Preferential Solvation of Ketoprofen in Some Co-solvent Binary Mixtures

The preferential solvation parameters of ketoprofen (KTP) in ethanol (EtOH) + water and propylene glycol (PG) + water binary solvent mixtures were obtained from their thermodynamic properties by means of the inverse Kirkwood–Buff integrals (IKBI) and quasi-lattice quasi-chemical methods. According to the IKBI method, it is found that KTP is very sensitive to specific solvation effects, so the preferential solvation parameter by co-solvents, δx _1,3, is negative in the water-rich mixtures of both binary systems but positive in the other compositions at temperatures of 293.15, 303.15 and 313.15 K. From this it can be assumed that, in water-rich mixtures, hydrophobic hydration around the aromatic rings and the methyl group, present in the drug, plays a relevant role in the solvation. The bigger amount of drug solvation by the co-solvent in mixtures of similar solvent proportions and in co-solvent-rich mixtures could be due mainly to polarity effects. Moreover, in these mixtures the solute will be acting as a Lewis acid with the co-solvent molecules, because they are more basic than water.     

Excited state hydrogen bond dynamics: coumarin 102 in acetonitrile-water binary mixtures

The time dependent change in the intermolecular response of solvent molecules following photoexcitation of Coumarin 102 (C102) has been measured in acetonitrile-water binary mixtures. Experiments were performed on mixtures of composition x(CH3CN) = 0.25, 0.50, 0.75, and 1.00. At low water concentrations (x(H2O) < or = 0.25) the solvent response is consistent with previous measurements probing dipolar solvation. With increasing water concentration (x(H2O) > or = 0.50) an additional response is found subsequent to dipolar solvation, exhibited as a rapid gain in the solvent's polarizability on a approximately 250 fs time scale. Monte Carlo simulations of the C102:binary mixture system were performed to quantify the number of hydrogen-bonding interactions between C102 and water. These simulations indicate that the probability of the C102 solute being hydrogen bound with two water molecules, both as donors at the carbonyl site, increases in a correlated fashion with the amplitude of the additional response in the measurements. We conclude that excitation of C102 simultaneously weakens and strengthens hydrogen bonding in complexes with two inequivalently bound waters.     

Solute-solvent friction kernels and solution properties of methyl oxazoline-phenyl oxazoline (MeOx-PhOx) copolymers in binary ethanol-water mixtures

Solvent mixtures often alter the solubility of polymeric substances. Statistical copolymers made from 2-methyl-2-oxazoline (MeOx) and 2-phenyl-2-oxazoline (PhOx) are known for their varying solubilities in pure ethanol, pure water and in binary mixtures of ethanol-water. Constrained Molecular Dynamics (MD) simulations have been carried out with an aim to explain the varying solubilities of the statistical MeOx-PhOx copolymers. The solute-solvent dynamic friction kernels calculated through constrained MD simulations corroborate the solubility pattern in these copolymers. The solvation characteristics have been analyzed in terms of the solute-solvent radial distribution functions (RDFs). The ethanol-soluble MeOx-PhOx copolymers exhibit characteristic solute-composition dependence in the dynamic solute-solvent friction kernels, indicating the strength of the solute-solvent correlations. The aggressive solvation by the ethanol molecules in the binary solvent mixtures has been brought out by the O(solute)-H(ethanol) RDFs which exhibit a characteristic dependence on the ethanol content in the solvent composition. The corresponding O(solute)-H(water) RDFs are devoid of any such composition dependence. For all the MeOx-PhOx copolymers, the O-site solvation is strongly dominated by the water molecules and the N-sites are solvated equally by both ethanol and water molecules.     

Ion-molecule interactions in solutions of lithium perchlorate in propylene carbonate + diethyl carbonate mixtures: an IR and molecular orbital study

FTIR spectra have been recorded and analyzed for solutions of lithium perchlorate in propylene carbonate (PC), diethyl carbonate (DEC), and PC + DEC mixtures. It has been shown that the carbonyl stretch bands for PC and DEC are very sensitive to the interaction between Li+ and the solvent molecules. They split with addition of LiClO4, indicating a strong interaction of Li+ with PC and DEC through the oxygen group of PC and both oxygen and ether oxygen atoms of DEC. In conjunction with molecular orbital calculation, the optimized geometries of solvation are given. In addition, solvent separated ion pairs and contact ion pairs were observed in LiClO4/DEC solutions, and no preferential solvation of Li+ in LiClO4/PC + DEC solutions were detected.     

