1. Department of Chemistry, University of Texas at Dallas, P.O. Box 830660, Richardson, Texas 75083, Macrocyclics, 2110 Research Row, Dallas, Texas 75235, Department of Inorganic and Analytical Chemistry, Lajos Kossuth University, H-4010, Debrecen, Hungary, and Rogers Magnetic Resonance Center, Department of Radiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390