Water-organic Mixtures Research Articles

Siloxane-urethane membranes for removal of volatile organic solvents by pervaporation

Aqueous dispersions of siloxane-urethane copolymers (polysiloxaneurethanes) containing 0–49% of siloxane moieties were synthesized by the modified prepolymer-ionomer method. The properties of the dispersions were determined. Dense membranes were prepared from those dispersions by crosslinking with a multifunctional aziridine derivative. The structure of the obtained membranes was investigated by FTIR, solid state 13C NMR, 29Si NMR and DSC. Prepared membranes were tested in vacuum pervaporation of the following water-organic mixtures: water-tert-butyl methyl ether (1.8% wt. MTBE) and water-butyl acetate (0.25% wt. BuAc) at a temperature of 313 K. It was found that pervaporation properties of the polysiloxaneurethane membranes depended on the content of siloxane moieties. The best separation and transport properties were observed for the membrane containing 49% of siloxane groups. For this membrane separation factor a was equal to 750 and 1370 for water-MTBE and water-BuAc mixtures, respectively. The ratio of organic to water partial molar fluxes (Jorg/Jwater) was 2.8 and 0.5, respectively. This membrane was highly hydrophobic, thus the measured flux of pure water was about half of that for the membrane with a lower content of siloxane moieties.

Sweeping gas pervaporation with hollow-fiber ion-exchange membranes

Selective and transport properties of an anion-exchange hollow-fiber membrane (Pervasiv Ltd., Israel) were determined in the sweeping gas pervaporation process used for the dehydration of different organic solvents. C2–C4 alcohols (i.e. ethanol—EtOH, propanol—nPrOH, isopropanol—iPrOH, n-butanol—nBuOH and isobutanol —iBuOH) and two esters (i.e. methyl acetate — MeAc and ethyl acetate — EtAc) were chosen for investigations. The water content in the feed mixture was in the range 1–8 wt.%. Pervasiv membrane possessed the hydrophilic properties in contact with water-organic mixtures investigated. The separation factor α of Pervasiv membrane was correlated with the dielectric constant of the organic solvent. It was found that α increased exponentially with the decrease of the dielectric constant of organic solvent. Such behaviour was caused not only by the decrease of the flux of the less polar organic component through the membrane but also by the substantial increase of the water flux. The concentration dependence of the permeate fluxes showed that the total flux increased when the amount of water in the feed increased. The molar partial fluxes of organic solvents were much higher for polar solvents (ethanol) when comparing with solvents of lower polarity (e.g. isobutanol, methyl acetate).

Purification and characterization of a type B feruloyl esterase (StFAE-A) from the thermophilic fungus Sporotrichum thermophile.

A feruloyl esterase (StFAE-A) produced by Sporotrichum thermophile was purified to homogeneity. The purified homogeneous preparation of native StFAE-A exhibited a molecular mass of 57.0+/-1.5 kDa, with a mass of 33+/-1 kDa on SDS-PAGE. The pI of the enzyme was estimated by cation-exchange chromatofocusing to be at pH 3.1. The enzyme activity was optimal at pH 6.0 and 55-60 degrees C. The purified esterase was stable at the pH range 5.0-7.0. The enzyme retained 70% of activity after 7 h at 50 degrees C and lost 50% of its activity after 45 min at 55 degrees C and after 12 min at 60 degrees C. Determination of k(cat)/ K(m) revealed that the enzyme hydrolyzed methyl p-coumarate 2.5- and 12-fold more efficiently than methyl caffeate and methyl ferulate, respectively. No activity on methyl sinapinate was detected. The enzyme was active on substrates containing ferulic acid ester linked to the C-5 and C-2 linkages of arabinofuranose and it hydrolyzed 4-nitrophenyl 5- O- trans-feruloyl-alpha- l-arabinofuranoside (NPh-5-Fe-Ara f) 2-fold more efficiently than NPh-2-Fe-Ara f. Ferulic acid (FA) was efficiently released from destarched wheat bran when the esterase was incubated together with xylanase from S. thermophile (a maximum of 34% total ferulic acid released after 1 h incubation). StFAE-A by itself could release FA, but at a level almost 47-fold lower than that obtained in the presence of xylanase. The potential of StFAE-A for the synthesis of various phenolic acid esters was tested using a ternary water-organic mixture consisting of n-hexane, 1-butanol and water as a reaction system.

