1. Department of Analytical Chemistry/Biochemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden, Department of Biochemistry and Molecular Biology, Eberly College of Science, Pennsylvania State University, 205 South Frear Laboratory, University Park, Pennsylvania, 16802-4500, and University of Siegen, Organic Chemistry 1, Adolf-Reichwein-Strasse 2, D-57068 Siegen, Germany