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1.
J. W. Hastings Shiao-Chun Tu James E. Becvar ‡ Robert P. Presswood 《Photochemistry and photobiology》1979,29(2):383-387
Abstract— The bioluminescent oxidation of reduced flavin mononucleotide by bacterial luciferase involves a long-lived flavoenzyme intermediate whose chromophore has been postulated to be the 4a-sub-stituted peroxy anion of reduced flavin. Reaction of long chain aldehyde with this intermediate results in light emission and formation of the corresponding acid. These experiments show that the typical aldehyde-dependent, luciferase-catalyzed bioluminescence can also be obtained starting with FMN and H2 O2 instead of FMNH2 and O2 . We postulate that the 4a-peroxy anion intermediate is formed directly by attack of H2 O2 on FMN. The latter may be bound to luciferase. An enzyme bound intermediate is formed which by kinetic analysis, flavin specificity for luminescence, aldehyde dependence, and bioluminescent emission spectrum appears to be identical with the species generated by reaction of FMNH, and O2 with luciferase. The quantum yield of the H2 O2 -- and FMN-initiated biolumlnescence is low but can be enhanced by certain metal ions, which also stimulate a chemiluminescent reaction of oxidized flavin with H2 O2 . The peak of this chemiluminescence. however, appears to be at a shorter wavelength than that (490 nm) of the bioluminescence. 相似文献
2.
Ravindra L. Arudi Benon H. J. Bielski Augustine O. Allen 《Photochemistry and photobiology》1984,39(5):703-706
Abstract— During the reaction HO2 + HO2 (or O2 - ) = H2 O2 + O2 in aqueous solution, no luminescence in the region 620–720 nm, expected if the product O2 were formed in a singlet state, could be detected. If any singlet O2 is formed, its yield must be less than 10%. Faint luminescence, sometimes found at shorter wavelengths, was shown to arise from reaction of HO2 with impurities in the reagents present. 相似文献
3.
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
4.
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
5.
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
6.
Abstract —In vivo participation of singlet excited oxygen (1 O2 , 1 Δ9) in the photodynamic inactivation and induction of genetic changes (gene conversion) in acridine orange-sensitized yeast cells was investigated by using N3 - , an efficient 1 O2 quencher, and D2 O, a known agent for the enhancement of the lifetime of 1 O2 . The addition of N3 - protected the cells from both photodynamic actions. From an analysis of the concentration-dependent protection, about 80% of the induction of the genetic change is explainable on the basis of 1 O2 mechanism. The quantitative estimation of the N3 - protection in the inactivation was not possible because of the sigmoidal nature of the inactivation curve. The replacement of H2 O with D2 O during illumination was effective in enhancing the photodynamic inactivation but almost completely ineffective for the gene conversion induction. The deuterium effect with the cell system was clearly not as large as would be expected from in vitro experiments. This, however, could be explained from the kinetic consideration that natural quenchers of l O2 in the cell would mask the deuterium effect. By experiments with different cell stages it was demonstrated that these two modifying effects were dependent on the intracellular reaction environment. The conclusion is that 1 O2 must be the major intermediate responsible for the photodynamic actions in acridine orangesensitized yeast cells. 相似文献
7.
PI-TAI CHOU SHANNON L. STUDER MARTY L. MARTINEZ EDWARD ORTON MARK YOUNG † 《Photochemistry and photobiology》1991,53(5):587-593
Abstract— We present an infrared study of 3-hydroxyflavone in 12 K Ar and O2 matrices. Although it is extremely photostable in an Ar matrix, a remarkable oxygenation reaction for 3-hydroxyflavone takes place upon photoexcitation in an O2 matrix. The primary photoproduct is concluded to be a keto-hydroperoxide. On further photolysis the keto-hydroperoxide affords the photostable secondary product 2-(benzoyloxyl)benzoic acid, as well as CO and CO2 through two independent pathways. 相似文献
8.
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
9.
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
10.
I. B. C. Matheson 《Photochemistry and photobiology》1979,29(5):875-878
Abstract— The chemical reaction rate constant of bilirubin with singlet oxygen in basic aqueous solution has been redetermined to be 3.5 × 108 M-1 s-1 by a competitive technique using a 1,3-diphenylisobenzofuran in sodium dodecyl sulfate micelles. Bilirubin also physically quenches a singlet oxygen with a rate constant of 9 × 108 M -1 s-1 . The lifetime of singlet oxygen in D2 O solution has been determined to be 35 μ s . The absorption cross-section for the molecular oxygen 3 ∑g -→1 δ g + 1 v electronic transition at 1.06μn in aqueous solution is unexpectedly larger than the gas paase cross-section. 相似文献
11.