Homogeneous Biocatalysis in Organic Solvents and Water-Organic Mixtures

Homogeneous Biocatalysis in Organic Solvents and Water-Organic Mixtures

Stimuli‐sensitive behaviour of novel betaine‐type polyampholytes

AbstractNovel linear and crosslinked polyampholytes of betaine structure based on acrylic acid and ethyl 3‐aminocrotonate (ethyl ester of 3‐amino‐2‐butenoic acid) have been synthesized by Michael addition reaction followed by radical copolymerization. The mechanism of formation of monomer and polymer betaines is discussed. The linear polyampholyte has been characterized by potentiometric titration, IR, NMR and GPC. Crosslinked polymeric betaines were synthesized in the presence of N,N′‐methylenebisacrylamide. The stimuli‐sensitive properties of amphoteric gels have been studied as a function of pH, ionic strength, water–organic mixture composition, electric, and combined electric and magnetic fields. The isoelectric points of linear and crosslinked polymeric betaines correspond to pH 2.0–2.1. The effect of ionic strength on the solution and gel properties of polybetaine has been interpreted on the basis of destruction of inter‐chain, intra‐chain and intra‐group salt bonds. Water–acetone, water–ethanol or water–DMF mixtures cause the shrinking of amphoteric gel due to change of the dielectric constant of the medium and decrease of the osmotic pressure. Electrocollapse is observed under the action of DC electric field. Simultaneously cross action of electric and magnetic fields enhances the collapsing rate. Appearance of pH gradient within the volume of polyampholyte gel under the externally imposed DC electric field has been observed. Copyright © 2003 Society of Chemical Industry

Liquid-phase hydrogenation of benzene to cyclohexene catalyzed by Ru/SiO 2 in the presence of water–organic mixtures

The liquid-phase hydrogenation of benzene to cyclohexene was studied using a Ru/SiO 2 catalyst prepared by reduction of ruthenium(III) chloride impregnated in a hydrophilic non-porous silica. In a biphasic water/benzene system at 423 K and 5 MPa of hydrogen pressure, a 14% cyclohexene yield was obtained at 60% benzene conversion. Increased cyclohexene yields and selectivities were observed in the presence of ethylene glycol/water and glycerol/water mixtures, which consist mainly of hydrated organic molecules that can enhance the hydrophilicity around the ruthenium particles favoring the cyclohexene desorption.

Homogeneous Biocatalysis in Organic Solvents and Water-Organic Mixtures

Biocatalysis in non-aqueous media has undergone tremendous development during the last decade, and numerous reactions have been introduced and optimized for synthetic applications. In contrast to aqueous enzymology, biotransformations in organic solvents offer unique industrially attractive advantages, such as: drastic changes in the enantioselectivity of the reaction, the reversal of the thermodynamic equilibrium of hydrolysis reactions, suppression of water-dependent side reactions, and resistance to bacterial contamination. Currently, the field is dominated by heterogeneous biocatalysis based primarily on lyophilized enzyme powders, cross-linked crystals, and enzymes immobilized on inert supports that are mainly applied in enantioselective synthesis. However, low reaction rates are an inherent problem of the heterogeneous biocatalysis, while the homogeneous systems have the advantage that the elimination of diffusional barriers of substrates and products between organic and water phases results in an increase in the reaction rate. Here the discussion is focused on the correlation between activity and structure of the intact enzymes dissolved in neat organic solvents, as well as modifications of natural enzymes, which make them soluble and catalytically active in non-aqueous environment. Factors that influence conformation and stability of the enzymes are also discussed. Current developments in non-aqueous biocatalysts that combine advantages of protein modification and immobilization, i.e., HIP plastics, enzyme chips, ionic liquids, are introduced. Finally, engineering enzymes for biotransformations in non-conventional media by directed evolution is summarized.

