Showing papers on "Solvent effects published in 2004"
TL;DR: In this article, a roadmap for the literature values of density, viscosity, melting and glass transition temperatures, thermal stability, empirical solvent parameters, absorption, toxicity, surface tension, heat capacity, and thermal conductivity is provided.
Abstract: Ionic liquids are good solvents for catalytic reactions. The rational selection of the appropriate ionic liquid solvent for a particular reaction requires general knowledge of the properties of ionic liquids, and the details of some properties of the specific ionic liquid solvents being considered. The solvent properties of ionic liquids that are relevant to catalysis are discussed, and sources of the values of those properties for ionic liquids are identified. A roadmap for the literature values of density, viscosity, melting and glass transition temperatures, thermal stability, empirical solvent parameters, absorption, toxicity, surface tension, heat capacity, and thermal conductivity is provided.
745 citations
TL;DR: The controversy as to whether the central keto-enol moiety or the peripheral phenolic hydroxyl groups of CU are involved in its radical trapping (antioxidant) activity is resolved and the SPLET process cannot occur in a nonionizing solvent.
Abstract: The rates of reaction of 1,1-diphenyl-2-picrylhydrazyl (dpph•) radicals with curcumin (CU, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione), dehydrozingerone (DHZ, “half-curcumin”), and isoeugenol (IE) have been measured in methanol and ethanol and in two non-hydroxylic solvents, dioxane and ethyl acetate, which have about the same hydrogen-bond-accepting abilities as the alcohols. The reactions of all three substrates are orders of magnitude faster in the alcohols, but these high rates can be suppressed to values essentially equal to those in the two non-hydroxylic solvents by the addition of acetic acid. The fast reactions in alcohols are attributed to the reaction of dpph• with the CU, DHZ, and IE anions (see J. Org. Chem. 2003, 68, 3433), a process which we herein name sequential proton loss electron transfer (SPLET). The most acidic group in CU is the central keto−enol moiety. Following CU's ionization to a monoanion, ET from the [−(O)CCHC(O)−]- moiety to dpph• yields the neutral [−(O)CCH...
381 citations
TL;DR: In this study, eight solvent parameters, including hydrogen bond acceptor propensity, hydrogen bond donor propensity, polarity/dipolarity, dipole moment, dielectric constant, viscosity, surface tension and cohesive energy density, of 96 solvents were collected and separated into 15 solvent groups.
327 citations
TL;DR: In particular, relatively polar solvents that are able to transport water through the emulsion continuous phase (Ostwald ripening) are shown to produce much lower surface areas than analogous resins prepared by homogeneous solution polymerization of divinylbenzene.
Abstract: Poly(divinylbenzene) emulsion-derived (PolyHIPE) solid foams prepared with porogens (toluene, chlorobenzene, (2-chloroethyl)benzene, 1,2-dichlorobenzene, and 1-chloro-3-phenylpropane) in the oil phase have morphologies and surface areas that are strongly influenced by the nature of the porogen. For the case where the surfactant employed is Span 80, we show that the solid foam structure depends on (i) the ability of the solvent to swell the growing network, (ii) the solvent polarity, and (iii) the ability of the solvent to adsorb at the emulsion interface. In particular, relatively polar solvents that are able to transport water through the emulsion continuous phase (Ostwald ripening) are shown to produce much lower surface areas than analogous resins prepared by homogeneous solution polymerization of divinylbenzene in the presence of the solvent in question alone. The influence of Ostwald ripening is further suggested by the observation that surface area decreases with increasing emulsion aqueous phase co...
295 citations
TL;DR: Mechanistic results support the idea that thiolate is the reacting species and that the reaction indeed proceeds through an uncomplicated S(N)2 transition state, and it was found that attack by thiol is much faster than previously assumed, if mediated through water chains.
