1. Department of Chemistry, University of Fribourg, Chemin de Musée 9, 1700 Fribourg (Switzerland)
2. Current address: Functional Genomics Center Zurich, Winterthurerstrasse 190, 8057 Zürich (Switzerland)
3. Institute for Geosciences, Eberhard Karls University Tübingen, Hölderlinstrasse 12, 72074 Tübingen (Germany)