1. Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, South Parks Road, OX1 3QZ Oxford, United Kingdom, Sanofi-Aventis, CRVA, 13 quai Jules Guesde, BP14, 94403 Vitry-sur-Seine, France, and the Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, OX1 3TA Oxford, United Kingdom