Showing papers on "Solvent published in 1987"

Process for the preparation of dispersible colloidal systems of a substance in the form of nanoparticles

Abstract: The process according to the invention comprises: (1) the preparation of a liquid phase consisting essentially of a solution of a substance A in a solvent or in a mixture of solvents, and containing the substance B in solution or as a dispersion, (2) the preparation of a second liquid phase consisting essentially of a non-solvent or a mixture of non-solvents for the substances A and B, and supplemented with one or more surfactants, the solvent or mixture of solvents of the first phase being miscible in all proportions with the non-solvent or mixture of non-solvents of the second phase, (3) the addition of the first phase to the second phase with moderate agitation so as to produce a colloidal suspension of nanocapsules, the wall of which is constituted by the substance A and the core by the substance B, (4) if desired, the removal of all or part of the solvent or the mixture of solvents and of the non-solvent or the mixture of non-solvents so as to produce a colloidal suspension of nanocapsules of the desired concentration or to produce a powder of nanocapsules following the addition of stabilizing substances.

Polymerization of phenols catalyzed by peroxidase in nonaqueous media

Abstract: Polymers produced by horseradish-peroxidase-catalyzed coupling of phenols have been explored as potential substitutes for phenol-formaldehyde resins. To overcome low substrate solubilities and product molecular weights in water, enzymatic polymerizations in aqueous-organic mixtures have been examined. Peroxidase vigorously polymerizes a number of phenols in mixtures of water with water-miscible solvents such as dioxane, acetone, di-methylformamide, and methyl formate with the solvent content up to 95%. As a result, various phenolic polymers with average molecular weights from 400 to 2.6 x 10(4) D were obtained depending on the reaction medium composition and the nature of the phenol. Peroxidase-catalyzed copolymerization of different phenols in 85% dioxane was demonstrated. Poly(p-phenylphenol) and poly(p-cresol) were enzymatically prepared on a gram scale. They had much higher melting points, and in addition, poly(p-phenylphenol) was found to have a much higher electrical conductivity than phenol-formaldehyde resins.

Biocatalysis in Organic Media

Abstract: The potentials of using organic reaction media in biotechnological conversions have already been demonstrated in several experimental studies. Examples of possible advantages are: possibility of higher substrate and/or product concentrations, favorable shift of reaction equilibria, reduced substrate and/or product inhibition, and facilitated product recovery. Especially water/organic solvent two-phase systems seem to possess several of these advantages. The solvent type will highly affect kinetics and stability of the (immobilized) biocatalyst, solubility and partitioning of reactants/products, and product recovery. Therefore the solvent choice can have a large influence on the economics of the two-liquid-phase biocatalytic process. Immobilization of the biocatalyst may be useful to provide protection against denaturating solvent effects. The polarity of the employed support material will also be decisive for the partitioning of substrates and products among the various phases. A classification of biphasic systems, which is based on the possible types of theoretical concentration profiles and aqueous phase configurations, is discussed. Reversed micelles and aqueous two-liquid-phase systems can be considered as special cases. The design of two-liquid-phase bioreactors is dependent on the state of the biocatalyst, free or immobilized, and on the necessity for emulsification of one of the two liquid phases in the other. Many mass-transfer resistances, e.g. across the liquid/liquid interface, in the aqueous phase, across the liquid/solid interface, and in the biocatalyst phase, can limit the overall reaction rate. The epoxidation of alkenes in water/solvent two-phase systems is discussed to give an example of the scope of biotechnological processes that is obtained by using organic media. Finally, a design calculation of a packed-bed organic-liquid-phasel immobilized-biocatalyst reactor for the epoxidation of propene is given to illustrate some of the above aspects.

Organic solvents for bioorganic synthesis : 1. Optimization of parameters for a chymotrypsin catalyzed process

Abstract: The influence of solvents on enzymatic activity and stability was investigated. As a model reaction the α-chymotrypsin-catalyzed esterification of N-acetyl-l-phenylalanine with ethanol was used. The enzyme was adsorbed on porous glass beads and used in various solvents. Small amounts of water were added to increase the enzymatic activity. These enzyme preparations obeyed. Michaelis-Menten kinetics. K m,app decreased slightly with the log P value of the solvent while V app increased markedly with the log P value. Log P values were also useful for generalizing the influence of solvents on enzyme stability. The enzyme preparations showed a markedly higher thermostability in dry solvents having log P values >0.7 than in less hydrophobic solvents. Also the operational stability was better in the more hydrophobic solvents. The amount of water added to the enzyme preparations greatly influenced the initial reaction rates. For some solvents optimal water contents were determined. The thermostability decreased with increasing water content. The observations are summarized in the conclusion that more hydrophobic solvents are preferable to less hydrophobic ones. The log P value gives a good guidance when selecting an organic solvent for enzymatic conversions.

