1. Department of Theoretical Chemistry, Lund University, Chemical Centre, P.O. Box 124, SE-221 00 Lund, Sweden, Biostructural Research Group, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen Ø, Denmark, and Department of Chemistry, Göteborg University, Kemigården 4, SE-412 96 Göteborg, Sweden