Interactions between ions and water-DMSO mixed solvent

Abstract

As a classical cryoprotectant, the cryoprotective mechanism of DMSO remains elusive. In this study, we explore the capability of DMSO to hinder the formation of salt hydrates in the water-DMSO-salt ternary system, given that, at low temperatures, salt hydrates are more prone to attach to surfaces than ice, potentially preventing mechanical damage to cell membranes. Using THz-TDS, we validate the ability of DMSO to suppress salt hydrate formation. Combining IR spectroscopy, we conclude that this inhibitory effect partly arises from the interaction between cations and the S=O groups in DMSO molecules. Semi-quantitative DR spectroscopy provides similar insights from the perspective of molecular reorientation dynamics. Taking into account the intensified ion-dipole interactions due to a higher ion surface charge density, we focus our discussion on MgCl2, while NaCl, more akin to biological processes, serves as a reference. Delving into the specific molecular mechanisms, we put forth conjectures regarding the direct interaction between cations and DMSO or the indirect influence of cations on DMSO through the modulation of hydrogen bonds in surrounding water molecules. These research findings contribute to a better understanding and mastery of cryoprotectants.