Strength Of Solute-solvent Interactions Research Articles

Typical at glance but interesting when analyzed in detail: A story of Tris hydration.

This paper provides results of dielectric relaxation (DR) spectroscopy of aqueous solutions of tris(hydroxymethyl)aminomethane (Tris) covering frequencies of 0.05 ≤ ν/GHz ≤89. The DR spectra can be well fit by a sum of Cole-Cole relaxation, assigned to the solute, and 2Debye modes already observed for neat water. Analysis of the amplitudes reveals that Tris is hydrated by 7 H2Os up to its solubility limit. However, the rather high effective solute dipole moment of ≈12D suggests that H2O dipoles in contact with Tris should reorient independently from it. Accordingly, an alternative description of the DR spectra with a superposition of 4Debyerelaxations was attempted. In this model, the slowest mode at ∼4GHz arises from solute reorientation and that at ∼8GHz was assigned to dynamically retarded hydration water, whereas relaxations at ∼18 and ∼500GHz are again those of (rather unperturbed) bulk water. Analysis of the solvent-related modes shows that Tris indeed slows down 7-8 H2O molecules. However, the solute-solvent interaction strength is rather weak, excluding the rotation of an alleged Tris-(7-8) H2O cluster as an entity. The now derived effective dipole moment of (6.3 ± 0.5) D for the bare Tris molecule allows speculations on its conformation. With the help of computational methods, we suggest that Tris dissolved in water most likely possesses an intramolecular H-bond between the nitrogen and hydrogen atoms of amino and hydroxyl groups, respectively. In addition, computational results indicate that the seven hydration H2Os found by DR bind directly to the Tris OH groups.

Understanding gas absorption in multivalent ionic liquids via solute-solvent interaction analyses

Solute-solvent interactions are often evaluated to understand and explain gas solubilities. This information is regularly used to interpret gas solubility and separation within ionic liquids (ILs). Here, we use several different quantum chemical and previous molecular dynamics simulation results to show that strong solute–solvent interactions neither lead to high solubility nor to high selectivity, with respect to other solutes. Instead, the solute–solvent interaction strength with different isolated IL ions is affected by the electrostatic extremes. Also, the solute–solvent interaction with different IL molecules is strongly correlated to the molecular volumes or polarizabilities (within a series of same-anion based ILs).

Unveiling the self-association and desolvation in crystal nucleation.

As the first step in the crystallization process, nucleation has been studied by many researchers. In this work, phenacetin (PHEN) was selected as a model compound to investigate the relationship between the solvent and nucleation kinetics. Induction times at different supersaturation in six solvents were measured. FTIR and NMR spectroscopy were employed to explore the solvent-solute interactions and the self-association properties in solution. Density functional theory (DFT) was adopted to evaluate the strength of solute-solvent interactions and the molecular conformations in different solvents. Based on these spectroscopy data, molecular simulation and nucleation kinetic results, a comprehensive understanding of the relationship between molecular structure, crystal structure, solution chemistry and nucleation dynamics is discussed. Both the solute-solvent interaction strength and the supramolecular structure formed by the self-association of solute molecules affect the nucleation rate. The findings reported here shed new light on the molecular mechanism of nucleation in solution.

Thermosolvatochromism of 7H-indolo[1,2-a]quinolinium dyes in pure solvents

Thermosolvatochromism of two dyes generated from hydroxyphenyl and hydroxynaphthyl derivatives of 7H-indolo[1,2-a]quinolinium salts was studied in 14 pure solvents with polarities ranging from 155.3 to 249.5 kJ mol−1 according to ET(30) polarity scale. The measurements were carried out at temperatures ranging from −5 °C to 80 °C. The UV–Vis spectra of both compounds were found to be sensitive to temperature changes. In polar solvents, a decrease in temperature caused a hypsochromic shift in the UV–Vis spectrum of the studied dyes. In less polar solvents, a hypsochromic shift in the UV–Vis spectra of hydroxynaphthyl derivative with decreasing temperature was still observed, but in the spectrum of hydroxyphenyl derivative, a bathochromic shift was recorded. The results were compared with the spectral properties of Reichardt's dye. The influence of temperature on the absorption band position of hydroxynaphthyl derivative in many solvents was even greater than that of Reichardt's dye. The strength of solute-solvent interaction, as well as solvatochromic sensitivity and the type of solvatochromism (positive or negative), which the studied dyes exhibited, were taken into account in order to explain the obtained results. The VBHB model appeared to be very useful for interpretation of thermosolvatochromic properties of the studied dyes.

Insight into the role of pre-assembly and desolvation in crystal nucleation: a case of p-nitrobenzoic acid.

