Search Results (28)

In this research, we investigate the interaction between the redox mediator ferrocene carboxylic acid (Fc-COOH) and glucose oxidase (GOD) in order to determine the thermodynamics parameters K_int, ΔG_int, ΔH_int, and ΔS_int using simple UV–visible experiments at different temperatures. Positive values of ΔH_int, ΔS_int, together with a negative value of ΔG_int indicate an entropy-driven hydrophobic interaction typical of spontaneous association processes. The homogeneous electron transfer rate constants between the oxidized organometallic mediator and the reduced enzyme (k_s), along with their activation parameters (ΔG_ET^≠, ΔH_ET^≠ and ΔS_ET^≠), were calculated using data obtained from foot of the wave analysis (FOWA) of cyclic voltammetry experiments performed at variable temperature. According to transition state theory, the obtained parameters indicate a low activation enthalpy that reflects minimal energetic requirements for electron transfer, while the large negative activation entropy suggests the formation of an ordered transition state. The positive activation free energy falls within the expected range for biological electron transfer processes. Variable temperature cyclic voltammetry experiments of ferrocene carboxylic acid (Fc-COOH) were also performed. The obtained ΔG°, ΔH°, and ΔS° parameters indicate strong stabilization of the redox pair, consistent with a small difference in solvation energy. Circular dichroism, UV–vis spectroscopy, and combined CD and UV–Vis Spectroelectrochemistry measurements performed during redox mediation demonstrate that no significant structural alterations occur in either the enzyme or the redox mediator before or during the electron transfer processes. Full article

Hydrophilic interaction liquid chromatography (HILIC) is widely used for the analysis of glycans and oligosaccharides, yet the molecular basis of retention remains incompletely understood. In this study, we investigated dextran ladders labelled with 2-aminobenzamide (2-AB) and Rapifluor-MS™ (Waters, Milford, MA, USA) across a wide range of degrees of polymerization (DP 2–15), temperature conditions (10 °C to 70 °C), and gradient programs using a Acquity™ Premier Glycan BEH Amide column (Bridged Ethylene Hybrid, Waters, Milford, MA, USA). Van’t Hoff analysis revealed distinct enthalpic and entropic contributions to retention, allowing identification of a mechanistic transition from enthalpy-dominated docking interactions at low DP to entropy-driven dynamic adsorption at higher DP. This transition occurred reproducibly between DP 4–6, depending on the fluorescent label, while gradient steepness primarily influenced the location of the minimum enthalpy. Molecular dynamics simulations provided additional evidence, showing increased conformational flexibility and end-to-end distance variability for longer oligomers. This finding is consistent with entropy-dominated adsorption accompanied by displacement of structured interfacial water. Together, these results establish a molecular-level framework linking retention thermodynamics, conformational behavior, and solvation effects, thereby advancing our mechanistic understanding of glycan separation in HILIC. Full article

Complexation of alkaline earth metal cations with fluorescent tertiary-amide lower-rim calix[4]arene derivative bearing two phenanthridine moieties was studied experimentally (UV spectrophotometry, fluorimetry, isothermal microcalorimetry, NMR spectroscopy) and computationally (classical molecular dynamics and DFT calculations) at 25 °C. The complexation reactions were studied in acetonitrile, methanol, and ethanol, whereby the solvent effect on cation-binding processes was particularly addressed. The complex stability constants and standard reaction thermodynamic quantities (Gibbs energies, enthalpies, and entropies) were determined. The receptor exhibited particularly high affinity towards alkaline earth metal cations in acetonitrile, with peak affinity for Ca²⁺. The stability of all complexes was significantly lower in ethanol and methanol, where the most stable complex was formed with Sr²⁺. The decrease in cation-binding abilities was a consequence of the differences in solvation of the reactants and products of the complexation reactions (involving inclusion of the solvent molecule in the calixarene cone), cation charge density, as well as the cation–ligand binding site compatibility. The reactions were enthalpically controlled in acetonitrile, whereas in methanol and ethanol, the binding processes were endothermic and thus entropy driven. The results of ¹H NMR measurements, MD simulations, and DFT calculations provided an insight into the structure of the complexes and the corresponding adducts with solvent molecules, as well as the structural aspects behind the differences in complexation thermodynamics. Due to the significant increase in its fluorescence upon cation binding, the studied calixarene derivative was proven to be a promising luminescent sensor for alkaline earth metal cations. Full article

