1. Department of Chemistry University College London, 20 Gordon Street London WC1H 0AJ UK
2. The Swedish NMR Centre Medicinaregatan 5 40530 Gothenburg Sweden
3. Institute of Structural and Molecular Biology Division of Biosciences University College London Gower Street London WC1E 6BT UK
4. Department of Chemistry–BMC Uppsala University Box 576 75123 Uppsala Sweden