1. Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK.
2. MRC Weatherall Institute of Molecular Medicine, Haematology Unit, University of Oxford, Oxford OX3 9DS, UK.
3. Micron Oxford Advanced Bioimaging Unit, University of Oxford, Oxford OX1 3QU, UK.
4. Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA.
5. Spectroscopy Department, Physics Division, National Research Centre, 12622 Dokki, Cairo, Egypt.