- Diffusion-Kinetic Modeling of the Electron Raiolysis of Water at Elevated Temperatures
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The temperature dependence of the chemistry in the track of a fast electron in water has been examined with a deterministic diffusion-kinetic model.The model calculations suggest that there is an increase in the yields of the hydrated electron and hydroxyl radical and a decrease in the yields of molecular hydrogen and hydrogen peroxide with increasing temperature.These results are consistent with most of the experimental data.It is found that the best fit to the experimental data occurs when the radius of the initial spatial distribution of the hydrated electron is dependent on a process which scales according to an Arrhenius-like equation with an activation energy similar to that for electron movement between potential traps in water.The radii of the initial spatial distributions of all the other species appear to be independent of the temperature.The predictions of the model suggest that the initial radiation chemical yields of the reactive species are independent of temperature.An additional thermally dependent reaction for the decomposition of water is not required for the model predictions to match the experimental data.
- LaVerne, Jay A.,Pimblott, Simon M.
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- Experimental Determination of the OH Product Yield from NH2 + NO at 300 K
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The branching ratio, α = k1b/k1a, has been experimentally determined at 300 K for two product channels of the NH2 + NO reaction: -->N2 + H2O (k1a) and --> N2H + OH (k1b).The reaction was studied in a fast-flow tube reactor coupled to a modulated-beam mass spectrometer.CO was added to scavenge hydroxyl radicals via OH + CO --> CO2 + H.Separate experiments and kinetic modeling results confirm that the scavenging efficiency is near unity so that is a good measure of .The branching ratio, α = / = /, was determined from CO2+ and H2O+ ion intensities to be 0.15 at 300 K.This result is discussed as it relates to previous measurements and to the atmospheric chemistry of ammonia.
- Dolson, David A.
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- A Flash Photolysis-Shock Tube Kinetic Study of the H Atom Reaction with O2: H+O2=OH+O (962 KHO2+Ar (746 K=T=987 K)
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Rate constants for the reactions H+O2->OH+O (1) and H+O2+M->HO2+M (2) were measured under pseudo-first-order conditions by the flash photolysis-shock tube technique that employs the atomic resonance absorption detection method to monitor t.Rate data for reaction 1 were obtained over the temperature range from 962 to 1705 K, and the results are well represented by the Arrhenius expression k1(T)=(2.79+/-0.32)*10-10 exp(-16132+/-276 cal mol-1/RT) cm3 molecule-1 s-1.The mean deviation of the experimentally measured rate constants from those calculated by using this expression is +/-16percent over the stated temperature range.The recent shock tube data of Frank and Just (1693-2577 K) were combined with the present results for k1(T) to obtain the following Arrhenius expression for the overall temperature span (962-2577 K): k1(T)=(3.18+/-0.24)*10-10 exp(-16439+/-186 cal mol-1/RT) cm3 molecule-1 s-1.The mean deviation of the experimentally measured rate constants from this expression is +/-15percent over the entire temperature range.Values for the rate constant for the reverse of reaction 1 were calculated from each of the experimentelly measured k1(T) values with expressions for the equilibrium constant derived by using the least JANAF thermochemical data.These k-1(T) values were also combined with similarly derived values from the Frank and Just data.This combined data base showed that k-1(T) was essentially constant between 962 and 2577 K with an average value of 2.05*10-11 cm3 molecule-1 s-1 and a one standard deviation uncertainty of 0.42*10-11 cm3 molecule-1 s-1.Kinetic results were also derived for reaction 2 from the difference between the experimental first-order t decays and the corresponding calculated k1(T) values.The temperature span over which k2 data could be determined was limited 746 Ka slight negative temperature dependence, the magnitude of the uncertainties in the k2 results and the limited temperature span that could be covered preclude the calculation of reliable Arrhenius parameters.Instead, a simple average value may be used to represent this rate constant, k2=(7.1+/-1.9)*10-33 cm6 molecule-2 s-1, where the error limit is given at the one standard deviation level.All the results obtained are compared with those of previous investigations.
- Pirraglia, A. N.,Michael, J. V.,Sutherland, J. W.,Klemm, R. B.
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- A Study of the Reaction Li + O2 + M (M = N2, He) over the Temperature Range 267-1100 K by Time-Resolved Laser-Induced Fluorescence of Li(22PJ-22S1/2)
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We present an investigation of the recombination reaction between lithium atoms and O2 in the presence of both N2 and He as bath gases.Lithium atoms were produced by the pulsed photolysis of either LiI, LiOH, or LiO2 molecules in the presence of an excess of O2 and the bath gas.The Li atom concentration was then monitored by laser-induced fluorescence of the metal atoms at λ = 670.7 nm using a pulsed nitrogen-pumped dye laser and boxcar integration of the fluorescence signal.Termolecular behavior was demontstrated in the case of both bath gases, and absolute third-order rate constants were obtained over the temperature range 267-1100 K.A fit of these data to the form AT-n yields k(M = N2) = (4.30 +/- 1.36) * 10-30(T/300 K)-(1.02 +/- 0.06) cm6 molecule-2 s-1 and k(M = He) = (1.25 +/- 0.48) * 10-30(T/300 K)-(0.38 +/- 0.08) cm6 molecule-2 s-1.It is demontstrated that these measurements are essentially in the low-pressure limit; the rate coefficients are then extrapolated from the experimental temperature range to ambient mesospheric temperatures ( 140 K a satisfactory fit to the Troe formalism.
- Plane, John M. C.,Rajasekhar, B.
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- Decay dynamics of H2O(A1B1) excitation by two photon absorption at 354.6 nm
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Water was photolyzed at 177.3 nm via a two-photon excitation by a frequency-tripled Nd:YAG laser (354.6 nm). The complete product state distribution of the ejected OH product was determined by LIF. The OH is produced in the vibrational ground state exclusively. OH shows a Boltzmann-type rotational distribution with a temperature parameter of about 350 K. No preferred population of A- or spin-orbit states was observed.
- Mikulecky,Gericke,Comes
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- Role of Hydrogen Bonding by Thiones in Protecting Biomolecules from Copper(I)-Mediated Oxidative Damage
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The sulfur-containing antioxidant molecule ergothioneine with an ability to protect metalloenzymes from reactive oxygen species (ROS) has attracted significant interest in both chemistry and biology. Herein, we demonstrated the importance of hydrogen bonding in S-oxygenation reactions between various thiones and H2O2 and its significance in protecting the metal ion from H2O2-mediated oxidation. Among all imidazole- and benzimidazole-based thiones (1-10), ImMeSH (2) showed the highest reactivity toward H2O2 - almost 10 and 75 times more reactive than N,N′-disubstituted ImMeSMe (5) and BzMeSMe (10), respectively. Moreover, metal-bound ImMeSH (2) of [TpmCu(2)]+ (13) was found to be 51 and 1571 times more reactive toward H2O2 than the metal-bound ImMeSMe (5) of [TpmCu(5)]+ (16), and BzMeSMe (10) of [TpmCu(10)]+ (21), respectively. The electron-donating N-Me substituent and the free N-H group at the imidazole ring played a very crucial role in the high reactivity of ImMeSH toward H2O2. The initial adduct formation between ImMeSH and H2O2 (ImMeSH·H2O2) was highly facilitated (-23.28 kcal mol-1) due to the presence of a free N-H group, which leads to its faster oxygenation than N,N′-disubstituted ImMeSMe (5) or BzMeSMe (10). As a result, ImMeSH (2) showed a promising effect in protecting the metal ion from H2O2-mediated oxidation. It protected biomolecules from Cu(I)-mediated oxidative damage of through coordination to the Cu(I) center of [TpmCu(CH3CN)]+ (11), whereas metal-bound ImMeSMe or BzMeSMe failed to protect biomolecules under identical reaction conditions.
- Rai, Rakesh Kumar,Chalana, Ashish,Karri, Ramesh,Das, Ranajit,Kumar, Binayak,Roy, Gouriprasanna
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- Formation of hydroxyl radical from the photolysis of frozen hydrogen peroxide
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Hydrogen peroxide (HOOH) in ice and snow is an important chemical tracer for the oxidative capacities of past atmospheres. However, photolysis in ice and snow will destroy HOOH and form the hydroxyl radical (·OH), which can react with snowpack trace species. Reactions of ·OH in snow and ice will affect the composition of both the overlying atmosphere (e.g., by the release of volatile species such as formaldehyde to the boundary layer) and the snow and ice (e.g., by the ·OH-mediated destruction of trace organics). To help understand these impacts, we have measured the quantum yield of ·OH from the photolysis of HOOH on ice. Our measured quantum yields (Φ(HOOH → ·OH)) are independent of ionic strength, pH, and wavelength, but are dependent upon temperature. This temperature dependence for both solution and ice data is best described by the relationship ln(Φ(HOOH → ·OH)) = -(684 ± 17)(1/T) + (2.27 ± 0.064) (where errors represent 1 standard error). The corresponding activation energy (Ea) for HOOH (5.7 kJ mol-1) is much smaller than that for nitrate photolysis, indicating that the photochemistry of HOOH is less affected by changes in temperature. Using our measured quantum yields, we calculate that the photolytic lifetimes of HOOH in surface snow grains under midday, summer solstice sunlight are approximately 140 h at representative sites on the Greenland and Antarctic ice sheets. In addition, our calculations reveal that the majority of ·OH radicals formed on polar snow grains are from HOOH photolysis, while nitrate photolysis is only a minor contributor. Similarly, HOOH appears to be much more important than nitrate as a photochemical source of ·OH on cirrus ice clouds, where reactions of the photochemically formed hydroxyl radical could lead to the release of oxygenated volatile organic compounds to the upper troposphere.
- Chu, Liang,Anastasio, Cort
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- The reaction of anthracene with OH radicals: An experimental study of the kinetics between 58 and 470 K
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The first direct measurement of the reaction rate constant of a polycyclic aromatic hydrocarbon in the gas phase in the temperature range 58-470 K is reported. The reaction is OH+ anthracene and the experiment has been performed in a continuous flow Cintique de Raction en Ecoulement Supersonique Uniforme apparatus, which had to be modified for this purpose. Pulsed laser photolysis of H2 O2 has been used to generate OH radicals and laser-induced fluorescence to observe the kinetic decay of the radicals and hence determine the rate coefficients. The reaction is found to be fast, and the rate constant increases monotonically as the temperature is lowered. The rate coefficients match the expression k (cm3 molecules-1 s-1) =1.12× 10-10 (T300) -0.46.
- Goulay,Rebrion-Rowe,Le Garrec,Le Picard,Canosa,Rowe
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- Measurements of ground-state OH rotational energy-transfer rates
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We have studied rotational energy transfer (RET) in collisions of OH with the bath gases Ar, N2, O2, and H2O at 293 K. Rotationally hot OH(X2Π3/2,v″=0,N ″=1-12) was generated by photolysis of H2O2 at 266 nm, and collisional relaxation of the nascent rotational distribution was monitored by laser-induced fluorescence. The data are remarkably well described by an exponential-gap model for the matrix of state-to-state RET rate constants. For Ar, N2, and O2, RET rates are significantly faster at low N″ than high N″; for H2O, RET is approximately an order of magnitude faster than for the other bath gases, and the rate is not as strongly dependent on N″. The rates of rotationally inelastic energy transfer are similar in the X and A states, but the X-state depopulation rate constants (including nearly elastic, Λ-doublet-changing collisions) are faster than the A-state values. By comparing the depopulation rates derived from the present experiment with previous linewidth measurements, we conclude that RET is the dominant source of pressure broadening for OH microwave transitions and makes a significant contribution for ultraviolet A-X transitions. While generally good agreement is found between the present results and previous OH RET studies for both the ground and excited electronic states, some significant discrepancies are noted.
- Kliner, Dahv A.V.,Farrow, Roger L.
