Interaction Forces and Functional Materials, Department of Interface Chemistry and Surface Engineering, Max-Planck-Institut für Eisenforschung GmbH , 40237 Düsseldorf, Germany.
Institut für Physikalische Chemie II, TU Bergakademie Freiberg , 09599 Freiberg, Germany.
Langmuir. 2018 Jan 23;34(3):766-772. doi: 10.1021/acs.langmuir.7b02844. Epub 2017 Nov 9.
The capabilities of atomic force microscopes and optical tweezers to probe unfolding or surface-to-molecule bond rupture at a single-molecular level are widely appreciated. These measurements are typically carried out unidirectionally under nonequilibrium conditions. Jarzynski's equality has proven useful to relate the work obtained along these nonequilibrium trajectories to the underlying free energy of the unfolding or unbinding process. Here, we quantify biases that arise from the molecular design of the bond rupture experiment for probing surface-to-molecule bonds. In particular, we probe the well-studied amine/gold bond as a function of the linker's length which is used to anchor the specific amine functionality during a single molecule unbinding experiment. With increasing linker length, we observe a significant increase in the average work spent on polymer stretching and a strongly biased estimated interaction free energy. Our data demonstrate that free energy estimates converge well for linker lengths below 20 nm, where the bias is <10-15%. With longer linkers severe methodical limits of the method are reached, and convergence within a reasonable number of realizations of the bond rupture is not feasible. Our results also provide new insights into stability and work dissipation mechanisms at adhesive interfaces at the single-molecular level, and offer important design and analysis aspects for single-molecular surface-to-molecule experiments.
原子力显微镜和光镊的功能可以在单分子水平上探测解折叠或表面-分子键的断裂，这一点得到了广泛的认可。这些测量通常在非平衡条件下单向进行。雅可比等式已被证明可用于将沿这些非平衡轨迹获得的功与解折叠或离解过程的基础自由能联系起来。在这里，我们量化了由于用于探测表面-分子键的键断裂实验的分子设计而产生的偏差。具体来说，我们研究了众所周知的胺/金键，作为链接器长度的函数，该长度用于在单个分子解键实验中锚定特定的胺官能团。随着链接器长度的增加，我们观察到聚合物拉伸上花费的平均功显著增加，并且估计的相互作用自由能存在严重的偏差。我们的数据表明，对于长度小于 20nm 的链接器，自由能估计值收敛良好，偏差小于 10-15%。对于更长的链接器，该方法的方法学限制非常严重，并且在合理数量的键断裂实现中收敛是不可行的。我们的结果还为单分子水平上的粘合界面的稳定性和功耗散机制提供了新的见解，并为单分子表面-分子实验提供了重要的设计和分析方面。
