Hydrated Sodium Ion Clusters [Na+(H2O)n (n = 1-6)]: An ab initio Study on Structures and Non-covalent Interaction.

Pengju Wang,Ruili Shi,Xiaoming Huang,Lingli Tang,Jijun Zhao,Yan Su

doi:10.3389/fchem.2019.00624

Abstract

Structural, thermodynamic, and vibrational characteristics of water clusters up to six water molecules incorporating a single sodium ion [Na+(H2O)n (n = 1–6)] are calculated using a comprehensive genetic algorithm combined with density functional theory on global search, followed by high-level ab initio calculation. For n ≥ 4, the coordinated water molecules number for the global minimum of clusters is 4 and the outer water molecules connecting with coordinated water molecules by hydrogen bonds. The charge analysis reveals the electron transfer between sodium ions and water molecules, providing an insight into the variations of properties of O–H bonds in clusters. Moreover, the simulated infrared (IR) spectra with anharmonic correction are in good agreement with the experimental results. The O–H stretching vibration frequencies show redshifts comparing with a free water molecule, which is attributed to the non-covalent interactions, including the ion–water interaction, and hydrogen bonds. Our results exhibit the comprehensive geometries, energies, charge, and anharmonic vibrational properties of Na+(H2O)n (n = 1–6), and reveal a deeper insight of non-covalent interactions.

Highlights

Hydrated ion clusters widely exist in oceans and living organisms, especially hydrated sodium ion clusters, which are important in the control of blood pressure, cell permeability, neuronal activity, and other somatic functions (Jensen, 1992; Feller et al, 1994; Pohl et al, 2013)
A global minimum can be determined by obtaining the stabilization energies of Hydrated Sodium Ion Clusters isomers
For Na+(H2O)5, 4+1+0 is supported as the global minimum by most ab initio calculations at 0 K (Hashimoto and Morokuma, 1994; Kim et al, 1995; Lee et al, 2004; Rao et al, 2008; Neela et al, 2012; Biring et al, 2013; Soniat et al, 2015; Fifen and Agmon, 2016), and 5+0+0 is deemed to be concomitant with 4+1+0 at 298 K (Kim et al, 1995; Fifen and Agmon, 2016)

Summary

INTRODUCTION

Hydrated ion clusters widely exist in oceans and living organisms, especially hydrated sodium ion clusters, which are important in the control of blood pressure, cell permeability, neuronal activity, and other somatic functions (Jensen, 1992; Feller et al, 1994; Pohl et al, 2013). For Na+(H2O)5, 4+1+0 (the structures of isomers are presented in the form of n1+n2+n3, where n1, n2, and n3 are the numbers of water molecules in the first, second, and third solvation shells, respectively) is supported as the global minimum by most ab initio calculations at 0 K (Hashimoto and Morokuma, 1994; Kim et al, 1995; Lee et al, 2004; Rao et al, 2008; Neela et al, 2012; Biring et al, 2013; Soniat et al, 2015; Fifen and Agmon, 2016), and 5+0+0 is deemed to be concomitant with 4+1+0 at 298 K (Kim et al, 1995; Fifen and Agmon, 2016). Charge transfer inside the clusters through NBO analysis and charge density difference are contained, aiming to reveal the principle of non-covalent interactions effecting on the O–H bonds

METHODS

RESULTS AND DISCUSSION

CONCLUSION