How are water’s material properties encoded within the structure of the water molecule? This is pertinent to understanding Earth’s living systems, its materials, its geochemistry and geophysics, and a broad spectrum of its industrial chemistry. Water has distinctive liquid and solid properties: It is highly cohesive. It has volumetric anomalies—water’s solid (ice) floats on its liquid; pressure can melt the solid rather than freezing the liquid; heating can shrink the liquid. It has more solid phases than other materials. Its supercooled liquid has divergent thermodynamic response functions. Its glassy state is neither fragile nor strong. Its component ions—hydroxide and protons—diffuse much faster than other ions. Aqueous solvation of ions or oils entails large entropies and heat capacities. We review how these properties are encoded within water’s molecular structure and energies, as understood from theories, simulations, and experiments. Like simpler liquids, water molecules are nearly spherical and interact with each other through van der Waals forces. Unlike simpler liquids, water’s orientation-dependent hydrogen bonding leads to open tetrahedral cage-like structuring that contributes to its remarkable volumetric and thermal properties.

Enthalpies of mixing of aliphatic 3,3 and 6,6-ionene fluorides with low molecular weight salts (sodium formate, acetate, nitrate, chlorate(v), and thiocyanate), all dissolved in water, were determined. In addition, to complement our previous study (Lukšičet al., Phys. Chem. Chem. Phys., 2012, 14, 2024), new measurements were performed where aqueous solutions of 3,3 and 6,6-ionene bromides were mixed with solutions of sodium fluoride, chloride, bromide, and iodide. Electrostatic theory, based on Manning's limiting law or the Poisson-Boltzmann equation, predicted the enthalpy of mixing to be endothermic in all the cases, while experiments showed that this is not always true. When an aqueous solution of 3,3-ionene fluoride was mixed with a solution of sodium fluoride (or formate and acetate) in water, the effect was indeed endothermic. For all other salts, i.e. sodium chlorate, nitrate, and thiocyanate, heat was released upon mixing. The situation was similar for 6,6-ionene fluoride solutions with an exception of mixing with sodium chlorate, where the effect was endothermic. The enthalpy of mixing was strongly correlated with the enthalpy of hydration of the counterion of the low molecular weight salt. A lyotropic series, similar to that of Hofmeister, was obtained. To examine also the effect of co-ions, ionene bromides were titrated with tetramethyl-, tetraethyl-, or tetrapropylammonium bromides. The enthalpy was exothermic for all mixtures while, somewhat unexpectedly, the co-ion specific effect was quite strong.

Disordered porous materials filled with liquid or solution may be considered as partly-quenched, i.e., as systems in which some of the degrees of freedom are quenched and others annealed. In such cases, the statistical-mechanical averages used to calculate the system's thermodynamical properties become double ensemble averages: first over the annealed degrees of freedom and then over all possible values of the quenched variables. In this respect, the quenched-annealed systems differ from regular mixtures. The multi-faceted applications of the partly-quenched systems to a kaleidoscope of technological and biological processes make the understanding of these systems important and of interest. Present contribution reviews recent developments in theory and simulation of partly-quenched systems containing charges. Specifically, two different models of such systems are discussed: (a) the model in which the nanoporous system (matrix subsystem) formed by charged obstacles is electroneutral, and (b) the model, where the subsystem of obstacles has some net charge. The latter model resembles, for example, the situation in ion exchange resins etc. Various theoretical methods are applied to investigate structural and dynamical peculiarities of such systems. One is the replica Ornstein-Zernike theory, especially adapted for charged systems, and the other is the Monte Carlo computer simulation method. These two approaches are well suited to study thermodynamical parameters, such as the mean activity coefficient of the annealed electrolyte or Donnan's exclusion parameter. Highly relevant issue of dynamics of ions in partly-quenched systems is also addressed. For this purpose, the Brownian dynamic method is used: the self-diffusion coefficients of ions are calculated for various model parameters and discussed in light of the experimental data. These results, together with the thermodynamical data mentioned above, provide additional evidence that properties of the adsorbed fluid substantially differ from those of its bulk counterpart.

Proteins function in crowded aqueous environments interacting with a diverse range of compounds, among them dissolved ions. These interactions are water mediated. In the present study we combine field dependent NMR relaxation (NMRD) and theory to probe water dynamics at the surface of protein in concentrated aqueous solutions of hen egg-white lysozyme (LZM) and bovine serum albumin (BSA). The experiments reveal that presence of salts (NaCl or NaI) leads to an opposite ion-specific response for the two proteins: an addition of salt to LZM solutions increases water relaxation rates with respect to the salt-free case, while for BSA solutions a decrease is observed. The magnitude of the change depends on the ion identity. The developed model accounts for the non-Lorentzian shape of the NMRD profiles and reproduces the experimental data over four decades in Larmor frequency (10 kHz to 110 MHz). It is applicable 1

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