Abstract: The mechanism for thiol/disulfide exchange has been studied with high-level theoretical calculations. Free energies, transition structures, charge densities, and solvent effects along the reaction pathway have been determined for the first time. Mechanistic results agree with experimental data, and support the idea that the thiolate is the reacting species and that the reaction indeed proceeds through an uncomplicated S(N)2 transition state. The transition structures have the charge density evenly concentrated in the attacking and leaving sulfur atoms. The charge densities allow us to rationalize the solvent effects. As transition structures have the charge density more widely distributed than reactants, hydrophobic environments catalyze the reaction. The effect can be so dramatic that disulfide exchange inside the active site of ribonucleotide reductase is estimated to be catalyzed 10(3) times faster than the reaction in water. It was also found that attack by thiol is much faster than previously assumed, if mediated through water chains. Although the present results, as well as experimental data, still suggest that thiolate is the main reaction species, water-mediated thiol attack is almost kinetically competitive, and can eventually become competitive under specific experimental conditions.
264 citations
245 citations
TL;DR: For the water system, the electric field method is superior to the potential approach, as judged by comparison with experiments for the absorption line shape, and for the N-methylacetamide system the two methods are comparable.
Abstract: Kwac and Cho [J. Chem. Phys. 119, 2247 (2003)] have recently developed a combined electronic structure/molecular dynamics approach to vibrational spectroscopy in liquids. The method involves fitting ab initio vibrational frequencies for a solute in a cluster of solvent molecules to a linear combination of the electrostatic potentials on the solute atoms due to the charges on the solvent molecules. These authors applied their method to the N-methylacetamide-D/D(2)O system. We (S. A. Corcelli, C. P. Lawrence, and J. L. Skinner, [J. Chem. Phys. 120, 8107 (2004)]) have recently explored a closely related method, where instead of the electrostatic potential, the solute vibrational frequencies are fit to the components of the electric fields on the solute atoms due to the solvent molecules. We applied our method to the HOD/D(2)O and HOD/H(2)O systems. In order to make a direct comparison of these two approaches, in this paper we apply their method to the water system, and our method to the N-methylacetamide system. For the water system we find that the electric field method is superior to the potential approach, as judged by comparison with experiments for the absorption line shape. For the N-methylacetamide system the two methods are comparable.
243 citations
TL;DR: In this paper, a halide ligand from the deactivator in ATRP reactions in the presence of water or other coordinating compounds can be suppressed by the addition of halide salts allowing the regeneration of the dissociated CuII−X species and therefore increasing the deactivation rate.
Abstract: Copper-mediated ATRP in protic solvents is characterized by inefficient deactivation due to reversible dissociation of a halide ligand from the ATRP deactivator CuIILnX (L = bipyridine or another amine or imine, X = Br, Cl), which may be followed by competitive coordination of solvent to the CuII center. This process is strongly solvent-dependent and leads to fast and often poorly controlled polymerizations. The loss of a halide ligand from the deactivator in ATRP reactions in the presence of water or other coordinating compounds can be suppressed by the addition of halide salts allowing the regeneration of the dissociated CuII−X species and, therefore, increasing the deactivation rate. The deactivation step in ATRP, which is of primary importance for control over the polymerization, can also be accelerated by employing a catalyst system initially containing a sufficiently large amount of CuII−halide complex. These approaches are illustrated by conducting the controlled radical polymerization of 2-hydroxy...
237 citations
TL;DR: In this article, the microdomain structure in symmetric diblock copolymer poly(styrene-b-methyl methacrylate), P(Sb-MMA), ultrathin films via PMMA-selective solvent vapor treatment by atomic force microscopy was analyzed.
Abstract: We have followed the time development of the microdomain structure in symmetric diblock copolymer poly(styrene-b-methyl methacrylate), P(S-b-MMA), ultrathin films via PMMA-selective solvent vapor treatment by atomic force microscopy (AFM). After preparation on a substrate preferentially attracting the PMMA block, PS forms a continuous layer at a film's free surface. With subsequent solvent vapor treatment, the film gradually shows a well-ordered hexagonally packed nanocylinders structure. It is shown that only when the film thickness is less than the 1/2L0 (lamellar repeat spacing), and exposed to PMMA block selective solvent for an appropriate time, can the well-ordered hexagonally packed nanocylinders form. On an extended solvent vapor treatment, a mixed morphology containing nanocylinders and stripes appears, followed by the striped morphologies. When the annealing time is long enough, the film comes back to the flat surface again, however, with PMMA instead of PS dominating the free surface. Thickness...
