1. Institut für Mikrotechnik Mainz GmbH, Carl-Zeiss-Str. 18-20, 55129 Mainz, Germany; Department of Chemistry and Chemical Engineering, Eindhoven University of Technology, 5600 MB Eindhoven, P.O. Box 513, The Netherlands; Department of Chemical Engineering, University College London, Torrington Place, London WC1E 7JE, UK; and Department of Chemistry, Pharmaceutics and Earth Sciences, Institute of Organic Chemistry, Johannes-Gutenberg-Universität Mainz, Duesbergweg 10−14, 55128 Mainz