Showing papers on "Solvent published in 1996"
TL;DR: This procedure provides a nonhazardous alternative to distillations and vacuum transfers and does not require undue supervision or cooling, yet allows for the rapid collection of large quantities of extremely pure solvents on demand.
2,663 citations
TL;DR: An analytical technique is described which combines solvent extraction with gas chromatographic (GC) analysis in a simple and inexpensive apparatus involving very little solvent consumption and is in good agreement with a convective-diffusive kinetic model.
Abstract: An analytical technique is described which combines solvent extraction with gas chromatographic (GC) analysis in a simple and inexpensive apparatus involving very little solvent consumption. A small drop (8 μL) of a water-immiscible organic solvent, containing an internal standard, is located at the end of a Teflon rod which is immersed in a stirred aqueous sample solution. After the solution has been stirred for a prescribed period of time, the probe is withdrawn from the aqueous solution, and the organic phase is sampled with a microsyringe and injected into the GC for quantification. The observed rate of solvent extraction is in good agreement with a convective−diffusive kinetic model. Analytically, the relative standard deviation of the method is 1.7% for a 5.00-min extraction of the analyte 4-methylacetophenone into n-octane.
1,191 citations
TL;DR: In this paper, the authors describe a new technique for sample preparation, accelerated solvent extraction (ASE), that combines elevated temperatures and pressures with liquid solvents, and investigate the effects of various operational parameters (i.e., temperature, pressure, and volume of solvent used) on the performance of ASE.
Abstract: We describe a new technique for sample preparation, accelerated solvent extraction (ASE), that combines elevated temperatures and pressures with liquid solvents. The effects of various operational parameters (i.e., temperature, pressure, and volume of solvent used) on the performance of ASE were investigated. The solvents used are those normally used for standard liquid extraction techniques like Soxhlet or sonication. We found the recoveries of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and total petroleum hydrocarbons from reference materials using ASE to be quantitative. The extraction time for 1−30-g samples is less than 15 min, and the volume of solvent is 1.2−1.5 times that of the extraction cell containing the sample. No evidence was seen for thermal degradation during the extraction of temperature-sensitive compounds.
1,109 citations
TL;DR: This new method has shown that Streptococcus thermophilus B and Leuconostoc mesenteroides NCDO 523 (LM 523) display maximal affinity for an acidic solvent and a low affinity for basic solvents, which demonstrate that both bacteria are strong electron donors and very weak electron acceptors.
472 citations
TL;DR: FTIR spectroscopy was used to quantitatively assess the secondary structure of proteins in aqueous−organic mixtures ranging from pure water to a pure solvent and found that the protein secondary structure was much more native-like in pure organic solvents than in most water−solvent mixtures.
Abstract: FTIR spectroscopy was used to quantitatively assess the secondary structure of proteins in aqueous−organic mixtures ranging from pure water to a pure solvent. For every such solution/suspension, the α-helix content of the protein was independently calculated from the amide I and amide III spectral regions (which gave essentially identical results). In all cases studied (two unrelated enzymic proteinslysozyme and subtilisin; three dissimilar water-miscible solventsacetonitrile, tetrahydrofuran, and 1-propanol), the protein secondary structure was much more native-like in pure organic solvents than in most water−solvent mixtures, e.g., 60% (v/v) organic solvents. In fact, placing lyophilized (or crystalline) proteins in the anhydrous solvents tested had no appreciable effect on the α-helix content, whereas the latter declined markedly in the 60% (v/v) solvents. This behavior was found to be kinetically controlled, i.e., to be due to inherent restrictions on protein conformational mobility in anhydrous, in c...
393 citations
TL;DR: In this article, the properties of dendrimers under varying solvent conditions are studied using molecular dynamics simulations, and it is shown that the dendrigers have a compact (space filling) structure under all solvent conditions, with a radius of gyration which scales with the number of monomers as RG ∝ N 1/3.
