Bubble points of hydrogen chloride–water–isopropanol and hydrogen chloride–water–isopropanol–benzene systems and liquid–liquid equilibria of hydrogen chloride–water–benzene and hydrogen chloride–water–isopropanol–benzene systems

Bubble points of the HCl–water–isopropanol and the HCl–water–isopropanol–benzene systems and liquid–liquid equilibria (LLE) of the HCl–water–benzene and the HCl–water– isopropanol–benzene systems were measured at 25–85°C and 30–70°C, respectively. The electrolyte nonrandom two-liquid model proposed by Chen et al. [C.-C. Chen, H.I. Britt, J.F. Boston, L.B. Evans, AIChE J. 28 (1982) 588–596] can satisfactorily correlate bubble points and liquid–liquid equilibria of the present mixed-solvent electrolyte systems over the entire range of temperature and concentrations using only binary adjustable parameters.     

Bulk properties and hydration numbers of components of water–salt,water–urea,and water–urea–salt systems

With an increase in the concentration of additives, the hydration numbers of compounds decrease. Thus, in a saturated 54.6% solution, urea loses approximately 3/4 of the initial amount of water, forming an aquacomplex of the composition (NH₂)₂CO?H₂O. In a supersaturated 44% solution, the sodium chloride aquacomplex is dehydrated by 2/3, and in a supersaturated 67% solution, sodium sulfate is dehydrated by 5/6. The density of these solutions is 1.354÷1.360 g/cm³ (44% NaCl) and 1.800÷1.849 g/cm³ (67% Na₂SO₄). In a saturated urea solution, NaNO₃, NaCl, and Na₂SO₄ complexes lose 53÷55% of hydration water. It is shown that the interactions in the binary water–urea system somewhat increase the hydration number of the salts (structural hydration). The hydration water density, a structurally important characteristic, increases in the series of solutions of urea, NaNO₃, NaCl, and Na₂SO₄. In the same series of additives, the excess volume of binary water–urea and water–salt systems becomes more negative.     

Surface tension isotherms of the dioxane–acetone–water and glycerol–ethanol–water ternary systems

The results of the experimental and theoretical studies of the concentration dependence of surface tension of aqueous solutions of the 1,4-dioxane–acetone–water and glycerol–ethanol–water ternary systems were given. The studies were performed by the hanging-drop method on a DSA100 tensiometer. The maximum error of surface tension was 1%. The theoretical models for calculating the surface tension of the ternary systems of organic solutions were analyzed.     

Temperatures of liquid–liquid separation and excess molar volumes of {N-methylpiperidine–water} and {2-methylpiperidine–water} systems

Partial miscibility in binary systems {N-methylpiperidine–water} and {2-methylpiperidine–water} was studied. The temperatures of liquid–liquid separation were determined as function of composition using both calorimetric technique and phase equilibrium cell. The densities of {amine–water} mixtures were determined in the domain of total miscibility at temperatures between 288 K and 338 K. Excess molar volumes were derived from experimental density data and fit to a Redlich–Kister polynomial.     

Characteristics of sodium alginate membranes for the pervaporation dehydration of ethanol–water and isopropanol–water mixtures

Alginate membranes for the pervaporation dehydration of ethanol–water and isopropanol–water mixtures were prepared and tested. The sodium alginate membrane was water soluble and mechanically weak but it showed promising performance for the pervaporation dehydration. To control the water solubility the sodium alginate membrane was crosslinked ionically using various divalent and trivalent ions. Among them the alginate membrane crosslinked with Ca²⁺ ion showed the highest pervaporation performance in terms of the flux and separation factors.     

Rayleigh and Raman light scattering in hydrogen-bonded acetonitrile–water

The structure, vibrational frequencies, light scattering activities and binding energies of CH₃CNH₂O are obtained from ab initio methods. The hydrogen NH bond distance is calculated as 2.06 Å, the dipole moment as 5.77 D and our best estimate for the binding energy is 3.5 kcal mol^–1 (14.7 kJ mol^–1), after correcting for zero-point vibrations. The calculated average dipole polarizability is 39.67 au and the anisotropy is fairly large, corresponding to 21.78 au. The changes in intramolecular vibrational frequencies are analyzed. The scattering activities and depolarization of the Rayleigh and Raman light scattered are calculated. In the Raman case the depolarization due to the intense NC stretching vibration is increased by 20% after the hydrogen bond. For the OH symmetric stretch of water there is a large redshift of 75 cm^–1 and a great intensification of the Raman scattering activity by a factor of 2 and a considerable increase of the depolarization by a factor of nearly 4.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002)     

Ultrathin dynamic networks formed by the surfactant SPAN 65 at the air–water and oil–water interface

