EFFECT OF IMIDAZOLE SUBSTITUTION ON THE DIMERIZATION REACTION OF MANGANESE(III) PORPHYRIN IN AQUEOUS ENVIRONMENTS - TEMPERATURE JUMP STUDY

Equilibrium constants for ligand binding and rate constants for a dimerization reaction in the presence of the ligand imidazole were determined for the manganese(III) porphyrin in 0.1M KNO3. Imidazole binds to the manganese porphyrin in stepwise equilibria to form the diligated dimer (MnPL)D and further to the di-imidazole monomer, MnP2. Analysis of temperature jump kinetic data, supported by spectrophotometric studies, showed that the phenomenon responsible for the relaxation is the dissociation of the ligated dimer. The mechanism proposed involves a self dissociation of the imidazole bound dimer and a ligand induced dimer dissociation viz: {A figure is presented} At 302°K, the rate constants evaluated are k1 = 4.8 × 106 M-1 S-1, k-1 = 200 S-1k2 = 5.4 × 107M-1 S-1 and k-2 = 2500 M-1 S-1. © 1979.