Thermodynamic properties (enthalpy, bond energy, entropy, and heat capacity) and internal rotor potentials of vinyl alcohol, methyl vinyl ether, and their corresponding radicals.

PubMed

da Silva, Gabriel; Kim, Chol-Han; Bozzelli, Joseph W

2006-06-29

Vinyl alcohols (enols) have been discovered as important intermediates and products in the oxidation and combustion of hydrocarbons, while methyl vinyl ethers are also thought to occur as important combustion intermediates. Vinyl alcohol has been detected in interstellar media, while poly(vinyl alcohol) and poly(methyl vinyl ether) are common polymers. The thermochemical property data on these vinyl alcohols and methyl vinyl ethers is important for understanding their stability, reaction paths, and kinetics in atmospheric and thermal hydrocarbon-oxygen systems. Enthalpies , entropies , and heat capacities (C(p)()(T)) are determined for CH(2)=CHOH, C(*)H=CHOH, CH(2)=C(*)OH, CH(2)=CHOCH(3), C(*)H=CHOCH(3), CH(2)=C(*)OCH(3), and CH(2)=CHOC(*)H(2). Molecular structures, vibrational frequencies, , and C(p)(T) are calculated at the B3LYP/6-31G(d,p) density functional calculation level. Enthalpies are also determined using the composite CBS-Q, CBS-APNO, and G3 methods using isodesmic work reactions to minimize calculation errors. Potential barriers for internal rotors are calculated at the B3LYP/6-31G(d,p) level and used to determine the hindered internal rotational contributions to entropy and heat capacity. The recommended ideal gas phase values calculated in this study are the following (in kcal mol(-1)): -30.0, -28.9 (syn, anti) for CH(2)=CHOH; -25.6, -23.9 for CH(2)=CHOCH(3); 31.3, 33.5 for C(*)H=CHOH; 27.1 for anti-CH(2)=C(*)OH; 35.6, 39.3 for C(*)H=CHOCH(3); 33.5, 32.2 for CH(2)=C(*)OCH(3); 21.3, 22.0 for CH(2)=CHOC(*)H(2). Bond dissociation energies (BDEs) and group additivity contributions are also determined. The BDEs reveal that the O-H, O-CH(3), C-OH, and C-OCH(3) bonds in vinyl alcohol and methyl vinyl ether are similar in energy to those in the aromatic molecules phenol and methyl phenyl ether, being on average around 3 kcal mol(-1) weaker in the vinyl systems. The keto-enol tautomerization enthalpy for the interconversion of vinyl alcohol to acetaldehyde is determined to be -9.7 kcal mol(-1), while the activation energy for this reaction is calculated as 55.9 kcal mol(-1); this is the simplest keto-enol tautomerization and is thought to be important in the reactions of vinyl alcohol. Formation of the formyl methyl radical (vinoxy radical/vinyloxy radical) from both vinyl alcohol and methyl vinyl ether is also shown to be important, and its reactions are discussed briefly.

Role of water and carbonates in photocatalytic transformation of CO{sub 2} to CH{sub 4} on titania.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dimitrijevic, N. M.; Vijayan, B. K.; Poluektov, O. G.

Using the electron paramagnetic resonance technique, we have elucidated the multiple roles of water and carbonates in the overall photocatalytic reduction of carbon dioxide to methane over titania nanoparticles. The formation of H atoms (reduction product) and {center_dot}OH radicals (oxidation product) from water, and CO{sub 3}{sup -} radical anions (oxidation product) from carbonates, was detected in CO{sub 2}-saturated titania aqueous dispersion under UV illumination. Additionally, methoxyl, {center_dot}OCH{sub 3}, and methyl, {center_dot}CH{sub 3}, radicals were identified as reaction intermediates. The two-electron, one-proton reaction proposed as an initial step in the reduction of CO{sub 2} on the surface of TiO{sub 2} ismore » supported by the results of first-principles calculations.« less

Role of Water and Carbonates in Photocatalytic Transformation of CO2 to CH4 on Titania

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dimitrijevic, Nada; Vijayan, Baiju K.; Poluektov, Oleg G.

Using the electron paramagnetic resonance technique, we have elucidated the multiple roles of water and carbonates in the overall photocatalytic reduction of carbon dioxide to methane over titania nanoparticles. The formation of H atoms (reduction product) and {sm_bullet}OH radicals (oxidation product) from water, and CO{sub 3}{sup -} radical anions (oxidation product) from carbonates, was detected in CO{sub 2}-saturated titania aqueous dispersion under UV illumination. Additionally, methoxyl, {sm_bullet}OCH{sub 3}, and methyl, {sm_bullet}CH{sub 3}, radicals were identified as reaction intermediates. The two-electron, one-proton reaction proposed as an initial step in the reduction of CO{sub 2}, on the surface of TiO{sub 2}, ismore » supported by the results of first-principles calculations.« less

Atmospheric fate of hydrofluoroolefins, CxF2x+1CHCH2 (x = 1,2,3,4 and 6): Kinetics with Cl atoms and products.

PubMed

Ballesteros, Bernabé; Jiménez, Elena; Moreno, Alberto; Soto, Amparo; Antiñolo, María; Albaladejo, José

2017-01-01

Rate coefficients for the gas-phase reactions of C x F 2x+1 CHCH 2 (x = 1, 2, 3, 4 and 6) with Cl atoms were determined at (298 ± 2) K and (710 ± 5) Torr of air using a relative rate technique. Two experimental setups with simulation chambers were employed with Fourier Transform Infrared (FTIR) spectroscopy and Gas Chromatography coupled to Mass Spectrometry (GC-MS) as detection techniques. The Cl-rate coefficients obtained were (in 10 -10  cm 3  molecule -1  s -1 ): (0.85 ± 0.11) for CF 3 CHCH 2 , (1.11 ± 0.08) for C 2 F 5 CHCH 2 , (1.12 ± 0.18) for C 3 F 7 CHCH 2 , (0.97 ± 0.09) for C 4 F 9 CHCH 2 , and (0.99 ± 0.08) for C 6 F 13 CHCH 2 . Additionally, the gas-phase products were identified and quantified, when possible, by FTIR spectroscopy or GC-MS. The main reaction product was reported to be C x F 2x+1 C(O)CH 2 Cl. The fluorinated species, C x F 2x+1 CHO and C x F 2x+1 C(O)CH 2 Cl, were identified. CF 3 C(O)CH 2 Cl and CF 3 CHO were found to be formed with molar yield of (69 ± 5)% and (9 ± 1)%, respectively. The global lifetime of the investigated C x F 2x+1 CHCH 2 due to their Cl-reaction is more than 100 days so this route does not compete with the removal by OH radicals. This lifetime is long enough for C x F 2x+1 CHCH 2 to be transported to remote areas where they can be degraded. However, at a local scale, in marine regions at dawn the removal of C x F 2x+1 CHCH 2 is expected to occur in ca. 1 day. The atmospheric degradation of these hydrofluoroolefins by Cl atoms is not expected to be a source of bioaccumulative perfluorinated carboxylic acids, C x F 2x+1 C(O)OH. Additionally, the UV absorption cross sections of CF 3 C(O)CH 2 Cl were determined together with the rate coefficient of the OH reaction by an absolute kinetic method at room temperature. Copyright © 2016 Elsevier Ltd. All rights reserved.

Theoretical studies on atmospheric chemistry of HFE-245mc and perfluoro-ethyl formate: Reaction with OH radicals, atmospheric fate of alkoxy radical and global warming potential

NASA Astrophysics Data System (ADS)

Lily, Makroni; Baidya, Bidisha; Chandra, Asit K.

2017-02-01

Theoretical studies have been performed on the kinetics, mechanism and thermochemistry of the hydrogen abstraction reactions of CF3CF2OCH3 (HFE-245mc) and CF3CF2OCHO with OH radical using DFT based M06-2X method. IRC calculation shows that both hydrogen abstraction reactions proceed via weakly bound hydrogen-bonded complex preceding to the formation of transition state. The rate coefficients calculated by canonical transition state theory along with Eckart's tunnelling correction at 298 K: k1(CF3CF2OCH3 + OH) = 1.09 × 10-14 and k2(CF3CF2OCHO + OH) = 1.03 × 10-14 cm3 molecule-1 s-1 are in very good agreement with the experimental values. The atmospheric implications of CF3CF2OCH3 and CF3CF2OCHO are also discussed.

Energetics of the O-H bond and of intramolecular hydrogen bonding in HOC6H4C(O)Y (Y = H, CH3, CH2CH=CH2, C[triple bond]CH, CH2F, NH2, NHCH3, NO2, OH, OCH3, OCN, CN, F, Cl, SH, and SCH3) compounds.

PubMed

Bernardes, Carlos E S; Minas da Piedade, Manuel E

2008-10-09

The energetics of the phenolic O-H bond in a series of 2- and 4-HOC 6H 4C(O)Y (Y = H, CH3, CH 2CH=CH2, C[triple bond]CH, CH2F, NH2, NHCH 3, NO2, OH, OCH3, OCN, CN, F, Cl, SH, and SCH3) compounds and of the intramolecular O...H hydrogen bond in 2-HOC 6H 4C(O)Y, was investigated by using a combination of experimental and theoretical methods. The standard molar enthalpies of formation of 2-hydroxybenzaldehyde (2HBA), 4-hydroxybenzaldehyde (4HBA), 2'-hydroxyacetophenone (2HAP), 2-hydroxybenzamide (2HBM), and 4-hydroxybenzamide (4HBM), at 298.15 K, were determined by micro- or macrocombustion calorimetry. The corresponding enthalpies of vaporization or sublimation were also measured by Calvet drop-calorimetry and Knudsen effusion measurements. The combination of the obtained experimental data led to Delta f H m (o)(2HBA, g) = -238.3 +/- 2.5 kJ.mol (-1), DeltafHm(o)(4HBA, g) = -220.3 +/- 2.0 kJ.mol(-1), Delta f H m (o)(2HAP, g) = -291.8 +/- 2.1 kJ.mol(-1), DeltafHm(o)(2HBM, g) = -304.8 +/- 1.5 kJ.mol (-1), and DeltafHm(o) (4HBM, g) = -278.4 +/- 2.4 kJ.mol (-1). These values, were used to assess the predictions of the B3LYP/6-31G(d,p), B3LYP/6-311+G(d,p), B3LYP/aug-cc-pVDZ, B3P86/6-31G(d,p), B3P86/6-311+G(d,p), B3P86/aug-cc-pVDZ, and CBS-QB3 methods, for the enthalpies of a series of isodesmic gas phase reactions. In general, the CBS-QB3 method was able to reproduce the experimental enthalpies of reaction within their uncertainties. The B3LYP/6-311+G(d,p) method, with a slightly poorer accuracy than the CBS-QB3 approach, achieved the best performance of the tested DFT models. It was further used to analyze the trends of the intramolecular O...H hydrogen bond in 2-HOC 6H 4C(O)Y evaluated by the ortho-para method and to compare the energetics of the phenolic O-H bond in 2- and 4-HOC 6H 4C(O)Y compounds. It was concluded that the O-H bond "strength" is systematically larger for 2-hydroxybenzoyl than for the corresponding 4-hydroxybenzoyl isomers mainly due to the presence of the intramolecular O...H hydrogen bond in the 2-isomers. The observed differences are, however, significantly dependent on the nature of the substituent Y, in particular, when an intramolecular H-bond can be present in the radical obtained upon cleavage of the O-H bond.

Characterization of a distonic isomer C6H5C+(OH)OCH2 of methyl benzoate radical cation by associative ion-molecule reactions

NASA Astrophysics Data System (ADS)

Dechamps, Noémie; Flammang, Robert; Gerbaux, Pascal; Nam, Pham-Cam; Nguyen, Minh Tho

2006-03-01

The C6H5C+(OH)OCH2 radical cation, formally a distonic isomer of ionized methyl benzoate, has been prepared by dissociative ionization of neopentyl benzoate, as earlier suggested by Audier et al. [H.E. Audier, A. Milliet, G. Sozzi, S. Hammerum, Org. Mass. Spectrom. 25 (1990) 44]. Its distonic character has now been firmly established by its high reactivity towards neutral methyl isocyanide (ionized methylene transfer) producing N-methyl ketenimine ions. Other mass spectrometric experiments and ab initio quantum chemical calculations also concur with each other pointing toward the existence of a stable distonic radical cation.

Hydrogen Migration and Vinylidene Pathway for Formation of Methane in the 193 nm Photodissociation of Propene: CH3CH=CH2 and CD3CD=CD2

NASA Technical Reports Server (NTRS)

Zhao, Yi-Lei; Laufer, Allan H.; Halpern, Joshua B.; Fahr, Askar

2007-01-01

Photodissociation channels and the final product yields from the 193 nm photolysis of propene-h6 (CH2=CHCH3) and propene-d6 (CD2=CDCD3) have been investigated, employing gas chromatography, mass spectroscopy, and flame ionization (GC/MS/FID) detection methods. The yields of methane as well as butadiene relative to ethane show considerable variations when propene-h6 or propene-d6 are photolyzed. This suggests significant variances in the relative importance of primary photolytic processes and/or secondary radical reactions, occurring subsequent to the photolysis. Theoretical calculations suggest the potential occurrence of an intramolecular dissociation through a mechanism involving vinylidene formation, accompanied by an ethylenic H-migration through the pi-orbitals. This process affects the final yields of methane-h4 versus methane-d4 with respect to other products. The product yields from previous studies of the 193 nm photolysis of methyl vinyl ketone-h6 and -d6 (CH2=CHCOCH3, CD2=CDCOCD3), alternative precursors for generating methyl and vinyl radicals, are compared with the current results for propene.

ORGANONICKEL CHEMISTRY IN THE CATALYTIC HYDRODECHLORINATION OF POLYCHLOROBIPHENYLS (PCBS): LIGAND STERIC EFFECTS AND MOLECULAR STRUCTURE OF REACTION INTERMEDIATES. (R823526)

EPA Science Inventory

Abstract

Soluble homogeneous organophosphorus_¯¯nickel complexes have been used to detoxify polychlorinated biphenyls (PCBs) by catalyzed hydrodechlorination using NaBH₂(OCH₂CH₂OCH₃)₂ as the hyd...

On the Formation of the C{sub 2}H{sub 6}O Isomers Ethanol (C{sub 2}H{sub 5}OH) and Dimethyl Ether (CH{sub 3}OCH{sub 3}) in Star-forming Regions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bergantini, Alexandre; Maksyutenko, Pavlo; Kaiser, Ralf I., E-mail: ralfk@hawaii.edu

The structural isomers ethanol (CH{sub 3}CH{sub 2}OH) and dimethyl ether (CH{sub 3}OCH{sub 3}) were detected in several low-, intermediate-, and high-mass star-forming regions, including Sgr B2, Orion, and W33A, with the relative abundance ratios of ethanol/dimethyl ether varying from about 0.03 to 3.4. Until now, no experimental data regarding the formation mechanisms and branching ratios of these two species in laboratory simulation experiments could be provided. Here, we exploit tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) to detect and analyze the production of complex organic molecules (COMs) resulting from the exposure of water/methane (H{sub 2}O/CH{sub 4}) ices to energetic electrons.more » The main goal is to understand the formation mechanisms in star-forming regions of two C{sub 2}H{sub 6}O isomers: ethanol (CH{sub 3}CH{sub 2}OH) and dimethyl ether (CH{sub 3}OCH{sub 3}). The results show that the experimental branching ratios favor the synthesis of ethanol versus dimethyl ether (31 ± 11:1). This finding diverges from the abundances observed toward most star-forming regions, suggesting that production routes on interstellar grains to form dimethyl ether might be missing; alternatively, ethanol can be overproduced in the present simulation experiments, such as via radical–radical recombination pathways involving ethyl and hydroxyl radicals. Finally, the PI-ReTOF-MS data suggest the formation of methylacetylene (C{sub 3}H{sub 4}), ketene (CH{sub 2}CO), propene (C{sub 3}H{sub 6}), vinyl alcohol (CH{sub 2}CHOH), acetaldehyde (CH{sub 3}CHO), and methyl hydroperoxide (CH{sub 3}OOH), in addition to ethane (C{sub 2}H{sub 6}), methanol (CH{sub 3}OH), and CO{sub 2} detected from infrared spectroscopy. The yield of all the confirmed species is also determined.« less

OH Production from Reactions of Organic Peroxy Radicals with HO2 : Recent Studies on Ether-Derived Peroxy Radicals

NASA Astrophysics Data System (ADS)

Orlando, J. J.; Tyndall, G. S.; Kegley Owen, C. S.; Reynoldson, N.

2013-12-01

There is now ample evidence supporting significant formation of OH radicals in the reaction of HO2 with certain organic peroxy radicals (RO2). These reaction channels serve to promote radical propagation, and thus have the potential to alter HOx budgets and partitioning and hence tropospheric oxidative capacity. While much focus has been placed on OH production from reactions involving carbonyl-containing RO2 species, it is also the case that other oxygen- substituted peroxy species (e.g., CH3OCH2OO, HOCH2OO) likely generate OH in their reactions with HO2 (see ref. 1 and refs therein). In this work, the Cl-atom-initiated oxidation of two ethers, diethyl and diisopropyl ether, is investigated over ranges of conditions in an environmental chamber, using both FTIR and GC-FID methods for product quantification. Preliminary analysis suggests that significant OH production is occurring in the reaction of HO2 with CH3CH2OCH(OO)CH3, and also provides evidence for a rapid unimolecular reaction of diisopropyl ether-derived peroxy radicals. Details of these and other results will be described. 1. Orlando, J. J., and G. S. Tyndall, 2012: Laboratory studies of organic peroxy radical chemistry: an overview with emphasis on recent issues of atmospheric significance, Chemical Society Reviews, 41, 6294-6317, doi: 10.1039/C2CS35166H.

Synthesis of nano grade hollow silica sphere via a soft template method.

PubMed

Tsai, Ming-Shyong; Li, Miao Ju; Yen, Fu-Hsu

2008-06-01

The nano grade hollow silica sphere (HSS) was synthesized by a novel soft template method. We found that the precipitate of aluminate had a porous structure that could be the soft template for HSS. After mixing the colloidal silica with the aluminate precipitate, the bubble trapped in this porous structure could form the nano grade HSS. The aluminate precipitate was removed by adjusting the pH of the slurry to approximately 1. The outside diameter, the specific surface, and the mean pore size diameter of the forming HSS were 60-90 nm, 571 m2/g, and 3 nm, respectively. The formed HSS was collected by modifying the surface with Si(OCH3)3CHCH2 (VTMO) and then filtrating the precipitated gel in the n-butanol and ethanol solvent system.

Reaction between aminoalkyl radicals and akyl halides: Dehalogenation by electron transfer?

NASA Astrophysics Data System (ADS)

Lalevée, J.; Fouassier, J. P.; Blanchard, N.; Ingold, K. U.

2011-07-01

Aminoalkyl radicals, such as Et2NCrad HCH3, have low oxidation potentials and are therefore powerful reducing agents. We have found that Et2NCrad HCH3 reacts with CCl4 and CBr4 in di-tert-butyl peroxide with bimolecular rate constants (measured by LFP) close, or equal, to the diffusion-controlled limit. For the less reactive halide, CH2Br2, the reaction rate is increased substantially by the addition of acetonitrile as a co-solvent. It is tentatively concluded that these reactions occur by electron-transfer from the aminoalkyl to the organohalide with formation of the iminium ion, Et2N+dbnd CHCH3 (NMR detection), halide ion and a halomethyl radical, e.g., rad CCl3 and rad CHCl2 (ESR, spin-trapping detection).

Resist Rolymers. 8. Thermolysis of Bromine Containing Acrylate Polymers.

DTIC Science & Technology

1987-06-01

bromine containing polymers is particularly interesting because of their role as proven flame retardants . The bromine ...BrI IC COOH I -co2 (1 CH MeI I Br --- CH 2 ---- The presence of bromine on ester units apparently alters the principal mode of degradation of the...CH2---C C--- I I I I C-O C-O C C=O 0’ OCH2CH2Br 0 0 + ’OCH2CH 2Br (6) As described earlier6 bromoethoxy radical loose bromine atom at

Discovery of interstellar ketenyl (HCCO), a surprisingly abundant radical

NASA Astrophysics Data System (ADS)

Agúndez, Marcelino; Cernicharo, José; Guélin, Michel

2015-05-01

We conducted radioastronomical observations of 9 dark clouds with the IRAM 30 m telescope. We present the first identification in space of the ketenyl radical (HCCO) toward the starless core Lupus-1A and the molecular cloud L483 and the detection of the related molecules ketene (H2CCO) and acetaldehyde (CH3CHO) in these two sources and 3 additional dark clouds. We also report the detection of the formyl radical (HCO) in the 9 targeted sources and of propylene (CH2CHCH3) in 4 of the observed sources, which significantly extends the number of dark clouds where these molecules are known to be present. We have derived a beam-averaged column density of HCCO of ~5 × 1011 cm-2 in both Lupus-1A and L483, which means that the ketenyl radical is just ~10 times less abundant than ketene in these sources. The non-negligible abundance of HCCO found implies that there must be a powerful formation mechanism able to counterbalance the efficient destruction of this radical through reactions with neutral atoms. The column densities derived for HCO, (0.5-2.7) ×1012 cm-2, and CH2CHCH3, (1.9-4-2) ×1013 cm-2, are remarkably uniform across the sources where these species are detected, confirming their ubiquity in dark clouds. Gas phase chemical models of cold dark clouds can reproduce the observed abundances of HCO, but cannot explain the presence of HCCO in Lupus-1A and L483 and the high abundances derived for propylene. The chemistry of cold dark clouds needs to be revised in light of these new observational results. Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Tables 3-6 are available in electronic form at http://www.aanda.org

Infrared absorption of trans-1-chloromethylallyl and trans-1-methylallyl radicals produced in photochemical reactions of trans-1,3-butadiene and Cl2 in solid para-hydrogen.

PubMed

Bahou, Mohammed; Wu, Jen-Yu; Tanaka, Keiichi; Lee, Yuan-Pern

2012-08-28

The reactions of chlorine and hydrogen atoms with trans-1,3-butadiene in solid para-hydrogen (p-H(2)) were investigated with infrared (IR) absorption spectra. When a p-H(2) matrix containing Cl(2) and trans-1,3-butadiene was irradiated with ultraviolet light at 365 nm, intense lines at 650.3, 809.0, 962.2, 1240.6 cm(-1), and several weaker ones due to the trans-1-chloromethylallyl radical, ●(CH(2)CHCH)CH(2)Cl, appeared. Observed wavenumbers and relative intensities agree with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++g(2d, 2p) method. That the Cl atom adds primarily to the terminal carbon atom of trans-1,3-butadiene is in agreement with the path of minimum energy predicted theoretically, but in contrast to the reaction of Cl + propene in solid p-H(2) [J. Amicangelo and Y.-P. Lee, J. Phys. Chem. Lett. 1, 2956 (2010)] in which the addition of Cl to the central C atom is favored, likely through steric effects in a p-H(2) matrix. A second set of lines, intense at 781.6, 957.9, 1433.6, 2968.8, 3023.5, 3107.3 cm(-1), were observed when the UV-irradiated Cl(2)/trans-1,3-butadiene/p-H(2) matrix was further irradiated with IR light from a SiC source. These lines are assigned to the trans-1-methylallyl radical, ●(CH(2)CHCH)CH(3), produced from reaction of 1,3-butadiene with a H atom resulted from the reaction of Cl atoms with solid p-H(2) exposed to IR radiation.

Low-k SiOCH Film Etching Process and Its Diagnostics Employing Ar/C5F10O/N2 Plasma

NASA Astrophysics Data System (ADS)

Nagai, Mikio; Hayashi, Takayuki; Hori, Masaru; Okamoto, Hidekazu

2006-09-01

We proposed an environmental harmonic etching gas of C5F10O (CF3CF2CF2OCFCF2), and demonstrated the etching of low-k SiOCH films employing a dual-frequency capacitively coupled etching system. Dissociative ionization cross sections for the electron impact ionizations of C5F10O and c-C4F8 gases have been measured by quadrupole mass spectroscopy (QMS). The dissociative ionization cross section of CF3+ from C5F10O gas was much higher than those of other ionic species, and 10 times higher than that of CF3+ from C4F8 gas. CF3+ is effective for increasing the etching rate of SiO2. As a result, the etching rate of SiOCH films using Ar/C5F10O/N2 plasma was about 1000 nm/min, which is much higher than that using Ar/C4F8/N2 plasma. The behaviours of fluorocarbon radicals in Ar/C5F10O/N2 plasma, which were measured by infrared diode laser absorption spectroscopy, were similar to those in Ar/C4F8/N2 plasma. The densities of CF and CF3 radicals were markedly decreased with increasing N2 flow rate. Etching rate was controlled by N2 flow rate. A vertical profile of SiOCH with a high etching rate and less microloading was realized using Ar/C5F10O/N2 plasma chemistry.

H-atom addition and abstraction reactions in mixed CO, H2CO and CH3OH ices - an extended view on complex organic molecule formation

NASA Astrophysics Data System (ADS)

Chuang, K.-J.; Fedoseev, G.; Ioppolo, S.; van Dishoeck, E. F.; Linnartz, H.

2016-01-01

Complex organic molecules (COMs) have been observed not only in the hot cores surrounding low- and high-mass protostars, but also in cold dark clouds. Therefore, it is interesting to understand how such species can be formed without the presence of embedded energy sources. We present new laboratory experiments on the low-temperature solid state formation of three complex molecules - methyl formate (HC(O)OCH3), glycolaldehyde (HC(O)CH2OH) and ethylene glycol (H2C(OH)CH2OH) - through recombination of free radicals formed via H-atom addition and abstraction reactions at different stages in the CO→H2CO→CH3OH hydrogenation network at 15 K. The experiments extend previous CO hydrogenation studies and aim at resembling the physical-chemical conditions typical of the CO freeze-out stage in dark molecular clouds, when H2CO and CH3OH form by recombination of accreting CO molecules and H-atoms on ice grains. We confirm that H2CO, once formed through CO hydrogenation, not only yields CH3OH through ongoing H-atom addition reactions, but is also subject to H-atom-induced abstraction reactions, yielding CO again. In a similar way, H2CO is also formed in abstraction reactions involving CH3OH. The dominant methanol H-atom abstraction product is expected to be CH2OH, while H-atom additions to H2CO should at least partially proceed through CH3O intermediate radicals. The occurrence of H-atom abstraction reactions in ice mantles leads to more reactive intermediates (HCO, CH3O and CH2OH) than previously thought, when assuming sequential H-atom addition reactions only. This enhances the probability to form COMs through radical-radical recombination without the need of UV photolysis or cosmic rays as external triggers.

Competing 1πσ* mediated dynamics in mequinol: O-H versus O-CH3 photodissociation pathways.

PubMed

Hadden, David J; Roberts, Gareth M; Karsili, Tolga N V; Ashfold, Michael N R; Stavros, Vasilios G

2012-10-14

Deactivation of excited electronic states through coupling to dissociative (1)πσ* states in heteroaromatic systems has received considerable attention in recent years, particularly as a mechanism that contributes to the ultraviolet (UV) photostability of numerous aromatic biomolecules and their chromophores. Recent studies have expanded upon this work to look at more complex species, which involves understanding competing dynamics on two different (1)πσ* potential energy surfaces (PESs) localized on different heteroatom hydride coordinates (O-H and N-H bonds) within the same molecule. In a similar spirit, the work presented here utilizes ultrafast time-resolved velocity map ion imaging to study competing dissociation pathways along (1)πσ* PESs in mequinol (p-methoxyphenol), localized at O-H and O-CH(3) bonds yielding H atoms or CH(3) radicals, respectively, over an excitation wavelength range of 298-238 nm and at 200 nm. H atom elimination is found to be operative via either tunneling under a conical intersection (CI) (298 ≥ λ ≥ 280 nm) or ultrafast internal conversion through appropriate CIs (λ ≤ 245 nm), both of which provide mechanisms for coupling onto the dissociative state associated with the O-H bond. In the intermediate wavelength range of 280 ≥ λ ≥ 245 nm, mediated H atom elimination is not observed. In contrast, we find that state driven CH(3) radical elimination is only observed in the excitation range 264 ≥ λ ≥ 238 nm. Interpretation of these experimental results is guided by: (i) high level complete active space with second order perturbation theory (CASPT2) calculations, which provide 1-D potential energy cuts of the ground and low lying singlet excited electronic states along the O-H and O-CH(3) bond coordinates; and (ii) calculated excitation energies using CASPT2 and the equation-of-motion coupled cluster with singles and doubles excitations (EOM-CCSD) formalism. From these comprehensive studies, we find that the dynamics along the O-H coordinate generally mimic H atom elimination previously observed in phenol, whereas O-CH(3) bond fission in mequinol appears to present notably different behavior to the CH(3) elimination dynamics previously observed in anisole (methoxybenzene).

Reaction of singlet-excited 2,3-diazabicyclo[2.2.2]oct-2-ene and tert-butoxyl radicals with aryl-substituted benzofuranones.

PubMed

Lundgren, Cecilia Vannesjö; Koner, Apurba L; Tinkl, Michael; Pischel, Uwe; Nau, Werner M

2006-03-03

5,7-Di-tert-butyl-3-aryl-3H-benzofuran-2-ones are lactones with potential antioxidant activity, owing to their abstractable benzylic C-H hydrogens. The fluorescence quenching of the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), an established probe for the hydrogen-donor propensity of chain-breaking antioxidants, was investigated for 16 aryl-substituted benzofuranone derivatives [m,m-(CF3)2, p-CN, m-CN, p-CF3, p-COOCH3, m-CF3, p-Cl, p-F, H, m-CH3, p-CH3, m,p-(CH3)2, p-OCH3, o-CH3, o-CF3, o,m-(CH3)2]. Analysis of the rate data in terms of a linear free energy relationship yielded a reaction constant of rho = +0.35. This implies that n,pi*-excited DBO acts as nucleophilic species. In contrast, hydrogen abstraction of tert-butoxyl radicals from the benzofuranones was accelerated by electron-donating substituents (rho = -0.23), in conformity with the electrophilic character of oxygen-centered alkoxyl radicals. Possible implications for the optimization of the hydrogen-donor propensity of antioxidants through structural variation are discussed.

Enthalpy of formation of anisole: implications for the controversy on the O-H bond dissociation enthalpy in phenol.

PubMed

Simões, Ricardo G; Agapito, Filipe; Diogo, Hermínio P; da Piedade, Manuel E Minas

2014-11-20

Significant discrepancies in the literature data for the enthalpy of formation of gaseous anisole, ΔfHmo(PhOCH3, g), have fueled an ongoing controversy regarding the most reliable enthalpy of formation of the phenoxy radical and of the gas phase O-H bond dissociation enthalpy, DHo(PhO-H), in phenol. In the present work ΔfHmo(PhOCH3, g) was reassessed using a combination of calorimetric determinations and high-level (W2-F12) ab initio calculations. Static-bomb combustion calorimetry led to the standard molar enthalpy of formation of liquid anisole at 298.15 K, ΔfHmo(PhOCH3, l) = −(117.1 ± 1.4) kJ·mol(-1). The corresponding enthalpy of vaporization was obtained as, ΔvapHmo(PhOCH3) = 46.41 ± 0.26 kJ·mol(-1), by Calvet-drop microcalorimetry. These results give ΔfHmo(PhOCH3, g) = −(70.7 ± 1.4) kJ·mol(-1), in excellent agreement with ΔfHmo(PhOCH3, g) = −(70.8 ± 3.2) kJ·mol(-1), obtained from the W2-F12 calculations. The ΔfHmo(PhOCH3, g) here recommended leads to ΔfHmo(PhO•, g) = 55.5 ± 2.4 kJ·mol(-)1 and DH°(PhO-H) = 368.1 ± 2.6 kJ·mol(-1).

Peter J Derrick and the Grand Scale 'Magnificent Mass Machine' mass spectrometer at Warwick.

PubMed

Colburn, A W; Derrick, Peter J; Bowen, Richard D

2017-12-01

The value of the Grand Scale 'Magnificent Mass Machine' mass spectrometer in investigating the reactivity of ions in the gas phase is illustrated by a brief analysis of previously unpublished work on metastable ionised n-pentyl methyl ether, which loses predominantly methanol and an ethyl radical, with very minor contributions for elimination of ethane and water. Expulsion of an ethyl radical is interpreted in terms of isomerisation to ionised 3-pentyl methyl ether, via distonic ions and, possibly, an ion-neutral complex comprising ionised ethylcyclopropane and methanol. This explanation is consistent with the closely similar behaviour of the labelled analogues, C 3 H 7 CH 2 CD 2 OCH 3 +. and C 3 H 7 CD 2 CH 2 OCH 3 +. , and is supported by the greater kinetic energy release associated with loss of ethane from ionised n-propyl methyl ether compared to that starting from directly generated ionised 3-pentyl methyl ether.

Mechanism of the Skraup and Doebner-von Miller quinoline syntheses: Cyclization of. alpha. ,. beta. -unsaturated N-aryliminium salts via 1,3-dizaetidinium ion intermediates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eisch, J.J.; Dluzniewski, T.

1989-03-17

The hydrochlorides of cinnamaldehyde anils of the type ArCH=CHCH=NAr{prime}, where Ar and Ar{prime} are phenyl or p-tolyl groups, have been shown to react between 25{degree}C and 100{degree}C, in a toluene suspension or in a solution of DMSO or acetonitrile, to yield 2-substituted quinolines and N-cinnamylanilines ArCH=CHCH{sub 2}NHAr{prime}. The reaction proceeds under anhydrous conditions by cyclization of the anil hydrochlorides themselves to produce ultimately 2-substituted quinolines. The kinetics of the reaction follow a first-order dependence on the anil hydrochloride. Rapid exchange occurring between dissimilar anil hydrochlorides suggests that such anil metatheses take place by way of 1,3-diazetidinium ion intermediates, which previousmore » studies have shown would possess the requisite metastability. The foregoing experimental observations are reconciled in terms of a novel mechanism for the formation of quinolines directly from anils under acidic conditions, namely, the reversible formation of diazetidinium ions and their irreversible cyclization to quinolines. It is proposed that this pathway is the operative mechanism in the classic Skraup and Doehner-von Miller quinoline syntheses. 28 refs., 2 tabs.« less

Assessing thermochemical data

NASA Astrophysics Data System (ADS)

Holmes, John L.; Aubry, Christiane; Wang, Xian

2007-11-01

This paper describes, with examples, a critical assessment of thermochemical data for some small molecules and free radicals. The available heats of formation, [Delta]fH° (all 298 K values). for simple alkyl hydroperoxides and di-alkyl peroxides were compared and new data are provided. The [Delta]fH° values, all ±5 kJ/mol, are: CH3OOH, -135; CH3CH2OOH, -168; n-C3H7OOH, -189; s-C3H7OOH, -205; t-C4H9OOH, -240; CH3OOCH3, -132; CH3CH2OOCH3, -165; C2H5OOC2H5, -198; n-C3H7OOn-C3H7, -240; s-C3H7OOs-C3H7, -272; t-C4H9OOt-C4H9, -342. These are consistent with established O-O bond dissociation energies and with additivity considerations. [Delta]fH° values for the corresponding alkoxy radicals are also addressed. A similar survey was applied to the homologous n-alkyl aldehydes, C2 to C8, for which recommended [Delta]fH° values, all ±1.5 kJ/mol, are: -166.5, -189, -207.5, -227, -248, -268 and -289, respectively. Particular attention was given to [Delta]fH°(CH3CO) = -10.3 ± 1.8 kJ/mol. The current NIST WebBook datum, [Delta]fH°(CS) = 280.3 kJ/mol, is arguably the best value, being consistent with related thermochemical data. Finally the [Delta]fH° values for the allylic free radicals CH2CHCH2, 174 ± 3 kJ/mol, CH2CHCH(OH), 4.5 ± 4 kJ/mol, and (CH2CH)2C(OH), 37 ± 4 kJ/mol, derived from experimental data and results of computational chemistry are described, together with some related homolytic bond strengths.

Kinetic and mechanistic study of the gas-phase reaction of CxF2x+1CHCH2 (x=1, 2, 3, 4 and 6) with O3 under atmospheric conditions.

PubMed

Soto, A; Ballesteros, B; Jiménez, E; Antiñolo, M; Martínez, E; Albaladejo, J

2018-06-01

The relative-rate technique has been used to determine the rate coefficient for the reaction of C x F 2x+1 CHCH 2 (x = 1, 2, 3, 4 and 6) with ozone at (298 ± 2) K and (720 ± 5) Torr of air by FTIR (Fourier Transform Infrared Spectroscopy) and by GC-MS/SPME (Gas Chromatography-Mass Spectroscopy with Solid Phase Micro Extraction) in two different atmospheric simulation chambers. The following rate coefficients, in units of 10 -19  cm 3 molecule -1 s -1 , were obtained: (3.01 ± 0.10) for CF 3 CHCH 2 , (2.11 ± 0.35) for C 2 F 5 CHCH 2 , (2.34 ± 0.42) for C 3 F 7 CHCH 2 , (2.05 ± 0.31) for C 4 F 9 CHCH 2 and (2.07 ± 0.39) for C 6 F 13 CHCH 2 , where uncertainties represent ±2σ statistical error. The atmospheric lifetime of C x F 2x+1 CHCH 2 due to reaction with ozone was estimated from the reported rate coefficients. Additionally, the gaseous products formed in these reactions were investigated in the presence of synthetic air simulating a clean atmosphere. Perfluoroaldehydes, C x F 2x+1 C(O)H (PFALs), formaldehyde, formic acid and CF 2 O were identified as reaction products in the investigated reactions. The identified products made possible to propose a reaction mechanism that justifies the observed products. The atmospheric implications of these results are discussed in terms of the potential contribution of the atmospheric degradation of these species to PFAL and PFCA burden. Copyright © 2018 Elsevier Ltd. All rights reserved.

The effect of natural iron oxide and oxalic acid on the photocatalytic degradation of isoproturon: a kinetics and analytical study.

PubMed

Boucheloukh, H; Remache, W; Parrino, F; Sehili, T; Mechakra, H

2017-05-17

The photocatalytic degradation of isoproturon, a persistent toxic herbicide, was investigated in the presence of natural iron oxide and oxalic acid and under UV irradiation. The influence of the relevant parameters such as the pH and the iron oxide and oxalic acid concentrations has been studied. The presence of natural iron oxide and oxalic acid in the system effectively allow the degradation of isoproturon, whereas the presence of t-butyl alcohol adversely affects the phototransformation of the target pollutant, thus indicating that an OH radical initiated the degradation mechanism. The degradation mechanism of isoproturon was investigated by means of GC-MS analysis. Oxidation of both the terminal N-(CH 3 ) 2 and isopropyl groups is the initial process leading to N-monodemethylated (NHCH 3 ), N-formyl (N(CH 3 )CHO), and CHCH 3 OH as the main intermediates. The substitution of the isopropyl group by an OH group is also observed as a side process.

Protein-functionalized hairy diamond nanoparticles.

PubMed

Dahoumane, Si Amar; Nguyen, Minh Ngoc; Thorel, Alain; Boudou, Jean-Paul; Chehimi, Mohamed M; Mangeney, Claire

2009-09-01

Diazonium salt chemistry and atom transfer radical polymerization (ATRP) were combined in view of preparing new bioactive hairy diamond nanoparticles containing, or potentially containing, nitrogen-vacancy (NV) fluorescent centers (fluorescent nanodiamonds, or fNDs). fNDs were modified by ATRP initiators using the electroless reduction of the diazonium salt BF(4)(-),(+)N(2)-C(6)H(4)-CH(CH(3))-Br. The strongly bound aryl groups -C(6)H(4)-CH(CH(3))-Br efficiently initiated the ATRP of tert-butyl methacrylate (tBMA) at the surface of the nanodiamonds, which resulted in obtaining ND-PtBMA hybrids. The grafted chain thickness, estimated from X-ray photoelectron spectroscopy (XPS), was found to increase linearly with respect to time before reaching a plateau value of ca. 2 nm. These nanoobjects were further hydrolyzed into ND-PMAA (where PMAA is the poly(methacrylic acid) graft) and further decorated by bovine serum albumin through the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) coupling procedure.

Site reactivity in the free radicals induced damage to leucine residues: a theoretical study.

PubMed

Medina, M E; Galano, A; Alvarez-Idaboy, J R

2015-02-21

Several recent computational studies have tried to explain the observed selectivity in radical damage to proteins. In this work we use Density Functional Theory and Transition State Theory including tunnelling corrections, reaction path degeneracy, the effect of diffusion, and the role of free radicals to get further insights into this important topic. The reaction between a leucine derivative and free radicals of biological significance, in aqueous and lipid media, has been investigated. Both thermochemical and kinetic analyses, in both hydrophilic and hydrophobic environments, have been carried out. DPPH, ˙OOH, ˙OOCH3, ˙OOCH2Cl, ˙OOCHCl2 and ˙OOCHCH2 radicals do not react with the target molecule. The reactions are proposed to be kinetically controlled. The leucine gamma site was the most reactive for the reactions with ˙N3, ˙OOCCl3, ˙OCH3, ˙OCH2Cl, and ˙OCHCl2 radicals, with rate constants equal to 1.97 × 10(5), 3.24 × 10(4), 6.68 × 10(5), 5.98 × 10(6) and 8.87 × 10(8) M(-1) s(-1), respectively, in aqueous solution. The ˙Cl, ˙OH and ˙OCCl3 radicals react with leucine at the beta, gamma, and delta positions at rates close to the diffusion limit with the alpha position which is the slowest path and the most thermodynamically favored. The presented results confirm that the Bell-Evans-Polanyi principle does not apply for the reactions between amino acid residues and free radicals. Regarding the influence of the environment on the reactivity of the studied series of free radicals towards leucine residues, it is concluded that hydrophilic media slightly lower the reactivity of the studied radicals, compared to hydrophobic ones, albeit the trends in reactivity are very similar.

(Phosphinoalkyl)silanes. 4.(1) Hydrozirconation as a Non-Photochemical Route to (Phosphinopropyl)silanes: Facile Assembly of the Bis(3-(diphenylphosphino)propyl)silyl ("biPSi") Ligand Framework. Access to the Related Poly(3-(dimethylsilyl)propyl)phosphines R(n)()P(CH(2)CH(2)CH(2)SiMe(2)H)(3)(-)(n)() (n = 1, R = Ph; n = 0).

PubMed

Zhou, Xiaobing; Stobart, Stephen R.; Gossage, Robert A.

1997-08-13

Treatment of SiEt(3)(CH=CH(2)) with ZrCp(2)HCl (Schwartz's reagent) followed by reaction with PPh(2)Cl provides a high-yield (75%) route to Ph(2)PCH(2)CH(2)SiEt(3), and accordingly hydrozirconation of CH(2)=CHCH(2)SiHMe(2) affords the intermediate ZrCp(2)(CH(2)CH(2)CH(2)SiHMe(2))Cl (2). The latter, which is very sensitive to hydrolysis and reacts with HCl forming SiHMe(2)Pr(n)() and with NBS or I(2) affording SiHMe(2)CH(2)CH(2)CH(2)X (X = Br (3), I (4)), behaves similarly with PPh(2)Cl, PPhCl(2), or PBr(3) undergoing cleavage to the known Ph(2)PCH(2)CH(2)CH(2)SiMe(2)H (i.e. chelH, A) and the novel bis- and tris(silylpropyl)phosphines PhP(CH(2)CH(2)CH(2)SiMe(2)H)(2) (5) and P(CH(2)CH(2)CH(2)SiMe(2)H)(3) (6), respectively, with concomitant formation of ZrCp(2)Cl(2). Corresponding hydroboration of allylsilanes is facile, but subsequent phosphine halide cleavage yields (phosphinoalkyl)silanes only as constituents of intractable mixtures. Hydrozirconation followed by phosphination with PPh(2)Cl also converts SiHMe(CH(2)CH=CH(2))(2) to SiHMe(CH(2)CH(2)CH(2)PPh(2))(2) (i.e. biPSiH, B) together with a propyl analogue Ph(2)PCH(2)CH(2)CH(2)SiMe(Pr(n)())H (7) of A (ca. 2:1 ratio), as well as SiH(CH(2)CH=CH(2))(3) to a mixture (ca. 5:2:1 ratio) of SiH(CH(2)CH(2)CH(2)PPh(2))(3) (i.e. triPSiH, C), a new analogue SiH(Pr(n)())(CH(2)CH(2)CH(2)PPh(2))(2) (8) of B, and a further analogue Ph(2)PCH(2)CH(2)CH(2)SiHPr(n)()(2) (9) of A. A further analogue SiH(2)(CH(2)CH(2)CH(2)PPh(2))(2) (10) of biPSiH (B) is obtained similarly starting from SiH(2)(CH(2)CH=CH(2))(2). Steric control of silylalkyl cleavage from 2 is indicated by the fact that, like PPh(2)Cl (which forms B), two further biPSiH analogues SiH(Me)[CH(2)CH(2)CH(2)P(n-hex)(2)](2) (11) and SiH(Me)(CH(2)CH(2)CH(2)PPhBz)(2) (12) were obtained using P(n-hex)(2)Cl (i.e. n-hex = CH(3)(CH(2))(4)CH(2)-) or PPhBzCl (i.e. Bz = -CH(2)C(6)H(5)), respectively, whereas neither PPr(i)(2)Cl nor PBu(t)(2)Cl led to (phosphinoalkyl)silane formation. The surface-substrate linking reagent Ph(2)PCH(2)CH(2)CH(2)Si(OEt)(3) (D) is formed efficiently by similar means from Si(OEt)(3)(CH(2)CH=CH(2)). NMR data ((1)H, (13)C, (29)Si, (31)P) for 2-12 have been measured and are discussed.

Disproportionation and thermochemical sulfate reduction reactions in S-H20-Ch4 and S-D2O-CH4 systems from 200 to 340 °C at elevated pressures

USGS Publications Warehouse

Yuan, Shunda; Chou, I-Ming; Burruss, Robert A.

2013-01-01

Elemental sulfur, as a transient intermediate compound, by-product, or catalyst, plays significant roles in thermochemical sulfate reduction (TSR) reactions. However, the mechanisms of the reactions in S-H2O-hydrocarbons systems are not clear. To improve our understanding of reaction mechanisms, we conducted a series of experiments between 200 and 340 °C for S-H2O-CH4, S-D2O-CH4, and S-CH4-1m ZnBr2 systems in fused silica capillary capsules (FSCC). After a heating period ranging from 24 to 2160 hours (hrs), the quenched samples were analyzed by Raman spectroscopy. Combined with the in situ Raman spectra collected at high temperatures and pressures in the S-H2O and S-H2O-CH4 systems, our results showed that (1) the disproportionation of sulfur in the S-H2O-CH4 system occurred at temperatures above 200 °C and produced H2S, SO42-, and possibly trace amount of HSO4-; (2) sulfate (and bisulfate), in the presence of sulfur, can be reduced by methane between 250 and 340 °C to produce CO2 and H2S, and these TSR temperatures are much closer to those of the natural system (2O-CH4 system may take place simultaneously, with TSR being favored at higher temperatures; and (4) in the system S-D2O-CH4, both TSR and the competitive disproportionation reactions occurred simultaneously at temperatures above 300 °C, but these reactions were very slow at lower temperatures. Our observation of methane reaction at 250 °C in a laboratory time scale suggests that, in a geologic time scale, methane may be destroyed by TSR reactions at temperatures > 200 °C that can be reached by deep drilling for hydrocarbon resources.

Infrared Laser Spectroscopy of the n-PROPYL and i-PROPYL Radicals in Helium Droplets: Significant Bend-Stretch Coupling Revealed in the CH Stretch Region

NASA Astrophysics Data System (ADS)

Moradi, Christopher P.; Douberly, Gary E.; Tabor, Daniel P.; Sibert, Edwin

2016-06-01

The n-propyl and i-propyl radicals were generated in the gas phase via pyrolysis of n-butyl nitrite (CH3(CH2)3ONO) and i-butyl nitrite (CH3CH(CH3)CH2ONO) precursors, respectively. Nascent radicals were promptly solvated by a beam of He nanodroplets, and the infrared spectra of the radicals were recorded in the C-H stretching region. In addition to three vibrations of n-propyl previously measured in an Ar matrix, we observe many unreported bands between 2800 and 3150 wn, which we attribute to propyl radicals. The C-H stretching modes observed above 2960 wn for both radicals are in excellent agreement with anharmonic frequencies computed using VPT2. Between 2800 and 2960 wn, however, the spectra of n-propyl and i-propyl radicals become quite congested and difficult to assign due to the presence of multiple anharmonic resonances. Computations employing a local mode Hamiltonian reveal the origin of the spectral congestion to be strong coupling between the high frequency C-H stretching modes and the lower frequency bending/scissoring motions. The only significant local coupling is between stretches and bends on the same CH2/CH3 group.

Theoretical insight into OH- and Cl-initiated oxidation of CF3OCH(CF3)2 and CF3OCF2CF2H & fate of CF3OC(X•)(CF3)2 and CF3OCF2CF2X• radicals (X=O, O2)

PubMed Central

Bai, Feng-Yang; Ma, Yuan; Lv, Shuang; Pan, Xiu-Mei; Jia, Xiu-Juan

2017-01-01

In this study, the mechanistic and kinetic analysis for reactions of CF3OCH(CF3)2 and CF3OCF2CF2H with OH radicals and Cl atoms have been performed at the CCSD(T)//B3LYP/6-311++G(d,p) level. Kinetic isotope effects for reactions CF3OCH(CF3)2/CF3OCD(CF3)2 and CF3OCF2CF2H/CF3OCF2CF2D with OH and Cl were estimated so as to provide the theoretical estimation for future laboratory investigation. All rate constants, computed by canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT), are in reasonable agreement with the limited experimental data. Standard enthalpies of formation for the species were also calculated. Atmospheric lifetime and global warming potentials (GWPs) of the reaction species were estimated, the large lifetimes and GWPs show that the environmental impact of them cannot be ignored. The organic nitrates can be produced by the further oxidation of CF3OC(•)(CF3)2 and CF3OCF2CF2• in the presence of O2 and NO. The subsequent decomposition pathways of CF3OC(O•)(CF3)2 and CF3OCF2CF2O• radicals were studied in detail. The derived Arrhenius expressions for the rate coefficients over 230–350 K are: k T(1) = 5.00 × 10−24T3.57 exp(−849.73/T), k T(2) = 1.79 × 10−24T4.84 exp(−4262.65/T), kT(3) = 1.94 × 10−24 T4.18 exp(−884.26/T), and k T(4) = 9.44 × 10−28T5.25 exp(−913.45/T) cm3 molecule−1 s−1. PMID:28067283

Theoretical insight into OH- and Cl-initiated oxidation of CF3OCH(CF3)2 and CF3OCF2CF2H & fate of CF3OC(X•)(CF3)2 and CF3OCF2CF2X• radicals (X=O, O2)

NASA Astrophysics Data System (ADS)

Bai, Feng-Yang; Ma, Yuan; Lv, Shuang; Pan, Xiu-Mei; Jia, Xiu-Juan

2017-01-01

In this study, the mechanistic and kinetic analysis for reactions of CF3OCH(CF3)2 and CF3OCF2CF2H with OH radicals and Cl atoms have been performed at the CCSD(T)//B3LYP/6-311++G(d,p) level. Kinetic isotope effects for reactions CF3OCH(CF3)2/CF3OCD(CF3)2 and CF3OCF2CF2H/CF3OCF2CF2D with OH and Cl were estimated so as to provide the theoretical estimation for future laboratory investigation. All rate constants, computed by canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT), are in reasonable agreement with the limited experimental data. Standard enthalpies of formation for the species were also calculated. Atmospheric lifetime and global warming potentials (GWPs) of the reaction species were estimated, the large lifetimes and GWPs show that the environmental impact of them cannot be ignored. The organic nitrates can be produced by the further oxidation of CF3OC(•)(CF3)2 and CF3OCF2CF2• in the presence of O2 and NO. The subsequent decomposition pathways of CF3OC(O•)(CF3)2 and CF3OCF2CF2O• radicals were studied in detail. The derived Arrhenius expressions for the rate coefficients over 230-350 K are: k T(1) = 5.00 × 10-24T3.57 exp(-849.73/T), k T(2) = 1.79 × 10-24T4.84 exp(-4262.65/T), kT(3) = 1.94 × 10-24 T4.18 exp(-884.26/T), and k T(4) = 9.44 × 10-28T5.25 exp(-913.45/T) cm3 molecule-1 s-1.

The Coupled Photochemistry of Ammonia and Acetylene: Applications to the Atmospheric Chemistry on Jupiter

NASA Astrophysics Data System (ADS)

Keane, Thomas Christopher

1995-01-01

The existence of hydrogen cyanide (HCN) in the highly reducing atmosphere of Jupiter was a surprising discovery (Tokunaga et al., 1981). Previous studies that tested the theoretical proposal of Kaye and Strobel (1983a) that the HCN observed on Jupiter is the result of NH _3 photolysis in the presence of C _2H_2 established that acetonitrile (CH_3CN) and acetaldazine (CH _3CH=NN=CHCH_3) are important intermediates in HCN formation (Ferris and Ishikawa, 1988). In this study the rates of formation of these compounds, and of other recently detected intermediates, have been determined in static photolysis experiments at 296 K and at temperatures which are closer to those found in the Jovian atmosphere. Experiments were also performed, using a photochemical flow reactor, that allowed for a better approximation of the mixing ratios of reactant gases (8 times 10^{ -4} for NH_3 and 1 times 10^{-5} for C_2H_2) and the process of advection in the Jovian atmosphere. An overall reaction pathway for HCN formation is proposed. Major intermediates and products found in these laboratory simulations that have not yet been observed on Jupiter are acetonitrile (CH_3CN), acetaldazine (CH_3CH=NN=CHCH _3), acetaldehyde hydrazone (CH_3 CH=NNH_2), N-ethylethylideneimine (CH_3CH=NC_2H _5), ethylamine (C_2H _5NH_2) and methylamine (CH _3NH_2). HCN is formed by the photolysis of NH_3/C _2H_2 mixtures (40:5 torr) at 296 K and at low temperature (208 K, 195 K and 180 K) with the highest quantum efficiency for HCN formation observed at 180 K. In static experiments using a high partial pressure of H_2 the quantum yield for HCN formation decreased three-fold relative to the 296 K photolyses when no H_2 was used. An additional ten-fold decrease in the quantum yield for HCN formation occurred when using the flow system. The quantum yields for acetaldazine and acetaldehyde hydrazone formation were found to vary inversely to that for HCN formation. For those static experiments which best simulate Jovian reaction conditions (H_2: NH_3 : C_2H_2 = 600: 7.5: 5 torr, 180 K) the following products and their quantum yields for formation were obtained: C_2H_4 (0.129), CH_3 CH=NN=CHCH_3 (0.079), CH _3CH=NNH_2 (0.049), C_2H_5NH_2 (0.038), CH_3NH_2 (0.003), CH_3CN (0.002), HCN (0.001) and CH_3CH=NC _2H_5 (0.001).

Reactions of gas phase H atoms with ethylene, acetylene and ethane adsorbed on Ni( 1 1 1 )

NASA Astrophysics Data System (ADS)

Bürgi, T.; Trautman, T. R.; Gostein, M.; Lahr, D. L.; Haug, K. L.; Ceyer, S. T.

2002-03-01

The products of the reaction of the most energetic form of hydrogen, gas phase H atoms, with ethylene, acetylene and ethane adsorbed on a Ni(1 1 1) surface at 60 K are probed. Adsorbed ethylidyne (CCH 3) is identified by high resolution electron energy loss spectroscopy to be the major product (30% yield) in all three cases. Adsorbed acetylene is a minor product (3% yield) and arises as a consequence of a dynamic equilibrium between CCH 3 and C 2H 2 in the presence of gas phase H atoms. The observation of the same product for the reaction of H atoms with all three hydrocarbons implies that CCH 3 is the most stable C 2 species in the presence of coadsorbed hydrogen. The rates of CCH 3 production are measured as a function of the time of exposure of H atoms to each hydrocarbon. A simple kinetic model treating each reaction as a pseudo-first order reaction in the hydrocarbon coverage is fit to these data. A mechanism for the formation of CCH 3 via a CHCH 2 intermediate common to all three reactants is proposed to describe this model. The observed instability of the CH 2CH 3 species relative to C 2H 4 plays a role in the formulation of this mechanism as does the observed stability of CHCH 2 species in the presence of coadsorbed hydrogen. The CH 2CH 3 and the CHCH 2 species are produced by the translational activation of ethane and the dissociative ionization of ethane and ethylene, respectively. In addition, the binding energy and the vibrational spectrum of ethane adsorbed on Ni(1 1 1) are determined and exceptionally high resolution vibrational spectra of adsorbed ethylene and acetylene are presented.

Infrared laser spectroscopy of the helium-solvated allyl and allyl peroxy radicals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leavitt, Christopher M.; Moradi, Christopher P.; Acrey, Bradley W.

2013-12-16

Infrared spectra in the C–H stretch region are reported for the allyl (CH 2CHCH 2) and allyl peroxy (CH 2=CH–CH 2OO·) radicals solvated in superfluid helium nanodroplets. Nine bands in the spectrum of the allyl radical have resolved rotational substructure. We have assigned three of these to the ν 1 (a 1), ν 3 (a 1), and ν 13 (b 2) C–H stretch bands and four others to the ν 14/(ν 15+2ν 11) (b 2) and ν 2/(ν 4+2ν 11) (a 1) Fermi dyads, and an unassigned resonant polyad is observed in the vicinity of the ν 1 band. Experimentalmore » coupling constants associated with Fermi dyads are consistent with quartic force constants obtained from density functional theory computations. The peroxy radical was formed within the He droplet via the reaction between allyl and O 2 following the sequential pick-up of the reactants. Five stable conformers are predicted for the allyl peroxy radical, and a computed two-dimensional potential surface for rotation about the CC–OO and CC–CO bonds reveals multiple isomerization barriers greater than ≈300 cm –1. Furthermore, the C–H stretch infrared spectrum is consistent with the presence of a single conformer following the allyl + O 2 reaction within helium droplets.« less

The gas phase origin of complex organic molecules precursors in prestellar cores

NASA Astrophysics Data System (ADS)

Bacmann, A.; Faure, A.

2015-05-01

Complex organic molecules (COMs) have long been observed in the warm regions surrounding nascent protostars. The recent discovery of oxygen-bearing COMs like methyl formate or dimethyl ether in prestellar cores (Bacmann et al. [2]), where gas and dust temperatures rarely exceed 10-15 K, has challenged the previously accepted models according to which COM formation relied on the diffusion of heavy radicals on warm (˜30 K) grains. Following these detections, new questions have arisen: do non-thermal processes play a role in increasing radical mobility or should new gas-phase routes be explored? The radicals involved in the formation of the aforementioned COMs, HCO and CH3O represent intermediate species in the grain-surface synthesis of methanol which proceeds via successive hydrogenations of CO molecules in the ice. We present here observations of methanol and its grain-surface precursors HCO, H2CO, CH3O in a sample of prestellar cores and derive their relative abundances. We find that the relative abundances HCO:H2CO:CH3O:CH3OH are constant across the core sample, close to 10:100:1:100. Our results also show that the amounts of HCO and CH3O are consistent with a gas-phase synthesis of these species from H2CO and CH3OH via radical-neutral or ion-molecule reactions followed by dissociative recombinations. Thus, while grain chemistry is necessary to explain the abundances of the parent volatile CH3OH, and possibly H2CO, the reactive species HCO and CH3O might be daughter molecules directly produced in the gas-phase.

Using a non-spin flip model to rationalize the irregular patterns observed in the activation of the C-H and Si-H bonds of small molecules by CpMCO (M = Co, Rh) complexes.

PubMed

Castro, Guadalupe; Colmenares, Fernando

2017-09-20

The activation of the C-H and Si-H bonds of CH(CH 3 ) 3 and SiH(CH 3 ) 3 molecules by organometallic compounds CpMCO (M = Co, Rh) has been investigated through DFT and CASSCF-MRMP2 calculations. In particular, we have analyzed the pathways joining the lowest-lying triplet and singlet states of the reactants with the products arising from the insertion of the metal atom into the C-H or Si-H bonds of the organic molecules. Channels connecting the reactants with the inserted structure Cp(CO)H-M-C(CH 3 ) 3 through the oxidative addition of the C-H bond of the organic molecule to the metal fragment were found only for the reaction CpRhCO + CH(CH 3 ) 3 . However, inserted structures could also be obtained for the interactions of SiH(CH 3 ) 3 with CpCoCO and CpRhCO by two sequential reactions involving the formation and rebounding of the radical fragments Cp(CO)H-M + Si(CH 3 ) 3 . According to this two-step reaction scheme, the complex CpCoCO is unable to activate the C-H bond of the CH(CH 3 ) 3 molecule due to the high energy at which the radical fragments Cp(CO)H-M + C(CH 3 ) 3 are located. The picture attained for these interactions is consistent with the available experimental data for this kind of reaction and allows rationalization of the differences in the reactivity patterns determined for them without using spin-flip models, as has been proposed in previous studies.

Glyceryl ether sulfonates for use in oil recovery fluids and processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCoy, D.R.

1984-08-21

Petroleum may be recovered from petroleum containing formations having high salinity by injecting into the formation an aqueous fluid containing an effective amount of a surface active agent characterized by the formula: R/sub 1/(OCH/sub 2/CH(OH)CH/sub 2/) /SUB m/ (R/sub 2/) /SUB n/ OR/sub 3/SO/sub 3/X wherein R/sub 1/ is an alkyl or alkylaryl radical, m is an integer of from 1 to 10, R/sub 2/ is an ethoxy radical and/or 1,2-propoxy radical, n is an integer of from 0 to 10, R/sub 3/ is an ethylene or 1,3-propylene radical, X is a sodium, potassium or ammonium cation; and driving themore » fluid through the formation and thereby displacing and recovering petroleum from the formation.« less

Atmospheric Chemistry of (CF3)2CHOCH3, (CF3)2CHOCHO, and CF3C(O)OCH3.

PubMed

Østerstrøm, Freja From; Wallington, Timothy J; Sulbaek Andersen, Mads P; Nielsen, Ole John

2015-10-22

Smog chambers with in situ FTIR detection were used to measure rate coefficients in 700 Torr of air and 296 ± 2 K of: k(Cl+(CF3)2CHOCH3) = (5.41 ± 1.63) × 10(-12), k(Cl+(CF3)2CHOCHO) = (9.44 ± 1.81) × 10(-15), k(Cl+CF3C(O)OCH3) = (6.28 ± 0.98) × 10(-14), k(OH+(CF3)2CHOCH3) = (1.86 ± 0.41) × 10(-13), and k(OH+(CF3)2CHOCHO) = (2.08 ± 0.63) × 10(-14) cm(3) molecule(-1) s(-1). The Cl atom initiated oxidation of (CF3)2CHOCH3 gives (CF3)2CHOCHO in a yield indistinguishable from 100%. The OH radical initiated oxidation of (CF3)2CHOCH3 gives the following products (molar yields): (CF3)2CHOCHO (76 ± 8)%, CF3C(O)OCH3 (16 ± 2)%, CF3C(O)CF3 (4 ± 1)%, and C(O)F2 (45 ± 5)%. The primary oxidation product (CF3)2CHOCHO reacts with Cl atoms to give secondary products (molar yields): CF3C(O)CF3 (67 ± 7)%, CF3C(O)OCHO (28 ± 3)%, and C(O)F2 (118 ± 12)%. CF3C(O)OCH3 reacts with Cl atoms to give: CF3C(O)OCHO (80 ± 8)% and C(O)F2 (6 ± 1)%. Atmospheric lifetimes of (CF3)2CHOCH3, (CF3)2CHOCHO, and CF3C(O)OCH3 were estimated to be 62 days, 1.5 years, and 220 days, respectively. The 100-year global warming potentials (GWPs) for (CF3)2CHOCH3, (CF3)2CHOCHO, and CF3C(O)OCH3 are estimated to be 6, 121, and 46, respectively. A comprehensive description of the atmospheric fate of (CF3)2CHOCH3 is presented.

Infrared Spectroscopy of 1-CHOLOROMETHYLALLYL and 1-METHYLALLYL Radicals Produced in a Solid Para-Hydrogen Matrix.

NASA Astrophysics Data System (ADS)

Bahou, Mohammed; Wu, Jen-Yu; Tanaka, Keiichi; Lee, Yuan-Pern

2012-06-01

The reaction of chlorine atoms with trans-1,3-butadiene in solid para-hydrogen (p-H_2) matrix has been studied using Fourier transform infrared spectroscopy. When a mixture of Cl_2, trans-1,3-butadiene and p-H_2 was deposited onto a cold target at 3 K and irradiated by UV light at 365 nm, new intense lines at 809.0, 962.1, 1240.6 cm-1 and several weaker ones appeared. The carrier of this spectrum was assigned to the 1-chloromethylallyl radical, - (CH_2CHCH)CH_2Cl, based on the anharmonic vibrational frequencies calculated with the DFT method, indicating that the addition of the Cl atom to trans-1,3-butadiene occurs primarily at the terminal carbon atom. This is in sharp contrast to the reaction of chlorine atoms with propene in a solid p-H_2 matrix in which the addition of Cl to the central carbon atom to produce selectively the 2-chloropropyl is favored due to the steric effects. The energy diagram calculated with B3PW91 method supports this selective reaction process because 1) the channel from trans-1,3-butadiene to 1-chloro-methylallyl is almost barrierless (0.4 kcal/mol), and 2) isomereization from 1-chloromethylally to the 2-chloro-3-buten-1-yl radical, CH_2CHCHClCH_2 - by migration of Cl atom from the terminal to the central C atom, hardly occur in the p-H_2 matrix because of the isomerization barrier height (18.8 kcal/mol). We also observed a second set of lines with intense ones at 781.6, 957.93, 1433.6 cm-1 and several weaker ones when the UV-irradiated Cl_2/trans-1,3-butadiene/p-H_2 matrix was further irradiated with infrared light from a globar source. These lines are assigned to the 1-methylallyl radical, - (CH_2CHCH)CH_3, produced from reaction of 1,3-butadiene with an H atom that was produced from the reaction of Cl atoms with IR-irradiated p-H_2, Cl + H_2^* → H + HCl. The energy diagram calculated at the G3//B3LYP level similarly supports the reaction process to form selectively 1-methylallyl in the p-H_2 matrix. J. C. Amicangelo and Y. P. Lee, J. Phys. Chem. Lett. 1, 1956 (2010). J. L. Millerngelo, J. Phys. Chem. A 108, 2268 (2004).

Propenyl ether monomers for photopolymerization

DOEpatents

Crivello, J.V.

1996-10-22

Propenyl ether monomers of formula A(OCH{double_bond}CHCH{sub 3}){sub n} wherein n is an integer from one to six and A is selected from cyclic ethers, polyether and alkanes are disclosed. The monomers are readily polymerized in the presence of cationic photoinitiators, when exposed to actinic radiation, to form poly(propenyl ethers) that are useful for coatings, sealants, varnishes and adhesives. Compositions for preparing polymeric coatings comprising the compounds of the above formula together with particular cationic photoinitiators are also disclosed, as are processes for making the monomers from allyl halides and readily available alcohols. The process involves rearranging the resulting allyl ethers to propenyl ethers.

Propenyl ether monomers for photopolymerization

DOEpatents

Crivello, James V.

1996-01-01

Propenyl ether monomers of formula V A(OCH.dbd.CHCH.sub.3).sub.n wherein n is an integer from one to six and A is selected from cyclic ethers, polyether and alkanes are disclosed. The monomers are readily polymerized in the presence of cationic photoinitiators, when exposed to actinic radiation, to form poly(propenyl ethers) that are useful for coatings, sealants, varnishes and adhesives. Compositions for preparing polymeric coatings comprising the compounds of formula V together with particular cationic photoinitiators are also disclosed, as are processes for making the monomers from allyl halides and readily available alcohols. The process involves rearranging the resulting allyl ethers to propenyl ethers.

Process for making propenyl ethers and photopolymerizable compositions containing them

DOEpatents

Crivello, James V.

1996-01-01

Propenyl ether monomers of formula V A(OCH.dbd.CHCH.sub.3).sub.n wherein n is an integer from one to six and A is selected from cyclic ethers, polyether and alkanes are disclosed. The monomers are readily polymerized in the presence of cationic photoinitiators, when exposed to actinic radiation, to form poly(propenyl ethers) that are useful for coatings, sealants, varnishes and adhesives. Compositions for preparing polymeric coatings comprising the compounds of formula V together with particular cationic photoinitiators are also disclosed, as are processes for making the monomers from allyl halides and readily available alcohols. The process involves rearranging the resulting allyl ethers to propenyl ethers.

On the formation of the ·CH 2CH 2CH=NH 2+ distonic radical cation upon ionization of cyclopropylamine and allylamine

NASA Astrophysics Data System (ADS)

Nguyen, Minh Tho; Creve, Steven; Ha, Tae-Kyu

1998-08-01

Ab initio molecular orbital and density functional theory calculations have been applied to determine the relative stability of the cyclopropylamine 1 and allylamine (CH 2=CHCH 2NH 2+·2) radical cations and their isomers. It is confirmed that, upon ionization, 1 undergoes barrier-free ring-opening giving the distonic species ·CH 2CH 2CH=NH 2+3. 2 also rearranges by a 1,2-H-shift to the more stable 3 (by 70 kJ/mol) which is, however, less stable than the 1-aminopropene ion (CH 3-CH=CH-NH 2+·4) by 60 kJ/mol. The transition structure TS 2/3 lies 40 kJ/mol higher in energy than TS 3/4. Although QCISD and B3LYP calculations of isotropic hyperfine coupling constants agree reasonably with observed values, supporting the presence of the distonic 3 in ESR matrix experiments, the exclusive observation of 3, but not 4, is intriguing. This emphasizes the role of the matrix in stabilizing 3.

A Mechanistical Study on the Formation of Dimethyl Ether (CH3OCH3) and Ethanol (CH3CH2OH) in Methanol-containing Ices and Implications for the Chemistry of Star-forming Regions

NASA Astrophysics Data System (ADS)

Bergantini, Alexandre; Góbi, Sándor; Abplanalp, Matthew J.; Kaiser, Ralf I.

2018-01-01

The underlying formation mechanisms of complex organic molecules (COMs)—in particular, structural isomers—in the interstellar medium (ISM) are largely elusive. Here, we report new experimental findings on the role of methanol (CH3OH) and methane (CH4) ices in the synthesis of two C2H6O isomers upon interaction with ionizing radiation: ethanol (CH3CH2OH) and dimethyl ether (CH3OCH3). The present study reproduces the interstellar abundance ratios of both species with ethanol to dimethyl ether branching ratios of (2.33 ± 0.14):1 suggesting that methanol and methane represents the key precursor to both isomers within interstellar ices. Exploiting isotopic labeling combined with reflectron time-of-flight mass spectrometry (Re-TOF-MS) after isomer selective vacuum ultra-violet (VUV) photoionization of the neutral molecules, we also determine the formation mechanisms of both isomers via radical–radical recombination versus carbene (CH2) insertion with the former pathway being predominant. Formation routes to higher molecular weight reaction products such as ethylene glycol (HOCH2CH2OH), dimethyl peroxide (CH3OOCH3), and methoxymethanol (CH3OCH2OH) are discussed briefly as well.

ALMA Detection of Interstellar Methoxymethanol (CH3OCH2OH)

NASA Astrophysics Data System (ADS)

McGuire, Brett A.; Shingledecker, Christopher N.; Willis, Eric R.; Burkhardt, Andrew M.; El-Abd, Samer; Motiyenko, Roman A.; Brogan, Crystal L.; Hunter, Todd R.; Margulès, Laurent; Guillemin, Jean-Claude; Garrod, Robin T.; Herbst, Eric; Remijan, Anthony J.

2017-12-01

We report the detection of interstellar methoxymethanol (CH3OCH2OH) in Atacama Large Millimeter/submillimeter Array (ALMA) Bands 6 and 7 toward the MM1 core in the high-mass star-forming region NGC 6334I at ∼0.″1–1″ spatial resolution. A column density of 4(2) × 1018 cm‑2 at T ex = 200 K is derived toward MM1, ∼34 times less abundant than methanol (CH3OH), and significantly higher than predicted by astrochemical models. Probable formation and destruction pathways are discussed, primarily through the reaction of the CH3OH photodissociation products, the methoxy (CH3O) and hydroxymethyl (CH2OH) radicals. Finally, we comment on the implications of these mechanisms on gas-phase versus grain-surface routes operative in the region, and the possibility of electron-induced dissociation of CH3OH rather than photodissociation.

Natural bond orbital approach to the transmission of substituent effect through the fulvene and benzene ring systems.

PubMed

Oziminski, Wojciech P; Krygowski, Tadeusz M

2011-03-01

Electronic structure of 22 monosubstituted derivatives of benzene and exocyclically substituted fulvene with substituents: B(OH)(2), BH(2), CCH, CF(3), CH(3), CHCH(2), CHO, Cl, CMe(3), CN, COCH(3), CONH(2), COOH, F, NH(2), NMe(2), NO, NO(2), OCH(3), OH, SiH(3), SiMe(3) were studied theoretically by means of Natural Bond Orbital analysis. It is shown, that sum of π-electron population of carbon atoms of the fulvene and benzene rings, pEDA(F) and pEDA(B), respectively correlate well with Hammett substituent constants [Formula in text] and aromaticity index NICS. The substituent effect acting on pi-electron occupation at carbon atoms of the fulvene ring is significantly stronger than in the case of benzene. Electron occupations of ring carbon atoms (except C1) in fulvene plotted against each other give linear regressions with high correlation coefficients. The same is true for ortho- and para-carbon atoms in benzene. Positive slopes of the regressions indicate similar for fulvene and benzene kind of substituent effect - mostly resonance in nature. Only the regressions of occupation at the carbon atom in meta- position of benzene against ortho- and para-positions gives negative slopes and low correlation coefficients.

Hydrogen peroxide and dioxygen activation by dinuclear copper complexes in aqueous solution: hydroxyl radical production initiated by internal electron transfer.

PubMed

Zhu, Qing; Lian, Yuxiang; Thyagarajan, Sunita; Rokita, Steven E; Karlin, Kenneth D; Blough, Neil V

2008-05-21

Dinuclear Cu(II) complexes, CuII2Nn (n = 4 or 5), were recently found to specifically cleave DNA in the presence of a reducing thiol and O2 or in the presence of H2O2 alone. However, CuII2N3 and a closely related mononuclear Cu(II) complex exhibited no selective reaction under either condition. Spectroscopic studies indicate an intermediate is generated from CuII2Nn (n = 4 or 5) and mononuclear Cu(II) solutions in the presence of H2O2 or from CuI2Nn (n = 4 or 5) in the presence of O2. This intermediate decays to generate OH radicals and ligand degradation products at room temperature. The lack of reactivity of the intermediate with a series of added electron donors suggests the intermediate discharges through a rate-limiting intramolecular electron transfer from the ligand to the metal peroxo center to produce an OH radical and a ligand-based radical. These results imply that DNA cleavage does not result from direct reaction with a metal-peroxo intermediate but instead arises from reaction with either OH radicals or ligand-based radicals.

Atmospheric chemical reactions of monoethanolamine initiated by OH radical: mechanistic and kinetic study.

PubMed

Xie, Hong-Bin; Li, Chao; He, Ning; Wang, Cheng; Zhang, Shaowen; Chen, Jingwen

2014-01-01

Monoethanolamine (MEA) is a benchmark and widely utilized solvent in amine-based postcombustion CO2 capture (PCCC), a leading technology for reducing CO2 emission from fossil fuel power plants. The large-scale implementation of PCCC would lead to inevitable discharges of amines to the atmosphere. Therefore, understanding the kinetics and mechanisms of the transformation of representative amine MEA in the atmosphere is of great significance for risk assessment of the amine-based PCCC. In this study, the H-abstraction reaction of MEA with ·OH, and ensuing reactions of produced MEA-radicals, including isomerization, dissociation, and bimolecular reaction MEA-radicals+O2, were investigated by quantum chemical calculation [M06-2X/aug-cc-pVTZ//M06-2X/6-311++G(d,p)] and kinetic modeling. The calculated overall rate constant [(7.27 × 10(-11)) cm(3) molecule(-1) s(-1)] for H-abstraction is in excellent agreement with the experimental value [(7.02 ± 0.46) × 10(-11) cm(3) molecule(-1) s(-1)]. The results show that the product branching ratio of NH2CH2 · CHOH (MEA-β) (43%) is higher than that of NH2 · CHCH2OH (MEA-α) (39%), clarifying that MEA-α is not an exclusive product. On the basis of the unveiled reaction mechanisms of MEA-radicals + O2, the proton transfer reaction mass spectrometry signal (m/z 60.044), not recognized in the experiment, was identified.

Process for making propenyl ethers and photopolymerizable compositions containing them

DOEpatents

Crivello, J.V.

1996-01-23

Propenyl ether monomers of formula A(OCH{double_bond}CHCH{sub 3}){sub n} (V) wherein n is an integer from one to six and A is selected from cyclic ethers, polyether, and alkanes are disclosed. The monomers are readily polymerized in the presence of cationic photoinitiators, when exposed to actinic radiation, to form poly(propenyl ethers) that are useful for coatings, sealants, varnishes and adhesives. Compositions for preparing polymeric coatings comprising the compounds of formula V together with particular cationic photoinitiators are also disclosed, as are processes for making the monomers from allyl halides and readily available alcohols. The process involves rearranging the resulting allyl ethers to propenyl ethers.

Photodissociation of anisole and absolute photoionization cross-section of the phenoxy radical.

PubMed

Xu, Hong; Pratt, S T

2013-11-21

We have studied the photodissociation dynamics of anisole (C6H5OCH3) at 193 nm and determined the absolute photoionization cross-section of the phenoxy radical at 118.2 nm (10.486 eV) relative to the known cross-section of the methyl radical. Even at this energy, there is extensive fragmentation of the phenoxy radical upon photoionization, which is attributed to ionizing transitions that populate low-lying excited electronic states of the cation. For phenoxy radicals with less than ∼1 eV of internal energy, we find a cross-section for the production of the phenoxy cation of 14.8 ± 3.8 Mb. For radicals with higher internal energy, dissociative ionization is the dominant process, and for internal energies of ∼2.7-3.7 eV, we find a total cross-section (photoionization plus dissociative ionization) of 22.3 ± 4.1 Mb. The results are discussed relative to the recently reported photoionization cross-section of phenol.

Infrared laser spectroscopy of the n-propyl and i-propyl radicals: Stretch-bend Fermi coupling in the alkyl CH stretch region

DOE PAGES

Franke, Peter R.; Tabor, Daniel P.; Moradi, Christopher P.; ...

2016-12-13

The n-propyl and i-propyl radicals were generated in the gas phase via pyrolysis of n-butyl nitrite [CH 3(CH 2) 3ONO] and i-butyl nitrite [(CH 3) 2CHCH 2ONO], respectively. Nascent radicals were promptly solvated by a beam of He nanodroplets, and the infrared spectra of the radicals were recorded in the CH stretching region. Several previously unreported bands are observed between 2800 and 3150 cm –1. The CH stretching modes observed above 3000 cm –1 are in excellent agreement with CCSD(T) anharmonic frequencies computed using second-order vibrational perturbation theory. However, between 2800 and 3000 cm –1, the spectra of n- andmore » i-propyl radicals become congested and difficult to assign due to the presence of multiple anharmonic resonance polyads. To model the spectrally congested region, Fermi and Darling-Dennison resonances are treated explicitly using “dressed” Hamiltonians and CCSD(T) quartic force fields in the normal mode representation, and the agreement with experiment is less than satisfactory. Computations employing local mode effective Hamiltonians reveal the origin of the spectral congestion to be strong coupling between the high frequency CH stretching modes and the lower frequency CH n bending/scissoring motions. The most significant coupling is between stretches and bends localized on the same CH 2/CH 3 group. As a result, spectral simulations using the local mode approach are in excellent agreement with experiment.« less

Infrared laser spectroscopy of the n-propyl and i-propyl radicals: Stretch-bend Fermi coupling in the alkyl CH stretch region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franke, Peter R.; Tabor, Daniel P.; Moradi, Christopher P.

The n-propyl and i-propyl radicals were generated in the gas phase via pyrolysis of n-butyl nitrite [CH 3(CH 2) 3ONO] and i-butyl nitrite [(CH 3) 2CHCH 2ONO], respectively. Nascent radicals were promptly solvated by a beam of He nanodroplets, and the infrared spectra of the radicals were recorded in the CH stretching region. Several previously unreported bands are observed between 2800 and 3150 cm –1. The CH stretching modes observed above 3000 cm –1 are in excellent agreement with CCSD(T) anharmonic frequencies computed using second-order vibrational perturbation theory. However, between 2800 and 3000 cm –1, the spectra of n- andmore » i-propyl radicals become congested and difficult to assign due to the presence of multiple anharmonic resonance polyads. To model the spectrally congested region, Fermi and Darling-Dennison resonances are treated explicitly using “dressed” Hamiltonians and CCSD(T) quartic force fields in the normal mode representation, and the agreement with experiment is less than satisfactory. Computations employing local mode effective Hamiltonians reveal the origin of the spectral congestion to be strong coupling between the high frequency CH stretching modes and the lower frequency CH n bending/scissoring motions. The most significant coupling is between stretches and bends localized on the same CH 2/CH 3 group. As a result, spectral simulations using the local mode approach are in excellent agreement with experiment.« less

Theoretical study on the gas-phase reaction mechanism between palladium monoxide and methane.

PubMed

Yang, Hua-Qing; Hu, Chang-Wei; Gao, Chao; Yang, Meng-Yao; Li, Fang-Ming; Li, Cai-Qin; Li, Xiang-Yuan

2011-12-01

The gas-phase reaction mechanism between palladium monoxide and methane has been theoretically investigated on the singlet and triplet state potential energy surfaces (PESs) at the CCSD(T)/AVTZ//B3LYP/6-311+G(2d, 2p), SDD level. The major reaction channel leads to the products PdCH(2) + H(2)O, whereas the minor channel results in the products Pd + CH(3)OH, CH(2)OPd + H(2), and PdOH + CH(3). The minimum energy reaction pathway for the formation of main products (PdCH(2) + H(2)O), involving one spin inversion, prefers to start at the triplet state PES and afterward proceed along the singlet state PES, where both CH(3)PdOH and CH(3)Pd(O)H are the critical intermediates. Furthermore, the rate-determining step is RS-CH(3) PdOH → RS-2-TS1cb → RS-CH(2)Pd(H)OH with the rate constant of k = 1.48 × 10(12) exp(-93,930/RT). For the first C-H bond cleavage, both the activation strain ΔE(≠)(strain) and the stabilizing interaction ΔE(≠)(int) affect the activation energy ΔE(≠), with ΔE(≠)(int) in favor of the direct oxidative insertion. On the other hand, in the PdCH(2) + H(2) O reaction, the main products are Pd + CH(3)OH, and CH(3)PdOH is the energetically preferred intermediate. In the CH(2)OPd + H(2) reaction, the main products are Pd + CH(3)OH with the energetically preferred intermediate H(2)PdOCH(2). In the Pd + CH(3)OH reaction, the main products are CH(2)OPd + H(2), and H(2)PdOCH(2) is the energetically predominant intermediate. The intermediates, PdCH(2), H(2) PdCO, and t-HPdCHO are energetically preferred in the PdC + H(2), PdCO + H(2), and H(2)Pd + CO reactions, respectively. Besides, PdO toward methane activation exhibits higher reaction efficiency than the atom Pd and its first-row congener NiO. Copyright © 2011 Wiley Periodicals, Inc.

Formation of ethylene glycol and other complex organic molecules in star-forming regions

NASA Astrophysics Data System (ADS)

Rivilla, V. M.; Beltrán, M. T.; Cesaroni, R.; Fontani, F.; Codella, C.; Zhang, Q.

2017-02-01

Context. The detection of complex organic molecules related with prebiotic chemistry in star-forming regions allows us to investigate how the basic building blocks of life are formed. Aims: Ethylene glycol (CH2OH)2 is the simplest sugar alcohol and the reduced alcohol of the simplest sugar glycoladehyde (CH2OHCHO). We study the molecular abundance and spatial distribution of (CH2OH)2, CH2OHCHO and other chemically related complex organic species (CH3OCHO, CH3OCH3, and C2H5OH) towards the chemically rich massive star-forming region G31.41+0.31. Methods: We analyzed multiple single-dish (Green Bank Telescope and IRAM 30 m) and interferometric (Submillimeter Array) spectra towards G31.41+0.31, covering a range of frequencies from 45 to 258 GHz. We fitted the observed spectra with a local thermodynamic equilibrium (LTE) synthetic spectra, and obtained excitation temperatures and column densities. We compared our findings in G31.41+0.31 with the results found in other environments, including low- and high-mass star-forming regions, quiescent clouds and comets. Results: We report for the first time the presence of the aGg' conformer of (CH2OH)2 towards G31.41+0.31, detecting more than 30 unblended lines. We also detected multiple transitions of other complex organic molecules such as CH2OHCHO, CH3OCHO, CH3OCH3, and C2H5OH. The high angular resolution images show that the (CH2OH)2 emission is very compact, peaking towards the maximum of the 1.3 mm continuum. These observations suggest that low abundance complex organic molecules, like (CH2OH)2 or CH2OHCHO, are good probes of the gas located closer to the forming stars. Our analysis confirms that (CH2OH)2 is more abundant than CH2OHCHO in G31.41+0.31, as previously observed in other interstellar regions. Comparing different star-forming regions we find evidence of an increase of the (CH2OH)2/CH2OHCHO abundance ratio with the luminosity of the source. The CH3OCH3/CH3OCHO and (CH2OH)2/C2H5OH ratios are nearly constant with luminosity. We also find that the abundance ratios of pairs of isomers (CH2OHCHO/CH3OCHO and C2H5OH/CH3OCH3) decrease with the luminosity of the sources. Conclusions: The most likely explanation for the behavior of the (CH2OH)2/CH2OHCHO ratio is that these molecules are formed by different chemical formation routes not directly linked, although different formation and destruction efficiencies in the gas phase cannot be ruled out. The most likely formation route of (CH2OH)2 is by combination of two CH2OH radicals on dust grains. We also favor that CH2OHCHO is formed via the solid-phase dimerization of the formyl radical HCO. The interpretation of the observations also suggests a chemical link between CH3OCHO and CH3OCH3, and between (CH2OH)2 and C2H5OH. The behavior of the abundance ratio C2H5OH/CH3OCH3 with luminosity may be explained by the different warm-up timescales in hot cores and hot corinos. The reduced spectra (ASCII files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A59

Reactive sulfur species: kinetics and mechanism of the oxidation of cystine by hypochlorous acid to give N,N'-dichlorocystine.

PubMed

Nagy, Péter; Ashby, Michael T

2005-06-01

Cystine and HOCl (a neutrophil-derived oxidant) react to form an intermediate that has a half-life of ca. 5 min at pH 7.5. The intermediate subsequently decomposes to eventually yield a mixture of cystine, higher oxides of Cys, and other uncharacterized species. Spectral titrations, transitory (1)H NMR and UV-vis spectra, and the reaction properties of the intermediate are consistent with a formulation of N,N'-dichlorocystine {NDC = [-SCH(2)CH(NHCl)(CO(2)H)](2)}. The reaction of equimolar amounts of HOCl with cystine at pH 11.3 does not yield N-chlorocystine [NCC = (-O2C)(H3N+)CHCH(2)SSCH(2)CH(NHCl)(CO(2)H)] but rather a 1:1 mixture of NDC and cystine. This result could be explained by two mechanisms: rapid disproportionation of NCC to produce NDC and cystine or a faster reaction of the second equivalent of HOCl with NCC than the first equivalent of HOCl reacts with cystine. The latter mechanism is favored because of our observation by NMR spectroscopy that NDC decomposes via a species that we have assigned as NCC. Thus, disproportionation of NCC is apparently a relatively slow process. The rates of reaction of cystine(0) = [-SCH(2)CH(NH(3)(+))(CO(2)(-))](2) degrees , cystine(1-) = [((-)O(2)C)(H(2)N)CHCH(2)SSCH(2)CH(NH(3)(+))(CO(2)(-))](-), and cystine(2-) = [-SCH(2)CH(NH2)(CO2)(-))]2(2-) have been investigated, and it is clear that cystine(0) is unreactive, whereas cystine(2-) is about four times more reactive than cystine(1-). Accordingly, the following mechanism is proposed (constants for 5 degrees C): HOCl = H+ + OCl-, pK1 = 7.47; cystine(0) = cystine(1-) + H+, pK2 = 8.15; cystine(1-) = cystine(2-) + H+, pK3 = 9.00; cystine(1-) + HOCl --> NCC(1-) + H2O, k4 = 4.3(2) x 10(6) M(-1) s(-1); cystine(2-) + HOCl --> NCC(2)(-) + H2O, k5 = 1.6(2) x 10(7) M(-1) s(-1); NCC(1-) --> NCC(2-) + H+, k6 = fast; NCC(2-) + HOCl --> NDC(2-) + H2O, k7 = fast. At physiologic pH, the k4 pathway dominates. The generation of long-lived chloramine derivatives of cystine may have physiological consequences, since such compounds are known to react with nucleophiles via mechanisms that are also characteristic of HOCl, electrophilic transfer C+.

