1. Carolina Environmental Bioinformatics Research Center, Laboratory for Molecular Modeling, Division of Medicinal Chemistry and Natural Products, School of Pharmacy, University of North Carolina at Chapel Hill, Campus Box 7568, 327 Beard Hall, Chapel Hill, North Carolina 27599-7568, and Sustainable Technology Division, National Risk Management Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, Ohio 45268