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The structure and interaction patterns of a kind of N,N-dimethylformamide-based (DMF-based) ionic liquid, [[DMFH.sup.}][N[O.sub.3.sup.-]] are examined by using density function theory method. Results reveal that neutral pairs are more stable than the ion pairs.

Quantum chemical calculations were used to investigate the interaction between water molecules and ionic liquids based on the imidazolium cation with anions [Cl.sup.-], [Br.sup.-] and B[F.sub.4.sup.-]. The water molecules interact with anions to form [X.sup.-]...W, 2[X.sup.-]...2W, B[F.sub.4.sup.-]...W (X=Cl or Br, W=water) complexes and the strength of the interactions follow the trend anion-W>cation-W>ion pair -W.

A study computed the adsorption and dissociation of thiophene on the MoP(001), [gamma]-Mo2N(100), and Ni2P(001) surfaces by using the density functional theory method. Results reveal that thiophene adsorbs dissociatively on MoP(001), while nondissociatively on [gamma]-Mo2N(100) and Ni2(001).

Density functional theory (DFT) is used to study the CO adsorption on the Fe3O4(111) surfaces, which are considered as active catalysts in water-gas shift reaction. The results have shown that the adsorbed CO can migrate from the on-top site to the bridge site or 3-fold site and the oxidation of CO through surface oxygen atoms is feasible.

Mechanistic aspects of acetaldehyde hydroxylation by Compound I model active species of cytochrome P450 2E1 (CYP2E1) were investigated by means of B3LYP density function theory calculations. The results demonstrate that acetaldehyde hydroxylation by CYP2E1 is in accord with the effectively concerted mechanisms both on the high quartet spin state and on the low doublet spin state.

Ordered macroporous carbon with a three-dimensional (3D) interconnected pore structure and a graphitic pore wall was prepared by chemical vapor deposition (CVD) of benzene using inverse silica as the template. The enhancement of these electrochemical characteristics is presumably related to the graphitic nature and the 3D interconnected open pore structures of the carbon materials and it is anticipated that the nanostructured carbon can be used as the novel anode material for electrochemical energy conversion and storage devices.

CO2 chemisorption on the Ni(111), Ni(100), and Ni(110) surfaces is investigated at the level of density functional theory. The ability of CO2 chemisorption is in order of Ni(110) > Ni(100) > Ni(111) where CO2 has exothremic chemisorption on Ni(110) and endothermic chemisorption on Ni(111) while it is thermally neutral on Ni(100).

Density functional theory calculation was carried out for hydrogen adsorption on the (001), (110), and (100) surfaces of Fe(sub 5)C(sub 2) and found that the most stable hydrogen species is C(sub S)H at 1/3 and 2/3 monolayer (ML) on (001). On the metallic Fe(Sub 5)C(sub 2)(100) surface which lacks surface carbon atoms on the surface monolayer, dissociated hydrogen is found at 1/2 ML, while both dissociated hydrogen and activated H(sub 2) are found at 1 ML.

The two-dimensional correlation spectroscopy technique is employed to study the solvation and structural properties of ionic liquids (ILs) in water. The C-H stretching vibration of the ionic liquid cation is shown to exhibit systematic blue-shifts with an increase in the water content.

Molecular dynamics simulations are used for investigating the solubility of the S[O.sub.2] and C[O.sub.2] gases in the 1,1,3,3-tetramethylguanidium lactate (TMG) lactic acid (LAC) ionic liquid (TMGL). The results have shown strong organization of S[O.sub.2] about the TMG cation and the LAC anion, but weak organization of C[O.sub.2] about the cation and the anion of the TMGL, which has explained the selectivity of the TMGL toward the S[O.sub.2] and C[O.sub.2].

The structures and energies of [Mo.sub.27][S.sub.x][C.sub.y] cluster models are computed by density functional theory (DFT) in order to understand the carburization processes of Mo[S.sub.x] catalysts. The results have shown that the model cluster, [Mo.sub.27][S.sub.24][C.sub.30], with a fully carbonized S edge and [S.sub.1] bulky sulfur, is the most favored full carburization.

NO probe molecule adsorption on the stoichiometric (Mo16S32) and nonstoichometric (Mo16S34 and Mo16S29) clusters is investigated using density functional theory (DFT) method. The calculated adsorption energies indicate that the stoichiometric cluster has stronger NO affinity than the nonstoichiometric surfaces.

Density functional theory (DFT) calculations are used to investigate C[O.sub.2] reforming of C[H.sub.4] on Ni(111). The computed energy barriers of the most favorable elementary reaction have identified the C[H.sub.4] activation into C[H.sub.3] and H as the rate-determining step of C[O.sub.2] reforming of C[H.sub.4] on Ni(111).

The possible reaction pathways of nitroethylene with the Si(100)-2 by 1 surface are examined by unrestricted density functional theory. The isomerization reactions of the addition products are investigated and the obtained results help in examining the factors governing the competition and selectivity to organic reactions on the reconstructed Si(100) surface.

