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Paolo Di Mascio - One of the best experts on this subject based on the ideXlab platform.
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Cholesterol Hydroperoxides Generate Singlet Molecular Oxygen [O2 (1Δg)]: Near-IR Emission, 18O-Labeled Hydroperoxides, and Mass Spectrometry
Chemical research in toxicology, 2011Co-Authors: Miriam Uemi, Graziella E. Ronsein, Sayuri Miyamoto, Marisa H. G. Medeiros, Fernanda M. Prado, Flávia Daniela Motta, Paolo Di MascioAbstract:In mammalian membranes, cholesterol is concentrated in lipid rafts. The generation of cholesterol hydroperoxides (ChOOHs) and their decomposition products induces various types of cell damage. The decomposition of some organic hydroperoxides into peroxyl radicals is known to be a potential source of singlet molecular Oxygen [O2 (1Δg)] in biological systems. We report herein on evidence of the generation of O2 (1Δg) from ChOOH isomers in solution or in liposomes containing ChOOHs, which involves a cyclic mechanism from a linear tetraoxide intermediate originally proposed by Russell. Characteristic light emission at 1270 nm, corresponding to O2 (1Δg) monomolecular decay, was observed for each ChOOH isomer or in liposomes containing ChOOHs. Moreover, the presence of O2 (1Δg) was unequivocally demonstrated using the direct spectral characterization of near-infrared light emission. Using 18O-labeled cholesterol hydroperoxide (Ch18O18OH), we observed the formation of 18O-labeled O2 (1Δg) [18O2 (1Δg)] by the che...
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Generation of Cholesterol Carboxyaldehyde by the Reaction of Singlet Molecular Oxygen [O2 (1Δg)] as Well as Ozone with Cholesterol
Chemical research in toxicology, 2009Co-Authors: Miriam Uemi, Sayuri Miyamoto, Graziella E. Ronsein, Marisa H. G. Medeiros, Paolo Di MascioAbstract:A few years ago, it was reported that ozone is produced in human atherosclerotic arteries, on the basis of the identification of 3β-hydroxy-5-oxo-5,6-secocholestan-6-al and 3β-hydroxy-5β-hydroxy-B-norcholestane-6β-carboxaldehyde (ChAld) as their 2,4-dinitrophenylhydrazones. The formation of endogenous ozone was attributed to water oxidation catalyzed by antibodies, with the formation of dihydrogen trioxide as a key intermediate. We now report that ChAld is also generated by the reaction of cholesterol with singlet molecular Oxygen [O2 (1Δg)] that is produced by photodynamic action or by the thermodecomposition of 1,4-dimethylnaphthalene endoperoxide, a defined pure chemical source of O2 (1Δg). On the basis of 18O-labeled ChAld mass spectrometry, NMR, light emission measurements, and derivatization studies, we propose that the mechanism of ChAld generation involves the formation of the well-known cholesterol 5α-hydroperoxide (5α-OOH) (the major product of O2 (1Δg)-oxidation of cholesterol) and/or a 1,2-dio...
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Tryptophan Oxidation by Singlet Molecular Oxygen [O2 (1Δg)]: Mechanistic Studies Using 18O-Labeled Hydroperoxides, Mass Spectrometry, and Light Emission Measurements
Chemical research in toxicology, 2008Co-Authors: Graziella E. Ronsein, Mauricio César Bof De Oliveira, Sayuri Miyamoto, Marisa H. G. Medeiros, Paolo Di MascioAbstract:Proteins have been considered important targets for reactive Oxygen species. Indeed, tryptophan (W) has been shown to be a highly susceptible amino acid to many oxidizing agents, including singlet molecular Oxygen [O2 (1Δg)]. In this study, two cis- and trans-tryptophan hydroperoxide (WOOH) isomers were completely characterized by HPLC/mass spectrometry and NMR analyses as the major W-oxidation photoproducts. These photoproducts underwent thermal decay into the corresponding alcohols. Additionally, WOOHs were shown to decompose under heating or basification, leading to the formation of N-formylkynurenine (FMK). Using 18O-labeled hydroperoxides (W18O18OH), it was possible to confirm the formation of two Oxygen-labeled FMK molecules derived from W18O18OH decomposition. This result demonstrates that both Oxygen atoms in FMK are derived from the hydroperoxide group. In addition, these reactions are chemiluminescent (CL), indicating a dioxetane cleavage pathway. This mechanism was confirmed since the CL spectr...
