1. Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, Institut für Mathematik, Freie Universität Berlin, Arnimallee 6, D-14195, Berlin, Germany, Physical Chemistry Institute, Zürich University, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland, and Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, U.S.A.