1. Department of Chemistry, University of California, Riverside, California 92521, United States
2. Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, United States
3. Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143, United States
4. College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, P. R. China