Abstract: The properties of dendrimers (“starburst” molecules) under varying solvent conditions are studied using molecular dynamics simulations. The dendrimers are found to have a compact (space filling) structure under all solvent conditions, with a radius of gyration which scales with the number of monomers as RG ∝ N1/3. For high generation number dendrimers, there is a distinct region of constant monomer density. The density in this region depends only on the solvent quality and is independent of the generation number. When the contributions of the different generations to the overall density profile are separated, we find that the monomers which belong to the first few generations are stretched and spatially localized. Later generations are less localized and penetrate well into the central regions of the dendrimer. The different primary branches (“dendrons”) of the dendrimers are found to be segregated. The amount of spatial overlap between the different dendrons decreases with increasing generation number of...
324 citations
TL;DR: In this paper, solid dispersions of piroxicam were prepared with polyvinylpyrrolidone (PVP) K-17 PF and PVP K-90 by solvent method.
310 citations
TL;DR: In this paper, the influence of the nature of solvent on the reactivity and selectivity features of the large pore Ti-beta catalyst has been studied during the oxidation of 1-hexene and cyclohexanol, as representative substrates, using aqueous hydrogen peroxide as oxidant and under single liquid phase conditions.
266 citations
TL;DR: The spectrophotometric method, as revised by us, provides an easy, rapid, sensitive, and complete measure of hydroperoxidation of lipids.
237 citations
TL;DR: In this paper, the importance of a solvent in regulating the adhesion forces between surfaces is studied quantitatively with scanning force microscopy Both samples and tips are coated with alkyl thiolate monolayers of type HS(CH2)10Y and force measurements are conducted as a function of terminal group Y (Y = CH2CH3, CH2OCH 3, CO2 CH3, CO(NH2), CO2H, and CH2OH) and solvent (water, ethanol, and n-hexadecane) and force data are used
Abstract: The importance of a solvent in regulating the adhesion forces between surfaces is studied quantitatively with scanning force microscopy Both samples and tips are coated with alkyl thiolate monolayers of type HS(CH2)10Y and force measurements are conducted as a function of terminal group Y (Y = CH2CH3, CH2OCH3, CO2CH3, CO(NH2), CO2H, and CH2OH) and solvent (water, ethanol, and n-hexadecane) Adhesive forces in water span the greatest range (030−125 nN), with hydrophobic surfaces adhering most strongly and hydrophilic surfaces most weakly In ethanol the adhesive forces are substantially smaller and in n-hexadecane they are negligible In water, these adhesive forces are consistent with the work required to exclude solvent from the tip−sample interface, indicating that solvent exclusion dominates adhesion Such macroscopic solvent exclusion cannot fully explain the adhesive forces in ethanol This force data is used to evaluate the tip−sample interfacial energies (γts) of like CH3- and CH2OCH3-terminated
203 citations
TL;DR: In this paper, a total of 202 organic solvents and the gas phase were placed on a solvent basicity scale for hydrogen bond acceptor based on parameter SB, which can be readily determined from the UV/Vis spectrum for an appropriate acid probe (5-nitroindoline) (NI) and its non-acid homomorph (1-methyl-5nitrogen) (MNI).
Abstract: A total of 202 organic solvents and the gas phase were placed on a solvent basicity scale for hydrogen bond acceptor based on parameter SB. The value of such a parameter can readily be determined from the UV/Vis spectrum for an appropriate acid probe (5-nitroindoline) (NI) and its non-acid homomorph (1-methyl-5-nitroindoline) (MNI). The proposed scale can advantageously substitute the more widely used solvent scales such as Gutmann's donor number (DN), the Koppel-Palm B(MeOD) scale, and the Taft-Kamlet β scale. While data for the proposed scale are derived only from electronic transitions, they are accurately descriptive of solvent basicity in both spectroscopy (UV/Vis, IR and NMR) and miscellaneous chemical areas (thermodynamic, kinetics, and electrochemistry).
TL;DR: In this paper, two simple free energy increments were derived describing the ΔGt values of 58 complexes within 1.8 kJ mol-1, irrespective of whether the latter is attractive or repulsive.
