1. Contribution from the Department of Medical Biochemistry and Genetics, The Texas A&M University System Health Science Center, College Station, Texas 77843-1114, Chemistry Research Laboratory, Department of Chemistry, Oxford University, Mansfield Road, Oxford OX1 3TA, United Kingdom, Department of Physics, Syracuse University, 201 Physics Building, Syracuse, New York 13244-1130, and Structural Biology, Biochemistry, and Biophysics Program, Syracuse University, 111 College Place, Syracuse, New York 13244-4100