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1.
The singlet oxygen quantum yield (φ1 o2 ) of 11 purified fluorescein derivatives was determined by reaction with singlet oxygen acceptors in aqueous and ethanolic solutions; in both solvents φ1 o2 was enhanced with increasing halogenation. Tryptophan and 2,2,6,6-tetramethylpiperidone were found to be unadapted for the determination of φ1 o2 , in our systems; however, the use of 9.10-dipropionic anthracene acid andp-nitrosodimethylaniline in conjunction with imidazole derivatives was suitable for 1 O2 detection in water. Both methods lead to results in excellent agreement. As in ethanol. φ1 o2 , was equal to the triplet state quantum yield (φT ), the comparison between the two solvents showed that φT in water was greater than in ethanol. The comparison between our values obtained with polychromatic light with published data obtained with monochromatic light suggests that the triplet quantum yield of fluorescein derivatives is wavelength independent. 相似文献
2.
Abstract A continuous argon laser has been used to study the self-sensitized photooxidation of potassium rubrene-2,3,8,9-tetracarboxylate in oxygen-saturated H2 O and D2 O. An analysis of the data obtained in concentrated solutions leads to an unexpected high value of the ratio of 1 O2 lifetimes in D2 O and H2 O, T d 2 o/T h 2 o =17 ± 1. Results obtained in diluted aqueous solutions are interpreted in terms of a re-encounter of 1 O2 and ground state substrate molecules generated in the same triplet—triplet annihilation act. 相似文献
3.
Abstract— The yield of the primary products of the liquid water photolysis at 1236 and 1470 Å is reported. It was found that besides the dissociation of the excited water molecules into H and OH radicals probably e− aq is also formed. The H and OH radicals were scavenged by means of formate, and the e− aq together with a part of H2 O* by adding carbon dioxide. The quantum yields determined at 1236 Å, are: Φ(H, OH) = 1.03 & 0.02, 0.06 <Φ( e− aq , H2 O*) < 0.12 and at 1470 Å,: Φ(H, OH)=0.72±0.02, 0.037 < Φ( e− aq , H2 O*) <0.075. The quantum yield of high purity water at 1849 Å in the absence of any scavengers is Φ(H, OH)=0.022. Previously published data by us for 1849 Å are also given: Φ(H, OH)=0.33 ± 0.01 and 0.02 < Φ ( e− aq H2 O*) < 0.04. Reaction mechanisms are proposed. 相似文献
4.
Willem H. Koppenol John Butler‡ Johan W. van Leeuwen 《Photochemistry and photobiology》1978,28(4-5):655-658
Abstract— The Haber-Weiss cycle:
was investigated at low pH by radiolysis of oxygen or nitrogen saturated solutions of hydrogen peroxide. It was found that reaction 2 has a low rate constant: k2 = 3.0 ± 0.6 M -1 s-1 (pH 2.3, 22°C). The rate determining step of reaction 2 is most probably the transfer of an electron from a π8 * orbital of HO2 to the empty u * orbital of H2 O2 . Overlap between these two orbitals is hindered by the filled π8 * orbitals of H2 O2 . Fe(HI)EDTA catalyses reaction 2. 相似文献
was investigated at low pH by radiolysis of oxygen or nitrogen saturated solutions of hydrogen peroxide. It was found that reaction 2 has a low rate constant: k
5.
Abstract— Polymer rose bengal derivatives are converted to their C-6 ammonium salts. The φ1 O2 derived in CH2 C12 is a function of the K B of the neutralizing amine. 相似文献
6.