Abstract: Association energies ΔGt in chloroform, in part also in carbon tetrachloride, were determined by NMR titrations of suitably substituted nucleosides and several synthetic analogues. Based on these and on many literature data, two simple free energy increments were derived describing the ΔGt values of 58 complexes within 1.8 kJ mol-1. With chloroform as solvent the increment for the primary interaction between donor and acceptor is 7.9 kJ mol-1, for the secondary one 2.9 kJ mol-1, irrespective of whether the latter is attractive or repulsive. Addition of only 1% methanol to CCl4 led to a decrease in association constants by a factor of 25. Calorimetric titrations of G-C nucleoside derivatives in CCl4 showed substantial contributions from G dimers, in line with NMR titrations, and surprisingly small decreases in entropy. Preliminary NOE measurements allowed us to single out some of the possible association modes; they are also in line with expected self- and triple-association modes of the nucleobases. These modes are generally in accord with nucleobase associations predicted by MM calculations in the literature, which in turn agree with predictions based solely on the increments derived in the present work.
TL;DR: In this paper, the peroxide hydroxylation of benzene to phenol in the absence of a solvent was investigated using hexagonal mesoporous silicas. But they were not shown to be catalytically active.
TL;DR: In this paper, the extraction of grape seed oil by means of liquid and supercritical carbon dioxide as solvent is described, and the operating conditions to determine the maximum extraction yield were studied.
Abstract: In this work the extraction of grape seed oil by means of liquid and supercritical carbon dioxide as solvent is described. The operating conditions to determine the maximum extraction yield were studied. The efficiency of supercritical fluid extraction (SFE) was similar to that obtained by conventional liquid extraction, but the quality of the supercritically extracted oil was higher, equivalent to a degummed, liquid- extracted oil. It is considered that SFE is competitive with conventional liquid extraction, because the solvent distillation and oil refining stages can be omitted.
TL;DR: Gold colloids are homogeneously coated with silica via a three-step deposition process; the thickness of the silica layer can be completely controlled, and the particles can be transferred into practically any solvent.
TL;DR: Solvent-tolerant and -sensitive Pseudomonas putida strains were studied to determine their cell envelope changes following exposure to o-xylene and it is suggested that these envelope modifications aid in survival at high concentrations of organic solvents.
Abstract: Solvent-tolerant and -sensitive Pseudomonas putida strains were studied to determine their cell envelope changes following exposure to o-xylene. Both strains produced trans-unsaturated fatty acids. The tolerant strain showed an increase in total fatty acids, an increase in saturated fatty acids, and modified lipopolysaccharide. It is suggested that these envelope modifications aid in survival at high concentrations of organic solvents.
TL;DR: In this paper, the solubility of paracetamol was studied at 25°C in mixtures of amphiprotic and aprotic solvents of varying polarity (ethyl acetate-ethanol, ethanol-water, dioxane-water).
Abstract: The solubility of paracetamol was studied at 25°C in mixtures of amphiprotic and aprotic solvents of varying polarity (ethyl acetate-ethanol, ethanol-water, dioxane-water). A plot of the solubility mole fraction of the drug versus the solubility parameter of the solvent mixtures reached a peak in dioxane-water, and two solubility maxima within the polarity range provided by the ethanol-water and ethanol-ethyl acetate mixtures. This "chameleonic effect" can be quantitatively described in terms of cavity formation, nonspecific and specific interactions, represented by the Hildebrand solubility parameter and the acidic and basic solubility parameters of the solvent mixtures. The model predicts two solubility maxima, as found experimentally. The behavior of paracetamol in dioxane-water mixtures is similar to that of other drugs, showing a single maximum, although a small peak and a valley are also observed near the solubility parameter region where the maximum in ethanol-water appears. An increase in the temperature of fusion of the solid phase by about eight degrees was observed after equilibration of the powder with ethanol, ethyl acetate and dioxane. No changes in the solid phase were observed in water and aqueous mixtures below 50% water. The same change in the solid phase was also found in ethanol-ethyl acetate mixtures; it was independent of the nature and cosolvent ratio and had little effect on the relative variation of solubility with solvent composition. The solid phase contributes as a constant to the total solubility.
TL;DR: In this paper, an ab initio study of specific and non-specific solvent effects on the glycine zwitterion energetics and formation mechanism is presented, which is carried out at the HF an MP2 levels with the 6-31 + G ∗∗ basis set.
TL;DR: Results indicate that formamide has a destabilizing effect on the helical state, and that sequence-dependent variations in hydration patterns are primarily responsible for small variations in sensitivity to the denaturant.
