1. Contribution from the Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON, Canada, M5S 1A8, Program in Molecular Structure and Function, Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada, M5G 1X8, Department of Chemistry, University of Toronto, UTM, 3359 Mississauga Road North, Mississauga, ON, Canada, L5L 1C6, and Department of Biochemistry, University of Toronto, 1 King's College Circle, Toronto, ON, Canada, M5S 1X8