RNA hydrolysis by cobalt(III) complexes1

Abstract

Adenylyl(3′-5′)adenosine (ApA) and uridylyl(3′-5′)uridine (UpU) are hydrolyzed at pH 7.0 and 50 °C by [Co(N)₄(OH₂)₂]³⁺ complexes (N: coordinated nitrogen atom). The pseudo-first-order rate constants for ApA hydrolysis by the triethylenetetramine and the tris(2-aminoethyl)amine complexes (0.1 mol dm^–3) are 1.5 × 10^–2 h^–1, corresponding to 10⁵-fold acceleration. The Co^III complexes are also active for the hydrolysis of 2′,3′-cyclic monophosphates of ribonucleotides. The pH–rate constant profile for ApA hydrolysis is bell-shaped with a maximum around pH 7, and a notable D₂O solvent isotope effect (2.0) is observed. It is proposed that the coordination water molecules on the Co^III ions promote (as general acid catalysts) the departure of the alkoxide ion of 5′-OH from the phosphorus atom.