Photo-CIDNP Reveals Different Protonation Sites Depending on the Primary Step of the Photoinduced Electron-/Proton-Transfer Process with Ru(II) Polyazaaromatic Complexes

Troian‐Gautier, Ludovic; Mugeniwabagara, Epiphanie; Fusaro, Luca; Cauët, Émilie; Mesmaeker, Andrée Kirsch‐De; Luhmer, Michel

doi:10.1021/jacs.7b09513

Cited by 8 publications

(14 citation statements)

References 32 publications

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“…First, the 2 LMCT character of 1 + * leads to a mono-reduced complex with a reduced iron(II) metal center. This is unlike prototypical MLCT excited states where the reduced photocatalyst has an electron localized on a bipyridine ligand. − Hence reductive quenching of an LMCT excited state results in vectorial electron transfer away from the donor, a process desired for applications in photoredox chemistry and solar energy conversion. In contrast, reductive quenching of an MLCT excited state results in non-vectorial electron transfer that leaves a ligand-localized electron proximate to the electron donor, which may promote strong electronic coupling and enhance charge recombination.…”

Section: Results and Discussionmentioning

confidence: 99%

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

et al. 2021

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Efficient excited-state electron transfer between an iron(III) photosensitizer and organic electron donors was realized with green light irradiation. This advance was enabled by the use of the previously reported iron photosensitizer, [Fe(phtmeimb)2]+ (phtmeimb = {phenyl[tris(3-methyl-imidazolin-2-ylidene)]borate}, that exhibited long-lived and luminescent ligand-to-metal charge-transfer (LMCT) excited states. A benchmark dehalogenation reaction was investigated with yields that exceed 90% and an enhanced stability relative to the prototypical photosensitizer [Ru(bpy)3]2+. The initial catalytic step is electron transfer from an amine to the photoexcited iron sensitizer, which is shown to occur with a large cage-escape yield. For LMCT excited states, this reductive electron transfer is vectorial and may be a general advantage of Fe(III) photosensitizers. In-depth time-resolved spectroscopic methods, including transient absorption characterization from the ultraviolet to the infrared regions, provided a quantitative description of the catalytic mechanism with associated rate constants and yields.

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Section: Results and Discussionmentioning

confidence: 99%

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

et al. 2021

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“…26 An isotope effect is also observed when [Ru(TAP)2(dppz)] 2+ oxidizes 5′-GMP 12 and CIDNP studies with other [Ru(TAP)2L 2+ complexes suggest that this process might proceed by PCET within the solvent cage resulting in the formation of Ru(TAP)(TAPH)(dppz)] 2+ (equation 4). [13][14][15][16] [Ru(TAP)2(dppz)]…”

Section: Dft Calculations On the Electronic And Vibrational Absorptiomentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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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 photo-electron 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 1ereduced 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 are electronic transitions 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 both [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 photo-excitation of [Ru(TAP)2(dppz)] 2+ intercalated in guanine-containing DNA. This suggests that the photochemical process in DNA proceeds by photo-electron 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′-GMP. Additional infrared spectroelectrochemical 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).

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“…This showed the formation of a covalent photoadduct between the exocyclic amine of the guanine nucleobase and one of the TAP ligands ( Scheme 7 ) [ 125 , 126 ]. The mechanism involves the radical recombination of the protonated reduced ruthenium complex [ 127 , 128 ] and the deprotonated radical cation of guanine and rearomatisation of the nucleobase leads to the formation of the observed photoadduct. Interestingly, no bonding to the O6 centre of guanine was observed despite that radicals centred on O6 are usually the most stable.…”

Section: Ru-dna and The Antigene And Antisense Strategiesmentioning

confidence: 99%

Applications of Ruthenium Complexes Covalently Linked to Nucleic Acid Derivatives

et al. 2018

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Oligonucleotides are biopolymers that can be easily modified at various locations. Thereby, the attachment of metal complexes to nucleic acid derivatives has emerged as a common pathway to improve the understanding of biological processes or to steer oligonucleotides towards novel applications such as electron transfer or the construction of nanomaterials. Among the different metal complexes coupled to oligonucleotides, ruthenium complexes, have been extensively studied due to their remarkable properties. The resulting DNA-ruthenium bioconjugates have already demonstrated their potency in numerous applications. Consequently, this review focuses on the recent synthetic methods developed for the preparation of ruthenium complexes covalently linked to oligonucleotides. In addition, the usefulness of such conjugates will be highlighted and their applications from nanotechnologies to therapeutic purposes will be discussed.

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Photo-CIDNP Reveals Different Protonation Sites Depending on the Primary Step of the Photoinduced Electron-/Proton-Transfer Process with Ru(II) Polyazaaromatic Complexes

Cited by 8 publications

References 32 publications

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

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

Applications of Ruthenium Complexes Covalently Linked to Nucleic Acid Derivatives

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Photo-CIDNP Reveals Different Protonation Sites Depending on the Primary Step of the Photoinduced Electron-/Proton-Transfer Process with Ru(II) Polyazaaromatic Complexes

Cited by 8 publications

References 32 publications

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

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

Applications of Ruthenium Complexes Covalently Linked to Nucleic Acid Derivatives

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