1. Department of Pharmaceutics, The School of Pharmacy, University of London, 29/39 Brunswick Square, London WC1N 1AX, Faculty of Medicine, Imperial College London, Hammersmith Hospital, Ducane Road, London W12 0NN, and Department of Pharmaceutical and Biological Chemistry, The School of Pharmacy, University of London, 29/39 Brunswick Square, London WC1N 1AX, U.K