1. Contribution from the Quantum Chemistry Group, Faculty of Chemistry, A. Mickiewicz University, ul. Grunwaldzka 6, 60-780 Poznan, Poland, Institute of Bioorganic Chemistry, Polish Academy of Sciences, ul. Noskowskiego, Poznan, Poland, and Department of Physical Chemistry, K. Marcinkowski University of Medical Science, ul. Swiecickiego 6, 60-781 Poznan, Poland