Assessment of dynamic properties of water aroung a monovalent ion: A classical molecular dynamics simulation study
Ikuo Kurisakia, Takuya Takahashia,b,*
a Research Organization of Science and Engineering, Ritsumeikan University, 1-1-1, Noju-Higashi, Kusatsu, 525-8577 Shiga-ken, Japan
b Department of Bioscience and Bioinformatics, Ritsumeikan University, 1-1-1, Noju-Higashi, Kusatsu, 525-8577 Shiga-ken, Japan
This paper shows the behavior of and the dynamic properties of water molecules under the influence of monovalent ions. Terahertz microscopy has also shown the dynamic properties of water in monovalent ions solution. There are few simulation studies on it. So, this paper, rather than experimental results, shows modeling aspect. Moreover, quantum mechanics and molecular mechanics studies could reproduce the dynamic properties of water in the solution of monovalent ions. In this study, seven different rigid water models (SPC/E, TIP3P, TIP4P, TIP5P, TIP3P-F, TIP4P-EW, and TIP5P-E) were used. MD simulation was done in AMBER. Simulation time was 20 ps under constant volume at 298 K. The density was fixed to 1 g/cm3 at a pressure of 1 bar.
D1/Dbulk and τ1/τbulk were studied with the change in the atomic number of the ion. D1, Dbulk, τ1, and τbulk represent the self- diffusion coefficient in first hydration layer and bulk water and rotational relaxation time constants of water in the first hydration layer and bulk water respectively. When D1/Dbulk (τ1/τbulk) was greater than unity, it was named fast water because mobility increases and slow water was named for the opposite case. The figures below explain the results.
The results indicate that the use of conventional water models and AMBER ion parameters were unable to reproduce fast water molecules thus classical molecular dynamics was used to understand the mechanism. Moreover TIP5P water model was found best to explain the hydration of water molecules in the presence of monovalent ions.
Reviewer: Aamir Alaud Din