1. Department of Pharmaceutical Sciences and Experimental Therapeutics College of Pharmacy University of Iowa 180 S Grand Avenue, CPB 538 Iowa City IA 52245 USA
2. Present address: Beckman Coulter Indianapolis IN 46268 USA
3. NMR Facility, Roy J. and Lucille A. Carver College of Medicine University of Iowa 285 Newton Rd Iowa City IA 52245 USA
4. Present address: Bruker Biospin Corporation Billerica MA 01821–3991 USA
5. Iowa Neuroscience Institute Roy J. and Lucille A. Carver College of Medicine University of Iowa Iowa City IA 52242 USA