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PubMed1983

Singlet oxygen formation detected by low-level chemiluminescence during enzymatic reduction of prostaglandin G2 to H2.

Addition of arachidonic acid to a suspension of ram vesicular gland microsomes or purified prostaglandin synthase, causes a rapid burst of light emission in the range 600-750 nm, as detected by single-photon counting. Maximal light emission intensity is obtained within 15-30 s after the addition of arachidonic acid and is followed by a rapid decay to the background level. The intensity of chemiluminescence is dependent on the amount of ram vesicular gland microsomes or isolated prostaglandin synthase and arachidonic acid concentration (Km about 6 microM). Spectral analysis of arachidonic acid-induced photoemission of isolated prostaglandin synthase in the range 600-750 nm showed two distinctive peaks at about 634 and 703 nm. The similar relative intensities of these peaks, along with the lower intensity at about 668 nm is indicative of singlet oxygen dimol emission. Chemiluminescence with arachidonate is enhanced by 1,4-diazabicyclo[2,2,2]octane and inhibited by azide, indomethacin, acetylsalicylic acid and beta-carotene. Cooxygenation substrates such as phenol, hydroquinone and reduced glutathione, inhibited the arachidonic acid-induced chemiluminescence. Dioxygen is a requirement for the observation of singlet oxygen dimol emission with arachidonic acid as a substrate for ram vesicular gland microsomes or purified prostaglandin synthase. However, when prostaglandin G2 is substituted for arachidonic acid, light emission is not dependent on oxygen. Thus, singlet oxygen can be formed in the dismutation reaction, 2 PGG2 leads to 2 PGH2 + 1O2, catalysed by prostaglandin hydroperoxidase.

Animals↗
PubMed2006

Ultrafast carotenoid-to-chlorophyll singlet energy transfer in the cytochrome b6f complex from Bryopsis corticulans.

Ultrafast carotenoid-to-chlorophyll (Car-to-Chl) singlet excitation energy transfer in the cytochrome b(6)f (Cyt b(6)f) complex from Bryopsis corticulans is investigated by the use of femtosecond time-resolved absorption spectroscopy. For all-trans-alpha-carotene free in n-hexane, the lifetimes of the two low-lying singlet excited states, S(1)(2A(g)(-)) and S(2)(1B(u)(+)), are determined to be 14.3 +/- 0.4 ps and 230 +/- 10 fs, respectively. For the Cyt b(6)f complex, to which 9-cis-alpha-carotene is bound, the lifetime of the S(1)(2A(g)(-)) state remains unchanged, whereas that of the S(2)(1B(u)(+)) state is significantly reduced. In addition, a decay-to-rise correlation between the excited-state dynamics of alpha-carotene and Chl a is clearly observed. This spectroscopic evidence proves that the S(2)(1B(u)(+)) state is able to transfer electronic excitations to the Q(x) state of Chl a, whereas the S(1)(2A(g)(-)) state remains inactive. The time constant and the partial efficiency of the energy transfer are determined to be 240 +/- 40 fs and (49 +/- 4)%, respectively, which supports the overall efficiency of 24% determined with steady-state fluorescence spectroscopy. A scheme of the alpha-carotene-to-Chl a singlet energy transfer is proposed based on the excited-state dynamics of the pigments.

Carotenoids↗
PubMed2001

Time-resolved detection of singlet oxygen in a transmission microscope.

The time-resolved absorption spectrum of singlet oxygen [O2(a1 delta g)-->O2(b1 sigma g+)] has been recorded in the region approximately 5100-5300 cm-1 from air-saturated polystyrene samples using a microscope attached to a step-scan Fourier transform IR spectrometer. Singlet oxygen signals were observed with a time resolution of approximately 160 ns from sample volumes of approximately 20 nL using moderate data-acquisition times. These data indicate that it is reasonable and worthwhile to consider the further development of a transmission microscope as a viable tool to create singlet oxygen images of inhomogeneous samples including samples of biological importance.

