Aqueous Mixtures Of Methanol Research Articles

Synthesis, Characterization and Antifungal Activity of Manganese (II) Complex with Schiff Base Derived from Acetylacetone and Leucine

This study was aimed at synthesizing, characterizing and evaluating the antifungal activity of the Schiff base and Mn (II) complex. The reaction of the mixture of ethanol solution of acetylacetone and leucine yielded a Schiff base. The interaction between the Schiff base in hot aqueous methanol mixture and manganese (II) chloride in ethanol gave the manganese (II) Schiff base complex. The complex was characterized by decomposition/melting point temperatures, solubility test, IR spectrophotometry, colour determination, dissociation constant of Schiff base and antifungal activity. The Schiff base obtained has yellow colour, with a melting point of 250°C and percentage yield of 54.67% while the manganese (II) complex obtained had a pink colour with decomposition temperature of 167°C and percentage yield of 76.40%. The Schiff base and the complex was soluble in some solvents but slightly soluble in others. The Infrared spectra of the Schiff base showed a band at a range of 1600cm -1 - 1622cm -1 attributed to v (C=N) stretching frequencies establishing it being a Schiff base. Similar bands were observed in the spectra of Manganese (II) Schiff base complex but in lower frequencies indicating that the Schiff base has coordinated to the Mn ion. The antifungal activity of manganese (II) complex showed significant activity on the fungal isolates Candida albican and Sacchromyces cerevisiae . The study concludes that Schiff base synthesized was a weak acid and the Schiff base was not an active drug against the fungal pathogens used but Mn (II) complex was active against the pathogens used.

Determination of Abraham model solute descriptors and preferential solvation from measured solubilities for 4-nitropyrazole dissolved in binary aqueous-organic solvent mixtures

ABSTRACTAbraham model solute descriptors are determined for 4-nitropyrazole based on published solubility data for 4-nitropyrazole dissolved in binary aqueous-methanol and aqueous-ethanol solvent mixtures at 298.15 K. The calculated solute descriptors enable the solubility of 4-nitropyrazole to be estimated in more than 80 different organic solvents. Also calculated from the published solubility data are the preferential solvation parameters, obtained from the inverse Kirkwood–Buff integrals, for describing the solvent distribution around the dissolved 4-nitropyrazole solute molecule.

The microscopic structure of cold aqueous methanol mixtures

The evolution of the micro-segregated structure of aqueous methanol mixtures, in the temperature range 300 K-120 K, is studied with computer simulations, from the static structural point of view. The structural heterogeneity of water is reinforced at lower temperatures, as witnessed by a pre-peak in the oxygen-oxygen structure factor. Water tends to form predominantly chain-like clusters at lower temperatures and smaller concentrations. Methanol domains have essentially the same chain-like cluster structure as the pure liquid at high concentrations and becomes monomeric at smaller ones. Concentration fluctuations decrease with temperature, leading to quasi-ideal Kirkwood-Buff integrals, despite the enhanced molecular interactions, which we interpret as the signature of non-interacting segregated water and methanol clusters. This study throws a new light on the nature of the micro-heterogeneous structure of this mixture: the domain segregation is essentially based on the appearance of linear water clusters, unlike other alcohol aqueous mixtures, such as with propanol or butanol, where the water domains are more bulky.

Some thermophysical properties of methanol and aqueous methanol mixtures at sub- and supercritical conditions

Expressions for the composition dependence of the critical constants of mixtures or water and methanol are presented as are expressions of the vapor pressure, the molar enthalpy of vaporization, and the molar volume of methanol along its saturation curve. The internal pressure of saturated methanol is compared with it cohesive energy density, reflecting the diminishing strength of its intermolecular hydrogen bonding as the temperature is increased. Thermophysical properties (molar volumes, isobaric expansibilities, isothermal compressibilities, and internal pressures) of mixtures of methanol and water at subcritical temperatures at saturation and at the fixed pressures of 7 and 20MPa have been calculated and are presented in a table. The self- and mutual association of water and methanol in their mixtures at sub-critical temperatures is examined.

Temperature of maximum density and excess thermodynamics of aqueous mixtures of methanol.

