Kinetics and product distribution of p-nitrophenyl phosphate dianion solvolysis in ternary DMSO/alcohol/water mixtures are compatible with metaphosphate formation

The rate of solvolysis of p-nitrophenyl phosphate (PNPP) dianion in DMSO/water strongly decreases by increasing water concentration. Addition of linear alcohols (methanol, propanol, butanol, pentanol, and hexanol) at constant DMSO/water molar ratio produced an even sharper rate decrease. Alkyl phosphate formation, resulting from PNPP solvolysis in ternary DMSO/water/alcohol mixtures, increased with alcohol concentration and was essentially temperature independent. Methanol and hexanol were the poorest nucleophiles under all conditions. Activation energies and enthalpies for solvolysis in ternary mixtures were similar and entropies varied with alcohol concentration. Taken together these results can be best interpreted in terms of a dissociative mechanism with the intervention of metaphosphate. Copyright (C) 2011 John Wiley & Sons, Ltd.

A dissolution and reaction modeling for hydrolysis of TEOS in heterogeneous TEOS-water-HCl mixtures under ultrasound stimulation

A simplified dissolution and reaction modeling was employed to study the hydrolysis of heterogeneous tetraethoxysilane (TEOS)-water-HCl mixtures under ultrasound stimulation. The nominal pH was changed from 0.8 to 2.0. The acid specific hydrolysis rate constant was determined as k = 6.1 mol(-1) 1 min(-1) [H+](-1) at 39 degreesC, in good agreement with the literature. Along the heterogeneous step of the reaction, the ultrasound maintains an additional quantity of water under a virtual state of dissolution besides the water dissolved due to the homogenizing effect of the alcohol produced in the reaction. The forced virtually dissolved water is probably represented by water at the TEOS-water interface during the heterogeneous step of the reaction. The mean radius of the heterogeneity represented by water dispersed in TEOS phase, while hydrolysis has not started yet, was evaluated as about 290 A. The HCl concentration accordingly increases the hydrolysis rate constant but its fundamental role on the immiscibility gap of the TEOS-water-ethanol system has not been unequivocally established. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Unusual 1,6-diphenyl-1,3,5-hexatriene (DPH) spectrophotometric behavior in water/ethanol and water/DMSO mixtures

The absorption spectra of DPH at fixed concentration do not change with water content in organic solvents. It exhibits monomer bands, such as those obtained in ethanol. The absorption did not change for solutions up to 54 and 46% of water in ethanol and DMSO, respectively, for [DPH] = 5.0 × 10-6 mol L-1 at 30 °C. However, at the same experimental conditions, a gradual sharp decay of the DPH fluorescence is observed. It is proposed that water molecules below these water concentration limits act as quenchers of the excited states of DPH. Stern-Volmer quenching constants by intensities measurements are 7.4 × 10-2 (water/ethanol) and 2.6 × 10-2 L mol-1 (water/DMSO). DPH lifetime measurements in the absence and presence of water resulted in 7.1 × 10-2 L mol-1 in water/ethanol, which pointed out that the process is a dynamic quenching by water molecules. For experiments using DPH as probe, this process can affect data, leading to misunderstanding interpretation.

Effect of acute treatment with a water-alcohol extract of Erythrina mulungu on anxiety-related responses in rats

We investigated the effect of acute oral treatment with a water-alcohol extract of the inflorescence of Erythrina mulungu (EM, Leguminosae-Papilionaceae) (100, 200 and 400 mg/kg) on rats submitted to different anxiety models: the elevated T-maze (for inhibitory avoidance and escape measurements), the light/dark transition, and the cat odor test. These models were selected for their presumed capacity to demonstrate specific subtypes of anxiety disorders as recognized in clinical practice. Treatment with 200 mg/kg EM impaired avoidance latencies (avoidance 1 - 200 mg/kg EM: 18 ± 7 s, control group: 40 ± 9 s; avoidance 2 - 200 mg/kg EM: 15 ± 4 s, control group: 110.33 ± 38 s) in a way similar to the reference drug diazepam (avoidance 1: 3 ± 0.79 s; avoidance 2: 3 ± 0.76 s), without altering escape. Additionally, the same treatments increased the number of transitions (200 mg/kg EM: 6.33 ± 0.90, diazepam: 10 ± 1.54, control group: 2.78 ± 0.60) between the two compartments and the time spent in the lighted compartment in the light/dark transition model (200 mg/kg EM: 39 ± 7 s; diazepam: 61 ± 9 s; control group: 14 ± 4 s). The dose of 400 mg/kg EM also increased this last measurement (38 ± 8 s). These results were not due to motor alterations since no significant effects were detected in the number of crossings or rearings in the arena. Furthermore, neither EM nor diazepam altered the behavioral responses of rats to a cloth impregnated with cat odor. These observations suggest that EM exerts anxiolytic-like effects on a specific subset of defensive behaviors, particularly those that have been shown to be sensitive to low doses of benzodiazepines.

