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

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journal contribution
posted on 08.10.1997, 00:00 by Thomas W. Welch, Suzanne A. Ciftan, P. S. White, H. Holden Thorp
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 RuIVO2+ and RuIIIOH2+ redox forms relative to other (polypyridyl)oxoruthenium(IV) complexes. As a result, the oxidations of both sec-phenylethanol and trans-stilbene are ∼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 RuIVO2+ form with no contribution from direct oxidation by the RuIIIOH2+ intermediate, which greatly simplifies the kinetic analysis. The RuIVO2+ 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 RuIIIOH2+ 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.

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