Showing papers on "Solvent published in 2006"
TL;DR: It is proposed that surface Cd vacancies function as nonradiative recombination centers and the adsorption of a Lewis base to the QD raises the surface vacancy energy close to, or above, the conduction band edge and eliminates electron capture by the surface vacancies.
Abstract: We report on the effects of Lewis bases and other ligands on radiative recombination in CdSe quantum dots (QDs) in several solvents. Long-chain primary amines are found to be the most efficacious capping agents for CdSe QDs in nonpolar solvents. Primary alkylamines are superior to secondary and tertiary alkylamines. The kinetics of chemisorption and desorption in less polar solvents, such as hexane or chloroform, are temperature controlled and obey a Langmuir isotherm. Mercaptan adsorption also obeys a Langmuir isotherm, and alkylmercaptans rapidly displace amines, leading to luminescence quenching. In more polar solvents, such as toluene, ligands desorb, leading to luminescence quenching. It is proposed that surface Cd vacancies function as nonradiative recombination centers. The adsorption of a Lewis base to the QD raises the surface vacancy energy close to, or above, the conduction band edge and eliminates electron capture by the surface vacancies. Solvent polarity has a strong effect on luminescence since the solvent determines the extent of ligand adsorption to the QD surface.
495 citations
TL;DR: In this article, the acid-catalyzed dehydration of fructose was performed in a microbatch reactor at 90°C using 1-H-3-methyl imidazolium chloride, HMIM+Cl−, acting both as solvent and catalyst.
Abstract: The acid-catalyzed dehydration of fructose was performed in a microbatch reactor at 90 °C using 1-H-3-methyl imidazolium chloride, HMIM+Cl−, acting both as solvent and catalyst. A yield in 5-hydroxymethylfurfural (HMF) as high as 92% is achieved within 15–45 min. A productivity of 0.02 mmol of HMF, per min and per mmol of ionic liquid, can then be obtained. A remarkable feature, as compared with other catalytic systems, is the absence of decomposition of 5-hydroxymethylfurfural which can then be separately or continuously extracted in a simple manner with diethyl ether, thus allowing easier recycling of the ionic liquid after water removal. The absence of decomposition of 5-hydroxymethylfurfural is due to the lower free energy of activation calculated in the presence of the ionic liquid compared to other homogeneous or heterogeneous catalysts, which then makes, in a consecutive reaction network, the formation of the 5-hydroxymethylfurfural intermediate nearly quantitative. Under similar operating conditions, sucrose is nearly quantitatively transformed into HMF and unreacted glucose.
333 citations
TL;DR: The interaction of calixpyrrole with several chloride salts has been studied in the solid state by X-ray crystallography as well as in solution by isothermal titration calorimetry (ITC) and (1)H NMR spectroscopic titrations, and the resulting affinity constants were found to be highly dependent on the choice of solvent.
Abstract: The interaction of calixpyrrole with several chloride salts has been studied in the solid state by X-ray crystallography as well as in solution by isothermal titration calorimetry (ITC) and 1H NMR spectroscopic titrations. The titration results in dimethylsulfoxide, acetonitrile, nitromethane, 1,2-dichloroethane, and dichloromethane, carried out using various chloride salts, specifically tetraethylammonium (TEA), tetrapropylammonium (TPA), tetrabutylammonium (TBA), tetraethylphosphonium (TEP), tetrabutylphosphonium (TBP), and tetraphenylphosphonium (TPhP), showed no dependence on method of measurement. The resulting affinity constants (Ka), on the other hand, were found to be highly dependent on the choice of solvent with Ka's ranging from 102−105 M-1 being recorded in the test solvents used for this study. In dichloromethane, a strong dependence on the countercation was also seen, with the Ka's for the interaction with chloride ranging from 102−104 M-1. In the case of TPA, TBA, and TBP, the ITC data coul...
305 citations
TL;DR: The parallels between organic reactions conducted with water as the solvent and reactions conducted under high pressure can be understood in light of theories of aqueous solvation and hydrophobic effects to promote reactions of nonpolar compounds.
