Studies on p-nitrophenyl picolinate cleavage by mono-Schiff base complexes with aza-crown ether or morpholino pendants

Abstract

Mono-Schiff base manganese(III) and cobalt(II) complexes with either benzo-10-aza-crown ether pendants (MnL1 2 Cl, CoL1 2) or morpholino pendants (MnL2 2Cl, CoL2 2) have been employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of catalytic PNPP hydrolysis have been also examined. The rate increases with pH of the buffer solution; all four complexes exhibited high activity in the catalytic PNPP hydrolysis. Compared with the crown-free analogues MnL2 2Cl and CoL2 2, the crowned Schiff base complexes (MnL1 2Cl, CoL1 2) exhibit higher catalytic activity. The pseudo-first-order-rate ( k obs ) for the PNPP hydrolysis catalyzed by the complex MnL1 2Cl containing benzo-10-aza-crown ether is 1.06 × 103 times that of spontaneous hydrolysis of PNPP at pH = 7.00, 25 °C, [S] = 2.0 × 10−4 mol dm−3. Studies on p-nitrophenyl picolinate cleavage by mono-Schiff base complexes with aza-crown ether or morpholino pendants Jian-zhang Li*, Fa-mei Feng, Bin Xu,Wei-dong Jiang Key Laboratory of Green and Technology, Department of Chemistry, Sichuan University of Science & Engineering, Zigong, Sichuan, 643000, P.R. China Sheng-ying Qin Department of Chemistry, Sichuan University, Chengdu, Sichuan, 610064, P.R. China Mono-Schiff base manganese(III) and cobalt(II) complexes with either benzo-10-aza-crown ether pendants (MnL1 2Cl, CoL1 2) or morpholino pendants (MnL2 2Cl, CoL2 2) have been employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with PNPP. A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. Compared with the crown-free analogy MnL2 2Cl and CoL2 2, the crowned Schiff base complexes (MnL1 2Cl, CoL1 2) exhibit higher catalytic activity.