1. Chemistry Department, The University of Texas at Dallas, Richardson, TX 75083–0688, U.S.A.
2. Pre-Clinical Science Unit of the Department of Veterans Affairs Medical Center, The University of Texas Southwestern Medical Center at Dallas, 4500 South Lancaster Road, Dallas, TX 75216, U.S.A.
3. The Mary Nell & Ralph B. Rogers N.M.R. Center, The University of Texas Southwestern Medical Center at Dallas, 4500 South Lancaster Road, Dallas, TX 75216, U.S.A.
4. Department of Biochemistry, The University of Texas Southwestern Medical Center at Dallas, 4500 South Lancaster Road, Dallas, TX 75216, U.S.A.