Thermodynamics of Na + ion solvation in water–organic mixtures studied by the method of Volta potential differences

The features of the solvation of the Na+ ion compared with the Cl– ion in mixtures of water with various organic solvents have been elucidated on the basis of the analysis of chemical Gibbs energies of Na+ transfer from water to mixed solvents.

New approach in the treatment of data from an acid-base potentiometric titrationI. Monocomponent systems of monofunctional acids and bases.

Based on precise analysis of the acid-base equilibrium, a new approach in the treatment of experimental data from a potentiometric titration is proposed. A new general formula giving explicitly the relation V=f([H(+)]) is derived, valid for every acid-base titration, which includes mono- and polyfunctional protolytes and their mixtures. The present study is the first practical application of this formula for the simplest case, the analysis of one monofunctional protolyte. The collected mV data during the titration are converted into pH-values by means of an auto pH-calibration procedure, thus avoiding preliminary preparation of the measuring system. The mentioned pH-calibration method is applicable also in water-organic mixtures and allows the quantitative determination of sparingly soluble substances (particularly pharmaceuticals). The treatment of the data is performed by means of ready-to-use software products, which makes the proposed approach accessible for a wide range of applications.

Conformational changes and inactivation of rabbit muscle creatine kinase in dimethyl sulfoxide solutions.

The effects of dimethyl sulfoxide (DMSO) on creatine kinase (CK) conformation and enzymatic activity were studied by measuring activity changes, aggregation, and fluorescence spectra. The results showed that at low concentrations (< 65% v/v), DMSO had little effect on CK activity and structure. However, higher concentrations of DMSO led to CK inactivation, partial unfolding, and exposure of hydrophobic surfaces and thiol groups. DMSO caused aggregation during CK denaturation. A 75% DMSO concentration induced the most significant aggregation of CK. The CK inactivation and unfolding kinetics were single phase. The unfolding of CK was an irreversible process in the DMSO solutions. The results suggest that to a certain extent, an enzyme can maintain catalytic activity and conformation in water-organic mixture environments. Higher concentrations of DMSO affected the enzyme structure but not its active site. Inactivation occurred along with noticeable conformational change during CK denaturation. The inactivation and unfolding of CK in DMSO solutions differed from other denaturants such as guanidine, urea, and sodium dodecyl sulfate. The exposure of hydrophobic surfaces was a primary reason for the protein aggregation.

Formation and properties of polyelectrolyte complexes of chitosan hydrochloride and sodium dextransulfate

Methods of potentiometry, turbidimetry, colorimetry, IR spectroscopy, and element analysis were used to investigate the conditions of formation and the properties of non-stoichiometric polyelectrolyte complexes of chitosan hydrochloride (CHC) and sodium dextransulfate (the molecules of both polysaccharides appear as semirigid chains, but their charges are opposite). It was determined that the complexes' formation of polyelectrolytes studied is predominantly electrostatic in the presence of urea. As was also found turbidity and stability of the polycomplexes solutions depended markedly on pH value of CHC and a nature of the low-molecular-weight salts added. The complexes obtained were soluble in water, aqueous urea, and water-organic mixtures. The extent of solubility depended on the composition of the complexes and could be influenced by addition of appropriate concentrations of certain low-molecular-weight salts.

