1. Faculty of Chemistry, University of Gdańsk, Sobieskiego 18, 80-952 Gdańsk, Poland, Baker Laboratory of Chemistry and Chemical Biology, Cornell University, Ithaca, N.Y., 14853-1301, U.S.A., and Academic Computer Center in Gdańsk TASK, Narutowicza 11/12, 80-952 Gdańsk, Poland