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BP: Fachverband Biologische Physik

BP 1: Statistical Physics of Biological Systems I (joint BP, DY)

BP 1.8: Vortrag

Montag, 22. März 2010, 12:15–12:30, H45

All-or-none protein-like folding transition of a flexible homopolymer chain — •Wolfgang Paul¹, Mark Talor², and Kurt Binder³ — ¹Institut für Physik, Martin-Luther-Universität, 06099 Halle — ²Department of Physics, Hiram College, Hiram, Ohio 44234, USA — ³Institut für Physik, Johannes-Gutenberg-Universität, 55099 Mainz

We report a first-order all-or-none transition from an expanded coil to a compact crystallite for a flexible polymer chain. Wang-Landau sampling is used to construct the complete density of states for square-well chains up to length 256. Analysis within both the microcanonical and canonical ensembles shows a direct freezing transition for finite length chains with sufficiently short-range interactions. This type of transition is a distinctive feature of "one-step" protein folding and our findings demonstrate that a simple homopolymer model can exhibit protein-folding thermodynamics. We also discuss how this finding depends on the range of the attractive interaction. Chains assume an expanded coil conformation at high temperatures and a crystallite structure at low temperatures. For large well diameters, with decreasing temperature a chain undergoes a continuous coil-globule (collapse) transition followed by a discontinuous globule-crystal (freezing) transition. For small well diameters the collapse transition is preempted by the freezing transition and thus there is a direct first-order coil-crystal phase transition.