Yu. I. Khurgin

Construction and X-ray reflectivity study of self-assembled lysozyme/polyion multilayers

Abstract The process of multilayer assembly via layer-by-layer deposition of linear polyions and lysozyme have been studied. The films were fabricated on glass slides by alternate electrostatic adsorption of anionic poly(styrenesulfonate) (PSS), cationic poly(allylamine) (PAA) polyions and hen egg-white lysozyme. The multilayer build-up was monitored by the small-angle X-ray diffraction method. X-ray reflectivity curves from the films measured at different steps of the assembly reveal Kiessig fringes. From their periodicity the film thickness was calculated. The growth step for a PSS/PAA bilayer equals 37 A. The thickness of the lysozyme layer equals 45 A, which is close to dimensions of the lysozyme molecule determined by X-ray crystallography. An analysis of surface charges of the lysozyme molecule shows some preferentially positive charged regions, which are the most probable sites of interactions with negatively charged PSS.

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).

Urea-generated free rotating water molecules are active in the protein unfolding process

The critical urea concentration (C3 ∗) which destabilizes the structure of bovine serum albumin and chymotrypsinogen was determined by UV difference spectroscopy. The increase of the relative content of mobile rotating water molecules in aqueous urea was formerly shown by millimeter spectroscopy [1]. The rise of rotator content at a urea concentration C3⩾ C3 ∗ when the bulk water is practically exhausted is suggested as a main driving force of protein unfolding.

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.

HYDROPHOBIC HYDRATION OF ALIPHATIC AMINO ACIDS

Indexes of hydrophobic hydration of aliphatic amino acids derived by millimeter spectroscopy (31.42 GHz) give a linear correlation with the accessible surface area of the side chains.

Investigation of hydration of α-amino acids by means of absorption millimeter spectroscopy

The hydration indexes for 19 protein α-amino acids are measured by means of absorption millimeter spectroscopy (AMS) at 31.42 GHz. The plot of the hydration indexes on the area of surface of aliphatic amino acid molecules accessible for water is a straight line located above the points corresponding to aromatic or polar amino acids. The contribution of nonpolar groups in the hydration index is greater than that of polar groups provided that their accessible surface areas are equal. The contribution to hydration of -OH and-CONH2 groups in Ser. Gin, and Asn coincides in sign with that of pure hydrophobic hydration but the value of the contribution is significantly smaller. The change in mobility of water molecules, which is the basis of the AMS method, may serve as the physicochemical foundation for the construction of a new hydrophobicity scale for amino acids comparable with the already existing scales.

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.

Compression-induced phase transition in antibody monolayers

Abstract The formation of monolayers of immunoglobulin G macromolecules at the air-water interface was studied using a Langmuir trough. A pressure-induced phase transition was detected in the monolayers

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.

Quantum-chemical study of interaction of water with urea

Conclusions1.Theab initio quantum-chemical method STO-3GF has been used to calculate the structure and heat of formation of urea complexes with water molecules.2.The most stable urea-water complex is that with a structure in which the water molecule exists in a broad potential well, where it can almost freely move in space to distances up to 3 Å. Therefore, the addition of urea increases the mobility of the molecules in liquid water and breaks down the water structure.