TY - JOUR

T1 - Acid-alkaline properties of triplet state and radical of kynurenic acid

AU - Zhuravleva, Yuliya S.

AU - Tsentalovich, Yuri P.

N1 - Publisher Copyright: © 2018 Elsevier B.V.

PY - 2018/10/1

Y1 - 2018/10/1

N2 - Kynurenic acid (KNA), a degradation product of endogenous UV filter of the human lens kynurenine, is a convenient model compound for studying reactions of photoexcited chromophores with amino acids, peptides and proteins. In this work, transient absorption spectra of triplet KNA (TKNA) and KNA radical (KNA[rad]−) were obtained for aqueous solutions with different pH's, and the dissociation constants for TKNA (pKa = 3.7) and KNA[rad]− (pKa = 5.5) have been determined. The quenching of TKNA by oxygen, tryptophan and ascorbate proceeds with nearly diffusion rate constants, weakly dependent on the charge on TKNA and on quencher. The quenching by tyrosine and histidine are much slower, and the quenching rate constants depend on solution pH's. The most pronounced pH-dependence was found for TKNA quenching by thiols cysteine and glutathione, which can be attributed to the switch of the quenching mechanism from the electron transfer in alkaline solutions to the hydrogen atom transfer under neutral and acidic conditions.

AB - Kynurenic acid (KNA), a degradation product of endogenous UV filter of the human lens kynurenine, is a convenient model compound for studying reactions of photoexcited chromophores with amino acids, peptides and proteins. In this work, transient absorption spectra of triplet KNA (TKNA) and KNA radical (KNA[rad]−) were obtained for aqueous solutions with different pH's, and the dissociation constants for TKNA (pKa = 3.7) and KNA[rad]− (pKa = 5.5) have been determined. The quenching of TKNA by oxygen, tryptophan and ascorbate proceeds with nearly diffusion rate constants, weakly dependent on the charge on TKNA and on quencher. The quenching by tyrosine and histidine are much slower, and the quenching rate constants depend on solution pH's. The most pronounced pH-dependence was found for TKNA quenching by thiols cysteine and glutathione, which can be attributed to the switch of the quenching mechanism from the electron transfer in alkaline solutions to the hydrogen atom transfer under neutral and acidic conditions.

KW - Acid

KW - Eye lens

KW - Free radicals

KW - Kynurenic

KW - Photochemistry

KW - Triplet state

KW - AQUEOUS-SOLUTIONS

KW - TIME-RESOLVED CIDNP

KW - LASER FLASH-PHOTOLYSIS

KW - AROMATIC-AMINO-ACIDS

KW - ELECTRON-TRANSFER

KW - PULSE-RADIOLYSIS

KW - CATARACTOUS HUMAN LENSES

KW - TRYPTOPHAN OXIDATION

KW - UV FILTERS

KW - SKIN-CANCER

UR - http://www.scopus.com/inward/record.url?scp=85050219909&partnerID=8YFLogxK

U2 - 10.1016/j.jphotochem.2018.07.029

DO - 10.1016/j.jphotochem.2018.07.029

M3 - Article

AN - SCOPUS:85050219909

VL - 365

SP - 7

EP - 12

JO - Journal of Photochemistry and Photobiology A: Chemistry

JF - Journal of Photochemistry and Photobiology A: Chemistry

SN - 1010-6030

ER -