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Emma L D'Ambro, Kristian H Møller, Felipe D Lopez-Hilfiker, Siegfried Schobesberger, Jiumeng Liu, John E Shilling, Ben Hwan Lee, Henrik G Kjaergaard, Joel A Thornton
We report chamber measurements of secondary organic aerosol (SOA) formation from isoprene photochemical oxidation, where radical concentrations were systematically varied and the molecular composition of semi to low volatility gases and SOA were measured online. Using a detailed chemical kinetics box model, we find that to explain the behavior of low volatility products and SOA mass yields relative to input H2O2 concentrations, the second generation dihydroxy hydroperoxy peroxy radical (C5H11O6•) must undergo an intra-molecular H-shift with a net forward rate constant of order 0...
April 7, 2017: Environmental Science & Technology
Qian Yao, Xiao-Hui Sun, Ze-Rong Li, Fang-Fang Chen, Xiang-Yuan Li
Intramolecular H-migration reaction of hydroperoxyalkylperoxy radicals ((•)O2QOOH) is one of the most important reaction families in the low-temperature oxidation of hydrocarbon fuels. This reaction family is first divided into classes depending upon H atom transfer from -OOH bonded carbon or non-OOH bonded carbon, and then the two classes are further divided depending upon the ring size of the transition states and the types of the carbons from which the H atom is transferred. High pressure limit rate rules and pressure-dependent rate rules for each class are derived from the rate constants of a representative set of reactions within each class using electronic structure calculations performed at the CBS-QB3 level of theory...
April 13, 2017: Journal of Physical Chemistry. A
D V Yanykin, A A Khorobrykh, V V Terentyev, V V Klimov
Earlier the catalase-insensitive formation of organic hydroperoxides (via the interaction of organic radicals produced due to redox activity of P680(+·) (or TyrZ(·)) with molecular oxygen) has been found in Mn-depleted PS2 preparations (apo-WOC-PS2) by Khorobrykh et al. (Biochemistry 50:10658-10665, 2011). The present work describes a second pathway of the photoproduction of organic peroxides on the donor side of PS2. It was shown that illumination of CaCl2-treated PS2 membranes (deprived of the PS2 extrinsic proteins without removal of the Mn-containing water-oxidizing complex) (CaCl2-PS2) led to the photoproduction of highly lipophilic organic hydroperoxides (LP-OOH) (in amount corresponding to 1...
March 27, 2017: Photosynthesis Research
Shuo Li, Zhansheng Lu, Yi Zhang, Dongwei Ma, Zongxian Yang
Hydrogen peroxide (H2O2) is an important chemical commodity, with demand growing significantly in chemical synthesis due to its green characteristics. The mechanisms of the direct synthesis of hydrogen peroxide (DSHP) on metal-free silicon and phosphorus dual-doped graphene (Si-P-G) catalyst, based on a dispersion-corrected density functional theory (DFT-D) method, are systematically investigated. The most stable Si-P-G catalyst is presented, with the local region of dopants shown to play an important role in the adsorption and reduction of oxygen...
March 17, 2017: Physical Chemistry Chemical Physics: PCCP
Karen Busk Nørøxe, Linda Huibers, Grete Moth, Peter Vedsted
BACKGROUND: Optimal utilisation of the out-of-hours primary care (OOH-PC) services remains a concern in public health policy. We need more knowledge on potentially avoidable contacts. This study examines the frequency of medically assessed inappropriate OOH-PC calls from adults, explores factors associated with such assessment, and examines the relation to patient-assessed severity of health problem and fulfilment of expectations. METHODS: We performed secondary analyses of data from a large cross-sectional survey on contacts to Danish OOH-PC...
