scispace - formally typeset
Search or ask a question

Showing papers on "Solvent effects published in 2015"


Journal ArticleDOI
TL;DR: The addition of water or methanol to the electrolyte allows a shift of oxidation potentials in a specific range, creating suitable systems for selective anodic cross-coupling reactions, and this driving force for selectivity in oxidative coupling might also explain previous findings using HFIP and hypervalent iodine reagents.
Abstract: Solvents such as 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) with a high capacity for donating hydrogen bonds generate solvates that enter into selective cross-coupling reactions of aryls upon oxidation. When electric current is employed for oxidation, reagent effects can be excluded and a decoupling of nucleophilicity from oxidation potential can be achieved. The addition of water or methanol to the electrolyte allows a shift of oxidation potentials in a specific range, creating suitable systems for selective anodic cross-coupling reactions. The shift in the redox potentials depends on the substitution pattern of the substrate employed. The concept has been expanded from arene-phenol to phenol-phenol as well as phenol-aniline cross-coupling. This driving force for selectivity in oxidative coupling might also explain previous findings using HFIP and hypervalent iodine reagents.

170 citations


Journal ArticleDOI
TL;DR: In this paper, an accurate and general solvation model that includes a cavity that is a nonlocal functional of both solute electron density and potential, local dielectric response on this non-locally determined cavity, and non-local approximations to the cavity-formation and dispersion energies is presented.
Abstract: Many important applications of electronic structure methods involve molecules or solid surfaces in a solvent medium. Since explicit treatment of the solvent in such methods is usually not practical, calculations often employ continuum solvation models to approximate the effect of the solvent. Previous solvation models either involve a parametrization based on atomic radii, which limits the class of applicable solutes, or based on solute electron density, which is more general but less accurate, especially for charged systems. We develop an accurate and general solvation model that includes a cavity that is a nonlocal functional of both solute electron density and potential, local dielectric response on this nonlocally determined cavity, and nonlocal approximations to the cavity-formation and dispersion energies. The dependence of the cavity on the solute potential enables an explicit treatment of the solvent charge asymmetry. With four parameters per solvent, this “CANDLE” model simultaneously reproduces solvation energies of large datasets of neutral molecules, cations, and anions with a mean absolute error of 1.8 kcal/mol in water and 3.0 kcal/mol in acetonitrile.

138 citations


Journal ArticleDOI
TL;DR: In this article, the structural properties of H-ZSM-5, in conjunction with increased reaction performance using the polar aprotic solvent THF, are used for furfuryl alcohol hydrolysis to levulinic acid.
Abstract: Furfuryl alcohol in high concentrations (1 M) was hydrolyzed to levulinic acid in high yields (>70%) using H-ZSM-5 zeolite as the catalyst in monophasic tetrahydrofuran (THF)–water solvent systems. Reaction kinetics studies using H-ZSM-5 were carried out, and combined with results obtained for other Bronsted acid catalysts, we suggest that the structural properties of H-ZSM-5, in conjunction with increased reaction performance using the polar aprotic solvent THF, are effective for furfuryl alcohol hydrolysis to levulinic acid while inhibiting furfuryl alcohol polymerization reactions. In addition, on the basis of results obtained for a wide range of THF–H2O solvent systems (19:1–1:2 w/w), we suggest that the hydrophobic nature of H-ZSM-5 alters the internal solvent microenvironment within the zeolite framework, allowing for high levulinic acid yields, even at low THF solvent concentrations (e.g., 1:2 THF–H2O w/w).

