1. Catalan Institute of Nanoscience and Nanotechnology (ICN2) CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra 08193 Barcelona Spain
2. Centre de Biophysique Moléculaire, CNRS Université d'Orléans Rue Charles Sadron 45071 Orléans France
3. Departament de Química Universitat Autònoma de Barcelona, Campus UAB, Bellaterra 08193 Barcelona Spain
4. Departament de Bioquímica i Biologia Molecular Institut de Biotecnologia i Biomedicina (IBB), Campus UAB 08193 Bellaterra Spain
5. ALBA Synchrotron, Cerdanyola del Vallès 08290 Barcelona Spain
6. Department of Applied Physics and Applied Mathematics Columbia University New York USA
7. ICREA, Pg. Lluís Companys 23 08010 Barcelona Spain