STRUCTURE-PROPERTY RELATIONSHIP BETWEEN HALF-WAVE POTENTIALS OF ORGANIC-COMPOUNDS AND THEIR TOPOLOGY

A significant correlation was found between half-wave potentials of organic compounds and their topological indices, A(x1), A(x2), and A(x3). The simplicity of calculation of the index from the connectivity in the molecular skeleton, together with the significant correlation, indicates its practical value. Good results have been obtained by using them to predict the half-wave potentials of some organic compounds.

STUDIES ON STRUCTURE-PROPERTY RELATIONSHIP BETWEEN COLOR REAGENTS AND SENSITIVITY OF THEIR COLOR-REACTIONS WITH YTTERBIUM BY TOPOLOGICAL INDEXES

In this paper A, topological indices and molecular connectivity inidces have been applied to multivariate analysis in structure-property studies. The topological indices of twenty asymmetrical phosphone bisazo derivatives of chromotropic acid have been calculated. The structure-property relationships between color reagents and molar absorptivity of color reactions with ytterbium have been studied by A(m) indices and molecular connectivity indices. Good results have been obtained.

QUANTITATIVE STRUCTURE-ACTIVITY-RELATIONSHIPS FOR TOXICITY OF PHENOLS USING REGRESSION-ANALYSIS AND COMPUTATIONAL NEURAL NETWORKS

Quantitative structure-toxicity models were developed that directly link the molecular structures of a et of 50 alkYlated and/or halogenated phenols with their polar narcosis toxicity, expressed as the negative logarithm of the IGC50 (50% growth inhibitor

STUDY ON STRUCTURE-PROPERTY RELATIONSHIP OF POLYIMIDE BLENDS .2. STRUCTURE AND MISCIBILITY OF POLYIMIDE PBPI-E/PTI-E BLENDS

The structure and miscibility of polyimide PBPI-E/PTI-E blends were studied by wide- and small-angle X-ray scattering and dynamic mechanical analysis, where PBPI-E is a biphenyl-dianhydride-based polyimide, and PTI-E is a polyimide from 4,4'-thiodiphthalic anhydride and 4,4'-oxydianiline. The results obtained show that there exists a paracrystalline structure in the blends with high content of PBPI-E, but this does not affect the miscibility of the blends. The blends are miscible over the entire composition range, since only one T(g) was observed for each blend. Meanwhile, the segregation of PTI-E during crystallization of PBPI-E in the blends is interlamellar.

STUDY ON STRUCTURE-PROPERTY RELATIONSHIP OF POLYIMIDE BLENDS .1. A DYNAMIC MECHANICAL STUDY OF THE MISCIBILITY OF POLYIMIDE POLYIMIDE BLENDS

Three pairs of polyimide/polyimide blends (50/50 wt%) with different molecular structures were prepared by two ways, i.e. mixing of the polyamic acid precursors with subsequent imidization, and direct solution mixing of the polyimides. The blends were studied with DMA technique. The results obtained show that all the blends prepared with these two different ways are miscible, as there existed only one glass transition temperature(Tg) for all the blends. It is suggested that the miscibility of these polyimide/polyimide blends is a result of the strong inter-molecular charge-transfer interaction between the chains of their components.

Molecular docking and 3D-QSAR study of pyranmycin derivatives against 16S rRNA A site

To understand pharmacophore properties of pyranmycin derivatives and to design novel inhibitors of 16S rRNA A site, comparative molecular field analysis (CoMFA) approach was applied to analyze three-dimensional quantitative structure-activity relationship (3D-QSAR) of 17 compounds. AutoDock 3.0.5 program was employed to locate the orientations and conformations of the inhibitors interacting with 16S rRNA A site. The interaction mode was demonstrated in the aspects of inhibitor conformation, hydrogen bonding and electrostatic interaction. Similar binding conformations of these inhibitors and good correlations between the calculated binding free energies and experimental biological activities suggest that the binding conformations of these inhibitors derived from docking procedure were reasonable. Robust and predictive 3D-QSAR model was obtained by CoMFA with q(2) values of 0.723 and 0.993 for cross-validated and noncross-validated, respectively. The 3D-QSAR model built here will provide clear guidelines for novel inhibitors design based on the Pyranmycin derivatives against 16S rRNA A site. (c) 2005 Elsevier B.V. All rights reserved.

Comparison of steroid substrates and inhibitors of P-glycoprotein by 3D-QSAR analysis

Steroid derivatives show a complex interaction with P-glycoprotein (Pgp). To determine the essential structural requirements of a series of structurally related and functionally diverse steroids for Pgp-mediated transport or inhibition, a three-dimensional quantitative structure activity relationship study was performed by comparative similarity index analysis modeling. Twelve models have been explored to well correlate the physiochemical features with their biological functions with Pgp on basis of substrate and inhibitor datasets, in which the best predictive model for substrate gave cross-validated q(2) = 0.720, non-cross-validated r(2) = 0.998, standard error of estimate SEE = 0.012, F = 257.955, and the best predictive model for inhibitor gave q(2) = 0.536, r(2) = 0.950, SEE = 1.761 and F = 45.800. The predictive ability of all models was validated by a set of compounds that were not included in the training set. The physiochemical similarities and differences of steroids as Pgp substrate and inhibitor, respectively, were analyzed to be helpful in developing new steroid-like compounds. (C) 2004 Elsevier B.V. All rights reserved.

