Exploring Photoreactions between Polyazaaromatic Ru(II) Complexes and Biomolecules by Chemically Induced Dynamic Nuclear Polarization Measurements

Abstract

Steady-state (1)H 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 (1)H 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 (1)H NMR signal broadening and photo-CIDNP extinction. The (1)H 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.

Luminescent Ruthenium(II) Polypyridine Complexes for a Wide Variety of Biomolecular and Cellular Applications

“…Complex 41 determined that the mechanism of linkage of a guanine to the polyazaaromatic ruthenium (II) complex involves the C-2 or C-7 of a tap ligand. 45 After demonstrating guanine linkage to oxidizing polyazaaromatic ruthenium(II) complexes, Ghizdavu et al designed a new strategy for the photo-cross-linking of two strands of an oligonucleotide (ODN) duplex. 46 The strategy involves irradiation of complex 42 to facilitate adduct formation on a guanine base of one ODN strand, followed by photoaddition of the same ruthenium complex onto a separate guanine base from the complementary strand.…”

Spectro-electrochemical Studies on [Ru(TAP)2(dppz)]2+—Insights into the Mechanism of its Photosensitized Oxidation of Oligonucleotides

“…More recently a series of detailed photo-CIDNP (chemically induced dynamic nuclear polarization) studies of the reduction of various [Ru(TAP)2(L)] 2+ with 5′-GMP and other reducing biomolecules have been reported by Kirsch-De Mesmaeker, Luhmer and coworkers. [13][14][15][16] With 5′-GMP as quencher, strongly enhanced absorption signals are found, predominantly for the 2,7-TAP protons (much weaker for the 3,6-TAP protons and absent for the 9,10-TAP protons) (see Figure 1 for the numbering of atoms in TAP), while a strong effect is also observed for the H8 of the GMP. This result is consistent with formation of the reduced metal complex and the oxidized nucleotide in the solvent cage; the CIDNP signal arises because of the competition between the back-electron transfer and the escape of the two radical species.…”

Photochemical pump and NMR probe to monitor the formation and kinetics of hyperpolarized metal dihydrides

“…Our p -H 2 approach also brings the sensitivity of NMR spectroscopy into a similar range to time-resolved UV/vis absorption spectroscopy. The nearest comparable measurements by NMR spectroscopy have been made by photo-CIDNP 34,35 or by stopped-flow NMR. 36 …”