1. Fakultät für Chemie und Mineralogie, Institut für Organische Chemie, University of Leipzig, Johannisallee 29, 04103 Leipzig, Germany, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), Department of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, and Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le Aldo Moro 5, 00185 Roma, Italy