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

Abstract

The kinetics and equilibria for the axial ligation of pyridine and substituted pyridines to bromomethyl(aqua)cobaloxime have been measured spectrophotometrically in aqueous solutions of ionic strength l⋅0 M (KC1) at 25°C as a function of pH. The binding constants and rate of formation increase in the order 4-NH 2 Py > 4-EtPy > 4-MePy > Py > 2-NH 2 Py > 2-EtPy. The data have been interpreted based on the basicity of the ligand, π-back bonding from Co(III) → L and hard and soft interactions. The rate of substitution of H 2 O varies with the pKa of the incoming ligand, thus establishing the existence of nucleophilic participation of the ligand in the transition state. We have investigated the DNA binding of bromomethyl(aqua)cobaloxime with DNA. Bromomethyl(ligand)cobaloximes were isolated and characterized by elemental analysis, IR and NMR (1 H, 13 C) spectra.