Many structure-property/activity studies use graph theoretical indices, which are based on the topological properties of a molecule viewed as a graph. Since topological indices can be derived directly from the molecul...Many structure-property/activity studies use graph theoretical indices, which are based on the topological properties of a molecule viewed as a graph. Since topological indices can be derived directly from the molecular structure without any experimental effort, they provide a simple and straightforward method for property prediction. In this work the flash point of alkanes was modeled by a set of molecular connectivity indices （Х）, modified molecular connectivity indices （ ^mХ^v ） and valance molecular connectivity indices （ ^mХ^v ）, with ^mХ^v calculated using the hydrogen perturbation. A stepwise Multiple Linear Regression （MLR） method was used to select the best indices. The predicted flash points are in good agreement with the experimental data, with the average absolute deviation 4.3 K.展开更多
A quantitative structure-property relationship (QSPR) study has been made for the prediction of the surface tension of nonionic surfactants in aqueous solution. The regressed model includes a topological descriptor, ...A quantitative structure-property relationship (QSPR) study has been made for the prediction of the surface tension of nonionic surfactants in aqueous solution. The regressed model includes a topological descriptor, the Kier & Hall index of zero order (KH0) of the hydrophobic segment of surfactant and a quantum chemical one, the heat of formation (fHD) of surfactant molecules. The established general QSPR between the surface tension and the descriptors produces a correlation coefficient of multiple determination, 2r=0.9877, for 30 studied nonionic surfactants.展开更多
Based on the quantum chemical descriptors,quantitative structure-property relationship（QSPR） models have been developed to estimate and predict the photodegradation rate constant（logK） of polycyclic aromatic hydro...Based on the quantum chemical descriptors,quantitative structure-property relationship（QSPR） models have been developed to estimate and predict the photodegradation rate constant（logK） of polycyclic aromatic hydrocarbons（PAHs） by use of linear method（multiple linear regression,MLR） and non-linear method（back propagation artificial neural network,BP-ANN）.A BP-ANN with 3-3-1 architecture was generated by using three quantum chemical descriptors appearing in the MLR model.The standard heat of formation（HOF）,the gap of frontier molecular orbital energies（ΔELH） and total energy（TE） were inputs and its output was logK.Leave-One-Out（LOO） Cross-Validated correlation coefficient（R^2CV） of the established MLR and BP-ANN models were 0.6383 and 0.7843,respectively.The nonlinear BP-ANN model has better predictive ability compared to the linear MLR model with the root mean square error（RMSE） for training and validation sets to be 0.1071,0.1514 and the squared correlation coefficient（R^2） of 0.9791,0.9897,respectively.In addition,some insights into the molecular structural features affecting the photodegradation of PAHs were also discussed.展开更多
以物质的电子、空间等结构性质为基础,运用Gaussian98和Cerius2程序包对偶极距(Dipole)、最高占据轨道能量(EHOMO)、最低空轨道能量(ELUMO)、分子总能量(E)、旋转键(Rotlbonds)、最弱的R-NO2键长(R-NO2 bond length,R为C或N)、氢键供体(...以物质的电子、空间等结构性质为基础,运用Gaussian98和Cerius2程序包对偶极距(Dipole)、最高占据轨道能量(EHOMO)、最低空轨道能量(ELUMO)、分子总能量(E)、旋转键(Rotlbonds)、最弱的R-NO2键长(R-NO2 bond length,R为C或N)、氢键供体(Hbond donor)和中点势(Vmid)8种描述符进行了计算,采用Cerius2程序包中的QSPR方法建立了芳香系炸药密度与8种描述符之间的构效关系式,相关系数R为0.909,30个化合物所构成的训练集和15个化合物所构成的预测集预测密度与实测密度之间的平均误差分别为3.33%和2.94%。展开更多
In this paper, according to the peak numbers of the nuclear magnetic resonance and the Randic embranchment degree (δ_i) of carbon atom i, the carbon atom’s environment valence g_i is defined as: g_i=(t_i+δ_i)/2.The...In this paper, according to the peak numbers of the nuclear magnetic resonance and the Randic embranchment degree (δ_i) of carbon atom i, the carbon atom’s environment valence g_i is defined as: g_i=(t_i+δ_i)/2.The g_i reflect the characteristic of each carbon atom, and as well as the conjunction detail of the carbon atom with other carbon atoms.So, the g_ i could distinguish better the chemical environment of each carbon atom in the molecule than δ_i.A connectivity index of environment valence ( mS) and its athwart index ( mS′) are proposed based on the adjacency matrix and the carbon atom’s environment valence g_i.Among them, the 0S and 0S′ include the characteristic and the connectivity of each carbon atom, the 1S and 1S′ reflect the second conjunction between carbon atoms.Based on 0S′ and N(the number of carbon atom), a new structural parameter——symmetry degree (N_ ec), is defined as: N_ ec=[(0S′_S/0S′_C)N] 2/3,and the N_ ec reflect the size of the molecule as well as the symmetry of the molecule.The N_ ec, 0S and R_n(the biggest ring’s edge numbers of cycloalkanes) of 474 saturated hydrocarbons (216 paraffins and 258 cycloalkanes) were calculated and correlated with their boiling points.The best regression equation was obtained as follow: ln(1056-T_b)=6.9480-0.1040N_ ec -0.0086890S-0.009614R_ n+0.01998R 0.5_n,n=474,R=0.9989,F=52627,S=5.63K.The model was checked up by the Jackknife’s method.It should have overall steadiness and could be used for predicting the boiling point of saturated hydrocarbons.展开更多
文摘Many structure-property/activity studies use graph theoretical indices, which are based on the topological properties of a molecule viewed as a graph. Since topological indices can be derived directly from the molecular structure without any experimental effort, they provide a simple and straightforward method for property prediction. In this work the flash point of alkanes was modeled by a set of molecular connectivity indices （Х）, modified molecular connectivity indices （ ^mХ^v ） and valance molecular connectivity indices （ ^mХ^v ）, with ^mХ^v calculated using the hydrogen perturbation. A stepwise Multiple Linear Regression （MLR） method was used to select the best indices. The predicted flash points are in good agreement with the experimental data, with the average absolute deviation 4.3 K.
