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Sample records for aromatic radical anions

  1. Direct determination of rate constants for coupling between aromatic radical anions and alkyl and benzyl radicals by laser-flash photolysis

    DEFF Research Database (Denmark)

    Lund, T.; Christensen, P.; Wilbrandt, Robert Walter

    2003-01-01

    Coupling rates between the radicals methyl, n-, sec-, tert-butyl and benzyl (R-.) and the aromatic radical anions of 1,4-dicyanonaphthalene, 9,10-dicyanoanthracene and fluorenone (A(-.)) have been obtained using a new laser-flash photolysis method. The radicals R-. and the radical anions A(-.) were...... generated by a photoinduced electron transfer reaction between the aromatic compound A and the alkyl or benzyl triphenylborate anion RB(Ph)(3)(-). For the first time the rate constants of the coupling reaction between methyl and benzyl radicals with aromatic radical anions have been obtained. For all...... of the radicals and the structure and standard potentials of the aromatic radical anions....

  2. Electron affinities of aromatic hydrocarbons and disproportionation of their radical-anions

    Energy Technology Data Exchange (ETDEWEB)

    Szwarc, M.

    1986-09-01

    Electron affinities of aromatic hydrocarbons measured in the gas-phase and in solutions are compared. The experimental methods used for their determination are briefly reviewed. The reduction yields the respective radical-anions. Radical-anions may undergo disproportionation, a reaction described by the scheme: 2A/sup -/ . , Cat/sup =/ in equilibrium A + A/sup 2-/, 2 Cat/sup +/, K/sub dipr/. The disproportionation constant, K/sub dipr/, is greatly affected by the nature of aromatic hydrocarbon, of the cation, and of the solvent. Variation of each of these factors is illustrated. Variation of the cation and solvent results in changes of the disproportionation constant as large as factors of 10/sup 25/. The causes of these variations are rationalized and discussed in terms of the respective ..delta..H and ..delta..S. Kinetics of disproportionation was investigated by flash-photolysis techniques. The experimental approach is described. The peculiarities of Ba salts deserved some discussion to clarify the nature of those salts. The effect of disproportionation on reactions of radical-anions are described: namely on cis-trans isomerization of stilbenes, on protonation of radical-anions of anthracene an perylene, on dissociation of radical anions of aromatic derivatives ethane, etc.

  3. Calculation of electron affinities of polycyclic aromatic hydrocarbons and solvation energies of their radical anion.

    Science.gov (United States)

    Betowski, Leon D; Enlow, Mark; Riddick, Lee; Aue, Donald H

    2006-11-30

    Electron affinities (EAs) and free energies for electron attachment (DeltaGo(a,298K)) have been directly calculated for 45 polynuclear aromatic hydrocarbons (PAHs) and related molecules by a variety of theoretical methods, with standard regression errors of about 0.07 eV (mean unsigned error = 0.05 eV) at the B3LYP/6-31 + G(d,p) level and larger errors with HF or MP2 methods or using Koopmans' Theorem. Comparison of gas-phase free energies with solution-phase reduction potentials provides a measure of solvation energy differences between the radical anion and neutral PAH. A simple Born-charging model approximates the solvation effects on the radical anions, leading to a good correlation with experimental solvation energy differences. This is used to estimate unknown or questionable EAs from reduction potentials. Two independent methods are used to predict DeltaGo(a,298K) values: (1) based upon DFT methods, or (2) based upon reduction potentials and the Born model. They suggest reassignments or a resolution of conflicting experimental EAs for nearly one-half (17 of 38) of the PAH molecules for which experimental EAs have been reported. For the antiaromatic molecules, 1,3,5-tri-tert-butylpentalene and the dithia-substituted cyclobutadiene 1, the reduction potentials lead to estimated EAs close to those expected from DFT calculations and provide a basis for the prediction of the EAs and reduction potentials of pentalene and cyclobutadiene. The Born model has been used to relate the electrostatic solvation energies of PAH and hydrocarbon radical anions, and spherical halide anions, alkali metal cations, and ammonium ions to effective ionic radii from DFT electron-density envelopes. The Born model used for PAHs has been successfully extended here to quantitatively explain the solvation energy of the C60 radical anion.

  4. Long-range intramolecular electron transfer in aromatic radical anions and binuclear transition metal complexes

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    1981-01-01

    Intramolecular electron transfer (ET) over distances up to about 10 Å between states in which the electron is localized on donor and acceptor groups by interaction with molecular or external solvent nuclear motion occurs, in particular, in two classes of systems. The excess electron in anionic...... in the intermediate states. We have furthermore provided criteria for the distinction between direct ET, ET through high-energy (superexchange), and low-energy (''radical'' intermediate mechanism) intermediate states on the basis of experimental rate data and illustrated this with data for organic radical anions...

  5. Cyclization by intramolecular carbolithiation of alkyl- and vinyllithiums prepared by the action of aromatic radical anions on phenyl thioethers. High stereoselectivity in the cyclization accelerated by an allylic lithium oxyanion.

    Science.gov (United States)

    Deng, Kai; Bensari-Bouguerra, Ahlem; Whetstone, Joseph; Cohen, Theodore

    2006-03-17

    The reductive lithiation of alkyl and vinyl phenyl thioethers by aromatic radical anions is shown to be the most general method yet known for preparing organolithiums capable of intramolecular carbometalation of unactivated alkenes to produce five-membered rings and in one case a four-membered ring (in a far higher yield than known cases). The relative rates of cyclization for alkyllithiums are secondary > tertiary > primary, and the yields are very high. In the secondary case, the stereoselectivity is extremely high, producing a cyclopentylmethyllithium with a trans-2-alkyl substituent. A remarkable finding is that for all of the organolithiums a lithium oxyanionic group in the proximal allylic position to the alkene greatly accelerates the cyclization and leads almost exclusively to a trans relationship between the CH(2)Li group and the OLi group, the opposite relationship from that observed in intramolecular carbolithiations by allyllithiums. A mechanistic rationale for this divergence is discussed. One of the two types of proximal homoallylic lithium oxyanions exerts an analogous effect. An intriguing limitation, even occurring with the highly reactive secondary organolithium and in the presence of an allylic oxyanionic group, is the failure of intramolecular carbolithiation when a methyl group is at the terminus of the alkene.

  6. Anion photoelectron spectroscopy of radicals and clusters

    Energy Technology Data Exchange (ETDEWEB)

    Travis, Taylor R. [Univ. of California, Berkeley, CA (United States)

    1999-12-01

    Anion photoelectron spectroscopy is used to study free radicals and clusters. The low-lying 2Σ and 2π states of C2nH (n = 1--4) have been studied. The anion photoelectron spectra yielded electron affinities, term values, and vibrational frequencies for these combustion and astrophysically relevant species. Photoelectron angular distributions allowed the author to correctly assign the electronic symmetry of the ground and first excited states and to assess the degree of vibronic coupling in C2H and C4H. Other radicals studied include NCN and I3. The author was able to observe the low-lying singlet and triplet states of NCN for the first time. Measurement of the electron affinity of I3 revealed that it has a bound ground state and attachment of an argon atom to this moiety enabled him to resolve the symmetric stretching progression.

  7. Aromatic-radical oxidation chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Glassman, I.; Brezinsky, K. [Princeton Univ., NJ (United States)

    1993-12-01

    The research effort has focussed on discovering an explanation for the anomalously high CO{sub 2} concentrations observed early in the reaction sequence of the oxidation of cyclopentadiene. To explain this observation, a number of plausible mechanisms have been developed which now await experimental verification. One experimental technique for verifying mechanisms is to probe the reacting system by perturbing the radical concentrations. Two forms of chemical perturbation of the oxidation of cyclopentadiene were begun during this past year--the addition of NO{sub 2} and CO to the reacting mixture.

  8. Protonation Reaction of Benzonitrile Radical Anion and Absorption of Product

    DEFF Research Database (Denmark)

    Holcman, Jerzy; Sehested, Knud

    1975-01-01

    The rate constant for the protonation of benzonitrile radical anions formed in pulse radiolysis of aqueous benzonitrile solutions is (3.5 ± 0.5)× 1010 dm3 mol–1 s–1. A new 270 nm absorption band is attributed to the protonated benzonitrile anion. The pK of the protonation reaction is determined...

  9. Methylglyoxal as a scavenger for superoxide anion-radical.

    Science.gov (United States)

    Shumaev, K B; Lankin, V Z; Konovalova, G G; Grechnikova, M A; Tikhaze, A K

    2016-07-01

    Methylglyoxal at a concentration of 5 mM caused a significant inhibition of superoxide anion radical (O2 (·-)) comparable to the effect of Tirone. In the process of O2 (·-) generation in the system of egg phosphatidylcholine liposome peroxidation induced by the azo-initiator AIBN, a marked inhibition of chemiluminescence in the presence of 100 mM methylglyoxal was found. At the same time, methylglyoxal did not inhibit free radical peroxidation of low-density lipoprotein particles, which indicates the absence of interaction with methylglyoxal alkoxyl and peroxyl polyenoic lipid radicals. These findings deepen information about the role of methylglyoxal in the regulation of free radical processes.

  10. Inhibitory effects of chitosan on superoxide anion radicals and lipid free radicals

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    With the electron spin resonance (ESR) technique, the inhibitory effects of chitosan on superoxide anion radicals and linoleic acid lipid radicals were found. The inhibitory ratio E for these two kinds of radicals is in proportion to the concentration of chitosan. It was also observed that E for linoleic acid lipid radicals increased with the increase of the degree of deacetylation and decreased with the increase of the molecular weight of chitosan.

  11. Isoprene, sulphoxy radical-anions and acidity

    Directory of Open Access Journals (Sweden)

    K. J. Rudziński

    2008-12-01

    Full Text Available Transformation of isoprene coupled with autoxidation of SIV in aqueous solutions was studied experimentally and by chemical-kinetic modelling over broad range of solution acidities (pH=3–9 to complement the research on aqueous-phase and heterogeneous transformation of isoprene reported recently by many laboratories. Isoprene significantly slowed down the autoxidation in acidic and basic solutions, and accelerated it slightly in neutral solutions. Simultaneously, production of sulphate ions and formation of solution acidity were significantly reduced. Formation of sulphite and sulphate derivatives of isoprene – sulphurous acid mono-(2-methyl-4-oxo-but-2-enyl ester (m/z=162.9, sulphurous acid mono-(4-hydroxy-2-methyl-but-2-enyl ester (m/z=164.9, sulphuric acid mono-(2-methyl-4-oxo-but-2-enyl ester (m/z=178.9, sulphuric acid mono-(4-hydroxy-2-methyl-but-2-enyl ester (m/z=180.9 – was indicated by mass spectroscopic analysis of post-reaction mixtures. The results of experiments were explained by changes in a subtle quantitative balance of three superimposed processes whose rates depended in different manner on the acidity of reacting solutions – the scavenging of sulphoxy radicals by isoprene, the formation of sulphoxy radicals during further reactions of isoprene radicals, and the autoxidation of SIV itself. A chemical mechanism based on this idea was explored numerically to show good agreement with experimental data. Interaction of isoprene with sulphur(IV species and oxygen can possibly result in formation of new organosulphate components of atmospheric aerosols and waters, and influence distribution of reactive sulphur and oxygen species in isoprene-emitting organisms exposed to SIV pollutants.

  12. Repair effect of thymine radical anion by echinocoside using pulse radiolysis

    Institute of Scientific and Technical Information of China (English)

    李雯艳; 郑荣梁; 赵松岭; 姜岳; 林念芸

    1996-01-01

    Repair activities of thymine radical anion by echinocoside, isolated from Pedicularis plicata. were studied using pulse radiolysis technique. The thymine radical anion was produced by the reaction of hydrated electron with thymine. Echinocoside. one of the polyphenols of phenylpropanoid glycoside, was added to the thymine aqueous solution saturated with N2. Kinetic analysis by transient absorption spectrum showed that thymine radical anion was formed at first, and then after several decades of microseconds of pulse radiolysis. the spectrum of thymine radical anion was changed to that of echinocoside radical anion. The evidence indicated that thymine radical anion was repaired through one-electron-transfer between the DNA base radical anion and echinocoside. The rate constant of electron transfer by echinocoside was 1.45× 109 dm3 · mol1 · s 1.

  13. Oxidation of silicon surface with atomic oxygen radical anions

    Institute of Scientific and Technical Information of China (English)

    Wang Lian; Song Chong-Fu; Sun Jian-Qiu; Hou Ying; Li Xiao-Guang; Li Quan-Xin

    2008-01-01

    The surface oxidation of silicon (Si) wafers by atomic oxygen radical anions (O- anions) and the preparation of metal-oxide-semiconductor (MOS) capacitors on the O--oxidized Si substrates have been examined for the first time. The O- anions are generated from a recently developed O- storage-emission material of [Ca24Al28O64]4+.4O- (C12A7-O- for short). After it has been irradiated by an O- anion beam (0.5 μA/cm2) at 300℃ for 1-10 hours, the Si wafer achieves an oxide layer with a thickness ranging from 8 to 32 nm. X-ray photoelectron spectroscopy (XPS) results reveal that the oxide layer is of a mixture of SiO2, Si2O3, and Si2O distributed in different oxidation depths. The features of the MOS capacitor of are investigated by measuring capacitance-voltage (C - V) and current-voltage (Ⅰ - Ⅴ) curves. The oxide charge density is about 6.0×1011 cm-2 derived from the C - V curves. The leakage current density is in the order of 10-6 A/cm2 below 4 MV/cm, obtained from the Ⅰ - Ⅴ curves. The Oanions formed by present method would have potential applications to the oxidation and the surface-modification of materials together with the preparation of semiconductor devices.

  14. Charge transfer from 2-aminopurine radical cation and radical anion to nucleobases: A pulse radiolysis study

    Energy Technology Data Exchange (ETDEWEB)

    Manoj, P. [School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686 560, Kerala (India); Mohan, H. [Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Mittal, J.P. [Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Manoj, V.M. [School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686 560, Kerala (India); Aravindakumar, C.T. [School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686 560, Kerala (India)], E-mail: CT-Aravindakumar@rocketmail.com

    2007-01-08

    Pulse radiolysis study has been carried out to investigate the properties of the radical cation of 2-aminopurine (2AP) and the probable charge transfer from the radical cation and radical anion of 2AP to natural nucleobases in aqueous medium. The radical cation of 2AP was produced by the reaction of sulfate radical anion (SO{sub 4}{sup dot-}). The time resolved absorption spectra obtained by the reaction of SO{sub 4}{sup dot-} with 2AP at neutral pH have two distinct maxima at 380 and 470nm and is assigned to the formation of a neutral radical of the form 2AP-N{sup 2}(-H){sup dot} (k{sub 2}=4.7x10{sup 9}dm{sup 3}mol{sup -1}s{sup -1} at pH 7). This neutral radical is formed from the deprotonation reaction of a very short-lived radical cation of 2AP. The transient absorption spectra recorded at pH 10.2 have two distinct maxima at 400 and 480nm and is assigned to the formation of a nitrogen centered radical (2AP-N(9){sup dot}). As the hole transport from 2AP to guanine is a highly probable process, the reaction of SO{sub 4}{sup dot-} is carried out in the presence of guanosine, adenosine and inosine. The spectrum obtained in the presence of guanosine was significantly different from that in the absence and it showed prominent absorption maxima at 380 and 470nm, and a weak broad maximum centered around 625nm which match well with the reported spectrum of a neutral guanine radical (G(-H){sup dot}). The electron transfer reaction from the radical anion of 2AP to thymine (T), cytidine (Cyd) and uridine (Urd) was also investigated at neutral pH. Among the three pyrimidines, only the transient spectrum in the presence of T gave a significant difference from the spectral features of the electron adduct of 2AP, which showed a prominent absorption maximum at 340nm and this spectrum is similar to the electron adduct spectrum of T. The preferential reduction of thymine by 2AP{sup dot-} and the oxidation of guanosine by 2AP{sup dot+} clearly follow the oxidation

  15. Ammoniated electron as a solvent stabilized multimer radical anion

    CERN Document Server

    Shkrob, I A

    2005-01-01

    The excess electron in liquid ammonia ("ammoniated electron") is commonly viewed as a cavity electron in which the s-type wave function fills the interstitial void between 6-9 ammonia molecules. Herewith an alternative model is examined in which the ammoniated electron is regarded as a solvent stabilized multimer radical anion, as was originally suggested by Symons [Chem. Soc. Rev. 1976, 5, 337]. In this model, most of the excess electron density resides in the frontier orbitals of N atoms in the ammonia molecules forming the solvation cavity; a fraction of this spin density is transferred to the molecules in the second solvation shell. The cavity is formed due to the repulsion between negatively charged solvent molecules. Using density functional theory calculations for small ammonia cluster anions in the gas phase, it is demonstrated that such core anions would quantitatively account for the observed pattern of Knight shifts for 1H and 14N nuclei as observed by NMR spectroscopy and the downshifted stretchin...

  16. Generation of naphthoquinone radical anions by electrospray ionization: solution, gas-phase, and computational chemistry studies.

    Science.gov (United States)

    Vessecchi, Ricardo; Naal, Zeki; Lopes, José N C; Galembeck, Sérgio E; Lopes, Norberto P

    2011-06-02

    Radical anions are present in several chemical processes, and understanding the reactivity of these species may be described by their thermodynamic properties. Over the last years, the formation of radical ions in the gas phase has been an important issue concerning electrospray ionization mass spectrometry studies. In this work, we report on the generation of radical anions of quinonoid compounds (Q) by electrospray ionization mass spectrometry. The balance between radical anion formation and the deprotonated molecule is also analyzed by influence of the experimental parameters (gas-phase acidity, electron affinity, and reduction potential) and solvent system employed. The gas-phase parameters for formation of radical species and deprotonated species were achieved on the basis of computational thermochemistry. The solution effects on the formation of radical anion (Q(•-)) and dianion (Q(2-)) were evaluated on the basis of cyclic voltammetry analysis and the reduction potentials compared with calculated electron affinities. The occurrence of unexpected ions [Q+15](-) was described as being a reaction between the solvent system and the radical anion, Q(•-). The gas-phase chemistry of the electrosprayed radical anions was obtained by collisional-induced dissociation and compared to the relative energy calculations. These results are important for understanding the formation and reactivity of radical anions and to establish their correlation with the reducing properties by electrospray ionization analyses.

  17. Structure and reactivity of the N-acetyl-cysteine radical cation and anion: does radical migration occur?

    NARCIS (Netherlands)

    Osburn, S.; Berden, G.; Oomens, J.; O'Hair, R.A.J.; Ryzhov, V.

    2011-01-01

    The structure and reactivity of the N-acetyl-cysteine radical cation and anion were studied using ion-molecule reactions, infrared multi-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. The radical cation was generated by first nitrosylating the thiol of N-

  18. Structure and Reactivity of the N-Acetyl-Cysteine Radical Cation and Anion: Does Radical Migration Occur?

    NARCIS (Netherlands)

    Osburn, S.; G. Berden,; Oomens, J.; O' Hair, R. A. J.; Ryzhov, V.

    2011-01-01

    The structure and reactivity of the N-acetyl-cysteine radical cation and anion were studied using ion-molecule reactions, infrared multi-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. The radical cation was generated by first nitrosylating the thiol of N-

  19. Activation/driving force relationships for cyclopropylcarbinyl --> homoallyl-type rearrangements of radical anions.

    Science.gov (United States)

    Chahma, M'hamed; Li, Xiangzhong; Phillips, J Paige; Schwartz, Phillip; Brammer, Larry E; Wang, Yonghui; Tanko, James M

    2005-04-21

    By using direct and indirect electrochemical methods, rate constants (ko) for cyclopropane ring opening of radical anions derived from the one-electron reduction of trans-1-benzoyl-2-phenylcyclopropane, trans-1-benzoyl-2-vinylcyclopropane, 2-methylenecyclopropyl phenyl ketone, spiro[anthracene-9,1'-cyclopropan-10-one], 3-cyclopropylcyclohex-2-en-1-one, and 3-(1-methylcyclopropyl)cyclohex-2-en-1-one were determined. Qualitatively, rate constants for ring opening of these (and other cyclopropyl- and cyclobutyl-containing radical anions) can be rationalized on the basis of the thermodynamic stability of the radical anion, the ability of substituents on the cyclopropyl group to stabilize the radical portion of the distonic radical anion, and the stability of the enolate portion of the distonic radical anion. On the basis of this notion, a thermochemical cycle for estimating deltaG(o) for ring opening was presented. For simple cyclopropyl-containing ketyl anions, a reasonable correlation between log(ko) and deltaG(o) was found, and stepwise dissociative electron transfer theory was applied to rationalize the results. Activation energies calculated with density functional theory (UB3LYP/6-31+G*) correlate reasonably well with measured log(ko). The derived log(ko) and deltaG(o) and log(ko) vs E(a) plots provide the basis for a "calibration curve" to predict rate constants for ring opening of radical anions derived from carbonyl compounds, in general.

  20. Inactivation of Bacillus Subtilis by Atomic Oxygen Radical Anion

    Institute of Scientific and Technical Information of China (English)

    LI Longchun; WANG Lian; YU Zhou; LV Xuanzhong; LI Quanxin

    2007-01-01

    UAtomic oxygen radical anion (O- ) is one of the most active oxygen species, and has extremely high oxidation ability toward small-molecules of hydrocarbons. However, to our knowledge, little is known about the effects of O- on cells of micro-organisms. This work showed that O- could quickly react with the Bacillus subtilis cells and seriously damage the cell walls a s well as their other contents, leading to a fast and irreversible inactivation. SEM micrographs revealed that the cell structures were dramatically destroyed by their exposure to O-. The inactivation efficiencies of B. subtilis depend on the O-- intensity, the initial population of cells and the treatment temperature, but not on the pH in the range of our investigation. For a cell concentration of 106 cfu/ml, the number of survived cells dropped from 106 cfu/ml to 103 cfu/ml after about five-minute irradiation by an O- flux in an intensity of 233 nA/cm2 under a dry argon environment (30 ℃, 1 atm, exposed size: 1.8 cm2). The inactivation mechanism of micro-organisms induced by O- is also discussed.

  1. OD ESR detection of the radical anions of cyclic nitrones in liquid solutions

    Science.gov (United States)

    Barlukova, M. M.; Gritsan, N. P.; Bagryansky, V. A.; Starichenko, V. F.; Grigor'ev, I. A.; Molin, Yu. N.

    2005-01-01

    The radical anions of five-membered cyclic nitrone spin traps, 3,3,5,5-tetramethyl-1-pyrroline-1-oxide and 1,2,2,5,5-pentamethyl-3-imidazoline-3-oxide, formed under radiolysis of liquid squalane solutions at 250-268 K, were registered by the method of optically detected ESR, and the hfc constants and g-values of the radical anions were determined. The hfc constants of these radical anions were predicted by DFT calculations and were found to be in quantitative agreement with experiment. It was demonstrated that radical anions of the five-membered cyclic nitrones have non-planar geometry with the spin density localized in the C dbnd N sbnd O fragment.

  2. Membrane Separator for Redox Flow Batteries that Utilize Anion Radical Mediators.

    Energy Technology Data Exchange (ETDEWEB)

    Delnick, Frank M.

    2014-10-01

    A Na + ion conducting polyethylene oxide membrane is developed for an organic electrolyte redox flow battery that utilizes anion radical mediators. To achieve high specific ionic conductivity, tetraethyleneglycol dimethylether (TEGDME) is used as a plasticizer to reduce crystallinity and increase the free volume of the gel film. This membrane is physically and chemically stable in TEGDME electrolyte that contains highly reactive biphenyl anion radical mediators.

  3. Kinetics and mechanism of protection of thymine from sulphate radical anion under anoxic conditions

    Indian Academy of Sciences (India)

    M Sudha Swaraga; M Adinarayana

    2003-04-01

    The rates of photooxidation of thymine in presence of peroxydisulphate (PDS) have been determined by measuring the absorbance of thymine at 264 nm spectrophotometrically. The rates and the quantum yields () of oxidation of thymine by sulphate radical anion have been determined in the presence of different concentrations of caffeic acid. Increase in [caffeic acid] is found to decrease the rate of oxidation of thymine suggesting that caffeic acid acts as an efficient scavenger of SO$^{\\bullet -}_{4}$ and protects thymine from it. Sulphate radical anion competes for thymine as well as for caffeic acid. The rate constant of sulphate radical anion with caffeic acid has been calculated to be 1.24 × 1010 dm3 mol-1 s-1. The quantum yields of photooxidation of thymine have been calculated from the rates of oxidation of thymine and the light intensity absorbed by PDS at 254 nm, the wavelength at which PDS is activated to sulphate radical anion. From the results of experimentally determined quantum yields (exptl) and the quantum yields calculated (cl) assuming caffeic acid acting only as a scavenger of SO$^{\\bullet -}_{4}$ radicals show that exptl values are lower than cl values. The ' values, which are experimentally found quantum yield values at each caffeic acid concentration and corrected for SO$^{\\bullet-}_{4}$ scavenging by caffeic acid, are also found to be greater than exptl values. These observations suggest that the thymine radicals are repaired by caffeic acid in addition to scavenging of sulphate radical anions.

  4. Mechanism of protection of adenosine from sulphate radical anion and repair of adenosine radicals by caffeic acid in aqueous solution

    Indian Academy of Sciences (India)

    M Sudha Swaraga; L Charitha; M Adinarayana

    2005-07-01

    The photooxidation of adenosine in presence of peroxydisulphate (PDS) has been studied by spectrophotometrically measuring the absorbance of adenosine at 260 nm. The rates of oxidation of adenosine by sulphate radical anion have been determined in the presence of different concentrations of caffeic acid. Increase in [caffeic acid] is found to decrease the rate of oxidation of adenosine suggesting that caffeic acid acts as an efficient scavenger of $SO_{4}^{\\bullet-}$ and protects adenosine from it. Sulphate radical anion competes for adenosine as well as for caffeic acid. The quantum yields of photooxidation of adenosine have been calculated from the rates of oxidation of adenosine and the light intensity absorbed by PDS at 254 nm, the wavelength at which PDS is activated to sulphate radical anion. From the results of experimentally determined quantum yields (exptl) and the quantum yields calculated (cal) assuming caffeic acid acting only as a scavenger of $SO_{4}^{\\bullet-}$ show that exptl values are lower than cal values. The ' values, which are experimentally found quantum yield values at each caffeic acid concentration and corrected for $SO_{4}^{\\bullet-}$ scavenging by caffeic acid, are also found to be greater than exptl values. These observations suggest that the transient adenosine radicals are repaired by caffeic acid in addition to scavenging of sulphate radical anions.

  5. Reactions between the (SO·4-) radical and some common anions in atmospheric aqueous droplets

    Institute of Scientific and Technical Information of China (English)

    OUYANG Bin; FANG Hao-jie; ZHU Cheng-zhu; DONG Wen-bo; HOU Hui-qi

    2005-01-01

    The rate constants of reactions between the SO4·- radical and some common anions in atmospheric aqueous droplets e.g. Cl-,NO3-, HSO3- and HCO3- were determined using the laser flash photolysis technique. Absorption spectra of SO4·- and the product radicals were also reported. The chloride ion was evaluated among all the anions to be the most efficient scavenger of SO4·- . The results may supply useful information for a better understanding of the vigorous radical-initiated reactions in atmospheric aqueous droplets such as clouds, rains or fogs.

  6. The strong influence of the solvent on the electron spin resonance spectra of semiquinone radical anions

    DEFF Research Database (Denmark)

    Spanget-Larsen, Jens

    2013-01-01

    The hyperfine constants of the chrysazin radical anion and the anthralin-10-yl radical were studied by UB3LYP Density Functional Theory (DFT) calculations, using the basis sets EPR-II or EPR-III and representing the influence of the solvent by the Isodensity Polarizable Continuum Model (IPCM......). The proton hyperfine constants predicted for the chrysazin semiquinone radical anion were highly sensitive to the assumed dielectric constant ε of the solvent continuum, inverting the relative magnitudes of the hyperfine constants and thereby leading to agreement with the observed data published by Stegmann...

  7. Screening of radical scavenging activity of some medicinal and aromatic plant extracts

    NARCIS (Netherlands)

    Miliauskas, G.; Venskutonis, R.P.; Beek, van T.A.

    2004-01-01

    Extracts of 12 medicinal and aromatic plants were investigated for their radical scavenging activity using DPPH and ABTS assays: Salvia sclarea, Salvia glutinosa, Salvia pratensis, Lavandula angustifolia, Calendula officinalis, Matricaria recutita, Echinacea purpurea, Rhaponticum carthamoides, Jugla

  8. Formation of radical anions of radiosensitizers and related model compounds via electrospray ionization

    DEFF Research Database (Denmark)

    Feketeová, Linda; Albright, Abigail L; Sørensen, Brita Singers

    2014-01-01

    Radiosensitizers are used in radiotherapy to enhance tumour control of radioresistant hypoxic tumours. While the detailed mechanism of radiosensitization is still unknown, the formation of radical anions is believed to be a key step. Thus understanding the ionization reactions of radiosensitizers......, misonidazole and related compounds using a hybrid linear ion trap – Fourier Transform Ion Cyclotron Resonance mass spectrometer (Finnigan-LTQ-FT). A key finding is that negative electrospray ionization of these radiosensitizers leads to the formation of radical anions, allowing their fragmentation reactions...

  9. Resonance Raman Spectrum of the Transient (SCN)2 Free Radical Anion

    DEFF Research Database (Denmark)

    Wilbrandt, Robert Walter; Jensen, N. H.; Pagsberg, Palle Bjørn

    1979-01-01

    The resonance Raman spectrum of the transient species (λmax = 475 nm, τ½ = 1.6 μs) formed by pulse radiolysis of aqueous solutions of thiocyanate, SCN2−, is reported. The spectrum is discussed in terms of the previous assignment of this transient to the radical anion, (SCN)−2. The observed...... vibrational frequencies of the radical anion are consistent with substantial weakening of the S---S and the Ctriple bond; length as m-dashN bonds are compared with neutral thiocyanogen....

  10. The AHA Moment: Assessment of the Redox Stability of Ionic Liquids Based on Aromatic Heterocyclic Anions (AHAs) for Nuclear Separations and Electric Energy Storage.

    Science.gov (United States)

    Shkrob, Ilya A; Marin, Timothy W

    2015-11-19

    Because of their extended conjugated bond network, aromatic compounds generally have higher redox stability than less saturated compounds. We conjectured that ionic liquids (ILs) consisting of aromatic heterocyclic anions (AHAs) may exhibit improved radiation and electrochemical stability. Such properties are important in applications of these ILs as diluents in radionuclide separations and electrolytes in the electric energy storage devices. In this study, we systematically examine the redox chemistry of the AHAs. Three classes of these anions have been studied: (i) simple 5-atom ring AHAs, such as the pyrazolide and triazolides, (ii) AHAs containing an adjacent benzene ring, and (iii) AHAs containing electron-withdrawing groups that were introduced to reduce their basicity and interaction with metal ions. It is shown that fragmentation in the reduced and oxidized states of these AHAs does not generally occur, and the two main products, respectively, are the H atom adduct and the imidyl radical. The latter species occurs either as an N σ-radical or as an N π-radical, depending on the length of the N-N bond, and the state that is stabilized in the solid matrix is frequently different from that having the lowest energy in the gas phase. In some instances, the formation of the sandwich π-stack dimer radical anions has been observed. For trifluoromethylated anions, H adduct formation did not occur; instead, there was facile loss of fluoride from their fluorinated groups. The latter can be problematic in nuclear separations, but beneficial in batteries. Overall, our study suggests that AHA-based ILs are viable candidates for use as radiation-exposed diluents and electrolytes.

  11. Resonance Raman Spectra of the Transient Cl2 and Br2 Radical Anions

    DEFF Research Database (Denmark)

    Wilbrandt, Robert Walter; Jensen, Niels-Henrik; Sillesen, Alfred Hegaard

    1984-01-01

    The resonance Raman spectra of the short-lived radical anions ClImage 2− and BrImage − in aqueous solution are reported. The observed wavenumbers of 279 cm−1 for ClImage − and 177 cm−1 for BrImage − are about 10% higher than those published for the corresponding species isolated in solid argon...

  12. Spectroscopically resolved competition between dissociation and detachment from nitrobenzene radical anion

    NARCIS (Netherlands)

    Steill, J. D.; Oomens, J.

    2011-01-01

    We report the vibrational spectrum of the gas-phase isolated nitrobenzene radical anion. The spectrum has been acquired by infrared multiple-photon absorption induced dissociation and electron detachment using the FT mass spectrometer coupled to the infrared free-electron laser FELIX. Upon wavelengt

  13. Superoxide Anion Radical Scavenging Ability of Quaternary Ammonium Salt of Chitosan

    Institute of Scientific and Technical Information of China (English)

    Xiao Yan ZHU; Jian Min WU; Zhi Shen JIA

    2004-01-01

    A series of N-alkyl or N-aryl chitosan quaternary ammonium salt were prepared using 96% deacetylated chitosan. Their scavenging activities against superoxide anion radical were investigated by chemiluminescence. The IC50 values of these compounds range from 280 to 880 μg/mL, which should be attributed to their different substitutes.

  14. Oxidation of caffeine by phosphate radical anion in aqueous solution under anoxic conditions

    Indian Academy of Sciences (India)

    Maram Ravi Kumar; Mundra Adinarayana

    2000-10-01

    The photooxidation of caffeine in presence of peroxydiphosphate (PDP) in aqueous solution at natural H (∼7 5) has been carried out in a quantum yield reactor using a high-pressure mercury lamp. The reactions were followed spectrophotometrically by measuring the absorbance of caffeine at max (272 nm). The rates of reaction were calculated under different experimental conditions. The quantum yields were calculated from the rates of oxidation of caffeine and the intensity of light at 254 nm which was measured by using peroxydisulphate solution as a standard chemical actinometer. The reaction rates of oxidation of caffeine by PDP increase with increase in [PDP] as well as with increase in light intensity, while they are independent of [caffeine]. The quantum yields of oxidation of caffeine by PDP are independent of [PDP] as well as light intensity. However, quantum yields of oxidation of caffeine by PDP increase with increase in caffeine concentration. On the basis of these experimental results and product analysis, a probable mechanism has been suggested in which PDP is activated to phosphate radical anions (PO$_{4}^{\\bullet 2-}$) by direct photolysis of PDP and also by the sensitizing effect of caffeine. The phosphate radical anions thus produced react with caffeine by electron transfer reaction, resulting in the formation of caffeine radical cation, which deprotonates in a fast step to produce C8OH adduct radicals. These radicals might react with PDP to give final product 1,3,7-trimethyluric acid and PO$_{4}^{\\bullet 2-}$ radicals, the latter propagates the chain reaction.

  15. Reactions of CF3O radicals with selected alkenes and aromatics under atmospheric conditions

    DEFF Research Database (Denmark)

    Kelly, C.; Sidebottom, H.W.; Treacy, J.;

    1994-01-01

    Rate data for the reactions of CF3O radicals with alkenes and aromatic compounds have been determined at 298 K using a relative rate method. The data are analyzed in terms of structure-reactivity relationships, and their importance to the atmospheric chemistry of CF3O discussed.......Rate data for the reactions of CF3O radicals with alkenes and aromatic compounds have been determined at 298 K using a relative rate method. The data are analyzed in terms of structure-reactivity relationships, and their importance to the atmospheric chemistry of CF3O discussed....

  16. Time-dependent density functional study of the electronic excited states of polycyclic aromatic hydrocarbon radical ions

    Energy Technology Data Exchange (ETDEWEB)

    Hirata, So; Head-Gordon, Martin P; Szczepanski, Jan; Vala, Martin

    2003-06-19

    A uniform, comprehensive theoretical interpretation of spectroscopic data is presented for 53 radical ion species of polycyclic aromatic hydrocarbons (PAHs) with the aid of (Tamm–Dancoff) time-dependent density functional theory (TDDFT). TDDFT is capable of predicting the transition energies to the low-lying excited states of PAH ions with quantitative accuracy (the standard deviation from experimental results being less than 0.3 eV) and their intensity patterns qualitatively correctly. The accuracy is hardly affected by the sizes of PAH ions (azulene through dinaphthocoronene), the types of transitions (Koopmans or satellite transitions), the types of orbi-tals involved (π* ← π, π* ← σ, or σ* ← π transitions), the types of ions (cations or anions), or other geometrical or electronic perturbations (non-planarity, sp3 carbons, or heterocyclic or non-benzenoid rings).

  17. Electrochemical investigations of antioxidant interactions with radical anion and dianion of 1,3-dinitrobenzene

    Energy Technology Data Exchange (ETDEWEB)

    Arshad, Nasima [Department of Chemistry, Allama Iqbal Open University, Islamabad (Pakistan); Janjua, Naveed Kausar [Department of Chemistry, Quaid-i-Azam University, Islamabad (Pakistan)], E-mail: nkausarjanjua@yahoo.com; Ahmed, Safeer [Department of Chemistry, Quaid-i-Azam University, Islamabad (Pakistan); Khan, Athar Yaseen [Department of Chemistry, Allama Iqbal Open University, Islamabad (Pakistan); Skibsted, Leif H. [Food Chemistry, Department of Food Science, University of Copenhagen (Denmark)

    2009-11-01

    Interactions of five antioxidants (AO), quercetin (Q), morin (M), rutin (R), ascorbic acid (AA) and {beta}-carotene ({beta}-C) with anion radical and dianion of 1,3-dinitrobenzene (1,3-DNB) in two aprotic solvents - dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) - have been studied by cyclic voltammetry using glassy carbon electrode. Electrochemical parameters - peak potential (E{sub p}), half-wave potential (E{sub 1/2}), and peak current (i{sub p}) - for the reduction of 1,3-DNB before and after the addition of various concentrations of antioxidants, were evaluated. A gradual decrease in the oxidation peak current and finally irreversibility in 1,3-DNB radical anion and dianion systems upon the addition of antioxidant, reveals their interactions. The homogeneous bi-molecular rate constant (k{sub 2}) was determined from electrochemical data. In comparison to all other antioxidants used, enhanced homogeneous second order rate constant for the interaction of morin with 1,3-DNB anion radical and dianion, was observed. This aspect is attributable to protonation initiated by hydrogen bonding and greater acidic nature of morin.

  18. Polymorphism and Metallic Behavior in BEDT-TTF Radical Salts with Polycyano Anions

    Directory of Open Access Journals (Sweden)

    Carlos J. Gómez-García

    2012-04-01

    Full Text Available Up to five different crystalline radical salts have been prepared with the organic donor BEDT-TTF and three different polynitrile anions. With the polynitrile dianion tcpd2− (=C[C(CN2]32−, two closely related radical salts: α'-(ET4tcpd·THF (1 (THF = tetrahydrofurane and α'-(ET4tcpd·H2O (2 have been prepared, depending on the solvent used in the synthesis. With the mono-anion tcnoetOH− (=[(NC2CC(OCH2CH2OHC(CN2]− two polymorphs with similar physical properties but different crystal packings have been synthesized: θ-(ET2(tcnoetOH (3 and β''-(ET2(tcnoetOH (4. Finally, with the mono-anion tcnoprOH− (=[(NC2CC(OCH2CH2CH2OHC(CN2]− we have prepared a metallic radical salt: β''-(ET2(tcnoprOH(CH2Cl2CH3Cl0.5 (5. Salts 1‑4 are semiconductors with high room temperature conductivities and activation energies in the range 0.1–0.5 eV, whereas salt 5 is metallic down to 0.4 K although it does not show any superconducting transition above this temperature.

  19. Radical cations of aromatic selenium compounds: role of Se···X nonbonding interactions.

    Science.gov (United States)

    Singh, Beena G; Thomas, Elizabeth; Sawant, Shilpa N; Takahashi, Kohei; Dedachi, Kenchi; Iwaoka, Michio; Priyadarsini, K Indira

    2013-09-26

    Selenium centered radical cations in aliphatic selenium compounds are stabilized by formation of two-center-three electron (2c-3e) hemi bonds either with nearby heteroatoms forming monomer radicals or with selenium atoms of the parent molecules forming dimer radicals. Such radicals in aromatic selenium compounds would generally be stabilized as monomers by the delocalization of the spin density along the aromatic ring. To test the assumption if aromatic selenides having Se···X nonbonding interactions can show different types of radical cations, we have performed pulse radiolysis studies of three structurally related aromatic selenium compounds and the results have been substantiated with cyclic voltammetry and quantum chemical calculations. The three aromatic selenium compounds have functional groups like -CH2N(CH3)2 (1), -CH2OH (2), and -CH3 (3) at ortho position to the -SeCH3 moiety. The energy of Se···X nonbonding interactions (E(nb)) for these compounds is in the order 1 (Se···N) > 2 (Se···O) > 3 (Se···H). Radical cations, 1(•+), 2(•+) and 3(•+) were produced by the one-electron oxidation of 1, 2 and 3 by radiolytically generated (•)OH and Br2(•-) radicals. Results on transient spectra, lifetime, and secondary reactions of 1(•+), 2(•+), and 3(•+) indicated that 1(•+) shows a significantly different absorption spectrum, longer lifetime, and less oxidizing power compared to those of 2(•+) or 3(•+). Quantum chemical calculations suggested that 1(•+) is stabilized by the formation of a 2c-3e bond between Se and N atoms, whereas 2(•+) and 3(•+) acquire stability through the delocalization of the spin density on the aromatic ring. These results provide evidence for the first time that stronger nonbonding interactions between Se···N in the ground state, facilitate the formation of stabilized radical cations, which can significantly influence the redox chemistry and the biological activity of aromatic selenium compounds.

  20. Vibrational Spectroscopy of Transient Dipolar Radicals via Autodetachment of Dipole-Bound States of Cold Anions

    Science.gov (United States)

    Huang, Dao-Ling; Liu, Hong-Tao; Dau, Phuong Diem; Wang, Lai-Sheng

    2014-06-01

    High-resolution vibrational spectroscopy of transient species is important for determining their molecular structures and understanding their chemical reactivity. However, the low abundance and high reactivity of molecular radicals pose major challenges to conventional absorption spectroscopic methods. The observation of dipole-bound states (DBS) in anions extend autodetachment spectroscopy to molecular anions whose corresponding neutral radicals possess a large enough dipole moment (>2.5 D).1,2 However, due to the difficulty of assigning the congested spectra at room temperature, there have been only a limited number of autodetachment spectra via DBS reported. Recently, we have built an improved version of a cold trap3 coupled with high-resolution photoelectron imaging.4 The first observation of mode-specific auotodetachment of DBS of cold phenoxide have shown that not only vibrational hot bands were completely suppressed, but also rotational profile was observed.5 The vibrational frequencies of the DBS were found to be the same as those of the neutral radical, suggesting that vibrational structures of dipolar radicals can be probed via DBS.5 More significantly, the DBS resonances allowed a number of vibrational modes with very weak Frank-Condon factors to be "lightened" up via vibrational autodetachment.5 Recently, our first high-resolution vibrational spectroscopy of the dehydrogenated uracil radical, with partial rotational resolution, via autodetachment from DBS of cold deprotonated uracil anions have been reported.6 Rich vibrational information is obtained for this important radical species. The resolved rotational profiles also allow us to characterize the rotational temperature of the trapped anions for the first time.6 1 K. R. Lykke, D. M. Neumark, T. Andersen, V. J. Trapa, and W. C. Lineberger, J. Chem. Phys. 87, 6842 (1987). 2 D. M. Wetzel, and J. I. Brauman, J. Chem. Phys. 90, 68 (1989). 3 P. D. Dau, H. T. Liu, D. L. Huang, and L. S. Wang, J. Chem. Phys

  1. Superoxide Anion Radical Production in the Tardigrade Paramacrobiotus richtersi, the First Electron Paramagnetic Resonance Spin-Trapping Study.

    Science.gov (United States)

    Savic, Aleksandar G; Guidetti, Roberto; Turi, Ana; Pavicevic, Aleksandra; Giovannini, Ilaria; Rebecchi, Lorena; Mojovic, Milos

    2015-01-01

    Anhydrobiosis is an adaptive strategy that allows withstanding almost complete body water loss. It has been developed independently by many organisms belonging to different evolutionary lines, including tardigrades. The loss of water during anhydrobiotic processes leads to oxidative stress. To date, the metabolism of free radicals in tardigrades remained unclear. We present a method for in vivo monitoring of free radical production in tardigrades, based on electron paramagnetic resonance and spin-trap DEPMPO, which provides simultaneous identification of various spin adducts (i.e., different types of free radicals). The spin trap can be easily absorbed in animals, and tardigrades stay alive during the measurements and during 24-h monitoring after the treatment. The results show that hydrated specimens of the tardigrade Paramacrobiotus richtersi produce the pure superoxide anion radical ((•)O2(-)). This is an unexpected result, as all previously examined animals and plants produce both superoxide anion radical and hydroxyl radical ((•)OH) or exclusively hydroxyl radical.

  2. Roles of free radicals in type 1 phototherapeutic agents: aromatic amines, sulfenamides, and sulfenates.

    Science.gov (United States)

    Lin, Tien-Sung; Rajagopalan, Raghavan; Shen, Yuefei; Park, Sungho; Poreddy, Amruta R; Asmelash, Bethel; Karwa, Amolkumar S; Taylor, John-Stephen A

    2013-07-03

    Detailed analyses of the electron spin resonance (ESR) spectra, cell viability, and DNA degradation studies are presented for the photolyzed Type I phototherapeutic agents: aromatic amines, sulfenamides, and sulfenates. The ESR studies provided evidence that copious free radicals can be generated from these N-H, N-S, and S-O containing compounds upon photoirradiation with UV/visible light. The analyses of spectral data allowed us to identify the free radical species. The cell viability studies showed that these agents after exposure to light exert cytotoxicity to kill cancer cells (U937 leukemia cell lines HTC11, KB, and HT29 cell lines) in a dosage- and time-dependent manner. We examined a possible pathway of cell death via DNA degradation by a plasmid cleavage assay for several compounds. The effects of photosensitization with benzophenone in the presence of oxygen were examined. The studies indicate that planar tricyclic amines and sulfenamides tend to form π-electron delocalized aminyl radicals, whereas nonplanar ones tend to yield nitroxide radicals resulting from the recombination of aminyl radicals with oxygen. The ESR studies coupled with the results of cell viability measurements and DNA degradation reveal that planar N-centered radicals can provide higher potency in cell death and allow us to provide some insights on the reaction mechanisms. We also found the formation of azatropylium cations possessing high aromaticity derived from azepines can facilitate secondary electron transfer to form toxic O2(•-) radicals, which can further exert oxidative stress and cause cell death.

  3. Excited states in electron-transfer reaction products : ultrafast relaxation dynamics of an isolated acceptor radical anion.

    OpenAIRE

    D. A. Horke; Roberts, G.M.; Verlet, J. R. R.

    2011-01-01

    The spectroscopy and ultrafast relaxation dynamics of excited states of the radical anion of a representative charge-transfer acceptor molecule, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, have been studied in the gas phase using time-resolved photoelectron spectroscopy. The photoelectron spectra reveal that at least two anion excited states are bound. Time-resolved studies show that both excited states are very short-lived and internally convert to the anion ground state, with the ...

  4. Effect of the Structure of Cations and Anions of Ionic Liquids on Separation of Aromatics from Hydrocarbon Mixtures

    Institute of Scientific and Technical Information of China (English)

    Liu Yansheng; Zhang Zhongxin; Zhang Guofu; Liu Zhichang; Hu Yufeng; Shi Quan; Ji Dejun

    2006-01-01

    The effects of the structure of typical cations and anions of ionic liquids on the separation of benzene and toluene from aromatic/paraffin mixtures were studied. The results showed that the corresponding separation factors were considerably larger than those of the traditional solvents (Benzene+Hexane+sulfolane), and that the ionic liquids could be used as novel solvents for the separation of aromatics from hydrocarbon mixtures. The key parameters governing the ability of ionic liquids for separating aromatics from hydrocarbon sources were investigated. It was found that the effectiveness of the ionic liquids, based on the same anion, changed in the cation order of [BIqu]+< [BPy]+< [BMIM]+. The selectivity of the ionic liquid toward aromatics decreased apparently with the increasing length of the substituted alkyl chain of its cationic head ring. The separation factors, based on the same cation, changed in the anion order of [Tf2N]-<[PF6]-<[BF4]-<[C2H5SO4]-. The solubilities of the aromatics were greater in the ionic liquids based on the former three anions than that in the ionic liquids involving [C2H5SO4]-.

  5. Revisiting the electrochemical formation, stability and structure of radical and biradical anionic structures in dinitrobenzenes

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Munoz, Lindsay S.; Gonzalez, Felipe J. [Departamento de Quimica, Centro de Investigacion y Estudios Avanzados, Av. I.P.N. 2508. Col. San Pedro Zacatenco, 07360, D.F. (Mexico); Gonzalez, Ignacio [Departamento de Quimica, Universidad Autonoma Metropolitana-Iztapalapa, Area de Electroquimica, Apartado Postal 55-534, 09340, D.F. (Mexico); Goulart, Marilia O.F.; Abreu, Fabiane Caxico de; Ribeiro, Adriana Santos [Instituto de Quimica e Biotecnologia, Universidade Federal de Alagoas, Tabuleiro do Martins, Maceio, AL, 57072-970 (Brazil); Ribeiro, Rogerio Tavares; Longo, Ricardo L. [Departamento de Quimica Fundamental, Universidade Federal de Pernambuco, Av. Prof. Luiz Freire, s/n, Cid. Universitaria, Recife, PE, 50740-540 (Brazil); Navarro, Marcelo, E-mail: navarro@ufpe.b [Departamento de Quimica Fundamental, Universidade Federal de Pernambuco, Av. Prof. Luiz Freire, s/n, Cid. Universitaria, Recife, PE, 50740-540 (Brazil); Frontana, Carlos, E-mail: ultrabuho@yahoo.com.m [Departamento de Quimica, Centro de Investigacion y Estudios Avanzados, Av. I.P.N. 2508. Col. San Pedro Zacatenco, 07360, D.F. (Mexico)

    2010-11-30

    The effects of the position of a second nitroaromatic group (orthovs.paravs.meta) during reduction of nitrobenzenes were analysed. Cyclic voltammetric experiments in acetonitrile solution revealed that ortho-, meta- and para-dinitrobenzenes show two reversible reduction processes. An Electrochemical-Electron Spin Resonance (E-ESR) study showed that the corresponding radical anions of the ortho and para derivatives, electrogenerated during the first electron transfer uptake, remain the same even after the second monoelectronic process, increasing their intensity due to the presence of a comproportionation process (A{sup 2-} + A {yields} 2A{center_dot}{sup -}). For the case of the meta derivative, the electrogenerated radical anion at the first reduction peak is consumed at the second reduction step, forming a secondary radical species. During the electrochemical study of methyl 3,5-dinitrobenzoate, two successive and reversible electron processes were also observed; however, in this case, a very rare biradical dianion structure was found. The use of ESR-spectroelectrochemistry shed some light on controversial aspects of nitroaromatic reduction, especially concerning the second and further waves. These results were corroborated and interpreted with quantum chemical calculations of the molecular and electronic structures, electron affinities and spin densities. As a result, electrochemical mechanisms are presented and discussed.

  6. SYNTHESIS OF BLOCK COPOLYMER BY INTEGRATED LIVING ANIONIC POLYMERIZATION-ATOM TRANSFER RADICAL POLYMERIZATION (ATRP)

    Institute of Scientific and Technical Information of China (English)

    Bing Liu; Feng Liu; Ning Luo; Sheng-kang Ying; Qing Liu

    2000-01-01

    Alpha-trichloroacetoxy terminated polystyrene oligomer (PS-CH2CH2OCOCCl3) and poly-(styrene-b-butadiene)oligomer [P(S-b-B)-CH2CH2OCOCCl3)] were synthesized by living anionic polymeri-zation using n-butyllithium as initiator.Then the PS-CH2CH2OCOCCl3 (PS-Cl3) or P(S-b-B)-CH2CH2O-COCCl3 (PSB-Cl3) was used as the macroinitiator in the polymerization of (meth)acrylates in the presence of CuX/bpy. AB diblock and ABC triblock copolymers were prepared by the integrated living anionic polymerization (LAP)-atom transfer radical polymerization (ATRP). The structures of the PSB-Cl3 and the P(S-b-MMA) were identified by FTIR and 1H-NMR spectrum, respectively. A new way to design block copolymers (the combination of LAP and ATRP) was developed.

  7. Formation of environmentally persistent free radicals from the heterogeneous reaction of ozone and polycyclic aromatic compounds.

    Science.gov (United States)

    Borrowman, Cuyler K; Zhou, Shouming; Burrow, Timothy E; Abbatt, Jonathan P D

    2016-01-01

    In the 1980s long-lived radical species were identified in cigarette tar. Since then, environmentally persistent free radicals (EPFRs) have been observed in ambient particulate matter, and have been generated in particulate matter generated from internal combustion engines. For the first time, we measure in situ the formation and decay of EPFRs through the heterogeneous reaction of ozone and several polycyclic aromatic compounds (PAC). Solid anthracene (ANT), pyrene (PY), benzo[a]pyrene (BAP), benzo[ghi]perylene (BGHIP), 1,4-naphthoquinone (1,4NQ), and 9,10-anthraquinone (AQ) were reacted with gas-phase ozone in a flow system placed in the active cavity of an electron paramagnetic resonance (EPR) spectrometer, and the formation of radicals was measured on the timescale of tens of minutes at ambient levels of ozone down to 30 ppb. For most substrates the net radical production is initially rapid, slows at intermediate times, and is followed by a slow decay. For oxidized solid BAP, radical signal persists for many days in the absence of ozone. To evaluate the effect of substrate phase, the solid PAHs were also dissolved in squalane, an organic oil inert to ozone, which yielded a much higher maximum radical concentration and faster radical decay when exposed to ozone. With higher mobility, reactants were apparently able to more easily diffuse and react with each other, yielding the higher radical concentrations. The EPR spectra exhibit three radicals types, two of which have been assigned to semiquinone species and one to a PAH-derived, carbon-centered radical. Although our system uses levels of PAC not typically found in the environment it is worth noting that the amounts of radical formed, on the order of 10(18) radicals per g, are comparable to those observed in ambient particulate matter.

  8. Gas-phase Reactions of Polycyclic Aromatic Hydrocarbon Anions with Molecules of Interstellar Relevance

    Science.gov (United States)

    Demarais, Nicholas J.; Yang, Zhibo; Martinez, Oscar; Wehres, Nadine; Snow, Theodore P.; Bierbaum, Veronica M.

    2012-02-01

    We have studied reactions of small dehydrogenated polycyclic aromatic hydrocarbon anions with neutral species of interstellar relevance. Reaction rate constants are measured at 300 K for the reactions of phenide (C6H- 5), naphthalenide (C10H- 7), and anthracenide (C14H- 9) with atomic H, H2, and D2 using a flowing afterglow-selected ion flow tube instrument. Reaction rate constants of phenide with neutral molecules (CO, O2, CO2, N2O, C2H2, CH3OH, CH3CN, (CH3)2CO, CH3CHO, CH3Cl, and (CH3CH2)2O) are also measured under the same conditions. Experimental measurements are accompanied by ab initio calculations to provide insight into reaction pathways and enthalpies. Our measured reaction rate constants should prove useful in the modeling of astrophysical environments, particularly when applied to dense regions of the interstellar and circumstellar medium.

  9. Anion-radical oxygen centers in small (AgO)n clusters: density functional theory predictions

    CERN Document Server

    Trushin, Egor V

    2012-01-01

    Anion-radical form of the oxygen centers O(-) is predicted at the DFT level for small silver oxide particles having the AgO stoichiometry. Model clusters (AgO)n appear to be ferromagnetic with appreciable spin density at the oxygen centers. In contrast to these clusters, the Ag2O model cluster have no unpaired electrons in the ground state. The increased O/Ag ratio in the oxide particles is proved to be responsible for the spin density at oxygen centers.

  10. Homoleptic 2,2'-bipyridine metalates(-I) of iron and cobalt, one cocrystallized with an anthracene radical anion and the other with neutral anthracene.

    Science.gov (United States)

    Brennessel, William W; Ellis, John E

    2014-08-01

    Homoleptic 2,2'-bipyridine (bipy) metalates of iron and cobalt have been synthesized directly from the corresponding homoleptic anthracene metalates. In the iron structure, bis[([2.2.2]cryptand)potassium(I)] tris(2,2'-bipyridine)ferrate(-I) anthracene(-I), [K(C18H36N2O6)]2[Fe(C10H8N2)3](C14H10), the asymmetric unit contains one potassium complex cation in a general position, the Fe center and one and a half bipy ligands of the ferrate complex on a crystallographic twofold axis that includes the Fe atom, and one half of an anthracene radical anion whose other half is generated by a crystallographic inversion center. The cations and anions are well separated and the geometry about the Fe center is essentially octahedral. In the cobalt structure, ([2.2.2]cryptand)potassium(I) bis(2,2'-bipyridine)cobaltate(-I) anthracene hemisolvate tetrahydrofuran (THF) disolvate, [K(C18H36N2O6)][Co(C10H8N2)2]·0.5C14H10·2C4H8O, the asymmetric unit contains the cation, anion, and both cocrystallized THF solvent molecules in general positions, and one half of a cocrystallized anthracene molecule whose other half is generated by a crystallographic inversion center. The cation and anion are well separated and the ligand planes in the cobaltate anion are periplanar. Each anthracene molecule is midway between and is oriented perpendicular to a pair of symmetry-related bipy ligands such that aromatic donor-acceptor interactions may play a role in the packing arrangement. The lengths of the bonds that connect the bipy rings support the assertion that the ligands are bipy radical anions in the iron structure. However, in the case of cobalt, these lengths are between the known ranges for a bipy radical anion and a bipy dianion, and therefore no conclusion can be made from the crystallography alone. One cocrystallized THF solvent molecule in the cobalt structure was modeled as disordered over three positions with appropriate geometric and thermal restraints, which resulted in a refined

  11. Ab initio study of long-range electron transfer between biphenyl anion radical and naphthalene

    Institute of Scientific and Technical Information of China (English)

    李象远; 肖顺清; 何福城

    1999-01-01

    After the separation of the donor, the aeceptor, and the σ-type bridge from the π-σ-π system, the geometries of biphenyl, biphenyl anion radical, naphthalene, and naphthalene anion radical are optimized, and then the reorganization energy for the intermolecular electron transfer (ET) at the levels of HF/4-31G and HF/DZP is calculated. The ET matrix elements of the self-exchange reactions of the π-σ-π systems have been calculated by means of both the direct calculation based on the variational principle, and the transition energy between the molecular orbitals at the linear coordinate R=0.5. For the cross reactions, the ET matrix element and the geometry of the transition state are determined by searching the minimum energy splitting △min along the reaction coordinate. In the evaluation of the solvent reorganization energy of the ET in solution, the Marcus’ two-sphere model has been invoked. A few of ET rate constants for the intramolecular ET reactions for the π-σ-π systems, which contain

  12. Insights in the radical scavenging mechanism of syringaldehyde and generation of its anion

    Science.gov (United States)

    Yancheva, D.; Velcheva, E.; Glavcheva, Z.; Stamboliyska, B.; Smelcerovic, A.

    2016-03-01

    The ability of syringaldehyde, a naturally occurring phenolic antioxidant and medicinally important compound, to scavenge free radicals according different mechanisms was elucidated by computing the respective reaction enthalpies at DFT B3LYP/6-311++G** level. Bond dissociation enthalpy, ionization potentials and proton affinities were calculated in gas phase, benzene, water and DMSO in order to account for different environment (nonpolar lipid membranes and polar physiological liquids) where the antioxidant action in the living organism could take place and various experimental in vitro conditions. Molecular and electronic properties influencing the reactivity of syringaldehyde according to the different mechanisms were discussed in the light of the reported radical scavenging activities in crocin bleaching, oxidation potential of the first anodic peak and DPPH test. According to the calculated reaction enthalpies, in polar environment the syringaldehyde reacts preferably by sequential proton loss electron transfer which is related to the formation of a phenoxy anion. Such phenoxy anion was generated in DMSO solution and the changes in the force field, steric and electronic structure, resulting from the conversion, were described in detail based on the IR spectral data and DFT computations.

  13. The Production of Polycyclic Aromatic Hydrocarbon Anions in Inert Gas Matrices Doped with Alkali Metals. Electronic Absorption Spectra of the Pentacene Anion (C22H14(-))

    Science.gov (United States)

    Halasinski, Thomas M.; Hudgins, Douglas M.; Salama, Farid; Allamandola, Louis J.; Mead, Susan (Technical Monitor)

    1999-01-01

    The absorption spectra of pentacene (C22H14) and its radical cation (C22H14(+)) and anion (C22H14(-)) isolated in inert-gas matrices of Ne, Ar, and Kr are reported from the ultraviolet to the near-infrared. The associated vibronic band systems and their spectroscopic assignments are discussed together with the physical and chemical conditions governing ion (and counterion) production in the solid matrix. In particular, the formation of isolated pentacene anions is found to be optimized in matrices doped with alkali metal (Na and K).

  14. Polycyclic aromatic hydrocarbon (PAH) formation from benzyl radicals: a reaction kinetics study.

    Science.gov (United States)

    Sinha, Sourab; Raj, Abhijeet

    2016-03-21

    The role of resonantly stabilized radicals such as propargyl, cyclopentadienyl and benzyl in the formation of aromatic hydrocarbons such as benzene and naphthalene in the high temperature environments has been long known. In this work, the possibility of benzyl recombination to form three-ring aromatics, phenanthrene and anthracene, is explored. A reaction mechanism for it is developed, where reaction energetics are calculated using density functional theory (B3LYP functional with 6-311++G(d,p) basis set) and CBS-QB3, while temperature-dependent reaction kinetics are evaluated using transition state theory. The mechanism begins with barrierless formation of bibenzyl from two benzyl radicals with the release of 283.2 kJ mol(-1) of reaction energy. The further reactions involve H-abstraction by a H atom, H-desorption, H-migration, and ring closure to gain aromaticity. Through mechanism and rate of production analyses, the important reactions leading to phenanthrene and anthracene formation are determined. Phenanthrene is found to be the major product at high temperatures. Premixed laminar flame simulations are carried out by including the proposed reactions for phenanthrene formation from benzyl radicals and compared to experimentally observed species profiles to understand their effects on species concentrations.

  15. Study of radicals, clusters and transition state species by anion photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Arnold, D.W.

    1994-08-01

    Free radicals, elemental and van der Waals clusters and transition state species for bimolecular chemical reactions are investigated using anion photoelectron spectroscopy. Several low-lying electronic states of ozone have been identified via photoelectron spectroscopy of O{sub 3}{sup {minus}}. A characterization of these states is important to models for atmospheric ozone reaction kinetics. The fluoroformyloxyl radical, FCO{sub 2}, has been investigated, providing vibrational frequencies and energies for two electronic states. The technique has also been employed to make the first direct observation and characterization of the NNO{sub 2} molecule. Several electronic states are observed for this species which is believed to play a role as a reactive intermediate in the N + NO{sub 2} reaction. The experimental results for all three of these radicals are supplemented by ab initio investigations of their molecular properties. The clusters investigations include studies of elemental carbon clusters (C{sub 2}{sup {minus}} {minus} C{sub 11}{sup {minus}}), and van der Waals clusters (X{sup {minus}}(CO{sub 2}){sub n}, X = I, Br, Cl; n {le} 13 and I{sup {minus}} (N{sub 2}O){sub n=1--11}). Primarily linear clusters are observed for the smaller carbon clusters, while the spectra of the larger clusters contain contribution from cyclic anion photodetachment. Very interesting ion-solvent interactions are observed in the X{sup {minus}}(CO{sub 2})n clusters. The transition state regions for several bimolecular chemical reactions have also been investigated by photodetachment of a negative ion precursor possessing a geometry similar to that of the transition state species. These spectra show features which are assigned to motions of the unstable neutral complex existing between reactants and products.

  16. Study of organic radicals through anion photoelectron velocity-map imaging spectroscopy

    Science.gov (United States)

    Dixon, Andrew Robert

    We report preliminary results on the photoelectron imaging of phenylcarbene, cyanophenylcarbene, and chlorophenylcarbene anions. Triplet phenylcarbene is observed to have an EA of ≤ 0.83 eV, considerably lower than the previously indirectly-determined value. Transitions to the singlet and triplet ground state of both cyanophenylcarbene and chlorophenylcarbene are observable, though unidentified bands make full assignment difficult. Cyanophenylcarbene is found to have a triplet ground-state, with a tentative EA of 2.04 eV. Chlorophenylcarbene is found to have a singlet ground-state. The phenyl-group is found to favor the singlet state slightly. The cyanofluoromethyl radical, FC(H)CN, was estimated to have an EA of 1.53 +/- 0.08 eV, by a combination of experimental and theoretical results.. With similar methodology, we report the adiabatic electron affinity of the cyanobenzyl radical, EA(PhCHCN) = 1.90 +/- 0.01 eV, and assign an upper limit of the EA for the chlorobenzyl radical, EA(PhCHCl) ≤ 1.12 eV. These values were used to estimate the C-H bond dissociation energy (BDE)s for these substituted methanes. Fluoroacetonitrile was found to have a BDE of D H198 = 90.7 +/- 2.8 kcal mol□1. The C-H bond dissociation energies at the benzyl-alpha sites of the phenylmethanes are determined as 80.9 +/- 2.3 kcal mol-1 for benzyl nitrile and an upper limit of 84.2 kcal mol-1 for benzyl chloride. These results are discussed in terms of substituent interactions in a simple MO framework and in relation to other similar molecules, including recently reported results for chloroacetonitrile. The 532 nm photoelectron spectrum of glyoxal provides the first direct spectroscopic determination of the adiabatic electron affinity, EA = 1.10(2) eV. This assignment is supported by a Franck-Condon simulation of the experimental spectrum that successfully reproduces the observed spectral features. The vertical detachment energy (VDE) of the glyoxal radical anion is determined as VDE = 1

  17. Ab initio ro-vibronic spectroscopy of the 2Π PCS radical and +1ΣPCS- anion

    Science.gov (United States)

    Finney, Brian; Mitrushchenkov, Alexander O.; Francisco, Joseph S.; Peterson, Kirk A.

    2016-12-01

    Near-equilibrium potential energy surfaces have been calculated for both the PCS radical and its anion using a composite coupled cluster approach based on explicitly correlated F12 methods in order to provide accurate structures and spectroscopic properties. These transient species are still unknown and the present study provides theoretical predictions of the radical and its anion for the first time. Since these species are strongly suggested to play an important role as intermediates in the interstellar medium, the rotational and vibrational spectroscopic parameters are presented to help aid in the identification and assignment of these spectra. The rotational constants produced will aid in ground-based observation. Both the PCS radical and the PCS- anion are linear. In the PCS- anion, which has a predicted adiabatic electron binding energy (adiabatic electron affinity of PCS) of 65.6 kcal/mol, the P-C bond is stronger than the corresponding neutral radical showing almost triple bond character, while the C-S bond is weaker, showing almost single bond character in the anion. The PCS anion shows a smaller rotational constant than that of the neutral. The ω3 stretching vibrational frequencies of PCS- are red-shifted from the radical, while the ω1 and ω2 vibrations are blue-shifted with ω1 demonstrating the largest blue shift. The ro-vibronic spectrum of the PCS radical has been accurately calculated in variational nuclear motion calculations including both Renner-Teller (RT) and spin-orbit (SO) coupling effects using the composite potential energy near-equilibrium potential energy and coupled cluster dipole moment surfaces. The spectrum is predicted to be very complicated even at low energies due to the presence of a strong Fermi resonance between the bending mode and symmetric stretch, but also due to similar values of the bending frequency, RT, and SO splittings.

  18. Theoretical Infrared Spectra for Polycyclic Aromatic Hydrocarbon Neutrals, Cations and Anions

    Science.gov (United States)

    Langhoff, Stephen R.

    1995-01-01

    Calculations are carried out using density functional theory (DFT) to determine the harmonic frequencies and intensities of the neutrals and cations of thirteen polycyclic aromatic hydrocarbons (PAHs) up to the size of ovalene. Calculations are also carried out for a few PAH anions. The DFT harmonic frequencies, when uniformly scaled by the factor of 0.958 to account primarily for anharmonicity, agree with the matrix isolation fundamentals to within an average error of about 10 per centimeter. Electron correlation is found to significantly reduce the intensities of many of the cation harmonics, bringing them into much better agreement with the available experimental data. While the theoretical infrared spectra agree well with the experimental data for the neutral systems and for many of the cations, there are notable discrepancies with the experimental matrix isolation data for some PAH cations that are difficult to explain in terms of limitations in the calculations. In agreement with previous theoretical work, the present calculations show that the relative intensities for the astronomical unidentified infrared (UIR) bands agree reasonably well with those for a distribution of polycyclic aromatic hydrocarbon (PAH) cations, but not with a distribution of PAH neutrals. We also observe that the infrared spectra of highly symmetrical cations such as coronene agree much better with astronomical observations than do those of, for example, the polyacenes such as tetracene and pentacene. The total integrated intensities for the neutral species are found to increase linearly with size, while the total integrated intensities are much larger for the cations and scale more nearly quadratically with size. We conclude that emission from moderate-sized highly symmetric PAH cations such as coronene and larger could account for the UIR bands.

  19. 1,1-Diphenyl-2-picrylhydrazyl radical and superoxide anion scavenging activity of Rhizophora mangle (L. bark

    Directory of Open Access Journals (Sweden)

    Janet Calero Sánchez

    2010-01-01

    Full Text Available Background: Rhizophora mangle (L. produce a variety of substances that possesses pharmacological actions. Although it shown antioxidant properties in some assays, there is no available information about its effect on some free radical species. So the objective of the present research is to evaluate the DPPH radical and superoxide anion scavenging properties of R. mangle extract and its polyphenol fraction. Methods: Rhizophora mangle (L. bark aqueous extract and its major constituent, polyphenols fraction, were investigated for their antioxidant activities employing 2 in vitro assay systems: 1,1-diphenyl-2-picrylhydrazyl (DPPH and superoxide anion radicals scavenging. Results: IC 50 for DPPH radical-scavenging activity was 6.7 μg tannins/mL for extract and 7.6 μg tannins/mL for polyphenolic fraction. The extract showed better activity than its fraction (P < 0.05 in the DPPH radicals reducing power. Polyphenolic fraction exhibited better superoxide anion scavenging ability (IC 50 = 21.6 μg tannins/mL than the extract (IC 50 = 31.9 μg tannins/mL. Antioxidant activities of both samples increased with the rise of tannins concentration. The comparison of regression lines showed significant differences (P < 0.05 between extract and its polyphenolic fraction in both assays, indicating that extract was more effective in DPPH radical scavenging than its fraction at tannin concentrations below the crossing point of both lines, while that fraction was more effective than extract inhibiting the superoxide anions generation. Conclusions: R. mangle aqueous extract showed a potent antioxidant activity, achieved by the scavenging ability observed against DPPH radicals and superoxide anions. Regarding its polyphenolic composition, the antioxidant effects observed in this study are due, most probably, to the presence of polyphenolic compounds.