Chrysodeixis chalcites nucleopolyhedrovirus (ChchNPV): Natural occurrence and efficacy as a biological insecticide on young banana plants in greenhouse and open-field conditions on the Canary Islands

PubMed Central

Fuentes, Ernesto Gabriel; Hernández-Suárez, Estrella

2017-01-01

Chrysodeixis chalcites, an important pest of banana crops on the Canary Islands, is usually controlled by chemical insecticides. The present study aimed to evaluate the efficacy of the most prevalent isolate of the Chrysodeixis chalcites nucleopolyhedrovirus (ChchNPV, Baculoviridae) as a biological insecticide. Overall the prevalence of ChchNPV infection in C. chalcites populations was 2.3% (103 infected larvae out of 4,438 sampled), but varied from 0–4.8% on Tenerife and was usually low (0–2%) on the other islands. On Tenerife, infected larvae were present at 11 out of 17 plantations sampled. The prevalence of infection in larvae on bananas grown under greenhouse structures was significantly higher (3%) than in open-field sites (1.4%). The ChchNPV-TF1 isolate was the most abundant and widespread of four genetic variants of the virus. Application of 1.0x109 viral occlusion bodies (OBs)/l of ChchNPV-TF1 significantly reduced C. chalcites foliar damage in young banana plants as did commonly used pesticides, both in greenhouse and open-field sites. The insecticidal efficacy of ChchNPV-TF1 was similar to that of indoxacarb and a Bacillus thuringiensis (Bt)-based insecticide in one year of trials and similar to Bt in the following year of trails in greenhouse and field crops. However, larvae collected at different time intervals following virus treatments and reared in the laboratory experienced 2–7 fold more mortality than insects from conventional insecticide treatments. This suggests that the acquisition of lethal dose occurred over an extended period (up to 7 days) compared to a brief peak in larvae on plants treated with conventional insecticides. These results should prove useful for the registration of a ChchNPV-based insecticide for integrated management of this pest in banana crops on the Canary Islands. PMID:28750003

Chrysodeixis chalcites nucleopolyhedrovirus (ChchNPV): Natural occurrence and efficacy as a biological insecticide on young banana plants in greenhouse and open-field conditions on the Canary Islands.

PubMed

Fuentes, Ernesto Gabriel; Hernández-Suárez, Estrella; Simón, Oihane; Williams, Trevor; Caballero, Primitivo

2017-01-01

Chrysodeixis chalcites, an important pest of banana crops on the Canary Islands, is usually controlled by chemical insecticides. The present study aimed to evaluate the efficacy of the most prevalent isolate of the Chrysodeixis chalcites nucleopolyhedrovirus (ChchNPV, Baculoviridae) as a biological insecticide. Overall the prevalence of ChchNPV infection in C. chalcites populations was 2.3% (103 infected larvae out of 4,438 sampled), but varied from 0-4.8% on Tenerife and was usually low (0-2%) on the other islands. On Tenerife, infected larvae were present at 11 out of 17 plantations sampled. The prevalence of infection in larvae on bananas grown under greenhouse structures was significantly higher (3%) than in open-field sites (1.4%). The ChchNPV-TF1 isolate was the most abundant and widespread of four genetic variants of the virus. Application of 1.0x109 viral occlusion bodies (OBs)/l of ChchNPV-TF1 significantly reduced C. chalcites foliar damage in young banana plants as did commonly used pesticides, both in greenhouse and open-field sites. The insecticidal efficacy of ChchNPV-TF1 was similar to that of indoxacarb and a Bacillus thuringiensis (Bt)-based insecticide in one year of trials and similar to Bt in the following year of trails in greenhouse and field crops. However, larvae collected at different time intervals following virus treatments and reared in the laboratory experienced 2-7 fold more mortality than insects from conventional insecticide treatments. This suggests that the acquisition of lethal dose occurred over an extended period (up to 7 days) compared to a brief peak in larvae on plants treated with conventional insecticides. These results should prove useful for the registration of a ChchNPV-based insecticide for integrated management of this pest in banana crops on the Canary Islands.

Radical Ions of 3-Styryl-quinoxalin-2-one Derivatives Studied by Pulse Radiolysis in Organic Solvents.

PubMed

Skotnicki, Konrad; De la Fuente, Julio R; Cañete, Álvaro; Berrios, Eduardo; Bobrowski, Krzysztof

2018-04-12

The absorption-spectral and kinetic behaviors of radical ions and neutral hydrogenated radicals of seven 3-styryl-quinoxalin-2(1 H)-one (3-SQ) derivatives, one without substituents in the styryl moiety, four others with electron-donating (R = -CH 3 , -OCH 3 , and -N(CH 3 ) 2 ) or electron-withdrawing (R = -OCF 3 ) substituents in the para position in their benzene ring, and remaining two with double methoxy substituents (-OCH 3 ), however, at different positions (meta/para and ortho/meta) have been studied by UV-vis spectrophotometric pulse radiolysis in neat acetonitrile saturated with argon (Ar) and oxygen (O 2 ) and in 2-propanol saturated with Ar, at room temperature. In acetonitrile solutions, the radical anions (4R-SQ •- ) are characterized by two absorption maxima located at λ max = 470-490 nm and λ max = 510-540 nm, with the respective molar absorption coefficients ε 470-490 = 8500-13 100 M -1 cm -1 and ε 510-540 = 6100-10 300 M -1 cm -1 , depending on the substituent (R). All 4R-SQ •- decay in acetonitrile via first-order kinetics, with the rate constants in the range (1.2-1.5) × 10 6 s -1 . In 2-propanol solutions, they decay predominantly through protonation by the solvent, forming neutral hydrogenated radicals (4R-SQH • ), which are characterized by weak absorption bands with λ max = 480-490 nm. Being oxygen-insensitive, the radical cations (4R-SQ •+ ) are characterized by a strong absorption with λ max = 450-630 nm, depending on the substituent (R). They are formed in a charge-transfer reaction between a radical cation derived from acetonitrile (ACN •+ ) and substituted 3-styryl-quinoxalin-2-one derivatives (4R-SQ) with a pseudo-first-order rate constant k = (2.7-4.7) × 10 5 s -1 measured in solutions containing 0.1 mM 4R-3-SQ. The Hammett equation plot gave a very small negative slope (ρ = -0.08), indicating a very weak influence of the substituents in the benzene ring on the rate of charge-transfer reaction. The decay of 4R-SQ •+ in Ar-saturated acetonitrile solutions occurs with a pseudo-first-order rate constant k = (1.6-6.2) × 10 4 s -1 and, in principle, is not affected by the presence of O 2 , suggesting charge-spin delocalization over the whole 3-SQ molecule. Most of the radiolytically generated transient spectra are reasonably well-reproduced by semiempirical PM3-ZINDO/S (for 4R-SQ •- ) and density functional theory quantum mechanics calculations employing M06-2x hybrid functional together with the def2-TZVP basis set (for 4R-SQ •+ ).

A nanoscale Zr-based fluorescent metal-organic framework for selective and sensitive detection of hydrogen sulfide

NASA Astrophysics Data System (ADS)

Li, Yanping; Zhang, Xin; Zhang, Ling; Jiang, Ke; Cui, Yuanjing; Yang, Yu; Qian, Guodong

2017-11-01

Hydrogen sulfide (H2S) has been commonly viewed as a gas signaling molecule in various physiological and pathological processes. However, the highly efficient H2S detection still remains challenging. Herein, we designed a new robust nano metal-organic framework (MOF) UiO-66-CH=CH2 as a fluorescent probe for rapid, sensitive and selective detection of biological H2S. UiO-66-CH=CH2 was prepared by heating ZrCl4 and 2-vinylterephthalic acid via a simple method. UiO-66-CH=CH2 displayed fluorescence quenching to H2S and kept excellent selectivity in the presence of biological relevant analytes especially the cysteine and glutathione. This MOF-based probe also exhibited fast response (10 s) and high sensitivity with a detection limit of 6.46 μM which was within the concentration range of biological H2S in living system. Moreover, this constructed MOF featured water-stability, nanoscale (20-30 nm) and low toxicity, which made it a promising candidate for biological H2S sensing.

Experimental measurements of low temperature rate coefficients for neutral-neutral reactions of interest for atmospheric chemistry of Titan, Pluto and Triton: reactions of the CN radical.

PubMed

Morales, Sébastien B; Le Picard, Sébastien D; Canosa, André; Sims, Ian R

2010-01-01

The kinetics of the reactions of cyano radical, CN (X2sigma+) with three hydrocarbons, propane (CH3CH2CH3), propene (CH3CH=CH2) and 1-butyne (CH[triple band]CCH2CH3) have been studied over the temperature range of 23-298 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. These reactions are of interest for the cold atmospheres of Titan, Pluto and Triton, as they might participate in the formation of nitrogen and carbon bearing molecules, including nitriles, that are thought to play an important role in the formation of hazes and biological molecules. All three reactions are rapid with rate coefficients in excess of 10(-10) cm3 molecule(-1) s(-1) at the lowest temperatures of this study and show behaviour characteristic of barrierless reactions. Temperature dependences, different for each reaction, are compared to those used in the most recent photochemical models of Titan's atmosphere.

Evidence for Formation of a Radical-Mediated Flavin-N5 Covalent Intermediate.

PubMed

Dai, Yumin; Valentino, Hannah R; Sobrado, Pablo

2018-05-18

The redox-neutral reaction catalyzed by 2-haloacrylate hydratase (2-HAH) leads to the conversion of 2-chloroacrylate to pyruvate. Previous mechanistic studies demonstrated formation of a flavin-iminium ion as an important intermediate in the 2-HAH catalytic cycle. Time-resolved flavin absorbance studies were performed in this study and the data showed that the enzyme is capable of stabilizing both anionic and neutral flavin semiquinone species. The presence of a radical scavenger decreases the activity in a concentration-dependent manner. These data are consistent with the flavin iminium intermediate occurring via radical recombination. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Formation of a Criegee intermediate in the low-temperature oxidation of dimethyl sulfoxide.

PubMed

Asatryan, Rubik; Bozzelli, Joseph W

2008-04-07

Dimethyl sulfoxide (DMSO) is the major sulfur-containing constituent of the Marine Boundary Layer. It is a significant source of H2SO4 aerosol/particles and methane sulfonic acid via atmospheric oxidation processes, where the mechanism is not established. In this study, several new, low-temperature pathways are revealed in the oxidation of DMSO using CBS-QB3 and G3MP2 multilevel and B3LYP hybrid density functional quantum chemical methods. Unlike analogous hydrocarbon peroxy radicals the chemically activated DMSO peroxy radical, [CH3S(=O)CH2OO*]*, predominantly undergoes simple dissociation to a methylsulfinyl radical CH3S*(=O) and a Criegee intermediate, CH2OO, with the barrier to dissociation 11.3 kcal mol(-1) below the energy of the CH3S(=O)CH2* + O2 reactants. The well depth for addition of O2 to the CH3S(=O)CH2 precursor radical is 29.6 kcal mol(-1) at the CBS-QB3 level of theory. We believe that this reaction may serve an important role in atmospheric photochemical and irradiated biological (oxygen-rich) media where formation of initial radicals is facilitated even at lower temperatures. The Criegee intermediate (carbonyl oxide, peroxymethylene) and sulfinyl radical can further decompose, resulting in additional chain branching. A second reaction channel important for oxidation processes includes formation (via intramolecular H atom transfer) and further decomposition of hydroperoxide methylsulfoxide radical, *CH2S(=O)CH2OOH over a low barrier of activation. The initial H-transfer reaction is similar and common in analogous hydrocarbon radical + O2 reactions; but the subsequent very low (3-6 kcal mol(-1)) barrier (14 kcal mol(-1) below the initial reagents) to beta-scission products is not common in HC systems. The low energy reaction of the hydroperoxide radical is a beta-scission elimination of *CH2S(=O)CH2OOH into the CH2=S=O + CH2O + *OH product set. This beta-scission barrier is low, because of the delocalization of the *CH2 radical center through the -S(=O) group, to the -CH2OOH fragment in the transition state structure. The hydroperoxide methylsulfoxide radical can also decompose via a second reaction channel of intramolecular OH migration, yielding formaldehyde and a sulfur-centered hydroxymethylsulfinyl radical HOCH2S*(=O). The barrier of activation relative to initial reagents is 4.2 kcal mol(-1). Heats of formation for DMSO, DMSO carbon-centered radical and Criegee intermediate are evaluated at 298 K as -35.97 +/- 0.05, 13.0 +/- 0.2 and 25.3 +/- 0.7 kcal mol(-1) respectively using isodesmic reaction analysis. The [CH3S*(=O) + CH2OO] product set is shown to form a van der Waals complex that results in O-atom transfer reaction and the formation of new products CH3SO2* radical and CH2O. Proper orientation of the Criegee intermediate and methylsulfinyl radical, as a pre-stabilized pre-reaction complex, assist the process. The DMSO radical reaction is also compared to that of acetonyl radical.

Alternating copolymerization of fluoroalkenes with carbon monoxide.

PubMed

Fujita, Tomoyuki; Nakano, Koji; Yamashita, Makoto; Nozaki, Kyoko

2006-02-15

The palladium-catalyzed alternating copolymerization of fluoroalkenes, represented as CH(2)=CH-CH(2)-C(n)F(2n+1), with CO was performed using (R,S)-BINAPHOS (2e) as a ligand. The CH(2)-C(n)F(2n+1) group is the most electronegative substituent ever reported for the copolymerization (Taft's sigma value of 0.90 for CH(2)CF(3)). The copolymer obtained from CH(2)=CH-CH(2)-C(8)F(17) (1a) existed as a mixture of polyspiroketal and polyketone, while that from CH(2)=CH-CH(2)-C(4)F(9) (1b) was a pure polyspiroketal, as was revealed by infrared and (13)C-CP/MAS NMR spectroscopies. The terminal structure of the polymer from 1b was confirmed by MALDI-TOF MS spectrometry. Detailed NMR studies suggested that the much higher reactivity with (R,S)-BINAPHOS (2e) than that with the conventional ligand DPPP (2a) can be attributed to the unique 1,2-insertion of the fluoroalkene into acylpalladium species. The existence of an electronegative substituent on the alpha-carbon of the palladium center is successfully avoided in the 1,2-insertion mechanism.

Aqueous Phase Non Enzymatic Chemistry of Cyanide, Formaldehyde and RNH2

NASA Technical Reports Server (NTRS)

Lerner, Narcinda R.; Chang, Sherwood (Technical Monitor)

1994-01-01

It is postulated that amino acids were produced on the early earth from dilute aqueous solution of cyanide, carbonyls and ammonia (the Strecker synthesis RNH2 + R"R""C=O + KCN yields H-N(R)-C(R")(R"")-CO2H. We have studied the products obtained from dilute aqueous solutions of cyanide, formaldehyde (R"=R""=H), ammonia (R=H) and amino acids. Solutions in the pH range from 8 to 10. at room temperature and at reactant concentrations from 0.001 M to 0.3 M have been studied. With R= H product yields were low (less than 3%). Only with R"=R""=H and R represented by the following: CH2CO2H (glycine); CH(CH3)CO2H (alanine); CH(CH2CH3)CO2H (a-amino n=butyric acids); C(CH3)2(CO2H) (a-aminoisobutyric acid); CH(CH(CH3)2)CO2H (valine); and CH(CH2CO2H)CO2H (aspartic acid), were product yields high (greater than 10%). The yields of glycine were larger with R not equal to H. The prebiotic implications of these findings will be discussed.

CNN pincer ruthenium catalysts for hydrogenation and transfer hydrogenation of ketones: experimental and computational studies.

PubMed

Baratta, Walter; Baldino, Salvatore; Calhorda, Maria José; Costa, Paulo J; Esposito, Gennaro; Herdtweck, Eberhardt; Magnolia, Santo; Mealli, Carlo; Messaoudi, Abdelatif; Mason, Sax A; Veiros, Luis F

2014-10-13

Reaction of [RuCl(CNN)(dppb)] (1-Cl) (HCNN=2-aminomethyl-6-(4-methylphenyl)pyridine; dppb=Ph2 P(CH2 )4 PPh2 ) with NaOCH2 CF3 leads to the amine-alkoxide [Ru(CNN)(OCH2 CF3 )(dppb)] (1-OCH2 CF3 ), whose neutron diffraction study reveals a short RuO⋅⋅⋅HN bond length. Treatment of 1-Cl with NaOEt and EtOH affords the alkoxide [Ru(CNN)(OEt)(dppb)]⋅(EtOH)n (1-OEt⋅n EtOH), which equilibrates with the hydride [RuH(CNN)(dppb)] (1-H) and acetaldehyde. Compound 1-OEt⋅n EtOH reacts reversibly with H2 leading to 1-H and EtOH through dihydrogen splitting. NMR spectroscopic studies on 1-OEt⋅n EtOH and 1-H reveal hydrogen bond interactions and exchange processes. The chloride 1-Cl catalyzes the hydrogenation (5 atm of H2 ) of ketones to alcohols (turnover frequency (TOF) up to 6.5×10(4) h(-1) , 40 °C). DFT calculations were performed on the reaction of [RuH(CNN')(dmpb)] (2-H) (HCNN'=2-aminomethyl-6-(phenyl)pyridine; dmpb=Me2 P(CH2 )4 PMe2 ) with acetone and with one molecule of 2-propanol, in alcohol, with the alkoxide complex being the most stable species. In the first step, the Ru-hydride transfers one hydrogen atom to the carbon of the ketone, whereas the second hydrogen transfer from NH2 is mediated by the alcohol and leads to the key "amide" intermediate. Regeneration of the hydride complex may occur by reaction with 2-propanol or with H2 ; both pathways have low barriers and are alcohol assisted. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Oxidative C-H/C-H Cross-Coupling Reactions between N-Acylanilines and Benzamides Enabled by a Cp*-Free RhCl3/TFA Catalytic System.

PubMed

You, Jingsong; Shi, Yang; Zhang, Luoqiang; Lan, Jingbo; Zhang, Min; Zhou, Fulin; Wei, Wenlong

2018-06-03

Using the dual chelation-assisted strategy, a completely regiocontrolled oxidative C-H/C-H cross-coupling reaction between an N-acylaniline and a benzamide has been accomplished for the first time, which enables a step-economical and highly efficient pathway to 2-amino-2'-carboxybiaryl scaffolds from readily available substrates. A Cp*-free RhCl3/TFA catalytic system has been developed to replace the generally used [Cp*RhCl2]2/AgSbF6 (Cp* = pentamethyl cyclopentadienyl) in oxidative C-H/C-H cross-coupling reactions between two (hetero)arenes. The RhCl3/TFA system avoids the use of expensive Cp* ligand and AgSbF6. As an illustrative example, the protocol developed herein greatly streamlines access to naturally occurring benzo[c]phenanthridine alkaloid oxynitidine in an excellent overall yield. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis, Crystal Structure, Antioxidant, and α-Glucosidase Inhibitory Activities of Methoxy-substituted Benzohydrazide Derivatives

NASA Astrophysics Data System (ADS)

Prachumrat, P.; Kobkeatthawin, T.; Ruanwas, P.; Boonnak, N.; Laphookhieo, S.; Kassim, M. B.; Chantrapromma, S.

2018-05-01

Eight methoxy substituted at the benzylidene moiety benzohydrazide derivatives [ R = 2-OCH3 ( 1), 3-OCH3 ( 2), 4-OCH3 ( 3), 2,3-(OCH3)2 ( 4), 3,4-(OCH3)2 ( 5), 2,4,5-(OCH3)3 ( 6), 2,4,6-(OCH3)3 ( 7), and 3,4,5-(OCH3)3 ( 8)] were synthesized and characterized by 1H NMR, FT-IR and UV-Vis spectroscopy. The crystal structure of 4 was determined by single crystal X-ray diffraction (sp. gr. Pbca, Z = 8). The molecule is slightly twisted with the dihedral angle between the two phenyl rings being 9.33(14)°. The methoxy group at the ortho position is twisted [C-O-C-C angle is-109.2(3)°] whereas the other at meta position is co-planar with the attached benzene ring. In the crystal packing, the molecules are linked into two-dimensional network parallel to the (001) plane by O-H···O, O-H···N, and N-H···O hydrogen bonds. Compounds 1-8 were evaluated for an antioxidant and α-glucosidase inhibitory activities and the results suggested that the -OCH3 substituent was ineffective for bioactivity enhancement.

Thermochemical and kinetic analyses on oxidation of isobutenyl radical and 2-hydroperoxymethyl-2-propenyl radical.

PubMed

Zheng, X L; Sun, H Y; Law, C K

2005-10-13

In recognition of the importance of the isobutene oxidation reaction in the preignition chemistry associated with engine knock, the thermochemistry, chemical reaction pathways, and reaction kinetics of the isobutenyl radical oxidation at low to intermediate temperature range were computationally studied, focusing on both the first and the second O2 addition to the isobutenyl radical. The geometries of reactants, important intermediates, transition states, and products in the isobutenyl radical oxidation system were optimized at the B3LYP/6-311G(d,p) and MP2(full)/6-31G(d) levels, and the thermochemical properties were determined on the basis of ab initio, density functional theory, and statistical mechanics. Enthalpies of formation for several important intermediates were calculated using isodesmic reactions at the DFT and the CBS-QB3 levels. The kinetic analysis of the first O2 addition to the isobutenyl radical was performed using enthalpies at the CBS-QB3 and G3(MP2) levels. The reaction forms a chemically activated isobutenyl peroxy adduct which can be stabilized, dissociate back to reactants, cyclize to cyclic peroxide-alkyl radicals, and isomerize to the 2-hydroperoxymethyl-2-propenyl radical that further undergoes another O2 addition. The reaction channels for isomerization and cyclization and further dissociation on this second O2 addition were analyzed using enthalpies at the DFT level with energy corrections based on similar reaction channels for the first O2 addition. The high-pressure limit rate constants for each reaction channel were determined as functions of temperature by the canonical transition state theory for further kinetic model development.

Nucleophilic substitution at silicon (SN2@Si) via a central reaction barrier.

PubMed

Bento, A Patrícia; Bickelhaupt, F Matthias

2007-03-16

It is textbook knowledge that nucleophilic substitution at carbon (SN2@C) proceeds via a central reaction barrier which disappears in the corresponding nucleophilic substitution reaction at silicon (SN2@Si). Here, we address the question why the central barrier disappears from SN2@C to SN2@Si despite the fact that these processes are isostructural and isoelectronic. To this end, we have explored and analyzed the potential energy surfaces (PES) of various Cl-+CR3Cl (R=H, CH3) and Cl-+SiR3Cl model reactions (R=H, CH3, C2H5, and OCH3). Our results show that the nature of the SN2 reaction barrier is in essence steric, but that it can be modulated by electronic factors. Thus, simply by increasing the steric demand of the substituents R around the silicon atom, the SN2@Si mechanism changes from its regular single-well PES (with a stable intermediate transition complex, TC), via a triple-well PES (with a pre- and a post-TS before and after the central TC), to a double-well PES (with a TS; R=OCH3), which is normally encountered for SN2@C reactions.

Methyl-perfluoroheptene-ethers (CH3OC7F13): measured OH radical reaction rate coefficients for several isomers and enantiomers and their atmospheric lifetimes and global warming potentials.

PubMed

Jubb, Aaron M; Gierczak, Tomasz; Baasandorj, Munkhbayar; Waterland, Robert L; Burkholder, James B

2014-05-06

Mixtures of methyl-perfluoroheptene-ethers (CH3OC7F13, MPHEs) are currently in use as replacements for perfluorinated alkanes (PFCs) and poly-ether heat transfer fluids, which are persistent greenhouse gases with lifetimes >1000 years. At present, the atmospheric processing and environmental impact from the use of MPHEs is unknown. In this work, rate coefficients at 296 K for the gas-phase reaction of the OH radical with six key isomers (including stereoisomers and enantiomers) of MPHEs used commercially were measured using a relative rate method. Rate coefficients for the six MPHE isomers ranged from ∼ 0.1 to 2.9 × 10(-12) cm(3) molecule(-1) s(-1) with a strong stereoisomer and -OCH3 group position dependence; the (E)-stereoisomers with the -OCH3 group in an α- position relative to the double bond had the greatest reactivity. Rate coefficients measured for the d3-MPHE isomer analogues showed decreased reactivity consistent with a minor contribution of H atom abstraction from the -OCH3 group to the overall reactivity. Estimated atmospheric lifetimes for the MPHE isomers range from days to months. Atmospheric lifetimes, radiative efficiencies, and global warming potentials for these short-lived MPHE isomers were estimated based on the measured OH rate coefficients along with measured and theoretically calculated MPHE infrared absorption spectra. Our results highlight the importance of quantifying the atmospheric impact of individual components in an isomeric mixture.

Reaction between peroxynitrite and boronates: EPR spin-trapping, HPLC analyses, and quantum mechanical study of the free radical pathway

PubMed Central

Sikora, Adam; Zielonka, Jacek; Lopez, Marcos; Dybala-Defratyka, Agnieszka; Joseph, Joy; Marcinek, Andrzej; Kalyanaraman, Balaraman

2013-01-01

Recently we showed that peroxynitrite (ONOO−) reacts directly and rapidly with aromatic and aliphatic boronic acids (k ≈ 106 M−1s−1). Product analyses and substrate consumption data indicated that ONOO− reacts stoichiometrically with boronates, yielding the corresponding phenols as the major product (~85–90%), and the remaining products (10–15%) were proposed to originate from free radical intermediates (phenyl and phenoxyl radicals). Here we investigated in detail the minor, free radical pathway of boronate reaction with ONOO−. The electron paramagnetic resonance (EPR) spin-trapping technique was used to characterize the free radical intermediates formed from the reaction between boronates and ONOO−. Using 2-methyl-2-nitrosopropane (MNP) and 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO) spin traps, phenyl radicals were trapped and detected. Although phenoxyl radicals were not detected, the positive effects of molecular oxygen, and inhibitory effects of hydrogen atom donors (acetonitrile, and 2-propanol) and general radical scavengers (GSH, NADH, ascorbic acid and tyrosine) on the formation of phenoxyl radical-derived nitrated product, suggest that phenoxyl radical was formed as the secondary species. We propose that the initial step of the reaction involves the addition of ONOO− to the boron atom in boronates. The anionic intermediate undergoes both heterolytic (major pathway) and homolytic (minor pathway) cleavage of the peroxy (O-O) bond to form phenol and nitrite as a major product (via a non-radical mechanism), or a radical pair PhB(OH)2O•−…•NO2 as a minor product. It is conceivable that phenyl radicals are formed by the fragmentation of PhB(OH)2O•− radical anion. According to the DFT quantum mechanical calculations, the energy barrier for the dissociation of PhB(OH)2O•− radical anion to form phenyl radicals is only a few kcal/mol, suggesting rapid and spontaneous fragmentation of PhB(OH)2O•− radical anion in aqueous media. Biological implications of the minor free radical pathway are discussed in the context of ONOO− detection, using the boronate probes. PMID:21434648

A substrate radical intermediate in the reaction between ribonucleotide reductase from Escherichia coli and 2'-azido-2'-deoxynucleoside diphosphates.

PubMed

Sjöberg, B M; Gräslund, A; Eckstein, F

1983-07-10

The B2 subunit of ribonucleotide reductase from Escherichia coli contains a tyrosine radical which is essential for enzyme activity. In the reaction between ribonucleotide reductase and the substrate analogue 2'-azido-2'-deoxycytidine 5'-diphosphate a new transient radical is formed. The EPR characteristics of this new radical species are consistent with a localization of the unpaired electron at the sugar moiety of the nucleotide. The radical shows hyperfine couplings to a hydrogen and a nitrogen nucleus, the latter probably being part of the azide substituent. The formation of the nucleotide radical in this suicidal reaction is concomitant with the decay of the tyrosine radical of the B2 subunit. Kinetic data argue for a first (pseudosecond) order decay of the B2 radical via generation of the nucleotide radical followed by a slower first order decay of the nucleotide radical. End products in the reaction are cytosine and radical-free protein B2. In the reaction between bacteriophage T4 ribonucleotide reductase and 2'-azido-2'-deoxycytidine 5'-diphosphate an identical nucleotide radical is formed. The present results are consistent with the hypothesis that the appearance and structure of the transient radical mimic stages in the normal reaction pathway of ribonucleotide reductase, postulated to proceed via 3'-hydrogen abstraction and cation radical formation of the substrate nucleotide (Stubbe, J., and Ackles, D. (1980) J. Biol. Chem. 255, 8027-8030). The nucleotide radical described here might be equivalent to such a cation radical intermediate.

Thermal Decomposition of Potential Ester Biofuels. Part I: Methyl Acetate and Methyl Butanoate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Porterfield, Jessica P.; Bross, David H.; Ruscic, Branko

2017-06-09

Two methyl esters have been examined as models for the pyrolysis of biofuels. Dilute samples (0.06 - 0.13%) of methyl acetate (CH 3COOCH 3) and methyl butanoate (CH 3CH 2CH 2COOCH 3) were entrained in (He, Ar) carrier gas and decomposed in a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from the methyl esters were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by matrix infrared absorption spectroscopy. Pyrolysis pressures in the pulsed micro-reactor were roughly 20 Torr and residence times through the reactors were approximately 25 - 150 µs. Reactor temperatures ofmore » 300 – 1600 K were explored. Decomposition of CH 3COOCH 3 commences at 1000 K and the initial products are (CH 2=C=O and CH 3OH). As the micro-reactor is heated to 1300 K, a mixture of (CH 2=C=O and CH 3OH, CH 3, CH 2=O, H, CO, CO 2) appears. The thermal cracking of CH 3CH 2CH 2COOCH 3 begins at 800 K with the formation of (CH 3CH 2CH=C=O, CH 3OH). By 1300 K, the pyrolysis of methyl butanoate yields a complex mixture of (CH 3CH 2CH=C=O, CH 3OH, CH 3, CH 2=O, CO, CO 2, CH 3CH=CH 2, CH 2CHCH 2, CH 2=C=CH 2, HCCCH 2, CH 2=C=C=O, CH 2=CH 2, HCΞCH, CH 2=C=O). Based on the results from the thermal cracking of methyl acetate and methyl butanoate, we predict several important decomposition channels for the pyrolysis of fatty acid methyl esters, R CH 2-COOCH 3. The lowest energy fragmentation will be a 4-center elimination of methanol to form the ketene, RCH=C=O. At higher temperatures, concerted fragmentation to radicals will ensue to produce a mixture of species: (RCH 2 + CO 2 + CH 3) and (RCH 2 + CO + CH 2=O + H). Thermal cracking of the β C-C bond of the methyl ester will generate the radicals (R and H) as well as CH 2=C=O + CH 2=O. The thermochemistry of methyl acetate and its fragmentation products have been obtained via the Active Thermochemical Tables (ATcT) approach, resulting in Δ fH 298(CH 3COOCH 3) = -98.7 ± 0.2 kcal mol -1, Δ fH 298(CH 3CO 2) = -45.7 ± 0.3 kcal mol -1, and Δ fH 298(COOCH 3) = -38.3 ± 0.4 kcal mol -1.« less

The effect of VUV radiation from Ar/O2 plasmas on low-k SiOCH films

NASA Astrophysics Data System (ADS)

Lee, J.; Graves, D. B.

2011-08-01

The degradation of porous low-k materials, like SiOCH, under plasma processing continues to be a problem in the next generation of integrated-circuit fabrication. Due to the exposure of the film to many species during plasma treatment, such as photons, ions, radicals, etc, it is difficult to identify the mechanisms responsible for plasma-induced damage. Using a vacuum beam apparatus with a calibrated Xe vacuum ultraviolet (VUV) lamp, we show that 147 nm VUV photons and molecular O2 alone can damage these low-k materials. Using Fourier-transform infrared (FTIR) spectroscopy, we show that VUV/O2 exposure causes a loss of methylated species, resulting in a hydrophilic, SiOx-like layer that is susceptible to H2O absorption, leading to an increased dielectric constant. The effect of VUV radiation on chemical modification of porous SiOCH films in the vacuum beam apparatus and in Ar and O2 plasma exposure was found to be a significant contributor to dielectric damage. Measurements of dielectric constant change using a mercury probe are consistent with chemical modification inferred from FTIR analysis. Furthermore, the extent of chemical modification appears to be limited by the penetration depth of the VUV photons, which is dependent on wavelength of radiation. The creation of a SiOx-like layer near the surface of the material, which grows deeper as more methyl is extracted, introduces a dynamic change of VUV absorption throughout the material over time. As a result, the rate of methyl loss is continuously changing during the exposure. We present a model that attempts to capture this dynamic behaviour and compare the model predictions to experimental data through a fitting parameter that represents the effective photo-induced methyl removal. While this model accurately simulates the methyl loss through VUV exposure by the Xe lamp and Ar plasma, the methyl loss from VUV photons in O2 plasma are only accurately depicted at longer exposure times. We conclude that other species, such as oxygen radicals or ions, may play a major role in chemical modification at short times near the surface of the material, while VUV photons contribute to the majority of the damage in the bulk.

Thermal Decomposition Mechanisms of Lignin Model Compounds: From Phenol to Vanillin

NASA Astrophysics Data System (ADS)

Scheer, Adam Michael

Lignin is a complex, aromatic polymer abundant in cellulosic biomass (trees, switchgrass etc.). Thermochemical breakdown of lignin for liquid fuel production results in undesirable polycyclic aromatic hydrocarbons that lead to tar and soot byproducts. The fundamental chemistry governing these processes is not well understood. We have studied the unimolecular thermal decomposition mechanisms of aromatic lignin model compounds using a miniature SiC tubular reactor. Products are detected and characterized using time-of-flight mass spectrometry with both single photon (118.2 nm; 10.487 eV) and 1 + 1 resonance-enhanced multiphoton ionization (REMPI) as well as matrix isolation infrared spectroscopy. Gas exiting the heated reactor (300 K--1600 K) is subject to a free expansion after a residence time of approximately 100 micros. The expansion into vacuum rapidly cools the gas mixture and allows the detection of radicals and other highly reactive intermediates. By understanding the unimolecular fragmentation patterns of phenol (C6H5OH), anisole (C6H 5OCH3) and benzaldehyde (C6H5CHO), the more complicated thermocracking processes of the catechols (HO-C 6H4-OH), methoxyphenols (HO-C6H4-OCH 3) and hydroxybenzaldehydes (HO-C6H4-CHO) can be interpreted. These studies have resulted in a predictive model that allows the interpretation of vanillin, a complex phenolic ether containing methoxy, hydroxy and aldehyde functional groups. This model will serve as a guide for the pyrolyses of larger systems including lignin monomers such as coniferyl alcohol. The pyrolysis mechanisms of the dimethoxybenzenes (H3C-C 6H4-OCH3) and syringol, a hydroxydimethoxybenzene have also been studied. These results will aid in the understanding of the thermal fragmentation of sinapyl alcohol, the most complex lignin monomer. In addition to the model compound work, pyrolyisis of biomass has been studied via the pulsed laser ablation of poplar wood. With the REMPI scheme, aromatic lignin decomposition products are directly and selectively detected. A number of these products are the lignin model compounds listed above, providing a direct link between the model compound studies and the pyrolysis of actual biomass.

Highly durable organic electrode for sodium-ion batteries via a stabilized α-C radical intermediate

NASA Astrophysics Data System (ADS)

Wu, Shaofei; Wang, Wenxi; Li, Minchan; Cao, Lujie; Lyu, Fucong; Yang, Mingyang; Wang, Zhenyu; Shi, Yang; Nan, Bo; Yu, Sicen; Sun, Zhifang; Liu, Yao; Lu, Zhouguang

2016-11-01

It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized α-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the α-radical demonstrates reversible transformation between three states: C=C α-C.radical and α-C- anion. Such transformation provides additional Na+ storage equal to more than 0.83 Na+ insertion per α-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.

Growth of metal oxide thin films by laser-induced metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Tokita, Koji; Okada, Fumio

1996-12-01

The growth of metal oxide thin films by laser-induced metalorganic chemical vapor deposition was investigated by changing wavelength, power, repetition rate, and irradiation angle of the excimer laser. When O2 was used as an oxidizing gas with 193 or 248 nm irradiation, amorphous TiO2 and crystalline PbO films were obtained in the laser-irradiated area of Si substrates from the parent metalorganic compounds, Ti(O-iC3H7)4 and (C2H5)3PbOCH2C(CH3)3, respectively. In contrast, no ZrO2 film could be formed from Zr(O-tC4H9)4. One-photon formation of TiO2 films was confirmed from laser power dependence measurements. The maximum growth rate of 0.05 Å per laser pulse was compared with that estimated by a simple surface reaction model, according to which the slow growth rate is due to the small absorption cross section of Ti(O-iC3H7)4 and mild fluence of laser irradiation. In experiments of ozone gas excitation by KrF laser, a SiO2 film was obtained by gas-phase reactions of the oxygen radical, O(1D), with Si(O-C2H5)4. The direct patterning of TiO2 and PbO films as well as the possibility of producing patterned PbTiO3 film was demonstrated. The growth of the patterned SiO2 film was prevented by gas-phase diffusion of intermediates.

Gallium oxide thin films from the AACVD of [Ga(NMe2)3]2 and donor functionalised alcohols.

PubMed

Basharat, Siama; Carmalt, Claire J; Binions, Russell; Palgrave, Robert; Parkin, Ivan P

2008-02-07

Thin films of Ga(2)O(3) have been produced from [Ga(NMe(2))(3)](2) and ROH (R = CH(2)CH(2)NMe(2), CH(CH(2)NMe(2))(2), CH(CH(3))CH(2)NMe(2), CH(2)CH(2)OMe and C(CH(3))(2)CH(2)OMe) by aerosol assisted chemical vapour deposition on glass. Transparent, unreflective films were obtained at a deposition temperature of 550 degrees C using toluene as solvent. The gallium oxide films were analyzed by Scanning electron microscopy (SEM), Raman spectroscopy, wavelength dispersive analysis of X-rays (WDX) and X-ray photoelectron spectroscopy (XPS). The gallium oxide films obtained were X-ray amorphous. Gas-sensing experiments indicated that the films showed an n-type response to ethanol at a variety of temperatures.

CH3OCH3 in Orion-KL: a striking similarity with HCOOCH3

NASA Astrophysics Data System (ADS)

Brouillet, N.; Despois, D.; Baudry, A.; Peng, T.-C.; Favre, C.; Wootten, A.; Remijan, A. J.; Wilson, T. L.; Combes, F.; Wlodarczak, G.

2013-02-01

Context. Orion-KL is a remarkable, nearby star-forming region where a recent explosive event has generated shocks that could have released complex molecules from the grain mantles. Aims: A comparison of the distribution of the different complex molecules will help in understanding their formation and constraining the chemical models. Methods: We used several data sets from the Plateau de Bure Interferometer to map the dimethyl ether emission with different arcsec spatial resolutions and different energy levels (from Eup = 18 to 330 K) to compare with our previous methyl formate maps. Results: Our data show remarkable similarity between the dimethyl ether (CH3OCH3) and the methyl formate (HCOOCH3) distributions even on a small scale (1.8″ × 0.8″ or ~500 AU). This long suspected similarity, seen from both observational and theoretical arguments, is demonstrated with unprecedented confidence, with a correlation coefficient of maps ~0.8. Conclusions: A common precursor is the simplest explanation of our correlation. Comparisons with previous laboratory work and chemical models suggest the major role of grain surface chemistry and a recent release, probably with little processing, of mantle molecules by shocks. In this case the CH3O radical produced from methanol ice would be the common precursor (whereas ethanol, C2H5OH, is produced from the radical CH2OH). The alternative gas phase scheme, where protonated methanol CH3OH+2 is the common precursor to produce methyl formate and dimethyl ether through reactions with HCOOH and CH3OH, is also compatible with our data. Our observations cannot yet definitely allow a choice between the different chemical processes, but the tight correlation between the distributions of HCOOCH3 and CH3OCH3 strongly contrasts with the different behavior we observe for the distributions of ethanol and formic acid. This provides a very significant constraint on models. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

The Gaseous Phase as a Probe of the Astrophysical Solid Phase Chemistry

NASA Astrophysics Data System (ADS)

Abou Mrad, Ninette; Duvernay, Fabrice; Isnard, Robin; Chiavassa, Thierry; Danger, Grégoire

2017-09-01

In support of space missions and spectroscopic observations, laboratory experiments on ice analogs enable a better understanding of organic matter formation and evolution in astrophysical environments. Herein, we report the monitoring of the gaseous phase of processed astrophysical ice analogs to determine if the gaseous phase can elucidate the chemical mechanisms and dominant reaction pathways occurring in the solid ice subjected to vacuum ultra-violet (VUV) irradiation at low temperature and subsequently warmed. Simple (CH3OH), binary (H2O:CH3OH, CH3OH:NH3), and ternary ice analogs (H2O:CH3OH:NH3) were VUV-processed and warmed. The evolution of volatile organic compounds in the gaseous phase shows a direct link between their relative abundances in the gaseous phase, and the radical and thermal chemistries modifying the initial ice composition. The correlation between the gaseous and solid phases may play a crucial role in deciphering the organic composition of astrophysical objects. As an example, possible solid compositions of the comet Lovejoy are suggested using the abundances of organics in its comae.

Trimethyl phosphite as a trap for alkoxy radicals formed from the ring opening of oxiranylcarbinyl radicals. Conversion to alkenes. Mechanistic applications to the study of C-C versus C-O ring cleavage.

PubMed

Ding, Bangwei; Bentrude, Wesley G

2003-03-19

Trimethyl phosphite, (MeO)(3)P, is introduced as an efficient and selective trap in oxiranylcarbinyl radical (2) systems, formed from haloepoxides 8-13 under thermal AIBN/n-Bu(3)SnH conditions at about 80 degrees C. Initially, the transformations of 8-13, in the absence of phosphite, to allyl alcohol 7 and/or vinyl ether 5 were measured quantitatively (Table 1). Structural variations in the intermediate oxiranylcarbinyl (2), allyloxy (3), and vinyloxycarbinyl (4) radicals involve influences of the thermodynamics and kinetics of the C-O (2 --> 3, k(1)) and C-C (2 --> 4, k(2)) radical scission processes and readily account for the changes in the amounts of product vinyl ether (5) and allyl alcohol (7) formed. Added (MeO)(3)P is inert to vinyloxycarbinyl radical 4 and selectively and rapidly traps allyloxy radical 3, diverting it to trimethyl phosphate and allyl radical 6. Allyl radicals (6) dimerize or are trapped by n-Bu(3)SnH to give alkenes, formed from haloepoxides 8, 9, and 13 in 69-95% yields. Intermediate vinyloxycarbinyl radicals (4), in the presence or absence of (MeO)(3)P, are trapped by n-Bu(3)SnH to give vinyl ethers (5). The concentrations of (MeO)(3)P and n-Bu(3)SnH were varied independently, and the amounts of phosphate, vinyl ether (5), and/or alkene from haloepoxides 10, 11, and 13 were carefully monitored. The results reflect readily understood influences of changes in the structures of radicals 2-4, particularly as they influence the C-O (k(1)) and C-C (k(2)) cleavages of intermediate oxiranylcarbinyl radical 2 and their reverse (k(-1), k(-2)). Diversion by (MeO)(3)P of allyloxy radicals (3) from haloepoxides 11 and 12 fulfills a prior prediction that under conditions closer to kinetic control, products of C-O scission, not just those of C-C scission, may result. Thus, for oxiranylcarbinyl radicals from haloepoxides 11, 12, and 13, C-O scission (k(1), 2 --> 3) competes readily with C-C cleavage (k(2), 2 --> 4), even though C-C scission is favored thermodynamically.

Identification of the substrate radical intermediate derived from ethanolamine during catalysis by ethanolamine ammonia-lyase.

PubMed

Bender, Güneş; Poyner, Russell R; Reed, George H

2008-10-28

Rapid-mix freeze-quench (RMFQ) methods and electron paramagnetic resonance (EPR) spectroscopy have been used to characterize the steady-state radical in the deamination of ethanolamine catalyzed by adenosylcobalamin (AdoCbl)-dependent ethanolamine ammonia-lyase (EAL). EPR spectra of the radical intermediates formed with the substrates, [1-13C]ethanolamine, [2-13C]ethanolamine, and unlabeled ethanolamine were acquired using RMFQ trapping methods from 10 ms to completion of the reaction. Resolved 13C hyperfine splitting in EPR spectra of samples prepared with [1-13C]ethanolamine and the absence of such splitting in spectra of samples prepared with [2-13C]ethanolamine show that the unpaired electron is localized on C1 (the carbinol carbon) of the substrate. The 13C splitting from C1 persists from 10 ms throughout the time course of substrate turnover, and there was no evidence of a detectable amount of a product like radical having unpaired spin on C2. These results correct an earlier assignment for this radical intermediate [Warncke, K., et al. (1999) J. Am. Chem. Soc. 121, 10522-10528]. The EPR signals of the substrate radical intermediate are altered by electron spin coupling to the other paramagnetic species, cob(II)alamin, in the active site. The dipole-dipole and exchange interactions as well as the 1-13C hyperfine splitting tensor were analyzed via spectral simulations. The sign of the isotropic exchange interaction indicates a weak ferromagnetic coupling of the two unpaired electrons. A Co2+-radical distance of 8.7 A was obtained from the magnitude of the dipole-dipole interaction. The orientation of the principal axes of the 13C hyperfine splitting tensor shows that the long axis of the spin-bearing p orbital on C1 of the substrate radical makes an angle of approximately 98 degrees with the unique axis of the d(z2) orbital of Co2+.

Human 2-Oxoglutarate Dehydrogenase Complex E1 Component Forms a Thiamin-derived Radical by Aerobic Oxidation of the Enamine Intermediate*

PubMed Central

Nemeria, Natalia S.; Ambrus, Attila; Patel, Hetalben; Gerfen, Gary; Adam-Vizi, Vera; Tretter, Laszlo; Zhou, Jieyu; Wang, Junjie; Jordan, Frank

2014-01-01

Herein are reported unique properties of the human 2-oxoglutarate dehydrogenase multienzyme complex (OGDHc), a rate-limiting enzyme in the Krebs (citric acid) cycle. (a) Functionally competent 2-oxoglutarate dehydrogenase (E1o-h) and dihydrolipoyl succinyltransferase components have been expressed according to kinetic and spectroscopic evidence. (b) A stable free radical, consistent with the C2-(C2α-hydroxy)-γ-carboxypropylidene thiamin diphosphate (ThDP) cation radical was detected by electron spin resonance upon reaction of the E1o-h with 2-oxoglutarate (OG) by itself or when assembled from individual components into OGDHc. (c) An unusual stability of the E1o-h-bound C2-(2α-hydroxy)-γ-carboxypropylidene thiamin diphosphate (the “ThDP-enamine”/C2α-carbanion, the first postdecarboxylation intermediate) was observed, probably stabilized by the 5-carboxyl group of OG, not reported before. (d) The reaction of OG with the E1o-h gave rise to superoxide anion and hydrogen peroxide (reactive oxygen species (ROS)). (e) The relatively stable enzyme-bound enamine is the likely substrate for oxidation by O2, leading to the superoxide anion radical (in d) and the radical (in b). (f) The specific activity assessed for ROS formation compared with the NADH (overall complex) activity, as well as the fraction of radical intermediate occupying active centers of E1o-h are consistent with each other and indicate that radical/ROS formation is an “off-pathway” side reaction comprising less than 1% of the “on-pathway” reactivity. However, the nearly ubiquitous presence of OGDHc in human tissues, including the brain, makes these findings of considerable importance in human metabolism and perhaps disease. PMID:25210035

Probing Combustion Chemistry in a Miniature Shock Tube with Synchrotron VUV Photo Ionization Mass Spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lynch, Patrick T.; Troy, Tyler P.; Ahmed, Musahid

2015-01-29

Tunable synchrotron-sourced photoionization time-of-flight mass spectrometry (PI-TOF-MS) is an important technique in combustion chemistry, complementing lab-scale electron impact and laser photoionization studies for a wide variety of reactors, typically at low pressure. For high-temperature and high-pressure chemical kinetics studies, the shock tube is the reactor of choice. Extending the benefits of shock tube/TOF-MS research to include synchrotron sourced PI-TOF-MS required a radical reconception of the shock tube. An automated, miniature, high-repetition-rate shock tube was developed and can be used to study high-pressure reactive systems (T > 600 K, P < 100 bar) behind reflected shock waves. In this paper, wemore » present results of a PI-TOF-MS study at the Advanced Light Source at Lawrence Berkeley National Laboratory. Dimethyl ether pyrolysis (2% CH3OCH3/Ar) was observed behind the reflected shock (1400 < T-5 < 1700 K, 3 < P-5 < 16 bar) with ionization energies between 10 and 13 eV. Individual experiments have extremely low signal levels. However, product species and radical intermediates are well-resolved when averaging over hundreds of shots, which is ordinarily impractical in conventional shock tube studies. The signal levels attained and data throughput rates with this technique are comparable to those with other synchrotron-based PI-TOF-MS reactors, and it is anticipated that this high pressure technique will greatly complement those lower pressure techniques.« less

Biological effects of 2,4-pentadiene-1-ol.

PubMed

Benesová, O; Sprincl, L; Ulbrich, K; Obereigner, B; Drobník, J; Kálal, J; Kopecek

1977-07-01

The biological effects of 2,4-pentadiene-1-ol (CH2 = CH--CH = CH--CH2--OH) the starting monomer in the preparation of a biocompatible polymer were studied. The experiments in rats revealed both a high local (oedema, necrosis) and systemic toxicity. Within 5-10 min after dermal application of 0.2 ml the compound evoked intensive hyperaemia of acral parts (ears, snout, paws) and induced severe breathing difficulties which led to death in half of the animals after a single administration. The most evident macroscopic and microscopic pathologic changes were found in the place of application and in the lungs (haemorrhage in alveolae). Both clinical and histological findings indicated that the toxicity is due to an increased permeability of capillaries.

On the nature of Ni···Ni interaction in a model dimeric Ni complex.

PubMed

Kamiński, Radosław; Herbaczyńska, Beata; Srebro, Monika; Pietrzykowski, Antoni; Michalak, Artur; Jerzykiewicz, Lucjan B; Woźniak, Krzysztof

2011-06-07

A new dinuclear complex (NiC(5)H(4)SiMe(2)CHCH(2))(2) (2) was prepared by reacting nickelocene derivative [(C(5)H(4)SiMe(2)CH=CH(2))(2)Ni] (1) with methyllithium (MeLi). Good quality crystals were subjected to a high-resolution X-ray measurement. Subsequent multipole refinement yielded accurate description of electron density distribution. Detailed inspection of experimental electron density in Ni···Ni contact revealed that the nickel atoms are bonded and significant deformation of the metal valence shell is related to different populations of the d-orbitals. The existence of the Ni···Ni bond path explains the lack of unpaired electrons in the complex due to a possible exchange channel.

Tin(II) alkoxide hydrolysis products for use as base catalysts

DOEpatents

Boyle, Timothy J.

2002-01-01

Tin alkoxide compounds are provided with accessible electrons. The compounds are a polymeric tin alkoxide, [Sn(OCH.sub.2 C(CH.sub.3).sub.3).sub.2 ].sub.n, and the hydrolysis products Sn.sub.6 O.sub.4 (OCH.sub.2 C(CH.sub.3).sub.3).sub.4 and Sn.sub.5 O.sub.2 (OCH.sub.2 C(CH.sub.3).sub.3).sub.6. The hydrolysis products are formed by hydrolyzing the [Sn(OCH.sub.2 C(CH.sub.3).sub.3).sub.2 ].sub.n in a solvent with controlled amounts of water, between 0.1 and 2 moles of water per mole of the polymeric tin alkoxide.

Intramolecular Oxidative O-Demethylation of an Oxoferryl Porphyrin Complexed with a Per-O-methylated β-Cyclodextrin Dimer.

PubMed

Kitagishi, Hiroaki; Kurosawa, Shun; Kano, Koji

2016-11-22

The intramolecular oxidation of ROCH 3 to ROCH 2 OH, where the latter compound spontaneously decomposed to ROH and HCHO, was observed during the reaction of the supramolecular complex (met-hemoCD3) with cumene hydroperoxide in aqueous solution. Met-hemoCD3 is composed of meso-tetrakis(4-sulfonatophenyl)porphinatoiron(III) (Fe III TPPS) and a per-O-methylated β-cyclodextrin dimer having an -OCH 2 PyCH 2 O- linker (Py=pyridine-3,5-diyl). The O=Fe IV TPPS complex was formed by the reaction of met-hemoCD3 with cumene hydroperoxide, and isolated by gel-filtration chromatography. Although the isolated O=Fe IV TPPS complex in the cyclodextrin cage was stable in aqueous solution at 25 °C, it was gradually converted to Fe II TPPS (t 1/2 =7.6 h). This conversion was accompanied by oxidative O-demethylation of an OCH 3 group in the cyclodextrin dimer. The results indicated that hydrogen abstraction by O=Fe IV TPPS from ROCH 3 yields HO-Fe III TPPS and ROCH 2 . . This was followed by radical coupling to afford Fe II TPPS and ROCH 2 OH. The hemiacetal (ROCH 2 OH) immediately decomposed to ROH and HCHO. This study revealed the ability of oxoferryl porphyrin to induce two-electron oxidation. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

An Oxyferrous Heme/Protein-based Radical Intermediate Is Catalytically Competent in the Catalase Reaction of Mycobacterium tuberculosis Catalase-Peroxidase (KatG)*S⃞

PubMed Central

Suarez, Javier; Ranguelova, Kalina; Jarzecki, Andrzej A.; Manzerova, Julia; Krymov, Vladimir; Zhao, Xiangbo; Yu, Shengwei; Metlitsky, Leonid; Gerfen, Gary J.; Magliozzo, Richard S.

2009-01-01

A mechanism accounting for the robust catalase activity in catalase-peroxidases (KatG) presents a new challenge in heme protein enzymology. In Mycobacterium tuberculosis, KatG is the sole catalase and is also responsible for peroxidative activation of isoniazid, an anti-tuberculosis pro-drug. Here, optical stopped-flow spectrophotometry, rapid freeze-quench EPR spectroscopy both at the X-band and at the D-band, and mutagenesis are used to identify catalase reaction intermediates in M. tuberculosis KatG. In the presence of millimolar H2O2 at neutral pH, oxyferrous heme is formed within milliseconds from ferric (resting) KatG, whereas at pH 8.5, low spin ferric heme is formed. Using rapid freeze-quench EPR at X-band under both of these conditions, a narrow doublet radical signal with an 11 G principal hyperfine splitting was detected within the first milliseconds of turnover. The radical and the unique heme intermediates persist in wild-type KatG only during the time course of turnover of excess H2O2 (1000-fold or more). Mutation of Met255, Tyr229, or Trp107, which have covalently linked side chains in a unique distal side adduct (MYW) in wild-type KatG, abolishes this radical and the catalase activity. The D-band EPR spectrum of the radical exhibits a rhombic g tensor with dual gx values (2.00550 and 2.00606) and unique gy (2.00344) and gz values (2.00186) similar to but not typical of native tyrosyl radicals. Density functional theory calculations based on a model of an MYW adduct radical built from x-ray coordinates predict experimentally observed hyperfine interactions and a shift in g values away from the native tyrosyl radical. A catalytic role for an MYW adduct radical in the catalase mechanism of KatG is proposed. PMID:19139099

Etching Enhancement Followed by Nitridation on Low-k SiOCH Film in Ar/C5F10O Plasma

NASA Astrophysics Data System (ADS)

Miyawaki, Yudai; Shibata, Emi; Kondo, Yusuke; Takeda, Keigo; Kondo, Hiroki; Ishikawa, Kenji; Okamoto, Hidekazu; Sekine, Makoto; Hori, Masaru

2013-02-01

The etching rates of low-dielectric-constant (low-k), porous SiOCH (p-SiOCH) films were increased by nitrogen-added Ar/C5F10O plasma etching in dual-frequency (60 MHz/2 MHz)-excited parallel plate capacitively coupled plasma. Previously, perfluoropropyl vinyl ether [C5F10O] provided a very high density of CF3+ ions [Nagai et al.: Jpn. J. Appl. Phys. 45 (2006) 7100]. Surface nitridation on the p-SiOCH surface exposed to Ar/N2 plasma led to the etching of larger amounts of p-SiOCH in Ar/C5F10O plasma, which depended on the formation of bonds such as =C(sp2)=N(sp2)- and -C(sp)≡N(sp).

Computational Study on the Unimolecular Decomposition of JP-8 Jet Fuel Surrogates III: Butylbenzene Isomers ( n-, s-, and t-C14H10).

PubMed

Belisario-Lara, Daniel; Mebel, Alexander M; Kaiser, Ralf I

2018-04-26

Ab initio G3(CCSD,MP2)//B3LYP/6-311G(d,p) calculations of potential energy surfaces have been carried out to unravel the mechanism of the initial stages of pyrolysis of three C 10 H 14 isomers: n-, s-, and t-butylbenzenes. The computed energy and molecular parameters have been utilized in RRKM-master equation calculations to predict temperature- and pressure-dependent rate constants and product branching ratios for the primary unimolecular decomposition of these molecules and for the secondary decomposition of their radical fragments. The results showed that the primary dissociation of n-butylbenzene produces mostly benzyl (C 7 H 7 ) + propyl (C 3 H 7 ) and 1-phenyl-2-ethyl (C 6 H 5 C 2 H 4 ) + ethyl (C 2 H 5 ), with their relative yields strongly dependent on temperature and pressure, together with a minor amount of 1-phenyl-prop-3-yl (C 9 H 11 ) + methyl (CH 3 ). Secondary decomposition reactions that are anticipated to occur on a nanosecond scale under typical combustion conditions split propyl (C 3 H 7 ) into ethylene (C 2 H 4 ) + methyl (CH 3 ), ethyl (C 2 H 5 ) into ethylene (C 2 H 4 ) + hydrogen (H), 1-phenyl-2-ethyl (C 6 H 5 C 2 H 4 ) into mostly styrene (C 8 H 8 ) + hydrogen (H) and to a lesser extent phenyl (C 6 H 5 ) + ethylene (C 2 H 4 ), and 1-phenyl-prop-3-yl (C 9 H 11 ) into predominantly benzyl (C 7 H 7 ) + ethylene (C 2 H 4 ). The primary decomposition of s-butylbenzene is predicted to produce 1-phenyl-1-ethyl (C 6 H 5 CHCH 3 ) + ethyl (C 2 H 5 ) and a minor amount of 1-phenyl-prop-1-yl (C 9 H 11 ) + methyl (CH 3 ), and then 1-phenyl-1-ethyl (C 6 H 5 CHCH 3 ) and 1-phenyl-prop-1-yl (C 9 H 11 ) rapidly dissociate to styrene (C 8 H 8 ) + hydrogen (H) and styrene (C 8 H 8 ) + methyl (CH 3 ), respectively. t-Butylbenzene decomposes nearly exclusively to 2-phenyl-prop-2-yl (C 9 H 11 ) + methyl (CH 3 ), and further, 2-phenyl-prop-2-yl (C 9 H 11 ) rapidly eliminates a hydrogen atom to form 2-phenylpropene (C 9 H 10 ). If hydrogen atoms or other reactive radicals are available to make a direct hydrogen-atom abstraction from butylbenzenes possible, the C 10 H 13 radicals (1-phenyl-but-1-yl, 2-phenyl-but-2-yl, and t-phenyl-isobutyl) can be formed as the primary products from n-, s-, and t-butylbenzene, respectively. The secondary decomposition of 1-phenyl-but-1-yl leads to styrene (C 8 H 8 ) + ethyl (C 2 H 5 ), whereas 2-phenyl-but-2-yl and t-phenyl-isobutyl dissociate to 2-phenylpropene (C 9 H 10 ) + methyl (CH 3 ). Thus, the three butylbenzene isomers produce distinct but overlapping nascent pyrolysis fragments, which likely affect the successive oxidation mechanism and combustion kinetics of these JP-8 fuel components. Temperature- and pressure-dependent rate constants generated for the initial stages of pyrolysis of butylbenzenes are recommended for kinetic modeling.

Isolation and characterization of charge-tagged phenylperoxyl radicals in the gas phase: direct evidence for products and pathways in low temperature benzene oxidation.

PubMed

Kirk, Benjamin B; Harman, David G; Kenttämaa, Hilkka I; Trevitt, Adam J; Blanksby, Stephen J

2012-12-28

The phenylperoxyl radical has long been accepted as a critical intermediate in the oxidation of benzene and an archetype for arylperoxyl radicals in combustion and atmospheric chemistry. Despite being central to many contemporary mechanisms underpinning these chemistries, reports of the direct detection or isolation of phenylperoxyl radicals are rare and there is little experimental evidence connecting this intermediate with expected product channels. We have prepared and isolated two charge-tagged phenyl radical models in the gas phase [i.e., 4-(N,N,N-trimethylammonium)phenyl radical cation and 4-carboxylatophenyl radical anion] and observed their reactions with dioxygen by ion-trap mass spectrometry. Measured reaction rates show good agreement with prior reports for the neutral system (k(2)[(Me(3)N(+))C(6)H(4)˙ + O(2)] = 2.8 × 10(-11) cm(3) molecule(-1) s(-1), Φ = 4.9%; k(2)[((-)O(2)C)C(6)H(4)˙ + O(2)] = 5.4 × 10(-11) cm(3) molecule(-1) s(-1), Φ = 9.2%) and the resulting mass spectra provide unequivocal evidence for the formation of phenylperoxyl radicals. Collisional activation of isolated phenylperoxyl radicals reveals unimolecular decomposition by three pathways: (i) loss of dioxygen to reform the initial phenyl radical; (ii) loss of atomic oxygen yielding a phenoxyl radical; and (iii) ejection of the formyl radical to give cyclopentadienone. Stable isotope labeling confirms these assignments. Quantum chemical calculations for both charge-tagged and neutral phenylperoxyl radicals confirm that loss of formyl radical is accessible both thermodynamically and entropically and competitive with direct loss of both hydrogen atom and carbon dioxide.

Rotational Spectrum, Conformational Composition, and Quantum Chemical Calculations of Cyanomethyl Formate (HC(O)OCH2C≡N), a Compound of Potential Astrochemical Interest.

PubMed

Samdal, Svein; Møllendal, Harald; Carles, Sophie

2015-08-27

The rotational spectrum of cyanomethyl formate (HC(O)OCH2C≡N) has been recorded in the 12–123 GHz spectral range. The spectra of two conformers were assigned. The rotamer denoted I has a symmetry plane and two out-of plane hydrogen atoms belonging to the cyanomethyl (CH2CN) moiety. In the conformer called II, the cyanomethyl group is rotated 80.3° out of this plane. Conformer I has an energy that is 1.4(6) kJ/mol lower than the energy of II according to relative intensity measurements. A large number of rotational transitions have been assigned for the ground and vibrationally excited states of the two conformers and accurate spectroscopic constants have been obtained. These constants should predict frequencies of transitions outside the investigated spectral range with a very high degree of precision. It is suggested that cyanomethyl formate is a potential interstellar compound. This suggestion is based on the fact that its congener methyl formate (HC(O)OCH3) exists across a large variety of interstellar environments and the fact that cyanides are very prevalent in the Universe. The experimental work has been augmented by high-level quantum chemical calculations. The CCSD/cc-pVQZ calculations are found to predict structures of the two forms that are very close to the Born–Oppenheimer equilibrium structures. MP2/cc-pVTZ predictions of several vibration–rotation interaction constants were generally found to be rather inaccurate. A gas-phase reaction between methyl formate and the cyanomethyl radical CH2CN to produce a hydrogen atom and cyanomethyl formate was mimicked using MP2/cc-pVTZ calculations. It was found that this reaction is not favored thermodynamically. It is also conjectured that the possible formation of cyanomethyl formate might be catalyzed and take place on interstellar particles.

Forming a Two-Ring Polycyclic Aromatic Hydrocarbon without a Benzene Intermediate: the Reaction of Propargyl with Acetylene

NASA Astrophysics Data System (ADS)

Osborn, David; Savee, John; Selby, Talitha; Welz, Oliver; Taatjes, Craig

The reaction of acetylene (HCCH) with a resonance-stabilized free radical is a commonly invoked mechanism for the generation of polycyclic aromatic hydrocarbons (PAH), which are likely precursors of soot particles in combustion. In this work, we examine the sequential addition of acetylene to the propargyl radical (H2CCCH) at temperatures of 800 and 1000 K. Using time-resolved multiplexed photoionization mass spectrometry with tunable ionizing radiation, we identified the isomeric forms of the C5H5 and C7H7 intermediates in this reaction sequence, and confirmed that the final C9H8 product is the two-ring aromatic compound indene. We identified two different resonance-stabilized C5H5 intermediates, with different temperature dependencies. Furthermore, the C7H7 intermediate is the tropyl radical (c-C7H7) , not the benzyl radical (C6H5CH2) , as is usually assumed in combustion environments. These experimental results are in general agreement with the latest electronic structure / master equation results of da Silva et al. This work shows a pathway for PAH formation that bypasses benzene / benzyl intermediates.

Electrochemical storage cell containing a substituted anisole or di-anisole redox shuttle additive for overcharge protection and suitable for use in liquid organic and solid polymer electrolytes

DOEpatents

Kerr, John B.; Tian, Minmin

2000-01-01

A electrochemical cell is described comprising an anode, a cathode, a solid polymer electrolyte, and a redox shuttle additive to protect the cell against overcharging and a redox shuttle additive to protect the cell against overcharging selected from the group consisting of: (a) a substituted anisole having the general formula (in an uncharged state): ##STR1## where R.sub.1 is selected from the group consisting of H, OCH.sub.3, OCH.sub.2 CH.sub.3, and OCH.sub.2 phenyl, and R.sub.2 is selected from the group consisting of OCH.sub.3, OCH.sub.2 CH.sub.3, OCH.sub.2 phenyl, and O.sup.- Li.sup.+ ; and (b) a di-anisole compound having the general formula (in an uncharged state): ##STR2## where R is selected from the group consisting of -OCH.sub.3 and -CH.sub.3, m is either 1 or 0, n is either 1 or 0, and X is selected from the group consisting of -OCH.sub.3 (methoxy) or its lithium salt --O.sup.- Li.sup.+. The lithium salt of the di-anisole is the preferred form of the redox shuttle additive because the shuttle anion will then initially have a single negative charge, it loses two electrons when it is oxidized at the cathode, and then moves toward the anode as a single positively charged species where it is then reduced to a single negatively charged species by gaining back two electrons.

Quantification of the Keto-Hydroperoxide (HOOCH2OCHO) and Other Elusive Intermediates during Low-Temperature Oxidation of Dimethyl Ether.

PubMed

Moshammer, Kai; Jasper, Ahren W; Popolan-Vaida, Denisia M; Wang, Zhandong; Bhavani Shankar, Vijai Shankar; Ruwe, Lena; Taatjes, Craig A; Dagaut, Philippe; Hansen, Nils

2016-10-04

This work provides new temperature-dependent mole fractions of elusive intermediates relevant to the low-temperature oxidation of dimethyl ether (DME). It extends the previous study of Moshammer et al. [ J. Phys. Chem. A 2015 , 119 , 7361 - 7374 ] in which a combination of a jet-stirred reactor and molecular beam mass spectrometry with single-photon ionization via tunable synchrotron-generated vacuum-ultraviolet radiation was used to identify (but not quantify) several highly oxygenated species. Here, temperature-dependent concentration profiles of 17 components were determined in the range of 450-1000 K and compared to up-to-date kinetic modeling results. Special emphasis is paid toward the validation and application of a theoretical method for predicting photoionization cross sections that are hard to obtain experimentally but essential to turn mass spectral data into mole fraction profiles. The presented approach enabled the quantification of the hydroperoxymethyl formate (HOOCH 2 OCH 2 O), which is a key intermediate in the low-temperature oxidation of DME. The quantification of this keto-hydroperoxide together with the temperature-dependent concentration profiles of other intermediates including H 2 O 2 , HCOOH, CH 3 OCHO, and CH 3 OOH reveals new opportunities for the development of a next-generation DME combustion chemistry mechanism.

Thermal Chemistry of Cp*W(NO)(CH2CMe3)(H)(L) Complexes (L = Lewis Base).

PubMed

Fabulyak, Diana; Handford, Rex C; Holmes, Aaron S; Levesque, Taleah M; Wakeham, Russell J; Patrick, Brian O; Legzdins, Peter; Rosenfeld, Devon C

2017-01-03

The complexes trans-Cp*W(NO)(CH 2 CMe 3 )(H)(L) (Cp* = η 5 -C 5 Me 5 ) result from the treatment of Cp*W(NO)(CH 2 CMe 3 ) 2 in n-pentane with H 2 (∼1 atm) in the presence of a Lewis base, L. The designation of a particular geometrical isomer as cis or trans indicates the relative positions of the alkyl and hydrido ligands in the base of a four-legged piano-stool molecular structure. The thermal behavior of these complexes is markedly dependent on the nature of L. Some of them can be isolated at ambient temperatures [e.g., L = P(OMe) 3 , P(OPh) 3 , or P(OCH 2 ) 3 CMe]. Others undergo reductive elimination of CMe 4 via trans to cis isomerization to generate the 16e reactive intermediates Cp*W(NO)(L). These intermediates can intramolecularly activate a C-H bond of L to form 18e cis complexes that may convert to the thermodynamically more stable trans isomers [e.g., Cp*W(NO)(PPh 3 ) initially forms cis-Cp*W(NO)(H)(κ 2 -PPh 2 C 6 H 4 ) that upon being warmed in n-pentane at 80 °C isomerizes to trans-Cp*W(NO)(H)(κ 2 -PPh 2 C 6 H 4 )]. Alternatively, the Cp*W(NO)(L) intermediates can effect the intermolecular activation of a substrate R-H to form trans-Cp*W(NO)(R)(H)(L) complexes [e.g., L = P(OMe) 3 or P(OCH 2 ) 3 CMe; R-H = C 6 H 6 or Me 4 Si] probably via their cis isomers. These latter activations are also accompanied by the formation of some Cp*W(NO)(L) 2 disproportionation products. An added complication in the L = P(OMe) 3 system is that thermolysis of trans-Cp*W(NO)(CH 2 CMe 3 )(H)(P(OMe) 3 ) results in it undergoing an Arbuzov-like rearrangement and being converted mainly into [Cp*W(NO)(Me)(PO(OMe) 2 )] 2 , which exists as a mixture of two isomers. All new complexes have been characterized by conventional and spectroscopic methods, and the solid-state molecular structures of most of them have been established by single-crystal X-ray crystallographic analyses.

Absence of an effect of vitamin E on protein and lipid radical formation during lipoperoxidation of LDL by lipoxygenase

PubMed Central

Ganini, Douglas; Mason, Ronald P.

2014-01-01

LDL oxidation is the primary event in atherosclerosis, where LDL lipoperoxidation leads to modifications in the apolipoprotein B-100 (apo B-100) and lipids. Intermediate species of lipoperoxidation are known to be able to generate amino acid-centered radicals. Thus, we hypothesized that lipoperoxidation intermediates induce protein-derived free radical formation during LDL oxidation. Using DMPO and immuno spin-trapping, we detected the formation of protein free radicals on LDL incubated with Cu2+ or the soybean lipoxidase (LPOx)/phospholipase A2 (PLA2). With low concentrations of DMPO (1 mM), Cu2+ dose-dependently induced oxidation of LDL and easily detected apo B-100 radicals. Protein radical formation in LDL incubated with Cu2+ showed maximum yields after 30 minutes. In contrast, the yields of apo B-100-radicals formed by LPOx/PLA2 followed a typical enzyme-catalyzed kinetics that was unaffected by DMPO concentrations of up to 50 mM. Furthermore, when we analyzed the effect of antioxidants on protein radical formation during LDL oxidation, we found that ascorbate, urate and Trolox dose-dependently reduced apo B-100-free radical formation in LDL exposed to Cu2+. In contrast, Trolox was the only antioxidant that even partially protected LDL from LPOx/PLA2. We also examined the kinetics of lipid radical formation and protein radical formation induced by Cu2+ or LPOx/PLA2 for LDL supplemented with α-tocopherol. In contrast to the potent antioxidant effect of α-tocopherol on the delay of LDL oxidation induced by Cu2+, when we used the oxidizing system LPOx/PLA2, no significant protection was detected. The lack of protection of α-tocopherol on the apo B-100 and lipid free radical formation by LPOx may explain the failure of vitamin E as a cardiovascular protective agent for humans. PMID:25091900

Role of the ancillary ligand N,N-dimethylaminoethanol in the sensitization of Eu(III) and Tb(III) luminescence in dimeric beta-diketonates.

PubMed

Eliseeva, Svetlana V; Kotova, Oxana V; Gumy, Frédéric; Semenov, Sergey N; Kessler, Vadim G; Lepnev, Leonid S; Bünzli, Jean-Claude G; Kuzmina, Natalia P

2008-04-24

Two types of dimeric complexes [Ln2(hfa)6(mu2-O(CH2)2NHMe2)2] and [Ln(thd)2(mu2,eta2-O(CH2)2NMe2)]2 (Ln = YIII, EuIII, GdIII, TbIII, TmIII, LuIII; hfa- = hexafluoroacetylacetonato, thd- = dipivaloylmethanato) are obtained by reacting [Ln(hfa)3(H2O)2] and [Ln(thd)3], respectively, with N,N-dimethylaminoethanol in toluene and are fully characterized. X-ray single crystal analysis performed for the TbIII compounds confirms their dimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of the beta-diketonate. In [Tb2(hfa)6(mu2-O(CH2)2NHMe2)2], eight-coordinate TbIII ions adopt distorted square antiprismatic coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a Tb1...Tb2 separation of 3.684(1) A. In [Tb(thd)2(mu2,eta2-O(CH2)2NMe2)]2, the N,N-dimethylaminoethanol acts as chelating-bridging O,N-donor anion and the TbIII ions are seven-coordinate; the Tb1...Tb1A separation amounts to 3.735(2) A within centrosymmetric dimers. The dimeric complexes are thermally stable up to 180 degrees C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The EuIII and TbIII dimers display metal-centered luminescence, particularly [Eu2(hfa)6(O(CH2)2NHMe2)2] (quantum yield Q(L)Ln = 58%) and [Tb(thd)2(O(CH2)2NMe2)]2 (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and EuIII- or TbIII-doped (0.01-0.1 mol %) LuIII analogues, leads to the conclusion that both the beta-diketone and N,N-dimethylaminoethanol ligands contribute significantly to the sensitization process of the EuIII luminescence. The ancillary ligand increases considerably the luminescence of [Eu2(hfa)6(O(CH2)2NHMe2)2], compared to [Ln(hfa)3(H2O)2], through the formation of intra-ligand states while it is detrimental to TbIII luminescence in both beta-diketonates. Thin films of the most luminescent compound [Eu2(hfa)6(O(CH2)2NHMe2)2] obtained by vacuum sublimation display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for applications in electroluminescent devices.

Photoproduction of One-Electron Reducing Intermediates by Chromophoric Dissolved Organic Matter (CDOM): Relation to O2- and H2O2 Photoproduction and CDOM Photooxidation.

PubMed

Zhang, Yi; Blough, Neil V

2016-10-06

A molecular probe, 3-amino-2,2,5,5,-tetramethy-1-pyrrolydinyloxy (3ap), was employed to determine the formation rates of one-electron reducing intermediates generated photochemically from both untreated and borohydride-reduced Suwanee River fulvic and humic acids (SRFA and SRHA, respectively). This stable nitroxyl radical reacts rapidly with reducing radicals and other one-electron reductants to produce a relatively stable product, the hydroxylamine, which can be derivatized with fluorescamine, separated by HPLC and quantified fluorimetrically. We provide evidence that O 2 and 3ap compete for the same pool(s) of photoproduced reducing intermediates, and that under appropriate experimental conditions, the initial rate of hydroxylamine formation (R H ) can provide an estimate of the initial rate of superoxide (O 2 - ) formation. However, comparison of the initial rates of H 2 O 2 formation (R H2O2 ) to that of R H show far larger ratios of R H /R H2O2 (∼6-13) than be accounted for by simple O 2 - dismutation (R H /R H2O2 = 2), implying a significant oxidative sink of O 2 - (∼67-85%). Because of their high reactivity with O 2 - and their likely importance in the photochemistry of CDOM, we suggest that coproduced phenoxy radicals could represent a viable oxidative sink. Because O 2 - /phenoxy radical reactions can lead to more highly oxidized products, O 2 - could be playing a far more significant role in the photooxidation of CDOM than has been previously recognized.

Vitamin K3 analogs induce selective tumor cytotoxicity in neuroblastoma.

PubMed

Kitano, Toru; Yoda, Hiroyuki; Tabata, Keiichi; Miura, Motofumi; Toriyama, Masaharu; Motohashi, Shigeyasu; Suzuki, Takashi

2012-01-01

We investigated the cytotoxicity of eight vitamin K3 (VK3) analogs against neuroblastoma cell lines (IMR-32, LA-N-1, NB-39, and SK-N-SH) and normal cell lines (human umbilical vein endothelial cells (HUVEC) and human dermal fibroblasts (HDF)) using a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. 2-[(2-Methoxy)ethylthio]-3-methyl-1,4-naphthoquinone (VK3-OCH(3)) showed especially potent cytotoxic activities against neuroblastoma cells compared with normal cells. In a Hoechst 33342 staining experiment, apoptotic morphologies characterized by cell shrinkage, nuclear condensation, and nuclear fragmentation were observed in IMR-32 and LA-N-1 cells after 48 h of treatment with 10(-5) M of VK3-OCH(3). To clarify the molecular mechanisms of apoptosis induced by VK3-OCH(3), we examined the expression of apoptosis related proteins using a Proteome Profiler Array and western blotting. Heme oxygenase (HO)-1 was remarkably increased by VK3-OCH(3) compared with the control (173% in IMR-32 and 170% in LA-N-1 at 24 h). Moreover, caveolin-1 was induced by VK3-OCH(3) at 48 h. In addition, VK3-OCH(3) arrested the cell cycle at the G2/M phase in IMR-32 cells. These results suggest that VK3-OCH(3) exhibited a selective antitumor activity via HO-1-related mechanisms.

Relative stability of radicals derived from artemisinin: A semiempirical and DFT study

NASA Astrophysics Data System (ADS)

Arantes, C.; de Araujo, M. T.; Taranto, A. G.; de M. Carneiro, J. W.

The semiempirical AM1 and PM3 methods, as well as the density functional (DFT/B3LYP) approach using the 6-31g(d) basis set, were employed to calculate the relative stability of intermediate radicals derived from artemisinin, a sesquiterpene lactone having an endoperoxide bridge that is essential for its antimalarial activity. The compounds studied have their nonperoxidic oxygen atom of the trioxane ring and/or the carbonyl group replaced by a CH2 unit. Relative stabilities were calculated by means of isodesmic equations using artemisinin as reference. It was found that replacement of oxygen atoms decreases the relative stability of the anionic radical intermediates. In contrast, for compounds with inverted stereochemistry the intermediate radicals were found to be more stable than those with the artemisinin-like stereochemistry. These relative stabilities may modulate the antimalarial potency. Radicals centered on carbon are always more stable than the corresponding radicals centered on oxygen.

The reactions of cytidine and 2'-deoxycytidine with SO4.- revisited. Pulse radiolysis and product studies.

PubMed

Aravindakumar, Charuvila T; Schuchmann, Man Nien; Rao, Balijepalli S; von Sonntag, Justus; von Sonntag, Clemens

2003-01-21

The reactions of SO4.- with 2'-deoxycytidine 1a and cytidine 1b lead to very different intermediates (base radicals with 1a, sugar radicals with 1b). The present study provides spectral and kinetic data for the various intermediates by pulse radiolysis as well as information on final product yields (free cytosine). Taking these and literature data into account allows us to substantiate but also modify in essential aspects the current mechanistic concept (H. Catterall, M. J. Davies and B. C. Gilbert, J. Chem. Soc., Perkin Trans. 2, 1992, 1379). SO4.- radicals have been generated radiolytically in the reaction of peroxodisulfate with the hydrated electron (and the H. atom). In the reaction of SO4.- with 1a (k = 1.6 x 10(9) dm3 mol-1 s-1), a transient (lambda max = 400 nm, shifted to 450 nm at pH 3) is observed. This absorption is due to two intermediates. The major component (lambda max approximately 385 nm) does not react with O2 and has been attributed to an N-centered radical 4a formed upon sulfate release and deprotonation at nitrogen. The minor component, rapidly wiped out by O2, must be due to C-centered OH-adduct radical(s) 6a and/or 7a suggested to be formed by a water-induced nucleophilic replacement. These radicals decay by second-order kinetics. Free cytosine is only formed in low yields (G = 0.14 x 10(-7) mol J-1 upon electron-beam irradiation). In contrast, 1b gives rise to an intermediate absorbing at lambda max = 530 nm (shifted to 600 nm in acid solution) which rapidly decays (k = 6 x 10(4) s-1). In the presence of O2, the decay is much faster (k approximately 1.3 x 10(9) dm3 mol-1 s-1) indicating that this species must be a C-centered radical. This has been attributed to the C(5)-yl radical 8 formed upon the reaction of the C(2')-OH group with the cytidine SO4(.-)-adduct radical 2b. This reaction competes very effectively with the corresponding reaction of water and the release of sulfate and a proton generating the N-centered radical. Upon the decay of 8, sugar radical 11 is formed with the release of cytosine. The latter is formed with a G value of 2.8 x 10(-7) mol J-1 (85% of primary SO4.-) at high dose rates (electron beam irradiation). At low dose rates (gamma-radiolysis) its yield is increased to 7 x 10(-7) mol J-1 due to a chain reaction involving peroxodisulfate and reducing free radicals. Phosphate buffer prevents the formation of the sugar radical at the SO4(.-)-adduct stage by enhancing the rate of sulfate release by deprotonation of 2b and also by speeding up the decay of the C(5)-yl radical into another (base) radical. Cytosine release in cytidine is mechanistically related to strand breakage in poly(C). Literature data on the effect of dioxygen on strand breakage yields in poly(C) induced by SO4.- (suppressed) and upon photoionisation (unaltered) lead us to conclude that in poly(C) and also in the present system free radical cations are not involved to a major extent. This conclusion modifies an essential aspect of the current mechanistic concept.

Photogeneration of H2O2 in Water-Swollen SPEEK/PVA Polymer Films.

PubMed

Lockhart, PaviElle; Little, Brian K; Slaten, B L; Mills, G

2016-06-09

Efficient reduction of O2 took place via illumination with 350 nm photons of cross-linked films containing a blend of sulfonated poly(ether etherketone) and poly(vinyl alcohol) in contact with air-saturated aqueous solutions. Swelling of the solid macromolecular matrices in H2O enabled O2 diffusion into the films and also continuous extraction of the photogenerated H2O2, which was the basis for a method that allowed quantification of the product. Peroxide formed with similar efficiencies in films containing sulfonated polyketones prepared from different precursors and the initial photochemical process was found to be the rate-determining step. Generation of H2O2 was most proficient in the range of 4.9 ≤ pH ≤ 8 with a quantum yield of 0.2, which was 10 times higher than the efficiencies determined for solutions of the polymer blend. Increases in temperature as well as [O2] in solution were factors that enhanced the H2O2 generation. H2O2 quantum yields as high as 0.6 were achieved in H2O/CH3CN mixtures with low water concentrations, but peroxide no longer formed when film swelling was suppressed. A mechanism involving reduction of O2 by photogenerated α-hydroxy radicals from the polyketone in competition with second-order radical decay processes explains the kinetic features. Higher yields result from the films because cross-links present in them hinder diffusion of the radicals, limiting their decay and enhancing the oxygen reduction pathway.

Characterization of the product radical structure in the Co(II)-product radical pair state of coenzyme B12-dependent ethanolamine deaminase by using three-pulse 2H ESEEM spectroscopy.

PubMed

Warncke, Kurt

2005-03-08

Molecular structural features of the product radical in the Co(II)-product radical pair catalytic intermediate state in coenzyme B(12)- (adenosylcobalamin-) dependent ethanolamine deaminase from Salmonella typhimurium have been characterized by using X-band three-pulse electron spin-echo envelope modulation (ESEEM) spectroscopy in the disordered solid state. The Co(II)-product radical pair state was prepared by cryotrapping holoenzyme during steady-state turnover on excess 1,1,2,2-(2)H(4)-aminoethanol or natural abundance, (1)H(4)-aminoethanol. Simulation of the (2)H/(1)H quotient ESEEM (obtained at two microwave frequencies, 8.9 and 10.9 GHz) from the interaction of the unpaired electron localized at C2 of the product radical with nearby (2)H nuclei requires four types of coupled (2)H, which are assigned as follows: (a) a single strongly coupled (effective dipole distance, r(eff) = 2.3 A) (2)H in the C5' methyl group of 5'-deoxyadenosine, (b) two weakly coupled (r(eff) = 4.2 A) (2)H in the C5' methyl group, (c) one (2)H coupling from a beta-(2)H bonded to C1 of the product radical (isotropic hyperfine coupling, A(iso) = 4.7 MHz), and (d) a second type of C1 beta-(2)H coupling (A(iso) = 7.7 MHz). The two beta-(2)H couplings are proposed to arise from two C1-C2 rotamer states of the product radical that are present in approximately equal proportion. A model is presented, in which C5' is positioned at a distance of 3.3 A from C2, which is comparable with the C1-C5' distance in the Co(II)-substrate radical pair intermediate. Therefore, the C5'methyl group remains in close (van der Waals) contact with the substrate and product radical species during the radical rearrangement step of the catalytic cycle, and the C5' center is the sole mediator of radical pair recombination in ethanolamine deaminase.

Ethylene Glycol Adsorption and Reaction over CeOX(111) Thin Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mullins, David R; Chen, Tsung-Liang

2011-01-01

This study reports the interaction of ethylene glycol with well-ordered CeO{sub x}(111) thin film surfaces. Ethylene glycol initially adsorbs on fully oxidized CeO{sub 2}(111) and reduced CeO{sub 2-x}(111) through the formation of one C-O-Ce bond and then forms a second alkoxy bond after annealing. On fully oxidized CeO{sub 2}(111) both recombination of ethylene glycol and water desorption occur at low temperature leaving stable -OCH{sub 2}CH{sub 2}O- (ethylenedioxy) intermediates and oxygen vacancies on the surface. This ethylenedioxy intermediate goes through C-C bond scission to produce formate species which then react to produce CO and CO{sub 2}. The formation of water resultsmore » in the reduction of the ceria. On a reduced CeO{sub 2-x}(111) surface the reaction selectivity shifts toward a dehydration process. The ethylenedioxy intermediate decomposes by breaking a C-O bond and converts into an enolate species. Similar to the reaction of acetaldehyde on reduced CeO{sub 2-x}(111), the enolate reacts to produce acetaldehyde, acetylene, and ethylene. The loss of O from ethylene glycol leads to a small amount of oxidation of the reduced ceria.« less

Ethylene Glycol Adsorption and Reaction over CeOX(111) Thin Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

T Chen; D Mullins

2011-12-31

This study reports the interaction of ethylene glycol with well-ordered CeO{sub x}(111) thin film surfaces. Ethylene glycol initially adsorbs on fully oxidized CeO{sub 2}(111) and reduced CeO{sub 2-x}(111) through the formation of one C-O-Ce bond and then forms a second alkoxy bond after annealing. On fully oxidized CeO{sub 2}(111) both recombination of ethylene glycol and water desorption occur at low temperature leaving stable -OCH{sub 2}CH{sub 2}O- (ethylenedioxy) intermediates and oxygen vacancies on the surface. This ethylenedioxy intermediate goes through C-C bond scission to produce formate species which then react to produce CO and CO{sub 2}. The formation of water resultsmore » in the reduction of the ceria. On a reduced CeO{sub 2-x}(111) surface the reaction selectivity shifts toward a dehydration process. The ethylenedioxy intermediate decomposes by breaking a C-O bond and converts into an enolate species. Similar to the reaction of acetaldehyde on reduced CeO{sub 2-x}(111), the enolate reacts to produce acetaldehyde, acetylene, and ethylene. The loss of O from ethylene glycol leads to a small amount of oxidation of the reduced ceria.« less

Methemoglobin formation from butylated hydroxyanisole and oxyhemoglobin. Comparison with butylated hydroxytoluene and p-hydroxyanisole.

