1. The Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames 50011, Iowa, United States
2. Manchester Institute of Biotechnology and Department of Chemistry, The University of Manchester, 131 Princess Street, Manchester M1 7DN, U.K.
3. Institute of Physical and Theoretical Chemistry, University of Regensburg, Regensburg 93040, Germany
4. SUPA School of Physics and Astronomy and BSRC, The University of St Andrews, St Andrews KY16 9SS, U.K.