As one of the most important phenomena in crystallization, the crystal nucleation process has always been the focus of research. In this work, influences of pre-assembly species and the desolvation process on the crystal nucleation process were studied. p-Nitrobenzoic acid (PNBA) was taken as a model compound to investigate the relationship between solution chemistry and nucleation kinetics in seven different solvents. One unsolvated form and four solvates of PNBA were obtained and one of the solvates was newly discovered. The nucleation behaviours and nucleation kinetics of PNBA in the seven solvents were studied and analyzed. Density functional theory (DFT) and solvation energy calculation were adopted to evaluate the strength of solute-solvent interactions. Vibrational spectroscopy combined with molecular simulation was applied to reveal the pre-assembly species in the solution. Based on these results, a comprehensive understanding of the relationship between molecular structure, crystal structure, solution chemistry and nucleation dynamics was proposed and discussed. It was found that the structural similarity between solution chemistry and crystal structure, the interaction between specific sites and the overall strength of solvation will jointly affect the nucleation process.

Uncovering the solubility behavior of vitamin B6 hydrochloride in three aqueous binary solvents by thermodynamic analysis and molecular dynamic simulation

Solubility of vitamin B6 hydrochloride (VB6H) in three water-organic binary mixed solvents from 278.15 K to 313.15 K at atmospheric pressure was investigated by experiments and molecular simulations. The solvation free energy suggests that the solubility of VB6H increases with solute-solvent interaction strength increasing and there exists the strongest interaction energy at co-solvency composition in binary solvents. Radial distribution function (RDF) shows the tendency to aggregation of two solvent molecules as the molar fraction of organic solvent in mixtures increases, which suggests, to some extent, the interaction between solute and solvent molecules would be weaken and the solubility of VB6H decreases. It could be concluded that the solubility behavior of VB6H is a result from both solute-solvent and solvent-solvent interactions. Then the experimental data were correlated by the modified Apelblat model, the λh model, the CNIBS/R–K model and the NRTL model, respectively. And all of the models present a good consistency with the data. Furthermore, the calculations of mixing thermodynamic properties show that the mixing process of VB6H in the investigated solvents is exothermic and spontaneous. The experimental data can be used as basic data in the industrial production and scientific research of VB6H, a high value-added product. MD simulations and correlation models herein are helpful to understanding of solid-liquid equilibrium of compounds in binary solvent systems, then prediction of solubility which is the target of considerable researches.

Thermophysical properties of ionic liquid, 1‑ethyl-3-methylimidazolium ethyl sulfate in organic solvents at dilute region

This paper reports the density, speed of sound, viscosity and refractive index data of the ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate in some polar organic solvents, 1-propanol, ethanol, methanol and acetonitrile in dilute region of the ionic liquid concentration at temperature ranges T = (288.15 to 318.15) K and at atmospheric pressure. On the basis of density and speed of sound data, the apparent molar volume Vφ and apparent molar isentropic compressibility κφ were calculated. From these quantities and with help of Redlich-Mayer equation, the standard partial molar volumes and partial molar isentropic compressibility were obtained. The obtained parameters show that the strength of solute-solvent interactions. The Jones-Dole equation was used for correlating of viscosity data. In addition, the solvation numbers was estimated using the obtained values for the viscosity B-coefficient and the standard partial molar volume for the systems studied at various temperatures. Molar refractions were obtained by using the Lorentz-loran's equation which used to interpret the polarizability of the solutions.

A Parameterization of Empirical Sigma Enlarging Bridge Correction of Kovalenko-Hirata Closure in Ornstein-Zernike Theory for Lennard-Jones Fluids

Abstract We report the parameter values included in the sigma enlarging bridge (SEB) function for two-component Lennard-Jones fluids within the Ornstein-Zernike (OZ) integral equation framework, which was first proposed in our previous study [T. Miyata, Y. Ebato, J. Molec. Liquids, 217 (2016) 75] to improve the accuracy of the solvation free energy (SFE). In this article, we consider a wide range of thermodynamic states, with varying the solute size and the solute-solvent interaction strength. The SEB parameter was evaluated via the least square fitting of the first rising region of the radial distribution function obtained from OZ theory to that from molecular dynamics simulation. The SEB function was applied to both the hypernetted chain (HNC) and Kovalenko-Hirata (KH) closures. It is found that the SEB parameter increases monotonically with the solute size, whereas it hardly depends on the solute-solvent interaction strength. Also, the performance of bare HNC, bare KH, Percus-Yevick, and Verlet-modified closures are also examined, to report the relationship between the solute volume and the error of the SFE obtained from OZ theory. We found that the SFE errors under both HNC and KH closures are not necessarily proportional to the solute volume.

