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Sample records for alkane radical cations

  1. Infrared Spectroscopic Investigation on CH Bond Acidity in Cationic Alkanes

    NASA Astrophysics Data System (ADS)

    Matsuda, Yoshiyuki; Xie, Min; Fujii, Asuka

    2016-06-01

    We have demonstrated large enhancements of CH bond acidities in alcohol, ether, and amine cations through infrared predissociation spectroscopy based on the vacuum ultraviolet photoionization detection. In this study, we investigate for the cationic alkanes (pentane, hexane, and heptane) with different alkyl chain lengths. The σ electrons are ejected in the ionization of alkanes, while nonbonding electrons are ejected in ionization of alcohols, ethers, and amines. Nevertheless, the acidity enhancements of CH in these cationic alkanes have also been demonstrated by infrared spectroscopy. The correlations of their CH bond acidities with the alkyl chain lengths as well as the mechanisms of their acidity enhancements will be discussed by comparison of infrared spectra and theoretical calculations.

  2. Early events following radiolytic and photogeneration of radical cations in hydrocarbons

    SciTech Connect

    Werst, D.W.; Trifunac, A.D.

    1992-11-01

    Real-time studies in hydrocarbons have revealed a richness of chemistry involving the initial ionic species produced in radiolysis and photoionization. A modified radical cation mechanism patterned after the core mechanism for alkane radiolysis-formation of radical cations and their disappearance via ion-molecule reactions - is capable of explaining a wide range of observations in high-energy photochemistry, and thus unifies two high-energy regimes. Fundamental studies of radical cations suggest strategies for mitigating radiation effects in materials.

  3. Early events following radiolytic and photogeneration of radical cations in hydrocarbons

    SciTech Connect

    Werst, D.W.; Trifunac, A.D.

    1992-01-01

    Real-time studies in hydrocarbons have revealed a richness of chemistry involving the initial ionic species produced in radiolysis and photoionization. A modified radical cation mechanism patterned after the core mechanism for alkane radiolysis-formation of radical cations and their disappearance via ion-molecule reactions - is capable of explaining a wide range of observations in high-energy photochemistry, and thus unifies two high-energy regimes. Fundamental studies of radical cations suggest strategies for mitigating radiation effects in materials.

  4. Arene-thioether mixed complex radical cations

    SciTech Connect

    Werst, D.W.

    1994-03-01

    Studies of radiolytically generated radical cations in aromatic hydrocarbon solvents have led to the first direct characterization of monomeric thioether radical cations in liquid solution. Observation of these very reactive chemical intermediates is made possible by the great sensitivity of fluorescence-detected magnetic resonance (FDMR) and by solvent stabilization of the thioether radical cations via electron donation. Monomeric thioether radical cations in arene solvents such as toluene exist as arene-thioether mixed complex radical cations -- the first {pi}-lone pair mixed complex radical cations ever observed. Such orbital interactions are of fundamental importance for open-shell intermediates as they have consequences for both electronic structure and reactivity. Thioether radical cations provide a valuable test system to probe the chemical influence of orbital interactions that are generic to all {pi}-type and heteroatom-containing organic radical cations, and magnetic resonance provides unsurpassed structural resolution for condensed-phase paramagnetic intermediates.

  5. Halogenated silanes, radicals, and cations

    NASA Astrophysics Data System (ADS)

    Wang, Liming; He, Yi-Liang

    2008-09-01

    Quantum chemistry study has been carried out on the structure and energetics of halogenated silanes, radicals, and cations (SiHxXy0,+1, X = F, Cl, Br; x + y = 1-4). The geometries are optimized at B3LYP/6-31+G(2df,p) level. The adiabatic ionization energiess (IEas), relative energetics of cations, proton affinities (PAs) of silanes, and the enthalpies of formation are predicted using G3(CC) model chemistry. Non-classical ion complex structures are found for hydrogenated cations and transition states connecting classical and non-classical structures are also located. The most stable cations for silylene and silyl radicals have their classical divalent and trivalent structures, and those for silanes have non-classical structures except for SiH3Br+ and SiH2Br2+. The non-classical structures for halosilane cations imply difficulty in experimentally measurement of the adiabatic ionization energies using photoionization or photoelectron studies. For SiH3X, SiH2X2, and SiHX3, the G3(CC) adiabatic IEas to classical ionic structures closest to their neutrals agree better with the photoelectron spectroscopic measurements. The transition states between classical and non-classical structures also hamper the photoionization determination of the appearance energies for silylene cations from silanes. The G3(CC) results for SiHx0,+1 agree excellently with the photoionization mass spectrometric study, and the results for fluorinated and chlorinated species also agree with the previous theoretical predictions at correlation levels from BAC-MP4 to CCSD(T)/CBS. The predicted enthalpy differences between SiH2Cl+, SiHCl2+, and SiCl3+ are also in accordance with previous kinetics study. The G3(CC) results show large discrepancies to the collision-induced charge transfer and/or dissociation reactions involving SiFx+ and SiClx+ ions, for which the G3(CC) enthalpies of formation are also significantly differed from the previous theoretical predictions, especially on SiFx+ (x = 2-4). The G3

  6. Trapping of neutral radicals by aromatic and heterocyclic cation radicals

    SciTech Connect

    Shine, H.J.; Soroka, M.

    1986-09-01

    A considerable amount of knowledge has been accrued during the last 15-20 years on the chemistry of polynuclear aromatic and heterocyclic cation radicals. For the most part, the reactions that have been studied have been of cation radicals with neutral and anionic nucleophiles which lead to addition or substitution products. Classic examples among these reactions are, for example, the reaction of water with the cation radical of 9,10-diphenylanthracene and perylene, and that of water with the thianthrene cation radical. Reactions such as these have been among foundation-establishing studies in the scope and mechanism of cation-radical reactions. Cation radicals can also undergo another type reaction with nucleophies, that is, electron transfer. This possibility leads to two far-reaching and connected questions: can addition and substitution reactions of aromatic cation radicals with nucleophiles be preceded by single electron transfer (SET).; and, can such cation radicals trap neutral radicals. These questions are also then related to another question having even greater impact on organic chemistry: can electrophilic aromatic substitution (ArH + E/sup +/ ..-->.. ArE + H/sup +/) be preceded by SET. The authors have been trying to answer the first two questions about SET and trapping of radicals by combining the two possibilities. That is, they have chosen the reaction of the thianthrene cation radical (represented by the symbol S/sup +./) with grignard reagents, for which two possible routes could be anticipated: either direct addition at sulfur or addition preceded by SET.

  7. Role of defects in radiation chemistry of crystalline organic materials. 3. Geometrical and electronic structures of alkene radical anion and cation in alkene/n-alkane mixed crystals as studied by ESR spectroscopy

    SciTech Connect

    Matsuura, Kaoru; Muto, Hachizo; Nunome, Keichi )

    1991-11-14

    An ESR study has been made in order to elucidate the electronic structures of alkene radical anions and cations, the former radicals being first detected in the hexene/n-hexene mixed crystals irradiated at 4.2 K along with the cation. The present work extended to the hexene and butene isomers has resulted in evidence that both anions with vinylene and vinylidene groups have pyramidal structures with {sigma}-character, which differ from the planar or twisted structures of corresponding cations. The proton hyperfine couplings of their anions were only about one-third as large as those for the cations: {vert bar}A{vert bar}(two {alpha}-H) = {vert bar}0.45, 0.1, {minus}0.25{vert bar} mT; a (two pairs of {beta}-H) = 1.38 and 0.56 mT for the 3-hexene anion, and a(two {alpha}-H) = 1.3 mT and a(two pairs of {beta}-H) = 4.6 and 2.9 mT for the cation. The differences in the geometrical structures and in the sizes of the proton couplings of the anion and cation radicals were discussed on the basis of a simple molecular orbital calculation. It has been found that the anion is stabilized by admixing {vert bar}2s;C> atomic orbitals (AO) with a lower core integral than {vert bar}2p;C> AO to the unpaired electron orbital and that the small {beta}-proton couplings mainly originate from low extent of hyperconjugation due to a wide energy separation of C{double bond}C {pi}-antibonding and C-H pseudo-{pi}-bonding orbitals.

  8. Radical Cation/Radical Reactions: A Fourier Transform Ion Cyclotron Resonance Study of Allyl Radical Reacting with Aromatic Radical Cations

    PubMed Central

    Russell, Amber L.; Rohrs, Henry W.; Read, David; Giblin, Daryl E.; Gaspar, Peter P.; Gross, Michael L.

    2010-01-01

    A method for the study of reactions of open-shell neutrals (radicals) and radical cations is described. Pyrolysis (25–1500 °C) of thermally labile compounds, such as, 1,5-hexadiene via a Chen nozzle yields a seeded beam of reactive species in helium. The pyrolysis products are then analyzed by electron ionization (EI) or reacted with stored ions. Electron ionization of the pyrolysis products of 1,5-hexadiene shows that both the allyl radical and allene are generated. Reactions of benzene radical cations and the pyrolysis products of 1,5-hexadiene result in carbon-carbon bond formation. Those reactions of allyl radical with the benzene radical cation yield the C7H7+ ion of m/z 91, permitting an unusual entry into arenium ions. The reaction of allene with benzene radical cation in contrast yields C9H10+. and C9H9+. PMID:20401179

  9. Radical cations in radiation chemistry of liquid hydrocarbons

    SciTech Connect

    Trifunac, A.D.; Sauer, M.C., Jr.; Shkrob, I.A.; Werst, D.W.

    1996-07-01

    The state of knowledge concerning radical cations in liquid alkanes is discussed with particular emphasis on those which exhibit high mobility. Uncertainty has existed in the interpretation of previous results with respect to the nature and reactivity of high mobility ions, especially for cyclohexane. Recent time-resolved studies on pulse radiolysis/transient absorption, photoconductivity, and magnetic resonance in these systems have led us to propose new mechanisms for the high mobility ions. In decalins, scavenging of these ions by solutes is a pseudo-first-order reaction. In cyclohexane, the behavior is more complex and is indicative of the involvement of two species. This bimodality is rationalized in terms of a dynamic equilibrium between two conformers of the solvent radical cation. Several experimental tests supporting these views include a recent study on two-color laser photoionization in cyclohexane.

  10. Radiolytic generation of radical cations in xenon matrices. Tetramethylcyclopropane radical cation and its transformations

    SciTech Connect

    Qin, X.Z.; Trifunac, A.D. )

    1990-04-05

    Radiolytic generation of radical cations in xenon matrices containing electron scavengers is illustrated by studying the 1,1,2,2-tetramethylcyclopropane radical cation. Dilute and concentrated solutions of tetramethylcyclopropane in xenon without electron scavengers and neat tetramethylcyclopropane yielded neutral radicals upon {gamma}-irradiation. Speculation on the mechanisms of radical formation is presented. The radical species observed in the {gamma}-irradiation of neat tetramethylcyclopropane appears to be identical with the paramagnetic species observed in CF{sub 2}ClCFCl{sub 2} above 120 K, suggesting that a neutral radical rather than the ring-opened distonic radical cation is observed in the CF{sub 2}ClCFCl{sub 2} matrix.

  11. Gas-Phase Reactions of Atomic Gold Cations with Linear Alkanes (C2-C9).

    PubMed

    Zhang, Ting; Li, Zi-Yu; Zhang, Mei-Qi; He, Sheng-Gui

    2016-06-30

    To develop proper ionization methods for alkanes, the reactivity of bare or ligated transition metal ions toward alkanes has attracted increasing interests. In this study, the reactions of the gold cations with linear alkanes from ethane up to nonane (CnH2n+2, n = 2-9) under mild conditions have been characterized by mass spectrometry and density functional theory calculations. When reacting with Au(+), small alkanes (n = 2-6) were confirmed to follow specific reaction channels of dehydrogenation for ethane and hydride transfer for others to generate product ions characteristic of the original alkanes, which indicates that Au(+) can act as a reagent ion to ionize alkanes from ethane to n-hexane. Strong dependence of the chain length of alkanes was observed for the rate constants and reaction efficiencies. Extensive fragmentation took place for larger alkanes (n > 6). Theoretical results show that the fragmentation induced by the hydride transfer occurs after the release of AuH. Moreover, the fragmentation of n-heptane was successfully avoided when the reaction took place in a high-pressure reactor. This implies that Au(+) is a potential reagent ion to ionize linear and even the branched alkanes. PMID:27266670

  12. Electronic spectrum of 9-methylanthracenium radical cation

    NASA Astrophysics Data System (ADS)

    O'Connor, Gerard D.; Sanelli, Julian A.; Dryza, Vik; Bieske, Evan J.; Schmidt, Timothy W.

    2016-04-01

    The predissociation spectrum of the cold, argon-tagged, 9-methylanthracenium radical cation is reported from 8000 cm-1 to 44 500 cm-1. The reported spectrum contains bands corresponding to at least eight electronic transitions ranging from the near infrared to the ultraviolet. These electronic transitions are assigned through comparison with ab initio energies and intensities. The infrared D1←D0 transitions exhibit significant vibronic activity, which is assigned through comparison with TD-B3LYP excited state frequencies and intensities, as well as modelled vibronic interactions. Dissociation of 9-methylanthracenium is also observed at high visible-photon energies, resulting in the loss of either CH2 or CH3. The relevance of these spectra, and the spectra of other polycyclic aromatic hydrocarbon radical cations, to the largely unassigned diffuse interstellar bands, is discussed.

  13. Radical cations of quadricyclane and norbornadiene in polar ZSM-5 matrices: Radical cation photochemical transformations without photons

    SciTech Connect

    Barnabas, M.V.; Trifunac, A.D.

    1994-06-01

    Radical cations of quadricyclane (Q) and norbornadiene (NBD) are produced by {gamma}-radiolysis in zeolites. In polar ZSM-5, only one radical cation is initially observed below 100K. Increasing the temperature above 200K gives rise to the cyclopentadiene radical cation. Higher temperatures (>360K) give rise to the cyclopenten-4-yl radical. The observation of cyclopentadiene radical cation implies the occurrence of the reverse Diels-Alder reaction. This is a thermally forbidden, photochemically allowed, process, which is made possible by the interaction of the polar zeolite matrix sites with parent NBD and Q radical cations.

  14. Electromers of the benzene dimer radical cation.

    PubMed

    Błoch-Mechkour, Anna; Bally, Thomas

    2015-04-28

    The well-studied benzene dimer radical cation, which is prototypical for this class of species, has been reinvestigated computationally. Thereby it turned out that both the σ-hemibonded and the half-shifted sandwich structures of the benzene dimer cation, which had been independently proposed, represent stationary points on the B2PLYP-D potential energy surfaces. However, these structures belong to distinct electronic states, both of which are associated with potential surfaces that are very flat with regard to rotation of the two benzene rings in an opposite sense relative to each other. The surfaces of these two "electromers" of the benzene dimer cation are separated by only 3-4 kcal mol(-1) and do not intersect along the rotation coordinate, which represents a rather unique electronic structure situation. When moving on either of the two surfaces the title complex is an extremely fluxional species, in spite of its being bound by over 20 kcal mol(-1).

  15. Electron spin resonance spectroscopic studies of radical cation reactions

    SciTech Connect

    Dai, S.

    1990-01-01

    A spin Hamiltonian suitable for theoretical analyses of ESR spectra is derived using the general effective Hamiltonian theory in the usual Schroedinger representation. The Permutation Indices method is extended to obtain the dynamic exchange equations used in ESR lineshape simulation. The correlation between [beta]-hydrogen coupling constants and their geometric orientations are derived using a perturbation method. The three electron bond model is extended to rationalize unimolecular rearrangements of radical cations. The ring-closed radical cations of 9,10-octalin oxide and synsesquinorbornene oxide have been characterized by ESR spectroscopy in the CFCl[sub 3] matrix at low temperature. The self-electron-transfer rate constants between the methyl viologen dication and cation have been determined by dynamic ESR lineshape simulations at room temperature in allyl alcohol, water, methanol and propargyl alcohol solvents. The radical cation formed by the radiolytic oxidation of allylamine in Freon matrices at 77 K is the 3-iminiopropyl distonic species(3-iminium-1-propyl radical). The nucleophilic endocylization of the but-3-en-1-ol radical cation to the protonated tetrahydrofuran-3-yl radical was observed in the radiolytic oxidation of but-3-en-1-ol in Freon matrices. ESR studies of the radiolytic oxidation of 1,5-hexdiyne have resulted in characterization the 1,5-hexadiyne radical cation isomerizing to the 1,2,4,5-hexatetraene radical cation. The symmetric (C[sub 2v]) bicyclo[3.3.0]-octa-2,6-diene-4,8-diyl(a bridged 1,4-bishomobenzene species) radical cation is produced by the radiolytic oxidation of semibullvalene in Freon matrices. The ring-opening 3,4-dimethylenecyclobutene radical cation to 1,2,4,5-hexatetraene radical cation was observed in the photolysis of 3,4-dimethylenecyclobutene radical cation. The cyclooctatetraene radical cation generated by radiolytic oxidation photoisomerizes to bicyclo[3.3.0]octa-2,6-diene-4,8-diyl radical cation.

  16. Fragmentation Pathways in the Uracil Radical Cation

    SciTech Connect

    Zhou, Congyi; Matsika, Spiridoula; Kotur, Marija; Weinacht, Thomas C.

    2012-08-24

    We investigate pathways for fragmentation in the uracil radical cation using ab initio electronic structure calculations. We focus on the main fragments produced in pump–probe dissociative ionization experiments. These are fragments with mass to charge ratios (m/z) of 69, 28, 41, and 42. Barriers to dissociation along the ground ionic surface are reported, which provide an estimate of the energetic requirements for the production of the main fragments. Finally, direct and sequential fragmentation mechanisms have been analyzed, and it is concluded that sequential fragmentation after production of fragment with m/z 69 is the dominant mechanism for the production of the smaller fragments.

  17. Infrared Spectroscopic Investigation of the Acidic CH Bonds in Cationic n-Alkanes: Pentane, Hexane, and Heptane.

    PubMed

    Xie, Min; Matsuda, Yoshiyuki; Fujii, Asuka

    2016-08-18

    Radical cations of n-alkanes (pentane, hexane, and heptane) in the gas phase are investigated by infrared predissociation spectroscopy with the argon or nitrogen tagging. All-trans and gauche-involving conformers are identified for these cations by comparisons of observed infrared spectra and vibrational simulations. Intense CH stretch bands are observed in the frequency region lower than the normal alkyl CH stretch frequency. These low frequencies and high intensities of the CH stretch bands are caused by the CH bond weakening and the enhanced positive charge of the hydrogen atoms through the delocalization of the σ electron in the CH bonds. These effects of the delocalization of the σ electron result in the enhanced acidity of the CH bonds. The conformation as well as alkyl chain length dependence of the acidity of the CH bonds is demonstrated by the CH stretch frequency shift trend. PMID:27467194

  18. Transition-Metal Hydride Radical Cations.

    PubMed

    Hu, Yue; Shaw, Anthony P; Estes, Deven P; Norton, Jack R

    2016-08-10

    Transition-metal hydride radical cations (TMHRCs) are involved in a variety of chemical and biochemical reactions, making a more thorough understanding of their properties essential for explaining observed reactivity and for the eventual development of new applications. Generally, these species may be treated as the ones formed by one-electron oxidation of diamagnetic analogues that are neutral or cationic. Despite the importance of TMHRCs, the generally sensitive nature of these complexes has hindered their development. However, over the last four decades, many more TMHRCs have been synthesized, characterized, isolated, or hypothesized as reaction intermediates. This comprehensive review focuses on experimental studies of TMHRCs reported through the year 2014, with an emphasis on isolated and observed species. The methods used for the generation or synthesis of TMHRCs are surveyed, followed by a discussion about the stability of these complexes. The fundamental properties of TMHRCs, especially those pertaining to the M-H bond, are described, followed by a detailed treatment of decomposition pathways. Finally, reactions involving TMHRCs as intermediates are described. PMID:26828562

  19. Transition-Metal Hydride Radical Cations.

    PubMed

    Hu, Yue; Shaw, Anthony P; Estes, Deven P; Norton, Jack R

    2016-08-10

    Transition-metal hydride radical cations (TMHRCs) are involved in a variety of chemical and biochemical reactions, making a more thorough understanding of their properties essential for explaining observed reactivity and for the eventual development of new applications. Generally, these species may be treated as the ones formed by one-electron oxidation of diamagnetic analogues that are neutral or cationic. Despite the importance of TMHRCs, the generally sensitive nature of these complexes has hindered their development. However, over the last four decades, many more TMHRCs have been synthesized, characterized, isolated, or hypothesized as reaction intermediates. This comprehensive review focuses on experimental studies of TMHRCs reported through the year 2014, with an emphasis on isolated and observed species. The methods used for the generation or synthesis of TMHRCs are surveyed, followed by a discussion about the stability of these complexes. The fundamental properties of TMHRCs, especially those pertaining to the M-H bond, are described, followed by a detailed treatment of decomposition pathways. Finally, reactions involving TMHRCs as intermediates are described.

  20. Effect of alkane chain length and counterion on the freezing transition of cationic surfactant adsorbed film at alkane mixture - water interfaces.

    PubMed

    Tokiwa, Yuhei; Sakamoto, Hiroyasu; Takiue, Takanori; Aratono, Makoto; Matsubara, Hiroki

    2015-05-21

    Penetration of alkane molecules into the adsorbed film gives rise to a surface freezing transition of cationic surfactant at the alkane-water interface. To examine the effect of the alkane chain length and counterion on the surface freezing, we employed interfacial tensiometry and ellipsometry to study the interface of cetyltrimethylammonium bromide and cetyltrimethylammonium chloride aqueous solutions against dodecane, tetradecane, hexadecane, and their mixtures. Applying theoretical equations to the experimental results obtained, we found that the alkane molecules that have the same chain length as the surfactant adsorb preferentially into the surface freezing film. Furthermore, we demonstrated that the freezing transition temperature of cationic surfactant adsorbed film was independent of the kind of counterion. PMID:25932500

  1. Two phosphaalkene radical cations with inverse spin density distributions.

    PubMed

    Pan, Xiaobo; Wang, Xingyong; Zhang, Zaichao; Wang, Xinping

    2015-09-14

    Two phosphaalkene radical cations 1(•+) and 2(•+) have been reported. 1(•+) is stable in the solid state and has been structurally characterized. 2(•+) only remains persistent in solution. 1(•+) is described as a phosphorus-centered radical, while 2(•+) as a delocalized radical with little contribution from phosphorus.

  2. Radical-radical interactions among oxidized guanine bases including guanine radical cation and dehydrogenated guanine radicals.

    PubMed

    Zhao, Jing; Wang, Mei; Yang, Hongfang; Zhang, Meng; Liu, Ping; Bu, Yuxiang

    2013-09-19

    We present here a theoretical investigation of the structural and electronic properties of di-ionized GG base pairs (G(•+)G(•+),G(-H1)(•)G(•+), and G(-H1)(•)G(-H1)(•)) consisting of the guanine cation radical (G(•+)) and/or dehydrogenated guanine radical (G(-H1)(•)) using density functional theory calculations. Different coupling modes (Watson-Crick/WC, Hoogsteen/Hoog, and minor groove/min hydrogen bonding, and π-π stacking modes) are considered. We infer that a series of G(•+)G(•+) complexes can be formed by the high-energy radiation. On the basis of density functional theory and complete active space self-consistent (CASSCF) calculations, we reveal that in the H-bonded and N-N cross-linked modes, (G(•+)G(•+))WC, (G(-H1)(•)G(-H1)(•))WC, (G(-H1)(•)G(-H1)(•))minI, and (G(-H1)(•)G(-H1)(•))minIII have the triplet ground states; (G(•+)G(•+))HoogI, (G(-H1)(•)G(•+))WC, (G(-H1)(•)G(•+))HoogI, (G(-H1)(•)G(•+))minI, (G(-H1)(•)G(•+))minII, and (G(-H1)(•)G(-H1)(•))minII possess open-shell broken-symmetry diradical-characterized singlet ground states; and (G(•+)G(•+))HoogII, (G(•+)G(•+))minI, (G(•+)G(•+))minII, (G(•+)G(•+))minIII, (G(•+)G(•+))HoHo, (G(-H1)(•)G(•+))minIII, (G(-H1)(•)G(•+))HoHo, and (G(-H1)(•)G(-H1)(•))HoHo are the closed-shell systems. For these H-bonded diradical complexes, the magnetic interactions are weak, especially in the diradical G(•+)G(•+) series and G(-H1)(•)G(-H1)(•) series. The magnetic coupling interactions of the diradical systems are controlled by intermolecular interactions (H-bond, electrostatic repulsion, and radical coupling). The radical-radical interaction in the π-π stacked di-ionized GG base pairs ((G(•+)G(•+))ππ, (G(-H1)(•)G(•+))ππ, and (G(-H1)(•)G(-H1)(•))ππ) are also considered, and the magnetic coupling interactions in these π-π stacked base pairs are large. This is the first theoretical prediction that some di

  3. DFT study on the cycloreversion of thietane radical cations.

    PubMed

    Domingo, Luis R; Pérez-Ruiz, Raúl; Argüello, Juan E; Miranda, Miguel A

    2011-06-01

    The molecular mechanism of the cycloreversion (CR) of thietane radical cations has been analyzed in detail at the UB3LYP/6-31G* level of theory. Results have shown that the process takes place via a stepwise mechanism leading to alkenes and thiobenzophenone; alternatively, formal [4+2] cycloadducts are obtained. Thus, the CR of radical cations 1a,b(•+) is initiated by C2-C3 bond breaking, giving common intermediates INa,b. At this stage, two reaction pathways are feasible involving ion molecule complexes IMCa,b (i) or radical cations 4a,b(•+) (ii). Calculations support that 1a(•+) follows reaction pathway ii (leading to the formal [4+2] cycloadducts 5a). By contrast, 1b(•+) follows pathway i, leading to trans-stilbene radical cation (2b(•+)) and thiobenzophenone.

  4. DFT study on the cycloreversion of thietane radical cations.

    PubMed

    Domingo, Luis R; Pérez-Ruiz, Raúl; Argüello, Juan E; Miranda, Miguel A

    2011-06-01

    The molecular mechanism of the cycloreversion (CR) of thietane radical cations has been analyzed in detail at the UB3LYP/6-31G* level of theory. Results have shown that the process takes place via a stepwise mechanism leading to alkenes and thiobenzophenone; alternatively, formal [4+2] cycloadducts are obtained. Thus, the CR of radical cations 1a,b(•+) is initiated by C2-C3 bond breaking, giving common intermediates INa,b. At this stage, two reaction pathways are feasible involving ion molecule complexes IMCa,b (i) or radical cations 4a,b(•+) (ii). Calculations support that 1a(•+) follows reaction pathway ii (leading to the formal [4+2] cycloadducts 5a). By contrast, 1b(•+) follows pathway i, leading to trans-stilbene radical cation (2b(•+)) and thiobenzophenone. PMID:21561127

  5. Picosecond photolysis of azo compounds in liquid alkanes: germinate recombination kinetics for polyatomic free radical pairs

    NASA Astrophysics Data System (ADS)

    Scott, Thomas W.; Doubleday, Charles, Jr.

    1991-03-01

    Picosecond optical absorption transients for the photolysis products of azocumene and the cyclic azo compound 3,8-diphenyl-1,2-diaza-1-cyclooctene have been measured in a series of alkane solvents having different liquid viscosities. The transient intermediate produced from azocumene decays through a diffusion influenced process which is interpreted as secondary recombination of geminate free radical pairs. This assignment is based on the wavelength dependence of the transient absorption signal, the viscosity dependence of the decay kinetics and the complementary decay profiles seen for free and tethered radical pairs. The long time limit of the survival probability for geminate cumyl free radicals follows the reciprocal square root fo time decay predicted by the Smoluchowski diffusion equation.

  6. Pyridine radical cation and its fluorine substituted derivatives

    USGS Publications Warehouse

    Bondybey, V.E.; English, J.H.; Shiley, R.H.

    1982-01-01

    The spectra and relaxation of the pyridine cation and of several of its fluorinated derivatives are studied in low temperature Ne matrices. The ions are generated by direct photoionization of the parent compounds. Of the compounds studied, laser induced → and → fluorescence is observed only for the 2, 6‐difluoropyridine cation. The analysis of the spectrum indicates that the ion is planar both in the and states. The large variety in the spectroscopic and relaxation behavior of fluoropyridine radical cations is explained in terms of their electronic structure and of the differential shifts of the individual electronic states caused by the fluorine substitution.

  7. Measurement of antioxidant activity with trifluoperazine dihydrochloride radical cation.

    PubMed

    Asghar, M N; Khan, I U

    2008-06-01

    A novel, rapid and cost-effective trifluoperazine dihydrochloride (TFPH) decolorization assay is described for the screening of antioxidant activity. A chromogenic reaction between TFPH and potassium persulfate at low pH produces an orange-red radical cation with maximum absorption at 502 nm in its first-order derivative spectrum. TFPH was dissolved in distilled water to give a 100 mM solution. The TFPH radical cation solution was made by reacting 0.5 mL of the solution with K2S2O8 (final concentration: 0.1 mM) and diluting to 100 mL with 4 M H2SO4 solution. A linear inhibition of color production was observed with linearly increasing amounts of antioxidants, with correlation coefficients (R(2)) ranging from 0.999 to 0.983. The antioxidant capacity of standard solutions of an antioxidant was evaluated by comparing with the inhibition curve using Trolox as the standard. Comparison of antioxidant capacity determined with this newly developed TFPH assay and with the well-known 2,2'-azinobis-[3-ethylbenzthiazoline-6-sulfonic acid] (ABTS)-persulfate decolorization assay indicated the efficacy and sensitivity of the procedure. The proposed assay is less expensive (costs about US$4 per 100 assays) and requires only 20 min for preparation of radical cation solution in comparison with ABTS assay, in which almost 12-16 h are required for preparation of a stable ABTS radical cation solution. The present assay has the advantage over ABTS assay that it can be used to measure the antioxidant activity of the samples, which are naturally found at a pH as low as 1, because the radical cation itself has been stabilized at low pH.

  8. A semiconducting organic radical cationic host-guest complex.

    PubMed

    Fahrenbach, Albert C; Sampath, Srinivasan; Late, Dattatray J; Barnes, Jonathan C; Kleinman, Samuel L; Valley, Nicholas; Hartlieb, Karel J; Liu, Zhichang; Dravid, Vinayak P; Schatz, George C; Van Duyne, Richard P; Stoddart, J Fraser

    2012-11-27

    The self-assembly and solid-state semiconducting properties of single crystals of a trisradical tricationic complex composed of the diradical dicationic cyclobis(paraquat-p-phenylene) (CBPQT(2(•+))) ring and methyl viologen radical cation (MV(•+)) are reported. An organic field effect transistor incorporating single crystals of the CBPQT(2(•+))⊂MV(•+) complex was constructed using lithographic techniques on a silicon substrate and shown to exhibit p-type semiconductivity with a mobility of 0.05 cm(2) V(-1) s(-1). The morphology of the crystals on the silicon substrate was characterized using scanning electron microscopy which revealed that the complexes self-assemble into "molecular wires" observable by the naked-eye as millimeter long crystalline needles. The nature of the recognition processes driving this self-assembly, radical-radical interactions between bipyridinium radical cations (BIPY(•+)), was further investigated by resonance Raman spectroscopy in conjunction with theoretical investigations of the vibrational modes, and was supported by X-ray structural analyses of the complex and its free components in both their radical cationic and dicationic redox states. These spectroscopic investigations demonstrate that the bond order of the BIPY(•+) radical cationic units of host and guest components is not changed upon complexation, an observation which relates to its conductivity in the solid-state. We envision the modularity inherent in this kind of host-guest complexation could be harnessed to construct a library of custom-made electronic organic materials tailored to fit the specific needs of a given electronic application.

  9. Formation and Dissociation of Phosphorylated Peptide Radical Cations

    NASA Astrophysics Data System (ADS)

    Kong, Ricky P. W.; Quan, Quan; Hao, Qiang; Lai, Cheuk-Kuen; Siu, Chi-Kit; Chu, Ivan K.

    2012-12-01

    In this study, we generated phosphoserine- and phosphothreonine-containing peptide radical cations through low-energy collision-induced dissociation (CID) of the ternary metal-ligand phosphorylated peptide complexes [CuII(terpy) p M]·2+ and [CoIII(salen) p M]·+ [ p M: phosphorylated angiotensin III derivative; terpy: 2,2':6',2''-terpyridine; salen: N, N '-ethylenebis(salicylideneiminato)]. Subsequent CID of the phosphorylated peptide radical cations ( p M·+) revealed fascinating gas-phase radical chemistry, yielding (1) charge-directed b- and y-type product ions, (2) radical-driven product ions through cleavages of peptide backbones and side chains, and (3) different degrees of formation of [M - H3PO4]·+ species through phosphate ester bond cleavage. The CID spectra of the p M·+ species and their non-phosphorylated analogues featured fragment ions of similar sequence, suggesting that the phosphoryl group did not play a significant role in the fragmentation of the peptide backbone or side chain. The extent of neutral H3PO4 loss was influenced by the peptide sequence and the initial sites of the charge and radical. A preliminary density functional theory study, at the B3LYP 6-311++G(d,p) level of theory, of the neutral loss of H3PO4 from a prototypical model— N-acetylphosphorylserine methylamide—revealed several factors governing the elimination of neutral phosphoryl groups through charge- and radical-induced mechanisms.

  10. DFT and ENDOR Study of Bixin Radical Cations and Neutral Radicals on Silica-Alumina.

    PubMed

    Tay-Agbozo, Sefadzi S; Krzyaniak, Matthew D; Bowman, Michael K; Street, Shane; Kispert, Lowell D

    2015-06-18

    Bixin, a carotenoid found in annatto (Bixa orellana), is unique among natural carotenoids by being water-soluble. We stabilized free radicals from bixin on the surface of silica-alumina (Si-Al) and characterized them by pulsed electron-nuclear double resonance (ENDOR). DFT calculations of unpaired electron spin distribution for various bixin radicals predict the EPR hyperfine couplings. Least-square fitting of experimental ENDOR spectra by spectra calculated from DFT hyperfine couplings characterized the radicals trapped on Si-Al. DFT predicts that the trans bixin radical cation is more stable than the cis bixin radical cation by 1.26 kcal/mol. This small energy difference is consistent with the 26% trans and 23% cis radical cations in the ENDOR spectrum. The remainder of the ENDOR spectrum is due to several neutral radicals formed by loss of a H(+) ion from the 9, 9', 13, or 13' methyl group, a common occurrence in all water-insoluble carotenoids previously studied. Although carboxyl groups of bixin strongly affect its solubility relative to other natural carotenoids, they do not alter properties of its free radicals based on DFT calculations and EPR measurements which remain similar to typical water-insoluble carotenoids.

  11. DFT and ENDOR Study of Bixin Radical Cations and Neutral Radicals on Silica-Alumina.

    PubMed

    Tay-Agbozo, Sefadzi S; Krzyaniak, Matthew D; Bowman, Michael K; Street, Shane; Kispert, Lowell D

    2015-06-18

    Bixin, a carotenoid found in annatto (Bixa orellana), is unique among natural carotenoids by being water-soluble. We stabilized free radicals from bixin on the surface of silica-alumina (Si-Al) and characterized them by pulsed electron-nuclear double resonance (ENDOR). DFT calculations of unpaired electron spin distribution for various bixin radicals predict the EPR hyperfine couplings. Least-square fitting of experimental ENDOR spectra by spectra calculated from DFT hyperfine couplings characterized the radicals trapped on Si-Al. DFT predicts that the trans bixin radical cation is more stable than the cis bixin radical cation by 1.26 kcal/mol. This small energy difference is consistent with the 26% trans and 23% cis radical cations in the ENDOR spectrum. The remainder of the ENDOR spectrum is due to several neutral radicals formed by loss of a H(+) ion from the 9, 9', 13, or 13' methyl group, a common occurrence in all water-insoluble carotenoids previously studied. Although carboxyl groups of bixin strongly affect its solubility relative to other natural carotenoids, they do not alter properties of its free radicals based on DFT calculations and EPR measurements which remain similar to typical water-insoluble carotenoids. PMID:25333911

  12. Reaction of bovine cytochrome c oxidase with hydrogen peroxide produces a tryptophan cation radical and a porphyrin cation radical.

    PubMed

    Rigby, S E; Jünemann, S; Rich, P R; Heathcote, P

    2000-05-23

    Oxidized bovine cytochrome c oxidase reacts with hydrogen peroxide to generate two electron paramagnetic resonance (EPR) free radical signals (Fabian, M., and Palmer, G. (1995) Biochemistry 34, 13802-13810). These radicals are associated with the binuclear center and give rise to two overlapped EPR signals, one signal being narrower in line width (DeltaHptp = 12 G) than the other (DeltaHptp = 45 G). We have used electron nuclear double resonance (ENDOR) spectrometry to identify the two different chemical species giving rise to these two EPR signals. Comparison of the ENDOR spectrum associated with the narrow signal with that of compound I of horseradish peroxidase (formed by reaction of that enzyme with hydrogen peroxide) demonstrates that the two species are virtually identical. The chemical species giving rise to the narrow signal is therefore identified as an exchange-coupled porphyrin cation radical similar to that formed in horseradish peroxidase compound I. Comparison of the ENDOR spectrum of compound ES (formed by the reaction of hydrogen peroxide with cytochrome c peroxidase) with that of the broad signal indicates that the chemical species giving rise to the broad EPR signal in cytochrome c oxidase is probably an exchange coupled tryptophan cation radical. This is substantiated using H(2)O/D(2)O solvent exchange experiments where the ENDOR difference spectrum of the broad EPR signal of cytochrome c oxidase shows a feature consistent with hyperfine coupling to the exchangeable N(1) proton of a tryptophan cation radical.

  13. Electronic structure and photochemical interconversions of dihydropentalene radical cations

    SciTech Connect

    Bally, T.; Truttmann, L.; Wang, J.T.; Williams, F.

    1995-08-02

    Starting from the recently characterized radical cation of bicyclo[3,3,0]octa-2,6-diene-4,8-diyl, four additional dihydropentalene radical cations (DHP{sup -4}) can be formed by phototautomerization in Freon glasses and argon matrices where they can be characterized by optical (Freon, argon) and ESR spectroscopy (Freon). Two of these DHP isomers can be prepared independently, while the cations of the other two are identified by analogy of their spectra with those of related compounds. The electronic structure of 1,2-, 1,4-, and 1,5-DHP{sup +}, which have linear and cross-conjugated triene {pi}-systems is discussed on the basis of their photoelectron and optical spectra and INDO/S calculations. The part of the C{sub 8}H{sub 8}{sup +} potential surface comprising all ten possible DHP{sup +} tautomers and some related valence isomers is explored by high-level ab initio calculations. An FMO-based set of rules for sigmatropic rearrangements in radical cations is presented and serves to rationalize the observed H-shifts. 40 refs., 12 figs., 4 tabs.

  14. Changes in fluorescent emission of cationic fluorophores in the presence of n-alkanes and alcohols in different polarity solvents

    NASA Astrophysics Data System (ADS)

    Delgado-Camón, Arantzazu; Garriga, Rosa; Mateos, Elena; Cebolla, Vicente L.; Galbán, Javier; Membrado, Luis; Marcos, Susana de; Gálvez, Eva M.

    2011-01-01

    Berberine and coralyne experience either fluorescence enhancement or quenching when long hydrocarbon chain compounds (e.g., n-alkanes or alcohols) are added to their solutions, depending on solvent polarity. In polar solvents, as methanol or acetonitrile, the added compounds provide an apolar microenvironment that hinders alternative relaxation mechanisms, favouring fluorescence emission. However, alkane additions produce quenching in dichloromethane, which has been explained taking into account ion pairing between cationic fluorophore and counterion. The strong quenching measured after alcohol additions in dichloromethane suggests reversed micelle formation. Procedures and results described here may find practical applications in the development of analytical methods.

  15. Oxoferryl porphyrin cation radicals in model systems: Evidence for variable metal-radical spin coupling

    NASA Astrophysics Data System (ADS)

    Bill, E.; Bominaar, E. L.; Ding, X.-Q.; Trautwein, A. X.; Winkler, H.; Mandon, D.; Weiss, R.; Gold, A.; Jayaraj, K.; Toney, G. E.

    1990-07-01

    Magnetic properties of frozen solutions of highly oxidized iron porphyrin complexes were investigated by EPR and Mössbauer spectroscopy. The Mössbauer spectra, recorded at low temperatures in various magnetic fields, were analyzed on the basis of spin Hamiltonian simulations. Spin coupling between ferryl iron (FeIV) and porphyrin cation radical was taken into account explicitly. Hyperfine and spin-coupling parameters are given for several complexes, together with zero-field parameters. One of the complexes exhibits weak spin coupling, it is the first model system exhibiting properties comparable to those of the oxoferryl cation radical enzyme Horse Radish Peroxidase I.

  16. Kinetics for Tautomerizations and Dissociations of Triglycine Radical Cations

    SciTech Connect

    Siu, Chi-Kit; Zhao, Junfang; Laskin, Julia; Chu, Ivan K.; Hopkinson, Alan C.; Siu , K W Michael

    2009-06-01

    Fragmentations of tautomers of the α-centered radical triglycine radical cation, [GGG*]+, [GG*G]+, and [G*GG]+, are charge-driven, giving b-type ions; these are processes that are facilitated by a mobile proton, as in the fragmentation of protonated triglycine (Rodriquez, C.F. et al. J. Am. Chem. Soc. 2001, 123, 3006 - 3012). By contrast, radical centers are less mobile. Two mechanisms have been examined theoretically utilizing density functional theory and Rice-Ramsperger-Kassel-Marcus modeling: (1) a direct hydrogen-atom migration between two α-carbons, and (2) a two-step proton migration involving a canonical [GGG]*+ as an intermediate. Predictions employing the latter mechanism are in good agreement with results of recent CID experiments (Chu, I.K. et al. J. Am. Chem. Soc. 2008, 130, 7862 - 7872).

  17. Theoretical studies on the dimerization of substituted paraphenylenediamine radical cations

    NASA Astrophysics Data System (ADS)

    Punyain, Kraiwan; Kelterer, Anne-Marie; Grampp, Günter

    2011-12-01

    Organic radical cations form dicationic dimers in solution, observed experimentally as diamagnetic species in temperature-dependent EPR and low temperature UV/Vis spectroscopy. Dimerization of paraphenylenediamine, N,N-dimethyl-paraphenylenediamine and 2,3,5,6-tetramethyl-paraphenylenediamine radical cation in ethanol/diethylether mixture was investigated theoretically according to geometry, energetics and UV/Vis spectroscopy. Density Functional Theory including dispersion correction describes stable dimers after geometry optimization with conductor-like screening model of solvation and inclusion of the counter-ion. Energy corrections were done on double-hybrid Density Functional Theory with perturbative second-order correlation (B2PLYP-D) including basis set superposition error (BSSE), and multireference Møller-Plesset second-order perturbation theory method (MRMP2) based on complete active space method (CASSCF(2,2)) single point calculation, respectively. All three dication π-dimers exhibit long multicenter π-bonds around 2.9 ± 0.1 Å with strongly interacting orbitals. Substitution with methyl groups does not influence the dimerization process substantially. Dispersion interaction and electrostatic attraction from counter-ion play an important role to stabilize the dication dimers in solution. Dispersion-corrected double hybrid functional B2PLYP-D and CASSCF(2,2) can describe the interaction energetics properly. Vertical excitations were computed with Tamm-Dancoff approximation for time-dependent Density Functional Theory (TDA-DFT) at the B3LYP level with the cc-pVTZ basis set including ethanol solvent molecules explicitly. A strong interaction of the counter-ion and the solvent ethanol with the monomeric species is observed, whereas in the dimers the strong interaction of both radical cation species is the dominating factor for the additional peak in UV/Vis spectra.

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

    NASA Astrophysics Data System (ADS)

    Osburn, Sandra; Berden, Giel; Oomens, Jos; O'Hair, Richard A. J.; Ryzhov, Victor

    2011-10-01

    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-acetyl-cysteine followed by the homolytic cleavage of the S-NO bond in the gas phase. IRMPD spectroscopy coupled with DFT calculations revealed that for the radical cation the radical migrates from its initial position on the sulfur atom to the α-carbon position, which is 2.5 kJ mol-1 lower in energy. The radical migration was confirmed by time-resolved ion-molecule reactions. These results are in contrast with our previous study on cysteine methyl ester radical cation (Osburn et al., Chem. Eur. J. 2011, 17, 873-879) and the study by Sinha et al. for cysteine radical cation ( Phys. Chem. Chem. Phys. 2010, 12, 9794-9800) where the radical was found to stay on the sulfur atom as formed. A similar approach allowed us to form a hydrogen-deficient radical anion of N-acetyl-cysteine, (M - 2H) •- . IRMPD studies and ion-molecule reactions performed on the radical anion showed that the radical remains on the sulfur, which is the initial and more stable (by 63.6 kJ mol-1) position, and does not rearrange.

  19. Magnetic Resonance Studies of Proton Loss from Carotenoid Radical Cations

    SciTech Connect

    Kispert, Lowell D; Focsan, A Ligia; Konovalova, Tatyana A; Lawrence, Jesse; Bowman, Michael K; Dixon, David A; Molnar, Peter; Deli, Jozsef

    2007-06-11

    Carotenoids, intrinsic components of reaction centers and pigment-protein complexes in photosynthetic membranes, play a photoprotective role and serve as a secondary electron donor. Before optimum use of carotenoids can be made in artificial photosynthetic systems, their robust nature in living materials requires extensive characterization of their electron transfer, radical trapping ability, stability, structure in and on various hosts, and photochemical behavior. Pulsed ENDOR and 2D-HYSCORE studies combined with DFT calculations reveal that photo-oxidation of natural zeaxanthin (I) and violaxanthin (II) on silica-alumina produces not only the carotenoid radical cations (Car•+) but also neutral radicals (#Car•) by proton loss from the methyl groups at positions 5 or 5', and possibly 9 or 9' and 13 or 13'. Notably, the proton loss favored in I at the 5 position by DFT calculations, is unfavorable in II due to the epoxide at the 5, 6 position. DFT calculations predict the isotropic methyl proton couplings of 8-10 MHz for Car•+ which agree with the ENDOR for carotenoid α-conjugated radical cations. Large α-proton hyperfine coupling constants (>10 MHz) determined from HYSCORE are assigned from the DFT calculations to neutral carotenoid radicals. Proton loss upon photolysis was also examined as a function of carotenoid polarity [Lycopene (III) versus 8'-apo-β-caroten-8'-al (IV)]; hydrogen bonding [Lutein (V) versus III]; host [silica-alumina versus MCM-41 molecular sieve]; and substituted metal in MCM-41. Loss of H+ from the 5(5'), 9(9') or 13(13') methyl positions has importance in photoprotection. Photoprotection involves nonphotochemical quenching (NPQ) in which 1Ch1* decays via energy transfer to the carotenoid which returns to the ground state by thermal dissipation; or via electron transfer to form a charge transfer state (I •+…Chl•-), lower in energy than 1Chl*. Formation of I •+ results in bond lengthening, a mechanism for nonradiative energy

  20. Gas-Phase Reactions of Doubly Charged Lanthanide Cations with Alkanes and Alkenes. Trends in Metal(2+) Reactivity

    SciTech Connect

    Gibson, John K.; Marcalo, Joaquim; Santos, Marta; Pires de Matos, Antonio; Haire, Richard G.

    2008-12-08

    The gas-phase reactivity of doubly-charged lanthanide cations, Ln2+ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), with alkanes (methane, ethane, propane, n-butane) and alkenes (ethene, propene, 1-butene) was studied by Fourier transform ion cyclotron resonance mass spectrometry. The reaction products consisted of different combinations of doubly-charged organometallic ions?adducts or species formed via metal-ion-induced hydrogen, dihydrogen, alkyl, or alkane eliminations from the hydrocarbons?and singly-charged ions that resulted from electron, hydride, or methide transfers from the hydrocarbons to the metal ions. The only lanthanide cations capable of activating the hydrocarbons to form doubly-charged organometallic ions were La2+, Ce2+, Gd2+, and Tb2+, which have ground-state or low-lying d1 electronic configurations. Lu2+, with an accessible d1 electronic configuration but a rather high electron affinity, reacted only through transfer channels. The remaining Ln2+ reacted via transfer channels or adduct formation. The different accessibilities of d1 electronic configurations and the range of electron affinities of the Ln2+ cations allowed for a detailed analysis of the trends for metal(2+) reactivity and the conditions for occurrence of bond activation, adduct formation, and electron, hydride, and methide transfers.

  1. Stabilization of the veratryl alcohol cation radical by lignin peroxidase.

    PubMed

    Khindaria, A; Yamazaki, I; Aust, S D

    1996-05-21

    Lignin peroxidase (LiP) catalyzes the H2O2-dependent oxidation of veratryl alcohol (VA) to veratryl aldehyde, with the enzyme-bound veratryl alcohol cation radical (VA.+) as an intermediate [Khindaria et al. (1995) Biochemistry 34, 16860-16869]. The decay constant we observed for the enzyme generated cation radical did not agree with the decay constant in the literature [Candeias and Harvey (1995) J. Biol. Chem. 270, 16745-16748] for the chemically generated radical. Moreover, we have found that the chemically generated VA.+ formed by oxidation of VA by Ce(IV) decayed rapidly with a first-order mechanism in air- or oxygen-saturated solutions, with a decay constant of 1.2 x 10(3) s-1, and with a second-order mechanism in argon-saturated solution. The first-order decay constant was pH- independent suggesting that the rate-limiting step in the decay was deprotonation. When VA.+ was generated by oxidation with LiP the decay also occurred with a first-order mechanism but was much slower, 1.85 s-1, and was the same in both oxygen- and argon-saturated reaction mixtures. However, when the enzymatic reaction mixture was acid-quenched the decay constant of VA.+ was close to the one obtained in the Ce(IV) oxidation system, 9.7 x 10(2) s-1. This strongly suggested that the LiP-bound VA.+ was stabilized and decayed more slowly than free VA.+. We propose that the stabilization of VA.+ may be due to the acidic microenvironment in the enzyme active site, which prevents deprotonation of the radical and subsequent reaction with oxygen. We have also obtained reversible redox potential of VA.+/VA couple using cyclic voltammetery. Due to the instability of VA.+ in aqueous solution the reversible redox potential was measured in acetone, and was 1.36 V vs normal hydrogen electrode. Our data allow us to propose that enzymatically generated VA.+ can act as a redox mediator but not as a diffusible oxidant for LiP-catalyzed lignin or pollutant degradation.

  2. Reactions and structural investigation of chlorpromazine radical cation

    NASA Astrophysics Data System (ADS)

    Joshi, Ravi; Ghanty, Tapan K.; Mukherjee, T.

    2008-10-01

    Experimental and theoretical studies have been carried out to understand pro-oxidant behaviour of chlorpromazine radical cation (CPZ rad + ). Pulse radiolysis studies have shown that CPZ rad + oxidizes physiological antioxidants (uric acid and bilirubin), and biomolecules like, tyrosine and proteins (bovine serum albumin and casein), thereby acting as a pro-oxidant. Ab-initio quantum chemical calculations suggest structural and electronic changes on oxidation of CPZ. The calculations with Hartree-Fock and density functional methods show that ring nitrogen atom is the site of electron removal from CPZ and sulfur atom is the site of maximum spin in CPZ rad + . The calculations also suggest that oxidation of CPZ leads to increase in planarity of the tricyclic ring as well as tilting of alkyl side chain towards chlorine containing ring. The structural changes on oxidation of CPZ and spin delocalization in CPZ rad + fairly explain the pro-oxidant activity of CPZ.

  3. Spectroscopy of free-base N-confused tetraphenylporphyrin radical anion and radical cation.

    PubMed

    Alemán, Elvin A; Manríquez Rocha, Juan; Wongwitwichote, Wongwit; Godínez Mora-Tovar, Luis Arturo; Modarelli, David A

    2011-06-23

    The radical anions and radical cations of the two tautomers (1e and 1i) of 5,10,15,20-tetraphenyl N-confused free-base porphyrin have been studied using a combination of cyclic voltammetry, steady state absorption spectroscopy, and computational chemistry. N-Confused porphyrins (NCPs), alternatively called 2-aza-21-carba-5,10,15,20-tetraphenylporphyrins or inverted porphyrins, are of great interest for their potential as building blocks in assemblies designed for artificial photosynthesis, and understanding the absorption spectra of the corresponding radical ions is paramount to future studies in multicomponent arrays where electron-transfer reactions are involved. NCP 1e was shown to oxidize at a potential of E(ox) 0.65 V vs Fc(+)|Fc in DMF and reduce at E(red) -1.42 V, while the corresponding values for 1i in toluene were E(ox) 0.60 V and E(red) -1.64 V. The geometries of these radical ions were computed at the B3LYP/6-31+G(d)//B3LYP/6-31G(d) level in the gas phase and in solution using the polarizable continuum model (PCM). From these structures and that of H(2)TPP and its corresponding radical ions, the computed redox potentials for 1e and 1i were calculated using the Born-Haber cycle. While the computed reduction potentials and electron affinities were in excellent agreement with the experimental reduction potentials, the calculated oxidation potentials displayed a somewhat less ideal relationship with experiment. The absorption spectra of the four radical ions were also measured experimentally, with radical cations 1e(•+) and 1i(•+) displaying significant changes in the Soret and Q-band regions as well as new low energy absorption bands in the near-IR region. The changes in the absorption spectra of radical anions 1e(•-) and 1i(•-) were not as dramatic, with the changes occurring only in the Soret and Q-band regions. These results were favorably modeled using time-dependent density functional calculations at the TD-B3LYP/6-31+G(d)//B3LYP/6-31G

  4. Electronic spectra of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation and radical

    DOE PAGES

    Peter R. Craig; Miller, John R.; Havlas, Zdenek; Trujillo, Marianela; Rempala, Pawel; Kirby, James P.; Noll, Bruce C.; Michl, Josef

    2016-05-02

    In this study, properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation 1 and its tetra-o-fluoro derivative 1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation 1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF–4 anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of 1 and 1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results. Reduction or pulse radiolysis lead to a neutral 19-electron radical,more » whose visible absorption and MCD spectra have been recorded and interpreted as well. The reduction is facilitated by ~0.1 V upon going from 1 to 1a« less

  5. Observation of radical cations by swiftness or by stealth.

    SciTech Connect

    Werst, D. W.; Trifunac, A. D.; Chemistry

    1998-01-01

    David W. Werst was born in Missouri and educated at the University of Missouri (B.S.) and the University of Minnesota (Ph.D.). His thesis work was carried out under the supervision of Paul Barbara and Ronald Gentry. He joined the Chemistry Division of Argonne National Laboratory in 1985 to conduct postdoctoral research in the group of Alexander Trifunac and has been a staff member of the Radiation and Photochemistry Group since 1989. His primary research interests are in the study of radical cation structure and reactivity and ionization processes in ordered and amorphous solids. Alexander D. Trifunac was born in Yugoslavia. He was educated at Columbia University (B.A.) and the University of Chicago (Ph.D.). His thesis work was on CIDNP, radical pair theory and experiments, with Gerhard L. Closs. He joined the Chemistry Division of Argonne National Laboratory in 1972 in a postdoctoral position. He is a senior scientist and is (since 1982) a group leader of the Radiation and Photochemistry Group. His research interests are in the study of chemistry of transient paramagnetic species involved in energy and charge-transfer processes occurring in radiolysis and in photoionization in liquids, glasses, and amorphous solids.

  6. Are the Radical Centers in Peptide Radical Cations Mobile? The Generation, Tautomerism, and Dissociation of Isomeric α-Carbon-Centered Triglycine Radical Cations in the Gas Phase

    SciTech Connect

    Chu, Ivan K.; Zhao, Junfang; Xu, Minjie; Siu, Shiu On; Hopkinson, Alan C.; Siu , K W Michael

    2008-05-31

    The mobility of the radical center in three isomeric triglycine radical cationss[G•GG]+, [GG•G]+, and [GGG•]+shas been investigated theoretically via density functional theory (DFT) and experimentally via tandem mass spectrometry. These radical cations were generated by collision-induced dissociations (CIDs) of Cu(II)-containing ternary complexes that contain the tripeptides YGG, GYG, and GGY, respectively (G and Y are the glycine and tyrosine residues, respectively). Dissociative electron transfer within the complexes led to observation of [Y•GG]+, [GY•G]+, and [GGY•]+; CID resulted in cleavage of the tyrosine side chain as p-quinomethide, yielding [G•GG]+, [GG•G]+, and [GGG•]+, respectively. Interconversions between these isomeric triglycine radical cations have relatively high barriers (g44.7 kcal/mol), in support of the thesis that isomerically pure [G•GG]+, [GG•G]+, and [GGG•]+ can be experimentally produced. This is to be contrasted with barriers < 17 kcal/mol that were encountered in the tautomerism of protonated triglycine [Rodriquez C. F. et al. J. Am. Chem. Soc. 2001, 123, 3006-3012]. The CID spectra of [G•GG]+, [GG•G]+, and [GGG•]+ were substantially different, providing experimental proof that initially these ions have distinct structures. DFT calculations showed that direct dissociations are competitive with interconversions followed by dissociation.

  7. The chemistry of amine radical cations produced by visible light photoredox catalysis

    PubMed Central

    Hu, Jie; Wang, Jiang; Nguyen, Theresa H

    2013-01-01

    Summary Amine radical cations are highly useful reactive intermediates in amine synthesis. They have displayed several modes of reactivity leading to some highly sought-after synthetic intermediates including iminium ions, α-amino radicals, and distonic ions. One appealing method to access amine radical cations is through one-electron oxidation of the corresponding amines under visible light photoredox conditions. This approach and subsequent chemistries are emerging as a powerful tool in amine synthesis. This article reviews synthetic applications of amine radical cations produced by visible light photocatalysis. PMID:24204409

  8. Halogenated benzene radical cations and ground state degeneracy splitting by asymmetric substitution

    USGS Publications Warehouse

    Bondybey, V.E.; Vaughn, C.R.; Miller, T.A.; English, J.H.; Shiley, R.H.

    1981-01-01

    The absorption and laser induced fluorescence of several halogenated benzene radical cations were studied in solid Ne matrices. The spectra of 1,2,4-trifluorobenzene, l,3-dichloro-5-fluorobenzene, and l-chloro-3,5- difluorobenzene radical cations are observed and analyzed. Studies of fluorescence polarization and a photoselection technique were used to examine the splitting of the degeneracy of the benzene cation ground state by asymmetric subsitution. ?? 1981 American Institute of Physics.

  9. Gas-phase electronic spectrum of the indole radical cation

    NASA Astrophysics Data System (ADS)

    Chalyavi, N.; Catani, K. J.; Sanelli, J. A.; Dryza, V.; Bieske, E. J.

    2015-08-01

    The visible and near-UV electronic spectrum of the indole radical cation is measured in the gas phase by photodissociation of indole+-Ar and indole+-He complexes in a tandem mass spectrometer. A series of resolved vibronic transitions extending from 610 to 460 nm are assigned to the D2 ← D0 band system, while weak transitions between 390 and 360 nm are assigned to the D3 ← D0 system, and a stronger, broad, unresolved absorption between 350 and 300 nm is attributed to the D4 ← D0 system. Time-dependent density functional theory calculations are used to assign vibronic structure of the D2 ← D0 band system, and show that the main active vibrational modes correspond to in-plane ring deformations. The strongest D2 ← D0 vibronic transitions of indole+-He do not correspond with any catalogued diffuse interstellar bands, even considering band displacements of up to 50 cm-1possibly caused by the attached He atom.

  10. The Prowess of Photogenerated Amine Radical Cations in Cascade Reactions: From Carbocycles to Heterocycles.

    PubMed

    Morris, Scott A; Wang, Jiang; Zheng, Nan

    2016-09-20

    Cascade reactions represent a class of ideal organic reactions because they empower efficiency, elegance, and novelty. However, development of cascade reactions remains a daunting task for synthetic chemists. Radicals are known to be well suited for cascade reactions. Compared with widely used carbon-based radicals, nitrogen-based radicals, such as neutral aminyl radicals and protonated aminyl radicals (amine radical cations), are underutilized, although they are behind some notable synthetic methods such as the Hofmann-Löffler-Freytag reaction. The constraint on their usage is generally attributed to the limited number of available stable precursors. Since amine radical cations offer increased reactivity and selectivity in chemical transformations compared with neutral aminyl radicals, their generation is of utmost importance. Recently, a surge of reports has been revealed using visible light photoredox catalysis. It has been demonstrated that amines can act as an electron donor in a reductive quenching cycle while the amine itself is oxidized to the amine radical cation. Although a number of methods exist to generate amine radical cations, the photochemical formation of these species offers many practical advantages. In this Account, we discuss our journey to the development of annulation reactions with various π-bonds and electrophilic addition reactions to alkenes using photogenerated amine radical cations. Various carbocycles and heterocycles are produced by these reactions. In our annulation work, we first show that single electron photooxidation of cyclopropylanilines to the amine radical cations triggers ring opening of the strained carbocycle, producing distonic radical cations. These odd-electron species are shown to react with alkenes and alkynes to yield the corresponding cyclopentanes and cyclopentenes in an overall redox neutral process. Further development of this annulation reaction allows us to achieve the [4 + 2] annulation of cyclobutylanilines

  11. The Prowess of Photogenerated Amine Radical Cations in Cascade Reactions: From Carbocycles to Heterocycles.

    PubMed

    Morris, Scott A; Wang, Jiang; Zheng, Nan

    2016-09-20

    Cascade reactions represent a class of ideal organic reactions because they empower efficiency, elegance, and novelty. However, development of cascade reactions remains a daunting task for synthetic chemists. Radicals are known to be well suited for cascade reactions. Compared with widely used carbon-based radicals, nitrogen-based radicals, such as neutral aminyl radicals and protonated aminyl radicals (amine radical cations), are underutilized, although they are behind some notable synthetic methods such as the Hofmann-Löffler-Freytag reaction. The constraint on their usage is generally attributed to the limited number of available stable precursors. Since amine radical cations offer increased reactivity and selectivity in chemical transformations compared with neutral aminyl radicals, their generation is of utmost importance. Recently, a surge of reports has been revealed using visible light photoredox catalysis. It has been demonstrated that amines can act as an electron donor in a reductive quenching cycle while the amine itself is oxidized to the amine radical cation. Although a number of methods exist to generate amine radical cations, the photochemical formation of these species offers many practical advantages. In this Account, we discuss our journey to the development of annulation reactions with various π-bonds and electrophilic addition reactions to alkenes using photogenerated amine radical cations. Various carbocycles and heterocycles are produced by these reactions. In our annulation work, we first show that single electron photooxidation of cyclopropylanilines to the amine radical cations triggers ring opening of the strained carbocycle, producing distonic radical cations. These odd-electron species are shown to react with alkenes and alkynes to yield the corresponding cyclopentanes and cyclopentenes in an overall redox neutral process. Further development of this annulation reaction allows us to achieve the [4 + 2] annulation of cyclobutylanilines

  12. Photoinactivation of PS2 secondary donors by PS2 cation radicals and superoxide radicals

    SciTech Connect

    Chen, G.X.; Cheniae, G.M.; Blubaugh, D.J.; Golbeck, J.H.

    1991-12-31

    Illumination of Mn- and Cl-depleted PS2 causes rapid irreversible inactivation of specific redox-active components on the donor side of the PS2 Reaction Center (RC). Under aerobic conditions, weak light preillumination of NH{sub 2}OH-PS2 causes rapid loss of Y{sub Z}{sup {plus_minus}} formation, Y{sub Z} {yields} P{sub 680}{sup +}, the A{sub T}-band thermoluminescence emission, the Y{sub Z}{sup +}-dependent (Site 1) photooxidation of exogenous e{sup {minus}} donors, and the capability to photoligate Mn{sup 2+} into the water oxidizing enzyme (photoactivation), all without significantly affecting P{sub 680}{sup +}/Q{sub A}{sup {minus}} charge separation. In contrast, aerobic high light preillumination of Mn-depleted PS2 promotes very rapid and parallel loss of photoactivation and A{sub T}-band emission capabilities significantly than loss of either Y{sub Z}{sup +}-formation or P{sub 680}{sup +}/Q{sub A}{sup {minus}} charge separation capabilities. These photodamages and those to Cl-depleted thylakoids (4,5) generally are believed to be caused by reactions between the highly oxidizing cation radicals (P{sub 680}{sup +}/Chl{sup +}) and nearby amino acid residues of D{sub 1}>D{sub 2}. The reported promotion of the photodamages by e{sup {minus}} acceptors of Q{sub A}{sup {minus}}/Q{sub B}{sup {minus}} their inhibition by e{sup {minus}} donors to Y{sub Z}{sup +} and their occurrence under strict anaerobic conditions all tend to support the idea of direct damage by P{sub 680}{sup +}/Chl{sup +}. Our studies lead us to conclude that the photodamages to the donor side components are caused minimally by a rapid mechanism requiring both superoxide and PS2 cation radicals; and by a slower mechanism driven by the PS2 cation radicals only.

  13. Catalytic Carbocation Generation Enabled by the Mesolytic Cleavage of Alkoxyamine Radical Cations.

    PubMed

    Zhu, Qilei; Gentry, Emily C; Knowles, Robert R

    2016-08-16

    A new catalytic method is described to access carbocation intermediates via the mesolytic cleavage of alkoxyamine radical cations. In this process, electron transfer between an excited state oxidant and a TEMPO-derived alkoxyamine substrate gives rise to a radical cation with a remarkably weak C-O bond. Spontaneous scission results in the formation of the stable nitroxyl radical TEMPO(.) as well as a reactive carbocation intermediate that can be intercepted by a wide range of nucleophiles. Notably, this process occurs under neutral conditions and at comparatively mild potentials, enabling catalytic cation generation in the presence of both acid sensitive and easily oxidized nucleophilic partners. PMID:27403637

  14. Radical formation in the [MeReO3]-catalyzed aqueous peroxidative oxidation of alkanes: a theoretical mechanistic study.

    PubMed

    Kuznetsov, Maxim L; Pombeiro, Armando J L

    2009-01-01

    Plausible mechanisms of radical formation in the catalytic system [MeReO(3)]/H(2)O(2)/H(2)O-CH(3)CN for the oxidation of alkanes to alcohols and ketones, via radical pathways, are investigated extensively at the density functional theory level. The most favorable route is based on the monoperoxo complex [MeReO(2)(O(2))(H(2)O)] and includes the formation of an H(2)O(2) adduct, water-assisted H-transfer from H(2)O(2) to the peroxo ligand, and generation of HOO(*). The thus formed reduced Re(VI) complex [MeReO(2)(OOH)(H(2)O)] reacts with H(2)O(2), resulting, upon water-assisted H-transfer and O-OH bond homolysis, in the regeneration of the oxo-Re(VII) catalyst and formation of the HO(*) radical that reacts further with the alkane. Water plays a crucial role by (i) stabilizing transition states for the proton migrations and providing easy intramolecular H-transfers in the absence of any N,O-ligands and (ii) saturating the Re coordination sphere what leads to a decrease of the activation barrier for the formation of HOO(*). The activation energy of the radical formation calculated for [MeReO(3)] (17.7 kcal/mol) is compatible with that determined experimentally [Shul'pin et al. J. Chem. Soc., Perkin Trans. 2 2001, 1351 .] for oxo-V-based catalytic systems (17 +/- 2 kcal/mol), and the overall type of mechanism proposed for such V catalysts is also effective for [MeReO(3)]. PMID:19049432

  15. Products and Kinetics of the Reactions of an Alkane Monolayer and a Terminal Alkene Monolayer with NO₃ Radicals

    SciTech Connect

    Gross, Simone; Bertram, Allan K.

    2009-01-27

    The reactions of an alkanethiol and a terminal alkenethiol self-assembled monolayer with NO₃ radicals (in the presence of NO₂ and O₂) were studied. For the alkane monolayer, infrared (IR) spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirmed the formation of organonitrates (RONO₂). The observation of organonitrates is in contrast to the recent X-ray photoelectron spectroscopy (XPS) data, which showed very little nitrogen-containing surface species. The identification of organonitrates may help explain why significant volatilization of the organic chain was not observed in recent studies of alkane monolayer oxidation by NO₃ radicals. The reactive uptake coefficient (g) of NO₃ on alkene monolayers determined in our study is higher than the values obtained in a recent study using liquid and solid alkene bulk films. A possible reason for this difference may be the location of the double bond at the interface. Using the g value determined in our studies, we show that under conditions where NO₃ is high the lifetime of an alkene monolayer in the atmosphere may be short (approximately 20 min). XPS, IR, and ToF-SIMS were used to identify surface functional groups after the oxidation of the alkene monolayers by NO₃. The results are consistent with the formation of C-O, aldehyde/ketone, carboxylic groups, and nitrogen containing species.

  16. Electronic absorption spectroscopy of polycyclic aromatic hydrocarbons (PAHs) radical cations generated in oleum: a superacid medium.

    PubMed

    Cataldo, Franco; Iglesias-Groth, Susana; Manchado, Arturo

    2010-12-01

    Oleum (fuming sulphuric acid), a well known superacid, was used as medium for the generation of the radical cation of a series of selected PAHs. The resulting radical cation spectra were studied by electronic absorption spectroscopy. Not only common PAHs like naphthalene, anthracene, tetracene, pentacene, perylene, pyrene, benzo[a]pyrene, phenanthrene and picene were studied but also the less common and very large PAHs relevant also for the astrochemical research, like coronene, hexabenzocoronene, quaterrylene, dicoronylene and a coronene oligomer. A correlation between the first ionization potential (IP1) of the PAHs studied and the energy to the so-called A-type band of the radical cations observed in oleum has led to the equation IP1=1.30EA+4.39 (in eV) which permits to estimate the energy of the PAHs radical cation transition (EA) in the VIS-NIR knowing the relative ionization potential or vice versa. PMID:20863743

  17. [Yield of pigment cation-radicals in the reaction of quinone photooxidation of chlorophyll].

    PubMed

    Kostikov, A P; Sadovnikova, N A; Evstigneev, V B

    1976-01-01

    Photoinduced transfer of electrons in alkohol solutions of chlorophyll and its deuterated analog, deuterochlorophyll containing the quinoses: p-benzoquinone, chloranyl, duroquinone, 1,4-naftoquinone and ubiquinone (coenzyme Q6) is studied. It is shown that pigment cation-radical and quinone anion-radical are the primary products of photoreaction. A relationship between stationary concentrations of deuterochlorophyll and p-benzoquinone radicals and quinone concentration in solution is obtained. The reaction mechanism and causes of other authors' (G. Tollin et al.) failure in finding pigment cation-radicals which are formed in the reaction of the latter with quinoses are discussed. It is shown that optimal conditions for accumulating photoinduced cation-radicals of the pigment in pigment solutions of chlorophyll with quinones are lowered temperature, high viscosity of the solvent, low pH of the solution, careful purification of the quinone from hydroquinone admixture.

  18. UV/Vis Action Spectroscopy and Structures of Tyrosine Peptide Cation Radicals in the Gas Phase.

    PubMed

    Viglino, Emilie; Shaffer, Christopher J; Tureček, František

    2016-06-20

    We report the first application of UV/Vis photodissociation action spectroscopy for the structure elucidation of tyrosine peptide cation radicals produced by oxidative intramolecular electron transfer in gas-phase metal complexes. Oxidation of Tyr-Ala-Ala-Ala-Arg (YAAAR) produces Tyr-O radicals by combined electron and proton transfer involving the phenol and carboxyl groups. Oxidation of Ala-Ala-Ala-Tyr-Arg (AAAYR) produces a mixture of cation radicals involving electron abstraction from the Tyr phenol ring and N-terminal amino group in combination with hydrogen-atom transfer from the Cα positions of the peptide backbone. PMID:27159034

  19. Comparing the gas-phase fragmentation reactions of protonated and radical cations of the tripeptides GXR

    NASA Astrophysics Data System (ADS)

    Wee, Sheena; O'Hair, Richard A. J.; McFadyen, W. David

    2004-05-01

    Electrospray ionization (ESI) mass spectrometry of methanolic solutions of mixtures of the copper salt (2,2':6',2''-terpyridine)copper(II) nitrate monohydrate ([Cu(II)(tpy)(NO3)2].H2O) and a tripeptide GXR (where X = 1 of the 20 naturally occurring amino acids) yielded [Cu(II)(tpy)(GXR)][radical sign]2+ ions, which were then subjected to collision induced dissociation (CID). In all but one case (GRR), these [Cu(II)(tpy)(GXR)][radical sign]2+ ions fragment to form odd electron GXR[radical sign]+ radical cations with sufficient abundance to examine their gas-phase fragmentation reactions. The GXR[radical sign]+ radical cations undergo a diverse range of fragmentation reactions which depend on the nature of the side chain of X. Many of these reactions can be rationalized as arising from the intermediacy of isomeric distonic ions in which the charge (i.e. proton) is sequestered by the highly basic arginine side chain and the radical site is located at various positions on the tripeptide including the peptide back bone and side chains. The radical sites in these distonic ions often direct the fragmentation reactions via the expulsion of small radicals (to yield even electron ions) or small neutrals (to form radical cations). Both classes of reaction can yield useful structural information, allowing for example, distinction between leucine and isoleucine residues. The gas-phase fragmentation reactions of the GXR[radical sign]+ radical cations are also compared to their even electron [GXR+H]+ and [GXR+2H]2+ counterparts. The [GXR+H]+ ions give fewer sequence ions and more small molecule losses while the [GXR+2H]2+ ions yield more sequence information, consistent with the [`]mobile proton model' described in previous studies. In general, all three classes of ions give complementary structural information, but the GXR[radical sign]+ radical cations exhibit a more diverse loss of small species (radicals and neutrals). Finally, links between these gas-phase results and key

  20. Strategies for generating peptide radical cations via ion/ion reactions.

    PubMed

    Gilbert, Joshua D; Fisher, Christine M; Bu, Jiexun; Prentice, Boone M; Redwine, James G; McLuckey, Scott A

    2015-02-01

    Several approaches for the generation of peptide radical cations using ion/ion reactions coupled with either collision induced dissociation (CID) or ultraviolet photo dissociation (UVPD) are described here. Ion/ion reactions are used to generate electrostatic or covalent complexes comprised of a peptide and a radical reagent. The radical site of the reagent can be generated multiple ways. Reagents containing a carbon-iodine (C-I) bond are subjected to UVPD with 266-nm photons, which selectively cleaves the C-I bond homolytically. Alternatively, reagents containing azo functionalities are collisionally activated to yield radical sites on either side of the azo group. Both of these methods generate an initial radical site on the reagent, which then abstracts a hydrogen from the peptide while the peptide and reagent are held together by either electrostatic interactions or a covalent linkage. These methods are demonstrated via ion/ion reactions between the model peptide RARARAA (doubly protonated) and various distonic anionic radical reagents. The radical site abstracts a hydrogen atom from the peptide, while the charge site abstracts a proton. The net result is the conversion of a doubly protonated peptide to a peptide radical cation. The peptide radical cations have been fragmented via CID and the resulting product ion mass spectra are compared to the control CID spectrum of the singly protonated, even-electron species. This work is then extended to bradykinin, a more broadly studied peptide, for comparison with other radical peptide generation methods. The work presented here provides novel methods for generating peptide radical cations in the gas phase through ion/ion reaction complexes that do not require modification of the peptide in solution or generation of non-covalent complexes in the electrospray process.

