Hydrolytic Metalloenzyme Models. Effects of AOT Reverse Micelles on the Hydrolysis of p-Nitrophenyl Picolinate Catalyzed by Zn2+ and Cu2+ Complexes of N-Alkyl-2-hydroxymethylimidazoles

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Abstract
The catalytic effects of bivalent metal ion (Zn2+ and Cu2+) complexes of N-alkyl-2-hydroxymethylimidazoles on the hydrolysis of p-nitrophenyl picolinate (PNPP) have been studied kinetically in the reverse micelles of AOT/hexane/water at 25 °C. The results were compared with those obtained in the non-micellar aqueous media and aqueous micelles. The hydrolysis was observed to occur through the acyl group transfer from PNPP to the ligand hydroxyl group in both cases of Zn2+ and Cu2+ ions and in all three non-micellar and micellar systems. However, the ligand:metal ion ratio in the kinetically active complexes was found to differ significantly in the three systems: there seems to exist general trends of 1 : 1, 2 : 1, and 4 : 1 stoichiometry in the ligand:metal ion ratio, depending on non-micellar aqueous media, aqueous micelles and reverse micelles, respectively. It was also noticed that the hydrolysis is always faster in micellar systems than in non-micellar aqueous media. Furthermore, a lipophilic ligand (N-dodecyl, Lig-12) was found to be more active than a hydrophilic ligand (N-methyl, Lig-1) under two micellar conditions.