1. Contribution from the NMR Program, National High Magnetic Field Laboratory (NHMFL), Tallahassee, Florida 32310, Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, Vanderbilt Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee 37232, Department of Chemistry & Biochemistry, Florida State University, Tallahassee, Florida 32306, and Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306