Density functional theory computations are carried out to study the structure and stability of MoS(sub x) clusters with the change of sulfur coverage at both Mo and S edges. The interaction between Mo and S edges under the variation of sulfur coverage is analyzed with the change of Mo(sub 27)S(sub x) clusters and the stability of triangular MoS(sub x) clusters are discussed.

A systematic density functional theory (DFT) of hydrogen adsorption on Fe(111) at various coverages is presented. The coverage effects on the adsorption configrations and adsorption energies are addressed.

A systematic density functional study on the structure and stability of triangular molybdenum sulfide [MoS(sub x)] models is carried out. It is found that CO adsorption at the corner site represents the most stable conformation.

Density functional theory calculations are carried out on the CO/H2 coadsorption on the (001), (110), and (100) surfaces of Fe5C2 for the understanding of the Fischer-Tropsch synthesis (FTS) mechanism. The stable surface species changes with the variation of the H2 and CO coverage.

Copper tetra-(octly-alkoxy-carbonyl)-pthalocyanine and 3,4,9,10-tetra-(octyl-alkoxy-carbonyl)-perylene attached with long alkyl chains by covalent bonds were synthesized. Atomic force microscopy demonstrated the formation of the bulk heterojunction structure in their cast-coated films.

Possible mechanisms of the [2+2] cycloaddition reactions of ethylene, propylene, vinyl chloride, and styrene with the Si(100)-2 X 1 surface are investigated by theoretical calculations with the unrestricted density functional theory and the second-order Moller-Plesset perturbation theory. The reactions follow the diradical mechanism of thermal [2+2] cycloaddition reactions between pi-electron donors and acceptors through a pi-complex precursor and a singlet diradical intermediate.

A route to the fabrication of unique flowerlike polymer superstructures with uniform petals at the nanoscale is reported. Polymer/zeolite composite is first prepared by loading corresponding monomer and initiator into the channels of the host zeolite with the aid of supercritical (SC) CO(sub 2) followed by thermal polymerization of monomers in the channels of the zeolite.

CO adsorption on four MoSx clusters is investigated by using density functional method. It is found that CO prefers adsorption on the coordinatively unsaturated (1010) surface.

The nonhydrothermal synthesis of SnO2 nanorods at moderate temperatures (320 or 700 degree Celsius), and the application of these nanorods as a Li storage compound for Li-ion batteries are reported. Some possible reasons for the high capacity are suggested, based on the observation of morphology changes in the nanorods during cycling.

Density functional theory calculations are carried out to study CO adsorption on the (001), (100), and (110) surfaces of Fe5C2, which are considered as active catalysts in Fischer-Tropsch synthesis. Study indicates that CO prefers to adsorb at three 3--fold sites (three iron atoms) on the three surfaces at low coverage with maximum adsorption energies of -2.10, -2.21 and -2.34 eV, respectively.

The adsorption of Ni8 clusters on the anionic (Mg25O (sub 25) (super 0/+/2+,), F (sub 8) (Super 0/+/2+)) and cationic (Mg24O(sub 25)(super0/-/2-), V(sub 8)(super 0/-02-)) vacancies, as well as on the regular sites (Mg25O25, Mg2+ and NiMg24O25, Ni2+) of the MgO(001) surface is investigated at the PW91/DND level of density functional theory. The electronic property of the vacancies is analyzed.

The hydrogen bond acceptor capability of halogens has long been underappreciated in the field of biology. In this work, we have surveyed structures of protein complexes with halogenated ligands to characterize geometrical preferences of C−X···H contacts and contributions of such interactions to protein−ligand binding affinity. Notably, F···H interactions in biomolecules exhibit a remarkably different behavior as compared to three other kinds of X···H (X = Cl, Br, I) interactions, which has been rationalized by means of ab initio calculations using simple model systems. The C−X···H contacts in biological systems are characterized as weak hydrogen bonding interactions. Furthermore, the electrophile “head on” and nucleophile “side on” interactions of halogens have been extensively investigated through the examination of interactions in protein structures and a two-layer ONIOM-based QM/MM method. In biomolecular systems, C−X···H contacts are recognized as secondary interaction contributions to C−X···O halogen bonds that play important roles in conferring specificity and affinity for halogenated ligands. The results presented here are within the context of their potential applications in drug design, including relevance to the development of accurate force fields for halogens. [ABSTRACT FROM AUTHOR]

The blue-shifted C−D stretching vibrations (νCD) of deuteriated dimethyl sulfoxide (DMSO-d6) in mixtures of DMSO-d6/ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) were carefully investigated and compared with those in DMSO-d6/water. Results from FTIR studies indicate that the direct interaction of C−D···F between DMSO-d6and the anion [BF4−] plays a minor role in the blue-shift of νCDin the mixtures of DMSO-d6/IL. They also show that the indirect influence of the hydrogen bond formed by the nearby functional group SO with C2−H of the cation significantly contributes to the blue-shift of νCD, as can be inferred from the significant differences of the blue-shift in [Bmim][BF4] and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([Bm2im][BF4]). In contrast, in the case of DMSO-d6/water mixtures, direct hydration of C−H···O between the methyl groups of DMSO-d6with the oxygen atom of water is mainly responsible for the blue shift of νCD. Furthermore, theoretical calculations revealed that charge migrations as well as rehybridization have a dominant effect on the blue-shift in both mixtures. [ABSTRACT FROM AUTHOR]