Communication: Uncovering correlated vibrational cooling and electron transfer dynamics with multidimensional spectroscopy.

Analogues of 2D photon echo methods in which two population times are sampled have recently been used to expose heterogeneity in chemical kinetics. In this work, the two population times sampled for a transition metal complex are transformed into a 2D rate spectrum using the maximum entropy method. The 2D rate spectrum suggests heterogeneity in the vibrational cooling (VC) rate within the ensemble. In addition, a cross peak associated with VC and back electron transfer (BET) dynamics reveals correlation between the two processes. We hypothesize that an increase in the strength of solute-solvent interactions, which accelerates VC, drives the system toward the activationless regime of BET.

A molecular dynamics study of intramolecular proton transfer reaction of malonaldehyde in solution based upon a mixed quantum-classical approximation. II. Proton transfer reaction in non-polar solvent.

The intramolecular proton transfer reaction of malonaldehyde in neon solvent has been investigated by mixed quantum-classical molecular dynamics (QCMD) calculations and fully classical molecular dynamics (FCMD) calculations. Comparing these calculated results with those for malonaldehyde in water reported in Part I [A. Yamada, H. Kojima, and S. Okazaki, J. Chem. Phys. 141, 084509 (2014)], the solvent dependence of the reaction rate, the reaction mechanism involved, and the quantum effect therein have been investigated. With FCMD, the reaction rate in weakly interacting neon is lower than that in strongly interacting water. However, with QCMD, the order of the reaction rates is reversed. To investigate the mechanisms in detail, the reactions were categorized into three mechanisms: tunneling, thermal activation, and barrier vanishing. Then, the quantum and solvent effects were analyzed from the viewpoint of the reaction mechanism focusing on the shape of potential energy curve and its fluctuations. The higher reaction rate that was found for neon in QCMD compared with that found for water solvent arises from the tunneling reactions because of the nearly symmetric double-well shape of the potential curve in neon. The thermal activation and barrier vanishing reactions were also accelerated by the zero-point energy. The number of reactions based on these two mechanisms in water was greater than that in neon in both QCMD and FCMD because these reactions are dominated by the strength of solute-solvent interactions.

Composition and Temperature Dependence of Excess Properties of Binary Mixtures of Imidazolium Based Ionic Liquids: II ([C n mim][PF6]) + Propylamine

The experimental data of densities, ρ, speeds of sound, u, and refractive indices, $$ n_{\text{D}} $$ , for pure ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]) and their binary mixtures with propylamine were measured by an Anton Paar DSA 5000 densimeter and Abbemat 300 refractometer, respectively. The measurements were performed as a function of concentration and at temperatures between 293.15 and 313.15 K and at 0.1 MPa. From these measured values, the excess molar volumes $$ V_{\text{m}}^{\text{E}} $$ , excess molar isentropic compressibilities $$ K_{S,\text{m}}^{\text{E}} $$ , and refractive index deviations $$ \Delta_{\varphi } n_{\text{D}} $$ were derived and correlated with the Redlich–Kister polynomial equation. The values of $$ V_{\text{m}}^{\text{E}} $$ and $$ K_{S,\text{m}}^{\text{E}} $$ are negative and decrease with increase in temperature whereas the $$ \Delta_{\varphi } n_{\text{D}} $$ are positive and increase with temperature for all studied systems. $$ V_{\text{m}}^{\text{E}} $$ and $$ K_{S,\text{m}}^{\text{E}} $$ decrease with increasing alkyl chain length of ILs. The variations in excess properties are discussed with respect to increases in temperature, addition of –CH2 groups in alkyl chain of ILs and the strength of solute-solvent interactions existing in the ILs + amine mixtures. $$ V_{\text{m}}^{\text{E}} $$ was also predicted from the Prigogine–Flory–Patterson theory.

Adsorption of solutes at liquid–vapor interfaces: insights from lattice gas models

The adsorption behavior of ions at liquid-vapor interfaces exhibits several unexpected yet generic features. In particular, energy and entropy are both minimum when the solute resides near the surface, for a variety of ions in a range of polar solvents, contrary to predictions of classical theories. Motivated by this generality, and by the simple physical ingredients implicated by computational studies, we have examined interfacial solvation in highly schematic models, which resolve only coarse fluctuations in solvent density and cohesive energy. Here we show that even such lattice gas models recapitulate surprising thermodynamic trends observed in detailed simulations and experiments. Attention is focused on the case of two dimensions, for which approximate energy and entropy profiles can be calculated analytically. Simulations and theoretical analysis of the lattice gas highlight the role of capillary wave-like fluctuations in mediating adsorption. They further point to ranges of temperature and solute-solvent interaction strength where surface propensity is expected to be strongest.

