The Opposite Effect of Metal Ions on Short-/Long-Range Water Structure: A Multiple Characterization Study

Inorganic electrolyte solutions are very important in our society as they dominate many biochemical and geochemical processes. Herein, an in-depth study was performed to illustrate the ion-induced effect on water structure by coupling NMR, viscometer, Raman and Molecular Dynamic (MD) simulations. The NMR coefficient (BNMR) and diffusion coefficient (D) from NMR, and viscosity coefficient (Bvis) from a viscometer all proved that dissolved metal ions are capable of enhancing the association degree of adjacent water molecules, and the impact on water structure decreased in the order of Cr(3+) > Fe(3+) > Cu(2+) > Zn(2+). This regularity was further evidenced by Raman analysis; however, the deconvoluted Raman spectrum indicated the decrease in high association water with salt concentration and the increase in low association water before 200 mmol·L(-1). By virtue of MD simulations, the opposite changing manner proved to be the result of the opposite effect on short-/long-range water structure induced by metal ions. Our results may help to explain specific protein denaturation induced by metal ions.