tests of biologi- 

 cal activities rather than the more exact classical chemical and physical 

 comparisons. When samples wci'e compared by these latter methods, it 

 became evident that the designations \dtamins Bi2a and Bi2b were two names 

 for the same substance (see Fig. 4). Other forms of the vitamin Bi2 group 

 from isolation programs, vitamins Bi2c and Bi2d (later retracted^^), have 

 been described,'^ and in the light of present knowledge many more forms 

 maj'- exist. Fortunately, the early complexity of the forms has been greatly 

 simplified by a better understanding of the nature of the cobalt complex in 

 this group of compounds. 



Vitamin B12 is a cyanocobalt coordination complex in which the coordina- 

 tively bound cyano group is replaceable by other ions^^-^^ or molecules. 

 The number of \dtamin B12 modifications possible is then limited only by 

 the number of ions or molecules which can replace cyanide in the cobalt 

 coordination complex. Treatment of vitamin B12 with hydrochloric acid 

 or aqueous oxalic acid liberates hj^drogen cyanide whereas sulfuric acid 

 fails to bring about its formation. This is evidently due to the greater co- 

 ordination tendency of chloride and oxalate ions as compared to sulfate. 

 In the foiTuation of vitamin Bi2a (B^b) the cyanide ion is evidently liberated 

 and replaced by a hydroxo group; in confirmation, it has been found that 

 vitamin Bi2a in aqueous solution has a pH of about 9 and behaves on titra- 

 tion as a weak base.'*^ Further proof of the correctness of this interpretation 

 is the fact that treatment of vitamin Bi2a (Bi2b) with cyanide ions brought 

 about its conversion to vitamin Bio.*"*- ^^'^^ On the basis of the evident nature 

 of the cobalt complex in vitamin Bi2, a system of nomenclature has been 

 devised which can be applied to the modifications of vitamin Bi2.^® Under 

 this system, the name cohalamin designates all the vitamin Bi2 molecule 

 except the cyano group. Vitamin B]2 is then cyanocobalamin, vitamin Bi2a 

 (Bi2b) is hydroxocobalamin, and vitamin Bi2c is nitritocobalamin.^^ Other 

 modifications can be readily designated by this system. Chloro-, bromo-, 

 sulfato-, cyanato- thiocyanato-, and nitrocobalamin have been de- 

 scribed.'*^- ^^' ^^ A sulfur-containing cobalamin of unknown group identity 

 results from the reaction of cyanocobalamin with hydrogen sulfide.^®- ^^ 



Another naturally occurring modification of vitamin Bi2, pseudovitamin 



« N. G. Brink, F. A. Kuehl, and K. Folkers, Science 112, 354 (1950). 



" E. A. Kaczka, D. E. Wolf, F. A. Kuehl, and K. Folkers, Science 112, 354 (1950). 



" B. Ellis, V. Petrow, G. H. Beaven, E. R. Holiday, and E. A. Johnson, J. Pharm. 



Pharmacol. 2, 735 (1950). 

 " W. L. C. Veer, J. 11. Edelhausen, H. G. Wijmenga, and J. Lens, Biochim. et Bio- 



phys. Acta 6, 225 (1950). 

 " E. A. Kaczka, D. E. Wolf, F. A. Kuehl, and K. Folkers, J. Am. Chem. Soc. 73, 3569 



(1951). 

 "> R. P. Buhs, E. G. Newstead, and N. R. Trenner, Science 113, 625 (1951). 



