1. Laboratorium für Anorganische Chemie, Departement Chemie und Angewandte Biowissenschaften, ETH Zürich, CH-8093 Zürich, Switzerland, Department of Pharmacy, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NN, United Kingdom, and Department of Pharmacology, University of Linköping, SE-581 85 Linköping, Sweden