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1.
The photodecomposition of sulfanilamide (4-aminobenzenesulfonamide), sulfacetamide. sulfathiazole. sulfadiazine, carbutamide and tolbutamide has been studied using the spin traps 2-methyl-2-nitrosopropanc and 5,5-dimethyl-l-pyrroline-l-oxide. The following radicals were trapped during the photolysis of sulfanilamide in aqueous solution: H' and HNC6H4SO2NH, (α-fission). SO2NH2 and C6H4NH2 (δ fission). H2NC6H4SO2 and NH2 (δ-fission). Although the C.,H4SO2NH2 and the SO; radicals were also detected these were not formed directly by homolytic bond fission. Homolytic bond fission was also observed during the irradiation of sulfacetamide (α.δ), sulfadiazine (α). carbutamide (α,δ) and tolbutamide (δ). All of the analogs, with the exception of tolbutamide, generated the SO; radical. Sulfacetamide, sulfadiazine and carbutamide generated the C6H4SO2;NHR radical by some process that did not involve homolytic bond fission. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects.  相似文献   

2.
The menadione photosensitized reactions of nucleic acid and protein constituents were studied by ESR and spin trapping. Thymine, thymidine, cytosine, 2'-deoxycytidine,5'-dCMP, uracil and several N-acetyl amino acids and dipeptides were investigated. Photolysis at 335 nm was carried out in air-saturated or Ar saturated DMSO : H2O (1 : 1, vol/vol) containing 10 3 M menadione and 10-2 M 2-methyl-2-nitrosopropane as the spin trap. The observed spin adducts were explained in terms of electron transfer from the substrate to the excited triplet state of menadione to form the radical cation of the substrate and the anion radical of menadione which was also detected by ESR.  相似文献   

3.
Abstract— The photodecomposition of sulfanilamide, 4-aminobenzoic acid and related analogs in aqueous solution has been studied with the aid of spin traps 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and CH3NO2 as well as by direct electron spin resonance techniques. The NH2 radical was trapped by DMPO during the photolysis of aqueous solutions of sulfanilamide with a Xe arc lamp. Studies with [15N1]-sulfanilamide indicated that the NH2 radical was generated by homolytic fission of the sulfur-nitrogen bond. Under the same conditions DMPO trapped the H and SO3 radicals during photolysis of sulfanic acid. Direct photolysis of sulfanilamide, sulfanilic acid and Na2SO3 in the absence of any spin trap yielded the SO3 radical. Photolysis of 4-aminobenzoic acid at pH 7 gave the H radical which was trapped by DMPO. At low pH values OH and C6H4COOH radicals were generated during the photolysis of 4-aminobenzoic acid. No eaq were trapped by CH3NO2 when acid (pH 4) and neutral aqueous solutions of sulfanilamide or 4-aminobenzoic acid were photoirradiated. The mechanism of formation of known photoproducts from the free radicals generated by sulfanilamide and 4-aminobenzoic acid during irradiation are discussed. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects.  相似文献   

4.
Abstract— The oxidation of 3, 4-dihydroxyphenylalanine (dopa) photosensitized by hematoporphyrin has been studied by ESR spectroscopy. The nitroxide free radical 2, 2, 6, 6-tetramethyl-4-piperidone-I-oxyl (TEMPONE) is shown to be a convenient probe for monitoring oxygen consumption during the reaction. Isotope and azide effects on oxygen consumption suggest that photooxidation in D2O proceeds mainly by a singler oxygen mechanism, whereas in H2O both singlet oxygen and free radical mechanisms are important. The relative importance of these mechanisms can change as oxygen is consumed during the photoreaction. TEMPONE also can be used as an indicator of the presence of reducing radicals (in this case hematoporphyrin radical anions) in the system, but only at low oxygen levels: in aerated solutions efficient reaction of these radical ions with oxygen is proposed.  相似文献   

5.
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 eaq is also formed. The H and OH radicals were scavenged by means of formate, and the eaq together with a part of H2O* by adding carbon dioxide. The quantum yields determined at 1236 Å, are: Φ(H, OH) = 1.03 & 0.02, 0.06 <Φ( eaq , H2O*) < 0.12 and at 1470 Å,: Φ(H, OH)=0.72±0.02, 0.037 < Φ( eaq , H2O*) <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 ( eaq H2O*) < 0.04. Reaction mechanisms are proposed.  相似文献   

