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1.
A COMPARATIVE STUDY OF PHOTODYNAMIC OXIDATION AND RADIOFREQUENCY-DISCHARGE-GENERATED 1 O2 OXIDATION OF GUANOSINE 总被引:2,自引:0,他引:2
A. Kornhauser N. I. Krinsky P.-K. C. Huang D. C. Clagett 《Photochemistry and photobiology》1973,18(1):63-69
Abstract— Guanosine-2-14 C and guanosine-8-14 C were subjected, under similar environmental conditions, to oxidation either by radiofrequency-discharge-generated singlet oxygen or by a methylene-blue-sensitized photodynamic reaction. The reaction products in both cases were compared chromatographically. The product distributions were not identical, indicating differing modes of oxidation in these two systems. It is suggested that both Type I and Type II oxidation mechanisms are operative in the photodynamic system, whereas only Type II-like reactions occur in the radio-frequency-discharge system. 相似文献
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T. Gillbro P. O. Andersson R. S. H. Liu A. E. Asato S. Takaishi R. J. Cogdell 《Photochemistry and photobiology》1993,57(1):44-48
The location of the carotenoid 2Ag-state (S1) was studied by fluorescence spectroscopy in two series of carotenoids. One consisted of natural polyenes like phytoene, phytofluene, β-carotene, and neurosporene, and the other of minicarotenes, i.e., compounds similar to β-carotene, but with a smaller number of double bonds (n=3–9). A decrease of the S1-S0 energy gap with n was observed in both series, and extrapolation to n= 11 gave the energies 14 500 and 13 200 cm?1 for β-carotene and lycopene, respectively. The neurosporene S1 state was located at ca 16 000 cm?1. A good relationship between the nonradiative relaxation rate and the number of conjugation was observed. The rate increased by a factor of 2.5 per double bond. The possible role of the S1 state in reversible carotenoid ← chlorophyll electron-exchange energy transfer is discussed. 相似文献
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Abstract A rubrene derivative has been synthesized as a new trap for singlet oxygen in aqueous solution. Photooxygenation and evolution of the endoperoxide under various conditions have been investigated. This trap may be used either as a colorimetric test or as a specific one by isolation of the endoperoxide. 相似文献
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Abstract— The rate constant for quenching of 1 O2 by azide ion in water was determined to be (5.0 ± 0.4) × 108 M −1 s−1 using a variety of sensitizers (including humic acids) and 1 O2 acceptors. The apparent second-order rate constant decreases with pH below pH 5.5 in accordance with the protonation of azide ion to form hydrazoic acid (p K a = 4.6). Quenching by hydrazoic acid is at least 2 orders of magnitude slower than by azide ion. Greater than 99% of all interactions between 1 O2 and azide ion involve physical quenching rather than chemical reaction. Humic acid triplets are not significantly quenched by azide ion at concentrations less than 2 m M , allowing azide ion quenching to be used as a diagnostic test for the intermediacy of 1 O2 in photosensitized oxidations in natural surface waters. 相似文献
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J. Marko G. Vermeersch N. Febvay-Garot S. Caplain A. Lablache-Comboer 《Photochemistry and photobiology》1983,38(2):169-175
Abstract— The photochemical reaction in aqueous solutions of several phenothiazines with an N-alkylamine chain, and their salts, is studied by means of Chemically Induced Dynamic Nuclear Polarization (CIDNP)¶ . The particular behaviour of chlorpromazine hydrochloride is outlined and evidence is shown for the existence of a substitution product with the solvent at the α-carbon atom of the side-chain, and an aldehydic derivative resulting in the cleavage of that one. Radical-ions pairs of CPZ are involved in both processes. 相似文献
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Meyrick J. Peak Jennifer S. Johnson R. W. Tuveson Jennifer G. Peak 《Photochemistry and photobiology》1987,45(4):473-478
