Simulations of Single-Molecule Friction at Hydrophilic Surfaces

利用原子力显微镜可以研究单肽链在不同表面上的吸附自由能和摩擦效应。在以前的合作中，研究了单一的蜘蛛丝肽链在疏水钻石上的吸附。在这项建议中，我们将重点放在生物学上更相关的亲水性表面，目的是获得有关动力学效应的完整微观了解。I)通过广泛的模拟和Fokker-Planck模型的结合，我们将提取亲水表面上的肽链在实验上相关的线性响应(即低速)区域的迁移率。这将使我们能够量化单个氢键的迁移率(或摩擦系数)，这与β-折叠和α-螺旋形成的动力学有关。Ii)通过对吸附聚合物施加法向力，我们将建立单分子在水中摩擦的阿蒙顿定律的纳米版本。我们还将改变多肽的亲水性程度、表面和链长。Iii)我们将研究多肽-多肽的摩擦效应，目的是预测高密度吸附层中的有效聚合物迁移率。Iv)我们将研究不同聚合物模型下吸附聚合物的破裂长度关系，即等长的L的聚合物自发从吸附表面解吸的悬臂高度D*。

Adsorption free energies and friction effects of single peptide chains on different surfaces can be studied with the AFM. In the previous collaboration, the adsorption of a single spider-silk peptide chain on hydrophobic diamond was studied. In this proposal we concentrate on biologically more relevant hydrophilic surfaces with the goal to gain complete microscopic understanding of the involved kinetic effects. I) By a combination of extensive simulations and Fokker-Planck-modeling, we will extract the mobility of peptide chains on hydrophilic surfaces in the experimentally relevant linearresponse (i.e. low velocity) regime. This will allow us to quantify the mobility (or friction coefficient) of a single hydrogen bond, which is relevant for the kinetics of beta-sheet and alpha-helix formation. II) By applying normal forces to adsorbing polymers, we will formulate the nanoscopic version of Amonton’s law for single molecule friction in water. We will also vary the degree of hydrophilicity of the peptides, the surfaces and the chain length. III) We will study peptide-peptide friction effects with the goal to predict effective polymer mobilities in dense adsorbed layers. IV) We will study the rupture length dependence of adsorbed polymers for different polymer models, i.e. the cantilever height D* at which a polymer of contour length L spontaneously desorbs from an adsorbing surface.