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1.
Abstract —The photoreduction of thionine by water has been studied, using a technique applied in earlier work on photoreduction of methylene blue. It is found for thionine as for methylene blue, that a long-lived excited intermediate is formed, and that two such intermediates react to produce a single reduced molecule, thus providing adequate energy for the reaction. The mechanism proposed for methylene blue photoreduction is shown to be applicable to thionine photoreduction as well, indicating the unimportance of the amine methyl groups. Although in previous work it was suggested that H2 O was the reducing agent, none of them, however, could determine the H2 O2 formed. The formation of H2 O2 is confirmed in this work, and the kinetics of its formation are shown to be in accordance with the mechanism. 相似文献
2.
CATALYTIC ACTION AND DESTRUCTION OF PROTOHEMATIN DURING PEROXIDE DEPENDENT LUMINOL CHEMILUMINESCENCE
Abstract— The catalytic action of protohematin was studied during the H2 O2 -dependent chemiluminescent luminol reaction. In spite of the fact that the catalyst was ultimately inactivated, the average protohematin molecule catalyzed the consumption of about 103 molecules of luminol. The inactivation of catalyst and the initial consumption of luminol were studied during the luminescent reaction with different concentrations of reactants. A scheme accounting for the experimental observations is proposed. The formation of a primary protohematin-H2 O2 complex is followed by binding of luminol, resulting in a ternary complex. A nucleophilic attack by a second molecule of H2 O2 on the luminol molecule results in light emission from excited aminophthalate via a hypothetical peroxide adduct. The destruction of protohematin occurs via the attack of H2 O2 on the porphyrin structure of the protohematin-H2 O2 complex. Second order rate constants for the destruction of protohematin, the formation of the luminol complex and the nucleophilic attack of H2 O2 are presented. 相似文献
3.
U. Steiner M. Hafner S. Schreiner H. E. A. Kramer 《Photochemistry and photobiology》1974,19(2):119-128
Abstract— While studying the photoreduction of some dyes (D) by reducing agents (R), it was observed that the quantum yield of the photoreduction increases considerably upon addition of a third substance (C), whereas it is very small when the dye is photoreduced by C alone (catalytic effect), (see Table 1).
The system thionine (D), allylthiourea (R), and azulene (C) was investigated in detail using both flash photolysis and continuous illumination. On photolysis, thionine is converted into its photo-reduced form, leucothionine. Azulene reacts with the basic form of the thionine triplet3 TH + to produce the semithionine radical. In the system thionine and azulene, most of these radicals revert back to thionine. When ATU (˜ 102- M ) is added to thionine and azulene (3 × 10-4 M ), the semithionine radicals are reduced to leucothionine; the quantum yield of this reduction is considerably higher than in the system thionine and allylthiourea. Flash experiments demonstrate that allylthiourea does not react with the semithionine radicals.
At very high ATU concentrations (≥ 10-1 M ), however, the primary reaction is between thionine triplet and allylthiourea; under these conditions the quantum yield is not influenced by azulene (3 × 10-4 M ). 相似文献
The system thionine (D), allylthiourea (R), and azulene (C) was investigated in detail using both flash photolysis and continuous illumination. On photolysis, thionine is converted into its photo-reduced form, leucothionine. Azulene reacts with the basic form of the thionine triplet
At very high ATU concentrations (≥ 10
4.
Abstract— The apparent K m for O2 in the photoreduction of molecular oxygen by spinach class II chloroplasts and photosystem I subchloroplast fragments was determined. In both cases, a value of 2 ∼ 3 μ M O2 was obtained. The reaction rate constant between O2 and P-430, the primary electron acceptor of PS I, is estimated to be ∼ 1.5 × 107 M -1 s-1 and the factors affecting the production of superoxide by the photoreduction of O2 in chloroplasts are discussed. Preliminary evidence is presented indicating the occurrence of an azide-insensitive scavenging system for H2 O2 in chloroplast stroma. 相似文献
5.
A series of phage with different genomes (both single-stranded and double-stranded RNA and DNA) was inactivated with hydrogen peroxide (H2 O2 ) in various combinations with far-ultraviolet (FUV) and near-ultraviolet (NUV) radiations. In every case but one (a lipid-coated phage), a sublethal H2 O2 concentration greatly enhanced killing by NUV but not FUV. Moreover, this NUV/H2 O2 synergism was oxygen independent and there was little if any host cell reactivation upon NUV plus H2 O2 inactivation. These results suggest that these phage are inactivated by a common mechanism irrespective of nucleic acid composition, but that some phage genomes may be more vulnerable to NUV/H2 O2 inactivation than others. 相似文献
6.
