Thermodynamics of solvation and solvophobic effect in formamide

Using semi-adiabatic calorimetry, we measured the enthalpies of solution for various low-polar compounds including alkanes, aromatic hydrocarbons and their halogenated derivatives in formamide at temperature of 298 K. For the same compounds, the values of limiting activity coefficients in formamide were determined using GC headspace analysis at 298 K, and Gibbs free energies of solution and solvation were calculated. Based on these data and the available literature values of the Gibbs free energy of solvation in formamide for a number of other low-polar solutes, a study of the solvophobic effect in this solvent is performed, and its resemblance to the hydrophobic effect in aqueous solutions is demonstrated. It is shown that the contribution of the solvophobic effect into the solvation Gibbs free energy in formamide is much higher than that in aliphatic alcohols, but lower than that in water. Like in water, the magnitude of this contribution for different solutes linearly increases with the solute molecular volume. Solvophobic effect also significantly affects the enthalpies of dissolution in formamide, causing them to be more negative in the case of alkanes and more positive in the case of arenes. © 2013 Elsevier Ltd. All rights reserved

Evaluation of the contribution to hydration of nonelectrolytes from the hydrophobic effect

A new method was suggested for estimating the hydrophobic effect of contributions to the Gibbs energies and enthalpies of hydration of hydrocarbons, inorganic gases and rare gases. In accordance with this method the hydrophobic effect contribution to the Gibbs energy was evaluated from the difference between the hydration Gibbs energy of a solute and the non hydrophobic contribution. To estimate the latter value, the known dependence connecting the Gibbs energies of solvation of a solute in a number of aprotic solvents to the Hildebrand solubility parameter for these solvents was used. The non hydrophobic contribution to the Gibbs energy of hydration was calculated for various solutes from such dependences extended to water as solvent. The Hildebrand solubility parameter for water used in the calculation was corrected for the effect of association through hydrogen bonding. This correction was made by subtraction of the water self-association enthalpy from the enthalpy of vaporization of water. The evaluated Gibbs energies of the hydrophobic effect are positive for saturated hydrocarbons, inorganic gases and rare gases and linearly depend on the solute molecular refraction. The hydrophobic contribution to the hydration enthalpies of the solutes was calculated in the same manner as was made to calculate the hydrophobic contribution to Gibbs energies of hydration. Enthalpies of the hydrophobic effect for the solutes under study are negative. © 1995 Plenum Publishing Corporation

Interactions of water with human serum albumin suspended in water-organic mixtures

Calorimetric enthalpy changes on suspending a partially hydrated preparation of human serum albumin (HSA) in various water-organic mixtures are discussed together with the water sorption isotherms. Experimental data indicate that suspending the HSA preparation is accompanied mainly by two processes. The first is water desorption-sorption which superficially obeys the Langmuir model. The influence of the medium on the thermodynamic parameters of water sorption can be described approximately by thermodynamic data on the solvation of water at infinite dilution. The second effect is a non-sorption process attributed tentatively to rupture of protein-protein contacts in the HSA preparation on suspending it. Depending on the nature of the solvent and its water content, such transformation of the HSA preparation can result in deviations from the Langmuir isotherm of water sorption by the suspended protein. This transformation is accompanied by the corresponding increase in the accessible surface area of the protein preparation and a significant enthalpy change. Experimental data cast doubt on the validity of the traditional opinion that the significant increase in water sorption by proteins at high water activities results from the various kinds of water-water interaction on the protein surface. It appears that the imposition of the transformation of the protein preparation on water sorption-desorption can determine both the calorimetric profile and thermodynamic data on suspending the protein preparation in various solvents

Thermodynamics of water binding by human serum albumin suspended in acetonitrile

Heat effects resulting from the introduction of solid human serum albumin (HSA) into various water-acetonitrile mixtures were measured calorimetrically at 298 K. The amount of water bound to the suspended HSA as a function of the water content of the solvent was also determined. Introducing HSA into water-acetonitrile mixtures involves water binding according to the Langmuir isotherm with an adsorption constant Kc = 1.0 ± 0.1 M-1, enthalpy Δh = -9.0 ± 1.5 kJ mol-1 and entropy ΔS = -30 ± 6 J mol-1 K-1. Placing HSA in the solvent has an additional heat effect of 46 ± 19 J g-1, which is attributed to an unknown transformation of the protein preparation. © 1995

Synthesis of lipophilic triazacycloalkanes and their platinum(II) complexes

A series of cyclic lipophilic polyamines: 1,4,7-triethyl-1,4,7- triazacyclodecane, 1,4,7-triethyl-1,4,7-triazacycloundecane, 1,4,7-trimethyl-1,4,7-triazacycloundecane, and 1,4,8-triisopropyl-1,4,8- triazacycloundecane, as well as their complexes with dimethylplatinum(II) were synthesized for the first time. Features of complex formation of triazacyclanes with platinum and their manifestation in NMR spectra were discussed. © Nauka/Interperiodica 2006

