1. Department of Physical Chemistry, University of Freiburg, Albertstrasse 21, D-79104 Freiburg, Germany, Department of Physical Chemistry, University of Padova, Via Loredan 2, I-35131 Padova, Italy, J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia, and Department of Pharmaceutical Technology, University of Freiburg, Hermann-Herder-Strasse 9, D-79104 Freiburg, Germany