1. Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012, Bruker Daltonics, 40 Manning Road, Billerica, Massachusetts 01821, and Department of Chemistry and Biochemistry, and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0358