N-dimethyl Formamide Research Articles

Fabrication of polyimide microspheres with high precursor polymer concentration

Polyimide (PI) microspheres with high precursor polymer concentration were successfully prepared using non-aqueous reverse emulsion polymerisation. The emulsion was composed of N, N-dimethyl formamide and liquid paraffin, in which Span85 was used as surfactant. The effect of Span85 concentration on the resulting PI product has been investigated. The results indicated that with the increase in Span85 concentration, the average diameter declined, and the size distribution became narrow. When the concentration of surfactant Span85 was around 0.15 w/w, a yellow-to-brown-coloured powder of PI microfine spheres was obtained, with an average particle size of 25.6 µm. As an emulsifier and a chain termination agent, surfactant Span85 chemically bonded to the growing polymer chains, and not only formed stable non-aqueous inverse emulsion but also increased precursor polymer concentration.

Thermodynamic solvation of a series of homologous α-amino acids in non-aqueous mixture of ethylene-glycol and N,N-dimethyl formamide

Standard free energies (ΔG0t(i) ) and entropies (ΔS0t(i)) of transfer of some homologous α-amino acids viz. glycine (gly), dl-alanine (ala), dl-α-amino butyric acid (aba) and dl-nor-valine (nor-val) from protic ethylene glycol (EG) to dipolar aprotic N,N-dimethyl formamide (DMF) have been evaluated from solubility measure-ments at five equidistant temperatures i.e from 15 to 350C. The observed ΔG0t(i) and TΔS0t(i) Vs composition profiles are complicated because of the various interaction effects. The chemical effects of the transfer Gibbs energies (ΔG0t.ch(i)) and entropies of transfer (ΔS0t.ch(i)) have been obtained after elimination of cavity effect, estimated by the scaled particle theory and dipole-dipole interaction effects, estimated by the use of Keesom-orientation expression. The chemical contributions of transfer energetics of homologous α-amino acids are guided by the composite effects of increased dispersion interaction, basicity and decreased acidity, hydrogen bonding effects and solvophobic solvation of ethylene glycol and N, N-dimethyl formamide mixed solvent as compared to that of reference solvent (ethylene glycol).

Synthesis and Characterization of Hyperbranched Polyesters Based on Isophthalic Acid and Trimethylolpropane

Hydroxyl-terminated hyperbranched polyesters (HBPEs) with aromatic/aliphatic structure were synthesized at three different monomer mole ratios (A2/B3=1, 0.9, and 0.6, respectively) by melt polycondensation of isophthalic acid and trimethylolpropane via A2+ B3 approach. Fourier transform infrared (FTIR) spectroscopy indicated that the expected HBPEs, which showed excellent solubility in a variety of polar solvents such as N, N-dimethyl formamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), and terahydrofuran (THF), were produced without gelation during the polymerization. The weight-average molecular weight of HBPEs ranged from 7014 to 8306 and their inherent viscosities were varied from 0.17 to 0.34 dL/g. The degree of branching of the HBPEs was estimated to be 0.39–0.49 by1H-NMR and 13C-NMR measurement. Their glass transition temperature measured by differential scanning calorimetry (DSC) was between 64 and 86°C. The thermogravimetric analysis (TGA) measurement revealed that HBPEs had ca 8.5% weight-loss at 300°C in N2.

Bubble point measurements of binary mixtures formed by 1-hexanol with selected nitro-compounds and substituted benzenes at 95.6 kPa

Bubble point measurements (at 95.6 kPa) over the entire composition range are carried out for the binary mixtures formed by 1-hexanol with the: nitro-compounds (acetonitrile, acrylonitrile N, N-dimethyl formamide and aniline) and substituted benzenes ( o-xylene, chlorobenzene, and nitrobenzene), employing a Swietoslawski type ebulliometer. Wilson model is found to represent the measured liquid phase composition versus bubble point temperature data well. Computed values of the vapor phase mole fractions and liquid phase activity coefficients are tabulated and briefly discussed.