A new method, based on quantum chemical calculations, is proposed for the thermodynamically consistent reformulation of QSPR-type Linear Free-Energy Relationship (LFER) models. This reformulation permits the extraction of valuable information on intermolecular interactions and its transfer in other LFER-type models, in acidity/basicity scales, or even in equation-of-state models. New molecular descriptors of electrostatic interactions are derived from the distribution of molecular surface charges obtained from COSMO-type quantum chemical calculations. The widely used and very successful Abraham’s Linear Solvation Energy Relationship (LSER) model is selected as the reference LSER model for the calculations in solute–solvent systems as well as in solute self-solvation. Hydrogen-bonding free energies, enthalpies, and entropies are now derived for a variety of common solutes. The capacity of the method to address the role of conformational changes in solvation quantities is discussed. The perspectives of the LSER model with the implementation of the new descriptors are also discussed. Full article

This work focused on the solubility of ethane in three promising ionic liquids {1-Hexyl-3-methylimidazolium bis(trifluormethylsulfonyl) imide [HMIM][Tf2N], 1-Butyl-3-methyl-imidazolium dimethyl-phosphate [BMIM][DMP], and 1-Propyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)-imide [PMIM][Tf2N]}. The solubilities were measured at 303.15 K to 343.15 K and pressures up to 1.4 MPa using a gravimetric microbalance. The overall ranking of ethane solubility in the ionic liquids from highest to lowest is the following: [HMIM][Tf2N] > [PMIM][Tf2N] > [BMIM][DMP]. The Peng–Robinson equation of state was used to model the experimental data using three different mixing rules: van der Waals one, van der Waals two, and Wong–Sandler mixing rules combined with the Non-Random Two-Liquid model. The average absolute deviations for the three mixing rules for the ionic liquids at the three temperatures were 4.39, 2.45, and 2.45%, respectively. Henry’s Law constants for ethane in [BMIM] [DMP] were the highest (lowest solubility) amongst other ionic liquids studied in this work. The solubility ranking for the 3 ILs was confirmed by calculating their overall polarity parameter (N) using COSMO-RS. The selectivity of CO₂ over C₂H₆ was estimated at three temperatures, and the overall ranking of the selectivity was in the following order: [PMIM][Tf2N] > [BMIM][DMP] > [HMIM][Tf2N] > Selexol. Selexol is an efficient and widely used physical solvent in gas sweetening. It has lower selectivity than the three ionic liquids studied. [PMIM][Tf2N], a promising solvent, has the highest selectivity among the three ILs studied and would, therefore, be the best choice if, in addition to carbon dioxide capture, ethane co-absorption was to be avoided. The enthalpy and entropy of solvation at infinite dilution were also estimated. Full article

Exploiting the van der Waals model of liquids, it is possible to derive analytical formulas for the thermodynamic functions governing solvation, the transfer of a solute molecule from a fixed position in the ideal gas phase to a fixed position in the liquid phase. The solvation Gibbs free energy change consists of two contributions: (a) the high number density of all liquids and the repulsive interactions due to the basic fact that each molecule has its own body leading to the need to spend free energy to produce an appropriate cavity to contain the solute molecule; (b) the ubiquitous intermolecular attractive interactions lead to a gain in free energy for switching-on attractions between the solute molecule and neighboring liquid molecules. Also the solvation entropy change consists of two contributions: (a) there is an entropy loss in all liquids because the cavity presence limits the space accessible to liquid molecules during their continuous translations; (b) there is an entropy gain in all liquids, at room temperature, due to the liquid structural reorganization as a response to the perturbation represented by solute addition. The latter entropy contribution is balanced by a corresponding enthalpy term. The scenario that emerged from the van der Waals model is in qualitative agreement with experimental results. Full article

Cabozantinib malate (CBZM), a new anticancer medication, has been studied for its solubility and thermodynamic properties in a variety of {dimethyl sulfoxide (DMSO) + water (H₂O)} mixtures at 298.2–318.2 K and 101.1 kPa. Using the shake flask technique, the solubility of CBZM was assessed and the results were correlated to the van’t Hoff, Apelblat, Buchowski–Ksiazczak λh, Yalkowsky–Roseman, Jouyban–Acree, and Jouyban–Acree-van’t Hoff models. There was a significant correlation between the experimental CBZM solubility data and all computational models, as evidenced by the error values for all computational models being less than 5.0%. Temperature and DMSO mass percentage improved the CBZM mole fraction solubility in the cosolvent solutions of {DMSO + H₂O}. At 318.2 K, pure DMSO had the highest mole fraction solubility of CBZM (4.38 × 10⁻²), whereas pure H₂O had the lowest mole fraction solubility (2.24 × 10⁻⁷ at 298.2 K). The positive values of computed thermodynamic parameters indicated that the dissolution of CBZM was endothermic and entropy-driven in all of the {DMSO + H₂O} solutions investigated. It was found that the CBZM solvation in {DMSO + H₂O} solutions is governed by enthalpy. When compared to CBZM-H₂O, CBZM-DMSO showed the highest molecular interactions. The findings of this investigation demonstrated that DMSO has a great deal of potential for CBZM solubilization in H₂O. Full article