Water coordination structures and the excess free energy of the liquid

We assess the contribution of each coordination state to the hydration free energy of a distinguished water molecule, the solute water. We define a coordination sphere, the inner-shell, and separate the hydration free energy into packing, outer-shell, and local, solute-specific (chemical) contributions. The coordination state is defined by the number of solvent water molecules within the coordination sphere. The packing term accounts for the free energy of creating a solute-free coordination sphere in the liquid. The outer-shell contribution accounts for the interaction of the solute with the fluid outside the coordination sphere and it is accurately described by a Gaussian model of hydration for coordination radii greater than the minimum of the oxygen-oxygen pair-correlation function: theory helps identify the length scale to parse chemical contributions from bulk, nonspecific contributions. The chemical contribution is recast as a sum over coordination states. The nth term in this sum is given by the probability p(n) of observing n water molecules inside the coordination sphere in the absence of the solute water times a factor accounting for the free energy, W(n), of forming an n-water cluster around the solute. The p(n) factors thus reflect the intrinsic properties of the solvent while W(n) accounts for the interaction between the solute and inner-shell solvent ligands. We monitor the chemical contribution to the hydration free energy by progressively adding solvent ligands to the inner-shell and find that four-water molecules are needed to fully account for the chemical term. For a chemically meaningful coordination radius, we find that W(4) ≈ W(1) and thus the interaction contribution is principally accounted for by the free energy for forming a one-water cluster, and intrinsic occupancy factors alone account for over half of the chemical contribution. Our study emphasizes the need to acknowledge the intrinsic solvent properties in interpreting the hydration structure of any solute, with particular care in cases where the solute-solvent interaction strength is similar to that between the solvent molecules.

The role of specific interactions on dynamical processes in a room temperature ionic liquid

This article describes our ongoing efforts to comprehend the role of specific interactions on the dynamical processes such as rotational diffusion and photoisomerization in a typical room temperature ionic liquid. Rotational diffusion studies carried out with a pair of structurally similar non-dipolar solutes indicate that organic solutes do experience strong specific interactions even with the highly associative ionic liquids such that their rotation is hindered. Similar measurements carried out with a non-polar and a dipolar solute in an ionic liquid and a conventional solvent reveal that even in ionic liquids, apart from the viscosity of the medium, the important parameters, which govern the solute rotation are the solvent-size and free volume in case of non-polar solutes, whereas for charged and dipolar solutes, it is the solute-solvent interaction strength. Photoisomerization studies dealing with a pair of carbocyanine derivatives have shed light on the influence of solvent viscosity and specific interactions on the rates of photoisomerization. Our results point to the fact that the positively charged as well as the negatively charged cyanine derivatives do not experience specific interactions with the ionic liquid such that the isomerization rates are affected. However, when the isomerization rates are compared with a conventional isoviscous solvent, it has been noticed that the rates of isomerization are solely governed by viscosity of the medium in case of the positively charged cyanine derivative. In contrast, photoisomerization rates of the negatively charged cyanine derivative are significantly faster in a conventional isoviscous solvent compared to the ionic liquid due to the specific interactions between the solute and the former, which lower the barrier height for isomerization.

Structural and dynamical properties of a core-softened fluid in a supercritical region

We present a theoretical study of the structural, thermodynamic, and transport properties of a supercritical fluid comprising particles interacting via isotropic attractive core-softened potential. The shear viscosity and self-diffusion coefficient are computed on the basis of the mode-coupling theory, with required structural input obtained from the thermodynamically self-consistent integral equation theory. We also consider dilute solutes in a core-softened fluid and use the anisotropic integral equation theory to obtain the solute-solute potential of mean force, which yields the second virial coefficient. We analyze its dependence on the solvent density and solute-solvent interaction strength.

Solvent density inhomogeneities and solvation free energies in supercritical diatomic fluids: A density functional approach

Density functional theory is used to explore the solvation properties of a spherical solute immersed in a supercritical diatomic fluid. The solute is modeled as a hard core Yukawa particle surrounded by a diatomic Lennard-Jones fluid represented by two fused tangent spheres using an interaction site approximation. The authors' approach is particularly suitable for thoroughly exploring the effect of different interaction parameters, such as solute-solvent interaction strength and range, solvent-solvent long-range interactions, and particle size, on the local solvent structure and the solvation free energy under supercritical conditions. Their results indicate that the behavior of the local coordination number in homonuclear diatomic fluids follows trends similar to those reported in previous studies for monatomic fluids. The local density augmentation is particularly sensitive to changes in solute size and is affected to a lesser degree by variations in the solute-solvent interaction strength and range. The associated solvation free energies exhibit a nonmonotonous behavior as a function of density for systems with weak solute-solvent interactions. The authors' results suggest that solute-solvent interaction anisotropies have a major influence on the nature and extent of local solvent density inhomogeneities and on the value of the solvation free energies in supercritical solutions of heteronuclear molecules.

