Exploring Photoreactions between Polyazaaromatic Ru(II) Complexes and Biomolecules by Chemically Induced Dynamic Nuclear Polarization Measurements
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- 作者：Sandrine Perrier ; Epiphanie Mugeniwabagara ; Andre Kirsch-De Mesmaeker ; P. J. Hore ; Michel Luhmer
- 刊名：Journal of the American Chemical Society
- 出版年：2009
- 出版时间：September 2, 2009
- 年：2009
- 卷：131
- 期：34
- 页码：12458-12465
- 全文大小：293K
- 年卷期：v.131,no.34(September 2, 2009)
- ISSN：1520-5126
文摘
Steady-state 1H photo-chemically induced dynamic nuclear polarization (CIDNP) experiments were conducted at 14.1 T on deoxygenated (buffered pH 7) aqueous solutions of [Ru(phen)3]2+, [Ru(tap)2(phen)]2+, and [Ru(tap)3]2+ (tap = 1,4,5,8-tetraazaphenanthrene; phen = 1,10-phenanthroline) in the presence of guanosine-5′-monophosphate or N-acetyltyrosine. For the first time, CIDNP arising from photo-oxidation by polyazaaromatic Ru(II) complexes is reported. In agreement with the occurrence of a photo-electron-transfer process, photo-CIDNP effects are observed with [Ru(tap)3]2+ and [Ru(tap)2(phen)]2+ but not with [Ru(phen)3]2+. With [Ru(tap)2(phen)]2+, no significant photo-CIDNP is observed for the 1H nuclei of the phen ligand, consistent with the fact that the metal-to-ligand charge-transfer triplet excited states responsible for the photo-oxidation involve a tap ligand. Successive experiments with [Ru(tap)3]2+ highlight the accumulation of long-lived radical species in solution that cause 1H NMR signal broadening and photo-CIDNP extinction. The 1H photo-CIDNP observed for the biomolecules is rather weak, less than about 30% of the equilibrium magnetization. However, up to 60% polarization enhancement is observed for H-2 and H-7 of the tap ligands, which indicates high unpaired electron density in the vicinity of these atoms in the transient radical pair. This is consistent with the structure of known photoadducts formed, for instance, between the metallic compounds and the guanine base of mono- and polynucleotides. Indeed, in these adducts the covalent bond involves carbon C-2 or C-7 of a tap ligand. The occurrence of photo-CIDNP with polyazaaromatic Ru(II) complexes opens new perspectives for the study of this type of compound.