  1. Kinetic investigation of the reactions of NCO radicals with alkanes in the temperature range 294 to 1,113 K

    SciTech Connect

    Schuck, A.; Volpp, H.R.; Wolfrum, J. . Physikalisch-Chemisches Inst.)

    1994-12-01

    Absolute rate coefficients for the reaction of NCO radicals with methane (k[sub 1]), ethane (k[sub 2]), and propane (k[sub 3]) were measured as a function of temperature in a heatable quartz reactor by means of the laser photolysis/laser-induced fluorescence (LP/LIF) pump-probe technique. NCO radicals were produced by the fast precursor reaction NH(a[sup 1] [Delta]) + HNCO [yields] NH[sub 2] + NCO, following the 193-nm photolysis of isocyanic acid. The measure rate coefficients can be described by the following expressions: k[sub 1](512 < T < 1,113 K) = 10[sup 12.99 [+-] 0.12] [times] exp(-34.0[+-]1.8 kJ/mol/RT) cm[sup 3]/mol s; k[sub 2](296 < T < 922 K) = 10[sup 8.21] [times] (T/298 K)[sup (6.89[+-]0.02)] [times] exp(12.2[+-]0.5 kJ/mol/RT)cm[sup 3]/mol s; and k[sub 3](300 < T < 849 K) = 10[sup 11.49] [times] (T/298 K)[sup (2.15[+-]0.02)] [times] exp(-1.8[+-]0.4 kJ/mol/RT)cm[sup 3]/mol s. A comparison with the corresponding reactions of CN, Cl, and OH radicals with alkanes suggests that all these title reactions also proceed predominantly via a hydrogen atom abstraction mechanism to form HNCO.

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

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

    Electron paramagnetic resonance and electron-nuclear double resonance methods were used to study the polycyclic aromatic radical cations produced in a Friedel-Crafts alkylating system, 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 hydrocarbons, 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 using the B3LYP/6-31G(d,p)//B3LYP/6-31G(d) approach. The theoretical coupling constants support the experimental assignment of the observed radicals.

  3. p53 Mutagenesis by benzo[a]pyrene derived radical cations.

    PubMed

    Sen, Sushmita; Bhojnagarwala, Pratik; Francey, Lauren; Lu, Ding; Penning, Trevor M; Field, Jeffrey

    2012-10-15

    Benzo[a]pyrene (B[a]P), a major human carcinogen in combustion products such as cigarette smoke and diesel exhaust, is metabolically activated into DNA-reactive metabolites via three different enzymatic pathways. The pathways are the anti-(+)-benzo[a]pyrene 7,8-diol 9,10-epoxide pathway (P450/epoxide hydrolase catalyzed) (B[a]PDE), the benzo[a]pyrene o-quinone pathway (aldo ketose reductase (AKR) catalyzed) and the B[a]P radical cation pathway (P450 peroxidase catalyzed). We used a yeast p53 mutagenesis system to assess mutagenesis by B[a]P radical cations. Because radical cations are short-lived, they were generated in situ by reacting B[a]P with cumene hydroperoxide (CuOOH) and horse radish peroxidase (HRP) and then monitoring the generation of the more stable downstream products, B[a]P-1,6-dione and B[a]P-3,6-dione. On the basis of B[a]P-1,6 and 3,6-dione formation, approximately 4 μM of radical cation was generated. In the mutagenesis assays, the radical cations produced in situ showed a dose-dependent increase in mutagenicity from 0.25 μM to 10 μM B[a]P with no significant increase seen with further escalation to 50 μM B[a]P. However, mutagenesis was 200-fold less than with the AKR pathway derived B[a]P, 7-8-dione. Mutant p53 plasmids, which yield red colonies, were recovered from the yeast to study the pattern and spectrum of mutations. The mutation pattern observed was G to T (31%) > G to C (29%) > G to A (14%). The frequency of codons mutated by the B[a]P radical cations was essentially random and not enriched at known cancer hotspots. The quinone products of radical cations, B[a]P-1,6-dione and B[a]P-3,6-dione were more mutagenic than the radical cation reactions, but still less mutagenic than AKR derived B[a]P-7,8-dione. We conclude that B[a]P radical cations and their quinone products are weakly mutagenic in this yeast-based system compared to redox cycling PAH o-quinones. PMID:22768918

  4. Berberine cation: A fluorescent chemosensor for alkanes and other low-polarity compounds. An explanation of this phenomenon

    PubMed

    Cossio; Arrieta; Cebolla; Membrado; Vela; Garriga; Domingo

    2000-07-27

    Alkanes in the presence of berberine sulfate provide an enhancement of fluorescent signal, which depends on alkane concentration and structure, when the system is irradiated with monochromatic UV light. Computational analysis suggests that an ion-induced dipole between alkanes and berberine sulfate is responsible for this phenomenon. This interaction can properly model the experimentally obtained fluorescent response. The proposed explanation allows other interacting systems to be designed, which have been experimentally confirmed. PMID:10930271

  5. Berberine cation: A fluorescent chemosensor for alkanes and other low-polarity compounds. An explanation of this phenomenon

    PubMed

    Cossio; Arrieta; Cebolla; Membrado; Vela; Garriga; Domingo

    2000-07-27

    Alkanes in the presence of berberine sulfate provide an enhancement of fluorescent signal, which depends on alkane concentration and structure, when the system is irradiated with monochromatic UV light. Computational analysis suggests that an ion-induced dipole between alkanes and berberine sulfate is responsible for this phenomenon. This interaction can properly model the experimentally obtained fluorescent response. The proposed explanation allows other interacting systems to be designed, which have been experimentally confirmed.

  6. Theoretical study of second-order hyperpolarizability for nitrogen radical cation

    NASA Astrophysics Data System (ADS)

    Tarazkar, Maryam; Romanov, Dmitri A.; Levis, Robert J.

    2015-05-01

    We report calculations of the static and dynamic hyperpolarizabilities of the nitrogen radical cation in doublet state. The electronic contributions were computed analytically using density functional theory and multi-configurational self-consistent field method with extended basis sets for non-resonant excitation. The open-shell electronic system of nitrogen radical cation provides negative second-order optical nonlinearity, suggesting that the hyperpolarizability coefficient, {{γ }(2)}, in the non-resonant regime is mainly composed of combinations of virtual one-photon transitions rather than two-photon transitions. The second-order optical properties of nitrogen radical cation have been calculated as a function of bond length starting with the neutral molecular geometry (S0 minimum) and stretching the N-N triple bond, reaching the ionic D0 relaxed geometry all the way toward dissociation limit, to investigate the effect of internuclear bond distance on second-order hyperpolarizability.

  7. Fingerprinting DNA oxidation processes: IR characterization of the 5-methyl-2'-deoxycytidine radical cation.

    PubMed

    Bucher, Dominik B; Pilles, Bert M; Pfaffeneder, Toni; Carell, Thomas; Zinth, Wolfgang

    2014-02-24

    Methylated cytidine plays an important role as an epigenetic signal in gene regulation. Its oxidation products are assumed to be involved in active demethylation processes but also in damaging DNA. Here, we report the photochemical production of the 5-methyl-2'-deoxycytidine radical cation via a two-photon ionization process. The radical cation is detected by time-resolved IR spectroscopy and identified by band assignment using density functional theory calculations. Two final oxidation products are characterized with liquid chromatography coupled to mass spectrometry.

  8. The isolable cation radical of disilene: synthesis, characterization, and a reversible one-electron redox system.

    PubMed

    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.

  9. Oxidation of a model alkane aerosol by OH radical: the emergent nature of reactive uptake.

    PubMed

    Houle, F A; Hinsberg, W D; Wilson, K R

    2015-02-14

    An accurate description of the evolution of organic aerosol in the Earth's atmosphere is essential for climate models. However, the complexity of multiphase chemical and physical transformations has been challenging to describe at the level required to predict aerosol lifetimes and changes in chemical composition. In this work a model is presented that reproduces experimental data for the early stages of oxidative aging of squalane aerosol by hydroxyl radical (OH), a process governed by reactive uptake of gas phase species onto the particle surface. Simulations coupling free radical reactions and Fickian diffusion are used to elucidate how the measured uptake coefficient reflects the elementary steps of sticking of OH to the aerosol as a result of a gas-surface collision, followed by very rapid abstraction of hydrogen and subsequent free radical reactions. It is found that the uptake coefficient is not equivalent to a sticking coefficient or an accommodation coefficient: it is an intrinsically emergent process that depends upon particle size, viscosity, and OH concentration. An expression is derived to examine how these factors control reactive uptake over a broad range of atmospheric and laboratory conditions, and is shown to be consistent with simulation results. Well-mixed, liquid behavior is found to depend on the reaction conditions in addition to the nature of the organic species in the aerosol particle.

  10. Spectroscopy and decay dynamics of several methyl-and fluorine-substituted benzene radical cations

    USGS Publications Warehouse

    Bondybey, V.E.; Vaughn, C.; Miller, T.A.; English, J.H.; Shiley, R.H.

    1981-01-01

    Spectra of several fluorobenzene cation radicals containing 1-3 methyl substituents were observed in solid Ne matrix and analyzed. Comparisons between these compounds and other fluorobenzenes studied previously as well as comparisons between the B?? state lifetimes in the gas phase and in the matrix are used to gain a deeper insight into the B?? state decay dynamics. ?? 1981 American Chemical Society.

  11. Gas-phase structure and reactivity of the keto tautomer of the deoxyguanosine radical cation.

    PubMed

    Feketeová, Linda; Chan, Bun; Khairallah, George N; Steinmetz, Vincent; Maître, Philippe; Radom, Leo; O'Hair, Richard A J

    2015-10-21

    Guanine radical cations are formed upon oxidation of DNA. Deoxyguanosine (dG) is used as a model, and the gas-phase infrared (IR) spectroscopic signature and gas-phase unimolecular and bimolecular chemistry of its radical cation, dG˙(+), A, which is formed via direct electrospray ionisation (ESI/MS) of a methanolic solution of Cu(NO3)2 and dG, are examined. Quantum chemistry calculations have been carried out on 28 isomers and comparisons between their calculated IR spectra and the experimentally-measured spectra suggest that A exists as the ground-state keto tautomer. Collision-induced dissociation (CID) of A proceeds via cleavage of the glycosidic bond, while its ion–molecule reactions with amine bases occur via a number of pathways including hydrogen-atom abstraction, proton transfer and adduct formation. A hidden channel, involving isomerisation of the radical cation via adduct formation, is revealed through the use of two stages of CID, with the final stage of CID showing the loss of CH2O as a major fragmentation pathway from the reformed radical cation, dG˙(+). Quantum chemistry calculations on the unimolecular and bimolecular reactivity are also consistent with A being present as a ground-state keto tautomer. PMID:25942055

  12. Medium effect on the Jahn-Teller distortions of the tetramethylallene radical cation

    SciTech Connect

    Qin, X.Z.; Trifunac, A.D. )

    1991-08-22

    The Jahn-Teller distortion of the delocalized {pi}-radical cation tetramethylallene{sm bullet}{sup +} (TMA{sm bullet}{sup +}) was found to be medium dependent. TMA{sup {sm bullet}} was studied in liquid hydrocarbons (195-295 K) by time-resolved fluorescence-detected magnetic resonance (FDMR) spectroscopy and in freon matrices (80-160 K) and zeolite Na-Y (80-298 K) by EPR spectroscopy. The observed coupling constants for the twelve protons of the four methyl groups of the radical cation are 11.3, 8.1, and 14.4 G, respectively. AM1 and INDO calculations suggest that different coupling constants can be explained by different twist angles in TMA{sup {sm bullet}+}. It is suggested that interaction between TMA{sup {sm bullet}+} and the chlorine or fluorine atoms of freon matrices or between TMA{sup {sm bullet}+} and the sodium atoms of the zeolite can influence the charge and spin distribution in the radical cation so that the structures that differ from that found in hydrocarbon solution can be stabilized. This is the first example of a Jahn-Teller-active radical cation that has been studied in several media.

  13. Participation of cationic intermediates in radical-induced homopolymerization of maleic anhydride

    SciTech Connect

    Gaylord, N.G.; Koo, J.Y.

    1981-03-01

    Since the failure to promote MAH polymerization in the presence of amine-containing redox catalyst systems suggested the presence of cationic intermediates, the radical-induced polymerization of MAH was carried out in the absence and in the presence of N,N-dimethylformamide (DMF) and N, N-dimethylaniline (DMA).

  14. A combined EPR and DFT study of the overcrowded aromatic radical cations from Friedel-Crafts alkylation reactions

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Tang, Fu Ming; Wu, Yi Fang

    2011-09-01

    Electron paramagnetic resonance and electron-nuclear double resonance methods were used to study the polycyclic aromatic radical cations produced in a Friedel-Crafts alkylating system, and the following radical cations were indentified: 3,6,11,14-tetramethyl dibenzo (a, c) triphylene and 2,6-dimethyl-9,10-di(p-methylbenzyl) anthracene radical cations. The results indicate that the observed electron paramagnetic resonance spectra are due to overcrowded polycyclic aromatic radical cations formed from the parent hydrocarbons. It is suggested that benzyl halides produced in the Friedel-Crafts alkylation reactions undergo Scholl condensation to give polycyclic aromatic hydrocarbons, which are converted into corresponding polycyclic aromatic radical cations in the presence of AlCl 3. We carried out the theoretical calculation of the isotropic 1H hyperfine coupling constants for studied both PAHs radical cations. The results indicate that the IEFPCM-DFT calculation at B3LYP level with 6-31++G(d,p), EPRII and EPRIII basis sets could well support the experimental hfcc assignment of the observed radicals. Optimized geometry indicates that the aromatic rings in both PAHs radical cations twisted significantly out of co-planarity.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  16. Total synthesis of cephalosporolide E via a tandem radical/polar crossover reaction. The use of the radical cations under nonoxidative conditions in total synthesis.

    PubMed

    Cortezano-Arellano, Omar; Quintero, Leticia; Sartillo-Piscil, Fernando

    2015-03-01

    The present work reports the first example of the use of the chemistry of radical cations under nonoxidative conditions in total synthesis. Using a late-stage tandem radical/polar crossover reaction, a highly stereoselective total synthesis of cephalosporolide E (which is typically obtained admixed with cephalosporolide F) was accomplished. The reaction of a phthalimido derivative with triphenyltin radical in refluxing toluene engenders a contact ion-pair (radical cation) that leads, in the first instance, to the cephalosporolide F, which is transformed into the cephalosporolide E via a stereocontrolled spiroketal isomerization promoted by the diphenylphosphate acid that is formed during the tandem transformation.

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

    PubMed

    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.

  18. Efficient scavenging of β-carotene radical cations by antiinflammatory salicylates.

    PubMed

    Cheng, Hong; Liang, Ran; Han, Rui-Min; Zhang, Jian-Ping; Skibsted, Leif H

    2014-02-01

    The radical cation generated during photobleaching of β-carotene is scavenged efficiently by the anion of methyl salicylate from wintergreen oil in a second-order reaction approaching the diffusion limit with k2 = 3.2 × 10(9) L mol(-1) s(-1) in 9 : 1 v/v chloroform-methanol at 23 °C, less efficiently by the anion of salicylic acid with 2.2 × 10(8) L mol(-1) s(-1), but still of possible importance for light-exposed tissue. Surprisingly, acetylsalicylate, the aspirin anion, reacts with an intermediate rate in a reaction assigned to the anion of the mixed acetic-salicylic acid anhydride formed through base induced rearrangements. The relative scavenging rate of the β-carotene radical cation by the three salicylates is supported by DFT-calculations.

  19. The role of organic solvent radical cations in separations ligand degradation

    SciTech Connect

    Mezyk, Stephen P.; Mincher, Bruce J.; Dhiman, Surajdevprakash B.; Layne, Bobby; Wishart, James F.

    2015-11-04

    The dodecane radical cation reaction rate constant with CMPO was measured using ps electron pulse radiolysis/absorption spectroscopy as k = (1.30 ± 0.11) x 1010 M-1 s-1 in dodecane/0.10 M CH2Cl2 solution. No reactivity increase occurred when these solutions were pre-contacted with nitric acid, similar to the behavior observed for TODGA. To corroborate these kinetic data with steady-state radiolysis measurements, where acid pre contacted CMPO showed significantly less degradation, it is proposed that the dodecane radical cation always reacts directly with TODGA, but for CMPO the charge-transfer occurs with the CMPO•HNO3 complex formed in the acid contacted solvent.

  20. The role of organic solvent radical cations in separations ligand degradation

    DOE PAGES

    Mezyk, Stephen P.; Mincher, Bruce J.; Dhiman, Surajdevprakash B.; Layne, Bobby; Wishart, James F.

    2015-11-04

    The dodecane radical cation reaction rate constant with CMPO was measured using ps electron pulse radiolysis/absorption spectroscopy as k = (1.30 ± 0.11) x 1010 M-1 s-1 in dodecane/0.10 M CH2Cl2 solution. No reactivity increase occurred when these solutions were pre-contacted with nitric acid, similar to the behavior observed for TODGA. To corroborate these kinetic data with steady-state radiolysis measurements, where acid pre contacted CMPO showed significantly less degradation, it is proposed that the dodecane radical cation always reacts directly with TODGA, but for CMPO the charge-transfer occurs with the CMPO•HNO3 complex formed in the acid contacted solvent.

  1. Radical cations from dipyridinium derivatives: a combined EPR and DFT study.

    PubMed

    Stipa, Pierluigi

    2006-06-01

    The monoelectronic reduction of 1,1'-dimethyl-2,2'-dicyano-4,4'-bipyridinium (DCMV++) bis-methylsulphate, conducted directly in the cavity of the electron paramagnetic resonance (EPR) spectrometer at room temperature and in DMSO solution, gave the signal of the corresponding radical cation (DCMV.+) whose interpretation has been carried out with the aid of density functional theory (DFT) calculations run at different levels. The model chemistries considered yielded in general hyperfine coupling constants (hfcc) in good agreement with the experimental ones, except for the methyl protons directly bonded to the pyridinium nitrogens. The use of various computational methods accounting for solvent-solute interactions did not give significant improvements with respect to the gas phase results, while the geometry optimizations performed showed that the two pyridinium rings are coplanar in the radical cation but staggered in the parent dication, although the corresponding energy barrier involved is very low.

  2. Intramolecular Electron Transfer in Bis(tetraalkyl Hydrazine) and Bis(hydrazyl) Radical Cations.

    NASA Astrophysics Data System (ADS)

    Chang, Hao

    A series of multicyclic bis(hydrazine) and bis(diazenium) compounds connected by relatively rigid hydrocarbon frameworks were prepared for the study of intramolecular electron transfer. The thermodynamics of electron removal of these compounds was investigated by cyclic voltammetry. The difference between the first and second oxidation potentials for the 4 sigma-bonded species was found to be larger for the bis(hydrazyl) radical systems than for the bis(hydrazines) by ca. 0.2 V (4.6 kcal/mol). This indicates a greater degree of interaction between the two nitrogen moieties for the hydrazyl systems, which is consistent with a greater degree of electronic coupling (H _{rm AB}) in these systems. The ESR spectra of the 4 sigma -bonded bis(hydrazine) radical cations indicate localized radical cations, which corresponds to slow intramolecular electron transfer on the ESR timescale. Conversely, the ESR spectra of the corresponding bis(hydrazyl) radical cation systems show nitrogen hyperfine splittings of a(4N) of ca. 4.5 G. This indicates that intramolecular electron transfer between the two nitrogen moieties is fast on the ESR timescale; the rate of exchange, k_ {rm ex} was estimated to be well above 1.9 times 10^8 s^{-1}. The contrast in exchange rates is consistent with the large geometry change upon oxidation which is characteristic of hydrazines. The hydrazyls undergo a smaller geometry change upon oxidation, and thus are expected to exhibit smaller inner-sphere reorganization energies. The optical spectra of these radical species was investigated in hopes of observing absorption bands corresponding to intramolecular electron transfer, as predicted by Hush theory. A broad absorption band was observed in the near IR region for the saturated bis(hydrazyl) radical cation system at 1060 nm (9420 cm^{-1} ) in acetonitrile at room temperature, and was accompanied by a narrower band at 1430 nm (6993 cm^ {-1}). The width of this band was estimated to be 545 nm (6496 cm^{-1

  3. Cytosine neutral molecules and cation-radicals in the gas-phase

    NASA Astrophysics Data System (ADS)

    Wolken, Jill K.; Yao, Chunxiang; Turecek, Frantisek; Polce, Michael J.; Wesdemiotis, Chrys

    2007-11-01

    Gas-phase cytosine molecules and cation-radicals represent a complex system of several nearly isoenergetic tautomers within each group. Computational methods differ in ordering the relative enthalpies of neutral cytosine tautomers. At our highest level of theory, CCSD(T)/aug-cc-pVTZ calculations find an enol form, anti-2-hydroxy-4-aminopyrimidine (2), to be the most stable neutral tautomer in the gas-phase, followed by its rotamer, syn-2-hydroxy-4-aminopyrimidine (3), the canonical oxo-form, 4-amino-1,2-dihydropyrimidin-2(1H)-one (1), imino-forms, 2-oxo-4-iminodihydro(1H,3H)pyrimidine (4 and 5), and another oxo-form, 4-amino-dihydropyrimidin-2(3H)-one (6). Other tautomers, such as anti-anti, syn-syn and syn-anti-2-hydroxy-4-iminodihydro(3H,4H)pyrimidines (7-9), are less stable. The adiabatic ionization energies of the major cytosine tautomers have been calculated to be 8.71, 8.64, 8.62, 8.58, 8.64, and 8.31 eV for 1, 2, 3, 4, 5, and 6, respectively. Cytosine cation-radicals show very close relative energies that increase in the order of 6+ (most stable) <2+ [approximate] 3+ < 4+ [approximate] 7+ [approximate] 1+ < 5+. In addition, distonic ions having radical centers at C-5 (10+) and C-6 (11+ are found as low-energy isomers of 1+-7+. Metastable cytosine cation-radicals undergo ring-cleavage dissociations by eliminations of CO (major) and HNCO (minor). The energetics of these and other higher-energy dissociations, including the pertinent transition states, have been established by high-level ab initio and density functional theory calculations and plausible mechanisms have been proposed. Collisional neutralization of cytosine cation-radicals with trimethylamine and dimethyldisulfide as electron donors forms stable molecules that are detected as cation-radicals following collisional reionization. The dissociations observed upon neutralization-reionization mainly include ring-cleavages followed by loss of NCO, HNCO, and formation of C2H3N, C2H2N, and CO neutral

  4. Basal Plane Fluorination of Graphene by XeF2 via a Radical Cation Mechanism.

    PubMed

    Liu, Yijun; Noffke, Benjamin W; Qiao, Xiaoxiao; Li, Qiqi; Gao, Xinfeng; Raghavachari, Krishnan; Li, Liang-shi

    2015-09-17

    Graphene fluorination with XeF2 is an attractive method to introduce a nonzero bandgap to graphene under mild conditions for potential electro-optical applications. Herein, we use well-defined graphene nanostructures as a model system to study the reaction mechanism of graphene fluorination by XeF2. Our combined experimental and theoretical studies show that the reaction can proceed through a radical cation mechanism, leading to fluorination and sp(3)-hybridized carbon in the basal plane.

  5. Maleimide Glycidyl Ether: A Bifunctional Monomer for Orthogonal Cationic and Radical Polymerizations.

    PubMed

    Klein, Rebecca; Übel, Fabian; Frey, Holger

    2015-10-01

    A novel bifunctional monomer, namely maleimide glycidyl ether (MalGE), prepared in a four-step reaction sequence is introduced. This monomer allows for selective (co)polymerization of the epoxide group via cationic ring-opening polymerization, preserving the maleimide functionality. On the other hand, the maleimide functionality can be copolymerized via radical techniques, preserving the epoxide moiety. Cationic ring-opening multibranching copolymerization of MalGE with glycidol was performed, and a MalGE content of up to 24 mol% could be incorporated into the hyperbranched polymer backbone (Mn = 1000-3000 g mol(-1)). Preservation of the maleimide functionality during cationic copolymerization was verified via NMR spectroscopy. Subsequently, the maleimide moiety was radically crosslinked to generate hydrogels and additionally employed to perform Diels-Alder (DA) "click" reactions with (functional) dienes after the polymerization process. Radical copolymerization of MalGE with styrene (Mn = 5000-9000 g mol(-1)) enabled the synthesis of a styrene copolymer with epoxide functionalities that are useful for versatile crosslinking and grafting reactions.

  6. Maleimide Glycidyl Ether: A Bifunctional Monomer for Orthogonal Cationic and Radical Polymerizations.

    PubMed

    Klein, Rebecca; Übel, Fabian; Frey, Holger

    2015-10-01

    A novel bifunctional monomer, namely maleimide glycidyl ether (MalGE), prepared in a four-step reaction sequence is introduced. This monomer allows for selective (co)polymerization of the epoxide group via cationic ring-opening polymerization, preserving the maleimide functionality. On the other hand, the maleimide functionality can be copolymerized via radical techniques, preserving the epoxide moiety. Cationic ring-opening multibranching copolymerization of MalGE with glycidol was performed, and a MalGE content of up to 24 mol% could be incorporated into the hyperbranched polymer backbone (Mn = 1000-3000 g mol(-1)). Preservation of the maleimide functionality during cationic copolymerization was verified via NMR spectroscopy. Subsequently, the maleimide moiety was radically crosslinked to generate hydrogels and additionally employed to perform Diels-Alder (DA) "click" reactions with (functional) dienes after the polymerization process. Radical copolymerization of MalGE with styrene (Mn = 5000-9000 g mol(-1)) enabled the synthesis of a styrene copolymer with epoxide functionalities that are useful for versatile crosslinking and grafting reactions. PMID:26301777

  7. Carotenoid radical cations as a probe for the molecular mechanism of nonphotochemical quenching in oxygenic photosynthesis.

    PubMed

    Amarie, Sergiu; Standfuss, Jörg; Barros, Tiago; Kühlbrandt, Werner; Dreuw, Andreas; Wachtveitl, Josef

    2007-04-01

    Nonphotochemical quenching (NPQ) is a fundamental mechanism in photosynthesis which protects plants against excess excitation energy and is of crucial importance for their survival and fitness. Recently, carotenoid radical cation (Car*+) formation has been discovered to be a key step for the feedback deexcitation quenching mechanism (qE), a component of NPQ, of which the molecular mechanism and location is still unknown. We have generated and characterized carotenoid radical cations by means of resonant two color, two photon ionization (R2C2PI) spectroscopy. The Car*+ bands have maxima located at 830 nm (violaxanthin), 880 nm (lutein), 900 nm (zeaxanthin), and 920 nm (beta-carotene). The positions of these maxima depend strongly on solution conditions, the number of conjugated C=C bonds, and molecular structure. Furthermore, R2C2PI measurements on the light-harvesting complex of photosystem II (LHC II) samples with or without zeaxanthin (Zea) reveal the violaxanthin (Vio) radical cation (Vio*+) band at 909 nm and the Zea*+ band at 983 nm. The replacement of Vio by Zea in the light-harvesting complex II (LHC II) has no influence on the Chl excitation lifetime, and by exciting the Chls lowest excited state, no additional rise and decay corresponding to the Car*+ signal observed previously during qE was detected in the spectral range investigated (800-1050 nm). On the basis of our findings, the mechanism of qE involving the simple replacement of Vio with Zea in LHC II needs to be reconsidered.

  8. Formation, isomerization, and dissociation of alpha-carbon-centered and pi-centered glycylglycyltryptophan radical cations

    SciTech Connect

    Ng, Dominic C.; Song, Tao; Siu, Shiu On; Siu, Chi-Kit; Laskin, Julia; Chu, Ivan K.

    2010-02-11

    Gas phase fragmentations of two isomeric radical cationic tripeptides of glycylglycyltryptophan-G•GW+ and [GGW]•+—with well-defined initial radical sites at the α-carbon atom and the 3-methylindole ring, respectively, have been studied using collision-induced dissociation (CID), density functional theory (DFT), and Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Substantially different low-energy CID spectra were obtained for these two isomeric GGW structures, suggesting that they did not interconvert on the time scale of these experiments. DFT and RRKM calculations were used to investigate the influence of the kinetics, stabilities, and locations of the radicals on the competition between the isomerization and dissociation channels. The calculated isomerization barrier between the GGW radical cations (>35.4 kcal/mol) was slightly higher than the barrier for competitive dissociation of these species (<30.5 kcal/mol); the corresponding microcanonical rate constants for isomerization obtained from RRKM calculations were all considerably lower than the dissociation rates at all internal energies. Thus, interconversion between the GGW isomers examined in this study cannot compete with their fragmentations.

  9. Solvent effects on the resonance Raman spectra of bacteriochlorophyll a cation radical

    NASA Astrophysics Data System (ADS)

    Misono, Yasuhito; Nishizawa, Ei-ichi; Limantara, Leenawaty; Koyama, Yasushi; Itoh, Koichi

    1995-04-01

    Resonance Raman (RR) spectra were measured for the cation radical of bacteriochlorophyll a in acetone, methanol, dichloromethane and mixed solvents of acetone and methanol. The ring-breathing (C a-C m stretching) frequency of the radical (abbreviated as vr+) was observed at 1601 cm -1 in acetone (forming a penta-coordinated monomer), at 1587 cm -1 in a methanol (forming a hexa-coordinated monomer) and at 1600 cm -1 in dichloromethane (forming a penta-coordinated aggregate). The RR spectrum of the radical in dichloromethane is almost identical to the transient RR spectrum ascribed to 'the aggregated T 1 species of Bchl a' formed in the particular solvent by Nishizawa, Limantara, Nanjou, Nagae, Kakuno and Koyama, indicating that their interpretation needs to be revised.

  10. High-field EPR study of carotenoid and chlorophyll cation radicals in photosystem II.

    SciTech Connect

    Lakshmi, K. V.; Reifler, M. J.; Brudvig, G. W.; Poluektov, O. G.; Wagner, A. M.; Thurnuaer, M. C.; Chemistry; Yale Univ.

    2000-11-16

    In photosystem II (PS II), chlorophyll, {beta}-carotene, and cytochrome b{sub 559} are alternate electron donors that may be involved in a photoprotection mechanism. The present study describes the use of high-field EPR spectroscopy to characterize the low-temperature photooxidation of Chl{sub z} and Car cofactors in PS II. The EPR signals of the individual species, previously not resolved at X-band frequency (9 GHz), are resolved at higher D-band frequency (130 GHz) in deuterated Synechococcus lividus PS II. Deuteration of PS II results in significant narrowing of the EPR lines, yielding well-resolved EPR spectra of the Car{sup +} and Chl{sub z}{sup +} radicals at 130 GHz. The g tensors of the individual species were determined by EPR spectral simulations. The g tensor determined for the Car{sup +} radical (g{sub xx} = 2.00335, g{sub yy} = 2.00251, g{sub zz} = 2.00227) is similar to that previously observed for a canthaxanthin cation radical but with a slightly rhombic tensor. The Chl{sub z}{sup +} g tensor (g{sub xx} = 2.00312, g{sub yy} = 2.00263, g{sub zz} = 2.00202) is similar to that of a chlorophyll a cation radical. This study shows that both the carotenoid and chlorophyll radicals are generated in PS II by illumination at temperatures from 6 to 190 K and that there is no interconversion of Car{sup +} and Chl{sub z}{sup +} radicals upon dark annealing at temperatures up to 160 K. This study also establishes the feasibility of using deuteration and high-field EPR to resolve previously unresolvable cofactor signals in PS II.

  11. Increased yields of radical cations by arene addition to irradiated 1,2-dichloroethane

    NASA Astrophysics Data System (ADS)

    Funston, Alison M.; Miller, John R.

    2005-04-01

    Pulse radiolysis in chlorinated hydrocarbon liquids such as 1,2-dichloroethane is a versatile and effective method for the generation of solute radical cations. The addition of a large concentration of toluene or benzene to solutions of 1,2-dichloroethane is found to increase the yield of solute radical cations ( G=0.68 molecules 100 eV -1 in 1,2-dichloroethane (J. Phys. Chem. 83(15) (1979) 1944) by a factor of 2.5. The increased yield is found for solutes which have a potential of ˜1.1 V (vs. SCE) or below for the S + rad /S couple and is due to reaction of the chlorine atom:toluene (π-Cl rad ) complex with the solute. A similar species forms with benzene. π-Cl rad is formed with a yield of G=3.0, and arises principally as a result of geminate recombination of ions. It has an absorption in the visible with λ max 460 nm, ɛ max=1800 M -1 cm -1 and decays with an observed first-order rate constant k=1.12×10 6 s -1. The rate of reaction of the π-Cl • with added solutes ranges from 2.5 to 5×10 9 M -1 s -1. The other oxidant present in the 1,2-dichloroethane/toluene solutions is identified as the toluene cation dimer. This is formed from the 1,2-dichloroethane radical cation with bimolecular rate constant k=1.35×10 10 M -1 s -1 with a radiation chemical yield G=0.5. The rate of reaction of this species with the added solutes is diffusion controlled, k=1-2×10 10 M -1 s -1.

  12. Synchrotron vacuum ultraviolet (VUV) photo-induced fragmentation of cyclic dipeptides radical cations.

    PubMed

    Zhang, Liyun; Jia, Liangyuan; Zhang, Lidong; Guo, Huijun; Zhou, Zhongyue; Weng, Junjie; Qi, Fei

    2012-07-01

    Cyclic dipeptides, due to their chemical properties and various bioactivities, are very attractive for medicinal chemistry. Fragmentations of three simple cyclic dipeptides including cyclo(Gly-Gly), cyclo(Ala-Ala) and cyclo(Gly-Val) in the gas-phase are determined with synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (VUV PIMS) and theoretical calculations. Cyclo(Gly-Gly) and cyclo(Ala-Ala) show the similar fragmentation pathways. The primary decomposition reactions of cyclo(Gly-Gly) and cyclo(Ala-Ala) radical cations are found to be HNCO loss and CO elimination. The appearance energies (AEs) of fragment ions [CH2NHCOCH2]+• and [CH3CHNHCOCHCH3]+• are measured to be 10.21 and 9.66±0.05 eV, respectively, which are formed from cyclo(Gly-Gly) and cyclo(Ala-Ala) radical cations with HNCO elimination. Due to the stabilization of the radical cation of cyclo(Gly-Val) with isopropyl side group, the dominant fragment ion m/z 114 assigned as [C4H6N2O2]+• is produced by γ-H migration and i cleavage to lose propylene. The ionization energies (IEs) of three cyclic dipeptides decrease in the order cyclo(Gly-Gly) (9.33±0.05 eV)>cyclo(Ala-Ala) (9.21±0.05 eV)>cyclo(Gly-Val) (9.09±0.05 eV) from measurements of photoionization efficiency spectra. It implies that IEs of cyclic dipeptides are affected by substituent groups and symmetrical characterization of molecular structures. These observations of the chemical properties of cyclic dipeptides radical ion (M+•) may be important for understanding gas-phase molecular reactivity of 2,5-diketopiperazines and guiding diketopiperazine-based drug design. PMID:21918875

  13. Multimetallic catalysed radical oxidative C(sp3)–H/C(sp)–H cross-coupling between unactivated alkanes and terminal alkynes

    PubMed Central

    Tang, Shan; Wang, Pan; Li, Haoran; Lei, Aiwen

    2016-01-01

    Radical involved transformations are now considered as extremely important processes in modern organic synthetic chemistry. According to the demand by atom-economic and sustainable chemistry, direct C(sp3)–H functionalization through radical oxidative coupling represents an appealing strategy for C–C bond formations. However, the selectivity control of reactive radical intermediates is still a great challenge in these transformations. Here we show a selective radical oxidative C(sp3)–H/C(sp)–H cross-coupling of unactivated alkanes with terminal alkynes by using a combined Cu/Ni/Ag catalytic system. It provides a new way to access substituted alkynes from readily available materials. Preliminary mechanistic studies suggest that this reaction proceeds through a radical process and the C(sp3)–H bond cleavage is the rate-limiting step. This study may have significant implications for controlling selective C–C bond formation of reactive radical intermediates by using multimetallic catalytic systems. PMID:27339161

  14. In vitro antioxidant and radical-scavenging capacities of Citrullus colocynthes (L) and Artemisia absinthium extracts using promethazine hydrochloride radical cation and contemporary assays.

    PubMed

    Asghar, M Nadeem; Khan, I Ullah; Bano, N

    2011-10-01

    A new, quick and economical decolorization assay based upon the generation of a radical cation made from promethazine hydrochloride (PMZH) is described for screening of antioxidant activity of plants/herbal extracts. PMZH radical cations, produced through a reaction between PMZH and potassium persulfate (K(2)S(2)O(8)) in phosphoric acid medium, have maximum absorption at 515 nm in their first-order derivative spectrum. Theconcentrations of chromagen and K(2)S(2)O(8) were optimized (final concentration of PMZH and K₂S₂O₈ were 0.166 mM and 0.11 mM, respectively) for better stability and sensitivity of the radical cation produced. Agood linear correlation was found between the percentage inhibition and the increasing amounts of standard antioxidants, with correlation coefficients ranging from 0.989 to 0.999. The newly developed assay was employed to evaluate the antioxidant capacity of Citrullus colocynthes L. and Artemisia absinthium extracts. The proposed assay involved a more stable radical cation and required only 1 h for preparation of a working solution in comparison to the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation decolorizaion assay, which was reported to be less sensitive at low pH and almost 12-16 h were required for preparation of a working ABTS solution. Other assays employed to evaluate the antioxidant potential andradical-scavenging capacities of the extracts were the ferric-reducing antioxidant power, 2,2'-diphenyl-1-picrylhydrazyl radical scavenging, total phenolic contents assay, total flavonoid contents and metal-chelating activity assays, and the lipid peroxidation value in linoleic acid emulsion systems. The results indicate that boththe plants have potent free radical-scavenging activity and the ability to prevent lipid peroxidation and radical chain reactions.

  15. External electric field promotes proton transfer in the radical cation of adenine-thymine

    NASA Astrophysics Data System (ADS)

    Zhang, Guiqing; Xie, Shijie

    2016-07-01

    According to pKa measurements, it has been predicted that proton transfer would not occur in the radical cation of adenine-thymine (A:T). However, recent theoretical calculations indicate that proton transfer takes place in the base pair in water below the room temperature. We have performed simulations of proton transfer in the cation of B-DNA stack composed of 10 A:T base pairs in water from 20 K to 300 K. Proton transfer occurs below the room temperature, meanwhile it could also be observed at the room temperature under the external electric field. Another case that interests us is that proton transfer bounces back after ˜300 fs from the appearance of proton transfer at low temperatures.

  16. Simultaneous occurrence of three different valence tautomers in meso-vinylruthenium-modified zinc porphyrin radical cations.

    PubMed

    Chen, Jing; Wuttke, Evelyn; Polit, Walther; Exner, Thomas; Winter, Rainer F

    2013-03-01

    The mixed-valent radical cation of a styrylruthenium-modified meso-tetraarylzinc porphyrin forms a mixture of three different valence tautomers (VTs) in CH2Cl2 or 1,2-C2H4Cl2 solutions. One of these VTs has the charge and spin delocalized over the porphyrin and the styrylruthenium moieties, while the other two display charge and spin localization on just one of the different redox sites. The relative amounts of the three different VTs were determined by EPR and IR spectroscopies at variable temperatures, while delocalization in the ground state was confirmed by DFT calculations.

  17. Collision-induced dissociation (CID) of guanine radical cation in the gas phase: an experimental and computational study.

    PubMed

    Cheng, Ping; Li, Yanni; Li, Shuqi; Zhang, Mingtao; Zhou, Zhen

    2010-05-14

    Gas-phase guanine (G) radical cations were generated by electrospraying a solution of guanosine (L) and Cu(NO(3))(2). Collision-induced dissociation (CID) for guanine radical cations yielded five competing dissociation channels, corresponding to the elimination neutral molecules of NH(3), HCN, H(2)NC[triple bond]N (HN=C=NH), HNCO and the neutral radical N=C=NH, respectively. The primary product ions were further characterized by their relevant fragmentions. Ab initio and density functional theory (DFT) calculations were employed to explain the experimental observations. Ten stable radical cation isomers were optimized and the potential energy surfaces (PESs) for the isomerization processes were explored in detail. Starting with the most stable isomer, the primary dissociation channels of guanine radical cations were theoretically investigated. DFT calculations show that the energy barriers for the eliminations of NH(3), HCN, H(2)NC[triple bond]N (HN=C=NH), HNCO and N=C=NH are 397 kJ mol(-1), 479 kJ mol(-1), 294 kJ mol(-1) (298 kJ mol(-1)), 306 kJ mol(-1), and 275 kJ mol(-1), respectively. The results are consistent with the energy-resolved CID of guanine radical cation, in which the eliminations of NH(3) and HCN are less abundant than the other channels. PMID:20428546

  18. Pulse radiolysis of alkanes: A time-resolved electron paramagnetic resonance study

    SciTech Connect

    Shkrob, I.A.; Trifunac, A.D.

    1994-02-14

    Time-resolved spin-echo-detected electron paramagnetic resonance (EPR) was applied to examine short-lived alkyl radicals formed in pulse radiolysis of liquid alkanes. It was found that the ratio of yields of penultimate and interior radicals in n-alkanes at the instant of their generation is temperature-independent and is ca. 1.25 times greater than the statistical quantity. This higher-than-statistical production of penultimate radicals indicates that the fast ion molecule reactions involving radical cations are a significant route of radical generation. The analysis of spin-echo kinetics in n-alkanes suggests that the alkyl radicals are emissively polarized in spur reactions. this initial polarization rapidly increases with shortening of the aliphatic chain. Another finding is that a long-chain structure of these radicals results in much higher rate of Heisenberg spin exchange relative to the recombination rate. The relative yields of hydrogen abstraction and fragmentation for various branched alkanes are estimated. It is concluded that the fragmentation occurs prior to the formation of radicals in an excited precursor species. Effects of phenolic and alkene additives in radiolysis of n-alkanes are examined. It is demonstrated that phenoxy radicals are produced in dissociative capture of electrons and alkane holes. Another route is a reaction of phenols with free hydrogen atoms. A rapid transfer of singlet correlation from the geminate radical ion pairs is responsible for unusual polarization patterns in the phenoxy and cyclohexadienyl radicals. The significance of these results in the context of cross-linking in polyethylene and higher paraffins is discussed. 56 refs.

  19. The first BETS radical cation salts with dicyanamide anion: Crystal growth, structure and conductivity study

    NASA Astrophysics Data System (ADS)

    Kushch, N. D.; Buravov, L. I.; Chekhlov, А. N.; Spitsina, N. G.; Kushch, P. P.; Yagubskii, E. B.; Herdtweck, E.; Kobayashi, A.

    2011-11-01

    Electrochemical oxidation of bis(ethylenedithio)tetraselenafulvalene (BETS) has been investigated. Simple and complex dicyanamides of transition metals (Mn 2+, Ni 2+ and Fe 2+) were used as electrolytes. The correlation between composition of prepared radical cation salts and metal nature in electrolytes was established. Manganese dicyanamides provide the formation of BETS salts with the {Mn[N(CN) 2] 3}- and [N(CN) 2]-XH 2O anions. When Ni- or Fe-containing electrolytes were used only metalless BETS salts, α″-BETS 2[N(CN) 2]·2H 2O ( I) and θ-BETS 2[N(CN) 2]·3.6H 2O ( II), formed. Structures and conducting properties of these salts were analyzed. Both salts exhibit layered structure. Conducting radical cation layers have α″ (I)- or θ -type ( II). Anion sheets appear as two-dimensional polymer networks of different types. These networks are formed by [N(CN)] 2- anions and water molecules interlinked by hydrogen bonds. Salt I is a semiconductor and II demonstrates resistance drop down to150 K at normal pressure and down to 72 K at ˜0.4 kbar pressure.

  20. Zeaxanthin Radical Cation Formation in Minor Light-Harvesting Complexes of Higher Plant Antenna

    SciTech Connect

    Avenson, Thomas H.; Ahn, Tae Kyu; Zigmantas, Donatas; Niyogi, Krishna K.; Li, Zhirong; Ballottari, Matteo; Bassi, Roberto; Fleming, Graham R.

    2008-01-31

    Previous work on intact thylakoid membranes showed that transient formation of a zeaxanthin radical cation was correlated with regulation of photosynthetic light-harvesting via energy-dependent quenching. A molecular mechanism for such quenching was proposed to involve charge transfer within a chlorophyll-zeaxanthin heterodimer. Using near infrared (880-1100 nm) transient absorption spectroscopy, we demonstrate that carotenoid (mainly zeaxanthin) radical cation generation occurs solely in isolated minor light-harvesting complexes that bind zeaxanthin, consistent with the engagement of charge transfer quenching therein. We estimated that less than 0.5percent of the isolated minor complexes undergo charge transfer quenching in vitro, whereas the fraction of minor complexes estimated to be engaged in charge transfer quenching in isolated thylakoids was more than 80 times higher. We conclude that minor complexes which bind zeaxanthin are sites of charge transfer quenching in vivo and that they can assume Non-quenching and Quenching conformations, the equilibrium LHC(N)<--> LHC(Q) of which is modulated by the transthylakoid pH gradient, the PsbS protein, and protein-protein interactions.

  1. The Effect of the Secondary Structure on Dissociation of Peptide Radical Cations: Fragmentation of Angiotensin III and Its Analogues

    SciTech Connect

    Yang, Zhibo; Lam, Corey; Chu, Ivan K.; Laskin, Julia

    2008-09-28

    Fragmentation of protonated RVYIHPF and RVYIHPF-OMe and the corresponding radical cations was studied using time- and collision energy-resolved surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially equipped to perform SID experiments. Peptide radical cations were produced by gas-phase fragmentation of CoIII(salen)-peptide complexes. Both the energetics and mechanisms of dissociation of even-electron and odd-electron angiotensin III ions are quite different. Protonated molecules are much more stable towards fragmentation than the corresponding radical cations. RRKM modeling of the experimental data suggests that this stability is largely attributed to differences in threshold energies for dissociation while activation entropies are very similar. Detailed analysis of the experimental data obtained for radical cations demonstrated the presence of two distinct structures separated by a high free-energy barrier. The two families of structures were ascribed to the canonical and zwitterionic forms of the radical cations produced in our experiments.

  2. Novel Cβ-Cγ bond cleavages of tryptophan-containing peptide radical cations.

    PubMed

    Song, Tao; Hao, Qiang; Law, Chun-Hin; Siu, Chi-Kit; Chu, Ivan K

    2012-02-01

    In this study, we observed unprecedented cleavages of the C(β)-C(γ) bonds of tryptophan residue side chains in a series of hydrogen-deficient tryptophan-containing peptide radical cations (M(•+)) during low-energy collision-induced dissociation (CID). We used CID experiments and theoretical density functional theory (DFT) calculations to study the mechanism of this bond cleavage, which forms [M - 116](+) ions. The formation of an α-carbon radical intermediate at the tryptophan residue for the subsequent C(β)-C(γ) bond cleavage is analogous to that occurring at leucine residues, producing the same product ions; this hypothesis was supported by the identical product ion spectra of [LGGGH - 43](+) and [WGGGH - 116](+), obtained from the CID of [LGGGH](•+) and [WGGGH](•+), respectively. Elimination of the neutral 116-Da radical requires inevitable dehydrogenation of the indole nitrogen atom, leaving the radical centered formally on the indole nitrogen atom ([Ind](•)-2), in agreement with the CID data for [WGGGH](•+) and [W(1-CH3)GGGH](•+); replacing the tryptophan residue with a 1-methyltryptophan residue results in a change of the base peak from that arising from a neutral radical loss (116 Da) to that arising from a molecule loss (131 Da), both originating from C(β)-C(γ) bond cleavage. Hydrogen atom transfer or proton transfer to the γ-carbon atom of the tryptophan residue weakens the C(β)-C(γ) bond and, therefore, decreases the dissociation energy barrier dramatically. PMID:22135037

  3. Gas-phase reactions of doubly charged actinide cations with alkanes and alkenes--probing the chemical activity of 5f electrons from Th to Cm.

    PubMed

    Marçalo, Joaquim; Santos, Marta; Gibson, John K

    2011-11-01

    Small alkanes (methane, ethane, propane, n-butane) and alkenes (ethene, propene, 1-butene) were used to probe the gas-phase reactivity of doubly charged actinide cations, An(2+) (An = Th, Pa, U, Np, Pu, Am, Cm), by means of Fourier transform ion cyclotron resonance mass spectrometry. Different combinations of doubly and singly charged ions were observed as reaction products, comprising species formed via metal-ion induced eliminations of small molecules, simple adducts and ions resulting from electron, hydride or methide transfer channels. Th(2+), Pa(2+), U(2+) and Np(2+) preferentially yielded doubly charged products of hydrocarbon activation, while Pu(2+), Am(2+) and Cm(2+) reacted mainly through transfer channels. Cm(2+) was also capable of forming doubly charged products with some of the hydrocarbons whereas Pu(2+) and Am(2+) were not, these latter two ions conversely being the only for which adduct formation was observed. The product distributions and the reaction efficiencies are discussed in relation to the electronic configurations of the metal ions, the energetics of the reactions and similar studies previously performed with doubly charged lanthanide and transition metal cations. The conditions for hydrocarbon activation to occur as related to the accessibility of electronic configurations with one or two 5f and/or 6d unpaired electrons are examined and the possible chemical activity of the 5f electrons in these early actinide ions, particularly Pa(2+), is considered.

  4. Gas-phase reactions of aryl radicals with 2-butyne: experimental and theoretical investigation employing the N-methyl-pyridinium-4-yl radical cation.

    PubMed

    Lam, A K Y; Li, C; Khairallah, G; Kirk, B B; Blanksby, S J; Trevitt, A J; Wille, U; O'Hair, R A J; da Silva, G

    2012-02-21

    Aromatic radicals form in a variety of reacting gas-phase systems, where their molecular weight growth reactions with unsaturated hydrocarbons are of considerable importance. We have investigated the ion-molecule reaction of the aromatic distonic N-methyl-pyridinium-4-yl (NMP) radical cation with 2-butyne (CH(3)C≡CCH(3)) using ion trap mass spectrometry. Comparison is made to high-level ab initio energy surfaces for the reaction of NMP and for the neutral phenyl radical system. The NMP radical cation reacts rapidly with 2-butyne at ambient temperature, due to the apparent absence of any barrier. The activated vinyl radical adduct predominantly dissociates via loss of a H atom, with lesser amounts of CH(3) loss. High-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry allows us to identify small quantities of the collisionally deactivated reaction adduct. Statistical reaction rate theory calculations (master equation/RRKM theory) on the NMP+2-butyne system support our experimental findings, and indicate a mechanism that predominantly involves an allylic resonance-stabilized radical formed via H atom shuttling between the aromatic ring and the C(4) side-chain, followed by cyclization and/or low-energy H atom β-scission reactions. A similar mechanism is demonstrated for the neutral phenyl radical (Ph˙)+2-butyne reaction, forming products that include 3-methylindene. The collisionally deactivated reaction adduct is predicted to be quenched in the form of a resonance-stabilized methylphenylallyl radical. Experiments using a 2,5-dichloro substituted methyl-pyridiniumyl radical cation revealed that in this case CH(3) loss from the 2-butyne adduct is favoured over H atom loss, verifying the key role of ortho H atoms, and the shuttling mechanism, in the reactions of aromatic radicals with alkynes. As well as being useful phenyl radical analogues, pyridiniumyl radical cations may form in the ionosphere of Titan, where they could undergo rapid

  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

    NASA Astrophysics Data System (ADS)

    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. Single-Crystal X-ray Structures of conductive π-Stacking Dimers of Tetrakis(alkylthio)benzene Radical Cations.

    PubMed

    Chen, Xiaoyu; Gao, Feng; Yang, Wuqin

    2016-01-01

    Salts containing radical cations of 1,2,4,5-tetrakis(isopropylthio)benzene (TPB) and 1,2,4,5-tetrakis(ethylthio) benzene (TEB) have been successfully synthesized with . These newly synthesized salts have been characterized by UV-Vis absorption, EPR spectroscopy, conductivity measurement, single crystal X-ray diffraction analysis as well as DFT calculation. This study raises the first crystal structure of conductive π-stacking radical cation with single phenyl ring and reveals their conductivity has relationship with the stack structure which affected by the substituent. PMID:27403720

  7. The structure and photochemical transformation of cyclopropylacetylene radical cation as revealed by matrix EPR and quantum chemical study

    NASA Astrophysics Data System (ADS)

    Shiryaeva, Ekaterina S.; Tyurin, Daniil A.; Feldman, Vladimir I.

    2012-05-01

    The primary radical cation of cyclopropylacetylene was first characterized by EPR spectroscopy in low-temperature freon matrices. The assignment was confirmed by specific deuteration and quantum-chemical calculations at PBE0 and CCSD(T) levels. Photolysis with visible light led to irreversible transformation of the initial species to a ring-open structure. Detailed computational analysis of energy and magnetic resonance parameters of possible reaction products justified formation of pent-3-en-1-yne radical cation (presumably, a (Z)-isomer). This conclusion was also supported by the effect of specific deuteration.

  8. Single-Crystal X-ray Structures of conductive π-Stacking Dimers of Tetrakis(alkylthio)benzene Radical Cations

    NASA Astrophysics Data System (ADS)

    Chen, Xiaoyu; Gao, Feng; Yang, Wuqin

    2016-07-01

    Salts containing radical cations of 1,2,4,5-tetrakis(isopropylthio)benzene (TPB) and 1,2,4,5-tetrakis(ethylthio) benzene (TEB) have been successfully synthesized with . These newly synthesized salts have been characterized by UV-Vis absorption, EPR spectroscopy, conductivity measurement, single crystal X-ray diffraction analysis as well as DFT calculation. This study raises the first crystal structure of conductive π-stacking radical cation with single phenyl ring and reveals their conductivity has relationship with the stack structure which affected by the substituent.

  9. Single-Crystal X-ray Structures of conductive π-Stacking Dimers of Tetrakis(alkylthio)benzene Radical Cations.

    PubMed

    Chen, Xiaoyu; Gao, Feng; Yang, Wuqin

    2016-07-11

    Salts containing radical cations of 1,2,4,5-tetrakis(isopropylthio)benzene (TPB) and 1,2,4,5-tetrakis(ethylthio) benzene (TEB) have been successfully synthesized with . These newly synthesized salts have been characterized by UV-Vis absorption, EPR spectroscopy, conductivity measurement, single crystal X-ray diffraction analysis as well as DFT calculation. This study raises the first crystal structure of conductive π-stacking radical cation with single phenyl ring and reveals their conductivity has relationship with the stack structure which affected by the substituent.

  10. Single-Crystal X-ray Structures of conductive π-Stacking Dimers of Tetrakis(alkylthio)benzene Radical Cations

    PubMed Central

    Chen, Xiaoyu; Gao, Feng; Yang, Wuqin

    2016-01-01

    Salts containing radical cations of 1,2,4,5-tetrakis(isopropylthio)benzene (TPB) and 1,2,4,5-tetrakis(ethylthio) benzene (TEB) have been successfully synthesized with . These newly synthesized salts have been characterized by UV-Vis absorption, EPR spectroscopy, conductivity measurement, single crystal X-ray diffraction analysis as well as DFT calculation. This study raises the first crystal structure of conductive π-stacking radical cation with single phenyl ring and reveals their conductivity has relationship with the stack structure which affected by the substituent. PMID:27403720

  11. Chain branching and termination in the low-temperature combustion of n-alkanes: 2-pentyl radical + O2, isomerization and association of the second O2.

    PubMed

    Asatryan, Rubik; Bozzelli, Joseph W

    2010-07-29

    Association of alkyl radicals with ground-state oxygen (3)Sigma(g)(+)(O(2)) generates chemically activated peroxy intermediates, which can isomerize or further react to form new products before collisional stabilization. The lowest-energy reaction (approximately 19 kcal mol(-1)) for alkylperoxy derivatives of C(3) and larger n-hydrocarbons is an isomerization (intramolecular H-atom transfer) that forms a hydroperoxide alkyl radical, and there is a approximately 30 kcal mol(-1) barrier path to olefin plus HO(2), which is a termination step at lower temperatures. The low-energy-barrier product, hydroperoxide alkyl radical intermediate, can experience additional chemical activation via association with a second oxygen molecule, where there are three important paths that result in chain branching. The competition between this HO(2) + olefin termination step of the first O(2) association and the chain branching processes from the second chemical activation step plays a dominant role at temperatures below 1000 K. Secondary n-pentyl radicals are used in this study as surrogates to analyze the thermochemistry and detailed kinetics of the chemical activation and stabilized adduct reactions important to chain branching and termination. As these radicals provide six- member ring transition states for H-atom transfer between secondary carbons, they represent the detailed kinetics of larger alkane radicals, such as the common fuel components n-heptane and n-decane. Comprehensive potential energy diagrams developed from multilevel CBS-QB3, G3MP2, and CBS-APNO and single-level ab initio and density functional theory methods are used to analyze secondary 2-pentyl (n-pentan-2-yl) and interrelated 2-hydroperoxide-pentan-4-yl radical interactions with O(2). The thermochemistry and kinetics of the chemical activation and stabilized adduct reactions important to chain branching and termination are reported and discussed. Results show that the chain branching reactions have faster

  12. Formation and decomposition of distonic o-, m-, and p-benzyne radical cations from photolysis of Mg(+)(o-, m-, p-C(6)H(4)F(2)).

    PubMed

    Liu, Hai-Chuan; Wang, Chang-Sheng; Guo, Wenyue; Wu, Yun-Dong; Yang, Shihe

    2002-04-10

    Distonic o-, m-, and p-benzyne radical cations (1-3) have been generated by a novel photolysis reaction of mass-selected Mg(+)-difluorobenzene complexes. The energy required for the formation of these radical cations is within 2.2 eV. The formation of o-benzyne cation is most facile. The benzyne radical cations dissociate further to yield ethyne and 1,3-butadiyne radical cation as major products given a sufficient amount of energy. The whole process involves only a single photon, and is very efficient. The calculated threshold for the formation of 1,3-butadiyne radical cation from Mg(+)(o-C(6)H(4)F(2)) is about 4.6 eV, quite comparable with the experimental estimate.

  13. Jahn-Teller and pseudo-Jahn-Teller effects in trifluoromethane radical cation

    NASA Astrophysics Data System (ADS)

    Ghanta, Susanta

    2016-08-01

    Jahn-Teller (JT) and pseudo-Jahn-Teller (PJT) effects in the ground, first and second excited electronic states of the trifluoromethane radical cation are theoretically examined here. Extensive ab initio computation of electronic potential energy surfaces and their coupling surfaces are performed. Full quantum dynamics are obtained by both time-independent and time-dependent quantum mechanical methods. This system belongs to (E+A)⊗e JT-PJT family. Our results compare well with the experimental data. JT interactions are fairly strong in the second excited B˜2 E electronic state and the PJT interaction between A˜2A2 - B˜2 E electronic states is stronger which cause an increase of the spectral line density of the vibronic spectrum.

  14. Aqueous oxidation of sulfonamide antibiotics: aromatic nucleophilic substitution of an aniline radical cation.

    PubMed

    Tentscher, Peter R; Eustis, Soren N; McNeill, Kristopher; Arey, J Samuel

    2013-08-19

    Sulfonamide antibiotics are an important class of organic micropollutants in the aquatic environment. For several, sulfur dioxide extrusion products have been previously reported upon photochemical or dark oxidation. Using quantum chemical modeling calculations and transient absorption spectroscopy, it is shown that single-electron oxidation from sulfadiazine produces the corresponding aniline radical cation. Density functional theory calculations indicate that this intermediate can exist in four protonation states. One species exhibits a low barrier for an intramolecular nucleophilic attack at the para position of the oxidized aniline ring, in which a pyrimidine nitrogen acts as a nucleophile. This attack can lead to a rearranged structure, which exhibits the same connectivity as the SO2 -extruded oxidation product that was previously observed in the aquatic environment and characterized by NMR spectroscopy. We report a detailed reaction mechanism for this intramolecular aromatic nucleophilic substitution, and we discuss the possibility of this reaction pathway for other sulfonamide drugs. PMID:23828254

  15. Electron transfer pathways in mixed-valence paracyclophane-bridged bis-triarylamine radical cations.

    PubMed

    Kaupp, Martin; Gückel, Simon; Renz, Manuel; Klawohn, Sascha; Theilacker, Kolja; Parthey, Matthias; Lambert, Christoph

    2016-01-01

    A series of paracyclophane (PC) bridged mixed-valence (MV) bis-triarylamine radical cations with different ([2.2], [3.3], [4.4]) linkers, with and without additional ethynyl spacers, have been studied by quantum-chemical calculations (BLYP35-D3/TZVP/COSMO) of ground-state structures, thermal electron-transfer barriers, hyperfine couplings, and lowest-lying excited states. Such PC-bridged MV systems are important intra-molecular model systems for inter-molecular electron transfer (ET) via π-stacked aromatics, since they allow enforcement of a more or less well-defined geometrical arrangement. Closely comparable ET barriers and electronic couplings for all [2.2] and [3.3] bridges are found for these class-II MV systems, irrespective of the use of pseudo-para and pseudo-meta connections. While the latter observation contradicts notions of quantum interference for off-resonant conduction through molecular wires, it agrees with the less intricate nodal structures of the highest occupied molecular orbitals. The ET in such MV systems may be more closely connected with hole conduction in the resonant regime. Computations on model cations, in which the [2.2] linkers have been truncated, confirm predominant through-space π-π electronic coupling. Systems with [4.4] PC bridges exhibit far more structural flexibility and concomitantly weaker electronic interactions between the redox centers.

  16. Manifestation of Nonadiabatic Effects in the IR Spectrum of Para-Benzoquinone Radical Cation

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    X-irradiation of an Ar matrix doped with p-benzoquinone (PBQ) at 10 K leads to formation of the PBQ radical cation (PBQ^{bullet +}) and radical anion (PBQ^{bullet -}). The IR spectrum of PBQ^{bullet +} exhibits broad and dense absorption bands in the 2000 cm^{-1} and higher energy region. Another characteristic of the spectrum is the presence of three intense peaks in the lower energy region. Equation-of-motion coupled-cluster calculations have been performed to analyze the spectrum with the quasi-diabatic model Hamiltonian technique. A spectral simulation based on the model Hamiltonian reproduces the observed IR spectrum very well, revealing that the electronic transition to the low-lying excited state, {˜ A} ^2B_{2u} ← {˜ X} ^2B_{3g}, is severely affected by nonadiabatic interaction of the two states, to which the aforementioned features are attributed. In particular, three b_{1u} fundamental peaks for {˜ X} ^2B_{3g} PBQ^{bullet +} gain large intensities from the electronic transition through the vibronic coupling. On the other hand, transition to another b_{1u} fundamental level (anti-symmetric CO stretch) in the {˜ X} state has a diminished intensity due to cancellation of the electronic contribution and the usual dipole derivative contribution. Furthermore, this b_{1u} level is significantly scrambled with nearby vibronic states of b_{2u} symmetry, which accounts for the weak broad band experimentally observed in the 1560-1600 cm^{-1} region.

  17. Synthesis of the iron phthalocyaninate radical cation μ-nitrido dimer and its interaction with hydrogen peroxide

    NASA Astrophysics Data System (ADS)

    Grishina, E. S.; Makarova, A. S.; Kudrik, E. V.; Makarov, S. V.; Koifman, O. I.

    2016-03-01

    The iron phthalocyaninate μ-nitrido dimer radical cation, as well as the μ-nitrido dimer complexes of iron phthalocyaninate, was found to have high catalytic activity in the oxidation of organic compounds. It was concluded that this compound is of interest as a model of active intermediates—catalase and oxidase enzymes.

  18. Spectroscopic Evidence for Through-Space Arene-Sulfur-Arene Bonding Interaction in m-Terphenyl Thioether Radical Cations.

    PubMed

    Monney, Nicolas P-A; Bally, Thomas; Yamamoto, Takuhei; Glass, Richard S

    2015-12-31

    Electronic absorption spectra and quantum chemical calculations of the radical cations of m-terphenyl tert-butyl thioethers, where the S-t-Bu bond is forced to be perpendicular to the central phenyl ring, show the occurrence of through-space [π···S···π](+) bonding interactions which lead to a stabilization of the thioether radical cations. In the corresponding methyl derivatives there is a competition between delocalization of the hole that is centered on a p-AO of the S atom into the π-system of the central phenyl ring or through space into the flanking phenyl groups, which leads to a mixture of planar and perpendicular conformations in the radical cation. Adding a second m-terphenyl tert-butyl thioether moiety does not lead to further delocalization; the spin and charge remain in one of the two halves of the radical cation. These findings have interesting implications with regard to the role of methionines as hopping stations in electron transfer through proteins.

  19. Direct observation of hexamethylbenzenium radical cations generated during zeolite methanol-to-olefin catalysis: an ESR study.

    PubMed

    Kim, Sun Jung; Jang, Hoi-Gu; Lee, Jun Kyu; Min, Hyung-Ki; Hong, Suk Bong; Seo, Gon

    2011-09-01

    The generation of hexamethylbenzenium radical cations as the key reaction intermediate in chabazite-type molecular sieve acids (i.e., H-SAPO-34 and H-SSZ-13) during the methanol-to-olefin process has been directly evidenced by ESR spectroscopy. PMID:21766115

  20. Kinetics of ABTS derived radical cation scavenging by bucillamine, cysteine, and glutathione. Catalytic effect of Cu(2+) ions.

    PubMed

    Valent, Ivan; Topolská, Dominika; Valachová, Katarína; Bujdák, Juraj; Šoltés, Ladislav

    2016-05-01

    Kinetics of reduction of the stable radical cation derived from 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) in reaction with the anti-rheumatic drug bucillamine (BUC) and two reference thiols - cysteine (Cys) and glutathione (GSH) was followed spectrophotometrically in acidic medium with 10-fold molar excess of the reductant. Decay of the radical is governed by pseudo-first order kinetics with small deviation in the case of GSH. H(+) ions displayed second order inhibition of the reaction with all the studied compounds. The reaction of BUC exhibits zero order kinetics to the radical at lower acidities with a moderate acceleration of the reaction rate by H(+) ions. A significant catalytic effect of Cu(2+) ions on the reactions with all the reductants was observed. The most sensitive to Cu(2+)-catalysis was the reaction of BUC with the radical cation, while Cu(2+) ions showed much lower effect on the reaction with GSH. The presence of EDTA strongly inhibited the reactions and equalized the reaction rates for all the reductants. A Cu(I) selective chelator bathocuproine disulfonate reduced the reaction rate with Cys, but accelerated the reaction with BUC at the lower acidities. The experimental results were rationalized in the framework of the mechanism of reductive chelation. The conclusions may have important consequences for interpretation of antioxidant capacity assays, such as TEAC, utilizing the ABTS derived radical cation.

  1. The first BETS radical cation salts with dicyanamide anion: Crystal growth, structure and conductivity study

    SciTech Connect

    Kushch, N.D.; Buravov, L.I.; Chekhlov, A.N.; Spitsina, N.G.; Kushch, P.P.; Yagubskii, E.B.; Herdtweck, E.; Kobayashi, A.

    2011-11-15

    Electrochemical oxidation of bis(ethylenedithio)tetraselenafulvalene (BETS) has been investigated. Simple and complex dicyanamides of transition metals (Mn{sup 2+}, Ni{sup 2+} and Fe{sup 2+}) were used as electrolytes. The correlation between composition of prepared radical cation salts and metal nature in electrolytes was established. Manganese dicyanamides provide the formation of BETS salts with the {l_brace}Mn[N(CN){sub 2}]{sub 3}{r_brace}- and [N(CN){sub 2}]-XH{sub 2}O anions. When Ni- or Fe-containing electrolytes were used only metalless BETS salts, {alpha}''-BETS{sub 2}[N(CN){sub 2}].2H{sub 2}O (I) and {theta}-BETS{sub 2}[N(CN){sub 2}].3.6H{sub 2}O (II), formed. Structures and conducting properties of these salts were analyzed. Both salts exhibit layered structure. Conducting radical cation layers have {alpha}'' (I)- or {theta}-type (II). Anion sheets appear as two-dimensional polymer networks of different types. These networks are formed by [N(CN)]{sub 2}{sup -} anions and water molecules interlinked by hydrogen bonds. Salt I is a semiconductor and II demonstrates resistance drop down to150 K at normal pressure and down to 72 K at {approx}0.4 kbar pressure. - Graphical abstract: We studied electrochemical oxidation of BETS donor in the presence of simple and/or complex dicyanamides of transition metals (Ni, Fe, Mn) as electrolytes. New conducting salts {alpha}''-BETS{sub 2}[N(CN){sub 2}].2H{sub 2}O and {theta}-BETS{sub 2}[N(CN){sub 2}].3.8H{sub 2}O have been synthesized and characterized. Highlights: > We studied electrochemical oxidation of BETS donor. > Dicyanamides of transition metals (Ni, Fe, Mn) were used as electrolytes. > We found a well-reproducible synthesis of magnetic superconductor BETS{sub 2}Mn[N(CN){sub 2}]{sub 3}. > Two new metalless BETS salts form when Ni and Fe electrolytes were used. > Their structure and conductivity were investigated.

  2. The guanine cation radical: investigation of deprotonation states by ESR and DFT.

    PubMed

    Adhikary, Amitava; Kumar, Anil; Becker, David; Sevilla, Michael D

    2006-11-30

    This work reports ESR studies that identify the favored site of deprotonation of the guanine cation radical (G*+) in an aqueous medium at 77 K. Using ESR and UV-visible spectroscopy, one-electron oxidized guanine is investigated in frozen aqueous D2O solutions of 2'-deoxyguanosine (dGuo) at low temperatures at various pHs at which the guanine cation radical, G*+ (pH 3-5), singly deprotonated species, G(-H)* (pH 7-9), and doubly deprotonated species, G(-2H)*- (pH > 11), are found. C-8-deuteration of dGuo to give 8-D-dGuo removes the major proton hyperfine coupling at C-8. This isolates the anisotropic nitrogen couplings for each of the three species and aids our analyses. These anisotropic nitrogen couplings were assigned to specific nitrogen sites by use of 15N-substituted derivatives at N1, N2, and N3 atoms in dGuo. Both ESR and UV-visible spectra are reported for each of the species: G*+, G(-H)*, and G(-2H)*-. The experimental anisotropic ESR hyperfine couplings are compared to those obtained from DFT calculations for the various tautomers of G(-H)*. Using the B3LYP/6-31G(d) method, the geometries and energies of G*+ and its singly deprotonated state in its two tautomeric forms, G(N1-H)* and G(N2-H)*, were investigated. In a nonhydrated state, G(N2-H)* is found to be more stable than G(N1-H)*, but on hydration with seven water molecules G(N1-H)* is found to be more stable than G(N2-H)*. The theoretically calculated hyperfine coupling constants (HFCCs) of G*+, G(N1-H)*, and G(-2H)*- match the experimentally observed HFCCs best on hydration with seven or more waters. For G(-2H)*-, the hyperfine coupling constant (HFCC) at the exocyclic nitrogen atom (N2) is especially sensitive to the number of hydrating water molecules; good agreement with experiment is not obtained until nine or 10 waters of hydration are included.

  3. Fragmentation of singly, doubly, and triply charged hydrogen deficient peptide radical cations in infrared multiphoton dissociation and electron induced dissociation.

    PubMed

    Kalli, Anastasia; Hess, Sonja

    2012-02-01

    Gas phase fragmentation of hydrogen deficient peptide radical cations continues to be an active area of research. While collision induced dissociation (CID) of singly charged species is widely examined, dissociation channels of singly and multiply charged radical cations in infrared multiphoton dissociation (IRMPD) and electron induced dissociation (EID) have not been, so far, investigated. Here, we report on the gas phase dissociation of singly, doubly and triply charged hydrogen deficient peptide radicals, [M + nH]((n+1)+·) (n=0, 1, 2), in MS(3) IRMPD and EID and compare the observed fragmentation pathways to those obtained in MS(3) CID. Backbone fragmentation in MS(3) IRMPD and EID was highly dependent on the charge state of the radical precursor ions, whereas amino acid side chain cleavages were largely independent of the charge state selected for fragmentation. Cleavages at aromatic amino acids, either through side chain loss or backbone fragmentation, were significantly enhanced over other dissociation channels. For singly charged species, the MS(3) IRMPD and EID spectra were mainly governed by radical-driven dissociation. Fragmentation of doubly and triply charged radical cations proceeded through both radical- and charge-driven processes, resulting in the formation of a wide range of backbone product ions including, a-, b-, c-, y-, x-, and z-type. While similarities existed between MS(3) CID, IRMPD, and EID of the same species, several backbone product ions and side chain losses were unique for each activation method. Furthermore, dominant dissociation pathways in each spectrum were dependent on ion activation method, amino acid composition, and charge state selected for fragmentation.

