Equilibrium conformations of polymer chains Part II. Conformons in networks

With regard to the ideal network it is shown that the concept ofN non-interacting polymer chains can be transformed in a problem of non interacting excitations (called conformons) for rubber elasticity. Modelling the interaction on permanent crosslinks as a scattering problem and taking the finite chain length into account, an interpretation of the second Mooney coefficient can be given. There is some evidence that the junctions move by constrained self diffusion.Dedicated to Prof. Dr. W. Ruland on the occasion of his 60th birthday.     

Room Temperature Solid State Reaction Involving Structural Transformation of Covalent Oxide Network

An interesting structural transformation from a two dimensional (2d) covalent oxide network with a layered structure to a three-dimensional (3d) network with a tunnel structure was found at room temperature in the mixture of hydrated alkali-metal molybdenum bronze and amorphous alkali-metal molybdate. From various experimental results it was concluded that the transformation was due to a room temperature solid state reaction.     

阴离子嵌段共聚的交联聚苯乙烯的网络链长多分散性与网络结构非均一性

用链长分布不同的活性聚苯乙烯子聚物与二乙烯基苯进行阴离子嵌段共聚,合成了一系列两相模型交联网络。以作者等提出的方法测定了所合成网络的结构非均一因子Z。实验测定的网络结构非均一因子Z与交联前聚苯乙烯活性链的分子量分布宽度指数d之间有平行的相应变化规律,表明所给予的非均一因子Z的物理意义是合理的。同时说明,子聚物链长分布较宽时,在网络的高交联区中除了二乙烯基苯外,还有一些对溶胀无贡献的子聚物以悬挂链的形式存在。     

人工神经元网络辅助丙烷氨氧化催化剂设计

报道了利用人工神经元网络辅助丙烷氨氧化制丙烯腈催化剂设计的研究进展结果．通过筛选得到了可以拟合该反应体系的神经元网络模型，从而使丙烷转化率和丙烯腈选择性可以表示为催化剂组成的函数，利用培训后的神经元网络模型所得到的权值文件，结合作者自编的优化程序，该网络可用于预测最优的催化剂组成．实验得到丙烯腈收率和选择性可分别达到４３．０％和５６．２４％．     

Antibody synthesis induced by endogenous internal images

In this study, immunization with a vaccine consisting of multiple F(abt’)₂ fragments of affinity-purified antitetanus toxoid antibodies covalently bound to a carrier protein successfully induced antitetanus toxoid antibodies. Further studies showed that this vaccine preparation contained no biologically detectable tetanus antigen. The induced antitetanus antibody (Ab1t’) titer was higher than the titer of antibodies binding control antigens. The immunizing F(abt’)₂ preparation did not elicit a secondary antitetanus response from mice primed with tetanus toxoid and, hence, appeared free of tetanus epitopes. The specificity of Ab1t’ was established by absorption and inhibition with antigen. Immunization with antitetanus F(abt’)₂ (Ab1t’) fragments appears to have elicited naturally occurring autologous antitetanus toxoid antibody (Ab1t’) through an idiotypic pathway. As predicted by network theory, anti-idiotype (Ab2) and antitetanus (Ab1t’) cycled reciprocally. Clonotypic characterization of Ab1t’ using isoelectric focusing and affinity immunoblotting showed increases in Ab1t’ titer to be the result of increased synthesis by limited subsets of antitetanus toxoid B-cell clones and not increased synthesis by multiple clones, as is characteristic of antigen-driven Ab1 responses. Many Ab1 and Ab1t’ clonotypes had identical pIs, suggesting that they either share V region genes or are the product of the same B-cell clones. These findings indicate that immunization with polyclonal multivalent Ab1 preparations can trigger active synthesis of antibodies with the same specificity. The results provide further evidence for naturally occurring idiotypic cascades that could be exploited for studies of catalytic antibodies.     

An <Emphasis Type="BoldItalic">in silico</Emphasis> approach for screening flavonoids as P-glycoprotein inhibitors based on a Bayesian-regularized neural network

Summary 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.     

Lithium insertion into In2S3 studied by perturbed γ-γ angular correlation

Li_xIn₂S₃ was electrochemically prepared with different small amounts x of lithium (0?x?0.13) in order to maintain the initial crystallographic structure of the thiospinel In₂S₃. About 10¹² radioactive ¹¹¹In ions have been implanted into these samples at 400 keV to perform PAC experiments in the temperature range from 10 to 773 K. The results are compared to previous experiments with undoped In₂S₃ samples. According to the structure of In₂S₃ in the β-phase, which belongs to the I4₁/amd space group having a unit cell with 32 In and 48 S atoms and the cell parameters α=7.61 Å and c=32.28 Å, three different electric field gradients were observed. Within two different temperature ranges dynamical EFGs occur, which are clearly influenced by the insertion of Lithium. The strong dependence of one EFG on the Li concentration x can be correlated to the effective charge of the In ions. This correlation is discussed with respect to XRD analyses of the Li_xIn₂S₃ samples and to XANES measurements on a similar sample.     

Hyperbranched polycyclocarbosiloxane

A new cross-linkable naphthalene-cyclocarbosiloxane was synthesised starting from bis[1,4-bis(methylhydrosiloxanyl)-dihydronaphthalene] via catalytic addition of the Si-H reactive groups to the unsaturated bond of triethoxyvinylsilane. Hyperbranched polycyclocarbosiloxane networks were formed by condensation of the alcoxyl groups in the presence of dibutyltin dilaurate as catalyst. The cross-linking process was studied in order to obtain information concerning the values of the reaction parameters and to determine the position of the gelation point relative to conversion.GPC analysis, IR, and 1H-NMR spectral analysis techniques were used to investigate the chemical structures of the intermediates and of the product.     

Ion-exchange selectivity of a network calixarene-containing polymer obtained by the template synthesis on Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, and Ba<Superscript>2+</Superscript> matrices

The ion-exchange equilibrium in network polymers obtained from cis-2,8,14,20-tetraphenyl-4,6,10,12,16,18,22,24-octahydroxycalix[4]arene by template synthesis on cations Na⁺, K⁺, and Ba²⁺ as matrices was studied. The selectivity coefficients of ion exchanges Ba²⁺-H⁺, Na⁺-H⁺, K⁺-H⁺, Na⁺-K⁺, and Na⁺-NH₄ ⁺ were determined. The template synthesis enhanced the affinity of the polymers to matrix-forming cations by 6–8 kJ mol⁻¹. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1919–1922, August, 2005.     

Location of saddle points and minimum energy paths by a constrained simplex optimization procedure

Two methods are proposed, one for the location of saddle points and one for the calculation of steepest-descent paths on multidimensional surfaces. Both methods are based on a constrained simplex optimization technique that avoids the evaluation of gradients or second derivative matrices. Three chemical reactions of increasing structural complexity are studied within the PRDDO SCF approximation. Predicted properties of reaction hypersurfaces are in good overall agreement with those determined by gradient minimization and gradient following algorithms in connection with various ab initio SCF methods. Computational efforts required by the new procedures are discussed.