1. Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland; Fachbereich 9Theoretische Chemie, Bergische Universität-Gesamthochschule Wuppertal, Gaussstr. 20, D-42097 Wuppertal, Germany; and Center for Advanced Research in Biotechnology, NIST, 9600 Gudelsky Drive, Rockville, Maryland 20850