107 citations


Journal ArticleDOI
TL;DR: Ni/Al2O3 catalysts were tested for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) as an important bio-based platform molecule for chemical products based on renewable feedstocks as discussed by the authors.
Abstract: Ni/Al2O3 catalysts were tested for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) as an important bio-based platform molecule for chemical products based on renewable feedstocks. The catalysts were prepared by wet impregnation, incipient wetness impregnation, precipitation, and flame spray pyrolysis; both the influence of different solvents (monovalent alcohols and water) as well as solvent free reaction conditions were screened in batch autoclaves. Whereas alcohols led to a number of side reactions that could only be suppressed by high hydrogen pressures (>20 bar), water as solvent resulted in a GVL selectivity of 100%. The GVL yields reached 57%. Further improvement was achieved without any solvent, whereby the GVL yield increased to 92% at 100% LA conversion. Reuse of the Ni catalysts resulted in a significant drop in activity. The catalysts were thoroughly characterized by temperature programmed reduction (TPR), X-ray diffraction (XRD), linear combination analysis of X-ray absorption near edge structure (XANES) spectra and extended X-ray absorption fine structure (EXAFS). The results indicated that incorporated Ni2+, as present in flame-derived catalysts, was less active for GVL synthesis compared to supported Ni particles, as present in the wet impregnated catalyst.

86 citations


Journal ArticleDOI
TL;DR: In this article, a new reaction pathway involving propargyl amines as intermediates that do not undergo rearrangement is presented, which is driven by inductive and solvent effects, with a wide array of both being reported.
Abstract: Copper nanoparticles supported on activated carbon have been found to catalyze the multicomponent synthesis of indolizines from pyridine-2-carbaldehyde derivatives, secondary amines, and terminal alkynes in dichloromethane; in the absence of solvent, however, heterocyclic chalcones are formed. We provide compelling evidence that both processes take place through aldehyde–amine–alkyne coupling intermediates. In contrast to other well-known mechanisms for chalcone formation from aldehydes and alkynes, a new reaction pathway involving propargyl amines as intermediates that do not undergo rearrangement is presented. The formation of indolizines or chalcones is driven by inductive and solvent effects, with a wide array of both being reported. In both reactions, the nanoparticulate catalyst has been shown to be superior to some commercially available copper catalysts, and it could be recycled in the case of the chalcone synthesis.

85 citations


Journal ArticleDOI
TL;DR: P Powder X-ray diffraction confirmed that MIL-53(Al) synthesized in DMF at 120°C remains in the large-pore form under all conditions, while the other material synthesized at 220°C undergoes a more gradual breathing transition than is observed for MIL- 53(Al), prepared by traditional methods.

81 citations


Journal ArticleDOI
TL;DR: An improved LED-based illumination device can be used to obtain NMR reaction profiles of photocatalytic reactions under synthetic conditions and perform both photo-CIDNP and intermediate studies, which demonstrates the importance of downstream intermediates and NMR-accessible complementary information in photocatalyst reactions and suggests the control of photoorganic reactions by solvent effects.
Abstract: Mechanistic insights into chemical photocatalysis are mainly the domain of UV/Vis spectroscopy, because NMR spectroscopy has been limited by the type of illumination so far. An improved LED-based illumination device can be used to obtain NMR reaction profiles of photocatalytic reactions under synthetic conditions and perform both photo-CIDNP and intermediate studies. Flavin-catalyzed photooxidations of alcohols show the potential of this setup. After identical initial photoreaction steps the stabilization of a downstream intermediate is the key to the further reaction mechanism and the reactivity. As a chemical photocatalyst flavin can act either as a one- or a two-electron mediator when the stability of the zwitterionic radical pair is moldulated in different solvents. This demonstrates the importance of downstream intermediates and NMR-accessible complementary information in photocatalytic reactions and suggests the control of photoorganic reactions by solvent effects.