Microscopy↗
PubMed1995

Singlet oxygen-trapping reaction as a method of (1)O2 detection: role of some reducing agents.

The production of singlet oxygen by H2O2 disproportionation and via the oxidation of H2O2 by NaOCl in a neutral medium was monitored by spin trapping with 2,2,6,6 tetramethyl-4-piperidone (TMPone). The singlet oxygen formed in both reactions oxidized 2,2,6,6 tetramethyl-4-piperidone to give nitroxide radicals. However the production of nitroxide radicals was relatively small considering the concentrations of H2O2 and NaOCl used in the reaction systems. Addition of electron donating agents: ascorbate, Fe2+ and desferrioxamine leads to an increase in the production of nitroxide radicals. We assumed that a very slow step of the reaction sequence, the homolytic breaking of the O-O bond of N-hydroperoxide (formed as an intermediate product during the reaction of 1O2 with TMPone) could be responsible for the relatively small production of nitroxide radicals. Electron donating agents added to the reaction system probably raise the rate of the hydroperoxide decomposition by allowing a more rapid heterolytic cleavage of the O-O bond leading to a greater production of nitroxide radicals. The largest effect was observed in the presence of desferrioxamine. Its participation in this process is proved by the concomitant appearance of desferrioxamine nitroxide radicals. The results obtained demonstrate that the method proposed by several authors and tested in this study to detect singlet oxygen is not convenient for precise quantitative studies. The reactivity of TMPone towards O2.-/HO2. and .OH has been also investigated. It has been found that both O2.-/HO2. and .OH radicals formed in a phosphate buffer solution (pH 7.4, 37 degrees C), respectively by a xanthine-oxidase/hypoxanthine system and via H2O2 UV irradiation, do not oxidize 2,2,6,6 tetramethyl-4-piperidone to nitroxide radicals.

Ascorbic Acid↗
PubMedDate not supplied

[Coherent singlet-triplet transitions at the initial step of tubulin assembly into microtubules].

Quantum chemistry calculations [DFT-B3LYP QM/MM method, 6-31G** basis set, + ab initio molecular dynamics] were used to study the action of Mg2+ on tubulin properties. It was shown that the hydration of the guanosine triphosphate-tubulin forms a protein zone structure, which includes a electron-occupied zone and a conductivity zone. The binding of Mg2+ to guanosine triphosphate-tubulin results in the unpairing of electrons in the occupied zone (triplet state formation) followed by their transition to the conductivity zone in which the inversion of spin occurs (singlet state formation). The formation of triplet state is the initial step in the subsequent protein dynamics in the picosecond range of time. The dynamics shows up as a coherent oscillating transition of tubulin between the triplet and singlet states, which is evidence of a simultaneous adjustment between nuclear and electron configurations of the protein (ab initio molecular dynamics calculations). The barrier between the triplet and singlet states does not exceed 0.60 kcal x mol(-1). The barrier overcome is considered as electron tunneling through the Fermi surface, which separates the occupied and conductivity zones. Zone formation occurs in the presence of the shell of biological water surrounding the protein.

Microtubules↗
PubMed1977

Singlet oxygen as a mediator in the hematoporphyrin-catalyzed photooxidation of NADPH to NADP+ in deuterium oxide.

The oxygen-dependent photooxidation of NADPH in the presence of hematoporphyrin in D2O results in the production of enzymatically active NADP+. The reaction is not inhibited by benzoate, mannitol, superoxide dismutase, or catalase. Moreover, addition of either potassium superoxide or H2O2 does not potentiate the reaction. This suggests OH-, H2O2, and O-2 are not likely to be the reactive oxygen species in this system. The oxidation is inhibited by various singlet oxygen quenchers and inhibitors such as 1,4-diazabicyclo[2.2.2]octane, 2,5-dimethylfuran plus methanol, histidine, and methionine. In addition, the rate of oxidation in H2O is less than one-fifth of that in D2O. The results suggest a singlet oxygen-mediated process. During the oxidation, no superoxide radical production could be detected with either ferricytochrome c or nitroblue tetrazolium. However, H2O2 has been found as one of the products. These observations are consistent with an oxidation-reduction reaction between singlet oxygen and NADPH to form H2O2 and NADP+, catalyzed by the light-activated photosensitizer hematoporphyrin.