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Quenching of Singlet Molecular Oxygen, O2( 1 Dg), by Dipyridamole and Derivatives
2007Co-Authors: Marilene Silva Oliveira, Paolo Di Mascio, Michelle S. Lima, Divinomar Severino, Marcel TabakAbstract:Dipyridamole (DIP) is known for its vasodilating and antiplatelet activity, exhibiting also a potent antioxidant effect, strongly inhibiting lipid peroxidation. This effect has been studied in mitochondria and a correlation between the DIP derivatives’ structure, the ability to bind to micelles and biological activity has been suggested. In the present work, the quenching of singlet molecular Oxygen, O2( 1 Dg), by DIP and RA47 and RA25 derivatives was analyzed in acetonitrile (ACN) and aqueous acid solutions. Laser flash photolysis excitation of methylene blue (MB) was made at 532 nm and monomol light emission of O2( 1 Dg) was monitored at 1270 nm. Bimolecular quenching constants in ACN are consistent with an efficient physical quenching, presenting values a bit lower than the diffusion limit (kt = 3.4–6.8 · 10 8 M )1 s )1 ). The quenching process probably occurs via reversible charge transfer with the formation of an exciplex. Calculation of DGet associated with O2( 1 Dg) quenching corroborates with uncompleted electron transfer. In aqueous acid solutions (pH = 3.0), the kt values for DIP and derivatives are 20-fold smaller when compared with ACN. The electrochemical properties of DIP in ACN are characterized by two consecutive one-electron processes with half-wave oxidation potentials of 0.30 and 0.67 V vs saturated calomel electrode (SCE). However, in an aqueous acid medium, a single oxidation wave is observed involving a two-electron process (0.80 V vs SCE). Therefore, O2( 1 Dg) quenching is consistent with electrochemical data.
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Direct Evidence of Singlet Molecular Oxygen [O2 (1Δg)] Production in the Reaction of Linoleic Acid Hydroperoxide with Peroxynitrite
Journal of the American Chemical Society, 2003Co-Authors: Sayuri Miyamoto, Marisa H. G. Medeiros, Glaucia R. Martinez, Ana Paula Bortoletto Martins, Paolo Di MascioAbstract:Peroxynitrite (ONOO-), a biologically active species, can induce lipid peroxidation in biological membranes, thereby leading to the formation of various hydroperoxides. We report herein on the formation of singlet molecular Oxygen [O2 (1Δg)] in the reaction of peroxynitrite with linoleic acid hydroperoxide (LAOOH) or 18O-labeled LAOOH. The formation of O2 (1Δg) was characterized by (i) dimol light emission in the red spectral region (λ > 570 nm) using a red-sensitive photomultiplier; (ii) monomol light emission in the near-infrared region (λ = 1270 nm) with a liquid nitrogen-cooled germanium diode or a photomultiplier coupled to a monochromator; (iii) the enhacing effect of deuterium oxide on chemiluminescence intensity, as well as the quenching effect of sodium azide; and (iv) chemical trapping of O2 (1Δg) or 18O-labeled O2 (1Δg) with the 9,10-diphenylanthracene (DPA) and detection of the corresponding DPAO2 or 18O-labeled DPA endoperoxide by HPLC coupled to tandem mass spectrometry. Moreover, the presen...
Peter R. Ogilby - One of the best experts on this subject based on the ideXlab platform.
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Singlet Oxygen: there is indeed something new under the sun
Chemical Society reviews, 2010Co-Authors: Peter R. OgilbyAbstract:Singlet Oxygen, O2(a1Δg), the lowest excited electronic state of molecular Oxygen, has been known to the scientific community for ∼80 years. It has a characteristic chemistry that sets it apart from the triplet ground state of molecular Oxygen, O2(X3Σ−g), and is important in fields that range from atmospheric chemistry and materials science to biology and medicine. For such a “mature citizen”, singlet Oxygen nevertheless remains at the cutting-edge of modern science. In this critical review, recent work on singlet Oxygen is summarized, focusing primarily on systems that involve light. It is clear that there is indeed still something new under the sun (243 references).
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Singlet Sigma: The “Other” Singlet Oxygen in Solution
Photochemistry and Photobiology, 1999Co-Authors: Dean Weldon, Tina D. Poulsen, Kurt V. Mikkelsen, Peter R. OgilbyAbstract:The lowest excited electronic state of molecular Oxygen, O2(a1-DLg), is often called simply singlet Oxygen. This singlet delta state is an acknowledged and well-studied intermediate in many solution-phase photosystems. However, the second excited electronic state of Oxygen, O2(b1δg+), is also a singlet. It has recently become possible to monitor this singlet sigma state in solution, which, in combination with studies of the singlet delta state, contributes to a better understanding of a variety of general problems in chemistry.