77 citations


Journal ArticleDOI
TL;DR: Synthetic molecular balances are used to measure solvent effects on aromatic, aliphatic, and fluorous nonpolar interactions to establish ced as a readily accessible, quantitative descriptor of solvophobic association in a range of chemical contexts.
Abstract: The hydrophobic effect plays a central role in determining the structure, activity, and properties of biomolecules and materials. In contrast, the general manifestation of this phenomenon in other solvents—the solvophobic effect—although widely invoked, is currently poorly defined because of the lack of a universally accepted descriptor. Here we have used synthetic molecular balances to measure solvent effects on aromatic, aliphatic, and fluorous nonpolar interactions. Our solvent screening data combined with independent experimental measurements of supramolecular association, single-molecule folding, and bulk phase transfer energies were all found to correlate well with the cohesive energy density (ced) of the solvent. Meanwhile, other measures of solvent cohesion, such as surface tension and internal pressure, gave inferior correlations. Thus, we establish ced as a readily accessible, quantitative descriptor of solvophobic association in a range of chemical contexts.

74 citations


Journal ArticleDOI
01 Jan 2015-Small
TL;DR: Five alternative solvents are investigated, namely, tetrahydrofuran, decalin, tetralin, m- xylene, and o-xylene, for the dispersion of semiconducting SWCNTs by poly(3-dodecylthiophene) P3DDT, and a general mechanism is proposed to explain the selective dispersion by conjugated polymers.
Abstract: Regioregular poly(3-alkylthiophene) (P3AT) polymers have been previously reported for the selective, high-yield dispersion of semiconducting single-walled carbon nanotubes (SWCNTs) in toluene. Here, five alternative solvents are investigated, namely, tetrahydrofuran, decalin, tetralin, m-xylene, and o-xylene, for the dispersion of SWCNTs by poly(3-dodecylthiophene) P3DDT. The dispersion yield could be increased to over 40% using decalin or o-xylene as the solvents while maintaining high selectivity towards semiconducting SWCNTs. Molecular dynamics (MD) simulations in explicit solvents are used to explain the improved sorting yield. In addition, a general mechanism is proposed to explain the selective dispersion of semiconducting SWCNTs by conjugated polymers. The possibility to perform selective sorting of semiconducting SWCNTs using various solvents provides a greater diversity of semiconducting SWCNT ink properties, such as boiling point, viscosity, and surface tension as well as toxicity. The efficacy of these new semiconducting SWCNT inks is demonstrated by using the high boiling point and high viscosity solvent tetralin for inkjet-printed transistors, where solvent properties are more compatible with the inkjet printing head and improved droplet formation.

69 citations


Journal ArticleDOI
TL;DR: In this paper, the relationship between the redox potential in solution and the gas-phase ionization energy and the volume of an organic electron donor was investigated, and it was shown that the intrinsic reduction power, which neglects the environment, has to be separated from extrinsic (e.g., solvent) effects.
Abstract: Organic electron donors are of importance for a number of applications. However, the factors that are essential for a directed design of compounds with desired reduction power are not clear. Here, we analyze these factors in detail. The intrinsic reduction power, which neglects the environment, has to be separated from extrinsic (e.g., solvent) effects. This power could be quantified by the gas-phase ionization energy. The experimentally obtained redox potentials in solution and the calculated ionization energies in a solvent (modeled with the conductor-like screening model (COSMO)) include both intrinsic and extrinsic factors. An increase in the conjugated π-system of organic electron donors leads to an increase in the intrinsic reduction power, but also decreases the solvent stabilization. Hence, intrinsic and extrinsic effects compete against each other; generally the extrinsic effects dominate. We suggest a simple relationship between the redox potential in solution and the gas-phase ionization energy and the volume of an organic electron donor. We finally arrive at formulas that allow for an estimate of the (gas-phase) ionization energy of an electron donor or the (gas-phase) electron affinity of an electron acceptor from the measured redox potentials in solution. The formulas could be used for neutral organic molecules with no or only small static dipole moment and relatively uniform charge distribution after oxidation/reduction.

