1. Department of Chemistry, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, England, ICREA, Life Science Department, Barcelona Supercomputing Center, Jordi Girona 29, 08034 Barcelona, Spain, Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England, and Protein and Nucleic Acid Chemistry Laboratory, Hodgkin Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England