Evaluation of cryoprotectant and cooling rate for sperm cryopreservation in the euryhaline fish medaka Oryzias latipes

Medaka Oryzias latipes is a well-recognized biomedical fish model because of advantageous features such as small body size, transparency of embryos, and established techniques for gene knockout and modification. The goal of this study was to evaluate two critical factors, cryoprotectant and cooling rate, for sperm cryopreservation in 0.25-ml French straws. The objectives were to: (1) evaluate the acute toxicity of methanol, 2-methoxyethanol (ME), dimethyl sulfoxide (Me 2SO), N, N-dimethylacetamide (DMA), N, N-dimethyl formamide (DMF), and glycerol with concentrations of 5%, 10%, and 15% for 60 min of incubation at 4 °C; (2) evaluate cooling rates from 5 to 25 °C/min for freezing and their interaction with cryoprotectants, and (3) test fertility of thawed sperm cryopreserved with selected cryoprotectants and associated cooling rates. Evaluation of cryoprotectant toxicity showed that methanol and ME (5% and 10%) did not change the sperm motility after 30 min; Me 2SO, DMA, and DMF (10% and 15%) and glycerol (5%, 10% and 15%) significantly decreased the motility of sperm within 1 min after mixing. Based on these results, methanol and ME were selected as cryoprotectants (10%) to evaluate with different cooling rates (from 5 to 25 °C/min) and were compared to Me 2SO and DMF (10%) (based on their use as cryoprotectants in previous publications). Post-thaw motility was affected by cryoprotectant, cooling rate, and their interaction ( P ⩽ 0.000). The highest post-thaw motility (50 ± 10%) was observed at a cooling rate of 10 °C/min with methanol as cryoprotectant. Comparable post-thaw motility (37 ± 12%) was obtained at a cooling rate of 15 °C/min with ME as cryoprotectant. With DMF, post-thaw motility at all cooling rates was ⩽10% which was significantly lower than that of methanol and ME. With Me 2SO, post-thaw motilities were less than 1% at all cooling rates, and significantly lower compared to the other three cryoprotectants ( P ⩽ 0.000). When sperm from individual males were cryopreserved with 10% methanol at a cooling rate of 10 °C/min and 10% ME with a rate of 15 °C/min, no difference was found in post-thaw motility. Fertility testing of thawed sperm cryopreserved with 10% methanol at a rate of 10 °C/min showed average hatching of 70 ± 30% which was comparable to that of fresh sperm (86 ± 15%). Overall, this study established a baseline for high-throughput sperm cryopreservation of medaka provides an outline for protocol standardization and use of automated processing equipment in the future.

The use of cryomicroscopy in guppy sperm freezing

The present study employed cryomicroscopy to derive an optimal sperm freezing protocol for guppy ( Poecilia reticulata) sperm. Evaluation criteria during the freezing–thawing process were assessed for nucleation temperature (Tn), temperature when more than 50% of sperm display bending mid-piece (Tb), temperature when more than 80% of sperm stop moving (Tm), thawing temperature (Tt), and post-thaw motility. We compared four different cryoprotectants: 5% N-dimethyl formamide (DMF), 6% methanol (MEOH), 10% dimethyl sulfoxide (DMSO), and 14% glycerol, as well as glycerol at different concentrations of 7–50%; cooling and rewarming rates ranged from 5 to 100 °C/min. The protocol that yielded the highest post-thaw motility was samples suspended in 14% glycerol, cooled at 25 °C/min, and thawed at 100 °C/min, which was in complete agreement with our previous findings derived from a controlled-rate freezer. In addition, Tb and Tm were found to be negatively correlated with post-thaw motility, suggesting their possible role in predicting freezing success. The present study for the first time demonstrated the usefulness of cryomicroscopy in deriving an optimal sperm freezing protocol for aquatic species.

Influences of organic-modified Fe-montmorillonite on structure, morphology and properties of polyacrylonitrile nanocomposite fibers

