Liquid structure of the ionic liquid, 1-methyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide determined from neutron scattering and molecular dynamics simulations

The liquid structure of 1-methyl-4-cyanopyridinium bis {(trifluoromethyl)sulfonyl}imide, a prototypical ionic liquid containing an electron-withdrawing group on the cation, has been investigated at 368 K. Experimental neutron scattering combined with empirical potential structure refinement analysis of the data and classical molecular dynamics simulations have been used to probe the liquid structure in detail. Both techniques generated highly consistent results that provide valuable validation of the force fields and refinement approaches. A significant degree of apparent charge ordering is found in the liquid structure, although the nonspherical shape of the ions results in interpenetration of cations into the first shell of adjacent cations, with much shorter closest contact distances than the averaged center-of-mass cation-cation and cation-anion separations.

Behavior of the heterogeneous electron-transfer rate constants of arenes and substituted anthracenes in room-temperature ionic liquids

We report the anodic oxidation of several arenes and anthracenes within room-temperature ionic liquids (RTILs). In particular, the heterogeneous electron-transfer rates (k(0)) for substituted anthracenes and arenes are also investigated in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(2)mim][NTf2]) and found not to obey the outer-sphere Marcus-type behavior of these compounds in contrast to the behavior in traditional organic solvents,in particular the predictions for k(0) with molecular size and solvent static dielectric constant. To obtain the electron-transfer rate for 9-phenylanthracene, the dimerization and heterogeneous electron-transfer kinetics of its electrogenerated radical cations is studied in [C(2)mim][NTf2] and eight other RTILs and are both found to be largely independent of the solution viscosity.

Glucose solvation by the ionic liquid 1,3-dimethylimidazolium chloride: A simulation study

Simulations of beta-glucose in the ionic liquid 1,3-dimethylimidazoliurn chloride have been performed in order to examine the solvation environment of the carbohydrate. Both single molecule and 1:5 glucose:ionic liquid (16.7 wt %) solutions are Studied, and the hydrogen bonding between sugar and solvent is examined. The primary solvation shell around the perimeter of the glucose ring consists predominantly of chloride anions which hydrogen bond to the hydroxyl groups. A small presence of the cation is also found, with the association Occurring through the weakly acidic hydrogen at the 2-position of the imidazolium ring interacting with the oxygen atoms of the sugar secondary hydroxyls. An average chloride coordination number of 4 is found around the glucose for both the single molecule and high concentration Simulations, despite the reduced chloride:glucose ratio in the latter case. In relation to the cation, the glucose molecules occupy positions above and below the plane of the imidazolium ring. Importantly, even at high glucose concentrations, no significant change in the anion-cation interactions and overall liquid structure of the ionic liquid is found, indicating that the glucose is readily accommodated by the solvent at this concentration. Dominant contributions to the sugar-ionic liquid interaction energy come from favorable hydrogen bonding (electrostatic) interactions between hydroxyls and chlorides, although a small favorable van der Waals energy contribution is also seen between the sugar and cations suggesting that the cation could be tailored in order to further improve the dissolution of glucose/cellulose in ionic liquid systems.

Elucidation of the electrochemical oxidation pathway of ammonia in dimethylformamide and the room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

The direct electrochemical oxidation of ammonia has been examined in both the organic solvent dimethylformamide (DMF) and the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][N(Tf)(2)]. The corresponding voltammetric responses have been shown to be similar in each solvent with a broad oxidative wave occurring upon the introduction of ammonia to the solution and the appearance of a new reductive wave following the oxidation. The oxidative reaction process has been examined and a suitable reaction pathway has been deduced, corresponding to the formation of ammonium cations after oxidation of the ammonia. A linear response of limiting current against vol% ammonia was observed in both DMF and [EMIM][N(Tf)(2)], suggesting potential application for analytical methods.

