平菇多糖稀溶液行为的研究

平菇多糖属生物高分子, 文章对平菇多糖稀溶液性质进行了研究。实验系采用Elias浊点滴定法测定平菇多糖溶液的θ组成, 用快速动态膜渗透计和粘度法测定平菇多糖的数均分子量、维利系数与分子链的构型参数。探讨其在θ条件下的分子形态及用Tung函数法等处理分级数据, 从而获得平菇多糖的分子量分布。     

Self-assembly of 5,11,17,23-tetranitro-25,26,27,28-tetramethoxythiacalix[4]arene with neutral molecules and its use for anion recognition

Methylation of 5,11,17,23-tetranitrothiacalix[4]arene with diazomethane leads to the tetramethoxy derivative, which was studied using single-crystal X-ray crystallography. It revealed that this compound, albeit in the 1,3-alternate conformation, can form the inclusion complexes with various solvent molecules possessing acidic methyl groups (ethyl acetate, nitromethane, acetone, acetonitrile) and creates interesting infinite channels filled with solvent molecules. The subsequent transformation of nitro groups into the ureido moieties gave receptors capable of anion recognition even in a highly HB-competitive solvent like DMSO.     

Thermal analysis of the combustion of charcoals from Eucalyptus dunnii obtained at different pyrolysis temperatures

DSC and TG/DTA were used to study charcoals obtained from eucalyptus wood at different pyrolysis temperatures, as well as the exchanged energy, and the transformations involved during the pyrolysis process. Charcoals DSC curves showed two exothermic peaks, at ~610 and ~750 K. The first peak was squashed for those charcoals obtained at higher final pyrolysis temperatures, and it disappeared in the charcoals obtained at 873 and 923 K. The second peak intensity increased and its location changed at the higher temperatures. Charcoal characterization showed a rise of heat values with the pyrolysis temperature.     

Full-range optical pH sensor based on imaging techniques

A new colour-based disposable sensor array for a full pH range (0-14) is described. The pH sensing elements are a set of different pH indicators immobilized in plasticized polymeric membranes working by ion-exchange or co-extraction. The colour changes of the 11 elements of the optical array are obtained from a commercial scanner using the hue or H component of the hue, saturation, value (HSV) colour space, which provides a robust and precise parameter, as the analytical parameter. Three different approaches for pH prediction from the hue H of the array of sensing elements previously equilibrated with an unknown solution were studied: Linear model, Sigmoid competition model and Sigmoid surface model providing mean square errors (MSE) of 0.1115, 0.0751 and 0.2663, respectively, in the full-range studied (0-14). The performance of the optical disposable sensor was tested for pH measurement, validating the results against a potentiometric reference procedure. The proposed method is quick, inexpensive, selective and sensitive and produces results similar to other more complex optical approaches for broad pH sensing.     

Synthesis and characterization of WO3 nanoparticles prepared by the precipitation method: Evaluation of photocatalytic activity under vis-irradiation

WO₃ nanoparticles were synthesized by the precipitation method varying the time employed in the formation of their precursor in aqueous media and the calcination temperature. The WO₃ crystallization process and morphology of the synthesized samples were followed by the XRD, TEM and SEM techniques. The effects of the calcination temperature on the surface area and optical properties of the WO₃ nanoparticles were also investigated. Nanoparticles with morphologies such as square and rectangular plates and ovoid forms were observed for the different experimental conditions. WO₃ nanoparticles with different morphologies were tested for the photocatalytic degradation of organic dyes. In general, the photocatalysts showed a capacity to bleach the dye solution in the following sequence: indigo carmine (IC) > rhodamine B (rhB) > congo red (CR). The extent of mineralization was determined by means of total organic carbon (TOC) measurements, which showed a satisfactory TOC reduction (93%, within 75 h) only for IC. This value was even better than the one concerning the P-25 Degussa reference.     

Advances in theoretical and experimental XAFS studies of thermodynamic properties,anharmonic effects and structural determination of fcc crystals

Thermodynamic properties, anharmonic effects and structural determination of fcc crystals have been studied based on the theoretical and experimental Debye–Waller factors presented in terms of cumulant expansion up to the third order, thermal expansion coefficient, X-ray absorption fine structure (XAFS) spectra and their Fourier transform magnitudes. The advances in these studies are performed by the further development of the anharmonic correlated Einstein model primary only for approximating three first XAFS cumulants into the method using that all the considered theoretical and experimental XAFS parameters have been provided based on only the calculated and measured second cumulants. The obtained cumulants describe the anharmonic effects in XAFS contributing to the accurate structural determination. Numerical results for Cu are found to be in good agreement with the experimental values extracted by using the present advanced method and with those obtained by the other measurements.     

Living Polymerization of N,N‐Diphenylacrylamide with Triisobutylaluminum

Summary: N,N‐Diphenylacrylamide was polymerized in a living fashion with triisobutylaluminum in THF at 0 °C. The polymerization results showed an increase of molecular weight proportional to the amount of monomer consumed and a first‐order kinetics at −78 °C. The intermediates obtained with excess initiator at −78 °C revealed that the polymerization was initiated through 1,4‐addition of hydride from a triisobutyl group in the triisobutylaluminum and then proceeded through aluminum‐oxygen bond interchange.

N,N‐Diphenylacrylamide was polymerized in a living fashion with triisobutylaluminum in THF at 0 °C.     

Unusual stoichiometry of urea-derivatized calix[4]arenes induced by anion complexation

Calix[4]arenes bearing two p-nitrophenyl-ureido functions at the upper rim are effective anion binders. The stoichiometry of complexation depends on the substitution pattern (distal vs proximal) and anion concentration. While the distally substituted receptor forms 1:1 complexes with anions, the corresponding proximal derivative prefers the 2:1 stoichiometry (calixarene:anion) under identical conditions.