FT-Raman spectroscopic evidences for the preferential solvation of sodium tetrafluorobrate in acetonitrile-based mixed solvents

Solutions of sodium tetrafluorobrate in acetonitrile-dimethylformamide, and acetonitrile-dimethylsulfoxide mixtures have been studied by FT-Raman spectroscopy for three solvent compositions, respectively. New bands due to solvent molecules in the first solvation shell of Na(+) were detected in the region of the O=C--N deformation and CH(3) rocking mode for amide and of the S=O and C--S stretching modes for sulfoxide. The individual solvation numbers of sodium cation in different environment were deduced. In all the cases, it is found that the sodium ion was preferentially solvated by DMF or DMSO in respective binary solvents. This result was further supported by ab initio calculations.     

Enthalpies of Transfer of Tetraalkylammonium Bromides and CsBr from water to Aqueous DMF at 298.15 K

Enthalpies of transfer of tetraalkylammonium bromides and CsBr from water to aqueous DMF mixtures are reported and analyzed in terms of a new solvation theory. It was found that a previous equation could not reproduce these data over the whole range of solvent compositions. Using a new solvation theory to model the enthalpies of transfer shows excellent agreement between experimental and calculated values over the entire range of solvent compositions. The analyses show that tetrapropylammonium bromide, Pr₄NBr, and tetrapentylammonium bromide, Pen₄NBr, are preferentially solvated by water; in contrast tetrabutylammonium bromide, Bu₄NBr, is preferentially solvated by DMF. The solvation of tetramethylammonium bromide, Me₄NBr, and cesium bromide, CsBr, is random. The extent to which the tetraalkylammonium bromides disrupt solvent–solvent bonds increases systematically in going from Me₄NBr to Pen₄NBr.     

Li＋在PC＋DMF混合溶剂中优先溶剂化的13C NMR研究

利用¹³C NMR光谱技术研究了Li^＋在碳酸丙烯酯(PC)＋N,N-二甲基甲酰胺(DMF)混合溶剂中的优先溶剂化现象. 根据溶剂分子中碳原子的化学位移随锂盐浓度的变化关系, 确定了与Li^＋发生配位的原子. 碳原子的配位位移值随混合溶剂组成的变化关系表明, 在LiClO₄＋PC＋DMF混合物中, DMF分子对Li^＋的溶剂化作用较PC分子强. 定量计算得到, 在n(PC)∶n(DMF)＝1∶1(摩尔比)的混合溶剂中, PC与DMF分子数在Li^＋第一溶剂化层中的比率为0.12, 说明Li^＋优先被DMF分子溶剂化.     

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.     

Solvation of decane and benzene in mixtures of 1-octanol and <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylformamide

The heats of dissolution of decane and benzene in a model system of octanol-1 (OctOH) and N,N-dimethylformamide (DMF) at 308 K are measured using a variable temperature calorimeter equipped with an isothermal shell. Standard enthalpies are determined and standard heat capacities of dissolution in the temperature range of 298–318 K are calculated using data obtained in [1, 2]. The state of hydrocarbon molecules in a binary mixture is studied in terms of the enhanced coordination model (ECM). Benzene is shown to be preferentially solvated by DMF over the range of physiological temperatures. The solvation shell of decane is found to be strongly enriched with 1-octanol. It is obvious that although both hydrocarbons are nonpolar, the presence of the aromatic π-system in benzene leads to drastic differences in their solvation in a lipid–protein medium.     

Determination of compositions of NaI solid solvates obtained from the solutions in mixtures of water with acetonitrile and N,N-dimethylformamide at 25°C

The thermogravimetric method was applied to determine the compositions of solid NaI existing in equilibrium with saturated salt solutions over the whole range of the compositions of the mixtures of water with AN and DMF at 25°C. It was concluded that NaI is preferentially hydrated in water-rich region only for both investigated systems, i.e. forx _AN<0.15 andx _DMF<0.25. Above the mentioned organic solvent content the significant differences in solvation of NaI are observed for both systems. In water-AN system for 0.15<x _AN<0.95 NaI is weakly preferentially hydrated and the composition of the solvate is: NaI·H₂O·CH₃CN. In pure AN, NaI is not solvated. In water-DMF system in the ranges of composition 0.25<x _DMF<0.50 and 0.50<x _DMF<0.80 two types of mixed solvates are observed: NaI·4H₂O·2DMF, and NaI·2H₂O·2DMF, respectively. So, NaI is strongly solvated by both components of mixed solvent. Forx _DMF>0.80 like in pure DMF, NaI is solvated by two molecules of DMF.     