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- The nascent OH detection in photodissociation of 2-(bromomethyl)hexafluoro- 2-propanol at 193 nm: Laser-induced fluorescence study
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Photodissociation of 2-(bromomethyl)hexafluoro-2-propanol (BMHFP) and 3-bromo-1-propanol (BP), involving σC-BrnBr transition at 193 nm, has been investigated by measuring laser-induced fluorescence spectra of the expected OH product. The OH channel is a minor dissociation pathway with a quantum yield of 0.17 ± 0.05 in BMHFP, whereas it was not observed in BP. Partitioning of the available energy into translation, rotation, and vibration of the photoproducts has been measured by state selective detection of the nascent OH product in BMHFP. OH is produced mostly in the ground vibrational level (v″ = 0), with a rotational distribution being characterized by a temperature of 465 ± 25 K. But, a significant fraction of the available energy of 30.2 kcal mol-1 is partitioned into translation of OH (14.6 kcal mol-1). The OH(v″ = 0, J″) populations in the spin-orbit states as well as in the Λ-doublet states are statistical. A plausible mechanism of OH formation on excitation of BMHFP at 193 nm is suggested, with the primary reaction channel being elimination of Br atom by direct C-Br bond dissociation from a repulsive surface. The Br radical is detected using (2 + 1) resonance-enhanced multiphoton ionization (REMPI) at ~234 nm. It is produced in both the ground (2P3/2) and the excited (2P1/2) spin-orbit states with the relative quantum yield of the latter to be 0.36. The co-fragment of Br undergoes secondary C-O bond dissociation to produce OH and F3C-C(CH 2)-CF3, with the reaction having a barrier located in the exit channel. In this two-step three-body dissociation process, a major fraction of the available energy is released into translation (〈fT〉 ~ 0.75), resulting from an impulsive C-Br bond dissociation in the primary step and presence of an exit barrier in the secondary process. Experimental results combined with theoretical calculations provide a clear picture of the dynamics of OH formation from BMHFP at 193 nm. In addition, the energetics of another channel, competing with OH, have been calculated from the primary product F3C-C(CH2)(OH)-CF3. In contrast to BMHFP, the OH product could not be observed from the photolysis of 3-bromo-1-propanol (another saturated halogenated propanol) at 193 nm under the detection limit of the present experimental condition, although it has a higher absorption cross-section at 193 nm.
- Indulkar, Yogesh N.,Upadhyaya, Hari P.,Kumar, Awadhesh,Waghmode, Suresh B.,Naik, Prakash D.
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- Relaxation of H2O from its |04〉- vibrational state in collisions with H2O, Ar, H2, N2, and O2
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Collisional relaxation of water molecules from the highly excited |04- vibrational states in collisions with water, argon, hydrogen, nitrogen and oxygen was analyzed. It was found that delay between the pulse from the pump laser and those from
- Barnes, Peter W.,Sims, Ian R.,Smith, Ian W.M.
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- A novel catalyst of Cu-Bi-V-O complex in phenol hydroxylation with hydrogen peroxide
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A new catalyst of Cu-Bi-V-O complex oxide was hydrothermally synthesized in a Bi2O3-V2O5-CuO-H2O system, and its was found that this compound is very active for phenol hydroxylation by H2O2, which was comparable to titanium silicalite (TS-1). Investigation using the ESR spin-trapping technique on the catalyst indicated that Cu2+ species are major active sites, and hydroxyl radicals are the major active intermediates in phenol hydroxylation. The key factors for phenol conversion and product selectivity were reaction temperature, solvent, phenol/H2O2 molar ratio, reaction time, catalyst amount, and method of H2O2 addition.
- Sun, Jianmin,Meng, Xiangju,Shi, Yanhui,Wang, Runwei,Feng, Shouhua,Jiang, Dazhen,Xu, Ruren,Xiao, Feng-Shou
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- Formation of HO2 and OH in photolytically initiated oxidation of dimethyl ether
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Time-resolved measurements of HO2 and OH have been conducted in 355 nm photolysis of dimethyl ether/Cl2/O2 mixture at elevated temperature, using near-infrared frequency modulation spectroscopy. A part of OH was found to be produced at a timescale of several microseconds by the methoxymethyl with O2 reaction, while HO2 is formed mainly in milliseconds with the yield increasing up to 60% between 500 and 600 K. It was rationalized that HO2 is not a direct product of the O2 adduct decomposition, but a secondary product through HCHO + OH reaction. Another pathway through HCO formation from the adduct is also discussed.
- Suzaki, Kotaro,Kanno, Nozomu,Tonokura, Kenichi,Koshi, Mitsuo,Tsuchiya, Kentaro,Tezaki, Atsumu
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- Gas-Phase Hydroxyl Radical Generation by the Surface Reactions over Basic Metal Oxides
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Hydroxyl radical desorption in the heterogeneous catalytic reactions of water or hydrogen with oxygen was examined by laser-induced fluorescence spectroscopy. The catalytic activities of Pt, Al2O3, and basic metal oxides (MgO, CaO, SrO, BaO) supported on Al2O3 were studied in the pressure range 0.1-10 Torr and the temperature range 1100-1300 K. In the case of OH generation from water, the catalytic activities of Pt and all oxides except Al2O3 were very high and the OH concentration reached the equilibrium value within a residence time of 4 ms. In the case of hydrogen oxidation, differences in the catalytic behavior were clearly observed. The surface reaction mechanisms and the effects of Al2O3 and MgO on gas-phase ignition are discussed.
- Noda, Suguru,Nishioka, Masateru,Harano, Azuchi,Sadakata, Masayoshi
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- PRODUCTION OF OH ON POLYCRYSTALLINE NICKEL STUDIED BY THERMAL DESORPTION/LASER-INDUCED FLUORESCENCE
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The production of hydroxyl radical following either the reaction of H2/O2 mixtures or the dissociation of H2O on polycrystalline nickel has been studied in a flow system.The hydroxyl radicals were detected in the gas phase by laser-induced fluorescence (LIF) following desorption from the catalyst surface at temperatures above 850 K.The apparent activation energy for OH desorption from nickel varied from 26 to 40 kcal/mol depending upon the O/H ratio.The effect of the partial pressure of O2 and H2 on the OH production rate was measured and a mechanism to explain these results is proposed.The reaction of CO+H2 over polycrystalline nickel was also studied.However, no OH radicals were detected desorbing from the surface at temperatures up to 1350 K.
- Keiser, J. T.,Hoffbauer, M. A.,Lin, M. C.
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- High temperature rate coefficient measurements of H + O2 chain-branching and chain-terminating reaction
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Rate coefficients for H + O2 → OH + O (R1) and H + O2 + M → HO2 + M (R9) were measured via OH absorption behind reflected shock waves, being: k1 = 6.73 × 1015 T-0.50 e
- Hwang,Ryu, Si-Ok,Witt, K.J. De,Rabinowitz
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- Oxidation of Aqueous Polyselenide Solutions. A Mechanistic Pulse Radiolysis Study
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The oxidation of aqueous polyselenide solutions was studied by pulse radiolysis in the presence of N2O at pH 12.3; the hydroxyl radical OH was the predominant oxidant, while hydrogen selenide anions HSe- and triselenide dianions Se32- were the major selenide species in the starting solution. The progress of the oxidation was monitored by optical spectroscopy. Transient polyselenides appeared immediately after the electron pulse and rapidly proceeded to form adducts with HSe-, i.e., HSe22- and H2Se2-, and a fairly long-lived intermediate that was identified as the diselenide radical anion Se2-. These radicals recombine to give eventually the tetraselenide dianion, Se42-.
- Goldbach, Andreas,Saboungi, Marie-Louise,Johnson,Cook, Andrew R.,Meisel, Dan
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- Vibrationally mediated dissociation dynamics of H2O in the vOH=2 polyad
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The 193 nm photodissociation dynamics of gas-phase H2O molecules was examined from selected rotational and vibrational quantum states within the vOH=2 polyad. Data suggest a somewhat more restricted regime of applicability for the spectator model, specifically for vibrational states of H2O at relatively high levels of local mode excitation.
- Nizkorodov, Sergey A.,Ziemkiewicz, Michael,Myers, Tanya L.,Nesbitt, David J.
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- OH detection by absorption of frequency-doubled diode laser radiation at 308 nm
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Radiation at 308 nm has been obtained by frequency doubling the output of a commercial diode laser cooled to 165 K. A single pass through a crystal of LiIO3 converted 1 mW of 616 nm radiation to 50 pW of UV, and this was used to detect the OH radical in absorption in a flow tube. Possible extensions of the method for detection of OH in the atmosphere are discussed.
- Barry, Hugh R.,Bakowski, Ben,Corner, Laura,Freegarde, Tim,Hawkins, Oliver T.W.,Hancock, Gus,Jacobs, Robert M.J.,Peverall, Robert,Ritchie, Grant A.D.
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- An intense pulsed electrical discharge source for OH molecular beams
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In this Letter we describe and characterize a pulsed DC discharge source for a molecular beam of OH radicals. The absolute line-integrated OH density has been measured by cavity ring-down spectroscopy, while the off-axis distribution of the radicals has been determined by 1-dimensional laser-induced fluorescence spectroscopy. Combining both measurements the total OH centerline flux at the maximum of the pulse was determined to be (2.2±0.1)×1017 molecules/sr s. No anomalous population distribution was found for the Λ-doublet components of the rotational ground state.
- Van Beek,Ter Meulen
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- Sinomenine Protects PC12 Neuronal Cells against H2O2-induced Cytotoxicity and Oxidative Stress via a ROS-dependent Up-regulation of Endogenous Antioxidant System
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Sinomenine (SN), a purified alkaloid from Chinese herb Sinomenium acutum that was used preferentially in the treatment of rheumatoid diseases, has exerted neuroprotective effects and anti-inflammatory properties in many previous studies. Some studies have revealed that the antioxidant property of SN, acting mainly through inhibiting NADPH oxidase activation, was involved in the beneficial effects of SN. However, SN belongs to the family of dextrorotatory morphinan analogues, which may initiate elevation of reactive oxygen species (ROS) levels. Thus in the present report, we conducted studies to examine its impact and mechanism on the resistance of PC12 neuronal cells to oxidative stress. Precondition with SN (0.1–5?μM) for 12?h significantly decreased H2O2-induced cytotoxicity and remarkably alleviated oxidative injury. However, SN exhibited little direct free radical scavenging property in vitro and induced “appropriate” production of ROS in PC12 cell. Interestingly, the SN-triggering ROS production served as a signal to activate the Nrf2 antioxidant system including Nrf2, HO-1, and NQO-1, which was inhibited by the antioxidant trolox. Furthermore, Nrf2 knockdown largely attenuated the beneficial effects of SN precondition on oxidative stress. In conclusion, our findings suggested that SN increased the resistance to oxidative stress in neuronal cells via a ROS-dependent up-regulation of endogenous antioxidant system, and this mechanism may be involved in the neuroprotection of SN.
- Fan, Hua,Shu, Qing,Guan, Xinlei,Zhao, Jiegang,Yan, Junqiang,Li, Xiangming,Liu, Jiangbo,Jia, Zhaohui,Shi, Jian,Li, Juan
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- Photofragment angular momentum polarization from dissociation of hydrogen peroxide near 355 nm
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The measurements on the dissociation of hydrogen peroxide (H2O2) around 355 nm, in the long-wavelength tail of the ultraviolet (UV) absorption spectrum were reported. Measurements of angular momentum polarization give a detailed picture of state-specific dissociation from nonequilibrium configuration of the ground-state parent molecule occurs. In addition, evidence for interference between multiple dissociating electronic states was reported as well.
- Alexander, Andrew J.
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- Low catalytic activity of the Cu(II)-binding motif (Xxx-Zzz-His; ATCUN) in reactive oxygen species production and inhibition by the Cu(i)-chelator BCS
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The catalytic redox activity of Cu(ii) bound to the motif NH2-Xxx-Zzz-His (ATCUN) with ascorbate and H2O2/O2 is very low and can be stopped via Cu(i)-chelation. This impacts its application as an artificial Cu-enzyme to degrade biomolecules via production of reactive oxygen species in a Cu(i)-chelator rich environment like the cytosol.
