Liquids, Volume 4, Issue 1 (March 2024) – 14 articles

Solvation properties are key for understanding the interactions between solvents and solutes, making them critical for optimizing chemical synthesis and biochemical applications. Designable solvents for targeted optimization of these end-uses could, therefore, play a big role in the future of the relevant industries. The tailorable nature of protic ionic liquids (PILs) as designable solvents makes them ideal candidates. By alteration of their constituent structural groups, their solvation properties can be tuned as required. The solvation properties are determined by the polar and non-polar interactions of the PIL, but they remain relatively unknown for PILs as compared to aprotic ILs and their characterization is non-trivial. Here, we use solvatochromic dyes as probe molecules to investigate the solvation properties of nine previously uncharacterized alkyl- and dialkylammonium PILs. These properties include the Kamlet–Aboud–Taft (KAT) parameters: π* (dipolarity/polarizability), α (H-bond acidity) and β (H-bond basicity), along with the E_T(30) scale (electrophilicity/polarizability). We then used molecular dynamics simulations to calculate the radial distribution functions (RDF) of 21 PILs, which were correlated to their solvation properties and liquid nanostructure. It was identified that the hydroxyl groups on the PIL cation increase α, π* and E_T(30), and correspondingly increase the cation–anion distance in their RDF plots. The hydroxyl group, therefore, reduces the strength of the ionic interaction but increases the polarizability of the ions. An increase in the alkyl chain length on the cation led to a decrease in the distances between cations, while also increasing the β value. The effect of the anion on the PIL solvation properties was found to be variable, with the nitrate anion greatly increasing π*, α and anion–anion distances. The research presented herein advances the understanding of PIL structure–property relationships while also showcasing the complimentary use of molecular dynamics simulations and solvatochromic analysis together. Full article

The solvent-dependent intensity changes in the first UV/Vis absorption band of the three polyenes DPH, DPHb, and ttbP3 dissolved in a hydrocarbon solvent with temperature allow for the conclusion that, at temperatures above 233 K, the two phenyl groups of DPH are rotated out-of-plane to yield a non-coplanar molecular structure. This leads to the conclusion that DPH becomes increasingly less coplanar as the temperature rises above 233 K. When the phenyl groups rotate out-of-plane, the polarizability decreases, and the energy of the first electronic transition increases by an extra value. Therefore, below 233 K, the correlation lines between the absorption energy of the 0–0 component of the UV/Vis absorption band and the solvent polarizability, as measured by the SP values, show bilinear behavior. The unexpected behavior shown by DPH dissolved in tetrachloro- and dichloromethane is discussed. We dedicate this research as a tribute to the very important contribution to the solvent effect made by Prof. Christian Reichardt and also to his generous and altruistic scientific help that he has always shown. Full article

A computational model that can accurately describe the thermodynamics of a hydrocarbon system and its properties under various conditions is a prerequisite for running reservoir and pipeline simulations. Cubic Equations of State (EoS) are mathematical tools used to model the phase and volumetric behavior of reservoir fluids when compositional effects need to be considered. To anticipate uncertainty and enhance the quality of their predictions, EoS models must be adjusted to adequately match the available lab-measured PVT values. This task is challenging given that there are many potential tuning parameters, thus leading to various tuning results of questionable validity. In this paper, we present an automated EoS tuning workflow that employs a Generalized Pattern Search (GPS) optimizer for efficient tuning of a cubic EoS model. Specifically, we focus on the Peng–Robinson (PR) model, which is the oil and gas industry standard, to accurately capture the behavior of diverse multicomponent, complex hydrocarbon mixtures encountered in subsurface reservoirs. This approach surpasses the limitations of conventional gradient-based (GB) methods, which are susceptible to getting trapped in local optima. The proposed technique also allows physical constraints to be imposed on the optimization procedure. A gas condensate and an H₂S-rich oil were used to demonstrate the effectiveness of the GPS algorithm in finding an optimized solution for high-dimensional search spaces, and its superiority over conventional gradient-based optimization was confirmed by automatically tracking globally optimal and physically sound solutions. Full article

