1. CAS Key Laboratory of Chemistry of Northwestern Plant Resources and Key Laboratory for Natural Medicine of Gansu ProvinceLanzhou Institute of Chemical Physics, Chinese Academy of Sciences Lanzhou P. R. China
2. University of Chinese Academy of Sciences 19A Yuquan Road Beijing 100049 P. R. China
3. College of Chemistry and Chemical EngineeringNorthwest Normal University Lanzhou P. R. China
4. Centre of Resource Chemical and New MaterialLanzhou Institute of Chemical PhysicsChinese Academy of Sciences Qingdao P. R. China