1. Dipartimento di Biotecnologie, Chimica e Farmacia, Università di Siena, via A. Moro 2, I-53100 Siena, Italy
2. Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States,
3. Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States and
4. Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, Université de Strasbourg-CNRS, F-67034 Strasbourg, France