202 citations
TL;DR: The study shows that by only taking into account both bulk effects and explicit solvent molecules it is possible to reproduce solvent effects on the energy and the intensities of the electronic spectra, especially for what concerns pi/pi* transition.
Abstract: Here we present the first computations of fluorescence spectra in aqueous solution at an accurate quantum mechanical level. From a methodological point of view, our study shows that by only taking into account both bulk effects and explicit solvent molecules it is possible to reproduce solvent effects on the energy and the intensities of the electronic spectra, especially for what concerns π/π* transition. The computed absorption and fluorescence spectra are in a good agreement with the available experimental results. The energy ordering between the lowest energy n-π* and the π/π* transitions in uracil strongly depends on the nature of the embedding medium. The geometry of the first solvation shell is remarkably sensitive to the specific electronic state, suggesting that solvent degrees of freedom can act as S1/S2 coupling modes.
176 citations
TL;DR: It is clearly shown that macroscopic gelation can be related to a solvent polar solubility parameter for this system and the role of the solvent environment in terms of dendron--dendron intermolecular hydrogen bonding and its impact on the supramolecular chiral organization of the assembled superstructure is demonstrated.
Abstract: The self-assembly of diaminododecane with dendritic l-lysine-based peptides to form gel-phase materials was investigated in a range of different solvents. The degree of structuring was modulated by the solvent employed, an effect which induced subtle changes in the mesoscale aggregate morphology and macroscopic behavior of the self-assembled state. In this paper a range of different solvent parameters are investigated, and it is clearly shown that macroscopic gelation can be related to a solvent polar solubility parameter for this system. The results also show a dependence on Kamlet-Taft hydrogen bonding parameters, and this clearly demonstrates the role of the solvent environment in terms of dendron--dendron intermolecular hydrogen bonding and its impact on the supramolecular chiral organization of the assembled superstructure.
TL;DR: In this article, a comprehensive theoretical study of the reaction mechanisms for the conversion between spiropyrans (SPs) and the open form of merocyanines (MCs) has been conducted by theoretical calculations.
Abstract: A comprehensive theoretical study of the reaction mechanisms for the conversion between spiropyrans (SPs) and the open form of merocyanines (MCs) has been conducted by theoretical calculations. The reaction mechanisms on the ground- and triplet-state potential energy surfaces (PESs) were investigated using the density functional method. Time-dependent density functional theory (TD-DFT) calculations using the CIS optimized excited-state geometries were carried out to study the reaction mechanisms on the lowest excited singlet-state PES. Two possible reaction mechanisms for the thermal conversion between SPs to MCs were found on the ground-state PES. The geometrical parameter, BLA (Bond Length Alternation), which correlates the strengths of the substituents and the polarities of solvents, was used to explain the changes in the reaction mechanism induced by the different donor−acceptor pairs and solvents. In addition, the reaction mechanisms of spiropyran⇆merocyanine conversion on the triplet and the lowest ...
TL;DR: The gas-phase S(N)2 reactions of chloride with ethyl and neopentyl chlorides and their alpha-cyano derivatives have been explored with B3LYP, CBS-QB3, and PDDG/PM3 calculations, and theoretical results contrast with previous conclusions that were based upon gas- phase rate measurements.