In this work, we present a study of representative excess thermodynamic properties of aqueous mixtures of methanol over the complete concentration range, based on extensive computer simulation calculations. In addition to test various existing united atom model potentials, we have developed a new force-field which accurately reproduces the excess thermodynamics of this system. Moreover, we have paid particular attention to the behavior of the temperature of maximum density (TMD) in dilute methanol mixtures. The presence of a temperature of maximum density is one of the essential anomalies exhibited by water. This anomalous behavior is modified in a non-monotonous fashion by the presence of fully miscible solutes that partly disrupt the hydrogen bond network of water, such as methanol (and other short chain alcohols). In order to obtain a better insight into the phenomenology of the changes in the TMD of water induced by small amounts of methanol, we have performed a new series of experimental measurements and computer simulations using various force fields. We observe that none of the force-fields tested capture the non-monotonous concentration dependence of the TMD for highly diluted methanol solutions.

Temperature dependent solubility of vanillic acid in aqueous methanol mixtures: Measurements and thermodynamic modeling

The solid-liquid equilibrium data of vanillic acid (VA) in pure ethanol and in various (methanol+water) mixed solvents were measured over the temperature range from (293.15 to 318.15) K at atmosphere pressure using a thermostatted reactor and UV/vis spectrophotometer analysis. The effects of the composition of binary systems and temperature on the solubility were discussed. The obtained solubility data were correlated with the Van't Hoff model, the modified Apelblat equation and the λh equation. In general, the regressed results with the three models were all within the acceptable limit for the solubility of vanillic acid in the (methanol+water) mixed solvents. Furthermore, thermodynamic properties of dissolution of the vanillic acid in the selected systems were estimated. Consequently, the experimental data and model parameters would be useful for optimizing the process of purification of vanillic acid in industry.

Relating side chain organization of PNIPAm with its conformation in aqueous methanol.

Combining nuclear magnetic resonance (NMR), dynamic light scattering (DLS), and μs long all-atom simulations with two million particles, we establish a delicate correlation between increased side chain organization of PNIPAm and its collapse in aqueous methanol mixtures. We find that the preferential binding of methanol with PNIPAm side chains, bridging distal monomers along the polymer backbone, results in increased organization. Furthermore, methanol-PNIPAm preferential binding is dominated by hydrogen bonding. Our findings reveal that the collapse of PNIPAm is dominated by enthalpic interactions and that the standard poor solvent (entropic) effects play no major role.

Solvatochromism and Preferential Solvation of Deferiprone in Some Water–Organic Mixed Solvents

The molar transition energy (E T) values for deferiprone as a solvatochromic probe were measured in different aqueous binary mixtures of methanol, ethanol, 2-propanol, and 1-propanol (as HBD solvents) and acetonitrile and dioxane (as HBA solvents). Plots of E T as a function of mole fraction of the organic solvents were obtained and the data were analyzed to investigate preferential solvation of the drug in terms of both solute–solvent and solvent–solvent interactions. Also, the local mole fraction of each solvent composition was calculated in the cybotactic region of the probe. The molar transition energy of deferiprone in different binary mixtures was also analyzed in terms of Kamlet, Abboud, and Taft parameters. Dual and multiparameter correlation showed better results in HBD and HBA solvents, respectively.

Ion association and solvation behavior of copper sulfate in binary aqueous–methanol mixtures at different temperatures

The specific conductance (κ) of copper sulfate in binary mixtures (methanol–water) with the alcohol mass fractions of 0%, 20% and 40% at different temperatures of (298.15, 303.15, 308.15 and 313.15) K was measured experimentally. The conductivity data have been analyzed using the Fuoss–Shedlovsky conductivity equation. The molar conductance (ΛM), the limiting molar conductance (Λ0), the association constants (KA), the Walden product (Λ0η0), and the standard thermodynamic parameters of association (ΔG°A, ΔH°A and ΔS°A) were calculated and discussed. The results show that, the molar conductance and the limiting molar conductance values were decreased as the relative permittivity of the solvent decreased while, the association constant increased. Also the results show that the values of the molar conductance, the limiting molar conductance and the association constant were increased as the temperature increased indicating that the association process is an endothermic one.

