1. Department of Pharmaceutics; School of Pharmacy; Shenyang Pharmaceutical University; Shenyang 110016 P. R. China
2. Municipal Key Laboratory of Biopharmaceutics; School of Pharmacy; Shenyang Pharmaceutical University; Shenyang 110016 P. R. China
3. Key Laboratory of Structure-Based Drug Design and Discovery; Shenyang Pharmaceutical University; Shenyang 110016 P. R. China
4. Division of Molecular Pharmaceutics and Center of Nanotechnology in Drug Delivery; Eshelman School of Pharmacy; University of North Carolina at Chapel Hill; Chapel Hill NC 27599 USA