68 citations


Journal ArticleDOI
TL;DR: A database of new solvent parameters describing empirically solute/solvent interactions, with the main advantage over previous parametrizations is the easiness of extension of this database to newly designed solvents, since only three probes are required.
Abstract: For about 300 solvents, we propose a database of new solvent parameters describing empirically solute/solvent interactions: DI for dispersion and induction, ES for electrostatic interactions between permanent multipoles, α1 for solute Lewis base/solvent Lewis acid interactions, and β1 for solute hydrogen-bond donor/solvent hydrogen-bond acceptor interactions. The main advantage over previous parametrizations is the easiness of extension of this database to newly designed solvents, since only three probes, the betaine dye 30, 4-fluorophenol, and 4-fluoroanisole are required. These parameters can be entered into the linear solvation energy relationship A = A0 + di(DI) + eES + aα1 + bβ1 to predict a large number of varied physicochemical properties A and to rationalize the multiple intermolecular forces at the origin of solvent effects through a simple examination of the sign and magnitude of regression coefficients di, e, a, and b. Such a rationalization is illustrated for conformational and tautomeric equi...

15 Jun 2015
TL;DR: It is suggested that an aprotic organic solvent affects the reaction kinetics by changing the stabilization of the acidic proton relative to the protonated transition state in Brønsted acid catalysts, such as H-mordenite and H-beta.
Abstract: Reaction kinetics were studied to quantify the effects of polar aprotic organic solvents on the acid-catalyzed conversion of xylose into furfural. A solvent of particular importance is γ-valerolactone (GVL), which leads to significant increases in reaction rates compared to water in addition to increased product selectivity. GVL has similar effects on the kinetics for the dehydration of 1,2-propanediol to propanal and for the hydrolysis of cellobiose to glucose. Based on results obtained for homogeneous Brønsted acid catalysts that span a range of pKa values, we suggest that an aprotic organic solvent affects the reaction kinetics by changing the stabilization of the acidic proton relative to the protonated transition state. This same behavior is displayed by strong solid Brønsted acid catalysts, such as H-mordenite and H-beta.

Journal ArticleDOI
TL;DR: The optical spectra and the radiative and nonradiative decay rate constants have been investigated theoretically for TPA-NZP in hexane, ethyl ether, tetrahydrofuran, and dimethylformamide solvents, in comparison with the gas phase and it is found that upon increasing the solvent polarity, the amount of red shift in the absorption peak is much less than that of emission, resulting in breakdown of the mirror symmetry.
Abstract: The triphenylamine-thiadiazole molecule (TPA-NZP) is a newly popular, highly efficient OLED fluorescent emitter with exciton utilization efficiency exceeding the upper limit of spin statistics (25%). In this work, the optical spectra and the radiative and nonradiative decay rate constants have been investigated theoretically for TPA-NZP in hexane, ethyl ether, tetrahydrofuran, and dimethylformamide solvents, in comparison with the gas phase. We observed the evolutions of the excited states from the hybridized local and charge-transfer (HLCT) character to complete intramolecular charge transfer (CT) character with the increase of the solvent polarities. It is found that upon increasing the solvent polarity, the amount of red shift in the absorption peak is much less than that of emission, resulting in breakdown of the mirror symmetry. This is because that 0-0 transition energy is red-shifted but the vibrational relaxation increases with the solvent polarity, leading to subtraction in absorption while addition in emission. The radiative decay rate constant is calculated to be almost independent of polarity. The nonradiative decay rate increases by almost one order of magnitude from that in nonpolar hexane to the strongly polarized dimethylformamide, which is attributed to the dual effects of the red shift in the gap and enhancement of the vibrational relaxation by solvent polarity.

