Sinha Supurna
Raman Research Institute, Bangalore, India.
Phys Rev E Stat Nonlin Soft Matter Phys. 2008 Jun;77(6 Pt 1):061903. doi: 10.1103/PhysRevE.77.061903. Epub 2008 Jun 4.
We investigate the role of fluctuations in single-molecule measurements of torque-link (t-lk) curves. For semiflexible polymers of finite persistence length (i.e., polymers with contour length L comparable to the persistence length LP), the torque versus link curve in the constant-torque (isotorque) ensemble is distinct from the one in the constant-link (isolink) ensemble. Thus, one encounters the conceptually interesting issue of a "free energy of transition" in switching ensembles while making torque-link measurements. We predict the dependence on the semiflexibility parameter beta=L/LP of this extra contribution to the free energy, which shows up as an area in the torque-link plane. This can be tested against future torque-link experiments with single biopolymers. We bring out the inequivalence of torque-link curves for a stiff polymer and present explicit analytical expressions for the distinct torque-link relations in the two ensembles and the free-energy difference in switching ensembles in this context. The predictions of our work can be tested against single-molecule experiments on torsionally constrained biopolymers.
我们研究了扭矩-链长（t-lk）曲线单分子测量中涨落的作用。对于具有有限持久长度的半柔性聚合物（即轮廓长度L与持久长度LP相当的聚合物），恒扭矩（等扭矩）系综中的扭矩与链长曲线不同于恒链长（等链长）系综中的曲线。因此，在进行扭矩-链长测量时，在切换系综时会遇到一个概念上有趣的“转变自由能”问题。我们预测了这种对自由能额外贡献的对半柔性参数β = L/LP的依赖性，它表现为扭矩-链长平面中的一个面积。这可以通过未来对单个生物聚合物的扭矩-链长实验来检验。我们揭示了刚性聚合物扭矩-链长曲线的不等价性，并给出了两种系综中不同扭矩-链长关系以及在此背景下切换系综时自由能差的明确解析表达式。我们工作的预测可以通过对受扭转约束生物聚合物的单分子实验来检验。