Aerobiosis↗
PubMed1980

Studies on lipid peroxidation using isolated rat liver cells: the role of singlet oxygen in the propagation of lipid peroxidation ADP-Fe3+ or CCl4 induced.

The separation of lipid peroxidation reactions in two sequential parts, initiation and propagation, has been proposed. Furthermore, it has been shown that some of the propagation reactions following the peroxidative breakdown of membrane lipids may produce singlet oxygen, a highly excited, energetic species of molecular oxygen. To investigate whether singlet oxygen is involved in the propagation of ADP-Fe3+ or CCl4-induced lipid peroxidation, hepatocytes in single cell suspension were treated with the two mentioned drugs in the presence or in the absence of 1,4-diazabicyclo-[2,2,2]octane (DABCO), a known scavenger of singlet oxygen. Only the stimulation of malonaldehyde production due to ADP-Fe3+ was partially prevented by high concentrations of the scavenger, while the CCl4-induced increase of malonaldehyde was not influenced. The results reported here suggest that ADP-iron complex stimulates lipid peroxidation in a way that is somehow different from that occurring in the case of CCl4 poisoning.

Adenosine Diphosphate↗
PubMed1995

The specificity and product of quenching singlet oxygen by 2,2,6,6-tetramethylpiperidine.

The specificity of 2,2,6,6-tetramethylpiperidine to singlet oxygen was shown using Rose Bengal as a singlet oxygen generator, and Xanthine-Xanthine Oxidase and KO2 as the sources for the superoxide radical. The highest concentration of produced-singlet oxygen occurred at 25% of O2 by Rose Bengal photosensitization. The linewidth of the EPR signal for photosensitized nitroxyl radical, increasing solvent polarity. Deuterated solvents enlarge the EPR signal intensity in a dose-dependent manner. No EPR signal increase was observed in xanthine-xanthine oxidase reaction or KO2 systems, indicating that TEMP does not react with the superoxide anion. Thus, reaction of TEMP with 1O2 is highly specific.

Cyclic N-Oxides↗
PubMedDate not supplied

The effect of pH on chemiluminescence of different probes exposed to superoxide and singlet oxygen generators.

The compromised optima for high intensity chemiluminescence (CL), using superoxide generators, were all above pH 9.0 for the CL probes luminol and lucigenin. With luminol the optima were at pH 9.0 and 9.4 for the generators KO2 and hypoxanthine/xanthine oxidase (HX/XO), respectively. Lucigenin, with the same generators, produced optima at pH 9.5 and 10.0, respectively. The probe methyl-Cypridina-luciferin analogue (MCLA) produced optima closer to neutral pH, which is preferred for physiological assessments. MCLA had optima at pH 6.0, 8.7 and 9.5 with KO2 and with HX/XO optima at pH 4.8, 6.0, 7.0 and 8.7. When CL was assessed at physiological pH, MCLA observed superoxide radicals with a sensitivity of 100- and 330-fold more than luminol or luicigenin respectively. For singlet oxygen, the sensitivity of MCLA at this pH was 45- and 5465-fold more than for the said probes respectively. H2O2 did not elicit CL between pH 4 and 9.5 with any of the probes and did not influence the production of superoxide or singlet oxygen when co-assessed. Therefore CL could only be obtained when enzymes were used as converters. The optima for the enzyme-conversion system horseradish peroxidase (HRP)/H2O2, and luminol, were at pH 8.0 and 9.2. Lucigenin and HRP/H2O2 also had a biphasic CL profile with optima at pH 7.4 and 9.6. MCLA and HRP/H2O2 had five optima, with the major ones at pH 6.1 and beyond 10. The optima for the myeloperoxidase/H2O system were at 8.6 and beyond 10.0 when luminol and 0.15 mol/L NaBr were used.

