Anisotropic effective core potentials

We present a convenient method for accounting for the anisotropy of partially filled d shells that are incorporated in effective core potentials by including the leading anisotropy term of the d-type electron density, which is the quadrupole moment, as an electrostatic potential energy operator in the model Hamiltonian. We present sample calculations on the cobalt hydride and dicobalt systems. We find the quadrupole anisotropy to have a very large effect in the distance regime of CoH. In the dicobalt system, which has a relatively long internuclear distance, the quadrupole anisotropy shifts the equilibrium bond length by nearly 0.02 bohr.     

Enhanced electrical and mechanical properties of multiwall carbon nanotube rubber composites

Multiwall carbon nanotube‐filled elastomers are prepared by solution blending using a sonication process. It is shown that the processing conditions have a strong effect on the composite properties especially on electrical properties, which are very sensitive to nanotube dispersion within the elastomeric matrix. The percolation threshold is seen to be shifted to a lower nanotube content than that previously reported. With regard to the unfilled elastomer, large increases in the elastic and tensile moduli are obtained with the nanotube loading, thus highlighting the potential of this type of particles as reinforcing fillers for elastomeric matrices. Raman spectroscopy under strain has been used to evaluate the strength of the polymer–filler interface. Weak interfacial interactions are deduced, but the debundling of the nanotubes and the orientational effects of the polymeric chains are observed when the composite is submitted to a uniaxial deformation. Copyright © 2012 John Wiley & Sons, Ltd.     

Prediction analysis and quality assessment of microwell array images

Microwell arrays are widely used for the analysis of fluorescent‐labelled biomaterials. For rapid detection and automated analysis of microwell arrays, the computational image analysis is required. Support Vector Machines (SVM) can be used for this task. Here, we present a SVM‐based approach for the analysis of microwell arrays consisting of three distinct steps: labeling, training for feature selection, and classification into three classes. The three classes are filled, partially filled, and unfilled microwells. Next, the partially filled wells are analyzed by SVM and their tendency towards filled or unfilled tested through applying a Gaussian filter. Through this, all microwells can be categorized as either filled or unfilled by our algorithm. Therefore, this SVM‐based computational image analysis allows for an accurate and simple classification of microwell arrays.     

Relativistic four-component DFT calculations of 1H NMR chemical shifts in transition-metal hydride complexes: unusual high-field shifts beyond the Buckingham-Stephens model

State-of-the-art relativistic four-component DFT-GIAO-based calculations of (1)H NMR chemical shifts of a series of 3d, 4d, and 5d transition-metal hydrides have revealed significant spin-orbit-induced heavy atom effects on the hydride shifts, in particular for several 4d and 5d complexes. The spin-orbit (SO) effects provide substantial, in some cases even the dominant, contributions to the well-known characteristic high-field hydride shifts of complexes with a partially filled d-shell, and thereby augment the Buckingham-Stephens model of off-center paramagnetic ring currents. In contrast, complexes with a 4d(10) and 5d(10) configuration exhibit large deshielding SO effects on their hydride (1)H NMR shifts. The differences between the two classes of complexes are attributed to the dominance of π-type d-orbitals for the true transition-metal systems compared to σ-type orbitals for the d(10) systems.     

Syntheses, properties and cellular studies of metalloisoporphyrins

b-Bilene hydrochlorides are shown to be improved intermediates for the synthesis of metallo-isoporphyrins in enhanced yields (28% vs. 6%). Several new diamagnetic zinc(II) and a novel paramagnetic copper(II) isoporphyrin salts were also obtained using this approach. Metal-free isoporphyrins were also isolated. In vitro studies using human carcinoma HEp2 cells show that all metallo-isoporphyrins accumulate within cells and localize partially in the mitochondria. The zinc-isoporphyrins were found to be moderately phototoxic while the copper complex showed the lowest phototoxicity, maybe as a result of its paramagnetic nature.     

