1. Laboratoire Physico-Chimie; Institut Curie, CNRS UMR168, Paris-Science Lettres; Universite Pierre et Marie Curie-Paris 6; 75005 Paris France
2. Department of Biology/Chemistry; Division of Biophysics; University of Osnabrück; 49076 Osnabrück Germany
3. Laboratoire de Physique de la Matière Condensée; École Polytechnique; 91128 Palaiseau France