Metal-ion-promoted hydrolysis of uridylyl(3′,5′)uridine: internal vs. external general base catalysis

Abstract

The hydrolysis of uridylyl(3′,5′)uridine promoted by Mg²⁺, Zn²⁺ and Zn²⁺[12]aneN₃([12]aneN₃= 1,5,9-triazacyclododecane) has been studied in imidazole, HEPES and triethanolamine buffers and the origin of marked electrolyte effects observed with Zn²⁺[12]ane N₃ has been examined. The results obtained suggest that the basic buffer constituent does not serve as an external general base, but the catalytic activity of the metal ion species is influenced by the coordination to the buffer base and other Lewis bases present in the solution. The data lend additional support to a bifunctional mechanism, which consist of coordination of the metal ion to the anionic phosphodiester and intracomplex general base (or nucleophilic) catalysis by its hydroxo ligand.