  20. A study on scavenging effects of Chinese medicine on superoxide anion radicals by pulse radiolysis

    Energy Technology Data Exchange (ETDEWEB)

    Li Fengmei; Liu Andong; Gu Hongchun; Di Shaojie (Beijing Normal Univ., BJ (China). Inst. of Low Energy Nuclear Physics)

    A study on scavenging and dismutation effects on superoxide anion radical ([center dot]O[sub 2][sup -]) using two Chinese antiaging medicines - Salvia miltiorrhiza injection (S.M.) and Sulekang capsule (S.C.) was carried out using pulse radiolysis. The absorption spectra of [center dot] OH[sub 2][sup -] was redetermined by radiolysis of an aqueous solution of sodium format. The absorption maximum is at about 250 nm. The results suggested that S.M. and S.C. can dismutate and scavenge [center dot]O[sub 2][sup -]. The experimental scavenging rates of S.M. (150[mu]g/ml) and S.C. (250[mu]g/ml) were 89.6% and 69.5% respectively. (author).

  1. Ubiquitous trisulfur radical anion: fundamentals and applications in materials science, electrochemistry, analytical chemistry and geochemistry.

    Science.gov (United States)

    Chivers, Tristram; Elder, Philip J W

    2013-07-21

    The trisulfur radical anion [S3]˙(-) is well-known from inorganic chemistry textbooks as the blue chromophore in ultramarine blues in which this highly reactive species is trapped in a zeolitic framework. Recent findings have revealed that [S3]˙(-) has a multi-faceted role in a variety of media, including alkali metal-sulfur batteries, aqueous solutions at high temperatures and pressures, and ionic liquids; it has also been used to detect trace amounts of water in organic solvents. This tutorial review illustrates how various physical techniques are used to identify a reactive species in solution and shows how elucidation of electronic structures can be used to explain spectroscopic and structural properties. Examples of the function of [S3]˙(-) in materials science, electrochemistry, analytical chemistry and geochemistry are used to illustrate the widespread influence of this fundamentally important triatomic sulfur species.

  2. PCL assay application in superoxide anion-radical scavenging capacity of tea Camellia sinensis extracts

    Directory of Open Access Journals (Sweden)

    Anna Gramza-Michałowska

    2015-12-01

    Full Text Available Background. Plant polyphenols are known for their limiting of adverse effects on reactive oxygen species (ROS in biological systems. The photochemiluminescence (PCL assay allows to evaluate the antiradical activity of a compound in the presence of a superoxide anion-radical (O •-, which is one of the ROS directly associated with the human body. In this work, determination of the superoxide anion radical scavenging ac- tivity of different tea extracts using the PCL assay was performed. Material and methods. Investigations were conducted on different tea leaves extracts. The study included five kinds of tea leaves subjected to aqueous and ethanol extraction procedure. Catechins content was evalu- ated using HPLC. Antiradical activity of the samples was conducted with use of Photochem assay. Results. Analysis of total catechins content in tea aqueous extracts enabled them to be arranged as follows: yellow > green > white > red > black, while for ethanol extracts it was: yellow = green > white > red > black. The examined tea extracts were ranked from highest to lowest water-soluble antioxidative capacity (ACW values as follows: yellow > green > white > red > black. The results of lipid-soluble antioxidative capacity (ACL values for aqueous extracts were similar; however, were approximately 50% lower than those pre- sented as ACW. The second examined group were ethanol extracts, which ranked for ACW values: yellow > green = red = white > black, while ACL values ranked as follows: yellow > white = black = red > green. PCL assay results were correlated with total catechin content in aqueous extracts. Conclusions. Antiradical activity of different tea leaves extracts in PCL assay, showed that the highest activ- ity was found in extracts of yellow tea; the lowest, however, was identified in black tea extracts.

  3. THERMODYNAMIC STUDY ON ADSORPTION OF AROMATIC SULFONIC ACIDS ONTO MACROPOROUS WEAK BASE ANION EXCHANGER FROM AQUEOUS SOLUTIONS

    Institute of Scientific and Technical Information of China (English)

    Chao Long; Quan-xing Zhang; Ai-min Li; Jin-long Chen

    2004-01-01

    The adsorption equilibrium isotherms of three aromatic sulfonic acid compounds, 2-naphthalenesulfonic acid, ptoluenesulfonic acid and p-chlorobenzenesulfonic acid, from aqueous solutions by macroporous weak base anion exchanger within the temperature range of 293 K-313 K were obtained. Several isotherm equations were correlated with the equilibrium data, and the experimental data was found to fit the three-parameter Redlich-Peterson equation best within the entire range of concentrations. The study showed that the hydrophobicity of solute has distinct influence on adsorption capacity of the anion exchanger for the aromatic sulfonic acid. Moreover, estimations of the isosteric enthalpy, free energy,and entropy change of adsorption were also reported. The positive isosteric enthalpy and entropy change for adsorption indicate an endothermic and entropy driven process in the present study.

  4. Concerted effects of substituents in the reaction of •OH radicals with aromatics: The hydroxybenzaldehydes

    Science.gov (United States)

    Albarran, Guadalupe; Mendoza, Edith; Schuler, Robert H.

    2016-07-01

    In the present work, we have examined the distribution of products in the radiolytic hydroxylation of 2-, 3- and 4-hydroxybenzaldehyde to obtain information on the concerted effect of the -CHO and -OH groups at the addition site of •OH radicals. The •OH radical was found to selectively add to the free positions of the aromatic ring. Furthermore, the •OH radical reacts by substitution at the ipso position followed by elimination of the substituent, producing dihydroxybenzene compounds. Additionally, the formation of carboxylic acids as an initial product has been conclusively identified by retention times and UV and mass spectra. These acids are formed as a result of the radiolytic oxidation of the initial radical formed by the addition reaction of the •OH radicals to the meso position (exocyclic carbon). The identification of the products, dihydroxybenzaldehydes, dihydroxybenzenes and hydroxybenzoic acids and calculation of their yields were achieved through HPLC. The G values of each product are given, which reflect the charge distributions in the hydroxybenzaldehydes, such that the formyl group modifies the ortho-para directing effect of the -OH substituent. The 3 and 5 positions in 2- and 4-hydroxybenzaldehyde showed increased the electronic density compared to that of phenol, indicating that the formyl group has a significant effect on the electronic structure of those hydroxybenzaldehydes. In 3-hydroxybenzaldehyde, the -OH substituent had a dominant ortho-directing effect similar to that observed for phenol.

  5. Chemistry of polycyclic aromatic hydrocarbons formation from phenyl radical pyrolysis and reaction of phenyl and acetylene.

    Science.gov (United States)

    Comandini, A; Malewicki, T; Brezinsky, K

    2012-03-15

    An experimental investigation of phenyl radical pyrolysis and the phenyl radical + acetylene reaction has been performed to clarify the role of different reaction mechanisms involved in the formation and growth of polycyclic aromatic hydrocarbons (PAHs) serving as precursors for soot formation. Experiments were conducted using GC/GC-MS diagnostics coupled to the high-pressure single-pulse shock tube present at the University of Illinois at Chicago. For the first time, comprehensive speciation of the major stable products, including small hydrocarbons and large PAH intermediates, was obtained over a wide range of pressures (25-60 atm) and temperatures (900-1800 K) which encompass the typical conditions in modern combustion devices. The experimental results were used to validate a comprehensive chemical kinetic model which provides relevant information on the chemistry associated with the formation of PAH compounds. In particular, the modeling results indicate that the o-benzyne chemistry is a key factor in the formation of multi-ring intermediates in phenyl radical pyrolysis. On the other hand, the PAHs from the phenyl + acetylene reaction are formed mainly through recombination between single-ring aromatics and through the hydrogen abstraction/acetylene addition mechanism. Polymerization is the common dominant process at high temperature conditions.

  6. Anion-π Catalysis of Enolate Chemistry: Rigidified Leonard Turns as a General Motif to Run Reactions on Aromatic Surfaces.

    Science.gov (United States)

    Cotelle, Yoann; Benz, Sebastian; Avestro, Alyssa-Jennifer; Ward, Thomas R; Sakai, Naomi; Matile, Stefan

    2016-03-18

    To integrate anion-π, cation-π, and ion pair-π interactions in catalysis, the fundamental challenge is to run reactions reliably on aromatic surfaces. Addressing a specific question concerning enolate addition to nitroolefins, this study elaborates on Leonard turns to tackle this problem in a general manner. Increasingly refined turns are constructed to position malonate half thioesters as close as possible on π-acidic surfaces. The resulting preorganization of reactive intermediates is shown to support the disfavored addition to enolate acceptors to an absolutely unexpected extent. This decisive impact on anion-π catalysis increases with the rigidity of the turns. The new, rigidified Leonard turns are most effective with weak anion-π interactions, whereas stronger interactions do not require such ideal substrate positioning to operate well. The stunning simplicity of the motif and its surprisingly strong relevance for function should render the introduced approach generally useful.

  7. A study of quasi reversible nitro radical anion from -nitrostyrene at wax-impregnated carbon paste electrode

    Indian Academy of Sciences (India)

    Ronald J Mascarenhas; Irishi N Namboothiri; B S Sherigara; Vijayakumar K Reddy

    2006-05-01

    A comprehensive study of the electrochemical reduction of -nitrostyrene and the corresponding heterocyclic analogue has been carried out in aprotic media using wax-impregnated carbon paste electrodes. Nitrostyrene exhibits quasi-reversible reduction process in aprotic medium at the waximpregnated carbon paste electrodes as compared to other electrodes reported in the literature. The nitroradical anion couple detected in the presence of tetrabutyl ammonium perchlorate is found to be stable only in aprotic media. Though, as reported, the pharmacological activity related to this nitro radical anion and its therapeutic value are related to the stability of the nitro radical anion, the stability itself depends on the electrode system employed. Added benzoic acid is found to bring about a positive shift in cathodic peak potential.

  8. Ferrous Ion Chelating, Superoxide Anion Radical Scavenging and Tyrosinase Inhibitory Properties of Pure and Commercial Essential Oils of Anetrhum Graveolens

    Directory of Open Access Journals (Sweden)

    Sh Darvish Alipour Astaneh

    2013-04-01

    Full Text Available Introduction: Despite slight toxicities of essential oils, they are not under strict control in many countries. Anethum graveolens is widely consumed and its essential oils are at public reach. This study was designed to study essential oils of Anethum graveolens. Methods: The biological properties of pure and commercial essential oils of Anethum graveolens were investigated. In fact, Ferrous ion chelating activity, superoxide anion radical scavenging property, tyrosinase inhibition and total flavonoids of the oils were determined. Results: Chelating activity of 7.8 µg of EDTA was equivalent to 2 µg of the pure oil. The oils had superoxide anion radical scavenging activities which may be related to their total phenol and flavonoid contents. IC50 of ferrous ion chelating, antityrosiase and superoxide anion radical scavenging activities of pure and commercial oils were 1.3, 1.4, 1 and (171.6, 589, 132 µg respectively. Antityrosiase activity of 6.4 µg pure oil was equal to 1000 µg of the commercial oil. Conclusion: Anethum possesses antioxidative and free radical scavenging properties. This oil chelates ferrous ions and superoxide radicals. It is effective in formation of reactive toxic products. Anethum has good potentials regarding its applications in food and drug industries.

  9. Study on the Retention Behavior of Aromatic Carboxylic and Sulfonic acid on a New Anion Exchange Column

    Institute of Scientific and Technical Information of China (English)

    SHI,Ya-Li; CAI,Ya-Qi; MOU,Shi-Fen

    2008-01-01

    Ion chromatography (IC) has gradually developed into a preferred method for the determination of inorganic anions. And in recent years some low molecular aliphatic acid can be also separated in the ion exchange column with the development of stationary phase. But for the determination of aromatic ionic compounds there are some problems. The aromatic anions show enhanced retention due to interaction with the π electrons of the aromatic backbone. Although the addition of an organic modifier can alleviate the difficulty, it is not the ultimate solution.IonPac AS20 column was developed using a unique polymer bonding technology and its substrate coating is aliphatic backbone. The polymer is completely free of any π electron-containing substituents in the AS20 column. In this paper, the retention behavior of aromatic carboxylic and sulfonic acid on two hydroxide-selective columns,IonPac AS11-HC, AS16, and the new column AS20 was also studied. The result showed that the retentions of ten compounds on three columns were different with each other because of their different column characteristics.Among them 4-chlorobenzene sulfonic acid, 3,5-dihydric benzoic acid and salicylic acid obviously exhibited the weakest retention on the IonPac AS20. It was showed that π-π bond function between anion and stationary phases was weakened in AS20 column because its polymer was completely free of any π electron-containing substituents.So in this paper the AS20 was selected as an analytical column to separate ten aromatic ionic compounds, fumaric acid with conjugate bond included. The retention behavior, separation of the ten compounds and effect of temperature on their retention in the anion-exchange column AS20 (2 mm) were studied. The result showed that those compounds could be separated with each other when running in gradient program and the organic modifier was unnecessary during the separation. So it is showed that AS20 column can be used as a separating column because its

  10. EPR and DFT Study of the Polycyclic Aromatic Radical Cations from FriedeI-Crafts Alkylation Reactions

    Institute of Scientific and Technical Information of China (English)

    Tao Wang; An-an Wu; Li-guo Gao; Han-qing Wang

    2009-01-01

    Electron paramagnetic resonance and electron-nuclear double resonance methods were used to study the polycyclic aromatic radical cations produced in a Friedel-Crafts alkylating sys-tem, with m-xylene, or p-xylene and alkyl chloride. The results indicate that the observed electron paramagnetic resonance spectra are due to polycyclic aromatic radicals formed from the parent hydrocarbons. It is suggested that benzyl halides produced in the Friedel-Crafts alkylation reactions undergo Scholl self-condensation to give polycyclic aromatic hydrocar-bons, which are converted into corresponding polycyclic aromatic radical cations in the presence of AlCl3. The identification of observed two radicals 2,6-dimethylanthracene and 1,4,5,8-tetramethylanthracene were supported by density functional theory calculations us-ing the B3LYP/6-31G(d,p)//B3LYP/6-31G(d) approach. The theoretical coupling constants support the experimental assignment of the observed radicals.

  11. Micellar electrokinetic chromatography of aromatic anions and non-ionic aromatic compounds with stepwise changes of the concentration of cetyltrimethylammonium chloride.

    Science.gov (United States)

    Esaka, Yukihiro; Kobayashi, Miki; Murakami, Hiroya; Uno, Bunji

    2012-05-04

    Micellar electrokinetic chromatography in which the concentration of cetyltrimetylammmonium chloride (CTAC) was sequentially changed in the separation system was investigated using 10 aromatic anions and 11 non-ionic aromatic compounds as model analytes. All separations were performed in the absence of electroosmotic flow (EOF), and thus, analytes were detected in the order of their strength of interaction with micelles in the system. In isocratic elutions without EOF, the model analytes could be separated better with lower concentrations of CTAC but migration times of the analytes possessing relatively higher polarities increased markedly, and thus, long analysis times were required. Therefore, we attempted to increase the concentration of CTAC during a single measurement to reduce the analysis time without hindering the resultant separation of analytes obtained with lower concentrations. Briefly, the present surfactant stepwise elution can be performed by a sequential increase in CTAC concentrations of the running solution in the anodic reservoir from 30 to 50mM for the anions and from 20 to 50 mM for the non-ionic compounds. Additionally, to perform expected gradient separations with good reproducibility, each running solution with a different CTAC concentration was treated with tetraethylammmonium chloride as an additive to adjust electric conductivities of each running solution to be equal. Under this condition, CTAC micelles of each zone of different CTAC concentrations would migrate with practically the same velocity. Consequently, by the present stepwise method, both the 10 anionic analytes and the 11 non-ionic analytes were well separated within reasonable periods which corresponded approximately to two-third and less than half of those by the isocratic elutions, respectively.

  12. Vibronic spectra of the p-benzoquinone radical anion and cation: a matrix isolation and computational study

    OpenAIRE

    Piech, Krzysztof; Bally, Thomas; Ichino, Takatoshi; Stanton, John

    2014-01-01

    The electronic and vibrational absorption spectra of the radical anion and cation of p-benzoquinone (PBQ) in an Ar matrix between 500 and 40 000 cm⁻¹ are presented and discussed in detail. Of particular interest is the radical cation, which shows very unusual spectroscopic features that can be understood in terms of vibronic coupling between the ground and a very low-lying excited state. The infrared spectrum of PBQ˙⁺ exhibits a very conspicuous and complicated pattern of features above 1900 ...

  13. Excited states in electron-transfer reaction products: ultrafast relaxation dynamics of an isolated acceptor radical anion.

    Science.gov (United States)

    Horke, Daniel A; Roberts, Gareth M; Verlet, Jan R R

    2011-08-04

    The spectroscopy and ultrafast relaxation dynamics of excited states of the radical anion of a representative charge-transfer acceptor molecule, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, have been studied in the gas phase using time-resolved photoelectron spectroscopy. The photoelectron spectra reveal that at least two anion excited states are bound. Time-resolved studies show that both excited states are very short-lived and internally convert to the anion ground state, with the lower energy state relaxing within 200 fs and a near-threshold valence-excited state relaxing on a 60 fs time scale. These excited states, and in particular the valence-excited state, present efficient pathways for electron-transfer reactions in the highly exergonic inverted region which commonly displays rates exceeding predictions from electron-transfer theory.

  14. Comparison of (η6-Fluoroarene)tricarbonylchromium Complexes with Their Chloro-analogs in Radical Aromatic Substitutions

    Institute of Scientific and Technical Information of China (English)

    林和春; 杨立; 李超忠

    2003-01-01

    Reactions of fluoroarene-Cr(CO)3 complexes with SmI2 and earbonyl compounds in THF/HMPA at -40~- 60℃ afforded the correspoDdin~ radical aromatic substitution products in high yield. Compared to the corresponding chloroarene-Cr(CO)3 complexes, fluoroarene-Cr(CO)3 complexes showed a higher efficiency and slightly lower regioselectivity.

  15. Anion size control of the packing in the metallic versus semiconducting chiral radical cation salts (DM-EDT-TTF)2XF6 (X = P, As, Sb).

    Science.gov (United States)

    Pop, Flavia; Auban-Senzier, Pascale; Canadell, Enric; Avarvari, Narcis

    2016-10-13

    Control of the structural type in metallic enantiopure and racemic radical cation salts is achieved through hydrogen bonding interactions between the chiral donor DM-EDT-TTF and the XF6 anions (X = P, As, Sb), determined by the anion size and the chiral information.

  16. Mechanism of Action of Sulforaphane as a Superoxide Radical Anion and Hydrogen Peroxide Scavenger by Double Hydrogen Transfer: A Model for Iron Superoxide Dismutase.

    Science.gov (United States)

    Prasad, Ajit Kumar; Mishra, P C

    2015-06-25

    The mechanism of action of sulforaphane as a scavenger of superoxide radical anion (O2(•-)) and hydrogen peroxide (H2O2) was investigated using density functional theory (DFT) in both gas phase and aqueous media. Iron superoxide dismutase (Fe-SOD) involved in scavenging superoxide radical anion from biological media was modeled by a complex consisting of the ferric ion (Fe(3+)) attached to three histidine rings. Reactions related to scavenging of superoxide radical anion by sulforaphane were studied using DFT in the presence and absence of Fe-SOD represented by this model in both gas phase and aqueous media. The scavenging action of sulforaphane toward both superoxide radical anion and hydrogen peroxide was found to involve the unusual mechanism of double hydrogen transfer. It was found that sulforaphane alone, without Fe-SOD, cannot scavenge superoxide radical anion in gas phase or aqueous media efficiently as the corresponding reaction barriers are very high. However, in the presence of Fe-SOD represented by the above-mentioned model, the scavenging reactions become barrierless, and so sulforaphane scavenges superoxide radical anion by converting it to hydrogen peroxide efficiently. Further, sulforaphane was found to scavenge hydrogen peroxide also very efficiently by converting it into water. Thus, the mechanism of action of sulforaphane as an excellent antioxidant has been unravelled.

  17. A Molecular Precursor to Phosphaethyne and Its Application in Synthesis of the Aromatic 1,2,3,4-Phosphatriazolate Anion

    Energy Technology Data Exchange (ETDEWEB)

    Transue, Wesley J.; Velian, Alexandra; Nava, Matthew; Martin-Drumel, Marie-Aline; Womack, Caroline C.; Jiang, Jun; Hou, Gao-Lei; Wang, Xue-Bin; McCarthy, Michael C.; Field, Robert W.; Cummins, Christopher C.

    2016-06-01

    Dibenzo-7-phosphanorbornadiene Ph3PC(H)PA (1, A = C14H10, anthracene) is reported as a molecular precursor to phosphaethyne (HC≡P), produced together with anthracene and triphenylphosphine. HCP generated by thermolysis of 1 has been characterized by molecular beam mass spectrometry (MBMS), laser-induced fluorescence (LIF), microwave spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. In toluene, fragmentation of 1 has been found to proceed with activation parameters of ΔH = 25.5 kcal/mol and ΔS = ₋2.43 e.u., and is accompanied by formation of an orange insoluble precipitate. Results from computational studies of the mechanism of HCP generation are in good agreement with experimental data. This high temperature method of HCP generation has pointed to new reaction chemistry with azide anion to produce the 1,2,3,4-phosphatriazolate anion, HCPN3- , for which structural data have been obtained in a single-crystal Xray diffraction study. Negative ion photoelectron spectroscopy has shown the adiabatic detachment energy for this anion to be 3.555(10) eV. The aromaticity of HCPN3- has been assessed using nucleus-independent chemical shift (NICS), quantum theory of atoms in molecules (QTAIM), and natural bond orbital (NBO) methods.

  18. Hydration Leads to Efficient Reactions of the Carbonate Radical Anion with Hydrogen Chloride in the Gas Phase.

    Science.gov (United States)

    Tang, Wai Kit; van der Linde, Christian; Siu, Chi-Kit; Beyer, Martin K

    2017-01-12

    The carbonate radical anion CO3(•-) is a key intermediate in tropospheric anion chemistry. Despite its radical character, only a small number of reactions have been reported in the literature. Here we investigate the gas-phase reactions of CO3(•-) and CO3(•-)(H2O) with HCl under ultrahigh vacuum conditions. Bare CO3(•-) forms OHCl(•-) with a rate constant of 4.2 × 10(-12) cm(3) s(-1), which corresponds to an efficiency of only 0.4%. Hydration accelerates the reaction, and ligand exchange of H2O against HCl proceeds with a rate of 2.7 × 10(-10) cm(3) s(-1). Quantum chemical calculations reveal that OHCl(•-) is best described as an OH(•) hydrogen bonded to Cl(-), while the ligand exchange product is Cl(-)(HCO3(•)). Under tropospheric conditions, where CO3(•-)(H2O) is the dominant species, Cl(-)(HCO3(•)) is efficiently formed. These reactions must be included in models of tropospheric anion chemistry.

  19. Chloride anion effect on the advanced oxidation processes of methidathion and dimethoate: role of Cl2(·-) radical.

    Science.gov (United States)

    Caregnato, Paula; Rosso, Janina A; Soler, Juán M; Arques, Antonio; Mártire, Daniel O; Gonzalez, Mónica C

    2013-01-01

    The reaction of phosphor-containing pesticides such as methidathion (MT) and dimethoate (DM) with dichloride radical anions (Cl(2)(·-)) was investigated. The second order rate constants (1.3 ± 0.4) × 10(8) and (1.1 ± 0.4) × 10(8) M(-1) s(-1) were determined for the reaction of Cl(2)(·-) with MT and DM, respectively. A reaction mechanism involving an initial charge transfer from the sulfide groups of the insecticides to Cl(2)(·-) is proposed and supported by the identified transient intermediates and reaction products. The formation of chlorinated byproducts was determined. The unexpected consequences of an efficient Cl(2)(·-) reactivity towards MT and DM on the degradation capacity by Advanced Oxidation Procedures applied to polluted waters containing the insecticides and Cl(-) anions is discussed.

  20. Formation and decay of fluorobenzene radical anions affected by their isomeric structures and the number of fluorine atoms.

    Science.gov (United States)

    Higashino, Saki; Saeki, Akinori; Okamoto, Kazumasa; Tagawa, Seiichi; Kozawa, Takahiro

    2010-08-12

    Aryl fluoride has attracted much attention as a resist component for extreme ultraviolet (EUV) lithography, because of the high absorption cross section of fluorine for EUV photons; however, less is known about electron attachment to fluorobenzene (FBz) and the stability of the reduced state. Picosecond and nanosecond pulse radiolysis of tetrahydrofuran solutions of FBz from mono-, di-, tri-, tetra-, penta-, and hexafluorobenzene was performed, and the effects of isomeric structure and number of fluorine atoms were examined. Scavenging of solvated electrons was found to correlate with the electron affinity obtained by density functional theory in the gas phase, whereas the decay of FBz radical anions was dominated by the activation energy of fluorine anion dissociation calculated using a polarized continuum model (PCM). A sharp contrast in the lifetimes of ortho-, meta-, and para-position difluorobenzene was observed, which could provide information on the molecular design of functional materials.

  1. Effects of gamma-irradiation on the free radical and antioxidant contents in nine aromatic herbs and spices.

    Science.gov (United States)

    Calucci, Lucia; Pinzino, Calogero; Zandomeneghi, Maurizio; Capocchi, Antonella; Ghiringhelli, Silvia; Saviozzi, Franco; Tozzi, Sabrina; Galleschi, Luciano

    2003-02-12

    Nine spice and aromatic herb samples (i.e., basil, bird pepper, black pepper, cinnamon, nutmeg, oregano, parsley, rosemary, and sage) were gamma-irradiated at a dose of 10 kGy according to commercial practices. The effects of the disinfection treatment on the content of organic radicals and some nutrients (namely, vitamin C and carotenoids) in the samples were investigated by chromatographic and spectroscopic techniques. Irradiation resulted in a general increase of quinone radical content in all of the investigated samples, as revealed by electron paramagnetic resonance spectroscopy. The fate of these radicals after storage for 3 months was also investigated. The cellulose radical was clearly observed in a few samples. Significant losses of total ascorbate were found for black pepper, cinnamon, nutmeg, oregano, and sage, whereas a significant decrease of carotenoids content was observed for cinnamon, oregano, parsley, rosemary, bird pepper, and sage.

  2. Proton transfer from water to ketyl radical anion: Assessment of critical size of hydrated cluster and free energy barrier in solution from first principles simulations

    Science.gov (United States)

    Biswas, Sohag; Dasgupta, Teesta; Mallik, Bhabani S.

    2016-09-01

    We present the reactivity of an organic intermediate by studying the proton transfer process from water to ketyl radical anion using gas phase electronic structure calculations and the metadynamics method based first principles molecular dynamics (FPMD) simulations. Our results indicate that during the micro solvation of anion by water molecules systematically, the presence of minimum three water molecules in the gas phase cluster is sufficient to observe the proton transfer event. The analysis of trajectories obtained from initial FPMD simulation of an aqueous solution of the anion does not show any evident of complete transfer of the proton from water. The cooperativity of water molecules and the relatively weak anion-water interaction in liquid state prohibit the full release of the proton. Using biasing potential through first principles metadynamics simulations, we report the observation of proton transfer reaction from water to ketyl radical anion with a barrier height of 16.0 kJ/mol.

  3. Role of phenyl radicals in the growth of polycyclic aromatic hydrocarbons.

    Science.gov (United States)

    Shukla, Bikau; Susa, Akio; Miyoshi, Akira; Koshi, Mitsuo

    2008-03-20

    To investigate the role of phenyl radical in the growth of PAHs (polycyclic aromatic hydrocarbons), pyrolysis of toluene with and without benzene has been studied by using a heatable tubular reactor couple with an in-situ sampling vacuum ultraviolet (VUV) single photon ionization (SPI) time-of-flight mass spectrometer (TOFMS) at temperatures 1155-1467 K and a pressure of 10.02 Torr with 0.56 s residence time. When benzene was added, a significant increase of phenyl addition products (biphenyl, terphenyl, and triphenylene) was observed and the mass spectra showed a clear regular sequence with an interval of approximately 74 mass number, corresponding to the phenyl addition (+C6H5) followed by H-elimination (-H) and cyclization (-H2). The analysis showed that the PAC (phenyl addition/cylization) mechanism is efficient for the growth of PAHs without a triple fusing site, for which the HACA (hydrogen abstraction/C2H2 addition) step is inefficient, and produces PAHs with five-membered rings. The PAC process was also suggested to be efficient in the subsequent growth of PAHs with five-membered rings. The role of the PAC mechanism in combustion conditions is discussed in relation to the importance of disordered five-membered ring structure in fullerene or soot core.

  4. Aqueous-Phase Reactions of Isoprene with Sulfoxy Radical Anions as a way of Wet Aerosol Formation in the Atmosphere

    Science.gov (United States)

    Kuznietsova, I.; Rudzinski, K. J.; Szmigielski, R.; Laboratory of the Environmental Chemistry

    2011-12-01

    Atmospheric aerosols exhibit an important role in the environment. They have implications on human health and life, and - in the larger scale - on climate, the Earth's radiative balance and the cloud's formation. Organic matter makes up a significant fraction of atmospheric aerosols (~35% to ~90%) and may originate from direct emissions (primary organic aerosol, POA) or result from complex physico-chemical processes of volatile organic compounds (secondary organic aerosol, SOA). Isoprene (2-methyl-buta-1,3-diene) is one of the relevant volatile precursor of ambient SOA in the atmosphere. It is the most abundant non-methane hydrocarbon emitted to the atmosphere as a result of living vegetation. According to the recent data, the isoprene emission rate is estimated to be at the level of 500 TgC per year. While heterogeneous transformations of isoprene have been well documented, aqueous-phase reactions of this hydrocarbon with radical species that lead to the production of new class of wet SOA components such as polyols and their sulfate esters (organosulfates), are still poorly recognized. The chain reactions of isoprene with sulfoxy radical-anions (SRA) are one of the recently researched route leading to the formation of organosulfates in the aqueous phase. The letter radical species originate from the auto-oxidation of sulfur dioxide in the aqueous phase and are behind the phenomenon of atmospheric acid rain formation. This is a complicated chain reaction that is catalyzed by transition metal ions, such as manganese(II), iron(III) and propagated by sulfoxy radical anions . The presented work addresses the chemical interaction of isoprene with sulfoxy radical-anions in the water solution in the presence of nitrite ions and nitrous acid, which are important trace components of the atmosphere. We showed that nitrite ions and nitrous acid significantly altered the kinetics of the auto-oxidation of SO2 in the presence of isoprene at different solution acidity from 2 to 8

  5. Anionaromatic neutral tweezers complexes: are they stable in polar solvents?

    Science.gov (United States)

    Sánchez-Lozano, Marta; Otero, Nicolás; Hermida-Ramón, Jose M; Estévez, Carlos M; Mandado, Marcos

    2011-03-17

    The impact of the solvent environment on the stabilization of the complexes formed by fluorine (T-F) and cyanide (T-CN) substituted tweezers with halide anions has been investigated theoretically. The study was carried out using computational methodologies based on density functional theory (DFT) and symmetry adapted perturbation theory (SAPT). Interaction energies were obtained at the M05-2X/6-31+G* level. The obtained results show a large stability of the complexes in solvents with large dielectric constant and prove the suitability of these molecular tweezers as potential hosts for anion recognition in solution. A detailed analysis of the effects of the solvent on the electron withdrawing ability of the substituents and its influence on the complex stability has been performed. In particular, the interaction energy in solution was split up into intermonomer and solvent-complex terms. In turn, the intermonomer interaction energy was partitioned into electrostatic, exchange, and polarization terms. Polar resonance structures in T-CN complexes are favored by polar solvents, giving rise to a stabilization of the intermonomer interaction, the opposite is found for T-F complexes. The solvent-complex energy increases with the polarity of the solvent in T-CN complexes, nonetheless the energy reaches a maximum and then decreases slowly in T-F complexes. An electron density analysis was also performed before and after complexation, providing an explanation to the trends followed by the interaction energies and their different components in solution.

  6. Proton transfer from 1,4-pentadiene to superoxide radical anion: a QTAIM analysis

    Directory of Open Access Journals (Sweden)

    Angela Rodríguez-Serrano

    2014-04-01

    Full Text Available We studied the bis-allylic proton transferreaction from 1,4-pentadiene to superoxideradical anion (O2·־. Minima andtransition state geometries, as well asthermochemical parameters were computedat the B3LYP/6-311+G(3df,2plevel of theory. The electronic wavefunctions of reactants, intermediates,and products were analyzed within theframework of the Quantum Theory ofAtoms in Molecules. The results showthe formation of strongly hydrogen bondedcomplexes between the 1,4-pentadien-3-yl anion and the hydroperoxylradical as the reaction products. Theseproduct complexes (PCs are more stablethan the isolated reactants and muchmore stable than the isolated products.This reaction occurs via pre-reactivecomplexes which are more stable thanthe PCs and the transition states. This isin agreement with the fact that the netproton transfer reaction that leads to freeproducts is an endothermic and nonspontaneousprocess.

  7. Polyimido sulphur anions S(NR)$^{m-}_{n}$: Free radicals and coordination behaviour

    Indian Academy of Sciences (India)

    Dietmar Stalke

    2000-06-01

    In a reaction sequence of amide addition followed by halogen oxidation the triazasulphite S(NR)$^{2-}_{3}$ and the tetrazasulphate S(NR)$^{2-}_{4}$ are readily accessible from sulphur diimide S(NR)2 via sulphur triimide S(NR)3. Addition of lithium organics to sulphur triimide provides a general route to triazasulphonates RS(NR)$^{2-}_{3}$. All these anions resemble potential tripodal coordination behaviour because of their nitrogen donor centres. Furthermore, the sulphur polyimido ligands are capable of responding to the various requirements of different metals (even in mixed metal species) by charge (de)localization. This paper deals with the synthetic routes of the sulphur nitrogen anions and their coordination behaviour. Their reactivity, mainly towards main group metal synthons, is also discussed.

  8. Theoretical and experimental studies of the spin trapping of inorganic radicals by 5,5-dimethyl-1-pyrroline N-oxide (DMPO). 1. Carbon dioxide radical anion.

    Science.gov (United States)

    Villamena, Frederick A; Locigno, Edward J; Rockenbauer, Antal; Hadad, Christopher M; Zweier, Jay L

    2006-12-14

    The carbon dioxide radical anion (CO2*-) is known to be generated in vivo through various chemical and biochemical pathways. Electron paramagnetic resonance (EPR) spin trapping with the commonly used spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO), has been employed in the detection of CO2*-. The thermodynamics of CO2*- addition to DMPO was predicted using density functional theory (DFT) at the B3LYP/6-31++G**//B3LYP/6-31G* and B3LYP/6-311+G* levels with the polarizable continuum model (PCM) to simulate the effect of the bulk dielectric effect of water on the calculated energetics. Three possible products of CO2*- addition to DMPO were predicted: (1) a carboxylate adduct, (2) pyrroline-alcohol and (3) DMPO-OH. Experimentally, UV photolysis of H2O2 in the presence of sodium formate (NaHCO2) and DMPO gave an EPR spectrum characteristic of a C-centered carboxylate adduct and is consistent with the theoretically derived hyperfine coupling constants (hfcc). The pKa of the carboxylate adduct was estimated computationally to be 6.4. The mode of CO2*- addition to DMPO is predicted to be governed predominantly by the spin (density) population on the radical, whereas electrostatic effects are not the dominant factor for the formation of the persistent adduct. The thermodynamic behavior of CO2*- in the aqueous phase is predicted to be similar to that of mercapto radical (*SH), indicating that formation of CO2*- in biological systems may have an important role in the initiation of oxidative damage in cells.

  9. Viral infection correlated with superoxide anion radicals production and natural and synthetic copper complexes.

    Science.gov (United States)

    Tomas, E; Popescu, A; Titire, A; Cajal, N; Cristescu, C; Tomas, S

    1989-01-01

    Studies conducted on asymmetric triazine derivatives synthetized at the Chemical and Pharmaceutical Research Institute showed that products S1, S16, S17, S19, S20 and S22 have a remarkable O2- radical scavenger activity. Among these derivatives, the product S1 is the most efficient as an antiviral agent.

  10. Mechanistic aspects of the oxidative and reductive fragmentation of n-nitrosoamines: a new method for generating nitrenium cations, amide anions, and aminyl radicals

    OpenAIRE

    Piech, Krzysztof; Bally, Thomas; Sikora, Adam; Marcinek, Andrzej

    2008-01-01

    A new method for investigating the mechanisms of nitric oxide release from NO donors under oxidative and reductive conditions is presented. Based on the fragmentation of N-nitrosoamines, it allows generation and spectroscopic characterization of nitrenium cations, amide anions, and aminyl radicals. X-irradiation of N-nitroso-N,N-diphenylamine 1 in Ar matrices at 10 K is found to yield the corresponding radical ions, which apparently undergo spontaneous loss of NO° under the conditions of this...

  11. Reactions of superoxide dismutases with HS(-)/H2S and superoxide radical anion: An in vitro EPR study.

    Science.gov (United States)

    Bolić, Bojana; Mijušković, Ana; Popović-Bijelić, Ana; Nikolić-Kokić, Aleksandra; Spasić, Snežana; Blagojević, Duško; Spasić, Mihajlo B; Spasojević, Ivan

    2015-12-01

    Interactions of hydrogen sulfide (HS(-)/H2S), a reducing signaling species, with superoxide dimutases (SOD) are poorly understood. We applied low-T EPR spectroscopy to examine the effects of HS(-)/H2S and superoxide radical anion O2.- on metallocenters of FeSOD, MnSOD, and CuZnSOD. HS(-)/H2S did not affect FeSOD, whereas active centers of MnSOD and CuZnSOD were open to this agent. Cu(2+) was reduced to Cu(1+), while manganese appears to be released from MnSOD active center. Untreated and O2.- treated FeSOD and MnSOD predominantly show 5 d-electron systems, i.e. Fe(3+) and Mn(2+). Our study provides new details on the mechanisms of (patho)physiological effects of HS(-)/H2S.

  12. Mechanisms of oxidation of guanine in DNA by carbonate radical anion, a decomposition product of nitrosoperoxycarbonate.

    Science.gov (United States)

    Lee, Young Ae; Yun, Byeong Hwa; Kim, Seog K; Margolin, Yelena; Dedon, Peter C; Geacintov, Nicholas E; Shafirovich, Vladimir

    2007-01-01

    Peroxynitrite is produced during inflammation and combines rapidly with carbon dioxide to yield the unstable nitrosoperoxycarbonate, which decomposes (in part) to CO(3) (.-) and (.)NO(2) radicals. The CO(3) (.-) radicals oxidize guanine bases in DNA through a one-electron transfer reaction process that ultimately results in the formation of stable guanine oxidation products. Here we have explored these mechanisms, starting with a spectroscopic study of the kinetics of electron transfer from 20-22mer double-stranded oligonucleotides to CO(3) (.-) radicals, together with the effects of base sequence on the formation of the end-products in runs of one, two, or three contiguous guanines. The distributions of these alkali-labile lesions were determined by gel electrophoresis methods. The cascade of events was initiated through the use of 308 nm XeCl excimer laser pulses to generate CO(3) (.-) radicals by an established method based on the photodissociation of persulfate to sulfate radicals and the oxidation of bicarbonate. Although the Saito model (Saito et al., J. Am. Chem. Soc. 1995, 117, 6406-6407) predicts relative ease of one-electron oxidations in DNA, following the trend 5'-GGG > 5'-GG > 5'-G, we found that the rate constants for CO(3) (.-)-mediated oxidation of guanines in these sequence contexts (k(5)) showed only small variation within a narrow range [(1.5-3.0)x10(7) M(-1) s(-1)]. In contrast, the distributions of the end-products are dependent on the base sequence context and are higher at the 5'-G in 5'-GG sequences and at the first two 5'-guanines in the 5'-GGG sequences. These effects are attributed to a combination of initial hole distributions among the contiguous guanines and the subsequent differences in chemical reaction yields at each guanine. The lack of dependence of k(5) on sequence context indicates that the one-electron oxidation of guanine in DNA by CO(3) (.-) radicals occurs by an inner-sphere mechanism.

  13. Role of Kekul\\'e and Non-Kekul\\'e Structures in the Radical Character of Alternant Polycyclic Aromatic Hydrocarbons: A TAO-DFT Study

    CERN Document Server

    Yeh, Chia-Nan

    2016-01-01

    We investigate the role of Kekul\\'e and non-Kekul\\'e structures in the radical character of alternant polycyclic aromatic hydrocarbons (PAHs) using thermally-assisted-occupation density functional theory (TAO-DFT), an efficient electronic structure method for the study of large ground-state systems with strong static correlation effects. Our results reveal that the studies of Kekul\\'e and non-Kekul\\'e structures qualitatively describe the radical character of alternant PAHs, which could be useful when electronic structure calculations are infeasible due to the expensive computational cost. In addition, our results support previous findings on the increase in radical character with increasing system size. For alternant PAHs with the same number of aromatic rings, the geometrical arrangements of aromatic rings are responsible for their radical character.

  14. OH-radical induced degradation of hydroxybenzoic- and hydroxycinnamic acids and formation of aromatic products-A gamma radiolysis study

    Energy Technology Data Exchange (ETDEWEB)

    Krimmel, Birgit; Swoboda, Friederike [University of Vienna, Department of Nutritional Sciences, Section Radiation Biology (Austria); Solar, Sonja, E-mail: sonja.solar@univie.ac.a [University of Vienna, Department of Nutritional Sciences, Section Radiation Biology (Austria); Reznicek, Gottfried [Department of Pharmacognosy, Althanstrasse 14, A-1090 Vienna (Austria)

    2010-12-15

    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{sub 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.

  15. OH-radical induced degradation of hydroxybenzoic- and hydroxycinnamic acids and formation of aromatic products—A gamma radiolysis study

    Science.gov (United States)

    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.

  16. Electron attachment to solvated dGpdG: effects of stacking on base-centered and phosphate-centered valence-bound radical anions.

    Science.gov (United States)

    Gu, Jiande; Liang, Guoming; Xie, Yaoming; Schaefer, Henry F

    2012-04-23

    To explore the nature of electron attachment to guanine-centered DNA single strands in the presence of a polarizable medium, a theoretical investigation of the DNA oligomer dinucleoside phosphate deoxyguanylyl-3',5'-deoxyguanosine (dGpdG) was performed by using density functional theory. Four different electron-distribution patterns for the radical anions of dGpdG in aqueous solution have been located as local minima on the potential energy surface. The excess electron is found to reside on the proton of the phosphate group (dGp(H-)dG), or on the phosphate group (dGp(.-)dG), or on the nucleobase at the 5' position (dG(.-)pdG), or on the nucleobase at the 3' position (dGpdG(.-)), respectively. These four radical anions are all expected to be electronically viable species under the influence of the polarizable medium. The predicted energetics of the radical anions follows the order dGp(.-)dG>dG(.-)pdG>dGpdG(.-)>dGp(H-)dG. The base-base stacking pattern in DNA single strands seems unaffected by electron attachment. On the contrary, intrastrand H-bonding is greatly influenced by electron attachment, especially in the formation of base-centered radical anions. The intrastrand H-bonding patterns revealed in this study also suggest that intrastrand proton transfer might be possible between successive guanines due to electron attachment to DNA single strands.

  17. Sonochemiluminescence of lucigenin: Evidence of superoxide radical anion formation by ultrasonic irradiation

    Science.gov (United States)

    Matsuoka, Masanori; Takahashi, Fumiki; Asakura, Yoshiyuki; Jin, Jiye

    2016-07-01

    The sonochemiluminescence (SCL) behavior of lucigenin (Luc2+) has been studied in aqueous solutions irradiated with 500 kHz ultrasound. Compared with the SCL of a luminol system, a tremendously increased SCL intensity is observed from 50 µM Luc2+ aqueous solution (pH =11) when small amounts of coreactants such as 2-propanol coexist. It is shown that SCL intensity strongly depends on the presence of dissolved gases such as air, O2, N2, and Ar. The highest SCL intensity is obtained in an O2-saturated solution, indicating that molecular oxygen is required to generate SCL. Since SCL intensity is quenched completely in the presence of superoxide dismutase (SOD), an enzyme that can catalyze the disproportionation of O2 •-, the generation of O2 •- in the ultrasonic reaction field is important in the SCL of Luc2+. In this work, the evidence of O2 •- production is examined by a spectrofluorometric method using 2-(2-pyridyl)benzothiazoline as the fluorescent probe. The results indicate that the yield of O2 •- is markedly increased in the O2-saturated solutions when a small amount of 2-propanol coexists, which is consistent with the results of SCL measurements. 2-Propanol in the interfacial region of a cavitation bubble reacts with a hydroxyl radical (•OH) to form a 2-propanol radical, CH3C•(OH)CH3, which can subsequently react with dissolved oxygen to generate O2 •-. The most likely pathways for SCL as well as the spatial distribution of SCL in a microreactor are discussed in this study.

  18. Superoxide anion radicals induce IGF-1 resistance through concomitant activation of PTP1B and PTEN.

    Science.gov (United States)

    Singh, Karmveer; Maity, Pallab; Krug, Linda; Meyer, Patrick; Treiber, Nicolai; Lucas, Tanja; Basu, Abhijit; Kochanek, Stefan; Wlaschek, Meinhard; Geiger, Hartmut; Scharffetter-Kochanek, Karin

    2015-01-01

    The evolutionarily conserved IGF-1 signalling pathway is associated with longevity, metabolism, tissue homeostasis, and cancer progression. Its regulation relies on the delicate balance between activating kinases and suppressing phosphatases and is still not very well understood. We report here that IGF-1 signalling in vitro and in a murine ageing model in vivo is suppressed in response to accumulation of superoxide anions (O2∙-) in mitochondria, either by chemical inhibition of complex I or by genetic silencing of O2∙--dismutating mitochondrial Sod2. The O2∙--dependent suppression of IGF-1 signalling resulted in decreased proliferation of murine dermal fibroblasts, affected translation initiation factors and suppressed the expression of α1(I), α1(III), and α2(I) collagen, the hallmarks of skin ageing. Enhanced O2∙- led to activation of the phosphatases PTP1B and PTEN, which via dephosphorylation of the IGF-1 receptor and phosphatidylinositol 3,4,5-triphosphate dampened IGF-1 signalling. Genetic and pharmacologic inhibition of PTP1B and PTEN abrogated O2∙--induced IGF-1 resistance and rescued the ageing skin phenotype. We thus identify previously unreported signature events with O2∙-, PTP1B, and PTEN as promising targets for drug development to prevent IGF-1 resistance-related pathologies.

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

    Science.gov (United States)

    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.

  20. Radical chemistry in the thermal decomposition of anisole and deuterated anisoles: an investigation of aromatic growth.

    Science.gov (United States)

    Scheer, Adam M; Mukarakate, Calvin; Robichaud, David J; Ellison, G Barney; Nimlos, Mark R

    2010-09-02

    The pyrolyses of anisole (C(6)H(5)OCH(3)), d(3)-anisole (C(6)H(5)OCD(3)), and d(8)-anisole (C(6)D(5)OCD(3)) have been studied using a hyperthermal tubular reactor and photoionization reflectron time-of-flight mass spectrometer. Gas exiting the reactor is subject to an immediate supersonic expansion after a residence time of approximately 65 mus. This allows the detection of highly reactive radical intermediates. Our results confirm that the first steps in the thermal decomposition of anisole are the loss of a methyl group to form phenoxy radical, followed by ejection of a CO to form cyclopentadienyl radical (c-C(5)H(5)); C(6)H(5)OCH(3) --> C(6)H(5)O + CH(3); C(6)H(5)O --> c-C(5)H(5) + CO. At high temperatures (T(wall) = 1200 degrees C - 1300 degrees C) the c-C(5)H(5) decomposes to propargyl radical (CH(2)CCH) and acetylene; c-C(5)H(5) --> CH(2)CCH + C(2)H(2). The formation of benzene and naphthalene is demonstrated with 1 + 1 resonance-enhanced multiphoton ionization. Propargyl radical recombination is a significant benzene formation channel. However, we show the majority of benzene is formed by a ring expansion reaction of methylcyclopentadiene (C(5)H(5)CH(3)) resulting from methyl radical addition to cyclopentadienyl radical; CH(3) + c-C(5)H(5) --> C(5)H(5)CH(3) --> C(6)H(6) + 2H. The naphthalene is generated from cyclopentadienyl radical recombination; 2c-C(5)H(5) --> C(5)H(5)-C(5)H(5) --> C(10)H(8) + 2H. The respective intermediate amu 79 and 129 species associated with these reactions are detected, confirming the stepwise nature of the decompositions. These reactions are verified by pyrolysis studies of cyclopentadiene (C(5)H(6)) and C(5)H(5)CH(3) obtained from rapid thermal dissociation of the respective dimer compounds, as well as pyrolysis studies of propargyl bromide (BrCH(2)CCH).

  1. EPR studies of the vitamin K 1 semiquinone radical anion. Comparison to the electron acceptor A 1 in green plant photosystem I

    Science.gov (United States)

    Thurnauer, Marion C.; Brown, James W.; Gast, P.; Feezel, Laura L.

    Suggestions that the electron acceptor, A 1, in Photosystem I is a quinone have come from both optical and epr experiments. Vitamin K 1 (phylloquinone) is present in the PSI complex with a stoichiometry of two molecules per reaction center. In order to determine if A 1 can be identified with vitamin K 1, X-band and Q-band epr properties of the vitamin K 1 radical anion in frozen alcohol solutions are examined. The results are compared to the epr properties that have been observed for the reduced A 1 acceptor in vivo. The g-values obtained for the vitamin K 1 radical anion are consistent with identifying A 1 with vitamin K 1.

  2. Dehalogenation of aromatics by nucleophilic aromatic substitution.

    Science.gov (United States)

    Sadowsky, Daniel; McNeill, Kristopher; Cramer, Christopher J

    2014-09-16

    Nucleophilic aromatic substitution has been implicated as a mechanism for both the biotic and abiotic hydrodehalogenation of aromatics. Two mechanisms for the aqueous dehalogenation of aromatics involving nucleophilic aromatic substitution with hydride as a nucleophile are investigated using a validated density functional and continuum solvation protocol. For chlorinated and brominated aromatics, nucleophilic addition ortho to carbon-halogen bonds via an anionic intermediate is predicted to be the preferred mechanism in the majority of cases, while concerted substitution is predicted to be preferred for most fluorinated aromatics. Nucleophilic aromatic substitution reactions with the hydroxide and hydrosulfide anions as nucleophiles are also investigated and compared.

  3. Importance of fundamental sp, sp2, and sp3 hydrocarbon radicals in the growth of polycyclic aromatic hydrocarbons.

    Science.gov (United States)

    Shukla, Bikau; Koshi, Mitsuo

    2012-06-05

    The most basic chemistry of products formation in hydrocarbons pyrolysis has been explored via a comparative experimental study on the roles of fundamental sp, sp(2), and sp(3) hydrocarbon radicals/intermediates such as ethyne/ethynyl (C(2)H(2)/C(2)H), ethene/ethenyl (C(2)H(4)/C(2)H(3)), and methane/methyl (CH(4)/CH(3)) in products formations. By using an in situ time-of-flight mass spectrometry technique, gas-phase products of pyrolysis of acetylene (ethyne, C(2)H(2)), ethylene (ethene, C(2)H(4)), and acetone (propanone, CH(3)COCH(3)) were detected and found to include small aliphatic products to large polycyclic aromatic hydrocarbons (PAHs) of mass 324 amu. Observed products mass spectra showed a remarkable sequence of mass peaks at regular mass number intervals of 24, 26, or 14 indicating the role of the particular corresponding radicals, ethynyl (C(2)H), ethenyl (C(2)H(3)), or methyl (CH(3)), in products formation. The analysis of results revealed the following: (a) product formation in hydrocarbon pyrolysis is dominated by hydrogen abstraction and a vinyl (ethenyl, C(2)H(3)) radical addition (HAVA) mechanism, (b) contrary to the existing concept of termination of products mass growth at cyclopenta fused species like acenaphthylene, novel pathways forming large PAHs were found succeeding beyond such cyclopenta fused species by the further addition of C(2)H(x) or CH(3) radicals, (c) production of cyclopenta ring-fused PAHs (CP-PAHs) such as fluoranthene/corannulene appeared as a preferred route over benzenoid species like pyrene/coronene, (d) because of the high reactivity of the CH(3) radical, it readily converts unbranched products into products with aliphatic chains (branched product), and (e) some interesting novel products such as dicarbon monoxide (C(2)O), tricarbon monoxide (C(3)O), and cyclic ketones were detected especially in acetone pyrolysis. These results finally suggest that existing kinetic models of product formation should be modified to include

  4. The activity of 3- and 7-hydroxyflavones as scavengers of superoxide radical anion generated from photo-excited riboflavin

    Energy Technology Data Exchange (ETDEWEB)

    Montana, P.; Pappano, N.; Debattista, N. [Universidad Nacional de San Luis, Area de Quimica Fisica, San Luis (Argentina); Avila, V.; Posadaz, A.; Bertolotti, S.G.; Garcia, N.A. [Universidad Nacional de Rio Cuarto, Dto. de Quimica, Rio Cuarto (Argentina)

    2003-08-01

    The visible-light irradiation of the system Riboflavin plus 3-hydroxyflavone or plus 7-hydroxyflavone, under aerobic conditions, produces a series of competitive processes that depend on the relative concentrations of the pigment and the flavones. The picture comprises photochemical mechanisms that potentially operate in nature. They mainly include the quenching of Rf singlet ({sup 1}Rf*) and triplet ({sup 3}Rf*) excited states (with bimolecular rate constants in the order of 10{sup 9} M{sup -1} s{sup -1}) and superoxide radical anion-mediated reactions. The participation of the oxidative species singlet molecular oxygen was not detected. The overall result shows chemical transformations in both Rf and 3-hydroxyflavone. No experimental evidence was found indicating any chemical reaction involving 7-hydroxyflavone. The fate of the pigment also depends on the amount of the dissolved flavonoid. At 50 mM concentrations of these compounds or higher, practically no photochemistry occurs, owing to the extensive quenching of ({sup 1}Rf*) When the concentration of the flavones is in the mM range or lower, ({sup 3}Rf*) is photogenerated. Then, the excited triplet species can be quenched mainly by the flavones through an electron-transfer process, yielding the semireduced pigment. The latter interacts with dissolved oxygen producing O{sub 2}{sup .-}, which reacts with both the pigment and 3-hydroxyflavone. In summary, 3-hydroxyflavone and 7-hydroxyflavone participate in the generation of superoxide ion in an Rf-sensitized process, and simultaneously 3-hydroxyflavone constitutes a degradable quencher of the oxidative species. (author)

  5. Anion-induced Ag(I) self-assemblies with electron deficient aromatic ligands: anion-π-system interactions as a driving force for templated coordination networks.

    Science.gov (United States)

    Safin, Damir A; Pialat, Amélie; Leitch, Alicea A; Tumanov, Nikolay A; Korobkov, Ilia; Filinchuk, Yaroslav; Brusso, Jaclyn L; Murugesu, Muralee

    2015-06-11

    Three novel 1D, 2D and 3D coordination polymers were successfully isolated using nitrogen based 3,6-bis(2'-pyrimidyl)-1,2,4,5-tetrazine (BPymTz) and 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (TPymT) ligands with Ag(I) ions. The formation of these supramolecular assemblies was templated through anion-π-system interactions.

  6. Photocatalytic Anion Oxidation and Applications in Organic Synthesis.

    Science.gov (United States)

    Hering, Thea; Meyer, Andreas Uwe; König, Burkhard

    2016-08-19

    Ions and radicals of the same kind differ by one electron only. The oxidation of many stable inorganic anions yields their corresponding highly reactive radicals, and visible light excitable photocatalysts can provide the required oxidation potential for this transformation. Air oxygen serves as the terminal oxidant, or cheap sacrificial oxidants are used, providing a very practical approach for generating reactive inorganic radicals for organic synthesis. We discuss in this perspective several recently reported examples: Nitrate radicals are obtained by one-electron photooxidation of nitrate anions and are very reactive toward organic molecules. The photooxidation of sulfinate salts yields the much more stable sulfone radicals, which smoothly add to double bonds. A two-electron oxidation of chloride anions to electrophilic chlorine species reacting with arenes in aromatic substitutions extends the method beyond radical reactions. The chloride anion oxidation proceeds via photocatalytically generated peracidic acid as the oxidation reagent. Although the number of reported examples of photocatalytically generated inorganic radical intermediates for organic synthesis is still small, future extension of the concept to other inorganic ions as radical precursors is a clear perspective.

  7. Calculation of the properties of the S3- radical anion and its complexes with Cu+ in aqueous solution

    Science.gov (United States)

    Tossell, J. A.

    2012-10-01

    A species observed in aqueous sulfidic solutions at high T and P has recently been identified as the anion radical S3-, based on the Raman spectrum obtained in a hydrothermal diamond-anvil cell (Pokrovski and Dubrovinsky, 2011, Science, 331, 1052-1054). Such a species had not been expected to occur in such environments, although S3- as an component of lapis lazuli, other solids and even albite melt has been well studied (Winther et al., 1998; Reinen and Lindner, 1999; Arieli et al., 2004; Shnitko et al., 2008; Bacci et al., 2009). We have calculated the structures, energetics, vibrational and UV-visible spectra of S3- and several other similar species and confirm the species identification of Pokrovski and Dubrovinsky, although we are still somewhat concerned about the apparent lack of a third peak which we calculate to be present in the Raman spectrum of S3-. Our calculations indicate that the reaction: S6-2⇒2S3- in aqueous solution has a free energy change of +3 kcal/mol at 298 K and 1 atm pressure but -13 kcal/mol at 723 K and 1 atm pressure, consistent with the disappearance of disulfide species and the appearance of S3-at high T. Likewise, the free energy for the reaction: 2HS+SO4-2+H⇒S3-+.75O+2.5HO decreases from 44.1 to 19.0 kcal/mol between 298 and 723 K (again at 1 atm). This is consistent with the decrease in concentrations of SH- and SO4-2 and the formation of S3- observed by Pokrovski and Dubrovinski over this temperature range. The corresponding log K values are in semiquantitative agreement with those found by Pokrovski and Dubrovinsky. The main contribution to these changes in reaction free energy with temperature come from the VRT (vibrational-rotational-translational) contribution to the gas-phase free energy, while the hydration free energy difference changes little. Calculation of 34S-32S isotopic fractionations for S3- at 298 K give δ values of around +4.3% relative to H2S, a value intermediate between that of S3 and S3-2. Calculated free

  8. Superoxide anion radical (O2(-)) degrades methylmercury to inorganic mercury in human astrocytoma cell line (CCF-STTG1).

    Science.gov (United States)

    Mailloux, Ryan J; Yumvihoze, Emmanuel; Chan, Hing Man

    2015-09-05

    Methylmercury (MeHg) is a global pollutant that is affecting the health of millions of people worldwide. However, the mechanism of MeHg toxicity still remains somewhat elusive and there is no treatment. It has been known for some time that MeHg can be progressively converted to inorganic mercury (iHg) in various tissues including the brain. Recent work has suggested that cleavage of the carbon-metal bond in MeHg in a biological environment is facilitated by reactive oxygen species (ROS). However, the oxyradical species that actually mediates this process has not been identified. Here, we provide evidence that superoxide anion radical (O2(-)) can convert MeHg to iHg. The calculated second-order rate constant for the degradation of 1μM MeHg by O2(-) generated by xanthine/xanthine oxidase was calculated to be 2×10(5)M(-1)s(-1). We were also able to show that this bioconversion can proceed in intact CCF-STTG1 human astrocytoma cells exposed to paraquat (PQ), a O2(-) generating viologen. Notably, exposure of cells to increasing amounts of PQ led to a dose dependent increase in both MeHg and iHg. Indeed, a 24h exposure to 500μM PQ induced a ∼13-fold and ∼18-fold increase in intracellular MeHg and iHg respectively. These effects were inhibited by superoxide dismutase mimetic MnTBAP. In addition, we also observed that a 24h exposure to a biologically relevant concentration of MeHg (1μM) did not induce cell death, oxidative stress, or even changes in cellular O2(-) and H2O2. However, co-exposure to PQ enhanced MeHg toxicity which was associated with a robust increase in cell death and oxidative stress. Collectively our results show that O2(-) can bioconvert MeHg to iHg in vitro and in intact cells exposed to conditions that simulate high intracellular O2(-) production. In addition, we show for the first time that O2(-) mediated degradation of MeHg to iHg enhances the toxicity of MeHg by facilitating an accumulation of both MeHg and iHg in the intracellular

  9. Fluorinated Dodecaphenylporphyrins: Synthetic and Electrochemical Studies Including the First Evidence of Intramolecular Electron Transfer Between an Fe(II) Porphyrin -Anion Radical and an Fe(I) Porphyrin

    Energy Technology Data Exchange (ETDEWEB)

    D' Souza, F.; Forsyth, T.P.; Fukuzumi, S.; Kadish, K.M.; Krattinger, B.; Lin, M.; Medforth, C.J.; Nakanishi, I.; Nurco, D.J.; Shelnutt, J.A.; Smith, K.M.; Van Caemelbecke, E.

    1998-10-19

    Dodecaphenylporphyrins with varying degrees of fluorination of the peripheral phenyl rings (FXDPPS) were synthesized as model compounds for studying electronic effects in nonplan~ porphyrins, and detailed electrochemical studies of the chloroiron(HI) complexes of these compounds were undertaken. The series of porphyrins, represented as FeDPPCl and as FeFXDPPCl where x = 4, 8 (two isomers), 12, 20,28 or 36, could be reversibly oxidized by two electrons in dichloromethane to give n-cation radicals and n-dications. All of the compounds investigated could also be reduced by three electrons in benzonitrile or pyridine. In benzonitrile, three reversible reductions were observed for the unfluorinated compound FeDPPC1, whereas the FeFXDPPCl complexes generally exhibited irreversible first and second reductions which were coupled to chemical reactions. The chemical reaction associated with the first reduction involved a loss of the chloride ion after generation of Fe FXDPPC1. The second chemical reaction involved a novel intramolecular electron transfer between the initially generated Fe(H) porphyrin n-anion radical and the final Fe(I) porphyrin reduction product. In pyridine, three reversible one electron reductions were observed with the second reduction affording stable Fe(II) porphyrin o - anion radicals for ail of the complexes investigated.

  10. Preparation of high-capacity, weak anion-exchange membranes by surface-initiated atom transfer radical polymerization of poly(glycidyl methacrylate) and subsequent derivatization with diethylamine

    Science.gov (United States)

    Qian, Xiaolei; Fan, Hua; Wang, Chaozhan; Wei, Yinmao

    2013-04-01

    Ion-exchange membrane is of importance for the development of membrane chromatography. In this work, a high-capacity anion-exchange membrane was prepared by grafting of glycidyl methacrylate (GMA) onto the surface of regenerated cellulose (RC) membranes via surface-initiated atom transfer radical polymerization (SI-ATRP) and subsequent derivatization with diethylamine. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterize changes in the chemical functionality, surface topography and pore morphology of the modified membranes. The static capacity of the prepared anion-exchange membrane was evaluated with bovine serum albumin (BSA) as a model protein. The results indicated that the anion-exchange membrane which could reach a maximum capacity of 96 mg/mL for static adsorption possesses a higher adsorption capacity, and the adsorption capacity increases with the polymerization time. The effect of pH and salt concentration confirmed that the adsorption of BSA followed ion-exchange mechanism. The established method would have potential application in the preparation of anion-exchange membrane.

  11. Trapped Hydronium Radical Produced by Ultraviolet Excitation of Substituted Aromatic Molecule.

    Science.gov (United States)

    Hernández, Federico J; Capello, Marcela C; Naito, Ayumi; Manita, Shun; Tsukada, Kohei; Miyazaki, Mitsuhiko; Fujii, Masaaki; Broquier, Michel; Gregoire, Gilles; Dedonder-Lardeux, Claude; Jouvet, Christophe; Pino, Gustavo A

    2015-12-24

    The gas phase structure and excited state dynamics of o-aminophenol-H2O complex have been investigated using REMPI, IR-UV hole-burning spectroscopy, and pump-probe experiments with picoseconds laser pulses. The IR-UV spectroscopy indicates that the isomer responsible for the excitation spectrum corresponds to an orientation of the OH bond away from the NH2 group. The water molecule acts as H-bond acceptor of the OH group of the chromophore. The complexation of o-aminophenol with one water molecule induced an enhancement in the excited state lifetime on the band origin. The variation of the excited state lifetime of the complex with the excess energy from 1.4 ± 0.1 ns for the 0-0 band to 0.24 ± 0.3 ns for the band at 0-0 + 120 cm(-1) is very similar to the variation observed in the phenol-NH3 system. This experimental result suggests that the excited state hydrogen transfer reaction is the dominant channel for the non radiative pathway. Indeed, excited state ab initio calculations demonstrate that H transfer leading to the formation of the H3O(•) radical within the complex is the main reactive pathway.

  12. Ion distribution in quaternary-ammonium-functionalized aromatic polymers: effects on the ionic clustering and conductivity of anion-exchange membranes.

    Science.gov (United States)

    Weiber, E Annika; Jannasch, Patric

    2014-09-01

    A series of copoly(arylene ether sulfone)s that have precisely two, three, or four quaternary ammonium (QA) groups clustered directly on single phenylene rings along the backbone are studied as anion-exchange membranes. The copolymers are synthesized by condensation polymerizations that involve either di-, tri-, or tetramethylhydroquinone followed by virtually complete benzylic bromination using N-bromosuccinimide and quaternization with trimethylamine. This synthetic strategy allows excellent control and systematic variation of the local density and distribution of QA groups along the backbone. Small-angle X-ray scattering of these copolymers shows extensive ionic clustering, promoted by an increasing density of QA on the single phenylene rings. At an ion-exchange capacity (IEC) of 2.1 meq g(-1), the water uptake decreases with the increasing local density of QA groups. Moreover, at moderate IECs at 20 °C, the Br(-) conductivity of the densely functionalized copolymers is higher than a corresponding randomly functionalized polymer, despite the significantly higher water uptake of the latter. Thus, the location of multiple cations on single aromatic rings in the polymers facilitates the formation of a distinct percolating hydrophilic phase domain with a high ionic concentration to promote efficient anion transport, despite probable limitations by reduced ion dissociation. These findings imply a viable strategy to improve the performance of alkaline membrane fuel cells.

  13. Novel oxidation of aromatic aldehydes catalyzed by Preyssler's anion, [NaP{sub 5}W{sub 30}O{sub 110}]{sup 14-}

    Energy Technology Data Exchange (ETDEWEB)

    Bamoharram, F.F.; Roshani, M.; Moghayadi, M. [Islamic Azad University-Mashhad Branch, Mashhad (Iran, Islamic Republic of). Dept. of Chemistry]. E-mail: abamoharram@yahoo.com; Alizadeh, M.H. [Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of). Dept. of Chemistry; Razavi, H. [Georgetown University, Washington, DC (United States). Dept. of Chemistry

    2006-05-15

    Preyssler's anion, with formula [NaP{sub 5}W{sub 30}O{sub 110}]{sup 14-}, catalyzes the oxidation of aromatic aldehydes to related carboxylic acids by hydrogen peroxide as oxidizing agent, under microwave irradiation, or at 70 deg C. Both homogeneous and heterogeneous Preyssler's catalysts (as H{sub 14}[NaP{sub 5}W{sub 30}O{sub 110}]) were used and had their activity compared with those of some Keggin structures. Our data indicate that Sodium30-tungsto pentaphosphate, the so-called Preyssler's anion, with high hydrolytic (pH=0-12) and thermal stability is the best catalyst with high yield and good selectivity. Under microwave irradiation, this polyanion supported on SiO{sub 2} was found to be an excellent catalyst for aldehydes with low loss factor in 1-2 min (the loss factor is a measure of the ability of the material to dissipate energy). The effects of various parameters, including catalyst type, nature of the substituent in the aldehyde and temperature, on the yield of the carboxylic acids were studied. (author)

  14. Spectroscopic Properties of Novel Aromatic Metal Clusters: NaM4 (M=Al, Ga, In) and their Cations and Anions

    Energy Technology Data Exchange (ETDEWEB)

    Balasubramanian, K; Zhao, C

    2004-03-17

    The ground and several excited states of metal aromatic clusters, namely NaM4 and NaM{sub 4}{sup {+-}} (M=Al, Ga, In) clusters have been investigated by employing complete activespace self-consistent-field (CASSCF) followed by Multi-reference singles and doubles configuration interaction (MRSDCI) computations that included up to 10 million configurations and other methods. The ground states NaM{sub 4}{sup -} of aromatic anions are found to be symmetric C{sub 4v} ({sup 1}A{sub 1}) electronic states with ideal square pyramid geometries. While the ground state of NaIn4 is also predicted to be a symmetric C{sub 4v} ({sup 2}A{sub 1}) square pyramid, the ground state of the NaAl4 cluster is found to have a C{sub 2v} ({sup 2}A{sub 1}) pyramid with a rhombus base and the ground state of NaGa{sub 4} possesses a C{sub 2v} ({sup 2}A{sub 1}) pyramid with a rectangle base. In general these structures exhibit 2 competing geometries, viz., an ideal C{sub 4v} structure and a distorted rhomboidal or rectangular pyramid structure (C{sub 2v}). All of the ground states of the NaM{sub 4}{sup +} (M= Al, Ga, In) cations are computed to be C{sub 2v} ({sup 3}A{sub 2}) pyramids with rhombus bases. The equilibrium geometries, vibrational frequencies, dissociation energies, adiabatic ionization potentials, adiabatic electron affinities for the electronic states of NaM{sub 4} (M=Al, Ga, In) and their ions are computed and compared with experimental results and other theoretical calculations. On the basis of our computed excited states energy separations, we have tentatively suggested assignments to the observed X and A states in the anion photoelectron spectra of Al{sub 4}Na{sup -} reported by Li et al. The X state can be assigned to a C{sub 2v} ({sup 2}A{sub 1}) rhomboidal pyramid. The A state observed in the anion spectrum is assigned to the first excited state ({sup 2}B{sub 1}) of the neutral NaAl{sub 4} with the C{sub 4v} symmetry. The assignments of the excited states are consistent with

  15. Aromatic C-H Bond Functionalization Induced by Electrochemically in Situ Generated Tris(p-bromophenyl)aminium Radical Cation: Cationic Chain Reactions of Electron-Rich Aromatics with Enamides.