Monte Carlo investigations of intermolecular interactions in water-amide mixtures

Monte Carlo simulations of water-amides (amide=fonnamide-FOR, methylfonnamide-NMF and dimethylformamide-DMF) solutions have been carried out in the NpT ensemble at 308 K and 1 atm. The structure and excess enthalpy of the mixtures as a function of the composition have been investigated. The TIP4P model was used for simulating water and six-site models previously optimized in this laboratory were used for simulating the liquid amides. The intermolecular interaction energy was calculated using the classical 6-12 Lennard-Jones potential plus a Coulomb term. The interaction energy between solute and solvent has been partitioned what leads to a better understanding of the behavior of the enthalpy of mixture obtained for the three solutions experimentally. Radial distribution functions for the water-amides correlations permit to explore the intermolecular interactions between the molecules. The results show that three, two and one hydrogen bonds between the water and the amide molecules are formed in the FOR, NMF and DMF-water solutions, respectively. These H-bonds are, respectively, stronger for DMF-water, NMF-water and FOR-water. In the NMF-water solution, the interaction between the methyl group of the NMF and the oxygen of the water plays a role in the stabilization of the aqueous solution quite similar to that of an H-bond in the FOR-water solution. (c) 2005 Elsevier B.V. All rights reserved.

Monte Carlo simulation of water-tetrahydrofuran mixtures

Monte Carlo simulations of water-tetrahydrofuran (THF) mixtures were performed in the isothermal-isobaric ensemble (NPT) at T = 298 K and p = 1 atm. The interaction energy was calculated using the TIP4P model for water and a five-site united atom representation for the THF molecule. The potential energy surfaces for water-THF interactions were obtained by using combining rules and the original potential functions used for pure liquids. Theoretical values obtained for the average interaction energy as a function of concentration are in good agreement with available experimental data. Results from the partitioning of the total interaction energy into water-water, water-THF and THF-THF contributions are presented. These results are useful to distinguish between the quantitative contributions of these molecular interactions to the energetic behavior of the water-THF mixing process. The radial distribution functions for HW-OTHF and OW-OTHF site-site interactions show the salient features of hydrogen-bonded liquids. Comparison of the average number of water-water complexes interacting through hydrogen bonding in water-THF and water-methanol mixtures shows an enhancement of the water-water coordination number in a THF rich environment. © 1995.

Solvation in aqueous binary mixtures: consequences of the hydrophobic character of the ionic liquids and the solvatochromic probes

Information on the solvation in mixtures of water, W, and the ionic liquids, ILs, 1-allyl-3-R-imidazolium chlorides; R = methyl, 1-butyl, and 1-hexyl, has been obtained from the responses of the following solvatochromic probes: 2,6-dibromo-4-[(E)-2-(1-R-pyridinium-4-yl)ethenyl] phenolate, R = methyl, MePMBr2; 1-octyl, OcPMBr(2), and the corresponding quinolinium derivative, MeQMBr(2). A model developed for solvation in binary mixtures of W and molecular solvents has been extended to the present mixtures. Our objective is to assess the relevance to solvation of hydrogen-bonding and the hydrophobic character of the IL and the solvatochromic probe. Plots of the medium empirical polarity, E-T(probe) versus its composition revealed non-ideal behavior, attributed to preferential solvation by the IL and, more efficiently, by the IL-W hydrogen-bonded complex. The deviation from linearity increases as a function of increasing number of carbon atoms in the alkyl group of the IL, and is larger than that observed for solvation by W plus molecular solvents (1-propanol and 2-(1-butoxy)ethanol) that are more hydrophobic than the ILs investigated. This enhanced deviation is attributed to the more organized structure of the ILs proper, which persists in their aqueous solutions. MeQMBr(2) is more susceptible to solvent lipophilicity than OcPMBr(2), although the former probe is less lipophilic. This enhanced susceptibility agrees with the important effect of annelation on the contributions of the quinonoid and zwitterionic limiting structures to the ground and excited states of the probe, hence on its response to both medium composition and lipophilicity of the IL.

Defects in ZnO nanoparticles laser-ablated in water-ethanol mixtures at different pressures

The effect of liquid medium and its pressure on the photoluminescence of ZnO nanoparticles prepared via laser ablation of Zn targets in various water-ethanol mixtures is studied. As the ethanol content increases, the photoluminescence of the product changes, while metallic zinc is observed to emerge in nanomaterials prepared in ethanol-rich environments. The applied pressure had a less profound effect, mainly affecting materials produced in water or water-ethanol, and much less those generated in pressurized ethanol. Tuning the reactivity of the liquid and pressurizing it during laser ablation is demonstrated to be promising for tailoring the emission properties of the product.

