TY - JOUR

T1 - Disproportionation and dimerisation of kynurenic acid under UV light

AU - Morozova, Olga B.

AU - Zhuravleva, Yuliya S.

AU - Geniman, Maksim P.

AU - Yurkovskaya, Alexandra V.

AU - Sherin, Peter S.

N1 - Fundings: We acknowledge financial support from the Ministry of Science and Higher Education of the Russian Federation (Grant No. 075-15-2021-580) for optical measurements, and RFBR (project number 21-53-12023) for CIDNP measurements. Authors acknowledge Agilent Measurements Suite (AMS) of the Chemical Department of Imperial College London for access to HPLC-MS equipment.

PY - 2023/11/1

Y1 - 2023/11/1

N2 - In this work, we report on the photo-induced oxidation of kynurenic acid (KNA) by the triplet-excited KNA in a neutral aqueous solution. This reaction is confirmed by two different time-resolved methods: optical spectroscopy and chemically induced dynamic nuclear polarization (CIDNP). The disproportionation reaction proceeds with the rate constant of (6.0 ± 1.2) × 107 M−1s−1 via the mechanism of H-atom transfer to the photoexcited KNA in the triplet state, yielding the reduced and oxidized forms of KNA, KNAH2[rad]− and KNA(-H)[rad]−, respectively. The formation of these radicals is confirmed by a good proportionality relationship between the calculated proton hyperfine coupling constants of both radicals and the signal intensities in 1H CIDNP spectra detected after the recombination of the geminate radical pairs formed immediately after the laser pulse. The oxidized forms of KNA recombine yielding dimeric KNA-KNA products crosslinked via different positions within aromatic systems. The oxidized form of KNA, KNA(-H)[rad]−, could be of high biological interest due to its ability to recombine with other electron-deficient radicals, including tryptophan and tyrosine radicals, unravelling a radical pathway for the covalent attachment of KNA to proteins in living tissues.

AB - In this work, we report on the photo-induced oxidation of kynurenic acid (KNA) by the triplet-excited KNA in a neutral aqueous solution. This reaction is confirmed by two different time-resolved methods: optical spectroscopy and chemically induced dynamic nuclear polarization (CIDNP). The disproportionation reaction proceeds with the rate constant of (6.0 ± 1.2) × 107 M−1s−1 via the mechanism of H-atom transfer to the photoexcited KNA in the triplet state, yielding the reduced and oxidized forms of KNA, KNAH2[rad]− and KNA(-H)[rad]−, respectively. The formation of these radicals is confirmed by a good proportionality relationship between the calculated proton hyperfine coupling constants of both radicals and the signal intensities in 1H CIDNP spectra detected after the recombination of the geminate radical pairs formed immediately after the laser pulse. The oxidized forms of KNA recombine yielding dimeric KNA-KNA products crosslinked via different positions within aromatic systems. The oxidized form of KNA, KNA(-H)[rad]−, could be of high biological interest due to its ability to recombine with other electron-deficient radicals, including tryptophan and tyrosine radicals, unravelling a radical pathway for the covalent attachment of KNA to proteins in living tissues.

KW - Crosslinking

KW - H-atom transfer

KW - Kynurenic acid

KW - Photo-oxidation

KW - Photo-reduction

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85165532699&origin=inward&txGid=34b43d0f7474b3c27f10af25f8ff124b

UR - https://www.mendeley.com/catalogue/b5ea2829-53e7-343c-8655-1f320e5feb4b/

U2 - 10.1016/j.jphotochem.2023.115009

DO - 10.1016/j.jphotochem.2023.115009

M3 - Article

VL - 445

JO - Journal of Photochemistry and Photobiology A: Chemistry

JF - Journal of Photochemistry and Photobiology A: Chemistry

SN - 1010-6030

M1 - 115009

ER -