1. Research Group for Peptide Chemistry, Hungarian Academy of Science, Eötvös L. University, P.O. Box 32, Budapest 112, Hungary, H-1518, Physicochemical Unit, Faculty Pharmacy, Pza. Puis XII s/n 08028, Barcelona, Spain, and Department of Peptide and Protein Chemistry, Research Council, CID. CSIC. Jordi Girona 16. 08034, Barcelona, Spain