Studies on thermodynamics, dynamics, structure and anomalies of water in cryopreserving solutions

The aim of this PhD thesis is to study through molecular dynamics simulations the properties of supercooled water in solutions with cryoprotectant molecules, such as trehalose and dimethyl sulphoxide (DMSO), to determine how the anomalous properties of water are affected by the presence of these solutes and how to exploit these properties for cryopreservation. The system examined in this thesis are aqueous solutions of trehalose, aqueous solutions of DMSO, and systems composed by a lysozyme protein in water and in trehalose and/or DMSO aqueous solutions. Also aqueous solutions of lithium chloride (LiCl), an electrolyte, were studied. In particular, for the trehalose aqueous solutions we present the thermodynamics findings for concentrations of 20 wt\% and 40 wt\% in trehalose in the normal liquid and supercooled region, detailing estimations of the temperature of maximum density (TMD) and minimum density (TmD) lines, the lines of maxima of the isothermal compressibility, and the liquid-liquid critical point (LLCP). Also a structural analysis on these solutions is done through the study of the water oxygen - water oxygen and the water oxygen - trehalose oxygen radial distribution functions. For the DMSO aqueous solution we studied the traslational dynamics of water upon cooling through the analysis of the water oxygen self intermediate scattering functions, with a particular focus on the Mode Coupling Theory behavior, and we compared the results with those for pure water. The effect of DMSO on the hydrogen bond network of water upon cooling is also analyzed. For the systems containing the lysozyme protein we studied the structural properties of the hydration water of the protein through the radial distribution functions, and we analized water local structures, that derive from the presence of molecules coordinated in a tetrahedral manner with four hydrogen bonds and molecules which present a disruption in the tetrahedral network, through the V4S parameter. We analyzed the effect that DMSO and trehalose have on the local structures of protein hydration water. Finally, presents also the thermodynamics findings on LiCl supercooled aqueous solutions through the analysis of the isochores curves to estimate the TMD and TmD lines, the lines of maxima of the isothermal compressibility, and the LLCP, and the structural findings through the analysis of the radial distribution functions, to study the effect of this electrolyte on the properties of water. These findings highlight how the presence of DMSO and of trehalose favor the high-density phase of water, and how the behavior of water in the analyzed solutions is closely related to that of pure water, demonstrating how its unique and distinctive properties significantly influence the behavior of these mixtures.