The Fe-montmorillonite (Fe-MMT) combined catalysis effects of Fe ion with barrier effects of silicate clays, was firstly synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The organic-modified Fe-montmorillonite (Fe-OMT) was dispersed in the N, N-dimethyl formamide (DMF) and then compounded with polyacrylonitrile (PAN) solution which was dissolved in DMF. The composite solutions were electrospun to form PAN/Fe-OMT nanocomposite fibers. The influences of the Fe-OMT on the structure, morphology, thermal, flammability and mechanical properties of PAN nanocomposite fibers were respectively characterized by X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM), Thermogravimetric analyses (TGA), Micro Combustion Calorimeter (MCC) and Electronic Single Yarn Strength Tester. It was found from XRD curves that there was not observable diffraction peak of silicate clay, indicating that the silicate clay layers were well dispersed within the PAN nanofibers. The HRTEM image indicated that the multilayer stacks of nanoclays could be found within the nanofibers and were aligned almost along the axis of the nanofibers. The SEM images showed that the diameters of nanocomposite fibers were decreased with the loading of the Fe-OMT. The TGA analyses revealed that the onset temperature of thermal degradation and charred residue at 700°C of PAN nanocomposite fibers were notably increased compared with the pure PAN nanofibers, contributing to the improved thermal stability properties. It was also observed from MCC analyses that the decreased peak of heat release rate (PHRR) of the PAN nanocomposite fibers reduced the flammability properties. The loadings of Fe-OMT increased the tensile strength of PAN nanocomposite fibers, but the elongation at break of PAN nanocomposite fibers was lower than that of the PAN nanofibers.

Grafting of chitosan as a biopolymer onto wool fabric using anhydride bridge and its antibacterial property

Weak binding of chitosan on the wool constitutes the main problem in its application. In this paper, the surface modification of wool fabric using anhydrides to graft the chitosan was studied. Weight gain, antibacterial and antifelting properties of the chitosan grafted-acylated wool fabric were investigated. Wool fabrics were acylated with two anhydrides, succinic anhydride (SA) and phthalic anhydride (PA), using different solvents (dimethylsulfoxide (DMSO) and N, N-dimethyl formamide (DMF)). The effects of anhydrides, solvents, anhydride concentration, liquor ratio (L:R) and reaction time on acylation of wool were investigated. Chitosan was grafted to the acylated wool and the effects of pH, chitosan concentration, and reaction time on chitosan grafting of acylated wool were evaluated. Fourier transform infra-red (FTIR), scanning electron microscope (SEM), differential scanning colorimetry (DSC) and weight gain analyses provided evidence that chitosan was grafted on to the acylated wool through the formation of new covalent bonds. The grafted samples have antibacterial potential due to existence of the antibacterial property of chitosan. In addition, the chitosan grafted-acylated wool samples have antifelting property. The findings of this research support the potential production of new environmentally friendly textile fabrics.

Electrospinning of α,β-poly( N-2-hydroxyethyl)- dl-aspartamide- graft-polylactic acid to produce a fibrillar scaffold

α,β-Poly( N-2-hydroxyethyl)- dl-aspartamide grafted with polylactic acid (PHEA- g-PLA) is a biocompatible and biodegradable amphiphilic copolymer that has been already employed to prepare a drug delivery system. In this study we have prepared for the first time a fibrillar scaffold from PHEA- g-PLA by the electrospinning of a solution of this copolymer in a mixture of N, N-dimethyl formamide (DMF) and acetone (80:20 vol/vol). The average diameter and the morphology of electrospun fibers were detected by scanning electron microscopy. Chemical degradation studies in phosphate buffer solution pH 7.4 have been performed until 15 days in order to obtain a preliminary information about the hydrolytic resistance of the prepared scaffold.

Synthesis and characterization of polyethersulfone membranes

Phase inversion method was used to prepare polyethersulfone (PES) ultrafiltration (UF) membranes. Polyethylene glycol (PEG); N, N-dimethyl formamide (DMF) and water were utilized as pore-forming additive, solvent and non-solvent, respectively. Effects of PES and PEG concentrations in the casting solution, PEG molecular weight (MW) and coagulation bath temperature (CBT) on morphology of the prepared membranes were investigated. Taguchi experimental design was applied to run a minimum number of experiments. 18 membranes were synthesized and their permeation and rejection properties to pure water and human serum albumin (HSA) solution were studied. It was found out that increasing PEG concentration, PEG MW and CBT, accelerates diffusional exchange rate of solvent (DMF) and non-solvent (water) and consequently facilitates formation of macrovoids in the membrane structure. The results showed that, increasing PES concentration, however, slows down the demixing process. This prevents instantaneous growth of nucleuses in the membrane structure. Hence, a large number of small nucleuses are created and distributed throughout the polymer film and denser membranes are synthesized. A trade-off between water permeation and HSA rejection was involved, with membranes having higher water permeation exhibited lower HSA rejection, and vice versa. Hence, optimizing preparation variables to achieve high pure water permeation flux along with reasonable HSA rejection was inevitable. Analysis of variance (ANOVA) showed that all parameters have significant effects on the response (water flux and HSA rejection). However, CBT and PES concentration were more influential factors than PEG concentration and MW on the responses.