PubMed

Stolze, K; Nohl, H

1992-01-01

The widely used food additives butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) react with oxyhemoglobin, thereby forming methemoglobin. The reaction rates were measured using visible spectroscopy, and second order rate constants were established for BHA and compared with p-hydroxyanisole. Using ESR we investigated the involvement of free radical reaction intermediates. The expected one-electron oxidation product of BHA and BHT, the phenoxyl radical, could only be detected with pure 3-t-butyl-4-hydroxyanisole and oxyhemoglobin. With the commercial mixture of 2- and 3-t-butyl-4-hydroxyanisole a very strong ESR signal of a secondary free radical species was observed, similar to the one observed earlier with p-hydroxyanisole and dependent on the presence of free thiol groups, so that we assumed the intermediate existence of a perferryl species, the MetHb-H2O2 adduct. In a second series of experiments we investigated the reactivity of this postulated intermediate with BHA and BHT, starting with a pure MetHb/H2O2-phenol mixture in a stopped-flow apparatus linked to the ESR spectrometer, detecting the expected phenoxyl radicals from BHA and p-hydroxyanisole. Due to the low solubility and decreased reactivity of BHT only traces of phenoxyl type radical were found together with a high concentration of unreacted perferryl species. The reactivity of BHA, BHT and p-hydroxyanisole with free thiol groups is demonstrated by an increased reaction rate in the presence of the thiol group blocking substance NEM.

Atmospheric Oxidation Mechanism of Furfural Initiated by Hydroxyl Radicals.

PubMed

Zhao, Xiaocan; Wang, Liming

2017-05-04

Furfural is emitted into the atmosphere because of its potential applications as an intermediate to alkane fuels from biomass, industrial usages, and biomass burning. The kinetic and mechanistic information on the furfural chemistry is necessary to assess the fate of furfural in the atmosphere and its impact on the air quality. Here we studied the atmospheric oxidation mechanisms of furfural initiated by the OH radicals using quantum chemistry and kinetic calculations. The reaction of OH and furfural was initiated mainly by OH additions to C 2 and C 5 positions, forming R2 and R5 adducts, which could undergo rapid ring-breakage to form R2B and R5B, respectively. Our calculations showed that these intermediate radicals reacted rather slowly with O 2 under the atmospheric conditions because the additions of O 2 to these radicals are only slightly exothermic and highly reversible. Alternatively, these radicals would react directly with O 3 , NO 2 , HO 2 /RO 2 , etc. Namely, the atmospheric oxidation of furfural would unlikely result in ozone formation. Under typical atmospheric conditions, the main products in OH-initiated furfural oxidation include 2-oxo-3-pentene-1,5-dialdehyde, 5-hydroxy-2(5H)-furanone, 4-oxo-2- butenoic acid, and 2,5-furandione. These compounds will likely stay in the gas phase and are subject to further photo-oxidation.

Electron Paramagnetic Resonance Spectroscopic Study on Nonequilibrium Reaction Pathways in the Photolysis of Solid Nitromethane (CH3NO2) and D3-Nitromethane (CD3NO2).

PubMed

Tsegaw, Yetsedaw Andargie; Sander, Wolfram; Kaiser, Ralf I

2016-03-10

Thin films of nitromethane (CH3NO2) along with its isotopically labeled counterpart D3-nitromethane (CD3NO2) were photolyzed at discrete wavelength between 266 nm (4.7 eV) and 121 nm (10.2 eV) to explore the underlying mechanisms involved in the decomposition of model compounds of energetic materials in the condensed phase at 5 K. The chemical modifications of the ices were traced in situ via electron paramagnetic resonance, thus focusing on the detection of (hitherto elusive) reaction intermediates and products with unpaired electrons. These studies revealed the formation of two carbon-centered radicals [methyl (CH3), nitromethyl (CH2NO2)], one oxygen-centered radical [methoxy (CH3O)], two nitrogen-centered radicals [nitrogen monoxide (NO), nitrogen dioxide (NO2)], as well as atomic hydrogen (H). The decomposition products of these channels and the carbon-centered nitromethyl (CH2NO2) radical in particular represent crucial reaction intermediates leading via sequential molecular mass growth processes in the exposed nitromethane samples to complex organic molecules as predicted previously by dynamics calculations. The detection of the nitromethyl (CH2NO2) radical along with atomic hydrogen (H) demonstrated the existence of a high-energy decomposition pathway, which is closed under collisionless conditions in the gas phase.

Photodissociation of CF2ICF2I in solid para-hydrogen: infrared spectra of anti- and gauche-˙C2F4I radicals.

PubMed

Haupa, Karolina Anna; Lim, Manho; Lee, Yuan-Pern

2018-05-09

The photolysis of 1,2-diiodotetrafluoroethane (CF2ICF2I) has served as a prototypical system in ultrafast reaction dynamics. Even though the intermediates, anti- and gauche-iodotetrafluoroethyl (˙C2F4I) radicals, have been characterized with electron diffraction and X-ray diffraction, their infrared spectra are unreported. We report the formation and infrared identification of these radical intermediates upon ultraviolet photodissociation of CF2ICF2I in solid para-hydrogen (p-H2) at 3.3 K. Lines at 1364.9/1358.5, 1283.2, 1177.1, 1162.2, 1126.8, 837.3, 658.0, 574.2, and 555.2 cm-1 are assigned to anti-˙C2F4I, and lines at 1325.9, 1259.7, 1143.4, 1063.4, 921.0, and 765.3 cm-1 to gauche-˙C2F4I. A secondary photodissociation leading to C2F4 was also observed. The assignments were derived according to behavior on secondary photolysis, comparison of the vibrational wavenumbers and the IR intensities of the observed lines with values predicted with the B3PW91/aug-cc-pVTZ-pp method. This spectral identification provides valuable information for future direct spectral probes of these important intermediates.

Magnetic properties of diruthenium(II,III) carboxylate compounds. Crystal structures of Ru2Cl(mu-O2CCH=CHCH=CHMe)4 and Ru2Cl(mu-O2CCH2OMe)4.

PubMed

Barral, M C; Jiménez-Aparicio, R; Pérez-Quintanilla, D; Priego, J L; Royer, E C; Torres, M R; Urbanos, F A

2000-01-10

The reaction of Ru2Cl(mu-O2CMe)4 with 2,4-hexadienoic and 2-methoxyacetic acids affords the compounds Ru2Cl(mu-O2CR)4 [R = CH=CHCH=CHCH3 (1), CH2OMe (2)]. The structures of both complexes have been determined by X-ray crystallography. 1 crystallizes in the triclinic space group P-1 with a = 9.264(1) A, b = 12.661(8) A, c = 12.839(5) A, alpha = 106.09(3) degrees, beta = 77.89(2) degrees, gamma = 97.73(3) degrees, and Z = 2. 2 crystallizes in the nonstandard monoclinic space group P2(1)/c with a = 12.132(4) A, b = 11.570(2) A, c = 13.674(2) A, beta = 91.18(2) degrees, and Z = 4. Complexes 1 and 2 show [Ru2(mu-O2CR)4]+ units linked by chloride ions, giving zigzag chains with Ru-Cl-Ru angles of 119.43(4) degrees and 110.11(7) degrees, respectively. The Ru-Ru bond distances are 2.2857(9) A (1) and 2.290(1) A (2). A magnetic study, in the 2-300 K temperature range, of the new compounds and the previously described Ru2Cl(mu-O2CR)4 [R = CHMe2 (3), CMe3 (4), C4H4N (5)] is described. The polymeric complexes 1 and 2 and the nonpolymeric 3-5 show a large zero-field splitting which varies from 53.9 to 68.1 cm-1. These complexes also show a weak, but not negligible, through-space intermolecular antiferromagnetic coupling not observed in the previous magnetic studies carried out on these types of compounds.

The C- and N-Terminal Residues of Synthetic Heptapeptide Ion Channels Influence Transport Efficacy Through Phospholipid Bilayers

PubMed Central

Djedovič, Natasha; Ferdani, Riccardo; Harder, Egan; Pajewska, Jolanta; Pajewski, Robert; Weber, Michelle E.; Schlesinger, Paul H.; Gokel, George W.

2008-01-01

The synthetic peptide, R2N-COCH2OCH2CO-Gly-Gly-Gly-Pro-Gly-Gly-Gly-OR’, was shown to be selective for Cl- over K+ when R is n-octadecyl and R’ is benzyl. Nineteen heptapeptides have now been prepared in which the N-terminal and C-terminal residues have been varied. All of the N-terminal residues are dialkyl but the C-terminal chains are esters, 2° amides, or 3° amides. The compounds having varied N-terminal anchors and C-terminal benzyl groups are as follows: 1, R = n-propyl; 2, R = n-hexyl; 3, R = n-octyl; 4, R = n-decyl; 5, R = n-dodecyl; 6, R = n-tetradecyl; 7, R = n-hexadecyl; 8, R = n-octadecyl. Compounds 9-19 have R = n-octadecyl and C-terminal residues as follows: 9, OR’ = OCH2CH3; 10, OR’ = OCH(CH3)2; 11, OR’ = O(CH2)6CH3; 12, OR’ = OCH2-c-C6H11; 13, OR’ = O(CH2)9CH3; 14, OR’ = O (CH2)17CH3; 15, NR’2 = N[(CH2)6CH3]2; 16, NHR’ = NH(CH2)9CH3; 17, NR’2 = N[(CH2)9CH3]2; 18, NHR’ = NH(CH2)17CH3; 19, NR’2 = N[(CH2)17CH3]2. The highest anion transport activities were observed as follows. For the benzyl esters whose N-terminal residues were varied, i.e. 1-8, compound 3 was most active. For the C18 anchored esters 10-14, n-heptyl ester 11 was most active. For the C18 anchored, C-terminal amides 15-19, di-n-decylamide 17 was most active. It was concluded that both the C- and N-terminal anchors were important for channel function in the bilayer but that activity was lost unless only one of the two anchoring groups was dominant. PMID:19633728

The mechanism of the photochemical oxidation of water to oxygen with silver chloride colloids

NASA Astrophysics Data System (ADS)

Chandrasekaran, K.; Thomas, J. K.

1983-05-01

Photoexcitation of silver chloride colloids in the presence of excess silver ions, leads to the decomposition of water. Hydroxyl radicals were found to be intermediates in the decomposition process. Irradiation leads to hydroxyl radicals, which recombine to give hydrogen peroxide, on the colloidal particle surface. Subsequent decomposition of H 2O 2 to give O 2 is catalyzed by silver ions. Addition of alcohols such as methanol and isopropanol reduce the oxygen yield, as they react with OH radicals and reduce the H 2O 2 yield.

AAPH-mediated antioxidant reactions of secoisolariciresinol and SDG.

PubMed

Hosseinian, Farah S; Muir, Alister D; Westcott, Neil D; Krol, Ed S

2007-02-21

Secoisolariciresinol (SECO ) is the major lignan found in flaxseed (Linum usitatissimum L.) and is present in a polymer that contains secoisolariciresinol diglucoside (SDG ). SECO, SDG and the polymer are known to have a number of health benefits, including reduction of serum cholesterol levels, delay in the onset of type II diabetes and decreased formation of breast, prostate and colon cancers. The health benefits of SECO and SDG may be partially attributed to their antioxidant properties. To better understand their antioxidant properties, SECO and SDG were oxidized using 2,2'-azobis(2-amidinopropane), an in vitro model of radical scavenging. The major lignan radical-scavenging oxidation products and their formation over time were determined. SDG was converted to four major products, which were the result of a phenoxyl radical intermediate. One of these products, a dimer of SDG, decomposed under the reaction conditions to form two of the other major products, and . SECO was converted to five major products, two of which were also the result of a phenoxyl radical intermediate. The remaining products were the result of an unexpected alkoxyl radical intermediate. The phenol oxidation products were stable under the reaction conditions, whereas two of the alcohol oxidation products decomposed. In general, only one phenol group on the lignans was oxidized, suggesting that the number of phenols per molecule may not predict radical scavenging antioxidant ability of lignans. Finally, SECO is a superior antioxidant to SDG, and it may be that the additional alcohol oxidation pathway contributes to its greater antioxidant ability.

Distribution of free radicals and intermediates during the photodegradation of polychlorinated biphenyls strongly affected by cosolvents and TiO₂ catalyst.

PubMed

Zhu, Xiangdong; Wang, Yujun; Qin, Wenxiu; Zhang, Shicheng; Zhou, Dongmei

2016-02-01

Polychlorinated biphenyls (PCBs) pose potential ecological risk because of their high toxicity and carcinogenicity. Photodegradation, which is an important process for the removal of PCBs, is greatly influenced by the cosolvent and catalyst. Hence, it is important to explore their effects on the photodegradation behavior of PCBs. In this study, 2,4,4'-trichlorobiphenyl (PCB28) was selected as a model compound, and the effects of two typical cosolvents, namely acetone and ethanol, and TiO2 catalyst on the distributions of free radicals and intermediates were investigated. Interestingly, the TiO2 catalyst did not promote PCB28 photodegradation. Moreover, the free radical distribution was greatly influenced in the presence of the TiO2 catalyst, while was only slightly affected in its absence by the cosolvent kinds. The main photodegradation pathways are proposed on the basis of the distribution of detected intermediates, which were significantly regulated by both the cosolvent and TiO2 catalyst. The results provide novel insights into the photodegradation of PCBs and may have important implications for choosing cosolvent in desorbing soil PCBs and consequently enhancing PCBs degradation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Noncanonical Radical SAM Enzyme Chemistry Learned from Diphthamide Biosynthesis.

PubMed

Dong, Min; Zhang, Yugang; Lin, Hening

2018-05-10

Radical S-adenosylmethionine (SAM) enzymes are a superfamily of enzymes that use SAM and reduced [4Fe-4S] cluster to generate a 5'-deoxyadenosyl radical to catalyze numerous challenging reactions. We have reported a type of noncanonical radical SAM enzymes in the diphthamide biosynthesis pathway. These enzymes also use SAM and reduced [4Fe-4S] clusters, but generate a 3-amino-3-carboxypropyl (ACP) radical to modify the substrate protein, translation elongation factor 2. The regioselective cleavage of a different C-S bond of the sulfonium center of SAM in these enzymes comparing to canonical radical SAM enzymes is intriguing. Here, we highlight some recent findings in the mechanism of these types of enzymes, showing that the diphthamide biosynthetic radial SAM enzymes bound SAM with a distinct geometry. In this way, the unique iron of the [4Fe-4S] cluster in the enzyme can only attack the carbon on the ACP group to form an organometallic intermediate. The homolysis of the organometallic intermediate releases the ACP radical and generates the EF2 radial.

Oxidation of dimethyl-ether and ethylene in the atmosphere and combustion environment and thermodynamic studies on hydrofluorocarbons usingab initio calculation methods

NASA Astrophysics Data System (ADS)

Yamada, Takahiro

1999-08-01

Reaction pathways and kinetics are analyzed on CH3OC.H2 unimolecular decay and on the complete CH3OC.H2 + O2 reaction system using thermodynamic properties DHdegf 298,Sdeg 298, and Cp(T) 300 <= T/K <= 1500) derived by two ab initio calculation methods, CBS-q and G2. These are used to determine thermodynamic properties of reactants, intermediate radicals and transition state (TS) compounds. Quantum Rice-Ramsperger-Kassel (QRRK) analysis is used to calculate energy dependent rate constants, k(E), and master equation is used to account for collisional stabilization. Comparison of calculated fall-off with experiment indicates that the CBS-q and G2 calculated Ea,rxn for the rate controlling transition state (β-scission reaction to CH 2O + C.H2OOH) needs to be lowered by factor of 3.3 kcal/mol and 4.0 kcal/mol respectively in order to match the data of Sehested et al. Experimental results on dimethyl-ether pyrolysis and oxidation reaction systems are compared with a detailed reaction mechanism model. The computer code CHEMKIN II is used for numerical integration. Overall agreement of the model data with experimental data is very good. Reaction pathways are analyzed and kinetics are determined on formation and reactions of the adduct resulting from OH addition to ethylene using the above ab initio methods. Hydrogen atom tunneling is included by use of Eckart formalism. Rate constants are compared with experimentally determined product branching ratios (C.H2CH 2OH stabilization: CH2O + CH3: CH3CHO + H). ab initio calculations are performed to estimate thermodynamic properties of nine fluorinated ethane compounds (fluoroethane to hexafluoroethane), eight fluoropropane (1-fluoropropane, 1,1- and 1,2- difluoropropane, 1,1,1- and 1,1,2-trifluoropropane, 1,1,1,2- and 1,1,2,2-tetrafluoropropane and 1,1,1,2,2- pentafluoropropane), and 2-fluoro,2-methylpropane. Standard entropies and heat capacities are calculated using the rigid-rotor-harmonic-oscillator approximation with direct integration over energy levels of the intramolecular rotation potential energy curve. Enthalpies of formation are estimated using G2MP2 total energies and isodesmic reactions. Thermodynamic properties for fluorinated carbon groups C/C/F/H2, C/C/F2/H, C/C/F3, C/C2/F/H, C/C2/F2 and C/C3/F for fluorinated alkane compounds, CD/F/H and CD/F2 for fluorinated alkene compounds and CT/F for fluorinated alkyne compounds are estimated. Fluorine-fluorine interaction terms F/F, 2F/F, 3F/F, 2F/2F, 3F/2F and 3F/3F for alkane compounds, F//F, 2F//F and 2F/2F for alkene compounds, and F///F for alkyne compound are also estimated.

Synthesis, structure and reactivity of rare-earth metallacarborane alkyls [η(1):η(5)-O(CH2)2C2B9H9]Ln(σ:η(1)-CH2C6H4-o-NMe2)(THF)2.

PubMed

Yang, Jingying; Xie, Zuowei

2015-04-14

Rare-earth metallacarborane alkyls can be stabilized by the incorporation of a functional sidearm into both π and σ ligands. Reaction of [Me3NH][7,8-O(CH2)2-7,8-C2B9H10] with one equiv. of Ln(CH2C6H4-o-NMe2)3 gave metallacarborane alkyls [η(1):η(5)-O(CH2)2C2B9H9]Ln(σ:η(1)-CH2C6H4-o-NMe2)(THF)2 (Ln = Y (), Gd (), Er ()) via alkane elimination. They represent the first examples of rare-earth metallacarborane alkyls. Treatment of with RN[double bond, length as m-dash]C[double bond, length as m-dash]NR (R = Cy, (i)Pr) or 2-benzoylpyridine afforded the corresponding mono-insertion products [η(1):η(5)-O(CH2)2C2B9H9]Y[η(2)-(RN)2C(CH2C6H4-o-NMe2)](DME) (R = Cy (), (i)Pr ()) or [η(1):η(5)-O(CH2)2C2B9H9]Y[C5H4NC(Ph)(CH2C6H4-o-NMe2)O](THF)2 (), respectively. Complex also reacted with ArNCO or ArNC (Ar = 2,6-diisopropylphenyl, 2,6-dimethylphenyl) to give di-insertion products [η(1):η(5)-O(CH2)2C2B9H9]Y[OC([double bond, length as m-dash]NC6H3Me2)N(C6H3Me2)C(CH2C6H4-o-NMe2)O](THF)2 () or [η(1):η(5)-O(CH2)2C2B9H9]Y[C([double bond, length as m-dash]NC6H3(i)Pr2)C([double bond, length as m-dash]NC6H3(i)Pr2)(CH2C6H4-o-NMe2)](DME) (). These results showed that the reactivity pattern of the Ln-C σ bond in rare-earth metallacarborane alkyls was dependent on the nature of the unsaturated organic molecules. New complexes were characterized by various spectroscopic techniques and elemental analysis. Some were further confirmed by single-crystal X-ray analysis.

Vinylcyclopropylacyl and polyeneacyl radicals. Intramolecular ketene alkyl radical additions in ring synthesis.

PubMed

De Boeck, Benoit; Herbert, Nicola M A; Harrington-Frost, Nicole M; Pattenden, Gerald

2005-01-21

Treatment of a variety of substituted vinylcyclopropyl selenyl esters, e.g. 11, with Bu(3)SnH-AIBN in refluxing benzene leads to the corresponding acyl radical intermediates, which undergo rearrangement and intramolecular cyclisations via their ketene alkyl radical equivalents producing cyclohexenones in 50-60% yield. By contrast, treatment of conjugated triene selenyl esters, e.g. 32, with Bu(3)SnH-AIBN produces substituted 2-cyclopentenones via intramolecular cyclisations of their ketene alkyl radical intermediates. Under the same radical-initiating conditions the selenyl esters derived from o-vinylbenzoic acid and o-vinylcinnamic acid undergo intramolecular cyclisations producing 1-indanone and 5,6-dihydrobenzocyclohepten-7-one respectively in 60-70% yields. A tandem radical cyclisation from the alpha,beta,gamma,delta-diene selenyl ester 31 provides an expeditious synthesis of the diquinane 35 in 69% yield.

Unusual spin-trap chemistry for the reaction of hydroxyl radical with the carcinogen N-nitrosodimethylamine

NASA Astrophysics Data System (ADS)

Wink, David A.; Desrosiers, Marc F.

The reaction of the potent carcinogen N-nitrosodimethylamine (NDMA) with hydroxyl radical generated via radiolysis was studied using EPR techniques. Attempts to spin trap NDMA radical intermediates with 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) produced only unusual DBNBS radicals. One of these radicals was shown to be generated by both reaction of DBNBS with nitric oxide, and direct oxidation of DBNBS with an inorganic oxidant ( .Br -2). Another DBNBS radical was identified as a sulfite spin adduct resulting from the degradation of DBNBS by a NDMA reactive intermediate. In the absence of DBNBS, hydroxyl radical reaction with NDMA gave the dimethylnitroxide radical. Unexpectedly, addition of DBNBS to a solution containing dimethylnitroxide produced an EPR spectrum nearly identical to that of NDMA solutions with DBNBS added before radiolysis. A proposed mechanism accounting for these observations is presented.

Antioxidant properties of di-tert-butylhydroxylated flavonoids.

PubMed

Lebeau, J; Furman, C; Bernier, J L; Duriez, P; Teissier, E; Cotelle, N

2000-11-01

Epidemiological evidence suggests an inverse relationship between dietary intake of flavonoids and cardiovascular risk. The biological activities of flavonoids are related to their antioxidative effects, but they also can be mutagenic, due to the prooxidant activity of the catechol pattern. To prevent these problems, we synthesized new flavonoids where one or two di-tert-butylhydroxyphenyl (DBHP) groups replaced catechol moiety at position 2 of the benzopyrane heterocycle. Two DBHP moieties can also be arranged in an arylidene structure or one DBHP fixed on a chalcone structure. Position 7 on the flavone and arylidene or position 4 on the chalcone was substituted by H, OCH(3), or OH. New structures were compared with quercetin and BHT in an LDL oxidation system induced by Cu(II) ions. Arylidenes and chalcones had the best activities (ED(50) = 0.86 and 0.21) compared with vitamin E, BHT, and quercetin (ED(50) = 10.0, 7. 4, and 2.3 microM). Activity towards stable free radical 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) was measured by log Z and ECR(50) parameters. Synthesized flavones proved to be poor DPPH radical scavengers, the activity increasing with the number of DBHP units. In contrast, arylidenes and chalcones were stronger DPPH radical scavengers (log Z > 3, 0.3 < ECR(50) < 2.12) than BHT (log Z = 0.75, ECR(50) = 12.56) or quercetin (log Z = 2.76, ECR(50) = 0.43). Unlike quercetin, synthesized compounds neither chelated nor reduced copper, proving that these new flavonoids had no prooxidant activity in vitro.

Zwitterionic metal carboxylate complexes: In solid state

NASA Astrophysics Data System (ADS)

Nath, Bhaskar; Kalita, Dipjyoti; Baruah, Jubaraj B.

2012-07-01

A flexible dicarboxylic acid having composition [(CH(o-C5H4N)(p-C6H4OCH2CO2H)2] derived from corresponding bis-phenol reacts with various metal(II) acetates such as manganese(II), cobalt(II) and nickel(II) acetate leads to zwtterionic complexes with compositions [CH(o-C5H4N)(p-C6H4OCH2CO2){p-C6H4OCH2CO2M(H2O)5}].6H2O (where M = Mn, Co, Ni). The complexes are characterised by X-ray crystallography. These complexes have chiral center due to unsymmetric structure conferred to the ligand through coordination at only one carboxylate group of the ligand. In solid state these complexes are racemic.

A Chrysodeixis chalcites Single-Nucleocapsid Nucleopolyhedrovirus Population from the Canary Islands Is Genotypically Structured To Maximize Survival

PubMed Central

Bernal, Alexandra; Simón, Oihane; Williams, Trevor; Muñoz, Delia

2013-01-01

A Chrysodeixis chalcites single-nucleocapsid nucleopolyhedrovirus wild-type isolate from the Canary Islands, Spain, named ChchSNPV-TF1 (ChchTF1-wt), appears to have great potential as the basis for a biological insecticide for control of the pest. An improved understanding of the genotypic structure of this wild-type strain population should facilitate the selection of genotypes for inclusion in a bioinsecticidal product. Eight genetically distinct genotypes were cloned in vitro: ChchTF1-A to ChchTF1-H. Quantitative real-time PCR (qPCR) analysis confirmed that ChchTF1-A accounted for 36% of the genotypes in the wild-type population. In bioassays, ChchTF1-wt occlusion bodies (OBs) were significantly more pathogenic than any of the component single-genotype OBs, indicating that genotype interactions were likely responsible for the pathogenicity phenotype of wild-type OBs. However, the wild-type population was slower killing and produced higher OB yields than any of the single genotypes alone. These results strongly suggested that the ChchTF1-wt population is structured to maximize its transmission efficiency. Experimental OB mixtures and cooccluded genotype mixtures containing the most abundant and the rarest genotypes, at frequencies similar to those at which they were isolated, revealed a mutualistic interaction that restored the pathogenicity of OBs. In OB and cooccluded mixtures containing only the most abundant genotypes, ChchTF1-ABC, OB pathogenicity was even greater than that of wild-type OBs. The ChchTF1-ABC cooccluded mixture killed larvae 33 h faster than the wild-type population and remained genotypically and biologically stable throughout five successive passages in vivo. In conclusion, the ChchTF1-ABC mixture shows great potential as the active ingredient of a bioinsecticide to control C. chalcites in the Canary Islands. PMID:24096419

Synthesis and characterisation of new types of side chain cholesteryl polymers.

PubMed

Wang, Bin; Du, Haiyan; Zhang, Junhua

2011-01-01

A series of cholesterol derivatives have been synthesised via the alkylation reaction of the 3-hydroxyl group with the aliphatic bromide compounds with different chain lengths, namely 3β-alkyloxy-cholesterol. The double bond between the C5 and C6 positions in these cholesterol derivatives was oxidised into epoxy, followed by an epoxy-ring-opening reaction with the treatment with acrylic acid, resulting in a series of 3β-alkyloxy-5α-hydroxy-6β-acryloyloxycholesterol, C(n)OCh (n=1, 2, 4, 6, 8, 10, 12), The acrylate group is connected to the C6 position, which is confirmed by the single crystal structure analysis. The corresponding polymers, PC(n)OCh, were prepared via free radical polymerisation. The structure of monomers and the resulting polymers were characterised with nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). The thermal properties of PC(n)OCh were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). To determine the secondary structure of polymers, circular dichroism (CD) spectra were performed. It was found that not all monomers produce high-molecular-weight polymers because of steric hindrance. However, all polymers have a helical structure, which can be enhanced by increasing the alkoxy chain length. In addition, increasing the alkoxy chain length decreases the glass transition temperature and increases the decomposition temperature of the polymers. Copyright © 2010 Elsevier Inc. All rights reserved.

Intramolecular and Lattice Dynamics in V6-nIVVnV O7(OCH3)12 Crystal

NASA Astrophysics Data System (ADS)

Yablokov, Yu. V.; Augustyniak-Jabłokow, M. A.; Borshch, S.; Daniel, C.; Hartl, H.

2006-08-01

Multi-nuclear mixed-valence clusters V4IVV2VO7(OCH3)12 were studied by X-band EPR in the temperature range 4.2-300 K. An isotropic exchange interactions between four VIV ions with individual spin Si=1/2 determine the energy levels structure of the compound with the total spin states S=0, 1, and 2, which are doubled and split due to the extra electron transfer. The spin-Hamiltonian approach was used for the analysis of the temperature dependences of the EPR spectra parameters and the cluster dynamics. Two types of the electron transfer are assumed: the single jump transfer leading to the splitting of the total spin states by intervals comparable in magnitude with the exchange parameter J≈100-150cm-1 and the double jump one resulting in dynamics. The dependence of the transition ratesνtr on the energy of the total spin states was observed. In particular, in the range 300-220 K the νtr ≈0.7×1010 cm-1 and below 180 K the νtr≈1×1010 cm-1 was estimated. The g-factors of the spin states were shown to depend on the values of the intermediate spins. A phase transition in the T-range 210-180 K leading to the change in the initial VIV ions localization was discovered.

Conformational and spectroscopic study of xanthogen ethyl formates, ROC(S)SC(O)OCH2CH3. Isolation of CH3CH2OC(O)SH

NASA Astrophysics Data System (ADS)

Juncal, Luciana C.; Cozzarín, Melina V.; Romano, Rosana M.

2015-03-01

ROC(S)SC(O)OCH2CH3, with R = CH3sbnd , (CH3)2CHsbnd and CH3(CH2)2sbnd , were obtained through the reaction between potassium xanthate salts, ROC(S)SK, and ethyl chloroformate, ClC(O)OCH2CH3. The liquid compounds were identified and characterized by 1H and 13C NMR and mass spectrometry. The conformations adopted by the molecules were studied by DFT methods. 6 conformers were theoretically predicted for R = CH3sbnd and (CH3)2CHsbnd , while the conformational flexibility of the n-propyl substituent increases the total number of feasible rotamers to 21. For the three molecules, the conformers can be associated in 3 groups, being the most stable the AS forms - the Cdbnd S double bond anti (A) with respect to the Csbnd S single bond and the Ssbnd C single bond syn (S) with respect to the Cdbnd O double bond - followed by AA and SS conformers. The vibrational spectra were interpreted in terms of the predicted conformational equilibrium, presenting the ν(Cdbnd O) spectral region signals corresponding to the three groups of conformers. A moderated pre-resonance Raman enhancement of the ν(Cdbnd S) vibrational mode of CH3(CH2)2OC(S)SC(O)OCH2CH3 was detected, when the excitation radiation approaches the energy of a n → π∗ electronic transition associated with the Cdbnd S chromophore. UV-visible spectra in different solvents were measured and interpreted in terms of TD-DFT calculations. The unknown molecule CH3CH2OC(O)SH was isolated by the UV-visible photolysis of CH3OC(S)SC(O)OCH2CH3 isolated in Ar matrix, and also obtained as a side-product of the reaction between potassium xanthate salts, ROC(S)SK, and ethyl chloroformate, ClC(O)OCH2CH3.

The Synthesis and Characterization of Aromatic Hybrid Anderson–Evans POMs and their Serum Albumin Interactions: The Shift from Polar to Hydrophobic Interactions

PubMed Central

Al-Sayed, Emir; Blazevic, Amir; Roller, Alexander; Rompel, Annette

2015-01-01

Four aromatic hybrid Anderson polyoxomolybdates with Fe3+ or Mn3+ as the central heteroatom have been synthesized by using a pre-functionalization protocol and characterized by using single-crystal X-ray diffraction, FTIR, ESI-MS, 1H NMR spectroscopy, and elemental analysis. Structural analysis revealed the formation of (TBA)3[FeMo6O18{(OCH2)3CNHCOC6H5}2]⋅3.5 ACN (TBA-FeMo6-bzn; TBA=tetrabutylammonium, ACN=acetonitrile, bzn=TRIS-benzoic acid alkanolamide, TRIS–R=(HOCH2)3C–R)), (TBA)3[FeMo6O18{(OCH2)3CNHCOC8H7}2]⋅2.5 ACN (TBA-FeMo6-cin; cin=TRIS-cinnamic acid alkanolamide), (TBA)3[MnMo6O18{(OCH2)3CNHCOC6H5}2]⋅3.5 ACN (TBA-MnMo6-bzn), and (TBA)3[MnMo6O18{(OCH2)3CNHCOC8H7}2]⋅2.5 ACN (TBA-MnMo6-cin). To make these four compounds applicable in biological systems, an ion exchange was performed that gave the water-soluble (up to 80 mm) sodium salts Na3[FeMo6O18{(OCH2)3CNHCOC6H5}2] (Na-FeMo6-bzn), Na3[FeMo6O18{(OCH2)3CNHCOC8H7}2] (Na-FeMo6-cin), Na3[MnMo6O18{(OCH2)3CNHCOC6H5}2] (Na-MnMo6-bzn), and Na3[MnMo6O18{(OCH2)3CNHCOC8H7}2] (Na-MnMo6-cin). The hydrolytic stability of the sodium salts was examined by applying ESI-MS in the pH range of 4 to 9. Sodium dodecylsulfate–polyacrylamide gel electrophoresis (SDS-PAGE) showed that human and bovine serum albumin (HSA and BSA) remain intact in solutions that contain up to 100 equivalents of the sodium salts over more than 4 d at 20 °C. Tryptophan (Trp) fluorescence quenching was applied to study the interactions between the sodium salts and HSA and BSA at pH 5.5 and 7.4. The quenching constants were extracted by using Stern–Volmer analysis, which suggested the formation of a 1:1 POM–protein complex in all samples. It is suggested that the aromatic hybrid POM approaches subdomain IIA of HSA and exhibits hydrophobic interactions with its hydrophobic tails, whereas the Anderson core is stabilized through electrostatic interactions with polar amino acid side chains from, for example, subdomain IB. PMID:26527418

Dimethylalkoxygallane incorporating a donor-functionalised alkoxide: the monomeric gas-phase structure.

PubMed

Knapp, Caroline E; Carmalt, Claire J; McMillan, Paul F; Wann, Derek A; Robertson, Heather E; Rankin, David W H

2008-12-28

The structure of the vapour produced upon heating the dimethylalkoxygallane [Me(2)GaOCH(2)CH(2)NMe(2)](2) has been studied by gas-phase electron diffraction and ab initio molecular orbital calculations; only the monomeric form [Me(2)GaOCH(2)CH(2)NMe(2)] is observed in the vapour, with the nitrogen atom forming a dative bond with the metal centre.

Kinetics and thermochemistry of 2,5-dimethyltetrahydrofuran and related oxolanes: next next-generation biofuels.

PubMed

Simmie, John M

2012-05-10

The enthalpies of formation, entropies, specific heats at constant pressure, enthalpy functions, and all carbon-hydrogen and carbon-methyl bond dissociation energies have been computed using high-level methods for the cyclic ethers (oxolanes) tetrahydrofuran, 2-methyltetrahydrofuran, and 2,5-dimethyltetrahydrofuran. Barrier heights for hydrogen-abstraction reactions by hydrogen atoms and the methyl radical are also computed and shown to correlate with reaction energy change. The results show a pleasing consistency and considerably expands the available data for these important compounds. Abstraction by ȮH is accompanied by formation of both pre- and postreaction weakly bound complexes. The resulting radicals formed after abstraction undergo ring-opening reactions leading to readily recognizable intermediates, while competitive H-elimination reactions result in formation of dihydrofurans. Formation enthalpies of all 2,3- and 2,5-dihydrofurans and associated radicals are also reported. It is probable that the compounds at the center of this study will be relatively clean-burning biofuels, although formation of intermediate aldehydes might be problematic.

Ginsenoside 25-OCH3-PPD promotes activity of LXRs to ameliorate P2X7R-mediated NLRP3 inflammasome in the development of hepatic fibrosis.

PubMed

Han, Xin; Song, Jian; Lian, Li-Hua; Yao, You-Li; Shao, Dan-Yang; Fan, Ying; Hou, Li-Shuang; Wang, Ge; Zheng, Shuang; Wu, Yan-Ling; Nan, Ji-Xing

2018-06-22

Ginseng is widely used in energy drinks, dietary supplements and herbal medicines, and its pharmacological actions are related with energy metabolism. As an important modulating energy metabolism pathway, liver X receptors (LXRs) can promote the resolving of hepatic fibrosis and inflammation. The present study aims to evaluate the regulation of 25-OCH3-PPD, a ginsenoside isolated from Panax ginseng, against hepatic fibrosis and inflammation in thioacetamide (TAA)-stimulated mice by activating LXRs pathway. 25-OCH3-PPD decreases serum ALT/AST levels and improves the histological pathology of liver in TAA-induced mice; attenuates transcripts of pro-fibrogenic markers associated with hepatic stellate cell activation; attenuates the levels of pro-Inflammatory cytokines and blocks apoptosis happened in liver; inhibits NLRP3 inflammasome by affecting P2X7R activation; regulates PI3K/Akt and LKB1/AMPK-SIRT1. 25-OCH3-PPD also facilitates LX25Rs and FXR activities decreased by TAA stimulation. 25-OCH3-PPD also decreases α-SMA via regulation of LXRs and P2X7R-NLRP3 in vitro. Our data suggest the possibility that 25-OCH3-PPD promotes activity of LXRs to ameliorate P2X7R-mediated NLRP3 inflammasome in the development of hepatic fibrosis.

Effects of preoperative oral carbohydrate supplementation on postoperative metabolic stress response of patients undergoing elective abdominal surgery.

PubMed

Viganò, Jacopo; Cereda, Emanuele; Caccialanza, Riccardo; Carini, Roberta; Cameletti, Barbara; Spampinato, Marcello; Dionigi, Paolo

2012-08-01

The goal of the present study was to evaluate the effects of preoperative oral carbohydrate supplementation (OCH) on the postoperative metabolic stress response of patients undergoing elective abdominal surgery. The study was designed as a controlled, prospective, cohort study including 38 patients treated with OCH (800 mL the day before surgery and 400 mL within 3 h before the induction of anesthesia) and 38 controls matched for surgical procedure. Fasting glucose, insulin, insulin resistance (HOMA-IR index), cortisol, and interleukin 6 (IL-6) were assessed before and after surgery (postoperative day (POD) 1, 2, and 3). The administration of OCH resulted in lower fasting glucose, HOMA-IR index, cortisol, and IL-6 on both POD 1 and POD 2. At multivariable regression analyses, the reduction of these parameters was independent of sex, age, body mass index, and major abdominal surgery. Particularly, models including OCH treatment explained 70, 63, and 66 % of the variance of the increase in IL-6 levels at POD 1, POD 2, and POD 3, respectively. The effect of OCH on changes in glucose, insulin resistance, and cortisol on POD 1 and POD 2 disappeared after the inclusion of IL-6 in the models. Treatment with OCH was associated with attenuation of the postoperative metabolic stress response. We hypothesize that modulation of the inflammatory response is one of the mechanisms involved.

Copper-Catalyzed Intermolecular Amidation and Imidation of Unactivated Alkanes

PubMed Central

2015-01-01

We report a set of rare copper-catalyzed reactions of alkanes with simple amides, sulfonamides, and imides (i.e., benzamides, tosylamides, carbamates, and phthalimide) to form the corresponding N-alkyl products. The reactions lead to functionalization at secondary C–H bonds over tertiary C–H bonds and even occur at primary C–H bonds. [(phen)Cu(phth)] (1-phth) and [(phen)Cu(phth)2] (1-phth2), which are potential intermediates in the reaction, have been isolated and fully characterized. The stoichiometric reactions of 1-phth and 1-phth2 with alkanes, alkyl radicals, and radical probes were investigated to elucidate the mechanism of the amidation. The catalytic and stoichiometric reactions require both copper and tBuOOtBu for the generation of N-alkyl product. Neither 1-phth nor 1-phth2 reacted with excess cyclohexane at 100 °C without tBuOOtBu. However, the reactions of 1-phth and 1-phth2 with tBuOOtBu afforded N-cyclohexylphthalimide (Cy-phth), N-methylphthalimide, and tert-butoxycyclohexane (Cy-OtBu) in approximate ratios of 70:20:30, respectively. Reactions with radical traps support the intermediacy of a tert-butoxy radical, which forms an alkyl radical intermediate. The intermediacy of an alkyl radical was evidenced by the catalytic reaction of cyclohexane with benzamide in the presence of CBr4, which formed exclusively bromocyclohexane. Furthermore, stoichiometric reactions of [(phen)Cu(phth)2] with tBuOOtBu and (Ph(Me)2CO)2 at 100 °C without cyclohexane afforded N-methylphthalimide (Me-phth) from β-Me scission of the alkoxy radicals to form a methyl radical. Separate reactions of cyclohexane and d12-cyclohexane with benzamide showed that the turnover-limiting step in the catalytic reaction is the C–H cleavage of cyclohexane by a tert-butoxy radical. These mechanistic data imply that the tert-butoxy radical reacts with the C–H bonds of alkanes, and the subsequent alkyl radical combines with 1-phth2 to form the corresponding N-alkyl imide product. PMID:24405209

The effect of high dose on residual radicals in open air irradiated α-T UHMWPE resin powder

NASA Astrophysics Data System (ADS)

Mehmood, Malik S.; Shah, Jahan M.; Mishra, Sanjay R.; Walters, Benjamin M.

2013-03-01

Powder samples of UHMWPE (GUR 1020) containing 0.1 wt%. vitamin E (α-tocopherol, α-T) were irradiated at room temperature in air for doses of 30-kGy, 65-kGy or 100-kGy (60Co). After irradiation, they were stored at -78.5 °C (dry ice temperature) for 1 year and then opened to air at room temperature. Following the decay of the primary alkyl and allyl radicals (at room temperature in air), growth of the carbon-centered polyenyl R1 (-˙CH-[-CHCH-]m-, m≥3), and the oxygen-centered di- or tri-enyl R2 (-˙OCH-[-CHCH-]m-, m≤3) residual radicals were measured for 8 weeks. An X-band electron spin resonance (ESR) spectrometer was used for radical measurements. The initial relative radical concentrations (R2/R1) were found to be 10.13, 4.6 and 3.7 for the 65-kGy, 30-kGy and 100-kGy samples, respectively. R1 and R2 were both found to grow significantly in the 65-kGy sample while they grew only slightly in the 30-kGy and 100-kGy samples. In 65-kGy sample, R1 grew faster than R2 and the relative concentration R2/R1 was reduced from 10.13 to 2.9 for the 65-kGy sample while those for the 30-kGy and 100-kGy samples reduced only slightly, from 4.6 to 3.5 and 3.7 to 3.2, respectively. The behavior of the residual radicals can be explained by Raman spectroscopic data which suggest that the 65-kGy samples had a higher percentage of amorphous regions when compared to the 30-kGy or 100-kGy ones (21.7 compared to 15.7 or 17.9) and also suggest a lower percentage of interfacial regions (16.4 compared to 25.6 or 17.5) and a lower level of structural disorder (0.26 compared to 0.44 or 0.27).

Direct observation of unimolecular decay of CH 3 CH 2 CHOO Criegee intermediates to OH radical products

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Yi; Liu, Fang; Klippenstein, Stephen J.

2016-07-28

The unimolecular decay of carbonyl oxide intermediates, known as Criegee intermediates, produced in alkene ozonolysis is a significant source of OH radicals in the troposphere. Here, the rate of appearance of OH radical products is examined directly in the time-domain for a prototypical alkyl-substituted Criegee intermediate, CH3CH2CHOO, following vibrational activation under collision-free conditions. Complementary statistical Rice-Ramsperger-Kassel-Marcus calculations of the microcanonical unimolecular decay rate for CH3CH2CHOO are also carried out at energies in the vicinity of the barrier for 1,4 hydrogen atom transfer that leads to OH products. Tunneling through the barrier, derived from high level electronic structure calculations, contributes significantlymore » to the decay rate. Infrared transitions of CH3CH2CHOO are identified in the CH stretch overtone region, which are detected by ultraviolet laser-induced fluorescence of the resultant OH products. The features observed are attributed to CH vibrational excitations and conformational forms utilizing insights from theory. Both experiment and theory yield unimolecular decay rates for CH3CH2CHOO of ca. 10(7) s(-1), which are slower than those obtained for syn-CH3CHOO or (CH3)(2)COO reported previously [Fang et al., J. Chem. Phys. 144, 061102 (2016)] at similar energies. Master equation modeling is also utilized to predict the thermal decay rate of CH3CH2CHOO under atmospheric conditions, giving a rate of 279 s(-1) at 298 K.« less

EPR characterization of ascorbyl and sulfur dioxide anion radicals trapped during the reaction of bovine Cytochrome c Oxidase with molecular oxygen

NASA Astrophysics Data System (ADS)

Yu, Michelle A.; Egawa, Tsuyoshi; Yeh, Syun-Ru; Rousseau, Denis L.; Gerfen, Gary J.

2010-04-01

The reaction intermediates of reduced bovine Cytochrome c Oxidase (CcO) were trapped following its reaction with oxygen at 50 μs-6 ms by innovative freeze-quenching methods and studied by EPR. When the enzyme was reduced with either ascorbate or dithionite, distinct radicals were generated; X-band (9 GHz) and D-band (130 GHz) CW-EPR measurements support the assignments of these radicals to ascorbyl and sulfur dioxide anion radical (SO2-rad), respectively. The X-band spectra show a linewidth of 12 G for the ascorbyl radical and 11 G for the SO2-rad radical and an isotropic g-value of 2.005 for both species. The D-band spectra reveal clear distinctions in the g-tensors and powder patterns of the two species. The ascorbyl radical spectrum displays approximate axial symmetry with g-values of gx = 2.0068, gy = 2.0066, and gz = 2.0023. The SO2-rad>/SUP> radical has rhombic symmetry with g-values of gx = 2.0089, gy = 2.0052, and gz = 2.0017. When the contributions from the ascorbyl and SO2-rad radicals were removed, no protein-based radical on CcO could be identified in the EPR spectra.

Multicomponent kinetic analysis and theoretical studies on the phenolic intermediates in the oxidation of eugenol and isoeugenol catalyzed by laccase.

PubMed

Qi, Yan-Bing; Wang, Xiao-Lei; Shi, Ting; Liu, Shuchang; Xu, Zhen-Hao; Li, Xiqing; Shi, Xuling; Xu, Ping; Zhao, Yi-Lei

2015-11-28

Laccase catalyzes the oxidation of natural phenols and thereby is believed to initialize reactions in lignification and delignification. Numerous phenolic mediators have also been applied in laccase-mediator systems. However, reaction details after the primary O-H rupture of phenols remain obscure. In this work two types of isomeric phenols, EUG (eugenol) and ISO (trans-/cis-isoeugenol), were used as chemical probes to explore the enzymatic reaction pathways, with the combined methods of time-resolved UV-Vis absorption spectra, MCR-ALS, HPLC-MS, and quantum mechanical (QM) calculations. It has been found that the EUG-consuming rate is linear to its concentration, while the ISO not. Besides, an o-methoxy quinone methide intermediate, (E/Z)-4-allylidene-2-methoxycyclohexa-2,5-dienone, was evidenced in the case of EUG with the UV-Vis measurement, mass spectra and TD-DFT calculations; in contrast, an ISO-generating phenoxyl radical, a (E/Z)-2-methoxy-4-(prop-1-en-1-yl) phenoxyl radical, was identified in the case of ISO. Furthermore, QM calculations indicated that the EUG-generating phenoxyl radical (an O-centered radical) can easily transform into an allylic radical (a C-centered radical) by hydrogen atom transfer (HAT) with a calculated activation enthalpy of 5.3 kcal mol(-1) and then be fast oxidized to the observed eugenol quinone methide, rather than an O-radical alkene addition with barriers above 12.8 kcal mol(-1). In contrast, the ISO-generating phenoxyl radical directly undergoes a radical coupling (RC) process, with a barrier of 4.8 kcal mol(-1), while the HAT isomerization between O- and C-centered radicals has a higher reaction barrier of 8.0 kcal mol(-1). The electronic conjugation of the benzyl-type radical and the aromatic allylic radical leads to differentiation of the two pathways. These results imply that competitive reaction pathways exist for the nascent reactive intermediates generated in the laccase-catalyzed oxidation of natural phenols, which is important for understanding the lignin polymerization and may shed some light on the development of efficient laccase-mediator systems.

Mutual synergy between catalase and peroxidase activities of the bifunctional enzyme KatG is facilitated by electron hole-hopping within the enzyme.

PubMed

Njuma, Olive J; Davis, Ian; Ndontsa, Elizabeth N; Krewall, Jessica R; Liu, Aimin; Goodwin, Douglas C

2017-11-10

KatG is a bifunctional, heme-dependent enzyme in the front-line defense of numerous bacterial and fungal pathogens against H 2 O 2 -induced oxidative damage from host immune responses. Contrary to the expectation that catalase and peroxidase activities should be mutually antagonistic, peroxidatic electron donors (PxEDs) enhance KatG catalase activity. Here, we establish the mechanism of synergistic cooperation between these activities. We show that at low pH values KatG can fully convert H 2 O 2 to O 2 and H 2 O only if a PxED is present in the reaction mixture. Stopped-flow spectroscopy results indicated rapid initial rates of H 2 O 2 disproportionation slowing concomitantly with the accumulation of ferryl-like heme states. These states very slowly returned to resting ( i.e. ferric) enzyme, indicating that they represented catalase-inactive intermediates. We also show that an active-site tryptophan, Trp-321, participates in off-pathway electron transfer. A W321F variant in which the proximal tryptophan was replaced with a non-oxidizable phenylalanine exhibited higher catalase activity and less accumulation of off-pathway heme intermediates. Finally, rapid freeze-quench EPR experiments indicated that both WT and W321F KatG produce the same methionine-tyrosine-tryptophan (MYW) cofactor radical intermediate at the earliest reaction time points and that Trp-321 is the preferred site of off-catalase protein oxidation in the native enzyme. Of note, PxEDs did not affect the formation of the MYW cofactor radical but could reduce non-productive protein-based radical species that accumulate during reaction with H 2 O 2 Our results suggest that catalase-inactive intermediates accumulate because of off-mechanism oxidation, primarily of Trp-321, and PxEDs stimulate KatG catalase activity by preventing the accumulation of inactive intermediates. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Strong intramolecular Si-N interactions in the chlorosilanes Cl3-nHnSiOCH2CH2NMe2 (n = 1-3).

PubMed

Hagemann, Michael; Mix, Andreas; Berger, Raphael J F; Pape, Tania; Mitzel, Norbert W

2008-11-17

The compounds Cl 3SiOCH 2CH 2NMe 2 ( 1) and Cl 2HSiOCH 2CH 2NMe 2 ( 2) were prepared by reactions of lithium 2-(dimethylamino)ethanolate with SiCl 4 and HSiCl 3. The analogous reaction with H 2SiCl 2 gave ClH 2SiOCH 2CH 2NMe 2 ( 3), but only in a mixture with Cl 2HSiOCH 2CH 2NMe 2 ( 2), from which it could not be separated. All compounds were characterized by IR and NMR ( (1)H, (13)C, (29)Si) spectroscopy, 1 and 2 by elemental analyses and by determination of their crystal structures. Cl 3SiOCH 2CH 2NMe 2 ( 1) and Cl 2HSiOCH 2CH 2NMe 2 ( 2) crystallize as monomeric ring compounds with pentacoordinate silicon atoms participating in intramolecular Si-N bonds [2.060(2) A ( 1), 2.037(2) A ( 2)]. The dative bonds in 1 and 2 between the silicon and nitrogen atoms could also be proven to exist at low temperatures in solution in (1)H, (29)Si-HMBC-NMR experiments by detection of the scalar coupling between the (29)Si and the protons of the NCH 2 and NCH 3 groups. A function describing the chemical shift delta exp (29)Si dependent on the chemical shifts of the individual equilibrium components, the temperature, and the free enthalpy of reaction was worked out and fitted to the experimental VT-NMR data of 1 and 2. This provided values of the free reaction enthalpies of Delta G = -28.8 +/- 3.9 kJ x mol (-1) for 1 and Delta G = -22.3 +/- 0.4 kJ x mol (-1) for 2 and estimates for the chemical shifts of open-chain (index o) and ring conformers (index r) for 1 of delta r = -94 +/- 2 ppm and delta o = -36 +/- 5 ppm and for 2 of delta r = -82 +/- 1 ppm and delta o = -33 +/- 4 ppm. The value of delta r for 1 is very close to that obtained from a solid-state (29)Si MAS NMR spectrum. Quantumchemical calculations (up to MP2/TZVPP) gave largely differing geometries for 1 (with a Si...N distance of 3.072 A), but well reproduced the geometry of 2. These differences are due to Cl...H and Cl...C repulsions and solid state effects, which can be modeled by conductor-like screening model calculations and also rationalized in terms of the topology of the electron density, which was analyzed in terms of the quantum theory of atoms in molecules.

Reactivity of [K₃(phen)₈][Cu(NPh₂)₂]₃--a possible intermediate in the copper(I)-catalyzed N-arylation of N-phenylaniline.

PubMed

Tseng, Chia-Kai; Lee, Chi-Rung; Tseng, Mei-Chun; Han, Chien-Chung; Shyu, Shin-Guang

2014-05-21

Complex [K3(phen)8][Cu(NPh2)2]3 (1, phen = phenanthroline) was isolated from the catalytic C-N cross coupling reaction based on the CuI-phen-tBuOK catalytic system. Complex 1 can react with 4-iodotoluene to give 4-methyl-N,N-diphenylaniline (3a) in 50% yield (based on all available NPh2(-) ligands of complex 1). In addition, 1 can also work as an effective catalyst for the C-N coupling reactions under the same reaction conditions, indicating that 1 may be an effective intermediate of the catalytic system. In the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), a radical scavenger, the stoichiometric reaction between complex 1 and 4-iodotoluene was significantly quenched to give a low yield of 12%. The results suggest that the radical path dominates in the reaction, with (phen)KNPh2 as the possible radical source. The structures of 1 and (phen)KNPh2 were both determined by single crystal X-ray diffraction studies.

Computational Study of the Thermodynamics of Atmospheric Nitration of PAHs via OH-Radical-Initiated Reaction

NASA Astrophysics Data System (ADS)

Jariyasopit, N.; Cheong, P.; Simonich, S. L.

2011-12-01

Nitrated polycyclic aromatic hydrocarbons (NPAHs) are an important class of PAH derivatives that are more toxic than their parent PAHs (1) and are emitted from direct emission and secondary emission to the atmosphere. The secondary emissions, particularly the OH-radical initiated and NO3-radical-initiated reactions, have been shown to influence the NPAH concentrations in the atmosphere. Gas-phase reactions are thought to be the major sources of NPAHs containing four or fewer rings (2). Besides NPAHs, PAHs lead to a number of other products including oxygenated, hydroxy substituted and ring-opened PAH derivatives (3). For some PAHs, the OH-initiated and NO3-initiated reactions result in the formation of different NPAH isomers, allowing the ratio of these isomers to be used in the determination of direct or secondary emission sources. Previous studies have shown that the PAH gas-phase reactions with OH radical is initiated by the addition of OH radical to the aromatic ring to form hydroxycyclohexadienyl radicals (4). In the presence of NO2, these reactive intermediates readily nitrate with the elimination of water (4). The hydroxycyclohexadienyl-type radical intermediates are also prone to react with other species in the atmosphere or revert back to the original compound (3). The objective of this study was to investigate the thermodynamics of PAH nitration through day-time OH-radical-initiated reactions. The theoretical investigation were carried out using Density Functioanl Theory (B3LYP) and the 6-31G(d) basis set, as implemented in Gaussian03. A number of different PAHs were studied including fluoranthene, pyrene, as well as the molecular weight 302 PAHs such as dibenzo[a,l]pyrene. Computations were also used to predict unknown NPAHs formed by OH-radical-initiated reaction. All intermediates for the OH-radical addition and the following nitration were computed. We have discovered that the thermodynamic stability of the intermediates involved in the PAH oxygenation and nitration pathways are critical in explaining the atmospheric abundances of NPAHs. Specifically, we have found that the experimentally most abundant species had the most stable intermediates. Interestingly, the overall free energy of reaction was not a factor in determining the relative abundances of NPAHs.

From CO2 to dimethyl carbonate with dialkyldimethoxystannanes: the key role of monomeric species.

PubMed

Kalhor, Mahboubeh Poor; Chermette, Henry; Chambrey, Stéphane; Ballivet-Tkatchenko, Danielle

2011-02-14

The formation of dimethyl carbonate (DMC) from CO(2) and methanol with the dimer [n-Bu(2)Sn(OCH(3))(2)](2) was investigated by experimental kinetics in support of DFT calculations. Under the reaction conditions (357-423 K, 10-20 MPa), identical initial rates are observed with three different reacting mixtures, CO(2)/toluene, supercritical CO(2), and CO(2)/methanol, and are consistent with the formation of monomeric di-n-butyltin(iv) species. An intramolecular mechanism is, therefore, proposed with an Arrhenius activation energy amounting to 104 ± 10 kJ mol(-1) for DMC synthesis. DFT calculations on the [(CH(3))(2)Sn(OCH(3))(2)](2)/CO(2) system show that the exothermic insertion of CO(2) into the Sn-OCH(3) bond occurs by a concerted Lewis acid-base interaction involving the tin center and the oxygen atom of the methoxy ligand. The Gibbs energy diagrams highlight that, under the reaction conditions, the dimer-monomer equilibrium is significantly shifted towards monomeric species, in agreement with the experimental kinetics. Importantly, the two Sn-OCH(3) bonds are prompt to insert CO(2). These results provide new insight into the reaction mechanism and catalyst design to enhance the turnover numbers.

The Synthesis and Characterization of Aromatic Hybrid Anderson-Evans POMs and their Serum Albumin Interactions: The Shift from Polar to Hydrophobic Interactions.

PubMed

Al-Sayed, Emir; Blazevic, Amir; Roller, Alexander; Rompel, Annette

2015-12-01

Four aromatic hybrid Anderson polyoxomolybdates with Fe(3+) or Mn(3+) as the central heteroatom have been synthesized by using a pre-functionalization protocol and characterized by using single-crystal X-ray diffraction, FTIR, ESI-MS, (1) H NMR spectroscopy, and elemental analysis. Structural analysis revealed the formation of (TBA)3 [FeMo6 O18 {(OCH2 )3 CNHCOC6 H5 }2 ]⋅3.5 ACN (TBA-FeMo6 -bzn; TBA=tetrabutylammonium, ACN=acetonitrile, bzn=TRIS-benzoic acid alkanolamide, TRISR=(HOCH2 )3 CR)), (TBA)3 [FeMo6 O18 {(OCH2 )3 CNHCOC8 H7 }2 ]⋅2.5 ACN (TBA-FeMo6 -cin; cin=TRIS-cinnamic acid alkanolamide), (TBA)3 [MnMo6 O18 {(OCH2 )3 CNHCOC6 H5 }2 ]⋅3.5 ACN (TBA-MnMo6 -bzn), and (TBA)3 [MnMo6 O18 {(OCH2 )3 CNHCOC8 H7 }2 ]⋅2.5 ACN (TBA-MnMo6 -cin). To make these four compounds applicable in biological systems, an ion exchange was performed that gave the water-soluble (up to 80 mM) sodium salts Na3 [FeMo6 O18 {(OCH2 )3 CNHCOC6 H5 }2 ] (Na-FeMo6 -bzn), Na3 [FeMo6 O18 {(OCH2 )3 CNHCOC8 H7 }2 ] (Na-FeMo6 -cin), Na3 [MnMo6 O18 {(OCH2 )3 CNHCOC6 H5 }2 ] (Na-MnMo6 -bzn), and Na3 [MnMo6 O18 {(OCH2 )3 CNHCOC8 H7 }2 ] (Na-MnMo6 -cin). The hydrolytic stability of the sodium salts was examined by applying ESI-MS in the pH range of 4 to 9. Sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that human and bovine serum albumin (HSA and BSA) remain intact in solutions that contain up to 100 equivalents of the sodium salts over more than 4 d at 20 °C. Tryptophan (Trp) fluorescence quenching was applied to study the interactions between the sodium salts and HSA and BSA at pH 5.5 and 7.4. The quenching constants were extracted by using Stern-Volmer analysis, which suggested the formation of a 1:1 POM-protein complex in all samples. It is suggested that the aromatic hybrid POM approaches subdomain IIA of HSA and exhibits hydrophobic interactions with its hydrophobic tails, whereas the Anderson core is stabilized through electrostatic interactions with polar amino acid side chains from, for example, subdomain IB. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Synthesis and Free Radical Scavenging Activity of New Hydroxybenzylidene Hydrazines.

PubMed

Sersen, Frantisek; Gregan, Fridrich; Kotora, Peter; Kmetova, Jarmila; Filo, Juraj; Loos, Dusan; Gregan, Juraj

2017-05-29

Hydroxybenzylidene hydrazines exhibit a wide spectrum of biological activities. Here, we report synthesis and free radical scavenging activity of nine new N-(hydroxybenzylidene)-N'-[2,6-dinitro-4-(trifluoromethyl)]phenylhydrazines. The chemical structures of these compounds were confirmed by 1H-NMR, 13C-NMR, 19F-NMR, IR spectroscopy, LC-MS, and elemental analysis. The prepared compounds were tested for their activity to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH), galvinoxyl radical (GOR), and 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) radicals. The free radical scavenging activity expressed as SC50 values of these compounds varied in a wide range, from a strong to no radical scavenging effect. The most effective radical scavengers were hydroxybenzylidene hydrazines containing three hydroxyl groups in the benzylidene part of their molecules. The prepared compounds were also tested for their activity to inhibit photosynthetic electron transport in spinach chloroplasts. IC50 values of these compounds varied in wide range, from an intermediate to no inhibitory effect.

EPR spin trapping evidence of radical intermediates in the photo-reduction of bicarbonate/CO2 in TiO2 aqueous suspensions.

PubMed

Molinari, Alessandra; Samiolo, Luca; Amadelli, Rossano

2015-05-01

Using the EPR spin trapping technique, we prove that simultaneous reactions take place in illuminated suspensions of TiO2 in aqueous carbonate solutions (pH ≈ 7). The adsorbed HCO3(-) is reduced to formate as directly made evident by the detection of formate radicals (˙CO2(-)). In addition, the amount of OH˙ radicals from the photo-oxidation of water shows a linear dependence on the concentration of bicarbonate, indicating that electron scavenging by HCO3(-) increases the lifetime of holes. In a weakly alkaline medium, photo-oxidation of HCO3(-)/CO3(2-) to ˙CO3(-) interferes with the oxidation of water. A comparative analysis of different TiO2 samples shows that formation of ˙CO2(-) is influenced by factors related to the nature of the surface, once expected surface area effects are accounted for. Modification of the TiO2 surface with noble metal nanoparticles does not have unequivocal benefits: the overall activity improves with Pd and Rh but not with Ru, which favours HCO3(-) photo-oxidation even at pH = 7. In general, identification of radical intermediates of oxidation and reduction reactions can provide useful mechanistic information that may be used in the development of photocatalytic systems for the reduction of CO2 also stored in the form of carbonates.

Analysis of Investigational Drugs in Biological Fluids. Method Development and Routine Assay. Appendix A.

DTIC Science & Technology

1997-02-13

AMINOPROPIOPHENONE IN DOG PLASMA 0 OCH 3 CH2 CH3 OCH2CHOHCH 2 OH H2 N& p-Aminopropiophenone Guaifenesin (WR 000,302) Internal Standard APPROVALS: This Analytical...40 - 80 il VOLUME: RUN TIME: 14 min (PAPP: 10.7 min; Guaifenesin (Internal Standard): 8.5 min) DETECTOR Wavelength: 316 nm SETTINGS: Absorption Range

Fluorescence emission induced by the femtosecond filament transmitting through the butane/air flame

NASA Astrophysics Data System (ADS)

Li, Suyu; Li, Yanhua; Shi, Zhe; Sui, Laizhi; Li, He; Li, Qingyi; Chen, Anmin; Jiang, Yuanfei; Jin, Mingxing

2018-01-01

We measure the backward fluorescence spectra generated by the femtosecond filament transmitting through the butane/air flame, and study the fluorescence emission from combustion intermediates (CN, CH and C2 radicals), air (mainly N2 and N2+). It is found that the fluorescence emission from combustion intermediates, N2 and N2+ shows difference when the femtosecond filament transmits through different parts of the butane/air flame, and we attempt to analyze it in this paper. This study demonstrates that the filament-induced fluorescence technique can be utilized to sense the combustion intermediates.

Durable Fluorocarbon-Based Coatings for Aircraft

DTIC Science & Technology

2000-11-01

synthesized two novel monomers, 2-fluoro-2- perfluorooctyl - 1,3-propanediol and 2-fluoro-2- perfluoro (2-ethylhexyl)-1,3-propanediol, and demonstrated that...propanediols, two branched perfluoroalkyl methanols, perfluoro -1H,1H-2-ethylhexanol (pefluoro-1-ethylpentyl methanol) and perfluoro - 1H,1H-2,2...malonates. Reduction of the perfluorinated malonates gave the perfluoroalkyl -branched 1,3-propanediols. R-OH + HBr R-Br cat. O O OCH 2CH3 OCH 2CH3 + O O

Low-energy (<20 eV) and high-energy (1000 eV) electron-induced methanol radiolysis of astrochemical interest

NASA Astrophysics Data System (ADS)

Sullivan, Kristal K.; Boamah, Mavis D.; Shulenberger, Katie E.; Chapman, Sitara; Atkinson, Karen E.; Boyer, Michael C.; Arumainayagam, Christopher R.

2016-07-01

We report the first infrared study of the low-energy (<20 eV) electron-induced reactions of condensed methanol. Our goal is to simulate processes which occur when high-energy cosmic rays interact with interstellar and cometary ices, where methanol, a precursor of several prebiotic species, is relatively abundant. The interactions of high-energy radiation, such as cosmic rays (Emax ˜ 1020 eV), with matter produce large numbers of low-energy secondary electrons, which are known to initiate radiolysis reactions in the condensed phase. Using temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS), we have investigated low-energy (5-20 eV) and high-energy (˜1000 eV) electron-induced reactions in condensed methanol (CH3OH). IRAS has the benefit that it does not require thermal processing prior to product detection. Using IRAS, we have found evidence for the formation of ethylene glycol (HOCH2CH2OH), formaldehyde (CH2O), dimethyl ether (CH3OCH3), methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), and the hydroxyl methyl radical (·CH2OH) upon both low-energy and high-energy electron irradiation of condensed methanol at ˜85 K. Additionally, TPD results, presented herein, are similar for methanol films irradiated with both 1000 eV and 20 eV electrons. These IRAS and TPD findings are qualitatively consistent with the hypothesis that high-energy condensed phase radiolysis is mediated by low-energy electron-induced reactions. Moreover, methoxymethanol (CH3OCH2OH) could serve as a tracer molecule for electron-induced reactions in the interstellar medium. The results of experiments such as ours may provide a fundamental understanding of how complex organic molecules are synthesized in cosmic ices.

Direct production of OH radicals upon CH overtone activation of (CH{sub 3}){sub 2}COO Criegee intermediates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Fang; Beames, Joseph M.; Lester, Marsha I., E-mail: milester@sas.upenn.edu

2014-12-21

Ozonolysis of alkenes, a principle non-photolytic source of atmospheric OH radicals, proceeds through unimolecular decay of energized carbonyl oxide intermediates, known as Criegee intermediates. In this work, cold dimethyl-substituted Criegee intermediates are vibrationally activated in the CH stretch overtone region to drive the 1,4 hydrogen transfer reaction that leads to OH radical products. IR excitation of (CH{sub 3}){sub 2}COO reveals the vibrational states with sufficient oscillator strength, coupling to the reaction coordinate, and energy to surmount the effective barrier (≤ 16.0 kcal mol{sup −1}) to reaction. Insight on the dissociation dynamics is gleaned from homogeneous broadening of the spectral features,more » indicative of rapid intramolecular vibrational energy redistribution and/or reaction, as well as the quantum state distribution of the OH X{sup 2}Π (v = 0) products. The experimental results are compared with complementary electronic structure calculations, which provide the IR absorption spectrum and geometric changes along the intrinsic reaction coordinate. Additional theoretical analysis reveals the vibrational modes and couplings that permit (CH{sub 3}){sub 2}COO to access to the transition state region for reaction. The experimental and theoretical results are compared with an analogous recent study of the IR activation of syn-CH{sub 3}CHOO and its unimolecular decay to OH products [F. Liu, J. M. Beames, A. S. Petit, A. B. McCoy, and M. I. Lester, Science 345, 1596 (2014)].« less

Direct observation of unimolecular decay of CH{sub 3}CH{sub 2}CHOO Criegee intermediates to OH radical products

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Yi; Liu, Fang; Lester, Marsha I., E-mail: milester@sas.upenn.edu

2016-07-28

The unimolecular decay of carbonyl oxide intermediates, known as Criegee intermediates, produced in alkene ozonolysis is a significant source of OH radicals in the troposphere. Here, the rate of appearance of OH radical products is examined directly in the time-domain for a prototypical alkyl-substituted Criegee intermediate, CH{sub 3}CH{sub 2}CHOO, following vibrational activation under collision-free conditions. Complementary statistical Rice–Ramsperger–Kassel–Marcus calculations of the microcanonical unimolecular decay rate for CH{sub 3}CH{sub 2}CHOO are also carried out at energies in the vicinity of the barrier for 1,4 hydrogen atom transfer that leads to OH products. Tunneling through the barrier, derived from high level electronicmore » structure calculations, contributes significantly to the decay rate. Infrared transitions of CH{sub 3}CH{sub 2}CHOO are identified in the CH stretch overtone region, which are detected by ultraviolet laser-induced fluorescence of the resultant OH products. The features observed are attributed to CH vibrational excitations and conformational forms utilizing insights from theory. Both experiment and theory yield unimolecular decay rates for CH{sub 3}CH{sub 2}CHOO of ca. 10{sup 7} s{sup −1}, which are slower than those obtained for syn-CH{sub 3}CHOO or (CH{sub 3}){sub 2}COO reported previously [Fang et al., J. Chem. Phys. 144, 061102 (2016)] at similar energies. Master equation modeling is also utilized to predict the thermal decay rate of CH{sub 3}CH{sub 2}CHOO under atmospheric conditions, giving a rate of 279 s{sup −1} at 298 K.« less

Heterogeneous Nucleation of Trichloroethylene Ozonation Products in the Formation of New Fine Particles

NASA Astrophysics Data System (ADS)

Wang, Ning; Sun, Xiaomin; Chen, Jianmin; Li, Xiang

2017-02-01

Free radicals in atmosphere have played an important role in the atmospheric chemistry. The chloro-Criegee free radicals are produced easily in the decomposition of primary ozonide (POZ) of the trichloroethylene, and can react with O2, NO, NO2, SO2 and H2O subsequently. Then the inorganic salts, polar organic nitrogen and organic sulfur compounds, oxygen-containing heterocyclic intermediates and polyhydroxy compounds can be obtained. The heterogeneous nucleation of oxidation intermediates in the formation of fine particles is investigated using molecular dynamics simulation. The detailed nucleation processes are reported. According to molecular dynamics simulation, the nucleation with a diameter of 2 nm is formed in the Organic Compounds-(NH4)2SO4-H2O system. The spontaneous nucleation is an important process in the formation of fine particles in atmosphere. The model study gives a good example from volatile organic compounds to new fine particles.

Novel Reagents for Multi-Component Reactions

NASA Astrophysics Data System (ADS)

Wang, Yanguang; Basso, Andrea; Nenajdenko, Valentine G.; Gulevich, Anton V.; Krasavin, Mikhail; Bushkova, Ekaterina; Parchinsky, Vladislav; Banfi, Luca; Basso, Andrea; Cerulli, Valentina; Guanti, Giuseppe; Riva, Renata; Rozentsveig, Igor B.; Rozentsveig, Gulnur N.; Popov, Aleksandr V.; Serykh, Valeriy J.; Levkovskaya, Galina G.; Cao, Song; Shen, Li; Liu, Nianjin; Wu, Jingjing; Li, Lina; Qian, Xuhong; Chen, Xiaopeng; Wang, Hongbo; Feng, Jinwu; Wang, Yanguang; Lu, Ping; Heravi, Majid M.; Sadjadi, Samaheh; Kazemizadeh, Ali Reza; Ramazani, Ali; Kudyakova, Yulia S.; Goryaeva, Marina V.; Burgart, Yanina V.; Saloutin, Victor I.; Mossetti, Riccardo; Pirali, Tracey; Tron, Gian Cesare; Rozhkova, Yulia S.; Mayorova, Olga A.; Shklyaev, Yuriy V.; Zhdanko, Alexander G.; Nenajdenko, Valentine G.; Stryapunina, Olga G.; Plekhanova, Irina V.; Glushkov, Vladimir A.; Shklyaev, Yurii V.

Ketenimines are a class of versatile and highly reactive intermediates that can participate in a variety of organic reactions, such as nucleophilic additions, radical additions, [2 + 2] and [2 + 4] cycloadditions, and sigmatropic rearrangements. In this presentation, we report on a series of multi-component reactions that involve a ketenimine intermediate. These reactions could furnish diverse heterocyclic compounds, including functionalized iminocoumarin, iminodihydroqunolines, iminothiochromens, pyrrolines, isoquinolines, pyridines, β-lactams, imino-1,2-dihydrocoumarins, and benzimidazoles.

Synthesis, antityrosinase activity of curcumin analogues, and crystal structure of (1 E,4 E)-1,5-bis(4-ethoxyphenyl)penta-1,4-dien-3-one

NASA Astrophysics Data System (ADS)

Chantrapromma, S.; Ruanwas, P.; Boonnak, N.; Chantrapromma, K.; Fun, H.-K.

2016-12-01

Five derivatives of curcumin analogue ( R = OCH2CH3 ( 1), R = N(CH3)2 ( 2), R = 2,4,5-OCH3 ( 3), R = 2,4,6-OCH3 ( 4), and R = 3,4,5-OCH3 ( 5)) were synthesized and characterized by 1H NMR, FT-IR and UV-Vis spectroscopy. The synthesized derivatives were screened for antityrosinase activity, and found that 4 and 5 possess such activity. The crystal structure of 1 was determined by single crystal X-ray diffraction: monoclinic, sp. gr. P21/ c, a = 17.5728(15) Å, b = 5.9121(5) Å, c = 19.8269(13) Å, β = 121.155(5)°, Z = 4. The molecule 1 is twisted with the dihedral angle between two phenyl rings being 15.68(10)°. In the crystal packing, the molecules 1 are linked into chains by C-H···π interactions and further stacked by π···π interactions with the centroid-centroid distance of 3.9311(13) Å.

Natural Product Ginsenoside 25-OCH3-PPD Inhibits Breast Cancer Growth and Metastasis through Down-Regulating MDM2

PubMed Central

Wang, Wei; Zhang, Xu; Qin, Jiang-Jiang; Voruganti, Sukesh; Nag, Subhasree Ashok; Wang, Ming-Hai; Wang, Hui; Zhang, Ruiwen

2012-01-01

Although ginseng and related herbs have a long history of utility for various health benefits, their application in cancer therapy and underlying mechanisms of action are not fully understood. Our recent work has shown that 20(S)-25-methoxyl-dammarane-3β, 12β, 20-triol (25-OCH3-PPD), a newly identified ginsenoside from Panax notoginseng, exerts activities against a variety of cancer cells in vitro and in vivo. This study was designed to investigate its anti-breast cancer activity and the underlying mechanisms of action. We observed that 25-OCH3-PPD decreased the survival of breast cancer cells by induction of apoptosis and G1 phase arrest and inhibited the growth of breast cancer xenografts in vivo. We further demonstrated that, in a dose- and time-dependent manner, 25-OCH3-PPD inhibited MDM2 expression at both transcriptional and post-translational levels in human breast cancer cells with various p53 statuses (wild type and mutant). Moreover, 25-OCH3-PPD inhibited in vitro cell migration, reduced the expression of epithelial-to-mesenchymal transition (EMT) markers, and prevented in vivo metastasis of breast cancer. In summary, 25-OCH3-PPD is a potential therapeutic and anti-metastatic agent for human breast cancer through down-regulating MDM2. Further preclinical and clinical development of this agent is warranted. PMID:22911819

Natural product ginsenoside 25-OCH3-PPD inhibits breast cancer growth and metastasis through down-regulating MDM2.

PubMed

Wang, Wei; Zhang, Xu; Qin, Jiang-Jiang; Voruganti, Sukesh; Nag, Subhasree Ashok; Wang, Ming-Hai; Wang, Hui; Zhang, Ruiwen

2012-01-01

Although ginseng and related herbs have a long history of utility for various health benefits, their application in cancer therapy and underlying mechanisms of action are not fully understood. Our recent work has shown that 20(S)-25-methoxyl-dammarane-3β, 12β, 20-triol (25-OCH(3)-PPD), a newly identified ginsenoside from Panax notoginseng, exerts activities against a variety of cancer cells in vitro and in vivo. This study was designed to investigate its anti-breast cancer activity and the underlying mechanisms of action. We observed that 25-OCH(3)-PPD decreased the survival of breast cancer cells by induction of apoptosis and G1 phase arrest and inhibited the growth of breast cancer xenografts in vivo. We further demonstrated that, in a dose- and time-dependent manner, 25-OCH(3)-PPD inhibited MDM2 expression at both transcriptional and post-translational levels in human breast cancer cells with various p53 statuses (wild type and mutant). Moreover, 25-OCH(3)-PPD inhibited in vitro cell migration, reduced the expression of epithelial-to-mesenchymal transition (EMT) markers, and prevented in vivo metastasis of breast cancer. In summary, 25-OCH(3)-PPD is a potential therapeutic and anti-metastatic agent for human breast cancer through down-regulating MDM2. Further preclinical and clinical development of this agent is warranted.

Imaging spectroscopy of the missing REMPI bands of methyl radicals: Final touches on all vibrational frequencies of the 3p Rydberg states

NASA Astrophysics Data System (ADS)

Pan, Huilin; Liu, Kopin

2018-01-01

(2 + 1) resonance-enhanced multiphoton ionization (REMPI) detection of methyl radicals, in particular that via the intermediate 3p Rydberg states, has shown to be a powerful method and thus enjoyed a wide range of applications. Methyl has six vibrational modes. Among them—including partially and fully deuterated isotopologs—four out of twenty vibrational frequencies in the intermediate 3p states have so far eluded direct spectroscopic determination. Here, by exploiting the imaging spectroscopy approach to a few judiciously selected chemical reactions, the four long-sought REMPI bands—CHD2(611), CH2D(311), CH2D(511), and CH2D(611)—are discovered, which complete the REMPI identification for probing any vibrational mode of excitation of methyl radical and its isotopologs. These results, in conjunction with those previously reported yet scattered in the literature, are summarized here for ready reference, which should provide all necessary information for further spectral assignments and future studies of chemical dynamics using this versatile REMPI scheme.

An ab initio investigation of possible intermediates in the reaction of the hydroxyl and hydroperoxyl radicals

NASA Technical Reports Server (NTRS)

Jackels, C. F.

1985-01-01

Ab initio quantum chemical techniques are used to investigate covalently-bonded and hydrogen-bonded species that may be important intermediates in the reaction of hydroxyl and hydroperoxyl radicals. Stable structures of both types are identified. Basis sets of polarized double zeta quality and large scale configuration interaction wave functions are utilized. Based on electronic energies, the covalently bonded HOOOH species is 26.4 kcal/mol more stable than the OH and HO2 radicals. Similarly, the hydrogen bonded HO---HO2 species has an electronic energy 4.7 kcal/mol below that of the component radicals, after correction is made for the basis set superposition error. The hydrogen bonded form is planar, possesses one relatively normal hydrogen bond, and has the lowest energy 3A' and 1A' states that are essentially degenerate. The 1A" and 3A" excited states produced by rotation of the unpaired OH electron into the molecular plane are very slightly bound.

Synthesis of heterocyclic analogues of epibatidine via 7-azabicyclo[2.2.1]hept-2-yl radical intermediates. 1. Intermolecular reactions.

PubMed

Gómez-Sánchez, Elena; Soriano, Elena; Marco-Contelles, José

2008-09-05

The synthesis and reactivity of the 7-azabicyclo[2.2.1]hept-2-yl radical has been extensively investigated in inter- and intramolecular reaction processes for the first time. In this work we will present the preparation of the radical and its successful intermolecular reaction with radical acceptors such as tert-butylisocyanide and acrylonitrile. Computational analyses have been carried out to show and explain the mechanisms and stereochemical outcome of these transformations. Overall and from the chemical point of view, a new and convenient synthetic approach has been developed for the synthesis of exo-2-(cyano)alkyl substituted 7-azabicyclo[2.2.1]heptane derivatives, a series of compounds of wide interest for the synthesis of heterocyclic analogues of epibatidine. As a result, we describe here the synthesis of the tetrazoloepibatidines (8 and 15) and the oxadiazoloepibatidine (10).

Trapping and spectroscopic characterization of an FeIII-superoxo intermediate from a nonheme mononuclear iron-containing enzyme

PubMed Central

Mbughuni, Michael M.; Chakrabarti, Mrinmoy; Hayden, Joshua A.; Bominaar, Emile L.; Hendrich, Michael P.; Münck, Eckard; Lipscomb, John D.

2010-01-01

intermediates are well known in heme enzymes, but none have been characterized in the nonheme mononuclear FeII enzyme family. Many steps in the O2 activation and reaction cycle of FeII-containing homoprotocatechuate 2,3-dioxygenase are made detectable by using the alternative substrate 4-nitrocatechol (4NC) and mutation of the active site His200 to Asn (H200N). Here, the first intermediate (Int-1) observed after adding O2 to the H200N-4NC complex is trapped and characterized using EPR and Mössbauer (MB) spectroscopies. Int-1 is a high-spin (S1 = 5/2) FeIII antiferromagnetically (AF) coupled to an S2 = 1/2 radical (J ≈ 6 cm-1 in ). It exhibits parallel-mode EPR signals at g = 8.17 from the S = 2 multiplet, and g = 8.8 and 11.6 from the S = 3 multiplet. These signals are broadened significantly by hyperfine interactions (A17O ≈ 180 MHz). Thus, Int-1 is an AF-coupled species. The experimental observations are supported by density functional theory calculations that show nearly complete transfer of spin density to the bound O2. Int-1 decays to form a second intermediate (Int-2). MB spectra show that it is also an AF-coupled FeIII-radical complex. Int-2 exhibits an EPR signal at g = 8.05 arising from an S = 2 state. The signal is only slightly broadened by (< 3% spin delocalization), suggesting that Int-2 is a peroxo-FeIII-4NC semiquinone radical species. Our results demonstrate facile electron transfer between FeII, O2, and the organic ligand, thereby supporting the proposed wild-type enzyme mechanism. PMID:20837547

Nitroaliphatic difluoroformals

DOEpatents

Peters, Howard M.; Simon, Jr., Robert L.

1978-01-01

Nitroaliphatic difluoroformals of the formula RCH.sub.2 OCF.sub.2 OCH.sub.2 R' wherein R = FC(NO.sub.2).sub.2 -- and R' = F.sub.2 C(NO.sub.2)-- or CF.sub.3 --; or R = R' = CF.sub.3 OCH.sub.2 C(NO.sub.2).sub.2 --. The compounds are prepared in accordance with the following reaction: ##STR1## carried out at temperatures of from about 95.degree. C to about 150.degree. C. The compounds are especially useful as energetic plasticizers in explosive compositions.

RRKM and master equation kinetic analysis of parallel addition reactions of isomeric radical intermediates in hydrocarbon flames

NASA Astrophysics Data System (ADS)

Winter, Pierre M.; Rheaume, Michael; Cooksy, Andrew L.

2017-08-01

We have calculated the temperature-dependent rate coefficients of the addition reactions of butadien-2-yl (C4H5) and acroylyl (C3H3O) radicals with ethene (C2H4), carbon monoxide (CO), formaldehyde (H2CO), hydrogen cyanide (HCN), and ketene (H2CCO), in order to explore the balance between kinetic and thermodynamic control in these combustion-related reactions. For the C4H5 radical, the 1,3-diene form of the addition products is more stable than the 1,2-diene, but the 1,2-diene form of the radical intermediate is stabilized by an allylic delocalization, which may influence the relative activation energies. For the reactions combining C3H3O with C2H4, CO, and HCN, the opposite is true: the 1,2-enone form of the addition products is more stable than the 1,3-enone, whereas the 1,3-enone is the slightly more stable radical species. Optimized geometries and vibrational modes were computed with the QCISD/aug-cc-pVDZ level and basis, followed by single-point CCSD(T)-F12a/cc-pVDZ-F12 energy calculations. Our findings indicate that the kinetics in all cases favor reaction along the 1,3 pathway for both the C4H5 and C3H3O systems. The Rice-Ramsperger-Kassel-Marcus (RRKM) microcanonical rate coefficients and subsequent solution of the chemical master equation were used to predict the time-evolution of our system under conditions from 500 K to 2000 K and from 10-5 bar to 10 bars. Despite the 1,3 reaction pathway being more favorable for the C4H5 system, our results predict branching ratios of the 1,2 to 1,3 product as high as 0.48 at 1 bar. Similar results hold for the acroylyl system under these combustion conditions, suggesting that under kinetic control the branching of these reactions may be much more significant than the thermodynamics would suggest. This effect may be partly attributed to the low energy difference between 1,2 and 1,3 forms of the radical intermediate. No substantial pressure-dependence is found for the overall forward reaction rates until pressures decrease below 0.1 bar.

Intermediates in the Formation of Aromatics in Hydrocarbon Combustion

NASA Technical Reports Server (NTRS)

Walch, Stephen P.; Langhoff, S. R. (Technical Monitor)

1994-01-01

The formation of the first benzene ring is believed to be the rate limiting step in soot formation. Two different mechanisms have been proposed for formation of cyclic C6 species. The first involves the reaction of two acetylenes to give CH2CHCCH (vinyl acetylene), the loss of a H to give CHCHCCH (n-C41-13) or CH2CCCH (iso-C4H3), and addition of another acetylene to n-C4H3, followed by ring closure to give phenyl radical. Miller and Melius argue that only n-C4H3 leads to phenyl radical and since iso-C4H3 is more stable than n-C4H3 this mechanism is unlikely. An alternative mechanism proposed by them is formation of benzene from the dimerization of two CH2CCH (propargyl) radicals (formed by the reaction of singlet methylene with C2H2). We report reaction pathways and accurate energetics (from CASSCF/internally contracted CI calculations) for the reactions of CH(pi-2) and CH2-1 with acetylene, the reaction of vinylidene with acetylene, and the reaction of n-C4H3 and iso-C4H3 with acetylene. These calculations identify two new reactive intermediates CHCHCH ( a A"-2 ground state in Cs symmetry; spin coupling is a doublet from three singly occupied orbitals) and CHCCH (B-3 ground state in C2 symmetry) from the reaction of CH with acetylene. These species dimerize with no barrier to form benzene and para-benzyne, respectively. CHCCH is proposed as a reactive intermediate which can add to benzene to give higher polynuclear aromatic hydrocarbons or fullerenes. The addition of a C3H2 unit releases two C-C bond energies and thus the resulting addition product contains sufficient energy to break several CH bonds leading to a reduction in the H to C ratio as the cluster size increases. It is found that iso-C4H3 adds to acetylene to initially give a fulvene radical but that this species rearranges to phenyl radical. Thus, the reaction of acetylene with iso-C4H3 does lead to phenyl radical and the cyclization pathway may also contribute to formation of the initial benzene ring.

Thermal decomposition of FC(O)OCH3 and FC(O)OCH2CH3.

PubMed

Berasategui, M; Argüello, G A; Burgos Paci, M A

2018-05-09

The thermal decomposition of methyl and ethyl formates has been extensively studied due to their importance in the oxidation of several fuels, pesticidal properties and their presence in interstellar space. We hitherto present the study of the thermal decomposition of methyl and ethyl fluoroformates, which could help in the elucidation of the reaction mechanisms. The reaction mechanisms were studied using FTIR spectroscopy in the temperature range of 453-733 K in the presence of different pressures of N2 as bath gas. For FC(O)OCH3 two different channels were observed; the unimolecular decomposition which is favored at higher temperatures and has a rate constant kFC(O)OCH3 = (5.3 ± 0.5) × 1015 exp[-(246 ± 10 kJ mol-1/RT)] (in units of s-1) and a bimolecular channel with a rate constant kFC(O)OCH3 = (1.6 ± 0.5) × 1011 exp[-(148 ± 10 kJ mol-1/RT)] (in units of s-1 (mol L)-1). However for ethyl formate, only direct elimination of CO2, HF and ethylene operates. The rate constants of the homogeneous first-order process fit the Arrhenius equation kFC(O)OCH2CH3 = (2.06 ± 0.09) × 1013 exp[-(169 ± 6 kJ mol-1/RT)] (in units of s-1). The difference between the mechanisms of the two fluoroformates relies on the stabilization of a six-centered transition state that only exists for ethyl formate. First principles calculations for the different channels were carried out to understand the dynamics of the decomposition.

The benzylperoxyl radical as a source of hydroxyl and phenyl radicals.