Journal ArticleDOI
TL;DR: In this paper, the optical properties of two triphenylamine (TPA)-based donor-acceptor fluorophores were investigated in nine different organic solvents as dilute solutions in order to analyze the effect of solvent on their linear and nonlinear optical properties.
Abstract: In this work we present a systematic investigation on the optical properties of two triphenylamine (TPA)-based donor–acceptor fluorophores: TPA-PA (phenylaldehyde) and TPA-BMO ((Z)-4-benzylidene-2-methyloxazol-5(4H)-one). The two compounds are dissolved in nine different organic solvents as dilute solutions in order to analyze the effect of solvent on their linear and nonlinear optical properties. For each compound under one-photon excitation, its fluorescence emission spectrum red-shifts more than 160 nm as the solvent polarity increases from hexane to MeCN, while the fluorescence quantum efficiency and lifetime reach maximum magnitudes in solvents with medium polarity. The quantum efficiency reaches as high as 0.72 in dioxane for TPA-PA and 0.69 in Et2O for TPA-BMO, respectively. These TPA-PA and TPA-BMO solutions are also strongly emissive upon appropriate two photon excitation, with fluorescence emission spectra identical to those under corresponding one-photon excitation. The maximum two-photon absor...

Journal ArticleDOI
TL;DR: A new experimental approach is presented in which two separate cryogenic ion traps are used to reproducibly form weakly bound solvent clusters around electrosprayed ions and messenger-tag them for single-photon infrared photodissociation spectroscopy, enabling the vibrational characterization of ionic clusters comprised of a solvent network around large and non-volatile ions.
Abstract: A new experimental approach is presented in which two separate cryogenic ion traps are used to reproducibly form weakly bound solvent clusters around electrosprayed ions and messenger-tag them for single-photon infrared photodissociation spectroscopy. This approach thus enables the vibrational characterization of ionic clusters comprised of a solvent network around large and non-volatile ions. We demonstrate the capabilities of the instrument by clustering water, methanol, and acetone around a protonated glycylglycine peptide. For water, cluster sizes with greater than twenty solvent molecules around a single ion are readily formed. We further demonstrate that similar water clusters can be formed around ions having a shielded charge center or those that do not readily form hydrogen bonds. Finally, infrared photodissociation spectra of D2-tagged GlyGlyH(+)⋅(H2O)1-4 are presented. They display well-resolved spectral features and comparisons with calculations reveal detailed information on the solvation structures of this prototypical peptide.

Journal ArticleDOI
TL;DR: In this article, the authors evaluate relative C-H reactivity and solvent quality of seven aromatic solvents for the DAP of defect-free naphthalene diimide (NDI)-based copolymers of different solubility.
Abstract: The solvent for direct arylation polycondensation (DAP) is of crucial importance. For conjugated polymers exhibiting reduced solubility, the choice of solvent decides on the maximum molecular weight that can be achieved, hence, good aromatic solvents are generally desirable. However, unintentional activation of C–H bonds present in aromatic solvents under DAP conditions leads to in situ solvent termination which competes with step growth. Here we evaluate relative C–H reactivity and solvent quality of seven aromatic solvents for the DAP of defect-free naphthalene diimide (NDI)-based copolymers of different solubility. C–H reactivity is strongly reduced with increasing degree of substitution for both chlorine and methyl substituents. Mesitylene is largely C–H unreactive and, thus, albeit being a moderate solvent, enables very high molecular weights at elevated temperature for NDI copolymers with limited solubility.

Journal ArticleDOI
TL;DR: An optimized procedure of synthesis that leads to the preparation of glutarimidoxioxime in the absence of other amidoxime byproducts is described in this paper.
Abstract: The complex formation between a cyclic ligand glutarimidoxioxime (denoted as HLIII in this paper) and UO22+ is studied by potentiometry and microcalorimetry. Glutarimidoxioxime (HLIII), together with glutarimidedioxime (H2LI) and glutardiamidoxime (H2LII), belongs to a family of amidoxime derivatives with prospective applications as binding agents for the recovery of uranium from seawater. An optimized procedure of synthesis that leads to the preparation of glutarimidoxioxime in the absence of other amidoxime byproducts is described in this paper. Speciation models based on the thermodynamic results from this study indicate that, compared with H2LI and H2LII, HLIII forms a much weaker complex with UO22+, UO2(LIII)+, and cannot effectively compete with the hydrolysis equilibria of UO22+ under neutral or alkaline conditions. DFT computations, taking into account the solvation by including discrete hydration water molecules and bulk solvent effects, were performed to evaluate the structures and energies of the possible isomers of UO2(LIII)+. Differing from the tridentate or η2-coordination modes previously found in the U(VI) complexes with amidoxime-related ligands, a bidentate mode, involving the oxygen of the oxime group and the nitrogen of the imino group, is found to be the most probable mode in UO2(LIII)+. The bidentate coordination mode seems to be stabilized by the formation of a hydrogen bond between the carbonyl group of HLIII and a water molecule in the hydration sphere of UO22+.

