血清胆红素的光敏氧化

竹红菌乙素是一种芘醌类的光敏剂.实验结果表明在可见光的照射下.它能加速血清胆红素的光氧化,氧化速率提高5倍以上.比较在不同溶剂中各种活性氧淬灭剂对胆红素光氧化的抑制作用,指出血清胆红素光敏氧化反应包括自由基氧化反应(Ⅰ型反应)和单态氧氧化反应(Ⅱ型反应)等多重机制.     

Methylene blue photosensitized oxidation of cysteine sulfinic acid and other sulfinates: the involvement of singlet oxygen and the azide paradox

The methylene blue photosensitized oxidation of cysteine sulfinic acid is investigated. Enhancement of the oxygen consumption rate in deuterium oxide suggests the involvement of singlet oxygen ((1)O(2)) in oxidation. Addition of the (1)O(2) quencher azide produced an unusual enhancement of the oxidation rate of all the sulfinates assayed. It is assumed that azide works as a one-electron carrier between (1)O(2) and the sulfur compounds. Analyses of the products indicate that the photochemical oxidation of cysteine sulfinic acid proceeds through two simultaneous mechanisms. The Type II (singlet oxygen) mechanism is responsible for oxidation of the sulfinic group to the sulfonic group with production of cysteic acid, stable to the photooxidation system, whereas the Type I (electron transfer) mechanism is involved in the degradation of cysteine sulfinic acid to acetaldehyde. Other products detected were ammonia, sulfate, and hydrogen peroxide which account for the degradation of cysteine sulfinic acid and for the excess of oxygen consumption detected during the oxidative reaction.     

Photosensitized formation of ascorbate radicals by chloroaluminum phthalocyanine tetrasulfonate: an electron spin resonance study.

The chloroaluminum phthalocyanine tetrasulfonate sensitized photooxidation of ascorbic acid to ascorbate radical (A.-) was followed by electron spin resonance (ESR) spectroscopy. In air saturated aqueous media, steady-state amounts of A.- are rapidly established upon irradiation. The ESR signal disappears within a few seconds after the light is extinguished--more slowly under constant irradiation as oxygen is depleted. No photooxidation was observed in deaerated media. The effect of added superoxide dismutase, catalase, desferrioxamine, and singlet oxygen scavengers (NaN3 and tryptophan) was studied, as was replacement of water by D2O and saturation with O2. The results are indicative of free radical production by direct reaction between ascorbate ion and sensitized phthalocyanine (a Type I mechanism) in competition with the (Type II) reaction of HA- with singlet oxygen, a reaction which does not produce ascorbate radical intermediates.     

The cytotoxic activity of hematoheme: evidence for two different mechanisms

Hematoheme displays a potent cytolytic activity toward erythrocytes either in the presence of hydrogen peroxide and a halide ion (system I) or in the presence of oxygen and a reducing agent (system II). In system I it resembles the cytotoxic activity of various peroxidases, whereas in system II it resembles the destructive activity of bleomycin and a variety of metal complexes. Both types of reactions presumably involve the generation of active oxygen species, which are responsible for the damaging effects. In a first attempt to compare the chemical mechanisms of the two types of reactions we used various traps and scavengers of active oxygen species. Tryptophan as well as tyrosine and uric acid were found to be potent inhibitors of the hematoheme-H2O2-halide reaction but do not significantly inhibit the hematoheme-O2-ascorbate reaction. Pyridine, on the other hand, inhibits the oxygen-mediated reaction, but does not affect the peroxide-halide-mediated activity. The cytolytic activity of photoactivated hematoporphyrin, which involves the generation of singlet oxygen, is activated by pyridine and is strongly inhibited by diphenylisobenzofuran. The latter compound is a weak activator of both hematoheme reactions. We conclude that the two hematoheme reactions proceed by two different mechanisms and probably generate different toxic intermediates. The results further suggest that the toxic intermediate generated by photoactivated hematoporphyrin (singlet oxygen) does not play a dominant role in either of the two hematoheme reactions.     

Photosensitized transformation of adrenochrome

The methylene blue-sensitized photooxidation of adrenochrome was studied by steady-state kinetics. The buffered, aqueous system was irradiated with light longer than 600 nm, wavelengths at which only the sensitizer absorbs. During irradiation, disappearance of adrenochrome and the formation of adrenochrome-melanin was observed. Calculated rate constants were determined on the basis of spectroscopic measurements. It was found that the observed transformation reaction steps are pH dependent. The participation of two types of photosensitized mechanism has been evidenced. Type II, singlet oxygen mechanism, predominates at pH below 9, whereas above pH 9, Type I applies. We observed the so-called "isotope effect" and a decrease of photooxidation rate in the presence of azide ion, a well-known singlet oxygen quencher, indicating the participation of singlet oxygen.     