PubMed

Sander, Wolfram; Roy, Saonli; Bravo-Rodriguez, Kenny; Grote, Dirk; Sanchez-Garcia, Elsa

2014-09-26

The benzyl radical (1) is a key intermediate in the combustion and tropospheric oxidation of toluene. Because of its relevance, the reaction of 1 with molecular oxygen was investigated by matrix-isolation IR and EPR spectroscopy as well as computational methods. The primary reaction product of 1 and O2 is the benzylperoxyl radical (2), which exists in several conformers that can easily interconvert even at cryogenic temperatures. Photolysis of radical 2 at 365 nm results in a formal [1,3]-H migration and subsequent cleavage of the O-O bond to produce a hydrogen-bonded complex between the hydroxyl radical and benzaldehyde (4). Prolonged photolysis produces the benzoyl radical (5) and water, which finally yield the phenyl radical (7), CO, and H2O. Thus, via a sequence of exothermic reactions 1 is transformed into radicals of even higher reactivity, such as OH and 7. Our results have implications for the development of models for the highly complicated process of combustion of aromatic compounds. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Standard Gibbs free energies of reactions of ozone with free radicals in aqueous solution: quantum-chemical calculations.

PubMed

Naumov, Sergej; von Sonntag, Clemens

2011-11-01

Free radicals are common intermediates in the chemistry of ozone in aqueous solution. Their reactions with ozone have been probed by calculating the standard Gibbs free energies of such reactions using density functional theory (Jaguar 7.6 program). O(2) reacts fast and irreversibly only with simple carbon-centered radicals. In contrast, ozone also reacts irreversibly with conjugated carbon-centered radicals such as bisallylic (hydroxycylohexadienyl) radicals, with conjugated carbon/oxygen-centered radicals such as phenoxyl radicals, and even with nitrogen- oxygen-, sulfur-, and halogen-centered radicals. In these reactions, further ozone-reactive radicals are generated. Chain reactions may destroy ozone without giving rise to products other than O(2). This may be of importance when ozonation is used in pollution control, and reactions of free radicals with ozone have to be taken into account in modeling such processes.

Calculational and Experimental Investigations of the Pressure Effects on Radical - Radical Cross Combinations Reactions: C2H5 + C2H3

NASA Technical Reports Server (NTRS)

Fahr, Askar; Halpern, Joshua B.; Tardy, Dwight C.

2007-01-01

Pressure-dependent product yields have been experimentally determined for the cross-radical reaction C2H5 + C2H3. These results have been extended by calculations. It is shown that the chemically activated combination adduct, 1-C4H8*, is either stabilized by bimolecular collisions or subject to a variety of unimolecular reactions including cyclizations and decompositions. Therefore the "apparent" combination/disproportionation ratio exhibits a complex pressure dependence. The experimental studies were performed at 298 K and at selected pressures between about 4 Torr (0.5 kPa) and 760 Torr (101 kPa). Ethyl and vinyl radicals were simultaneously produced by 193 nm excimer laser photolysis of C2H5COC2H3 or photolysis of C2H3Br and C2H5COC2H5. Gas chromatograph/mass spectrometry/flame ionization detection (GC/MS/FID) were used to identify and quantify the final reaction products. The major combination reactions at pressures between 500 (66.5 kPa) and 760 Torr are (1c) C2H5 + C2H3 yields 1-butene, (2c) C2H5 + C2H5 yields n-butane, and (3c) C2H3 + C2H3 yields 1,3-butadiene. The major products of the disproportionation reactions are ethane, ethylene, and acetylene. At moderate and lower pressures, secondary products, including propene, propane, isobutene, 2-butene (cis and trans), 1-pentene, 1,4-pentadiene, and 1,5-hexadiene are also observed. Two isomers of C4H6, cyclobutene and/or 1,2-butadiene, were also among the likely products. The pressure-dependent yield of the cross-combination product, 1-butene, was compared to the yield of n-butane, the combination product of reaction (2c), which was found to be independent of pressure over the range of this study. The [ 1-C4H8]/[C4H10] ratio was reduced from approx.1.2 at 760 Torr (101 kPa) to approx.0.5 at 100 Torr (13.3 kPa) and approx.0.1 at pressures lower than about 5 Torr (approx.0.7 kPa). Electronic structure and RRKM calculations were used to simulate both unimolecular and bimolecular processes. The relative importance of C-C and C-H bond ruptures, cyclization, decyclization, and complex decompositions are discussed in terms of energetics and structural properties. The pressure dependence of the product yields were computed and dominant reaction paths in this chemically activated system were determined. Both modeling and experiment suggest that the observed pressure dependence of [1-C4H8]/[C4H10] is due to decomposition of the chemically activated combination adduct 1-C4H8* in which the weaker allylic C-C bond is broken: H2C=CHCH2CH3 yields C3H5 + CH3. This reaction occurs even at moderate pressures of approx.200 Torr (26 kPa) and becomes more significant at lower pressures. The additional products detected at lower pressures are formed from secondary radical-radical reactions involving allyl, methyl, ethyl, and vinyl radicals. The modeling studies have extended the predictions of product distributions to different temperatures (200-700 K) and a wider range of pressures (10(exp -3) - 10(exp 5) Torr). These calculations indicate that the high-pressure [1-C4H8]/[C4H10] yield ratio is 1.3 +/- 0.1.

Theoretical study of the reactions of the hydroselenyl radical (HSe●) with the selenenic radical (HSeO●).

PubMed

Vega-Teijido, Mauricio Angel; Kieninger, Martina; Ventura, Oscar N

2017-12-05

The formation of selenium species in some biological processes involves the generation of ionic and radical intermediates such as RSe ● , RSe - , RSeO ● , and RSeO - , among others. We performed a theoretical study of the possible mechanisms for the reaction of the two simplest Se radicals-the hydroselenyl (HSe ● ) and selenenic (HSeO ● ) radicals, in which the possible products, intermediates, and transition-state structures were investigated. Density functional theory (DFT) was applied at the B3LYP/6-311++G(3df,3pd) level and the Ahlrichs Coulomb fitting basis sets were employed with an effective core potential (ECP) for both Se atoms. The same procedure was used to calculate the electronic density. All calculations were also performed using the M06-2X functional, which describes weaker bonds better than B3LYP does. In the reaction of interest, the so-called CR complex (HSe····SeOH) is formed initially. After passing through the transition state TS1, cis-HSeSeOH is obtained as a product. If a low barrier is then overcome (passing through the transition state TS32), the trans-HSeSeOH species is obtained. The CR complex can also rearrange into the intermediate INT after overcoming the barrier presented by the transition state TS2. Additionally, the decomposition of INT to H 2 O and 1 Se 2 is possible through another transition state. This reaction is not included in this study. We also observed a second possible route for the conversion of INT to one of the HSeSeOH species; this route occurs through two pathways (with transition states TS31 and TS32). A comparison of some of the results with those obtained for sulfur analogs along the same pathways is also presented in this work. Graphical abstract Electronic envelopes for HSeO ● and HSe ● radicals.

A computational study of the addition of ReO3L (L = Cl(-), CH3, OCH3 and Cp) to ethenone.

PubMed

Aniagyei, Albert; Tia, Richard; Adei, Evans

2016-01-01

The periselectivity and chemoselectivity of the addition of transition metal oxides of the type ReO3L (L = Cl, CH3, OCH3 and Cp) to ethenone have been explored at the MO6 and B3LYP/LACVP* levels of theory. The activation barriers and reaction energies for the stepwise and concerted addition pathways involving multiple spin states have been computed. In the reaction of ReO3L (L = Cl(-), OCH3, CH3 and Cp) with ethenone, the concerted [2 + 2] addition of the metal oxide across the C=C and C=O double bond to form either metalla-2-oxetane-3-one or metalla-2,4-dioxolane is the most kinetically favored over the formation of metalla-2,5-dioxolane-3-one from the direct [3 + 2] addition pathway. The trends in activation and reaction energies for the formation of metalla-2-oxetane-3-one and metalla-2,4-dioxolane are Cp < Cl(-) < OCH3 < CH3 and Cp < OCH3 < CH3 < Cl(-) and for the reaction energies are Cp < OCH3 < Cl(-) < CH3 and Cp < CH3 < OCH3 < Cl CH3. The concerted [3 + 2] addition of the metal oxide across the C=C double of the ethenone to form species metalla-2,5-dioxolane-3-one is thermodynamically the most favored for the ligand L = Cp. The direct [2 + 2] addition pathways leading to the formations of metalla-2-oxetane-3-one and metalla-2,4-dioxolane is thermodynamically the most favored for the ligands L = OCH3 and Cl(-). The difference between the calculated [2 + 2] activation barriers for the addition of the metal oxide LReO3 across the C=C and C=O functionalities of ethenone are small except for the case of L = Cl(-) and OCH3. The rearrangement of the metalla-2-oxetane-3-one-metalla-2,5-dioxolane-3-one even though feasible, are unfavorable due to high activation energies of their rate-determining steps. For the rearrangement of the metalla-2-oxetane-3-one to metalla-2,5-dioxolane-3-one, the trends in activation barriers is found to follow the order OCH3 < Cl(-) < CH3 < Cp. The trends in the activation energies for the most favorable [2 + 2] addition pathways for the LReO3-ethenone system is CH3 > CH3O(-) > Cl(-) > Cp. For the analogous ethylene-LReO3 system, the trends in activation and reaction energies for the most favorable [3 + 2] addition pathway is CH3 > CH3O(-) > Cl(-) > Cp [10]. Even though the most favored pathway in the ethylene-LReO3 system is the [3 + 2] addition pathway and that on the LReO3-ethenone is the [2 + 2] addition pathway, the trends in the activation energies for both pathways are the same, i.e. CH3 > CH3O(-) > Cl(-) > Cp. However, the trends in reaction energies are quite different due to different product stabilities. The formation of the acetic acid precursor through the direct addition pathways was unsuccessful for all the ligands studied. The formation of the acetic acid precursor through the cyclization of the metalla-2-oxetane-3-one is only possible for the ligands L = Cl(-), CH3 whiles for the cyclization of metalla-2-oxetane-4-one to the acetic acid precursor is only possible for the ligand L = CH3. Although there are spin-crossover reaction observed for the ligands L = Cl(-), CH3 and CH3O(-), the reactions occurring on the single surfaces have been found to occur with lower energies than their spin-crossover counterparts.

Synthesis, antityrosinase activity of curcumin analogues, and crystal structure of (1E,4E)-1,5-bis(4-ethoxyphenyl)penta-1,4-dien-3-one

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chantrapromma, S., E-mail: suchada.c@psu.ac.th; Ruanwas, P.; Boonnak, N.

2016-12-15

Five derivatives of curcumin analogue (R = OCH{sub 2}CH{sub 3} (1), R = N(CH{sub 3}){sub 2} (2), R = 2,4,5-OCH{sub 3} (3), R = 2,4,6-OCH{sub 3} (4), and R = 3,4,5-OCH{sub 3} (5)) were synthesized and characterized by {sup 1}H NMR, FT-IR and UV–Vis spectroscopy. The synthesized derivatives were screened for antityrosinase activity, and found that 4 and 5 possess such activity. The crystal structure of 1 was determined by single crystal X-ray diffraction: monoclinic, sp. gr. P2{sub 1}/c, a = 17.5728(15) Å, b = 5.9121(5) Å, c = 19.8269(13) Å, β = 121.155(5)°, Z = 4. The molecule 1more » is twisted with the dihedral angle between two phenyl rings being 15.68(10)°. In the crystal packing, the molecules 1 are linked into chains by C−H···π interactions and further stacked by π···π interactions with the centroid–centroid distance of 3.9311(13) Å.« less

Criegee intermediates in the indoor environment. New insights

DOE PAGES

Shallcross, D. E.; Taatjes, C. A.; Percival, C. J.

2014-03-25

Criegee intermediates are formed in the ozonolysis of alkenes and play an important role in indoor chemistry, notably as a source of OH radicals. Recent studies have shown that these Criegee intermediates react very quickly with NO 2, SO 2, and carbonyls, and in this study, steady-state calculations are used to inspect the potential impact of these data on indoor chemistry. It is shown that these reactions could accelerate NO 3 formation and SO 2 removal in the indoor environment significantly. In addition, reaction between Criegee intermediates and halogenated carbonyls could provide a significant loss process indoors, where currently onemore » does not exist.« less

Enzyme-like catalysis via ternary complex mechanism: alkoxy-bridged dinuclear cobalt complex mediates chemoselective O-esterification over N-amidation.

PubMed

Hayashi, Yukiko; Santoro, Stefano; Azuma, Yuki; Himo, Fahmi; Ohshima, Takashi; Mashima, Kazushi

2013-04-24

Hydroxy group-selective acylation in the presence of more nucleophilic amines was achieved using acetates of first-row late transition metals, such as Mn, Fe, Co, Cu, and Zn. Among them, cobalt(II) acetate was the best catalyst in terms of reactivity and selectivity. The combination of an octanuclear cobalt carboxylate cluster [Co4(OCOR)6O]2 (2a: R = CF3, 2b: R = CH3, 2c: R = (t)Bu) with nitrogen-containing ligands, such as 2,2'-bipyridine, provided an efficient catalytic system for transesterification, in which an alkoxide-bridged dinuclear complex, Co2(OCO(t)Bu)2(bpy)2(μ2-OCH2-C6H4-4-CH3)2 (10), was successfully isolated as a key intermediate. Kinetic studies and density functional theory calculations revealed Michaelis-Menten behavior of the complex 10 through an ordered ternary complex mechanism similar to dinuclear metallo-enzymes, suggesting the formation of alkoxides followed by coordination of the ester.

Environmental risk assessment of hydrofluoroethers (HFEs).

PubMed

Tsai, Wen-Tien

2005-03-17

Hydrofluoroethers (HFEs) are being used as third generation replacements to chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and perfluorocarbons (PFCs) because of their nearly zero stratospheric ozone depletion and relatively low global warming potential. HFEs have been developed under commercial uses as cleaning solvents (incl., HFE-7500, C7F15OC2H5; HFE-7200, C4F9OC2H5; HFE-7100, C4F9CH3; HFE-7000, n-C3F7OCH3), blowing agents (incl., HFE-245mc, CF3CF2OCH3; HFC-356mec, CF3CHFCF2OCH3), refrigerants (incl., HFE-143a, CF3OCH3; HFE-134, CHF2OCHF2; HFE-245mc, CF3CF2OCH3), and dry etching agents in semiconductor manufacturing, (incl., HFE-227me, CF3OCHFCF3). From the environmental, ecological, and health points of view, it is important to understand their environmental risks for these HFEs from a diversity of commercial applications and industrial processes. This paper aims to introduce these HFEs with respect to physiochemical properties, commercial uses, and environmental hazards (i.e. global warming, photochemical potential, fire and explosion hazard, and environmental partition). Further, it addresses the updated data on the human toxicity, occupational exposure and potential health risk of commercial HFEs. It is concluded that there are few HFEs that still possess some environmental hazards, including global warming, flammability hazard and adverse effect of exposure. The partition coefficient for these HFEs has been estimated using the group contribution method; the values of logKow for commercial HFEs have been estimated to be below 3.5.

Carboxylate and amino group coated silver nanoparticles as joining materials for copper-to-copper silver joints.

PubMed

Oestreicher, A; Röhrich, T; Lerch, M

2012-12-01

Organic silver complexes are introduced where silver is linked either with a carboxyl group or with an amino group. Upon heating, nanoparticles are generated if the respective ligands are long enough to act as stabilizing agents in the nanoparticulate regime. With decomposition and volatilization of the organic material, the sintering of silver occurs. The thermal characteristics of the carboxylates silver-n-octanoate, silver-n-decanoate, and AgOOC(CH2OCH2)2CH2OCH3 are compared with silver-n-alkylamines (n = 8, 9, and 12), and their thermal behavior is discussed based on thermogravimetry (TG) measurements. The consecutive stages of a metallization process are addressed based on the properties of AgOOC(CH2OCH2)2CH2OCH3, and the usable effects of the individual phases of this metal organic compound are analyzed by cross-sectional scanning electron microscope (SEM) images of silver joints. Selection criteria are addressed based on the thermal behavior. A mechanism for the joining process is proposed, considering formation and sintering of the nanoparticles. It was found that the bulk material can be used for low-temperature joining processes. Strong adherence to copper as a basic material can be achieved.

Theoretical investigation of the oxidation pathways of the Cl-initiated reaction of 2-methyl-3-buten-2-ol

NASA Astrophysics Data System (ADS)

Zhang, Weichao; Zhang, Dongju

2012-12-01

The mechanism and products of the reaction of 2-methyl-3-buten-2-ol (MBO232) with Cl atoms in the presence of O2 have been elucidated by performing high-level quantum chemistry calculations. The geometries of the reactants, intermediates, transition states, and products are optimized at the MP2(full)/6-311G(d, p) level, and their single-point energies are refined at the CCSD(T)/6-311 + G(d, p) level. The potential energy surface profiles have been constructed at the CCSD(T)/6-311 + G(d, p)//MP2(full)/6-311G(d, p) + 0.95 × ZPE level of theory, and the possible channels involved in the reaction are also discussed. The calculations indicate that the reaction predominantly proceeds via the addition of Cl atoms to the double bond rather than the direct abstraction of the H atoms in MBO232. The nascent adducts (CH3)2C(OH)CHCH2Cl (IM1) and (CH3)2C(OH)CHClCH2 (IM2) do not undergo subsequent isomerization and dissociation reactions, but rather react with O2. The theoretical results show that the major products are CH2ClCHO and CH3C(O)CH3 for the reaction of MBO232 + Cl in the presence of O2, which is in good agreement with the experimental finding.

Oxidation mechanisms of CF2Br2 and CH2Br2 induced by air nonthermal plasma.

PubMed

Schiorlin, Milko; Marotta, Ester; Dal Molin, Marta; Paradisi, Cristina

2013-01-02

Oxidation mechanisms in air nonthermal plasma (NTP) at room temperature and atmospheric pressure were investigated in a corona reactor energized by +dc, -dc, or +pulsed high voltage.. The two bromomethanes CF(2)Br(2) and CH(2)Br(2) were chosen as model organic pollutants because of their very different reactivities with OH radicals. Thus, they served as useful mechanistic probes: they respond differently to the presence of humidity in the air and give different products. By FT-IR analysis of the postdischarge gas the following products were detected and quantified: CO(2) and CO in the case of CH(2)Br(2), CO(2) and F(2)C ═ O in the case of CF(2)Br(2). F(2)C ═ O is a long-lived oxidation intermediate due to its low reactivity with atmospheric radicals. It is however removed from the NTP processed gas by passage through a water scrubber resulting in hydrolysis to CO(2) and HF. Other noncarbon containing products of the discharge were also monitored by FT-IR analysis, including HNO(3) and N(2)O. Ozone, an important product of air NTP, was never detected in experiments with CF(2)Br(2) and CH(2)Br(2) because of the highly efficient ozone depleting cycles catalyzed by BrOx species formed from the bromomethanes. It is concluded that, regardless of the type of corona applied, CF(2)Br(2) reacts in air NTP via a common intermediate, the CF(2)Br radical. The possible reactions leading to this radical are discussed, including, for -dc activation, charge exchange with O(2)(-), a species detected by APCI mass spectrometry.

Photoisomerization and photodissociation dynamics of reactive free radicals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bise, Ryan T.

2000-08-01

The photofragmentation pathways of chemically reactive free radicals have been examined using the technique of fast beam photofragment translational spectroscopy. Measurements of the photodissociation cross-sections, product branching ratios, product state energy distributions, and angular distributions provide insight into the excited state potential energy surfaces and nonadiabatic processes involved in the dissociation mechanisms. Photodissociation spectroscopy and dynamics of the predissociativemore » $$\\tilde{A}$$ 2A 1 and $$\\tilde{B}$$ 2A 2 states of CH 3S have been investigated. At all photon energies, CH 3 + S( 3P j), was the main reaction channel. The translational energy distributions reveal resolved structure corresponding to vibrational excitation of the CH 3 umbrella mode and the S( 3P j) fine-structure distribution from which the nature of the coupled repulsive surfaces is inferred. Dissociation rates are deduced from the photofragment angular distributions, which depend intimately on the degree of vibrational excitation in the C-S stretch. Nitrogen combustion radicals, NCN, CNN and HNCN have also been studied. For all three radicals, the elimination of molecular nitrogen is the primary reaction channel. Excitation to linear excited triplet and singlet electronic states of the NCN radical generates resolved vibrational structure of the N 2 photofragment. The relatively low fragment rotational excitation suggests dissociation via a symmetric C 2V transition state. Resolved vibrational structure of the N 2 photofragment is also observed in the photodissociation of the HNCN radical. The fragment vibrational and rotational distributions broaden with increased excitation energy. Simple dissociation models suggest that the HNCN radical isomerizes to a cyclic intermediate (c-HCNN) which then dissociates via a tight cyclic transition state. In contrast to the radicals mentioned above, resolved vibrational structure was not observed for the ICNN radical due to extensive fragment rotational excitation, suggesting that intermediate bent states are strongly coupled along the dissociation pathway. The measurements performed in this Thesis have additionally refined the heats of formation and bond dissociation energies of these radicals and have unambiguously confirmed and added to the known electronic spectroscopy.« less

Double C-H activation of ethane by metal-free SO2*+ radical cations.

PubMed

de Petris, Giulia; Cartoni, Antonella; Troiani, Anna; Barone, Vincenzo; Cimino, Paola; Angelini, Giancarlo; Ursini, Ornella

2010-06-01

The room-temperature C-H activation of ethane by metal-free SO(2)(*+) radical cations has been investigated under different pressure regimes by mass spectrometric techniques. The major reaction channel is the conversion of ethane to ethylene accompanied by the formation of H(2)SO(2)(*+), the radical cation of sulfoxylic acid. The mechanism of the double C-H activation, in the absence of the single activation product HSO(2)(+), is elucidated by kinetic studies and quantum chemical calculations. Under near single-collision conditions the reaction occurs with rate constant k=1.0 x 10(-9) (+/-30%) cm(3) s(-1) molecule(-1), efficiency=90%, kinetic isotope effect k(H)/k(D)=1.1, and partial H/D scrambling. The theoretical analysis shows that the interaction of SO(2)(*+) with ethane through an oxygen atom directly leads to the C-H activation intermediate. The interaction through sulfur leads to an encounter complex that rapidly converts to the same intermediate. The double C-H activation occurs by a reaction path that lies below the reactants and involves intermediates separated by very low energy barriers, which include a complex of the ethyl cation suitable to undergo H/D scrambling. Key issues in the observed reactivity are electron-transfer processes, in which a crucial role is played by geometrical constraints. The work shows how mechanistic details disclosed by the reactions of metal-free electrophiles may contribute to the current understanding of the C-H activation of ethane.

Radicals and molecular products from the gas-phase pyrolysis of lignin model compounds. Cinnamyl alcohol

PubMed Central

Khachatryan, Lavrent; Xu, Meng-xia; Wu, Ang-jian; Pechagin, Mikhail; Asatryan, Rubik

2016-01-01

The experimental results on detection and identification of intermediate radicals and molecular products from gas-phase pyrolysis of cinnamyl alcohol (CnA), the simplest non-phenolic lignin model compound, over the temperature range of 400–800 °C are reported. The low temperature matrix isolation – electron paramagnetic resonance (LTMI-EPR) experiments along with the theoretical calculations, provided evidences on the generation of the intermediate carbon and oxygen centered as well as oxygen-linked, conjugated radicals. A mechanistic analysis is performed based on density functional theory to explain formation of the major products from CnA pyrolysis; cinnamaldehyde, indene, styrene, benzaldehyde, 1-propynyl benzene, and 2-propenyl benzene. The evaluated bond dissociation patterns and unimolecular decomposition pathways involve dehydrogenation, dehydration, 1,3-sigmatropic H-migration, 1,2-hydrogen shift, C—O and C—C bond cleavage processes. PMID:28344372

A radical pathway in catecholase activity with nickel(II) complexes of phenol based "end-off" compartmental ligands.

PubMed

Ghosh, Totan; Adhikary, Jaydeep; Chakraborty, Prateeti; Sukul, Pradip K; Jana, Mahendra Sekhar; Mondal, Tapan Kumar; Zangrando, Ennio; Das, Debasis

2014-01-14

Seven dinuclear and one dinuclear based dicyanamide bridged polymeric Ni(II) complexes of phenol based compartmental ligands (HL(1)-HL(4)) have been synthesized with the aim to investigate their catecholase-like activity and to evaluate the most probable mechanistic pathway involved in this process. The complexes have been characterized by routine physicochemical studies as well as by X-ray single crystal structure analyses namely [Ni2(L(2))(SCN)3(H2O)(CH3OH)] (), [Ni2(L(4))(SCN)3(CH3OH)2] (), [Ni2(L(2))(SCN)2(AcO)(H2O)] (), [Ni2(L(4))(SCN)(AcO)2] (), [Ni2(L(2))(N3)3(H2O)2] (), [Ni2(L(4))(N3)3(H2O)2] (), [Ni2(L(1))(AcO)2(N(CN)2)]n () and [Ni2(L(3))(AcO)2(N(CN)2)] (), [SCN = isothiocyanate, AcO = acetate, N3 = azide, and N(CN)2 = dicyanamide anion; L(1-4) = 2,6-bis(R2-iminomethyl)-4-R1-phenolato, where R1 = methyl and tert-butyl, R2 = N,N-dimethyl ethylene for L(1-2) and R1 = methyl and tert-butyl, R2 = 2-(N-ethyl) pyridine for L(3-4)]. A UV-vis spectrophotometric study using 3,5-di-tert butylcatechol (3,5-DTBC) reveals that all the complexes are highly active in catalyzing the aerobic oxidation of (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) in methanol medium with the formation of hydrogen peroxide. An EPR study confirms the generation of radicals during the catalysis. Cyclic voltammetric studies of the complexes in the presence and absence of 3,5-DTBC have been performed. Reduction of Ni(II) to Ni(I) and that of the imine bond of the ligand system have been detected at ∼-1.0 V and ∼-1.5 V, respectively. Coulometric separation of the species at -1.5 V followed by the EPR study at 77 K confirms the species as an organic radical and thus most probably reduced imine species. Spectroelectrochemical analysis at -1.5 V clearly indicates the oxidation of 3,5-DTBC and thus suggests that the radical pathway is supposed to be responsible for the catecholase-like activity exhibited by the nickel complexes. The ligand centred radical generation has further been verified by density functional theory calculation.

Homogeneous and heterogeneous noncovalent dimers of formaldehyde and thioformaldehyde: structures, energetics, and vibrational frequencies.

PubMed

Van Dornshuld, Eric; Holy, Christina M; Tschumper, Gregory S

2014-05-08

This work provides the first characterization of five stationary points of the homogeneous thioformaldehyde dimer, (CH2S)2, and seven stationary points of the heterogeneous formaldehyde/thioformaldehyde dimer, CH2O/CH2S, with correlated ab initio electronic structure methods. Full geometry optimizations and corresponding harmonic vibrational frequencies were computed with second-order Møller-Plesset perturbation theory (MP2) and 13 different density functionals in conjunction with triple-ζ basis sets augmented with diffuse and multiple sets of polarization functions. The MP2 results indicate that the three stationary points of (CH2S)2 and four of CH2O/CH2S are minima, in contrast to two stationary points of the formaldehyde dimer, (CH2O)2. Single-point energies were also computed using the explicitly correlated MP2-F12 and CCSD(T)-F12 methods and basis sets as large as heavy-aug-cc-pVTZ. The (CH2O)2 and CH2O/CH2S MP2 and MP2-F12 binding energies deviated from the CCSD(T)-F12 binding energies by no more than 0.2 and 0.4 kcal mol(-1), respectively. The (CH2O)2 and CH2O/CH2S global minimum is the same at every level of theory. However, the MP2 methods overbind (CH2S)2 by as much as 1.1 kcal mol(-1), effectively altering the energetic ordering of the thioformaldehyde dimer minima relative to the CCSD(T)-F12 energies. The CCSD(T)-F12 binding energies of the (CH2O)2 and CH2O/CH2S stationary points are quite similar, with the former ranging from around -2.4 to -4.6 kcal mol(-1) and the latter from about -1.1 to -4.4 kcal mol(-1). Corresponding (CH2S)2 stationary points have appreciably smaller CCSD(T)-F12 binding energies ranging from ca. -1.1 to -3.4 kcal mol(-1). The vibrational frequency shifts upon dimerization are also reported for each minimum on the MP2 potential energy surfaces.

Radical-mediated reduction of the dithiocarbamate group under tin-free conditions.

PubMed

McMaster, Claire; Bream, Robert N; Grainger, Richard S

2012-06-28

Reductive desulfurisation of dithiocarbamates is conveniently achieved using H(3)PO(2)-Et(3)N-ACCN in refluxing dioxane. Fused and spirocyclic β-lactams, prepared through 4-exo trig carbamoyl radical cyclisation-dithiocarbamate group transfer reactions, are reduced without fragmentation of the strained 4-membered ring. Diethyl tetraacetyl-d-glucopyranosyl dithiocarbamate is selectively reduced with or without acyloxy group migration depending on reaction conditions and choice of reductant. Deuterium incorporation from D(3)PO(2)-Et(3)N is observed for a system involving a nucleophilic radical intermediate, but not in the case of the electrophilic radical obtained through acyloxy group migration on a glucose derivative.

Geraniol (2,6-dimethyl-2,6-octadien-8-ol) reactions with ozone and OH radical: Rate constants and gas-phase products

NASA Astrophysics Data System (ADS)

Forester, Crystal D.; Ham, Jason E.; Wells, J. R.

The bimolecular rate constants, kOH+geraniol, (231±58)×10 -12 cm 3 molecule -1 s -1 and k+geraniol, (9.3±2.3)×10 -16 cm 3 molecule -1 s -1, were measured using the relative rate technique for the reaction of the hydroxyl radical (OH) and ozone (O 3) with 2,6-dimethyl-2,6-octadien-8-ol (geraniol) at (297±3) K and 1 atmosphere total pressure. To more clearly define part of geraniol's indoor environment degradation mechanism, the products of the geraniol+OH and geraniol+O 3 reactions were also investigated. The identified geraniol+OH and geraniol+O 3 reaction products were: acetone, hydroxyacetaldehyde (glycolaldehyde, HC( dbnd O)CH 2OH), ethanedial (glyoxal, HC( dbnd O)C( dbnd O)H), and 2-oxopropanal (methylglyoxal, CH 3C( dbnd O)C( dbnd O)H). The use of derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and N,O-bis(trimethylsilyl) trifluoroacetamide (BSTFA) were used to propose 4-oxopentanal as the other major geraniol+OH and geraniol+O 3 reaction product. The elucidation of this other reaction product was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible geraniol+OH and geraniol+O 3 reaction mechanisms based on previously published volatile organic compound+OH and volatile organic compound+O 3 gas-phase reaction mechanisms.

Radical Cationic Pathway for the Decay of Ionized Glyme Molecules in Liquid Solution.

PubMed

Taletskiy, Konstantin S; Borovkov, Vsevolod I; Schegoleva, Lyudmila N; Beregovaya, Irina V; Taratayko, Andrey I; Molin, Yuriy N

2015-11-12

Chemical stability of primary radical cations (RCs) generated in irradiated matter determines substantially the radiation resistance of organic materials. Transformations of the RCs of the glyme molecules, R(-O-CH2-CH2-)nO-R (R = CH3, n = 1-4) has been studied on the nanosecond time scale by measuring the magnetic field effects in the recombination fluorescence from irradiated liquid solutions of the glymes. In all cases, the RCs observed were different from that expected for the primary ones and revealed very similar hyperfine couplings independent of the poly(ethylene oxide) chain length and of the substitution of terminal methyl groups by C2H5 or CH2CH2Cl, as has been shown with diglyme as an example. Quantum chemical analysis of possible chemical transformations for the monoglyme RC as a model system allowed us to discover the reaction pathway yielding the methyl vinyl ether RC. The pathway involves intramolecular proton transfer followed by C-O bond cleavage. Only one (-O-CH2-CH2-O-) fragment is involved in this transformation, which is nearly barrierless due to the catalytic effect of adjacent glyme molecules. The rapid formation of the methyl vinyl ether RC in the irradiated monoglyme was confirmed by the numerical simulation of the experimental curves of the time-resolved magnetic field effect. These findings suggest that the R'-O-CH═CH2(•+) formation is a typical decay pathway for the primary RCs in irradiated liquid glymes.

Risk Prediction Models of Locoregional Failure After Radical Cystectomy for Urothelial Carcinoma: External Validation in a Cohort of Korean Patients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ku, Ja Hyeon; Kim, Myong; Jeong, Chang Wook

2014-08-01

Purpose: To evaluate the predictive accuracy and general applicability of the locoregional failure model in a different cohort of patients treated with radical cystectomy. Methods and Materials: A total of 398 patients were included in the analysis. Death and isolated distant metastasis were considered competing events, and patients without any events were censored at the time of last follow-up. The model included the 3 variables pT classification, the number of lymph nodes identified, and margin status, as follows: low risk (≤pT2), intermediate risk (≥pT3 with ≥10 nodes removed and negative margins), and high risk (≥pT3 with <10 nodes removed ormore » positive margins). Results: The bootstrap-corrected concordance index of the model 5 years after radical cystectomy was 66.2%. When the risk stratification was applied to the validation cohort, the 5-year locoregional failure estimates were 8.3%, 21.2%, and 46.3% for the low-risk, intermediate-risk, and high-risk groups, respectively. The risk of locoregional failure differed significantly between the low-risk and intermediate-risk groups (subhazard ratio [SHR], 2.63; 95% confidence interval [CI], 1.35-5.11; P<.001) and between the low-risk and high-risk groups (SHR, 4.28; 95% CI, 2.17-8.45; P<.001). Although decision curves were appropriately affected by the incidence of the competing risk, decisions about the value of the models are not likely to be affected because the model remains of value over a wide range of threshold probabilities. Conclusions: The model is not completely accurate, but it demonstrates a modest level of discrimination, adequate calibration, and meaningful net benefit gain for prediction of locoregional failure after radical cystectomy.« less

Accretion Product Formation from Self- and Cross-Reactions of RO2 Radicals in the Atmosphere.

PubMed

Berndt, Torsten; Scholz, Wiebke; Mentler, Bernhard; Fischer, Lukas; Herrmann, Hartmut; Kulmala, Markku; Hansel, Armin

2018-03-26

Hydrocarbons are emitted into the Earth's atmosphere in very large quantities by human and biogenic activities. Their atmospheric oxidation processes almost exclusively yield RO 2 radicals as reactive intermediates whose atmospheric fate is not yet fully unraveled. Herein, we show that gas-phase reactions of two RO 2 radicals produce accretion products composed of the carbon backbone of both reactants. The rates for accretion product formation are very high for RO 2 radicals bearing functional groups, competing with those of the corresponding reactions with NO and HO 2 . This pathway, which has not yet been considered in the modelling of atmospheric processes, can be important, or even dominant, for the fate of RO 2 radicals in all areas of the atmosphere. Moreover, the vapor pressure of the formed accretion products can be remarkably low, characterizing them as an effective source for the secondary organic aerosol. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theoretical insight into reaction mechanisms of 2,4-dinitroanisole with hydroxyl radicals for advanced oxidation processes.

PubMed

Zhou, Yang; Liu, Xiaoqiang; Jiang, Weidong; Shu, Yuanjie

2018-01-24

The detailed degradation mechanism of an insensitive explosive, 2,4-dinitroanisole (DNAN), in advanced oxidation processes (AOPs) was investigated computationally at the M06-2X/6-311 + G(d,p)/SMD level of theory. Results obtained show that the addition-elimination reaction is the dominant mechanism. The phenol products formed can continue to be oxidized to benzoquinone radicals that are often detected by experiments and may be the initial reactants of ring-opening reactions. The H-abstraction reaction is an unavoidable competing mechanism; the intermediate generated can also undergo the process of addition-elimination reaction. The nitro departure reaction involves not only hydroxyl radical (•OH), but also other active substances (such as •H). More importantly, we found that AOP technology can easily degrade DNAN, similar to TNT and DNT. Thus, this method is worth trying in experiments. The conclusions of this work provide theoretical support for such experimental research. Graphical abstract Possible pathways of degradation by •OH radicals in advanced oxidation processes (AOPs) of the typical insensitive explosive 2,4-dinitroanisole (DNAN) were investigated by density functional theory (DFT) methods. Based on the Gibbs free energy barriers and intermediates, the dominant reaction mechanism was determined. The conclusions will be helpful in utilizing AOP technology to remove DNAN pollution.

Oxygen Activation and Radical Transformations in Heme Proteins and Metalloporphyrins

PubMed Central

2017-01-01

As a result of the adaptation of life to an aerobic environment, nature has evolved a panoply of metalloproteins for oxidative metabolism and protection against reactive oxygen species. Despite the diverse structures and functions of these proteins, they share common mechanistic grounds. An open-shell transition metal like iron or copper is employed to interact with O2 and its derived intermediates such as hydrogen peroxide to afford a variety of metal–oxygen intermediates. These reactive intermediates, including metal-superoxo, -(hydro)peroxo, and high-valent metal–oxo species, are the basis for the various biological functions of O2-utilizing metalloproteins. Collectively, these processes are called oxygen activation. Much of our understanding of the reactivity of these reactive intermediates has come from the study of heme-containing proteins and related metalloporphyrin compounds. These studies not only have deepened our understanding of various functions of heme proteins, such as O2 storage and transport, degradation of reactive oxygen species, redox signaling, and biological oxygenation, etc., but also have driven the development of bioinorganic chemistry and biomimetic catalysis. In this review, we survey the range of O2 activation processes mediated by heme proteins and model compounds with a focus on recent progress in the characterization and reactivity of important iron–oxygen intermediates. Representative reactions initiated by these reactive intermediates as well as some context from prior decades will also be presented. We will discuss the fundamental mechanistic features of these transformations and delineate the underlying structural and electronic factors that contribute to the spectrum of reactivities that has been observed in nature as well as those that have been invented using these paradigms. Given the recent developments in biocatalysis for non-natural chemistries and the renaissance of radical chemistry in organic synthesis, we envision that new enzymatic and synthetic transformations will emerge based on the radical processes mediated by metalloproteins and their synthetic analogs. PMID:29286645

High Temperature Superconducting Compounds

DTIC Science & Technology

1992-11-30

broadened interest in superconductivity in both the engineering and scientific communities. Superconducting materials may be offered as a solution to a...YBa2Cu307- has been made. For yttrium, the tris( isopropoxide ) was used exclusively, while the use of both Ba(O-i-Pr)2 and Ba(OCH2Ch2OEt)2 (prepared in... solutions of Cu(acac)2, Ba(OCH2CH 2OEt)2 , and Y(O-i-Pr)3 were spin coated on SrTiO 3 (100) and fired under oxygen to give oriented (b axis normal to the

Structure and energetics of vinoxide and the X({sup 2}A{double{underscore}prime}) and A({sup 2}A{prime}) vinoxy radicals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alconcel, L.S.; Deyerl, H.J.; Zengin, V.

1999-11-18

Enolate anions are intermediates in many organic reactions that involve carbon-carbon or carbon-oxygen food formation. They also play a key role in the development of stereoselective and stereocontrolled syntheses of complex compounds. Enolate radicals are important intermediates in combustion and photochemical smog cycles. In particular, the vinoxy radical, C{sub 2}H{sub 3}O{sup {sm{underscore}bullet}} is a major product of the reaction of odd oxygen and ethylene. The photoelectron spectrum of binoxide, C{sub 2}H{sub 3}O{sup {minus}}, at 355 nm is reported, showing photodetachment to both the X({sup 2}A{double{underscore}prime}) ground and first excited A({sup 2}A{prime}) states of the vinoxy radical. Both direct interpretations andmore » Franck-Condon simulations of the photoelectron spectrum of this simple enolate anion have been used to obtain insights into the energetics and structures of the anion and the ground and first excited state of the neutral radical. Franck-Condon simulations were generated from ab initio geometry and frequency calculations using the CASSCF method and showed good agreement with the vibrational structure visible in the experimental spectrum. The electron affinity (E.A.{sub exp} = 1.795 {+-} 0.015 eV; E.A.{sub calc} = 1.82 eV) and separation energy of the ground and first excited states (T{sub 0,exp} = 1.015 {+-} 0.015 eV; T{sub 0,calc} = 0.92 eV) obtained from the ab initio calculations are in good accord with the experimental values.« less

Free radical generation by non-equilibrium atmospheric pressure plasma in alcohol-water mixtures: an EPR-spin trapping study

NASA Astrophysics Data System (ADS)

Uchiyama, Hidefumi; Ishikawa, Kenji; Zhao, Qing-Li; Andocs, Gabor; Nojima, Nobuyuki; Takeda, Keigo; Krishna, Murali C.; Ishijima, Tatsuo; Matsuya, Yuji; Hori, Masaru; Noguchi, Kyo; Kondo, Takashi

2018-03-01

Free radical species in aqueous solution—various alcohol-water reaction mixtures—by exposure to non-equilibrium cold atmospheric pressure Ar plasma (CAP), were monitored using electron paramagnetic resonance spin-trapping techniques with 3, 5-dibromo-4-nitrosobenzene sulfonate as a water soluble nitroso spin trap. The major radical species were formed by H-abstraction from alcohol molecules due to ·OH radicals. In the ethanol-water mixture ·CH2CH2OH produced by H abstraction from CH3 group of the ethanol and ·CH3 radicals were detected. The latter was due to the decomposition of unstable CH3·CHOH to form the ·CH3 radicals and the stable formaldehyde by C-C bond fission. These intermediates are similar to those observed by reaction with ·OH radicals generation in the H2O2-UV photolysis of the reaction mixtures. The evidence of ·CH3 radical formation in the pyrolytic decomposition of the reaction mixtures by exposure to ultrasound or in methane irradiated with microwave plasma have been reported previously. However, the pyrolytic ·CH3 radicals were not found in both plasma and H2O2-UV photolysis condition. These results suggests that free radicals produced by Ar-CAP are most likely due to the reaction between abundant ·OH radicals and alcohol molecules.

Mechanism of Air Oxidation of the Fragrance Terpene Geraniol.

PubMed

Bäcktorp, Carina; Hagvall, Lina; Börje, Anna; Karlberg, Ann-Therese; Norrby, Per-Ola; Nyman, Gunnar

2008-01-01

The fragrance terpene geraniol autoxidizes upon air exposure and forms a mixture of oxidation products, some of which are skin sensitizers. Reactions of geraniol with O2 have been studied with DFT (B3LYP) and the computational results compared to experimentally observed product ratios. The oxidation is initiated by hydrogen abstraction, forming an allylic radical which combines with an O2 molecule to yield an intermediate peroxyl radical. In the subsequent step, geraniol differs from previously studied cases, in which the radical chain reaction is propagated through intermolecular hydrogen abstraction. The hydroxy-substituted allylic peroxyl radical prefers an intramolecular rearrangement, producing observable aldehydes and the hydroperoxyl radical, which in turn can propagate the radical reaction. Secondary oxidation products like epoxides and formates were also considered, and plausible reaction pathways for formation are proposed.

The flash-quench technique in protein-DNA electron transfer: reduction of the guanine radical by ferrocytochrome c.

PubMed

Stemp, E D; Barton, J K

2000-08-21

Electron transfer from a protein to oxidatively damaged DNA, specifically from ferrocytochrome c to the guanine radical, was examined using the flash-quench technique. Ru(phen)2dppz2+ (dppz = dipyridophenazine) was employed as the photosensitive intercalator, and ferricytochrome c (Fe3+ cyt c), as the oxidative quencher. Using transient absorption and time-resolved luminescence spectroscopies, we examined the electron-transfer reactions following photoexcitation of the ruthenium complex in the presence of poly(dA-dT) or poly(dG-dC). The luminescence-quenching titrations of excited Ru(phen)2dppz2+ by Fe3+ cyt c are nearly identical for the two DNA polymers. However, the spectral characteristics of the long-lived transient produced by the quenching depend strongly upon the DNA. For poly(dA-dT), the transient has a spectrum consistent with formation of a [Ru(phen)2dppz3+, Fe2+ cyt c] intermediate, indicating that the system regenerates itself via electron transfer from the protein to the Ru(III) metallointercalator for this polymer. For poly(dG-dC), however, the transient has the characteristics expected for an intermediate of Fe2+ cyt c and the neutral guanine radical. The characteristics of the transient formed with the GC polymer are consistent with rapid oxidation of guanine by the Ru(III) complex, followed by slow electron transfer from Fe2+ cyt c to the guanine radical. These experiments show that electron holes on DNA can be repaired by protein and demonstrate how the flash-quench technique can be used generally in studying electron transfer from proteins to guanine radicals in duplex DNA.

Broadband Microwave Study of Reaction Intermediates and Products Through the Pyrolysis of Oxygenated Biofuels

NASA Astrophysics Data System (ADS)

Abeysekera, Chamara; Hernandez-Castillo, Alicia O.; Fritz, Sean; Zwier, Timothy S.

2017-06-01

The rapidly growing list of potential plant-derived biofuels creates a challenge for the scientific community to provide a molecular-scale understanding of their combustion. Development of accurate combustion models rests on a foundation of experimental data on the kinetics and product branching ratios of their individual reaction steps. Therefore, new spectroscopic tools are necessary to selectively detect and characterize fuel components and reactive intermediates generated by pyrolysis and combustion. Substituted furans, including furanic ethers, are considered second-generation biofuel candidates. Following the work of the Ellison group, an 8-18 GHz microwave study was carried out on the unimolecular and bimolecular decomposition of the smallest furanic ether, 2-methoxy furan, and it`s pyrolysis intermediate, the 2-furanyloxy radical, formed in a high-temperature pyrolysis source coupled to a supersonic expansion. Details of the experimental setup and analysis of the spectrum of the radical will be discussed.

Predicting the effect of angular momentum on the dissociation dynamics of highly rotationally excited radical intermediates.

PubMed

Brynteson, Matthew D; Butler, Laurie J

2015-02-07

We present a model which accurately predicts the net speed distributions of products resulting from the unimolecular decomposition of rotationally excited radicals. The radicals are produced photolytically from a halogenated precursor under collision-free conditions so they are not in a thermal distribution of rotational states. The accuracy relies on the radical dissociating with negligible energetic barrier beyond the endoergicity. We test the model predictions using previous velocity map imaging and crossed laser-molecular beam scattering experiments that photolytically generated rotationally excited CD2CD2OH and C3H6OH radicals from brominated precursors; some of those radicals then undergo further dissociation to CD2CD2 + OH and C3H6 + OH, respectively. We model the rotational trajectories of these radicals, with high vibrational and rotational energy, first near their equilibrium geometry, and then by projecting each point during the rotation to the transition state (continuing the rotational dynamics at that geometry). This allows us to accurately predict the recoil velocity imparted in the subsequent dissociation of the radical by calculating the tangential velocities of the CD2CD2/C3H6 and OH fragments at the transition state. The model also gives a prediction for the distribution of angles between the dissociation fragments' velocity vectors and the initial radical's velocity vector. These results are used to generate fits to the previously measured time-of-flight distributions of the dissociation fragments; the fits are excellent. The results demonstrate the importance of considering the precession of the angular velocity vector for a rotating radical. We also show that if the initial angular momentum of the rotating radical lies nearly parallel to a principal axis, the very narrow range of tangential velocities predicted by this model must be convoluted with a J = 0 recoil velocity distribution to achieve a good result. The model relies on measuring the kinetic energy release when the halogenated precursor is photodissociated via a repulsive excited state but does not include any adjustable parameters. Even when different conformers of the photolytic precursor are populated, weighting the prediction by a thermal conformer population gives an accurate prediction for the relative velocity vectors of the fragments from the highly rotationally excited radical intermediates.

Stable Aluminum Metal-Organic Frameworks (Al-MOFs) for Balanced CO2 and Water Selectivity.

PubMed

Li, Haiwei; Feng, Xiao; Ma, Dou; Zhang, Mengxi; Zhang, Yuanyuan; Liu, Yi; Zhang, Jinwei; Wang, Bo

2018-01-31

Three new Al-MOFs in the formation of [Al 4 (OH) 2 (OCH 3 ) 4 (OH-BDC) 3 ]·xH 2 O (BIT-72), [Al 4 (OH) 2 (OCH 3 ) 4 (CH 3 -BDC) 3 ]·xH 2 O (BIT-73) and {Al 4 (OH) 2 (OCH 3 ) 4 [(CH 3 ) 2 -BDC] 3 }·xH 2 O (BIT-74) have been synthesized by assembling Al 3+ ion with terephthalic acid ions decorated with monohydroxyl, monomethyl or dimethyl groups, respectively. All of these three MOFs exhibit high stability in boiling water and acidic conditions. Among them, BIT-72 shows the highest surface area of 1618 m 2 ·g -1 and IAST CO 2 /N 2 selectivity of 48, while BIT-73 and BIT-74 present moderate IAST CO 2 /N 2 selectivity and much lower H 2 O capacity below P/P 0 = 0.3. The high CO 2 /N 2 selectivity together with alleviative H 2 O sorption at low water relative pressure may provide promising potential in postcombustion CO 2 capture.

Non-photochemical production of singlet oxygen via activation of persulfate by carbon nanotubes.

PubMed

Cheng, Xin; Guo, Hongguang; Zhang, Yongli; Wu, Xiao; Liu, Yang

2017-04-15

The reaction between persulfate (PS) and carbon nanotubes (CNTs) for the degradation of 2,4-dichlorophenol (2,4-DCP) was investigated. It was demonstrated that CNTs could efficiently activate PS for the degradation of 2,4-DCP. Results suggested that the neither hydroxyl radical (OH) nor sulfate radical (SO 4 - ) was produced therein. For the first time, the generation of singlet oxygen ( 1 O 2 ) was proved by several methods including electron paramagnetic resonance spectrometry (EPR) and liquid chromatography mass spectrometry measurements. Moreover, the generation of the superoxide radical as a precursor of the singlet oxygen was also confirmed by using certain scavengers and EPR measurement, in which the presence of molecular oxygen was not required as a precursor of 1 O 2 . The efficient generation of 1 O 2 using the PS/CNTs system without any light irradiation can be employed for the selective oxidation of aqueous organic compounds under neutral conditions with the mineralization and toxicity evaluated. A kinetic model was developed to theoretically evaluate the adsorption and oxidation of 2,4-DCP on the CNTs. Accordingly, a catalytic mechanism was proposed involving the formation of a dioxirane intermediate between PS and CNTs, and the subsequent decomposition of this intermediate into 1 O 2 . Copyright © 2017 Elsevier Ltd. All rights reserved.

Radical routes to interstellar glycolaldehyde. The possibility of stereoselectivity in gas-phase polymerization reactions involving CH(2)O and ˙CH(2)OH.

PubMed

Wang, Tianfang; Bowie, John H

2010-10-21

A previous report that the interstellar molecule glycolaldehyde (HOCH(2)CHO) can be made from hydroxymethylene (HOCH:) and formaldehyde has been revisited at the CCSD(T)/6-311++G(3df,2p)//MP2/6-311++G(3df,2p) level of theory. This reaction competes with the formation of acetic acid and methylformate, molecules which have also been detected in interstellar clouds. Other possible modes of formation of glycolaldehyde by radical/radical reactions have been shown to be viable theoretically as follows: HO˙+˙CH2CHO -->HOCH2CHO [ΔG(Γ)(298K)=-303kJ mol⁻¹] HOCH2˙+˙CHO-->HOCH2CHO (-259kJ mol⁻¹). The species in these two processes are known interstellar molecules. Key radicals ˙CH(2)CHO and ˙CH(2)OH in these sequences have been shown to be stable for the microsecond duration of neutralization/reionization experiments in the dual collision cells of a VG ZAB 2HF mass spectrometer. The polymerization reaction HOCH(2)CH˙OH + nCH(2)O → HOCH(2)[CH(OH)](n)˙CHOH (n = 1 to 3) has been studied theoretically and shown to be energetically feasible, as is the cyclization reaction of HOCH(2)[(CH(2)OH)(4)]˙CHOH (in the presence of one molecule of water at the reacting centre) to form glucose. The probability of such a reaction sequence is small even if polymerization were to occur in interstellar ice containing a significant concentration of CH(2)O. The large number of stereoisomers produced by such a reaction sequence makes the formation of a particular sugar, again for example glucose, an inefficient synthesis. The possibility of stereoselectivity occurring during the polymerization was investigated for two diastereoisomers of HOCH(2)[(CHOH)](2)˙CHOH. No significant difference was found in the transition state energies for addition of CH(2)O to these two diastereoisomers, but a barrier difference of 12 kJ mol(-1) was found for the H transfer reactions ˙OCH(2)[(CHOH)](2)CH(2)OH → HOCH(2)[(CHOH)(2)˙CHOH of the two diastereoisomers.

Helium Nanodroplet Isolation of the Cyclobutyl, 1-Methylallyl, and Allylcarbinyl Radicals: Infrared Spectroscopy and Ab Initio Computations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Alaina R.; Franke, Peter R.; Douberly, Gary E.

Gas-phase cyclobutyl radical (*C 4H 7) is produced via pyrolysis of cyclobutylmethyl nitrite (C 4H 7(CH 2)ONO). Other (C 4H 7)-C-center dot radicals, such as 1-methylallyl and allylcarbinyl, are similarly produced from nitrite precursors. Nascent radicals are promptly solvated in liquid He droplets, allowing for the acquisition of infrared spectra in the CH stretching region. For the cyclobutyl and 1-methylallyl radicals, anharmonic frequencies are predicted by VPT2+K simulations based upon a hybrid CCSD(T) force field with quadratic (cubic and quartic) force constants computed using the ANO1 (ANO0) basis set. A density functional theoretical method is used to compute the forcemore » field for the allylcarbinyl radical. For all *C 4H 7 radicals, resonance polyads in the 2800-3000 cm -1 region appear as a result of anharmonic coupling between the CH stretching fundamentals and CH, bend overtones and combinations. Upon pyrolysis of the cyclobutylmethyl nitrite precursor to produce the cyclobutyl radical, an approximately 2-fold increase in the source temperature leads to the appearance of spectral signatures that can be assigned to 1-methylallyl and 1,3-butadiene. On the basis of a previously reported *C 4H 7 potential energy surface, this result is interpreted as evidence for the unimolecular decomposition of the cyclobutyl radical via ring opening, prior to it being captured by helium droplets. On the *C 4H 7 potential surface, 1,3-butadiene is formed from cyclobutyl ring opening and H atom loss, and the 1-methylallyl radical is the most energetically stable intermediate along the decomposition pathway. Here, the allylcarbinyl radical is a higher-energy (C 4H 7)-C-center dot intermediate along the ring-opening path, and the spectral signatures of this radical are not observed under the same conditions that produce 1-methylallyl and 1,3-butadiene from the unimolecular decomposition of cyclobutyl.« less

Helium Nanodroplet Isolation of the Cyclobutyl, 1-Methylallyl, and Allylcarbinyl Radicals: Infrared Spectroscopy and Ab Initio Computations

DOE PAGES

Brown, Alaina R.; Franke, Peter R.; Douberly, Gary E.

2017-09-22

Gas-phase cyclobutyl radical (*C 4H 7) is produced via pyrolysis of cyclobutylmethyl nitrite (C 4H 7(CH 2)ONO). Other (C 4H 7)-C-center dot radicals, such as 1-methylallyl and allylcarbinyl, are similarly produced from nitrite precursors. Nascent radicals are promptly solvated in liquid He droplets, allowing for the acquisition of infrared spectra in the CH stretching region. For the cyclobutyl and 1-methylallyl radicals, anharmonic frequencies are predicted by VPT2+K simulations based upon a hybrid CCSD(T) force field with quadratic (cubic and quartic) force constants computed using the ANO1 (ANO0) basis set. A density functional theoretical method is used to compute the forcemore » field for the allylcarbinyl radical. For all *C 4H 7 radicals, resonance polyads in the 2800-3000 cm -1 region appear as a result of anharmonic coupling between the CH stretching fundamentals and CH, bend overtones and combinations. Upon pyrolysis of the cyclobutylmethyl nitrite precursor to produce the cyclobutyl radical, an approximately 2-fold increase in the source temperature leads to the appearance of spectral signatures that can be assigned to 1-methylallyl and 1,3-butadiene. On the basis of a previously reported *C 4H 7 potential energy surface, this result is interpreted as evidence for the unimolecular decomposition of the cyclobutyl radical via ring opening, prior to it being captured by helium droplets. On the *C 4H 7 potential surface, 1,3-butadiene is formed from cyclobutyl ring opening and H atom loss, and the 1-methylallyl radical is the most energetically stable intermediate along the decomposition pathway. Here, the allylcarbinyl radical is a higher-energy (C 4H 7)-C-center dot intermediate along the ring-opening path, and the spectral signatures of this radical are not observed under the same conditions that produce 1-methylallyl and 1,3-butadiene from the unimolecular decomposition of cyclobutyl.« less

Formation mechanism of glycolaldehyde and ethylene glycol in astrophysical ices from HCO• and •CH2OH recombination: an experimental study

NASA Astrophysics Data System (ADS)

Butscher, T.; Duvernay, F.; Theule, P.; Danger, G.; Carissan, Y.; Hagebaum-Reignier, D.; Chiavassa, T.

2015-10-01

Among all existing complex organic molecules, glycolaldehyde HOCH2CHO and ethylene glycol HOCH2CH2OH are two of the largest detected molecules in the interstellar medium. We investigate both experimentally and theoretically the low-temperature reaction pathways leading to glycolaldehyde and ethylene glycol in interstellar grains. Using infrared spectroscopy, mass spectroscopy and quantum calculations, we investigate formation pathways of glycolaldehyde and ethylene glycol based on HCO• and •CH2OH radical-radical recombinations. We also show that •CH2OH is the main intermediate radical species in the H2CO to CH3OH hydrogenation processes. We then discuss astrophysical implications of the chemical pathway we propose on the observed gas-phase ethylene glycol and glycolaldehyde.

Conformational and spectroscopic study of xanthogen ethyl formates, ROC(S)SC(O)OCH₂CH₃. Isolation of CH₃CH₂OC(O)SH.

PubMed

Juncal, Luciana C; Cozzarín, Melina V; Romano, Rosana M

2015-03-15

ROC(S)SC(O)OCH2CH3, with R=CH3-, (CH3)2CH- and CH3(CH2)2-, were obtained through the reaction between potassium xanthate salts, ROC(S)SK, and ethyl chloroformate, ClC(O)OCH2CH3. The liquid compounds were identified and characterized by (1)H and (13)C NMR and mass spectrometry. The conformations adopted by the molecules were studied by DFT methods. 6 conformers were theoretically predicted for R=CH3- and (CH3)2CH-, while the conformational flexibility of the n-propyl substituent increases the total number of feasible rotamers to 21. For the three molecules, the conformers can be associated in 3 groups, being the most stable the AS forms - the C=S double bond anti (A) with respect to the C-S single bond and the S-C single bond syn (S) with respect to the C=O double bond - followed by AA and SS conformers. The vibrational spectra were interpreted in terms of the predicted conformational equilibrium, presenting the ν(C=O) spectral region signals corresponding to the three groups of conformers. A moderated pre-resonance Raman enhancement of the ν(C=S) vibrational mode of CH3(CH2)2OC(S)SC(O)OCH2CH3 was detected, when the excitation radiation approaches the energy of a n→π∗ electronic transition associated with the C=S chromophore. UV-visible spectra in different solvents were measured and interpreted in terms of TD-DFT calculations. The unknown molecule CH3CH2OC(O)SH was isolated by the UV-visible photolysis of CH3OC(S)SC(O)OCH2CH3 isolated in Ar matrix, and also obtained as a side-product of the reaction between potassium xanthate salts, ROC(S)SK, and ethyl chloroformate, ClC(O)OCH2CH3. Copyright © 2014 Elsevier B.V. All rights reserved.

Atmospheric degradation of industrial fluorinated acrylates and methacrylates with Cl atoms at atmospheric pressure and 298 K

NASA Astrophysics Data System (ADS)

Rivela, Cynthia B.; Blanco, María B.; Teruel, Mariano A.

2018-04-01

The gas-phase reaction of Cl atom with 2,2,2-trifluoroethylacrylate (k1), 1,1,1,3,3,3-hexafluoroisopropylacrylate (k2), 2,2,2-trifluoroethylmethacrylate (k3) and 1,1,1,3,3,3-hexafluoroisopropylmethacrylate (k4), have been investigated at 298 K and 1 atm using the relative method by gas chromatography coupled with flame ionization detection (GC-FID). The values obtained are (in cm3 molecule-1 s-1): k1(Cl+CH2=CHC(O)OCH2CF3) = (2.41 ± 0.57) × 10-10, k2(Cl+CH2=CHC(O)OCH(CF3)2) = (1.39 ± 0.34) × 10-10, k3(Cl+CH2=C(CH3)C(O)OCH2CF3) = (2.22 ± 0.45) × 10-10, and k4(Cl +CH2=C(CH3)C(O)OCH(CF3)2 = (2.44 ± 0.52) × 10-10. Products identification studies were performed by solid-phase microextraction (SPME) method, with on-fiber products derivatization using o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride, coupled with gas chromatography with mass spectrometry detection (GC-MS). Chloroacetone, trifluoroacetaldehyde and formaldehyde were observed as degradation products and a general mechanism is proposed. Additionally, reactivity trends and atmospheric implications are discussed. Significant ozone photochemical potentials (POCP) and acidification potentials lead to local and or regional impact of the esters under study although is expected to a have a minor impact on global warming and climate change.

Determination of 25-OCH3-PPD and the related substances by UPLC-MS/MS and their cytotoxic activity.

PubMed

Ding, Meng; Lu, Jingjing; Zhao, Chen; Zhang, Sainan; Zhao, Yuqing

2016-06-01

20(R)-25-methoxyl-dammarane-3β,12β,20-triol (25-OCH3-PPD) is a promising antitumor compound belonging to triterpenoid saponins isolated from radix notoginseng. A systematic research on the related impurities in raw material of 25-OCH3-PPD has not been conducted. In this study, three impurities obtained by HPLC-ELSD and characterized by (13)C NMR and MS were observed in the raw material of 25-OCH3-PPD. Cytotoxic activities of the related substances were also evaluated, of which impurity B with 25-OCH3-PPD showed synergistic inhibitory activity against BGC-823 with IC50 values of 8.33μM. Furthermore, a rapid and selective UPLC-MS/MS method was developed for simultaneous determination of the principal component and three related substances in the raw material of 25-OCH3-PPD. Multiple reaction monitoring scan mode was used for the quantification of 20(R)-25-OCH3-PPD and its three related substances. The four constituents were separated within 11min on a BEH C18 column (100 mm×2.1mm, 1.7μm) using a mobile phase comprising methanol and 0.03% formic acid water (82:18, v/v) at a flow rate of 0.2mL/min. The proposed UPLC-MS/MS method displayed acceptable levels of linearity, precision, repeatability, and accuracy. In addition, the proposed method was successfully applied for the establishment of a rational quality control standard for the raw material of 25-OCH3-PPD. Copyright © 2016 Elsevier B.V. All rights reserved.

Thermochemical and kinetic analysis on the reactions of O2 with products from OH addition to isobutene, 2-hydroxy-1,1-dimethylethyl, and 2-hydroxy-2-methylpropyl radicals: HO2 formation from oxidation of neopentane, Part II.

PubMed

Sun, Hongyan; Bozzelli, Joseph W; Law, Chung K

2007-06-14

Unimolecular dissociation of a neopentyl radical to isobutene and methyl radical is competitive with the neopentyl association with O2 ((3)Sigma(g)-) in thermal oxidative systems. Furthermore, both isobutene and the OH radical are important primary products from the reactions of neopentyl with O2. Consequently, the reactions of O2 with the 2-hydroxy-1,1-dimethylethyl and 2-hydroxy-2-methylpropyl radicals resulting from the OH addition to isobutene are important to understanding the oxidation of neopentane and other branched hydrocarbons. Reactions that correspond to the association of radical adducts with O2((3)Sigma(g)-) involve chemically activated peroxy intermediates, which can isomerize and react to form one of several products before stabilization. The above reaction systems were analyzed with ab initio and density functional calculations to evaluate the thermochemistry, reaction paths, and kinetics that are important in neopentyl radical oxidation. The stationary points of potential energy surfaces were analyzed based on the enthalpies calculated at the CBS-Q level. The entropies, S(degrees)298, and heat capacities, C(p)(T), (0

Thermochemistry and kinetics for 2-butanone-1-yl radical (CH2·C(═O)CH2CH3) reactions with O2.

PubMed

Sebbar, N; Bozzelli, J W; Bockhorn, H

2014-01-09

Thermochemistry of reactants, intermediates, transition state structures, and products along with kinetics on the association of CH2·C(═O)CH2CH3 (2-butanone-1-yl) with O2 and dissociation of the peroxy adduct isomers are studied. Thermochemical properties are determined using ab initio (G3MP2B3 and G3) composite methods along with density functional theory (B3LYP/6-311g(d,p)). Entropy and heat capacity contributions versus temperature are determined from structures, vibration frequencies, and internal rotor potentials. The CH2·C(═O)CH2CH3 radical + O2 association results in a chemically activated peroxy radical with 27 kcal mol(-1) excess of energy. The chemically activated adduct can react to stabilized peroxy or hydroperoxide alkyl radical adducts, further react to lactones plus hydroxyl radical, or form olefinic ketones and a hydroperoxy radical. Kinetic parameters are determined from the G3 composite methods derived thermochemical parameters, and quantum Rice-Ramsperger-Kassel (QRRK) analysis to calculate k(E) with master equation analysis to evaluate falloff in the chemically activated and dissociation reactions. One new, not previously reported, peroxy chemistry reaction is presented. It has a low barrier path and involves a concerted reaction resulting in olefin formation, H2O elimination, and an alkoxy radical.

Atmospheric chemistry of HFE-7000 (CF(3)CF (2)CF (2)OCH (3)) and 2,2,3,3,4,4,4-heptafluoro-1-butanol (CF (3)CF (2)CF (2)CH (2)OH): kinetic rate coefficients and temperature dependence of reactions with chlorine atoms.

PubMed

Díaz-de-Mera, Yolanda; Aranda, Alfonso; Bravo, Iván; Rodríguez, Diana; Rodríguez, Ana; Moreno, Elena

2008-10-01

The adverse environmental impacts of chlorinated hydrocarbons on the Earth's ozone layer have focused attention on the effort to replace these compounds by nonchlorinated substitutes with environmental acceptability. Hydrofluoroethers (HFEs) and fluorinated alcohols are currently being introduced in many applications for this purpose. Nevertheless, the presence of a great number of C-F bonds drives to atmospheric long-lived compounds with infrared absorption features. Thus, it is necessary to improve our knowledge about lifetimes and global warming potentials (GWP) for these compounds in order to get a complete evaluation of their environmental impact. Tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase. Nevertheless, Cl atoms reaction may also be important since rate constants are generally larger than those of OH. In the present work, we report the results obtained in the study of the reactions of Cl radicals with HFE-7000 (CF(3)CF(2)CF(2)OCH(3)) (1) and its isomer CF(3)CF(2)CF(2)CH(2)OH (2). Kinetic rate coefficients with Cl atoms have been measured using the discharge flow tube-mass spectrometric technique at 1 Torr of total pressure. The reactions of these chlorofluorocarbons (CFCs) substitutes have been studied under pseudo-first-order kinetic conditions in excess of the fluorinated compounds over Cl atoms. The temperature ranges were 266-333 and 298-353 K for reactions of HFE-7000 and CF(3)CF(2)CF(2)CH(2)OH, respectively. The measured room temperature rate constants were k(Cl+CF(3)CF(2)CF(2)OCH(3)) = (1.24 +/- 0.28) x 10(-13) cm(3) molecule(-1) s(-1)and k(Cl+CF(3)CF(2)CF(2)CH(2)OH) = (8.35 +/- 1.63) x 10(-13) cm(3) molecule(-1) s(-1) (errors are 2sigma + 10% to cover systematic errors). The Arrhenius expression for reaction 1 was k (1)(266-333 K) = (6.1 +/- 3.8) x 10(-13)exp[-(445 +/- 186)/T] cm(3) molecule(-1) s(-1) and k (2)(298-353 K) = (1.9 +/- 0.7) x 10(-12)exp[-(244 +/- 125)/T] cm(3) molecule(-1) s(-1) (errors are 2sigma). The reactions are reported to proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl radical. At 298 K and 1 Torr, yields on HCl of 0.95 +/- 0.38 and 0.97 +/- 0.16 (errors are 2sigma) were obtained for CF(3)CF(2)CF(2)OCH(3) and CF(3)CF(2)CF(2)CH(2)OH, respectively. The obtained kinetic rate constants are related to the previous data in the literature, showing a good agreement taking into account the error limits. Comparing the obtained results at room temperature, k (1) and k (2), HFE-7000 is significantly less reactive than its isomer C(3)F(7)CH(2)OH. A similar behavior has been reported for the reactions of other fluorinated alcohols and their isomeric fluorinated ethers with Cl atoms. Literature data, together with the results reported in this work, show that, for both fluorinated ethers and alcohols, the kinetic rate constant may be considered as not dependent on the number of -CF(2)- in the perfluorinated chain. This result may be useful since it is possible to obtain the required physicochemical properties for a given application by changing the number of -CF(2)- without changes in the atmospheric reactivity. Furthermore, lifetimes estimations for these CFCs substitutes are calculated and discussed. The average estimated Cl lifetimes are 256 and 38 years for HFE-7000 and C(3)H(7)CH(2)OH, respectively. The studied CFCs' substitutes are relatively short-lived and OH reaction constitutes their main reactive sink. The average contribution of Cl reactions to global lifetime is about 2% in both cases. Nevertheless, under local conditions as in the marine boundary layer, tau (Cl) values as low as 2.5 and 0.4 years for HFE-7000 and C(3)H(7)CH(2)OH, respectively, are expected, showing that the contribution of Cl to the atmospheric degradation of these CFCs substitutes under such conditions may constitute a relevant sink. In the case of CF(3)CF(2)CF(2)OCH(3), significant activation energy has been measured, thus the use of kinetic rate coefficient only at room temperature would result in underestimations of lifetimes and GWPs. The results obtained in this work may be helpful within the database used in the modeling studies of coastal areas. The knowledge of the atmospheric behavior and the structure-reactivity relationship discussed in this work may also contribute to the development of new environmentally acceptable chemicals. New volatile materials susceptible of emission to the troposphere should be subject to the study of their reactions with OH and Cl in the range of temperature of the troposphere. The knowledge of the temperature dependence of the kinetic rate constants, as it is now reported for the case of reactions 1 and 2, will allow more accurate lifetimes and related magnitudes like GWPs. Nevertheless, a better knowledge of the vertical Cl tropospheric distribution is still required.

Calix

PubMed

Frkanec; Visnjevac; Kojic-Prodic; Zinic

2000-02-04

Chiral calix[4]arene derivatives with four O-(N-acetyl-PhgOMe), (1), (Phg denotes R-phenylglycine), or O-(N-acetyl-LeuOMe) (2) strands have been synthesised. Both compounds exist in chloroform in stable cone conformations with a noncovalently organised cavity at the lower rim that is formed by circular interstrand amidic hydrogen bonds. Such organisation affects both the selectivity and extraction/transport properties of 1 and 2 toward metal cations. Calix[4]arene derivatives with one OCH2COPhgOMe strand (3), two OCH2COPhgOMe strands (5) and with 1,3-OMe-2,4-(O-CH2COPhgOMe) substituents (4) at the lower rim have also been prepared. For 3, a conformation stabilised by a circular hydrogen-bond arrangement is found in chloroform, while 4 exists as a time-averaged C2 conformation with two intramolecular NH ...OCH3 hydrogen bonds. Compound 5 has a unique hydrogen-bonding motif in solution and in the solid state with two three-centred NH-.. O and two OH...O hydrogen bonds at the lower rim. This motif keeps 5 in the flattened cone conformation in chloroform. The X-ray structure analysis of 1 revealed a molecular structure with C2 symmetry; this structure is organised in infinite chains by intra- and intermolecular H bonds. The solid-state and solution structures of the [1-Na]ClO4 complex are identical, C4 symmetric cone conformations.

Photosensitized degradation of acetaminophen in natural organic matter solutions: The role of triplet states and oxygen.

PubMed

Li, Yanyun; Pan, Yanheng; Lian, Lushi; Yan, Shuwen; Song, Weihua; Yang, Xin

2017-02-01

The photolysis of acetaminophen, a widely used pharmaceutical, in simulated natural organic matter solutions was investigated. The triplet states of natural organic matter ( 3 NOM*) were found to play the dominant role in its photodegradation, while the contributions from hydroxyl radicals and singlet oxygen were negligible. Dissolved oxygen (DO) plays a dual role. From anaerobic to microaerobic (0.5 mg/L DO) conditions, the degradation rate of acetaminophen increased by 4-fold. That suggests the involvement of DO in reactions with the degradation intermediates. With increasing oxygen levels to saturated conditions (26 mg/L DO), the degradation rate became slower, mainly due to DO's quenching effect on 3 NOM*. Superoxide radical (O 2 - ) did not react with acetaminophen directly, but possibly quenched the intermediates to reverse the degradation process. The main photochemical pathways were shown to involve phenoxyl radical and N-radical cations, finally yielding hydroxylated derivatives, dimers and nitrosophenol. A reaction mechanism involving 3 NOM*, oxygen and O 2 - is proposed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Peroxidase-type reactions suggest a heterolytic/nucleophilic O–O joining mechanism in the heme-dependent chlorite dismutase†

PubMed Central

Mayfield, Jeffrey A.; Blanc, Béatrice; Rodgers, Kenton R.; Lukat-Rodgers, Gudrun S.; DuBois, Jennifer L.

2015-01-01

Heme-containing chlorite dismutases (Clds) catalyze a highly unusual O–O bond forming reaction. The O–O cleaving reactions of hydrogen peroxide and peracetic acid (PAA) with the Cld from Dechloromonas aromatica (DaCld) were studied to better understand the Cl–O cleavage of the natural substrate and subsequent O–O bond formation. While reactions with H2O2 resulted in slow destruction of the heme, at acidic pH, heterolytic cleavage of the O–O bond of PAA cleanly yielded the ferryl porphyrin cation radical (Compound I). At alkaline pH, the reaction proceeds more rapidly and the first observed intermediate is a ferryl heme. Freezequench EPR confirmed that the latter has an uncoupled protein-based radical, indicating that Compound I is the first intermediate formed at all pH values and that radical migration is faster at alkaline pH. These results suggest by analogy that two-electron Cl–O bond cleavage to yield a ferryl-porphyrin cation radical is the most likely initial step in O–O bond formation from chlorite. PMID:24001266

Experimental and theoretical study of 2,6-difluorophenylnitrene, its radical cation, and their rearrangement products in argon matrices.

PubMed

Carra, Claudio; Nussbaum, Rafael; Bally, Thomas

2006-06-12

2,6-Difluorophenylnitrene was reinvestigated both experimentally, in Ar matrices at 10 K, and computationally, by DFT and CASSCF/CASPT2 calculations. Almost-pure samples of both neutral rearrangement products (the bicyclic azirine and the cyclic ketenimine) of a phenylnitrene were prepared and characterized for the first time. These samples were then subjected to X-irradiation in the presence of CH2Cl2 as an electron scavenger, which led to ionization of the neutral intermediates. Thereby, it was shown that only the phenylnitrene and the cyclic ketenimine yield stable radical cations, whereas the bicyclic azirine decays to both of these compounds on ionization. The cyclic ketenimine yields a novel aromatic azatropylium-type radical cation. The electronic structure of the title compound is discussed in detail, and its relation to those of the iso-pi-electronic benzyl radical and phenylcarbene is traced.

Properties of Intermediates in the Catalytic Cycle of Oxalate Oxidoreductase and Its Suicide Inactivation by Pyruvate

PubMed Central

2017-01-01

Oxalate:ferredoxin oxidoreductase (OOR) is an unusual member of the thiamine pyrophosphate (TPP)-dependent 2-oxoacid:ferredoxin oxidoreductase (OFOR) family in that it catalyzes the coenzyme A (CoA)-independent conversion of oxalate into 2 equivalents of carbon dioxide. This reaction is surprising because binding of CoA to the acyl-TPP intermediate of other OFORs results in formation of a CoA ester, and in the case of pyruvate:ferredoxin oxidoreductase (PFOR), CoA binding generates the central metabolic intermediate acetyl-CoA and promotes a 105-fold acceleration of the rate of electron transfer. Here we describe kinetic, spectroscopic, and computational results to show that CoA has no effect on catalysis by OOR and describe the chemical rationale for why this cofactor is unnecessary in this enzymatic transformation. Our results demonstrate that, like PFOR, OOR binds pyruvate and catalyzes decarboxylation to form the same hydroxyethylidine–TPP (HE–TPP) intermediate and one-electron transfer to generate the HE–TPP radical. However, in OOR, this intermediate remains stranded at the active site as a covalent inhibitor. These and other results indicate that, like other OFOR family members, OOR generates an oxalate-derived adduct with TPP (oxalyl-TPP) that undergoes decarboxylation and one-electron transfer to form a radical intermediate remaining bound to TPP (dihydroxymethylidene–TPP). However, unlike in PFOR, where CoA binding drives formation of the product, in OOR, proton transfer and a conformational change in the “switch loop” alter the redox potential of the radical intermediate sufficiently to promote the transfer of an electron into the iron–sulfur cluster network, leading directly to a second decarboxylation and completing the catalytic cycle. PMID:28514140

Neutral and ionic platinum compounds containing a cyclometallated chiral primary amine: synthesis, antitumor activity, DNA interaction and topoisomerase I-cathepsin B inhibition.

PubMed

Albert, Joan; Bosque, Ramon; Crespo, Margarita; Granell, Jaume; López, Concepción; Martín, Raquel; González, Asensio; Jayaraman, Anusha; Quirante, Josefina; Calvis, Carme; Badía, Josefa; Baldomà, Laura; Font-Bardia, Mercè; Cascante, Marta; Messeguer, Ramon

2015-08-14

The synthesis and preliminary biological evaluation of neutral and cationic platinum derivatives of chiral 1-(1-naphthyl)ethylamine are reported, namely cycloplatinated neutral complexes [PtCl{(R or S)-NH(2)CH(CH(3))C(10)H(6)}(L)] [L = SOMe(2) ( 1-R or 1-S ), L = PPh(3) (2-R or 2-S), L = P(4-FC(6)H(4))(3) (3-R), L = P(CH(2))(3)N(3)(CH(2))(3) (4-R)], cycloplatinated cationic complexes [Pt{(R)-NH(2)CH(CH(3))C(10)H(6)}{L}]Cl [L = Ph(2)PCH(2)CH(2)PPh(2) (5-R), L = (C(6)F(5))(2)PCH(2)CH(2)P(C(6)F(5))(2) (6-R)] and the Pt(ii) coordination compound trans-[PtCl(2){(R)-NH(2)CH(CH(3))C(10)H(6)}(2)] (7-R). The X-ray molecular structure of 7-R is reported. The cytotoxic activity against a panel of human adenocarcinoma cell lines (A-549 lung, MDA-MB-231 and MCF-7 breast, and HCT-116 colon), cell cycle arrest and apoptosis, DNA interaction, topoisomerase I and cathepsin B inhibition, and Pt cell uptake of the studied compounds are presented. Remarkable cytotoxicity was observed for most of the synthesized Pt(ii) compounds regardless of (i) the absolute configuration R or S, and (ii) the coordinated/cyclometallated (neutral or cationic) nature of the complexes. The most potent compound 2-R (IC(50) = 270 nM) showed a 148-fold increase in potency with regard to cisplatin in HCT-116 colon cancer cells. Preliminary biological results point out to different biomolecular targets for the investigated compounds. Neutral cyclometallated complexes 1-R and 2-R, modify the DNA migration as cisplatin, cationic platinacycle 5-R was able to inhibit topoisomerase I-promoted DNA supercoiling, and Pt(ii) coordination compound 7-R turned out to be the most potent inhibitor of cathepsin B. Induction of G-1 phase ( 2-R and 5-R ), and S and G-2 phases (6-R) arrests are related to the antiproliferative activity of some representative compounds upon A-549 cells. Induction of apoptosis is also observed for 2-R and 6-R.

Reassessment of the risk factors for biochemical recurrence in D'Amico intermediate-risk prostate cancer treated using radical prostatectomy.

PubMed

Narita, Shintaro; Mitsuzuka, Koji; Tsuchiya, Norihiko; Koie, Takuya; Kawamura, Sadafumi; Ohyama, Chikara; Tochigi, Tatsuo; Yamaguchi, Takuhiro; Arai, Yoichi; Habuchi, Tomonori

2015-11-01

To assess the risk factors for biochemical recurrence in D'Amico intermediate-risk prostate cancer patients treated using radical prostatectomy. We retrospectively reviewed the medical records of 1268 men with prostate cancer treated using radical prostatectomy without neoadjuvant therapy. The association between various risk factors and biochemical recurrence was then statistically evaluated. The Kaplan-Meier method, log-rank tests and Cox proportional hazards models were used for statistical analysis. In the intermediate-risk group, 96 patients (14.5%) experienced biochemical recurrence during a median follow up of 41 months. In the intermediate-risk group, preoperative prostate-specific antigen level, prostate volume and prostate-specific antigen density were significant preoperative risk factors for biochemical recurrence, whereas other factors including age, primary Gleason 4, clinical stage >T2 and percentage of positive biopsies were not. In multivariate analysis, higher preoperative prostate-specific antigen level and density, and a smaller prostate volume were independent risk factors for biochemical recurrence in the intermediate-risk group. Biochemical recurrence-free survival of patients in the intermediate-risk group with a higher prostate-specific antigen level and density (≥15 ng/mL, ≥0.6 ng/mL/cm(3), respectively), and lower prostate volume (≤10 mL) was comparable with that of high-risk group individuals (P = 0.632, 0.494 and 0.961, respectively). Preoperative prostate-specific antigen, prostate volume and prostate-specific antigen density are significant risk factors for biochemical recurrence in D'Amico intermediate-risk prostate cancer patients treated using radical prostatectomy. Using these variables, a subset of the intermediate-risk patients can be identified as having equivalent outcomes to high-risk patients. © 2015 The Japanese Urological Association.

Formation of OH radicals in the gas phase ozonolysis of alkenes: the unexpected role of carbonyl oxides

NASA Astrophysics Data System (ADS)

Gutbrod, Roland; Schindler, Ralph N.; Kraka, Elfi; Cremer, Dieter

1996-04-01

According to CCSD(T)/TZ + 2P calculations, the decomposition of carbonyl oxide, H 2COO to HCO and OH radicals is unlikely in view of an activation enthalpy ΔΔHf0(298) of 31 kcal/mol. However, for dimethylcarbonyl oxide there is a low energy rearrangement mode ( ΔΔHf0(298): 14.4 kca/mol) which involves a H atom of ghe methyl group and which leads to a hydroperoxy methyl ethene intermediate, which in turn can decompose to OH and CH 2COCH 3 radicals ( ΔΔHf0(298): 23 kcal/mol). In the gas phase ozonolysis of alkyl substituted alkenes the formation of OH radicals is the most likely process. This has important consequences for the chemistry of the atmosphere.

Oxidation of aqueous polyselenide solutions. A mechanistic pulse radiolysis study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldbach, A.; Saboungi, M.L.; Johnson, J.A.

2000-05-04

The oxidation of aqueous polyselenide solutions was studied by pulse radiolysis in the presence of N{sub 2}O at pH 12.3; the hydroxyl radical OH was the predominant oxidant, while hydrogen selenide anions HSe{sup {minus}} and triselenide dianions Se{sub 3}{sup 2{minus}} 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{sup {minus}}, i.e., HSe{sub 2}{sup 2{minus}} and H{sub 2}Se{sub 2}{sup {minus}}, and a fairly long-lived intermediate that was identified as the diselenide radical anion Se{sub 2}{supmore » {minus}}. These radicals recombine to give eventually the tetraselenide dianion, Se{sub 4}{sup 2{minus}}.« less

Monitoring the Softening of Aluminum-Alloy V95ochT2 Shapes by a Nondestructive Method

NASA Astrophysics Data System (ADS)

Shigapov, A. I.; Klimova, T. A.; Il'inkova, T. A.

2015-09-01

Correlation relations between the strength and the electrical conductivity of aluminum shapes are determined. The properties of alloy V95ochT2 are studied after different temperature-and-time actions. It is shown that the "dark spots" appearing on the surface of such shapes can be evaluated by a nondestructive eddy-current method.

Synthesis of 2-Aryl- and 2-Vinylpyrrolidines via Copper-Catalyzed Coupling of Styrenes and Dienes with Potassium β-Aminoethyl Trifluoroborates.

PubMed

Um, Chanchamnan; Chemler, Sherry R

2016-05-20

2-Arylpyrrolidines occur frequently in bioactive compounds, and thus, methods to access them from readily available reagents are valuable. We report a copper-catalyzed intermolecular carboamination of vinylarenes with potassium N-carbamoyl-β-aminoethyltrifluoroborates. The reaction occurs with terminal, 1,2-disubstituted, and 1,1-disubstituted vinylarenes bearing a number of functional groups. 1,3-Dienes are also good substrates, and their reactions give 2-vinylpyrrolidines. Radical clock mechanistic experiments are consistent with the presence of carbon radical intermediates and do not support participation of carbocations.

VAPOR PRESSURES, LIQUID MOLAR VOLUMES, VAPOR NON- IDEALITIES, AND CRITICAL PROPERTIES OF SOME FLUORINATED ETHERS: CF3OCF2OCF3, CF3OCF2 CF2H, c-CF2CF2CF2O, CF3OCF2H, AND CF3OCH3; AND OF CCl3F AND CF2ClH

EPA Science Inventory

Vapor pressures, compressibilities, expansivities, and molar volumes of the liquid phase have been measured between room temperature and the critical temperature for a series of fluorinated ethers: CF3OCF2OCF3, CF3OCF2CF2H, c-CF2CF2CF2O, CF3OCF2H, and CF3OCH3. Vapor-phase non-ide...

C-H activations at iridium(I) square-planar complexes promoted by a fifth ligand.

PubMed

Martín, Marta; Torres, Olga; Oñate, Enrique; Sola, Eduardo; Oro, Luis A

2005-12-28

In the presence of ligands such as acetonitrile, ethylene, or propylene, the Ir(I) complex [Ir(1,2,5,6-eta-C8H12)(NCMe)(PMe3)]BF4 (1) transforms into the Ir(III) derivatives [Ir(1-kappa-4,5,6-eta-C8H12)(NCMe)(L)(PMe3)]BF4 (L = NCMe, 2; eta2-C2H4, 3; eta2-C3H6, 4), respectively, through a sequence of C-H oxidative addition and insertion elementary steps. The rate of this transformation depends on the nature of L and, in the case of NCMe, the pseudo-first-order rate constants display a dependence upon ligand concentration suggesting the formation of five-coordinate reaction intermediates. A similar reaction between 1 and vinyl acetate affords the Ir(III) complex [Ir(1-kappa-4,5,6-eta-C8H12){kappa-O-eta2-OC(Me)OC2H3}(PMe3)]BF4 (7) via the isolable five-coordinate Ir(I) compound [Ir(1,2,5,6-eta-C8H12){kappa-O-eta2-OC(Me)OC2H3}(PMe3)]BF4 (6). DFT (B3LYP) calculations in model complexes show that reactions initiated by acetonitrile or ethylene five-coordinate adducts involve C-H oxidative addition transition states of lower energy than that found in the absence of these ligands. Key species in these ligand-assisted transformations are the distorted (nonsquare-planar) intermediates preceding the intramolecular C-H oxidative addition step, which are generated after release of one cyclooctadiene double bond from the five-coordinate species. The feasibility of this mechanism is also investigated for complexes [IrCl(L)(PiPr3)2] (L = eta2-C2H4, 27; eta2-C3H6, 28). In the presence of NCMe, these complexes afford the C-H activation products [IrClH(CH=CHR)(NCMe)(PiPr3)2] (R = H, 29; Me, 30) via the common cyclometalated intermediate [IrClH{kappa-P,C-P(iPr)2CH(CH3)CH2}(NCMe)(PiPr3)] (31). The most effective C-H oxidative addition mechanism seems to involve three-coordinate intermediates generated by photochemical release of the alkene ligand. However, in the absence of light, the reaction rates display dependences upon NCMe concentration again indicating the intermediacy of five-coordinate acetonitrile adducts.

The CRDS method application for study of the gas-phase processes in the hot CVD diamond thin film.

NASA Astrophysics Data System (ADS)

Buzaianumakarov, Vladimir; Hidalgo, Arturo; Morell, Gerardo; Weiner, Brad; Buzaianu, Madalina

2006-03-01

For detailed analysis of problem related to the hot CVD carbon-containing nano-material growing, we have to detect different intermediate species forming during the growing process as well as investigate dependences of concentrations of these species on different experimental parameters (concentrations of the CJH4, H2S stable chemical compounds and distance from the filament system to the substrate surface). In the present study, the HS and CS radicals were detected using the Cavity Ring Down Spectroscopic (CRDS) method in the hot CVD diamond thin film for the CH4(0.4 %) + H2 mixture doped by H2S (400 ppm). The absolute absorption density spectra of the HS and CS radicals were obtained as a function of different experimental parameters. This study proofs that the HS and CS radicals are an intermediate, which forms during the hot filament CVD process. The kinetics approach was developed for detailed analysis of the experimental data obtained. The kinetics scheme includes homogenous and heterogenous processes as well as processes of the chemical species transport in the CVD chamber.