OscarH Will III David E. Sawtelle Pamela Iverson Kara Jorve 《Photochemistry and photobiology》1988,48(3):305-309
Abstract— The accumulation of (J-carotene in the ph/ph + y diploid strain of the smut fungus Ustilago violacea was associated with reduced killing and lower levels of induced mitotic recombination compared to the β-carotene lacking ph/ph+ w strain in response to both incandescent photosensitization and treatment with H2 02 . The ph/ph+ y strain was only slightly more resistant to killing by exogenous toluidine blue (TB) photosensitization. The ph/ph+ y strain exhibited significantly greater levels of survival when exposed to incandescent radiation and 1.5 μ.M TB for 15 min, as well as 3.0. 0.3, 0.03, 0.003% H2 02 in the dark. The ph/ph+ y strain also exhibited lower levels of mitotic recombination after endogenous TB photosensitization and the latter two H2 02 treatments. Similar survival results were obtained for the carotene accumulating haploid strain l.C2y and the carotene lacking haploid strain l.C2iv in response to H2 02 exposure. 相似文献
7.
K. Wyrzykowska M. Grodowski K. Weiss T. Latowski † 《Photochemistry and photobiology》1978,28(3):311-318
Abstract. The quantum yields of HCI (φHC1 ) formation have been measured for the photolysis of N -methyldiphenylamine (MeDPA), triphenylamine (TPA) and diphenylamine (DPA) in the presence of CCl4 in polar solvents. The quantum yields of N-methylcarbazole formation (φmφca ) have also been determined for the system MeDPA-CCl4 . With increasing CCl4 concentration, φHCl increases as φMeCA decreases, and φHCl reaches maximum values 2.7 at 1 M CCl4 . Using laser photolysis, transient spectra have been recorded for MeDPA in the absence and presence of CCl4 in polar and non-polar solvents, and for TPA. Transient absorption due to the triplet states and photocyclization products (without CCU), exciplexes, the (C6 H5 )2 NCHi radical, the MeDPA+ cation radical, the (TPA+ ., CCl4 ) ion pair, and the TPA+ cation radical have been identified. The mechanistic implications of these results are discussed. 相似文献
8.
Abstract— The extinction coefficient εT , of triplet benzophenone in benzene has been directly determined by absolute measurements of absorbed energy and triplet absorbance, Δ D 0 T , under demonstrably linear conditions where incident excitation energy, E 0 , and ground state absorbance, A 0 , are both extrapolated to zero. The result, 7220 ± 320 M -1 cm-1 at 530 nm, validates and slightly corrects many measurements relative to benzophenone of triplet extinction coefficients made by the energy transfer technique, and of triplet yields obtained by the comparative method.
As E0 and A 0 both decrease, Δ D 0 T becomes proportional to their product. In this situation, the ratio R = (1/ A 0 )(dΔ D 0 T /d E 0 ) = (εT - εG )φT . Measurements of R , referred to benzophenone, give (εT - εG )φT for any substance, without necessity for absolute energy calibration.
Both absolute and relative laser flash measurements on zinc tetraphenyl porphyrin (εT - εG at 470 nm = 7.3 × 104 M -1 cm-1 ) give φT = 0.83 ± 0.04. 相似文献
As E
Both absolute and relative laser flash measurements on zinc tetraphenyl porphyrin (ε
9.
-The luminescence at 1.27 μm from the 3 →→1 δg transition of the oxygen molecule has been detected from a variety of liquid systems. A Q-switched laser delivering pulses of 532 nm light was the excitation source, a germanium photodiode was the detector and substituted porphyrins were used as photosensitizers. Protio- and deutero- forms of several solvents were studied and the singlet oxygen lifetimes determined directly agreed well with published values. Tδ in D2 O was found to be 55 μs and, by extrapolation from a series of H2 O - D2 O mixtures, a value of 3.3 μs was obtained for Tδ in H2 O. The technique was shown to be useful in measuring Tδ values in several microheterogeneous systems such as surfactant micelles, vesicles and human serum albumin. 相似文献
10.
