1. Centre for Research in Molecular Modeling and Department of Chemistry & Biochemistry, Concordia University, Montréal, Québec, Canada H4B 1R6, Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, Département de Chimie, Ecole Normale Supérieure, UMR 8640 PASTEUR, 24 rue Lhomond, 75213 Paris, France, and Department of Chemistry & Biochemistry, University of Colorado, Boulder, Colorado 80309-0215