Free Radical Scavengers↗
PubMedDate not supplied

Rapid determination of rice seed vigour by spontaneous chemiluminescence and singlet oxygen generation during early imbibition.

Using a highly sensitive single photon counter, a spontaneous chemiluminescence (CL) study on rice (Oryza sativa L.) seeds stored in different years was carried out. We first observed that the degree of ageing in rice seeds was related to the intensity of spontaneous CL during early imbibition (0-30 min). Rice seeds stored for a shorter time had a stronger intensity of CL in early imbibition. The germination rate of rice seeds showed an obvious positive correlation with the intensity of spontaneous CL. Singlet oxygen ((1)O(2)) in rice seeds during early imbibition was investigated by a CL method using a cypridina luciferin analogue, 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo [1,2alpha] pyrazin-3-one (MCLA), as a selective CL probe. Additional experimental evidence for the formation of (1)O(2) came from the quenching effect of sodium azide (NaN(3)) on MCLA-mediated rice seeds' CL. Analysis based on the experimental results demonstrated that spontaneous CL in rice seeds during early imbibition was mainly contributed by singlet oxygen ((1)O(2)).

Germination↗
PubMedDate not supplied

Singlet oxygen generation from lophine hydroperoxides.

Singlet oxygen was detected from the reaction of lophine hydroperoxides 2 in the presence of 1,3-diphenyl-isobenzofuran as a singlet oxygen detector. In order to examine the substituent effect on the formation of (1)O(2), 2-(p-substituted phenyl) lophine peroxides 2a-c were tested. It was found that an electron-attracting group contributed to the efficient formation of (1)O(2) (80% for a NO(2) group), while an electron-donating group enhanced the efficiency of chemiluminescence.

Benzofurans↗
PubMed2005

Illustrating the power of singlet oxygen chemistry in a synthetic context: biomimetic syntheses of litseaverticillols A-G, I and J and the structural reassignment of litseaverticillol E.

Biomimetic syntheses of the litseaverticillols A-G, I and J are reported herein. The syntheses rely heavily on the application of two different modes of reaction for photochemically generated singlet oxygen, namely, the [4+2] cycloaddition of singlet oxygen (1O2) with furans and the ene reaction of 1O2 with double bonds. The highlight of these syntheses is a one-pot cascade sequence, involving five synthetic operations initiated by a [4+2] reaction, to form the fully functionalised litseaverticillol core. A series of regioselective ene reactions are then used to appositely functionalise the side chains. The synthesis of litseaverticillol E (both its originally proposed and its actual structures) allows a structural reassignment of this natural product.

Magnetic Resonance Spectroscopy↗
PubMed1993

Evidence for singlet oxygen-induced cross-links and aggregation of collagen.

Singlet oxygen, generated by a hematoporphyrin-photosensitized reaction, was shown to cause insolubilization and an increase in molecular weight of acid soluble type I collagen and vitreous collagen as manifested in sodium dodecyl sulfate polyacrylamide gel electrophoresis. No such changes in the molecular properties of collagen could be observed when the irradiation was carried out in the presence of sodium azide, a singlet oxygen quencher. The increase in molecular weight and insolubilization of the collagen solution was attributed to extensive cross-links in the protein molecules.

Animals↗
PubMed2000

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.

Aerobiosis↗
PubMed1984

Singlet oxygen in copper-catalyzed lipid peroxidation in erythrocyte membranes.