Abstract: Formamide lowers melting temperatures (Tm) of DNAs linearly by 2.4-2.9 degrees C/mole of formamide (C(F)) depending on the (G+C) composition, helix conformation and state of hydration. The inherent cooperativity of melting is unaffected by the denaturant. dTm/dC(F)for 11 plasmid domains of 0.23 coil transitions. Results indicate that formamide has a destabilizing effect on the helical state, and that sequence-dependent variations in hydration patterns are primarily responsible for small variations in sensitivity to the denaturant. The average unit transition enthalpy delta H(m)[see text for complete expression], exhibits a biphasic dependence on formamide concentration. The initial drop of -0.8 kcal/mol bp at low formamide concentrations is attributable to a delta delta H(m)[see text for complete expression], for exchange of solvent in the vicinity of the helix: displacement by formamide of weakly bound hydrate or counterion. The phenomenological effects are equivalent to lowering the bulk counterion concentration. Poly(dA.dT) exhibits a much lower sensitivity to formamide, due to the specific pattern of tightly bound, immobilized water bridges that buttress the helix from within the narrow minor groove. Tracts of three (A.T)-pairs behave normally, but tracts of six exhibit the same level of reduced sensitivity as the polymer, suggesting a conformational shift as tracts are elongated beyond some critical length [McCarthy J.G. and Rich,A. (1991) Nucleic Acids Res. 19, 3421-3429].
TL;DR: In this paper, the authors describe the use of HFP as a solvent for EPR spectroscopy and mechanistic studies of radical cations as intermediates in electrophilic aromatic substitution, photochemistry and spin trapping.
TL;DR: In this article, the authors report atomistically detailed molecular dynamics simulations of benzene−polystyrene systems (0−84.2 wt % polystyrene) and calculate solvent diffusion coefficients and find that their composition dependence not only shows good agreement with experiment but also follows quite well the predictions by lattice models.
Abstract: We report atomistically detailed molecular dynamics simulations of benzene−polystyrene systems (0−84.2 wt % polystyrene). We have calculated solvent diffusion coefficients and have found that their composition dependence not only shows good agreement with experiment but also follows quite well the predictions by lattice models. We also show that, for the polystyrene−benzene system studied here, it is not possible to separate solvent molecules into slow ones, tightly bound to the polymer, and fast ones, not bound to the polymer. This would suggest that, in a gel, the polymer chains alone act as obstacles to solvent diffusion and not polymer decorated by a shell of solvent molecules. We have found the reorientation of benzene molecules in the gel to be nonexponential and anisotropic, the reorientation of the ring normal being slower than the in-plane reorientation. This anisotropy increases dramatically with polystyrene concentration. At the highest polymer concentration, the time scales for the two motions...
TL;DR: In this paper, the solubility of H2 has been measured as a function of pressure in ethanol + water and various solvents at (298 and 323) K. The results are compared with theoretical predictions for H2 in different solivas and some mixtures and found to agree within ±10% error, except for acetonitrile.
Abstract: The solubility of H2 has been measured as a function of pressure in ethanol + water and various solvents at (298 and 323) K. The results are compared with theoretical predictions for H2 in different solvents and some mixtures and found to agree within ±10% error, except for acetonitrile. The solubility of CO in 1-octene has also been measured. Liquid−liquid equilibrium for the 1-octene + water + ethanol system was measured at (298 and 323) K, but the predictions of these data by the UNIFAC−UNIQUAC models were not found to be satisfactory, except for higher 1-octene concentrations in water (>6% w/w) for which the predictions were within 10% error.
Patent•
12 Jul 1996
TL;DR: In this paper, an α-olefin and a diene monomer are polymerized in a process comprising the step of contacting (1) ethylene, (2) at least one C 3 -C 20 aliphatic α -olefin, (3) optionally, at least C 4 −C 20 diene, (4) a catalyst comprising (a) a metallocene complex, and (b) an activator, and(5) a solvent.
Abstract: Ethylene, an α-olefin and, optionally, a diene monomer are polymerized in a process comprising the step of contacting (1) ethylene, (2) at least one C 3 -C 20 aliphatic α-olefin, (3) optionally, at least one C 4 -C 20 diene, (4) a catalyst comprising (a) a metallocene complex, and (b) an activator, and (5) a solvent. The process is conducted in either a single reactor or in multiple reactors, the latter configured either in series or parallel. Solvent is removed from the polymer stream in an anhydrous, first stage solvent recovery operation such that the solids concentration of the product stream is increased by at least 100 percent. Additional solvent is removed in an anhydrous, second stage solvent recovery operation from the product of the first stage solvent recovery operation such that the solids concentration of the product stream is in excess of 65 weight percent.
