1. Departament de Química, Universitat de Lleida, Departament de Matemàtica, Universitat de Lleida, Av. Rovira Roure, 191. E-25198 Lleida, Catalonia, Spain, Department of Chemistry, University of Southern Denmark, Campusvej 55, Odense, DK-5230, Denmark, and Laboratory of Physical Chemistry and Colloid Science, Wageningen University, P.O. Box 8038, Dreijenplein 6, 6703 HB Wageningen, The Netherlands