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1.
Abstract— The photosensitized oxidation of 10–100 μ M N -acetyl-L-tryptophanamide (NATA) in neutral aqueous solution and in the presence of various dyes proceeds by a pure O2 (1 Δg )-involving mechanism. Incorporation of the tryptophyl (Trp) residue into the polypeptide chain of human serum albumin (HSA) has no influence on the mechanism and efficiency of Trp photooxidation when sensitized either by methylene blue, a non-binding dye, or by rose bengal, a dye that gives non-covalent 1: 1 complexes with HSA. This is due to the location of the Trp residue in close proximity of the protein surface and, in the case of rose bengal, to the coincidence of the photophysical properties (including the quantum yield of O2 (1 Δg ) generation) for the free and HSA-bound dye. Hematoporphyrin also binds to HSA with 1: 1 stoichiometry, although at a different site from rose bengal. Bound Hp again displays photophysical properties very similar with those of free Hp; however, the efficiency of Trp photo-oxidation in HSA is about 5-fold higher than in NATA owing to a limited rearrangement of the protein structure, induced by Hp binding, which enhances the probability of chemical quenching of O2 (1 Δg ) by the indole ring. 相似文献
2.
COOPERATION OF CHARGES IN PHOTOSYNTHETIC O2 EVOLUTION–I. A LINEAR FOUR STEP MECHANISM 总被引:30,自引:0,他引:30
Abstract— Using isolated chloroplasts and techniques as described by Joliot and Joliot[6] we studied the evolution of O2 in weak light and light flashes to analyze the interactions between light induced O2 precursors and their decay in darkness. The following observations and conclusions are reported: 1. Light flashes always produce the same number of oxidizing equivalents either as precursor or as O2 . 2. The number of unstable precursor equivalents present during steady state photosynthesis is ∼ 1.2 per photochemical trapping center. 3. The cooperation of the four photochemically formed oxidizing equivalents occurs essentially in the individual reaction centers and the final O2 evolution step is a one quantum process. 4. The data are compatible with a linear four step mechanism in which a trapping center, or an associated catalyst, ( S ) successively accumulates four + charges. The S 4+ state produces O2 and returns to the ground state S 0 . 5. Besides S 0 also the first oxidized state S + is stable in the dark, the two higher states, S2+ and S3+ are not. 6. The relaxation times of some of the photooxidation steps were estimated. The fastest reaction, presumably S *1 ← S 2 , has a (first) half time ≤ 200 μsec. The S *2 state and probably also the S *0 state are processed somewhat more slowly (˜ 300–400 μsec). 相似文献
3.
Abstract —The pulsed ruby laser (347 nm) flash photolysis technique has been used to measure the triplet-triplet absorption spectra and triplet lifetimes of trans -retinal, N-frans -retinylidene- n -butylamine (NRBA), and protonated NRBA (NRBAH+ ) at room temperature. In methylcyclohexane solution, the triplet lifetimes are in the range 10–20 μs and decrease in the order NRBAH+ > NRBA > trans -retinal. Intersy stem-crossing efficiencies (φISC ) were determined by a comparison technique using anthracene and 1,2-benzanthracene as reference compounds. For trans -retinal, φISC is 0–50 pM 0–05 in methylcyclohexane and 0–08 in methanol, which confirms that earlier values of 0–11 and 0–017 in these solvents are in error. For NRBA and NRBAH+ in methylcyclohexane, ΦISC values are 0008 and < 0–001, respectively. Evidence is presented for a significant solvent effect in the isomerization of retinal via the triplet state, and that cis φ trans isomerization occurs from the triplet state of NRBAH+ . The relation between the intersystem-crossing properties of model compounds and the photochemistry of rhodopsin is discussed. 相似文献
4.
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
5.
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
6.
Asaad Salehi nthony Oertling aroldN. Fonda erald T. Babcock C. K. Chang 《Photochemistry and photobiology》1988,48(4):525-530
Abstract— By using excitation at 363.8 nm, resonance Raman (RR) spectra were obtained for Cu(II), Co(II), and Ni(II) complexes of methyloctaethylchlorin (MeOEC) and their ir-cation radicals. Additionally, the Raman spectra of the Cu(II) derivatives of (rarcs-octaethylchlorin (r-OEC) were included for comparison. The alkyl-substituted CuMeOEC exhibits a Raman spectrum that is nearly identical to that of the simpler (-CuOEC in both the neutral and oxidized states. Unlike the latter species, the cation radical of CuMeOEC is immune to oxidative dehydrogenation to porphyrin, and this has facilitated vibrational characterization of the ring-oxidized species. This study aims to compare the vibrational characteristics in the 1450 to 1700 cm-t region of the metallochlorin ir-cation radicals to those of the corresponding oxidized metalloporphyrins. We focus on two modes in the1500–1520 cm-1 and1620–1650 cm-1 region that are analogous to the v3 and v10 vibrations, respectively, in the metalloporphyrin analogs. These vibrational modes are clearly defined in all species and exhibit a strong core-size dependency in the porphyrin complexes. The core-size study as well as the frequency changes upon oxidation support the conclusion that the v3 -like vibration in the chlorin species features substantial Cb Cb in addition to Ca Cm stretching character. The v,0 -like mode of the chlorin macrocycle, on the other hand, displays characteristics that closely resembles that of the porphyrin analog; consequently, these vibrations are of predominantly Ca Cm stretching character in both cases. 相似文献
7.