Oxidation State Specific Generation of Arsines from Methylated Arsenicals Based on L- Cysteine Treatment in Buffered Media for Speciation Analysis by Hydride Generation - Automated Cryotrapping - Gas Chromatography-Atomic Absorption Spectrometry with the Multiatomizer

An automated system for hydride generation - cryotrapping- gas chromatography - atomic absorption spectrometry with the multiatomizer is described. Arsines are preconcentrated and separated in a Chromosorb filled U-tube. An automated cryotrapping unit, employing nitrogen gas formed upon heating in the detection phase for the displacement of the cooling liquid nitrogen, has been developed. The conditions for separation of arsines in a Chromosorb filled U-tube have been optimized. A complete separation of signals from arsine, methylarsine, dimethylarsine, and trimethylarsine has been achieved within a 60 s reading window. The limits of detection for methylated arsenicals tested were 4 ng l(-1). Selective hydride generation is applied for the oxidation state specific speciation analysis of inorganic and methylated arsenicals. The arsines are generated either exclusively from trivalent or from both tri- and pentavalent inorganic and methylated arsenicals depending on the presence of L-cysteine as a prereductant and/or reaction modifier. A TRIS buffer reaction medium is proposed to overcome narrow optimum concentration range observed for the L-cysteine modified reaction in HCl medium. The system provides uniform peak area sensitivity for all As species. Consequently, the calibration with a single form of As is possible. This method permits a high-throughput speciation analysis of metabolites of inorganic arsenic in relatively complex biological matrices such as cell culture systems without sample pretreatment, thus preserving the distribution of tri- and pentavalent species.     

Systematic optimization of exhaustive electrokinetic injection combined with micellar sweeping in capillary electrophoresis

The combination of exhaustive electrokinetic injection and sweeping micellar electrokinetic chromatography (sweeping-MEKC) in capillary electrophoresis often provides a several thousand-fold improvement in concentration detection limit. However, reproducibility of this method has been a major issue that often prevents its use as a quantitative tool for the analysis of ultra-trace analytes in complex matrices. In this paper, we demonstrate that such a technique can be systematically optimized with five key factors: the conductivity of the sample solution, the conductivities of the separation buffers, the fraction of the capillary that is filled with the high conductivity buffer, the electrokinetic injection time, and the surfactant concentration. By controlling the sample conductivity, we were able to achieve highly reproducible results, while still maintaining the sensitivity of field-amplified sample injection. At optimal conditions, we were able to analyze three amine drugs (amphetamine, methamphetamine, and methylenedioxymethamphetamine) with limits of detection of 6 to 8 pg ml(-1) (ppt), which is a several thousand-fold improvement over normal sample injection using CE with a photodiode array detector.     

Flow-through partial-filling affinity capillary electrophoresis can estimate binding constants of neutral ligands to receptors via a competitive assay technique

This work evaluates the use of a competitive binding assay using flow-through partial-filling affinity capillary electrophoresis (FTPFACE) to estimate binding constants of neutral ligands to a receptor. We demonstrate this technique using, as a model system, carbonic anhydrase B (CAB, EC 4.2.1.1) and arylsulfonamides. In this technique, the capillary is first partially filled with a negatively charged ligand, a sample containing CAB and two noninteracting standards, and a neutral ligand, then electrophoresed. Upon application of a voltage the sample plug migrates into the plug of negatively charged ligand (L(-)) resulting in the formation of a CAB-L(-) complex. Continued electrophoresis results in mixing between the neutral ligand (L(0)) and the CAB-L(-) complex. L(0) successfully competes out L(-) to form the new CAB-L(0) complex. Analysis of the change in the relative migration time ratio (RMTR) of CAB relative to the noninteracting standards, as a function of neutral ligand concentration, yields a value for the binding constant. These values are in agreement with those estimated using other binding and ACE techniques. Data demonstrating the quantitative potential of this method is presented.     

Time-resolved self-assembly of a fullerene-topology core-shell cluster containing 68 uranyl polyhedra

A complex core-shell cluster consisting of 68 uranyl peroxo polyhedra, 16 nitrate groups, and ~44 K(+) and Na(+) cations was obtained by self-assembly in alkaline aqueous solution under ambient conditions. Crystals formed after a month and were characterized. The cluster, designated as {U(1)?U(28)?U(40R)}, contains a fullerene-topology cage built from 28 uranyl polyhedra. A ring consisting of 40 uranyl polyhedra linked into five-membered rings and 16 nitrate groups surrounds this cage cluster. Topological pentagons in the cage and ring are aligned, and their corresponding rings of uranyl bipyramids are linked through K(+) cations located between the two shells. A partially occupied U site is located at the center of the cluster. Time-resolved small-angle X-ray scattering and electrospray ionization mass spectrometry demonstrated that the U(28) cage cluster formed in solution within an hour, whereas the U(40R) shell formed around the cage cluster after more than several days.     

