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FREE RADICALS PRODUCED IN A RIGID SOLUTION OF TRYPTOPHAN BY A BIPHOTONIC PROCESS
Author(s) -
STEEN H. B.
Publication year - 1969
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.1751-1097.1969.tb07317.x
Subject(s) - radical , photochemistry , chemistry , absorption (acoustics) , radiolysis , quantum yield , phosphorescence , irradiation , photodissociation , ethylene glycol , molecule , materials science , fluorescence , organic chemistry , optics , physics , nuclear physics , composite material
— Free radicals were trapped by irradiation of tryptophan in an ethylene glycol/water glass with 250 nm U.V. light at 77°K. The ESR‐spectrum was attributed to approximately equal amounts of trapped electrons and ethyl radicals. The electrons could be transformed into the ethyl type radicals by heating or bleaching with near u.v. or visible light. The quantum yield of trapped radicals increased with increasing intensity of the irradiation by more than one order of magnitude over the range of intensities studied. A kinetic model was formulated on the assumption that the radicals were produced by the successive absorption of two light quanta, the absorption of the first giving rise to a transient intermediate which subsequently absorbs a second quantum to produce the radicals. The experiments confirmed the applicability of this model to the present case. The decay time obtained for the intermediate was 6.8 sec which equals the phosphorescence decay time of tryptophan under similar conditions, indicating that the intermediate involved was the lowest triplet level of this molecule. The absorption cross section of this intermediate at 250 nm with regard to the formation of trapped radicals was found to be 8000 l./mol cm.