V. A. Zavizion

Investigation of intermolecular interactions in solutions by means of millimeter-wave spectroscopy 4. Negative and positive hydration in aqueous solutions of urea

Measurements have been made of the absorption of EHF radiation (μ 5 cm−1) by aqueous solutions of urea at 20–70°C, over the entire interval of urea solubility. Excess absorption has been found in comparison with the additive magnitude, and this has been attributed to an increase in the fraction of water molecules in the solution with rotational degrees of freedom. A model has been proposed for the hydration of urea, based on the concept of inhomogeneity of the hydrate shell of urea: stabilization of the structure of water under the influence of carbonyl oxygen and Hcis atoms (positive hydration) and a simultaneous breakdown of the structure of water in the region of two Htrans atoms that have approached to a distance of 2.14 » (negative hydration).

Study of intermolecular interactions in aqueous solutions by millimeter spectroscopy

The absorption of millimeter electromagnetic radiation (v=1.4, 1.71, and 5 cm−1) by aqueous solutions of glycine (pH 6.1–6.2) in the concentration range of 0.5–2.5 mol L−1 was measured. It was found that the absorbing ability of the water present in the solutions, is higher than that of pure water. This phenomenon is explained by the presence of a center of negative hydration in the structure of the glycine zwitterion, which results in an increase in the rotational mobility of water molecules immobilized in the hydrate shell of the glycine zwitterion.

Investigation of intermolecular interactions in solutions by means of millimeter spectroscopy. Communication 2. Aqueous solutions of ethanol

Conclusions1.Measurements have been made of the concentration dependence of the absorption of electromagnetic ultrahigh-frequency radiation (λ ≈ 2 mm) in the water/ethanol system, and it has been demonstrated that the contributions of water and ethanol to the absorption by the solutions are nonadditive.2.Three characteristic intervals of concentration have been found, in which different types of interaction between water and ethanol molecules are predominant.3.Ethanol hydration numbers have been evaluated, and the contributions to the absorption deficit from polar and hydrophobic hydration have been segregated.

Millimeter spectroscopic study of intermolecular interactions in solutions

The absorption of 5 cm−1 electromagnetic radiation by aqueous solutions of methyl, ethyl, n-, and isopropyl, sec-, iso-, and tert-butyl, and tert-amyl alcohols and ethylene glycol was measured within their solubility limits in water at 20°C. It was found that the observed nonadditivity of absorption (absorption deficit) is a qualitative measure of hydration of alcohols of two types: hydrophilic and hydrophobic. The possibility of distinguishing these effects by millimeter spectroscopy was demonstrated. Hydrophobic hydration makes the basic contribution to the hydration number of aliphatic alcohols. On the example of solutions of ethanol and tert-butanol, it was shown that hydrophobic hydration decreases with an increase in the temperature of the solution due to intensification of hydrophobic interactions between the hydrocarbon radicals.

Effect of urea on the structure and functional activity of proteins. Chymotrypsinogen A and α-chymotrypsin

The effect of urea on the structural stability and functional activity of globular proteins,viz., chymotrypsinogen A (ChtG) and α-chymotrypsin (Cht), was studied over a wide range of concentrations (0.5–6 rnol L-1), and the existence of two different mechanisms of the action of urea on these proteins was demonstrated. No changes in the spatial structure of ChtG were observed in the concentration range from 0,5 to 3 mol L−1 (region 1). Differential UV spectroscopy shows tile redistribution of aromatic groups between the inner volume and the outer surface of a protein molecule (protein denaturation) at concentrations >3 mol L−1 (regionII), In regionI, urea changes the kinetic parameters of enzymatic reactions involving Cht, which is explained on the basis of millimeter spectroscopy data by its action on the structure and nucleophilic reactivity of water.

Interaction of EHF radiation with biomolecular systems

Data on the absorption of EHF electromagnetic energy by aqueous solutions are summarized. Experimental tests for positive (hydrophilic and hydrophobic) and negative (hydrophilic) hydration are formulated. The applicability of the proposed approach to the study of the hydration of high-molecular-weight systems, including aqueous solutions of proteins, is demonstrated. A model is proposed that explains the interaction of EHF radiation with real biological systems, including under conditions of EHF therapy. The experimental data on the absorption of EHF radiation by aqueous solutions of organic and inorganic electrolytes and nonelectrolytes as well as globular proteins are used to construct a model that explains certain details of EHF therapy. The fraction of mobile water molecules in the skin is considered the primary molecular target for EHF radiation; they are capable of transporting the EHF energy to primary physiological targets of the protein type.