Ground and Excited-Electronic-State Dissociations of Hydrogen-Rich and Hydrogen-Deficient Tyrosine Peptide Cation Radicals

NASA Astrophysics Data System (ADS)

Viglino, Emilie; Lai, Cheuk Kuen; Mu, Xiaoyan; Chu, Ivan K.; Tureček, František

2016-09-01

We report a comprehensive study of collision-induced dissociation (CID) and near-UV photodissociation (UVPD) of a series of tyrosine-containing peptide cation radicals of the hydrogen-rich and hydrogen-deficient types. Stable, long-lived, hydrogen-rich peptide cation radicals, such as [AAAYR + 2H]+● and several of its sequence and homology variants, were generated by electron transfer dissociation (ETD) of peptide-crown-ether complexes, and their CID-MS3 dissociations were found to be dramatically different from those upon ETD of the respective peptide dications. All of the hydrogen-rich peptide cation radicals contained major (77%-94%) fractions of species having radical chromophores created by ETD that underwent photodissociation at 355 nm. Analysis of the CID and UVPD spectra pointed to arginine guanidinium radicals as the major components of the hydrogen-rich peptide cation radical population. Hydrogen-deficient peptide cation radicals were generated by intramolecular electron transfer in CuII(2,2 ':6 ',2 ″-terpyridine) complexes and shown to contain chromophores absorbing at 355 nm and undergoing photodissociation. The CID and UVPD spectra showed major differences in fragmentation for [AAAYR]+● that diminished as the Tyr residue was moved along the peptide chain. UVPD was found to be superior to CID in localizing Cα-radical positions in peptide cation radical intermediates.

Hydrolysis and coordination behavior of ferrocenyl-phosphonodithiolate: Synthesis and structure of Cu 4[FcP(OCH 3)( μ-S)( μ3-S)] 4 [Fc = Fe( η5-C 5H 4)( η5-C 5H 5)

NASA Astrophysics Data System (ADS)

Liu, Shu-Lei; Wang, Xi-Ying; Duan, Taike; Leung, Wa-Hung; Zhang, Qian-Feng

2010-02-01

Treatment of the dimeric [FcP(S)( μ-S)] 2 [Fc = Fe( η5-C 5H 4)( η5-C 5H 5)] with the organic base Et 3N in methylene chloride solution resulted in the isolation of a multi-component compound [Et 3NH] 2[(FcPO 2S) 2CH 2][FcPS(OH) 2] 2·CH 2Cl 2 ( 1·CH 2Cl 2). The formation of the [(FcPO 2S) 2CH 2] 2- anion was due to the dechlorination of methylene chloride, it consists of two [FcPO 2S] 2- units bridging by a methylene group. Reaction of Na[FcP(OCH 3)S 2] with equal equivalent of [Cu(MeCN) 4][ClO 4] in methanol afforded a sole tetranuclear copper(I) complex Cu 4[FcP(OCH 3)( μ-S)( μ3-S)] 4 ( 2). The neutral complex 2 consists of a crystallographically centrosymmetric tetramer containing four CuS 3 arrays each of which has one μ-sulfur and two μ3-sulfur bridges.

25-OCH3-PPD induces the apoptosis of activated t-HSC/Cl-6 cells via c-FLIP-mediated NF-κB activation.

PubMed

Wu, Yan-ling; Wan, Ying; Jin, Xue-Jun; OuYang, Bing-Qing; Bai, Ting; Zhao, Yu-Qing; Nan, Ji-Xing

2011-11-15

25-OCH(3)-PPD is a dammarane-type triterpene sapogenin isolated from the roots, leaves and seeds of Panax notoginseng, which has shown anti-tumor effects in several human cancer lines. In this study, we evaluated the effects of 25-OCH(3)-PPD on apoptosis of activated t-HSC/Cl-6 cells induced by tumor necrosis factor-α (TNF-α). The inhibitory effects of eleven compounds isolated from Panax ginseng and P. notoginseng were detected in activated t-HSC/Cl-6 cells. 25-OCH(3)-PPD produced a significant inhibitory effect on activated t-HSC/Cl-6 cells. However, 25-OCH(3)-PPD showed almost no effect on the cell viability of Chang liver cells, a type of normal human hepatic cell line. Therefore, we aimed to determine the anti-fibrotic potential of 25-OCH(3)-PPD and to characterize the signal transduction pathways involved in activated HSCs. 25-OCH(3)-PPD decreased the fibrosis markers, including α-smooth muscle actin (α-SMA), transforming growth factor β-1 (TGF-β1) and tissue inhibitors of metalloproteinases-1 (TIMP-1). 25-OCH(3)-PPD elevated the level of cellular GSH in activated HSCs, which demonstrated that 25-OCH(3)-PPD might inhibit HSC activation by its antioxidant capacity. Further analyses revealed that 25-OCH(3)-PPD increased the levels of cleaved caspase-3, decreased the ratio of Bcl-2/Bax and the expression of survivin via c-FLIP-mediated NF-κB activation and shed light on the regulation of apoptosis. Therefore, 25-OCH(3)-PPD may prove to be an excellent candidate agent for the therapy of hepatic fibrosis. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

A kinetic study of enhancing effect by phenolic compounds on the hydroxyl radical generation during ozonation.

PubMed

Han, Y H; Ichikawa, K; Utsumi, H

2004-01-01

Ozone decomposition in aqueous solution proceeds through a radical type chain mechanism. These reactions involve the very reactive and catalytic intermediates O2- radical, OH radical, HO2 radical, OH-, H2O2, etc. OH radical is proposed as an important factor in the ozonation of water among them. In the present study, the enhancing effects of several phenolic compounds; phenol, 2-, 3-, 4-monochloro, 2,4-dichloro, 2,4,6-trichlorophenol on OH radical generation were mathematically evaluated using the electron spin resonance (ESR)/spin-trapping technique. OH radical was trapped with a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a stable adduct, DMPO-OH. The initial velocities of DMPO-OH generation in ozonated water containing phenolic compounds were quantitatively measured using a combined system of ESR spectroscopy with stopped-flow apparatus, which was controlled by homemade software. The initial velocities of DMPO-OH generation increased as a function of the ozone concentration. The relation among ozone concentration, amount of phenolic compounds and the initial velocity (v0) of DMPO-OH generation was mathematically analyzed and the following equation was obtained, v0 (10(-6) M/s) = (A' x [PhOHs (10(-9) M)] + 0.0005) exp (60 x [ozone (10(-9) M)]). The equation fitted very well with the experimental results, and the correlation coefficient was larger than 0.98.

Formation of singlet oxygen by decomposition of protein hydroperoxide in photosystem II.

PubMed

Pathak, Vinay; Prasad, Ankush; Pospíšil, Pavel

2017-01-01

Singlet oxygen (1O2) is formed by triplet-triplet energy transfer from triplet chlorophyll to O2 via Type II photosensitization reaction in photosystem II (PSII). Formation of triplet chlorophyll is associated with the change in spin state of the excited electron and recombination of triplet radical pair in the PSII antenna complex and reaction center, respectively. Here, we have provided evidence for the formation of 1O2 by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex. Protein hydroperoxide is formed by protein oxidation initiated by highly oxidizing chlorophyll cation radical and hydroxyl radical formed by Type I photosensitization reaction. Under highly oxidizing conditions, protein hydroperoxide is oxidized to protein peroxyl radical which either cyclizes to dioxetane or recombines with another protein peroxyl radical to tetroxide. These highly unstable intermediates decompose to triplet carbonyls which transfer energy to O2 forming 1O2. Data presented in this study show for the first time that 1O2 is formed by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex.

Formation of singlet oxygen by decomposition of protein hydroperoxide in photosystem II

PubMed Central

Pathak, Vinay; Prasad, Ankush

2017-01-01

Singlet oxygen (1O2) is formed by triplet-triplet energy transfer from triplet chlorophyll to O2 via Type II photosensitization reaction in photosystem II (PSII). Formation of triplet chlorophyll is associated with the change in spin state of the excited electron and recombination of triplet radical pair in the PSII antenna complex and reaction center, respectively. Here, we have provided evidence for the formation of 1O2 by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex. Protein hydroperoxide is formed by protein oxidation initiated by highly oxidizing chlorophyll cation radical and hydroxyl radical formed by Type I photosensitization reaction. Under highly oxidizing conditions, protein hydroperoxide is oxidized to protein peroxyl radical which either cyclizes to dioxetane or recombines with another protein peroxyl radical to tetroxide. These highly unstable intermediates decompose to triplet carbonyls which transfer energy to O2 forming 1O2. Data presented in this study show for the first time that 1O2 is formed by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex. PMID:28732060

Specific Function of the Met-Tyr-Trp Adduct Radical and Residues Arg-418 and Asp-137 in the Atypical Catalase Reaction of Catalase-Peroxidase KatG*

PubMed Central

Zhao, Xiangbo; Khajo, Abdelahad; Jarrett, Sanchez; Suarez, Javier; Levitsky, Yan; Burger, Richard M.; Jarzecki, Andrzej A.; Magliozzo, Richard S.

2012-01-01

Catalase activity of the dual-function heme enzyme catalase-peroxidase (KatG) depends on several structural elements, including a unique adduct formed from covalently linked side chains of three conserved amino acids (Met-255, Tyr-229, and Trp-107, Mycobacterium tuberculosis KatG numbering) (MYW). Mutagenesis, electron paramagnetic resonance, and optical stopped-flow experiments, along with calculations using density functional theory (DFT) methods revealed the basis of the requirement for a radical on the MYW-adduct, for oxyferrous heme, and for conserved residues Arg-418 and Asp-137 in the rapid catalase reaction. The participation of an oxyferrous heme intermediate (dioxyheme) throughout the pH range of catalase activity is suggested from our finding that carbon monoxide inhibits the activity at both acidic and alkaline pH. In the presence of H2O2, the MYW-adduct radical is formed normally in KatG[D137S] but this mutant is defective in forming dioxyheme and lacks catalase activity. KatG[R418L] is also catalase deficient but exhibits normal formation of the adduct radical and dioxyheme. Both mutants exhibit a coincidence between MYW-adduct radical persistence and H2O2 consumption as a function of time, and enhanced subunit oligomerization during turnover, suggesting that the two mutations disrupting catalase turnover allow increased migration of the MYW-adduct radical to protein surface residues. DFT calculations showed that an interaction between the side chain of residue Arg-418 and Tyr-229 in the MYW-adduct radical favors reaction of the radical with the adjacent dioxyheme intermediate present throughout turnover in WT KatG. Release of molecular oxygen and regeneration of resting enzyme are thereby catalyzed in the last step of a proposed catalase reaction. PMID:22918833

Effects of potassium iodide, colchicine and dapsone on the generation of polymorphonuclear leukocyte-derived oxygen intermediates.

PubMed

Miyachi, Y; Niwa, Y

1982-08-01

The effects of potassium iodide, colchicine and dapsone on the in vitro generation of polymorphonuclear leukocyte (PMN)-derived oxygen intermediates were investigated. These three drugs have beneficial effects on those conditions in which PMNs play an important pathogenetic role. Three oxygen intermediates, superoxide anion (O2-), hydrogen peroxide (H2O2), hydroxyl radical (OH.) and chemiluminescence were included in assay studies. Dose response studies were performed with therapeutic doses of the drugs (10 microM--mM). We found that both potassium iodide and dapsone significantly suppressed the generation of oxygen intermediates, except for O2-. Colchicine decreased OH. production. Our results show tha these agents to some extent exert their anti-inflammatory effects by interfering with the PMN-dependent production of oxygen intermediates, thus conferring protection from auto-oxidative tissue injury. This may account for their clinical efficacy in many PMN-mediated dermatological diseases.

Generation of hydroxyl radicals and singlet oxygen during oxidation of rhododendrol and rhododendrol-catechol.

PubMed

Miyaji, Akimitsu; Gabe, Yu; Kohno, Masahiro; Baba, Toshihide

2017-03-01

The generation of hydroxyl radicals and singlet oxygen during the oxidation of 4-(4-hydroxyphenyl)-2-butanol (rhododendrol) and 4-(3,4-dihydroxyphenyl)-2-butanol (rhododendrol-catechol) with mushroom tyrosinase in a phosphate buffer (pH 7.4) was examined as the model for the reactive oxygen species generation via the two rhododendrol compounds in melanocytes. The reaction was performed in the presence of 5,5-dimethyl-1-pyrroline- N -oxide (DMPO) spin trap reagents for hydroxyl radical or 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TEMP), an acceptor of singlet oxygen, and their electron spin resonances were measured. An increase in the electron spin resonances signal attributable to the adduct of DMPO reacting with the hydroxyl radical and that of 4-oxo-TEMP reacting with singlet oxygen was observed during the tyrosinase-catalyzed oxidation of rhododendrol and rhododendrol-catechol, indicating the generation of hydroxyl radical and singlet oxygen. Moreover, hydroxyl radical generation was also observed in the autoxidation of rhododendrol-catechol. We show that generation of intermediates during tyrosinase-catalyzed oxidation of rhododendrol enhances oxidative stress in melanocytes.

Catalytic Antibodies for Prophylaxis/Treatment of Cyanide Poisoning

DTIC Science & Technology

1993-05-28

Other Synthetic Work As described in detail in the midterm report, the synthesis of a 2-napthyl-3-methylcyclo- hex-2-en- 1 -one derivative (E-l, Chart E...OCH 2-); 3.74 (t. 2H, J = 6.06 Hz, -OCH 2-); 3.4 (br s, 1 H, -OH); 1.96 (q, 2 H, J = 6.11 Hz, -CH2-). Synthesis of 4..[4-(3-Hydroxy- 1 -propyloxy)phenylj...2.05 (q, 2H. J = 6.0 Hz, -OH2.). Synthesis of 4-14-(3-Acetoxy- 1 .propyloxy)phenylJ-4-oxo-3-phenylbutflb-itrile. The ke’one C-3 (100 mg, 0.32 inmol) was

Isomerization and Fragmentation of Cyclohexanone in a Heated Micro-Reactor

NASA Astrophysics Data System (ADS)

Porterfield, Jessica P.; Nguyen, Thanh Lam; Baraban, Joshua H.; Buckingham, Grant; Troy, Tyler; Kostko, Oleg; Ahmed, Musahid; Stanton, John F.; Daily, John W.; Ellison, Barney

2016-06-01

he thermal decomposition of cyclohexanone (C_6H10=O) has been studied in a set of flash-pyrolysis micro-reactors. Samples of C_6H10=O were first observed to decompose at 1200 K. Short residence times of 100 μsec and dilution of samples (<0.1%) isolate unimolecular decomposition. Products were identified by tunable VUV photoionization mass spectroscopy, photoionization appearance thresholds, and complementary matrix infrared absorption spectroscopy. Thermal cracking of cyclohexanone appeared to result from a variety of competing pathways pictured to the right. Isomerization of cyclohexanone to the enol, cyclohexen-1-ol (C_6H_9OH), is followed by retro-Diels-Alder cleavage to CH_2=CH_2 and CH_2=C(OH)-CH=CH_2. Further isomerization of CH_2=C(OH)CH=CH_2 to methyl vinyl ketone (CH_3COCH=CH_2, MVK) was also observed. Photoionization spectra identified both enols, C_6H_9OH and CH=C(OH)CH=CH_2, and the ionization threshold of C_6H_9OH was measured to be 8.2 ± 0.1 eV. At 1200 K, the products of cyclohexanone pyrolysis were found to be: C_6H_9OH, CH_2=C(OH)CH=CH_2, MVK, CH_2CHCH_2, CO, CH_2=C=O, CH_3, CH_2=C=CH_2, CH_2=CH-CH=CH_2, CH_2=CHCH_2CH_3, CH_2=CH_2, and HCCH.

Vibrational non-equilibrium in the hydrogen-oxygen reaction. Comparison with experiment

NASA Astrophysics Data System (ADS)

Skrebkov, Oleg V.

2015-03-01

A theoretical model is proposed for the chemical and vibrational kinetics of hydrogen oxidation based on consistent accounting of the vibrational non-equilibrium of the HO2 radical that forms as a result of the bimolecular recombination H+O2 → HO2. In the proposed model, the chain branching H+O2 = O+OH and inhibiting H+O2+M = HO2+M formal reactions are treated (in the terms of elementary processes) as a single multi-channel process of forming, intramolecular energy redistribution between modes, relaxation, and unimolecular decay of the comparatively long-lived vibrationally excited HO2 radical, which is able to react and exchange energy with the other components of the mixture. The model takes into account the vibrational non-equilibrium of the starting (primary) H2 and O2 molecules, as well as the most important molecular intermediates HO2, OH, O2(1Δ), and the main reaction product H2O. It is shown that the hydrogen-oxygen reaction proceeds in the absence of vibrational equilibrium, and the vibrationally excited HO2(v) radical acts as a key intermediate in a fundamentally important chain branching process and in the generation of electronically excited species O2(1Δ), O(1D), and OH(2Σ+). The calculated results are compared with the shock tube experimental data for strongly diluted H2-O2 mixtures at 1000 < T < 2500 K, 0.5 < p < 4 atm. It is demonstrated that this approach is promising from the standpoint of reconciling the predictions of the theoretical model with experimental data obtained by different authors for various compositions and conditions using different methods. For T < 1500 K, the nature of the hydrogen-oxygen reaction is especially non-equilibrium, and the vibrational non-equilibrium of the HO2 radical is the essence of this process. The quantitative estimation of the vibrational relaxation characteristic time of the HO2 radical in its collisions with H2 molecules has been obtained as a result of the comparison of different experimental data on induction time measurements with the relevant calculations.

Synthesized TiO2/ZSM-5 composites used for the photocatalytic degradation of azo dye: Intermediates, reaction pathway, mechanism and bio-toxicity

NASA Astrophysics Data System (ADS)

Zhou, Kefu; Hu, Xin-Yan; Chen, Bor-Yann; Hsueh, Chung-Chuan; Zhang, Qian; Wang, Jiajie; Lin, Yu-Jung; Chang, Chang-Tang

2016-10-01

In this study, a one-step solid dispersion method was used to synthesize titanium dioxide (TiO2)/Zeolite Socony Mobil-5 (ZSM-5) composites with substantially reduced time and energy consumption. A degradation efficiency of more than 95% was achieved within 10 min using 50% PTZ (synthesized TiO2/ZSM-5 composites with TiO2 contents of 50 wt% loaded on ZSM-5) at pH 7 and 25 °C. The possible degradation pathway of azo-dye Reactive Black 5 (RB5) was investigated using gas chromatography-mass spectrometry and ion chromatography (IC). The bonds between the N atoms and naphthalene groups are likely attacked first and cleaved by hydroxyl radicals, ultimately resulting in the decolorization and mineralization of the azo dye. A comparative assessment of the characteristics of abiotic and biotic dye decolorization was completed. In addition, the toxicity effects of the degradation intermediates of azo-dye RB5 on cellular respiratory activity were analyzed. The bio-toxicity results showed that the decay rate constants of CO2 production from the azo-dye RB5 samples at different degradation times increased initially and subsequently decreased, indicating that intermediates of higher toxicity could adhere to the catalyst surface and gradually destroyed by further photocatalytic oxidation. Additionally, EDTA (hole scavengers) and t-BuOH (radical scavengers) were used to detect the main active oxidative species in the system. The results showed that the hydroxyl radicals are the main oxidation species in the photocatalytic process.

Mechanistic Insights from Reaction of α-Oxiranyl-Aldehydes with Cyanobacterial Aldehyde Deformylating Oxygenase

PubMed Central

Das, Debasis; Ellington, Benjamin; Paul, Bishwajit; Marsh, E. Neil G.

2014-01-01

The biosynthesis of long-chain aliphatic hydrocarbons, which are derived from fatty acids, is widespread in Nature. The last step in this pathway involves the decarbonylation of fatty aldehydes to the corresponding alkanes or alkenes. In cyanobacteria this is catalyzed by an aldehyde deformylating oxygenase. We have investigated the mechanism of this enzyme using substrates bearing an oxirane ring adjacent to the aldehyde carbon. The enzyme catalyzed the deformylation of these substrates to produce the corresponding oxiranes. Performing the reaction in D2O allowed the facial selectivity of proton addition to be examined by 1H-NMR spectroscopy. The proton is delivered with equal probability to either face of the oxirane ring, indicating the formation of an oxiranyl radical intermediate that is free to rotate during the reaction. Unexpectedly, the enzyme also catalyzes a side reaction in which oxiranyl-aldehydes undergo tandem deformylation to furnish alkanes two carbons shorter. We present evidence that this involves the rearrangement of the intermediate oxiranyl radical formed in the first step, resulting an aldehyde that is further deformylated in a second step. These observations provide support for a radical mechanism for deformylation and, furthermore, allow the lifetime of the radical intermediate to be estimated based on prior measurements of rate constants for the rearrangement of oxiranyl radicals. PMID:24313866

Radiolysis of paracetamol in dilute aqueous solution

NASA Astrophysics Data System (ADS)

Szabó, László; Tóth, Tünde; Homlok, Renáta; Takács, Erzsébet; Wojnárovits, László

2012-09-01

Using radiolytic experiments hydroxyl radical (main reactant in advanced oxidation processes) was shown to effectively destroy paracetamol molecules. The basic reaction is attachment to the ring. The hydroxy-cyclohexadienyl radical produced in the further reactions may transform to hydroxylated paracetamol derivatives or to quinone type molecules and acetamide. The initial efficiency of aromatic ring destruction in the absence of dissolved O2 is c.a. 10%. The efficiency is 2-3 times higher in the presence of O2 due to its reaction with intermediate hydroxy-cyclohexadienyl radical and the subsequent ring destruction reactions through peroxi radical. Upon irradiation the toxicity of solutions at low doses increases with the dose and then at higher doses it decreases. This is due to formation of compounds with higher toxicity than paracetamol (e.g. acetamide, hidroquinone). These products, however, are highly sensitive to irradiation and degrade easily.

Impact of ambient gases on the mechanism of [Cs8Nb6O19]-promoted nerve-agent decomposition† †Dedicated to the memory of Prof. Keiji Morokuma. ‡ ‡Electronic supplementary information (ESI) available: (1) The calculated transition states, intermediates and products of the GB hydrolysis and their important geometry parameters (in Å) for X = SO2, (2) the calculated adsorption energies (in kcal mol–1) of NO2 radicals to Cs8Nb6O19, (3) Cartesian coordinates for all reported structures in xyz format. (structure.xyz). See DOI: 10.1039/c7sc04997h

PubMed Central

Kaledin, Alexey L.; Driscoll, Darren M.; Troya, Diego; Collins-Wildman, Daniel L.

2018-01-01

The impact of ambient gas molecules (X), NO2, CO2 and SO2 on the structure, stability and decontamination activity of Cs8Nb6O19 polyoxometalate was studied computationally and experimentally. It was found that Cs8Nb6O19 absorbs these molecules more strongly than it adsorbs water and Sarin (GB) and that these interactions hinder nerve agent decontamination. The impacts of diamagnetic CO2 and SO2 molecules on polyoxoniobate Cs8Nb6O19 were fundamentally different from that of NO2 radical. At ambient temperatures, weak coordination of the first NO2 radical to Cs8Nb6O19 conferred partial radical character on the polyoxoniobate and promoted stronger coordination of the second NO2 adsorbent to form a stable diamagnetic Cs8Nb6O19/(NO2)2 species. Moreover, at low temperatures, NO2 radicals formed stable dinitrogen tetraoxide (N2O4) that weakly interacted with Cs8Nb6O19. It was found that both in the absence and presence of ambient gas molecules, GB decontamination by the Cs8Nb6O19 species proceeds via general base hydrolysis involving: (a) the adsorption of water and the nerve agent on Cs8Nb6O19/(X), (b) concerted hydrolysis of a water molecule on a basic oxygen atom of the polyoxoniobate and nucleophilic addition of the nascent OH group to the phosphorus center of Sarin, and (c) rapid reorganization of the formed pentacoordinated-phosphorus intermediate, followed by dissociation of either HF or isopropanol and formation of POM-bound isopropyl methyl phosphonic acid (i-MPA) or methyl phosphonofluoridic acid (MPFA), respectively. The presence of the ambient gas molecules increases the energy of the intermediate stationary points relative to the asymptote of the reactants and slightly increases the hydrolysis barrier. These changes closely correlate with the Cs8Nb6O19–X complexation energy. The most energetically stable intermediates of the GB hydrolysis and decontamination reaction were found to be Cs8Nb6O19/X-MPFA-(i-POH) and Cs8Nb6O19/X-(i-MPA)-HF both in the absence and presence of ambient gas molecules. The high stability of these intermediates is due to, in part, the strong hydrogen bonding between the adsorbates and the protonated [Cs8Nb6O19/X/H]+-core. Desorption of HF or/and (i-POH) and regeneration of the catalyst required deprotonation of the [Cs8Nb6O19/X/H]+-core and protonation of the phosphonic acids i-MPA and MPFA. This catalyst regeneration is shown to be a highly endothermic process, which is the rate-limiting step of the GB hydrolysis and decontamination reaction both in the absence and presence of ambient gas molecules. PMID:29719688

Synthesis of amino acids

DOEpatents

Davis, J.W. Jr.

1979-09-21

A method is described for synthesizing amino acids preceding through novel intermediates of the formulas: R/sub 1/R/sub 2/C(OSOC1)CN, R/sub 1/R/sub 2/C(C1)CN and (R/sub 1/R/sub 2/C(CN)O)/sub 2/SO wherein R/sub 1/ and R/sub 2/ are each selected from hydrogen and monovalent hydrocarbon radicals of 1 to 10 carbon atoms. The use of these intermediates allows the synthesis steps to be exothermic and results in an overall synthesis method which is faster than the synthesis methods of the prior art.

Synthesis of alpha-amino acids

DOEpatents

Davis, Jr., Jefferson W.

1983-01-01

A method for synthesizing alpha amino acids proceeding through novel intermediates of the formulas: R.sub.1 R.sub.2 C(OSOCl)CN, R.sub.1 R.sub.2 C(Cl)CN and [R.sub.1 R.sub.2 C(CN)O].sub.2 SO wherein R.sub.1 and R.sub.2 are each selected from hydrogen monovalent substituted and unsubstituted hydrocarbon radicals of 1 to 12 carbon atoms. The use of these intermediates allows the synthesis steps to be exothermic and results in an overall synthesis method which is faster than the synthesis methods of the prior art.

Synthesis of alpha-amino acids

DOEpatents

Davis, J.W. Jr.

1983-01-25

A method is described for synthesizing alpha amino acids proceeding through novel intermediates of the formulas: R[sub 1]R[sub 2]C(OSOCl)CN, R[sub 1]R[sub 2]C(Cl)CN and [R[sub 1]R[sub 2]C(CN)O][sub 2]SO wherein R[sub 1] and R[sub 2] are each selected from hydrogen monovalent substituted and unsubstituted hydrocarbon radicals of 1 to 10 carbon atoms. The use of these intermediates allows the synthesis steps to be exothermic and results in an overall synthesis method which is faster than the synthesis methods of the prior art. No Drawings

Synthesis of alpha-amino acids

DOEpatents

Davis, Jr., Jefferson W.

1983-01-01

A method for synthesizing alpha amino acids proceding through novel intermediates of the formulas: R.sub.1 R.sub.2 C(OSOCl)CN, R.sub.1 R.sub.2 C(Cl)CN and [R.sub.1 R.sub.2 C(CN)O].sub.2 SO wherein R.sub.1 and R.sub.2 are each selected from hydrogen monovalent substituted and unsubstituted hydrocarbon radicals of 1 to 10 carbon atoms. The use of these intermediates allows the synthesis steps to be exothermic and results in an overall synthesis method which is faster than the snythesis methods of the prior art.

Synthesis of alpha-amino acids

DOEpatents

Davis, Jr., Jefferson W.

1983-01-01

A method for synthesizing alpha amino acids proceding through novel intermediates of the formulas: R.sub.1 R.sub.2 C(OSOCl)CN, R.sub.1 R.sub.2 C(Cl)CN and [R.sub.1 R.sub.2 C(CN)O].sub.2 SO wherein R.sub.1 and R.sub.2 are each selected from hydrogen monovalent substituted and unsubstituted hydrocarbon radicals of 1 to 12 carbon atoms. The use of these intermediates allows the synthesis steps to be exothermic and results in an overall synthesis method which is faster than the synthesis methods of the prior art.

Formation of hydroxyl radicals and Co3+ in the reaction of Co(2+)-EDTA with hydrogen peroxide. Catalytic effect of Fe3+.

PubMed

Eberhardt, M K; Santos, C; Soto, M A

1993-05-07

Co2+ ions (Co(NO3)2.6H2O) react with H2O2 only in presence of EDTA to yield OH radicals and Co3+. This reaction was carried out in unbuffered aqueous solutions (pH = 2.6). The formation of Co3+ was confirmed by spectroscopy. The Co(3+)-EDTA complex shows two typical absorptions at 382 nm and 532 nm. The Co(3+)-EDTA complex can be prepared by a number of oxidizing agents, like Fe3+, Fe(3+)-EDTA, Ag+, Ag2+, Ce4+, and hydroxyl radicals. Since Fe3+ oxidizes Co(2+)-EDTA to Co(3+)-EDTA and Fe2+ we initiate a chain reaction for .OH formation. Our results show that there are two modes for H2O2 decomposition: (1) One electron transfer to give OH radicals and (2) Decomposition of H2O2 to H2O and O2 without intermediate .OH formation. This reaction depends strongly on the pH of the buffer. The H2O2 decomposition increases with increasing pH and increasing Co2+ concentration.

Identification of oxidative coupling products of xylenols arising from laboratory-scale phytoremediation.

PubMed

Poerschmann, J; Schultze-Nobre, L; Ebert, R U; Górecki, T

2015-01-01

Oxidative coupling reactions take place during the passage of xylenols through a laboratory-scale helophyte-based constructed wetland system. Typical coupling product groups including tetramethyl-[1,1'-biphenyl] diols and tetramethyl diphenylether monools as stable organic intermediates could be identified by a combination of pre-chromatographic derivatization and GC/MS analysis. Structural assignment of individual analytes was performed by an increment system developed by Zenkevich to pre-calculate retention sequences. The most abundant analyte turned out to be 3,3',5,5'-tetramethyl-[1,1'-biphenyl]-4,4'-diol, which can be formed by a combination of radicals based on 2,6-xylenol or by an attack of a 2,6-xylenol-based radical on 2,6-xylenol. Organic intermediates originating from oxidative coupling could also be identified in anaerobic constructed wetland systems. This finding suggested the presence of (at least partly) oxic conditions in the rhizosphere. Copyright © 2014 Elsevier Ltd. All rights reserved.

Vibrational Spectroscopy of Ions and Radicals Present in the Interstellar Medium and in Planetary Atmospheres: A Theoretical Study

NASA Technical Reports Server (NTRS)

Chaban, Galina M.

2004-01-01

Anharmonic vibrational frequencies and intensities are calculated for OH(H2O)n and H(H2O)n radicals (that form on icy particles of the interstellar medium), HCO radical (the main intermediate in the synthesis of organic molecules in space), NH2(-) and C2H(-) anions, H5(+) cation, and other systems relevant to interstellar chemistry. In addition to pure ions and radicals, their complexes with water are studied to assess the effects of water environment on infrared spectra. The calculations are performed using the correlation-corrected vibrational self-consistent field (CC-VSCF) method with ab initio potential surfaces at the MP2 and CCSD(T) levels. Fundamental, overtone, and combination excitations are computed. The results are in good agreement with available experimental data and provide reliable predictions for vibrational excitations not yet measured in laboratory experiments. The data should be useful for interpretation of astronomically observed spectra and identification of ions and radicals present in the interstellar medium and in planetary atmospheres.

Radiolysis of berberine or palmatine in aqueous solution

NASA Astrophysics Data System (ADS)

Marszalek, Milena; Wolszczak, Marian

2011-01-01

The reactions of hydrated electron (eaq-), hydrogen atom (H rad ) (reducing species) and Cl2•-, Br2•-, N,O•H radicals (oxidizing species) with berberine or palmatine in aqueous solution have been studied by steady-state and pulse radiolysis. The spectra of transient intermediates, leading to the final products, are presented. The rate constants of the reaction of eaq- and rad OH radical with both alkaloids in the homogenous solution and in the presence of DNA are reported. It is demonstrated that the primary products of the reaction of berberine and palmatine with eaq- and radicals generated during radiolysis are unstable and undergo further reactions.

Gas-phase tropospheric chemistry of 2,3,7,8-tetrafuorinated dibenzo-p-dioxin.

PubMed

Zhang, Chenxi; Sun, Xiaomin

2014-01-15

Growing attention has been devoted to understanding the formation and destruction of polyfluorinated dibenzo-p-dioxins (PFDDs). High-accuracy molecular orbital calculations have been performed to investigate the tropospheric oxidation reaction of 2,3,7,8-tetrafuorinated dibenzo-p-dioxin (TFDD) initiated by OH radical, NO3 radical and O3. The rate constant of TFDD reaction triggered by the OH radical, NO3 radical and O3 is about 2.30 × 10(-11)cm(3) molecule(-l) s(-l), 3.18 × 10(-13)cm(3) molecule(-l) s(-l), and 3.30 × 10(-19)cm(3) molecule(-l) s(-l), respectively. OH radical is the major gas phase tropospheric sink for TFDD. Once TFDD-OH intermediates are produced in the initial reactions, they can react with tropospheric O2 subsequently to generate peroxy radical isomers. The TFDD-OH-O2 can further react with tropospheric NO via isomerization or combination, resulting that the dioxin ring will be ruptured completely. This study can serve as a template for tropospheric degradation of the gaseous PFDDs, which is beneficial for assessing their tropospheric behaviors. © 2013 Elsevier B.V. All rights reserved.

The Development, Implementation and Application of Accurate Quantum Chemical Methods for Molecular Structure, Spectra and Reaction Paths

DTIC Science & Technology

2016-02-02

Bartlett, Nigel G. J. Richards, Robert W. Molt, Alison M. Lecher. Facile Csp2 Csp2 bond cleavage in oxalic acid -derived radicals: Implications for...sway a strong bond link in oxalate can be broken by manganese containing enzymes. The intermediate steps involved the formation of either a radical or...catalysis by oxalate decarboxylase, Journal of the American Chemical Society, (03 2015): 3248. doi: 10.1021/ja510666r Erik Deumens, Victor F. Lotrich

The inverse podant [Li3(NBut)3S)]+ stabilises a single ethylene oxide OCH=CH2 anion as a high- and low-temperature polymorph of [(thf)3Li3(OCH=CH2)(NBut)3S)].

PubMed

Walfort, B; Pandey, S K; Stalke, D

2001-09-07

A single ethylene oxide anion derived from the ether cleavage reaction of thf with ButLi is stabilised by the inverse podant [Li3(NBut)3S)]+ to give a high- and a low-temperature polymorph with a considerable difference in conformation and packing.

Gas-Phase Ozonolysis of Cycloalkenes: Formation of Highly Oxidized RO2 Radicals and Their Reactions with NO, NO2, SO2, and Other RO2 Radicals.

PubMed

Berndt, Torsten; Richters, Stefanie; Kaethner, Ralf; Voigtländer, Jens; Stratmann, Frank; Sipilä, Mikko; Kulmala, Markku; Herrmann, Hartmut

2015-10-15

The gas-phase reaction of ozone with C5-C8 cycloalkenes has been investigated in a free-jet flow system at atmospheric pressure and a temperature of 297 ± 1 K. Highly oxidized RO2 radicals bearing at least 5 O atoms in the molecule and their subsequent reaction products were detected in most cases by means of nitrate-CI-APi-TOF mass spectrometry. Starting from a Criegee intermediate after splitting-off an OH-radical, the formation of these RO2 radicals can be explained via an autoxidation mechanism, meaning RO2 isomerization (ROO → QOOH) and subsequently O2 addition (QOOH + O2 → R'OO). Time-dependent RO2 radical measurements concerning the ozonolysis of cyclohexene indicate rate coefficients of the intramolecular H-shifts, ROO → QOOH, higher than 1 s(-1). The total molar yield of highly oxidized products (predominantly RO2 radicals) from C5-C8 cycloalkenes in air is 4.8-6.0% affected with a calibration uncertainty by a factor of about two. For the most abundant RO2 radical from cyclohexene ozonolysis, O,O-C6H7(OOH)2O2 ("O,O" stands for two O atoms arising from the ozone attack), the determination of the rate coefficients of the reaction with NO2, NO, and SO2 yielded (1.6 ± 0.5) × 10(-12), (3.4 ± 0.9) × 10(-11), and <10(-14) cm(3) molecule(-1) s(-1), respectively. The reaction of highly oxidized RO2 radicals with other peroxy radicals (R'O2) leads to detectable accretion products, RO2 + R'O2 → ROOR' + O2, which allows to acquire information on peroxy radicals not directly measurable with the nitrate ionization technique applied here. Additional experiments using acetate as the charger ion confirm conclusively the existence of highly oxidized RO2 radicals and closed-shell products. Other reaction products, detectable with this ionization technique, give a deeper insight in the reaction mechanism of cyclohexene ozonolysis.

Tuning the reactivity of Fe(V)(O) toward C-H bonds at room temperature: effect of water.

PubMed

Singh, Kundan K; Tiwari, Mrityunjay k; Ghosh, Munmun; Panda, Chakadola; Weitz, Andrew; Hendrich, Michael P; Dhar, Basab B; Vanka, Kumar; Sen Gupta, Sayam

2015-02-16

The presence of an Fe(V)(O) species has been postulated as the active intermediate for the oxidation of both C-H and C═C bonds in the Rieske dioxygenase family of enzymes. Understanding the reactivity of these high valent iron-oxo intermediates, especially in an aqueous medium, would provide a better understanding of these enzymatic reaction mechanisms. The formation of an Fe(V)(O) complex at room temperature in an aqueous CH3CN mixture that contains up to 90% water using NaOCl as the oxidant is reported here. The stability of Fe(V)(O) decreases with increasing water concentration. We show that the reactivity of Fe(V)(O) toward the oxidation of C-H bonds, such as those in toluene, can be tuned by varying the amount of water in the H2O/CH3CN mixture. Rate acceleration of up to 60 times is observed for the oxidation of toluene upon increasing the water concentration. The role of water in accelerating the rate of the reaction has been studied using kinetic measurements, isotope labeling experiments, and density functional theory (DFT) calculations. A kinetic isotope effect of ∼13 was observed for the oxidation of toluene and d8-toluene showing that C-H abstraction was involved in the rate-determining step. Activation parameters determined for toluene oxidation in H2O/CH3CN mixtures on the basis of Eyring plots for the rate constants show a gain in enthalpy with a concomitant loss in entropy. This points to the formation of a more-ordered transition state involving water molecules. To further understand the role of water, we performed a careful DFT study, concentrating mostly on the rate-determining hydrogen abstraction step. The DFT-optimized structure of the starting Fe(V)(O) and the transition state indicates that the rate enhancement is due to the transition state's favored stabilization over the reactant due to enhanced hydrogen bonding with water.

Radical SAM catalysis via an organometallic intermediate with an Fe-[5'-C]-deoxyadenosyl bond.

PubMed

Horitani, Masaki; Shisler, Krista; Broderick, William E; Hutcheson, Rachel U; Duschene, Kaitlin S; Marts, Amy R; Hoffman, Brian M; Broderick, Joan B

2016-05-13

Radical S-adenosylmethionine (SAM) enzymes use a [4Fe-4S] cluster to cleave SAM to initiate diverse radical reactions. These reactions are thought to involve the 5'-deoxyadenosyl radical intermediate, which has not yet been detected. We used rapid freeze-quenching to trap a catalytically competent intermediate in the reaction catalyzed by the radical SAM enzyme pyruvate formate-lyase activating enzyme. Characterization of the intermediate by electron paramagnetic resonance and (13)C, (57)Fe electron nuclear double-resonance spectroscopies reveals that it contains an organometallic center in which the 5' carbon of a SAM-derived deoxyadenosyl moiety forms a bond with the unique iron site of the [4Fe-4S] cluster. Discovery of this intermediate extends the list of enzymatic bioorganometallic centers to the radical SAM enzymes, the largest enzyme superfamily known, and reveals intriguing parallels to B12 radical enzymes. Copyright © 2016, American Association for the Advancement of Science.

Anti-lung cancer effects of novel ginsenoside 25-OCH(3)-PPD.

PubMed

Wang, Wei; Rayburn, Elizabeth R; Hang, Jie; Zhao, Yuqing; Wang, Hui; Zhang, Ruiwen

2009-09-01

20(S)-25-methoxyl-dammarane-3beta, 12beta, 20-triol (25-OCH(3)-PPD), a newly identified natural product from Panax notoginseng, exhibits activity against a variety of cancer cells. Herein, we report the effects of this compound on human A549, H358, and H838 lung cancer cells, and compare these effects with a control lung epithelial cell line, BEAS-2B. 25-OCH(3)-PPD decreased survival, inhibited proliferation, and induced apoptosis and G1 cell cycle arrest in the lung cancer cell lines. The P. notoginseng compound also decreased the levels of proteins associated with cell proliferation and cell survival. Moreover, 25-OCH(3)-PPD inhibited the growth of A549 lung cancer xenograft tumors. 25-OCH(3)-PPD demonstrated low toxicity to non-cancer cells, and no observable toxicity was seen when the compound was administered to animals. In conclusion, our preclinical data indicate that 25-OCH(3)-PPD is a potential therapeutic agent in vitro and in vivo, and further preclinical and clinical development of this agent for lung cancer is warranted.

Nitrolysis of the CN Single Bond and Related Chemistry of Nitro and Nitroso Groups.

DTIC Science & Technology

1988-03-01

oxime of be 4,5-diphenyl-l-triphenylmethoxy-l,23- triazole (11). It was benzoyl cyanide (Scheme 6), for which radical intermediates hydrolysed by...S-Pnitroxide (a radical scavenger) or benzoyl peroxide (a radical *PhC CCN)- NO2 Ag PhCON--CPh suc)I I source). A partial extension of the overall...two anomethylenenitronate anion. (Attempts to prepare the pathways for fragmentation of the ester (3) (C,.H,0 N.O,): one ketenimine (15) by a

Low temperature (550-700 K) oxidation pathways of cyclic ketones: Dominance of HO 2-elimination channels yielding conjugated cyclic coproducts

DOE PAGES

Scheer, Adam M.; Welz, Oliver; Vasu, Subith S.; ...

2015-04-13

The low-temperature oxidation of three cyclic ketones, cyclopentanone (CPO; C 5H 8O), cyclohexanone (CHO; C 6H 10 O), and 2-methyl-cyclopentanone (2-Me-CPO; CH 3–C 5H7 O), is studied between 550 and 700 K and at 4 or 8 Torr total pressure. Initial fuel radicals R are formedvia fast H-abstraction from the ketones by laser-photolytically generated chlorine atoms. Intermediates and products from the subsequent reactions of these radicals in the presence of excess O 2 are probed with time and isomeric resolution using multiplexed photoionization mass spectrometry with tunable synchrotron ionizing radiation. For CPO and CHO the dominant product channel in themore » R + O 2 reactions is chain-terminating HO 2-elimination yielding the conjugated cyclic coproducts 2-cyclopentenone and 2-cyclohexenone, respectively. Results on oxidation of 2-Me-CPO also show a dominant contribution from HO 2-elimination. Moreover, the photoionization spectrum of the co-product suggests formation of 2-methyl-2-cyclopentenone and/or 2-cyclohexenone, resulting from a rapid Dowd–Beckwith rearrangement, preceding addition to O 2, of the initial (2-oxocyclopentyl)methyl radical to 3-oxocyclohexyl. Cyclic ethers, markers for hydroperoxyalkyl radicals (QOOH), key intermediates in chain-propagating and chain-branching low-temperature combustion pathways, are only minor products. The interpretation of the experimental results is supported by stationary point calculations on the potential energy surfaces of the associated R + O 2 reactions at the CBS-QB3 level. Furthermore, the calculations indicate that HO 2-elimination channels are energetically favored and product formation via QOOH is disfavored. Lastly, the prominence of chain-terminating pathways linked with HO 2 formation in low-temperature oxidation of cyclic ketones suggests little low-temperature reactivity of these species as fuels in internal combustion engines.« less

Low temperature (550-700 K) oxidation pathways of cyclic ketones: Dominance of HO 2-elimination channels yielding conjugated cyclic coproducts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scheer, Adam M.; Welz, Oliver; Vasu, Subith S.

The low-temperature oxidation of three cyclic ketones, cyclopentanone (CPO; C 5H 8O), cyclohexanone (CHO; C 6H 10 O), and 2-methyl-cyclopentanone (2-Me-CPO; CH 3–C 5H7 O), is studied between 550 and 700 K and at 4 or 8 Torr total pressure. Initial fuel radicals R are formedvia fast H-abstraction from the ketones by laser-photolytically generated chlorine atoms. Intermediates and products from the subsequent reactions of these radicals in the presence of excess O 2 are probed with time and isomeric resolution using multiplexed photoionization mass spectrometry with tunable synchrotron ionizing radiation. For CPO and CHO the dominant product channel in themore » R + O 2 reactions is chain-terminating HO 2-elimination yielding the conjugated cyclic coproducts 2-cyclopentenone and 2-cyclohexenone, respectively. Results on oxidation of 2-Me-CPO also show a dominant contribution from HO 2-elimination. Moreover, the photoionization spectrum of the co-product suggests formation of 2-methyl-2-cyclopentenone and/or 2-cyclohexenone, resulting from a rapid Dowd–Beckwith rearrangement, preceding addition to O 2, of the initial (2-oxocyclopentyl)methyl radical to 3-oxocyclohexyl. Cyclic ethers, markers for hydroperoxyalkyl radicals (QOOH), key intermediates in chain-propagating and chain-branching low-temperature combustion pathways, are only minor products. The interpretation of the experimental results is supported by stationary point calculations on the potential energy surfaces of the associated R + O 2 reactions at the CBS-QB3 level. Furthermore, the calculations indicate that HO 2-elimination channels are energetically favored and product formation via QOOH is disfavored. Lastly, the prominence of chain-terminating pathways linked with HO 2 formation in low-temperature oxidation of cyclic ketones suggests little low-temperature reactivity of these species as fuels in internal combustion engines.« less

Optical and magnetic properties for metal halide-based organic-inorganic layered perovskites

NASA Astrophysics Data System (ADS)

Shikoh, Eiji; Ando, Yasuo; Era, Masanao; Miyazaki, Terunobu

2001-05-01

Layered perovskites (RNH 3) 2CuCl 4, where R was methyl-benzene C 6H 5-CH 2, 1-methyl-naphthalene 1-C 10H 9-CH 2, 1-propyl-naphthalene 1-C 10H 9-O(CH 2) 3 and 1-butyl-naphthalene 1-C 10H 9-O(CH 2) 4, were synthesized. These complexes showed ferromagnetism, with different Curie temperatures, TC, depending on the structure of the molecule. The change of TC by taking into account the overlap of the electronic states between the organic and the inorganic layers were discussed.

Characterization of supramolecular (H2O)18 water morphology and water-methanol (H2O)15(CH3OH)3 clusters in a novel phosphorus functionalized trimeric amino acid host.

PubMed

Raghuraman, Kannan; Katti, Kavita K; Barbour, Leonard J; Pillarsetty, Nagavarakishore; Barnes, Charles L; Katti, Kattesh V

2003-06-11

Phosphorus functionalized trimeric alanine compounds (l)- and (d)-P(CH(2)NHCH(CH(3))COOH)(3) 2 are prepared in 90% yields by the Mannich reaction of Tris(hydroxymethyl)phosphine 1 with (l)- or (d)- Alanine in aqueous media. The hydration properties of (l)-2 and (d)-2 in water and water-methanol mixtures are described. The crystal structure analysis of (l)-2.4H(2)O, reveals that the alanine molecules pack to form two-dimensional bilayers running parallel to (001). The layered structural motif depicts two closely packed monolayers of 2 each oriented with its phosphorus atoms projected at the center of the bilayer and adjacent monolayers are held together by hydrogen bonds between amine and carboxylate groups. The water bilayers are juxtaposed with the H-bonded alanine trimers leading to 18-membered (H(2)O)(18) water rings. Exposure of aqueous solution of (l)-2 and (d)-2 to methanol vapors resulted in closely packed (l)-2 and (d)-2 solvated with mixed water-methanol (H(2)O)(15)(CH(3)OH)(3) clusters. The O-O distances in the mixed methanol-water clusters of (l)-2.3H(2)O.CH(3)OH and (d)-2.3H(2)O.CH(3)OH (O-O(average) = 2.857 A) are nearly identical to the O-O distance observed in the supramolecular (H(2)O)(18) water structure (O-O(average) = 2.859 A) implying the retention of the hydrogen bonded structure in water despite the accommodation of hydrophobic methanol groups within the supramolecular (H(2)O)(15)(CH(3)OH)(3) framework. The O-O distances in (l)-2.3H(2)O.CH(3)OH and (d)-2.3H(2)O.CH(3)OH and in (H(2)O)(18) are very close to the O-O distance reported for liquid water (2.85 A).

The [C{sub 6}H{sub 10}]{sup {sm{underscore}bullet}+} hypersurface: The parent radical cation Diels-Alder reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffmann, M.; Schaefer, H.F. III

1999-07-21

Various possible reaction pathways between ethene and butadiene radical cation (cis- and trans-), have been investigated at different levels of theory up to UCCSD(T)/DZP/UMP2(fc)/DZP and with density functional theory at B3LYP/DZP. A stepwise addition involving open chain intermediates and leading to the Diels-Alder product, the cyclohexene radical cation, was found to have a total activation barrier {Delta}G{sup 298{ne}} = 6.3 kcal mol{sup {minus}1} and a change in free Gibbs energy, {Delta}G{sup 298}, of {minus}33.5 kcal mol{sup {minus}1}. On the E{degree} potential energy surface, all transition states are lower in energy than separated ethene and butadiene, the exothermicity {Delta}E = -45.6more » kcal mol{sup {minus}1}. A more direct path could be characterized as stepwise with one intermediate only at the SCF level but not at electron-correlated levels and hence might actually be a concerted strongly asynchronous addition with a very small or no activation barrier (UCCSD(T)/DZP/UHF/6-31G* gives a {Delta}G{sup 298{ne}} of 0.8 kcal mol{sup {minus}1}). The critical step for another alternative, the cyclobutanation-vinylcyclobutane/cyclohexene rearrangement, is a 1,3-alkyl shift which involves a barrier ({Delta}G{sup 298{ne}}) only 1.7 kcal mol{sup {minus}1} higher than that of stop use addition for both cis-, and trans-butadiene radical cation. However, from the (ethene and trans-butadiene) reactions, ring expansion of the vinylcyclobutane radical cation intermediate, to a methylene cyclopentane radical cation, requires an activation only 1.3 kcal mol{sup {minus}1} larger than for (trans-butadiene radical). While cis/trans isomerization of free butadiene radical cation requires a high activation (24.9 kcal mol{sup {minus}1}), a reaction sequence involving addition of ethene (to stepwise give an open chain intermediate and vinyl cyclobutane radical cation) has a barrier of only 3.5 kcal mol{sup {minus}1} ({Delta}G{sup 298{ne}}). This sequence also makes ethene and butadiene radical cations to exchange terminal methylene groups.« less

Dispersed-Fluorescence Spectroscopy of Jet-Cooled Calcium Ethoxide Radical (CaOC_2H_5)

NASA Astrophysics Data System (ADS)

Paul, Anam C.; Reza, Md Asmaul; Liu, Jinjun

2016-06-01

Metal-containing free radicals are important intermediates in metal-surface reactions and in the interaction between metals and organic molecules. In the present work, dispersed fluorescence (DF) spectra of the calcium ethoxide radical (CaOC_2H_5) have been obtained by pumping the {tilde A^2}{A}' ← {tilde X^2}{A}' and the {tilde B^2}{A}'' ← {tilde X^2}{A}' origin bands in its laser-induced fluorescence (LIF) spectrum. CaOC_2H_5 radicals were produced by 1064 nm laser ablation of calcium grains in the presence of ethanol under jet-cooled conditions. Dominant transitions in the vibrationally resolved DF spectra are well reproduced using Franck-Condon factors predicted by complete active space self-consistent (CASSCF) calculations. Differences in transition intensities between the {tilde A^2}{A}' → {tilde X^2}{A}' and the {tilde B^2}{A}'' → {tilde X^2}{A}' DF spectra are attributed to the pseudo-Jahn-Teller interaction between the tilde A ^2 A' and the tilde B ^2 A'' states. Collision-induced population transfer between these two excited electronic states results in additional peaks in the DF spectra.

Mechanism for degradation of Nafion in PEM fuel cells from quantum mechanics calculations.

PubMed

Yu, Ted H; Sha, Yao; Liu, Wei-Guang; Merinov, Boris V; Shirvanian, Pezhman; Goddard, William A

2011-12-14

We report results of quantum mechanics (QM) mechanistic studies of Nafion membrane degradation in a polymer electrolyte membrane (PEM) fuel cell. Experiments suggest that Nafion degradation is caused by generation of trace radical species (such as OH(●), H(●)) only when in the presence of H(2), O(2), and Pt. We use density functional theory (DFT) to construct the potential energy surfaces for various plausible reactions involving intermediates that might be formed when Nafion is exposed to H(2) (or H(+)) and O(2) in the presence of the Pt catalyst. We find a barrier of 0.53 eV for OH radical formation from HOOH chemisorbed on Pt(111) and of 0.76 eV from chemisorbed OOH(ad), suggesting that OH might be present during the ORR, particularly when the fuel cell is turned on and off. Based on the QM, we propose two chemical mechanisms for OH radical attack on the Nafion polymer: (1) OH attack on the S-C bond to form H(2)SO(4) plus a carbon radical (barrier: 0.96 eV) followed by decomposition of the carbon radical to form an epoxide (barrier: 1.40 eV). (2) OH attack on H(2) crossover gas to form hydrogen radical (barrier: 0.04 eV), which subsequently attacks a C-F bond to form HF plus carbon radicals (barrier as low as 1.00 eV). This carbon radical can then decompose to form a ketone plus a carbon radical with a barrier of 0.86 eV. The products (HF, OCF(2), SCF(2)) of these proposed mechanisms have all been observed by F NMR in the fuel cell exit gases along with the decrease in pH expected from our mechanism. © 2011 American Chemical Society

A stable Fe{sup III}-Fe{sup IV} replacement of tyrosyl radical in a class I ribonucleotide reductase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voevodskaya, N.; Lendzian, F.; Graeslund, A.

2005-05-20

Ribonucleotide reductase (RNR) of Chlamydia trachomatis is a class I RNR enzyme composed of two homodimeric components, proteins R1 and R2. In class I RNR, R1 has the substrate binding site, whereas R2 has a diferric site and normally in its active form a stable tyrosyl free radical. C. trachomatis RNR is unusual, because its R2 component has a phenylalanine in the place of the radical carrier tyrosine. Replacing the tyrosyl radical, a paramagnetic Fe{sup III}-Fe{sup IV} species (species X, normally a transient intermediate in the process leading to radical formation) may provide the oxidation equivalent needed to start themore » catalytic process via long range electron transfer from the active site in R1. Here EPR spectroscopy shows that in C. trachomatis RNR, species X can become essentially stable when formed in a complete RNR (R1/R2/substrate) complex, adding further weight to the possible role of this species X in the catalytic reaction.« less

On the formation of niacin (vitamin B3) and pyridine carboxylic acids in interstellar model ices

NASA Astrophysics Data System (ADS)

McMurtry, Brandon M.; Turner, Andrew M.; Saito, Sean E. J.; Kaiser, Ralf I.

2016-06-01

The formation of pyridine carboxylic acids in interstellar ice grains was simulated by electron exposures of binary pyridine (C5H5N)-carbon dioxide (CO2) ice mixtures at 10 K under contamination-free ultrahigh vacuum conditions. Chemical processing of the pristine ice and subsequent warm-up phase was monitored on line and in situ via Fourier transform infrared spectroscopy to probe for the formation of new radiation induced species. In the infrared spectra of the irradiated ice, bands assigned to nicotinic acid (niacin; vitamin B3; m-C5H4NCOOH) along with 2,3-, 2,5-, 3,4-, and 3,5-pyridine dicarboxylic acid (C5H3N(COOH)2) were unambiguously identified along with the hydroxycarbonyl (HOCO) radical. Our study suggests that the reactive pathway responsible for pyridine carboxylic acids formation involves a HOCO intermediate, which forms through the reaction of suprathermal hydrogen ejected from pyridine with carbon dioxide. The newly formed pyridinyl radical may then undergo radical-radical recombination with a hydroxycarbonyl radical to form a pyridine carboxylic acid.

Microwave-assisted rapid photocatalytic degradation of malachite green in TiO2 suspensions: mechanism and pathways.

PubMed

Ju, Yongming; Yang, Shaogui; Ding, Youchao; Sun, Cheng; Zhang, Aiqian; Wang, Lianhong

2008-11-06

Microwave-assisted photocatalytic (MPC) degradation of malachite green (MG) in aqueous TiO2 suspensions was investigated. A 20 mg/L sample of MG was rapidly and completely decomposed in 3 min with the corresponding TOC removal efficiency of about 85%. To gain insight into the degradation mechanism, both GC-MS and LC-ESI-MS/MS techniques were employed to identify the major intermediates of MG degradation, including N-demethylation intermediates [(p-dimethylaminophenyl)(p-methylaminophenyl)phenylmethylium (DM-PM), (p-methylaminophenyl)(p-methylaminophenyl)phenylmethylium (MM-PM), (p-methylaminophenyl)(p-aminophenyl)phenylmethylium (M-PM)]; a decomposition compound of the conjugated structure (4-dimethylaminobenzophenone (DLBP)); products resulting from the adduct reaction of hydroxyl radical; products of benzene removal; and other open-ring intermediates such as phenol, terephthalic acid, adipic acid, benzoic acid, etc. The possible degradation mechanism of MG included five processes: the N-demethylation process, adduct products of the hydroxyl radical, the breakdown of chromophores such as destruction of the conjugated structure intermediate, removal of benzene, and an open-ring reaction. To the best of our knowledge, it is the first time the whole MG photodegradation processes have been reported.

Differentiation of HL-60 cells distinguishes between cytostatic and cytotoxic effects of the alkylphospholipid ET-18-OCH3.

PubMed

Civoli, F; Pauig, S B; Daniel, L W

1996-01-01

The synthetic dialkylphospholipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) inhibits growth of the acute myelogenous leukemia cell line HL-60. Incubation of HL-60 cells with demethyl-sulfoxide causes the cells to differentiate to a granulocyte-like phenotype and become quiescent. Incubation of the DMSO-treated cells with ET-18-OCH3 results in a reduction in cell numbers due to cytotoxicity. In contrast, treatment of undifferentiated HL-60 cells with lower concentrations of ET-18-OCH3 leads to growth inhibition. These data indicate that the model of differentiated HL-60 cells currently used for the study of resistance to growth inhibition is inappropriate. HL-60 cells can be used to measure growth inhibition and at higher doses cytotoxicity. However, the differentiated, nonproliferative, cells can only be used to measure direct cytotoxicity. Therefore, the results of studies directly comparing the effects of ET-18-OCH3 in proliferative HL-60 cells and quiescent DMSO-treated HL-60 cells should be reevaluated. An evaluation of the effects of low concentrations of ET-18-OCH3 (0.5-1.5 microM) in proliferative HL-60 cells indicated that ET-18-OCH3 was an effective cytostatic agent at nontoxic concentrations. In summary, studies on the mechanism of action of ET-18-OCH3, or related ether lipids, should carefully investigate differences in the effects at cytostatic versus cytotoxic concentrations.

Direct dynamics simulation of dioxetane formation and decomposition via the singlet .O-O-CH2-CH2. biradical: Non-RRKM dynamics

NASA Astrophysics Data System (ADS)

Sun, Rui; Park, Kyoyeon; de Jong, Wibe A.; Lischka, Hans; Windus, Theresa L.; Hase, William L.

2012-07-01

Electronic structure calculations and direct chemical dynamics simulations are used to study the formation and decomposition of dioxetane on its ground state singlet potential energy surface. The stationary points for 1O2 + C2H4, the singlet .O-O-CH2-CH2. biradical, the transition state (TS) connecting this biradical with dioxetane, and the two transition states and gauche .O-CH2-CH2-O. biradical connecting dioxetane with the formaldehyde product molecules are investigated at different levels of electronic structure theory including UB3LYP, UMP2, MRMP2, and CASSCF and a range of basis sets. The UB3LYP/6-31G* method was found to give representative energies for the reactive system and was used as a model for the simulations. UB3LYP/6-31G* direct dynamics trajectories were initiated at the TS connecting the .O-O-CH2-CH2. biradical and dioxetane by sampling the TS's vibrational energy levels, and rotational and reaction coordinate energies, with Boltzmann distributions at 300, 1000, and 1500 K. This corresponds to the transition state theory model for trajectories that pass the TS. The trajectories were directed randomly towards both the biradical and dioxetane. A small fraction of the trajectories directed towards the biradical recrossed the TS and formed dioxetane. The remainder formed 1O2 + C2H4 and of these ˜ 40% went directly from the TS to 1O2 + C2H4 without getting trapped and forming an intermediate in the .O-O-CH2-CH2. biradical potential energy minimum, a non-statistical result. The dioxetane molecules which are formed dissociate to two formaldehyde molecules with a rate constant two orders of magnitude smaller than that predicted by Rice-Ramsperger-Kassel-Marcus theory. The reaction dynamics from dioxetane to the formaldehyde molecules do not follow the intrinsic reaction coordinate or involve trapping in the gauche .O-CH2-CH2-O. biradical potential energy minimum. Important non-statistical dynamics are exhibited for this reactive system.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borg, D.C.; Schaich, K.M.; Forman, A.

Several laboratoreies contend that sometimes reducing free radicals reach directly with H/sub 2/O/sub 2/ to afford OH. in a metal-independent fashion, and others propose that often the strongly electrophilic reaction intermediate is either a metal-oxy complex or a crypto-hydroxyl radical (crypto-OH.) rather than OH., especially when lipid peroxidation is initiated. Our data imply that metal-independent OH. formation is not competitively significant in vivo and that adventitious metals probably were unrecognized in the reactions that prompted others to the contrary conclusion, while the confusing patterns of initiator and inhibitor reactivity that led to inferences of ferryl (or cupryl) intermediation or tomore » the concept of crypto-OH. are explicable by the extremely short reaction radius of OH., which we show can be formed in lipid milieux that are inaccessible to hydrophilic or macromolecular scavengers.« less

Experimental and DFT computational study of β-Me and β-H elimination coupled with proton transfer: From amides to enamides in Cp* 2MX (M = La, Ce)

DOE PAGES

Rozenel, Sergio S.; Perrin, Lionel; Eisenstein, Odile; ...

2016-10-26

The thermal rearrangement of the f-block metallocene amides Cp* 2MNR 1R 2, where R 1 is CHMe 2, R 2 is either CHMe 2 or CMe 3, and M is either La or Ce, to the corresponding enamides Cp* 2MNR 1[C(Me)=CH 2] and H 2 or CH 4, respectively, occurs when the solid amides are heated in sealed evacuated ampules at 160–180 °C for 1–2 weeks. The net reaction is a β-H or β-Me elimination followed by a γ-abstraction of a proton at the group from which the β-elimination occurs. When R 1 is either SiMe 3 or SiMe 2CMemore » 3 and R 2 is CMe 3, the enamide Cp* 2MNR 1[C(Me)=CH 2] is isolated, the result of β-Me elimination, but when R 2 is CHMe 2, the enamides Cp* 2MNR 1[C(Me)=CH 2] and Cp* 2NR 1[C(H)=CH 2] are isolated, the result of β-H and β-Me elimination. In the latter cases, both enamides are formed in similar amounts and the rates of the β-H and β-Me elimination steps must be similar. A two-step mechanism is developed from DFT calculations. The first step is migration of a hydride or a methyl anion to the Cp* 2M fragment, forming M–H or M–Me bonds as the N=C bond in the intermediate imine forms. Furthermore, the enamide evolves from the metal-coordinated imine by abstraction of a proton from the γ-carbon of the intermediate imine. The two elementary steps involve significant geometrical changes within the N αC βC γ set of atoms during the two-step elimination process that are in large part responsible for the relatively high activation barriers for the net reaction, which may be classified as a proton-coupled hydride or methyl anion transfer reaction.« less

Experimental and DFT computational study of β-Me and β-H elimination coupled with proton transfer: From amides to enamides in Cp* 2MX (M = La, Ce)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rozenel, Sergio S.; Perrin, Lionel; Eisenstein, Odile

The thermal rearrangement of the f-block metallocene amides Cp* 2MNR 1R 2, where R 1 is CHMe 2, R 2 is either CHMe 2 or CMe 3, and M is either La or Ce, to the corresponding enamides Cp* 2MNR 1[C(Me)=CH 2] and H 2 or CH 4, respectively, occurs when the solid amides are heated in sealed evacuated ampules at 160–180 °C for 1–2 weeks. The net reaction is a β-H or β-Me elimination followed by a γ-abstraction of a proton at the group from which the β-elimination occurs. When R 1 is either SiMe 3 or SiMe 2CMemore » 3 and R 2 is CMe 3, the enamide Cp* 2MNR 1[C(Me)=CH 2] is isolated, the result of β-Me elimination, but when R 2 is CHMe 2, the enamides Cp* 2MNR 1[C(Me)=CH 2] and Cp* 2NR 1[C(H)=CH 2] are isolated, the result of β-H and β-Me elimination. In the latter cases, both enamides are formed in similar amounts and the rates of the β-H and β-Me elimination steps must be similar. A two-step mechanism is developed from DFT calculations. The first step is migration of a hydride or a methyl anion to the Cp* 2M fragment, forming M–H or M–Me bonds as the N=C bond in the intermediate imine forms. Furthermore, the enamide evolves from the metal-coordinated imine by abstraction of a proton from the γ-carbon of the intermediate imine. The two elementary steps involve significant geometrical changes within the N αC βC γ set of atoms during the two-step elimination process that are in large part responsible for the relatively high activation barriers for the net reaction, which may be classified as a proton-coupled hydride or methyl anion transfer reaction.« less

Mineralization of aniline using hydroxyl/sulfate radical-based technology in a waterfall reactor.

PubMed

Durán, A; Monteagudo, J M; San Martín, I; Amunategui, F J; Patterson, D A

2017-11-01

The aim of this work is to study the applicability of a UV/H 2 O 2 process intensified with persulfate (PS) as a source of SO 4 - radicals to efficiently mineralize a synthetic effluent containing aniline in a glass reactor arranged in a cascade configuration. pH conditions were studied and the concentration of PS was optimized. The synergism for aniline mineralization between the UV/H 2 O 2 process and the combined UV/H 2 O 2 /PS process was quantified in 10.1%. Aniline degradation reached 100% under the UV/H2O2/PS process after 20 min. Its mineralization is favored under acidic conditions and with the presence of persulfate (optimal conditions: 49% in 90 min; pH = 4; [PS] = 250 ppm). On the contrary, the worst conditions were found at pH = 11, since hydrogen peroxide decomposes and carbonates were formed increasing the scavenging effect. The different mechanisms involved (formulated from intermediates identified by mass spectrometry) confirm these results. Aniline was found to follow a degradation pathway where phenol is the main intermediate. The presence of sulfate radicals increases phenol degradation rate leading to a higher mineralization extent. Benzoquinone was identified as the main aromatic oxidation product of phenol, whereas succinic, 4-oxo-pentanoic, fumaric and oxalic acids were detected as aliphatic oxidation products for both UV/H2O2 and UV/H2O2/PS oxidation processes. Copyright © 2017 Elsevier Ltd. All rights reserved.

Simultaneous and spectroscopic redox molecular imaging of multiple free radical intermediates using dynamic nuclear polarization-magnetic resonance imaging.

PubMed

Hyodo, Fuminori; Ito, Shinji; Yasukawa, Keiji; Kobayashi, Ryoma; Utsumi, Hideo

2014-08-05

Redox reactions that generate free radical intermediates are essential to metabolic processes. However, their intermediates can produce reactive oxygen species, which may promote diseases related to oxidative stress. We report here the use of dynamic nuclear polarization-magnetic resonance imaging (DNP-MRI) to conduct redox molecular imaging. Using DNP-MRI, we obtained simultaneous images of free radical intermediates generated from the coenzyme Q10 (CoQ10), flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD) involved in the mitochondrial electron transport chain as well as the radicals derived from vitamins E and K1. Each of these free radicals was imaged in real time in a phantom comprising a mixture of free radicals localized in either lipophilic or aqueous environments. Changing the frequency of electron spin resonance (ESR) irradiation also allowed each of the radical species to be distinguished in the spectroscopic images. This study is the first to report the spectroscopic DNP-MRI imaging of free radical intermediates that are derived from endogenous species involved in metabolic processes.

Alcohols as alkylating agents in heteroarene C–H functionalization

PubMed Central

Jin, Jian; MacMillan, David W. C.

2015-01-01

Redox processes and radical intermediates are found in many biochemical processes, including deoxyribonucleotide synthesis and oxidative DNA damage1. One of the core principles that underlies DNA biosynthesis is the radical-mediated elimnation of H2O to deoxygenate ribonucleotides, an example of ‘spin-center shift’ (SCS)2, during which an alcohol C–O bond is cleaved, resulting in a carbon-centered radical intermediate. While SCS is a well-understood biochemical process, it is underutilized by the synthetic organic chemistry community. We wondered whether it would be possible to take advantage of this naturally occurring process to accomplish mild, non-traditional alkylations using alcohols as radical precursors. Considering traditional radical-based alkylation methods require the use of stoichiometric oxidants, elevated temperatures, or peroxides3–7, the development of a mild protocol using simple and abundant alkylating agents would have significant utility in the synthesis of diversely functionalized pharmacophores. In this manuscript, we describe the successful execution of this idea via the development of a dual catalytic alkylation of heteroarenes using alcohols as mild alkylating reagents. This method represents the first broadly applicable use of unactivated alcohols as latent alkylating reagents, achieved via the successful merger of photoredox and hydrogen atom transfer (HAT) catalysis. The utility of this multi-catalytic protocol has been demonstrated through the late-stage functionalization of the medicinal agents, fasudil and milrinone. PMID:26308895

The Rise of Radicals in Bioinorganic Chemistry.

PubMed

Gray, Harry B; Winkler, Jay R

2016-10-01

Prior to 1950, the consensus was that biological transformations occurred in two-electron steps, thereby avoiding the generation of free radicals. Dramatic advances in spectroscopy, biochemistry, and molecular biology have led to the realization that protein-based radicals participate in a vast array of vital biological mechanisms. Redox processes involving high-potential intermediates formed in reactions with O 2 are particularly susceptible to radical formation. Clusters of tyrosine (Tyr) and tryptophan (Trp) residues have been found in many O 2 -reactive enzymes, raising the possibility that they play an antioxidant protective role. In blue copper proteins with plastocyanin-like domains, Tyr/Trp clusters are uncommon in the low-potential single-domain electron-transfer proteins and in the two-domain copper nitrite reductases. The two-domain muticopper oxidases, however, exhibit clusters of Tyr and Trp residues near the trinuclear copper active site where O 2 is reduced. These clusters may play a protective role to ensure that reactive oxygen species are not liberated during O 2 reduction.

Reaction of atomic hydrogen with formic acid.

PubMed

Cao, Qian; Berski, Slawomir; Latajka, Zdzislaw; Räsänen, Markku; Khriachtchev, Leonid

2014-04-07

We study the reaction of atomic hydrogen with formic acid and characterize the radical products using IR spectroscopy in a Kr matrix and quantum chemical calculations. The reaction first leads to the formation of an intermediate radical trans-H2COOH, which converts to the more stable radical trans-cis-HC(OH)2via hydrogen atom tunneling on a timescale of hours at 4.3 K. These open-shell species are observed for the first time as well as a reaction between atomic hydrogen and formic acid. The structural assignment is aided by extensive deuteration experiments and ab initio calculations at the UMP2 and UCCSD(T) levels of theory. The simplest geminal diol radical trans-cis-HC(OH)2 identified in the present work as the final product of the reaction should be very reactive, and further reaction channels are of particular interest. These reactions and species may constitute new channels for the initiation and propagation of more complex organic species in the interstellar clouds.

Chemistry within Molecular van der Waals Clusters

DTIC Science & Technology

1990-07-18

and Discussion 1) Stabilizing an Unstable Reagent within a Cluster a) 1, 1- Difluoroethane Clusters 2) Providing New Chemical Pathways a) Ammonia...1- difluoroethane clusters 24, the generation of (CH3 OCH 3 )nH3 O+ & (CH3 OCH 3 )nCH3 OH2 + ions from dimethyl ether dusters25 ,26, the generation of...Stabilizing an Unstable Reagent within a Cluster a) 1.1- Difluoroethane Clusters 24 The dominant reactive process which occurs within the majority of cluster

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

PubMed Central

Liu, Neng; Moumanis, Khalid; Dubowski, Jan J.

2015-01-01

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75°. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15°, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer’s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103°. The XPS results indicate ArF laser induced formation of Si–(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals. PMID:26575362

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment.

PubMed

Liu, Neng; Moumanis, Khalid; Dubowski, Jan J

2015-11-09

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75°. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm(2), respectively, has decreased the CA to near 15°, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer's surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm(2) and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103°. The XPS results indicate ArF laser induced formation of Si-(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

Oxidation of carbon monoxide, hydrogen peroxide and water at a boron doped diamond electrode: the competition for hydroxyl radicals.

PubMed

Kisacik, Izzet; Stefanova, Ana; Ernst, Siegfried; Baltruschat, Helmut

2013-04-07

Boron doped diamond (BDD) electrodes have an extremely high over-voltage for oxygen evolution from water, which favours its use in oxidation processes of other compounds at high potentials. We used a rotating ring disc (RRDE) assembly and differential electrochemical mass spectrometry (DEMS) in order to monitor the consumption or the production of species in the course of the electrode processes. By intercepting the intermediate of the electrochemical water oxidation with chemical reactions we demonstrate clearly, albeit indirectly, that in the water oxidation process at BDD above 2.5 V the first step is the formation of ˙OH radicals. The electro-oxidation of CO to CO2 at BDD electrodes proceeds only via a first attack by ˙OH radicals followed by a further electron transfer to the electrode. At potentials below the onset of oxygen evolution from water, H2O2 is oxidised by a direct electron transfer to the BDD electrode, while at higher potentials, two different reactions paths compete for the ˙OH radicals formed in the first electron transfer from water: one, where these ˙OH radicals react with each other followed by further electron transfers leading to O2 on the one hand and one, where ˙OH radicals react with other species like H2O2 or CO with subsequent electron transfers on the other hand.

Mechanisms of strand break formation in DNA due to the direct effect of ionizing radiation: the dependency of free base release on the length of alternating CG oligodeoxynucleotides.

PubMed

Sharma, Kiran K; Razskazovskiy, Yuriy; Purkayastha, Shubhadeep; Bernhard, William A

2009-06-11

The question of how NA base sequence influences the yield of DNA strand breaks produced by the direct effect of ionizing radiation was investigated in a series of oligodeoxynucleotides of the form (d(CG)(n))(2) and (d(GC)(n))(2). The yields of free base release from X-irradiated DNA films containing 2.5 waters/nucleotide were measured by HPLC as a function of oligomer length. For (d(CG)(n))(2), the ratio of the Gua yield to Cyt yield, R, was relatively constant at 2.4-2.5 for n = 2-4 and it decreased to 1.2 as n increased from 5 to 10. When Gua was moved to the 5' end, for example going from d(CG)(5) to d(GC)(5), R dropped from 1.9 +/- 0.1 to 1.1 +/- 0.1. These effects are poorly described if the chemistry at the oligomer ends is assumed to be independent of the remainder of the oligomer. A mathematical model incorporating charge transfer through the base stack was derived to explain these effects. In addition, EPR was used to measure the yield of trapped-deoxyribose radicals at 4 K following X-irradiation at 4 K. The yield of free base release was substantially greater, by 50-100 nmol/J, than the yield of trapped-deoxyribose radicals. Therefore, a large fraction of free base release stems from a nonradical intermediate. For this intermediate, a deoxyribose carbocation formed by two one-electron oxidations is proposed. This reaction pathway requires that the hole (electron loss site) transfers through the base stack and, upon encountering a deoxyribose hole, oxidizes that site to form a deoxyribose carbocation. This reaction mechanism provides a consistent way of explaining both the absence of trapped radical intermediates and the unusual dependence of free base release on oligomer length.

Bis-propargyl thermosets

DOEpatents

Douglas, Elliot P.; Langlois, David A.; Benicewicz, Brian C.

1995-01-01

The present invention provides (1) curable bispropargyl-containing monomers represented by the formula: B.sup.1 --A.sup.1.sub.m --R--A.sup.2.sub.n --B.sup.2 wherein R is a radical selected from the group consisting of 1,4-phenylene, 4,4'-biphenyl, 2,6-naphthalene, --C.sub.6 H.sub.4 --CR.sup.2 .dbd.CR.sup.2 --C.sub.6 H.sub.4 -- wherein R.sup.2 is H or CH.sub.3, and the same where said groups contain one or more substituents selected from the group consisting of halo, nitro, lower alkyl, lower alkoxy, fluoroalkyl or fluoroalkoxy, A.sup.1 and A.sup.2 are selected from the group consisting of --C.sub.6 H.sub.4 --C(O)--O-- and --C.sub.6 H.sub.4 --O--C(O)--, m and n are 0 or 1, m+n is 0, 1 or 2, and B.sup.1 and B.sup.2 are --OCH.sub.2 --C.tbd.C--H, (2) thermoset compositions comprised of cured segments derived from monomers represented by the formula: B.sup.1 --A.sup.1.sub.m --R--A.sup.2.sub.n --B.sup.2 as described above, and (3) curable blends of at least two of the monomers.

Hydrolysis of Mg(BH4)2 and its coordination compounds as a way to obtain hydrogen

NASA Astrophysics Data System (ADS)

Solovev, Mikhail V.; Chashchikhin, Oleg V.; Dorovatovskii, Pavel V.; Khrustalev, Victor N.; Zyubin, A. S.; Zyubina, T. S.; Kravchenko, O. V.; Zaytsev, Alexey A.; Dobrovolsky, Yu. A.

2018-02-01

Three ligand-stabilized Mg(BH4)2-based complexes have been synthesized and evaluated as potential hydrogen storage media for portable fuel cell applications. The new borohydrides: Mg(BH4)2 × 0.5Et2O and Mg(BH4)2 × diglyme (diglyme - CH3O(CH2)2O(CH2)2OCH3) have been synthesized and examined by X-ray single crystal diffraction method. Hydrolysis reactions of the compounds liberate hydrogen in quantities ranging from 46 to 96% of the theoretical yield. The hydrolysis of Mg(BH4)2 and other borohydrides is also accompanied by the diborane formation. The amount of liberated diborane depends on the Mg-coordination environment. To explain this fact quantum-chemical calculations have been performed. It is shown that formation of Mg-O-Mg-bridges enables the side process of diborane generation. It means that the size and denticity of the ligand directly affects the amount of released diborane. In general, the larger the ligand and the higher its denticity, the smaller is amount of diborane produced. The new compound Mg(BH4)2 × diglyme decomposes without diborane formation that allows one to be considered as a new promising chemical hydrogen storage compound for the practical usage.

Intermediates in the reaction of substrate-free cytochrome P450cam with peroxy acetic acid.

PubMed

Schünemann, V; Jung, C; Trautwein, A X; Mandon, D; Weiss, R

2000-08-18

Freeze-quenched intermediates of substrate-free cytochrome 57Fe-P450(cam) in reaction with peroxy acetic acid as oxidizing agent have been characterized by EPR and Mossbauer spectroscopy. After 8 ms of reaction time the reaction mixture consists of approximately 90% of ferric low-spin iron with g-factors and hyperfine parameters of the starting material; the remaining approximately 10% are identified as a free radical (S' = 1/2) by its EPR and as an iron(IV) (S= 1) species by its Mossbauer signature. After 5 min of reaction time the intermediates have disappeared and the Mossbauer and EPR-spectra exhibit 100% of the starting material. We note that the spin-Hamiltonian analysis of the spectra of the 8 ms reactant clearly reveals that the two paramagnetic species, e.g. the ferryl (iron(IV)) species and the radical, are not exchanged coupled. This led to the conclusion that under the conditions used, peroxy acetic acid oxidized a tyrosine residue (probably Tyr-96) into a tyrosine radical (Tyr*-96), and the iron(III) center of substrate-free P450(cam) to iron(IV).

Utilisation of an eta(3)-allyl hydride complex, formed by UV irradiation, as a controlled source of 16-electron (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe).

PubMed

Sexton, Catherine J; López-Serrano, Joaquín; Lledós, Agustí; Duckett, Simon B

2008-10-21

Low temperature UV irradiation of solutions of (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe)(2) yields (eta(5)-C(5)Me(5))Rh(eta(3)-CH(2)CHCH(2))(H), which provides controlled access to the 16-electron fragment (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe).

Chemiluminescent reaction of oxygen atoms with some nitrile compounds

NASA Astrophysics Data System (ADS)

Upadhyaya, Hari P.; Pavanaja, Ubaradka B.; Sapre, Avinash V.; Rama Rao, Kuchimanchi V. S.; Mittal, Jai P.

1994-09-01

In a discharge-flow experiment, chemiluminescent reactions of oxygen atoms (O( 3P)) with organic nitriles (RCN) are studied. For unsaturated nitriles RCN (R: CH 2=CH; CH 2=C(CH 3); CH 2=CH(CH 2)) the observed emission is attributed to CN * (B→X) and NO * (γ:A→X and β: B→X, bands). For saturated and phenyl nitriles (R: CH 3; C 2H 5; C 6H 5) emission is only observed from CN * (B 2Σ +). A suitable reaction mechanism for the observed emission is proposed.

Experimental study and detailed modeling of toluene degradation in a low-pressure stoichiometric premixed CH4/O2/N2 flame.

PubMed

Bakali, A El; Dupont, L; Lefort, B; Lamoureux, N; Pauwels, J F; Montero, M

2007-05-17

Temperature and mole fraction profiles have been measured in laminar stoichiometric premixed CH4/O2/N2 and CH4/1.5%C6H5CH3/O2/N2 flames at low pressure (0.0519 bar) by using thermocouple, molecular beam/mass spectrometry (MB/MS), and gas chromatography/mass spectrometry (GC/MS) techniques. The present study completes our previous work performed on the thermal degradation of benzene in CH4/O2/N2 operating at similar conditions. Mole fraction profiles of reactants, final products, and reactive and stable intermediate species have been analyzed. The main intermediate aromatic species analyzed in the methane-toluene flame were benzene, phenol, ethylbenzene, benzylalcohol, styrene, and benzaldehyde. These new experimental results have been modeled with our previous model including submechanisms for aromatics (benzene up to p-xylene) and aliphatic (C1 up to C7) oxidation. Good agreement has been observed for the main species analyzed. The main reaction paths governing the degradation of toluene in the methane flame were identified, and it occurs mainly via the formation of benzene (C6H5CH3 + H = C6H6 + CH3) and benzyl radical (C6H5CH3 + H = C6H5CH2 + H2). Due to the abundance of methyl radicals, it was observed that recombination of benzyl and methyl is responsible for main monosubstitute aromatic species analyzed in the methane-toluene flame. The oxidation of these substitute species led to cyclopentadienyl radical as observed in a methane-benzene flame.

Oral Chloral Hydrate Compare with Rectal Thiopental in Pediatric Procedural Sedation and Analgesia; a Randomized Clinical Trial.

PubMed

Azizkhani, Reza; Kanani, Soheila; Sharifi, Ali; Golshani, Keihan; Masoumi, Babak; Ahmadi, Omid

2014-01-01

The increasing use of diagnostic imaging in pediatric medicine has resulted in growing need for procedural sedation and analgesia (PSA) to minimize motion artifacts during procedures. The drug of choice in pediatric PSA was not introduced until now. The aim of the present study was comparison of oral chloral hydrate (OCH) and rectal sodium thiopental (RST) in pediatric PSA. In the present randomized clinical trial, 2-6 years old pediatrics who referred for performing brain computed tomography scan was enrolled and were randomly divided in to two groups. OCH (50mg/kg) and RST (25mg/kg) were prescribed and a trained nurse recorded the time from drug prescription to receiving the conscious sedation (onset of action), the total period which the patient has the Ramsay score≥4 (duration of action), and adverse effect of agents. Mann-Whitney U test and chi-squared test, and Non-parametric analysis of covariance (ANCOVA) were used for comparisons. One hundred and forty children were entered to two groups of OCH and RST, randomly. The patients of two groups had similar age, sex, weight, and baseline vital signs except for diastolic blood pressure (p<0.001). The onset of action in OCH and RST groups were 24.5±6.1and 28.7±5.2 minutes, respectively (p<0.001). Duration of action in OCH and RST groups were 12.9±2.8 minutes and 13.7±2.6 minutes, respectively (p=0.085). Non-parametric ANCOVA revealed that only diastolic blood pressure was affected by drug prescription (p=0.001). In 11(15.7%) patients in RST group, diarrhea was observed during 24 hours (p=0.001). Oxygen desaturation was observed only in two patients, both in OCH group. Each of the sedative has advantages and disadvantages that should be considered when selecting one for inducing short-term sedation. It seems that rectal sodium thiopental and oral chloral hydrate are equally effective in pediatric PSA and based on patient's condition we can administrate one of these agents.

A computational study of the catalytic aerobic epoxidation of propylene over the coordinatively unsaturated metal-organic framework Fe3(btc)2: formation of propylene oxide and competing reactions.

PubMed

Maihom, Thana; Sawangphruk, Montree; Probst, Michael; Limtrakul, Jumras

2018-02-28

The aerobic epoxidation of propylene over the metal-organic framework Fe 3 (btc) 2 (btc = 1,3,5-benzentricarboxylate) as catalyst has been investigated by means of density functional calculations. The mechanisms of the reaction towards propylene oxide, carbonylic products (acetone and propanal) and a pi-allyl radical were investigated to assess the efficiency of Fe 3 (btc) 2 for the selective formation of propylene oxide. Propylene oxide and carbonylic products are formed on Fe 3 (btc) 2 by proceeding via propyleneoxy intermediates in the first step. Subsequently, the intermediates can then either be transformed to propylene oxide by way of ring closure of the intermediate or to the carbonylic compounds of propanal and acetone via 1,2-hydride shift. The results show that the formation of propylene oxide is favored over the formation of carbonylic products mainly due to the activation barriers being 2-3 times smaller. The activation barriers for the formation of the propyleneoxy intermediates on the Fe 3 (btc) 2 catalyst for the first and second reaction cycle are also lower than the barriers obtained for the formation of the pi-allyl radical that acts as the precursor to combustion products. On the basis of these computational results, we therefore expect a high catalytic selectivity of the Fe 3 (btc) 2 catalyst with respect to the formation of propylene oxide. We also compared the catalytic activities of Fe 3 (btc) 2 and Cu 3 (btc) 2 . The activation energy of the rate-determining step is almost 2 times lower for Fe 3 (btc) 2 than that for Cu 3 (btc) 2 , due to a larger charge transfer from the catalytic site to the O 2 molecule in the case of Fe 3 (btc) 2 .

Influence of oxidative and nitrosative stress on accumulation of diphosphate intermediates of the non-mevalonate pathway of isoprenoid biosynthesis in corynebacteria and mycobacteria.

PubMed

Artsatbanov, V Yu; Vostroknutova, G N; Shleeva, M O; Goncharenko, A V; Zinin, A I; Ostrovsky, D N; Kapreliants, A S

2012-04-01

Artificial generation of oxygen superoxide radicals in actively growing cultures of Mycobacterium tuberculosis, Myc. smegmatis, and Corynebacterium ammoniagenes is followed by accumulation in the bacterial cells of substantial amounts of 2-C-methyl-D-erythritol-2,4-cyclodiphosphate (MEcDP) - an intermediate of the non-mevalonate pathway of isoprenoid biosynthesis (MEP) - most possibly due to the interaction of the oxygen radicals with the 4Fe-4S group in the active center and inhibition of the enzyme (E)-4-oxy-3-methylbut-2-enyl diphosphate synthase (IspG). Cadmium ions known to inhibit IspG enzyme in chloroplasts (Rivasseau, C., Seemann, M., Boisson, A. M., Streb, P., Gout, E., Douce, R., Rohmer, M., and Bligny, R. (2009) Plant Cell Environ., 32, 82-92), when added to culture of Myc. smegmatis, substantially increase accumulation of MEcDP induced by oxidative stress with no accumulation of other organic phosphate intermediates in the cell. Corynebacterium ammoniagenes'', well-known for its ability to synthesize large amounts of MEcDP, was also shown to accumulate this unique cyclodiphosphate in actively growing culture when NO at low concentration is artificially generated in the medium. A possible role of the MEP-pathway of isoprenoid biosynthesis and a role of its central intermediate MEcDP in bacterial response to nitrosative and oxidative stress is discussed.

