Van Gogh’s Painting Grounds: Quantitative Determination of Bulking Agents (Extenders) Using SEM/EDX

A pre-concentration procedure using cloud point extraction is presented for the determination of uranium in natural water using molecular absorption spectrometry. The ligand used was 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) and the micellar phase was obtained using the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) and centrifugation. Interferences were eliminated using a masking solution containing trans-1,2-cyclohexanediaminetetraacetic acid (CDTA), sodium fluoride and sulphosalicylic acid. The optimization step was performed using a two-level factorial design and a Doehlert matrix, involving the factors pH, centrifugation time and buffer concentration. The method allows the determination of uranium in water samples with a detection limit of 0.15 μg L⁻¹, a quantification limit of 0.50 μg L⁻¹ and a precision expressed as relative standard deviation of 1.8 and 2.3% for uranium concentrations of 5 and 10 μg L⁻¹, respectively (n = 8). The accuracy was confirmed by analysis of two certified samples of natural water. This method was applied to the determination of uranium in superficial water samples collected at a uranium mine in Brazil. For five samples analyzed, the concentration of uranium varied between 1.1 and 18.1 μg L⁻¹. Tests of addition/recovery were performed for all these samples, and the results varying between 98 and 105% also proved that this procedure is not affected by the matrix and can be applied satisfactorily to the determination of uranium in water samples.     

Aspects of transmetallation reactions of 2-Me2NCH2C6H4- and 2,6-(Me2NCH2)C6H3-Metal (Pd,Pt, Hg,Tl) complexes with metal carboxylates and low-valent metal (Pd,Pt) complexes

A study has been made of reactions involving organometallic compounds containing ortho-Me₂NCH₂ substituted aryl ligands. The single step syntheses of the new compounds [(2-Me₂NCH₂C₆H₄)₂TlCl], [ [{(S)-2-Me₂NCH(Me)C₆H₄}₂TlCl], [{(S)-2-Me₂NCH(Me)C₆H₄}TlCl₂], [{2,6-(Me₂NCH₂)₂C₆H₃}TlClBr] and [{2,6-(Me₂NCH₂)₂C₆H₃}HgCl] are described. Stable internal NTl coordination at low temperatures has been established for the C-chiral thallium compounds. Reactions of the other Tl and Hg compounds and of [(2-Me₂NCH₂C₆H₄)₂Hg] with Pd(O₂CMe)₂, and also of the reverse reaction of cis-[(2-Me₂NCH₂C₆H₄)₂Pd] with Hg(O₂CR)₂ or Tl(O₂CR)₃, gave transmetallation of one organo ligand and led to a single mono-organopalladium compound and corresponding by-products. Reaction of cis-[(₂-Me₂NCH₂C₆H₄)₂Pd] with Pd(O₂CR)₂ gave the dimeric compound [{(2-Me₂NCH₂C₆H₄)Pd(O₂CR)}₂]. cis-[(2-Me₂NCH₂C₆H₄)₂Pt] did not react with Pd(O₂CMe)₂, while reaction of trans-[(2-Me₂NCH₂C₆H₄)₂Pt] or cis-[(2-Me₂NC₆H₄CH₂)₂Pt] with Pd(O₂CMe)₂ resulted in decomposition. Upon heating, trans-[(2-Me₂NCH₂C₆H₄)₂Pt] was isomerized to cis-isomer. A redox reaction between [(2-Me₂NCH₂C₆H₄)₂Hg] and [Pt(COD)₂] (COD  1,5-cyclo-octadiene) and [Pd₂(DBA)₃] (DBA  dibenzylideneacetone) gave the cis-isomers of [(2-Me₂NCH₂C₆H₄)₂M] (M  Pd, Pt).The results are discussed in terms of influence of internal coordination of the CH₂NMe₂ group. It is concluded that although internal coordination of the CH₂NMe₂ ligand can stabilize metal—carbon bonds it cannot prevent cleavage of such bonds by electrophiles. In this respect, there is no difference in the behaviour of Hg(O₂CR)₂ and Tl(O₂CR)₃. The reactions are influenced by the metal—nitrogen bond strength, which follows the order PtN > PdN > HgN, TlN. The reactivity of Pt compounds is greatly influenced by their structure and type of ligand. It is proposed that cleavege of PdC bonds occurs mainly by a mechanism involving direct electrophilic attack at the carbon centre.     

Fluxional nickel(II)- and palladium (II)-triazenido (C5H5)(L)(RN3R)M complexes; Evidence for a triplet-state intermediate

Summary The (⁵-C₅H₅)(L)(RN₃R)Ni and (⁵-C₅H₅)(PPh₃)(RN₃R)Pd compounds, with L = PPh₃, CO, CNR, and RN₃R = diaryltriazenido anion, were prepared. The bonding mode of the triazenido ligand is monodentate in the (⁵-C₅H₅)(PPh₃)(RN₃R)M phosphine compounds. The carbonyl and isonitrile groups are inserted into the nickel-nitrogen bond and a five-membered heteronuclear ring is formed in (⁵-C₅-C₅H₅)(L)(RN₃R)Ni, when L= CO and CNR.Most compounds are fluxional, involving site exchange of the triazenidoaryl-groupsvia intermediates with a chelating bonding mode of the triazenido ligand. The (⁵-C₅H₅)(PPh₃)(RN₃R)Ni compound shows anomalous solution paramagnetism, that is correlated with the fluxional mechanism. The temperature dependence of contact shifts in the n.m.r. spectrum was determined and E-values were calculated.     

