1. Laboratory for Physical Chemistry, ETH Zürich, 8093 Zürich, Switzerland, Department of Chemistry, Bielefeld University, Universitätsstrasse 25, D-33615 Bielefeld, Germany, Max Planck Institute for Polymer Research, Postfach 3148, 55021 Mainz, Germany, and Max Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany