1. Centre for Biomolecular Sciences, EastChem, The University, St Andrews, Scotland, KY16 9ST, U.K., Department of Chemistry, EastChem, The University of Edinburgh, Scotland EH9 3JJ, Biochemie, Technische Universität Dresden, D-01062 Dresden, Germany, and Department of Chemistry, Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602