IR Spectroscopy of Solutions of Dimethylsulfoxide in Monoethanolamine
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ICAL CHEMISTRY OF SOLUTIONS
IR Spectroscopy of Solutions of Dimethylsulfoxide in Monoethanolamine E. G. Kononovaa, M. N. Rodnikovab,*, I. A. Soloninab, and E. V. Shirokovab aNesmeyanov bKurnakov
Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, 199991 Russia Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected] Received December 12, 2019; revised December 12, 2019; accepted April 14, 2020
Abstract—Solutions of dimethylsulfoxide (DMSO) in monoethanolamine (MEA) are studied via IR spectroscopy on a Bruker Tensor 37 FT-IR spectrometer in the wavenumber range of 900–4000 cm−1. The concentrations of DMSO are 2–66 mol %. The region of the stretching vibrations of hydrogen-bonded OH and NH2 groups (2800–4000 cm−1) and the region of the S=O vibrations of DMSO (900–1100 cm−1) are studied in detail. The obtained data are compared to the IR spectra of solutions of DMSO in ethylene glycol in the regions of OH and S=O stretching vibrations. The effect the NH2 group in the MEA molecule has on the interaction in the DMSO–MEA system and the physicochemical properties of this system as compared to ethylene glycol solutions of DMSO are discussed. DOI: 10.1134/S0036024420110151
INTRODUCTION Aqueous solutions of DMSO and MEA are widely used in cryobiology. Both aqueous systems have a low freezing point that allows biological objects to be stored in them [1, 2]. The lowest freezing point in H2O‒DMSO is around −72°C at a component ratio of 2 : 1 [1], while the one in H2O–MEA is −50°С at 3 : 1 [3]. An aqueous solution of DMSO can induce cell fusion [4] and act as a cryoprotector for membranes and proteins [5, 6]. An aqueous solution of MEA can be used as a cryoprotector for the vitrification of biological materials [2]. The DMSO molecule is a distorted pyramid with the S atom in the vertex. It has been studied by both electronography [7] and quantum chemistry [8]. Geometric data on this molecule in the gas phase, obtained via microwave microscopy, are presented in Fig. 1 and Table 1 [7]. The dipole moment of the molecule in the liquid phase is 3.96 D, and the donor strength is 29.8 [3]. The IR spectrum of liquid DMSO is shown in Fig. 2 in the range of the S=O stretching band most susceptible to interactions (900– 1100 cm−1).
10]. The molecule has three proton donor centers and two proton acceptor centers, so the MEA molecule in liquid forms a 3D hydrogen-bond network [11] that largely governs the physicochemical properties of this solvent. The physicochemical properties of DMSO and MEA are given in Table 2 (the properties of EG and H2O are given for reference) [12]. We can draw several conclusions from the data in Table 2. The MEA molecule has the highest electron-donor strength of the considered solvents, but its dipole moment is lower than that of EG and higher than the one of water. Due to the NH2 group in the molecule, MEA has a considerable ionization constant: pKb = 4.75 [13]. On the one hand, this results from the contribution of
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