TL;DR: An enhanced mass transfer of polycyclic aromatic hydrocarbon compounds to microorganisms by suitable hydrophobic solvents might allow the development of solvent-augmented biodegradation techniques for use in aqueous or slurry-type bioreactors.
Abstract: The biodegradation of polycyclic aromatic hydrocarbon pollutants is constrained, in part, by their solid physical state and very low water solubility. Searching for ways to overcome these limitations, we isolated from soil a bacterium capable of growing on pyrene as a sole source of carbon and energy. Acid-fast stain, morphology, and fatty acid profile identified it as a Mycobacterium sp. In a mineral salts solution, the isolate mineralized 50% of a 250-(mu)g/ml concentration of [(sup14)C]pyrene in 2 to 3 days. Detergent below the critical micelle concentration increased the pyrene mineralization rate to 154%, but above the critical micelle concentration, the detergent severely inhibited pyrene mineralization. The water-miscible solvent polyethylene glycol was inhibitory. The hydrophobic solvents heptamethylnonane, decalin, phenyldecane, and diphenylmethane were also inhibitory at several concentrations tested, but the addition of paraffin oil, squalene, squalane, tridecylcyclohexane, and cis-9-tricosene at 0.8% (vol/vol) doubled pyrene mineralization rates by the Mycobacterium sp. without being utilized themselves. The Mycobacterium sp. was found to have high cell surface hydrophobicity and adhered to the emulsified solvent droplets that also contained the dissolved pyrene, facilitating its mass transfer to the degrading bacteria. Cells physically adhering to solvent droplets metabolized pyrene 8.5 times as fast as cells suspended in the aqueous medium. An enhanced mass transfer of polycyclic aromatic hydrocarbon compounds to microorganisms by suitable hydrophobic solvents might allow the development of solvent-augmented biodegradation techniques for use in aqueous or slurry-type bioreactors.
TL;DR: The femtosecond optical-heterodyne-detected optical Kerr effect/Raman-induced Kerr effect (OHD OKE/RIKE) dynamics of CS2 dissolved in a series of alkane solvents are reported in this article.
Abstract: The femtosecond optical-heterodyne-detected optical Kerr effect/Raman-induced Kerr effect (OHD OKE/RIKE) dynamics of CS2 dissolved in a series of alkane solvents are reported. The data reveal that the nondiffusive (subpicosecond) dynamics of simple molecular liquids are determined largely by the details of the local, microscopic environment, rather than by the bulk solution properties, with no correlation observed between the short-time, nondiffusive dynamics and the bulk solution viscosity. For each solvent investigated, the vibrational spectral density is observed to narrow and shift to lower frequency with increasing dilution. While the same general trend is observed for each solvent, deviations of magnitude are observed for the longer-chain n-alkanes. This, coupled with the markedly nonexponential decay of the orientational anisotropy observed for the higher-alkane dilutions, suggests the presence of two distinct environments in which isolated pockets of CS2 exist. The observed spectral evolution is d...
TL;DR: In this paper, a novel class of low-molecular-weight organic gels has been developed; N,N′,N″-tristearyltrimesamide (TSTA) forms gels with various organic solvents, immobilizing solvent at a low concentration of TSTA.
Abstract: A novel class of low-molecular-weight organic gels has been developed; N,N′,N″-tristearyltrimesamide (TSTA) forms gels with various organic solvents, immobilizing solvent at a low concentration of TSTA. The gels, which form fibrous bundles leading to three-dimensional networks, exhibit well-defined sol-gel transitions. Both intermolecular hydrogen bonding and intermolecular inteactions between long alkyl chains are suggested to be responsible for the formation of gels.
TL;DR: In this article, an efficient fluorescence quenching caused by rapid internal conversion from the first excited singlet state is observed in alcohol solutions of 2-(2‘-pyridyl)indoles, molecules which may simultaneously act as hydrogen bonding donors and acceptors.
