Dinuclear Zn2+ complexes in the hydrolysis of the phosphodiester linkage in a diribonucleoside monophosphate diester

Abstract

Dizinc complexes that were formed from 2 ∶ 1 mixtures of Zn(NO₃)₂ and dinucleating ligands TPHP (1), TPmX (2) or TPpX (3) in aqueous solutions efficiently hydrolyzed diribonucleoside monophosphate diesters (NpN) under mild conditions. The dinucleating ligand affected the structure of the aquo-hydroxo-dizinc core, resulting in different characteristics in the catalytic activities towards NpN cleavage. The pH-rate profile of ApA cleavage in the presence of (Zn²⁺)₂-1 was sigmoidal, whereas those of (Zn²⁺)₂-2 and (Zn²⁺)₂-3 were bell-shaped. The pH titration study indicated that (Zn²⁺)₂-1 dissociates only one aquo proton (up to pH 12), whereas (Zn²⁺)₂-2 dissociates three aquo protons (up to pH 10.7). The observed differences in the pH-rate profile are attributable to the various distributions of the monohydroxo-dizinc species, which are responsible for NpN cleavage. As compared to that using (Zn²⁺)₂-1, the NpN cleavage using (Zn²⁺)₂-2 showed a greater rate constant, with a higher product ratio of 3′-NMP/2′-NMP. The saturation behaviors of the rate, with regard to the concentration of NpN, were analyzed by Michaelis–Menten type kinetics. Although the binding of (Zn²⁺)₂-2 to ApA was weaker than that of (Zn²⁺)₂-1, (Zn²⁺)₂-2 showed a greater k_cat value than (Zn²⁺)₂-1, resulting in higher ApA cleavage activity of the former.