Journal article
Aggregation of 12-Hydroxystearic Acid and Its Lithium Salt in Hexane: Molecular Dynamics Simulations
The journal of physical chemistry. B, v 120(29), pp 7164-7173
28 Jul 2016
PMID: 27387154
Featured in Collection : UN Sustainable Development Goals @ Drexel
Abstract
12-Hydroxystearic acid (12HSA) is a well-known organogelator, and its metal salts and derivatives find roles in many important applications. The structures of aggregates of 12-hydroxysteric acid and its salts depend sensitively on cation type, but a fundamental understanding of this phenomenon is lacking. In this study, molecular dynamics simulations were conducted on the microsecond long time scales for (1) 12HSA and (2) its lithium salt, each at 12.5 wt % in explicit hexane solvent. Self-assembly was accelerated by using a modified potential to prohibit alkane chain dihedral gauche states (all-trans-12HSA) and then verified by continuation using standard force-field parameters. In three independent simulation, acceleration using "gauche-less" potentials resulted in self-assembled pseudocrystalline aggregates through formation of polarized five- and six-membered rings between inter-12-hydroxyl groups and head-to-head carboxylic acid dimerization. When subjected to the unmodified dihedral potential, two of the three structures remained stable after 1 μs of MD. Stable structures exhibited a "ring-of-rings" motif, composed of two six-membered acetic acid-dimerized ring bundles with six satellite rings, while the unstable structure did not. In strong contrast, the lithium salt produced a network of fibrils that spanned the volume of the sample. When lithium ions were substituted for carboxylic acid protons in the stable acid structures, they remained intact but lost their chiral nature. Both the acid and lithium structures displayed scattering peaks that agreed with experiment. Taken together, our results suggest that this ring-of-rings structure could be a primary feature of the self-assembly of 12HSA in organic solvents.
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Details
- Title
- Aggregation of 12-Hydroxystearic Acid and Its Lithium Salt in Hexane: Molecular Dynamics Simulations
- Creators
- Ryan Gordon - Department of Chemical and Biological Engineering, Drexel University , Philadelphia, Pennsylvania 19104, United StatesSpencer T Stober - ExxonMobil Research and Engineering, Annandale, New Jersey 08801, United StatesCameron F Abrams - Department of Chemical and Biological Engineering, Drexel University , Philadelphia, Pennsylvania 19104, United States
- Publication Details
- The journal of physical chemistry. B, v 120(29), pp 7164-7173
- Publisher
- American Chemical Society; Washington, DC
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Chemical and Biological Engineering
- Web of Science ID
- WOS:000380730300014
- Scopus ID
- 2-s2.0-84979881265
- Other Identifier
- 991014969877304721
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- Collaboration types
- Industry collaboration
- Domestic collaboration
- Web of Science research areas
- Biophysics
- Chemistry, Physical