Abstract— Many inorganic oxidation reactions involving a variety of oxidizing agents show chemiluminescence in the spectral region of 400–600 mp. Excited O2 O2 -associates are assumed to be the emitting molecules formed by bimolecular recombination of HO x O2 -radicals. Oxidation of sodium sulfite with molecular oxygen in the presence of Cu- and Fe-basic oxides shows chemiluminescence which originates from the reactions of the heavy metal complexes of OH- and O, H-radicals with O2 . The simplest way of producing a radical from O2 is by the uptake of one electron. Suitable electron donors, such as hydro-quinones and semiquinones, emit light if treated with oxygen. In certain organic solvents OH- can also act as electron donor. Its presence causes the formation of semiquinones from quinones in the absence of oxygen. The chemiluminescence which is observable upon treatment of alkaline dimethylsulfoxide, dioxane, pyridine-water and alcohol-water mixtures with oxygen is also attributable to electron transfer from OH- to O2 . 相似文献
8.
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
9.
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
10.
Abstract— The hematoporphyrin-sensitized production of singlet molecular oxygen, O2 (1 Δg ), has been investigated in methanol and in aqueous solution. The quantum yield for formation of O2 (1 Δg ) (ΦΔ ) has been measured by both steady-state (oxygen consumption) and time-resolved (near-infrared luminescence) methods. In methanol, both techniques indicate that ΦΔ = 0.76 and the value remains independent of sensitizer concentration over a wide range. This finding is consistent with the dye persisting in a monomelic form in methanol solution. In contrast, ΦΔ decreases markedly with increasing sensitizer concentration in water due to dimerization of the dye. Analysis of the steady-state data indicates ΦΔ values of 0.74 and 0.12, respectively, for monomer and dimer. It is further shown that the efficiency whereby quenching of the triplet state by O2 results in generation of O2 (1 Δg ) is substantially lower for the dimer than for the corresponding monomer. Because monomer and dimer possess quite different absorption spectral profiles, the efficacy for photodynamic action with hematoporphyrin exhibits a pronounced wavelength dependence. 相似文献
11.
Abstract— The possibility of 1 O2 (1 Δg ) 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 H2 O2 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 (1 Δg ) → 2O2 (3 Σ- g ). Emission bands in the range 475–540 nm arise from the superposition of the 2O2 (1 Δg ) → 2O2 (3 Σ- 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 D2 O in which 1 O2 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 1 O2 in the chemiluminescence of both systems. 相似文献
12.
Abstract— The acid-base equilibria of the excited singlet and triplet states of acridine orange (AO) were studied by flash-photolysis and fluorometric methods. The dye is a stronger base in the first excited singlet state (pKs = 13.3) than in the triplet and ground states (pKr = 10.3: pKc , = 10.2); acridine orange follows the trend observed with some other heterocyclic compounds, viz. pKs > pKr = pK,c . At room temperature, an anomalous fluorescence occurs from the dye in basic media: the assignment of this emission is discussed.
The semi-reduced dye was studied as a function of pH. In a large pH range (3–14), only the protolytic equilibrium between the cationic (AOH2 + ) and the neutral (AOH) radicals was observed; the pK value corresponding to this equilibrium was found to be in the range of pH 5–6. 相似文献
The semi-reduced dye was studied as a function of pH. In a large pH range (3–14), only the protolytic equilibrium between the cationic (AOH
13.
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
14.
Abstract— Photolysis of acridine-orange-heparin complexes in N2 - and O2 -saturated solution results in permanent photooxidation of AO with little or no concomitant change in the heparin moiety. The major photoproduct is mono- N -demethylated acridine orange; in O2 -saturated solution an additional minor oxygenated product, most likely the 10-oxide (N-oxide) or the 9-acridanone (acridone) is also formed. The results suggest an intermolecular electron transfer between adjacently adsorbed dye molecules. The heparin moiety plays a significant role in the photochemistry by bringing dye molecules into favorable geometric orientation for biomolecular reaction and by means of specific dye-polymer interactions. 相似文献
15.
