1. Department of Environmental Sciences and Engineering CB7431, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7431, School of Pharmacy CB7360, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7360, and Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, P.O. Box 12233, MD F0-03, Research Triangle Park, North Carolina 27709