GARY J. BACHOWSKI KIM M. MOREHOUSE ALBERT W. GIROTTI 《Photochemistry and photobiology》1988,47(5):635-645
Abstract— Photooxidation reactions in ascorbate (AH)-containing erythrocyte membrane suspensions have been studied in broad perspective by simultaneously monitoring lipid peroxidation in the membrane compartment and formation of hydrogen peroxide (H2 O2 ) and hydroxyl radical (OH) in the aqueous compartment. Non-bound uroporphyrin (UP) and membrane-bound protoporphyrin (PP) were used as sensitizers. Photoreduction of UP to the radical anion (UP- ) was detected by electron spin resonance when UP/AH/membrane mixtures were irradiated anaerobically. Aerobic irradiation resulted in a strong AH- -stimulation of lipid peroxidation, H2 O2 formation, and OH- generation (detected with 2-deoxyribose (DOR) and the spin trap 5,5-dimethyl-l-pyrroline-N-oxide). Use of diagnostic agents (e.g. catalase, desferrioxamine, mannitol) revealed that OH- is involved in light-stimulated DOR oxidation, but not in lipid peroxidation. Similar irradiation in the presence of PP resulted in far greater lipid peroxidation than observed with UP, but less DOR oxidation, and insignificant accumulation of H2 O2 . This suggests that photoreduction of membrane-bound PP is less efficient, possibly due to hindered access of AH- . 相似文献
7.
J. Van Steveninck K. Tijssen J. P. J. Boegheim J. Van der Zee T. M. A. R. Dubbelman 《Photochemistry and photobiology》1986,44(6):711-716
In a reaction mixture containing hematoporphyrin derivative, deoxyribose, Fe3+ -EDTA and either methionine or tryptophan, hydroxyl radicals were formed during illumination with visible light. When either hematoporphyrin derivative, Fe3+ -EDTA or the amino acid was omitted from the reaction mixture, the generation of hydroxyl radicals ceased. These observations suggest an iron-catalyzed Haber-Weiss reaction, involving superoxide and hydrogen peroxide in the generation of hydroxyl radicals. It could be shown that with methionine H2 O2 was indeed an essential intermediate in the reaction sequence. With tryptophan, however, H2 O2 , was not generated. Apparently a photooxidation product of tryptophan could replace H2 O2 in the OH-generating reaction with Fe2+ -EDTA. Although superoxide was generated in the reaction mixture, it was not an indispensable intermediate. Apparently a porphyrin radical, formed via photoexcitation of hematoporphyrin derivative, could replace superoxide in the Haber-Weiss reaction. 相似文献
8.
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
9.
Abstract In the presence of the photosensitizer riboflavin at high fluence rates a photoproduct, most probably H2 O2 , is formed which causes negative phototaxis in the colorless flagellate Polytomella magna . The aim of this study was to find out whether H2 O2 is produced in a type I or II reaction. As has been shown, 1 O2 quenchers either do not influence the photodynamic action of riboflavin (furfuryl ethanol, DPBF, l -histidine, crocetin) or show slight quenching effects only at very high concentrations ≧ 10−2 M (DABCO, DMF, imidazole). D2 O is toxic to P. magna even in 1:1 and 1:2 mixtures with H2 O. On the other hand, the quenching effect of 1,4-benzoquinone, highly indicative for the type I pathway, is more than two orders of magnitude stronger than the one of the above mentioned 1 O2 quenchers. The results suggest that H2 O2 is produced in a type I reaction. Superoxide does not seem to be involved since superoxide dismutase does not diminish the photodynamic effect of riboflavin. 相似文献
10.
Abstract— In many biological systems, the role of O2 - in hydroxylation and toxic processes was assumed to be due to the formation of OH radicals. The Haber-Weiss reaction (Haber and Weiss, 1934)—(H2 O2 + O2 - → OH + OH- + O2 ) was suggested as the origin of this activity.
In this study it is shown that this reaction pathway is too slow, and that OH is probably formed from the reaction of complexed superoxide with H2 O2 or/and from the reduction of Fe(III), bound to biological compounds, by O2 - ; the reduced Fe(II) can then react with H2 O2 as a Fenton reagent, to yield OH.
It is also shown that singlet oxygen cannot be formed in these biological systems neither from the dismutation of OJ nor from the reaction of O2 - with OH. Singlet oxygen may be formed from the reduction of metal complexes by O2 - . 相似文献
In this study it is shown that this reaction pathway is too slow, and that OH is probably formed from the reaction of complexed superoxide with H
It is also shown that singlet oxygen cannot be formed in these biological systems neither from the dismutation of OJ nor from the reaction of O
11.