    Science.gov (United States)

    Li, Long-Ji; Jiang, Yang-Ye; Lam, Chiu Marco; Zeng, Cheng-Chu; Hu, Li-Ming; Little, R Daniel

    2015-11-01

    An effective Friedel-Crafts alkylation reaction of electron-rich aromatics with N-vinylamides, induced by electrochemically in situ-generated TBPA radical cation, has been developed; the resulting adducts are produced in good to excellent yields. In the "ex-cell" type electrolysis, TBPA is transformed to its oxidized form in situ and subsequently employed as an electron transfer reagent to initiate a cationic chain reaction. An easily recoverable and reusable polymeric ionic liquid-carbon black (PIL-CB) composite was also utilized as a supporting electrolyte for the electrochemical generation of TBPA cation radical, without sacrificing efficiency or stability after four electrolyses. Cyclic voltammetry analysis and the results of control experiments demonstrate that the reaction of electron-rich aromatics and N-vinylamides occurs via a cationic chain reaction, which takes place though an oxidative activation of a C-H bond of electron-rich aromatics instead of oxidation of the N-vinylamide as previously assumed.

  16. Anion conductive aromatic block copolymers containing diphenyl ether or sulfide groups for application to alkaline fuel cells.

    Science.gov (United States)

    Yokota, Naoki; Ono, Hideaki; Miyake, Junpei; Nishino, Eriko; Asazawa, Koichiro; Watanabe, Masahiro; Miyatake, Kenji

    2014-10-08

    A novel series of aromatic block copolymers composed of fluorinated phenylene and biphenylene groups and diphenyl ether (QPE-bl-5) or diphenyl sulfide (QPE-bl-6) groups as a scaffold for quaternized ammonium groups is reported. The block copolymers were synthesized via aromatic nucleophilic substitution polycondensation, chloromethylation, quaternization, and ion exchange reactions. The block copolymers were soluble in organic solvents and provided thin and bendable membranes by solution casting. The membranes exhibited well-developed phase-separated morphology based on the hydrophilic/hydrophobic block copolymer structure. The membranes exhibited mechanical stability as confirmed by DMA (dynamic mechanical analyses) and low gas and hydrazine permeability. The QPE-bl-5 membrane with the highest ion exchange capacity (IEC = 2.1 mequiv g(-1)) exhibited high hydroxide ion conductivity (62 mS cm(-1)) in water at 80 °C. A noble metal-free fuel cell was fabricated with the QPE-bl-5 as the membrane and electrode binder. The fuel cell operated with hydrazine as a fuel exhibited a maximum power density of 176 mW cm(-2) at a current density of 451 mA cm(-2).

  17. [Reliability of electron-transport membranes and the role of oxygen anion-radicals in aging: stochastic modulation of the genetic program].

    Science.gov (United States)

    Kol'tover, V K

    2010-01-01

    All biomolecular constructions and nanorecators are designed to perform preset functions. All of them operate with limited reliability, namely, for each and every device or bionanoreactor normal operation alternates with accidental malfunctions (failures). Timely preventive maintenance replacement (prophylaxis) of functional elements in cells and tissues, the so-called turnover, is the main line of assuring high system reliability of organism as a whole. There is a finite number of special groups of genes (reliability assuring structures, RAS) that perform supervisory functions over the preventive maintenance. In a hierarchic pluricellular organism, RAS are genetic regulatory networks of a special group of cells, like hypothalamic neurons in the suprachiasmatic nucleus of mammals. Of the primary importance is limited reliability of mitochondrial nanoreactors, since the random malfunctions of electron transport chains produce reactive anion-radicals of oxygen (superoxide radical, O2*(-)). With time, O2*(-) radicals initiate accumulation of irreparable damages in RAS. When these damages accumulate up to preset threshold level, a fatal decrease in reliability of RAS occurs. Thus, aging is the stochastic consequence of programmed deficiency in reliability of biomolecular constructions and nanoreactors including the genetically preset limit of the system reliability. This reliability approach provides the realistic explanation of the data on prolongation of life of experimental animals with antioxidants as well as the explanation of similar "hormetic" effects of ionizing radiation in low doses.

  18. Competitive Deprotonation and Superoxide [O2 -•] Radical-Anion Adduct Formation Reactions of Carboxamides under Negative-Ion Atmospheric-Pressure Helium-Plasma Ionization (HePI) Conditions

    Science.gov (United States)

    Hassan, Isra; Pinto, Spencer; Weisbecker, Carl; Attygalle, Athula B.

    2016-03-01

    Carboxamides bearing an N-H functionality are known to undergo deprotonation under negative-ion-generating mass spectrometric conditions. Herein, we report that N-H bearing carboxamides with acidities lower than that of the hydroperoxyl radical (HO-O•) preferentially form superoxide radical-anion (O2 -•) adducts, rather than deprotonate, when they are exposed to the glow discharge of a helium-plasma ionization source. For example, the spectra of N-alkylacetamides show peaks for superoxide radical-anion (O2 -•) adducts. Conversely, more acidic amides, such as N-alkyltrifluoroacetamides, preferentially undergo deprotonation under similar experimental conditions. Upon collisional activation, the O2 -• adducts of N-alkylacetamides either lose the neutral amide or the hydroperoxyl radical (HO-O•) to generate the superoxide radical-anion ( m/z 32) or the deprotonated amide [ m/z (M - H)-], respectively. For somewhat acidic carboxamides, the association between the two entities is weak. Thus, upon mildest collisional activation, the adduct dissociates to eject the superoxide anion. Superoxide-adduct formation results are useful for structure determination purposes because carboxamides devoid of a N-H functionality undergo neither deprotonation nor adduct formation under HePI conditions.

  19. Prion-derived copper-binding peptide fragments catalyze the generation of superoxide anion in the presence of aromatic monoamines

    Directory of Open Access Journals (Sweden)

    Tomonori Kawano

    2007-01-01

    Full Text Available Objectives: Studies have proposed two opposing roles for copper-bound forms of prion protein (PrP as an anti-oxidant supporting the neuronal functions and as a pro-oxidant leading to neurodegenerative process involving the generation of reactive oxygen species. The aim of this study is to test the hypothesis in which putative copper-binding peptides derived from PrP function as possible catalysts for monoamine-dependent conversion of hydrogen peroxide to superoxide in vitro. Materials and methods: Four peptides corresponding to the copper (II-binding motifs in PrP were synthesized and used for analysis of peptide-catalyzed generation of superoxide in the presence of Cu (II and other factors naturally present in the neuronal tissues. Results: Among the Cu-binding peptides tested, the amino acid sequence corresponding to the Cu-binding site in the helical region was shown to be the most active for superoxide generation in the presence of Cu(II, hydrogen peroxide and aromatic monoamines, known precursors or intermediates of neurotransmitters. Among monoamines tested, three compounds namely phenylethylamine, tyramine and benzylamine were shown to be good substrates for superoxide-generating reactions by the Cu-bound helical peptide. Conclusions: Possible roles for these reactions in development of prion disease were suggested.

  20. Application of dissolvable layered double hydroxides as sorbent in dispersive solid-phase extraction and extraction by co-precipitation for the determination of aromatic acid anions.

    Science.gov (United States)

    Tang, Sheng; Lee, Hian Kee

    2013-08-06

    Three types of magnesium-aluminum layered double hydroxides were synthesized and employed as solid-phase extraction (SPE) sorbents to extract several aromatic acids (protocatechuic acid, mandelic acid, phthalic acid, benzoic acid, and salicylic acid) from aqueous samples. An interesting feature of these sorbents is that they dissolve when the pH of the solution is lower than 4. Thus, the analyte elution step, as needed in conventional sorbent-based extraction, was obviated by dissolving the sorbent in acid after extraction and separation from the sample solution. The extract was then directly injected into a high-performance liquid chromatography-ultraviolet detection system for analysis. In the key adsorption process, both dispersive SPE and co-precipitation extraction with the sorbents were conducted and experimental parameters such as pH, temperature, and extraction time were optimized. The results showed that both extraction methods provided low limits of detection (0.03-1.47 μg/L) and good linearity (r(2) > 0.9903). The optimized extraction conditions were applied to human urine and sports drink samples. This new and interesting extraction approach was demonstrated to be a fast and efficient procedure for the extraction of organic anions from aqueous samples.

  1. Reaction of sulphate radical anion (SO{sub 4}{sup {center_dot}}{sup -}) with cyanuric acid. A potential reaction for its degradation?

    Energy Technology Data Exchange (ETDEWEB)

    Manoj, P.; Varghese, R.; Manoj, V.M.; Aravindakumar, C.T. [Mahatma Gandhi University, School of Chemical Sciences, Kottayam (India)

    2002-01-01

    A novel reaction between sulfate radical anion (SO{sub 4}{sup {center_dot}}{sup -}) and cyanuric acid (CA), a non-degradable end product of the oxidative degradation of the triazine based herbicide, atrazine, is presented using laser flash photolysis and steady state radiolysis techniques at pH 5. A second order rate constant of 1.9x10{sup 7} dm{sup 3} mol{sup -1} s{sup -1} has been determined and the transient intermediate ({lambda}{sub max}=330 nm) is assigned to a radical cation of CA (CA{sup {center_dot}}{sup +}). The degradation profile indicated that about 76% of CA have been decomposed after an absorbed {gamma}-radiation dose of 18 kGy. It is therefore proposed that the reaction of SO{sub 4}{sup {center_dot}}{sup -} could be utilised for the degradation of CA in aqueous medium which is normally stable to any Advanced Oxidation Processes. (author)

  2. 氧脱木素过程中超氧阴离子自由基的控制%Regulation of Superoxide Anion Radical During the Oxygen Delignification Process

    Institute of Scientific and Technical Information of China (English)

    曹石林; 詹怀宇; 付时雨; 陈礼辉

    2007-01-01

    In this study, the superoxide anion radicals were generated by the auto-oxidation of 1,2,3-trihydroxybenzene and determined by UV spectrophotometry, and the reaction was found to be facilitated by anthraquinone-2-sulfonic acid sodium salt. The bamboo kraft pulps were treated by the 1,2,3-trihydroxybenzene auto-oxidation method or the 1,2,3-trihydroxybenzene auto-oxidation combined with anthraquinone-2-suffonic acid sodium salt to show the effect of the superoxide anion radicals during the oxygen delignification of bamboo kraft pulp and the enhancing affect of anthraquinone compounds as an additive on delignification. The results indicated that the superoxide anion radicals could react with lignin and remove it from pulp with negligible damage on cellulose, and the anthraquinone-2-sulfonic acid sodium salt could facilitate the generation of superoxide anion radical to enhance delignification of pulps. The oxygen delignification selectivity could be improved using the 1,2,3-trihydroxybenzene auto-oxidation system combined with anthraquinone-2-sulfonic acid sodium salt.

  3. Construction of a highly sensitive non-enzymatic sensor for superoxide anion radical detection from living cells.

    Science.gov (United States)

    Liu, Yuelin; Liu, Xiuhui; Liu, Yidan; Liu, Guoan; Ding, Lan; Lu, Xiaoquan

    2017-04-15

    A novel non-enzymatic superoxide anion (O2•(-)) sensor was fabricated based on Ag nanoparticles (NPs)/L-cysteine functioned carbon nanotubes (Cys-MWCNTs) nanocomposites and used to measure the release of O2•(-) from living cells. In this strategy, AgNPs could be uniformly electrodeposited on the MWCNTs surface with average diameter of about 20nm as exhibited by scanning electronmicroscopy (SEM). Electrochemical study demonstrated that the AgNPs/Cys-MWCNTs modified glassy carbon electrode exhibited excellent catalytic activity toward the reduction of O2•(-) with a super wide linear range from 7.00×10(-11) to 7.41×10(-5)M and a low detection limit (LOD) of 2.33×10(-11)M (S/N=3). Meanwhile, the mechanism for O2•(-) reduction was also proposed for the first time. Importantly, this novel non-enzymatic O2•(-) sensor can detect O2•(-) release from cancer cells under both the external stimulation and the normal condition, which has the great potential application in clinical diagnostics to assess oxidative stress of living cells.

  4. Transition Metal Complexes and Radical Anion Salts of 1,10-Phenanthroline Derivatives Annulated with a 1,2,5-Tiadiazole and 1,2,5-Tiadiazole 1,1-Dioxide Moiety: Multidimensional Crystal Structures and Various Magnetic Properties

    Directory of Open Access Journals (Sweden)

    Yoshiaki Shuku

    2014-01-01

    Full Text Available Advances in the molecular variety and the elucidation of the physical properties of 1,10-phenanthroline annulated with 1,2,5-thiadiazole and 1,2,5-thiadiazole 1,1-dioxide moieties have been achieved, and are described herein. A 1,2,5-thiadiazole compound, [1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline (tdap, was used as a ligand to create multidimensional network structures based on S•••S and S•••N intermolecular interactions. A 1,2,5-thiadiazole 1,1-dioxide compound, [1,2,5] thiadiazolo[3,4-f][1,10]phenanthroline, 1,1-dioxide (tdapO2, was designed to create a stable radical anion, as well as good network structures. Single crystal X-ray structure analyses revealed that transition metal complexes of tdap, and radical anion salts of tdapO2 formed multidimensional network structures, as expected. Two kinds of tdap iron complexes, namely [Fe(tdap2(NCS2] and [Fe(tdap2(NCS2]•MeCN exhibited spin crossover transitions, and their transition temperatures showed a difference of 150 K, despite their similar molecular structures. Magnetic measurements for the tdapO2 radical anion salts revealed that the magnetic coupling constants between neighboring radical species vary from strongly antiferromagnetic (J = −320 K to ferromagnetic (J = 24 K, reflecting the differences in their π overlap motifs.

  5. Mulliken Hush elucidation of the encounter (precursor) complex in intermolecular electron transfer via self-exchange of tetracyanoethylene anion-radical

    Science.gov (United States)

    Rosokha, S. V.; Newton, M. D.; Head-Gordon, M.; Kochi, J. K.

    2006-05-01

    The paramagnetic [1:1] encounter complex (TCNE)2-rad is established as the important precursor in the kinetics and mechanism of electron-transfer for the self-exchange between tetracyanoethylene acceptor ( TCNE) and its radical-anion as the donor. Spectroscopic observation of the dimeric complex (TCNE)2-rad by its intervalence absorption band at the solvent-dependent wavelength of λIV ˜ 1500 nm facilitates the application of Mulliken-Hush theory which reveals the significant electronic interaction extant between the pair of cofacial TCNE moieties with the sizable coupling of HDA = 1000 cm -1. The transient existence of such an encounter complex provides the critical link in the electron-transfer kinetics by lowering the classical Marcus reorganization barrier by the amount of HDA in this strongly adiabatic system. Ab initio quantum-mechanical methods as applied to independent theoretical computations of both the reorganization energy ( λ) and the electronic coupling element ( HDA) confirm the essential correctness of the Mulliken-Hush formalism for fast electron transfer via strongly coupled donor/acceptor encounter complexes.

  6. Compounds having aromatic rings and side-chain amide-functionality and a method for transporting monovalent anions across biological membranes using the same

    Science.gov (United States)

    Davis, Jeffery T.; Sidorov, Vladimir; Kotch, Frank W.

    2008-04-08

    A compound containing at least two aromatic rings covalently bonded together, with each aromatic ring containing at least one oxyacetamide-based side chain, the compound being capable of forming a chloride ion channel across a lipid bilayer, and transporting chloride ion across the lipid bilayer.

  7. The Negative Ion Photoelectron Spectrum of meta -Benzoquinone Radical Anion (MBQ •– ): A Joint Experimental and Computational Study

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Bo; Hrovat, David A.; Deng, S. H. M.; Zhang, Jian; Wang, Xue-Bin; Borden, Weston Thatcher

    2014-03-05

    Negative ion photoelectron (NIPE) spectra of the radical anion of meta-benzoquinone (MBQ, m-OC6H4O) have been obtained at 20 K, using both 355 and 266 nm lasers for electron photodetachment. The spectra show well-resolved peaks and complex spectral patterns. The electron affinity of MBQ is determined from the first resolved peak to be 2.875 ±17 0.010 eV. Single-point, CASPT2/aug-cc-pVTZ//CASPT2/ aug-cc-pVDZ calculations predict accurately the positions of the 0-0 bands in the NIPE spectrum for formation of the four lowest electronic states of neutral MBQ from the 2A2 state of MBQ•-. In addition, the Franck-Condon factors that are computed from the CASPT2/aug-cc-pVDZ optimized geometries,vibrational frequencies, and normal mode vectors, successfully simulate the intensities and frequencies of the vibrational peaks in the NIPE spectrum that are associated with each of these electronic states. The successful simulation of the NIPE spectrum of MBQ•- allows the assignment of 3B2 as the ground state of MBQ, followed by the 1B2 and 1A1 electronic states, respectively 9.0 ± 0.2 and 16.6 ± 0.2 kcal/mol higher in energy than the triplet. These experimental energy differences are in good agreement with the calculated values of 9.7 and 15.7 kcal/mol. The relative energies of these two singlet states in MBQ confirm the previous prediction that their relative energies would be reversed from those in meta-benzoquinodimethane (MBQDM, m-CH2C6H4CH2).

  8. Dissociations of copper(II)-containing complexes of aromatic amino acids: radical cations of tryptophan, tyrosine, and phenylalanine.

    Science.gov (United States)

    Siu, Chi-Kit; Ke, Yuyong; Guo, Yuzhu; Hopkinson, Alan C; Siu, K W Michael

    2008-10-14

    The dissociations of two types of copper(II)-containing complexes of tryptophan (Trp), tyrosine (Tyr), or phenylalanine (Phe) are described. The first type is the bis-amino acid complex, [Cu(II)(M)(2)].(2+), where M = Trp, Tyr, or Phe; the second [Cu(II)(4Cl-tpy)(M)].(2+), where 4Cl-tpy is the tridendate ligand 4'-chloro-2,2':6',2''-terpyridine. Dissociations of the Cu(ii) bis-amino acid complexes produce abundant radical cation of the amino acid, M.(+), and/or its secondary products. By contrast, dissociations of the 4Cl-tpy-bearing ternary complexes give abundant M.(+) only for Trp. Density functional theory (DFT) calculations show that for Tyr and Phe, amino-acid displacement reactions by H(2)O and CH(3)OH (giving [Cu(II)(4Cl-tpy)(H(2)O)].(2+) and [Cu(II)(4Cl-tpy)(CH(3)OH)].(2+)) are energetically more favorable than dissociative electron transfer (giving M.(+) and [Cu(I)(4Cl-tpy)](+)). The fragmentation pathway common to all these [Cu(II)(4Cl-tpy)(M)].(2+) ions is the loss of NH(3). DFT calculations show that the loss of NH(3) proceeds via a "phenonium-type" intermediate. Dissociative electron transfer in [Cu(II)(4Cl-tpy)(M-NH(3))].(2+) results in [M-NH(3)].(+). The [Phe-NH(3)] (+) ion dissociates facilely by eliminating CO(2) and giving a metastable phenonium-type ion that rearranges readily into the styrene radical cation.

  9. SOA Formation form the NO3 radicals Chemistry of Isoprene, Monoterpenes, Sesquiterpenes, Biogenic Oxygenated Compounds, and Aromatics

    Science.gov (United States)

    Kleindienst, T. E.; Jaoui, M.; Docherty, K.; Corse, E.; Offenberg, J. H.; Lewandowski, M.

    2011-12-01

    Volatile organic compounds (VOCs) are oxidized in the atmosphere primarily by hydroxyl radicals (OH) during daylight hours but also by nitrate radicals (NO3) during overnight, photochemically inactive periods. While reactions with OH have received considerable attention with regard to gas-phase reaction products and secondary organic aerosol (SOA) formation, less is known about the mechanisms and products resulting from nighttime NO3 reactions despite their potential for SOA formation. To date, there have been limited studies on the chemical characteristics of aerosol reaction products formed from VOCs oxidation with NO3, and few SOA reaction products have been identified. Nighttime reactions have nevertheless been incorporated into some air quality models despite the limited information available and substantial uncertainties which still exist. The National Exposure Research Laboratory of the U.S. Environmental Protection Agency recently undertook an integrated laboratory research effort to better understand the contribution of NO3 reactions to nighttime SOA formation. Isoprene, methacrolein, a-pinene, b-pinene, d-limonene, b-caryophyllene, farnesene, a-humulene, 2-methyl-3-buten-2-ol, toluene, m-xylene, and naphthalene were reacted with NO3 under a wide range of conditions in a series of separate photochemical reaction chamber experiments. These hydrocarbons are thought to contribute to ambient SOA formation. NO3 was formed through thermal decomposition of N2O5. The yield, physical characteristics, and composition of SOA formed in each experiment was analyzed by a suite of instruments including a scanning mobility particle sizer, a Sunset Labs semi continuous EC-OC monitor, a volatility differential mobility analyzer, a direct insertion probe-mass spectrometer, a high resolution time-of-flight aerosol mass spectrometer, and a gas-chromatography-mass spectrometer. To understand the relative contributions of nighttime versus daytime VOCs reactions, a similar

  10. Exploitation of the photochromic nitroprusside anion [ FeNO(CN){5}] 2- as counterion for constructing molecular conductors: The first radical cation salts based on BDH-TTP and the amide functionalized derivatives of EDT-TTF

    Science.gov (United States)

    Shibaeva, R.; Khasanov, S.; Zorina, L.; Simonov, S.; Shevyakova, I.; Kushch, L.; Buravov, L.; Yagubskii, E.; Baudron, S.; Mézière, C.; Batail, P.; Canadell, E.; Yamada, J.

    2004-04-01

    The radical cation salts based on BDH-TTP and the mono- and diamide functionalized derivatives of EDT-TTF with the double charged nitroprusside anion [ FeNO(CN){5}] 2- (NP): kappa -(BDH-TTP){4}[NP]C{6}H{5}NO{2} (1), kappa -(BDH-TTP){4}[NP] (2), (BDH-TTP){2}[NP] (3), α -[ EDT-TTF-CONH{2}] {4}[NP] (4), β -[ EDT-TTF-(CONH{2})2] {2}[NP]{0.5}(C{6}H{5}NO{2})0.5 (5) have been synthesized. The crystal structures and transport properties of 1 5, as well as electronic band structures of 1and 2 have been studied. Key words. organic conductors based on radical cation salts X-ray and band structure conductivity.

  11. Superoxide generated by pyrogallol reduces highly water-soluble tetrazolium salt to produce a soluble formazan: a simple assay for measuring superoxide anion radical scavenging activities of biological and abiological samples.

    Science.gov (United States)

    Xu, Chen; Liu, Shu; Liu, Zhiqiang; Song, Fengrui; Liu, Shuying

    2013-09-02

    Superoxide anion radical (O2(˙-)) plays an important role in several human diseases. The xanthine/xanthine oxidase system is frequently utilized to produce O2(˙-). However, false positive results are easily got by using this system. The common spectrophotometric probes for O2(˙-) are nitroblue tetrazolium (NBT) and cytochrome c. Nevertheless, the application of NBT method is limited because of the water-insolubility of NBT formazan and the assay using cytochrome c lacks sensitivity and is not suitable for microplate measurement. We overcome these problems by using 1,2,3-trihydroxybenzene (pyrogallol) as O2(˙-)-generating system and a highly water-soluble tetrazolium salt, 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium sodium salt (WST-1) which can be reduced by superoxide anion radical to a stable water-soluble formazan with a high absorbance at 450 nm. The method is simple, rapid and sensitive. Moreover, it can be adapted to microplate format. In this study, the O2(˙-) scavenging activities of superoxide dismutase (SOD), L-ascorbic acid, N-acetyl-L-cysteine (NAC), albumin from human serum, flavonoids and herbal extracts were assessed by using this method. Meanwhile, the activities of tissue homogenates and serum were determined by using this validated method. This method, applicable to tissue homogenates, serum and herbal extracts, proved to be efficient for measuring O2(˙-) scavenging activities of biological and abiological samples.

  12. Oxidative catalysis using the stoichiometric oxidant as a reagent: an efficient strategy for single-electron-transfer-induced tandem anion-radical reactions.

    Science.gov (United States)

    Kafka, František; Holan, Martin; Hidasová, Denisa; Pohl, Radek; Císařová, Ivana; Klepetářová, Blanka; Jahn, Ullrich

    2014-09-01

    Oxidative single-electron transfer-catalyzed tandem reactions consisting of a conjugate addition and a radical cyclization are reported, which incorporate the mandatory terminal oxidant as a functionality into the product.

  13. Theoretical and Experimental Studies of the Spin Trapping of Inorganic Radicals by 5,5-Dimethyl-1-Pyrroline N-Oxide (DMPO). 3. Sulfur Dioxide, Sulfite and Sulfate Radical Anions

    Science.gov (United States)

    Zamora, Pedro L.; Villamena, Frederick A.

    2012-01-01

    Radical forms of sulfur dioxide (SO2), sulfite (SO32−), sulfate (SO42−), and their conjugate acids are known to be generated in vivo through various chemical and biochemical pathways. Oxides of sulfur are environmentally pervasive compounds and are associated with a number of health problems. There is growing evidence that their toxicity may be mediated by their radical forms. Electron paramagnetic resonance (EPR) spin trapping using the commonly used spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO), has been employed in the detection of SO3•− and SO4•−. The thermochemistries of SO2•−, SO3•−, SO4•−, and their respective conjugate acids addition to DMPO were predicted using density functional theory (DFT) at the PCM/B3LYP/6-31+G**//B3LYP/6-31G* level. No spin adduct was observed for SO2•− by EPR but an S-centered adduct was observed for SO3•− and an O-centered adduct for SO4•−. Determination of adducts as S- or O-centered was made via comparison based on qualitative trends of experimental hfcc’s with theoretically calculated ones. The thermodynamics of the non-radical addition of SO32− and HSO3− to DMPO followed by conversion to the corresponding radical adduct via the Forrester-Hepburn mechanism was also calculated. Adduct acidities and decomposition pathways were investigated as well, including an EPR experiment using H217O to determine the site of hydrolysis of O-centered adducts. The mode of radical addition to DMPO is predicted to be governed by several factors, including spin population density, and geometries stabilized by hydrogen bonds. The thermodynamic data supports evidence for the radical addition pathway over the nucleophilic addition mechanism. PMID:22668066

  14. Forgotten Radicals in Biology

    OpenAIRE

    2008-01-01

    Redox reactions play key roles in intra- and inter-cellular signaling, and in adaptative processes of tissues towards stress. Among the major free radicals with essential functions in cells are reactive oxygen species (ROS) including superoxide anion (O2 •-), hydroxyl radical (•OH) and reactive nitrogen species (RNS) such as nitric oxide (•NO). In this article, we review the forgotten and new radicals with potential relevance to cardiovascular pathophysiology. Approximately 0.3% of O2 •- pres...

  15. EPR Study of Radicals in Irradiated Ionic Liquids and Implications for the Radiation Stability of Ionic Liquid-Based Extraction Systems

    CERN Document Server

    Shkrob, I A; Wishart, J F; Chemerisov, Sergey D.; Shkrob, Ilya A.; Wishart, James F.

    2007-01-01

    The radiation- and photo- chemistry of room temperature ionic liquids (ILs) composed of ammonium, phosphonium, pyrrolidinium, and imidazolium cations and bis(triflyl)amide, dicyanamide, and bis(oxalato)borate anions, have been studied using low-temperature Electron Paramagnetic Resonance (EPR). Several classes of radicals have been identified and related to reactions of the primary radiolytically generated electrons and holes. Large yields of terminal and penultimate C-centered radicals are observed in the aliphatic chains of the phosphonium, ammonium and pyrrolidinium cations, but not for imidazolium cation. This pattern can be accounted for by efficient deprotonation of a hole trapped on the cation (the radical dication) that competes with rapid charge transfer to a nearby anion. The latter leads to the formation of stable N- or O-centered radicals. The electrons either react with the protic impurity (for nonaromatic cations) yielding H atoms or the aromatic moiety (for imidazolium cations). Excitation of b...

  16. Chemistry of carbonization - I. A theoretical study of free radical formation from starting materials

    Energy Technology Data Exchange (ETDEWEB)

    Ruette, F.; Sierraalta, A.; Castells, V.; Laya, M. (Instituto Venezolano de Investigaciones Cientificas, Caracas (Venezuela). Laboratorio de Quimica Computacional)

    1993-01-01

    The effect of size, shape, and aromaticity in the formation of radicals from model polyaromatic hydrocarbons (PAH) was theoretically studied using the MINDO/3 method. The results were interpreted in terms of hydrogen transfer on carbonization and liquefaction processes of coal-related compounds. Additives that donate or withdraw electrons were modeled by calculating negatively or positively charged systems. The results show that the hydrogen donating properties of PAHs increase with the increase of their molecular weights. The formation of anionic [pi]-radicals is thermodynamically favoured, contrary to cationic [pi]-radicals. Negative charge favoured the formation of low molecular weight radicals, and therefore, the hydrogen transfer from light to heavy PAHs. Positive charges, in general, do not facilitate the hydrogen transfer. 42 refs., 2 figs., 4 tabs.

  17. Studies on structures and electron affinities of the simplest alkyl dithio radicals and their anions with gaussian-3 theory and density functional theory.

    Science.gov (United States)

    Gao, Aifang; Du, Hongli; Li, Aiguo; Pei, Huiyi

    2013-06-01

    The equilibrium geometries and electron affinities of the R-SS/R-SS(-)(R=CH₃, C₂H₅, n-C₃H7, i-C₃H₇, n-C₄H₉, t-C₄H₉, n-C₅H₁₁) species have been studied using the higher level of the Gaussian-3(G3) theory and 21 carefully calibrated pure and hybrid density functionals (five generalized gradient approximation (GGA) methods, seven hybrid GGAs, three meta GGA methods, and six hybrid meta GGAs) in conjunction with diffuse function augmented double-ζ plus polarization (DZP++) basis sets. The geometries are fully optimized with each method and discussed. The reliable adiabatic electron affinity has been presented by means of the high level of G3 technique. With the DZP++ DFT method, three measures of neutral/anion energy differences reported in this work are the adiabatic electron affinity, the vertical electron affinity, and the vertical detachment energy. The adiabatic electron affinities, obtained at the BP86, M05-2X, B3LYP, M06, B98, M06-2X, mPW1PW91, HCTH, B97-1, M05, PBE1PBE, and VSXC methods, are in agreement with the G3 results. These methods perform better for EA prediction and are considered to be reliable.

  18. Infrared Spectra of Polycyclic Aromatic Hydrocarbons (PAHs)

    Science.gov (United States)

    Bauschlicher, Charles W., Jr.; Bakes, E. L. O.

    2000-01-01

    We have computed the synthetic infrared spectra of some polycyclic aromatic hydrocarbons containing up to 54 carbon atoms. The species studied include ovalene, circumcoronene, dicoronylene, and hexabenzocoronene. We report spectra for anions, neutrals, cations, and multiply charged cations.

  19. Free Radical Scavenging Fingerprints of Selected Aromatic and Medicinal Tunisian Plants Assessed by Means of TLC-DPPH(•) Test and Image Processing.

    Science.gov (United States)

    El Euch, Salma Kammoun; Cieśla, Łukasz; Bouzouita, Nabiha

    2014-01-01

    Aqueous-methanol extracts prepared from 10 Tunisian plant species were analyzed for the presence of potent direct antioxidants. The analyzed species included: Anacyclus clavatus Desf., Erica multiflora L., Cistus salvifolius L., Centaurium erythraea Rafn., Marrubium vulgare L., Lavandula stoechas L., Artemisia campestris L., Origanum majorana L., Salvia officinalis L., and Pistacia lentiscus L. All the extracts were chromatographed on the RP18 W plates with methanol-water-acetic acid (48 + 47 + 5, v/v/v) mobile phase. Upon completion of the chromatographic development and the drying step, the plates were stained with a chloroform solution of 2, 2-diphenyl-1-picrylhydrazyl radical (DPPH(•)). An image processing protocol, with use of Sorbfil TLC Videodensitometer, was applied to quantitatively measure the activity of polyphenols and to screen complex samples for the presence of free radical scavengers. The activity of the individual compounds was compared with that of rutin, used as a standard. The TLC-DPPH(•) test showed that C. salvifolius had the most potent antioxidant activity, as it possessed the highest activity coefficient (calculated as the sum of the areas under the peaks of all active compounds/area under peak of rutin). The proposed procedure may be used to differentiate potent chain-breaking antioxidants and compounds propagating radical chain reactions.

  20. Anion photoelectron imaging spectroscopy of glyoxal

    Science.gov (United States)

    Xue, Tian; Dixon, Andrew R.; Sanov, Andrei

    2016-09-01

    We report a photoelectron imaging study of the radical-anion of glyoxal. The 532 nm photoelectron spectrum provides the first direct spectroscopic determination of the adiabatic electron affinity of glyoxal, EA = 1.10 ± 0.02 eV. This assignment is supported by a Franck-Condon simulation of the experimental spectrum that successfully reproduces the observed spectral features. The vertical detachment energy of the radical-anion is determined as VDE = 1.30 ± 0.04 eV. The reported EA and VDE values are attributed to the most stable (C2h symmetry) isomers of the neutral and the anion.

  1. The Negative Ion Photoelectron Spectrum of Cyclopropane-1,2,3-Trione Radical Anion, (CO) 3 •– — A Joint Experimental and Computational Study

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Bo; Hrovat, David A.; West, Robert; Deng, Shihu H. M.; Wang, Xue-Bin; Borden, Weston Thatcher

    2014-09-03

    Negative Ion Photoelectron (NIPE) spectra of the radical anion of cyclopropane-1,2,3-trione, (CO)3•-, have been obtained at 20 K, using both 355 and 266 nm lasers for electron photodetachment. The spectra show broadened bands, due to the short lifetimes of both the singlet and triplet states of (CO)3. The smaller intensity of the band with the lower electron binding energy suggests that the singlet is the ground state of (CO)3. From the NIPE spectra, the electron affinity (EA) and the singlet-triplet energy gap of (CO)3 are estimated to be, respectively, EA = 3.1 ± 0.1 eV and ΔEST = -14 ± 3 kcal/mol. High-level, (U)CCSD(T)/aug-cc-pVQZ//(U)CCSD(T)/aug-cc-pVTZ, calcu-lations give EA = 3.04 eV for the 1A1´ ground state of (CO)3 and ΔEST = -13.8 kcal/mol for the energy gap between the 1A1´ and 3A2 states, in excellent agreement with values from the NIPE spectra. In addition, simulations of the vibrational structures for formation of these states of (CO)3 from the 2A2'' state of (CO)3•- provide a good fit to the shapes of broad bands in the 266 nm NIPE spectrum. The NIPE spectrum of (CO)3•- and the analysis of the spectrum by high-quality electronic structure calculations demonstrate that NIPES can not only access and provide information about transition structures, but NIPES can also access and provide information about hilltops on potential energy surfaces.

  2. Ultrafast studies on the photophysics of matrix-isolated radical cations of polycyclic aromatic hydrocarbons: implications for the Diffuse Interstellar Bands (DIB) problem

    CERN Document Server

    Zhao, L; Shkrob, I A; Crowell, R A; Pommeret, S; Chronister, E L; Liu, A D; Trifunac, A D; Zhao, Liang; Lian, Rui; Shkrob, Ilya A.; Crowell, Robert A.; Pommeret, Stanislas; Chronister, Eric L.; Liu, An Dong; Trifunac, Alexander D.

    2004-01-01

    Rapid, efficient deactivation of the photoexcited PAH cations accounts for their remarkable photostability and have important implications for astrochemistry, as these cations are the leading candidates for the species responsible for the diffuse interstellar bands (DIB) observed throughout the Galaxy.Ultrafast relaxation dynamics for photoexcited PAH cations isolated in boric acid glass have been studied using femtosecond and picosecond transient grating spectroscopy. With the exception of perylene+, the recovery kinetics for the ground doublet (D0) states of these radical cations are biexponential, containing a fast (< 200 fs) and a slow (3-20 ps) components. No temperature dependence or isotope effect was observed for the fast component, whereas the slow component exhibits both the H/D isotope effect (1.1-1.3) and strong temperature dependence (15 to 300 K). We suggest that the fast component is due to internal Dn to D0 conversion and the slow component is due to vibrational energy transfer (VET) from a...

  3. One-electron oxidation of ferrocenes by short-lived N-oxyl radicals. The role of structural effects on the intrinsic electron transfer reactivities.

    Science.gov (United States)

    Baciocchi, Enrico; Bietti, Massimo; D'Alfonso, Claudio; Lanzalunga, Osvaldo; Lapi, Andrea; Salamone, Michela

    2011-06-07

    A kinetic study of the one electron oxidation of substituted ferrocenes (FcX: X = H, COPh, COMe, CO(2)Et, CONH(2), CH(2)OH, Et, and Me(2)) by a series of N-oxyl radicals (succinimide-N-oxyl radical (SINO), maleimide-N-oxyl radical (MINO), 3-quinazolin-4-one-N-oxyl radical (QONO) and 3-benzotriazin-4-one-N-oxyl radical (BONO)), has been carried out in CH(3)CN. N-oxyl radicals were produced by hydrogen abstraction from the corresponding N-hydroxy derivatives by the cumyloxyl radical. With all systems, the rate constants exhibited a satisfactory fit to the Marcus equation allowing us to determine self-exchange reorganization energy values (λ(NO˙/NO(-))) which have been compared with those previously determined for the PINO/PINO(-) and BTNO/BTNO(-) couples. Even small modification of the structure of the N-oxyl radicals lead to significant variation of the λ(NO˙/NO(-)) values. The λ(NO˙/NO(-)) values increase in the order BONO < BTNO < QONO < PINO < SINO < MINO which do not parallel the order of the oxidation potentials. The higher λ(NO˙/NO(-)) values found for the MINO and SINO radicals might be in accordance with a lower degree of spin delocalization in the radicals MINO and SINO and charge delocalization in the anions MINO(-) and SINO(-) due to the absence of an aromatic ring in their structure.

  4. Isolation and assessment of the molecular and electronic structures of azo-anion-radical complexes of chromium and molybdenum. Experimental and theoretical characterization of complete electron-transfer series.

    Science.gov (United States)

    Joy, Sucheta; Krämer, Tobias; Paul, Nanda D; Banerjee, Priyabrata; McGrady, John E; Goswami, Sreebrata

    2011-10-17

    The reaction of 3 equiv of the ligand 2-[(2-chlorophenyl)azo]pyridine (L(a)) or 2-[(4-chlorophenyl)azo]pyridine (L(b)) with 1 equiv of Cr(CO)(6) or Mo(CO)(6) in boiling n-octane afforded [Cr(L(a/b))(3)](0) (1a and 1b) and [Mo(L(a/b))(3)](0) (2a and 2b). The chemical oxidation reaction of these neutral complexes with I(2) in CH(2)Cl(2) provided access to air-stable one-electron-oxidized species as their triiodide (I(3)(-)) salts. The electronic structures of chromium and molybdenum centers coordinated by the three redox noninnocent ligands L(a/b) along with their redox partners have been elucidated by using a host of physical methods: X-ray crystallography, magnetic susceptibility measurements, nuclear magnetic resonance, cyclic voltammetry, absorption spectroscopy, electron paramagnetic resonance spectroscopy, and density functional theory. The four representative complexes, 1a, [1a]I(3), 2a, and [2a]I(3), have been characterized by X-ray crystallography. The results indicate a predominant azo-anion-radical description of the ligands in the neutral chromium(III) species, [Cr(III)(L(•-))(3)], affording a singlet ground state through strong metal-ligand antiferromagnetic coupling. All of the electrochemical processes are ligand-based; i.e., the half-filled (t(2g))(3) set of the Cr(III) d(3) ion remains unchanged throughout. The description of the molybdenum analogue is less clear-cut because mixing between metal- and ligand-based orbitals is more significant. On the basis of variations in net spin densities and orbital compositions, we argue that the oxidation events are again primarily ligand-based, although the electron density at the molybdenum center is clearly more variable than that at the chromium center in the corresponding series [1a](+), 1a, and [1a](-).

  5. Electrical and magnetic properties of new compounds of the conductor anion [Ni(dmit2]- and nitronyl nitroxide magnetic radicals Propriedades elétricas e magnéticas de novos compostos com o ânion condutor [Ni(dmit2]- e radicais magnéticos nitronil nitróxido

    Directory of Open Access Journals (Sweden)

    Mauro Cesar Dias

    2007-08-01

    Full Text Available Three compounds have been synthesized with formulae [3-MeRad][Ni(dmit2] (1, [4-MeRad][Ni(dmit2] (2 and [4-PrRad][Ni(dmit2] (3 where [Ni(dmit2]- is an anionic pi-radical (dmit = 1,3-dithiol-2-thione-4,5-dithiolate and [3-MeRad]+ is 3-N-methylpyridinium alpha-nitronyl nitroxide, [4-MeRad]+ is 4-N-methylpyridinium alpha-nitronyl nitroxide and [4-PrRad]+ is 4-N-propylpyridinium alpha-nitronyl nitroxide. The temperature-dependent magnetic susceptibility of 1 revealed that an antiferromagnetic interaction operates between the 3-MeRad+ radical cations with exchange coupling constants of J1 = - 1.72 cm-1 and antiferromagnetism assigned to the spin ladder chains of the Ni(dmit2 radical anions. Compound 1 exhibits semiconducting behavior and 3 presents capacitor behavior in the temperature range studied (4 - 300 K.

  6. Survey of organic acid eluents for anion chromatography

    Energy Technology Data Exchange (ETDEWEB)

    Book, D.E.

    1981-10-01

    Of all the potential eluents surveyed (including aromatic, sulfonic, phosphonic, among other acids), only the carboxylic acids and the nitrophenols are recommended as eluents for anion chromatography. The concentration of the eluent should be in the range 5 x 10/sup -5/ to 1 x 10/sup -3/ M. The eluent should have the same charge as inorganic anions, a higher charge than organic acid samples. Choice of eluents for separation of halides, chloride and sulfate, multivalent inorganic anions, small alkyl acids, and aromatic acids is discussed. (DLC)

  7. Understanding and modeling removal of anionic organic contaminants (AOCs) by anion exchange resins.

    Science.gov (United States)

    Zhang, Huichun; Shields, Anthony J; Jadbabaei, Nastaran; Nelson, Maurice; Pan, Bingjun; Suri, Rominder P S

    2014-07-01

    Ionic organic contaminants (OCs) are a growing concern for water treatment and the environment and are removed inefficiently by many existing technologies. This study examined removal of anionic OCs by anion exchange resins (AXRs) as a promising alternative. Results indicate that two polystyrene AXRs (IRA910 and IRA96) have higher sorption capacities and selectivity than a polyacrylate resin (A860). For the polystyrene resins, selectivity follows: phenolates ≥ aromatic dicarboxylates > aromatic monocarboxylates > benzenesulfonate > aliphatic carboxylates. This trend can be explained based on hydration energy, the number of exchange groups, and aromaticity and hydrophobicity of the nonpolar moiety (NPM) of the anions. For A860, selectivity only varies within a narrow range (0.13-1.64). Despite the importance of the NPM of the anions, neutral solutes were sorbed much less, indicating synergistic combinations of electrostatic and nonelectrostatic interactions in the overall sorption. By conducting multiple linear regression between Abraham's descriptors and nature log of selectivity, induced dipole-related interactions and electrostatic interactions were found to be the most important interaction forces for sorption of the anions, while solute H-bond basicity has a negative effect. A predictive model was then developed for carboxylates and phenolates based on the poly parameter linear free energy relationships established for a diverse range of 16 anions and 5 neutral solutes, and was validated by accurate prediction of sorption of five test solutes within a wide range of equilibrium concentrations and that of benzoate at different pH.

  8. Aromatic Radicals-Acetylene Particulate Matter Chemistry

    Science.gov (United States)

    2011-12-01

    atmosphere1. In addition to acute respiratory problems, long-term effects include lung cancer and cardiopulmonary diseases , as studied by Pope at al...problems such as ischemic heart disease , fatal arrhythmia, and congestive heart failure4,5. Strategies to reduce fine particulate matter (PM...acetylene reaction have been made by Fahr and Stein15, who deduced an Arrhenius expression in a 4 temperature range between 1000 and 1330 K in

  9. Active Oxygen Radical Scavenging Ability of Water-Soluble β-Alanine C60 Adducts

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Water-soluble β-alanine C60 adducts were synthesized, and the scavenging ability to superoxygen anion radical O2-and hydroxyl radicalOH were studied by autoxidation ofpyrogallol and chemiluminescence, respectively. It was found that β-alanine C60 adducts showed an excellent efficiency in eliminating superoxygen anion radical and hydroxyl radical. The 50% inhibition concentration (IC50) for superoxygen anion radical and hydroxyl radical were 0.15 mg/mL and 0.048 mg/mL, respectively. The difference should be mainly attributed to the different scavenging mechanisms.

  10. Channeling the SmI₂ reactions to the radical path: radicals resisting reduction by SmI₂.

    Science.gov (United States)

    Yella, Ramesh; Hoz, Shmaryahu

    2014-08-01

    Studies on the reaction of 4-(2,2-diphenylvinyl)pyridine with SmI2 revealed that the intermediate radical strongly resists further reduction to the corresponding anion. The resistance of the radical to accepting another electron is traced to its stabilization by the nitrogen lone pair. The literature suggests that oxygen may also play a role similar to that of nitrogen in directing the course of the reaction toward radical rather than to anionic chemistry.

  11. Molecular structure, optical and magnetic properties of metal-free phthalocyanine radical anions in crystalline salts (H2Pc˙-)(cryptand[2,2,2][Na(+)])·1.5C6H4Cl2 and (H2Pc˙-)(TOA+)·C6H4Cl2 (TOA+ is tetraoctylammonium cation).

    Science.gov (United States)

    Konarev, Dmitri V; Zorina, Leokadiya V; Khasanov, Salavat S; Litvinov, Aleksey L; Otsuka, Akihiro; Yamochi, Hideki; Saito, Gunzi; Lyubovskaya, Rimma N

    2013-05-21

    Ionic compounds containing radical anions of metal-free phthalocyanine (H2Pc˙(-)): (H2Pc˙(-))(cryptand[2,2,2][Na(+)])·1.5C6H4Cl2 (1) and (H2Pc˙(-))(TOA(+))·C6H4Cl2 (2) have been obtained as single crystals for the first time. Their crystal structures have been determined, and optical and magnetic properties have been investigated. The H2Pc˙(-) radical anions have a slightly bowl-like shape with four pyrrole nitrogen atoms located below the molecular plane, while four phenylene substituents are located above this plane. Changes in the average length of N-C and C-C bonds in H2Pc˙(-) in comparison with those in neutral H2Pc indicate that negative charge is mainly delocalized over the 24-atom phthalocyanine ring rather than the phenylene substituents. The H2Pc˙(-) formation is accompanied by a shift of up to 10 cm(-1) and disappearance of some intense IR-active bands whereas the band of the N-H stretching mode is shifted by 21-27 cm(-1) to larger wavenumbers. New bands attributed to H2Pc˙(-) appear in the NIR spectra of the salts with maxima at 1033 and 1028 nm for 1 and 2, respectively. The formation of H2Pc˙(-) is accompanied by the splitting of the Soret and Q-bands of H2Pc into several bands and their blue-shift up to 32 nm. Narrow EPR signals with g = 2.0033 and linewidth of 0.16-0.24 mT at room temperature in the spectra of the salts were attributed to the H2Pc˙(-) radical anions. According to SQUID measurements they have S = 1/2 spin states with effective magnetic moments of 1.73 (1) and 1.78 (2) μB at 300 K. Magnetic behavior of 1 and 2 follows the Curie-Weiss law with negative Weiss temperatures of -0.9 and -0.5 K, respectively, indicating weak antiferromagnetic interactions of spins. The EPR signal splits into two lines below 120 and 80 K for 1 and 2, respectively and these lines are noticeably broadened below 25 K.

  12. 酶法制备鲽鱼鱼皮胶原蛋白肽及其清除超氧阴离子自由基的研究%Study on the Enzymatic Preparation and Superoxide Anion Radical Scavenging Activity of Collagen Peptide from Plaice Skin

    Institute of Scientific and Technical Information of China (English)

    王群; 郑海涛; 葛尧; 何计国

    2011-01-01

    采用碱性蛋白酶酶解鲽鱼鱼皮胶原蛋白制备胶原蛋白肽,对其清除超氧阴离子自由基的能力进行研究.通过单因素试验和响应面法分析不同酶解条件对超氧阴离子自由基清除率的影响,优化得到最佳酶解工艺条件:pH 9.5,加酶量158l U/g,底物浓度10 mg/mL,酶解时间为6h,酶解温度60℃,最高清除率为75.51%,半数清除浓度(IC5o)为7.98 mg/mL.%Alcalase was used to hydrolyze plaice skin for preparing collagen peptide, and the superoxide anion radical scavenging activity of this collagen peptide was studied. Effect of the different enzymatic hydrolysis conditions on superoxide anion radical scavenging activity were analyzed by single factor experiment and response surface method. The optimal hydrolytic conditions of plaice skin collagen using Alcalase with high scavenging rate were pH=9.5, enzyme dosage 1581 U/g, concentration of substrate 10 mg/mL, hydrolysis time 6 h, temperature 60℃. The maximum scavenging rate of 75.51% and half scavenging concentration (IC50) of 7.98 mg/mL were obtained.

  13. Core-modified octaphyrins: Syntheses and anion-binding properties

    Indian Academy of Sciences (India)

    Rajneesh Misra; Venkataramanarao G Anand; Harapriya Rath; Tavarekere K Chandrashekar

    2005-03-01

    In this paper, a brief review of the syntheses, characterization and anion-binding properties of core-modified octaphyrins is presented. It has been shown that the core-modified octaphyrins exhibit aromaticity both in solution and in solid state, confirming the validity of the (4 + 2) Huckel rule for larger -electron systems. Solid-state binding characteristics of TFA anions of two core-modified octaphyrins are also described.

  14. Aromatic graphene

    Science.gov (United States)

    Das, D. K.; Sahoo, S.

    2016-04-01

    In recent years graphene attracts the scientific and engineering communities due to its outstanding electronic, thermal, mechanical and optical properties and many potential applications. Recently, Popov et al. [1] have studied the properties of graphene and proved that it is aromatic but without fragrance. In this paper, we present a theory to prepare graphene with fragrance. This can be used as scented pencils, perfumes, room and car fresheners, cosmetics and many other useful household substances.

  15. Quantum chemical calculations of anion complex [B12Hx(NF2)12-x]2-, x = 9 – 12

    Science.gov (United States)

    Koblova, E. A.; Saldin, V. I.; Ustinov, A. Yu

    2017-01-01

    The geometric, energetic, spectral and electronic properties of various isomers of B12Hх(NF2)12-х 2‑ anion complex with x = 9 ‑ 12 have been studied using Density Functional Theory (B3LYP/6-311++G**). It was shown that the most stable isomers are characterized by the preference to form the most symmetric structures with uniformly distributed charge densities. However, when replacing a hydrogen atom with difluoramino group, an inductive effect occurs. NF2 group pulls a part of electron density that leads to the polarization of the boron core. Blue shifts in the IR spectrum compared to the vibrations of the free radical NF2 ranging from 5 to 69 cm‑1 for the most stable isomers with the minimum total energy are characteristic and points to the stability of B12Hх(NF2)12-х 2‑ anions. The obtained results broaden the idea of aromaticity of B12H12 2‑ anion and will be useful in synthesis of new B12H12 2‑ derivatives.

  16. Anion exchange membrane

    Science.gov (United States)

    Verkade, John G; Wadhwa, Kuldeep; Kong, Xueqian; Schmidt-Rohr, Klaus

    2013-05-07

    An anion exchange membrane and fuel cell incorporating the anion exchange membrane are detailed in which proazaphosphatrane and azaphosphatrane cations are covalently bonded to a sulfonated fluoropolymer support along with anionic counterions. A positive charge is dispersed in the aforementioned cations which are buried in the support to reduce the cation-anion interactions and increase the mobility of hydroxide ions, for example, across the membrane. The anion exchange membrane has the ability to operate at high temperatures and in highly alkaline environments with high conductivity and low resistance.

  17. cis-Diaquabis(di-2-pyrimidinyl sulfide- K2N,N) Cobalt(II) Ditetrafluoridoborate: Lone Pair-aromatic and Anion-П Interactions in the Self-assembly of Coordination Complex%cis-Diaquabis(di-2-pyrimidinyl sulfide- K2N,N) Cobalt(II) Ditetrafluoridoborate: Lone Pair-aromatic and Anion-П Interactions in the Self-assembly of Coordination Complex

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    The title complex, [Co(DprS)2(H20)2]2(BF4)4 (DprS is di-2-pyrimidinyl sulfide), was obtained and characterized by elemental analysis, FT-IR and X-ray crystallography. The complex crystallizes in space group P21/c with a = 11.742(1), b = 22,439(2), c = 20.538(2) A, β = 109.713(5)°, Z = 4, V = 5094.3(3)A, Dc = 1.692 g.cm-3, μ = 0.929 mm-I, F(000) = 2600, R = 0.0756 and wR = 0.1929. The asymmetric unit of the title complex is comprised of two isomeric cobalt(II) centers (Co(l) and Co(2)) with a cis-[Co(DprS)2(H20)2]2+ moiety. Each Co(II) center exhibits a similar distorted N402-octahedral coordination geometry surrounded by a pair of DprS in a N,N'-chelate mode and two aqua ligands in a cis-relationship. Unconventional S-π(pyrimidinyl), N-π(pyrimidinyl), and anion(BF4)...π(pyrimidinyl) are found to combine with the C-H-.-F and O-H...F interactions to stabilize a whole three-dimensional framework with the mononuclear units (Co(l) and Co(2)). The ligand conformation will be also discussed.

  18. Anions in Cometary Comae

    Science.gov (United States)

    Charnley, Steven B.

    2011-01-01

    The presence of negative ions (anions) in cometary comae is known from Giotto mass spectrometry of IP/Halley. The anions 0-, OH-, C-, CH- and CN- have been detected, as well as unidentified anions with masses 22-65 and 85-110 amu (Chaizy et al. 1991). Organic molecular anions are known to have a significant impact on the charge balance of interstellar clouds and circumstellar envelopes and have been shown to act as catalysts for the gas-phase synthesis of larger hydrocarbon molecules in the ISM, but their importance in cometary comae has not yet been explored. We present details of the first attempt to model the chemistry of anions in cometary comae. Based on the combined chemical and hydro dynamical model of Rodgers & Charnley (2002), we investigate the role of large carbon-chain anions in cometary coma chemistry. We calculate the effects of these anions on coma thermodynamics, charge balance and examine their impact on molecule formation.

  19. DNA binding hydroxyl radical probes

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Vicky J.; Konigsfeld, Katie M.; Aguilera, Joe A. [Department of Radiology, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610 (United States); Milligan, Jamie R., E-mail: jmilligan@ucsd.edu [Department of Radiology, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610 (United States)

    2012-01-15

    The hydroxyl radical is the primary mediator of DNA damage by the indirect effect of ionizing radiation. It is a powerful oxidizing agent produced by the radiolysis of water and is responsible for a significant fraction of the DNA damage associated with ionizing radiation. There is therefore an interest in the development of sensitive assays for its detection. The hydroxylation of aromatic groups to produce fluorescent products has been used for this purpose. We have examined four different chromophores, which produce fluorescent products when hydroxylated. Of these, the coumarin system suffers from the fewest disadvantages. We have therefore examined its behavior when linked to a cationic peptide ligand designed to bind strongly to DNA. - Highlights: > Examined four aromatic groups as a means to detect hydroxyl radicals by fluorescence. > Coumarin system suffers from the fewest disadvantages. > Characterized its reactivity when linked to a hexa-arginine peptide.

  20. THERMOCHEMISTRY OF HYDROCARBON RADICALS

    Energy Technology Data Exchange (ETDEWEB)

    Kent M. Ervin, Principal Investigator

    2004-08-17

    Gas phase negative ion chemistry methods are employed to determine enthalpies of formation of hydrocarbon radicals that are important in combustion processes and to investigate the dynamics of ion-molecule reactions. Using guided ion beam tandem mass spectrometry, we measure collisional threshold energies of endoergic proton transfer and hydrogen atom transfer reactions of hydrocarbon molecules with negative reagent ions. The measured reaction threshold energies for proton transfer yield the relative gas phase acidities. In an alternative methodology, competitive collision-induced dissociation of proton-bound ion-molecule complexes provides accurate gas phase acidities relative to a reference acid. Combined with the electron affinity of the R {center_dot} radical, the gas phase acidity yields the RH bond dissociation energy of the corresponding neutral molecule, or equivalently the enthalpy of formation of the R{center_dot} organic radical, using equation: D(R-H) = {Delta}{sub acid}H(RH) + EA(R) - IE(H). The threshold energy for hydrogen abstraction from a hydrocarbon molecule yields its hydrogen atom affinity relative to the reagent anion, providing the RH bond dissociation energy directly. Electronic structure calculations are used to evaluate the possibility of potential energy barriers or dynamical constrictions along the reaction path, and as input for RRKM and phase space theory calculations. In newer experiments, we have measured the product velocity distributions to obtain additional information on the energetics and dynamics of the reactions.

  1. Catalytic Radical Domino Reactions in Organic Synthesis

    Science.gov (United States)

    Sebren, Leanne J.; Devery, James J.; Stephenson, Corey R.J.

    2014-01-01

    Catalytic radical-based domino reactions represent important advances in synthetic organic chemistry. Their development benefits synthesis by providing atom- and step-economical methods to complex molecules. Intricate combinations of radical, cationic, anionic, oxidative/reductive, and transition metal mechanistic steps result in cyclizations, additions, fragmentations, ring-expansions, and rearrangements. This Perspective summarizes recent developments in the field of catalytic domino processes. PMID:24587964

  2. 白藜芦醇对衰老小鼠GSH和抗超氧阴离子自由基含量变化的影响%Effect of resveratrol on content of GSH and anti super oxide anion radical of naturally senile mice

    Institute of Scientific and Technical Information of China (English)

    张效莉; 吴景东

    2011-01-01

    目的:研究白藜芦醇对皮肤的抗衰老作用.方法:健康4月龄昆明种小鼠12只,作为青年对照组(A);健康18月龄昆明种小鼠60只,随机分成5组:老年空白对照组(B)、老年阳性对照组(C)、老年绞股蓝皂苷时照组(D)、老年白藜芦醇高剂量组(E)、老年白藜芦醇低剂量组(F).每日灌胃给药,以生化分析方法测定GSH及抗超氧阴离子自由基含量.结果:与青年对照组对比其余五个老年组的GSH和抗超氧阴离子自由基含量在药物的作用下明显提高.结论:白藜芦醇能够延缓小鼠的衰老.%Objective To study if resveratrol have function on delaying naturally senile mice or not. Methods 12 kind of Kunming age in four-month female small mice contrast a group as youth (A),60 kind of Kunmlng age in eighteen-month female small mice at random divides 5 group, 12 for a group: Old age blank group (B),old age masculine group(C),old age gypenoside group(D),resveratrol high dose(E),resveratrol low dose(F).Filling the stomach with medicine. Determine the content of GSH and anti super oxide anion radical. Results Compares with the youth group,the other five old age group can enhance the content of GSH and anti super oxide anion radical. Conclusion Resveratrol have function on delaying naturally senile mice.

  3. Anion exchange polymer electrolytes

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Yu Seung; Kim, Dae Sik; Lee, Kwan-Soo

    2013-07-23

    Solid anion exchange polymer electrolytes and compositions comprising chemical compounds comprising a polymeric core, a spacer A, and a guanidine base, wherein said chemical compound is uniformly dispersed in a suitable solvent and has the structure: ##STR00001## wherein: i) A is a spacer having the structure O, S, SO.sub.2, --NH--, --N(CH.sub.2).sub.n, wherein n=1-10, --(CH.sub.2).sub.n--CH.sub.3--, wherein n=1-10, SO.sub.2-Ph, CO-Ph, ##STR00002## wherein R.sub.5, R.sub.6, R.sub.7 and R.sub.8 each are independently --H, --NH.sub.2, F, Cl, Br, CN, or a C.sub.1-C.sub.6 alkyl group, or any combination of thereof; ii) R.sub.9, R.sub.10, R.sub.11, R.sub.12, or R.sub.13 each independently are --H, --CH.sub.3, --NH.sub.2, --NO, --CH.sub.nCH.sub.3 where n=1-6, HC.dbd.O--, NH.sub.2C.dbd.O--, --CH.sub.nCOOH where n=1-6, --(CH.sub.2).sub.n--C(NH.sub.2)--COOH where n=1-6, --CH--(COOH)--CH.sub.2--COOH, --CH.sub.2--CH(O--CH.sub.2CH.sub.3).sub.2, --(C.dbd.S)--NH.sub.2, --(C.dbd.NH)--N--(CH.sub.2).sub.nCH.sub.3, where n=0-6, --NH--(C.dbd.S)--SH, --CH.sub.2--(C.dbd.O)--O--C(CH.sub.3).sub.3, --O--(CH.sub.2).sub.n--CH--(NH.sub.2)--COOH, where n=1-6, --(CH.sub.2).sub.n--CH.dbd.CH wherein n=1-6, --(CH.sub.2).sub.n--CH--CN wherein n=1-6, an aromatic group such as a phenyl, benzyl, phenoxy, methylbenzyl, nitrogen-substituted benzyl or phenyl groups, a halide, or halide-substituted methyl groups; and iii) wherein the composition is suitable for use in a membrane electrode assembly.

  4. A theoretical investigation into the cooperativity effect involving anionic hydrogen bond and aromaticity in Cl-…benzonitrile…H2 O ternary complex%Cl-…苯氰…H2O中阴离子氢键协同效应与芳香性理论研究

    Institute of Scientific and Technical Information of China (English)

    宋慧; 李斌; 赵光明; 武红娟; 龙泽清

    2015-01-01

    本文采用DFT-B3LYP和MP2(full)方法对三聚体Cl–…苯氰…H2O中O/C–H…Cl–阴离子氢键与传统氢键O–H…N和C–H…O之间的协同效应、热力学性质以及芳香性进行了研究.结果表明阴离子氢键O/C–H…Cl–对O–H…N或 C–H…O相互作用的影响更显著.在线性结构中发生正协同效应,熵变是促进热力学协同效应的主要因素,而在环状结构中发生反协同效应,焓变成为主要因素.在三聚体形成过程中,苯氰环的芳香性是减弱的,而苯氰中π→π∗共轭效应是增强的.结果表明,协同效应能Ecoop.分别与 Rc ( NICS (1) ternary/NICS (1) binary ),ΔΔδ(Δδternary -Δδbinary ), Rc′(( NICS (1) ternary - NICS (1)binary)/NICS (1)binary)和RBDE(C–CN)(BDE(C–CN)ternary/BDE(C–CN)binary)均具有良好的线性关系.同时, AIM的分析也佐证了协同效应的存在.%The cooperativity effects between the O/C–H…Cl–anionic H-bonding and O–H…N and C–H…O H-bonding interactions, thermodynamic properties and aromaticities in Cl–…benzonitrile…H2 O comple-xes are investigated using the B3LYP and MP2(full) methods. The result shows that the influence of the O/C–H…Cl–anionic H-bonding interaction on the C–H…O is more pronounced than that on the O–H…N in-teraction. The cooperativity effect appears in the linear conformation while the anti-cooperativity effect is found in the cyclic structure. The enthalpy change is the major factor driving the cooperativity in forming the linear ter-nary complex while entropy change turns into the favorable factor in forming the cyclic system. The aromaticity of the benzonitrile ring is weakened and theπ→π∗conjugative effect between the ring and C≡N bond is strength-ened upon the ternary-complex formation. To our interest, the cooperativity effect correlates well with Rc(NICS (1)ternary/NICS (1)binary),ΔΔδ (Δδternary– Δδbinary), Rc′((NICS (1)ternary– NICS (1

  5. Ion-radical intermediates of the radiation-chemical transformations of organic carbonates

    Science.gov (United States)

    Shiryaeva, Ekaterina S.; Sosulin, Ilya S.; Saenko, Elizaveta V.; Feldman, Vladimir I.

    2016-07-01

    The spectral features and reactions of ion-radical intermediates produced from organic carbonates in low-temperature matrices were investigated by EPR spectroscopy and quantum-chemical calculations. It was shown that radical cations of diethyl carbonate and dimethyl carbonate underwent intramolecular hydrogen transfer to yield alkyl-type species, as was suggested previously. Meanwhile, radical cation of EC demonstrates a ring cleavage even at 77 K, while radical cation of PC is probably intrinsically stable and undergo an ion-molecule reaction with a neighboring neutral molecule in dimers or associates. Radical anions were obtained in glassy matrices of diethyl ether or perdeuteroethanol. The radical anions of linear carbonates show photoinduced fragmentation to yield the corresponding alkyl radicals; such process may also occur directly under radiolysis. Radical anions of cyclic carbonates are relatively stable and yield only trace amounts of fragmentation products under similar conditions.

  6. Fast Resonance Raman Spectroscopy of Short-Lived Radicals

    DEFF Research Database (Denmark)

    Pagsberg, Palle Bjørn; Wilbrandt, Robert Walter; Hansen, Karina Benthin

    1976-01-01

    We report the first application of pulsed resonance Raman spectroscopy to the study of short-lived free radicals produced by pulse radiolysis. A single pulse from a flash-lamp pumped tunable dye laser is used to excite the resonance Raman spectrum of the p-terphenyl anion radical with an initial...

  7. Hydration and sorption characteristics of a polyfunctional weak-base anion exchanger after the sorption of vanillin and ethylvanillin

    Science.gov (United States)

    Rodionova, D. O.; Voronyuk, I. V.; Eliseeva, T. V.

    2016-07-01

    Features of the sorption of substituted aromatic aldehydes by a weak-base anion exchanger under equilibrium conditions are investigated using vanillin and ethylvanillin as examples. Analysis of the sorption isotherms of carbonyl compounds at different temperatures allows us to calculate the equilibrium characteristics of their sorption and assess the entropy and enthalpy contributions to the energy of the process. Hydration characteristics of the macroporous weak-base anion exchanger before and after the sorption of aromatic aldehydes are compared.

  8. Evaluation of the radical scavenging activity of a series of synthetic hydroxychalcones towards the DPPH radical

    Directory of Open Access Journals (Sweden)

    STOYAN P. PARUSHEV

    2011-04-01

    Full Text Available Sixteen hydroxychalcones were synthesized in sufficient purity by the Claisen–Schmidt condensation between appropriate acetophenones and aromatic aldehydes. All the compounds were evaluated for their ability to scavenge the stable free 2,2-diphenyl-1-picrylhydrazyl (DPPH radical. Important structure–activity relationships were observed that strongly contribute to the knowledge for the design of DPPH radical scavenging chalcones. Relevant theoretical parameters were computed in an attempt to understand and explain the obtained experimental results.

  9. SIMULTANEOUS DTERMINATION OF CHROMATE AND AROMATIC HYDROCARBONS IN ENVIRONMENTAL SAMPLES BY CAPILLARY ELECTROPHORESIS

    Science.gov (United States)

    An analytical method was developed to determine simultaneously, the inorganic anion CrO2-4, and organic aromatic compounds including benzoate, 2-Cl-benzoate, phenol, m-cresol and o-/p-cresol by capillary electrophoresis (CE). Chromate and the aromatics were separated in a relativ...

  10. Radical prostatectomy

    DEFF Research Database (Denmark)

    Fode, Mikkel; Sønksen, Jens; Jakobsen, Henrik

    2014-01-01

    OBJECTIVE: The aim of this study was to compare oncological and functional outcomes between robot-assisted laparoscopic radical prostatectomy (RALP) and retropubic radical prostatectomy (RRP) during the initial phase with RALP at a large university hospital. MATERIAL AND METHODS: Patient and tumour...... surgery and at follow-up and they were asked to report their use of pads/diapers. Potency was defined as an IIEF-5 score of at least 17 with or without phosphodiesterase-5 inhibitors. Patients using up to one pad daily for security reasons only were considered continent. Positive surgical margins, blood...... loss and functional outcomes were compared between groups. RESULTS: Overall, 453 patients were treated with RRP and 585 with RALP. On multivariate logistic regression analyses, the type of surgery did not affect surgical margins (p = 0.96) or potency at 12 months (p = 0.7). Patients who had undergone...

  11. BENZO[a]PYRENE METABOLITES EXAGGERATE DNA OXIDATIVE DAMAGE UPON THE INVOLVEMENT OF FREE RADICALS%苯并[a]比代谢产物在自由基参与下加速DNA的氧化损伤

    Institute of Scientific and Technical Information of China (English)

    罗云敬; GAO Da-yuan; WEI Hua-chen

    2003-01-01

    @@ Polycyclic aromatic hydrocarbons (PAHs),which constitute a major class of environmental pollu tants are posing a threat to human health. Benzopyrene,an index of PAH levels omnipresent in the everyday environment ,becomes toxic only when being metabolically and/or photo-activated,i. e. ,in the pres ence of UV light. Free radicals such as superoxide anions ('O2),hydrogen peroxide (H2O2),hydroxyl radicals ('OH) and singlet oxygen (1O2) are involved in carcinogenesis. Wei CE etc[1] studied the effects of different scavengers of active oxygen species (superoxide dismutase,catalase,mannitol and dimethyfu ran) on promoting B[a]P mutagenicity. Bryla P ete[2] investigated the roles of several ROS scavengers in the oxidation and binding of B[a]P to calf thymus DNA using the 32p-postlabeling assay.

  12. The direct aromatization of methane

    Energy Technology Data Exchange (ETDEWEB)

    Marcelin, G.; Oukaci, R.; Migone, R.A.; Kazi, A.M. [Altamira Instruments, Pittsburgh, PA (United States)

    1995-12-31

    The thermal decomposition of methane shows significant potential as a process for the production of higher unsaturated and aromatic hydrocarbons when the extent of the reaction is limited. Thermodynamic calculations have shown that when the reaction is limited to the formation of C{sub 2} to C{sub 10} products, yields of aromatics can exceed 40% at temperatures of 1200{degrees}C. Preliminary experiments have shown that when the reaction is limited to the formation of C{sub 2} to C{sub 10} products, yields of aromatics can exceed 40% at temperatures of 1200{degrees}C. Preliminary experiments have shown that cooling the product and reacting gases as the reaction proceeds can significantly reduce or eliminate the formation of solid carbon and heavier (C{sub 10+}) materials. Much work remains to be done in optimizing the quenching process and this is one of the goals of this program. Means to lower the temperature of the reaction are being studied as this result in a more feasible commercial process due to savings realized in energy and material of construction costs. The use of free-radical generators and catalysts will be investigated as a means of lowering the reaction temperature thus allowing faster quenching. It is highly likely that such studies will lead to a successful direct methane to higher hydrocarbon process.

