Flow-through microdispenser for interfacing micro-HPLC to Raman and mid-IR spectroscopic detection

A flow-through microdispenser has been coupled to a micro HPLC separation system and used as a solvent elimination interface for Fourier transform infrared (FTIR) and Raman spectroscopic detection of the separated compounds. Using the microdispenser picoliter sized droplets can be generated and deposited on an appropriate target placed on a computerized x, y-stage. Evaporation of volatile solvent and buffer is rapid and allows analysis of the obtained dry deposits by various techniques. Due to the destruction free character of Raman and FTIR spectroscopy they can be applied sequentially to interrogate the same deposit. In the reported application five phenolic acids typically present in wine have been separated on a C-18 column technique using a mixture of water, methanol and acetic acid as mobile phase. For spectrum acquisition infrared and Raman microscopes have been used. The spectra recorded from the dried deposits of the separated compounds agreed well with the reference spectra of corresponding components.     

Lead tetraacetate-iodine oxidation of 23-spirostanols

Reactions of 23R- and 23S-23-spirostanols in the 25R and 25S series with lead tetraacetate-iodine were studied. The reactions carried out at low temperature afforded d-seco-iododialdehydes and C₂₂ lactones, while similar reactions performed in refluxing tetrachloromethane yielded 20-chlorolactones and their 21-acetoxy derivatives irrespective of the hydroxyl group configuration at C-23. The reaction mechanisms are discussed.     

1‐Chloro‐2‐nitro­benzene: N—O⋯Cl halogen bonds and aromatic π–π stacking,and thermal vibrations in the vicinity of the melting point

The crystal structure of 1‐chloro‐2‐nitro­benzene, C₆H₄ClNO₂, is made up of mol­ecules which are linked by N—O⋯Cl halogen bonds. These mol­ecular chains are involved in aromatic π–π stacking; the inter­molecular O⋯Cl distance is 3.09 Å. Such short halogen bonds are not common. A rigid‐body analysis including the non‐rigidly attached rigid group provides the mean‐square amplitudes of the mol­ecular translations and librations, and of the inter­nal torsional vibrations of the nitro group. The results reveal the driving role of the torsional vibrations of the nitro group in the phase transition to the liquid phase.     

金纳米粒子在TiO2气凝胶基质上的行为: 光催化活性评价和结构研究

TiO2 -Au aerogels containing different amounts of gold nanoparticles of different sizes (5 and 16 nm) were successfully synthesized using a sol-gel procedure, and were tested for salicylic acid photodegradation under UV irradiation. The structure and morphology of the obtained materials were investigated using X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption measurements. UV-Vis spectroscopy was used to study the optical properties. The effects of the gold nanoparticles on the TiO2 crystallization process were twofold, as follows: (i) the number of crystallized zones was strongly related to the concentration of the gold nanoparticles, and (ii) the smaller gold particles increased the time taken for the crystallization of the samples. It was found that the noble metal-doped samples exhibited higher degradation rates compared with bare titania. It was found that the most active photocatalyst in each studied system was the sample with the highest concentration of gold nanoparticles. Additionally, the highest degradation rate value was obtained with the smallest Au nanoparticles (46.4 10-3 μmol/(L·s).     

Nanoscale Organolanthanum Clusters: Nuclearity-Directing Role of Cyclopentadienyl and Halogenido Ligands

Tetramethylaluminato/halogenido(X) ligand exchange reactions in half-sandwich complexes [Cp^RLa(AlMe₄)₂] are feasible in non-coordinating solvents and provide access to large coordination clusters of the type [Cp^RLaX₂]_x. Incomplete exchange reactions generate the hexalanthanum clusters [Cp^R₆La₆X₈(AlMe₄)₄] (Cp^R=Cp*=C₅Me₅, X=I; Cp^R=Cp′=C₅H₄SiMe₃, X=Br, I). Treatment of [Cp*La(AlMe₄)₂] with two equivalents Me₃SiI gave the nonalanthanum cluster [Cp*LaI₂]₉, while the exhaustive reaction of [Cp′La(AlMe₄)₂] with the halogenido transfer reagents Me₃GeX and Me₃SiX (X=I, Br, Cl) produced a series of monocyclopentadienyl rare-earth-metal clusters with distinct nuclearity. Depending on the halogenido ion size the homometallic clusters [Cp′LaCl₂]₁₀ and [Cp′LaX₂]₁₂ (X=Br, I) could be isolated, whereas different crystallization techniques led to the aggregation of clusters of distinct structural motifs, including the desilylated cyclopentadienyl-bridged cluster [(μ-Cp)₂Cp′₈La₈I₁₄] and the heteroaluminato derivative [Cp′₁₀La₁₀Br₁₈(AlBr₂Me₂)₂]. The use of the Cp′ ancillary ligand facilitates cluster characterization by means of NMR spectroscopy.     

