Aqueous Mixtures Of Methanol Research Articles

Studies of Partial Molar Volumes of Some Narcotic-Analgesic Drugs in Aqueous-Alcoholic Mixtures at 25°C

Partial molar volumes of the drugs Parvon Spas, Parvon Forte, Tramacip, and Parvodex in aqueous mixtures of methanol (MeOH), ethanol (EtOH), and propan-1-ol (1-PrOH) have been determined. The data have been evaluated using the Masson equation. The parameters, apparent molar volumes \({(\phi_{\rm v})}\), partial molar volumes \({(\phi_{\rm v}^{0})}\), and Sv values (experimental slopes) have been interpreted in terms of solute–solvent interactions. In addition, these studies have also been extended to determine the effect of these drugs on the solvation behavior of an electrolyte (sodium chloride), a surfactant (sodium dodecyl sulfate), and a non-electrolyte (sucrose). It can be inferred from these studies that all drug cations can be regarded as structure makers/promoters due to hydrophobic hydration. Furthermore, the results are correlated to understand the solution behavior of drugs in aqueous-alcoholic systems, as a function of the nature of the alcohol and solutes.

On the solvent role in alcohol-induced α-helix formation of chymotrypsin inhibitor 2

Abstract The circular dichroism (CD) spectra of chymotrypsin inhibitor 2 (CI2) have been measured as a function of alcohol mole fraction in aqueous mixtures of methanol, ethanol, trifluoroethanol (TFE), and hexafluoro-iso-propanol (HFIP). Small-angle X-ray and neutron scattering (SAXS and SANS) of CI2 was also measured as a function of ethanol mole fraction in ethanol-water mixtures. The CD spectra have shown that the secondary structure of CI2 changes from β-strand to α-helical structure at alcohol mole fractions characteristic of the individual alcohols in an order of HFIP > TFE > ethanol > methanol in effectiveness, where the structure transition of solvent clusters takes place from the typical tetrahedral-like water to the chain-like alcohol clusters in alcohol-water mixtures previously reported. The radius of gyration of CI2, obtained from the analysis of the SANS data, increased with an increase in ethanol mole fraction up to around 0.2 and then gradually decreased. The SAXS data have shown that the shape of CI2 changes from a sphere to a rod-like one at a 0.1 ethanol mole fraction. A possible role of solvent clusters played in alcohol-induced α-helix formation of CI2 is discussed from a viewpoint of the solvent clusters.

Solubility of sodium diclofenac in binary water + alcohol solvent mixtures at 25°C

Solubility of sodium diclofenac in aqueous binary mixtures of methanol, ethanol and 2-propanol was determined at 25°C. The maximum solubility of the drug was observed at volume fractions of 0.85, 0.90 and 0.50 for methanol, ethanol and 2-propanol mixtures, respectively. The produced data was fitted to the Jouyban-Acree model and its constants were computed, then the back-calculated solubilities were compared with the corresponding experimental values by calculating the mean percentage deviation (MPD) and the overall MPD for three cosolvent systems was 12.6%. The solubility data in water + ethanol mixtures was predicted using a previously trained version of the Jouyban-Acree model and the prediction MPD was 32.0%. The model successfully predicted the solvent composition providing the maximum solubility of the drug, which is an important data in the formulation studies, especially in the early stages of drug discovery investigations.

Determination of the Acidity Constants of Methyl Red and Phenol Red Indicators in Binary Methanol− and Ethanol−Water Mixtures

The conditional acidity constants, pKa, of methyl red and phenol red were determined in (10, 30, and 50) wt % binary aqueous mixtures of methanol and ethanol at 298.15 K and at constant low ionic strength (2.5·10−3 mol·dm−3) by a spectrophotometric method. For methyl red and phenol red and in the studied cosolvent + water systems, pKa ranged from 3.78 ± 0.06 to 5.50 ± 0.04 and 8.50 ± 0.1 to 6.71 ± 0.03, respectively. Variations in the pKa of methyl red and phenol red as functions of wt % cosolvents are discussed in terms of solvent properties.