March 14, 2017: BMC Family Practice
Tarali Devi, Yong-Min Lee, Jieun Jung, Muniyandi Sankaralingam, Wonwoo Nam, Shunichi Fukuzumi
Metal-superoxo species are involved in a variety of enzymatic oxidation reactions, and multi-electron oxidation of substrates is frequently observed in those enzymatic reactions. A Cr(III) -superoxo complex, [Cr(III) (O2 )(TMC)(Cl)](+) (1; TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), is described that acts as a novel three-electron oxidant in the oxidation of dihydronicotinamide adenine dinucleotide (NADH) analogues. In the reactions of 1 with NADH analogues, a Cr(IV) -oxo complex, [Cr(IV) (O)(TMC)(Cl)](+) (2), is formed by a heterolytic O-O bond cleavage of a putative Cr(II) -hydroperoxo complex, [Cr(II) (OOH)(TMC)(Cl)], which is generated by hydride transfer from NADH analogues to 1...
March 7, 2017: Angewandte Chemie
Filipe Natalio, Stefanie Wiese, Wolfgang Brandt, Ludger Wessjohann
Boron's unusual properties inspired major advances in chemistry. In nature, the existence and importance of boron has been fairly explored (e.g. bacterial signaling, plant development) but its role as biological catalyst was never reported. Here, we show that boric acid [B(OH)3 ] can restore chloroperoxidase activity of Curvularia inaequalis recombinant apo-haloperoxidase's (HPO) in the presence of hydrogen peroxide and chloride ions. Molecular modeling and semi-empirical PM7 calculations support a thermodynamically highly favored (bio)catalytic mechanism similarly to vanadium haloperoxidases (V-HPO) in which [B(OH)3 ] is assumedly located in apo-HPO's active site and a monoperoxyborate [B(OH)3 (OOH)(-) ] intermediate is formed and stabilized by interaction with specific active site amino acids leading ultimately to the formation of HOCl...
March 1, 2017: Chemistry: a European Journal
Kenta Arai, Ayako Tashiro, Yuui Osaka, Michio Iwaoka
We previously reported that water-soluble cyclic selenides can mimic the antioxidative function of glutathione peroxidase (GPx) in water through a simple catalytic cycle, in which the selenide (>Se) is oxidized by H₂O₂ to the selenoxide (>Se=O) and the selenoxide is reduced by a thiol back to the selenide. In methanol, however, the GPx-like activity could not be explained by this simple scenario. To look into the reasons for the unusual behaviors in methanol, monoamino-substituted cyclic selenides with a variable ring size were synthesized, and the intermediates of the catalytic cycle were characterized by means of (77)Se-NMR and LC-MS spectroscopies...
February 25, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Padmaja Krishnan, Minghui Liu, Pierre A Itty, Zhi Liu, Vanessa Rheinheimer, Min-Hong Zhang, Paulo J M Monteiro, Liya E Yu
Consecutive eight study phases under the successive presence and absence of UV irradiation, water vapor, and oxygen were conducted to characterize surface changes in the photocatalytic TiO2 powder using near-ambient-pressure X-ray photoelectron spectroscopy (XPS). Both Ti 2p and O 1s spectra show hysteresis through the experimental course. Under all the study environments, the bridging hydroxyl (OHbr) and terminal hydroxyl (OHt) are identified at 1.1-1.3 eV and 2.1-2.3 eV above lattice oxygen, respectively...
February 27, 2017: Scientific Reports
Naoki Shimizu, Hannah Bersabe, Junya Ito, Shunji Kato, Ryo Towada, Takahiro Eitsuka, Shigefumi Kuwahara, Teruo Miyazawa, Kiyotaka Nakagawa
Squalene (SQ), a main component of human sebum, is readily photooxidized by exposure to sunlight, producing six squalene monohydroperoxide (SQ-OOH) isomers. Despite its known connection to various skin conditions, few studies have sought to analyze SQ-OOH at the isomeric level. In this study, we aimed to develop a method to discriminate each SQ-OOH isomer with the use of tandem mass spectrometry (MS/MS). The six standard SQ-OOH isomers were prepared by photooxidizing SQ in the presence of rose bengal, a photosensitizer, and isolated by semipreparative high-performance liquid chromatography (HPLC)...
