排序方式: 共有29条查询结果,搜索用时 15 毫秒
21.
Abstract— The decay of the indole triplet of single tryptophan-containing proteins and model compounds can be readily measured at room temperature in aqueous solution by monitoring the triplet-triplet absorption or phosphorescence emission following a 265 nm exciting laser pulse. The quenching action of acrylamide on the triplet excited state of indole side chains was studied in an analogous fashion to that previously done at the singlet level (Eftink and Ghiron, 1977). The acrylamide triplet quenching constant (tkq) ranged from a high of 7.8 times 108M-1 s-1 for the exterior indole of corticotropin (ACTH) to a low of 2 times 105 Af-1 s-1 for the interior indole of ribonuclease T, (RNase T,). The ratio (7) of these values with their respective acrylamide singlet quenching constants (tkq),(γ=tkq8Kq) ranged from a high of 0.22 for ACTH to a low of 0.001 for RNase T1,. Acrylamide is also an inefficient quencher of model indoles in various solvents (i.e. it has a γ less than 1). The magnitude of γ varied from a high of 0.3 in H20 to a low of 0.02 in acetonitrile, but did not correlate with viscosity, dielectric constant or polarity. The lower efficiency observed for internal indole groups can not be explained by that class of models which predict the presence of static quenching at the triplet level, since none was observed. The present results confirm the observation of Calhoun et al. of a large discrepancy between acrylamide's singlet and triplet quenching constants for buried indole side chains, but suggest that it may be largely explained by the fact that acrylamide is an inefficient quencher of the indole triplet state (1983). The magnitude of this inefficiency is probably determined by specific microenvironmental factors. Thus, unlike 8Kq, the environmentally sensitive lkH cannot be easily used to characterize the dynamics of proteins. 相似文献
22.
Abstract— The microsecond flash photolysis of 5-methoxyindole in aqueous solutions has been studied at γexc ≥ 290 nm. Transients identified in this time realm in neutral solutions are: eaq - , the 5-methoxyindole radical cation (γmax ≅ 440 nm), the neutral transient with γmax ≅ 530 nm) and an unidentified oxygen sensitive transient with γmax ≅ 435 nm. Radical cations and e- aq are shown to be produced in equal amounts consistent with a photoionization process as the only source of both transients. H+ quenching of fluorescence and radical cation production gives equivalent Stern-Volmer constants indicating that photoionization occurs from the fluorescent state. The unidentified oxygen sensitive transient exhibits a pK a of2–2.5 and is quenched at lower pH values indicating that it also has a fluorescent state precursor. 相似文献
23.
Abstract— The kinetics of the photoinactivation of trypsin as sensitized by methylene blue and by eosin Y were investigated. The time-course of inactivation was first-order. The rates of inactivation were essentially identical as measured by three methods: the casein assay, the benzoyl-L-arginine ethyl ester assay, and the hemoglobin (in 5 M urea) assay. This is in sharp contrast to the results of earlier studies with flavins as photosensitizers, where the rate of inactivation was found to be much greater when measured by the hemoglobin assay than when measured by the other two assays. These differences are interpreted as indicating the production of a urea-sensitive 'damaged class' of trypsin molecules during photodynamic inactivation with flavins as sensitizers, but not with methylene blue and eosin Y. The results presented indicate that the mechanism of the photodynamic inactivation of enzymes might be different with different photosensitizing dyes. 相似文献
24.
25.
W. A. Volkert R. R. Kuntz C. A. Ghiron † R. F. Evans † R. Santus M. Bazin 《Photochemistry and photobiology》1977,26(1):3-9
Abstract— Electronic spectra of indoles are very sensitive to solvents. These solvent effects are particularly pronounced in the case of the fluorescence spectra of indoles. In order to elucidate the solvent band shifts during the relaxation of the excited states, particularly in polar solvents, the dipole moments of the excited singlet states have been estimated from the data of solvent-dependent Stokes shifts. In addition to indole, indole-5-carboxylic acid, indole-3-carboxylic acid, indole-2-carboxylic acid, 5-cyano- and 5-bromo-indoles have been investigated. All indoles showed a substantial increase in dipole moment upon excitation to the emitting state. These results are generally consistent with the Pariser-Parr-Pople SCF MO calculations. 相似文献
26.
R.F. Evans C.A. Ghiron W.A. Volkert R.R. Kuntz R. Santus M. Bazin 《Chemical physics letters》1976,42(1):39-42
Electron counting methods show that approximately 50% of the neutral radicals produced in the flash photolysis of N-acety-L-tryptophanamide (NATA) are not accompanied by hydrated electron formation. Thus, the neutral radical cannot originate solely from the photoionization reaction. 相似文献
27.
28.
Proton quenching of fluorescence, radical and electron production in the flash photolysis of N-acetyl-L-tryptophanamide indicates these processes originate from a common state. An indole photolysis model consistent with these and earlier observations is suggested. 相似文献
29.