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1.
Abstract— The rapid bimolecular reaction SO + O3 = SO2 +O2 + 106 kcal/mole
yields electronically excited SO2 in the 3 B 1 and 1 B2 states with some vibrational excitation, as well as SO2 in its electronic ground state. It is shown that k1 = 1.5 x 1012 exp (-2100/ RT ) cm2 mole-1 s-1 and that the formation of electronically excited SO2 involves higher activation energies. 相似文献
yields electronically excited SO
2.
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
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.
Kinetic and mechanistic aspects of the vitamin B2 (riboflavin [Rf])-sensitized photo-oxidation of the imidazoline derivates (IDs) naphazoline (NPZ) and tetrahydrozoline (THZ) were investigated in aqueous solution. The process appears as important on biomedical grounds, considering that the vitamin is endogenously present in humans, and IDs are active components of ocular medicaments of topical application. Under aerobic visible light irradiation, a complex picture of competitive interactions between sensitizer, substrates and dissolved oxygen takes place: the singlet and triplet (3 Rf*) excited states of Rf are quenched by the IDs: with IDs concentrations ca. 5.0 m m and 0.02 m m Rf, 3 Rf* is quenched by IDs, in a competitive fashion with dissolved ground state oxygen. Additionally, the reactive oxygen species: O2 (1 Δg ), O2 •− , HO• and H2 O2 , generated from 3 Rf* and Rf •− , were detected with the employment of time-resolved methods or specific scavengers. Oxygen uptake experiments indicate that, for NPZ, only H2 O2 was involved in the photo-oxidation. In the case of THZ, O2 •− , HO• and H2 O2 were detected, whereas only HO• was unambiguously identified as THZ oxidative agents. Upon direct UV light irradiation NPZ and THZ generate O2 (1 Δg. ), with quantum yields of 0.2 (literature value, employed as a reference) and 0.08, respectively, in acetonitrile. 相似文献
5.
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
6.
Abstract— Polymer rose bengal derivatives are converted to their C-6 ammonium salts. The φ1 O2 derived in CH2 C12 is a function of the K B of the neutralizing amine. 相似文献
7.
Taras K. Antal Wayne Lo William H. Armstrong Esa Tyystjärvi 《Photochemistry and photobiology》2009,85(3):663-668
We measured the photosensitivity of an artificial tetranuclear oxo–Mn(IV) complex, [Mn4 O6 (bpea)4 ]Br4 , which has an adamantane-shaped {Mn4 O6 }4+ core. Illumination caused changes in the absorption spectrum of the compound consistent with a one-electron reduction in the compound. Bromide appears to be the most probable electron donor in the reaction system. Chemical modification of the cluster appears to destabilize it, predisposing it to reductive degradation. UV light was more efficient than visible light in causing the changes. The data support the suggestion that the natural oxygen-evolving Mn complex is photosensitive and can oxidize components of the oxygen-evolving complex in its excited state causing photoinhibition, and that photostability is an important issue in designing Mn complexes for artificial photosynthesis. Furthermore, light-induced oxidation of bromide by [Mn4 O6 (bpea)4 ]4+ may suggest that oxidation of chloride is involved in natural water splitting or has been involved during the evolution of the water-splitting enzyme. 相似文献
8.
PULSE RADIOLYSIS STUDIES IN MODEL LIPID SYSTEMS: FORMATION AND BEHAVIOR OF PEROXY RADICALS IN FATTY ACIDS 总被引:1,自引:0,他引:1
Abstract— Radiolytic formation and peroxidation of fatty acid radicals have been investigated by pulse radiolysis techniques in oleate, linoleate, linolenate and arachidonate systems. A strong absorption band at 280 nm associated with conjugated radicals, Rconj , formed in polyunsaturated fatty acid moieties has been used as a probe for kinetic processes occurring at doubly allylic sites in the hydrocarbon chain. Formation of Rconj by O- has been found to be more efficient than the less selective OH radical. Peroxidation of Rconj is shown to be somewhat slower, ( k R + O2 ˜ 3 × 108 M -1 s-1 ), than O2 reactions with radicals in oleate ( k R + O2 = 1 × 109 M -1 s-1 ). Peroxy radicals generated in these reactions disappear slowly by essentially second order processes (2 k RO1 ˜ 107 M -1 s-1 ). The superoxide radical, O- 2 , shows little if any reactivity towards 0.01 M linolenate or arachidonate over periods of 20 s. 相似文献
9.
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
10.
Abstract— A direct process for an activationless electron transfer from photoexcited tryptophan to molecular oxygen is proposed. By photodetachment of mass-selected indole-O2 - clusters in gas phase a neutral indole+ O2 - charge-separated exciplex state is found at 2.25 0.2 eV above the neutral ground state. By theory also, the existence of an excited charge separated state at 3.05 0.2 eV is postulated. In gas phase both charge-separated cluster states are energetically below the first singlet states 1 Lb and 1 La and the lower even below the first triplet state T1 of indole. In gas-phase clusters these energetics imply a very efficient quenching of photoexcited indole by fast electron transfer to oxygen. We discuss a similar mechanism for tryptophan-O2 in aqueous environment and find it without activation barrier and presumably extremely fast. In the collisional tryptophan* -O2 complex the efficiency and the time scale of the charge transfer process should be mostly solvent independent. In polar solvent a complete charge separation and free superoxide formation are expected. We correlate this model with previous fluorescence and phosphorescence quenching data of excited tryptophan by O2 and propose electron transfer to be the relevant process. 相似文献
11.
