Galbraith Madeline L, Madura Jeffry D
Department of Physics, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, United States.
Department of Chemistry & Biochemistry, Center for Computational Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, United States.
J Mol Graph Model. 2017 Nov;78:168-175. doi: 10.1016/j.jmgm.2017.09.021. Epub 2017 Oct 6.
Poly(n-isopropylacrylamide), PNIPAM, is a thermo-responsive polymer that has been thoroughly studied for its many applications, such as drug delivery and actuators. Below the lower critical solution temperature (LCST), PNIPAM is well hydrated in the elongated conformation. The transition occuring at the LCST results in a less hydrated collapsed state above the LCST. This volume phase transition is dependent upon the hydration of the polymer and its hydrophobicity. Some research has been done on potential modifications of PNIPAM for applications, but until now there has not been a study of the hydration properties as a function of hydrophobicity. The work presented in this paper applies a Voronoi analysis of the hydration of PNIPAM, as well as PNIPAM with other alkyl substituents. We show from classical MD simulations that increasing hydrophobicity can increase the volume phase change, but there is a lower limit to this trend. Additionally, replica exchange molecular dynamics were conducted on PNIPAM showing a fluctuation between elongated and collapsed states near the LCST.
聚（N-异丙基丙烯酰胺），即PNIPAM，是一种热响应性聚合物，因其在药物递送和致动器等诸多应用中的表现而得到了深入研究。在低临界溶液温度（LCST）以下，PNIPAM以伸长构象充分水合。在LCST发生的转变导致在LCST以上形成水合程度较低的塌缩状态。这种体积相变取决于聚合物的水合作用及其疏水性。针对PNIPAM在应用方面的潜在改性已经开展了一些研究，但到目前为止，尚未有关于水合性质随疏水性变化的研究。本文所展示的工作对PNIPAM以及带有其他烷基取代基的PNIPAM的水合作用进行了Voronoi分析。我们从经典分子动力学模拟中发现，增加疏水性会增大体积相变，但这种趋势存在下限。此外，对PNIPAM进行了副本交换分子动力学模拟，结果显示在LCST附近PNIPAM在伸长态和塌缩态之间波动。