  4. Isolation and Characterization of the 2,2'-Azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) Radical Cation-Scavenging Reaction Products of Arbutin.

    PubMed

    Tai, Akihiro; Ohno, Asako; Ito, Hideyuki

    2016-09-28

    Arbutin, a glucoside of hydroquinone, has shown strong 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation-scavenging activity, especially in reaction stoichiometry. This study investigated the reaction mechanism of arbutin against ABTS radical cation that caused high stoichiometry of arbutin in an ABTS radical cation-scavenging assay. HPLC analysis of the reaction mixture of arbutin and ABTS radical cation indicated the existence of two reaction products. The two reaction products were purified and identified to be a covalent adduct of arbutin with an ABTS degradation fragment and 3-ethyl-6-sulfonate benzothiazolone. A time-course study of the radical-scavenging reactions of arbutin and the two reaction products suggested that one molecule of arbutin scavenges three ABTS radical cation molecules to generate an arbutin-ABTS fragment adduct as a final reaction product. The results suggest that one molecule of arbutin reduced two ABTS radical cation molecules to ABTS and then cleaved the third ABTS radical cation molecule to generate two products, an arbutin-ABTS fragment adduct and 3-ethyl-6-sulfonate benzothiazolone.

  5. Isolation and Characterization of the 2,2'-Azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) Radical Cation-Scavenging Reaction Products of Arbutin.

    PubMed

    Tai, Akihiro; Ohno, Asako; Ito, Hideyuki

    2016-09-28

    Arbutin, a glucoside of hydroquinone, has shown strong 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation-scavenging activity, especially in reaction stoichiometry. This study investigated the reaction mechanism of arbutin against ABTS radical cation that caused high stoichiometry of arbutin in an ABTS radical cation-scavenging assay. HPLC analysis of the reaction mixture of arbutin and ABTS radical cation indicated the existence of two reaction products. The two reaction products were purified and identified to be a covalent adduct of arbutin with an ABTS degradation fragment and 3-ethyl-6-sulfonate benzothiazolone. A time-course study of the radical-scavenging reactions of arbutin and the two reaction products suggested that one molecule of arbutin scavenges three ABTS radical cation molecules to generate an arbutin-ABTS fragment adduct as a final reaction product. The results suggest that one molecule of arbutin reduced two ABTS radical cation molecules to ABTS and then cleaved the third ABTS radical cation molecule to generate two products, an arbutin-ABTS fragment adduct and 3-ethyl-6-sulfonate benzothiazolone. PMID:27607833

  6. Products and mechanism of secondary organic aerosol formation from reactions of n-alkanes with OH radicals in the presence of NOx.

    PubMed

    Lim, Yong Bin; Ziemann, Paul J

    2005-12-01

    Secondary organic aerosol (SOA) formation from reactions of n-alkanes with OH radicals in the presence of NOx was investigated in an environmental chamber using a thermal desorption particle beam mass spectrometer for particle analysis. SOA consisted of both first- and higher-generation products, all of which were nitrates. Major first-generation products were sigma-hydroxynitrates, while higher-generation products consisted of dinitrates, hydroxydinitrates, and substituted tetrahydrofurans containing nitrooxy, hydroxyl, and carbonyl groups. The substituted tetrahydrofurans are formed by a series of reactions in which sigma-hydroxycarbonyls isomerize to cyclic hemiacetals, which then dehydrate to form substituted dihydrofurans (unsaturated compounds) that quickly react with OH radicals to form lower volatility products. SOA yields ranged from approximately 0.5% for C8 to approximately 53% for C15, with a sharp increase from approximately 8% for C11 to approximately 50% for C13. This was probably due to an increase in the contribution of first-generation products, as well as other factors. For example, SOA formed from the C10 reaction contained no first-generation products, while for the C15 reaction SOA was approximately 40% first-generation and approximately 60% higher-generation products, respectively. First-generation sigma-hydroxycarbonyls are especially important in SOA formation, since their subsequent reactions can rapidly form low volatility compounds. In the atmosphere, substituted dihydrofurans created from sigma-hydroxycarbonyls will primarily react with O3 or NO3 radicals, thereby opening reaction pathways not normally accessible to saturated compounds.

  7. The role of the position of the basic residue in the generation and fragmentation of peptide radical cations

    NASA Astrophysics Data System (ADS)

    Wee, Sheena; O'Hair, Richard A. J.; McFadyen, W. David

    2006-03-01

    Using simple di- and tripeptides GX, GGX, GXG, XG and XGG, the influence of the position of the basic residue, X (X = R, K and H), on the formation of peptide radical cations (M+) from [CuII(tpy)M]2+ complexes (where tpy = 2,2':6',2''-terpyridine) was probed. It was found that M+ is formed with greatest abundance when the basic residue is at the C-terminus. For arginine containing peptides, this may be due to further fragmentation of GRG+, RG+ and RGG+ at the MS2 stage. For lysine and histidine containing peptides, when the basic residue is not located at the C-terminus, competing fragmentation pathways that lead to peptide backbone cleavage are more facile than M+ formation. In order to gain some insights into the binding modes of these peptides to [CuII(tpy)]2+, the formation and fragmentation of copper(II) complexes of tripeptides protected as their carboxy methyl/ethyl esters (M-OR', R' = Me/Et) were also probed. The products of the competing fragmentation pathways of [CuII(tpy)M]2+, as well as the formation and fragmentation of [CuII(tpy)(M-OR')]2+, suggest that the unprotected peptides, M, mainly bind as zwitterions to [CuII(tpy)]2+. The fragmentation reactions of the radical cations (M+) were also studied. Radical driven side chain fragmentation reactions of M+ are dependent on both the position of the residue as well as the identity of other residues present in the peptide radical cations. GR and RG, which undergo rearrangement to form a mixed anhydride in their protonated forms, do not undergo the same rearrangement in their radical cation forms.

  8. Formation of a porphyrin pi-cation radical in the fluoride complex of horseradish peroxidase.

    PubMed

    Farhangrazi, Z S; Sinclair, R; Powers, L; Yamazaki, I

    1995-11-21

    Horseradish peroxidase (HRP) was oxidized by IrCl6(2-) to a mixture of compounds I and II, the rate of oxidation and the ratio of the mixture being greatly affected by pH (Hayashi & Yamazaki, 1979). Oxidation of HRP by IrCl6(2-) in the presence of fluoride was significantly accelerated. This resulted in the formation of a new compound which is a ferric fluoride complex containing a porphyrin pi-cation radical. The spectrum of the new compound showed a decreased absorption band in the Soret region and a broad band at 570 nm; which was converted to that of the original ferric fluoride complex by addition of ascorbate or hydroquinone. Addition of cyanide slowed down the oxidation of HRP by IrCl6(2-), and the oxidation product was the same as that obtained in the absence of cyanide. Compound I was formed when H2O2 was added to HRP in the presence of fluoride or cyanide. The one-electron reduction potential (Eo') of the oxidized HRP-fluoride complex was measured at several pH values, the Eo' value at pH 7 being 861 +/- 4 mV. The ratio of delta Eo' to delta pH was 49 mV/pH unit.

  9. Reactive Pathways in the Chlorobenzene-Ammonia Dimer Cation Radical: New Insights from Experiment and Theory

    NASA Astrophysics Data System (ADS)

    Nyambo, Silver; Uhler, Brandon; Kalume, Aimable; Muzangwa, Lloyd; Reid, Scott

    2014-06-01

    Previously, we have studied non-covalent interactions in mono-halogenated benzene clusters using mass selected resonant 2-photon ionization methods. We have extended our studies by investigating the interaction between these mono-halobenzenes with a prototypical N atom donor (NH_3). Thus, we have obtained electronic spectra of PhX…(NH_3)n ( X=F, Cl, Br and n=1,2….) complexes in the region of the PhX monomer S_0-S_1 (ππ*) transition. Here we are mainly focusing on PhCl…NH_3 dimer. We found that upon ionization of the dimer, three reactive pathways of the [PhCl…NH_3]+. have been evidenced. The primary pathway is the Cl atom elimination, previously evidenced. The second and third pathways, HCl elimination and H atom elimination are identified for the first time in the R2PI studies of the dimer. Electronic spectra obtained for the three pathways shows that they originate from a common precursor. The reactive pathways in this system were extensively characterized computationally. We used DFT and post-Hartree Fock electronic structure calculations, Frank-Condon analysis to support our experimental findings. The results were consistent with previous direct ab initio molecular dynamics calculations, we found two nearly iso-energetic Wheland intermediates which lie significantly lower in energy than the initially formed dimer cation radical [PhCl…NH_3]+..

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

    PubMed

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

    2015-11-12

    Chemical stability of primary radical cations (RCs) generated in irradiated matter determines substantially the radiation resistance of organic materials. Transformations of the RCs of the glyme molecules, R(-O-CH2-CH2-)nO-R (R = CH3, n = 1-4) has been studied on the nanosecond time scale by measuring the magnetic field effects in the recombination fluorescence from irradiated liquid solutions of the glymes. In all cases, the RCs observed were different from that expected for the primary ones and revealed very similar hyperfine couplings independent of the poly(ethylene oxide) chain length and of the substitution of terminal methyl groups by C2H5 or CH2CH2Cl, as has been shown with diglyme as an example. Quantum chemical analysis of possible chemical transformations for the monoglyme RC as a model system allowed us to discover the reaction pathway yielding the methyl vinyl ether RC. The pathway involves intramolecular proton transfer followed by C-O bond cleavage. Only one (-O-CH2-CH2-O-) fragment is involved in this transformation, which is nearly barrierless due to the catalytic effect of adjacent glyme molecules. The rapid formation of the methyl vinyl ether RC in the irradiated monoglyme was confirmed by the numerical simulation of the experimental curves of the time-resolved magnetic field effect. These findings suggest that the R'-O-CH═CH2(•+) formation is a typical decay pathway for the primary RCs in irradiated liquid glymes. PMID:26472520

  11. Distance dependence of hole transfer rates from G radical cations to GGG traps in DNA.

    PubMed

    Kalosakas, G; Spanou, E

    2013-10-01

    Relative reaction rates for hole transfer between G radical cations and GGG triplets in DNA, through different bridges of varying lengths, are numerically calculated and the obtained results are compared with corresponding experimental observations [Giese et al., 2001, Nature, 412, 318; Angew. Chem., Int. Ed., 1999, 38, 996]. Hole donors and acceptors are separated either by (T-A)n bridges or by N repeated barriers consisting of (T-A,T-A) double base-pairs which are connected through single G-C base-pairs. In the former case, hole transfer rates show a strong exponential decrease with the length of the bridge for short bridges, while a switching to weak distance dependence has been observed for longer bridges. In the latter case, a power law seems to better describe the distance dependence of charge transfer rates. All these experimental observations are qualitatively reproduced by our simulations without any adjustable parameter, considering only tunneling as the charge transfer mechanism. Physical insights into the mechanism providing the switching behavior in the case of (T-A)n bridges are presented through an analysis of the eigenfunctions of the system. PMID:23928688

  12. The o-, m-, and p-benzyne radical cations: a theoretical study.

    PubMed

    Li, Hua; Huang, Ming-Bao

    2008-09-21

    On the basis of the CASPT2 (multiconfigurational second-order perturbation theory) geometry optimization calculations, the ground states of the o-C6H4+ (C2v), m-C6H4+ (C2v), and p-C6H4+ (D2h) radical cations were determined to be 1 2B1, 1 2A2, and 1 2B1u, respectively. For o-C6H4+ and m-C6H4+, the first excited states (1 2A2 and 1 2A1, respectively) lie very close to the respective ground states. The small distance value of 1.419 A between the two dehydrocarbons in the ground-state geometry of m-C6H4+ indicates that there is a real chemical bond between the two dehydrocarbons (the distance in the 1 2A1 geometry of m-C6H4+ is very long as in the m-C6H4 molecule). The (U)B3LYP isotropic proton hfcc (hyperfine coupling constant) calculation results imply that the ground and first excited states of o-C6H4+ will have similar ESR spectrum patterns while the ground and first excited states of m-C6H4+ will have completely different ESR spectrum patterns.

  13. Oxidation of thioanisole and p-methoxythioanisole by lignin peroxidase: kinetic evidence of a direct reaction between compound II and a radical cation.

    PubMed Central

    Brück, Thomas B; Gerini, Maria Francesca; Baciocchi, Enrico; Harvey, Patricia J

    2003-01-01

    The reaction of H2O2 with thioanisole and p-methoxythioanisole catalysed by lignin peroxidase from Phanerochaete chrysosporium has been studied spectrophotometrically under turnover and single turnover conditions with a stopped-flow apparatus. Pre-formed lignin peroxidase compounds I and II are each able to react with the sulphides to form a sulphide radical cation. The radical cation is then converted into the sulphoxide either by reaction with the medium or by reaction with compound II. This is the first report of a direct reaction between compound II and the substrate radical cation. With thioanisole, significant enantiomeric selectivity and high oxygen incorporation in the sulphoxide are obtained because compound II is preferentially reduced by the enzyme-bound thioanisole radical cation compared with the neutral substrate. By contrast, with p-methoxythioanisole, the data imply formation of an intermediate ternary complex comprising compound II, radical cation and neutral substrate, such that a chain of electron transfer reactions starting from neutral molecule and progressing to oxidized haem via substrate radical cation is facilitated, yielding the native enzyme and two molecules of p-methoxythioanisole radical cation as products. The reactions of compounds I and II with sulphides imply flexing of the apoprotein moiety during catalysis. PMID:12803544

  14. Photosensitized oxidation of aryl benzyl sulfoxides. Evidence for nucleophilic assistance to the C-s bond cleavage of aryl benzyl sulfoxide radical cations.

    PubMed

    Del Giacco, Tiziana; Lanzalunga, Osvaldo; Lapi, Andrea; Mazzonna, Marco; Mencarelli, Paolo

    2015-02-20

    The radical cations of a series of aryl benzyl sulfoxides (4-X-C6H4CH2SOC6H4Y(+•)) have been generated by photochemical oxidation of the parent sulfoxides sensitized by 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)ClO4(-)). Steady-state photolysis experiments showed the prevailing formation of benzylic products deriving from the C-S fragmentation in the radical cations, together with sulfur-containing products. Formation of sulfoxide radical cations was unequivocally established by laser flash photolysis experiments showing the absorption bands of 3-CN-NMQ(•) (λmax = 390 nm) and of the radical cations (λmax = 500-620 nm). The decay rate constants of radical cations, determined by LFP experiments, decrease by increasing the electron-donating power of the arylsulfinyl Y substituent and to a smaller extent by increasing the electron-withdrawing power of the benzylic X substituent. A solvent nucleophilic assistance to the C-S bond cleavage has been suggested, supported by the comparison of substituent effects on the same process occurring in aryl tert-butyl sulfoxide radical cations. DFT calculations, performed to determine the bond dissociation free energy in the radical cations, the transition state energies associated with the unimolecular C-S bond cleavage, and the charge and spin delocalized on their structures, were also useful to endorse the nucleophilic assistance to the C-S scission.

  15. Role of. pi. -cation radicals in the enzymatic cycles of peroxidases, catalases, and nitrite and sulfite reductases

    SciTech Connect

    Hanson, L K; Chang, C K; Davis, M S; Fajer, J

    1980-01-01

    Charge iterative extended Hueckel calculations, and magnetic and optical results on porphyrins, chlorins, and isobacteriochlorins (1) suggest that the catalytic cycles of the enzymes horseradish peroxidase, catalase, Neurospora crassa catalase, and nitrite and sulfite reductases proceed via ..pi..-cation radicals of their prosthetic groups; (2) offer distinguishing features for the optical and magnetic spectra of these radicals, pertinent to their detection as enzymatic intermediates; (3) reconcile the seemingly contradictory optical and NMR data on Compounds I of horseradish peroxidase; and (4) predict that the axial ligation of the heme differs for horseradish peroxidase and catalase.

  16. Unconventional hydrogen bonding to organic ions in the gas phase: stepwise association of hydrogen cyanide with the pyridine and pyrimidine radical cations and protonated pyridine.

    PubMed

    Hamid, Ahmed M; El-Shall, M Samy; Hilal, Rifaat; Elroby, Shaaban; Aziz, Saadullah G

    2014-08-01

    Equilibrium thermochemical measurements using the ion mobility drift cell technique have been utilized to investigate the binding energies and entropy changes for the stepwise association of HCN molecules with the pyridine and pyrimidine radical cations forming the C5H5N(+·)(HCN)n and C4H4N2 (+·)(HCN)n clusters, respectively, with n = 1-4. For comparison, the binding of 1-4 HCN molecules to the protonated pyridine C5H5NH(+)(HCN)n has also been investigated. The binding energies of HCN to the pyridine and pyrimidine radical cations are nearly equal (11.4 and 12.0 kcal/mol, respectively) but weaker than the HCN binding to the protonated pyridine (14.0 kcal/mol). The pyridine and pyrimidine radical cations form unconventional carbon-based ionic hydrogen bonds with HCN (CH(δ+)⋯NCH). Protonated pyridine forms a stronger ionic hydrogen bond with HCN (NH(+)⋯NCH) which can be extended to a linear chain with the clustering of additional HCN molecules (NH(+)⋯NCH··NCH⋯NCH) leading to a rapid decrease in the bond strength as the length of the chain increases. The lowest energy structures of the pyridine and pyrimidine radical cation clusters containing 3-4 HCN molecules show a strong tendency for the internal solvation of the radical cation by the HCN molecules where bifurcated structures involving multiple hydrogen bonding sites with the ring hydrogen atoms are formed. The unconventional H-bonds (CH(δ+)⋯NCH) formed between the pyridine or the pyrimidine radical cations and HCN molecules (11-12 kcal/mol) are stronger than the similar (CH(δ+)⋯NCH) bonds formed between the benzene radical cation and HCN molecules (9 kcal/mol) indicating that the CH(δ+) centers in the pyridine and pyrimidine radical cations have more effective charges than in the benzene radical cation.

  17. First estimation of C4-H bond dissociation energies of NADH and its radical cation in aqueous solution.

    PubMed

    Zhu, Xiao-Qing; Yang, Yuan; Zhang, Min; Cheng, Jin-Pei; Zhang, Ming

    2003-12-17

    The heterolytic and homolytic C4-H bond dissociation energies of NADH and its radical cation (NADH*+) in aqueous solution were estimated according to the reaction of NADH with N,N,N',N'-tetramethyl-p-phenylenediamine radical cation perchlorate (TMPA*+) in aqueous solution. The results show that the values of the heterolytic and homolytic C4-H bond dissociation energies of NADH in aqueous solution are 53.6 and 79.3 kcal/mol, respectively; the values of the heterolytic and homolytic C4-H bond dissociation energies of NADH*+*+ in aqueous solution are 5.1 and 36.3 kcal/mol, respectively, which, to our knowledge, is first reported. This energetic information disclosed in the present work should be believed to furnish hints to the understanding of the mechanisms for the redox interconversions of coenzyme couple NADH/NAD+ in vivo.

  18. DFT study on the molecular mechanism of the [4 + 2] cycloaddition between thiobenzophenone and arylalkenes via radical cations.

    PubMed

    Domingo, Luis R; Pérez-Ruiz, Raúl; Argüello, Juan E; Miranda, Miguel A

    2009-05-14

    The mechanistic aspects of the radical cationic version of the [4 + 2] cycloaddition between thiobenzophenone 1 and three aryl-substituted alkenes 2a-c have been studied using DFT methods at the UB3LYP/6-31G* level of theory. In the ground state, the Diels-Alder reaction follows an asynchronous concerted mechanism; the large activation energy associated with bond formation prevents this process. After generation of the radical cation (RC), formation of a molecular complex (MC) between 1 and 2a-c initiates a stepwise mechanism, with attack of the sulfur atom of 1 to the aryl-conjugated position of 2a-c. Subsequent ring closure is the rate-determining step of these cycloadditions. Methoxy or dimethylamino substitution at the aryl group, while stabilizing the corresponding RC, results in a less exothermic formation of MC and a significant increase of the cycloaddition barrier.

  19. Investigation of the molecular structure of radical cation of s-trioxane: quantum chemical calculations and low-temperature EPR results

    NASA Astrophysics Data System (ADS)

    Janovský, I.; Naumov, S.; Knolle, W.; Mehnert, R.

    2003-06-01

    s-Trioxane radical cation was radiolytically generated in freon matrix and the changes of the EPR spectra with temperature, arising from conformational interconversion involving ring, were observed. The equilibration, leading to six equivalent protons (hfs splitting constant 5.9 mT) characteristic of the average planar geometry of the radical cation, occurs at ˜120 K in CF 3CCl 3. Supplementary experiments with 1,3-dioxane, which forms a radical cation with a similar electronic structure, were also performed. DFT quantum chemical calculations were used to support the experimental results.

  20. The Guanine Cation Radical: Investigation of Deprotonation States by ESR and DFT

    PubMed Central

    Adhikary, Amitava; Kumar, Anil; Becker, David; Sevilla, Michael D.

    2008-01-01

    This work reports ESR studies that identify the favored site of deprotonation of the guanine cation radical (G•+) in an aqueous medium at 77 K. Using ESR and UV-visible spectroscopy, one-electron oxidized guanine is investigated in frozen aqueous D2O solutions of 2′-deoxyguanosine (dGuo) at low temperatures at various pHs at which the guanine cation, G•+ (pH 3–5), singly deprotonated species, G(-H)• (pH 7–9) and doubly deprotonated species, G(-2H)•− (pH>11) are found. C-8-deuteration of dGuo to give 8-D-dGuo removes the major proton hyperfine coupling at C-8. This isolates the anisotropic nitrogen couplings for each of the three species and aids our analyses. These anisotropic nitrogen couplings were assigned to specific nitrogen sites by use of 15N substituted derivatives at N1, N2 N3 atoms in dGuo. Both ESR and UV-visible spectra are reported for each of the species: G•+, G(-H)•, and G(-2H)•−. The experimental anisotropic ESR hyperfine couplings are compared to those obtained from DFT calculations for the various tautomers of G(-H)•. Using the B3LYP/6–31G(d) method, the geometries and energies of G•+ and its singly deprotonated state in its two tautomeric forms, G(N1-H)• and G(N2-H)•, were investigated. In a non-hydrated state G(N2-H)• is found to be more stable than G(N1-H)• but on hydration with 7 water molecules G(N1-H)• is found to be more stable than G(N2-H)•. The theoretically calculated hyperfine coupling constants (HFCC) of G•+, G(N1-H)• and G(-2H)•− match the experimentally observed HFCCs best on hydration with 7 or more waters. For G(-2H)•−, the hyperfine coupling constant (HFCC) at the exocyclic nitrogen atom (N2) is especially sensitive to the number of hydrating water molecules; good agreement with experiment is not obtained until 9 or 10 waters of hydration are included. PMID:17125389

  1. The dynamical behavior of the s-trioxane radical cation-A low-temperature EPR and theoretical study.

    PubMed

    Naumov, Sergej S; Knolle, Wolfgang; Naumov, Sergej P; Pöppl, Andreas; Janovský, Igor

    2014-01-01

    The radical cation of s-trioxane, radiolytically generated in a freon (CF3CCl3) matrix, was studied in the 10-140 K temperature region. Reversible changes of the EPR spectra were observed, arising from both ring puckering and ring inversion through the molecular plane. The ESREXN program based on the Liouville density matrix equation, allowing the treatment of dynamical exchange, has been used to analyze the experimental results. Two limiting conformer structures of the s-trioxane radical cation were taken into account, namely "rigid" half-boat and averaged planar ones, differing strongly in their electron distribution. The spectrum due to the "rigid" half-boat conformer can be observed only at very low (<60 K) temperatures, when the exchange of conformers is very slow. Two transition states for interconversion by puckering and ring-inversion were identified, close in activation energy (2.3 and 3.0 kJ/mol calculated). Since the energy difference is very small, both processes set on at a comparable temperature. In the case of nearly complete equilibration (fast exchange) between six energetically equivalent structures at T > 120 K in CF3CCl3, a septet due to six equivalent protons (hfs splitting constant 5.9 mT) is observed, characteristic of the dynamically averaged planar geometry of the radical cation. DFT quantum chemical calculations and spectral simulation including intramolecular dynamical exchange support the interpretation. PMID:25353382

  2. To jump or not to jump? Cα hydrogen atom transfer in post-cleavage radical-cation complexes.

    PubMed

    Bythell, Benjamin J

    2013-02-14

    Conventionally, electron capture or transfer to a polyprotonated peptide ion produces an initial radical-cation intermediate which dissociates "directly" to generate complementary c(n)' and z(m)(•) sequence ions (or ions and neutrals). Alternatively, or in addition, the initial radical-cation intermediate can undergo H(•) migration to produce c(n)(•) (or c(n) - H(•)) and z(m)' (or z(m)(•) + H(•)) species prior to complex separation ("nondirect"). This reaction significantly complicates spectral interpretation, creates ambiguity in peak assignment, impairs effective algorithmic processing (reduction of the spectrum to solely (12)C m/z values), and reduces sequence ion signal-to-noise. Experimental evidence indicates that the products of hydrogen atom transfer reactions are substantially less prevalent for higher charge state precursors. This effect is generally rationalized on the basis of decreased complex lifetime. Here, we present a theoretical study of these reactions in post N-C(α) bond cleavage radical-cation complexes as a function of size and precursor charge state. This approach provides a computational estimate of the barriers associated with these processes for highly charged peptides with little charge solvation. The data indicate that the H(•) migration is an exothermic process and that the barrier governing this reaction rises steeply with precursor ion charge state. There is also some evidence for immediate product separation following N-C(α) bond cleavage at higher charge state. PMID:22809411

  3. The dynamical behavior of the s-trioxane radical cation-A low-temperature EPR and theoretical study.

    PubMed

    Naumov, Sergej S; Knolle, Wolfgang; Naumov, Sergej P; Pöppl, Andreas; Janovský, Igor

    2014-01-01

    The radical cation of s-trioxane, radiolytically generated in a freon (CF3CCl3) matrix, was studied in the 10-140 K temperature region. Reversible changes of the EPR spectra were observed, arising from both ring puckering and ring inversion through the molecular plane. The ESREXN program based on the Liouville density matrix equation, allowing the treatment of dynamical exchange, has been used to analyze the experimental results. Two limiting conformer structures of the s-trioxane radical cation were taken into account, namely "rigid" half-boat and averaged planar ones, differing strongly in their electron distribution. The spectrum due to the "rigid" half-boat conformer can be observed only at very low (<60 K) temperatures, when the exchange of conformers is very slow. Two transition states for interconversion by puckering and ring-inversion were identified, close in activation energy (2.3 and 3.0 kJ/mol calculated). Since the energy difference is very small, both processes set on at a comparable temperature. In the case of nearly complete equilibration (fast exchange) between six energetically equivalent structures at T > 120 K in CF3CCl3, a septet due to six equivalent protons (hfs splitting constant 5.9 mT) is observed, characteristic of the dynamically averaged planar geometry of the radical cation. DFT quantum chemical calculations and spectral simulation including intramolecular dynamical exchange support the interpretation.

  4. Examination of the chemical behavior of the quercetin radical cation towards some bases.

    PubMed

    Marković, Zoran; Amić, Dragan; Milenković, Dejan; Dimitrić-Marković, Jasmina M; Marković, Svetlana

    2013-05-21

    It has been generally accepted that, due to high ionization potential values, single electron transfer followed by proton transfer (SET-PT) is not a plausible mechanism of antioxidant action in flavonoids. In this paper the SET-PT mechanism of quercetin (Q) was examined by revealing possible reaction paths of the once formed quercetin radical cation (Q(+)˙) at the M0-52X/6311+G(d,p) level of theory. The deprotonation of Q(+)˙ was simulated by examining its chemical behavior in the presence of three bases: methylamine (representative of neutral bases), the MeS anion (CH3S(-)) and the hydroxide anion (representative of anionic bases). It was found that Q(+)˙ will spontaneously be transformed into Q in the presence of bases whose HOMO energies are higher than the SOMO energy of Q(+)˙ in a given medium, implying that Q cannot undergo the SET-PT mechanism in such an environment. In the reaction with the MeS anion in both gaseous and aqueous phases and the hydroxide anion in the gaseous phase Q(+)˙ accepts an electron from the base, and so-formed Q undergoes the hydrogen atom transfer mechanism. On the other hand, SET-PT is a plausible mechanism of Q in the presence of bases whose HOMO energies are lower than the SOMO energy of Q(+)˙ in a given medium. In such cases Q(+)˙ spontaneously donates a proton to the base, with energetic stabilization of the system. Our investigation showed that Q conforms to the SET-PT mechanism in the presence of methylamine, in both gaseous and aqueous phases, and in the presence of the hydroxide anion, in the aqueous solution.

  5. Proton Transfer of Guanine Radical Cations Studied by Time-Resolved Resonance Raman Spectroscopy Combined with Pulse Radiolysis.

    PubMed

    Choi, Jungkweon; Yang, Cheolhee; Fujitsuka, Mamoru; Tojo, Sachiko; Ihee, Hyocherl; Majima, Tetsuro

    2015-12-17

    The oxidation of guanine (G) is studied by using transient absorption and time-resolved resonance Raman spectroscopies combined with pulse radiolysis. The transient absorption spectral change demonstrates that the neutral radical of G (G(•)(-H(+))), generated by the deprotonation of G radical cation (G(•+)), is rapidly converted to other G radical species. The formation of this species shows the pH dependence, suggesting that it is the G radical cation (G(•+))' formed from the protonation at the N7 of G(•)(-H(+)). On one hand, most Raman bands of (G(•+))' are up-shifted relative to those of G, indicating the increase in the bonding order of pyrimidine (Pyr) and imidazole rings. The (G(•+))' exhibits the characteristic CO stretching mode at ∼1266 cm(-1) corresponding to a C-O single bond, indicating that the unpaired electron in (G(•+))' is localized on the oxygen of the Pyr ring. PMID:26632994

  6. Collision cross-sections of [C,H,O] cations and radical cations from aliphatic [C,H,O] compounds

    NASA Astrophysics Data System (ADS)

    van Houte, J. J.; van Thuijl, J.

    1994-05-01

    Over 260 collision cross-section [sigma]ot, expressed in »ngströms squared, have been determined for the studied ions at 20 and 70 eV by extrapolation of [sigma]t to zero target gas pressure, and these yield two types of structural information. The first type concerns occurrence and detection of cyclic ions, the second isomerization of parent molecular ions and different product ion distributions at 20 and 70 eV. In addition, examples of two distinct fragmentation mechanisms operative in the formation of identical daughter ions from a given precursor could be traced. Formation of cyclic daughter ions is, for instance, observed for C2H3O+ from oxirane, C3H5O+ from oxetane, C4H7O+2 from 4-methyl-1,3-dioxolane. Cyclic molecular ions are formed in varying proportions from oxirane, tetrahydrofuran, 2- and 4-methyl-1,3-dioxolane but not from porpylene oxide, oxetane and 1,3-dioxolane. Isomerization of the parent molecular ion is proposed for the following fragmentations: CH2 from allyl alcohol, CHO2+ from formic acid, C2H2O·+ from oxirane, and C3H6O·+ from 3-methyl butanal and 2-methyl pentanal. Different product ion distributions at 20 and 70 eV were found for C3H5O+ from ethyl propionate and 2-pentanone, C2H4O·+ and C4H8O·+ from butane-1,3-diol, and C3H6O·+ from 2- and 4-methyl-1,3-dioxolane. Two distinct fragmentation mechanisms were traced for the following processes: CH2OH, C2H2O·+ and C2H3O+ from methyl vinyl ether, CH2 and C2H5O+ from butane-1,3-diol and C2H2O·+ from butanone. Self protonation of acetaldehyde also appears to take place by two mechanisms. Energy partitioning is evident in the formation of formyl cations HCO+ but wears off for processes in which larger daughter ions are formed. For formyl cations from straight chain aldehydes, the 70 eV collision cross-section is linearly related to the logarithm of the reciprocal of the number of degrees of freedom in the parent molcule, log (1/DFp). One example of a proton-bound dimer is given, that of

  7. Non-photochemical Fluorescence Quenching in Photosystem II Antenna Complexes by the Reaction Center Cation Radical.

    PubMed

    Paschenko, V Z; Gorokhov, V V; Grishanova, N P; Korvatovskii, B N; Ivanov, M V; Maksimov, E G; Mamedov, M D

    2016-06-01

    efficiency for non-photochemical antenna fluorescence quenching by RC cation radical in comparison to that of photochemical quenching are discussed. PMID:27301286

  8. The loss of NH2O from the N-hydroxyacetamide radical cation CH3C(O)NHOH+

    NASA Astrophysics Data System (ADS)

    Jobst, Karl J.; Burgers, Peter C.; Ruttink, Paul J. A.; Terlouw, Johan K.

    2006-08-01

    A previous study [Ch. Lifshitz, P.J.A. Ruttink, G. Schaftenaar, J.K. Terlouw, Rapid Commun. Mass Spectrom. 1 (1987) 61] shows that metastable N-hydroxyacetamide ions CH3C(O)NHOH+ (HA-1) do not dissociate into CH3CO+ + NHOH by direct bond cleavage but rather yield CH3CO+ + NH2OE The tandem mass spectrometry based experiments of the present study on the isotopologue CH3C(O)NDOD+ reveal that the majority of the metastable ions lose the NH2O radical as NHDO rather than ND2O. A mechanistic analysis using the CBS-QB3 model chemistry shows that the molecular ions HA-1 rearrange into hydrogen-bridged radical cations [OCC(H2)H...N(H)OH]+ whose acetyl cation component then catalyses the transformation NHOH --> NH2O prior to dissociation. The high barrier for the unassisted 1,2-H shift in the free radical, 43 kcal mol-1, is reduced to a mere 7 kcal mol-1 for the catalysed transformation which can be viewed as a quid-pro-quo reaction involving two proton transfers.

  9. Solution-phase mechanistic study and solid-state structure of a tris(bipyridinium radical cation) inclusion complex.

    PubMed

    Fahrenbach, Albert C; Barnes, Jonathan C; Lanfranchi, Don Antoine; Li, Hao; Coskun, Ali; Gassensmith, Jeremiah J; Liu, Zhichang; Benítez, Diego; Trabolsi, Ali; Goddard, William A; Elhabiri, Mourad; Stoddart, J Fraser

    2012-02-15

    The ability of the diradical dicationic cyclobis(paraquat-p-phenylene) (CBPQT(2(•+))) ring to form inclusion complexes with 1,1'-dialkyl-4,4'-bipyridinium radical cationic (BIPY(•+)) guests has been investigated mechanistically and quantitatively. Two BIPY(•+) radical cations, methyl viologen (MV(•+)) and a dibutynyl derivative (V(•+)), were investigated as guests for the CBPQT(2(•+)) ring. Both guests form trisradical complexes, namely, CBPQT(2(•+))⊂MV(•+) and CBPQT(2(•+))⊂V(•+), respectively. The structural details of the CBPQT(2(•+))⊂MV(•+) complex, which were ascertained by single-crystal X-ray crystallography, reveal that MV(•+) is located inside the cavity of the ring in a centrosymmetric fashion: the 1:1 complexes pack in continuous radical cation stacks. A similar solid-state packing was observed in the case of CBPQT(2(•+)) by itself. Quantum mechanical calculations agree well with the superstructure revealed by X-ray crystallography for CBPQT(2(•+))⊂MV(•+) and further suggest an electronic asymmetry in the SOMO caused by radical-pairing interactions. The electronic asymmetry is maintained in solution. The thermodynamic stability of the CBPQT(2(•+))⊂MV(•+) complex was probed by both isothermal titration calorimetry (ITC) and UV/vis spectroscopy, leading to binding constants of (5.0 ± 0.6) × 10(4) M(-1) and (7.9 ± 5.5) × 10(4) M(-1), respectively. The kinetics of association and dissociation were determined by stopped-flow spectroscopy, yielding a k(f) and k(b) of (2.1 ± 0.3) × 10(6) M(-1) s(-1) and 250 ± 50 s(-1), respectively. The electrochemical mechanistic details were studied by variable scan rate cyclic voltammetry (CV), and the experimental data were compared digitally with simulated data, modeled on the proposed mechanism using the thermodynamic and kinetic parameters obtained from ITC, UV/vis, and stopped-flow spectroscopy. In particular, the electrochemical mechanism of association

  10. Photo-excitation of adenine cation radical [A•+] in the near UV-vis region produces sugar radicals in Adenosine and in its nucleotides

    PubMed Central

    Adhikary, Amitava; Khanduri, Deepti; Kumar, Anil; Sevilla, Michael D.

    2011-01-01

    In this study, we report the formation of ribose sugar radicals in high yields (85 – 100%) via photo-excitation of adenine cation radical (A•+) in Ado and its ribonucleotides. Photo-excitation of A•+ at low temperatures in homogenous aqueous glassy samples of Ado, 2′-AMP, 3′-AMP and 5′-AMP forms sugar radicals predominantly at C5′- and also at C3′-sites. The C5′• and C3′• sugar radicals were identified employing Ado deuterated at specific carbon sites: C1′, C2′, and at C5′. Phosphate substitution is found to deactivate sugar radical formation at the site of substitution. Thus, in 5′-AMP, C3′• is observed to be the main radical formed via photo-excitation at ca. 143 K whereas in 3′-AMP, C5′• is the only species found. These results were supported by results obtained employing 5′-AMP with specific deuteration at C5′-site (i.e., 5′,5′-D,D-5′-AMP). Moreover, contrary to the C5′• observed in 3′-dAMP, we find that C5′• in 3′-AMP shows a clear pH dependent conformational change as evidenced by a large increase in the C4′ β–hyperfine coupling on increasing the pH from 6 to 9. Calculations performed employing DFT (B3LYP/6-31G*) for C5′• in 3′-AMP show that the two conformations of C5′• result from strong hydrogen bond formation between the O5′-H and the 3′-phosphate dianion at higher pHs. Employing time-dependent density functional theory [TD-DFT, B3LYP/6-31G(d)] we show that in the excited state, the hole transfers to the sugar moiety and has significant hole localization at the C5′-site in a number of allowed transitions. This hole localization is proposed to lead to the formation of the neutral C5′-radical (C5′•) via deprotonation. PMID:19367991

  11. Time-resolved fluorescence-detected magnetic resonance and fluorescence studies of trialkylamines irradiated by pulse radiolysis in alkane solvents

    SciTech Connect

    Lefkowitz, S.M.; Trifunac, A.D.

    1984-01-05

    Time-resolved fluorescence-detected magnetic resonance (FDMR) studies of irradiated alkane solutions of trialkylamines and scintillators reveal the EPR spectra of the trialkylaminium radicals, formed by scavenging solvent radical cations. A qualitative kinetic analysis indicates that the growth of the triethylaminium radical (TEA/sup +/-) FDMR signal occurs on similar time scales in both n-hexane and cyclohexane, suggesting that, in cyclohexane, TEA/sup +/- is formed by scavenging the lower mobility ''trapped'' cyclohexane radical cations. Fluorescence results indicate that TEA quenches both scintillator fluorescence and total FDMR intensities to a greater extent than is expected from amine scavenging of solvent holes. TEA also exhibits an intense, relatively long-lived fluorescence which is apparently not produced by radical ion recombination or energy transfer. 6 figures

  12. Key Role of End-Capping Groups in Optoelectronic Properties of Poly-p-phenylene Cation Radicals

    PubMed Central

    2015-01-01

    Poly-p-phenylenes (PPs) are prototype systems for understanding the charge transport in π-conjugated polymers. In a combined computational and experimental study, we demonstrate that the smooth evolution of redox and optoelectronic properties of PP cation radicals toward the polymeric limit can be significantly altered by electron-donating iso-alkyl and iso-alkoxy end-capping groups. A multiparabolic model (MPM) developed and validated here rationalizes this unexpected effect by interplay of the two modes of hole stabilization: due to the framework of equivalent p-phenylene units and due to the electron-donating end-capping groups. A symmetric, bell-shaped hole in unsubstituted PPs becomes either slightly skewed and shifted toward an end of the molecule in iso-alkyl-capped PPs or highly deformed and concentrated on a terminal unit in PPs with strongly electron-donating iso-alkoxy capping groups. The MPM shows that the observed linear 1/n evolution of the PP cation radical properties toward the polymer limit originates from the hole stabilization due to the growing chain of p-phenylene units, while shifting of the hole toward electron-donating end-capping groups leads to early breakdown of these 1/n dependencies. These insights, along with the readily applicable and flexible multistate parabolic model, can guide studies of complex donor–spacer–acceptor systems and doped molecular wires to aid the design of the next generation materials for long-range charge transport and photovoltaic applications. PMID:25264475

  13. Enhancement of a Lewis acid-base interaction via solvation: ammonia molecules and the benzene radical cation.

    PubMed

    Chiang, Chi-Tung; Freindorf, Marek; Furlani, Thomas; DeLeon, Robert L; Richard, John P; Garvey, James F

    2007-07-12

    The interaction between ammonia and the benzene radical cation has been investigated by gas-phase studies of mass selected ion clusters {C(6)H(6)-(NH(3))(n=0-8)}(+) via tandem quadrupole mass spectrometry and through calculations. Experiments show a special stability for the cluster ion that contains four ammonias: {C(6)H(6)(NH(3))(4)}(+). Calculations provide evidence that the first ammonia forms a weak dative bond to the cyclohexadienyl radical cation, {C(6)H(6)-NH(3)}(+), where there is a transfer of electrons from ammonia to benzene. Additional solvating ammonia molecules form stabilizing hydrogen bonds to the ring-bound ammonia {C(6)H(6)-NH(3)}(+).(NH(3))(n), which cause cooperative changes in the structure of the cluster complex. Free ammonia is a weak hydrogen bond donor, but electron transfer from NH(3) to the benzene ring that strengthens the dative bond will increase the hydrogen acidity and the strength of the cluster hydrogen bonds to the added ammonia. A progressive "tightening" of this dative bond is observed upon addition of the first, second, and third ammonia to give a cluster stabilized by three N-(+)H x N hydrogen bonds. This shows that the energetic cost of tightening the dative bond is recovered with dividends in the formation of stable cluster hydrogen bonds.

  14. Electrochemical Behavior of meso-Substituted Porphyrins: The Role of Cation Radicals to the Half-Wave Oxidation Potential Splitting.

    PubMed

    Tran, Thai T H; Chang, Yan-Ru; Hoang, Tuan K A; Kuo, Ming-Yu; Su, Yuhlong O

    2016-07-21

    In this study, the electrochemical behavior of free base and zinc meso-substituted porphyrins is examined by cyclic voltammetry (CV) and density functional theory (DFT). The results show that the half-wave oxidation potential splitting of the two oxidation states (ΔE= second E1/2 - first E1/2) of tetraphenylporphyrin (H2TPP) and its zinc complex (ZnTPP) are higher than those of porphyrins and their zinc complexes with meso-substituted five-membered heterocylic rings. The ΔE values follow the trend of TPP > T(3'-thienyl)P > T(3'-furyl)P > T(2'-thienyl)P for both meso-porphyrins and their respective zinc complexes. By employing DFT calculations, we have found that the trend of ΔE values is consistent with that of highest spin density (HSD) distribution and HOMO-LUMO energy gaps of cationic radicals as well as the π-conjugation between central porphyrin and meso-substituted rings. Also, they exhibit the better resonance between the porphyrin ring with meso-substituted rings as moving from porphyrins and their zinc complexes with phenyl rings to five-membered heterocyclic rings. A good agreement between calculated and experimental results indicates that cationic radicals, especially their spin density distribution, do play an important role in half-wave oxidation potential splitting of meso-porphyrins and their zinc complexes. PMID:27379447

  15. Emergent functionality of nucleobase radical cations in duplex DNA: prediction of reactivity using qualitative potential energy landscapes.

    PubMed

    Joseph, Joshy; Schuster, Gary B

    2006-05-10

    The one-electron oxidation of a series of DNA oligonucleotides was examined. Each oligomer contains a covalently linked anthraquinone (AQ) group. Irradiation of the AQ group with near-UV light results in a one-electron oxidation of the DNA that generates a radical cation (electron "hole"). The radical cation migrates through the DNA by a hopping mechanism and is trapped by reaction with water or molecular oxygen, which results in chemical reaction at particular nucleobases. This reaction is revealed as strand cleavage when the irradiated oligonucleotide is treated with piperidine. The specific oligomers examined reveal the existence of three categories of nucleobase sequences: charge shuttles, charge traps, and barriers to charge migration. The characterization of a sequence is not independent of the identity of other sequences in the oligonucleotide, and for this reason, the function of a particular sequence emerges from an analysis of the entire structure. Qualitative potential energy landscapes are introduced as a tool to assist in the rationalization and prediction of the reactions of nucleobases in oxidized DNA. PMID:16669676

  16. Unconventional hydrogen bonding to organic ions in the gas phase: Stepwise association of hydrogen cyanide with the pyridine and pyrimidine radical cations and protonated pyridine

    SciTech Connect

    Hamid, Ahmed M.; El-Shall, M. Samy; Hilal, Rifaat; Elroby, Shaaban; Aziz, Saadullah G.

    2014-08-07

    Equilibrium thermochemical measurements using the ion mobility drift cell technique have been utilized to investigate the binding energies and entropy changes for the stepwise association of HCN molecules with the pyridine and pyrimidine radical cations forming the C{sub 5}H{sub 5}N{sup +·}(HCN){sub n} and C{sub 4}H{sub 4}N{sub 2}{sup +·}(HCN){sub n} clusters, respectively, with n = 1–4. For comparison, the binding of 1–4 HCN molecules to the protonated pyridine C{sub 5}H{sub 5}NH{sup +}(HCN){sub n} has also been investigated. The binding energies of HCN to the pyridine and pyrimidine radical cations are nearly equal (11.4 and 12.0 kcal/mol, respectively) but weaker than the HCN binding to the protonated pyridine (14.0 kcal/mol). The pyridine and pyrimidine radical cations form unconventional carbon-based ionic hydrogen bonds with HCN (CH{sup δ+}⋯NCH). Protonated pyridine forms a stronger ionic hydrogen bond with HCN (NH{sup +}⋯NCH) which can be extended to a linear chain with the clustering of additional HCN molecules (NH{sup +}⋯NCH··NCH⋯NCH) leading to a rapid decrease in the bond strength as the length of the chain increases. The lowest energy structures of the pyridine and pyrimidine radical cation clusters containing 3-4 HCN molecules show a strong tendency for the internal solvation of the radical cation by the HCN molecules where bifurcated structures involving multiple hydrogen bonding sites with the ring hydrogen atoms are formed. The unconventional H-bonds (CH{sup δ+}⋯NCH) formed between the pyridine or the pyrimidine radical cations and HCN molecules (11–12 kcal/mol) are stronger than the similar (CH{sup δ+}⋯NCH) bonds formed between the benzene radical cation and HCN molecules (9 kcal/mol) indicating that the CH{sup δ+} centers in the pyridine and pyrimidine radical cations have more effective charges than in the benzene radical cation.

  17. Electronic and vibrational spectra of matrix isolated anthracene radical cations - Experimental and theoretical aspects

    NASA Technical Reports Server (NTRS)

    Szczepanski, Jan; Vala, Martin; Talbi, Dahbia; Parisel, Olivier; Ellinger, Yves

    1993-01-01

    The IR vibrational and visible/UV electronic absorption spectra of the anthracene cation, An(+), were studied experimentally, in argon matrices at 12 K, as well as theoretically, using ab initio calculations for the vibrational modes and enhanced semiempirical methods with configuration interaction for the electronic spectra. It was found that both approaches predicted well the observed photoelectron spectrum. The theoretical IR intensities showed some remarkable differences between neutral and ionized species (for example, the CH in-plane bending modes and CC in-plane stretching vibrations were predicted to increase by several orders of magnitude upon ionization). Likewise, estimated experimental IR intensities showed a significant increase in the cation band intensities over the neutrals. The implication of these findings for the hypothesis that polycyclic aromatic hydrocarbon cations are responsible for the unidentified IR emission bands from interstellar space is discussed.

  18. Mechanistic Examination of Cβ–Cγ Bond Cleavages of Tryptophan Residues during Dissociations of Molecular Peptide Radical Cations

    SciTech Connect

    Song, Tao; Ma, Ching-Yung; Chu, Ivan K.; Siu, Chi-Kit; Laskin, Julia

    2013-02-14

    In this study, we used collision-induced dissociation (CID) to examine the gas-phase fragmentations of [GnW]•+ (n = 2-4) and [GXW]•+ (X = C, S, L, F, Y, Q) species. The Cβ–Cγ bond cleavage of a C-terminal decarboxylated tryptophan residue ([M - CO2]•+) can generate [M - CO2 - 116]+, [M - CO2 - 117]•+, and [1H-indole]•+ (m/z 117) species as possible product ions. Competition between the formation of [M - CO2 - 116]+ and [1H-indole]•+ systems implies the existence of a proton-bound dimer formed between the indole ring and peptide backbone. Formation of such a proton-bound dimer is facile via a protonation of the tryptophan γ-carbon atom as suggested by density functional theory (DFT) calculations. DFT calculations also suggested the initially formed ion 2--the decarboxylated species that is active against Cβ–Cγ bond cleavage -can efficiently isomerize to form a more-stable -radical isomer (ion 9) as supported by Rice-Ramsperger-Kassel-Marcus (RRKM) modeling. The Cβ–Cγ bond cleavage of a tryptophan residue also can occur directly from peptide radical cations containing a basic residue. CID of [WGnR]•+ (n = 1-3) radical cations consistently resulted in predominant formation of [M-116]+ product ions. It appears that the basic arginine residue tightly sequesters the proton and allows the charge-remote Cβ–Cγ bond cleavage to prevail over the charge-directed one. DFT calculations predicted the barrier for the former is 6.2 kcal mol -1 lower than that of the latter. Furthermore, the pathway involving a salt-bridge intermediate also was accessible during such a bond cleavage event.

  19. Stabilization of long-chain intermediates in solution. Tridecyl radicals and cations

    NASA Astrophysics Data System (ADS)

    Teodorović, Aleksandar V.; Badjuk, Dalibor M.; Stevanović, Nenad; Pavlović, Radoslav Z.

    2015-03-01

    Tetradecanoic acid was decarboxylated by means of lead(IV) acetate (LTA) under thermal (81 °C) and photolytic (r.t.) conditions in benzene solution. The mixture of products, obtained in thermal reaction, consists of esters (acetoxyalkanes and carboxylates), tridecenes, tridecane and phenyltridecane. Additionally, tetradecane and hexacosane, under photolytic conditions, were formed. The classes of products and their distribution might be explained by presence of intermediate 1-tridecyl radical which can undergo intramolecular (result in formation of rearranged carbon centered radicals) and intermolecular stabilization pathways. Experimentally obtained results were used as input data for computational Monte Carlo simulation study of the reaction. On the basis of these results, radical rearrangements, as well as hydride shifts in tridecyl system are discussed.

  20. Theoretical study of electronically excited radical cations of naphthalene and anthracene as archetypal models for astrophysical observations. Part I. Static aspects.

    PubMed

    Ghanta, S; Reddy, V Sivaranjana; Mahapatra, S

    2011-08-28

    Motivated by the recent discovery of new diffuse interstellar bands and results from laboratory experiments, ab initio quantum chemistry calculations are carried out for the lowest six electronic states of naphthalene and anthracene radical cations. The calculated adiabatic electronic energies are utilized to construct suitable diabatic electronic Hamiltonians in order to perform nuclear dynamics studies in Part II. Complex entanglement of the electronic states is established for both the radical cations and the coupling surfaces among them are also derived in accordance with the symmetry selection rules. Critical examination of the coupling parameters of the Hamiltonian suggests that 29 (out of 48) and 31 (out of 66) vibrational modes are relevant in the nuclear dynamics in the six lowest electronic states of naphthalene and anthracene radical cations, respectively. PMID:21750790

  1. Xe-bearing hydrocarbon ions: Observation of Xe.acetylene+rad and Xe.benzene+rad radical cations and calculations of their ground state structures

    NASA Astrophysics Data System (ADS)

    Cui, Zhong-hua; Attah, Isaac K.; Platt, Sean P.; Aziz, Saadullah G.; Kertesz, Miklos; El-Shall, M. S.

    2016-04-01

    This work reports evidence for novel types of Xe-bearing hydrocarbon radical cations. The Xe.acetylene+rad radical cation adduct is observed at nearly room temperature using the mass-selected drift cell technique. The irreversible addition of the Xe atom and the lack of back dissociation to HCCH+rad + Xe is consistent with the calculated binding energy of 0.85 eV to be contrasted with the metastable nature of the neutral Xe.acetylene adduct. The observed Xe.benzene+rad radical cation appears to be a weakly bound complex stabilized mainly by ion-induced dipole interaction consistent with a calculated binding energy in the range of 0.14-0.17 eV.

  2. Pentachlorophenol radical cations generated on Fe(III)-montmorillonite initiate octachlorodibenzo-p-dioxin formation in clays: DFT and FTIR studies

    PubMed Central

    Gu, Cheng; Liu, Cun; Johnston, Cliff T.; Teppen, Brian J.; Li, Hui; Boyd, Stephen A.

    2011-01-01

    Octachlorodibenzodioxin (OCDD) forms spontaneously from pentachlorophenol (PCP) on the surfaces of Fe(III)-saturated smectite clay (1). Here, we used in situ FTIR methods and quantum mechanical calculations to determine the mechanism by which this reaction is initiated. As the clay was dehydrated, vibrational spectra showed new peaks that grew and then reversibly disappeared as the clay rehydrated. First principle DFT calculations of hydrated Fe-PCP clusters reproduced these transient FTIR peaks when inner-sphere complexation and concomitant electron transfer produced Fe(II) and PCP radical cations. Thus, our experimental (FTIR) and theoretical (quantum mechanical) results mutually support the hypothesis that OCDD formation on Fe-smectite surfaces is initiated by the reversible formation of metastable PCP radical cations via single electron transfer from PCP to Fe(III). The negatively charged clay surface apparently selects for this reaction mechanism by stabilizing PCP radical cations. PMID:21254769

  3. Ne matrix spectra of the sym-C6Br3F3+ radical cation

    USGS Publications Warehouse

    Bondybey, V.E.; Sears, T.J.; Miller, T.A.; Vaughn, C.; English, J.H.; Shiley, R.S.

    1981-01-01

    The electronic absorption and laser excited, wavelength resolved fluorescence spectra of the title cation have been observed in solid Ne matrix and vibrationally analysed. The vibrational structure of the excited B2A2??? state shows close similarity to the parent compound. The X2E??? ground state structure is strongly perturbed and irregular owing to a large Jahn-Teller distortion. The data are analysed in terms of a recently developed, sophisticated multimode Jahn-Teller theoretical model. We have generated the sym-C6Br3F3+ cations in solid Ne matrix and obtained their wavelength resolved emission and absorption spectra. T ground electronic X2E??? state exhibits an irregular and strongly perturbed vibrational structure, which can be successfully modeled using sophisticated multimode Jahn-Teller theory. ?? 1981.

  4. Hydration of the pyrimidine radical cation and stepwise solvation of protonated pyrimidine with water, methanol, and acetonitrile.

    PubMed

    Hamid, Ahmed M; Sharma, Pramod; El-Shall, M Samy; Hilal, Rifaat; Elroby, Shaaban; Aziz, Saadullah G; Alyoubi, Abdulrahman O

    2013-08-28

    Equilibrium thermochemical measurements using an ion mobility drift cell technique have been utilized to investigate the binding energies and entropy changes associated with the stepwise hydration of the biologically significant ions pyrimidine radical cation and protonated pyrimidine. The binding energy of the hydrated pyrimidine radical cation is weaker than that of the proton-bound dimer pyrimidineH(+)(H2O) consistent with the formation of a weak carbon-based CH(δ+)··OH2 hydrogen bond (11.9 kcal/mol) and a stronger NH(+)··OH2 hydrogen bond (15.6 kcal/mol), respectively. Other proton-bound dimers such as pyrimidineH(+)(CH3OH) and pyrimidineH(+)(CH3CN) exhibit higher binding energies (18.2 kcal/mol and 22.8 kcal/mol, respectively) due to the higher proton affinities and dipole moments of acetonitrile and methanol as compared to water. The measured collisional cross sections of the proton-bound dimers provide experimental-based support for the DFT calculated structures at the M06-2x/6-311++G (d,p) level. The calculations show that the hydrated pyrimidine radical cation clusters form internally solvated structures in which the water molecules are bonded to the C4N2H4(●+) ion by weak CH(δ+)··OH2 hydrogen bonds. The hydrated protonated pyrimidine clusters form externally solvated structures where the water molecules are bonded to each other and the ion is external to the water cluster. Dissociative proton transfer reactions C4N2H4(●+)(H2O)(n-1) + H2O → C4N2H3(●) + (H2O)(n)H(+) and C4N2H5(+)(H2O)(n-1) + H2O → C4N2H4 + (H2O)(n)H(+) are observed for n ≥ 4 where the reactions become thermoneutral or exothermic. The absence of the dissociative proton transfer reaction within the C4N2H5(+)(CH3CN)n clusters results from the inability of acetonitrile molecules to form extended hydrogen bonding structures such as those formed by water and methanol due to the presence of the methyl groups which block the extension of hydrogen bonding networks.

  5. Theoretical study of the electronically excited radical cations of naphthalene and anthracene as archetypal models for astrophysical observations. Part II. Dynamics consequences.

    PubMed

    Ghanta, S; Reddy, V Sivaranjana; Mahapatra, S

    2011-08-28

    Nuclear dynamics is investigated theoretically from first principles by employing the ab initio vibronic models of the prototypical naphthalene and anthracene radical cations developed in Part I. This Part is primarily aimed at corroborating a large amount of available experimental data with a specific final goal to establish an unambiguous link with the current observations in astrophysics and astronomy. The detailed analyses presented here perhaps establish that these two prototypical polycyclic aromatic hydrocarbon radical cations are indeed potential carriers of the observed diffuse interstellar bands. PMID:21750791

  6. Role of configurational gating in intracomplex electron transfer from cytochrome c to the radical cation in cytochrome c peroxidase.

    PubMed

    Mei, H; Wang, K; Peffer, N; Weatherly, G; Cohen, D S; Miller, M; Pielak, G; Durham, B; Millett, F

    1999-05-25

    Electron transfer within complexes of cytochrome c (Cc) and cytochrome c peroxidase (CcP) was studied to determine whether the reactions are gated by fluctuations in configuration. Electron transfer in the physiological complex of yeast Cc (yCc) and CcP was studied using the Ru-39-Cc derivative, in which the H39C/C102T variant of yeast iso-1-cytochrome c is labeled at the single cysteine residue on the back surface with trisbipyridylruthenium(II). Laser excitation of the 1:1 Ru-39-Cc-CcP compound I complex at low ionic strength results in rapid electron transfer from RuII to heme c FeIII, followed by electron transfer from heme c FeII to the Trp-191 indolyl radical cation with a rate constant keta of 2 x 10(6) s-1 at 20 degrees C. keta is not changed by increasing the viscosity up to 40 cP with glycerol and is independent of temperature. These results suggest that this reaction is not gated by fluctuations in the configuration of the complex, but may represent the elementary electron transfer step. The value of keta is consistent with the efficient pathway for electron transfer in the crystalline yCc-CcP complex, which has a distance of 16 A between the edge of heme c and the Trp-191 indole [Pelletier, H., and Kraut, J. (1992) Science 258, 1748-1755]. Electron transfer in the complex of horse Cc (hCc) and CcP was examined using Ru-27-Cc, in which hCc is labeled with trisbipyridylruthenium(II) at Lys-27. Laser excitation of the Ru-27-Cc-CcP complex results in electron transfer from RuII to heme c FeII with a rate constant k1 of 2.3 x 10(7) s-1, followed by oxidation of the Trp-191 indole to a radical cation by RuIII with a rate constant k3 of 7 x 10(6) s-1. The cycle is completed by electron transfer from heme c FeII to the Trp-191 radical cation with a rate constant k4 of 6.1 x 10(4) s-1. The rate constant k4 decreases to 3.4 x 10(3) s-1 as the viscosity is increased to 84 cP, but the rate constants k1 and k3 remain the same. The results are consistent with a

  7. Role of configurational gating in intracomplex electron transfer from cytochrome c to the radical cation in cytochrome c peroxidase.

    PubMed

    Mei, H; Wang, K; Peffer, N; Weatherly, G; Cohen, D S; Miller, M; Pielak, G; Durham, B; Millett, F

    1999-05-25

    Electron transfer within complexes of cytochrome c (Cc) and cytochrome c peroxidase (CcP) was studied to determine whether the reactions are gated by fluctuations in configuration. Electron transfer in the physiological complex of yeast Cc (yCc) and CcP was studied using the Ru-39-Cc derivative, in which the H39C/C102T variant of yeast iso-1-cytochrome c is labeled at the single cysteine residue on the back surface with trisbipyridylruthenium(II). Laser excitation of the 1:1 Ru-39-Cc-CcP compound I complex at low ionic strength results in rapid electron transfer from RuII to heme c FeIII, followed by electron transfer from heme c FeII to the Trp-191 indolyl radical cation with a rate constant keta of 2 x 10(6) s-1 at 20 degrees C. keta is not changed by increasing the viscosity up to 40 cP with glycerol and is independent of temperature. These results suggest that this reaction is not gated by fluctuations in the configuration of the complex, but may represent the elementary electron transfer step. The value of keta is consistent with the efficient pathway for electron transfer in the crystalline yCc-CcP complex, which has a distance of 16 A between the edge of heme c and the Trp-191 indole [Pelletier, H., and Kraut, J. (1992) Science 258, 1748-1755]. Electron transfer in the complex of horse Cc (hCc) and CcP was examined using Ru-27-Cc, in which hCc is labeled with trisbipyridylruthenium(II) at Lys-27. Laser excitation of the Ru-27-Cc-CcP complex results in electron transfer from RuII to heme c FeII with a rate constant k1 of 2.3 x 10(7) s-1, followed by oxidation of the Trp-191 indole to a radical cation by RuIII with a rate constant k3 of 7 x 10(6) s-1. The cycle is completed by electron transfer from heme c FeII to the Trp-191 radical cation with a rate constant k4 of 6.1 x 10(4) s-1. The rate constant k4 decreases to 3.4 x 10(3) s-1 as the viscosity is increased to 84 cP, but the rate constants k1 and k3 remain the same. The results are consistent with a

  8. Formaldehyde mediated proton-transport catalysis in the ketene-water radical cation CH2C(O)OH2+

    NASA Astrophysics Data System (ADS)

    Lee, Richard; Ruttink, Paul J. A.; Burgers, Peter C.; Terlouw, Johan K.

    2006-09-01

    Previous studies have shown that the solitary ketene-water ion CH2C(O)OH2+ (1) does not isomerize into CH2C(OH)2+ (2), its more stable hydrogen shift isomer. Tandem mass spectrometry based collision experiments reveal that this isomerization does take place in the CH2O loss from low-energy 1,3-dihydroxyacetone ions (HOCH2)2CO+. A mechanistic analysis using the CBS-QB3 model chemistry shows that such molecular ions rearrange into hydrogen-bridged radical cations [CH2C(O)O(H)-H...OCH2]+ in which the CH2O molecule catalyzes the transformation 1 --> 2 prior to dissociation. The barrier for the unassisted reaction, 29 kcal mol-1, is reduced to a mere 0.6 kcal mol-1 for the catalysed transformation. Formaldehyde is an efficient catalyst because its proton affinity meets the criterion for facile proton-transport catalysis.

  9. Umbrella motion of the methyl cation, radical, and anion molecules. I. Potentials, energy levels and partition functions

    NASA Astrophysics Data System (ADS)

    Ragni, Mirco; Bitencourt, Ana Carla P.; Prudente, Frederico V.; Barreto, Patricia R. P.; Posati, Tamara

    2016-03-01

    A study of the umbrella motion of the methyl cation, radical, and anion molecules is presented. This is the floppiest mode of vibration of all three species and its characterization is of fundamental importance for understanding their reactivity. Minimum Energy Paths of the umbrella motions according to the hyperspherical treatment were obtained, by single point calculations, at the CCSD(T)/aug-cc-pVQT level of theory in the Born-Oppenheimer approximation. These energy profiles permit us to calculate the vibrational levels through the Hyperquantization algorithm, which is shown appropriated for the description of the umbrella motion of these three molecules. The adiabatic electron affinity and ionization potentials were estimated to good accuracy. Partition functions are also calculated in order to obtain information on the reaction rates involving these groups.

  10. Topological and spectroscopic study of three-electron bonded compounds as models of radical cations of methionine-containing dipeptides

    NASA Astrophysics Data System (ADS)

    Fourré, Isabelle; Bergès, Jacqueline; Braïda, Benoît; Houée-Levin, Chantal

    2008-12-01

    Small models of radical cations of methionine-containing dipeptides, which are stabilized by formation of two-centre three-electron (2c-3e) S∴X bonds (X = S, N and O), were investigated at the BH&HLYP/6-31G(d) level and by means of topological tools. The SX distance is not so important for stability but the relative orientation of both fragments is. The AIM and ELF topological analyses shows that the nature of the S∴X bond varies with X, from purely 2c-3e in S∴S + entities to electrostatic in S∴O + ones. The σSX → σSX∗ wavelengths, obtained at the TD-BH&HLYP/cc-pVTZ level, strongly depend on X and on conformation.

  11. Hg(2+) -induced in situ generated radical cation of (S)-BINOL-based polymer for highly enantioselective recognition of phenylalaninol.

    PubMed

    Jiao, Jiemin; Li, Fei; Zhang, Shuwei; Quan, Yiwu; Zheng, Wenhua; Cheng, Yixiang; Zhu, Chengjian

    2014-08-01

    Phenylalaninol enantiomers are one of the most important chiral compounds due to its presence in biologically active molecules and pharmaceutical products. In this paper, a novel chiral fluorescence polymer sensor incorporating (S)-BINOL and oligomeric aniline via a nucleophilic addition-elimination reaction is designed and synthesized. Polymer sensor exhibits "turn-off" fluorescence quenching response upon the addition of Hg(2+) , and "turn-on" moderate fluorescence enhancement behavior towards phenylalaninol enantiomers. Meanwhile, this kind of (S)-BINOL-based polymer sensor can exhibit highly selective enantioselective recognition response towards (L)-phenylalaninol upon the addition of Hg(2+) and the value of ef can reach as high as 5.4, which can be attributed to the formation of in situ generated radical cation arisen from oligomeric aniline moiety by Hg(2+) induction. PMID:25048009

  12. Efficient radical cation stabilization of PANI-ZnO and PANI-ZnO-GO composites and its optical activity

    NASA Astrophysics Data System (ADS)

    Mathavan, T.; Divya, A.; Archana, J.; Ramasubbu, A.; Benial, A. Milton Franklin; Jothirajan, M. A.

    2016-05-01

    Polyaniline (PANI) and its composites PANI-ZnO (Zinc oxide) and PANI-ZnO-GO (Graphene oxide) were successfully constructed. These materials were characterized by electron spin resonance (ESR) technique and ultraviolet visible spectrometry. The parameters such as line width, g-factor and spin concentration were deduced from ESR spectra, from the results the radical cation stabilization of PANI, PANI-ZnO and PANI-ZnO-GO composites were compared by the polaron and bipolaron formation. The absorption features obtained in the UV absorption spectra reveal the band gap of these modified PANI composites and also predicted the information of increasing and decreasing features of signal intensity and spin concentration.

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

    PubMed

    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.

  14. Fluorescence of the perylene radical cation and an inaccessible D0/D1 conical intersection: An MMVB, RASSCF, and TD-DFT computational study

    NASA Astrophysics Data System (ADS)

    Tokmachev, Andrei M.; Boggio-Pasqua, Martial; Mendive-Tapia, David; Bearpark, Michael J.; Robb, Michael A.

    2010-01-01

    The photophysics of the perylene radical cation (Pe•+) was studied using the molecular mechanics-valence bond (MMVB) hybrid force field. Potential energy surfaces of the first three electronic states were investigated. Geometry optimizations of critical points—including conical intersections between the relevant electronic states—were performed using the MMVB analytical energy gradient for cations. No accessible planar conical intersection between the D0 and D1 states of Pe•+ was found; this is consistent with the experimentally observed D1 lifetimes and the observation of D1 emission from this cation in the condensed phase. Benchmark RASSCF and TD-DFT calculations support the reliability of the MMVB results.

  15. Water-catalyzed hydrolysis of the radical cation of ketene in the gas phase: theory and experiment.

    PubMed

    Orlova, Galina; Blagojevic, Voislav; Bohme, Diethard K

    2006-07-13

    Both theoretical and experimental investigations are reported for the gas-phase hydrolysis of the radical cation of ketene, H(2)CCO(*+). Density functional theory (DFT) with the B3LYP/6-311++G(d,p) method indicates that a second water molecule is required as a catalyst for the addition of water across the C=O bond in H(2)CCO(*+) by eliminating the activation barrier for the conversion of [H(2)CCO.H(2)O](*+) to [H(2)CC(OH)(2)](*+). Theory further indicates that [H(2)CC(OH)(2).H(2)O](*+) may recombine with electrons to produce neutral acetic acid. Experimental results of flow-reactor tandem mass spectrometer experiments in which CH(2)CO(*+) ions were produced either directly from ketene by electron transfer or by the chemical reaction of CH(2)(*+) with CO are consistent with formation of an (C(2),H(4),O(2))(*+) ion in a reaction second-order in H(2)O. Furthermore, comparative multi-CID experiments indicate that this ion is likely to be the enolic CH(2)C(OH)(2)(*+) cation. The results suggest a possible mechanism for the formation of acetic acid from ketene and water on icy surfaces in hot cores and interstellar clouds.

  16. A 1,2,3-dithiazolyl-o-naphthoquinone: a neutral radical with isolable cation and anion oxidation states.

    PubMed

    Smithson, Chad S; MacDonald, Daniel J; Matt Letvenuk, T; Carello, Christian E; Jennings, Michael; Lough, Alan J; Britten, James; Decken, Andreas; Preuss, Kathryn E

    2016-06-21

    Under aprotic conditions, the reaction of 4-amino-1,2-naphthoquinone with excess S2Cl2 generates 4,5-dioxo-naphtho[1,2-d][1,2,3]dithiazol-2-ium chloride in a typical Herz condensation. By contrast, prior literature reports an imine (NH) product, 4,5-dioxo-1H-naphtho[1,2-d][1,2,3]dithiazole, for the same reaction performed in acetic acid. Herein, the cation product is isolated with four different counter-anions (Cl(-), GaCl4(-), FeCl4(-) and OTf(-)). Reduction of the cation generates a neutral radical 1,2,3-dithiazolyl-o-naphthoquinone, with potential ligand properties. Further reduction generates a closed shell anion, isolated as a water-stable Li(+) complex and exhibiting O,O-bidentate chelation. The hydroxy (OH) isomer of the original imine (NH) product is reported, and this can be readily deprotonated and acylated (OAc). All species are structurally characterized. Solution redox behaviour and EPR are discussed where appropriate. PMID:27216412

  17. Fragmentation Chemistry of [Met-Gly]•+, [Gly-Met]•+, and [Met-Met]•+ Radical Cations

    NASA Astrophysics Data System (ADS)

    Lau, Justin Kai-Chi; Lo, Seydina; Zhao, Junfang; Siu, K. W. Michael; Hopkinson, Alan C.

    2013-04-01

    Radical cations [Met-Gly]•+, [Gly-Met]•+, and [Met-Met]•+ have been generated through collision-induced dissociation (CID) of [CuII(CH3CN)2(peptide)]•2+ complexes. Their fragmentation patterns and dissociation mechanisms have been studied both experimentally and theoretically using density functional theory at the UB3LYP/6-311++G(d,p) level. The captodative structure, in which the radical is located at the α-carbon of the N-terminal residue and the proton is on the amide oxygen, is the lowest energy structure on each potential energy surface. The canonical structure, with the charge and spin both located on the sulfur, and the distonic ion with the proton on the terminal amino group, and the radical on the α-carbon of the C-terminal residue have similar energies. Interconversion between the canonical structures and the captodative isomers is facile and occurs prior to fragmentation. However, isomerization to produce the distonic structure is energetically less favorable and cannot compete with dissociation except in the case of [Gly-Met]•+. Charge-driven dissociations result in formation of [ b n - H]•+ and a 1 ions. Radical-driven dissociation leads to the loss of the side chain of methionine as CH3-S-CH = CH2 producing α-glycyl radicals from both [Gly-Met]•+ and [Met-Met]•+. For [Met-Met]•+, loss of the side chain occurs at the C-terminal as shown by both labeling experiments and computations. The product, the distonic ion of [Met-Gly]•+, NH3 +CH(CH2CH2SCH3)CONHCH•COOH dissociates by loss of CH3S•. The isomeric distonic ion NH3 +CH2CONHC•(CH2CH2SCH3)COOH is accessible directly from the canonical [Gly-Met]•+ ion. A fragmentation pathway that characterizes this ion (and the distonic ion of [Met-Met]•+) is homolytic fission of the Cβ-Cγ bond to lose CH3SCH2 •.

