1. Department of Polymer Sciences, M.V. Lomonosov Moscow State University, Leninskie Gory, Moscow V-234, 119899 Russia; Department of Pharmaceutical Sciences, University of Nebraska Medical Center, 986025 Nebraska Medical Center, Omaha, Nebraska 68198-6025; and Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec, Canada H3A 2K6