  13. Application of Ionic Liquids with Carboxyl and Aromatic Ring Conjugated Anions in Dye-Sensitized Solar Cells%阴离子为羧酸根和芳环共轭的离子液体在染料敏化太阳能电池中的应用

    Institute of Scientific and Technical Information of China (English)

    王海; 徐雪青; 史继富; 徐刚

    2013-01-01

      提出了利用p-π共轭效应设计离子液体的方法, p-π共轭效应可以有效分散阴离子的负电荷,降低离子液体中阴阳离子之间的库仑引力,以得到低粘度的离子液体.所设计的离子液体为1-乙基-3-甲基咪唑苯甲酸(EMIB)和1-乙基-3-甲基咪唑异烟酸(EMIIN)(它们的阴离子中羧酸根和芳环为p-π共轭结构),这两种离子液体都达到了较低的粘度(EMIB为42 mPa·s, EMIIN为27 mPa·s).进一步将这两种离子液体做成电解质,应用在染料敏化太阳能电池中,通过优化电解质的组成, EMIB基电解质达到了1.43 mS·cm-1的电导率和1.45×10-7 cm2·s-1的I-3的扩散系数,而EMIIN基电解质的电导率和I-3扩散系数分别为1.63 mS·cm-1和2.01×10-7 cm2·s-1,后者电导性能的提高主要和EMIIN粘度较低有关系.进一步将这两种电解质组装成电池,在300 W·m-2的光强下测得EMIB基电池和EMIIN基电池的效率分别为2.85%和4.30%.%A method of utilizing p-π conjugation effects for obtaining low-viscosity ionic liquids is presented. p-π conjugation effectively disperses anionic charge and reduces Coulombic interactions. Ionic liquids prepared in this study were 1-ethyl-3-methylimidazolium benzoate (EMIB) and 1-ethyl-3-methylimidazolium isonicotinate (EMIIN). They have carboxyl and aromatic ring p-π conjugated anions, and achieve low viscosities of 42 and 27 mPa·s, respectively. EMIB and EMIIN were employed as electrolytes, which were used to construct dye-sensitized solar cel s (DSCs). After optimizing the composition, the ionic conductivity and tri odide ionic diffusion constant for the EMIB-based electrolyte were 1.43 mS·cm-1 and 1.45 × 10-7 cm2·s-1, respectively. For the EMIIN-based electrolyte, the ionic conductivity and tri odide ionic diffusion constant were 1.63 mS·cm-1 and 2.01×10-7 cm2·s-1, respectively. These were higher than the corresponding values for the EMIB-based electrolyte because of EMIINʹs lower

  14. Pathways of arachidonic acid peroxyl radical reactions and product formation with guanine radicals.

    Science.gov (United States)

    Crean, Conor; Geacintov, Nicholas E; Shafirovich, Vladimir

    2008-02-01

    Peroxyl radicals were derived from the one-electron oxidation of polyunsaturated fatty acids by sulfate radicals that were generated by the photodissociation of peroxodisulfate anions in air-equilibrated aqueous solutions. Reactions of these peroxyl and neutral guanine radicals, also generated by oxidation with sulfate radicals, were investigated by laser kinetic spectroscopy, and the guanine oxidation products were identified by HPLC and mass spectrometry methods. Sulfate radicals rapidly oxidize arachidonic (ArAc), linoleic (LnAc), and palmitoleic (PmAc) acids with similar rate constants, (2-4) x 10 (9) M (-1) s (-1). The C-centered radicals derived from the oxidation of ArAc and LnAc include nonconjugated Rn(.) ( approximately 80%) and conjugated bis-allylic Rba(.) ( approximately 20%) radicals. The latter were detectable in the absence of oxygen by their prominent, narrow absorption band at 280 nm. The Rn(.) radicals of ArAc (containing three bis-allylic sites) transform to the Rba(.) radicals via an intramolecular H-atom abstraction [rate constant (7.5 +/- 0.7) x 10 (4) s (-1)]. In contrast, the Rn(.) radicals of LnAc that contain only one bis-allylic site do not transform intramolecularly to the Rba(.) radicals. In the case of PmAc, which contains only one double bond, the Rba(.) radicals are not observed. The Rn(.) radicals of PmAc rapidly combine with oxygen with a rate constant of (3.8 +/- 0.4) x 10(9) M(-1) s(-1). The Rba(.) radicals of ArAc are less reactive and react with oxygen with a rate constant of (2.2 +/- 0.2) x 10 (8) M (-1) s (-1). The ArAc peroxyl radicals formed spontaneously eliminate superoxide radical anions [rate constant = (3.4 +/- 0.3) x 10 (4) M (-1) s (-1)]. The stable oxidative lesions derived from the 2',3',5'-tri- O-acetylguanosine or 2',3',5'-tri- O-acetyl-8-oxo-7,8-dihydroguanosine radicals and their subsequent reactions with ArAc peroxyl radicals were also investigated. The major products found were the 2,5-diamino-4 H

  15. Transmembrane anion transport and cytotoxicity of synthetic tambjamine analogs.

    Science.gov (United States)

    Hernando, Elsa; Soto-Cerrato, Vanessa; Cortés-Arroyo, Susana; Pérez-Tomás, Ricardo; Quesada, Roberto

    2014-03-21

    Ten synthetic analogs of the marine alkaloids tambjamines, bearing aromatic enamine moieties, have been synthesized. These compounds proved to be highly efficient transmembrane anion transporters in model liposomes. Changes in the electronic nature of the substituents of the aromatic enamine or the alkoxy group of the central pyrrole group did not affect this anionophore activity. The in vitro activity of these compounds has also been studied. They trigger apoptosis in several cancer cell lines with IC50 values in the low micromolar range as well as modify the intracellular pH, inducing the basification of acidic organelles.

  16. Anion-π catalysis.

    Science.gov (United States)

    Zhao, Yingjie; Beuchat, César; Domoto, Yuya; Gajewy, Jadwiga; Wilson, Adam; Mareda, Jiri; Sakai, Naomi; Matile, Stefan

    2014-02-05

    The introduction of new noncovalent interactions to build functional systems is of fundamental importance. We here report experimental and theoretical evidence that anion-π interactions can contribute to catalysis. The Kemp elimination is used as a classical tool to discover conceptually innovative catalysts for reactions with anionic transition states. For anion-π catalysis, a carboxylate base and a solubilizer are covalently attached to the π-acidic surface of naphthalenediimides. On these π-acidic surfaces, transition-state stabilizations up to ΔΔGTS = 31.8 ± 0.4 kJ mol(-1) are found. This value corresponds to a transition-state recognition of KTS = 2.7 ± 0.5 μM and a catalytic proficiency of 3.8 × 10(5) M(-1). Significantly increasing transition-state stabilization with increasing π-acidity of the catalyst, observed for two separate series, demonstrates the existence of "anion-π catalysis." In sharp contrast, increasing π-acidity of the best naphthalenediimide catalysts does not influence the more than 12 000-times weaker substrate recognition (KM = 34.5 ± 1.6 μM). Together with the disappearance of Michaelis-Menten kinetics on the expanded π-surfaces of perylenediimides, this finding supports that contributions from π-π interactions are not very important for anion-π catalysis. The linker between the π-acidic surface and the carboxylate base strongly influences activity. Insufficient length and flexibility cause incompatibility with saturation kinetics. Moreover, preorganizing linkers do not improve catalysis much, suggesting that the ideal positioning of the carboxylate base on the π-acidic surface is achieved by intramolecular anion-π interactions rather than by an optimized structure of the linker. Computational simulations are in excellent agreement with experimental results. They confirm, inter alia, that the stabilization of the anionic transition states (but not the neutral ground states) increases with the π-acidity of the

  17. Interaction of anions with substituted buckybowls. The anion's nature and solvent effects.

    Science.gov (United States)

    Campo-Cacharrón, Alba; Cabaleiro-Lago, Enrique M; González-Veloso, Iván; Rodríguez-Otero, Jesús

    2014-08-07

    Complexes formed by CN-substituted corannulene and sumanene with monovalent anions have been computationally studied to evaluate the effect of anion's nature and solvent upon the interaction. The results indicate that the most stable complex arrangement corresponds in all cases to the anion located by the center of the concave face of the bowl. All complexes are remarkably stable in the gas phase, with interaction energies ranging from -47 to -24 kcal/mol depending on the anion and the bowl considered. The order of stability for the different anion complexes in the gas phase is CO2H(-) > Cl(-) > Br(-) > NO3(-) ≫ ClO4(-) > BF4(-). Regarding the bowl employed, the intensity of the interaction is largest with the sumanene derivative substituted in the C-H aromatic groups. The weakest interactions are obtained with the sumanene derivative substituted in the CH2 groups, whereas complexes with the corannulene derivative give intermediate values. NO3(-) is oriented parallel to the bowl in the most stable complexes, whereas CO2H(-) prefers being oriented perpendicular to the bowl; ClO4(-) and BF4(-) arrange themselves with three bonds pointing to the bowl. These orientations are preferred on the basis of larger electrostatic and dispersion interactions. The preference of anions for the concave face of the bowl not only is mainly related to larger electrostatic interactions but also is because dispersion and induction are larger than in other arrangements considered. The presence of solvent modeled with a continuum model has a deep impact on the interaction energies already in solvents with low dielectric constant. All complexes remain stable, though energies in water hardly reach -7 kcal/mol. Br(-) complexes are the most stable in solvent, whereas CO2H(-) ones suffer a large penalty in solvent, becoming among the least stable complexes despite being the most stable in the gas phase.

  18. Aromatics Oxidation and Soot Formation in Flames

    Energy Technology Data Exchange (ETDEWEB)

    Howard, J. B.; Richter, H.

    2005-03-29

    This project is concerned with the kinetics and mechanisms of aromatics oxidation and the growth process to polycyclic aromatic hydrocarbons (PAH) of increasing size, soot and fullerenes formation in flames. The overall objective of the experimental aromatics oxidation work is to extend the set of available data by measuring concentration profiles for decomposition intermediates such as phenyl, cyclopentadienyl, phenoxy or indenyl radicals which could not be measured with molecular-beam mass spectrometry to permit further refinement and testing of benzene oxidation mechanisms. The focus includes PAH radicals which are thought to play a major role in the soot formation process while their concentrations are in many cases too low to permit measurement with conventional mass spectrometry. The radical species measurements are used in critical testing and improvement of a kinetic model describing benzene oxidation and PAH growth. Thermodynamic property data of selected species are determined computationally, for instance using density functional theory (DFT). Potential energy surfaces are explored in order to identify additional reaction pathways. The ultimate goal is to understand the conversion of high molecular weight compounds to nascent soot particles, to assess the roles of planar and curved PAH and relationships between soot and fullerenes formation. The specific aims are to characterize both the high molecular weight compounds involved in the nucleation of soot particles and the structure of soot including internal nanoscale features indicative of contributions of planar and/or curved PAH to particle inception.

  19. Zn-Al LAYERED DOUBLE HYDROXIDE PILLARED BY DIFFERENT DICARBOXYLATE ANIONS

    Directory of Open Access Journals (Sweden)

    S. Gago

    2004-12-01

    Full Text Available Zn-Al layered double hydroxides (LDHs intercalated by terephthalate (TPH and biphenyl-4,4'-dicarboxylate (BPH anions have been synthesized by direct co-precipitation from aqueous solution. The Zn/Al ratio in the final materials was 1.8. The products were characterized by powder X-ray diffraction, thermogravimetric analysis, FTIR and FT Raman spectroscopy, and MAS NMR spectroscopy. The basal spacing for the TPH-LDH intercalate was 14.62 Å, indicating that the guest anions stack to form a monolayer with the aromatic rings perpendicular to the host layers. For the LDH intercalate containing BPH anions, a basal spacing of at least 19.2 Å would be expected if the anions adopted an arrangement similar to that for the TPH anions. The observed spacing was 18.24 Å, suggesting that the anions are tilted slightly with respect to the host layers.

  20. A Joint Experimental and Computational Study of the Negative Ion Photoelectron Spectroscopy of the 1-Phospha-2,3,4-triazolate Anion, HCPN 3

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Gao-Lei; Chen, Bo; Transue, Wesley J.; Hrovat, David A.; Cummins, Christopher C.; Borden, Weston Thatcher; Wang, Xue-Bin

    2016-08-11

    We report here the results of a combined experimental and computational study of the negative ion photoelectron spectroscopy (NIPES) of the recently synthesized, planar, aromatic, HCPN3– ion. The adiabatic electron detachment energy of HCPN3– (electron affinity of HCPN3•) was measured to be 3.555 ± 0.010 eV, a value that is intermediate between the electron detachment energies of the closely related (CH)2N3– and P2N3– ions. High level electronic structure calculations and Franck–Condon factor (FCF) simulations reveal that transitions from the ground state of the anion to two nearly degenerate, low-lying, electronic states, of the neutral HCPN3• radical are responsible for the congested peaks at low binding energies in the NIPE spectrum. The best fit of the simulated NIPE spectrum to the experimental spectrum indicates that the ground state of HCPN3• is a 5π-electron 2A" π radical state, with a 6π-electron, 2A', σ radical state being at most ~1.0 kcal/mol higher in energy. This assignment contrasts with our recent finding that the ground state of P2N3• is a 6π-electron σ radical state

  1. Measurement of radical-species concentrations and polycyclic aromatic hydrocarbons in flames by fluorescence and absorption using a tunable dye laser. Progress report, March 1, 1980-February 28, 1981

    Energy Technology Data Exchange (ETDEWEB)

    Lucht, R.P.; Sweeney, D.W.; Laurendeau, N.M.

    1981-03-01

    A theoretical and experimental investigation of OH saturated fluorescence is described. The goal of the research is to develop a saturated fluorescence technique which will yield accurate molecular number densities over a wide range of flame pressure, temperature, and composition. Experimentally, OH is excited by a ten nanosecond pulse from a Nd:YAG-pumped dye laser tuned to an isolated rotational transition in the (0,0) band of the A/sup 2/..sigma../sup +/-X/sup 2/ pi electronic system. The resulting fluorescence signal is resolved both spectrally and temporally. Total OH number densities are calculated by collecting fluorescence from the directly excited upper rotational level, and using the balanced cross-rate model to analyze the experimental data. Fluorescence measurements of OH number density agree to within a factor of three with the results of independent OH absorption measurements. Significantly, the ratio of the fluorescence signal to the number density measured by absorption is nearly the same in 30, 100 and 250 torr H/sub 2//O/sub 2//N/sub 2/ flat flames, demonstrating the insensitivity of the saturated fluorescence signal to the quenching environment of the radical. Collisional transfer in excited OH is studied by recording the time development of OH fluorescence spectrum. The experimental spectra are compared with the results of time-dependent computer modeling. By varying rotational transfer rates until the calculated and experimental spectra agree, rotational transfer cross sections can be calculated. The signal processing system was thoroughly checked by comparing the photomultiplier output to that of a fast photodiode, and by comparing single pulse Rayleigh scattering and fluorescence traces with sampling oscilloscope traces.

  2. (Hetero)aromatics from dienynes, enediynes and enyne-allenes.

    Science.gov (United States)

    Raviola, Carlotta; Protti, Stefano; Ravelli, Davide; Fagnoni, Maurizio

    2016-08-01

    The construction of aromatic rings has become a key objective for organic chemists. While several strategies have been developed for the functionalization of pre-formed aromatic rings, the direct construction of an aromatic core starting from polyunsaturated systems is yet a less explored field. The potential of such reactions in the formation of aromatics increased at a regular pace in the last few years. Nowadays, there are reliable and well-established procedures to prepare polyenic derivatives, such as dienynes, enediynes, enyne-allenes and hetero-analogues. This has stimulated their use in the development of innovative cycloaromatizations. Different examples have recently emerged, suggesting large potential of this strategy in the preparation of (hetero)aromatics. Accordingly, this review highlights the recent advancements in this field and describes the different conditions exploited to trigger the process, including thermal and photochemical activation, as well as the use of transition metal catalysis and the addition of electrophiles/nucleophiles or radical species.

  3. Potentiometric anion selective sensors

    NARCIS (Netherlands)

    Antonisse, Martijn M.G.; Reinhoudt, David N.

    1999-01-01

    In comparison with selective receptors (and sensors) for cationic species, work on the selective complexation and detection of anions is of more recent date. There are three important components for a sensor, a transducer element, a membrane material that separates the transducer element and the aqu

  4. Polycyclic Aromatic Hydrocarbons

    Science.gov (United States)

    Salama, Farid

    2010-01-01

    Carbonaceous materials play an important role in space. Polycyclic Aromatic Hydrocarbons (PAHs) are a ubiquitous component of the carbonaceous materials. PAHs are the best-known candidates to account for the IR emission bands. They are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge is to reproduce in the laboratory the physical conditions that exist in the emission and absorption interstellar zones. The harsh physical conditions of the ISM -low temperature, collisionless, strong UV radiation fields- are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions and radicals are formed from the neutral precursors in an isolated environment at low temperature and probed with high-sensitivity cavity ringdown spectroscopy in the NUV-NIR range. Carbon nanoparticles are also formed during the short residence time of the precursors in the plasma and are characterized with time-offlight mass spectrometry. These experiments provide unique information on the spectra of large carbonaceous molecules and ions in the gas phase that can now be directly compared to interstellar and circumstellar observations (IR emission bands, DIBs, extinction curve). These findings also hold great potential for understanding the formation process of interstellar carbonaceous grains. We will review recent progress in the experimental and theoretical studies of PAHs, compare the laboratory data with astronomical observations and discuss the global implications.

  5. Resonance ionization detection of combustion radicals

    Energy Technology Data Exchange (ETDEWEB)

    Cool, T.A. [Cornell Univ., Ithaca, NY (United States)

    1993-12-01

    Fundamental research on the combustion of halogenated organic compounds with emphasis on reaction pathways leading to the formation of chlorinated aromatic compounds and the development of continuous emission monitoring methods will assist in DOE efforts in the management and disposal of hazardous chemical wastes. Selective laser ionization techniques are used in this laboratory for the measurement of concentration profiles of radical intermediates in the combustion of chlorinated hydrocarbon flames. A new ultrasensitive detection technique, made possible with the advent of tunable VUV laser sources, enables the selective near-threshold photoionization of all radical intermediates in premixed hydrocarbon and chlorinated hydrocarbon flames.

  6. Corticosteroids increase superoxide anion production by rat liver microsomes.

    Science.gov (United States)

    Nelson, D H; Ruhmann-Wennhold, A

    1975-01-01

    Superoxide anion production by liver microsomes from intact, adrenalectomized, and cortisoltreated adrenalectomized rats has been determined. The amount formed was roughly proportionate to the amount of cortisol given, and a similar response was seen in the activity of NADPH-cytochrome c reductase. The amount of measurable superoxide anion was markedly reduced by the addition of superoxide dismutase. The increased production of this potent free radical with cortisol therapy suggests that its formation may contribute to some of the harmful effects of corticosteroids given in more than physiologic amounts. PMID:239969

  7. Perspective: Electrospray photoelectron spectroscopy: From multiply-charged anions to ultracold anions

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Lai-Sheng, E-mail: Lai-Sheng-Wang@brown.edu [Department of Chemistry, Brown University, Providence, Rhode Island 02912 (United States)

    2015-07-28

    Electrospray ionization (ESI) has become an essential tool in chemical physics and physical chemistry for the production of novel molecular ions from solution samples for a variety of spectroscopic experiments. ESI was used to produce free multiply-charged anions (MCAs) for photoelectron spectroscopy (PES) in the late 1990 s, allowing many interesting properties of this class of exotic species to be investigated. Free MCAs are characterized by strong intramolecular Coulomb repulsions, which create a repulsive Coulomb barrier (RCB) for electron emission. The RCB endows many fascinating properties to MCAs, giving rise to meta-stable anions with negative electron binding energies. Recent development in the PES of MCAs includes photoelectron imaging to examine the influence of the RCB on the electron emission dynamics, pump-probe experiments to examine electron tunneling through the RCB, and isomer-specific experiments by coupling PES with ion mobility for biological MCAs. The development of a cryogenically cooled Paul trap has led to much better resolved PE spectra for MCAs by creating vibrationally cold anions from the room temperature ESI source. Recent advances in coupling the cryogenic Paul trap with PE imaging have allowed high-resolution PE spectra to be obtained for singly charged anions produced by ESI. In particular, the observation of dipole-bound excited states has made it possible to conduct vibrational autodetachment spectroscopy and resonant PES, which yield much richer vibrational spectroscopic information for dipolar free radicals than traditional PES.

  8. Ignorance Radicalized

    Directory of Open Access Journals (Sweden)

    Gergo Somodi

    2009-12-01

    Full Text Available The aim of this paper is twofold. I criticize Michael Devitt's linguistic---as opposed to Chomsky's psychological---conception of linguistics on the one hand, and I modify his related view on linguistic intuitions on the other. I argue that Devitt's argument for the linguistic conception is in conflict with one of the main theses of that very conception, according to which linguistics should be about physical sentence tokens of a given language rather than about the psychologically real competence of native speakers. The basis of this conflict is that Devitt's view on language, as I will show, inherits too much from the criticized Chomskian view. This is also the basis of Devitt's strange claim that it is the linguist, and not the ordinary speaker, whose linguistic intuition should have an evidential role in linguistics. I will argue for the opposite by sketching a view on language that is more appropriate to the linguistic conception. That is, in criticizing Devitt, I am not defending the Chomskian approach. My aim is to radicalize Devitt's claims.

  9. Antioxidant, Anti-5-lipoxygenase and Antiacetylcholinesterase Activities of Essential Oils and Decoction Waters of Some Aromatic Plants

    Directory of Open Access Journals (Sweden)

    Sílvia M. Albano

    2012-01-01

    Full Text Available The scavenging of free radicals and superoxide anion, the inhibition of 5-lipoxygenase and the antiacetylcholinesterase activities of essential oils and decoction waters of eight aromatic plants (Dittrichia viscosa , Foeniculum vulgare, Origanum vulgare, Salvia officinalis, Thymbra capitata , Thymus camphoratus, Thymus carnosus and Thymus mastichina were studied. The essential oils were dominated by 1,8-cineole in S. officinalis (59%, T. mastichina (49% and T. camphoratus (21%; borneol (20% in T. carnosus; carvacrol in Thymbra capitata (68%; γ -terpinene (49% in O. vulgare; α -pinene (26% in F. vulgare; and trans-nerolidol (8% + β -oplopenone (7% in D. viscosa. O. vulgare decoction waters had the highest amount of phenols (4 5 ± 3 mg GAE/mL while F. vulgare only had 5 ± 0 mg GAE/mL. The decoction waters showed higher radical scavenging activity than the essential oils. O. vulgare decoction water showed the best antioxidant activity (IC 50= 3 ± 0 m g/mL, while the most effective essential oils were those of Thymbra capitata (IC 50=61 ± 2 m g/mL and O. vulgare (IC 50=15 6 ± 5 m g/mL. Thymbra capitata (IC 50= 6 ± 0 m g/mL decoction water showed the best superoxide anion scavenging activity. F. vulgare decoction water and essential oil revealed the best 5-lipoxygenase inhibition capacity (IC 50=2 7 ± 1 m g/mL and IC 50=6 8 ± 2 m g/mL, respectively. T. mastichina (IC 50=4 6 ± 4 m g/mL, S. officinalis (IC 50=5 1 ± 4 m g/mL, Thymbra capitata (IC 50=5 2 ± 1 m g/mL and T. camphoratus (IC 50=13 7 ± 2 m g/mL essential oils showed the best antiacetylcholinesterase activity.

  10. Aromater i drikkevand

    DEFF Research Database (Denmark)

    Nyeland, B. A.; Hansen, A. B.

    DMU har den 10. Juni 1997 afholdt en præstationsprøvning: Aromater i drikkevand. Der deltog 21 laboratorier i præstationsprøvningen. Prøvningen omfattede 6 vandige prøver og 6 ampuller indeholdende 6 aromater. Laboratorierne spikede de tilsendte vandprøver med indholdet fra ampullerne...

  11. Effect of anions on the electrochemistry of zinc tetraphenylporphyrin

    Energy Technology Data Exchange (ETDEWEB)

    Seely, G.R.; Gust, D.; Moore, T.A.; Moore, A.L. (Arizona State Univ., Tempe, AZ (United States))

    1994-10-13

    Accurate measurements of porphyrin redox potentials are essential for the prediction and rationalization of the rates of electron transfer reactions involving these biologically important electron-donating and accepting chromophores. The present work describes a survey of redox potentials of zinc tetraphenylporphyrin obtained by cyclic voltammetry in dichloromethane, with tetrabutylammonium salts containing a variety of anions as electrolytes. Of the anions tested, hexafluorophosphate appears to have the least ability to ligate the metal, so that potentials measured in its presence as electrolyte should most closely approach those of the unligated porphyrin. With perchlorate electrolyte, the potential for one-electron oxidation is approximately 80 mV lower, enough to affect the interpretation of photochemical electron transfer rates. In general, anions bind much more strongly to the cation radical than to zinc tetraphenylporphyrin itself. The use of reference redox systems based on thymoquinone and ferrocene carboxylate enabled comparison of potentials measured with different electrolytes. 30 refs., 2 tabs.

  12. Cathodic Aromatic C,C Cross-Coupling Reaction via Single Electron Transfer Pathway.

    Science.gov (United States)

    Qu, Yang; Tateno, Hiroyuki; Matsumura, Yoshimasa; Kashiwagi, Tsuneo; Atobe, Mahito

    2017-03-07

    We have successfully developed a novel cathodic cross-coupling reaction of aryl halides with arenes. Utilization of the cathodic single electron transfer (SET) mechanism for activation of aryl halides enables the cross-coupling reaction to proceed without the need for any transition metal catalysts or single electron donors in a mild condition. The SET from a cathode to an aryl halide initiates a radical chain by giving an anion radical of the aryl halide. The following propagation cycle also consists entirely of anion radical intermediates.

  13. Cathodic Aromatic C,C Cross-Coupling Reaction via Single Electron Transfer Pathway

    Directory of Open Access Journals (Sweden)

    Yang Qu

    2017-03-01

    Full Text Available We have successfully developed a novel cathodic cross-coupling reaction of aryl halides with arenes. Utilization of the cathodic single electron transfer (SET mechanism for activation of aryl halides enables the cross-coupling reaction to proceed without the need for any transition metal catalysts or single electron donors in a mild condition. The SET from a cathode to an aryl halide initiates a radical chain by giving an anion radical of the aryl halide. The following propagation cycle also consists entirely of anion radical intermediates.

  14. A Supramolecular Sensing Platform for Phosphate Anions and an Anthrax Biomarker in a Microfluidic Device

    NARCIS (Netherlands)

    Eker, Bilge; Yilmaz, Mahmut Deniz; Schlautmann, Stefan; Gardeniers, Johannes G.E.; Huskens, Jurriaan

    2011-01-01

    A supramolecular platform based on self-assembled monolayers (SAMs) has been implemented in a microfluidic device. The system has been applied for the sensing of two different analyte types: biologically relevant phosphate anions and aromatic carboxylic acids, which are important for anthrax detecti

  15. Resonant spectra of quadrupolar anions

    CERN Document Server

    Fossez, K; Nazarewicz, W; Michel, N; Garrett, W R; Płoszajczak, M

    2016-01-01

    In quadrupole-bound anions, an extra electron is attached at a sufficiently large quadrupole moment of a neutral molecule, which is lacking a permanent dipole moment. The nature of the bound states and low-lying resonances of such anions is of interest for understanding the threshold behavior of open quantum systems in general. In this work, we investigate the properties of quadrupolar anions as extreme halo systems, the formation of rotational bands, and the transition from a subcritical to supercritical electric quadrupole moment. We solve the electron-plus-molecule problem using a non-adiabatic coupled-channel formalism by employing the Berggren ensemble, which explicitly contains bound states, narrow resonances, and the scattering continuum. We demonstrate that binding energies and radii of quadrupolar anions strictly follow the scaling laws for two-body halo systems. Contrary to the case of dipolar anions, ground-state band of quadrupolar anions smoothly extend into the continuum, and many rotational ban...

  16. Spectroscopic detection, reactivity, and acid-base behavior of ring-dimethoxylated phenylethanoic acid radical cations and radical zwitterions in aqueous solution.

    Science.gov (United States)

    Bietti, Massimo; Capone, Alberto

    2004-01-23

    A product and time-resolved kinetic study of the one-electron oxidation of ring-dimethoxylated phenylethanoic acids has been carried out at different pH values. Oxidation leads to the formation of aromatic radical cations or radical zwitterions depending on pH, and pK(a) values for the corresponding acid-base equilibria have been measured. The radical cations undergo decarboxylation with first-order rate constants (k(dec)) ranging from <10(2) to 5.6 x 10(4) s(-1) depending on radical cation stability. A significant increase in k(dec) (between 10 and 40 times) is observed on going from the radical cations to the corresponding radical zwitterions. The results are discussed in terms of the ease of intramolecular side chain to ring electron transfer required for decarboxylation, in both the radical cations and radical zwitterions.

  17. Glutathione--hydroxyl radical interaction: a theoretical study on radical recognition process.

    Directory of Open Access Journals (Sweden)

    Béla Fiser

    Full Text Available Non-reactive, comparative (2 × 1.2 μs molecular dynamics simulations were carried out to characterize the interactions between glutathione (GSH, host molecule and hydroxyl radical (OH(•, guest molecule. From this analysis, two distinct steps were identified in the recognition process of hydroxyl radical by glutathione: catching and steering, based on the interactions between the host-guest molecules. Over 78% of all interactions are related to the catching mechanism via complex formation between anionic carboxyl groups and the OH radical, hence both terminal residues of GSH serve as recognition sites. The glycine residue has an additional role in the recognition of OH radical, namely the steering. The flexibility of the Gly residue enables the formation of further interactions of other parts of glutathione (e.g. thiol, α- and β-carbons with the lone electron pair of the hydroxyl radical. Moreover, quantum chemical calculations were carried out on selected GSH/OH(• complexes and on appropriate GSH conformers to describe the energy profile of the recognition process. The relative enthalpy and the free energy changes of the radical recognition of the strongest complexes varied from -42.4 to -27.8 kJ/mol and from -21.3 to 9.8 kJ/mol, respectively. These complexes, containing two or more intermolecular interactions, would be the starting configurations for the hydrogen atom migration to quench the hydroxyl radical via different reaction channels.

  18. Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

    Energy Technology Data Exchange (ETDEWEB)

    Gottlieb, C.A.; Thaddeus, P. [Harvard Univ., Cambridge, MA (United States)

    1993-12-01

    Highly reactive carbenes and carbon-chain radicals are studied at millimeter wavelengths by observing their rotational spectra. The purpose is to provide definitive spectroscopic identification, accurate spectroscopic constants in the lowest vibrational states, and reliable structures of the key intermediates in reactions leading to aromatic hydrocarbons and soot particles in combustion.

  19. Aromatics oxidation and soot formation in flames

    Energy Technology Data Exchange (ETDEWEB)

    Howard, J.B.; Pope, C.J.; Shandross, R.A.; Yadav, T. [Massachusetts Institute of Technology, Cambridge (United States)

    1993-12-01

    This project is concerned with the kinetics and mechanisms of aromatics oxidation and soot and fullerenes formation in flames. The scope includes detailed measurements of profiles of stable and radical species concentrations in low-pressure one-dimensional premixed flames. Intermediate species identifications and mole fractions, fluxes, and net reaction rates calculated from the measured profiles are used to test postulated reaction mechanisms. Particular objectives are to identify and to determine or confirm rate constants for the main benzene oxidation reactions in flames, and to characterize fullerenes and their formation mechanisms and kinetics.

  20. Hydroxyl radical generation by red tide algae.

    Science.gov (United States)

    Oda, T; Akaike, T; Sato, K; Ishimatsu, A; Takeshita, S; Muramatsu, T; Maeda, H

    1992-04-01

    The unicellular marine phytoplankton Chattonella marina is known to have toxic effects against various living marine organisms, especially fishes. However, details of the mechanism of the toxicity of this plankton remain obscure. Here we demonstrate the generation of superoxide and hydroxyl radicals from a red tide unicellular organism, C. marina, by using ESR spectroscopy with the spin traps 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and N-t-butyl-alpha-phenylnitrone (PBN), and by using the luminol-enhanced chemiluminescence response. The spin-trapping assay revealed productions of spin adduct of superoxide anion (O2-) (DMPO-OOH) and that of hydroxyl radical (.OH) (DMPO-OH) in the algal suspension, which was not observed in the ultrasonic-ruptured suspension. The addition of superoxide dismutase (500 U/ml) almost completely inhibited the formation of both DMPO-OOH and DMPO-OH, and carbon-centered radicals were generated with the disappearance of DMPO-OH after addition of 5% dimethyl sulfoxide (Me2SO) and 5% ethanol. Furthermore, the generation of methyl and methoxyl radicals, which are thought to be produced by the reaction of hydroxyl radical and Me2SO under aerobic condition, was identified using spin trapping with a combination of PBN and Me2SO. Luminol-enhanced chemiluminescence assay also supported the above observations. These results clearly indicate that C. marina generates and releases the superoxide radical followed by the production of hydroxyl radical to the surrounding environment. The velocity of superoxide generation by C. marina was about 100 times faster than that by mammalian phagocytes per cell basis. The generation of oxygen radical is suggested to be a pathogenic principle in the toxication of red tide to susceptible aquaculture fishes and may be directly correlated with the coastal pollution by red tide.

  1. Modeling Carbon Chain Anions in L1527

    CERN Document Server

    Harada, Nanase

    2008-01-01

    The low-mass protostellar region L1527 is unusual because it contains observable abundances of unsaturated carbon-chain molecules including CnH radicals, H2Cn carbenes, cyanopolyynes, and the negative ions C4H- and C6H-, all of which are more associated with cold cores than with protostellar regions. Sakai et al. suggested that these molecules are formed in L1527 from the chemical precursor methane, which evaporates from the grains during the heat-up of the region. With the gas-phase osu.03.2008 network extended to include negative ions of the families Cn-, and CnH-, as well as the newly detected C3N-, we modeled the chemistry that occurs following methane evaporation at T~ 25-30 K. We are able to reproduce most of the observed molecular abundances in L1527 at a time of ~5000 yr. At later times, the overall abundance of anions become greater than that of electrons, which has an impact on many organic species and ions. The anion-to-neutral ratio in our calculation is in good agreement with observation for C6H-...

  2. Anionic surface binders

    Directory of Open Access Journals (Sweden)

    Aljaž-Rožič Mateja

    2004-01-01

    Full Text Available The MELAMIN Chemical Factory in Kočevje manufactures synthetic resins and binders for the paper industry. Binders based on AKD (alkyl ketene dimer are produced which are used for binding paper and cardboard in the range of neutral and partially basic pH. Cationic and, lately, anionic binders are mostly used for the bulk binding of paper and board. The possibility of using AKD binders on paper or board surfaces is presented. In this case partially cationic AKD binders may be applied. When optical whiteners are used, the application of AKD binders is recommended. In the case of paper it is possible to substitute acrylate binders by AKD binders. The best results are obtained when the paper is first partly treated in bulk and subsequently surface treated.

  3. Genomic and molecular mechanisms for efficient biodegradation of aromatic dye.

    Science.gov (United States)

    Sun, Su; Xie, Shangxian; Chen, Hu; Cheng, Yanbing; Shi, Yan; Qin, Xing; Dai, Susie Y; Zhang, Xiaoyu; Yuan, Joshua S

    2016-01-25

    Understanding the molecular mechanisms for aromatic compound degradation is crucial for the development of effective bioremediation strategies. We report the discovery of a novel phenomenon for improved degradation of Direct Red 5B azo dye by Irpex lacteus CD2 with lignin as a co-substrate. Transcriptomics analysis was performed to elucidate the molecular mechanisms of aromatic degradation in white rot fungus by comparing dye, lignin, and dye/lignin combined treatments. A full spectrum of lignin degradation peroxidases, oxidases, radical producing enzymes, and other relevant components were up-regulated under DR5B and lignin treatments. Lignin induced genes complemented the DR5B induced genes to provide essential enzymes and redox conditions for aromatic compound degradation. The transcriptomics analysis was further verified by manganese peroxidase (MnP) protein over-expression, as revealed by proteomics, dye decolorization assay by purified MnP and increased hydroxyl radical levels, as indicated by an iron reducing activity assay. Overall, the molecular and genomic mechanisms indicated that effective aromatic polymer degradation requires synergistic enzymes and radical-mediated oxidative reactions to form an effective network of chemical processes. This study will help to guide the development of effective bioremediation and biomass degradation strategies.

  4. A radical approach to radical innovation

    OpenAIRE

    Deichmann, Dirk; van der Ende, Jan

    2014-01-01

    textabstractInnovation pays. Amazon, Apple, Facebook, Google – nearly every one of today’s most successful companies has a talent for developing radical new ideas. But how best to encourage radical initiative taking from employees, and does their previous success or failure at it play a role?

  5. Resonant spectra of quadrupolar anions

    Science.gov (United States)

    Fossez, K.; Mao, Xingze; Nazarewicz, W.; Michel, N.; Garrett, W. R.; Płoszajczak, M.

    2016-09-01

    In quadrupole-bound anions, an extra electron is attached at a sufficiently large quadrupole moment of a neutral molecule, which is lacking a permanent dipole moment. The nature of the bound states and low-lying resonances of such anions is of interest for understanding the threshold behavior of open quantum systems in general. In this work, we investigate the properties of quadrupolar anions as halo systems, the formation of rotational bands, and the transition from a subcritical to supercritical electric quadrupole moment. We solve the electron-plus-rotor problem using a nonadiabatic coupled-channel formalism by employing the Berggren ensemble, which explicitly contains bound states, narrow resonances, and the scattering continuum. The rotor is treated as a linear triad of point charges with zero monopole and dipole moments and nonzero quadrupole moment. We demonstrate that binding energies and radii of quadrupolar anions strictly follow the scaling laws for two-body halo systems. Contrary to the case of dipolar anions, ground-state band of quadrupolar anions smoothly extend into the continuum, and many rotational bands could be identified above the detachment threshold. We study the evolution of a bound state of an anion as it dives into the continuum at a critical quadrupole moment and we show that the associated critical exponent is α =2 . Everything considered, quadrupolar anions represent a perfect laboratory for the studies of marginally bound open quantum systems.

  6. Synthesis of water-soluble cystine C60 derivative with catalyst and its active oxygen radical scavenging ability

    Institute of Scientific and Technical Information of China (English)

    Wen Chao Guan; Xiang Ying Tang; Li Zhen Huang; Hong Xu

    2007-01-01

    A novel water-soluble cystine C60 derivative was synthesized in the presence of the catalyst, tetrabutylammonium hydroxide (TBAH). The product was characterized by FT-IR, UV, 1H NMR, 13C NMR, MS and elemental analysis. Furthermore, the that cystine C60 derivative showed an excellent efficiency in eliminating superoxygen anion radical and hydroxyl radical. The 50%inhibition concentration (IC50) for superoxygen anion radical and hydroxyl radical were 0.167 and 0.008 mg/mL, respectively.

  7. Predicting the Strength of Anion-π Interactions of Substituted Benzenes: the Development of Anion-π Binding Substituent Constants.

    Science.gov (United States)

    Bagwill, Christina; Anderson, Christa; Sullivan, Elizabeth; Manohara, Varun; Murthy, Prithvi; Kirkpatrick, Charles C; Stalcup, Apryll; Lewis, Michael

    2016-11-23

    A computational study aimed at accurately predicting the strength of the anion-π binding of substituted benzenes is presented. The anion-π binding energies (Ebind) of 37 substituted benzenes and the parent benzene, with chloride or bromide were investigated at the MP2(full)/6-311++G** level of theory. In addition, energy decomposition analysis was performed on 27 selected chloride-arene complexes via symmetry adapted perturbation theory (SAPT), using the SAPT2+ approach. Initial efforts aimed to correlate the anion-π Ebind values with the sum of the Hammett constants σp (Σσp) or σm (Σσm), as done by others. This proved a decent approach for predicting the binding strength of aromatics with electron-withdrawing substituents. For the Cl(-)-substituted benzene Ebind values, the correlation with the Σσp and Σσm values of aromatics with electron-withdrawing groups had r(2) values of 0.89 and 0.87 respectively. For the Br(-)-substituted benzene Ebind values, the correlation with the Σσp and Σσm values of aromatics with electron-withdrawing groups had r(2) values of 0.90 and 0.87. However, adding aromatics with electron-donating substituents to the investigation caused the correlation to deteriorate. For the Cl(-)-substituted benzene complexes the correlation between Ebind values and the Hammett constants had r(2) = 0.81 for Σσp and r(2) = 0.84 for Σσm. For the Br(-)-substituted benzene complexes, the respective r(2) values were 0.71 for Σσp and 0.79 for Σσm. The deterioration in correlation upon consideration of substituted benzenes with electron-donating substituents is due to the anion-π binding energies becoming more attractive regardless of what type of substituent is added to the aromatic. A similar trend has been reported for parallel face-to-face substituted benzene-benzene binding. This is certainly counter to what electrostatic arguments would predict for trends in anion-π binding energies, and this discrepancy is further highlighted

  8. Influence of Aqueous Inorganic Anions on the Reactivity of Nanoparticles in TiO2 Photocatalysis.

    Science.gov (United States)

    Farner Budarz, Jeffrey; Turolla, Andrea; Piasecki, Aleksander F; Bottero, Jean-Yves; Antonelli, Manuela; Wiesner, Mark R

    2017-03-21

    The influence of inorganic anions on the photoreactivity and aggregation of titanium dioxide nanoparticles (NPs) was assessed by dosing carbonate, chloride, nitrate, phosphate, and sulfate as potassium salts at multiple concentrations. NP stability was monitored in terms of aggregate morphology and electrophoretic mobility (EPM). Aggregate size and fractal dimension were measured over time by laser diffraction, and the isoelectric point (IEP) as a function of anion and concentration was obtained by measuring EPM versus pH. Phosphate, carbonate, and to a lesser extent, sulfate decreased the IEP of TiO2 and stabilized NP suspensions owing to specific surface interactions, whereas this was not observed for nitrate and chloride. TiO2 NPs were exposed to UV-A radiation, and the photoreactivity was assessed by monitoring the production of reactive species over time both at the NP surface (photogenerated holes) and in the bulk solution (hydroxyl radicals) by observing their reactions with the selective probe compounds iodide and terephthalic acid, respectively. The generation of photogenerated holes and hydroxyl radicals was influenced by each inorganic anion to varying degrees. Carbonate and phosphate inhibited the oxidation of iodide, and this interaction was successfully described by a Langmuir-Hinshelwood mechanism and related to the characteristics of TiO2 aggregates. Chloride and nitrate do not specifically interact with TiO2, and sulfate creates relatively weak interactions with the TiO2 surface such that no decrease in photogenerated hole reactivity was observed. A decrease in hydroxyl radical generation was observed for all inorganic anions. Quenching rate constants for the reaction of hydroxyl radicals with each inorganic anion do not provide a comprehensive explanation for the magnitude of this decrease, which arises from the interplay of several physicochemical phenomena. This work shows that the reactivity of NPs will be strongly influenced by the makeup of

  9. Antioxidative effect of some hydroxy substituted aromatic bisimines.

    Science.gov (United States)

    Sersen, Frantisek; Walko, Martin; Loos, Dusan

    2009-06-01

    This work deals with antioxidative properties of some derivatives 4,4'-bis(dihydroxybenzylanilidenamino) diphenylmethanes and diphenylethers, which structure is similar to resveratrol. Four derivatives of above-mentioned compounds were synthesized with hydroxyl (OH) groups in various positions. It was found that derivatives with two OH groups in 2 and 5 positions were very good scavengers of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals in both methanol and chloroform. On the other hand derivatives with OH groups in positions 2 and 4 did not scavenge DPPH radicals. The calculation of free enthalpies (by quantum chemical method AM1) necessary for the formations of anions or radicals support above mentioned findings because the enthalpies for effective derivatives were lesser, than for ineffective ones. Also, it was found that studied compounds did not scavenge hydroxyl radicals whereas resveratrol did it.

  10. Synthesis and anion recognition of neutral receptors based on multiamide calix[4]arene

    Institute of Scientific and Technical Information of China (English)

    LIU; Shunying; WANG; Fajun; WEI; Lanhua; XIAO; Wang; MENG

    2004-01-01

    Two multiamide calix[4]arenes (5, 6) were synthesized and characterized by IR, 1H NMR, MS and elemental analysis. The binding properties of receptors with some anions (p-O2NPhOPO2-3, p-O2NPhO-, H2PO-4, Ac-, Cl-, Br- and I-) were studied by UV-Vis spectra. The results indicate that the tetraamide calix[4]arenes (5, 6) have a good selectivity to the anions containing aromatic ring (p-O2NPhOPO32 , p-O2NPhO-). The 1 : 1 complexes between host and guest were formed through multiple hydrogen bonding and π-π interactions. The hosts 5 and 6also show a definite binding ability for the anions (H2 PO-4, Ac-, Cl-) that have no ultraviolet absorption, which provides a simple method of spectrum detection for these anions.

  11. Radical theory of rings

    CERN Document Server

    Gardner, JW

    2003-01-01

    Radical Theory of Rings distills the most noteworthy present-day theoretical topics, gives a unified account of the classical structure theorems for rings, and deepens understanding of key aspects of ring theory via ring and radical constructions. Assimilating radical theory's evolution in the decades since the last major work on rings and radicals was published, the authors deal with some distinctive features of the radical theory of nonassociative rings, associative rings with involution, and near-rings. Written in clear algebraic terms by globally acknowledged authorities, the presentation

  12. Phosphazene-promoted anionic polymerization

    KAUST Repository

    Zhao, Junpeng

    2014-01-01

    In the recent surge of metal-free polymerization techniques, phosphazene bases have shown their remarkable potential as organic promoters/catalysts for the anionic polymerization of various types of monomers. By complexation with the counterion (e.g. proton or lithium cation), phosphazene base significantly improve the nucleophilicity of the initiator/chain-end resulting in rapid and usually controlled anionic/quasi-anionic polymerization. In this review, we will introduce the general mechanism, i.e. in situ activation (of initiating sites) and polymerization, and summarize the applications of such a mechanism on macromolecular engineering toward functionalized polymers, block copolymers and complex macromolecular architectures.

  13. [Lavoisier and radicals].

    Science.gov (United States)

    Lafont, Olivier

    2007-01-01

    Lavoisier and his co-workers (Guyton de Morveau, Bertholet, Fourcroy) considered that acids were constituted of oxygen and of something else that they called radicals. These radicals were known in some cases, i.e. nitrogen for nitrous acid, carbon for carbonic acid, phosphorus for phosphoric acid. In the case of sulfur, the sulfuric radical could be associated with different quantities of oxigen leading to sulfuric or sulfurous acids. In other cases radicals remained unknown at the time i.e. muriatic radical for muriatic acid, or benzoyl radical for benzoic acid. It is interesting to notice that Lavoisier evoked the case of compound radicals constituted of different substances such as carbon and hydrogen.

  14. Free radical scavenging abilities of polypeptide from Chlamys farreri

    Science.gov (United States)

    Han, Zhiwu; Chu, Xiao; Liu, Chengjuan; Wang, Yuejun; Mi, Sun; Wang, Chunbo

    2006-09-01

    We investigated the radical scavenging effect and antioxidation property of polypeptide extracted from Chlamys farreri (PCF) in vitro using chemiluminescence and electron spin resonance (ESR) methods. We examined the scavenging effects of PCF on superoxide anions (O{2/-}), hydroxyl radicals (OH·), peroxynitrite (ONOO-) and the inhibiting capacity of PCF on peroxidation of linoleic acid. Our experiment suggested that PCF could scavenge oxygen free radicals including superoxide anions (O{2/-}) (IC50=0.3 mg/ml), hydroxyl radicals (OH·) (IC50=0.2 μg/ml) generated from the reaction systems and effectively inhibit the oxidative activity of ONOO- (IC50=0.2 mg/ml). At 1.25 mg/ml of PCF, the inhibition ratio on lipid peroxidation of linoleic acid was 43%. The scavenging effect of PCF on O{2/-}, OH· and ONOO- free radicals were stronger than those of vitamin C but less on lipid peroxidation of linoleic acid. Thus PCF could scavenge free radicals and inhibit the peroxidation of linoleic acid in vitro. It is an antioxidant from marine products and potential for industrial production in future.

  15. Free radical scavenging abilities of polypeptide from Chlamys farreri

    Institute of Scientific and Technical Information of China (English)

    HAN Zhiwu; CHU Xiao; LIU Chengjuan; WANG Yuejun; SUN Mi; WANG Chunbo

    2006-01-01

    We investigated the radical scavenging effect and antioxidation property of polypeptide extracted from Chlamys farreri (PCF) in vitro using chemiluminescence and electron spin resonance (ESR) methods. We examined the scavenging effects of PCF on superoxide anions (O-2), hydroxyl radicals (OH·), peroxynitrite (ONOO-) and the inhibiting capacity of PCF on peroxidation of linoleic acid. Our experiment suggested that PCF could scavenge oxygen free radicals including superoxide anions (O-2) (IC50 =0.3 mg/ml), hydroxyl radicals (OH·) (IC50 = 0.2 μg/ml) generated from the reaction systems and effectively inhibit the oxidative activity of ONOO- (IC50 = 0.2 mg/ml). At 1.25 mg/ml of PCF, the inhibition ratio on lipid peroxidation of linoleic acid was 43 %. The scavenging effect of PCF on (O-2), OH·and ONOO- free radicals were stronger than those of vitamin C but less on lipid peroxidation of linoleic acid. Thus PCF could scavenge free radicals and inhibit the peroxidation of linoleic acid in vitro. It is an antioxidant from marine products and potential for industrial production in future.

  16. Radicals in {gamma}-irradiated wool

    Energy Technology Data Exchange (ETDEWEB)

    Baeva, N.N.; Sadova, S.F.; Sharpatyi, V.A.

    1992-01-01

    Radicals were identified in wool fiber {gamma}-irradiated at 77 K by EPR: products of reaction of an electron e and H atom with amino acid residues and a polypeptide chain, and their partial yields at 77 K and the reactivity scale of e with respect to the individual fragments of the protein molecule were determined: [RSSR]: [>C=O{sub p.b.}]:[NH{sub 3}{sup +}-R]:[aromatic ring] = 4:3: > 1:1. 10 refs., 1 fig., 1 tab.

  17. Pentaarylfullerenes as noncoordinating cyclopentadienyl anions

    NARCIS (Netherlands)

    Bouwkamp, Marco W.; Meetsma, Auke

    2009-01-01

    The first example of an early-transition-metal complex involving a pentaarylfullerene was prepared. Instead of half-sandwich complexes, solvent separated ion pairs were obtained in which the pentaarylfullerene moiety acts as noncoordinating cyclopentadienyl anion.

  18. Theoretical modeling of infrared emission from neutral and charged polycyclic aromatic hydrocarbons. II.

    NARCIS (Netherlands)

    Bakes, ELO; Tielens, AGGM; Bauschlicher, CW; Hudgins, DM; Allamandola, LJ

    2001-01-01

    The nature of the carriers of the interstellar infrared (IR) emission features between 3.3 and 12.7 mum is complex. We must consider emission from a family of polycyclic aromatic hydrocarbons (PAHs) in a multiplicity of cationic charge states (+1, +2, +3, and so on), along with neutral and anionic P

  19. Contemporary Radical Prostatectomy

    Directory of Open Access Journals (Sweden)

    Qiang Fu

    2011-01-01

    Full Text Available Purpose. Patients diagnosed with clinically localized prostate cancer have more surgical treatment options than in the past. This paper focuses on the procedures' oncological or functional outcomes and perioperative morbidities of radical retropubic prostatectomy, radical perineal prostatectomy, and robotic-assisted laparoscopic radical prostatectomy. Materials and Methods. A MEDLINE/PubMed search of the literature on radical prostatectomy and other new management options was performed. Results. Compared to the open procedures, robotic-assisted radical prostatectomy has no confirmed significant difference in most literatures besides less blood loss and blood transfusion. Nerve sparing is a safe means of preserving potency on well-selected patients undergoing radical prostatectomy. Positive surgical margin rates of radical prostatectomy affect the recurrence and survival of prostate cancer. The urinary and sexual function outcomes have been vastly improved. Neoadjuvant treatment only affects the rate of positive surgical margin. Adjuvant therapy can delay and reduce the risk of recurrence and improve the survival of the high risk prostate cancer. Conclusions. For the majority of patients with organ-confined prostate cancer, radical prostatectomy remains a most effective approach. Radical perineal prostatectomy remains a viable approach for patients with morbid obesity, prior pelvic surgery, or prior pelvic radiation. Robot-assisted laparoscopic prostatectomy (RALP has become popular among surgeons but has not yet become the firmly established standard of care. Long-term data have confirmed the efficacy of radical retropubic prostatectomy with disease control rates and cancer-specific survival rates.

  20. Charge-transfer-directed radical substitution enables para-selective C-H functionalization

    Science.gov (United States)

    Boursalian, Gregory B.; Ham, Won Seok; Mazzotti, Anthony R.; Ritter, Tobias

    2016-08-01

    Efficient C-H functionalization requires selectivity for specific C-H bonds. Progress has been made for directed aromatic substitution reactions to achieve ortho and meta selectivity, but a general strategy for para-selective C-H functionalization has remained elusive. Herein we introduce a previously unappreciated concept that enables nearly complete para selectivity. We propose that radicals with high electron affinity elicit arene-to-radical charge transfer in the transition state of radical addition, which is the factor primarily responsible for high positional selectivity. We demonstrate with a simple theoretical tool that the selectivity is predictable and show the utility of the concept through a direct synthesis of aryl piperazines. Our results contradict the notion, widely held by organic chemists, that radical aromatic substitution reactions are inherently unselective. The concept of radical substitution directed by charge transfer could serve as the basis for the development of new, highly selective C-H functionalization reactions.

  1. Facile modification of multi-walled carbon nanotubes-polymeric ionic liquids-coated solid-phase microextraction fibers by on-fiber anion exchange.

    Science.gov (United States)

    Feng, Juanjuan; Sun, Min; Bu, Yanan; Luo, Chuannan

    2015-05-08

    In situ anion exchange has been proved to be an efficient method for facile modification of polymeric ionic liquids (PILs)-based stationary phases. In this work, an on-fiber anion exchange process was utilized to tune the extraction performance of a multi-walled carbon nanotubes (MWCNTs)-poly(1-vinyl-3-octylimidazolium bromide) (poly(VOIm(+)Br(-)))-coated solid-phase microextraction (SPME) fiber. MWCNTs were first coated onto the stainless steel wire through a layer-by-layer fabrication method and then the PILs were coated onto the MWCNTs physically. Anion of the MWCNTs-poly(VOIm(+)Br(-)) fiber was changed into bis(triflroromethanesulfonyl)imide (NTf2(-)) and 2-naphthalene-sulfonate (NapSO3(-)) by on-fiber anion exchange. Coupled to gas chromatography, the MWCNTs-poly(VOIm(+)Br(-)) fiber showed acceptable extraction efficiency for hydrophilic and hydrogen-bonding-donating alcohols, with limits of detection (LODs) in the range of 0.005-0.05μgmL(-1); after the anion exchange with NTf2(-), the obtained MWCNTs-poly(VOIm(+)NTf2(-)) fiber brought wide linear ranges for hydrophobic n-alkanes with correlation coefficient (R) ranging from 0.994 to 0.997; aromatic property of the fiber was enhanced by aromatic NapSO3(-) anions to get sufficient extraction capacity for phthalate esters and halogenated aromatic hydrocarbons. The MWCNTs-poly(VOIm(+)NapSO3(-)) fiber was finally applied to determine several halogenated aromatic hydrocarbons in groundwater of industrial park.

  2. Bound anionic states of adenine

    Energy Technology Data Exchange (ETDEWEB)

    Haranczyk, Maciej; Gutowski, Maciej S; Li, Xiang; Bowen, Kit H

    2007-03-20

    Anionic states of nucleic acid bases are involved in DNA damage by low-energy electrons and in charge transfer through DNA. Previous gas phase studies of free, unsolvated nucleic acid base parent anions probed only dipole-bound states, which are not present in condensed phase environments, but did not observe valence anionic states, which for purine bases, are thought to be adiabatically unbound. Contrary to this expectation, we have demonstrated that some thus far ignored tautomers of adenine, which result from enamine-imine transformations, support valence anionic states with electron vertical detachment energies as large as 2.2 eV, and at least one of these anionic tautomers is adiabatically bound. Moreover, we predict that the new anionic tautomers should also dominate in solutions and should be characterized by larger values of electron vertical detachment energy than the canonical valence anion. All of the new-found anionic tautomers might be formed in the course of dissociative electron attachment followed by a hydrogen atom attachment to a carbon atom, and they might affect the structure and properties of DNA and RNA exposed to low-energy electrons. The discovery of these valence anionic states of adenine was facilitated by the development of: (i) a new experimental method for preparing parent anions of nucleic acid bases for photoelectron experiments, and (ii) a new combinatorial/ quantum chemical approach for identification of the most stable tautomers of organic molecules. The computational portion of this work was supported by the: (i) Polish State Committee for Scientific Research (KBN) Grants: DS/8000-4-0140-7 (M.G.) and N204 127 31/2963 (M.H.), (ii) European Social Funds (EFS) ZPORR/2.22/II/2.6/ARP/U/2/05 (M.H.), and (iii) US DOE Office of Biological and Environmental Research, Low Dose Radiation Research Program (M.G.). M.H. holds the Foundation for Polish Science (FNP) award for young scientists. The calculations were performed at the Academic

  3. Amide-based Fluorescent Macrocyclic Anion Receptors

    Institute of Scientific and Technical Information of China (English)

    ZENG, Zhen-Ya(曾振亚); XU, Kuo-Xi(徐括喜); HE, Yong-Bing(何永炳); LIU, Shun-Ying(刘顺英); WU, Jin-Long(吴进龙); WEI, Lan-Hua(隗兰华); MENG, Ling-Zhi(孟令芝)

    2004-01-01

    Two fluorescent anion receptors (1 and 2) based on amide macrocycle were synthesized and corresponding fluorescence quenching induced by anion complexation was observed in different degree. Receptors form 1: 1 complexes with anions by hydrogen bonding interactions. Receptor 1 bound anions in the order of F->Cl->H2PO4->CH3COO->>Br-, I- and receptor 2 showed high selectivity to F- over other anions.

  4. Free radicals and antioxidants at a glance using EPR spectroscopy.

    Science.gov (United States)

    Spasojević, Ivan

    2011-01-01

    The delicate balance between the advantageous and detrimental effects of free radicals is one of the important aspects of human (patho)physiology. The controlled production of reactive oxygen and nitrogen species has an essential role in the regulation of various signaling switches. On the other hand, imbalanced generation of radicals is highly correlated with the pathogenesis of many diseases which require the application of selected antioxidants to regain the homeostasis. In the era of growing interest for redox processes, electron paramagnetic resonance (EPR) spectroscopy is arguably the best-suited technique for such research due to its ability to provide a unique insight into the world of free radicals and antioxidants. Herein, I present the principles of EPR spectroscopy and the applications of this method in assessing: (i) the oxidative status of biological systems, using endogenous long-lived free radicals (ascorbyl radical (Asc(•)), tocopheroxyl radical (TO(•)), melanin) as markers; (ii) the production of short-lived radicals (hydroxyl radical (OH(•)), superoxide radical anion (O(2)(•-)), sulfur- and carbon-centered radicals), which are implicated in both, oxidative stress and redox signaling; (iii) the metabolism of nitric oxide (NO(•)); (iv) the antioxidative properties of various drugs, compounds, and natural products; (v) other redox-relevant parameter. Besides giving a comprehensive survey of up-to-date literature, I also provide illustrative examples in sufficient detail to provide a means to exploit the potential of EPR in biochemical/physiological/medical research. The emphasis is on the features and characteristics (both positive and negative) relevant for EPR application in clinical sciences. My aim is to encourage fellow colleagues interested in free radicals and antioxidants to expand their base knowledge or methods used in their laboratories with data acquired by EPR or some of the EPR techniques outlined in this review, in order to

  5. Towards the Rational Design of Ionic Liquid Matrices for Secondary Ion Mass Spectrometry: Role of the Anion

    Science.gov (United States)

    Dertinger, Jennifer J.; Walker, Amy V.

    2013-08-01

    The role of the ionic liquid (IL) anion structure on analyte signal enhancements has been systematically investigated in secondary ion mass spectrometry (SIMS) using a variety of samples, including lipids, sterols, polymers, and peptides. Twenty-four ILs were synthesized. The 12 matrix acids were cinnamic acid derivatives. Two bases were employed: 1-methylimidazole and tripropylamine. Three matrices, methylimmidazolium o-coumarate, tripropylammonium o-coumarate, and tripropylammonium 3,4,5-trimethoxycinnamate, were "universal" matrices enhancing all analytes tested. The pKa of the matrix acid does not appear to have a strong effect on analyte ion intensities. Rather, it is observed that a single hydroxyl group on the anion aromatic ring leads to significantly increased molecular ion intensities. No analyte signal enhancements were observed for -CH3, -CF3 and -OCH3 groups present on the aromatic ring. The position of the -OH group on the aromatic ring also alters molecular ion intensity enhancements. As well as the chemical identity and position of substituents, the number of moieties on the aromatic ring may affect the analyte signal enhancements observed. These observations suggest that the activation of the IL anion aromatic ring is important for optimizing analyte signal intensities. The implications for SIMS imaging of complex structures, such as biological samples, are discussed.

  6. Inhibitory effects of cardols and related compounds on superoxide anion generation by xanthine oxidase.

    Science.gov (United States)

    Masuoka, Noriyoshi; Nihei, Ken-ichi; Maeta, Ayami; Yamagiwa, Yoshiro; Kubo, Isao

    2015-01-01

    5-Pentadecatrienylresorcinol, isolated from cashew nuts and commonly known as cardol (C₁₅:₃), prevented the generation of superoxide radicals catalysed by xanthine oxidase without the inhibition of uric acid formation. The inhibition kinetics did not follow the Michelis-Menten equation, but instead followed the Hill equation. Cardol (C₁₀:₀) also inhibited superoxide anion generation, but resorcinol and cardol (C₅:₀) did not inhibit superoxide anion generation. The related compounds 3,5-dihydroxyphenyl alkanoates and alkyl 2,4-dihydroxybenzoates, had more than a C9 chain, cooperatively inhibited but alkyl 3,5-dihydroxybenzoates, regardless of their alkyl chain length, did not inhibit the superoxide anion generation. These results suggested that specific inhibitors for superoxide anion generation catalysed by xanthine oxidase consisted of an electron-rich resorcinol group and an alkyl chain having longer than C9 chain.

  7. Orgasm after radical prostatectomy

    NARCIS (Netherlands)

    Koeman, M; VanDriel, MF; Schultz, WCMW; Mensink, HJA

    1996-01-01

    Objective To evaluate the ability to obtain and the quality of orgasm after radical prostatectomy, Patients and methods The orgasms experienced after undergoing radical prostatectomy were evaluated in 20 men (median age 65 years, range 56-76) using a semi-structured interview and a self-administered

  8. The Radicalization Puzzle [video

    OpenAIRE

    Mohammed Hafez; Center for Homeland Defense and Security Naval Postgraduate School

    2015-01-01

    This 20 minute lecture, by Dr. Mohammad Hafez of the Naval Postgraduate School examines the driving factors behind the process of radicalization, turning seemingly ordinary men and women into potential terrorists. The lecture is based on the article "The Radicalization Puzzle: A Theoretical Synthesis of Empirical Approaches to Homegrown Extremism" in Studies in Conflict and Terrorism, by Mohammad Hafez and Creighton Mullins.

  9. Pioneering Metal-Free Oxidative Coupling Strategy of Aromatic Compounds Using Hypervalent Iodine Reagents.

    Science.gov (United States)

    Kita, Yasuyuki; Dohi, Toshifumi

    2015-10-01

    We started our hypervalent iodine research about 30 years ago in the mid-1980s. We soon successfully developed the single-electron-transfer oxidation ability of a hypervalent iodine reagent, specifically, phenyliodine(III) bis(trifluoroacetate) (PIFA), toward aromatic rings of phenyl ethers for forming aromatic cation radicals. This was one of the exciting and unexpected events in our research studies so far, and the discovery was reported in 1991. It also led to the next challenge, developing the metal-free oxidative couplings for C-H functionalizations and direct couplings between the C-H bonds of valuable aromatic compounds in organic synthesis. In order to realize the effective oxidative coupling, pioneering new aromatic ring activations was essential and several useful methodologies have been found for oxidizable arenes. The achievements regarding this objective obtained in our continuous research are herein summarized with classification of the aromatic ring activation strategies.

  10. Pu Anion Exchange Process Intensification

    Energy Technology Data Exchange (ETDEWEB)

    Taylor-Pashow, K. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2015-10-08

    This project seeks to improve the efficiency of the plutonium anion-exchange process for purifying Pu through the development of alternate ion-exchange media. The objective of the project in FY15 was to develop and test a porous foam monolith material that could serve as a replacement for the current anion-exchange resin, Reillex® HPQ, used at the Savannah River Site (SRS) for purifying Pu. The new material provides advantages in efficiency over the current resin by the elimination of diffusive mass transport through large granular resin beads. By replacing the large resin beads with a porous foam there is much more efficient contact between the Pu solution and the anion-exchange sites present on the material. Several samples of a polystyrene based foam grafted with poly(4-vinylpyridine) were prepared and the Pu sorption was tested in batch contact tests.

  11. Anions in Nucleic Acid Crystallography.

    Science.gov (United States)

    D'Ascenzo, Luigi; Auffinger, Pascal

    2016-01-01

    Nucleic acid crystallization buffers contain a large variety of chemicals fitting specific needs. Among them, anions are often solely considered for pH-regulating purposes and as cationic co-salts while their ability to directly bind to nucleic acid structures is rarely taken into account. Here we review current knowledge related to the use of anions in crystallization buffers along with data on their biological prevalence. Chloride ions are frequently identified in crystal structures but display low cytosolic concentrations. Hence, they are thought to be distant from nucleic acid structures in the cell. Sulfate ions are also frequently identified in crystal structures but their localization in the cell remains elusive. Nevertheless, the characterization of the binding properties of these ions is essential for better interpreting the solvent structure in crystals and consequently, avoiding mislabeling of electron densities. Furthermore, understanding the binding properties of these anions should help to get clues related to their potential effects in crowded cellular environments.

  12. Tris-[8]annulenyl Isocyanurate Trianion Triradical and Hexa-anion from the Alkali Metal Reduction of [8]Annulenyl Isocyanate.

    Science.gov (United States)

    Peters, Steven J; Klen, Joseph R

    2015-06-05

    The solution phase alkali metal reduction of [8]annulenyl isocyanate (C8H7NCO) yields an EPR spectrum, which reveals electron couplings to seven protons and only one nitrogen. Although this strongly suggested that the C8H7NCO anion radical was generated, experiments on the oxidized product reveal the actual reduced species to be tris-[8]annulenyl isocyanurate. Unlike the previously studied phenyl isocyanurate anion radical, the unpaired electron(s) is now localized within an [8]annulenyl moiety. Further exposure to metal results in the formation of an equilibrium mixture of trianion triradical and trianion radical species. The cyclotrimerization to form the isocyanurate is proposed to be driven by a reactive C8H7NCO dianion, which is produced from the large equilibrium disproportionation of the anion radical. Exhaustive reduction of the tris-[8]annulenyl isocyanurate with potassium in THF generates the first-ever observed hexa-anion of an isocyanurate. NMR analysis reveals that the polarity of the carbonyl bonds within this hexa-anion is augmented and is caused by the close proximity of K(+) ions, which are tightly ion paired to the three [8]annulenyl dianion rings. These preliminary studies on the reduction of C8H7NCO suggest that polymeric materials (e.g., polyisocyanates) made from this isocyanate might exhibit unique properties.

  13. Site-Specific Description of the Enhanced Recognition Between Electrogenerated Nitrobenzene Anions and Dihomooxacalix[4]arene Bidentate Ureas.

    Science.gov (United States)

    Martínez-González, Eduardo; Armendáriz-Vidales, Georgina; Ascenso, José R; Marcos, Paula M; Frontana, Carlos

    2015-05-01

    Electron transfer controlled hydrogen bonding was studied for a series of nitrobenzene derivative radical anions, working as large guest anions, and substituted ureas, including dihomooxacalix[4]arene bidentate urea derivatives, in order to estimate binding constants (Kb) for the hydrogen-bonding process. Results showed enhanced Kb values for the interaction with phenyl-substituted bidentate urea, which is significantly larger than for the remaining compounds, e.g., in the case of 4-methoxynitrobenzene a 28-fold larger Kb value was obtained for the urea bearing a phenyl (Kb ∼ 6888) vs tert-butyl (Kb ∼ 247) moieties. The respective nucleophilic and electrophilic characters of the participant anion radical and urea hosts were parametrized with global and local electrodonating (ω(-)) and electroaccepting (ω(+)) powers, derived from DFT calculations. ω(-) data were useful for describing trends in structure–activity relationships when comparing nitrobenzene radical anions. However, ω(+) for the host urea structures lead to unreliable explanations of the experimental data. For the latter case, local descriptors ωk(+)(r) were estimated for the atoms within the urea region in the hosts [∑kωk(+)(r)]. By compiling all the theoretical and experimental data, a Kb-predictive contour plot was built considering ω(-) for the studied anion radicals and ∑kωk(+)(r) which affords good estimations.

  14. Closed-Shell Polycyclic Aromatic Hydrocarbon Cations: A New Category of Interstellar Polycyclic Aromatic Hydrocarbons

    Science.gov (United States)

    Hudgins, Douglas M.; Bauschlicher, Charles W., Jr.; Allamandola, Louis J.; DeVincenzi, Donald (Technical Monitor)

    2001-01-01

    Density functional theory has been employed to calculate the harmonic frequencies and intensities of a range of polycyclic aromatic hydrocarbon (PAH) cations that explore both size and electronic structure effects of the infrared spectroscopic properties of these species. The sample extends the size range of PAH species considered to more than 50 carbon atoms and includes several representatives from each of two heretofore unexplored categories of PAH cations: (1) fully benzenoid PAH cations whose carbon skeleton is composed of an odd number of carbon atoms (C(sub odd) PAHs); and (2) protonated PAH cations (HPAH+). Unlike the radical electronic structures of the PAH cations that have been the subject of previous theoretical and experimental work, the species in these two classes have a closed-shell electronic configuration. The calculated spectra of circumcoronene, C54H18 in both neutral and (radical) cationic form are also reported and compared with those of the other species. Overall, the C(sub odd) PAHs spectra are dominated by strong CC stretching modes near 1600 cm(exp -1) and display spectra that are remarkably insensitive to molecular size. The HPAH+ species evince a more complex spectrum consistent with the added contributions of aliphatic modes and their generally lower symmetry. Finally, for both classes of closed-shell cations, the intensity of the aromatic CH stretching modes is found to increase with molecular size far out of proportion with the number of CH groups, approaching a value more typical of neutral PAHs for the largest species studied.

  15. The many ways of making anionic clays

    Indian Academy of Sciences (India)

    Michael Rajamathi; Grace S Thomas; P Vishnu Kamath

    2001-10-01

    Together with hydrotalcite-like layered double hydroxides, bivalent and trivalent metal hydroxides and their hydroxy salts are actually anionic clays consisting of positively charged hydroxide layers with anions intercalated in the interlayer region. The anionic clays exhibit anion sorption, anion diffusion and exchange properties together with surface basicity making them materials of importance for many modern applications. In this article, we discuss many different ways of making anionic clays and compare and contrast the rich diversity of this class of materials with the better-known cationic clays.

