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1.
Abstract— All -trans retinal is dissolved in alcohols and illuminated at 365 nm in the presence of a singlet oxygen acceptor, 2,5-dimethylfuran. Illumination produces the photosensitized oxidation of the acceptor which is measured by the disappearance of its 215 nm absorption band. A kinetic study is carried out and βDMF is 1.6 × 10--4 M . The quantum yield of 1O2 production from the light-excited retinal is estimated to 0.096. The retinal sensitized photooxidation of dimethylfuran is inhibited by a 1O2 quencher, 1,4-diazabicyclo(2,2,2)-octane, and enhanced by deuteration of the solvent. Deuterated solvents are known to increase 1O2 lifetime.
The production of 1O2 from retinal is briefly discussed in relation to the damage which may be induced by light in the visual cells.  相似文献   

2.
Abstract— We report the detection of a weak near-infrared light emission originating from 8 nM singlet molecular oxygen (1O2) produced in a mixture of 1 m M hypochlorite (OC1-) and 8 n M hydrogen peroxide (H2O2). The measurements were made with a highly sensitive detection system for ultraweak light emission in the 1.0-1.5 μm wavelength region. The emission intensity exhibited linear dependence for H2O2 concentrations in the range of 8-670 n M . The mixture containing a lower concentration (33 μ M ) of OCl- pseudocontinuously emitted near-infrared light for 5 s. The rate constant for 1O2 production obtained from the kinetic analysis agrees with that previously reported. Our results demonstrate the possibility of measuring very low concentrations of 1O2 in a OCi-/H2O2 mixture as well as 1O2 production in intact living systems.  相似文献   

3.
Abstract— The formation of singlet molecular oxygen (1O2) by sensitization of the furocoumarins 5-methoxypsoralen (5-MOP), 8-methoxypsoralen (8-MOP) and psoralen complexed with DNA was investigated. From the results it is concluded that 5-MOP complexed with native DNA is able to generate 1O2, even in a larger extent than 5-MOP free in solution. Also, with 8-MOP and especially with psoralen, 1O2 formation by the complexed compound could be observed. The 1O2 formation sensitized by covalently bound furocoumarin was demonstrated with psoralen as a model compound. 4',5'-Dihydropsoralen, a model compound for the UVA light absorbing 4',5'monoadducts of furocoumarins to DNA, is also able to generate 1O2.  相似文献   

4.
A NEW METHOD FOR THE DETECTION OF SINGLET OXYGEN IN AQUEOUS SOLUTIONS   总被引:4,自引:0,他引:4  
Abstract— In experiments on the interception of reactive intermediates of strongly oxidizing character in dye (S) sensitized photooxidations using p -nitrosodimethylaniline (RNO) as a selective scavenger, it has been observed that some substrates (A) or 1O2 acceptors (like imidazole derivatives) induce the bleaching of RNO as followed spectrophotometrically at 440 nm. Since singlet oxygen (1O2) does not react chemically with RNO, this bleaching is a consequence of 1O2 capture by the imidazole ring which results in the formation of a trans-annular peroxide intermediate [1O2] capable of inducing the bleaching of RNO (-RNO). In the absence of RNO, [1O2] decomposes or rearranges into the final oxygenation product 1O2: 1Δg Thus, the system imidazole plus RNO can be used as a sensitive and selective test for the presence of 1O2 in aqueous solutions. The method can also be applied in the presence of sensitizing dyes which, under visible irradiation, can partially bleach RNO even in the absence of imidazole derivatives. In such a case, the bleaching of RNO is strongly increased by the presence of imidazoles with a characteristic dependence on their concentration. The separation of the product of RNO bleaching by thin layer chromatography can serve as additional proof of the presence of 1O2 in the system. The imidazole plus RNO method has been applied to a number of sensitizing and non-sensitizing dyes.  相似文献   

5.
Abstract —In vivo participation of singlet excited oxygen (1O2, 1Δ9) in the photodynamic inactivation and induction of genetic changes (gene conversion) in acridine orange-sensitized yeast cells was investigated by using N3-, an efficient 1O2 quencher, and D2O, a known agent for the enhancement of the lifetime of 1O2. 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 1O2 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 H2O with D2O 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 lO2 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 1O2 must be the major intermediate responsible for the photodynamic actions in acridine orangesensitized yeast cells.  相似文献   

6.
7.
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, 1O2. But the reaction between 1O2 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 1O2 processes, though appreciable 1O2 was formed.  相似文献   

