Mechanism of Intramolecular Nucleophilic Substitution in the Catalytic Hydrolysis of Bis(4-Nitrophenyl) Phosphate Ester in a Metallomicelle

A macrocyclic Schiff base ligand and the corresponding Cu(II) and Ni(II) complexes were synthesized and characterized. The catalytic ability of metallomicelles, made from these complexes and micelles, as mimic hydrolytic metalloenzymes, was investigated in the catalytic hydrolysis of bis(p-nitrophenyl) phosphate (BNPP). The rate of the BNPP catalytic reaction in the metallomicelles is ca 2.0 × 106-fold faster than that of the spontaneous hydrolysis of BNPP in aqueous solution under the same conditions. The analysis of absorption spectra of the hydrolytic reaction systems indicates that key intermediates, comprising BNPP and the Ni(II) or Cu(II) complexes, have been formed and the catalytic hydrolysis of BNPP is an intramolecular nucleophilic substitution reaction. Based on the analysis of the absorption spectrum, a mechanism for the catalytic hydrolysis of BNPP has been proposed and a kinetic mathematical model has been established.