Formation and selected reactions of some binuclear oxygen complexes

Abstract

Chelate formation and amide deprotonation reactions of 1:1 cobaltous complexes of glycyl-L-histidine, glycylhistamine, glycyl-L-aspartic acid, L-histidyl-L-histidine, L-histidylglycine, and L-aspartylglycine have been investigated by potentiometric equilibrium measurements and the corresponding equilibrium constants are reported. The coordinating R groups affect these equilibria not only by direct interaction with the metal, but also through an inductive effect on the acidity of the amide nitrogen. Potentiometric equilibrium measurement have also been made for a series of new pentadentate ligands composed of 1, 9-bis (4-imidazolyl)-2,5,8-triazanonane, 1, 11-bis(4-imidazolyl)-2,6,10-triazaundecane, 1, 9-bis (2-pyridyl)-2, 5,8-triazanonane, 1, 11-bis (2-pyridyl)- 2,6,10-triazaundecane, and 2,6-bis(5-(1,4-diazahexyl)) pyridine with Co²⁺, Ni²⁺, Cu²⁺,and Zn²⁺. Oxygenation equilibrium constants have been measured for the 1:1 cobaltous complexes of the dipeptides and polyamines listed above and also for the 2:1 cobalt (II) complexes of glycylglycine, glycyl-L-alanine, glycyl-L-serine, L-serylglycine, L-alanyl-L-alanine, L-alanylglycine and glycyl-L-tyrosine. The cobalt systems of the polyamine pentacoordinate ligands listed above have been investigated electrochemically. The oxidation potentials of the cobaltous chelates and the reduction potentials of the dioxygen complexes have been measured polarographically, and both potentials show a strong positive correlation with the logarithm of the oxygenation equilibrium constant. Oxidation potentials of the dioxygen complexes have been measured by cyclic voltammetry..