Contribution of omega-3 fatty acids to the thermodynamics of membrane protein solvation

Recent NMR experiments and molecular dynamics simulations have indicated that rhodopsin is preferentially solvated by omega-3 fatty acids compared to saturated chains. However, to date no physical theory has been advanced to explain this phenomenon. The present work presents a novel thermodynamic explanation for this preferential solvation based on statistical analysis of 26,100 ns all-atom molecular dynamics simulations of rhodopsin in membranes rich in polyunsaturated chains. The results indicate that the preferential solvation by omega-3 chains is entropically driven; all chains experience an entropic penalty when associating with the protein, but the penalty is significantly larger for saturated chains.     

Preferential solvation of poly(methyl methacrylate) and a bisphenol A diglycidyl ether by size-exclusion chromatography

The preferential adsorption coefficient, lambda, of poly(methyl methacrylate), PMMA, in solutions formed by an epoxy resin in tetrahydrofuran (THF), was studied by size-exclusion chromatography (SEC). Only PMMA of lowest molar mass was preferentially solvated by epoxy but at low concentrations of epoxy in the mixture. At higher epoxy content PMMA was preferentially solvated by THF. A simultaneous and competitive solvation between the specific interactions PMMA-epoxy and the self association of epoxy at high concentrations would be the responsible of this inversion point. The more compacted coil of PMMA of higher molecular weights in solution could explain the lack of interaction of these polymers with epoxy. The results also indicated that lambda decreased with the molar mass. This variation has been attributed to the influence of the coil segment density on preferential adsorption.     

Copolymérisations de l'acrylonitrile. XII. Phénomènes de solvatation préférentielle et effet de conversion dans la copolymérisation (acrylonitrile–styrène)

Kinetic deviations with the conversion observed in free-radical-initiated [acrylonitrile (A)–styrene (S)] copolymerization carried out in DMF solution have been interpreted in terms of preferential solvation of the polymer by one of the monomers or the solvent. First it is well established that the initial styrene content of the PAS copolymer increases if a slight amount of polymer is introduced before the beginning of polymerization. Next the preferential solvation has been studied and characterized in various solvents (toluene or DMF) from the results of differential refractometry at dialysis equilibrium of the ternary solution (solvent–monomer–polymer) versus its solvent mixture. It was found that the most polar monomer, acrylonitrile, is already adsorbed by the polymer, mostly in copolymerizations carried out in DMF, from initially rich acrylonitrile mixtures. It is suggested that this phenomenon implies a heterogeneous repartition of the monomer mixture in the solution, which may affect the kinetic copolymerization when the conversion increases.     

Preferential solvation of some antiepileptic drugs in {cosolvent (1) + water (2)} mixtures at 298.15 K

The solubility of lamotrigine (LTG), clonazepam (CZP) and diazepam (DZP) in some {cosolvent (1) + water (2)} mixtures expressed in mole fraction at 298.15 K was calculated from reported solubility values expressed in molarity by using the densities of the saturated solutions. Aqueous binary mixtures of ethanol, propylene glycol and N-methyl-2-pyrrolidone were considered. From mole fraction solubilities and some thermodynamic properties of the solvent mixtures, the preferential solvation of these drugs by both solvents in the mixtures was analysed by using the inverse Kirkwood–Buff integrals. It is observed that LTG, CZP and DZP are preferentially solvated by water in water-rich mixtures in all the three binary systems analysed. In {ethanol (1) + water (2)} mixtures, preferential solvation by water is also observed in ethanol-rich mixtures. Nevertheless, in {propylene glycol (1) + water (2)} and {N-methyl-2-pyrrolidone (1) + water (2)} mixtures preferential solvation by the cosolvent was observed in cosolvent-rich mixtures.     

Solvation of perfluorooctane and octane in water, methanol, acetonitrile, and aqueous mixtures of methanol and acetonitrile

Molecular dynamics simulations are used to examine the local solvation structure of single octane and perfluorooctane molecules in liquid water, methanol, acetonitrile, and aqueous mixtures of methanol and acetonitrile. The motivation is to obtain baseline information about the solvation of perfluorooctane by liquids used as the mobile phase in liquid chromatography and how it differs from the solvation of octane. While octane is uniformly solvated by both water and the second component, perfluorooctane is solvated by methanol and acetonitrile with the exclusion of water from the first solvation layer when the solvent is a mixture.     