Kinetics and Near-Infrared Spectroscopy of Organic Peroxy Radicals

NASA Astrophysics Data System (ADS)

Smarte, M. D.; Okumura, M.

2016-12-01

Organic peroxy radicals are important intermediates in atmospheric chemistry with fates that control the rate of radical propagation in an oxidation mechanism. Laboratory methods for detecting peroxy radicals are essential to measuring precise rate constants that constrain these fates. In this work, we discuss the use of near-infrared cavity ringdown spectroscopy to detect organic peroxy radicals for the purpose of laboratory kinetics measurements. We focus on chlorine-substituted peroxy radicals generated in the oxidation of alkenes by chlorine, a minor tropospheric oxidant found in marine and coastal regions. Previous kinetics experiments on peroxy radicals have largely used UV absorption spectroscopy via the dissociative B-X transition. However, the spectra produced are featureless and exhibit substantial overlap; determining the concentration profile of an individual peroxy radical can be an arduous task. In our work, we probe the forbidden peroxy radical A-X transition in the near-infrared. While this approach requires overcoming small cross sections ( 10-21 cm2), the A state is bound and leads to structured absorption spectra that may be useful in constraining the kinetics of mixtures of organic peroxy radicals formed in the oxidation of complex hydrocarbons. Only a few kinetics studies utilizing the A-X transition exist in the literature and they are focused on small, unsubstituted species. This presentation explores the ability of the A-X transition to unravel the kinetics of more complex peroxy radicals in laboratory experiments using several example systems: (1) Determining rate constants for the self and cross reactions of β-chloroethylperoxy and HO2. (2) Detecting the second generation of peroxy radicals formed from alkoxy radical decomposition in the chlorine-initiated oxidation of 2-butene. (3) Observing different rates of reactivity with NO across the pool of peroxy radical isomers formed in the chlorine-initiated oxidation of isoprene.

Reduction mechanisms of additives on Si anodes of Li-ion batteries.

PubMed

Martínez de la Hoz, Julibeth M; Balbuena, Perla B

2014-08-28

Solid-electrolyte interphase (SEI) layers are films deposited on the surface of Li-ion battery electrodes during battery charge and discharge processes. They are due to electrochemical instability of the electrolyte which causes electron transfer from (to) the anode (cathode) surfaces. The films could have a protective passivating role and therefore understanding the detailed reduction (oxidation) processes is essential. Here density functional theory and ab initio molecular dynamics simulations are used to investigate the reduction mechanisms of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) on lithiated silicon surfaces. These species are frequently used as "additives" to improve the SEI properties. It is found that on lithiated Si anodes (with low to intermediate degrees of lithiation) VC may be reduced via a 2e(-) mechanism yielding an opened VC(2-) anion. At higher degrees of lithiation, such a species receives two extra electrons from the surface resulting in an adsorbed CO(2-)(ads) anion and a radical anion ˙OC2H2O(2-). Additionally, in agreement with experimental observations, it is shown that CO2 can be generated from reaction of VC with the CO3(2-)anion, a product of the reduction of the main solvent, ethylene carbonate (EC). On the other hand, FEC reduction on LixSiy surfaces is found to be independent of the degree of lithiation, and occurs through three mechanisms. One of them leads to an adsorbed VC(2-) anion upon release from the FEC molecule and adsorption on the surface of F(-) and one H atom. Thus in some cases, the reduction of FEC may lead to the exact same reduction products as that of VC, which explains similarities in SEI layers formed in the presence of these additives. However, FEC may be reduced via two other multi-electron transfer mechanisms that result in formation of either CO2(2-), F(-), and ˙CH2CHO(-) or CO(2-), F(-), and ˙OCH2CHO(-). These alternative reduction products may oligomerize and form SEI layers with different components than those formed in the presence of VC. In all cases, FEC reduction also leads to formation of LiF moieties on the anode surface, in agreement with reported experimental data. The crucial role of the surface in each of these mechanisms is thoroughly explained.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santamaria, J.; Pasquier, C.; Ferradini, C.

The oxidation in aqueous solutions of hypoxanthine into xanthine and xanthine into uric acid by OH radicals has been investigated using pulse radiolysis and fast kinetic absorption spectrophotometry. After hypoxanthine irradiations the spectrum of transient R/sub 1/ has been characterized. This radical is formed with a rate constant k/sub (Hyx+OH) = 6.5 x 10/sup 9/ M/sup -1/ sec/sup -1/ and disappears by disproportionation leading to xanthine and hypoxanthine with a rate constant 2K/sub (R/sub 1/+ r/sub 1// = 1.3 x 10/sup 8/ M/sup -1/ sec/sup -//sub 1/. After xanthine irradiations a radical intermediate R/sub 2/ is formed with a ratemore » constant k/sub(X+ OH)/= 5.2 x 10/sup 8/ M/sup -1/ sec/sup -1/ and disappears through a second-order reaction 2K/sub (R/sub 2/+ R/sub 2/)/ = 2.0 x 10/sup 8/ M/sup -1/ sec/sup -1/. Finally, after aeration only uric acid and xanthine are measured.« less

Magnetic field effects on coenzyme B12- and B6-dependent lysine 5,6-aminomutase: switching of the J-resonance through a kinetically competent radical-pair intermediate.

PubMed

Chen, Jun-Ru; Ke, Shyue-Chu

2018-05-09

The environmental magnetic field is beneficial to migratory bird navigation through the radical-pair mechanism. One of the continuing challenges in understanding how magnetic fields may perturb biological processes is that only a very few field-sensitive examples have been explored despite the prevalence of radical pairs in enzymatic reactions. We show that the reaction of adenosylcobalamin- and pyridoxal-5'-phosphate-dependent lysine 5,6-aminomutase proceeds via radical-pair intermediates and is magnetic field dependent. The 5'-deoxyadenosyl radical from adenosylcobalamin abstracts a C5(H) from the substrate to yield a {cob(ii)alamin - substrate} radical pair wherein the large spin-spin interaction (2J = 8000 gauss) locks the radical pair in a triplet state, as evidenced by electron paramagnetic resonance spectroscopy. Application of an external magnetic field in the range of 6500 to 8500 gauss triggers intersystem crossing to the singlet {cob(ii)alamin - substrate} radical-pair state. Spin-conserved H back-transfer from deoxyadenosine to the substrate radical yields a singlet {cob(ii)alamin-5'-deoxyadenosyl} radical pair. Spin-selective recombination to adenosylcobalamin decreased the enzyme catalytic efficiency kcat/Km by 16% at 7600 gauss. As a mechanistic probe, observation of magnetic field effects successfully demonstrates the presence of a kinetically significant radical pair in this enzyme. The study of a pronounced high-field level-crossing characteristic through an immobilized radical pair with a constant exchange interaction deepens our understanding of how a magnetic field may interact with an enzyme.

[Inhibiting properties of stable nitroxyl radicals in reactions of linoleic acid and linoleyl alcohol oxidation catalyzed by 5-lipoxygenase].

PubMed

Kharchenko, O V; Kharitonenko, A I; Vovk, A I; Kukhar', V P; Babiĭ, L V; Khil'chevskiĭ, A N; Mel'nik, A K

2005-01-01

The inhibiting effects of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its 4-substituted derivatives in reactions of linoleyl acid or linoleyl alcohol oxidation catalyzed by potato tuber 5-lipoxygenase were investigated. Inhibiting properties of stable nitroxyl radicals in presence of lubrol and SDS were reduced at the transition from TEMPO to 4-hydroxy-TEMPO or 4-amino-TEMPO and increased at use of adamantane-1-carboxylic or 3-methyladamantane-1-carboxylic acid 1-oxyl-2,2,6,6-tetramethylpiperidine-4-yl esters. Enzyme activity at saturating concentrations of inhibitor was not suppressed completely, and decreased up to the certain level determined by the substrate nature. The dependence of partial inhibition efficiency on rotational correlation time of stable nitroxides in model micellar systems were analysed. It was supposed that 5-lipoxygenase inhibition includes the interaction of hydrophobic nitroxide with radical intermediate formed in enzymatic process.

Inhibition effects of flavonoids on 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline and 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline formation and alkoxy radical scavenging capabilities of flavonoids in a model system.

PubMed

Shao, Zeping; Han, Zhonghui; Zhang, Jinhui; Zhang, Yan; Wang, Shuo

2018-06-01

Heterocyclic aromatic amines (HAAs) have been considered as carcinogenic and mutagenic chemicals generated during thermal processing of protein-rich foods that can be inhibited by some flavonoids. Free radical scavenging is a major characteristic of flavonoids. The half-maximal inhibitory concentration (IC 50 ) values of nine flavonoids were determined by evaluating their capacity to inhibit 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline (7,8-DiMeIQx) formation in a model system. The results of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) test validated that MeIQx and 7,8-DiMeIQx formed via a free radical pathway. Electron spin resonance (ESR) spectroscopic analysis with spin trapping (α-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN) spin adduct, a N  = 15.2 G and a H  = 2.7 G) revealed that an alkoxy radical was the generated intermediate. The scavenging capacities of the nine flavonoids on alkoxy radicals were then evaluated based on the ESR spectra of the POBN spin adducts. The weak correlation between the alkoxy radical scavenging capacities and IC 50 of the flavonoids suggested that their inhibitory activity against MeIQx and 7,8-DiMeIQx formation operates by a more complex mechanism than simply scavenging alkoxy radicals. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

Electrochemical treatment of 2, 4-dichlorophenol using a nanostructured 3D-porous Ti/Sb-SnO2-Gr anode: Reaction kinetics, mechanism, and continuous operation.

PubMed

Asim, Sumreen; Zhu, Yunqing; Batool, Aisha; Hailili, Reshalaiti; Luo, Jianmin; Wang, Yuanhao; Wang, Chuanyi

2017-10-01

2, 4-dichlorophenol (2, 4-DCP) is considered to be a highly toxic, mutagenic, and possibly carcinogenic pollutant. This study is focused on the electrochemical oxidation of 2, 4-DCP on nanostructured 3D-porous Ti/Sb-SnO 2 -Gr anodes, with the aim of presenting a comprehensive elucidation of mineralization process through the investigation of influential kinetics, the reactivity of hydroxyl radical's and analysis of intermediates. High efficiency was achieved at pH of 3 using Na 2 SO 4 electrolytes at a current density of 30 mA cm -2 . Under the optimized conditions, a maximum removal of 2, 4-DCP of up to 99.9% was reached, whereas a TOC removal of 81% was recorded with the lowest EC TOC (0.49 kW h g -1 ) within 40 min of electrolysis. To explore the stability of the 3D-Ti/Sb-SnO 2 -Gr electrodes, a continuous electrochemical operation was established, and the consistent mineralization results indicated the effectiveness of the 3D-Ti/Sb-SnO 2 -Gr system concerning its durability and practical utilization. EPR studies demonstrated the abundant generation of OH radicals on 3D-Ti/Sb-SnO 2 -Gr, resulting in fast recalcitrant pollutant incineration. From dechlorination and the reactivity of the OH radicals, several intermediates including six cyclic byproducts and three aliphatic carboxylic acids were detected, and two possible degradation pathways were proposed that justify the complete mineralization of 2, 4-DCP. Copyright © 2017 Elsevier Ltd. All rights reserved.

Rubber-Modified Epoxies: Morphology and Mechanical Properties.

DTIC Science & Technology

1980-09-01

matrix and enhances ductility. The elastomers used in the present study are carboxyl-terminated copolymers of butadiene and acrylonitrile ( CTBN ). The...marketed under the trade name Hycar CTBN . The structure of Hycar CTBN is HO - C(CH2CH = CHCH2)x--(CH2-CH) ) -C-OH o CN 0 where x : 5, y = I and z = 10...for a typical copolymer. (Properties of CTBN rubbers are found in ref. 8.) Two rubber modifiers, CTBN (X]3) and CTBN (X8), with 27 and 17 wt

Synthesis of Antidotes and Prophylactics for Organophosphorus Acetylcholinesterase Inhibitors

DTIC Science & Technology

1996-01-01

Choline A nalogs .............................................. 13 D . M iscellaneous Com pounds...27b 27c (PN-III-28) CH(CH3 )2 TsO 28a 28b 28c (PN-II-258) Ph I C. Carbamoyl enolates of Choline Analogs The enolates of 1-methyl-3-piperidone and 1...sodium bicarbonate solution. The crystalline solid obtained was filtered and dried to give 4.5 g (77%) of the amine. 6-Benzoyloxyimidazo[1,2-a]pyridine

Measuring sunscreen protection against solar-simulated radiation-induced structural radical damage to skin using ESR/spin trapping: development of an ex vivo test method.

PubMed

Haywood, Rachel; Volkov, Arsen; Andrady, Carima; Sayer, Robert

2012-03-01

The in vitro star system used for sunscreen UVA-testing is not an absolute measure of skin protection being a ratio of the total integrated UVA/UVB absorption. The in vivo persistent-pigment-darkening method requires human volunteers. We investigated the use of the ESR-detectable DMPO protein radical-adduct in solar-simulator-irradiated skin substitutes for sunscreen testing. Sunscreens SPF rated 20+ with UVA protection, reduced this adduct by 40-65% when applied at 2 mg/cm(2). SPF 15 Organic UVA-UVB (BMDBM-OMC) and TiO(2)-UVB filters and a novel UVA-TiO(2) filter reduced it by 21, 31 and 70% respectively. Conventional broad-spectrum sunscreens do not fully protect against protein radical-damage in skin due to possible visible-light contributions to damage or UVA-filter degradation. Anisotropic spectra of DMPO-trapped oxygen-centred radicals, proposed intermediates of lipid-oxidation, were detected in irradiated sunscreen and DMPO. Sunscreen protection might be improved by the consideration of visible-light protection and the design of filters to minimise radical leakage and lipid-oxidation.

Homogeneous reduction of CO2 by photogenerated pyridinyl radicals.

PubMed

Riboni, Francesca; Selli, Elena; Hoffmann, M R; Colussi, A J

2015-05-14

We report that 1-hydropyridinyl radicals (1-PyH(•)) photogenerated in solution react with dissolved CO2 en route to its 2e(-) reduction into carboxylic acids. The 254 nm excitation of pyridine (Py) in deaerated 2-PrOH/H2O mixtures saturated with 1 atm of CO2 yields a suite of products, among which we identified Na(HCOO)2(-) (m/z(-) = 113), C5H6NCOO(-) (m/z(-) = 124), and C5H10O2NCOO(-) (m/z(-) = 160) species by electrospray ionization mass spectrometry. These products demonstrably contain carboxylate functionalities that split CO2 neutrals via collisionally induced dissociation. We infer that 1-PyH(•) [from (1) (3)Py* + 2-PrOH → 1-PyH(•) + (•)PrOH] adds to CO2, in competition with radical-radical reactions, leading to intermediates that are in turn reduced by (•)PrOH into the observed species. The formation of carboxylates in this system, which is shown to require CO2, Py, 2-PrOH, and actinic radiation, amounts to the homogeneous 2e(-) reduction of CO2 by 2-PrOH initiated by Py*. We evaluate a rate constant (2) k2(1-PyH(•) + CO2 → (•)Py-1-COOH) ≈ O (10) M(-1) s(-1) and an activation energy E2 ≥ 9 kcal mol(-1) that are compatible with thermochemical estimates for this reaction.

UV Photodesorption of Methanol in Pure and CO-rich Ices: Desorption Rates of the Intact Molecule and of the Photofragments

NASA Astrophysics Data System (ADS)

Bertin, Mathieu; Romanzin, Claire; Doronin, Mikhail; Philippe, Laurent; Jeseck, Pascal; Ligterink, Niels; Linnartz, Harold; Michaut, Xavier; Fillion, Jean-Hugues

2016-02-01

Wavelength-dependent photodesorption rates have been determined using synchrotron radiation for condensed pure and mixed methanol ice in the 7-14 eV range. The VUV photodesorption of intact methanol molecules from pure methanol ices is found to be of the order of 10-5 molecules/photon, that is two orders of magnitude below what is generally used in astrochemical models. This rate gets even lower (<10-6 molecules/photon) when the methanol is mixed with CO molecules in the ices. This is consistent with a picture in which photodissociation and recombination processes are at the origin of intact methanol desorption from pure CH3OH ices. Such low rates are explained by the fact that the overall photodesorption process is dominated by the desorption of the photofragments CO, CH3, OH, H2CO, and CH3O/CH2OH, whose photodesorption rates are given in this study. Our results suggest that the role of the photodesorption as a mechanism to explain the observed gas phase abundances of methanol in cold media is probably overestimated. Nevertheless, the photodesorption of radicals from methanol-rich ices may stand at the origin of the gas phase presence of radicals such as CH3O, therefore, opening new gas phase chemical routes for the formation of complex molecules.

Spectroscopic and Kinetic Characterization of Peroxidase-Like π-Cation Radical Pinch-Porphyrin-Iron(III) Reaction Intermediate Models of Peroxidase Enzymes.

PubMed

Hernández Anzaldo, Samuel; Arroyo Abad, Uriel; León García, Armando; Ramírez Rosales, Daniel; Zamorano Ulloa, Rafael; Reyes Ortega, Yasmi

2016-06-27

The spectroscopic and kinetic characterization of two intermediates from the H₂O₂ oxidation of three dimethyl ester [(proto), (meso), (deuteroporphyrinato) (picdien)]Fe(III) complexes ([FePPPic], [FeMPPic] and [FeDPPic], respectively) pinch-porphyrin peroxidase enzyme models, with s = 5/2 and 3/2 Fe(III) quantum mixed spin (qms) ground states is described herein. The kinetic study by UV/Vis at λmax = 465 nm showed two different types of kinetics during the oxidation process in the guaiacol test for peroxidases (1-3 + guaiacol + H₂O₂ → oxidation guaiacol products). The first intermediate was observed during the first 24 s of the reaction. When the reaction conditions were changed to higher concentration of pinch-porphyrins and hydrogen peroxide only one type of kinetics was observed. Next, the reaction was performed only between pinch-porphyrins-Fe(III) and H₂O₂, resulting in only two types of kinetics that were developed during the first 0-4 s. After this time a self-oxidation process was observed. Our hypotheses state that the formation of the π-cation radicals, reaction intermediates of the pinch-porphyrin-Fe(III) family with the ligand picdien [N,N'-bis-pyridin-2-ylmethyl-propane-1,3-diamine], occurred with unique kinetics that are different from the overall process and was involved in the oxidation pathway. UV-Vis, ¹H-NMR and ESR spectra confirmed the formation of such intermediates. The results in this paper highlight the link between different spectroscopic techniques that positively depict the kinetic traits of artificial compounds with enzyme-like activity.

Pulse radiolysis in model studies toward radiation processing

NASA Astrophysics Data System (ADS)

Von Sonntag, C.; Bothe, E.; Ulanski, P.; Deeble, D. J.

1995-02-01

Using the pulse radiolysis technique, the OH-radical-induced reactions of poly(vinyl alcohol) PVAL, poly(acrylic acid) PAA, poly(methacrylic acid) PMA, and hyaluronic acid have been investigated in dilute aqueous solution. The reactions of the free-radical intermediates were followed by UV-spectroscopy and low-angle laser light-scattering; the scission of the charged polymers was also monitored by conductometry. For more detailed product studies, model systems such as 2,4-dihydroxypentane (for PVAL) and 2,4-dimethyl glutaric acid (for PAA) was also investigated. With PVA, OH-radicals react predominantly by abstraction of an H-atom in α-position to the hydroxyl group (70%). The observed bimolecular decay rate constant of the PVAL-radicals decreases with time. This has been interpreted as being due to an initially fast decay of proximate radicals and a decrease of the probability of such encounters with time. Intramolecular crosslinking (loop formation) predominates at high doses per pulse. In the presence of O 2, peroxyl radicals are formed which in the case of the α-hydroxyperoxyl radicals can eliminate HO 2-radicals in competition with bimolecular decay processes which lead to a fragmentation of the polymer. In PAA, radicals both in α-position (characterized by an absorption near 300 nm) and in β-position to the carboxylate groups are formed in an approximately 1:2 ratio. The lifetime of the radicals increases with increasing electrolytic dissociation of the polymer. The β-radicals undergo a slow (intra- as well as intermolecular) H-abstraction yielding α-radicals, in competition to crosslinking and scission reactions. In PMA only β-radicals are formed. Their fragmentation has been followed by conductometry. In hyaluronic acid, considerable fragmeentation is observed even in the absence of oxygen which, in fact, has some protective effect against this process. Thus free-radical attack on this important biopolymer makes it especially vulnerable with respect to a reduction of its viscosity, and in rheumatic diseases this effect may be the reason for their painfulnes.

Reactions of the linear tetranuclear complex Ru sub 4 (CO) sub 10 (CH sub 3 C double bond C(H)C(H) double bond N-i-Pr) sub 2 with oxidizing reagents. Syntheses of halide-bridged (Ru(CO) sub 2 X(CH sub 3 C double bond C(H)C(H) double bond N-i-Pr)) sub 2 and fac-Ru(CO) sub 3 X(CH sub 3 C double bond C(H)C(H) double bond N-i-Pr)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mul, W.P.; Elsevier, C.J.; van Leijen, M.

1991-01-01

The linear tetranuclear complex Ru{sub 4}(CO){sub 10}(CH{sub 3}C{double bond}C(H)C(H){double bond}N-i-Pr){sub 2} (1), containing two {eta}{sup 5}-azaruthenacyclopentadienyl systems, reacts with oxidizing reagents (I{sub 2}, Br{sub 2}, NBS, CCl{sub 4}) at elevated temperatures (40-90C) in heptane or benzene to give the new dimeric halide-bridged organoruthenium(II) complexes (Ru(CO){sub 2}X(CH{sub 3}C{double bond}C(H)C(H){double bond}N-i-Pr)){sub 2} (X = I (3a), X = Br (3b), Cl (3c); yield 30-80%) together with (Ru(CO){sub 3}X{sub 2}){sub 2}. The reactions of 1 with CX{sub 4} (X = I, Br, Cl) are accelerated by CO, probably because Ru{sub 4}(CO){sub 12}(CH{sub 3}C{double bond}C(H)C(H){double bond}N-i-Pr){sub 2} (5), which contains two unbridged metal-metal bonds,more » is formed prior to oxidation. The halide-bridged dimers 3a-c are obtained as mixtures of four isomers, the configurations of which are discussed. Splitting of the halide bridges takes place when a solution of 3a-c is saturated with CO, whereby mononuclear fac-Ru(CO){sub 3}X(CH{sub 3}C{double bond}C(H)C(H){double bond}N-i-Pr) (4a-c) is obtained. This process is reversible; ie., passing a stream of nitrogen through a solution of 4a-c or removal of the solvent under vacuum causes the reverse reaction with reformation of 3a-c. Compounds 3a-c and 4a-c have been characterized by IR (3, 4), FD mass (3), {sup 1}H (3, 4), and {sup 13}C{l brace}H{r brace} NMR (4) spectroscopy and satisfactory elemental analyses have been obtained for 3a-c. Compounds 3 and 4 are suitable precursors for the preparation of new homo- and heteronuclear transition-metal complexes.« less

Radical Abstraction Reactions with Concerted Fragmentation in the Chain Decay of Nitroalkanes

NASA Astrophysics Data System (ADS)

Denisov, E. T.; Shestakov, A. F.

2018-05-01

Reactions of the type X• + HCR2CH2NO2 → XH + R2C=CH2 + N•O2 are exothermic, due to the breaking of weak C-N bonds and the formation of energy-intensive C=C bonds. Quantum chemistry calculations of the transition state using the reactions of Et• and EtO• with 2-nitrobutane shows that such reactions can be categorized as one-step, due to the extreme instability of the intermediate nitrobutyl radical toward decay with the formation of N•O2. Kinetic parameters that allow us to calculate the energy of activation and rate constant of such a reaction from its enthalpy are estimated using a model of intersecting parabolas. Enthalpies, energies of activation, and rate constants are calculated for a series of reactions with the participation of Et•, EtO•, RO•2, N•O2 radicals on the one hand and a series of nitroalkanes on the other. A new kinetic scheme of the chain decay of nitroalkanes with the participation of abstraction reactions with concerted fragmentation is proposed on the basis of the obtained data.

Missing Peroxy Radical Sources Within a Rural Forest Canopy

NASA Technical Reports Server (NTRS)

Wolfe, G. M.; Cantrell, C.; Kim, S.; Mauldin, R. L., III; Karl, T.; Harley, P.; Turnipseed, A.; Zheng, W.; Flocke, F.; Apel, E. C.;

High-intensity focused ultrasound (HIFU) in prostate cancer: a single centre experience in patients with low, intermediate or high-risk of progression.

PubMed

Callea, Andrea; Piccinni, Roberto; Zizzi, Vito; Sblendorio, Domenico; Berardi, Bartolomeo; Tempesta, Antonio; Gala, Francesco Giuseppe; Traficante, Antonio

2010-12-01

High-intensity focused ultrasound (HIFU) is a minimally invasive treatment based on thermal ablation of tissues which are warmed up to 85 degrees C in the focal area. Clinical studies have shown such treatment modality to be safe and effective in the management of localised prostate cancer as well as of local recurrences after radical prostatectomy or radiotherapy. From May 2002 to June 2010, 171 patients with no previous treatment for prostate cancer, aged 44 to 86 years (mean 74.7) underwent 197 HIFU treatments; 22 patients needed a second treatment as the first was incomplete (4 patients) or because of recurrence (18 patients). The prognosis subgroups were defined as low-risk in 29 patients (clinical stage T1-T2a, PSA < or = 10 ng/mL and Gleason score lower than 7), intermediate-risk in 47 patients (clinical stage T2b or PSA 10 - 20 ng/mL or Gleason score of 7), and high-risk in 95 patients (clinical stage > or = T2c or PSA > 20 ng/mL or Gleason score higher than 7). At a mean follow-up of 67.9 months, biochemical success rate (PSA constantly < 0.5 ng/ml) was obtained in 84.2% of low and intermediate risk patients and in 43.1% of high risk patients; post-treatment biopsies (6 months after treatment) revealed no residual tumour in 93.4% of low or intermediate risk patients and in 63.1% of high risk patients. Radical prostatectomy remains the "gold standard" for localised prostate cancer. However, HIFU seems to be a promising alternative and less invasive treatment modality with an encouraging success rate, at least in the short-term, in patients with low and medium risk of progression, not candidates for radical surgery; in cancers with clinical stage > or = T2c, or PSA > 20 ng/mL, or Gleason score higher than 7 seems to get good results in about half of patients.

Reaction Paths and Chemical Activation Reactions of 2-Methyl-5-Furanyl Radical with 3O2.

PubMed

Hudzik, Jason M; Bozzelli, Joseph W

2017-10-05

Interest in high-energy substituted furans has been increasing due to their occurrence in biofuel production and their versatility in conversion to other useful products. Methylfurans are the simplest substituted furans and understanding their reaction pathways, thermochemical properties, including intermediate species stability, and chemical kinetics would aid in the study of larger furans. Furan ring C-H bonds have been shown to be extremely strong, approximately 120 kcal mol -1 , due in part to the placement of the oxygen atom and aromatic-like resonance, both within the ring. The thermochemistry and kinetics of the oxidation of 2-methyfuran radical at position 5 of the furan ring, 2-methyl-5-furanyl radical (2MF5j), is analyzed. The resulting chemically activated species, 2MF5OOj radical, has a well depth of 51 kcal mol -1 below the 2MF5j + O 2 reactants; this is 4-5 kcal mol -1 deeper than that of phenyl and vinyl radical plus O 2 , with both of these reactions known to undergo chain branching. Important, low-energy reaction pathways include chain branching dissociations, intramolecular abstractions, group transfers, and radical oxygen additions. Enthalpies of formation, entropies, and heat capacities for the stable molecules, radicals, and transition-state species are analyzed using computational methods. Calculated ΔH ° f 298 values were determined using an isodesmic work reaction from the CBS-QB3 composite method. Elementary rate parameters are from saddle point transition-state structures and compared to variational transition-state analysis for the barrierless reactions. Temperature- and pressure-dependent rate constants which are calculated using QRRK and master equation analysis is used for falloff and stabilization.

Activation of C-O and C-C bonds and formation of novel HAlOH-ether complexes: an EPR study of the reaction of ground-state Al atoms with methylethyl ether and diethyl ether.

PubMed

Brunet, François D; Feola, Julie C; Joly, Helen A

2012-03-15

Reaction mixtures, containing Al atoms and methylethyl ether (MEE) or diethyl ether (DEE) in an adamantane matrix, were prepared with the aid of a metal-atom reactor known as a rotating cryostat. The EPR spectra of the resulting products were recorded from 77-260 K, at 10 K intervals. Al atoms were found to insert into methyl-O, ethyl-O, and C-C bonds to form CH(3)AlOCH(2)CH(3), CH(3)OAlCH(2)CH(3), and CH(3)OCH(2)AlCH(3), respectively, in the case of MEE while DEE produced CH(3)CH(2)AlOCH(2)CH(3) and CH(3)AlCH(2)OCH(2)CH(3), respectively. From the intensity of the transition lines attributed to the Al atom C-O insertion products of MEE, insertion into the methyl-O bond is preferred. The Al hyperfine interaction (hfi) extracted from the EPR spectra of the C-O insertion products was greater than that of the C-C insertion products, that is, 5.4% greater for the DEE system and 7% greater for the MEE system. The increase in Al hfi is thought to arise from the increased electron-withdrawing ability of the substituents bonded to Al. Besides HAlOH, resulting from the reaction of Al atoms with adventitious water, novel mixed HAlOH:MEE and HAlOH:DEE complexes were identified with the aid of isotopic studies involving H(2)(17)O and D(2)O. The Al and H hfi of HAlOH were found to decrease upon complex formation. These findings are consistent with the nuclear hfi calculated using a density functional theory (DFT) method with close agreement between theory and experiment occurring at the B3LYP level using a 6-311+G(2df,p) basis set.

PLA2 mediated arachidonate free radicals: PLA2 inhibition and neutralization of free radicals by anti-oxidants--a new role as anti-inflammatory molecule.

PubMed

Nanda, B L; Nataraju, A; Rajesh, R; Rangappa, K S; Shekar, M A; Vishwanath, B S

2007-01-01

PLA2 enzyme catalyses the hydrolysis of cellular phospholipids at the sn-2 position to liberate arachidonic acid and lysophospholipid to generate a family of pro-inflammatory eicosanoids and platelet activating factor. The generation of pro-inflammatory eicosanoids involves a series of free radical intermediates with simultaneous release of reactive oxygen species (superoxide and hydroxyl radicals). Reactive oxygen species formed during arachidonic acid metabolism generates lipid peroxides and the cytotoxic products such as 4-hydroxy nonenal and acrolein, which induces cellular damage. Thus PLA2 catalyzes the rate-limiting step in the production of pro-inflammatory eicosanoids and free radicals. These peroxides and reactive oxygen species in turn activates PLA2 enzyme and further attenuates the inflammatory process. Therefore scavenging these free radicals and inhibition of PLA2 enzyme simultaneously by a single molecule such as antioxidants is of great therapeutic relevance for the development of anti-inflammatory molecules. PLA2 enzymes have been classified into calcium dependent cPLA2 and sPLA2 and calcium independent iPLA2 forms. In several inflammatory diseases sPLA2 group IIA is the most abundant isoform identified. This isoform is therefore targeted for the development of anti-inflammatory molecules. Many secondary metabolites from plants and marine sponges exhibit both anti-inflammatory and antioxidant properties. Some of them include flavonoids, terpenes and alkaloids. But in terms of PLA2 inhibition and antioxidant activity, the structural aspects of flavonoids are well studied rather than terpenes and alkaloids. In this line, molecules having both anti-oxidant and PLA2 inhibitions are reviewed. A single molecule with dual activities may prove to be a powerful anti-inflammatory drug.

Impact of ambient gases on the mechanism of [Cs8Nb6O19]-promoted nerve-agent decomposition.

PubMed

Kaledin, Alexey L; Driscoll, Darren M; Troya, Diego; Collins-Wildman, Daniel L; Hill, Craig L; Morris, John R; Musaev, Djamaladdin G

2018-02-28

The impact of ambient gas molecules (X), NO 2 , CO 2 and SO 2 on the structure, stability and decontamination activity of Cs 8 Nb 6 O 19 polyoxometalate was studied computationally and experimentally. It was found that Cs 8 Nb 6 O 19 absorbs these molecules more strongly than it adsorbs water and Sarin (GB) and that these interactions hinder nerve agent decontamination. The impacts of diamagnetic CO 2 and SO 2 molecules on polyoxoniobate Cs 8 Nb 6 O 19 were fundamentally different from that of NO 2 radical. At ambient temperatures, weak coordination of the first NO 2 radical to Cs 8 Nb 6 O 19 conferred partial radical character on the polyoxoniobate and promoted stronger coordination of the second NO 2 adsorbent to form a stable diamagnetic Cs 8 Nb 6 O 19 /(NO 2 ) 2 species. Moreover, at low temperatures, NO 2 radicals formed stable dinitrogen tetraoxide (N 2 O 4 ) that weakly interacted with Cs 8 Nb 6 O 19 . It was found that both in the absence and presence of ambient gas molecules, GB decontamination by the Cs 8 Nb 6 O 19 species proceeds via general base hydrolysis involving: (a) the adsorption of water and the nerve agent on Cs 8 Nb 6 O 19 /(X), (b) concerted hydrolysis of a water molecule on a basic oxygen atom of the polyoxoniobate and nucleophilic addition of the nascent OH group to the phosphorus center of Sarin, and (c) rapid reorganization of the formed pentacoordinated-phosphorus intermediate, followed by dissociation of either HF or isopropanol and formation of POM-bound isopropyl methyl phosphonic acid (i-MPA) or methyl phosphonofluoridic acid (MPFA), respectively. The presence of the ambient gas molecules increases the energy of the intermediate stationary points relative to the asymptote of the reactants and slightly increases the hydrolysis barrier. These changes closely correlate with the Cs 8 Nb 6 O 19 -X complexation energy. The most energetically stable intermediates of the GB hydrolysis and decontamination reaction were found to be Cs 8 Nb 6 O 19 /X-MPFA-(i-POH) and Cs 8 Nb 6 O 19 /X-(i-MPA)-HF both in the absence and presence of ambient gas molecules. The high stability of these intermediates is due to, in part, the strong hydrogen bonding between the adsorbates and the protonated [Cs 8 Nb 6 O 19 /X/H] + -core. Desorption of HF or/and (i-POH) and regeneration of the catalyst required deprotonation of the [Cs 8 Nb 6 O 19 /X/H] + -core and protonation of the phosphonic acids i-MPA and MPFA. This catalyst regeneration is shown to be a highly endothermic process, which is the rate-limiting step of the GB hydrolysis and decontamination reaction both in the absence and presence of ambient gas molecules.

Synthesis of the (N2)3- radical from Y2+ and its protonolysis reactivity to form (N2H2)2- via the Y[N(SiMe3)2]3/KC8 reduction system.

PubMed

Fang, Ming; Lee, David S; Ziller, Joseph W; Doedens, Robert J; Bates, Jefferson E; Furche, Filipp; Evans, William J

2011-03-23

Examination of the Y[N(SiMe(3))(2)](3)/KC(8) reduction system that allowed isolation of the (N(2))(3-) radical has led to the first evidence of Y(2+) in solution. The deep-blue solutions obtained from Y[N(SiMe(3))(2)](3) and KC(8) in THF at -35 °C under argon have EPR spectra containing a doublet at g(iso) = 1.976 with a 110 G hyperfine coupling constant. The solutions react with N(2) to generate (N(2))(2-) and (N(2))(3-) complexes {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-η(2):η(2)-N(2)) (1) and {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-η(2):η(2)-N(2))[K(THF)(6)] (2), respectively, and demonstrate that the Y[N(SiMe(3))(2)](3)/KC(8) reaction can proceed through an Y(2+) intermediate. The reactivity of (N(2))(3-) radical with proton sources was probed for the first time for comparison with the (N(2))(2-) and (N(2))(4-) chemistry. Complex 2 reacts with [Et(3)NH][BPh(4)] to form {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-N(2)H(2)), the first lanthanide (N(2)H(2))(2-) complex derived from dinitrogen, as well as 1 as a byproduct, consistent with radical disproportionation reactivity.

Mitigation of 3-Monochloro-1,2-propanediol Ester Formation by Radical Scavengers.

PubMed

Zhang, Hai; Jin, Pengwei; Zhang, Min; Cheong, Ling-Zhi; Hu, Peng; Zhao, Yue; Yu, Liangli; Wang, Yong; Jiang, Yuanrong; Xu, Xuebing

2016-07-27

The present study investigated the possible mechanism of free radical scavengers on mitigation of 3-monochloro-1,2-propanediol (3-MCPD) fatty acid ester formation in vegetable oils. The electron spin resonance investigation showed that the concentration of free radicals could be clearly decreased in 1,2-distearoyl-sn-glycerol (DSG) samples by all four antioxidants (l-ascorbyl palmitate, α-tocopherol, lipophilic tea polyphenols, and rosemary extract) at 120 °C for 20 min under a N2 atmosphere. Moreover, the rosemary extract exhibited the highest inhibition efficiency. The Fourier transform infrared spectroscopy examination of DSG with α-tocopherol at 25 and 120 °C revealed that α-tocopherol could prevent the involvement of an ester carbonyl group of DSG in forming the cyclic acyloxonium free radical intermediate. Furthermore, the ultraperformance liquid chromatography-quadrupole-time-of-flight mass spectrometry analysis showed that α-tocopherol could suppress the formation of 3-MCPD di- and monoesters. Finally, the four antioxidants could decrease 3-MCPD esters in the palm oil during deodorization. Particularly, the rosemary extract also showed the highest efficiency in 3-MCPD ester mitigation.

Why are sec-alkylperoxyl bimolecular self-reactions orders of magnitude faster than the analogous reactions of tert-alkylperoxyls? The unanticipated role of CH hydrogen bond donation.

PubMed

Lee, Richmond; Gryn'ova, Ganna; Ingold, K U; Coote, Michelle L

2016-08-24

High-level ab initio calculations are used to identify the mechanism of secondary (and primary) alkylperoxyl radical termination and explain why their reactions are much faster than their tertiary counterparts. Contrary to existing literature, the decomposition of both tertiary and non-tertiary tetroxides follows the same asymmetric two-step bond cleavage pathway to form a caged intermediate of overall singlet multiplicity comprising triplet oxygen and two alkoxyl radicals. The alpha hydrogen atoms of non-tertiary species facilitate this process by forming unexpected CHO hydrogen bonds to the evolving O2. For non-tertiary peroxyls, subsequent alpha hydrogen atom transfer then yields the experimentally observed non-radical products, ketone, alcohol and O2, whereas for tertiary species, this reaction is precluded and cage escape of the (unpaired) alkoxyl radicals is a likely outcome with important consequences for autoxidation.

Radical-induced chemistry from VUV photolysis of interstellar ice analogues containing formaldehyde

NASA Astrophysics Data System (ADS)

Butscher, Teddy; Duvernay, Fabrice; Danger, Grégoire; Chiavassa, Thierry

2016-09-01

Surface processes and radical chemistry within interstellar ices are increasingly suspected to play an important role in the formation of complex organic molecules (COMs) observed in several astrophysical regions and cometary environments. We present new laboratory experiments on the low-temperature solid state formation of complex organic molecules - glycolaldehyde, ethylene glycol, and polyoxymethylene - through radical-induced reactivity from VUV photolysis of formaldehyde in water-free and water-dominated ices. Radical reactivity and endogenous formation of COMs were monitored in situ via infrared spectroscopy in the solid state and post photolysis with temperature programmed desorption (TPD) using a quadripole mass spectrometer. We show the ability of free radicals to be stored when formed at low temperature in water-dominated ices, and to react with other radicals or on double bonds of unsaturated molecules when the temperature increases. It experimentally confirms the role of thermal diffusion in radical reactivity. We propose a new pathway for formaldehyde polymerisation induced by HCO radicals that might explain some observations made by the Ptolemy instrument on board the Rosetta lander Philae. In addition, our results seem to indicate that H-atom additions on H2CO proceed preferentially through CH2OH intermediate radicals rather than the CH3O radical.

A Study of Structural Changes in Pressed Semiproducts from Aluminum Alloy V95ochT2 in the Range of Dark Spots

NASA Astrophysics Data System (ADS)

Shigapov, A. I.; Il'inkova, T. A.; Kuryntsev, S. V.; Petrova, E. P.

2017-01-01

Seven heats of alloy V95ochT2 are studied after a heat treatment imitating the conditions of the appearance of dark spots in the production process and anodic oxidizing (anodizing). The mechanical properties, the hardness, the structure, and the electrical conductivity of the alloy are determined. The causes and conditions of the appearance of dark spots are analyzed. The transparence of the film is shown to worsen upon formation of particles of second phase in the alloy.

The rotational spectrum of the water-hydroperoxy radical (H2O-HO2) complex.

PubMed

Suma, Kohsuke; Sumiyoshi, Yoshihiro; Endo, Yasuki

2006-03-03

Peroxy radicals and their derivatives are elusive but important intermediates in a wide range of oxidation processes. We observed pure rotational transitions of the water-hydroperoxy radical complex, H2O-HO2, in a supersonic jet by means of a Fourier transform microwave spectrometer combined with a double-resonance technique. The observed rotational transitions were found to split into two components because of the internal rotation of the water moiety. The molecular constants for the two components were determined precisely, supporting a molecular structure in which HO2 acts as a proton donor to form a nearly planar five-membered ring, and one hydrogen atom of water sticks out from the ring plane. The structure and the spectral splittings due to internal rotation provide information on the nature of the bonding interaction between open- and closed-shell species, and they also provide accurate transition frequencies that are applicable to remote sensing of this complex, which may elucidate its potential roles in atmospheric and combustion chemistry.

Anharmonic Effect in CH3CH2C(=O)OCH2CH3 Decomposition

NASA Astrophysics Data System (ADS)

Ding, Yang; Song, Liguo; Yao, Li; Xia, Wenwen

2017-12-01

In this paper, using the B3LYP functional and CCSD(T) method with 6-311++G** basis set, the harmonic and anharmonic rate constants in the unimolecular dissociation of ethyl propanoate have been calculated using Rice-Ramsperger-Kassel-Marcus theory. The anharmonic rate constants of the title reaction have also been examined, the comparison shows that, the anharmonic effect especially in the case of high total energies and temperature for channels 3 to 6 is significant, so that the anharmonic effect cannot be neglected for unimolecular dissociation reaction of CH3CH2C(=O)OCH2CH3 both in microcanonical and canonical systems.

Identification of combustion intermediates in low-pressure premixed pyridine/oxygen/argon flames.

PubMed

Tian, Zhenyu; Li, Yuyang; Zhang, Taichang; Zhu, Aiguo; Qi, Fei

2008-12-25

Combustion intermediates of two low-pressure premixed pyridine/oxygen flames with respective equivalence ratios of 0.56 (C/O/N = 1:4.83:0.20) and 2.10 (C/O/N = 1:1.29:0.20) have been identified with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry techniques. About 80 intermediates in the rich flame and 60 intermediates in the lean flame, including nitrogenous, oxygenated, and hydrocarbon intermediates, have been identified by measurements of photoionization mass spectra and photoionization efficiency spectra. Some radicals and new nitrogenous intermediates are identified in the present work. The experimental results are useful for studying the conversion of volatile nitrogen compounds and understanding the formation mechanism of NO(x) in flames of nitrogenous fuels.

Reactivity of chemiluminescence reagents toward oxidants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khevelev, M.; Weinstein-Loyd, J.B.

Hydroperoxyl radical (HO{sub 2}) and its conjugate base, superoxide radical (O{sub 2}{sup -}) are important chemical intermediates. O{sub 2}{sup -} is ubiquitous in aerobic cells and has been implicated in arthritis, cancer, and aging, among other biological processes. HO{sub 2} plays a central role in atmospheric photochemistry. Because of their short lifetime, there are few reliable analytical methods for the detection of HO{sub 2}/O{sub 2}{sup -}. In a number of recent publications, the chemiluminescence reagent CLA has been exploited as a specific marker for these species. Using UV/visible spectroscopy, we have investigated the stability of CLA and several of itsmore » analogs in the presence of oxidants, including O{sub 2}, H{sub 2}O{sub 2}, OH and HO{sub 2}/O{sub 2}{sup -}. The spectral changes observed suggest that the reaction with HO{sub 2}/O{sub 2}{sup -} is rather nonspecific.« less

Mechanistic studies related to the safety of Li/SOCl2 cells

NASA Technical Reports Server (NTRS)

Carter, B. J.; Williams, R. M.; Tsay, F. D.; Rodriguez, A.; Kim, S.; Evans, M. M.; Frank, H.

1985-01-01

Mechanistic studies of the reactions in Li-SOCl2 cells have been undertaken to improve understanding of the safety problems of these cells. The electrochemical reduction of 1.5M LiAlCl4/SOCl2 has been investigated using gas chromatography, electron spin resonance spectroscopy, and infrared spectroscopy. Cl2 and S2Cl2 have been identified as intermediates in the reduction of SOCl2, along with a radical species (g/xx/ = 2.004, g/yy/ = 2.016, g/zz/ = 2.008) and the proposed triplet ground-state dimer of this radical. SO2 and sulfur have been identified as products. Based upon these findings, a mechanism for the electrochemical reduction of 1.5M LiAlCl4/SOCl2 has been proposed, and its implications for safety of Li-SOCl2 cells during discharge to +0.5V at 25-30 C are discussed.

Free-radical mediated synthesis of enantiomerically pure, highly functionalized inositols from carbohydrates.

PubMed

Marco-Contelles, J; Pozuelo, C; de Opazo, E

2001-06-15

We report the synthesis, free-radical cyclization of precursors 1,2,7-trideoxy-7-iodo-3,4:5,6-di-O-isopropylidene-D-gluco-hept-1-enitol (1), methyl 7-O-acetyl-6-O-benzyl-8-bromo-2,3,8-trideoxy-4,5-O-isopropylidene-D-gluco-oct-2-enonate (2) and 5-O-acetyl-4-O-benzyl-6-bromo-6-deoxy-2,3-O-isopropylidene-D-glucose-O-benzyloxime (3), readily prepared from D-glucose, and some selected transformations of the carbocycles obtained from these intermediates. In compound 1 we have installed a terminal double bond and an iodide as radical acceptor and leaving group, respectively. Compounds 2 and 3 are epsilon-bromo aldehydes substituted with alpha,beta-unsaturated ester and oxime ether functions as radical traps, respectively. The tributyltin hydride mediated ring closure of these radical precursors have afforded a series of interesting, diverse and highly functionalized carbocycles which can be considered useful building blocks for the synthesis of branched-chain cyclitols, aminocyclitols and aminoconduritols. In these processes, a good chemical yield and high stereoselectivity has been found in the newly formed stereocenters. Particularly interesting has been the finding that the stereochemical outcome of the free-radical cyclization is independent of the ratio of isomers (E or Z) in oxime ether 3. These results show the power and the state of art of this strategy for the stereocontrolled synthesis of enantiomerically pure inositols from carbohydrates.

Two tyrosyl radicals stabilize high oxidation states in cytochrome c oxidase for efficient energy conservation and proton translocation

NASA Astrophysics Data System (ADS)

Rousseau, Denis

2012-02-01

The reaction of hydrogen peroxide (H2O2) with oxidized bovine cytochrome c oxidase (bCcO) was studied by electron paramagnetic resonance (EPR) to determine the properties of radical intermediates. Two distinct radicals with widths of 12 and 46 G are directly observed by X-band CW-EPR in the reaction of bCcO with H2O2 at pH 6 and pH 8. High-frequency EPR (D-band) provides assignments to tyrosine for both radicals based on well-resolved g-tensors. The 46 G wide radical has extensive hyperfine structure and can be fit with parameters consistent with Y129. However, the 12 G wide radical has minimal hyperfine structure and can be fit using parameters unique to the post-translationally modified Y244 in CcO. The results are supported by mixed quantum mechanics and molecular mechanics calculations. This study reports spectroscopic evidence of a radical formed on the modified tyrosine in CcO and resolves the much debated controversy of whether the wide radical seen at low pH in the bovine system is a tyrosine or tryptophan. A model is presented showing how radical formation and migration may play an essential role in proton translocation. This work was done in collaboration with Michelle A. Yu, Tsuyoshi Egawa, Syun-Ru Yeh and Gary J. Gerfen from Albert Einstein College of Medicine; Kyoko Shinzawa-Itoh and Shinya Yoshikawa from the University of Hyogo; and Victor Guallar from the Barcelona Supercomputing Center.

Deoxygenation of Palmitic Acid on Unsupported Transition-Metal Phosphides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peroni, Marco; Lee, Insu; Huang, Xiaoyang

Abstract Highly active bulk transition metal phosphides (WP, MoP, and Ni2P) were synthesized for the catalytic hydrodeoxygenation of palmitic acid, hexadecanol, hexadecanal, and microalgae oil. The specific activities positively correlated with the concentration of exposed metal sites, although the relative rates changed with temperature due to activation energies varying from 57 kJ·mol-1 for MoP to 142 kJ·mol-1 for WP. The reduction of the fatty acid to the aldehyde occurs through a Langmuir-Hinshelwood mechanism, where the rate-determining step is the addition of the second H to the hydrocarbon. On WP, the conversion of palmitic acid proceeds via R-CH2COOH R-CH2CHO R-CH2CH2OH R-CHCH2more » R-CH2CH3 (hydrodeoxygenation). Decarbonylation of the intermittently formed aldehyde (R-CH2COOH R-CH2CHO R-CH3) was an important pathway on MoP and Ni2P. Conversion via dehydration to a ketene, followed by its decarbonylation occurred only on Ni2P. The rates of alcohol dehydration (R-CH2CH2OH R-CHCH2) correlate with the concentration of Lewis acid sites of the phosphides. Acknowledgements The authors would like to thank Roel Prins for the critical discussion of the results. We are also grateful to Xaver Hecht for technical support. Funding by the German Federal Ministry of Food and Agriculture in the framework of the Advanced Biomass Value project (03SF0446A) is gratefully acknowledged. J.A.L. acknowledges support for his contribution by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences for exploring non-oxidic supports for deoxygenation reactions.« less

Release of Reactive Oxygen Intermediates (Superoxide Radicals, Hydrogen Peroxide, and Hydroxyl Radicals) and Peroxidase in Germinating Radish Seeds Controlled by Light, Gibberellin, and Abscisic Acid1

PubMed Central

Schopfer, Peter; Plachy, Claudia; Frahry, Gitta

2001-01-01

Germination of radish (Raphanus sativus cv Eterna) seeds can be inhibited by far-red light (high-irradiance reaction of phytochrome) or abscisic acid (ABA). Gibberellic acid (GA3) restores full germination under far-red light. This experimental system was used to investigate the release of reactive oxygen intermediates (ROI) by seed coats and embryos during germination, utilizing the apoplastic oxidation of 2′,7′-dichlorofluorescin to fluorescent 2′,7′-dichlorofluorescein as an in vivo assay. Germination in darkness is accompanied by a steep rise in ROI release originating from the seed coat (living aleurone layer) as well as the embryo. At the same time as the inhibition of germination, far-red light and ABA inhibit ROI release in both seed parts and GA3 reverses this inhibition when initiating germination under far-red light. During the later stage of germination the seed coat also releases peroxidase with a time course affected by far-red light, ABA, and GA3. The participation of superoxide radicals, hydrogen peroxide, and hydroxyl radicals in ROI metabolism was demonstrated with specific in vivo assays. ROI production by germinating seeds represents an active, developmentally controlled physiological function, presumably for protecting the emerging seedling against attack by pathogens. PMID:11299341

Preparation of new crosslinking agents and additives for use in polymer electrolyte membranes (PEMs) for fuel cell applications

NASA Astrophysics Data System (ADS)

Zhou, Yangliu

The most commonly used proton conductive membrane in polymer electrolyte membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) studies to date is DuPont's NafionRTM, which is a perfluorinated copolymer of tetrafluoroethylene (TFE) and perfluorovinyl ether with a pendant sulfonic acid group. A focus of this work is to find ways to improve the performance of NafionRTM membranes. Crosslinking the TFE chains of fluorinated ionomeric copolymers to improve their thermal and mechanical stability is a proven route to this goal. A straightforward synthetic route to perfluorinated divinyl ethers of the formula CF2=CFO(CF 2)3[OCF(CF3)CF2]mOCF=CF 2 (m = 0-1) has been demonstrated. The compounds CF2=CFO(CF 2)3OCF=CF2 and CF2=CFO(CF2) 3OCF(CF3)CF2OCF=CF2 were prepared and characterized by GC-MS, 13C and 19F NMR, and gas-IR spectroscopy. Synthetic routes to fluorosulfato-tetrafluoropropionyl fluoride [FSO3CF2CF2C(O)F] and difluoromalonyl difluoride [F(O)CCF2C(O)F] with improved yields were found. The second focus of the dissertation was the development of fluorous triarylphosphines for use as new doping materials for the modification of NafionRTM membranes and for use as ligands in catalysts for biphasic catalysis. The synthesis and characterization of a series of new polyhexafluoropropylene oxide derivatives for preparation of fluorous triarylphosphines and phosphonium salts was studied, such as F[CF(CF3)CF2O] 4CF(CF3)CH2CH2I, F[CF(CF3)CF 2O]4CF(CF3)CH=CH2, F[CF(CF3)CF 2O]4CF(CF3) CH2CH2C6H5, and F[CF(CF 3)CF2O]4CF(CF3)CH2CH 2C6H4Br. In a separate study, the photochlorination of 2,2,3,3-tetrafluoro-1-propanol (HCF2CF2CH2OH) and 2,2,3,3-tetrafluoropropyl 2,2,3,3-tetrafluoropropionate [HCF2CF2C(O)OCH2 CF2CF2H] with super diazo blue light (lambda max = 420 nm) were investigated. The photochemical products are different from those obtained under mercury light (lambda = 253.7nm). A new compound ClCF2CF2C(O)OC(H)ClCF2CF2Cl was prepared and characterized by GC-MS, elemental analysis, 1H, 13C and 19F NMR, and gas-IR spectroscopy.

A Cost-Benefit Analysis of Hollow Water's Community Holistic Circle Healing Process.

ERIC Educational Resources Information Center

Couture, Joe; Parker, Ted; Couture, Ruth; Laboucane, Patti

Four Native American communities in Manitoba (Canada) known as Hollow Water devised a healing system for sexual abuse--the Hollow Water First Nation Community Holistic Circle Healing (CHCH). While integrating elements of a number of federal and provincially funded services, the 13-step CHCH healing process is based on the seven Midewin teachings…

Disproportionation of hydroxylamine by water-soluble iron(III) porphyrinate compounds.

PubMed

Bari, Sara E; Amorebieta, Valentín T; Gutiérrez, María M; Olabe, José A; Doctorovich, Fabio

2010-01-01

The reactions of hydroxylamine (HA) with several water-soluble iron(III) porphyrinate compounds, namely iron(III) meso-tetrakis-(N-ethylpyridinium-2yl)-porphyrinate ([Fe(III)(TEPyP)](5+)), iron(III) meso-tetrakis-(4-sulphonatophenyl)-porphyrinate ([Fe(III)(TPPS)](3-)), and microperoxidase 11 ([Fe(III)(MP11)]) were studied for different [Fe(III)(Porph)]/[HA] ratios, under anaerobic conditions at neutral pH. Efficient catalytic processes leading to the disproportionation of HA by these iron(III) porphyrinates were evidenced for the first time. As a common feature, only N(2) and N(2)O were found as gaseous, nitrogen-containing oxidation products, while NH(3) was the unique reduced species detected. Different N(2)/N(2)O ratios obtained with these three porphyrinates strongly suggest distinctive mechanistic scenarios: while [Fe(III)(TEPyP)](5+) and [Fe(III)(MP11)] formed unknown steady-state porphyrinic intermediates in the presence of HA, [Fe(III)(TPPS)](3-) led to the well characterized soluble intermediate, [Fe(II)(TPPS)NO](4-). Free-radical formation was only evidenced for [Fe(III)(TEPyP)](5+), as a consequence of a metal centered reduction. We discuss the catalytic pathways of HA disproportionation on the basis of the distribution of gaseous products, free radicals formation, the nature of porphyrinic intermediates, the Fe(II)/Fe(III) redox potential, the coordinating capabilities of each complex, and the kinetic analysis. The absence of NO(2)(-) revealed either that no HAO-like activity was operative under our reaction conditions, or that NO(2)(-), if formed, was consumed in the reaction milieu.

Mineralization of the textile dye acid yellow 42 by solar photoelectro-Fenton in a lab-pilot plant.

PubMed

Espinoza, Carolina; Romero, Julio; Villegas, Loreto; Cornejo-Ponce, Lorena; Salazar, Ricardo

2016-12-05

A complete mineralization of a textile dye widely used in the Chilean textile industry, acid yellow 42 (AY42), was studied. Degradation was carried out in an aqueous solution containing 100mgL(-1) of total organic carbon (TOC) of dye using the advanced solar photoelectro-Fenton (SPEF) process in a lab-scale pilot plant consisting of a filter press cell, which contains a boron doped diamond electrode and an air diffusion cathode (BDD/air-diffusion cell), coupled with a solar photoreactor for treat 8L of wastewater during 270min of electrolysis. The main results obtained during the degradation of the textile dye were that a complete transformation to CO2 depends directly on the applied current density, the concentration of Fe(2+) used as catalyst, and the solar radiation intensity. The elimination of AY42 and its organic intermediates was due to hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between electrogenerated H2O2 and added Fe(2+). The application of solar radiation in the process (SPEF) yield higher current efficiencies and lower energy consumptions than electro-Fenton (EF) and electro-oxidation with electrogenerated H2O2 (E OH2O2) by the additional production of hydroxyl radicals from the photolysis of Fe(III) hydrated species and the photodecomposition of Fe(III) complexes with organic intermediates. Moreover, some products and intermediates formed during mineralization of dye, such as inorganic ions, carboxylic acids and aromatic compounds were determined by photometric and chromatographic methods. An oxidation pathway is proposed for the complete conversion to CO2. Copyright © 2016 Elsevier B.V. All rights reserved.

Time- and isomer-resolved measurements of sequential addition of acetylene to the propargyl radical

DOE PAGES

Savee, John D.; Selby, Talitha M.; Welz, Oliver; ...

2015-10-06

Soot formation in combustion is a complex process in which polycyclic aromatic hydrocarbons (PAHs) are believed to play a critical role. Recent works concluded that three consecutive additions of acetylene (C 2H 2) to propargyl (C 3H 3) create a facile route to the PAH indene (C 9H 8). However, the isomeric forms of C 5H 5 and C 7H 7 intermediates in this reaction sequence are not known. We directly investigate these intermediates using time- and isomer-resolved experiments. Both the resonance stabilized vinylpropargyl ( vp-C 5H 5) and 2,4-cyclopentadienyl ( c-C 5H 5) radical isomers of C 5H 5more » are produced, with substantially different intensities at 800 K vs 1000 K. In agreement with literature master equation calculations, we find that c-C 5H 5 + C 2H 2 produces only the tropyl isomer of C 7H 7 ( tp-C 7H 7) below 1000 K, and that tp-C 7H 7 + C 2H 2 terminates the reaction sequence yielding C 9H 8 (indene) + H. Lastly, this work demonstrates a pathway for PAH formation that does not proceed through benzene.« less

UV + V UV double-resonance studies of autoionizing Rydberg states of the hydroxyl radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Green, Amy M.; Liu, Fang; Lester, Marsha I., E-mail: milester@sas.upenn.edu

2016-05-14

The hydroxyl radical (OH) is a key oxidant in atmospheric and combustion chemistry. Recently, a sensitive and state-selective ionization method has been developed for detection of the OH radical that utilizes UV excitation on the A{sup 2}Σ{sup +}–X{sup 2}Π transition followed by fixed 118 nm vacuum ultraviolet (VUV) radiation to access autoionizing Rydberg states [J. M. Beames et al., J. Chem. Phys. 134, 241102 (2011)]. The present study uses tunable VUV radiation generated by four-wave mixing to examine the origin of the enhanced ionization efficiency observed for OH radicals prepared in specific A{sup 2}Σ{sup +} intermediate levels. The enhancement ismore » shown to arise from resonant excitation to distinct rotational and fine structure levels of two newly identified {sup 2}Π Rydberg states with an A{sup 3}Π cationic core and a 3d electron followed by ionization. Spectroscopic constants are derived and effects due to uncoupling of the Rydberg electron are revealed for the OH {sup 2}Π Rydberg states. The linewidths indicate a Rydberg state lifetime due to autoionization on the order of a picosecond.« less

Highly selective transformation of ammonia nitrogen to N2 based on a novel solar-driven photoelectrocatalytic-chlorine radical reactions system.

PubMed

Ji, Youzhi; Bai, Jing; Li, Jinhua; Luo, Tao; Qiao, Li; Zeng, Qingyi; Zhou, Baoxue

2017-11-15

A highly selective method for transforming ammonia nitrogen to N 2 was proposed, based on a novel solar-driven photoelectrocatalytic-chlorine radical reactions (PEC-chlorine) system. The PEC-chlorine system was facilitated by a visible light response WO 3 nanoplate array (NPA) electrode in an ammonia solution containing chloride ions (Cl - ). Under illumination, photoholes from WO 3 promote the oxidation of Cl - to chlorine radical (Cl). This radical can selectively transform ammonia nitrogen to N 2 (79.9%) and NO 3 - (19.2%), similar to the breakpoint chlorination reaction. The ammonia nitrogen removal efficiency increased from 10.6% (PEC without Cl - ) to 99.9% with the PEC-chlorine system within 90 min operation, which can be attributed to the cyclic reactions between Cl - /Cl and the reaction intermediates (NH 2 , NHCl, etc.) that expand the degradation reactions from the surface of the electrodes to the whole solution system. Moreover, Cl is the main radical species contributing to the transformation of ammonia nitrogen to N 2 , which is confirmed by the tBuOH capture experiment. Compared to conventional breakpoint chlorination, the PEC-chlorine system is a more economical and efficient means for ammonia nitrogen degradation because of the fast removal rate, no additional chlorine cost, and its use of clean energy (since it is solar-driven). Copyright © 2017 Elsevier Ltd. All rights reserved.

Method for synthesizing thin film electrodes

DOEpatents

Boyle, Timothy J [Albuquerque, NM

2007-03-13

A method for making a thin-film electrode, either an anode or a cathode, by preparing a precursor solution using an alkoxide reactant, depositing multiple thin film layers with each layer approximately 500 1000 .ANG. in thickness, and heating the layers to above 600.degree. C. to achieve a material with electrochemical properties suitable for use in a thin film battery. The preparation of the anode precursor solution uses Sn(OCH.sub.2C(CH.sub.3).sub.3).sub.2 dissolved in a solvent in the presence of HO.sub.2CCH.sub.3 and the cathode precursor solution is formed by dissolving a mixture of (Li(OCH.sub.2C(CH.sub.3).sub.3)).sub.8 and Co(O.sub.2CCH.sub.3).H.sub.2O in at least one polar solvent.

Hot-hole extraction from quantum dot to molecular adsorbate.

PubMed

Singhal, Pallavi; Ghosh, Hirendra N

2015-03-09

Ultrafast thermalized and hot-hole-transfer processes have been investigated in CdSe quantum dot (QD)/catechol composite systems in which hole transfer from photoexcited QDs to the catechols is thermodynamically favorable. A series of catechol derivatives were selected with different electron-donating and -withdrawing groups, and the effect of these groups on hole transfer and charge recombination (CR) dynamics has been investigated. The hole-transfer time was determined using the fluorescence upconversion technique and found to be 2-10 ps depending on the molecular structure of the catechol derivatives. The hot-hole-transfer process was followed after monitoring 2S luminescence of CdSe QDs. Interestingly, hot-hole extraction was observed only in the CdSe/3-methoxycatechol (3-OCH3) composite system owing to the higher electron-donating property of the 3-methoxy group. To confirm the extraction of the hot hole and to monitor the CR reaction in CdSe QD/catechol composite systems, ultrafast transient absorption studies have been carried out. Ultrafast transient-absorption studies show that the bleach recovery kinetics of CdSe QD at the 2S excitonic position is much faster in the presence of 3-OCH3. This faster bleach recovery at the 2S position in CdSe/3-OCH3 suggests hot-hole transfer from CdSe QD to 3-OCH3. CR dynamics in CdSe QD/catechol composite systems was followed by monitoring the excitonic bleach at the 1S position and was found to decrease with free energy of the CR reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular identification and functional characterization of rabbit MATE1 and MATE2-K.

PubMed

Zhang, Xiaohong; Cherrington, Nathan J; Wright, Stephen H

2007-07-01

An electroneutral organic cation (OC)/proton exchanger in the apical membrane of proximal tubules mediates the final step of renal OC excretion. Two members of the multidrug and toxin extrusion family, MATE1 and MATE2-K, were recently identified in human and rodent kidney and proposed to be the molecular basis of renal OC/H(+) exchange. To take advantage of the comparative value of the large database on the kinetic and selectivity characteristics of OC/H(+) exchange that exists for rabbit kidney, we cloned rbMATE1 and rbMATE2-K. The rabbit homologs have 75% (MATE1) and 74% (MATE2-K) amino acid identity to their human counterparts (and 51% identity with each other). rbMATE1 and rbMATE2-K exhibited H(+) gradient-dependent uptake and efflux of tetraethylammonium (TEA) when expressed in Chinese hamster ovary cells. Both transporters displayed similar affinities for selected compounds [IC(50) values within 2-fold for TEA, 1-methyl-4-phenylpyridinium, and quinidine] and very different affinities for others (IC(50) values differing by 8- to 80-fold for choline and cimetidine, respectively). These results indicate that rbMATE1 and rbMATE2-K are multispecific OC/H(+) exchangers with similar, but distinct, functional characteristics. Overall, the selectivity of MATE1 and MATE2-K correlated closely with that observed in rabbit renal brush-border membrane vesicles.

The Molecular Mechanism of the Catalase-like Activity in Horseradish Peroxidase.

PubMed

Campomanes, Pablo; Rothlisberger, Ursula; Alfonso-Prieto, Mercedes; Rovira, Carme

2015-09-02

Horseradish peroxidase (HRP) is one of the most relevant peroxidase enzymes, used extensively in immunochemistry and biocatalysis applications. Unlike the closely related catalase enzymes, it exhibits a low activity to disproportionate hydrogen peroxide (H2O2). The origin of this disparity remains unknown due to the lack of atomistic information on the catalase-like reaction in HRP. Using QM(DFT)/MM metadynamics simulations, we uncover the mechanism for reduction of the HRP Compound I intermediate by H2O2 at atomic detail. The reaction begins with a hydrogen atom transfer, forming a peroxyl radical and a Compound II-like species. Reorientation of the peroxyl radical in the active site, concomitant with the transfer of the second hydrogen atom, is the rate-limiting step, with a computed free energy barrier (18.7 kcal/mol, ∼ 6 kcal/mol higher than the one obtained for catalase) in good agreement with experiments. Our simulations reveal the crucial role played by the distal pocket residues in accommodating H2O2, enabling formation of a Compound II-like intermediate, similar to catalases. However, out of the two pathways for Compound II reduction found in catalases, only one is operative in HRP. Moreover, the hydrogen bond network in the distal side of HRP compensates less efficiently than in catalases for the energetic cost required to reorient the peroxyl radical at the rate-determining step. The distal Arg and a water molecule in the "wet" active site of HRP have a substantial impact on the reaction barrier, compared to the "dry" active site in catalase. Therefore, the lower catalase-like efficiency of heme peroxidases compared to catalases can be directly attributed to the different distal pocket architecture, providing hints to engineer peroxidases with a higher rate of H2O2 disproportionation.

A nuclear magnetic double resonance study of N-beta-bis-(beta'-chloroethyl) phosphonylethyl-DL-phenylalanine.

PubMed

Friedman, M; Boyd, W A

1977-01-01

Studies were carried out on the effect of decoupling, deuterium labeling, concentration, temperature, and solvent media on the NMR parameters of the vinyl phosphonate adduct of phenylalanine, C6H5CH2CH(COO-)NH2+CH2CH2PO(OCH2CH2C1)2. The results permit assignments of chemical shifts and coupling constants to the various protons of this molecule which contains unique structural features. The NH2+-CH2-protons are deshielded by more than 1 ppm than the CH2-PO-protons. The -OCH2-protons are nonequivalent exhibiting a fine split. Possible sources of the fine split include NH...O=P hydrogen bonding. The deuterium-labeling method should be applicable for synthesizing deuterium-and tritium-labeled crosslinked amino acids such as lysinoalanine and lanthionine and demonstrating analgous dehydroalanine-alpha-amino group-crosslinking.

Spectroscopic evidence for an engineered, catalytically active Trp radical that creates the unique reactivity of lignin peroxidase.

PubMed

Smith, Andrew T; Doyle, Wendy A; Dorlet, Pierre; Ivancich, Anabella

2009-09-22

The surface oxidation site (Trp-171) in lignin peroxidase (LiP) required for the reaction with veratryl alcohol a high-redox-potential (1.4 V) substrate, was engineered into Coprinus cinereus peroxidase (CiP) by introducing a Trp residue into a heme peroxidase that has similar protein fold but lacks this activity. To create the catalytic activity toward veratryl alcohol in CiP, it was necessary to reproduce the Trp site and its negatively charged microenvironment by means of a triple mutation. The resulting D179W+R258E+R272D variant was characterized by multifrequency EPR spectroscopy. The spectra unequivocally showed that a new Trp radical [g values of g(x) = 2.0035(5), g(y) = 2.0027(5), and g(z) = 2.0022(1)] was formed after the [Fe(IV)=O Por(*+)] intermediate, as a result of intramolecular electron transfer between Trp-179 and the porphyrin. Also, the EPR characterization crucially showed that [Fe(IV)=O Trp-179(*)] was the reactive intermediate with veratryl alcohol. Accordingly, our work shows that it is necessary to take into account the physicochemical properties of the radical, fine-tuned by the microenvironment, as well as those of the preceding [Fe(IV)=O Por(*+)] intermediate to engineer a catalytically competent Trp site for a given substrate. Manipulation of the microenvironment of the Trp-171 site in LiP allowed the detection by EPR spectroscopy of the Trp-171(*), for which direct evidence has been missing so far. Our work also highlights the role of Trp residues as tunable redox-active cofactors for enzyme catalysis in the context of peroxidases with a unique reactivity toward recalcitrant substrates that require oxidation potentials not realized at the heme site.

Nano-MnO2-mediated transformation of triclosan with humic molecules present: kinetics, products, and pathways.

PubMed

Sun, Kai; Li, Shunyao; Waigi, Michael Gatheru; Huang, Qingguo

2018-05-01

It has been shown that manganese dioxide (MnO 2 ) can mediate transformation of phenolic contaminants to form phenoxyl radical intermediates, and subsequently, these intermediates intercouple to form oligomers via covalent binding. However, the reaction kinetics and transformation mechanisms of phenolic contaminants with humic molecules present in nano-MnO 2 -mediated systems were still unclear. In this study, it was proven that nano-MnO 2 were effective in transforming triclosan under acidic conditions (pH 3.5-5.0) during manganese reduction, and the apparent pseudo first-order kinetics rate constants (k = 0.0599-1.5314 h -1 ) increased as the pH decreased. In particular, the transformation of triclosan by nano-MnO 2 was enhanced in the presence of low-concentration humic acid (1-10 mg L -1 ). The variation in the absorption of humic molecules at 275 nm supported possible covalent binding between humic molecules and triclosan in the nano-MnO 2 -mediated systems. A total of four main intermediate products were identified by high-resolution mass spectrometry (HRMS), regardless of humic molecules present in the systems or not. These products correspond to a suite of radical intercoupling reactions (dimers and trimers), ether cleavage (2,4-dichlorophenol), and oxidation to quinone-like products, triggered by electron transfer from triclosan molecules to nano-MnO 2 . A possible reaction pathway in humic acid solutions, including homo-coupling, decomposition, oxidation, and cross-coupling, was proposed. Our findings provide valuable information regarding the environmental fate and transformation mechanism of triclosan by nano-MnO 2 in complex water matrices.

Self-Assembled Amphiphilic Water Oxidation Catalysts: Control of O-O Bond Formation Pathways by Different Aggregation Patterns.

PubMed

Yang, Bing; Jiang, Xin; Guo, Qing; Lei, Tao; Zhang, Li-Ping; Chen, Bin; Tung, Chen-Ho; Wu, Li-Zhu

2016-05-17

The oxidation of water to molecular oxygen is the key step to realize water splitting from both biological and chemical perspective. In an effort to understand how water oxidation occurs on a molecular level, a large number of molecular catalysts have been synthesized to find an easy access to higher oxidation states as well as their capacity to make O-O bond. However, most of them function in a mixture of organic solvent and water and the O-O bond formation pathway is still a subject of intense debate. Herein, we design the first amphiphilic Ru-bda (H2 bda=2,2'-bipyridine-6,6'-dicarboxylic acid) water oxidation catalysts (WOCs) of formula [Ru(II) (bda)(4-OTEG-pyridine)2 ] (1, OTEG=OCH2 CH2 OCH2 CH2 OCH3 ) and [Ru(II) (bda)(PySO3 Na)2 ] (2, PySO3 (-) =pyridine-3-sulfonate), which possess good solubility in water. Dynamic light scattering (DLS), scanning electron microscope (SEM), critical aggregation concentration (CAC) experiments and product analysis demonstrate that they enable to self-assemble in water and form the O-O bond through different routes even though they have the same bda(2-) backbone. This work illustrates for the first time that the O-O bond formation pathway can be regulated by the interaction of ancillary ligands at supramolecular level. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhancing and inhibiting effects of aromatic compounds on luminol-dimethylsulfoxide-OH(-) chemiluminescence and determination of intermediates in oxidative hair dyes by HPLC with chemiluminescence detection.

PubMed

Zhou, Jian; Xu, Hong; Wan, Guo-Hui; Duan, Chun-Feng; Cui, Hua

2004-10-08

The effect of 36 aromatic compounds on the luminol-dimethylsulfoxide-OH(-) chemiluminescence (CL) was systematically studied. It was found that dihydroxybenzenes, and ortho- and para-substituted aminophenols and phenylenediamines inhibited the CL and phenols with three or more than three hydroxyls except phloroglucin tended to enhance the CL. The CL inhibition and enhancement was proposed to be dependent on whether superoxide anion radical (O(2)(-)) was competitively consumed by compounds in the CL system. Trihydroxybenzenes were capable of generating superoxide anion radical, leading to the CL enhancement, whereas dihydroxybenzenes were superoxide anion radical scavenger, causing the CL inhibition. Based on the inhibited CL, a novel method for the simultaneous determination of p-phenylenediamine, o-phenylenediamine, p-aminophenol, o-aminophenol, resorcinol and hydroquinone by high-performance liquid chromatography coupled with chemiluminescence detection was developed. The method has been successfully applied to determine intermediates in oxidative hair dyes and wastewater of shampooing after hair dyed.

Reaction kinetics and mechanisms of organosilicon fungicide flusilazole with sulfate and hydroxyl radicals.

PubMed

Mercado, D Fabio; Bracco, Larisa L B; Arques, Antonio; Gonzalez, Mónica C; Caregnato, Paula

2018-01-01

Flusilazole is an organosilane fungicide used for treatments in agriculture and horticulture for control of diseases. The reaction kinetics and mechanism of flusilazole with sulfate and hydroxyl radicals were studied. The rate constant of the radicals with the fungicide were determined by laser flash photolysis of peroxodisulfate and hydrogen peroxide. The results were 2.0 × 10 9 s -1 M -1 for the reaction of the fungicide with HO and 4.6 × 10 8  s -1  M -1 for the same reaction with SO 4 - radicals. The absorption spectra of organic intermediates detected by laser flash photolysis of S 2 O 8 2- with flusilazole, were identified as α-aminoalkyl and siloxyl radicals and agree very well with those estimated employing the time-dependent density functional theory with explicit account for bulk solvent effects. In the continuous photolysis experiments, performed by photo-Fenton reaction of the fungicide, the main degradation products were: (bis(4-fluorophenyl)-hydroxy-methylsilane) and the non-toxic silicic acid, diethyl bis(trimethylsilyl) ester, in ten and twenty minutes of reaction, respectively. Copyright © 2017. Published by Elsevier Ltd.

Inhibitors of choline uptake and metabolism cause developmental abnormalities in neurulating mouse embryos.

PubMed

Fisher, M C; Zeisel, S H; Mar, M H; Sadler, T W

2001-08-01

Choline is an essential nutrient in methylation, acetylcholine and phospholipid biosynthesis, and in cell signaling. The demand by an embryo or fetus for choline may place a pregnant woman and, subsequently, the developing conceptus at risk for choline deficiency. To determine whether a disruption in choline uptake and metabolism results in developmental abnormalities, early somite staged mouse embryos were exposed in vitro to either an inhibitor of choline uptake and metabolism, 2-dimethylaminoethanol (DMAE), or an inhibitor of phosphatidylcholine synthesis, 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH(3)). Cell death following inhibitor exposure was investigated with LysoTracker Red and histology. Embryos exposed to 250-750 microM DMAE for 26 hr developed craniofacial hypoplasia and open neural tube defects in the forebrain, midbrain, and hindbrain regions. Embryos exposed to 125-275 microM ET-18-OCH(3) exhibited similar defects or expansion of the brain vesicles. ET-18-OCH(3)-affected embryos also had a distended neural tube at the posterior neuropore. Embryonic growth was reduced in embryos treated with either DMAE (375, 500, and 750 microM) or ET-18-OCH(3) (200 and 275 microM). Whole mount staining with LysoTracker Red and histological sections showed increased areas of cell death in embryos treated with 275 microM ET-18-OCH(3) for 6 hr, but there was no evidence of cell death in DMAE-exposed embryos. Inhibition of choline uptake and metabolism during neurulation results in growth retardation and developmental defects that affect the neural tube and face. Copyright 2001 Wiley-Liss, Inc.

Production of Hydroxyl Radical via the Activation of Hydrogen Peroxide by Hydroxylamine.

PubMed

Chen, Liwei; Li, Xuchun; Zhang, Jing; Fang, Jingyun; Huang, Yanmin; Wang, Ping; Ma, Jun

2015-09-01

The production of the hydroxyl radical (HO·) is important in environmental chemistry. This study reports a new source of HO· generated solely from hydrogen peroxide (H2O2) activated by hydroxylamine (HA). Electron paramagnetic resonance analysis and the oxidation of a HO· probe, benzoic acid, were used to confirm the production of HO·. The production of HO· increased with increasing concentrations of either HA or H2O2 as well as decreasing pH. The second-order rate constant for the reaction was (2.2 ± 0.2) × 10(-4) M(-1) s(-1). HO· was probably produced in two steps: the activation of H2O2 by protonated HA and then reaction between the H2O2 and the intermediate protonated aminoxyl radical generated in the first step. Such a two-step oxidation can possibly be ascribed to the ionizable hydroxyl moiety in the molecular structure of HA, as is suggested by comparing the reactivity of a series of HA derivatives in HO· production. The results shed light on a previously unknown source of HO· formation, which broadens the understanding of its role in environmental processes.

Syntheses, structures, and magnetic properties of three new MnII-[MoIII(CN)7]4- molecular magnets.

PubMed

Wei, Xiao-Qin; Pi, Qian; Shen, Fu-Xing; Shao, Dong; Wei, Hai-Yan; Wang, Xin-Yi

2018-05-22

By reaction of K4[MoIII(CN)7]·2H2O, Mn(ClO4)2·6H2O and bidentate chelating ligands, three new cyano-bridged compounds, namely Mn2(3-pypz)(H2O)(CH3CN)[Mo(CN)7] (1), Mn2(1-pypz)(H2O)(CH3CN)[Mo(CN)7] (2) and Mn2(pyim)(H2O)(CH3CN)[Mo(CN)7] (3) (3-pypz = 2-(1H-pyrazol-3-yl)pyridine, 1-pypz = 2-(1H-pyrazol-1-yl)pyridine, pyim = 2-(1H-imidazol-2-yl)pyridine), have been synthesized and characterized structurally and magnetically. Single crystal X-ray analyses revealed that although the chelating ligands are different, compounds 1 to 3 are isomorphous and crystallize in the same monoclinic space group C2/m. Connected by the bridging cyano groups, one crystallographically unique [Mo(CN)7]4- unit and three crystallographically unique MnII ions of different coordination environments form similar three-dimensional frameworks, which have a four-nodal 3,4,4,7-connecting topological net with a vertex symbol of {43}{44·62}2{410·611}. Magnetic measurements revealed that compounds 1-3 display long-range magnetic ordering with critical temperatures of 64, 66 and 62 K, respectively. These compounds are rare examples of a small number of chelating co-ligand coordinated [Mo(CN)7]4--based magnetic materials. Specifically, the bidentate chelating ligands were successfully introduced into the heptacyanomolybdate system for the first time.

Tunneling effects in the unimolecular decay of (CH 3) 2COO Criegee intermediates to OH radical products

DOE PAGES

Fang, Yi; Barber, Victoria P.; Klippenstein, Stephen J.; ...

2017-04-04

Unimolecular decay of the dimethyl substituted Criegee intermediate (CH 3) 2COO is observed at energies significantly below the transition state barrier associated with hydrogen atom transfer with time-resolved detection of the resultant OH radical products. (CH 3) 2COO is prepared at specific energies in the 3900-4600 cm -1 region through IR excitation of combination bands involving CH stretch and another lower frequency mode, and the OH products are detected by UV laser-induced fluorescence. OH appearance times on the order of microseconds are observed in this deep tunneling regime, which are about 100 times slower than that in the vicinity ofmore » the barrier. The experimental rates are in good accord with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the microcanonical dissociation rates for (CH 3) 2COO that include tunneling. Master equation modeling based on these microcanonical rates is used to predict the thermal decay rate of (CH 3) 2COO to OH products under atmospheric conditions of 276 s -1 at 298 K (high pressure limit). Furthermore, thermal unimolecular decay of (CH 3) 2COO to OH products is shown to have significant contributions from tunneling at energies much below the barrier to H-atom transfer.« less

Tunneling effects in the unimolecular decay of (CH 3) 2COO Criegee intermediates to OH radical products

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Yi; Barber, Victoria P.; Klippenstein, Stephen J.

Unimolecular decay of the dimethyl substituted Criegee intermediate (CH 3) 2COO is observed at energies significantly below the transition state barrier associated with hydrogen atom transfer with time-resolved detection of the resultant OH radical products. (CH 3) 2COO is prepared at specific energies in the 3900-4600 cm -1 region through IR excitation of combination bands involving CH stretch and another lower frequency mode, and the OH products are detected by UV laser-induced fluorescence. OH appearance times on the order of microseconds are observed in this deep tunneling regime, which are about 100 times slower than that in the vicinity ofmore » the barrier. The experimental rates are in good accord with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the microcanonical dissociation rates for (CH 3) 2COO that include tunneling. Master equation modeling based on these microcanonical rates is used to predict the thermal decay rate of (CH 3) 2COO to OH products under atmospheric conditions of 276 s -1 at 298 K (high pressure limit). Furthermore, thermal unimolecular decay of (CH 3) 2COO to OH products is shown to have significant contributions from tunneling at energies much below the barrier to H-atom transfer.« less

Missing Peroxy Radical Sources within a Summertime Ponderosa Pine Forest

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wolfe, G. M.; Cantrell, Chris; Kim, S.

2014-05-13

Organic peroxy (RO2) and hydroperoxy (HO2) radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of peroxy radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present peroxy radical observations acquired within a Ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen – Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total peroxy radical mixing ratios reach as high as 180 pptvmore » and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of peroxy radicals below the forest canopy. The base chemical mechanism underestimates total peroxy radicals by as much as a factor of 3. Peroxy radical sinks are unlikely to be overestimated, suggesting missing sources. A close comparison of model results with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (~120 and 50 pptv min-1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within the forest, and we conclude that a similar mechanism may underlie many such anomalous findings.« less

Reaction between peroxynitrite and triphenylphosphonium-substituted arylboronic acid isomers–Identification of diagnostic marker products and biological implications

PubMed Central

Sikora, Adam; Zielonka, Jacek; Adamus, Jan; Debski, Dawid; Dybala-Defratyka, Agnieszka; Michalowski, Bartosz; Joseph, Joy; Hartley, Richard C.; Murphy, Michael P.; Kalyanaraman, Balaraman

2013-01-01

Aromatic boronic acids react rapidly with peroxynitrite (ONOO−) to yield phenols as major products. This reaction was used to monitor ONOO− formation in cellular systems. Previously, we proposed that the reaction between ONOO− and arylboronates (PhB(OH)2) yields a phenolic product (major pathway) and a radical pair PhB(OH)2O•−…•NO2 (minor pathway). [Sikora A. et al., Chem Res Toxicol 24, 687-97, 2011]. In this study, we investigated the influence of a bulky triphenylphosphonium (TPP) group on the reaction between ONOO− and mitochondria-targeted arylboronate isomers (o-, m-, and p-MitoPhB(OH)2). Results from the electron paramagnetic resonance (EPR) spin-trapping experiments unequivocally showed the presence of a phenyl radical intermediate from meta and para isomers, and not from the ortho isomer. The yield of o-MitoPhNO2 formed from the reaction between o-MitoPhB(OH)2 and ONOO− was not diminished by phenyl radical scavengers, suggesting a rapid fragmentation of the o-MitoPhB(OH)2O•− radical anion with subsequent reaction of the resulting phenyl radical with •NO2 in the solvent cage. The DFT quantum mechanical calculations showed that the energy barrier for the dissociation of o-MitoPhB(OH)2O•− radical anion is significantly lower than that of m-MitoPhB(OH)2O•− and p-MitoPhB(OH)2O•− radical anions. The nitrated product, o-MitoPhNO2, is not formed by nitrogen dioxide radical generated by myeloperoxidase in the presence of nitrite anion and hydrogen peroxide, indicating that this specific nitrated product may be used as a diagnostic marker product for ONOO−. Incubation of o-MitoPhB(OH)2 with RAW 264.7 macrophages activated to produce ONOO− yielded the corresponding phenol o-MitoPhOH as well as the diagnostic nitrated product, o-MitoPhNO2. We conclude that the ortho isomer probe reported here is most suitable for specific detection of ONOO− in biological systems. PMID:23611338

Analysis of the Rotational Structure of ˜{B}^2A' ← ˜{X}^2A' Transition of Isopropoxy Radical: Isolated State vs. Coupled States Model

NASA Astrophysics Data System (ADS)

Melnik, Dmitry G.; Miller, Terry A.; Liu, Jinjun

2013-06-01

Isopropoxy radicals are reactive intermediates in atmospheric and combustion chemistry. From the theoretical point of view, they represent an extreme case of ``isotopically'' substituted methoxy radicals with two methyl groups playing the role of heavy hydrogen isotopes. Previously the rotationally resolved spectra of ˜{B}^2A' ← ˜{X}^2A' electronic transition were successfully analyzed using a simple effective rotational Hamiltonian of the isolated ˜{X} and ˜{B} states. However, a number of the experimentally determined parameters appeared dramatically inconsistent with the quantum chemistry calculations and theoretical predictions based on the symmetry arguments. Recently, we analyzed these spectra using a coupled two state model, which explicitly includes interactions between the ground ˜{X}^2A' state and low-lying excited ˜{A}^2A^'' state. In this presentation we will discuss the results of this analysis and compare the parameters of both models and their physical significance. D. G. Melnik, T. A. Miller and J. Liu, TI15, 67^{th Molecular Spectroscopy Symposium}, Columbus, 2012

Chlorine atom-initiated low-temperature oxidation of prenol and isoprenol: The effect of C=C double bonds on the peroxy radical chemistry in alcohol oxidation

DOE PAGES

Welz, Oliver; Savee, John D.; Osborn, David L.; ...

2014-07-04

The chlorine atom-initiated oxidation of two unsaturated primary C5 alcohols, prenol (3-methyl-2-buten-1-ol, (CH 3) 2CCHCH 2OH) and isoprenol (3-methyl-3-buten-1-ol, CH 2C(CH 3)CH 2CH 2OH), is studied at 550 K and low pressure (8 Torr). The time- and isomer-resolved formation of products is probed with multiplexed photoionization mass spectrometry (MPIMS) using tunable vacuum ultraviolet ionizing synchrotron radiation. The peroxy radical chemistry of the unsaturated alcohols appears much less rich than that of saturated C4 and C5 alcohols. The main products observed are the corresponding unsaturated aldehydes – prenal (3-methyl-2-butenal) from prenol oxidation and isoprenal (3-methyl-3-butenal) from isoprenol oxidation. No significant productsmore » arising from QOOH chemistry are observed. These results can be qualitatively explained by the formation of resonance stabilized allylic radicals via H-abstraction in the Cl + prenol and Cl + isoprenol initiation reactions. The loss of resonance stabilization upon O 2 addition causes the energies of the intermediate wells, saddle points, and products to increase relative to the energy of the initial radicals and O 2. These energetic shifts make most product channels observed in the peroxy radical chemistry of saturated alcohols inaccessible for these unsaturated alcohols. The experimental findings are underpinned by quantum-chemical calculations for stationary points on the potential energy surfaces for the reactions of the initial radicals with O 2. Under our conditions, the dominant channels in prenol and isoprenol oxidation are the chain-terminating HO 2-forming channels arising from radicals, in which the unpaired electron and the –OH group are on the same carbon atom, with stable prenal and isoprenal co-products, respectively. These results suggest that the presence of C=C double bonds in alcohols will reduce low-temperature reactivity during autoignition.« less

Alcohols as alkylating agents in heteroarene C-H functionalization

NASA Astrophysics Data System (ADS)

Jin, Jian; MacMillan, David W. C.

