Photolysis mechanism of aqueous tryptophan
Flash photolysis experiments indicate that monophotonic photoionization is the principal initial photolysis act in aqueous tryptophan under high intensity, 265-nm laser excitation, leading to the Trp/sup +/ radical cation (lambda/sub max/ 580 nm) with quantum yield 0.12 +- 0.01 and e/sub aq//sup -/ with quantum yield 0.10 +- 0.01 from pH 4 to 8. The neutral Trp radical (lambda/sub max/ 510 nm) is formed by deprotonation with rate constant 1.5 x 10/sup 6/ s/sup -1/. The disappearance of e/sub aq//sup -/ follows a complex decay inconsistent with homogeneous kinetics. The results are in agreement with a recombination model in which the electron diffuses through the medium as a quasi-free entity, during which period back reactions with the original radical, or electrons and radicals generated in nearby pairs, compete with scavenging by tryptophan or added solutes. The well-established result that Trp yield observed after electron decay is not enhanced by oxygen or other e/sub aq//sup -/ scavengers is attributed to the formation of an unstable intermediate product of the electron-radical back reaction which subsequently oxidizes additional tryptophan to Trp.
- Research Organization:
- Illinois Inst. of Tech., Chicago
- OSTI ID:
- 7300569
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 81:14; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400500* -- Photochemistry
AMINO ACIDS
AQUEOUS SOLUTIONS
AZOLES
CARBOXYLIC ACIDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DECOMPOSITION
DISPERSIONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INDOLES
KINETICS
MIXTURES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PYRROLES
REACTION KINETICS
SOLUTIONS
TRYPTOPHAN