P. F. HEELIS B. J. PARSONS G. O. PHILLIPS A. J. SWALLOW 《Photochemistry and photobiology》1991,53(1):21-23
Abstract— The one-electron reduction and oxidation of 5,10-methenyltetrahydrofolate has been studied in aqueous solution in the acidity range H0 = -1 to pH = 7 using the reducing species CO- 2 and (CH3 )2 -COH and oxidising species Br- 2 , and H2 SeO+3 . The spectral and other properties of the radicals so formed were found to be indcpendent of the reductant/oxidant used. Two protolytic forms of both the oxidised and reduced radicals were observed with approximate p K , values of 0.5 ± 0.3 being determined. Both the bridged form (5.10-methenyltetrahydrofolate) and the unbridged form (5- formyltetrahydrofolate) were found to be easily oxidised, whereas only the former could be reduced. 相似文献
11.
HYDROGEN PEROXIDE INDUCED RESISTANCE TO BROAD-SPECTRUM NEAR-ULTRAVIOLET LIGHT(300–400 nm) INACTIVATION IN Escherichia coli 总被引:5,自引:0,他引:5
Abstract— Strains of Escherichia coli carrying the four possible combinations of the alleles nur, nur+ , uvrAb, and uvrA + were either untreated or pretreated with a sublethal dose of H2 02 prior to inactivation with NUV radiation. Pretreated cells exhibited a greater resistance to NUV than did untreated cells. Pretreatment with H2 O2 did not induce resistance to FUV radiation. The induction of resistance to NUV inactivation by H2 O2 pretreatment apparently leads to protection against the damage caused by NUV radiation. Although pretreatment of cells with H2 02 leads to resistance of such cells to inactivation by H2 O2 and NUV, survival of H2 O2 treated bacteriophage PI cml clr100 is not enhanced when assayed on H2 O2 pretreated E. coli host cells. 相似文献
12.
Abstract— Bacteriorhodopsin is a light activated proton pump which generates proton and electric gradients across the cytoplasmic membrane of Halobacterium halobium. In this study, a dye whose fluorescence intensity responds rapidly to membrane potential was used to follow the evolution of the potential on liposomes reconstituted with bacteriorhodopsin, in the microseconds time domain. By comparing the formation kinetics of the potential to those of the long-lived intermediate species in the bacteriorhodopsin photocycle, M412 , both in H2 O and 2 H2 O suspensions, we can draw the following conclusion: the electric potential onset time is 20 μs after initiation of the illumination. The triggering of the potential is not the formation of the M412 intermediate, which was hitherto considered to be the first species in the bacteriorhodopsin cycle which has an unprotonated Schiff base linkage at the retinal chromophore. Rather, the potential forms at the transition of the L550 intermediate to the species X which precedes M412 or even at the preceding conversion of K590 to L550 . 相似文献
13.
C. Chahidi M. Aubailly A. Momzikoff M. Bazin R. Santus 《Photochemistry and photobiology》1981,33(5):641-649
Abstract— The characteristics of the fluorescence and phosphorescence emission of 2-amino-4 (3H) pteridinone (or pterin) in aqueous solutions are pH dependent. The room temperature fluorescence quantum yield is low and is maximum at pH = 10 (φF ∼ 0.057). The 77K phosphorescence emission consists of two overlapping emissions originating from τ* triplet states. In agreement with low temperature results, the 353nm laser flash photolysis makes it possible to detect at pH 9.2, two transient triplet absorptions (τ1 ∼ 0.3 μs and τ2 ∼ 2.3 μs). The longer lived triplet is characterized by φTM ∼ 0.20 and ∼ (550nm) = 2000 M −1 cm−1 . It reacts with the solvent forming the semireduced pterin with a quantum yield φR ∼ 0.06. The photosensitizing properties of pterin have been studied by laser flash spectroscopy and steady state irradiations. Photoreactions implying singlet oxygen formation are shown to occur. Laser flash spectroscopy indicates that the pterin triplet is reduced by amino acids and nucleic acid bases. Corresponding bimolecular reaction rate constants have been measured. 相似文献
14.
