1. Departments of Organic Chemistry and Structural Biology, Weizmann Institute of Science, IL-76100 Rehovot, Israel
2. Institute of Nanotechnology, Forschungszentrum Karlsruhe, P.O. Box 3640, D-76021 Karlsruhe, Germany
3. Department of Organic Chemistry, Weizmann Institute of Science, IL-76100 Rechovot, Israel