Measurement of the a.c. impedance of aluminium samples by holographic interferometry

In the present investigation, holographic interferometry was utilized for the first time to measure the alternating current (a.c.) impedance of aluminium samples during the initial stage of anodization processes in aqueous solution without any physical contact. The anodization process (oxidation) of the aluminium samples was carried out chemically in different sulphuric acid concentrations (0.5–3.125% H₂SO₄) at room temperature. In the mean time, a method of holographic interferometric was used to measure the thickness of anodization (oxide film) of the aluminium samples in aqueous solutions. Along with the holographic measurement, a mathematical model was derived in order to correlate the a.c. impedance of the aluminium samples in solutions to the thickness of the oxide film of the aluminium samples which forms due to the chemical oxidation. The thickness of the oxide film of the aluminium samples was measured by the real-time holographic interferometry. Consequently, holographic interferometry is found very useful for surface finish industries especially for monitoring the early stage of anodization processes of metals, in which the thickness of the anodized film as well as the a.c. impedance of the aluminium samples can be determined in situ. In addition, a comparison was made between the a.c. impedance values obtained from the holographic interferometry measurements and from measurements of electrochemical impedance spectroscopy. The comparison indicates that there is good agreement between the data from both techniques.     

Wireless electrochemical preparation of gradient nanoclusters consisting of copper(II), stearic acid and montmorillonite on a copper wire for headspace in-tube microextraction of chlorobenzenes

This work introduces a new gradient fiber coating for microextraction of chlorobenzenes. Nanoclusters of organoclay-Cu(II) on a copper wire were fabricated by wireless electrofunctionalization. The resultant gradient coatings are more robust, and thermally and mechanically stable. Wireless electrofunctionalization was carried out in a bipolar cell under a constant deposition potential and using an ethanolic electrolyte solution containing stearic acid and montmorillonite. Stearic acid acts as an inexpensive and green coating while montmorillonite acts as a modifier to impart thermal stability. The gradient morphology of the nanoclusters was investigated by scanning electron microscopy, thermogravimetric analysis and energy dispersive X-ray spectroscopy. The coated wire was placed in a hollow needle and used for headspace in-tube microextraction (HS–ITME) of chlorobenzenes (CBs). Effects of various parameters affecting synthesis and extraction were optimized. Following extraction, the needles were directly inserted into the GC injector, and the CBs (chlorobenzene, 1,4-dichlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, 1,2,3,4-tetrachlorobenzene) were quantified by GC–MS. The limits of detection under optimized conditions range from 0.5 to 10 ng.L^?1. The intra– and inter–day relative standard deviations (RSDs) (for n?=?10, 5 respectively) using a single fiber are 6–10 and 10–15%, respectively. The fiber–to–fiber RSDs (for n?=?3) is between 17 and 24%. The method was successfully applied to the extraction of CBs from real water samples, and relative recoveries are between 91 and 110%.

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Graphical abstract A gradient coating of organoclay–Cu nanoclusters was fabricated on a copper wire by wireless electrofunctionalization. The oxidation of copper takes place at the anodic pole (red) while dissolved oxygen in ethanol solution is reduced at the cathodic pole (blue).

     

New Hybrid Material: (C<Subscript>3</Subscript>H<Subscript>6</Subscript>N<Subscript>3</Subscript>)<Subscript>4</Subscript>Bi<Subscript>2</Subscript>Cl<Subscript>10</Subscript>. Synthesis,Structural Study and Spectroscopic Behavior

The structure of (C₃H₆N₃)₄Bi₂Cl₁₀ was determined by single crystal X-ray diffraction at room temperature. It crystallizes in the orthorhombic space group Pcmn, with a = 9.430 (1) Å, b = 17.426 (3) Å, c = 19.883(5) Å, V = 3267.3 (11) ų and Z = 4. The structure consists of discrete binuclear [Bi₂Cl₁₀]^4– anions and 3-aminopyrazolium cations. The crystal packing is governed by weak N–H···Cl hydrogen bonds, π–π and electrostatic Cl···Cl interactions. Infrared spectrum is used to gain more information on the title compound. An assignment of the observed vibration modes is reported. The crystal morphology is studied using the BFDH laws. The calculated HOMO and LUMO energies show that charge transfer occur within organic and inorganic molecules. The optical absorption of the zero-dimensional hybrid was also investigated.     

Stereoselectivity in Reactions of Metal Complexes. Part XV. Structure and stability of chiral cobalt(III) complexes with pentadentate ligands