Preferential Solvation of Ions in Mixed Solvents. 5. The Alkali Metal, Silver, and Thallium(I) Cations in Aqueous Organic Solvents According to the Inverse Kirkwood-Buff Integral (IKBI) Approach

The inverse Kirkwood-Buff integral (IKBI) approach is applied, as far as the relevant data exist in the literature, to the preferential solvation of Li+, Na+, K+, Rb+, Cs+, Ag+, and Tl+ in aqueous mixtures of methanol, ethanol, 1,2-ethanediol (EG), acetonitrile, formamide, N,N,-dimethylformamide (DMF), N,N,N′,N′,N″,N″-hexamethyl phosphoric triamide (HMPT), and dimethyl sulfoxide (DMSO). In aqueous EG and formamide the preferential solvation is very small. Water is the preferred solvent in the solvation shells in aqueous methanol, ethanol and acetonitrile (except for Ag+ in the latter solvent) but the co-solvent is preferred in aqueous mixtures of DMF, HMPT, and DMSO over most or all of the composition range. For the latter three mixtures the larger donicity of the co-solvents causes their preference, whereas where water is preferred over other protic solvents, it is the small size of the water molecules that appears to be the cause.

Methodology Optimization for Quantification of Total Phenolics and Individual Phenolic Acids in Sweetpotato (Ipomoea batatas L.) Roots

Phenolic acids are one of the several classes of naturally occurring antioxidant compounds found in sweetpotatoes. Simplified, robust, and rapid methodologies were optimized to quantify total and individual phenolic acids in sweetpotato roots. Total phenolic acid content was quantified spectrophotometrically using both Folin-Denis and Folin-Ciocalteu reagents. The Folin-Ciocalteu reagent gave an overestimation of total phenolic acids due to the absorbance of interfering compounds (that is, reducing sugars and ascorbic acid). Individual phenolic acids were quantified by high-performance liquid chromatography (HPLC) using the latest in column technology. Four reversed-phase C18 analytical columns with different properties (dimensions, particle size, particle shape, pore size, and carbon load) were compared. Three different mobile phases using isocratic conditions were also evaluated. A column (4.6 x 150 mm) packed with 5-microm spherical silica particles of pore size 110 A combined with 14% carbon load provided the best and fast separation of individual phenolic acids (that is, chlorogenic acid, caffeic acid, and 3 isomers of dicaffeoylquinic acid) with a total analysis time of less than 7 min. Among the 3 mobile phases tested, a mobile phase consisting of 1% (v/v) formic acid aqueous solution: acetonitrile: 2-propanol, pH 2.5 (70:22:8, v/v/v) gave adequate separation. Among the solvents tested, aqueous mixtures (80:20, solvent:water) of methanol and ethanol provided higher phenolic acid extraction efficiency than the aqueous mixture of acetone.

Molecular Solvation in Water−Methanol and Water−Sorbitol Mixtures: The Roles of Preferential Hydration, Hydrophobicity, and the Equation of State

