1. Department of Chemical Sciences University of Padova Via Marzolo 1 35131 Padova Italy
2. Department of Chemistry Carnegie Mellon University 4400 Fifth Avenue Pittsburgh Pennsylvania 15213 USA
3. Present address: Centre for Mechanical Engineering Materials and Processes (CEMMPRE) Department of Chemical Engineering University of Coimbra Rua Silvio Lima, Polo II 3030-790 Coimbra Portugal