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
12.
Abstract— The kinetics of the oxidation of a homologous series of 4,4'-di(n-alkyl)-bipyridinium (viologen) radicals by Ru(NH3 )6 3+ in vesicle suspensions was studied using laser flash photolysis. The viologen radicals were produced photochemically in the bilayer membrane phase of the vesicles by electron transfer from the triplet state of chlorophyll-α. At high concentrations of Ru(NH3 )6 3+ , the rate of oxidation of the viologen radicals in the aqueous phase was limited by the rate at which the radicals diffused from the membrane to the aqueous phase. The exit rate constant decreased from 2 × 105 s−1 for the methyl viologen radical to 4 × 103 s−1 for the pentyl viologen radical. Both the exit rate constants and the calculated values for the equilibrium association constants of the viologen radicals were unexpectedly insensitive to the length of their alkyl substituents. This, as well as other data, suggests that the radicals that diffused into the aqueous phase tended to remain associated with the membrane-water interface. 相似文献
13.
Giuliana Valduga Santiago Nonell Elena Reddi Giulio Jori Silvia E. Braslavsky 《Photochemistry and photobiology》1988,48(1):1-5
Abstract— Zn(II)phthalocyanine (ZnPc) generates O2 (1 Δg ) with a quantum yield of ca. 0.4 upon photocxcitation at 354 or 600 nm in ethanolic solution as determined by time-resolved phosphorescence studies at 1270 nm and photooxidation experiments using 1,3-diphenylisobenzofuran (DPBF) as substrate. The quantum yield of photooxidation slightly increases upon incorporation of ZnPc into unilamellar liposomes of dipalmitoylphosphatidylcholine. Under our irradiation conditions (600 nm, 18° C, and short light exposure times), DPBF(5–50 μM) undergoes photooxidation by a pure Type II mechanism; the rate constant for the O2 (1 Δg ) + DPBF reaction is (1.1 ±0.1) x 109 M-1 s_1 in ethanol solution and determined to be about two orders of magnitude smaller when both ZnPc and DPBF are embedded into liposomes. 相似文献
14.
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
15.
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
16.
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
17.
Abstract— The fluoroquinolone antibiotics can induce skin photosensitivity in some patients and this has been ascribed to the generation of reactive oxygen species, such as singlet oxygen (O2 [1 Δg ]). We have studied the photochemical properties of the different ionized forms of the fluoroquinolone norfloxacin upon complexation with Mg2 + and Ca2 + ions, as it is proposed that the antibiotic exists mainly as a complex in the blood plasma. We found that the norfloxacin cation (pH < 6) shows no photodegradation after UVA irradiation and has a low quantum yield of O2 (1 Δg ) generation. The norfloxacin cation does not complex. Ca2 + or Mg2 + ions; when these ions are added to the solution, we observed no changes in the fluorescence quantum yields (φflu ) and singlet oxygen yields (φΔ ). In contrast, the neutral (6 ± pH > 8.5) and anionic (pH > 9) forms of norfloxacin are able to complex calcium and magnesium, and their generation of O2 (1 Δg ) is decreased by complexation. The neutral zwitterionic form and the anionic form also quench singlet oxygen by both chemical and physical pathways regardless of complex formation, while physical quenching is observed for the cation. At pH > 7.4, norfloxacin photobleaches and complexation to Ca2 + and Mg2 + increases the rate at which photobleaching occurs. Thus, both the pH of the medium and complexation with metal cations may affect the phototoxic potential of this antibiotic. 相似文献
18.
–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
19.
Abstract— The rate constant k5 / > for physical quenching of singlet oxygen O2 (δ1 ;) by the sensitizer in dye-sensitized photooxygenations is determined in the case of chlorophylls a and b (7.3 times 108 , 4.2 times 108 M-1 s-1 respectively), pheophytins a and b (7.4 times 107 , 3.0 times 107 M-1 s_1 respectively), tetraphenylporphyrin (4.4 times 107 M-1 s_1 ), magnesium tetraphenylporphyrin (5.0 times 108 M-1 s_1 ), zinc tetraphenylporphyrin (1.5 times 108 M-1 s_l ) and protoporphyrin IX-dimethylester (9.1 times 107 M -1 s_1 ) in benzene. These sensitizers show a linear correlation between log ks O , and their half-wave oxidation potentials and the value of the slope is similar to that observed for various compounds such as phenols. It is concluded that (i) the interaction between chlorophylls and related compounds with singlet oxygen may involve an exciplex as for phenols, and (ii) physical quenching may be envisaged as a spin-orbit-induced intersystem crossing within the exciplex. 相似文献
20.
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