Abstract: The parallels between organic reactions conducted with water as the solvent and reactions conducted under high pressure can be understood in light of theories of aqueous solvation and hydrophobic effects. Such parallels provide powerful tools for promoting reactions of nonpolar compounds.
305 citations
TL;DR: In this article, the effect of sample solvent in the antioxidant capacity of foods measured by the four most widely used procedures (ABTS, FRAP, DPPH and ORAC) has not been systematically studied.
260 citations
TL;DR: In this article, the authors focused on a study of sulfolane and four ionic liquids as solvents in liquid-liquid extraction, and the experimental data for the binary and ternary systems were well correlated with the NRTL model.
255 citations
TL;DR: In this paper, the effects of several parameters (ligand, solvent, reducing agent, metal) on click coupling of low-molecular-weight α,ω-diazido-terminated polystyrene prepared by atom transfer radical polymerization (ATRP) were studied using step-growth click coupling.
Abstract: CuI-catalyzed azide−alkyne cycloadditions were conducted in organic media under various conditions. The effects of several parameters (ligand, solvent, reducing agent, metal) on these reactions were studied using the step-growth click coupling of low-molecular-weight α,ω-diazido-terminated polystyrene prepared by atom transfer radical polymerization (ATRP). These reactions were typically conducted in DMF, monitored by size exclusion chromatography (SEC), and semiquantitatively analyzed by Gaussian multipeak fitting and subsequent peak integration. Both the electronic properties of the ligand and the number of coordinating atoms had significant influence on the rates of the click coupling reactions. Aliphatic amine ligands led to significantly faster rates as compared to pyridine-based ligands. Faster rates were also observed with tridentate vs tetradentate ligands. A further rate enhancement was observed when the reactions were conducted in a noncoordinating solvent (toluene) vs a coordinating solvent (DM...
219 citations
TL;DR: The Catalán solvent scales are found to be the most suitable for describing the solvatochromic shifts of the fluorescence emission, which are dominated by polarity/polarizability effects, as confirmed by quantum-chemical calculations performed in the dielectric continuum approximation.
Abstract: Steady-state and time-resolved fluorescence techniques have been used to study the photophysical properties of the fluorescent BODIPY-derived dye 3-{2-[4-(dimethylamino)phenyl]ethenyl}-4,4-difluoro-8-(4-methoxyphenyl)-1,5,7-trimethyl-3a,4a-diaza-4-bora-s-indacene. This compound has been synthesized via a microwave-assisted condensation of p-N,N-dimethylaminobenzaldehyde with the appropriate 1,3,5,7-tetramethyl substituted borondipyrromethene unit. The fluorescence properties of the dye are strongly solvent dependent: increasing the solvent polarity leads to lower fluorescence quantum yields and lifetimes, and the wavelength of maximum fluorescence emission shifts to the red. The Catalan solvent scales are found to be the most suitable for describing the solvatochromic shifts of the fluorescence emission. These are dominated by polarity/polarizability effects, as confirmed by quantum-chemical calculations performed in the dielectric continuum approximation. Fluorescence decay profiles of the dye can be de...
217 citations
TL;DR: The effect of solvent on the two-dimensional (2D) supramolecular ordering of monodendron 1 at the liquid-solid interface has been systematically investigated by means of scanning tunneling microscopy (STM).
Abstract: The effect of solvent on the two-dimensional (2D) supramolecular ordering of monodendron 1 at the liquid-solid interface has been systematically investigated by means of scanning tunneling microscopy (STM). Solvents range from those with hydrophilic solvating properties, such as alkylated alcohols and acids, to hydrophobic solvents such as alkylated aromatics and alkanes. Dramatic differences in the 2D ordering are observed depending on the nature of the solvent. Of particular interest is the fact that in hydrophobic solvating solvents, such as aliphatic and aromatic hydrocarbons, solvent molecules are coadsorbed in the 2D molecular network while this is not the case for alkylated alcohols or acids. Furthermore, in the case of the coadsorbing solvents, a striking influence of the alkyl chain length has been observed on the 2D pattern formed. The solvent and alkyl chain length dependences are discussed in terms of molecule-molecule interactions (homo and hetero) and molecule-substrate interactions.