Chemiluminescence of the peroxomonosulphate-cobalt(II)-aliphatic monocarboxylic acids system.

A weak chemiluminescence (CL) emission was observed due to the production of singlet oxygen ((1)O(2)) during the decomposition of peroxomonosulphate (HSO(5)(-)) catalysed by cobalt(II). Low molecular mass aliphatic monocarboxylic acids, such as formic, acetic, propionic, butyric and valeric acids, influenced the CL emission, and the reaction of aliphatic monocarboxylic acids with HSO(5)(-)/Co(2+) solution was further investigated using a flow injection analysis (FIA) CL method. The results indicated that the CL intensities of aliphatic monocarboxylic acids were improved with increase in the carbon chain length in the potassium peroxomonosulphate-cobalt(II) sulphate system. Generation of singlet oxygen was confirmed by the fact that the CL emission of aliphatic monocarboxylic acids with the HSO(5)(-)/Co(2+) solution was quenched by NaN(3), and from the CL spectrum of the reaction system. Additionally, a possible mechanism of aliphatic monocarboxylic acids CL emission enhancement was proposed.     

Photo- and thermal-oxidation studies on methyl and phenyl linoleate: anti-oxidant behaviour and rates of reaction

Photo-peroxidation of methyl and phenyl linoleate in methanol solutions at 25 degrees C, in the presence of methylene blue or 5,10,15,20-tetra(4-pyridyl)-porphyrin (TPP) as sensitisers of singlet oxygen, was found to proceed at more than 30 times the rate of the same polyunsaturated fatty acid (PUFA) ester species undergoing thermal-peroxidation in the bulk phase at 50 degrees C. The addition of anti-oxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) quench the thermal-oxidation effectively but appear to only partially inhibit the photosensitized peroxidation reactions. The kinetics of the overall peroxidation reactions were followed by ultraviolet spectroscopy, measurements of hydroperoxide concentration and by high performance liquid chromatography (HPLC). The photo-peroxidation reaction proceeds more rapidly in chloroform solution as the lifetime of singlet oxygen is shown to be over ten times longer in chloroform than methanol. The initial fast reaction kinetics of the photo-peroxidation reactions were evaluated using a pulsed laser technique to show that singlet oxygen reacts competitively with both the anti-oxidants and the polyunsaturated fatty acid ester. Second order kinetic rate constants (in the range 10(5)-10(7) dm(3) mol(-1) s(-1)) were evaluated for the reactivity of singlet oxygen with a range of anti-oxidants and a singlet oxygen quencher, and the results used to explain the effect of anti-oxidants at different concentrations on the rate of the linoleate photo-peroxidation reaction.     

Molecular mechanisms of photosensitization

The first part of this article is devoted to basic concepts of photosensitization and to the primary photophysical and photochemistry processes involved in the reaction. The electronic configuration of molecular oxygen in its ground or activated states, which intervene in numerous photosensitized reactions, is reviewed. Finally, the main photosensitized reactions are reviewed and classified into three different groups: reactions due to radicals (type I), reactions due to singlet oxygen (type II) and those which do not involve oxygen (type III).     

Singlet oxygen production in photosynthesis

A photosynthetic organism is subjected to photo-oxidative stress when more light energy is absorbed than is used in photosynthesis. In the light, highly reactive singlet oxygen can be produced via triplet chlorophyll formation in the reaction centre of photosystem II and in the antenna system. In the antenna, triplet chlorophyll is produced directly by excited singlet chlorophyll, while in the reaction centre it is formed via charge recombination of the light-induced charge pair. Changes of the mid-point potential of the primary quinone acceptor in photosystem II modulate the pathway of charge recombination in photosystem II and influence the yield of singlet oxygen production. Singlet oxygen can be quenched by beta-carotene, alpha-tocopherol or can react with the D1 protein of photosystem II as target. If not completely quenched, it can specifically trigger the up-regulation of the expression of genes which are involved in the molecular defence response of plants against photo-oxidative stress.     