Comparison of batch and in‐line PECVD of a‐Si:H passivation layers for silicon heterojunction solar cells

We present PECVD deposition of i‐a‐Si:H in an in‐line configuration for the fabrication of silicon heterojunction solar cells. For industry, in‐line processing has the potential to increase production throughput and yield. We compared batch and in‐line fabrication of i‐a‐Si:H passivation samples with identical plasma conditions and observed that the a‐Si:H material properties do not significantly differ. In batch‐type production the substrate is in the plasma zone at the moment of ignition, whereas for in‐line deposition the substrate is introduced into the plasma zone when steady plasma conditions have been reached. Our preliminary results show that there are depositions conditions that result both for in‐line and batch‐type deposition in good i‐a‐Si:H passivation layers. Therefore both methods can equally well be considered for the production of silicon heterojunction solar cells. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Application of Precipitation-based and Nanoparticle-based Techniques for Fabrication of Potentiometric Sensors for Nano Molar Determination of Chitosan and Polyvinyl Pyrrolidone in Pharmaceutical Formulations and Biological Fluids

Chitosan (CH) is one of the most abundant biopolymers with multiple applications. Polyvinyl pyrrolidone (PVP) has specific binding and detoxification properties that are of great interest in health care. Hence, it arises a crucial urge to develop economic sensors to analyze CH and PVP in pharmaceutical formulations and biological samples. Two portable sensors were fabricated using precipitation-based technique, and nanoparticles-based technique, for determination of CH and PVP in sensor 1 and 2; respectively. Linear responses of 10⁻⁵ to10⁻⁷ M and 10⁻² to10⁻⁷ M at pH 3.6–4.8 and 7.2–8.4, with ideal Nernstian slopes of 60.00 and 59.83 mV /decade, and nanomolar LODs of 94.90 and 81.20 nM were observed for CH and PVP; respectively. The percentage recoveries were 100.40±1.03 and 100.19±0.64 for sensors 1 and 2; respectively. Both sensors were successfully applied in biological fluids without pre-treatment. Accurate results were obtained using sensor 1, in pure form, pharmaceutical formulations, human plasma, rat liver and rat brain, as well as sensor 2, in pure form, pharmaceutical formulations and urine samples. The results were statistically compared with the reported methods and no significant difference was observed.     

Fabrication and Visualization of Metal‐Ion Patterns on Glass by Dip‐Pen Nanolithography

Fluorescent self‐assembled monolayers (SAMs) are used as dip‐pen nanolithography (DPN) substrates for the fabrication of patterns of Ca²⁺ and Cu²⁺ ions. The driving force for the transfer of these ions from an atomic force microscopy (AFM) tip to the surface is their complexation to organic ligands on the monolayer. By means of fluorescent surfaces, the patterns can be visualized under a fluorescence microscope. We use a custom‐built atomic force fluorescence microscope (AFFM), a combination of atomic force and confocal fluorescence microscopes, to deposit the metal ions onto the sensing SAMs by DPN and to subsequently visualize modulations of fluorescence intensity in a sequential write–read mode.     

Dynamic modulation transfer function: a method to characterize the temporal performance of liquid-crystal displays

A method to measure the dynamic modulation transfer function (DMTF) of a liquid-crystal display (LCD) is proposed to characterize its performance when rendering motion images. The method includes a measurement system to capture the temporal luminance variation of a LCD while using a well-designed input data sequence and a simulation model based on smooth pursuit eye tracking and temporal light integration at the human retina. It predicts the perceived performance of a moving sine wave pattern on a LCD and subsequently calculates the DMTF. With this approach, several technologies to reduce motion blur were evaluated and discussed.     

ADAPTIVE PARALLEL MULTIGRID SOLUTION OF 2D INCOMPRESSIBLE NAVIER–STOKES EQUATIONS

In this paper an adaptive parallel multigrid method and an application example for the 2D incompressible Navier–Stokes equations are described. The strategy of the adaptivity in the sense of local grid refinement in the multigrid context is the multilevel adaptive technique (MLAT) suggested by Brandt. The parallelization of this method on scalable parallel systems is based on the portable communication library CLIC and the message-passing standards: PARMACS, PVM and MPI. The specific problem considered in this work is a two-dimensional hole pressure problem in which a Poiseuille channel flow is disturbed by a cavity on one side of the channel. Near geometric singularities a very fine grid is needed for obtaining an accurate solution of the pressure value. Two important issues of the efficiency of adaptive parallel multigrid algorithms, namely the data redistribution strategy and the refinement criterion, are discussed here. For approximate dynamic load balancing, new data in the adaptive steps are redistributed into distributed memories in different processors of the parallel system by block remapping. Among several refinement criteria tested in this work, the most suitable one for the specific problem is that based on finite-element residuals from the point of view of self-adaptivity and computational efficiency, since it is a kind of error indicator and can stop refinement algorithms in a natural way for a given tolerance. Comparisons between different global grids without and with local refinement have shown the advantages of the self-adaptive technique, as this can save computer memory and speed up the computing time several times without impairing the numerical accuracy. © 1997 By John Wiley & Sons, Ltd. Int. J. Numer. Methods Fluids 24, 875–892, 1997.     

KHCoP2O7·2H2O: a novel acidic pyrophosphate

Potassium cobalt hydrogenpyrophosphate dihydrate, KHCoP₂O₇·2H₂O, crystallizes in the orthorhombic space group Pnma. This salt is isotypic with KHMP₂O₇·2H₂O (M = Mn and Zn). The structure consists of alternating layers, built from HP₂O₇³⁻ acidic pyrophosphate groups and CoO₆ octahedra, joined by potassium ions and bridging hydrogen bonds. The Co, K and water O atoms lie on mirror planes. The pyrophosphate group consists of two symmetry‐related PO₄ groups, with the bridging O atom on a mirror plane.