1. Department of Chemistry, University of Southampton, Highfield, Southampton S09 5NH, UK
2. Medical Research Council Collaborative Centre, 1-3 Burtonhole Lane, Mill Hill, London NW7 1AD, UK
3. National Institute for Medical Research, The Ridgeway, London NW7 1AA, UK
4. Department of Haematology, Clinical School, University of Cambridge, Hills Road, Cambridge CB2 2QL, UK