SPHERULITIC STRUCTURE AND MORPHOLOGY OF POLY(ETHYLENE SUCCINATE)/POLY(ETHYLENE OXIDE) (PES/PEO) BLENDS WITH ONE-STEP CRYSTALLIZATION

The spherulitic structure and morphology development of poly(ethylene succinate)/poly(ethylene oxide) (PES/PEO) blends with one-step crystallization behavior were observed by means of polarizing optical microscope.It was found that the pure PES spherulite in which the adequate quantity of PEO melt existed in the interlamellar regions,and the blending spherulite formed by both PES and PEO lamellae could form simultaneously.When the two types of spherulites contacted with each other the front of the blendi...     

原位交联明胶电纺纤维的制备工艺研究

提出一种原位交联工艺,用于一步制备交联明胶电纺纤维膜,克服目前该电纺膜交联工艺繁琐以及交联过程破坏纤维形态等缺点.通过一系列实验,找出明胶-三氟乙醇-戊二醛三元溶液体系的稳定电纺条件.所得的纤维直径在1μm左右,远大于单纺明胶的纤维直径.同时发现,在电纺过程中,由于纤维表面戊二醛迅速挥发,使得纤维形成"伪核壳"结构.利用流变仪对三元溶液交联速率进行分析,结果表明戊二醛加入明胶溶液后,体系黏度瞬间增大,10 min后维持稳定.最后,通过耐水性试验评价纤维膜交联效果,发现纤维膜有10%左右的溶解,但在水介质中仍可保持很好的纤维形态.     

Co-isolation of deoxynivalenol and zearalenone with sol–gel immunoaffinity columns for their determination in wheat and wheat products

The paper describes a sample clean-up method for the co-isolation of deoxynivalenol (DON) and zearalenone (ZON), two mycotoxins naturally co-occurring in wheat. The method is based on immunoaffinity columns prepared by co-immobilising anti-DON and anti-ZON antibodies in a porous sol–gel glass. The main task in developing the method consisted in finding a loading medium allowing retention of both analytes as well as a common elution medium for the dissociation of both antigen–antibody complexes formed. This can be achieved by co-extracting DON and ZON with ACN–water (60:40, v/v), reducing the acetonitril concentration to 2.5% before loading an aliquot of the diluted sample extract onto the DON/ZON column. The columns are washed with 5 ml of MeOH–water (10:90, v/v) before DON and ZON are co-eluted with 4 ml of ACN–water (50:50, v/v). Concentrations of DON and ZON are determined with HPLC-UV and HPLC-fluorescence detection, respectively. The sample clean-up method was shown to be applicable to wheat and wheat products, e.g., cornflakes, milk wheat mash and rusk. Spiking experiments (spike level 500 μg DON/kg and 50 μg ZON/kg) resulted in recovery rates from 82% to 111%.     

Domino-Knoevenagel-hetero-Diels-Alder reactions: an efficient one-step synthesis of indole-annulated thiopyranobenzopyran derivatives

Rapid one-step synthesis of hitherto unreported indole-annulated pentacyclic heterocycles containing oxygen, nitrogen, and sulfur has been described by domino-Knoevenagel-hetero-Diels-Alder reaction. The reaction sequence provides a route to the synthesis of a novel type of polyheterocycles in excellent yields with high stereoselectivity.     

Conditional Logistic Regression With Longitudinal Follow-up and Individual-Level Random Coefficients: A Stable and Efficient Two-Step Estimation Method

The analysis of data generated by animal habitat selection studies, by family studies of genetic diseases, or by longitudinal follow-up of households often involves fitting a mixed conditional logistic regression model to longitudinal data composed of clusters of matched case-control strata. The estimation of model parameters by maximum likelihood is especially difficult when the number of cases per stratum is greater than one. In this case, the denominator of each cluster contribution to the conditional likelihood involves a complex integral in high dimension, which leads to convergence problems in the numerical maximization. In this article we show how these computational complexities can be bypassed using a global two-step analysis for nonlinear mixed effects models. The first step estimates the cluster-specific parameters and can be achieved with standard statistical methods and software based on maximum likelihood for independent data. The second step uses the EM-algorithm in conjunction with conditional restricted maximum likelihood to estimate the population parameters. We use simulations to demonstrate that the method works well when the analysis is based on a large number of strata per cluster, as in many ecological studies. We apply the proposed two-step approach to evaluate habitat selection by pairs of bison roaming freely in their natural environment. This article has supplementary material online.     

Oriented single crystalline TiO2 nano-pillar arrays directly grown on titanium substrate in tetramethylammonium hydroxide solution

Oriented single crystalline titanium dioxide (TiO₂) nano-pillar arrays were directly synthesized on the Ti plate in tetramethylammonium hydroxide (TMAOH) solution by one-pot hydrothermal method. The samples were characterized respectively by means of field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). Results showed that the TiO₂ nano-pillar with a tetrahydral bipyramidal tip grew vertically on the titanium substrate. HRTEM and Raman results confirmed that the TiO₂ nano-pillar arrays were single crystalline anatase. The controls of morphology, size, and orientation of the nano-pillar could be achieved by varying the solution concentration and hydrothermal temperature. Furthermore, the special morphology of the TiO₂ nano-pillar arrays was caused by the selectively absorption of the tetramethylammonium (TMA) through hydrogen bonds on the lattice planes parallel to (0 0 1) of anatase TiO₂. Less grain boundaries and direct electrical pathway for electron transferring were crucial for the superior photoelectrochemical properties of the single anatase TiO₂ nano-pillar arrays. This approach provides a facile in situ method to synthesize TiO₂ nano-pillar arrays with a special morphology on titanium substrate.     