  16. [Research progress on free radicals in human body].

    Science.gov (United States)

    Wang, Q B; Xu, F P; Wei, C X; Peng, J; Dong, X D

    2016-08-10

    Free radicals are the intermediates of metabolism, widely exist in the human bodies. Under normal circumstances, the free radicals play an important role in the metabolic process on human body, cell signal pathway, gene regulation, induction of cell proliferation and apoptosis, so as to maintain the normal growth and development of human body and to inhibit the growth of bacteria, virus and cancer. However, when organic lesion occurs affected by external factors or when equilibrium of the free radicals is tipped in the human body, the free radicals will respond integratedly with lipids, protein or nucleic acid which may jeopardize the health of human bodies. This paper summarizes the research progress of the free radicals conducted in recent years, in relations to the perspective of the types, origins, test methods of the free radicals and their relationship with human's health. In addition, the possible mechanisms of environmental pollutants (such as polycyclic aromatic hydrocarbons) mediating oxidative stress and free radicals scavenging in the body were also summarized.

  17. Salvage robotic radical prostatectomy

    Directory of Open Access Journals (Sweden)

    Samuel D Kaffenberger

    2014-01-01

    Full Text Available Failure of non-surgical primary treatment for localized prostate cancer is a common occurrence, with rates of disease recurrence ranging from 20% to 60%. In a large proportion of patients, disease recurrence is clinically localized and therefore potentially curable. Unfortunately, due to the complex and potentially morbid nature of salvage treatment, radical salvage surgery is uncommonly performed. In an attempt to decrease the morbidity of salvage therapy without sacrificing oncologic efficacy, a number of experienced centers have utilized robotic assistance to perform minimally invasive salvage radical prostatectomy. Herein, we critically evaluate the existing literature on salvage robotic radical prostatectomy with a focus on patient selection, perioperative complications and functional and early oncologic outcomes. These results are compared with contemporary and historical open salvage radical prostatectomy series and supplemented with insights we have gained from our experience with salvage robotic radical prostatectomy. The body of evidence by which conclusions regarding the efficacy and safety of robotic salvage radical prostatectomy can be drawn comprises fewer than 200 patients with limited follow-up. Preliminary results are promising and some outcomes have been favorable when compared with contemporary open salvage prostatectomy series. Advantages of the robotic platform in the performance of salvage radical prostatectomy include decreased blood loss, short length of stay and improved visualization. Greater experience is required to confirm the long-term oncologic efficacy and functional outcomes as well as the generalizability of results achieved at experienced centers.

  18. Aromaticity Competition in Differentially Fused Borepin-Containing Polycyclic Aromatics.

    Science.gov (United States)

    Messersmith, Reid E; Siegler, Maxime A; Tovar, John D

    2016-07-01

    This report describes the synthesis and characterization of a series of borepin-based polycyclic aromatics bearing two different arene fusions. The borepin synthesis features streamlined Ti-mediated alkyne reduction, leading to Z-olefins, followed by direct lithiation and borepin formation. These molecules allow for an assessment of aromatic competition between the fused rings and the central borepin core. Crystallographic, magnetic, and computational studies yielded insights about the aromaticity of novel, differentially fused [b,f]borepins and allowed for comparison to literature compounds. Multiple borepin motifs were also incorporated into polycyclic aromatics with five or six rings in the main backbone, and their properties were also evaluated.

  19. Anion binding in biological systems

    Science.gov (United States)

    Feiters, Martin C.; Meyer-Klaucke, Wolfram; Kostenko, Alexander V.; Soldatov, Alexander V.; Leblanc, Catherine; Michel, Gurvan; Potin, Philippe; Küpper, Frithjof C.; Hollenstein, Kaspar; Locher, Kaspar P.; Bevers, Loes E.; Hagedoorn, Peter-Leon; Hagen, Wilfred R.

    2009-11-01

    We compare aspects of biological X-ray absorption spectroscopy (XAS) studies of cations and anions, and report on some examples of anion binding in biological systems. Brown algae such as Laminaria digitata (oarweed) are effective accumulators of I from seawater, with tissue concentrations exceeding 50 mM, and the vanadate-containing enzyme haloperoxidase is implicated in halide accumulation. We have studied the chemical state of iodine and its biological role in Laminaria at the I K edge, and bromoperoxidase from Ascophyllum nodosum (knotted wrack) at the Br K edge. Mo is essential for many forms of life; W only for certain archaea, such as Archaeoglobus fulgidus and the hyperthermophilic archaeon Pyrococcus furiosus, and some bacteria. The metals are bound and transported as their oxo-anions, molybdate and tungstate, which are similar in size. The transport protein WtpA from P. furiosus binds tungstate more strongly than molybdate, and is related in sequence to Archaeoglobus fulgidus ModA, of which a crystal structure is known. We have measured A. fulgidus ModA with tungstate at the W L3 (2p3/2) edge, and compared the results with the refined crystal structure. XAS studies of anion binding are feasible even if only weak interactions are present, are biologically relevant, and give new insights in the spectroscopy.

  20. Anion binding in biological systems

    Energy Technology Data Exchange (ETDEWEB)

    Feiters, Martin C [Department of Organic Chemistry, Institute for Molecules and Materials, Faculty of Science, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen (Netherlands); Meyer-Klaucke, Wolfram [EMBL Hamburg Outstation at DESY, Notkestrasse 85, D-22607 Hamburg (Germany); Kostenko, Alexander V; Soldatov, Alexander V [Faculty of Physics, Southern Federal University, Sorge 5, Rostov-na-Donu, 344090 (Russian Federation); Leblanc, Catherine; Michel, Gurvan; Potin, Philippe [Centre National de la Recherche Scientifique and Universite Pierre et Marie Curie Paris-VI, Station Biologique de Roscoff, Place Georges Teissier, BP 74, F-29682 Roscoff cedex, Bretagne (France); Kuepper, Frithjof C [Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban, Argyll PA37 1QA, Scotland (United Kingdom); Hollenstein, Kaspar; Locher, Kaspar P [Institute of Molecular Biology and Biophysics, ETH Zuerich, Schafmattstrasse 20, Zuerich, 8093 (Switzerland); Bevers, Loes E; Hagedoorn, Peter-Leon; Hagen, Wilfred R, E-mail: m.feiters@science.ru.n [Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft (Netherlands)

    2009-11-15

    We compare aspects of biological X-ray absorption spectroscopy (XAS) studies of cations and anions, and report on some examples of anion binding in biological systems. Brown algae such as Laminaria digitata (oarweed) are effective accumulators of I from seawater, with tissue concentrations exceeding 50 mM, and the vanadate-containing enzyme haloperoxidase is implicated in halide accumulation. We have studied the chemical state of iodine and its biological role in Laminaria at the I K edge, and bromoperoxidase from Ascophyllum nodosum (knotted wrack) at the Br K edge. Mo is essential for many forms of life; W only for certain archaea, such as Archaeoglobus fulgidus and the hyperthermophilic archaeon Pyrococcus furiosus, and some bacteria. The metals are bound and transported as their oxo-anions, molybdate and tungstate, which are similar in size. The transport protein WtpA from P. furiosus binds tungstate more strongly than molybdate, and is related in sequence to Archaeoglobus fulgidus ModA, of which a crystal structure is known. We have measured A. fulgidus ModA with tungstate at the W L{sub 3} (2p{sub 3/2}) edge, and compared the results with the refined crystal structure. XAS studies of anion binding are feasible even if only weak interactions are present, are biologically relevant, and give new insights in the spectroscopy.

  1. Radical chemistry of artemisinin

    Energy Technology Data Exchange (ETDEWEB)

    Denisov, Evgenii T; Solodova, S L; Denisova, Taisa G [Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region (Russian Federation)

    2010-12-29

    The review summarizes physicochemical characteristics of the natural sesquiterpene peroxide artemisinin. The kinetic schemes of transformations of artemisinin radicals under anaerobic conditions are presented and analyzed. The sequence of radical reactions of artemisinin in the presence of oxygen is considered in detail. Special emphasis is given to the intramolecular chain oxidation resulting in the transformation of artemisinin into polyatomic hydroperoxide. The kinetic characteristics of elementary reaction steps involving alkyl, alkoxyl, and peroxyl radicals generated from artemisinin are discussed. The results of testing of artemisinin and its derivatives for the antimalarial activity and the scheme of the biochemical synthesis of artemisinin in nature are considered.

  2. Radical chemistry of artemisinin

    Science.gov (United States)

    Denisov, Evgenii T.; Solodova, S. L.; Denisova, Taisa G.

    2010-12-01

    The review summarizes physicochemical characteristics of the natural sesquiterpene peroxide artemisinin. The kinetic schemes of transformations of artemisinin radicals under anaerobic conditions are presented and analyzed. The sequence of radical reactions of artemisinin in the presence of oxygen is considered in detail. Special emphasis is given to the intramolecular chain oxidation resulting in the transformation of artemisinin into polyatomic hydroperoxide. The kinetic characteristics of elementary reaction steps involving alkyl, alkoxyl, and peroxyl radicals generated from artemisinin are discussed. The results of testing of artemisinin and its derivatives for the antimalarial activity and the scheme of the biochemical synthesis of artemisinin in nature are considered.

  3. Synthesis, structure and electrical conductivity of fulvalenium salts of cobalt bis(dicarbollide) anion and its derivatives

    Indian Academy of Sciences (India)

    Vladimir Bregadze; Igor Sivaev; Irina Lobanova; Olga Kazheva; Grigorii Alexandrov; Andrey Kravchenko; Vladimir Starodub; Lev Buravov; Lev Titov; Oleg Dyachenko

    2010-01-01

    TTF, TTF-BMDT, TTF-BEDT and TMTSF cation radical salts of cobalt bis(dicarbollide) anion [3,3'-Co(1,2-C2B9H11)2]- and its derivatives are prepared and their crystal structures and electrical conductivities are determined. Some regularities in the crystal structures of the TTF-based radical cation salts prepared are also discussed.

  4. Proton and hydride affinities in excited states: magnitude reversals in proton and hydride affinities between the lowest singlet and triplet states of annulenyl and benzannulenyl anions and cations

    DEFF Research Database (Denmark)

    Rosenberg, Martin; Ottosson, Henrik; Kilså, Kristine

    2010-01-01

    Aromaticity has importance for proton and hydride affinities in the singlet ground state (S(0)) of annulenyl anions and cations so that, e.g., cyclopentadiene is an acidic hydrocarbon. For the lowest pipi* excited triplet state (T(1)), Baird's rule concludes that annulenes with 4n pi-electrons ar......Aromaticity has importance for proton and hydride affinities in the singlet ground state (S(0)) of annulenyl anions and cations so that, e.g., cyclopentadiene is an acidic hydrocarbon. For the lowest pipi* excited triplet state (T(1)), Baird's rule concludes that annulenes with 4n pi......-electrons are aromatic and those with 4n+2 pi-electrons are antiaromatic, opposite to Huckel's rule for aromaticity in S(0). Our hypothesis is now that the relative magnitudes of proton and hydride affinities of annulenyl anions and cations reverts systematically as one goes from S(0) to T(1) as a result of the opposite...... electron counting rules for aromaticity in the two states. Using quantum chemical calculations at the G3(MP2)//(U)B3LYP/6-311+G(d,p) level we have examined the validity of this hypothesis for eight proton and eight hydride addition reactions of anions and cations, respectively, of annulenyl...

  5. Investigation of hybrid molecular material prepared by ionic liquid and polyoxometalate anion

    Indian Academy of Sciences (India)

    T Rajkumar; G Ranga Rao

    2008-11-01

    A solid hybrid molecular material containing 1-butyl 3-methyl imidazolium cations and Keggin anions of phosphotungstic acid has been synthesized. It is fully characterized by CHN analysis, FTIR, XRD, UV-Vis-NIR DRS, 31P MAS NMR, TGA and SEM. The FTIR spectrum of the compound shows the fingerprint vibrational bands of both Keggin molecular anions and imidazolium cations. The aromatic C-H stretch region (2700-3250 cm-1) of imidazolium cation is split due to the interaction between the ring C-H and bulky Keggin anion. The red-shift in the UV-Vis spectra and the downfield 31P MAS NMR chemical shift also confirm the electrostatic interaction between the ions in the compound. Near IR spectral region (1000-2500 nm) shows the elimination of water in the compound which is hydrophobic.

  6. Asymmetric Anion-π Catalysis: Enamine Addition to Nitroolefins on π-Acidic Surfaces.

    Science.gov (United States)

    Zhao, Yingjie; Cotelle, Yoann; Avestro, Alyssa-Jennifer; Sakai, Naomi; Matile, Stefan

    2015-09-16

    Here we provide experimental evidence for anion-π catalysis of enamine chemistry and for asymmetric anion-π catalysis. A proline for enamine formation on one side and a glutamic acid for nitronate protonation on the other side are placed to make the enamine addition to nitroolefins occur on the aromatic surface of π-acidic naphthalenediimides. With increasing π acidity of the formally trifunctional catalysts, rate and enantioselectivity of the reaction increase. Mismatched and more flexible controls reveal that the importance of rigidified, precisely sculpted architectures increases with increasing π acidity as well. The absolute configuration of stereogenic sulfoxide acceptors at the edge of the π-acidic surface has a profound influence on asymmetric anion-π catalysis and, if perfectly matched, affords the highest enantio- and diastereoselectivity.

  7. Tar balls from Deep Water Horizon oil spill: environmentally persistent free radicals (EPFR) formation during crude weathering.

    Science.gov (United States)

    Kiruri, Lucy W; Dellinger, Barry; Lomnicki, Slawo

    2013-05-07

    Tar balls collected from the Gulf of Mexico shores of Louisiana and Florida after the BP oil spill have shown the presence of electron paramagnetic resonance (EPR) spectra characteristic of organic free radicals as well as transition metal ions, predominantly iron(III) and manganese(II). Two types of organic radicals were distinguished: an asphaltene radical species typically found in crude oil (g = 2.0035) and a new type of radical resulting from the environmental transformations of crude (g = 2.0041-47). Pure asphaltene radicals are resonance stabilized over a polyaromatic structure and are stable in air and unreactive. The new radicals were identified as products of partial oxidation of crude components and result from the interaction of the oxidized aromatics with metal ion centers. These radicals are similar to semiquinone-type, environmentally persistent free radicals (EPFRs) previously observed in combustion-generated particulate and contaminated soils.

  8. Tripodal Receptors for Cation and Anion Sensors

    NARCIS (Netherlands)

    Kuswandi, Bambang; Nuriman,; Verboom, Willem; Reinhoudt, David N.

    2006-01-01

    This review discusses different types of artificial tripodal receptors for the selectiverecognition and sensing of cations and anions. Examples on the relationship between structure andselectivity towards cations and anions are described. Furthermore, their applications as potentiometricion sensing

  9. Contorted polycyclic aromatics.

    Science.gov (United States)

    Ball, Melissa; Zhong, Yu; Wu, Ying; Schenck, Christine; Ng, Fay; Steigerwald, Michael; Xiao, Shengxiong; Nuckolls, Colin

    2015-02-17

    CONSPECTUS: This Account describes a body of research in the design, synthesis, and assembly of molecular materials made from strained polycyclic aromatic molecules. The strain in the molecular subunits severely distorts the aromatic molecules away from planarity. We coined the term "contorted aromatics" to describe this class of molecules. Using these molecules, we demonstrate that the curved pi-surfaces are useful as subunits to make self-assembled electronic materials. We have created and continue to study two broad classes of these "contorted aromatics": discs and ribbons. The figure that accompanies this conspectus displays the three-dimensional surfaces of a selection of these "contorted aromatics". The disc-shaped contorted molecules have well-defined conformations that create concave pi-surfaces. When these disc-shaped molecules are substituted with hydrocarbon side chains, they self-assemble into columnar superstructures. Depending on the hydrocarbon substitution, they form either liquid crystalline films or macroscopic cables. In both cases, the columnar structures are photoconductive and form p-type, hole- transporting materials in field effect transistor devices. This columnar motif is robust, allowing us to form monolayers of these columns attached to the surface of dielectrics such as silicon oxide. We use ultrathin point contacts made from individual single-walled carbon nanotubes that are separated by a few nanometers to probe the electronic properties of short stacks of a few contorted discs. We find that these materials have high mobility and can sense electron-deficient aromatic molecules. The concave surfaces of these disc-shaped contorted molecules form ideal receptors for the molecular recognition and assembly with spherical molecules such as fullerenes. These interfaces resemble ball-and-socket joints, where the fullerene nests itself in the concave surface of the contorted disc. The tightness of the binding between the two partners can be

  10. Radical prostatectomy - discharge

    Science.gov (United States)

    ... to 6 months. You will learn exercises (called Kegel exercises) that strengthen the muscles in your pelvis. ... Radical prostatectomy Retrograde ejaculation Urinary incontinence Patient Instructions Kegel exercises - self-care Suprapubic catheter care Urinary catheters - ...

  11. Traditional Chinese medicine formula Qing Huo Yi Hao as superoxide anion scavenger in high glucosetreated endothelial cells

    Institute of Scientific and Technical Information of China (English)

    Qiong xu; Bin ZHANG; Xiao-mu LI; Xin GAO

    2012-01-01

    Aim:To investigate the effects of a traditional Chinese medicine formula Qing Huo Yi Hao (QHYH)and its components on hydroxyl radical (HO·)production in vitro and the activity of QHYH against free radicals in cultured endothelial cells induced by high glucose.Methods:Hydroxyl radicals (HO·)were generated through Fenton reactions in vitro,and 5,5-dimethyl-1-pyrroline N-oxide (DMPO)was used as a spin trap to form DMPO/HO·adducts detected using electron paramagnetic resonance (EPR).Immortalized mouse cerebral microvascular endothelial (bEnd.3)cells were treated with high glucose (35 mmol/L).The free radical scavenging ability of QHYH in the cells was evaluated using EPR.Superoxide dismutase (SOD)was used to identify the free radicals scavenged by QHYH in the cells.Results:QHYH and its 8 components concentration-dependently reduced DMPO/HO· signaling.The DMPO/HO· adduct scavenging ability of QHYH was 82.2%,which was higher than each individual component.The free radical scavenging ability of 1% QHYH in high glucose-treated bEnd.3 cells was approximately 70%.In these cells,the free radicals were also specifically reduced by SOD (400 U/mL),implying that the free radicals were primarily superoxide anions.Conclusion:The results demonstrate that the QHYH formula is potent antioxidant acting as scavenge of superoxide anions in high glucose-treated endothelial cells.

  12. The Possible Interstellar Anion CH2CN-: Spectroscopic Constants, Vibrational Frequencies, and Other Considerations

    Science.gov (United States)

    Fortenberry, Ryan C.; Crawford, T. Daniel; Lee, Timothy J.

    2012-01-01

    The A 1B1 anion (CH2CN??) has been hypothesized as the carrier for one di use interstellar band. However, this particular molecular system has not been detected in the interstellar medium even though the related cyanomethyl radical and the isoelectronic ketenimine molecule have been found. In this study we are employing the use of proven quartic force elds and second-order vibrational perturbation theory to compute accurate spectroscopic constants and fundamental vibrational frequencies for X 1A0 CH2CN?? in order to assist in laboratory studies and astronomical observations. Keywords: Astrochemistry, ISM: molecular anions, Quartic force elds, Rotational constants, Vibrational frequencies

  13. Petrochemistry - Aromatics; Petrochimie - Aromatiques

    Energy Technology Data Exchange (ETDEWEB)

    Anon.

    2005-09-01

    The assignment of Unipetrol chemical activities to the Czech group Agrofert by the Polish PKN Orlen is suspended and would be renegotiated. Oman Oil Company (OOC) is joining in the Korean LG International and in its subsidiary company Oman Refinery Company (ORC) for the construction of its new aromatics complex on its site of Sohar (Oman). This plan represents an investment of one milliard of dollars; it will produce 800000 t/year of para-xylene and 210000 t/year of benzene. The unit would be operational at the third trimester 2008. (O.M.)

  14. Fluorinated aromatic diamine

    Science.gov (United States)

    Jones, Robert J. (Inventor); O'Rell, Michael K. (Inventor); Hom, Jim M. (Inventor)

    1980-01-01

    This invention relates to a novel aromatic diamine and more particularly to the use of said diamine for the preparation of thermally stable high-molecular weight polymers including, for example, polyamides, polyamideimides, polyimides, and the like. This diamine is obtained by reacting a stoichometric amount of a disodium salt of 2,2-bis(4-hydroxyphenyl) hexafluoropropane with 4-chloronitrobenzene to obtain an intermediate, 2,2-bis[4-(4-nitrophenoxy)phenyl] hexafluoropropane, which is reduced to the corresponding 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoropropane.

  15. Study on the Free Radical Scavenging Activity of Sea Cucumber (Paracaudina chinens var.) Gelatin Hydrolysate

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Gelatin from the sea cucumber (Paracaudina chinens var.) was hydrolyzed by bromelain and the hydrolysate was found to have a high free radical scavenging activity. The hydrolysate was fractionated through an ultrafiltration membrane with 5 kDa molecular weight cutoff (MWCO). The portion (less than 5 kDa) was further separated by Sephadex G-25. The active peak was collected and assayed for free radical scavenging activity. The scavenging rates for superoxide anion radicals (O2·-) and hydroxyl radicals (·OH) of the fraction with the highest activity were 29.02% and 75.41%, respectively. A rabbit liver mitochondrial free radical damage model was adopted to study the free radical scavenging activity of the fraction. The results showed that the sea cucumber gelatin hydrolysate can prevent the damage of rabbit liver and mitochondria.

  16. Methods and systems for measuring anions

    KAUST Repository

    Masih, Dilshad

    2016-08-18

    Embodiments of the present disclosure provide for methods for detecting the presence and/or concentration of anions in a solution, systems for detecting the presence and/or concentration of anions in a solution, anion sensor systems, and the like.

  17. Efficient Amide Based Halogenide Anion Receptors

    Institute of Scientific and Technical Information of China (English)

    Hong Xing WU; Feng Hua LI; Hai LIN; Shou Rong ZHU; Hua Kuan LIN

    2005-01-01

    In this paper, we present the synthesis and anion recognition properties of the amide based phenanthroline derivatives 1, 2 and 3. In all cases 1:1 receptor: anion complexes were observed. The receptors were found to be selective for fluoride and chloride respectively over other putative anionic guest species.

  18. Binding Hydrated Anions with Hydrophobic Pockets.

    Science.gov (United States)

    Sokkalingam, Punidha; Shraberg, Joshua; Rick, Steven W; Gibb, Bruce C

    2016-01-13

    Using a combination of isothermal titration calorimetry and quantum and molecular dynamics calculations, we demonstrate that relatively soft anions have an affinity for hydrophobic concavity. The results are consistent with the anions remaining partially hydrated upon binding, and suggest a novel strategy for anion recognition.

  19. Developing principles for predicting ionic liquid effects on reaction outcome. The importance of the anion in controlling microscopic interactions.

    Science.gov (United States)

    Keaveney, Sinead T; Haines, Ronald S; Harper, Jason B

    2015-03-28

    A series of ionic liquids containing anions of differing coordination strength were investigated as solvents for the condensation reaction of an alkyl amine and an aromatic aldehyde. As predicted, the rate constant of the process was found to increase with the proportion of the ionic liquid in the reaction mixture. Temperature-dependent kinetic analyses demonstrated that by varying the ability of the anion to interact with the cation the magnitude of both the enthalpy and entropy of activation could be controlled in a predictable manner, with the activation parameters being linearly dependent on the ionic liquid basicity. Interestingly, the unexpected trend in the rate constants observed when altering the anion of the ionic liquid highlighted the presence of more subtle secondary microscopic interactions involving the anion, further emphasizing the fragility of the enthalpy - entropy balance.

  20. Aromaticity of Heterofullerenes C18BxNy (x + y = 2) and Their Molecular Ions

    Science.gov (United States)

    Chen, Jia-li; Kerim, Ablikim

    2008-04-01

    The aromaticity of all possible substituted fullerene isomers of C18N2, C18B2, C18BN, and their molecular ions which originate from the C20 (Ih) cage were studied by the topological resonance energy (TRE) and the percentage topological resonance energy methods. The relationship between the aromaticity of C18BxNy isomers and the sites where the heteroatoms dope at the C20 (Ih) cage is discussed. Calculation results show that at the neutral and cationic states all the isomers are predicted to be antiaromatic with negative TREs, but their polyvalent anions are predicted to be aromatic with positive TREs. The most stable isomer is formed by heteroatom doping at the 1, 11-sites in C18N2, C18B2, and C18BN. Heterofullerenes are more aromatic than C20. The stability order in the neutral states is C18N2 > C18 BN > C18 B2 > C20. The stability order in closed-shell is C18B28- > C206- > C18BN6- > C18N24-. This predicts theoretically that their polyvalent anions have high aromaticity.

  1. Hydroxyl radical reactivity at the air-ice interface

    Directory of Open Access Journals (Sweden)

    T. F. Kahan

    2010-01-01

    Full Text Available Hydroxyl radicals are important oxidants in the atmosphere and in natural waters. They are also expected to be important in snow and ice, but their reactivity has not been widely studied in frozen aqueous solution. We have developed a spectroscopic probe to monitor the formation and reactions of hydroxyl radicals in situ. Hydroxyl radicals are produced in aqueous solution via the photolysis of nitrite, nitrate, and hydrogen peroxide, and react rapidly with benzene to form phenol. Similar phenol formation rates were observed in aqueous solution and bulk ice. However, no reaction was observed at air-ice interfaces, or when bulk ice samples were crushed prior to photolysis to increase their surface area. We also monitored the heterogeneous reaction between benzene present at air-water and air-ice interfaces with gas-phase OH produced from HONO photolysis. Rapid phenol formation was observed on water surfaces, but no reaction was observed at the surface of ice. Under the same conditions, we observed rapid loss of the polycyclic aromatic hydrocarbon (PAH anthracene at air-water interfaces, but no loss was observed at air-ice interfaces. Our results suggest that the reactivity of hydroxyl radicals toward aromatic organics is similar in bulk ice samples and in aqueous solution, but is significantly suppressed in the quasi-liquid layer (QLL that exists at air-ice interfaces.

  2. "Carbo-aromaticity" and novel carbo-aromatic compounds.

    Science.gov (United States)

    Cocq, Kévin; Lepetit, Christine; Maraval, Valérie; Chauvin, Remi

    2015-09-21

    While the concept of aromaticity is being more and more precisely delineated, the category of "aromatic compounds" is being more and more expanded. This is illustrated by an introductory highlight of the various types of "aromaticity" previously invoked, and by a focus on the recently proposed "aromatic character" of the "two-membered rings" of the acetylene and butatriene molecules. This serves as a general foundation for the definition of "carbo-aromaticity", the relevance of which is surveyed through recent results in the synthetic, physical, and theoretical chemistry of carbo-mers and in particular macrocyclic-polycyclic representatives constituting a natural family of "novel aromatic compounds". With respect to their parent molecules, carbo-mers are constitutionally defined as "carbon-enriched", and can also be functionally regarded as "π-electron-enriched". This is exemplified by recent experimental and theoretical results on functional, aromatic, rigid, σ,π-macrocyclic carbo-benzene archetypes of various substitution patterns, with emphasis on the quadrupolar pattern. For the purpose of comparison, several types of non-aromatic references of carbo-benzenes are then considered, i.e. freely rotating σ,π-acyclic carbo-n-butadienes and flexible σ-cyclic, π-acyclic carbo-cyclohexadienes, and to "pro-aromatic" congeners, i.e. rigid σ,π-macrocyclic carbo-quinoids. It is shown that functional carbo-mers are entering the field of "molecular materials" for properties such as linear or nonlinear optical properties (e.g. dichromism and two-photon absorption) and single molecule conductivity. Since total or partial carbo-mers of aromatic carbon-allotropes of infinite size such as graphene (graphynes and graphdiynes) and graphite ("graphitynes") have long been addressed at the theoretical or conceptual level, recent predictive advances on the electrical, optical and mechanical properties of such carbo-materials are surveyed. Very preliminary experimental results

  3. Polymerization of anionic wormlike micelles.

    Science.gov (United States)

    Zhu, Zhiyuan; González, Yamaira I; Xu, Hangxun; Kaler, Eric W; Liu, Shiyong

    2006-01-31

    Polymerizable anionic wormlike micelles are obtained upon mixing the hydrotropic salt p-toluidine hydrochloride (PTHC) with the reactive anionic surfactant sodium 4-(8-methacryloyloxyoctyl)oxybenzene sulfonate (MOBS). Polymerization captures the cross-sectional radius of the micelles (approximately 2 nm), induces micellar growth, and leads to the formation of a stable single-phase dispersion of wormlike micellar polymers. The unpolymerized and polymerized micelles were characterized using static and dynamic laser light scattering, small-angle neutron scattering, 1H NMR, and stopped-flow light scattering. Stopped-flow light scattering was also used to measure the average lifetime of the unpolymerized wormlike micelles. A comparison of the average lifetime of unpolymerized wormlike micelles with the surfactant monomer propagation rate was used to elucidate the mechanism of polymerization. There is a significant correlation between the ratio of the average lifetime to the monomer propagation rate and the average aggregation number of the polymerized wormlike micelles.

  4. Laser Cooling of Molecular Anions

    CERN Document Server

    Yzombard, Pauline; Gerber, Sebastian; Doser, Michael; Comparat, Daniel

    2015-01-01

    We propose a scheme for laser cooling of negatively charged molecules. We briefly summarise the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with C$\\_2^-$, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photo-detachment process is present, as well as Doppler laser cooling of trapped C$\\_2^-$, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources and antimatter physics.

  5. Free Radical Reactions in Food.

    Science.gov (United States)

    Taub, Irwin A.

    1984-01-01

    Discusses reactions of free radicals that determine the chemistry of many fresh, processed, and stored foods. Focuses on reactions involving ascorbic acid, myoglobin, and palmitate radicals as representative radicals derived from a vitamin, metallo-protein, and saturated lipid. Basic concepts related to free radical structure, formation, and…

  6. Anionic access to silylated and germylated binuclear heterocycles.

    Science.gov (United States)

    Boddaert, Thomas; François, Cyril; Mistico, Laetitia; Querolle, Olivier; Meerpoel, Lieven; Angibaud, Patrick; Durandetti, Muriel; Maddaluno, Jacques

    2014-08-04

    A simple access to silylated and germylated binuclear heterocycles, based on an original anionic rearrangement, is described. A set of electron-rich and electron-poor silylated aromatic and heteroaromatic substrates were tested to understand the mechanism and the factors controlling this rearrangement, in particular its regioselectivity. This parameter was shown to follow the rules proposed before from a few examples. Then, the effect of the substituents borne by the silicon itself, in particular the selectivity of the ligand transfer, was studied. Additionally, this chemistry was extended to germylated substrates. A hypervalent germanium species, comparable to the putative intermediate proposed with silicon, seems to be involved. However, a pathway implicating the elimination of LiCH2Cl was observed for the first time with this element, leading to unexpected products of the benzo-oxa (or benzo-aza) germol-type.

  7. IONIC CONDUCTIVITY IN THE COMPLEXES OF COMB-SHAPED POLYETHER WITH LITHIUM AROMATIC SULFONATE

    Institute of Scientific and Technical Information of China (English)

    ZHANG Shengshui; QIU Weihua; XUE Dacui; LIU Qingguo

    1993-01-01

    Complexes of comb-shaped polyether and lithium aromatic sulfonates bearing different negative charge number were prepared by in situ thermal polymerization. Their conductivity depends deeply on salt content, ambient temperature and negative charge number of the added salts. Results show that anions can be partly immobilized by increasing their negative charges at lower temperature.Against discharge time the short circuit current of the battery (Li/complex film/Lix V3O8) is stabilized by increasing the anionic charge number of the complex.

  8. Hosting anions. The energetic perspective.

    Science.gov (United States)

    Schmidtchen, Franz P

    2010-10-01

    Hosting anions addresses the widely spread molecular recognition event of negatively charged species by dedicated organic compounds in condensed phases at equilibrium. The experimentally accessible energetic features comprise the entire system including the solvent, any buffers, background electrolytes or other components introduced for e.g. analysis. The deconvolution of all these interaction types and their dependence on subtle structural variation is required to arrive at a structure-energy correlation that may serve as a guide in receptor construction. The focus on direct host-guest interactions (lock-and-key complementarity) that have dominated the binding concepts of artificial receptors in the past must be widened in order to account for entropic contributions which constitute very significant fractions of the total free energy of interaction. Including entropy necessarily addresses the ambiguity and fuzziness of the host-guest structural ensemble and requires the appreciation of the fact that most liquid phases possess distinct structures of their own. Apparently, it is the perturbation of the intrinsic solvent structure occurring upon association that rules ion binding in polar media where ions are soluble and abundant. Rather than specifying peculiar structural elements useful in anion binding this critical review attempts an illumination of the concepts and individual energetic contributions resulting in the final observation of specific anion recognition (95 references).

  9. Voltammetric studies on free radicals of lower fatty alco- hols

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In this work, both generation and reduction processes of the a-radicals of lower fatty alcohols were studied by voltammetry in lower fatty alcohols/peroxydisul- fate/phosphate buffer system. Experimental results showed that such three reactions were successively completed at negative potential on mercury electrode surface: (ⅰ) sulfate radical anion was generated electrochemically from one-electron reduction of peroxydisulfate ion , (ⅱ) the oxidized lower fatty alcohols to the corresponding a-radicals and (ⅲ) the a-radicals were reduced in one-electron and one-proton addition to produce their own re-duction waves. The apparent free energy ΔrGm of the a-radicals of lower straight-chain fatty alcohols such as metha-nol, ethanol, propanol, butanol and pentanol obtained were 107.09, 116.74, 122.53, 126.39 and 129.28 kJ·mol/L, respec-tively. The proposed method is more simple and convenient than the current approaches based on the radical-chain reac-tion for studying alcohol oxidation.

  10. Bacterial Degradation of Aromatic Compounds

    Directory of Open Access Journals (Sweden)

    Qing X. Li

    2009-01-01

    Full Text Available Aromatic compounds are among the most prevalent and persistent pollutants in the environment. Petroleum-contaminated soil and sediment commonly contain a mixture of polycyclic aromatic hydrocarbons (PAHs and heterocyclic aromatics. Aromatics derived from industrial activities often have functional groups such as alkyls, halogens and nitro groups. Biodegradation is a major mechanism of removal of organic pollutants from a contaminated site. This review focuses on bacterial degradation pathways of selected aromatic compounds. Catabolic pathways of naphthalene, fluorene, phenanthrene, fluoranthene, pyrene, and benzo[a]pyrene are described in detail. Bacterial catabolism of the heterocycles dibenzofuran, carbazole, dibenzothiophene, and dibenzodioxin is discussed. Bacterial catabolism of alkylated PAHs is summarized, followed by a brief discussion of proteomics and metabolomics as powerful tools for elucidation of biodegradation mechanisms.

  11. Stable radical content and anti-radical activity of roasted Arabica coffee: from in-tact bean to coffee brew.

    Directory of Open Access Journals (Sweden)

    Gordon J Troup

    Full Text Available The roasting of coffee beans generates stable radicals within melanoidins produced by non-enzymatic browning. Roasting coffee beans has further been suggested to increase the antioxidant (AO capacity of coffee brews. Herein, we have characterized the radical content and AO capacity of brews prepared from Coffea arabica beans sourced directly from an industrial roasting plant. In-tact beans exhibited electron paramagnetic resonance signals arising from Fe3+, Mn2+ and at least three distinct stable radicals as a function of roasting time, whose intensity changed upon grinding and ageing. In coffee brews, the roasting-induced radicals were harboured within the high molecular weight (> 3 kD melanoidin-containing fraction at a concentration of 15 nM and was associated with aromatic groups within the melanoidins. The low molecular weight (< 3 kD fraction exhibited the highest AO capacity using DPPH as an oxidant. The AO activity was not mediated by the stable radicals or by metal complexes within the brew. While other non-AO functions of the roasting-induced radical and metal complexes may be possible in vivo, we confirm that the in vitro antiradical activity of brewed coffee is dominated by low molecular weight phenolic compounds.

  12. The formation of polycyclic aromatic hydrocarbons in evolved circumstellar environments

    CERN Document Server

    Cherchneff, Isabelle

    2010-01-01

    The formation of Polycyclic Aromatic Hydrocarbons in the circumstellar outflows of evolved stars is reviewed, with an emphasis on carbon stars on the Asymptotic Giant Branch. Evidence for PAHs present in their winds is provided by meteoritic studies and recent observations of the Unidentified Infrared bands. We detail the chemical processes leading to the closure of the first aromatic ring as well as the growth mechanisms leading to amorphous carbon grains. Existing studies on PAH formation in evolved stellar envelopes are reviewed and new results for the modelling of the inner wind of the archetype carbon star IRC+10216 are presented. Benzene, C6H6, forms close to the star, as well as water, H2O, as a result of non-equilibrium chemistry induced by the periodic passage of shocks. The growth process of aromatic rings may thus resemble that active in sooting flames due to the presence of radicals like hydroxyl, OH. Finally, we discuss possible formation processes for PAHs and aromatic compounds in the hydrogen-...

  13. Anion

    Directory of Open Access Journals (Sweden)

    A. Vadivel Murugan

    2003-01-01

    . Its characterization is investigated by Fourier Transform Infrared Spectroscopy (FT-IR and Scanning Electron Microscopy (SEM. The hybrid material presents predominantly high electronic conductivities of around 2.0 and 7.0 S cm-1 at 300 and 400K respectively.

  14. Inorganic chemistry. Synthesis and characterization of P₂N₃⁻: an aromatic ion composed of phosphorus and nitrogen.

    Science.gov (United States)

    Velian, Alexandra; Cummins, Christopher C

    2015-05-29

    Aromaticity is predominantly associated with carbon-rich compounds but can also occur in all-inorganic ones. We report the synthesis of the diphosphatriazolate anion, a rare example of a planar aromatic inorganic species. Treatment of azide (N3(-)) in tetrahydrofuran solution with P2A2 (A = C14H10), a source of P2, produced P2N3(-), which we isolated as its [Na-kryptofix-221](+) salt in 22% yield and characterized by single-crystal x-ray diffraction. Salts [Na-kryptofix-221] [P2N3] and [Na-kryptofix-221] [P2(15)NN2] were analyzed by infrared and Raman spectroscopy, (15)N and (31)P nuclear magnetic resonance spectroscopy, and mass spectrometry. The formation of the P2N3(-) anion was investigated using density functional theory, and its aromatic character was confirmed by NICS (nucleus-independent chemical shift) and QTAIM (quantum theory of atoms in molecules) methods.

  15. Gangs, Terrorism, and Radicalization

    Directory of Open Access Journals (Sweden)

    Scott Decker

    2011-01-01

    Full Text Available What can street gangs tell us about radicalization and extremist groups? At first glance, these two groups seem to push the boundaries of comparison. In this article, we examine the important similarities and differences across criminal, deviant, and extremist groups. Drawing from research on street gangs, this article explores issues such as levels of explanation,organizational structure, group process, and the increasingly important role of technology and the Internet in the context of radicalization. There are points of convergence across these groups, but it is important to understand the differences between these groups. This review finds little evidence to support the contention that American street gangs are becoming increasingly radicalized. This conclusion is based largely on organizational differences between gangs and terror groups.

  16. Sexuality Following Radical Prostatectomy

    DEFF Research Database (Denmark)

    Fode, Mikkel; Serefoglu, Ege C; Albersen, Maarten;

    2017-01-01

    INTRODUCTION: Radical prostatectomies can result in urinary incontinence and sexual dysfunction. Traditionally, these issues have been studied separately, and the sexual problem that has received the most focus has been erectile dysfunction. AIM: To summarize the literature on sexually related side...... effects and their consequences after radical prostatectomy and focus on the occurrence and management of problems beyond erectile dysfunction. METHODS: The literature on sexuality after radical prostatectomy was reviewed through a Medline search. Original research using quantitative and qualitative...... methodologies was considered. Priority was given to studies exploring aspects of sexuality other than erectile function. MAIN OUTCOME MEASURES: The prevalence, predictive factors, and management of post-prostatectomy sexual problems beyond erectile dysfunction. RESULTS: Most patients will develop urinary...

  17. Substrate-dependent aromatic ring fission of catechol and 2-aminophenol with O2 catalyzed by a nonheme iron complex of a tripodal N4 ligand.

    Science.gov (United States)

    Lakshman, Triloke Ranjan; Chatterjee, Sayanti; Chakraborty, Biswarup; Paine, Tapan Kanti

    2016-06-07

    The catalytic reactivity of an iron(ii) complex [(TPA)Fe(II)(CH3CN)2](2+) (1) (TPA = tris(2-pyridylmethyl)amine) towards oxygenative aromatic C-C bond cleavage of catechol and 2-aminophenol is presented. Complex 1 exhibits catalytic and regioselective C-C bond cleavage of 3,5-di-tert-butylcatechol (H2DBC) to form intradiol products, whereas it catalyzes extradiol-type C-C bond cleavage of 2-amino-4,6-di-tert-butylphenol (H2AP). The catalytic reactions are found to be pH-dependent and the complex exhibits maximum turnovers at pH 5 in acetonitrile-phthalate buffer. An iron(iii)-catecholate complex [(TPA)Fe(III)(DBC)](+) (2) is formed in the ring cleavage of catechol. In the extradiol-type cleavage of H2AP, an iron(iii)-2-iminobenzosemiquinonate complex [(TPA)Fe(III)(ISQ)](2+) (3) (ISQ = 4,6-di-tert-butyl-2-iminobenzosemiquinonate radical anion) is observed in the reaction pathway. This work shows the importance of the nature of 'redox non-innocent' substrates in governing the mode of ring fission reactivity.

  18. Conformation-Selective Resonant Photoelectron Spectroscopy via Dipole-Bound States of Cold Anions.

    Science.gov (United States)

    Huang, Dao-Ling; Liu, Hong-Tao; Ning, Chuan-Gang; Wang, Lai-Sheng

    2015-06-18

    Molecular conformation is important in chemistry and biochemistry. Conformers connected by low energy barriers can only be observed at low temperatures and are difficult to be separated. Here we report a new method to obtain conformation-selective spectroscopic information about dipolar molecular radicals via dipole-bound excited states of the corresponding anions cooled in a cryogenic ion trap. We observed two conformers of cold 3-hydroxyphenoxide anions [m-HO(C6H4)O(-)] in high-resolution photoelectron spectroscopy and measured different electron affinities, 18,850(8) and 18,917(5) cm(-1), for the syn and anti 3-hydroxyphenoxy radicals, respectively. We also observed dipole-bound excited states for m-HO(C6H4)O(-) with different binding energies for the two conformers due to the different dipole moments of the corresponding 3-hydroxyphenoxy radicals. Excitations to selected vibrational levels of the dipole-bound states result in conformation-selective photoelectron spectra. This method should be applicable to conformation-selective spectroscopic studies of any anions with dipolar neutral cores.

  19. Effect of low concentrations of synthetic surfactants on polycyclic aromatic hydrocarbons (PAH) biodegradation

    OpenAIRE

    A. C. Rodrigues; Nogueira, R; Melo, L. F.; A. G. Brito

    2013-01-01

    The present study is focused on the effect of synthetic surfactants, at low concentration, on the kinetics of polycyclic aromatic hydrocarbons (PAH) biodegradation by Pseudomonas putida ATCC 17514 and addresses the specific issue of the effect of the surfactant on bacterial adhesion to PAH, which is believed to be an important mechanism for the uptake of hydrophobic compounds. For that purpose, three surfactants were tested, namely, the nonionic Tween 20, the anionic sodium dodecyl sulphate (...

  20. Carbon–carbon bond cleavage for Cu-mediated aromatic trifluoromethylations and pentafluoroethylations

    Directory of Open Access Journals (Sweden)

    Tsuyuka Sugiishi

    2015-12-01

    Full Text Available This short review highlights the copper-mediated fluoroalkylation using perfluoroalkylated carboxylic acid derivatives. Carbon–carbon bond cleavage of perfluoroalkylated carboxylic acid derivatives takes place in fluoroalkylation reactions at high temperature (150–200 °C or under basic conditions to generate fluoroalkyl anion sources for the formation of fluoroalkylcopper species. The fluoroalkylation reactions, which proceed through decarboxylation or tetrahedral intermediates, are useful protocols for the synthesis of fluoroalkylated aromatics.

  1. Beyond Radical Educational Cynicism.

    Science.gov (United States)

    Wood, George H.

    1982-01-01

    An alternative is presented to counter current radical arguments that the schools cannot bring about social change because they are instruments of capitalism. The works of Samuel Bowles, Herbert Gintis, and Louis Althusser are discussed. Henry Giroux's "Ideology, Culture and the Process of Schooling" provides an alternative to cynicism.…

  2. Radically enhanced molecular recognition

    KAUST Repository

    Trabolsi, Ali

    2009-12-17

    The tendency for viologen radical cations to dimerize has been harnessed to establish a recognition motif based on their ability to form extremely strong inclusion complexes with cyclobis(paraquat-p-phenylene) in its diradical dicationic redox state. This previously unreported complex involving three bipyridinium cation radicals increases the versatility of host-guest chemistry, extending its practice beyond the traditional reliance on neutral and charged guests and hosts. In particular, transporting the concept of radical dimerization into the field of mechanically interlocked molecules introduces a higher level of control within molecular switches and machines. Herein, we report that bistable and tristable [2]rotaxanes can be switched by altering electrochemical potentials. In a tristable [2]rotaxane composed of a cyclobis(paraquat-p-phenylene) ring and a dumbbell with tetrathiafulvalene, dioxynaphthalene and bipyridinium recognition sites, the position of the ring can be switched. On oxidation, it moves from the tetrathiafulvalene to the dioxynaphthalene, and on reduction, to the bipyridinium radical cation, provided the ring is also reduced simultaneously to the diradical dication. © 2010 Macmillan Publishers Limited. All rights reserved.

  3. Electromeric rhodium radical complexes

    NARCIS (Netherlands)

    Puschmann, F.F.; Harmer, J.; Stein, D.; Rüegger, H.; de Bruin, B.; Grützmacher, H.

    2010-01-01

    Radical changes: One single P-Rh-P angle determines whether the odd electron in the paramagnetic complex [Rh(trop2PPh)(PPh3)] is delocalized over the whole molecule (see picture, blue) or is localized on the P—Rh unit (red). The two energetically almost degenerate electromers exist in a fast equilib

  4. Violent Radicalization in Europe

    DEFF Research Database (Denmark)

    Dalgaard-Nielsen, Anja

    2010-01-01

    When, why, and how do people living in a democracy become radicalized to the point of being willing to use or directly support the use of terrorist violence against fellow citizens? This question has been at the center of academic and public debate over the past years as terrorist attacks...

  5. Radical School Reform.

    Science.gov (United States)

    Gross, Beatrice, Ed.; Gross, Ronald, Ed.

    This book provides a comprehensive examination of the nature of the school crisis and the ways in which radical thinkers and educators are dealing with it. Excerpts from the writings of Jonathan Kozol, John Holt, Kenneth Clark, and others are concerned with the realities of education in ghettos and suburbs. Paul Goodman, Marshall McLuhan, Sylvia…

  6. Homegrown religious radicalization

    DEFF Research Database (Denmark)

    Khawaja, Iram

    and their families. Existing literature and ways of thinking about the social psychological process of radicalization will be reviewed, such as social identity theory and transformative learning theory, and a theoretical framework based on a focus on belonging, recognition and the sense of community will be proposed...

  7. On Radical Feminism

    Institute of Scientific and Technical Information of China (English)

    翟良锴

    2015-01-01

    <正>All men are created equal.For centuries,human have been struggling for their rights.Women,as a special social force,are fighting vigorously for their equal rights with men.According to an introduction to feminism,there are three main types of feminism:socialist,reformist and radical(Feminism 101).In order

  8. Schlenk Techniques for Anionic Polymerization

    KAUST Repository

    Ratkanthwar, Kedar

    2015-09-01

    Anionic polymerization-high vacuum techniques (HVTs) are doubtlessly the most prominent and reliable experimental tools to prepare polymer samples with well-defined and, in many cases, complex macromolecular architectures. Due to the high demands for time and skilled technical personnel, HVTs are currently used in only a few research laboratories worldwide. Instead, most researchers in this filed are attracted to more facile Schlenk techniques. The basic principle of this technique followed in all laboratories is substantially the same, i.e. the use of alternate vacuum and inert gas atmosphere in glass apparatus for the purification/charging of monomer, solvents, additives, and for the manipulation of air-sensitive compounds such as alkyl metal initiators, organometallic or organic catalysts. However, it is executed quite differently in each research group in terms of the structure of Schlenk apparatus (manifolds, connections, purification/storage flasks, reactors, etc.), the use of small supplementary devices (soft tubing, cannulas, stopcocks, etc.) and experimental procedures. The operational methods are partly purpose-oriented while also featured by a high flexibility, which makes it impossible to describe in detail each specific one. In this chapter we will briefly exemplify the application of Schlenk techniques for anionic polymerization by describing the performance of a few experiments from our own work.

  9. Advances towards aromatic oligoamide foldamers

    DEFF Research Database (Denmark)

    Hjelmgaard, Thomas; Plesner, Malene; Dissing, Mette Marie;

    2014-01-01

    We have efficiently synthesized 36 arylopeptoid dimers with ortho-, meta-, and para-substituted aromatic backbones and tert-butyl or phenyl side chains. The dimers were synthesized by using a "submonomer method" on solid phase, by applying a simplified common set of reaction conditions. X......-ray crystallographic analysis of two of these dimers disclosed that the tert-butyl side chain invokes a cis amide conformation with a comparatively more closely packed structure of the surrounding aromatic backbone while the phenyl side chain results in a trans amide conformation with a more open, extended structure...... of the surrounding aromatic backbone. Investigation of the X-ray structures of two arylopeptoid dimers disclosed that the tert-butyl side chain invokes a cis amide conformation with a closely packed structure of the surrounding aromatic backbone while the phenyl side chain results in a trans amide conformation...

  10. Free Radicals and Extrinsic Skin Aging

    Directory of Open Access Journals (Sweden)

    Borut Poljšak

    2012-01-01

    Full Text Available Human skin is constantly directly exposed to the air, solar radiation, environmental pollutants, or other mechanical and chemical insults, which are capable of inducing the generation of free radicals as well as reactive oxygen species (ROS of our own metabolism. Extrinsic skin damage develops due to several factors: ionizing radiation, severe physical and psychological stress, alcohol intake, poor nutrition, overeating, environmental pollution, and exposure to UV radiation (UVR. It is estimated that among all these environmental factors, UVR contributes up to 80%. UV-induced generation of ROS in the skin develops oxidative stress, when their formation exceeds the antioxidant defence ability of the target cell. The primary mechanism by which UVR initiates molecular responses in human skin is via photochemical generation of ROS mainly formation of superoxide anion (O2−•, hydrogen peroxide (H2O2, hydroxyl radical (OH•, and singlet oxygen (1O2. The only protection of our skin is in its endogenous protection (melanin and enzymatic antioxidants and antioxidants we consume from the food (vitamin A, C, E, etc.. The most important strategy to reduce the risk of sun UVR damage is to avoid the sun exposure and the use of sunscreens. The next step is the use of exogenous antioxidants orally or by topical application and interventions in preventing oxidative stress and in enhanced DNA repair.

  11. Bioassay of polycyclic aromatic hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Van Kirk, E.A.

    1980-08-01

    A positive relationship was found between the photodynamic activity of 24 polycyclic aromatic hydrocarbons versus published results on the mutagenicity, carcinogenicity, and initiation of unscheduled DNA synthesis. Metabolic activation of benzo(a)pyrene resulted in detection of increased mutagenesis in Paramecium tetraurelia as found also in the Ames Salmonella assay. The utility of P. tetraurelia as a biological detector of hazardous polycyclic aromatic hydrocarbons is discussed.

  12. Tunable electronic interactions between anions and perylenediimide.

    Science.gov (United States)

    Goodson, Flynt S; Panda, Dillip K; Ray, Shuvasree; Mitra, Atanu; Guha, Samit; Saha, Sourav

    2013-08-07

    Over the past decade anion-π interaction has emerged as a new paradigm of supramolecular chemistry of anions. Taking advantage of the electronic nature of anion-π interaction, we have expanded its boundaries to charge-transfer (CT) and formal electron transfer (ET) events by adjusting the electron-donating and accepting abilities of anions and π-acids, respectively. To establish that ET, CT, and anion-π interactions could take place between different anions and π-acids as long as their electronic and structural properties are conducive, herein, we introduce 3,4,9,10-perylenediimide (PDI-1) that selectively undergoes thermal ET from strong Lewis basic hydroxide and fluoride anions, but remains electronically and optically silent to poor Lewis basic anions, as ET and CT events are turned OFF. These interactions have been fully characterized by UV/Vis, NMR, and EPR spectroscopies. These results demonstrate the generality of anion-induced ET events in aprotic solvents and further refute a notion that strong Lewis basic hydroxide and fluoride ions can only trigger nucleophilic attack to form covalent bonds instead of acting as sacrificial electron donors to π-acids under appropriate conditions.

  13. Adsorption affinity of anions on metal oxyhydroxides

    Science.gov (United States)

    Pechenyuk, S. I.; Semushina, Yu. P.; Kuz'mich, L. F.

    2013-03-01

    The dependences of anion (phosphate, carbonate, sulfate, chromate, oxalate, tartrate, and citrate) adsorption affinity anions from geometric characteristics, acid-base properties, and complex forming ability are generalized. It is shown that adsorption depends on the nature of both the anions and the ionic medium and adsorbent. It is established that anions are generally grouped into the following series of adsorption affinity reduction: PO{4/3-}, CO{3/2-} > C2O{4/2-}, C(OH)(CH2)2(COO){3/3-}, (CHOH)2(COO){2/2-} > CrO{4/2-} ≫ SO{4/2-}.

  14. The role of free radicals in traumatic brain injury.

    Science.gov (United States)

    O'Connell, Karen M; Littleton-Kearney, Marguerite T

    2013-07-01

    Traumatic brain injury (TBI) is a significant cause of death and disability in both the civilian and the military populations. The primary impact causes initial tissue damage, which initiates biochemical cascades, known as secondary injury, that expand the damage. Free radicals are implicated as major contributors to the secondary injury. Our review of recent rodent and human research reveals the prominent role of the free radicals superoxide anion, nitric oxide, and peroxynitrite in secondary brain injury. Much of our current knowledge is based on rodent studies, and the authors identified a gap in the translation of findings from rodent to human TBI. Rodent models are an effective method for elucidating specific mechanisms of free radical-induced injury at the cellular level in a well-controlled environment. However, human TBI does not occur in a vacuum, and variables controlled in the laboratory may affect the injury progression. Additionally, multiple experimental TBI models are accepted in rodent research, and no one model fully reproduces the heterogeneous injury seen in humans. Free radical levels are measured indirectly in human studies based on assumptions from the findings from rodent studies that use direct free radical measurements. Further study in humans should be directed toward large samples to validate the findings in rodent studies. Data obtained from these studies may lead to more targeted treatment to interrupt the secondary injury cascades.

  15. Mechanism and kinetics for scavenging superoxide anion by progesterone

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The chemical reaction of progesterone with superoxide anion in 0.1 mol/L NaHCO3 medium is studied by polarography. Differing from the indirect inhibition of generation by synthesized glucocorticoids in mechanism, the function that progesterone scavenges is ascribed to that directly oxidizes the C == C double bond conjugated with the carbonyl moiety of progesterone molecule to a free radical, and then is reduced to H2O2. The result obtained in this work gives new evidence for biomedical research. The equation of rate constant of the oxidization reaction is de-duced, and the apparent rate constant obtained is 308 L·mol-1·s-1.

  16. Metabolic activation of aromatic amines and azo dyes.

    Science.gov (United States)

    Bartsch, H

    1981-01-01

    Aromatic amines, amides and nitro compounds are a class of chemicals that produce tumors in a wide variety of tissues in experimental animals, including liver, urinary bladder, forestomach, small intestine, Zymbal's gland, subcutaneous tissue or skin. In man, exposure to some aromatic amines is associated with tumours of the urinary bladder and carcinoma of the renal pelvis. Their biological activity as carcinogens or genotoxic agents is, in all the cases that have been studied in detail, dependent on metabolic activation in vivo, occurring by multiple pathways. Differences in these metabolic pathways may largely account for the differences in tissues and species susceptibilities to cancer induction. Carcinogenicity of aromatic amines or amides is dependent on their oxidation to N-hydroxy derivatives, whilst the carcinogenicity of aromatic nitro compounds is linked to their reduction to hydroxylamines. Further conversion of the N-hydroxylamine or N-hydroxyamide to reactive intermediates can occur in several ways, which include (i) esterification of the N-hydroxy group, (ii) non-enzymic protonation of the nitrogen of the hydroxylamine and (iii) oxidation to a free radical of arylhydroxamic acids. Following generation of such reactive electrophilic intermediates in tissues or cells, macromolecular binding has been observed to nucleic acids and proteins. In many cases, arylamidated and arylaminated products are formed with nucleic acid bases; in the case of the well-studied 2-acetylaminofluorene, nucleophilic atoms of guanine are the predominant site of reaction. Relatively little is known of the structure and biological consequences of DNA adducts formed from other aromatic amines, amides or nitro compounds; more research in these directions is warranted.

  17. Aromaticity of Heterofullerenes C18BxNy (x+y=2) and Their Molecular Ions

    Institute of Scientific and Technical Information of China (English)

    Jia-li Chen; Ablikim Kerim

    2008-01-01

    The axomaticity of all possible substituted fullerene isomers of C18N2,C18N2,C18BN,and their molecular ions which originate from the C20 (Ih) cage were studied by the topological resonance energy (TRE) and the percentage topological resonance energy methods.The relationship between the aromaticity of C18BxNy isomers and the sites where the heteroatoms dope at the C20 (Ih) cage is discussed.Calculation results show that at the neutral and cationic states all the isomers axe predicted to be antiaromatic with negative TREs,but their polyvalent anions are predicted to be aromatic with positive TREs.The most stable isomer is formed by heteroatom doping at the 1,11-sites in C18N2,C18B2,and C18BN.Heterofullerenes are more aromatic than C20.The stability order in the neutral states is C18N2>C18BN>C18B2>C20.The stability order in closed-shell is C18B28->C206->C18BN6->C18N24-.This predicts theoretically that their polyvalent anions have high aromaticity.

  18. C-H and N-H bond dissociation energies of small aromatic hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Barckholtz, C.; Barckholtz, T.A.; Hadad, C.M.

    1999-01-27

    A survey of computational methods was undertaken to calculate the homolytic bond dissociation energies (BDEs) of the C-H and N-H bonds in monocyclic aromatic molecules that are representative of the functionalities present in coal. These include six-membered rings (benzene, pyridine, pyridazine, pyrimidine, pyrazine) and five-membered rings (furan, thiophene, pyrrole, oxazole). By comparison of the calculated C-H BDEs with the available experimental values for these aromatic molecules, the B3LYP/6-31G(d) level of theory was selected to calculate the BDEs of polycyclic aromatic hydrocarbons (PAHs), including carbonaceous PAHs (naphthalene, anthracene, pyrene, coronene) and heteroatomic PAHs (benzofuran, benzothiophene, indole, benzoxazole, quinoline, isoquinoline, dibenzofuran, carbazole). The cleavage of a C-H or a N-H bond generates a {sigma} radical that is, in general, localized at the site from which the hydrogen atom was removed. However, delocalization of the unpaired electron results in {approximately} 7 kcal {center{underscore}dot} mol{sup {minus}1} stabilization of the radical with respect to the formation of phenyl when the C-H bond is adjacent to a nitrogen atom in the azabenzenes. Radicals from five-membered rings are {approximately} 6 kcal {center{underscore}dot} mol{sup {minus}1} less stable than those formed from six-membered rings due to both localization of the spin density and geometric factors. The location of the heteroatoms in the aromatic ring affects the C-H bond strengths more significantly than does the size of the aromatic network. Therefore, in general, the monocyclic aromatic molecules can be used to predict the C-H BDE of the large PAHs within 1 kcal {center{underscore}dot} mol{sup {minus}1}.

  19. Toward Molecular Magnets of Organic Origin via Anion-π Interaction Involving m-Aminyl Diradical: A Theoretical Study.

    Science.gov (United States)

    Bhattacharya, Debojit; Shil, Suranjan; Misra, Anirban; Bytautas, Laimutis; Klein, Douglas J

    2016-11-17

    Here we study a set of novel magnetic organic molecular species with different halide ions (fluoride, chloride, bromide) absorbed ∼2 Å above or below the center of an aromatic π-ring in an m-aminyl diradical. Focus is on the nature of anion-π interaction and its impact on magnetic properties, specifically on magnetic anisotropy and on intramolecular magnetic exchange coupling. In the development of single molecule magnets, magnetic anisotropy is considered to be the most influential factor. A new insight regarding the magnetic anisotropy that determines the barrier height for relaxation of magnetization of m-aminyl diradical-derived anionic complexes is obtained from calculations of the axial zero-field-splitting (ZFS) parameter D. The noncovalent anion-π interaction strongly influences magnetic anisotropy in m-aminyl-halide diradical complexes. In particular, the change of D values from positive (for the m-aminyl diradical, m-aminyl diradical/fluoride, and m-aminyl diradical/chloride complexes) to negative D-values in m-aminyl diradical complexes containing bromide signals a change from oblate to prolate type of spin-density distribution. Furthermore, the noncovalent halide-π interactions lead to large values of intramolecular magnetic exchange coupling coefficients J exhibiting a ferromagnetic sign. The magnitude of J steadily increases going from anionic complexes containing fluoride to chloride and then to bromide. Relations are sought between the magnetic exchange coupling coefficients J and aromaticity, namely structural HOMA (harmonic oscillator model of aromaticity) and magnetic NICS (nucleus independent chemical shift) aromaticity indices, in particular, the NICSzz(+1) component. Finally, possible numerical checks on the conditions relating to validity of the well-known Yamaguchi's formula for calculating the exchange coupling coefficient J in diradical systems are discussed.

  20. Investigation of the antioxidant and radical scavenging activities of some phenolic Schiff bases with different free radicals.

    Science.gov (United States)

    Marković, Zoran; Đorović, Jelena; Petrović, Zorica D; Petrović, Vladimir P; Simijonović, Dušica

    2015-11-01

    The antioxidant properties of some phenolic Schiff bases in the presence of different reactive particles such as (•)OH, (•)OOH, (CH2=CH-O-O(•)), and (-•)O2 were investigated. The thermodynamic values, ΔH BDE, ΔH IP, and ΔH PA, were used for this purpose. Three possible mechanisms for transfer of hydrogen atom, concerted proton-electron transfer (CPET), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) were considered. These mechanisms were tested in solvents of different polarity. On the basis of the obtained results it was shown that SET-PT antioxidant mechanism can be the dominant mechanism when Schiff bases react with radical cation, while SPLET and CPET are competitive mechanisms for radical scavenging of hydroxy radical in all solvents under investigation. Examined Schiff bases react with the peroxy radicals via SPLET mechanism in polar and nonpolar solvents. The superoxide radical anion reacts with these Schiff bases very slowly.

  1. Stable radical content and anti-radical activity of roasted Arabica coffee: from in-tact bean to coffee brew.

    Science.gov (United States)

    Troup, Gordon J; Navarini, Luciano; Suggi Liverani, Furio; Drew, Simon C

    2015-01-01

    The roasting of coffee beans generates stable radicals within melanoidins produced by non-enzymatic browning. Roasting coffee beans has further been suggested to increase the antioxidant (AO) capacity of coffee brews. Herein, we have characterized the radical content and AO capacity of brews prepared from Coffea arabica beans sourced directly from an industrial roasting plant. In-tact beans exhibited electron paramagnetic resonance signals arising from Fe3+, Mn2+ and at least three distinct stable radicals as a function of roasting time, whose intensity changed upon grinding and ageing. In coffee brews, the roasting-induced radicals were harboured within the high molecular weight (> 3 kD) melanoidin-containing fraction at a concentration of 15 nM and was associated with aromatic groups within the melanoidins. The low molecular weight (brew. While other non-AO functions of the roasting-induced radical and metal complexes may be possible in vivo, we confirm that the in vitro antiradical activity of brewed coffee is dominated by low molecular weight phenolic compounds.

  2. Probability and radical behaviorism

    Science.gov (United States)

    Espinosa, James M.

    1992-01-01

    The concept of probability appears to be very important in the radical behaviorism of Skinner. Yet, it seems that this probability has not been accurately defined and is still ambiguous. I give a strict, relative frequency interpretation of probability and its applicability to the data from the science of behavior as supplied by cumulative records. Two examples of stochastic processes are given that may model the data from cumulative records that result under conditions of continuous reinforcement and extinction, respectively. PMID:22478114

  3. Probability and radical behaviorism

    OpenAIRE

    Espinosa, James M.

    1992-01-01

    The concept of probability appears to be very important in the radical behaviorism of Skinner. Yet, it seems that this probability has not been accurately defined and is still ambiguous. I give a strict, relative frequency interpretation of probability and its applicability to the data from the science of behavior as supplied by cumulative records. Two examples of stochastic processes are given that may model the data from cumulative records that result under conditions of continuous reinforc...

  4. Radical chic, javisst!

    NARCIS (Netherlands)

    Hartle, J.F.

    2012-01-01

    Det är lätt att raljera över engagerade människor, i synnerhet när engagemanget framstår som ytligt och chict snarare än grundläggande och autentiskt. Men vad ligger bakom ett sådant avfärdande? Johan Frederik Hartle läser om Tom Wolfes klassiska essä "Radical Chic" och visar hur Wolfe −− genom att

  5. Women and radicalization

    OpenAIRE

    Badran, Margot

    2006-01-01

    The paper focuses on women and radicalization within the context of Muslim societies (majority, minority, and half Muslim) societies and groups, mainly in Asia and Africa. The basic argument advanced in this paper is that Islamic feminism with its gender-egalitarian discourse and practices has a major role to play in the empowerment of Muslim women—and of men and society as a whole—and should be brought to bear in devising policy, strategy, and tools.

  6. Radical substitution with azide

    DEFF Research Database (Denmark)

    Pedersen, Christian Marcus; Marinescu, Lavinia Georgeta; Bols, Mikael

    2005-01-01

    and the substrate. A primary deuterium kinetic isotope effect was found for the azidonation of benzyl ethers both with TMSN3-PhI(OAc)2 and with IN3. Also a Hammett free energy relationship study of this reaction showed good correlation with sigma+ constants giving with rho-values of -0.47 for TMSN3-PhI(OAc)2 and -0.......39 for IN3. On this basis a radical mechanism of the reaction was proposed....

  7. [Radical prostatectomy - pro robotic].

    Science.gov (United States)

    Gillitzer, R

    2012-05-01

    Anatomical radical prostatectomy was introduced in the early 1980s by Walsh and Donker. Elucidation of key anatomical structures led to a significant reduction in the morbidity of this procedure. The strive to achieve similar oncological and functional results to this gold standard open procedure but with further reduction of morbidity through a minimally invasive access led to the establishment of laparoscopic prostatectomy. However, this procedure is complex and difficult and is associated with a long learning curve. The technical advantages of robotically assisted surgery coupled with the intuitive handling of the device led to increased precision and shortening of the learning curve. These main advantages, together with a massive internet presence and aggressive marketing, have resulted in a rapid dissemination of robotic radical prostatectomy and an increasing patient demand. However, superiority of robotic radical prostatectomy in comparison to the other surgical therapeutic options has not yet been proven on a scientific basis. Currently robotic-assisted surgery is an established technique and future technical improvements will certainly further define its role in urological surgery. In the end this technical innovation will have to be balanced against the very high purchase and running costs, which remain the main limitation of this technology.

  8. Ursodeoxycholic acid and superoxide anion

    Institute of Scientific and Technical Information of China (English)

    Predrag Ljubuncic; Omar Abu-Salach; Arieh Bomzon

    2005-01-01

    AIM: To investigate the ability of ursodeoxycholic acid (UDCA) to scavenge superoxide anion (O2-).METHODS: We assessed the ability of UDCA to scavenge (O2-) generated by xanthine-xanthine oxidase (X-XO) in a cell-free system and its effect on the rate of O2--induced ascorbic acid (AA) oxidation in hepatic post-mitochondrial supernatants.RESULTS: UDCA at a concentration as high as 1 mmol/Ldid not impair the ability of the X-XO system to generate O2-, but could scavenge O2- at concentrations of 0.5 and 1 mmol/L, and decrease the rate of AA oxidation at a concentration of 100 μmol/L.CONCLUSION: UDCA can scavenge O2-, an action that may be beneficial to patients with primary biliary cirrhosis.

  9. Bosentan, a mixed endothelin receptor antagonist, inhibits superoxide anion-induced pain and inflammation in mice.

    Science.gov (United States)

    Serafim, Karla G G; Navarro, Suelen A; Zarpelon, Ana C; Pinho-Ribeiro, Felipe A; Fattori, Victor; Cunha, Thiago M; Alves-Filho, Jose C; Cunha, Fernando Q; Casagrande, Rubia; Verri, Waldiceu A

    2015-11-01

    Bosentan is a mixed endothelin receptor antagonist widely used to treat patients with pulmonary arterial hypertension, and the emerging literature suggests bosentan as a potent anti-inflammatory drug. Superoxide anion is produced in large amounts during inflammation, stimulates cytokine production, and thus contributes to inflammation and pain. However, it remains to be determined whether endothelin contributes to the inflammatory response triggered by the superoxide anion. The present study investigated the effects of bosentan in a mouse model of inflammation and pain induced by potassium superoxide, a superoxide anion donor. Male Swiss mice were treated with bosentan (10-100 mg/kg) by oral gavage, 1 h before potassium superoxide injection, and the inflammatory response was evaluated locally and at spinal cord (L4-L6) levels. Bosentan (100 mg/kg) inhibited superoxide anion-induced mechanical and thermal hyperalgesia, overt pain-like behavior (abdominal writhings, paw flinching, and licking), paw edema, myeloperoxidase activity (neutrophil marker) in the paw skin, and leukocyte recruitment in the peritoneal cavity. Bosentan also inhibited superoxide anion-induced interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) production, while it enhanced IL-10 production in the paw skin and spinal cord. Bosentan inhibited the reduction of antioxidant capacity (reduced glutathione, ferric reducing antioxidant power, and ABTS radical scavenging ability) induced by the superoxide anion. Finally, we demonstrated that intraplantar injection of potassium superoxide induces the mRNA expression of prepro-endothelin-1 in the paw skin and spinal cord. In conclusion, our results demonstrated that superoxide anion-induced inflammation, pain, cytokine production, and oxidative stress depend on endothelin; therefore, these responses are amenable to bosentan treatment.