Structured emulsion-based delivery systems: Controlling the digestion and release of lipophilic food components

There is a need for edible delivery systems to encapsulate, protect and release bioactive and functional lipophilic constituents within the food and pharmaceutical industries. These delivery systems could be used for a number of purposes: controlling lipid bioavailability; targeting the delivery of bioactive components within the gastrointestinal tract; and designing food matrices that delay lipid digestion and induce satiety. Emulsion technology is particularly suited for the design and fabrication of delivery systems for lipids. In this article we provide an overview of a number of emulsion-based technologies that can be used as edible delivery systems by the food and other industries, including conventional emulsions, nanoemulsions, multilayer emulsions, solid lipid particles, and filled hydrogel particles. Each of these delivery systems can be produced from food-grade (GRAS) ingredients (e.g., lipids, proteins, polysaccharides, surfactants, and minerals) using relatively simple processing operations (e.g., mixing, homogenizing, and thermal processing). The structure, preparation, and utilization of each type of delivery system for controlling lipid digestion are discussed. This knowledge can be used to select the most appropriate emulsion-based delivery system for specific applications, such as encapsulation, controlled digestion, and targeted release.     

Analysis of coumarins by micro high-performance liquid chromatography-mass spectrometry with a particle beam interface

Coumarins are a large group of compounds that are naturally present in plant tissues and that exhibit a wide range of pharmacological properties. Analytical methods based on chromatographic techniques and conventional detectors are inadequate to accurately analyze coumarins in complex matrices such as plant extracts. In this article a new method based on a modified particle beam liquid chromatography-mass spectrometry interface is described. The method allows specific and accurate determination of several coumarins in biological matrices. An application regarding the analysis of 18 coumarins in the extract of Smyrnium perfoliatum L. is also reported.     

On-line coupling of ion chromatography and atomic spectrometry and use of direct graphite furnace atomic absorption spectrometry as new tools for ultra trace determinations in refractory metals

On-line coupling of inductively coupled plasma (ICP) techniques such as ICP-AES and ICP-MS with ion chromatography (IC) offers unique features for ultra-trace analysis. An on-line preconcentration procedure based on cation exchange enables sub-ng/g analysis in complex matrices like molybdenum and tungsten. The best dissolution reagent for these matrices is hydrogen peroxide, which can be cleaned to ultra high purity with the same metal free chromatography equipment used for the preconcentration. Preconcentration is possible for elements that show cationic reactions within acidic peroxide containing solutions. In this study 28 elements detrimental for microelectronics applications are observed. A comparison of the combinations IC-ICP-AES and IC-ICP-MS with glow discharge mass spectrometry (GDMS) for the analysis of today's purest tungsten samples shows the analytical power and accuracy of the coupled devices. Graphite furnace atomic absorption spectrometry (GFAAS) as an extremely sensitive analytical technique is applied with and without the same sample pretreatment as used for the on-line coupling. Direct GFAAS measurements of alkali metals are complementary to IC-ICP techniques. The data evaluated with these wet chemical techniques are compared to the usual manufacturers characterisation technique GDMS. With respect to the low concentrations present in these high purity materials (ng/g level in the solid) the discrepancies between all methods are acceptable. The sensitivity of IC-ICP-MS is in most cases far superior to IC-ICP-AES and for some elements also to GDMS. Furthermore the specific advantages of on-line coupling such as the elimination of isobaric interferences in ICP-MS or spectral interferences in ICP-AES are shown for ICP-AES and ICP-MS determinations.     