  18. On the dissociation of the naphthalene radical cation: new iPEPICO and tandem mass spectrometry results.

    PubMed

    West, Brandi; Joblin, Christine; Blanchet, Valerie; Bodi, Andras; Sztáray, Bálint; Mayer, Paul M

    2012-11-15

    The dissociation of the naphthalene radical cation has been reinvestigated here by a combination of tandem mass spectrometry and imaging photoelectron photoion coincidence spectroscopy (iPEPICO). Six reactions were explored: (R1) C(10)H(8)(•+) → C(10)H(7)(+) + H (m/z = 127); (R2) C(10)H(8)(•+) → C(8)H(6)(•+) + C(2)H(2) (m/z = 102); (R3) C(10)H(8)(•+) → C(6)H(6)(•+) + C(4)H(2) (m/z = 78); (R4) C(10)H(8)(•+) → C(10)H(6)(•+) + H(2) (m/z = 126); (R5) C(10)H(7)(+) → C(6)H(5)(+) + C(4)H(2) (m/z = 77); (R6) C(10)H(7)(+) → C(10)H(6)(•+) + H (m/z = 126). The E(0) activation energies for the reactions deduced from the present measurements are (in eV) 4.20 ± 0.04 (R1), 4.12 ± 0.05 (R2), 4.27 ± 0.07 (R3), 4.72 ± 0.06 (R4), 3.69 ± 0.26 (R5), and 3.20 ± 0.13 (R6). The corresponding entropies of activation, ΔS(‡)(1000K), derived in the present study are (in J K(-1) mol(-1)) 2 ± 2 (R1), 0 ± 2 (R2), 4 ± 4 (R3), 11 ± 4 (R4), 5 ± 15 (R5), and -19 ± 11 (R6). The derived E(0) value, combined with the previously reported IE of naphthalene (8.1442 eV) results in an enthalpy of formation for the naphthyl cation, Δ(f)H°(0K) = 1148 ± 14 kJ mol(-1)/Δ(f)H°(298K) = 1123 ± 14 kJ mol(-1) (site of dehydrogenation unspecified), slightly lower than the previous estimate by Gotkis and co-workers. The derived E(0) for the second H-loss leads to a Δ(f)H° for ion 7, the cycloprop[a]indene radical cation, of Δ(f)H°(0K) =1457 ± 27 kJ mol(-1)/Δ(f)H°(298K)(C(10)H(6)(+)) = 1432 ± 27 kJ mol(-1). Detailed comparisons are provided with values (experimental and theoretical) available in the literature. PMID:23088182

  19. Observation of the cation radicals of pyrrole and of some substituted pyrroles in fast-scan cyclic voltammetry. Standard potentials and lifetimes

    SciTech Connect

    Andrieux, C.P.; Audebert, P.; Hapiot, P.; Saveant, J. )

    1990-03-14

    Polypyrroles and polysubstituted pyrroles have attracted considerable and increasing attention over the past 10 years in view of their remarkable conducting and electrocatalytic properties. Oxidative electropolymerization of pyrrolic monomers is a convenient and attractive route to polypyrrole electrode coatings and free-standing films. Although valuable information has been gained about the nucleation processes following the initial generation of dimeric and polymeric species, the mechanism by which these dimers are formed has not been ascertained. Likewise, the standard potentials at which the cation radicals are formed as well as their lifetimes are not known. The reason for this lack of information concerning the reactivity of the electrochemically generated pyrrole cation radical is that the measurement times employed in the experimental studies carried out by potential-step and cyclic voltammetric techniques were too long to allow the observation of the cation radical by means of its rereduction current. In the present preliminary report, they show that it is possible to overcome these difficulties by use of recently developed ultramicroelectrode techniques and thus to observe the pyrrolic cation radicals through their rereduction wave in fast-scan cyclic voltammetry.

  20. Chronoamperometric study of the films formed by 4,4'-bipyridyl cation radical salts on mercury in the presence of iodide ions: consecutive two-dimensional phase transitions.

    PubMed

    Gómez, L; Ruiz, J J; Camacho, L; Rodríguez-Amaro, R

    2005-01-01

    This paper reports a new mathematical model for consecutive two-dimensional phase transitions that accounts for the chronoamperometric behavior observed in the formation of electrochemical phases by 4,4'-bipyridyl cation radical (BpyH(2)(*)(+)) on mercury in aqueous iodide solutions. Also, a new interpretation for the induction time is proposed. PMID:15620326

  1. Chronoamperometric study of the films formed by 4,4'-bipyridyl cation radical salts on mercury in the presence of iodide ions: consecutive two-dimensional phase transitions.

    PubMed

    Gómez, L; Ruiz, J J; Camacho, L; Rodríguez-Amaro, R

    2005-01-01

    This paper reports a new mathematical model for consecutive two-dimensional phase transitions that accounts for the chronoamperometric behavior observed in the formation of electrochemical phases by 4,4'-bipyridyl cation radical (BpyH(2)(*)(+)) on mercury in aqueous iodide solutions. Also, a new interpretation for the induction time is proposed.

  2. 15N electron nuclear double resonance of the primary donor cation radical P+.865 in reaction centers of Rhodopseudomonas sphaeroides: additional evidence for the dimer model.

    PubMed Central

    Lubitz, W; Isaacson, R A; Abresch, E C; Feher, G

    1984-01-01

    Four 15N hyperfine coupling constants, including signs, have been measured by electron nuclear double resonance (ENDOR) and electron nuclear nuclear triple resonance (TRIPLE) for the bacteriochlorophyll a radical cation, BChla+., in vitro and for the light-induced primary donor radical cation, P+.865, in reaction centers of Rhodopseudomonas sphaeroides R-26. A comparison of the data shows that the hyperfine coupling constants have the same sign in both radicals and are, on the average, smaller by a factor of 2 in P+.865. These results provide additional evidence that P+.865 is a bacteriochlorophyll dimer and are in contradiction with the monomer structure of P+.865 recently proposed by O'Malley and Babcock. The reduction factors of the individual 15N couplings, together with the evidence from proton ENDOR data and molecular orbital calculations, indicate a dimer structure in which only two rings (either I and I or III and III) of the bacteriochlorophyll macrocycles overlap. PMID:6096857

  3. Where Does the Electron Go? Stable and Metastable Peptide Cation Radicals Formed by Electron Transfer

    NASA Astrophysics Data System (ADS)

    Pepin, Robert; Layton, Erik D.; Liu, Yang; Afonso, Carlos; Tureček, František

    2016-10-01

    Electron transfer to doubly and triply charged heptapeptide ions containing polar residues Arg, Lys, and Asp in combination with nonpolar Gly, Ala, and Pro or Leu generates stable and metastable charge-reduced ions, (M + 2H)+●, in addition to standard electron-transfer dissociation (ETD) fragment ions. The metastable (M + 2H)+● ions spontaneously dissociate upon resonant ejection from the linear ion trap, giving irregularly shaped peaks with offset m/z values. The fractions of stable and metastable (M + 2H)+● ions and their mass shifts depend on the presence of Pro-4 and Leu-4 residues in the peptides, with the Pro-4 sequences giving larger fractions of the stable ions while showing smaller mass shifts for the metastables. Conversion of the Asp and C-terminal carboxyl groups to methyl esters further lowers the charge-reduced ion stability. Collisional activation and photodissociation at 355 nm of mass-selected (M + 2H)+● results in different dissociations that give sequence specific MS3 spectra. With a single exception of charge-reduced (LKGLADR + 2H)+●, the MS3 spectra do not produce ETD sequence fragments of the c and z type. Hence, these (M + 2H)+● ions are covalent radicals, not ion-molecule complexes, undergoing dramatically different dissociations in the ground and excited electronic states. The increased stability of the Pro-4 containing (M + 2H)+● ions is attributed to radicals formed by opening of the Pro ring and undergoing further stabilization by hydrogen atom migrations. UV-VIS photodissociation action spectroscopy and time-dependent density functional theory calculations are used in a case in point study of the stable (LKGPADR + 2H)+● ion produced by ETD. In contrast to singly-reduced peptide ions, doubly reduced (M + 3H)+ ions are stable only when formed from the Pro-4 precursors and show all characteristics of even electron ions regarding no photon absorption at 355 nm or ion-molecule reactions, and exhibiting proton driven collision

  4. Analysis of diarylmethylamine compounds using electrospray mass spectrometry: formation mechanisms of radical ions and dehydro cations.

    PubMed

    Cai, Tian; Xu, Xiao-Ying; Wu, Zhi-Jun

    2015-12-01

    A series of diarylmethylamine compounds were analyzed using electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). [M](+)˙ and [M - H](+) were both observed, but showed different abundances. A possible mechanism for the formation of [M](+)˙ and [M - H](+) was proposed to explicate the rule for the ratio change of I([M](+)˙)/I([M-H](+)). The [M](+)˙ has two structures, which can interconvert into each other in the gas phase. The substituted groups on the benzene rings play a crucial role in the transfer between the two structures. Electron withdrawing groups can prevent the formation of carbocations, thus nitro-containing diarylmethylamines remained mainly as structure I and were detected as [M](+)˙. On the contrary, electron donating groups help to stabilize carbocations. This makes structure I transfer to structure II, and structure II prefers to further generate [M - H](+) by loss of an H radical. Nuclear magnetic resonance and D-labelled MS experiments indicate that the 1-C-H bond has strong activity.

  5. Incorporation of anthracene into zeolites: confinement effect on the recombination rate of photoinduced radical cation-electron pair.

    PubMed

    Marquis, Séverine; Moissette, Alain; Brémard, Claude

    2006-07-17

    FT-Raman spectrometry in combination with diffuse reflectance UV/Vis absorption (DRUVv) and fluorescence emission indicate that complete anthracene (ANT) sorption as intact molecules takes place over 6 months in the medium pores of non-Brønsted acidic M(n)ZSM-5 zeolites (n=0.0, 3.4, 6.6; M=Na+, K+, Rb+, Cs+) with 1 ANT per unit cell loading. The combined effect of confinement and electrostatic field induced by bulky cations (Rb+, Cs+) leads to specific changes in the occluded ANT Raman spectra after very long organization periods (one year). The laser photolysis (266 nm, 355 nm) of ANT@M(n)ZSM-5 equilibrated samples generates long-lived charge separated species in aluminum rich zeolites (n=3.4, 6.6). The very long-lived radical pairs are characterized by conventional DRUVv and CW-EPR spectroscopy. The direct charge recombination rates of ANT.+-electron pairs are dispersive, extending over a broad range of timescales. The kinetic constant values are found to increase dramatically with the aluminum content and increase markedly with M+ according to the following order Na+ < K+ < Rb+ < Cs+. The small reorganization energy (lambda) of ZSM-5 zeolite pores coupled with large negative free energy changes (-DeltaG degrees ) between the ground state ANT oxidation potential and Fermi level of aluminum rich M(n)ZSM-5 explain the observed trends of the ANT.+@M(n)ZSM-5.- charge recombination rates.

  6. Long-lived radical cation-electron pairs generated by anthracene sorption in non Brønsted acidic zeolites.

    PubMed

    Marquis, Séverine; Moissette, Alain; Vezin, Hervé; Brémard, Claude

    2005-03-10

    The sorption of anthracene (ANT) in non Brønsted acidic ZSM-5 zeolite through the mere exposure at room temperature of solid ANT and dehydrated zeolite crystals with Li(3.4)(AlO2)n(SiO2)(96-n) chemical formulas per unit cell generates spontaneous ionization of ANT (IP 7.44 eV in the gas phase). In contrast, ANT was found to be sorbed as an intact molecule in M(3.4)ZSM-5 with M = Na+, K+, Rb+, and Cs+. The radical cation (ANT*+) of the long-lived ANT*+@Li(3.4)ZSM-5*- pair was characterized by conventional diffuse reflectance UV-visible and resonance Raman spectrometry. In contrast, the X-band continuous wave (CW) EPR signal was found to be typical of a weakly coupled spin correlated ion pair. The two-dimension hyperfine sublevel correlation (2D-HYSCORE) spectra provide a detailed description of the microenvironment of the trapped electron of the ANT*+@Li(n)ZSM-5*- pair. The trapped electron appears localized in close proximity of occluded ANT*+, Li+, and the Si-O-Al nearest group of the zeolite framework.

  7. Dimerization of the octaethylporphyrin {pi} cation radical complex of cobalt(II): Thermodynamic, kinetic, and spectroscopic studies

    SciTech Connect

    Ni, Y.; Lee, S.; Wayland, B.B.

    1999-08-23

    One electron oxidation of cobalt(II) can occur from either the cobalt d or porphyrin {pi} orbitals depending on the choice of porphyrin and reaction media. Oxidation of (octaethylporphyrinato)cobalt(II), (OEP)Co{sup II} (1), in the presence of ligands such as H{sub 2}O and CO produces diamagnetic five and six coordinate complexes of cobalt(III). In the absence of additional ligands to coordinate with Co(III) the first oxidation of [(OEP)Co{sup II}]{sup +} (2). Metalloporphyrin {pi} cation radical complexes and dimers of the OEP derivatives have been extensively investigated. This article reports on the interconversion of the paramagnetic (S = 1) monomer, [(OEP)Co{sup II}]{sup +} (2), with a diamagnetic dimer, [(OEP)-Co{sup II}]{sub 2}{sup 2+} (3), in dichloromethane solvant. {sup 1}H NMR shift and line width studies in CD{sub 2}Cl{sub 2} are applied in evaluating the thermodynamic and activation parameters for homolytic dissociation of the diamagnetic dimer (3).

  8. 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.

    PubMed

    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.

  9. 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.

    PubMed

    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. PMID:26444498

  10. Generation of Trityl Radicals by Nucleophilic Quenching of Tris(2,3,5,6-tetrathiaaryl)methyl Cations and Practical and Convenient Large-Scale Synthesis of Persistent Tris(4-carboxy-2,3,5,6-tetrathiaaryl)methyl Radical

    PubMed Central

    Rogozhnikova, Olga Yu.; Vasiliev, Vladimir G.; Troitskaya, Tatiana I.; Trukhin, Dmitry V.; Mikhalina, Tatiana V.; Halpern, Howard J.; Tormyshev, Victor M.

    2014-01-01

    Tris(2,3,5,6-tetrathiaaryl)methyl cations, which were generated from the corresponding triarylmethanols in the presence of strong acids, underwent reaction with nucleophiles to give trityl radicals, as the product of a one-electron reduction of the carbocation. Depending on the nature of the nucleophile, the only byproducts were either diamagnetic quinone methides or asymmetrical monosubstituted trityl radicals. Herein, we report a protocol for the large-scale synthesis of the Finland trityl, which has the advantage of high overall yield and reproducibility. PMID:24772001

  11. Radical cation of star-shaped condensed oligofluorenes having isotruxene as a core: importance of rigid planar structure on charge delocalization.

    PubMed

    Fujitsuka, Mamoru; Cho, Dae Won; Tojo, Sachiko; Choi, Jungkweon; Huang, Hsin-Hau; Yang, Jye-Shane; Majima, Tetsuro

    2014-03-27

    Because of their excellent optical and electronic properties, oligofluorenes and polyfluorenes have been investigated for years. Recently developed star-shaped oligomers bearing a truxene or isotruxene core are interesting two-dimensional oligomers. Since employment of a condensed ring system will be effective in further extension of π-conjugation system, we studied electronic and vibrational properties of radical cation of CITFn, star-shaped condensed oligomer with isotruxene core and fluorene unit, by means of the radiation chemical methods. Absorption spectra of radical cation of CITFn were measured in the wide spectral range, which revealed extended π-conjugation of CITFn. Furthermore, time-resolved resonance Raman spectra during pulse radiolysis revealed that the oxidation of CITFn induced structural change to enhance quinoidal character. The Raman data and theoretical calculation indicated that the rigid framework of the present star-shaped oligomer which makes the oligomer a planar structure is quite important in extension of the conjugation pathway.

  12. Communication: Ion mobility of the radical cation dimers: (Naphthalene)2+• and naphthalene+•-benzene: Evidence for stacked sandwich and T-shape structures

    NASA Astrophysics Data System (ADS)

    Platt, Sean P.; Attah, Isaac K.; Aziz, Saadullah; El-Shall, M. Samy

    2015-05-01

    Dimer radical cations of aromatic and polycyclic aromatic molecules are good model systems for a fundamental understanding of photoconductivity and ferromagnetism in organic materials which depend on the degree of charge delocalization. The structures of the dimer radical cations are difficult to determine theoretically since the potential energy surface is often very flat with multiple shallow minima representing two major classes of isomers adopting the stacked parallel or the T-shape structure. We present experimental results, based on mass-selected ion mobility measurements, on the gas phase structures of the naphthalene+ṡ ṡ naphthalene homodimer and the naphthalene+ṡ ṡ benzene heterodimer radical cations at different temperatures. Ion mobility studies reveal a persistence of the stacked parallel structure of the naphthalene+ṡ ṡ naphthalene homodimer in the temperature range 230-300 K. On the other hand, the results reveal that the naphthalene+ṡ ṡ benzene heterodimer is able to exhibit both the stacked parallel and T-shape structural isomers depending on the experimental conditions. Exploitation of the unique structural motifs among charged homo- and heteroaromatic-aromatic interactions may lead to new opportunities for molecular design and recognition involving charged aromatic systems.

  13. Photostability via sloped conical intersections: a computational study of the excited states of the naphthalene radical cation.

    PubMed

    Hall, Katherine F; Boggio-Pasqua, Martial; Bearpark, Michael J; Robb, Michael A

    2006-12-21

    On the basis of an extensive ab initio electronic structure study of the ground and excited-state potential energy surfaces of the naphthalene radical cation (N*+), we propose a mechanism for its ultrafast nonradiative relaxation from the second excited state (D2) down to the ground state (D0), which could explain the experimentally observed photostability [Zhao, L.; Lian, R.; Shkrob I. A.; Crowell, R. A.; Pommeret, S.; Chronister, E. L.; Liu, A. D.; Trifunac, A. D. J. Phys. Chem. A., 2004, 108, 25]. The proposed photophysical relaxation pathway involves internal conversion from the D2 state down to the D0 state via two consecutive, accessible, sloped conical intersections (CIs). The two crossings, D0/D1 and D1/D2, are characterized at the complete active space self-consistent field (CASSCF) level. At this level of theory, the D0/D1 crossing is energetically readily accessible, while the D1/D2 CI appears too high in energy to be involved in internal conversion. However, the inclusion of dynamic correlation effects, via single point CASPT2 calculations including excitations out of the valence pi- and sigma-orbitals, lowers the D0 and D2 state energies with respect to D1. Extrapolations at the CASPT2 level predict that the D1/D2 crossing is then significantly lower in energy than with CASSCF indicating that with a higher-level treatment of dynamic correlation it may be energetically accessible following vertical excitation to D2. N*+ is proposed as one of the species contributing to a series of diffuse infrared absorption bands originating from interstellar clouds. Understanding the mechanism for photostability in the gas phase, therefore, has important consequences for astrophysics.

  14. Electronic Characterization of Reaction Intermediates: The Fluorenylium, Phenalenylium, and Benz[f]indenylium Cations and Their Radicals.

    PubMed

    Fulara, Jan; Chakraborty, Arghya; Maier, John P

    2016-03-01

    Three vibrationally resolved absorption systems commencing at 538, 518, and 392 nm were detected in a 6 K neon matrix after mass-selected deposition of C13 H9 (+) ions (m/z=165) produced from fluorene in a hot-cathode discharge ion source. The benz[f]indenylium (BfI(+) : 538 nm), fluorenylium (FL9(+) : 518 nm), and phenalenylium (PHL(+) : 392 nm) cations are the absorbing molecules. Two electronic systems corresponding to neutral species are apparent at 490 and 546 nm after irradiation of the matrix with λ<260 nm photons and were assigned to the FL9 and BfI radicals, respectively. The strongest peak at 518 nm is the origin of the 2 (1) B2 ←X̃ (1) A1 absorption of FL9(+) , and the 490 nm band is the 2 (2) A2 ←X̃ (2) B1 origin of FL9. The electronic systems commencing at 538 nm and 546 nm were assigned to the 1 (1) A1 ←X̃ (1) A1 and 1 (2) A2 ←X̃ (2) A2 transitions of BfI(+) and BfI. The 392 nm band is the 1 (1) E'←X̃ (1) A1 ' transition of PHL(+). The electronic spectra of C13 H9 (+) /C13 H9 were assigned on the basis of the vertical excitation energies calculated with SAC-CI and MS-CASPT2 methods. PMID:26845059

  15. Alkyl nitrate formation from the reactions of C8-C14 n-alkanes with OH radicals in the presence of NO(x): measured yields with essential corrections for gas-wall partitioning.

    PubMed

    Yeh, Geoffrey K; Ziemann, Paul J

    2014-09-18

    In this study, C8-C14 n-alkanes were reacted with OH radicals in the presence of NO(x) in a Teflon film environmental chamber and isomer-specific yields of alkyl nitrates were determined using gas chromatography. Because results indicated significant losses of alkyl nitrates to chamber walls, gas-wall partitioning was investigated by monitoring the concentrations of a suite of synthesized alkyl nitrates added to the chamber. Gas-to-wall partitioning increased with increasing carbon number and with proximity of the nitrooxy group to the terminal carbon, with losses as high as 86%. The results were used to develop a structure-activity model to predict the effects of carbon number and isomer structure on gas-wall partitioning, which was used to correct the measured yields of alkyl nitrate isomers formed in chamber reactions. The resulting branching ratios for formation of secondary alkyl nitrates were similar for all isomers of a particular carbon number, and average values, which were almost identical to alkyl nitrate yields, were 0.219, 0.206, 0.254, 0.291, and 0.315 for reactions of n-octane, n-decane, n-dodecane, n-tridecane, and n-tetradecane, respectively. The increase in average branching ratios and alkyl nitrate yields with increasing carbon number to a plateau value of ∼0.30 at about C13-C14 is consistent with predictions of a previously developed model, indicating that the model is valid for alkane carbon numbers ≥C3.

  16. Alkyl nitrate formation from the reactions of C8-C14 n-alkanes with OH radicals in the presence of NO(x): measured yields with essential corrections for gas-wall partitioning.

    PubMed

    Yeh, Geoffrey K; Ziemann, Paul J

    2014-09-18

    In this study, C8-C14 n-alkanes were reacted with OH radicals in the presence of NO(x) in a Teflon film environmental chamber and isomer-specific yields of alkyl nitrates were determined using gas chromatography. Because results indicated significant losses of alkyl nitrates to chamber walls, gas-wall partitioning was investigated by monitoring the concentrations of a suite of synthesized alkyl nitrates added to the chamber. Gas-to-wall partitioning increased with increasing carbon number and with proximity of the nitrooxy group to the terminal carbon, with losses as high as 86%. The results were used to develop a structure-activity model to predict the effects of carbon number and isomer structure on gas-wall partitioning, which was used to correct the measured yields of alkyl nitrate isomers formed in chamber reactions. The resulting branching ratios for formation of secondary alkyl nitrates were similar for all isomers of a particular carbon number, and average values, which were almost identical to alkyl nitrate yields, were 0.219, 0.206, 0.254, 0.291, and 0.315 for reactions of n-octane, n-decane, n-dodecane, n-tridecane, and n-tetradecane, respectively. The increase in average branching ratios and alkyl nitrate yields with increasing carbon number to a plateau value of ∼0.30 at about C13-C14 is consistent with predictions of a previously developed model, indicating that the model is valid for alkane carbon numbers ≥C3. PMID:24654572

  17. Where does the electron go? Electron distribution and reactivity of peptide cation radicals formed by electron transfer in the gas phase.

    PubMed

    Turecek, Frantisek; Chen, Xiaohong; Hao, Changtong

    2008-07-01

    We report the first detailed analysis at correlated levels of ab initio theory of experimentally studied peptide cations undergoing charge reduction by collisional electron transfer and competitive dissociations by loss of H atoms, ammonia, and N-C alpha bond cleavage in the gas phase. Doubly protonated Gly-Lys, (GK + 2H) (2+), and Lys-Lys, (KK + 2H) (2+), are each calculated to exist as two major conformers in the gas phase. Electron transfer to conformers with an extended lysine chain triggers highly exothermic dissociation by loss of ammonia from the Gly residue, which occurs from the ground ( X ) electronic state of the cation radical. Loss of Lys ammonium H atoms is predicted to occur from the first excited ( A ) state of the charge-reduced ions. The X and A states are nearly degenerate and show extensive delocalization of unpaired electron density over spatially remote groups. This delocalization indicates that the captured electron cannot be assigned to reduce a particular charged group in the peptide cation and that superposition of remote local Rydberg-like orbitals plays a critical role in affecting the cation-radical reactivity. Electron attachment to ion conformers with carboxyl-solvated Lys ammonium groups results in spontaneous isomerization by proton-coupled electron transfer to the carboxyl group forming dihydroxymethyl radical intermediates. This directs the peptide dissociation toward NC alpha bond cleavage that can proceed by multiple mechanisms involving reversible proton migrations in the reactants or ion-molecule complexes. The experimentally observed formations of Lys z (+*) fragments from (GK + 2H) (2+) and Lys c (+) fragments from (KK + 2H) (2+) correlate with the product thermochemistry but are independent of charge distribution in the transition states for NC alpha bond cleavage. This emphasizes the role of ion-molecule complexes in affecting the charge distribution between backbone fragments produced upon electron transfer or capture

  18. Photocatalytic degradation of 1,10-dichlorodecane in aqueous suspensions of TiO{sub 2}: A reaction of adsorbed chlorinated alkane with surface hydroxyl radicals

    SciTech Connect

    El-Morsi, T.M.; Bubakowski, W.R.; Abd-El-Aziz, A.S.; Friesen, K.J.

    2000-03-15

    1,10-Dichlorodecane (D{sub 2}C{sub 10}) is shown to be effectively photodegraded in aqueous suspensions of TiO{sub 2} using a photoreactor equipped with 300 nm lamps. Solutions exposed to UV light intensities of 3.6 x 10{sup {minus}5} Ein L{sup {minus}1} min{sup {minus}1}, established by ferrioxalate actinometry, showed negligible direct photolysis in the absence of TiO{sub 2} and a D{sub 2}C{sub 10} concentration approaching its solubility limit. Kinetics of photodegradation followed a Langmuir-Hinshelwood model suggesting that the reaction occurred on the surface of the photocatalyst. The presence of h{sup +}{sub vb} and OH{sm_bullet} radical scavengers, including methanol and iodide, inhibited the degradation supporting a photooxidation reaction. Electron scavengers (Ag{sup +}, Cu{sup 2+}, and Fe{sup 3+}) had small effects on the degradation rate. The lack of transformation of D{sub 2}C{sub 10} in acetonitrile as solvent indicated that the major oxidants were OH{sm_bullet} radicals. The presence of tetranitromethane, effectively eliminating the formation of free OH{sm_bullet} radicals, did not affect the degradation rates significantly. This result, combined with observed increases in photolysis rates with the degree of adsorption of D{sub 2}C{sub 10} onto the surface of the photocatalyst, confirmed that the reaction involved adsorbed 1,10-dichlorodecane and surface bound OH{sm_bullet} radicals.

  19. Exploiting time-resolved magnetic field effects for determining radical ion reaction rates

    NASA Astrophysics Data System (ADS)

    Bessmertnykh, A. O.; Borovkov, V. I.; Bagryansky, V. A.; Molin, Yu N.

    2016-07-01

    The capabilities of the method of time-resolved magnetic field effect in determining the rates of charge transfer reactions between radical ions and molecules on a nanosecond time scale have been investigated. The approach relies on the electron spin coherence in radical pair's partners generated by ionizing radiation. The spin evolution of the pair is sensitive to the reaction since the latter results in changing magnetic interactions of the unpaired electron. This process can be monitored by magnetic-field-sensitive fluorescence from an irradiated sample that is illustrated using reactions involving alkane radical cations. The accuracy and limitations of the approach are discussed.

  20. Negative and positive ion trapping by isotopic molecules in cryocrystals in case of solid parahydrogen containing electrons and H(6) (+) radical cations.

    PubMed

    Shimizu, Yuta; Inagaki, Makoto; Kumada, Takayuki; Kumagai, Jun

    2010-06-28

    We performed electron spin resonance studies of trapped electrons and H(6) (+) radical cations produced by radiolysis of solid parahydrogen (p-H(2)), p-H(2)-ortho-D(2) (o-D(2)), and p-H(2)-HD mixtures. Yields of trapped electrons, H(6) (+) radical cations, and its isotopic analogs H(6-n)D(n) (+) (4>or=n>or=1) increased with increasing o-D(2) and HD concentrations in solid p-H(2). Electrons were found trapped near an o-D(2) or an HD in solid p-H(2) due to the long-range charge-induced dipole and quadrupole interactions between electrons and isotopic hydrogen molecules. H(6) (+) radical cations diffuse in solid p-H(2) by repetition of H(6) (+)+H(2)-->H(2)+H(6) (+) and are trapped by ortho-D(2) or HD to form H(6-n)D(n) (+) (4>or=n>or=1) as isotope condensation reactions. Decay behaviors of these cations by the repetition, isotope condensation, and geminate recombination between electrons and H(6-n)D(n) (+) (4>or=n>or=0) were reproduced by determining the corresponding reaction rate constants k(1), k(2), and k(3). Values of 0.045 and 0.0015 L mol(-1) min(-1) were obtained for k(1) (H(6) (+)+D(2)-->H(2)+H(4)D(2) (+)) and k(2) (H(4)D(2) (+)+D(2)-->H(2)+H(2)D(4) (+)), respectively, and the value was quasinull for k(3) (H(2)D(4) (+)+D(2)-->H(2)+D(6) (+)). These rate constants suggest that hole mobility drastically decreased in the repetition reaction when H(6) (+) radical cations acting as hole carriers formed H(4)D(2) (+) or H(2)D(4) (+). HD and D(2) molecules, therefore, act as electron and hole acceptors in irradiated solid p-H(2)-o-D(2) and p-H(2)-HD mixtures.

  1. On the Electronic Spectroscopy of Closed Shell Cations Derived from Resonance Stabilized Radicals: Insights from Theory and Franck-Condon Analysis

    NASA Astrophysics Data System (ADS)

    Troy, Tyler P.; Kable, Scott H.; Schmidt, Timothy W.; Reid, Scott A.

    2012-06-01

    Recent attention has been directed on closed shell aromatic cations as potential carriers of the diffuse interstellar bands. The spectra of mass-selected, matrix-isolated benzylium and tropylium cations were recently reported [Nagy, A., Fulara, J., Garkusha, I. and Maier, J. P. (2011), Angew. Chem. Int. Ed., 50: 3022-3025]. The benzylium spectrum shows an extended progression in a low frequency (510 cm-1) ring distortion mode. Modeling of the benzylium spectrum using (TD)DFT and MCSCF-PT2 methods in concert with multidimensional Franck-Condon (FC) analysis is found to yield excellent agreement with the experimental spectrum. We extended this analysis to larger (2 and 3 ring) PAH cations derived from resonance stabilized radicals, which are predicted to show strong S0 → Sn transitions in the visible region. The FC progression is significantly quenched in the larger species, and our results for 1-napthylmethylium are in excellent agreement with very recent experiments [Nagy, A., Fulara, J., and Maier, J. P. (2011), J. Am. Chem. Soc., 133, 19796]. Since carriers of the DIBs should exhibit spectra dominated by a single vibronic transition, our results demonstrate that closed-shell cations may present spectra with the required properties. Furthermore, the calculated ionization energies of a range of CSCs were found to be in the 13-14 eV range, consistent with variations in behaviour of the DIB carriers with respect to various astrophysical environments.

  2. Structural investigation of asymmetrical dimer radical cation system (H2O-H2S)+: proton-transferred or hemi-bonded?

    PubMed

    Joshi, Ravi; Ghanty, Tapan K; Naumov, Sergej; Mukherjee, Tulsi

    2007-03-29

    Ab initio molecular orbital and hybrid density functional methods have been employed to characterize the structure and bonding of (H2O-H2S)+, an asymmetrical dimer radical cation system. A comparison has been made between the two-center three-electron (2c-3e) hemi-bonded system and the proton-transferred hydrogen-bonded systems of (H2O-H2S)+. Geometry optimization of these systems was carried out using unrestricted Hartree Fock (HF), density functional theory with different functionals, and second-order Møller-Plesset perturbation (MP2) methods with 6-311++G(d,p) basis set. Hessian calculations have been done at the same level to check the nature of the equilibrium geometry. Energy data were further improved by calculating basis set superposition error for the structures optimized through MP2/6-311++G(d,p) calculations. The calculated results show that the dimer radical cation structure with H2O as proton acceptor is more stable than those structures in which H2O acts as a proton donor or the 2c-3e hemi-bonded (H2O thereforeSH2)+ system. This stability trend has been further confirmed by more accurate G3, G3B3, and CCSD(T) methods. On the basis of the present calculated results, the structure of H4OS+ can best be described as a hydrogen-bonded complex of H3O+ and SH with H2O as a proton acceptor. It is in contrast to the structure of neutral (H2O...H2S) dimer where H2O acts as a proton donor. The present work has been able to resolve the ambiguity in the nature of bonding between H2O and H2S in (H2O-H2S)+ asymmetrical dimer radical cation.

  3. A search for blues brothers: X-ray crystallographic/spectroscopic characterization of the tetraarylbenzidine cation radical as a product of aging of solid magic blue.

    PubMed

    Talipov, Marat R; Hossain, Mohammad M; Boddeda, Anitha; Thakur, Khushabu; Rathore, Rajendra

    2016-03-14

    Magic blue (MB+˙ SbCl6− salt), i.e. tris-4-bromophenylamminium cation radical, is a routinely employed one-electron oxidant that slowly decomposes in the solid state upon storage to form so called ‘blues brothers’, which often complicate the quantitative analyses of the oxidation processes. Herein, we disclose the identity of the main ‘blues brother’ as the cation radical and dication of tetrakis-(4-bromophenyl)benzidine (TAB) by a combined DFT and experimental approach, including isolation of TAB+˙ SbCl6− and its X-ray crystallography characterization. The formation of TAB in aged magic blue samples occurs by a Scholl-type coupling of a pair of MB followed by a loss of molecular bromine. The recognition of this fact led us to the rational design and synthesis of tris(2-bromo-4-tert-butylphenyl)amine, referred to as ‘blues cousin’ (BC: Eox1 = 0.78 V vs. Fc/Fc+, λmax(BC+˙) = 805 nm, εmax = 9930 cm−1 M−1), whose oxidative dimerization is significantly hampered by positioning the sterically demanding tert-butyl groups at the para-positions of the aryl rings. A ready two-step synthesis of BC from triphenylamine and the high stability of its cation radical (BC+˙) promise that BC will serve as a ready replacement for MB and an oxidant of choice for mechanistic investigations of one-electron transfer processes in organic, inorganic, and organometallic transformations.

  4. Discovery and Mechanistic Studies of Facile N-Terminal Cα–C Bond Cleavages in the Dissociation of Tyrosine-Containing Peptide Radical Cations

    SciTech Connect

    Mu, Xiaoyan; Song, Tao; Xu, Minjie; Lai, Cheuk-Kuen; Siu, Chi-Kit; Laskin, Julia; Chu, Ivan K.

    2014-03-28

    Gas phase fragmentations of protein and peptide (M) ions in a mass spectrometer—induced by, for example, electron-capture dissociation1-2 and electron-transfer dissociation3-422 —form the foundation for top-down amino acid sequencing approaches for the rapid identification of protein components in complex biological samples. During these processes, protonated protein and peptide radicals ([M + nH]•(n – 1)+)5–8 are generated; their fragmentations are governed largely by the properties of the unpaired electron. Because of their importance in modern bioanalytical chemistry, considerable attention has been drawn recently toward understanding the radical cation chemistry behind the fragmentations of these odd-electron biomolecular ions in the gas phase.

  5. Magneto-structural relationships for radical cation and neutral pyridinophane structures with intrabridgehead nitrogen atoms. An integrated experimental and quantum mechanical study.

    PubMed

    Williams, Ffrancon; Chen, Guo-Fei; Mattar, Saba M; Scudder, Paul H; Trieber, Dwight A; Saven, Jeffery G; Whritenour, David C; Cimino, Paola; Barone, Vincenzo

    2009-07-01

    An integrated experimental and computational approach was used to compare the properties of representative molecules containing intrabridgehead nitrogen atoms with those of the corresponding radical cations issuing from one-electron oxidation with the aim of unraveling the characteristics of the three-electron sigma-bonds formed in the open-shell species. From a quantitative point of view, last-generation density functional methods coupled with proper basis sets and, when needed, continuum models for describing bulk solvent effects confirm their reliability for the computation of structures and magnetic properties of organic free radicals. From an interpretative point of view, different hybridizations of nitrogen atoms tuned by their chemical environment lead to markedly different magnetic properties that represent reliable and sensitive probes of structural and electronic characteristics.

  6. A complete map of the ion chemistry of the naphthalene radical cation? DFT and RRKM modeling of a complex potential energy surface

    NASA Astrophysics Data System (ADS)

    Solano, Eduardo A.; Mayer, Paul M.

    2015-09-01

    The fragmentation mechanisms of the naphthalene molecular ion to [M-C4H2]+•, [M-C2H2]+•, [M-H2]+•, and [M-H•]+ were obtained at the UB3LYP/6-311+G(3df,2p)//UB3LYP/6-31G(d) level of theory and were subsequently used to calculate the microcanonical rate constants, k(E)'s, for all the steps by the Rice-Ramsperger-Kassel-Marcus formalism. The pre-equilibrium and steady state approximations were applied on different regions of the potential energy profiles to obtain the fragmentation k(E)'s and calculate the relative abundances of the ions as a function of energy. These results reproduce acceptably well the imaging photoelectron-photoion coincidence spectra of naphthalene, in the photon-energy range 14.0-18.8 eV that was previously reported by our group. Prior to dissociation, the molecular ion rapidly equilibrates with a set of isomers that includes the Z- and E-phenylvinylacetylene (PVA) radical cations. The naphthalene ion is the predominant isomer below 10 eV internal energy, with the other isomers remaining at steady state concentrations. Later on, new steady-state intermediates are formed, such as the azulene and 1-phenyl-butatriene radical cations. The naphthalene ion does not eject an H atom directly but eliminates an H2 molecule in a two-step fragmentation. H• loss occurs instead from the 1-phenyl-butatriene ion. The PVA ions initiate the ejection of diacetylene (C4H2) to yield the benzene radical cation. Acetylene elimination yields the pentalene cation at low energies (where it can account for 45.9%-100.0% of the rate constant of this channel), in a three-step mechanism starting from the azulene ion. However, above 7.6 eV, the major [M-C2H2]+• structure is the phenylacetylene cation.

  7. A complete map of the ion chemistry of the naphthalene radical cation? DFT and RRKM modeling of a complex potential energy surface

    SciTech Connect

    Solano, Eduardo A.; Mayer, Paul M.

    2015-09-14

    The fragmentation mechanisms of the naphthalene molecular ion to [M–C{sub 4}H{sub 2}]{sup +•}, [M–C{sub 2}H{sub 2}]{sup +•}, [M–H{sub 2}]{sup +•}, and [M–H{sup •}]{sup +} were obtained at the UB3LYP/6-311+G(3df,2p)//UB3LYP/6-31G(d) level of theory and were subsequently used to calculate the microcanonical rate constants, k(E)’s, for all the steps by the Rice-Ramsperger-Kassel-Marcus formalism. The pre-equilibrium and steady state approximations were applied on different regions of the potential energy profiles to obtain the fragmentation k(E)’s and calculate the relative abundances of the ions as a function of energy. These results reproduce acceptably well the imaging photoelectron-photoion coincidence spectra of naphthalene, in the photon-energy range 14.0–18.8 eV that was previously reported by our group. Prior to dissociation, the molecular ion rapidly equilibrates with a set of isomers that includes the Z- and E-phenylvinylacetylene (PVA) radical cations. The naphthalene ion is the predominant isomer below 10 eV internal energy, with the other isomers remaining at steady state concentrations. Later on, new steady-state intermediates are formed, such as the azulene and 1-phenyl-butatriene radical cations. The naphthalene ion does not eject an H atom directly but eliminates an H{sub 2} molecule in a two-step fragmentation. H{sup •} loss occurs instead from the 1-phenyl-butatriene ion. The PVA ions initiate the ejection of diacetylene (C{sub 4}H{sub 2}) to yield the benzene radical cation. Acetylene elimination yields the pentalene cation at low energies (where it can account for 45.9%–100.0% of the rate constant of this channel), in a three-step mechanism starting from the azulene ion. However, above 7.6 eV, the major [M–C{sub 2}H{sub 2}]{sup +•} structure is the phenylacetylene cation.

  8. A complete map of the ion chemistry of the naphthalene radical cation? DFT and RRKM modeling of a complex potential energy surface.

    PubMed

    Solano, Eduardo A; Mayer, Paul M

    2015-09-14

    The fragmentation mechanisms of the naphthalene molecular ion to [M-C4H2](+•), [M-C2H2](+•), [M-H2](+•), and [M-H(•)](+) were obtained at the UB3LYP/6-311+G(3df,2p)//UB3LYP/6-31G(d) level of theory and were subsequently used to calculate the microcanonical rate constants, k(E)'s, for all the steps by the Rice-Ramsperger-Kassel-Marcus formalism. The pre-equilibrium and steady state approximations were applied on different regions of the potential energy profiles to obtain the fragmentation k(E)'s and calculate the relative abundances of the ions as a function of energy. These results reproduce acceptably well the imaging photoelectron-photoion coincidence spectra of naphthalene, in the photon-energy range 14.0-18.8 eV that was previously reported by our group. Prior to dissociation, the molecular ion rapidly equilibrates with a set of isomers that includes the Z- and E-phenylvinylacetylene (PVA) radical cations. The naphthalene ion is the predominant isomer below 10 eV internal energy, with the other isomers remaining at steady state concentrations. Later on, new steady-state intermediates are formed, such as the azulene and 1-phenyl-butatriene radical cations. The naphthalene ion does not eject an H atom directly but eliminates an H2 molecule in a two-step fragmentation. H(•) loss occurs instead from the 1-phenyl-butatriene ion. The PVA ions initiate the ejection of diacetylene (C4H2) to yield the benzene radical cation. Acetylene elimination yields the pentalene cation at low energies (where it can account for 45.9%-100.0% of the rate constant of this channel), in a three-step mechanism starting from the azulene ion. However, above 7.6 eV, the major [M-C2H2](+•) structure is the phenylacetylene cation.

  9. Reactions of 5-methylcytosine cation radicals in DNA and model systems: thermal deprotonation from the 5-methyl group vs. excited state deprotonation from sugar

    PubMed Central

    Adhikary, Amitava; Kumar, Anil; Palmer, Brian J.; Todd, Andrew D.; Heizer, Alicia N.; Sevilla, Michael D.

    2014-01-01

    Purpose To study the formation and subsequent reactions of the 5-methyl-2′-deoxycytidine cation radical (5-Me-2′-dC•+) in nucleosides and DNA-oligomers and compare to one electron oxidized thymidine. Materials and methods Employing electron spin resonance (ESR), cation radical formation and its reactions were investigated in 5-Me-2′-dC, thymidine (Thd) and their derivatives, in fully double stranded (ds) d[GC*GC*GC*GC*]2 and in the 5-Me-C/A mismatched, d[GGAC*AAGC:CCTAATCG], where C* = 5-Me-C. Results We report 5-Me-2′-dC•+ production by one-electron oxidation of 5-Me-2′-dC by Cl2•− via annealing in the dark at 155 K. Progressive annealing of 5-Me-2′-dC•+ at 155 K produces the allylic radical (C-CH2•). However, photoexcitation of 5-Me-2′-dC•+ by 405 nm laser or by photoflood lamp leads to only C3′• formation. Photoexcitation of N3-deprotonated thyminyl radical in Thd and its 5′-nucleotides leads to C3′• formation but not in 3′-TMP which resulted in the allylic radical (U-CH2•) and C5′• production. For excited 5-Me-2′,3′-ddC•+, absence of the 3′-OH group does not prevent C3′• formation. For d[GC*GC*GC*GC*]2 and d[GGAC*AAGC:CCTAATCG], intra-base paired proton transferred form of G cation radical (G(N1-H)•:C(+H+)) is found with no observable 5-Me-2′-dC•+ formation. Photoexcitation of (G(N1-H)•:C(+H+)) in d[GC*GC*GC*GC*]2 produced only C1′• and not the expected photoproducts from 5-Me-2′-dC•+. However, photoexcitation of (G(N1-H)•:C(+H+)) in d[GGAC*AAGC:CCTAATCG] led to C5′• and C1′• formation. Conclusions C-CH2• formation from 5-Me-2′-dC•+ occurs via ground state deprotonation from C5-methyl group on the base. In the excited 5-Me-2′-dC•+ and 5-Me-2′,3′-ddC•+, spin and charge localization at C3′ followed by deprotonation leads to C3′• formation. Thus, deprotonation from C3′ in the excited cation radical is kinetically controlled and sugar C-H bond energies are

  10. Polymerization of ionized acetylene clusters into covalent bonded ions: evidence for the formation of benzene radical cation.

    PubMed

    Momoh, Paul O; Abrash, Samuel A; Mabrouki, Ridha; El-Shall, M Samy

    2006-09-27

    Since the discovery of acetylene and benzene in protoplanetary nebulae under powerful ultraviolet ionizing radiation, efforts have been made to investigate the polymerization of ionized acetylene. Here we report the efficient formation of benzene ions within gas-phase ionized acetylene clusters (C2H2)n+ with n = 3-60. The results from experiments, which use mass-selected ion mobility techniques, indicate that the (C2H2)3+ ion has unusual stability similar to that of the benzene cation; its primary fragment ions are similar to those reported from the benzene cation, and it has a collision cross section of 47.4 A2 in helium at 300 K, similar to the value of 47.9 A2 reported for the benzene cation. In other words, (C2H2)3+ structurally looks like benzene, it has stability similar to that of benzene, it fragments such as benzene, therefore, it must be benzene! PMID:16984178

  11. Acid-base equilibria involved in secondary reactions following the 4-carboxybenzophenone sensitized photooxidation of methionylglycine in aqueous solution. Spectral and time resolution of the decaying (S...N){sup +} radical cation

    SciTech Connect

    Hug, G.L.; Marciniak, B. |; Bobrowski, K. ||

    1996-09-05

    A radical cation with an intramolecular sulfur-nitrogen bond was formed in the photoinitiated transfer of an electron from the sulfur atom of the dipeptide Met-Gly to 4-carboxybenzophenone in its triplet state. The sulfur-nitrogen coupling involved two-center, three-electron bonds. The kinetics of the reactions of these radical cations, which were initiated by a laser flash, were followed over time. The principal method of implementing the spectral resolutions was accomplished through a multiple linear regression technique. This spectral analysis was repeated for numerous time windows during the lifetime of the transients` decays. The resulting concentrations of the transients were consistent with an independent factor analysis. It was found that the decay of the radical cations was multiexponential and that the decay varied with pH. A simplified reaction scheme was proposed whereby the absorbing radical cations can alternatively decay by an irreversible channel or react reversibly with OH{sup -}. Rate constants for the three elementary reactions of this scheme were determined from an analysis of the decay of the concentration of the radical cations. In addition, the equilibrium constant for the reversible reaction was determined by two separate procedures. 35 refs., 7 figs., 2 tabs.

  12. Density functional theory study of conformation-dependent properties of neutral and radical cationic L-tyrosine and L-tryptophan.

    PubMed

    Baek, K Y; Fujimura, Y; Hayashi, M; Lin, S H; Kim, S K

    2011-09-01

    Conformation-dependent properties of L-tyrosine and L-tryptophan in neutral and radical cations were studied by using the density functional theory (DFT) with a new density functional M05-2X. The results are compared with those obtained by using the conventional DFT (B3LYP). Results obtained by both types of DFT were in qualitative accord, including the existence of two conformational subgroups and their subgroup-dependent adiabatic ionization energy and hydrogen bonding. On the other hand, quantitative differences were found between the two DFT methods as well: the M05-2X method successfully reproduced experimental adiabatic ionization energy, whereas the B3LYP functional consistently yielded significantly lower values by 0.2-0.3 eV. More importantly, natural bond orbital (NBO) analysis for cationic conformers showed that all conformers of L-tyrosine and L-tryptophan undergo charge localization upon ionization regardless of the presence of intramolecular hydrogen bonding, unlike the case of L-phenylalanine that was treated earlier by other studies. Different degrees of charge localization among all three aromatic amino acids are explained by employing a simple model in which the aromatic amino acid is assumed to consist of two submoieties of distinct cationic core: the backbone and aromatic side chain. The difference in adiabatic ionization energy between these two submoieties is found to govern the degree of charge localization. PMID:21539381

  13. Bis[bis-(4-alkoxyphenyl)amino] derivatives of dithienylethene, bithiophene, dithienothiophene and dithienopyrrole: palladium-catalysed synthesis and highly delocalised radical cations.

    PubMed

    Odom, Susan A; Lancaster, Kelly; Beverina, Luca; Lefler, Kelly M; Thompson, Natalie J; Coropceanu, Veaceslav; Brédas, Jean-Luc; Marder, Seth R; Barlow, Stephen

    2007-01-01

    Five diamines with thiophene-based bridges--(E)-1,2-bis{5-[bis(4-butoxyphenyl)amino]-2-thienyl}ethylene (1), 5,5'-bis[bis(4-methoxyphenyl)amino]-2,2'-bithiophene (2), 2,6-bis[bis(4-butoxyphenyl)amino]dithieno[3,2-b:2',3'-d]thiophene (3), N-(4-tert-butylphenyl)-2,6-bis[bis(4-methoxyphenyl)amino]dithieno[3,2-b:2',3'-d]pyrrole (4 a) and N-tert-butyl-2,6-bis[bis(4-methoxyphenyl)amino]dithieno[3,2-b:2',3'-d]pyrrole (4 b)--have been synthesised. The syntheses make use of the palladium(0)-catalysed coupling of brominated thiophene species with diarylamines, in some cases accelerated by microwave irradiation. The molecules all undergo facile oxidation, 4 b being the most readily oxidised at about -0.4 V versus ferrocenium/ferrocene, and solutions of the corresponding radical cations were generated by addition of tris(4-bromophenyl)aminium hexachloroantimonate to the neutral species. The near-IR spectra of the radical cations show absorptions characteristic of symmetrical delocalised species (that is, class III mixed-valence species); analysis of these absorptions in the framework of Hush theory indicates strong coupling between the two amine redox centres, stronger than that observed in species with phenylene-based bridging groups of comparable length. The strong coupling can be attributed to high-lying orbitals of the thiophene-based bridging units. ESR spectroscopy indicates that the coupling constant to the amino nitrogen atoms is somewhat reduced relative to that in a stilbene-bridged analogue. The neutral species and the corresponding radical cations have been studied with the aid of density functional theory and time-dependent density functional theory. The DFT-calculated ESR parameters are in good agreement with experiment, while calculated spin densities suggest increased bridge character to the oxidation in these species relative to that in comparable species with phenylene-based bridges.

  14. Effect of Base Stacking on the Acid-Base Properties of the Adenine Cation Radical [A•+] in Solution: ESR and DFT Studies

    PubMed Central

    Adhikary, Amitava; Kumar, Anil; Khanduri, Deepti

    2015-01-01

    In this study, the acid–base properties of the adenine cation radical are investigated by means of experiment and theory. Adenine cation radical (A•+) is produced by one-electron oxidation of dAdo and of the stacked DNA-oligomer (dA)6 by Cl2•− in aqueous glass (7.5 M LiCl in H2O and in D2O) and investigated by ESR spectroscopy. Theoretical calculations and deuterium substitution at C8–H and N6–H in dAdo aid in our assignments of structure. We find the pKa value of A•+ in this system to be ca. 8 at 150 K in seeming contradiction to the accepted value of ≤ 1 at ambient temperature. However, upon thermal annealing to ≥160 K, complete deprotonation of A•+ occurs in dAdo in these glassy systems even at pH ca. 3. A•+ found in (dA)6 at 150 K also deprotonates on thermal annealing. The stability of A•+ at 150 K in these systems is attributed to charge delocalization between stacked bases. Theoretical calculations at various levels (DFT B3LYP/6-31G*, MPWB95, and HF-MP2) predict binding energies for the adenine stacked dimer cation radical of 12 to 16 kcal/mol. Further DFT B3LYP/6-31G* calculations predict that, in aqueous solution, monomeric A•+ should deprotonate spontaneously (a predicted pKa of ca. −0.3 for A•+). However, the charge resonance stabilized dimer AA•+ is predicted to result in a significant barrier to deprotonation and a calculated pKa of ca. 7 for the AA•+ dimer which is 7 pH units higher than the monomer. These theoretical and experimental results suggest that A•+ isolated in solution and A•+ in adenine stacks have highly differing acid–base properties resulting from the stabilization induced by hole delocalization within adenine stacks. PMID:18611019

  15. Radical Cations of the Monomer and van der Waals Dimer of a Methionine Residue as Prototypes of (2 Center-3 Electron) SN and SS Bonds. Molecular Simulations of Their Absorption Spectra in Water.

    PubMed

    Archirel, Pierre; Bergès, Jacqueline; Houée-Lévin, Chantal

    2016-09-22

    Oxidation of peptides or proteins by the OH(•) radicals produced by pulse radiolysis yields species identified by their absorption spectra in the UV-visible domain. However, the case of methionine (Met) in peptides is complex because its oxidation can lead to various free radicals with 2 center-3 electron (2c-3e) bonds. We have performed Monte Carlo/density functional theory molecular simulations of the radical cation of the methylated methionine aminoacid, Met(•+), taken as a model of the methonine residue of peptides, and of the radical cation of its van der Waals dimer, Met2(•+). The cation of the methionine residue displays a 2c-3e SN bond. The cation of dimer Met2(•+) displays three quasidegenerate conformers, one stabilized by a 2c-3e SS bond and the other two stabilized by ion-molecule interactions and made up of a neutral and a cationic unit. These conformers are characterized by their charge and spin density localization and their UV-visible absorption spectra. These spectra enable a discussion of the absorption spectra of the literature; in particular, we emphasize the role of dimers before and after the oxidation process. PMID:27564585

  16. [Effect of calcium cations on acid-base properties and free radical oxidation of dopamine and pyrocatechol].

    PubMed

    Lebedev, A V; Ivanova, M V; Timoshin, A A; Ruuge, E K

    2008-01-01

    Ca2+-induced increase in the rate of pyrocatechol and dopamine oxidation by dioxygen and Ca2+-dependent acid-base properties of the catechols were studied by potentiometric titration, UV/Vis-spectrophotometry, EPR-spectroscopy, and by measurement of oxygen consumption. The effect of Ca2+ on the chain reactions of oxidation can be explained by additional deprotonation (decrease in pKai) of the catechols that accelerates one electron transport to dioxygen and formation of calcium semiquinonate, undergoing further oxidation. The described Ca2+-dependent redox-conversion of ortho-phenols proposes that an additional function of calcium in the cell can be its involvement in free radical oxidoreductive reactions at pH > pKai.

  17. Fragmentation of peptide radical cations containing a tyrosine or tryptophan residue: structural features that favor formation of [x(n-1) + H]˙⁺ and [z(n-1) + H]˙⁺ ions.

    PubMed

    Mädler, Stefanie; Lau, Justin Kai-Chi; Williams, Declan; Wang, Yating; Saminathan, Irine S; Zhao, Junfang; Siu, K W Michael; Hopkinson, Alan C

    2014-06-12

    Peptide radical cations A(n)Y(•+) (where n = 3, 4, or 5) and A5W(•+) have been generated by collision-induced dissociation (CID) of [Cu(II)(tpy)(peptide)](•2+) complexes. Apart from the charge-driven fragmentation at the N-Cα bond of the hetero residue producing either [c + 2H](+) or [z - H](•+) ions and radical-driven fragmentation at the Cα-C bond to give a(+) ions, unusual product ions [x + H](•+) and [z + H](•+) are abundant in the CID spectra of the peptides with the hetero residue in the second or third position of the chain. The formation of these ions requires that both the charge and radical be located on the peptide backbone. Energy-resolved spectra established that the [z + H](•+) ion can be produced either directly from the peptide radical cation or via the fragment ion [x + H](•+). Additionally, backbone dissociation by loss of the C-terminal amino acid giving [b(n-1) - H](•+) increases in abundance with the length of the peptides. Mechanisms by which peptide radical cations dissociate have been modeled using density functional theory (B3LYP/6-31++G** level) on tetrapeptides AYAG(•+), AAYG(•+), and AWAG(•+).

  18. Photolysis of alpha-xylyl chlorides: an efficient deep-UV photoinitiating system for radical and cationic polymerization.

    PubMed

    Ponce, Patricia; Catalani, Luiz Henrique

    2004-07-01

    Photoacid generators (PAG) are chemical systems where light absorption renders strong acid formation, typically with quantum yields greater than one. Many compounds bearing halogen atoms are reported to produce hydrogen halides upon photolysis. Here, alpha-chloroxylene derivatives (ortho, meta and para) were subject of a photolysis study in order to: (i) determine the operative mechanism, (ii) identify the products formed and (iii) quantify the amount of HCl formed. Product structure and quantum yields of HCl formation where determined for the photolysis of alpha-chloro-o-xylene (1), alpha-chloro-m-xylene (2), alpha-chloro-p-xylene (3), alpha, alpha'-dichloro-o-xylene (4), alpha, alpha'-dichloro-m-xylene (5) and alpha, alpha'-dichloro-p-xylene (6) in apolar (benzene, cumene, ethylbenzene, toluene and isooctane) and polar (methanol, n-propanol, isopropyl alcohol) solvents. Some of these compounds were analysed by laser flash photolysis in argon-purged isooctane as solvent to examine the possible reaction intermediates involved. The observed products are derived from typical radical reactions like recombination, dimerization and hydrogen abstraction from the starting compound or from solvents. The formation of HCl is expected as the result of C-Cl homolysis followed by hydrogen abstraction by chlorine atom. The results showed yields ranging from 1.2 to 18, depending on the conditions used. These numbers indicate the potential use of these compounds as PAG systems for the deep UV region.

  19. Cascade dissociations of peptide cation-radicals. Part 1. Scope and effects of amino acid residues in penta-, nona-, and decapeptides.

    PubMed

    Chung, Thomas W; Hui, Renjie; Ledvina, Aaron; Coon, Joshua J; Tureček, Frantisek

    2012-08-01

    Amino acid residue-specific backbone and side-chain dissociations of peptide z ions in MS(3) spectra were elucidated for over 40 pentapeptides with arginine C-terminated sequences of the AAXAR and AAHXR type, nonapeptides of the AAHAAXX"AR and AAHAXAX"AR type, and AAHAAXX"AAR decapeptides. Peptide z(n) ions containing amino acid residues with readily transferrable benzylic or tertiary β-hydrogen atoms (Phe, Tyr, His, Trp, Val) underwent facile backbone cleavages to form dominant z(n-2) or z(n-3) ions. These backbone cleavages are thought to be triggered by a side-chain β-hydrogen atom transfer to the z ion C(α) radical site followed by homolytic dissociation of the adjacent C(α)-CO bond, forming x(n-2) cation-radicals that spontaneously dissociate by loss of HNCO. Amino acid residues that do not have readily transferrable β-hydrogen atoms (Gly, Ala) do not undergo the z(n) → z(n-2) dissociations. The backbone cleavages compete with side-chain dissociations in z ions containing Asp and Asn residues. Side-chain dissociations are thought to be triggered by α-hydrogen atom transfers that activate the C(β)-C(γ) or C(β)-heteroatom bonds for dissociations that dominate the MS(3) spectra of z ions from peptides containing Leu, Cys, Lys, Met, Ser, Arg, Glu, and Gln residues. The Lys, Arg, Gln, and Glu residues also participate in γ-hydrogen atom transfers that trigger other side-chain dissociations. PMID:22669761

  20. Chemistry of carotenoid neutral radicals.

    PubMed

    Ligia Focsan, A; Magyar, Adam; Kispert, Lowell D

    2015-04-15

    Proton loss from the carotenoid radical cations (Car(+)) to form neutral radicals (#Car) was investigated by numerous electrochemical, EPR, ENDOR and DFT studies described herein. The radical cation and neutral radicals were formed in solution electrochemically and stabilized on solid silica-alumina and MCM-41 matrices. Carotenoid neutral radicals were recently identified in Arabidopsis thaliana plant and photosystem II samples. Deprotonation at the terminal ends of a zeaxanthin radical cation could provide a secondary photoprotection pathway which involves quenching excited state chlorophyll by the long-lived zeaxanthin neutral radicals formed. PMID:25687648

  1. Structures and stabilities of hemi-bonded vs proton-transferred isomers of dimer radical cation systems (XH3sbnd YH3)+ (X,Y = N, P, As)

    NASA Astrophysics Data System (ADS)

    Ji, Li Fei; Li, An Yong; Li, Zhuo Zhe

    2015-01-01

    Structures, bonding and relative stabilities of the radical dimer cations (XH3sbnd YH3)+ (X,Y = N, P, As) have been studied theoretically. Two kinds of structures (hemi-bonded and proton-transferred isomers) are obtained for each system. For (NH3sbnd N/P/AsH3)+ the stable conformer is the proton-transferred structure; for (PH3sbnd PH3)+ and (AsH3sbnd AsH3)+ the stable structure is the hemi-bonded one; for (PH3sbnd AsH3)+ three proton-transferred and one hemi-bonded isomers were found with the stability order: (Hsbnd PH3+⋯AsH2) I > (H3PH+⋯AsH2) II > (H3P⋯AsH3+) > (H3AsH+⋯PH2) III. The hemi-bonds have large interaction energies 25.2-35.1 kcal/mol and are partially covalent in nature, while the proton-transferred structures have moderate interaction energies 6.5-22.2 kcal/mol.

  2. Detection and removal of contaminating hydroxylamines from the spin trap DEPMPO, and re-evaluation of its use to indicate nitrone radical cation formation and S(N)1 reactions.

    PubMed

    Jackson, Simon K; Liu, Ke Jian; Liu, Miao; Timmins, Graham S

    2002-02-01

    A previous report that the spin trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO) allows DEPMPO radical cation formation to be detected via the production of a carbon-centred radical adduct (assigned as the cis-hydroxyethyl species, formed by an intramolecular process) is shown to be incorrect. Rather, this and other paramagnetic species arise from the facile oxidation of trace hydroxylamine impurities present in commercial DEPMPO samples. As a result, techniques for the detection and elimination of such hydroxylamine impurities from DEPMPO solutions were developed and are described; these should prove to be of general use in EPR spin trapping experiments.

  3. Full dimensional quantum-mechanical simulations for the vibronic dynamics of difluorobenzene radical cation isomers using the multilayer multiconfiguration time-dependent Hartree method

    NASA Astrophysics Data System (ADS)

    Meng, Qingyong; Faraji, Shirin; Vendrell, Oriol; Meyer, Hans-Dieter

    2012-10-01

    Full dimensional multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) calculations of the dynamics of the three difluorobenzene cationic isomers in five lowest-lying doublet electronic states using the ab initio multistate multimode vibronic coupling Hamiltonian (MMVCH) model are carried out using the Heidelberg MCTDH package. The same dynamical problems, but treated with the MCTDH scheme and using a reduced dimensional ab initio MMVCH model, have been previously reported [S. Faraji, H.-D. Meyer, and H. Köppel, "Multistate vibronic interactions in difluorobenzene radical cations. II Quantum dynamical simulations," J. Chem. Phys. 129, 074311 (2008), 10.1063/1.2958918]. For easy comparison with the reduced dimensional results, 11D or 10D ML-MCTDH calculations are also performed. Extensive ML-MCTDH test calculations are performed to find appropriate ML-MCTDH wavefunction structures (ML-trees), and the convergence of the ML-MCTDH calculations are carefully checked to ensure accurate results. Based on the appropriate ML-trees, the photoelectron (PE) spectrum and the mass analyzed threshold ionization (MATI) spectrum are simulated, analyzed, and compared with corresponding experimental spectra. Because of its efficient simulation capability for large systems, ML-MCTDH calculations save a considerable amount of central processing unit (CPU)-time, even when a reduced dimensional MMVCH is used, i.e., the same reduced model as in the corresponding MCTDH calculations. Simulations of the experimental PE spectra by full dimensional ML-MCTDH calculations reproduced main peaks, which originate from different electronic states. The agreement is improved as compared to the reduced dimensionality calculations. Unfortunately, the experimental PE spectra are not very well resolved. Therefore, we compare our calculations additionally with highly resolved MATI spectra, which, however, are only available for the tilde{X} state. Based on a series of ML-MCTDH simulations with

  4. Full dimensional quantum-mechanical simulations for the vibronic dynamics of difluorobenzene radical cation isomers using the multilayer multiconfiguration time-dependent Hartree method.

    PubMed

    Meng, Qingyong; Faraji, Shirin; Vendrell, Oriol; Meyer, Hans-Dieter

    2012-10-01

    Full dimensional multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) calculations of the dynamics of the three difluorobenzene cationic isomers in five lowest-lying doublet electronic states using the ab initio multistate multimode vibronic coupling Hamiltonian (MMVCH) model are carried out using the Heidelberg MCTDH package. The same dynamical problems, but treated with the MCTDH scheme and using a reduced dimensional ab initio MMVCH model, have been previously reported [S. Faraji, H.-D. Meyer, and H. Köppel, "Multistate vibronic interactions in difluorobenzene radical cations. II Quantum dynamical simulations," J. Chem. Phys. 129, 074311 (2008)]. For easy comparison with the reduced dimensional results, 11D or 10D ML-MCTDH calculations are also performed. Extensive ML-MCTDH test calculations are performed to find appropriate ML-MCTDH wavefunction structures (ML-trees), and the convergence of the ML-MCTDH calculations are carefully checked to ensure accurate results. Based on the appropriate ML-trees, the photoelectron (PE) spectrum and the mass analyzed threshold ionization (MATI) spectrum are simulated, analyzed, and compared with corresponding experimental spectra. Because of its efficient simulation capability for large systems, ML-MCTDH calculations save a considerable amount of central processing unit (CPU)-time, even when a reduced dimensional MMVCH is used, i.e., the same reduced model as in the corresponding MCTDH calculations. Simulations of the experimental PE spectra by full dimensional ML-MCTDH calculations reproduced main peaks, which originate from different electronic states. The agreement is improved as compared to the reduced dimensionality calculations. Unfortunately, the experimental PE spectra are not very well resolved. Therefore, we compare our calculations additionally with highly resolved MATI spectra, which, however, are only available for the X̃ state. Based on a series of ML-MCTDH simulations with longer propagation time

  5. Conformational Distortions of π-Cation Radical (β-Oxoporphyrin)copper(II) Derivatives: [Cu(2,7,12-TrioxoOEHP)][SbCl(6)] and [Cu(2,7-DioxoOEiBC)][SbCl(6)].

    PubMed

    Turowska-Tyrk, Ilona; Kang, Seong-Joo; Scheidt, W Robert

    2011-03-01

    The preparation and characterization of two π-cation radical derivatives of copper β-oxo porphyrins is described. [3,3,8,8,13,13,17,18-Octaethyl-(3H,8H,13H)-porphine-2,7,12-trionato (2-)] copper π-cation radical, [Cu(2,7,12-trioxoOEHP(.))](+), and [3,3,8,8,12,13,17,18-octaethyl-(3H,8H)-porphine-2,7-dionato(2-)] copper π-cation radical, [Cu(2,7-dioxoOEiBC(.))](+), have been prepared and characterized by single-crystal X-ray determinations, UV/vis/NIR, and IR spectroscopies. Both molecules have modest distortion from the planarity and show monomeric units in the solid state. [Cu(2,7-dioxoOEiBC(.))](+) shows a concentration dependent near-IR band at 1410 nm. Crystal data for [Cu(2,7,12-trioxoOEHP(.))][SbCl(6)]: tetragonal, space group P4(2)/n, a = 31.085 (14) Å, c = 9.410 (4) Å, V = 9093 Å(3), Z = 8, T = 127 K. Crystal data for [Cu(2,7-dioxoOEiBC(.))][SbCl(6)]: monoclinic, space group P2(1)/n, a = 9.655 (4) Å, b = 20.592 (8) Å, c = 43.347 (17) Åβ = 89.97(1)(°), V = 8618. Å(3), Z = 8, T = 100 K.

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

    PubMed

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

    2016-06-27

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

  7. C---lH...O and O...H...O bonded intermediates in the dissociation of low energy methyl glycolate radical cations

    NASA Astrophysics Data System (ADS)

    Suh, Dennis; Kingsmill, Carol A.; Ruttink, Paul J. A.; Burgers, Peter C.; Terlouw, Johan K.

    1995-08-01

    Low energy methyl glycolate radical cations HOCH2C(=O)OCH3+, 1, abundantly lose HCO, yielding protonated methyl formate H---C(OH)OCH3+. Tandem mass spectrometry based experiments on 2H, 13C and 18O labelled isotopologues show that this loss is largely (about 75%) atom specific. Analysis of the atom connectivity in the product ions indicates that the reaction proceeds analogously to the loss of HCO and CH3CO from ionized acetol HOCH2C(=O)CH3+ and acetoin HOCH(CH3)C(=O)CH3+, respectively. The mechanism, it is proposed, involves isomerization of 1 to the key intermediate CH2=O... H---C(=O)OCH3+, an H-bridged ion-dipole complex of neutral formaldehyde and ionized methyl formate. Next, charge transfer takes place to produce CH3OC(H)=O...HC(H)=O+, an H-bridged ion-dipole complex of ionized formaldehyde and neutral methyl formate, followed by proton transfer to generate the products. Preliminary ab initio calculations executed at the UMP3/6-31G*//6-31G*+ZPVE level of theory are presented in support of this proposal. The non-specific loss of HCO from 1 (about 25%) is rationalized to occur via the same mechanism, but after communication with isomeric dimethyl carbonate ions CH3OC(=O)OCH3+, 2, via the O...H...O bonded intermediate [CH2=O...H...O=C---OCH3]+. The latter pathway is even more important in the formation of CH2OH+ ions from 1 which, it is shown, is not a simple bond cleavage reaction, but may involve consecutive or concerted losses of CH3 and CO2 from the above O...H...O bonded species. Ionized methyl lactate HOCH(CH3)C(=O)OCH3+, the higher homologue of 1, shows a unimolecular chemistry which is akin to that of 1.

  8. A unified description of the electrochemical, charge distribution, and spectroscopic properties of the special-pair radical cation in bacterial photosynthesis.

    PubMed

    Reimers, Jeffrey R; Hush, Noel S

    2004-04-01

    We apply our four-state 70-vibration vibronic-coupling model for the properties of the photosynthetic special-pair radical cation to: (1) interpret the observed correlations between the midpoint potential and the distribution of spin density between the two bacteriochlorophylls for 30 mutants of Rhodobacter sphaeroides, (2) interpret the observed average intervalence hole-transfer absorption energies as a function of spin density for six mutants, and (3) simulate the recently obtained intervalence electroabsorption Stark spectrum of the wild-type reaction center. While three new parameters describing the location of the sites of mutation with respect to the special pair are required to describe the midpoint-potential data, a priori predictions are made for the transition energies and the Stark spectrum. In general, excellent predictions are made of the observed quantities, with deviations being typically of the order of twice the experimental uncertainties. A unified description of many chemical and spectroscopic properties of the bacterial reaction center is thus provided. Central to the analysis is the assumption that the perturbations made to the reaction center, either via mutations of protein residues or by application of an external electric field, act only to independently modify the oxidation potentials of the two halves of the special pair and hence the redox asymmetry E0. While this appears to be a good approximation, clear evidence is presented that effects of mutation can be more extensive than what is allowed for. A thorough set of analytical equations describing the observed properties is obtained using the Born-Oppenheimer adiabatic approximation. These equations are generally appropriate for intervalence charge-transfer problems and include, for the first time, full treatment of both symmetric and antisymmetric vibrational motions. The limits of validity of the adiabatic approach to the full nonadiabatic problem are obtained.

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

    PubMed

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

    2016-01-01

    The spectroscopic and kinetic characterization of two intermediates from the H₂O₂ oxidation of three dimethyl ester [(proto), (meso), (deuteroporphyrinato) (picdien)]Fe(III) complexes ([FePPPic], [FeMPPic] and [FeDPPic], respectively) pinch-porphyrin peroxidase enzyme models, with s = 5/2 and 3/2 Fe(III) quantum mixed spin (qms) ground states is described herein. The kinetic study by UV/Vis at λmax = 465 nm showed two different types of kinetics during the oxidation process in the guaiacol test for peroxidases (1-3 + guaiacol + H₂O₂ → oxidation guaiacol products). The first intermediate was observed during the first 24 s of the reaction. When the reaction conditions were changed to higher concentration of pinch-porphyrins and hydrogen peroxide only one type of kinetics was observed. Next, the reaction was performed only between pinch-porphyrins-Fe(III) and H₂O₂, resulting in only two types of kinetics that were developed during the first 0-4 s. After this time a self-oxidation process was observed. Our hypotheses state that the formation of the π-cation radicals, reaction intermediates of the pinch-porphyrin-Fe(III) family with the ligand picdien [N,N'-bis-pyridin-2-ylmethyl-propane-1,3-diamine], occurred with unique kinetics that are different from the overall process and was involved in the oxidation pathway. UV-Vis, ¹H-NMR and ESR spectra confirmed the formation of such intermediates. The results in this paper highlight the link between different spectroscopic techniques that positively depict the kinetic traits of artificial compounds with enzyme-like activity. PMID:27355940

  10. Selective hydroxylation of alkanes by an extracellular fungal peroxygenase.

    PubMed

    Peter, Sebastian; Kinne, Matthias; Wang, Xiaoshi; Ullrich, René; Kayser, Gernot; Groves, John T; Hofrichter, Martin

    2011-10-01

    Fungal peroxygenases are novel extracellular heme-thiolate biocatalysts that are capable of catalyzing the selective monooxygenation of diverse organic compounds, using only H(2)O(2) as a cosubstrate. Little is known about the physiological role or the catalytic mechanism of these enzymes. We have found that the peroxygenase secreted by Agrocybe aegerita catalyzes the H(2)O(2)-dependent hydroxylation of linear alkanes at the 2-position and 3-position with high efficiency, as well as the regioselective monooxygenation of branched and cyclic alkanes. Experiments with n-heptane and n-octane showed that the hydroxylation proceeded with complete stereoselectivity for the (R)-enantiomer of the corresponding 3-alcohol. Investigations with a number of model substrates provided information about the route of alkane hydroxylation: (a) the hydroxylation of cyclohexane mediated by H(2)(18)(2) resulted in complete incorporation of (18)O into the hydroxyl group of the product cyclohexanol; (b) the hydroxylation of n-hexane-1,1,1,2,2,3,3-D(7) showed a large intramolecular deuterium isotope effect [(k(H)/k(D))(obs)] of 16.0 ± 1.0 for 2-hexanol and 8.9 ± 0.9 for 3-hexanol; and (c) the hydroxylation of the radical clock norcarane led to an estimated radical lifetime of 9.4 ps and an oxygen rebound rate of 1.06 × 10(11) s(-1). These results point to a hydrogen abstraction and oxygen rebound mechanism for alkane hydroxylation. The peroxygenase appeared to lack activity on long-chain alkanes (> C(16)) and highly branched alkanes (e.g. tetramethylpentane), but otherwise exhibited a broad substrate range. It may accordingly have a role in the bioconversion of natural and anthropogenic alkane-containing structures (including alkyl chains of complex biomaterials) in soils, plant litter, and wood. PMID:21812933

  11. Crystalline bipyridinium radical complexes and uses thereof

    SciTech Connect

    Fahrenbach, Albert C.; Barnes, Jonathan C.; Li, Hao; Stoddart, J. Fraser; Basuray, Ashish Neil; Sampath, Srinivasan

    2015-09-01

    Described herein are methods of generating 4,4'-bipyridinium radical cations (BIPY.sup..cndot.+), and methods for utilizing the radical-radical interactions between two or more BIPY.sup..cndot.+ radical cations that ensue for the creation of novel materials for applications in nanotechnology. Synthetic methodologies, crystallographic engineering techniques, methods of physical characterization, and end uses are described.

