Liquid–liquid phase separation of N-isopropylpropionamide aqueous solutions above the lower critical solution temperature

Liquid–liquid phase separation of N-isopropylpropionamide aqueous solutions above the lower critical solution temperature

We investigate driving forces of the liquid–liquid phase separation of N-isopropylpropionamide (NiPPA) aqueous solutions above the lower critical solution temperature using molecular dynamics simulations. Spontaneous phase separations of the model aqueous solution with a modified OPLS-AA force field...

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Main Authors: Mochizuki, Kenji, Sumi, Tomonari, Koga, Kenichiro
Format: Online
Language:English
Published: Nature Publishing Group 2016
Online Access:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4838917/
id pubmed-4838917
recordtype oai_dc
spelling pubmed-48389172016-04-27 Liquid–liquid phase separation of N-isopropylpropionamide aqueous solutions above the lower critical solution temperature Mochizuki, Kenji Sumi, Tomonari Koga, Kenichiro Article We investigate driving forces of the liquid–liquid phase separation of N-isopropylpropionamide (NiPPA) aqueous solutions above the lower critical solution temperature using molecular dynamics simulations. Spontaneous phase separations of the model aqueous solution with a modified OPLS-AA force field are observed above the experimentally determined cloud point. The destabilization toward the phase separation is confirmed by temperature dependence of the long-wavelength limit of the concentration-concentration structure factor, the dominant component of which is found to be an increasing effective attraction between NiPPA molecules. At varying temperatures, the potentials of mean force (PMFs) between a pair of NiPPA molecules at infinite dilution are obtained and decomposed into the nonpolar and Coulombic contributions. The nonpolar contribution, arising essentially from molecular volume, promotes association of NiPPA molecules with increasing temperature while the Coulombic one antagonizes the association. Thus, our analysis leads to a conclusion that the driving force of thermally induced aggregation of NiPPA molecules is the temperature dependence of the nonpolar contribution in PMF between NiPPA molecules, not the temperature dependence of the number or strength of hydrogen bonds between NiPPA and water molecules. Nature Publishing Group 2016-04-21 /pmc/articles/PMC4838917/ /pubmed/27098236 http://dx.doi.org/10.1038/srep24657 Text en Copyright © 2016, Macmillan Publishers Limited http://creativecommons.org/licenses/by/4.0/ This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
repository_type Open Access Journal
institution_category Foreign Institution
institution US National Center for Biotechnology Information
building NCBI PubMed
collection Online Access
language English
format Online
author Mochizuki, Kenji
Sumi, Tomonari
Koga, Kenichiro
spellingShingle Mochizuki, Kenji
Sumi, Tomonari
Koga, Kenichiro
Liquid–liquid phase separation of N-isopropylpropionamide aqueous solutions above the lower critical solution temperature
author_facet Mochizuki, Kenji
Sumi, Tomonari
Koga, Kenichiro
author_sort Mochizuki, Kenji
title Liquid–liquid phase separation of N-isopropylpropionamide aqueous solutions above the lower critical solution temperature
title_short Liquid–liquid phase separation of N-isopropylpropionamide aqueous solutions above the lower critical solution temperature
title_full Liquid–liquid phase separation of N-isopropylpropionamide aqueous solutions above the lower critical solution temperature
title_fullStr Liquid–liquid phase separation of N-isopropylpropionamide aqueous solutions above the lower critical solution temperature
title_full_unstemmed Liquid–liquid phase separation of N-isopropylpropionamide aqueous solutions above the lower critical solution temperature
title_sort liquid–liquid phase separation of n-isopropylpropionamide aqueous solutions above the lower critical solution temperature
description We investigate driving forces of the liquid–liquid phase separation of N-isopropylpropionamide (NiPPA) aqueous solutions above the lower critical solution temperature using molecular dynamics simulations. Spontaneous phase separations of the model aqueous solution with a modified OPLS-AA force field are observed above the experimentally determined cloud point. The destabilization toward the phase separation is confirmed by temperature dependence of the long-wavelength limit of the concentration-concentration structure factor, the dominant component of which is found to be an increasing effective attraction between NiPPA molecules. At varying temperatures, the potentials of mean force (PMFs) between a pair of NiPPA molecules at infinite dilution are obtained and decomposed into the nonpolar and Coulombic contributions. The nonpolar contribution, arising essentially from molecular volume, promotes association of NiPPA molecules with increasing temperature while the Coulombic one antagonizes the association. Thus, our analysis leads to a conclusion that the driving force of thermally induced aggregation of NiPPA molecules is the temperature dependence of the nonpolar contribution in PMF between NiPPA molecules, not the temperature dependence of the number or strength of hydrogen bonds between NiPPA and water molecules.
publisher Nature Publishing Group
publishDate 2016
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4838917/
_version_ 1613568784760569856

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