1. Institut de Chimie des Surfaces et Interfaces, CNRS UPR 9069, Jean Starcky, 15, F-68057, Mulhouse, France, Applied Science & Technology/Analytical Sciences, Dow Olefinverbund GmbH, Schkopau, D16/1.04, Germany, Laboratoire de Physicochimie des Polymères, Université de Mons-Hainaut, Place du Parc, 20, B-7000 Mons, Belgium, and European Molecular Biology Laboratory, Hamburg Outstation, EMBL c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany