1. Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180, Department of Biological Sciences, State University of New York at Albany, 1400 Washington Avenue, Albany, New York 12222, and Department of Biology, Chemistry, and Physics, Southern Polytechnic State University, 1100 South Marietta Parkway, Marietta, Georgia 30060