Showing papers on "Solvent published in 1990"

Very low temperature casting of controlled release microspheres

Abstract: A process for preparing microspheres using very cold temperatures to freeze polymer-biologically active agent mixtures into polymeric microspheres with very high retention of biological activity and material. Polymer is dissolved in a solvent together with an active agent that can be either dissolved in the solvent or dispersed in the solvent in the form of microparticles. The polymer/active agent mixture is atomized into a vessel containing a liquid non-solvent, alone or frozen and overlayered with a liquified gas, at a temperature below the freezing point of the polymer/active agent solution. The cold liquified gas or liquid immediately freezes the polymer droplets. As the droplets and non-solvent for the polymer is warmed, the solvent in the droplets thaws and is extracted into the non-solvent, resulting in hardened microspheres.

Lipase catalyzed alcoholysis of sunflower oil

Abstract: Lipase-catalyzed alcoholysis of sunflower oil under anhydrous conditions was examined. Lipases fromPseudomonas fluorescens and 2 immobilized enzymes fromMucor miehei and aCandida sp. gave sufficient conversion with petroleum ether as the solvent, even when methanol and ethanol were used. The overall content of tri-, di- and monoglycerides, as well as the corresponding alkyl esters, was measured. BecausePseudomonas lipase led to almost quantitative esterification, further studies were carried out with that enzyme varying the amounts of enzyme or the alcohols. Acceptable conversions were achieved even without solvent. Reaction rates of alcoholysis with 5 homologous alcohols, with or without the addition of water, were measured, and in all cases the reaction rates increased with higher chain length of the alcohol. In the case of methanol the highest rate was obtained without any addition of water, but a significantly higher rate was observed with 96% ethanol as opposed to absolute ethanol. The main advantages of lipasecatalyzed, nonaqueous alcoholysis as compared to classical procedures are the mild reaction conditions, the isolation of glycerin without further purification and without the formation of chemical waste, and the ability of lipases to catalyze the esterification of free fatty acids.

Preferential interactions determine protein solubility in three-component solutions: the MgCl2 system.

Abstract: The correlation between protein solubility and the preferential interactions of proteins with solvent components was critically examined with aqueous MgCl2 as the solvent system. Preferential interaction and solubility measurements with three proteins, beta-lactoglobulin, bovine serum albumin, and lysozyme, resulted in similar patterns of interaction. At acid pH (pH 2-3) and lower salt concentrations (less than 2 M), the proteins were preferentially hydrated, while at higher salt concentrations, the interaction was either that of preferential salt binding or low salt exclusion. At pH 4.5-5, all three proteins exhibited either very low preferential hydration or preferential binding of MgCl2. These results were analyzed in terms of the balance between salt binding and salt exclusion attributed to the increase in the surface tension of water by salts, which is invariant with conditions. It was shown that the increase in salt binding at high salt concentration is a reflection of mass action, while its decrease at acid pH is due to the electrostatic repulsion between Mg2+ ions and the high net positive charge on the protein. The preferential interaction pattern was paralleled by the variation of protein solubility with solvent conditions. Calculation of the transfer free energies from water to the salt solutions for proteins in solution and in the precipitate showed dependencies on salt concentration. This indicates that the nature of interactions between proteins and solvent components is the same in solution and in the solid state, which implies no change in protein structure during precipitation. Analysis of the transfer free energies and preferential interaction parameter in terms of the salting-in, salting-out, and weak ion binding contributions has led to the conclusions that, when the weak ion binding contribution is small, the predominant protein-salt interaction must be that of preferential salt exclusion most probably caused by the increase of the surface tension of water by addition of the salt. A necessary consequence of this is salting-out of the protein, if the protein structure is to remain unaltered.

Preparation of liposome and lipid complex compositions

Abstract: Liposome and lipidic particle formulations of compounds are prepared by dissolving in a solution of liposome-forming lipids in an aprotic solvent such as DMSO, optionally containing a lipid-solubilizing amount of a lower alkanol, and either injecting the resulting solution into an aqueous solution, or the aqueous solution into the resulting solution. The resulting liposome or lipidic particle suspension may then be dialyzed or otherwise concentrated. This method is particularly useful for compounds which are poorly-soluble in aqueous solution, but is generally useful for any compound or combination of compounds which can be dissolved in the aprotic solvent or aprotic solvent/lower alkanol mixture.

Encapsulation of water-soluble drugs by a modified solvent evaporation method. I. Effect of process and formulation variables on drug entrapment.