Molecular dynamics simulations of aqueous mixtures of methanol and sorbitol were performed over a wide range of binary composition, density (pressure), and temperature to study the equation of state and solvation of small apolar solutes. Experimentally, methanol is a canonical solubilizing agent for apolar solutes and a protein denaturant in mixed-aqueous solvents; sorbitol represents a canonical "salting-out" or protein-stabilizing cosolvent. The results reported here show increasing sorbitol concentration under isothermal, isobaric conditions results in monotonic increases in apolar solute excess chemical potential (mu2ex) over the range of experimentally relevant temperatures. For methanol at elevated temperatures, increasing cosolvent composition results in monotonically decreasing mu2ex. However, at lower temperatures mu2ex exhibits a maximum versus cosolvent concentration, as seen experimentally for Ar in ethanol-water solutions. Both density anomalies and hydrophobic effects--characterized by temperatures of density maxima and apolar solute solubility minima, respectively--are suppressed upon addition of either sorbitol or methanol at all temperatures and compositions simulated here. Thus, the contrasting effects of sorbitol and methanol on solute chemical potential cannot be explained by qualitative differences in their ability to enhance or suppress hydrophobic effects. Rather, we find mu2ex values across a broad range of temperatures and cosolvent composition can be quantitatively explained in terms of isobaric changes in solvent density--i.e., the equation of state--along with the corresponding packing fraction of the solvent. Analysis in terms of truncated preferential interaction parameters highlights that care must be taken in interpreting cosolvent effects on solvation in terms of local preferential hydration.

Computational Models for Structure-Hydrophobicity Relationships of 4-Carboxyl-2,6-Dinitrophenyl Azo Hydroxynaphthalenes

Some phenyl azo hydroxynaphthalene dyes (e.g., sunset yellow) are certified as approved colorants for food, cosmetics, and drug formulations. The hydrophobicity of 4 newly synthesized azo dyes of the phenyl azo hydroxynaphthalene class was investigated, as a training set, with the goal of developing models for quantitative structure-property relationships (QSPR). Retention behavior of the molecules reversed-phase thin-layer chromatography (RPTLC) was investigated using liquid paraffin-coated silica gel as the stationary phase. Mobile phases consisted of aqueous mixtures of methanol, acetone, and dimethylformamide (DMF). Basic hydrophobicity parameter (Rmw), specific hydrophobic surface area (S), and isocratic chromatographic hydrophobicity index (phio) were computed from the chromatographic data. The hydrophobicity index (Rm) decreased linearly with increasing concentration of organic modifiers. Extrapolated Rmw values obtained by using DMF and acetone differ significantly from the value obtained by using methanol as organic modifier [P < 0.05, 1-way analysis of variance (ANOVA), Tukey's multiple comparison test]. Structure-property relationships showed that hydrophobicity was dependent on type and position of naphthalene ring substituents. Rm decreased with the presence of a highly polar substituent (e.g., COOH). Owing to intramolecular interaction, Rm increased when the common hydroxyl group (OH) is positioned ortho to the azo group, relative to para positioning, in 2 positional isomers. Pattern recognition data analysis underscores the utility of phio as a more accurate hydrophobicity descriptor than Rmw. Phio is negatively correlated with theoretically calculated density, surface tension, and refractive index for the molecules. These models could be used to predict toxicity (absorption, distribution, metabolism, excretion, toxicity; ADMET) properties of the azo dyes and may also play useful roles in computer-assisted molecular discovery of nontoxic azo dyes.

Effect of Chromatographic Conditions on the Separation of Selected Alkaloids on Phenyl Stationary Phase by an HPLC Method

Some alkaloid standards and synthetic or natural alkaloid mixtures were chromatographed on phenyl‐silica stationary phases using various aqueous eluents: aqueous methanol or acetonitrile mixture, buffered aqueous mobile phases at pH 3 to suppress silanols' ionisation, or at pH 8 to suppress alkaloids' ionisation. Strong silanophilic interactions that can occur with these analytes and the adsorbent surface can lead to poor peak shape and resolution. Mobile phases with anionic ion‐pairs such as sodium dodecyl sulphate, octanesulfonic acid sodium salt, or HDEHP were used to improve efficiency, peak shape, and selectivity. The effect of silanol blockers – different amines on the retention, efficiency, and peak shape for RP systems, was analysed.

Excess properties of aqueous mixtures of methanol: Simple models versus experiment

Molecular simulations on water–methanol mixtures were performed over the entire concentration range using primitive models that descend from realistic molecular models of both compounds. Since the primitive models reproduce, even semi-quantitatively, the structure of the pure compounds, the primary goal was to examine what thermodynamic features they are able to capture. Comparison of simulation data shows that the primitive and realistic models yield, qualitatively, the same behavior and that both fail to produce a minimum of the partial molar volume of methanol at low concentrations. Reasons for this failure along with details on the relation between specific intermolecular interactions and observed phenomena are discussed.