Preferential solvation of etoricoxib in some aqueous binary cosolvent mixtures at 298.15 K

Preferential solvation parameters of etoricoxib in several aqueous cosolvent mixtures were calculated from solubilities and other thermodynamic properties by using the IKBI method. Cosolvents studied were as follows: 1,4-dioxane, N,N-dimethylacetamide, 1,4-butanediol, N,N-dimethylformamide, ethanol and dimethyl sulfoxide. Etoricoxib exhibits solvation effects, being the preferential solvation parameter δx_1,3, negative in water-rich and cosolvent-rich mixtures but positive in mixtures with similar proportions of both solvents. It is conjecturable that the hydrophobic hydration in water-rich mixtures plays a relevant role in drug solvation. In mixtures of similar solvent proportions where etoricoxib is preferentially solvated by the cosolvents, the drug could be acting as Lewis acid with the more basic cosolvents. Finally, in cosolvent-rich mixtures the preferential solvation by water could be due to the more acidic behaviour of water. Nevertheless, the specific solute–solvent interactions in the different binary systems remain unclear because no relation between preferential solvation magnitude and cosolvent polarities has been observed.     

Solvation of halide ions and the iodine molecule in binary mixtures of water + oxydipropionitrile application to extraction

In water-rich mixtures, the addition of oxydipropionitrile (ODPN) does not alter the solvation of halide ions, they are preferentially solvated by water. In ODPN-rich media, the addition of water to the poor solvent increases the solvation of halide ions by forming hydrogen bonds with water molecules. The iodine molecule is solvated mainly by ODPN and addition of water to the solvent has little influence. The triiodide complex, a highly polarisable species behaves in the same way as the iodine molecule. On demixing, the halide ions are solvated in a similar way in the water-rich phase and very differently in the solvent-rich phase. Advantage is taken of this property to extract cationic complexes quantitatively from their aqueous solutions with ODPN.     

Effect of Base–Acid Properties of Mixtures of Ethanol with Water on the Enthalpy of Solution of Cyclic Ethers in these Mixtures at <Emphasis Type="Italic">T</Emphasis> = 298.15 K

The enthalpies of solution of the cyclic ethers 1,4-dioxane, 12-crown-4 and 18-crown-6 in mixtures of ethanol and water have been measured within the whole mole fraction range at T = 298.15 K. The enthalpy of solvation has been calculated. In pure ethanol and pure water, the solvation enthalpy of the investigated cyclic ethers depends linearity on the number of –CH₂CH₂– groups in the cyclic ether molecules. Based on the analysis of the preferential solvation model proposed by Waghorne, it can be concluded that the 1,4-dioxane, 15C5 and 18C6 molecules are preferentially solvated by water molecules in the range of low water content in these mixtures. The effect of base–acid properties of ethanol–water mixtures on the enthalpy of solution of cyclic ethers in these mixtures has been analyzed. The enthalpy of solution of cyclic ethers correlates with the acidic properties of ethanol–water mixtures in the range of high and medium water content. The results presented are compared with analogous data obtained for the methanol–water and propan-1-ol–water mixtures.     

The Standard Partial Molar Volumes of Ions in Solution. Part 3. Volumes in Solvent Mixtures Where Preferential Solvation Takes Place

Standard partial molar volumes of 1:1 salts in aqueous mixtures of ethanol (EtOH), dimethyl sulfoxide (DMSO) and acetonitrile (MeCN) at 298.15 K were obtained from the literature. In such mixtures there is evidence that preferential solvation occurs in the solvent shell around the ion where electrostriction takes place. Specifically, the anions are better solvated by the water whereas the cations are generally solvated by both the water and the nonaqueous component of the mixtures to various extents. There are no clear-cut criteria for how the measured volumes are to be apportioned between the ions in such mixtures. Various solvation models were used to estimate the volumes of the salts by calculation of the electrostriction around the ions. Only the taking into account of the preferential solvation of the ions in the solvation shell yielded calculated results of the standard partial molar volumes of the salts in agreement with the experimental data.     

Enthalpies of transfer of N-methylformamide,formamide, and N,N-dimethylformamide from methanol to methanol+dimethylsulfoxide mixtures

The enthalpies of transfer of formamide, N-methylformamide and N,N-dimethylformamide from methanol to methanol+dimethylsulfoxide solvent systems have been measured. These data are analysed in terms of a recently developed model of solvation in mixed solvents. The results of the data analyses indicate that preferential solvation of the different functional groups of the amides differs, the carbonyl oxygen being preferentially solvated by methanol and the nitrogen protons are by dimethylsulfoxide.     

