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Photogeneration and quenching of reactive oxygen species by urocanic acid

Haralampus-Grynaviski, N., Ransom, C., Ye, T., Rozanowska, Malgorzata Barbara, Wrona, M., Sarna, T. and Simon, J. D. 2002. Photogeneration and quenching of reactive oxygen species by urocanic acid. Journal of the American Chemical Society 124 (13) , pp. 3461-3468. 10.1021/ja016902x

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Urocanic acid, UCA, is characterized by two electronic transitions in the UV-B (280−320 nm) which comprise its broad absorption spectrum and give rise to wavelength-dependent isomerization quantum yields. The absorption spectrum of UCA extends into the UV-A (320−400 nm). Given the UV-A component of sunlight is significantly greater than the UV-B component it is hypothesized even weak UV-A photochemistry of UCA could be important for in vivo responses to UV radiation. Degenerate pump−probe experiments performed on t-UCA at several wavelengths in the UV-A reveal an excited-state absorption that undergoes a rapid, 1 ps decay. Photoacoustic experiments performed on both the cis and trans isomers reveal the formation of a long-lived intermediate following UV-A excitation. The efficiency and action spectra for this latter photoactive process are presented and are similar for both isomers of UCA. Cholesterol hydroperoxide assays designed to investigate the nature of the UV-A photoreactivity of t-UCA confirm the production of reactive oxygen species. The bimolecular rate constant for the quenching of singlet oxygen by t-UCA is determined to be 3.5 × 106 M-1 s-1. Taking into consideration recent theoretical calculations and jet expansion studies of the electronic structure of gas-phase t-UCA, a model is proposed to explain the isomerization and photoreactivity of t-UCA in solution over the UV-A region.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Optometry and Vision Sciences
Subjects: R Medicine > RE Ophthalmology
Publisher: American Chemical Society
ISSN: 0002-7863
Last Modified: 04 Jun 2017 04:45

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