1. Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, Department of Radiology, New York University School of Medicine, 530 1st Avenue, New York, New York 10016, and Department of Molecular Genetics and Microbiology, University of New Mexico Health Sciences Center, 915 Camino de Salud NE, Albuquerque, New Mexico 87131