Reaction kinetics and solubility in water-organic binary solutions are governed by similar solvation equilibria

The solvation effects observed in water-organic solutions were studied by combining data for reaction kinetics and dissolution equilibria by means of a linear free-energy (similarity) analysis. Kinetic data for the pH-independent hydrolysis of (4-methoxyphenyl)-2,2-dichloroacetate measured in this work and solubility data for naphthalene, and other substrates of low polarity, in aqueous binary mixtures of methanol, ethanol, acetonitrile, dimethyl sulfoxide (DMSO), and 1,4-dioxane were used. Linear similarity relationships were discovered for these data over the full range of solvent compositions studied. To gain insight into the similarities observed between these different phenomena, molecular dynamics simulations were carried out for naphthalene and an ester in water–acetonitrile solutions. The results revealed considerable preferential solvation of these substrates by the co-solvent. Linear relationships between the experimental data and the mole fractions of acetonitrile in the solvation shells of substrates were found. Surprisingly, a linear relationship was found between the mole fractions of acetonitrile in the solvation shells of the ester and naphthalene. This linearity indicated that a similar solvation mechanism governs even such different phenomena as dissolution and reaction kinetics. The relationships between the experimental data and the results of the molecular dynamics calculations found in this work explained the solvent effect observed in water-organic solutions on the molecular level. Copyright © 2015 John Wiley & Sons, Ltd.

On the nature of the molecular ordering of water in aqueous DMSO mixtures.

Computer simulation studies of aqueous dimethyl sulfoxyde (DMSO) mixtures show micro-heterogeneous structures, just like aqueous alcohol mixtures. However, there is a marked difference in the aggregate structure of water between the two types of systems. While water molecules form multiconnected globular clusters in alcohols, we report herein that the typical water aggregates in aqueous DMSO mixtures are linear, favouring a 2 hydrogen bond structure per water molecule, and for all DMSO mole fractions ranging from 0.1 to 0.9. This linear-aggregate structure produces a particular signature in the water site-site structure factors, in the form of a pre-peak at k ≈ 0.2-0.8 Å(-1), depending on DMSO concentration. This pre-peak is either absent in other aqueous mixtures, such as aqueous methanol mixtures, or very difficult to see through computer simulations, such as in aqueous-t-butanol mixtures. This difference in the topology of the aggregates explains why the Kirkwood-Buff integrals of aqueous-DMSO mixture look nearly ideal, in contrast with those of aqueous alcohol mixtures, suggesting a connection between the shape of the water aggregates, its fluctuations, and the concentration fluctuations. In order to further study this discrepancy between aqueous DMSO and aqueous alcohol mixture, two models of pseudo-DMSO are introduced, where the size of the sulfur atom is increased by a factor 1.6 and 1.7, respectively, hence increasing the hydrophobicity of the molecule. The study shows that these mixtures become closer to the emulsion type seen in aqueous alcohol mixtures, with more globular clustering of the water molecules, long range domain oscillations in the water-water correlations and increased water-water Kirkwood-Buff integrals. It demonstrates that the local ordering of the water molecules is influenced by the nature of the solute molecules, with very different consequences for structural properties and related thermodynamic quantities. This study illustrates the unique plasticity of water in presence of different types of solutes.

Tautomeric and Microscopic Protonation Constants of Alanine and Valine in Different Aqueous Solutions of Methanol and Tetrahydrofuran

The solute–solvent interactions of alanine and valine were investigated potentiometrically in different aqueous solvent mixtures (0–50 % v/v) of methanol (an amphiprotic solvent) and tetrahydrofuran (a dipolar aprotic solvent). The macroscopic and microscopic protonation constants as well as the tautomeric constants were determined and correlated with either a macroscopic parameter such as dielectric constant or a microscopic parameter such as a Kamlet, Abboud, and Taft (KAT) solvatochromic parameter. The obtained results show that the protonation constants of the amino group (in log10 scale) are linearly related to the reciprocal of the dielectric constants of the water–organic solvent mixtures but this is not true for the protonation of the carboxylic acid group of the amino acids in both systems. Finally, the results are discussed in terms of the effect of solvent on the protonation and tautomeric constants.

Effect of solute–solvent interactions on DPPH radical scavenging efficiency of some flavonoid antioxidants in various binary water–methanol mixtures

Scavenging ability of three kinds of natural flavonoid antioxidants including chrysin, naringenin, and quercetin against the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical was evaluated by the UV-vis spectrophotometric technique in different aqueous mixtures of methanol (50%–90% v/v) at physiological pH. The studied flavonoids showed their activity to be comparable with ascorbic acid (vitamin C), which is used as a standard reference material in most testing methods. Our findings indicated that an increase in the organic solvent percentage (v/v) has different effects on the radical scavenging efficiency of flavonoids presumably due to solute–solvent interactions. These variations were analyzed in light of various simple and multiple regression equations using the normalized polarity parameter ([Formula: see text]) and Kamlet, Abboud, and Taft solvatochromic parameters. Moreover, The IC50 values of the samples were then obtained by the Yasuda–Shedlovsky extrapolation procedure in pure water.