  12. Strong Inhibition of O-Atom Transfer Reactivity for Mn(IV)(O)(π-Radical-Cation)(Lewis Acid) versus Mn(V)(O) Porphyrinoid Complexes.

    PubMed

    Zaragoza, Jan Paulo T; Baglia, Regina A; Siegler, Maxime A; Goldberg, David P

    2015-05-27

    The oxygen atom transfer (OAT) reactivity of two valence tautomers of a Mn(V)(O) porphyrinoid complex was compared. The OAT kinetics of Mn(V)(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato(3-)) reacting with a series of triarylphosphine (PAr3) substrates were monitored by stopped-flow UV-vis spectroscopy, and revealed second-order rate constants ranging from 16(1) to 1.43(6) × 10(4) M(-1) s(-1). Characterization of the OAT transition state analogues Mn(III)(OPPh3)(TBP8Cz) and Mn(III)(OP(o-tolyl)3)(TBP8Cz) was carried out by single-crystal X-ray diffraction (XRD). A valence tautomer of the closed-shell Mn(V)(O)(TBP8Cz) can be stabilized by the addition of Lewis and Brønsted acids, resulting in the open-shell Mn(IV)(O)(TBP8Cz(•+)):LA (LA = Zn(II), B(C6F5)3, H(+)) complexes. These Mn(IV)(O)(π-radical-cation) derivatives exhibit dramatically inhibited rates of OAT with the PAr3 substrates (k = 8.5(2) × 10(-3) - 8.7 M(-1) s(-1)), contrasting the previously observed rate increase of H-atom transfer (HAT) for Mn(IV)(O)(TBP8Cz(•+)):LA with phenols. A Hammett analysis showed that the OAT reactivity for Mn(IV)(O)(TBP8Cz(•+)):LA is influenced by the Lewis acid strength. Spectral redox titration of Mn(IV)(O)(TBP8Cz(•+)):Zn(II) gives Ered = 0.69 V vs SCE, which is nearly +700 mV above its valence tautomer Mn(V)(O)(TBP8Cz) (Ered = -0.05 V). These data suggest that the two-electron electrophilicity of the Mn(O) valence tautomers dominate OAT reactivity and do not follow the trend in one-electron redox potentials, which appear to dominate HAT reactivity. This study provides new fundamental insights regarding the relative OAT and HAT reactivity of valence tautomers such as M(V)(O)(porph) versus M(IV)(O)(porph(•+)) (M = Mn or Fe) found in heme enzymes.

  13. Identity and mechanisms of alkane-oxidizing metalloenzymes from deep-sea hydrothermal vents.

    PubMed

    Bertrand, Erin M; Keddis, Ramaydalis; Groves, John T; Vetriani, Costantino; Austin, Rachel Narehood

    2013-01-01

    Six aerobic alkanotrophs (organism that can metabolize alkanes as their sole carbon source) isolated from deep-sea hydrothermal vents were characterized using the radical clock substrate norcarane to determine the metalloenzyme and reaction mechanism used to oxidize alkanes. The organisms studied were Alcanivorax sp. strains EPR7 and MAR14, Marinobacter sp. strain EPR21, Nocardioides sp. strains EPR26w, EPR28w, and Parvibaculum hydrocarbonoclasticum strain EPR92. Each organism was able to grow on n-alkanes as the sole carbon source and therefore must express genes encoding an alkane-oxidizing enzyme. Results from the oxidation of the radical-clock diagnostic substrate norcarane demonstrated that five of the six organisms (EPR7, MAR14, EPR21, EPR26w, and EPR28w) used an alkane hydroxylase functionally similar to AlkB to catalyze the oxidation of medium-chain alkanes, while the sixth organism (EPR92) used an alkane-oxidizing cytochrome P450 (CYP)-like protein to catalyze the oxidation. DNA sequencing indicated that EPR7 and EPR21 possess genes encoding AlkB proteins, while sequencing results from EPR92 confirmed the presence of a gene encoding CYP-like alkane hydroxylase, consistent with the results from the norcarane experiments.

  14. Effect of iridium(IV) oxides on the decay of zinc tetrakis(N-methylpyridinium-4-yl)porphyrin. pi. -radical cation in the presence of poly(styrenesulfonate)

    SciTech Connect

    Nahor, G.S. )

    1989-07-27

    The {pi}-radical cation of zinc tetrakis(N-methylpyridinium-4-yl)porphyrin(ZnTMPyP{sup 5+}) has been produced by pulse radiolysis and its decay reactions have been followed in the presence of oxoiridium(IV) hydrate species and a negatively charged polyelectrolyte, poly(styrenesulfonate) (PSS). The iridium oxide species were produced from hexachloroiridate, and the nature of the product strongly depended on the pH during preparation. A hexahydroxoiridate species that was produced at high pH was found to be very reactive, and its reactions account for most decay processes observed. {gamma}-Radiolysis experiments suggest that this decay involves oxidation of the iridium species in a catalytic process. PSS-stabilized IrO{sub x} hydrosols did not react with the radical cation fast enough to compete with its disproportionation, although such hydrosols were highly reactive when stabilized with neutral or positively charged polymers. The lack of reactivity is attributed to the low mobility of the positively charged porphyrin in the domain of the negatively charged polyelectrolyte as well as to the absence of interpolymer processes. However, under {gamma}-radiolysis conditions, a redox reaction between the hydrosols and the radical becomes feasible.

  15. A simple, post-additional antioxidant capacity assay using adenosine triphosphate-stabilized 2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) radical cation in a G-quadruplex DNAzyme catalyzed ABTS-H2O2 system.

    PubMed

    Jia, Shu-Min; Liu, Xiao-Fei; Kong, De-Ming; Shen, Han-Xi

    2012-05-15

    The scavenging of 2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) radical cation (ABTS(+)) by antioxidants has been widely used in antioxidant capacity assay. Because of ABTS(+) disproportionation, however, this radical cannot be prepared on a large scale and stored long-term, making it unsuitable for high-throughput detection and screening of antioxidants. We developed a modified "post-additional" antioxidant capacity assay. This method possessed two remarkable features: First, instead of natural peroxidases, an artificial enzyme, G-quadruplex DNAzyme, was used for the preparation of ABTS(+), thus greatly reducing the cost of the assay, and eliminating the strict demand for the storage of enzymes. Second, an ABTS(+) stabilizer, adenosine triphosphate (ATP), was used. In the presence of ATP, the disproportionation of ABTS(+) was effectively inhibited, and the lifetime of this radical cation was prolonged about 6-fold (12 days versus 2 days), making the large-scale preparation of ABTS(+) possible. Utilizing this method, the antioxidant capacities of individual antioxidants and real samples can be quantified and compared easily. In addition, this method can be developed as a high-throughput screening method for antioxidants. The screening results could even be judged by the naked eye, eliminating the need for expensive instruments.

  16. Metabolism of Hydrocarbons in n-Alkane-Utilizing Anaerobic Bacteria.

    PubMed

    Wilkes, Heinz; Buckel, Wolfgang; Golding, Bernard T; Rabus, Ralf

    2016-01-01

    The glycyl radical enzyme-catalyzed addition of n-alkanes to fumarate creates a C-C-bond between two concomitantly formed stereogenic carbon centers. The configurations of the two diastereoisomers of the product resulting from n-hexane activation by the n-alkane-utilizing denitrifying bacterium strain HxN1, i.e. (1-methylpentyl)succinate, were assigned as (2S,1'R) and (2R,1'R). Experiments with stereospecifically deuterated n-(2,5-2H2)hexanes revealed that exclusively the pro-S hydrogen atom is abstracted from C2 of the n-alkane by the enzyme and later transferred back to C3 of the alkylsuccinate formed. These results indicate that the alkylsuccinate-forming reaction proceeds with an inversion of configuration at the carbon atom (C2) of the n-alkane forming the new C-C-bond, and thus stereochemically resembles a SN2-type reaction. Therefore, the reaction may occur in a concerted manner, which may avoid the highly energetic hex-2-yl radical as an intermediate. The reaction is associated with a significant primary kinetic isotope effect (kH/kD ≥3) for hydrogen, indicating that the homolytic C-H-bond cleavage is involved in the first irreversible step of the reaction mechanism. The (1-methylalkyl)succinate synthases of n-alkane-utilizing anaerobic bacteria apparently have very broad substrate ranges enabling them to activate not only aliphatic but also alkyl-aromatic hydrocarbons. Thus, two denitrifiers and one sulfate reducer were shown to convert the nongrowth substrate toluene to benzylsuccinate and further to the dead-end product benzoyl-CoA. For this purpose, however, the modified β-oxidation pathway known from alkylbenzene-utilizing bacteria was not employed, but rather the pathway used for n-alkane degradation involving CoA ligation, carbon skeleton rearrangement and decarboxylation. Furthermore, various n-alkane- and alkylbenzene-utilizing denitrifiers and sulfate reducers were found to be capable of forming benzyl alcohols from diverse alkylbenzenes

  17. Alkane desaturation by concerted double hydrogen atom transfer to benzyne.

    PubMed

    Niu, Dawen; Willoughby, Patrick H; Woods, Brian P; Baire, Beeraiah; Hoye, Thomas R

    2013-09-26

    The removal of two vicinal hydrogen atoms from an alkane to produce an alkene is a challenge for synthetic chemists. In nature, desaturases and acetylenases are adept at achieving this essential oxidative functionalization reaction, for example during the biosynthesis of unsaturated fatty acids, eicosanoids, gibberellins and carotenoids. Alkane-to-alkene conversion almost always involves one or more chemical intermediates in a multistep reaction pathway; these may be either isolable species (such as alcohols or alkyl halides) or reactive intermediates (such as carbocations, alkyl radicals, or σ-alkyl-metal species). Here we report a desaturation reaction of simple, unactivated alkanes that is mechanistically unique. We show that benzynes are capable of the concerted removal of two vicinal hydrogen atoms from a hydrocarbon. The discovery of this exothermic, net redox process was enabled by the simple thermal generation of reactive benzyne intermediates through the hexadehydro-Diels-Alder cycloisomerization reaction of triyne substrates. We are not aware of any single-step, bimolecular reaction in which two hydrogen atoms are simultaneously transferred from a saturated alkane. Computational studies indicate a preferred geometry with eclipsed vicinal C-H bonds in the alkane donor.

  18. Process for functionalizing alkanes

    DOEpatents

    Bergman, R.G.; Janowicz, A.H.; Periana, R.A.

    1988-05-24

    Process for functionalizing saturated hydrocarbons comprises: (a) reacting said saturated hydrocarbons of the formula: R[sub 1]H wherein H represents a hydrogen atom; and R[sub 1] represents a saturated hydrocarbon radical, with a metal complex of the formula: CpRh[P(R[sub 2])[sub 3

  19. Modelling the bacterial photosynthetic reaction center. V. Assignment of the electronic transition observed at 2200 cm-1 in the special-pair radical-cation as a second-highest occupied molecular orbital to highest occupied molecular orbital transition

    NASA Astrophysics Data System (ADS)

    Reimers, Jeffrey R.; Shapley, Warwick A.; Hush, Noel S.

    2003-08-01

    Primary charge separation in photoexcited photosynthetic reaction centers produces the radical cation P+ of a bacteriochlorophyll dimer known as the special-pair P. P+ has an intense electronic transition in the vicinity of 1800-5000 cm-1 which is usually assigned to the interchromophore hole-transfer excitation of the dimer radical cation; in principle, this spectrum can give much insight into key steps of the solar-to-electrical energy-conversion process. The extent to which this transition is localized on one-half of the dimer or delocalized over both is of utmost importance; an authoritative deduction of this quantity from purely spectroscopic arguments requires the detailed assignment of the observed high to medium resolution spectra. For reaction centers containing bacteriochlorophylls a or b, a shoulder is observed at 2200 cm-1 on the low-energy side of the main hole-transfer absorption band, a band whose maximum is near 2700 cm-1. Before quantitative analysis of the hole-transfer absorption in these well-studied systems can be attempted, the nature of the processes leading to this shoulder must be determined. We interpret it as arising from an intrachromophore SHOMO to HOMO transition whose intensity arises wholly through vibronic coupling with the hole-transfer band. A range of ab initio and density-functional calculations are performed to estimate the energy of this transition both for monomeric cations and for P+ of Blastochloris viridis, Rhodobacter sphaeroides, Chlorobium limicola, Chlorobium tepidum, Chlamydomonas reinhardtii, Synochocystis S.6803, spinach photosystems I and II, Heliobacillus mobilis, and finally Heliobacterium modesticaldum, with the results found to qualitatively describe the available experimental data. Subsequent papers in this series provide quantitative analyses of the vibronic coupling and complete spectral simulations based on the model developed herein.

  20. Copper-Catalyzed Intermolecular Amidation and Imidation of Unactivated Alkanes

    PubMed Central

    2015-01-01

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

  1. Process for functionalizing alkanes

    DOEpatents

    Bergman, Robert G.; Janowicz, Andrew H.; Periana, Roy A.

    1988-01-01

    Process for functionalizing saturated hydrocarbons comprising: (a) reacting said saturated hydrocarbons of the formula: R.sub.1 H wherein H represents a hydrogen atom; and R.sub.1 represents a saturated hydrocarbon radical, with a metal complex of the formula: CpRh[P(R.sub.2).sub.3 ]H.sub.2 wherein Cp represents a cyclopentadienyl or alkylcyclopentadienyl radical; Rh represents a rhodium atom; P represents a phosphorus atom; R.sub.2 represents a hydrocarbon radical; H represents a hydrogen atom, in the presence of ultraviolet radiation to form a hydridoalkyl complex of the formula: CpRh[P(R.sub.2).sub.3 ](R.sub.1)H (b) reacting said hydridoalkyl complex with an organic halogenating agent such as a tetrahalomethane or a haloform of the formulas: CX'X''X'''X'''' or CHX'X''X''' wherein X', X'', X'", X"" represent halogens selected from bromine, iodine or chlorine atom, at a temperature in the range of about -60.degree. to -17.degree. C. to form the corresponding haloalkyl complex of step (a) having the formula: CpRhPMe.sub.3 RX; and, (c) reacting said haloalkyl complex formed in (b) with halogen (X.sub.2) at a temperature in the range of about -60.degree. to 25.degree. C. (i.e., ambient) to form a functional haloalkyl compound.

  2. Notable effects of the metal salts on the formation and decay reactions of α-tocopheroxyl radical in acetonitrile solution. The complex formation between α-tocopheroxyl and metal cations.

    PubMed

    Kohno, Yutaro; Fujii, Miyabi; Matsuoka, Chihiro; Hashimoto, Haruka; Ouchi, Aya; Nagaoka, Shin-ichi; Mukai, Kazuo

    2011-08-18

    The measurement of the UV-vis absorption spectrum of α-tocopheroxyl (α-Toc(•)) radical was performed by reacting aroxyl (ArO(•)) radical with α-tocopherol (α-TocH) in acetonitrile solution including four kinds of alkali and alkaline earth metal salts (MX or MX(2)) (LiClO(4), LiI, NaClO(4), and Mg(ClO(4))(2)), using stopped-flow spectrophotometry. The maximum wavelength (λ(max)) of the absorption spectrum of the α-Toc(•) at 425.0 nm increased with increasing concentration of metal salts (0-0.500 M) in acetonitrile, and it approached constant values, suggesting an [α-Toc(•)-M(+) (or M(2+))] complex formation. The stability constants (K) were determined to be 9.2, 2.8, and 45 M(-1) for LiClO(4), NaClO(4), and Mg(ClO(4))(2), respectively. By reacting ArO(•) with α-TocH in acetonitrile, the absorption of ArO(•) disappeared rapidly, while that of α-Toc(•) appeared and then decreased gradually as a result of the bimolecular self-reaction of α-Toc(•) after passing through the maximum. The second-order rate constants (k(s)) obtained for the reaction of α-TocH with ArO(•) increased linearly with an increasing concentration of metal salts. The results indicate that the hydrogen transfer reaction of α-TocH proceeds via an electron transfer intermediate from α-TocH to ArO(•) radicals followed by proton transfer. Both the coordination of metal cations to the one-electron reduced anions of ArO(•) (ArO:(-)) and the coordination of counteranions to the one-electron oxidized cations of α-TocH (α-TocH(•)(+)) may stabilize the intermediate, resulting in the acceleration of electron transfer. A remarkable effect of metal salts on the rate of bimolecular self-reaction (2k(d)) of the α-Toc(•) radical was also observed. The rate constant (2k(d)) decreased rapidly with increasing concentrations of the metal salts. The 2k(d) value decreased at the same concentration of the metal salts in the following order: no metal salt > NaClO(4) > LiClO(4) > Mg

  3. Radical cations as precursors in the metabolic formation of quinones from benzo[a]pyrene and 6-fluorobenzo[a]pyrene. Fluoro substitution as a probe for one-electron oxidation in aromatic substrates.

    PubMed

    Cavalieri, E L; Rogan, E G; Cremonesi, P; Devanesan, P D

    1988-06-01

    Three classes of products are formed when benzo[a]pyrene (BP) is metabolized by cytochrome P-450: dihydrodiols, phenols and the quinones, BP 1,6-, 3,6- and 6,12-dione. These products have been thought to arise from attack of a catalytically-activated electrophilic oxygen atom. In this paper we report chemical and biochemical experiments which demonstrate that BP quinones arise from an initial one-electron oxidation of BP to form its radical cation. BP, 6-fluorobenzo[a]pyrene (6-FBP), 6-chlorobenzo[a]pyrene (6-ClBP), and 6-bromobenzo[a]pyrene (6-BrBP) were metabolized by uninduced and 3-methylcholanthrene-induced rat liver microsomes in the presence of NADPH or cumene hydroperoxide (CHP) as cofactor. BP and 6-FBP produced similar metabolic profiles with induced microsomes in the presence of NADPH or 2 mM CHP. With NADPH both compounds produced dihydrodiols, phenols and quinones, whereas with CHP, they yielded only quinones. Metabolism of BP and 6-FBP was also similar with uninduced microsomes and 2 mM CHP, yielding the same BP quinones. With uninduced microsomes in the presence of NADPH, BP produced all three classes of metabolites, whereas 6-FBP afforded only quinones. At a low concentration of CHP (0.10 mM), BP was metabolized to phenols and quinones, whereas 6-FBP gave only quinones. 6-ClBP and 6-BrBP were poor substrates, forming metabolites only with induced microsomes and NADPH. One-electron oxidation of BP by Mn(OAc)3 occurred exclusively at C-6 with predominant formation of 6-acetoxyBP and small amounts of BP quinones. In the one-electron oxidation of 6-FBP by Mn(OAc)3, the major products obtained were 6-acetoxyBP, a mixture of 1,6- and 3,6-diacetoxyBP, and BP quinones. Reaction of BP and 6-FBP radical cation perchlorates with water produced the same BP quinones. Conversely, electrophilic substitution of 6-FBP with bromine or deuterium ion afforded C-1 and/or C-3 derivatives with retention of the fluoro substituent at C-6. These results indicate that

  4. Studies of radiation-produced radicals and radical ions

    SciTech Connect

    Williams, T.F.

    1991-01-01

    The radiolytic oxidation of anti-5-methylbicyclo(2.1.0)pentane gives the 1-methylcyclopentene radical cation as the sole rearrangement product H migration whereas oxidation of its syn isomer results in the highly selective formation of the 3-methylcyclopentene radical cation by methyl group migration. Since exactly the same stereoselectivity of olefin formation was observed in corresponding PET (photosensitized electron transfer) studies in the liquid phase, it is concluded that the rearrangement in this case also occurs through the intermediacy of radical cations. Clearly, the radical cation rearrangement must occur very rapidly (10{sup {minus}8}--10{sup {minus}9}s) under liquid-phase conditions at room temperature to compete with back electron transfer, and therefore the hydrogen (or methyl) migration is a fast process under these conditions. An intramolecular cycloaddition reaction was demonstrated in the radical cation rearrangement of 4-vinylcyclohexene to bicyclo(3.2.1)oct-2-ene. ESR studies show that the radiolytic oxidation of quadricyclane in Freon matrices under conditions of high substrate dilution leads to the bicyclo(3.2.0)hepta-2,6-diene radical cation as well as the previously reported norbornadiene radical cation, the former species predominating at sufficiently low concentrations.

  5. Process for functionalizing alkanes

    SciTech Connect

    Bergman, R. G.; Janowicz, A. H.; Periana-Pillai, R. A.

    1985-04-16

    Process for functionalizing saturated hydrocarbons selectively in the terminal position comprising: (a) reacting said saturated hydrocarbons of the formula: RH where: H represents a hydrogen atom, and R represents a saturated hydrocarbon radical, with a metal complex of the formula: C /SUB p/ RhPMe/sub 3/H/sub 2/ where: C /SUB p/ represents a pentamethylated cyclopentadienyl radical, Rh represents a rhodium atom, P represents a phosphorous atom, Me represents a methyl group, H represents a hydrogen atom, in the presence of ultraviolet radiation at a temperature maintained at about -60/sup 0/ to -17/sup 0/ C. to form a hydridoalkyl complex of the formula: C /SUB p/ RhPMe/sub 3/RH (b) reacting said hydridoalkyl complex with a haloform of the formula: CHX/sub 3/ where: X represents a bromine, iodine or chlorine atom, at a temperature in the range of about -60/sup 0/ to -17/sup 0/ C. to form the corresponding haloalkyl complex of step (a) having the formula: C /SUB p/ RhMe/sub 3/RX; and, (c) reacting said haloalkyl complex formed in (b) with halogen (X/sub 2/) at a temperature in the range of about -60/sup 0/ to 25/sup 0/ C. (i.e. ambient) to form a functional haloalkyl compound.

  6. Process for functionalizing alkanes

    DOEpatents

    Bergman, Robert G.; Janowicz, Andrew H.; Periana-Pillai, Roy A.

    1985-01-01

    Process for functionalizing saturated hydrocarbons selectively in the terminal position comprising: (a) reacting said saturated hydrocarbons of the formula: RH where: H represents a hydrogen atom, and R represents a saturated hydrocarbon radical, with a metal complex of the formula: CpRhPMe.sub.3 H.sub.2 where: Cp represents a pentamethylated cyclopentadienyl radical, Rh represents a rhodium atom, P represents a phosphorous atom, Me represents a methyl group, H represents a hydrogen atom, in the presence of ultraviolet radiation at a temperature maintained at about -60.degree. to -17.degree. C. to form a hydridoalkyl complex of the formula: CpRhPMe.sub.3 RH (b) reacting said hydridoalkyl complex with a haloform of the formula: CHX.sub.3 where: X represents a bromine, iodine or chlorine atom, at a temperature in the range of about -60.degree. to -17.degree. C. to form the corresponding haloalkyl complex of step (a) having the formula: CpRhPMe.sub.3 RX; and, (c) reacting said haloalkyl complex formed in (b) with halogen (X.sub.2) at a temperature in the range of about -60.degree. to 25.degree. C. (i.e. ambient) to form a functional haloalkyl compound.

  7. Cascade Dissociations of Peptide Cation-Radicals. Part2. Infrared Multiphoton Dissociation and Mechanistic Studies of z-Ions from Pentapeptides

    PubMed Central

    Ledvina, Aaron R.; Chung, Thomas W.; Hui, Renjie; Coon, Joshua J.

    2013-01-01

    Dissociations of z4 ions from pentapeptides AAXAR, where X = H, Y, F, W, and V, produce dominant z2 ions that account for >50% of the fragment ion intensity. The dissociation has been studied in detail by experiment and theory and found to involve several isomerization and bond-breaking steps. Isomerizations in z4 ions proceed by amide transcis rotations followed by radical-induced transfer of a β-hydrogen atom from the side chain, forming stable Cβ radical intermediates. These undergo rate-determining cleavage of the Cα—CO bond at the X residue followed by loss of the neutral AX fragment, forming x2 intermediates. The latter were detected by energy-resolved resonant excitation collision-activated dissociation (CAD) and infrared multiphoton dissociation (IRMPD) experiments. The x2 intermediates undergo facile loss of HNCO to form z2 fragment ions, as also confirmed by energy-resolved CAD and IRMPD MS4 experiments. The loss of HNCO from the x2 ion from AAHWR is kinetically hampered by the Trp residue that traps the OCNH radical group in a cyclic intermediate. PMID:22669762

  8. Cascade dissociations of peptide cation-radicals. Part 2. Infrared multiphoton dissociation and mechanistic studies of z-ions from pentapeptides.

    PubMed

    Ledvina, Aaron R; Chung, Thomas W; Hui, Renjie; Coon, Joshua J; Tureček, Frantisek

    2012-08-01

    Dissociations of z(4) ions from pentapeptides AAXAR where X=H, Y, F, W, and V produce dominant z(2) ions that account for >50 % of the fragment ion intensity. The dissociation has been studied in detail by experiment and theory and found to involve several isomerization and bond-breaking steps. Isomerizations in z(4) ions proceed by amide trans→cis rotations followed by radical-induced transfer of a β-hydrogen atom from the side chain, forming stable C(β) radical intermediates. These undergo rate-determining cleavage of the C(α)-CO bond at the X residue followed by loss of the neutral AX fragment, forming x(2) intermediates. The latter were detected by energy-resolved resonant excitation collision-induced dissociation (CID) and infrared multiphoton dissociation (IRMPD) experiments. The x(2) intermediates undergo facile loss of HNCO to form z(2) fragment ions, as also confirmed by energy-resolved CID and IRMPD MS(4) experiments. The loss of HNCO from the x(2) ion from AAHWR is kinetically hampered by the Trp residue that traps the OCNH radical group in a cyclic intermediate. PMID:22669762

  9. Liquid-liquid interfaces of semifluorinated alkane diblock copolymers with water, alkanes, and perfluorinated alkanes.

    SciTech Connect

    Perahia, Dvora, Dr.; Pierce, Flint; Tsige, Mesfin; Grest, Gary Stephen, Dr.

    2008-08-01

    The liquid-liquid interface between semifluorinated alkane diblock copolymers of the form F3C(CF2)n-1-(CH2)m-1CH3 and water, protonated alkanes, and perfluorinated alkanes are studied by fully atomistic molecular dynamics simulations. A modified version of the OPLS-AA (Optimized Parameter for Liquid Simulation All-Atom) force field of Jorgensen et al. has been used to study the interfacial behavior of semifluorinated diblocks. Aqueous interfaces are found to be sharp, with correspondingly large values of the interfacial tension. Due to the reduced hydrophobicity of the protonated block compared to the fluorinated block, hydrogen enhancement is observed at the interface. Water dipoles in the interfacial region are found to be oriented nearly parallel to the liquid-liquid interface. A number of protonated alkanes and perfluorinated alkanes are found to be mutually miscible with the semifluorinated diblocks. For these liquids, interdiffusion follows the expected Fickian behavior, and concentration-dependent diffusivities are determined.

  10. Formation of C10H+8 from the benzene radical cation: a case for the growth of polycyclic aromatic hydrocarbon ions by ion/molecule reactions in the gas phase?

    NASA Astrophysics Data System (ADS)

    Bohme, D. K.; Wlodek, S.; Zimmerman, J. A.; Eyler, J. R.

    1991-11-01

    Experimental results are reported which show that diacetylene, but not acetylene, adds rapidly to C6H+6 in the gas phase in helium at 0.35 Torr and 296 ± 2 K when C6H+6 is produced by the chemical ionisation of benzene with NO+. The experiments were performed with the selected-ion flow tube and Fourier transform ion cyclotron resonance techniques. Chemical reactivity and ion photodissociation methods were employed to investigate the identity of the C10H+8 ion produced by the addition reaction. Results were obtained for the reactions of this cation with deuterium, acetylene, diacetylene, styrene, trimethylamine, nitric oxide, 1,2,4,5-tetramethylbenzene and p-methylaniline, and were compared with the results of the reactions of these same molecules with the C10H+8 radical cation produced directly from naphthalene by chemical ionisation with Si+ and electron ionisation. Laser photodissociation experiments at 355 nm were also carried out on the C10H+8 ion produced from the addition reaction, and by electron ionisation of naphthalene and azulene. The chemical and photophysical behavior of the former two ions was found to be identical which suggests that ionised naphthalene is formed in the addition reaction of ionised benzene and diacetylene. The implications of this result for the growth of polycyclic aromatic hydrocarbons in hydrocarbon flames and in interstellar regions are briefly discussed.

  11. Low temperature rate coefficients for reactions of the butadiynyl radical, C4H, with various hydrocarbons. Part I: reactions with alkanes (CH4, C2H6, C3H8, C4H10).

    PubMed

    Berteloite, Coralie; Le Picard, Sébastien D; Balucani, Nadia; Canosa, André; Sims, Ian R

    2010-04-21

    The kinetics of the reactions of the linear butadiynyl radical, C4H (CCCCH), with methane, ethane, propane and butane have been studied over the temperature range of 39-300 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. The rate coefficients, except for the reaction with methane, show a negative temperature dependence and can be fitted with the following expressions over the temperature range of this study: k(C2H6) = 0.289 x 10(-10) (T/298 K)(-1.23) exp(-24.8 K/T) cm3 molecule(-1) s(-1); k(C3H8) = 1.06 x 10(-10) (T/298 K)(-1.36) exp(-56.9 K/T) cm3 molecule(-1) s(-1); k(C4H10) = 2.93 x 10(-10) (T/298 K)(-1.30) exp(-90.1 K/T) cm3 molecule(-1) s(-1). The rate coefficients for the reaction with methane were measured only at 200 K and 300 K yielding a positive temperature dependence: k(CH4) = 1.63 x 10(-11) exp(-610 K/T) cm3 molecule(-1) s(-1). Possible reaction mechanisms and product channels are discussed in detail for each of these reactions. Potential implications of these results for models of low temperature chemical environments, in particular cold interstellar clouds and planetary atmospheres such as that of Titan, are considered.

  12. Actinide cation-cation complexes

    SciTech Connect

    Stoyer, N.J.; Seaborg, G.T.

    1994-12-01

    The +5 oxidation state of U, Np, Pu, and Am is a linear dioxo cation (AnO{sub 2}{sup +}) with a formal charge of +1. These cations form complexes with a variety of other cations, including actinide cations. Other oxidation states of actinides do not form these cation-cation complexes with any cation other than AnO{sub 2}{sup +}; therefore, cation-cation complexes indicate something unique about AnO{sub 2}{sup +} cations compared to actinide cations in general. The first cation-cation complex, NpO{sub 2}{sup +}{center_dot}UO{sub 2}{sup 2+}, was reported by Sullivan, Hindman, and Zielen in 1961. Of the four actinides that form AnO{sub 2}{sup +} species, the cation-cation complexes of NpO{sub 2}{sup +} have been studied most extensively while the other actinides have not. The only PuO{sub 2}{sup +} cation-cation complexes that have been studied are with Fe{sup 3+} and Cr{sup 3+} and neither one has had its equilibrium constant measured. Actinides have small molar absorptivities and cation-cation complexes have small equilibrium constants; therefore, to overcome these obstacles a sensitive technique is required. Spectroscopic techniques are used most often to study cation-cation complexes. Laser-Induced Photacoustic Spectroscopy equilibrium constants for the complexes NpO{sub 2}{sup +}{center_dot}UO{sub 2}{sup 2+}, NpO{sub 2}{sup +}{center_dot}Th{sup 4+}, PuO{sub 2}{sup +}{center_dot}UO{sub 2}{sup 2+}, and PuO{sub 2}{sup +}{center_dot}Th{sup 4+} at an ionic strength of 6 M using LIPAS are 2.4 {plus_minus} 0.2, 1.8 {plus_minus} 0.9, 2.2 {plus_minus} 1.5, and {approx}0.8 M{sup {minus}1}.

  13. Reactivity of oxygen radical anions bound to scandia nanoparticles in the gas phase: C-H bond activation.

    PubMed

    Tian, Li-Hua; Meng, Jing-Heng; Wu, Xiao-Nan; Zhao, Yan-Xia; Ding, Xun-Lei; He, Sheng-Gui; Ma, Tong-Mei

    2014-01-20

    The activation of C-H bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O(-·)) is an important species in C-H activation. The mechanistic details of C-H activation by O(-·) radicals can be well understood by studying the reactions between O(-·) containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n-butane was studied by using a high-resolution time-of-flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n-butane by (Sc2O3)(N)O(-) (N=1-18) clusters was observed. The reactivity of (Sc2O3)(N)O(-) (N=1-18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc8O13(-)) and 12 (Sc24O37(-)). Larger (Sc2O3)(N)O(-) clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc2O3)(N)O(-) (N=1-5) clusters, which were found to contain the O(-·) radicals as the active sites. The local charge environment around the O(-·) radicals was demonstrated to control the experimentally observed size-dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O(-·) containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the C-H bond activation. PMID:24338790

  14. Communication: Oscillating charge migration between lone pairs persists without significant interaction with nuclear motion in the glycine and Gly-Gly-NH-CH{sub 3} radical cations

    SciTech Connect

    Vacher, Morgane; Bearpark, Michael J.; Robb, Michael A.

    2014-05-28

    Coupled electron-nuclear dynamics has been studied, using the Ehrenfest method, for four conformations of the glycine molecule and a single conformation of Gly-Gly-NH-CH{sub 3}. The initial electronic wavepacket was a superposition of eigenstates corresponding to ionization from the σ lone pairs associated with the carbonyl oxygens and the amine nitrogen. For glycine, oscillating charge migration (when the nuclei were frozen) was observed for the 4 conformers studied with periods ranging from 2 to 5 fs, depending on the energy gap between the lone pair cationic states. When coupled nuclear motion was allowed (which was mainly NH{sub 2} partial inversion), the oscillations hardly changed. For Gly-Gly-NH-CH{sub 3}, charge migration between the carbonyl oxygens and the NH{sub 2} lone pair can be observed with a period similar to glycine itself, also without interaction with nuclear motion. These simulations suggest that charge migration between lone pairs can occur independently of the nuclear motion.

  15. Catalytic conversion of light alkanes

    SciTech Connect

    Lyons, J.E.

    1992-06-30

    The second Quarterly Report of 1992 on the Catalytic Conversion of Light Alkanes reviews the work done between April 1, 1992 and June 31, 1992 on the Cooperative Agreement. The mission of this work is to devise a new catalyst which can be used in a simple economic process to convert the light alkanes in natural gas to oxygenate products that can either be used as clean-burning, high octane liquid fuels, as fuel components or as precursors to liquid hydrocarbon uwspomdon fuel. During the past quarter we have continued to design, prepare, characterize and test novel catalysts for the mild selective reaction of light hydrocarbons with air or oxygen to produce alcohols directly. These catalysts are designed to form active metal oxo (MO) species and to be uniquely active for the homolytic cleavage of the carbon-hydrogen bonds in light alkanes producing intermediates which can form alcohols. We continue to investigate three molecular environments for the active catalytic species that we are trying to generate: electron-deficient macrocycles (PHASE I), polyoxometallates (PHASE II), and regular oxidic lattices including zeolites and related structures as well as other molecular surface structures having metal oxo groups (PHASE I).

  16. Comproportionation of Cationic and Anionic Tungsten Complexes Having an N -Heterocyclic Carbene Ligand To Give the Isolable 17-Electron Tungsten Radical CpW(CO) 2 (IMes)

    SciTech Connect

    Roberts, John A. S.; Franz, James A.; van der Eide, Edwin F.; Walter, Eric D.; Petersen, Jeffrey L.; DuBois, Daniel L.; Bullock, R. Morris

    2011-09-21

    A series consisting of a tungsten anion, radical and cation, supported by the N-heterocyclic carbene IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and spanning formal oxidation states W(0), W(I) and W(II), has been synthesized, isolated, and characterized. Reaction of the hydride CpW(CO)2(IMes)H with KH and 18 crown 6 gives the tungsten anion [CpW(CO)2(IMes)]-[K(18 crown 6)]+. The crystal structure of this complex shows that the K+ interacts not only with the oxygen atoms in the crown ether, but also with the carbonyl oxygens. The electrochemical oxidation of [CpW(CO)2(IMes)]- in acetonitrile is fully reversible (E½ = -1.65 V vs Cp2Fe+•/0) at all scan rates, indicating that CpW(CO)2(IMes)• is a persistent radical. Hydride transfer from CpW(CO)2(IMes)H to Ph3C+PF6 affords [cis-CpW(CO)2(IMes)(MeCN)]+PF6 . Comproportionation of [CpW(CO)2(IMes)]- with [CpW(CO)2(IMes)(MeCN)]+ gives the 17-electron tungsten radical CpW(CO)2(IMes)•. This complex shows paramagnetically shifted resonances in 1H NMR spectra and has been characterized by IR spectroscopy, low-temperature EPR spectroscopy, and X-ray diffraction. CpW(CO)2(IMes)• is very stable with respect to disproportionation and dimerization. NMR studies of degenerate electron transfer between CpW(CO)2(IMes)• and [CpW(CO)2(IMes)]- are reported. DFT calculations were carried out on CpW(CO)2(IMes)H, as well as on related complexes bearing NHC ligands with N,N´ substituents Me [CpW(CO)2(IMe)H] or H [CpW(CO)2(IH)H] to compare to the experimentally studied IMes complexes with mesityl substituents. These calculations reveal W H homolytic bond dissociation energies (BDEs) to decrease with increasing steric bulk of the NHC ligand, from 67 for CpW(CO)2(IH)H to 64 for CpW(CO)2(IMe)H to 63 kcal/mol for CpW(CO)2(IMes)H. The calculated spin density at W for CpW(CO)2(IMes)• is 0.63. The W radicals CpW(CO)2(IMe)• and CpW(CO)2(IH)• are calculated to form weak W W bonds. The weakly bonded complexes [CpW(CO)2(IMe)]2

  17. An ESR and NMR study of the radiolysis of n-alkanes: Crystal structure dependence

    NASA Astrophysics Data System (ADS)

    Toriyama, K.; Okazaki, M.; Nunome, K.; Matsuura, K.

    The process of radiation damage for long-chain n-alkanes was investigated to elucidate that for polyethylene. Chain-end alkyl radicals were preferentially formed not only through primary C-H scission but also through a hydrogen atom reaction in odd- n-alkane, as was shown by analysis of the ESR spectra for isotopic mixtures of tridecane- h28/tridecane- d28 and nonadecane- h40/nonadecane- d40. To elucidate the mode of alkyl radical migration in solids through intermolecular hydrogen atom abstraction, D/H exchange was detected in mixed crystals of eicosane- d42/eicosane- h42. The chain-end region was found to be more reactive than the inner region for radical site migration. In addition, formation of a microscopic amorphous island by destruction of the crystal lattice was also detected. The influences of molecular packing were large in all cases.

  18. Calorimetric study of cationic photopolymerization

    NASA Astrophysics Data System (ADS)

    Czajlik, I.; Hedvig, P.; Ille, A.; Dobó, J.

    1996-03-01

    The photopolymerization of penta-erythritol tetra-glycidyl ether (initiator Degacure KI-85) was studied by a du Pont 910 type DSC. From our experimental results the following conclusions can be drawn: (1) During the cationic polymerization reaction the lifetime of the initiating centers are long compared to the lifetime of free radicals in case of radical polymerization. (2) The rate of deactivation of the initiating centers increases with increasing temperature.

  19. Alkane-Based Urethane Potting Compounds

    NASA Technical Reports Server (NTRS)

    Morris, D. E.

    1986-01-01

    New low viscosity urethanes easily mixed, molded, and outgassed. Alkane-based urethanes resist hydrolysis and oxidation and have excellent dielectric properties. Low-viscosity alkane-based urethane prepolymer prepared by one-step reaction of either isophorone diisocyanate or methyl-bis (4-cyclohexyl isocyanate) with hydrogenated, hydroxy-terminated polybutadiene (HTPBD).

  20. The anaerobic degradation of gaseous, nonmethane alkanes — From in situ processes to microorganisms

    PubMed Central

    Musat, Florin

    2015-01-01

    The short chain, gaseous alkanes ethane, propane, n- and iso-butane are released in significant amounts into the atmosphere, where they contribute to tropospheric chemistry and ozone formation. Biodegradation of gaseous alkanes by aerobic microorganisms, mostly bacteria and fungi isolated from terrestrial environments, has been known for several decades. The first indications for short chain alkane anaerobic degradation were provided by geochemical studies of deep-sea environments around hydrocarbon seeps, and included the uncoupling of the sulfate-reduction and anaerobic oxidation of methane rates, the consumption of gaseous alkanes in anoxic sediments, or the enrichment in 13C of gases in interstitial water vs. the source gas. Microorganisms able to degrade gaseous alkanes were recently obtained from deep-sea and terrestrial sediments around hydrocarbon seeps. Up to date, only sulfate-reducing pure or enriched cultures with ethane, propane and n-butane have been reported. The only pure culture presently available, strain BuS5, is affiliated to the Desulfosarcina–Desulfococcus cluster of the Deltaproteobacteria. Other phylotypes involved in gaseous alkane degradation have been identified based on stable-isotope labeling and whole-cell hybridization. Under anoxic conditions, propane and n-butane are activated similar to the higher alkanes, by homolytic cleavage of the C—H bond of a subterminal carbon atom, and addition of the ensuing radical to fumarate, yielding methylalkylsuccinates. An additional mechanism of activation at the terminal carbon atoms was demonstrated for propane, which could in principle be employed also for the activation of ethane. PMID:25904994

  1. The anaerobic degradation of gaseous, nonmethane alkanes - From in situ processes to microorganisms.

    PubMed

    Musat, Florin

    2015-01-01

    The short chain, gaseous alkanes ethane, propane, n- and iso-butane are released in significant amounts into the atmosphere, where they contribute to tropospheric chemistry and ozone formation. Biodegradation of gaseous alkanes by aerobic microorganisms, mostly bacteria and fungi isolated from terrestrial environments, has been known for several decades. The first indications for short chain alkane anaerobic degradation were provided by geochemical studies of deep-sea environments around hydrocarbon seeps, and included the uncoupling of the sulfate-reduction and anaerobic oxidation of methane rates, the consumption of gaseous alkanes in anoxic sediments, or the enrichment in (13)C of gases in interstitial water vs. the source gas. Microorganisms able to degrade gaseous alkanes were recently obtained from deep-sea and terrestrial sediments around hydrocarbon seeps. Up to date, only sulfate-reducing pure or enriched cultures with ethane, propane and n-butane have been reported. The only pure culture presently available, strain BuS5, is affiliated to the Desulfosarcina-Desulfococcus cluster of the Deltaproteobacteria. Other phylotypes involved in gaseous alkane degradation have been identified based on stable-isotope labeling and whole-cell hybridization. Under anoxic conditions, propane and n-butane are activated similar to the higher alkanes, by homolytic cleavage of the C-H bond of a subterminal carbon atom, and addition of the ensuing radical to fumarate, yielding methylalkylsuccinates. An additional mechanism of activation at the terminal carbon atoms was demonstrated for propane, which could in principle be employed also for the activation of ethane. PMID:25904994

  2. Supported organoiridium catalysts for alkane dehydrogenation

    SciTech Connect

    Baker, R. Thomas; Sattelberger, Alfred P.; Li, Hongbo

    2013-09-03

    Solid supported organoiridium catalysts, a process for preparing such solid supported organoiridium catalysts, and the use of such solid supported organoiridium catalysts in dehydrogenation reactions of alkanes is provided. The catalysts can be easily recovered and recycled.

  3. Solar photothermochemical alkane reverse combustion

    PubMed Central

    Chanmanee, Wilaiwan; Islam, Mohammad Fakrul; Dennis, Brian H.; MacDonnell, Frederick M.

    2016-01-01

    A one-step, gas-phase photothermocatalytic process for the synthesis of hydrocarbons, including liquid alkanes, aromatics, and oxygenates, with carbon numbers (Cn) up to C13, from CO2 and water is demonstrated in a flow photoreactor operating at elevated temperatures (180–200 °C) and pressures (1–6 bar) using a 5% cobalt on TiO2 catalyst and under UV irradiation. A parametric study of temperature, pressure, and partial pressure ratio revealed that temperatures in excess of 160 °C are needed to obtain the higher Cn products in quantity and that the product distribution shifts toward higher Cn products with increasing pressure. In the best run so far, over 13% by mass of the products were C5+ hydrocarbons and some of these, i.e., octane, are drop-in replacements for existing liquid hydrocarbons fuels. Dioxygen was detected in yields ranging between 64% and 150%. In principle, this tandem photochemical–thermochemical process, fitted with a photocatalyst better matched to the solar spectrum, could provide a cheap and direct method to produce liquid hydrocarbons from CO2 and water via a solar process which uses concentrated sunlight for both photochemical excitation to generate high-energy intermediates and heat to drive important thermochemical carbon-chain-forming reactions. PMID:26903631

  4. Solar photothermochemical alkane reverse combustion.

    PubMed

    Chanmanee, Wilaiwan; Islam, Mohammad Fakrul; Dennis, Brian H; MacDonnell, Frederick M

    2016-03-01

    A one-step, gas-phase photothermocatalytic process for the synthesis of hydrocarbons, including liquid alkanes, aromatics, and oxygenates, with carbon numbers (Cn) up to C13, from CO2 and water is demonstrated in a flow photoreactor operating at elevated temperatures (180-200 °C) and pressures (1-6 bar) using a 5% cobalt on TiO2 catalyst and under UV irradiation. A parametric study of temperature, pressure, and partial pressure ratio revealed that temperatures in excess of 160 °C are needed to obtain the higher Cn products in quantity and that the product distribution shifts toward higher Cn products with increasing pressure. In the best run so far, over 13% by mass of the products were C5+ hydrocarbons and some of these, i.e., octane, are drop-in replacements for existing liquid hydrocarbons fuels. Dioxygen was detected in yields ranging between 64% and 150%. In principle, this tandem photochemical-thermochemical process, fitted with a photocatalyst better matched to the solar spectrum, could provide a cheap and direct method to produce liquid hydrocarbons from CO2 and water via a solar process which uses concentrated sunlight for both photochemical excitation to generate high-energy intermediates and heat to drive important thermochemical carbon-chain-forming reactions.

  5. Structural insights into diversity and n-alkane biodegradation mechanisms of alkane hydroxylases

    PubMed Central

    Ji, Yurui; Mao, Guannan; Wang, Yingying; Bartlam, Mark

    2013-01-01

    Environmental microbes utilize four degradation pathways for the oxidation of n-alkanes. Although the enzymes degrading n-alkanes in different microbes may vary, enzymes functioning in the first step in the aerobic degradation of alkanes all belong to the alkane hydroxylases. Alkane hydroxylases are a class of enzymes that insert oxygen atoms derived from molecular oxygen into different sites of the alkane terminus (or termini) depending on the type of enzymes. In this review, we summarize the different types of alkane hydroxylases, their degrading steps, and compare typical enzymes from various classes with regard to their three-dimensional structures, in order to provide insights into how the enzymes mediate their different roles in the degradation of n-alkanes and what determines their different substrate ranges. Through the above analyzes, the degrading mechanisms of enzymes can be elucidated and molecular biological methods can be utilized to expand their catalytic roles in the petrochemical industry or in bioremediation of oil-contaminated environments. PMID:23519435

  6. Carbon and hydrogen isotopic composition of methane and C2+ alkanes in electrical spark discharge: implications for identifying sources of hydrocarbons in terrestrial and extraterrestrial settings.

    PubMed

    Telling, Jon; Lacrampe-Couloume, Georges; Sherwood Lollar, Barbara

    2013-05-01

    The low-molecular-weight alkanes--methane, ethane, propane, and butane--are found in a wide range of terrestrial and extraterrestrial settings. The development of robust criteria for distinguishing abiogenic from biogenic alkanes is essential for current investigations of Mars' atmosphere and for future exobiology missions to other planets and moons. Here, we show that alkanes synthesized during gas-phase radical recombination reactions in electrical discharge experiments have values of δ(2)H(methane)>δ(2)H(ethane)>δ(2)H(propane), similar to those of the carbon isotopes. The distribution of hydrogen isotopes in gas-phase radical reactions is likely due to kinetic fractionations either (i) from the preferential incorporation of (1)H into longer-chain alkanes due to the more rapid rate of collisions of the smaller (1)H-containing molecules or (ii) by secondary ion effects. Similar δ(13)C(C1-C2+) and δ(2)H(C1-C2+) patterns may be expected in a range of extraterrestrial environments where gas-phase radical reactions dominate, including interstellar space, the atmosphere and liquid hydrocarbon lakes of Saturn's moon Titan, and the outer atmospheres of Jupiter, Saturn, Neptune, and Uranus. Radical recombination reactions at high temperatures and pressures may provide an explanation for the combined reversed δ(13)C(C1-C2+) and δ(2)H(C1-C2+) patterns of terrestrial alkanes documented at a number of high-temperature/pressure crustal sites.

  7. Carbon and hydrogen isotopic composition of methane and C2+ alkanes in electrical spark discharge: implications for identifying sources of hydrocarbons in terrestrial and extraterrestrial settings.

    PubMed

    Telling, Jon; Lacrampe-Couloume, Georges; Sherwood Lollar, Barbara

    2013-05-01

    The low-molecular-weight alkanes--methane, ethane, propane, and butane--are found in a wide range of terrestrial and extraterrestrial settings. The development of robust criteria for distinguishing abiogenic from biogenic alkanes is essential for current investigations of Mars' atmosphere and for future exobiology missions to other planets and moons. Here, we show that alkanes synthesized during gas-phase radical recombination reactions in electrical discharge experiments have values of δ(2)H(methane)>δ(2)H(ethane)>δ(2)H(propane), similar to those of the carbon isotopes. The distribution of hydrogen isotopes in gas-phase radical reactions is likely due to kinetic fractionations either (i) from the preferential incorporation of (1)H into longer-chain alkanes due to the more rapid rate of collisions of the smaller (1)H-containing molecules or (ii) by secondary ion effects. Similar δ(13)C(C1-C2+) and δ(2)H(C1-C2+) patterns may be expected in a range of extraterrestrial environments where gas-phase radical reactions dominate, including interstellar space, the atmosphere and liquid hydrocarbon lakes of Saturn's moon Titan, and the outer atmospheres of Jupiter, Saturn, Neptune, and Uranus. Radical recombination reactions at high temperatures and pressures may provide an explanation for the combined reversed δ(13)C(C1-C2+) and δ(2)H(C1-C2+) patterns of terrestrial alkanes documented at a number of high-temperature/pressure crustal sites. PMID:23683048

  8. Silicon based radicals, radical ions, diradicals and diradicaloids.

    PubMed

    Chandra Mondal, Kartik; Roy, Sudipta; Roesky, Herbert W

    2016-02-21

    Radicals are an important class of species which act as intermediates in numerous chemical and biological processes. Most of the radicals have short lifetimes. However, radicals with longer lifetimes can be isolated and stored in a pure form. They are called stable radicals. Over the last five decades, the syntheses of several stable radicals have been reported. Recently, highly unstable radicals have been successfully stabilized via strong σ-donation of singlet carbenes. Cyclic aklyl(amino) carbene (cAAC) is regarded as a stronger σ-donor and a better π-acceptor when compared with that of an N-heterocyclic carbene (NHC). In this article we review preferentially the results of our group to generate stable radical centers on the carbene carbon atoms by employing the so far hidden and unique ability of the cAACs. We focus on the development of new synthetic routes to stable and isolable radicals containing silicon atoms. All the compounds have been well characterized by single crystal X-ray analysis; the mono-radicals have been distinguished by EPR spectroscpy and the ground state of the diradicals has been studied by magnetic susceptibility measurements and theoretical calculations. Many of these compounds are studied by cyclic voltammetry and are often converted to their corresponding radical cations or radical anions via electron abstraction or addition processes. Some of them are stable, having long lifetimes and hence are isolated and characterized thoroughly. Not much information has been obtained on the short lived persistent radical species. Herein, we discuss some of the examples of such a type of species and focus on what kind of chemical reactions are initiated by these short-lived radical species in solution. We also briefly mention the syntheses and charaterization of the so far reported stable silicon centered radicals. PMID:26585359

  9. The hydrodeoxygenation of bioderived furans into alkanes

    NASA Astrophysics Data System (ADS)

    Sutton, Andrew D.; Waldie, Fraser D.; Wu, Ruilian; Schlaf, Marcel; ‘Pete' Silks, Louis A.; Gordon, John C.

    2013-05-01

    The conversion of biomass into fuels and chemical feedstocks is one part of a drive to reduce the world's dependence on crude oil. For transportation fuels in particular, wholesale replacement of a fuel is logistically problematic, not least because of the infrastructure that is already in place. Here, we describe the catalytic defunctionalization of a series of biomass-derived molecules to provide linear alkanes suitable for use as transportation fuels. These biomass-derived molecules contain a variety of functional groups, including olefins, furan rings and carbonyl groups. We describe the removal of these in either a stepwise process or a one-pot process using common reagents and catalysts under mild reaction conditions to provide n-alkanes in good yields and with high selectivities. Our general synthetic approach is applicable to a range of precursors with different carbon content (chain length). This allows the selective generation of linear alkanes with carbon chain lengths between eight and sixteen carbons.

  10. The hydrodeoxygenation of bioderived furans into alkanes.

    PubMed

    Sutton, Andrew D; Waldie, Fraser D; Wu, Ruilian; Schlaf, Marcel; Silks, Louis A Pete; Gordon, John C

    2013-05-01

    The conversion of biomass into fuels and chemical feedstocks is one part of a drive to reduce the world's dependence on crude oil. For transportation fuels in particular, wholesale replacement of a fuel is logistically problematic, not least because of the infrastructure that is already in place. Here, we describe the catalytic defunctionalization of a series of biomass-derived molecules to provide linear alkanes suitable for use as transportation fuels. These biomass-derived molecules contain a variety of functional groups, including olefins, furan rings and carbonyl groups. We describe the removal of these in either a stepwise process or a one-pot process using common reagents and catalysts under mild reaction conditions to provide n-alkanes in good yields and with high selectivities. Our general synthetic approach is applicable to a range of precursors with different carbon content (chain length). This allows the selective generation of linear alkanes with carbon chain lengths between eight and sixteen carbons. PMID:23609095

  11. Enzymes and genes involved in aerobic alkane degradation

    PubMed Central

    Wang, Wanpeng; Shao, Zongze

    2013-01-01

    Alkanes are major constituents of crude oil. They are also present at low concentrations in diverse non-contaminated because many living organisms produce them as chemo-attractants or as protecting agents against water loss. Alkane degradation is a widespread phenomenon in nature. The numerous microorganisms, both prokaryotic and eukaryotic, capable of utilizing alkanes as a carbon and energy source, have been isolated and characterized. This review summarizes the current knowledge of how bacteria metabolize alkanes aerobically, with a particular emphasis on the oxidation of long-chain alkanes, including factors that are responsible for chemotaxis to alkanes, transport across cell membrane of alkanes, the regulation of alkane degradation gene and initial oxidation. PMID:23755043

  12. Improved Alkane Production in Nitrogen-Fixing and Halotolerant Cyanobacteria via Abiotic Stresses and Genetic Manipulation of Alkane Synthetic Genes.

    PubMed

    Kageyama, Hakuto; Waditee-Sirisattha, Rungaroon; Sirisattha, Sophon; Tanaka, Yoshito; Mahakhant, Aparat; Takabe, Teruhiro

    2015-07-01

    Cyanobacteria possess the unique capacity to produce alkane. In this study, effects of nitrogen deficiency and salt stress on biosynthesis of alkanes were investigated in three kinds of cyanobacteria. Intracellular alkane accumulation was increased in nitrogen-fixing cyanobacterium Anabaena sp. PCC7120, but decreased in non-diazotrophic cyanobacterium Synechococcus elongatus PCC7942 and constant in a halotolerant cyanobacterium Aphanothece halophytica under nitrogen-deficient condition. We also found that salt stress increased alkane accumulation in Anabaena sp. PCC7120 and A. halophytica. The expression levels of two alkane synthetic genes were not upregulated significantly under nitrogen deficiency or salt stress in Anabaena sp. PCC7120. The transformant Anabaena sp. PCC7120 cells with additional alkane synthetic gene set from A. halophytica increased intracellular alkane accumulation level compared to control cells. These results provide a prospect to improve bioproduction of alkanes in nitrogen-fixing halotolerant cyanobacteria via abiotic stresses and genetic engineering.

  13. Crossed-beam DC slice imaging of fluorine atom reactions with linear alkanes

    SciTech Connect

    Shi, Yuanyuan; Kamasah, Alexander; Joalland, Baptiste; Suits, Arthur G.

    2015-05-14

    We report the reaction dynamics of F atom with selected alkanes studied by crossed beam scattering with DC slice ion imaging. The target alkanes are propane, n-butane, and n-pentane. The product alkyl radicals are probed by 157 nm single photon ionization following reaction at a collision energy of ∼10 kcal mol{sup −1}. The analyzed data are compared with the corresponding theoretical studies. Reduced translational energy distributions for each system show similar trends with little of the reaction exoergicity appearing in translation. However, the pentane reaction shows a somewhat smaller fraction of available energy in translation than the other two, suggesting greater energy channeled into pentyl internal degrees of freedom. The center-of-mass angular distributions all show backscattering as well as sharp forward scattering that decreases in relative intensity with the size of the molecule. Possible reasons for these trends are discussed.

  14. Nitrated metalloporphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, P.E. Jr.; Lyons, J.E.

    1994-01-18

    Compositions of matter comprising nitro-substituted metal complexes of porphyrins are catalysts for the oxidation of alkanes. The metal is iron, chromium, manganese, ruthenium, copper or cobalt. The porphyrin ring has nitro groups attached thereto in meso and/or [beta]-pyrrolic positions.

  15. Reflectance spectroscopy of organic compounds: 1. Alkanes

    USGS Publications Warehouse

    Clark, R.N.; Curchin, J.M.; Hoefen, T.M.; Swayze, G.A.

    2009-01-01

    Reflectance spectra of the organic compounds comprising the alkane series are presented from the ultraviolet to midinfrared, 0.35 to 15.5 /??m. Alkanes are hydrocarbon molecules containing only single carbon-carbon bonds, and are found naturally on the Earth and in the atmospheres of the giant planets and Saturn's moon, Titan. This paper presents the spectral properties of the alkanes as the first in a series of papers to build a spectral database of organic compounds for use in remote sensing studies. Applications range from mapping the environment on the Earth, to the search for organic molecules and life in the solar system and throughout the. universe. We show that the spectral reflectance properties of organic compounds are rich, with major diagnostic spectral features throughout the spectral range studied. Little to no spectral change was observed as a function of temperature and only small shifts and changes in the width of absorption bands were observed between liquids and solids, making remote detection of spectral properties throughout the solar system simpler. Some high molecular weight organic compounds contain single-bonded carbon chains and have spectra similar to alkanes even ' when they fall into other families. Small spectral differences are often present allowing discrimination among some compounds, further illustrating the need to catalog spectral properties for accurate remote sensing identification with spectroscopy.

  16. Nitrated metalloporphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, Jr., Paul E.; Lyons, James E.

    1992-01-01

    Alkanes are oxidized by contact with oxygen-containing gas in the presence as catalyst of a metalloporphyrin in which hydrogen atoms in the porphyrin ring have been replaced with one or more nitro groups. Hydrogen atoms in the porphyrin ring may also be substituted with halogen atoms.

  17. Nitrated metalloporphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, Jr., Paul E.; Lyons, James E.

    1994-01-01

    Compositions of matter comprising nitro-substituted metal complexes of porphyrins are catalysts for the oxidation of alkanes. The metal is iron, chromium, manganese, ruthenium, copper or cobalt. The porphyrin ring has nitro groups attached thereto in meso and/or .beta.-pyrrolic positions.

  18. Accelerated Molecular Dynamics Simulation of Alkane Desorption

    NASA Astrophysics Data System (ADS)

    McLaughlin, Kelly; Fichthorn, Kristen

    2006-03-01

    Thermal desorption has been the focus of much surface science research. Studies of alkanes on graphite^1 and gold^2 have shown prefactors that are constant with alkane chain length but vary by over six orders of magnitude. Other studies on magnesium oxide^3 and gold^4 show a prefactor that increases with increasing chain length. We have developed an all-atom model to study alkane desorption from graphite. Transition state theory is used to obtain rate constants from the simulation. Accelerated MD is used to extend the desorption simulation to experimentally relevant temperatures. Our results show a prefactor that increases with increasing chain length. We predict that it will become constant as internal conformational changes occur significantly. We examine the effect of desorption environment through varying the alkane surface coverage. 1. K.R. Paserba and A.J. Gellman, J. Chem. Phys. 115, 6737 (2001). 2. S.M. Wetterer et al., J. Phys. Chem. 102, 9266 (1998). 3. S.L. Tait et al., J. Chem. Phys. 122, 164707 (2005). 4. K.A. Fichthorn and R.A. Miron, Phys. Rev. Lett. 89, 196103 (2002).

  19. Trans-4,4{prime}-dichloro-1,1{prime},2,2{prime},3,3{prime}-tetrathiadiazafulvalene (DC-TAF) and its 1:1 radical cation salts [DC-TAF][X]: Preparation and solid-state properties of BF{sub 4{minus}}, ClO{sub 4{minus}}, and FSO{sub 3{minus}} derivatives

    SciTech Connect

    Barclay, T.J.; Beer, L.; Cordes, A.W.; Haddon, R.C.; Itkis, M.I.; Oakley, R.T.; Preuss, K.E.; Reed, R.W.

    1999-07-21

    Reductive coupling of 4,5-dichloro-1,2,3-dithiazolylium chloride yields trans-4,4{prime}-dichloro-1,1{prime},2,2{prime},3,3{prime}-tetrathiadiazafulvalene (DC-TAF), the first example of this heterofulvalene system. Ab initio molecular orbital (B3LYP/6-31G**) calculations on prototypal TAF confirm that the closed shell {sup 1}A{sub g} state lies 22 kcal mol{sup {minus}1} below the {sup 3}B{sub u} diradical triplet. Cyclic voltammetry on DC-TAF reveals two reversible oxidation waves at 0.80and 1.25 V (in CH{sub 3}CN, reference SCE). The EST signal (g = 2.0117) of the radical cation [DC-TAF]{sup +} (in SO{sub 2}(1)) exhibits a five=line hyperfine coupling pattern with a{sub n} = 0.096 mT. DC-TAF forms a series of 1:1 radical ion salts [DC-TAF][X] by electrooxidation in the presence of tetrahedral counterions (X{sup {minus}} = BF{sub 4}{sup {minus}}, ClO{sub 4}{sup {minus}}, FSO{sub 3}{sup {minus}}). The crystal structures of these salts are isomorphous, monoclinic space group P2{sub 1}/n. and consist of one-dimensional ladder-like arrays of [DC-TAF]{sup +} radical cations bridged by S---S contacts ranging from 3.5 to 3.7 {angstrom}. Variable-temperature conductivity and magnetic measurements on [DC-TAF][ClO{sub 4}] indicate Mott insulator behavior, with a measured band gap of 0.30 eV.

  20. Structural and Kinetic Studies of Novel Cytochrome P450 Small-Alkane Hydroxylases

    SciTech Connect

    Arnold, Frances H.

    2012-02-27

    The goals of this project are to investigate (1) the kinetics and stabilities of engineered cytochrome P450 (P450) small alkane hydroxylases and their evolutionary intermediates, (2) the structural basis for catalytic proficiency on small alkanes of these engineered P450s, and (3) the changes in redox control resulting from protein engineering. To reach these goals, we have established new methods for determining the kinetics and stabilities of multicomponent P450s such as CYP153A6. Using these, we were able to determine that CYP153A6 is proficient for hydroxylation of alkanes as small as ethane, an activity that has never been observed previously in any natural P450. To elucidate the structures of the engineered P450s, we obtained x-ray diffraction data for two variants in the P450PMO (propane monooxygenase) lineage and a preliminary structure for the most evolved variant. This structure shows changes in the substrate binding regions of the enzyme and a reduction in active site volume that are consistent with the observed changes in substrate specificity from fatty acids in the native enzyme to small alkanes in P450PMO. We also constructed semi-rational designed libraries mutating only residues in the enzyme active site that in one round of mutagenesis and screening produced variants that achieved nearly half of the activity of the most evolved enzymes of the P450PMO lineage. Finally, we found that changes in redox properties of the laboratory-evolved P450 alkane hydroxylases did not reflect the improvement in their electron transfer efficiency. The heme redox potential remained constant throughout evolution, while activity increased and coupling efficiency improved from 10% to 90%. The lack of correlation between heme redox potential and enzyme activity and coupling efficiency led us to search for other enzyme properties that could be better predictors for activity towards small alkanes, specifically methane. We investigated the oxidation potential of the radical

  1. The influence of molecular structure and aerosol phase on the heterogeneous oxidation of normal and branched alkanes by OH.

    PubMed

    Ruehl, Christopher R; Nah, Theodora; Isaacman, Gabriel; Worton, David R; Chan, Arthur W H; Kolesar, Katheryn R; Cappa, Christopher D; Goldstein, Allen H; Wilson, Kevin R

    2013-05-16

    Insights into the influence of molecular structure and thermodynamic phase on the chemical mechanisms of hydroxyl radical-initiated heterogeneous oxidation are obtained by identifying reaction products of submicrometer particles composed of either n-octacosane (C28H58, a linear alkane) or squalane (C30H62, a highly branched alkane) and OH. A common pattern is observed in the positional isomers of octacosanone and octacosanol, with functionalization enhanced toward the end of the molecule. This suggests that relatively large linear alkanes are structured in submicrometer particles such that their ends are oriented toward the surface. For squalane, positional isomers of first-generation ketones and alcohols also form in distinct patterns. Ketones are favored on carbons adjacent to tertiary carbons, while hydroxyl groups are primarily found on tertiary carbons but also tend to form toward the end of the molecule. Some first-generation products, viz., hydroxycarbonyls and diols, contain two oxygen atoms. These results suggest that alkoxy radicals are important intermediates and undergo both intramolecular (isomerization) and intermolecular (chain propagation) hydrogen abstraction reactions. Oxidation products with carbon number less than the parent alkane's are observed to a much greater extent for squalane than for n-octacosane oxidation and can be explained by the preferential cleavage of bonds involving tertiary carbons.

  2. A new approach to the non-oxidative conversion of gaseous alkanes in a barrier discharge and features of the reaction mechanism

    NASA Astrophysics Data System (ADS)

    Kudryashov, S.; Ryabov, A.; Shchyogoleva, G.

    2016-01-01

    A new approach to the non-oxidative conversion of C1-C4 alkanes into gaseous and liquid products in a barrier discharge is proposed. It consists in inhibiting the formation of deposits on the reactor electrode surfaces due to the addition of distilled water into the flow of hydrocarbon gases. The energy consumption on hydrocarbon conversion decreases from methane to n-butane from ~46 to 35 eV molecule-1. The main gaseous products of the conversion of light alkanes are hydrogen and C2-C4 hydrocarbons. The liquid reaction products contain C5+ alkanes with a predominantly isomeric structure. The results of modeling the kinetics of chemical reactions show that an increase in the molecular weight of the reaction products is mainly due to processes involving CH2 radical and the recombination of alkyl radicals.

  3. The origin of alkanes found in human skin surface lipids

    SciTech Connect

    Bortz, J.T.; Wertz, P.W.; Downing, D.T. )

    1989-12-01

    Lipids extracted from human skin contain variable amounts of paraffin hydrocarbons. Although the composition of these alkanes strongly resembles petroleum waxes, it has been proposed that they are biosynthetic products of human skin. To investigate this question, skin surface lipids from 15 normal subjects were analyzed for the amount and composition of alkanes, using quantitative thin-layer chromatography and quartz capillary gas chromatography. The alkanes were found to constitute 0.5% to 1.7% of the skin lipids. Subjects differed greatly in the chain length distribution of their alkanes between 15 and 35 carbon atoms, and in the relative amounts of normal alkanes (like those in petroleum waxes) and branched chain alkanes (like those in petroleum lubricating oils). In 6 subjects, the alkane content of cerumen from each ear was examined to investigate whether alkanes arrive at the skin surface by a systemic route or by direct contact with environmental surfaces. No trace of alkanes was found in 11 of the 12 cerumen samples. Using a tandem accelerator mass spectrometer for carbon-14 dating, a combined sample of the skin surface alkanes was found to have a theoretical age of 30,950 years, similar to that of a sample of petrolatum. These analyses indicate that the alkanes found on the surface of human skin are mixtures of a variety of petroleum distillation fractions that are acquired by direct contamination from the environment.

  4. Studies of radiation-produced radicals and radical ions. Progress report, September 1, 1990--October 15, 1991

    SciTech Connect

    Williams, T.F.

    1991-12-31

    The radiolytic oxidation of anti-5-methylbicyclo[2.1.0]pentane gives the 1-methylcyclopentene radical cation as the sole rearrangement product H migration whereas oxidation of its syn isomer results in the highly selective formation of the 3-methylcyclopentene radical cation by methyl group migration. Since exactly the same stereoselectivity of olefin formation was observed in corresponding PET (photosensitized electron transfer) studies in the liquid phase, it is concluded that the rearrangement in this case also occurs through the intermediacy of radical cations. Clearly, the radical cation rearrangement must occur very rapidly (10{sup {minus}8}--10{sup {minus}9}s) under liquid-phase conditions at room temperature to compete with back electron transfer, and therefore the hydrogen (or methyl) migration is a fast process under these conditions. An intramolecular cycloaddition reaction was demonstrated in the radical cation rearrangement of 4-vinylcyclohexene to bicyclo[3.2.1]oct-2-ene. ESR studies show that the radiolytic oxidation of quadricyclane in Freon matrices under conditions of high substrate dilution leads to the bicyclo[3.2.0]hepta-2,6-diene radical cation as well as the previously reported norbornadiene radical cation, the former species predominating at sufficiently low concentrations.

  5. OH-initiated heterogeneous oxidation of cholestane: a model system for understanding the photochemical aging of cyclic alkane aerosols.

    PubMed

    Zhang, Haofei; Ruehl, Christopher R; Chan, Arthur W H; Nah, Theodora; Worton, David R; Isaacman, Gabriel; Goldstein, Allen H; Wilson, Kevin R

    2013-11-27

    Aerosols containing aliphatic hydrocarbons play a substantial role in the urban atmosphere. Cyclic alkanes constitute a large fraction of aliphatic hydrocarbon emissions originating from incomplete combustion of diesel fuel and motor oil. In the present study, cholestane (C27H48) is used as a model system to examine the OH-initiated heterogeneous oxidation pathways of cyclic alkanes in a photochemical flow tube reactor. Oxidation products are collected on filters and analyzed by a novel soft ionization two-dimensional gas chromatography/mass spectrometry technique. The analysis reveals that the first-generation functionalization products (cholestanones, cholestanals, and cholestanols) are the dominant reaction products that account for up to 70% by mass of the total speciated compounds. The ratio of first-generation carbonyls to alcohols is near unity at every oxidation level. Among the cholestanones/cholestanals, 55% are found to have the carbonyl group on the rings of the androstane skeleton, while 74% of cholestanols have the hydroxyl group on the rings. Particle-phase oxidation products with carbon numbers less than 27 (i.e., "fragmentation products") and higher-generation functionalization products are much less abundant. Carbon bond cleavage was found to occur only on the side chain. Tertiary-carbon alkoxy radicals are suggested to play an important role in governing both the distribution of functionalization products (via alkoxy radical isomerization and reaction with oxygen) and the fragmentation products (via alkoxy radical decomposition). These results provide new insights into the oxidation mechanism of cyclic alkanes.

  6. OH-initiated heterogeneous oxidation of cholestane: a model system for understanding the photochemical aging of cyclic alkane aerosols.

    PubMed

    Zhang, Haofei; Ruehl, Christopher R; Chan, Arthur W H; Nah, Theodora; Worton, David R; Isaacman, Gabriel; Goldstein, Allen H; Wilson, Kevin R

    2013-11-27

    Aerosols containing aliphatic hydrocarbons play a substantial role in the urban atmosphere. Cyclic alkanes constitute a large fraction of aliphatic hydrocarbon emissions originating from incomplete combustion of diesel fuel and motor oil. In the present study, cholestane (C27H48) is used as a model system to examine the OH-initiated heterogeneous oxidation pathways of cyclic alkanes in a photochemical flow tube reactor. Oxidation products are collected on filters and analyzed by a novel soft ionization two-dimensional gas chromatography/mass spectrometry technique. The analysis reveals that the first-generation functionalization products (cholestanones, cholestanals, and cholestanols) are the dominant reaction products that account for up to 70% by mass of the total speciated compounds. The ratio of first-generation carbonyls to alcohols is near unity at every oxidation level. Among the cholestanones/cholestanals, 55% are found to have the carbonyl group on the rings of the androstane skeleton, while 74% of cholestanols have the hydroxyl group on the rings. Particle-phase oxidation products with carbon numbers less than 27 (i.e., "fragmentation products") and higher-generation functionalization products are much less abundant. Carbon bond cleavage was found to occur only on the side chain. Tertiary-carbon alkoxy radicals are suggested to play an important role in governing both the distribution of functionalization products (via alkoxy radical isomerization and reaction with oxygen) and the fragmentation products (via alkoxy radical decomposition). These results provide new insights into the oxidation mechanism of cyclic alkanes. PMID:24152093

  7. Oxidative dehydrogenation of alkanes to unsaturated hydrocarbons

    DOEpatents

    Kung, Harold H.; Chaar, Mohamed A.