Abstract— Escherichia coli strain RT8 hemA8 [blocked in biosynthesis of δ-aminolevulinic acid (δ-ALA), and unable to manufacture porphyrins unless exogenously supplied with δ-ALA] is inactivated more efficiently by monochromatic 334- and 405-nm radiations if the cells are grown with δ-ALA supplementation. The fiuence enhancement factor for δ-ALA sensitization is larger for light at 405 nm than at 334 nm. Both irradiation conditions (plus or minus δ-ALA) showed prominent oxygen enhancement ratios, which were also larger at 405 nm than at 334 nm. At 334 nm, δ-ALA supplementation did not affect the accumulation of DNA breaks, while at 405 nm, the induction of DNA breaks doubled for cells supplemented with δ-ALA. Rubidium leakage caused by 405-nm radiation occurred at a smaller fiuence in cells supplemented with higher concentrations of δ-ALA than in cells supplemented with a lower concentration. The results suggest that (1) porphyrin derivatives may have a role in cell killing by near-UV radiations, and (2) damage to cytomembranes may be a critical lesion produced by these events, whereas DNA breakage may not. 相似文献
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E xposure of pig kidney cells in monolayer culture to far-red light (FRL), near 750 nm, was found to increase the incidence of chromatid aberrations and aberrant cells [1]. Dose–response curves for cell populations predominantly in early S reached a maximum at incident energies of ca. 50 mJ cm-2 . We show here that the incorporation of tritiated thymidine by the nuclei of pig kidney cells in monolayer also is inhibited by FRL, with a similar dose-response maximum. 相似文献
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Abstract— Although the mechanism of bioluminescent reactions in various species, such as fireflies, ostracod crustaceans ( Cypridina ), sea pansies ( Renilla ), and the deep-sea shrimp Oplophorus , are thought to involve dioxetanone intermediates, studies reported in the past from different laboratories have included widely different experimental results, most likely due to various factors including the effects of contaminating CO2 . With the improved technique employed in the present study, bioluminescent reactions of the firefly and Cypridina in 18 O2 gas resulted in an incorporation of over 75% of 18 O into one oxygen of the product CO2 . with a reproducibility within a few per cent. When 13 CO2 . instead of the product CO2 of the bioluminescent reaction, was studied in an H2 18 O medium, the exchange of one oxygen of 13 CO2 with H2 O was 64%. and the effect of contaminant CO2 amounted to 1418% of the total CO2 . These results suggest that every molecule of CO2 formed in the bioluminescent reactions of the firefly and Cypridina had intially contained 1 oxygen atom derived from O2 . 相似文献
10.
Abstract— A mutant of Chlamydomonas reinhardtii (NL–11) isolated from a wild type (137c+) was inactivated in the light in the presence of methionine at concentrations where the wild type was not inactivated. The inactivation was suppressed by either catalase or superoxide dismutase (SOD). Light-induced H2 O2 formation and nitroblue tetrazolium (NBT) reduction inNL–11 were greater than those in the wild type. Methionine stimulated both the H2 O2 formation and the NBT reduction inNL–11 as well as the wild type. The light-induced NBT reduction inNL–11 in the presence of methionine was partially suppressed by externally added SOD suggesting the participation of O- 2 . These results suggest that the hypersensitivity ofNL–11 to methionine in the light is due to stimulated formation of H2 O2 and O- 2 . 相似文献
11.
beta-Crystallins (beta 1-, beta 2- and beta 3-crystallin) comprise nearly half the protein of the human lens. The effect of near-UV radiation, which is one of the possible risk factors in cataract formation, on the beta-crystallins is investigated in this study. Protein intersubunit crosslinking, change in charge of the protein subunits to more acidic species and changes in protein tertiary structure (conformation) by 300 nm irradiation are reported. The fluorescence yield of protein tryptophan residues decreases by 300 nm irradiation. There is an increase in nontryptophan fluorescence (lambda cx 340 nm, lambda cm 400-600 nm), and in protein absorption at 340 nm, due to the formation of tryptophan photooxidation products. Both tryptophan and its oxidation products can be photoexcited by 300 nm irradiation and the latter are known to be good photosensitizers. The results provide evidence for the generation of H2O2 in the irradiated human beta-crystallin solutions by the Type I photosensitizing action of the chromophores absorbing at 300 nm. The H2O2 is generated via the intermediate production of O2 anion; the latter spontaneously dismutates to H2O2, presumably via O2- protein interactions. The amount of H2O2 generated per absorbed photon is compared for various solutions of beta 1-, beta 2- and beta 3-crystallins from human lenses of different age. 相似文献
12.
