II. CHEMISTRY 



411 



(II.O)' 



Co+++ 

 



+ X- 



— — X- 



Co+++ 

 



+ 11=0 



Other modilications of \'itainiii B12 are readily prepared by treatment of 

 hydroxocobalamin with the desired reagent as, for example, hydrochloric 

 acid to form chlorocobalamin, and hydrobromic acid to give bromocobala- 



min.'' 



The photochemical reaction which liberates CN" from the cyanocobala- 

 min complex has been described as one reaction which leads to the forma- 

 tion of hydroxocobalamin,''^ and it is claimed that irradiation in the 3G5-m/x 

 range is specific for this photochemical conversion. An excellent method 

 has been developed for the (luantitative determination of cyanocobalamin 

 based on the measurement of CN~ liberated by the use of visible light. ^^ 

 It was found that irradiation of solutions of cyanocobalamin with visible 

 light from an electric bulb catalyzed the liberation of hydrogen cyanide 

 which could be swept out by a stream of nitrogen and determined colori- 

 metrically. The reaction is reversible, and addition of cyanide ions forms 

 first an unstable purple complex involving two additional cyanide ions; 

 when the solution is acidified or the excess cyanide ion is otherwise removed, 

 cyanocobalamin results.^^' *'-• ^^ 



An extended study of the ultraviolet absorption spectrum of vitamin B12 

 and also of the spectral contribution of the benzimidazole moiety has led 

 to certain suggestions as to the spatial arrangement of the benzimidazole 

 nucleus in the cobalt complex. ^^ These spectroscopic data, which bear only 

 upon the coordination features, have led to the proposed formulation (X); 



CH2OH 



Nr^CHj 



P^COH) 5h \UcH 



(Propanolamine?) 



"G. E. Boxer and J. C. Rickards, Arch. Biochem. 30, 372, 382, 392 (1951). 

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

 Pharmacol. 2, 733, 944 (1950). 