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Chemical Reactivity of Singlet Sigma Oxygen (b1Σg+) in Solution
Journal of the American Chemical Society, 1996Co-Authors: Rodger D. Scurlock, And Bojie Wang, Peter R. OgilbyAbstract:Spectroscopic data are presented to indicate that, in solution, chemical reactions of singlet sigma Oxygen, O2(b1Σg+), do not compete effectively with the physical deactivation channels that produce O2(a1Δg).
Norman A. García - One of the best experts on this subject based on the ideXlab platform.
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Effect of Cu(2+)-complexation on the scavenging ability of chrysin towards photogenerated singlet molecular Oxygen (O2((1)Δg)). Possible biological implications.
Journal of photochemistry and photobiology. B Biology, 2016Co-Authors: Vanesa Muñoz, Sandra Miskoski, Gabriela V. Ferrari, M. Paulina Montaña, Norman A. GarcíaAbstract:Visible-light irradiation of aqueous-ethanolic solutions of Riboflavin (Rf) in the individual presence of the flavone chrysin (Chr) and its complex with Cu(2+) ([Chr2Cu]; 2:1 L:M) generates singlet molecular Oxygen O2((1)Δg), that concomitantly interact with both flavone derivatives. Overall (kt) and reactive (kr) rate constants in the order of 10(7)M(-1)s(-1) were determined for the process. Metal chelation greatly enhances the scavenging ability of [Chr2Cu] towards O2((1)Δg) through a mechanism dominated, in >80%, by the physical component. In this way, practically all O2((1)Δg) is deactivated by the complex without significant loss of the quencher. The isolated flavone quenches O2((1)Δg) in a prevailing reactive fashion. The very low value exhibited by [Chr2Cu] for the kr/kt ratio constitutes a positive quality for antioxidative protectors in biological media, where elevated local concentration and high reactivity of significant molecules make them initial targets for O2((1)Δg) aggression. Finally, two interesting properties in the field of free radicals scavenging by [Chr2Cu] must be mentioned. In first place metal chelation itself, in the obvious sense of free metal ion withdrawal from the oxidizable medium, prevents the initiation of a free radical-mediated oxidation processes through mechanisms of Fenton or lipid peroxidation. In addition, the incorporation of Cu adds to [Chr2Cu] the ability of a free radical scavenger, already described for similar Cu-chelate compounds. This collection of beneficial properties positions the complex as a remarkably promising bioprotector towards ROS-mediated oxidation. A quantification of the efficiency on the initial anti-oxidative effect exerted by Chr and [Chr2Cu] towards tryptophan was carried out. The amino acid is an archetypal molecular model, commonly employed to monitor oxidative degradation of proteinaceous media. It was efficiently photoprotected against O2((1)Δg)-mediated photooxidation by [Chr2Cu].
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Singlet molecular Oxygen [O2(1Δg)]-mediated photodegradation of tyrosine derivatives in the presence of cationic and neutral micellar systems
Amino acids, 2007Co-Authors: Susana Criado, Juan P. Escalada, Adriana Pajares, Norman A. GarcíaAbstract:The kinetics of rose bengal-sensitized photooxidation of tyrosine and several tyrosine-derivatives (tyr-D) named tyrosine methyl ester, tyrosine ethyl ester and tyrosine benzyl ester was studied in buffered pH 11 water, and buffered pH 11 micellar aqueous solutions of 0.01 M cetyltrimethylammonium chloride (CTAC) and 0.01 M-octylphenoxypolyethoxyethanol [triton X100 (TX100)]. Through time-resolved phosphorescence detection of singlet molecular Oxygen (O2(1Δg)) and polarographic determination of Oxygen consumption, the respective bimolecular rate constants for reactive (kr) and overall (kt) quenching of the oxidative species by tyr-D were evaluated. Both rate constants behave in different fashion depending on the particular reaction medium. kr/kt values, increase in the sense CTAC≪TX100 < water, indicating, for the tyr-D family studied, an excellent degree of self-protection against O2(1Δg)-attack in the CTAC micellar system and a high photooxidability level in water. Results were interpreted in terms of a competition between solvent polarity effects, local substrate concentration and electron donating capabilities of the substrates in the different media that can contribute to predict the extent of photodynamic damage in biological environments.