Optimal Environment for Glucose Oxidase in Perfluorosulfonated Ionomer Membranes: Improvement of First-Generation Biosensors

An optimal environment for glucose oxidase (GOx) in Nafion membranes is achieved using an advanced immobilization protocol based on a nonaqueous immobilization route. Exposure of glucose oxidase to water-organic mixtures with a high (85-95%) content of the organic solvent resulted in stabilization of the enzyme by a membrane-forming polyelectrolyte. Such an optimal environment leads to the highest enzyme specific activity in the resulting membrane, as desired for optimal use of the expensive oxidases. Casting solution containing glucose oxidase and Nafion is completely stable over 5 days in a refrigerator, providing almost absolute reproducibility of GOx-Nafion membranes. A glucose biosensor was prepared by casting the GOx-Nafion membranes over Prussian Blue-modified glassy carbon disk electrodes. The biosensor operated in the FIA mode allows the detection of glucose down to the 0.1 microM level, along with high sensitivity (0.05 A M(-1) cm(-2)), which is only 10 times lower than the sensitivity of the hydrogen peroxide transducer used. A comparison with the recently reported enzyme electrodes based on similar H2O2 transducers (transition metal hexacyanoferrates) shows that the proposed approach displays a dramatic (100-fold) improvement in sensitivity of the resulting biosensor. Combined with the attractive performance of a Prussian Blue-based hydrogen peroxide transducer, the proposed immobilization protocol provides a superior performance for first-generation glucose biosensors in term of sensitivity and detection limits.

Basicity of a novel macrocycle containing thiopyrimidine and uracil moieties in various water-organic mixtures

The acid–base behavior of the novel macrocycle, containing thiopyrimidine and uracil moieties 32-trimethyl-23,36-dioxo-15,19-dithio-2,9,13,20,24,31,34,35-octaazatatracyclo [28,3,110,14,120,24]hexatriacontaheptaen-1(34),10(35),11,13,21,30,32 (1) and the acyclic 1,6-bis[4-(N,N-dimethylamino)-6-methylpyrimidinile-2-thio]hexane (2) were studied by potentiometric, UV-Vis, 1H, NMR spectroscopic methods in water–dimethyl sulfoxide (methanol, 1,4-dioxane) solutions and at the interface between water and chloroform phases. The data obtained indicate, that thiopyrimidine nitrogens are the protonation sites of both 1 and 2. The protonation of 2 occurs in one step, while 1 is protonated stepwise in the pH range 9–2.5. The NMR data indicate that the intramolecular interaction between protonated pyrimidine and uracil moieties is the main reason for the stabilization of protonated forms of 1. The protonation constants of 1 were found to be different in various water–organic mixtures, which is in accord with the different 1H NMR spectra of 1 in various solvents. The protonation of 1 at the water–organic phase boundary is effected by the extraction of [1·2H]2+ into the aqueous phase, which can be regarded as a way of obtaining its water -soluble form.

Surfactant-free emulsion electrosynthesis via power ultrasound: electrocatalytic formation of carbon–carbon bonds

Proof-of-concept of the mediated electrosynthesis of carbon–carbon bonds in totally ‘green’ surfactant-free emulsion media generated by application of power ultrasound to a biphasic water–organic mixture is illustrated by reference to three systems, some requiring further activation by light, and each catalysed by vitamin B12. The voltammetry of aqueous vitamin B12 solutions at an electrode modified with microdroplets of the organic reactant is employed to gain an insight into the electrocatalytic pathway and readily permits the identification of optimum reaction parameters, such as starting material ratios and wavelength of light. The latter are employed in proof-of-concept emulsion electrosynthesis under conditions of triple activation (electron transfer, ultrasound and light).

A computational chemical study of penetration and displacement of water films near mineral surfaces

A series of molecular dynamics simulations have been performed on organic–water mixtures near mineral surfaces. These simulations show that, in contrast to apolar compounds, small polar organic compounds such as phenols can penetrate through thin water films to adsorb on these mineral surfaces. Furthermore, additional simulations involving demixing of an organic–water mixture near a surfactant-covered mineral surface demonstrate that even low concentrations of adsorbed polar compounds can induce major changes in mineral surface wettability, allowing sorption of apolar molecules. This strongly supports a two-stage adsorption mechanism for organic solutes, involving initial migration of small polar organic molecules to the mineral surface followed by water film displacement due to co-adsorption of the more apolar organic compounds, thus converting an initial water-wet mineral system to an organic-covered surface. This has profound implications for studies of petroleum reservoir diagenesis and wettability changes.

