1. Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 135, CZ-61265 Brno, Czech Republic, School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, U.K., and Department of Chemistry, University of Warwick, Gibbet Hill Road, Warwick CV4 7AL, U.K.