Electrostatic contribution from solvent in modulating single-walled carbon nanotube association.

Content Provider	Europe PMC
Author	Ou, Shu-Ching Patel, Sandeep
Copyright Year	2014
Description	We perform all-atom molecular dynamics simulations to compute the potential of mean force (PMF) between two (10,10) single-walled carbon nanotubes solvated in pure nonpolarizable SPC/E and polarizable TIP4P-FQ water, at various temperatures. In general, the reversible work required to bring two nanotubes from a dissociated state (free energy reference) to contact state (free energy minimum) is more favorable and less temperature-dependent in TIP4P-FQ than in SPC/E water models. In contrast, molecular properties and behavior of water such as the spatially-resolved water number density (intertube, intratube, or outer regions), for TIP4P-FQ are more sensitive to temperature than SPC/E. Decomposition of the solvent-induced PMF into different spatial regions suggests that TIP4P-FQ has stronger temperature dependence; the opposing destabilizing/stabilizing contributions from intertube water and more distal water balance each other and suppress the temperature dependence of total association free energy. Further investigation of hydrogen bonding network in intertube water reveals that TIP4P-FQ retains fewer hydrogen bonds than SPC/E, which correlates with the lower water number density in this region. This reduction of hydrogen bonds affects the intertube water dipoles. As the intertube volume decreases, TIP4P-FQ dipole moment approaches the gas phase value; the distribution of dipole magnitude also becomes narrower due to less average polarization/perturbation from other water molecules. Our results imply that the reduction of water under confinement may seem trivial, but underlying effects to structure and free energetics are non-negligible.
Abstract	We perform all-atom molecular dynamics simulations to compute the potential of mean force (PMF)between two (10,10) single-walled carbon nanotubes solvated in pure nonpolarizable SPC/E andpolarizable TIP4P-FQ water, at various temperatures. In general, the reversible work required tobring two nanotubes from a dissociated state (free energy reference) to contact state (free energyminimum) is more favorable and less temperature-dependent in TIP4P-FQ than in SPC/E water models. Incontrast, molecular properties and behavior of water such as the spatially-resolved water numberdensity (intertube, intratube, or outer regions), for TIP4P-FQ are more sensitive to temperaturethan SPC/E. Decomposition of the solvent-induced PMF into different spatial regions suggests thatTIP4P-FQ has stronger temperature dependence; the opposing destabilizing/stabilizing contributionsfrom intertube water and more distal water balance each other and suppress the temperaturedependence of total association free energy. Further investigation of hydrogen bonding network inintertube water reveals that TIP4P-FQ retains fewer hydrogen bonds than SPC/E, which correlates withthe lower water number density in this region. This reduction of hydrogen bonds affects theintertube water dipoles. As the intertube volume decreases, TIP4P-FQ dipole moment approaches thegas phase value; the distribution of dipole magnitude also becomes narrower due to less averagepolarization/perturbation from other water molecules. Our results imply that the reduction of waterunder confinement may seem trivial, but underlying effects to structure and free energetics arenon-negligible.
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Page Count	14
ISSN	00219606
Volume Number	141
DOI	10.1063/1.4892566
PubMed Central reference number	PMC4187323
Issue Number	11
PubMed reference number	25240371
Journal	The Journal of Chemical Physics [J Chem Phys]
e-ISSN	10897690
Language	English
Publisher	American Institute of Physics
Publisher Date	2014-09-01
Access Restriction	Open
Rights License	0021-9606/2014/141(11)/114906/14/$30.00 Copyright © 2014 AIP Publishing LLC
Content Type	Text
Resource Type	Article
Subject	Physics and Astronomy Medicine Physical and Theoretical Chemistry