Gibbs excess and the calculation of the absolute surface composition of liquid binary mixtures.

Adsorption at the liquid-vapor interphase of a liquid binary mixture is traditionally quantified by means of the Gibbs solute excess. Despite several theoretical reviews on the meaning of Gibbs excess defined by the Gibbs dividing surface, it is still misinterpreted as the excess concentration under Guggenheim's finite-depth surface layer approach. In this work, both concepts are clarified in a practical way, aided by a graphical representation without loss of generality. The understanding of both quantities led to the development of a thermodynamic procedure for the calculation of the actual number of solute and solvent molecules at a finite-depth surface layer (not a monolayer), what is called the absolute surface composition. From surface tension and density data, the absolute surface composition of the binary aqueous mixtures of methanol, ethanol, 1-propanol, and 1-butanol was calculated. Results show thermodynamic consistency and agree with experimental reports and with an empirical mixing rule. The increasing alcohol surface concentration throughout the entire concentration range casts doubt on the formation of an alcohol monolayer, as was suggested by other authors. Furthermore, the use of Guggenheim's monolayer model does not reproduce the experimental data, nor does it show thermodynamic consistency.

Comparison of the free and bound phenolic profiles and cellular antioxidant activities of litchi pulp extracts from different solvents

BackgroundThe phenolic contents and antioxidant activities of fruits could be underestimated if the bound phenolic compounds are not considered. In the present study, the extraction efficiencies of various solvents were investigated in terms of the total content of the free and bound phenolic compounds, as well as the phenolic profiles and antioxidant activities of the extracts.MethodsFive different solvent mixtures were used to extract the free phenolic compounds from litchi pulp. Alkaline and acidic hydrolysis methods were compared for the hydrolysis of bound phenolic compounds from litchi pulp residue. The phenolic compositions of the free and bound fractions from the litchi pulp were identified using HPLC-DAD. The antioxidant activities of the litchi pulp extracts were determined by oxygen radical absorbance capacity (ORAC) and cellular antioxidant activity (CAA) assays.ResultsOf the solvents tested, aqueous acetone extracted the largest amount of total free phenolic compounds (210.7 mg GAE/100 g FW) from litchi pulp, followed sequentially by aqueous mixtures of methanol, ethanol and ethyl acetate, and water itself. The acid hydrolysis method released twice as many bound phenolic compounds as the alkaline hydrolysis method. Nine phenolic compounds were detected in the aqueous acetone extract. In contrast, not all of these compounds were found in the other four extracts. The classification and content of the bound phenolic compounds released by the acid hydrolysis method were higher than those achieved by the alkaline hydrolysis. The aqueous acetone extract showing the highest ORAC value (3406.9 μmol TE/100 g FW) for the free phenolic extracts. For the CAA method, however, the aqueous acetone and methanol extracts (56.7 and 55.1 μmol QE/100 g FW) showed the highest levels of activity of the five extracts tested. The ORAC and CAA values of the bound phenolic compounds obtained by acid hydrolysis were 2.6- and 1.9-fold higher than those obtained using the alkaline hydrolysis method.ConclusionsThe free and bound phenolic contents and profiles and antioxidant activities of the extracts were found to be dependent on the extraction solvent used. Litchi exhibited good cellular antioxidant activity and could be a potentially useful natural source of antioxidants.

Impact of the nature and composition of the mobile phase on the mass transfer mechanism in chiral reversed phase liquid chromatography. Application to the minimization of the solvent cost in chiral separations

The mechanism of mass transfer was studied on a cellulose-based chiral stationary phase (CSP, Lux Cellulose-1) using aqueous mixtures of acetonitrile (50/50–90/10, v/v) or methanol (90/10 and 100/0, v/v) as the mobile phase. An experimental protocol validated in RPLC and HILIC chromatography and recently extended to chiral RPLC was applied. The five mass-transfer contributions (longitudinal diffusion, short-range and long-range eddy dispersion, solid–liquid mass transfer resistances due to finite intra-particle diffusivity and slow adsorption–desorption) to the reduced height equivalent to a theoretical plate (HETP) were measured. The experimental results show that the adsorption rate constants kads of trans-stilbene enantiomers onto the CSP are three times larger with acetonitrile than with methanol as the organic modifier. This is correlated to the decrease of enantioselectivity from 1.4 (in methanol) to only 1.1 (in acetonitrile). The amount of solvent needed to achieve a separation factor of exactly 2.0 was determined. This showed that analysis cost could be reduced seven times by selecting pure methanol as the eluent for a 5cm long column rather than an acetonitrile–water mixture for a longer (20–45cm) column.