Current status and future trends on automated multidimensional separation techniques employing sorbent‐based extraction columns

Determination of target analytes present in complex matrices requires a suitable sample preparation approach to efficiently remove the analytes of interest from a medium containing several interferers while at the same time preconcentrating them aiming to improve the output signal detection. Online multidimensional solid‐phase separation techniques have been widely used for the analysis of different contaminants in complex matrices such as food, environmental, and biological samples, among others. These online techniques usually consist of two steps performed in two different columns (extraction and analytical column), the first being employed to extract the analytes of interest from the original medium and the latter to separate them from the interferers. The extraction column in multidimensional techniques presents a relevant role since their variations as building material (usually a tube), sorbent material, modes of application, and so on can significantly influence the extraction success. The main features of such columns are subject of constant research aiming improvements directly related to the performance of the separation techniques that utilize multidimensional analysis. The present review highlights the main features of extraction columns online coupled to chromatographic techniques, inclusive for in‐tube solid‐phase microextraction, online solid phase and turbulent flow, aiming the determination of analytes present at very low concentrations in complex matrices. It will critically describe and discuss some of the most common instrumental set up as well as comments on recent applications of these multidimensional techniques. Besides that, the authors have described some properties and enhancements of the extraction columns that are used as first dimension on these systems, such as type of column material (poly (ether ether ketone), fused silica, stainless steel, and other materials) and the way that the extractive phase is accommodated inside the tubing (filled and open tubular). Practical applications of this approach in fields such as environment, food, and bioanalysis are also presented and discussed.     

Protons solvated in noble-gas matrices: interaction with nitrogen

The interaction of a (NgHNg)(+) cation (Ng = Ar and Kr) with a nitrogen molecule is studied. The structure, energetics, and vibrational properties of these complexed systems are computationally studied at the MP2/6-311++G(2d,2p) level of theory. The computations reveal two stable structures, linear and T-shaped configurations, with BSSE corrected interaction energies of the order of -1000 cm(-1). The (NgHNg)(+)[dot dot dot]N(2) complexes are characterized experimentally by IR absorption spectroscopy in solid Ar and Kr matrices. The spectra show that only one complex structure is present, as evidenced by the single nitrogen-induced nu(3) band. According to the computational results, the linear structure is more probable in the experiments. However, our results show that the one-to-one complex at the present computational level does not accurately agree with the matrix-isolation experiments, the differences originating possibly from the influence of the surrounding matrix. Based on the current data, the mechanism of cation decay in noble-gas matrices is discussed. The observed similar decay of (NgHNg)(+) and its N(2) complex indicates that the solvated proton is unable to tunnel and is therefore immobile in noble-gas matrices. The observations for the cation decay are consistent with the electron neutralization mechanism.     

Ultrafast hybridization screening in Fe3+ aqueous solution

We report here on the electron binding energies and ultrafast electronic relaxation of the Fe(3+)(aq) complex in FeCl(3) aqueous solution as measured by soft X-ray photoelectron (PE) spectroscopy from a vacuum liquid microjet. Covalent mixing between the 3d valence orbitals of the iron cation and the molecular orbitals of water in the ground-state solution is directly revealed by spectroscopy of the highest partially occupied molecular orbitals. Valence PE spectra, obtained for photon energies near the iron 2p absorption edge, exhibit large resonant enhancements. These resonant PE features identify 3d-O2p transient hybridization between iron and water-derived orbitals and are an indication of charge transfer within the electronically excited Fe(3+)(aq)* complex. Charge transfer from water to iron is also revealed by the 2p core-level PE spectrum, and the asymmetric peak shape additionally identifies the characteristic multiplet interactions in the 2p core-hole state. The electronic structure of water molecules in the first hydration shell is selectively probed by Auger decay from water molecules, at excitation energies well below the O1s absorption edge of neat water. These experiments lay the groundwork for establishing resonant PE spectroscopy for the study of electronic-structure dynamics in the large family of transition metal (aqueous) solutions.     

Antimony in the environment as a global pollutant: a review on analytical methodologies for its determination in atmospheric aerosols

This review summarizes and discusses the research carried out on the determination of antimony and its predominant chemical species in atmospheric aerosols. Environmental matrices such as airborne particulate matter, fly ash and volcanic ash present a number of complex analytical challenges as very sensitive analytical techniques and highly selective separation methodologies for speciation studies. Given the diversity of instrumental approaches and methodologies employed for the determination of antimony and its species in environmental matrices, the objective of this review is to briefly discuss the most relevant findings reported in the last years for this remarkable element and to identify the future needs and trends. The survey includes 92 references and covers principally the literature published over the last decade.     

