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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Concentration Dependent Specific Rotations of Chiral Surfactants: Experimental and Computational Studies
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Concentration Dependent Specific Rotations of Chiral Surfactants: Experimental and Computational Studies

机译:手性表面活性剂的浓度依赖性比旋光度:实验和计算研究

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摘要

Recent experimental studies have shown unexpected chiroptical response from some chiral surfactant molecules, where the specific rotations changed significantly as a function of concentration. To establish a theoretical understanding of this experimentally observed phenomena, a novel methodology for studying chiral surfactants via combined molecular dynamics (MD) and quantum mechanical (QM) calculations is presented. MD simulations on the +10 000 atom surfactant systems have been performed using MD and QM/molecular mechanics (MM) approaches. QM calculations performed on MD snapshots coupled with extensive analysis on lauryl ester of phenylalanine (LEP) surfactant system indicate that the experimentally observed variation of specific rotation with concentration may be due to the conformational differences of the surfactant monomers in the aggregates. Though traditional MM simulations did not show significant differences in the conformer populations, QM/MM simulations using the forces derived from the PM6 method did predict conformational differences between aggregated and nonaggregated LEP molecules, which is consistent with experimental data. Additionally the electrostatic environment of charged surfactants may also be important, since dramatic changes in the Boltzmann populations of surfactant monomers can be noted in the presence of an electric field generated by the chiral ionic aggregates.
机译:最近的实验研究表明,一些手性表面活性剂分子具有出乎意料的手性反应,其中比旋光度随浓度的变化而显着变化。为了建立对该实验观察到的现象的理论理解,提出了一种通过结合分子动力学(MD)和量子力学(QM)计算研究手性表面活性剂的新方法。已经使用MD和QM /分子力学(MM)方法对+10000原子表面活性剂系统进行了MD模拟。对MD快照进行的QM计算以及对苯丙氨酸(LEP)表面活性剂系统的月桂酸酯的广泛分析表明,实验观察到的比旋光度随浓度的变化可能是由于聚集物中表面活性剂单体的构象差异所致。尽管传统的MM模拟并未显示构象种群之间的显着差异,但是使用PM6方法衍生的力进行的QM / MM模拟确实预测了聚集的LEP分子与未聚集的LEP分子之间的构象差异,这与实验数据一致。另外,带电荷的表面活性剂的静电环境也可能是重要的,因为在由手性离子聚集体产生的电场存在下可以注意到表面活性剂单体的玻尔兹曼群体的急剧变化。

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