1. Ottawa Carleton Institutes of Chemistry and Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
2. Departamento de Farmacia, Facultad de Quimica, Universidad Nacional Autonoma de México, Coyoacan 041510, México
3. Department of Chemistry, University of Delhi, Delhi 110007, India
4. Universidad Nacional, Heredia, apdo 86—3000, Costa Rica