The syntheses and characterization of four new linear pentadentate ligands and their Co^III complexes are described: N,N′-[(pyridine-2,6-diy)bis(methylene)]bis[sarcosine] (sarmp), N,N′-[(pyridine-2,6-diyl)bis(methylene)]bis[(R)- or (S)-proline] ((R,R)- or (S,S)-promp), N,N′-[(pyridine-2,6-diyl)bis(methylene)]bis[N-(methyl)-(R)- or (S)-alanine] ((R,R)- or (S,S)-malmp); 2,2′-[pyridine-2,6-diyl]bis[(S)- or rac-N-(acetic acid)pyrrolidine] ((S,S)- or rac-bapap). The complexes were characterized and, with but one exception, complex formation is stereospecific: Δ-exo-(R,R) (or Λ-exo-(S,S)) for promp and Λ-(R,R) (or Δ-(S,S)) for bapap. The exception is [Co((R,R)- or (S,S)-malmp)H₂O]ClO₄ for which two forms are obtained, to which Λ-endo-(R,R) (or Δ-endo-(S,S)) and, tentatively, Δ-unsymmetric-(R,R)- (or Λ-unsymmetric-(S,S)-) configurations are assigned. X-Ray crystal structures are presented for the complexes [Co(sarmp)H₂O]ClO₄, [Co((S,S)-promp)H₂O]ClO₄, [Co(rac-bapap)H₂O]ClO₄ and endo-[Co(rac-malmp)H₂O]ClO₄. Ligand acid dissociation and Co^II and Fe^II complex-formation constants are reported.     

Synthesis, properties and thermal studies of oxorhenium(V) complexes with 3-hydrazino-5,6-diphenyl-1,2,4-triazine, benzimidazolethione and 2-hydrazinobenzimidazole. Mixed ligand complexes, pyrolytical products and biological activity

A series of biologically active complexes of oxorhenium(V), were prepared by using the organic ligands 3-hydrazino-5,6-diphenyl-1,2,4-triazine (HL1), benzimidazolethione (H2L2) and 2-hydrazinobenzimidazole (H2L3). The mixed ligand complexes of oxorhenium(V) with the previous ligands and one of the following ligands: NH4SCN, 1,10-phenanthroline (1,10-phen), 8-hydroxyquinoline (8-OHquin) or glycine (Gly), were isolated. All the binary and mixed ligand complexes have monomeric structures and exist in the octahedral configuration. Thermal studies on these complexes showed the possibility of structural transformation from mononuclear into binuclear ones. The structures of all complexes and the corresponding thermal products were elucidated by elemental analyses, IR, electronic absorption and 1H NMR spectra, magnetic moments, conductance and TG-DSC measurements. The antifungal activities of the metal complexes towards Alternaria alternata and Aspergilus niger were tested and showed comparable behaviour with some well known antibiotics.     

Determination of antibilharzial antimony compounds by direct current, differential pulse, square-wave and alternating current anodic stripping voltammetry

A simple, rapid and sensitive method has been developed for the determination of Sb(III) in five antimonial antibilharzial drugs using anodic stripping voltammetry. The method is based on the reduction of Sb(III) on the HMDE, followed by a selected mode of oxidative sweep, i.e. direct current, differential pulse, square-wave or first harmonic alternating current sweep, using 2 mol/L HCl as a supporting electrolyte. Voltammograms for various sample concentrations in the range 3–47 ppb Sb(III) were recorded and the respective calibration graphs constructed. To overcome the expected effect of adsorption of surface active organic compounds on the mercury drop, the standard addition technique of Sb₂O₃ solution was applied to calculate the recoveries of all the tested antimonials. The method gave reproducible results within 2% and the limit of detection for all measurement modes was 3 ppb. SW and AC modes seem to achieve lower detection limits than the other two modes. The four modes proved to be of equal accuracy and precision.     

Bi-parametric optimal partition invariancy sensitivity analysis in linear optimization

In bi-parametric linear optimization (LO), perturbation occurs in both the right-hand-side and the objective function data with different parameters. In this paper, the bi-parametric LO problem is considered and we are interested in identifying the regions where the optimal partitions are invariant. These regions are referred to as invariancy regions. It is proved that invariancy regions are separated by vertical and horizontal lines and generate a mesh-like area. It is proved that the boundaries of these regions can be identified in polynomial time. The behavior of the optimal value function on these regions is investigated too.     

An MEDT study of the mechanism and selectivities of the [3+2] cycloaddition reaction of tomentosin with benzonitrile oxide

The [3+2] cycloaddition (32CA) reaction of tomentosin with benzonitrile oxide yielding a spiro-isoxazoline has been studied within the Molecular Electron Density Theory at the B3LYP/6-31(d,p) computational level. Given the multifunctionality of tomentosin, this 32CA reaction can take place along 16 competitive reaction paths. The chemo-, regio-, and stereoisomeric reaction paths involving the two C C double bonds of tomentosin have been studied. Density functional theory (DFT) calculations account for the total chemo- and regioselectivity, in complete agreement with the experimental outcomes, being suggestive of low diastereofacial selectivity. Analysis of the conceptual DFT indices accounts for the nonpolar character of this 32CA reaction. On the other hand, the topological analysis of the electron localization function of the selected points of the intrinsic reaction coordinate associated with the formation of the C C and C O single bonds emphasizes the zw-type reactivity of the phenyl nitrile oxide; the reaction taking place through a non-concerted two-stage one-step mechanism initialized with the formation of the C C single bond involving the β-conjugated carbon of tomentosin.     

Skew Killing spinors in four dimensions

Annals of Global Analysis and Geometry - This paper is devoted to the classification of 4-dimensional Riemannian spin manifolds carrying skew Killing spinors. A skew Killing spinor $$\psi $$ is a...