An all-atom force field is developed using a combination of density functional theory calculations and OPLS force field parameter values for the 1,1,3,3-tetramethylguanidium lactate (TMG) lactic acid (LAC) ionic liquid (TMGL). The computed density of the TMGL is in good agreement with available experimental values. The internal energy components, cohesive energy density, and the self-diffusion constants are also discussed. Molecular dynamics simulations are then conducted to investigate the solubility of the SO2and CO2gases in the TMGL. The simulation results show strong organization of SO2about the TMG cation and the LAC anion, especially the LAC anion, but relatively weak organization of CO2about the cation and the anion of the TMGL, which explained well the selectivity of the TMGL toward the SO2and CO2. [ABSTRACT FROM AUTHOR]

The mechanism of N-demethylation of N,N-dimethylanilines (DMAs) by cytochrome P450, a highly debated topic in mechanistic bioinorganic chemistry (Karki, S. B.; Dinnocenczo, J. P.; Jones, J. P.; Korzekwa, K. R. J. Am. Chem. Soc.1995, 117, 3657), is studied here using DFT calculations of the reactions of the active species of the enzyme, Compound I (Cpd I), with four para-(H, Cl, CN, NO2) substituted DMAs. The calculations resolve mechanistic controversies, offer a consistent mechanistic view, and reveal the following features:  (a) the reaction pathways involve C−H hydroxylation by Cpd I followed by a nonenzymatic carbinolamine decomposition. (b) C−H hydroxylation is initiated by a hydrogen atom transfer (HAT) step that possesses a “polar” character. As such, the HAT energy barriers correlate with the energy level of the HOMO of the DMAs. (c) The series exhibits a switch from spin-selective reactivity for DMA and p-Cl-DMA to two-state reactivity, with low- and high-spin states, for p-CN-DMA and p-NO2-DMA. (d) The computed kinetic isotope effect profiles (KIEPs) for these scenarios match the experimentally determined KIEPs. Theory further shows that the KIEs and TS structures vary in a manner predicted by the Melander−Westheimer postulate:  as the substituent becomes more electron withdrawing, the TS is shifted to a later position along the H-transfer coordinate and the corresponding KIEs increases. (e) The generated carbinolaniline can readily dissociate from the heme and decomposes in a nonenzymatic environment, which involves water assisted proton shift. [ABSTRACT FROM AUTHOR]

The density functional theory (DFT) method has been used to investigate NO probe molecule adsorption on the stoichiometric (Mo16S32) and nonstoichiometric (Mo16S34and Mo16S29) clusters. The calculated adsorption energies indicate that the stoichiometric cluster has stronger NO affinity than the nonstoichiometric surfaces. It is also found that mononitrosyl adsorption is favored at low NO coverage, while dinitrosyl (germinal) and (NO)2dimer adsorption at high NO coverage are possible. Strong repulsive interaction has been found for the adsorbed dinitrosyl and (NO)2dimer species. In addition, the computed NO stretching frequencies for the mononitrosyl and dinitrosyl species agree well with the experimental data, while those of the dimer species are much lower than the suggested experimental data. [ABSTRACT FROM AUTHOR]

Possible reaction pathways of nitroethylene with the Si(100)-2 × 1 surface have been investigated by unrestricted density functional theory. The facile occurrence of the studied reactions was demonstrated by the low activation energies of the rate-determining steps (1.07−5.23 kcal/mol). It was found that the [6b+ 2] cycloaddition reaction of nitroethylene is most kinetically favorable. The isomerization reactions of the addition products were also investigated. The [1b+ 2] cycloaddition product may further undergo a rearrangement by overcoming a 12.37 kcal/mol activation energy barrier into an isomer, with an oxygen atom of the nitryl group inserted between two silicon atoms of the Si(100) surface. [ABSTRACT FROM AUTHOR]

Spin-polarized density functional theory calculations have been performed to characterize the hydrogen adsorption and diffusion on the Fe(111) surface at 2/3-, 1-, and 2-monolayer (ML) coverages. It is found that the most favored adsorption site for atomic hydrogen (H) is the top-shallow bridge site (tsb), followed by the quasi 4-fold site (qff) with the energy difference of about 0.1 eV, while the top site (t) is not competitive. Furthermore, the adsorbed atomic hydrogen (H) has a high mobility, as indicated by the small diffusion barriers. The local density of state (LDOS) analysis reveals that the Fe−H (tsb or qff) bond involves mainly the Fe 4s and 4p and H 1s orbitals with less contribution of the Fe 3d orbital, while the Fe 4s, 4p, and 3d orbitals all participate in the Fe−H (top) bond. In addition, the coverage effects on the adsorption configurations and adsorption energies are addressed. [ABSTRACT FROM AUTHOR]