1. Institute of Organic and Biomolecular Chemistry, University of Göttingen, Tammannstrasse 2, D-37077 Göttingen, Germany, Oncotest GmbH, Am Flughafen 12-14, D-79108 Freiburg, Germany, Fachhochschule Ostfriesland, Constantiaplatz 4, D-26726 Emden, Germany, and Alfred-Wegener-Institute for Polar and Marine Research, D-27570 Bremerhaven, Germany