Molecular dynamics and EPR spectroscopic studies of 8CB liquid crystal
Molecular dynamics and EPR spectroscopic studies of 8CB liquid crystal
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DOI：
10.1039/c2sm25429h
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发表时间：
2012-01-01
期刊：
影响因子：
3.4
通讯作者：
Oganesyan, V. S.
中科院分区：
文献类型：
--
作者：
Chami, F.;Wilson, M. R.;Oganesyan, V. S.
我们报告成功地模拟的运动EPR谱的液晶8 CB掺杂胆甾烷氮氧化物自旋探针从全原子分子动力学（MD）模拟。的光谱计算直接和完全从MD轨迹使用我们的新MD-EPR方法。预测的分子顺序，动力学和EPR光谱的变化在整个N-I相变与实验结果显示出良好的一致性。在N-I转变点处，发现了无序和部分有序亚稳态之间的纳秒级交换动力学，并通过EPR测量得到证实。这项研究表明，一个独特的组合，国家的最先进的分子建模在原子水平和EPR光谱，引入顺磁探针，允许精确估计的本地秩序和运动参数的介晶。特别是，它示出的旋转相关时间的准确估计为不同的分子轴在液晶中可以实现和相关的自旋探针的运动直接。我们还展示了在8 CB中的低温近晶-A液晶相的成功模拟。在这里，模拟正确地预测实验层间距在8 CB和直接显示存在一个强烈的局部偏好的反平行排列的分子。后者导致D的层间距接近1.4分子长度。
We report successful simulation of motional EPR spectra of the liquid crystal 8CB doped with a cholestane nitroxide spin probe from fully atomistic molecular dynamics (MD) simulations. The spectra are calculated directly and completely from MD trajectories using our novel MD-EPR methodology. Predicted changes in molecular order, dynamics and EPR spectra across the N-I phase transitions show excellent agreement with experimental results. A nanosecond exchange dynamics between disordered and partially ordered meta-stable states is revealed at the N-I transition point and is confirmed by EPR measurements. This study demonstrates that a unique combination of state-of-the- art molecular modelling at the atomistic level and EPR spectroscopy, with introduced paramagnetic probes, allows accurate estimation of the local order and motional parameters of the mesogens. In particular, it is shown that an accurate estimation of the rotation correlation times for different molecular axes in liquid crystals can be achieved and correlated directly with the motions of the spin probe. We also demonstrate the successful simulation of a low temperature smectic-A liquid crystal phase in 8CB. Here, the simulations correctly predict the experimental layer spacing in 8CB and show directly the presence of a strong local preference for anti-parallel arrangements of molecules. The latter leads to a layer-spacing of D approximate to 1.4 molecular lengths.