Reactivity trends of the base hydrolysis of coumarin and thiocoumarin in binary aqueous–methanol mixtures at different temperatures

Rate constants for base hydrolysis of both coumarin and thiocoumarin have been studied in different binary aqueous–methanol mixtures at temperature range from 288 to 313 K. The activation parameters of the reactions were evaluated. Moreover, the change in the activation barrier of the investigated compounds from water to water–methanol mixtures were estimated from the kinetic data.

Enthalpies of transfer of acetonitrile from water to aqueous methanol, ethanol and dimethylsulphoxide mixtures at 298.15 K

Previous studies have established that the extended coordination model of solvation can satisfactorily account for the variation in the transfer enthalpies of solutes in mixed-solvent systems. The model parameter relating to the solute-induced disruption of the solvent structure shows a marked dependence on the nature of the mixed solvent. In the present paper we report the transfer enthalpies of acetonitrile from water to aqueous methanol, ethanol and dimethylsulphoxide (DMSO) systems. Analysis of these in terms of the extended coordination model confirms both the model's ability to account for the experimental data, and the variability of the structural disruption parameter. The solvation parameters recovered from the analyses indicate that the net effect of acetonitrile on the solvent structure is a breaking of solvent–solvent bonds. The extent of bond breaking of the solvent increases from MeOH to EtOH.

A new equation to reproduce the enthalpies of transfer of formamide, N-methylformamide and N, N-dimethylformamide from water to aqueous methanol mixtures at 298 K

The enthalpies of transfer of formamide (Form) N-methylformamide (NMF) and N, N-dimethylformamide (DMF) from water to aqueous methanol mixtures are reported and analysed in terms of the new solvation theory. It was found that a previous equation could not reproduce these data over the whole range of solvent compositions. Using the new solvation theory to reproduce the enthalpies of transfer shows excellent agreement between the experimental and calculated data over the entire range of solvent compositions. The analyses show that the solvation of DMF is random in the aqueous methanol mixtures while Form and NMF are preferentially solvated by methanol. It is also found that the interaction of the solutes is stronger with methanol than with water.

Excess properties of aqueous mixtures of methanol: Simulation versus experiment

We report molecular simulation results for both the excess mixing and partial molar properties of water–methanol mixtures over the entire concentration range with the particular emphasis on the low concentration ends. It is shown that the mixing properties are very sensitive to potential models and that the used realistic potentials (TIP4P for water and OPLS for methanol) give a reasonably good agreement with experiment only for volumetric properties although the qualitative trend of the partial molar volume at low concentrations is not reproduced. As regards excess enthalpy, the results are rather bad and only its sign is predicted correctly.

17O NMR relaxation study of dynamics of water molecules in aqueous mixtures of methanol, ethanol, and 1-propanol over a temperature range of 283–403 K

17O NMR spin-lattice relaxation time ( T 1) of water molecules was measured in aqueous mixtures of methanol, ethanol, and 1-propanol over a temperature range of 283–403 K. At temperatures below ∼ 303 K, the relaxation rate R 1 (= 1/ T 1) in the aqueous mixtures of methanol and ethanol sharply increased with increasing alcohol concentration up to characteristic alcohol mole fractions x Me and x Et of ∼ 0.3 and ∼ 0.2, respectively, showing that the rotation of water molecules is gradually retarded in the water-rich region due to hydrophobic hydration. With increasing x Me and x Et up to ∼ 0.7 the R 1 values slightly decreased and/or remained almost constant, and then increased again when x Et > 0.7. With increasing temperature, the degree of the retardation in the water-rich region became insignificant, and the R 1 values monotonously increased with increasing alcohol concentration. The relaxation rates in the 1-propanol–water mixtures monotonously increased with increasing alcohol content at all temperatures investigated. These results are discussed in view of microscopic structure of the alcohol–water mixtures previously obtained from X-ray diffraction measurements.

