1. Leiden Institute of Chemistry (LIC), Leiden University, 2333 CD Leiden, The Netherlands
2. Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, 80138 Naples, Italy
3. Département de Biochimie, Université de Lausanne, CH-1015 Epalinges, Switzerland
4. Department of Theoretical Physics, Georg-August University of Goettingen, 37077 Goettingen, Germany