1. Department of Chemistry, University of Rome “La Sapienza”, Piazzale A. Moro 5, 00185 Rome, Italy, Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Schmiedelstrasse 6, A-8042 Graz, Austria, and Genetic Immunization Laboratory, Department of Molecular Cellular and Animal Biology, University of Camerino, Via Gentile III da Varano, 62032 Camerino (MC), Italy