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