La(III) complex of phenanthroline bridging polyamine as efficient catalyst for the hydrolysis of ATP

Abstract

The hydrolysis of ATP catalyzed by protonated ligand 2, 9-di[(2'-ethylamino)ethylene-aminomethyl]-1, 10-phenanthroline·4HCl.H₂O(L) or its La(III) complex has been studied at <i>p</i>H 7.6 using ³¹P NMR spectroscopy. The two systems have a rate of 12.1×10^-4 mol.dm^-3 and 159×10^-4 mol.dm^-3 , which is about 5- and 59-fold as fast as that of free ATP respectively. La(III) complex of L is a more efficient catalyst for ATP hydrolysis than metal ion alone, which has a rate enhancement ratio about 5. High catalytic efficiency has been achieved through the effective activation of ATP by La(III) complex and the availability of a good intramolecular nucleophile. The phosphoramidate intermediate at 2.88 ppm in L/ATP system has not been observed in La(III)/L/ATP system. The mechanism for ATP hydrolysis catalyzed by complex of ‘‘hard’’ metal ion has been given. The effects of metal ion mediated by polyaza ligand in controlling the recognition of the substrate and the attacking on phosphorous counter have been discussed.