title: Why charged molecules move across a temperature gradient: the role of electric fields.
abstract: Methods to move solvated molecules are rare. Apart from electric fields, only thermal gradients are effective enough to move molecules inside a fluid. This effect is termed thermophoresis, and the underlying mechanisms are still poorly understood. Nevertheless, it is successfully used to quantify biomolecule binding in complex liquids. Here we show experiments that reveal that thermophoresis in water is dominated by two electric fields, both established by the salt ions of the solution. A local field around the molecule drives molecules along an energy gradient, whereas a global field moves the molecules by a combined thermoelectrophoresis mechanism known as the Seebeck effect. Both mechanisms combined predict the thermophoresis of DNA and RNA polymers for a wide range of experimental parameters. For example, we correctly predict a complex, nonlinear size transition, a salt-species-dependent offset, a maximum of thermophoresis over temperature, and the dependence of thermophoresis on the molecule concentration.
authors.affiliation: Systems Biophysics, Physics Department, Nanosystems Initiative Munich and Center for NanoScience Ludwig-Maximilians-Universität München, Amalienstrasse 54, 80799 München, Germany.
authors.forename: Maren
authors.initials: M
authors.lastname: Reichl
authors.affiliation: Systems Biophysics, Physics Department, Nanosystems Initiative Munich and Center for NanoScience Ludwig-Maximilians-Universität München, Amalienstrasse 54, 80799 München, Germany.
authors.forename: Mario
authors.initials: M
authors.lastname: Herzog
authors.affiliation: Systems Biophysics, Physics Department, Nanosystems Initiative Munich and Center for NanoScience Ludwig-Maximilians-Universität München, Amalienstrasse 54, 80799 München, Germany.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Götz
authors.affiliation: Systems Biophysics, Physics Department, Nanosystems Initiative Munich and Center for NanoScience Ludwig-Maximilians-Universität München, Amalienstrasse 54, 80799 München, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Braun
mesh_terms: D004247:DNA / Q000032:analysis* / Q000737:chemistry; D004058:Diffusion; D004574:Electromagnetic Fields; D004586:Electrophoresis / Q000379:methods*; D007477:Ions / Q000737:chemistry; D008956:Models, Chemical; D011189:Potassium Chloride / Q000737:chemistry; D012330:RNA, Double-Stranded / Q000032:analysis* / Q000737:chemistry; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D007477:Ions; D012330:RNA, Double-Stranded; D014867:Water; D011189:Potassium Chloride; D004247:DNA