Solvation

The Henry's Law constants of CO2, CH4 and N2 in 2701 ionic liquids (ILs) of widely varying structures at (283.15, 298.15, and 323.15) K, the molar volumes and the relative polarity of ILs at 298.15 K are predicted using the thermodynamic method COSMO-RS. Structural variations in the cations and anions that enhance or diminish solubility and selectivity are identified. The trends in Henry's Law constants are explained in the light of molecular interactions qualitatively through sigma profiles and sigma-potentials of ILs. The relationships between the Henry's Law constants and the properties of ionic liquids are also investigated. In general, the Henry's Law constants of CO2 decrease with increase in molar volume, and decrease in polarity of ILs. Both the solubility of CO2 and selectivity decrease as temperature is increased. Activity coefficients at infinite dilution, enthalpies and entropies of solvation are also used to elucidate gas–liquid interactions. COSMOtherm ...

An understanding of molecular interactions is essential for insight into biological systems at the molecular scale. Among the various components of molecular interactions, electrostatics are of special importance because of their long-range nature and their influence on polar or charged molecules, including water, aqueous ions, proteins, nucleic acids, carbohydrates, and membrane lipids. In particular, robust models of electrostatic interactions are essential for understanding the solvation properties of biomolecules and the effects of solvation upon biomolecular folding, binding, enzyme catalysis, and dynamics. Electrostatics, therefore, are of central importance to understanding biomolecular structure and modeling interactions within and among biological molecules. This review discusses the solvation of biomolecules with a computational biophysics view toward describing the phenomenon. While our main focus lies on the computational aspect of the models, we provide an overview of t...

The solubilities of the analgesic drug meloxicam (MEL) in ethanol + water cosolvent mixtures were determined at several temperatures from 293.15 to 313.15 K. The Gibbs energy, enthalpy, and entropy of solution and of mixing were obtained from these solubility data. The solubility was maximal in 0.85 mass fraction of ethanol at several temperatures and very low in pure water at all the temperatures studied. A non-linear plot of ΔHsoln0 vs. ΔGsoln0 with negative slope from pure water up to 0.85 mass fraction of ethanol and positive beyond this composition up to neat ethanol was obtained. Accordingly, the driving mechanism for MEL solubility in almost all mixtures is the entropy, probably due to water-structure loss around the drug non-polar moieties caused by the ethanol. The preferential solvation of MEL by the components of the solvent was estimated by means of the quasi-lattice quasi-chemical and by the inverse Kirkwood–Buff integral method, showing the preferential solvation of MEL by ethanol except at very low water contents, where water preferentially solvates the drug.► Solubility of meloxicam in ethanol + water mixtures is highly dependent on solvent composition. ► The driving mechanism for meloxicam dissolution is the entropy in almost all mixtures. ► Meloxicam is preferentially solvated by ethanol except at very low water contents.

An investigation of the interrelationship of cycling performance, solution structure, and electrode surface film structure has been conducted for electrolytes composed of different concentrations of LiPF6 in propylene carbonate (PC) with a binder-free (BF) graphite electrode. Varying the concentration of LiPF6 changes the solution structure, altering the predominant mechanism of electrolyte reduction at the electrode interface. The change in mechanism results in a change in the structure of the solid electrolyte interface (SEI) and the reversible cycling of the cell. At low concentrations of LiPF6 in PC (1.2 M), electrochemical cycling and cyclic voltammetry (CV) of BF graphite electrodes reveal continuous electrolyte reduction and no lithiation/delithiation of the graphite. The solution structure is dominated by solvent-separated ion pairs (Li+(PC)4//PF6–), and the primary reduction product of the electrolyte is lithium propylene dicarbonate (LPDC). At high concentrations of LiPF6 in PC (3.0–3.5 M), electrochemical cycling and CV reveal reversible lithiation/delithiation of the graphite electrode. The solution structure is dominated by contact ion pairs (Li+(PC)3PF6–), and the primary reduction product of the electrolyte is LiF.

We have quantum chemically investigated how solvation influences the competition between the SN2 and E2 pathways of the model F– + C2H5Cl reaction. The system is solvated in a stepwise manner by going from the gas phase, then via microsolvation of one to three explicit solvent molecules, then last to bulk solvation using relativistic density functional theory at (COSMO)-ZORA-OLYP/QZ4P. We explain how and why the mechanistic pathway of the system shifts from E2 in the gas phase to SN2 upon strong solvation of the Lewis base (i.e., nucleophile/protophile). The E2 pathway is preferred under weak solvation of the system by dichloromethane, whereas a switch in reactivity from E2 to SN2 is observed under strong solvation by water. Our activation strain and Kohn–Sham molecular orbital analyses reveal that solvation of the Lewis base has a significant impact on the strength of the Lewis base. We show how strong solvation furnishes a weaker Lewis base that is unable to overcome the high characteristic distortivity associated with the E2 pathway, and thus the SN2 pathway becomes viable.

A Raman spectroscopic study was carried out on water in gelatin at 4% w/v in gel (25 °C) and sol (40–60 °C) states at various concentrations (0.5, 1, 5, 10 and 15 mM) of anionic surfactant, sodium dodecyl sulfate (SDS). The in-phase collective stretching mode vibration of hydrogen-bonded -OH oscillators, centered around 3250 cm−1 in a tetrahedral network of water molecules, was observed to be significantly affected by temperature and the presence of SDS. According to our observation this may be due to the thinning of the hydration water around the gelatin molecules due to strong thermal agitation. The peak center of the collective bands of water decreased linearly with SDS concentration in the gel state which implied that with the increase in concentration of SDS, the -OH oscillators gradually lost their attachment to gelatin chains and were replaced by SDS molecules. Ultimately this resulted in a thinning of the hydration layer around the gelatin and the oscillation frequency of -OH oscillators moved towards 3250 cm−1 at 1 mM SDS concentration resulting in increased coupling of -OH oscillators to form the tetrahedral network at the critical micelle concentration (cmc) of SDS. The variation in the peak amplitudes and the systematic reversal of their trend about the cmc axis was surprising. At 40 °C the amplitude of the peak at 3250 cm−1 increased drastically due to a possible coil expansion by about 7–8% which accommodated more interstitial water into the pseudonetwork leading to an increase in the number of nearest neighbors and for about 6% increase in the C value. However, at the cmc the peak amplitude was observed to be independent of temperature. Continuous shifting of the peak center and full width at half-maxima towards lower values was observed with increasing SDS concentrations in the gel state.