Department of Physics , University of Basel , Klingelbergstrasse 82 , 4056 Basel , Switzerland.
Department of Chemistry and Biochemistry , University of Bern , Freiestrasse 3 , Bern , CH 3012 , Switzerland.
Nano Lett. 2020 Jan 8;20(1):652-657. doi: 10.1021/acs.nanolett.9b04418. Epub 2019 Dec 6.
Bending and twisting around carbon-carbon single bonds are ubiquitous in natural and synthetic polymers. Force-induced changes were so far not measured at the single-monomer level, owing to limited ways to apply local forces. We quantified down to the submolecular level the mechanical response within individual poly-pyrenylene chains upon their detachment from a gold surface with an atomic force microscope at 5 K. Computer simulations based on a dedicated force field reproduce the experimental traces and reveal symmetry-broken bent and rotated conformations of the sliding physisorbed segment besides steric hindrance of the just lifted monomer. Our study also shows that the tip-molecule bond remains intact but remarkably soft and links force variations to complex but well-defined conformational changes.
在天然和合成聚合物中，碳-碳单键的弯曲和扭曲是普遍存在的。由于施加局部力的方法有限，迄今为止，还没有在单体水平上测量力诱导的变化。我们在 5 K 下使用原子力显微镜将单个多并苯链从金表面分离时，在亚分子水平上定量测量了其机械响应。基于专门力场的计算机模拟再现了实验轨迹，并揭示了滑动物理吸附段的对称破缺弯曲和旋转构象，以及刚刚提起的单体的空间位阻。我们的研究还表明，尖端-分子键保持完整，但非常柔软，并将力的变化与复杂但明确的构象变化联系起来。
