Elastic Properties of Guanidine Hydrochloride Solutions with Various Concentrations in the Gigahertz Frequency Range
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OLYMERS DYNAMICS
Elastic Properties of Guanidine Hydrochloride Solutions with Various Concentrations in the Gigahertz Frequency Range A. I. Fedoseeva, I. P. Koludarova,b, A. V. Fronttseka, A. V. Dmitrieva, and S. G. Lushnikova,* a
b Ecology
Ioffe Institute, St. Petersburg, 194021 Russia and Evolution Unit, Okinawa Institute of Science and Technology, Onna, Kunigami-gun, Okinawa, 904-0495 Japan *e-mail: [email protected] Received February 10, 2020; revised February 10, 2020; accepted February 17, 2020
Abstract—The temperature dependences of the veloсity of hypersound (V(T)) in solutions with various concentrations of guanidine hydrochloride (GndHCl) are studied by Brillouin–Mandelstam light scattering spectroscopy in the temperature range from 263 to 353 K. It is shown that the temperature dependence of the sound velocity has a pronounced maximum at low concentrations of GndHCl. An increase in the concentration of GndHCl in a solution is accompanied by a shift of the maximum to the low-temperature region and an increase in the absolute values of the sound velocity, which means a decrease in the adiabatic compressibility over the entire range of studied temperatures. The temperature dependence of the adiabatic compressibility is constructed at low concentrations of GndHCl. The contribution of relaxation processes to the temperature behavior of the attenuation of hypersound in solutions of GndHCl is determined. It is shown that their behavior is activated thermally and described by the Arrhenius law. The values of the activation energy of relaxation processes are calculated. Possible mechanisms that underlie the observed phenomena are discussed. DOI: 10.1134/S1063784220090170
INTRODUCTION To study the stability of proteins and the mechanisms and kinetics of folding and unfolding, protein denaturation under the influence of various factors (temperature, pressure, and chemical denaturants) is usually studied. In chemical denaturation, one of the derivatives of guanidine, namely, guanidine hydrochloride (GdnHCl), is among the most common protein denaturants. The widespread use of guanidine is determined by the fact that it is an important raw material in organic and inorganic synthesis for the preparation of numerous derivatives (for example, N-substituted guanidine) that have recently attracted attention as nonionic bases, organic catalysts, and N-donors for metal ions [1–4]. However, despite the widespread use of this substance, its physical properties and the properties of its aqueous solutions are relatively poorly understood. Only recently, the crystalline form of guanidine was obtained and its structure was studied in detail by the X-ray diffraction method [5]. Guanidine (NH2)2C(=NH) is a compound that contains a CH3 core to which two amino groups (NH2) and one imino group are covalently bonded. In an aqueous solution, guanidine is protonated and exists as a Gdm+ cation ([CH6N3]+). The molecule has a rigid planar structure. By studying solutions with
various concentrations of GdnHCl, the osmotic co
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