Femtosecond electronic relaxation of excited metalloporphyrins in the gas phase

A systematic study of the ultrafast decay of metalloporphyrins containing various transition metals with partially filled 3d shells and zinc (3d filled) is reported here after excitation in the second excited state of the system (Soret band). Both time-of-flight mass spectrometry and velocity map imaging have been used for detection. A general biexponential decay with a short time constant tau1 approximately 100 fs is observed for the transition metal porphyrins, followed by a tau2 approximately 1 ps time decay. This evolution is interpreted as a porphyrin-to-metal charge transfer, tau1, followed by a back transfer, tau2, which leads to an excited state (d,d*) localized on the metal. These conclusions stem from the different behaviors of zinc and the transition metal porphyrins. A porphyrin-to-metal charge transfer model is chosen to describe the relaxation mechanism, based upon the fact that transition metalloporphyrins can accept electrons on the metal site, in contrast to zinc porphyrins.     

铜锌镁铝四元水滑石的微观结构及其姜-泰勒畸变

采用密度泛函理论(DFT),选取CASTEP程序模块,对铜锌镁铝四元水滑石[(M)-IV-LDHs(M=Cu,Zn,Mg,Al)]周期性模型进行几何全优化,从各体系的结构参数、电子排布、Mulliken电荷布居、结合能、氢键等方面,研究了体系中的姜-泰勒效应、氯离子位置对层板畸变及体系稳定性的影响.优化结果表明,姜-泰勒效应不仅存在于d轨道未排满的Cu2+中,也存在于理论上d轨道排满的Zn2+与p轨道未排满的Mg2+中.氯离子排在金属上方的体系,其金属畸变程度大于氯离子排在非金属上方的体系.同时,对于本文选取的8个CuAl-IV-LDHs体系,结合能绝对值按照1-8号逐渐降低,体系的稳定性下降,最终转变为不稳定的压扁的八面体构型.这有助于从理论上对含铜四元水滑石的姜-泰勒效应进一步认识.     

Solvent dependence of the g-anisotropy in the ESR of cyanide-bridged mixed-valence complexes

The low temperature (approximately 5 K) X-band ESR spectra are reported of the cyanide-bridged mixed-valence complexes [(OC)5Cr(mu-CN)M(NH3)5]X2 (M = Ru, Os; X = PF6(-)) in frozen matrices formed from nitromethane, acetonitrile and dimethylformamide with toluene. The anisotropy (g paralell-g perpendicular) is greater for the ruthenium than for the osmium complex. It is positive in all cases and is strongly dependent on the hydrogen-bonding interaction between the solvent matrix and the metal-ammine fragment, decreasing in the order nitromethane > acetonitrile > dimethylformamide. The axial ligand field parameter, Delta, is quite insensitive to the ammine metal (M) and is mainly determined by the solvent matrix. Density functional calculations, together with a simplified MO model, show that: (a) The value of Delta is dominated by the interaction between the filled cyanide pi-orbitals and the ammine-metal d(xz,yz) orbitals, (b) Delta decreases with increasing solvent donicity because the resulting positive shift of the d-orbital energies reduces this interaction, (c) the insensitivity of Delta to the ammine-metal arises because an increase in the energy mismatch between the cyanide pi-orbitals and the d-orbitals in osmium compound is offset by an increase in the 5d resonance integrals relative to those in the 4d shell. Semi-quantitative values are obtained for the pi and pi* resonance integrals. We point out that g paralell determines that portion of the ammine-metal spin population that interacts with the cyanide bridge, and should therefore be correlated with the degree of metal-metal charge transfer in low-spin d6-d5 intervalence compounds. X-band ESR spectra of the polycrystalline powders (M = Ru, Os; X = CF3SO3(-)) are rhombic with similar axial and rhombic ligand field parameters. The rhombicity is interpreted as resulting from asymmetric cation-anion hydrogen-bonding that is apparent in the crystal structures of these isomorphous compounds.