On the nature of the silver phases of Ag/Al2O3 catalysts for reactions involving nitric oxide

The nature of the silver phases of Ag/Al2O3 catalysts (prepared by silver nitrate impregnation followed by calcination) was investigated by X-ray diffractograms (XRD), transmission electron microscopy (TEM) and UV-VIS analyses and related to the activity of the corresponding materials for the oxidation of NO to NO2. The UV-VIS spectrum of the 1.2 wt.% Ag/Al2O3 exhibited essentially one band associated with Ag+ species and the NO2 yields measured over this material were negligible. A 10 wt.% Ag/Al2O3 material showed the presence of oxidic species of silver (as isolated Ag+ cations and silver aluminate), but the UV-VIS data also revealed the presence of some metallic silver. The activity for the NO oxidation to NO2 of this sample was moderate. The same 10% sample either reduced in H-2 or used for the C3H6-selective catalytic reduction (SCR) of NO showed a significantly larger proportion of silver metallic phases and these samples displayed a high activity for the formation of NO2. These data show that the structure and nature of the silver phases of Ag/Al2O3 catalysts can markedly change under reaction feed containing only a fraction of reducing agent (i.e. 500 ppm of propene) in net oxidizing conditions (2.5% O-2). The low activity for N-2 formation during the C3H6-SCR of NO (reported in an earlier study) over the high loading sample can. therefore, he related to the presence of metallic silver. which is yet a good catalyst for NO oxidation to NO2. The reverse observations apply for the oxide species observed over the low loading sample, which is a good SCR catalyst but do not oxidize NO to NO2. (C) 2002 Elsevier Science B.V. All rights reserved.

Examination of the conformational restraints to a chiral diimine bridged 2,2 '-bipyridine

The synthesis of a new bis(2,2-bipyridine), bridged by a Schiff base cyclohexane moiety is described. Surprisingly, this compound does not appear to form discrete oligonuclear metal complexes on the addition of zinc(II) and iron(II) cations. In order to rationalise this behaviour, the compound's conformation has been explored using a combination of circular dichroism, X-ray crystallography and DFT calculations, indicating that at least two energy barriers need to be overcome to orientate the ligand in a suitable conformation to permit the formation of coordination helicates with control over the metal centred stereochemistry. (C) 2004 Elsevier Ltd. All rights reserved.

Density-Enhanced Gas and Dust Shells in a New Chemical Model for IRC+10216

A new chemical model is presented for the carbon-rich circumstellar envelope (CSE) of the asymptotic giant branch star IRC+10216. The model includes shells of matter with densities that are enhanced relative to the surrounding circumstellar medium. The chemical model uses an updated reaction network including reactions from the RATE06 database and a more detailed anion chemistry. In particular, new mechanisms are considered for the formation of CN-, C3N-, and C2H-, and for the reactions of hydrocarbon anions with atomic nitrogen and with the most abundant cations in the CSE. New reactions involving H- are included which result in the production of significant amounts of C2H- and CN- in the inner envelope. The calculated radial molecular abundance profiles for the hydrocarbons C2H, C4H, and C6H and the cyanopolyynes HC3N and HC5N show narrow peaks which are in better agreement with observations than previous models. Thus, the narrow rings observed in molecular microwave emission surrounding IRC+10216 are interpreted as arising in regions of the envelope where the gas and dust densities are greater than the surrounding circumstellar medium. Our models show that CN- and C2H- may be detectable in IRC+10216 despite the very low theorized radiative electron attachment rates of their parent neutral species. We also show that magnesium isocyanide (MgNC) can be formed in the outer envelope through radiative association involving Mg+ and the cyanopolyyne species.

Biochemical characterization of arterivirus nonstructural protein 11 reveals the nidovirus-wide conservation of a replicative endoribonuclease

Nidoviruses (arteriviruses, coronaviruses, and roniviruses) are a phylogenetically compact but diverse group of positive-strand RNA viruses that includes important human and animal pathogens. Nidovirus RNA synthesis is mediated by a cytoplasmic membrane-associated replication/transcription complex that includes up to 16 viral nonstructural proteins (nsps), which carry common enzymatic activities, like the viral RNA polymerase, but also unusual and poorly understood RNA-processing functions. Of these, a conserved endoribonuclease (NendoU) is a major genetic marker that is unique to nidoviruses. NendoU activity was previously verified in vitro for the coronavirus nsp15, but not for any of its distantly related orthologs from other nidovirus lineages, like the arterivirus nsp11. Here, we show that the bacterially expressed nsp11 proteins of two arteriviruses, equine arteritis virus and porcine respiratory and reproductive syndrome virus, possess pyrimidine-specific endoribonuclease activity. RNA cleavage was independent of divalent cations in vitro and was greatly reduced by replacement of residues previously implicated in catalysis. Comparative characterization of the NendoU activity in arteriviruses and severe acute respiratory syndrome coronavirus revealed common and distinct features of their substrate requirements and reaction mechanism. Our data provide the first biochemical evidence of endoribonuclease activity associated with arterivirus nsp11 and support the conclusion that this remarkable RNA-processing enzyme, whose substrate in the infected cell remains to be identified, distinguishes nidoviruses from all other RNA viruses.