Assessment of the environmental impact of organic chemicals has become an important subject in chemical science. Efficient quantitative descriptors of their impact are their partition coefficients logP_ow, logK_oa and logK_aw. We present a group-additivity method that has proven its versatility for the reliable prediction of many other molecular descriptors for the calculation of the first two partition coefficients and indirectly of the third with high dependability. Based on the experimental logP_ow data of 3332 molecules and the experimental logK_oa data of 1900 molecules at 298.15 K, the respective partition coefficients have been calculated with a cross-validated standard deviation S of only 0.42 and 0.48 log units and a goodness of fit Q² of 0.9599 and 0.9717, respectively, in a range of ca. 17 log units for both descriptors. The third partition coefficient logK_aw has been derived from the calculated values of the former two descriptors and compared with the experimentally determined logK_aw value of 1937 molecules, yielding a standard deviation σ of 0.67 log units and a correlation coefficient R² of 0.9467. This approach enabled the quick calculation of 29,462 logP_ow, 27,069 logK_oa and 26,220 logK_aw values for the more than 37,100 molecules of ChemBrain’s database available to the public. Full article

The UV/Vis absorption energies (ν_max) of different solvatochromic probes measured in co-solvent/water mixtures are re-analyzed as a function of the average molar concentration (N_av) of the solvent composition compared to the use of the mole fraction. The empirical E_T(30) parameter of Reichardt’s dye B30 is the focus of the analysis. The Marcus classification of aqueous solvent mixtures is a useful guide for co-solvent selection. Methanol, ethanol, 1,2-ethanediol, 2-propanol, 2-methyl-2-propanol, 2-butoxyethanol, formamide, N-methylformamide (NMF), N,N-dimethylformamide (DMF), N-formylmorpholine (NFM), 1,4-dioxane and DMSO were considered as co-solvents. The E_T(30) values of the binary solvent mixtures are discussed in relation to the physical properties of the co-solvent/water mixtures in terms of quantitative composition, refractive index, thermodynamics of the mixture and the non-uniformity of the mixture. Significant linear dependencies of E_T(30) as a function of N_av can be demonstrated for formamide/water, 1,2-ethanediol/water, NMF/water and DMSO/water mixtures over the entire compositional range. These mixtures belong to the group of solvents that do not enhance the water structure according to the Marcus classification. The influence of the solvent microstructure on the non-linearity E_T(30) as a function of N_av is particularly clear for alcohol/water mixtures with an enhanced water structure. Full article

This article contains a comparative spectral analysis corroborated with the quantum mechanical computations of four cycloimmonium ylids. The spectral shift of the visible electronic absorption band of the studied molecules in 20 solvents with different empirical parameters is expressed by linear multi-parametric dependences that emphasize the intramolecular charge transfer (ICT) process. The nature of molecular interactions and their contribution to the spectral shift of the visible ICT band of solutes are also established in this manuscript. The results of the statistical analysis are used to estimate the cycloimmonium ylids’ excited dipole moment by the variational method, using the hypothesis of McRae. The importance of the structure of both the heterocycle and carbanion substituents to the stability and reactivity of the studied cycloimmonium ylids is underlined by the quantum mechanical computations of the molecular descriptors. Full article

Catalan’s SPP^N, a measure of solvent polarity/polarizability has been analysed in terms of molecular properties derived from computational chemistry. The results show that SPP^N correlates positively with the molecular dipole moment and quadrupolar amplitude and negatively with the molecular polarizability. These correlations are shared with Kamet and Taft’s π* and Reichardt and Dimroth’s E_T(30). Thus, one can associate the solvent polarity with non-specific interactions involving the permanent charges on solvent molecules. It is also noted that the opposite correlations, all three parameters increasing with increasing solvent polarity but decreasing with increasing solvent polarizability, creates an ambiguity in their use, for example, in linear free energy relationships. Full article

