Flash Photolysis and Inactivation of Aqueous Lysozyme*

Abstract— The photochemical and photosensitizing properties of N‐formylkynurenine (FK) and related compounds have been investigated using the laser flash photolysis technique by exciting water solutions with 265 nm or 353 nm radiation. The FK molecules in their first excited singlet state readily react with water leading probably to OH formation. FK triplet state reacts with many biological compounds including vitamins, amino acids and nucleic acid bases. The semi‐reduced FK thus formed can, in turn, reduce substrates such as cytochrome c or O2.

Section: Primary Photochemical Processesmentioning

confidence: 99%

ON THE PHOTOSENSITIZING PROPERTIES OF N‐FORMYLKYNURENINE AND RELATED COMPOUNDS

Pileni

Santús

Land

1978

“…These numbers may measure the true yields from outright electron ejection from E* but these are other alternatives. Flash-photolysis studies by Czapski and Ottolenghi [29] with phenolate, Grossweiner and Usui with tryptophan [30], and Goldschmidt and Stein with pnaphtholate [ 131 suggest that low yields of solvated electrons are produced from prefluorescent excited states. In exciplex-forming systems this prefluorescent state may be the excited singlet, I*.…”

Section: Solvent Effectsmentioning

confidence: 99%

Exciplex Studies–v. Electron Ejection From Indole and Methyl‐indole Derivatives*

Hopkins

Lumry

1972

Abstract— Electron‐scavenging experiments with N2O as scavenger demonstrate at least two electron‐producing reactions of the excited singlet states of the exciplex species formed by indole or 1 ‐methyl‐indole with water. Most electrons reacting with N2O result from collision of the scavenger with a metastable state formed from the initial exciplex state but finite electron yields from indole and 1‐methyl‐indole at limiting scavenger concentrations suggest that the intermediate states also eject electrons directly into the solvent. The formation of the first metastable state from the fluorescent exciplex state has an activation energy, EM, estimated to be about 13 kcal/mole for both indole and 1 ‐methyl‐indole water exciplexes. The EM values for 1‐methyl‐indole from fluorescence and electron yields are the same, Indicating that at neutral and alkaline pH fluorescence quenching and electron extraction are both being controlled by the formation of the first metastable intermediate. Observed electron yields from indole‐water and indole‐methanol exciplexes are less than predicted using fluorescence data, although EM values of 1 kcal/mole are obtained for the indole‐methanol exciplex by both methods. At pH 12·0 and 28°C the total electron yields for indole‐water and 1 ‐methyl‐indole‐water exciplexes are 0·30 and 0·25, respectively. The residual yields attributed to outright formation of hydrated electrons from the initial exciplex excited stateare 0·11 and 0·05, respectively. Electron yields from the indole‐water exciplex are strongly pH dependent only near pH 1 where the fluorescence yields as well as the electron yields decrease rapidly with increasing acidity. The 1‐methyl‐indole‐water exciplex shows an additional pH dependence which is first‐order in hydrogen‐ion activity and has an effective pKa of about 11·5. Comparable yields for indole and 1‐methyl‐indole are found only above pH 12. High electron yields are found with indole in the exciplex‐forming solvent dioxane and in the non‐exciplex forming solvent cyclohexane. For the latter system electrons are probably derived only from the lowest excited state of indole on collision with N2O.

“…1 1 show that AF' for oxidation of tyrosine and tryptophan by triplet eosin and semi-oxidized eosin should be the order of -13 kcal/ mole and -20 kcal/mole respectively. Oxidation by T has been shown to produce the same initial radical products as ultraviolet photolysis [6], which have been identified with the p-alanylphenoxyl radical [32] and the tryptophan radical formed by ejection of an electron from the pyrrole ring N atom of tryptophan [33]. The hydrated electron is a product of both processes [6].…”

Section: Photodynamic Oxidation Of I -mentioning

confidence: 99%

“…Recent calcuIations of Reinisch et uf. [34] indicate that two-photon excitation is required to overcome the high activation energy for dissociation of the tyrosine and tryptophan triplet states to give the radical products, although this may not be the case for the photoionization pathway if electron release takes place from another intermediate [33]. The aromatic products of oxidation by X are not known.…”

Section: Photodynamic Oxidation Of I -mentioning

confidence: 99%

Photodynamic Oxidation of Iodide Ion and Aromatic Amino Acids by Eosin*

Kępka

Grossweiner

1971

Self Cite

Abstract— The photosensitized oxidation of I‐, tyrosine, and tryptophan by aqueous eosin has been investigated with a photostationary technique, in which the system is irradiated with sinusoidally modulated light and phase sensitive detection is used to measure the spectra of short‐lived intermediates and their rate constants. It has been shown that the principal oxidizing agent for I‐ is semi‐oxidized eosin (X) produced by the reduction of oxygen by triplet state eosin. The same mechanism obtains when femcyanide ion is substitued for oxygen. A second oxidizing agent is effective in oxygenated solutions at high I‐ concentrations, attributed to O2‐. The X mechanism controls when tyrosine or tryptophan are irradiated at low substrate concentrations in the presence of oxygen or femcyanide. However, at high substrate concentrations, or in the absence of the electron accepting agents, the mechanism switches to the ‘dye‐substrate’ process where triplet state eosin oxidizes the aromatic substrate and is reduced to the semiquinone. The conversion quantum yields agree with the predictions based on the measured quenching and reaction rate constants.