Triplex selective 2-(2-naphthyl)quinoline compounds: Origins of affinity and new design principles

A novel competition dialysis assay was used to investigate the structural selectivity of a series of substituted 2-(2-naphthyl)quinoline compounds designed to target triplex DNA. The interaction of 14 compounds with 13 different nucleic acid sequences and structures was studied. A striking selectivity for the triplex structure poly dA:[poly dT](2) was found for the majority of compounds studied. Quantitative analysis of the competition dialysis binding data using newly developed metrics revealed that these compounds are among the most selective triplex-binding agents synthesized to date. A quantitative structure-affinity relationship (QSAR) was derived using triplex binding data for all 14 compounds used in these studies. The QSAR revealed that the primary favorable determinant of triplex binding free energy is the solvent accessible surface area. Triplex binding affinity is negatively correlated with compound electron affinity and the number of hydrogen bond donors. The QSAR provides guidelines for the design of improved triplex-binding agents.

Synthesis and QSAR studies of novel triazole compounds containing thioamide as potential antifungal agents

Eighteen novel triazole compounds containing thioamide were designed and synthesized. Their structures were confirmed by elemental analysis, H-1 NMR, IR, and MS. The title compounds exhibited certain antifungal activity. And the geometry structures of the title compounds were optimized by means of the density functional theory (DFT) method at B3LYP/6-31G* level. The quantitative structure-activity relationship (QSAR) of the title compounds was systematically investigated. A correlative equation between FA and DELH, V was well established by using the multiple linear regression (MLR). (c) 2006 Elsevier Ltd. All rights reserved.

An in silico approach for screening flavonoids as P-glycoprotein inhibitors based on a Bayesian-regularized neural network

P-glycoprotein (P-gp), an ATP-binding cassette (ABC) transporter, functions as a biological barrier by extruding cytotoxic agents out of cells, resulting in an obstacle in chemotherapeutic treatment of cancer. In order to aid in the development of potential P-gp inhibitors, we constructed a quantitative structure-activity relationship (QSAR) model of flavonoids as P-gp inhibitors based on Bayesian-regularized neural network (BRNN). A dataset of 57 flavonoids collected from a literature binding to the C-terminal nucleotide-binding domain of mouse P-gp was compiled. The predictive ability of the model was assessed using a test set that was independent of the training set, which showed a standard error of prediction of 0.146 +/- 0.006 (data scaled from 0 to 1). Meanwhile, two other mathematical tools, back-propagation neural network (BPNN) and partial least squares (PLS) were also attempted to build QSAR models. The BRNN provided slightly better results for the test set compared to BPNN, but the difference was not significant according to F-statistic at p = 0.05. The PLS failed to build a reliable model in the present study. Our study indicates that the BRNN-based in silico model has good potential in facilitating the prediction of P-gp flavonoid inhibitors and might be applied in further drug design.

A novel short neurotoxin, cobrotoxin c, from monocellate cobra (Naja kaouthia) venom: isolation and purification, primary and secondary structure determination, and tertiary structure modeling

A novel short neurotoxin, cobrotoxin c (CBT C) was isolated from the venom of monocellate cobra (Naja kaouthia) using a combination of ion-exchange chromatography and FPLC. Its primary structure was determined by Edman degradation. CBT C is composed of 61 amino acid residues. It differs from cobrotoxin b (CBT B) by only two amino acid substitutions, Thr/Ala11 and Arg/Thr56, which are not located on the functionally important regions by sequence similarity. However, the LD50 is 0.08 mg/g to mice, i.e. approximately five-fold higher than for CBT B. Strikingly, a structure-function relationship analysis suggests the existence of a functionally important domain on the outside of Loop III of CBT C. The functionally important basic residues on the outside of Loop III might have a pairwise interaction with alpha subunit, instead of gamma or delta subunits of the nicotinic acetylcholine receptor (nAChR). (C) 2002 Elsevier Science Inc. All rights reserved.

