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Alterations in Water Structure Induced by Guanidinium and Sodium Ions



Raymond D. Mountain, D Thirumalai


Using molecular dynamics simulations we have probed the ion-induced changes in the water structure as the concentration of ion is varied. We consider two ions, namely, sodium chloride and guanadinium chloride. As the concentration of sodium ions, Na^+, is increased the water structure is greatly perturbed. When the mole fraction of water is less than about 0.93 the tetrahedral network of water is affected. At the smallest water mole fraction considered there is a total disruption of the tetrahdedral structure of water just as found in water at high pressures. The number of water-water hydrogen bonds per water molecule is greatly diminished as Na^+ concentration increases. Surprisingly, we find that the number of water molecules that are coordinated to Na^+ is nearly independent of the sodium chloride concentration. In contrast to the the kosmotropic ion Na^+, the weakly hydrated chaotropic ion Gdm^+ does not alter the water structure as dramatically. At all Gdm^+ concentrations the water hydrogen bonds are fully preserved. We find that the tetrahedral network of water is compromised nnly at the highest Gdm^+ concentration. The differences in the interaction of these two ions with water as their concentration is varied are used to propose a mechanism by which Gdm^+ denatures proteins.
Journal of Physical Chemistry B
No. 51


guandinium chloride, molecular dynamics, molecular simulation, sodium chloride, solvations, water


Mountain, R. and Thirumalai, D. (2004), Alterations in Water Structure Induced by Guanidinium and Sodium Ions, Journal of Physical Chemistry B (Accessed February 23, 2024)
Created November 1, 2004, Updated February 17, 2017