Multiparameter correlations for description of thermodynamic parameters of solvation: I. Enthalpy of nonspecific solvation

Applicability of a linear solvation-energy approach for descripition of the solvation enthalpies of nonelectrolytes is examined. In most cases a good fit of experimental solvation enthalpies can be attained. However, the resulting data are difficult to interpret in terms of different types of intermolecular interactions

Multiparameter correlations for describing thermodynamic parameters of solvation: II. Enthalpy of specific interaction

The applicability of the approach based on the linear solvation energy relationship to describing the enthalpies of specific solvent-solute interactions was examined. In associated solvents, this approach reflects the contribution of specific interaction incorrectly. Although the enthalpies of solvation as a whole are described well, this is an "occasional" result and is due to averaging over different compounds and redistribution of contributions from other types of interactions. A modification of this approach was suggested to take into account the effect of reorganization of an associated solvent

Commercial Concession: Issues of Conceptual Apparatus

The article discusses the theoretical issues of correlation of terms used to refer to the agreement of commercial concession, as well as related issues arising from legal practice and theory of civil law

Quantum-chemical estimation of the stability and reactivity of diphosphonium salts

For a series of diphosphonium salts containing two positively charged covalently bonded phosphorus atoms, XnY3-nP +P+XnY3-n (X = alkyl substituent, Y = amino group, n = 0-3), the stability, reactivity, and P-P bond strength were evaluated by various physicochemical methods. The P-P bond energy is appreciably influenced by both steric factors and donor properties of the substituents. The calculations confirmed that transformations of diphosphonium salts can involve cleavage of both P-P and P-N (or P-C) bonds

Calorimetric and FTIR-spectroscopic study of solvent effect on the state of dry solid bovine pancreatic α-chymotrypsin immersed in anhydrous organic solvents

Calorimetric heat effects and structural rearrangements accompanying the immersion of dry solid bovine pancreatic α-chymotrypsin in anhydrous organic solvents and water were measured at 298 K. It was found that the enthalpy and IR-absorbance changes being put together obey good linear correlation. According to the extent of their influence on the protein structure and thermodynamic state the solvents could be divided into two groups. The first group exhibiting nearly zero effects consists of carbon tetrachloride, benzene, nitromethane, acetonitrile, 1, 4-dioxane, n-butanol, n-propanol and pyridine. Dry solid protein is suggested to be stable in such media due to kinetic reasons. Immersion of the protein into a second group solvents, namely, dimethyl sulfoxide, methanol, ethanol, and in pure water as well, is followed by swelling of the protein and accompanied with significant exothermic enthalpy change and structural rearrangements. It was shown that attribution of the solvent to the first or the second group is determined by its thermody-namic hydrophilicity (partial excess molar Gibbs free energy of water in a given solvent at infinite dilution). The first group consists of liquids with thermodynamic hydrophilicities all above 2.7 kJ/mol. The thermodynamic hydrophilicities of the second group solvents are lower than 2.3 kJ/mol. At close hydrophilicities the presence of mobile protons in the solvent molecule sufficiently accelerates the solid protein swelling. It is deduced that thermodynamic hydrophilicity and proton donating ability could be principal factors controlling the stability of dry solid proteins and kinetics of swelling in liquids examined at room temperature

Calorimetric determination of hydrogen-bonding enthalpy for neat aliphatic alcohols

Hydrogen bonding in pure aliphatic alcohols is investigated using a novel calorimetric approach. Average enthalpies of hydrogen bonding were determined for methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, hexan-1-ol and octan-1-ol. For all the studied alcohols except methanol the average hydrogen-bonding enthalpies fall in the range from -16.9 to -17.7kJ mol -1. A slightly smaller value of -15.1 kJ mol-1 was observed for methanol. From the enthalpies of the specific interactions of the alcohols and chloroform (as proton donors) formed with the alcohols and diethyl ether (as proton acceptors), the dimerization enthalpies were determined for the investigated alcohols: -8.6±0.7 kJ mol-1. The specific interaction and dimerization enthalpies obtained are concurrent with the Badger-Bauer rule and the hydrogen-bond cooperativity effects. The calorimetric data obtained are supported by literature Fourier transform infrared data on dimer and multimer formation for ethanol and octan-1-ol in tetrachloromethane solution. Copyright © 2005 John Wiley & Sons, Ltd

Quantum-chemical estimation of the stability and reactivity of diphosphonium salts

For a series of diphosphonium salts containing two positively charged covalently bonded phosphorus atoms, XnY3-nP +P+XnY3-n (X = alkyl substituent, Y = amino group, n = 0-3), the stability, reactivity, and P-P bond strength were evaluated by various physicochemical methods. The P-P bond energy is appreciably influenced by both steric factors and donor properties of the substituents. The calculations confirmed that transformations of diphosphonium salts can involve cleavage of both P-P and P-N (or P-C) bonds

New thermochemical parameter for describing solvent effects on IR stretching vibration frequencies. Communication 1. Assessment of van der Waals interactions

Solvent effects on O{single bond}H stretching vibrations in several complexes with hydrogen bonding have been investigated by FTIR spectroscopy. To assess the influence of van der Waals (vdW) interactions on frequency shifts, a new parameter of solvent, sqrt(δcav hS), is proposed. This parameter has been derived from equations describing enthalpy of non-specific solvation. Linear correlation was established between the O{single bond}H frequency shift (with respect to the gas phase) and parameter sqrt(δcav hS) for a series of complexes of aliphatic alcohols with standard proton acceptors. Linear correlations with sqrt(δcav hS) were also observed for a series of "free" O{single bond}H and also C{double bond, long}O, P{double bond, long}O, S{double bond, long}O and C{single bond}Br stretching vibrations. A new method is proposed for estimating the gas-phase stretching frequency from IR spectra of solutions. In addition, frequencies of "free" X{single bond}H groups in neat bases were deduced from the experimental data. © 2005 Elsevier B.V. All rights reserved

Interaction enthalpies of solid bovine pancreatic α-chymotrypsin with organic solvents: Comparison with FTIR- spectroscopic data

Calorimetric heat effects and integral absorbance changes observed in the FTIR spectra were measured at immersing solid bovine pancreatic α-chymotrypsin in organic solvents and water at 298 K. Enthalpy changes upon the immersion of the enzyme in different media are in a good linear correlation with the corresponding IR-absorbance changes. Based on calorimetric and FTIR data, all the solvents were divided into two groups. The first group of solvents includes carbon tetrachloride, benzene, nitromethane, acetonitrile, 1,4-dioxane, n-butanol, n-propanol and pyridine in which no significant heat evolution and structural changes were found at the solid enzyme immersion. Second group of the solvents includes dimethyl sulfoxide, methanol, ethanol, and water. Immersion into these media, results in the solid protein swelling and involves significant exothermic heat evolution and structural changes in the protein. Dividing of different media in these two groups is in a qualitative correlation with the solvent hydrophilicity which is defined as partial excess molar Gibbs free energy of water at infinite dilution in a given solvent. The first group of solvents includes liquids with hydrophilicity exceeding 2.7 kJ/mol. The hydrophilicity of the second group solvents is <2.3 kJ/mol. Hydrogen bond donating ability of the solvents assists in the protein swelling. Hydrogen bonding between protein and solvent is assumed to be a main factor controlling the swelling of solid protein preparation in the solvents at room temperature. © 2002 Elsevier Science B.V. All rights reserved