A lipase catalyzed condensation reaction with a tricyclic diketone: yet another example of biocatalytic promiscuity

Novozym 435 (a commercially available immobilized form of Candida antarctica lipase B) was found to catalyze a condensation reaction of 5-hydroxy-endo-tricyclo[5.2.1.0 2,6]deca-4,8-dien-3-one with acetaldehyde (enzymatically produced from vinyl acetate in situ) under low water conditions, in presence of 10% organic co-solvent ( N, N-dimethyl formamide or pyridine), to form a bis-adduct. Even though the condensation reaction occurred with pyridine (acting as a base catalyst) in the presence of acetaldehyde and in the absence of enzyme, the reaction was very slow as compared to the enzymatic process. Thus, while the non-enzymatic process took 4 days to achieve 100% conversion; in presence of enzyme it was possible within 4 h.

Determination of penicillin V potassium in pharmaceuticals and spiked human urine by chemiluminescence

AbstractA simple and selective method for penicillin V potassium (PVK) determination by chemiluminescence (CL) was developed. Oxidation of PVK by alkaline hydrogen peroxide produces CL, which is greatly enhanced by N, N-dimethyl formamide (DMF) and N-cetyl-N,N,N-trimethylammonium bromide (CTMAB). Optimum conditions were established using luminometry. There is a linear relationship between the chemiluminescent peak height and the amount of PVK within the range 0.5–129.5 mg L−1, with a detection limit of 0.2 mg L−1. The coefficient of variation was 1.2% for 40 mg L−1 PVK solution (n = 7). The method is very simple, has high sensitivity and good selectivity, and is usable for process control. It was successfully utilized for the determination of PVK in pharmaceuticals and spiked human urine.

PREPARATION OF PVDF ISLAND THIN FILMS BASED ON A PHASE SEPARATION METHOD

ABSTRACT By mixture of amount of poly (vinylidene fluoride) (PVDF) and poly-vinylpyrrolidone (PVP) into N, N-dimethyl formamide (DMF), we present a novel technique of preparing PVDF island thin films on Pt/Ti/SiO2/Si substrates during spin-coating process based on the process of phase separation. After treated at vacuum condition, the samples were immerged in the ethanol solvent to dissolve PVP, which leads the formation of PVDF island thin films. The X-ray diffractometer, Fourier transform infrared spectroscopy and atomic force microscope were employed to determine the PVDF island thin films. In addition, the formative mechanism of polymer resin with island structure was also investigated.

Synthesis, characterization and constitutional isomerism study of new aromatic polyamides containing pendant groups based on asymmetrically substituted meta-phenylene diamines

Four new aromatic polyamides containing pendant groups were synthesized by low temperature interfacial polycondensation of two asymmetrically substituted diamine monomers, namely, 4-[4-(1-methyl-1-phenylethyl) phenoxy]-1,3-diamino benzene and 4-{4-[(4-methylphenyl) sulphonyl]phenoxy}-1,3-diamino benzene with two aromatic diacid chlorides, namely isophthaloyl chloride and terephthaloyl chloride. Inherent viscosities of polyamides were in the range 0.64–0.72 dL/g indicating formation of medium molecular weight polymers. The weight average molecular weights and number average molecular weights, determined by gel permeation chromatography (polystyrene standard), were in the range 54,500–65,000 and 19,750–27,000, respectively. The constitutional isomerism of synthesized polyamides was investigated by 1H and 13C NMR spectroscopy, where as the constitutional order was calculated from 1H NMR spectroscopy and was found to be in the range 0.35–0.37. Polyamides containing pendant groups were essentially amorphous and were soluble in polar aprotic solvents such as N, N-dimethyl acetamide, N-methyl-2-pyrrolidone, N, N-dimethyl formamide and dimethyl sulfoxide. Polyamides exhibited glass-transition temperature in the range 237–254 °C. The initial decomposition temperature, determined by TGA in nitrogen atmosphere, of polyamides was in the range 371–410 °C indicating their good thermal stability.

