1. Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, U.K., Institute of Organic Chemistry, Biochemistry and Biotechnology, Wroclaw University of Technology, Wroclaw, Poland, and Department of Biophysics, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801