1. Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China), Hunan Normal University, Changsha, Hunan 410081, P. R. China
2. Institute of Biomedical Research, Yunnan University, Kunming 650500, P. R. China
3. Research Computing Center, University of North Carolina, Chapel Hill, NC 27599-3420, USA
4. Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599-3290, USA