Studies on p-Nitrophenyl Picolinate Cleavage by Unsymmetrical Bis-Schiff Base Manganese(III) and Cobalt(II) Complexes in CTAB Surfactant Micellar Solution

Abstract

The unsymmetrical bis-Schiff base manganese(III) and cobalt(II) complexes with either benzo-10-aza-crown ether pendants (MnL¹Cl, MnL²Cl) or morpholino pendant (MnL³Cl, CoL³) have been employed as models for hydrolase by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP) in the buffered CTAB micellar solution. A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of PNPP hydrolysis have been examined. All four complexes exhibit higher catalytic activity in the buffered CTAB micellar solution and the rate increases with pH of the buffered CTAB micellar solution under 25°C. The complexes containing a crown ether group exhibit higher catalytic activities than the free-crown analogues. The catalytic activity of manganese(III) complex is superiority over cobalt(II) complex in catalyzing hydrolysis of PNPP under the same ligand.

Keywords:

• Benzo-10-aza-crown ether
• CTAB micellar solution
• mimic hydrolase
• p-nitrophenyl picolinate
• unsymmetrical bis-Schiff base complexes

Acknowledgments

The authors gratefully acknowledge financial support from China National Natural Science Foundation (No: 20072025) and the Opening Project of Key Laboratory of Green Catalysis of Sichuan Institutes of High Education (No. LZJ1101).

Notes

Condition: 25 ± 0.1°C, I = 0.1 mol · dm⁻³ KNO₃, [complex] = 1.0 × 10⁻⁵ mol · dm⁻³, [Tris] = 0.1 mol · dm⁻³, [CTAB] = 1.0 × 10⁻³ mol · dm⁻³.