- Santoro, Alice,Walke, Gulshan,Vileno, Bertrand,Kulkarni, Prasad P.,Raibaut, Laurent,Faller, Peter
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- Temperature-dependent kinetics of the gas-phase reactions of OH with Cl2, CH4, and C3H8
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The reactions of OH with molecular chlorine (reaction 1), methane (reaction 2), and propane (reaction 3) have been studied experimentally using a pulsed laser photolysis/pulsed-laser-induced fluorescence technique over wide ranges of temperatures (297-826, 298-1009, and 296-908 K, respectively) and at pressures between 6.68 and 24.15 kPa. The rate coefficients obtained for reactions 1-3 demonstrate no dependence on pressure and exhibit positive temperature dependences that can be represented with modified three-parameter Arrhenius expressions within their corresponding experimental temperature ranges: k 1 = 3.59 × 10-16 T1.35 exp(-745 K/T) cm3 molecule-1 s-1, k2 = 3.82 × 10-19 T2.38 exp(-1136 K/T) cm3 molecule-1 s-1, and k3 = 6.64 × 10 -16 T1.46 exp(-271 K/T) cm3 molecule -1 s-1. For the OH + Cl2 reaction, the potential energy surface has been studied using quantum chemical methods, and a transition-state theory model has been developed on the basis of calculations and experimental data. Model predictions suggest OH + Cl2 → HOCl + Cl as the main channel of this reaction. The model results in the expression k1 = 1.35 × 10-16 T1.50 exp(-723 K/T) cm3 molecule-1 s-1 for the temperature dependence of the reaction 1 rate coefficient extrapolation outside the experimental range to low temperatures down to 200 K and to high temperatures up to 3000 K. A temperature dependence of the rate coefficient of the HOCl + Cl → OH + Cl2 reaction has been derived on the basis of the experimental data, modeling, and thermochemical information.
- Bryukov, Mikhail G.,Knyazev, Vadim D.,Lomnicki, Slawomir M.,McFerrin, Cheri A.,Dellinger, Barry
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- Rate Constants for the Reactions OH + HOCl -> H2O + ClO and H + HOCl -> Products
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A new laboratory source of gaseous hypochlorous acid (HOCl) has been used in two kinetics investigations in a mass spectrometry-resonance fluorescence discharge flow system.Two potential removal reactions of stratospheric HOCl were studied.The rate constant for the reaction OH + HOCl -> H2O + ClO (1) at 298 K was found to be lower than the NASA estimate by a factor of about 2-12; a value in the range (1.7-9.5)E-l3 cm3 molecule-1 s-1 for k1 is reported here.The reaction of Cl2O + OH interfered in the study of k1 and was the subject of a preliminary investigation.Its rate constant was determined to be (9.4 +/- 1.0) E-12) cm3 molecule-1 s-1 at 298 K.The rate constant for the reaction H + HOCl -> products (2) was determined to be (5.0 +/- 1.4)E-12 cm3 molecule-1 s-1 at 298 K.Although branching ratios for three possible product channels could not be determined, OH was identified as a product.The results of this work imply that reactions 1 and 2 are not competitive with direct photolysis in the removal of HOCl from the stratosphere.
- Ennis, C. A.,Birks, J. W.
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- Vibrational relaxation of OH by oxygen atoms
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The collisional removal of OH(v = 1) by O(3P) atoms is investigated. OH is generated by 193 nm photolysis of H2O 2, and O(3P) atoms are generated by a microwave discharge in O2 diluted in Ar. OH(v = 0 and 1) concentrations are monitored by laser-induced fluorescence vs. the time after the photolysis laser pulse. From comparison of these concentrations with kinetic simulations, the room-temperature total removal rate constant for OH(v = 1) in collisions with O(3P) is determined to be (3.9 ± 0.6) × 10 -11 cm3 molecule-1 s-1. This value is slightly larger than the OH(v = 0)-O(3P) reaction rate constant, but the difference is within the experimental uncertainty.
- Khachatrian, Ani,Dagdigian, Paul J.
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- Correlation between Gas-Phase and Solution-Phase Reactivities of Hydroxyl Radicals toward Saturated Organic Compounds
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The gas-phase and aqueous-solution-phase reactivities of hydroxyl radicals with a wide variety of organic compounds are compared.When kinetic data are available for the same reaction occuring in both phases, this comparison provides useful information about the reaction mechanism.Through this comparison we can demonstrate a linear correlation between the gas/solution-phase OH reactivities for numerous saturated organic compounds.This empirical relationship can be used together with mechanistic information to estimate the OH reactivity in one phase from the measured rate constant in the other.In order to develop and extend the correlation, we have used the flash photolysis resonance fluorescence technique to measure rate constants for the gas-phase reactions of OH radicals with methanol-d4, ethanol-d6, 2-chloroethanol, 2,2,2-trichloroethanol, 2,2,2-trifluoroethanol, acetone-d6, 1,1,1-trifluoroacetone,and 1,2-butylene oxide at 298 K.These results are reported herein.
- Wallington, Timothy J.,Dagaut, Philippe,Kurylo, Michael J.
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- Hydrogen-oxygen reactions behind shock waves assisted by OH(2Σ+) formation
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The results of the OH(2Σ+) → OH(2Π) luminescence registration at 1000≤ T≤2500 K and 2.0≥p≥0.3 atm during the ignition-combustion process behind incident shock waves in (2H2 + O 2) + Ar mixtures were s
- Skrebkov,Karkach,Vasil'ev,Smirnov
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- Mechanism of the O(3P) + H2S Reaction. Abstraction or Addition?
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The question of whether the reaction of O(3P) with H2S proceeds by absraction, O + H2S -> OH + SH, or by addition, O + H2S -> * -> products, was investigated by quntitative gas chromatographic analysis of N2 and CO2 produced in mercury-photosensitized mixtutes of N2O, H2S, and CO.Reactant pressures were chosen so that less than 5 percent of the O atoms formed from N2O would react with CO, but a large fraction of any OH radicals formed from reaction of O with H2S would react with CO to form CO2.The CO2 yields were compared with those calculated from an expression derived by steady-state treatment of a simple mechanism.The CO2 yields indicated that 52 percent of the O + H2S reaction proceeds by abstraction, although it could be as much as 100 percent depending on the extent of H2S2 formation by SH radical recombination and the rate constant for the reaction of O atoms with H2S2.
- Singleton, Donald L.,Paraskevopoulos, George,Irwin, Robert S.
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- State resolved photodissociation of vibrationally excited water: Rotations, stretching vibrations, and relative cross sections
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The state resolved photodissociation of highly vibrationally excited water molecules using laser induced fluorescence detection of the OH product demonstrates the control that the initially selected state exerts over product state populations.These vibrationally mediated photodissociation experiments, in which one photon prepares a highly vibrationally excited molecule and a second photon dissociates it, determine the role of overall rotations and of O-H stretching vibrations as well as measure the relative cross section for the photodissociation of water.The rotational state of the vibrationally excited water molecule governs the rotational state of the OH product of the dissociation, in agreement with ab initio calculations and previous measurements on single rotational states excited in the fundamental asymmetric stretching vibration band.The initially selected vibrational state of the water molecule determines the vibrational energy disposal in the products, which agrees with a simple qualitative model based on the pattern of the initially selected vibrational wave function.Dissociating vibrational states with similar energies but very different nuclear motions produces dramatically different product vibrational state populations.The vibrational energy initially present in the surviving bond primarily appears as vibrational excitation of the product.Dissociation of the 04>- state produces no vibrationally excited OH, but dissociation of the 13>- state produces mostly vibrationally excited products.These qualitative notions agree well with recently detailed ab initio calculations.The relative photodissociation cross section of the highly vibrationally excited molecule shows structure over the wavelength range of 218.5 to 266 nm that reflects the nodal pattern of the intermediate vibrational state in the dissociation and confirms the predictions of theoretical calculations.
- Wal, R. L. Vander,Scott, J. L.,Crim, F. F.
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- Low temperature relaxation of OH in the X2U and a2Σ states in an argon free-jet
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Low temperature (translational temperatures below 10 K) relaxation of OH in the X 2Π and A 2Σ states has been studied in an argon free jet. We determine upper limits on υ = 1 relaxation in the X 2Π manifold from laser induced fluorescence (LIF). We measure absolute relaxation rate coefficients for υ = 2(N), υ = 1(N), and υ = 0(N) levels in the A 2Σ state manifold. In addition, from comparison of the dispersed LIF we obtain state-to-state rate coefficients for υ = 1, N=0 and N = 1 going to υ′ = 0,N′ levels in the A 2Σ manifold. Bimolecular rate coefficients are reported which are all much greater than similar measurements at room temperature. Rates for vibrational relaxation at these low temperatures are 5.7(±0.7) × 10-1 cm3/s for υ(2-1) relaxation, 3.2 (± 1) × 10-10 cm3/s for υ(1-0) relaxation, and we report rotational relaxation rates for N = 1 and 2 of υ = 0, 1 and 2 excited states, all near the collision limited values.
- Ahern, Michael M.
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- Dynamics of H2O2 photodissociation: OH product state and momentum distribution characterized by sub-Doppler and polarization spectroscopy
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Hydrogen peroxide has been optically excited at a wavelength of 266 nm and the OH photofragment completely characterized by Doppler and polarization spectroscopy using the laser-induced fluorescence technique.The entire internal state distribution (vibration, rotation, spin, and A components), translational energy, angular distribution, rotational alignment, and vector correlations between rotational and translation motions of OH products is measured.The hydroxyl radicals are formed in the X2Π3/2,1/2 ground state with 90percent of the available energy (248 kJ/mol) being released as OH recoil translation.The angular distribution is nearly a sin2θ distribution about the electric vector of the photolysis laser.The internal motion of OH is vibrationally cold (no vibrationally excited OH was found) while the rotational excitation in v = 0 can be described by a Boltzmann distribution with a temperature parameter of Trot = (1530 +/- 150) K.The two spin states are found to be populated nearly statistically, in contrast to the A components which show an increasing inversion with increasing OH rotation.The observed profiles of recoil Doppler broadened spectral lines are strongly dependent on the nature of the transition, the excitation-detection geometry, and the relative polarizations of the dissociating and analyzing laser light.However, the line intensities show only a minor dependence on geometry and polarization indicating a low alignment of OH photofragments (A0(2)0.1).For the first time the vector correlation between product rotational and translational motions was analyzed and evaluated in terms of the three bipolar moments β02(20), β00(22), and β02(22).The bipolar moment β02(20) corresponds to the conventionally defined anisotropy parameter β = 2β02(20) = -0.71.The angular distribution peaks in the direction perpendicular to the electric vector of the dissociating laser light, indicating the predominant electronic excited state in H2O2 being of 1A symmetry.The moment β00(22) increases with JOH showing a bias towards vOH and JOH being parallel to one another.The moment β00(22) is a measure of the mutual correlation of the fragment translational and rotational vectors and the transition dipole vector W in the parent molecule.The positive value of this moment 02(22) = 0.11> indicates that the expectation value of y2> should be very small when μ is parallel to the z axis and vOH perpendicular to μ (x axis). X2> originates in the torsional motion in the H2O2 parent molecule, while z2> reflects the bending vibration of nearly planar H2O2 where the H atoms are in the trans position.
- Gericke, Karl-Heinz,Klee, Stefan,Comes, Franz Josef,Dixon, Richard N.
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- Spin-Trapping Studies on the Reaction of Iron Complexes with Peroxides and the Effects of Water-Soluble Antioxidants
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Using ESR spin-trapping techniques we measured the levels of free radical species generated from six different systems (hypoxanthine-xanthine oxidase, iron(II)-hydrogen peroxide, iron(III)-hydrogen peroxide, iron(II)-t-butyl hydroperoxide, iron(III)-t-but
- Kohno, Masahiro,Yamada, Masako,Mitsuta, Keiichi,Mizuta, Yokio,Yoshikawa, Toshikazu
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- State-to-state photodissociation of the fundamental symmetric stretch vibration of water prepared by stimulated Raman excitation
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The state-to-state photodissociation at 193 nm of the fundamental symmetric stretch vibration of water, H2O (1,0,0), is studied.Stimulated Raman excitation and coherent anti-Stokes Raman scattering are used to prepare and detect, respectively, particular rotational states of H2O (1,0,0).Laser induced fluorescence is used for monitoring the OH species which are formed from particularly selected rotational states of the H2O (1,0,0) and also from photodissociation of all accupied rotational states of the ground vibrational state, H2O (0,0,0), at room temperature.The cross section for photodissociation from a particular rotation of H2O (1,0,0) at 193 nm is found to be ca. 550 times greater than that for H2O (0,0,0).The formation of the OH product in different rotational, Λ-doublet and spin-orbit states is analyzed for the photodissociation of H2O (0,0,0) and for the photodissociation of the 101, 110 + 111, 212 + 211, and 303 rotational states of H2O (1,0,0).The rotational distribution of the OH resulting from photodissociation of H2O (1,0,0) shows a structured distribution that is dependent on the particular rotation of the vibrationally excited state, while that resulting from photodissociation of H2O (0,0,0) presents a smooth distribution.The Λ-doublet ratio in the two spin-orbit states shows preference of the A component for photodissociation from the above rotational states of H2O (1,0,0), while only a small preference at high N is observed for photodissociation from the ground vibrational state.The results are compared to available theoretical calculations based on the Franck-Condon model and show reasonable agreement between experiment and theory.
