1. Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0820, Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0820, and National Centre for Aquatic Biodiversity and Biosecurity, National Institute of Water and Atmospheric Research, Newmarket, Auckland, New Zealand