余甘子、细叶草乌及土荆皮化学成分研究

本论文由三部分共6 章组成。第一部分报道了余甘子、细叶草乌和土荆皮等三种药用植物的化学成分研究成果；第二部分报道了细叶草乌和土荆皮中分离得到的化合物的活性测试，以及这两种植物的质谱分析；第三部分概述了土荆皮的研究现状。第一部分包括1－3 章。在第1 章、第2 章和第3 章中分别报道了余甘子(Phyllanthus emblica L.) 、细叶草乌(Aconitum richardsonianum var.pseudosessiliflorum) 和土荆皮( pseudolarix kaempferi) 的化学成分。采用正、反相硅胶柱层析等各种分离方法，从余甘子中共分离出10 个化合物，其中1 个为新化合物，另外还有2 个为首次从该植物中分离得到。细叶草乌的化学成分研究尚未见报道，我们从该植物中共分离出15 个化合物，其中6 个为二萜生物碱，9个为非生物碱成分。从土荆皮中分离得到16 个化合物，其中8 个二萜、1 个三萜和7 个其它类型化合物，其中有4 个化合物为首次在该植物中分离得到；从土荆皮挥发油中分离鉴定出了22 个化合物，占挥发油总量的90%。第二部分包括4－5 章。第4 章报道了从细叶草乌和土荆皮中分离得到的13个化合物的药理活性研究，结果显示，展花乌头宁和土荆乙酸葡萄糖苷等表现出较高的组织蛋白酶K 抑制活性；土荆乙酸葡萄糖苷表现出较高的组织蛋白酶B抑制活性；8-去乙酰滇乌碱表现出较高的蛋白质酪氨酸磷酸酶抑制活性。第5 章报道了细叶草乌和土荆皮总浸膏的质谱( ESI-MS ) 分析，研究结果表明，ESI-MS 法可以简单快速地检测这两种植物的主要成分；通过ESI-MS2 分析初步探讨了一些化合物的裂解规律，尝试质谱在其结构测定中的具体应用。第三部分为第6 章。从化学成分、药理、构效关系、主要成分的定量分析、及其合成研究等方面概述了土荆皮的研究进展。 This dissertation consists of three parts. The first part elaborate thephytochemical investigation of three medicinal plants, Phyllanthus emblica L.,Aconitum richardsonianum var. pseudosessiliflorum and pseudolarix kaempferi. Thesecond part reported the bioassay of 13 constituents from Aconitum richardsonianumvar. pseudosessiliflorum and pseudolarix kaempferi, and ESI-MS analysis of these twoplant . The third part is a review on the research progress of pseudolarix kaempferi.The first part is composed of three chapters. Chapters 1-3 focus on the isolationand identification of chemical constituents from Phyllanthus emblica L., Aconitumrichardsonianum var. pseudosessiliflorum and pseudolarix kaempferi. 10 compoundsincluding a new tannin were isolated from the fruits of Phyllanthus emblica by repeatcolumn chromatography over normal and reversed phase silica gel, 2 of them werefirstly reported in this plant. The chemical constituents of Aconitum richardsonianumvar. pseudosessiliflorum never reported before, 15 compounds including 6 diterpenealkaloids were isolated and identified from the roots of this plant. 16 compoundsincluding 8 diterpenes , 1 triterpene and 7 other compounds were isolated from the bark of pseudolarix kaempferi, among them, 4 compounds were firstly reported fromthe EtOH extracts of this plant, and 22 compounds were identified from its essentialoil, representing 90% of the total essential oil.The second part includes chapters 4 and 5. Chapter 4 reported thepharmacological activities of 13 compounds isolated from Aconitum richardsonianumvar. pseudosessiliflorum and pseudolarix kaempferi. Results demonstrated that chasmanine and pseudolaric acid B-β-D-glucoside exhibit relatively high anti-Cathepsin K activities; pseudolaric acid B-β-D-glucoside exhibits relatively highanti-Cathepsin B activity; 8-deacetyl-yunaconitine exhibits relatively high anti-PTP1Bactivity. Chapter 5 reported the ESI-MS analysis of extractions from Aconitumrichardsonianum var. pseudosessiliflorum and pseudolarix kaempferi, it was showedthat ESI-MS can be used as an useful tool in analyzing the major constituents of thesetwo plant much quick and easy, in addition, the fragmentation rules of somecompounds were discussed, in order to find some applications of ESI-MS2 method in their structure determination.The third part is a review on the research progress of pseudolarix kaempferi,including the chemical constituents, pharmacology, structure-activity relationship(SAP), quantitative analysis and synthesis of the major constituents.

Comparison of different methods for variable selection

In chemistry for chemical analysis of a multi-component sample or quantitative structure-activity/property relationship (QSAR/QSPR) studies, variable selection is a key step. In this study, comparisons between different methods were performed. These methods include three classical methods such as forward selection, backward elimination and stepwise regression; orthogonal descriptors; leaps-and-bounds regression and genetic algorithm. Thirty-five nitrobenzenes were taken as the data set. From these structures quantum chemical parameters, topological indices and indicator variable were extracted as the descriptors for the comparisons of variable selections. The interesting results have been obtained. (C) 2001 Elsevier Science B.V. All rights reserved.

Study on the structure and miscibility of PBPI-E/PTI-E blends

The crystallization, miscibility and structure of polyimide PBPI-E/PTI-E blends were studied by DSC, DMA, NMR and fluorescence techniques, where PBPI-E is a biphenyldianhydride-based polyimide, and PTI-E is a polyimide from 4,4'-thiodiphthalic anhydride and 4,4'-oxydianiline. The results obtained show that PBPI-E/PTI-E blends are miscible at a molecular level for all the compositions studied. However, the glass transition temperature of the blends is well below the value predicted by the Fox equation, and the blends are not stable at high temperature, i.e. phase separation will occur when the blends are annealed about T-g. Moreover, the melting point T-m, differential enthalpy Delta H and spin-lattice relaxation time T-l(c) of the blends increase with the annealing time. (C) 1997 Elsevier Science Ltd. All rights reserved.