Local polarity of solvent mixtures in the field of electronically excited molecules and exciplexes

Abstract: In mixtures of solvents of different dielectric polarities a process of preferential solvation described as ‘dielectric enrichment’ occurs in the solvation shell of dipolar solute molecules. Dielectric enrichment requires the diffusion of solvent molecules, and its extent depends on solvent viscosity and on time; in the case of electronically excited molecules it may be limited by their lifetime. Measurements on short-lived ( 10 ns) fluorescers show that in non-viscous liquid media dielectric enrichment reaches equilibrium in times of 1 ns to over 20 ns depending on the polar solvent mole fraction in the mixture. In the case of exciplexes the process of dielectric enrichment is complicated by the quenching action of polar solvents, which reduces the exciplex lifetime.

Extreme solvent effects on reaction rate constants at supercritical fluid conditions

Abstract: The reaction rate constant was adjusted continuously over two orders of magnitude for the unimolecular decomposition of α-chlorobenzyl methyl ether using the supercritical fluid solvent 1, 1 diffluoroethane. Activation volumes were observed as low as −6,000 cm3/mol, which is about an order of magnitude more negative than those reported previously in the literature for a homogeneous reaction. Spectral shift (solvatochromic) data were measured for phenol blue in the same fluid in order to interpret the rate data. A method is presented to predict solvent effects on rate constants at supercritical fluid conditions.

Biological activities of phthalocyanines--VI. Photooxidation of L-tryptophan by selectively sulfonated gallium phthalocyanines: singlet oxygen yields and effect of aggregation.

Abstract: — The photosensitized oxidation of L-tryptophan by gallium phthalocyanines sulfonated to different degrees is studied as a function of both substrate and sensitizer concentrations in water and 50% MeOH-H2O solutions. The maximum quantum yield of singlet oxygen was found to be nearly 0.5 for all sulfonated gallium complexes. The effect of adding sulfonate groups in the phthalocyanine backbone is to change the tendency of dye molecules to dimerize or aggregate in a particular solvent. A shift in the chemical equilibrium away from the monomeric state, which occurs at high dye concentrations and at lower degrees of dye sulfonation, results in a reduced photochemical yield. The variation of quantum yields in different solvent systems and at several wavelengths is similarly accounted for by the fraction of light absorbed by the productive monomer state.

Acid Fermentation in Water-Organic Solvent Two-Liquid Phase Systems

Abstract: In search of an optimal system for extractive fermentation of an organic acid, fermentations of lactic, citric, and acetic acids were studied in a broth saturated with an organic solvent and in a broth-organic solvent two-liquid phase system. Among the 13 solvents tested, only long-chain hydrocarbons, perfluorodecalin, and methyl oleate were found to be nontoxic to the cells of L. delbrueckii in two-liquid phase systems. However, a distinction was made between toxicity due to dissolved solvent molecules and that due to a separate solvent phase. Thus, cells of L. delbrueckii, which were not inhibited in n-dodecanol-saturated broth, but inhibited in a two-phase system, were successfully protected by immobilization in carrageenan beads. The same solvent however, partially inhibited the growth of A. niger and A. aceti when present at saturated levels in the broth. The effect of tridodecylamine on lactic acid fermentation in a two-liquid phase system was investigated in view of enhancing the acid extraction. Since extraction of an acid is favored by low pH, an extractive fermentation of an acid is practical for microorganisms that can grow at pH < pKa, such as A. aceti and A. niger. The amine was found to be toxic to L. delbrueckii above a concentration of 222 mM, and at a level of 50%v, it was deleterious to all cell microorganisms tested, either free or gel entrapped.

