Catalytic cleavage of p-nitrophenyl picolinate by metallomicelles made up of copper(II) complexes of small molecular ligands bearing hydroxyl or carboxyl groups

Abstract

The esterolytic activities of Cu2+ complexes (Cu2+L1, Cu2+L2 and Cu2+L3) of three small molecular ligands: N-(2-hydroxyethyl)ethylenediamine (L1), 2,2′-iminodiethanol (L2) and iminodiacetic acid (L3), in the presence of the nonionic micelle (Brij35) towards the substrate p-nitrophenyl picolinate (PNPP) have been investigated. The catalytic reactivity order is: Cu2+L1 > Cu2+L2 > Cu2+L3, which can be attributed to the similarity of and the difference between their catalytic mechanisms, most likely resulting from the analogy and the discrepancy of the structure of the three complexes. The critical feature of the catalytic process is, quite likely, the formation of a ternary complex involving a binary metal ion complex and the substrate, followed by pseudo-intramolecular nucleophilic attack of the alcoholic hydroxyl (for Cu2+L1 and Cu2+L2) or metal ion bound hydroxide ion (for Cu2+L3), at carbonyl of the substrate. Detailed kinetic analyses are given for the hydrolysis of PNPP catalyzed by the three complexes.