Thermochemical Investigations of Tautomeric Equilibrium. Variation of the Calculated Equilibrium Constant with Binary Solvent Composition

Abstract

A conventional nonelectrolyte solution model which has led to successful predictive equations for solute solubility and infinite dilution chromatographic partition coefficients is extended to systems containing a tautomeric solute dissolved in a binary solvent mixture. The derived expression predicts that the tautomeric solute concentration in a binary solvent is a geometric average of the pure solvent ratios and permits calculation of solute-solvent association constants from variation of the stoichiometric tautomeric solute concentration ratios as a function of binary solvent composition. Experimental data for phenylazonaphthol dissolved in aqueous-ethanol and aqueous-acetone solvent mixtures is discussed in relation to the theoretical model.     

Enthalpies of dissolution of propylene carbonate,acetonitrile, and 1,4-dioxane in mixtures of water with acetone or dimethyl sulfoxide

Enthalpies of dissolution of acetonitrile, propylene carbonate, and 1,4-dioxane in mixtures of water with acetone or DMSO were measured in the whole concentration range of the mixed solvents. Standard enthalpies of dissolution and enthalpies of transfer of solutes from water to its mixtures with acetone or DMSO were determined. In the region of small proportions of the nonaqueous component, the enthalpy of cavity formation in the mixed solvent makes the main contribution to the variation of the enthalpy of dissolution. An increase in the proportion of the nonaqueous component leads to competition between the contributions of cavity formation and specific interaction between the solute and the solvent during solvation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1747–1752, September, 1995.     

Preferential Solvation of Some Sulfonamides in Propylene Glycol + Water Solvent Mixtures According to the IKBI and QLQC Methods

The preferential solvation parameters, which represent differences between the local and bulk mole fractions of the solvents near to the solute, in solutions of some sulfonamides in propylene glycol + water binary mixtures are derived from their thermodynamic properties by means of the inverse Kirkwood?Buff integrals (IKBI) and the Quasi-Lattice Quasi-Chemical (QLQC) method. From solvent effect studies, it is found that sulfonamides are sensitive to solvation effects; the preferential solvation parameter, δx _PG,S, is negative in water-rich mixtures but positive in compositions from 0.20 to 1.00 in mole fraction of propylene glycol according to IKBI method and positive in all co-solvent compositions if the QLQC method is considered. It is conjecturable that in water-rich mixtures, hydrophobic hydration around the aromatic ring and/or other non-polar groups plays a relevant role in the solvation. The greater solvation by propylene glycol mixtures of similar solvent compositions and in co-solvent-rich mixtures could be due mainly to polarity effects and acidic behavior of the sulfonamides, in contrast to the more basic solvent propylene glycol.     

Single particle and pair dynamics in water-formic acid mixtures containing ionic and neutral solutes: nonideality in dynamical properties

A series of molecular dynamics simulations of water-formic acid mixtures containing either an ionic solute or a neutral hydrophobic solute has been performed to study the extent of nonideality in the dynamics of these solutes for varying composition of the mixtures. The diffusion coefficients of the charged solutes, both cationic and anionic, are found to show nonideal behavior with variation of composition, and similar nonideality is also observed for the diffusion and orientational relaxation of solvent molecules in these mixtures. The diffusion coefficient of a neutral hydrophobic solute, however, decreases monotonically with increase in water concentration. We have also investigated some of the pair dynamical properties such as water-water and water-formic acid hydrogen bond relaxation and residence dynamics of water molecules in water and formic acid hydration shells. The lifetimes of water-water hydrogen bonds are found to be longer than those between formic acid carbonyl oxygen-water hydrogen bonds, whereas the lifetimes of formic acid hydroxyl hydrogen-water hydrogen bonds are longer than those of water-water hydrogen bonds. In general, the hydrogen bond lifetimes for both water-water and water-formic acid hydrogen bonds are found to decrease with increase in water concentration. Residence times of water molecules also show the same trend with increase in formic acid concentration. Interestingly, these pair dynamical properties show a monotonic dependence on composition without any maximum or minimum and behave almost ideally with respect to changes in the composition of the mixtures. The present calculations are performed with fixed-charge nonpolarizable models of the solvent and solute molecules without taking into account many-body polarization effects in an explicit manner.     

UV-visible spectroscopic study of solvation in ternary solvent mixtures: ketocyanine dye in methanol + acetone + water and methanol + acetone + benzene

Solvation characteristics of a ketocyanine dye have been studied in completely miscible ternary solvent mixtures, namely, methanol + acetone + water and methanol + acetone + benzene, by monitoring the solvatochromic absorption band of the dye. The maximum energy of absorption (E) of the solute in a ternary solvent mixture differs significantly from the mole fraction average of the E values in the component solvents. Results in the corresponding binary solvent mixtures also show a deviation of the E value from the mole fraction averaged E values. The results have been explained in terms of preferential solvation using a two phase model of solvation. The excess or deficit over the bulk composition of a solvent component in the vicinity of the solute molecule in a ternary solvent mixture has been estimated using the knowledge of solvation in the corresponding binary mixtures.     

