1. Department of Chemistry and the Center of Nanoscale Science and Technology, Rice University, P.O. Box 1892, Houston, Texas 77251-1892, Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, and Department of Molecular Virology and Microbiology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030