School of Pharmaceutical Sciences and School of Mathematics and Statistics, Central South University, Changsha 410083, P. R. China.|School of Pharmaceutical Sciences and School of Mathematics and Statistics, Central South University, Changsha 410083, P. R. China.|School of Pharmaceutical Sciences and School of Mathematics and Statistics, Central South University, Changsha 410083, P. R. China.|School of Pharmaceutical Sciences and School of Mathematics and Statistics, Central South University, Changsha 410083, P. R. China.