Aspects of biocatalyst stability in organic solvents

Abstract: The stability of biocatalysis in systems containing organic solvents is reviewed. Among the examples presented are homogeneous mixtures of water and water-miscible organic solvents, aqueous/organic two-phase systems, solid biocatalysts suspended in organic solvents, enzymes in reverse micelles and modified enzymes soluble in water immiscible solvents. The stability of biocatalysts in organic solvents depends very much on the conditions. The hydrophobicity or the polarity of the solvent is clearly of great importance. More hydrophobic solvents (higher log P values) are less harmful to enzymes than less hydrophobic solvents. The water content of the system is a very important parameter. Some water is essential for enzymatic activity; however, the stability of enzymes decreases with increasing water content. Mechanisms of enzyme inactivation are discussed.

Process for upgrading diesel oils

Abstract: A process for upgrading diesel oil comprising the steps of: (1) reacting the diesel oil with a nitrogenous treating agent; (2) contacting the diesel oil from step (1) above with (a) a primary solvent selected from the group consisting of organic solvents having a dipole moment of about 1.3 or greater and mixtures thereof, with the proviso that alkyl amines and alkanol amines are excluded, or a water mixture of the primary solvent comprising about 50% by weight or less water and; (b) a cosolvent different from the primary solvent selected from the group consisting of an alcohol having 1 to 4 carbon atoms, an aldehyde having 1 or 2 carbon atoms, a ketone having 3 carbon atoms, a carboxylic acid having 1 or 2 carbon atoms and mixtures thereof, or a water mixture of the cosolvent comprising about 50% by weight or less water; wherein the primary solvent and cosolvent are each immiscible with the diesel oil or are in combination immiscible with the diesel oil, and (3) separating the diesel oil from step (2) above from the primary solvent and from the cosolvent to recover upgraded diesel fuel.

The role of solvent-accessible surface area in determining partition coefficients.

Abstract: The logarithm of the partition coefficient (log P) of low-molecular-weight organic compounds is a physicochemical parameter used extensively in structure-biological activity studies to model interactions of the compounds with nonpolar phases in vitro and in vivo. The partition coefficient can be determined between water and a number of nonpolar solvents. The most common nonpolar solvent is 1-octanol, but solvents such as benzene, carbon tetrachloride, and chloroform are frequently used as models for the nonpolar phases. The functional relationship between chemical structure and partitioning is not well-understood. In this paper, partition coefficient data for 50 solutes in six nonpolar solvent systems are analyzed by using principal components analysis. The objective of the work is to explore the relationship between solute structure and partitioning behavior for simple organic compounds. Two structural factors are found to be important, with the isotropic surface area being the most important. The isotropic surface area can be used to estimate log P in some solvents and as an independent variable in quantitative structure-activity relationships (QSAR). This is illustrated by estimating the rate of epidermal diffusion of steroids.

Abnormal solubility behavior of .beta.-lactoglobulin: salting-in by glycine and sodium chloride

Abstract: The causes of the salting-in of beta-lactoglobulin by glycine and NaCl, a solubility behavior contrary to expectations, were probed by a detailed study of the interactions between these solvent components and the protein. The preferential interactions of beta-lactoglobulin with solvent components in aqueous glycine and NaCl systems have been compared with those of bovine serum albumin and lysozyme. At neutral pH, beta-lactoglobulin exhibited insignificant preferential interactions in glycine and NaCl at low cosolvent concentrations and an increasing preferential hydration at higher concentrations, the levels approaching the values expected from the other two proteins. These results indicate considerable binding of the electrolytes to beta-lactoglobulin, sufficient to compensate for the exclusion due to perturbation of the solvent surface tension. The difference between the preferential interactions of beta-lactoglobulin and the other proteins with these two solvent additives was shown to be the cause of the increase of beta-lactoglobulin solubility even at high concentrations of the additives, at which they have salting-out effects on the other proteins. The preferential interactions of NaCl with the three proteins were examined as a function of pH. The results showed no pH dependence of the preferential hydration for bovine serum albumin and lysozyme, while this parameter increased significantly for beta-lactoglobulin at lower pH. This suggests that the binding of electrolytes to beta-lactoglobulin is due to a unique charge distribution on the surface of the protein around neutral pH, which imparts to this protein a large dipole moment.

