1. Department of Chemistry, University of Coimbra, Coimbra, P-3004-535, Portugal, Faculty of Pharmacy and Biochemistry, University of Buenos Aires, C.P. 1113 Buenos Aires, Argentina, Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow, Poland, and Department of Chemistry and Biochemistry, F.C.T., and CCMAR, University of Algarve, Campus de Gambelas, 8005-039 Faro, Portugal