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ELECTRON TRANSFER FROM THE EXCITED STATE OF TYROSINE TO COMPOUNDS CONTAINING DISULFIDE LINKAGES
Author(s) -
FEITELSON J.,
HAYON E.
Publication year - 1973
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.1751-1097.1973.tb06355.x
Subject(s) - chemistry , excited state , photochemistry , electron transfer , tyrosine , flash photolysis , photodissociation , singlet state , ion , radical , triplet state , molecule , kinetics , reaction rate constant , organic chemistry , atomic physics , biochemistry , physics , quantum mechanics
— The flash photolysis of aqueous solutions of tyrosine has been studied in the presence of various concentrations of the cyclic disulfide sodium lipoate (thioctic acid, Na + salt). In addition to the formation of phenoxyl radicals and hydrated electrons (and possibly H atoms) from the photoionization of tyrosine, the characteristic spectrum of the radical anion RSSR ‐ of lipoate was also observed in neutral as well as in alkaline solutions. From the dependence of these yields upon the concentration of lipoate, it was found that a long–lived triplet excited state of tyrosine, rather than the singlet excited state, is involved in these reactions. The negative radical ions RSSR ‐ are formed by two distinct pathways: (a) Na + –lipoate reacts with the solvated electrons which are ejected from the tyrosine triplets 3 Tyr → RO.+ e ‐ aq + H + followed by e ‐ aq + RSSR → RSSR ‐ , and (b) by direct interaction of lipoate with triplet excited tyrosine, resulting in the transfer of a negative charge from tyrosine to the disulfide linkage. At high lipoate concentrations, the singlet excited state of lipoate is quenched, k 4 = 1.6 × 10 10 M ‐1 sec ‐1 , but this reaction does not lead to the formation of RSSR ‐ radical ions.