打结高分子链穿孔行为的研究

A knotted polymer chain passing through a pore

以三叶草型结(即31结)为例,采用分子动力学(MD)方法,研究打结高分子链在外场力作用下穿越微孔的动力学过程.模拟发现,在拉动打结高分子链的过程中,结的大小呈涨落变化,直至最后散结.定性讨论了结的存在对高分子链穿孔速率的影响.在外场力作用下,打结高分子链平均穿孔时间(τ)与链长(N)满足标度关系τ～Nα,其中标度系数α随外场力f增大而增大.对于短链,外场力越大,平均穿孔时间越短;而对于较长的链,外场力越大,平均穿孔时间反而越长.本文还研究了结在高分子链中所处的位置对平均穿孔时间的影响.结点位置不同,高分子链平均穿孔时间也不同.初始时,结越靠近第一个穿孔原子,其平均穿孔时间就越长.通过这些研究,可对打结高分子链(特别是打结DNA)穿越微孔的微观过程有一定认识,从而加深对生物大分子穿孔行为的理解。

A knotted polymer chain passing through a pore is investigated by molecule dynamics method.In this paper,we take 31 knot as an example.It is found that,during the process of translocation,the size of the knot fluctuates until the knot is unknotted.In addition,the effect of the knot on the translocation velocity of the knotted chain is also discussed.For the given external force,the average translocation time τ satisfies the scaling relation：τ-Nα,and the scaling exponent α increases with the external force f.For short knotted polymer chains,the average translocation time τ decreases when the external force f increases.However,for very long knotted polymer chains,the average translocation time τ increases when the external force f increases.In the meantime,the position of knot in a knotted polymer chain also affects the average translocation time τ strongly.The closer the knot approaches the first translocated monomer,the longer the average translocation time.This investigation can provide some insights into the translocation of knotted polymer chains（especially knotted DNA） through the nanopore,and help us understand the translocation behavior of biomacromolecules.