6.
Abstract— Photooxidation reactions in ascorbate (AH)-containing erythrocyte membrane suspensions have been studied in broad perspective by simultaneously monitoring lipid peroxidation in the membrane compartment and formation of hydrogen peroxide (H2O2) and hydroxyl radical (OH) in the aqueous compartment. Non-bound uroporphyrin (UP) and membrane-bound protoporphyrin (PP) were used as sensitizers. Photoreduction of UP to the radical anion (UP-) was detected by electron spin resonance when UP/AH/membrane mixtures were irradiated anaerobically. Aerobic irradiation resulted in a strong AH--stimulation of lipid peroxidation, H2O2 formation, and OH- generation (detected with 2-deoxyribose (DOR) and the spin trap 5,5-dimethyl-l-pyrroline-N-oxide). Use of diagnostic agents (e.g. catalase, desferrioxamine, mannitol) revealed that OH- is involved in light-stimulated DOR oxidation, but not in lipid peroxidation. Similar irradiation in the presence of PP resulted in far greater lipid peroxidation than observed with UP, but less DOR oxidation, and insignificant accumulation of H2O2. This suggests that photoreduction of membrane-bound PP is less efficient, possibly due to hindered access of AH-.  相似文献   

7.
Abstract— Studies have been made of the inactivation of potato virus X (PVX), free PVX-RNA, and a phenotypically mixed virus particle composed of PVX-RNA and tobacco mosiac virus (U-1 strain) protein (PVXRNA: TMVPRO) by ultraviolet radiation of 254, 280 and 302 nm wavelengths. Rate constants and quantum yields of inactivation have been determined under conditions of photoreactivation and non-photoreactivation in H2O and D2O. The ratios of the rate constants in H2O to those in D2O obtained for PVX-RNA were greater than unity at the above three wavelengths, as was the case for PVX at 254 and 302 nm. The ratios of the rate constants were, within experimental error, equal to unity for PVXRNA:TMVPRO at all three wavelengths and for PVX at 280 nm. It is concluded that, in contrast to the situation observed with TMV and PVXRNA:TMVPRO, the behavior of the intact PVX viron upon irradiation closely approximates the behavior of free RNA in solution, on the basis of quantum yields of inactivation, photoreactivated sector, and the ratio of kinetic isotope effects in H2O and D2O.  相似文献   

8.
Free radicals were trapped and observed by ESR when photoallergens bithionol and fentichlor were irradiated in the presence of spin traps N- t -butyl-α-phenylnitrone (PBN) and 5,5-dimethyl-pyrroline-N-oxide (DMPO). In the absence of air, both PBN and DMPO trapped a carbon-centered radical. The carbon-centered radical, which was capable of abstracting a hydrogen atom from cysteine, glutathione, ethanol and formate, was identified as an aryl radical derived from the homolytic cleavage of the carbon-chlorine bond. In the presence of air, both carbon-centered radicals and hydroxyl radicals were trapped by DMPO. Under similar conditions, the yield of the hydroxyl radicals was greater from bithionol than from fentichlor. The presence of the hydroxyl radical was confirmed by kinetic experiments employing hydroxyl radical scavengers (ethanol, formate). Superoxide and H2O2 were not involved. Experiments with oxygen-17O indicated that the hydroxyl radicals came exclusively from dissolved oxygen. The precursor of the hydroxyl radical is postulated to be a peroxy intermediate (ArOO*) derived from the reaction of an aryl radical (Ar*) with molecular oxygen. Both bithionol and fentichlor photoionized only when excited in the UVC (<270 nm) region. Free radicals have long been postulated in the photodechlorination of bithionol and fentichlor and the present study provides supporting evidence for such a mechanism. Aryl and hydroxyl radicals are reactive chemical species which may trigger a series of events that culminate in photoallergy.  相似文献   

9.
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 % D2O, 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 D2O than in H2O. Half maximal inhibitions are obtained by 1.3 mM azide in H2O and by 0.1 mAf azide in D2O. Isotope effects and azide sensitivities point to photooxidation of epinephrine in D2O primarily by a singlet oxygen pathway; in H2O, non-singlet oxygen pathways become more predominant. Superoxide dismutase (SOD) markedly inhibits rates of the photooxidations in H2O and in D2O; about 25% at 10-9 M SOD, and 50% at 10-6 M SOD in H2O. In the photooxidation in H2O, 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   

