Local and Global Effects of Dissolved Sodium Chloride on the Structure of Water

Abstract

Determining how the structure of water is modified by the presence of salts is instrumental to understanding the solvation of biomolecules and, in general, the role played by salts in biochemical processes. However, the extent of hydrogen bonding disruption induced by salts remains controversial. We performed extensive first-principles simulations of solutions of a simple salt (NaCl) and found that, while the cation does not significantly change the structure of water beyond the first solvation shell, the anion has a further reaching effect, modifying the hydrogen-bond network even outside its second solvation shell. We found that a distinctive fingerprint of hydrogen bonding modification is the change in polarizability of water molecules. Molecular dipole moments are instead insensitive probes of long-range modifications induced by Na and Cl ions. Though noticeable, the long-range effect of Cl is expected to be too weak to affect solubility of large biomolecules.

Communication: Dielectric properties of condensed systems composed of fragments

“…Using the DFT method, we also calculated the molecular polarizabilities of water in the first solvation shell of the Na + ion at ambient conditions [22]:ᾱ mol is 1.62Å 3 , which is again slightly larger than that obtained by the DID approximation by ∼3%. For water molecules with dangling bonds in the basal surface layer of ice Ih [23,24], the difference inᾱ mol given by the DFT and DID approaches is even smaller: 1.62Å 3 vs 1.61Å 3 , only ∼1%.…”

Cationic and Anionic Impact on the Electronic Structure of Liquid Water

“…A considerable number of experiments have been performed to elucidate the water-ion interaction 3 and the interpretations of the data suggest sometimes a complex picture about the nature of the ion solvation. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Studies from X-ray scattering, 7 dielectric relaxations, 8,9 infrared, [10][11][12][13] and terahertz spectroscopy 15 showed that the impact on water molecules by solvated ions is mainly restricted to water molecules in close vicinity to the ion. Only for specific combinations of strongly hydrated salt ions it has been reported that the impact on the orientation of water molecules may extend beyond the first solvation shell.…”

Anionic effects on the structure and dynamics of water in superconcentrated aqueous electrolytes

“…13 Hence the effects of ions on the structure and dynamics of water have been extensively investigated both experimentally and theoretically. [14][15][16][17][18][19][20][21][22][23][24] For example, there is a subject of ongoing discussion about the spatial extent of the inuence of the dissolved ions on the structure of the surrounding water molecules in solutions. Recent studies have shown that long-range orientational order between water molecules exists in dilute salt solutions.…”