Metallomicellar Catalysis. Effects of Bridge-Connecting Ligands on the Hydrolysis of PNPP Catalyzed by Zn(II), Co(II), and Ni(II) Complexes of Ethoxyl-diamine Ligands in Micellar Solution

Abstract

The syntheses of three ligands are reported: N,N,N',N'-tetra(2-hydroxyethyl)-1,3-propylene-diamine (1), N,N,N',N'-tetra(2-hydroxyethyl)-1,10-decadiamine (2), and N,N,N',N'-tetra(2-hydroxy-ethyl)-1,4-xylyldiamine (3). The catalytic hydrolysis ofp-nitrophenyl picolinate (PNPP) by bivalent metal ions Zn(II), Ni(II), and Co(II) was studied kinetically in the buffered CTAB and Brij35 micellar solution at 25 °C and different pH values. The results indicate that 1:2 and 2:1 complexes of these ligands and metal ions in CATB and Brij35 micellar solution are the active species for the catalytic hydrolysis of PNPP, respectively. A ternary complex kinetic model for metallomicellar catalysis was employed to interpret the results to obtain relative kinetic and thermodynamic parameters. The comparison of these parameters indicates that the catalytic activity of different metal complexes catalyzed hydrolysis of PNPP depends on the rigidity of the bridge-connecting ligand and the microenvironment. The effect of the structure of the ligands on the hydrolytic reaction of PNPP has been discussed in detail.