2015-09-01

Redox processes and radical intermediates are found in many biochemical processes, including deoxyribonucleotide synthesis and oxidative DNA damage. One of the core principles underlying DNA biosynthesis is the radical-mediated elimination of H2O to deoxygenate ribonucleotides, an example of `spin-centre shift', during which an alcohol C-O bond is cleaved, resulting in a carbon-centred radical intermediate. Although spin-centre shift is a well-understood biochemical process, it is underused by the synthetic organic chemistry community. We wondered whether it would be possible to take advantage of this naturally occurring process to accomplish mild, non-traditional alkylation reactions using alcohols as radical precursors. Because conventional radical-based alkylation methods require the use of stoichiometric oxidants, increased temperatures or peroxides, a mild protocol using simple and abundant alkylating agents would have considerable use in the synthesis of diversely functionalized pharmacophores. Here we describe the development of a dual catalytic alkylation of heteroarenes, using alcohols as mild alkylating reagents. This method represents the first, to our knowledge, broadly applicable use of unactivated alcohols as latent alkylating reagents, achieved via the successful merger of photoredox and hydrogen atom transfer catalysis. The value of this multi-catalytic protocol has been demonstrated through the late-stage functionalization of the medicinal agents, fasudil and milrinone.

Alcohols as alkylating agents in heteroarene C-H functionalization.

PubMed

Jin, Jian; MacMillan, David W C

2015-09-03

Redox processes and radical intermediates are found in many biochemical processes, including deoxyribonucleotide synthesis and oxidative DNA damage. One of the core principles underlying DNA biosynthesis is the radical-mediated elimination of H2O to deoxygenate ribonucleotides, an example of 'spin-centre shift', during which an alcohol C-O bond is cleaved, resulting in a carbon-centred radical intermediate. Although spin-centre shift is a well-understood biochemical process, it is underused by the synthetic organic chemistry community. We wondered whether it would be possible to take advantage of this naturally occurring process to accomplish mild, non-traditional alkylation reactions using alcohols as radical precursors. Because conventional radical-based alkylation methods require the use of stoichiometric oxidants, increased temperatures or peroxides, a mild protocol using simple and abundant alkylating agents would have considerable use in the synthesis of diversely functionalized pharmacophores. Here we describe the development of a dual catalytic alkylation of heteroarenes, using alcohols as mild alkylating reagents. This method represents the first, to our knowledge, broadly applicable use of unactivated alcohols as latent alkylating reagents, achieved via the successful merger of photoredox and hydrogen atom transfer catalysis. The value of this multi-catalytic protocol has been demonstrated through the late-stage functionalization of the medicinal agents, fasudil and milrinone.

Synthesis of Organic Compounds (Selected Articles)

DTIC Science & Technology

1990-10-03

OH+TiCI,+4NH3 - (CH2+CHCH 2 0)4 Ti+4NH4 Cl Allyl ester of-orthotitanium acid is obtained for the first time [1]. The proposed method is based on the...reaction of allyl alcohol with titanium tetrachloride in the presence of ammonia in the medium of benzene. DESCRIPTION OF SYNTHESIS Synthesis is...point 141-1420 at I mm: it is hygroscopic and easily hydrolized. NOTE Synthesis can be carried out in the absence of benzene in the medium of allyl

Exploring the intrinsic polar [4+2(+)] cycloaddition reactivity of gaseous carbosulfonium and carboxonium ions.

PubMed

Basher, Muftah M; Corilo, Yuri E; Sparrapan, Regina; Benassi, Mario; Augusti, Rodinei; Eberlin, Marcos N; Riveros, José M

2012-11-01

Gas-phase reactions of model carbosulfonium ions (CH(3)-S(+)=CH(2;) CH(3)CH(2)-S(+)=CH(2) and Ph-S(+)=CH(2)) and an O-analogue carboxonium ion (CH(3)-O(+)=CH(2)) with acyclic (isoprene, 1,3-butadiene, methyl vinyl ketone) and cyclic (1,3-cyclohexadiene, thiophene, furan) conjugated dienes were systematically investigated by pentaquadrupole mass spectrometry. As corroborated by B3LYP/6-311 G(d,p) calculations, the carbosulfonium ions first react at large extents with the dienes forming adducts via simple addition. The nascent adducts, depending on their stability and internal energy, react further via two competitive channels: (1) in reactions with acyclic dienes via cyclization that yields formally [4+2(+)] cycloadducts, or (2) in reactions with the cyclic dienes via dissociation by HSR loss that yields methylenation (net CH(+) transfer) products. In great contrast to its S-analogues, CH(3)-O(+)=CH(2) (as well as C(2)H(5)-O(+)=CH(2) and Ph-O(+)=CH(2) in reactions with isoprene) forms little or no adduct and proton transfer is the dominant reaction channel. Isomerization to more acidic protonated aldehydes in the course of reaction seems to be the most plausible cause of the contrasting reactivity of carboxonium ions. The CH(2)=CH-O(+)=CH(2) ion forms an abundant [4+2(+)] cycloadduct with isoprene, but similar to the behavior of such α,β-unsaturated carboxonium ions in solution, seems to occur across the C=C bond. Copyright © 2012 John Wiley & Sons, Ltd.

Multiheteromacrocycles that Complex Metal Ions. Second Progress Report, 1 May 1975 -- 30 April 1976

DOE R&D Accomplishments Database

Cram, D. J.

1976-01-15

Objective is to develop cyclic and polycyclic host organic compounds to complex and lipophilize metal ions. Macrorings were synthesized: (OCH{sub 2} CH{sub 2} O CH{sub 2}COCH{sub 2} COCH{sub 2}){sub 2} and (OCH{sub 2} CH{sub 2} O CH{sub 2} COCH{sub 2} COCH{sub 2}){sub 3}. The smaller ring complexes divalent metals 10{sup 1+9} times better than the open-chain model CH{sub 3} O CH{sub 2} CO CH{sub 2} COCH{sub 2} O CH{sub 3}, and the order in which metal ions are complexed is Cu{sup 2+}, UO{sub 2}{sup 2+} greater than Ni{sup 2+} greater than Fe{sup 2+}, Co{sup 2+}, Zn{sup 2+}, Cd{sup 2+} greater than Mn{sup 2+}. The UO{sub 2}{sup 2+} and Cu{sup 2+} complexes were isolated and characterized. The larger ring complexes trivalent metals 10{sup 0.9-1.7} times better than the open- chain model compound, and the order is La{sup 3+}, Ce{sup 3+} greater than Cr{sup 3+}. Five other macrocycles were also synthesized, and their binding constants with Na, K, NH{sub 4}, and Cs picrates were measured. Six compounds containing one macroring and two inward-pointing ArOH or ArOCH{sub 3} groups were also prepared and tested for binding of Li, Na, K, Rb, and NH{sub 4} picrates. Racemic compounds containing two binaphthyls and its sulfur analog were prepared. Cage-shaped multiheteromacrocycles containing ten O ligand sites or four S and six O ligand sites were prepared and the binding capability of the first compound for picrates studied. Two ring systems with phosphonate ester groups were also prepared. (DLC)

Sugar Radical Formation by a Proton Coupled Hole Transfer in 2′-Deoxyguanosine Radical Cation (2′-dG•+): A Theoretical Treatment

PubMed Central

Kumar, Anil; Sevilla, Michael D.

2009-01-01

Previous experimental and theoretical work has established that electronic excitation of a guanine cation radical in nucleosides or in DNA itself leads to sugar radical formation by deprotonation from the dexoxyribose sugar. In this work we investigate a ground electronic state pathway for such sugar radical formation in a hydrated one electron oxidized 2′-deoxyguanosine (dG•+ + 7H2O), using density functional theory (DFT) with the B3LYP functional and the 6-31G* basis set. We follow the stretching of the C5′-H bond in dG•+ to gain an understanding of the energy requirements to transfer the hole from the base to sugar ring and then to deprotonate to proton acceptor sites in solution and on the guanine ring. The geometries of reactant (dG•+ + 7H2O), transition state (TS) for deprotonation of C5′ site and product (dG(•C5′, N7-H+) + 7 H2O) were fully optimized. The zero point energy (ZPE) corrected activation energy (TS) for the proton transfer (PT) from C5′ is calculated to be 9.0 kcal/mol and is achieved by stretching the C5′-H bond by 0.13 Å from its equilibrium bond distance (1.099 Å). Remarkably, this small bond stretch is sufficient to transfer the “hole” (positive charge and spin) from guanine to the C5′ site on the deoxyribose group. Beyond the TS, the proton (H+) spontaneously adds to water to form a hydronium ion (H3O+) as an intermediate. The proton subsequently transfers to the N7 site of the guanine (product). The 9 kcal/mol barrier suggests slow thermal conversion of the cation radical to the sugar radical but also suggests that localized vibrational excitations would be sufficient to induce rapid sugar radical formation in DNA base cation radicals. PMID:19754084

Flavonoid oxidation by the radical generator AIBN: a unified mechanism for quercetin radical scavenging.

PubMed

Krishnamachari, Venkat; Levine, Lanfang H; Paré, Paul W

2002-07-17

Four oxidized flavonoid derivatives generated from reacting quercetin (a pentahydroxylated flavone) with the peroxyl radical generator 2,2'-azobis-isobutyronitrile (AIBN) were isolated by chromatographic methods and identified by NMR and MS analyses. Compounds included 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (2); 1,3,11a-trihydroxy-9-(3,5,7-trihydroxy-4H-1-benzopyran-4-on-2-yl)-5a-(3,4-dihydroxyphenyl)-5,6,11-hexahydro-5,6,11-trioxanaphthacene-12-one (3); 2-(3,4-dihydroxybenzoyloxy)-4,6-dihydroxybenzoic acid (4); and methyl 3,4-dihydroxyphenylglyoxylate (5). Product ratios under different hydrogen ion concentrations and external nucleophiles revealed that two of the products, namely the substituted benzofuranone (2) and the depside (4), are generated from a common carbocation intermediate. Indirect evidence for the operation of a cyclic concerted mechanism in the formation of the dimeric product (3) is provided. The identification of these products supports the model that the principal site of scavenging reactive oxygen species (ROS) in quercetin is the o-dihydroxyl substituent in the B-ring, as well as the C-ring olefinic linkage.

Oxysterols from Free Radical Chain Oxidation of 7-Dehydrocholesterol: Product and Mechanistic Studies

PubMed Central

Xu, Libin; Korade, Zeljka; Porter, Ned A.

2010-01-01

Free radical chain oxidation of highly oxidizable 7-dehydrocholesterol (7-DHC) initiated by 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) was carried out at 37°C in benzene for 24 hours. Fifteen oxysterols derived from 7-DHC were isolated and characterized with 1D- and 2D-NMR spectroscopy and mass spectrometry. A mechanism that involves abstraction of hydrogen atoms at C-9 and/or C-14 is proposed to account for the formation of all of the oxysterols and the reaction progress profile. In either the H-9 or H-14 mechanism, a pentadienyl radical intermediate is formed after abstraction of H-9 or H-14 by a peroxyl radical. This step is followed by the well-precedented transformations observed in peroxidation reactions of polyunsaturated fatty acids such as oxygen addition, peroxyl radical 5-exo cyclization, and SHi carbon radical attack on the peroxide bond. The mechanism for peroxidation of 7-DHC also accounts for the formation of numerous oxysterol natural products isolated from fungal species, marine sponges, and cactaceous species. In a cell viability test, the oxysterol mixture from 7-DHC peroxidation was found to be cytotoxic to Neuro2a neuroblastoma cells in the micromolar concentration range. We propose that the high reactivity of 7-DHC and the oxysterols generated from its peroxidation may play important roles in the pathogenesis of Smith-Lemli-Opitz syndrome (SLOS), X-linked dominant chondrodysplasia punctata (CDPX2), and cerebrotendinous xanthomatosis (CTX), all of these being metabolic disorders having an elevated level of 7-DHC. PMID:20121089

Laser studies of the photodissociation dynamics of cometary radicals

NASA Technical Reports Server (NTRS)

Jackson, William M.

1991-01-01

In the past year, it was shown that in the 193 nm photolysis of C2H, the C2 radical is produced in a variety of electronic, vibrational, and rotational states. The relative population of the vibrational and rotational states of C2(A 1 Pi u), C2(B 1 Sigma g +), and C2(A 3 Pi u) were determined in a static gas cell and in a pulsed molecular beam. It seems as though the original angular momentum of the C2H molecule appears as part of the angular momentum of the C2 radical. A attempt is being made to discover the mathematical relationship that governs this mapping. New information about the bond dissociation energy of the C2 radical was produces. C2(b 3 Sigma g -) and C2( 1 Delta g) were detected in the photolysis of C2H via time resolved infrared emission spectroscopy. In the former case, vibrational excitation up to v'' = 4 is observed. All of the results suggest that the C2 models in comets need to consider the presence of vibrationally excited C2 radicals in comets. The laser induced fluorescence spectra of the C3 was observed as a product of the 193 nm photolysis of allene and propyne. The populations of the rotational levels are identical in both cases. This result has led us to conclude that an isomerization reaction occurs in the photolysis of propyne which leads to the same C3H2 intermediate that is formed in the photolysis of C3H4. Since the former molecule is one of the most abundant in the interstellar medium it is also likely that its precursor is also present in comets. This would explain why C3 is observed in comets.

Photogenerated radical intermediates of vitamin K 1: a time-resolved resonance Raman study

NASA Astrophysics Data System (ADS)

Balakrishnan, G.; Umapathy, S.

1999-01-01

Quinones play a vital role in the process of electron transfer in bacterial photosynthetic reaction centers. It is of interest to investigate the photochemical reactions involving quinones with a view to elucidating the structure-function relationships in the biological processes. Resonance Raman spectra of radical anions and the time-resolved resonance Raman spectra of vitamin K 1 (model compound for Q A in Rhodopseudomonas viridis, a bacterial photosynthetic reception center) are presented. The photochemical intermediates of vitamin K 1, viz. radical anion, ketyl radical and o-quinone methide have been identified. The vibrational assignments of all these intermediates are made on the basis of comparison with our earlier TR3 studies on radical anions of naphthoquinone and menaquinone.

Experimental demonstration of radicaloid character in a RuV=O intermediate in catalytic water oxidation

PubMed Central

Moonshiram, Dooshaye; Alperovich, Igor; Concepcion, Javier J.; Meyer, Thomas J.; Pushkar, Yulia

2013-01-01

Water oxidation is the key half reaction in artificial photosynthesis. An absence of detailed mechanistic insight impedes design of new catalysts that are more reactive and more robust. A proposed paradigm leading to enhanced reactivity is the existence of oxyl radical intermediates capable of rapid water activation, but there is a dearth of experimental validation. Here, we show the radicaloid nature of an intermediate reactive toward formation of the O-O bond by assessing the spin density on the oxyl group by Electron Paramagnetic Resonance (EPR). In the study, an 17O-labeled form of a highly oxidized, short-lived intermediate in the catalytic cycle of the water oxidation catalyst cis,cis-[(2,2-bipyridine)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+ was investigated. It contains Ru centers in oxidation states [4,5], has at least one RuV = O unit, and shows |Axx| = 60G 17O hyperfine splittings (hfs) consistent with the high spin density of a radicaloid. Destabilization of π-bonding in the d3 RuV = O fragment is responsible for the high spin density on the oxygen and its high reactivity. PMID:23417296

Quantum Chemical Molecular Dynamics Simulations of 1,3-Dichloropropene Combustion.

PubMed

Ahubelem, Nwakamma; Shah, Kalpit; Moghtaderi, Behdad; Page, Alister J

2015-09-03

Oxidative decomposition of 1,3-dichloropropene was investigated using quantum chemical molecular dynamics (QM/MD) at 1500 and 3000 K. Thermal oxidation of 1,3-dichloropropene was initiated by (1) abstraction of allylic H/Cl by O2 and (2) intra-annular C-Cl bond scission and elimination of allylic Cl. A kinetic analysis shows that (2) is the more dominant initiation pathway, in agreement with QM/MD results. These QM/MD simulations reveal new routes to the formation of major products (H2O, CO, HCl, CO2), which are propagated primarily by the chloroperoxy (ClO2), OH, and 1,3-dichloropropene derived radicals. In particular, intra-annular C-C/C-H bond dissociation reactions of intermediate aldehydes/ketones are shown to play a dominant role in the formation of CO and CO2. Our simulations demonstrate that both combustion temperature and radical concentration can influence the product yield, however not the combustion mechanism.

Temperature-Dependent Rate Constants and Substituent Effects for the Reactions of Hydroxyl Radicals With Three Partially Fluorinated Ethers

NASA Technical Reports Server (NTRS)

Hsu, K.-J.; DeMore, W. B.

1995-01-01

Rate constants and temperature dependencies for the reactions of OH with CF3OCH3 (HFOC-143a), CF2HOCF2H (HFOC-134), and CF3OCF2H (HFOC-125) were studied using a relative rate technique in the temperature range 298-393 K. The following absolute rate constants were derived: HFOC-143a, 1.9E-12 exp(-1555/T); HFOC-134, 1.9E-12 exp(-2006/T); HFOC-125, 4.7E-13 exp(-2095/T). Units are cm(exp 3)molecule(exp -1) s(exp -1). Substituent effects on OH abstraction rate constants are discussed, and it is shown that the CF3O group has an effect on the OH rate constants similar to that of a fluorine atom. The effects are related to changes in the C-H bond energies of the reactants (and thereby the activation energies) rather than changes in the preexponential factors. On the basis of a correlation of rate constants with bond energies, the respective D(C-H) bond strengths in the three ethers are found to be 102, 104, and 106 kcal/mol, with an uncertainty of about 1 kcal/mol.

Development of a fed-batch process for a recombinant Pichia pastoris Δoch1 strain expressing a plant peroxidase.

PubMed

Gmeiner, Christoph; Saadati, Amirhossein; Maresch, Daniel; Krasteva, Stanimira; Frank, Manuela; Altmann, Friedrich; Herwig, Christoph; Spadiut, Oliver

2015-01-08

Pichia pastoris is a prominent host for recombinant protein production, amongst other things due to its capability of glycosylation. However, N-linked glycans on recombinant proteins get hypermannosylated, causing problems in subsequent unit operations and medical applications. Hypermannosylation is triggered by an α-1,6-mannosyltransferase called OCH1. In a recent study, we knocked out OCH1 in a recombinant P. pastoris CBS7435 Mut(S) strain (Δoch1) expressing the biopharmaceutically relevant enzyme horseradish peroxidase. We characterized the strain in the controlled environment of a bioreactor in dynamic batch cultivations and identified the strain to be physiologically impaired. We faced cell cluster formation, cell lysis and uncontrollable foam formation.In the present study, we investigated the effects of the 3 process parameters temperature, pH and dissolved oxygen concentration on 1) cell physiology, 2) cell morphology, 3) cell lysis, 4) productivity and 5) product purity of the recombinant Δoch1 strain in a multivariate manner. Cultivation at 30°C resulted in low specific methanol uptake during adaptation and the risk of methanol accumulation during cultivation. Cell cluster formation was a function of the C-source rather than process parameters and went along with cell lysis. In terms of productivity and product purity a temperature of 20°C was highly beneficial. In summary, we determined cultivation conditions for a recombinant P. pastoris Δoch1 strain allowing high productivity and product purity.

Substrate-Tuned Catalysis of the Radical S-Adenosyl-L-Methionine Enzyme NosL Involved in Nosiheptide Biosynthesis.

PubMed

Ji, Xinjian; Li, Yongzhen; Ding, Wei; Zhang, Qi

2015-07-27

NosL is a radical S-adenosyl-L-methionine (SAM) enzyme that converts L-Trp to 3-methyl-2-indolic acid, a key intermediate in the biosynthesis of a thiopeptide antibiotic nosiheptide. In this work we investigated NosL catalysis by using a series of Trp analogues as the molecular probes. Using a benzofuran substrate 2-amino-3-(benzofuran-3-yl)propanoic acid (ABPA), we clearly demonstrated that the 5'-deoxyadenosyl (dAdo) radical-mediated hydrogen abstraction in NosL catalysis is not from the indole nitrogen but likely from the amino group of L-Trp. Unexpectedly, the major product of ABPA is a decarboxylated compound, indicating that NosL was transformed to a novel decarboxylase by an unnatural substrate. Furthermore, we showed that, for the first time to our knowledge, the dAdo radical-mediated hydrogen abstraction can occur from an alcohol hydroxy group. Our study demonstrates the intriguing promiscuity of NosL catalysis and highlights the potential of engineering radical SAM enzymes for novel activities. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-Catalyzed Atom-Transfer Radical Cyclization at Remote Unactivated C(sp3 )-H Sites: Hydrogen-Atom Transfer of Hybrid Vinyl Palladium Radical Intermediates.

PubMed

Ratushnyy, Maxim; Parasram, Marvin; Wang, Yang; Gevorgyan, Vladimir

2018-03-01

A novel mild, visible-light-induced palladium-catalyzed hydrogen atom translocation/atom-transfer radical cyclization (HAT/ATRC) cascade has been developed. This protocol involves a 1,5-HAT process of previously unknown hybrid vinyl palladium radical intermediates, thus leading to iodomethyl carbo- and heterocyclic structures. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Elucidation of the electronic states in polyethylene glycol by attenuated Total reflectance spectroscopy in the far-ultraviolet region

NASA Astrophysics Data System (ADS)

Ueno, Nami; Wakabayashi, Tomonari; Morisawa, Yusuke

2018-05-01

We measured the attenuated total reflectance-far ultraviolet (ATR-FUV) spectra of poly(ethylene glycol) (PEG; average molecular weights of 200, 300, and 400) and related materials in the liquid state in the 145-200-nm wavelength region. For appropriately assigning the absorption bands, we also performed theoretical simulation of the unit-number dependent electronic spectra. The FUV spectra of PEGs contain three bands, which are assigned to the transitions between n(CH2OCH2)-3s Rydberg state (176 nm), n(CH2OCH2)-3p Rydberg state (163 nm), and n(OH)-3p Rydberg state (153 nm). Since the contribution of n(OH) decreases compared to n(CH2OCH2) with increase in the number of units, the ratios of the molar absorption coefficients, ε, at 153 nm relative to 163 nm, decrease. On the other hand, the ratio of ε at 176 nm to that at 163 nm increases with increase in the number of units, because of the difference in the number of unoccupied orbitals in the transitions. The calculated results suggest that n orbitals form two electronic bands. In the upper band, the electrons expand over the ether chain, whereas in the lower band, the electrons are localized in the terminal OH in the PEGs.

A detailed kinetic modeling study of toluene oxidation in a premixed laminar flame

PubMed Central

Tian, Zhenyu; Pitz, William J.; Fournet, René; Glaude, Pierre-Alexander; Battin-Leclerc, Frédérique

2013-01-01

An improved chemical kinetic model for the toluene oxidation based on experimental data obtained in a premixed laminar low-pressure flame with vacuum ultraviolet (VUV) photoionization and molecular beam mass spectrometry (MBMS) techniques has been proposed. The present mechanism consists of 273 species up to chrysene and 1740 reactions. The rate constants of reactions of toluene decomposition, reaction with oxygen, ipso-additions and metatheses with abstraction of phenylic H-atom are updated; new pathways of C4 + C2 species giving benzene and fulvene are added. Based on the experimental observations, combustion intermediates such as fulvenallene, naphtol, methylnaphthalene, acenaphthylene, 2-ethynylnaphthalene, phenanthrene, anthracene, 1-methylphenanthrene, pyrene and chrysene are involved in the present mechanism. The final toluene model leads to an overall satisfactory agreement between the experimentally observed and predicted mole fraction profiles for the major products and most combustion intermediates. The toluene depletion is governed by metathese giving benzyl radicals, ipso-addition forming benzene and metatheses leading to C6H4CH3 radicals. A sensitivity analysis indicates that the unimolecular decomposition via the cleavage of a methyl C-H bond has a strong inhibiting effect, while decomposition via C-C bond breaking, ipso-addition of H-atom to toluene, decomposition of benzyl radicals and reactions related to C6H4CH3 radicals have promoting effect for the consumption of toluene. Moreover, flow rate analysis is performed to illustrate the formation pathways of mono- and polycyclic aromatics. PMID:23762016

Interactions of short-acting, intermediate-acting and pre-mixed human insulins with free radicals--Comparative EPR examination.

PubMed

Olczyk, Paweł; Komosinska-Vassev, Katarzyna; Ramos, Paweł; Mencner, Łukasz; Olczyk, Krystyna; Pilawa, Barbara

2015-07-25

Electron paramagnetic resonance (EPR) spectroscopy was used to examine insulins interactions with free radicals. Human recombinant DNA insulins of three groups were studied: short-acting insulin (Insuman Rapid); intermediate-acting insulins (Humulin N, Insuman Basal), and pre-mixed insulins (Humulin M3, Gensulin M50, Gensulin M40, Gensulin M30). The aim of an X-band (9.3GHz) study was comparative analysis of antioxidative properties of the three groups of human insulins. DPPH was used as a stable free radical model. Amplitudes of EPR lines of DPPH as the paramagnetic free radical reference, and DPPH interacting with the individual tested insulins were compared. For all the examined insulins kinetics of their interactions with free radicals up to 60 min were obtained. The strongest interactions with free radicals were observed for the short-acting insulin - Insuman Rapid. The lowest interactions with free radicals were characteristic for intermediate-acting insulin - Insuman Basal. The pre-mixed insulins i.e. Humulin M3 and Gensulin M50 revealed the fastest interactions with free radicals. The short acting, intermediate acting and premixed insulins have been found to be effective agents in reducing free radical formation in vitro and should be further considered as potential useful tools in attenuation of oxidative stress in diabetic patients. Copyright © 2015 Elsevier B.V. All rights reserved.

OH-radical induced degradation of hydroxybenzoic- and hydroxycinnamic acids and formation of aromatic products—A gamma radiolysis study

NASA Astrophysics Data System (ADS)

Krimmel, Birgit; Swoboda, Friederike; Solar, Sonja; Reznicek, Gottfried

2010-12-01

The OH-radical induced degradation of hydroxybenzoic acids (HBA), hydroxycinnamic acids (HCiA) and methoxylated derivatives, as well as of chlorogenic acid and rosmarinic acid was studied by gamma radiolysis in aerated aqueous solutions. Primary aromatic products resulting from an OH-radical attachment to the ring (hydroxylation), to the position occupied by the methoxyl group (replacement -OCH 3 by -OH) as well as to the propenoic acid side chain of the cinnamic acids (benzaldehyde formations) were analysed by HPLC-UV and LC-ESI-MS. A comparison of the extent of these processes is given for 3,4-dihydroxybenzoic acid, vanillic acid, isovanillic acid, syringic acid, cinnamic acid, 4-hydroxycinnamic acid, caffeic acid, ferulic acid, isoferulic acid, chlorogenic acid, and rosmarinic acid. For all cinnamic acids and derivatives benzaldehydes were significant oxidation products. With the release of caffeic acid from chlorogenic acid the cleavage of a phenolic glycoside could be demonstrated. Reaction mechanisms are discussed.

Copper-catalyzed oxidative Heck reactions between alkyltrifluoroborates and vinyl arenes.

PubMed

Liwosz, Timothy W; Chemler, Sherry R

2013-06-21

We report herein that potassium alkyltrifluoroborates can be utilized in oxidative Heck-type reactions with vinyl arenes. The reaction is catalyzed by a Cu(OTf)2/1,10-phenanthroline with MnO2 as the stoichiometric oxidant. In addition to the alkyl Heck, amination, esterification, and dimerization reactions of alkyltrifluoroborates are demonstrated under analogous reaction conditions. Evidence for an alkyl radical intermediate is presented.

Hydrogen-bonding Interactions between Apigenin and Ethanol/Water: A Theoretical Study

NASA Astrophysics Data System (ADS)

Zheng, Yan-Zhen; Zhou, Yu; Liang, Qin; Chen, Da-Fu; Guo, Rui; Lai, Rong-Cai

2016-10-01

In this work, hydrogen-bonding interactions between apigenin and water/ethanol were investigated from a theoretical perspective using quantum chemical calculations. Two conformations of apigenin molecule were considered in this work. The following results were found. (1) For apigenin monomer, the molecular structure is non-planar, and all of the hydrogen and oxygen atoms can be hydrogen-bonding sites. (2) Eight and seven optimized geometries are obtained for apigenin (I)-H2O/CH3CH2OH and apigenin (II)-H2O/CH3CH2OH complexes, respectively. In apigenin, excluding the aromatic hydrogen atoms in the phenyl substituent, all other hydrogen atoms and the oxygen atoms form hydrogen-bonds with H2O and CH3CH2OH. (3) In apigenin-H2O/CH3CH2OH complexes, the electron density and the E(2) in the related localized anti-bonding orbital are increased upon hydrogen-bond formation. These are the cause of the elongation and red-shift of the X-H bond. The sum of the charge change transfers from the hydrogen-bond acceptor to donor. The stronger interaction makes the charge change more intense than in the less stable structures. (4) Most of the hydrogen-bonds in the complexes are electrostatic in nature. However, the C4-O5···H, C9-O4···H and C13-O2···H hydrogen-bonds have some degree of covalent character. Furthermore, the hydroxyl groups of the apigenin molecule are the preferred hydrogen-bonding sites.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Xianhui; Ngo, Huong T.; Walker, Devin M.

The performance of catalytic tri-reforming under industrially relevant situations (e.g., pellet catalysts, pressurized reactor) was investigated using surrogate biogas as the feedstock. Tri-reforming using Ni/Mg/Ce 0.6Zr 0.4O 2/Al 2O 3 pellet catalysts was studied in a bench scale fixed-bed reactor. The feed molar ratio for CH 4: CO 2: air was fixed as 1.0: 0.70: 0.95. The effects of temperature (800 – 860 °C), pressure (1 – 6 bar), and H 2O/CH 4 molar feed ratio (0.23 – 0.65) were examined. Pressure has substantial impact on the reaction and transport rates and equilibrium conversions, making it a key variable. Atmore » 860 °C, CO 2 conversion increased from 4 to 61% and H 2/CO molar ratio decreased from 2.0 to 1.1 as the pressure changed from 1 to 6 bar. CO 2 conversion and H 2/CO molar ratio were also influenced by the temperature and H 2O/CH 4 molar ratio. At 3 bar, CO 2 conversion varied between 4 and 43% and the H 2/CO molar ratio varied between 1.2 and 1.9 as the temperature changed from 800 to 860 °C. At 3 bar and 860 °C, CO 2 conversion decreased from 35 to 8% and H 2/CO molar ratio increased from 1.7 to 2.4 when the H 2O/CH 4 molar ratio was increased from 0.23 to 0.65. This work demonstrates that the tri-reforming technology is feasible for converting biogas under scaled-up conditions in a fixed-bed reactor.« less

Tri-reforming of surrogate blogs over Ni/Mg/ceria-zirconia/alumina pellet catalysts

DOE PAGES

Zhao, Xianhui; Ngo, Huong T.; Walker, Devin M.; ...

2018-01-23

The performance of catalytic tri-reforming under industrially relevant situations (e.g., pellet catalysts, pressurized reactor) was investigated using surrogate biogas as the feedstock. Tri-reforming using Ni/Mg/Ce 0.6Zr 0.4O 2/Al 2O 3 pellet catalysts was studied in a bench scale fixed-bed reactor. The feed molar ratio for CH 4: CO 2: air was fixed as 1.0: 0.70: 0.95. The effects of temperature (800 – 860 °C), pressure (1 – 6 bar), and H 2O/CH 4 molar feed ratio (0.23 – 0.65) were examined. Pressure has substantial impact on the reaction and transport rates and equilibrium conversions, making it a key variable. Atmore » 860 °C, CO 2 conversion increased from 4 to 61% and H 2/CO molar ratio decreased from 2.0 to 1.1 as the pressure changed from 1 to 6 bar. CO 2 conversion and H 2/CO molar ratio were also influenced by the temperature and H 2O/CH 4 molar ratio. At 3 bar, CO 2 conversion varied between 4 and 43% and the H 2/CO molar ratio varied between 1.2 and 1.9 as the temperature changed from 800 to 860 °C. At 3 bar and 860 °C, CO 2 conversion decreased from 35 to 8% and H 2/CO molar ratio increased from 1.7 to 2.4 when the H 2O/CH 4 molar ratio was increased from 0.23 to 0.65. This work demonstrates that the tri-reforming technology is feasible for converting biogas under scaled-up conditions in a fixed-bed reactor.« less

Magnetic field affects enzymatic ATP synthesis.

PubMed

Buchachenko, Anatoly L; Kuznetsov, Dmitry A

2008-10-01

The rate of ATP synthesis by creatine kinase extracted from V. xanthia venom was shown to depend on the magnetic field. The yield of ATP produced by enzymes with 24Mg2+ and 26Mg2+ ions in catalytic sites increases by 7-8% at 55 mT and then decreases at 80 mT. For enzyme with 25Mg2+ ion in a catalytic site, the ATP yield increases by 50% and 70% in the fields 55 and 80 mT, respectively. In the Earth field the rate of ATP synthesis by enzyme, in which Mg2+ ion has magnetic nucleus 25Mg, is 2.5 times higher than that by enzymes, in which Mg2+ ion has nonmagnetic, spinless nuclei 24Mg or 26Mg. Both magnetic field effect and magnetic isotope effect demonstrate that the ATP synthesis is an ion-radical process, affected by Zeeman interaction and hyperfine coupling in the intermediate ion-radical pair.

Electro-fenton and photoelectro-fenton degradation of sulfanilic acid using a boron-doped diamond anode and an air diffusion cathode.

PubMed

El-Ghenymy, Abdellatif; Garrido, José Antonio; Centellas, Francesc; Arias, Conchita; Cabot, Pere Lluís; Rodríguez, Rosa María; Brillas, Enric

2012-04-05

The mineralization of sulfanilic acid has been studied by electro-Fenton (EF) and photoelectro-Fenton (PEF) reaction with UVA light using an undivided electrochemical cell with a boron-doped diamond (BDD) anode and an air diffusion cathode able to generate H(2)O(2). Organics were then oxidized by hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between generated H(2)O(2) and added Fe(2+). The UVA irradiation in PEF enhanced the production of hydroxyl radicals in the bulk, accelerating the removal of organics and photodecomposed intermediates like Fe(III)-carboxylate complexes. Partial decontamination of 1.39 mM sulfanilic acid solutions was achieved by EF until 100 mA cm(-2) at optimum conditions of 0.4 mM Fe(2+) and pH 3.0. The increase in current density and substrate content led to an almost total mineralization. In contrast, the PEF process was more powerful, yielding almost complete mineralization in less electrolysis time under comparable conditions. The kinetics for sulfanilic acid decay always followed a pseudo-first-order reaction. Hydroquinone and p-benzoquinone were detected as aromatic intermediates, whereas acetic, maleic, formic, oxalic, and oxamic acids were identified as generated carboxylic acids. NH(4)(+) ion was preferentially released in both treatments, along with NO(3)(-) ion in smaller proportion.

Experimentally Determined Site-Specific Reactivity of the Gas-Phase OH and Cl + i-Butanol Reactions Between 251 and 340 K.

PubMed

McGillen, Max R; Tyndall, Geoffrey S; Orlando, John J; Pimentel, Andre S; Medeiros, Diogo J; Burkholder, James B

2016-12-22

Product branching ratios for the gas-phase reactions of i-butanol, (CH 3 ) 2 CHCH 2 OH, with OH radicals (251, 294, and 340 K) and Cl atoms (294 K) were quantified in an environmental chamber study and used to interpret i-butanol site-specific reactivity. i-Butyraldehyde, acetone, acetaldehyde, and formaldehyde were observed as major stable end products in both reaction systems with carbon mass balance indistinguishable from unity. Product branching ratios for OH oxidation were found to be temperature-dependent with the α, β, and γ channels changing from 34 ± 6 to 47 ± 1%, from 58 ± 6 to 37 ± 9%, and from 8 ± 1 to 16 ± 4%, respectively, between 251 and 340 K. Recommended temperature-dependent site-specific modified Arrhenius expressions for the OH reaction rate coefficient are (cm 3 molecule -1 s -1 ): k α (T) = 8.64 × 10 -18 × T 1.91 exp(666/T); k β (T) = 5.15 × 10 -19 × T 2.04 exp(1304/T); k γ (T) = 3.20 × 10 -17 × T 1.78 exp(107/T); k OH (T) = 2.10 × 10 -18 × T 2 exp(-23/T), where k Total (T) = k α (T) + k β (T) + k γ (T) + k OH (T). The expressions were constrained using the product branching ratios measured in this study and previous total phenomenological rate coefficient measurements. The site-specific expressions compare reasonably well with recent theoretical work. It is shown that use of i-butanol would result in acetone as the dominant degradation product under most atmospheric conditions.

Characterization of intermediate products of solar photocatalytic degradation of ranitidine at pilot-scale.

PubMed

Radjenović, Jelena; Sirtori, Carla; Petrović, Mira; Barceló, Damià; Malato, Sixto

2010-04-01

In the present study the mechanisms of solar photodegradation of H(2)-receptor antagonist ranitidine (RNTD) were studied in a well-defined system of a pilot plant scale Compound Parabolic Collector (CPC) reactor. Two types of heterogeneous photocatalytic experiments were performed: catalysed by titanium-dioxide (TiO(2)) semiconductor and by Fenton reagent (Fe(2+)/H(2)O(2)), each one with distilled water and synthetic wastewater effluent matrix. Complete disappearance of the parent compounds and discreet mineralization were attained in all experiments. Furthermore, kinetic parameters, main intermediate products, release of heteroatoms and formation of carboxylic acids are discussed. The main intermediate products of photocatalytic degradation of RNTD have been structurally elucidated by tandem mass spectrometry (MS(2)) experiments performed at quadrupole-time of flight (QqToF) mass analyzer coupled to ultra-performance liquid chromatograph (UPLC). RNTD displayed high reactivity towards OH radicals, although a product of conduction band electrons reduction was also present in the experiment with TiO(2). In the absence of standards, quantification of intermediates was not possible and only qualitative profiles of their evolution could be determined. The proposed TiO(2) and photo-Fenton degradation routes of RNTD are reported for the first time. (c) 2010 Elsevier Ltd. All rights reserved.

Formation of methemoglobin and phenoxyl radicals from p-hydroxyanisole and oxyhemoglobin.

PubMed

Stolze, K; Nohl, H

1991-01-01

The reaction of p-hydroxyanisole with oxyhemoglobin was investigated using electron spin resonance spectroscopy (ESR) and visible spectroscopy. As a reactive reaction intermediate we found the p-methoxyphenoxyl radical, the one-electron oxidation product of p-hydroxyanisole. Detection of this species required the rapid flow device elucidating the instability of this radical intermediate. The second reaction product formed is methemoglobin. Catalase or SOD had no effect upon the reaction kinetics. Accordingly, reactive oxygen species such as hydroxyl radicals or superoxide could not be observed although the spin trapping agent DMPO was used to make these short-lived species detectable. When the sulfhydryl blocking agents N-ethylmaleimide or mersalyl acid were used, an increase of the methemoglobin formation rate and of the phenoxyl radical concentration were observed. We have interpreted this observation in terms of a side reaction of free radical intermediates with thiol groups.

Hydrocarbon oxidation by beta-halogenated dioxoruthenium(VI) porphyrin complexes: effect of reduction potential (RuVI/V) and C-H bond-dissociation energy on rate constants.

PubMed

Che, Chi-Ming; Zhang, Jun-Long; Zhang, Rui; Huang, Jie-Sheng; Lai, Tat-Shing; Tsui, Wai-Man; Zhou, Xiang-Ge; Zhou, Zhong-Yuan; Zhu, Nianyong; Chang, Chi Kwong

2005-11-18

beta-Halogenated dioxoruthenium(VI) porphyrin complexes [Ru(VI)(F(28)-tpp)O(2)] [F(28)-tpp=2,3,7,8,12,13, 17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(VI)(beta-Br(8)-tmp)O(2)] [beta-Br(8)-tmp=2,3,7,8,12,13,17,18-octabromo-5,10,15,20- tetrakis(2,4,6-trimethylphenyl)porphyrinato(2-)] were prepared from reactions of [Ru(II)(por)(CO)] [por=porphyrinato(2-)] with m-chloroperoxybenzoic acid in CH(2)Cl(2). Reactions of [Ru(VI)(por)O(2)] with excess PPh(3) in CH(2)Cl(2) gave [Ru(II)(F(20)-tpp)(PPh(3))(2)] [F(20)-tpp=5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(II)(F(28)-tpp)(PPh(3))(2)]. The structures of [Ru(II)(por)(CO)(H(2)O)] and [Ru(II)(por)(PPh(3))(2)] (por=F(20)-tpp, F(28)-tpp) were determined by X-ray crystallography, revealing the effect of beta-fluorination of the porphyrin ligand on the coordination of axial ligands to ruthenium atom. The X-ray crystal structure of [Ru(VI)(F(20)-tpp)O(2)] shows a Ru=O bond length of 1.718(3) A. Electrochemical reduction of [Ru(VI)(por)O(2)] (Ru(VI) to Ru(V)) is irreversible or quasi-reversible, with the E(p,c)(Ru(VI/V)) spanning -0.31 to -1.15 V versus Cp(2)Fe(+/0). Kinetic studies were performed for the reactions of various [Ru(VI)(por)O(2)], including [Ru(VI)(F(28)-tpp)O(2)] and [Ru(VI)(beta-Br(8)-tmp)O(2)], with para-substituted styrenes p-X-C(6)H(4)CH=CH(2) (X=H, F, Cl, Me, MeO), cis- and trans-beta-methylstyrene, cyclohexene, norbornene, ethylbenzene, cumene, 9,10-dihydroanthracene, xanthene, and fluorene. The second-order rate constants (k(2)) obtained for the hydrocarbon oxidations by [Ru(VI)(F(28)-tpp)O(2)] are up to 28-fold larger than by [Ru(VI)(F(20)-tpp)O(2)]. Dual-parameter Hammett correlation implies that the styrene oxidation by [Ru(VI)(F(28)-tpp)O(2)] should involve rate-limiting generation of a benzylic radical intermediate, and the spin delocalization effect is more important than the polar effect. The k(2) values for the oxidation of styrene and ethylbenzene by [Ru(VI)(por)O(2)] increase with E(p,c)(Ru(VI/V)), and there is a linear correlation between log k(2) and E(p,c)(Ru(VI/V)). The small slope (approximately 2 V(-1)) of the log k(2) versus E(p,c)(Ru(VI/V)) plot suggests that the extent of charge transfer is small in the rate-determining step of the hydrocarbon oxidations. The rate constants correlate well with the C-H bond dissociation energies, in favor of a hydrogen-atom abstraction mechanism.

Definition of compartment-based radical surgery in uterine cancer: modified radical hysterectomy in intermediate/high-risk endometrial cancer using peritoneal mesometrial resection (PMMR) by M Höckel translated to robotic surgery.

PubMed

Kimmig, Rainer; Aktas, Bahriye; Buderath, Paul; Wimberger, Pauline; Iannaccone, Antonella; Heubner, Martin

2013-08-16

The technique of compartment-based radical hysterectomy was originally described by M Höckel as total mesometrial resection (TMMR) for standard treatment of stage I and II cervical cancer. However, with regard to the ontogenetically-defined compartments of tumor development (Müllerian) and lymph drainage (Müllerian and mesonephric), compartments at risk may also be defined consistently in endometrial cancer. This is the first report in the literature on the compartment-based surgical approach to endometrial cancer. Peritoneal mesometrial resection (PMMR) with therapeutic lymphadenectomy (tLNE) as an ontogenetic, compartment-based oncologic surgery could be beneficial for patients in terms of surgical radicalness as well as complication rates; it can be standardized for compartment-confined tumors. Supported by M Höckel, PMMR was translated to robotic surgery (rPMMR) and described step-by-step in comparison to robotic TMMR (rTMMR). Patients (n = 42) were treated by rPMMR (n = 39) or extrafascial simple hysterectomy (n = 3) with/without bilateral pelvic and/or periaortic robotic therapeutic lymphadenectomy (rtLNE) for stage I to III endometrial cancer, according to International Federation of Gynecology and Obstetrics (FIGO) classification. Tumors were classified as intermediate/high-risk in 22 out of 40 patients (55%) and low-risk in 18 out of 40 patients (45%), and two patients showed other uterine malignancies. In 11 patients, no adjuvant external radiotherapy was performed, but chemotherapy was applied. No transition to open surgery was necessary. There were no intraoperative complications. The postoperative complication rate was 12% with venous thromboses, (n = 2), infected pelvic lymph cyst (n = 1), transient aphasia (n = 1) and transient dysfunction of micturition (n = 1). The mean difference in perioperative hemoglobin concentrations was 2.4 g/dL (± 1.2 g/dL) and one patient (2.4%) required transfusion. During follow-up (median 17 months), one patient experienced distant recurrence and one patient distant/regional recurrence of endometrial cancer (4.8%), but none developed isolated locoregional recurrence. There were two deaths from endometrial cancer during the observation period (4.8%). We conclude that rPMMR and rtLNE are feasible and safe with regard to perioperative morbidity, thus, it seems promising for the treatment of intermediate/high-risk endometrial cancer in terms of surgical radicalness and complication rates. This could be particularly beneficial for morbidly obese and seriously ill patients.

Hypochlorite and superoxide radicals can act synergistically to induce fragmentation of hyaluronan and chondroitin sulphates

PubMed Central

2004-01-01

Activated phagocytes release the haem enzyme MPO (myeloperoxidase) and also generate superoxide radicals (O2•−), and hence H2O2, via an oxidative burst. Reaction of MPO with H2O2 in the presence of chloride ions generates HOCl (the physiological mixture of hypochlorous acid and its anion present at pH 7.4). Exposure of glycosaminoglycans to a MPO–H2O2–Cl− system or reagent HOCl generates long-lived chloramides [R-NCl-C(O)-R′] derived from the glycosamine N-acetyl functions. Decomposition of these species by transition metal ions gives polymer-derived amidyl (nitrogen-centred) radicals [R-N•-C(O)-R′], polymer-derived carbon-centred radicals and site-specific strand scission. In the present study, we have shown that exposure of glycosaminoglycan chloramides to O2•− also promotes chloramide decomposition and glycosaminoglycan fragmentation. These processes are inhibited by superoxide dismutase, metal ion chelators and the metal ion-binding protein BSA, consistent with chloramide decomposition and polymer fragmentation occurring via O2•−-dependent one-electron reduction, possibly catalysed by trace metal ions. Polymer fragmentation induced by O2•− [generated by the superoxide thermal source 1, di-(4-carboxybenzyl)hyponitrite] was demonstrated to be entirely chloramide dependent as no fragmentation occurred with the native polymers or when the chloramides were quenched by prior treatment with methionine. EPR spin-trapping experiments using 5,5-dimethyl1-pyrroline-N-oxide and 2-methyl-2-nitrosopropane have provided evidence for both O2•− and polymer-derived carbon-centred radicals as intermediates. The results obtained are consistent with a mechanism involving one-electron reduction of the chloramides to yield polymer-derived amidyl radicals, which subsequently undergo intramolecular hydrogen atom abstraction reactions to give carbon-centred radicals. The latter undergo fragmentation reactions in a site-specific manner. This synergistic damage to glycosaminoglycans induced by HOCl and O2•− may be of significance at sites of inflammation where both oxidants are generated concurrently. PMID:15078224

Synthesis of ketones from biomass-derived feedstock.

PubMed

Meng, Qinglei; Hou, Minqiang; Liu, Huizhen; Song, Jinliang; Han, Buxing

2017-01-31

Cyclohexanone and its derivatives are very important chemicals, which are currently produced mainly by oxidation of cyclohexane or alkylcyclohexane, hydrogenation of phenols, and alkylation of cyclohexanone. Here we report that bromide salt-modified Pd/C in H 2 O/CH 2 Cl 2 can efficiently catalyse the transformation of aromatic ethers, which can be derived from biomass, to cyclohexanone and its derivatives via hydrogenation and hydrolysis processes. The yield of cyclohexanone from anisole can reach 96%, and the yields of cyclohexanone derivatives produced from the aromatic ethers, which can be extracted from plants or derived from lignin, are also satisfactory. Detailed study shows that the Pd, bromide salt and H 2 O/CH 2 Cl 2 work cooperatively to promote the desired reaction and inhibit the side reaction. Thus high yields of desired products can be obtained. This work opens the way for production of ketones from aromatic ethers that can be derived from biomass.

Radical production from the interaction of ozone and PUFA as demonstrated by electron spin resonance spin-trapping techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pryor, W.A.; Prier, D.G.; Church, D.F.

1981-02-01

There is considerable evidence that indicates that a fraction of the damage caused by ozone to cellular systems involves radical-mediated reactions. The most direct method for probing the mechanism by which ozone reacts with target molecules such as polyunsaturated fatty acids involves the use of electron spin resonance. In 1968, Goldstein et al. reported that ESR signals were observed when 40 ppM ozone in air is bubbled through linoleic acid. We have repeated this experiment and have performed several experiments modified from this design; in none of these do we observe ESR signals. We have studied the reaction of ozonemore » with PUFA at -78/sup 0/C using spin traps. Spin traps themselves react with ozone, but the following protocol avoids that reaction. (1) Ozone in air or oxygen-free ozone is allowed to bubble through the sample in Freon-11 in an ESR tube at -78/sup 0/C; no ESR absorption is observed. (2) Unreacted ozone is flushed out with argon or nitrogen. (3) The spin trap in Freon-11 is added to give a 0.1 M solution, still at -78/sup 0/C; no ESR signal is observed. (4) The tube is allowed to warm slowly. At about -45/sup 0/C, the ESR spectra of spin adducts appear. Using this method with methyl linoleate we observe spin adducts of alkoxy radicals and also a signal that is consistent with a carbon radical with one ..cap alpha..-H. We hypothesize that an intermediate is formed from the reaction of ozone with PUFA that is stable at -78/sup 0/Cbut decomposes to form radicals at about -45/sup 0/C. We tentatively identify the intermediate as a trioxide on the basis of analogies and its temperature profile for decomposition to radicals. It appears reasonable to suggest that the reaction(s) responsible for the production of radicals under these low-temperature conditions also occurs at room temperature. Although the low-temperature intermediate cannot be observed at ambient temperatures, radicals from it could be responsible for the effects on autoxidation that are induced by ozone.« less

[Mechanism and performance of styrene oxidation by O3/H2O2].

PubMed

He, Jue-Cong; Huang, Qian-Ru; Ye, Qi-Hong; Luo, Yu-Wei; Zhang, Zai-Li; Fan, Qing-Juan; Wei, Zai-Shan

2013-10-01

It can produce a large number of free radicals in O3/H2O2, system, ozone and free radical coupling oxidation can improve the styrene removal efficiency. Styrene oxidation by O3/H2O2 was investigated. Ozone dosage, residence time, H2o2 volume fraction, spray density and molar ratio of O3/C8H8 on styrene removal were evaluated. The experimental results showed that styrene removal efficiency achieved 85.7%. The optimal residence time, H2O2, volume fraction, spray density and O3/C8H8 molar ratio were 20. 6 s, 10% , 1.72 m3.(m2.h)-1 and 0.46, respectively. The gas-phase degradation intermediate products were benzaldehyde(C6H5CHO) and benzoic acid (C6H5 COOH) , which were identified by means of gas chromatography-mass spectrometry(GC-MS). The degradation mechanism of styrene is presented.

Electrochemical mineralization pathway of quinoline by boron-doped diamond anodes.

PubMed

Wang, Chunrong; Ma, Keke; Wu, Tingting; Ye, Min; Tan, Peng; Yan, Kecheng

2016-04-01

Boron-doped diamond anodes were selected for quinoline mineralization, and the resulting intermediates, phenylpropyl aldehyde, phenylpropionic acid, and nonanal were identified and followed during quinoline oxidation by gas chromatography-mass spectrometry and high-performance liquid chromatography. The evolutions of formic acid, acetic acid, oxalic acid, NO2(-), NO3(-), and NH4(+) were quantified. A new reaction pathway for quinoline mineralization by boron-doped diamond anodes has been proposed, where the pyridine ring in quinoline is cleaved by a hydroxyl radical giving phenylpropyl aldehyde and NH4(+). Phenylpropyl aldehyde is quickly oxidized into phenylpropionic acid, and the benzene ring is cleaved giving nonanal. This is further oxidized to formic acid, acetic acid, and oxalic acid. Finally, these organic intermediates are mineralized to CO2 and H2O. NH4(+) is also oxidized to NO2(-) and on to NO3(-). The results will help to gain basic reference for clearing intermediates and their toxicity. Copyright © 2016 Elsevier Ltd. All rights reserved.

Chemical instability of graphene oxide following exposure to highly reactive radicals in advanced oxidation processes.

PubMed

Wang, Zhaohui; Sun, Linyan; Lou, Xiaoyi; Yang, Fei; Feng, Min; Liu, Jianshe

2017-12-01

The rapidly increasing and widespread use of graphene oxide (GO) as catalyst supports, requires further understanding of its chemical stability in advanced oxidation processes (AOPs). In this study, UV/H 2 O 2 and UV/persulfate (UV/PS) processes were selected to test the chemical instability of GO in terms of their performance in producing highly reactive hydroxyl radicals (OH) and sulfate radicals (SO 4 - ), respectively. The degradation intermediates were characterized using UV-visible absorption spectra (UV-vis), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Experimental data indicate that UV/PS process was more effective in enhancing GO degradation than the UV/H 2 O 2 system. The overall oxygen-containing functionalities (e.g. CO, CO and OCO groups) dramatically declined. After radical attack, sheet-like GO was destructed into lots of flakes and some low-molecular-weight molecules were detected. The results suggest GO is most vulnerable against SO 4 - radical attack, which deserves special attention while GO acts as a catalyst support or even as a catalyst itself. Therefore, stability of GO and its derivatives should be carefully assessed before they are applied to SO 4 - -based AOPs. Copyright © 2017 Elsevier Inc. All rights reserved.

Polynuclear complexes of copper(I) halides: coordination chemistry and catalytic transformations of alkynes

NASA Astrophysics Data System (ADS)

Mykhalichko, B. M.; Temkin, Oleg N.; Mys'kiv, M. G.

2000-11-01

Characteristic features of the coordination chemistry of Cu(I) and mechanisms of catalytic conversions of alkynes in the CuCl-MCl-H2O-HC≡CR system (MCl is alkali metal or ammonium chloride or amine hydrochloride; R=H, CH2OH, CH=CH2, etc.) are analysed based on studies of the compositions and structures of copper(I) chloride (bromide) complexes, alkyne π-complexes and ethynyl organometallic polynuclear compounds formed in this system in solutions and in the crystalline state. The role of polynuclear complexes in various reactions of alkynes is discussed. The bibliography includes 149 references.

The human Krebs cycle 2-oxoglutarate dehydrogenase complex creates an additional source of superoxide/hydrogen peroxide from 2-oxoadipate as alternative substrate.

PubMed

Nemeria, Natalia S; Gerfen, Gary; Guevara, Elena; Nareddy, Pradeep Reddy; Szostak, Michal; Jordan, Frank

2017-07-01

Recently, we reported that the human 2-oxoglutarate dehydrogenase (hE1o) component of the 2-oxoglutarate dehydrogenase complex (OGDHc) could produce the reactive oxygen species superoxide and hydrogen peroxide (detected by chemical means) from its substrate 2-oxoglutarate (OG), most likely concurrently with one-electron oxidation by dioxygen of the thiamin diphosphate (ThDP)-derived enamine intermediate to a C2α-centered radical (detected by Electron Paramagnetic Resonance) [Nemeria et al., 2014 [17]; Ambrus et al. 2015 [18

Gas-Phase Formation Rates of Nitric Acid and Its Isomers Under Urban Conditions

NASA Technical Reports Server (NTRS)

Okumura, M.; Mollner, A. K.; Fry, J. L.; Feng, L.

2005-01-01

Ozone formation in urban smog is controlled by a complex set of reactions which includes radical production from photochemical processes, catalytic cycles which convert NO to NO2, and termination steps that tie up reactive intermediates in long-lived reservoirs. The reaction OH + NO2 + M -4 HONO2 + M (la) is a key termination step because it transforms two short-lived reactive intermediates, OH and NO2, into relatively long-lived nitric acid. Under certain conditions (low VOC/NOx), ozone production in polluted urban airsheds can be highly sensitive to this reaction, but the rate parameters are not well constrained. This report summarizes the results of new laboratory studies of the OH + NO2 + M reaction including direct determination of the overall rate constant and branching ratio for the two reaction channels under atmospherically relevant conditions.

Controlling Stereoselectivity and Chemoselectivity of Cyclopropyl Ketyl Radical Anions with Visible Light Photocatalysis

NASA Astrophysics Data System (ADS)

Amador, Adrian Gabriel

A defining characteristic of research in the Yoon laboratory is a focus on the formation and utilization of high-energy reactive intermediates to accomplish difficult transformations. Recent efforts have been aimed at controlling the reactivity of open-shell radical intermediates; both in terms of chemoselectivity and stereoselectivity. Transition metal photocatalysis has proven to be a particularly successful strategy for accomplishing a wide variety of transformations ranging from net redox neutral as well as net reductive and oxidative transformations. This thesis describes one such approach where the combination of a photocatalyst and a Lewis acid can be used to achieve highly selective and high yielding [3 + 2] cycloadditions between aryl cyclopropyl ketones and a wide range of unsaturated (e.g. olefin and imine) coupling partners. Key to the success of these studies was understanding and carefully optimizing both photocatalyst and Lewis acid to achieve the desired reactivity. These studies have resulted in the development of a highly enantioselective [3 + 2] cycloaddition between cyclopropyl ketones and olefins for the synthesis of cyclopentanes as well as the development of a more general redox-auxiliary approach for the [3 + 2] cycloaddition of cyclopropyl ketones and simple olefins and imine derivatives.

Abatement of trichloroethylene using DBD plasma

NASA Astrophysics Data System (ADS)

Vesali-Naseh, M.; Xu, S.; Xu, L.; Khodadadi, A.; Mortazavi, Y.; Ostrikov, K.

2014-08-01

Dielectric barrier discharge plasma was used to oxidize trichloroethylene (TCE) in 21% of O2 in carriers of N2 and He. The degradation products of TCE were analyzed using gas chromatography mass spectrometry. TCE was decomposed completely at optimum energy density of 260 and 300 J/l for He and N2, respectively and its conversion followed zero order reaction. The TCE removal efficiency is decreased in humid air due to interception of reactive intermediates by OH radicals.

Elucidating reactivity regimes in cyclopentane oxidation: Jet stirred reactor experiments, computational chemistry, and kinetic modeling

DOE PAGES

Al Rashidi, Mariam J.; Thion, Sebastien; Togbe, Casimir; ...

2016-06-22

This study is concerned with the identification and quantification of species generated during the combustion of cyclopentane in a jet stirred reactor (JSR). Experiments were carried out for temperatures between 740 and 1250 K, equivalence ratios from 0.5 to 3.0, and at an operating pressure of 10 atm. The fuel concentration was kept at 0.1% and the residence time of the fuel/O 2/N 2 mixture was maintained at 0.7 s. The reactant, product, and intermediate species concentration profiles were measured using gas chromatography and Fourier transform infrared spectroscopy. The concentration profiles of cyclopentane indicate inhibition of reactivity between 850-1000 Kmore » for φ=2.0 and φ=3.0. This behavior is interesting, as it has not been observed previously for other fuel molecules, cyclic or non-cyclic. A kinetic model including both low- and high-temperature reaction pathways was developed and used to simulate the JSR experiments. The pressure-dependent rate coefficients of all relevant reactions lying on the PES of cyclopentyl + O 2, as well as the C-C and C-H scission reactions of the cyclopentyl radical were calculated at the UCCSD(T)-F12b/cc-pVTZ-F12//M06-2X/6-311++G(d,p) level of theory. The simulations reproduced the unique reactivity trend of cyclopentane and the measured concentration profiles of intermediate and product species. Furthermore, sensitivity and reaction path analyses indicate that this reactivity trend may be attributed to differences in the reactivity of allyl radical at different conditions, and it is highly sensitive to the C-C/C-H scission branching ratio of the cyclopentyl radical decomposition.« less

Pyrimidine Nucleobase Radical Reactivity in DNA and RNA.

PubMed

Greenberg, Marc M

2016-11-01

Nucleobase radicals are major products of the reactions between nucleic acids and hydroxyl radical, which is produced via the indirect effect of ionizing radiation. The nucleobase radicals also result from hydration of cation radicals that are produced via the direct effect of ionizing radiation. The role that nucleobase radicals play in strand scission has been investigated indirectly using ionizing radiation to generate them. More recently, the reactivity of nucleobase radicals resulting from formal hydrogen atom or hydroxyl radical addition to pyrimidines has been studied by independently generating the reactive intermediates via UV-photolysis of synthetic precursors. This approach has provided control over where the reactive intermediates are produced within biopolymers and facilitated studying their reactivity. The contributions to our understanding of pyrimidine nucleobase radical reactivity by this approach are summarized.

Pyrimidine nucleobase radical reactivity in DNA and RNA

NASA Astrophysics Data System (ADS)

Greenberg, Marc M.

2016-11-01

Nucleobase radicals are major products of the reactions between nucleic acids and hydroxyl radical, which is produced via the indirect effect of ionizing radiation. The nucleobase radicals also result from hydration of cation radicals that are produced via the direct effect of ionizing radiation. The role that nucleobase radicals play in strand scission has been investigated indirectly using ionizing radiation to generate them. More recently, the reactivity of nucleobase radicals resulting from formal hydrogen atom or hydroxyl radical addition to pyrimidines has been studied by independently generating the reactive intermediates via UV-photolysis of synthetic precursors. This approach has provided control over where the reactive intermediates are produced within biopolymers and facilitated studying their reactivity. The contributions to our understanding of pyrimidine nucleobase radical reactivity by this approach are summarized.

The OH-Initiated Oxidation of CS2 in the Presence of NO: FTIR Matrix-Isolation and Theoretical Studies.

PubMed

Bil, A; Grzechnik, K; Sałdyka, M; Mielke, Z

2016-09-01

We studied the photochemistry of the carbon disulfide-nitrous acid system with the help of Fourier transform infrared (FTIR) matrix isolation spectroscopy and theoretical methods. The irradiation of the CS2···HONO complexes, isolated in solid argon, with the filtered output of the mercury lamp (λ > 345 nm) was found to produce OCS, SO2, and HNCS; HSCN was also tentatively identified. The (13)C, (15)N, and (2)H isotopic shifts as well as literature data were used for product identifications. The evolution of the measured FTIR spectra with irradiation time and the changes in the spectra after matrix annealing indicated that the identified molecules are the products of different reaction channels: OCS being a product of another reaction path than SO2 and HNCS or HSCN. The possible reaction channels between SC(OH)S/SCS(OH) radicals and NO were studied using DFT/B3LYP/aug-cc-pVTZ method. The SC(OH)S and/or SCS(OH) intermediates are formed when HONO attached to CS2 photodissociates into OH and NO. The calculations indicated that SC(OH)S radical can form with NO two stable adducts. The more stable SC(OH)S···NO structure is a reactant for a simple one-step process leading to OCS and HONS molecules. An alternative, less-stable complex formed between SC(OH)S and NO leads to formation of OCS and HSNO. The calculations predict only one stable complex between SCS(OH) radical and NO, which can dissociate along two channels leading to HNCS and SO2 or HSCN and SO2 as the end products. The identified photoproducts indicate that both SC(OH)S and SCS(OH) adducts are intermediates in the CS2 + OH + NO reaction leading to different reaction products.

Sulfate radical degradation of acetaminophen by novel iron-copper bimetallic oxidation catalyzed by persulfate: Mechanism and degradation pathways

NASA Astrophysics Data System (ADS)

Zhang, Yuanchun; Zhang, Qian; Hong, Junming

2017-11-01

A novel iron coupled copper oxidate (Fe2O3@Cu2O) catalyst was synthesized to activate persulfate (PS) for acetaminophen (APAP) degradation. The catalysts were characterized via field-emission scanning electron microscopy and energy-dispersive X-ray spectrometry. The effects of the catalyst, PS concentration, catalyst dosage, initial pH, dissolved oxygen were analyzed for treatment optimization. Results indicated that Fe2O3@Cu2O achieved higher efficiency in APAP degradation than Fe2O3/PS and Cu2O/PS systems. The optimal removal efficiency of APAP (90%) was achieved within 40 min with 0.6 g/L PS and 0.3 g/L catalyst. To clarify the mechanism for APAP degradation, intermediates were analyzed with gas chromatography-mass spectrometry. Three possible degradation pathways were identified. During reaction, Cu(I) was found to react with Fe(III) to generate Fe(II), which is the most active phase for PS activation. Through the use of methanol and tert-butyl alcohol (TBA) as radical trappers, SO4rad - was identified as the main radical species that is generated during oxidation.

Pathological and 3 Tesla Volumetric Magnetic Resonance Imaging Predictors of Biochemical Recurrence after Robotic Assisted Radical Prostatectomy: Correlation with Whole Mount Histopathology.

PubMed

Tan, Nelly; Shen, Luyao; Khoshnoodi, Pooria; Alcalá, Héctor E; Yu, Weixia; Hsu, William; Reiter, Robert E; Lu, David Y; Raman, Steven S

2018-05-01

We sought to identify the clinical and magnetic resonance imaging variables predictive of biochemical recurrence after robotic assisted radical prostatectomy in patients who underwent multiparametric 3 Tesla prostate magnetic resonance imaging. We performed an institutional review board approved, HIPAA (Health Insurance Portability and Accountability Act) compliant, single arm observational study of 3 Tesla multiparametric magnetic resonance imaging prior to robotic assisted radical prostatectomy from December 2009 to March 2016. Clinical, magnetic resonance imaging and pathological information, and clinical outcomes were compiled. Biochemical recurrence was defined as prostate specific antigen 0.2 ng/cc or greater. Univariate and multivariate regression analysis was performed. Biochemical recurrence had developed in 62 of the 255 men (24.3%) included in the study at a median followup of 23.5 months. Compared to the subcohort without biochemical recurrence the subcohort with biochemical recurrence had a greater proportion of patients with a high grade biopsy Gleason score, higher preoperative prostate specific antigen (7.4 vs 5.6 ng/ml), intermediate and high D'Amico classifications, larger tumor volume on magnetic resonance imaging (0.66 vs 0.30 ml), higher PI-RADS® (Prostate Imaging-Reporting and Data System) version 2 category lesions, a greater proportion of intermediate and high grade radical prostatectomy Gleason score lesions, higher pathological T3 stage (all p <0.01) and a higher positive surgical margin rate (19.3% vs 7.8%, p = 0.016). On multivariable analysis only tumor volume on magnetic resonance imaging (adjusted OR 1.57, p = 0.016), pathological T stage (adjusted OR 2.26, p = 0.02), positive surgical margin (adjusted OR 5.0, p = 0.004) and radical prostatectomy Gleason score (adjusted OR 2.29, p = 0.004) predicted biochemical recurrence. In this cohort tumor volume on magnetic resonance imaging and pathological variables, including Gleason score, staging and positive surgical margins, significantly predicted biochemical recurrence. This suggests an important new imaging biomarker. Copyright © 2018 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

Structural requirements and reaction pathways in dimethyl ether combustion catalyzed by supported Pt clusters.

PubMed

Ishikawa, Akio; Neurock, Matthew; Iglesia, Enrique

2007-10-31

The identity and reversibility of the elementary steps required for catalytic combustion of dimethyl ether (DME) on Pt clusters were determined by combining isotopic and kinetic analyses with density functional theory estimates of reaction energies and activation barriers to probe the lowest energy paths. Reaction rates are limited by C-H bond activation in DME molecules adsorbed on surfaces of Pt clusters containing chemisorbed oxygen atoms at near-saturation coverages. Reaction energies and activation barriers for C-H bond activation in DME to form methoxymethyl and hydroxyl surface intermediates show that this step is more favorable than the activation of C-O bonds to form two methoxides, consistent with measured rates and kinetic isotope effects. This kinetic preference is driven by the greater stability of the CH3OCH2* and OH* intermediates relative to chemisorbed methoxides. Experimental activation barriers on Pt clusters agree with density functional theory (DFT)-derived barriers on oxygen-covered Pt(111). Measured DME turnover rates increased with increasing DME pressure, but decreased as the O2 pressure increased, because vacancies (*) on Pt surfaces nearly saturated with chemisorbed oxygen are required for DME chemisorption. DFT calculations show that although these surface vacancies are required, higher oxygen coverages lead to lower C-H activation barriers, because the basicity of oxygen adatoms increases with coverage and they become more effective in hydrogen abstraction from DME. Water inhibits reaction rates via quasi-equilibrated adsorption on vacancy sites, consistent with DFT results indicating that water binds more strongly than DME on vacancies. These conclusions are consistent with the measured kinetic response of combustion rates to DME, O2, and H2O, with H/D kinetic isotope effects, and with the absence of isotopic scrambling in reactants containing isotopic mixtures of 18O2-16O2 or 12CH3O12CH3-13CH3O13CH3. Turnover rates increased with Pt cluster size, because small clusters, with more coordinatively unsaturated surface atoms, bind oxygen atoms more strongly than larger clusters and exhibit lower steady-state vacancy concentrations and a consequently smaller number of adsorbed DME intermediates involved in kinetically relevant steps. These effects of cluster size and metal-oxygen bond energies on reactivity are ubiquitous in oxidation reactions requiring vacancies on surfaces nearly saturated with intermediates derived from O2.

Synthesis of Improved Antileishmanial and Antitrypanosomal Drugs Treatment and Prophylaxis

DTIC Science & Technology

1986-11-01

for a diphenyl ether analog ((2) p. 44). 16 - -r , ü$$m&±ysc$c .<v£*^Ä VV’-Orfs aB9*>ratfe>^v CHART NO. 1 8-[(6-AMIDOXIMINOHEXYL)AMINO]-6-METHOXY...MALEATE (SNL-130) cico—(f)V-ci A1C1 CS 1 (58%) • Brü 1) »3PCH2CH2NMe2/n-BuLi 2) H30* 3) Oxalic Acid 4) OH 0 «CHCH,NMe 2ŕ,c2 2 (79%), Free base... diphenyl ether analog ((2) p. 44). A mixture of sodium amide (11.6 g, O.J mol), acetonitrile (15 mL, 11.8 g> 0.29 mol) and dry benzene (1 L) was heated

Synthesis of truncated analogues of the iNKT cell agonist, α-galactosyl ceramide (KRN7000), and their biological evaluation

PubMed Central

Veerapen, Natacha; Reddington, Faye; Salio, Mariolina; Cerundolo, Vincenzo; Besra, Gurdyal S.

2011-01-01

Stimulation of iNKT cells by α-galactosyl ceramide (α-GalCer), also known as KRN7000, and its truncated analogue OCH induces both Th1- and Th2-cytokines, with OCH inducing a Th2-cytokine bias. Skewing of the iNKT cells’ response towards either a Th1- or Th2-cytokine profile offers potential therapeutic benefits. The length of both the acyl and the sphingosine chains in α-galactosyl ceramides is known to influence the cytokine release profile. We have synthesized analogues of α-GalCer with truncated sphingosine chains for biological evaluation, with particular emphasis on the Th1/Th2 distribution. Starting from a common precursor, d-lyxose, the sphingosine derivatives were synthesised via a straightforward Wittig condensation. PMID:21145749

Reaction mechanisms of DNT with hydroxyl radicals for advanced oxidation processes-a DFT study.

PubMed

Zhou, Yang; Yang, Zhilin; Yang, Hong; Zhang, Chaoyang; Liu, Xiaoqiang

2017-04-01

In advanced oxidation processes (AOPs), the detailed degradation mechanisms of a typical explosive of 2,4-dinitrotoluene (DNT) can be investigated by the density function theory (DFT) method at the SMD/M062X/6-311+G(d) level. Several possible degradation routes for DNT were explored in the current study. The results show that, for oxidation of the methyl group, the dominant degradation mechanism of DNT by hydroxyl radicals (•OH) is a series of sequential H-abstraction reactions, and the intermediates obtained are in good agreement with experimental findings. The highest activation energy barrier is less than 20 kcal mol -1 . Other routes are dominated by an addition-elimination mechanism, which is also found in 2,4,6-trinitrotoluene, although the experiment did not find the corresponding products. In addition, we also eliminate several impossible mechanisms, such as dehydration, HNO 3 elimination, the simultaneous addition of two •OH radials, and so on. The information gained about these degradation pathways is helpful in elucidating the detailed reaction mechanism between nitroaromatic explosives and hydroxyl radicals for AOPs. Graphical Abstract The degradation mechanism of an important explosive, 2,6-dinitrotoluene (DNT), by the hydroxyl radical for advanced oxidation progresses.

Radical-Mediated Enzymatic Carbon Chain Fragmentation-Recombination

PubMed Central

Zhang, Qi; Li, Yuxue; Chen, Dandan; Yu, Yi; Duan, Lian; Shen, Ben; Liu, Wen

2010-01-01

The radical S-adenosylmethionine (S-AdoMet) superfamily contains thousands of proteins that catalyze highly diverse conversions, most of which are poorly understood due to a lack of information regarding chemical products and radical-dependent transformations. We here report that NosL, involved in forming the indole side ring of the thiopeptide nosiheptide (NOS), is a radical S-AdoMet 3-methyl-2-indolic acid (MIA) synthase. NosL catalyzed an unprecedented carbon chain reconstitution of L-Trp to give MIA, showing removal of the Cα-N unit and shift of the carboxylate to the indole ring. Dissection of the enzymatic process upon the identification of products and a putative glycyl intermediate uncovered a radical-mediated, unusual fragmentation-recombination reaction. This finding unveiled a key step in radical S-AdoMet enzyme-catalyzed structural rearrangements during complex biotransformations. Additionally, NosL tolerated fluorinated L-Trps as the substrates, allowing for production of a regiospecifically halogenated thiopeptide that has not been found in over 80 entity-containing, naturally occurring thiopeptide family. PMID:21240261

Searching for trans ethyl methyl ether in Orion KL★,★★

PubMed Central

Tercero, B.; Cernicharo, J.; López, A.; Brouillet, N.; Kolesniková, L.; Motiyenko, R. A.; Margulès, L.; Alonso, J. L.; Guillemin, J.-C.

2015-01-01

We report on the tentative detection of trans ethyl methyl ether (tEME), t-CH3CH2OCH3, through the identification of a large number of rotational lines from each one of the spin states of the molecule towards Orion KL. We also search for gauche-trans-n-propanol, Gt-n-CH3CH2CH2OH, an isomer of tEME in the same source. We have identified lines of both species in the IRAM 30 m line survey and in the ALMA Science Verification data. We have obtained ALMA maps to establish the spatial distribution of these species. Whereas tEME mainly arises from the compact ridge component of Orion, Gt-n-propanol appears at the emission peak of ethanol (south hot core). The derived column densities of these species at the location of their emission peaks are ≤(4.0 ± 0.8) × 1015 cm−2 and ≤(1.0 ± 0.2)× 1015 cm−2 for tEME and Gt-n-propanol, respectively. The rotational temperature is ~100 K for both molecules. We also provide maps of CH3OCOH, CH3CH2OCOH, CH3OCH3, CH3OH, and CH3CH2OH to compare the distribution of these organic saturated O-bearing species containing methyl and ethyl groups in this region. Abundance ratios of related species and upper limits to the abundances of non-detected ethers are provided. We derive an abundance ratio N(CH3OCH3)/N(tEME) ≥ 150 in the compact ridge of Orion. PMID:26869726

Searching for trans ethyl methyl ether in Orion KL.

PubMed

Tercero, B; Cernicharo, J; López, A; Brouillet, N; Kolesniková, L; Motiyenko, R A; Margulès, L; Alonso, J L; Guillemin, J-C

2015-10-01

We report on the tentative detection of trans ethyl methyl ether (tEME), t-CH 3 CH 2 OCH 3 , through the identification of a large number of rotational lines from each one of the spin states of the molecule towards Orion KL. We also search for gauche-trans-n-propanol, Gt-n-CH 3 CH 2 CH 2 OH, an isomer of tEME in the same source. We have identified lines of both species in the IRAM 30 m line survey and in the ALMA Science Verification data. We have obtained ALMA maps to establish the spatial distribution of these species. Whereas tEME mainly arises from the compact ridge component of Orion, Gt-n-propanol appears at the emission peak of ethanol (south hot core). The derived column densities of these species at the location of their emission peaks are ≤(4.0 ± 0.8) × 10 15 cm -2 and ≤(1.0 ± 0.2)× 10 15 cm -2 for tEME and Gt-n-propanol, respectively. The rotational temperature is ~100 K for both molecules. We also provide maps of CH 3 OCOH, CH 3 CH 2 OCOH, CH 3 OCH 3 , CH 3 OH, and CH 3 CH 2 OH to compare the distribution of these organic saturated O-bearing species containing methyl and ethyl groups in this region. Abundance ratios of related species and upper limits to the abundances of non-detected ethers are provided. We derive an abundance ratio N (CH 3 OCH 3 )/ N (tEME) ≥ 150 in the compact ridge of Orion.

Inhibition of free radical-induced erythrocyte hemolysis by 2-O-substituted ascorbic acid derivatives.

PubMed

Takebayashi, Jun; Kaji, Hiroaki; Ichiyama, Kenji; Makino, Kazutaka; Gohda, Eiichi; Yamamoto, Itaru; Tai, Akihiro

2007-10-15

Inhibitory effects of 2-O-substituted ascorbic acid derivatives, ascorbic acid 2-glucoside (AA-2G), ascorbic acid 2-phosphate (AA-2P), and ascorbic acid 2-sulfate (AA-2S), on 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH)-induced oxidative hemolysis of sheep erythrocytes were studied and were compared with those of ascorbic acid (AA) and other antioxidants. The order of the inhibition efficiency was AA-2S> or =Trolox=uric acid> or =AA-2P> or =AA-2G=AA>glutathione. Although the reactivity of the AA derivatives against AAPH-derived peroxyl radical (ROO(*)) was much lower than that of AA, the derivatives exerted equal or more potent protective effects on AAPH-induced hemolysis and membrane protein oxidation. In addition, the AA derivatives were found to react per se with ROO(*), not via AA as an intermediate. These findings suggest that secondary reactions between the AA derivative radical and ROO(*) play a part in hemolysis inhibition. Delayed addition of the AA derivatives after AAPH-induced oxidation of erythrocytes had already proceeded showed weaker inhibition of hemolysis compared to that of AA. These results suggest that the AA derivatives per se act as biologically effective antioxidants under moderate oxidative stress and that AA-2G and AA-2P may be able to act under severe oxidative stress after enzymatic conversion to AA in vivo.

Mechanism insight of PFOA degradation by ZnO assisted-photocatalytic ozonation: Efficiency and intermediates.

PubMed

Wu, Dan; Li, Xukai; Tang, Yiming; Lu, Ping; Chen, Weirui; Xu, Xiaoting; Li, Laisheng

2017-08-01

Zinc oxide (ZnO) nanorods were prepared by a directly pyrolysis method and employed as catalyst for perfluorooctanoic acid (PFOA) degradation. Comparative experiments were conducted to discuss the catalytic activity and flexibility of ZnO. After ZnO addition, the best PFOA degradation efficiency (70.5%) was achieved by ZnO/UV/O 3 system, only 9.5% by sole ozonation and 18.2% by UV 254 light irradiation. PFOA degradation was sensitive with pH value and temperature. The better PFOA removal efficiency was achieved at acidic condition. A novel relationship was found among PFOA degradation efficiency with hydroxyl radicals and photo-generated holes. Hydroxyl radicals generated on the surfaces of ZnO nanorods played dominant roles in PFOA degradation. PFOA degradation was found to follow the photo-Kolbe reaction mechanism. C 2 -C 7 shorter-chain perfluorocarboxylic acids and fluoride ion were detected as main intermediates during PFOA degradation process. Based on the results, a proposal degradation pathway was raised. Copyright © 2017 Elsevier Ltd. All rights reserved.

On the cleavage of the peroxide O---O bond in methyl hydroperoxide and dimethyl peroxide upon protonation

NASA Astrophysics Data System (ADS)

Schalley, Christoph A.; Dieterle, Martin; Schröder, Detlef; Schwarz, Helmut; Uggerud, Einar

1997-04-01

The unimolecular decays of protonated methyl hydroperoxide and dimethyl peroxide have been studied by tandem mass spectrometric techniques in combination with isotopic labeling as well as computational methods. The potential-energy surfaces calculated at the BECKE3LYP/6-311++G** level of theory are in good agreement with the experimental findings. The decomposition of the protonated peroxides can be described by a general mechanistic scheme which involves rearrangement to proton-bridged complexes, i.e. [CH2O-H-OH2]+ and [CH2O-H-O(H)CH3]+, respectively. When formed unimolecularly via rearrangement of the protonated peroxides, these complexes are rovibrationally highly excited; consequently, their fragmentations are affected remarkably as compared to proton-bound complexes of lower internal energy which are independently generated from the corresponding alcohol and carbonyl compounds in a chemical ionization plasma. For methyl hydroperoxide, both oxygen atoms can be protonated, giving rise to two isomeric cations with rather similar heats of formation but entirely different fragmentation behaviors. Cleavage of the O---O bond in dimethyl peroxide upon protonation results in proton- as well as methyl-cation-bridged intermediates, e.g. [CH2O-H-O(H)CH3]+ and [CH2O-CH3-OH2]+.

Pulse radiolysis study of the reactions of catechins with nitrogen dioxide

NASA Astrophysics Data System (ADS)

Gebicki, Jerzy L.; Meisner, Piotr; Stawowska, Katarzyna; Gebicka, Lidia

2012-12-01

Nitrogen dioxide (•NO2), one of the oxidizing radicals formed in vivo is suspected to play a role in various pathophysiological processes. The reactions of •NO2 with dietary catechins, the group of flavonoids present in high amounts in green tea and red wine, have been investigated by pulse radiolysis method. The kinetics of the reaction of •NO2 with gallic acid have been also studied for comparison. The spectra of transient intermediates are presented. The rate constants of the reaction of •NO2 with catechin, epigallocatechin, epigallocatechin gallate and gallic acid determined by the competition method with 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) at pH 7.0 and room temperature have been found to be 0.9, 1.0, 2.3 and 0.5×108 M-1 s-1, respectively. The values for catechins are among the highest reported for the reactions of •NO2 with non-radical compounds.

Theoretical study of the gas-phase ozonolysis of beta-pinene (C10H16).

PubMed

Nguyen, T L; Peeters, J; Vereecken, L

2009-07-21

The O3-initiated oxidation of beta-pinene, a monoterpene emitted in forested areas, was theoretically characterized using DFT, CBS-QB3 and CASPT2 quantum chemical calculations combined with statistical kinetic RRKM/master equation analysis and transition state theory. The first-principles based rate coefficient of the initial 03 attack on the exocyclic double bond shows a slight positive temperature dependence, k(tot)T = 1.27 x 10(-22) x T2.64 x exp(-714 K/T) cm3 molecule(-1) s(-1) and is in close agreement with experiment. The resulting primary ozonides are found to give rise to two distinct, non-interconvertible conformers of the predominant Criegee intermediate (CI-1 and CI-2), with subsequent chemistries that are shown to be very different; this crucial aspect of beta-pinene ozonolysis was not taken into account in earlier studies. One of the conformers CI-2--carrying nearly half the total reaction flux--cannot undergo the usual "hydroperoxide channel", thus rationalizing why the OH yield from beta-pinene is barely half of that from alpha-pinene. The predicted first-generation product distribution for atmospheric conditions is consistent with the available experimental data on the overall products. Our final results predict 5% of nopinone formation, 28% OH radicals with 2-oxo-alkyl radical coproducts, 37% of stabilized Criegee intermediates (SCI), 17% lactones, 10% CO2 formed after an intersystem crossing, and 3% of a newly proposed biradical formed from prompt ring opening in the CI. In atmospheric conditions, additional OH production is expected from the stabilized CI-1 conformer via the thermal unimolecular "hydroperoxide channel", whereas the stabilized CI-2 can react with H2O and its dimer, to produce additional nopinone. The expected subsequent chemistries of the large coproduct radicals formed from reactions of the two CI are also addressed in extenso.

Kinetic and mechanistic aspects of hydroxyl radical‒mediated degradation of naproxen and reaction intermediates.

PubMed

Luo, Shuang; Gao, Lingwei; Wei, Zongsu; Spinney, Richard; Dionysiou, Dionysios D; Hu, Wei-Ping; Chai, Liyuan; Xiao, Ruiyang

2018-06-15

Hydroxyl radical ( • OH) based advanced oxidation technologies (AOTs) are effective for removing non‒steroidal anti-inflammatory drugs (NSAIDs) during water treatment. In this study, we systematically investigated the degradation kinetics of naproxen (NAP), a representative NSAID, with a combination of experimental and theoretical approaches. The second-order rate constant (k) of • OH oxidation of NAP was measured to be (4.32 ± 0.04) × 10 9  M -1  s -1 , which was in a reasonable agreement with transition state theory calculated k value (1.08 × 10 9  M -1  s -1 ) at SMD/M05-2X/6-311++G**//M05-2X/6-31+G** level of theory. The calculated result revealed that the dominant reaction intermediate is 2‒(5‒hydroxy‒6‒methoxynaphthalen‒2‒yl)propanoic acid (HMNPA) formed via radical adduct formation pathway, in which • OH addition onto the ortho site of the methoxy-substituted benzene ring is the most favorable pathway for the NAP oxidation. We further investigated the subsequent • OH oxidation of HMNPA via a kinetic modelling technique. The k value of the reaction of HMNPA and • OH was determined to be 2.22 × 10 9  M -1  s -1 , exhibiting a similar reactivity to the parent NAP. This is the first study on the kinetic and mechanistic aspects of NAP and its reaction intermediates. The current results are valuable in future study evaluating and extending the application of • OH based AOTs to degrade NAP and other NSAIDs of concern in water treatment plants. Copyright © 2018 Elsevier Ltd. All rights reserved.

Artifacts in measuring aerosol uptake kinetics: the roles of time, concentration and adsorption

NASA Astrophysics Data System (ADS)

Renbaum, L. H.; Smith, G. D.

2011-07-01

In laboratory studies of organic aerosol particles reacting with gas-phase oxidants, high concentrations of radicals are often used to study on the timescale of seconds reactions which may be occurring over days or weeks in the troposphere. Implicit in this approach is the assumption that radical concentration and time are interchangeable parameters, though this has not been established. Here, the kinetics of OH- and Cl-initiated oxidation reactions of model single-component liquid (squalane) and supercooled (brassidic acid and 2-octyldodecanoic acid) organic aerosols are studied by varying separately the radical concentration and the reaction time. Two separate flow tubes with residence times of 2 and 66 s are used, and [OH] and [Cl] are varied by adjusting either the laser photolysis fluence or the radical precursor concentration ([O3] or [Cl2], respectively) used to generate the radicals. It is found that the rates measured by varying the radical concentration and the reaction time are equal only if the precursor concentrations are the same in the two approaches. Further, the rates depend on the concentrations of the precursor species with a Langmuir-type functional form suggesting that O3 and Cl2 saturate the surface of the liquid particles. It is believed that the presence of O3 inhibits the rate of OH reaction, perhaps by reacting with OH radicals or by O3 or intermediate species blocking surface sites, while Cl2 enhances the rate of Cl reaction by participating in a radical chain mechanism. These results have important implications for laboratory experiments in which high concentrations of gas-phase oxidants are used to study atmospheric reactions over short timescales and may explain the variability in recent measurements of the reactive uptake of OH on squalane particles in reactor systems used in this and other laboratories.