Mixing method influence on compatibility and polymorphism studies by DSC and statistical analysis

Most of the pharmaceutical products are formulated as solid dosage form, which may present drug–excipient interactions that lead to changes in the chemical nature of the drug, such as solubility and bioavailability and may compromise its safety and effectiveness. Differential scanning calorimetry (DSC) is a widely used method for the rapid evaluation of the drug-excipient compatibility and the stability of the mixture formed; however, there is no consensus on the preparation methods of the drug–excipient mixtures. The aim of this study was to investigate the influence of the mixing method on the drug–excipient compatibility studies by means of DSC analysis, using tenofovir disoproxil fumarate as a drug model. Statistical analysis revealed significant differences in the heat of fusion of the drug in the mixtures prepared by several mixing methods. Vortex Mixer with a Pop-Off Cup used for 3 min proved to be very satisfactory for these studies. A polymorphic transition was observed in the mixture prepared with the mortar and pestle. Therefore, this method should be avoided since it may induce errors in the interpretation of DSC results. In this way, the mixing method used to prepare a mixture for studies of interactions between the API and the excipients in a pharmaceutical formulation has a great influence on the results and it must be chosen carefully.     

Investigation of nanostructured Fe3O4 polypyrrole core-shell composites by X-ray absorbtion spectroscopy and X-ray diffraction using synchrotron radiation

In this article, we focus on the structural peculiarities of nanosized Fe₃O₄ in the core-shell nanocomposites obtained by polymerization of conducting polypyrrole shell around Fe₃O₄ nanoparticles. The local structure of Fe atoms was determined from the Extended X-ray Absorption Fine Structure analysis using our own package computer programs. An X-ray diffraction method that is capable to determine average particle size, microstrains, as the particle size distribution of Fe₃O₄ nanoparticles is presented. The method is based on the Fourier analysis of a single X-ray diffraction profile using a new fitting method based on the generalized Fermi function facilities. The crystallites size obtained by X-ray diffraction spectra analysis was estimated between 3.2 and 10.3 nm. Significant changes in the first and the second Fe coordination shell in comparison with standard bulk were observed. The global and local structure of the nanosized Fe₃O₄ are correlated with the synthesis conditions of the core-shell polypyrrole nanocomposites.     

Spectra of certain types of polynomials and tiling of integers with translates of finite sets

We investigate Fuglede's spectral set conjecture in the special case when the set in question is a union of finitely many unit intervals in dimension 1. In this case, the conjecture can be reformulated as a statement about multiplicative properties of roots of associated with the set polynomials with (0,1) coefficients. Let be an N-term polynomial. We say that {θ₁,θ₂,…,θ_N−1} is an N-spectrum for A(x) if the θ_j are all distinct and

     

Sol-gel synthesis of ZnO/Zn<Subscript>2-x</Subscript>Fe<Subscript>x</Subscript>TiO<Subscript>4</Subscript> powders: structural properties,electrical conductivity and dielectric behavior

The aim of this work was an investigation of structural and electrical properties of ZnO/Zn_2-xFe_xTiO₄ (x?=?0.7, 1, 1.4) powders. The compounds obtained by sol-gel method are characterized by several techniques: X-ray diffraction (XRD), N₂ adsorption–desorption isotherms, scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), electrical and dielectrical measurements. The XRD, SEM and XPS analysis confirmed the formation of ZnFeTiO₄ inverse spinel structure. The electrical and dielectrical properties of ZnO/Zn_2-xFe_xTiO₄ (x?=?0.7, 1, 1.4) were measured by impedance spectroscopy, revealing a decrease in the electrical conductivity and the dielectric constant with Fe content.

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Application of thin titanium/titanium oxide layers deposited on gold for infrared reflection absorption spectroscopy: structural studies of lipid bilayers

Ultrathin titanium layers when deposited on the surface of gold can be successfully applied for infrared reflection absorption spectroscopy (IRRAS) investigations. It was shown that the reflectivity, the phase shift, and the mean square electric field of the p- and s-polarized IR radiation in up to 20 nm thick titanium layers covered with a 3-4 nm thick layer of native oxide are comparable to those of the air/gold interface. The surface selection rule is fulfilled. Thus, qualitative and quantitative analysis of 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) bilayers transferred in liquid expanded (LE) and liquid condensed (LC) states can be performed. Differences are found in the hydration state and molecular arrangement of the two investigated bilayers. In the DMPC bilayer in the LE state, the C-N bond in the positively charged choline moiety is inclined by approximately 70 degrees toward the surface of the negatively charged titanium substrate. In the phosphate moiety, the in-plane vector of the O-P-O group makes a small angle of approximately 15 degrees to the surface normal. This open structure of the lipid molecule corresponds to the B crystal structure of the DMPC molecule and provides space for strong hydration of the polar headgroup. In the DMPC bilayer in the LC state, the intermolecular distances are reduced; the C-N bond of the choline group makes a smaller angle to the surface normal, and the in-plane vector of the O-P-O group in the phosphate moiety displays a larger tilt. The degree of hydration is reduced. The arrangement of the polar headgroup region corresponds to the A crystal structure of the DMPC molecule.