Correlation of Kinetic and Thermodynamic Quantities of Tl(I)/Tl(Hg) Electroreduction with Parameters of Binary Mixtures of Water with Acetone, Acetonitrile, Methanol, and N,N-dimethylformamide

The diffusion coefficient of Tl+ ions, the standard potential, the size factor of the activated complex, and the standard rate constant of the overall reaction Tl(I)/Tl(Hg) in aqueous mixtures of acetone, methanol, acetonitrile, and dimethylformamide are related to parameters representing the composition, polarity, electron pair, and hydrogen-bond donor ability of these mixtures. The dependencies on mixture composition, and the linear and multilinear correlation with solvatochromic parameters are interpreted by assuming a heterosolvation effect in combination with a two-step ion transfer – ion adsorption mechanism.

Stoichiometric Solvation Effects. Solvolysis of Trifluoromethanesulfonyl Chloride

Solvolyses of trifluoromethanesulfonyl chloride (TFMSC) in water and in aqueous binary mixtures of acetone, ethanol and methanol are investigated at 25, 35 and 45 . The Grunwald-Winstein plot of first-order rate constants for the solvolytic reaction of TFMSC with YCl (based on 2-adamantyl chloride) shows marked dispersions into three separate curves for three aqueous mixtures. The extended Grunwald-Winstein plots for the solvolysis of TFMSC show better correlation. The large negative and relatively small positive reveals that the solvolytic reaction proceeds via a typical bimolecular reaction mechanism. The l and m values determined in various solvents are consistent with the proposed mechanism of the general base catalysis reaction mechanism for TFMSC solvolyses based on mass law and stoichiometric solvation effect studies.

A Kirkwood−Buff Derived Force Field for Methanol and Aqueous Methanol Solutions

A force field for the simulation of methanol and aqueous methanol mixtures is presented. The force field was specifically designed to reproduce the experimental Kirkwood-Buff integrals as a function of methanol mole fraction, thereby ensuring a reasonable description of the methanol cosolvent and water solvent activities. Other thermodynamic and physical properties of pure methanol and aqueous methanol solutions, including the density, enthalpy of mixing, translational diffusion constants, compressibility, thermal expansion, and dielectric properties, were also well reproduced.

Stereoselectivity ratios in a simple Diels–Alder reaction in aqueous salt solutions of alcohols

This is the first exhaustive report on the variation of stereoselectivity ratios for a simple Diels–Alder reaction between cyclopentadiene and methyl acrylate. The reaction was carried out in aqueous mixtures of methanol, ethanol, propan-1-ol and butan-1-ol in presence of LiClO 4, LiCl, NaCl, KCl, CaCl 2 and MgCl 2. The endo stereoisomer decreases with the increase in carbon chain length of the alcohol. However, LiClO 4, a salting-in agent in water becomes salting-out in aqueous mixtures of alcohols. The solvent properties, thus can be attuned by adjusting the amount of solvents and salts.

Solvent effect on alkaline fading of crystal violet in pure and aqueous mixtures of alcohols

Chemical kinetics of alkaline fading of crystal violet has been studied in aqueous mixtures of methanol, ethanol, isopropanol and t-butanol by measuring the specific rate constant of the reactions spect rophotometrically in these solvent systems. The kinetic solvent effect has been analyzed in the light of Gibb's free energies of transfer of reactants and transition states from water to aqueous mixtures of alcohols, derived thereof. The observed variation of transfer free energy parameters, characteristic of the S N 2 reaction, with cosoivent compositions have been interpreted In terms of various specific and non-specific interactions of media with the reacting species and the transitions state Involved in this reaction.