1. Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, The Quantum Electronics Laboratory, Faculty of Physics, Adam Mickiewicz University, 85 Umultowska, Poznan 61-614, Poland, and Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Virginia Biotech I, Suite 212, 800 East Leigh Street, Richmond, Virginia 23219