共查询到20条相似文献,搜索用时 765 毫秒
1.
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
2.
Yotaro Morishima Toru Kitani Takaomi Kobayashi Yasuhiro Saeki Shun-ichi Nozakura Takeshi Ohno Shunji Kato 《Photochemistry and photobiology》1985,42(5):457-464
Abstract— Anionic polyelectrolytes functionalized with the 5-deazaflavin group (dFl) were synthesized. The lifetime of the triplet excited dFl in the polyelectrolytes with a 2-mol% dFl content (AdFl-2) was about 10 times longer than that of a low molecular weight analog (AdFl-M). 2-Mercaptoethanol (RSH) reduced the triplet dFl with the rate constant of k red = 2.01 × 108 M −1 s−1 for AdFl-M and k red = 4.4 × 107 M −1 s−1 for AdFl-2. A zwitterionic viologen (SPV) oxidized the triplet dFl with the rate constant of k red = 3.69 × 109 M −1 s−1 for AdFl-M and k ox = 7.4 × 108 M−1 s−1 for AdFl-2. The smaller rate constants for the polymer system were discussed in terms of the hindering effect of the macromolecular microenvironment. The back electron transfer was shown to be drastically slowed in the AdFl-2-SPV system as a result of the intensive electrostatic effect of the polyelectrolytes. The buildup of the viologen radicals was studied under the steady-state illumination of the three component systems including viologen and RSH. The dFl group was demonstrated to serve as a very efficient photosensitizer in the oxidative cycle in case back electron transfer was retarded. This is the case of the AdFl-2-SPV system which gave the quantum yield of about 0.4 for the SPV− buildup. By comparison, the AdFl-2-MV2 + system resulted in a much slower buildup of MV +radicals. 相似文献
3.
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
4.
J. C. Lima Parvin Danesh Paulo Figueiredo Fernando S. Pina António Maçanita 《Photochemistry and photobiology》1994,59(4):412-418
Abstract The excited state properties of the chalcone isomers of malvidin 3,5-diglucoside (malvin) in acidic aqueous solution (0 < pH < 4) were investigated using steady-state and time-resolved fluorescence spectroscopy. The two chalcone isomers of malvin were first isolated by high-performance liquid chromatography and then characterized by UV/visible absorption and fluorescence spectroscopy. The results were supported by molecular orbital calculations. The rate constants for photodeprotonation ( k 1 = 1 × 109 s−l ) and protonation ( k −1 = 1.3 × 1010 L mol−1 s−l ) were determined, both from the multiexponential fluorescence decays and the fluorescence intensities measured at the emission wavelengths of the neutral and ionized chalcone forms. The results here obtained are relevant for the understanding of the photoreactivity of anthocyanins in acidic medium. 相似文献
5.
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
6.
Irina G. Gazaryan Maya Yu. Rubtsova Yuri L. Kapeliuch José Neptuno Rodriguez-Lopez L. Mark Lagrimini Roger N. F. Thorneley 《Photochemistry and photobiology》1998,67(1):106-110
The properties of a newly isolated anionic tobacco peroxidase from transgenic tobacco plants overexpressing the enzyme have been studied with respect to the chemiluminescent reaction of luminol oxidation. These were compared to the properties of horseradish peroxidase in the cooxidation of luminol and p -iodophenol, the enhanced chemiluminescence reaction. The pH, luminol and hydrogen peroxide concentrations were optimized for maximum sensitivity using the tobacco enzyme. The detection limit for the latter under the optimal conditions (2.5 m M luminol, 2 m M hydrogen peroxide, 100 m M Naborate buffer, pH 9.3) was about 0.1 p M , which is at least five times lower than that for horseradish peroxidase in enhanced chemiluminescence with p -iodophenol. The rate constants for the elementary steps of the enzyme-catalyzed reaction have been determined: k 1 = 4.9 × 106 M −1 s1 , k 2 = 7.3 × 106 M −1 s−1 , k 3 = 2.1 × 106 M −1 s−1 (pH 9.3). The similarity of these rate constants is unusual for plant peroxidases. The high catalytic activity of tobacco peroxidase in the luminescent reaction is explained by the high reactivity of its Compound II toward luminol and the high stability of the holoenzyme with respect to heme dissociation. This seems to be a unique property of this particular enzyme among other plant peroxidases. 相似文献
7.