Swelling properties of alkali-metal doped polymeric anion-exchange membranes in alcohol media for application in fuel cells

Swelling properties of four commercial anion-exchange membranes with different structure have been analyzed in several hydro-organic media. With this target, the liquid uptake and the surface expansion of the membranes in contact with different pure liquids, water and alcohols (methanol, ethanol and 1-propanol), and with water alcohol mixtures with different concentrations have been experimentally determined in presence and in absence of an alkaline medium (LiOH, NaOH and KOH of different concentrations). The alkali-metal doping effect on the membrane water uptake has also been investigated, analyzing the influence of the hydroxide concentration and the presence of an alcohol in the doping solution. The results show that the membrane structure plays an essential role in the influence that alcohol nature and alkaline media has on the selective properties of the membrane. The heterogeneous membranes, with lower density, show higher liquid uptakes and dimensional changes than the homogeneous membranes, regardless of the doping conditions. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Influence of stationary phase and eluent properties on chromatographic separation of carbohydrates

In this thesis, the sorption and elastic properties of the cation-exchange resins were studied to explain the liquid chromatographic separation of carbohydrates. Na+, Ca2+ and La3+ form strong poly(styrene-co-divinylbenzene) (SCE) as well as Na+ and Ca2+ form weak acrylic (WCE) cation-exchange resins at different cross-link densities were treated within this work. The focus was on the effects of water-alcohol mixtures, mostly aqueous ethanol, and that of the carbohydrates. The carbohydrates examined were rhamnose, xylose, glucose, fructose, arabinose, sucrose, xylitol and sorbitol. In addition to linear chromatographic conditions, non-linear conditions more typical for industrial applications were studied. Both experimental and modeling aspectswere covered. The aqueous alcohol sorption on the cation-exchangers were experimentally determined and theoretically calculated. The sorption model includes elastic parameters, which were obtained from sorption data combined with elasticity measurements. As hydrophilic materials cation-exchangers are water selective and shrink when an organic solvent is added. At a certain deswelling degree the elastic resins go through glass transition and become as glass-like material. Theincreasing cross-link level and the valence of the counterion decrease the sorption of solvent components in the water-rich solutions. The cross-linkage or thecounterions have less effect on the water selectivity than the resin type or the used alcohol. The amount of water sorbed is higher in the WCE resin and, moreover, the WCE resin is more water selective than the corresponding SCE resin. Theincreased aliphatic part of lower alcohols tend to increase the water selectivity, i.e. the resins are more water selective in 2-propanol than in ethanol solutions. Both the sorption behavior of carbohydrates and the sorption differences between carbohydrates are considerably affected by the eluent composition and theresin characteristics. The carbohydrate sorption was experimentally examined and modeled. In all cases, sorption and moreover the separation of carbohydrates are dominated by three phenomena: partition, ligand exchange and size exclusion. The sorption of hydrophilic carbohydrates increases when alcohol is added into the eluent or when carbohydrate is able to form coordination complexes with the counterions, especially with multivalent counterions. Decreasing polarity of the eluent enhances the complex stability. Size exclusion effect is more prominent when the resin becomes tighter or carbohydrate size increases. On the other hand,the elution volumes between different sized carbohydrates decreases with the decreasing polarity of the eluent. The chromatographic separation of carbohydrateswas modeled, using rhamnose and xylose as target molecules. The thermodynamic sorption model was successfully implemented in the rate-based column model. The experimental chromatographic data were fitted by using only one adjustable parameter. In addition to the fitted data also simulated data were generated and utilized in explaining the effect of the eluent composition and of the resin characteristics on the carbohydrate separation.