Abstract— The photooxidation of epinephrine, sensitized by methylene blue or by chlorophylls, excited with red light, involves the reduction of two molecules of oxygen to hydrogen peroxide per molecule of epinephrine oxidized to adrenochrome. The initial rates of these reactions are not affected by low concentrations of catalase. In 99 mol % D2 O, rates of methylene blue sensitized photooxidations are accelerated as much as 5.2 times over rates in ordinary water. Azide anion is a more effective inhibitor of this reaction in D2 O than in H2 O. Half maximal inhibitions are obtained by 1.3 mM azide in H2 O and by 0.1 mAf azide in D2 O. Isotope effects and azide sensitivities point to photooxidation of epinephrine in D2 O primarily by a singlet oxygen pathway; in H2 O, non-singlet oxygen pathways become more predominant. Superoxide dismutase (SOD) markedly inhibits rates of the photooxidations in H2 O and in D2 O; about 25% at 10-9 M SOD, and 50% at 10-6 M SOD in H2 O. In the photooxidation in H2 O, both by non-singlet and singlet oxygen mechanisms, the amount of superoxide produced is equivalent to the amount of O2 consumed in the photooxidation of epinephrine; the superoxide thus formed participates in the oxidation of epinephrine. 相似文献
15.
Abstract In the presence of the photosensitizer riboflavin at high fluence rates a photoproduct, most probably H2 O2 , is formed which causes negative phototaxis in the colorless flagellate Polytomella magna . The aim of this study was to find out whether H2 O2 is produced in a type I or II reaction. As has been shown, 1 O2 quenchers either do not influence the photodynamic action of riboflavin (furfuryl ethanol, DPBF, l -histidine, crocetin) or show slight quenching effects only at very high concentrations ≧ 10−2 M (DABCO, DMF, imidazole). D2 O is toxic to P. magna even in 1:1 and 1:2 mixtures with H2 O. On the other hand, the quenching effect of 1,4-benzoquinone, highly indicative for the type I pathway, is more than two orders of magnitude stronger than the one of the above mentioned 1 O2 quenchers. The results suggest that H2 O2 is produced in a type I reaction. Superoxide does not seem to be involved since superoxide dismutase does not diminish the photodynamic effect of riboflavin. 相似文献
16.
S. A. Bezman P. A. Burtis T. P. J. Izod M. A. Thayer 《Photochemistry and photobiology》1978,28(3):325-329
Abstract. The photodynamic inactivation of E. coli by visible light and O2 was found to occur in the presence of the sensitizer rose bengal, immobilized by covalent bonding to polystyrene beads. The demonstrated absence of significant amounts of dissolved rose bengal indicated that an inactivation mechanism based on penetration of sensitizer molecules into the cell's interior could not be operating. Survival curves typically exhibited induction periods followed by rapid exponential death, with 99.99% kill requiring 1–2 h depending on conditions. A mechanism involving the participation of photo-generated singlet excited oxygen O2 (1 δ) in inactivation of E. coli is proposed. The photodynamic inactivation rate increased significantly in H2 O compared with H2 O, which is evidence supporting singlet oxygen as an active intermediate, since O2 (1 δ) has a much longer lifetime in H2 O than in H2 O. H2 O did not act as a short term poison in the absence of sensitizer. 相似文献
17.
R. Bonnett C. Lambert † E. J. Land + P. A. Scourides R. S. Sinclair † T. G. Truscott § 《Photochemistry and photobiology》1983,38(1):1-8
Abstract— Nanosecond laser flash photolysis and pulse radiolysis have been used to generate and characterise the triplet state, and semioxidised and semireduced radicals of haematoporphyrin, and three 0 -acyl compounds derived from it (the monoacetate, the diacetate and the disuccinate).