    1988-01-01

    Oxidative dehydrogenation of alkanes to unsaturated hydrocarbons is carried out over metal vanadate catalysts under oxidizing conditions. The vanadate catalysts are represented by the formulas M.sub.3 (VO.sub.4).sub.2 and MV.sub.2 O.sub.6, M representing Mg, Zn, Ca, Pb, or Cd. The reaction is carried out in the presence of oxygen, but the formation of oxygenate by-products is suppressed.

  8. Oxidative dehydrogenation of alkanes to unsaturated hydrocarbons

    DOEpatents

    Kung, H.H.; Chaar, M.A.

    1988-10-11

    Oxidative dehydrogenation of alkanes to unsaturated hydrocarbons is carried out over metal vanadate catalysts under oxidizing conditions. The vanadate catalysts are represented by the formulas M[sub 3](VO[sub 4])[sub 2] and MV[sub 2]O[sub 6], M representing Mg, Zn, Ca, Pb, or Cd. The reaction is carried out in the presence of oxygen, but the formation of oxygenate by-products is suppressed.

  9. Mechanically Stabilized Tetrathiafulvalene Radical Dimers

    SciTech Connect

    Coskun, Ali; Spruell, Jason M.; Barin, Gokhan; Fahrenbach, Albert C.; Forgan, Ross S.; Colvin, Michael T.; Carmieli, Raanan; Benitez, Diego; Tkatchouk, Ekaterina; Friedman, Douglas C.; Sarjeant, Amy A.; Wasielewski, Michael R.; Goddard, William A.; Stoddart, J. Fraser

    2011-01-01

    Two donor-acceptor [3]catenanes—composed of a tetracationic molecular square, cyclobis(paraquat-4,4'-biphenylene), as the π-electron deficient ring and either two tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) containing macrocycles or two TTF-butadiyne-containing macrocycles as the π-electron rich components—have been investigated in order to study their ability to form TTF radical dimers. It has been proven that the mechanically interlocked nature of the [3]catenanes facilitates the formation of the TTF radical dimers under redox control, allowing an investigation to be performed on these intermolecular interactions in a so-called “molecular flask” under ambient conditions in considerable detail. In addition, it has also been shown that the stability of the TTF radical-cation dimers can be tuned by varying the secondary binding motifs in the [3]catenanes. By replacing the DNP station with a butadiyne group, the distribution of the TTF radical-cation dimer can be changed from 60% to 100%. These findings have been established by several techniques including cyclic voltammetry, spectroelectrochemistry and UV-vis-NIR and EPR spectroscopies, as well as with X-ray diffraction analysis which has provided a range of solid-state crystal structures. The experimental data are also supported by high-level DFT calculations. The results contribute significantly to our fundamental understanding of the interactions within the TTF radical dimers.

  10. Radical Hysterectomy

    MedlinePlus

    ... the base of her partner’s penis during intercourse. Orgasm after radical hysterectomy Women who have had a ... the surgery will affect their ability to have orgasms. This has not been studied a great deal, ...

  11. Alkane metathesis by tandem alkane-dehydrogenation-olefin-metathesis catalysis and related chemistry.

    PubMed

    Haibach, Michael C; Kundu, Sabuj; Brookhart, Maurice; Goldman, Alan S

    2012-06-19

    Methods for the conversion of both renewable and non-petroleum fossil carbon sources to transportation fuels that are both efficient and economically viable could greatly enhance global security and prosperity. Currently, the major route to convert natural gas and coal to liquids is Fischer-Tropsch catalysis, which is potentially applicable to any source of synthesis gas including biomass and nonconventional fossil carbon sources. The major desired products of Fischer-Tropsch catalysis are n-alkanes that contain 9-19 carbons; they comprise a clean-burning and high combustion quality diesel, jet, and marine fuel. However, Fischer-Tropsch catalysis also results in significant yields of the much less valuable C(3) to C(8)n-alkanes; these are also present in large quantities in oil and gas reserves (natural gas liquids) and can be produced from the direct reduction of carbohydrates. Therefore, methods that could disproportionate medium-weight (C(3)-C(8)) n-alkanes into heavy and light n-alkanes offer great potential value as global demand for fuel increases and petroleum reserves decrease. This Account describes systems that we have developed for alkane metathesis based on the tandem operation of catalysts for alkane dehydrogenation and olefin metathesis. As dehydrogenation catalysts, we used pincer-ligated iridium complexes, and we initially investigated Schrock-type Mo or W alkylidene complexes as olefin metathesis catalysts. The interoperability of the catalysts typically represents a major challenge in tandem catalysis. In our systems, the rate of alkane dehydrogenation generally limits the overall reaction rate, whereas the lifetime of the alkylidene complexes at the relatively high temperatures required to obtain practical dehydrogenation rates (ca. 125 -200 °C) limits the total turnover numbers. Accordingly, we have focused on the development and use of more active dehydrogenation catalysts and more stable olefin-metathesis catalysts. We have used thermally

  12. Catalytic Radical Domino Reactions in Organic Synthesis

    PubMed Central

    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

  13. Thermal conductivity of liquid n-alkanes

    SciTech Connect

    Calado, J.C.G.; Fareleira, J.M.N.A.; Mardolcar, U.V.; Nieto de Castro, C.A.

    1988-05-01

    The thermal conductivity of liquids has been shown in the past to be difficult to predict with a reasonable accuracy, due to the lack of accurate experimental data and reliable prediction schemes. However, data of a high accuracy, and covering wide density ranges, obtained recently in laboratories in Boulder, Lisbon, and London with the transient hot-wire technique, can be used to revise an existing correlation scheme and to develop a new universal predictive technique for the thermal conductivity of liquid normal alkanes. The proposed correlation scheme is constructed on a theoretically based treatment of the van der Waals model of a liquid, which permits the prediction of the density dependence and the thermal conductivity of liquid n-alkanes, methane to tridecane, for temperatures between 110 and 370 K and pressures up to 0.6 MPa, i.e., for 0.3 less than or equal to T/T/sub c/ less than or equal to 0.7 and 2.4 less than or equal to rho/rho/sub c/ less than or equal to 3.7, with an accuracy of +/-1%, given a known value of the thermal conductivity of the fluid at the desired temperature. A generalization of the hard-core volumes obtained, as a function of the number of carbon atoms, showed that it was possible to predict the thermal conductivity of pentane to tetradecane +/- 2%, without the necessity of available experimental measurements.

  14. Products of Chemistry: Alkanes: Abundant, Pervasive, Important, and Essential.

    ERIC Educational Resources Information Center

    Seymour, Raymond B.

    1989-01-01

    Discusses the history and commercialization of alkanes. Examines the nomenclature and uses of alkanes. Studies polymerization and several types of polyethylenes: low-density, high-density, low-molecular-weight, cross-linked, linear low-density, and ultrahigh-molecular-weight. Includes a glossary of hydrocarbon terms. (MVL)

  15. 40 CFR 721.536 - Halogenated phenyl alkane.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Halogenated phenyl alkane. 721.536 Section 721.536 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) TOXIC SUBSTANCES CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.536 Halogenated phenyl alkane....

  16. 40 CFR 721.535 - Halogenated alkane (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.535 Halogenated alkane (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halogenated alkane (PMN P-01-433) is...

  17. 40 CFR 721.535 - Halogenated alkane (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.535 Halogenated alkane (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halogenated alkane (PMN P-01-433) is...

  18. 40 CFR 721.536 - Halogenated phenyl alkane.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.536 Halogenated phenyl alkane. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halogenated phenyl alkane (PMN P-89-867)...

  19. 40 CFR 721.536 - Halogenated phenyl alkane.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.536 Halogenated phenyl alkane. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halogenated phenyl alkane (PMN P-89-867)...

  20. Sophorolipids from Torulopsis bombicola: possible relation to alkane uptake.

    PubMed Central

    Ito, S; Inoue, S

    1982-01-01

    Torulopsis bombicola produces extracellular sophorolipids when it is grown on water-insoluble alkanes. Sophorolipids and related model compounds, which were not themselves used for growth, were found to stimulate markedly the growth of T. bombicola on alkanes. This stimulatory effect was restricted to growth on C10 to C20 alkanes, whereas no significantly influence was observed for growth on fatty alcohols, fatty acids, glucose, or glycerol. The nonionic methyl ester of the glycolipid supported the greatest cell yield. However, a number of synthetic nonionic surfactants were unable to replace the glycolipid. When organisms were grown on hexadecane, stimulation of growth by sophorolipids was observed almost exclusively with strains of Torulopsis yeasts. In contrast, the growth of other typical alkane-utilizing yeasts, such as candida and Pichia strains, was inhibited or not affected. It appears that sophorolipids are involved in alkane dissimilation by T. bombicola through an undetermined mechanism. PMID:7201782

  1. Alkanes in benthic organisms from the Buccaneer oil field

    SciTech Connect

    Middleditch, B.S.; Basile, B.

    1980-06-01

    About 200 g per day of alkanes are present in brine discharged from each of two production platforms in the Buccaneer oil field in the NW Gulf of Mexico. These alkanes disperse rapidly in the water column, so that seawater concentrations of petroleum alkanes in this region are generally very low. They can be taken up to some extent by plankton, fish, and barnacles, but the petroleum alkane concentrations in these organisms are also relatively low. The largest pool of petroleum alkanes is in the surficial sediments, where concentrations of up to 25 ppM are observed, with concentration gradients extending more than 20 m from the production platforms. Organisms are examined which are exposed to these sediments and, for comparison, other specimens from control sites around structures from which there are no discharges.

  2. Utilization of n-Alkanes by Cladosporium resinae

    PubMed Central

    Teh, J. S.; Lee, K. H.

    1973-01-01

    Four different isolates of Cladosporium resinae from Australian soils were tested for their ability to utilize liquid n-alkanes ranging from n-hexane to n-octadecane under standard conditions. The isolates were unable to make use of n-hexane, n-heptane, and n-octane for growth. In fact, these hydrocarbons, particularly n-hexane, exerted an inhibitory effect on spore germination and mycelial growth. All higher n-alkanes from n-nonane to n-octadecane were assimilated by the fungus, although only limited growth occurred on n-nonane and n-decane. The long chain n-alkanes (C14 to C18) supported good growth of all isolates, but there was no obvious correlation between cell yields and chain lengths of these n-alkanes. Variation in growth responses to individual n-alkane among the different isolates was also observed. The cause of this variation is unknown. PMID:4735447

  3. Spectroscopy of the tilde A state of NO-alkane complexes (alkane = methane, ethane, propane, and n-butane)

    NASA Astrophysics Data System (ADS)

    Tamé-Reyes, Victor M.; Gardner, Adrian M.; Harris, Joe P.; McDaniel, Jodie; Wright, Timothy G.

    2012-12-01

    We have recorded (1+1) resonance-enhanced multiphoton ionization spectra of complexes formed between NO and the alkanes: CH4, C2H6, C3H8, and n-C4H10. The spectra correspond to the tilde A ← tilde X transition, which is a NO-localized 3s ← 2pπ* transition. In line with previous work, the spectrum for NO-CH4 has well-defined structure, but this is only partially resolved for the other complexes. The spectra recorded in the NO+-alkane mass channels all show a slowly rising onset, followed by a sharp offset, which is associated with dissociation of NO-alkane, from which binding energies in the tilde X and tilde A states are deduced. Beyond this sharp offset, there is a further rise in signal, which is attributed to fragmentation of higher complexes, NO-(alkane)n. Analysis of these features allows binding energies for (NO-alkane) ... alkane to be estimated, and these suggest that in the NO-(alkane)2 complexes, the second alkane molecule is bound to the first, rather than to NO. Calculated structures for the 1:1 complexes are reported, as well as binding energies.

  4. Simultaneous Interaction of Hydrophilic and Hydrophobic Solvents with Ethylamino Neurotransmitter Radical Cations: Infrared Spectra of Tryptamine(+)-(H2O)m-(N2)n Clusters (m,n ≤ 3).

    PubMed

    Schütz, Markus; Sakota, Kenji; Moritz, Raphael; Schmies, Matthias; Ikeda, Takamasa; Sekiya, Hiroshi; Dopfer, Otto

    2015-10-01

    Solvation of biomolecules by a hydrophilic and hydrophobic environment strongly affects their structure and function. Here, the structural, vibrational, and energetic properties of size-selected clusters of the microhydrated tryptamine cation with N2 ligands, TRA(+)-(H2O)m-(N2)n (m,n ≤ 3), are characterized by infrared photodissociation spectroscopy in the 2800-3800 cm(-1) range and dispersion-corrected density functional theory calculations at the ωB97X-D/cc-pVTZ level to investigate the simultaneous solvation of this prototypical neurotransmitter by dipolar water and quadrupolar N2 ligands. In the global minimum structure of TRA(+)-H2O generated by electron ionization, H2O is strongly hydrogen-bonded (H-bonded) as proton acceptor to the acidic indolic NH group. In the TRA(+)-H2O-(N2)n clusters, the weakly bonded N2 ligands do not affect the H-bonding motif of TRA(+)-H2O and are preferentially H-bonded to the OH groups of the H2O ligand, whereas stacking to the aromatic π electron system of the pyrrole ring of TRA(+) is less favorable. The natural bond orbital analysis reveals that the H-bond between the N2 ligand and the OH group of H2O cooperatively strengthens the adjacent H-bond between the indolic NH group of TRA(+) and H2O, while π stacking is slightly noncooperative. In the larger TRA(+)-(H2O)m clusters, the H2O ligands form a H-bonded solvent network attached to the indolic NH proton, again stabilized by strong cooperative effects arising from the nearby positive charge. Comparison with the corresponding neutral TRA-(H2O)m clusters illustrates the strong impact of the excess positive charge on the structure of the microhydration network.

  5. Simultaneous Interaction of Hydrophilic and Hydrophobic Solvents with Ethylamino Neurotransmitter Radical Cations: Infrared Spectra of Tryptamine(+)-(H2O)m-(N2)n Clusters (m,n ≤ 3).

    PubMed

    Schütz, Markus; Sakota, Kenji; Moritz, Raphael; Schmies, Matthias; Ikeda, Takamasa; Sekiya, Hiroshi; Dopfer, Otto

    2015-10-01

    Solvation of biomolecules by a hydrophilic and hydrophobic environment strongly affects their structure and function. Here, the structural, vibrational, and energetic properties of size-selected clusters of the microhydrated tryptamine cation with N2 ligands, TRA(+)-(H2O)m-(N2)n (m,n ≤ 3), are characterized by infrared photodissociation spectroscopy in the 2800-3800 cm(-1) range and dispersion-corrected density functional theory calculations at the ωB97X-D/cc-pVTZ level to investigate the simultaneous solvation of this prototypical neurotransmitter by dipolar water and quadrupolar N2 ligands. In the global minimum structure of TRA(+)-H2O generated by electron ionization, H2O is strongly hydrogen-bonded (H-bonded) as proton acceptor to the acidic indolic NH group. In the TRA(+)-H2O-(N2)n clusters, the weakly bonded N2 ligands do not affect the H-bonding motif of TRA(+)-H2O and are preferentially H-bonded to the OH groups of the H2O ligand, whereas stacking to the aromatic π electron system of the pyrrole ring of TRA(+) is less favorable. The natural bond orbital analysis reveals that the H-bond between the N2 ligand and the OH group of H2O cooperatively strengthens the adjacent H-bond between the indolic NH group of TRA(+) and H2O, while π stacking is slightly noncooperative. In the larger TRA(+)-(H2O)m clusters, the H2O ligands form a H-bonded solvent network attached to the indolic NH proton, again stabilized by strong cooperative effects arising from the nearby positive charge. Comparison with the corresponding neutral TRA-(H2O)m clusters illustrates the strong impact of the excess positive charge on the structure of the microhydration network. PMID:26353045

  6. Comparative study of alkali-vapour cells with alkane-, alkeneand 1-nonadecylbenzene-based antirelaxation wall coatings

    SciTech Connect

    Balabas, M V; Tretiak, O Yu

    2013-12-31

    The dependence of both longitudinal and transverse relaxation times of ground-state magnetic polarisation in alkali atoms on the coating temperature is experimentally studied for the first time in a rubidium-vapour cell with 1-nonadecylbenzene antirelaxation coating of inner walls. The comparison of these times with the relaxation times in a caesium-vapour cell with alkane wall coatings is presented. It is found that within the studied temperature range (294 – 340K) the transverse relaxation time decreases with increasing temperature of alkene and 1-nonadecylbenzene coatings. For the alkane coating such a dependence was not explicitly found. The longitudinal relaxation time begins to decrease in all cases when passing a certain critical temperature of the coating material. It is found that the unsaturated radical structure of the coating material molecules strongly affects its antirelaxation properties. (optical pumping)

  7. Radical Ions of Cycloparaphenylenes: Size Dependence Contrary to the Neutral Molecules.

    PubMed

    Fujitsuka, Mamoru; Tojo, Sachiko; Iwamoto, Takahiro; Kayahara, Eiichi; Yamago, Shigeru; Majima, Tetsuro

    2014-07-01

    Cycloparaphenylenes (CPPs) have attracted wide attention because of their interesting properties owing to distorted and strained aromatic systems and radially oriented p orbitals. For application of CPPs, information on their charged states (radical cation and radical anion) is essential. Here, we measured absorption spectra of the radical cations and the radical anions of CPPs with various ring sizes over a wide spectral region by means of radiation chemical methods. The peak position of the near-IR bands for both the radical cation and the radical anion shifted to lower energies with an increase in the ring size. This trend is contrary to what is observed for transitions between the HOMO and LUMO of the neutral CPP. The observed spectra of the CPP radical ions were reasonably assigned based on time-dependent density functional theory. These results indicate that the next HOMO and the next LUMO levels are important in the electronic transitions of radical ions. PMID:26279550

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

    NASA Astrophysics Data System (ADS)

    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.

  9. Photochemical properties of some Cl-containing halogenated alkanes.

    PubMed

    Orkin, V L; Khamaganov, V G; Kasimovskaya, E E; Guschin, A G

    2013-07-01

    Rate constants for the gas-phase reactions of OH radicals with three partially halogenated alkanes, CH3Cl (kMC), CHFClCFCl2 (k122a), and CH2FCFCl2 (k132c), were measured using a discharge flow-electron paramagnetic resonance technique over the temperature range from 298 to 460 K. The temperature dependences of the rate constants can be represented by the expressions kMC(298-460 K) = (3.09 ± 0.94) × 10(-12) exp[-(1411 ± 85)/T] cm(3) molecule(-1) s(-1), k122a(298-460 K) = (1.26 ± 0.24) × 10(-12) exp[-(1298 ± 66)/T] cm(3) molecule(-1) s(-1), and k132c(298-370 K) = (8.1 ± 2.2) × 10(-13) exp[-(1247 ± 89)/T] cm(3) molecule(-1) s(-1). The atmospheric lifetimes of CH3Cl, CHFClCFCl2, and CH2FCFCl2 due to their reaction with OH were estimated to be 1.6, 3.5, and 4.5 years, respectively. The UV absorption cross sections of halogenated ethanes, CHFClCFCl2, and CH2FCFCl2, were measured at T = 295 K between 190 and 240 nm, as were those for CHCl2CF2Cl (HCFC-122), CHCl2CF3 (HCFC-123), CHFClCF2Cl (HCFC-123a), and CH3CFCl2 (HCFC-141b). The atmospheric lifetimes due to stratospheric photolysis were also estimated. PMID:23725515

  10. Oligorotaxane Radicals under Orders

    PubMed Central

    2016-01-01

    A strategy for creating foldameric oligorotaxanes composed of only positively charged components is reported. Threadlike components—namely oligoviologens—in which different numbers of 4,4′-bipyridinium (BIPY2+) subunits are linked by p-xylylene bridges, are shown to be capable of being threaded by cyclobis(paraquat-p-phenylene) (CBPQT4+) rings following the introduction of radical-pairing interactions under reducing conditions. UV/vis/NIR spectroscopic and electrochemical investigations suggest that the reduced oligopseudorotaxanes fold into highly ordered secondary structures as a result of the formation of BIPY•+ radical cation pairs. Furthermore, by installing bulky stoppers at each end of the oligopseudorotaxanes by means of Cu-free alkyne–azide cycloadditions, their analogous oligorotaxanes, which retain the same stoichiometries as their progenitors, can be prepared. Solution-state studies of the oligorotaxanes indicate that their mechanically interlocked structures lead to the enforced interactions between the dumbbell and ring components, allowing them to fold (contract) in their reduced states and unfold (expand) in their fully oxidized states as a result of Coulombic repulsions. This electrochemically controlled reversible folding and unfolding process, during which the oligorotaxanes experience length contractions and expansions, is reminiscent of the mechanisms of actuation associated with muscle fibers. PMID:27163033

  11. High-order harmonic generation in alkanes

    SciTech Connect

    Altucci, C.; Velotta, R.; Heesel, E.; Springate, E.; Marangos, J. P.; Vozzi, C.; Benedetti, E.; Calegari, F.; Sansone, G.; Stagira, S.; Nisoli, M.; Tosa, V.

    2006-04-15

    We have investigated the process of high-order harmonic generation in light alkanes by using femtosecond laser pulses. We show the experimental results cannot be matched by a model that assumes a single active electron only in a hydrogenic s orbital. Clear evidences are shown of the important role played by the p-like character originating from the covalent C-H bond. By constructing a suitable mixture of s-type and p-type atomic wave functions, an excellent agreement between measurements in methane and simulations is found, thus confirming the validity of the developed method as a general tool for the analysis of high-order harmonic generation in complex molecules.

  12. Novel phase behavior in normal alkanes

    SciTech Connect

    Sirota, E.B.; King, H.E. Jr.; Hughes, G.J.; Wan, W.K. )

    1992-01-27

    X-ray scattering studies on aligned films of binary mixtures of the normal alkanes C{sub 23}H{sub 48} and C{sub 28}H{sub 58} reveal, for the first time in such materials, the existence of a new equilibrium phase having the symmetry of a smectic crystal, possibly a hexatic. This phase occurs between the hexagonally packed {ital R}{sub II} and the lower-temperature orthorhombic {ital R}{sub I}, plastic crystalline, layered, rotator phases. We argue that this loss of order is due to local distortion fluctuations in the hexagonal phase. Furthermore, we have identified an {ital ABC}-to-{ital ABAB} restacking transition within the ordered {ital R}{sub II} phase.

  13. Formation of ions and radicals from icy grains in comets

    NASA Technical Reports Server (NTRS)

    Jackson, William M.

    1992-01-01

    Two theoretical models for the formation of radicals from ice grains are examined to determine if this can explain the jets in comets. It is shown that the production rates for these radicals by the photolysis of molecules in the icy grains are not high enough to explain the jets. A new mechanism is proposed involving the release of cations and anions in the gas phase as the icy mantle surrounding the grains is evaporated. Solar visible radiation can then form radicals by photodetachment of the electrons from these anions. The production rate of radicals formed in this manner is in accord with the production rates of the observed radicals.

  14. The vapor-particle partitioning of n-alkanes

    SciTech Connect

    Doskey, P.V.

    1994-04-01

    A mixed-phase partitioning model has been proposed to predict the distribution of n-alkanes between the vapor and particle phases in the atmosphere. n-Alkanes having terrestrial plant wax and petroleum origins are assumed to be associated with atmospheric particles as microcrystalline solids and subcooled liquids, respectively. The fraction of n-alkanes on atmospheric particles having plant wax and petroleum origins is estimated with carbon preference indices. Hypothetical terrestrial plant wax and petroleum mixtures are used to estimate the mole fractions of the n-alkanes in each phase and the molecular weights of the phases. Solid and subcooled liquid phase n-alkane vapor pressures are used in the model to predict the fraction of n-alkanes associated with particles in the atmosphere. Trends in the prediction of vapor-particle partitioning using these assumptions agree well with field observations. However, the fraction of particle phase n-alkanes predicted by the model was significantly different from the field observations.

  15. Long-chain alkane production by the yeast Saccharomyces cerevisiae.

    PubMed

    Buijs, Nicolaas A; Zhou, Yongjin J; Siewers, Verena; Nielsen, Jens

    2015-06-01

    In the past decade industrial-scale production of renewable transportation biofuels has been developed as an alternative to fossil fuels, with ethanol as the most prominent biofuel and yeast as the production organism of choice. However, ethanol is a less efficient substitute fuel for heavy-duty and maritime transportation as well as aviation due to its low energy density. Therefore, new types of biofuels, such as alkanes, are being developed that can be used as drop-in fuels and can substitute gasoline, diesel, and kerosene. Here, we describe for the first time the heterologous biosynthesis of long-chain alkanes by the yeast Saccharomyces cerevisiae. We show that elimination of the hexadecenal dehydrogenase Hfd1 and expression of a redox system are essential for alkane biosynthesis in yeast. Deletion of HFD1 together with expression of an alkane biosynthesis pathway resulted in the production of the alkanes tridecane, pentadecane, and heptadecane. Our study provides a proof of principle for producing long-chain alkanes in the industrial workhorse S. cerevisiae, which was so far limited to bacteria. We anticipate that these findings will be a key factor for further yeast engineering to enable industrial production of alkane based drop-in biofuels, which can allow the biofuel industry to diversify beyond bioethanol.

  16. Long-chain alkane production by the yeast Saccharomyces cerevisiae.

    PubMed

    Buijs, Nicolaas A; Zhou, Yongjin J; Siewers, Verena; Nielsen, Jens

    2015-06-01

    In the past decade industrial-scale production of renewable transportation biofuels has been developed as an alternative to fossil fuels, with ethanol as the most prominent biofuel and yeast as the production organism of choice. However, ethanol is a less efficient substitute fuel for heavy-duty and maritime transportation as well as aviation due to its low energy density. Therefore, new types of biofuels, such as alkanes, are being developed that can be used as drop-in fuels and can substitute gasoline, diesel, and kerosene. Here, we describe for the first time the heterologous biosynthesis of long-chain alkanes by the yeast Saccharomyces cerevisiae. We show that elimination of the hexadecenal dehydrogenase Hfd1 and expression of a redox system are essential for alkane biosynthesis in yeast. Deletion of HFD1 together with expression of an alkane biosynthesis pathway resulted in the production of the alkanes tridecane, pentadecane, and heptadecane. Our study provides a proof of principle for producing long-chain alkanes in the industrial workhorse S. cerevisiae, which was so far limited to bacteria. We anticipate that these findings will be a key factor for further yeast engineering to enable industrial production of alkane based drop-in biofuels, which can allow the biofuel industry to diversify beyond bioethanol. PMID:25545362

  17. Expanding the product profile of a microbial alkane biosynthetic pathway.

    PubMed

    Harger, Matthew; Zheng, Lei; Moon, Austin; Ager, Casey; An, Ju Hye; Choe, Chris; Lai, Yi-Ling; Mo, Benjamin; Zong, David; Smith, Matthew D; Egbert, Robert G; Mills, Jeremy H; Baker, David; Pultz, Ingrid Swanson; Siegel, Justin B

    2013-01-18

    Microbially produced alkanes are a new class of biofuels that closely match the chemical composition of petroleum-based fuels. Alkanes can be generated from the fatty acid biosynthetic pathway by the reduction of acyl-ACPs followed by decarbonylation of the resulting aldehydes. A current limitation of this pathway is the restricted product profile, which consists of n-alkanes of 13, 15, and 17 carbons in length. To expand the product profile, we incorporated a new part, FabH2 from Bacillus subtilis , an enzyme known to have a broader specificity profile for fatty acid initiation than the native FabH of Escherichia coli . When provided with the appropriate substrate, the addition of FabH2 resulted in an altered alkane product profile in which significant levels of n-alkanes of 14 and 16 carbons in length are produced. The production of even chain length alkanes represents initial steps toward the expansion of this recently discovered microbial alkane production pathway to synthesize complex fuels. This work was conceived and performed as part of the 2011 University of Washington international Genetically Engineered Machines (iGEM) project.

  18. Heterogeneity of Alkane Chain Length in Freshwater and Marine Cyanobacteria

    PubMed Central

    Shakeel, Tabinda; Fatma, Zia; Fatma, Tasneem; Yazdani, Syed Shams

    2015-01-01

    The potential utilization of cyanobacteria for the biological production of alkanes represents an exceptional system for the next generation of biofuels. Here, we analyzed a diverse group of freshwater and marine cyanobacterial isolates from Indian culture collections for their ability to produce both alkanes and alkenes. Among the 50 cyanobacterial isolates screened, 32 isolates; 14 freshwater and 18 marine isolates; produced predominantly alkanes. The GC-MS/MS profiles revealed a higher percentage of pentadecane and heptadecane production for marine and freshwater strains, respectively. Oscillatoria species were found to be the highest producers of alkanes. Among the freshwater isolates, Oscillatoria CCC305 produced the maximum alkane level with 0.43 μg/mg dry cell weight, while Oscillatoria formosa BDU30603 was the highest producer among the marine isolates with 0.13 μg/mg dry cell weight. Culturing these strains under different media compositions showed that the alkane chain length was not influenced by the growth medium but was rather an inherent property of the strains. Analysis of the cellular fatty acid content indicated the presence of predominantly C16 chain length fatty acids in marine strains, while the proportion of C18 chain length fatty acids increased in the majority of freshwater strains. These results correlated with alkane chain length specificity of marine and freshwater isolates indicating that alkane chain lengths may be primarily determined by the fatty acid synthesis pathway. Moreover, the phylogenetic analysis showed clustering of pentadecane-producing marine strains that was distinct from heptadecane-producing freshwater strains strongly suggesting a close association between alkane chain length and the cyanobacteria habitat. PMID:25853127

  19. Copper-Catalyzed Oxidative Dehydrogenative Carboxylation of Unactivated Alkanes to Allylic Esters via Alkenes

    PubMed Central

    2015-01-01

    We report copper-catalyzed oxidative dehydrogenative carboxylation (ODC) of unactivated alkanes with various substituted benzoic acids to produce the corresponding allylic esters. Spectroscopic studies (EPR, UV–vis) revealed that the resting state of the catalyst is [(BPI)Cu(O2CPh)] (1-O2CPh), formed from [(BPI)Cu(PPh3)2], oxidant, and benzoic acid. Catalytic and stoichiometric reactions of 1-O2CPh with alkyl radicals and radical probes imply that C–H bond cleavage occurs by a tert-butoxy radical. In addition, the deuterium kinetic isotope effect from reactions of cyclohexane and d12-cyclohexane in separate vessels showed that the turnover-limiting step for the ODC of cyclohexane is C–H bond cleavage. To understand the origin of the difference in products formed from copper-catalyzed amidation and copper-catalyzed ODC, reactions of an alkyl radical with a series of copper–carboxylate, copper–amidate, and copper–imidate complexes were performed. The results of competition experiments revealed that the relative rate of reaction of alkyl radicals with the copper complexes follows the trend Cu(II)–amidate > Cu(II)–imidate > Cu(II)–benzoate. Consistent with this trend, Cu(II)–amidates and Cu(II)–benzoates containing more electron-rich aryl groups on the benzamidate and benzoate react faster with the alkyl radical than do those with more electron-poor aryl groups on these ligands to produce the corresponding products. These data on the ODC of cyclohexane led to preliminary investigation of copper-catalyzed oxidative dehydrogenative amination of cyclohexane to generate a mixture of N-alkyl and N-allylic products. PMID:25389772

  20. Copper-catalyzed oxidative dehydrogenative carboxylation of unactivated alkanes to allylic esters via alkenes.

    PubMed

    Tran, Ba L; Driess, Matthias; Hartwig, John F

    2014-12-10

    We report copper-catalyzed oxidative dehydrogenative carboxylation (ODC) of unactivated alkanes with various substituted benzoic acids to produce the corresponding allylic esters. Spectroscopic studies (EPR, UV-vis) revealed that the resting state of the catalyst is [(BPI)Cu(O2CPh)] (1-O2CPh), formed from [(BPI)Cu(PPh3)2], oxidant, and benzoic acid. Catalytic and stoichiometric reactions of 1-O2CPh with alkyl radicals and radical probes imply that C-H bond cleavage occurs by a tert-butoxy radical. In addition, the deuterium kinetic isotope effect from reactions of cyclohexane and d12-cyclohexane in separate vessels showed that the turnover-limiting step for the ODC of cyclohexane is C-H bond cleavage. To understand the origin of the difference in products formed from copper-catalyzed amidation and copper-catalyzed ODC, reactions of an alkyl radical with a series of copper-carboxylate, copper-amidate, and copper-imidate complexes were performed. The results of competition experiments revealed that the relative rate of reaction of alkyl radicals with the copper complexes follows the trend Cu(II)-amidate > Cu(II)-imidate > Cu(II)-benzoate. Consistent with this trend, Cu(II)-amidates and Cu(II)-benzoates containing more electron-rich aryl groups on the benzamidate and benzoate react faster with the alkyl radical than do those with more electron-poor aryl groups on these ligands to produce the corresponding products. These data on the ODC of cyclohexane led to preliminary investigation of copper-catalyzed oxidative dehydrogenative amination of cyclohexane to generate a mixture of N-alkyl and N-allylic products. PMID:25389772

  1. Alkanes-filled photonic crystal fibers as sensor transducers

    NASA Astrophysics Data System (ADS)

    Marć, P.; Przybysz, N.; Stasiewicz, K.; Jaroszewicz, L. R.

    2015-09-01

    In this paper we propose alkanes-filled PCFs as the new class of transducers for optical fiber sensors. We investigated experimentally thermo-optic properties of a commercially available LMA8 partially filled with different alkanes with a higher number of carbon atoms. A partially filled PCF spliced with standard SMFs constitutes one of the newest type transducer. We have selected a group of eight alkanes which have melting points in different temperatures. An analysis of temperature spectral characteristics of these samples will allow to design an optical fiber sensor with different temperature thresholds at specific wavelengths.

  2. Copper-homoscorpionate complexes as active catalysts for atom transfer radical addition to olefins.

    PubMed

    Muñoz-Molina, José María; Caballero, Ana; Díaz-Requejo, M Mar; Trofimenko, Swiatoslaw; Belderraín, Tomas R; Pérez, Pedro J

    2007-09-17

    Cu(I) complexes containing trispyrazolylborate ligands efficiently catalyze the atom transfer radical addition (ATRA) of polyhalogenated alkanes to various olefins under mild conditions. The catalytic activity is enhanced when bulky and electron donating Tpx ligands are employed. Kinetic data have allowed the proposal of a mechanistic interpretation that includes a Cu(II) pentacoordinated species that regulates the catalytic cycle.

  3. Hydrogen-transferring pyrolysis of long-chain alkanes and thermal stability improvement of jet fuels by hydrogen donors

    SciTech Connect

    Song, C.; Lai, W.C.; Schobert, H.H. . Fuel Science Program)

    1994-03-01

    Hydrogen-transferring pyrolysis refers to the thermal decomposition of hydrocarbons in the presence of hydrogen donors. Relative to the pyrolysis of pure n-tetradecane (C[sub 14]H[sub 28]) at 450 C, adding 10 vol % of H-donor tetralin suppressed n-C[sub 14] conversion by 68 % after 12 min of residence time, by about 66% after 21 min, and by 37% after 30 min. The presence of tetralin not only inhibited the n-C[sub 14] decomposition, but also altered the product distribution. The decomposition and isomerization of primary radicals are strongly suppressed, leading to a much higher ratio of the 1-alkene to n-alkane with 12 carbon atoms and slightly higher alkene/alkane ratio for the other product groups. The overall reaction mechanism for the initial stage of hydrogen-transferring pyrolysis is characterized by a one-step [beta]-scission of secondary radical followed by H-abstraction of the resulting primary radical. Moreover, desirable effects of the H-donor are also observed even after 240 min at 450 C, especially for inhibiting solid deposition. The authors also examined the effect of tetralin addition on the deposit formation from a paraffinic jet fuel JP-8 which is rich in C[sub 9]-C[sub 16] long-chain alkanes, and an aromatic compound, n-butylbenzene. Adding 10 vol % tetralin to a JP-8 jet fuel, n-C[sub 14], and n-butylbenzene reduced the formation of deposits by 90% (from 3.1 to 0.3 wt %), 77 % (from 3.0 to 0.7 wt %), and 54 % (from 5.6 to 2.6 wt %), respectively. These results suggest that, by taking advantage of H-transferring pyrolysis, hydrocarbon jet fuels may be used at high operating temperatures with little or no solid deposition.

  4. Process for converting light alkanes to higher hydrocarbons

    DOEpatents

    Noceti, Richard P.; Taylor, Charles E.

    1988-01-01

    A process is disclosed for the production of aromatic-rich, gasoline boiling range hydrocarbons from the lower alkanes, particularly from methane. The process is carried out in two stages. In the first, alkane is reacted with oxygen and hydrogen chloride over an oxyhydrochlorination catalyst such as copper chloride with minor proportions of potassium chloride and rare earth chloride. This produces an intermediate gaseous mixture containing water and chlorinated alkanes. The chlorinated alkanes are contacted with a crystalline aluminosilicate catalyst in the hydrogen or metal promoted form to produce gasoline range hydrocarbons with a high proportion of aromatics and a small percentage of light hydrocarbons (C.sub.2 -C.sub.4). The light hydrocarbons can be recycled for further processing over the oxyhydrochlorination catalyst.

  5. Influence of alkane chain length on adsorption on an α-alumina surface by MD simulations

    NASA Astrophysics Data System (ADS)

    Turgut, C.; Pandiyan, S.; Mether, L.; Belmahi, M.; Nordlund, K.; Philipp, P.

    2015-06-01

    Plasma surface techniques provide both an efficient and ecological tool for the functionalization of surfaces. Hence, a proper understanding of the plasma-surface interactions of precursors and radicals during the deposition process is of great importance. Especially during the initial deposition process, the deposition of molecules and fragments is difficult to investigate by experimental techniques and import insights can be obtained by molecular dynamics simulations. In this work, the reactive force field developed by the group of Kieffer at the University of Michigan was used to study the adsorption of single linear alkane chains on an α-alumina surface. The chain length was changed from 6 backbone carbon atoms to 16 carbon atoms, the deposition energy from 0.01 to 10 eV and the incidence angle from 0° to 60° with respect to the surface normal. Results show that the adsorption depends a lot on the ratio of deposition energy to alkane chain length and the incidence angle. More grazing incidence reduces the adsorption probability and a low ratio of energy to chain length increases it.

  6. Contribution of cyanobacterial alkane production to the ocean hydrocarbon cycle.

    PubMed

    Lea-Smith, David J; Biller, Steven J; Davey, Matthew P; Cotton, Charles A R; Perez Sepulveda, Blanca M; Turchyn, Alexandra V; Scanlan, David J; Smith, Alison G; Chisholm, Sallie W; Howe, Christopher J

    2015-11-01

    Hydrocarbons are ubiquitous in the ocean, where alkanes such as pentadecane and heptadecane can be found even in waters minimally polluted with crude oil. Populations of hydrocarbon-degrading bacteria, which are responsible for the turnover of these compounds, are also found throughout marine systems, including in unpolluted waters. These observations suggest the existence of an unknown and widespread source of hydrocarbons in the oceans. Here, we report that strains of the two most abundant marine cyanobacteria, Prochlorococcus and Synechococcus, produce and accumulate hydrocarbons, predominantly C15 and C17 alkanes, between 0.022 and 0.368% of dry cell weight. Based on global population sizes and turnover rates, we estimate that these species have the capacity to produce 2-540 pg alkanes per mL per day, which translates into a global ocean yield of ∼ 308-771 million tons of hydrocarbons annually. We also demonstrate that both obligate and facultative marine hydrocarbon-degrading bacteria can consume cyanobacterial alkanes, which likely prevents these hydrocarbons from accumulating in the environment. Our findings implicate cyanobacteria and hydrocarbon degraders as key players in a notable internal hydrocarbon cycle within the upper ocean, where alkanes are continually produced and subsequently consumed within days. Furthermore we show that cyanobacterial alkane production is likely sufficient to sustain populations of hydrocarbon-degrading bacteria, whose abundances can rapidly expand upon localized release of crude oil from natural seepage and human activities.

  7. Contribution of cyanobacterial alkane production to the ocean hydrocarbon cycle

    PubMed Central

    Lea-Smith, David J.; Biller, Steven J.; Davey, Matthew P.; Cotton, Charles A. R.; Perez Sepulveda, Blanca M.; Turchyn, Alexandra V.; Scanlan, David J.; Smith, Alison G.; Chisholm, Sallie W.; Howe, Christopher J.

    2015-01-01

    Hydrocarbons are ubiquitous in the ocean, where alkanes such as pentadecane and heptadecane can be found even in waters minimally polluted with crude oil. Populations of hydrocarbon-degrading bacteria, which are responsible for the turnover of these compounds, are also found throughout marine systems, including in unpolluted waters. These observations suggest the existence of an unknown and widespread source of hydrocarbons in the oceans. Here, we report that strains of the two most abundant marine cyanobacteria, Prochlorococcus and Synechococcus, produce and accumulate hydrocarbons, predominantly C15 and C17 alkanes, between 0.022 and 0.368% of dry cell weight. Based on global population sizes and turnover rates, we estimate that these species have the capacity to produce 2–540 pg alkanes per mL per day, which translates into a global ocean yield of ∼308–771 million tons of hydrocarbons annually. We also demonstrate that both obligate and facultative marine hydrocarbon-degrading bacteria can consume cyanobacterial alkanes, which likely prevents these hydrocarbons from accumulating in the environment. Our findings implicate cyanobacteria and hydrocarbon degraders as key players in a notable internal hydrocarbon cycle within the upper ocean, where alkanes are continually produced and subsequently consumed within days. Furthermore we show that cyanobacterial alkane production is likely sufficient to sustain populations of hydrocarbon-degrading bacteria, whose abundances can rapidly expand upon localized release of crude oil from natural seepage and human activities. PMID:26438854

  8. Effect of substituents on different channels of rad OH radical reaction with substituted organic sulfides

    NASA Astrophysics Data System (ADS)

    Mohan, Hari; Mittal, Jai P.

    2005-10-01

    Pulse radiolysis technique has been employed to study the nature of rad OH radical reaction in aqueous solutions of substituted organic sulfides. The transient absorption band at 345 nm observed on reaction of rad OH radicals in neutral aqueous solution of 3,3'-thiodipropionitrile is assigned to OH-adduct at sulfur. OH-adduct is observed to have high reactivity with oxygen ( k=8.8×10 8 dm 3 mol -1 s -1). The reaction of rad OH radicals in neutral aqueous solution of methyl propyl sulfide has shown the formation of sulfur-centered dimer radical cation with a small fraction (˜10%) of α-(alkylthio)alkyl radicals. The reaction of rad OH radicals with thiodiglycolic acid showed an absorption band at 285 nm, which is assigned to α -(alkylthio)alkyl radicals. The reaction of rad OH radicals with dimethyl 2,2'-thiodiethanoic acid has been assigned to OH-adduct at sulfur, whereas the transient absorption band at 390 observed with 3,3'-thiodipropionic acid is assigned to intra-molecular radical cation formed on p-orbital overlap of oxidized sulfur with oxygen. In acidic solutions, sulfur-centered dimer radical cation is the only transient species observed with substituted alkyl sulfides. The concentration of acid required to observe the formation of dimer radical cation is found to depend on the electron-withdrawing power of the substituted group. The reaction of rad OH radicals in neutral aqueous solution of substituted aryl sulfides has shown the formation of monomer radical cation and OH-adduct at benzene ring. Sulfur-centered dimer radical cations are not observed even in acidic conditions.

  9. Dynamics of CN+alkane reactions by crossed-beam dc slice imaging

    SciTech Connect

    Huang Cunshun; Li Wen; Estillore, Armando D.; Suits, Arthur G.

    2008-08-21

    The hydrogen atom abstraction reactions of CN (X {sup 2}{sigma}{sup +}) with alkanes have been studied using the crossed molecular beam technique with dc slice ion imaging at collision energies of 7.5 and 10.8 kcal/mol. The product alkyl radical images were obtained via single photon ionization at 157 nm for the reactions of CN (X {sup 2}{sigma}{sup +}) with n-butane, n-pentane, n-hexane, and cyclohexane. From analysis of the images, we obtained the center-of-mass frame product angular distributions and translational energy distributions directly. The results indicate that the products are largely backscattered and that most of the available energy ({approx}80%-85%) goes to the internal energy of the products. The reaction dynamics is discussed in light of recent kinetics data, theoretical calculations, and results for related halogen and oxygen atom reactions.

  10. A Comparison of the Monolayer Dynamics of the Branched Alkane Squalane and the Normal Alkane Tetracosane Adsorbed on Graphite

    NASA Astrophysics Data System (ADS)

    Enevoldsen, A. D.; Hansen, F. Y.; Diama, A.; Taub, H.

    2004-03-01

    Squalane is a branched alkane (C_30H_62) with 24 carbon atoms in its backbone, like the normal alkane tetracosane ( n-C_24H_50), and six symmetrically placed methyl side groups. In general, branched alkanes such as squalane are better lubricants than n-alkanes. We have studied the dynamics of the squalane and tetracosane monolayers by quasielastic neutron scattering and molecular dynamics (MD) simulations on two different time scales. Both experiments and simulations showed that diffusion at 260 K is about 2.5 times faster in the squalane than in the tetracosane system. It is somewhat surprising that the diffusion in a system with a branched alkane is faster than with a normal alkane. A possible explanation is that the squalane molecule does not bind as strongly to the surface as tetracosane, because the MD simulations have shown that the adsorbed molecules have a distorted backbone. This may also explain why the slow intramolecular motions associated with conformational changes are seen at lower temperatures in the squalane than the tetracosane monolayer where they are only observed near melting.

  11. Variation in n-Alkane Distributions of Modern Plants: Questioning Applications of n-Alkanes in Chemotaxonomy and Paleoecology

    NASA Astrophysics Data System (ADS)

    Bush, R. T.; McInerney, F. A.

    2010-12-01

    Long chain n-alkanes (n-C21 to n-C37) are synthesized as part of the epicuticular leaf wax of terrestrial plants and are among the most recognizable and widely used plant biomarkers. n-Alkane distributions have been utilized in previous studies on modern plant chemotaxonomy, testing whether taxa can be identified based on characteristic n-alkane profiles. Dominant n-alkanes (e.g. n-C27 or n-C31) have also been ascribed to major plant groups (e.g. trees or grasses respectively) and have been used in paleoecology studies to reconstruct fluctuations in plant functional types. However, many of these studies have been based on relatively few modern plant data; with the wealth of modern n-alkane studies, a more comprehensive analysis of n-alkanes in modern plants is now possible and can inform the usefulness of n-alkane distributions as paleoecological indicators. The work presented here is a combination of measurements made using plant leaves collected from the Chicago Botanic Garden and a compilation of published literature data from six continents. We categorized plants by type: angiosperms, gymnosperms, woody plants, forbs, grasses, ferns and pteridophytes, and mosses. We then quantified n-alkane distribution parameters such as carbon preference index (CPI), average chain length (ACL), and dispersion (a measure of the spread of the profile over multiple chain lengths) and used these to compare plant groups. Among all plants, one of the emergent correlations is a decrease in dispersion with increasing CPI. Within and among plant groups, n-alkane distributions show a very large range of variation, and the results show little or no correspondence between broad plant groups and a single dominant n-alkane or a ratio of n-alkanes. These findings are true both when data from six continents are combined and when plants from a given region are compared (North America). We also compared the n-alkane distributions of woody angiosperms, woody gymnosperms, and grasses with one

  12. Electrochemistry and spectroelectrochemistry of nitroxyl free radicals

    SciTech Connect

    Fish, J.R.; Swarts, S.G.; Sevilla, M.D.; Malinski, T.

    1988-06-30

    This work reports electrochemical and spectroelectrochemical studies of the two nitroxyl radicals 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy (3-carbamoyl-PROXYL). Oxidation and reduction reactions have been observed in aqueous media over the pH range 2-12 in the potential range -0.8 to +0.8 V by differential pulse voltammetry, cyclic voltammetry, and thin-layer UV-visible spectroelectrochemistry, and the reaction products have been characterized by IR, NMR, and ESR spectrometry. At pH values less than 10, characteristic electrochemical behavior is observed to be analogous for both radicals, and the products from electron transfer compare quite favorably with those found by pulse radiolysis of aqueous solutions of nitroxyl radicals. At pH 2-9, a stable cation from a reversible oxidation and hydroxylamine following an irreversible reduction, as well as hydroxylated cation at pH higher than 9, are the same as those obtained in pulse radiolysis experiments. Spectroscopic evidence indicates that behavior following reduction at high pH differs for the two radicals. At pH 12, reduced TEMPO may undergo structural changes leading to the formation of a new radical consisting of a seven-membered ring.

  13. Antioxidant, electrochemical, thermal, antimicrobial and alkane oxidation properties of tridentate Schiff base ligands and their metal complexes

    NASA Astrophysics Data System (ADS)

    Ceyhan, Gökhan; Çelik, Cumali; Uruş, Serhan; Demirtaş, İbrahim; Elmastaş, Mahfuz; Tümer, Mehmet

    2011-10-01

    In this study, two Schiff base ligands (HL 1 and HL 2) and their Cu(II), Co(II), Ni(II), Pd(II) and Ru(III) metal complexes were synthesized and characterized by the analytical and spectroscopic methods. Alkane oxidation activities of the metal complexes were studied on cyclohexane as substrate. The ligands and their metal complexes were evaluated for their antimicrobial activity against Corynebacterium xerosis, Bacillus brevis, Bacillus megaterium, Bacillus cereus, Mycobacterium smegmatis, Staphylococcus aureus, Micrococcus luteus and Enterococcus faecalis (as Gram-positive bacteria) and Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Yersinia enterocolitica, Klebsiella fragilis, Saccharomyces cerevisiae, and Candida albicans (as Gram-negative bacteria). The antioxidant properties of the Schiff base ligands were evaluated in a series of in vitro tests: 1,1-diphenyl-2-picrylhydrazyl (DPPH rad ) free radical scavenging and reducing power activity of superoxide anion radical generated non-enzymatic systems. Electrochemical and thermal properties of the compounds were investigated.

  14. Diffusion of Benzene and Alkylbenzenes in n-Alkanes.

    PubMed

    Kowert, Bruce A; Register, Paul M

    2015-10-01

    The translational diffusion constants, D, of benzene and a series of alkylbenzenes have been determined in four n-alkanes at room temperature using capillary flow techniques. The alkylbenzenes are toluene, ethylbenzene, 1-phenylpropane, 1-phenylpentane, 1-phenyloctane, 1-phenylundecane, 1-phenyltetradecane, and 1-phenylheptadecane. The n-alkanes are n-nonane, n-decane, n-dodecane, and n-pentadecane. Ratios of the solutes' D values are independent of solvent and in general agreement with the predictions of diffusion models for cylinders and lollipops. For the latter, an alkylbenzene's phenyl ring is the lollipop's candy; the alkyl chain is its handle. A model that considers the solutes to be spheres with volumes determined by the van der Waals increments of their constituent atoms is not in agreement with experiment. The diffusion constants of 1-alkene and n-alkane solutes in n-alkane solvents also are compared with the cylinder model; reasonably good agreement is found. The n-alkanes are relatively extended, and this appears to be the case for the alkyl chains of the 1-alkenes and alkylbenzenes as well. PMID:26417941

  15. Surface freezing in binary alkane-alcohol mixtures

    SciTech Connect

    Ofer, E.; Sloutskin, E.; Tamam, L.; Deutsch, M.; Ocko, B. M.

    2006-08-15

    Surface freezing was detected and studied in mixtures of alcohol and alkane molecules, using surface tensiometry and surface-specific x-ray scattering methods. Considering that surface freezing in pure alkanes forms an ordered monolayer and in alcohols it forms an ordered bilayer, the length mismatch repulsion was minimized by varying the carbon number of the alkane component around 2n, where n is the carbon number of the alcohol molecule. A solutionlike behavior was found for all mixtures, where the ideal liquid mixture phase-separates upon freezing both in the bulk and the surface. The solid exhibits a herringbone crystalline phase below an alkane mole fraction {phi}{sub t}{approx_equal}0.8 and a rotator phase above it. The surface frozen film below {phi}{sub t} is an alkane monolayer exhibiting a next-nearest neighbor molecular tilt of a composition-dependent magnitude. Above {phi}{sub t}, no diffraction peaks were observed. This could be explained by the intrinsically shorter-range order of the rotator phase and a possible proliferation of defects.

  16. Additional chain-branching pathways in the low-temperature oxidation of branched alkanes

    DOE PAGES

    Wang, Zhandong; Zhang, Lidong; Moshammer, Kai; Popolan-Vaida, Denisia M.; Shankar, Vijai Shankar Bhavani; Lucassen, Arnas; Hemken, Christian; Taatjes, Craig A.; Leone, Stephen R.; Kohse-Hoinghaus, Katharina; et al

    2015-12-31

    Chain-branching reactions represent a general motif in chemistry, encountered in atmospheric chemistry, combustion, polymerization, and photochemistry; the nature and amount of radicals generated by chain-branching are decisive for the reaction progress, its energy signature, and the time towards its completion. In this study, experimental evidence for two new types of chain-branching reactions is presented, based upon detection of highly oxidized multifunctional molecules (HOM) formed during the gas-phase low-temperature oxidation of a branched alkane under conditions relevant to combustion. The oxidation of 2,5-dimethylhexane (DMH) in a jet-stirred reactor (JSR) was studied using synchrotron vacuum ultra-violet photoionization molecular beam mass spectrometry (SVUV-PI-MBMS).more » Specifically, species with four and five oxygen atoms were probed, having molecular formulas of C8H14O4 (e.g., diketo-hydroperoxide/keto-hydroperoxy cyclic ether) and C8H16O5 (e.g., keto-dihydroperoxide/dihydroperoxy cyclic ether), respectively. The formation of C8H16O5 species involves alternative isomerization of OOQOOH radicals via intramolecular H-atom migration, followed by third O2 addition, intramolecular isomerization, and OH release; C8H14O4 species are proposed to result from subsequent reactions of C8H16O5 species. The mechanistic pathways involving these species are related to those proposed as a source of low-volatility highly oxygenated species in Earth's troposphere. At the higher temperatures relevant to auto-ignition, they can result in a net increase of hydroxyl radical production, so these are additional radical chain-branching pathways for ignition. Furthermore, the results presented herein extend the conceptual basis of reaction mechanisms used to predict the reaction behavior of ignition, and have implications on atmospheric gas-phase chemistry and the oxidative stability of organic substances.« less

  17. Peroxyl radical reactions with carotenoids in microemulsions: Influence of microemulsion composition and the nature of peroxyl radical precursor.

    PubMed

    El-Agamey, Ali; McGarvey, David J

    2016-01-01

    The reactions of acetylperoxyl radicals with different carotenoids (7,7'-dihydro-β-carotene and ζ-carotene) in SDS and CTAC microemulsions of different compositions were investigated using laser flash photolysis (LFP) coupled with kinetic absorption spectroscopy. The primary objective of this study was to explore the influence of microemulsion composition and the type of surfactant used on the yields and kinetics of various transients formed from the reaction of acetylperoxyl radicals with carotenoids. Also, the influence of the site (hydrocarbon phases or aqueous phase) of generation of the peroxyl radical precursor was examined by using 4-acetyl-4-phenylpiperidine hydrochloride (APPHCl) and 1,1-diphenylacetone (11DPA) as water-soluble and lipid-soluble peroxyl radical precursors, respectively. LFP of peroxyl radical precursors with 7,7'-dihydro-β-carotene (77DH) in different microemulsions gives rise to the formation of three distinct transients namely addition radical (λmax=460 nm), near infrared transient1 (NIR, λmax=700 nm) and 7,7'-dihydro-β-carotene radical cation (77DH(•+), λmax=770 nm). In addition, for ζ-carotene (ZETA) two transients (near infrared transient1 (NIR1, λmax=660 nm) and ζ-carotene radical cation (ZETA(•+), λmax=730-740 nm)) are generated following LFP of peroxyl radical precursors in the presence of ζ-carotene (ZETA) in different microemulsions. The results show that the composition of the microemulsion strongly influences the observed yield and kinetics of the transients formed from the reactions of peroxyl radicals (acetylperoxyl radicals) with carotenoids (77DH and ZETA). Also, the type of surfactant used in the microemulsions influences the yield of the transients formed. The dependence of the transient yields and kinetics on microemulsion composition (or the type of surfactant used in the microemulsion) can be attributed to the change of the polarity of the microenvironment of the carotenoid. Furthermore, the nature of

  18. Electrostatic control of the tryptophan radical in cytochrome c peroxidase.

    PubMed

    Barrows, Tiffany P; Bhaskar, B; Poulos, Thomas L

    2004-07-13

    Previously a K(+)-binding site, analogous to that found in ascorbate peroxidase (APX), was engineered into cytochrome c peroxidase (CcP) to test the hypothesis that the bound K(+) influences the stability of the Trp191 cation radical formed during the CcP catalytic cycle (Bonagura et al., (1996) Biochemistry 35, 6107 and Bonagura et al., (1999) Biochemistry 38, 5528). Characterization of this mutant, designated CcPK2, showed that the stability of the Trp191 cation radical is dependent on the occupancy of the engineered K(+) site and that the Trp191 radical was much less stable in this mutant than in wild-type CcP. The mutations Met230Leu, Met231Gln, and Met172Ser have now been constructed on the CcPK2 mutant template to test if the Met residues also contribute to the stabilization of the Trp191 cation radical. Crystal structures show that the mutations affect only the local structure near the sites of mutation. Removal of these electronegative residues located less than 8 A from the Trp radical results in a further destabilization of the Trp radical. The characteristic EPR signal associated with the Trp radical is significantly narrowed and is characteristic of a tyrosine radical signal. Double-mixing stopped-flow experiments, where the delay time between the formation of CcP compound I and its mixing with horse heart ferrocytochrome c is varied, show that the stability of the Trp radical decreases as the Met residues are removed from the proximal cavity. When taken together, these results demonstrate a strong correlation between the experimentally determined stability of the Trp191 radical, the enzyme activity, and the calculated electrostatic stabilization of the Trp191 radical. PMID:15236591

  19. Isolation and structural characterization of a mainly ligand-based dimetallic radical.

    PubMed

    Li, Shuyu; Wang, Xingyong; Zhang, Zaichao; Zhao, Yue; Wang, Xinping

    2015-12-14

    A radical cation of ruthenium was isolated and structurally characterized. The EPR spectrum and theoretical calculations indicate that the spin density mainly resides on ligands. The X-ray structure shows that the change in metal-metal bond lengths is negligible upon one-electron oxidation. sp(3) C-H bond activation was observed during the reaction of the parent molecule with the trityl cation, which possibly occurs via an oxidative EC mechanism: a thermodynamically favorable electron-transfer to give the radical cation intermediate, followed by the hydrogen atom abstraction to afford a cationic tetramethylfulvene complex with formation of a metal-carbon bond.

  20. Microbial production of short-chain alkanes.

    PubMed

    Choi, Yong Jun; Lee, Sang Yup

    2013-10-24

    Increasing concerns about limited fossil fuels and global environmental problems have focused attention on the need to develop sustainable biofuels from renewable resources. Although microbial production of diesel has been reported, production of another much in demand transport fuel, petrol (gasoline), has not yet been demonstrated. Here we report the development of platform Escherichia coli strains that are capable of producing short-chain alkanes (SCAs; petrol), free fatty acids (FFAs), fatty esters and fatty alcohols through the fatty acyl (acyl carrier protein (ACP)) to fatty acid to fatty acyl-CoA pathway. First, the β-oxidation pathway was blocked by deleting the fadE gene to prevent the degradation of fatty acyl-CoAs generated in vivo. To increase the formation of short-chain fatty acids suitable for subsequent conversion to SCAs in vivo, the activity of 3-oxoacyl-ACP synthase (FabH), which is inhibited by unsaturated fatty acyl-ACPs, was enhanced to promote the initiation of fatty acid biosynthesis by deleting the fadR gene; deletion of the fadR gene prevents upregulation of the fabA and fabB genes responsible for unsaturated fatty acids biosynthesis. A modified thioesterase was used to convert short-chain fatty acyl-ACPs to the corresponding FFAs, which were then converted to SCAs by the sequential reactions of E. coli fatty acyl-CoA synthetase, Clostridium acetobutylicum fatty acyl-CoA reductase and Arabidopsis thaliana fatty aldehyde decarbonylase. The final engineered strain produced up to 580.8 mg l(-1) of SCAs consisting of nonane (327.8 mg l(-1)), dodecane (136.5 mg l(-1)), tridecane (64.8 mg l(-1)), 2-methyl-dodecane (42.8 mg l(-1)) and tetradecane (8.9 mg l(-1)), together with small amounts of other hydrocarbons. Furthermore, this platform strain could produce short-chain FFAs using a fadD-deleted strain, and short-chain fatty esters by introducing the Acinetobacter sp. ADP1 wax ester synthase (atfA) and the E. coli mutant

  1. Alkanes in shrimp from the Buccaneer Oil Field

    SciTech Connect

    Middleditch, B.S.; Basile, B.; Chang, E.S.

    1982-07-01

    A total of 36 samples of shrimp were examined from the region of the Buccaneer oil field, eighteen of which were representatives of the commercial species Penaeus aztecus and the rest were various other species: Penaeus duorarum (pink shrimp), Trachypenaeus duorarum (sugar shrimp), Squilla empusa (mantis shrimp), and Sicyonia dorsalis (chevron shrimp). The alkanes and deuteriated alkanes were completely separated by GC, so a mass spectrometer was not required for their detection and quantitation. To confirm the identities of individual compounds, however, some samples were examined by combined gas chromatography-mass spectrometry. Results show that only thirteen of the forty shrimp collected from the region of the Buccaneer oil field contained petroleum alkanes, and the majority of these were obtained from trawls immediately adjacent to the production platforms. It appears that shrimp caught in the region of the Buccaneer oil field are not appreciably tainted with hydrocarbons discharged from the production platforms. (JMT)

  2. High Temperature Chemical Kinetic Combustion Modeling of Lightly Methylated Alkanes

    SciTech Connect

    Sarathy, S M; Westbrook, C K; Pitz, W J; Mehl, M

    2011-03-01

    Conventional petroleum jet and diesel fuels, as well as alternative Fischer-Tropsch (FT) fuels and hydrotreated renewable jet (HRJ) fuels, contain high molecular weight lightly branched alkanes (i.e., methylalkanes) and straight chain alkanes (n-alkanes). Improving the combustion of these fuels in practical applications requires a fundamental understanding of large hydrocarbon combustion chemistry. This research project presents a detailed high temperature chemical kinetic mechanism for n-octane and three lightly branched isomers octane (i.e., 2-methylheptane, 3-methylheptane, and 2,5-dimethylhexane). The model is validated against experimental data from a variety of fundamental combustion devices. This new model is used to show how the location and number of methyl branches affects fuel reactivity including laminar flame speed and species formation.

  3. Thermal decomposition of n-alkanes under supercritical conditions

    SciTech Connect

    Yu, J.; Eser, S.

    1996-10-01

    The future aircraft fuel system may be operating at temperatures above the critical points of fuels. Currently there is very limited information on the thermal stability of hydrocarbon fuels under supercritical conditions. In this work, the thermal stressing experiments of n-decane, n-dodecane, n-tetradecane, their mixtures, and an n-paraffin mixture, Norpar-13, was carried out under supercritical conditions. The experimental results indicated that the thermal decomposition of n-alkanes can be represented well by the first-order kinetics. Pressure has significant effects on the first-order rate constant and product distribution in the near-critical region. The major products are a series of n-alkanes and 1-alkenes. The relative yields of n-alkanes and 1-alkenes depend on the reaction conditions. The first-order rate constants for the thermal decomposition of individual compounds in a mixture are different from those obtained for the decomposition of pure compounds.

  4. Surface crystallization in normal-alkanes and alcohols

    SciTech Connect

    Deutsch, M.; Ocko, B.M.; Wu, X.Z. |; Sirota, E.B.; Sinha, S.K.

    1995-06-01

    A new, rare surface freezing, phenomenon is observed in molten normal-alkanes and their derivatives (alcohols, thiols, etc.). X-ray and surface tension measurements show the formation of a crystalline monolayer on the surface of the liquid alkane at temperatures up to 3 C above the bulk solidification temperature, T{sub f}. For alcohols, a single bilayer is formed. In both cases, the molecules in the layer are hexagonally packed and oriented normal to the surface for short chain lengths, and tilted for long ones. In both cases the single layer persists down to T{sub f}. In terms of wetting theory, this constitutes a very limited partial wetting of the liquid surface by the crystalline layer. The new surface phase is obtained only for chain lengths 14 < n {le} 50 in alkanes, and 16 < n < 30 in alcohols. The measurements are satisfactorily accounted for within a simple theory based on surface energy considerations.

  5. Alkanes and alkenes conversion to high octane gasoline

    SciTech Connect

    Harandi, M.N.; Owen, H.

    1989-07-25

    This patent describes a process for the conversion of lower alkane and alkene hydrocarbons to high octane gasoline. It comprises: contacting a hydrocarbon feedstock comprising lower alkanes and alkenes with a fluidized bed of acidic, shape selective metallosiliate catalyst in a first conversion zone under high temperature alkane conversion conditions wherein the feedstock contains an amount of lower alkene sufficient to provide an exotherm sufficient to maintain near isothermal reaction conditions whereby an effluent stream is produced comprising higher aliphatic hydrocarbons rich in aromatics; contacting the effluent stream with a fluidized bed of acidic, medium pore metallosilicate catalyst in a second conversion zone at moderate temperature under oligonerization and alkylation conditions whereby a C/sub 5/ + gasoline boiling range product is produced rich in alkylated aromatics.

  6. Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether

    NASA Technical Reports Server (NTRS)

    DeMore, W.; Bayes, K.

    1998-01-01

    Relative rate experiements were used to measure rate constants and temperature denpendencies of the reactions of OH with propane, n-butane, n-pentane, n-hexane, cyclopropane, cyclobutane, cyclopentane, and dimethyl ether.

  7. Photolytic formation of free radicals and their effect on hydrocarbon pyrolysis chemistry in a concentrated solar environment: Final report

    SciTech Connect

    Hunjan, M.; Mok, W.S.; Antal, M.J. Jr.

    1987-01-01

    The objective of this research was two-fold: (1) to determine whether uv photons available in a concentrated solar environment can be used as a photolytic source to dissociate vapor phase acetone; and (2) to explore the effects of photolysis on rate and selectivity of free radical reactions. The experiments were conducted in a 1 kW arc image furnace/tubular flow reactor system. The results obtained conclusively showed that acetone readily photodissociates in a 1000 sun environment, leading to the formation of free radicals. It was further observed that Beer-Lambert law can be used to predict the rate of photolysis of acetone. Furthermore, acetone, when used as source of methyl radicals, sensitized the reaction chemistry of alkanes and alkenes at a temperature of 350/sup 0/C. The methyl radicals from photolysis of acetone enhanced the cracking reactions of the alkanes yielding smaller alkanes and alkenes. When the initial hydrocarbon reactant was an alkene, a sensitization of the addition reaction was observed leading to formation of next higher alkene. To gain a theoretical insight into the reaction chemistry of alkanes, a numerical simulation model was developed to study the photosensitized decomposition of n-butane and the simulation results thus obtained were found to be in close agreement with experimental results. 64 refs., 10 figs., 22 tabs.

  8. Catalytic, mild, and selective oxyfunctionalization of linear alkanes: current challenges.

    PubMed

    Bordeaux, Mélanie; Galarneau, Anne; Drone, Jullien

    2012-10-22

    Selective catalysts for sustainable oxidation of alkanes are highly demanded because of the abundance of these molecules in the environment, the possibility to transform them into higher-value compounds, such as chemicals or synthetic fuels, and the fact that, kinetically speaking, this is a difficult reaction. Numerous chemical and biological catalysts have been developed in the lasts decades for this purpose, rendering the overview over this field of chemistry difficult. After giving a definition of the ideal catalyst for alkane oxyfunctionalization, this review aims to present the catalysts available today that are closest to ideal.

  9. Assimilation of chlorinated alkanes by hydrocarbon-utilizing fungi

    SciTech Connect

    Murphy, G.L.; Perry, J.J.

    1984-12-01

    The fatty acid compositions of two filamentous fungi (Cunninghamella elegans and Penicillium zonatum) and a yeast (Candida lipolytica) were determined after the organisms were grown on 1-chlorohexadecane or 1-chlorooctadecane. These organisms utilized the chlorinated alkanes as sole sources of carbon and energy. Analyses of the fatty acids present after growth on the chlorinated alkanes indicated that 60 to 70% of the total fatty acids in C. elegans were chlorinated. Approximately 50% of the fatty acids in C. lipolytica were also chlorinated. P. zonatum contained 20% 1-chlorohexadecanoic acid after growth on either substrate but did not incorporate C/sub 18/ chlorinated fatty acids.

  10. Regioselective alkane hydroxylation with a mutant AlkB enzyme

    DOEpatents

    Koch, Daniel J.; Arnold, Frances H.

    2012-11-13

    AlkB from Pseudomonas putida was engineered using in-vivo directed evolution to hydroxylate small chain alkanes. Mutant AlkB-BMO1 hydroxylates propane and butane at the terminal carbon at a rate greater than the wild-type to form 1-propanol and 1-butanol, respectively. Mutant AlkB-BMO2 similarly hydroxylates propane and butane at the terminal carbon at a rate greater than the wild-type to form 1-propanol and 1-butanol, respectively. These biocatalysts are highly active for small chain alkane substrates and their regioselectivity is retained in whole-cell biotransformations.

  11. Modeling of alkane emissions from a wood stain

    SciTech Connect

    Chang, J.C.S.; Guo, Z.

    1993-01-01

    The article discusses full-scale residential house tests to evaluate the effects of organic emissions from a wood finishing product--wood stain--on indoor air quality (IAQ). The test house concentrations of three alkane species, nonane, decane, and undecane, were measured as a function of time after the application of the wood stain. It was found that the test house concentrations can be simulated by an integrated IAQ model which takes into consideration source, sink, and ventilation effects. The alkane emissions were controlled by an evaporation-like process.

  12. 40 CFR 721.785 - Halogenated alkane aromatic compound (generic name).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Halogenated alkane aromatic compound... Specific Chemical Substances § 721.785 Halogenated alkane aromatic compound (generic name). (a) Chemical... as a halogenated alkane aromatic compound (PMN P-94-1747) is subject to reporting under this...

  13. 40 CFR 721.785 - Halogenated alkane aromatic compound (generic name).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Halogenated alkane aromatic compound... Specific Chemical Substances § 721.785 Halogenated alkane aromatic compound (generic name). (a) Chemical... as a halogenated alkane aromatic compound (PMN P-94-1747) is subject to reporting under this...

  14. 40 CFR 721.785 - Halogenated alkane aromatic compound (generic name).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Halogenated alkane aromatic compound... Specific Chemical Substances § 721.785 Halogenated alkane aromatic compound (generic name). (a) Chemical... as a halogenated alkane aromatic compound (PMN P-94-1747) is subject to reporting under this...

  15. 40 CFR 721.785 - Halogenated alkane aromatic compound (generic name).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Halogenated alkane aromatic compound... Specific Chemical Substances § 721.785 Halogenated alkane aromatic compound (generic name). (a) Chemical... as a halogenated alkane aromatic compound (PMN P-94-1747) is subject to reporting under this...

  16. 40 CFR 721.4464 - Mixture of hydrofluoro alkanes and hydrofluoro alkene.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Mixture of hydrofluoro alkanes and... Specific Chemical Substances § 721.4464 Mixture of hydrofluoro alkanes and hydrofluoro alkene. (a) Chemical... as a mixture of hydrofluoro alkanes and hydrofluoro alkene (PMNs P-96-945/946/947/948) are subject...

  17. 40 CFR 721.4464 - Mixture of hydrofluoro alkanes and hydrofluoro alkene.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Mixture of hydrofluoro alkanes and... Specific Chemical Substances § 721.4464 Mixture of hydrofluoro alkanes and hydrofluoro alkene. (a) Chemical... as a mixture of hydrofluoro alkanes and hydrofluoro alkene (PMNs P-96-945/946/947/948) are subject...

  18. 40 CFR 721.4464 - Mixture of hydrofluoro alkanes and hydrofluoro alkene.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Mixture of hydrofluoro alkanes and... Specific Chemical Substances § 721.4464 Mixture of hydrofluoro alkanes and hydrofluoro alkene. (a) Chemical... as a mixture of hydrofluoro alkanes and hydrofluoro alkene (PMNs P-96-945/946/947/948) are subject...

  19. 40 CFR 721.4464 - Mixture of hydrofluoro alkanes and hydrofluoro alkene.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Mixture of hydrofluoro alkanes and... Specific Chemical Substances § 721.4464 Mixture of hydrofluoro alkanes and hydrofluoro alkene. (a) Chemical... as a mixture of hydrofluoro alkanes and hydrofluoro alkene (PMNs P-96-945/946/947/948) are subject...

  20. 40 CFR 721.4464 - Mixture of hydrofluoro alkanes and hydrofluoro alkene.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Mixture of hydrofluoro alkanes and... Specific Chemical Substances § 721.4464 Mixture of hydrofluoro alkanes and hydrofluoro alkene. (a) Chemical... as a mixture of hydrofluoro alkanes and hydrofluoro alkene (PMNs P-96-945/946/947/948) are subject...