  10. Reactions of substituted benzene anions with N and O atoms: Chemistry in Titan's upper atmosphere and the interstellar medium

    Science.gov (United States)

    Wang, Zhe-Chen; Bierbaum, Veronica M.

    2016-06-01

    The likely existence of aromatic anions in many important extraterrestrial environments, from the atmosphere of Titan to the interstellar medium (ISM), is attracting increasing attention. Nitrogen and oxygen atoms are also widely observed in the ISM and in the ionospheres of planets and moons. In the current work, we extend previous studies to explore the reactivity of prototypical aromatic anions (deprotonated toluene, aniline, and phenol) with N and O atoms both experimentally and computationally. The benzyl and anilinide anions both exhibit slow associative electron detachment (AED) processes with N atom, and moderate reactivity with O atom in which AED dominates but ionic products are also formed. The reactivity of phenoxide is dramatically different; there is no measurable reaction with N atom, and the moderate reactivity with O atom produces almost exclusively ionic products. The reaction mechanisms are studied theoretically by employing density functional theory calculations, and spin conversion is found to be critical for understanding some product distributions. This work provides insight into the rich gas-phase chemistry of aromatic ion-atom reactions and their relevance to ionospheric and interstellar chemistry.

  11. Preparation a new sorbent based on polymeric ionic liquid for stir cake sorptive extraction of organic compounds and inorganic anions.

    Science.gov (United States)

    Huang, Xiaojia; Wang, Yulei; Hong, Qiuyun; Liu, Yi; Yuan, Dongxing

    2013-11-01

    A new multi-interaction sorbent (MIS) based on polymeric ionic liquid was prepared and used as extractive medium of stir cake sorptive extraction (SCSE). In the presence of dimethyl sulfoxide, an ionic liquid, 1-vinylbenzyl-3-methylimidazolium chloride was used as monomer to copolymerize in situ with divinylbenzene to form the MIS. The influences of the content of monomer and the porogen solvent in the polymerization mixture on the extraction performance were investigated thoroughly. The MIS was characterized by infrared spectroscopy, elemental analysis, scanning electron microscopy and mercury intrusion porosimetry. Parabens and aromatic amines were used to investigate the extraction performance of MIS-SCSE for apolar and strongly polar analytes, respectively. The extraction parameters for parabens and aromatic amines were optimized. At the same time, simple and sensitive analytical methods for parabens and aromatic amines in real samples were developed by the combination of MIS-SCSE and HPLC/DAD. Some inorganic anions, such as F(-), Br(-), NO3(-), PO4(3-) and SO4(2-), were used to test the extraction performance of MIS-SCSE for anions. Results indicated that mechanism involved in the extraction of MIS is the multi-interaction modes including π-π, hydrophobic, hydrogen-bonding, dipole-dipole and anion-exchange interactions.

  12. Effect of counter ions of arginine as an additive for the solubilization of protein and aromatic compounds.

    Science.gov (United States)

    Yoshizawa, Shunsuke; Arakawa, Tsutomu; Shiraki, Kentaro

    2016-10-01

    Arginine is widely used in biotechnological application, but mostly with chloride counter ion. Here, we examined the effects of various anions on solubilization of aromatic compounds and reduced lysozyme and on refolding of the lysozyme. All arginine salts tested increased the solubility of propyl gallate with acetate much more effectively than chloride. The effects of arginine salts were compared with those of sodium or guanidine salts, indicating that the ability of anions to modulate the propyl gallate solubility is independent of the cation. Comparison of transfer free energy of propyl gallate between sodium and arginine salts indicates that the interaction of propyl gallate is more favorable with arginine than sodium. On the contrary, the solubility of aromatic amino acids is only slightly modulated by anions, implying that there is specific interaction between acetic acid and propyl gallate. Unlike their effects on the solubility of small aromatic compounds, the solubility of reduced lysozyme was much higher in arginine chloride than in arginine acetate or sulfate. Consistent with high solubility, refolding of reduced lysozyme was most effective in arginine chloride. These results suggest potential broader applications of arginine modulated by different anions.

  13. Vibrational Spectroscopy of Microhydrated Conjugate Base Anions

    NARCIS (Netherlands)

    Asmis, K. R.; Neumark, D. M.

    2012-01-01

    Conjugate-base anions are ubiquitous in aqueous solution. Understanding the hydration of these anions at the molecular level represents a long-standing goal in chemistry. A molecular-level perspective on ion hydration is also important for understanding the surface speciation and reactivity of aeros

  14. Bacterial degradation of monocyclic aromatic amines

    Directory of Open Access Journals (Sweden)

    Pankaj Kumar Arora

    2015-08-01

    Full Text Available Aromatic amines are an important group of industrial chemicals, which are widely used for manufacturing of dyes, pesticides, drugs, pigments, and other industrial products. These compounds have been considered highly toxic to human beings due to their carcinogenic nature. Three groups of aromatic amines have been recognized: monocyclic, polycyclic and heterocyclic aromatic amines. Bacterial degradation of several monocyclic aromatic compounds has been studied in a variety of bacteria, which utilizes monocyclic aromatic amines as their sole source of carbon and energy. Several degradation pathways have been proposed and the related enzymes and genes have also been characterized. Many reviews have been reviewed toxicity of monocyclic aromatic amines; however, there is lack of review on biodegradation of monocyclic aromatic amines. The aim of this review is to summarize bacterial degradation of monocyclic aromatic amines. This review will increase our current understanding of biochemical and molecular basis of bacterial degradation of monocyclic aromatic amines.

  15. Creating molecular macrocycles for anion recognition

    Directory of Open Access Journals (Sweden)

    Amar H. Flood

    2016-03-01

    Full Text Available The creation and functionality of new classes of macrocycles that are shape persistent and can bind anions is described. The genesis of triazolophane macrocycles emerges out of activity surrounding 1,2,3-triazoles made using click chemistry; and the same triazoles are responsible for anion capture. Mistakes made and lessons learnt in anion recognition provide deeper understanding that, together with theory, now provides for computer-aided receptor design. The lessons are acted upon in the creation of two new macrocycles. First, cyanostars are larger and like to capture large anions. Second is tricarb, which also favors large anions but shows a propensity to self-assemble in an orderly and stable manner, laying a foundation for future designs of hierarchical nanostructures.

  16. Anion- interactions in layered structures of salts of 5-(hydroxyimino) quinolin-8-one and related salts

    Indian Academy of Sciences (India)

    Prithiviraj Khakhlary; Jubaraj B Baruah

    2015-01-01

    Relevance of anion- interactions in chloride, bromide, nitrate and perchlorate salts of 5-(hydroxyimino)quinolin-8-one are discussed. Structures of nitrate salt of 5-aminoquinoline as well as nitrate salt of 4-hydroxyquinazoline are compared with the structure of nitrate salt of 5-(hydroxyimino)quinolin-8-one. From such a comparison, two different arrangements of nitrate ions with respect to the respective cations are discerned. Nitrate ions are sandwiched between aromatic planes of cations in nitrate salts of 5-(hydroxyimino)quinolin-8-one or 4-hydroxyquinazoline; whereas, nitrate ions are in oblique positions with respect to aromatic planes of counter cations in nitrate salt of 5-aminoquinoline. Binding constants of different nitrate salts in solution are determined by UV-visible spectroscopic titrations. Solution study shows formation of ion-pairs of these salts in solution.

  17. Impact of induced levels of specific free radicals and malondialdehyde on chicken semen quality and fertility.

    Science.gov (United States)

    Rui, Bruno R; Shibuya, Fábio Y; Kawaoku, Allison J T; Losano, João D A; Angrimani, Daniel S R; Dalmazzo, Andressa; Nichi, Marcilio; Pereira, Ricardo J G

    2017-03-01

    Over the past decades, scientists endeavored to comprehend oxidative stress in poultry spermatozoa and its relationship with fertilizing ability, lipid peroxidation (LPO), free-radical scavenging systems, and antioxidant therapy. Although considerable progress has been made, further improvement is needed in understanding how specific reactive oxygen species (ROS) and malondialdehyde (MDA, a toxic byproduct of LPO) disrupt organelles in avian spermatozoon. Hence, this study examined functional changes in chicken spermatozoa after incubation with different ROS, and their implications for the fertility. First, semen samples from 14 roosters were individually diluted and aliquoted into five equal parts: control, superoxide anion, hydrogen peroxide (H2O2), hydroxyl radicals, and MDA. After incubation with these molecules, aliquots were analyzed for motility, plasma membrane and acrosome integrity, mitochondrial activity, and LPO and DNA damage. Hydrogen peroxide was more detrimental for sperm motility than hydroxyl radicals, whereas the superoxide anion and MDA exhibited no differences compared with controls. In turn, plasma membrane and acrosome integrity, mitochondrial activity, LPO and DNA integrity rates were only affected by hydroxyl radicals. Thereafter, semen aliquots were incubated under the same conditions and used for artificial insemination. In accordance to our in vitro observations, H2O2 and hydroxyl radicals sharply reduced egg fertility, whereas superoxide anion and MDA only induced slight declines. Thus, chicken sperm function was severely impaired by H2O2 and hydroxyl radicals, but their mechanisms of action seemingly comprise different pathways. Further analysis regarding susceptibility of spermatozoon organelles to specific radicals in other poultry will help us to understand the development of interspecific differences in scavenging systems and to outline more oriented antioxidant approaches.

  18. Anion stripping as a general method to create cationic porous framework with mobile anions.

    Science.gov (United States)

    Mao, Chengyu; Kudla, Ryan A; Zuo, Fan; Zhao, Xiang; Mueller, Leonard J; Bu, Xianhui; Feng, Pingyun

    2014-05-28

    Metal-organic frameworks (MOFs) with cationic frameworks and mobile anions have many applications from sensing, anion exchange and separation, to fast ion conductivity. Despite recent progress, the vast majority of MOFs have neutral frameworks. A common mechanism for the formation of neutral frameworks is the attachment of anionic species such as F(-) or OH(-) to the framework metal sites, neutralizing an otherwise cationic scaffolding. Here, we report a general method capable of converting such neutral frameworks directly into cationic ones with concurrent generation of mobile anions. Our method is based on the differential affinity between distinct metal ions with framework anionic species. Specifically, Al(3+) is used to strip F(-) anions away from framework Cr(3+) sites, leading to cationic frameworks with mobile Cl(-) anions. The subsequent anion exchange with OH(-) further leads to a porous network with mobile OH(-) anions. New materials prepared by anion stripping can undergo ion exchange with anionic organic dyes and also exhibit much improved ionic conductivity compared to the original unmodified MOFs.

  19. Toward Molecular Magnets of Organic Origin via Anion-π Interaction Involving m-Aminyl Diradical: A Theoretical Study

    DEFF Research Database (Denmark)

    Bhattacharya, Debojit; Shil, Suranjan; Misra, Anirban;

    2016-01-01

    Here we study a set of novel magnetic organic molecular species with different halide ions (fluoride, chloride, bromide) absorbed ∼2 Å above or below the center of an aromatic π-ring in an m-aminyl diradical. Focus is on the nature of anion-π interaction and its impact on magnetic properties......, specifically on magnetic anisotropy and on intramolecular magnetic exchange coupling. In the development of single molecule magnets, magnetic anisotropy is considered to be the most influential factor. A new insight regarding the magnetic anisotropy that determines the barrier height for relaxation...... of magnetization of m-aminyl diradical-derived anionic complexes is obtained from calculations of the axial zero-field-splitting (ZFS) parameter D. The noncovalent anion-π interaction strongly influences magnetic anisotropy in m-aminyl-halide diradical complexes. In particular, the change of D values from positive...

  20. Aromatic-Aromatic Interactions in Biological System: Structure Activity Relationships

    Energy Technology Data Exchange (ETDEWEB)

    Rajagopal, Appavu; Deepa, Mohan [Molecular Biophysics Unit, Indian Institute of Sciences-Bangalore, Karnataka (India); Govindaraju, Munisamy [Bio-Spatial Technology Research Unit, Department of Environmental Biotechnology, School of Environmental Sciences, Bharathidasan University, Tiruchirappalli, Tamil Nadu (India)

    2016-02-26

    While, intramolecular hydrogen bonds have attracted the greatest attention in studies of peptide conformations, the recognition that several other weakly polar interactions may be important determinants of folded structure has been growing. Burley and Petsko provided a comprehensive overview of the importance of weakly polar interactions, in shaping protein structures. The interactions between aromatic rings, which are spatially approximate, have attracted special attention. A survey of the proximal aromatic residue pairs in proteins, allowed Burley and Petsko to suggest that, “phenyl ring centroids are separated by a preferential distance of between 4.5 and 7 Å, and dihedral angles approximately 90° are most common”.

  1. Thermodynamic stabilities of carbon-and nitrogen-centered radicals

    Institute of Scientific and Technical Information of China (English)

    程津培; 赵永昱; 还振威

    1995-01-01

    The gas-phase homolytic C-H and N-H bond dissociation energies(BDE)of the substi-tuted phenoacetonitrile families,aromatic amines,and semicarbazone derivatives were systematically investigatedor reinvestigated based on a cycle utilizing the thermodynamic quantities determined in DMSO solution.Theexperimental evidence collected in.this work dearly indicates that the radicals derived from the above familiesare of the‘Class O’type,i.e.to be stabilized by a remote electron-donating substituent but destabilized by anelectron-withdrawing substituent.

  2. Catalysis of Radical Reactions: A Radical Chemistry Perspective.

    Science.gov (United States)

    Studer, Armido; Curran, Dennis P

    2016-01-04

    The area of catalysis of radical reactions has recently flourished. Various reaction conditions have been discovered and explained in terms of catalytic cycles. These cycles rarely stand alone as unique paths from substrates to products. Instead, most radical reactions have innate chains which form products without any catalyst. How do we know if a species added in "catalytic amounts" is a catalyst, an initiator, or something else? Herein we critically address both catalyst-free and catalytic radical reactions through the lens of radical chemistry. Basic principles of kinetics and thermodynamics are used to address problems of initiation, propagation, and inhibition of radical chains. The catalysis of radical reactions differs from other areas of catalysis. Whereas efficient innate chain reactions are difficult to catalyze because individual steps are fast, both inefficient chain processes and non-chain processes afford diverse opportunities for catalysis, as illustrated with selected examples.

  3. Hydroxyl radical induced transformation of phenylurea herbicides: A theoretical study

    Science.gov (United States)

    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.

  4. Reductive Umpolung of Carbonyl Derivatives with Visible-Light Photoredox Catalysis: Direct Access to Vicinal Diamines and Amino Alcohols via α-Amino Radicals and Ketyl Radicals

    KAUST Repository

    Fava, Eleonora

    2016-05-02

    Visible-light-mediated photoredox-catalyzed aldimine-aniline and aldehyde-aniline couplings have been realized. The reductive single electron transfer (SET) umpolung of various carbonyl derivatives enabled the generation of intermediary ketyl and α-amino radical anions, which were utilized for the synthesis of unsymmetrically substituted 1,2-diamines and amino alcohols. Anilines can be coupled with aldimines or aldehydes in a visible-light-mediated photoredox-catalyzed process. Reductive single electron transfer (SET) umpolung of the carbonyl derivatives leads to the generation of intermediary ketyl and α-amino radical anions, which were used for the synthesis of unsymmetrically substituted 1,2-diamines and amino alcohols.

  5. Evidence of Reactive Aromatics As a Major Source of Peroxy Acetyl Nitrate over China

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Zhen; Wang, Yuhang; Gu, Dasa; Zhao, Chun; Huey, L. G.; Stickel, Robert; Liao, Jin; Shao, Min; Zhu, T.; Zeng, Limin; Liu, Shaw C.; Chang, Chih-Chung; Amoroso, Antonio; Costabile, Francesa

    2010-09-15

    We analyze the observations of near-surface peroxy acetyl nitrate (PAN) and its precursors in Beijing, China in August of 2007. The levels of PAN are remarkably high (up to 14 ppbv), surpassing those measured over other urban regions in recent years. Analyses employing a 1-D version of a chemical transport model (Regional chEmical and trAnsport Model, REAM) indicate that aromatic non-methane hydrocarbons (NMHCs) are the dominant (55-75%) PAN source. The major oxidation product of aromatics that produces acetyl peroxy radicals is methylglyoxal (MGLY). PAN and O3 in the observations are correlated at daytime; aromatic NMHCs appear to play an important role in O3 photochemistry. Previous NMHC measurements indicate the presence of reactive aromatics at high levels over broad polluted regions of China. Aromatics are often ignored in global and (to a lesser degree) regional 3D photochemical transport models; their emissions over China as well as photochemistry are quite uncertain.Our findings suggest that critical assessments of aromatics emissions and chemistry (such as the yields of MGLY) are necessary to understand and assess ozone photochemistry and regional pollution export in China.

  6. Gnosticism and Radical Feminism

    DEFF Research Database (Denmark)

    Cahana, Jonathan

    2016-01-01

    and place demand an explanation; my attempt to do so also takes into account the important differences between the gnostic and the radical feminist postures, notably the latter belief in progress and the former nostalgia for an ungendered era. Both the similarities and the differences, however, may offer...... support for approaching Gnosticism as first and foremost a cultural phenomenon (albeit exhibiting religious “symptoms”), and I attempt to show that such an approach can help to solve the recurrent problem of defining Gnosticism....

  7. First examples of intramolecular addition of primary amidyl radicals to olefins

    Energy Technology Data Exchange (ETDEWEB)

    Gaudreault, P.; Drouin, C.; Lessard, J. [Sherbrooke Univ., PQ (Canada). Dept. de Chimie

    2005-07-01

    This paper presents the first examples of radical cyclization involving a primary amidyl radical and a pendant olefin. Amidyl radicals have attracted interest in terms of their structure, reactivity, and ways to generate them. The intramolecular addition of an amidyl radical on a pendant olefin appears to be a powerful synthetic tool for creating nitrogen-containing heterocycles. Although several examples of cyclization involving secondary amidyl radicals are cited in the the literature, there are no examples of a successful cyclization involving a primary amidyl radical. This is because all attempts to prepare the usual radical precursors have failed when applied to olefinic primary amides. This study reveals that N-(phenylthio) derivatives of olefinic primary amides can be easily prepared and that nitrogen heterocycles resulting from their radical cyclization can be obtained in good to very good yields. Four olefinic primary amides were chosen as models for radical cyclization of primary amidyl radicals. They were prepared from the corresponding carboxylic acids via the acid chlorides. Conversion of primary amides into suitable amidyl radical precursors was also examined. The study showed that N-(phenylthio) amides could be easily prepared by following a slightly modified protocol developed by Esker and Newcomb, by reacting the anion of the amide with phenylsulfenyl chloride. In particular, olefinic N-(phenylthio) amides were prepared and used as primary amidyl radical precursors in a reaction with a solution of 2,2'-azobis(isobutyronitrile) in catalytic quantities and tributyltin hydride in benzene. The resulting yields of cyclic products ranged from 63 to 85 per cent. The intent of the study was to demonstrate that it is no longer necessary to prepare an N-protected precursor and then remove the protecting group after cyclization. Further studies are currently underway. 10 refs., 1 tab.

  8. Anion conductance selectivity mechanism of the CFTR chloride channel.

    Science.gov (United States)

    Linsdell, Paul

    2016-04-01

    All ion channels are able to discriminate between substrate ions to some extent, a process that involves specific interactions between permeant anions and the so-called selectivity filter within the channel pore. In the cystic fibrosis transmembrane conductance regulator (CFTR) anion-selective channel, both anion relative permeability and anion relative conductance are dependent on anion free energy of hydration--anions that are relatively easily dehydrated tend to show both high permeability and low conductance. In the present work, patch clamp recording was used to investigate the relative conductance of different anions in CFTR, and the effect of mutations within the channel pore. In constitutively-active E1371Q-CFTR channels, the anion conductance sequence was Cl(-) > NO3(-) > Br(-) > formate > SCN(-) > I(-). A mutation that disrupts anion binding in the inner vestibule of the pore (K95Q) disrupted anion conductance selectivity, such that anions with different permeabilities showed almost indistinguishable conductances. Conversely, a mutation at the putative narrowest pore region that is known to disrupt anion permeability selectivity (F337A) had minimal effects on anion relative conductance. Ion competition experiments confirmed that relatively tight binding of permeant anions resulted in relatively low conductance. These results suggest that the relative affinity of ion binding in the inner vestibule of the pore controls the relative conductance of different permeant anions in CFTR, and that the pore has two physically distinct anion selectivity filters that act in series to control anion conductance selectivity and anion permeability selectivity respectively.

  9. Bursectomy at radical gastrectomy

    Institute of Scientific and Technical Information of China (English)

    Cuneyt; Kayaalp

    2015-01-01

    Radical gastrectomy with extended lymph node dissec tion and prophylactic resection of the omentum, peri toneum over the posterior lesser sac, pancreas and/o spleen was advocated at the beginning of the 1960 s in Japan. In time, prophylactic routine resections of the pancreas and/or spleen were abandoned because of the high incidence of postoperative complications. However omentectomy and bursectomy continued to be standard parts of traditional radical gastrectomy. The bursaomentalis was thought to be a natural barrier against invasion of cancer cells into the posterior part of the stomach. The theoretical rationale for bursectomy was to reduce the risk of peritoneal recurrences by eliminating the peritoneum over the lesser sac, which might include free cancer cells or micrometastases. Over time, the indication for bursectomy was gradually reduced to only patients with posterior gastric wall tumors penetrating the serosa. Despite its theoretical advantages, its benefit for recurrence or survival has not been proven yet. The possible reasons for this inconsistency are discussed in this review. In conclusion, the value of bursectomy in the treatment of gastric cancer is still under debate and large-scale randomized studies are necessary. Until clear evidence of patient benefit is obtained, its routine use cannot be recommended.

  10. Radically innovative steelmaking technologies

    Science.gov (United States)

    Szekely, Julian

    1980-09-01

    The steel industry is faced with serious problems caused by the increasing cost of energy, labor and capital and by tough overseas competition, employing new highly efficient process plants. The very high cost of capital and of capital equipment renders the construction of new green field site plants, exemplifying the best available technology economically unattractive. For this reason, over the long term the development radically innovative steelmaking technologies appears to be the only satisfactory resolution of this dilemma. The purpose of this article is to present a critical review of some of the radically innovative steelmaking technologies that have been proposed during the past few years and to develop the argument that these indeed do deserve serious consideration at the present time. It should be stressed, however, that these innovative technologies can be implemented only as part of a carefully conceived long range plan, which contains as a subset short term solutions, such as trigger prices improved investment credits, and so forth and intermediate term solutions, such as more extensive use of continuous casting, external desulfurization and selective modernization in general.

  11. Nanostructured cobalt phosphates as excellent biomimetic enzymes to sensitively detect superoxide anions released from living cells.

    Science.gov (United States)

    Wang, Min-Qiang; Ye, Cui; Bao, Shu-Juan; Xu, Mao-Wen; Zhang, Yan; Wang, Ling; Ma, Xiao-Qing; Guo, Jun; Li, Chang-Ming

    2017-01-15

    Monitoring superoxide anion radicals in living cells has been attracting much academic and industrial interest due to the dual roles of the radicals. Herein, we synthesized a novel nanostructured cobalt phosphate nanorods (Co3(PO4)2 NRs) with tunable pore structure using a simple and effective micro-emulsion method and explored their potential utilization in the electrochemical sensing of superoxide anions. As an analytical and sensing platform, the nanoscale biomimetic enzymes Co3(PO4)2 NRs exhibited excellent selectivity and sensitivity towards superoxide anion (O2(•-)) with a low detection limit (2.25nM), wide linear range (5.76-5396nM), and long-term stability. Further, the nanoscale biomimetic enzyme could be efficiently applied in situ to electrochemically detect O2(•-) released from human malignant melanoma cells and normal keratinocyte, showing excellent real time quantitative detection capability. This material open up exciting opportunities for implementing biomimetic enzymes in nanoscale transition metal phosphates and designing enzyme-free biosensors with much higher sensitivity and durability in health and disease analysis than those of natural one.

  12. Study of ionic equilibria of indotricarbocyanines in aromatic hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Dyadyusha, G.G.; Ishchenko, A.A.; Derevyanko, N.A.; Tolmachev, A.I.

    1982-05-01

    Study of the equilibria in nonpolar solvents is very complicated by the poor solubility of the salt-like dyes. Indotricarbocyanines I and II were found to be fairly soluble in aromatic hydrocarbons for solving these problems by means of electronic spectra. In the present work, their absorption spectra were studied in benzene, toluene, and m-xylene (the absorption spectra were measured on the SF-8 spectrophotometer). It was shown that the dyes studied in these solvents have spectral bands of unusual form of polymethine dyes. At the long wave edge of the spectra of indotricarbocyanines, a distinct band appears, whose intensity is very dependent on the nature of the anion. In the case of perchlorate I, it has a lower intensity, and in the case of iodide II, the intensity is higher.

  13. Aromaticity of group 14 organometallics: experimental aspects.

    Science.gov (United States)

    Lee, Vladimir Ya; Sekiguchi, Akira

    2007-01-01

    The long story of aromatic compounds has extended over almost two centuries, since the discovery by Faraday of "bicarburet of hydrogen", or C(6)H(6), now called benzene. Since then, the chemistry of aromatic compounds has been developed extensively; this is reflected in the synthesis of novel classes of aromatic derivatives including charged species, nonclassical (Möbius, three-dimensional, homo-, metalla-) aromatics, and fullerenes. The theory of aromaticity has also undergone a spectacular evolution since the first definition of aromaticity by Hückel; the classification of aromaticity now requires the consideration of versatile criteria: energetic, structural, magnetic, among others. In this Review, we discuss the current state of affairs in the chemistry of aromatic compounds of the heavier Group 14 elements, the latest experimental achievements, as well as future prospects in the field.

  14. Histidine-containing radicals in the gas phase.

    Science.gov (United States)

    Turecek, Frantisek; Yao, Chunxiang; Fung, Y M Eva; Hayakawa, Shigeo; Hashimoto, Mami; Matsubara, Hiroshi

    2009-05-21

    Radicals containing the histidine residue have been generated in the gas phase by femtosecond electron transfer to protonated histidine-N-methylamide (1H+), Nalpha-acetylhistidine-N-methylamide (2H+), Nalpha-glycylhistidine (3H+), and Nalpha-histidylglycine (4H+). Radicals generated by collisional electron transfer from dimethyldisulfide to ions 1H+ and 2H+ at 7 keV collision energies were found to dissociate completely on the microsecond time scale, as probed by reionization to cations. The main dissociations produced fragments from the imidazole side chain and the cleavage of the C(alpha)CO bond, whereas products of NCalpha bond cleavage were not observed. Electron transfer from gaseous potassium atoms to ions 3H+ and 4H+ at 2.97 keV collision energies not only caused backbone NCalpha bond dissociations but also furnished fractions of stable radicals that were detected after conversion to anions. Ion structures, ion-electron recombination energies, radical structures, electron affinities, and dissociation and transition-state energies were obtained by combined density functional theory and Møller-Plesset perturbational calculations (B3-PMP2) and basis sets ranging from 6-311+G(2d,p) to aug-cc-pVTZ. The Rice-Ramsperger-Kassel-Marcus theory was used to calculate rate constants on the B3-PMP2 potential energy surfaces to aid interpretation of the mass spectrometric data. The stability of Nalpha-histidylglycine-derived radicals is attributed to an exothermic isomerization in the imidazole ring, which is internally catalyzed by reversible proton transfer from the carboxyl group. The isomerization depends on the steric accessibility of the histidine side chain and the carboxyl group and involves a novel cation radical-COO salt-bridge intermediate.

  15. Thermal Decomposition of C7H7 Radicals; Benzyl, Tropyl, and Norbornadienyl

    Science.gov (United States)

    Buckingham, Grant; Ellison, Barney; Daily, John W.; Ahmed, Musahid

    2015-06-01

    Benzyl radical (C6H5CH2) and two other C7H7 radicals are commonly encountered in the combustion of substituted aromatic compounds found in biofuels and gasoline. High temperature pyrolysis of benzyl radical requires isomerization to other C7H7 radicals that may include cycloheptatrienyl (tropyl) radical (cyc-C7H7) and norbornadienyl radical. The thermal decomposition of all three radicals has now been investigated using a micro-reactor that heats dilute gas-phase samples up to 1600 K and has a residence time of about 100 μ-sec. The pyrolysis products exit the reactor into a supersonic expansion and are detected using synchrotron-based photoionization mass spectrometry and matrix-isolation IR spectroscopy. The products of the pyrolysis of benzyl radical (C6H5CH2) along with three isotopomers (C6H513CH2, C6D5CH2, and C6H5CD2) were detected and identified. The distribution of 13C atoms and D atoms indicate that multiple different decomposition pathways are active. Buckingham, G. T., Ormond, T. K., Porterfield, J. P., Hemberger, P., Kostko, O., Ahmed, M., Robichaud, D. J., Nimlos, M. R., Daily, J. W., Ellison, G. B. 2015, Journal of Chemical Physics 142 044307

  16. Interaction between fulvic acids of different origins and active oxygen radicals

    Institute of Scientific and Technical Information of China (English)

    王春霞; 王子健; 彭安; 侯京武; 忻文娟

    1996-01-01

    Using the spin trapping technique, the interaction between fulvic acids (FAs) of different origins and the active oxygen radicals was studied. The active oxygen radicals under study included superoxide anion (O2 · -) produced by xanthine oxidase (XOD) and stimulated polymorphonuclear leukocytes (PMN) of human being and hydroxyl radical ( ·OH) produced from Fenton’s reaction. It has been found that the FAs from both Kaschin-Beck disease (KBD) region and non-KBD region can accelerate the production of ·OH and scavenge O2 ·- . FA from peat can scavenge both O2·- and ·OH. The results show that the behavior of KBD and non-KBD FAs differs clearly from peat FA. It has been concluded that the superoxidation damage of KBD induced by FA is mainly due to hydroxyl radical reaction initiated in biological system.

  17. THE EFFECTS OF S-3-1 ON LIPID PEROXIDATION AND SCAVENGING FREE RADICALS IN VITRO

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    S-3-1 is a simplified synthetic analogue of the active principle of Salvia miltiorrhioza. Electron spin resonance spectrometry using 5,5′-dimethyl-1-pyrroline-N-oxide as a scavenger of free radicals indicated that 200 μg/ml of S-3-1 scavenged 1,1-diphenyl-2-picrylhydrazyl radicals completely. 25μg/ml of this compound quenched 100% of superoxide anion and a concentration of 250 μg/ml of S-3-1 quenched 63% of hydroxyl radicals. It was also shown that 3.56 mg/ml of S-3-1 could inhibit lipid peroxidation in microsome fraction from rat liver induced by FeSO4 and cysteine. These results show that S-3-1 is an effective antioxidant by scavenging free radicals.

  18. Reactivity and acid-base behavior of ring-methoxylated arylalkanoic acid radical cations and radical zwitterions in aqueous solution. Influence of structural effects and pH on the benzylic C-H deprotonation pathway.

    Science.gov (United States)

    Bietti, Massimo; Capone, Alberto

    2006-07-07

    A product and time-resolved kinetic study of the one-electron oxidation of ring-methoxylated phenylpropanoic and phenylbutanoic acids (Ar(CH2)nCO2H, n = 2, 3) has been carried out at different pH values. Oxidation leads to the formation of aromatic radical cations (Ar.+(CH2)nCO2H) or radical zwitterions (Ar.+(CH2)nCO2-) depending on pH, and pKa values for the corresponding acid-base equilibria have been measured. In the radical cation, the acidity of the carboxylic proton decreases by increasing the number of methoxy ring substituents and by increasing the distance between the carboxylic group and the aromatic ring. At pH 1.7 or 6.7, the radical cations or radical zwitterions undergo benzylic C-H deprotonation as the exclusive side-chain fragmentation pathway, as clearly shown by product analysis results. At pH 1.7, the first-order deprotonation rate constants measured for the ring-methoxylated arylalkanoic acid radical cations are similar to those measured previously in acidic aqueous solution for the alpha-C-H deprotonation of structurally related ring-methoxylated alkylaromatic radical cations. In basic solution, the second-order rate constants for reaction of the radical zwitterions with (-)OH (k-OH)) have been obtained. These values are similar to those obtained previously for the (-)OH-induced alpha-C-H deprotonation of structurally related ring-methoxylated alkylaromatic radical cations, indicating that under these conditions the radical zwitterions undergo benzylic C-H deprotonation. Very interestingly, with 3,4-dimethoxyphenylethanoic acid radical zwitterion, that was previously observed to undergo exclusive decarboxylation up to pH 10, competition between decarboxylation and benzylic C-H deprotonation is observed above pH 11.

  19. Synthesis of 1-Bromo-3-methoxy-4-propoxy-5-iodobenzene-A Novel Efficient Process for the Synthesis of Brominated Aromatic Compound

    Institute of Scientific and Technical Information of China (English)

    Hong Xin SHI; Hui LIN; Gérard MANDVILLE

    2004-01-01

    The reaction of aromatic carboxylic acid with oxalyl chloride gives rise to the corres- ponding acid chloride which without purification is treated with the sodium salt of mercapto- pyridine oxide in the presence of 2,2-azo-bisisobutyronitrile (AIBN), radical initiator to give a brominated aromatic compound. After etherification and oxidation, 5-iodovaniline was converted to trisubstituted benzene carboxylic acid which give 1-bromo-3-methoxy-4-propoxy-5-iodo- benzene by this new brominating process with a yield of 74 %.

  20. Effects of common inorganic anions on the rates of photocatalytic degradation of sodium dodecylbenzenesulfonate over illuminated titanium dioxide

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Experiments were carried out to study the effects of several anions on the photocatalytic degradation rates of sodium dodecylbenzene sulphonate (DBS) with TiO2 as catalyst. The anions were added as Na2 SO4, NaNO3, NaCl, NaHCO3, NaH2 PO4 and Na3 PO4, and two levels of anion content, i.e. 12 mmol/L and 36 mmol/L in terms of Na+ , were studied. The results revealed that: Cl , SO24- , NO-3 and HCO3-retarded the rates of DBS degradation to different degrees; PO43 - increased the DBS degradation rate at low concentration and decreased the rate at high concentration; H2PO-4 accelerated the rate of DBS degradation. The mechanism of the effects of anions on DBS degradation was concluded as the following three aspects: anions compete for the radicals; anions are absorbed on the surface of catalyst and block the active site catalyst.

  1. Anion conductance of the human red cell is carried by a maxi-anion channel

    DEFF Research Database (Denmark)

    Glogowska, Edyta; Dyrda, Agnieszka; Cueff, Anne

    2010-01-01

    Historically, the anion transport through the human red cell membrane has been perceived to be mediated by Band 3, in the two-component concept with the large electroneutral anion exchange accompanied by the conductance proper, which dominated the total membrane conductance. The status of anion...... that the diversity of anionic channel activities recorded in human erythrocytes corresponds to different kinetic modalities of a unique type of maxi-anion channel with multiple conductance levels and probably multiple gating properties and pharmacology, depending on conditions. It demonstrates the role of activator...... played by serum in the recruitment of multiple new conductance levels showing very complex kinetics and gating properties upon serum addition. These channels, which seem to be dormant under normal physiological conditions, are potentially activable and could confer a far higher anion conductance...

  2. Gas-Phase Reactivity of Microsolvated Anions

    DEFF Research Database (Denmark)

    Thomsen, Ditte Linde

    intrinsic factors and solvent effects is the enhanced reactivity of α-nucleophiles – nucleophiles with a lone-pair adjacent to the attacking site – referred to as the α-effect. This thesis concerns the reactivity of microsolvated anions and in particular how the presence of a single solvent molecule affects...... the gas-phase α-effect. The experimental studies are performed by means of the flowing after glow selected ion flow tube technique, and these are supplemented by electronic structure calculations. The α-nucleophile employed is the microsolvated hydrogen peroxide anion whose reactivity is compared...... to that of a series of microsolvated oxygen centered anions. The association of the nucleophiles with a single water or methanol molecule allows the α-effect to be observed in the SN2 reaction with methyl chloride; this effect was not apparent in the reactions of the unsolvated anions. The results suggest...

  3. Renal elimination of organic anions in cholestasis

    Institute of Scientific and Technical Information of China (English)

    Adriana Mónica Tortes

    2008-01-01

    The disposition of most drugs is highly dependent on specialized transporters.OAT1 and OAT3 are two organic anion transporters expressed in the basolateral membrane of renal proximal tubule cells,identified as contributors to xenobiotic and endogenous organic anion secretion.It is well known that cholestasis may cause renal damage.Impairment of kidney function produces modifications in the renal elimination of drugs.Recent studies have demonstrated that the renal abundance of OAT1 and OAT3 plays an important role in the renal elimination of organic anions in the presence of extrahepatic cholestasis.Time elapsed after obstructive cholestasis has an important impact on the regulation of both types of organic anion transporters.The renal expression of OAT1 and OAT3 should be taken into account in order to improve pharmacotherapeutic efficacy and to prevent drug toxicity during the onset of this hepatic disease.

  4. EPR study of the astaxanthin n-octanoic acid monoester and diester radicals on silica-alumina.

    Science.gov (United States)

    Focsan, A Ligia; Bowman, Michael K; Shamshina, Julia; Krzyaniak, Matthew D; Magyar, Adam; Polyakov, Nikolay E; Kispert, Lowell D

    2012-11-08

    The radical intermediates of the n-octanoic monoester and n-octanoic diester of astaxanthin were detected by pulsed EPR measurements carried out on the UV-produced radicals on silica-alumina artificial matrix and characterized by density functional theory (DFT) calculations. Previous Mims ENDOR for astaxanthin detected the radical cation and neutral radicals formed by proton loss from the C3 (or C3') position and from the methyl groups. Deprotonation of the astaxanthin neutral radical formed at the C3 (or C3') position resulted in a radical anion. DFT calculations for astaxanthin showed that the lowest energy neutral radical forms by proton loss at the C3 (or C3') position of the terminal ring followed by proton loss at the methyl groups of the polyene chain. Contrary to astaxanthin where proton loss can occur at either end of the symmetrical radical, for the diester of astaxanthin, this loss is prevented at the cyclohexene ends and is favored for its methyl groups. The monoester of astaxanthin, however, allows formation of the neutral radical at C3' and prevents its formation at the opposite end where the ester group is attached. At the terminal ring without the ester group attached, migration of proton from hydroxyl group to carbonyl group facilitates resonance stabilization, similarly to already published results for astaxanthin. However, cw EPR shows no evidence of a monoester radical anion formed. This study suggests the different radicals of astaxanthin and its esters that would form in a preferred environment, either hydrophobic or hydrophilic, depending on their structure.

  5. Dynamics of radical cations of poly(4-hydroxystyrene) in the presence and absence of triphenylsulfonium triflate as determined by pulse radiolysis of its highly concentrated solution

    Science.gov (United States)

    Okamoto, Kazumasa; Ishida, Takuya; Yamamoto, Hiroki; Kozawa, Takahiro; Fujiyoshi, Ryoko; Umegaki, Kikuo

    2016-07-01

    Pulse radiolysis of highly concentrated poly(4-hydroxystyrene) (PHS) solutions in cyclohexanone and p-dioxane was performed both with and without an onium-type photoacid generator (PAG). With increasing PHS concentration, the rate constant of deprotonation of PHS radical cations was found to decrease. In the presence of PAG, the yield of the multimer radical cation of PHS was shown to decrease. We found that pairing between the anions produced by the attachment of dissociative electrons of PAGs and the monomer PHS radical cations restrict local molecular motions, leading to the formation of the multimer PHS radical cations.

  6. pi-dimerization of pleiadiene radical cations at low temperatures revealed by UV-vis spectroelectrochemistry and quantum theory

    NARCIS (Netherlands)

    van het Goor, Layo; van Duijnen, Piet Th.; Koper, Carola; Jenneskens, Leonardus W.; Havenith, Remco W. A.; Hartl, Frantisek

    2011-01-01

    One-electron oxidation of the non-alternant polycyclic aromatic hydrocarbon pleiadiene and related cyclohepta[c,d]pyrene and cyclohepta[c,d]fluoranthene in THF produces corresponding radical cations detectable in the temperature range of 293-263 K only on the subsecond time scale of cyclic voltammet

  7. Fluorescence-lifetime-based sensors for anions

    Science.gov (United States)

    Teichmann, Maria; Draxler, Sonja; Kieslinger, Dietmar; Lippitsch, Max E.

    1997-05-01

    Sensing of anions has been investigated using the fluorescence decaytime as the information carrier. The sensing mechanism is based on the coextraction of an anion and a proton, and the presence of a fluorophore with a rather long fluorescence decaytime inside the membrane to act as a pH indicator. The relevant theory is discussed shortly. As an example a sensor for nitrate is shown, and the influence of ionic additives on the working function has been investigated.

  8. A new class of organocatalysts: sulfenate anions.

    Science.gov (United States)

    Zhang, Mengnan; Jia, Tiezheng; Yin, Haolin; Carroll, Patrick J; Schelter, Eric J; Walsh, Patrick J

    2014-09-26

    Sulfenate anions are known to act as highly reactive species in the organic arena. Now they premiere as organocatalysts. Proof of concept is offered by the sulfoxide/sulfenate-catalyzed (1-10 mol%) coupling of benzyl halides in the presence of base to generate trans-stilbenes in good to excellent yields (up to 99%). Mechanistic studies support the intermediacy of sulfenate anions, and the deprotonated sulfoxide was determined to be the resting state of the catalyst.

  9. Radicals in Berkeley?

    Science.gov (United States)

    Linn, Stuart

    2015-04-03

    In a previous autobiographical sketch for DNA Repair (Linn, S. (2012) Life in the serendipitous lane: excitement and gratification in studying DNA repair. DNA Repair 11, 595-605), I wrote about my involvement in research on mechanisms of DNA repair. In this Reflections, I look back at how I became interested in free radical chemistry and biology and outline some of our bizarre (at the time) observations. Of course, these studies could never have succeeded without the exceptional aid of my mentors: my teachers; the undergraduate and graduate students, postdoctoral fellows, and senior lab visitors in my laboratory; and my faculty and staff colleagues here at Berkeley. I am so indebted to each and every one of these individuals for their efforts to overcome my ignorance and set me on the straight and narrow path to success in research. I regret that I cannot mention and thank each of these mentors individually.

  10. Radical Chemistry and Cytotoxicity of Bioreductive 3-Substituted Quinoxaline Di-N-Oxides.

    Science.gov (United States)

    Anderson, Robert F; Yadav, Pooja; Shinde, Sujata S; Hong, Cho R; Pullen, Susan M; Reynisson, Jóhannes; Wilson, William R; Hay, Michael P

    2016-08-15

    The radical chemistry and cytotoxicity of a series of quinoxaline di-N-oxide (QDO) compounds has been investigated to explore the mechanism of action of this class of bioreductive drugs. A series of water-soluble 3-trifluoromethyl (4-10), 3-phenyl (11-19), and 3-methyl (20-21) substituted QDO compounds were designed to span a range of electron affinities consistent with bioreduction. The stoichiometry of loss of QDOs by steady-state radiolysis of anaerobic aqueous formate buffer indicated that one-electron reduction of QDOs generates radicals able to initiate chain reactions by oxidation of formate. The 3-trifluoromethyl analogues exhibited long chain reactions consistent with the release of the HO(•), as identified in EPR spin trapping experiments. Several carbon-centered radical intermediates, produced by anaerobic incubation of the QDO compounds with N-terminal truncated cytochrome P450 reductase (POR), were characterized using N-tert-butyl-α-phenylnitrone (PBN) and 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO) spin traps and were observed by EPR. Experimental data were well simulated for the production of strongly oxidizing radicals, capable of H atom abstraction from methyl groups. The kinetics of formation and decay of the radicals produced following one-electron reduction of the parent compounds, both in oxic and anoxic solutions, were determined using pulse radiolysis. Back oxidation of the initially formed radical anions by molecular oxygen did not compete effectively with the breakdown of the radical anions to form oxidizing radicals. The QDO compounds displayed low hypoxic selectivity when tested against oxic and hypoxic cancer cell lines in vitro. The results from this study form a kinetic description and explanation of the low hypoxia-selective cytotoxicity of QDOs against cancer cells compared to the related benzotriazine 1,4-dioxide (BTO) class of compounds.

  11. The Expanding Family of Natural Anion Channelrhodopsins Reveals Large Variations in Kinetics, Conductance, and Spectral Sensitivity

    Science.gov (United States)

    Govorunova, Elena G.; Sineshchekov, Oleg A.; Rodarte, Elsa M.; Janz, Roger; Morelle, Olivier; Melkonian, Michael; Wong, Gane K.-S.; Spudich, John L.

    2017-01-01

    Natural anion channelrhodopsins (ACRs) discovered in the cryptophyte alga Guillardia theta generate large hyperpolarizing currents at membrane potentials above the Nernst equilibrium potential for Cl− and thus can be used as efficient inhibitory tools for optogenetics. We have identified and characterized new ACR homologs in different cryptophyte species, showing that all of them are anion-selective, and thus expanded this protein family to 20 functionally confirmed members. Sequence comparison of natural ACRs and engineered Cl−-conducting mutants of cation channelrhodopsins (CCRs) showed radical differences in their anion selectivity filters. In particular, the Glu90 residue in channelrhodopsin 2, which needed to be mutated to a neutral or alkaline residue to confer anion selectivity to CCRs, is nevertheless conserved in all of the ACRs identified. The new ACRs showed a large variation of the amplitude, kinetics, and spectral sensitivity of their photocurrents. A notable variant, designated “ZipACR”, is particularly promising for inhibitory optogenetics because of its combination of larger current amplitudes than those of previously reported ACRs and an unprecedentedly fast conductance cycle (current half-decay time 2–4 ms depending on voltage). ZipACR expressed in cultured mouse hippocampal neurons enabled precise photoinhibition of individual spikes in trains of up to 50 Hz frequency. PMID:28256618

  12. Preparation of Anion Exchange Membrane Based on Imidazolium Functionalized Poly(arylene ether ketone)

    Institute of Scientific and Technical Information of China (English)

    ZHOU Hao; ZHANG Na; MA Wen-jia; ZHAO Cheng-ji; NA Hui

    2013-01-01

    The authors presented a novel synthetic route for the imidazolium functionalized poly(arylene ether ketone)s,derived from an engineering plastics polymer,a poly(arylene ether ketone) with 3,3',5,5'-tetramethyl-4,4'-dihydroxybiphenyl moiety(PAEK-TM).The preparation of anion exchange membranes comprised converting benzylic methyl groups to bromomethyl groups by a radical reaction,followed by the functionalization of bromomethylated PAEK with alkyl imidazoles,i.e.,methyl,butyl or vinyl imidazole.The structure of imidazolium functionalized PAEK was proved by 1H NMR spectra.A class of flexible and tough membranes was then achieved by subsequent film-forming and anion exchange processes.The water uptake and hydroxide conductivities of membranes are comparable or superior to those of quaternary ammonium(QA) anion exchange membranes.This work demonstrated a new route for non-QA anion exchange membrane design,avoiding the chloromethylation reagent and precisely controlling the degree and location of imidazolium groups.

  13. Solubilization isotherms of aromatic solutes in surfactant aggregates

    Energy Technology Data Exchange (ETDEWEB)

    Gadelle, F.; Koros, W.J.; Schechter, R.S. (Univ. of Texas, Austin, TX (United States). Dept. of Chemical Engineering)

    1995-03-01

    Several factors affecting solubilization of aromatic solutes in surfactant micelles have been investigated. Solubilization isotherms of benzene, toluene, and chlorobenzene in various aqueous micellar solutions were determined using head space gas chromatography. Cationic surfactants such as cetylpyridinium chloride or cetyltrimethylammonium bromide present high solubilization capacities. Comparable anionic surfactants exhibit lower solubilization and a greater tendency to precipitate. It was observed that nonionic surfactants show high solubilization on a molar basis. Solubilization in mixed cationic-anionic micelles was also investigated. It also appears that the molecular size of the solute determines the extent of the solubilization. Finally, the shape of the different isotherms indicates that knowing the amount solubilized at saturation of the micellar solution is not sufficient to estimate solubilization at solute concentrations lower than the solute aqueous solubility. Solubilization of organics in surfactant micelles is of major importance in many applications. One new application is micellar-enhanced ultrafiltration. Another application of interest is the surfactant-enhanced aquifer remediation, a process in which a micellar aqueous solution is flushed into contaminated groundwaters to enhance recovery of pollutants by micellar solubilization.

  14. Anion complexation with cyanobenzoyl substituted first and second generation tripodal amide receptors: crystal structure and solution studies.

    Science.gov (United States)

    Hoque, Md Najbul; Gogoi, Abhijit; Das, Gopal

    2015-09-14

    Anion complexation properties of two new tripodal amide receptors have been extensively studied here. Two tripodal receptors have been synthesized from the reaction of cyanobenzoyl acid chloride with two tri-amine building blocks such as (i) tris(2-aminoethyl)amine and (ii) tris(2-(4-aminophenoxy)ethyl)amine, which resulted in the first (L1) and second (L2) generation tripodal amides respectively. A detailed comparison of their coordination behavior with anions is also described by crystallographic and solution state experiments. The crystal structure demonstrates various types of spatial orientations of tripodal arms in two receptors and concomitantly interacts with anions distinctively. Intramolecular H-bonding between amide N–H and CO prevents opening of the receptor cavity in the crystal, which leads to a locked conformation of L1 having C(3v) symmetry and makes amide hydrogen unavailable for the anion which results in side cleft anion binding. However, in L2 we conveniently shift the anion binding sites to a distant position which increases cavity size as well as rules out any intramolecular H-bonding between amide N–H and CO. The crystal structure shows a different orientation of the arms in L2; it adopts a quasi-planar arrangement with C(2v) symmetry. In the crystal structure two arms are pointed in the same direction and while extending the contact the third arm is H-bonded with the apical N-atom through a –CN group, making a pseudo capsular cavity where the anion interacts. Most importantly spatial reorientation of the receptor L2 from a C(2v) symmetry to a folded conformation with a C(3v) symmetry was observed only in the presence of an octahedral SiF6(2-) anion and forms a sandwich type complex. Receptors L1 and L2 are explored for their solution state anion binding abilities. The substantial changes in chemical shifts were observed for the amide (-NH) and aromatic hydrogen (-CH) (especially for F(-)), indicating the role of these hydrogens in

  15. Study on biodegradable aromatic/aliphatic copolyesters

    Energy Technology Data Exchange (ETDEWEB)

    Yiwang Chen; Licheng Tan; Lie Chen; Yan, Yang; Xiaofeng Wang [Nanchang University, Nanchang (China). School of Materials Science and Engineering. Inst. of Polymer Materials]. E-mail: ywchen@ncu.edu.cn

    2008-04-15

    Progress on biodegradable aromatic/aliphatic copolyesters based on aliphatic and aromatic diacids, diols and ester monomers was reviewed. The aromatic/aliphatic copolyesters combined excellent mechanical properties with biodegradability. Physical properties and biodegradability of copolyesters varied with chain length of the aliphatic polyester segment and atacticity of copolyesters. The process ability of copolyesters could be improved significantly after incorporating a stiff chain segment through copolymerization of aliphatic polyesters with an aromatic liquid crystal element. The aromatic/aliphatic copolyesters as a new type of biodegradable materials could replace some general plastics in certain applications, namely biomedical and environmental friendly fields. (author)

  16. Evaluation of the thermal effect on separation selectivity in anion-exchange processes using superheated water ion-exchange chromatography.

    Science.gov (United States)

    Shibukawa, Masami; Taguchi, Akihiko; Suzuki, Yusuke; Saitoh, Kazunori; Hiaki, Toshihiko; Yarita, Takashi

    2012-07-07

    The thermal effect on retention and separation selectivity of inorganic anions and aromatic sulfonate ions in anion-exchange chromatography is studied on a quaternized styrene-divinylbenzene copolymer anion-exchange column in the temperature range of 40-120 °C using superheated water chromatography. The selectivity coefficient for a pair of identically charged anions approaches unity as temperature increases provided the ions have the same effective size, such that the retention of an analyte ion decreases with an increase in temperature when the analyte ion has stronger affinity for the ion-exchanger than that of the eluent counterion, whereas it increases when it has weaker affinity. The change in anion-exchange selectivity with temperature observed with superheated water chromatography has been discussed on the basis of the effect of temperature on hydration of the ions. At elevated temperatures, especially in superheated water, the electrostatic interaction or association of the ions with the fixed ion in the resin phase becomes a predominant factor resulting in a different separation selectivity from that obtained at ambient temperature.

  17. Radical chic? Yes we are!

    OpenAIRE

    Hartle, J.F.

    2012-01-01

    Ever since Tom Wolfe in a classical 1970 essay coined the term "radical chic", upper-class flirtation with radical causes has been ridiculed. But by separating aesthetics from politics Wolfe was actually more reactionary than the people he criticized, writes Johan Frederik Hartle.

  18. Muoniated acyl and thioacyl radicals

    Energy Technology Data Exchange (ETDEWEB)

    McKenzie, Iain [TRIUMF and Department of Chemistry, 8888 University Drive, Simon Fraser University, Burnaby B.C., V5A 1S6 (Canada); Brodovitch, Jean-Claude [TRIUMF and Department of Chemistry, 8888 University Drive, Simon Fraser University, Burnaby B.C., V5A 1S6 (Canada); Ghandi, Khashayar [TRIUMF and Department of Chemistry, 8888 University Drive, Simon Fraser University, Burnaby B.C., V5A 1S6 (Canada); Percival, Paul W. [TRIUMF and Department of Chemistry, 8888 University Drive, Simon Fraser University, Burnaby B.C., V5A 1S6 (Canada)]. E-mail: percival@sfu.ca

    2006-03-31

    The product of the reaction of muonium with tert-butylisocyanate was previously assigned as the muoniated tert-butylaminyl radical (I. McKenzie, J.-C. Brodovitch, K. Ghandi, S. Kecman, P. W. Percival, Physica B 326 (2003) 76). This assignment is incorrect since the muon and {sup 14}N hyperfine-coupling constants (hfcc) of this radical would have the opposite sign, which is in conflict with the experimental results. The radical is now reassigned as the muoniated N-tert-butylcarbamoyl radical, based on the similarities between the experimental muon and {sup 14}N hfcc and hfcc calculated at the UB3LYP/6-311G(d,p)//UB3LYP/EPR-III level. The large zero-point energy in the N-Mu bond results in the dissociation barrier of the muoniated N-tert-butylcarbamoyl radical being above the combined energy of the reactants, in contrast to the N-tert-butylcarbamoyl radical where the dissociation barrier lies below the combined energy of the reactants. The reaction of muonium with tert-butylisothiocyanate produced both conformers of the muoniated N-tert-butylthiocarbamoyl radical and their assignment was based on the similarities between the experimental and calculated muon hfcc. These are the first acyl and thioacyl radicals to be directly detected by muon spin spectroscopy.

  19. Melatonin scavenges phenylglyoxylic ketyl radicals.

    Science.gov (United States)

    Sersen, F; Vencel, T; Annus, J

    2004-12-01

    The antioxidant properties of melatonin were tested in this work by EPR technique. It was found that melatonin scavenges phenylglyoxylic ketyl radicals. Its effectiveness was 10-times lower than that of vitamin C. A new method of generation of phenylglyoxylic ketyl radicals by spontaneous decomposition of D,L-2,3-diphenyltartaric acid in propan-2-ol was used.

  20. A Supramolecular Sensing Platform for Phosphate Anions and an Anthrax Biomarker in a Microfluidic Device

    Directory of Open Access Journals (Sweden)

    Jurriaan Huskens

    2011-10-01

    Full Text Available A supramolecular platform based on self-assembled monolayers (SAMs has been implemented in a microfluidic device. The system has been applied for the sensing of two different analyte types: biologically relevant phosphate anions and aromatic carboxylic acids, which are important for anthrax detection. A Eu(III-EDTA complex was bound to β-cyclodextrin monolayers via orthogonal supramolecular host-guest interactions. The self-assembly of the Eu(III-EDTA conjugate and naphthalene β-diketone as an antenna resulted in the formation of a highly luminescent lanthanide complex on the microchannel surface. Detection of different phosphate anions and aromatic carboxylic acids was demonstrated by monitoring the decrease in red emission following displacement of the antenna by the analyte. Among these analytes, adenosine triphosphate (ATP and pyrophosphate, as well as dipicolinic acid (DPA which is a biomarker for anthrax, showed a strong response. Parallel fabrication of five sensing SAMs in a single multichannel chip was performed, as a first demonstration of phosphate and carboxylic acid screening in a multiplexed format that allows a general detection platform for both analyte systems in a single test run with µM and nM detection sensitivity for ATP and DPA, respectively.

  1. Neutral pyrimidine C-H donor as anion receptor

    Institute of Scientific and Technical Information of China (English)

    袁迎雪; 吴娜娜; 韩逸飞; 宋相志; 王洪波

    2016-01-01

    Anion receptors including pyrimidine subunit were designed and synthesized and their binding abilities with various anions were investigated by fluorescence and 1H NMR titration experiments. DFT calculations provided some information for anion recognition. It is confirmed that both of two new pyrimidine anion receptors have the selectivity for Cl−.

  2. Anaerobic degradation of homocyclic aromatic compounds via arylcarboxyl-coenzyme A esters: organisms, strategies and key enzymes.

    Science.gov (United States)

    Boll, Matthias; Löffler, Claudia; Morris, Brandon E L; Kung, Johannes W

    2014-03-01

    Next to carbohydrates, aromatic compounds are the second most abundant class of natural organic molecules in living organic matter but also make up a significant proportion of fossil carbon sources. Only microorganisms are capable of fully mineralizing aromatic compounds. While aerobic microbes use well-studied oxygenases for the activation and cleavage of aromatic rings, anaerobic bacteria follow completely different strategies to initiate catabolism. The key enzymes related to aromatic compound degradation in anaerobic bacteria are comprised of metal- and/or flavin-containing cofactors, of which many use unprecedented radical mechanisms for C-H bond cleavage or dearomatization. Over the past decade, the increasing number of completed genomes has helped to reveal a large variety of anaerobic degradation pathways in Proteobacteria, Gram-positive microbes and in one archaeon. This review aims to update our understanding of the occurrence of aromatic degradation capabilities in anaerobic microorganisms and serves to highlight characteristic enzymatic reactions involved in (i) the anoxic oxidation of alkyl side chains attached to aromatic rings, (ii) the carboxylation of aromatic rings and (iii) the reductive dearomatization of central arylcarboxyl-coenzyme A intermediates. Depending on the redox potential of the electron acceptors used and the metabolic efficiency of the cell, different strategies may be employed for identical overall reactions.

  3. The Effect of Nitrogen-Doped ATO Nanotubes on Radical Multiplication of Buffer Media by Visible Light Photocatalysis Rather UV

    Directory of Open Access Journals (Sweden)

    Kan-Hung Hu

    2012-01-01

    Full Text Available The use of TiO2 in photodynamic therapy for the treatment of cancer has generally been studied in cultured cancer cells in serum-containing RPMI 1640 medium under visible light application rather than ultraviolet (UV light. An ordered channel array of N-doped anodic titanium dioxide (ATO has been successfully made for visible light application. ATO nanotubes in the anatase form with a length of 10 μm are more effective than nanotubes of 1.8 μm in length as a photocatalyst for radical multiplication in buffer solution by generating hydroxyl radicals and superoxide radical anions under UV-A exposure. Only the N-doped ATO is applicable to visible light photocatalysis for radical multiplication in RPMI 1640+1% FBS and acrylamide, a free radical carrier.

  4. A comparison of transition state of phenol in H-atom abstraction by methyl and methylperoxyl radicals

    Institute of Scientific and Technical Information of China (English)

    SUN YouMin; WU JunSen; LIU ChengBu

    2007-01-01

    DFT method was employed to locate transition state for H-atom transfer from phenol by methyl radical and methylperoxyl radical. The reaction pathway energy profiles and the structure of transition state show that a common feature is the out-of-plane structure of the transition state: in contrast to the energetic minima of a hydrogen-bonded intermediate, the hydrogen bond in transition structures is considerably twisted out of the aromatic ring. From the values of enthalpy (△H) and activation energy (Ea)obtained, it is found that the rate of the reaction of peroxyl radical with phenolic antioxidant is higher than that of alkyl radical with antioxidant. Spin density distributions show that the electron transmission is between methyl (methylperoxyl) radical and phenol.

  5. Studies of anions sorption on natural zeolites.

    Science.gov (United States)

    Barczyk, K; Mozgawa, W; Król, M

    2014-12-10

    This work presents results of FT-IR spectroscopic studies of anions-chromate, phosphate and arsenate - sorbed from aqueous solutions (different concentrations of anions) on zeolites. The sorption has been conducted on natural zeolites from different structural groups, i.e. chabazite, mordenite, ferrierite and clinoptilolite. The Na-forms of sorbents were exchanged with hexadecyltrimethylammonium cations (HDTMA(+)) and organo-zeolites were obtained. External cation exchange capacities (ECEC) of organo-zeolites were measured. Their values are 17mmol/100g for chabazite, 4mmol/100g for mordenite and ferrierite and 10mmol/100g for clinoptilolite. The used initial inputs of HDTMA correspond to 100% and 200% ECEC of the minerals. Organo-modificated sorbents were subsequently used for immobilization of mentioned anions. It was proven that aforementioned anions' sorption causes changes in IR spectra of the HDTMA-zeolites. These alterations are dependent on the kind of anions that were sorbed. In all cases, variations are due to bands corresponding to the characteristic Si-O(Si,Al) vibrations (occurring in alumino- and silicooxygen tetrahedra building spatial framework of zeolites). Alkylammonium surfactant vibrations have also been observed. Systematic changes in the spectra connected with the anion concentration in the initial solution have been revealed. The amounts of sorbed CrO4(2-), AsO4(3-) and PO4(3-) ions were calculated from the difference between their concentrations in solutions before (initial concentration) and after (equilibrium concentration) sorption experiments. Concentrations of anions were determined by spectrophotometric method.

  6. Thermal Decomposition of Furan Generates Propargyl Radicals

    Energy Technology Data Exchange (ETDEWEB)

    Vasiliou, A.; Nimlos, M. R.; Daily, J. W.; Ellison, G. B.

    2009-07-01

    The thermal decomposition of furan has been studied by a 1 mm x 2 cm tubular silicon carbide reactor, C{sub 4}H{sub 4}O + {Delta} {yields} products. Unlike previous studies, these experiments are able to identify the initial furan decomposition products. Furan is entrained in either He or Ar carrier gas and is passed through a heated (1600 K) SiC tubular reactor. Furan decomposes during transit through the tubular reactor (approximately 65 {micro}s) and exits to a vacuum chamber. Within one nozzle diameter of leaving the nozzle, the gases cool to less than 50 K, and all reactions cease. The resultant molecular beam is interrogated by photoionization mass spectroscopy as well as infrared spectroscopy. Earlier G2(MP2) electronic structure calculations predicted that furan will thermally decompose to acetylene, ketene, carbon monoxide, and propyne at lower temperatures. At higher temperatures, these calculations forecast that propargyl radical could result. We observe all of these species (see Scheme 1). As the pressure in the tubular reactor is raised, the photoionization mass spectra show clear evidence for the formation of aromatic hydrocarbons.

  7. Nucleophilic fluorination of aromatic compounds

    Energy Technology Data Exchange (ETDEWEB)

    Satyamurthy, Nagichettiar; Barrio, Jorge R

    2014-03-18

    Iodylbenzene derivatives substituted with electron donating as well as electron withdrawing groups on the aromatic ring are used as precursors in aromatic nucleophilic substitution reactions. The iodyl group (IO.sub.2) is regiospecifically substituted by nucleophilic fluoride to provide the corresponding fluoroaryl derivatives. No-carrier-added [F-18]fluoride ion derived from anhydrous [F-18](F/Kryptofix, [F-18]CsF or a quaternary ammonium fluoride (e.g., Me.sub.4NF, Et.sub.4NF, n-Bu.sub.4NF, (PhCH.sub.2).sub.4NF) exclusively substitutes the iodyl moiety in these derivatives and provides high specific activity F-18 labeled fluoroaryl analogs. Iodyl derivatives of a benzothiazole analog and 6-iodyl-L-dopa derivatives have been synthesized as precursors and have been used in the preparation of no-carrier-added [F-18]fluorobenzothiazole as well as 6-[F-18]fluoro-L-dopa.

  8. Alkylation of organic aromatic compounds

    Science.gov (United States)

    Smith, L.A. Jr.

    1989-07-18

    Aromatic compounds are alkylated in a catalytic distillation, wherein the catalyst structure also serves as a distillation component by contacting the aromatic compound with a C[sub 2] to C[sub 10] olefin in the catalyst bed under 0.25 to 50 atmospheres of pressure and at temperatures in the range of 80 C to 500 C, using as the catalyst a mole sieve characterized as acidic or an acidic cation exchange resin. For example, ethyl benzene is produced by feeding ethylene below the catalyst bed while benzene is conveniently added through the reflux in molar excess to that required to react with ethylene, thereby reacting substantially all of the ethylene and recovering benzene as the principal overhead and ethyl benzene in the bottoms. 1 fig.

  9. Photochemical synthesis of simple organic free radicals on simulated planetary surfaces - An ESR study

    Science.gov (United States)

    Tseng, S.-S.; Chang, S.

    1975-01-01

    Electron spin resonance (ESR) spectroscopy provided evidence for formation of hydroxyl radicals during ultraviolet photolysis (254 nm) at -170 C of H2O adsorbed on silica gel or of silica gel alone. The carboxyl radical was observed when CO or CO2 or a mixture of CO and CO2 adsorbed on silica gel at -170 C was irradiated. The ESR signals of these radicals slowly disappeared when the irradiated samples were warmed to room temperature. However, reirradiation of CO or CO2, or the mixture CO and CO2 on silica gel at room temperature then produced a new species, the carbon dioxide anion radical, which slowly decayed and was identical with that produced by direct photolysis of formic acid adsorbed on silica gel. The primary photochemical process may involve formation of hydrogen and hydroxyl radicals. Subsequent reactions of these radicals with adsorbed CO or CO2 or both yield carboxyl radicals, CO2H, the precursors of formic acid. These results confirm the formation of formic acid under simulated Martian conditions and provide a mechanistic basis for gauging the potential importance of gas-solid photochemistry for chemical evolution on other extraterrestrial bodies, on the primitive earth, and on dust grains in the interstellar medium.

  10. Antioxidative capacity and enzyme activity in Haematococcus pluvialis cells exposed to superoxide free radicals

    Institute of Scientific and Technical Information of China (English)

    刘建国; 张晓丽; 孙延红; 林伟

    2010-01-01

    The antioxidative capacity of astaxanthin and enzyme activity of reactive oxygen eliminating enzymes such as superoxide dismutase (SOD),peroxidase (POD),catalase (CAT) and ascorbate peroxidase (APX) were studied in three cell types of Haematococcus pluvialis exposed to high concentrations of a superoxide anion radical (O2ˉ).The results show that defensive enzymes and astaxanthin-related mechanisms were both active in H.pluvialis during exposure to reactive oxygen species (ROS) such as Oˉ2.Astaxanthin reacte...

  11. Development of linear free energy relationships for aqueous phase radical-involved chemical reactions.

    Science.gov (United States)

    Minakata, Daisuke; Mezyk, Stephen P; Jones, Jace W; Daws, Brittany R; Crittenden, John C

    2014-12-02

    Aqueous phase advanced oxidation processes (AOPs) produce hydroxyl radicals (HO•) which can completely oxidize electron rich organic compounds. The proper design and operation of AOPs require that we predict the formation and fate of the byproducts and their associated toxicity. Accordingly, there is a need to develop a first-principles kinetic model that can predict the dominant reaction pathways that potentially produce toxic byproducts. We have published some of our efforts on predicting the elementary reaction pathways and the HO• rate constants. Here we develop linear free energy relationships (LFERs) that predict the rate constants for aqueous phase radical reactions. The LFERs relate experimentally obtained kinetic rate constants to quantum mechanically calculated aqueous phase free energies of activation. The LFERs have been applied to 101 reactions, including (1) HO• addition to 15 aromatic compounds; (2) addition of molecular oxygen to 65 carbon-centered aliphatic and cyclohexadienyl radicals; (3) disproportionation of 10 peroxyl radicals, and (4) unimolecular decay of nine peroxyl radicals. The LFERs correlations predict the rate constants within a factor of 2 from the experimental values for HO• reactions and molecular oxygen addition, and a factor of 5 for peroxyl radical reactions. The LFERs and the elementary reaction pathways will enable us to predict the formation and initial fate of the byproducts in AOPs. Furthermore, our methodology can be applied to other environmental processes in which aqueous phase radical-involved reactions occur.

  12. STUDIES ON THE POLYMERIZATION OF ACRYLONITRILE INITIATED BY METAVANADATE- CONTAINING ANION EXCHANGER-THIOUREA REDOX SYSTEM

    Institute of Scientific and Technical Information of China (English)

    YANG Chaoxiong; WU Jinyuan; WU Yuxian

    1991-01-01

    The polymerization of acrylonitrile (AN) in aqueous nitric acid initiated by metavanadate-containing anion exchange resin (PV)-thiourea (TU) redox system at 20- 40 ℃. has been investigated. The overall rate of polymerization (Rp) is given by Rp= 1.92 × 104 e -6,860/RT [AN]1.2[PV]0.44[TU]1.0[HNO3]1.0 The kinetic parameters differed from those of V5+-TU system indicated that the generation of the primary radicals is mainly a difffusion-controlled reaction . The effect of macromolecular field arisen from the polymer matrix exerts a great influence on the polymerization process.

  13. Isatinphenylsemicarbazones as efficient colorimetric sensors for fluoride and acetate anions - anions induce tautomerism.

    Science.gov (United States)

    Jakusová, Klaudia; Donovalová, Jana; Cigáň, Marek; Gáplovský, Martin; Garaj, Vladimír; Gáplovský, Anton

    2014-04-05

    The anion induced tautomerism of isatin-3-4-phenyl(semicarbazone) derivatives is studied herein. The interaction of F(-), AcO(-), H2PO4(-), Br(-) or HSO4(-) anions with E and Z isomers of isatin-3-4-phenyl(semicarbazone) and N-methylisatin-3-4-phenyl(semicarbazone) as sensors influences the tautomeric equilibrium of these sensors in the liquid phase. This tautomeric equilibrium is affected by (1) the inter- and intra-molecular interactions' modulation of isatinphenylsemicarbazone molecules due to the anion induced change in the solvation shell of receptor molecules and (2) the sensor-anion interaction with the urea hydrogens. The acid-base properties of anions and the difference in sensor structure influence the equilibrium ratio of the individual tautomeric forms. Here, the tautomeric equilibrium changes were indicated by "naked-eye" experiment, UV-VIS spectral and (1)H NMR titration, resulting in confirmation that appropriate selection of experimental conditions leads to a high degree of sensor selectivity for some investigated anions. Sensors' E and Z isomers differ in sensitivity, selectivity and sensing mechanism. Detection of F(-) or CH3COO(-) anions at high weakly basic anions' excess is possible.