Ionic liquids for the nuclear industry: A radiochemical, structural, and electrochemical investigation

The applicability of ionic liquids within the nuclear industry has been investigated. The radiation stability of ionic liquids containing dialkylimidazolium cations has been tested through with alpha, beta and gamma irradiation. The results of these tests suggest that imidazolium salts have stabilities similar to alkylbenzenes and greater than tetrabutylphosphate / odorless kerosene (TBP/OK) mixtures. The oxidative dissolution of uranium dioxide and the anodic dissolution of uranium metal and plutonium metal have been carried out in various ionic liquid media (C) 2002 American Chemical Society.

YF[MoO4] and YCl[MoO4]: Two halide derivatives of yttrium ortho-oxomolybdate: Syntheses, structures, and luminescence properties

The halide derivatives of yttrium ortho-oxomolybdate YX[MoO4] (X = F, Cl) both crystallize in the monoclinic system with four formula units per unit cell. YF[MoO4] exhibits a primitive cell setting (space group P2(1)/c, a = 519.62(2) pm, b = 1225.14(7) pm, c = 663.30(3) pm, beta = 112.851(4)degrees), whereas the lattice of YCl[MoO4] shows face-centering (space group C2/m; a = 1019.02(5) pm, b = 720.67(4) pm, c = 681.50(3) pm, beta = 107.130(4)degrees). The two compounds each contain crystallographically unique Y3+ cations, which are found to have a coordination environment of six oxide and two halide anions. In the case of YF[MoO4], the coordination environment is seen as square antiprisms, and for YCl[MoO4], trigon-dodecahedra. are found. The discrete tetrahedral [MoO4](2-) units of the fluoride derivative are exclusively bound by six terminal Y3+ cations, while those of the chloride compound show a 5-fold coordination around the tetrahedra with one edge-bridging and four terminal Y3+ cations. The halide anions in each compound exhibit a coordination number of two, building up isolated planar rhombus-shaped units according to [Y2F2](4+) in YF[MoO4] and [Y2Cl2](4+) in YCl[MoO4], respectively. Both compounds were synthesized at high temperatures using Y2O3, MoO3, and the corresponding yttrium trihalide in a molar ratio of 1:3:1. Single crystals of both are insensitive to moist air and are found to be coarse shaped and colorless with optical band gaps situated in the near UV around 3.78 eV for the fluoride and 3.82 eV for the chloride derivative. Furthermore, YF[MoO4] seems to be a suitable material for doping to obtain luminescent materials because the Eu3+-doped compound shows an intense red luminescence, which has been spectroscopically investigated.

Tris(1-ethyl-3-methylimidazolium) hexabromidoeuropate(III)

The crystal structure of the title compound, (C6H11N2)(3-)[EuBr6], consists of 1-ethyl-3-methylimidazolium cations and centrosymmetric octahedral hexabromidoeuropate anions. The [EuBr6](3-) anions are located at the corners and face-centres of the monoclinic unit cell. Characteristic hydrogen-bonding interactions can be observed between the bromide anions and the acidic H atoms of the imidazolium cations.

Ionic liquid characteristics of 1-alkyl-n-cyanopyridinium and 1-alkyl-n-(trifluoromethyl) pyridinium salts

1-Alkyl-n-cyanopyridinium and 1-alkyl-n-(trifluoromethyl) pyridinium salts have been synthesised and characterised in order to compare the effects of different electron-withdrawing functional groups on their ability to form ionic liquids. The presence of the electron-withdrawing nitrile or trifluoromethyl substituent on the pyridinium ring leads to salts with higher melting points than with the corresponding 1-alkylpyridinium or 1-alkylpicolinium cations. Solid-state structures were determined by single crystal X-ray crystallography for seven salts; 1-methyl-4-cyanopyridinium methylsulfate, and 1-methyl-3-cyanopyridinium, 1-methyl-4-cyanopyridinium, 1-ethyl-2-cyanopyridinium, 1-ethyl-3-cyanopyridinium, 1-ethyl-4-cyanopyridinium and 1-ethyl-4-(trifluormethyl) pyridinium bis{(trifluoromethyl) sulfonyl} imide, and show the effects of ring-substitution position on hydrogen-bonding in the solid-state and on melting points.