基金the National Natural Science Foundation of China(to grant No.29903006 and 29973023)the Visiting Scholar Foundation of Key Laboratory in University of China for their financial support
文摘A quantitative structure-property relationship (QSPR) study has been made for the prediction of the surface tension of nonionic surfactants in aqueous solution. The regressed model includes a topological descriptor, the Kier & Hall index of zero order (KH0) of the hydrophobic segment of surfactant and a quantum chemical one, the heat of formation (fHD) of surfactant molecules. The established general QSPR between the surface tension and the descriptors produces a correlation coefficient of multiple determination, 2r=0.9877, for 30 studied nonionic surfactants.
基金supported by the Natural Science Foundation of Fujian Province (D0710019)the Natural Science Foundation of Overseas Chinese Affairs Office of the State Council (06QZR09)
文摘Based on the quantum chemical descriptors,quantitative structure-property relationship（QSPR） models have been developed to estimate and predict the photodegradation rate constant（logK） of polycyclic aromatic hydrocarbons（PAHs） by use of linear method（multiple linear regression,MLR） and non-linear method（back propagation artificial neural network,BP-ANN）.A BP-ANN with 3-3-1 architecture was generated by using three quantum chemical descriptors appearing in the MLR model.The standard heat of formation（HOF）,the gap of frontier molecular orbital energies（ΔELH） and total energy（TE） were inputs and its output was logK.Leave-One-Out（LOO） Cross-Validated correlation coefficient（R^2CV） of the established MLR and BP-ANN models were 0.6383 and 0.7843,respectively.The nonlinear BP-ANN model has better predictive ability compared to the linear MLR model with the root mean square error（RMSE） for training and validation sets to be 0.1071,0.1514 and the squared correlation coefficient（R^2） of 0.9791,0.9897,respectively.In addition,some insights into the molecular structural features affecting the photodegradation of PAHs were also discussed.
文摘以物质的电子、空间等结构性质为基础,运用Gaussian98和Cerius2程序包对偶极距(Dipole)、最高占据轨道能量(EHOMO)、最低空轨道能量(ELUMO)、分子总能量(E)、旋转键(Rotlbonds)、最弱的R-NO2键长(R-NO2 bond length,R为C或N)、氢键供体(Hbond donor)和中点势(Vmid)8种描述符进行了计算,采用Cerius2程序包中的QSPR方法建立了芳香系炸药密度与8种描述符之间的构效关系式,相关系数R为0.909,30个化合物所构成的训练集和15个化合物所构成的预测集预测密度与实测密度之间的平均误差分别为3.33%和2.94%。
文摘In this paper, according to the peak numbers of the nuclear magnetic resonance and the Randic embranchment degree (δ_i) of carbon atom i, the carbon atom’s environment valence g_i is defined as: g_i=(t_i+δ_i)/2.The g_i reflect the characteristic of each carbon atom, and as well as the conjunction detail of the carbon atom with other carbon atoms.So, the g_ i could distinguish better the chemical environment of each carbon atom in the molecule than δ_i.A connectivity index of environment valence ( mS) and its athwart index ( mS′) are proposed based on the adjacency matrix and the carbon atom’s environment valence g_i.Among them, the 0S and 0S′ include the characteristic and the connectivity of each carbon atom, the 1S and 1S′ reflect the second conjunction between carbon atoms.Based on 0S′ and N(the number of carbon atom), a new structural parameter——symmetry degree (N_ ec), is defined as: N_ ec=[(0S′_S/0S′_C)N] 2/3,and the N_ ec reflect the size of the molecule as well as the symmetry of the molecule.The N_ ec, 0S and R_n(the biggest ring’s edge numbers of cycloalkanes) of 474 saturated hydrocarbons (216 paraffins and 258 cycloalkanes) were calculated and correlated with their boiling points.The best regression equation was obtained as follow: ln(1056-T_b)=6.9480-0.1040N_ ec -0.0086890S-0.009614R_ n+0.01998R 0.5_n,n=474,R=0.9989,F=52627,S=5.63K.The model was checked up by the Jackknife’s method.It should have overall steadiness and could be used for predicting the boiling point of saturated hydrocarbons.
