1. Contribution from the Physical Organic Chemistry Unit, Stratingh Institute, University of Groningen, 4 Nijenborgh, 9747 AG Groningen, The Netherlands, DUBBLE CRG/ESRF, Netherlands Organization for Scientific Research (NWO), c/o ESRF BP 220, F-38043 Grenoble Cedex, France, Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 4 Nijenborgh, 9747 AG Groningen, The Netherlands, and Department of Organic Chemistry, University of Nijmegen, 1 Toernooiveld,...