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Ion enrichment on the hydrophobic carbon-based surface in aqueous salt solutions due to cation-? interactions.

ABSTRACT: By incorporating cation-? interactions to classic all-atoms force fields, we show that there is a clear enrichment of Na(+) on a carbon-based ? electron-rich surface in NaCl solutions using molecular dynamics simulations. Interestingly, Cl(-) is also enriched to some extend on the surface due to the electrostatic interaction between Na(+) and Cl(-), although the hydrated Cl(-)-? interaction is weak. The difference of the numbers of Na(+) and Cl(-) accumulated at the interface leads to a significant negatively charged behavior in the solution, especially in nanoscale systems. Moreover, we find that the accumulation of the cations at the interfaces is universal since other cations (Li(+), K(+), Mg(2+), Ca(2+), Fe(2+), Co(2+), Cu(2+), Cd(2+), Cr(2+), and Pb(2+)) have similar adsorption behaviors. For comparison, as in usual force field without the proper consideration of cation-? interactions, the ions near the surfaces have a similar density of ions in the solution.

SUBMITTER: Shi G

PROVIDER: S-EPMC3853681 | biostudies-literature | 2013 Dec

REPOSITORIES: biostudies-literature

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Ion enrichment on the hydrophobic carbon-based surface in aqueous salt solutions due to cation-π interactions.

Shi Guosheng G Liu Jian J Wang Chunlei C Song Bo B Tu Yusong Y Hu Jun J Fang Haiping H

Scientific reports 20131206

By incorporating cation-π interactions to classic all-atoms force fields, we show that there is a clear enrichment of Na(+) on a carbon-based π electron-rich surface in NaCl solutions using molecular dynamics simulations. Interestingly, Cl(-) is also enriched to some extend on the surface due to the electrostatic interaction between Na(+) and Cl(-), although the hydrated Cl(-)-π interaction is weak. The difference of the numbers of Na(+) and Cl(-) accumulated at the interface leads to a signific ...[more]

PMID: 24310448

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Project description:In this study, we examine the temperature dependence of free energetics of nanotube association using graphical processing unit-enabled all-atom molecular dynamics simulations (FEN ZI) with two (10,10) single-walled carbon nanotubes in 3 m NaI aqueous salt solution. Results suggest that the free energy, enthalpy and entropy changes for the association process are all reduced at the high temperature, in agreement with previous investigations using other hydrophobes. Via the decomposition of free energy into individual components, we found that solvent contribution (including water, anion, and cation contributions) is correlated with the spatial distribution of the corresponding species and is influenced distinctly by the temperature. We studied the spatial distribution and the structure of the solvent in different regions: intertube, intratube and the bulk solvent. By calculating the fluctuation of coarse-grained tube-solvent surfaces, we found that tube-water interfacial fluctuation exhibits the strongest temperature dependence. By taking ions to be a solvent-like medium in the absence of water, tube-anion interfacial fluctuation shows similar but weaker dependence on temperature, while tube-cation interfacial fluctuation shows no dependence in general. These characteristics are discussed via the malleability of their corresponding solvation shells relative to the nanotube surface. Hydrogen bonding profiles and tetrahedrality of water arrangement are also computed to compare the structure of solvent in the solvent bulk and intertube region. The hydrophobic confinement induces a relatively lower concentration environment in the intertube region, therefore causing different intertube solvent structures which depend on the tube separation. This study is relevant in the continuing discourse on hydrophobic interactions (as they impact generally a broad class of phenomena in biology, biochemistry, and materials science and soft condensed matter research), and interpretations of hydrophobicity in terms of alternative but parallel signatures such as interfacial fluctuations, dewetting transitions, and enhanced fluctuation probabilities at interfaces.

Dataset Information

Ion enrichment on the hydrophobic carbon-based surface in aqueous salt solutions due to cation-? interactions.

Publications

Ion enrichment on the hydrophobic carbon-based surface in aqueous salt solutions due to cation-π interactions.

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