Liquids, Volume 5, Issue 3 (September 2025) – 7 articles

Experimental data on the folding and unfolding of small globular proteins are often well described assuming a two-state equilibrium process. It means that after careful analysis by a combination of experimental techniques, only folded and unfolded states of the protein are found to be populated under various external conditions with no detectable intermediates. One of the consequences of the two-state behavior is that the equilibrium ratio of the folded to unfolded protein states follows a simple thermodynamic relation, and the enthalpy difference between states can be obtained from the temperature dependence of the equilibrium constant. In this paper, we theoretically investigate the criteria for the two-state equilibrium behavior and discuss the thermodynamic constraint on the properties of the “hidden” folding intermediates. The literature data on the folding mechanism of lysozyme in water and glycerol, which follows a two-state equilibrium behavior but includes kinetic intermediates, is analysed in light of this constraint. Full article

Clove oil is an essential oil used in food and pharmaceutical applications, with a market value of 300+ million dollars per year. Microemulsions have been used as effective clove oil delivery vehicles and could also be used to develop new extraction processes from clove buds. Eugenol, the main component of clove oil, is a polar oil that behaves as a surfactant and as an oil. This bifunctional behavior makes formulating clove oil microemulsions a challenging task. Here, we used a version of the Hydrophilic–Lipophilic Difference (HLD) + Net-Average Curvature (NAC) model that incorporates the bifunctional polar oil model to predict and fit the phase behavior of lecithin (surfactant) + polyglycerol-10 caprylate (hydrophilic linker) microemulsions using mixtures of heptane and clove oil as the oil phase. Using HLD-NAC parameters from the literature, the predicted HLD-NAC curves reproduced the expected phase transitions and the trends in Eugenol segregation toward the surfactant layer. Using these literature parameters as an initial guess to fit the experimental phase volumes produced accurate calculated phase volumes, and predicted interfacial tensions. This work demonstrates the application of heuristics and databases of HLD-NAC parameters in predicting the complex phase behavior of surfactant–oil–water (SOW) systems. Full article

This paper shows that low concentrations of either a low-molecular-weight or a recyclable polymeric cosolvent can be used to design recyclable, tunable alkane polymeric solvent systems. We have shown that dyes experience a microheterogeneous environment that is ca. 40–50% like that of a polar solvent with as little as 0.1 M added cosolvent. Dyes like Nile red or a polyisobutylene (PIB)-bound dansyl fluorophore both detected microheterogeneity in macrohomogeneous mixtures of heptane or a poly(α-olefin) (PAO) with 0.1–2.0 M added polar solvents. H-Bonding cosolvents have greater effects than cosolvents that only interact with dyes by dipole–dipole interactions. Microheterogeneity was also seen when a PIB-bound version of a low-molecular-weight solvent is used as the added polar cosolvent. These microheterogeneous environments can advantageously be used in synthetic and catalytic reactions. This was demonstrated in transesterification and S_N2 chemistry. Reactions in PAO solutions polarized by 2 M added THF or by 0.5 M of a PIB-bound HMPA analog both had enhanced reactivity versus reactions in a PAO solution without added cosolvent. In the latter case, the catalyst, the PAO solvent, and the PIB-bound cosolvent were all fully recyclable. Full article

Peng–Robinson equation of state (PR EoS) has good prediction accuracy for phase diagrams of pure substances or mixtures, but liquid density, especially for high polar substances, is known to be ~20% lower value compared with experimental data at standard atmospheric temperature and pressure (SATP) conditions. To overcome this issue, translation via entropy-based solubility parameter (eSP) Peng–Robinson EoS (eSPT-PR EoS) is proposed in this work. The technique uses eSP for the liquid phase at SATP conditions and correlates the ideal value and a constant C for each substance as a correction. As a result, the C value can be linearly correlated with critical compressibility factor (Z_C). Finally, the liquid density was improved and gave an average relative deviation (ARD) value of 4.2% for the generally used 27 chemicals selected at SATP condition. Furthermore, critical density was also improved and gave ARD values of 3.9% compared with the original PR EoS of 21.8%. Thus, a universal calculation method based on PR EoS was developed for improving liquid density representation with the eSPT-PR EoS. Full article

The utilisation of empirical correlations for the estimation of thermodynamic functions is a valuable approach for reducing experimental effort and for validating existing data. Established correlations and group contribution methods provide reliable heat capacity estimates for simple organic compounds. The present work assesses the extent of deviations introduced by employing conventional heat capacity correlations for diols. For this purpose, heat capacity differences between the solid, liquid and gas phases are evaluated based on experimentally determined vapour pressures, enthalpies of vaporisation, heat capacities in the solid and liquid phases, and quantum chemical calculations. It is demonstrated that the structural characteristics of diols result in a significant overestimation of heat capacities when conventional empirical methods are applied. Deviations in the range of 30–50 J·K⁻¹·mol⁻¹ were observed when compared to consistent experimental data. As part of the evaluation, new group contribution parameters were developed for calculating heat capacities in the solid and liquid phases. Based on these improved data, inconsistencies in literature values for enthalpies of vaporisation (on the order of 10–15 kJ mol⁻¹) could be resolved. Furthermore, a new correlation was derived that allows for the reliable prediction of enthalpies of vaporisation for α,ω-alkanediols from pentanediol to decanediol. The resulting data provide significant advantages for the design of technical processes involving diols as renewable sources and for the accurate modelling of their phase behaviour. Full article

This article presents a mini-review of the available data on the thermodynamics of the complexation of amino acids and peptides with some nucleic bases in a buffer medium. Data on changes in thermodynamic parameters (binding constants, Gibbs energy, enthalpy, entropy) during the complexation of nucleic bases with amino acids and peptides as a function of physicochemical properties are given at T = 298.15 K. The effects of complexation on the volumetric properties of nucleic bases, including apparent molar volumes, standard molar volumes, and limiting molar expansibility, over a temperature range of 288.15 to 313.15 K are considered in detail. Differences in the behavior of amino acids and peptides caused by different modes of coordination with nucleic bases are noted. These manifest in the stoichiometry of the formed complexes, the relationship with the acid dissociation constants of carboxyl and amino groups, enthalpy–entropy compensation in the complexation process, the temperature dependence of the transfer volumes, and the effect of hydrophobicity on volumetric characteristics. Full article

Concentrated suspensions exhibit intriguing behaviors under external forces, including vibration and shear. While previous studies have focused primarily on cornstarch suspensions, this paper reports a novel observation that colloidal silica suspensions also exhibit dancing, bouncing, solidification, and melting under vertical vibration. Unlike cornstarch, silica particles offer high stability, controlled size distribution, and tunable surface properties, making them an ideal system for investigating these phenomena. The 70 wt.% aqueous suspensions of spherical silica particles with a diameter of 0.55 μm were subjected to controlled vertical vibration (60–100 Hz, 100–500 m/s²). High-speed video analysis revealed dynamic transitions, including melting, fingering, squirming, fragmentation, and jumping. The solidified suspension retained its shape after vibration ceased but melted upon weak vibration. This study demonstrates that such dynamic state transitions are not exclusive to starch-based suspensions but can also occur in well-defined colloidal suspensions. Our findings provide a new platform for investigating shear-thickening, jamming, and vibrational solidification in suspensions with controllable parameters. Further work is required to elucidate the underlying mechanisms. Full article