  1. Diffusion of squalene in n-alkanes and squalane.

    PubMed

    Kowert, Bruce A; Watson, Michael B; Dang, Nhan C

    2014-02-27

    Squalene, an intermediate in the biosynthesis of cholesterol, has a 24-carbon backbone with six methyl groups and six isolated double bonds. Capillary flow techniques have been used to determine its translational diffusion constant, D, at room temperature in squalane, n-C16, and three n-C8-squalane mixtures. The D values have a weaker dependence on viscosity, η, than predicted by the Stokes-Einstein relation, D = kBT/(6πηr). A fit to the modified relation, D/T = ASE/η(p), gives p = 0.820 ± 0.028; p = 1 for the Stokes-Einstein limit. The translational motion of squalene appears to be much like that of n-alkane solutes with comparable chain lengths; their D values show similar deviations from the Stokes-Einstein model. The n-alkane with the same carbon chain length as squalene, n-C24, has a near-equal p value of 0.844 ± 0.018 in n-alkane solvents. The values of the hydrodynamic radius, r, for n-C24, squalene, and other n-alkane solutes decrease as the viscosity increases and have a common dependence on the van der Waals volumes of the solute and solvent. The possibility of studying squalene in lipid droplets and membranes is discussed.

  2. Catalytic production of branched small alkanes from biohydrocarbons.

    PubMed

    Oya, Shin-ichi; Kanno, Daisuke; Watanabe, Hideo; Tamura, Masazumi; Nakagawa, Yoshinao; Tomishige, Keiichi

    2015-08-10

    Squalane, C30 algae-derived branched hydrocarbon, was successfully converted to smaller hydrocarbons without skeletal isomerization and aromatization over ruthenium on ceria (Ru/CeO2 ). The internal CH2 CH2 bonds located between branches are preferably dissociated to give branched alkanes with very simple distribution as compared with conventional methods using metal-acid bifunctional catalysts.

  3. Cyano- and polycyanometallo-porphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, P.E. Jr.; Lyons, J.E.

    1993-05-18

    New compositions of matter comprising cyano-substituted metal complexes of porphyrins are catalysts for the oxidation of alkanes. The metal is iron, chromium, manganese, ruthenium, copper or cobalt. The porphyrin ring has cyano groups attached thereto in meso- and/or [beta]-pyrrolic positions.

  4. Cyano- and polycyanometallo-porphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, P.E. Jr.; Lyons, J.E.

    1995-01-17

    New compositions of matter comprising cyano-substituted metal complexes of porphyrins are catalysts for the oxidation of alkanes. The metal is iron, chromium, manganese, ruthenium, copper or cobalt. The porphyrin ring has cyano groups attached thereto in meso and/or [beta]-pyrrolic positions.

  5. Diffusion of squalene in n-alkanes and squalane.

    PubMed

    Kowert, Bruce A; Watson, Michael B; Dang, Nhan C

    2014-02-27

    Squalene, an intermediate in the biosynthesis of cholesterol, has a 24-carbon backbone with six methyl groups and six isolated double bonds. Capillary flow techniques have been used to determine its translational diffusion constant, D, at room temperature in squalane, n-C16, and three n-C8-squalane mixtures. The D values have a weaker dependence on viscosity, η, than predicted by the Stokes-Einstein relation, D = kBT/(6πηr). A fit to the modified relation, D/T = ASE/η(p), gives p = 0.820 ± 0.028; p = 1 for the Stokes-Einstein limit. The translational motion of squalene appears to be much like that of n-alkane solutes with comparable chain lengths; their D values show similar deviations from the Stokes-Einstein model. The n-alkane with the same carbon chain length as squalene, n-C24, has a near-equal p value of 0.844 ± 0.018 in n-alkane solvents. The values of the hydrodynamic radius, r, for n-C24, squalene, and other n-alkane solutes decrease as the viscosity increases and have a common dependence on the van der Waals volumes of the solute and solvent. The possibility of studying squalene in lipid droplets and membranes is discussed. PMID:24528091

  6. Improving alkane synthesis in Escherichia coli via metabolic engineering.

    PubMed

    Song, Xuejiao; Yu, Haiying; Zhu, Kun

    2016-01-01

    Concerns about energy security and global petroleum supply have made the production of renewable biofuels an industrial imperative. The ideal biofuels are n-alkanes in that they are chemically and structurally identical to the fossil fuels and can "drop in" to the transportation infrastructure. In this work, an Escherichia coli strain that produces n-alkanes was constructed by heterologous expression of acyl-acyl carrier protein (ACP) reductase (AAR) and aldehyde deformylating oxygenase (ADO) from Synechococcus elongatus PCC7942. The accumulation of alkanes ranged from 3.1 to 24.0 mg/L using different expressing strategies. Deletion of yqhD, an inherent aldehyde reductase in E. coli, or overexpression of fadR, an activator for fatty acid biosynthesis, exhibited a nearly twofold increase in alkane titers, respectively. Combining yqhD deletion and fadR overexpression resulted in a production titer of 255.6 mg/L in E. coli, and heptadecene was the most abundant product. PMID:26476644

  7. 40 CFR 721.10704 - Aryl-substituted alkane.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... reporting. (1) The chemical substance identified generically as an aryl-substituted alkane (PMN P-12-548) is subject to reporting under this section for the significant new uses described in paragraph (a)(2) of this... communication program. Requirements as specified in § 721.72(a), (b), (c), (d), (e) (concentration set at...

  8. MODELING OF ALKANE EMISSIONS FROM A WOOD STAIN

    EPA Science Inventory

    The article discusses full-scale residential house tests to evaluate the effects of organic emissions from a wood finishing product--wood stain--on indoor air quality (IAQ). The test house concentrations of three alkane species, nonane, decane, and undecane, were measured as a fu...

  9. Diverse alkane hydroxylase genes in microorganisms and environments

    PubMed Central

    Nie, Yong; Chi, Chang-Qiao; Fang, Hui; Liang, Jie-Liang; Lu, She-Lian; Lai, Guo-Li; Tang, Yue-Qin; Wu, Xiao-Lei

    2014-01-01

    AlkB and CYP153 are important alkane hydroxylases responsible for aerobic alkane degradation in bioremediation of oil-polluted environments and microbial enhanced oil recovery. Since their distribution in nature is not clear, we made the investigation among thus-far sequenced 3,979 microbial genomes and 137 metagenomes from terrestrial, freshwater, and marine environments. Hundreds of diverse alkB and CYP153 genes including many novel ones were found in bacterial genomes, whereas none were found in archaeal genomes. Moreover, these genes were detected with different distributional patterns in the terrestrial, freshwater, and marine metagenomes. Hints for horizontal gene transfer, gene duplication, and gene fusion were found, which together are likely responsible for diversifying the alkB and CYP153 genes adapt to the ubiquitous distribution of different alkanes in nature. In addition, different distributions of these genes between bacterial genomes and metagenomes suggested the potentially important roles of unknown or less common alkane degraders in nature. PMID:24829093

  10. Cyano- and polycyanometalloporphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, Jr., Paul E.; Lyons, James E.

    1992-01-01

    Alkanes are oxidized by contact with oxygen-containing gas in the presence as catalyst of a metalloporphyrin in which hydrogen atoms in the porphyrin ring have been substituted with one or more cyano groups. Hydrogen atoms in the porphyrin ring may also be substituted with halogen atoms.

  11. Cyano- and polycyanometallo-porphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, Jr., Paul E.; Lyons, James E.

    1995-01-01

    New compositions of matter comprising cyano-substituted metal complexes of porphyrins are catalysts for the oxidation of alkanes. The metal is iron, chromium, manganese, ruthenium, copper or cobalt. The porphyrin ring has cyano groups attached thereto in meso and/or .beta.-pyrrolic positions.

  12. Cyano- and polycyanometallo-porphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, Jr., Paul E.; Lyons, James E.

    1993-01-01

    New compositions of matter comprising cyano-substituted metal complexes of porphyrins are catalysts for the oxidation of alkanes. The metal is iron, chromium, manganese, ruthenium, copper or cobalt. The porphyrin ring has cyano groups attached thereto in meso and/or .beta.-pyrrolic positions.

  13. Improving alkane synthesis in Escherichia coli via metabolic engineering.

    PubMed

    Song, Xuejiao; Yu, Haiying; Zhu, Kun

    2016-01-01

    Concerns about energy security and global petroleum supply have made the production of renewable biofuels an industrial imperative. The ideal biofuels are n-alkanes in that they are chemically and structurally identical to the fossil fuels and can "drop in" to the transportation infrastructure. In this work, an Escherichia coli strain that produces n-alkanes was constructed by heterologous expression of acyl-acyl carrier protein (ACP) reductase (AAR) and aldehyde deformylating oxygenase (ADO) from Synechococcus elongatus PCC7942. The accumulation of alkanes ranged from 3.1 to 24.0 mg/L using different expressing strategies. Deletion of yqhD, an inherent aldehyde reductase in E. coli, or overexpression of fadR, an activator for fatty acid biosynthesis, exhibited a nearly twofold increase in alkane titers, respectively. Combining yqhD deletion and fadR overexpression resulted in a production titer of 255.6 mg/L in E. coli, and heptadecene was the most abundant product.

  14. Catalytic oxidation of light alkanes in presence of a base

    DOEpatents

    Bhinde, Manoj V.; Bierl, Thomas W.

    1998-01-01

    The presence of a base in the reaction mixture in a metal-ligand catalyzed partial oxidation of alkanes results in sustained catalyst activity, and in greater percent conversion as compared with oxidation in the absence of base, while maintaining satisfactory selectivity for the desired oxidation, for example the oxidation of isobutane to isobutanol.

  15. Catalytic oxidation of light alkanes in presence of a base

    DOEpatents

    Bhinde, M.V.; Bierl, T.W.

    1998-03-03

    The presence of a base in the reaction mixture in a metal-ligand catalyzed partial oxidation of alkanes results in sustained catalyst activity, and in greater percent conversion as compared with oxidation in the absence of base, while maintaining satisfactory selectivity for the desired oxidation, for example the oxidation of isobutane to isobutanol. 1 fig.

  16. Integrated process for preparing a carboxylic acid from an alkane

    SciTech Connect

    Benderly, Abraham; Chadda, Nitin; Sevon, Douglass

    2011-12-20

    The present invention relates to an integrated process for producing unsaturated carboxylic acids from the corresponding C.sub.2-C.sub.4 alkane. The process begins with performance of thermally integrated dehydrogenation reactions which convert a C.sub.2-C.sub.4 alkane to its corresponding C.sub.2-C.sub.4 alkene, and which involve exothermically converting a portion of an alkane to its corresponding alkene by oxidative dehydrogenation in an exothermic reaction zone, in the presence of oxygen and a suitable catalyst, and then feeding the products of the exothermic reaction zone to an endothermic reaction zone wherein at least a portion of the remaining unconverted alkane is endothermically dehydrogenated to form an additional quantity of the same corresponding alkene, in the presence of carbon dioxide and an other suitable catalyst. The alkene products of the thermally integrated dehydrogenation reactions are then provided to a catalytic vapor phase partial oxidation process for conversion of the alkene to the corresponding unsaturated carboxylic acid or nitrile. Unreacted alkene and carbon dioxide are recovered from the oxidation product stream and recycled back to the thermally integrated dehydrogenation reactions.

  17. Modular and selective biosynthesis of gasoline-range alkanes.

    PubMed

    Sheppard, Micah J; Kunjapur, Aditya M; Prather, Kristala L J

    2016-01-01

    Typical renewable liquid fuel alternatives to gasoline are not entirely compatible with current infrastructure. We have engineered Escherichia coli to selectively produce alkanes found in gasoline (propane, butane, pentane, heptane, and nonane) from renewable substrates such as glucose or glycerol. Our modular pathway framework achieves carbon-chain extension by two different mechanisms. A fatty acid synthesis route is used to generate longer chains heptane and nonane, while a more energy efficient alternative, reverse-β-oxidation, is used for synthesis of propane, butane, and pentane. We demonstrate that both upstream (thiolase) and intermediate (thioesterase) reactions can act as control points for chain-length specificity. Specific free fatty acids are subsequently converted to alkanes using a broad-specificity carboxylic acid reductase and a cyanobacterial aldehyde decarbonylase (AD). The selectivity obtained by different module pairings provides a foundation for tuning alkane product distribution for desired fuel properties. Alternate ADs that have greater activity on shorter substrates improve observed alkane titer. However, even in an engineered host strain that significantly reduces endogenous conversion of aldehyde intermediates to alcohol byproducts, AD activity is observed to be limiting for all chain lengths. Given these insights, we discuss guiding principles for pathway selection and potential opportunities for pathway improvement.

  18. Pathway of n-Alkane Oxidation in Cladosporium resinae

    PubMed Central

    Walker, J. D.; Cooney, J. J.

    1973-01-01

    Pathways of initial oxidation of n-alkanes were examined in two strains of Cladosporium resinae. Cells grow on dodecane and hexadecane and their primary alcohol and monoic acid derivatives. The homologous aldehydes do not support growth but are oxidized by intact cells and by cell-free preparations. Hexane and its derivatives support little or no growth, but cell extracts oxidize hexane, hexanol, and hexanal. Alkane oxidation by extracts is stimulated by reduced nicotinamide adenine dinucleotide (phosphate). Alcohol and aldehyde oxidation are stimulated by nicotinamide adenine dinucleotide (phosphate), and reduced coenzymes accumulate in the presence of cyanide or azide. Extracts supplied with 14C-hexadecane convert it to the alcohol, aldehyde, and acid. Therefore, the major pathway for initial oxidation of n-alkanes is via the primary alcohol, aldehyde, and monoic acid, and the system can act on short-, intermediate-, and long-chain substrates. Thus, filamentous fungi appear to oxidize n-alkanes by pathways similar to those used by bacteria and yeasts. PMID:4146874

  19. Two-stage process for conversion of alkanes to gasoline

    SciTech Connect

    Harandi, M.N.; Owen, H.

    1989-08-22

    This patent describes an improvement in a two-stage process for upgrading hydrocarbons in at least four reaction zones cooperating to produce gasoline range hydrocarbons from lower alkanes. The reaction zones comprising first reaction zone to crack gas oil range hydrocarbons utilizing a large pore cracking catalyst, a second reaction zone in which the large pore catalyst is oxidatively regenerated, a third reaction zone in which an external catalyst cooler autogeneously cools regenerated catalyst by dehydrogenation of the lower alkane stream to produce an olefinic effluent, and a fourth reaction zone in which the olefinic effluent is oligomerized to the gasoline range hydrocarbons. The improvement comprising: a first stage, comprising utilizing excess heat from the second reaction zone: contacting the hot fluid catalytic cracking catalyst with C/sub 3//sup +/ alkanes in the third reaction zone to provide conversion of the alkanes to olefins which leave the third reaction zone as the olefinic effluent separated from catalyst; returning a specified amount of separate fluid catalytic cracking catalyst from the third reaction zone directly to the first or second reaction zone; a second state comprising passing the olefinic effluent from the third reaction zone to a fourth reaction zone for oligomerizing olefins to gasoline range hydrocarbons contacting the olefinic effluent with a medium pore zeolite catalyst effective; recovering a gasoline range hydrocarbon stream from the effluent of the fourth reaction zone.

  20. Modular and selective biosynthesis of gasoline-range alkanes.

    PubMed

    Sheppard, Micah J; Kunjapur, Aditya M; Prather, Kristala L J

    2016-01-01

    Typical renewable liquid fuel alternatives to gasoline are not entirely compatible with current infrastructure. We have engineered Escherichia coli to selectively produce alkanes found in gasoline (propane, butane, pentane, heptane, and nonane) from renewable substrates such as glucose or glycerol. Our modular pathway framework achieves carbon-chain extension by two different mechanisms. A fatty acid synthesis route is used to generate longer chains heptane and nonane, while a more energy efficient alternative, reverse-β-oxidation, is used for synthesis of propane, butane, and pentane. We demonstrate that both upstream (thiolase) and intermediate (thioesterase) reactions can act as control points for chain-length specificity. Specific free fatty acids are subsequently converted to alkanes using a broad-specificity carboxylic acid reductase and a cyanobacterial aldehyde decarbonylase (AD). The selectivity obtained by different module pairings provides a foundation for tuning alkane product distribution for desired fuel properties. Alternate ADs that have greater activity on shorter substrates improve observed alkane titer. However, even in an engineered host strain that significantly reduces endogenous conversion of aldehyde intermediates to alcohol byproducts, AD activity is observed to be limiting for all chain lengths. Given these insights, we discuss guiding principles for pathway selection and potential opportunities for pathway improvement. PMID:26556131

  1. Crystallization features of normal alkanes in confined geometry.

    PubMed

    Su, Yunlan; Liu, Guoming; Xie, Baoquan; Fu, Dongsheng; Wang, Dujin

    2014-01-21

    How polymers crystallize can greatly affect their thermal and mechanical properties, which influence the practical applications of these materials. Polymeric materials, such as block copolymers, graft polymers, and polymer blends, have complex molecular structures. Due to the multiple hierarchical structures and different size domains in polymer systems, confined hard environments for polymer crystallization exist widely in these materials. The confined geometry is closely related to both the phase metastability and lifetime of polymer. This affects the phase miscibility, microphase separation, and crystallization behaviors and determines both the performance of polymer materials and how easily these materials can be processed. Furthermore, the size effect of metastable states needs to be clarified in polymers. However, scientists find it difficult to propose a quantitative formula to describe the transition dynamics of metastable states in these complex systems. Normal alkanes [CnH2n+2, n-alkanes], especially linear saturated hydrocarbons, can provide a well-defined model system for studying the complex crystallization behaviors of polymer materials, surfactants, and lipids. Therefore, a deeper investigation of normal alkane phase behavior in confinement will help scientists to understand the crystalline phase transition and ultimate properties of many polymeric materials, especially polyolefins. In this Account, we provide an in-depth look at the research concerning the confined crystallization behavior of n-alkanes and binary mixtures in microcapsules by our laboratory and others. Since 2006, our group has developed a technique for synthesizing nearly monodispersed n-alkane containing microcapsules with controllable size and surface porous morphology. We applied an in situ polymerization method, using melamine-formaldehyde resin as shell material and nonionic surfactants as emulsifiers. The solid shell of microcapsules can provide a stable three-dimensional (3-D

  2. Isolating the non-polar contributions to the intermolecular potential for water-alkane interactions.

    PubMed

    Ballal, Deepti; Venkataraman, Pradeep; Fouad, Wael A; Cox, Kenneth R; Chapman, Walter G

    2014-08-14

    Intermolecular potential models for water and alkanes describe pure component properties fairly well, but fail to reproduce properties of water-alkane mixtures. Understanding interactions between water and non-polar molecules like alkanes is important not only for the hydrocarbon industry but has implications to biological processes as well. Although non-polar solutes in water have been widely studied, much less work has focused on water in non-polar solvents. In this study we calculate the solubility of water in different alkanes (methane to dodecane) at ambient conditions where the water content in alkanes is very low so that the non-polar water-alkane interactions determine solubility. Only the alkane-rich phase is simulated since the fugacity of water in the water rich phase is calculated from an accurate equation of state. Using the SPC/E model for water and TraPPE model for alkanes along with Lorentz-Berthelot mixing rules for the cross parameters produces a water solubility that is an order of magnitude lower than the experimental value. It is found that an effective water Lennard-Jones energy ε(W)/k = 220 K is required to match the experimental water solubility in TraPPE alkanes. This number is much higher than used in most simulation water models (SPC/E-ε(W)/k = 78.2 K). It is surprising that the interaction energy obtained here is also higher than the water-alkane interaction energy predicted by studies on solubility of alkanes in water. The reason for this high water-alkane interaction energy is not completely understood. Some factors that might contribute to the large interaction energy, such as polarizability of alkanes, octupole moment of methane, and clustering of water at low concentrations in alkanes, are examined. It is found that, though important, these factors do not completely explain the anomalously strong attraction between alkanes and water observed experimentally. PMID:25134597

  3. Isolating the non-polar contributions to the intermolecular potential for water-alkane interactions.

    PubMed

    Ballal, Deepti; Venkataraman, Pradeep; Fouad, Wael A; Cox, Kenneth R; Chapman, Walter G

    2014-08-14

    Intermolecular potential models for water and alkanes describe pure component properties fairly well, but fail to reproduce properties of water-alkane mixtures. Understanding interactions between water and non-polar molecules like alkanes is important not only for the hydrocarbon industry but has implications to biological processes as well. Although non-polar solutes in water have been widely studied, much less work has focused on water in non-polar solvents. In this study we calculate the solubility of water in different alkanes (methane to dodecane) at ambient conditions where the water content in alkanes is very low so that the non-polar water-alkane interactions determine solubility. Only the alkane-rich phase is simulated since the fugacity of water in the water rich phase is calculated from an accurate equation of state. Using the SPC/E model for water and TraPPE model for alkanes along with Lorentz-Berthelot mixing rules for the cross parameters produces a water solubility that is an order of magnitude lower than the experimental value. It is found that an effective water Lennard-Jones energy ε(W)/k = 220 K is required to match the experimental water solubility in TraPPE alkanes. This number is much higher than used in most simulation water models (SPC/E-ε(W)/k = 78.2 K). It is surprising that the interaction energy obtained here is also higher than the water-alkane interaction energy predicted by studies on solubility of alkanes in water. The reason for this high water-alkane interaction energy is not completely understood. Some factors that might contribute to the large interaction energy, such as polarizability of alkanes, octupole moment of methane, and clustering of water at low concentrations in alkanes, are examined. It is found that, though important, these factors do not completely explain the anomalously strong attraction between alkanes and water observed experimentally.

  4. Radiation stability of cations in ionic liquids. 4. Task-specific antioxidant cations for nuclear separations and photolithography.

    PubMed

    Shkrob, Ilya A; Marin, Timothy W

    2013-11-27

    Three families of "task-specific" antioxidant organic cations that include designated sites to facilitate deprotonation following electronic excitation and ionization have been introduced. The deprotonation from the excited state is reversible, leading to minimal damage of the cation, whereas the deprotonation from the oxidized cation yields persistent aroxyl and trityl radicals. This protection improves radiation stability of ionic compounds in 2.5 MeV electron beam radiolysis. Apart from the use of such cations as structural components of room temperature ionic liquid (IL) diluents for nuclear separations, their ionic compounds involving bases of superacids are well suited for use as chemically amplified acid generator resists in electron beam lithography and extreme ultraviolet photolithography.

  5. Radical prostatectomy - discharge

    MedlinePlus

    ... prostatectomy - discharge; Laparoscopic radical prostatectomy - discharge; LRP - discharge; Robotic-assisted laparoscopic prostatectomy - discharge ; RALP - discharge; Pelvic lymphadenectomy - ...

  6. Gas-phase tyrosine-to-cysteine radical migration in model systems.

    PubMed

    Lesslie, Michael; Osburn, Sandra; van Stipdonk, Michael J; Ryzhov, Victor

    2015-01-01

    Radical migration, both intramolecular and intermolecular, from the tyrosine phenoxyl radical Tyr(O(∙)) to the cysteine radical Cys(S(∙)) in model peptide systems was observed in the gas phase. Ion-molecule reactions (IMRs) between the radical cation of homotyrosine and propyl thiol resulted in a fast hydrogen atom transfer. In addition, radical cations of the peptide LysTyrCys were formed via two different methods, affording regiospecific production of Tyr(O(∙)) or Cys(S(∙)) radicals. Collision-induced dissociation of these isomeric species displayed evidence of radical migration from the oxygen to sulfur, but not for the reverse process. This was supported by theoretical calculations, which showed the Cys(S(∙)) radical slightly lower in energy than the Tyr(O(∙)) isomer. IMRs of the LysTyrCys radical cation with allyl iodide further confirmed these findings. A mechanism for radical migration involving a proton shuttle by the C-terminal carboxylic group is proposed. PMID:26307738

  7. [Lavoisier and radicals].

    PubMed

    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.

  8. Organometallic model complexes elucidate the active gallium species in alkane dehydrogenation catalysts based on ligand effects in Ga K-edge XANES

    SciTech Connect

    Getsoian, Andrew “Bean”; Das, Ujjal; Camacho-Bunquin, Jeffrey; Zhang, Guanghui; Gallagher, James R.; Hu, Bo; Cheah, Singfoong; Schaidle, Joshua A.; Ruddy, Daniel A.; Hensley, Jesse E.; Krause, Theodore R.; Curtiss, Larry A.; Miller, Jeffrey T.; Hock, Adam S.

    2016-01-01

    Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order to better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. These findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.

  9. Flash Points of Secondary Alcohol and n-Alkane Mixtures.

    PubMed

    Esina, Zoya N; Miroshnikov, Alexander M; Korchuganova, Margarita R

    2015-11-19

    The flash point is one of the most important characteristics used to assess the ignition hazard of mixtures of flammable liquids. To determine the flash points of mixtures of secondary alcohols with n-alkanes, it is necessary to calculate the activity coefficients. In this paper, we use a model that allows us to obtain enthalpy of fusion and enthalpy of vaporization data of the pure components to calculate the liquid-solid equilibrium (LSE) and vapor-liquid equilibrium (VLE). Enthalpy of fusion and enthalpy of vaporization data of secondary alcohols in the literature are limited; thus, the prediction of these characteristics was performed using the method of thermodynamic similarity. Additionally, the empirical models provided the critical temperatures and boiling temperatures of the secondary alcohols. The modeled melting enthalpy and enthalpy of vaporization as well as the calculated LSE and VLE flash points were determined for the secondary alcohol and n-alkane mixtures. PMID:26491811

  10. Influence of high biomass concentrations on alkane solubilities.

    PubMed

    Davison, B H; Barton, J W; Klasson, K T; Francisco, A B

    2000-05-01

    Alkane solubilities were measured experimentally for high-density biomass. The resulting Henry's law constants for propane were found to decrease significantly for both dense yeast suspensions and an actual propane-degrading biofilm consortium. At the biomass densities of a typical biofilm, propane solubility was about an order of magnitude greater than that in pure water. For example, a dense biofilm had a propane Henry's law constant of 0.09+/-0.04 atm m(3) mol(-1) compared to 0.6+/-0.1 atm m(3) mol(-1) measured in pure water. The results were modeled with mixing rules and compared with octanol-water mixtures. Hydrogels (agar) and salts decreased the alkane solubility. By considering a theoretical solubility of propane in dry biomass, estimates were made of intrinsic Henry's law constants for propane in pure yeast and biomass, which were 13+/-2 and 5+/-2 atm kg biomass mol(-1) for yeast and biofilm consortium, respectively.

  11. Site isolation in vanadium phosphorus oxide alkane oxidation

    SciTech Connect

    Thompson, M R; Ebner, J R

    1991-06-01

    Single crystal X-ray diffraction studies of vanadyl pyrophosphate indicate that at least two polytypical structures exists for this active and selective alkane oxidation catalyst. The crystal structures of these materials differ with respect to the symmetry and direction of columns of vanadyl groups within the unit cell. Single crystals of vanadyl pyrophosphate have been generated at extreme temperatures not often experienced by microcrystalline catalysts. The crystallography of the system suggests that other crystalline modifications or disordered phases might also exist. Zeroth-order models of crystal surface termination of vanadyl pyrophosphate have been constructed which conceptually illustrate the ability of vanadyl pyrophosphate to accommodate varying amounts of surface phosphorus parallel to (1,0,0), (0,1,0) and (0,2,4). Pyrophosphate termination of surfaces parallel to (1,0,0) likely results in the isolation of clusters of reactive centers and limits overoxidation of the alkane substrate. 23 refs., 6 figs.

  12. Surface crystallization and thin film melting in normal alkanes

    SciTech Connect

    Wu, X.Z. |; Shao, H.H. |; Ocko, B.M.; Deutsch, M.; Sinha, S.K.; Kim, M.W.; King, H.E. Jr.; Sirota, E.B.

    1994-12-31

    Normal alkanes of carbon number n > 14 exhibit surface crystallization at their liquid-vapor interface. This has been investigated with x-ray reflectivity, grazing incidence scattering and surface tension measurements. The structure and thermodynamics of the surface layer is consistent with a monolayer of the bulk rotator phase occurring at the surface above the bulk melting temperature. On the other hand, thin films of alkanes on SiO{sub 2}, exhibit a reduction of the melting temperature. The surface crystalline phase is observed for carbon number n > 14. The vanishing of surface phase for small n may be due to a transition from surface freezing to surface melting behavior. These measurements can yield the relative surface energies of the various phases. 41 refs.

  13. Multi-stage conversion of alkanes to gasoline

    SciTech Connect

    Harandi, M.N.; Owen, H.

    1991-09-17

    This patent describes improvement in a facility for converting alkanes into gasoline, the facility including a fluid catalytic cracking system and an olefin oligomerization reactor. The improvement comprises: a first valved conduit means for withdrawing a controlled stream of the regenerated catalyst from the first regenerator means; a dehydrogenation reactor in valved communication with the first regenerator means, through the first valved conduit means the dehydrogenation reactor having a dehydrogenation zone at a temperature below those prevailing in the first regeneration zone, the dehydrogenation reactor being located externally relative to the fluid catalytic cracker reactor and first regenerator; means for introducing a lower alkane feedstream into the dehydrogenation zone in an amount sufficient to maintain hot withdrawn catalyst in a state of fluidization in the dehydrogenation reactor while the catalyst is being cooled therein; a second valved conduit means for transporting cooled catalyst from the dehydrogenation zone to the first regeneration zone.

  14. Relative yields of radicals produced in deuterated methanol by irradiation

    NASA Astrophysics Data System (ADS)

    Nakagawa, Seiko

    2016-05-01

    The relative yields of radicals produced in four kinds of methanols; i.e., CH3OH, CH3OD, CD3OH and CD3OD, by γ-irradiation have been studied using ESR spin trapping with PBN. Both PBN-H and PBN-D were produced from CH3OD and CD3OH. This means that the proton transfer to the neutral methanol from the cationic one is one of the processes to produce both the methoxy and hydoxy-methyl radicals. The yield of the methoxy radical adduct relative to the hydroxy-methyl radical adduct decreased in the order CD3OH>CD3OD>CH3OH>CH3OD. The difference in the rates of the proton transfer and hydrogen abstraction reactions by substitution with deuterium is the reason for the variation in the relative radical yield.

  15. Reactions of C{sub 2}(a {sup 3} product {sub u}) with selected saturated alkanes: A temperature dependence study

    SciTech Connect

    Hu Renzhi; Zhang Qun; Chen Yang

    2010-04-28

    We present a temperature dependence study on the gas phase reactions of the C{sub 2}(a {sup 3} product {sub u}) radical with a selected series of saturated alkanes (C{sub 2}H{sub 6}, C{sub 3}H{sub 8}, n-C{sub 4}H{sub 10}, i-C{sub 4}H{sub 10}, and n-C{sub 6}H{sub 14}) by means of pulsed laser photolysis/laser-induced fluorescence technique. The bimolecular rate constants for these reactions were obtained between 298 and 673 K. A pronounced negative temperature effect was observed for n-C{sub 4}H{sub 10}, i-C{sub 4}H{sub 10}, and n-C{sub 6}H{sub 14} and interpreted in terms of steric hindrance of the more reactive secondary or tertiary C-H bonds by less reactive CH{sub 3} groups. Detailed analysis of our experimental results reveals quantitatively the temperature dependence of reactivities for the primary, secondary, and tertiary C-H bonds in these saturated alkanes and further lends support to a mechanism of hydrogen abstraction.

  16. At what chain length do unbranched alkanes prefer folded conformations?

    PubMed

    Byrd, Jason N; Bartlett, Rodney J; Montgomery, John A

    2014-03-01

    Short unbranched alkanes are known to prefer linear conformations, whereas long unbranched alkanes are folded. It is not known with certainty at what chain length the linear conformation is no longer the global minimum. To clarify this point, we use ab initio and density functional methods to compute the relative energies of the linear and hairpin alkane conformers for increasing chain lengths. Extensive electronic structure calculations are performed to obtain optimized geometries, harmonic frequencies, and accurate single point energies for the selected alkane conformers from octane through octadecane. Benchmark CCSD(T)/cc-pVTZ single point calculations are performed for chains through tetradecane, whereas approximate methods are required for the longer chains up to octadecane. Using frozen natural orbitals to unambiguously truncate the virtual orbital space, we are able to compute composite CCSD FNO(T) single point energies for all the chain lengths. This approximate composite method has significant computational savings compared to full CCSD(T) while retaining ∼0.15 kcal/mol accuracy compared to the benchmark results. More approximate dual-basis resolution-of-the-identity double-hybrid DFT calculations are also performed and shown to have reasonable 0.2-0.4 kcal/mol errors compared with our benchmark values. After including contributions from temperature dependent internal energy shifts, we find the preference for folded conformations to lie between hexadecane and octadecane, in excellent agreement with recent experiments [ Lüttschwager , N. O. ; Wassermann , T. N. ; Mata , R. A. ; Suhm , M. A. Angew. Chem. Int. Ed. 2013 , 52 , 463 ]. PMID:24524689

  17. Removal of alkanes from drinking water using membrane technologies

    SciTech Connect

    Fronk, C.A.

    1995-10-01

    Increasingly, the public is concerned about the quality of its drinking water. The chlorinated alkanes are saturated, aliphatic, synthetic organic compounds (SOC`s). When hydrocarbon feedstocks are chlorinated, a wide variety of chlorocarbons and chlorohydrocarbons are produced that are used as industrial solvents, degreasers and intermediaries. Because compounds such as Carbon Tetrachloride and 1,2-Dichloroethane are widely used, they often find their way into drinking water, particularly groundwaters. Surface waters are somewhat less affected bemuse of the high volatility of many chlorinated alkanes. The Drinking Water Research Division is responsible for evaluating various membrane technologies that may be feasible for meeting Maximum Contaminant Levels. Several membrane processes are under investigation to determine their effectiveness in removing SOC`s from drinking water. One study addressed the removal of a variety of alkanes from spiked groundwater by six reverse osmosis membranes: a cellulose acetate, a polyamide (hollow fiber), and four different types of thin-film composite membranes. Progressive chlorination of methanes, ethanes and propanes produces compounds that exhibit differing physicochemical properties. The differences in compound properties have an effect on the removal of these compounds by reverse osmosis membranes. For example only 25% of the methylene chloride (Dichloromethane) was removed by one thin-film composite versus 90% removal of the carbon tetrachloride. In addition, the various membranes are made of different polymeric materials and showed a wide range of removals. Generally, the thin-film composite membranes out performed the other membranes and the more highly chlorinated the compound the better the removal. Pervaporation is yet another membrane process that may prove effective in removal of alkanes and future studies will address its usefulness as a drinking water.

  18. Alkane production from biomass: chemo-, bio- and integrated catalytic approaches.

    PubMed

    Deneyer, Aron; Renders, Tom; Van Aelst, Joost; Van den Bosch, Sander; Gabriëls, Dries; Sels, Bert F

    2015-12-01

    Linear, branched and cyclic alkanes are important intermediates and end products of the chemical industry and are nowadays mainly obtained from fossil resources. In search for alternatives, biomass feedstocks are often presented as a renewable carbon source for the production of fuels, chemicals and materials. However, providing a complete market for all these applications seems unrealistic due to both financial and logistic issues. Despite the very large scale of current alkane-based fuel applications, biomass definitely has the potential to offer a partial solution to the fuel business. For the smaller market of chemicals and materials, a transition to biomass as main carbon source is more realistic and even probably unavoidable in the long term. The appropriate use and further development of integrated chemo- and biotechnological (catalytic) process strategies will be crucial to successfully accomplish this petro-to-bio feedstock transition. Furthermore, a selection of the most promising technologies from the available chemo- and biocatalytic tool box is presented. New opportunities will certainly arise when multidisciplinary approaches are further explored in the future. In an attempt to select the most appropriate biomass sources for each specific alkane-based application, a diagram inspired by van Krevelen is applied, taking into account both the C-number and the relative functionality of the product molecules.

  19. Alkane production from biomass: chemo-, bio- and integrated catalytic approaches.

    PubMed

    Deneyer, Aron; Renders, Tom; Van Aelst, Joost; Van den Bosch, Sander; Gabriëls, Dries; Sels, Bert F

    2015-12-01

    Linear, branched and cyclic alkanes are important intermediates and end products of the chemical industry and are nowadays mainly obtained from fossil resources. In search for alternatives, biomass feedstocks are often presented as a renewable carbon source for the production of fuels, chemicals and materials. However, providing a complete market for all these applications seems unrealistic due to both financial and logistic issues. Despite the very large scale of current alkane-based fuel applications, biomass definitely has the potential to offer a partial solution to the fuel business. For the smaller market of chemicals and materials, a transition to biomass as main carbon source is more realistic and even probably unavoidable in the long term. The appropriate use and further development of integrated chemo- and biotechnological (catalytic) process strategies will be crucial to successfully accomplish this petro-to-bio feedstock transition. Furthermore, a selection of the most promising technologies from the available chemo- and biocatalytic tool box is presented. New opportunities will certainly arise when multidisciplinary approaches are further explored in the future. In an attempt to select the most appropriate biomass sources for each specific alkane-based application, a diagram inspired by van Krevelen is applied, taking into account both the C-number and the relative functionality of the product molecules. PMID:26360875

  20. Modeling SOA production from the oxidation of intermediate volatility alkanes

    NASA Astrophysics Data System (ADS)

    Aumont, B.; Mouchel-Vallon, C.; Camredon, M.; Lee-Taylor, J.; Madronich, S.

    2012-12-01

    Secondary Organic Aerosols (SOA) production and ageing is a multigenerational oxidation process involving the formation of successive organic compounds with higher oxidation degree and lower vapour pressure. This process was investigated using the explicit oxidation model GECKO-A (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere). Results for the C8-C24 n-alkane series show the expected trends, i.e. (i) SOA yield grows with the carbon backbone of the parent hydrocarbon, (ii) SOA yields decreases with the decreasing pre-existing organic aerosol concentration, (iii) the number of generations required to describe SOA production increases when the pre-existing organic aerosol concentration decreases. Most SOA contributors were found to be not oxidized enough to be categorized as highly oxygenated organic aerosols (OOA) but reduced enough to be categorized as hydrocarbon like organic aerosols (HOA). Branched alkanes are more prone to fragment in the early stage of the oxidation than their corresponding linear analogues. Fragmentation is expected to alter both the yield and the mean oxidation state of the SOA. Here, GECKO-A is applied to generate highly detailed oxidation schemes for various series of branched and cyclised alkanes. Branching and cyclisation effects on SOA yields and oxidation states will be examined.

  1. Dielectric constant of liquid alkanes and hydrocarbon mixtures

    NASA Technical Reports Server (NTRS)

    Sen, A. D.; Anicich, V. G.; Arakelian, T.

    1992-01-01

    The complex dielectric constants of n-alkanes with two to seven carbon atoms have been measured. The measurements were conducted using a slotted-line technique at 1.2 GHz and at atmospheric pressure. The temperature was varied from the melting point to the boiling point of the respective alkanes. The real part of the dielectric constant was found to decrease with increasing temperature and correlate with the change in the molar volume. An upper limit to all the loss tangents was established at 0.001. The complex dielectric constants of a few mixtures of liquid alkanes were also measured at room temperature. For a pentane-octane mixture the real part of the dielectric constant could be explained by the Clausius-Mosotti theory. For the mixtures of n-hexane-ethylacetate and n-hexane-acetone the real part of the dielectric constants could be explained by the Onsager theory extended to mixtures. The dielectric constant of the n-hexane-acetone mixture displayed deviations from the Onsager theory at the highest fractions of acetone. The dipole moments of ethylacetate and acetone were determined for dilute mixtures using the Onsager theory and were found to be in agreement with their accepted gas-phase values. The loss tangents of the mixtures exhibited a linear relationship with the volume fraction for low concentrations of the polar liquids.

  2. Dielectric constant of liquid alkanes and hydrocarbon mixtures.

    PubMed

    Sen, A D; Anicich, V G; Arakelian, T

    1992-01-01

    The complex dielectric constants of n-alkanes with two to seven carbon atoms have been measured. The measurements were conducted using a slotted-line technique at 1.2 GHz and at atmospheric pressure. The temperature was varied from the melting point to the boiling point of the respective alkanes. The real part of the dielectric constant was found to decrease with increasing temperature and correlate with the change in the molar volume. An upper limit to all the loss tangents was established at 0.001. The complex dielectric constants of a few mixtures of liquid alkanes were also measured at room temperature. For a pentane-octane mixture the real part of the dielectric constant could be explained by the Clausius-Mosotti theory. For the mixtures of n-hexane-ethylacetate and n-hexane-acetone the real part of the dielectric constants could be explained by the Onsager theory extended to mixtures. The dielectric constant of the n-hexane-acetone mixture displayed deviations from the Onsager theory at the highest fractions of acetone. The dipole moments of ethylacetate and acetone were determined for dilute mixtures using the Onsager theory and were found to be in agreement with their accepted gas-phase values. The loss tangents of the mixtures exhibited a linear relationship with the volume fraction for low concentrations of the polar liquids.

  3. Synthesis and characterisation of cationically modified phospholipid polymers.

    PubMed

    Lewis, Andrew L; Berwick, James; Davies, Martyn C; Roberts, Clive J; Wang, Jin-Hai; Small, Sharon; Dunn, Anthony; O'Byrne, Vincent; Redman, Richard P; Jones, Stephen A

    2004-07-01

    Phospholipid-like copolymers based on 2-(methacryloyloxyethyl) phosphorylcholine were synthesised using monomer-starved free radical polymerisation methods and incorporating cationic charge in the form of the choline methacrylate monomer in amounts varying from 0 to 30 wt%, together with a 5 wt% silyl cross-linking agent in order to render them water-insoluble once thermally cured. Characterisation using a variety of techniques including nuclear magnetic resonance spectroscopy, high-pressure liquid chromatography and gel permeation chromatography showed the cationic monomer did not interfere with the polymerisation and that the desired amount of charge had been incorporated. Gravimetric and differential scanning calorimetry methods were used to evaluate the water contents of polymer membranes cured at 70 degrees C, which was seen to increase with increasing cation content, producing materials with water contents ranging from 50% to 98%. Surface plasmon resonance indicated that the coatings swelled rapidly in water, the rate and extent of swelling increasing with increasing cation level. Dynamic contact angle showed that coatings of all the polymers possessed a hydrophobic surface when dry in air, characteristic of the alkyl chains expressed at the surface (>100 degrees advancing angle). Rearrangement of the hydrophilic groups to the surface occurred once wet, to produce highly wettable surfaces with a decrease in advancing angle with increasing cation content. Atomic force microscopy showed all polymer films to be smooth with no features in topographical or phase imaging. Mechanical properties of the dry films were also unaffected by the increase in cation content.

  4. Additional chain-branching pathways in the low-temperature oxidation of branched alkanes

    SciTech Connect

    Wang, Zhandong; Zhang, Lidong; Moshammer, Kai; Popolan-Vaida, Denisia M.; Shankar, Vijai Shankar Bhavani; Lucassen, Arnas; Hemken, Christian; Taatjes, Craig A.; Leone, Stephen R.; Kohse-Hoinghaus, Katharina; Hansen, Nils; Dagaut, Philippe; Sarathy, S. Mani

    2015-12-31

    Chain-branching reactions represent a general motif in chemistry, encountered in atmospheric chemistry, combustion, polymerization, and photochemistry; the nature and amount of radicals generated by chain-branching are decisive for the reaction progress, its energy signature, and the time towards its completion. In this study, experimental evidence for two new types of chain-branching reactions is presented, based upon detection of highly oxidized multifunctional molecules (HOM) formed during the gas-phase low-temperature oxidation of a branched alkane under conditions relevant to combustion. The oxidation of 2,5-dimethylhexane (DMH) in a jet-stirred reactor (JSR) was studied using synchrotron vacuum ultra-violet photoionization molecular beam mass spectrometry (SVUV-PI-MBMS). Specifically, species with four and five oxygen atoms were probed, having molecular formulas of C8H14O4 (e.g., diketo-hydroperoxide/keto-hydroperoxy cyclic ether) and C8H16O5 (e.g., keto-dihydroperoxide/dihydroperoxy cyclic ether), respectively. The formation of C8H16O5 species involves alternative isomerization of OOQOOH radicals via intramolecular H-atom migration, followed by third O2 addition, intramolecular isomerization, and OH release; C8H14O4 species are proposed to result from subsequent reactions of C8H16O5 species. The mechanistic pathways involving these species are related to those proposed as a source of low-volatility highly oxygenated species in Earth's troposphere. At the higher temperatures relevant to auto-ignition, they can result in a net increase of hydroxyl radical production, so these are additional radical chain-branching pathways for ignition. Furthermore, the results presented herein extend the conceptual basis of reaction mechanisms used to predict the reaction behavior of ignition, and have

  5. Cesium cation affinities and basicities

    NASA Astrophysics Data System (ADS)

    Gal, Jean-François; Maria, Pierre-Charles; Massi, Lionel; Mayeux, Charly; Burk, Peeter; Tammiku-Taul, Jaana

    2007-11-01

    This review focuses on the quantitative data related to cesium cation interaction with neutral or negatively charged ligands. The techniques used for measuring the cesium cation affinity (enthalpies, CCA), and cesium cation basicities (Gibbs free energies, CCB) are briefly described. The quantum chemical calculations methods that were specifically designed for the determination of cesium cation adduct structures and the energetic aspects of the interaction are discussed. The experimental results, obtained essentially from mass spectrometry techniques, and complemented by thermochemical data, are tabulated and commented. In particular, the correlations between cesium cation affinities and lithium cation affinities for the various kinds of ligands (rare gases, polyatomic neutral molecules, among them aromatic compounds and negative ions) serve as a basis for the interpretation of the diverse electrostatic modes of interaction. A brief account of some recent analytical applications of ion/molecule reactions with Cs+, as well as other cationization approaches by Cs+, is given.

  6. Laboratory spectroscopic analyses of electron irradiated alkanes and alkenes in solar system ices

    NASA Astrophysics Data System (ADS)

    Hand, K. P.; Carlson, R. W.

    2012-03-01

    We report results from laboratory experiments of 10 keV electron irradiation of thin ice films of water and short-chain hydrocarbons at ˜10-8 Torr and temperatures ranging from 70-100 K. Hydrocarbon mixtures include water with C3H8, C3H6, C4H10 (butane and isobutane), and C4H8, (1-butene and cis/trans-2-butene). The double bonds of the alkenes in our initial mixtures were rapidly destroyed or converted to single carbon bonds, covalent bonds with hydrogen, bonds with -OH (hydroxyl), bonds with oxygen (C-O), or double bonds with oxygen (carbonyl). Spectra resulting from irradiation of alkane and alkene ices are largely indistinguishable; the initial differences in film composition are destroyed and the resulting mixture includes long-chain, branched aliphatics, aldehydes, ketones, esters, and alcohols. Methane was observed as a product during radiolysis but CO was largely absent. We find that while some of the carbon is oxidized and lost to CO2 formation, some carbon is sequestered into highly refractory, long-chain aliphatic compounds that remain as a thin residue even after the ice film has been raised to standard temperature and pressure. We conclude that the high availability of hydrogen in our experiments leads to the formation of the formyl radical which then serves as the precursor for formaldehyde and polymerization of longer hydrocarbon chains.

  7. Towards a practical development of light-driven acceptorless alkane dehydrogenation.

    PubMed

    Chowdhury, Abhishek Dutta; Weding, Nico; Julis, Jennifer; Franke, Robert; Jackstell, Ralf; Beller, Matthias

    2014-06-16

    The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter-chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom-efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans-[Rh(PMe3)2(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C4) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations. PMID:24829085

  8. Forgotten radicals in biology.

    PubMed

    Luc, Rochette; Vergely, Catherine

    2008-12-01

    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 (•-) present in cytosol exists in its protonated form: hydroperoxyl radical (HO2 (•)). Water (H2O) can be split into two free radicals: (•)OH and hydrogen radical (H(•)). Several free radicals, including thiyl radicals (RS(•)) and nitrogen dioxide (NO2 (•)) are known to isomerize double bonds. In the omega-6 series of poly-unsaturated fatty acids (PUFAs), cis-trans isomerization of γ-linolenate and arachidonate catalyzed by RS(•) has been investigated. Evidence is emerging that hydrogen disulphide (H2S) is a signaling molecule in vivo which can be a source of free radicals. The Cu-Zn superoxide dismutase (SOD) enzyme can oxidize the ionized form of H2S to hydro-sulphide radical: HS(•). Recent studies suggest that H2S plays an important function in cardiovascular functions. Carbonate radical, which can be formed when (•)OH reacts with carbonate or bicarbonate ions, is also involved in the activity of Cu-Zn-SOD. Recently, it has been reported that carbonate anion were potentially relevant oxidants of nucleic acids in physiological environments. In conclusion, there is solid evidence supporting the formation of many free radicals by cells leading which may play an important role in their homeostasis. PMID:23675099

  9. Photochemical dimerization and functionalization of alkanes, ethers, primary alcohols and silanes

    DOEpatents

    Crabtree, Robert H.; Brown, Stephen H.

    1988-01-01

    The space-time yield and/or the selectivity of the photochemical dimerization of alkanes, ethers, primary alcohols and tertiary silanes with Hg and U.V. light is enhanced by refluxing the substrate in the irradiated reaction zone at a temperature at which the dimer product condenses and remains condensed promptly upon its formation. Cross-dimerization of the alkanes, ethers and silanes with primary alcohols is disclosed, as is the functionalization to aldehydes of the alkanes with carbon monoxide.

  10. Photochemical dimerization and functionalization of alkanes, ethers, primary alcohols and silanes

    DOEpatents

    Crabtree, R.H.; Brown, S.H.

    1988-02-16

    The space-time yield and/or the selectivity of the photochemical dimerization of alkanes, ethers, primary alcohols and tertiary silanes with Hg and U.V. light is enhanced by refluxing the substrate in the irradiated reaction zone at a temperature at which the dimer product condenses and remains condensed promptly upon its formation. Cross-dimerization of the alkanes, ethers and silanes with primary alcohols is disclosed, as is the functionalization to aldehydes of the alkanes with carbon monoxide.

  11. Draft Genome Sequence of Gordonia sihwensis Strain 9, a Branched Alkane-Degrading Bacterium

    PubMed Central

    Brown, Lisa M.; Gunasekera, Thusitha S.; Striebich, Richard C.

    2016-01-01

    Gordonia sihwensis strain 9 is a Gram-positive bacterium capable of efficient aerobic degradation of branched and normal alkanes. The draft genome of G. sihwensis S9 is 4.16 Mb in size, with 3,686 coding sequences and 68.1% G+C content. Alkane monooxygenase and P-450 cytochrome genes required for alkane degradation are predicted in G. sihwensis S9. PMID:27340079

  12. Fundamental Flame Velocities of Pure Hydrocarbons I : Alkanes, Alkenes, Alkynes Benzene, and Cyclohexane

    NASA Technical Reports Server (NTRS)

    Gerstein, Melvin; Levine, Oscar; Wong, Edgar L

    1950-01-01

    The flame velocities of 37 pure hydrocarbons including normal and branched alkanes, alkenes, and alkynes; as well as benzene and cyclohexane, together with the experimental technique employed are presented. The normal alkanes have about the same flame velocity from ethane through heptane with methane being about 16 percent lower. Unsaturation increases the flame velocity in the order of alkanes, alkenes, and alkynes. Branching reduces the flame velocity.

  13. Observation of an aromatic radical anion dimer: (C{sub 10}F{sub 8}){sub 2}{sm_bullet}{sub {minus}}

    SciTech Connect

    Werst, D.W.

    1994-03-01

    Radical cation dimers are observed for many alkenes and aromatic hydrocarbons as products of the reaction between monomer radical cation and neutral molecule. In most cases, the dimer radical anions, formed via reaction of the monomer radical anion with a neutral molecule, have not been observed. Here we report the observation of the dimer radical anion of octafluoronaphthalene, formed by reaction of C{sub 10}F{sub 8}{sup {center_dot}{minus}} with the neutral parent molecules in nonpolar solvents following pulse radiolysis. Both monomer and dimer ions have been characterized by EPR spectra obtained by the time-resolved fluorescence-detected magnetic resonance.

  14. Molecular screening for alkane hydroxylase genes in Gram-negative and Gram-positive strains.

    PubMed

    Smits, T H; Röthlisberger, M; Witholt, B; van Beilen, J B

    1999-08-01

    We have developed highly degenerate oligonucleotides for polymerase chain reaction (PCR) amplification of genes related to the Pseudomonas oleovorans GPo1 and Acinetobacter sp. ADP1 alkane hydroxylases, based on a number of highly conserved sequence motifs. In all Gram-negative and in two out of three Gram-positive strains able to grow on medium- (C6-C11) or long-chain n-alkanes (C12-C16), PCR products of the expected size were obtained. The PCR fragments were cloned and sequenced and found to encode peptides with 43.2-93.8% sequence identity to the corresponding fragment of the P. oleovorans GPo1 alkane hydroxylase. Strains that were unable to grow on n-alkanes did not yield PCR products with homology to alkane hydroxylase genes. The alkane hydroxylase genes of Acinetobacter calcoaceticus EB104 and Pseudomonas putida P1 were cloned using the PCR products as probes. The two genes allow an alkane hydroxylase-negative mutant of Acinetobacter sp. ADP1 and an Escherichia coli recombinant containing all P. oleovorans alk genes except alkB, respectively, to grow on n-alkanes, showing that the cloned genes do indeed encode alkane hydroxylases. PMID:11207749

  15. Cloning and expression of three ladA-type alkane monooxygenase genes from an extremely thermophilic alkane-degrading bacterium Geobacillus thermoleovorans B23.

    PubMed

    Boonmak, Chanita; Takahashi, Yasunori; Morikawa, Masaaki

    2014-05-01

    An extremely thermophilic bacterium, Geobacillus thermoleovorans B23, is capable of degrading a broad range of alkanes (with carbon chain lengths ranging between C11 and C32) at 70 °C. Whole-genome sequence analysis revealed that unlike most alkane-degrading bacteria, strain B23 does not possess an alkB-type alkane monooxygenase gene. Instead, it possesses a cluster of three ladA-type genes, ladAαB23, ladAβB23, and ladB B23, on its chromosome, whose protein products share significant amino acid sequence identities, 49.8, 34.4, and 22.7 %, respectively, with that of ladA alkane monooxygenase gene found on a plasmid of Geobacillus thermodetrificans NG 80-2. Each of the three genes, ladAαB23, ladAβB23, and ladB B23, was heterologously expressed individually in an alkB1 deletion mutant strain, Pseudomonas fluorescens KOB2Δ1. It was found that all three genes were functional in P. fluorescens KOB2Δ1, and partially restored alkane degradation activity. In this study, we suggest that G. thermoleovorans B23 utilizes multiple LadA-type alkane monooxygenases for the degradation of a broad range of alkanes.

  16. HOCO radical chemistry.

    PubMed

    Francisco, Joseph S; Muckerman, James T; Yu, Hua-Gen

    2010-12-21

    Free radicals are important species in atmospheric chemistry, combustion, plasma environments, interstellar clouds, and biochemistry. Therefore, researchers would like to understand the formation mechanism, structure, stability, reactivity, spectroscopy, and dynamics of these chemical species. However, due to the presence of one or more unpaired electrons, radicals are often very reactive and have short lifetimes, which makes it difficult to conduct experiments. The HOCO radical appears in the atmosphere as well as in combustion environments and plays an important role in the conversion of CO to CO(2). Through the interplay between theoretical and experimental investigations, researchers have only recently understood the chemical role of the HOCO radical. In this Account, we systematically describe the current state of knowledge of the HOCO radical based on recent theoretical and experimental studies. This radical's two stable conformers, trans- and cis-HOCO, have been identified by high-level ab initio calculations and experimental spectroscopy. trans-HOCO is more stable by approximately 1.8 kcal/mol. The heat of formation of HOCO (298 K) was determined to be -43.0 ± 0.5 kcal/mol, giving a potential well depth of 30.1 ± 0.5 kcal/mol relative to the asymptote of the reactants OH + CO. The HOCO radical is very reactive. In most reactions between the HOCO radical and atoms, the HOCO radical acts as a hydrogen donor to reaction partners. Generally, the hydrogen is transferred through the formation of an association intermediate, which then proceeds through a molecular elimination step to produce the reaction products. The reaction rates of HOCO with some small radicals fall in the range of 10(-11)-10(-10) cm(3) molecule(-1) s(-1). These results clearly illustrate important features in the reactivity of the HOCO radical with other molecules.

  17. Identification and use of an alkane transporter plug-in for applications in biocatalysis and whole-cell biosensing of alkanes

    NASA Astrophysics Data System (ADS)

    Grant, Chris; Deszcz, Dawid; Wei, Yu-Chia; Martínez-Torres, Rubéns Julio; Morris, Phattaraporn; Folliard, Thomas; Sreenivasan, Rakesh; Ward, John; Dalby, Paul; Woodley, John M.; Baganz, Frank

    2014-07-01

    Effective application of whole-cell devices in synthetic biology and biocatalysis will always require consideration of the uptake of molecules of interest into the cell. Here we demonstrate that the AlkL protein from Pseudomonas putida GPo1 is an alkane import protein capable of industrially relevant rates of uptake of C7-C16 n-alkanes. Without alkL expression, native E.coli n-alkane uptake was the rate-limiting step in both the whole-cell bioconversion of C7-C16 n-alkanes and in the activation of a whole-cell alkane biosensor by C10 and C11 alkanes. By coexpression of alkL as a transporter plug-in, specific yields improved by up to 100-fold for bioxidation of >C12 alkanes to fatty alcohols and acids. The alkL protein was shown to be toxic to the host when overexpressed but when expressed from a vector capable of controlled induction, yields of alkane oxidation were improved a further 10-fold (8 g/L and 1.7 g/g of total oxidized products). Further testing of activity on n-octane with the controlled expression vector revealed the highest reported rates of 120 μmol/min/g and 1 g/L/h total oxidized products. This is the first time AlkL has been shown to directly facilitate enhanced uptake of C10-C16 alkanes and represents the highest reported gain in product yields resulting from its use.

  18. [Normal alkanes characteristic parameters of Jinzhou Bay surface sediments].

    PubMed

    Li, Ze-Li; Ma, Qi-Min; Cheng, Hai-Ou; Xu, Shao-Qing

    2011-11-01

    The concentration, composition and characteristic parameters of 18 surface sediment samples collected from Jinzhou Bay were studied. The samples were soxhlet-extracted with a mixture of 1: 1 (V/V) dichloromethane-hexane and analyzed by GC-MS after purification and concentration. Concentrations of n-alkanes vary from 1.9 to 4.2 microg x g(-1) with an average value of 2.6 microg x g(-1) dry weight. n-Alkanes distribution patterns of all positions were characterized by double peak-cluster, which means double sources from terrestrial and marine origin. The sum of nC25 to nC31 accounts for 20%-32% of the total n-alkanes, while the average value of L/H, C31/C19, TAR ratio are 0.67, 3.06, 2.02, respectively. All of these three indices suggest that the terrestrial contributions are higher than marine sources, especially for No. 2, 3 and 7 stations, which were influenced by riverinput nearby. Carbon Preference Index (CPI) ranges from 1.19 to 2.63 with an average value of 1.73, which is close to 1; the ratio of Pristane/Phytane (Pr/Ph) and unresolved/resolved compounds (U/R) range from 0.91 to 1.28, 2.2 to 4.3, respectively. All of these three parameters indicate that No. 13 and 15 stations are influenced by petroleum pollution. Comprehensive analysis of various parameters shows that Jinzhou Bay is threatened by both terrestrial inputs and petroleum hydrocarbons contaminations, which may relate to river discharging and port shipping in Jinzhou Bay. PMID:22295627

  19. DFT studies of all fluorothiophenes and their cations as candidate monomers for conductive polymers

    SciTech Connect

    Shirani, Hossein; Jameh-Bozorghi, Saeed; Yousefi, Ali

    2015-01-22

    In this paper, electronic, structural, and properties of mono-, di-, tri-, and tetrafluorothiophenes and their radical cations are studied using the density functional theory and B3LYP method with 6-311++G** basis set. Also, the effects of the number and position of the substituent of fluorine atoms on the properties of the thiophene ring have been studied using optimized structures obtained for these molecules and their radical cations; vibrational frequencies, spin-density distribution, size and direction of the dipole moment vector, ionization potential, electric Polarizabilities, HOMO–LUMO gaps and NICS values of these compounds have been calculated and analyzed.

  20. Radiation induced redox reactions and fragmentation of constituent ions in ionic liquids II. Imidazolium cations.

    SciTech Connect

    Shkrob, I. A.; Marin, T. W.; Chemerisov, S. D.; Hatcher, J.; Wishart, J.

    2011-04-14

    In part 1 of this study, radiolytic degradation of constituent anions in ionic liquids (ILs) was examined. The present study continues the themes addressed in part 1 and examines the radiation chemistry of 1,3-dialkyl substituted imidazolium cations, which currently comprise the most practically important and versatile class of ionic liquid cations. For comparison, we also examined 1,3-dimethoxy- and 2-methyl-substituted imidazolium and 1-butyl-4-methylpyridinium cations. In addition to identification of radicals using electron paramagnetic resonance spectroscopy (EPR) and selective deuterium substitution, we analyzed stable radiolytic products using {sup 1}H and {sup 13}C nuclear magnetic resonance (NMR) and tandem electrospray ionization mass spectrometry (ESMS). Our EPR studies reveal rich chemistry initiated through 'ionization of the ions': oxidation and the formation of radical dications in the aliphatic arms of the parent cations (leading to deprotonation and the formation of alkyl radicals in these arms) and reduction of the parent cation, yielding 2-imidazolyl radicals. The subsequent reactions of these radicals depend on the nature of the IL. If the cation is 2-substituted, the resulting 2-imidazolyl radical is relatively stable. If there is no substitution at C(2), the radical then either is protonated or reacts with the parent cation forming a C(2)-C(2) {sigma}{sigma}*-bound dimer radical cation. In addition to these reactions, when methoxy or C{sub {alpha}}-substituted alkyl groups occupy the N(1,3) positions, their elimination is observed. The elimination of methyl groups from N(1,3) was not observed. Product analyses of imidazolium liquids irradiated in the very-high-dose regime (6.7 MGy) reveal several detrimental processes, including volatilization, acidification, and oligomerization. The latter yields a polymer with m/z of 650 {+-} 300 whose radiolytic yield increases with dose (0.23 monomer units per 100 eV for 1-methyl-3-butylimidazolium

  1. Radiation induced redox reactions and fragmentation of constituent ions in ionic liquids. 2. Imidazolium cations.

    PubMed

    Shkrob, Ilya A; Marin, Timothy W; Chemerisov, Sergey D; Hatcher, Jasmine L; Wishart, James F

    2011-04-14

    In part 1 of this study, radiolytic degradation of constituent anions in ionic liquids (ILs) was examined. The present study continues the themes addressed in part 1 and examines the radiation chemistry of 1,3-dialkyl substituted imidazolium cations, which currently comprise the most practically important and versatile class of ionic liquid cations. For comparison, we also examined 1,3-dimethoxy- and 2-methyl-substituted imidazolium and 1-butyl-4-methylpyridinium cations. In addition to identification of radicals using electron paramagnetic resonance spectroscopy (EPR) and selective deuterium substitution, we analyzed stable radiolytic products using (1)H and (13)C nuclear magnetic resonance (NMR) and tandem electrospray ionization mass spectrometry (ESMS). Our EPR studies reveal rich chemistry initiated through "ionization of the ions": oxidation and the formation of radical dications in the aliphatic arms of the parent cations (leading to deprotonation and the formation of alkyl radicals in these arms) and reduction of the parent cation, yielding 2-imidazolyl radicals. The subsequent reactions of these radicals depend on the nature of the IL. If the cation is 2-substituted, the resulting 2-imidazolyl radical is relatively stable. If there is no substitution at C(2), the radical then either is protonated or reacts with the parent cation forming a C(2)-C(2) σσ*-bound dimer radical cation. In addition to these reactions, when methoxy or C(α)-substituted alkyl groups occupy the N(1,3) positions, their elimination is observed. The elimination of methyl groups from N(1,3) was not observed. Product analyses of imidazolium liquids irradiated in the very-high-dose regime (6.7 MGy) reveal several detrimental processes, including volatilization, acidification, and oligomerization. The latter yields a polymer with m/z of 650 ± 300 whose radiolytic yield increases with dose (~0.23 monomer units per 100 eV for 1-methyl-3-butylimidazolium trifluorosulfonate). Gradual

  2. Preliminary assessment of halogenated alkanes as vapor-phase tracers

    SciTech Connect

    Adams, Michael C.; Moore, Joseph N.; Hirtz, Paul

    1991-01-01

    New tracers are needed to evaluate the efficiency of injection strategies in vapor-dominated environments. One group of compounds that seems to meet the requirements for vapor-phase tracing are the halogenated alkanes (HCFCs). HCFCs are generally nontoxic, and extrapolation of tabulated thermodynamic data indicate that they will be thermally stable and nonreactive in a geothermal environment. The solubilities and stabilities of these compounds, which form several homologous series, vary according to the substituent ratios of fluorine, chlorine, and hydrogen. Laboratory and field tests that will further define the suitability of HCFCs as vapor-phase tracers are under way.

  3. Pulse radiolysis studies on reactions of hydroxyl radicals with selenocystine derivatives.

    PubMed

    Mishra, B; Kumbhare, L B; Jain, V K; Priyadarsini, K I

    2008-04-10

    Reactions of hydroxyl radicals (*OH) with selenocystine (SeCys) and two of its analogues, diselenodipropionic acid (SeP) and selenocystamine (SeA), have been studied in aqueous solutions at pHs of 1, 7, and 10 using the pulse radiolysis technique coupled with absorption detection. All of these diselenides react with *OH radicals with rate constants of approximately 10(10) M(-1) s(-1), producing diselenide radical cations ( approximately 1-5 micros after the pulse), with an absorption maximum at 560 nm, by elimination of H(2)O or OH(-) from hydroxyl radical adducts. Assignment of the 560 nm band to the diselenide radical cation was made by comparing the transient spectra with those produced upon reaction of diselenides with specific one-electron oxidants, Cl(2)(*-) (pH 1) and Br(2)(*-) radicals (pHs of 7 and 10). SeP having a carboxylic acid functionality showed quantitative conversion of hydroxyl radical adducts to radical cations. The compounds SeCys and SeA, having an amino functional group, in addition to the radical cations, produced a new transient with lambda(max) at 460 nm, at later time scales ( approximately 20-40 micros after the pulse). The rate and yield of formation of the 460 nm band increased with increasing concentrations of either SeCys or SeA. In analogy with similar studies reported for analogous disulfides, the 460 nm transient absorption band has been assigned to a triselenide radical adduct. The one-electron reduction potentials of the compounds were estimated to be 0.96, 1.3, and 1.6 V versus NHE, respectively, for SeP, SeCys, and SeA at pH 7. From these studies, it has been concluded that the electron-donating carboxylic acid group decreases the reduction potential and facilitates quantitative conversion of hydroxyl radical adducts to radical cations, while the electron-withdrawing NH(3)(+) group not only increases the reduction potential but also leads to fragmentation of the hydroxyl radical adduct to selenyl radicals, which are converted

  4. Cationic Antimicrobial Polymers and Their Assemblies

    PubMed Central

    Carmona-Ribeiro, Ana Maria; de Melo Carrasco, Letícia Dias

    2013-01-01

    Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications. PMID:23665898

  5. Toxicity of cationic lipids and cationic polymers in gene delivery.

    PubMed

    Lv, Hongtao; Zhang, Shubiao; Wang, Bing; Cui, Shaohui; Yan, Jie

    2006-08-10

    Gene therapy, as a promising therapeutics to treat genetic or acquired diseases, has achieved exciting development in the past two decades. Appropriate gene vectors can be crucial for gene transfer. Cationic lipids and polymers, the most important non-viral vectors, have many advantages over viral ones as non-immunogenic, easy to produce and not oncogenic. They hold the promise to replace viral vectors to be used in clinic. However, the toxicity is still an obstacle to the application of non-viral vectors to gene therapy. For overcoming the problem, many new cationic compounds have been developed. This article provides a review with respect to toxicity of cationic lipids and polymers in gene delivery. We evaluate the structural features of cationic compounds and summarize the relationship of toxicity and structure and hope to provide available suggestions on the development of these cationic compounds.

  6. Multiple sources of alkanes in Quaternary oceanic sediment of Antarctica

    USGS Publications Warehouse

    Kvenvolden, K.A.; Rapp, J.B.; Golan-Bac, M.; Hostettler, F.D.

    1987-01-01

    Normal alkanes (n-C13n-C36), isoprenoid hydrocarbons (i-C15, i-C16, i-C18, i-C19, and i-C20) triterpanes (C27C32), and (C27C29) are present in low concentrations offshore Antarctica in near-surface, Quaternary sediment of the Wilkes Land continental margin and of the western Ross Sea. The distributions of these hydrocarbons are interpreted relative to possible sources and processes. The hydrocarbons appear to be mixtures of primary and recycled material from marine and terrigenous sources. The n-alkanes are most abundant and are characterized by two distinct populations, one of probable marine origin and the other likely from terrigenous, vascular plant sources. Because the continent of Antarctica today is devoid of higher plants, the plant-derived hydrocarbons in these offshore sediments probably came from wind-blown material and recycled Antarctic sediment that contains land-plant remains from an earlier period of time. Isoprenoid hydrocarbons are partially recycled and mainly of marine origin; the dominance of pristane over phytane suggests oxic paleoenvironmental conditions. Both modern and ancient triterpanes and steranes are present, and the distribution of these indicates a mixture of primary and recycled bacterial, algal, and possible higher-plant materials. Although the sampled sediments were deposited during the Quaternary, they apparently contain a significant component of hydrocarbons of pre-Quaternary age. ?? 1987.

  7. Gas-phase study of Fe sup + -benzyne with alkanes

    SciTech Connect

    Yongqing Huang; Freiser, B.S. )

    1989-03-29

    The unimolecular chemistry of Fe{sup +}-benzyne and its reactivity with small alkanes in the gas phase are studied by Fourier transform mass spectrometry (FTMS). Collision-induced dissociation of Fe{sup +}-benzyne yields benzyne loss exclusively. In contrast, photodissociation of Fe{sup +}-benzyne yields not only cleavage of benzyne from Fe{sup +}, but competitive loss of C{sub 2}H{sub 2} and C{sub 4}H{sub 2} as well. The Fe{sup +}-benzyne is formed from chlorobenzene by loss of HCl. This dehydrochlorination of chlorobenzene also occurs in secondary reactions up to six times forming products of the type Fe{sup +}-polyphenylene. Fe{sup +}-benzyne reacts with alkanes larger than methane to form a wide variety of product ions by mechanisms including hydrogenation and methanation of the benzyne ligand. All of the product ions can be explained by mechanisms based on Fe{sup +} insertion into either C-C or C-H bonds as the reaction-initiating step, followed by either alkyl or H migration from Fe{sup +} onto the benzyne ligand or, alternatively, by the migratory insertion of benzyne into a metal-carbon or metal-hydrogen bond. Photodissociation and ion-molecule reaction studies yield a value for the metal-ligand bond energy of D{degree} (Fe{sup +}-benzyne) = 76 {plus minus} 10 kcal/mol.

  8. Direct hydrodeoxygenation of raw woody biomass into liquid alkanes.

    PubMed

    Xia, Qineng; Chen, Zongjia; Shao, Yi; Gong, Xueqing; Wang, Haifeng; Liu, Xiaohui; Parker, Stewart F; Han, Xue; Yang, Sihai; Wang, Yanqin

    2016-03-30

    Being the only sustainable source of organic carbon, biomass is playing an ever-increasingly important role in our energy landscape. The conversion of renewable lignocellulosic biomass into liquid fuels is particularly attractive but extremely challenging due to the inertness and complexity of lignocellulose. Here we describe the direct hydrodeoxygenation of raw woods into liquid alkanes with mass yields up to 28.1 wt% over a multifunctional Pt/NbOPO4 catalyst in cyclohexane. The superior performance of this catalyst allows simultaneous conversion of cellulose, hemicellulose and, more significantly, lignin fractions in the wood sawdust into hexane, pentane and alkylcyclohexanes, respectively. Investigation on the molecular mechanism reveals that a synergistic effect between Pt, NbOx species and acidic sites promotes this highly efficient hydrodeoxygenation of bulk lignocellulose. No chemical pretreatment of the raw woody biomass or separation is required for this one-pot process, which opens a general and energy-efficient route for converting raw lignocellulose into valuable alkanes.

  9. Geologic seepage of methane and light alkanes in Los Angeles

    NASA Astrophysics Data System (ADS)

    Doezema, L. A.; Chang, K.; Baril, R.; Nwachuku, I.; Contreras, P.; Marquez, A.; Howard, D.

    2013-12-01

    Natural geologic seepage of methane from underground oil and natural gas reservoirs has been suggested to be an underreported part of the global methane budget. Other light alkanes are also given off in combination with the methane seepage, making it possible that geologic seepage is also a potentially significant global source of these light alkanes. This study reports C1-C5 findings from geologic seepage made in the Los Angeles region. Microseepage, invisible escape of gases, was measured primarily at Kenneth Hahn Regional Park, while macroseepage, the visible release of gases, was measured at the La Brea Tar Pits. Samples were collected using stainless steel canisters and flux chambers and were analyzed using gas chromatography with flame ionization detectors (GC-FID). Average microseepage flux rates of 0.95 μg m-2 h-1 for ethane and 0.51 μg m-2 h-1 were found for propane, while average macroseepage rates for methane, ethane, and propane were 664, 19.8, and 18.1 mg m-2 h-1 respectively. Relationships between microseepage flux rate and location of underground oil and natural deposit and earthquake fault lines are presented. Additionally, the relative importance of findings in context with global budgets and local air quality is discussed.

