1. Department of Chemistry, School of Arts and Sciences, The Johns Hopkins University, Baltimore, Maryland 21218, Division of Toxicological Sciences, Department of Environmental Health Sciences, Bloomberg School of Hygiene, The Johns Hopkins University, Baltimore, Maryland 21205, Department of Medical Specialities, The University of Texas, M. D. Anderson Cancer Center, Houston, Texas 77030, and Cytochroma, Inc., Markham, Ontario, Canada L3R 8E4