Abstract: Pseudoephedrine HCl, a highly water-soluble drug, was entrapped within poly (methyl methacrylate) microspheres by a water/oil/water emulsification-solvent evaporation method. An aqueous drug solution was emulsified into a solution of the polymer in methylene chloride, followed by emulsification of this primary emulsion into an external aqueous phase to form a water/oil/water emulsion. The middle organic phase separated the internal drug-containing aqueous phase from the continuous phase. Microspheres were formed after solvent evaporation and polymer precipitation. The drug content of the microspheres increased with increasing theoretical drug loading, increasing amounts of organic solvent, polymer and polymeric stabilizer, and decreased with increasing stirring time, increasing pH of the continuous phase and increased volume of the internal and external aqueous phase.

Method for making uniformly-sized particles from insoluble compounds

Abstract: The invention involves a method for making uniformly sized particles from solid compounds. First, a suitable solid compound is dissolved in a suitable solvent. Then, a precipitating liquid is infused, precipitating non-aggregated particles with substantially uniform mean diameter. The particles are then separated from the solvent. Depending on the solid compound and the desired particle size, the parameters of temperature, ratio of non-solvent to solvent, infusion rate, stir rate, and volume can be varied according to the invention. The precipitating liquid may be aqueous or non-aqueous, depending upon the relative solubility of the compound and the desired suspending vehicle.

Partitioning of nonpolar solutes into bilayers and amorphous n-alkanes

Abstract: We have measured the partition coefficients for hexane between an aqueous solvent and phospholipid bilayer membranes as a function of the surface density of the bilayer chains. The surface density was varied by temperature, phospholipid chain length, and the incorporation of cholesterol and was monitored by 2H NMR. We observe that increasing surface density leads to expulsion of the solute: hexane partitioning decreases by a factor of 9 as the surface density of the bilayer chains increases from 50% to 90% of its maximum value, a range readily accessible in biomembranes under physiological conditions. Benzene as solute shows similar behavior; thus, the dependence of partitioning on surface density appears to be a general property of the organization of the bilayer chains. In order to determine the relative contributions to partitioning of (i) chain ordering and (ii) contact interactions, we have also performed reference-state experiments for benzene transfer between water and amorphous n-alkanes of different chain lengths. The widely accepted value of 25 cal/mol per A* of surface area for the free energy of oil/water transfer per methylene group is appropriate only when solute and solvent molecules are of the same size. We find that Flory-Huggins theory satisfactorily corrects for the molecular size differences of solutes and solvents. Comparisons of the bilayer/water and oil/water temperature dependencies of benzene partitioning show that there is an additional entropic expulsion of solute from the bilayer, consistent with recent statistical thermodynamic theory suggesting the importance of the chain ordering in the bilayer.

Butanol recovery from fermentations by liquid-liquid extraction and membrane solvent extraction

Abstract: Extraction can successfully be used for in-situ alcohol recovery in butanol fermentations to increase the substrate conversion. An advantage of extraction over other recovery methods may be the high capacity of the solvent and the high selectivity of the alcohol/water separation. Extraction, however, is a comprehensive operation, and the design of an extraction apparatus can be complex. The aim of this study is to assess the practical applicability of liquid-liquid extraction and membrane solvent extraction in butanol fermentations. In this view various aspects of extraction processes were investigated. Thirty-six chemicals were tested for the distribution coefficient for butanol, the selectivity of alcohol/water separation and the toxicity towards Clostridia. Convenient extractants were found in the group of esters with high molar mass. Liquid-liquid extraction was carried out in a stirred fermenter and a spray column. The formation of emulsions and the fouling of the solvent in a fermentation broth causes problems with the operation of this type of equipment. With membrane solvent extraction, in which the solvent is separated from the broth by a membrane, a dispersion-free extraction is possible, leading to an easy operation of the equipment. In this case the mass transfer in the membrane becomes important. With membrane solvent extraction the development of a process is emphasized in which the extraction characteristics of the solvent are combined with the property of silicone rubber membranes to separate butanol from water. In the case of apolar solvents with a high molar mass, the characteristics of the membrane process are determined completely by the solvent. In the case of polar solvents (e.g. ethylene glycol), the permselectivity of the membrane can profitably be used. This concept leads to a novel type of extraction process in which alcohol is extracted with a water-soluble solvent via a hydrophobic semipermeable membrane. This extraction process has been investigated for the recovery of butanol and ethanol from water. A major drawback in all processes with membrane solvent extraction was the permeation of part of the solvent to the aqueous phase. The extraction processes were coupled to batch, fed batch and continuous butanol fermentations to affirm the applicability of the recovery techniques in the actual process. In the batch and fed batch fermentations a three-fold increase in the substrate consumption could be achieved, in the continuous fermentation about 30% increase.