Abstract: The gas-phase SN2 reactions of chloride with ethyl and neopentyl chlorides and their α-cyano derivatives have been explored with B3LYP, CBS-QB3, and PDDG/PM3 calculations. Calculations predict that the steric effect of the tert-butyl group raises the activation energy by about 6 kcal/mol relative to methyl in both cases. Solvent effects have been computed with QM/MM Monte Carlo simulations for DMSO, methanol, and water, as well as with a polarizable continuum model, CPCM. Solvents cause a large increase in the activation energies of these reactions but have a very small differential effect on the ethyl and neopentyl substrates and their cyano derivatives. The theoretical results contrast with previous conclusions that were based upon gas-phase rate measurements.
TL;DR: In this article, the B3LYP density functional level of quercetin and its radicals were investigated at the B 3LYP functional level with the aim of determining the energetic and spectroscopic parameters and the factors that influence their antioxidant activity in the gas phase and in aqueous solution.
Abstract: Quercetin and its radicals were investigated at the B3LYP density functional level with the aim of determining the energetic and spectroscopic parameters and the factors that influence their antioxidant activity in the gas phase and in aqueous solution. The results indicated that the antioxidant ability of quercetin is mainly due to the orthodiphenolic moiety but also to the presence of the C=C double bond of the pyrone ring. Differences in the stability order of the isomers of quercetin’s radicals were found in going from vacuum to solvent. Hyperfine coupling constants were computed to help the interpretation of the intricate ESR spectrum of quercetin.
TL;DR: The enol imine ⇄ enaminone tautomerization constants, KT, and thermodynamic parameters, ΔHT and ΔST, of 1-hydroxy-2-naphthaldehyde Schiff bases are determined by UV/vis spectroscopy as discussed by the authors.
Abstract: The enol imine ⇄ enaminone tautomerization constants, KT, and thermodynamic parameters, ΔHT and ΔST, of 1-hydroxy-2-naphthaldehyde Schiff bases are determined by UV/vis spectroscopy. Polar solvents shift the equilibrium toward the quinone form (for the unsubstituted derivative 1c, KT = 0.20 (cyclohexane) and KT = 1.49 (ethanol)). Both donor (MeO, NMe2) and acceptor (CN, NO2) substituents lead to a decreased KT independent of solvent polarity. In apolar solvents, for all derivatives 1a−1e, the enol imine ⇄ enaminone equilibria are endergonic but exothermic. Linear solvation energy relationships allow extrapolation of ΔGT to the gas phase. Density functional theory calculations (B3LYP/6-311+G**) yield good agreement with these extrapolated ΔGT values. Solvent effects on 1c are also successfully reproduced by the calculations. Geometric (O···N distance) and energetic criteria (conformer energy differences, homodesmotic reactions) establish the importance of intramolecular hydrogen bonding for the tautomerism...
TL;DR: Analysis of Raman and neutron scattering spectra of lysozyme demonstrates that the protein dynamics follow the dynamics of the solvents glycerol and trehalose over the entire temperature range measured 100-350 K, giving insight into the effectiveness of glycersol as a biological cryopreservant.
Abstract: Analysis of Raman and neutron scattering spectra of lysozyme demonstrates that the protein dynamics follow the dynamics of the solvents glycerol and trehalose over the entire temperature range measured 100-350 K. The protein's fast conformational fluctuations and low-frequency vibrations and their temperature variations are very sensitive to behavior of the solvents. Our results give insight into previous counterintuitive observations that protein relaxation is stronger in solid trehalose than in liquid glycerol. They also provide insight into the effectiveness of glycerol as a biological cryopreservant.
TL;DR: A series of poly(alkyl methacrylate)s that contained either pendant carboxylic acid or self-complementary multiple hydrogen bonding (SCMHB) groups were synthesized to determine the influence of intermolecular associations on solution rheology and electrospinning performance.
TL;DR: N-Benzamido-N'-phenylthioureas represent a new generation of neutral thiourea-based anion receptors that show substantially improved anion binding performance important for anion sensing and recognition.