THE ROLE OF O2 - IN THE CHEMILUMINESCENCE OF LUMINOL* 总被引:1,自引:0,他引:1
Abstract— The chemiluminescence of luminol in buffered aqueous solutions is inhibited by superoxide dismutase. This occurs whether the luminescence is induced by ferricyanide, persulfate, hypochlorite, or by the action of xanthine oxidase on xanthine. Since superoxide dismutase inhibits reactions which involve O2 - , we conclude that this radical is a constant factor in the chemiluminescence of luminol in aqueous solutions. The kinetics of light production are discussed in terms of hypothetical mechanisms that fit the available data. The strong luminescence of luminol in aprotic solvents or in aqueous systems containing relatively high concentrations of H2 O2 could not be explored in this way, because superoxide dismutase is inactive under such conditions. 相似文献
12.
Pronounced aggregation of the photosystem II light-harvesting complex (LHC II) was observed in low-lightgrown tobacco plants stressed with a strong CO2 deficit for 2–3 days. The LHC II aggregates showed a typical band at 697–700 nm (F699 ) in low-temperature emission spectra. Its excitation spectrum corresponded to that of detergent-solubilized LHC II. Formation of F699 in stressed plants was not reversed in the dark and leaves did not contain any zeaxanthin showing that neither a light-induced transthylakoid pH gradient nor zeaxanthin was required for LHC II aggregation. The CO2 -stressed plants showed clear signs of photodamage: depression of the potential yield of photosystem II photochemistry (F,/FM ) by 50–70% and a decline in chlorophyll content by 10–15%. Therefore, we propose that the photodamage to the photosynthetic apparatus is the cause of the LHC II aggregation in plants. The F699 exhibited a reversible decrease of its intensity upon irradiation of leaves with intensive light. There was no or only slight decrease around 700 nm in unstressed plants. The nonphotochemical quenching of chlorophyll fluorescence showed the opposite relation, being higher before than after the strong CO2 deficit. This discrepancy was likely related to the different LHC II aggregation state in control and stressed plants. 相似文献
13.
Abstract— Laser flash photolysis of trans -[Rh(dppe)2 X2 ][PF6 ] (X=Br and I; dppe=bis(diphenylphosphino)ethane) in CH2 Cl2 or CH3 CN produces the d7 Rh(II) radicals, [Rh(dppe)2 X]+ , and halogen atoms. The kinetics of the disappearance of [Rh(dppe)2 X]+ radicals in CH2 Cl2 or CH3 CN were mixed order: H-atom abstraction from solvent to produce the rhodium hydrides, [RhH(dppe)2 X][PF6 ], and Rh/X recombination. In the poor H-atom donor solvent, benzonitrile, Rh/Br recombination was observed to be uncomplicated by competing H-atom abstraction. The hydride complexes [RhH(dppe)2 X][PF6 ], formed by H-atom abstraction were completely characterized by 31 P{1 H}-NMR, 1 H-NMR, and mass specrometry. Cyclohexene was used as an effective trap for photogenerated Br atoms and yielded bromocyclohexane and 3-bromocyclohexene in a relative yield, 1:9. The photochemical mechanism is discussed in light of the transient absorbance and trapping studies. 相似文献
14.
Abstract— From spectroscopic data and rate constants in the literature, equilibrium constants and rates of thermal formation of singlet oxygen (1 Δg and 1 Σg + ) were calculated for a number of conditions. For the gas phase we estimate K eq (1 Δg 3 Σg - ) = 1.67 exp(-94.31 KJ/RT) and K eq (1 Σg + /3 Σg - ) = 0.33 exp(-157.0 KJ/RT). The calculated rate constants for the 3 Σg + →1 Δg transition of O2 at 25°C varied from 2.5 × 10-11 s-1 in water to 4.8 × 10-16 s-1 in air, assuming equal solvent interactions with the ground and excited states. Physical quenchers for singlet oxygen are expected to be catalysts for its thermal formation. Equations are presented which allow one to estimate whether such catalysis by quenchers will result in a pro-oxidant effect. 相似文献
15.
