Suchergebnisse

While thermal rates of state transitions in classical systems have been studied for almost a century, associated transition-path times have only recently received attention. Uphill and downhill transition paths between states at different free energies should be statistically indistinguishable. Here, we systematically investigate transition-path-time symmetry and report evidence of its breakdown on the molecular- and meso-scale out of equilibrium. In automated Brownian dynamics experiments, we establish first-passage-time symmetries of colloids driven by femtoNewton forces in holographically-created optical landscapes confined within microchannels. Conversely, we show that transitions which couple in a path-dependent manner to fluctuating forces exhibit asymmetry. We reproduce this asymmetry in folding transitions of DNA-hairpins driven out of equilibrium and suggest a topological mechanism of symmetry breakdown. Our results are relevant to measurements that capture a single coordinate in a multidimensional free energy landscape, as encountered in electrophysiology and single-molecule fluorescence experiments. ; (J.G.) European Training Network (ETN) Grant No. 674979-NANOTRANS (J.G.) Winton Programme for the Physics of Sustainability (M.R.C.) European Unions Horizon 2020 Marie Skłodowska-Curie grant agreement No. 749944 (U.F.K.) ERC Consolidator Grant (DesignerPores 647144) (F.R.) Spanish Research Council [FIS2016-80458-P] (F.R.) Catalan Government [Icrea Academia prize 2013] (F.R.) EU [Proseqo, FETOPEN, Proposal 687089]

[EN] To our knowledge, we have developed a novel temperature-jump optical tweezers setup that changes the temperature locally and rapidly. It uses a heating laser with a wavelength that is highly absorbed by water so it can cover a broad range of temperatures. This instrument can record several force-distance curves for one individual molecule at various temper- atures with good thermal and mechanical stability. Our design has features to reduce convection and baseline shifts, which have troubled previous heating-laser instruments. As proof of accuracy, we used the instrument to carry out DNA unzipping experi- ments in which we derived the average basepair free energy, entropy, and enthalpy of formation of the DNA duplex in a range of temperatures between 5 C and 50 C. We also used the instrument to characterize the temperature-dependent elasticity of single-stranded DNA (ssDNA), where we find a significant condensation plateau at low force and low temperature. Oddly, the persistence length of ssDNA measured at high force seems to increase with temperature, contrary to simple entropic models. ; The authors thank J. Camunas and S. Frutos for contributing the molecules used in the experiments, and J.M. Huguet for helpful discussion. F.R. is supported by grant Institucio Catalana de Recerca i Estudis Avancats Academia 2013 and J.R. A.-G. by an Explora grant from MINECO (MAT2013-49455-EXP). The research that led to the results presented here was funded by the European Union Seventh Framework Programme (FP7/2007-2013) under grant 308850 INFERNOS and European Research Council grant MagReps (No. 267862). ; De Lorenzo, S.; Ribezzi-Crivellari, M.; Arias-Gonzalez, JR.; Smith, S.; Ritort, F. (2015). A Temperature-Jump Optical Trap for Single-Molecule Manipulation. Biophysical Journal. 108(12):2854-2864. https://doi.org/10.1016/j.bpj.2015.05.017 ; S ; 2854 ; 2864 ; 108 ; 12