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Photodegradation of Folate Sensitized by Riboflavin
Author(s) -
Scurachio Regina S.,
Skibsted Leif H.,
Metzker Gustavo,
Cardoso Daniel R.
Publication year - 2011
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2011.00916.x
Subject(s) - chemistry , photochemistry , electron transfer , quenching (fluorescence) , riboflavin , quantum yield , ionic strength , excited state , triplet state , singlet oxygen , singlet state , photodegradation , aqueous solution , inorganic chemistry , fluorescence , photocatalysis , organic chemistry , catalysis , molecule , oxygen , biochemistry , physics , quantum mechanics , nuclear physics
Folate is shown to react with singlet‐excited state of riboflavin in a diffusion controlled reaction and with triplet‐excited state of riboflavin in a somewhat slower reaction with 3 k q = 4.8 × 10 8 L mol −1 s −1 in aqueous phosphate buffer at pH 7.4, ionic strength of 0.2 mol L −1 , and 25°C. Singlet quenching is assigned as photo‐induced reductive electron transfer from ground state folate to singlet‐excited riboflavin, while triplet quenching is assigned as one‐electron transfer rather than hydrogen atom transfer from folate to triplet‐excited riboflavin, as the reaction quantum yield, φ = 0.32, is hardly influenced by solvent change from water to deuterium oxide, φ = 0.37. Cyclic voltammetry showed an irreversible two‐electron anodic process for folate, E = 1.14 V versus NHE at a scan‐rate of 50 mV s −1 , which appears to be kinetically controlled by the heterogeneous electron transfer from the substrates to the electrode. Main products of folate photooxidation sensitized by riboflavin were pterin‐6‐carboxylic acid and p‐aminobenzoyl‐ l ‐glutamic acid as shown by liquid chromatographic ion‐trap mass spectrometry (LC‐IT‐MS).