Studies on P -Nitrophenyl Picolinate Cleavage by Unsymmetrical Bis-Schiff Base Complexes with Aza-Crown Ether or Morpholino Pendants

The unsymmetrical bis-Schiff base manganese(III) and cobalt(II) complexes with either benzo-10-aza-crown ether pendants (MnL¹Cl, CoL¹, CoL²) or a morpholino pendant (MnL³Cl) have been demonstrated as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalysed 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 high catalytic activity and the rate increases with pH. The complexes of ligands containing a crown ether group exhibit higher catalytic activities than the non-crown analogue; the catalytic activity of the complexes follows the order Mn(III) > Co(II) (MnL¹Cl > CoL¹) with the same ligands.