1. Max Volmer Laboratory for Biophysical Chemistry, Institute of Chemistry, Technical University of Berlin, Secr. PC 14, Strasse des 17. Juni 135, D-10623 Berlin, Germany, Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max-von-Laue-Strasse 3, D-60438 Frankfurt/Main, Germany, and Chemical and Pharmaceutical Sciences Department, Johann Wolfgang Goethe University Frankfurt, Max-von-Laue-Strasse 1, 7-9, D-60439 Frankfurt/Main, Germany