1. Research Group EPR spectroscopy Max Planck Institute for Multidisciplinary Sciences Am Fassberg 11 37077 Göttingen Germany
2. Current address: Center for Biostructural Imaging of Neurodegeneration Medical Center Göttingen Von-Siebold-Straße 3a 37075 Göttingen Germany
3. NMR Signal Enhancement Group Max Planck Institute for Multidisciplinary Sciences Am Fassberg 11 37077 Göttingen Germany
4. Current address: Isotope Technologies Dresden Rossendorfer Ring 42 01328 Dresden Germany
5. Department of Chemistry University of Torino Via Giuria 9 10125 Torino Italy
6. Department of Chemistry Georg August University Göttingen Tammanstrasse 2 37077 Göttingen Germany