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Sensitized Photooxidation of Thyroidal Hormones. Evidence for Heavy Atom Effect on Singlet Molecular Oxygen [O2(1Δg)]-mediated Photoreactions¶
Photochemistry and photobiology, 2005Co-Authors: Sandra Miskoski, Antonio L. Zanocco, Arnaldo T. Soltermann, Patricia Gabriela Molina, Germán Günther, Norman A. GarcíaAbstract:Thyronine derivatives are essential indicators of thyroid gland diseases in clinical diagnosis and are currently used as standards for developing ordinary biochemical assays. Photooxidation of gland hormones of the thyronine (TN) family and structurally related compounds (TN, 3,5-diiodothyronine,3,3',5-triiodothyronine and 3,3',5,5'-tetraiodothyronine or thyroxine) was studied using rose bengal, eosin and perinaphthenone (PN) as dye sensitizers. Tyrosine (Tyr) and two iodinated derivatives (3-iodotyrosine and 3,5-diiodotyrosine) were also included in the study for comparative purposes. Irradiation of aqueous solutions of substrates containing xanthene dyes with visible light triggers a complex series of competitive interactions, which include the triplet excited state of the dye (3Xdye*) and singlet molecular Oxygen [O2(1Deltag)]-mediated and superoxide ion-mediated reactions. Rate constants for interaction with the 3Xdye*, attributed to an electron transfer process, are in the order of 10(8)-10(9) M-1 s-1 depending on the dye and the particular substrate. The photosensitization using PN follows a pure Type-II (O2(1Deltag) mediated) mechanism. The presence of the phenolic group in Tyr, TN and iodinated derivatives dominates the kinetics of photooxidation of these compounds. The reactive rate constants, k(r), and the quotient between reactive and overall rate constants (k(r)/k(t) values, in the range of 0.7-0.06) behave in an opposite fashion compared with the overall rate constants and oxidation potentials. This apparent inconsistency was interpreted on the basis of an internal heavy atom effect, favoring the intersystem-crossing deactivation route within the encounter complex with the concomitant reduction of effective photooxidation.
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Kinetic study of the oxidation of phenolic derivatives of α,α,α-trifluorotoluene by singlet molecular Oxygen [O2(1Δg)] and hydrogen phosphate radicals
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 2003Co-Authors: Janina A. Rosso, Norman A. García, Susana Criado, Sonia G. Bertolotti, Patricia E. Allegretti, Jorge J. P. Furlong, Mónica C. Gonzalez, Daniel O. MártireAbstract:The oxidation kinetics and mechanism of the phenolic derivatives of alpha,alpha,alpha-trifluorotoluene, 2-trifluoromethylphenol, 3-trifluoromethylphenol (3-TFMP), 4-trifluoromethylphenol and 3,5-bis(trifluoromethyl)phenol, mediated by singlet molecular Oxygen, O2(1delta(g)), and hydrogen phosphate radicals were studied, employing time-resolved O2(1delta(g)) phosphorescence detection, polarographic determination of dissolved Oxygen and flash photolysis. All the substrates are highly photo-oxidizable through a O2(1delta(g))-mediated mechanism. The phenols show overall quenching constants for O2(1delta(g)) of the order of 10(6) M(-1) s(-1) in D2O, while the values for the phenoxide ions in water range from 1.2 x 10(8) to 3.6 x 10(8) M(-1) s(-1). The effects of the pH and polarity of the medium on the kinetics of the photo-oxidative process suggest a charge-transfer mechanism. 2-Trifluoromethyl-1,4-benzoquinone is suspected to be the main photo-oxidation product for the substrate 3-TFMP. The absolute rate constants for the reactions of HPO4*- with the substrates range from 4 x 10(8) to 1 x 10(9) M(-1) s(-1). The 3-trifluoromethylphenoxyl radical was observed as the organic intermediate formed after reaction of 3-TFMP with HPO4*-, yielding 2,2'-bis(fluorohydroxymethyl)biphenyl-4,4'-diol as the end product. The observed results indicate that singlet molecular Oxygen and hydrogen phosphate radicals not only react at different rates with the phenols of alpha,alpha,alpha-trifluorotoluene, but the reactions also proceed through different reaction channels.
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Solvent effect on the reactivity of monosubstituted phenols towards singlet molecular Oxygen (O2(1Δg)) in alkaline media
Canadian Journal of Chemistry, 1993Co-Authors: Marta Luiz, María Isela Gutiérrez, Graciela Bocco, Norman A. GarcíaAbstract:The influence of solvent polarity on the dye-sensitized photooxidation (singlet molecular Oxygen (O2(1Δg)) mediated) of a series of para-substituted phenolates was studied. Kinetic evidence obtaine...