Journal ArticleDOI
TL;DR: The Passerini reaction mechanism is revisited using high-level DFT calculations and it is pointed out that this step is catalyzed by a second carboxylic acid molecule, as the subsequent Mumm rearrangement is.
Abstract: The Passerini reaction mechanism is revisited using high-level DFT calculations. Contrary to the common belief, the nitrilium intermediate is found to be stable in solution and its formation is rate-determining. The present results point out that this step is catalyzed by a second carboxylic acid molecule, as the subsequent Mumm rearrangement is. The solvent effect on the reaction rate was investigated. In a protic solvent like methanol, hydrogen bonds are responsible of the increasing barrier of the rate-determining step, compared to the commonly used solvent, the dichloromethane.

Journal ArticleDOI
TL;DR: It is shown how an enantiopure anion enforces a chiral conformation onto a catalytically relevant achiral cation, and VCD can be used to study solvent effects and that the obtained chiroptical data directly and quantitatively correlate with the experimentally observed enantioselectivity in an asymmetric olefin epoxidation reaction.
Abstract: Ionic interactions are increasingly appreciated as a key, asymmetry-inducing factor in enantioselective catalytic transformations, including those involving Bronsted acid or base catalysis, phase-transfer catalysis, and related processes However, a detailed understanding of these interactions is often lacking Herein, we show how an enantiopure anion enforces a chiral conformation onto a catalytically relevant achiral cation Specifically, we use vibrational circular dichroism (VCD) spectroscopy to monitor the transmission of stereochemical information from a chiral phosphate anion to a flexible manganese(III)-salen cation We show that VCD can be used to study solvent effects and that the obtained chiroptical data directly and quantitatively correlate with the experimentally observed enantioselectivity in an asymmetric olefin epoxidation reaction

Journal ArticleDOI
TL;DR: In this paper, the primary and secondary insertions of propylene into the activated ansa-zirconocene complex [Ph(H)C-(3,6-tBu2Flu)(3tBu-5-Me-C5H2)]ZrMe]+ were calculated with several DFT methods to find the most adequate methodology for the computation of metallocene-catalyzed olefin polymerization reactions.
Abstract: The primary insertion (or 1,2-insertion) of propylene into (C5Me5)2YCH2CH2CH(Me)2, as well as the primary and secondary (or 2,1) insertions of propylene into the activated ansa-zirconocene complex [{Ph(H)C-(3,6-tBu2Flu)(3-tBu-5-Me-C5H2)}ZrMe]+ were calculated with several DFT methods to find the most adequate methodology for the computation of metallocene-catalyzed olefin polymerization reactions. For the yttrium system, both solvent corrections and dispersion corrections are needed to determine energies of coordination and activation barriers in agreement with experimental data. Dispersion corrections were included directly via the use of specific functionals like B97D and M06 or were added as empirical corrections (GD3BJ) to the B3PW91 calculations. For the zirconocene system, the best method is a combination of B3PW91 with solvent corrections incorporated with the SMD continuum model. The dispersion corrections, included via both GD3BJ and M06, tend to overestimate the stabilization of the adducts beca...