10.
Abstract— Irradiation of daunomycin (or adriamycin) and the spin trap 5,5-dimethyl-l-pyrroline-1-oxide (DMPO) at 490 nm in the presence or in the absence of air generated the hydroxyl radical adduct (DMPO-OH). The observed DMPO-OH signal was not affected by the addition of hydroxyl radical scavengers (ethanol, formate), suggesting that direct trapping of the hydroxyl radical was not involved. The DMPO-OH signal was insensitive to superoxide dismutase and catalase, which ruled out the possibility of superoxide or H2O2 involvement. These findings demonstrate that daunomycin (or adriamycin) does not generate hydroxyl radicals or superoxide radical anions when subjected to 490-nm excitation. However, when daunomycin (or adriamycin) was irradiated at 310 nm DMPO adducts derived from two carbon-centered radicals, superoxide and the hydroxyl radical were detected. The superoxide adduct of DMPO was abolished by the addition of SOD, providing unequivocal evidence for the generation of the superoxide anion radical. The daunomycin semiquinone radical, observed upon 310-nm irradiation of daunomycin in the absence of DMPO, appears to be the precursor of the superoxide radical anion. One of the carbon-centered radicals trapped by DMPO exhibited a unique set of hyperfine parameters and was identified as an acyl radical. This suggests that the known photochemical deacylation of daunomycin occurs via a homolytic cleavage mechanism. The free radicals generated photolytically from adriamycin and daunomycin may be involved in the etiology of the skin ulceration and inflammation caused by these drugs. A knowledge of the dependence of these photogenerated radicals on the wavelength of excitation may be important in the development of adriamycin and daunomycin for photodynamic therapy.  相似文献   

11.
Abstract— Ethanol and ethanol-water matrices were exposed to X-rays at 77K and the photochemistry and paths of radical conversion were investigated by EPR methods. The main X-ray induced radical, CH3ĊHOH, is probably photoionized by 254 nm light. The following radicals are produced during prolonged UV-irradiation of CH3ĊHOH radicals: ĊH3, ĊHO, H and 2 types of radicals giving singlet EPR spectra. One of these radicals (d) is bleachable with 580 nm light, ĊH3 and ĊH3ĊHOH being formed during the bleaching, the other one (e) is unbleachable and the most stable radical in the matrix during annealing. The CH3 radicals decay at 77 K (τ∽ 10 min) and produce CH3-CHOH radicals and the unbleachable radical (e). Stable H-atom signals were seen in X-irradiated ethanol-water mixtures (volume ratio 2:1) at 77 K. The H-atom signals increased during photobleaching of the trapped electrons in the matrix and during UV-photolysis of CH3CHOH radicals.  相似文献   

12.
In a reaction mixture containing hematoporphyrin derivative, deoxyribose, Fe3+-EDTA and either methionine or tryptophan, hydroxyl radicals were formed during illumination with visible light. When either hematoporphyrin derivative, Fe3+-EDTA or the amino acid was omitted from the reaction mixture, the generation of hydroxyl radicals ceased. These observations suggest an iron-catalyzed Haber-Weiss reaction, involving superoxide and hydrogen peroxide in the generation of hydroxyl radicals. It could be shown that with methionine H2O2 was indeed an essential intermediate in the reaction sequence. With tryptophan, however, H2O2, was not generated. Apparently a photooxidation product of tryptophan could replace H2O2 in the OH-generating reaction with Fe2+-EDTA. Although superoxide was generated in the reaction mixture, it was not an indispensable intermediate. Apparently a porphyrin radical, formed via photoexcitation of hematoporphyrin derivative, could replace superoxide in the Haber-Weiss reaction.  相似文献   

13.
Abstract— Irradiation of bleomycin with light (λ > 320 nm) leads to a decrease in absorbance at 290 nm, which is suppressed by metal ions and by oxygen. Light-induced oxygen consumption is diminished by the enzymes superoxide dismutase and catalase, implying that toxic reduced species of oxygen (O2 and H2O2) are formed during irradiation. Spin-trapping measurements with 5,5-dimethyl-1-pyrroline-1-oxide and 2-methyl-2-nitrosopropane demonstrated that hydroxyl radical and methyl radical adducts also are generated in the system. In addition, direct ESR measurements have shown that methyl radicals are produced during irradiation of bleomycin solutions at low temperatures, together with radicals probably derived from the bithiazole moiety of the bleomycin. The latter are also produced from irradiation of the model compound bithia. Radical production is diminished by complexation of bleomycin with metal ions.  相似文献   

14.
Abstract— The mechanisms by which 4-substituted 2,6-di- t -butylphenols are oxygenated by base- and Co(II) Schiff base complex-catalysis into o - or p -peroxyquinols and their Co(III) complexes, respectively, have been investigated. For the base-catalyzed oxygenation, a one-step ionic mechanism involving no radical species is suggested to be the most probable one. For the formation of the peroxycobalt(III) complexes, the following stoichiometry is concluded: ArOH + Co(II) + 5/4 O2→ peroxycobalt(III) complex + 1/2 H2O. A mechanism involving an electron transfer between the phenols and the Co(II)-O2 complex followed by further electron transfer between the formed phenoxy radicals and the Co(II) complex to give the corresponding phenolate anions is proposed.  相似文献   

15.
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(1δ) in inactivation of E. coli is proposed. The photodynamic inactivation rate increased significantly in H2O compared with H2O, which is evidence supporting singlet oxygen as an active intermediate, since O2(1δ) has a much longer lifetime in H2O than in H2O. H2O did not act as a short term poison in the absence of sensitizer.  相似文献   