198 citations
TL;DR: A regression equation for predicting the carotenoid yield as a function of three processing variable (hexane % in solvent mixture, solvent-to-waste ratio and number of extractions) was derived by statistical analysis, and a model with predictive ability of 0.98 was obtained.
195 citations
TL;DR: In this article, the effect of solvent on organogel formation was investigated in selected ester, ketone, and alcoholic solvents using unique symmetrical trehalose diesters as gelators.
Abstract: Solvent−gelator interactions play a key role in mediating organogel formation and ultimately determine the properties of the gel. The effect of solvent on organogel formation was investigated in selected ester, ketone, and alcoholic solvents using unique symmetrical trehalose diesters as gelators. In solvents of the same class the gelation number (defined as the ratio of solvent molecules that gel per gelator molecule) decreased for trehalose 6,6‘-diacetate and 6,6‘-dibutyrate as the solvent Hildebrand solubility parameter increased. The opposite was observed for trehalose 6,6‘-didecanoate and 6,6‘-dimyristate. In general, the gelation numbers for all the gelators studied decreased in the order of esters > ketones > alcohols. Alcohols, which are capable of hydrogen bonding and can make substantial contribution to the total solvent−gelator interaction, significantly compromise gel formation. Optical microscopy and scanning electron microscopy revealed that for systems with high gelation numbers, such as tr...
TL;DR: In this article, a review summarizes the oxidation methods of organic compounds carried out in the presence of a catalyst using ionic liquids or molten ammonium salts as solvents, where the catalyst is efficiently immobilized in the solvent, thus leading to a reusable system.
Abstract: This review summarizes the oxidation methods of organic compounds carried out in the presence of a catalyst using ionic liquids or molten ammonium salts as solvents. From an ecological point of view, these procedures are particularly interesting when the catalyst is efficiently immobilized in the solvent, thus leading to a reusable system.
TL;DR: Water immiscible ionic liquids are shown to have no damaging effects on the cell membranes of Escherichia coli and Saccharomyces cerevisiae and can be used as biocompatible solvents for microbial biotransformations exemplified by an increase in yield of chiral alcohol synthesis.
Patent•
13 Oct 2006
TL;DR: In this paper, a lyophilization process which comprises dissolving a material in one or more solvents for said material to form a solution; forcing said material at least partially out of solution by combining the solution and a non-solvent for the material, which nonsolvent is miscible with either the solvent or solvent used and wherein said non solvent is volatilizable under freeze-drying conditions.
Abstract: A lyophilization process which comprises dissolving a material in one or more solvents for said material to form a solution; forcing said material at least partially out of solution by combining the solution and a non-solvent for the material, which non-solvent is miscible with the solvent or solvents used and wherein said non-solvent is volatilizable under freeze-drying conditions. In addition, for hydrophobic and/or lipophilic materials, the anti-solvent can be omitted, and the solution of the material in the solvent can be subjected directly to freeze drying. The lyophilizates can then be reconstituted with typical aqueous diluent in the case of hydrophilic materials. Hydrophobic and or lipophilic materials can be initially reconstituted with propylene glycol and/or polyethyleneglycol to form a high concentration solution therein and this is further diluted for use with a diluent of Intralipid, plasma, serum, or even whole blood.
TL;DR: It is shown that certain novel, biocompatible ionic liquids provide a stabilizing solvent for proteins, for example, cytochrome c, such that structure and activity are maintained even after 6 months of storage at room temperature.
Abstract: Proteins generally are only stable in vitro for short periods of time. This results in challenges during isolation and purification of recombinant proteins and reduces the shelf life of protein-based pharmaceuticals. Here we show that certain novel, biocompatible ionic liquids provide a stabilizing solvent for proteins, for example, cytochrome c, such that structure and activity are maintained even after 6 months of storage at room temperature. Normally, this protein would be rendered inactive after only 1 week in buffered aqueous solution. The effect of the ionic liquid solvent appears to be related to protection against hydrolysis.
