Zn(II) Coordination by Open-chain Polyamine Ligands Containing Dipyridine Units. Highly Active Dinuclear Zn(II) Complexes in Phosphate Ester Hydrolysis

Abstract

Abstract:The synthesis and characterization of two new open-chain ligands, L1 and L2, containing two 2,2'-dipyridine units connected respectively by a pentaethylenhexamine and a pentapropylenhexamine chain, is reported. Zn(II) complexation has been studied by means of potentiometric and UV-vis spectrophotometric measurements in aqueous solution. Both ligands form stable mono-and dinuclear complexes, the metal ions being coordinated by a single dipyridine unit and by the adjacent amine groups. The ability of the binuclear Zn(II) complexes as nucleophilic agents in hydrolytic processes has been tested by using bis(p-nitrophenyl) phosphate (BNPP) as substrate. Both complexes display high rate enhancements in BNPP cleavage in aqueous solution. The study outlines that different mechanisms are operative in BNPP cleavage in the presence of the L1 and L2 complexes.