Abstract: A series of neutral N-(substituted-benzamido)-N‘-phenylthioureas (substituent = p-OC2H5, p-CH3, m-CH3, H, p-Cl, p-Br, m-Cl, and p-NO2) were designed as anion receptors, in which the thiourea binding site was attached to the benzamido moiety via an N−N bond. The absorption spectra of these N-benzamidothioureas in acetonitrile peaked at ca. 270 nm were found to show unprecedented red shifts by 7 373 to 14 325 cm-1 in the presence of anions such as AcO-, F-, and H2PO4-. Under the same conditions, the classic neutral thiourea receptors, N-(substituted-phenyl)-N‘-phenylthioureas, showed absorption spectral shifts in most cases of less than 800 cm-1 with one exception of 6501 cm-1. Control experiments, effects of protic solvent, and 1H NMR titration confirmed the formation of hydrogen-bonding complexes between the new N-benzamidothiourea receptors and anions. The binding constants with AcO-, for example, are at 105−107 mol-1 L order of magnitude, which are 13 to 590 times those of the corresponding classic N-ph...
TL;DR: In this paper, the inductive and dispersive interactions of solvents were empirically evaluated for the first time by using 3,20-di-tert-butyl (ttbP9) as a probe, which exhibits a very strong first electronic transition with a marked vibronic structure that is very well resolved from the second electronic transition.
TL;DR: In this paper, the spectroscopic properties of lumichromes and lumiflavins were investigated and the results indicated that the predicted singlet−singlet and triplet−triplet transitions obtained for the various compounds studied, and the good correspondence between the predicted and measured transitions, indicate that the techniques applied provide an accurate description of the spectral properties of luminiferous compounds.
Abstract: Solvent effects on the spectroscopic properties of lumichromes and lumiflavins are presented. Fluorescence yields for lumiflavins are an order of magnitude larger than those for lumichromes, due to their lower nonradiative rate constants. Solvent effects on the absorption and emission band positions are explained on the basis of hydrogen-bonding interactions. TD-DFT calculations predicted that the lowest energy states are n,π* in the case of lumichromes, but π,π* in the case of the lumiflavins. The overall consistency of the predicted singlet−singlet and triplet−triplet transitions obtained for the various compounds studied, and the good correspondence between the predicted and measured transitions, indicate that the techniques applied provide an accurate description of the spectral properties of lumiflavins and lumichromes. The measured singlet oxygen yields have shown the lumichromes to be efficient singlet oxygen sensitizers.
TL;DR: Optically active acyclic ethynylhelicene oligomers were synthesized in high yields by a two-directional method involving Sonogashira coupling and deprotection, and vapor pressure osmometry studies indicated that the helical structure of the heptamer is dimeric in benzene, fluorobenzene, and trifluoromethylbenzene, while the random coil structure of in chloroform and toluene.
Abstract: Optically active acyclic ethynylhelicene oligomers were synthesized in high yields by a two-directional method involving Sonogashira coupling and deprotection. Their CD spectra in chloroform exhibited large differences between the oligomers with less than seven helicenes and their higher homologues, which indicated the formation of helical structures for the latter and random coil structures for the former. The helical heptamer gradually unfolded to a random coil structure in chloroform at room temperature. The unfolding rate was examined by CD in several aromatic solvents as well, and the rate constant k was found to be highly dependent on the type of aromatic substituent: k differed by seven orders of magnitude between iodobenzene and trifluoromethylbenzene. Several features of the rates are notable: The reaction rates in halobenzenes were in the order of iodobenzene > bromobenzene > chlorobenzene > benzene > fluorobenzene > m-difluorobenzene, those in alkylbenzenes were styrene > phenylacetylene > et...
TL;DR: This finding firmly establishes that the azine bridge indeed functions as a "conjugation stopper" in polar organic crystalline materials, an important design concept in the authors' polar materials research.
