Hydrolysis of p-nitrophenyl picolinate catalyzed by divalent metal ion complexes containing imidazole groups in micellar solution

The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by Zn(II), Cu(II) and Co(II) complexes of imidazole groups have been investigated kinetically in the pH range 6.0-8.0 at the presence of three kinds of surfactants and 25.0 +/- 0.01 degreesC, respectively. The results indicated that Zn(II) complex exhibit a great catalytic function in micellar solution with higher pH value, but when reactions were performed in weak acid solutions, Cu(II) complex catalyzed the hydrolysis of PNPP more efficiently than Zn(II) and CO(II) complexes did, which may be attributable to the different ionization states of the corresponding complexes in micellar media with different pH values and the different nucleophilic ability of active species in different complexes. In addition, these complexes showed more reactivity in zwitterionic (LSS) and nonionic (Brij35) micelles than that in cationic (CTAB) micelle, which may be explained by the electrostatic interaction between metal ions of these complexes and the head groups of surfactants or the substrate. The relative kinetic and thermodynamic parameters were obtained by kinetic analysis employing ternary complex model for metallomicellar catalysis. (C) 2003 Published by Elsevier B.V.