- David, D.,Strugano, A.,Bar, I.,Rosenwaks, S.
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- Bond-selective photofragmentation of jet-cooled HOD at 193 nm: Vibrationally mediated photochemistry with zero-point excitation
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Photofragment yields are reported for supersonically cooled H2O, D2O, and HOD via one photon, 193 nm photolysis in a slit jet expansion, with OH and OD fragments monitored by laser induced fluorescence methods. Detailed analysis of the dependence of OH vs OD photofragment signals on isotopic composition is used to extract relative photolysis cross sections and branching ratios for bond-selective cleavage in HOD, H2O, and D2O samples. Specified relative to the 193 nm cross sections for H2O→H+OH, the ratios are 0.392(20), 0.032(20), and 0.0157(19) for (i) HOD→H+OD, (ii) HOD→D+OH and D2O→D+OD channels, respectively. Specifically, these results indicate a propensity for H-OD vs D-OH bond cleavage in HOD of 12(8):1. This strong H/D isotopic selectivity reflects extreme non-Franck-Condon photolysis out of classically of forbidden regions of the ground-state wave function, i.e., bond-selective photochemistry mediated solely by zero-point vibrational excitation. However, when compared with theoretical predictions from full three-dimensional quantum scattering calculations on the ground (X1A1) and excited (A1B1) potential-energy surfaces (PES) of water, the observed HOD branching ratio is found to be too low by an order of magnitude. These results provide additional evidence that photodissociation of water in the extreme non-Franck-Condon region is not adequately explained by current theoretical models and suggest that contributions from other electronic surfaces may be important.
- Plusquellic, David F.,Votava, Ondrej,Nesbitt, David J.
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- Kinetics and Mechanism of the Reaction of OH with CS2 under Atmospheric Conditions
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A pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to study the reaction of OH with CS2 in the presence of He, N2, air, and O2 buffer gases and over the temperature range 250-350 K.In the absence of O2, evidence for rapid, reversible formation of a CS2OH adduct is observed.Analysis of observed OH temporal profiles gives the forward and reverse rates of adduct formation and hence the equilibrium constant.A heat of reaction of -9.9 +/- 1.2 kcal mol-1 is obtained from the temperature dependence of the equilibrium constant.The temperature dependence of the bimolecular rate coefficient for the forward addition reaction in 680 Torr of N2 + O2 is well-represented by the Arrhenius expression 6.9 * 10-14 exp(1150/T) cm3 molecule-1 s-1.A rapid reaction of OH with CS2 is observed in the presence of O2, confirming the observations reported in previous competitive rate studies.The observed bimolecular rate constant (kobsd) for the OH + CS2 reaction at 295 K in 700 Torr of air is found to be (1.5 +/- 0.1) * 1012 cm3 molecule-1 s-1; kobsd increases dramatically with decreasing temperature.All experimental observations are consistent with a simple three-step reaction mechanism: adduct formation followed by adduct decomposition in competition with an adduct + O2 reaction.Analysis of our data using a steady-state approximation based on the above three-step mechanism leads to a rate coefficient of (2.9 +/- 1.1) * 1014 cm3 molecule-1 s-1 for the adduct + O2 reaction.
- Hynes, A. J.,Wine, P. H.,Nicovich, J. M.
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- Vibrational relaxation of OH (X 2Πi, v=2)
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Vibrational relaxation rates for the v=2 level of the X 2Πi state of the OH radical have been measured in a low pressure flow system, using a novel two-laser pump-and-probe technique.The OH is prepared in the v=2 level by overtone pu
- Rensberger, Karen J.,Jeffries, Jay B.,Crosley, David R.
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- Pressure dependence of the absolute rate constant for the reaction OH+C2H2 from 228 to 413 K
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The pressure dependence of absolute rate constants for the reaction of OH+C2H2-> products has been examined at five temperatures ranging from 228 to 413 K.The experimental technique which was used is flash photolysis-resonance fluorescence (FP-RF).OH was produced by water photolysis and hydroxyl resonance fluorescent photons were measured by multiscaling techniques.The results indicate that the low pressure bimolecular rate constant is ca.4*10-13 cm3molecule-1s-1 over the temperature range studied.A substantial increase in the bimolecular rate constant withan increase in pressure was observed at all temperatures except 228 K.This indicates the importance of initial adduct formation and subsequent stabilization.The high pressure results are well represented by the Arrhenius expression (kbi)infinite=(6.83+/-1.19)*10-12 exp(-646+/-47/T) cm3molecule-1s-1.The present results are compared to previous investigations and are theoretically discussed.The implications of these results on modeling of terrestrial and planetary atmospheres and also in combustion chemistry are discussed.
- Michael, J. V.,Nava, D. F.,Borkowski, R. P.,Payne, W. A.,Stief, L. J.
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- Energy transfer from metastable electronically excited N2, Ar, Kr, and Xe to CH3OH, H2O2, CH3NH2, and N2H4
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The products of the reactions of metastable N2(A3Σu+) with the isoelectronic molecules CH3OH, H2O2, CH3NH2, and N2H4 have been studied using the discharge-flow technique, coupled with atomic resonance fiuorescence and laser induced fluorescence detection.In the reaction with H2O2, the weak central bond is broken efficiently, but in the other reactions, scission of the central bond is unimportant compared to that of the stronger terminal X-H bonds.The behavior for all four reagent molecules parallels their UV photochemistry, but contrasts with IR multiphoton dissociation of CH3OH and CH3NH2.The reactions of N2(A ) appear to parallel those of the excited metastable noble gases Ar(3P0.2), Kr(3P2), and Xe(3P2) , but scaled to the lower energy of N2(A) .
- Tao, Wen,Golde, Michael F.,Ho, Grace H.,Moyle, Alfred M.
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- Low-Temperature Kinetics of Reactions of OH Radical with Ethene, Propene, and 1-Butene
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The kinetics of the reactions of the OH radical with ethene (k 1), propene (k2), and 1-butene (k3) are studied over a temperature range of T = 96-296 K. The low-temperature environment is provided by a pulsed Laval nozzle supersonic expansion of nitrogen with admixed radical precursor and reactant gases. The OH radicals are produced by pulsed photolysis of H2O2 at 248 nm. Laser-induced fluorescence of the OH radicals excited in the (1,0) band of the A2σ+-X2∏i transition is used to monitor the OH decay kinetics to obtain the bimolecular rate coefficients. At T = 296 K, the rate constants k1, k2, and k3 are also measured as a function of total pressure. The room-temperature falloff parameters are used as the basis for extrapolation of the low-temperature kinetic data, obtained over a limited range of gas number density, to predict the high-pressure limits of all three rate coefficients at low temperatures. The temperature dependence of the measured high-pressure rate constants for T= 96-296 K can be expressed as follows: k1,∞ = (8.7 ± 0.7) × 10-12(T/300) (-0.85±0.11) cm3 molecule-1 s -1; k2,∞ = (2.95 ± 0.10) × 10 -11(T/300)(-1.06±0.13) cm3 molecule -1 s-1; k3,∞ = (3.02 ± 0.15) × 10-11(T/300)(-1.44±0.10) cm3 molecule-1 s-1. All three high-pressure rate constants show a slight negative temperature dependence, which is generally in agreement with both low-temperature and high-temperature kinetic data available in the literature. Implications to the atmospheric chemistry of Saturn are discussed. Incorporating the new experimental data on k1 in photochemical models of Saturn's atmosphere may significantly increase the predicted rate of photochemical conversion of H2O into C-O containing molecules.
- Vakhtin, Andrei B.,Murphy, James E.,Leone, Stephen R.
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- Geminate recombination of hydroxyl radicals generated in 200 nm photodissociation of aqueous hydrogen peroxide
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The picosecond dynamics of hydroxyl radicals generated in 200 nm photoinduced dissociation of aqueous hydrogen peroxide have been observed through their transient absorbance at 266 nm. It is shown that these kinetics are nearly exponential, with a decay time of ca. 30 ps. The prompt quantum yield for the decomposition of H2O2 is 0.56, and the fraction of hydroxyl radicals escaping from the solvent cage to the water bulk is 64-68%. These recombination kinetics suggest strong caging of the geminate hydroxyl radicals by water. Phenomenologically, these kinetics may be rationalized in terms of the diffusion of hydroxide radicals out of a shallow potential well (a solvent cage) with an Onsager radius of 0.24 nm.
- Crowell, Robert A.,Lian, Rui,Sauer Jr., Myran C.,Oulianov, Dmitri A.,Shkrob, Ilya A.
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- Measurement of orientation and alignment moment relaxation by polarization spectroscopy: Theory and experiment
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The measurement of orientation and alignment moment relaxation was discussed using polarization spectroscopy. The influences of Doppler motion, velocity-changing collisions, decay of population, orientation and alignment, and nuclear hyperfine depolarization on the calculated PS signal were also studied. The measurements were found to be analyzed using linearly polarized pump light on the Q1(2.5) transition of the OH A 2σ+ -X2π (0,0) band with He as the collision partner. Analysis shows that the collisional depolarization of rotational alignment was rapid, with a rate twice that of population transfer.
- Costen, Matthew L.,Crichton, Hilary J.,McKendrick, Kenneth G.
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- Effects of substituent and external pressure on spin trapping rates of carbon dioxide anion, sulfur trioxide anion, hydroxyl, and ethyl radicals with various PBN- and DMPO-type spin traps
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Using a competitive trapping method employing two different traps, the trapping rates of anionic radicals (CO2-· and SO3-·), hydroxyl, and ethyl were quantified for various PBN- and DMPO-type traps. We have examined the characteristic effects of substituent and external pressure on the spin trapping of anionic radicals and compared with those of neutral radicals such as ethyl and hydroxyl radicals. In DMPO-type traps, the effects of substituent on trapping rates of two anionic radicals were small compared with that of C2H5·. In PBN-type traps, the large effects of substituent on trapping rates of CO2-· and C2H5· were observed. Further, the activation volumes determined from the pressure dependence experiments for competitive reactions show a difference in pressure behavior between the two trapping reactions, and enable us to speculate on the reaction mechanism of substituted PBN and DMPO traps for anionic radicals.
- Sueishi, Yoshimi,Miyazono, Keitaro,Kozai, Kazuki
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- Catalytic patch with redox Cr/CeO2 nanozyme of noninvasive intervention for brain trauma
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Traumatic brain injury (TBI) is a sudden injury to the brain, accompanied by the production of large amounts of reactive oxygen and nitrogen species (RONS) and acute neuroinflammation responses. Although traditional pharmacotherapy can effectively decrease the immune response of neuron cells via scavenging free radicals, it always involves in short reaction time as well as rigorous clinical trial. Therefore, a noninvasive topical treatment method that effectively eliminates free radicals still needs further investigation. Methods: In this study, a type of catalytic patch based on nanozymes with the excellent multienzyme-like activity is designed for noninvasive treatment of TBI. The enzyme-like activity, free radical scavenging ability and therapeutic efficacy of the designed catalytic patch were assessed in vitro and in vivo. The structural composition was characterized by the X-ray diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy technology. Results: Herein, the prepared Cr-doped CeO2 (Cr/CeO2) nanozyme increases the reduced Ce3+ states, resulting in its enzyme-like activity 3-5 times higher than undoped CeO2. Furthermore, Cr/CeO2 nanozyme can improve the survival rate of LPS induced neuron cells via decreasing excessive RONS. The in vivo experiments show the Cr/CeO2 nanozyme can promote wound healing and reduce neuroinflammation of mice following brain trauma. The catalytic patch based on nanozyme provides a noninvasive topical treatment route for TBI as well as other traumas diseases. Conclusions: The catalytic patch based on nanozyme provides a noninvasive topical treatment route for TBI as well as other traumas diseases.
