Coenzyme B12 model studies: Equilibrium constants for the pH-dependent axial ligation of benzyl(aquo)cobaloxime by various N- and S-donor ligands

Abstract

Equilibria of the axial ligation of benzyl(aquo)cobaloximes by imidazole, 1-methyl imidazole, histidine, histamine, glycine, ethyl glycine ester, thiourea and urea have been spectrophotometrically measured in aqueous solutions of ionic strength 1⋅0 M (KCl) at 25°C as a function of pH. The equilibrium constants are in the order CN-> 1-methyl imidazole > imidazole > histidine > histamine > glycine > ethyl glycine ester > thiourea > urea. The order of stability of benzyl(ligand)cobaloxime is explained based on the basicity of the ligand, Co(III) → L dπ-pπ back bonding and soft-soft and soft-hard interaction. Imidazole, substituted imidazoles, histidine and histamine form more stable complexes than glycine, ethyl glycine ester in contrast to the basicity of the ligands. Benzyl(ligand)cobaloximes were isolated and characterized by elemental analysis, IR and 1 H NMR spectra.

The Synthesis of Diaminoanthraquinone Coloured Cross Linked Epoxy Resins and Their Application in Paint and Selected Polymers

“…All the compounds indicated -NH absorption bands at 2500 -3600 cm −1 and absorptions around 1630 -1680 cm −1 could be attributed to -C=N bonds [25] which could indicate some sought of tautomerism with the transfer of a proton from the NH group to the carbonyl oxygen on the anthraquinone. The 1630 -1680 cm −1 could also be attributed to intra-molecular hydrogen bonds [26].…”

Equilibria and kinetics for pH-dependent axial ligation of bromomethyl(aquo)cobaloxime by aliphatic amine ligands

“…[15][16][17] Recently, the equilibria and kinetics of axial ligation of alkyl(aquo)cobal-*For correspondence oximes with imidazole and substituted imidazoles were studied. [18][19][20][21] Compared to both cobalamins and other model systems, cobaloximes have stronger Co-C bonds 22 and shorter Co-L (L = pyridine, substituted pyridines) bonds. 13 Many model complexes [23][24][25][26][27][28] have shown that the ligand in the trans position to the Co-C bond can affect the kinetics and thermodynamic stability of the bond.…”

Kinetics and equilibria for the axial ligation of bromomethyl (aqua)cobaloxime with pyridines — Isolation characterization and DNA binding

“…Since binding of cobaloximes is closely related to the structural and binding characteristics of corrin systems involved in biological mechanisms and in continuation of our work, [10][11][12][13] we report here the isolation of bromomethyl(ligand) cobaloximes, equilibria and kinetics of the axial ligation of the bromomethyl(aqua) cobaloximes with pyridine and substituted pyridines. We have also investigated the interaction of bromomethyl cobaloxime with CT DNA.…”