1. Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (P.R. China), Fax: (+86) 411‐84379227
2. Key Laboratory of Preclinical Study for New Drugs of Gansu Province Department, Institute of Biochemistry and Molecular Biology, Lanzhou University, Lanzhou 730000 (P.R. China), Fax: (+86) 931‐8911255