Structure and thermodynamics of supercooled aqueous solutions: Ionic solutes compared with water in a hydrophobic environment

Molecular dynamics results are presented for bulk TIP4P water and for aqueous solutions of sodium chloride at two different concentrations. Thermodynamical and structural properties are calculated in the supercooled region. The behaviour in the thermodynamic plane is compared with the case of water in interaction with a hydrophobic environment. Structural modifications induced by the hydrophilic and hydrophobic interactions are discussed. It is found that the phase diagram of water is shifted in different directions in the case of the hydrophobic system and the ionic solutions. The region inside the temperatures of the maximum density curve is reduced upon increasing the concentration of ions.