1. Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K., Federal Institute of Materials Research and Testing (BAM), Richard Willstaeter Str. 11, D-12489, Germany, Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, U.K., Department of Medicine, Addenbrookes Hospital, Hills Road, Cambridge CB2 2QQ, U.K., and Animal Health Trust, Lanwades Park, Newmarket, Suffolk CB8 7UU, U.K.