The Experts below are selected from a list of 41127 Experts worldwide ranked by ideXlab platform
Jos Lelieveld - One of the best experts on this subject based on the ideXlab platform.
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Hydroxyl Radical buffered by isoprene oxidation over tropical forests
Nature Geoscience, 2012Co-Authors: Domenico Taraborrelli, Mark Lawrence, J N Crowley, Terry J Dillon, Sergey Gromov, C B M Gros, Luc Vereecken, Jos LelieveldAbstract:The Hydroxyl Radical is a key oxidant in the Earth’s atmosphere. The inclusion in an atmospheric chemistry model of a detailed mechanism of isoprene oxidation, involving the buffering of Hydroxyl Radical concentrations, improves agreement between model simulations of Hydroxyl Radical levels and observations.
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Hydroxyl Radical buffered by isoprene oxidation over tropical forests
Nature Geoscience, 2012Co-Authors: Domenico Taraborrelli, Mark Lawrence, J N Crowley, Terry J Dillon, Sergey Gromov, C B M Gros, Luc Vereecken, Jos LelieveldAbstract:The Hydroxyl Radical is a key oxidant in the Earth’s atmosphere. The inclusion in an atmospheric chemistry model of a detailed mechanism of isoprene oxidation, involving the buffering of Hydroxyl Radical concentrations, improves agreement between model simulations of Hydroxyl Radical levels and observations. The Hydroxyl Radical is a key oxidant in the Earth’s atmosphere. This short-lived highly reactive molecule plays an important role in the degradation of volatile organic compounds, leading to the production of ozone and the formation and growth of aerosol particles1,2,3. In this way, Hydroxyl Radicals influence air quality and regional climate. Measurements over tropical forests suggest that Hydroxyl Radicals are recycled following reaction with the volatile organic compound isoprene4,5, but the chemistry underpinning this observation is uncertain. Here, we propose a detailed chemical mechanism for the oxidation of isoprene by Hydroxyl Radicals. The photo-oxidation of unsaturated hydroperoxy-aldehydes—a product of isoprene oxidation—is a central part of the mechanism; their photolysis initiates a Hydroxyl Radical production cascade that is limited by the reaction of hydroperoxy-aldehydes with the Hydroxyl Radical itself. We incorporate this mechanism into a global atmospheric chemistry model and find that measurements of Hydroxyl Radical concentrations over a pristine region of the Amazon, and in moderately polluted conditions, are captured well. On the basis of this agreement, we suggest that isoprene oxidation can buffer Hydroxyl Radical concentrations, by serving as both a sink and source for these Radicals.
Christopher M Hadad - One of the best experts on this subject based on the ideXlab platform.
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on the electrophilicity of Hydroxyl Radical a laser flash photolysis and computational study
Journal of the American Chemical Society, 2005Co-Authors: Matthew P Dematteo, James S Poole, Xiaofeng Shi, Rakesh Sachdeva, Patrick G Hatcher, Christopher M HadadAbstract:The rate coefficients for reactions of Hydroxyl Radical with aromatic hydrocarbons were measured in acetonitrile using a novel laser flash photolysis method. Comparison of kinetic data obtained in acetonitrile with those obtained in aqueous solution demonstrates an unexpected solvent effect on the reactivity of Hydroxyl Radical. In particular, reactions of Hydroxyl Radical with benzene were faster in water than in acetonitrile, and by a significant factor of 65. Computational studies, at the B3LYP and CBS-QB3 levels, have confirmed the rate enhancement of Hydroxyl Radical addition to benzene via calculation of the transition states in the presence of explicit solvent molecules as well as a continuum dielectric field. The origin of the rate enhancement lies entirely in the structures of the transition states and not in the pre-reactive complexes. The calculations reveal that the Hydroxyl Radical moiety becomes more anionic in the transition state and, therefore, looks more like hydroxide anion. In the tran...
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reaction of Hydroxyl Radical with aromatic hydrocarbons in nonaqueous solutions a laser flash photolysis study in acetonitrile
Journal of Physical Chemistry A, 2005Co-Authors: James S Poole, Xiaofeng Shi, Christopher M HadadAbstract:Laser flash photolysis (LFP) of acetonitrile solutions of N-hydroxypyridin-2-thione in the presence of trans-stilbene generates a transient absorbance at 392 nm, attributed to the addition of Hydroxyl Radical to stilbene. The observed transient absorbance was used in competitive LFP experiments to determine relative rates of reaction for Hydroxyl Radical with a range of aromatic hydrocarbons in acetonitrile. Structure−reactivity relationships for the reaction of Hydroxyl Radical with arenes are derived. With these aromatic hydrocarbons, we observe a good correlation between the rates of Hydroxyl-Radical reaction and the ionization potential of the arene. Kinetic isotope effects are consistent with Hydroxyl-Radical addition being the dominant reaction pathway with the arene.