Pyrrolidinium Ionic Liquid Crystals

N-Alkyl-N-methylpyrrolidinium cations have been used for the design of ionic liquid crystals, including a new type of uranium-containing metallomesogen. Pyrrolidinium salts with bromide, bis(trifluoromethylsulfonyl)-imide, tetrafluoroborate, hexafluorophosphate, thiocyanate, tetrakis(2-thenoyltrifluoroacetonato)europate(III) and tetrabromouranyl] counteranions were prepared. For the bromide salts and tetrabromouranyl compounds, the chain length of the alkyl group CnH2n+1 was varied from eight to twenty carbon atoms (n =8. 10-20). The compounds show rich mesomorphic behaviour: highly ordered smectic phases (the crystal smectic E phase and the uncommon crystal smectic T phase), smectic A phases, and hexagonal. columnar phases were observed, depending on chain length and anion. This work gives better insight into the nature and formation of the crystal smectic T phase, and the Molecular requirements for the appearance of this highly ordered phase. This uncommon tetragonal mesophase is thoroughly discussed on the basis of detailed powder X-ray diffraction experiments and in relation to the existing literature. Structural models are proposed for self-assembly of the molecules within the smectic layers. In addition, the photophysical properties of the compounds containing a metal complex anion were investigated. For the uranium-containing mesogens, luminescence can be induced by dissolving them in an ionic: liquid matrix. The europium-containing compound shows intense red photoluminescence with high colour Purity.

Pyrrolidinium Ionic Liquid Crystals with Pendant Mesogenic Groups

New ionic liquid crystals (including ionic metallomesogens) based oil the pyrrolidinium core are presented. N-Methylpyrrolidine was quaternized with different mesogenic groups connected to a flexible, omega-bromosubstituted alkyl spacer. The length of the flexible alkyl spacer between the cationic head group and the rigid mesogenic group was varied. The substituted pyrrolidinium cations were combined with bromide, bis(trifluoromethylsulfonyl)imide, tetrakis (2-thenoyltrifluoroacetonato)europate(III), and tetrabromouranyl anions. The influence of the type of mesogenic unit, the lengths of the flexible spacer and terminal alkyl chain, the size of the mesogenic group, and the type of anion oil the thermotropic mesomorphic behavior was investigated. Furthermore, the phase behavior was thoroughly compared with the previously reported mesomorphism of N-alkyl-N-methylpyrrolidinium salts. Low-ordered smectic A phases of the de Vries type, smectic C phases, higher-ordered smectic F/I phases, as well its crystal smectic phases (E and G, J, H, or K) were observed and investigated by polarizing optical microscopy, differential scanning calorimetry, and powder X-ray diffraction.

In search of ionic liquids incorporating azolate anions

Twenty-eight novel salts with tetramethyl-, tetraethyl-, and tetrabutylammonium and 1-butyl-3-methylimidazolium cations paired with 3,5-dinitro-1,2,4-triazolate, 4-nitro-1,2,3-triazolate, 2,4-dinitroimidazolate, 4,5-dinitroimidazolate, 4,5-dicyanoimidazolate, 4-nitroimidazolate, and tetrazolate anions have been prepared and characterized by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and single-crystal Xray crystallography. The effects of cation and anion type and structure on the physicochemical properties of the resulting salts, including several ionic liquids, have been examined and discussed. Ionic liquids (defined as having m.p. <100 degrees C) were obtained with all combinations of the 1-butyl-3-methylimidazolium cation ([C(4)mim](+)) and the heterocyclic azolate anions studied, and with several combinations of tetraethyl or tetrabutylammonium cations and the azolate anions. The [C(4)mim](+) azolates were liquid at room temperature exhibiting large liquid ranges and forming glasses on cooling with glasstransition temperatures in the range of -53 to -82 degrees C (except for the 3,5-dinitro-1,2,4-triazolate salt with m.p. 33 degrees C). Six crystal structures of the corresponding tetraalkylammonium salts were determined and the effects of changes to the cations and anions on the packing of the structure have been investigated.