Simulations of Single-Molecule Friction at Hydrophilic Surfaces

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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.