Some surfactants tend to form ultrathin films at the surface of water or at the interface between oil and water. A representative of these surface-active compounds is SPAN 65 (trioctadecanyl ester of sorbic acid). Induced by attractive interactions these molecules can self-associate to form temporary networks. At the planar surface we measured the two-dimensional relaxation modulus, the storage modulus, the loss modulus and the relaxation spectrum. In addition to these measurements, we have also investigated the molecular structure of these networks with “Brewster-angle-microscopy”. The results indicate that temporary cross-linking points, which have lifetimes of the order of a few seconds, tend to stabilize these films. This dynamic network formation is also interesting for numerous technical applications, and it might be used for the preparation of emulsions, foams or microcapsules. Received: 23 October 2000 Accepted: 3 November 2000     

Dynamic and sub-ambient thermal transition relationships in water–sucrose solutions

This work was undertaken to investigate thermal and dynamic transitions observed in the temperature range close to the bulk ice melting temperature in sucrose solutions. Measurements of thermal (differential calorimetry) and dynamic (neutron scattering) properties were compared in order to give a physical interpretation of the thermal transitions observed during the thawing of amorphous sucrose solutions. In fact, the freezing of biological material leads to the distinction between different pools of water: bulk water which becomes ice after freezing, unfrozen water trapped in the glassy matrix or close to the interface of solutes can be considered, and finally freezable confined water with a lower melting point than bulk water and with properties depending on both the ice presence and the microstructure of the material. The transition temperatures such as glass transition or melting are dependent on the freezing protocol used and examples of annealing effects are presented, in order to underline the necessity of a good temperature control during freezing for the study of biological material with freezable water.     

Formation of a 1-D metal–water chain and a 2-D water–sulfate layer containing cyclic water octamers in a 3-D supramolecular network

A new tetranuclear complex, {[Cu(phen)(OH)]₄(H₂O)₂}?·?(SO₄)₂?·?8H₂O (1) (phen = 1,10-phenanthroline), has been synthesized and characterized by elemental analysis, UV-Vis, IR, TG, and single-crystal X-ray diffraction. Complex 1 exhibits a 3-D supramolecular network with a 1-D metal–water chain consisting of tetranuclear hydroxo-bridged copper(II) clusters and water octamers and a 2-D water–sulfate layer containing cyclic water octamers with five types of O–H?···?O hydrogen-bonding motifs. The free ligand and its complex were screened for antibacterial activity against Gram-positive and Gram-negative bacteria.     

Structures of an infinite helical water chain and discrete lattice water in metal–organic framework structures

Two supramolecular complexes Ni[(Py)₂C(OH)₂]₂·(CH₃COO)₂·4H₂O 1 and Co[(Py)₂C(OH)₂]₂·(CH₃COO)₂·2H₂O 2 have been synthesized under hydrothermal conditions and structurally characterized by elemental analysis, IR spectra, and X-ray single-crystal diffraction. The X-ray diffraction analysis indicates that the center metal (Ni²⁺ and Co²⁺) ions having the same coordination environments are chelated by two pyridyl N atoms and a hydroxyl O atom of the gem-diol ligand in an octahedral geometry. In 1, the lattice water molecules form infinite single helical chains, while in 2, two lattice water molecules are discrete. In their crystal structures, intermolecular O–H···O and C–H···O hydrogen bonds form an extensive three-dimensional network, which consolidates the crystal packing.     

Phase equilibria and critical phenomena in the cesium nitrate–water–pyridine ternary system

The solubilities of components, phase equilibria, and critical phenomena in the cesium nitrate–water–pyridine ternary system are studied in the 5–100°C temperature range by the visual–polythermal method. Cesium nitrate is found to exhibit a salting-out effect at temperatures above 79.9°C causing phase separation in homogeneous water–pyridine solutions. The temperature of formation of the critical monotectic tie line (79.9°C) and the compositions of solutions corresponding to the liquid–liquid critical points at three temperatures are determined. The pyridine distribution coefficients between the aqueous and organic phases of the monotectic state at 85.0, 90.0, and 100.0°C are calculated. Their values demonstrate that salting-out of pyridine from aqueous solutions by cesium nitrate increases at higher temperatures. The plotted isotherms of phase diagrams confirm the fragment of the scheme of topological transformation of the phase diagrams of salt–binary solvent ternary systems with salting-in and salting-out phenomena.     

Correlation and prediction of salt effects on vapor–liquid equilibrium in alcohol–water–salt systems

A modification of the solvation model of Ohe is proposed for the calculation of vapor–liquid equilibria (VLE) in alcohol–water–salt systems. The modified method employs the Bromley equation to calculate the activity of water in salt solutions, and a one-parameter empirical expression to calculate the activity of the alcohol. The single parameter is obtained by fitting ternary alcohol–water–salt data. The method is simple to use and does not require data on the vapor-pressures of alcohol–salt mixtures that are seldom available in the literature. Experimental data for 17 salts in 36 alcohol–water–salt systems, covering a temperature range from 298 to 375 K, and salt concentrations up to about 8 m, were correlated using the new approach. In all, 69 data sets and 1045 data points were correlated satisfactorily. The method was also used to predict VLE in four ternary alcohol–alcohol–salt systems and one quaternary alcohol–alcohol–water–salt system with satisfactory results.     

