Metallomicellar Catalysis: Hydrolysis of PNPP Catalyzed by Copper(II), Zinc(II), Cerium(IV) Complexes with Long Alkyl Pyridine Ligands in CTAB Micellar Solution

Abstract

A kind of new functional surfactant with substituted long alkyl pyridine was synthesized and its Ce(IV), Zn(II), and Cu(II) complexes were used as hydrolytic metalloenzyme models. The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by the metallomicelles in CTAB micellar solution was investigated at different pH and 30°C. Kinetic parameters of catalytic hydrolysis were obtained by employing the ternary complex kinetic model for metallomicellar catalysis. Effects of the structure of ligands and microenvironment of reaction on the hydrolytic reaction of PNPP have been discussed in detail. From the apparent rate constants (k _obsd ) of the catalytic hydrolysis of PNPP, it can be seen that the catalytic effect of complexes of ligand L² with long hydrocarbon chain was stronger than that of ligand L¹, and complex CuL² showed higher catalytic efficacy on the hydrolytic reaction than those of ZnL² and CeL². However, experiment results in this article showed that ZnL² and CeL² are more susceptible to environment than CuL². The catalytic mechanism was proposed, and the possibly active species for the catalytic hydrolysis of PNPP was determined to be the hydroxylated metal complex.

Keywords:

• Catalysis
• hydrolysis of PNPP
• kinetics
• metallomicelle
• pyridine

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant No. 20803050).

Notes

Note. In 0.01 mol L⁻¹ Tris-HCl buffer [µ = 0.1 (KCl)], [PNPP] = 2 × 10⁻⁵ mol L⁻¹, [ligand] = [Mⁿ⁺] = 1 × 10⁻⁴ mol L⁻¹, [CTAB] = 0.01 mol L⁻¹.

Note. [CTAB] = 0.01 mol L⁻¹, [PNPP] = 2 × 10⁻⁵ mol L⁻¹; correlation coefficients ≥ 0.98.