1. Department of Organic ChemistryUniversity of Duisburg Essen Universitätstr. 7 45141 Essen Germany
2. Department of Biomedical EngineeringEindhoven University of Technology P.O. Box 513 5600 MB Eindhoven The Netherlands
3. Departamento de Ciencias BiomédicasUniversidad de Alcalá 28805 Alcalá de Henares Spain
4. Present address: Institute of Theoretical ChemistryFaculty of ChemistryUniversity of Vienna Währinger Str. 17 1090 Vienna Austria
5. Centre for Medical BiotechnologyUniversity of Duisburg Essen Universitätstr. 7 45141 Essen Germany