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Effects of Optical Purity and Finite System Size on Self-Assembly of 12-Hydroxystearic Acid in Hexane: Molecular Dynamics Simulations
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2017-09-21 00:00:00 , DOI: 10.1021/acs.jpcb.7b05246 Ryan Gordon 1 , Spencer T. Stober 2 , Cameron F. Abrams 1
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2017-09-21 00:00:00 , DOI: 10.1021/acs.jpcb.7b05246 Ryan Gordon 1 , Spencer T. Stober 2 , Cameron F. Abrams 1
Affiliation
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12-Hydroxystearic acid (12HSA) and its derivatives are well-known organogelators, and they play critical roles in a variety of applications. The overall aggregate structure of 12HSA is sensitive to the chirality at the 12th carbon, but a fundamental understanding of this dependence is lacking. In this study, molecular dynamics simulations were conducted on microsecond long time scales for (1) (R)-12HSA, (2) (S)-12HSA, and (3) a 50/50 racemic mixture, each solvated at 12.5 wt % in explicit hexane. Self-assembly was accelerated by turning off alkyl chain dihedral gauche states and forcing the molecules to adopt an all-trans conformation. The stability of the resulting aggregates was tested by quenching them with access to gauche states restored. Ordered aggregates produced from optically pure (R)- and (S)-12HSA remained stable for at least 1 μs. The characteristic ordered structure observed is termed a “ring-of-rings” motif, and it contains two twisted six-membered ringlike bundles connected through acetic acid dimerization and surrounded by six satellite bundles. The chirality at the 12th carbon dictates the overall twist of the rings and thereby the handedness of the aggregates. Racemic mixtures did not produce stable ordered aggregates likely due to insufficient enantiomerically pure ring formation. The most prevalent finite-size effect observed was the stochastic formation of percolating aggregates, which were later avoided by using solvent-permeable, solute-impermeable, confining walls. The resulting ordered aggregates were in all important ways identical to those produced in unconfined systems. The combination of cycling off and on gauche states and the semipermeable walls may be an important new way to study the self-assembly underlying aggregation at industrially relevant concentrations of surfactants in organic solvents.
中文翻译：
光学纯度和有限体系尺寸对己烷中12-羟基硬脂酸自组装的影响：分子动力学模拟
12-羟基硬脂酸（12HSA）及其衍生物是众所周知的有机胶凝剂，它们在各种应用中都起着至关重要的作用。12HSA的总体聚集结构对第12个碳原子上的手性敏感，但缺乏对这种依赖性的基本了解。在这项研究中，对（1）（R）-12HSA，（2）（S）-12HSA和（3）50/50外消旋混合物（分别以12.5 wt％溶剂化）进行了微秒级长时间分子动力学模拟。在明确的己烷中。自组装通过关闭烷基链二面角加速笨拙状态和迫使分子采用一种清一色反式构象。通过将其淬灭，测试所得聚集体的稳定性。印第安州恢复。由光学纯（R）和（S产生的有序骨料。）-12HSA保持稳定至少1μs。观察到的特征性有序结构称为“环环”图案，它包含两个扭曲的六元环状束，这些束通过乙酸二聚作用连接，并被六个卫星束包围。在第12个碳原子上的手性决定了环的整体扭曲，从而决定了聚集体的旋向性。外消旋混合物未产生稳定的有序聚集体，这可能是由于对映体纯的环形成不足所致。观察到的最普遍的有限尺寸效应是渗流聚集体的随机形成，其后通过使用溶剂可渗透的，溶质不可渗透的封闭壁来避免。所得的有序聚集体在所有重要方面都与无约束系统中产生的有序聚集体相同。骑自行车断断续续的结合gauche状态和半渗透性壁可能是研究在有机溶剂中工业上相关浓度的表面活性剂下聚集的自组装基础的重要新方法。
更新日期：2017-09-21
中文翻译：
光学纯度和有限体系尺寸对己烷中12-羟基硬脂酸自组装的影响：分子动力学模拟
12-羟基硬脂酸（12HSA）及其衍生物是众所周知的有机胶凝剂，它们在各种应用中都起着至关重要的作用。12HSA的总体聚集结构对第12个碳原子上的手性敏感，但缺乏对这种依赖性的基本了解。在这项研究中，对（1）（R）-12HSA，（2）（S）-12HSA和（3）50/50外消旋混合物（分别以12.5 wt％溶剂化）进行了微秒级长时间分子动力学模拟。在明确的己烷中。自组装通过关闭烷基链二面角加速笨拙状态和迫使分子采用一种清一色反式构象。通过将其淬灭，测试所得聚集体的稳定性。印第安州恢复。由光学纯（R）和（S产生的有序骨料。）-12HSA保持稳定至少1μs。观察到的特征性有序结构称为“环环”图案，它包含两个扭曲的六元环状束，这些束通过乙酸二聚作用连接，并被六个卫星束包围。在第12个碳原子上的手性决定了环的整体扭曲，从而决定了聚集体的旋向性。外消旋混合物未产生稳定的有序聚集体，这可能是由于对映体纯的环形成不足所致。观察到的最普遍的有限尺寸效应是渗流聚集体的随机形成，其后通过使用溶剂可渗透的，溶质不可渗透的封闭壁来避免。所得的有序聚集体在所有重要方面都与无约束系统中产生的有序聚集体相同。骑自行车断断续续的结合gauche状态和半渗透性壁可能是研究在有机溶剂中工业上相关浓度的表面活性剂下聚集的自组装基础的重要新方法。
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