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
8.
G. T. MARKS E. D. LEE D. A. AIKENS H. H. RICHTOL 《Photochemistry and photobiology》1984,39(3):323-328
Abstract— Flash photolysis of neutral red between pH 1.3 and pH 11 yields the triplet species 3 DH2 +2 3 DH+ and 3 D. Both 3 DH2 +2 and 3 D exhibit first order decay with rate constants of 1.6 ± 0.3 × 104 s-1 but 3 DH+ decays within the lifetime of the flash. Over the entire pH range, ascorbic acid quenches the triplet, forming the semireduced radicals DH3 +2 DH2 + and DH, all of which exhibit second order decay with k = 1.8 ± 0.4 ± 108 M -1 s-1 most probably by recombination with semioxidized ascorbic acid. The dependence of the rate of decay of radical neutral red on the identity of reversible reductants supports the back-electron transfer mechanism, as does digital simulation of complex radical disproportionation schemes. In contrast to the efficient reduction of triplet neutral red by ascorbic acid, its reduction by EDTA is quite inefficient. 相似文献
9.
Piotr J. Bilski M. A. Wolak V. Zhang D. E. Moore C. F. Chignell 《Photochemistry and photobiology》2009,85(6):1327-1335
Lamotrigine (LTG) [3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine], an anticonvulsant and antidepressant drug Lamictal® , produces a (photo)toxic response in some patients. LTG absorbs UV light, generating singlet oxygen (1 O2 ) with a quantum yield of 0.22 in CH2 Cl2 , 0.11 in MeCN and 0.01 in D2 O. A small production of superoxide radical anion was also detected in acetonitrile. Thus, LTG is a moderate photosensitizer producing phototoxicity and oxidizing linoleic acid. LTG is a weak 1 O2 quencher ( k q = 3.2 × 105 m −1 s−1 in MeCN), but its photodecomposition products in dimethyl sulfoxide (DMSO) quenched 1 O2 very efficiently. Upon intense UV irradiation from a xenon lamp, LTG was photobleached rapidly in DMSO and slowly in acetonitrile, alcohol and water. The rate increased significantly when laser pulses at 266 nm were employed. The photobleaching products generated 1 O2 twice as strongly as LTG. Photobleaching was usually accompanied by the release of chloride anions, which increased in the presence of ascorbic acid. This suggests the formation of aryl radicals via dechlorination, a process which may be responsible for the photoallergic response observed in some patients. Our results demonstrate that LTG is a moderate generator of 1 O2 prone to photodechlorination, especially in a reducing environment, which can contribute to the reported phototoxicity of LTG. 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.
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
12.
Eberhard Bothe Man Nien Schuchmann Dietrich Schulte-Frohlinde Clemens von Sonntag 《Photochemistry and photobiology》1978,28(4-5):639-643
Abstract— In aqueous solutions α-hydroxyalkylperoxyl radicals undergo a spontaneous and a base catalysed HO2 elimination. From kinetic deuterium isotope effects, temperature dependence, and the influence of solvent polarity it was concluded that the spontaneous reaction occurs via an HO2 elimination followed by the dissociation of the latter into H+ and O2 - . The rate constant of the spontaneous HO2 elimination increases with increasing methyl substitution in α-position ( k (CH2 (OH)O2 ) < 10s-1 k (CH3 CH(OH)O2 ) = 52s-1 k ((CH3 )2 C(OH)O2 ) = 665 s-1 ). The OH- catalysed reaction is somewhat below diffusion controlled. The mixture of peroxyl radicals derived from polyhydric alcohols eliminate HO2 at two different rates. Possible reasons for this behaviour are discussed. The mixture of the six peroxyl radicals derived from d -glucose are observed to eliminate HO2 with at least three different rates. The fastest rate is attributed to the HO2 elimination from the peroxyl radical at C-l ( k > 7000s-1 ). Because of the HO2 eliminations the peroxyl radicals derived from d -glucose do not undergo a chain reaction in contrast to peroxyl radicals not containing an α-OH group. In competition with the first order elimination reactions the α-hydroxylalkylperoxyl radicals undergo a bimolecular decay. These reactions are briefly discussed. 相似文献
13.
