1. Institute of Chemical Sciences, University of Urbino, P.zza Rinascimento, 6, 61029 Urbino, Italy, Departments of Chemistry and Vegetal Biology, University of Florence, 50121 Firenze, Italy, Department of Chemistry, Columbia University, New York, New York 10027, and Center for Biologic Nanotechnology, University of Michigan, Ann Arbor, Michigan 48109