The intramolecular charge transfer behavior of push–pull dyes is the origin of their sensitivity to environment. Such compounds are of interest as probes for bioimaging and as biosensors to monitor cellular dynamics and molecular interactions. Those that are solvatochromic are of particular interest in studies of lipid dynamics and heterogeneity. The development of new solvatochromic probes has been driven largely by the need to tune desirable properties such as solubility, emission wavelength, or the targeting of a particular cellular structure. DFT calculations are often used to characterize these dyes. However, if a correlation between computed (dipole moment) and experimentally measured solvatochromic behavior can be established, they can also be used as a design tool that is accessible to students. Here, we examine this correlation and include case studies of the effects of probe modifications and conformation on dipole moments within families of solvatochromic probes. Indeed, the ground state dipole moment, an easily computed parameter, is correlated with experimental solvatochromic behavior and can be used in the design of new environment-sensitive probes before committing resources to synthesis. Full article

The thermodynamic and kinetic contributions to the over-extraction of extractables by nonpolar organic solvents relative to biological lipids in exhaustive and exaggerated extractions of medical devices are studied based on the Abraham solvation model and solvent–material interactions, using low-density polyethylene (LDPE) as an exemplary material. The thermodynamic effect is evaluated by the partition constant of extractables between LDPE and extraction solvents, hexane and lipids, defined as the concentration in the polymer phase divided by the concentration in the solvent phase. The Abraham solvation model is used to correlate the measured LDPE-lipid partition constant ($lo{g}_{10}{P}_{ldpe/lipid}$) to construct the predictive model. Similar models are also derived from the thermodynamic cycle conversion, using the system constants of LDPE-water and Lipid-water partition systems. These constructed models, together with the predictive LDPE-hexane ($lo{g}_{10}{P}_{ldpe/hexane}$) model established from a previous study, are used to predict and compare the ranges and values of $P_{ldpe/s}$ (s = lipids and hexane) for the observed LDPE extractables over a wide hydrophobicity range in $lo{g}_{10}{P}_{o/w}$ from zero to 30. The solvent-LDPE interactions are examined by the degree of swelling of LDPE by hexane (or other nonpolar solvents) and lipids, including the solvent diffusion rates into the material. These parameters allow the evaluation of kinetic effect on the over-extraction. The extent of over-extraction is compiled directly by experimental “overall” or “specific” migration data or indirectly calculated by the diffusion coefficient of extractables when extracted by hexane or lipids. It is concluded from this study that the extractables distribution between LDPE and lipids highly favors the lipid phase thermodynamically ($P_{ldpe/lipid}<1$), and the values of $P_{ldpe/lipid}$ are always lower than those of $P_{ldpe/hexane}$, thereby indicating that the thermodynamic effect is not the cause of over-extraction. It is the kinetic effect that dominantly contributes to the over-extraction, as supported by the material swelling and solvent diffusion rates. Finally, the extent of over-extraction has been established from a few folds to over a hundred-fold, and the median value is 7. Furthermore, the methods adopted and developed in this study can be invaluable tools in other disciplines such as the reliable prediction of extractables from other device materials and environmental sampling. Full article

This short review describes the expansion of the solvatochromic approach utilizing water-soluble solvatochromic dyes to the analysis of solvent features of aqueous media in solutions of various compounds. These solvent features (polarity/dipolarity, hydrogen bond donor ability (HBD acidity), and hydrogen bond acceptor ability (HBA basicity)) vary depending on the nature and concentration of a solute. Furthermore, the solvent features of water (the solvent dipolarity/polarizability and hydrogen bond donor ability) in solutions of various compounds describe multiple physicochemical properties of these solutions (such as the solubility of various compounds in aqueous solutions, salting-out and salting-in constants for polar organic compounds in the presence of different inorganic salts, as well as water activity, osmotic coefficients, surface tension, viscosity, and the relative permittivity of aqueous solutions of different individual compounds) and are likely related to changes in the arrangement of hydrogen bonds of water in these solutions. Full article

