1. Department of Inorganic and Analytical Chemistry, Loránd Eötvös University, Pázmány Péter sétány 1/a, H-1117 Budapest, Hungary, Department of Pharmaceutical Chemistry, Semmelweis University, Högyes E.u. 9, H-1092 Budapest, Hungary, Cooperative Research Center, Semmelweis University, POB 131, H-1367 Budapest, Hungary, and Peptide Research Group of the Hungarian Academy of Sciences, Department of Medical Chemistry, Semmelweis University, Puskin u. 9, H-1088 Budapest, Hungary