Hypocrellin A, a peryloquinone derivative, has recently been isolated from the sacs of the fungus Hypocrella bambusae. This pigment, in combination with phototherapy, has been used in human medicine to cure various skin diseases. The generation of singlet oxygen during photoirradiation of Hypocrellin A (HA) was detected as an oxidation product of a sterically hindered amine (tetramethylpiperidine oxide; TEMPO) by electron paramagnetic resonance (EPR) spectroscopic techniques. Azide inhibited the EPR signal intensity in a dose-dependent manner with a quenching rate constant of 3.86 x 10(8) M-1s-1 in ethanol. Deuterated solvents, known to increase the lifetime of singlet oxygen, augmented the EPR signal intensity. The rate of production of singlet oxygen was dependent not only upon the concentration of HA and the time of irradiation but also on the oxygen content of the reaction mixture. The hyperfine splitting constant (aN = 16.3 G) and g-value (g = 2.0056) of the photoproduct of TEMP-singlet oxygen and TEMPO were found to be identical. This indicates that the nitroxide species detected by EPR spectroscopy generated by reacting TEMP with photogenerated 1O2 is TEMPO. The rate constant (kT) for the reaction of singlet oxygen with TEMP to form TEMPO radical was found to be 5.3 x 10(5) M-1s-1. 相似文献
13.
John T. Barbas Michael E. Sigman† A. C. Buchanan III Eddie A. Chevis 《Photochemistry and photobiology》1993,58(2):155-158
Abstract— Photolysis of naphthalene on the surface of SiO2 under an atmosphere of air produces phthalic acid as the only major photoproduct, accounting for 49%o of the consumed naphthalene. Photolysis on Al2 O3 also produces phthalic acid, in 31% yield. Photolysis of 1 -methylnaphthalene on SiO2 proceeds under similar conditions to produce 2-acetylbenzoic acid (35%) as the major photoproduct with the production of a small amount of I-naphthaldchyde (6%). 1-Cyanonaphthalene does not photooxidize under similar conditions. The presence of oxygen is necessary for the photodecomposition of naphthalene and 1-methylnaphthalene to proceed. Superoxide formed from the photolysis of naphthalene at the SiO2 /air interface is readily observed by electron paramagnetic resonance spectroscopy. In the absence of naphthalene no superoxide is observed. A mechanism involving electron transfer from the S1 state of the naphthalene to O2 is proposed on the basis of these observations and related literature precedent. 相似文献
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Abstract— Radiation-induced covalent binding of labelled carcinogens to DNA has been investigated under a variety of conditions using ultrafiltration or millipore filtration of TCA precipitable complexes. High yields of carcinogen binding at high DNA concentrations are also observed for a variety of small molecules and are not carcinogen-specific. At high carcinogen concentrations, radiation-induced unstable electrophilic carcinogenic species are produced, and undergo free-radical reactions which simulate cellular redox reactions involved in metabolic carcinogen activation, leading to the formation of covalently bound carcinogen adducts to DNA as a potential target macromolecule. The yields of carcinogen-DNA adducts increase linearly with dose and depend upon carcinogen concentration. The results of scavenger studies indicate that the oxidising species O2 - and OH are the principal activating species. Rate constants for the selective radiation-induced oxidation reactions of various chemical carcinogens with superoxide have been measured by a competition kinetic method using pulse radiolysis. The relatively long-lived superoxide radical reacts with carcinogens at a rate which is two orders of magnitude slower than the diffusion-controlled rate for the hydroxyl radical, thus allowing a measure of O2 - specificity in the presence of competing reactants within the cell. 相似文献
16.
J. G. Parker 《Photochemistry and photobiology》1988,48(2):225-228
Abstract— Recent experimental data obtained using the separated sensitizer and substrate method to investigate the interaction of O2 (1 δg ) with various substances has been re-interpreted by means of a more complete theory. Comparison of experimental and recalculated values of the dependence of relative reaction rates on the sensitizer-substrate separation indicate general accord for experiments in which singlet oxygen acceptors in aqueous solution were used. The presumption is therefore that singlet molecular oxygen O2 (1 δg ) is indeed the active oxidizing agent and that the theory presented and experiment are entirely in agreement.