Kinetics of the solvolysis of thetrans-dichlorobis (Diaminoethane)-cobalt(III) ion in aqueous ethylene carbonate and aqueous propylene carbonate

The kinetics of the solvolysis of trans-[Coen₂Cl₂]⁺ have been followed in mixtures of water with either ethylene carbonate or propylene carbonate over a range of temperatures. Both the enthalpy and entropy of activation for the first order loss of a chloride ion to give [Coen₂Cl]²⁺ in water + ethylene carbonate show a maximum at low mole fractions of ethylene carbonate. As similar extrema in H and S for the same process for this complex and others in water +2-propanol and in water + t-butanol correlate well with extrema in the physical properties of the mixtures which are influenced by changes in solvent structure, it is suggested that these new extrema can be attributed to solvent structure effects. The application of a free energy cycle to the loss of the chloride ion in water and in the mixtures suggests that, although changes in solvent structure influence the cation in the transition state more than the cation in the initial state in water + ethylene carbonate, in water + propylene carbonate the influence of changes in solvent structure approximately balances. This is compared with the application of the free energy cycle to the same process in mixtures of water with a range of cosolvents using kinetic data available in the literature.     

Solute–solvent interactions of acid–1,4-dioxane mixtures—By dielectric, FTIR, UV–vis and 13C NMR spectrometric methods

Results of the dielectric studies carried out on the binary mixture of n-butyric and caprylic acids with 1,4-dioxane over the entire composition range and at temperatures 303 K, 308 K, 313 K and 318 K, and FTIR, UV–vis and 13C NMR spectral studies are presented in this paper. The excess permittivity and excess free energy were fitted with the Redlich–Kister polynomial. The variation of Kirkwood correlation factors, excess permittivity and excess free energy of mixing with the concentration and temperature has been investigated in view of understanding the ordering of dipoles of solute and solvent molecules. The FTIR, UV–vis and 13C NMR spectral analysis reveals the formation of complex between solute and solvent molecules. The parallel alignment of electric dipoles of the complex predicted by dielectric studies is well supported by UV–vis spectral analysis. The structure of the complex molecule present in the clusters has been deduced.     

Properties of L-ascorbic acid in water and binary aqueous mixtures of D-glucose and D-fructose at different temperatures

Using density and sound velocity partial molar volumes, partial molar adiabatic compressibilities, partial molar expansibilities and structure of L-ascorbic acid have been determined in water and aqueous mixtures of D-glucose and D-fructose at different concentrations and temperatures. Masson’s equation was used to analyze the measured data. The obtained parameters have been interpreted in terms of solute–solute and solute–solvent interactions. It is found that the L-ascorbic acid acts as structure breaker in water as well in binary studied mixtures.     

Vibrational spectroscopic studies on ion solvation of lithium perchlorate in propylene carbonate + N,N-dimethylformamide mixtures

The infrared (IR) and Raman spectra are reported for solutions of lithium perchlorate in propylene carbonate (PC), N,N-dimethylformamide (DMF) and PC + DMF mixtures. The band splittings of symmetric ring deformation for PC and O=CN deformation for DMF suggest that there is a strong interaction between lithium cations and solvent molecules. The solvent molecules have been assigned to two types, the free and complexed molecules. By a comparison of the intensity for the corresponding bands, it has been concluded that Li+ cations are preferentially solvated by DMF molecules in the LiClO4/PC-DMF solutions. This has been explained by the difference in values of donor number.     

Absorption spectral band width of charge transfer transition of E(T)(30) dye in homogeneous and heterogeneous media

Solvation characteristics in homogeneous and heterogeneous media have been probed by monitoring the band width of ICT band of 2,6-di-phenyl-4(2,4,6-triphenyl-1-pyridino) phenolate, the indicator solute for E(T)(30) scale, in pure, mixed binary solvents and aqueous micellar solution. Non-ideal solvation behaviour is observed in all the binary solvent mixtures. Index of preferential solvation has been calculated as a function of solvent composition. Study in micellar media indicates that the dye is located at the micelle-water interface. The effects of variation of micelle concentration, temperature and electrolyte concentration have also been studies.     

Use of a solvatochromic probe for study of solvation in ternary solvent mixture

Solvation characteristics of 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridino)phenolate in completely miscible ternary solvent mixtures (viz., methanol + acetone + water, methanol + acetone + benzene, and methanol + chloroform + benzene) have been studied by using an electronic spectroscopic procedure. The transition energy (E) corresponding to the charge-transfer band maximum of the solute in a ternary solvent mixture differs significantly from the average E-values in the component solvents weighted by the mole fraction of the solvents. A two-phase model of solvation has been invoked to explain the results. The excess or deficit of solvent components in the local region of the solute molecule over that in the bulk has been estimated using the knowledge of solvation in binary solvent mixtures.     