Mechanisms of reactions of iron(III) porphyrins with hydrogen peroxide and hydroperoxides: solvent and solvent isotope effects

Abstract: The effect of solvent polarity and acidity and the solvent isotope effects on the reaction of iron(III) porphyrins with hydrogen peroxide, tert-butyl hydroperoxide, and peracids have been investigated. Both the solvent isotope effects on the reactions of hydroperoxides with hemins are almost identical with these effects on the reactions of hydroperoxides with dialkyl sulfides and the effects on the reaction of peracids with iron(III) porphyrins. Since both of the latter reactions are known to involve heterolytic cleavage of the O-O bond, this similarity provides strong evidence for heterolytic cleavage of hydroperoxide by reaction with hemins. The strong alcohol catalysis of the studied reactions provides a mechanistic rationale for the O-O bond cleavage in cytochrome P-450 in terms of general-acid catalysis by water in the enzyme site.

Polymer recycling by selective dissolution

Abstract: A method for separating polymers from a physically commingled solid mixture containing a plurality of polymers comprises dissolving a first one of the polymers in a solvent at a first lower temperature to form a first preferably single phase solution and a remaining solid component. The solid component contains additional polymers which are not soluable to the solvent at the first temperature but which may be soluble at higher temperatures. The method includes subsequently heating the solvent to dissolve additional polymer from the solid component to form subsequent solutions. The polymers are then separated from their respective solution either using flash evaporation techniques when more than one polymer has been dissolved at a single temperature, or conventional techniques for extracting a polymer from a solvent in a solution.

Photodynamics of the S1 state of some hydroxy- and amino-substituted naphthoquinones and anthraquinones

Abstract: Photodynamics of the S1 state of the 1,4- and 1,8-disubstituted hydroxyquinones and aminoquinones have been studied in different organic solvents by absorption and fluorescence spectroscopy. The internal conversion process is the major deactivation path for the S1 state. The solvent and temperature dependence and deuterium isotope effect on the fluorescence dynamics suggest that hydrogen stretching vibrations in different intra- and inter-molecular hydrogen bonds are responsible for very fast non-radiative decay processes. Among the intra-molecular hydrogen-bonded molecules studied only the S1 state of 1,8-dihydroxy-9,10-anthraquinone showed the evidence of excited-state intramolecular proton-transfer process. Preliminary observations on the interaction of the S1 state of these quinones with benzene and other aromatic hydrocarbon solvents via the formation of an exciplex have also been reported.

Chromium compounds and uses thereof

Abstract: Novel chromlum-containing compounds, such as, for example, chromium pyrrolides, are prepared by forming a mixture of a chromium salt, a metal amide, and an electron pair donor solvent, such as, for example, an ether. These novel chromium-containing, or chromium pyrrolide, compounds can be used either unsupported or supported on an inorganic oxide support to trimerize and/or polymerize olefins.

Cosolvency and sorption of hydrophobic organic chemicals.

Abstract: Sorption of hydrophobic organic chemicals (HOCs) by two soils was measured from mixed solvents containing water plus completely miscible organic solvents (CMOSs) and partially miscible organic solvents (PMOSs). The utility of the log-linear cosolvency model for predicting HOC sorption from solvent mixtures was evaluated. Co-solvent effects of PMOSs on HOC solubility and sorption were compared. Nonpolar PMOSs (e.g., toluene, p-xylene, and TCE) have low aqueous solubilities and when present either as a cosolvent/cosolute in the aqueous phase or as separate liquid phase do not significantly influence HOC sorption by soils. In contrast, polar PMOSs (e.g., nitrobenzene and o-cresol) have sufficiently high aqueous solubilities that significant decreases in HOC sorption can be measured. The presence of a CMOS increases the PMOS solubility which, in turn, is reflected in increased solubility and decreased sorption of HOCs. Results presented suggest that water-PMOS and sorbent-PMOS interactions need to be considered in predicting the cosolvency of a polar PMOS.

