1. Oxford Centre for Molecular Sciences, Oxford University, New Chemistry Laboratory, South Parks Road, Oxford, OX1 3QT, U.K., Dyson Perrins Laboratory, Oxford University, South Parks Road, Oxford, OX1 3QY, U.K., Department of Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, U.K., and Biotechnology Research, Lonza A.G., CH-3930 Visp, Switzerland