Proton-coupled electron transfer as the mechanism of reaction between triplet state of kynurenic acid and tryptophan

Yuliya S. Zhuravleva, Olga B. Morozova, Yuri P. Tsentalovich, Peter S. Sherin

Research output: Contribution to journalArticlepeer-review

Abstract

Kynurenic acid (KNA) is an endogenous UV-A chromophore of the human eye lens able to sensitize photodamages to eye lens proteins. In the present work, we studied in details the mechanism of reaction between KNA triplet state (TKNA) and tryptophan (Trp), the most effective quencher of TKNA among aromatic and sulfur-containing amino acids, by nanosecond laser flash photolysis. Previous studies suggested electron transfer as the reaction mechanism without its direct spectroscopic confirmation. Time-resolved kinetics and spectral data of this work clearly evidence the formation of neutral tryptophanyl radicals immediately after the TKNA quenching by Trp that indicates either hydrogen transfer or proton-coupled electron transfer (PCET) as the reaction mechanism. Low kinetic isotope effect for the quenching rate constant, kH2O/kD2O = 1.3, speaks in favor of PCET mechanism of the quenching reaction, which includes the diffusion-controlled electron transfer as the primary step and the proton transfer in the radical cage as the final step.

Original languageEnglish
Article number112522
Number of pages6
JournalJournal of Photochemistry and Photobiology A: Chemistry
Volume396
DOIs
Publication statusPublished - 1 Jun 2020

Keywords

  • Kynurenic acid
  • Proton-coupled electron transfer
  • Radicals
  • Triplet state
  • Tryptophan
  • OXIDATION
  • TIME-RESOLVED CIDNP
  • TYROSINE
  • UV FILTER
  • AMINO-ACIDS
  • KINETICS
  • PHOTOCHEMISTRY
  • PROTEINS
  • WATER
  • PHOTOOXIDATION

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