Kinetics and mechanism of urethane reactions: Phenyl isocyanate–alcohol systems

Abstract: Urethane reactions of phenyl isocyanate alcohol systems with toluene as solvent and various aprotic polar solvents (including tertiary amines) as additives were carried out at constant temperature of 10–40°C. Analysis of the variation of the second order rate constants of these systems and those available in the literature indicates that formation of the hydrogen bonding complexes (alcohol with phenyl isocyanate and with aprotic solvent) and electron donor number (DN) of the aprotic solvent are the two factors allowing satisfactory explanation of the catalysis and inhibition effects of the wide range of aprotic solvents (including amines, amides, etc.). Based on these considerations, an ion-pair mechanism and the resulting kinetic equation for the urethane reaction are proposed. Verification on the kinetic equation with experimental results for the systems of phenyl isocyanate with alcohol in toluene (for the self catalysis of the alcohol), with dimethyl formamide and dimethyl sulfoxide in toluene (for the catalysis of the aprotic solvents), and with triethylamine in toluene (for the catalysis of the tertiary amines) shows satisfactory. In the mechanism, the aprotic solvent is considered to solvate the complex of phenyl isocyanate/alcohol at the active hydrogen to form an ion-pair which can undergo the urethane reaction more easily.

Fourier transform infrared studies of proteins using nonaqueous solvents. Effects of methanol and ethylene glycol on albumin and immunoglobulin G.

Abstract: An infrared/attenuated total reflection (ATR) technique has been utilized to study the structural changes in proteins induced by nonaqueous solvents, without the need of dissolving the protein in the nonaqueous solvent. For the two proteins studied, methanol and ethylene glycol caused similar changes in albumin, i.e., an increase in helix secondary structure. However, the two solvents had dissimilar effects on immunoglobulin G (IgG). Changes in the pH of aqueous solutions of IgG produced a third effect. By dissolving some IgG in ethylene glycol and then adsorbing IgG from this solution onto an ATR crystal, the time behavior of the adsorption process could be studied and a mechanism for the structural changes proposed.

Rotation and Solvation of Ammonium Ion

Abstract: From nitrogen-15 spin-lattice relaxation times and nuclear Overhauser enhancements, the rotational correlation time (c) for (15)NH(4)(+) was determined in a series of solvents. Values of (c) range from 0.46 to 20 picoseconds. The solvent dependence of (c) cannot be explained in terms of solvent polarity, molecular dipole moment, solvent basicity, solvent dielectric relaxation, or solvent viscosity. The rapid rotation and the variation with solvent can be accounted for by a model that involves hydrogen bonding of an NH proton to more than one solvent molecule in a disordered solvation environment.

Esterification in organic solvents: selection of hydrolases and effects of reaction conditions

Abstract: Fifty different hydrolases were screened for retention of high esterification activity in an organic solvent with citronellol as substrate. Although 22 hydrolases were very active as catalysts in the organic solvent, lipase from Candida cylindracea (lipase OF 360) was selected for further examination of the effects of reaction conditions on enzyme activity, with regard to catalyst availability and activity retention after immobilization. When the enzyme was entrapped in hydrophobic polyurethane gels, water-saturated isooctane was found to be the most suitable solvent, whereas polar solvents caused reversible catalyst inactivation. Entrapment significantly enhanced the operational stability of the lipase in the organic solvent.

Solvent bandwidth dependence and band asymmetry features of charge-transfer transitions in N-pyridinium phenolates

Abstract: They have investigated the shape of the solvatochromic absorption band for Betaine-26 2,4,6-triphenyl-N-(di-tert-butyl-4-hydroxyphenyl)pyridinium ion in a range of polar, apolar, protic, and aprotic solvents. Multiphonon band theory, including both molecular modes and a vibrationally dispersive solvent, indicates that the solvents fall in three categories: (1) The bandshape for polar, aprotic solvents is well reproduced by that for a structureless continuous dielectric and a single high-frequency molecular mode. Solvent broadening correlates with epsilon/sub o//sup -1/ - epsilon/sub s//sup -1/, epsilon/sub o/ being the optical and epsilon/sub s/ the static dielectric constant. The molecular frequency, Omega/sub c/, and displacement, ..delta../sub c/, are not very solvent dependent, emphasizing their molecular character, and the value Omega/sub c/ approx. = 1600 cm/sup -1/ suggests that C-O, C-N, and C-C stretching is involved. (2) Bands for apolar, aprotic solvents correspond to the same model. Omega/sub c/ and ..delta../sub c/ are again not very solvent dependent and coincide with the values for polar aprotic solvents. The solvent broadening is solvent independent, and wider than that for a structureless dielectric. This points to multipolar, dispersive, pressure, or pseudopotential forces as coupling mechanisms. (3) The bandshape for normal alcohols can only be produced by a model resting on twomore » molecular modes and a vibrational high-frequency solvent tail. Broadening, asymmetry, molecular frequencies, and deuterium isotope effects trace the protic solvent spectral entanglement to coupling between betaine-26 and a local mode group with features of both O-H stretching and bending and of librational solvent motion.« less

