1. Department of Cell Biology, Center for Integrative Molecular Biosciences, Department of Chemistry, and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, and Department of Electronic and Nanostructured Materials and Department of Materials Characterization, Sandia National Laboratory, Albuquerque, New Mexico 87185