Michael Price Stanley R. Terlecky David Kessel 《Photochemistry and photobiology》2009,85(6):1491-1496
Although the first reactive oxygen species (ROS) formed during irradiation of photosensitized cells is almost invariably singlet molecular oxygen (1 O2 ), other ROS have been implicated in the phototoxic effects of photodynamic therapy (PDT). Among these are superoxide anion radical (• O2 − ), hydrogen peroxide (H2 O2 ) and hydroxyl radical (• OH). In this study, we investigated the role of H2 O2 in the pro-apoptotic response to PDT in murine leukemia P388 cells. A primary route for detoxification of cellular H2 O2 involves the peroxisomal enzyme catalase. Inhibition of catalase activity by 3-amino-1,2,4-triazole led to an increased apoptotic response. PDT-induced apoptosis was impaired by addition of an exogenous recombinant catalase analog (CAT- skl) that was specifically designed to enter cells and more efficiently localize in peroxisomes. A similar effect was observed upon addition of 2,2'-bipyridine, a reagent that can chelate Fe+2 , a co-factor in the Fenton reaction that results in the conversion of H2 O2 to • OH. These results provide evidence that formation of H2 O2 during irradiation of photosensitized cells contributes to PDT efficacy. 相似文献
12.
Abstract— In order to gain further insight into the sensitized photooxygenation of the system thionine, allylthiourea, and oxygen, the influence of the leucothionine, which is formed during the photoreaction, was studied by flash photolysis. In the presence of leucothionine, additional thionine (Λobs = 598 nm) is reformed; i.e., leucothionine is oxidized to thionine by way of a semithionine intermediate (Λbs = 770 nm). This additional semithionine formation due to leucothionine is complete by 30 μsec after the flash. By varying the leucothionine concentration, the flash intensity and the pH it can be shown that the agent which oxidizes leucothionine to semithionine is identical to the agent which transforms semithionine to thionine. 相似文献
13.
The light-emitting principle of the brittle star Ophiopsila californica has been isolated and purified. It was found to be a green-fluorescent photoprotein (molecular weight 45000) which emits green light (λmax 500 nm) when H2 O2 is added, independently of the presence or absence of O2 . The green fluorescence (emission maximum 500 nm, excitation maximum 440 nm) spectrally coincided with the H2 O2 -triggered luminescence, indicating that the green fluorescent chromophore is the light-emitter of the photoprotein luminescence. 相似文献
14.
JANUSZ SLAWINSKI 《Photochemistry and photobiology》1971,13(6):489-497
Abstract— The oxidation of purpurogalline (PPG) by alkaline solution of H2 O2 pH 9–11 at 298°K is accompanied by chemiluminescence (CL) in the spectral range 400–600 nm with the maximum at 500 nm and quantum yield about 10-6 . The optimal concentrations of reactants with respect to maximal intensity are: 2 × 10-4 M PPG, 10-2 M NaOH, 1 M H2 O2 . Activation energy calculated from the maximum intensity of CL is 8.1×0.4 kcal/mole. Light emission occurs only when OH-groups of the phenolic ring of PPG undergo oxidation and the blue anion of o -PPG-quinone is formed. The rate that determines step in the reaction associated with luminescence is the nucleophilic attack of OOH- ion on the blue anion of o -PPG-quinone. In this exergonic step (-ΔH = 63 to 230kcal/mole) the o - and/or p -quinone ring is opened and carbonyl derivatives of α-tropolone are produced. They display fluorescence in the region 400–600 nm. The fluorescence spectrum of the reaction mixture after oxidation of PPG is very close to that of CL. It is likely that carbonyl derivatives of α-tropolone are emitters of CL. 相似文献
15.
HYDROGEN PEROXIDE INDUCED RESISTANCE TO BROAD-SPECTRUM NEAR-ULTRAVIOLET LIGHT(300–400 nm) INACTIVATION IN Escherichia coli 总被引:5,自引:0,他引:5
Abstract— Strains of Escherichia coli carrying the four possible combinations of the alleles nur, nur+ , uvrAb, and uvrA + were either untreated or pretreated with a sublethal dose of H2 02 prior to inactivation with NUV radiation. Pretreated cells exhibited a greater resistance to NUV than did untreated cells. Pretreatment with H2 O2 did not induce resistance to FUV radiation. The induction of resistance to NUV inactivation by H2 O2 pretreatment apparently leads to protection against the damage caused by NUV radiation. Although pretreatment of cells with H2 02 leads to resistance of such cells to inactivation by H2 O2 and NUV, survival of H2 O2 treated bacteriophage PI cml clr100 is not enhanced when assayed on H2 O2 pretreated E. coli host cells. 相似文献
16.