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
14.
–Methylviologen (MV2+ ) adsorbed on cellulose could be reduced photochemically in the solid phase sensitized by tris(2,2'-bipyridyl)ruthenium(II) complex, [Ru(II)(bpy)3 ], using disodium ethylene-diaminetetraacetic acid (Na2 EDTA) as a reducing agent. Formation of the cation radical (MV + .) was confirmed by visible and EPR spectra. The MV+ . formed on cellulose was remarkably stable against air oxidation and rapidly accumulated even by the irradiation under air. Water adsorbed on the cellulose greatly retarded the photoreaction. Action spectrum showed that the excitation of Ru(II)(byp)3 is responsible for the photochemical reaction. The quenching of the emission from Ru(II)(bpy)*3 by MV2+ . indicated that a primary photochemical reaction occurs between Ru(II)(bpy)*3 and MV2+ . The main reaction path is the reduction of MV2+ by Ru(II)(bpy)3 , giving MV+ . and Ru(III)(bpy)3 , followed by the reduction of Ru(III)(bpy)3 to Ru(II)(bpy)3 with Na2 EDTA, which in turn is oxidized to give carbon dioxide. 相似文献
15.
Abstract— The influence of chloride ion on the rate of decay of triplet methylene blue in 0.01 M acid in the absence and presence of ferrous ions was investigated by means of laser flash-photolysis monitored by kinetic spectrophotometry. Chloride weakly accelerates decay of 3 MBH2± in aqueous solution in the absence of Fe(II). Quenching of 3 MBH2+ by Fe(II) is more strongly catalyzed by Cl- in both water and 50 v/v% aq. CH3 CN. The uncatalyzed quenching constant, k 5 , is of the order of 1 × 106 M -1 s-1 while in 4.8 M aqueous chloride ( μ – 7.2 M ) k 5 = (37.2 ± 1.8) × 106 M -1 s-1 . A possible role of chloride is as a bridging species in quenching via electron transfer between 3 MBH2+ and Fe(II). 相似文献
16.
Colin F. Chignell B. Kalyanaraman Robert H. Sik Ronald P. Mason 《Photochemistry and photobiology》1981,34(2):147-156
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 CH3 NO2 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 [15 N1 ]-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 SO− 3 radicals during photolysis of sulfanic acid. Direct photolysis of sulfanilamide, sulfanilic acid and Na2 SO3 in the absence of any spin trap yielded the SO− 3 radical. Photolysis of 4-aminobenzoic acid at pH 7 gave the H radical which was trapped by DMPO. At low pH values OH and C6 H4 COOH radicals were generated during the photolysis of 4-aminobenzoic acid. No e− aq were trapped by CH3 NO2 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
17.
Abstract— The triplet-triplet absorption spectra in aqueous solution of the acid (3 LfH2 + ), the neutral (3 LfH) and the basic (3 Lf- ) forms of lumifiavin (6,7,9-trimethylisoalloxazine) were measured by flash photolysis. The p K a values of the corresponding protolytic equilibria of the lumifiavin triplet were found to be 4.45 ±0.1 and 9.8±0.15. 相似文献
18.
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
19.
Abstract— A comparison of the transient absorption spectra from the photolysis of disulfides in solution suggests that C-S bond breakage is a common primary photolytic process. This process becomes more important as the resulting carbon centered radical is stabilized by increasing alkyl substitution or resonance interaction with an aromatic system. The perthiyl radical product is characterized by λmax ∽380 nm,ε380 ∽1700 M −1 cm−1 and decays by second order kinetics with k 2 ∽3.7×108 M −1 s−1 in water.
In the presence of O2 , the photolysis of disulfides which produce the thiyl radical give transient absorptions in the 500–600 nm region. Possible identities of these transients are discussed. 相似文献
In the presence of O
20.
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