Regensburg 2013 – scientific programme

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KR: Fachgruppe Kristallographie

KR 4: Quantitative Materialanalyse (MI jointly with KR)

KR 4.8: Talk

Tuesday, March 12, 2013, 12:00–12:15, H5

Microscopic Understanding of Ionic Thermophoresis — Mario Herzog, •Maren Reichl, Alexandra Götz, and Dieter Braun — Systems Biophysics, LMU, München, Germany

A number of microscopic models for thermophoresis has been proposed recently. Here we measured short DNA and RNA molecules over a wide parameter range (0.4-14 nm Debye length, 5-75°C base temperature, 5-50 bases, 11 different electrolytes) [1]. The measurements confirm the capacitor model of thermophoresis with the following details [2]:

1. Thermophoresis is proportional to the Debye length when the latter is smaller than the molecule radius, but saturates for Debye lengths exceeding the molecule radius. This confirms the predicted size transition between the plate and spherical limit of the capacitor model. The fitted effective charges depend on DNA length predicted by molecular dynamics simulations of Manning condensation.

2. Depending on the electrolyte, a constant additive contribution for the Seebeck effect of the electrolyte is confirmed. It can be understood from literature data without fitting parameters.

The model allows non-trivial predictions of thermophoresis. Our work confirms in detail a local equilibrium approach to thermophoresis. The finding is likely to improve biomolecule binding studies using microscale thermophoresis (Nanotemper Technologies).

[1] Herzog M and Braun D, under review

[2] Dohnt J, Wiegand S, Duhr S and Braun D, Langmuir 23, 1674-1683 (2007)