Electron-Rich Oxoruthenium(IV) Cleavage Agents: A Zero-Order Rate Law for DNA Catalysis

A new family of oxoruthenium(IV) complexes based on [(DAMP)(L)RuO](2+) have been prepared where DAMP = 2,6-bis((dimethylamino)methyl)pyridine and L = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), or dipyridophenazine (dppz). The structures of [(DAMP)(bpy)RuO](2+) and [(DAMP)(phen)RuO](2+) were determined by X-ray crystallography. The Ru-O bond lengths (1.805(3) and 1.814(4) Å, respectively) are indicative of multiple bonding, as expected for oxoruthenium(IV), and clear steric protection of the Ru=O moiety is provided by the DAMP ligand. Cyclic voltammetry shows that the tertiary amine functionalities of the DAMP ligand stabilize both the Ru(IV)O(2+) and Ru(III)OH(2+) redox forms relative to other (polypyridyl)oxoruthenium(IV) complexes. As a result, the oxidations of both sec-phenylethanol and trans-stilbene are approximately 100 times slower for [(DAMP)(bpy)RuO](2+) than for [(bpy)(2)(py)RuO](2+). Accordingly, the reaction mechanisms involve oxidation of substrate only by the Ru(IV)O(2+) form with no contribution from direct oxidation by the Ru(III)OH(2+) intermediate, which greatly simplifies the kinetic analysis. The Ru(IV)O(2+) forms are not effective oxidants of the sugar moiety of mononucleotides; however, the base functionality of guanosine 5'-monophosphate is oxidized at detectable rates. In contrast, cleavage of a hairpin oligonucleotide is detected at both guanine and sugar functionalities, indicating that the oligomer promotes sugar oxidation by increasing the local concentration of the metal complex. The Ru(III)OH(2+) form of the DAMP complexes is stable in the absence of DNA but is reduced following a zero-order rate law in the presence of calf thymus DNA. Analysis using a model that resembles Michaelis-Menten kinetics indicates that the binding domain on DNA catalyzes the disproportionation of the complex. The model yields a binding constant and a calculated first-order rate constant that are in good agreement with independent measurements.