  14. Deuterated polycyclic aromatic hydrocarbons: Revisited

    CERN Document Server

    Doney, Kirstin D; Mori, Tamami; Onaka, Takashi; Tielens, A G G M

    2016-01-01

    The amount of deuterium locked up in polycyclic aromatic hydrocarbons (PAHs) has to date been an uncertain value. We present a near-infrared (NIR) spectroscopic survey of HII regions in the Milky Way, Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC) obtained with AKARI, which aims to search for features indicative of deuterated PAHs (PAD or Dn-PAH) to better constrain the D/H ratio of PAHs. Fifty-three HII regions were observed in the NIR (2.5-5 {\\mu}m), using the Infrared Camera (IRC) on board the AKARI satellite. Through comparison of the observed spectra with a theoretical model of deuterated PAH vibrational modes, the aromatic and (a)symmetric aliphatic C-D stretch modes were identified. We see emission features between 4.4-4.8 {\\mu}m, which could be unambiguously attributed to deuterated PAHs in only six of the observed sources, all of which are located in the Milky Way. In all cases, the aromatic C-D stretching feature is weaker than the aliphatic C-D stretching feature, and, in the case o...

  15. Characterization of transient species in laser photolysis of aromatic amino acids using acetone as photosensitizer

    Institute of Scientific and Technical Information of China (English)

    宋钦华; 徐业平; 俞书勤; 陈从香; 马兴孝; 王文锋; 姚思德; 林念芸

    1999-01-01

    The photochemical processes of aromatic amino acids were investigated in aqueous solution using acetone as photosensitizer by KrF (248 nm) laser flash photolysis. Laser-induced transient species were characterized according to kinetic analysis and quenching experiments. The intermediates recorded were assigned to the excited triplet state of tryptophan, the radicals of tryptophan and tyrosine. The excited triplet state of tryptophan produced via a triplet-triplet excitation transfer and the radicals arising from electron transfer reaction has been identified. Neither electron transfer nor energy transfer between triplet acetone and phenylalanine can occur in photolysis of phenylalanine aqueous solution which contains acetone. Furthermore, triplet acetone-induced radical transformation: Trp/N-Tyr→Trp-Tyr/O was observed directly in photolysis of dipeptide (Trp-Tyr) aqueous solution containing acetone, and the transformation resulting from intramolecular electron transfer was suggested.

  16. Free radicals and male reproduction.

    Science.gov (United States)

    Agarwal, Ashok; Allamaneni, Shyam S R

    2011-03-01

    Male factor accounts for almost 50% cases of infertility. The exact mechanism of sperm dysfunction is not known in many cases. Extensive research in the last decade has led to the identification of free radicals (reactive oxygen species) as mediators of sperm dysfunction in both specific diagnoses and idiopathic cases of male infertility. Elevated levels of reactive oxygen species are seen in up to 30-80% of men with male infertility. The role of free radicals has been studied extensively in the process of human reproduction. We know now that a certain level of free radicals is necessary for normal sperm function, whereas an excessive level of free radicals can cause detrimental effect on sperm function and subsequent fertilisation and offspring health. Oxidative stress develops when there is an imbalance between generation of free radicals and scavenging capacity of anti-oxidants in reproductive tract. Oxidative stress has been shown to affect both standard semen parameters and fertilising capacity. In addition, high levels of free radicals have been associated with lack of or poor fertility outcome after natural conception or assisted reproduction. Diagnostic techniques to quantify free radicals in infertile patients can assist physicians treating patients with infertility to plan for proper treatment strategies. In vivo anti-oxidants can be used against oxidative stress in male reproductive tract. Supplementation of in vitro anti-oxidants can help prevent the oxidative stress during sperm preparation techniques in assisted reproduction.

  17. An ESR study of the gamma radiolysis of aromatic polyesters containing isomeric naphthalene links

    Science.gov (United States)

    Hill, David J. T.; Choi, Bong-Ku; Ahn, Hung-Kun; Choi, E.-Joon

    2001-07-01

    Six polyesters were synthesised from 4,4'-oxy-bis(benzoyl chloride) and 1,4-, 1,5-, 1,6-, 2,3-, 2,6-, and 2,7-naphthalenediol isomers. The structures of the polyesters were characterised by means of IR, inherent viscosities in tetrachloroethane (TCE), solutions at 303 K and thermal analysis. The glass transition temperatures were in the range of 425-494 K by DSC thermal analysis. All of the polyesters were irradiated in an AECL Gammacell 220 unit at a dose rate of approximately 6.7 kGy/h to doses in the range of 0-15 kGy at 77 and 300 K. ESR spectroscopy was used to examine the radicals formed during radiolysis and to measure their yields. The G-values for radical formation in the polyesters were found to be in the range 0.18-1.41 at 77 K and 0.19-0.78 at 300 K. At 77 K, up to 15% of the radicals formed on radiolysis were found to be photo-bleachable anion radicals. Annealing experiments were carried out in order to identify the neutral radicals, which were assigned to naphthyl- or phenyl- and phenoxyl-type radicals.

  18. [Impact of biologically important anions on reactive oxygen species formation in water under the effect of non-ionizing physical agents].

    Science.gov (United States)

    Gudkov, S V; Ivanov, V E; Karp, O É; Chernikov, A V; Belosludtsev, K N; Bobylev, A G; Astashev, M E; Gapeev, A B; Bruskov, V I

    2014-01-01

    The influence of biologically relevant anions (succinate, acetate, citrate, chloride, bicarbonate, hydroorthophosphate, dihydroorthophosphate, nitrite, nitrate) on the formation of hydrogen peroxide and hydroxyl radicals in water was studied under the effect of non-ionizing radiation: heat, laser light with a wavelength of 632.8 nm, corresponding to the maximum absorption of molecular oxygen, and electromagnetic radiation of extremely high frequencies. It has been established that various anions may both inhibit the formation of reactive oxygen species and increase it. Bicarbonate and sulfate anions included in the biological fluids' and medicinal mineral waters have significant, but opposite effects on reactive oxygen species production. Different molecular mechanisms of reactive oxygen species formation are considered under the action of the investigated physical factors involving these anions, which may influence the biological processes by signal-regulatory manner and provide a healing effect in physical therapy.

  19. Guest Editorial: Processes of Radicalization and De-Radicalization

    Directory of Open Access Journals (Sweden)

    Donatella Della Porta

    2012-05-01

    Full Text Available The study of radicalization and de-radicalization, understood as processes leading towards the increased or decreased use of political violence, is central to the question of how political violence emerges, how it can be prevented, and how it can be contained. The focus section of this issue of the International Journal of Conflict and Violence addresses radicalization and de-radicalization, seeking to develop a more comprehensive understanding of the processes, dynamics, and mechanisms involved and taking an interdisciplinary approach to overcome the fragmentation into separate disciplines and focus areas. Contributions by Pénélope Larzillière, Felix Heiduk, Bill Kissane, Hank Johnston, Christian Davenport and Cyanne Loyle, Veronique Dudouet, and Lasse Lindekilde address repressive settings, legitimacy, institutional aspects, organizational outcomes, and dynamics in Europe, Asia, Africa, and North and South America.

  20. Benzo-thia-fused [n]Thienoacenequinodimethanes with Small to Moderate Diradical Characters: The Role of Pro-aromaticity versus Anti-aromaticity

    KAUST Repository

    Shi, Xueliang

    2016-01-19

    Open-shell singlet diradicaloids recently have received much attention due to their unique optical, electronic and magnetic properties and promising applications in materials science. Among various diradicaloids, quinoidal π-conjugated molecules have become the prevailing designs. However, there still lacks fundamental understanding on how the fusion mode and pro-aromaticity/anti-aromaticity affect their diradical character and physical properties. In this work, a series of pro-aromatic benzo-thia-fused [n]thienoacenequinodimethanes (Thn-TIPS (n=1-3) and BDTh-TIPS) were synthesized and compared with the previously reported anti-aromatic bisindeno-[n]thienoacenes (Sn-TIPS, n=1-4). The ground-state geometric and electronic structures of these new quinoidal molecules were systematically investigated by X-ray crystallographic analysis, variable temperature NMR, ESR, SQUID, Raman, and electronic absorption spectroscopy, assisted by DFT calculations. It was found that the diradical character index (y0) increased from nearly zero for Th1-TIPS to 2.4% for Th2-TIPS, 18.2% for Th3-TIPS, and 38.2% for BDTh-TIPS, due to the enhanced aromatic stabilization. Consequently, with the extension of molecular size, the one-photon absorption spectra are gradually red-shifted, the two-photon absorption (TPA) cross section values increase, and the singlet excited state lifetimes decrease. By comparison with the corresponding anti-aromatic analogues Sn-TIPS (n=1-3), the pro-aromatic Thn-TIPS (n=1-3) exhibit larger diradical character, longer singlet excited state lifetime and larger TPA cross section value. At the same time, they display distinctively different electronic absorption spectra and improved electrochemical amphotericity. Spectroelectrochemical studies revealed a good linear relationship between the optical energy gaps and the molecular length in the neutral, radical cationic and dicationic forms. Our research work disclosed the significant difference between the pro-aromatic

  1. HOCCO versus OCCO: Comparative spectroscopy of the radical and diradical reactive intermediates

    Science.gov (United States)

    Dixon, Andrew R.; Xue, Tian; Sanov, Andrei

    2016-06-01

    We present a photoelectron imaging study of three glyoxal derivatives: the ethylenedione anion (OCCO-), ethynediolide (HOCCO-), and glyoxalide (OHCCO-). These anions provide access to the corresponding neutral reactive intermediates: the OCCO diradical and the HOCCO and OHCCO radicals. Contrasting the straightforward deprotonation pathway in the reaction of O- with glyoxal (OHCCHO), which is expected to yield glyoxalide (OHCCO-), OHCCO- is shown to be a minor product, with HOCCO- being the dominant observed isomer of the m/z = 57 anion. In the HOCCO/OHCCO anion photoelectron spectrum, we identify several electronic states of this radical system and determine the adiabatic electron affinity of HOCCO as 1.763(6) eV. This result is compared to the corresponding 1.936(8) eV value for ethylenedione (OCCO), reported in our recent study of this transient diradical [A. R. Dixon, T. Xue, and A. Sanov, Angew. Chem., Int. Ed. 54, 8764-8767 (2015)]. Based on the comparison of the HOCCO-/OHCCO- and OCCO- photoelectron spectra, we discuss the contrasting effects of the hydrogen connected to the carbon framework or the terminal oxygen in OCCO.

  2. Noncomparative scaling of aromaticity through electron itinerancy

    Energy Technology Data Exchange (ETDEWEB)

    Paul, Satadal [Department of Chemistry, University of North Bengal, Raja Rammohunpur, Darjeeling 734013, West Bengal (India); Darjeeling Polytechnic, Kurseong, Darjeeling 734203, West Bengal (India); Goswami, Tamal; Misra, Anirban, E-mail: anirbanmisra@yahoo.com [Department of Chemistry, University of North Bengal, Raja Rammohunpur, Darjeeling 734013, West Bengal (India)

    2015-10-15

    Aromaticity is a multidimensional concept and not a directly observable. These facts have always stood in the way of developing an appropriate theoretical framework for scaling of aromaticity. In the present work, a quantitative account of aromaticity is developed on the basis of cyclic delocalization of π-electrons, which is the phenomenon leading to unique features of aromatic molecules. The stabilization in molecular energy, caused by delocalization of π-electrons is obtained as a second order perturbation energy for archetypal aromatic systems. The final expression parameterizes the aromatic stabilization energy in terms of atom to atom charge transfer integral, onsite repulsion energy and the population of spin orbitals at each site in the delocalized π-electrons. An appropriate computational platform is framed to compute each and individual parameter in the derived equation. The numerical values of aromatic stabilization energies obtained for various aromatic molecules are found to be in close agreement with available theoretical and experimental reports. Thus the reliable estimate of aromaticity through the proposed formalism renders it as a useful tool for the direct assessment of aromaticity, which has been a long standing problem in chemistry.

  3. Effect of copper oxide concentration on the formation and persistency of environmentally persistent free radicals (EPFRs) in particulates.

    Science.gov (United States)

    Kiruri, Lucy W; Khachatryan, Lavrent; Dellinger, Barry; Lomnicki, Slawo

    2014-02-18

    Environmentally persistent free radicals (EPFRs) are formed by the chemisorption of substituted aromatics on metal oxide surfaces in both combustion sources and superfund sites. The current study reports the dependency of EPFR yields and their persistency on metal loading in particles (0.25, 0.5, 0.75, 1, 2, and 5% CuO/silica). The EPFRs were generated through exposure of particles to three adsorbate vapors at 230 °C: phenol, 2-monochlorophenol (2-MCP), and dichlorobenzene (DCBz). Adsorption resulted in the formation of surface-bound phenoxyl- and semiquinoine-type radicals with characteristic EPR spectra displaying a g value ranging from ∼ 2.0037 to 2.006. The highest EPFR yield was observed for CuO concentrations between 1 and 3% in relation to MCP and phenol adsorption. However, radical density, which is expressed as the number of radicals per copper atom, was highest at 0.75-1% CuO loading. For 1,2-dichlorobenzene adsorption, radical concentration increased linearly with decreasing copper content. At the same time, a qualitative change in the radicals formed was observed--from semiquinone to chlorophenoxyl radicals. The two longest lifetimes, 25 and 23 h, were observed for phenoxyl-type radicals on 0.5% CuO and chlorophenoxyl-type radicals on 0.75% CuO, respectively.

  4. Vibrational spectroscopy of microhydrated conjugate base anions.

    Science.gov (United States)

    Asmis, Knut R; Neumark, Daniel M

    2012-01-17

    Conjugate-base anions are ubiquitous in aqueous solution. Understanding the hydration of these anions at the molecular level represents a long-standing goal in chemistry. A molecular-level perspective on ion hydration is also important for understanding the surface speciation and reactivity of aerosols, which are a central component of atmospheric and oceanic chemical cycles. In this Account, as a means of studying conjugate-base anions in water, we describe infrared multiple-photon dissociation spectroscopy on clusters in which the sulfate, nitrate, bicarbonate, and suberate anions are hydrated by a known number of water molecules. This spectral technique, used over the range of 550-1800 cm(-1), serves as a structural probe of these clusters. The experiments follow how the solvent network around the conjugate-base anion evolves, one water molecule at a time. We make structural assignments by comparing the experimental infrared spectra to those obtained from electronic structure calculations. Our results show how changes in anion structure, symmetry, and charge state have a profound effect on the structure of the solvent network. Conversely, they indicate how hydration can markedly affect the structure of the anion core in a microhydrated cluster. Some key results include the following. The first few water molecules bind to the anion terminal oxo groups in a bridging fashion, forming two anion-water hydrogen bonds. Each oxo group can form up to three hydrogen bonds; one structural result, for example, is the highly symmetric, fully coordinated SO(4)(2-)(H(2)O)(6) cluster, which only contains bridging water molecules. Adding more water molecules results in the formation of a solvent network comprising water-water hydrogen bonding in addition to hydrogen bonding to the anion. For the nitrate, bicarbonate, and suberate anions, fewer bridging sites are available, namely, three, two, and one (per carboxylate group), respectively. As a result, an earlier onset of water

  5. CONTINENT RADICAL PROSTATECTOMY

    Directory of Open Access Journals (Sweden)

    Yu. P. Sernyak

    2014-07-01

    Full Text Available Objective: to evaluate the impact of dissection of the dorsal venous complex without pre-ligation, suturing, or coagulation during radical prostatectomy (RPE in patients with localized prostate cancer (PC on the quality of surgery and the function of urinary retention.Subjects and methods. The data of 42 patients who had undergone posterior and anterior anatomical repair and vesicourethral anastomosis using a V-lock suture after prostatectomy were analyzed. All the patients were divided into 2 groups. Group 1 consisted of 22 patients in whom the dorsal venous complex was closed using a 3-0 vicryl suture before urethral dissection. Group 2 included 20 patients in whom the urethra was dissected without suturing the venous complex.Results. In group 1, complete urinary retention after catheter removal was noted in 9 (40.9 % and 15 (68 % patients within 24 hours and after 3 months, respectively. Following 12 months, two (9 % patients were observed to have partial mild urinary incontinence (as many as 2 pads per day. Group 2 patients showed complete urinary retention in 17 (85 % cases on the first day after catheter removal; all the patients retained urine 3 months later.Conclusion. In patients with localized PC, dissection of the dorsal venous complex without presuturing during laparoscopic RPE exerts a considerable impact on the preservation of urinary retention, namely 45% more of the patients reported complete urinary retention in early periods and 10 % more did this in later periods. At the same time, there was no statistically significant increase in intraoperative blood loss (p > 0.05, the number of positive edges, or biochemical recurrences.

  6. CONTINENT RADICAL PROSTATECTOMY

    Directory of Open Access Journals (Sweden)

    Yu. P. Sernyak

    2013-01-01

    Full Text Available Objective: to evaluate the impact of dissection of the dorsal venous complex without pre-ligation, suturing, or coagulation during radical prostatectomy (RPE in patients with localized prostate cancer (PC on the quality of surgery and the function of urinary retention.Subjects and methods. The data of 42 patients who had undergone posterior and anterior anatomical repair and vesicourethral anastomosis using a V-lock suture after prostatectomy were analyzed. All the patients were divided into 2 groups. Group 1 consisted of 22 patients in whom the dorsal venous complex was closed using a 3-0 vicryl suture before urethral dissection. Group 2 included 20 patients in whom the urethra was dissected without suturing the venous complex.Results. In group 1, complete urinary retention after catheter removal was noted in 9 (40.9 % and 15 (68 % patients within 24 hours and after 3 months, respectively. Following 12 months, two (9 % patients were observed to have partial mild urinary incontinence (as many as 2 pads per day. Group 2 patients showed complete urinary retention in 17 (85 % cases on the first day after catheter removal; all the patients retained urine 3 months later.Conclusion. In patients with localized PC, dissection of the dorsal venous complex without presuturing during laparoscopic RPE exerts a considerable impact on the preservation of urinary retention, namely 45% more of the patients reported complete urinary retention in early periods and 10 % more did this in later periods. At the same time, there was no statistically significant increase in intraoperative blood loss (p > 0.05, the number of positive edges, or biochemical recurrences.

  7. THE USE OF HAMMETT CONSTANTS TO UNDERSTAND THE NON-COVALENT BINDING OF AROMATICS

    Directory of Open Access Journals (Sweden)

    Michael Lewis

    2012-04-01

    Full Text Available Non-covalent interactions of aromatics are important in a wide range of chemical and biological applications. The past two decades have seen numerous reports of arene-arene binding being understood in terms Hammett substituent constants, and similar analyses have recently been extended to cation-arene and anion-arene binding. It is not immediately clear why electrostatic Hammett parameters should work so well in predicting the binding for all three interactions, given that different intermolecular forces dominate each interaction. This review explores such anomalies, and summarizes how Hammett substituent constants have been employed to understand the non-covalent binding in arene-arene, cation-arene and anion-arene interactions.

  8. Electron spin relaxation of a boron-containing heterocyclic radical

    Science.gov (United States)

    Eaton, Sandra S.; Huber, Kirby; Elajaili, Hanan; McPeak, Joseph; Eaton, Gareth R.; Longobardi, Lauren E.; Stephan, Douglas W.

    2017-03-01

    Preparation of the stable boron-containing heterocyclic phenanthrenedione radical, (C6F5)2B(O2C14H8), by frustrated Lewis pair chemistry has been reported recently. Electron paramagnetic resonance measurements of this radical were made at X-band in toluene:dichloromethane (9:1) from 10 to 293 K, in toluene from 180 to 293 K and at Q-band at 80 K. In well-deoxygenated 0.1 mM toluene solution at room temperature hyperfine splittings from 11B, four pairs of 1H, and 5 pairs of 19F contribute to an EPR spectrum with many resolved lines. Observed hyperfine couplings were assigned based on DFT calculations and account for all of the fluorines and protons in the molecule. Rigid lattice g values are gx = 2.0053, gy = 2.0044, and gz = 2.0028. Near the melting point of the solvent 1/Tm is enhanced due to motional averaging of g and A anisotropy. Increasing motion above the melting point enhances 1/T1 due to contributions from tumbling-dependent processes. The overall temperature dependence of 1/T1 from 10 to 293 K was modeled with the sum of contributions of a process that is linear in T, a Raman process, spin rotation, and modulation of g anisotropy by molecular tumbling. The EPR measurements are consistent with the description of this compound as a substituted aromatic radical, with relatively small spin density on the boron.

  9. Mechanistic studies on the OH-initiated atmospheric oxidation of selected aromatic hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Nehr, Sascha

    2012-07-01

    Benzene, toluene, the xylenes, and the trimethylbenzenes are among the most abundant aromatic trace constituents of the atmosphere mainly originating from anthropogenic sources. The OH-initiated atmospheric photo-oxidation of aromatic hydrocarbons is the predominant removal process resulting in the formation of O{sub 3} and secondary organic aerosol. Therefore, aromatics are important trace constituents regarding air pollution in urban environments. Our understanding of aromatic photo-oxidation processes is far from being complete. This work presents novel approaches for the investigation of OH-initiated atmospheric degradation mechanisms of aromatic hydrocarbons. Firstly, pulsed kinetic studies were performed to investigate the prompt HO{sub 2} formation from OH+ aromatic hydrocarbon reactions under ambient conditions. For these studies, the existing OH reactivity instrument, based on the flash photolysis/laser-induced fluorescence (FP/LIF) technique, was extended to the detection of HO{sub 2} radicals. The experimental design allows for the determination of HO{sub 2} formation yields and kinetics. Results of the pulsed kinetic experiments complement previous product studies and help to reduce uncertainties regarding the primary oxidation steps. Secondly, experiments with aromatic hydrocarbons were performed under atmospheric conditions in the outdoor atmosphere simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction chamber) located at Forschungszentrum Juelich. The experiments were aimed at the evaluation of up-to-date aromatic degradation schemes of the Master Chemical Mechanism (MCMv3.2). The unique combination of analytical instruments operated at SAPHIR allows for a detailed investigation of HO{sub x} and NO{sub x} budgets and for the determination of primary phenolic oxidation product yields. MCMv3.2 deficiencies were identified and most likely originate from shortcomings in the mechanistic representation of ring

  10. The role of anions on the indoor air quality; De rol van negatieve ionen op de binnenluchtkwaliteit

    Energy Technology Data Exchange (ETDEWEB)

    Havermans, J. [Afdeling Energie, Comfort en Binnenmilieu, TNO Bouw en Onderzoek, Delft (Netherlands)

    2010-11-15

    Anions may contribute to a more comfortable indoor environment. Even a simple apparatus as a lamp with semi conductor technique produces easily anions. Such ions will react with particles forming agglomerates that will precipitate. Also a reaction with oxygen and moist will result in the formation of a superoxide radical and peroxides. These radicals easily react with e.g. organic volatiles and possible also with spores and allergens. Depending on the concentration of the radicals, these compounds can be deteriorated fully. However, as a potential negative side effect the radicals can produce irritating substances by reaction with chemicals in the air. It is not clear yet if all cleaners, based on ionization, will cause this effect. Therefore more research is needed. [Dutch] Negatieve ionen (anionen) in de lucht kunnen een belangrijke bijdrage leveren aan een comfortabeler binnenmilieu en kunnen op een eenvoudige wijze worden geproduceerd. Bijvoorbeeld met lamp waarbij naast verlichting ook via (smd) halfgeleidertechniek negatieve ionen worden gevormd. Negatieve ionen reageren met deeltjes waardoor deze clusteren en deze uit de binnenlucht worden verwijderd. Ook kunnen ze met zuurstof en vocht reageren, waarbij reactief superoxide en peroxides worden gevormd. Deze radicalen zijn verantwoordelijk voor het verwijderen van bijvoorbeeld ongewenste geuren en mogelijk ook allergenen en schimmels. Ze kunnen ook als negatief bijeffect potentieel irriterende stoffen vormen door reactie met chemicalien in de lucht. Of dit het geval is met alle op ionisatie gebaseerde luchtzuiveringsapparaten dient nader te worden onderzocht.

  11. Identification and characterization of anion binding sites in RNA

    Energy Technology Data Exchange (ETDEWEB)

    Kieft, Jeffrey S.; Chase, Elaine; Costantino, David A.; Golden, Barbara L. (Purdue); (Colorado)

    2010-05-24

    Although RNA molecules are highly negatively charged, anions have been observed bound to RNA in crystal structures. It has been proposed that anion binding sites found within isolated RNAs represent regions of the molecule that could be involved in intermolecular interactions, indicating potential contact points for negatively charged amino acids from proteins or phosphate groups from an RNA. Several types of anion binding sites have been cataloged based on available structures. However, currently there is no method for unambiguously assigning anions to crystallographic electron density, and this has precluded more detailed analysis of RNA-anion interaction motifs and their significance. We therefore soaked selenate into two different types of RNA crystals and used the anomalous signal from these anions to identify binding sites in these RNA molecules unambiguously. Examination of these sites and comparison with other suspected anion binding sites reveals features of anion binding motifs, and shows that selenate may be a useful tool for studying RNA-anion interactions.

  12. Penile rehabilitation after radical prostatectomy

    DEFF Research Database (Denmark)

    Fode, Mikkel; Ohl, Dana A; Ralph, David;

    2013-01-01

    The pathophysiology of erectile dysfunction after radical prostatectomy (RP) is believed to include neuropraxia, which leads to temporarily reduced oxygenation and subsequent structural changes in penile tissue. This results in veno-occlusive dysfunction, therefore, penile rehabilitation programm...

  13. Redox Properties of Free Radicals.

    Science.gov (United States)

    Neta, P.

    1981-01-01

    Describes pulse radiolysis as a useful means in studing one-electron redox potentials. This method allows the production of radicals and the determination of their concentration and rates of reaction. (CS)

  14. High Vacuum Techniques for Anionic Polymerization

    KAUST Repository

    Ratkanthwar, Kedar

    2015-09-01

    Anionic polymerization high vacuum techniques (HVTs) are the most suitable for the preparation of polymer samples with well-defined complex macromolecular architectures. Though HVTs require glassblowing skill for designing and making polymerization reactor, it is the best way to avoid any termination of living polymers during the number of steps for the synthesis of polymers with complex structure. In this chapter, we describe the different polymerization reactors and HVTs for the purification of monomers, solvents, and other reagents for anionic polymerization as well as few model reactions for the synthesis of polymers with simple to complex structure.

  15. Krebs cycle anions in metabolic acidosis.

    Science.gov (United States)

    Bowling, Francis G; Morgan, Thomas J

    2005-10-05

    For many years it has been apparent from estimates of the anion gap and the strong ion gap that anions of unknown identity can be generated in sepsis and shock states. Evidence is emerging that at least some of these are intermediates of the citric acid cycle. The exact source of this disturbance remains unclear, because a great many metabolic blocks and bottlenecks can disturb the anaplerotic and cataplerotic pathways that enter and leave the cycle. These mechanisms require clarification with the use of tools such as gas chromatography-mass spectrometry.

  16. Templating irreversible covalent macrocyclization by using anions.

    Science.gov (United States)

    Kataev, Evgeny A; Kolesnikov, Grigory V; Arnold, Rene; Lavrov, Herman V; Khrustalev, Victor N

    2013-03-11

    Inorganic anions were used as templates in the reaction between a diamine and an activated diacid to form macrocyclic amides. The reaction conditions were found to perform the macrocyclization sufficiently slow to observe a template effect. A number of analytical methods were used to clarify the reaction mechanisms and to show that the structure of the intermediate plays a decisive role in determining the product distribution. For the macrocyclization under kinetic control, it was shown that the amount of a template, the conformational rigidity of building blocks, and the anion affinities of reaction components and intermediates are important parameters that one should take into consideration to achieve high yields.

  17. Utilizing the σ-complex stability for quantifying reactivity in nucleophilic substitution of aromatic fluorides

    Directory of Open Access Journals (Sweden)

    Magnus Liljenberg

    2013-04-01

    Full Text Available A computational approach using density functional theory to compute the energies of the possible σ-complex reaction intermediates, the “σ-complex approach”, has been shown to be very useful in predicting regioselectivity, in electrophilic as well as nucleophilic aromatic substitution. In this article we give a short overview of the background for these investigations and the general requirements for predictive reactivity models for the pharmaceutical industry. We also present new results regarding the reaction rates and regioselectivities in nucleophilic substitution of fluorinated aromatics. They were rationalized by investigating linear correlations between experimental rate constants (k from the literature with a theoretical quantity, which we call the sigma stability (SS. The SS is the energy change associated with formation of the intermediate σ-complex by attachment of the nucleophile to the aromatic ring. The correlations, which include both neutral (NH3 and anionic (MeO− nucleophiles are quite satisfactory (r = 0.93 to r = 0.99, and SS is thus useful for quantifying both global (substrate and local (positional reactivity in SNAr reactions of fluorinated aromatic substrates. A mechanistic analysis shows that the geometric structure of the σ-complex resembles the rate-limiting transition state and that this provides a rationale for the observed correlations between the SS and the reaction rate.

  18. Utilizing the σ-complex stability for quantifying reactivity in nucleophilic substitution of aromatic fluorides.

    Science.gov (United States)

    Liljenberg, Magnus; Brinck, Tore; Rein, Tobias; Svensson, Mats

    2013-01-01

    A computational approach using density functional theory to compute the energies of the possible σ-complex reaction intermediates, the "σ-complex approach", has been shown to be very useful in predicting regioselectivity, in electrophilic as well as nucleophilic aromatic substitution. In this article we give a short overview of the background for these investigations and the general requirements for predictive reactivity models for the pharmaceutical industry. We also present new results regarding the reaction rates and regioselectivities in nucleophilic substitution of fluorinated aromatics. They were rationalized by investigating linear correlations between experimental rate constants (k) from the literature with a theoretical quantity, which we call the sigma stability (SS). The SS is the energy change associated with formation of the intermediate σ-complex by attachment of the nucleophile to the aromatic ring. The correlations, which include both neutral (NH3) and anionic (MeO(-)) nucleophiles are quite satisfactory (r = 0.93 to r = 0.99), and SS is thus useful for quantifying both global (substrate) and local (positional) reactivity in SNAr reactions of fluorinated aromatic substrates. A mechanistic analysis shows that the geometric structure of the σ-complex resembles the rate-limiting transition state and that this provides a rationale for the observed correlations between the SS and the reaction rate.

  19. High-optical-quality blends of anionic polymethine salts and polycarbonate with enhanced third-order non-linearities for silicon-organic hybrid devices.

    Science.gov (United States)

    Li, Zhong'an; Liu, Yang; Kim, Hyeongeu; Hales, Joel M; Jang, Sei-Hum; Luo, Jingdong; Baehr-Jones, Tom; Hochberg, Michael; Marder, Seth R; Perry, Joseph W; Jen, Alex K-Y

    2012-11-20

    A series of anionic polymethine dyes with different aromatic counterions are prepared to improve their compatibility as guests in an amorphous polycarbonate host. When they are used as the cladding material for silicon hybrid slot waveguides, four-wave mixing wavelength conversion and two-photon absorption-based optical-power modulation are observed. Such guest-host materials may be attractive candidates for all-optical signal-processing applications.

  20. Hydride-induced anionic cyclization: an efficient method for the synthesis of 6-H-phenanthridines via a transition-metal-free process.

    Science.gov (United States)

    Chen, Wei-Lin; Chen, Chun-Yuan; Chen, Yan-Fu; Hsieh, Jen-Chieh

    2015-03-20

    A novel procedure for hydride-induced anionic cyclization has been developed. It includes the reduction of a biaryl bromo-nitrile with a nucleophilic aromatic substitution (S(N)Ar). A range of polysubstituted 6-H-phenanthridines were so obtained in moderate to good yield with good substrate tolerance. This method involves a concise transition-metal-free process and was applied to synthesize natural alkaloids.

  1. Global modeling of secondary organic aerosol formation from aromatic hydrocarbons: high- vs low-yield pathways

    Directory of Open Access Journals (Sweden)

    D. K. Henze

    2007-10-01

    Full Text Available Formation of SOA from the aromatic species toluene, xylene, and, for the first time, benzene, is added to a global chemical transport model. A simple mechanism is presented that accounts for competition between low and high-yield pathways of SOA formation, wherein secondary gas-phase products react further with either nitrogen oxide (NO or hydroperoxy radical (HO2 to yield semi- or non-volatile products, respectively. Aromatic species yield more SOA when they react with OH in regions where the [NO]/[HO2] ratios are lower. The SOA yield thus depends upon the distribution of aromatic emissions, with biomass burning emissions being in areas with lower [NO]/[HO2] ratios, and the reactivity of the aromatic with respect to OH, as a lower initial reactivity allows transport away from industrial source regions, where [NO]/[HO2] ratios are higher, to more remote regions, where this ratio is lower and, hence, the ultimate yield of SOA is higher. As a result, benzene is estimated to be the most important aromatic species with regards to formation of SOA, with a total production nearly equal that of toluene and xylene combined. In total, while only 39% percent of the aromatic species react via the low-NOx pathway, 72% of the aromatic SOA is formed via this mechanism. Predicted SOA concentrations from aromatics in the Eastern United States and Eastern Europe are actually largest during the summer, when the [NO]/[HO2] ratio is lower. Global production of SOA from aromatic sources is estimated at 3.5 Tg/yr, resulting in a global burden of 0.08 Tg, twice as large as previous estimates. The contribution of these largely anthropogenic sources to global SOA is still small relative to biogenic sources, which are estimated to comprise 90% of the global SOA burden, about half of which comes from isoprene. Compared to recent observations, it would appear there are additional pathways beyond those

  2. Rosemary Aromatization of Extra Virgin Olive Oil and Process Optimization Including Antioxidant Potential and Yield

    Directory of Open Access Journals (Sweden)

    Erkan Karacabey

    2016-08-01

    Full Text Available Aromatization of olive oil especially by spices and herbs has been widely used technique throughout the ages in Mediterranean diets. The present study was focused on aromatization of olive oil by rosemary (Rosmarinus officinalis L.. Aromatization process was optimized by response surface methodology as a function of malaxation’s conditions (temperature and time. According to authors’ best knowledge it was first time for examination of oil yield performance with antioxidant potential and pigments under effect of aromatization parameters. For all oil samples, values of the free acidity, peroxide, K232 and K270 as quality parameters fell within the ranges established for the highest quality category “extra virgin oil”. Oil yield (mL oil/kg olive paste changed from 158 to 208 with respect to design parameters. Total phenolic content and free radical scavenging activity as antioxidant potential of olive oil samples were varied in the range of 182.44 – 348.65 mg gallic acid equivalent/kg oil and 28.91 – 88.75 % inhibition of 2,2-Diphenyl-1-picrylhydrazyl-(DPPH•, respectively. Total contents of carotenoid, chlorophyll and pheophytin a as pigments in oil samples were found to be in between 0.09 – 0.48 mg carotenoid/kg oil, 0.11 – 0.96 mg chlorophyll/kg oil, 0.15 – 4.44 mg pheo α/kg oil, respectively. The proposed models for yield, pigments and antioxidant potential responses were found to be good enough for successful prediction of experimental results. Total phenolics, carotenoids and free radical scavenging activity of aromatized olive oil and oil yield were maximized to gather and optimal conditions were determined as 25°C, 84 min, and 2 % (Rosemary/olive paste; w/w.

  3. Communication: Solute Anisotropy Effects in Hydrated Anion and Neutral Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Wen, Hui; Hou, Gao-Lei; Kathmann, Shawn M.; Valiev, Marat; Wang, Xue B.

    2013-01-21

    Specific ion effects in solvation processes are often rationalized in terms of spherically symmetric models involving an ion’s size, charge, and polarizability. The effects of permanent charge anisotropy, related to the polyatomic nature of complex solutes, are expected to play a role in solvation but the extent of their importance remains unexplored. In this work we provide compelling experimental and theoretical evidence that the anisotropic nature of complex polyoxyanion solutes can have a critical influence on the solvation process. Combined photoelectron spectroscopy and theoretical modeling results show that the electron binding energy (EBE) of IO3-(H2O)n (n = 0 - 12) clusters is characterized by an anomalous drop at n = 10. Such behavior is unprecedented for rigid solute molecules, and is related to the anisotropy of the neutral iodate radical that displays a strong selectivity to solvent configurations generated by the charged anion complex. These results highlight the significance of solute anisotropy and its potential impact on ion specificity and selectivity in aqueous environments.

  4. Compactness Aromaticity of Atoms in Molecules

    Directory of Open Access Journals (Sweden)

    Mihai V. Putz

    2010-03-01

    Full Text Available A new aromaticity definition is advanced as the compactness formulation through the ratio between atoms-in-molecule and orbital molecular facets of the same chemical reactivity property around the pre- and post-bonding stabilization limit, respectively. Geometrical reactivity index of polarizability was assumed as providing the benchmark aromaticity scale, since due to its observable character; with this occasion new Hydrogenic polarizability quantum formula that recovers the exact value of 4.5 a03 for Hydrogen is provided, where a0 is the Bohr radius; a polarizability based–aromaticity scale enables the introduction of five referential aromatic rules (Aroma 1 to 5 Rules. With the help of these aromatic rules, the aromaticity scales based on energetic reactivity indices of electronegativity and chemical hardness were computed and analyzed within the major semi-empirical and ab initio quantum chemical methods. Results show that chemical hardness based-aromaticity is in better agreement with polarizability based-aromaticity than the electronegativity-based aromaticity scale, while the most favorable computational environment appears to be the quantum semi-empirical for the first and quantum ab initio for the last of them, respectively.

  5. Simultaneous anion and cation mobility in polypyrrole

    DEFF Research Database (Denmark)

    Skaarup, Steen; Bay, Lasse; Vidanapathirana, K.;

    2003-01-01

    Polypyrrole (PPy) polymer films permanently doped with large, immobile anion dodecyl benzene sulfonate (DBS) have been characterized by cyclic voltammetry in order to clarify the roles of cations and anions in the aqueous electrolyte as mobile ions in the film. Aqueous solutions of 0.05-0.1 M...... alkali metal chlorides as well as BaCl2, NaBr and (CH3CH2CH2)(4)NBr were used to investigate the effects of both the ionic charge, size and shape. In 1: 1 electrolytes using small ions only three peaks are present: a sharp cathodic peak at ca. - 0.6 V vs, SCE representing both the insertion of cations...... complicating reproducibility when employing PPy(DBS) polymers as actuators. When the cation is doubly charged, it enters the film less readily, and anions dominate the mobility. Using a large and bulky cation switches the mechanism to apparently total anion motion. The changes in area of the three peaks...

  6. Synthesis of azaphenanthridines via anionic ring closure

    DEFF Research Database (Denmark)

    Hansen, Henriette Møller; Lysén, M.; Begtrup, M.;

    2005-01-01

    A new and convergent synthesis of azaphenanthridines via an anionic ring closure is reported. Ortho-lithiation/in situ borylation of cyanopyridines produces the corresponding cyanopyridylboronic esters, which undergo a Suzuki-Miyaura cross-coupling to give the key intermediates. Addition of lithium...

  7. Donnan Membrane Technique (DMT) for Anion Measurement

    NARCIS (Netherlands)

    Alonso Vega, M.F.; Weng, L.P.; Temminghoff, E.J.M.; Riemsdijk, van W.H.

    2010-01-01

    Donnan membrane technique (DMT) is developed and tested for determination of free anion concentrations. Time needed to reach the Donnan membrane equilibrium depends on type of ions and the background. The Donnan membrane equilibrium is reached in 1 day for Cl-, 1-2 days for NO3-, 1-4 days for SO42-

  8. Anionic/cationic complexes in hair care.

    Science.gov (United States)

    O'Lenick, Tony

    2011-01-01

    The formulation of cosmetic products is always more complicated than studying the individual components in aqueous solution. This is because there are numerous interactions between the components, which make the formulation truly more than the sum of the parts. This article will look at interactions between anionic and cationic surfactants and offer insights into how to use these interactions advantageously in making formulations.

  9. Wigner photoemission time delay from endohedral anions

    Science.gov (United States)

    Kumar, Ashish; Varma, Hari R.; Deshmukh, Pranawa C.; Manson, Steven T.; Dolmatov, Valeriy K.; Kheifets, Anatoli

    2016-10-01

    Characteristic features of Wigner photoemission time delay from endohedral anions A@C60q along with their dependence on the anion charge q are unraveled. Specifically, significant enhancement of the time delay in the innermost dipole photoionization channels near threshold is found, owing to the presence of the Coulomb confined resonances (CRs). Moreover, it is shown that interchannel coupling of the inner-shell Coulomb CRs with outer-shell photoionization channels results in resonantly enhanced time delay in the release of the outer-shell photoelectron well above, several hundreds eV, the outer-shell thresholds. It is also demonstrated that, and explained why, photoionization cross sections of the innermost subshells as well as outer subshells (near the inner-subshell threshold) depends only very weakly on the anion charge q , but the dependence of the corresponding time delays on q can be significant. Furthermore, Coulomb CRs are found to emerge in the innermost quadrupole photoionization channels as well, thereby causing considerable time delay in the quadrupole photoemission. These findings are illustrated in calculations of the photoionization of inner and outer subshells of the endohedral anions Ne@C60-1 and Ne@C60-5 that were chosen as case studies.

  10. Stoichiometry of uranyl salophene anion complexes

    NARCIS (Netherlands)

    Antonisse, Martijn M.G.; Snellink-Ruel, Bianca H.M.; Engbersen, Johan F.J.; Reinhoudt, David N.

    1998-01-01

    In PVC/NPOE ion-selective membranes of potentiometric sensors, the guest-host stoichiometry of the anion complex of H2PO4 - and F- selective uranyl salophene derivatives is 2:1. This stoichiometry is different from the stoichiometry observed in DMSO solution (1H NMR) or solid state (X-ray crystal st

  11. Radical Compatibility with Nonaqueous Electrolytes and Its Impact on an All-Organic Redox Flow Battery

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Xiaoliang; Xu, Wu; Huang, Jinhua; Zhang, Lu; Walter, Eric D.; Lawrence, Chad W.; Vijayakumar, M.; Henderson, Wesley A.; Liu, Tianbiao L.; Cosimbescu, Lelia; Li, Bin; Sprenkle, Vincent L.; Wang, Wei

    2015-07-20

    Nonaqueous redox flow batteries hold the promise to achieve higher energy density ascribed to the broader voltage window than their aqueous counterparts, but their current performance is limited by low redox material concentration, poor cell efficiency, and inferior cycling stability. We report a new nonaqueous total-organic flow battery based on high concentrations of 9-fluorenone as negative and 2,5-di-tert-butyl-1-methoxy-4-[2’-methoxyethoxy]benzene as positive redox materials. The supporting electrolytes are found to greatly affect the cycling stability of flow cells through varying chemical stabilities of the charged radical species, especially the 9-fluorenone radical anions, as confirmed by electron spin resonance. Such an electrolyte optimization sheds light on mechanistic understandings of capacity fading in flow batteries employing organic radical-based redox materials and demonstrates that rational design of supporting electrolyte is vital for stable cyclability.

  12. Synthesis, Characterization, and Pharmacological Evaluation of Selected Aromatic Amines

    Directory of Open Access Journals (Sweden)

    Hammad Ismail

    2015-01-01

    Full Text Available Aromatic amines 1-amino-4-phenoxybenzene (A-1A, 2-(4-aminophenoxy naphthalene (A-2A, and 1-(4-aminophenoxy naphthalene (A-3A were synthesized by the reduction of corresponding nitroaromatics with hydrazine monohydrate and Pd/C 5% (w/w. The newly synthesized compounds were characterized by FTIR, 1H NMR, 13C NMR, UV-visible spectrophotometer, and mass spectrometry and their biological activities were investigated along with structurally similar 4-(4-aminophenyloxy biphenyl (A-A. Results of brine shrimp cytotoxicity assay showed that almost all of the compounds had LD50 values <1 μg/mL. The compounds also showed significant antitumor activity with IC50 values ranging from 67.45 to 12.2 µgmL−1. The cytotoxicity and antitumor studies correlate the results which suggests the anticancerous nature of compounds. During the interaction study of these compounds with DNA, all of the compounds showed hyperchromic effect indicating strong interaction through binding with the grooves of DNA. Moreover, A-3A also showed decrease in λmax confirming higher propensity for DNA groove binding. In DPPH free radical scavenging assay, all the compounds showed potential antioxidant capability. The compounds were highly active in protecting DNA against hydroxyl free radicals. DNA interaction and antioxidant results back up each other indicating that these compounds have potential to be used as cancer chemopreventive agents. Additionally, one compound (A-1A showed significant antibacterial and antifungal activity as well.

  13. Degradation of atrazine in aqueous medium by electrocatalytically generated hydroxyl radicals. A kinetic and mechanistic study.

    Science.gov (United States)

    Balci, Beytul; Oturan, Nihal; Cherrier, Richard; Oturan, Mehmet A

    2009-04-01

    Oxidative degradation of atrazine by hydroxyl radicals (()OH) was studied in aqueous medium. ()OH were formed in situ from electrochemically generating Fenton's reagent by an indirect electrochemical advanced oxidation process. Identification and evolution of seven main aromatic metabolites and four short-chain carboxylic acids were performed by using liquid chromatography analyses. Total organic carbon (TOC) and ionic chromatography were used in order to evaluate the mineralization efficiency of treated aqueous solutions. A high mineralization rate of 82% (never reported until now) was obtained. The oxidative degradation of cyanuric acid, the ultimate product of atrazine degradation, was highlighted for the first time. The absolute rate constant of the reaction between atrazine and hydroxyl radicals was evaluated by competition kinetics method as (2.54+/-0.22)x10(9)M(-1)s(-1). Considering all oxidation reaction intermediates and end products a general reaction sequence for atrazine degradation by hydroxyl radicals was proposed.

  14. Highly active and reusable catalyst from Fe-Mg-hydrotalcite anionic clay for Friedel-Crafts type benzylation reactions

    Indian Academy of Sciences (India)

    Vasant R Choudhary; Rani Jha; Pankaj A Choudhari

    2005-11-01

    Fe-Mg-hydrotalcite (Mg/Fe = 3) anionic clay with or without calcination (at 200-800°C) has been used for the benzylation of toluene and other aromatic compounds by benzyl chloride. Hydrotalcite before and after its calcination was characterized for surface area, crystalline phases and basicity. Both the hydrotalcite, particularly after its use in the benzylation reaction, and the catalyst derived from it by its calcination at 200-800°C show high catalytic activity for the benzylation of toluene and other aromatic compounds. The catalytically active species present in the catalyst in its most active form are the chlorides and oxides of iron on the catalyst surface.

  15. Anionic phospholipids modulate peptide insertion into membranes.

    Science.gov (United States)

    Liu, L P; Deber, C M

    1997-05-06

    While the insertion of a hydrophobic peptide or membrane protein segment into the bilayer can be spontaneous and driven mainly by the hydrophobic effect, anionic lipids, which comprise ca. 20% of biological membranes, provide a source of electrostatic attractions for binding of proteins/peptides into membranes. To unravel the interplay of hydrophobicity and electrostatics in the binding of peptides into membranes, we designed peptides de novo which possess the typical sequence Lys-Lys-Ala-Ala-Ala-X-Ala-Ala-Ala-Ala-Ala-X-Ala-Ala-Trp-Ala-Ala-X-Ala-Al a-Ala-Lys-Lys-Lys-Lys-amide, where X residues correspond to "guest" residues which encompass a range of hydrophobicity (Leu, Ile, Gly, and Ser). Circular dichroism spectra demonstrated that peptides were partially (40-90%) random in aqueous buffer but were promoted to form 100% alpha-helical structures by anionic lipid micelles. In neutral lipid micelles, only the relatively hydrophobic peptides (X = L and I) spontaneously adopted the alpha-helical conformation, but when 25% of negatively charged lipids were mixed in to mimic the content of anionic lipids in biomembranes, the less hydrophobic (X = S and G) peptides then formed alpha-helical conformations. Consistent with these findings, fluorescence quenching by the aqueous-phase quencher iodide indicated that in anionic (dimyristoylphosphatidylglycerol) vesicles, the peptide Trp residue was buried in the lipid vesicle hydrophobic core, while in neutral (dimyristoylphosphatidylcholine) vesicles, only hydrophobic (X = L and I) peptides were shielded from the aqueous solution. Trp emission spectra of peptides in the presence of phospholipids doxyl-labeled at the 5-, 7-, 10-, 12-, and 16-fatty acid positions implied not only a transbilayer orientation for inserted peptides but also that mixed peptide populations (transbilayer + surface-associated) may arise. Overall results suggest that for hydrophobic peptides with segmental threshold hydrophobicity below that which

  16. Cranberry flavonoids prevent toxic rat liver mitochondrial damage in vivo and scavenge free radicals in vitro.

    Science.gov (United States)

    Lapshina, Elena A; Zamaraeva, Maria; Cheshchevik, Vitali T; Olchowik-Grabarek, Ewa; Sekowski, Szymon; Zukowska, Izabela; Golovach, Nina G; Burd, Vasili N; Zavodnik, Ilya B

    2015-06-01

    The present study was undertaken for further elucidation of the mechanisms of flavonoid biological activity, focusing on the antioxidative and protective effects of cranberry flavonoids in free radical-generating systems and those on mitochondrial ultrastructure during carbon tetrachloride-induced rat intoxication. Treatment of rats with cranberry flavonoids (7 mg/kg) during chronic carbon tetrachloride-induced intoxication led to prevention of mitochondrial damage, including fragmentation, rupture and local loss of the outer mitochondrial membrane. In radical-generating systems, cranberry flavonoids effectively scavenged nitric oxide (IC50  = 4.4 ± 0.4 µg/ml), superoxide anion radicals (IC50  = 2.8 ± 0.3 µg/ml) and hydroxyl radicals (IC50  = 53 ± 4 µg/ml). The IC50 for reduction of 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH) was 2.2 ± 0.3 µg/ml. Flavonoids prevented to some extent lipid peroxidation in liposomal membranes and glutathione oxidation in erythrocytes treated with UV irradiation or organic hydroperoxides as well as decreased the rigidity of the outer leaflet of the liposomal membranes. The hepatoprotective potential of cranberry flavonoids could be due to specific prevention of rat liver mitochondrial damage. The mitochondria-addressed effects of flavonoids might be related both to radical-scavenging properties and modulation of various mitochondrial events.

  17. Atmospheric photochemistry of aromatic hydrocarbons: Analysis of OH budgets during SAPHIR chamber experiments and evaluation of MCMv3.2

    Science.gov (United States)

    Nehr, S.; Bohn, B.; Brauers, T.; Dorn, H.; Fuchs, H.; Häseler, R.; Hofzumahaus, A.; Li, X.; Lu, K.; Rohrer, F.; Tillmann, R.; Wahner, A.

    2012-12-01

    Aromatic hydrocarbons, almost exclusively originating from anthropogenic sources, comprise a significant fraction of volatile organic compounds observed in urban air. The photo-oxidation of aromatics results in the formation of secondary pollutants and impacts air quality in cities, industrialized areas, and districts of dense traffic. Up-to-date photochemical oxidation schemes of the Master Chemical Mechanism (MCMv3.2) exhibit moderate performance in simulating aromatic compound degradation observed during previous environmental chamber studies. To obtain a better understanding of aromatic photo-oxidation mechanisms, we performed experiments with a number of aromatic hydrocarbons in the outdoor atmosphere simulation chamber SAPHIR located in Jülich, Germany. These chamber studies were designed to derive OH turnover rates exclusively based on experimental data. Simultaneous measurements of NOx (= NO + NO2), HOx (= OH + HO2), and the total OH loss rate constant k(OH) facilitate a detailed analysis of the OH budgets during photo-oxidation experiments. The OH budget analysis was complemented by numerical model simulations using MCMv3.2. Despite MCM's tendency to overestimate k(OH) and to underpredict radical concentrations, the OH budgets are reasonably balanced for all investigated aromatics. However, the results leave some scope for OH producing pathways that are not considered in the current MCMv3.2. An improved reaction mechanism, derived from MCMv3.2 sensitivity studies, is presented. The model performance is basically improved by changes of the mechanistic representation of ring fragmentation channels.

  18. Birds and polycyclic aromatic hydrocarbons

    Science.gov (United States)

    Albers, P.H.

    2006-01-01

    Polycyclic aromatic hydrocarbons (PAH) are present throughout the global environment and are produced naturally and by activities of humans. Effects of PAH on birds have been determined by studies employing egg injection, egg immersion, egg shell application, single and multiple oral doses, subcutaneous injection, and chemical analysis of field-collected eggs and tissue. The four-to six-ring aromatic compounds are the most toxic to embryos, young birds, and adult birds. For embryos, effects include death, developmental abnormalities, and a variety of cellular and biochemical responses. For adult and young birds, effects include reduced egg production and hatching, increased clutch or brood abandonment, reduced growth, increased organweights, and a variety of biochemical responses. Trophic level accumulation is unlikely. Environmental exposure to PAH in areas of high human population or habitats affected by recent petroleum spills might be sufficient to adversely affect reproduction. Evidence of long-term effects of elevated concentrations of environmental PAH on bird populations is very limited and the mechanisms of effect are unclear.

  19. Antioxidant Activity of Magnolol and Honokiol: Kinetic and Mechanistic Investigations of Their Reaction with Peroxyl Radicals.

    Science.gov (United States)

    Amorati, Riccardo; Zotova, Julija; Baschieri, Andrea; Valgimigli, Luca

    2015-11-06

    Magnolol and honokiol, the bioactive phytochemicals contained in Magnolia officinalis, are uncommon antioxidants bearing isomeric bisphenol cores substituted with allyl functions. We have elucidated the chemistry behind their antioxidant activity by experimental and computational methods. In the inhibited autoxidation of cumene and styrene at 303 K, magnolol trapped four peroxyl radicals, with a kinh of 6.1 × 10(4) M(-1) s(-1) in chlorobenzene and 6.0 × 10(3) M(-1) s(-1) in acetonitrile, and honokiol trapped two peroxyl radicals in chlorobenzene (kinh = 3.8 × 10(4) M(-1) s(-1)) and four peroxyl radicals in acetonitrile (kinh = 9.5 × 10(3) M(-1) s(-1)). Their different behavior arises from a combination of intramolecular hydrogen bonding among the reactive OH groups (in magnolol) and of the OH groups with the aromatic and allyl π-systems, as confirmed by FT-IR spectroscopy and DFT calculations. Comparison with structurally related 3,3',5,5'-tetramethylbiphenyl-4,4'-diol, 2-allylphenol, and 2-allylanisole allowed us to exclude that the antioxidant behavior of magnolol and honokiol is due to the allyl groups. The reaction of the allyl group with a peroxyl radical (C-H hydrogen abstraction) proceeds with rate constant of 1.1 M(-1) s(-1) at 303 K. Magnolol and honokiol radicals do not react with molecular oxygen and produce no superoxide radical under the typical settings of inhibited autoxidations.

  20. Peroxy radical partitioning during the AMMA radical intercomparison exercise

    Directory of Open Access Journals (Sweden)

    M. D. Andrés-Hernández

    2010-04-01

    Full Text Available Peroxy radicals were measured onboard two scientific aircrafts during the AMMA (African Monsoon Multidisciplinary Analysis campaign in summer 2006. This paper reports results from the flight on 16 August 2006 during which measurements of HO2 by laser induced fluorescence spectroscopy at low pressure (LIF-FAGE and total peroxy radicals (RO2*=HO2+ΣRO2, R= organic chain by two similar instruments based on the peroxy radical chemical amplification (PerCA technique were subject of a blind intercomparison. The German DLR-Falcon and the British FAAM-BAe-146 flew wing tip to wing tip for about 30 min making concurrent measurements on 2 horizontal level runs at 697 and 485 hPa over the same geographical area in Burkina Faso. A full set of supporting measurements comprising photolysis frequencies, and relevant trace gases like CO, NO, NO2, NOy, O3 and a wider range of VOCs were collected simultaneously.

    Results are discussed on the basis of the characteristics and limitations of the different instruments used. Generally, no data bias are identified and the RO2* data available agree quite reasonably within the instrumental errors. The [RO2*]/[HO2] ratios, which vary between 1:1 and 3:1, as well as the peroxy radical variability, concur with variations in photolysis rates and in other potential radical precursors. Model results provide additional information about dominant radical formation and loss processes.

  1. Electron attachment and positive ion chemistry of monohydrogenated fluorocarbon radicals

    Energy Technology Data Exchange (ETDEWEB)

    Wiens, Justin P.; Shuman, Nicholas S.; Miller, Thomas M.; Viggiano, Albert A., E-mail: afrl.rvborgmailbox@kirtland.af.mil [Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, New Mexico 87117 (United States)

    2015-08-21

    Rate coefficients and product branching fractions for electron attachment and for reaction with Ar{sup +} are measured over the temperature range 300–585 K for three monohydrogenated fluorocarbon (HFC) radicals (CF{sub 3}CHF, CHF{sub 2}CF{sub 2}, and CF{sub 3}CHFCF{sub 2}), as well as their five closed-shell precursors (1-HC{sub 2}F{sub 4}I, 2-HC{sub 2}F{sub 4}I, 2-HC{sub 2}F{sub 4}Br, 1-HC{sub 3}F{sub 6}I, 2-HC{sub 3}F{sub 6}Br). Attachment to the HFC radicals is always fairly inefficient (between 0.1% and 10% of the Vogt–Wannier capture rate), but generally faster than attachment to analogous perfluorinated carbon radicals. The primary products in all cases are HF-loss to yield C{sub n}F{sub m−1}{sup −} anions, with only a minor branching to F{sup −} product. In all cases the temperature dependences are weak. Attachment to the precursor halocarbons is near the capture rate with a slight negative temperature dependence in all cases except for 2-HC{sub 2}F{sub 4}Br, which is ∼10% efficient at 300 K and becomes more efficient, approaching the capture rate at higher temperatures. All attachment kinetics are successfully reproduced using a kinetic modeling approach. Reaction of the HFC radicals with Ar{sup +} proceeds at or near the calculated collisional rate coefficient in all cases, yielding a wide variety of product ions.

  2. Standard Electrode Potentials Involving Radicals in Aqueous Solution: Inorganic Radicals

    Energy Technology Data Exchange (ETDEWEB)

    Armstrong, David A.; Huie, Robert E.; Koppenol, Willem H.; Lymar, Sergei V.; Merenyi, Gabor; Neta, Pedatsur; Ruscic, Branko; Stanbury, David M.; Steenken, Steen; Wardman, Peter

    2015-12-01

    Recommendations are made for standard potentials involving select inorganic radicals in aqueous solution at 25 °C. These recommendations are based on a critical and thorough literature review and also by performing derivations from various literature reports. The recommended data are summarized in tables of standard potentials, Gibbs energies of formation, radical pKa’s, and hemicolligation equilibrium constants. In all cases, current best estimates of the uncertainties are provided. An extensive set of Data Sheets is appended that provide original literature references, summarize the experimental results, and describe the decisions and procedures leading to each of the recommendations

  3. Radical formation by heavy metals

    Energy Technology Data Exchange (ETDEWEB)

    Beuter, W.

    1982-09-01

    Certain reduced heavy metal ions can convert oxygen to a ''reactive oxygen species'' by donation of an electron. The reactive oxygen then attacks structures susceptible to oxidation, in particular unsaturated fatty acids, and peroxidizes them in a radical reaction. This process is inhibited by the presence of vitamin E and by other means. Peroxidized lipids decay forming free radicals in the process which themselves can peroxidise neighbouring lipids in a radical chain reaction. This decay is, moreover, catalysed by reduced heavy metal ions but on the other hand retarded by selenium-containing glutathione peroxidase. Radical formation by heavy metals is considerably involved in (i) the production of parenteral iron poisoning of the piglet (ii) haemolytic crisis occurring in ruminants through chronic copper poisoning (iii) the production of lead poisoning in ruminants and other animals. These types of poisonings are made worse by a deficiency of vitamin E and/or selenium. Factors which increase the bio-availability of the free heavy metal ion or reduce the redox potential thereof can aid radical formation as well as factors which lead to a reduction of the heavy metal ion e.g. cysteine, ascorbic acid or glucose.

  4. Hückel's Rule of Aromaticity Categorizes Aromatic Closo Boron Hydride Clusters

    OpenAIRE

    Poater i Teixidor, Jordi; Solà i Puig, Miquel; Viñas, Clara; Teixidor, Francesc

    2016-01-01

    A direct connection is established between tridimensional aromatic closo boron hydride clusters and planar aromatic [n]annulenes for medium and large size boron clusters. In particular, our results prove the existence of a link between the two-dimensional Hückel rule followed by aromatic [n]-annulenes and Wade-Mingos' rule of three-dimensional aromaticity applied to the aromatic [BnHn]2- closo boron hydride clusters. Our results show that closo boron hydride clusters can be categorized into d...

  5. Equine digital veins are more sensitive to superoxide anions than digital arteries.

    Science.gov (United States)

    Lapo, Rock Allister; Gogny, Marc; Chatagnon, Gérard; Lalanne, Valérie; Harfoush, Khaled; Assane, Moussa; Desfontis, Jean-Claude; Mallem, Mohamed Yassine

    2014-10-05

    This work was designed to investigate (i) the effect of superoxide dismutase (SOD) inhibition on endothelial function and (ii) the free radical-induced endothelial dysfunction in equine digital veins (EDVs) and equine digital arteries (EDAs) isolated from healthy horses. EDV and EDA rings were suspended in a 5 ml organ bath containing Krebs solution. After a 60 min equilibration period, EDV and EDA rings were contracted with phenylephrine. Then, cumulative concentration-response curves (CCRCs) to acetylcholine were performed. In both EDVs and EDAs, acetylcholine (1 nM to 10 µM) produced concentration-dependent relaxation. We investigated the influence of SOD inhibition by diethyldithiocarbamate (DETC; 100 µM), a CuZnSOD inhibitor, on EDAs and EDVs relaxant responses to acetylcholine. Acetylcholine -mediated relaxation was impaired by DETC only in EDVs. SOD activity assayed by a xanthine-xanthine oxidase method was higher in EDAs compared with EDVs (Psuperoxide anions generating systems showed that in both EDVs and EDAs, the acetylcholine-mediated relaxation was significantly impaired by pyrogallol and homocysteine. This impairment was more pronounced in EDVs than in EDAs. Moreover, the pyrogallol-induced impairment of acetylcholine-mediated relaxation was potentiated by DETC to a greater extent in EDVs. We concluded that due to the lower activity of SOD, EDVs are more sensitive to superoxide anions than EDAs. So, any alteration of superoxide anions metabolism is likely to have a more important impact on venous rather than arterial relaxation.

  6. Anion-π interactions involving [MX(n)](m-) anions: a comprehensive theoretical study.

    Science.gov (United States)

    Estarellas, Carolina; Quiñonero, David; Deyà, Pere M; Frontera, Antonio

    2013-01-14

    In this manuscript we perform a systematic study on the geometric and energetic features of anion-π complexes, wherein the anion is a metal complex of variable shapes and charges. Such a study is lacking in the literature. For the calculations we used the ab initio RI-MP2/def2-TZVPP level of theory. A search in the Cambridge Structural Database (CSD) provides the experimental starting point that inspired the subsequent theoretical study. The influence of [MX(n)](m-) on the anion-π interaction was analyzed in terms of energetic, geometric, and charge transfer properties and Bader's theory of "atom-in-molecules" (AIM). The binding energy depends on the coordination index, geometric features and different orientations adopted by the metallic anion. The binding mode resembling a stacking interaction for linear, trigonal planar and square-planar anions is the most favorable. For tetrahedral and octahedral anions the most favorable orientation is the one with three halogen atoms pointing to the ring.

  7. Supramolecular Chemistry of Selective Anion Recognition for Anions of Environmental Relevance

    Energy Technology Data Exchange (ETDEWEB)

    Jonathan L. Sessler

    2007-09-21

    The major thrust of this project, led by the University of Kansas (Prof. Kristin Bowman-James), entails an exploration of the basic determinants of anion recognition and their application to the design, synthesis, and testing of novel sulfate extractants. A key scientific inspiration for the work comes from the need, codified in simple-to-appreciate terms by the Oak Ridge National Laboratory component of the team (viz. Dr. Bruce Moyer), for chemical entities that can help in the extractive removal of species that have low solubilities in borosilicate glass. Among such species, sulfate anion, has been identified as particularly insidious. Its presence interferes with the vitrification process, thus rendering the remediation of tank waste from, e.g., the Hanford site far more difficult and expensive. The availability of effective extractants, that would allow for the separation of separating sulfate from the major competing anions in the waste, especially nitrate, could allow for pre-vitrification removal of sulfate via liquid-liquid extraction. The efforts at The University of Texas, the subject of this report, have thus concentrated on the development of new sulfate receptors. These systems are designed to increase our basic understanding of anion recognition events and set the stage for the development of viable sulfate anion extractants. In conjunction with the Oak Ridge National Laboratory (ORNL) members of the research team, several of these new receptors were studied as putative extractants, with two of the systems being shown to act as promising synergists for anion exchange.

  8. Pulse radiolysis of solutions of stilbene. 2. Ionic and free radical species in benzene and cyclohexane

    Energy Technology Data Exchange (ETDEWEB)

    Robinson, E.A.; Salmon, G.A.

    1978-02-23

    The spectra of the radical cation and anion of trans-stilbene in benzene and cyclohexane have been resolved using various electron and positive charge scavengers. The decay of the ions is second order in both solvents. In cyclohexane only part of the yield of solvent cations is scavengeable by trans-stilbene; in benzene the stilbene cation is converted to the dimer in the presence of high stilbene concentrations. The electron scavengers N/sub 2/O and c-C/sub 6/F/sub 12/ compete directly with trans-stilbene for electrons and we deduce rate constants for the reactions of electrons with c-C/sub 6/F/sub 12/ and trans-stilbene of (1.2 +- 0.6) x 10/sup 12/ and (0.72 +- 0.5) x 10/sup 12/ M/sup -1/ s/sup -1/, respectively. SF/sub 6/ reduces the yield of trans-stilbene anion more efficiently than can be attributed solely to electron scavenging and it is shown that electron transfer from trans-stilbene anion to SF/sub 6/ occurs at a rate constant, k/sub 4/ = (3.9 +- 0.4) x 10/sup 9/ M/sup -1/ s/sup -1/. The presence of either aniline or n-butylamine causes enhancement of the yield of stilbene anion, the effect being particularly marked in the case of aniline. Possible explanations of the effect are considered. It is proposed that the UV absorptions are due to radical species, which in cyclohexane solution are most probably formed by the addition of cyclohexyl radicals to the olefinic double bond of the stilbenes.

  9. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Lu; Smith, Jeremy; Laskin, Alexander; Anastasio, Cort N.; Laskin, Julia; Zhang, Qi

    2014-01-01

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol and two methoxy-phenols (syringol and guaiacol) with two major aqueous phase oxidants – the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (•OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), desorption electrospray ionization mass spectrometry (DESIMS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O/C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than •OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenol had reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O/C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are likely an important source of brown carbon in the atmosphere, especially in regions influenced by biomass burning.

  10. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    Science.gov (United States)

    Yu, L.; Smith, J.; Laskin, A.; Anastasio, C.; Laskin, J.; Zhang, Q.

    2014-12-01

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol (compound with formula C6H5OH)), guaiacol (2-methoxyphenol), and syringol (2,6-dimethoxyphenol) with two major aqueous-phase oxidants - the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (· OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than · OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenolic compound has reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-visible region, suggesting that aqueous-phase reactions of phenols may contribute to formation of secondary brown carbon in the atmosphere, especially in regions influenced by biomass burning.

  11. Beyond organic chemistry: aromaticity in atomic clusters.

    Science.gov (United States)

    Boldyrev, Alexander I; Wang, Lai-Sheng

    2016-04-28

    We describe joint experimental and theoretical studies carried out collaboratively in the authors' labs for understanding the structures and chemical bonding of novel atomic clusters, which exhibit aromaticity. The concept of aromaticity was first discovered to be useful in understanding the square-planar unit of Al4 in a series of MAl4(-) bimetallic clusters that led to discoveries of aromaticity in many metal cluster systems, including transition metals and similar cluster motifs in solid compounds. The concept of aromaticity has been found to be particularly powerful in understanding the stability and bonding in planar boron clusters, many of which have been shown to be analogous to polycyclic aromatic hydrocarbons in their π bonding. Stimulated by the multiple aromaticity in planar boron clusters, a design principle has been proposed for stable metal-cerntered aromatic molecular wheels of the general formula, M@Bn(k-). A series of such borometallic aromatic wheel complexes have been produced in supersonic cluster beams and characterized experimentally and theoretically, including Ta@B10(-) and Nb@B10(-), which exhibit the highest coordination number in two dimensions.

  12. Heterogeneous photocatalytic reactions of sulfur aromatic compounds.

    Science.gov (United States)

    Samokhvalov, Alexander

    2011-11-18

    Sulfur aromatic compounds, such as mono-, di-, tri-, and tetraalkyl-substituted thiophene, benzothiophenes, dibenzothiophenes, are the molecular components of many fossils (petroleum, oil shale, tar sands, bitumen). Structural units of natural, cross-linked heteroaromatic polymers present in brown coals, turf, and soil are similar to those of sulfur aromatic compounds. Many sulfur aromatic compounds are found in the streams of petroleum refining and upgrading (naphthas, gas oils) and in the consumer products (gasoline, diesel, jet fuels, heating fuels). Besides fossils, the structural fragments of sulfur aromatic compounds are present in molecules of certain organic semiconductors, pesticides, small molecule drugs, and in certain biomolecules present in human body (pheomelanin pigments). Photocatalysis is the frontier area of physical chemistry that studies chemical reactions initiated by absorption of photons by photocatalysts, that is, upon electronic rather than thermal activation, under "green" ambient conditions. This review provides systematization and critical review of the fundamental chemical and physicochemical information on heterogeneous photocatalysis of sulfur aromatic compounds accumulated in the last 20-30 years. Specifically, the following topics are covered: physicochemical properties of sulfur aromatic compounds, major classes of heterogeneous photocatalysts, mechanisms and reactive intermediates of photocatalytic reactions of sulfur aromatic compounds, and the selectivity of these reactions. Quantum chemical calculations of properties and structures of sulfur aromatic compounds, their reactive intermediates, and the structure of adsorption complexes formed on the surface of the photocatalysts are also discussed.

  13. In situ direct sampling mass spectrometric study on formation of polycyclic aromatic hydrocarbons in toluene pyrolysis.

