Abstract
Hydrophobic cobyrinic acid heptamethyl ester corrinoids XCbs–Me (axial ligand X = CN−, , and vinyl) have been prepared from vitamin B12 by hydrolysis of the seven-amide chain and conversion to methyl ester. The solvents affect both the Soret band and the shape of the UV-Vis spectra of the hydrophobic corrinoids. The equilibrium constant, K, for the reactions of XCbs–Me (X = CN−, , and vinyl) with pyrazole (Pz) and imidazole (ImH) have been determined spectrophotometrically at 25°C. Value of K for Pz was less than that obtained for ImH in all the solvents used in the present study. The values of K increase as the solvent polarity increases, water > methanol > DMSO > DMF. The values of K for the two azoles decreases in the order X = CN− > > vinyl. This shows that the ligands coordinated at the trans position in the substitution site have a significant effect on the value of K.
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