Fluorescent dyes in the context of DNA‐binding: The case of Thioflavin T

Thioflavin T (ThT) is a dye characterized by a strong fluorescence light‐up on binding to biosubstrates. Although this effect is known to be related to the inhibition of intramolecular torsion on excitation, the binding modes and their role in affecting photoinduced processes are by no means adequately understood. Here, a combined molecular dynamics and quantum chemical modeling is used to study the tuning of the photophysical properties of ThT when moving from solution to DNA binding. The binding mechanism of ThT to B‐DNA was found to be very complex as a result of an uncommon interplay between different binding modes, for example, monomer intercalation and external binding but also groove binding of the dimer. The detailed analysis of the relation between the different binding modes and the structural and electronic properties of ThT can be used to better understand the interaction with other biosubstrates.     

Simultaneous liquid chromatography-fluorescence analysis of type A and type B trichothecenes as fluorescent derivatives via reaction with coumarin-3-carbonyl chloride

A method for the simultaneous LC-fluorescence detection (FLD) determination of eight trichothecenes A and B by pre-column derivatization with coumarin-3-carbonyl chloride, a highly fluorescent fluorophore, has been developed. The reaction conditions (temperature, reaction time, reactant ratios) were optimized to give a reproducible quantitative conversion. All derivatives were characterized by LC-MS. The chromatographic parameters were optimized (column, eluent) to give a very good separation of three type A (diacetoxyscirpenol, T-2 toxin, HT-2 toxin) and five type B trichothecenes [deoxynivalenol (DON), nivalenol, fusarenon-X, 3-acetyldeoxynivalenol, 15-acetyldeoxynivalenol]. The best conditions were obtained on a narrow-bore C18 column with a water-methanol gradient. The detection limits (S/N = 3:1) in grain samples, with an injected volume of 5 microl, were 0.2-1 ng/g for all trichothecenes. These values are more than one order of magnitude lower than those of other LC-FLD and LC-MS methods and are similar to those obtained by GC-MS. The calibration curves were linear between 100 and 2500 ng/g. The method was successfully applied to the analysis of a certified wheat reference material, after solvent extraction and clean-up on a Mycosep column, obtaining a good recovery (89% for DON) and a high accuracy (z-score value: 0.67).     

A packaging contaminant: isopropylthioxanthone (ITX) in dairy products

A fast, simple and very selective liquid chromatography-mass spectrometry (LC-MS) method for the detection of isopropylthioxanthone (ITX) in dairy products has been developed and validated. After addition of an ITX-d(3) as internal standard and a simple extraction from the sample with acetonitrile, the extract was centrifuged and directly injected into the LC-MS system. Chromatographic separation was achieved by means of a Gemini C18 column (100 mm x 2.0 mm i.d. 5 microm) using a gradient of aqueous 20 mM ammonium formiate at pH 4.5 and methanol as the mobile phase, at a flow rate of 0.25 mL min(-1). The method was validated according to the guidelines laid down by the Commission Decision 2002/657/EC using the parent ion [M+H](+) (m/z 255) as quantification ion, and the fragment ion (m/z 213) obtained by in-source collision-induced dissociation (IS-CID) as confirmation ion. Absolute and relative recoveries rates were verified at 5, 10, 15 microg kg(-1) in yoghurt samples and at 5 microg kg(-1) in milk and pudding: mean absolute recoveries were 77% in yoghurt, 50% in pudding and 67% in milk; relative recoveries (after internal standard correction) were always >97% in each matrix. The detection limit (CCalpha) and the detection capability (CCbeta) of method were 6.2 and 7.2 microg kg(-1), respectively.     

Use of decoupling to reduce the radiated noise generated by panels

Four types of sources that induce on a panel four different responses are considered. The differences show up also in the way the responses radiate to the far field. A decoupling device in a form of a layer is placed adjacent to the top surface of the panel. The decoupling layer modifies the radiated fields that the sources generate. The modifications in terms of radiation reduction factors and levels are defined. These factors and levels are analyzed for two kinds of decoupling layers. The first is a compliant coating and the second is a layer of a mixture of gas and fluid. The compliant coating may induce on the fluid a velocity field that is different from that of the panel. The mixture of gas and fluid introduces a surface impedance discontinuity between the top surface of the panel and the top surface of the layer, the top surface being in contact with the semi-infinite fluid above the panel.     

Gamma induced changes in Makrofol/CdSe nanocomposite films

We applied an ex-situ casting procedure to prepare a nanocomposite (NCP) from Makrofol polycarbonate (PC) and CdSe nanoparticles. The CdSe nanoparticles were prepared by a thermolysis procedure in the presence of N₂ gas flow. Rietveld refinement of x-ray data illustrated that the CdSe adopts a cubic zinc blend structure of 6.057 Å lattice parameter and 2 nm typical grain size. Samples from the prepared NCP were exposed to γ dosages (20 kGy-250 kGy). The modifications induced in the NCP films owing to γ dosages have been studied. The γ irradiation (50 kGy-250 kGy) causes crosslinks that reduce the optical bandgap from 4.15 eV to 3.81 eV, associated with an increase in dielectric parameters and refractive index. This is attributed to an increase in the mass fraction of the disordered regions as specified by x-ray diffraction. The PC-CdSe NCP was found to have a reaction to color modification which makes it suitable for saleable reproduction on a printing press.     

在硅胶表面制备牛血红蛋白分子印迹聚合物

采用表面印迹法, 以乙烯基三甲氧基硅烷修饰的硅胶为载体, 丙烯酰胺为功能单体, N,N-亚甲基双丙烯酰胺为交联剂, 并将改性聚乙烯醇(PVA)作为辅助识别聚合物链(ARPCs)引入聚合体系中, 制备了牛血红蛋白分子印迹聚合物(MIP). 实验使用红外光谱分析了改性PVA的结构特征, 用扫描电镜(SEM)观察MIP的表面形貌, 考察了ARPCs的含量对MIP吸附性能的影响. 吸附动力学实验研究表明, 聚合体系中ARPCs的引入使MIP对模板牛血红蛋白(BHb)的吸附量明显提高|十二烷基磺酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)结果显示, MIP对BHb的特异性吸附能力明显提高.     

TRANSFER MECHANISM OF QUININE DRUG ACROSS THE OIL/WATER (O/W) INTERFACE

The transfer phenomena of quinine drug at the aqueous 1,2- dichloroethane (DCE)interface have been studied by the current- scanning polarography. The relationships be-tween the wave height and pH of aqueous phase, concentration of quinine as well as therate of water drop are discussed. The effect of supporting electrolyte, buffer solution andthe nature of organic solvent on the polarographic wave is studied. The transfer char-acteristics of quinine in aqueous phase and in organic phase are compared, The mono- pro-tonated and diprotonated quinines can both transfer at the interface so as to produce twopolarographic waves. The transfer process of quinine at the interface is simultaneouslycontrolled by diffusion and reestablishment of the disturbed protonated equilibrium ofquinine. A further investigation is made by chronopotentiometry. On the basis of thetheoretical analysis, the formulae of the limiting current are derived and discussed. Thetheoretical results are in agreement with the experimental ones.