Esther Oliveros - One of the best experts on this subject based on the ideXlab platform.
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Singlet Oxygen (O2(1Δg)) quenching by dihydropterins
Journal of Physical Chemistry A, 2007Co-Authors: M. Laura Dántola, André M. Braun, Esther Oliveros, Andrés H. Thomas, Carolina LorenteAbstract:Pterins belong to a class of heterocyclic compounds present in a wide range of living systems. They participate in relevant biological functions and are involved in different photobiological processes. Dihydropterins are one of the biologically active forms of pterins. The photoinduced production and quenching of singlet Oxygen ( 1 O 2 ) by a series of dihydropterins (7,8-dihydrobiopterin (DHBPT), 7,8-dihydroneopterin (DHNPT), 6-formyl-7,8-dihydropterin (FDHPT), sepiapterin (SPT), 7,8-dihydrofolic acid (DHFA), and 7,8-dihydroxanthopterin (DHXPT)) in aqueous solution at physiological pH (∼7) were investigated, and the quantum yields of 1 O 2 production (Φ Δ ) and rate constants of total quenching (k t ) of 1 O 2 were determined. Studied compounds do not produce 1 O 2 under UV-A irradiation and are very efficient 1 O 2 quenchers. The chemical reactions between 1 O 2 and dihydropterin derivatives were investigated, and the corresponding rate constants (k r ) were found to be particularly high. The oxidized pterin derivatives, biopterin (BPT), neopterin (NPT), 6-formylpterin (FPT), and folic acid (FA), were identified and quantified during the reaction of 1 O 2 with DHBPT, DHNPT, FDHPT, and DHFA, respectively. Besides the oxidation of the dihydropyrazine ring to yield the corresponding oxidized pterins, a second oxidation pathway, leading to fragmentation of the dihydropterin and formation of non-pterinic products, was identified. Mechanisms and biological implications are discussed.
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Effect of the media on the quantum yield of singlet Oxygen (O2(1Δg)) production by 9H-fluoren-9-one: Microheterogeneous systems
Helvetica Chimica Acta, 2004Co-Authors: Claudia G. Martínez, André M. Braun, Esther OliverosAbstract:The quantum yield (ΦΔ) of singlet Oxygen (O2(1Δg) production by 9H-fluoren-9-one (FLU) is very sensitive to the nature of the solvent (0.02 in a highly polar and protic solvent, such as MeOH, to 1.0 in apolar solvents). This high sensitivity has been used for probing the interaction of FLU with micellar media and microemulsions based on anionic (sodium dodecyl sulfate, SDS; bis-(2-ethylhexyl)sodium sulfosuccinate, AOT), cationic (cetyltrimethylammonium chloride, CTAC) and nonionic (Triton X-100, TX) surfactants. Values of ΦΔ of FLU vary in a wide range (0.05–1.0) in both microheterogeneous media and neat solvent, and provide information on the microenvironment of FLU, i.e., on its localization within organized media. In ionic and nonionic micellar media, as well as in four-component microemulsions, FLU is, to various extents, exposed to solvation by the polar and protic components of the microheterogeneous systems (water and/or butan-1-ol) in the micellar interfacial region (ΦΔ=0.05–0.30). In contrast, in AOT reverse micelles (consisting of AOT as surfactant, cyclohexane as hydrophobic component, and water), FLU is located in the hydrophobic continuous pseudophase, and is totally separated from the micellar water pools (ΦΔ≈1.0).
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Effect of the Media on the Quantum Yield of Singlet Oxygen (O2(1Δg)) Production by 9H-Fluoren-9-one: Solvents and Solvent Mixtures
Helvetica Chimica Acta, 2003Co-Authors: Claudia G. Martínez, André M. Braun, Annette Neuner, Cristina Martí, Santi Nonell, Esther OliverosAbstract:We have investigated the effect of a series of 18 solvents and mixtures of solvents on the production of singlet molecular Oxygen (O2(1Δg), denoted as 1O2) by 9H-fluoren-9-one (FLU). The normalized empirical parameter E derived from ET(30) has been chosen as a measure of solvent polarity using Reichardt's betaine dyes. Quantum yields of 1O2 production (ΦΔ) decrease with increasing solvent polarity and protic character as a consequence of the decrease of the quantum yield of intersystem crossing (ΦISC). Values of ΦΔ of unity have been found in alkanes. In nonprotic solvents of increasing polarity, ΦISC and, therefore, ΦΔ decrease due to solvent-induced changes in the energy levels of singlet and triplet excited states of FLU. This compound is a poor 1O2 sensitizer in protic solvents, because hydrogen bonding considerably increases the rate of internal conversion from the singlet excited state, thus diminishing ΦΔ to values much lower than those in nonprotic solvents of similar polarity. In mixtures of cyclohexane and alcohols, preferential solvation of FLU by the protic solvent leads to a fast decrease of ΦΔ upon addition of increasing amounts of the latter.
