1. Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts 02115, Department of Chemistry, University of South Carolina, Columbia, South Carolina 29208, Department of Biochemistry, University of Illinois, Urbana, Illinois 61801, Department of Molecular Biology and Biochemistry, University of California, Irvine, California 92697, and Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284