- Zhang, Shaofang,Liu, Ying,Sun, Si,Wang, Junying,Li, Qifeng,Yan, Ruijuan,Gao, Yalong,Liu, Haile,Liu, Shuangjie,Hao, Wenting,Dai, Haitao,Liu, Changlong,Sun, Yuanming,Long, Wei,Mu, Xiaoyu,Zhang, Xiao-Dong
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p. 2806 - 2821
(2021/02/03)
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- A CaO2@Tannic Acid-FeIII Nanoconjugate for Enhanced Chemodynamic Tumor Therapy
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Chemodynamic therapy (CDT) is an effective tumor treatment strategy in which FeII reacts with hydrogen peroxide (H2O2) in tumor cells to produce highly toxic hydroxyl radical (.OH) through the Fenton reaction. However, the content of endogenous H2O2 in cells is limited, and the reaction between FeIII and H2O2 is inefficient, greatly limiting the efficiency of the Fenton reaction and reducing the effectiveness of tumor treatment. Therefore, in this work, we designed and synthesized a new type of nano-system (CaO2@TA-FeIII) for the enhanced CDT of tumors, in which the polyphenolic compound- tannic acid (TA) and FeIII formed a TA-Fe nano-coating on the surface of calcium peroxide (CaO2) nanospherical aggregates. When the CaO2@TA-FeIII nanoconjugates reach the tumor site, the CaO2 contained in the nanoconjugates produces H2O2 after disintegration in tumor cells, and the carried TA rapidly reduces FeIII to FeII, solving the two major shortcomings in CDT of (1) insufficient content of H2O2 in cancer cells, and (2) low catalytic efficiency of the Fenton reaction. Additionally, the .OH produced in the Fenton reaction induces oxidative stress for the tumor cells, promoting the occurrence of the “calcium overload” process, and thereby accelerating the death of tumor cells. Experimental results in vitro and in vivo showed that CaO2@TA-FeIII nanoconjugates can effectively kill cancer cells and display an excellent tumor therapeutic effect. We believe that the CaO2@TA-FeIII nanoconjugates are a promising new nano-platform for highly effective tumor treatment.
- Chen, Fei,Yang, Beibei,Xu, Lan,Yang, Jinfeng,Li, Jishan
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supporting information
p. 2278 - 2286
(2021/05/05)
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- Ag-doped Fe-metal-organic framework nanozymes for efficient antibacterial application
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Herein, we developed a Ag-doped Fe-based metal-organic framework nanozyme with excellent peroxidase-like activity, which catalyzes the decomposition of H2O2to produce highly toxic hydroxyl radicals, demonstrating excellent antibacterial properties against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria.
- Hu, Zhonglan,Liu, Xiao,Jiao, Lei,Wei, Xiaoqiong,Wang, Zhen,Huang, Nongyu,Li, Jiong
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supporting information
p. 17772 - 17776
(2021/10/12)
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- Nanoscale Metal-Organic Frameworks Stabilize Bacteriochlorins for Type i and Type II Photodynamic Therapy
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Herein we report the design of a bacteriochlorin-based nanoscale metal-organic framework, Zr-TBB, for highly effective photodynamic therapy via both type I and type II mechanisms. The framework of Zr-TBB stabilizes 5,10,15,20-tetra(p-benzoato)bacteriochlorin (TBB) ligands toward oxygen and light via geometrical constraint. Upon 740 nm light irradiation, Zr-TBB efficiently generates various reactive oxygen species, including singlet oxygen, superoxide anion, hydrogen peroxide, and hydroxyl radicals, to afford superb antitumor efficacy on mouse models of breast and colon cancers, with cure rates of 40% and 60%, respectively.
- Luo, Taokun,Ni, Kaiyuan,Culbert, August,Lan, Guangxu,Li, Zhe,Jiang, Xiaomin,Kaufmann, Michael,Lin, Wenbin
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supporting information
p. 7334 - 7339
(2020/08/21)
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- Ferrocene Functionalized Upconversion Nanoparticle Nanosystem with Efficient Near-Infrared-Light-Promoted Fenton-Like Reaction for Tumor Growth Suppression
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By taking advantage of the efficient F?rster resonance energy transfer (FRET) between near-infrared (NIR)-responsive lanthanide-doped upconversion nanoparticles (UCNPs) and Fenton reagent ferrocenyl compounds (Fc), a series of Fc-UCNPs was designed by functionalizing NaYF4:Yb,Tm nanoparticles with Fc1-Fc5 via surface-coordination chemistry. Fc-UCNP-Lipo nanosystems were then constructed by encapsulating Fc-UCNP inside liposomes for efficient delivery. Fc-UCNP can effectively release ·OH via a NIR-promoted Fenton-like reaction. In vitro and in vivo studies of Fc1-UCNP-Lipo confirmed the preferential accumulation in a tumor site followed by an enhanced uptake of cancer cells. After cellular internalization, the released Fc1-UCNP can effectively promote ·OH generation for tumor growth suppression. Such a Fc1-UCNP-Lipo nanosystem exhibits advantages such as easy fabrication, low drug dosage, and no ferrous ion release.
- Zhou, Jimin,Zhu, Xiangfeng,Cheng, Qianya,Wang, Yuxuan,Wang, Ruiqi,Cheng, Xingwen,Xu, Jiajia,Liu, Kuntang,Li, Lin,Li, Xueming,He, Mingfang,Wang, Jian,Xu, Heng,Jing, Su,Huang, Ling
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p. 9177 - 9187
(2020/06/08)
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- A Fast Photochemical Oxidation of Proteins (FPOP) platform for free-radical reactions: the carbonate radical anion with peptides and proteins
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Fast Photochemical Oxidation of Protein (FPOP), based on a pulsed KrF laser (248 nm) for free-radical generation, is a biophysical method that utilizes hydroxyl radicals to footprint proteins in solution. FPOP has been recognized for structural proteomics investigations, including epitope mapping, protein-aggregation characterization, protein-folding monitoring, and binding-affinity determination. The distinct merits of the platform are: i) the use of a scavenger to control radical lifetime and allow fast (“snapshot”) footprinting of solvent-accessible residues in a protein; ii) the employment of a flow system to enable single-shot irradiation of small plugs of the targeted sample; iii) the use of methionine and catalase after radical oxidation chemistry to prevent post-oxidation with residual oxidizing species; and iv) the utilization of mature mass spectrometry-based proteomic methods to afford detailed analysis. In addition to ?OH, other reactive reagents (e.g., carbenes, iodide, sulfate radical anion, and trifluoromethyl radical) can be implemented on this platform to increase the versatility and scope. In this study, we further elaborate the use of FPOP platform to generate secondary radicals and establish a workflow to answer fundamental questions regarding the intrinsic selectivity and reactivity of radicals that are important in biology. Carbonate radical anion is the example we chose owing to its oxidative character and important putative pathogenic roles in inflammation. This systematic study with model proteins/peptides gives consistent results with a previous study that evaluated reactivity with free amino acids and shows that methionine and tryptophan are the most reactive residues with CO3 -?. Other aromatic amino acids (i.e., tyrosine, histidine and phenylalanine) exhibit moderate reactivity, whereas, aliphatic amino acids are inert, unlike with ?OH. The outcome demonstrates this approach to be appropriate for studying the fast reactions of radicals with proteins.
- Zhang, Mengru Mira,Rempel, Don L.,Gross, Michael L.
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p. 126 - 132
(2018/12/13)
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- FeOCl/POM Heterojunctions with Excellent Fenton Catalytic Performance via Different Mechanisms
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To enhance the Fenton catalytic performance in a neutral solution under indoor sunlight, a novel FeOCl/polyoxometalate (POM) (FeOCl/POM-W and FeOCl/POM-Mo) composite was successfully synthesized for the first time, which shows significantly improved Fenton catalytic activity and stability for phenol degradation compared with FeOCl. Furthermore, the degradation constants (k) of FeOCl/POM-Mo (0.08 min-1) and FeOCl/POM-W (0.06 min-1) are a factor of 4 and 3 times greater than that of FeOCl (0.02 min-1), respectively. The enhanced catalytic activity is attributed to the formation of FeOCl/POM heterojunctions, which results in efficient separation of photoinduced electron-hole pairs and electron transfer from POM to FeOCl. Density functional theory calculations indicate a strong interface interaction of Fe-O-Mo and Fe-O-W in the FeOCl/POM heterojunctions. A Z-scheme mechanism for FeOCl/POM-Mo and a double-transfer mechanism for FeOCl/POM-W are proposed for the enhanced catalytic performance. This study sheds new light on the design and fabrication of high-performance photo-Fenton catalysts to overcome the environmental crisis.
- Zhang, Jian,Zhan, Mingyu,Zheng, Lulu,Zhang, Chen,Liu, Guodong,Sha, Jingquan,Liu, Shaojie,Tian, Shuo
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supporting information
p. 250 - 258
(2019/01/11)
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- Halogen-Mediated Membrane Transport: An Efficient Strategy for the Enhancement of Cellular Uptake of Synthetic Molecules
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The poor uptake of fluorescent probes and therapeutics by mammalian cells is a major concern in biological applications ranging from fluorescence imaging to drug delivery in living cells. Although gaseous molecules such as oxygen and carbon dioxide, hydrophobic substances such as benzene, and small polar but uncharged molecules such as water and ethanol can cross the cell plasma membrane by simple passive diffusion, many synthetic as well as biological molecules require specific membrane transporters and channel proteins that control the traffic of these molecules into and out of the cell. This work reports that the introduction of halogen atoms into a series of fluorescent molecules remarkably enhances their cellular uptake, and that their transport can be increased to more than 95 % by introducing two iodine atoms at appropriate positions. The nature of the fluorophore does not play a major role in the cellular uptake when iodine atoms are present in the molecules, as compounds bearing naphthalimide, coumarin, BODIPY, and pyrene moieties show similar uptakes. Interestingly, the introduction of a maleimide-based fluorophore bearing two hydroxyethylthio moieties allows the molecules to cross the plasma and nuclear membranes, and the presence of iodine atoms further enhances the transport across both membranes. Overall, this study provides a general strategy for enhancing the uptake of organic molecules by mammalian cells.
- Ungati, Harinarayana,Govindaraj, Vijayakumar,Nair, Chithra R.,Mugesh, Govindasamy
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p. 3391 - 3399
(2019/02/13)
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- ESIPT-based fluorescence probe for the ratiometric detection of superoxide
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A simple ESIPT-based fluorescence probe (HMBT-LW) was developed for the detection of superoxide (O2?). HMBT-LW was synthesised over two steps and was shown to rapidly detect low concentrations of O2? (limit of detection =
- Wu, Luling,Liu, Liyuan,Han, Hai-Hao,Tian, Xue,Odyniec, Maria L.,Feng, Lei,Sedgwick, Adam C.,He, Xiao-Peng,Bull, Steven D.,James, Tony D.
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supporting information
p. 2875 - 2877
(2019/02/17)
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- Titanium-Based Nanoscale Metal-Organic Framework for Type i Photodynamic Therapy
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Nanoscale metal-organic frameworks (nMOFs) have shown great potential as nanophotosensitizers for photodynamic therapy (PDT) owing to their high photosensitizer loadings, facile diffusion of reactive oxygen species (ROSs) through their porous structures, and intrinsic biodegradability. The exploration of nMOFs in PDT, however, remains limited to an oxygen-dependent type II mechanism. Here we report the design of a new nMOF, Ti-TBP, composed of Ti-oxo chain secondary building units (SBUs) and photosensitizing 5,10,15,20-tetra(p-benzoato)porphyrin (TBP) ligands, for hypoxia-tolerant type I PDT. Upon light irradiation, Ti-TBP not only sensitizes singlet oxygen production, but also transfers electrons from excited TBP? species to Ti4+-based SBUs to afford TBP?+ ligands and Ti3+ centers, thus propagating the generation of superoxide, hydrogen peroxide, and hydroxyl radicals. By generating four distinct ROSs, Ti-TBP-mediated PDT elicits superb anticancer efficacy with >98% tumor regression and 60% cure rate.