After 347 nm irradiation in water containing 2% Triton X-100, haematoporphyrin forms the triplet state (φT = 0.92) and photoionises monophotonically (φI = 0.03). For the O -acyl derivatives, φT approaches unity and photoionisation is reduced. In acetone the triplet yield of all four compounds are close to unity. The difference and corrected spectra for the triplet species are presented and decay rates ( k 1 ˜104 s-1 ) and oxygen quenching constants ( k Q ˜1.5times109 M -1 s-1 ) for the triplet state have been measured. The difference and corrected spectra for the semi-reduced species in methanol and semi-oxidised species in aqueous Triton X-100 are presented.
The photophysical characteristics in fluid solution of haematoporphyrin and its 0 -acyl derivatives are rather similar to those previously recorded for other photosensitising porphyrins. 相似文献
After 347 nm irradiation in water containing 2% Triton X-100, haematoporphyrin forms the triplet state (φ
The photophysical characteristics in fluid solution of haematoporphyrin and its 0 -acyl derivatives are rather similar to those previously recorded for other photosensitising porphyrins. 相似文献
18.
J. W. Eastman 《Photochemistry and photobiology》1967,6(1):55-72
Abstract— By idealizing the design of a typical spectrofluorimeter that measures fluorescence from dilute solutions, we are able to derive an equation that predicts the dependence of the observable amplitude on the concentration of the solute and on several instrumental parameters. The result of the derivation, the fluorescence function, is used together with measurements of rhodamine B fluorescence and colloidal silica scattering to calibrate a spectrofluorimeter.
The fluorescence function and the calibration data are used to determine the absolute fluorescence quantum yield of quinine sulfate in 0–1 N H2 So4 . The results, Ø250 =0.582 with excitation at 250 mμ, adn Ø350 =0.577 with excitation at 350mμ. agree well with the previous evaluation of Melhuish, Ø345 =0.546. 相似文献
The fluorescence function and the calibration data are used to determine the absolute fluorescence quantum yield of quinine sulfate in 0–1 N H
19.
Abstract— A novel method for the determination of singlet oxygen reaction rate constants is described and applied to studies of cyclohexadiene in methanol and gelatins in H2 O and D2 O. The technique uses tris (2,2'-bipyridine) ruthenium(II) dication (Ru(bipy)32+ ) as both singlet oxygen sensitizer and in situ oxygen concentration monitor during irradiation of sealed samples. Because of the high efficiency with which the luminescence of Ru(bipy)3 2+* can be detected, and the fact that emission lifetimes are used, the method offers some advantages over those previously described. The advantages and disadvantages of the method are discussed. A rate constant of 2.1 (±0.3) x 106 mol-1 dm3 s-1 has been determined for the reaction of 1 O2 with cyclohexadiene in methanol. For two different photographic gelatins the sums of reaction and quenching rate constants are 2.0 (±0.4) x 106 and 3.1 (±2.0) x 105 mol-1 dm3 s-1 ; for swine skin gelatin this value is 3.9 (±2.4) × 105 mol-1 dm3 s-1 . Chemical reaction, rather than physical quenching, is the dominant reaction route for gelatins and 1 O2 . 相似文献
20.
T. Melvin S. Cunniffe D. Papworth T. Roldan-Arjona P. O'Neill 《Photochemistry and photobiology》1997,65(4):660-665
Abstract— Irradiation of aqueous solutions of plasmid DNA (pUC18) at pH 7.6 with 193 nm laser light results in low yields of prompt single strand breakage (air-saturated sample φssb = [1.5 ± 0.1] ± 10−4 , argon-saturated sample φssb = [0.9 ± 0.1] ± 10−4 ). Treatment of the irradiated DNA samples with Escherichia coli formamidopyrimi-dine-DNA glycosylase (Fpg) protein results in an approximate 20-fold increase in the yield of single strand breakage (air-saturated sample φfpg = [33.1 ± 3.1] ± 10−4 , argon-saturated sample φfpg = [23.8 ± 2.6] × 10 4 ). This result indicates that 193 nm light induces other modification) (most likely of the purine moieties) that are 20 times more abundant than prompt strand breakage within the DNA matrix. 相似文献