Affiliation: | a College of Letters and Science, Department of Chemistry, F Daniels & JH Mathews 5327, 1101 University Avenue, Madison, WI 53706, USA;b University of Pennsylvania, Department of Biochemistry and Biophysics, Anatomy Chemistry Building, Philadelphia, PA 19104-6059, USA;c Abteilung Chemie, MPI Experimentelle Medizin, Herman Rein Strasse 3, Goettingen D–37075, Germany |