Abstract: Solvent effects on the NMR spectra of symmetrical (X = F (1), X = Cl (2), X = Br (3), X = I (4), X = NO2 (5), X = CN (6)) and unsymmetrical (X = I, Y = MeO (7), Y = PhO (8)) para-disubstituted acetophenone azines X−C6H4−CMeN−NCMe−C6H4−Y and of models X−C6H4−CMeN−Z (X = I, Z = H (9), Z = NH2 (10)), 4-iodoacetophenone (11), and iodobenzene (12) were measured in CDCl3, DMSO, THF, pyridine, and benzene to address one intramolecular and one intermolecular issue. Solvent effects on the 13C NMR spectra are generally small, and this finding firmly establishes that the azine bridge indeed functions as a “conjugation stopper,” an important design concept in our polar materials research. Since intermolecular halogen bonding of haloarenes do occur in polar organic crystalline materials, the NMR solution data pose the question as to whether the absence of solvent shifts indicates the absence of strong halogen bonding in solution. This question was studied by the theoretical analysis of the DMSO complexes of iodoarenes...
TL;DR: The origin of the enantioselectivity in the ruthenium-catalyzed transfer hydrogenation has been studied and electrostatic effects are of importance, not only in the T-shaped arene-aryl interaction in the favored transition state but also between the aryl of the substrate and the amine ligand in the disfavored TS.
Abstract: The origin of the enantioselectivity in the ruthenium-catalyzed transfer hydrogenation has been studied by means of experiment and density functional theory calculations. The results clearly show that electrostatic effects are of importance, not only in the T-shaped arene-aryl interaction in the favored transition state but also between the aryl of the substrate and the amine ligand in the disfavored TS. In addition, the electrostatic interaction between the alkyl substituent of the substrate and the catalyst is of importance to the enantioselectivity. The major cause of enantioselection is found to be of nonelectrostatic origin. This inherent property of the catalytic system is discussed in terms of dispersion forces and solvent effects. Finally, a minor but well-characterized steric effect was identified. The success of this class of catalysts in the reduction of alkyl aryl ketones is based on the fact that all factors work in the same direction.
TL;DR: The endo:exo ratio of 0.35:1 for the reaction of cyclopentadiene with methyl methacrylate observed in organic solvents can be converted to 3:1 in chloroaluminate ionic liquids with their effective reuse in Diels-Alder reactions.
Abstract: The endo:exo ratio of 0.35:1 for the reaction of cyclopentadiene with methyl methacrylate observed in organic solvents can be converted to 3:1 in chloroaluminate ionic liquids with their effective reuse in Diels-Alder reactions.
TL;DR: In this paper, the extreme polar morphology of the stable form of a steroid is explained by a molecular dynamics simulations approach, and the habit modification is caused by surface-solvent interactions, which affect the growth rate of the polar faces differently.
Abstract: The extreme polar morphology that has been observed for crystals of the stable form of a steroid is explained by a molecular dynamics simulations approach. The habit modification is caused by surface-solvent interactions, which affect the growth rate of the polar faces differently. The same effect was observed for the metastable polymorphic form. Depending on the solvent, the nature of the difference is mainly caused by the hydrogen bond interactions or the electrostatic part of the interactions.
TL;DR: It is suggested that explicit water–AD interactions may distort C5 and β (or αR and β) to an intermediate conformation in the strong polar solvents, and the energy surfaces may serve as the basis for developing of strategies enabling the inclusion of solvent polarization in the force field.
