1. National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Department of Chemistry, University of Jyväskylä, P. O. Box 35, FIN-40014, Finland, and Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-16206 Prague, Czech Republic