Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA.
J Chem Phys. 2012 Aug 14;137(6):064904. doi: 10.1063/1.4742970.
We present results on the sequence dependence of translocation kinetics for a partially charged heteropolymer moving through a very thin pore using theoretical tools and Langevin dynamics simulational techniques. The chain is composed of two types of monomers of differing frictional interaction with the pore and charge. We present exact analytical expressions for passage probability, mean first passage time, and mean successful passage times for both reflecting/absorbing and absorbing/absorbing boundary conditions, showing rich and unexpected dependence of translocation behavior on charge fraction, distribution along the chain, and electric field configuration. We find excellent qualitative and good quantitative agreement between theoretical and simulation results. Surprisingly, there emerges a threshold charge fraction of a diblock copolymer beyond which the success rate of translocation is independent of charge fraction. Also, the mean successful translocation time of a diblock copolymer displays non-monotonic behavior with increasing length of the charged block; there is an optimum length of the charged block where the mean translocation rate is the slowest; and there can be a substantial range of higher charge fractions which make the translocation slower than even a minimally charged chain. Additionally, we find for a fixed total charge on the chain, finer distribution along the backbone significantly decreases mean translocation time.
我们使用理论工具和 Langevin动力学模拟技术，展示了部分带电杂聚物通过非常细的孔时的迁移动力学的序列依赖性的结果。该链由两种具有不同摩擦相互作用和电荷的单体组成。我们给出了对于反射/吸收和吸收/吸收边界条件的通过概率、平均首次通过时间和平均成功通过时间的精确解析表达式，展示了迁移行为对电荷分数、沿链分布和电场配置的丰富而意外的依赖性。我们发现理论和模拟结果之间存在极好的定性和良好的定量一致性。令人惊讶的是，出现了一个二嵌段共聚物的临界电荷分数，超过该分数后，迁移成功率与电荷分数无关。此外，二嵌段共聚物的平均成功迁移时间随带电荷块的长度呈非单调变化；存在一个最佳的带电荷块长度，在此长度下，平均迁移速率最慢；并且可能存在一个较大的较高电荷分数范围，使迁移速度比甚至是最小带电荷的链还要慢。此外，我们发现对于链上固定的总电荷，沿骨架的更精细分布显著降低了平均迁移时间。
