Materials Department, University of California, Santa Barbara, California 93106, USA.
Phys Rev Lett. 2012 Jul 27;109(4):048301. doi: 10.1103/PhysRevLett.109.048301. Epub 2012 Jul 23.
We derive a thermodynamic identity that allows one to infer the change in the number of screening ions that are associated with a charged macromolecule as the macromolecule is continuously stretched. Applying this identity to force-extension data on both single-stranded and double-stranded DNA, we find that the number of polymer-associated ions depends nontrivially on both the bulk salt concentration and the bare rigidity of the polymer, with single-stranded DNA exhibiting a relatively large decrease in ion excess upon stretching. We rationalize these observations using simple models for polyelectrolyte extension.
我们推导出一个热力学恒等式，可以根据该恒等式推断当大分子连续拉伸时，与带电大分子相关的屏蔽离子数量的变化。将该恒等式应用于单链和双链 DNA 的力-伸长数据，我们发现与聚合物相关的离子数量不仅取决于本体盐浓度，还取决于聚合物的裸刚性，单链 DNA 在拉伸时离子过剩量相对较大。我们使用聚电解质拉伸的简单模型来解释这些观察结果。