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Photochemistry of the singlet Oxygen [O2(1Δg)] sensitizer perinaphthenone (phenalenone) in N,N′-dimethylacetamide and 1,4-dioxane
New Journal of Chemistry, 1999Co-Authors: Esther Oliveros, Claudia G. Martínez, Annette Neuner, Cristina Martí, Santi Nonell, Stefan H. Bossmann, Gernot Heit, Gabi Tröscher, André M. BraunAbstract:1H-Phenalen-1-one (perinaphthenone), an efficient singlet Oxygen [O2(1Δg)] sensitizer with a quantum yield of singlet Oxygen production (ΦΔ) close to unity, has been proposed as a universal standard for O2(1Δg) studies. However, data about the photochemical stability of phenalenone are limited to a few protic solvents. This parameter is of crucial interest for singlet Oxygen studies under continuous irradiation over long periods of time. In this contribution, we present experimental results demonstrating that, despite low quantum yields, significant photochemical decomposition of phenalenone occurs under steady-state irradiation in air equilibrated 1,4-dioxane and N,N′-dimethylacetamide (DMA), mainly due to hydrogen abstraction from the solvent by its triplet excited state. Furthermore, singlet Oxygen lifetime measurements as a function of irradiation time and comparison of the rates of decrease of the steady-state O2(1Δg) near-infrared (1270 nm) phosphorescence with those of phenalenone disappearance have led to the conclusion that at least one of the products formed during phenalenone irradiation contributes to singlet Oxygen sensitization. Quantum yields of singlet Oxygen production by phenalenone, determined using laser-induced optoacoustic calorimetry (LIOAC) and time-resolved near-infrared phosphorescence (TRPD), remain high in 1,4-dioxane and in DMA (0.99±0.05 and 0.87±0.05, respectively), confirming that this compound is a very efficient 1O2 sensitizer in a large variety of solvents (the ΦΔ value in DMA is the lowest measured so far). Photochimie de la pe′rinaphte′none (phe′nale′none), un sensibilisateur de l'Oxygene singulet [O2(1Δg)], dans le N , N ′-dime′thylace′tamide et le 1,4-dioxane. L'importance de la 1H-phe′nale′none-1 (ou pe′rinaphte′none) en tant que sensibilisateur de re′fe′rence pour la production d'Oxygene singulet [O2(1Δg)] est alle′e croissante ces dernieres anne′es. Cependant, la stabilite′ photochimique de ce compose′ a e′te′ seulement e′tudie′e dans un nombre limite′ de solvants protiques. Ce parametre est d'une grande importance pour des e′tudes impliquant la production d'Oxygene singulet sous irradiation prolonge′e du sensibilisateur. Dans cette contribution, nous pre′sentons des re′sultats montrant qu'une de′composition photochimique partielle de la phe′nale′none se produit sous irradiation en continue dans le 1,4-dioxane et dans le N,N′-dime′thylacetamide (DMA), principalement par suite de l'arrachement d'un atome d'hydrogene au solvant par l'e′tat excite′ triplet de la ce′tone. De plus, la de′termination des dure′es de vie de l'Oxygene singulet en fonction du temps d'irradiation et la comparaison des vitesses de la de′croissance de la production d'Oxygene singulet et de la disparition de la phe′nale′none nous ont conduit a la conclusion qu'au moins l'un des produits forme′s contribue a la production d'Oxygene singulet. Nous avons de′termine′ les rendements quantiques de production d'Oxygene singulet (ΦΔ) par la phe′nale′none en utilisant la combinaison de deux me′thodes diffe′rentes: la calorime′trie optoacoustique induite par impulsion laser et la de′tection de la phosphorescence de l'Oxygene singulet dans le proche infrarouge (1270 nm). Les valeurs de ΦΔ dans le 1,4-dioxane (0.99±0.05) et dans le DMA (0.87±0.05) confirment que ce compose′ est un sensibilisateur de l'Oxygene singulet tres efficace dans une grande varie′te′ de solvants (la valeur dans le DMA est la plus faible mesure′e jusqu'a pre′sent).
