1. Institute of Experimental Pharmacology, Slovak Academy of Sciences, SK-84104 Bratislava, Slovak Republic, Istituto per lo Studio delle Macromolecole, Consiglio Nazionale delle Ricerche, I-20133 Milan, Italy, Institute of Chemistry, Slovak Academy of Sciences, SK-84538 Bratislava, Slovak Republic, and Institute of Medical Physics and Biophysics, Faculty of Medicine, University of Leipzig, D-04107 Leipzig, Germany