1. Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, U.K.
2. Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, U.K.
3. Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, United States
4. Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
5. Department of Chemistry, University of Kentucky, Kentucky 40511, United States