For experiments in which bacterial targets were used a very distinct disagreement between theory and experiment is evident, the conclusion being that the kill rate does not depend linearly on the O2 (1 δg ) concentration in the immediate proximity of the bacteria. However, the data is consistent with a quadratic dependence on the 1 δg concentration. A possible conclusion therefore is that the cytotoxic species is actually O2 (1 σ+ g ), formed by an energy pooling reaction involving two O2 (1 δg ) molecules. 相似文献
For experiments in which bacterial targets were used a very distinct disagreement between theory and experiment is evident, the conclusion being that the kill rate does not depend linearly on the O
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Abstract—DNA crosslinks in Escherichia coli cells. exposed to 4.5',8-trimethylpsoralen plus 360 nm light, were measured using a rapid and sensitive new approach. The assay is based on the specificity of S1 nuclease from Aspergillus oryzae to single-stranded DNA. Bacterial cells were lysed and the DNA denatured by alkali. Following acid neutralization. crosslinked DNA undergoes spontaneous renaturation and is rendered S1 -nuclease resistant and therefore acid-precipitable. The single-stranded fraction after denaturation by alkali decreases with increasing near UV light exposure in the presence of TMP following first order kinetics. The kinetics were faster when exposure was at 4°C rather than at 20°C. This suggests that excision of crosslinks occurs during exposure at the higher temperature. Indeed. since the rate of DNA crosslinking in a uvr B mutant which is excision-deficient was higher than in wild type bacteria at 4°C, some excision must have occurred even in the cold. DNA from excision-proficient cells incubated at 37°C following exposure to TMP-plus-near UV at 4° showed a greater single stranded fraction than that from non-incubated cells. This indicates repair of DNA crosslinks. which proceeded with a half-time of 8 min at 37°C and was unaffected by substitution of thymine in DNA by 5-bromouracil. 相似文献
19.
Abstract— The spectra and molar absorbances of the HO2 and O2 - free radicals have been redetermined in aqueous formate solutions by pulse and stopped-flow radiolysis as well as by 60 Co gamma-ray studies. The extinction coefficients at the corresponding maxima and 23°C are 225 = 1400 ± 80 M -1 cm-1 and 225 = 2350 ± 120 M -1 cm-1 respectively. Reevaluation of earlier published rate data in terms of the new extinction coefficients yielded the following rate constants for the spontaneous decay of HO2 and O2 - : K Ho2+HO2 = (8.60 ± 0.62) × 105 M -1 s-1 ; K Ho2+O2- = (1.02 ± 0.49) × 108 M -1 s-1 ; K Ho2+O2- < 0.35 M -1 s-1 . For the equilibrium HO2 → O2 - + H+ the dissociation constant is K Ho2 = (2.05 ± 0.39) × 10-5 M or p K HO2 = 4.69 ± 0.08. G (O2 - ) has been evaluated as a function of formate concentration. 相似文献
20.
Abstract— The quantum yields and lifetimes of the fluorescence of tyrosine and tryptophan were determined in D2O-H2O and glycerol-H2O solvent mixtures of varying composition from 10 vol.% to 100% H2O at 15°C. Forboth amino acids the ratio of the quantum yields in D2O and H2O (i.e., qD/qH) was smaller than the ratio of the corresponding lifetimes (D/H). For tyrosine the ratio of the quantum yields in glycerol and H2O (qG/qH) was also smaller than the corresponding G/H ratio, but for tryptophan qG/gHG/H. The proximity of the q vs. plots for tyrosine in the two solvent mixtures indicates that at 15°C neither D2O nor glycerol, in the pure state or when diluted with H2O, quench tyrosine significantly. However, H2O quenches tyrosine by a dynamic process, which increases both the radiative and the nonradiative rate constant. The quenching action is attributed to a tyrosine-H2O exciplex, whose formation is independent of bulk viscosity and dielectric constant. Unlike tyrosine, tryptophan is quenched weakly by D2O by a static process at 15°C (i.e., involving no change in), but H2O quenches tryptophan much more efficiently by a dynamic process, which involves the nonradiative rate constant, but not the radiative constant. These results are explained on the basis of electrostatic complexation of the ammonium group to the carbon atom adjacent to the ring nitrogen with a lifetime which is longer thanin D2O but shorter thanin H2O, with solvent reorientation possibly also being an important factor in the quenching. This explanation is consistent with the fact that concentrated (8 M) urea increases q andof aqueous tryptophan ? 15–20%, while guanidine hydrochloride (6.4 M) has the opposite effect, i.e., it decreases q and t of tryptophan ? 15–20%, and with the fact that neither 8 M urea nor 6.4 M guanidine hydrochloride affects any fluorescence parameter of tyrosine at all. 相似文献