Atomistic simulations of cosolvent/water mixtures

In this thesis, atomistic simulations are performed to investigate hydrophobic solvation and hydrophobic interactions in cosolvent/water binary mixtures. Many cosolvent/water binary mixtures exhibit non-ideal behavior caused by aggregation at the molecular scale level although they are stable and homogenous at the macroscopic scale. Force-field based atomistic simulations provide routes to relate atomistic-scale structure and interactions to thermodynamic solution properties. The predicted solution properties are however sensitive to the parameters used to describe the molecular interactions. In this thesis, a force field for tertiary butanol (TBA) and water mixtures is parameterized by making use of the Kirkwood-Buff theory of solution. The new force field is capable of describing the alcohol-alcohol, water-water and alcohol-water clustering in the solution as well as the solution components’ chemical potential derivatives in agreement with experimental data. With the new force field, the preferential solvation and the solvation thermodynamics of a hydrophobic solute in TBA/water mixtures have been studied. First, methane solvation at various TBA/water concentrations is discussed in terms of solvation free energy-, enthalpy- and entropy- changes, which have been compared to experimental data. We observed that the methane solvation free energy varies smoothly with the alcohol/water composition while the solvation enthalpies and entropies vary nonmonotonically. The latter occurs due to structural solvent reorganization contributions which are not present in the free energy change due to exact enthalpy-entropy compensation. It is therefore concluded that the enthalpy and entropy of solvation provide more detailed information on the reorganization of solvent molecules around the inserted solute. Hydrophobic interactions in binary urea/water mixtures are next discussed. This system is particularly relevant in biology (protein folding/unfolding), however, changes in the hydrophobic interaction induced by urea molecules are not well understood. In this thesis, this interaction has been studied by calculating the free energy (potential of mean force), enthalpy and entropy changes as a function of the solute-solute distance in water and in aqueous urea (6.9 M) solution. In chapter 5, the potential of mean force in both solution systems is analyzed in terms of its enthalpic and entropic contributions. In particular, contributions of solvent reorganization in the enthalpy and entropy changes are studied separately to better understand what are the changes in interactions in the system that contribute to the free energy of association of the nonpolar solutes. We observe that in aqueous urea the association between nonpolar solutes remains thermodynamically favorable (i.e., as it is the case in pure water). This observation contrasts a long-standing belief that clusters of nonpolar molecules dissolve completely in the presence of urea molecules. The consequences of our observations for the stability of proteins in concentrated urea solutions are discussed in the chapter 6 of the thesis.

Thermodynamic study of the solubility of sodium naproxen in some ethanol + water mixtures

By using the van't Hoff and Gibbs equations the apparent thermodynamic functions Gibbs energy, enthalpy, and entropy of solution for sodium naproxen in ethanol + water cosolvent mixtures, were evaluated from solubility data determined at temperatures from (278.15 to 308.15) K. The drug solubility was greatest in neat water and lowest in neat ethanol at all the temperatures studied. By means of non-linear enthalpy-entropy compensation analysis, it follows that the dissolution process of this drug in ethanol-rich mixtures is entropy-driven, whereas, in water-rich mixtures the process is enthalpy-driven.

Pervaporation dehydration of isopropyl alcohol with NaY zeolite incorvorated hybrid membranes

With a solution technique, NaY zeolite incorporated, tetraethylorthosilicate-crosslinked poly(vinyl alcohol) membranes were prepared. The resulting membranes were tested for their ability to separate isopropyl alcohol/water mixtures by pervaporation in the temperature range of 30-50 degrees C. The effects of the zeolite content and feed composition on the pervaporation performance of the membranes were investigated. The experimental results demonstrated that both flux and selectivity increased simultaneously with increasing zeolite content in the membranes. This was explained on the basis of the enhancement of hydrophilicity, selective adsorption, and establishment of a molecular sieving action attributed to the creation of pores in the membrane matrix. The membrane containing 15 mass % zeolite exhibited the highest separation selectivity of 3991 with a flux of 5.39 X 10(-2) kg/m(2) h with 10 mass % water in the feed at 30 degrees C. The total flux and flux of water were close to each other for almost all the studied membranes, and this suggested that the membranes could be used effectively to break the azeotropic point of water/isopropyl alcohol mixtures to remove a small amount of water from isopropyl alcohol. From the temperature-dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water were significantly lower than those for isopropyl alcohol, and this suggested that the developed membranes had a higher separation efficiency for water/isopropyl alcohol systems. The activation energy values for total permeation and water permeation were found to be almost the same for all the membranes, and this signified that coupled transport was minimal because of the highly selective nature of the membranes. Positive heat of sorption values were observed in all the membranes, and this suggested that Henry's mode of sorption was predominant. (c) 2008 Wiley Periodicals, lnc.

Comparative exergy analysis of direct alcohol fuel cells using fuel mixtures

Within the last years there has been increasing interest in direct liquid fuel cells as power sources for portable devices and, in the future, power plants for electric vehicles and other transport media as ships will join those applications. Methanol is considerably more convenient and easy to use than gaseous hydrogen and a considerable work is devoted to the development of direct methanol fuel cells. But ethanol has much lower toxicity and from an ecological viewpoint ethanol is exceptional among all other types of fuel as is the only chemical fuel in renewable supply. The aim of this study is to investigate the possibility of using direct alcohol fuel cells fed with alcohol mixtures. For this purpose, a comparative exergy analysis of a direct alcohol fuel cell fed with alcohol mixtures against the same fuel cell fed with single alcohols is performed. The exergetic efficiency and the exergy loss and destruction are calculated and compared in each case. When alcohol mixtures are fed to the fuel cell, the contribution of each fuel to the fuel cell performance is weighted attending to their relative proportion in the aqueous solution. The optimum alcohol composition for methanol/ethanol mixtures has been determined.