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
17.
Jehuda Feitelson Avigdor Shafferman Gabriel Stein 《Photochemistry and photobiology》1973,18(2):113-118
Abstract— The photochemistry of dithioglycolic acid at 254 nm was investigated in deaerated aqueous solutions in the pH range 1.4–7.3. Initial yields of the primary photochemical products H2 S,–SH and aldehyde-(probably glyoxylic acid) were determined. The complex pH dependence of these simultaneously formed first stable products is interpreted in terms of the ground-state ionic equilibria, and in addition pH-dependent processes occurring in the excited state and labile intermediate sequence.
It is suggested that the photochemical mechanism involves two parallel pathways: one a hydrolytic splitting of S - S leading to H2 S formation (unaffected by the presence of O2 or isopropanol), the other a free radical mechanism via C–S breakage, which is affected by the presence of O2 or isopropanol. 相似文献
It is suggested that the photochemical mechanism involves two parallel pathways: one a hydrolytic splitting of S - S leading to H
18.
Angela Agostiano D. Christopher Goetze Robert Carpentier † 《Photochemistry and photobiology》1992,55(3):449-455
Abstract— In this paper, the technique of cyclic voltammetry has been used in a photoelectrochemical cell in order to follow the redox species formed in solution by the photo-induced electron transfer between the thylakoids and various acceptors and donors. The photoelectrochemical behavior of artificial electron acceptors (such as 2,5-dichlorobenzoquinone and methylviologen) and donors (such as sym -diphenylcarbazide and durohydroquinone) specific for either Photosystem I or Photosystem II has been investigated. The influence of inhibiting agents (such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea and Tris) on the cell photoresponse has also been characterized, together with the capability of donors to restore the photocurrent. Evidence for H2 O2 formation by way of a Mehler-type reaction has been provided and an electrochemical model of its coupled photochemical and electrochemical reactions in solution is reported. 相似文献
19.
Mariana Vignoni Franco M. Cabrerizo Carolina Lorente Andrés H. Thomas 《Photochemistry and photobiology》2009,85(1):365-373
New photochemical studies of the reactivity of biopterin (BPT) and neopterin (NPT) in acidic (pH = 5.5) and alkaline (pH = 10.5) aqueous solutions at 350 nm and room temperature were performed. The photochemical properties of BPT are of particular interest because the photolysis of this compound takes place in the white skin patches of patients affected by vitiligo. The photochemical reactions were followed by UV/VIS spectrophotometry, HPLC, electrochemical measurement of dissolved O2 and enzymatic methods for hydrogen peroxide (H2 O2 ) and superoxide anion (O2 •− ) determinations. When BPT or NPT are exposed to UVA radiation, a red intermediate, very likely 6-formyl-5,8-dihydropterin, is generated in an O2 -independent process. That product is rapidly oxidized on admission of O2 to yield 6-formylpterin and H2 O2 . When the photolysis takes place in aerobic conditions, no additional pathways exist. On the other hand, in the absence of O2 , the intermediate generated is not stable and leads to the formation of many products. O2 •− is also generated during photo-oxidation of BPT and NPT. The quantum yields of reactant consumption depends on the O2 concentration: the higher the O2 concentration, the lower the quantum yields. This behavior is discussed in connection with the excited state of the pterins. 相似文献
20.
Abstract— –In the light, isolated spinach thylakoids consumed O2 in the presence of methylviologen, and ascorbate was found to interact with this reaction in various ways. Chelating-resin was used to remove metal impurities from the assay medium. Ascorbate diminished the H2 02 pool in resin-untreated solutions, while in resin-treated solutions ascorbate had no effect on H2 O2 concentrations. A Fenton catalyst (Fe-EDTA) increased O2 uptake in the presence of ascorbate and decreased the amount of O2 recovered by catalase. Ascorbate tripled the rate of the methylviologen-mediated Mehler reaction, and the O2 consumed was liberated to 50% of its original concentration by catalase. Superoxide dismutase reversed the effects of ascorbate on the Mehler reaction rates. These results indicate that ascorbate can stimulate Mehler reactions indirectly by promoting a Fenton-type reaction as well as stimulating Mehler reactions directly by reducing 2O2 - to 2H2 O2 . The promotion of a Fenton-type reaction by ascorbate appears to be the cause of H2 O2 depletion in resin-untreated solutions. 相似文献