Henry’s law constants derived from equilibrium static cell measurements for dilute organic–water mixtures

The relationship of pressure and composition in the Henry’s law regime has been experimentally measured in an equilibrium static cell for a set of binary organic–water mixtures. The solutes range from hydrophilic materials, such as alcohol to extremely hydrophobic components, such as toluene and 1,2-dichloroethane. The goal of this study is to determine the effective concentration range over which Henry’s law reasonably approximates the gas–liquid partitioning. With the goal of obtaining accurate values of Henry’s law constant, several methodologies are critically compared for the aqueous solutes examined experimentally. The apparatus employed can determine gas–liquid partitioning coefficients through a variety of methods including direct phase concentration ratios, equilibrium partitioning in closed systems (EPICS), and application of the coexistence equation for γ ∞. Results to date indicate a more complex d P/d x behavior in the dilute region than previously assumed; and Henry’s law constant may not strictly apply to hydrophobic materials until the solute concentration is so low that analytical detection is problematic.

The peculiarities of high-molecular complex compounds of metal ions with fibrous complexites in water-organic mixtures

Abstract The results of equilibria studies of formation of high-molecular complex compounds (HMCC) of transition metal ions (Cu 2+ , Co 2+ , Ni 2+ ) with fibrous complexites when ionic strength is 0.05 at temperature range of 298–358 K in mixed solvents of variable composition are reported as the function of a solvent composition. The experiments were carried out by the potentiometric method in water — methanol and water — dimethylsulfoxide mixtures. Under a complexite the author implies a fibrous matrix formed on the basis of a cellulose that contains amidoxime and hydroxamic groups. The composition was stated, stability constants (log K st. ) and thermodynamic characteristics (ΔG 0 st. , ΔH 0 st. , ΔS 0 st. ) of complex formation were calculated. The HMCC are characterised by spectra of electronic reflection and infrared spectra. The values of log K st. increase with the decrease of the dielectric constant (ϵ) of the solvent. It was found that the dependence of a log K st. is not linear. The addition of the protolytic solvent that results in the stability increase of the complexes is stated. The influence of the addition of the aprotic polar component of a mixed solvent depends to some extent on the nature of the metal ion. The change of both HMCC structure and its geometry is shown not to be affected by the solvent. The results obtained are discussed in terms of the solvolytic ability of a solvent as well as of the effect of specific polymeric factors.

Vapor phase transport synthesis of zeolites from sol–gel precursors

A study of zeolite crystallization from sol–gel precursors using the vapor phase transport synthesis method has been performed. Zeolites (ZSM-5, ZSM-48, zeolite P, and sodalite) were crystallized by contacting vapor phase organic or organic–water mixtures with dried sodium silicate and dried sodium alumino-silicate gels. For each precursor gel, a ternary phase system of vapor phase organic reactant molecules was explored. The vapor phase reactant mixtures ranged from pure ethylene diamine, triethylamine, or water, to an equimolar mixture of each. In addition, a series of gels with varied physical and chemical properties were crystallized using the same vapor phase solvent mixture for each gel. The precursor gels and the crystalline products were analyzed via scanning electron microscopy, electron dispersive spectroscopy, X-ray mapping, powder X-ray diffraction, nitrogen surface area, Fourier transform infrared spectroscopy, and thermal analyses. The product phase and purity as a function of the solvent mixture, precursor gel structure, and precursor gel chemistry is discussed.

