1. Department of Chemistry, UMIST, P.O. Box 88, Manchester M60 1QD, U.K., School of Pharmacy, University of Nottingham, University Park, Nottingham NG7 2RD, U.K., Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, U.K., and Innoval Technology, Beaumont Close, Banbury OX16 1TQ, U.K.