Spectral investigations of preferential solvation and solute-solvent interactions of 1,4-dimethylamino anthraquinone in CH2Cl2/C2H5OH mixtures

The optical absorption and IR spectra of 1,4-dimethylamino anthraquinone (1,4-DMAAQ) in CH(2)Cl(2)/C(2)H(5)OH mixtures have been investigated. The preferential solvation of 1,4-DMAAQ in CH(2)Cl(2)/C(2)H(5)OH mixed solvents has been studied by monitoring the charge transfer band of 1,4-DMAAQ. The optical absorption spectral study indicates that 1,4-DMAAQ is preferentially solvated by CH(2)Cl(2) in CH(2)Cl(2)/C(2)H(5)OH mixtures. This can be confirmed by the observed index of preferential solvation value (delta(s1)) as well as higher mole fraction of CH(2)Cl(2) in the solvation microsphere (x(1)(L)) than in the bulk solvent (x(1)). The CH(2)Cl(2) molecules become more available to enter the solvation shell of 1,4-DMAAQ because of the hydrogen bonded clusters formed by ethanol molecules. This is also evident from the non-linear behavior of the transition energy (E(12)) as well as the absence of synergistic behavior. IR spectral studies show that the observed shifts in the nu(CO) and nu(NH) of 1,4-DMAAQ are due to the dipole-dipole interaction between the 1,4-DMAAQ and the associated ethanol.     

A first principles molecular dynamics study of lithium atom solvation in binary liquid mixture of water and ammonia: structural, electronic, and dynamical properties

The preferential solvation of solutes in mixed solvent systems is an interesting phenomenon that plays important roles in solubility and kinetics. In the present study, solvation of a lithium atom in aqueous ammonia solution has been investigated from first principles molecular dynamics simulations. Solvation of alkali metal atoms, like lithium, in aqueous and ammonia media is particularly interesting because the alkali metal atoms release their valence electrons in these media so as to produce solvated electrons and metal counterions. In the present work, first principles simulations are performed employing the Car-Parrinello molecular dynamics method. Spontaneous ionization of the Li atom is found to occur in the mixed solvent system. From the radial distribution functions, it is found that the Li(+) ion is preferentially solvated by water and the coordination number is mostly four in its first solvation shell and exchange of water molecules between the first and second solvation shells is essentially negligible in the time scale of our simulations. The Li(+) ion and the unbound electron are well separated and screened by the polar solvent molecules. Also the unbound electron is primarily captured by the hydrogens of water molecules. The diffusion rates of Li(+) ion and water molecules in its first solvation shell are found to be rather slow. In the bulk phase, the diffusion of water is found to be slower than that of ammonia molecules because of strong ammonia-water hydrogen bonds that participate in solvating ammonia molecules in the mixture. The ratio of first and second rank orientational correlation functions deviate from 3, which suggests a deviation from the ideal Debye-type orientational diffusion. It is found that the hydrogen bond lifetimes of ammonia-ammonia pairs is very short. However, ammonia-water H-bonds are found to be quite strong when ammonia acts as an acceptor and these hydrogen bonds are found to live longer than even water-water hydrogen bonds.     

Characterization of metal ions in coordinating solvent mixtures by means of Raman spectroscopy.

Titration Raman spectroscopy has been developed for studying the solvation structure of metal ions in solution. The method affords us the solvation number, and the value thus obtained in neat solvents is in good agreement with that determined by EXAFS. The method is then applied to solvent mixtures, and the individual solvation number for each solvent is extracted. In a solvent mixture of N,N-dimethylformamide (DMF) and N,N,N',N'-tetramethylurea (TMU), the metal ion prefers DMF to TMU, which is ascribed to the solvation steric effect. The same applies also for the solvent mixture of N,N-dimethylpropionamide (DMPA) and DMF. However, unlike TMU, DMPA changes its conformation from the planar cis to non-planar staggered upon solvation to the metal ion. The enthalpy for the conformational change of DMPA is positive in the bulk, while it is significantly negative in the coordination sphere of the manganese(II) ion. Here, we briefly describe the procedure of measurements and analyses for the titration Raman spectroscopy, and review the solvation structure of the alkaline earth, first transition metal(II) and lanthanide(III) ions in some solvent mixtures in view of solvation steric effect.     

Individual solvation numbers around the nickel(II) ion in an N,N-dimethylformamide and N,N-dimethylacetamide mixture determined by Raman spectrophotometry.

Individual solvation numbers around the nickel(II) ion have been determined by titration Raman spectroscopy in N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) mixtures at 298 K. The in-plane bending vibration (delta(O=C-N)) of DMF and the stretching vibration (v(N-CH3)) of DMA were used in the present analysis. These Raman bands of solvent molecules shift to higher frequencies upon coordination of the solvent molecules to the metal ion. By analyzing the band intensities of free and bound solvent molecules with increasing concentration of the metal ion, the solvation number around the metal ion can be evaluated. Because the individual solvation numbers of DMF and DMA around the nickel(II) ion in the mixture are determined independently, the total solvation number is obtained as their sum. It was found that the total solvation number remains 6 in all mixtures of the DMA mole fraction x = 0 - 1. Although DMF and DMA have practically the same electron-pair donor capacities, the nickel(II) ion prefers DMF to DMA, and an equal solvation number is attained at x = 0.75. This is ascribed to the solvation steric effect of DMA.