1. Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128, Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393, IRIBHN, Université Libre de Bruxelles, Campus Erasme, 808 route de Lennik, B-1070 Bruxelles, Belgium, and Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907