Abstract: The effects of solvation on the conformations and energies of alanine dipeptide (AD) have been studied by ab initio calculations up to MP2/cc-pVTZ//MP2/6-31G**, utilizing the polarizable continuum model (PCM) to mimic solvation effects. The energy surfaces in the gas phase, ether, and water bear similar topological features carved by the steric hindrance, but the details differ significantly due to the solvent effects. The gas-phase energy map is qualitatively consistent with the Ramachandran plot showing seven energy minima. With respect to the gas-phase map, the significant changes of the aqueous map include (1) the expanded low-energy regions, (2) the emergence of an energy barrier between C5-β and αR-β2 regions, (3) a clearly pronounced αR minimum, a new β-conformer, and the disappearance of the gas-phase global minimum, and (4) the shift of the dominant region in LEII from the gas-phase C7ax region to the αL region. These changes bring the map in water to be much closer to the Ramachandran plot than the gas-phase map. The solvent effects on the geometries include the elongation of the exposed NH and CO bonds, the shortening of the buried HNCO peptide bonds, and the enhanced planarity of the peptide bonds. The energy surface in ether has features similar to those both in the gas phase and in water. The free energy order computed in the gas phase and in ether is in good agreement with experimental studies that concluded that C5 and C7eq are the dominant species in both the gas phase and nonpolar solvents. The free energy order in water is consistent with the experimental observation that the dominant C7eq in the nonpolar solvent was largely replaced by PII-like (i.e., β) and αR in the strong polar solvents. Based on calculations on AD + 4H2O and other AD–water clusters, we suggest that explicit water–AD interactions may distort C5 and β (or αR and β) to an intermediate conformation. Our analysis also shows that the PCM calculations at the MP2/cc-pVTZ//MP2/6-31G** level give good descriptions to the bulk solvent polarization effect. The results presented in this article should be of sufficient quality to characterize the peptide bonds in the gas phase and solvents. The energy surfaces may serve as the basis for developing of strategies enabling the inclusion of solvent polarization in the force field. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1699–1716, 2004
TL;DR: The results show that specific interactions (hydrogen bonds) between solvent molecules and between polymer and solvent molecules play an important role in thermodiffusion for this system.
Abstract: Soret coefficients of the ternary system of poly(ethylene oxide) in mixed water/ethanol solvent were measured over a wide solvent composition range by means of thermal diffusion forced Rayleigh scattering. The Soret coefficient S(T) of the polymer was found to change sign as the water content of the solvent increases with the sign change taking place at a water mass fraction of 0.83 at a temperature of 22 degrees C. For high water concentrations, the value of S(T) of poly(ethylene oxide) is positive, i.e., the polymer migrates to the cooler regions of the fluid, as is typical for polymers in good solvents. For low water content, on the other hand, the Soret coefficient of the polymer is negative, i.e., the polymer migrates to the warmer regions of the fluid. Measurements for two different polymer concentrations showed a larger magnitude of the Soret coefficient for the smaller polymer concentration. The temperature dependence of the Soret coefficient was investigated for water-rich polymer solutions and revealed a sign change from negative to positive as the temperature is increased. Thermodiffusion experiments were also performed on the binary mixture water/ethanol. For the binary mixtures, the Soret coefficient of water was observed to change sign at a water mass fraction of 0.71. This is in agreement with experimental results from the literature. Our results show that specific interactions (hydrogen bonds) between solvent molecules and between polymer and solvent molecules play an important role in thermodiffusion for this system.
TL;DR: In this article, the applicability limits of the Srinivasan and Weidner model have been tested and the very strong influence of the solvent nature (viscosity and molar conductivity of the solution) on the characteristics of the nanoporous carbon electrode cells has been established.
TL;DR: A microscopic theory of solvent reorganization energy in polar molecular solvents is developed and a good agreement between the analytical procedure and the results of Monte Carlo simulations of model systems is achieved.
Abstract: A microscopic theory of solvent reorganization energy in polar molecular solvents is developed. The theory represents the solvent response as a combination of the density and polarization fluctuations of the solvent given in terms of the density and polarization structure factors. A fully analytical formulation of the theory is provided for a solute of arbitrary shape with an arbitrary distribution of charge. A good agreement between the analytical procedure and the results of Monte Carlo simulations of model systems is achieved. The reorganization energy splits into the contributions from density fluctuations and polarization fluctuations. The polarization part is dominated by longitudinal polarization response. The density part is inversely proportional to temperature. The dependence of the solvent reorganization energy on the solvent dipole moment and refractive index is discussed.
TL;DR: In this paper, the effect of the extraction solvent on the extraction yield and ash content in the HyperCoal was investigated, and it was shown that the polar compounds contained mainly consisted of quinoline-type ones.