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Effect of the microenvironment on the efficiency of singlet Oxygen (O2(1Δg)) production by photosensitizing anti-inflammatory drugs
Journal of photochemistry and photobiology. B Biology, 1998Co-Authors: Luis A. Martinez, André M. Braun, Esther OliverosAbstract:Abstract The influence of the medium on the quantum yields of singlet Oxygen (O2(1Δg)) production (ΦΔ) by a series of photosensitizing non-steroidal anti-inflammatory drugs (NSAID) derived from 2-arylpropionic acid (APA) has been investigated. Four-component oil-in-water and water-in-oil microemulsions, based on anionic and cationic surfactants, have been employed as the simplest models to mimic more complex biological environments. ΦΔ values have been determined by monitoring the singlet Oxygen (1O2) luminescence at 1270 nm upon continuous excitation of the drugs under air-equilibrated conditions. Results indicate that ΦΔ values are highly affected by the medium, being higher in microheterogeneous systems than in (homogeneous) solution. Some of the anti-inflammatory derivatives are very efficient 1O2 sensitizers: e.g., values of apparent ΦΔ as high as 0.86 (±0.04) and 0.70 (± 0.03) have been found for triaprofenic acid and suprofen, respectively. The location of the drugs in the interfacial region of the microemulsions combined with their high ΦΔ values suggest that type II reactions may play a significant role in the overall photodynamic process in more complex organized media, such as biological membranes.
Marisa H. G. Medeiros - One of the best experts on this subject based on the ideXlab platform.
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Cholesterol Hydroperoxides Generate Singlet Molecular Oxygen [O2 (1Δg)]: Near-IR Emission, 18O-Labeled Hydroperoxides, and Mass Spectrometry
Chemical research in toxicology, 2011Co-Authors: Miriam Uemi, Graziella E. Ronsein, Sayuri Miyamoto, Marisa H. G. Medeiros, Fernanda M. Prado, Flávia Daniela Motta, Paolo Di MascioAbstract:In mammalian membranes, cholesterol is concentrated in lipid rafts. The generation of cholesterol hydroperoxides (ChOOHs) and their decomposition products induces various types of cell damage. The decomposition of some organic hydroperoxides into peroxyl radicals is known to be a potential source of singlet molecular Oxygen [O2 (1Δg)] in biological systems. We report herein on evidence of the generation of O2 (1Δg) from ChOOH isomers in solution or in liposomes containing ChOOHs, which involves a cyclic mechanism from a linear tetraoxide intermediate originally proposed by Russell. Characteristic light emission at 1270 nm, corresponding to O2 (1Δg) monomolecular decay, was observed for each ChOOH isomer or in liposomes containing ChOOHs. Moreover, the presence of O2 (1Δg) was unequivocally demonstrated using the direct spectral characterization of near-infrared light emission. Using 18O-labeled cholesterol hydroperoxide (Ch18O18OH), we observed the formation of 18O-labeled O2 (1Δg) [18O2 (1Δg)] by the che...
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Generation of Cholesterol Carboxyaldehyde by the Reaction of Singlet Molecular Oxygen [O2 (1Δg)] as Well as Ozone with Cholesterol
Chemical research in toxicology, 2009Co-Authors: Miriam Uemi, Sayuri Miyamoto, Graziella E. Ronsein, Marisa H. G. Medeiros, Paolo Di MascioAbstract:A few years ago, it was reported that ozone is produced in human atherosclerotic arteries, on the basis of the identification of 3β-hydroxy-5-oxo-5,6-secocholestan-6-al and 3β-hydroxy-5β-hydroxy-B-norcholestane-6β-carboxaldehyde (ChAld) as their 2,4-dinitrophenylhydrazones. The formation of endogenous ozone was attributed to water oxidation catalyzed by antibodies, with the formation of dihydrogen trioxide as a key intermediate. We now report that ChAld is also generated by the reaction of cholesterol with singlet molecular Oxygen [O2 (1Δg)] that is produced by photodynamic action or by the thermodecomposition of 1,4-dimethylnaphthalene endoperoxide, a defined pure chemical source of O2 (1Δg). On the basis of 18O-labeled ChAld mass spectrometry, NMR, light emission measurements, and derivatization studies, we propose that the mechanism of ChAld generation involves the formation of the well-known cholesterol 5α-hydroperoxide (5α-OOH) (the major product of O2 (1Δg)-oxidation of cholesterol) and/or a 1,2-dio...