Vibrational relaxation in ionic liquids and ionic liquid reverse micelles

We report static and ultrafast IR studies of Fe(CN) 5NO 2− and W(CO) 6 in bulk ionic liquids and of ionic liquid reverse micelles. For Fe(CN) 5NO 2− and W(CO) 6 in ionic liquids, the vibrational frequencies appear to scale with solute–solvent interaction strength, but the vibrational energy relaxation (VER) times are longer than in methanol and DMSO. The VER times in the reverse micelles are consistent with a solvation environment that has mixed surfactant and ionic liquid and is more polar than the bulk ionic liquid. These results differ from previous ionic liquid reverse micelle studies.

Dependence of EXAFS (Extended X-Ray Absorption Fine Structure) Parameters of Iodide Anions in Various Solvents upon a Solvent Parameter

Abstract X-ray absorption spectra of I K-edge have been obtained for iodide ions dissolved in various solvents. Oscillation amplitudes of the extended X-ray absorption fine structure (EXAFS) evaluated from the peak intensities in the Fourier-transform spectra were found to correlate with the Mayer-Gutmann acceptor number (AN) of solvents studied. The correlation is quite similar to that for bromide ions, which has already been reported by the same authors (H. Tanida, H. Sakane, and I. Watanabe, J. Chem. Soc., Dalton Trans., 1994, 2321). Such results confirm that the EXAFS method is not only a tool to determine geometrical structures in liquids, but can also be used for evaluating solute-solvent interaction strength, similarly to AN. The I…O distances in protic solvents and I…C in aprotic solvents were determined to be 3.4—3.5 and 3.7—3.8 Å, respectively. In protic solvents, the larger the AN values, the shorter the I…O distances and the larger the co-ordination numbers of I-, which were determined to be 1—4. In aprotic solvents, the co-ordination numbers of I- were found to be 4—8. It seems that aprotic solvents having two methyl groups in a molecule are able to solvate I- through two methyl groups, which is similar to the conclusion reported for Br-.

Effect of solvent, temperature, and pressure on hydrogen bonding and reorientation of water molecules

On the basis of the study of the solvent, temperature, and pressure effects, we show how the NMR rotational correlation times τ 2R for a heavy water molecule in neat liquid and organic solvents are correlated with the strength of solute-solvent interactions, in particular, H bonds. At room temperature (30 °C), the correlation time is 2.1 ps in the random H-bond network in heavy water, whereas it is as small as 0.1 ps in such an apolar, hydrophobic solvent as carbon tetrachloride because of the absence of the H bonds between water molecules. Pressure distorts H bonds and accelerates the orientational motion of water molecules in neat liquid. Firm evidence is collected for the limitations of the Stokes-Einstein-Debye (SED) law in solution.

Dependence of the chemical dynamics of intercluster association reactions on the strength of the solute–solvent intermolecular potential

Classical trajectory calculations are performed to investigate how microscopic solvation influences the H+CH3→CH4 reaction mechanism, rate constant, energetics, product energy, and angular momentum partitioning; and how these solvation effects depend on the solute–solvent interaction strength. Without solvation, the final energy and rotational angular momentum of CH4 strongly depend on the H+CH3 relative translational energy. However, for HAr2+CH3 with a normal H–Ar Lennard-Jones interaction strength εHAr0, a spectator-stripping mechanism dominates the reactive collisions so that both the final CH4 energy and rotational angular momentum do not significantly depend on the relative translational energy. The association cross section to form CH4 is slightly larger for HAr2+CH3 than for H+CH3. When the H–Ar interaction strength for HAr2 is increased from 1 to 100εHAr0, it is found that (1) the association cross section to form CH4 is insensitive to the H–Ar interaction strength, suggesting a long-range transition state; (2) the reaction mechanism changes from a spectator-stripping model to a complex one, which alters the character of the CH4+Ar2 product energy and angular momentum partitioning; and (3) the formation of the Ar2–CH4 complex leads to stabilized CH4 product, with substantial energy transfer from CH4 for the strongest H–Ar interaction strength of 100εHAr0.