Infrared and Raman spectroscopies of monolayers at the air–water interface

Infrared and Raman spectroscopies are now currently used to obtain molecular information (orientation, conformation, organization) on monolayers at the air–water interface. In the past year, several original studies were performed on peptides and proteins and their interaction with phospholipidic monolayers.     

Refractivity and polarizability of mixtures of L-histidine–metformin hydrochloride–water at 30°C

The molar refractivity and polarizability of mixtures of L-histidine (0.01–0.11 mol L^–1)–metformin hydrochloride (0.03, 0.05, 0.07 mol L^–1)–water were calculated from density and refractive index data at 30°C. Enhancement in the polarizability has been observed with increase in L-histidine concentration as well as metformin hydrochloride content in the solution. The molar refractivity and polarizability of solutions increased appreciably after 0.09 mol L^–1 L-histidine in each aqueous solution.     

Determination of carbamates and organophosphorus pesticides by SDME–GC in natural water

Water contamination due to the wide variety of pesticides used in agriculture practices is a global environmental pollution problem. Analytical methods with low quantification limits are necessary. The application of a new extraction technique, solvent drop microextraction (SDME), followed by gas chromatography with a nitrogen-phosphorus detector, was assessed for determining carbamates and organophosphorus pesticides in natural water. Experimental parameters which control the performance of SDME such as selection of microextraction solvent, optimization of organic drop volume, effects of sample stirring, salt addition, and, finally, sorption time profiles were studied. Once SDME was optimized, analytical parameters such as linearity (r ²>0.99), precision (<13%), and detection limits (0.2 to 5 μg/L), plus matrix effects were evaluated (no matrix effects were found). SDME is a dynamic technique able to extract pesticides from water in 14 min; the use of organic solvents and water samples for SDME is negligible compared to other extraction techniques.     

Micellization and surface activity of Triton X-100 in water–orthophosphoric medium

The adsorption isotherms of Triton X-100 for air/water–orthophosphoric acid interfaces were determined by the stripping method. The surface chemical parameters, Γ_max, F and ΔG°_A, and the aggregation ones, CMC and the ΔG_M, are determined in different H₂O/H₃PO₄ mixtures. For concentrations higher than 4 M, the values of the CMC, ΔG_M, Γ_max and ΔG°_A increase with increasing acid concentrations due to the occurring changes in the medium structure. ©2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASsurface tension / non-ionic surfactant / micellization / orthophosphoric acid     

Enthalpic interaction coefficients of NaI–alkanediol pairs in methanol and in water

The dissolution enthalpies of NaI in the mixtures of methanol with 1,2-alkanediols (1,2-propanediol, 1,2-butanediol, 1,2-pentanediol) and with ??,??-alkanediols (1,3-propanediol, 1,4-butanediol, 1,5-pentanediol), as well NaI in the mixtures of water with 1,3-propanediol and 1,2-pentanediol, were determined at 298.15?K. The energetic effect of interactions between the investigated alkanediols and NaI in methanol and in water was calculated using the enthalpic pair interaction coefficients (h _xy ) model. These results along with the other data concerning the NaI?Cnon-electrolyte pairs taken from our earlier reports and from the literature were analyzed with respect to the effect of the non-electrolyte properties on the variations of the h _xy values. The group contributions illustrating the interactions of NaI with selected functional groups in non-electrolyte (alkanediol and alkanol) molecules, namely: CH₂ and OH groups were calculated and discussed.     

Laser Raman spectroscopic study of water in gelatin–surfactant solutions and gels

A Raman spectroscopic study was carried out on water in gelatin at 4% w/v in gel (25 °C) and sol (40–60 °C) states at various concentrations (0.5, 1, 5, 10 and 15 mM) of anionic surfactant, sodium dodecyl sulfate (SDS). The in-phase collective stretching mode vibration of hydrogen-bonded -OH oscillators, centered around 3250 cm⁻¹ in a tetrahedral network of water molecules, was observed to be significantly affected by temperature and the presence of SDS. According to our observation this may be due to the thinning of the hydration water around the gelatin molecules due to strong thermal agitation. The peak center of the collective bands of water decreased linearly with SDS concentration in the gel state which implied that with the increase in concentration of SDS, the -OH oscillators gradually lost their attachment to gelatin chains and were replaced by SDS molecules. Ultimately this resulted in a thinning of the hydration layer around the gelatin and the oscillation frequency of -OH oscillators moved towards 3250 cm⁻¹ at 1 mM SDS concentration resulting in increased coupling of -OH oscillators to form the tetrahedral network at the critical micelle concentration (cmc) of SDS. The variation in the peak amplitudes and the systematic reversal of their trend about the cmc axis was surprising. At 40 °C the amplitude of the peak at 3250 cm⁻¹ increased drastically due to a possible coil expansion by about 7–8% which accommodated more interstitial water into the pseudonetwork leading to an increase in the number of nearest neighbors and for about 6% increase in the C value. However, at the cmc the peak amplitude was observed to be independent of temperature. Continuous shifting of the peak center and full width at half-maxima towards lower values was observed with increasing SDS concentrations in the gel state. Received: 28 September 1998 Accepted in revised form: 8 March 1999