1. Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, Department of Chemistry, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada, Department of Chemistry and Biochemistry, Loyola Marymount University, 1 LMU Drive, MS 8225, Los Angeles, California 90045, and Department of Chemistry, Columbia University, 3000 Broadway, Mail Code 3119, New York, New York 10027