The solubility and solution thermodynamics of isotretinoin (ITN) (3) in numerous {dimethyl sulfoxide (DMSO) (1) + water (H₂O) (2)} combinations were studied at 298.2–318.2 K under fixed atmospheric pressure of 101.1 kPa. A shake flask methodology was used to determine ITN solubility, and correlations were made using the “van’t Hoff, Apelblat, Buchowski-Ksiazczak λh, Yalkowsky-Roseman, Jouyban-Acree, and Jouyban-Acree-van’t Hoff models”. In mixtures of {(DMSO (1) + H₂O (2)}, the solubility of ITN in mole fractions was enhanced with the temperature and DMSO mass fraction. The mole fraction solubility of ITN was highest in neat DMSO (1.02 × 10⁻¹ at 318.2 K) and lowest in pure H₂O (3.14 × 10⁻⁷ at 298.2 K). The output of computational models revealed good relationships between the solubility data from the experiments. The dissolution of ITN was “endothermic and entropy-driven” in all of the {(DMSO (1) + H₂O (2)} mixtures examined, according to the positive values of measured thermodynamic parameters. Enthalpy was discovered to be the driving force behind ITN solvation in {(DMSO (1) + H₂O (2)} combinations. ITN-DMSO displayed the highest molecular interactions when compared to ITN-H₂O. The outcomes of this study suggest that DMSO has a great potential for solubilizing ITN in H₂O. Full article

Protein unfolding is a ubiquitous process responsible for the loss of protein functionality (denaturation), which, in turn, can be accompanied by the death of cells and organisms. The nature of enthalpy–entropy compensation (EEC) in the kinetics of protein unfolding is a subject of debate. In order to investigate the nature of EEC, the “completely loose” transition state (TS) model has been applied to calculate the Arrhenius parameters for the unfolding of polyglycine dimers as a model process. The calculated Arrhenius parameters increase with increasing dimer length and demonstrate enthalpy–entropy compensation. It is shown that EEC results from the linear correlations of enthalpy and entropy of activation with dimer length, which are derived directly from the properties of the transition state. It is shown that EEC in solvated (hydrated, etc.) proteins is a direct consequence of EEC in proteins themselves. The suggested model allows us also to reproduce and explain “exotic” very high values of the pre-exponential factor measured for the proteins unfolding, which are drastically higher than those known for unimolecular reactions of organic molecules. A similar approach can be applied to analyzing the nature of EEC phenomena observed in other areas of chemistry. Full article

The solubility of the poorly soluble medicine febuxostat (FXT) (3) in various {polyethylene glycol 400 (PEG 400) (1) + water (H₂O) (2)} mixtures has been examined at 298.2–318.2 K and 101.1 kPa. FXT solubility was measured using an isothermal method and correlated with “van’t Hoff, Apelblat, Buchowski–Ksiazczak λh, Yalkowsky–Roseman, Jouyban–Acree, and Jouyban–Acree-van’t Hoff models”. FXT mole fraction solubility was enhanced via an increase in temperature and PEG 400 mass fraction in {(PEG 400 (1) + H₂O (2)} mixtures. Neat PEG 400 showed the highest mole fraction solubility of FXT (3.11 × 10^–2 at 318.2 K), while neat H₂O had the lowest (1.91 × 10^–7 at 298.2 K). The overall error value was less than 6.0% for each computational model, indicating good correlations. Based on the positive values of apparent standard enthalpies (46.72–70.30 kJ mol⁻¹) and apparent standard entropies (106.4–118.5 J mol⁻¹ K⁻¹), the dissolution of FXT was “endothermic and entropy-driven” in all {PEG 400 (1) + H₂O (2)} mixtures examined. The main mechanism for FXT solvation in {PEG 400 (1) + H₂O (2)} mixtures was discovered to be an enthalpy-driven process. In comparison to FXT-H₂O, FXT-PEG 400 showed the strongest molecular interactions. In conclusion, these results suggested that PEG 400 has considerable potential for solubilizing a poorly soluble FXT in H₂O. Full article

Access to the enthalpy and entropy of the formation of metal complexes in solution is essential for understanding the factors determining their thermodynamic stability and speciation. As a case study, in this report we systematically examine the complexation of silver(I) in acetonitrile (AN) with the following monoamines: n-propylamine (n-pr), n-butylamine (n-but), hexylamine (hexyl), diethylamine (di-et), dipropylamine (di-pr), dibutylamine (di-but), triethylamine (tri-et) and tripropylamine (tri-pr). The study shows that the complex stabilities are quite independent of the length of the substitution chain on the N atom and demonstrates that, in general, the overall enthalpy terms associated with the complex formation are strongly exothermic, whereas the entropy values oppose the complex formations. In addition, we examined the similarity of the formation constants of AgL complexes of the primary monoamines in AN, dimethylsulfoxide (DMSO) and water, which were unexpected on the basis of the difference between the donor properties of solvents. Full article