An experimental study of the stability of TiO 2 particles in organic–water mixtures

The stability of TiO 2 (Anatase) particles in various organic-water mixtures is examined experimentally. The results obtained reveal that the addition of AlCl 3 to a methanol–water dispersion leads to charge reversal on particle surface. If the concentration of methanol is high, CaCl 2 also leads to charge reversal, but NaCl does not have this effect. This implies that if the concentration of methanol is low, the coagulation between TiO 2 particles is due to double-layer compression for Na + and Ca 2+, and due to charge adsorption and neutralization for Al 3+. A methanol dispersion is unstable without the addition of electrolyte, and the addition of both CaCl 2 and AlCl 3 has the effect of stabilizing the dispersion; the addition of NaCl does not have this effect. The qualitative behaviors of an acetone–water dispersion are similar to those of a methanol–water dispersion. It is interesting to observe, however, that the absolute mobility of a pure acetone dispersion has a maximum as the concentrations of both CaCl 2 and AlCl 3 vary, but charge reversal does not occur. Among the dispersions without the addition of electrolyte, a 50% organic–water mixture is most stable. Also, a methanol–water dispersion is more stable than an acetone–water dispersion, which can be explained based on the degree of dissociation of an electrolyte.

ＳＡＰとミクロフィブリル状セルロースの複合構造体に関する研究 （第２報） 水と有機溶媒との混合溶媒系に於けるＭＦＣおよびＢＣの分散安定性に関する研究

By uniformly dispersing microfibrillated cellulose (the “MFC”) or bacterial cellulose (the “BC”) in a solvent mixture of water and hydrophilic organic solvent, a dispersion system of low concentration and high viscosity can be obtained. If super absorbent polymer particles (the “SAP”) are dispersed in this system, the SAP can be dispersed stably at a high concentration by virtue of such viscosity effect. The authors have found that, by forming a sheet from such a dispersion slurry and removing the solvent component therefrom, a SAP/MFC composite or a SAP/BC composite can be obtained efficiently where the MFC or the BC acts as the bonding agent. The MFC or the BC retains water stably in its microfibril structure when it is dispersed in water. That is to say, the MFC or the BC exhibits a similar behavior as it is in a so-called hydrating condition. Their hydrating condition, however, may vary very much depending on the kinds or amounts of organic solvents added. This report summarizes the results of the dispersing concentrations of the MFC or the BC with respect to the dispersion stability of the MFC or the BC in the solvent systems of water and organic solvents. The conclusions obtained are as follows : (1) Both of the S-MFC and the BC can be dispersed stably in organic solvents and water mixture systems where the SAP does not swell or coagulate. As an indication of the dispersion stability, the volumes of phase separation were measured.(2) Three kinds of fine fibers in the form of microfibrillated fibers (the “MF”), namely, the S-MFC, diluted BC and refined BC, were compared in terms of the dispersion stability, and found in the order of refined BC, the BC and the S-MFC. Thus, it was found that different dispersion stabilities were given different of the MF. This was probably because of different hydration capabilities, that is to say, different viscosities or amounts of water retained when they are dispersed in water.(3) The MF shows a very high dependence of dispersion stability on its concentration in water dispersion systems or in organic solvents/water mixture systems.(4) The dispersion stabilities of solvent systems were investigated when the ratios of organic solvent to water varied. It was consequently found that there existed a critical stability concentration value (Y value), beyond which the dispersion was stable. The Y value differs with the kinds of the MF. Specifically, the Y value of the S-MFC was around 0.3%, that of the BC was around 0.25%, and the value of refined BC was around 0.05%(5) As it was considered that increasing dispersion stability by the addition of an organic solvent was because of the viscosity of the system, changes in viscosity with three kinds of the MF, namely, the S-MFC, the BC and the refined BC, dispersed in an ethanol/water system, which is a standard condition, were investigated. The viscosity of any one of the these three MFs was higher as dispersed in an ethanol/water system than in a water dispersion system. It was confirmed that the maximum viscosity existed at around 50/50 of the ethanol/water ratio. From these results it was concluded that improved dispersion stability in solvent mixture systems was attributable to the increase in viscosity of the system.(6) If propylene glycol (the “PG”) is used as the organic solvent, the viscosity of the PG and the interaction of MF as dispersed in a solvent mixture so act in concert as to increase the viscosity of the MF dispersed system as the PG concentration increases so that the dispersion gets to be more stabilized. From this fact, the PG/water =70/30 system together with the ethanol/water =60/40 system was selected as a standard dispersion medium to be considered in future studies.