Lipid hydroperoxide was generated in human erythrocyte membranes by irradiation with near ultraviolet (UV) light in the presence of a photosensitizer, hematoporphyrin, but no production of 2-thiobarbituric acid-reactive materials (malonaldehyde and its precursors) was detected. Incubation of the irradiated membranes with CuSO4 led to increased levels of hydroperoxide and formation of malonaldehyde. Hydroperoxides were essential for initiating the Cu(II)-catalyzed peroxidation as no significant activity was observed with nonirradiated membranes and Cu(II) unless an organic peroxide, either t-butyl hydroperoxide or cumene hydroperoxide, was added. Catalytic activity was also found with Fe(II), but not with other metal ions tested. The peroxidation catalyzed with Cu(II) was partially inhibited by several singlet oxygen quenchers but was not affected by superoxide dismutase, catalase or OH radical scavengers. The possible involvement of singlet oxygen in the Cu(II)-catalyzed peroxidation reaction was further supported by a 3-fold enhancement of malonaldehyde production in D2O.

Copper↗
PubMed1994

Kinetic study of quenching reactions of singlet oxygen and scavenging reactions of free radicals by alpha-, beta-, gamma- and delta- tocopheramines in ethanol solution and micellar dispersion.

Quenching reactions of singlet oxygen and scavenging reactions of free radicals by alpha-, beta-, gamma- and delta-tocopheramines (Toc-amines) were investigated spectrophotometrically in ethanol and Triton X-100 micellar dispersions. The rate constants of quenching of singlet oxygen (kQ) by alpha-, beta-, gamma- and delta-Toc-amines increased as the total electron donating capacity of the methyl groups at the aromatic ring increased. A plot of logkQ vs. peak oxidation potential (Ep) was found to be linear and the slope was negative. Similar results were obtained for scavenging of a phenoxyl radical (PhO.). The results suggest that charge transfer plays an important role in these reactions. The kQ values were found to be 1.30-2.57 times as large as kQ for alpha-tocopherol (alpha-Toc). Although alpha-Toc has the highest antioxidant activity among natural tocopherols and related phenols, Toc-amines also can serve as antioxidants.

Antioxidants↗
PubMed2001

A novel putative reductase (Cpd1p) and the multidrug exporter Snq2p are involved in resistance to cercosporin and other singlet oxygen-generating photosensitizers in Saccharomyces cerevisiae.

Phytopathogenic Cercospora species produce cercosporin, a photoactivated perylenequinone toxin that belongs to a family of photosensitizers which absorb light energy and produce extremely cytotoxic, reactive oxygen species. In this work, we used Saccharomyces cerevisiae as a model system for the identification and cloning of genes whose products mediate cercosporin detoxification. Two genesexpressed in high-copy number vectors conferred cercosporin resistance to an otherwise sensitive strain. One gene codes for Snq2p, a well-characterized multidrug, ABC-type, efflux protein. The other, designated CPD1 (Cercosporin Photosensitizer Detoxification), encodes a novel protein with significant similarity to the FAD-dependent pyridine nucleotide reductases. We showed that over-expression of either of these proteins can also mediate resistance to other singlet oxygen-generating compounds. The involvement of Snq2p and Cpd1p in photosensitizer detoxification reinforces previous observations which suggested that singlet oxygen acts on membrane lipids and that cellular resistance to cercosporin is mediated by a mechanism involving toxin efflux and/or toxin reduction.

ATP-Binding Cassette Transporters↗
PubMed2006

Singlet oxygen quantum yield determination for a fluorene-based two-photon photosensitizer.

The quantum yield, Phi(Delta), of singlet oxygen generation under two-photon excitation has been determined for a fluorene derivative. A photochemical method was developed using 1,3-diphenylisobenzofuran (DPBF), a chemical quencher of 1O2, and 2-(9,9-didecyl-7-nitrofluoren-2-yl)benzothiazole (1) as a two-photon photosensitizer (PS). The photochemical kinetics of the quencher was measured by two different fluorescence methods. Fluorene 1 exhibited relatively high singlet oxygen quantum yield, Phi(Delta) approximately 0.4 +/- 0.1, and had a two-photon absorption cross-section of 28 +/- 5 GM. Thus, 1 may have potential for use as a two-photon PS in the near-IR spectral region for biomedical applications.

Benzofurans↗