- Lan, Guangxu,Ni, Kaiyuan,Veroneau, Samuel S.,Feng, Xuanyu,Nash, Geoffrey T.,Luo, Taokun,Xu, Ziwan,Lin, Wenbin
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supporting information
p. 4204 - 4208
(2019/03/11)
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- Morphology-and pH-dependent peroxidase mimetic activity of nanoceria
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The peroxidase mimetic properties of nanoceria have attracted extensive attention in recent years. In this work, the peroxidase mimetic properties of CeO2 nanocrystals with different morphologies, namely, nanocubes and nanorods, were investigated. Two types of oxidative species, HO radicals and peroxide-like intermediates, were identified in the CeO2/H2O2 systems. The formation of these oxidative species is strongly dependent on the pH value and the morphology of the CeO2 nanocrystals. The origin of the peroxidase mimetic activity of nanoceria was mainly ascribed to the presence of HO under acidic conditions, whereas the peroxide-like species also played a major role under neutral and basic conditions. CeO2 nanorods with excellent redox properties and higher concentration of Ce3+ and oxygen vacancies were more favorable for the generation of both HO and peroxide-like intermediates than that of CeO2 nanocubes, exhibiting excellent peroxidase mimetic activity toward 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), methylene blue (MB), and congo red (CR) in the presence of H2O2.
- Wei, Xiaoshu,Li, Xiaofeng,Feng, Yuqian,Yang, Sen
-
p. 11764 - 11770
(2018/04/05)
-
- Cold atmospheric plasma activated water as a prospective disinfectant: The crucial role of peroxynitrite
-
The socio-economic, environmental, and health implications of diseases caused by pathogenic microorganisms and their treatment using conventional antimicrobials are significant. The increasing resistance to antibiotics and detrimental biological side effects of many common antibiotics on human health and on the ecosystem have driven the search for new cost-effective and highly-efficient sterilization treatments and agents that are more environmentally benign. Plasma activated water (PAW), a product of cold atmospheric plasma reacting with water, is a promising broad-spectrum biocidal agent whose biochemical activity is attributed to the presence of a rich diversity of highly reactive oxygen and nitrogen species (RONS). The transient activity of PAW, where PAW reverts to water within days of storage and application, suggests that it can become a green alternative to conventional chemical treatment methods, yet the issues of scale up and the not fully understood mechanism of activity remain. In this study, we sought to explore the antibiotic potential of PAW generated from a plasma jet in a continuous flow reactor and determine the individual and combined contribution of thus-generated reactive chemistries in PAW for organism inactivation. Treatment of Escherichia coli with PAW led to more than a 4-log reduction, while exposure to an equivalent single dose of hydrogen peroxide (H2O2), nitrate (NO3-) or nitrite (NO2-) to that found in PAW failed to attain the same level of reduction. Peroxynitrite was identified as a critical bioactive species, particularly under acidic conditions, originating from the synergistic plasma effects (like the reactions of H2O2, NO3-, NO2- and other existing short-lived species like OH radicals in PAW). This research successfully demonstrated the possibility of PAW being an effective environmentally benign disinfectant, the activity of which is closely linked to the generation of peroxynitrite, providing much needed insights into the fundamental aspects of PAW chemistry required for optimisation of the biochemical activity of PAW and translation of this decontamination strategy into real life applications.
- Zhou, Renwu,Zhou, Rusen,Prasad, Karthika,Fang, Zhi,Speight, Robert,Bazaka, Kateryna,Ostrikov, Kostya
-
supporting information
p. 5276 - 5284
(2018/12/05)
-
- Gas-Phase Reaction of Methyl n-Propyl Ether with OH, NO3, and Cl: Kinetics and Mechanism
-
Rate constants at room temperature (293 ± 2 K) and atmospheric pressure for the reaction of methyl n-propyl ether (MnPE), CH3OCH2CH2CH3, with OH and NO3 radicals and the Cl atom have been determined in a 100 L FEP-Teflon reaction chamber in conjunction with gas chromatography-flame ionization detector (GC-FID) as the detection technique. The obtained rate constants k (in units of cm3 molecule-1 s-1) are (9.91 ± 2.30) × 10-12, (1.67 ± 0.32) × 10-15, and (2.52 ± 0.14) × 10-10 for reactions with OH, NO3, and Cl, respectively. The products of these reactions were investigated by gas chromatography-mass spectrometry (GC-MS), and formation mechanisms are proposed for the observed reaction products. Atmospheric lifetimes of the studied ether, calculated from rate constants of the different reactions, reveal that the dominant loss process for MnPE is its reaction with OH, while in coastal areas and in the marine boundary layer, MnPE loss by Cl reaction is also important.
- Zhu, Jianqiang,Wang, Shuyan,Tsona, Narcisse T.,Jiang, Xiaotong,Wang, Yifeng,Ge, Maofa,Du, Lin
-
p. 6800 - 6809
(2017/09/23)
-
- Catalytic decomposition of H2O2 over a Au/carbon catalyst: A dual intermediate model for the generation of hydroxyl radicals
-
The generation of hydroxyl radicals (HO) by H2O2 decomposition over solid catalysts (a Fenton-like reaction) will play an important role in the design of new processes for water treatment. More specifically, the understanding of H2O2 decomposition on Au nanoparticles (NPs) is crucial for the optimization of the structure of active sites and the evaluation of cytotoxicity of Au NPs. Here, the kinetic behavior of H2O2 decomposition over supported Au NPs was investigated in a buffer solution at pH ~ 6.8. Over a range of H2O2 concentrations, the decay of H2O2 followed a pseudo-first-order kinetic rate law with an apparent activation energy of 142 kJ/mol. The observed rate constant was linearly increased from (3.0 ± 1.0) × 10-3 to (66.7 ± 2.3) × 10-3 min-1 with the increase in the Au NPs concentration. Further increase in the surface concentration of H2O2 may reduce the HO generation efficiency. A dual intermediate model was proposed for the generation mechanism of HO.
- Yang, Xue-Jing,Tian, Peng-Fei,Wang, Hua-Lin,Xu, Jing,Han, Yi-Fan
-
p. 126 - 132
(2016/02/23)
-
- Boronate based fluorescence (ESIPT) probe for peroxynitrite
-
A simple probe for the detection of peroxynitrite was developed incorporating a benzyl boronic ester "protecting" unit. The "protecting" unit of the probe is removed by peroxynitrite to "turn-on" ESIPT fluorescence (4.5 fold enhancement). Furthermore, the probe was cell permeable and was used in cell imaging experiments showing an off-on response towards peroxynitrite, in HeLa and RAW 264.7 cells.
- Sedgwick, Adam C.,Sun, Xiaolong,Kim, Gyoungmi,Yoon, Juyoung,Bull, Steven D.,James, Tony D.
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p. 12350 - 12352
(2016/10/22)
-
- Absorption cross sections of 2?Nitrophenol in the 295?400 nm region and photolysis of 2?Nitrophenol at 308 and 351 nm
-
2-Nitrophenol is an important component of “brown carbon” in the atmosphere. Photolysis is its dominant gas phase removal process. We have determined the gas phase absorption cross sections of 2-nitrophenol in the 295?400 nm region by using cavity ring-down spectroscopy. 2-Nitrophenol exhibits a broad absorption band over the wavelength region studied, with the peak absorption located at 345 nm. Absorption cross section values range between (2.86 ± 0.18) × 10?18 and (2.63 ± 0.31) × 10?20 cm2/ molecule over the 295?400 nm range. We have investigated the HONO, NO2, and OH formation channels following the gas phase photolysis of 2-nitrophenol at 308 and 351 nm. Direct NO2 formation was not observed. HONO and OH are direct products from 2-nitrophenol photolysis. The average OH quantum yields from the photolysis of 0.5, 1.0, and 2.0 mTorr of 2-nitrophenol are 0.69 ± 0.07 and 0.70 ± 0.07 at 308 and 351 nm. The average HONO quantum yields are 0.34 ± 0.09 and 0.39 ± 0.07 at 308 and 351 nm. The OH and HONO quantum yields are independent of nitrogen carrier gas pressure in the 20?600 Torr range. Oxidant formation rate constants from 2-nitrophenol photolysis have been calculated. Discussions have been made concerning the role of 2-nitrophenol gas phase photolysis in the formation of atmospheric oxidants in regions of high anthropogenic emissions.
- Sangwan, Manuvesh,Zhu, Lei
-
p. 9958 - 9967
(2018/04/27)
-
- A turn-on fluorescent probe for hypochlorous acid based on HOCl-promoted removal of the C = N bond in BODIPY-hydrazone
-
A boron dipyrromethene-based fluorescent probe, BODH, has been successfully developed for hypochlorous acid detection based on the HOCl-promoted oxidative removal of the C = N bond in response to the amount of HOCl. The reaction is accompanied by a 6-fold
- Chen, Wei-Chieh,Venkatesan, Parthiban,Wu, Shu-Pao
-
p. 6892 - 6898
(2015/09/02)
-
- Radical product yields from the ozonolysis of short chain alkenes under atmospheric boundary layer conditions
-
The gas-phase reaction of ozone with unsaturated volatile organic compounds (VOCs), alkenes, is an important source of the critical atmospheric oxidant OH, especially at night when other photolytic radical initiation routes cannot occur. Alkene ozonolysis is also known to directly form HO2 radicals, which may be readily converted to OH through reaction with NO, but whose formation is poorly understood. We report a study of the radical (OH, HO 2, and RO2) production from a series of small alkenes (propene, 1-butene, cis-2-butene, trans-2-butene, 2-methylpropene, 2,3-dimethyl-2-butene (tetramethyl ethene, TME), and isoprene). Experiments were performed in the European Photoreactor (EUPHORE) atmospheric simulation chamber, with OH and HO2 levels directly measured by laser-induced fluorescence (LIF) and HO2 + ΣRO2 levels measured by peroxy-radical chemical amplification (PERCA). OH yields were found to be in good agreement with the majority of previous studies performed under comparable conditions (atmospheric pressure, long time scales) using tracer and scavenger approaches. HO2 yields ranged from 4% (trans-2-butene) to 34% (2-methylpropene), lower than previous experimental determinations. Increasing humidity further reduced the HO2 yields obtained, by typically 50% for an RH increase from 0.5 to 30%, suggesting that HOx production from alkene ozonolysis may be lower than current models suggest under (humid) ambient atmospheric boundary layer conditions. The mechanistic origin of the OH and HO2 production observed is discussed in the context of previous experimental and theoretical studies.
- Alam, Mohammed S.,Rickard, Andrew R.,Camredon, Marie,Wyche, Kevin P.,Carr, Timo,Hornsby, Karen E.,Monks, Paul S.,Bloss, William J.
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p. 12468 - 12483
(2014/01/06)
-
- Evidence for OH radical production during electrocatalysis of oxygen reduction on pt surfaces: Consequences and application
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Multielectronic O2 reduction reactions (ORR) at Pt surface (and at Au surface for comparison purpose) were examined both in water and in organic solvents using a strategy based on radical footprinting and scanning electrochemical microscopy (SECM). Experiments reveal a considerable and undocumented production of OH radicals when O2 is reduced at a Pt electrode. These observations imply that the generally admitted description of ORR as simple competitive pathways between 2-electron (O2 to H 2O2) and 4-electron (O2 to H2O) reductions is often inadequate and demonstrate the occurrence of another 3-electron pathway (O2 to OH radical). This behavior is especially observable at neutral and basic pH's in water and in organic solvents like dimethylformamide or dichloromethane. In view of the high reactivity of OH radical versus organic or living materials, this observation could have important consequences in several practical situations (fuel cells, sensors, etc.) as far as O2 reduction is concerned. This also appears as a simple way to locally produce highly reactive species as exemplified in the present work by the micropatterning of organic surfaces.
