Influence of surface interactions on folding and forced unbinding of semiflexible chains

We investigate the folding and forced-unbinding transitions of adsorbed semiflexible polymer chains using theory and simulations. These processes describe biologically relevant phenomena that include adhesive interactions between proteins and tethering of receptors to cell walls. The binding interface is modeled as a solid surface and the worm-like chain is used for the semiflexible chain. Using Langevin simulations we examine the ordering kinetics of racquet-like and toroidal structures in the presence of attractive interaction between the surface and the polymer chain. For a range of interactions, temperature, and the persistence length l_p we obtained the monomer density distribution n(x) for all the relevant morphologies. The simulated results for n(x) are in good agreement with theory. The formation of toroids on the surface appears to be a first order transition. Chain-surface interaction is probed by subjecting the surface structures to a pulling force f. The average extension x as a function of f exhibit sigmoidal profile with sharp all-or-none transition at the unfolding f_c which increases for more structured states. Simulated x compare well with the theoretical predictions. The critical force f_c is a function of l_s/l_c for a fixed temperature, where l_c, l_s are the length scales that express the strength of the intramolecular and chain-surface attraction, respectively. For a fixed l_s, f_c increases as l_p decreases.