1. Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143
2. Graduate Group in Biophysics, University of California, San Francisco, California 94143
3. Department of Physics, Arizona State University, Tempe, Arizona 85287;
4. Department of Chemical Engineering, University of California, Santa Barbara, California 93106;
5. Max Planck Institute of Colloids and Interfaces, Department of Theory and Bio-Systems, 14424 Potsdam, Germany;