1. Department of Physical Chemistry, Heinrich-Heine University, University-str. 1, D-40225 Düsseldorf, Germany
2. Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, D-12489 Berlin, Germany
3. Istituto Biostrutture e Bioimmagini-CNR, Via Mezzocannone 16, I-80134 Napoli, Italy