16.
Abstract— The photolysis of aqueous solutions of cis -[Cr(C2O4)2(H2O)2]- at 254 nm and pH 4 produced CO2 and H2 in nearly equal yields. The quantum yield of hydrogen, φ2, increased by 9% and the yield of carbon dioxide, φ, by 65% as the pH was lowered from 4 to I. The total gas yield, φgas, decreased in the presence of added oxalate or chromium (II) ions and when the light intensity was lowered. The gas yield in D2O was appreciably higher than in H2O. The variation of φgas with pH (D) and with added oxalate ion was roughly parallel in the two liquid media. The gas yield increased in the series:
A tentative mechanism is suggested to explain the results.  相似文献   

17.
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 H2O and D2O. An analysis of the data obtained in concentrated solutions leads to an unexpected high value of the ratio of 1O2 lifetimes in D2O and H2O, T d 2o/T h 2o =17 ± 1. Results obtained in diluted aqueous solutions are interpreted in terms of a re-encounter of 1O2 and ground state substrate molecules generated in the same triplet—triplet annihilation act.  相似文献   

18.
Abstract— Upon irradiation with ultraviolet light the isoflavonoid phytoalexins phaseollin, 3,6a, 9-trihydroxypterocarpan, glyceollin, tuberosin and pisatin, but not medicarpin, brought about inactivation ofglucose–6-phosphate dehydrogenase in an in vitro assay system. Photoinactivation of the enzyme by photoactivated pisatin in air-saturated solutions was hardly affected by singlet oxygen quenchers such as NaN3, bovine serum albumin, histidine or methionine. Neither addition of the hydroxyl radical scavengers mannitol, Na-benzoate and ethanol nor the presence of catalase or supcroxide dismutase protected the enzyme against photoinactivation, suggesting that OH, H2O2 and O2 are not the reactive oxygen species involved. However, the free radical scavenger S-(2-amino-ethyl)isothiouronium bromide hydrobromide (AET) protected the enzyme against inactivation by photoactivated pisatin. Direct evidence for the generation of free radicals was obtained by ESR measurements of solutions of phaseollin, pisatin and medicarpin in hexane irradiated with ultraviolet light in the presence or absence of O2. Phaseollin produced the most stable free radicals, whereas medicarpin hardly gave rise to free radical formation; pisatin took a somewhat intermediate position by producing a strong ESR signal which, however, decayed rather quickly. Photodegradation of all phytoalexins, except for medicarpin, was accompanied with loss of fungitoxicity, as shown in thin-layer chromatographic bioassays, and formation of new products.
These results indicate free radical formation as the causative process for photoinactivation of enzymes by photoactivated isoflavonoid phytoalexins.  相似文献   

19.
The characteristic fluorescence properties of quercetin-3- O -rhamnoside (QCRM) and quercetin-3- O -rutinoside (QCRT) were studied in CH3OH–H2O and CH3CN–H2O mixed solvents. Although QCRM and QCRT are known as nonfluorescent molecules, significant fluorescence emissions were discovered at 360 nm in CH3OH and CH3CN when they were promoted to the second excited state. The emission band is broad and structureless and the intensity decreases quickly as the H2O composition in the solvent increases. When the amount of H2O exceeds 60% in both mixed solvents, this emission disappears due to the formation of the distorted excited state. This state will be formed due to the strong intermolecular hydrogen bonding between the polar groups of solute and H2O. As the composition of CH3OH or CH3CN in solvent becomes large, the number of molecules having several intramolecular hydrogen bonding increases. Some of these molecules will be changed to a fluorescent species during the decay process, after excitation. The theoretical calculation further supports these results. The change of the lifetimes, quantum yields, and radiative and nonradiative rate constants of molecules was also examined as a function of solvatochromic parameters for CH3OH–H2O and CH3CN–H2O.  相似文献   

20.
Abstract— Semiquinone free radicals have been generated by the UV photolysis of aqueous solutions of melanin precursors (catechols and catecholamines) and characterized by electron spin resonance (ESR) spectroscopy. Hyperfine parameters of the semiquinones are sensitive to the nature of the substituents on the aromatic ring, reflecting (i) the ionization state of the substituent; (ii) restricted rotation of methylene protons; and (iii) the presence of a chiral carbon center. In the presence of complexing metal ions (Zn2+, Cd2+) the semiquinones form chelate complexes whose ESR spectra differ from those of the uncomplexed radicals. Satellite peaks demonstrating hyperfine coupling to metal isotopes (67Zn, 111Cd and 113Cd) present in natural abundance were detected in several instances. Concentrations of metal complexes are much higher than those of the uncomplexed radicals, suggesting that diamagnetic metal ions may be useful in identifying the presence of semiquinone radicals of this kind in various systems.  相似文献   

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