1. Institute of Physical and Theoretical Chemistry and Center of Biomolecular Magnetic Resonance, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt, Germany
2. Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik, Iceland
3. Centre for Biomolecular Sciences, Centre of Magnetic Resonance, University of St Andrews, North Haugh, KY16 9ST St Andrews, U.K.