用高效液相色谱法快速测定甜菊糖甙

本文介绍了用高效液相色谱法分离测定甜菊糖甙的四种成分,测定了各成分的相对百分含量及甜菊饮料制品中各糖甙成分及糖类的含量,并做了精密度和回收率的验证。该法简便快速,效果良好。色谱条件为:μ-Bondapak NH_2往,柱前加Bondapak AX/Corasil预柱;乙腈:0.02M(NH_4))2 HPO_4水溶液=75:25作流动相,流速为2.0ml·min~(-1);示差折光检测。     

A new differential scanning calorimetry based approach for the characterization of peracid resin

Differential scanning calorimetry was used to trace the heat of decomposition of the peracid groups (ΔH_d) in the oxidized EVA-g-AA resin. From the correlation between ΔH_d and the oxidation capacity measured by iodometry, it was found that 35 ± 5 cal of energy evolved per miliequivalent of peracid group decomposed. The ΔH_d values are also useful in finding the optimum condition for oxidation of acid groups and can be used to investigate the distribution of active peracid groups across the matrix. The stability and the activation energy of decomposition of grafted type peracid resin were also studied, where the activation energy of decomposition was calculated to be 13.4 kcal/mol.     

New supports for enzyme immobilization based on copolymers of vinylene carbonate and acrylamide

In this study, a series of beadlike and hydrophilic supports containing reactive cyclic carbonate groups for enzyme immobilization were prepared via reverse-phase suspension copolymerization of the aqueous solutions of vinylene carbonate (VCA), acrylamide (AA), and N,N′-methylene bisacrylamide in paraffin oil. The supports were used as a matrix for immobilization of trypsin and showed a considerable capacity to couple with trypsin and reasonable retention of activity for the immobilized trypsin, depending on the immobilization conditions, such as the content of VCA structural units, reaction time, and pH of the medium.     

线性低密度聚乙烯在与丁苯橡胶的共混体系中的结晶行为

本工作采用DSC、X-射线衍射、小角激光光散射、偏光显微镜等手段,研究了线性低密度聚乙烯/丁苯橡胶共混体系中聚乙烯的结晶结构、平衡熔点和结晶动力学。     

A NEW PEAK (T_4) IN THE ~(13)C-NMR SPECTRUM OF POLYBUTADIENE

A new peak at 39.0 ppm in the ~(13)C-NMR spectrum of polybutadiene (PBD) was discovered. This peak is assigned to the fourth peak (T_4) of trans-1,4-sequence marked with an asterisk as shown in Fig. 3 in the text.The occurrence of T_4 carbon nuclei is strongly affected by their neighboring 1,2-units. So long as both contents of trans-1,4- and 1,2-units attain their proper amounts the peak (T_4) with appear in the ~(13)C-NMR spectrum of PBD.     

The stereochemistry of bicyclo[3.2.1]-octane—XII The photohalogenation of bicyclo[3.2.1]octene-2 derivatives

The light-initiated halogenation of bicyclo[3.2.1]octene-2, its 3-phenyl and 3-bromo derivatives with N-bromosuccinimide and t-butyl hypochlorite resulted in the exclusive formation of the exo-4-halobicyclo[3.2.1]octene-2-derivatives.     

Cooperative Competition Clustering for Gene Selection

Clustering analysis of data from DNA microarray hybridization studies is an essential task for identifying biologically relevant groups of genes. Attribute cluster algorithm (ACA) has provided an attractive way to group and select meaningful genes. However, ACA needs much prior knowledge about the genes to set the number of clusters. In practical applications, if the number of clusters is misspecified, the performance of the ACA will deteriorate rapidly. We propose the Cooperative Competition Cluster Algorithm (CCCA) in this paper. In the algorithm, we assume that both cooperation and competition exist simultaneously between clusters in the process of clustering. By using this principle of Cooperative Competition, the number of clusters can be found in the process of clustering. Experimental results on a synthetic and gene expression data are demonstrated. The results show that CCCA can choose the number of clusters automatically and get excellent performance with respect to other competing methods.     

Dissociation behavior of doubly-charged tryptic peptides: correlation of gas-phase cleavage abundance with ramachandran plots

Analysis of fragmentation patterns from 5654 unique doubly charged tryptic peptides is obtained. Great variability of average relative abundance of bond cleavage is found between different amino acid combinations. There exist similarities as well as differences between b and y ions. Strong enhancement or suppression of cleavage gives insight into possible chemical interactions at reactive conformations formed by preferred phi-psi angles.     

Enhanced post-source decay and cross-ring fragmentation of oligosaccharides facilitated by conversion to amino derivatives

Post-source decay (PSD) fragmentation of chemically or enzymatically produced aminoglycans has been evaluated through matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Conversion of native glycans to their respective aminoglycan derivatives improved detection sensitivity of the usual fragments and promoted cross-ring fragmentation of linear oligosaccharides, facilitating linkage recognition. The cross-ring fragmentations for both dextrin and dextran oligosaccharides were not limited to the reducing-end glucose moiety, as they were extended throughout the entire molecule. When the amino group was generated for N-glycans derived from three different glycoproteins, an enhancement of PSD was observed, without a significant extent of cross-ring fragmentation.     

Cesium lead halide perovskite nanocrystals for ultraviolet and blue light blocking

Using cesium lead halide perovskite nanocrystals, CsPb(Cl/Br)_3, as a light absorber, we report a highly effective UV and blue light blocking film. The CsPb(Cl/Br)_3 nanocrystals are well dispersed in the ethyl cellulose(EC) matrix to compose a UV and blue light shielding film, and the absorption edge of the film is tunable by adjusting Cl to Br ratio using anion exchange. The CsPbCl_2 Br-EC film exhibits a transmittance of 5% at 459 nm, 90% at 478 nm and 95% in the range of 500–800 nm, which makes it excellent for UV and blue light shielding. In addition, the as-prepared EC-CsPb(Cl/Br)_3 film shows excellent photostability under UV irradiation. Results demonstrate that this EC-CsPb(Cl/Br)_3 based materials with sharp absorbance edges, tunable blocking wavelength, and high photostability can be useful for the applications in UV and blue light blocking and optical filters