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SINGLET OXYGEN YIELDS AND RADICAL CONTRIBUTIONS IN THE DYE‐SENSITISED PHOTO‐OXIDATION IN METHANOL OF ESTERS OF POLYUNSATURATED FATTY ACIDS (OLEIC, LINOLEIC, LINOLENIC AND ARACHIDONIC)
Author(s) -
Chacon Jorge N.,
McLearie James,
Sinclair Roy S.
Publication year - 1988
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.1751-1097.1988.tb02760.x
Subject(s) - singlet oxygen , chemistry , photochemistry , quenching (fluorescence) , singlet state , quantum yield , flash photolysis , linolenate , triplet state , oxygen , reaction rate constant , fluorescence , fatty acid , excited state , organic chemistry , kinetics , molecule , physics , quantum mechanics , nuclear physics
— The triplet state characteristics (spectrum, lifetime and quantum yield) for four dye sensi tisers [methylene blue (MB), erythrosin (ER), haematoporphyrin (HP) and riboflavin (RF)] were determined in methanol by laser flash photolysis and singlet oxygen yields (0.60 to 0.48) from time‐resolved measurements of the 1270 nm near infrared emission. The reaction of singlet oxygen with four long chain unsaturated phenyl esters [oleate (18: 1), linoleate (18: 2), linolenate (18: 3) and arachidonate (20: 4)] was followed quantitatively using the singlet oxygen luminescence technique and also, after continuous420–700 nm irradiation, by HPLC and other analysis of the isomeric product monohydroperoxides. The overall quantum yield of photooxidation (∼10 ‐2 ) was shown to be consistent with the observed singlet oxygen quenching constants(2–12 times 10 4 dm 3 mol ‐1 s ‐1 ) for the four esters studied and the singlet oxygen lifetime in methanol (τ∼ 9 μs). The isomer product distribution was interpreted in terms of a dual singlet oxygen and radical mechanism, the radical contribution increasing with sensitiser in the order ER = MB < HP ≪ RF, but also showing some dependence on substrate unsaturation. Evidence is presented for singlet oxygen quenching by MB and RF ( k O = 1.6 and 6.0 times 10 7 dm 3 mol ‐1 s ‐1 ) and for the accelerated photobleaching of the dye sensitisers in the presence of the unsaturated esters.