1. Contribution from the Kimika Fakultatea, Euskal Herriko Unibertsitatea, P.K. 1072, 20080 Donostia, Spain, Oxford Centre for Molecular Sciences, New Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom, Laboratoire de Chimie Biophysique, Institut le Bel, Université Louis Pasteur, 67000 Strasbourg, France, Laboratoire de Biologie et Génomique Structurales, Ecole Supérieure de Biotechnologie de Strasbourg 67400 Illkirch, France, and Department of Chemistry and Chemical Biology, Harvard...