1. Laboratoire de Chimie Inorganique et Bioinorganique, Ecole Polytechnique Fédérale de Lausanne, EPFL-BCH; CH-1015 Lausanne, Switzerland, Department of Chemistry, The Richard E. Smalley Center for Nanoscale Science and Technology, and the Center for Biological and Environmental Nanotechnology MS 60, Rice University, Houston, Texas 77251-1892, Centre de Biophysique Moléculaire, CNRS, rue Charles Sadron, 45071 Orléans, France, and TDA Research Incorporated, 12345 West 52nd Avenue, Wheat Ridge, Colorado, 80033