February 10, 2017: Journal of Oleo Science
Hasse C Knap, Solvejg Jørgensen
We have used quantum mechanical chemical calculations (CCSD(T)-F12a/cc-pVDZ-F12//M06-2X/aug-cc-pVTZ) to investigate the hydrogen shift (H-shift) reactions in acyl peroxy and hydroperoxy acyl peroxy radicals. We have focused on the H-shift reactions from a hydroperoxy group (OOH) (1,X-OOH H-shift with X = 6, 7, 8, or 9) in the hydroperoxy acyl peroxy radicals, this H-shift is a reversible reaction and it scrambles between two peroxides, hydroperoxy acyl peroxy and peroxy peroxoic acid radicals. The forward reaction rate constants of the 1,X-OOH H-shift reactions are estimated to be above 10(3) s(-1) with transition state theory corrected with Eckart quantum tunnelling correction...
February 13, 2017: Journal of Physical Chemistry. A
Nathalie Ségaud, Constance De Thomasson, Caroline Daverat, Katell Sénéchal-David, Amandine Dos Santos, Vincent Steinmetz, Philippe Maître, Jean-Noël Rebilly, Frédéric Banse, Olivia Reinaud
A heteroditopic ligand associated with a calix[6]arene scaffold bearing a tris(imidazole) coordinating site at its small rim and an amine/pyridine ligand at its large rim has been prepared, and its regioselective coordination to Zn(II) at the small rim and Fe(II) in the amine/pyridine ligand has been achieved. The heterodinuclear complex obtained displays an overall cone conformation capped by the tris(imidazole)Zn(II) moiety and bears a non-heme Fe(II) complex at its base. Each of the metal centers exhibits one labile position, allowing the coordination inside the cavity of a guest alkylamine at Zn(II) and the generation of reaction intermediates (Fe(III) (OOH) and Fe(IV) O) at the large rim...
February 24, 2017: Chemistry: a European Journal
Barbara Michiels, Van Kinh Nguyen, Samuel Coenen, Philippe Ryckebosch, Nathalie Bossuyt, Niel Hens
BACKGROUND: Annual influenza epidemics significantly burden health care. Anticipating them allows for timely preparation. The Scientific Institute of Public Health in Belgium (WIV-ISP) monitors the incidence of influenza and influenza-like illnesses (ILIs) and reports on a weekly basis. General practitioners working in out-of-hour cooperatives (OOH GPCs) register diagnoses of ILIs in an instantly accessible electronic health record (EHR) system. This article has two objectives: to explore the possibility of modelling seasonal influenza epidemics using EHR ILI data from the OOH GPC Deurne-Borgerhout, Belgium, and to attempt to develop a model accurately predicting new epidemics to complement the national influenza surveillance by WIV-ISP...
January 18, 2017: BMC Infectious Diseases
Emmanuel Giner, Lorenzo Tenti, Celestino Angeli, Nicolas Ferré
The present paper reports an original computational strategy for the computation of the isotropic hyperfine coupling constants (hcc). The algorithm proposed here is based on an approach recently introduced by some of the authors, namely, the first-order breathing orbital self-consistent field (FOBO-SCF). The approach is an almost parameter-free wave function method capable to accurately treat the spin delocalization together with the spin polarization effects while staying in a restricted formalism and avoiding spin contamination...
February 3, 2017: Journal of Chemical Theory and Computation
Shuo Zhao, Renxi Jin, Hadi Abroshan, Chenjie Zeng, Hui Zhang, Stephen D House, Eric Gottlieb, Hyung J Kim, Judith C Yang, Rongchao Jin
Electrocatalytic water splitting to produce hydrogen comprises the hydrogen and oxygen evolution half reactions (HER and OER), with the latter as the bottleneck process. Thus, enhancing the OER performance and understanding the mechanism are critically important. Herein, we report a strategy for OER enhancement by utilizing gold nanoclusters to form cluster/CoSe2 composites; the latter exhibit largely enhanced OER activity in alkaline solutions. The Au25/CoSe2 composite affords a current density of 10 mA cm(-2) at small overpotential of ∼0...