Application of solid-phase microextraction and gas chromatography–mass spectrometry for measuring chemicals in saliva of synthetic leather workers

Saliva is of interest as a diagnostic aid for oral and systemic diseases, to monitor therapeutic drugs, and detect illicit drug abuse. It is also attractive for biological monitoring of exposure to hazardous solvents. The major advantage of this indicator over other biological monitoring targets is that the saliva is noninvasive and less confidential in comparison with blood and urine. Salivary analysis is generally acceptable by study subjects and can be applied to investigation of a wide variety of compounds. However, very few studies have been conducted on the saliva matrix to monitor exposure to hazardous solvents. The aim of this study is to establish an analytical method, headspace solid-phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC–MS), by which the saliva matrix can be monitored for multiple compounds with various polarities, such as methyl ethyl ketone (MEK), isopropyl alcohol (IPA), and N, N-dimethyl formamide (DMF) (common solvents used in synthetic leather manufacture), as well as acetone (ACE) and N-methyl formamide (NMF) (metabolites of IPA and DMF, respectively). We studied this technique as an alternative biological monitoring method for investigating exposure to hazardous solvents. A Carboxen/Polydimethylsiloxane (CAR/PDMS 75 μm) fiber coating was employed for this study, and various extraction and desorption parameters were evaluated. The extraction efficiency and reproducibility of analyses was improved by pre-incubation. The limits of detection were 0.004, 0.003, 0.006, 0.05, and 0.10 μg/mL for ACE, MEK, IPA, DMF, and NMF, respectively. Method validation was performed on standards spiked in blank saliva, and a correlation was made between HS-SPME and traditional solvent pretreatment methods. It was found that correlation coefficients ( r) were greater than 0.996 for each analyte, with no significant differences ( p > 0.05) between two methods. However, the SPME method achieved lower limits of detection, with good accuracy (recovery 95.3–109.2%) and precision (1.17–8.22% CV) for both intra- and inter-assay, when quality control samples were analyzed for all five compounds. The partition coefficient for each compound between the headspace of the saliva sample and the CAR/PDMS fiber coating was 90.9, 170.1, 36.4, 3.70 and 0.92 for ACE, MEK, IPA, DMF and NMF, respectively. Real sample analyses were performed on workers in a synthetic leather factory. In summary, the SPME method is a highly versatile and flexible technique for chemical measurement, and we demonstrate its application for monitoring biological exposure to hazardous solvents. Saliva monitoring using sensitive SPME approaches for determining workplace exposure should prove useful as an alternative exposure monitoring method.

Environmentally friendly surface modification of silk fiber: Chitosan grafting and dyeing

In this paper, the surface modification of silk fiber using anhydrides to graft the polysaccharide chitosan and dyeing ability of the grafted silk were studied. Silk fiber was degummed and acylated with two anhydrides, succinic anhydride (SA) and phthalic anhydride (PA), in different solvents (dimethyl sulfoxide (DMSO) and N, N-dimethyl formamide (DMF)). The effects of anhydrides, solvents, anhydride concentration, liquor ratio (L:R) and reaction time on acylation of silk were studied. The polysaccharide chitosan was grafted to the acylated silk fiber and dyed by acid dye (Acid Black NB.B). The effects of pH, chitosan concentration, and reaction time on chitosan grafting of acylated silk were investigated. The physical properties show sensible changes regardless of weight gain. Scanning electron microscopy (SEM) analysis showed the presence of foreign materials firmly attached to the surface of silk. FTIR spectroscopy provided evidence that chitosan was grafted onto the acylated silk through the formation of new covalent bonds. The dyeing of the chitosan grafted-acylated silk fiber indicated the higher dye ability in comparison to the acylated and degummed silk samples. The mechanism of chitosan grafting over degummed silk through anhydride linkage was proposed. The findings of this research support the potential production of new environmentally friendly textile fibers. It is worthwhile to mention that the grafted samples have antibacterial potential due to the antibacterial property of chitosan molecules.