TL;DR: In this paper, the effect of type of organic phase solvents on the mean particle sizes of obtained poly( d,l -lactide-co-glycolide) (PLGA) nanoparticles were investigated by an emulsification-diffusion method.
TL;DR: In this article, molecularly imprinted polymer (MIP) powders were blended with PMMA and the blended films were coated on a piezoelectric quartz crystal with a view to preparing QCM-based VOC sensors.
Abstract: Cross-linked polymers made of methyl methacrylate (MMA) as a monomer and divinylbenzene (DVB) as a cross-linking agent were prepared in the presence of toluene or p-xylene as a solvent. The cross-linked polymer prepared in toluene tended to sorb toluene vapor preferably, while the cross-linked polymer prepared in p-xylene sorbed p-xylene vapor preferably. The observed molecular recognition ability can be explained on the bases of an imprinting effect by solvent molecules. Molecularly imprinted polymer (MIP) powders were blended with PMMA, and the blended films were coated on a piezoelectric quartz crystal with a view to preparing QCM-based VOC sensors. The imprint effect was clearly observed, even in these blended films. The response of the sensor towards toluene or p-xylene vapor was reversible; however, the response time was slow due to the existence of the matrix polymer around the MIP particles.
TL;DR: In this article, the ionic liquid [mebupy]BF4 is used as a solvent for liquid−liquid extraction and the experimental data for the binary and ternary systems were well-correlated with the NRTL model.
Abstract: This research focused on a study of the ionic liquid 4-methyl-N-butylpyridinium tetrafluoroborate ([mebupy]BF4) as a solvent in liquid−liquid extraction. Liquid−liquid equilibrium data were obtained for mixtures of 4-methyl-N-butylpyridinium tetrafluoroborate + (benzene or ethylbenzene or m-xylene) + (N-hexane or N-octane) at T = (313.2 and 348.2) K and T = (313.2 and 333.2) K for the ternary mixture with benzene and p = 0.1 MPa. The experimental data for the binary and ternary systems were well-correlated with the NRTL model. The aromatic/aliphatic selectivity values were comparable to those of toluene + N-heptane. The ionic liquid [mebupy]BF4 is therefore a suitable solvent for an industrial extraction process for the separation of aromatic and aliphatic hydrocarbons.
TL;DR: The performance of desorption electrospray ionization (DESI) in the analysis of a group of pharmaceuticals and their glucuronic acid conjugates is reported and polymethylmethacrylate (PMMA) was found to give the best performance in terms of sensitivity.
Abstract: The performance of desorption electrospray ionization (DESI) in the analysis of a group of pharmaceuticals and their glucuronic acid conjugates is reported. The suitability of different sprayer solvents and different surfaces was examined. In the positive ion mode, water/methanol/trifluoroacetic acid performed best, whereas, in the negative ion mode, water/methanol/ammonium hydroxide was found to be the most suitable spray solvent. Of the surfaces investigated, polymethylmethacrylate (PMMA) was found to give the best performance in terms of sensitivity. Spray solution flow rate and the distance of the sprayer tip from the surface were also found to have significant effects on the signal intensity. Analytes with basic groups efficiently formed the corresponding protonated molecules in the positive ion mode, whereas acidic analytes, such as the glucuronic acid conjugates, formed intense signals due to the deprotonated molecules in the negative ion mode. Ionization of neutral compounds was less efficient and in many cases it was achieved through adduct formation with simple anions or cations.
TL;DR: In this paper, quaternary ammonium ionic liquids have been synthesized and characterised and the results clearly demonstrate that these ILs can be easily separated and reused without losing their activity and quality.
TL;DR: In this paper, the effect of the solvent on the liquid-phase hydrogenation of citral on a Pt/SiO2 catalyst was examined by comparing the specific activity and the product selectivity in eight nonreactive solvents.
TL;DR: The aqueous iron(IV) ion, Fe(IV)(aq)O(2+), generated from O(3) and Fe(aq)( 2+), reacts rapidly with various oxygen atom acceptors (sulfoxides, a water-soluble triarylphosphine, and a thiolatocobalt complex).
