1. Department of Chemistry, Ecole Normale Supérieure, 24 rue Lhomond 75005 Paris, France, UMR ENS-CNRS-UPMC 8640, 24 rue Lhomond 75005 Paris, France, Fondation Pierre Gilles de Gennes pour la Recherche, Paris, France, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215