1. Oxford Centre for Molecular Sciences, Central Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QH, United Kingdom, Laboratory of Biophysical Chemistry, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands, and Laboratory of Physical Chemistry, Swiss Federal Institute of Technology Zurich, ETH Hönggerberg, CH-8093 Zürich, Switzerland