Molecular Descriptors Of Topology And Quantitative Structure Property Relationship

QSPR/ QSAR/ QSRR (quantitative structure- property relationships, quantitative structure- activity relationships, quantitative structure- retention relationships) have been a cutting-edge research in chemistry, environment, life science and so on. During recent years, in QSPR/QSAR/QSRR, developing topological index has been a promising approach. Topological index is a graph theoretical descriptor obtained by transforming molecular structures into the corresponding molecular graphs on the molecular level. Topological indexes have been an important method in QSPR/QSAR/QSRR. This work mainly concentrates on the follows:(1) In order to efficiently characterize structures of organic compounds, equilibrium electronegativities were calculated, in terms of the principle of the balanced electronegativities. The novel topological index Al was proposed by extending adjacent matrix employing the degrees of branching and equilibrium electronegativities which were utilized to dye hydrogen-suppressed graph. Possessing clear physical meaning, Al can distinguish compounds containing multiple bonds and/or heteroatoms. In addition, the path number P₂ and P₃ were involVed as well. Study was performed on the properties of alkanes (e. g., molar volume, molar refraction, critical volume and eccentric factor) and retention index of gas chromatography on different stationary phases at different temperatures(e. g, on squalane at 3(?), 5(?), 7(?); on H-1(?)PONA at 60; on J & W DB-5 a(?)60). The regression results indicated that the relationship between them can be quantitatively described as the following equation: P=a*AI+b*P₂+c*P₃+d, with all the correlation coefficients being larger than 0.99. The quantitative structure-property relationships (QSPR) were conducted of the thermodynamic properties (e. g.Δ_fH_m^θ, Sm^θ,Δ_fG_m^θ,ΔH_v,ΔH_s, C_p^θ, C_p, van der Waals constants a and b), boiling points (T_B), critical properties (e. g. T_C, P_C and V_C) for alkanes with the correlation coefficients ranging between 0.9916 and 0.9998. The cross validation demonstrated the models to be statistically significant and reliable. The models, with explicit physical meaning, indicated that size, equilibrium electronegativity, branching degree and shape of molecules can efficiently characterize the inherent structure information of alkanes. The .analyzing results with the Needham formula showed that NI was the most influential factor. The results showed that the models have wide application to study on QSPR and QSRR of alkanes.(2) A novel semi-empirical topological descriptor Nt was proposed by revising the traditional distance matrix based on the equilibrium electronegativity and the relative. bond length. Nt can not only efficiently distinguish structures of organic compounds containing multiple bonds and/or heteroatoms, but also possess good applications of QSPR/QSAR (quantitative structure-property/activity relationships) to a large diverse set of compounds, which are alkanes, alkenes, alkynes, aldehydes, ketones, thiols and alkoxy silicon chlorides with all the correlation coefficients of the models over 0.99 The LOO CV (leave-one-out cross-validation) method was used to testify the stability and predictive ability of the models. The validation results verified the good stability and predictive ability of the models employing the cross-validation parameters: R_CV, SEP_CV and S_CV, which demonstrated the wide potential of the N_t descriptor for applications to QSPR/QSAR.(3) A novel topological index NTI was proposed in terms of the principle of the topological theory by dyeing the suppressed-hydrogen graph and expanding the distance matrix. Taken into account the atomic characteristics of geometric structure as well as electron for compounds, the new index had excellent structural selectivity for organic compounds, which comprises 15 series of organic compounds with double bonds, triple bonds and hetero atoms (e. g., chain alkanes, cycloparaffin, alkenes, alkynes, alcohols, ketones, esters, ethers, alkyl halides, alkylbenzenes, benzene halides, phenol halides, dienes, p-anthranilates and p-hydroxybenzoates). Regression was performed between the index NTI and n-octanol/water partition coefficient of these compounds, demonstrating regression of excellence with the correlation coefficient ranging from 0.9900 to 0.9999. The relationship between log K_ow and NTI for organic, compounds can be quantitatively described as the following: log K_ow=aNTI+b (a and b are constants), which showed that the calculated values were in good agreement with the experimented ones.(4) We introduced the chemical behavior of topology for the first time which consists of the topological growing power and the topological blocking power. On the basis of the principle, the OET (orbital-energy topological index) was proposed by revising the valence electron distance matrix with the orbital energy. The results demonstrated that OET has good application to the physicochemical properties of lanthanide and actinide, especially to the spectral properties which have not been reported by means of QSPR (quantitative structure-property relationships). The results of LOO CV (leave-one-out cross-validation) verified the good stability and predictive ability of the models using the cross-validation parameters: PRESS/SSY, SEP_CV, R_CV, S_PRESS and PSE with the PRESS/SSY ratio ranging between 0.0006 and 0.1148. Compared with the other methods, this work provided an easier way yielding results close to or better than the others. It is on the basis of the chemical behavior of topology that leads to the good and wide application of this method.