- Noel, Jean-Marc,Latus, Alina,Lagrost, Corinne,Volanschi, Elena,Hapiot, Philippe
-
p. 2835 - 2841
(2012/03/22)
-
- Reaction OH + OH studied over the 298-834 K temperature and 1 - 100 bar pressure ranges
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Self-reaction of hydroxyl radicals, OH + OH → H2O + O (1a) and OH + OH → H2O2 (1b), was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 298-834 K temperature and 1-100 bar pressure ranges (bath gas He). A heatable high-pressure flow reactor was employed. Hydroxyl radicals were prepared using reaction of electronically excited oxygen atoms, O(1D), produced in photolysis of N2O at 193 nm, with H2O. The temporal behavior of OH radicals was monitored via transient absorption of light from a dc discharge in H2O/Ar low-pressure resonance lamp at ca. 308 nm. The absolute intensity of the photolysis light was determined by accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The results of this study combined with the literature data indicate that the rate constant of reaction 1a, associated with the pressure independent component, decreases with temperature within the temperature range 298-414 K and increases above 555 K. The pressure dependent rate constant for (1b) was parametrized using the Troe expression as k1b,inf = (2.4 ± 0.6) × 10-11(T/300)-0.5 cm3 molecule -1 s-1, k1b,0 = [He] (9.0 ± 2.2) × 10-31(T/300)-3.5±0.5 cm3 molecule -1 s-1, Fc = 0.37.
- Sangwan, Manuvesh,Chesnokov, Evgeni N.,Krasnoperov, Lev N.
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p. 6282 - 6294
(2012/08/29)
-
- A novel Electro-Fenton-Like system using PW11O 39Fe(III)(H2O)4- as an electrocatalyst for wastewater treatment
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A novel Electro-Fenton-Like (EFL) system was developed using the Keggin-type iron-substituted heteropolytungstate anion PW11O 39Fe(III)(H2O)4- to substitute for Fe 3+ in the conventional Electro-Fenton (EF) system for treatment of water polluted with organic compounds. The EFL system overcomes the drawback of low pH in conventional EF approaches and can be directly applied to neutral water treatment without any pH adjustment. Experimental results for dimethylphthalate (DMP) revealed complete degradation in a potential of -0.5 V and O2 flow rate of 60 mL min-1. Total organic carbon removal of ~56% was achieved at 120 min. Comparison with conventional EF oxidation revealed better efficiency of the present system for DMP degradation, suggesting its potential in treatment of water and wastewater with a relaxed pH requirement. The cumulative H2O2 concentration generated in situ at the electrode was monitored and the observed degradation rate constants k obs were determined for different initial DMP concentrations. The ligand exchange reaction of PW11O39Fe(III)(H 2O)4- with H2O2 and the electron transfer resulting in hydroxyl radicals were examined using HPLC and electrochemical impedance spectroscopy. An electrocatalytic model involving inner-sphere electron transfer and a reaction mechanism for PW 11O39Fe(III)(H2O)4- electrocatalytic reduction of H2O2 are proposed.
- Wang, Chongtai,Hua, Yingjie,Tong, Yexiang
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p. 6755 - 6760
(2011/01/11)
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- Bimolecular rate constants between levoglucosan and hydroxyl radical: Effects of pH and temperature
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Bimolecular rate constants for levoglucosan and hydroxyl radical were determined at various temperatures and pHs using competitive kinetics. Hydrogen peroxide was used as the radical source, and benzoic acid was used as a competitive radical scavenger. The rate constants at 20°C were 7.9 × 108 to 2.4 × 109M-1S-1 between pH 3.0 and 8.0 and showed little variation as a function of temperature between 10 and 40°C.
- Teraji, Takashi,Arakaki, Takemitsu
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p. 900 - 901
(2011/02/17)
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- Single and double reduction of C60 in 2:1 γ-cyclodextrin/[60]fullerene inclusion complexes by cyclodextrin radicals
-
Spectroscopic and chemical properties of γ-CD{radical dot} radicals, resulting from the abstraction by HO{radical dot} radicals of hydrogen atoms, have been investigated using pulse radiolysis. The reactions of γ-CD{radical dot}
- Quaranta, Annamaria,Zhang, Yongmin,Wang, Yali,Edge, Ruth,Navaratnam, Suppiah,Land, Edward J.,Bensasson, René V.
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p. 174 - 179
(2009/03/12)
-
- Excited state dynamics of liquid water: Insight from the dissociation reaction following two-photon excitation
-
The authors use transient absorption spectroscopy to monitor the ionization and dissociation products following two-photon excitation of pure liquid water. The primary decay mechanism changes from dissociation at an excitation energy of 8.3 eV to ionization at 12.4 eV. The two channels occur with similar yield for an excitation energy of 9.3 eV. For the lowest excitation energy, the transient absorption at 267 nm probes the geminate recombination kinetics of the H and OH fragments, providing a window on the dissociation dynamics. Modeling the OH geminate recombination indicates that the dissociating H atoms have enough kinetic energy to escape the solvent cage and one or two additional solvent shells. The average initial separation of H and OH fragments is 0.7±0.2 nm. Our observation suggests that the hydrogen bonding environment does not prevent direct dissociation of an O-H bond in the excited state. We discuss the implications of our measurement for the excited state dynamics of liquid water and explore the role of those dynamics in the ionization mechanism at low excitation energies.
- Elles, Christopher G.,Shkrob, Ilya A.,Crowell, Robert A.,Bradforth, Stephen E.
-
-
- HNO3 forming channel of the HO2 + NO reaction as a function of pressure and temperature in the ranges of 72-600 torr and 223-323 K
-
A high-pressure turbulent flow reactor coupled with a chemical ionization mass-spectrometer was used to determine the branching ratio of the HO 2 + NO reaction: HO2 + NO -OH + NO2 (1a), HO2 + N-O → HNO3 (1b). The branching ratio, β-k1b/k1a, was derived from the measurements of chemically amplified concentrations of the NO2 and HNO3 products in the presence of O2 and CO. The pressure and temperature dependence of βwas determined in the pressure range of 72-600 Torr of N2 carrier gas between 323 and 223 K. At each pressure, the branching ratio was found to increase with the decrease of temperature, the increase becoming less pronounced with the increase of pressure. In the 298-223 K range, the data could be fitted by the expression: β(T,P) = (530 ±10)/T(K) + (6.4 ±1.3) x 10-4P(Torr- (1.73 ±0.07), giving β 0.5% near the Earth's surface (298 K, 760 Torr) and 0.8% in the tropopause region (220 K, 200 Torr). The atmospheric implication of these results is briefly discussed.
- Butkovskaya, Nadezhda,Kukui, Alexandre,Le Bras, Georges
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p. 9047 - 9053
(2008/10/09)
-
- Atmospheric reaction of OH radicals with 1,3-butadiene and 4-hydroxy-2-butenal
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The gas-phase reaction of OH radicals with 1,3-butadiene and 4-hydroxy-2-butenal in the presence of NO has been studied in a flow tube operated at 295 ± 2 K and pressures of 950 mbar of synthetic air or 100 mbar of an O2/He mixture. OH radicals were generated using three different experimental approaches, namely, ozonolysis of tetramethylethylene (dark reaction), photolysis of methyl nitrite, or via the reaction of HO 2 with NO (HO2 from the reaction of H-atoms with O 2). Products of the reaction of OH radicals with 1,3-butadiene were HCHO (0.64 ± 0.08), acrolein (0.59 ± 0.06), 4-hydroxy-2-butenal (0.23 ± 0.10), furan (0.046 ± 0.014), and organic nitrates (0.06 ± 0.02) accounting for more than 90% of the reacted carbon. There was no significant dependence of product yields on experimental conditions which were varied in a wide range. The formation of the 1,4-addition product 4-hydroxy-2-butenal was confirmed unambiguously for the first time. The rate coefficient k(OH + 4-hydroxy-2-butenal) = (5.1 ± 0.8) x 10-11 cm3 molecule-1 s-1 was determined using a relative rate technique (p = 100 mbar, T = 295 ± 2 K). Products of the reaction of OH radicals with 4-hydroxy-2-butenal were glycolaldehyde (0.40 ± 0.06), glyoxal (0.17 ± 0.04), trans-butenedial (0.093 ± 0.033), and organic nitrates (0.043 ± 0.015) as well as further carbonylic substances remaining unidentified so far. Corresponding reaction mechanisms describing the formation of the detected products are proposed, and the relevance of these data for atmospheric conditions is discussed.
- Berndt, Torsten,Boege, Olaf
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p. 12099 - 12105
(2008/10/09)
-
- Kinetics of NO and NO2 evolution from illuminated frozen nitrate solutions
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The release of NO and NO2 from frozen aqueous NaNO3 irradiated at 313 nm was studied using time-resolved spectroscopic techniques. The kinetic behavior of NO and NO2 signals during on-and-off illumination cycles confirms that NO2 is a primary photoproduct evolving from the outermost ice layers and reveals that NO is a secondary species generated deeper in the ice, whence it eventually emerges due to its inertness and larger diffusivity. NO is shown to be more weakly held than NO2 by ice in thermal desorption experiments on preirradiated samples. The partial control of gaseous emissions by mass transfer, and hence by the morphology and metamorphisms of polycrystalline ice, is established by (1) the nonmonotonic temperature dependence of NO and NO2 signals upon stepwise warming under continuous illumination, (2) the fact that the NO, NO2 or NOx (NOx ≡ NO + NO2) amounts released in bright thermograms performed under various heating ramps fail to scale with photon dose, due to irreversible losses in the adsorbed state. Because present NO/NO2 ratios are up to 10-fold smaller than those determined over sunlit snowpacks, we infer that the immediate precursors to NO mostly absorb at λ > λmax (NO3 -) - 302 nm.
- Boxe,Colussi,Hoffmann,Perez,Murphy,Cohen
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p. 3578 - 3583
(2008/10/09)
-
- Kinetics of the OH + HCNO reaction
-
The kinetics of the OH + HCNO reaction was studied. The total rate constant was measured by LIF detection of OH using two different OH precursors, both of which gave identical results. We obtain k = (2.69 ± 0.41) × 10 -12 exp[(750.2 ± 49.8)/7] cm3 molecule-1 s-1 over the temperature range 298-386 K, with a value of k = (3.39 ± 0.3) × 10-11 cm3 molecule-1 s-1 at 296 K. CO, H2CO, NO, and HNO products were detected using infrared laser absorption spectroscopy. On the basis of these measurements, we conclude that CO + H2NO and HNO + HCO are the major product channels, with a minor contribution from H2CO + NO.
- Feng, Wenhui,Meyer, Justin P.,Hershberger, John F.
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p. 4458 - 4464
(2008/10/09)
-
- Rate coefficients for the reactions of OH with CF3CH 2CH3 (HFC-263fb), CF3CHFCH2F (HFC-245eb), and CHF2CHFCHF2 (HFC-245ea) between 238 and 375 K
-
Rate coefficients for reaction of the hydroxyl radical (OH) with three hydrofluorocarbons (HFCs) CF3CH2-CH3, HFC-263fb, (k1); CF3CHFCH2F, HFC-245eb, (k 2); and CHF2CHFCHF2, HFC-245ea, (k 3); which are suggested as potential substitutes to chlorofluorocarbons (CFCs), were measured using pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) between 235 and 375 K. The Arrhenius expressions obtained are k1(T) = (4.36 ± 0.72) × 10-12 exp[-(1290 ± 40)/T] cm3 molecule -1 s-1; k2(T) = (1.23 ± 0.18) × 10-12 exp[-(1250 ± 40)/T] cm3molecule-1 s-1; k3(7) = (1.91 ± 0.42) × 10-12 exp[-(1375 ± 100)/T] cm3 molecule-1 s -1. The quoted uncertainties are 95% confidence limits and include estimated systematic errors. The present results are discussed and compared with rate coefficients available in the literature. Our results are also compared with those calculated using structure activity relationships (SAR) for fluorinated compounds. The IR absorption cross-sections at room temperature for these compounds were measured over the range of 500 to 4000 cm-1. The global warming potentials (GWPs) of CF3CH2CH 3(HFC-263fb), CF3CHFCH2F(HFC-245eb), and CHF2CHFCHF2(HFC-245ea) were calculated to be 234, 962, and 723 for a 20-year horizon; 70, 286, and 215 for a 100-year horizon; and 22, 89, and 68 for a 500-year horizon; and the atmospheric lifetimes of these compounds are 0.8, 2.5, and 2.6 years, respectively. It is concluded that these compounds are acceptable substitutes for CFCs in terms of their impact on Earth's climate.
