共查询到20条相似文献,搜索用时 15 毫秒
1.
Abstract— The triplet state characteristics (spectrum, lifetime and quantum yield) for four dye sensi tisers [methylene blue (MB), erythrosin (ER), haematoporphyrin (HP) and riboflavin (RF)] were determined in methanol by laser flash photolysis and singlet oxygen yields (0.60 to 0.48) from time-resolved measurements of the 1270 nm near infrared emission. The reaction of singlet oxygen with four long chain unsaturated phenyl esters [oleate (18: 1), linoleate (18: 2), linolenate (18: 3) and arachidonate (20: 4)] was followed quantitatively using the singlet oxygen luminescence technique and also, after continuous420–700 nm irradiation, by HPLC and other analysis of the isomeric product monohydroperoxides. The overall quantum yield of photooxidation (∼10-2 ) was shown to be consistent with the observed singlet oxygen quenching constants(2–12 times 104 dm3 mol-1 s-1 ) for the four esters studied and the singlet oxygen lifetime in methanol (τ∼ 9 μs). The isomer product distribution was interpreted in terms of a dual singlet oxygen and radical mechanism, the radical contribution increasing with sensitiser in the order ER = MB < HP ≪ RF, but also showing some dependence on substrate unsaturation. Evidence is presented for singlet oxygen quenching by MB and RF ( kO = 1.6 and 6.0 times 107 dm3 mol-1 s-1 ) and for the accelerated photobleaching of the dye sensitisers in the presence of the unsaturated esters. 相似文献
2.
LUMIFLAVIN-SENSITIZED PHOTOOXYGENATION OF INDOLE 总被引:1,自引:0,他引:1
Abstract— The lumiflavin-sensitized photooxygenation of indole in aqueous solutions has been investigated by means of steady light photolysis and flash photolysis. The semiquinone of lumiflavin and the half-oxidized radical of indole were formed by the reaction between triplet lumiflavin and indole (3.7 times 109 M -1 s-1 ). The semiquinone anion radical of lumiflavin reacted with oxygen to form superoxide radical. The triplet state of lumiflavin also reacted with oxygen forming singlet oxygen, 1 O2 . But the reaction between 1 O2 and indole (7 times 107 M_l s_1 ; estimated from steady light photolysis using Rose Bengal as a sensitizer) was far less efficient than the reaction between indole and triplet lumiflavin. The quantum yield of the lumiflavin-sensitized photooxygenation of dilute indole via radical processes was much higher than that via 1 O2 processes, though appreciable 1 O2 was formed. 相似文献
3.
Abstract— Reactions of the triplet state of lumiflavin (3 LF) in water adjusted at pH 7.2 were reexamined by means of a Xe-flash photolysis and a laser photolysis. Measurements of the decay of 3 LF were made on solutions of LF ranging in the concentration from 4 to 61 times 10-6 mol/dm3 . A one-electron reduced and a one-electron oxidized species of lumiflavin (LF- and LF+ ) were produced in the first decay stage of 3 LF with a high efficiency (0.6 ± 0.1) in a bimolecular triplet-triplet reaction. The product radicals (LFH- and LF+ ) quench 3 LF very efficiently (3 ± 0.8 × 109 mol-1 dm3 s-1 ) compared with LF in the ground state (> 2 × 107 dm3 mol-1 ). 相似文献
4.
M. CRAW M. R. CHEDEKEL† T. G. TRUSCOTT § E. J. LAND† 《Photochemistry and photobiology》1984,39(2):155-159
Abstract— The photochemical interaction between 8-methoxypsoralen (8-MOP) and the melanin precursorL–3,4-dihydroxyphenylalanine(dopaH2 ) has been studied using laser flash photolysis. Triplet excited 8-MOP was thus found to abstract electrons from dopaH2 ( k ∼ 2 × 109 dm3 mol-1 s-1 ) to form semireduced 8-MOP and semioxidised dopaH2 .The technique of pulse radiolysis was used to establish separately the spectra of (a) the semi-reduced form of 8-MOP at pH 6.5 and (b) the semioxidised forms of dopaH2 at pH 6.5, 5.8, 4.6 and 3.3. The corresponding λmax and extinction coefficients found were: for 8-MOP at pH 6.5, λmax = 350 nm (= 9050 dm3 mol-1 cm-1 ); for dopa at pH 6.5, λmax = 305 nm (ε= 12000 dm3 mol-1 cm-1 ) and for dopaH at pH 3.3, λ= 305 nm (ε= 5900 dm3 mol-1 cm-1 ). 相似文献
5.