Abstract. The photooxidation of tetracyclone yielding dibenzoyl stilbene was studied by means of an 18 O labelling method recently used to study heme catabolism. Unlike heme degrading systems, the photooxidation of tetracyclone was found to proceed by a one-molecule mechanism whereby both oxygen atoms in dibenzoyl stilbene are derived from the same molecule of molecular oxygen. This is evidence for a dioxobridged intermediate. 相似文献
16.
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
17.
We have studied the hydrogenase-catalyzed production of H, when either its natural electron mediator cytochrome c3 (c3 ) or the artificial mediator methyl viologen (MV) was reduced by illumination of proflavin (PF) in the presence of ethylenediaminetetraacetate (EDTA). The reduction rates of MV and c3 were comparable at equivalent concentrations of PF, taking into account the four redox sites of c3 . However, when the concentration of c3 exceeded that of PF, the reduction rate decreased. We explain this by light quenching. In the H2 -producing system, MV was more efficient than c3 as electron mediator when the initial reaction rates were compared. However, under certain conditions with MV, the rate of H2 production decreased rapidly with time of illumination, whereas with c3 it consistently remained stable. Possible reasons for this difference are discussed.
Severe inactivation of hydrogenase was observed in the absence of the primary electron donor EDTA. It is concluded that this inactivation is caused by the excited state of PF 相似文献
Severe inactivation of hydrogenase was observed in the absence of the primary electron donor EDTA. It is concluded that this inactivation is caused by the excited state of PF 相似文献
18.
Abstract— The concentration dependence of the lifetimes of the charge transfer excited states of Cu(dmp)+ 2 and Cu(dpp) + 2 has been investigated in CH2 C12 solution at 20° C. (dmp denotes 2,9-dimethyf-1,10-phenanthroline, and dpp denotes 2,9-diphenyl-l,10-phenanthroline.) In dilute solution (< 30 μM) the lifetime of Cu(dmp)+ 2 , is 95 ± 5 ns, independent of the anion. At higher concentrations the lifetime decreases, in most cases, to a limiting value that depends upon the counterion. The measured limiting lifetimes range from 38 ± 3 ns for CIO- 4 to 78 ± 5 ns for PF- 6 . The anion-induced quenching is attributed to exciplex quenching which is mediated by an ion pair which exists in the ground state. The results imply that the quenching ability of the anions follows the order BPh-4 < PF -6 , < BF-4 < CIO -4 < NO-3 which is consistent with previous estimates of donor strength. The lifetime of Cu(dpp)+ 2 is also concentration dependent, but the effect is much smaller because the phenyl substituents impede attack by the anion. 相似文献
19.
Abstract— The photolysis of aqueous solutions of cis -[Cr(C2 O4 )2 (H2 O)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 D2 O was appreciably higher than in H2 O. 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
A tentative mechanism is suggested to explain the results. 相似文献
20.
Abstract— Photolyses at 485 or 490 nm of air saturated, H2 I7 O enriched, aqueous solutions of adriamycin (ADR) in the presence of 5,5-dimethyl-l-pyrroline-l-oxide (DMPO) produce a mixture of hydroxyl radical spin-adducts, i.e. DMPO-16 OH- and DMPO-17 OH-, as detected by electron spin resonance (ESR). DMPO-17 OH- was also observed during the irradiation at these same wavelengths of aqueous solutions of ADR or daunomycin (DA) containing DMPO and 17 O enriched oxygen. Therefore, the observed hydroxyl radical spin-adducts derive from both water and gaseous oxygen. It is concluded from the measured relative spin-adduct concentrations and from the enrichment fractions that most of the DMPO-OH adducts originate from water. However, if anaerobic diluted solutions of ADR (200 μ M ) or DA (600 μM) in the presence of DMPO (13 mM and 27 m M respectively) are irradiated at these same wavelengths no spin adduct is detected, indicating that oxygen is needed for the adduct formation, at these drug and spin trap concentrations. DMPO-OH- is always observed if relatively high concentrations of either the drug (1.1–2.9 mM) or the spin trap(100–150 m M ) are used in argon saturated solutions. A water photooxidation mediated mechanism is proposed in order to account for these results, analogous to previous observations in the photochemistry of other water soluble anthraquinone derivatives. 相似文献