KINETICS OF COPPER(2)-GLYCINE INTERACTIONS IN AQUEOUS SOLUTION

Rate constants for the formation of copper(II) complexes with the glycine anion have been measured by a combination of temperature-jump and close-to-equilibrium stopped-flow techniques. Measurements were carried out in moderately acid solutions to avoid complications due to copper-hydroxy species. Relaxation times, in the millisecond time region, could be interpreted only as reactions between metal ion and free anion, even though the zwitterion predominated at the pH's used. The forward rate constants for the mono and bis complexes with glycine were found to be 4 X 109 and 4 X 108 M1 sec-1, respectively, at 25° and I = 0.1. These constants, although large, were consistent with the Eigen-Tamm mechanism for the formation of metal complexes wherein the release of a water molecule from the inner hydration sphere of the metal ion is the rate-determining step. The unimolecular rate constants for ligand penetration into the inner hydration sphere of the copper ion were estimated to be 2 X 109 and 5 X108 sec-1 for the first and second steps, respectively. © 1968, American Chemical Society. All rights reserved.