1. Laboratory for Macromolecular and Organic Chemistry, and Department of Polymer Technology, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, Laboratory of Organic Chemistry, Radboud Universiteit Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands, and EM Unit, Department of Pathology, University of Maastricht, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands