Computational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid

In this work, molecular dynamics simulations were performed to study the pH-induced structural transitions for a CTAB/<i>p</i>-toluic acid solution. Spherical and cylindrical micelles were obtained for aqueous surfactants at pH 2 and 7, respectively, which agrees well with the experiment...

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Autores principales:	Tingyi Wang, Hui Yan, Li Lv, Yingbiao Xu, Lingyu Zhang, Han Jia
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	molecular dynamics simulation pH-induced structural transitions rodlike micelle sphecial micelle cationic surfactant Organic chemistry QD241-441
Acceso en línea:	https://doaj.org/article/7a5ef81e2f3c4242a6a246705062f1e2
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spelling	oai:doaj.org-article:7a5ef81e2f3c4242a6a246705062f1e22021-11-25T18:28:52ZComputational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid10.3390/molecules262269781420-3049https://doaj.org/article/7a5ef81e2f3c4242a6a246705062f1e22021-11-01T00:00:00Zhttps://www.mdpi.com/1420-3049/26/22/6978https://doaj.org/toc/1420-3049In this work, molecular dynamics simulations were performed to study the pH-induced structural transitions for a CTAB/<i>p</i>-toluic acid solution. Spherical and cylindrical micelles were obtained for aqueous surfactants at pH 2 and 7, respectively, which agrees well with the experimental observations. The structural properties of two different micelles were analyzed through the density distributions of components and the molecular orientations of CTA<sup>+</sup> and toluic acid inside the micelles. It was found that the bonding interactions between CTA<sup>+</sup> and toluic in spherical and cylindrical micelles are very different. Almost all the ionized toluic acid (PTA<sup>−</sup>) in the solution at pH 7 was solubilized into the micelles, and it was located in the CTA<sup>+</sup> headgroups region. Additionally, the bonding between surfactant CTA<sup>+</sup> and PTA<sup>−</sup> was very tight due to the electrostatic interactions. The PTA<sup>−</sup> that penetrated into the micelles effectively screened the electrostatic repulsion among the cationic headgroups, which is considered to be crucial for maintaining the cylindrical micellar shape. As the pH decreased, the carboxyl groups were protonated. The hydration ability of neutral carboxyl groups weakened, resulting in deeper penetration into the micelles. Meanwhile, their bonding interactions with surfactant headgroups also weakened. Accompanied by the strengthen of electrostatic repulsion among the positive headgroups, the cylindrical micelle was broken into spherical micelles. Our work provided an atomic-level insights into the mechanism of pH-induced structural transitions of a CTAB/<i>p</i>-toluic solution, which is expected to be useful for further understanding the aggregate behavior of mixed cationic surfactants and aromatic acids.Tingyi WangHui YanLi LvYingbiao XuLingyu ZhangHan JiaMDPI AGarticlemolecular dynamics simulationpH-induced structural transitionsrodlike micellesphecial micellecationic surfactantOrganic chemistryQD241-441ENMolecules, Vol 26, Iss 6978, p 6978 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	molecular dynamics simulation pH-induced structural transitions rodlike micelle sphecial micelle cationic surfactant Organic chemistry QD241-441
spellingShingle	molecular dynamics simulation pH-induced structural transitions rodlike micelle sphecial micelle cationic surfactant Organic chemistry QD241-441 Tingyi Wang Hui Yan Li Lv Yingbiao Xu Lingyu Zhang Han Jia Computational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid
description	In this work, molecular dynamics simulations were performed to study the pH-induced structural transitions for a CTAB/<i>p</i>-toluic acid solution. Spherical and cylindrical micelles were obtained for aqueous surfactants at pH 2 and 7, respectively, which agrees well with the experimental observations. The structural properties of two different micelles were analyzed through the density distributions of components and the molecular orientations of CTA<sup>+</sup> and toluic acid inside the micelles. It was found that the bonding interactions between CTA<sup>+</sup> and toluic in spherical and cylindrical micelles are very different. Almost all the ionized toluic acid (PTA<sup>−</sup>) in the solution at pH 7 was solubilized into the micelles, and it was located in the CTA<sup>+</sup> headgroups region. Additionally, the bonding between surfactant CTA<sup>+</sup> and PTA<sup>−</sup> was very tight due to the electrostatic interactions. The PTA<sup>−</sup> that penetrated into the micelles effectively screened the electrostatic repulsion among the cationic headgroups, which is considered to be crucial for maintaining the cylindrical micellar shape. As the pH decreased, the carboxyl groups were protonated. The hydration ability of neutral carboxyl groups weakened, resulting in deeper penetration into the micelles. Meanwhile, their bonding interactions with surfactant headgroups also weakened. Accompanied by the strengthen of electrostatic repulsion among the positive headgroups, the cylindrical micelle was broken into spherical micelles. Our work provided an atomic-level insights into the mechanism of pH-induced structural transitions of a CTAB/<i>p</i>-toluic solution, which is expected to be useful for further understanding the aggregate behavior of mixed cationic surfactants and aromatic acids.
format	article
author	Tingyi Wang Hui Yan Li Lv Yingbiao Xu Lingyu Zhang Han Jia
author_facet	Tingyi Wang Hui Yan Li Lv Yingbiao Xu Lingyu Zhang Han Jia
author_sort	Tingyi Wang
title	Computational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid
title_short	Computational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid
title_full	Computational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid
title_fullStr	Computational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid
title_full_unstemmed	Computational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid
title_sort	computational investigations of a ph-induced structural transition in a ctab solution with toluic acid
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/7a5ef81e2f3c4242a6a246705062f1e2
work_keys_str_mv	AT tingyiwang computationalinvestigationsofaphinducedstructuraltransitioninactabsolutionwithtoluicacid AT huiyan computationalinvestigationsofaphinducedstructuraltransitioninactabsolutionwithtoluicacid AT lilv computationalinvestigationsofaphinducedstructuraltransitioninactabsolutionwithtoluicacid AT yingbiaoxu computationalinvestigationsofaphinducedstructuraltransitioninactabsolutionwithtoluicacid AT lingyuzhang computationalinvestigationsofaphinducedstructuraltransitioninactabsolutionwithtoluicacid AT hanjia computationalinvestigationsofaphinducedstructuraltransitioninactabsolutionwithtoluicacid
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Computational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid

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