  10. Direct hydrodeoxygenation of raw woody biomass into liquid alkanes.

    PubMed

    Xia, Qineng; Chen, Zongjia; Shao, Yi; Gong, Xueqing; Wang, Haifeng; Liu, Xiaohui; Parker, Stewart F; Han, Xue; Yang, Sihai; Wang, Yanqin

    2016-01-01

    Being the only sustainable source of organic carbon, biomass is playing an ever-increasingly important role in our energy landscape. The conversion of renewable lignocellulosic biomass into liquid fuels is particularly attractive but extremely challenging due to the inertness and complexity of lignocellulose. Here we describe the direct hydrodeoxygenation of raw woods into liquid alkanes with mass yields up to 28.1 wt% over a multifunctional Pt/NbOPO4 catalyst in cyclohexane. The superior performance of this catalyst allows simultaneous conversion of cellulose, hemicellulose and, more significantly, lignin fractions in the wood sawdust into hexane, pentane and alkylcyclohexanes, respectively. Investigation on the molecular mechanism reveals that a synergistic effect between Pt, NbOx species and acidic sites promotes this highly efficient hydrodeoxygenation of bulk lignocellulose. No chemical pretreatment of the raw woody biomass or separation is required for this one-pot process, which opens a general and energy-efficient route for converting raw lignocellulose into valuable alkanes. PMID:27025898

  11. Direct hydrodeoxygenation of raw woody biomass into liquid alkanes

    PubMed Central

    Xia, Qineng; Chen, Zongjia; Shao, Yi; Gong, Xueqing; Wang, Haifeng; Liu, Xiaohui; Parker, Stewart F.; Han, Xue; Yang, Sihai; Wang, Yanqin

    2016-01-01

    Being the only sustainable source of organic carbon, biomass is playing an ever-increasingly important role in our energy landscape. The conversion of renewable lignocellulosic biomass into liquid fuels is particularly attractive but extremely challenging due to the inertness and complexity of lignocellulose. Here we describe the direct hydrodeoxygenation of raw woods into liquid alkanes with mass yields up to 28.1 wt% over a multifunctional Pt/NbOPO4 catalyst in cyclohexane. The superior performance of this catalyst allows simultaneous conversion of cellulose, hemicellulose and, more significantly, lignin fractions in the wood sawdust into hexane, pentane and alkylcyclohexanes, respectively. Investigation on the molecular mechanism reveals that a synergistic effect between Pt, NbOx species and acidic sites promotes this highly efficient hydrodeoxygenation of bulk lignocellulose. No chemical pretreatment of the raw woody biomass or separation is required for this one-pot process, which opens a general and energy-efficient route for converting raw lignocellulose into valuable alkanes. PMID:27025898

  12. On the Route to the Photogeneration of Heteroaryl Cations. The Case of Halothiophenes.

    PubMed

    Raviola, Carlotta; Chiesa, Francesco; Protti, Stefano; Albini, Angelo; Fagnoni, Maurizio

    2016-08-01

    2-Chloro-, 2-bromo-, and 2-iodothiophenes undergo photochemical dehalogenation via the triplet state. In the presence of suitable π-bond nucleophiles, thienylation occurs with modest yield from chloro and bromo derivatives (via photogenerated triplet 2-thienyl cation). Specific trapping by using oxygen along with computational analysis carried out by means of a density functional method support that, in the case of iodo derivatives, homolytic thienyl-I bond fragmentation occurs first and heteroaryl cations are formed by electron transfer within the triplet radical pair, thus opening an indirect access to such cations. PMID:27383725

  13. 40 CFR 721.2625 - Reaction product of alkane-diol and epichlorohydrin.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Reaction product of alkane-diol and... Specific Chemical Substances § 721.2625 Reaction product of alkane-diol and epichlorohydrin. (a) Chemical... as reaction product of alkanediol and epichlorohydrin (PMN P-89-760) is subject to reporting...

  14. 40 CFR 721.2625 - Reaction product of alkane-diol and epichlorohydrin.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Reaction product of alkane-diol and... Specific Chemical Substances § 721.2625 Reaction product of alkane-diol and epichlorohydrin. (a) Chemical... as reaction product of alkanediol and epichlorohydrin (PMN P-89-760) is subject to reporting...

  15. 40 CFR 721.2625 - Reaction product of alkane-diol and epichlorohydrin.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Reaction product of alkane-diol and... Specific Chemical Substances § 721.2625 Reaction product of alkane-diol and epichlorohydrin. (a) Chemical... as reaction product of alkanediol and epichlorohydrin (PMN P-89-760) is subject to reporting...

  16. 40 CFR 721.2625 - Reaction product of alkane-diol and epichlorohydrin.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Reaction product of alkane-diol and... Specific Chemical Substances § 721.2625 Reaction product of alkane-diol and epichlorohydrin. (a) Chemical... as reaction product of alkanediol and epichlorohydrin (PMN P-89-760) is subject to reporting...

  17. 40 CFR 721.2625 - Reaction product of alkane-diol and epichlorohydrin.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Reaction product of alkane-diol and... Specific Chemical Substances § 721.2625 Reaction product of alkane-diol and epichlorohydrin. (a) Chemical... as reaction product of alkanediol and epichlorohydrin (PMN P-89-760) is subject to reporting...

  18. Surfactant-induced phases in water-supported alkane monolayers: I. Thermodynamics.

    PubMed

    Yefet, Shai; Sloutskin, Eli; Tamam, Lilach; Sapir, Zvi; Cohen, Asaf; Deutsch, Moshe; Ocko, Benjamin M

    2014-07-15

    Alkanes longer than n = 6 carbons do not spread on the water surface, but condense in a macroscopic lens. However, adding trimethylammonium-based surfactants, C(m)TAB, in submillimolar concentrations causes the alkanes to spread and form a single Langmuir-Gibbs (LG) monolayer of mixed alkanes and surfactant tails, which coexists with the alkane lenses. Upon cooling, this LG film surface-freezes at a temperature T(s) above the bulk freezing temperature T(b). The thermodynamics of surface freezing (SF) of these LG films is studied by surface tension measurements for a range of alkanes (n = 12-21) and surfactant alkyl lengths (m = 14, 16, 18), at several concentrations c. The surface freezing range T(s)-T(b) observed is up to 25 °C, an order of magnitude larger than the temperature range of SF monolayers on the surface of pure alkane melts. The measured (n,T) surface phase diagram is accounted for well by a model based on mixtures' theory, which includes an interchange energy term ω. ω is found to be negative, implying attraction between unlike species, rather than the repulsion found for SF of binary alkane mixtures. Thus, the surfactant/alkane mixing is a necessary condition for the occurrence of SF in these LG films. The X-ray derived structure of the films is presented in an accompanying paper. PMID:24918482

  19. ESR study of stable radicals in an irradiated single crystal of deoxyguanosine 5'-phosphate (Na salt)

    SciTech Connect

    Rakvin, B.; Herak, J.N.

    1981-11-01

    Three different radical species have been identified in an irradiated single crystal of deoxyguanosine 5'-phosphate at room temperature. The dominating species is a hydrogen-addition radical with spectroscopic characteristics similar to those of the N(7)-protonated H-addition radical in guanine/sup ./HCl. The well-resolved quartet ESR pattern is believed to belong to a radical in the sugar moiety formed by breakage of the furanose ring in the same manner as that reported earlier for deoxycytidine 5'-phosphate. The third species present is either a protonated anion or a deprotonated cation located in this six-member ring of the guanine base.

  20. Geomicrobiological linkages between short-chain alkane consumption and sulfate reduction rates in seep sediments

    PubMed Central

    Bose, Arpita; Rogers, Daniel R.; Adams, Melissa M.; Joye, Samantha B.; Girguis, Peter R.

    2013-01-01

    Marine hydrocarbon seeps are ecosystems that are rich in methane, and, in some cases, short-chain (C2–C5) and longer alkanes. C2–C4 alkanes such as ethane, propane, and butane can be significant components of seeping fluids. Some sulfate-reducing microbes oxidize short-chain alkanes anaerobically, and may play an important role in both the competition for sulfate and the local carbon budget. To better understand the anaerobic oxidation of short-chain n-alkanes coupled with sulfate-reduction, hydrocarbon-rich sediments from the Gulf of Mexico (GoM) were amended with artificial, sulfate-replete seawater and one of four n-alkanes (C1–C4) then incubated under strict anaerobic conditions. Measured rates of alkane oxidation and sulfate reduction closely follow stoichiometric predictions that assume the complete oxidation of alkanes to CO2 (though other sinks for alkane carbon likely exist). Changes in the δ13C of all the alkanes in the reactors show enrichment over the course of the incubation, with the C3 and C4 incubations showing the greatest enrichment (4.4 and 4.5‰, respectively). The concurrent depletion in the δ13C of dissolved inorganic carbon (DIC) implies a transfer of carbon from the alkane to the DIC pool (−3.5 and −6.7‰ for C3 and C4 incubations, respectively). Microbial community analyses reveal that certain members of the class Deltaproteobacteria are selectively enriched as the incubations degrade C1–C4 alkanes. Phylogenetic analyses indicate that distinct phylotypes are enriched in the ethane reactors, while phylotypes in the propane and butane reactors align with previously identified C3–C4 alkane-oxidizing sulfate-reducers. These data further constrain the potential influence of alkane oxidation on sulfate reduction rates (SRRs) in cold hydrocarbon-rich sediments, provide insight into their contribution to local carbon cycling, and illustrate the extent to which short-chain alkanes can serve as electron donors and govern microbial

  1. Incorporation of chlorinated alkanes into fatty acids of hydrocarbon-utilizing mycobacteria.

    PubMed

    Murphy, G L; Perry, J J

    1983-12-01

    The cellular fatty acid composition of Mycobacterium vaccae JOB5 and Mycobacterium convolutum R22 was examined after growth on n-alkanes and compared with the fatty acids of the organisms after growth on 1-chlorohexadecane and 1-chlorooctadecane. Growth on n-alkanes resulted in normal fatty acid profiles. Mass spectral analyses indicated that, after growth on the terminally chlorinated n-alkanes, 75 to 86% of the fatty acids in M. convolutum and ca. 55% of the fatty acids in M. vaccae contained chlorine. Neither organism could utilize chloroacetate or 3-chloropropionate as sole source of carbon and energy. When these compounds were added to a growth medium with n-hexadecane as substrate, there was no evidence that chlorinated fatty acids were produced. Terminally chlorinated n-alkanes can be added to the list of n-alkanes, alkenes, and cyclohexylalkane derivatives that can be directly incorporated into cellular fatty acids of hydrocarbon-utilizing organisms.

  2. Possible origin of n -alkanes with a remarkable even-to-odd predominance in recent marine sediments

    NASA Astrophysics Data System (ADS)

    Nishimura, Mitsugu; Baker, Earl W.

    1986-02-01

    N- alkane distributions with a remarkable even-to-odd predominance (C 16-C 24) were found in marine surface sediments. The previously proposed diagenetic reduction of the corresponding n- fatty acids could not be considered as a source for these N- alkane. Based on a comparison of compositional features of n- alkane, n- fatty acid and n- alcohol distributions, carbon isotope analyses, and other geochemical parameters, the data indicate that the even-predominant n- alkanes were derived directly from marine bacteria.

  3. Radical-Mediated Fluoroalkylations.

    PubMed

    Cho, Eun Jin

    2016-02-01

    Recently, the development of eco-friendly radical processes has become of great interest in synthetic chemistry. In particular, visible-light photocatalysis has drawn tremendous attention for its environmental compatibility and versatility in promoting many synthetically important reactions. In addition, inorganic electrides as electron donors have emerged as new eco-friendly tools for radical transformations since they consist of non-toxic and naturally abundant main metals such as calcium. The design of new fluoroalkylation reactions has benefited greatly from recent advances in visible-light photocatalysis and the chemistry of inorganic electrides. Since adding fluoroalkyl groups can dramatically change the physical and chemical properties of organic compounds, using these processes to promote eco-friendly radical fluoroalkylations will have a major impact in areas such as pharmaceuticals, agrochemicals, and material sciences. This Personal Account reviews radical-mediated fluoroalkylations, such as trifluoromethylations and difluoroalkylations, recently developed in our laboratory. PMID:26497950

  4. Adsorption of proteins at the aqueous solution/alkane interface: Co-adsorption of protein and alkane.

    PubMed

    Miller, R; Aksenenko, E V; Zinkovych, I I; Fainerman, V B

    2015-08-01

    The equations of state, adsorption isotherms and functions of the distribution of protein molecules in liquid interfacial layers with respect to molar area and the equations for their viscoelastic behavior are presented. This theory was used to determine the adsorption characteristics of β-casein and β-lactoglobulin at water/oil interfaces. The experimental results are shown to be describable quite adequately by the proposed theory with consistent model parameters. The data analysis demonstrated that the β-casein molecule adsorbed at equilibrium conditions is more unfolded as compared with dynamic conditions, and this fact causes the significant increase of the adsorption equilibrium constant. The theory assumes the adsorption of protein molecules from the aqueous solution and a competitive adsorption of alkane molecules from the alkane phase. The comparison of the experimental equilibrium interfacial tension isotherms for β-lactoglobulin at the solution/hexane interface with data calculated using the proposed theoretical model demonstrates that the assumption of a competitive adsorption is essential, and the influence of the hexane molecules on the shape of the adsorption isotherm does in fact exist.

  5. Accelerated crystallization of zeolites via hydroxyl free radicals.

    PubMed

    Feng, Guodong; Cheng, Peng; Yan, Wenfu; Boronat, Mercedes; Li, Xu; Su, Ji-Hu; Wang, Jianyu; Li, Yi; Corma, Avelino; Xu, Ruren; Yu, Jihong

    2016-03-11

    In the hydrothermal crystallization of zeolites from basic media, hydroxide ions (OH(-)) catalyze the depolymerization of the aluminosilicate gel by breaking the Si,Al-O-Si,Al bonds and catalyze the polymerization of the aluminosilicate anions around the hydrated cation species by remaking the Si,Al-O-Si,Al bonds. We report that hydroxyl free radicals (•OH) are involved in the zeolite crystallization under hydrothermal conditions. The crystallization processes of zeolites-such as Na-A, Na-X, NaZ-21, and silicalite-1-can be accelerated with hydroxyl free radicals generated by ultraviolet irradiation or Fenton's reagent.

  6. 40 CFR 721.10625 - Distillation bottoms, alkylated benzene by-product, brominated and bromo diphenyl alkane (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... benzene by-product, brominated and bromo diphenyl alkane (generic). 721.10625 Section 721.10625 Protection... Distillation bottoms, alkylated benzene by-product, brominated and bromo diphenyl alkane (generic). (a... generically as distillation bottoms, alkylated benzene by-product, brominated and bromo diphenyl alkane...

  7. 40 CFR 721.10625 - Distillation bottoms, alkylated benzene by-product, brominated and bromo diphenyl alkane (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... benzene by-product, brominated and bromo diphenyl alkane (generic). 721.10625 Section 721.10625 Protection... Distillation bottoms, alkylated benzene by-product, brominated and bromo diphenyl alkane (generic). (a... generically as distillation bottoms, alkylated benzene by-product, brominated and bromo diphenyl alkane...

  8. 40 CFR 721.10178 - Distillates (Fischer-Tropsch), hydroisomerized middle, C10-13-branched alkane fraction.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...), hydroisomerized middle, C10-13-branched alkane fraction. 721.10178 Section 721.10178 Protection of Environment...), hydroisomerized middle, C10-13-branched alkane fraction. (a) Chemical substance and significant new uses subject... middle, C10-13-branched alkane fraction (PMN P-04-319; CAS No. 642928-30-1) is subject to reporting...

  9. 40 CFR 721.10178 - Distillates (Fischer-Tropsch), hydroisomerized middle, C10-13-branched alkane fraction.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...), hydroisomerized middle, C10-13-branched alkane fraction. 721.10178 Section 721.10178 Protection of Environment...), hydroisomerized middle, C10-13-branched alkane fraction. (a) Chemical substance and significant new uses subject... middle, C10-13-branched alkane fraction (PMN P-04-319; CAS No. 642928-30-1) is subject to reporting...

  10. Hydroxyl radicals in indoor environments

    NASA Astrophysics Data System (ADS)

    Sarwar, Golam; Corsi, Richard; Kimura, Yosuke; Allen, David; Weschler, Charles J.

    Indoor hydroxyl radical concentrations were estimated using a new indoor air quality model which employs the SAPRC-99 atmospheric chemistry model to simulate indoor homogenous reactions. Model results indicate that typical indoor hydroxyl radical concentrations are lower than typical outdoor summertime urban hydroxyl radical levels of 5-10×10 6 molecules cm -3; however, indoor levels can be similar to or greater than typical nighttime outdoor hydroxyl radical levels of approximately 5×10 4 molecules cm -3. Effects of selected parameters on indoor hydroxyl radical concentrations are presented herein. Indoor hydroxyl radical concentrations are predicted to increase non-linearly with increasing outdoor ozone concentrations, indoor alkene emission rates, and air exchange rates. Indoor hydroxyl radical concentrations decrease with increasing outdoor nitric oxide concentrations. Indoor temperature and indoor light intensity have moderate impacts on indoor hydroxyl radical concentrations. Outdoor hydroxyl radical concentrations, outdoor nitrate (NO 3rad ) radical concentrations, outdoor hydroperoxy radical concentrations, and hydroxyl radical removal by indoor surfaces are predicted to have no appreciable impact on indoor hydroxyl radical concentrations. Production of hydroxyl radicals in indoor environments appears to be controlled primarily by reactions of alkenes with ozone, and nitric oxide with hydroperoxy radical. Estimated indoor hydroxyl radical levels may potentially affect indoor air quality. Two examples are presented in which reactions of d-limonene and α-pinene with indoor hydroxyl radicals produce aldehydes, which may be of greater concern than the original compounds.

  11. Cation-induced stabilization of the engineered cation-binding loop in cytochrome c peroxidase (CcP).

    PubMed

    Bhaskar, B; Bonagura, Christopher A; Li, Huiying; Poulos, Thomas L

    2002-02-26

    We have previously shown that the K(+) site found in the proximal heme pocket of ascorbate peroxidase (APX) could be successfully engineered into the closely homologous cytochrome c peroxidase (CcP) [Bonagura et al., (1996) Biochemistry 35, 6107-6115; Bonagura et al. (1999) Biochemistry 38, 5538-5545]. In addition, specificity could be switched to binding Ca(2+) as found in other peroxidases [Bonagura et al. (1999) J. Biol. Chem. 274, 37827-37833]. The introduction of a proximal cation-binding site also promotes conversion of the Trp191 containing cation-binding loop from a "closed" to an "open" conformer. In the present study we have changed a crucial hinge residue of the cation-binding loop, Asn195, to Pro which stabilizes the loop, albeit, only in the presence of bound K(+). The crystal structure of this mutant, N195PK2, has been refined to 1.9 A. As predicted, introduction of this crucial hinge residue stabilizes the cation-binding loop in the presence of the bound K(+). As in earlier work, the characteristic EPR signal of Trp191 cation radical becomes progressively weaker with increasing [K(+)] and the lifetime of the Trp191 radical also has been considerably shortened in this mutant. This mutant CcP exhibits reduced enzyme activity, which could be titrated to lower levels with increasing [K(+)] when horse heart cytochrome c is the substrate. However, with yeast cytochrome c as the substrate, the mutant was as active as wild-type at low ionic strength, but 40-fold lower at high ionic strength. We attribute this difference to a change in the rate-limiting step as a function of ionic strength when yeast cytochrome c is the substrate. PMID:11851415

  12. Flow reactor studies of non-equilibrium plasma-assisted oxidation of n-alkanes.

    PubMed

    Tsolas, Nicholas; Lee, Jong Guen; Yetter, Richard A

    2015-08-13

    The oxidation of n-alkanes (C1-C7) has been studied with and without the effects of a nanosecond, non-equilibrium plasma discharge at 1 atm pressure from 420 to 1250 K. Experiments have been performed under nearly isothermal conditions in a flow reactor, where reactive mixtures are diluted in Ar to minimize temperature changes from chemical reactions. Sample extraction performed at the exit of the reactor captures product and intermediate species and stores them in a multi-position valve for subsequent identification and quantification using gas chromatography. By fixing the flow rate in the reactor and varying the temperature, reactivity maps for the oxidation of fuels are achieved. Considering all the fuels studied, fuel consumption under the effects of the plasma is shown to have been enhanced significantly, particularly for the low-temperature regime (T<800 K). In fact, multiple transitions in the rates of fuel consumption are observed depending on fuel with the emergence of a negative-temperature-coefficient regime. For all fuels, the temperature for the transition into the high-temperature chemistry is lowered as a consequence of the plasma being able to increase the rate of fuel consumption. Using a phenomenological interpretation of the intermediate species formed, it can be shown that the active particles produced from the plasma enhance alkyl radical formation at all temperatures and enable low-temperature chain branching for fuels C3 and greater. The significance of this result demonstrates that the plasma provides an opportunity for low-temperature chain branching to occur at reduced pressures, which is typically observed at elevated pressures in thermal induced systems. PMID:26170423

  13. Flow reactor studies of non-equilibrium plasma-assisted oxidation of n-alkanes.

    PubMed

    Tsolas, Nicholas; Lee, Jong Guen; Yetter, Richard A

    2015-08-13

    The oxidation of n-alkanes (C1-C7) has been studied with and without the effects of a nanosecond, non-equilibrium plasma discharge at 1 atm pressure from 420 to 1250 K. Experiments have been performed under nearly isothermal conditions in a flow reactor, where reactive mixtures are diluted in Ar to minimize temperature changes from chemical reactions. Sample extraction performed at the exit of the reactor captures product and intermediate species and stores them in a multi-position valve for subsequent identification and quantification using gas chromatography. By fixing the flow rate in the reactor and varying the temperature, reactivity maps for the oxidation of fuels are achieved. Considering all the fuels studied, fuel consumption under the effects of the plasma is shown to have been enhanced significantly, particularly for the low-temperature regime (T<800 K). In fact, multiple transitions in the rates of fuel consumption are observed depending on fuel with the emergence of a negative-temperature-coefficient regime. For all fuels, the temperature for the transition into the high-temperature chemistry is lowered as a consequence of the plasma being able to increase the rate of fuel consumption. Using a phenomenological interpretation of the intermediate species formed, it can be shown that the active particles produced from the plasma enhance alkyl radical formation at all temperatures and enable low-temperature chain branching for fuels C3 and greater. The significance of this result demonstrates that the plasma provides an opportunity for low-temperature chain branching to occur at reduced pressures, which is typically observed at elevated pressures in thermal induced systems.

  14. Green light radiation effects on free radicals inhibition in cellular and chemical systems.

    PubMed

    Comorosan, Sorin; Polosan, Silviu; Jipa, Silviu; Popescu, Irinel; Marton, George; Ionescu, Elena; Cristache, Ligia; Badila, Dumitru; Mitrica, Radu

    2011-01-10

    Free radicals generation is inhibited through green light (GL) irradiation in cellular systems and in chemical reactions. Standard melanocyte cultures were UV-irradiated and the induced cellular reactive oxygen species (ROS) were quantified by the fluorescence technique. The same cell cultures, previously protected by a 24h GL exposure, displayed a significantly lower ROS production. A simple chemical reaction is subsequently chosen, in which the production of free radicals is well defined. Paraffin wax and mineral oil were GL irradiated during thermal degradation and the oxidation products checked by chemiluminescence [CL] and Fourier transform infrared spectra [FT-IR]. The same clear inhibition of the radical oxidation of alkanes is recorded. A quantum chemistry modeling of these results is performed and a mechanism involving a new type of Rydberg macromolecular systems with implications for biology and medicine is suggested. PMID:20934350

  15. Free Radical Reactions in Food.

    ERIC Educational Resources Information Center

    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…

  16. Measurements of homogeneous nucleation in normal-alkanes

    NASA Astrophysics Data System (ADS)

    Kraack, H.; Sirota, E. B.; Deutsch, M.

    2000-04-01

    The homogeneous nucleation of normal-alkanes with carbon numbers 15⩽n⩽60 is studied by scanning calorimetry, using the droplet technique. Pure, nonemulsified samples show near-zero undercoolings below the melting point, Tm, except for both ends of the n-range, where undercoolings ΔT of up to 2 °C are observed. The emulsions have much larger undercoolings. The relative undercoolings show three regimes: A fast decreasing one, up to n=17, an anomalously low constant one, ΔT/Tm≈0.04, for 17⩽n⩽30, and a gradually increasing one for 32⩽n⩽60. A value of ΔT/Tm≈0.086 is reached at n=60. The connections of these results with the bulk rotator phases and the recently discovered surface freezing effect are discussed. Strong intrinsic interrelations among these are indicated.

  17. Morphological Transformations in Solid Domains of Alkanes on Surfactant Solutions.

    PubMed

    Matsubara, Hiroki; Takaichi, Tetsumasa; Takiue, Takanori; Aratono, Makoto; Toyoda, Aya; Iimura, Kenichi; Ash, Philip A; Bain, Colin D

    2013-03-21

    Alkanes on surfactant solutions can form three distinct phases at the air-solution interface, a liquid phase (L), a solid monolayer phase (S1), and a hybrid bilayer phase (S2). Phase coexistence between any two, or all three, of these phases has been observed by Brewster angle microscopy of tetradecane, hexadecane, and their mixtures on solutions of tetradecyltrimethylammonium bromide. The morphologies of the domains depend on the competition between line tension and electrostatic interactions, which are essentially different depending on the pair of phases in contact. Domains of S1 in the L phase are long and thin; however, long, thin domains of L in an S1 phase are not stable but break up into a string of small circular domains. The bilayer S2 domains are always circular, owing to the dominance of line tension on the morphology. PMID:26291344

  18. Thermal analysis of n-alkane phase change material mixtures

    SciTech Connect

    Chio, Y.I.; Choi, E.; Lorsch, H.G.

    1991-03-31

    Tests were performed to characterize the thermal behavior of it number of n-alkanes to be used as phase change materials (PCMs) in district cooling applications. Hexadecane and tetradecane were mixed in different fractions, and their thermal behavior was experimentally evaluated. Test results for melting temperature and fusion energy for laboratory grade hexadecane and tetradecane showed good agreement with datain the literature. However, values for commercial grade hexadecane were found to be considerably lower. In the range of temperatures of interest for district cooling, mixtures of tetradecane and hexadecane can be treated as homogeneous substances. However, their heats of fusion are slightly lower than those of the pure substances. Their melting temperatures are also lower by an amount that can be predicted.

  19. Environmental chemistry and toxicology of polychlorinated n-alkanes.

    PubMed

    Tomy, G T; Fisk, A T; Westmore, J B; Muir, D C

    1998-01-01

    Polychlorinated-n-alkanes (PCAs) or chlorinated paraffins consist of C10 to C30 n-alkanes with chlorine content from 30% to 70% by mass. PCAs are used as high-temperature lubricants, plasticizers, flame retardants, and additives in adhesives, paints, rubber, and sealants. This review presents the existing data on the environmental chemistry and toxicology of PCAs and a preliminary exposure and risk assessment. There is limited information on the levels, fate, or biological effects of PCAs in the environment. This results both from the difficulty associated with quantifying PCAs, because of the complexity inherent to commercial formulations, and from the limited knowledge of their physicochemical properties and biodegradation rates. There are indications that PCAs are widespread environmental contaminants at ng/L levels in surface waters and ng/g (wet wt) levels in biota. However, environmental measurements of PCAs are very limited in the U.S. and Canada, and are only slightly more detailed in western Europe. Assuming that reported water concentrations are mainly caused by the short chain (C10-C13) compounds, aquatic organisms may be at risk from exposure to PCAs. Fugacity level II modeling for two representative PCAs, using the best available physicochemical property data and estimated degradation rates, suggested that C16C24Cl10 would achieve higher concentrations in biota, sediment, and soil than C12H20Cl6 because of slower degradation rates and lower water solubility. Environmental residence time of C16H24Cl10 is estimated to be 520 d compared to 210 d for C12H20Cl6. Future studies will require better analytical methods and reference materials certified for PCA content. Additional data are needed to evaluate exposure of biota to PCAs in the environment, particularly in light of their continued production and usage around the globe. PMID:9751033

  20. The Cation-π Interaction

    PubMed Central

    DOUGHERTY, DENNIS A.

    2014-01-01

    CONSPECTUS The chemistry community now recognizes the cation-π interaction as a major force for molecular recognition, joining the hydrophobic effect, the hydrogen bond, and the ion pair in determining macromolecular structure and drug-receptor interactions. This Account provides the author’s perspective on the intellectual origins and fundamental nature of the cation-π interaction. Early studies on cyclophanes established that water-soluble, cationic molecules would forgo aqueous solvation to enter a hydrophobic cavity if that cavity was lined with π systems. Important gas phase studies established the fundamental nature of the cation-π interaction. The strength of the cation-π interaction – Li+ binds to benzene with 38 kcal/mol of binding energy; NH4+ with 19 kcal/mol– distinguishes it from the weaker polar-π interactions observed in the benzene dimer or water-benzene complexes. In addition to the substantial intrinsic strength of the cation-π interaction in gas phase studies, the cation-π interaction remains energetically significant in aqueous media and under biological conditions. Many studies have shown that cation-π interactions can enhance binding energies by 2 – 5 kcal/mol, making them competitive with hydrogen bonds and ion pairs in drug-receptor and protein-protein interactions. As with other noncovalent interactions involving aromatic systems, the cation-π interaction includes a substantial electrostatic component. The six (four) Cδ−–Hδ+ bond dipoles of a molecule like benzene (ethylene) combine to produce a region of negative electrostatic potential on the face of the π system. Simple electrostatics facilitate a natural attraction of cations to the surface. The trend for (gas phase) binding energies is Li+>Na+>K+>Rb+: as the ion gets larger the charge is dispersed over a larger sphere and binding interactions weaken, a classical electrostatic effect. On other hand, polarizability does not define these interactions. Cyclohexane

  1. Measuring long chain alkanes in diesel engine exhaust by thermal desorption PTR-MS

    NASA Astrophysics Data System (ADS)

    Erickson, M. H.; Gueneron, M.; Jobson, B. T.

    2013-07-01

    A method using thermal desorption sampling and analysis by PTR-MS to measure long chain alkanes (C12-C18) and other larger organics associated with diesel engine exhaust emissions is described. Long chain alkanes undergo dissociative proton transfer reactions forming a series of fragment ions with formula CnH2n+1. The PTR-MS is insensitive to n-alkanes less than C8 but displays an increasing sensitivity for larger alkanes. Fragment ion distribution and sensitivity is a function of drift conditions. At 80 Td the most abundant ion fragments from C10 to C16 n-alkanes were m/z 57, 71 and 85. The mass spectrum of gasoline and diesel fuel at 80 Td displayed ion group patterns that can be related to known fuel constituents, such as alkanes, alkylbenzenes and cycloalkanes, and other compound groups that are inferred from molecular weight distributions such as dihydronapthalenes and naphthenic monoaromatics. It is shown that thermal desorption sampling of gasoline and diesel engine exhausts at 80 Td allows for discrimination against light alkanes and alkenes which are a major constituent of both exhausts, allowing for quantification of higher molecular weight alkanes from the abundance of CnH2n+1 fragment ions. Using this approach, the molar abundance of C12-C18 alkanes in diesel engine exhaust was found to be 75% that of the total C1-C4 alkylbenzene abundance. While the PTR-MS mass spectra of gasoline and diesel exhaust looked similar, the abundance of higher molecular weight compounds relative to that of C4-alkylbenzenes was much greater in diesel engine exhaust. The abundance patterns of compounds determined by thermal desorption sampling may allow for emission profiles to be developed to better quantify the relative contributions of diesel and gasoline exhaust emissions of larger organic compounds to urban air concentrations.

  2. Light alkane conversion processes - Suprabiotic catalyst systems for selective oxidation of light alkane gases to fuel oxygenates.

    SciTech Connect

    Lyons, J.E.

    1992-07-01

    The objective of the work presented in this paper is to develop new, efficient catalysts for the selective transformation of the light alkanes in natural gas to alcohols for use as liquid transportation fuels, fuel precursors and chemical products. There currently exists no DIRECT one-step catalytic air-oxidation process to convert these substrates to alcohols. Such a one-step route would represent superior useful technology for the utilization of natural gas and similar refinery-derived light hydrocarbon streams. Processes for converting natural gas or its components (methane, ethane, propane, and the butanes) to alcohols for use as motor fuels, fuel additives or fuel precursors will not only add a valuable alternative to crude oil but will produce a clean-burning, high octane alternative to conventional gasoline.

  3. Light alkane conversion processes - Suprabiotic catalyst systems for selective oxidation of light alkane gases to fuel oxygenates

    SciTech Connect

    Lyons, J.E.

    1992-01-01

    The objective of the work presented in this paper is to develop new, efficient catalysts for the selective transformation of the light alkanes in natural gas to alcohols for use as liquid transportation fuels, fuel precursors and chemical products. There currently exists no DIRECT one-step catalytic air-oxidation process to convert these substrates to alcohols. Such a one-step route would represent superior useful technology for the utilization of natural gas and similar refinery-derived light hydrocarbon streams. Processes for converting natural gas or its components (methane, ethane, propane, and the butanes) to alcohols for use as motor fuels, fuel additives or fuel precursors will not only add a valuable alternative to crude oil but will produce a clean-burning, high octane alternative to conventional gasoline.

  4. Diarylferrocene tweezers for cation binding.

    PubMed

    Lima, Carlos F R A C; Fernandes, Ana M; Melo, André; Gonçalves, Luís M; Silva, Artur M S; Santos, Luís M N B F

    2015-10-01

    The host-guest chemistry of ferrocene derivatives was explored by a combined experimental and theoretical study. Several 1-arylferrocenes and 1,1'-diarylferrocenes were synthesized by the Suzuki-Miyaura cross-coupling reaction. The ability of these compounds to bind small cations in the gas phase was investigated experimentally by electrospray ionization mass spectrometry (ESI-MS). The results evidenced a noticeable ability of all 1,1'-diarylferrocenes studied to bind cations, while the same was not observed for the corresponding 1-arylferrocenes nor ferrocene. The 1,1'-diarylferrocenecation relative interaction energies were evaluated by ESI-MS and quantum chemical calculations and showed that cation binding in these systems follows electrostatic trends. It was found that, due to their unique molecular shape and smooth torsional potentials, 1,1'-diarylferrocenes can act as molecular tweezers of small-sized cations in the gas phase. PMID:26309143

  5. Prototheca zopfii Kruger strain UMK-13 growth on acetate or n-alkanes

    SciTech Connect

    Koenig, D.W.; Ward, H.B.

    1983-01-01

    A new strain of Prototheca zopfii Kruger was grown on acetate or on pure n-alkanes. A maximum acetate-supported exponential growth of 12 divisions day/sup -1/ occurred at pH 5 and 30/sup 0/C. At 25/sup 0/C, growth on n-alkanes was almost as fast, but no growth occurred at 30/sup 0/C. After 3 days at 25/sup 0/C, 34 to 45% of the n-alkanes had been removed, whereas at 21/sup 0/C and slower growth, utilization was twofold greater after 15 days. Rates of growth and utilization increased markedly after a point of sudden emulsification.

  6. Photochemical dimerization and functionalization of alkanes, ethers, primary and secondary alcohols, phosphine oxides and silanes

    DOEpatents

    Crabtree, Robert H.; Brown, Stephen H.

    1989-01-01

    The space-time yield and/or the selectivity of the photochemical dimerization of alkanes, ethers, primary and secondary alcohols, phosphine oxides and primary, secondary and tertiary silanes with Hg and U.V. light is enhanced by refluxing the substrate in the irradiated reaction zone at a temperature at which the dimer product condenses and remains condensed promptly upon its formation. Cross-dimerization of the alkanes, ethers and silanes with primary alcohols is disclosed, as is the functionalization to aldehydes of the alkanes with carbon monoxide.

  7. Photochemical dimerization and functionalization of alkanes, ethers, primary and secondary alcohols, phosphine oxides and silanes

    DOEpatents

    Crabtree, R.H.; Brown, S.H.

    1989-10-17

    The space-time yield and/or the selectivity of the photochemical dimerization of alkanes, ethers, primary and secondary alcohols, phosphine oxides and primary, secondary and tertiary silanes with Hg and U.V. light is enhanced by refluxing the substrate in the irradiated reaction zone at a temperature at which the dimer product condenses and remains condensed promptly upon its formation. Cross-dimerization of the alkanes, ethers and silanes with primary alcohols is disclosed, as is the functionalization to aldehydes of the alkanes with carbon monoxide.

  8. Adsorption and dissociation kinetics of alkanes on CaO(100)

    NASA Astrophysics Data System (ADS)

    Chakradhar, A.; Liu, Y.; Schmidt, J.; Kadossov, E.; Burghaus, U.

    2011-08-01

    The adsorption kinetics of ethane, butane, pentane, and hexane on CaO(100) have been studied by multi-mass thermal desorption (TDS) spectroscopy. The sample cleanliness was checked by Auger electron spectroscopy. A molecular and dissociative adsorption pathway was evident for the alkanes, except for ethane, which does not undergo bond activation. Two TDS peaks appeared when recording the parent mass, which are assigned to different adsorption sites/configurations of the molecularly adsorbed alkanes. Bond activation leads to desorption of hydrogen and several alkane fragments assigned to methane and ethylene formation. Only one TDS feature is seen in this case. Formation of carbon residuals was absent.

  9. Characterization of the Medium- and Long-Chain n-Alkanes Degrading Pseudomonas aeruginosa Strain SJTD-1 and Its Alkane Hydroxylase Genes

    PubMed Central

    Liu, Huan; Xu, Jing; Liang, Rubing; Liu, Jianhua

    2014-01-01

    A gram-negative aliphatic hydrocarbon-degrading bacterium SJTD-1 isolated from oil-contaminated soil was identified as Pseudomonas aeruginosa by comparative analyses of the 16S rRNA sequence, phenotype, and physiological features. SJTD-1 could efficiently mineralize medium- and long-chain n-alkanes (C12-C30) as its sole carbon source within seven days, showing the most optimal growth on n-hexadecane, followed by n-octadecane, and n-eicosane. In 36 h, 500 mg/L of tetradecane, hexadecane, and octadecane were transformed completely; and 2 g/L n-hexadecane was degraded to undetectable levels within 72 h. Two putative alkane-degrading genes (gene 3623 and gene 4712) were characterized and our results indicated that their gene products were rate-limiting enzymes involved in the synergetic catabolism of C12–C16 alkanes. On the basis of bioinformatics and transcriptional analysis, two P450 monooxygenases, along with a putative AlmA-like oxygenase, were examined. Genetically defective mutants lacking the characteristic alkane hydroxylase failed to degrade n-octadecane, thereby suggesting a different catalytic mechanism for the microbial transformation of alkanes with chain lengths over C18. PMID:25165808

  10. Characterization of the medium- and long-chain n-alkanes degrading Pseudomonas aeruginosa strain SJTD-1 and its alkane hydroxylase genes.

    PubMed

    Liu, Huan; Xu, Jing; Liang, Rubing; Liu, Jianhua

    2014-01-01

    A gram-negative aliphatic hydrocarbon-degrading bacterium SJTD-1 isolated from oil-contaminated soil was identified as Pseudomonas aeruginosa by comparative analyses of the 16S rRNA sequence, phenotype, and physiological features. SJTD-1 could efficiently mineralize medium- and long-chain n-alkanes (C12-C30) as its sole carbon source within seven days, showing the most optimal growth on n-hexadecane, followed by n-octadecane, and n-eicosane. In 36 h, 500 mg/L of tetradecane, hexadecane, and octadecane were transformed completely; and 2 g/L n-hexadecane was degraded to undetectable levels within 72 h. Two putative alkane-degrading genes (gene 3623 and gene 4712) were characterized and our results indicated that their gene products were rate-limiting enzymes involved in the synergetic catabolism of C12-C16 alkanes. On the basis of bioinformatics and transcriptional analysis, two P450 monooxygenases, along with a putative AlmA-like oxygenase, were examined. Genetically defective mutants lacking the characteristic alkane hydroxylase failed to degrade n-octadecane, thereby suggesting a different catalytic mechanism for the microbial transformation of alkanes with chain lengths over C18. PMID:25165808

  11. Calmodulin Methionine Residues are Targets For One-Electron Oxidation by Hydroxyl Radicals: Formation of S therefore N three-electron bonded Radical Complexes

    SciTech Connect

    Nauser, Thomas; Jacoby, Michael E.; Koppenol, Willem H.; Squier, Thomas C.; Schoneich, Christian

    2005-02-01

    The one-electron (1e) oxidation of organic sulfides and methionine (Met) constitutes an important reaction mechanism in vivo.1,2 Evidence for a Cu(II)-catalyzed oxidation of Met35 in the Alzheimer's disease -amyloid peptide was obtained,3 and, based on theoretical studies, Met radical cations were proposed as intermediates.4 In the structure of -amyloid peptide, the formation of Met radical cations appears to be facilitated by a preexisting close sulfur-oxygen (S-O) interaction between the Met35 sulfur and the carbonyl oxygen of the peptide bond C-terminal to Ile31.5 Substitution of Ile31 with Pro31 abolishes this S-O interaction,5 significantly reducing the ability of -amyloid to reduce Cu(II), and converts the neurotoxic wild-type -amyloid into a non-toxic peptide.6 The preexisting S-O bond characterized for wild-type -amyloid suggests that electron transfer from Met35 to Cu(II) is supported through stabilization of the Met radical cation by the electron-rich carbonyl oxygen, generating an SO-bonded7 sulfide radical cation (Scheme 1, reaction 1).5

  12. Numerical and experimental studies of ethanol flames and autoignition theory for higher alkanes

    NASA Astrophysics Data System (ADS)

    Saxena, Priyank

    oxides of nitrogen and other potential pollutants in similar partially premixed flames of ethanol and other fuels for comparison purposes. The computational results with the present mechanism are in reasonable agreement with experiment and perform as well as or better than predictions of other, generally much larger, mechanisms available in the literature. Further research is, however, warranted for providing additional and more stringent tests of the mechanism and its predictions, especially for condition at higher pressures. The second part of the dissertation consists of analytical study of autoignition of higher alkane fuels. It is shown that, above about 1000 K, ignition delay times for propane and all higher alkanes, as well as for a number of other fuels, can be calculated well by employing rate parameters of only three types of elementary steps, namely CmHn+HO2→C mHn-1+H2O2, H2O2+M→2OH+M and 2HO2→H2O2+O2, only the first of which is fuel-specific, the other two clearly being common to all fuels. The prediction of this remarkably simple result relies on a steady-state approximation for HO2, as well as steady states for more active radicals during induction. The resulting approximation to the chemistry exhibits a slow, finite-rate buildup of H2O2 and removal of fuel during the induction period. The criterion employed for termination of the induction period is the complete depletion of the original fuel subject to the approximations introduced. Numerical comparisons of the ignition-time formula with the experiments show that the predictions work well not only for higher alkanes but also for propene and JP-10. The analytical approximation thus produces reasonable results for a wide range of fuels. These results provide a new perspective on high-temperature autoignition chemistry and a general means of easily estimating ignition times of the large number of fuels of practical importance.

  13. The tricarbonylchromium template for stereocontrol in radical reactions of arenes.

    PubMed

    Merlic, C A; Walsh, J C

    2001-04-01

    Chromium tricarbonyl complexed aryl aldeyhydes and ketones underwent Sm(II)-promoted radical lactone formation in the presence of alpha,beta-unsaturated esters to produce diastereomerically pure lactones in good yields. The completely diastereoselective lactone formation involves capture of the benzylic ketyl radical by the ester anti to the chromium tricarbonyl moiety. The relative stereochemistry of the lactone and chromium tricarbonyl moieties was proven by X-ray crystallography and supports the proposed mechanism. Enantiopure chromium tricarbonyl complexed arenes afforded single enantiomers when subjected to Sm(II)-promoted radical lactone formation condiditions. The enantio- and diastereomerically pure chromium tricarbonyl complexed lactones were subsequently treated with BF3.OEt2 to generate a mixture of diastereomers via Lewis acid promoted chromium tricabonyl directed cationic rearrangement. The diastereomers were separated and individually decomplexed with I2 to afford both of the corresponding chromium-free enantiomerically pure lactones starting from a single enantiomerically pure chromium tricarbonyl complex. PMID:11281765

  14. Radical School Reform.

    ERIC Educational Resources Information Center

    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…

  15. Liquid alkanes with targeted molecular weights from biomass-derived carbohydrates.

    PubMed

    West, Ryan M; Liu, Zhen Y; Peter, Maximilian; Dumesic, James A

    2008-01-01

    Liquid transportation fuels must burn cleanly and have high energy densities, criteria that are currently fulfilled by petroleum, a non-renewable resource, the combustion of which leads to increasing levels of atmospheric CO(2). An attractive approach for the production of transportation fuels from renewable biomass resources is to convert carbohydrates into alkanes with targeted molecular weights, such as C(8)-C(15) for jet-fuel applications. Targeted n-alkanes can be produced directly from fructose by an integrated process involving first the dehydration of this C(6) sugar to form 5-hydroxymethylfurfural, followed by controlled formation of C-C bonds with acetone to form C(9) and C(15) compounds, and completed by hydrogenation and hydrodeoxygenation reactions to form the corresponding n-alkanes. Analogous reactions are demonstrated starting with 5-methylfurfural or 2-furaldehyde, with the latter leading to C(8) and C(13) n-alkanes. PMID:18702136

  16. Photocatalytic acceptorless alkane dehydrogenation: scope, mechanism, and conquering deactivation with carbon dioxide.

    PubMed

    Chowdhury, Abhishek Dutta; Julis, Jennifer; Grabow, Kathleen; Hannebauer, Bernd; Bentrup, Ursula; Adam, Martin; Franke, Robert; Jackstell, Ralf; Beller, Matthias

    2015-01-01

    Alkane dehydrogenation is of special interest for basic science but also offers interesting opportunities for industry. The existing dehydrogenation methodologies make use of heterogeneous catalysts, which suffer from harsh reaction conditions and a lack of selectivity, whereas homogeneous methodologies rely mostly on unsolicited waste generation from hydrogen acceptors. Conversely, acceptorless photochemical alkane dehydrogenation in the presence of trans-Rh(PMe3 )2 (CO)Cl can be regarded as a more benign and atom efficient alternative. However, this methodology suffers from catalyst deactivation over time. Herein, we provide a detailed investigation of the trans-Rh(PMe3 )2 (CO)Cl-photocatalyzed alkane dehydrogenation using spectroscopic and theoretical investigations. These studies inspired us to utilize CO2 to prevent catalyst deactivation, which leads eventually to improved catalyst turnover numbers in the dehydrogenation of alkanes that include liquid organic hydrogen carriers. PMID:25346450

  17. Draft Genome Sequence of the Versatile Alkane-Degrading Bacterium Aquabacterium sp. Strain NJ1

    PubMed Central

    Shiwa, Yuh; Yoshikawa, Hirofumi; Zylstra, Gerben J.

    2014-01-01

    The draft genome sequence of a soil bacterium, Aquabacterium sp. strain NJ1, capable of utilizing both liquid and solid alkanes, was deciphered. This is the first report of an Aquabacterium genome sequence. PMID:25477416

  18. Alkane oxidation with porphyrins and metal complexes thereof having haloalkyl side chains

    DOEpatents

    Wijesekera, Tilak; Lyons, James E.; Ellis, Jr., Paul E.; Bhinde, Manoj V.

    1998-01-01

    Transition metal complexes of meso-haloalkylporphyrins, wherein the haloalkyl groups contain 2 to 8 carbon atoms have been found to be highly effective catalysts for oxidation of alkanes and for the decomposition of hydroperoxides.

  19. Alkane oxidation with porphyrins and metal complexes thereof having haloalkyl side chains

    DOEpatents

    Wijesekera, T.; Lyons, J.E.; Ellis, P.E. Jr.; Bhinde, M.V.

    1998-06-23

    Transition metal complexes of meso-haloalkylporphyrins are disclosed, wherein the haloalkyl groups contain 2 to 8 carbon atoms have been found to be highly effective catalysts for oxidation of alkanes and for the decomposition of hydroperoxides. 7 figs.

  20. Modeling the Role of Alkanes, Polycyclic Aromatic Hydrocarbons, and Their Oligomers in Secondary Organic Aerosol Formation

    EPA Science Inventory

    A computationally efficient method to treat secondary organic aerosol (SOA) from various length and structure alkanes as well as SOA from polycyclic aromatic hydrocarbons (PAHs) is implemented in the Community Multiscale Air Quality (CMAQ) model to predict aerosol concentrations ...

  1. Conformational problem of alkanes in liquid crystals by NMR spectroscopy: a mini-review.

    PubMed

    Weber, Adrian C J; Chen, Daniel H J

    2014-10-01

    Recent discoveries of the role of alkane flexibility in determining liquid-crystal behaviour are surveyed. With the impetus for understanding the alkane conformational problem established, recent model dependent (1)H NMR work on the topic will be reviewed where progress is made but the need to circumvent models eventually becomes evident. A closer look at the rigid basic units of alkanes will provide the way forward where it is shown that the orientational ordering and anisotropic potentials of these molecules dissolved in liquid crystals scale with each other. Once this relationship is established, a series of works using anisotropic and isotropic (1)H NMR spectroscopy to study alkane conformational statistics will be covered, wherein the influence of the gas, isotropic condensed and anisotropic condensed phases will be described. PMID:25142124

  2. Regulation of the Alkane Hydroxylase CYP153 Gene in a Gram-Positive Alkane-Degrading Bacterium, Dietzia sp. Strain DQ12-45-1b

    PubMed Central

    Liang, Jie-Liang; JiangYang, Jing-Hong

    2015-01-01

    CYP153, one of the most common medium-chain n-alkane hydroxylases belonging to the cytochrome P450 superfamily, is widely expressed in n-alkane-degrading bacteria. CYP153 is also thought to cooperate with AlkB in degrading various n-alkanes. However, the mechanisms regulating the expression of the protein remain largely unknown. In this paper, we studied CYP153 gene transcription regulation by the potential AraC family regulator (CypR) located upstream of the CYP153 gene cluster in a broad-spectrum n-alkane-degrading Gram-positive bacterium, Dietzia sp. strain DQ12-45-1b. We first identified the transcriptional start site and the promoter of the CYP153 gene cluster. Sequence alignment of upstream regions of CYP153 gene clusters revealed high conservation in the −10 and −35 regions in Actinobacteria. Further analysis of the β-galactosidase activity in the CYP153 gene promoter-lacZ fusion cell indicated that the CYP153 gene promoter was induced by n-alkanes comprised of 8 to 14 carbon atoms, but not by derived decanol and decanic acid. Moreover, we constructed a cypR mutant strain and found that the CYP153 gene promoter activities and CYP153 gene transcriptional levels in the mutant strain were depressed compared with those in the wild-type strain in the presence of n-alkanes, suggesting that CypR served as an activator for the CYP153 gene promoter. By comparing CYP153 gene arrangements in Actinobacteria and Proteobacteria, we found that the AraC family regulator is ubiquitously located upstream of the CYP153 gene, suggesting its universal regulatory role in CYP153 gene transcription. We further hypothesize that the observed mode of CYP153 gene regulation is shared by many Actinobacteria. PMID:26567302

  3. Biodegradation of variable-chain-length n-alkanes in Rhodococcus opacus R7 and the involvement of an alkane hydroxylase system in the metabolism

    PubMed Central

    2014-01-01

    Rhodococcus opacus R7 is a Gram-positive bacterium isolated from a polycyclic aromatic hydrocarbon contaminated soil for its versatile metabolism; indeed the strain is able to grow on naphthalene, o-xylene, and several long- and medium-chain n-alkanes. In this work we determined the degradation of n-alkanes in Rhodococcus opacus R7 in presence of n-dodecane (C12), n-hexadecane (C16), n-eicosane (C20), n-tetracosane (C24) and the metabolic pathway in presence of C12. The consumption rate of C12 was 88%, of C16 was 69%, of C20 was 51% and of C24 it was 78%. The decrement of the degradation rate seems to be correlated to the length of the aliphatic chain of these hydrocarbons. On the basis of the metabolic intermediates determined by the R7 growth on C12, our data indicated that R. opacus R7 metabolizes medium-chain n-alkanes by the primary alcohol formation. This represents a difference in comparison with other Rhodococcus strains, in which a mixture of the two alcohols was observed. By GC-MSD analysis we also identified the monocarboxylic acid, confirming the terminal oxidation. Moreover, the alkB gene cluster from R. opacus R7 was isolated and its involvement in the n-alkane degradation system was investigated by the cloning of this genomic region into a shuttle-vector E. coli-Rhodococcus to evaluate the alkane hydroxylase activity. Our results showed an increased biodegradation of C12 in the recombinant strain R. erythropolis AP (pTipQT1-alkR7) in comparison with the wild type strain R. erythropolis AP. These data supported the involvement of the alkB gene cluster in the n-alkane degradation in the R7 strain. PMID:25401074

  4. Tyrosyl Radicals in Dehaloperoxidase

    PubMed Central

    Dumarieh, Rania; D'Antonio, Jennifer; Deliz-Liang, Alexandria; Smirnova, Tatyana; Svistunenko, Dimitri A.; Ghiladi, Reza A.

    2013-01-01

    Dehaloperoxidase (DHP) from Amphitrite ornata, having been shown to catalyze the hydrogen peroxide-dependent oxidation of trihalophenols to dihaloquinones, is the first oxygen binding globin that possesses a biologically relevant peroxidase activity. The catalytically competent species in DHP appears to be Compound ES, a reactive intermediate that contains both a ferryl heme and a tyrosyl radical. By simulating the EPR spectra of DHP activated by H2O2, Thompson et al. (Thompson, M. K., Franzen, S., Ghiladi, R. A., Reeder, B. J., and Svistunenko, D. A. (2010) J. Am. Chem. Soc. 132, 17501–17510) proposed that two different radicals, depending on the pH, are formed, one located on either Tyr-34 or Tyr-28 and the other on Tyr-38. To provide additional support for these simulation-based assignments and to deduce the role(s) that tyrosyl radicals play in DHP, stopped-flow UV-visible and rapid-freeze-quench EPR spectroscopic methods were employed to study radical formation in DHP when three tyrosine residues, Tyr-28, Tyr-34, and Tyr-38, were replaced either individually or in combination with phenylalanines. The results indicate that radicals form on all three tyrosines in DHP. Evidence for the formation of DHP Compound I in several tyrosine mutants was obtained. Variants that formed Compound I showed an increase in the catalytic rate for substrate oxidation but also an increase in heme bleaching, suggesting that the tyrosines are necessary for protecting the enzyme from oxidizing itself. This protective role of tyrosines is likely an evolutionary adaptation allowing DHP to avoid self-inflicted damage in the oxidative environment. PMID:24100039

  5. The Number of High-Energy Bands in the Photoelectron Spectrum of Alkanes

    NASA Astrophysics Data System (ADS)

    Merris, Russell; Gutman, Ivan

    2000-12-01

    It was observed that within the Bieri-Dill-Heilbronner-Schmelzer model for the calculation of the ion-ization energies of alkanes CnH2n+2, there are exactly n C2s -electron energy levels lying below the degenerate α-ß manifold. We now show that, indeed, this regularity is obeyed by practically all alkane species. Exceptions do exist, but they must possess a (chemically infeasible) group of more than six mutually connected quaternary carbon atoms.

  6. Measuring long chain alkanes in diesel engine exhaust by thermal desorption PTR-MS

    NASA Astrophysics Data System (ADS)

    Erickson, M. H.; Gueneron, M.; Jobson, B. T.

    2014-01-01

    A method using thermal desorption sampling and analysis by proton transfer reaction mass spectrometry (PTR-MS) to measure long chain alkanes (C12-C18) and other larger organics associated with diesel engine exhaust emissions is described. Long chain alkanes undergo dissociative proton transfer reactions forming a series of fragment ions with formula CnH2n+1. The PTR-MS is insensitive to n-alkanes less than C8 but displays an increasing sensitivity for larger alkanes. Fragment ion distribution and sensitivity is a function of drift conditions. At 80 Td the most abundant ion fragments from C10 to C16 n-alkanes were m/z 57, 71 and 85. The mass spectrum of gasoline and diesel fuel at 80 Td displayed ion group patterns that can be related to known fuel constituents, such as alkanes, alkylbenzenes and cycloalkanes, and other compound groups that are inferred from molecular weight distributions such as dihydronapthalenes and naphthenic monoaromatics. It is shown that thermal desorption sampling of gasoline and diesel engine exhausts at 80 Td allows for discrimination against volatile organic compounds, allowing for quantification of long chain alkanes from the abundance of CnH2n+1 fragment ions. The total abundance of long chain alkanes in diesel engine exhaust was measured to be similar to the total abundance of C1-C4 alkylbenzene compounds. The abundance patterns of compounds determined by thermal desorption sampling may allow for emission profiles to be developed to better quantify the relative contributions of diesel and gasoline exhaust emissions on organic compounds concentrations in urban air.

  7. Kinetics of CH(X 2Pi) radical reactions with cyclopropane, cyclopentane, and cyclohexane

    NASA Technical Reports Server (NTRS)

    Zabarnick, S.; Fleming, J. W.; Lin, M. C.

    1988-01-01

    Rate constants have been obtained for CH(X 2Pi) radical reactions with cyclopropane, cyclopentane, and cyclohexane in order to establish the rate of CH insertion into secondary C-H bonds in alkanes. Data indicate that there is no measurable dependence on photolysis laser energy. The reactions all exhibited rate constants that decrease with increasing temperature. It is suggested that a possible set of pathways for the cycloalkane reactions is a ring-opening process where the excited adduct decomposes to a hydrogen atom and a diene.

  8. Synthetic Utilization of α-Aminoalkyl Radicals and Related Species in Visible Light Photoredox Catalysis.

    PubMed

    Nakajima, Kazunari; Miyake, Yoshihiro; Nishibayashi, Yoshiaki

    2016-09-20

    Single electron oxidation of amines provides an efficient way to access synthetically useful α-aminoalkyl radicals as reactive intermediates. After the single electron oxidation of amines, fragmentation of the resulting radical cations proceeds to give the α-aminoalkyl radicals along with generation of a proton. In the synthetic utilization of the α-aminoalkyl radicals, precise control of single electron transfer is essential, because further oxidation of the α-aminoalkyl radicals occurs more easily than the starting amines and the α-aminoalkyl radicals are converted into the corresponding iminium ions. As a result, photoinduced single electron transfer is quite attractive in the synthetic utilization of the α-aminoalkyl radicals. Recently, visible light-photoredox catalysis using transition metal-polypyridyl complexes and other dyes as catalysts has attracted considerable attention, where useful molecular transformations can be achieved through the single electron transfer process between the excited catalysts and substrates. In this context, MacMillan et al. ( Science 2011, 334 , 1114 , DOI: 10.1126/science.1213920 ) reported an aromatic substitution reaction of cyanoarenes with amines, where α-aminoalkyl radicals work as key reactive intermediates. Pandey and Reiser et al. ( Org. Lett. 2012 , 14 , 672 , DOI: 10.1021/ol202857t ) and our group ( Nishibayashi et al. J. Am. Chem. Soc. 2012 , 134 , 3338 , DOI: 10.1021/ja211770y ) independently reported reactions of amines with α,β-unsaturated carbonyl compounds, where addition of α-aminoalkyl radicals to alkenes is a key step. After these earliest examples, nowadays, a variety of transformations using the α-aminoalkyl radicals as reactive intermediates have been reported by many groups. The α-aminoalkyl radicals are usually produced from amines by single electron oxidation and the subsequent deprotonation of the C-H bond adjacent to the nitrogen atom. In addition, the α-aminoalkyl radicals are also

  9. Synthetic Utilization of α-Aminoalkyl Radicals and Related Species in Visible Light Photoredox Catalysis.

    PubMed

    Nakajima, Kazunari; Miyake, Yoshihiro; Nishibayashi, Yoshiaki

    2016-09-20

    Single electron oxidation of amines provides an efficient way to access synthetically useful α-aminoalkyl radicals as reactive intermediates. After the single electron oxidation of amines, fragmentation of the resulting radical cations proceeds to give the α-aminoalkyl radicals along with generation of a proton. In the synthetic utilization of the α-aminoalkyl radicals, precise control of single electron transfer is essential, because further oxidation of the α-aminoalkyl radicals occurs more easily than the starting amines and the α-aminoalkyl radicals are converted into the corresponding iminium ions. As a result, photoinduced single electron transfer is quite attractive in the synthetic utilization of the α-aminoalkyl radicals. Recently, visible light-photoredox catalysis using transition metal-polypyridyl complexes and other dyes as catalysts has attracted considerable attention, where useful molecular transformations can be achieved through the single electron transfer process between the excited catalysts and substrates. In this context, MacMillan et al. ( Science 2011, 334 , 1114 , DOI: 10.1126/science.1213920 ) reported an aromatic substitution reaction of cyanoarenes with amines, where α-aminoalkyl radicals work as key reactive intermediates. Pandey and Reiser et al. ( Org. Lett. 2012 , 14 , 672 , DOI: 10.1021/ol202857t ) and our group ( Nishibayashi et al. J. Am. Chem. Soc. 2012 , 134 , 3338 , DOI: 10.1021/ja211770y ) independently reported reactions of amines with α,β-unsaturated carbonyl compounds, where addition of α-aminoalkyl radicals to alkenes is a key step. After these earliest examples, nowadays, a variety of transformations using the α-aminoalkyl radicals as reactive intermediates have been reported by many groups. The α-aminoalkyl radicals are usually produced from amines by single electron oxidation and the subsequent deprotonation of the C-H bond adjacent to the nitrogen atom. In addition, the α-aminoalkyl radicals are also

  10. Two distinct monooxygenases for alkane oxidation in Nocardioides sp. strain CF8.

    PubMed

    Hamamura, N; Yeager, C M; Arp, D J

    2001-11-01

    Alkane monooxygenases in Nocardioides sp. strain CF8 were examined at the physiological and genetic levels. Strain CF8 can utilize alkanes ranging in chain length from C(2) to C(16). Butane degradation by butane-grown cells was strongly inhibited by allylthiourea, a copper-selective chelator, while hexane-, octane-, and decane-grown cells showed detectable butane degradation activity in the presence of allylthiourea. Growth on butane and hexane was strongly inhibited by 1-hexyne, while 1-hexyne did not affect growth on octane or decane. A specific 30-kDa acetylene-binding polypeptide was observed for butane-, hexane-, octane-, and decane-grown cells but was absent from cells grown with octane or decane in the presence of 1-hexyne. These results suggest the presence of two monooxygenases in strain CF8. Degenerate primers designed for PCR amplification of genes related to the binuclear-iron-containing alkane hydroxylase from Pseudomonas oleovorans were used to clone a related gene from strain CF8. Reverse transcription-PCR and Northern blot analysis showed that this gene encoding a binuclear-iron-containing alkane hydroxylase was expressed in cells grown on alkanes above C(6). These results indicate the presence of two distinct monooxygenases for alkane oxidation in Nocardioides sp. strain CF8. PMID:11679317

  11. Marine hydrocarbonoclastic bacteria as whole-cell biosensors for n-alkanes.

    PubMed

    Sevilla, Emma; Yuste, Luis; Rojo, Fernando

    2015-07-01

    Whole-cell biosensors offer potentially useful, cost-effective systems for the in-situ monitoring of seawater for hydrocarbons derived from accidental spills. The present work compares the performance of a biosensor system for the detection of alkanes in seawater, hosted in either Escherichia coli (commonly employed in whole-cell biosensors but not optimized for alkane assimilation) or different marine bacteria specialized in assimilating alkanes. The sensor system was based on the Pseudomonas putida AlkS regulatory protein and the PalkB promoter fused to a gene encoding the green fluorescent protein. While the E. coli sensor provided the fastest response to pure alkanes (25-fold induction after 2 h under the conditions used), a sensor based on Alcanivorax borkumensis was slower, requiring 3-4 h to reach similar induction values. However, the A. borkumensis sensor showed a fourfold lower detection threshold for octane (0.5 μM), and was also better at sensing the alkanes present in petrol. At petrol concentrations of 0.0125%, the A. borkumensis sensor rendered a sevenfold induction, while E. coli sensor showed no response. We discuss possible explanations to this behaviour in terms of the cellular adaptations to alkane uptake and the basal fluorescence produced by each bacterial strain, which was lowest for A. borkumensis. PMID:25874658

  12. Alkanes in flower surface waxes of Momordica cochinchinensis influence attraction to Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae).

    PubMed

    Mukherjee, A; Sarkar, N; Barik, A

    2013-08-01

    Extraction, thin-layer chromatography, and gas chromatography-mass spectrophotometry analyses revealed 15 alkanes representing 97.14% of the total alkanes in the surface waxes of Momordica cochinchinensis Spreng flowers. Nonacosane was the prevailing alkane followed by hexatriacontane, nonadecane, heptacosane, and hentriacontane, accounting for 39.08%, 24.24%, 13.52%, 6.32%, and 5.12%, respectively. The alkanes from flower surface waxes followed by a synthetic mixture of alkanes mimicking alkanes of flower surface waxes elicited attraction of the female insect, Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) between 2 and 10-μg/mL concentrations in a Y-shaped glass tube olfactometer bioassay under laboratory conditions. Synthetic nonadecane from 178.28-891.37 ng, heptacosane from 118.14-590.72 ng, and nonacosane at 784.73 ng showed attraction of the insect. A synthetic mixture of 534.82 ng nonadecane, 354.43 ng heptacosane, and 2,354.18 ng nonacosane elicited highest attraction of A. foveicollis. PMID:23949856

  13. Alkanes in flower surface waxes of Momordica cochinchinensis influence attraction to Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae).

    PubMed

    Mukherjee, A; Sarkar, N; Barik, A

    2013-08-01

    Extraction, thin-layer chromatography, and gas chromatography-mass spectrophotometry analyses revealed 15 alkanes representing 97.14% of the total alkanes in the surface waxes of Momordica cochinchinensis Spreng flowers. Nonacosane was the prevailing alkane followed by hexatriacontane, nonadecane, heptacosane, and hentriacontane, accounting for 39.08%, 24.24%, 13.52%, 6.32%, and 5.12%, respectively. The alkanes from flower surface waxes followed by a synthetic mixture of alkanes mimicking alkanes of flower surface waxes elicited attraction of the female insect, Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) between 2 and 10-μg/mL concentrations in a Y-shaped glass tube olfactometer bioassay under laboratory conditions. Synthetic nonadecane from 178.28-891.37 ng, heptacosane from 118.14-590.72 ng, and nonacosane at 784.73 ng showed attraction of the insect. A synthetic mixture of 534.82 ng nonadecane, 354.43 ng heptacosane, and 2,354.18 ng nonacosane elicited highest attraction of A. foveicollis.

  14. Marine hydrocarbonoclastic bacteria as whole-cell biosensors for n-alkanes

    PubMed Central

    Sevilla, Emma; Yuste, Luis; Rojo, Fernando

    2015-01-01

    Whole-cell biosensors offer potentially useful, cost-effective systems for the in-situ monitoring of seawater for hydrocarbons derived from accidental spills. The present work compares the performance of a biosensor system for the detection of alkanes in seawater, hosted in either Escherichia coli (commonly employed in whole-cell biosensors but not optimized for alkane assimilation) or different marine bacteria specialized in assimilating alkanes. The sensor system was based on the Pseudomonas putida AlkS regulatory protein and the PalkB promoter fused to a gene encoding the green fluorescent protein. While the E. coli sensor provided the fastest response to pure alkanes (25-fold induction after 2 h under the conditions used), a sensor based on Alcanivorax borkumensis was slower, requiring 3–4 h to reach similar induction values. However, the A. borkumensis sensor showed a fourfold lower detection threshold for octane (0.5 μM), and was also better at sensing the alkanes present in petrol. At petrol concentrations of 0.0125%, the A. borkumensis sensor rendered a sevenfold induction, while E. coli sensor showed no response. We discuss possible explanations to this behaviour in terms of the cellular adaptations to alkane uptake and the basal fluorescence produced by each bacterial strain, which was lowest for A. borkumensis. PMID:25874658

  15. Marine hydrocarbonoclastic bacteria as whole-cell biosensors for n-alkanes.

    PubMed

    Sevilla, Emma; Yuste, Luis; Rojo, Fernando

    2015-07-01

    Whole-cell biosensors offer potentially useful, cost-effective systems for the in-situ monitoring of seawater for hydrocarbons derived from accidental spills. The present work compares the performance of a biosensor system for the detection of alkanes in seawater, hosted in either Escherichia coli (commonly employed in whole-cell biosensors but not optimized for alkane assimilation) or different marine bacteria specialized in assimilating alkanes. The sensor system was based on the Pseudomonas putida AlkS regulatory protein and the PalkB promoter fused to a gene encoding the green fluorescent protein. While the E. coli sensor provided the fastest response to pure alkanes (25-fold induction after 2 h under the conditions used), a sensor based on Alcanivorax borkumensis was slower, requiring 3-4 h to reach similar induction values. However, the A. borkumensis sensor showed a fourfold lower detection threshold for octane (0.5 μM), and was also better at sensing the alkanes present in petrol. At petrol concentrations of 0.0125%, the A. borkumensis sensor rendered a sevenfold induction, while E. coli sensor showed no response. We discuss possible explanations to this behaviour in terms of the cellular adaptations to alkane uptake and the basal fluorescence produced by each bacterial strain, which was lowest for A. borkumensis.

  16. Characterization of phospholipid+semifluorinated alkane vesicle system.

    PubMed

    Sabín, Juan; Ruso, Juan M; González-Pérez, Alfredo; Prieto, Gerardo; Sarmiento, Félix

    2006-01-15

    The aim of this study is to characterize vesicles obtained by the incorporation of the semifluorinated alkane, (perfluoro-n-hexyl)ethane (diblock F6H2) to a standard lipid, egg yolk phosphatidylcholine (PC). Large unilamellar vesicles (LUVs), prepared by extrusion, were characterized by fluorescence spectroscopy, zeta potential (zeta-potential) and light scattering. By using the fluorescence spectroscopy technique, the anisotropy of l,6-diphenyl-l,3,5-hexatriene (DPH) probe at different temperatures was determined. It was demonstrated that F6H2 is placed inside of the lipid bilayer and that the hydrocarbon acyl chain in the bilayers has higher viscosity in the presence of fluoroalkane. The zeta-potential of the PC-F6H2 system is negative and increases (in absolute value) from -10 to -19 mV when the temperature rises from 10 to 25 degrees C, this last value keeping practically constant with a further increase of temperature. The adsorption of K+ ions on the liposome surface was measured by zeta-potential. This adsorption originates a sudden increase of the initial zeta-potential followed by a slight decrease with K+ concentration. The application of the DLVO theory of colloidal stability showed a growing dependence of the DLVO potential with K+ concentration and consequently a increasing stability.

  17. Alkane functionalization at ([mu]-Oxo)diiron(III) centers

    SciTech Connect

    Leising, R.A.; Kim, J.; Perez, M.A.; Que, L. Jr. )

    1993-10-20

    The reactivity of ([mu]-oxo)diferric complexes with [sup t]BuOOH (TBHP) for the functionalization of alkanes in CH[sub 3]CN has been investigated as part of our efforts to model dinuclear sites in nonheme iron enzymes. [Fe[sub 2](TPA)[sub 2]O(OAc)](CIO[sub 4])[sub 3] (1) (TPA = tris(2-pyridylmethyl)amine, OAc = acetate) is an efficient catalyst for cyclohexane oxidation, affording cyclohexanol (A, 9 equiv), cyclohexanone (K, 11 equiv), and (tert-butylperoxy)cyclohexane (P, 16 equiv) in 0.25 h at ambient temperature and pressure under an argon atmosphere. The catalyst is remarkably robust, as indicated by the [sup 1]H NMR and UV-vis spectra of the reaction mixture during the catalytic reaction and by its ability to maintain its turnover efficiency with subsequent additions of oxidant. The catalytic mechanism for TBHP utilization was explored by observing the effects of varying the tripodal ligands on the ([mu]-oxo)([mu]-carboxylato)diferric catalysts and varying the bridge on Fe[sub 2]O(TPA)[sub 2] catalysts. The (A + K)/P ratio increased as the ligands became more electron donating. Solvent also played an important role in determining the partitioning of products between A + K and P, with benzonitrile favoring hydroxylated products at the expense of P and pyridine having the opposite effect. 49 refs., 2 figs., 3 tabs.

  18. Pulsed Dipolar Spectroscopy Reveals That Tyrosyl Radicals Are Generated in Both Monomers of the Cyclooxygenase-2 Dimer.

    PubMed

    Orlando, Benjamin J; Borbat, Peter P; Georgieva, Elka R; Freed, Jack H; Malkowski, Michael G

    2015-12-22

    Cyclooxygenases (COXs) are heme-containing sequence homodimers that utilize tyrosyl radical-based catalysis to oxygenate substrates. Tyrosyl radicals are formed from a single turnover of substrate in the peroxidase active site generating an oxy-ferryl porphyrin cation radical intermediate that subsequently gives rise to a Tyr-385 radical in the cyclooxygenase active site and a Tyr-504 radical nearby. We have utilized double-quantum coherence (DQC) spectroscopy to determine the distance distributions between Tyr-385 and Tyr-504 radicals in COX-2. The distances obtained with DQC confirm that Tyr-385 and Tyr-504 radicals were generated in each monomer and accurately match the distances measured in COX-2 crystal structures. PMID:26636181

  19. Free radical explosive composition

    DOEpatents

    Walker, Franklin E.; Wasley, Richard J.

    1979-01-01

    An improved explosive composition is disclosed and comprises a major portion of an explosive having a detonation velocity between about 1500 and 10,000 meters per second and a minor amount of a getter additive comprising a compound or mixture of compounds capable of capturing or deactivating free radicals or ions under mechanical or electrical shock conditions and which is not an explosive. Exemplary getter additives are isocyanates, olefins and iodine.

  20. Radicalism, Marxism, and medicine.

    PubMed

    Navarro, V

    1983-01-01

    This article presents a critique of recent radical interpretations of medicine and provides an alternative explanation of such interpretations. It analyzes 1) the articulation of medical practices, knowledge, and institutions within specific modes of production and social formations; 2) the dual functions of medicine within capitalist relations of production; 3) the reproduction of power within medicine; and 4) the meaning of capitalist, socialist, and communist medicine. The political practice derived from these analyses is also elaborated.