Studies on p-Nitrophenyl Picolinate (PNPP) Cleavage by Mono-Schiff Base Complexes with Aza-Crown Ether or Morpholino Pendants in CTAB Micellar Solution

Abstract

Two mono-Schiff base manganese (III) and cobalt (II) complexes with benzo-10-aza-crown ether pendants , and the analogous with morpholino pendants have been employed as models to mimic hydrolase in p-nitrophenyl picolinate (PNPP) in the buffered CTAB micellar solution. The kinetics and the mechanism on PNPP hydrolysis catalyzed by these complexes were investigated. The kinetic mathematical model of PNPP cleavage catalyzed by these complexes was proposed. The relative kinetic and thermodynamic parameters were determined. The effects of complexes structure and reactive temperature on the rate of catalytic PNPP hydrolysis have been also examined. The results showed that the rate for the catalytic PNPP hydrolysis was increased following the increase of pH of the buffered CTAB micellar solution; four complexes can efficiently accelerate the catalytic cleavage of PNPP in the buffered CTAB micellar solution. Compared with the crown-free analogous and , the crowned Schiff base complexes exhibit more high catalytic activity for promoting PNPP hydrolysis. The pseudo-first-order-rate ( k _obs ) for the PNPP hydrolysis catalyzed by the complex in the CTAB micellar solution is 2.02 × 10⁴ times than that of PNPP spontaneous hydrolysis in water at pH = 7.00, 25°C, [S] = 2.0 × 10⁻⁴ mol dm⁻³.

Keywords:

• Benzo-10-aza-crown ether
• catalytic kinetics
• mimic hydrolase
• mono-Schiff base complexes
• p-nitrophenyl picolinate

Acknowledgments

The authors gratefully acknowledge financial support from China National Natural Science Foundation (No. 20072025) and Key Project of Sichuan Province Education Office (No. 2005D007).

Notes

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