Ultrasensitive one-step rapid detection of ochratoxin A by the folding-based electrochemical aptasensor

A one-step electrochemical aptasensor using the thiol- and methylene blue- (MB-) dual-labeled aptamer modified gold electrode for determination of ochratoxin A (OTA) was presented in this research. The aptamer against OTA was covalently immobilized on the surface of the electrode by the self-assembly effect and used as recognition probes for OTA detection by the binding induced folding of the aptamer. Under the optimal conditions, the developed electrochemical aptasensor demonstrated a wide linear range from 0.1 pg mL⁻¹ to 1000 pg mL⁻¹ with the limit of detection (LOD) of 0.095 pg mL⁻¹, which was an extraordinary sensitivity compared with other common methods for OTA detection. Moreover, as a practical application, this proposed electrochemical aptasensor was used to monitor the OTA level in red wine samples without any special pretreatment and with satisfactory results obtained. Study results showed that this electrochemical aptasensor could be a potential useful platform for on-site OTA measurement in real complex samples.     

A systematic approach to quantitation of ephedra alkaloids in natural health products

A method for accurate determination of ephedrine (E) alkaloids in natural health products (NHP) is described. The NIST dietary supplement standard reference materials (SRMs) were selected for these studies. These SRMs comprise ground Ma Huang herb (Ephedra sinica Stapf.), a spray dried extract of the former, and commercial formulations derived from gel caps and a protein drink. The efficiency of sonication-assisted extraction and Soxhlet extraction was studied using both ammonium formate and potassium phosphate in 3% methanol as extraction media. The efficiency of SPE clean-up of the extract deteriorated rapidly when increasing amounts of sample matrix or analyte were processed, because of limited cartridge capacity. Quantitation by the method of additions was required to ensure the highest accuracy using both LC–UV and ES–LC–MS–MS techniques. Whereas the LC–UV method is more convenient and precise, the results are more questionable than ES–LC–MS–MS, because species-specific detection is not possible.     

Simultaneous determination of cefoxitin,cefuroxime, cephalexin and cephaloridine in plasma using HPLC and a column-switching technique

Summary A new high performance liquid chromatographic method was developed using a column-switching technique for the simultaneous determination of cephalexin, cefuroxime, cefoxitin and cephaloridine in plasma. The plasma samples were injected onto a precolumn packed with Corasil RP C₁₈ (37–50 m) after simple dilution with an internal standard solution in 0.01 M acetate buffer (pH 3.5). Polar plasma components were washed out using 0.01 M acetate buffer (pH 3.5). After valve switching, the concentrated drugs were desorbed in back-flush mode and separated on a Partisil ODS-3 column using acetonitrile in 0.02 M acetate buffer (pH 4.3) (1585, v/v) as the mobile phase. The method showed excellent precision with good sensitivity and speed with a detection limit of 0.5 g/ml. The total analysis time per sample was less than 25 min, and the mean coefficients of variation for intra- and inter-assay were both less than 4.9 %.This method has been successfully applied to plasma from rats after subcutaneous injection of cefuroxime.     

Study of the interference problems of dioxin-like chemicals with the bio-analytical method CALUX

The reporter gene expression method CALUX has proven to be a very valuable screening technique for assessing toxic equivalents of dioxins and dioxin-like compounds, because it detects all AhR ligands in a variety of sample matrices. However, the exact meaning of the CALUX response is difficult to evaluate for complex mixtures mainly since not all AhR ligands are known and since antagonistic or synergistic effects occurs.

In this paper, non-additive effects on the CALUX response of dioxins were investigated for a limited number of dioxin-like compounds in concentration ranges that are 10²–10⁸ times higher than that of 2,3,7,8-TCDD. Antagonistic effects are detected for three Aroclors (1242, 1254, 1260), Halowax 1014 (PCN), HCB and PBB 169. The ratios, Aroclor/dioxin, Halowax/dioxin and HCB/dioxin, needed to observe an antagonistic effect are 10 000, 5000 and 50 000, respectively. No significant deviation from additivity was observed for Aroclor 5442 (PCT) and PBB 77 in the concentration range investigated.

Two clean-up procedures have also been tested: in some cases the non-additive effects disappeared or were strongly reduced. Using only an acidic silica column, the classical dioxin-like compounds investigated here (PCB, PCT, PBB, PCN, HCB) as well as the dioxins are collected and analyzed altogether in one fraction. Consequently, no major alteration of the non-additive effects is expected. An acidic silica column combined with an activated carbon column allows the separation of PCDD/F and dioxin-like PCB in two different fractions, PBB 169 is completely eluted in the dioxin fraction and PBB 77 is distributed between the PCB and dioxin fraction. HCB is completely separated from the PCDD/F fraction.