Singlet oxygen production in thylakoid membranes during photoinhibition as detected by EPR spectroscopy

Exposure of isolated spinach thylakoids to high intensity illumination (photoinhibition) results in the well-characterized impairment of Photosystem II electron transport, followed by degradation of the D1 reaction centre protein. In the present study we demonstrate that this process is accompanied by singlet oxygen production. Singlet oxygen was detected by EPR spectroscopy, following the formation of stable nitroxide radicals from the trapping of singlet oxygen with a sterically hindered amine TEMP (2,2,6,6-tetramethylpiperidine). There was no detectable singlet oxygen production during anaerob photoinhibition or in the presence of sodium-azide. Comparing the kinetics of the loss of PS II function and D1 protein with that of singlet oxygen trapping suggests that singlet oxygen itself or its radical product initiates the degradation of D1.Abbreviations HEPES 4-(2-hydroxyethyl)-1-piperazine ethanesulphonle acid - PS Photosystem - TEMP 2,2,6,6-tetramethylpiperidine - TEMPO 2,2,6,6-tetramethylpiperidine-1-oxyl     

Photosensitization of aqueous model systems by hypericin.

Absorption and fluorescence measurements of purified hypericin (HY) were made in various media. Photosensitization of two aqueous systems was investigated: resealed red blood cell membranes (ghosts) and hen lysozyme (Lys). Solubilization of HY by ghost membranes was shown by means of diffuse reflectance spectroscopy. Visible light irradiation of the ghosts incorporating HY led to lipid peroxidation with evidence of singlet oxygen involvement. A binding model applicable for insoluble ligands is indicative of strong HY binding to HSA. The HY-HSA complex photosensitized inactivation of Lys. The pseudo-first-order reaction kinetics with protection by azide ion are consistent with a Type II mechanism mediated by singlet oxygen. The results are discussed in the context of the HY photodynamic and antiretroviral activities.     

Synthesis, photophysical and photochemical studies of new water-soluble indium(III) phthalocyanines.

The preparation of water-soluble indium(III)phthalocyanine complexes is described for the first time in this study. Peripherally and non-peripherally 3-hydroxypyridine tetrasubstituted indium(III) phthalocyanines (5a, 6a) and their quaternarized derivatives (5b, 6b) have been synthesized and characterized by elemental analysis, IR, 1H NMR spectroscopy, electronic spectroscopy and mass spectra. The quaternarized compounds (5b, 6b) show excellent solubility in water, which makes them potential photosensitizers for use in photodynamic therapy (PDT) applications. Photochemical and photophysical measurements were conducted on 3-pyridyloxy appended indium(III) phthalocyanines in dimethylsulfoxide (DMSO) for non-ionic (5a, 6a) and in both DMSO and water for quaternarized (5b, 6b) derivatives. General trends are described for quantum yields of photodegradation, fluorescence lifetimes, fluorescence quantum yields, triplet lifetimes and triplet quantum yields as well as singlet oxygen quantum yields of these compounds. The singlet oxygen quantum yields (Phi(Delta)), which give an indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required (Type II mechanism) are very high (Phi(Delta) > 0.55). Thus, these complexes may be useful as Type II photosensitizers.     

Tocopherol as singlet oxygen scavenger in photosystem II

Singlet oxygen is formed in the photosystem II reaction center in the quench of P680 triplets, and the yield is dependent on light intensity and the reduction level of plastoquinone. Singlet oxygen in PS II triggers the degradation of the D1 protein. We investigated the participation of tocopherol as a singlet oxygen scavenger in this system. For this purpose, we inhibited tocopherol biosynthesis at the level of the HPP-dioxygenase in the alga Chlamydomonas reinhardtii under conditions in which plastoquinone did not limit the photosynthesis rate. In the presence of the inhibitor and in high light for 2 h, photosynthesis in vivo and photosystem II was inactivated, the D1 protein was degraded, and the tocopherol pool was depleted and fell below its turnover rate/h. The inhibited system could be fully resuscitated upon the addition of a chemical singlet oxygen quencher (diphenylamine), and partly by synthetic cell wall permeable short chain alpha- and gamma-tocopherol derivatives. We conclude that under conditions of photoinhibition and extensive D1 protein turnover tocopherol has a protective function as a singlet oxygen scavenger.     

表没食子儿茶素没食子酸酯对活性氧的抑制作用

生物体内的活性氧(Reactive oxygen species,ROS)过量引起氧化应激将导致脂质、DNA和蛋白质氧化损伤,从而引发一系列生理和病理反应。绿茶中茶多酚的主要成分表没食子儿茶素没食子酸酯((-)-Epigallocatechin-3-gallate,EGCG)具有强抗氧化性,能有效抑制ROS。本文简要介绍了生物体内ROS的来源和EGCG的特性及其对ROS的抑制作用。通过检测玫瑰红水溶液在光敏化时所产生~1O_2的1 270 nm近红外发光,分析比较了EGCG和迭代钠(NaN_3)对~1O_2发光的淬灭过程,发现EGCG对~1O_2的淬灭效果比NaN_3更好,为EGCG淬灭~1O_2的定量研究提供理论依据。     