Crosslinked integrally skinned asymmetric polyaniline membranes for use in organic solvents

Solvent stable integrally skinned asymmetric nanofiltration membranes were prepared from polyaniline. These membranes were made by phase inversion and then crosslinked using two different chemical crosslinkers, α,α′-dichloro- p-xylene and glutaraldehyde. The resultant membranes were found to be stable in various organic solvents including acetone, methanol, ethyl acetate, tetrahydrofuran and N, N-dimethyl formamide. Nanofiltration experiments carried out in acetone and dimethyl formamide showed that the membranes gave stable permeate fluxes and good separation performances in the nanofiltration range. Molecular weight cut-off (MWCO) of the membranes was found to be between 150 and 250 g mol −1. These membranes were also found to be stable for operations at elevated temperatures up to 70 °C and possibly higher. Furthermore, no fillers or preservative agents are required to maintain the membranes in a dry state thereby increasing the ease of handling.

Effect of silica particles on cellulose acetate blend ultrafiltration membranes: Part I

This paper deals with the preparation of organic–inorganic ultrafiltration (UF) membranes by solution casting followed by phase separation method. The silica (SiO 2) particles were added to the cellulose acetate (CA) polymer with the increment of 10 wt.% from 0 to 40% by weight using N, N-dimethyl formamide (DMF) as polar solvent. The prepared organic–inorganic membranes were characterized for UF performance such as compaction, pure water flux, % water content, membrane hydraulic resistance, molecular weight cut-off (MWCO) and pore statistics. MWCO and pore statistics were investigated using protein solutions of different molecular weights. It is observed that by increasing the concentration of SiO 2 in CA polymer, the MWCO, pore radius, surface porosity and pore density has been increased. The mechanical stability of the CA/SiO 2 blend membranes increased initially and then declined with the addition of inorganic particle above 10 wt.% to the casting solution. The morphological structure was changed with the addition of SiO 2 particles in the casting solution. Further the permeate flux and % rejection of different molecular weight of proteins were investigated which showed an increased protein permeate flux with the decreased solute rejection. Meanwhile, the effect of SiO 2 content in the CA membranes on fouling-resistant ability was studied using BSA solution. The results indicated that increasing the SiO 2 content in the casting solution, the reversible fouling resistance dominated the total fouling resistance thereby improving the fouling resistance ability of the blend membranes.

Structures, thermal stability, and crystalline properties of polyamide6/organic-modified Fe-montmorillonite composite nanofibers by electrospinning

In the present work, Fe-montmorillonite (Fe-MMT) was synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The polyamide6 (PA6)/organic-modified Fe-montmorillonite (Fe-OMT) composite nanofibers were prepared by facile compounding and electrospinning. Fe-OMT was first dispersed in N, N-dimethyl formamide and then compounded with PA6 which was dissolved in formic acid. The composite solutions were electrospun to form PA6/Fe-OMT composite nanofibers. The structure, morphology, thermal stability, and crystalline properties of the composite nanofibers were characterized by Fourier transfer infrared (FTIR) spectra, Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), High-resolution electron microscopy (HREM), Scanning electron microscopy (SEM), and Thermogravimetric analyses (TGA), respectively. It was found that the silicate clay layers were well exfoliated within the composite nanofibers and were oriented along the fiber axis. The SEM images indicated that the loading of Fe-OMT decreased the diameters of composite nanofibers. TGA analyses revealed that the thermal stability was notably improved in the presence of silicate clay. It was also observed from wide-angle XRD analyses that the presence of nanoclays improved the γ-form crystals and induced the formations of α-form crystals of the PA6, attributed to effective nucleating effects of silicate clay platelets.

Activity coefficients and excess Gibbs energy of binary mixtures of N, N-dimethyl formamide with selected compounds at 95.5 kPa

Bubble point temperatures at 95.5 kPa, over the entire composition range, are measured for the binary mixtures of N, N-dimethyl formamide with: acetophenone, aniline, bromobenzene, chlorobenzene and N, N-dimethyl acetamide, employing a Swietoslawski-type ebulliometer. Liquid phase mole fraction versus bubble point temperature measurements are well represented by the Wilson model. Computed values of the activity coefficients and excess Gibbs energy are presented and discussed.