1. Faculty of Pharmacy, Department of Physicochemistry, Av. Joan XXIII s.n., 08028 Barcelona, Spain, Department of Peptide & Protein Chemistry, CID−CSIC, Jordi Girona 18, 08034 Barcelona, Spain, and Research Group of Peptide Chemistry, Hungarian Academy of Sciences, Eötvös L. University, P.O. Box 32, Budapest 112, Hungary H-1518