Abstract: The aqueous iron(IV) ion, FeIVaqO2+, generated from O3 and Feaq2+, reacts rapidly with various oxygen atom acceptors (sulfoxides, a water-soluble triarylphosphine, and a thiolatocobalt complex) In each case, FeIVaqO2+ is reduced to Feaq2+, and the substrate is oxidized to a product expected for oxygen atom transfer Competition methods were used to determine the kinetics of these reactions, some of which have rate constants in excess of 107 M-1 s-1 Oxidation of dimethyl sulfoxide (DMSO) has k = 126 × 105 M-1 s-1 and shows no deuterium kinetic isotope effect, k(DMSO-d6) = 123 × 105 M-1 s-1 The FeIVaqO2+/sulfoxide reaction is the product-forming step in a very efficient Feaq2+-catalyzed oxidation of sulfoxides by ozone This catalytic cycle, combined with labeling experiments in H218O, was used to determine the rate constant for the oxo-group exchange between FeIVaqO2+ and solvent water under acidic conditions, kexch = 14 × 103 s-1
TL;DR: The MSCS method allows probing of hot spots, plasticity and hydration simultaneously, providing a powerful complementary strategy to guide computational methods currently in development for binding site determination, ligand docking and design.
TL;DR: In this article, the polar characteristic of the solvent was proposed to be the main factor that affects both nucleation and growth of ZnO nanoparticles and, consequently, determines the aspect ratio of the products.
Abstract: Nanocrystalline ZnO powders were synthesized by a solvothermal method using various organic solvents as the reaction medium. Products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The aspect ratio of ZnO primary particles depended upon the solvent employed, such that the aspect ratio increased when the solvent with a low dielectric constant was employed. For the use of n-alkanes and aromatic compounds as solvent, ZnO nanorods were obtained. The polar characteristic of the solvent was proposed to be the main factor that affects both nucleation and growth of ZnO nanoparticles and, consequently, determines the aspect ratio of the products.
TL;DR: The Kamlet-Taft solvent descriptors have been used to analyze the rates of the reactions, which were found to have a strong inverse dependency on the alpha value of the solvent.
Abstract: In this paper, we report the effect of ionic liquids on substitution reactions using a variety of anionic nucleophiles. We have combined new studies of the reactivity of polyatomic anions, acetate, trifuoroacetate, cyanide, and thiocyanide, with our previous studies of the halides in [C4C1py][Tf2N], [C4C1py][TfO], and [C4C1im][Tf2N] (where [C4C1im]+ is 1-butyl-3-methylimidazolium and [C4C1py]+ is 1-butyl-1-methylpyrrolidinium) and compared their reactivities, k2, to the same reactions in the molecular solvents dichloromethane, dimethylsulfoxide, and methanol. The Kamlet-Taft solvent descriptors (alpha, beta, pi) have been used to analyze the rates of the reactions, which were found to have a strong inverse dependency on the alpha value of the solvent. This result is attributed to the ability of the solvent to hydrogen bond to the nucleophile, so reducing its reactivity. The Eyring activation parameters (DeltaH++ and DeltaS++), while confirming the reaction mechanism, do not offer obvious correlations with the Kamlet-Taft solvent descriptors.
TL;DR: Reflectance measurements during wash performance studies show that the purification and characterization of a single salt, solvent, detergent and bleach tolerant alkaline serine protease produced by a truly marine bacterium is capable of almost complete removal of recalcitrant blood and egg stains in both wet and dry wash operations.
TL;DR: For protic hydrogens, hydrogen bonding is the dominant interaction, but for the remaining protons solvent anisotropy and electric field effects appear to be the major factors.
Abstract: The 1H chemical shifts of 124 compounds containing a variety of functional groups have been recorded in CDCl3 and DMSO-d6 (henceforth DMSO) solvents. The 1H solvent shift Delta delta = delta(DMSO) - delta(CDCl3) varies from -0.3 to +4.6 ppm. This solvent shift can be accurately predicted (rms error 0.05 ppm) using the charge model of alpha, beta, gamma and long-range contributions. The labile protons of alcohols, acids, amines and amides give both, the largest solvent shifts and the largest errors. The contributions for the various groups are tabulated and it is shown that for H.C.C.X gamma-effects (X = OH, NH, =O, NH.CO) there is a dihedral angle dependence of the gamma-effect. The group contributions are discussed in terms of the possible solvent-solute interactions. For protic hydrogens, hydrogen bonding is the dominant interaction, but for the remaining protons solvent anisotropy and electric field effects appear to be the major factors.
