Abstract
The temperature-jump method has been used to determine the complexation rate constants for the reaction of L-carnosine with cobalt(II) at 25° and ionic strength 0.1 M. The association rate constant is consistent with a mechanism in which release of a water molecule from the metal ion’s inner coordination sphere is rate de- termining. The rate constants for the reaction, Co2+ + HL CoHL2+ (where HL represents the neutral form of the ligand), are ki = 4.2 X 10f (±20%) M~1 sec-1 and k-i = 87 (±20%) sec-1. Since the cobalt complex is a seven-membered ring system, the results are taken as evidence that the ligand entropy contribution to steric effects in fast metal-complex substitution reactions is considerably less significant than the ring-strain contribution.