Abstract: Efficient fluorescence quenching caused by rapid internal conversion from the first excited singlet state is observed in alcohol solutions of 2-(2‘-pyridyl)indoles, molecules which may simultaneously act as hydrogen bonding donors and acceptors. Electronic and infrared absorption studies show that upon adding alcohols to nonpolar solutions of pyridylindoles, 1:1 complexes are formed in the ground state, with hydrogen bonding occurring to the indole NH group. At higher alcohol concentrations 1:n (n ≥ 2) solvates dominate. Investigations of the fluorescence intensity as a function of temperature and deuterium substitution in the hydroxylic group of the alcohol, and the results obtained for the N-methylated derivatives and 2-phenylindole show that the quenching may be described by a stepwise mechanism. First, a 1:1 cyclic, doubly hydrogen-bonded complex between alcohol and pyridylindole is formed after photoexcitation. This process is controlled by solvent reorientation. Excited state double proton transfer ...
TL;DR: The rate constants for hydrogen atom abstraction by alkoxyl radicals from phenol, aniline, and diphenylamine have been measured in 14 solvents at room temperature by laser flash photolysis as mentioned in this paper.
Abstract: Absolute rate constants for hydrogen atom abstraction by alkoxyl radicals from phenol, aniline, and diphenylamine have been measured in 14 solvents at room temperature by laser flash photolysis. For all three substrates the rate constants decline as the solvent becomes a stronger hydrogen-bond acceptor (HBA). Thus, on changing the solvent from CCl4 to CH3CN the rate constants decline by factors of 148, 7.1, and 4.7 for PhOH, PhNH2, and Ph2NH, respectively. The kinetic solvent effect for phenol correlates rather well with Abraham's scale of relative HBA activities of the solvents we have employed as measured as solutes in CCl4 solvent. This correlation is not quite so good with aniline and it is almost nonexistent for diphenylamine. With all three substrates the “deviant” solvents produce higher rate constants than would be expected from the value of the solvent and, generally, these are the solvents in which steric hindrance to hydrogen-bond formation would appear probable. The kinetic data for the three ...
TL;DR: In this article, the changes in molecular weight distribution and quantity of soluble proteins in wheat extrudates as affected by extrusion temperature were investigated, and both aggregation and fragmentation of wheat proteins occurred during extrusion processing as indicated by SDS−PAGE analysis.
Abstract: To study the molecular mechanism of protein interactions during extrusion processing, the changes in molecular weight distribution and quantity of soluble proteins in wheat extrudates as affected by extrusion temperature were investigated. Wheat flour was extruded at die temperatures of 160, 170, and 185 °C. After extrusion, the solubility of wheat proteins decreased dramatically in all tested solvents [water, 0.01 M sodium hydroxide, 0.5 M sodium chloride, 70% ethanol, 0.1 M hydrochloric acid, 0.05 M sodium phosphate buffer (pH 7.0 and 8.0), 6 M urea, 1% SDS, 2% mercaptoethanol] except for an aqueous solvent containing 1% SDS and 2% 2-mercaptoethanol, in which they were almost completely soluble. In the soluble-protein fractions of the extrudates, the content of disulfide bonds decreased dramatically and the content of sulfhydryl groups varied slightly. Both aggregation and fragmentation of wheat proteins occurred during extrusion processing as indicated by SDS−PAGE analysis. The synergistic effect betwe...
Patent•
18 Sep 1996TL;DR: In this paper, a solvent-assisted method for mobilizing viscous heavy oil or bitumen in a reservoir under reservoir conditions without the need to adjust the temperature or pressure was proposed.
Abstract: The invention provides a solvent-assisted method for mobilizing viscous heavy oil or bitumen in a reservoir under reservoir conditions without the need to adjust the temperature or pressure. The invention utilizes mixtures of hydrocarbon solvents such as ethane, propane and butane, which dissolve in oil and reduce its viscosity. Two or more solvents are mixed in such proportions that the dew point of the solvent mixture corresponds with reservoir temperature and pressure conditions. The solvent mixture, when injected into a reservoir, exists predominantly in the vapor phase, minimizing the solvent requirement. The invention can be practised in the context of paired injector and producer wells, or a single well cyclic system.