1. University of York Department of Chemistry Heslington York YO10 5DD UK
2. University of York Department of Biology Heslington Wentworth Way YO10 5DD UK
3. University of York York Structural Biology Laboratory Heslington YO10 5DD UK
4. Anorganische Chemie Ruhr-Universität Bochum Universitätsstraße 150 44801 Bochum Germany