Abstract: Vitamin B 12 model molecule, dicyano cobyric mono acid hexamethylester 2f was synthesized from Vitamin B 12 by alcoholysis and acidic hydrolysis. Dicyano-a,b,c,d,e,g-α-f-N-(3-imidazoly) propylamido cobyrinate 3f was synthesized by the reaction between 2f and 3-imidazolylpropylamine hydrochloride. Compound 3f was treated with trifluoroacetic acid to give dimer-vitamin B 12 model molecule 5f. Compound 5f was treated with acidic buffers in methanol and the ring of 5f was opened to give compounds 6f. UV-Vis spectra were determined in buffers with different pH values. The equilibrium constants of Co-N bonds were calculated. K-value of 5f was 552×10³, which is much greater than that of monomer vitamin B₁₂ 4f. The strength of coordination bonds between the N atom in the side chain of cobyrinate and the Co atom in 5f was much weaker than that in monomer-vitamin B₁₂ 4f.

Key words: Vitamin B 12, Dimer Model molecule, UV-Vis spectrum, Equilibrium constants