8.
Abstract— Various nitrogen containing compounds have previously been shown to quench singlet oxygen (10z). When measuring the dimol 1O2 light emission arising from the H 2O2 /OCI- reaction, we found that certain cyclic diamines increase the emission of light, while other amines were inhibitory. This increase of light emission was seen with both 1, 4diazabicyclo[2.2.2]octane and N, N'-dimethylpi-perazine but not with acyclic analogues. Sodium azide inhibited both the normal and enhanced light emission. The enhanced light emission shows spectral properties characteristic of lO2 dimol emission.  相似文献   

9.
Abstract— The production of singlet oxygen (1O2) by a series of furocoumarins with different skin sensitizing abilities has been investigated with methods already proven to be suitable to establish the ability of 8-methoxypsoralen (8-MOP) to generate 1O2.
The following compounds: 5-methoxypsoralen (5-MOP), psoralen, 4,5',8-trimethylpsoralen (TMP) and 5,8–dimethoxypsoralen (5,8–DMOP), are able to generate 1O2 when irradiated with long–wave ultraviolet light. With the photobiologically inactive angelicin no 1O2 production has been found. The relative extent of 1O2 formation has been determined for the various furocoumarins and has been compared with literature data for the skin photosensitizing effect. The observed relation between experimental data on the one side and the literature data on the other side is discussed.  相似文献   

10.
Abstract— The self-sensitized photooxidation of mesodiphenylhelianthrene in various solvents has been investigated. The involvement of 1O2 as the reactive intermediate in the formation of the endoperoxide has been demonstrated by the quenching of the photooxidation by the efficient 1O2-quencher β-carotene. The rate constant for the addition of 1O2 to mesodiphenylhelianthrene has been determined to be k R≅ 1010 M -1 s-1, which is the highest value hitherto known in the literature. The probability factor p , which describes the concentration independent part of the overall quantum yield, has been measured to be p =0.17.  相似文献   

11.
The steady-state UVA (350 nm) photolysis of ( E )-β-ionone ( 1 ) in aerated toluene solutions was studied by 1H 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 1O2 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 1O2 ( Φ Δ = 0.16) and the isomeric α-pyran derivative ( 3 ), which was a reaction intermediate detected by NMR. In turn, the reaction of 1O2 with 1 and 3 occurred with rate constants of 1.0 × 106 and 2.5 × 108  m −1s−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 1O2.  相似文献   

12.
Abstract— Singlet oxygen (lO2) formed in the photolysis of neutral aqueous micellar (with Triton X-100) solution of chlorophyll a (dissolved inside the micelle) is detected in the aqueous phase by a test using imidazole in the presence of p -nitrosodimethylaniline. The quantum yield of lO2 diffusing out of the micelle into the aqueous phase is also determined [θ(lO2) ⋍ 0.70–0.85].  相似文献   

13.
Abstract— A very efficient quenching of singlet oxygen (1O2) by N3- ions has been applied to the determination of rate constants of reactions of 1O2 with various substrates (A). This determination has been made possible by choosing experimental conditions which give simple competition between N3- and A for 1O2 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 1O2 rate constants for reactions with biological substrates and some radiation protective agents have been determined.  相似文献   

14.
Abstract— The possibility of 1O2 (1Δg) participation in the oxidation of polyphenols and quinones has been investigated in two systems: (1) the system involving autooxidation leading to oxidative polymerization and destruction, and (2) the modified Trautz-Schorigin reaction, i.e. oxidation of polyphenols and HCHO with H2O2 in concentrated alkaline solutions. The red band with maximum at 635 nm observed in chemiluminescence of pyrocatechol, adrenaline, pyrogallol, gallic acid, adrenochrome and p -benzoquinone corresponds to the transition 2O2(1Δg) → 2O2(3Σ-g). Emission bands in the range 475–540 nm arise from the superposition of the 2O2(1Δg) → 2O2(3Σ-g) transition and radiative deactivation of excited oxidation products. In system (2) chemiluminescence has a broad band from 580 nm beyond 800 nm and much higher intensity than in system (1). Formaldehyde was found to enhance light emission in system (1) by a factor of about 30. The influence of solvents, including D2O in which 1O2 has varying lifetimes, on kinetics of chemiluminescence as well as quenching effect of β-carotene, hydroquinone, cysteine, bilirubin and biliverdin strongly support the involvement of 1O2 in the chemiluminescence of both systems.  相似文献   