Journal ArticleDOI
Cancan Wang1, Hong Jiang1, Changlin Chen1, Rizhi Chen1, Weihong Xing1 
TL;DR: In this article, the effect of solvent on the catalytic performance of glycerol hydrogenolysis to 1,2-propanediol over a Cu-ZnO catalyst prepared by a coprecipitation method was investigated.

Journal ArticleDOI
TL;DR: Several aspects of interfacial solvation are reviewed and ion transfer, electron transfer, and SN2 reactions are considered, showing that solvent effects on these reactions can be understood by examining the unique structure and dynamics of the liquid interface region.
Abstract: The liquid interface is a narrow, highly anisotropic region, characterized by rapidly varying density, polarity, and molecular structure. I review several aspects of interfacial solvation and show how these affect reactivity at liquid/liquid interfaces. I specifically consider ion transfer, electron transfer, and SN2 reactions, showing that solvent effects on these reactions can be understood by examining the unique structure and dynamics of the liquid interface region.

Journal ArticleDOI
TL;DR: The structural processes leading to dual fluorescence of 4-(dimethylamino)benzonitrile in the gas phase and in acetonitrile solvent were investigated and it is suggested that the main role in the dynamics is played by the nonadiabatic interaction of the LE and CT states.
Abstract: The structural processes leading to dual fluorescence of 4-(dimethylamino)benzonitrile in the gas phase and in acetonitrile solvent were investigated using a combination of multireference configuration interaction (MRCI) and the second-order algebraic diagrammatic construction (ADC(2)) methods. Solvent effects were included on the basis of the conductor-like screening model. The MRCI method was used for computing the nonadiabatic interaction between the two lowest excited ππ* states (S2(La, CT) and S1(Lb, LE)) and the corresponding minimum on the crossing seam (MXS) whereas the ADC(2) calculations were dedicated to assessing the role of the πσ* state. The MXS structure was found to have a twisting angle of ∼50°. The branching space does not contain the twisting motion of the dimethylamino group and thus is not directly involved in the deactivation process from S2 to S1. Polar solvent effects are not found to have a significant influence on this situation. Applying Cs symmetry restrictions, the ADC(2) calc...

Journal ArticleDOI
TL;DR: In this article, a novel process for the one-pot production of furan-based fuels, 2,5-dimethylfuran (DMF) and 2, 5-dihmethyltetrahydrofuran (DMTF), from fructose by optimizing the synergic effect of an ionic liquid promoted Ru/C catalyst and the solvent effect.

Journal ArticleDOI
TL;DR: In this article, the authors investigated selective hydrogenation of Acetophenone (AP) to 1-phenylethanol (PhE) in 13 solvents including water and conventional organic solvent, and observed strong solvent effects on the overall rate of AP conversion, depending on the catalysts used.

Journal ArticleDOI
TL;DR: Al, Si and Fe doped graphene are considered as potential materials for efficient As(III) removal by both chemical and physical interactions with high adsorption energies, even stable considering a solvent environment.
Abstract: On the basis of quantum chemistry calculations, the adsorption of As(III) onto graphene based adsorbents has been studied. The energetic and molecular properties that characterize the adsorption have been analyzed, and new adsorbents were proposed. The experimentally reported inefficient adsorption of As(III) by intrinsic graphene is theoretically characterized by a low adsorption energy (∼0.3 eV), which is decreased by solvent effects. Two stable conformations were found for the adsorbent–adsorbate systems. The As(III) removal by unmodified oxidized graphene (GO) reaches a medium size adsorption strength ( ∼1 eV), even stable considering a solvent environment. The efficiency of the adsorbents for As(III) removal is sorted as Al–G > Fe–G ≫ Si–G ≫ GO ≫ G. Therefore, Al, Si and Fe doped graphene are considered as potential materials for efficient As(III) removal.