I. B. C. Matheson R. D. Etheridge Nancy R. Kratowich John Lee 《Photochemistry and photobiology》1975,21(3):165-171
Abstract— The physical quenching of singlet molecular oxygen (1 Δg ) by amino acids and proteins in D2 O solution has been measured by their inhibition of the rate of singlet oxygen oxidation of the bilirubin anion. Steady-state singlet oxygen concentrations are produced by irradiating the oxygenated solution with the 1–06 μm output of a Nd-YAG laser, which absorbs directly in the electronic transition 1 Δg + 1 v →3 Σg - . The rate of quenching by most of the proteins studied is approximated by the sum of the quenching rates of their amino acids histidine, tryptophan and methionine, which implies that these amino acids in the protein structure are all about equally accessible to the singlet oxygen. The quenching constants differ from those obtained by the ruby-laser methylene-blue-photosensitized method of generating singlet oxygen, or from the results of steady-state methylene-blue-photosensitized oxidation, where singlet oxygen is assumed to be the main reactive species. The singlet oxygen quenching rates in D2 O, pD 8, are (107 ℒ mol-1 s-1 ): alanine 0–2, methionine 3, tryptophan 9, histidine 17, carbonic anhydrase 85, lysozyme 150, superoxide dismutase 260, aposuperoxide dismutase 250. 相似文献
6.
S. R. Fahrenholtz F. H. Doleiden A. M. Trozzolo A. A. Lamola 《Photochemistry and photobiology》1974,20(6):505-509
Abstract —D-α-tocopherol was found to be an effective quencher of 1 O2 molecules ( k = 2.5 times 108 →mol-1 s-1 in pyridine) by measuring its effect on the autosensitized photooxidation of rubrene. The quenching process was shown to be almost entirely 'physical', that is, α-tocopherol deactivated about 120 1 O2 molecules before being destroyed. The results suggest that this process may be a mechanism for the protective effect of α - tocopherol in photodynamic action. 相似文献
7.
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
8.
Abstract The water soluble carotenoid crocetin has been studied as a singlet molecular oxygen monitor in D2 O solution, pD 8.4. Crocetin reacts chemically with singlet molecular oxygen with a rate constant of 4 x 108 M -1 s-1 . The rate constant for total quenching, chemical and physical, is 2.5 x 109 M -1 s-1 . Crocetin shows evidence for a reversible reaction with singlet molecular oxygen, as demonstrated by a fairly rapid absorption recovery after bleaching. 相似文献
9.
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
10.
Abstract— Singlet oxygen has been generated directly in 1,1,2-trichloro, 1,2,2-trifluoroethane solution by irradiation of the oxygen dimol 23 ∑-g →21 δg transition with a pulsed dye laser and the 3 ∑g - →1 δg + lv transition with a continuous Nd-YAG laser. The rates of chemical reaction and physical quenching of singlet oxygen so generated has been measured for a series of substituted oxodipyrro-methenes. The results show that the oxodipyrromethenes react with singlet oxygen at rates comparable to that for 1,3-diphenylisobenzofuran. The rate of quenching of singlet oxygen by ground state oxygen has been measured to be 2.5±0.3 × 103 M-l s-1 . 相似文献
11.
