Spectro-electrochemical studies on [Ru(TAP)2(dppz)]2+ - insights into the mechanism of its photosensitized oxidation of oligonucleotides

Keane, P. M., Tory, J., Towrie, M., Sazanowich, I. V., Cardin, C. J. ORCID: https://orcid.org/0000-0002-2556-9995, Quinn, S. J., Hartl, F. ORCID: https://orcid.org/0000-0002-7013-5360, Kelly, J. M. and Long, C. (2019) Spectro-electrochemical studies on [Ru(TAP)2(dppz)]2+ - insights into the mechanism of its photosensitized oxidation of oligonucleotides. Inorganic Chemistry, 58 (1). pp. 663-671. ISSN 0020-1669 doi: 10.1021/acs.inorgchem.8b02859

Abstract/Summary

[Ru(TAP)2(dppz)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene; dppz = dipyrido[3,2-a:2′,3′-c]phenazine) is known to photo-oxidize guanine in DNA. Whether this oxidation proceeds by direct photoelectron transfer or by proton-coupled electron transfer is still unknown. To help distinguish between these mechanisms, spectro-electrochemical experiments have been carried out with [Ru(TAP)2(dppz)]2+ in acetonitrile. The UV–vis and mid-IR spectra obtained for the one-electron reduced product were compared to those obtained by picosecond transient absorption and time-resolved infrared experiments of [Ru(TAP)2(dppz)]2+ bound to guanine-containing DNA. An interesting feature of the singly reduced species is an electronic transition in the near-IR region (with λmax at 1970 and 2820 nm). Density functional and time-dependent density functional theory simulations of the vibrational and electronic spectra of [Ru(TAP)2(dppz)]2+, the reduced complex [Ru(TAP)2(dppz)]+, and four isomers of [Ru(TAP)(TAPH)(dppz)]2+ (a possible product of proton-coupled electron transfer) were performed. Significantly, these predict absorption bands at λ > 1900 nm (attributed to a ligand-to-metal charge-transfer transition) for [Ru(TAP)2(dppz)]+ but not for [Ru(TAP)(TAPH)(dppz)]2+. Both the UV–vis and mid-IR difference absorption spectra of the electrochemically generated singly reduced species [Ru(TAP)2(dppz)]+ agree well with the transient absorption and time-resolved infrared spectra previously determined for the transient species formed by photoexcitation of [Ru(TAP)2(dppz)]2+ intercalated in guanine-containing DNA. This suggests that the photochemical process in DNA proceeds by photoelectron transfer and not by a proton-coupled electron transfer process involving formation of [Ru(TAP)(TAPH)(dppz)]2+, as is proposed for the reaction with 5′-guanosine monophosphate. Additional infrared spectro-electrochemical measurements and density functional calculations have also been carried out on the free TAP ligand. These show that the TAP radical anion in acetonitrile also exhibits strong broad near-IR electronic absorption (λmax at 1750 and 2360 nm).

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/81480
Item Type	Article
Refereed	Yes
Divisions	Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry
Publisher	American Chemical Society
Download/View statistics	View download statistics for this item