- Rajakumar,Portmann,Burkholder, James B.,Ravishankara
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p. 6724 - 6731
(2008/10/09)
-
- Optical study of OH radical in a wire-plate pulsed corona discharge
-
In this study, the emission spectra of OH (A2Σ → X2Π, 0-0) emitted from the high-voltage pulsed corona discharge (HVPCD) of N2 and H2O mixture gas and humid air in a wire-plate reactor were successfully recorded against a severe electromagnetic interference coming from HVPCD at one atmosphere. The relative vibrational populations and the vibrational temperature of N2 (C, v′) were determined. The emission spectra of the Δv=+1 (1-0, 2-1, 3-2, 4-3) vibration transition band of N2 (C3Πu → B3Πg) is simulated through gauss distribution. The emission intensity of OH (A2Σ → X2Π, 0-0) has been exactly gotten by subtracting the emission intensity of the Δv=+1 vibration transition band of N2 (C3Π u → B3Πg) from the overlapping spectra. The relative population of OH (A2Σ) has been obtained by the emission intensity of OH (A2Σ → X2Π, 0-0) and Einstein's transition probability. The influences of pulsed peak voltage and pulse repetition rate on the relative population of OH (A 2Σ) radicals in N2 and H2O mixture gas and humid air are investigated separately. It is found that the relative population of OH (A2Σ) rises linearly with increasing the applied peak voltage and the pulse repetition rate. When the oxygen is added in N2 and H2O mixture gas, the relative population of OH (A2Σ) radicals decreases exponentially with increasing the added oxygen. The main involved physicochemical processes have also been discussed.
- Wang, Wenchun,Wang, Su,Liu, Feng,Zheng, Wei,Wang, Dezhen
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p. 477 - 482
(2007/10/03)
-
- Interaction of atomic hydrogen with Zn-polar and O-polar ZnO surfaces
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The interaction of Zn-polar and O-polar ZnO surfaces with atomic hydrogen produced by a remote rf plasma source is investigated in situ and in real time using spectroscopic ellipsometry. It is found that the reactivity of ZnO with atomic hydrogen depends on polarity. The interaction of O-polar surfaces with atomic hydrogen at 100 °C is suitable for producing clean surfaces, while Zn-polar surfaces strongly react with atomic hydrogen resulting in a disruption of the ZnO lattice with formation of Zn surface clusters.
- Losurdo, Maria,Giangregorio, Maria M.
-
-
- Determination of the reaction rate constants of antioxidants with the hydroxyl radical by a rapid-flow ESR method
-
The reaction rate constants of antioxidants with the hydroxyl radical (HO?) were determined by a rapid-flow ESR method. ESR spectra of the antioxidant radical formed by a reaction with HO? generated from the Ti3+ + H2O2 system were measured. When an antioxidant and ethanol were mixed with HO?, a superposed spectrum of the 1-hydroxyethyl radical and antioxidant radical was obtained. The intensity ratio of the signals of these radicals was calculated from the doubly integrated curve, and then the ratio of the reaction-rate constant of the antioxidant with HO? to that of ethanol was obtained. The ratios of pyrogallol, gallic acid, catechol, phloroglucinol, resorcinol, and methanol were 19, 17, 11, 1.5, 1.2, and 0.56, respectively. The dissociation energies of the bonds in antioxidant molecules were obtained by MO calculations, which demonstrated that phenoxy, hydroxymethyl, and 1-hydroxylethyl radicals were formed by the reactions with HO?, as expected from their spectra. The relationship between the relative activation energies obtained from the rate constants and the bond-dissociation energies showed that the Evans-Polanyi equation holds in polyphenol series, but the line was shifted from that of alcohols. This suggested that the structures of the transition state of alcohols were stabilized by a polar effect.
- Ohashi, Yasunori,Takeuchi, Yuya,Hirama, Mutsumi,Yoshioka, Hisashi,Yoshioka, Hiroe
-
p. 1757 - 1762
(2007/10/03)
-
- Synthesis and time-resolved fluorimetric application of a europium chelate-based phosphorescence probe specific for singlet oxygen
-
A new europium chelate, [4′-(9-anthryl)-2,2′:6′,2″- terpyridine-6,6″-diyl]bis(methylenenitrilo) tetrakis(acetate)-Eu 3+ (ATTA-Eu3+), has been designed and synthesized as a highly sensitive and selective time-resolved phosphorescence probe for singlet oxygen (1O2). The probe can specifically react with 1O2 to yield its endoperoxide (EP-ATTA-Eu3+) with a great increase of the luminescence quantum yield and a long phosphorescence lifetime of 1.21 ms, which renders the probe favorable to be used for highly sensitive time-resolved luminescence detection of 1O2. The new phosphorescence probe is highly water soluble with a large stability constant of ~1020 and a wide available pH range at pH > 3. Upon reactions with some reactive oxygen species including hydrogen peroxide, superoxide, hydroxyl radical and 1O2, the probe shows high specificity for 1O2. The probe was used for quantitative detection of 1O2 generated from a MoO42+-H2O2 system to give a detection limit of 2.8 nM. Furthermore, the good applicability of the probe was demonstrated by the real-time monitoring of the kinetic process of 1O2 generation in a horseradish peroxidase (HRP) catalyzed oxidation system of indole-3-acetic acid (IAA) in a weakly acidic buffer and in a photosensitization system of 5,10,15,20-tetrakis(N-methyl-4-pyridyl)-21H,23H- porphine (TMPyP) in a neutral buffer. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2005.
- Song, Bo,Wang, Guilan,Tan, Mingqian,Yuan, Jingli
-
p. 1431 - 1438
(2007/10/03)
-
- Low temperature NH(X 3Σ-) radical reactions with NO, saturated, and unsaturated hydrocarbons studied in a pulsed supersonic Laval nozzle flow reactor between 53 and 188 K
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The reactions of ground-state imidogen radicals (NH(X 3Σ -)) with NO and select saturated and unsaturated hydrocarbons have been measured in a pulsed supersonic expansion Laval nozzle flow reactor in the temperature range 53-188 K. The rate coefficients for the NH + NO system display negative temperature dependence in the temperature regime currently investigated and a global temperature-dependent fit is best represented in a modified power law functional form, with k1(NH + NO) = (4.11 ± 0.31) × 10-11 × (T/300)(-0.30±0.17) × exp(77±21/T) cm3/s. The reactions of NH with ethylene, acetylene, propene, and diacetylene were measured over the temperature range 53-135 K. In addition, the reactions of NH with methane and ethane were also measured at 53 K, for reasons discussed later. The temperature dependence of the reactions of NH with the unsaturated hydrocarbons are fit using power law expressions, k(T) = A(T/300)-n, and are as follows: k4, = (2.3 ± 1.2) × 10-12 × (T/300)(-1.09±0.333) cm3/s, k5 = (4.5 ± 0.3) × 10-12 × (T/300) (-1.07±0.04) cm3/s, k6 = (5.6 ± 1.9) × 10-12 × (T/300)(-1.23±0.21) cm3/s, and k7 = (7.4 ± 1.8) × 10 -12 × (T/300)(-1.23±0.15) cm3/s for ethylene, acetylene, propene, and diacetylene, respectively. The rate for NH + ethane at 53 K is measured to be k3 = (6.8 ± 1.7) × 10-12 cm3/s, while that for methane at the same temperature represents an upper bound of k2 ≤ (1.1 ± 4.3) × 10-12 cm3/s, as this is at the limits of measurement with our current technique. The behavior of these systems throughout the temperature range explored indicates that these reactions occur over a potential energy surface without an appreciable barrier through a complex formation mechanism. Implications for chemistry in low temperature environments where these species are found are briefly discussed.
- Mullen, Christopher,Smith, Mark A.
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p. 1391 - 1399
(2007/10/03)
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- Formation of nitric acid in the gas-phase HO2 + NO reaction: Effects of temperature and water vapor
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A high-pressure turbulent flow reactor coupled with a chemical ionization mass spectrometer was used to investigate the minor channel (Ib) producing nitric acid, HNO3, in the HO2 + NO reaction for which only one channel (la) is known so far: HO2 + NO → OH + NO 2 (la), HO2 + NO → HNO3 (1b). The reaction has been investigated in the temperature range 223-298 K at a pressure of 200 Torr of N2 carrier gas. The influence of water vapor has been studied at 298 K. The branching ratio, k1blk1a, was found to increase from (0.18+-0.06+0.04)% at 298 K to (0-87 -0.08+0.05)% at 223 K- corresponding to k1b = (1.6 ±0.5) x 10-14 and (10.4 ±1.7) ×10 -14 cm3 molecule -1 s-l, respectively at 298 and 223 K. The data could be fitted by the Arrhenius expression k1b = 6.4 × 10-17 exp((1644 ±76)l7) cm 3 molecule-1 s-1 at T = 223-298 K. The yield of HNO3 was found to increase in the presence of water vapor (by 90% at about 3 Torr of H2O). Implications of the obtained results for atmospheric radicals chemistry and chemical amplifiers used to measure peroxy radicals are discussed. The results show in particular that reaction Ib can be a significant loss process for the HOx (OH, HO2) radicals in the upper troposphere.
- Butkovskaya,Kukui,Pouvesle,Le Bras
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p. 6509 - 6520
(2008/10/09)
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- Product study of the reaction of CH3 with OH radicals at low pressures and temperatures of 300 and 612 K
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The product distribution for the title reaction was studied using our time-of-flight mass spectrometer (TOFMS) connected to a tubular flow reactor. The methyl and hydroxyl radicals were produced by an excimer laser pulse (?? = 193 nm) photolyzing acetone and nitrous oxide in the presence of excess water or hydrogen. Helium was used as the bath gas; the total density was held constant at 1.2 ?? 1017 cm-3. At 300 K the observations were consistent with singlet methylene (1CH2) and water as the main product channel with a small contribution of methanol. In contrast, at about 610 K three channels - formaldehyde isomers and methanol in addition to 1CH2 + H2O - are formed with similar yields. When acetone-d6 was used, the production of both CHDO and CD2O was observed, indicating that two different formaldehyde-producing channels are operating simultaneously. These experimental results are compared with RRKM and master equation calculations on the basis of the properties of the methanol potential energy surface from a recent ab initio study. ? 2005 American Chemical Society.
- Fockenberg, Christopher,Weston Jr., Ralph E.,Muckerman, James T.
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p. 8415 - 8427
(2008/10/09)
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- Acoustic emission from cavitating solutions: Implications for the mechanisms of sonochemical reactions
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The acoustic emission from collapsing cavitation bubbles generated using ultrasound of 20 kHz and 515 kHz frequencies in water has been measured and correlated with sonoluminescence and hydroxyl radical production to yield further information on the frequency dependence of sonochemical reactions. A reasonable correlation was found, and the results suggest differences in the predominant types of cavitation observed under laboratory conditions. ? 2005 American Chemical Society.
- Price, Gareth J.,Ashokkumar, Muthupandian,Hodnett, Mark,Zequiri, Bajram,Grieser, Franz
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p. 17799 - 17801
(2008/10/09)
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- A laser flash photolysis study of nitrous acid in the aqueous phase
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The OH quantum yield from the photolysis of nitrous acid in the aqueous phase by the 355 nm light was measured to be 0.25 ± 0.03. OH radical thus formed reacted readily with HNO2 to produce NO2, which sequentially reacted with HNO2 to form the HNO2-NO 2 adduct. The NO2 + HNO2 reaction was reversible with a forward rate constant of 3.76 × 107 dm 3 mol-1 s-1 and a backward rate constant of 1.06 × 105 s-1. Decay of the HNO2-NO 2 adduct would most likely generate HNO3 and NO at a rate constant of 3.0 × 103 s-1.
- Ouyang, Bin,Dong, Wenbo,Hou, Huiqi
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p. 306 - 311
(2008/10/09)
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