1. Laboratory of Molecular Biophysics and Oxford Centre for Molecular Sciences, University of Oxford, Rex Richards Building, South Parks Road, Oxford OX1 3QU, U.K., Department of Chemistry, University of British Columbia, Vancouver, BC, Canada V6T 1Z1, Laboratory of Organic Chemistry, ETH Zentrum, Universitatstrasse 16, CH 8092 Zurich, Switzerland, and Institute of Biological Research and Biotechnology, National Hellenic Research Foundation, 48 Vas. Constantinou Avenue, Athens 11635, Greece