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Tryptophan Oxidation by Singlet Molecular Oxygen [O2 (1Δg)]: Mechanistic Studies Using 18O-Labeled Hydroperoxides, Mass Spectrometry, and Light Emission Measurements
Chemical research in toxicology, 2008Co-Authors: Graziella E. Ronsein, Mauricio César Bof De Oliveira, Sayuri Miyamoto, Marisa H. G. Medeiros, Paolo Di MascioAbstract:Proteins have been considered important targets for reactive Oxygen species. Indeed, tryptophan (W) has been shown to be a highly susceptible amino acid to many oxidizing agents, including singlet molecular Oxygen [O2 (1Δg)]. In this study, two cis- and trans-tryptophan hydroperoxide (WOOH) isomers were completely characterized by HPLC/mass spectrometry and NMR analyses as the major W-oxidation photoproducts. These photoproducts underwent thermal decay into the corresponding alcohols. Additionally, WOOHs were shown to decompose under heating or basification, leading to the formation of N-formylkynurenine (FMK). Using 18O-labeled hydroperoxides (W18O18OH), it was possible to confirm the formation of two Oxygen-labeled FMK molecules derived from W18O18OH decomposition. This result demonstrates that both Oxygen atoms in FMK are derived from the hydroperoxide group. In addition, these reactions are chemiluminescent (CL), indicating a dioxetane cleavage pathway. This mechanism was confirmed since the CL spectr...
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Direct Evidence of Singlet Molecular Oxygen [O2 (1Δg)] Production in the Reaction of Linoleic Acid Hydroperoxide with Peroxynitrite
Journal of the American Chemical Society, 2003Co-Authors: Sayuri Miyamoto, Marisa H. G. Medeiros, Glaucia R. Martinez, Ana Paula Bortoletto Martins, Paolo Di MascioAbstract:Peroxynitrite (ONOO-), a biologically active species, can induce lipid peroxidation in biological membranes, thereby leading to the formation of various hydroperoxides. We report herein on the formation of singlet molecular Oxygen [O2 (1Δg)] in the reaction of peroxynitrite with linoleic acid hydroperoxide (LAOOH) or 18O-labeled LAOOH. The formation of O2 (1Δg) was characterized by (i) dimol light emission in the red spectral region (λ > 570 nm) using a red-sensitive photomultiplier; (ii) monomol light emission in the near-infrared region (λ = 1270 nm) with a liquid nitrogen-cooled germanium diode or a photomultiplier coupled to a monochromator; (iii) the enhacing effect of deuterium oxide on chemiluminescence intensity, as well as the quenching effect of sodium azide; and (iv) chemical trapping of O2 (1Δg) or 18O-labeled O2 (1Δg) with the 9,10-diphenylanthracene (DPA) and detection of the corresponding DPAO2 or 18O-labeled DPA endoperoxide by HPLC coupled to tandem mass spectrometry. Moreover, the presen...
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Oxidation of melatonin by singlet molecular Oxygen (O2(1deltag)) produces N1-acetyl-N2-formyl-5-methoxykynurenine.
Journal of pineal research, 2003Co-Authors: Eduardo Alves De Almeida, Marisa H. G. Medeiros, Glaucia R. Martinez, Clécio F. Klitzke, Paolo Di MascioAbstract:It has been shown that melatonin exhibits antioxidant properties. Chemical structures of some of the products formed by the interaction of melatonin with reactive Oxygen and nitrogen species have been elucidated. Despite some evidence that the reaction of melatonin with singlet molecular Oxygen (O2(1deltag)) produces N1-acetyl-N2-formyl-5-methoxykynurenine (AFMK), it has not been fully documented. In this investigation, melatonin was oxidized by photosensitization with methylene blue or by a clean chemical source of O2(1deltag), the thermodecomposition of N,N'-di(2,3-dihydroxypropyl)-1,4-naphtalenedipropanamide (DHPNO2). The resulting product was characterized by high performance liquid chromatography, coupled to electrospray ionization mass spectrometry and also by 1H, 13C and dept135 nuclear magnetic resonance spectroscopy. An isotopically labeled DHPN18O2 was also prepared and used as a chemical source of labeled 18[O2(1deltag)] to unequivocally characterize the end product. The results uncovered by this work confirm the hypothesis that oxidation of melatonin by O2(1deltag) produces AFMK.