The effect of aqueous alcohols (methanol, t-butanol) and sulfolane on the dissociation constants and thermodynamic properties of alkanolamines

The dissociation constants of protonated monoethanolamine, N-methyldiethanolamine have been determined in aqueous mixtures of methanol, t-butanol–water and sulfolane solvents. The mole fractions of the organic compounds ranged from (0.2 to 0.95) and the temperatures from (283 to 353)K. Standard state thermodynamic properties like ΔrG, were derived from the results. The basic strength of the protonated alkanolamine decreased with decreasing dielectric constant and increase in temperature of the solvent.

Monitoring the effects of homogeneity methanol/water/monomer on the mode of polymerization of styrene: dispersion polymerization versus emulsion polymerization

The polymerization of styrene (St) was carried out with varying amounts of methanol in aqueous medium. As methanol content decreased (to 50 %), the phase of polymerization mixture (methanol/water/monomer) changed to a heterogeneous state; the homogeneous state was obtained in samples that contain 75 and 100 % methanol. In order to verify the mechanism of polymerization in heterogeneous and homogeneous mixtures, the nucleus formation rate during polymerization, the stability equilibrium of the media and seeded particles, and the size of particles and their growth in polymerization were experimentally being monitored. With the homogeneous mixture in 75 wt% methanol, dumbbell, triangle, and peanut-like particles have been formed. On the other hand, the characteristics of the polymerization products were different from those typically obtained in the emulsion polymerization and in the sample with 100 wt% methanol dispersion polymerization. In the sample with 100 % methanol and in one with 50 % methanol, monodispersed spherical particles are formed in the final conversion. Thus, homogeneity in the aqueous methanol mixture can be a critical factor in determining the polymerization modes between dispersion and emulsion polymerization.

Effect of Colloidal Substrate Curvature on pH-Responsive Polyelectrolyte Brush Growth

Coatings consisting of polymer brushes are an effective way to modify solid interfaces. Polymer brush-modified hybrid particles have been prepared by surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP) of 2-(diethylamino)ethyl methacrylate (DEA) on silica particles. We have optimized the synthesis with respect to changing the reducing agent, temperature, and reaction solvent from an aqueous ethanol mixture to an aqueous methanol mixture. Our flexible electrostatically adsorbed macroinitiator approach allows for the modification of a variety of surfaces. Polybasic brushes have been grown on silica particles of different sizes, from 120 to 840 nm in diameter, as well as on wafers, and a comparison of the products has allowed the effect of surface curvature to be elucidated. An examination of the thickness of the dry brush and the aqueous hydrodynamic brush at both pH 7 and at 4 demonstrated that growth increased substantially with substrate curvature for particles with a diameter below 450 nm. This is attributed to the increasing separation between active chain ends, reducing the rate of termination. This is believed to be the first time that this effect has been demonstrated experimentally. Furthermore, we have seen that polymer brush growth on planar wafers was significantly reduced when the reaction mixture was stirred.

Molecular dynamics study on water self-diffusion in aqueous mixtures of methanol, ethylene glycol and glycerol: investigations from the point of view of hydrogen bonding

Molecular dynamics simulations have been performed to investigate the aqueous binary mixtures of alcohols, including methanol, ethylene glycol (EG) and glycerol of molalities ranging from 1 to 5 m at the temperatures of 273, 288 and 298 K, respectively. The primary purpose of this paper is to investigate the mechanism of water self-diffusion in water-alcohol mixtures from the point of view of hydrogen bonding. The effects of temperature and concentration on water self-diffusion coefficient are evaluated quantitatively in this work. Temperature and concentration to some extent affect the hydrogen bonding statistics and dynamics of the binary mixtures. It is shown that the self-diffusion coefficient of water molecules decreases as the concentration increases or the temperature decreases. Moreover, calculations of mean square displacements of water molecules initially with different number n of H-bonds indicate that the water self-diffusion coefficient decreases as n increases. We also studied the aggregation of alcohol molecules by the hydrophobic alkyl groups. The largest cluster size of the alkyl groups clearly increases as the concentration increases, implying the emergence of a closely connected network of water and alcohols. The clusters of water and alcohol that interacted could block the movement of water molecules in binary mixtures. These findings provide insight into the mechanisms of water self-diffusion in aqueous binary mixtures of methanol, EG and glycerol.