Electronic spectroscopic study of solvation of a ketocyanine dye in ternary solvent mixtures

Solvation characteristics in ternary solvent mixtures have been studied by monitoring the solvent-sensitive electronic absorption band of a ketocyanine dye in two ternary solvent mixtures, water + ethanol + benzene and water + ethanol + cyclohexane, in which one of the pairs are partially miscible. Investigations have been done in a completely miscible region including the binodal curve. The maximum energy of absorption (E) of the solute in a ternary solvent mixture differs significantly from the mole fraction average of the E-values in the component solvents. Results in the corresponding binary solvent mixtures also show a deviation of the E-value from the mole fraction averaged E-values, indicating preferential solvation by a component solvent. The results in ternary solvent mixture have been explained in terms of a realistic model of solvation using the results on binary solvation.     

Cooperative and synergistic solvent effects in SET‐LRP of MA

SET‐LRP requires a combination of ligand and solvent that mediates the disproportionation of Cu(I)X into Cu(0) activator, and Cu(II) deactivator. The solvent also modulates the kinetics of the reaction. More polar solvents, including mixtures of water and organic solvents enhance the rate of polymerization in accord with the Dimroth‐Reichardt parameter. Here, it is demonstrated that a similar effect is observed in binary mixtures of organic solvents, wherein the addition of a more polar solvent to a less polar solvent provides a linear increase in the apparent rate constant of propagation, k. However, this linear relationship does not hold for the entire range of volume fraction for binary mixtures when ethylene carbonate (EC) or MeOH are one of the two components. Results herein, suggest that the kinetics of SET‐LRP in these solvent mixtures is cooperatively and synergistically determined by polarity, degree of disproportionation, and also by another parameter related to the ability of the solvent to stabilize colloidal Cu(0) and determine its particle size. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5591–5605, 2009     

Solubility Parameter of Gatifloxacin and Its Correlation with Antibacterial Activity

The solubility parameter of gatifloxacin was calculated theoretically by Fedors’ method and also determined experimentally using the standard solubility method. The molar volume of gatifloxacin was determined experimentally by the flotation method. Three solvents, ethyl acetate, propylene glycol and water were used to prepare nine binary mixtures having different solubility parameter values varying from 8.9 to 23.4 H. The δ ₂ solubility parameter of gatifloxacin was found to be 12.4 H. The cumulative transport of gatifloxacin from the binary solvent mixtures (ethyl acetate–propylene glycol and propylene glycol–water) exhibited an inverse parabolic relationship to the solubility parameter of the solvent mixtures. Transport studies revealed that the extent of gatifloxacin rejection from solvent mixtures was dependent on its solubility parameter and system composition. In the selected organisms (bacteria), a minimum zone of inhibition was observed in a solvent mixture having the solubility parameter nearest to the solubility parameter of gatifloxacin. Two models were employed for the evaluation of the antibacterial activity of gatifloxacin in binary mixtures.     

Preferential solvation of methocarbamol in aqueous binary co-solvent mixtures at 298.15 K

The preferential solvation parameters of methocarbamol in dioxane + water, ethanol + water, methanol + water and propylene glycol + water mixtures are derived from their thermodynamic properties by using the inverse Kirkwood–Buff integrals (IKBI) method. This drug is sensitive to solvation effects, being the preferential solvation parameter δx_1,3, negative in water-rich and co-solvent-rich mixtures, but positive in mixtures with similar proportions of solvents, except in methanol + water mixtures, where positive values are found in all the methanol-rich mixtures. It is conjecturable that the hydrophobic hydration around the non-polar groups in water-rich mixtures plays a relevant role. Otherwise, in mixtures of similar solvent compositions, the drug is mainly solvated by co-solvent, probably due to the basic behaviour of the co-solvents; whereas, in co-solvent-rich mixtures, the preferential solvation by water could be due to the acidic behaviour of water. Nevertheless, the specific solute–solvent interactions present in the different binary systems remain unclear.     

Study of viscometric properties of L-ascorbic acid in binary aqueous mixtures of D-glucose and D-fructose

The relative viscosities and activation parameters of L-ascorbic acid have been determined in water and binary aqueous mixtures of D-glucose and D-fructose at different temperatures. A and B-coefficients of Jones–Dole equation are determined using density and viscosity data. Gibbs energy of activation of viscous flow per mole of solvent as well as per mole of solute along with activation enthalpy and entropy is also determined using Feakin’s transition-state theory. The obtained results are explained in terms of intermolecular interactions and in this study L-ascorbic acid has been found as structure breaker in binary aqueous mixtures of D-glucose and D-fructose.