Exploring mechanisms of a tropospheric archetype: CH{sub 3}O{sub 2} + NO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Launder, Andrew M.; Agarwal, Jay; Schaefer, Henry F., E-mail: ccq@uga.edu

Methylperoxy radical (CH{sub 3}O{sub 2}) and nitric oxide (NO) contribute to the propagation of photochemical smog in the troposphere via the production of methoxy radical (CH{sub 3}O) and nitrogen dioxide (NO{sub 2}). This reaction system also furnishes trace quantities of methyl nitrate (CH{sub 3}ONO{sub 2}), a sink for reactive NO{sub x} species. Here, the CH{sub 3}O{sub 2} + NO reaction is examined with highly reliable coupled-cluster methods. Specifically, equilibrium geometries for the reactants, products, intermediates, and transition states of the ground-state potential energy surface are characterized. Relative reaction enthalpies at 0 K (ΔH{sub 0K}) are reported; these values are comprisedmore » of electronic energies extrapolated to the complete basis set limit of CCSDT(Q) and zero-point vibrational energies computed at CCSD(T)/cc-pVTZ. A two-part mechanism involving CH{sub 3}O and NO{sub 2} production followed by radical recombination to CH{sub 3}ONO{sub 2} is determined to be the primary channel for formation of CH{sub 3}ONO{sub 2} under tropospheric conditions. Constrained optimizations of the reaction paths at CCSD(T)/cc-pVTZ suggest that the homolytic bond dissociations involved in this reaction path are barrierless.« less

Electrospray ionization tandem mass spectrometric study of protonated and alkali- cationized α/ε-hybrid peptides: differentiation of a pair of dipeptide positional isomers.

PubMed

Ramesh Babu, A; Raju, G; Purna Chander, C; Shoban Babu, B; Srinivas, R; Sharma, G V M

A new class of Boc-N-protected hybrid peptides derived from L- Ala and ε 6 -Caa (L-Ala = L-Alanine, Caa = C-linked carboamino acid derived from D-xylose) have been studied by positive ion electrospray ionization (ESI) ion-trap tandem mass spectrometry (MS/MS). MS n spectra of protonated and alkali-cationized hybrid peptides produce characteristic fragmentation involving the peptide backbone, the tert-butyloxycarbonyl (Boc) group, and the side chain. The dipeptide positional isomers are differentiated by the collision-induced dissociation (CID) of the protonated and alkali-cationized peptides. The CID of [M + H] + ion of Boc-NH-L-Ala-ε-Caa- OCH 3 (1) shows a prominent [M + H - C 4 H 8 ] + ion, which is totally absent for its positional isomer Boc-NH-ε-Caa-L-Ala-OCH 3 (6), which instead shows significant loss of t-butanol. The formation of the [M + Cat - C 4 H 8 ] + ion is totally absent and [M + Cat - Boc + H] + is prominent in the CID of the [M + Cat] + ion of Boc-NH-L-Ala-ε-Caa- OCH 3 (1), whereas the former is highly abundant and the latter is of low abundance for its positional isomer Boc-NH-ε-Caa-L-Ala-OCH 3 (6). It is observed that 'b' ions are abundant when oxazolone structures are formed through a five-membered cyclic transition state in tetra-, penta-, and hexapeptides and the cyclization process for larger 'b' ions led to an insignificant abundance. However, the significant 'b' ion is formed in ε,α-dipeptide, which may have a seven-membered substituted 2-oxoazepanium ion structure. The MS n spectra of [M + Cat - Boc + H] + ions of these peptides are found to be significantly different to those of [M + H - Boc + H] + ions. The CID spectra of [M + Cat - Boc + H] + ions of peptide acids containing L-Ala at the C-terminus show an abundant N-terminal rearrangement ion, [b n  + 17 + Cat] + , which is absent for the peptide acids containing ε-Caa at the C-terminus. Thus, the results of these hybrid peptides provide sequencing information, the structure of the cyclic intermediate involved in the formation of the rearrangement ion, and distinguish a pair of dipeptide positional isomers.

Quantum mechanics/molecular mechanics studies on the mechanism of action of cofactor pyridoxal 5'-phosphate in ornithine 4,5-aminomutase.

PubMed

Pang, Jiayun; Scrutton, Nigel S; Sutcliffe, Michael J

2014-09-01

A computational study was performed on the experimentally elusive cyclisation step in the cofactor pyridoxal 5'-phosphate (PLP)-dependent D-ornithine 4,5-aminomutase (OAM)-catalysed reaction. Calculations using both model systems and a combined quantum mechanics/molecular mechanics approach suggest that regulation of the cyclic radical intermediate is achieved through the synergy of the intrinsic catalytic power of cofactor PLP and the active site of the enzyme. The captodative effect of PLP is balanced by an enzyme active site that controls the deprotonation of both the pyridine nitrogen atom (N1) and the Schiff-base nitrogen atom (N2). Furthermore, electrostatic interactions between the terminal carboxylate and amino groups of the substrate and Arg297 and Glu81 impose substantial "strain" energy on the orientation of the cyclic intermediate to control its trajectory. In addition the "strain" energy, which appears to be sensitive to both the number of carbon atoms in the substrate/analogue and the position of the radical intermediates, may play a key role in controlling the transition of the enzyme from the closed to the open state. Our results provide new insights into several aspects of the radical mechanism in aminomutase catalysis and broaden our understanding of cofactor PLP-dependent reactions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

When Does Neoadjuvant Chemotherapy Really Avoid Radiotherapy? Clinical Predictors of Adjuvant Radiotherapy in Cervical Cancer.

PubMed

Papadia, Andrea; Bellati, Filippo; Bogani, Giorgio; Ditto, Antonino; Martinelli, Fabio; Lorusso, Domenica; Donfrancesco, Cristina; Gasparri, Maria Luisa; Raspagliesi, Francesco

2015-12-01

The aim of this study was to identify clinical variables that may predict the need for adjuvant radiotherapy after neoadjuvant chemotherapy (NACT) and radical surgery in locally advanced cervical cancer patients. A retrospective series of cervical cancer patients with International Federation of Gynecology and Obstetrics (FIGO) stages IB2-IIB treated with NACT followed by radical surgery was analyzed. Clinical predictors of persistence of intermediate- and/or high-risk factors at final pathological analysis were investigated. Statistical analysis was performed using univariate and multivariate analysis and using a model based on artificial intelligence known as artificial neuronal network (ANN) analysis. Overall, 101 patients were available for the analyses. Fifty-two (51 %) patients were considered at high risk secondary to parametrial, resection margin and/or lymph node involvement. When disease was confined to the cervix, four (4 %) patients were considered at intermediate risk. At univariate analysis, FIGO grade 3, stage IIB disease at diagnosis and the presence of enlarged nodes before NACT predicted the presence of intermediate- and/or high-risk factors at final pathological analysis. At multivariate analysis, only FIGO grade 3 and tumor diameter maintained statistical significance. The specificity of ANN models in evaluating predictive variables was slightly superior to conventional multivariable models. FIGO grade, stage, tumor diameter, and histology are associated with persistence of pathological intermediate- and/or high-risk factors after NACT and radical surgery. This information is useful in counseling patients at the time of treatment planning with regard to the probability of being subjected to pelvic radiotherapy after completion of the initially planned treatment.

Degradation of phenolic compounds with hydrogen peroxide catalyzed by enzyme from Serratia marcescens AB 90027.

PubMed

Yao, Ri-Sheng; Sun, Min; Wang, Chun-Ling; Deng, Sheng-Song

2006-09-01

In this paper, the degradation of phenolic compounds using hydrogen peroxide as oxidizer and the enzyme extract from Serratia marcescens AB 90027 as catalyst was reported. With such an enzyme/H2O2 combination treatment, a high chemical oxygen demand (COD) removal efficiency was achieved, e.g., degradation of hydroquinone exceeded 96%. From UV-visible and IR spectra, the degradation mechanisms were judged as a process of phenyl ring cleavage. HPLC analysis shows that in the degradation p-benzoquinone, maleic acid and oxalic acid were formed as intermediates and that they were ultimately converted to CO2 and H2O. With the enzyme/H2O2 treatment, vanillin, hydroquinone, catechol, o-aminophenol, p-aminophenol, phloroglucinol and p-hydroxybenzaldehyde were readily degraded, whereas the degradation of phenol, salicylic acid, resorcinol, p-cholorophenol and p-nitrophenol were limited. Their degradability was closely related to the properties and positions of their side chain groups. Electron-donating groups, such as -OH, -NH2 and -OCH3 enhanced the degradation, whereas electron-withdrawing groups, such as -NO2, -Cl and -COOH, had a negative effect on the degradation of these compounds in the presence of enzyme/H2O2. Compounds with -OH at ortho and para positions were more readily degraded than those with -OH at meta positions.

Polymerizable 2(2-hydroxynaphthyl)2H-benzotriazole compounds

DOEpatents

Gomez, P.M.; Neidlinger, H.H.

1991-07-16

Benzotriazole compounds having the formula: ##STR1## wherein R.sub.1 is H, Cl, or OCH.sub.3 ; R.sub.2 is a hydroxynaphthyl group; and R.sub.3 is a vinyl unsaturated polymerizable group. Homopolymers or copolymers thereof are effective as UV light stabilizers and absorbers.

Polymerizable 2(2-hydroxynaphthyl)2H-benzotriazole compounds

DOEpatents

Gomez, Peter M.; Neidlinger, Hermann H.

1991-01-01

Benzotriazole compounds having the formula: ##STR1## wherein R.sub.1 is H, Cl, or OCH.sub.3 ; R.sub.2 is a hydroxynaphthyl group; and R.sub.3 is a vinyl unsaturated polymerizable group. Homopolymers or copolymers thereof are effective as UV light stabilizers and absorbers.

Photosensitizing effects of nanometer TiO2 on chlorothalonil photodegradation in aqueous solution and on the surface of pepper.

PubMed

Tan, Yong Qiang; Xiong, Hai Xia; Shi, Tao Zhong; Hua, Ri Mao; Wu, Xiang Wei; Cao, Hai Qun; Li, Xue De; Tang, Jun

2013-05-29

The present study examined the effects of anatase nanometer TiO2 on photochemical degradation of chlorothalonil in aqueous solution and on the plant surface. Results showed that nanometer TiO2 exhibited a strong photosensitizing effect on the degradation of chlorothalonil both in aqueous solution and on the surface of green pepper. The photosensitization rate was the highest in the sunlight compared to illumination under high-pressure mercury and UV lamps. Use of distinct hydroxyl radical scavengers indicated that nanometer TiO2 acted by producing hydroxyl radicals with strong oxidizing capacity. Notably, nanometer TiO2 facilitated complete photodegradation of chlorothalonil with no detectable accumulation of the intermediate chlorothalonil-4-hydroxy. Nanometer TiO2 was also active on the surface of green pepper under natural sunlight both inside and outside of plastic greenhouse. These results together suggest that nanometer TiO2 can be used as a photosensitizer to accelerate degradation of the pesticides under greenhouse conditions.

Enhanced Synthesis of Alkyl Amino Acids in Miller's 1958 H2S Experiment

NASA Technical Reports Server (NTRS)

Parker, Eric T.; Cleaves, H. James; Callahan, Michael P.; Dworkin, James P.; Glavin, Daniel P.; Lazcano, Antonio; Bada, Jeffrey L.

2011-01-01

Stanley Miller's 1958 H2S-containing experiment, which included a simulated prebiotic atmosphere of methane (CH4), ammonia (NH3), carbon dioxide (CO2), and hydrogen sulfide (H2S) produced several alkyl amino acids, including the alpha-, beta-, and gamma-isomers of aminobutyric acid (ABA) in greater relative yields than had previously been reported from his spark discharge experiments. In the presence of H2S, aspariic and glutamic acids could yield alkyl amino acids via the formation of thioimide intermediates. Radical chemistry initiated by passing H2S through a spark discharge could have also enhanced alkyl amino acid synthesis by generating alkyl radicals that can help form the aldehyde and ketone precursors to these amino acids. We propose mechanisms that may have influenced the synthesis of certain amino acids in localized environments rich in H2S and lightning discharges, similar to conditions near volcanic systems on the early Earth, thus contributing to the prebiotic chemical inventory of the primordial Earth.

Perturbations in choline metabolism cause neural tube defects in mouse embryos in vitro.

PubMed

Fisher, Melanie C; Zeisel, Steven H; Mar, Mei-Heng; Sadler, Thomas W

2002-04-01

A role for choline during early stages of mammalian embryogenesis has not been established, although recent studies show that inhibitors of choline uptake and metabolism, 2-dimethylaminoethanol (DMAE), and 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3), produce neural tube defects in mouse embryos grown in vitro. To determine potential mechanisms responsible for these abnormalities, choline metabolism in the presence or absence of these inhibitors was evaluated in cultured, neurulating mouse embryos by using chromatographic techniques. Results showed that 90%-95% of 14C-choline was incorporated into phosphocholine and phosphatidylcholine (PtdCho), which was metabolized to sphingomyelin. Choline was oxidized to betaine, and betaine homocysteine methyltransferase was expressed. Acetylcholine was synthesized in yolk sacs, but 70 kDa choline acetyltransferase was undetectable by immunoblot. DMAE reduced embryonic choline uptake and inhibited phosphocholine, PtdCho, phosphatidylethanolamine (PtdEtn), and sphingomyelin synthesis. ET-18-OCH3 also inhibited PtdCho synthesis. In embryos and yolk sacs incubated with 3H-ethanolamine, 95% of recovered label was PtdEtn, but PtdEtn was not converted to PtdCho, which suggested that phosphatidylethanolamine methyltransferase (PeMT) activity was absent. In ET-18-OCH3 treated yolk sacs, PtdEtn was increased, but PtdCho was still not generated through PeMT. Results suggest that endogenous PtdCho synthesis is important during neurulation and that perturbed choline metabolism contributes to neural tube defects produced by DMAE and ET-18-OCH3.

Stabilization of the Simplest Criegee Intermediate from the Reaction between Ozone and Ethylene: A High-Level Quantum Chemical and Kinetic Analysis of Ozonolysis.

PubMed

Nguyen, Thanh Lam; Lee, Hyunwoo; Matthews, Devin A; McCarthy, Michael C; Stanton, John F

2015-06-04

The fraction of the collisionally stabilized Criegee species CH2OO produced from the ozonolysis of ethylene is calculated using a two-dimensional (E, J)-grained master equation technique and semiclassical transition-state theory based on the potential energy surface obtained from high-accuracy quantum chemical calculations. Our calculated yield of 42 ± 6% for the stabilized CH2OO agrees well, within experimental error, with available (indirect) experimental results. Inclusion of angular momentum in the master equation is found to play an essential role in bringing the theoretical results into agreement with the experiment. Additionally, yields of HO and HO2 radical products are predicted to be 13 ± 6% and 17 ± 6%, respectively. In the kinetic simulation, the HO radical product is produced mostly from the stepwise decomposition mechanism of primary ozonide rather than from dissociation of hot CH2OO.

The interaction of diamines and polyamines with the peroxidase-catalyzed metabolism of aromatic amines: a potential mechanism for the modulation of aniline toxicity.

PubMed

Michail, Karim; Aljuhani, Naif; Siraki, Arno G

2013-03-01

Synthetic and biological amines such as ethylenediamine (EDA), spermine, and spermidine have not been previously investigated in free-radical biochemical systems involving aniline-based drugs or xenobiotics. We aimed to study the influence of polyamines in the modulation of aromatic amine radical metabolites in peroxidase-mediated free radical reactions. The aniline compounds tested caused a relatively low oxidation rate of glutathione in the presence of horseradish peroxidase (HRP), and H2O2; however, they demonstrated marked oxygen consumption when a polyamine molecule was present. Next, we characterized the free-radical products generated by these reactions using spin-trapping and electron paramagnetic resonance (EPR) spectrometry. Primary and secondary but not tertiary polyamines dose-dependently enhanced the N-centered radicals of different aniline compounds catalyzed by either HRP or myeloperoxidase, which we believe occurred via charge transfer intermediates and subsequent stabilization of aniline-derived radical species as suggested by isotopically labeled aniline. Aniline/peroxidase reaction product(s) were monitored at 435 nm by kinetic spectrophotometry in the presence and absence of a polyamine additive. Using gas chromatography-mass spectrometry, the dimerziation product of aniline, azobenzene, was significantly amplified when EDA was present. In conclusion, di- and poly-amines are capable of enhancing the formation of aromatic-amine-derived free radicals, a fact that is expected to have toxicological consequences.

The photochemistry of anthropogenic nonmethane hydrocarbons in the troposphere

NASA Technical Reports Server (NTRS)

Brewer, D. A.; Augustsson, T. R.; Levine, J. S.

1983-01-01

A lumped, nonmethane hydrocarbon (NMHC) chemical mechanism is presently applied to a one-dimensional photochemical model of the troposphere. The profiles of OH, HO2, NO(x), and HNO3, showed only slight changes when NMHC chemistry was added. The integrated column of peroxyacetylnitrate (PAN), when NMHC chemistry was included, comprised 17 percent of the odd nitrogen budget. Advection is noted as an important possible mechanism for the removal of PAN at midlatitudes. The inclusion of such intermediate lifetime species as aldehydes and olefins has both provided additional sources of short-lived NMHC radicals, such as the peroxyacetyl radical that is the radical precursor of PAN, and offered a more detailed description of the concentrations of short-lived species and the overall NMHC chemistry.

Catalytic enantioselective alkene aminohalogenation/cyclization involving atom transfer.

PubMed

Bovino, Michael T; Chemler, Sherry R

2012-04-16

Problem solved: the title reaction was used for the synthesis of chiral 2-bromo, chloro, and iodomethyl indolines and 2-iodomethyl pyrrolidines. Stereocenter formation is believed to occur by enantioselective cis aminocupration and C-X bond formation is believed to occur by atom transfer. The ultility of the products as versatile synthetic intermediates was demonstrated, as was a radical cascade cyclization sequence. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Free Radical Mechanisms of Xenobiotic Mammalian Cytotoxicities

DTIC Science & Technology

1991-06-30

injury process was mediated through biotransformation of the halocarbons to a free radical intermediate, similar to what happens in the liver . However...peroxidation) of antioxidant agents - is not limited to the liver , but also occurs in vascular cells as well. Unlike the liver , where most of the injury is...frequent mechanism of xenobiotic liver toxicity is biotransformation by cytochrome P,5o-enzymes to toxic free radical intermediates. The primary objective

4′-CyanoPLP presents better prospect for the experimental detection of elusive cyclic intermediate radical in the reaction of lysine 5,6-aminomutase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maity, Amarendra Nath; Ke, Shyue-Chu, E-mail: ke@mail.ndhu.edu.tw

2015-02-06

Graphical abstract: The results of our calculations suggest that the reaction of 4′-cyanoPLP with lysine 5,6-aminomutase offers better prospect for the experimental detection of elusive cyclic azacyclopropylcarbinyl radical, which is proposed to be a key intermediate in the reaction of pyridoxal-5′-phosphate dependent radical aminomutases. - Highlights: • 4′-CyanoI{sup ·} is the lowest energy radical intermediate in the reaction of 5,6-LAM. • 4′-CyanoPLP offers good prospect for the experimental observation of elusive I{sup ·}. • The calculated HFCCs would help to characterize 4′-cyanoI{sup ·} by EPR. - Abstract: The results of our calculations suggest that the reaction of 4′-cyanoPLP with lysinemore » 5,6-aminomutase offers better prospect for the experimental detection of elusive cyclic azacyclopropylcarbinyl radical (I{sup ·}), which is proposed to be a key intermediate in the reaction of pyridoxal-5′-phosphate dependent radical aminomutases. We have calculated the corresponding hyperfine coupling constants (HFCCs) for {sup 14}N and {sup 13}C of cyano group using several basis sets to help the characterization of 4′-cyanoI{sup ·}.« less

Study of intermediates from transition metal excited-state electron-transfer reactions

NASA Astrophysics Data System (ADS)

Hoffman, M. Z.

1984-03-01

Attention during the past year focused on MV(+)., the reduced methyl viologen radical cation, which is a precursor to the formation of H2 in the photosensitized reduction of water. Through the use of photochemical and radiation chemical techniques, the efficiency of interaction of MV(+). with colloidal Pt, the stability of MV(+). as a function of pH, the quantum yield of formation of MV(+). in the Ru(bpy)3(2+)/MV(2+)/EDTA system, and the formation of photoactive charge-transfer complexes between MV(2+) and sacrificial electron donors were studied.

Ginsenoside-free molecules from steam-dried ginseng berry promote ethanol metabolism: an alternative choice for an alcohol hangover.

PubMed

Lee, Do Ik; Kim, Seung Tae; Lee, Dong Hoon; Yu, Jung Min; Jang, Su Kil; Joo, Seong Soo

2014-07-01

Ethanol metabolism produces harmful compounds that contribute to liver damage and cause an alcohol hangover. The intermediate metabolite acetaldehyde is responsible for alcohol hangover and CYP2E1-induced reactive oxygen species damage liver tissues. In this study, we examined whether ginsenoside-free molecules (GFMs) from steam-dried ginseng berries promote ethanol metabolism and scavenge free radicals by stimulating primary enzymes (alcohol dehydrogenase, aldehyde dehydrogenase, CYP2E1, and catalase) and antioxidant effects using in vitro and in vivo models. The results revealed that GFM effectively scavenged 2,2-diphenyl-1-picrylhydrazyl hydrate radicals and hydroxyl radicals. Notably, GFM significantly enhanced the expression of primary enzymes within 2 h in HepG2 cells. GFM clearly removed the consumed ethanol and significantly reduced the level of acetaldehyde as well as enhancement of primary gene expression in BALB/c mice. Moreover, GFM successfully protected HepG2 cells from ethanol attack. Of the major components identified in GFM, it was believed that linoleic acid was the most active ingredient. Based on these findings, we conclude that GFM holds promise for use as a new candidate for ethanol metabolism and as an antihangover agent. © 2014 Institute of Food Technologists®

Spectroscopic detection, characterization and dynamics of free radicals relevant to combustion processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, Terry

2015-06-04

Combustion chemistry is enormously complex. The chemical mechanisms involve a multitude of elementary reaction steps and a comparable number of reactive intermediates, many of which are free radicals. Computer simulations based upon these mechanisms are limited by the validity of the mechanisms and the parameters characterizing the properties of the intermediates and their reactivity. Spectroscopy can provide data for sensitive and selective diagnostics to follow their reactions. Spectroscopic analysis also provides detailed parameters characterizing the properties of these intermediates. These parameters serve as experimental gold standards to benchmark predictions of these properties from large-scale, electronic structure calculations. This work hasmore » demonstrated the unique capabilities of near-infrared cavity ringdown spectroscopy (NIR CRDS) to identify, characterize and monitor intermediates of key importance in complex chemical reactions. Our studies have focussed on the large family of organic peroxy radicals which are arguably themost important intermediates in combustion chemistry and many other reactions involving the oxidation of organic compounds. Our spectroscopic studies have shown that the NIR Ã - ˜X electronic spectra of the peroxy radicals allows one to differentiate among chemical species in the organic peroxy family and also determine their isomeric and conformic structure in many cases. We have clearly demonstrated this capability on saturated and unsaturated peroxy radicals and β-hydroxy peroxy radicals. In addition we have developed a unique dual wavelength CRDS apparatus specifically for the purpose of measuring absolute absorption cross section and following the reaction of chemical intermediates. The utility of the apparatus has been demonstrated by measuring the cross-section and self-reaction rate constant for ethyl peroxy.« less

Oligomerization reactions for precursors to secondary organic aerosol: Comparison between two formation mechanisms for the oligomeric hydroxyalkyl hydroperoxides

NASA Astrophysics Data System (ADS)

Zhao, Qiangli; Wang, Weina; Liu, Fengyi; Lü, Jian; Wang, Wenliang

2017-10-01

To better understand the formation mechanism of oligomeric hydroxyalkyl hydroperoxides HOROO(SCI)nH composed of stabilized Criegee intermediate (SCI) as a chain unit, the reactions of SCI with hydroxyalkyl hydroperoxides (HOROOH) and hydroxyalkylperoxy radical (HORO2) as well as HO2 radical were investigated. For the reactions of HORO2 + SCI, two preferred pathways involving a SCI insertion in HOROOH hydroperoxide bond can be found, and the formation of HOROO(SCI)H is the dominant pathway in the reaction of HOCH2(CH3)2COOH + (CH3)2COO. The structures of the HORO2, HOROOH as well as the SCIs play a crucial role in determining the reactivity of the oligomerization. Both the reactions of HORO2 + SCI + HO2 and HOROOH + SCI could be the source of the processors to the formation of secondary organic aerosol (SOA). But from the point of free energy barriers, the formation of HOROO(SCI)H prefers to follow the mechanism involving initiation by the reaction of a HORO2 and a SCI, sequential addition of SCIs, and termination by reaction with the HO2 radical. The rate coefficients show negative temperature dependence and vary in different systems depending on the reactants. The reaction process and constituents of the products can be regulated by temperature and reactants.

Mechanism of Cyclic Dye Regeneration During Eosin-Sensitized Photoinitiation in the Presence of Polymerization Inhibitors

PubMed Central

Avens, Heather J.; Bowman, Christopher N.

2009-01-01

A visible light photoinitiator, eosin, in combination with a tertiary amine coinitiator is found to initiate polymerization despite the presence of at least 1000-fold excess dissolved oxygen which functions as an inhibitor of radical polymerizations. Additionally, 0.4 µM eosin is able to overcome 100-fold excess (40 µM) 2,2,6,6-Tetramethyl-1-piperidinyloxy (TEMPO) inhibitor, initiating polymerization after only a 2 minute inhibition period. In contrast, 40 µM Irgacure-2959, a standard cleavage-type initiator, is unable to overcome even an equivalent amount of inhibitor (40 µM TEMPO). Through additional comparisons of these two initiation systems, a reaction mechanism is developed which is consistent with the kinetic data and provides an explanation for eosin’s relative insensitivity to oxygen, TEMPO and other inhibitors. A cyclic mechanism is proposed in which semi-reduced eosin radicals react by disproportionation with radical inhibitors and radical intermediates in the inhibition process to regenerate eosin and effectively consume inhibitor. In behavior similar to that of eosin, rose bengal, fluorescein, and riboflavin are also found to initiate polymerization despite the presence of excess TEMPO, indicating that cyclic regeneration likely enhances the photoinitiation kinetics of many dye photosensitizers. Selection of such dye initiation systems constitutes a valuable strategy for alleviating inhibitory effects in radical polymerizations. PMID:20098667

Efficient depletion of ascorbate by amino acid and protein radicals under oxidative stress.

PubMed

Domazou, Anastasia S; Zelenay, Viviane; Koppenol, Willem H; Gebicki, Janusz M

2012-10-15

Ascorbate levels decrease in organisms subjected to oxidative stress, but the responsible reactions have not been identified. Our earlier studies have shown that protein C-centered radicals react rapidly with ascorbate. In aerobes, these radicals can react with oxygen to form peroxyl radicals. To estimate the relative probabilities of the reactions of ascorbate with protein C- and O-centered radicals, we measured by pulse radiolysis the rate constants of the reactions of C-centered radicals in Gly, Ala, and Pro with O₂ and of the resultant peroxyl radicals with ascorbate. Calculations based on the concentrations of ascorbate and oxygen in human tissues show that the relative probabilities of reactions of the C-centered amino acid radicals with O₂ and ascorbate vary between 1:2.6 for the pituitary gland and 1:0.02 for plasma, with intermediate ratios for other tissues. The high frequency of occurrence of Gly, Ala, and Pro in proteins and the similar reaction rate constants of their C-centered radicals with O₂ and their peroxo-radicals with ascorbate suggest that our results are also valid for proteins. Thus, the formation of protein C- or O-centered radicals in vivo can account for the loss of ascorbate in organisms under oxidative stress. Copyright © 2012 Elsevier Inc. All rights reserved.

Protective effect of human recombinant copper-zinc superoxide dismutase on zone of stasis survival in burns in rats.

PubMed

Shalom, Avshalom; Kramer, Eyal; Westreich, Melvyn

2011-06-01

Superoxide dismutase, acting as a scavenger of oxygen free radicals, has shown mixed results in increasing burn wound survival. Originally, we demonstrated that human recombinant copper-zinc superoxide dismutase (Hr-CuZnSOD) could increase the survival of failing ischemic flaps in a rat model. Because of the possible similar pathophysiology of tissue ischemia in flaps and the zone of stasis in burns, we conducted a later study using 2 groups of rats with standardized intermediate burns, to ascertain whether Hr-CuZnSOD could increase zone of stasis survival in rats. The results showed that postburn Hr-CuZnSOD failed to improve zone of stasis survival in burns. We decided to undertake a new controlled study to ascertain whether there is a protective effect of Hr-CuZnSOD in cases of intermediate burns. We used 2 groups of rats, one of which received prophylactic treatments with Hr-CuZnSOD before the induction of standardized intermediate burns. Results showed that preburn Hr-CuZnSOD also failed to improve zone of stasis survival in burns. Further studies are needed to adequately understand the effect of oxygen free radicals in burn wound pathophysiology and to determine whether Hr-CuZnSOD has a role in the clinical management of burns or should be abandoned.

The reaction between CH 3O 2 and OH radicals: Product yields and atmospheric implications

DOE PAGES

Assaf, Emmanuel; Sheps, Leonid; Whalley, Lisa; ...

2017-01-25

The reaction between CH 3O 2 and OH radicals has been shown to be fast and to play an appreciable role for the removal of CH 3O 2 radials in remote environments such as the marine boundary layer. Two different experimental techniques have been used here to determine the products of this reaction. The HO 2 yield has been obtained from simultaneous time-resolved measurements of the absolute concentration of CH 3O 2, OH, and HO 2 radicals by cw-CRDS. The possible formation of a Criegee intermediate has been measured by broadband cavity enhanced UV absorption. A yield of Φ HO2more » = (0.8 ± 0.2) and an upper limit for Φ Criegee = 0.05 has been determined for this reaction, suggesting a minor yield of methanol or stabilized trioxide as a product. The impact of this reaction on the composition of the remote marine boundary layer has been determined by implementing these findings into a box model utilizing the Master Chemical Mechanism v3.2, and constraining the model for conditions found at the Cape Verde Atmospheric Observatory in the remote tropical Atlantic Ocean. Inclusion of the CH 3O 2+OH reaction into the model results in up to 30% decrease in the CH 3O 2 radical concentration while the HO 2 concentration increased by up to 20%. Finally, production and destruction of O 3 are also influenced by these changes, and the model indicates that taking into account the reaction between CH 3O 2 and OH leads to a 6% decrease of O 3.« less

The reaction between CH 3O 2 and OH radicals: Product yields and atmospheric implications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Assaf, Emmanuel; Sheps, Leonid; Whalley, Lisa

The reaction between CH 3O 2 and OH radicals has been shown to be fast and to play an appreciable role for the removal of CH 3O 2 radials in remote environments such as the marine boundary layer. Two different experimental techniques have been used here to determine the products of this reaction. The HO 2 yield has been obtained from simultaneous time-resolved measurements of the absolute concentration of CH 3O 2, OH, and HO 2 radicals by cw-CRDS. The possible formation of a Criegee intermediate has been measured by broadband cavity enhanced UV absorption. A yield of Φ HO2more » = (0.8 ± 0.2) and an upper limit for Φ Criegee = 0.05 has been determined for this reaction, suggesting a minor yield of methanol or stabilized trioxide as a product. The impact of this reaction on the composition of the remote marine boundary layer has been determined by implementing these findings into a box model utilizing the Master Chemical Mechanism v3.2, and constraining the model for conditions found at the Cape Verde Atmospheric Observatory in the remote tropical Atlantic Ocean. Inclusion of the CH 3O 2+OH reaction into the model results in up to 30% decrease in the CH 3O 2 radical concentration while the HO 2 concentration increased by up to 20%. Finally, production and destruction of O 3 are also influenced by these changes, and the model indicates that taking into account the reaction between CH 3O 2 and OH leads to a 6% decrease of O 3.« less

Speciated Monitoring of Gas-Phase Organic Peroxy Radicals by Chemical Ionization Mass Spectrometry: Cross-Reactions between CH3O2, CH3(CO)O2, (CH3)3CO2, and c-C6H11O2.

PubMed

Nozière, Barbara; Hanson, David R

2017-11-09

Organic peroxy radicals ("RO 2 ", with R organic) are key intermediates in most oxygen-rich systems, where organic compounds are oxidized (natural environment, flames, combustion engines, living organisms, etc). But, until recently, techniques able to monitor simultaneously and distinguish between RO 2 species ("speciated" detection) have been scarce, which has limited the understanding of complex systems containing these radicals. Mass spectrometry using proton transfer ionization has been shown previously to detect individual gas-phase RO 2 separately. In this work, we illustrate its ability to speciate and monitor several RO 2 simultaneously by investigating reactions involving CH 3 O 2 , CH 3 C(O)O 2 , c-C 6 H 11 O 2 , and (CH 3 ) 3 CO 2 . The detection sensitivity of each of these radicals was estimated by titration with NO to between 50 and 1000 Hz/ppb, with a factor from 3 to 5 of uncertainties, mostly due to the uncertainties in knowing the amounts of added NO. With this, the RO 2 concentration in the reactor was estimated between 1 × 10 10 and 1 × 10 12 molecules cm -3 . When adding a second radical species to the reactor, the kinetics of the cross-reaction could be studied directly from the decay of the first radical. The time-evolution of two and sometimes three different RO 2 was followed simultaneously, as the CH 3 O 2 produced in further reaction steps was also detected in some systems. The rate coefficients obtained are (in molecule -1 cm 3 s -1 ): k CH3O2+CH3C(O)O2 = 1.2 × 10 -11 , k CH3O2+t-butylO2 = 3.0 × 10 -15 , k c-hexylO2+CH3O2 = 1.2 × 10 -13 , k t-butylO2+CH3C(O)O2 = 3.7 × 10 -14 , and k c-hexylO2+t-butylO2 = 1.5 × 10 -15 . In spite of their good comparison with the literature and good reproducibility, large uncertainties (×5/5) are recommended on these results because of those in the detection sensitivities. This work is a first illustration of the potential applications of this technique for the investigation of organic radicals in laboratory and in more complex systems.

Study of the photon-induced formation and subsequent desorption of CH3OH and H2CO in interstellar ice analogs

NASA Astrophysics Data System (ADS)

Martín-Doménech, R.; Muñoz Caro, G. M.; Cruz-Díaz, G. A.

2016-05-01

Context. Methanol and formaldehyde are two simple organic molecules that are ubiquitously detected in the interstellar medium, in both the solid and gaseous phases. An origin in the solid phase and a subsequent nonthermal desorption into the gas phase is often invoked to explain their abundances in some of the environments where they are found. Experimental simulations under astrophysically relevant conditions have been carried out in the past four decades in order to find a suitable mechanism for that process. Aims: In particular, photodesorption from pure methanol ice (and presumably from pure formaldehyde ice) has been found to be negligible in previous works, probably because both molecules are very readily dissociated by vacuum-UV photons. Therefore, we explore the in situ formation and subsequent photon-induced desorption of these species, studying the UV photoprocessing of pure ethanol ice, and a more realistic binary H2O:CH4 ice analog. Methods: Experimental simulations were performed in an ultra-high vacuum chamber. Pure ethanol and binary H2O:CH4 ice samples deposited onto an infrared transparent window at 8 K were UV-irradiated using a microwave-discharged hydrogen flow lamp. Evidence of photochemical production of these two species and subsequent UV-photon-induced desorption into the gas phase were searched for by means of a Fourier transform infrared spectrometer and a quadrupole mass spectrometer, respectively. After irradiation, ice samples were warmed up to room temperature until complete sublimation was attained for detection of volatile products. Results: Formation of CH3OH was only observed during photoprocessing of the H2O:CH4 ice analog, accounting for ~4% of the initial CH4 ice column density, but no photon-induced desorption was detected. Photochemical production of H2CO was observed in both series of experiments. Formation of formaldehyde accounted for ≤45% conversion of the initial ethanol ice, but it could not be quantified during irradiation of the binary H2O:CH4 ice analogs. Photochemidesorption of formaldehyde, I.e., photon-induced formation on the ice surface and inmediate desorption, was observed, with a yield of ~6 × 10-5 (molecules/incident photon) in the case of the pure ethanol ice experiments, and ~4.4 × 10-5 (molecules/incident photon) when the H2O:CH4 ice analogs were photoprocessed. Photoprocessing of the ice analogs lead to formation of other species. Some of them were also found to desorb upon UV irradiation. Conclusions: While certain C-bearing species, in particular H2CO, were found to desorb upon irradiation, nonthermal desorption of CH3OH was not observed. So far, there is no experimental evidence of any efficient CH3OH desorption induced by UV photons. On the other hand, the observed photon-induced desorption of H2CO could account for the total formaldehyde abundance observed in the Horsehead photodissociation-dominated region.

Oxidative cyclization reactions: controlling the course of a radical cation-derived reaction with the use of a second nucleophile.

PubMed

Redden, Alison; Perkins, Robert J; Moeller, Kevin D

2013-12-02

Construction of new ring systems: Oxidative cyclizations (see picture; RVC=reticulated vitreous carbon) have been conducted that use two separate intramolecular nucleophiles to trap an enol ether-derived radical cation intermediate. The reactions provide a means for rapidly trapping the radical cation intermediate in a manner that avoids competitive decomposition reactions. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H 3CC≡C˙) with small alkenes and alkynes

DOE PAGES

Kirk, Benjamin B.; Savee, John D.; Trevitt, Adam J.; ...

2015-07-16

The reaction of small hydrocarbon radicals (i.e. ˙CN, ˙C 2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C 2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC≡C˙), a likely product frommore » the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d 4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (–H = 27%, –CH 3 = 73%) and (–H = 14%, –CH 3 = 86%), respectively. Altogether, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.« less

Molecular weight growth in Titan's atmosphere: branching pathways for the reaction of 1-propynyl radical (H3CC≡C˙) with small alkenes and alkynes.

PubMed

Kirk, Benjamin B; Savee, John D; Trevitt, Adam J; Osborn, David L; Wilson, Kevin R

2015-08-28

The reaction of small hydrocarbon radicals (i.e.˙CN, ˙C2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC[triple bond, length as m-dash]C˙), a likely product from the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (-H = 27%, -CH3 = 73%) and (-H = 14%, -CH3 = 86%), respectively. Together, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.

Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H 3CC≡C˙) with small alkenes and alkynes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirk, Benjamin B.; Savee, John D.; Trevitt, Adam J.

The reaction of small hydrocarbon radicals (i.e. ˙CN, ˙C 2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C 2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC≡C˙), a likely product frommore » the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d 4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (–H = 27%, –CH 3 = 73%) and (–H = 14%, –CH 3 = 86%), respectively. Altogether, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.« less

Hydrogen Bond Network between Amino Acid Radical Intermediates on the Proton-Coupled Electron Transfer Pathway of E. coli α2 Ribonucleotide Reductase

PubMed Central

2015-01-01

Ribonucleotide reductases (RNRs) catalyze the conversion of ribonucleotides to deoxyribonucleotides in all organisms. In all Class Ia RNRs, initiation of nucleotide diphosphate (NDP) reduction requires a reversible oxidation over 35 Å by a tyrosyl radical (Y122•, Escherichia coli) in subunit β of a cysteine (C439) in the active site of subunit α. This radical transfer (RT) occurs by a specific pathway involving redox active tyrosines (Y122 ⇆ Y356 in β to Y731 ⇆ Y730 ⇆ C439 in α); each oxidation necessitates loss of a proton coupled to loss of an electron (PCET). To study these steps, 3-aminotyrosine was site-specifically incorporated in place of Y356-β, Y731- and Y730-α, and each protein was incubated with the appropriate second subunit β(α), CDP and effector ATP to trap an amino tyrosyl radical (NH2Y•) in the active α2β2 complex. High-frequency (263 GHz) pulse electron paramagnetic resonance (EPR) of the NH2Y•s reported the gx values with unprecedented resolution and revealed strong electrostatic effects caused by the protein environment. 2H electron–nuclear double resonance (ENDOR) spectroscopy accompanied by quantum chemical calculations provided spectroscopic evidence for hydrogen bond interactions at the radical sites, i.e., two exchangeable H bonds to NH2Y730•, one to NH2Y731• and none to NH2Y356•. Similar experiments with double mutants α-NH2Y730/C439A and α-NH2Y731/Y730F allowed assignment of the H bonding partner(s) to a pathway residue(s) providing direct evidence for colinear PCET within α. The implications of these observations for the PCET process within α and at the interface are discussed. PMID:25516424

Radical scavenger can scavenge lipid allyl radicals complexed with lipoxygenase at lower oxygen content.

PubMed

Koshiishi, Ichiro; Tsuchida, Kazunori; Takajo, Tokuko; Komatsu, Makiko

2006-04-15

Lipoxygenases have been proposed to be a possible factor that is responsible for the pathology of certain diseases, including ischaemic injury. In the peroxidation process of linoleic acid by lipoxygenase, the E,Z-linoleate allyl radical-lipoxygenase complex seems to be generated as an intermediate. In the present study, we evaluated whether E,Z-linoleate allyl radicals on the enzyme are scavenged by radical scavengers. Linoleic acid, the content of which was greater than the dissolved oxygen content, was treated with soya bean lipoxygenase-1 (ferric form) in the presence of radical scavenger, CmP (3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl). The reaction rate between oxygen and lipid allyl radical is comparatively faster than that between CmP and lipid allyl radical. Therefore a reaction between linoleate allyl radical and CmP was not observed while the dioxygenation of linoleic acid was ongoing. After the dissolved oxygen was depleted, CmP stoichiometrically trapped linoleate-allyl radicals. Accompanied by this one-electron redox reaction, the resulting ferrous lipoxygenase was re-oxidized to the ferric form by hydroperoxylinoleate. Through the adduct assay via LC (liquid chromatography)-MS/MS (tandem MS), four E,Z-linoleate allyl radical-CmP adducts corresponding to regio- and diastereo-isomers were detected in the linoleate/lipoxygenase system, whereas E,E-linoleate allyl radical-CmP adducts were not detected at all. If E,Z-linoleate allyl radical is liberated from the enzyme, the E/Z-isomer has to reach equilibrium with the thermodynamically favoured E/E-isomer. These data suggested that the E,Z-linoleate allyl radicals were not liberated from the active site of lipoxygenase before being trapped by CmP. Consequently, we concluded that the lipid allyl radicals complexed with lipoxygenase could be scavenged by radical scavengers at lower oxygen content.

The anatomical location and laterality of orbital cavernous haemangiomas.

PubMed

McNab, Alan A; Selva, Dinesh; Hardy, Thomas G; O'Donnell, Brett

2014-10-01

To determine the anatomical location and laterality of orbital cavernous haemangiomas (OCH). Retrospective case series. The records of 104 patients with OCH were analyzed. The anatomical location of each OCH defined by the location of a point at the centre of the lesion, and its laterality. There were 104 patients included in the study. No patient had more than one lesion. Sixteen (15.4%) were located in the anterior third of the orbit, 74 (71.2%) were in the middle third, and 14 (13.5%) in the posterior third. In the middle third, 10 of 74 (13.5%) were extraconal and 64 intraconal (86.5%), with 30 of 64 (46.9%) middle third intraconal lesions lying lateral to the optic nerve. Of 104 lesions, 56 (53.8%) were left sided, showing a trend towards a predilection for the left side (p = 0.065). If data from other published series which included data on laterality is added to our own data and analysed, 270 of 468 (57.7%) OCH occurred in the left orbit (p < 0.005). OCH may occur at almost any location within the orbit. The commonest location is the middle third of the orbit, in the intraconal space lateral to the optic nerve. This may reflect an origin of these lesions from the arterial side of the circulation, as there are more small arteries in the intraconal space lateral to the optic nerve than in other locations. A predilection for the left orbit remains unexplained.

Optimization of pharmaceutical wastewater treatment by solar/ferrioxalate photo-catalysis.

PubMed

Monteagudo, J M; Durán, A; Culebradas, R; San Martín, I; Carnicer, A

2013-10-15

The degradation of a pharmaceutical wastewater using a ferrioxalate-assisted solar/photo-Fenton system has been studied. The photochemical reaction was carried out in a pilot plant consisting of a compound parabolic collector (CPC) solar reactor. An optimization study was performed combining a multivariate experimental design and Neuronal Networks that included the following variables: initial concentrations of H2O2, catalyst Fe (II) and oxalic acid (H2C2O4), temperature and solar power. Under optimal conditions, 84% TOC (Total Organic Carbon) removal was achieved in 115 min. Oxalic acid had a positive effect on mineralization when solar power was above 30 W m(-2). The minimum amount of H2O2 to degrade 1 mol of TOC was found to be 3.57 mol. Both the H2O2 conversion efficiency and the degree of mineralization were highest when the oxalic/Fe(II) initial molar relation was close to 3. HO radicals were the main oxidative intermediate species in the process, although hydroperoxyl radicals (HO(2)(·)) also played a role. Copyright © 2013 Elsevier Ltd. All rights reserved.

Emerging themes in radical SAM chemistry

PubMed Central

Shisler, Krista A; Broderick, Joan B

2014-01-01

Enzymes in the radical SAM (RS) superfamily catalyze a wide variety of reactions through unique radical chemistry. The characteristic markers of the superfamily include a [4Fe–4S] cluster coordinated to the protein via a cysteine triad motif, typically CX3CX2C, with the fourth iron coordinated by S-adenosylmethionine (SAM). The SAM serves as a precursor for a 5′-deoxyadenosyl radical, the central intermediate in nearly all RS enzymes studied to date. The SAM-bound [4Fe–4S] cluster is located within a partial or full triosephosphate isomerase (TIM) barrel where the radical chemistry occurs protected from the surroundings. In addition to the TIM barrel and a RS [4Fe–4S] cluster, many members of the superfamily contain additional domains and/or additional Fe–S clusters. Recently characterized superfamily members are providing new examples of the remarkable range of reactions that can be catalyzed, as well as new structural and mechanistic insights into these fascinating reactions. PMID:23141873

Solvent effects on the relative stability of radicals derived from artemisinin: DFT study using the PCM/COSMO approach

NASA Astrophysics Data System (ADS)

Araujo, M. T. De; Carneiro, J. W. De M.; Taranto, A. G.

The PCM/COSMO approach was employed to calculate the relative stability of radicals derived from the antimalarial artemisinin. The calculations were performed in polar (water) and apolar (THF) solvent at the density functional level [B3LYP/6-31g(d)]. Relative stabilities were calculated by means of isodesmic equations using artemisinin as reference. Replacement of oxygen atoms by CH2 unities was found to decrease the relative stability of the anionic radical intermediates. The degree of destabilization is reduced in the presence of solvent, being less in water than in THF. The dipole moment and the corresponding solvation free energies of these species modulate this effect. Derivatives with inverted stereochemistry are more stable than those with the artemisinin-like stereochemistry, although the solvent attenuates this stabilization effect. As was found in the in vacuo calculations, the radicals centered on carbon are always more stable than the corresponding radicals centered on oxygen.

Synthesis of a Novel Series of 2-Methylsulfanyl Fatty Acids and their Toxicity on the Human K-562 and U-937 Leukemia Cell Lines

PubMed Central

Carballeira, Néstor M.; Miranda, Carlos; Orellano, Elsie A.; González, Fernando A.

2006-01-01

The hitherto unknown 2-methylsulfanyldecanoic acid and 2-methylsulfanyldodecanoic acid were synthesized from methyl decanoate and methyl dodecanoate, respectively, through the reaction of lithium diisopropylamide and dimethyldisulfide in THF followed by saponification with potassium hydroxide in ethanol. Both α-methylsulfanylated FA were cytotoxic to the human chronic myelogenous leukemia K-562 and the human histiocytic lymphoma U-937 cell lines with EC50 values in the 200-300 μM range, which makes them more cytotoxic to these cell lines than either decanoic acid or dodecanoic acid. The cytotoxicity of the studied FA towards K-562 followed the order: 2-SCH3-12:0 > 2-SCH3-10:0 > 10:0 > 12:0 > 2-OCH3-12:0, while towards U-937 the cytotoxicity was found to be: 2-SCH3-10:0 > 2-SCH3-12:0 > 12:0 > 10:0 > 2-OCH3-12:0. These results indicate that the α-methylsulfanyl substitution increases the cytotoxicity of the C10 and C12 fatty acids towards the studied leukemia cell lines. PMID:16382579

Silica hydride intermediate for octadecylsilica and phenyl bonded phase preparation via heterogeneous hydrosilation in supercritical carbon dioxide.

PubMed

Scully, N M; Ashu-Arrah, B A; Nagle, A P; Omamogho, J O; O'Sullivan, G P; Friebolin, V; Dietrich, B; Albert, K; Glennon, J D

2011-04-15

Investigations into the preparation of silica hydride intermediate in supercritical carbon dioxide (sc-CO(2)) that avoids the use of organic solvents such as toluene or dioxane are described. The effects of reaction temperature, pressure and time on the surface coverage of the supercritical fluid generated silica hydride intermediate were studied. Under optimised supercritical conditions of 120°C, 483 bar and 3 h reaction time, silica hydride (Si-H) conversion efficiencies of ca. 40% were achieved for the hydride intermediate prepared from a monofunctional silane reagent (dimethylmethoxysilane). Si-H conversion efficiencies (as determined from (29)Si CP-MAS NMR spectral analysis) for the hydride intermediate prepared from triethoxysilane (TES) in sc-CO(2) were found to be comparable to those obtained using a TES silanisation approach in an organic solvent. (13)C and (29)Si CP-MAS-NMR spectroscopy was employed to provide a complete structural assignment of the silica hydride intermediates. Furthermore, supercritical CO(2) was subsequently employed as a reaction medium for the heterogenous hydrosilation of silica hydride with octadecene and with styrene, in the presence of a free radical initiator. These supercritical fluid generated reversed-phase materials were prepared in a substantially reduced reaction time (3 h) compared to organic solvent based methods (100 h reaction time). Silica functionalisation in sc-CO(2) presents an efficient and clean alternative to organic solvent based methods for the preparation of important silica hydride intermediate and silica bonded stationary phases via a hydrosilation approach. Copyright © 2010 Elsevier B.V. All rights reserved.

Highly Chemoselective Reduction of Amides (Primary, Secondary, Tertiary) to Alcohols using SmI2/Amine/H2O under Mild Conditions

PubMed Central

2014-01-01

Highly chemoselective direct reduction of primary, secondary, and tertiary amides to alcohols using SmI2/amine/H2O is reported. The reaction proceeds with C–N bond cleavage in the carbinolamine intermediate, shows excellent functional group tolerance, and delivers the alcohol products in very high yields. The expected C–O cleavage products are not formed under the reaction conditions. The observed reactivity is opposite to the electrophilicity of polar carbonyl groups resulting from the nX → π*C=O (X = O, N) conjugation. Mechanistic studies suggest that coordination of Sm to the carbonyl and then to Lewis basic nitrogen in the tetrahedral intermediate facilitate electron transfer and control the selectivity of the C–N/C–O cleavage. Notably, the method provides direct access to acyl-type radicals from unactivated amides under mild electron transfer conditions. PMID:24460078

40 CFR Table 2 to Subpart F of... - Organic Hazardous Air Pollutants

Code of Federal Regulations, 2010 CFR

2010-07-01

... (N,N-) 121697 Diethyl sulfate 64675 Dimethylbenzidine (3,3″-) 119937 Dimethylformamide (N,N-) 68122... Hexachlorobenzene 118741 Hexachlorobutadiene 87683 Hexachloroethane 67721 Hexane 110543 Hydroquinone 123319... ethylene glycol, diethylene glycol, and triethylene glycol R-(OCH2 CH2n-OR where: n=1, 2, or 3; R=alkyl or...

40 CFR Table 2 to Subpart F of... - Organic Hazardous Air Pollutants

Code of Federal Regulations, 2012 CFR

2012-07-01

... (N,N-) 121697 Diethyl sulfate 64675 Dimethylbenzidine (3,3′-) 119937 Dimethylformamide (N,N-) 68122... Hexachlorobenzene 118741 Hexachlorobutadiene 87683 Hexachloroethane 67721 Hexane 110543 Hydroquinone 123319... ethylene glycol, diethylene glycol, and triethylene glycol R-(OCH2 CH2n-OR where: n=1, 2, or 3; R=alkyl or...

Metal cluster chemistry: Structure and stereochemistry in the polynuclear rhodium hydrides HnRhn[P(OR)3]2n

PubMed Central

Brown, R. K.; Williams, J. M.; Fredrich, M. F.; Day, V. W.; Sivak, A. J.; Muetterties, E. L.

1979-01-01

Crystallographic analyses of x-ray and neutron diffraction data have provided a definitive structural representation of {HRh[P(O-i-C3H7)3]2}2 and {HRh[P(OCH3)3]2}3. These polynuclear hydrides are generated from square planar H2Rh[P(OR)3]2 units by edge (hydrogen atom) sharing and by vertex (hydrogen atom) sharing to form the dimeric and trimeric structures, respectively. The square-planar units are held together through four-center and three-center two-electron Rh—H—Rh bonds in the dimer and trimer, respectively. The dimer and trimer molecules each add one molecule of hydrogen to form H[(i-C3H7O)3P]2RhH3Rh [P(O-i-C3H7)3]2 and H5Rh3[P(OCH3)3]6, respectively. NMR spectral information has served to define the stereochemical features of these polyhydrides. The significance of this chemistry in the metal cluster-metal surface analogy is described. PMID:16592645

Determination of Combustion Product Radicals in a Hydrocarbon Fueled Rocket Exhaust Plume

NASA Technical Reports Server (NTRS)

Langford, Lester A.; Allgood, Daniel C.; Junell, Justin C.

2007-01-01

The identification of metallic effluent materials in a rocket engine exhaust plume indicates the health of the engine. Since 1989, emission spectroscopy of the plume of the Space Shuttle Main Engine (SSME) has been used for ground testing at NASA's Stennis Space Center (SSC). This technique allows the identification and quantification of alloys from the metallic elements observed in the plume. With the prospect of hydrocarbon-fueled rocket engines, such as Rocket Propellant 1 (RP-1) or methane (CH4) fueled engines being considered for use in future space flight systems, the contributions of intermediate or final combustion products resulting from the hydrocarbon fuels are of great interest. The effect of several diatomic molecular radicals, such as Carbon Dioxide , Carbon Monoxide, Molecular Carbon, Methylene Radical, Cyanide or Cyano Radical, and Nitric Oxide, needs to be identified and the effects of their band systems on the spectral region from 300 nm to 850 nm determined. Hydrocarbon-fueled rocket engines will play a prominent role in future space exploration programs. Although hydrogen fuel provides for higher engine performance, hydrocarbon fuels are denser, safer to handle, and less costly. For hydrocarbon-fueled engines using RP-1 or CH4 , the plume is different from a hydrogen fueled engine due to the presence of several other species, such as CO2, C2, CO, CH, CN, and NO, in the exhaust plume, in addition to the standard H2O and OH. These species occur as intermediate or final combustion products or as a result of mixing of the hot plume with the atmosphere. Exhaust plume emission spectroscopy has emerged as a comprehensive non-intrusive sensing technology which can be applied to a wide variety of engine performance conditions with a high degree of sensitivity and specificity. Stennis Space Center researchers have been in the forefront of advancing experimental techniques and developing theoretical approaches in order to bring this technology to a more mature stage.

Radicals: Reactive Intermediates with Translational Potential.

PubMed

Yan, Ming; Lo, Julian C; Edwards, Jacob T; Baran, Phil S

2016-10-05

This Perspective illustrates the defining characteristics of free radical chemistry, beginning with its rich and storied history. Studies from our laboratory are discussed along with recent developments emanating from others in this burgeoning area. The practicality and chemoselectivity of radical reactions enable rapid access to molecules of relevance to drug discovery, agrochemistry, material science, and other disciplines. Thus, these reactive intermediates possess inherent translational potential, as they can be widely used to expedite scientific endeavors for the betterment of humankind.

Comparative Effectiveness of Cancer Control and Survival after Robot-Assisted versus Open Radical Prostatectomy.

PubMed

Hu, Jim C; O'Malley, Padraic; Chughtai, Bilal; Isaacs, Abby; Mao, Jialin; Wright, Jason D; Hershman, Dawn; Sedrakyan, Art

2017-01-01

Robot-assisted surgery has been rapidly adopted in the U.S. for prostate cancer. Its adoption has been driven by market forces and patient preference, and debate continues regarding whether it offers improved outcomes to justify the higher cost relative to open surgery. We examined the comparative effectiveness of robot-assisted vs open radical prostatectomy in cancer control and survival in a nationally representative population. This population based observational cohort study of patients with prostate cancer undergoing robot-assisted radical prostatectomy and open radical prostatectomy during 2003 to 2012 used data captured in the SEER (Surveillance, Epidemiology, and End Results)-Medicare linked database. Propensity score matching and time to event analysis were used to compare all cause mortality, prostate cancer specific mortality and use of additional treatment after surgery. A total of 6,430 robot-assisted radical prostatectomies and 9,161 open radical prostatectomies performed during 2003 to 2012 were identified. The use of robot-assisted radical prostatectomy increased from 13.6% in 2003 to 2004 to 72.6% in 2011 to 2012. After a median followup of 6.5 years (IQR 5.2-7.9) robot-assisted radical prostatectomy was associated with an equivalent risk of all cause mortality (HR 0.85, 0.72-1.01) and similar cancer specific mortality (HR 0.85, 0.50-1.43) vs open radical prostatectomy. Robot-assisted radical prostatectomy was also associated with less use of additional treatment (HR 0.78, 0.70-0.86). Robot-assisted radical prostatectomy has comparable intermediate cancer control as evidenced by less use of additional postoperative cancer therapies and equivalent cancer specific and overall survival. Longer term followup is needed to assess for differences in prostate cancer specific survival, which was similar during intermediate followup. Our findings have significant quality and cost implications, and provide reassurance regarding the adoption of more expensive technology in the absence of randomized controlled trials. Copyright © 2017 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

Joint experimental and DFT study of the gas-phase unimolecular elimination kinetic of methyl trifluoropyruvate.

PubMed

Tosta, María M; Mora, José R; Córdova, Tania; Chuchani, Gabriel

2010-08-05

The elimination kinetics of methyl trifluoropyruvate in the gas phase was determined in a static system, where the reaction vessel was always deactivated with allyl bromide, and in the presence of at least a 3-fold excess of the free-radical chain inhibitor toluene. The working temperature range was 388.5-430.1 degrees C, and the pressure range was 38.6-65.8 Torr. The reaction was found to be homogeneous and unimolecular and to obey a first-order rate law. The products of the reaction are methyl trifluoroacetate and CO gas. The Arrhenius equation of this elimination was found to be as follows: log k(1) (s(-1)) = (12.48 +/- 0.32) - (204.2 +/- 4.2) kJ mol(-1)(2.303RT)(-1) (r = 0.9994). The theoretical calculation of the kinetic and thermodynamic parameters and the mechanism of this reaction were carried out at the B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), PBEPBE/6-31G(d,p), and PBEPBE/6-31G++(d,p) levels of theory. The theoretical study showed that the preferred reaction channel is a 1,2-migration of OCH(3) involving a three-membered cyclic transition state in the rate-determining step.

Hydroxyl radical induced transformation of phenylurea herbicides: A theoretical study

NASA Astrophysics Data System (ADS)

Mile, Viktória; Harsányi, Ildikó; Kovács, Krisztina; Földes, Tamás; Takács, Erzsébet; Wojnárovits, László

2017-03-01

Aromatic ring hydroxylation reactions occurring during radiolysis of aqueous solutions are studied on the example of phenylurea herbicides by Density Functional Theory calculations. The effect of the aqueous media is taken into account by using the Solvation Model Based on Density model. Hydroxyl radical adds to the ring because the activation free energies (0.4-47.2 kJ mol-1) are low and also the Gibbs free energies have high negative values ((-27.4) to (-5.9) kJ mol-1). According to the calculations in most of cases the ortho- and para-addition is preferred in agreement with the experimental results. In these reactions hydroxycyclohexadienyl type radicals form. In a second type reaction, when loss of chlorine atom takes place, OH/Cl substitution occurs without cyclohexadienyl type intermediate.

Degradation and intermediates of diclofenac as instructive example for decomposition of recalcitrant pharmaceuticals by hydroxyl radicals generated with pulsed corona plasma in water.

PubMed

Banaschik, Robert; Jablonowski, Helena; Bednarski, Patrick J; Kolb, Juergen F

2018-01-15

Seven recalcitrant pharmaceutical residues (diclofenac, 17α-ethinylestradiol, carbamazepine, ibuprofen, trimethoprim, diazepam, diatrizoate) were decomposed by pulsed corona plasma generated directly in water. The detailed degradation pathway was investigated for diclofenac and 21 intermediates could be identified in the degradation cascade. Hydroxyl radicals have been found primarily responsible for decomposition steps. By spin trap enhanced electron paramagnetic resonance spectroscopy (EPR), OH-adducts and superoxide anion radical adducts were detected and could be distinguished applying BMPO as a spin trap. The increase of concentrations of adducts follows qualitatively the increase of hydrogen peroxide concentrations. Hydrogen peroxide is eventually consumed in Fenton-like processes but the concentration is continuously increasing to about 2mM for a plasma treatment of 70min. Degradation of diclofenac is inversely following hydrogen peroxide concentrations. No qualitative differences between byproducts formed during plasma treatment or due to degradation via Fenton-induced processes were observed. Findings on degradation kinetics of diclofenac provide an instructive understanding of decomposition rates for recalcitrant pharmaceuticals with respect to their chemical structure. Accordingly, conclusions can be drawn for further development and a first risk assessment of the method which can also be applied towards other AOPs that rely on the generation of hydroxyl radicals. Copyright © 2017 Elsevier B.V. All rights reserved.

Unusual pi-donating effects of pi-accepting substituents on the stabilities of benzylic cations: a theoretical study.

PubMed

Kim, Chang Kon; Han, In Suk; Ryu, Wang Sun; Lee, Hai Whang; Lee, Bon-Su; Kim, Chan Kyung

2006-02-23

The pi-donating effects of pi-accepting X-substituents in substituted benzylic cations, X-C(6)H(5)-CHR(+) where R = CF(3), H and OCH(3), and X = p-NH(2), p-OCH(3), p-CH(3), H, p-F, p-Cl, p-CHO, m-CN, p-CN, m-NO(2) or p-NO(2), have been studied theoretically by using isodesmic hydride transfer reactions at various levels of theory. It might be difficult to determine the pi-donating effects of pi-acceptors using the simple Hammett-type linear equation, because it is not sensitive enough to include small pi-donating effects. Therefore, this effect was estimated using the NBO deletion energy (DeltaE(D)) of the second-order charge-transfer interaction (DeltaE(ct)) between the pi-orbitals (or lone pair orbitals) of the X-substituent and the pi-orbitals of phenyl ring. The extents of pi-donating effects increased in the order X = p-NO(2) < p-CHO < p-CN < p-Cl for both neutral and cationic species, and these effects were found to be more important for para- than for meta-substituents. Moreover, this could represent a general trend for pi-donation by pi-acceptors. On the other hand, the effects of R-substituents on this pi-donating effect were found to be in the order R = OCH(3) < H congruent with CF(3), as predicted by natural resonance theory (NRT) analyses.

Optimization of the NO photooxidation and the role of relative humidity.

PubMed

Ângelo, Joana; Magalhães, Pedro; Andrade, Luísa; Madeira, Luís M; Mendes, Adélio

2018-05-11

Photocatalysis was recognised as a suitable process for the photoabatement of atmospheric pollutants. The photooxidation mechanism on TiO 2 has been widely studied. However, recent studies demonstrated that the very often-assumed photooxidation intermediated by the hydroxyl radical cannot explain all the experimental observations. Indeed, this study contributes for a new understanding of NO photooxidation. First, the adsorption equilibrium isotherms of NO, NO 2 and H 2 O on the photocatalyst, Aeroxide ® P25 from Evonik Industries, were obtained. Also, the concentration of hydroxyl radicals was determined by photoluminescence. A comprehensive design of experiments was then followed; NO conversion and selectivity were obtained as a function of the relative humidity, irradiance, NO inlet concentration and residence time, following a response surface methodology (RSM). These results were then used to discuss the photooxidation mechanism of NO. Copyright © 2018 Elsevier Ltd. All rights reserved.

Spectroscopic investigation on the mechanism of formation of molecular complexes of albendazole and trimethoprim with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

NASA Astrophysics Data System (ADS)

Ganesh, K.; Balraj, C.; Satheshkumar, A.; Elango, K. P.

2012-06-01

UV-vis, 1H NMR, FT-IR, mass and fluorescence spectral techniques were employed to investigate the mechanism of interaction of albendazole and trimethoprim with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and to characterize the reaction products. The interaction of DDQ with trimethoprim (TMP) and albenadazole (ALB) were found to proceed through the formation of donor-acceptor complex, containing DDQ radical anion and its conversion to the product. Fluorescence quenching studies indicated that the interaction between the donors and the acceptor are spontaneous and the interaction of TMP-DDQ (binding constant = 2.9 × 105) is found to be stronger than that the ALB-DDQ (binding constant = 3 × 103) system. Also, the binding constant increased with an increase in polarity of the medium indicating the involvement of radical anion as intermediate.

Volatile organic compound conversion by ozone, hydroxyl radicals, and nitrate radicals in residential indoor air: Magnitudes and impacts of oxidant sources

NASA Astrophysics Data System (ADS)

Waring, Michael S.; Wells, J. Raymond

2015-04-01

Indoor chemistry may be initiated by reactions of ozone (O3), the hydroxyl radical (OH), or the nitrate radical (NO3) with volatile organic compounds (VOC). The principal indoor source of O3 is air exchange, while OH and NO3 formation are considered as primarily from O3 reactions with alkenes and nitrogen dioxide (NO2), respectively. Herein, we used time-averaged models for residences to predict O3, OH, and NO3 concentrations and their impacts on conversion of typical residential VOC profiles, within a Monte Carlo framework that varied inputs probabilistically. We accounted for established oxidant sources, as well as explored the importance of two newly realized indoor sources: (i) the photolysis of nitrous acid (HONO) indoors to generate OH and (ii) the reaction of stabilized Criegee intermediates (SCI) with NO2 to generate NO3. We found total VOC conversion to be dominated by reactions both with O3, which almost solely reacted with D-limonene, and also with OH, which reacted with D-limonene, other terpenes, alcohols, aldehydes, and aromatics. VOC oxidation rates increased with air exchange, outdoor O3, NO2 and D-limonene sources, and indoor photolysis rates; and they decreased with O3 deposition and nitric oxide (NO) sources. Photolysis was a strong OH formation mechanism for high NO, NO2, and HONO settings, but SCI/NO2 reactions weakly generated NO3 except for only a few cases.

Thermodynamic and electron paramagnetic resonance characterization of flavin in succinate dehydrogenase.

PubMed

Ohnishi, T; King, T E; Salerno, J C; Blum, H; Bowyer, J R; Maida, T

1981-06-10

Thermodynamic parameters of succinate dehydrogenase flavin were determined potentiometrically from the analysis of free radical signal levels as a function of the oxidation-reduction potential. Midpoint redox potentials of consecutive 1-electron transfer steps are -127 and -31 mV at pH 7.0. This corresponds to a stability constant of intermediate stability, 2.5 x 10(-2), which suggests flavin itself may be a converter from n = 2 to n = 1 electron transfer steps. The pK values of the free radical (FlH . in equilibrium Fl . -) and the fully reduced form (FlH2 in equilibrium FlH-) were estimated as 8.0 +/- 0.2 and 7.7 +/- 0.2, respectively. Succinate dehydrogenase flavosemiquinone elicits an EPR spectrum at g = 2.00 with a peak to peak width of 1.2 mT even in the protonated form, suggesting the delocalization in the unpaired electron density. A close proximity of succinate dehydrogenase flavin and iron-sulfur cluster S-1 was demonstrated based on the enhancement of flavin spin relaxation by Center S-1.

Regulation of the nitric oxide oxidase activity of myeloperoxidase by pharmacological agents.

PubMed

Maiocchi, Sophie L; Morris, Jonathan C; Rees, Martin D; Thomas, Shane R

2017-07-01

The leukocyte-derived heme enzyme myeloperoxidase (MPO) is released extracellularly during inflammation and impairs nitric oxide (NO) bioavailability by directly oxidizing NO or producing NO-consuming substrate radicals. Here, structurally diverse pharmacological agents with activities as MPO substrates/inhibitors or antioxidants were screened for their effects on MPO NO oxidase activity in human plasma and physiological model systems containing endogenous MPO substrates/antioxidants (tyrosine, urate, ascorbate). Hydrazide-based irreversible/reversible MPO inhibitors (4-ABAH, isoniazid) or the sickle cell anaemia drug, hydroxyurea, all promoted MPO NO oxidase activity. This involved the capacity of NO to antagonize MPO inhibition by hydrazide-derived radicals and/or the ability of drug-derived radicals to stimulate MPO turnover thereby increasing NO consumption by MPO redox intermediates or NO-consuming radicals. In contrast, the mechanism-based irreversible MPO inhibitor 2-thioxanthine, potently inhibited MPO turnover and NO consumption. Although the phenolics acetaminophen and resveratrol initially increased MPO turnover and NO consumption, they limited the overall extent of NO loss by rapidly depleting H 2 O 2 and promoting the formation of ascorbyl radicals, which inefficiently consume NO. The vitamin E analogue trolox inhibited MPO NO oxidase activity in ascorbate-depleted fluids by scavenging NO-consuming tyrosyl and urate radicals. Tempol and related nitroxides decreased NO consumption in ascorbate-replete fluids by scavenging MPO-derived ascorbyl radicals. Indoles or apocynin yielded marginal effects. Kinetic analyses rationalized differences in drug activities and identified criteria for the improved inhibition of MPO NO oxidase activity. This study reveals that widely used agents have important implications for MPO NO oxidase activity under physiological conditions, highlighting new pharmacological strategies for preserving NO bioavailability during inflammation. Copyright © 2017 Elsevier Inc. All rights reserved.

Phenoxide and alkoxide complexes of Mg, Al and Zn, and their use for the ring-opening polymerization of ℇ-caprolactone with initiators of different natures.

PubMed

Minyaev, Mikhail E; Nifant'ev, Ilya E; Shlyakhtin, Andrey V; Ivchenko, Pavel V; Lyssenko, Konstantin A

2018-05-01

A new packing polymorph of bis(2,6-di-tert-butyl-4-methylphenolato-κO)bis(tetrahydrofuran-κO)magnesium, [Mg(C 15 H 23 O) 2 (C 4 H 8 O) 2 ] or Mg(BHT) 2 (THF) 2 , (BHT is the 2,6-di-tert-butyl-4-methylphenoxide anion and THF is tetrahydrofuran), (1), has the same space group (P2 1 ) as the previously reported modification [Nifant'ev et al. (2017d). Dalton Trans. 46, 12132-12146], but contains three crystallographically independent molecules instead of one. The structure of (1) exhibits rotational disorder of the tert-butyl groups and positional disorder of a THF ligand. The complex of bis(2,6-di-tert-butyl-4-methylphenolato-κO)bis(μ 2 -ethyl glycolato-κ 2 O,O':κO)dimethyldialuminium, [Al 2 (CH 3 ) 2 (C 4 H 7 O 3 ) 2 (C 15 H 23 O) 2 ] or [(BHT)AlMe(OCH 2 COOEt)] 2 , (2), is a dimer located on an inversion centre and has an Al 2 O 2 rhomboid core. The 2-ethoxy-2-oxoethanolate ligand (OCH 2 COOEt) displays a μ 2 -κ 2 O,O':κO semi-bridging coordination mode, forming a five-membered heteronuclear Al-O-C-C-O ring. The same ligand exhibits positional disorder of the terminal methyl group. The redetermined structure of the heptanuclear complex octakis(μ 3 -benzyloxo-κO:κO:κO)hexaethylheptazinc, [Zn 7 (C 2 H 5 ) 6 (C 7 H 7 O) 8 ] or [Zn 7 (OCH 2 Ph) 8 Et 6 ], (3), possesses a bicubic Zn 7 O 8 core located at an inversion centre and demonstrates positional disorder of one crystallographically independent phenyl group. Cambridge Structural Database surveys are given for complexes structurally analogous to (2) and (3). Complexes (2) and (3), as well as derivatives of (1), are of interest as catalysts for the ring-opening polymerization of ℇ-caprolactone, and polymerization results are reported.

Platinum anti-cancer drugs: Free radical mechanism of Pt-DNA adduct formation and anti-neoplastic effect.

PubMed

Fong, Clifford W

2016-06-01

The literature on the anti-neoplastic effects of Pt drugs provides substantial evidence that free radical may be involved in the formation of Pt-DNA adducts and other cytotoxic effects. The conditions specific to cancerous tumours are more conducive to free radical mechanisms than the commonly accepted hydrolysis nucleophilic-electrophilic mechanism of Pt-DNA adduct formation. Molecular orbital studies of the adiabatic attachment of hydrated electrons to Pt drugs reveal that there is a significant lengthening of the Pt-X bond (where X is Cl, O in cisplatin, carboplatin and some pyrophosphate-Pt drugs but not oxaliplatin) in the anion radical species. This observation is consistent with a dissociative electron transfer (DET) mechanism for the formation of Pt-DNA adducts. A DET reaction mechanism is proposed for the reaction of Pt drugs with guanine which involves a quasi-inner sphere 2 electron transfer process involving a transient intermediate 5 co-ordinated activated anion radical species {R2Pt---Cl(G)(Cl)•}*(-) (where R is an ammine group, and G is guanine) and the complex has an elongated Pt---Cl (or Pt---O) bond. A DET mechanism is also proposed when Pt drugs are activated by reaction with free radicals such as HO•, CO3•(-), O2•(-) but do not react with DNA bases to form adducts, but form Pt-protein adducts with proteins such ezrin, FAS, DR5, TNFR1 etc. The DET mechanism may not occur with oxaliplatin. Copyright © 2016 Elsevier Inc. All rights reserved.

Role of reactive oxygen intermediates in the interferon-mediated depression of hepatic drug metabolism and protective effect of N-acetylcysteine in mice.

PubMed

Ghezzi, P; Bianchi, M; Gianera, L; Landolfo, S; Salmona, M

1985-08-01

Interferon (IFN) and IFN inducers are known to depress hepatic microsomal cytochrome P-450 levels, and the liver toxicity of IFN was reported to be lethal in newborn mice. We have observed that administration to mice of IFN and IFN inducers caused a marked increase in liver xanthine oxidase activity. Because this enzyme is well known to produce reactive oxygen intermediates and cytochrome P-450 was reported to be sensitive to the oxidative damage, we have tested the hypothesis that a free radical mechanism could mediate the depression of cytochrome P-450 levels by IFN. Administration to mice of the IFN inducer polyinosinic-polycytidylic acid (2 mg/kg i.p.) caused a 29 to 52% decrease in liver cytochrome P-450. Concomitant p.o. administration of the free radical scavenger, N-acetylcysteine (as a 2.5% solution in drinking water), or the xanthine oxidase inhibitor, allopurinol (100 mg/kg), protected against the IFN-mediated depression of P-450 kg), protected against the IFN-mediated depression of P-450 levels. The results suggest that an increased endogenous generation of free radicals, possibly due to the induction of xanthine oxidase, is implicated in the IFN-mediated depression of liver drug metabolism. The relevance of these data also extends to cases in which this side effect is observed in pathological situations (e.g., viral diseases and administration of vaccines) associated with an induction of IFN.

A new mechanism-based inhibitor of photosynthetic water oxidation: Acetone hydrazone. I. Equilibrium reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tso, J.; Dismukes, G.C.; Petrouleas, V.

1990-08-21

The process of photosynthetic water oxidation has been investigated by using a new type of water oxidation inhibitor, the alkyl hydrazones. Acetone hydrazone (AceH), (CH{sub 3}){sub 2}CNNH{sub 2}, inhibits water oxidation by a mechanism that is analogous to that of NH{sub 2}OH. This involves binding to the water-oxidizing complex (WOC), followed by photoreversible reduction of manganese (loss of the S{sub 1} {yields} S{sub 2} reaction). At higher AceH concentrations the S{sub 1} state is reduced in the dark and Mn is released, albeit to a lesser extent than with NH{sup 2}OH. Following extraction of Mn, AceH is able to donatemore » electrons rapidly to the reaction center tyrosine radical Z{sup +} ({sup 161}Tyr-D{sub 1} protein), more slowly to a reaction center radical C{sup +}, and not at all to the dark-stable tyrosine radical D{sup +} ({sup 160}Tyr-D{sub 2} protein) which must be sequestered in an inaccessible site. Unexpectedly, Cl{sup {minus}} was found not to interfere or compete with AceH for binding to the WOC in the S{sub 1} state, in contrast to the reported rate of binding of N,N-dimethylhydroxylamine (CH{sub 3}){sub 2}NOH. The authors interpret the latter behavior as due to ionic screening of the thylakoid membrane, rather than a specific Cl site involved in water oxidation. AceH appears not to bind to the acceptor side of PSII as evidenced by normal EPR signals both for Q{sub A}{sup {minus}}Fe(II), the primary electron acceptor, and for the oxidized Fe(III) acceptor (Q{sub 400} species), in contrast to that observed with NH{sub 2}OH. AceH can be oxidized in solution by a variety of oxidants including Mn(III) to form a reactive diazo intermediate, (CH{sub 3}){sub 2}CNN, which reacts with carbonyl compounds. Oxidation to this diazo intermediate is postulated to be responsible for inhibition of the WOC.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Xianhui; Walker, Devin; Maiti, Debtanu

Cylindrical NiMg/Ce 0.6Zr 0.4O 2 pellet catalysts with two different sizes (large: radius = 1.59 mm; and small: radius = 0.75 mm) were produced by extrusion of powder catalysts. The small catalyst pellets had a higher specific surface area, pore volume, average pore size, radial crush strength, and resistance to breakage than the large ones. Tri-reforming tests with surrogate biogas were conducted at 3 bar and 882 °C, with the feed molar ratios of CH 4: CO 2: air fixed at 1.0: 0.7: 0.95 and the H 2O/CH 4 molar feed ratio (0.35 – 1.16) varied. The small catalyst pelletsmore » exhibited lower internal mass transfer resistance and higher coking resistance, compared to the large ones. CO 2 conversion decreased and H 2/CO molar ratio increased with the increase of H 2O/CH 4 molar feed ratio, which are consistent with the trends predicted by thermodynamic equilibrium calculations. Finally, the results indicate that the NiMg/Ce 0.6Zr 0.4O 2 catalyst pellets are promising for commercial scale applications.« less

Exploring the potential for spatio-temporal mapping of VOC-OH reactions from column measurements of CH2O and NO2

NASA Astrophysics Data System (ADS)

Valin, L. C.; Fiore, A. M.; Chance, K.; Nowlan, C. R.; Gonzalez Abad, G.; Browne, E. C.

2014-12-01

Reactions of OH with volatile organic compounds (VOC) such as CH4 and isoprene produce formaldehyde (CH2O). The concentration of OH and the chemistry of peroxy radicals, a reactive intermediate of VOC + OH reactions, depend strongly on the concentration of NOx. Here, we investigate the influence of NOx on the formation of CH2O in an isoprene-rich atmosphere (Martin Lake Power Plant, NE Texas) and in a "background" atmosphere (Navajo Power Plant, N Arizona) using conceptual models and the WRF-Chem regional chemistry-transport model alongside satellite-based (Aura-OMI) and flight-based (ARCTAS) measurements. In the conceptual model, the enhancement of CH2O in an NO2 plume is large and depends on the magnitude of the OH enhancement, the lifetime of the parent VOC, the concentration of intermediate oxidation products, and the impact of NOx on the branching ratios of peroxy radicals. Preliminary analysis of WRF-Chem results supports these findings. For a large point source of NOx in a low NOx-background, the enhancement of the CH2O concentration in the NOx plume is more than two times that of the surrounding region in both the isoprene-rich and the "background" WRF-Chem simulations. Furthermore, the spatial correlation of OH and CH2O in these simulated plumes suggests that simultaneous measurement of CH2O and NO2 offers the potential to better constrain the processes affecting the reaction of VOC with OH, and thus the factors controlling O3 production and the NOx lifetime. The precision of UV/Visible spectrometers planned for future geostationary missions, such as TEMPO, suggest that the routine measurement of these relationships will be possible.

Exploring the chemical kinetics of partially oxidized intermediates by combining experiments, theory, and kinetic modeling.

PubMed

Hoyermann, Karlheinz; Mauß, Fabian; Olzmann, Matthias; Welz, Oliver; Zeuch, Thomas

2017-07-19

Partially oxidized intermediates play a central role in combustion and atmospheric chemistry. In this perspective, we focus on the chemical kinetics of alkoxy radicals, peroxy radicals, and Criegee intermediates, which are key species in both combustion and atmospheric environments. These reactive intermediates feature a broad spectrum of chemical diversity. Their reactivity is central to our understanding of how volatile organic compounds are degraded in the atmosphere and converted into secondary organic aerosol. Moreover, they sensitively determine ignition timing in internal combustion engines. The intention of this perspective article is to provide the reader with information about the general mechanisms of reactions initiated by addition of atomic and molecular oxygen to alkyl radicals and ozone to alkenes. We will focus on critical branching points in the subsequent reaction mechanisms and discuss them from a consistent point of view. As a first example of our integrated approach, we will show how experiment, theory, and kinetic modeling have been successfully combined in the first infrared detection of Criegee intermediates during the gas phase ozonolysis. As a second example, we will examine the ignition timing of n-heptane/air mixtures at low and intermediate temperatures. Here, we present a reduced, fuel size independent kinetic model of the complex chemistry initiated by peroxy radicals that has been successfully applied to simulate standard n-heptane combustion experiments.

cis-Stilbene and (1 alpha,2 beta,3 alpha)-(2-ethenyl-3-methoxycyclopropyl)benzene as mechanistic probes in the Mn(III)(salen)-catalyzed epoxidation: influence of the oxygen source and the counterion on the diastereoselectivity of the competitive concerted and radical-type oxygen transfer.

PubMed

Adam, Waldemar; Roschmann, Konrad J; Saha-Möller, Chantu R; Seebach, Dieter

2002-05-08

cis-Stilbene (1) has been epoxidized by a set of diverse oxygen donors [OxD], catalyzed by the Mn(III)(salen)X complexes 3 (X = Cl, PF(6)), to afford a mixture of cis- and trans-epoxides 2. The cis/trans ratios range from 29:71 (extensive isomerization) to 92:8, which depends both on the oxygen source [OxD] and on the counterion X of the catalyst. When (1 alpha,2 beta,3 alpha)-(2-ethenyl-3-methoxycyclopropyl)-benzene (4) is used as substrate, a mechanistic probe which differentiates between radical and cationic intermediates, no cationic ring-opening products are found in this epoxidation reaction; thus, isomerized epoxide product arises from intermediary radicals. The dependence of the diastereoselectivity on the oxygen source is rationalized in terms of a bifurcation step in the catalytic cycle, in which concerted Lewis-acid-activated oxygen transfer competes with stepwise epoxidation by the established Mn(V)(oxo) species. The experimental counterion effect is attributed to the computationally assessed ligand-dependent reaction profiles and stereoselectivities of the singlet, triplet, and quintet spin states available to the manganese species.

Raman and infrared spectroscopy of carbohydrates: A review

NASA Astrophysics Data System (ADS)

Wiercigroch, Ewelina; Szafraniec, Ewelina; Czamara, Krzysztof; Pacia, Marta Z.; Majzner, Katarzyna; Kochan, Kamila; Kaczor, Agnieszka; Baranska, Malgorzata; Malek, Kamilla

2017-10-01

Carbohydrates are widespread and naturally occurring compounds, and essential constituents for living organisms. They are quite often reported when biological systems are studied and their role is discussed. However surprisingly, up till now there is no database collecting vibrational spectra of carbohydrates and their assignment, as has been done already for other biomolecules. So, this paper serves as a comprehensive review, where for selected 14 carbohydrates in the solid state both FT-Raman and ATR FT-IR spectra were collected and assigned. Carbohydrates can be divided into four chemical groups and in the same way is organized this review. First, the smallest molecules are discussed, i.e. monosaccharides (D-(-)-ribose, 2-deoxy-D-ribose, L-(-)-arabinose, D-(+)-xylose, D-(+)-glucose, D-(+)-galactose and D-(-)-fructose) and disaccharides (D-(+)-sucrose, D-(+)-maltose and D-(+)-lactose), and then more complex ones, i.e. trisaccharides (D-(+)-raffinose) and polysaccharides (amylopectin, amylose, glycogen). Both Raman and IR spectra were collected in the whole spectral range and discussed looking at the specific regions, i.e. region V (3600-3050 cm- 1), IV (3050-2800 cm- 1) and II (1200-800 cm- 1) assigned to the stretching vibrations of the OH, CH/CH2 and C-O/C-C groups, respectively, and region III (1500-1200 cm- 1) and I (800-100 cm- 1) dominated by deformational modes of the CH/CH2 and CCO groups, respectively. In spite of the fact that vibrational spectra of saccharides are significantly less specific than spectra of other biomolecules (e.g. lipids or proteins), marker bands of the studied molecules can be identified and correlated with their structure.

Perioperative and mid-term oncologic outcomes of robotic assisted radical cystectomy with totally intracorporeal neobladder: Results of a propensity score matched comparison with open cohort from a single-centre series.

PubMed

Simone, Giuseppe; Tuderti, Gabriele; Misuraca, Leonardo; Anceschi, Umberto; Ferriero, Mariaconsiglia; Minisola, Francesco; Guaglianone, Salvatore; Gallucci, Michele

2018-04-17

In this study, we compared perioperative and oncologic outcomes of patients treated with either open or robot-assisted radical cystectomy and intracorporeal neobladder at a tertiary care center. The institutional prospective bladder cancer database was queried for "cystectomy with curative intent" and "neobladder". All patients underwent robot-assisted radical cystectomy and intracorporeal neobladder or open radical cystectomy and orthotopic neobladder for high-grade non-muscle invasive bladder cancer or muscle invasive bladder cancer with a follow-up length ≥2 years were included. A 1:1 propensity score matching analysis was used. Kaplan-Meier method was performed to compare oncologic outcomes of selected cohorts. Survival rates were computed at 1,2,3 and 4 years after surgery and the log rank test was applied to assess statistical significance between the matched groups. Overall, 363 patients (299 open and 64 robotic) were included. Open radical cystectomy patients were more frequently male (p = 0.08), with higher pT stages (p = 0.003), lower incidence of urothelial histologies (p = 0.05) and lesser adoption of neoadjuvant chemotherapy (<0.001). After applying the propensity score matching, 64 robot-assisted radical cystectomy patients were matched with 46 open radical cystectomy cases (all p ≥ 0.22). Open cohort showed a higher rate of perioperative overall complications (91.3% vs 42.2%, p 0.001). At Kaplan-Meier analysis robotic and open cohorts displayed comparable disease-free survival (log-rank p = 0.746), cancer-specific survival (p = 0.753) and overall-survival rates (p = 0.909). Robot-assisted radical cystectomy and intracorporeal neobladder provides comparable oncologic outcomes of open radical cystectomy and orthotopic neobladder at intermediate term survival analysis. Copyright © 2018 Elsevier Ltd, BASO ~ The Association for Cancer Surgery, and the European Society of Surgical Oncology. All rights reserved.

Role of effluent organic matter in the photochemical degradation of compounds of wastewater origin.

PubMed

Bodhipaksha, Laleen C; Sharpless, Charles M; Chin, Yu-Ping; MacKay, Allison A

2017-03-01

The photoreactivity of treated wastewater effluent organic matter differs from that of natural organic matter, and the indirect phototransformation rates of micropollutants originating in wastewater are expected to depend on the fractional contribution of wastewater to total stream flow. Photodegradation rates of four common compounds of wastewater origin (sulfamethoxazole, sulfadimethoxine, cimetidine and caffeine) were measured in river water, treated municipal wastewater effluent and mixtures of both to simulate various effluent-stream water mixing conditions that could occur in environmental systems. Compounds were chosen for their unique photodegradation pathways with the photochemically produced reactive intermediates, triplet-state excited organic matter ( 3 OM*), singlet oxygen ( 1 O 2 ), and hydroxyl radicals (OH). For all compounds, higher rates of photodegradation were observed in effluent relative to upstream river water. Sulfamethoxazole degraded primarily via direct photolysis, with some contribution from OH and possibly from carbonate radicals and other unidentified reactive intermediates in effluent-containing samples. Sulfadimethoxine also degraded mainly by direct photolysis, and natural organic matter appeared to inhibit this process to a greater extent than predicted by light screening. In the presence of effluent organic matter, sulfadimethoxine showed additional reactions with OH and 1 O 2 . In all water samples, cimetidine degraded by reaction with 1 O 2 (>95%) and caffeine by reaction with OH (>95%). In river water mixtures, photodegradation rate constants for all compounds increased with increasing fractions of effluent. A conservative mixing model was able to predict reaction rate constants in the case of hydroxyl radical reactions, but it overestimated rate constants in the case of 3 OM* and 1 O 2 pathways. Finally, compound degradation rate constants normalized to the rate of light absorption by water correlated with E 2 /E 3 ratios (sample absorbance at 254 nm divided by sample absorbance at 365 nm), suggesting that organic matter optical properties may hold promise to predict indirect compound photodegradation rates for various effluent mixing ratios. Copyright © 2016 Elsevier Ltd. All rights reserved.