Journal ArticleDOI
TL;DR: In this paper, the H/D exchange of arenes in acidic media by transition-metal and main-group-metal complexes and common inorganic salts was studied, and the influence of Lewis acidity, anions, charge, and ligands was evaluated.
Abstract: The H/D exchange of arenes in acidic media by transition-metal and main-group-metal complexes and common inorganic salts was studied. The influence of Lewis acidity, anions, charge, and ligands was evaluated. The results indicate that the determination of H/D exchange activity in acidic media is not related to the formation of metal–carbon bonds (i.e., C–H activation). The combined experimental data (regioselectivity, activation energy, kinetics, isotope effects, solvent effects) and DFT calculations point toward a proton catalysis mechanism. Thus, highly Lewis acidic metal compounds, such as aluminum(III) triflate, were extraordinarily active for the H/D exchange reactions. Indeed, the degree of H/D exchange reactivity allows for a comparative measurement of Lewis acidities.

Journal ArticleDOI
TL;DR: In this paper, a two-site catalyst model is proposed whereby the aromatic ring hydrogenation occurs over the metal sites while carbonyl hydrogenation is thought to occur predominantly at interfacial sites, with oxygen vacancies in the titania support activating the carbonyls.

Journal ArticleDOI
TL;DR: The structure-reactivity relationships determined in this study may help in the optimization of the physical absorption process by means of ionic liquids, with dispersion forces playing an important role in CO2 solubility.
Abstract: The physical absorption of CO2 by protic and aprotic ionic liquids such as 1-ethyl-3-methyl-imidazolium tetrafluoroborate was examined at the molecular level using symmetry adapted perturbation theory (SAPT) and density functional techniques through comparison of interaction energies of noncovalently bound complexes between the CO2 molecule and a series of ionic liquid ions and ion pairs. These energies were contrasted with those for complexes with model amines such as methylamine, dimethylamine, and trimethylamine. Detailed analysis of the five fundamental forces that are responsible for stabilization of the complexes is discussed. It was confirmed that the nature of the anion had a greater effect upon the physical interaction energy in non functionalized ionic liquids, with dispersion forces playing an important role in CO2 solubility. Hydrogen bonding with protic cations was shown to impart additional stability to the noncovalently bound CO2···IL complex through inductive forces. Two solvation models, the conductor-like polarizable continuum model (CPCM) and the universal solvation model (SMD), were used to estimate the impact of solvent effects on the CO2 binding. Both solvent models reduced interaction energies for all types of ions. These interaction energies appeared to favor imidazolium cations and carboxylic and sulfonic groups as well as bulky groups (e.g., NTf2) in anions for the physical absorption of CO2. The structure-reactivity relationships determined in this study may help in the optimization of the physical absorption process by means of ionic liquids.

Journal ArticleDOI
01 Jan 2015-Langmuir
TL;DR: Different kinetic mechanisms are compared in terms of peptide secondary structures, solvent-accessible surface area, radius of gyration, relative shape anisotropy, intra/intermolecular interactions, and aggregate size dynamics to provide insightful information for the design of functional biomaterials.
Abstract: Peptide amphiphiles are known to form a variety of distinctive self-assembled nanostructures (including cylindrical nanofibers in hydrogels) dependent upon the solvent conditions. Using a novel coarse-grained model, large-scale molecular dynamics simulations are performed on a system of 800 peptide amphiphiles (sequence, palmitoyl-Val3Ala3Glu3) to elucidate kinetic mechanisms of molecular assembly as a function of the solvent conditions. The assembly process is found to occur via a multistep process with transient intermediates that ultimately leads to the stabilized nanostructures including open networks of β-sheets, cylindrical nanofibers, and elongated micelles. Different kinetic mechanisms are compared in terms of peptide secondary structures, solvent-accessible surface area, radius of gyration, relative shape anisotropy, intra/intermolecular interactions, and aggregate size dynamics to provide insightful information for the design of functional biomaterials.