1. Dipartimento di Scienze Chimiche, Università di Camerino, Via S. Agostino, 1, 62032 Camerino, Italy, Laboratory for Experimental Oncology, Indiana University School of Medicine, Indianapolis, Indiana 46202, Department of Chemistry, University of Rochester, Rochester, New York 14620, Department of Biophysics, University of Rochester Medical Center, Rochester, New York 14642, and Dipartimento di Biologia Sperimentale, Università di Cagliari, 09124 Cagliari, Italy