Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 15: Single Molecules
CPP 15.3: Vortrag
Dienstag, 26. Februar 2008, 17:30–17:45, C 230
Numeric force ramp spectroscopy for polymer stretching: the role of thermal fluctuations — •Felix Hanke1,2, Douglas B Staple2, and Hans Jürgen Kreuzer2 — 1Fritz-Haber Institut der MPG, Faradayweg 4-6, 14195 Berlin — 2Dept of Physics, Dalhousie University, Halifax, NS, B3H 3J5, Canada
Force ramp spectroscopy is aimed at stretching single polymer molecules in an Atomic Force Microscope (AFM) such that the external force applied to the molecule increases linearly. This approach differs from the more commonly used constant velocity experiments in the observed thermal noise of the molecule-cantilever system. Recent experiments on Dextran [1], doubted the applicability of the often-used Gibbs (or fixed force) ensemble based on a thermal fluctuations argument. Here we use a Transfer Matrix formalism to describe the Dextran-cantilever system [2], which is coupled to a master equation description of the pulling process [3]. This theory enables a numerical imitation of the force ramp experiment from which the molecular force response and thermal noise of the force ramp setup are calculated. We find that the thermodynamics governing the force ramp experiment always depends significantly on the AFM cantilever. Specifically, the thermal noise of the system always remains restricted by the cantilever. This leads us to suggest that the interpretation of every single-molecule AFM experiment must account explicitly for the effect both, molecule and cantilever. [1] Walther et al, Biophys J 90 3806 (2006); [2] Hanke, Kreuzer, Eur Phys J B, 22 163 (2007); [3] Hanke, Kreuzer, Phys Rev E, 72 031805 (2005)