Laser Flash Photolysis of Indole in the Presence of Amino Acids

Abstract

The laser flash photolysis of indole at 265 nm in the presence of glycine, proline and hydroxy proline was studied. The relative yields of c aq, triplet state, and indole cation radical were determined in the absence and in the presence of the amino acids. The yields were determined as a function of laser intensity and the values at very low intensity were compared with the fluorescence quenching results. It was concluded that in these conditions the photoionization of indole occurs via the fluorescent state. From the curves of triplet yield vs laser intensity, the triplet quantum yield extrapolated at low laser intensity was obtained, φr = 0.55 φ 0.05, relative to the literature value of 0.15 for φeag. This gives φF+φeaq= 1.0 ± 0.1 at room temperature. When proline and hydroxy proline were used as singlet quenchers, the yield of In was greater than the yield of caq. This was considered as evidence that a fraction of the quenching processes leads to complete electron transfer from indole to the amino acids.

PHOTO‐INDUCED ELECTRON EJECTION FROM THE REDUCED COPPER OF Pseudomonas aeruginosa AZURIN

“…Quenching of the 410 nm absorbance in the presence of N 2 0 suggests that the disulfide is formed by reactions of free hydrated electrons. Maxima at 430-440 nm have been observed in the transient absorbance spectra obtained upon pulsed excitation of both tryptophan (Bent and Hayon, 1975) and indole (Previtali, 1984) at 266 nm and have been assigned to the triplet states of these species. However, N 2 0 is not a triplet quencher, and the quenching behavior observed here strongly associates the observed absorption with reactions of the hydrated electron.…”

Radical Cation Production in the Photolysis of 5‐m‐ethoxy‐1‐m‐ethylindole

“…Thus, the fluorescent state could be the precursor, but vibrationally excited singlet states with lifetimes of to s are excluded. Support for the assignment of the fluorescent state as the precursor to photoionization and triplet state production has arisen from the recent low intensity laser studies of indole (Previtali, 1984;Bazin et al, 1983), and previous work on N-acetyltryptophanamide from this laboratory (Evans et al, 1978). The difficulty in making this assignment for 5-Me01 and its derivatives may arise because 5-MeOI, unlike other indoles, does not form solvent exciplexes (Herschberger and Lumry, 1976).…”

Energetics of Photoinduced Electron Transfer in the Indole‐O2 Cluster in Gas Phase: Possible Consequences for Photoexcited Tryptophan in Solution

“…In the following section the energetics for charge transfer from the indole side chain of tryptophan to 0, in water is discussed. Electron transfer from excited tryptophan to the peptide chain or to water was shown to exist but to be very inefficient (below 1%) (10,37) and to need thermal activation (0.34 eV) (16).…”

“…A conformer model was set up wherein different conformer populations exhibit different nonradiative processes (5,8). Several quenching mechanisms have been discussed: Proton transfer to the indole ring (9) and intramolecular electron transfer to nearby carboxyl groups (8,10), which might be enhanced by solvation (11,12) or zwitter-ion formation (13,14). The intersystem crossing quantum yields have been determined to be 0.28 (1).…”