1. Institute for Technical Chemistry and Environmental Chemistry, Friedrich-Schiller University Jena, Lessingstrasse 12, D-07743 Jena, Germany, R&D Chemical Process Technology, DSM Nutritional Products, P.O. Box 2676, CH-4002 Basel, Switzerland, and Institute for Physical Chemistry, Friedrich-Schiller University Jena, Helmholtzweg 4, D-07743 Jena, Germany