OscarH Will III David E. Sawtelle Pamela Iverson Kara Jorve 《Photochemistry and photobiology》1988,48(3):305-309
Abstract— The accumulation of (J-carotene in the ph/ph + y diploid strain of the smut fungus Ustilago violacea was associated with reduced killing and lower levels of induced mitotic recombination compared to the β-carotene lacking ph/ph+ w strain in response to both incandescent photosensitization and treatment with H2 02 . The ph/ph+ y strain was only slightly more resistant to killing by exogenous toluidine blue (TB) photosensitization. The ph/ph+ y strain exhibited significantly greater levels of survival when exposed to incandescent radiation and 1.5 μ.M TB for 15 min, as well as 3.0. 0.3, 0.03, 0.003% H2 02 in the dark. The ph/ph+ y strain also exhibited lower levels of mitotic recombination after endogenous TB photosensitization and the latter two H2 02 treatments. Similar survival results were obtained for the carotene accumulating haploid strain l.C2y and the carotene lacking haploid strain l.C2iv in response to H2 02 exposure. 相似文献
16.
S. A. Bezman P. A. Burtis T. P. J. Izod M. A. Thayer 《Photochemistry and photobiology》1978,28(3):325-329
Abstract. The photodynamic inactivation of E. coli by visible light and O2 was found to occur in the presence of the sensitizer rose bengal, immobilized by covalent bonding to polystyrene beads. The demonstrated absence of significant amounts of dissolved rose bengal indicated that an inactivation mechanism based on penetration of sensitizer molecules into the cell's interior could not be operating. Survival curves typically exhibited induction periods followed by rapid exponential death, with 99.99% kill requiring 1–2 h depending on conditions. A mechanism involving the participation of photo-generated singlet excited oxygen O2 (1 δ) in inactivation of E. coli is proposed. The photodynamic inactivation rate increased significantly in H2 O compared with H2 O, which is evidence supporting singlet oxygen as an active intermediate, since O2 (1 δ) has a much longer lifetime in H2 O than in H2 O. H2 O did not act as a short term poison in the absence of sensitizer. 相似文献
17.
MARIAN ELBANOWSKI MARIA PAETZ JANUSZ SIAWINSKI LESZEK CIELA 《Photochemistry and photobiology》1988,47(3):463-466
Abstract— Chemiluminescence of the Eu(II)/Eu(III)-adenine nucleotide-H2 O2 system and fluorescence of the Eu(III)-adenosine triphosphate system have been investigated. The spectral distribution of the chemiluminescence emission has shown an occurrence of three main bands (Λ=470–480,590–620 and ca. 700 nm). The energy transfer process from the adenosine triphosphate molecules to the Eu(III) ions has been observed in the fluorescence spectrum. The examined chemiluminescence and fluorescence spectra show that these both kinds of emission originate from the 5 D *** τ7 F*** ( n =1–4) transitions in the Eu(III) ions. 相似文献
18.
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
19.
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
20.
Bunsho Ohtani Makoto Nishida Sei-ichi Nishimoto Tsutomu Kagiya 《Photochemistry and photobiology》1986,44(6):725-732
Photooxygenation reaction of an unsaturated fatty acid ester, methyl linoleate (methyl 9- cis. 12- cis -octadecadienoate, ML-H), sensitized by porphyrins and several types of dyes has been studied in aqueous emulsion and acetonitrile solution under air at 40°C. The oxygen (O2 ) uptake proceeded slowly in the absence of sensitizers upon irradiation of an aqueous emulsion and an acetonitrile solution of ML-H (20 m M ) at ℷex > 290 nm (11.4 and 6.1 μmol h-1 , respectively). The rate of O2 uptake was enhanced by a catalytic amount (0.1 m M ) of porphyrins and dyes; hematoporphyrin (HP), zinc tetrakis(N-methyl-4-pyridiniumyi)porphyrin (ZnTMPyP), methylene blue (MB), rose bengal (RB), acridine orange (AO), and acriflavine (AF). In both systems, the sensitized photooxidation of ML-H by O2 proceeded equimolarly to produce isomeric mixture of C9 and C13 hydroperoxides having the trans,cis and trans,trans conjugated diene configurations, independent of the types of the sensitizers used. The yield ratio of trans,trans/ trans,cis products in the MB-sensitized photooxygenation in acetonitrile and aqueous emulsion were almost equal (0.32 and 0.35. respectively). The sensitizing activity of the sensitizers, as measured by the quantum yield of O2 uptake, increased in the order: MB (≃ 0) < ZnTMPyP < RB < HP < AF < AO in the aqueous emulsion and AO < AF < HP < RB = MB in the acetonitrile solution. The order in homogeneous acetonitrile solution was interpreted by the sensitizing ability of the dyes to produce singlet oxygen, while that in heterogeneous aqueous emulsion was correlated to the lipophilicity of dyes as well as the singlet-oxygen-producing ability. 相似文献