TL;DR: In this paper, the critical micelle concentration (CMC) of Cetyl trimethylammonium bromide (CTAB) in both water and ethanol-water-mixed solvent was determined using steady-state fluorescence techniques in order to investigate the effect of the self-assembling properties of the surfactant on the template synthesis of porous inorganic materials.
Abstract: The critical micelle concentration (CMC) of cetyl trimethylammonium bromide (CTAB) in both water and ethanol-water-mixed solvent was determined using steady-state fluorescence techniques in order to investigate the effect of the self-assembling properties of the surfactant on the template synthesis of porous inorganic materials. Results indicated that the CMC increased with the increase of ethanol concentration in the mixed solvent. The CMC of CTAB is 0.0009 mol/L in water, while it is 0.24 mol/L in ethanol. Furthermore, the dissipative particle dynamics (DPD) was adopted to simulate the aggregation of CTAB in water and ethanol/water mixtures, and the energy difference was calculated for the surfactant tail groups after mixing with the solvent. The simulation results reflected a regularity similar to the experimental data, i.e., tail groups of CTAB interacted more strongly with ethanol than with groups of CTAB interacted more strongly with ethanol than with water, which elucidates the reason that the micelle is difficult to form in ethanol.
TL;DR: In this article, the solvent-mediated phase transformation of anhydrous to dihydrated carbamazepine in ethanol−water mixtures was studied using an in-line Raman immersion probe.
Abstract: In-line monitoring of solid-state properties in crystallization processes is of great significance in controlling the quality of crystalline active pharmaceutical ingredients. In this work, the solvent-mediated phase transformation of anhydrous to dihydrated carbamazepine in ethanol−water mixtures was studied using an in-line Raman immersion probe. The solute concentration profile was measured by off-line sampling. The transformation experiments were conducted with different operation parameters in terms of solvent composition and temperature. The transformation rate depends on both solvent composition and temperature. The mechanism of the transition was interpreted with the two-step polymorphic form transformation mechanism. It was observed that the crystallization of the stable form was the rate-controlling step. The influence of the operation parameters on the transformation rate can be interpreted as the effects of solvent and supersaturation on the crystallization kinetics. Another interpretation is ...
TL;DR: Results suggest that the PEG-DXR conjugate method has the potential to open the way for the use of oxSWNHs as a clinically practical drug carrier.
Abstract: A procedure for dispersing oxidized single-wall carbon nanohorns (oxSWNHs) in aqueous solution using a polyethylene glycol-doxorubicin (PEG-DXR) conjugate is described. In this procedure, oxSWNHs were first incubated with PEG-DXR in dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF), two organic solvents with relatively high electric dipole moments, after which the solvent was gradually changed to an aqueous one via addition of water until the final concentration of DMSO or DMF reached 10%. The PEG-DXR-oxSWNH complex that was obtained was able to pass through dextran-based chromatographic media (Sephadex G25) equilibrated with water. By contrast, untreated oxSWNHs and DXR-treated or PEG-treated oxSWNHs were unable to penetrate the column, indicating that the PEG-DXR conjugate endowed oxSWNHs with dispersibility in aqueous solution. In gel filtration experiments, the presence of free DXR had an inhibitory effect on the penetrability of PEG-DXR-oxSWNH complexes, which is consistent with the idea that PEG-DXR interacts with the surfaces of oxSWNHs via its DXR moiety. Quantitative analyses showed that the complex contained more than 250 mg of PEG-DXR for each gram of oxSWNHs. The average diameter of the dispersed complex was estimated to be approximately 160 nm using dynamic light scattering analysis. These results suggest that our method has the potential to open the way for the use of oxSWNHs as a clinically practical drug carrier.