15.
Abstract— The use of cyclic 1,3-dienes and polycyclic aromatic hydrocarbons as xenobiotic substrates for the interception of electronically excited (singlet) molecular oxygen (1O2) in biological systems is reviewed and criticized, and the possibility of utilization of reactive endogenous substrates for 1O2 interception is considered. The common sterols, cholesterol, 5α-cholest-7-en-3β-ol, and 5α-lanost-8-en-3β-ol each give oxidation products with 1O2 different from those with ground-state molecular oxygen that can be distinguished from one another by simple chromatographic means.  相似文献   

16.
Abstract— The photogeneration of singlet oxygen (1O2) from thylakoids and the chromophores involved as endogenous sensitizers were investigated using chloroplasts and thylakoids isolated from spinach. The blue light-induced inhibition kinetics of photosynthetic electron transport and that of CTvCF, ATPase were also studied. The spectral dependence of the generation of 1O2 from thylakoid membranes, measured by the imidazole plus RNO method, clearly demonstrated that the Fe-S centers play an important role in 1O2 generation, acting as sensitizers in thylakoids. The photoinhibition of the electron transport in isolated chloroplasts was strikingly depressed by a lipid-soluble '02 quencher and enhanced by deuterium oxide substitution, indicating that the inhibition processes are mainly mediated by 1O2 which is produced via photodynamic activation. The involvement of chloroplast cytochromes in the production of 1O2 was deduced from the action spectrum for the photodynamic inhibition of the electron carrier chain. The results obtained from the kinetic studies appear consistent with the involvement of some components such as the Fe-S centers and cytochrome chromophores of the carrier chain in the generation of 1O2.  相似文献   

17.
Abstract The production of singlet oxygen (1O2) upon irradiation of several dyes in aqueous solution at pH 9.0, was quantitatively analyzed on the basis of the appearance of stable nitroxide radicals using the amine 2,2,6,6-tetramethyl-4-piperidone as 1O2 acceptor. The dyes were checked for purity, their concentrations uniformized in terms of absorbance values and a correction factor was introduced which took into account the amount of photons absorbed. The rates of 1O2 production (in arbitrary units per min) were: 71 with rose Bengal, 70 with methylene blue, 61 with eosin Y, 18 with thiopyronine, 10 with proflavine and 9 with acridine yellow. Production of 1O2 was not observed with 9-aminoacridine, acridine orange, quinacrine and ethidium bromide. Irradiated lumichrome initiated, with the same amine, another type of reaction. The rates of two other photoreactions were also determined under similar experimental conditions by following (i) the deoxyguanosine decomposition in which case the reaction was found to be less sensitive but largely parallel to the 1O2 production and (ii) the bacteriophage ØX174 inactivation in which case the dyes showed differences in their relative efficiencies. The proteinic capsid of the phage appeared as an effective impermeability barrier towards externally generated 1O2. Moreover, some of the dyes studied intercalated into the phage DNA, a process known to favor radicalar reactions.  相似文献   

18.
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 H2O and D2O. 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)32+* 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 1O2 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 1O2.  相似文献   

19.
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 (1O2) with a quantum yield of 0.22 in CH2Cl2, 0.11 in MeCN and 0.01 in D2O. 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 1O2 quencher ( k q = 3.2 × 105  m −1 s−1 in MeCN), but its photodecomposition products in dimethyl sulfoxide (DMSO) quenched 1O2 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 1O2 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 1O2 prone to photodechlorination, especially in a reducing environment, which can contribute to the reported phototoxicity of LTG.  相似文献   

20.
Abstract— A comparative study was carried out on the in situ susceptibilities to photoinactivation of the photosystem I (PS I) and II (PS II) complexes of spinach thylakoids treated with efficient type II sensitizers. While the presence of the exogenous sensitizers caused a substantial increase in the extent of photoinactivation of whole chain electron transport, it did not affect PS I activity of thylakoids in light but exerted an enhanced photoinactivating effect only on PS II. The measurements of the action spectrum for the inhibition of PS II activity of the sensitizer-incorporated thylakoids and that for the generation of singlet oxygen (1O2) from them revealed that photosensitized inactivation of PS II is directly related to the photoproduction of 1O2 in thylakoid membranes. The results obtained in the present work clearly demonstrate an exceptional sensitivity of PS II to 1O2, providing circumstantial evidence that high light-induced damage to PS II may result from photosensitization reactions mediated by 1O2, which is not necessarily produced within the PS II complex.  相似文献   

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