1. Department of Pharmaceutical Sciences, University of Nebraska Medical Center, 600 South 42nd Street, Omaha, Nebraska 68198-6025, Department of Polymer Sciences, M. V. Lomonosov, Moscow State University, Vorobievy Gory, Moscow V-234, Russia, and Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec, Canada H3A 2K6