Lourdes M Bastos - One of the best experts on this subject based on the ideXlab platform.
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antioxidative properties of cardoon cynara cardunculus l infusion against superoxide Radical Hydroxyl Radical and hypochlorous acid
Journal of Agricultural and Food Chemistry, 2002Co-Authors: Patricia Valentao, Félix Carvalho, Eduarda Fernandes, Rosa M Seabra, Paula B Andrade, Lourdes M BastosAbstract:Polyphenols are able to act as antioxidants by virtue of their hydrogen-donating and metal-chelating capacities. Cardoon (Cynara cardunculus L.) is a species containing considerable amounts of polyphenolic compounds, namely flavonoids and phenolic acids. This study examined the antioxidant activity of cardoon lyophilized infusion against superoxide Radical, Hydroxyl Radical, and hypochlorous acid. Superoxide Radical was generated either in an enzymatic system or nonenzymatically, and the scavenging ability was assessed by the inhibition of superoxide Radical-induced reduction of nitroblue tetrazolium. Hydroxyl Radical was generated by the Fe3+-EDTA/ascorbate Fenton system, and scavenging capacity was estimated by evaluating the inhibition of Hydroxyl Radical-induced deoxyribose degradation into thiobarbituric acid-reactive substances. Inhibition of hypochlorous acid-induced 5-thio-2-nitrobenzoic acid oxidation to 5,5‘-dithiobis(2-nitrobenzoic acid) was used in order to test the hypochlorous acid scavengin...
Patricia Valentao - One of the best experts on this subject based on the ideXlab platform.
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Hydroxyl Radical and hypochlorous acid scavenging activity of small centaury (Centaurium erythraea) infusion. A comparative study with green tea (Camellia sinensis)
Phytomedicine : international journal of phytotherapy and phytopharmacology, 2003Co-Authors: Patricia Valentao, Félix Carvalho, Eduarda Fernandes, Rosa M Seabra, Paula B Andrade, M L BastosAbstract:Small centaury (Centaurium erythraea Rafin.) is a herbal species with a long use in traditional medicine due to its digestive, stomachic, tonic, depurative, sedative and antipyretic properties. This species is reported to contain considerable amounts of polyphenolic compounds, namely xanthones and phenolic acids as the main constituents. Although the antiRadicalar activity of some pure polyphenolic compounds is already known, it remains unclear how a complex mixture obtained from plant extracts functions against reactive oxygen species. Thus, the ability of small centaury infusion to act as a scavenger of the reactive oxygen species Hydroxyl Radical and hypochlorous acid was studied and compared with that of green tea (Camellia sinensis L.). Hydroxyl Radical was generated in the presence of Fe3+-EDTA, ascorbate and H2O2 (Fenton system) and monitored by evaluating Hydroxyl Radical-induced deoxyribose degradation. The reactivity towards hypochlorous acid was determined by measuring the inhibition of hypochlorous acid-induced 5-thio-2-nitrobenzoic acid oxidation to 5,5'-dithiobis(2-nitrobenzoic acid). The obtained results demonstrate that small centaury infusion exhibits interesting antioxidant properties, expressed both by its capacity to effectively scavenge Hydroxyl Radical and hypochlorous acid, although with a lower activity against the second than that observed for green tea. Green tea exhibited a dual effect at the Hydroxyl Radical scavenging assay, stimulating deoxyribose degradation at lower dosages.
