1. Department of Chemistry and Biochemistry; Ruhr-University-Bochum; Universitätsstr. 150 44801 Bochum Germany
2. Department of Biology; Universität Duisburg-Essen; Universitätsstr. 2 45141 Essen Germany
3. Max-Planck-Institut für Kohlenforschung; Kaiser-Wilhelm-Platz 1 45470 Mülheim an der Ruhr Germany
4. Department of Chemistry and Molecular Biology and the Swedish NMR Centre; University of Gothenburg; Kemivägen 10 412 96 Göteborg Sweden