Philippe Richard Aleksander Blum Leonard I. Grossweiner 《Photochemistry and photobiology》1983,37(3):287-291
—The photosensitized inactivation of subtilisin BPN' by free hematoporphyrin (HP) followed exponential kinetics with positive mechanistic tests for the involvement of singlet oxygen (1 O2 ) as the principal intermediate. The photoinactivation quantum yield was 0.029 at 390 nm in oxygen-saturated, D2 O buffer at pH 7.0. The effects of HP binding were investigated for tryptophan oxidation in bovine serum albumin (BSA) and human serum albumin (HSA) at high protein:HP concentration ratios where the HP was > 97% complexed. The reaction kinetics were non-exponential and mimick a second-order process in the initial stages. The rate of HP photobleaching was 30-fold faster for complexed HP compared with free HP, which was shown to account for the observed kinetics. Mechanistic tests showed that 1 O2 was the dominant photooxidizing intermediate of tryptophan residues and that it was not involved in the accompanying photobleaching of HP. The quantum yield for tryptophan oxidation in BSA was 0.11 at 390 nm in oxygen-saturated, D2 O buffer at pH 8.0. The reactivity of HSA was approximately 2-fold lower than BSA for equivalent conditions. Estimates of the reaction cross sections led to 3 Å2 for the inactivation of subtilisin BPN' by 1 O2 and 20 Å2 for the oxidation of tryptophan in BSA. 相似文献
12.
STEADY-STATE NEAR-INFRARED DETECTION OF SINGLET MOLECULAR OXYGEN: A STERN-VOLMER QUENCHING EXPERIMENT WITH SODIUM AZIDE 总被引:2,自引:1,他引:2
Abstract— A sensitive near-infrared detection system incorporating improvements to existing methodologies has been used to characterize the sodium azide quenching of the steady-state luminescence of singlet molecular oxygen at 1270 nm. Stern-Volmer plots which were linear up to 80% quenching of the 1 O2 generated by rose bengal and eosin Y yielded a rate constant of 5.8 ± 0.1 times 108 M −1 s−1 for the quenching of 1 O2 in water, while the rate constants obtained in deuterium oxide with the same sensitizers were 6.28 times 108 M −1 s−1 and 6.91 times 108 M −1 s−1 respectively. A flow system minimized the effects of photobleaching of the rose bengal. With a mercury arc light source, the instrument can be used in photosensitization experiments to detect low levels of 1 O2 production in aqueous media. 相似文献
13.
L. Matisová-Rychlá O. N. Karpukhin T. O. Pochalok 《Photochemistry and photobiology》1973,18(4):303-309
Abstract— The inhibition by stable radicals having the structure (X-O)2 NO of the initiated oxidation of ethyl benzene was studied. According to a formal kinetic scheme, verified by both theoretical computer calculations and an experimental chemiluminescence method, the rate constants of the interaction of peroxyradicals with iminoxy radicals were estimated at 60°C to be: 2.4 times 105 litres mol-1 s-1 for X = OCH3 and 3.4 times 105 litres mol-1 s-1 for X = OCH2 CH3 . 相似文献
14.
Javier Catalán Juan C. Del Valle Fernando Fabero Norman A. Garcia 《Photochemistry and photobiology》1995,61(2):118-123
Abstract— The mechanism for photodegradation of the ultraviolet photostabilizer 2-(2'-hydroxy-5'-methylphenyl)benzotriazole (TIN P) upon direct and dye-sensitized (singlet molecular oxygen [O2 (1Δg )]-mediated) irradiation was studied. From the experimental TIN P photodegradation rate data, and low temperature (77 K) fluorescence and phosphorescence quantum yields, one can conclude that the photodegradative process involves phosphorescent states of TIN P. The open conformer of TIN P quenches O2 (1 Δg ) by physical scavenging with a rate constant (kq ) in dimethylsulfoxide of 2.8 times 106 M -1 s-1 . The intramolecular hydrogen-bonded conformer does not appreciably interact with O2 (1 Δg ). In the presence of a relatively high concentration of OH- (either 5 times 10-2 M KOH in ethanol or water at pH 13), the ionic form of TIN P (with an ionized phenol group) physically and chemically quenches O2 (1 Δg ). The reaction rate constant ( k r ) is 1 times 10 8 M -1 s-1 , and the ratio k q / k r is approximately three in alkaline aqueous media. 相似文献
15.