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studies on the antioxidant activity of lippia citriodora infusion scavenging effect on superoxide Radical Hydroxyl Radical and hypochlorous acid
Biological & Pharmaceutical Bulletin, 2002Co-Authors: Patricia Valentao, Félix Carvalho, Eduarda Fernandes, Rosa M Seabra, Paula B Andrade, Maria De Lourdes BastosAbstract:Lippia citriodora is an herbal species which contains several flavonoids and phenolic acids. In view of the pharmacological interest in natural phenolic compounds as antioxidants, this study examined the superoxide Radical, Hydroxyl Radical and hypochlorous acid scavenging activities of L. citriodora infusion. Superoxide Radical was generated either in an enzymatic or in a chemical system, and scavenging ability was assessed by the inhibition of nitroblue tetrazolium reduction. Hydroxyl Radical was generated by the reaction of an iron-EDTA complex with H 2 O 2 in the presence of ascorbic acid, and was assayed by evaluating deoxyribose degradation. Hypochlorous acid scavenging activity was tested by measuring the inhibition of 5-thio-2-nitrobenzoic acid oxidation. The results demonstrate that this infusion has a potent superoxide Radical scavenging activity and a moderate scavenging activity of Hydroxyl Radical and hypochlorous acid. The chemical composition of the lyophilized infusion was also determined in an attempt to establish its relationship with the antioxidant activity found in the present study.
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antioxidative properties of cardoon cynara cardunculus l infusion against superoxide Radical Hydroxyl Radical and hypochlorous acid
Journal of Agricultural and Food Chemistry, 2002Co-Authors: Patricia Valentao, Félix Carvalho, Eduarda Fernandes, Rosa M Seabra, Paula B Andrade, Lourdes M BastosAbstract:Polyphenols are able to act as antioxidants by virtue of their hydrogen-donating and metal-chelating capacities. Cardoon (Cynara cardunculus L.) is a species containing considerable amounts of polyphenolic compounds, namely flavonoids and phenolic acids. This study examined the antioxidant activity of cardoon lyophilized infusion against superoxide Radical, Hydroxyl Radical, and hypochlorous acid. Superoxide Radical was generated either in an enzymatic system or nonenzymatically, and the scavenging ability was assessed by the inhibition of superoxide Radical-induced reduction of nitroblue tetrazolium. Hydroxyl Radical was generated by the Fe3+-EDTA/ascorbate Fenton system, and scavenging capacity was estimated by evaluating the inhibition of Hydroxyl Radical-induced deoxyribose degradation into thiobarbituric acid-reactive substances. Inhibition of hypochlorous acid-induced 5-thio-2-nitrobenzoic acid oxidation to 5,5‘-dithiobis(2-nitrobenzoic acid) was used in order to test the hypochlorous acid scavengin...
Thomas D Tullius - One of the best experts on this subject based on the ideXlab platform.
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mapping nucleic acid structure by Hydroxyl Radical cleavage
Current Opinion in Chemical Biology, 2005Co-Authors: Thomas D Tullius, Jason A GreenbaumAbstract:Hydroxyl Radical footprinting is a widely used method for following the folding of RNA molecules in solution. This method has the unique ability to provide experimental information on the solvent accessibility of each nucleotide in an RNA molecule, so that the folding of all domains of the RNA species can be followed simultaneously at single-nucleotide resolution. In recent work, Hydroxyl Radical footprinting has been used, often in combination with other global measures of structure, to work out detailed folding pathways and three-dimensional structures for increasingly large and complicated RNA molecules. These include synthetic ribozymes, and group I and group II ribozymes, from yeast, the Azoarcus cyanobacterium and Tetrahymena thermophila. Advances have been made in methods for analysis of Hydroxyl Radical data, so that the large datasets that result from kinetic folding experiments can be analyzed in a semi-automated and quantitative manner.
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dna strand breaking by the Hydroxyl Radical is governed by the accessible surface areas of the hydrogen atoms of the dna backbone
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Bhavani Balasubramanian, Wendy Pogozelski, Thomas D TulliusAbstract:Despite extensive study, there is little experimental information available as to which of the deoxyribose hydrogen atoms of duplex DNA reacts most with the Hydroxyl Radical. To investigate this question, we prepared a set of double-stranded DNA molecules in which deuterium had been incorporated specifically at each position in the deoxyribose of one of the four nucleotides. We then measured deuterium kinetic isotope effects on the rate of cleavage of DNA by the Hydroxyl Radical. These experiments demonstrate that the Hydroxyl Radical reacts with the various hydrogen atoms of the deoxyribose in the order 5′ H > 4′ H > 3′ H ≈ 2′ H ≈ 1′ H. This order of reactivity parallels the exposure to solvent of the deoxyribose hydrogens. Our work therefore reveals the structural basis of the reaction of the Hydroxyl Radical with DNA. These results also provide information on the mechanism of DNA damage caused by ionizing radiation as well as atomic-level detail for the interpretation of Hydroxyl Radical footprints of DNA-protein complexes and chemical probe experiments on the structure of RNA and DNA in solution.