Conductivity of tetra-alkylammonium salts in polyaromatic solvents

Abstract: It is shown that the conductivity of tetra-alkylammonium salts in low dielectric constant media is not greatly affected by the length of the carbon chain of the cation. The effect upon the conductivity of varying the size of anions and cations has been analysed in several pure and mixed solvents using a modified Fuoss–Kraus theory to take into account the activity coefficient of the undissociated electrolyte. The interionic distance parameter of the ion pairs is calculated and shown to be fairly constant, indicating interpenetration of the ions. Also, following on from the preceding paper, the effect upon the conductivity of the local environment around the solute is found to be negligible. The bulk dielectric constant of the solvent is shown to be the major factor affecting the conductivity of salts.

The second‐generation polysulfone gas‐separation membrane. I. The use of lewis acid: Base complexes as transient templates to increase free volume

Abstract: The second-generation polysulfone (PSU) gas-separation membrane is seen as a trilayer that is considerably more permeable and at least as selective as the first-generation bilayer that it has replaced. In air separation, a fourfold increase in oxygen permeabiliy has been obtained with no loss in oxygen/nitrogen selectivity. The enhanced performance is the result of a membrane skin that is not only thinner, but also exhibits increased free volume and a graded density. The key to the emergency of the trilayer morphology was the discovery of a hitherto unsuspected relationship between the size of solvent molecules within a sol and the free volume and permeability in the resultant gel! Solvent molecules with a molar volume V > ˜ 147 cc/mol function as transient templates (spacers) that decrease macromolecular packing density. As a practical matter, the low diffusivity (difficult extractibility) of large solvent molecules is circumvented by the use of 1:1 Lewis acid: base (A:B) complexes such as propionic acid: N-methyl pyrrolidone instead of neat solvents. Complexes whose acid and base strengths, respectively, lie between (Gutmann 47 < AN < 53 and 27 < DN < 28) are sufficiently stable to function as templates, while at the same time exhibiting the hydrolytic instability that leads to their ready disassociation and extraction by water. Selectivity is maintained by the use of A:B complexes whose Hildebrand solubility parameters differ from that of PSU by less than ˜ 1.3 (cal/cc)½. The emergence of the trilayer membrane is considered to be the second decoupling of permeability from selectivity. By the formation of an anisotropic (graded density) skin, permeability has been increased and selectivity maintained. This is analogous to the first decoupling by Loeb and Sourirajan who essentially replaced a thick dense monolayer film with a bilayer consisting of a thin skin of uniform density in series with a thick porous substructure.

Dry high flux semipermeable membranes

Abstract: High flux semipermeable membranes which comprises the polymerized reaction product within and/or on a porous support backing material may be prepared by contacting the porous support such as a polysulfone with an aqueous solution of a polyamine which may, if so desired, contain a polar aprotic solvent not reactive with the amines, a polyhydric compound and an acid acceptor. The surface of the coated support is freed of excess solution and thereafter contacted with an organic solution of a polyacyl halide for a period of time sufficient to form a polymerized reaction product within and/or on the support material. The resulting composite is then treated with a hydroxy polycarboxylic acid, polyaminoalkylene polycarboxylic acid, suffonic acid, amine salts of acids, amino acid, amino acid salt, polymeric acid and inorganic acid, before drying of the membrane. This will enable the membrane to be stored in a dry manner prior to use thereof in a separation process. The resultant membrane composite may be used in separation processes such as desalination of brackish or sea water or the softening of domestic hard water.

Solvent effects in molecular recognition

Abstract: Synthetic cyclophane hosts form stable and highly structured inclusion complexes with organic molecules in aqueous solutions. The solution geometries of these complexes are determined in a conformational analysis using Monte Car10 methods. Solvation-desolvation processes are a central factor in determining the stability of apolar inclusion complexes. The tight binding of small aromatic solutes in water is entropically unfavorable and is predominantly enthalpy-driven. A large part of the favorable enthalpy term for strong complexation in water results from its specific contributions. Electron donor-acceptor interactions stabilize complexes between electron-rich cyclophane hosts and electron-deficient aromatic substrates; however, they may be masked by specific solvation effects. Computer liquid phase simulations are undertaken to evaluate at a microscopic level the origin of such solvation effects. The progress in the modeling studies is described. Apolar complexation also occurs in organic solvents. Solvents like 2,2,2-trifluoroethanol and ethylene glycol come close to water in their ability to promote apolar complexation. Binding strength decreases from water to polar protic to dipolar aprotic and to apolar solvents. Complexation strength in solvents of all polarity including water and in binary aqueous solvent mixtures is predictable according to a linear free energy relationship between the complexation free energy and the empirical solvent polarity parameter ET(30).

