1. Departments of Pharmaceutics and Pharmaceutical Chemistry and Bioengineering, University of Utah, Salt Lake City, Utah 84112-5820, Departments of Chemical Engineering and Bioengineering, Box 351750, University of Washington, Seattle, Washington 98195-1750, National ESCA and Surface Analysis Center for Biomedical Problems, University of Washington, Seattle, Washington 98195-1750, and Department of Chemistry, Tsinghua University, Beijing, 100084, China