    Science.gov (United States)

    Shukla, Bikau; Susa, Akio; Miyoshi, Akira; Koshi, Mitsuo

    2007-08-30

    The gas-phase reaction products of toluene pyrolysis with and without acetylene addition produced in a flow tube reactor at pressures of 8.15-15.11 Torr and temperatures of 1136-1507 K with constant residence time (0.56 s) have been detected in an in situ direct sampling mass spectrometric study by using a vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry technique. Those products range from methyl radical to large polycyclic aromatic hydrocarbons (PAHs) of mass 522 amu (C(42)H(18)) including smaller species, radicals, polyynes, and PAHs, together with ethynyl, methyl, and phenyl PAHs. On the basis of observed mass spectra, the chemical kinetic mechanisms of the formation of products are discussed. Especially, acetylene is mixed with toluene to understand the effect of the hydrogen abstraction and acetylene addition (HACA) mechanism on the formation pathways of products in toluene pyrolysis. The most prominent outputs of this work are the direct detection of large PAHs and new reaction pathways for the formation of PAHs with the major role of cyclopenta-fused radicals. The basis of this new reaction route is the appearance of different sequences of mass spectra that well explain the major role of aromatic radicals mainly cyclopenta fused radicals of PAHs resulting from their corresponding methyl PAHs, with active participation of c-C(5)H(5), C(6)H(5), C(6)H(5)CH(2) ,and C(9)H(7) in the formation of large PAHs. The role of the HACA only seemed important for the formation of stable condensed PAHs from unstable primary PAHs with zigzag structure (having triple fusing sites) in one step by ring growth with two carbon atoms.

  14. Three hydroxy aurone compounds as chemosensors for cyanide anions.

    Science.gov (United States)

    Chen, Huihui; Sun, Yunhui; Zhou, Chuanjian; Cao, Duxia; Liu, Zhiqiang; Ma, Lin

    2013-12-01

    Three new 4-hydroxy aurone compounds 1-3 with dimethylamino (1), bromine (2) and cyano (3) as terminal group have been synthesized. Their photophysical properties as well as recognition properties for cyanide anions in acetonitrile and aqueous solution have also been examined. These compounds exhibit remarkable response to cyanide anions with obvious color and fluorescence change owing to hydrogen bonding reaction between cyanide anions and the O-H moiety of the sensors, which allows naked eye detection of cyanide anions.

  15. Epistemological barriers to radical behaviorism.

    Science.gov (United States)

    O'Donohue, W T; Callaghan, G M; Ruckstuhl, L E

    1998-01-01

    The historian and philosopher of science Gaston Bachelard proposed the concept of epistemological barriers to describe the intellectual challenges encountered by scientists in their work. In order to embrace novel ways of approaching a problem in science, scientists must overcome barriers or obstacles posed by their prior views. For example, Einsteinian physics presents scientists with claims that space is curved and that time and space are on the same continuum. We utilize Bachelard's concept of epistemological barriers to describe the differences between the intellectual journeys students pursuing advanced studies face when attempting to accept cognitive psychology or radical behaviorism. We contend that the folk psychological beliefs that students typically hold when entering these studies pose less challenge to cognitive psychology than to radical behaviorism. We also suggest that these barriers may also partly be involved in the problematic exegesis that has plagued radical behaviorism. In close, we offer some suggestions for dealing with these epistemological barriers.

  16. Epistemological barriers to radical behaviorism

    Science.gov (United States)

    O'Donohue, William T.; Callaghan, Glenn M.; Ruckstuhl, L. E.

    1998-01-01

    The historian and philosopher of science Gaston Bachelard proposed the concept of epistemological barriers to describe the intellectual challenges encountered by scientists in their work. In order to embrace novel ways of approaching a problem in science, scientists must overcome barriers or obstacles posed by their prior views. For example, Einsteinian physics presents scientists with claims that space is curved and that time and space are on the same continuum. We utilize Bachelard's concept of epistemological barriers to describe the differences between the intellectual journeys students pursuing advanced studies face when attempting to accept cognitive psychology or radical behaviorism. We contend that the folk psychological beliefs that students typically hold when entering these studies pose less challenge to cognitive psychology than to radical behaviorism. We also suggest that these barriers may also partly be involved in the problematic exegesis that has plagued radical behaviorism. In close, we offer some suggestions for dealing with these epistemological barriers. PMID:22478314

  17. Determination of hydroxyl radicals in TiO2/Ti photoelectrocatalytic oxidation system using Fe(phen)3 2+ spectrophotometry

    Institute of Scientific and Technical Information of China (English)

    JIANG Yan-li; LIU Hui-ling; WANG Qun-hui; JIANG Zhao-hua

    2006-01-01

    A new method of determining the cumulate concentration of hydroxyl radicals in the TiO2/Ti photoelectrocatalytic(PEC)oxidation system was established by o-phenanthroline-Fe(Ⅱ)(Fe(phen)32+) spectrophotometry and using anion exchange membrane. Fe concentration of hydroxyl radicals can be calculated through determining the change of the Fe(phen)33+ absorbency at 509 nm. In addition, the research results showed the production rate of hydroxyl radicals was affected obviously by pH of solution, the cumulate concentration of hydroxyl radicals was the largest at nearby the initial pH 6.3 (isoelectric point), and the change direction of pH after illumination tended to nearby isoelectric point.

  18. Color Responses of a Tripodal Colorimetric Sensor toward Anions

    Institute of Scientific and Technical Information of China (English)

    WEI Lan-Hua; HE Yong-Bing; WU Jin-Long; QIN Hai-Juan; XU Kuo-Xi; MENG Ling-Zhi

    2005-01-01

    A thiourea-based tripodal colorimetric anion sensor was synthesized. Its binding abilities with AcO- and halide anions in DMSO were studied by UV-Vis spectra. The sensor showed different color responses to these anions. The association constants and different stoichiometries were deduced by nonlinear least-square curve fitting or linear fitting.

  19. A theoretical investigation on the HCCS radical and its ions

    Energy Technology Data Exchange (ETDEWEB)

    Puzzarini, Cristina [Dipartimento di Chimica ' G. Ciamician' , Universita di Bologna, Via Selmi 2, I-40126 Bologna (Italy)], E-mail: cristina.puzzarini@unibo.it

    2008-05-04

    The thioketenyl (HCCS) radical and its related cation, HCCS{sup +}, and anion, HCCS{sup -}, have been investigated at a high level of accuracy. The singles and doubles coupled-cluster method including a perturbational correction for connected triple excitations, CCSD(T), in conjunction with correlation consistent basis sets ranging in size from quadruple to sextuple zeta have been employed. Extrapolation to the complete basis set limit has been used with accurate treatments of core-valence correlation effects to accurately predict equilibrium structures, dipole moments as well as ionization potential and electron affinity. For all the species studied, harmonic vibrational frequencies have also been evaluated to obtain zero-point corrections to energies.

  20. Synthesis and DPPH Radical Scavenging Activity of Prenylated Phenol Derivatives

    Directory of Open Access Journals (Sweden)

    Héctor Carrasco

    2012-01-01

    Full Text Available The synthesis of twenty six prenylated phenols derivatives is reported. These compounds were obtained under mild conditions via Electrophilic Aromatic Substitution (EAS coupling reactions between phenol derivatives containing electron-donor subtituents and 3-methyl-2-buten-1-ol using BF3×OEt2. Dialkylations were also produced with this method. The formation of a chroman ring by intramolecular cyclization between a sp2 carbon from the prenyl group with the hydroxyl substituent in the ortho position occurred with some phenols. All the synthesized compounds were evaluated as antioxidants according to a DPPH radical scavenging activity assay. IC50 values of five synthesized compounds indicated they were as good antioxidants as Trolox™.

  1. Radical democratic politics and feminism

    Directory of Open Access Journals (Sweden)

    Martínez Labrin, Soledad

    2006-05-01

    Full Text Available In the article I present a reflection around the radical democratic project proposed by Chantal Mouffe and Ernesto Laclau. Specifically, I examine the application of the project in the context of the “new social movements” and especially, of feminist movement. I state the need of drawing attention to universalism and essentialism as the main obstacles to generate a collective proposal without margins. Nevertheless, doubts remind about the possibility of building up a feminism tailored by the radical democratic project, in a stage in which the political action of such a movement is characterized by categories that are closed and crystallized

  2. Vaginal radical trachelectomy: an update.

    Science.gov (United States)

    Plante, Marie

    2008-11-01

    The vaginal radical trachelectomy has emerged as a valuable fertility-preserving treatment option for young women with early-stage disease. Cancer-related infertility is associated with feelings of depression, grief, stress, and sexual dysfunction. Data have shown that the overall oncological outcome is safe and that the obstetrical outcome is promising. In this article, we analyze the data on the vaginal radical trachelectomy published over the last 10 years in the context of what we have learned, what issues remain unclear, and what the future holds.

  3. Exploring mild enzymatic sustainable routes for the synthesis of bio-degradable aromatic-aliphatic oligoesters.

    Science.gov (United States)

    Pellis, Alessandro; Guarneri, Alice; Brandauer, Martin; Acero, Enrique Herrero; Peerlings, Henricus; Gardossi, Lucia; Guebitz, Georg M

    2016-05-01

    The application of Candida antarctica lipase B in enzyme-catalyzed synthesis of aromatic-aliphatic oligoesters is here reported. The aim of the present study is to systematically investigate the most favorable conditions for the enzyme catalyzed synthesis of aromatic-aliphatic oligomers using commercially available monomers. Reaction conditions and enzyme selectivity for polymerization of various commercially available monomers were considered using different inactivated/activated aromatic monomers combined with linear polyols ranging from C2 to C12 . The effect of various reaction solvents in enzymatic polymerization was assessed and toluene allowed to achieve the highest conversions for the reaction of dimethyl isophthalate with 1,4-butanediol and with 1,10-decanediol (88 and 87% monomer conversion respectively). Mw as high as 1512 Da was obtained from the reaction of dimethyl isophthalate with 1,10-decanediol. The obtained oligomers have potential applications as raw materials in personal and home care formulations, for the production of aliphatic-aromatic block co-polymers or can be further functionalized with various moieties for a subsequent photo- or radical polymerization.

  4. Formation of Polycyclic Aromatic Hydrocarbons and Nitrogen Containing Polycyclic Aromatic Compounds in Titan's Atmosphere, the Interstellar Medium and Combustion

    Science.gov (United States)

    Landera, Alexander

    2013-12-01

    Several different mechanisms leading to the formation of (substituted) naphthalene and azanaphthalenes were examined using theoretical quantum chemical calculations. As a result, a series of novel synthetic routes to Polycyclic Aromatic Hydrocarbons (PAHs) and Nitrogen Containing Polycyclic Aromatic Compounds (N-PACs) have been proposed. On Earth, these aromatic compounds originate from incomplete combustion and are released into our environment, where they are known to be major pollutants, often with carcinogenic properties. In the atmosphere of a Saturn's moon Titan, these PAH and N-PACs are believed to play a critical role in organic haze formation, as well as acting as chemical precursors to biologically relevant molecules. The theoretical calculations were performed by employing the ab initio G3(MP2,CC)/B3LYP/6-311G** method to effectively probe the Potential Energy Surfaces (PES) relevant to the PAH and N-PAC formation. Following the construction of the PES, Rice-Ramsperger-Kassel-Markus (RRKM) theory was used to evaluate all unimolecular rate constants as a function of collision energy under single-collision conditions. Branching ratios were then evaluated by solving phenomenological rate expressions for the various product concentrations. The most viable pathways to PAH and N-PAC formation were found to be those where the initial attack by the ethynyl (C2H) or cyano (CN) radical toward a unsaturated hydrocarbon molecule led to the formation of an intermediate which could not effectively lose a hydrogen atom. It is not until ring cyclization has occurred, that hydrogen elimination leads to a closed shell product. By quenching the possibility of the initial hydrogen atom elimination, one of the most competitive processes preventing the PAH or N-PAC formation was avoided, and the PAH or N-PAC formation was allowed to proceed. It is concluded that these considerations should be taken into account when attempting to explore any other potential routes towards

  5. Specific anion effects in Artemia salina.

    Science.gov (United States)

    Lo Nostro, Pierandrea; Ninham, Barry W; Carretti, Emiliano; Dei, Luigi; Baglioni, Piero

    2015-09-01

    The specific anion effect on the vitality of Artemia salina was investigated by measuring the Lethal Time LT50 of the crustaceans in the presence of different sodium salts solutions at room temperature and at the same ionic strength as natural seawater. Fluoride, thiocyanate and perchlorate are the most toxic agents, while chloride, bromide and sulfate are well tolerated. The rates of oxygen consumption of brine shrimps were recorded in mixed NaCl+NaF or NaCl+NaSCN solutions as a function of time. The results are discussed in terms of the Hofmeister series, and suggest that, besides the biochemical processes that involve F(-), SCN(-) and ClO4(-), the different physico-chemical properties of the strong kosmotropic and chaotropic anions may contribute in determining their strong toxicity for A. salina.

  6. Electron anions and the glass transition temperature

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Lewis E.; Sushko, Peter V.; Tomota, Yudai; Hosono, Hideo

    2016-08-24

    Properties of glasses are typically controlled by judicious selection of the glass-forming and glass-modifying constituents. Through an experimental and computational study of the crystalline, molten, and amorphous [Ca12Al14O32]2+ ∙ (e)2, we demonstrate that electron anions in this system behave as glass-modifiers that strongly affect solidification dynamics, the glass transition temperature, and spectroscopic properties of the resultant amorphous material. Concentration of such electron anions is a consequential control parameter: it invokes materials evolution pathways and properties not available in conventional glasses, which opens a new avenue in rational materials design.

  7. Stability and Characteristics of the Halogen Bonding Interaction in an Anion-Anion Complex: A Computational Chemistry Study.

    Science.gov (United States)

    Wang, Guimin; Chen, Zhaoqiang; Xu, Zhijian; Wang, Jinan; Yang, Yang; Cai, Tingting; Shi, Jiye; Zhu, Weiliang

    2016-02-04

    Halogen bonding is the noncovalent interaction between the positively charged σ-hole of organohalogens and nucleophiles. In reality, both the organohalogen and nucleophile could be deprotonated to form anions, which may lead to the vanishing of the σ-hole and possible repulsion between the two anions. However, our database survey in this study revealed that there are halogen bonding-like interactions between two anions. Quantum mechanics calculations with small model complexes composed of halobenzoates and propiolate indicated that the anion-anion halogen bonding is unstable in vacuum but attractive in solvents. Impressively, the QM optimized halogen bonding distance between the two anions is shorter than that in a neutral system, indicating a possibly stronger halogen bonding interaction, which is verified by the calculated binding energies. Furthermore, natural bond orbital and quantum theory of atoms in molecule analyses also suggested stronger anion-anion halogen bonding than that of the neutral one. Energy decomposition by symmetry adapted perturbation theory revealed that the strong binding might be attributed to large induction energy. The calculations on 4 protein-ligand complexes from PDB by the QM/MM method demonstrated that the anion-anion halogen bonding could contribute to the ligands' binding affinity up to ∼3 kcal/mol. Therefore, anion-anion halogen bonding is stable and applicable in reality.

  8. Oxidation of Guanine by Carbonate Radicals Derived from Photolysis of Carbonatotetramminecobalt(III) Complexes and the pH Dependence of Intrastrand DNA Cross-links Mediated by Guanine Radical Reactions

    OpenAIRE

    Crean, Conor; Lee, Young Ae; Yun, Byeong Hwa; Geacintov, Nicholas E.; Shafirovich, Vladimir

    2008-01-01

    The carbonate radical anion CO3•− is a decomposition product of nitrosoperoxycarbonate derived from the combination of carbon dioxide and peroxynitrite, an important biological byproduct of the inflammatory response. The selective oxidation of guanine in DNA by CO3•− radicals is known to yield spiroiminodihydantoin (Sp), guanidinohydantoin (Gh), and a novel intrastrand cross-linked product, 5’-d(CCATCG*CT*ACC) between guanine C8 (G*) and thymine N3 (T*) atoms in the oligonucleotide (Crean et ...

  9. LOW TEMPERATURE FORMATION OF NITROGEN-SUBSTITUTED POLYCYCLIC AROMATIC HYDROCARBONS (PANHs)—BARRIERLESS ROUTES TO DIHYDRO(iso)QUINOLINES

    Energy Technology Data Exchange (ETDEWEB)

    Parker, Dorian S. N.; Yang, Tao; Dangi, Beni B.; Kaiser, Ralf I. [Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Bera, Partha P.; Lee, Timothy J., E-mail: ralfk@hawaii.edu, E-mail: Timothy.J.Lee@nasa.gov [Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, Mountain View, CA 94035 (United States)

    2015-12-20

    Meteorites contain bio-relevant molecules such as vitamins and nucleobases, which consist of aromatic structures with embedded nitrogen atoms. Questions remain over the chemical mechanisms responsible for the formation of nitrogen-substituted polycyclic aromatic hydrocarbons (PANHs) in extraterrestrial environments. By exploiting single collision conditions, we show that a radical mediated bimolecular collision between pyridyl radicals and 1,3-butadiene in the gas phase forms nitrogen-substituted polycyclic aromatic hydrocarbons (PANHs) 1,4-dihydroquinoline and to a minor amount 1,4-dihydroisoquinoline. The reaction proceeds through the formation of a van der Waals complex, which circumnavigates the entrance barrier implying it can operate at very low kinetic energy and therefore at low temperatures of 10 K as present in cold molecular clouds such as TMC-1. The discovery of facile de facto barrierless exoergic reaction mechanisms leading to PANH formation could play an important role in providing a population of aromatic structures upon which further photo-processing of ice condensates could occur to form nucleobases.

  10. Lowest autodetachment state of the water anion

    Science.gov (United States)

    Houfek, Karel; Čížek, Martin

    2016-05-01

    The potential energy surface of the ground state of the water anion H2O- is carefully mapped using multireference CI calculations for a large range of molecular geometries. Particular attention is paid to a consistent description of both the O-+H2 and OH-+H asymptotes and to a relative position of the anion energy to the ground state energy of the neutral molecule. The autodetachment region, where the anion state crosses to the electronic continuum is identified. The local minimum in the direction of the O- + H2 channel previously reported by Werner et al. [J. Chem. Phys. 87, 2913 (1987)] is found to be slighly off the linear geometry and is separated by a saddle from the autodetachment region. The autodetachment region is directly accessible from the OH-+H asymptote. For the molecular geometries in the autodetachment region and in its vicinity we also performed fixed-nuclei electron-molecule scattering calculations using the R-matrix method. Tuning of consistency of a description of the correlation energy in both the multireference CI and R-matrix calculations is discussed. Two models of the correlation energy within the R-matrix method that are consistent with the quantum chemistry calculations are found. Both models yield scattering quantities in a close agreement. The results of this work will allow a consistent formulation of the nonlocal resonance model of the water anion in a future publication. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.

  11. Politseiuuringud kooskõlastamisele / Liivia Anion

    Index Scriptorium Estoniae

    Anion, Liivia

    2003-01-01

    1. aprillil 2003. a. moodustatud uurimistööde kooskõlastamise komisjoni tegevuse eesmärk on saada ülevaade kõrgkoolides õppivate töötajate poolt politseis korraldatavatest uurimustest, kasutada saadud infot politsei kasuks ja vältida teenistujate tööd segavate uurimuste tegemist. Komisjoni liige Liivia Anion teeb ülevaate komisjoni otsustuspädevuse valdkondadest ja töökorraldusest

  12. From small aromatic molecules to functional nanostructured carbon by pulsed laser-induced photochemical stitching

    Directory of Open Access Journals (Sweden)

    R. R. Gokhale

    2012-06-01

    Full Text Available A novel route employing UV laser pulses (KrF Excimer, 248 nm to cleave small aromatic molecules and stitch the generated free radicals into functional nanostructured forms of carbon is introduced. The process differs distinctly from any strategies wherein the aromatic rings are broken in the primary process. It is demonstrated that this pulsed laser-induced photochemical stitching (PLPS process when applied to routine laboratory solvents (or toxic chemical wastes when discarded Chlorobenzene and o-Dichlorobenzene yields Carbon Nanospheres (CNSs comprising of graphene-like sheets assembled in onion-like configurations. This room temperature process implemented under normal laboratory conditions is versatile and clearly applicable to the whole family of haloaromatic compounds without and with additions of precursors or other nanomaterials. We further bring out its applicability for synthesis of metal-oxide based carbon nanocomposites.

  13. Consumption of peptide-included and free tryptophan induced by peroxyl radicals: A kinetic study.

    Science.gov (United States)

    Fuentes, E; López-Alarcón, C

    2014-10-01

    It is well-known that tryptophan residues are efficiently oxidized by peroxyl radicals, generating kynurenine, and N-formyl kynurenine as well as hydroperoxide derivatives as products. In the present work we studied the kinetic of such reaction employing free and peptide-included tryptophan. Two azocompounds were used to produce peroxyl radicals: AAPH (2,2'-Azobis(2-methylpropionamidine) dihydrochloride) and ABCVA (4,4'-Azobis(4-cyanovaleric acid)), which generate cationic and anionic peroxyl radicals, respectively. Tryptophan consumption was assessed by fluorescence spectroscopy and the reactions were carried out in phosphate buffer (75mM, pH 7.4) at 45°C. Only a slight effect of the peroxyl radical charge was evidenced on the consumption of free tryptophan and the dipeptide Gly-Trp. Employing AAPH as peroxyl radical source, at low free tryptophan concentrations (1-10µM) near 0.3 mol of tryptophan were consumed per each mol of peroxyl radicals introduced into the system. However, at high free tryptophan concentrations (100µM-1mM) such stoichiometry increased in a tryptophan concentration-way. At 1mM three moles of tryptophan were consumed per mol of AAPH-derived peroxyl radicals, evidencing the presence of chain reactions. A similar behavior was observed when di and tri-peptides (Gly-Trp, Trp-Gly, Gly-Trp-Gly, Trp-Ala, Ala-Trp-Ala) were studied. Nonetheless, at low initial concentration (5µM), the initial consumption rate of tryptophan included in the peptides was two times higher than free tryptophan. In contrast, at high concentration (1mM) free and peptide-included tryptophan showed similar initial consumption rates. These results could be explained considering a disproportionation process of tryptophanyl radicals at low free tryptophan concentrations, a process that would be inhibited when tryptophan is included in peptides.

  14. Donnan membrane technique (DMT) for anion measurement.

    Science.gov (United States)

    Vega, Flora Alonso; Weng, Liping; Temminghoff, Erwin J M; Van Riemsdijk, Willem H

    2010-04-01

    Donnan membrane technique (DMT) is developed and tested for determination of free anion concentrations. Time needed to reach the Donnan membrane equilibrium depends on type of ions and the background. The Donnan membrane equilibrium is reached in 1 day for Cl(-), 1-2 days for NO(3)(-), 1-4 days for SO(4)(2-) and SeO(4)(2-), and 1-14 days for H(2)PO(4)(-) in a background of 2-200 mM KCl or K(2)SO(4). The strongest effect of ionic strength on equilibrium time is found for H(2)PO(4)(-), followed by SO(4)(2-) and SeO(4)(2-), and then by Cl(-) and NO(3)(-). The negatively charged organic particles of fulvic and humic acids do not pass the membrane. Two approaches for the measurement of different anion species of the same element, such as SeO(4)(2-) and HSeO(3)(-), using DMT are proposed and tested. These two approaches are based on transport kinetics or response to ionic strength difference. A transport model that was developed previously for cation DMT is applied in this work to analyze the rate-limiting step in the anion DMT. In the absence of mobile/labile complexes, transport tends to be controlled by diffusion in solution at a low ionic strength, whereas at a higher ionic strength, diffusion in the membrane starts to control the transport.

  15. Radical-cationic gaseous amino acids: a theoretical study.

    Science.gov (United States)

    Sutherland, Kailee N; Mineau, Philippe C; Orlova, Galina

    2007-08-16

    Three major forms of gaseous radical-cationic amino acids (RCAAs), keto (COOH), enolic (C(OH)OH), and zwitterionic (COO(-)), as well as their tautomers, are examined for aliphatic Ala(.+), Pro(.+), and Ser(.+), sulfur-containing Cys(.+), aromatic Trp(.+), Tyr(.+), and Phe(.+), and basic His(.+). The hybrid B3LYP exchange-correlation functional with various basis sets along with the highly correlated CCSD(T) method is used. For all RCAAs considered, the main stabilizing factor is spin delocalization; for His(.+), protonation of the basic side chain is equally important. Minor stabilizing factors are hydrogen bonding and 3e-2c interactions. An efficient spin delocalization along the N-C(alpha)-C(O-)O moiety occurs upon H-transfer from C(alpha) to the carboxylic group to yield the captodative enolic form, which is the lowest-energy isomer for Ala(.+), Pro(.+), Ser(.+), Cys(.+), Tyr(.+), and Phe(.+). This H-transfer occurs in a single step as a 1,3-shift through the sigma-system. For His(.+), the lowest-energy isomer is formed upon H-transfer from C(alpha) to the basic side chain, which results in a keto form, with spin delocalized along the N-C(alpha)-C=O fragment. Trp(.+) is the only RCAA that favors spin delocalization over an aromatic system given the low ionization energy of indole. The lowest-energy isomer of Trp(.+) is a keto form, with no H-transfer.

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

    Science.gov (United States)

    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

  17. On the atmospheric degradation of multifunctional organic compounds by NO3 and SO4- radicals in aqueous solution

    Science.gov (United States)

    Schöne, Luisa; Stieger, Bastian; Weller, Christian; Herrmann, Hartmut

    2014-05-01

    The atmospheric decomposition and transformation of a large number of organic compounds is initiated by radicals in the gas and aqueous phase. With increasing degree of oxidation and functionalization, organics become less volatile and more water soluble and partition into aqueous particles and cloud droplets where the oxidation by radicals continues. NO3 and SO4- radicals dominate the atmospheric aqueous phase besides OH radicals. Within this work, temperature dependent kinetic investigations were conducted by use of a laser flash photolysis laser long path absorption (LFPLLPA) setup. Second order rate constants for the reactions of 3-methoxy-1-propanol, diethylether, methylpropylether, 2-methyloxirane-2-carbaldehyde, 2,3-dihydroxy-2-methylpropanal, pyruvic, glyoxylic and glycolic acid as well as glyoxal, methylglyoxal and glycolaldehyde with NO3 and SO4- radicals were measured in a temperature range of 278 and 318 K applying pseudo-first order kinetics. The reactivity of the acids and their anions were investigated separately adjusting the pH to pH 1 or pH 8 for the acid or the anion form, respectively. From these measurements, activation parameters were derived. Measured k2nd range from 106 - 108 M1 s1. The kinetic and thermodynamic parameters as well as reaction mechanisms will be discussed within this contribution.

  18. Radical Innovation and Network Evolution

    NARCIS (Netherlands)

    S.M.W. Phlippen (Sandra); M. Riccaboni

    2007-01-01

    textabstractThis paper examines how a radical technological innovation affects alliance formation of firms and subsequent network structures. We use longitudinal data of interfirm R&D collaborations in the biopharmaceutical industry in which a new technological regime is established. Our findings su

  19. Wild radical square zero algebras

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    It is shown that a radical square zero algebra is wild, if and only if it is of Corner's type, and it is strictly wild if and only if it is Endo-wild. This gives a negative answer to a problem posed by Simson.

  20. Is Radical Innovation Management Misunderstood?

    DEFF Research Database (Denmark)

    Kristiansen, Jimmi Normann; Gertsen, Frank

    2015-01-01

    This paper poses a critical view on radical innovation (RI) management research and practice. The study investigates how expected RI performance influences firms’ under- standing of their RI capability. RI performance is often based on output measures such as market shares or fiscal return...

  1. Exploring the Theories of Radicalization

    Directory of Open Access Journals (Sweden)

    Maskaliūnaitė Asta

    2015-12-01

    Full Text Available After the London bombings in July 2005, the concern of terrorism scholars and policy makers has turned to “home-grown” terrorism and potential for political violence from within the states. “Radicalization” became a new buzz word. This article follows a number of reviews of the literature on radicalization and offers another angle for looking at this research. First, it discusses the term “radicalization” and suggests the use of the following definition of radicalization as a process by which a person adopts belief systems which justify the use of violence to effect social change and comes to actively support as well as employ violent means for political purposes. Next, it proposes to see the theories of radicalization focusing on the individual and the two dimensions of his/her motivation: whether that motivation is internal or external and whether it is due to personal choice or either internal (due to some psychological traits or external compulsion. Though not all theories fall neatly within these categories, they make it possible to make comparisons of contributions from a variety of different areas thus reflecting on the interdisciplinary nature of the study of terrorism in general and radicalization as a part of it.

  2. Radical review of NHS funding.

    Science.gov (United States)

    1988-02-06

    The Government is to carry out a radical review of the way the NHS is funded, Prime Minister Margaret Thatcher confirmed last week. And she hinted that she herself would be taking a leading role in drawing up proposals for reform.

  3. Detecting Social Polarization and Radicalization

    DEFF Research Database (Denmark)

    Qureshi, Pir Abdul Rasool; Memon, Nasrullah; Wiil, Uffe Kock

    2011-01-01

    This paper proposes a novel system to detect social polarization and to estimate the chances of violent radicalization associated with it. The required processes for such a system are indicated; it is also analyzed how existing technologies can be integrated into the proposed system to fulfill...

  4. Students' Ideas and Radical Constructivism

    Science.gov (United States)

    Sánchez Gómez, Pedro J.

    2016-01-01

    In this article, I study, from the point of view of the analytic philosophy of mind, the compatibility of students' ideas studies (SIS) with radical constructivism (RC). I demonstrate that RC is based on a psychology of "narrow mental states"; that is, the idea that the mental content of an individual can be fully characterised without…

  5. A new polymeric ionic liquid-based magnetic adsorbent for the extraction of inorganic anions in water samples.

    Science.gov (United States)

    Chen, Lei; Huang, Xiaojia; Zhang, Yong; Yuan, Dongxing

    2015-07-17

    In this work, a novel type of polymeric ionic liquid (PIL)-based magnetic adsorbent was successfully synthesized and applied for the extraction and determination of seven inorganic anions in water samples by coupling with ion chromatography. The new adsorbent was synthesized by simple free radical copolymerization of 1-ally-3-vinylimidazolium chloride, ethylene glycol dimethacrylate and silica-coated magnetite. The adsorbent exhibited well-defined core-shell structure and good magnetic response ability. Furthermore, due to the presence of abundant anion-exchange groups in the PIL, the adsorbent displayed expected extraction performance for anions including F(-), Cl(-), Br(-), NO2(-), NO3(-), PO4(3-) and SO4(2-). Various experimental parameters that could affect the extraction performance, such as the amount of adsorbent, desorption solvent, extraction and desorption time, the pH value of sample solution were investigated in detail. Under the optimized conditions, low limits of detection (S/N=3) and quantification limits (S/N=10) of the proposed method for the target anions were achieved within the range of 0.061-0.73μg/L and 0.19-2.41μg/L, respectively. The repeatability was investigated by evaluating the intra-day, inter-day precisions and batch-to-batch reproducibility with relative standard deviations (RSDs) lower than 11%. At the same time, the method also showed high extraction speed, simplicity, practicality and low cost for the extraction inorganic anions. Finally, the proposed method was used to detect anions in different water samples successfully. The recoveries were in the range of 71.0-111%, and the RSDs were below 12% in the all cases.

  6. Oxidative capacity of the Mexico City atmosphere – Part 1: A radical source perspective

    Directory of Open Access Journals (Sweden)

    M. J. Molina

    2007-04-01

    Full Text Available A detailed analysis of OH, HO2 and RO2 radical sources is presented for the near field photochemical regime inside the Mexico City Metropolitan Area (MCMA. During spring of 2003 (MCMA-2003 field campaign an extensive set of measurements was collected to quantify time resolved ROx (sum of OH, HO2, RO2 radical production rates from day- and nighttime radical sources. The Master Chemical Mechanism (MCMv3.1 was constrained by measurements of (1 concentration time-profiles of photosensitive radical precursors, i.e., nitrous acid (HONO, formaldehyde (HCHO, ozone (O3, glyoxal (CHOCHO, and other oxygenated volatile organic compounds (OVOCs; (2 respective photolysis-frequencies (J-values; (3 concentration time-profiles of alkanes, alkenes, and aromatic VOCs (103 compound are treated and oxidants, i.e., OH- and NO3 radicals, O3; and (4 NO, NO2, meteorological and other parameters. The ROx production rate was calculated directly from these observations; MCM was used to estimate further ROx production from unconstrained sources, and express overall ROx production as OH-equivalents (i.e., taking into account the propagation efficiencies of RO2 and HO2 radicals into OH radicals. Daytime radical production is found to be about 10-25 times higher than at night; it does not track the abundance of sunlight. 12-h average daytime contributions of individual sources are: HCHO and O3 photolysis, each about 20%; O3/alkene reactions and HONO photolysis, each about 15%; unmeasured sources about 30%. While the direct contribution of O3/alkene reactions appears to be moderately small, source-apportionment of ambient HCHO and HONO identifies O3/alkene reactions as being largely responsible for jump-starting photochemistry about one hour after sunrise. The peak radical production is found to be higher than in any other urban influenced environment studied to date; further, differences exist in the timing of radical production. Our measurements and analysis comprise a

  7. Anion order in perovskites: a group-theoretical analysis.

    Science.gov (United States)

    Talanov, M V; Shirokov, V B; Talanov, V M

    2016-03-01

    Anion ordering in the structure of cubic perovskite has been investigated by the group-theoretical method. The possibility of the existence of 261 ordered low-symmetry structures, each with a unique space-group symmetry, is established. These results include five binary and 14 ternary anion superstructures. The 261 idealized anion-ordered perovskite structures are considered as aristotypes, giving rise to different derivatives. The structures of these derivatives are formed by tilting of BO6 octahedra, distortions caused by the cooperative Jahn-Teller effect and other physical effects. Some derivatives of aristotypes exist as real substances, and some as virtual ones. A classification of aristotypes of anion superstructures in perovskite is proposed: the AX class (the simultaneous ordering of A cations and anions in cubic perovskite structure), the BX class (the simultaneous ordering of B cations and anions) and the X class (the ordering of anions only in cubic perovskite structure). In most perovskites anion ordering is accompanied by cation ordering. Therefore, the main classes of anion order in perovskites are the AX and BX classes. The calculated structures of some anion superstructures are reported. Comparison of predictions and experimentally investigated anion superstructures shows coherency of theoretical and experimental results.

  8. Photocatalytic degradation kinetics and mechanism of pentachlorophenol based on superoxide radicals

    Institute of Scientific and Technical Information of China (English)

    Yang Li; Junfeng Niu; Lifeng Yin; Wenlong Wang; Yueping Bao; Jing Chen; Yanpei Duan

    2011-01-01

    The micron grade multi-metal oxide bismuth silicate (Bi12SiO20,BSO) was prepared by the chemical solution decomposition technique.Photocatalytic degradation of pentachlorophenol (PCP) was investigated in the presence of BSO under xenon lamp irradiation.The reaction kinetics followed pseudo first-order and the degradation ratio achieved 99.1% after 120 min at an initial PCP concentration of 2.0 mg/L.The pH decreased from 6.2 to 4.6 and the dechlorination ratio was 68.4% after 120 min at an initial PCP concentration of 8.0 mg/L.The results of electron spin resonance showed that superoxide radical (O2-) was largely responsible for the photocatalytic degradation of PCP.Interestingly,this result was different from that of previous photocatalytic reactions where valence band holes or hydroxyl radicals played the role of major oxidants.Some aromatic compounds and aliphatic carboxylic acids were determined by GC/MS as the reaction intermediates,which indicated that O2- can attack the bond between the carbon and chlorine atoms to form less chlorinated aromatic compounds.The aromatic compounds were further oxidized by O2- to generate aliphatic carboxylic acids which can be finally mineralized to CO2 and H2O.

  9. Oxidative capacity of the Mexico City atmosphere - Part 1: A radical source perspective

    Science.gov (United States)

    Volkamer, R.; Sheehy, P.; Molina, L. T.; Molina, M. J.

    2010-07-01

    A detailed analysis of OH, HO2 and RO2 radical sources is presented for the near field photochemical regime inside the Mexico City Metropolitan Area (MCMA). During spring of 2003 (MCMA-2003 field campaign) an extensive set of measurements was collected to quantify time-resolved ROx (sum of OH, HO2, RO2) radical production rates from day- and nighttime radical sources. The Master Chemical Mechanism (MCMv3.1) was constrained by measurements of (1) concentration time-profiles of photosensitive radical precursors, i.e., nitrous acid (HONO), formaldehyde (HCHO), ozone (O3), glyoxal (CHOCHO), and other oxygenated volatile organic compounds (OVOCs); (2) respective photolysis-frequencies (J-values); (3) concentration time-profiles of alkanes, alkenes, and aromatic VOCs (103 compound are treated) and oxidants, i.e., OH- and NO3 radicals, O3; and (4) NO, NO2, meteorological and other parameters. The ROx production rate was calculated directly from these observations; the MCM was used to estimate further ROx production from unconstrained sources, and express overall ROx production as OH-equivalents (i.e., taking into account the propagation efficiencies of RO2 and HO2 radicals into OH radicals). Daytime radical production is found to be about 10-25 times higher than at night; it does not track the abundance of sunlight. 12-h average daytime contributions of individual sources are: Oxygenated VOC other than HCHO about 33%; HCHO and O3 photolysis each about 20%; O3/alkene reactions and HONO photolysis each about 12%, other sources <3%. Nitryl chloride photolysis could potentially contribute ~15% additional radicals, while NO2* + water makes - if any - a very small contribution (~2%). The peak radical production of ~7.5 107 molec cm-3 s-1 is found already at 10:00 a.m., i.e., more than 2.5 h before solar noon. O3/alkene reactions are indirectly responsible for ~33% of these radicals. Our measurements and analysis comprise a database that enables testing of the representation of

  10. Oxidative capacity of the Mexico City atmosphere – Part 1: A radical source perspective

    Directory of Open Access Journals (Sweden)

    R. Volkamer

    2010-07-01

    Full Text Available A detailed analysis of OH, HO2 and RO2 radical sources is presented for the near field photochemical regime inside the Mexico City Metropolitan Area (MCMA. During spring of 2003 (MCMA-2003 field campaign an extensive set of measurements was collected to quantify time-resolved ROx (sum of OH, HO2, RO2 radical production rates from day- and nighttime radical sources. The Master Chemical Mechanism (MCMv3.1 was constrained by measurements of (1 concentration time-profiles of photosensitive radical precursors, i.e., nitrous acid (HONO, formaldehyde (HCHO, ozone (O3, glyoxal (CHOCHO, and other oxygenated volatile organic compounds (OVOCs; (2 respective photolysis-frequencies (J-values; (3 concentration time-profiles of alkanes, alkenes, and aromatic VOCs (103 compound are treated and oxidants, i.e., OH- and NO3 radicals, O3; and (4 NO, NO2, meteorological and other parameters. The ROx production rate was calculated directly from these observations; the MCM was used to estimate further ROx production from unconstrained sources, and express overall ROx production as OH-equivalents (i.e., taking into account the propagation efficiencies of RO2 and HO2 radicals into OH radicals.

    Daytime radical production is found to be about 10–25 times higher than at night; it does not track the abundance of sunlight. 12-h average daytime contributions of individual sources are: Oxygenated VOC other than HCHO about 33%; HCHO and O3 photolysis each about 20%; O3/alkene reactions and HONO photolysis each about 12%, other sources <3%. Nitryl chloride photolysis could potentially contribute ~15% additional radicals, while NO2* + water makes – if any – a very small contribution (~2%. The peak radical production of ~7.5 107 molec cm−3 s−1 is

  11. Conservation of medicinal and aromatic plants

    Directory of Open Access Journals (Sweden)

    Šveistytė, Laima

    2016-07-01

    Full Text Available The conservation of medicinal and aromatic plants includes ex situ and in situ methods. The genetic recourses of medicinal and aromatic plants are stored, studied and constantly maintained in the field collections of the Institute of Botany of Nature Research Centre, Kaunas Botanical Garden of Vytautas Magnus University and Aleksandras Stulginskis University of Agriculture. Presently seeds of 214 accessions representing 38 species of medicinal and aromatic plants are stored in a long-term storage in the Plant Gene Bank. The data about national genetic resources are collected and stored in the Central Database of the Plant Gene Bank.

  12. The Scavenging of Free Radical and Oxygen Species Activities and Hydration Capacity of Collagen Hydrolysates from Walleye Pollock (Theragra chalcogramma) Skin

    Institute of Scientific and Technical Information of China (English)

    ZHUANG Yongliang; LI Bafang; ZHAO Xue

    2009-01-01

    Fish skin collagen hydrolysates (FSCH) were prepared from walleye pollock (Theragra chalcogramma) using a mixture of enzymes, namely trypsin and flavourzyme. The degree of hydrolysis of the skin collagen was 27.3%. FSCH was mainly composed of low-molecular-weight peptides and the relative proportion of <1000Da fraction was 70.6%. Free radical and oxygen species scavenging activities of FSCH were investigated in four model systems, including diphenylpicrylhy-drazyl radical (DPPH), superox-ide anion radical, hydroxyl radical and hydrogen peroxide model, and compared with that of a native antioxidant, reduced glutathione (GSH). FSCH was also evaluated by water-absorbing and water-holding capacity. The results showed that FSCH was able to scav-enge free radical and oxygen species significantly and to enhance water-absorbing and water-holding capacity remarkably. Therefore, FSCH may have potential applications in the medicine and food industries.

  13. Study of the Formation of the First Aromatic Rings in the Pyrolysis of Cyclopentene.

    Science.gov (United States)

    Herbinet, Olivier; Rodriguez, Anne; Husson, Benoit; Battin-Leclerc, Frédérique; Wang, Zhandong; Cheng, Zhanjun; Qi, Fei

    2016-02-11

    The thermal decomposition of cyclopentene was studied in a jet-stirred reactor operated at constant pressure and temperature to provide new experimental information about the formation of the first aromatic rings from cyclic C5 species. Experiments were carried out at a residence time of 1 s, a pressure of 106.7 kPa, temperatures ranging from 773 to 1073 K and under diluted conditions (cyclopentene inlet mole fraction of 0.04). Species were quantified using three analytical methods: gas chromatography, synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), and single photon laser ionization mass spectrometry (SPI-MS). Several species could be quantified using both methods allowing comparison of experimental data obtained with the three apparatuses. Discrepancies observed in mole fraction profiles of some large aromatics suggest that the direct sampling in the gas phase (with a molecular beam or a capillary tube) provide more reliable results. The main reaction products are 1,3-cyclopentadiene and hydrogen. The formation of many unsaturated C2-C6 olefins, diolefins and alkynes was also observed but in smaller amounts. Benzene, toluene, styrene, indene, and naphthalene were detected from 923 K. SVUV-PIMS data allowed the identification of another C6H6 isomer which is 1,5-hexadien-3-yne rather than fulvene. The quantification of the cyclopentadienyl radical was obtained from SVUV-PIMS and SPI-MS data with some uncertainty induced by the possible contribution to the signal for m/z 65 of a fragment from the decomposition of a larger ion. This is the first time that a radical is quantified in a jet-stirred reactor using non-optical techniques. SPI-MS analyses allowed the detection of species likely being combination products of allyl and cyclopentadienyl radicals. A model was developed for the pyrolysis of cyclopentene. This model includes routes of formation of aromatics from the cyclopentadienyl radical. The comparison of experimental and

  14. Pickering emulsion templated interfacial atom transfer radical polymerization for microencapsulation.

    Science.gov (United States)

    Li, Jian; Hitchcock, Adam P; Stöver, Harald D H

    2010-12-01

    This Article describes a new microencapsulation method based on a Pickering emulsion templated interfacial atom transfer radical polymerization (PETI-ATRP). Cationic LUDOX CL nanoparticles were coated electrostatically with an anionic polymeric ATRP initiator, poly(sodium styrene sulfonate-co-2-(2-bromoisobutyryloxy)ethyl methacrylate) (PSB), prepared by radical copolymerization of sodium styrene sulfonate and 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM). The resulting PSB-modified CL particles were surface active and could be used to stabilize oil-in-water Pickering emulsions. ATRP of water-soluble cross-linking monomers, confined to the oil-water interface by the surface-bound PSB, then led to nanoparticle/polymer composite shells. This method allowed encapsulation of core solvents (xylene, hexadecane, perfluoroheptane) with different solubility parameters. The microcapsule (MC) wall chemistry could accommodate different monomers, demonstrating the versatility of this method. Double-walled MCs were formed by sequentially carrying out PETI-ATRP and in situ polymerization of encapsulated monomers. The double-walled structure was verified by both transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM).

  15. Expanded Porphyrin-Anion Supramolecular Assemblies: Environmentally Responsive Sensors for Organic Solvents and Anions.

    Science.gov (United States)

    Zhang, Zhan; Kim, Dong Sub; Lin, Chung-Yon; Zhang, Huacheng; Lammer, Aaron D; Lynch, Vincent M; Popov, Ilya; Miljanić, Ognjen Š; Anslyn, Eric V; Sessler, Jonathan L

    2015-06-24

    Porphyrins have been used frequently to construct supramolecular assemblies. In contrast, noncovalent ensembles derived from expanded porphyrins, larger congeners of naturally occurring tetrapyrrole macrocycles, are all but unknown. Here we report a series of expanded porphyrin-anion supramolecular assemblies. These systems display unique environmentally responsive behavior. Addition of polar organic solvents or common anions to the ensembles leads to either a visible color change, a change in the fluorescence emission features, or differences in solubility. The actual response, which could be followed easily by the naked eye, was found to depend on the specifics of the assembly, as well as the choice of analyte. Using the ensembles of this study, it proved possible to differentiate between common solvents, such as diethyl ether, THF, ethyl acetate, acetone, alcohol, acetonitrile, DMF, and DMSO, identify complex solvent systems, as well as distinguish between the fluoride, chloride, bromide, nitrate, and sulfate anions.

  16. Infrared spectroscopy of organic free radicals related to combustion processes

    Energy Technology Data Exchange (ETDEWEB)

    Weisshaar, J.C. [Univ. of Wisconsin, Madison (United States)

    1993-12-01

    The primary long-term goal of this work is to develop new techniques for measuring vibrational spectra of polyatomic neutral free radicals. The authors explore a variation of resonant two-photon ionization (R2PI) in which tunable {omega}{sub IR} excites the radical vibrationally and {omega}{sub UV} selectively ionizes only the vibrationally excited molecules. Development of the IR + UV R2PI experiment is underway. In the meantime, the authors have used optical R2PI and pulsed field ionization (PFI) detection to obtain new vibrational spectra of species such as the benzyl and phenylsilane cations. In benzyl, a great deal was learned about the vibronic coupling mechanism in the mixed q{sup 2}A{sub 2}-2{sup 2}B{sub 2} system near 450 nm by projecting the mixed states onto the manifold of cation vibrational states. In phenylsilane{sup +}, we find that the sixfold barrier to internal rotation of the silyl group is small (V{sub 6} = +19 cm{sup {minus}1}). We are beginning to understand the mechanisms of coupling of torsional states with vibration, overall rotation, and other electronic states. In addition, we are developing a new model of internal rotation in aromatic compounds based on Prof. Frank Weinhold`s natural resonance theory.

  17. Role of methyl radicals in the growth of PAHs.

    Science.gov (United States)

    Shukla, Bikau; Miyoshi, Akira; Koshi, Mitsuo

    2010-04-01

    The role of methyl radicals in the networking of sp(2) carbons has been explored through kinetic analysis of mass spectra of the gas-phase products of the pyrolysis of toluene and toluene/acetone mixtures. Pyrolytic reactions were performed in a flow tube reactor at temperatures of 1140-1320 K and a constant total pressure of 10.38 Torr with a residence time of 0.585 s. On addition of acetone, methyl substituted products and their derivatives were enhanced. Mass peaks were observed in several sequences at an interval of 14 mass units; these ions correspond to methyl substituted products formed as a result of hydrogen abstraction (-H) followed by methyl radical addition (+CH(3)). Each major peak was usually preceded by a peak at two mass units lower, which was likely produced through dehydrogenation/dehydrocyclization (-H(2)) of methyl substituted products. Detected species include a large number of alkyl, cyclotetrafused (CT), cyclopentafused (CP) mono-, di-, and polycyclic aromatic hydrocarbons (PAHs) along with primary PAHs. The analysis showed that MAC (methyl addition/cyclization) has a unique capacity to induce the sequential growth of hexagonal networks of sp(2) carbons from all fusing sites of a PAH. Moreover, MAC was found capable of answering an important question in PAH growth, which is expansion of the CT --> CP --> hexagonal network for which other reported mechanisms are inefficient.

  18. Role of the hydroxyl radical in soot formation

    Science.gov (United States)

    King, Galen B.; Laurendeau, Normand M.

    1983-01-01

    The goal of this project is to determine the role of the hydroxyl radical during formation of soot. Correlations will be sought between OH concentration and (1) the critical equivalence ratio for incipient soot formation and (2) soot yield as a function of higher equivalence ratios. The ultimate aim is the development of a quasi-global kinetic model for the pre-particulate chemistry leading to soot nucleation. Hydroxyl radical concentration profiles are measured directly in both laminar premixed and diffusion flames using the newly developed technique, laser saturated fluorescence (LSF). This method is capable of measuring OH in the presence of soot particles. Aliphatic and aromatic fuels will be used to assess the influence of fuel type on soot formation. The influence of flame temperature on the critical equivalence ratio and soot yield will be related to changes in the OH concentration profiles. LSF measurements will be augmented with auxiliary measurements of soot and PAH concentrations to allow the development of a quasi-global model for soot formation.

  19. Reaction between protein radicals and other biomolecules

    DEFF Research Database (Denmark)

    Østdal, Henrik; Davies, Michael Jonathan; Andersen, Henrik J

    2002-01-01

    oil-in-water emulsion resulted in additional formation of lipid hydroperoxides and conjugated dienes. The results clearly show that protein radicals have to be considered as dynamic species during oxidative processes in biological systems and that protein radicals should not be considered as end-products......The present study investigates the reactivity of bovine serum albumin (BSA) radicals towards different biomolecules (urate, linoleic acid, and a polypeptide, poly(Glu-Ala-Tyr)). The BSA radical was formed at room temperature through a direct protein-to-protein radical transfer from H(2)O(2....... Subsequent analysis showed a decrease in the concentration of urate upon reaction with the BSA radical, while the BSA radical in the presence of poly(Glu-Ala-Tyr) resulted in increased formation of the characteristic protein oxidation product, dityrosine. Reaction between the BSA radical and a linoleic acid...

  20. The isolable cation radical of disilene: synthesis, characterization, and a reversible one-electron redox system.

    Science.gov (United States)

    Inoue, Shigeyoshi; Ichinohe, Masaaki; Sekiguchi, Akira

    2008-05-14

    The highly twisted tetrakis(di-tert-butylmethylsilyl)disilene 1 was treated with Ph3C+.BAr4- (BAr4-: TPFPB = tetrakis(pentafluorophenyl)borate) in toluene, producing disilene cation radical 3 upon one-electron oxidation. Cation radical 3 was isolated in the form of its borate salt as extremely air- and moisture-sensitive red-brown crystals. The molecular structure of 3 was established by X-ray crystallography, which showed a highly twisted structure (twisting angle of 64.9 degrees) along the central Si-Si bond with a bond length of 2.307(2) A, which is 2.1% elongated relative to that of 1. The cation radical is stabilized by sigma-pi hyperconjugation by the four tBu2MeSi groups attached to the two central sp2-Si atoms. An electron paramagnetic resonance (EPR) study of the hyperfine coupling constants (hfcc) of the 29Si nuclei indicates delocalization of the spin over the central two Si atoms. A reversible one-electron redox system between disilene, cation radical, and anion radical is also reported.

  1. Manipulation of persistent free radicals in biochar to activate persulfate for contaminant degradation.

    Science.gov (United States)

    Fang, Guodong; Liu, Cun; Gao, Juan; Dionysiou, Dionysios D; Zhou, Dongmei

    2015-05-01

    This study investigated the effects of metals (Fe3+, Cu2+, Ni2+, and Zn2+) and phenolic compounds (PCs: hydroquinone, catechol, and phenol) loaded on biomass on the formation of persistent free radicals (PFRs) in biochar. It was found that metal and phenolic compound treatments not only increased the concentrations of PFRs in biochar but also changed the types of PFRs formed, which indicated that manipulating the amount of metals and PCs in biomass may be an efficient method to regulate PFRs in biochar. These results provided direct evidence to elucidate the mechanism of PFR formation in biochar. Furthermore, the catalytic ability of biochar toward persulfate activation for the degradation of contaminants was evaluated. The results indicated that biochar activates persulfate to produce sulfate radicals (SO4•-) and degraded polychlorinated biphenyls (PCBs) efficiently. It was found that both the concentration and type of PFRs were the dominant factors controlling the activation of persulfate by biochar and that superoxide radical anions account for 20-30% of sulfate radical generation in biochar/persulfate. This conclusion was supported by linear correlations between the concentration of PFRs consumed and the formation of SO4•- and between λ (λ=[formed sulfate radicals]/[consumed PFRs]) and g-factors. The findings of this study provide new methods to manipulate PFR concentration in biochar for the transformation of contaminants and development of new alternative activators for persulfate-based remediation of contaminated soils.

  2. Theoretical study on effects of curvature of graphene in conjunction with simultaneous anion- and - stacking interactions

    Directory of Open Access Journals (Sweden)

    Pouya Karimi

    2015-12-01

    Full Text Available A graphene sheet (C102H30 has been rolled up by computational quantum chemistry methods to construct single-walled carbon nanotube fragments (SWCNTFs. The anion-π interactions of F- anion together with π-π stacking interactions of benzene on inner face and outer face of the central rings of SWCNTFs have been concurrently investigated. Structural parameters and energy data of the ternary benzene-SWCNTF-F- complexes were considered. Also, effects of charge transfer and aromaticity were estimated to determine how curvature of graphene influences on simultaneous anion-π and π-π stacking interactions.  Results indicate that curvature of graphene leads to structural changes in SWCNTFs which effects on simultaneous interactions of F- anion and benzene with SWCNTFs. Also, results show that although p-p stacking is a weak interaction, but it can impact on order of binding energies in complexes involved both p-p stacking and anion-p interactions. 

  3. Raman and IR studies and DFT calculations of the vibrational spectra of 2,4-Dithiouracil and its cation and anion

    Science.gov (United States)

    Singh, R.; Yadav, R. A.

    2014-09-01

    Raman and FTIR spectra of solid 2,4-Dithiouracil (DTU) at room temperature have been recorded. DFT calculations were carried out to compute the optimized molecular geometries, GAPT charges and fundamental vibrational frequencies along with their corresponding IR intensities, Raman activities and depolarization ratios of the Raman bands for the neutral DTU molecule and its cation (DTU+) and anion (DTU-) using the Gaussian-03 software. Addition of one electron leads to increase in the atomic charges on the sites N1 and N3 and decrease in the atomic charges on the sites S8 and S10. Due to ionization of DTU molecule, the charge at the site C6 decreases in the cationic and anionic radicals of DTU as compared to its neutral species. As a result of anionic radicalization, the C5sbnd C6 bond length increases and loses its double bond character while the C4sbnd C5 bond length decreases. In the case of the DTU+ ion the IR and Raman band corresponding to the out-of-phase coupled Nsbnd H stretching mode is strongest amongst the three species. The anionic DTU radical is found to be the most stable. The two NH out-of-plane bending modes are found to originate due to out-of-phase and in-phase coupling of the two NH bonds in the anion and cation contrary to the case of the neutral DTU molecule in which the out-of-plane bending motions of the two NH bonds are not coupled.

  4. Pulse shape discrimination in non-aromatic plastics

    Energy Technology Data Exchange (ETDEWEB)

    Paul Martinez, H.; Pawelczak, Iwona; Glenn, Andrew M.; Leslie Carman, M.; Zaitseva, Natalia; Payne, Stephen

    2015-01-21

    Recently it has been demonstrated that plastic scintillators have the ability to distinguish neutrons from gamma rays by way of pulse shape discrimination (PSD). This discovery has lead to new materials and new capabilities. Here we report our work with the effects of aromatic, non-aromatic, and mixed aromatic/non-aromatic matrices have on the performance of PSD plastic scintillators.

  5. Silaphenolates and Silaphenylthiolates: Two Unexplored Unsaturated Silicon Compound Classes Influenced by Aromaticity

    Directory of Open Access Journals (Sweden)

    Henrik Ottosson

    2012-01-01

    Full Text Available Monosilicon analogs of phenolates and phenylthiolates are studied by quantum chemical calculations. Three different silaphenolates and three different silaphenylthiolates are possible; the ortho-, meta-, and para-isomers. For the silaphenolates, the meta-isomer is the thermodynamically most stable, regardless if the substituent R at Si is H, t-Bu or SiMe3. However, with R = H and SiMe3 the energy differences between the three isomers are small, whereas with R = t-Bu the meta-isomer is ~5 kcal/mol more stable than the ortho-isomer. For the silaphenylthiolates the ortho-isomer is of lowest energy, although with R = H the ortho- and meta-isomers are isoenergetic. The calculated nucleus independent chemical shifts (NICS indicate that the silaphenolates and silaphenylthiolates are influenced by aromaticity, but they are less aromatic than the parent silabenzene. The geometries and charge distributions suggest that all silaphenolates and silaphenylthiolates to substantial degrees are described by resonance structures with an exocyclic C=O double bond and a silapentadienyl anionic segment. Indeed, they resemble the all-carbon phenolate and phenylthiolate. Silaphenylthiolates are less bond alternate and have slightly more negative NICS values than analogous silaphenolates, suggesting that this compound class is a bit more aromatic. Dimerization of the silaphenolates and silaphenylthiolates is hampered due to intramolecular Coulomb repulsion in the dimers, and silaphenolates with a moderately bulky SiMe3 group as substituent at Si should prefer the monomeric form.

  6. Tetranuclear Heterometallic {Zn2Eu2} Complexes With 1-Naphthoate Anions: Synthesis, Structure and Photoluminescence Properties.

    Science.gov (United States)

    Goldberg, Anna; Kiskin, Mikhail; Shalygina, Olga; Kozyukhin, Sergey; Dobrokhotova, Zhanna; Nikolaevskii, Stanislav; Sidorov, Alexey; Sokolov, Sergey; Timoshenko, Victor; Goloveshkin, Alexander; Eremenko, Igor

    2016-02-18

    A series of new tetranuclear heterometallic Zn(II) -Eu(III) complexes have been synthesized, that is, (bpy)2 Zn2Eu2 (naph)10 (1), (bpy)2 Zn2Eu2 (naph)8 (NO3)2 (2), and (phen)2 Zn2Eu2 (naph)8 (NO3)2 (3), and other ones, where naph(-) is the 1-naphthoate anion, bpy=2,2'-bipyridyl, and phen=1,10-phenanthroline. The solid-phase complexes consist of large supramolecular ensembles due to stacking interactions between the aromatic ligands. Photoluminescence (PL) measurements were carried out to study PL spectra, lifetimes and quantum yields (QY) of the synthesized complexes at different temperatures. The external QY for the solid phases of complexes under UV excitation was found to exceed 20 %. It has been shown that partial replacement of naphthoate ligands in the coordination environment of Eu(3+) by NO3(-) anions influences the PL properties. To investigate the behavior of these complexes in solvent, we dissolved complex 3 in MeCN, put it on a transparent glass as a substrate, and studied the PL properties at room temperature.

  7. RADICAL POLYMERIZATION OF N, N-DI(2-2 '-METHYL-ACRYLOYLOXY-PROPYL) -PARA-TOLUIDINE FUNCTIONAL MONOMER

    Institute of Scientific and Technical Information of China (English)

    QIU Kunyuan; FU Jie

    1989-01-01

    Functional monomer ( MP )2PT having tertiary aromatic amino group was systhesized from the reaction of N, N-di ( 2 -hydroxypropyl )-p-toluidine with 2-methyl acryloyl chloride. In the presence of organic peroxide, the radical polymerization of ( MP )2PT in toluene took place. The kinetics of ( MP )2PT polymerization and the ESR spectra ofLPO-( MP )2PT-MNP systems were determined respectively.

  8. Comments on Coulomb pairing in aromatic hydrocarbons

    CERN Document Server

    Huber, D L

    2013-01-01

    Recently reported anomalies in the double-photonionization spectra of aromatic molecules such as benzene, naphthalene, anthracene and coronene are attributed to Coulomb-pair resonances of pi electrons.

  9. Silicone elastomers with aromatic voltage stabilizers

    DEFF Research Database (Denmark)

    A Razak, Aliff Hisyam; Skov, Anne Ladegaard

    modifications. In order to increase the electrical breakdown strength of polymers for e.g. the cable industry, additives like aromatic voltage stabilizers are used. Earlier works on using voltage stabilizers in polymers have mainly focused on polyethylene with the purpose of reducing power loss for high voltage...... insulation cables.3–5 As an alternative to utilise additives as voltage stabilizers, grafting aromatic compounds to silicone backbones may overcome the common problem of insolubility of the aromatic voltage stabilizer in the silicone elastomers due to phase separation. Preventing phase separation during...... via hydrosilylation by a vinyl-functional crosslinker. The mechanism of electron-trapping by aromatic compounds grafted to silicone backbones in a crosslinked PDMS is illustrated in Fig. 1. The electrical breakdown strength, the storage modulus and the loss modulus of the elastomer were investigated...

  10. Graphite Oxide and Aromatic Amines : Size Matters

    NARCIS (Netherlands)

    Spyrou, Konstantinos; Calvaresi, Matteo; Diamanti, Evmorfi A. K.; Tsoufis, Theodoros; Gournis, Dimitrios; Rudolf, Petra; Zerbetto, Francesco

    2015-01-01

    Experimental and theoretical studies are performed in order to illuminate, for first time, the intercalation mechanism of polycyclic aromatic molecules into graphite oxide. Two representative molecules of this family, aniline and naphthalene amine are investigated. After intercalation, aniline molec

  11. Volatilisation of aromatic hydrocarbons from soil

    DEFF Research Database (Denmark)

    Lindhardt, B.; Christensen, T.H.

    1996-01-01

    The non-steady-state fluxes of aromatic hydrocarbons were measured in the laboratory from the surface of soils contaminated with coal tar Four soil samples from a former gasworks site were used for the experiments. The fluxes were quantified for 11 selected compounds, 4 mono- and 7 polycyclic...... aromatic hydrocarbons, for a period of up to 8 or 16 days. The concentrations of the selected compounds in the soils were between 0.2 and 3,100 mu g/g. The study included the experimental determination of the distribution coefficient of the aromatic hydrocarbons between the sorbed phase and the water under...... saturated conditions. The determined distribution coefficients showed that the aromatic hydrocarbons were more strongly sorbed to the total organic carbon including the coal tar pitch - by a factor of 8 to 25 - than expected for natural organic matter. The fluxes were also estimated using an analytical...

  12. The Industrial Reduction of Aromatic Nitro Compounds.

    Science.gov (United States)

    Gilbert, G.

    1980-01-01

    Describes methods for enriching an A-level chemistry course with a series of chemical company visits. The rationale is discussed for an emphasis of the visits on the industrial reduction of aromatic nitro compounds. (CS)

  13. Activity relationships for aromatic crown ethers

    CERN Document Server

    Wilson, M J

    1998-01-01

    This thesis involves an investigation of aromatic crown ethers and a study of their binding constants for alkali metals. The study was motivated by the current needs of the semiconductor industry to improve the scavenging of mobile ions from fabricated circuits. A number of aromatic crown ethers have been sulphonated in an attempt to improve their water solubility and cation binding activity. These materials have been extensively studied and their binding activity determined. In collaboration with a molecular modelling study, the effect of ionisable sulphonate groups on the macrocycles' behaviour has been investigated. The broader issue of the effect of substituents in aromatic crown ethers has also been studied with the preparation of a wide range of substituted crown ethers. The cation binding activity of these materials has been found to bear a simple relationship to the electron withdrawing nature of the aromatic substituents. This relationship can be accurately monitored using electronic charge densities...

  14. Dehydrogenative Aromatization of Saturated Aromatic Compounds by Graphite Oxide and Molecular Sieves

    Institute of Scientific and Technical Information of China (English)

    张轩; 徐亮; 王希涛; 马宁; 孙菲菲

    2012-01-01

    Graphite oxide (GO) has attracted much attention of material and catalysis chemists recently. Here we describe a combination of GO and molecular sieves for the dehydrogenative aromatization. GO prepared through improved Hummers method showed high oxidative activity in this reaction. Partially or fully saturated aromatic compounds were converted to their corresponding dehydrogenated aromatic products with fair to excellent conversions and selectivities. As both GO and molecular sieves are easily available, cheap, lowly toxic and have good tolerance to various functional groups, this reaction provides a facile approach toward aromatic compounds from their saturated precursors

  15. Oxygen free radicals in rheumatoid arthritis

    NARCIS (Netherlands)

    P. Biemond (Pieter)

    1986-01-01

    textabstractCurrent knowledge strongly suggests that oxygen free radicals are involved in the pathogenesis of RA. Additional information about the mechanism of free radical attack is necessary in order to find out if interaction with the mechanism of free radical damage can be used in the treatment

  16. Stable carbon isotope ratios of ambient aromatic volatile organic compounds

    Science.gov (United States)

    Kornilova, Anna; Huang, Lin; Saccon, Marina; Rudolph, Jochen

    2016-09-01

    Measurements of mixing ratios and stable carbon isotope ratios of aromatic volatile organic compounds (VOC) in the atmosphere were made in Toronto (Canada) in 2009 and 2010. Consistent with the kinetic isotope effect for reactions of aromatic VOC with the OH radical the observed stable carbon isotope ratios are on average significantly heavier than the isotope ratios of their emissions. The change of carbon isotope ratio between emission and observation is used to determine the extent of photochemical processing (photochemical age, ∫ [OH]dt) of the different VOC. It is found that ∫ [OH]dt of different VOC depends strongly on the VOC reactivity. This demonstrates that for this set of observations the assumption of a uniform ∫ [OH]dt for VOC with different reactivity is not justified and that the observed values for ∫ [OH]dt are the result of mixing of VOC from air masses with different values for ∫ [OH]dt. Based on comparison between carbon isotope ratios and VOC concentration ratios it is also found that the varying influence of sources with different VOC emission ratios has a larger impact on VOC concentration ratios than photochemical processing. It is concluded that for this data set the use of VOC concentration ratios to determine ∫ [OH]dt would result in values for ∫ [OH]dt inconsistent with carbon isotope ratios and that the concept of a uniform ∫ [OH]dt for an air mass has to be replaced by the concept of individual values of an average ∫ [OH]dt for VOC with different reactivity.

  17. Studies of transition states and radicals by negative ion photodetachment

    Energy Technology Data Exchange (ETDEWEB)

    Metz, R.B.

    1991-12-01

    Negative ion photodetachment is a versatile tool for the production and study of transient neutral species such as reaction intermediates and free radicals. Photodetachment of the stable XHY{sup {minus}} anion provides a direct spectroscopic probe of the transition state region of the potential energy surface for the neutral hydrogen transfer reaction X + HY {yields} XH + Y, where X and Y are halogen atoms. The technique is especially sensitive to resonances, which occur at a specific energy, but the spectra also show features due to direct scattering. We have used collinear adiabatic simulations of the photoelectron spectra to evaluate trail potential energy surfaces for the biomolecular reactions and have extended the adiabatic approach to three dimensions and used it to evaluate empirical potential energy surfaces for the I + Hl and Br + HI reactions. In addition, we have derived an empirical, collinear potential energy surface for the Br + HBr reaction that reproduces our experimental results and have extended this surface to three dimensions. Photodetachment of a negative ion can be also used to study neutral free radicals. We have studied the vibrational and electronic spectroscopy of CH{sub 2}NO{sub 2} by photoelectron spectroscopy of CH{sub 2}NO{sub 2}{sup {minus}}, determining the electron affinity of CH{sub 2}NO{sub 2}, gaining insight on the bonding of the {sup 2}B{sub 1} ground state and observing the {sup 2}A{sub 2} excited state for the first time. Negative ion photodetachment also provides a novel and versatile source of mass-selected, jet-cooled free radicals. We have studied the photodissociation of CH{sub 2}NO{sub 2} at 270, 235, and 208 nm, obtaining information on the dissociation products by measuring the kinetic energy release in the photodissociation.

  18. Thoughts on Optimization of Aromatic Feedstock

    Institute of Scientific and Technical Information of China (English)

    Cao Jian

    2002-01-01

    This article refers to four cases of process unit combinations with different throughputs of aromatics unit for production of 450 kt/a paraxylene at a certain petrochemical complex in order to against a representative case (provided with an 800-kt/a CCR unit and a 600-kt/a disproportionation unit) and the feasibility and advantage of using prolysis gasoline as aromatic feedstock is studied.

  19. Aromatic amines sources, environmental impact and remediation

    OpenAIRE

    Pereira, Luciana; Mondal, P. K.; Alves, M. M.

    2015-01-01

    Aromatic amines are widely used industrial chemicals as their major sources in the environment include several chemical industry sectors such as oil refining, synthetic polymers, dyes, adhesives, rubbers, perfume, pharmaceuticals, pesticides and explosives. They result also from diesel exhaust, combustion of wood chips and rubber and tobacco smoke. Some types of aromatic amines are generated during cooking, special grilled meat and fish, as well. The intensive use and production of these comp...

  20. Organic superconductors with an incommensurate anion structure

    Directory of Open Access Journals (Sweden)

    Tadashi Kawamoto and Kazuo Takimiya

    2009-01-01

    Full Text Available Superconducting incommensurate organic composite crystals based on the methylenedithio-tetraselenafulvalene (MDT-TSF series donors, where the energy band filling deviates from the usual 3/4-filled, are reviewed. The incommensurate anion potential reconstructs the Fermi surface for both (MDT-TSF(AuI20.436 and (MDT-ST(I30.417 neither by the fundamental anion periodicity q nor by 2q, but by 3q, where MDT-ST is 5H-2-(1,3-dithiol-2-ylidene-1,3-diselena-4,6-dithiapentalene, and q is the reciprocal lattice vector of the anion lattice. The selection rule of the reconstructing vectors is associated with the magnitude of the incommensurate potential. The considerably large interlayer transfer integral and three-dimensional superconducting properties are due to the direct donor–donor interactions coming from the characteristic corrugated conducting sheet structure. The materials with high superconducting transition temperature, Tc, have large ratios of the observed cyclotron masses to the bare ones, which indicates that the strength of the many-body effect is the major determinant of Tc. (MDT-TS(AuI20.441 shows a metal–insulator transition at TMI=50 K, where MDT-TS is 5H-2-(1,3-diselenol-2-ylidene-1,3,4,6-tetrathiapentalene, and the insulating phase is an antiferromagnet with a high Néel temperature (TN=50 K and a high spin–flop field (Bsf=6.9 T. There is a possibility that this material is an incommensurate Mott insulator. Hydrostatic pressure suppresses the insulating state and induces superconductivity at Tc=3.2 K above 1.05 GPa, where Tc rises to the maximum, Tcmax=4.9 K at 1.27 GPa. This compound shows a usual temperature–pressure phase diagram, in which the superconducting phase borders on the antiferromagnetic insulating phase, despite the unusual band filling.