1. Contribution from the Department of Physics, Emory University, Atlanta, Georgia 30322, the Departamento de Química (and the Centro de Química Fina e Biotecnologia), Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2825 Monte de Caparica, Portugal, and the Department of Biochemistry and Molecular Biology, College of Medicine, Institute for Biomolecular Science, H. Lee Moffit Cancer Center and Research Institute, University of South Florida, Tampa, Florida 33612