Membrane formation: diffusion induced demixing processes in ternary polymeric systems

Abstract: In this thesis the mechanism of membrane formation by means of immersion precipitation is studied. Immersion of a concentrated polymer solution film into a nonsolvent bath induces an exchange of solvent and nonsolvent in the film by means of diffusion. This process results in an asymmetric polymer distribution and leads to metastable compositions in the immersed polymer solution film. Demixing processes occur, yielding polymer rich and polymer lean entities in the film. When the exchange of solvent and nonsolvent is completed, a solidified film with a dense toplayer and a porous sublayer is obtained. The thin toplayer determines the permselectivity and the permeability of the membrane. The objective of this study is to gain insight into diffusional mass transport and demixing phenomena occurring during the immersion precipitation process.

Solvent extraction of cobalt and nickel in bis (2,4,4-tri-methylpentyl) phosphinic acid, “cyanex -272”

Abstract: ABSTRACT A study has been made of the extraction of cobalt and nickel from sulfate solutions into bis(2,4,4 tri-methylpentyl) Phosphinic acid - “Cyanex 272”, diluent Esso solvent DX 3641, for both high and low metal loading in the organic phase. In dilute solution, 0.01 M, extraction constants and enthalpies were determined for both metals. The extraction of cobalt was always favored over that of nickel, increasing with increase in temperature. No structure change with temperature was found for the cobalt-Cyanex complex. Phase modifiers were found to effect the selectivity of “Cyanex 272” for cobalt. At high metal loading, equilibrium curves for cobalt were fitted using semi-empirical curve fitting, while for nickel a straight line variation was observed. Organic phase polymerization was observed for both metals the degree of aggregation increasing with increase in loading. A step change increase in the viscosity of the organic phase was observed at high cobalt loading. Phase modifiers proved to ...

Solvent-resistant polyphenylene ether resin composition

Abstract: A polyphenylene ether resin composition having improved solvent resistance comprising (A) a modified polyphenylene ether obtained by modifying a polyphenylene ether with a modifier such as maleic anhydride and (B) a modified polyolefin obtained by modifying a polyolefin with both a modifier such as maleic anhydride and a vinyl or vinylidene compound such as styrene, and optionally (C) a binder such as phenylenediamine.

Cleaning compositions containing a colorant stabilized against fading

Abstract: An aqueous cleaning composition comprising a surfactant; up to about 50% of a higher boiling solvent, typically an alkyl ether of an alkylene glycol, said solvent introducing impurities into the composition in an amount and of a nature normally chemically incompatible with oxidizable dye chromophores; a dye in an amount to provide a desired tinctorial value, and a stabilizer selected from the group consisting of salts suitable to provide iodide and thiosulfate anions in an amount effective to retard fading of the dye, said compositions having a basic pH when the stabilizer is the thiousulfate salt. In another aspect of the invention, the stabilizer incorporated into compositions containing a solvent, a surfactant, and water, and optionally a dye provides a beneficial cleaning result. In yet another aspect of the invention, the stabilizer beneficially retards the development of malodors when the compositions of the present invention are contained in a PVC container. Broadly, the incorporation of the stabilizer in said solvent can be employed to neutralize said impurities.

Process for treatment of organic contaminants in solid or liquid phase wastes

Abstract: Solid or liquid phase wastes containing organic contaminants which can be photodegraded are treated. The contaminants are extracted into a perfluorinated solvent which is inert to the photodegradation step. In the case of solid wastes, such as contaminated soils, sediments or sludges, the contaminant is preferably first extracted into a hydrophilic solvent, such as acetone or methanol, and/or water, and is then extracted into the perfluorinated solvent. Photo-oxidants such as ozone are preferably used in the photodegradation step.