1. Laboratory of Polymer Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, Department of Pathology, Electron Microscopy, University of Maastricht, P.O. Box 616, 6200 MD Maastricht, The Netherlands, Department of Chemistry, University of Leicester, Leicester LE1 7RH, United Kingdom, and MicroSpectroscopy Centre, Laboratory for Biochemistry, Wageningen University and Research Centre, P.O. Box 8128, 6700 ET Wageningen, The Netherlands