Department of Chemical Engineering and Materials Science, University of Minnesota - Twin Cities, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, USA.
Department of Polymer Science and Engineering, Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, 199 Ren-ai Road, Suzhou 215123, People's Republic of China.
J Chem Phys. 2014 Feb 28;140(8):084905. doi: 10.1063/1.4865965.
The properties of channel-confined semiflexible polymers are determined by a complicated interplay of chain stiffness and excluded volume effects. Using Pruned-Enriched Rosenbluth Method (PERM) simulations, we study the equilibrium properties of channel-confined polymers by systematically controlling chain stiffness and excluded volume. Our calculations of chain extension and confinement free energy for freely jointed chains with and without excluded volume show excellent agreement with theoretical predictions. For ideal wormlike chains, the extension is seen to crossover from Odijk behavior in strong confinement to zero-stretching, bulk-like behavior in weak confinement. In contrast, for self-avoiding wormlike chains, we always observe that the linear scaling of the extension with the contour length is valid in the long-chain limit irrespective of the regime of confinement, owing to the coexistence of stiffness and excluded volume effects. We further propose that the long-chain limit for the extension corresponds to chain lengths wherein the projection of the end-to-end distance along the axis of the channel is nearly equal to the mean span parallel to the axis. For DNA in nanochannels, this limit was identified using PERM simulations out to molecular weights of more than 1 megabase pairs; the molecular weight of λ-DNA is found to exhibit nearly asymptotic fractional extension for channels sizes used commonly in experiments.
通道限制的半柔性聚合物的性质由链刚性和排除体积效应的复杂相互作用决定。使用修剪富集罗森布鲁斯方法 (PERM) 模拟，我们通过系统地控制链刚性和排除体积来研究通道限制聚合物的平衡性质。我们对具有和不具有排除体积的自由连接链的链延伸和限制自由能的计算与理论预测非常吻合。对于理想的类蠕虫链，在强限制下，延伸从 Odijk 行为转变为弱限制下的零拉伸、类似体相的行为。相比之下，对于自回避类蠕虫链，无论限制的范围如何，我们始终观察到延伸与轮廓长度的线性标度在长链极限下是有效的，这是由于刚性和排除体积效应的共存。我们进一步提出，延伸的长链极限对应于末端到末端距离沿着通道轴的投影几乎等于与轴平行的平均跨度的链长度。对于纳米通道中的 DNA，使用 PERM 模拟在超过 100 万个碱基对的分子量下确定了这个极限；发现 λ-DNA 的分子量对于实验中常用的通道尺寸表现出几乎渐近的分数延伸。