Process for recovering alcohol with energy integration

Abstract: A process for recovering alcohol by a continuous process employing fermentation, solvent extraction of the alcohol product, extractive distillation of the alcohol-solvent extract to provide water fraction and vacuum stripping for separation of the alcohol and regenerated solvent. The solvent is recycled. An isoparaffin is used as a solvent and this solvent can be modified with a long chain fatty acid, alcohol or fatty alcohol or long-chain esters. Alternatively, many modifiers may be used neat.

Dispersion polymerization of styrene in polar solvents. IV. Solvency control of particle size from hydroxypropyl cellulose stabilized polymerizations

Abstract: Changing solvent has a dramatic effect on the outcome of HPC stabilized dispersion polymerization of styrene in polar solvents. In methoxyethanol/ethanol mixtures, particle size varies from essentially infinity for unstabilized reactions (below 30% ethanol) to about 3 microns in ethanol. In a series of n-alcohols, there was a maximum in particle size at intermediate chain length: particle size increased from 2 microns in methanol to 8.3 microns in pentanol, then decreased again to 1 micron in octadecanol. These results were rationalized in terms of the three-component Hansen solubility parameters. The largest particles were obtained in solvents with Hanson polarity and hydrogen bonding terms closest to HPC. The generality of the three-component solubility parameter approach was examined by reactions performed in eight mixed solvents with the same values of all three Hansen terms. Seven of the eight solvents gave particles of similar size and molecular weight. The two critical effects of solvent on both particle size and molecular weight appear to be: (a) the solubility properties of the grafted HPC-PS formed, and (b) the partitioning of monomer and initiator between solution and particle phases subsequent to nucleation.

Solvent-Induced Nitrile Frequency Shifts: Acetonitrile and Benzonitrile:

Abstract: The C≡N stretching frequency, vC≡N, is affected by change in the solvent and also by change in concentration in the same solvent. In the case of acetonitrile, vC≡N is in Fermi resonance with the combination tone (δsym. CH3 + vC-C), and the degree of Fermi resonance interaction changes with change in the solvent. With the exception of dimethyl sulfoxide, unperturbed vC≡N for acetonitrile exhibits a pseudo-linear correlation with the acceptor number of the solvent.

Solvent effect on thermal degradation of polystyrene

Abstract: The thermal degradation of polystyrene (PS) in various kinds of solvents was studied in the temperature range from 300 to 450°C. The conversion of PS to low molecular weight products was dependent on the hydrogen donating ability of the solvents used: Solvents with greater donating ability resulted in less conversion of PS. A different degradation behavior was evident when phenols or other kind of solvents were used. These reaction properties are explained with a proposed degradation mechanism that includes hydrogen transfer steps from solvents to Intermediate PS radicals and from PS to the solvent radicals.

Picosecond mass‐selective measurements of phenol‐(NH3)n acid–base chemistry in clusters

Abstract: The rate of proton transfer from the acidic S1 state of phenol to the basis solvent (NH3)n was measured as a function of solvent cluster size n. A distinct reaction threshold was observed for solvent size n=5 for 266 nm picosecond excitation. The proton transfer rate was measured to be ka=(60±10 ps)−1 for n=5–7. A competitive recombination rate of k−a =(350±100 ps)−1 occurs for n=5. Additional solvation stabilizes the product side causing the reaction enthalpy and consequently k−a to decrease. No evidence of proton transfer was observed when phenol was seeded in the less basic solvent clusters (CH3OH)n and (H2O)n.

Self‐consistent theory of block copolymer blends: Neutral solvent

Abstract: We present a theoretical study of the lamellar structure of diblock copolymers blended with neutral solvent. The calculations are based on numerical solutions of the equations of the mean field self‐consistent theory of incompressible polymer/solvent blends, from the weak through to the strong segregation limits. For idealized model systems of symmetric copolymers and perfectly nonselective solvent, we examine the variation of the equilibrium lamellar thickness with molecular weight, Flory χ parameter, solvent quality, and copolymer volume fraction, as well as the distribution of solvent and polymer within the subdomains. We also examine a real system which has been extensively studied experimentally, namely PS‐b‐PI with the (nearly) nonselective solvent toluene.