1. Institute of Pharmaceutical Technology and Biopharmaceutics, Martin-Luther-University, Halle-Wittenberg, Wolfgang-Langenbeck-Strasse 4, D-06120 Halle/Saale, Germany, and Institute of Physical Chemistry, Martin-Luther-University, Halle-Wittenberg, Muehlpforte 1, D-06108 Halle/Saale, Germany