1. Contribution from the Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, D-52056 Aachen, Germany, School of Chemistry and Collaborative Optical Spectroscopy, Micromanipulation and Imaging Centre, The University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK, The Scripps Research Institute, Department of Molecular Biology (MB19), La Jolla, California 92037, and Department 2.5 Biophysics/Structural Biology, Saarland University, Universitätsklinikum, Geb. 60, D-66421 Homburg/Saar,...