Chemiluminescence accompanied by the reaction of acridinium ester and manganese (II)

An acridinium ester (AE) alkaline solution can react with Mn(II) to generate a strong chemiluminescence (CL) centered at 435 nm. The effects of reaction conditions such as pH and Mn(II) concentration on CL intensity were examined. In order to explore the CL mechanism, the effect of oxygen on the CL reaction was examined and an X‐ray photoelectron spectroscopy study of the reaction precipitate was carried out. The results indicated that oxygen participated in the CL reaction and Mn(IV) was the primary product in the system. A possible mechanism was proposed that involved two pathways: (1) dissolved oxygen was reduced to reactive oxygen radicals by Mn(II), these reactive intermediates then reacted with AE to produce excited state acridone; (2) Mn(II) could reduce AE to partly reduced AE, which then reacted with oxygen to form excited state acridone. The reactions of other metal ions with AE were also tested, and only Mn(II) was shown to trigger strong CL emission of AE, which indicated that the system had good selectivity for Mn(II). Copyright © 2014 John Wiley & Sons, Ltd.     

The photodynamic action of eosin,a singlet-oxygen generator

Eosin, a known generator of singlet oxygen, applied to leaf discs of Pisum sativum L. sensitized the inhibition of photosynthesis. Analysis of partial photosynthetic electron-transport reactions and of the kinetics of variable chlorophyll fluorescence located the damage at photosystem II. This injury required the presence of oxygen and was also caused by the irradiation of eosin-treated leaf tissue with green light. The role of oxygen and photodynamic reactions in the susceptibility of photosystem II to damage by environmental stresses is discussed.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCPIP 2,6-dichlorophenolindophenol - DPC 1,5-diphenylcarbazide - PSI photosystem I - PSII photosystem II - ¹O₂ singlet oxygen - Tricine N-[2-hydroxyl-3,1-bis(hydroxymethyl)ethyl]-glycine     

Reactivities of diphenylfuran (a singlet oxygen trap) with singlet oxygen and hydroxyl radical in aqueous systems.

It has been studied whether 2,5-diphenylfuran is a specific singlet oxygen trap in aqueous systems. With certain ¹O₂ generating systems (Rose Bengal photooxygenation and NaOClH₂O₂ systems) and·OH generating systems (Fenton's reagent and acetaldehyde-xanthine oxidase system), diphenylfuran was chiefly converted in all cases to cis-dibenzoyl-ethylene, but not to trans-dibenzoylethylene. Low but detectable conversion of diphenylfuran to a hydroperoxide, probably a distinct ¹O₂-derived reaction in aqueous media, was found only in the Rose Bengal photooxygenation system.     

Rose Bengal located within liposome do not affect the activity of inside-out oriented Na,K-ATPase

DPPC:DPPE-proteoliposomes (in which the enzyme is inside-out oriented) and DLOPC:DLOPE-proteoliposomes (in which the enzyme is only 40% inside-out oriented) is an excellent model for studying the selective effect of the reactive oxygen species, produced by the photo-activation of Rose Bengal. Both proteoliposomes used, when submitted to photo-irradiation with laser using 1200 mJ/cm2 energy dose, in the absence of the Rose Bengal, did not shown any effect in the ATPase activity and in the integrity of its systems. Also, no effect was observed using 50 microM of Rose Bengal encapsulated in the interior of the DPPC:DPPE-proteoliposome system. But, when we use 50 microM of Rose Bengal, present only in the extravesicular environment, and photo-irradiation with a laser dose of 200 mJ/cm2, it results in the loss of 40-50% of the ATPase activity, with damage of the DPPC:DPPE-proteoliposome integrity. Using a dose of 400 mJ/cm2 the ATPase activity was totality lost. Consequently, these effects could be correlated with direct damage in the peptide structure. The photo-irradiation of the system constituted by DLOPC:DLOPE-proteoliposome in the presence of Rose Bengal, encapsulated only in the interior compartment or in the extra-liposomal environments, revealed a gradual decrease of the ATPase activity, maintaining it at 30% after a dose of 1200 mJ/cm2 and losing total ATPase activity at 800 mJ/cm2, respectively, with the loss of integrity of this vesicular system in both conditions studied. The generated singlet oxygen could attack the double linkage present in the fatty acid structure of the lipid instead of the amino acid in the protein structure and, in a second step, result in an indirect inactivation of the enzyme activity. In summary, these results indicated that singlet oxygen species produced by photo-oxidation of Rose Bengal using laser light could act in protein and lipid structure depending on its proportion or distribution.