The π–π interaction is a major driving force that stabilizes protein assemblies during protein folding. Recent studies have additionally demonstrated its involvement in the liquid–liquid phase separation (LLPS) of intrinsically disordered proteins (IDPs). As the participating residues in IDPs are exposed to water, π–π interactions for LLPS must be modeled in water, as opposed to the interactions that are often established at the hydrophobic domains of folded proteins. Thus, we investigated the association of free energies of benzene and phenol dimers in water by integrating van der Waals (vdW)-corrected density functional theory (DFT) and DFT in classical explicit solvents (DFT-CES). By comparing the vdW-corrected DFT and DFT-CES results with high-level wavefunction calculations and experimental solvation free energies, respectively, we established the quantitative credibility of these approaches, enabling a reliable prediction of the benzene and phenol dimer association free energies in water. We discovered that solvation influences dimer association free energies, but not significantly when no direct hydrogen-bond-type interaction exists between two monomeric units, which can be explained by the enthalpy–entropy compensation. Our comprehensive computational study of the solvation effect on π–π interactions in water could help us understand the molecular-level driving mechanism underlying the IDP phase behaviors. Full article

Meloxicam is widely prescribed as an analgesic and anti-inflammatory drug in human therapeutics. Owing the very low aqueous solubility of meloxicam, this property has been studied in dimethyl sulfoxide (DMSO)-aqueous solvent systems at several temperatures from 273.15 to 313.15 K to expand the solubility database about analgesic drugs in mixed solvents. The flask shake method followed by ultraviolet-visible (UV-vis) spectrophotometry analysis were used for meloxicam solubility determinations. A number of cosolvency models, including the Jouyban–Acree model, were challenged for solubility correlation/prediction of this drug in these mixtures. The van’t Hoff and Gibbs equations were employed to calculate the apparent standard thermodynamic quantities relative to dissolution and mixing processes. The inverse Kirkwood–Buff integral method was employed for calculating the preferential solvation parameters of meloxicam by DMSO in the mixtures. Meloxicam solubility increases with increasing temperature and maximum solubilities are observed in neat DMSO at all temperatures studied. Dissolution processes were endothermic in all cases and entropy-driven in the composition interval of 0.40 ≤ x₁ ≤ 1.00. A nonlinear enthalpy–entropy relationship was observed in the plot of enthalpy vs. Gibbs energy for drug transfer processes. Meloxicam is preferentially solvated by water in water-rich mixtures but preferentially solvated by DMSO in the composition interval of 0.21 < x₁ < 1.00. Full article

The equilibrium solubility of benzoic acid in water and ethanol, as well as in nine {ethanol (1) + water (2)} mixtures, was determined from T = (293.15 to 323.15) K. Benzoic acid mole fraction solubility in these aqueous-ethanolic mixtures was adequately correlated with some well-known correlation/prediction models, obtaining mean percentage deviations of 2.2 to 7.6%. Apparent thermodynamic quantities, namely, Gibbs energy, enthalpy, and entropy, for the dissolution, mixing and solvation processes, were computed by means of the van ’t Hoff and Gibbs equations. The enthalpy–entropy compensation plot of apparent enthalpy vs. apparent Gibbs energy of dissolution was not linear, indicating enthalpy and entropy mechanisms for transfer. Ultimately, by using the inverse Kirkwood–Buff integrals, it is observed that benzoic acid is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in those {ethanol (1) + water (2)} mixtures of 0.24 < x₁ < 1.00. Full article

The corannulene pincer (also known in the literature as the buckycatcher) is a fascinating system that may encapsulate, among other molecules, the $C_{60}$ and $C_{70}$ fullerenes. These complexes are held together by strong π-stacking interactions. Although these are quantum mechanical effects, their description by quantum chemical methods has proved very hard. We used three semi-empirical methods, PM6-D3H4X, PM6-D3H+ and GFN2-xTB, to model the interactions. Binding to fullerenes was extended to all open conformations of the buckycatcher, and with the proper choice of solvation model and partition functions, we obtained Gibbs free energies of binding that deviated by 1.0–1.5 kcal/mol from the experimental data. Adding three-body dispersion to PM6-D3H+ led to even better agreement. These results agree better with the experimental data than calculations using higher-level methods at a significantly lower fraction of the computational cost. Furthermore, the formation of adducts with $C_{60}$ was studied using dynamical simulations, which helped to build a more complete picture of the behavior of the corannulene pincer with fullerenes. We also investigated the use of exchange-binding models to recover more information on this system in solution. Though the final Gibbs free energies in solution were worsened, gas-phase enthalpies and entropies better mirrored the experimental data. Full article