Studies on PNPP Hydrolysis Catalyzed by Schiff Base Cobalt(II) Complexes Containing Benzoaza-15-crown-5

Three novel Schiff base cobalt(II) complexes containing benzoaza-15-crown-5, CoL¹, CoL² and CoL³ were synthesized and characterized, and these complexes were used in catalytic hydrolysis of carboxylic ester (PNPP, p-nitrophenyl picolinate) as mimic hydrolytic metalloenzyme. The analysis of specific absorption spectra of the hydrolytic reaction systems indicated that the catalytic hydrolysis involved the key intermediates formed by PNPP with cobalt(II) complexes. The CoL³ bearing the electron withdrawing group shows better catalytic activity due to its stabilization effect on active species MLS⁻. The catalytic mechanism of PNPP hydrolysis was also proposed. The kinetic parameter of PNPP catalytic hydrolysis has been calculated and the activation energy for the catalytic hydrolysis is 43.69, 39.76 and 35.44 kJ·mol⁻¹, respectively.