1. Contribution from the School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT U.K., School of Chemistry, University of Birmingham, Edgbaston, Birmingham, B15 2TT U.K., School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT U.K., and Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, M5S 3H6 Canada