1. Centre for Biomolecular Sciences, The University, St. Andrews KY16 9ST, U.K., Department of Chemistry, West Mains Road, The University of Edinburgh, Edinburgh EH9 3JJ, U.K., Department of Chemistry, University of Saskatchewan, Saskatoon, Canada S7N 5C9, and Department of Microbiology, University of Guelph, Guelph, Canada N1G 2W1