化学位移是核磁共振波谱(nuclear magnetic resonance spectrum,NMR)的一项重要参数,由于其对原子周围化学环境十分敏感,因此化学位移的理论计算在生物大分子的结构预测中扮演着重要的角色[1-2]。目前预测生物大分子NMR化学位移的理论...化学位移是核磁共振波谱(nuclear magnetic resonance spectrum,NMR)的一项重要参数,由于其对原子周围化学环境十分敏感,因此化学位移的理论计算在生物大分子的结构预测中扮演着重要的角色[1-2]。目前预测生物大分子NMR化学位移的理论方法主要分为两类:一类是从实验数据拟合得到的经验或者半经验方法[3-4];另一类是基于量子力学理论的从头计算方法[5-7]。与前者相比,量子力学方法不依赖数据集,针对不同体系具有很好的移植性。由于量子力学方法需要的计算时间随计算体系的大小呈多项式增长,因此人们基于“化学局域性”原理发展了分块量子化学方法来提高计算效率。本课题组长期致力于分块量子化学方法的发展,针对生物大分子的NMR化学位移精确预测发展了自动分块的大分子NMR化学位移计算方法(automated fragmentation,AF-NMR)。本文简要介绍本课题组在这方面的研究进展。展开更多
Atomic electronegativity interaction vector (AEIV) and atomic hybridization state index (AHSI) were used for establishing the quantitative structure-spectroscopy relationship(QSSR) model of 13C NMR chemical shifts of ...Atomic electronegativity interaction vector (AEIV) and atomic hybridization state index (AHSI) were used for establishing the quantitative structure-spectroscopy relationship(QSSR) model of 13C NMR chemical shifts of isodon diterpenoid compounds.Multiple linear regression (MLR) and computational neural network (CNN) were used to create the models,and the estimation stability and generalization ability of the models were strictly analyzed by both internal and external validations.The established MLR and CNN models were correlated with experimental values and the correlation coefficients of model estimation,leave-one-out (LOO)cross-validation (CV),and predicted values of external samples were Rcum=0.9724,RCV=0.9723,Qext=0.9738 (MLR);Rcum=0.9957,Qext=0.9956 (CNN),respectively.The results indicated that CNN gave significantly better prediction of 13C NMR chemical shifts for isodon diterpenoids than MLR.Satisfactory results showed that AEIV and AHSI were obviously good for modeling 13C NMR chemical shifts of isodon diterpenoid compounds.展开更多
2,4-diphenylpentane-and 2,4-di-p-tolylpentane-2,4-diols were investigated employing experimental and density functional theory(DFT) method at B3LYP/6-31G(d) level.The structure of syn-2,4-di-p-tolylpentane-2,4-diol(2b...2,4-diphenylpentane-and 2,4-di-p-tolylpentane-2,4-diols were investigated employing experimental and density functional theory(DFT) method at B3LYP/6-31G(d) level.The structure of syn-2,4-di-p-tolylpentane-2,4-diol(2b) was characterized by X-ray diffraction and compared with the crystal structures of anti-and syn-2,4-diphenylpentane-2,4-diols(1a and 1b).X-ray diffraction indicates that inter and intra-molecular hydrogen bonds are formed in the crystal structures.There is π-π staking interaction in 1b and 2b.Good linear correlations and similar results are found between the experimental 1H and 13C NMR chemical shifts(δexp) and GIAO(Gauge Independent Atomic Orbital) method calculated magnetic isotropic shielding tensors(σcalc),HOMO and LUMO molecular orbitals were calculated at the same levels with the different results.UV-vis absorption spectra of the compounds were recorded in EtOH,MeCN,n-BuOH and cyclohexane with different dielectric constants.It is found that the solvent effect is obvious when ε is 24.85(EtOH),35.69(MeCN) and it is weak when ε is decreased to 17.33(n-BuOH),1.18(cyclohexane).展开更多
文摘化学位移是核磁共振波谱(nuclear magnetic resonance spectrum,NMR)的一项重要参数,由于其对原子周围化学环境十分敏感,因此化学位移的理论计算在生物大分子的结构预测中扮演着重要的角色[1-2]。目前预测生物大分子NMR化学位移的理论方法主要分为两类:一类是从实验数据拟合得到的经验或者半经验方法[3-4];另一类是基于量子力学理论的从头计算方法[5-7]。与前者相比,量子力学方法不依赖数据集,针对不同体系具有很好的移植性。由于量子力学方法需要的计算时间随计算体系的大小呈多项式增长,因此人们基于“化学局域性”原理发展了分块量子化学方法来提高计算效率。本课题组长期致力于分块量子化学方法的发展,针对生物大分子的NMR化学位移精确预测发展了自动分块的大分子NMR化学位移计算方法(automated fragmentation,AF-NMR)。本文简要介绍本课题组在这方面的研究进展。
文摘Atomic electronegativity interaction vector (AEIV) and atomic hybridization state index (AHSI) were used for establishing the quantitative structure-spectroscopy relationship(QSSR) model of 13C NMR chemical shifts of isodon diterpenoid compounds.Multiple linear regression (MLR) and computational neural network (CNN) were used to create the models,and the estimation stability and generalization ability of the models were strictly analyzed by both internal and external validations.The established MLR and CNN models were correlated with experimental values and the correlation coefficients of model estimation,leave-one-out (LOO)cross-validation (CV),and predicted values of external samples were Rcum=0.9724,RCV=0.9723,Qext=0.9738 (MLR);Rcum=0.9957,Qext=0.9956 (CNN),respectively.The results indicated that CNN gave significantly better prediction of 13C NMR chemical shifts for isodon diterpenoids than MLR.Satisfactory results showed that AEIV and AHSI were obviously good for modeling 13C NMR chemical shifts of isodon diterpenoid compounds.
基金Projects(21072053,20772028)supported by the National Natural Science Foundation of ChinaProjects(10K025,11C0527)supported by the Scientific Research Fund of Hunan Provincial Education Department,ChinaProject(LKF0901)supported by the Open Foundation of Key Laboratory of Theoretical Chemistry and Molecular Simulation of Ministry of Education,Hunan University of Science and Technology,China
文摘2,4-diphenylpentane-and 2,4-di-p-tolylpentane-2,4-diols were investigated employing experimental and density functional theory(DFT) method at B3LYP/6-31G(d) level.The structure of syn-2,4-di-p-tolylpentane-2,4-diol(2b) was characterized by X-ray diffraction and compared with the crystal structures of anti-and syn-2,4-diphenylpentane-2,4-diols(1a and 1b).X-ray diffraction indicates that inter and intra-molecular hydrogen bonds are formed in the crystal structures.There is π-π staking interaction in 1b and 2b.Good linear correlations and similar results are found between the experimental 1H and 13C NMR chemical shifts(δexp) and GIAO(Gauge Independent Atomic Orbital) method calculated magnetic isotropic shielding tensors(σcalc),HOMO and LUMO molecular orbitals were calculated at the same levels with the different results.UV-vis absorption spectra of the compounds were recorded in EtOH,MeCN,n-BuOH and cyclohexane with different dielectric constants.It is found that the solvent effect is obvious when ε is 24.85(EtOH),35.69(MeCN) and it is weak when ε is decreased to 17.33(n-BuOH),1.18(cyclohexane).