Effect of chain length on interactions of aliphatic alcohols with suspended human serum albumin

Enthalpy changes on the immersion of human serum albumin (HSA) into n-butanol, n-propanol, ethanol and methanol containing different amounts of water have been measured calorimetrically at 25°C. Water sorption isotherms on HSA were also determined in water-n-butanol and water-ethanol mixtures. From comparison of the calorimetric and sorption data, it was concluded that there is a significant enthalpy change on the HSA immersion into methanol and ethanol even under conditions where there is no change in the quantity of adsorbed water. No similar contribution was found in the n-butanol based suspensions. Water monolayer capacity evaluated from the Langmuir model decreases also significantly when going from ethanol to n-butanol. Considering this non water sorption contribution, values of the monolayer capacity and the shape of the experimental dependences, it was inferred that a relatively small change of the solvent molecule structure (from n-propanol to ethanol) affects strongly the interactions of the protein with the solvent

Solvophobic effects and relationships between the Gibbs energy and enthalpy for the solvation process

An approach is suggested to describe the solvophobic effects in various solvents, qualitatively and quantitatively. We analyzed the relationships between the Gibbs energies and enthalpies of solvation of alkanes in various solvents on the basis of existing experimental data. It is shown that for a large group of solvents, there is a linear correlation between the two quantities. Other solvents, primarily self-associated, show deviations from this line. These deviations are always positive, leading to a decrease in solubility, and can be used as a measure of the strength of the solvophobic effects. It is also shown that the solvophobic effects is not the only factor determining the solubility, even for alkane solutes. The magnitudes of contributions of the solvophobic effect into the Gibbs energies of solvation of various compounds in monohydric alcohols are determined. These magnitudes are found to be linearly correlated with a characteristic molecular volume of a solute. The slope of correlation grows up with the concentration of hydrogen bonds in the liquid solvent. Copyright © 2011 John Wiley & Sons, Ltd

Thermodynamics of specific interactions of pyridines in aliphatic alcohols: Gibbs energy, entropy, and degree of binding

The activity coefficients at infinite dilution (T = 298.15 K) and Gibbs energy of solvation of pyridines in aliphatic alcohols were determined. The thermodynamic functions of specific interactions in these systems were calculated. © 2013 Pleiades Publishing, Ltd

Solvent effect on H-bond cooperativity factors in ternary complexes of methanol, octan-1-ol, 2,2,2-trifluoroethanol with some bases

Cooperative hydrogen bonds in ternary complexes (ROH)2⋯B (ROH-alcohols; B-bases) formed in pure bases (B) and solutions in n-hexane, carbon tetrachloride, benzene and 1,2-dichloroethane were studied by FTIR spectroscopy. Based on the observations, the authors were able to propose an original method of evaluating solvent effects on cooperativity factors in the complexes. Frequencies of cooperative hydrogen bonds OH⋯B (νb) were determined for ternary complexes of pyridine with aliphatic alcohols (methanol, octan-1-ol) and for 2,2,2-trifluoroethanol with three different bases (acetonitrile, diethyl ether, tetrahydrofuran). The solvent shifts of νb were found to correlate with an empirical thermochemical parameter of the solvent, SVW. The cooperativity factors were determined for the complexes (ROH)2⋯B in all studied media. It has been found that the cooperativity factors are almost independent of the solvent. In addition, a method was proposed of estimating the frequencies and cooperativity factors for ternary complexes (ROH)2⋯B in the gas phase. It has been found that in gas phase the cooperativity factors are practically the same as in condensed media. © 2007 Elsevier B.V. All rights reserved

Thermodynamics of hydrogen bonding of weak bases in alcohol solutions: Calorimetry of solution, IR-spectroscopy and vapor pressure analysis

The properties of solutes and their reactivity in aliphatic alcohols significantly depend on the formation of hydrogen bonds. In this work, calorimetric, FTIR-spectroscopic and gas chromatographic vapor pressure studies of hydrogen bonds of weak bases in solution of aliphatic alcohols were carried out. Enthalpies of solutions at infinite dilution of ketones, nitriles and acetates in methanol and octan-1-ol were measured. Obtained from the calorimetric data, the enthalpies of specific interaction of weak bases in aliphatic alcohols unexpectedly found to be positive. IR spectra of solutions of ketones in aliphatic alcohols at infinite dilution were measured at different temperatures. Enthalpies of specific interaction in studied systems obtained from the spectroscopic data confirmed the endothermic process and are in good agreement with calorimetric results. Gibbs energies and entropies of specific interaction of weak bases in aliphatic alcohols were determined. Obtained results show, that the hydrogen bonding process of weak bases in aliphatic alcohols differs substantially from the formation of complexes 1:1 ROH⋯B (B - weak proton acceptor) in aprotic media. The complicated process of hydrogen bonding of weak bases in aliphatic alcohols apparently is controlled by the entropy factor, because these values are above zero. © 2011 Elsevier B.V. All rights reserved