Molecular dynamics simulations have been used to investigate the structural changes in confined liquids. The density distribution functions for weakly and strongly interacting liquids were determined and compared to those of a non-interacting system in order to assess the impact of the entropic forces on the equilibrium state of the systems. The effect of the entropic forces was assessed by quantifying the layering on the liquid structure upon confinement. The more pronounced layering obtained for weakly interacting and non-interacting systems indicated that entropic forces are more effective in these systems where an increase in the multiplicity of states does not require a prohibitively high cost in energy. Full article

Many reactions are carried out in solvent mixtures, mainly because of practical reasons. For example, E2 eliminations are favored over S_N2 substitutions in aqueous organic solvents because the bases are desolvated. This example raises the question: how do we chose binary solvents to favor reaction outcomes? This important question is deceptively simple because it requires that we understand the details of all interactions within the system. Solvatochromism (solvent-dependent color change of a substance) has contributed a great deal to answer this difficult question, because it gives information on the interactions between solvents, solute-solvent, and presumably transition state-solvent. This wealth of information is achieved by simple spectroscopic measurements of selected (solvatochromic) substances, or probes. An important outcome of solvatochromism is that the probe solvation layer composition is almost always different from that of bulk mixed solvent. In principle, this difference can be exploited to “tune” the composition of solvent mixture to favor the reaction outcome. This minireview addresses the use of solvatochromic probes to quantify solute-solvent interactions, leading to a better understanding of the complex effects of solvent mixtures on chemical phenomena. Because of their extensive use in chemistry, we focus on binary mixtures containing protic-, and protic-dipolar aprotic solvents. Full article

This review article is devoted to the colloidal properties of fullerene solutions. According to generally accepted understandings, all solvents in relations to fullerenes are divided into “good”, “poor”, and “reactive”. We have consistently considered the state of fullerenes in these systems. In “good”, predominantly non-polar aromatic solvents and CS₂, non-equilibrium dissolution methods lead to the formation of colloidal aggregates, whereas the utilization of equilibrium methods results in the formation of molecular solutions. The latter, however, have some unusual properties; new results considered in this review confirm previously expressed ideas about colloidal properties of these solutions. In “poor” (polar) solvents, lyophobic colloidal systems appear. Both “bottom-up” and “top-down” methods of preparation are well documented in the literature. However, N-methylpyrrolidine-2-one, DMSO, and DMF dissolve fullerenes quite easily and with less energy consumption. These solvents can be considered a subset of “poor” solvents that have some features of being “reactive” at the expense of basic properties. New data confirm that hydrosols of fullerenes are typical hydrophobic colloids that obey the Schulze–Hardy rule and other regularities in the presence of electrolytes. Organosols in acetonitrile and methanol are much less stable with respect to the effects of electrolytes. This allows us to assume a non-DLVO stabilizing factor in the hydrosols. Accordingly, a new estimate of the Hamaker constant of fullerene–fullerene interaction is proposed. In DMSO and DMF, the coagulation of fullerene sols is hindered due to strong solvation with these basic solvents. Full article

The pivotal role of proteins in pharmaceuticals is challenged by stability issues, making the study of inclusion bodies—a source of insoluble protein aggregates—increasingly relevant. This review outlines the critical procedures in inclusion body processing, focusing on ’mild solubilization concepts’ and refolding methodologies. Attention is afforded to the emerging role of ionic liquids with unique and tunable physicochemical properties in optimizing protein unfolding and refolding processes. The review critically assesses the existing literature at the intersection of inclusion bodies and ionic liquids, identifying recent advancements, potential applications, and avenues for future research. This comprehensive analysis aims to elucidate the complexities in efficient protein processing from inclusion bodies. Full article