January 17, 2017: Journal of the American Chemical Society
Tao Cheng, William A Goddard, Qi An, Hai Xiao, Boris Merinov, Sergey Morozov
The sluggish oxygen reduction reaction (ORR) is a major impediment to the economic use of hydrogen fuel cells in transportation. In this work, we report the full ORR reaction mechanism for Pt(111) based on Quantum Mechanics (QM) based Reactive metadynamics (RμD) simulations including explicit water to obtain free energy reaction barriers at 298 K. The lowest energy pathway for 4 e(-) water formation is: first, *OOH formation; second, *OOH reduction to H2O and O*; third, O* hydrolysis using surface water to produce two *OH and finally *OH hydration to water...
January 9, 2017: Physical Chemistry Chemical Physics: PCCP
Grégory Durand, Marie Rosselin, Pierre-André Klein, Kamal Zéamari, Fanny Choteau, Béatrice Tuccio
Two bifunctional α-phenyl-N-cyclohexyl nitrones were synthesized with the expectation that the cyclohexyl ring will impart lipophilicity to the molecule, high reactivity to the nitronyl group, and stability to the spin adducts formed. The synthesis of the acid nitrone 4 and its corresponding tert-butyl ester 3 was initiated by a Michael reaction to introduce the cyclohexyl ring. A Zn/AcOH-mediated reduction of the nitro functionality followed by condensation onto benzaldehyde generated the nitronyl function...
December 20, 2016: Journal of Organic Chemistry
Torsten Berndt, Hartmut Herrmann, Mikko Sipilä, Markku Kulmala
The gas-phase reaction of OH radicals with isoprene has been investigated in an atmospheric pressure flow tube at 293 ± 0.5 K with special attention to the second-generation products. Reaction conditions were optimized to achieve a predominant reaction of RO2 radicals with HO2 radicals. Chemical ionization-atmospheric pressure interface-time-of-flight mass spectrometry served as the analytical technique in order to follow the formation of RO2 radicals and closed-shell products containing at least four O atoms in the molecule...
December 29, 2016: Journal of Physical Chemistry. A
Melanie J Scott, Timothy R Billiar, Detcho A Stoyanovsky
The electron spin resonance (EPR) spin-trapping technique allows detection of radical species with nanosecond half-lives. This technique is based on the high rates of addition of radicals to nitrones or nitroso compounds (spin traps; STs). The paramagnetic nitroxides (spin-adducts) formed as a result of reactions between STs and radical species are relatively stable compounds whose EPR spectra represent "structural fingerprints" of the parent radical species. Herein we report a novel protocol for the synthesis of N-tert-butylmethanimine N-oxide (EBN), which is the simplest nitrone containing an α-H and a tertiary α'-C atom...
December 12, 2016: Scientific Reports
Raquel Oliveira, Wiem Zouari, Christian Herrero, Frédéric Banse, Bernd Schöllhorn, Claire Fave, Elodie Anxolabéhère-Mallart
Reductive activation of O2 is achieved by using the [Fe(III)(F20TPP)Cl] (F20TPP = 5,10,15,20-tetrakis(pentafluorophenyl) porphyrinate) porphyrin through electrochemical reduction of the [Fe(III)(F20TPP)(O2(•-))] superoxo complex. Formation of the [Fe(III)(F20TPP)(OO)](-) peroxo species is monitored by using low-temperature electronic absorption spectroscopy, electron paramagnetic resonance, and cyclic voltammetry. Its subsequent protonation to yield the [Fe(III)(F20TPP)(OOH)] hydroperoxo intermediate is probed using low-temperature electronic absorption spectroscopy and electron paramagnetic resonance...
December 5, 2016: Inorganic Chemistry
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