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
16.
Abstract— A very efficient quenching of singlet oxygen (1 O2 ) by N3 - ions has been applied to the determination of rate constants of reactions of 1 O2 with various substrates (A). This determination has been made possible by choosing experimental conditions which give simple competition between N3 - and A for 1 O2 formed in the steady state irradiation of convenient sensitizing dye (S). The consumption of oxygen by the substrate, as followed with an oxygen analyzer, decreases in the presence of low concentrations of N3 - . Using neutral air saturated aqueous solutions containing the dye phenosafranine + A and varying concentrations of N3 - , the 1 O2 rate constants for reactions with biological substrates and some radiation protective agents have been determined. 相似文献
17.
The influence of singlet oxygen (1 O2 ), generated by red light irradiation of oxygenated suspensions containing aluminium phthalocyanine sulphonate, on the membrane bound enzyme β-hydroxybutyrate dehydrogenase was investigated. The inactivation rates were measured using a spectrophotometry assay which involves disruption of the mitochondria. A novel NMR assay was also used to measure the activity of the enzyme in intact mitochondria. Relatively high inactivation rates of around 109 M −1 s−1 were observed in H2 O buffer, and rates in D2 O were a factor of 1.7 faster. Significant differences in enzyme inactivation rates by 1 O2 were observed, not only between disrupted and intact mitochondria but also between the NMR assay results and the spectrophotometric assay results. The results indicate the value of a specific assay which does not require the disruption of the biological system. 相似文献
18.
The photooxidation of N,N -diethylhydroxylamine (DEHA) by Rose Bengal (RB) has been investigated in micellar and nonmicellar aqueous solutions. We measured the quantum yield of oxygen consumption forming H2 O2 and monitored two intermediates, the superoxide and diethylnitroxide radicals. When the pH was vaned, the quantum yield of oxidation remained constant for 6 < pH < 10.5, decreased in acidic pH, and increased considerably in NaOH solution; these changes could be attributed to the protonation and dissociation processes of the >N-OH moiety of DEHA. The formation of diethylnitroxide radical was enhanced by superoxide dismutase or strong alkaline solution. Around neutral pH, the oxidation proceeded mainly via electron transfer from DEHA to the RB triplet ( k q = 107 M -1 s-1 ) with little 1 O2 participation ( kq < 105 M -1 s-1 ). However, when RB was incorporated into micelles in alkaline solution, the contribution of the singlet oxygen pathway increased at the expense of electron transfer, which was inhibited by the less polar micellar environment. Dark autoxidation of DEHA was accelerated by heavy metal impurities and increased very strongly in NaOH solution. 相似文献
19.
The steady-state UVA (350 nm) photolysis of ( E )-β-ionone ( 1 ) in aerated toluene solutions was studied by 1 H NMR spectroscopy. The formation of the 1,2,4-trioxane ( 2 ) and 5,8-endoperoxide ( 5 ) derivatives in the ratio of 4:1 was observed. Time-resolved laser induced experiments at 355 nm, such as laser-flash photolysis, photoacoustic and singlet oxygen 1 O2 phosphorescence detection, confirmed the formation of the excited triplet state of 1 with a quantum yield Φ T = 0.50 as the precursor for the generation of singlet oxygen 1 O2 ( Φ Δ = 0.16) and the isomeric α-pyran derivative ( 3 ), which was a reaction intermediate detected by NMR. In turn, the reaction of 1 O2 with 1 and 3 occurred with rate constants of 1.0 × 106 and 2.5 × 108 m −1 s−1 to yield the oxygenated products 5 and 2 , respectively, indicating the relevance of the fixed s-cis configuration in the α-pyran ring in the concerted [2+4] cycloaddition of 1 O2 . 相似文献
20.
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