1. Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, U.K.
2. MRC Centre for Drug Safety Science, Department of Molecular and Clinical Pharmacology, University of Liverpool, Sherrington Building, Liverpool L69 3GE, U.K.
3. Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, U.K.
4. Laboratoire de Chimie de Coordination, Université de Toulouse, 31077 Toulouse Cedex 4, France