Galli Group analyzes structure of salt water from first principles

Alex Gaiduk, an NSERC Postdoctoral Fellow in the Galli Group, along with Liew Family Professor Giulia Galli, recently published a new paper in the Journal of Physical Chemistry Letters on the effects that dissolved salts have on the structure of water.

One of the intriguing questions about water is to what extent its structure is modified by the presence of these dissolved salts. This question has important implications, for example, for explaining the origin of the Hofmeister series, which ranks different salts on their ability to increase/decrease solubility of large biomolecules in water.

Using state-of-the-art first-principles simulations of a sodium chloride solution in water, they determined that the constituent ions affect the liquid in different ways. Na+ has a strong local but weak long-range effect on the structure of water, while Cl− has a weak local but noticeable long-range effect on the hydrogen bond network of water, which is observed even outside the second solvation shell of the ion.

They identified structural and electronic fingerprints of this effect, namely the modification of the number of hydrogen bonds in different solvation shells and changes in molecular polarizabilities. Molecular dipoles, extensively used in the past to analyze salty water, are instead found to be rather insensitive probes. Even though the effect of Cl− extends far from the ion, it is too weak to affect solubility of large biomolecules in water, suggesting that the Hofmeister series likely arises due to direct interaction of proteins with salts.