Sequential injection system with higher dimensional electrochemical sensor signals Part 1. Voltammetric e-tongue for the determination of oxidizable compounds

A sequential injection analysis (SIA) system was developed with the aim of obtaining an automatic and versatile way to prepare standards needed in the study of systems with higher dimensional sensor signals. To illustrate this, different analytical techniques were used in determinations of several analytes. Automated potentiometric calibrations of different potentiometric sensors, with and without interference, were carried out. Useful determinations of selectivity coefficients with two degrees of freedom were obtained. Simultaneous voltammetric determinations have also been done. Firstly, simultaneous determinations of lead and cadmium, using epoxy-graphite composite as the working electrode, have enabled a separate calibration for each metal to be obtained. Next, a voltammetric electronic tongue was designed and applied to the determination of oxidizable species. The use of artificial neural networks has solved the overlapped signal of ascorbic acid, 4-aminophenol and 4-acetamidophenol (paracetamol). A set of 63 data points was prepared automatically and has facilitated the training of an electronic tongue for these three analytes. Accurate predictions of test solutions, in the range of 12–410 μM for ascorbic acid, 17–530 μM for 4-aminophenol and 10–420 μM for paracetamol, have been achieved with RMSEs lower than 0.10 μM.     

Synthesis of 4‐(trihalomethyl)dipyrimidin‐2‐ylamines from β‐alkoxy‐α,β‐unsaturated trihalomethyl ketones

The synthesis of a novel series of twelve 4‐(trihalomethyl)dipyrimidin‐2‐ylamines, from the cyclo‐condensation reaction of 4‐(trichloromethyl)‐2‐guanidinopyrimidine, with β‐alkoxyvinyl trihalomethyl ketones, of general formula: X₃C‐C(O)‐C(R²)=C(R¹)‐OR, where: X = F, Cl; R = Me, Et, ‐(CH₂)₂‐, ‐(CH₂)₃‐; R¹ = H, Me; R² = H, Me, ‐(CH₂)₂‐, ‐(CH₂)₃‐, is reported. The reactions were carried out in acetonitrile under reflux for 16 hours, leading to the dipyrimidin‐2‐ylamines in 65‐90% yield. Depending on the substituents of the vinyl ketone, tetrahydropyrimidines or aromatic pyrimidine rings were obtained from the cyclization reaction. When X = Cl, elimination of the trichloromethyl group was observed during the cyclization step. The structure of 4‐(trihalomethyl)dipyrimidin‐2‐ylamines was studied in detail by ¹H‐, ¹³C‐ and 2D‐nmr spectroscopy.     

All-solid-state potentiometric sensors sensitive to nonionic surfactants based on ionophores containing ethoxylate units

Earlier work of potentiometric Ion-selective electrodes (ISEs) sensitive to nonionic surfactants of the polyethoxylate type is further extended. The ISEs constructed were all-solid-state sensors with plasticized PVC membranes. The sensing material was a tetraphenylborate salt of the barium complex with a polyethoxylate nonionic surfactant. As membrane component, the combinations of two polyethoxylates of the nonylphenoxy type, which differed in the number of oxyethylene units (5 or 12), and two different plasticizers, (o-nitrophenyloctyl ether and o-nitrophenylphenyl ether), were tested. The response of these electrodes to different nonionic surfactants and the interference effect of several species has been evaluated. For all the types of tested electrodes, the sensitivities shown were ca. 30.0 mV dec(-1) and the limit of detection, ca. 10(-5) M, when a nonylphenoxyde with 12 oxyethylene units was used as standard. The membrane with the best response characteristics was then applied in potentiometric titrations of this kind of surfactants in the presence of Ba(2+) ion and using tetraphenylborate as the titrant.     

Activation of the carbon—nitrogen triple bond of benzonitrile in the presence of triosmium clusters and acetic acid. Crystal structure of (μ-H)Os3(CO)10(μ-O2CCH3), a product of the reaction

The activation of the CN triple bond of benzonitrile in the presence of acetic acid and of Os₃(CO)₁₂ or H₂Os₃(CO)₁₀ has been studied. When Os₃(CO)₁₂ reacts with PhCN and acetic acid in refluxing n-octane the three main products are (μ-H)Os₃(CO)₁₀(μ-O₂CCH₃) (I), (μ-H)Os₃(CO)₁₀(μ-NCHPh) (II) and (μ-H)Os₃(CO)₁₀(μ-NHCH₂Ph) (III); II and III are analogues of (μ-H)Ru₃(CO)₁₀(μ-NCHPh) and (μ-H)Ru₃(CO)₁₀(μ-NHCH₂Ph) obtained from PhCN, Ru₃(CO)₁₂ or H₄Ru₄(CO)]₁₂, and acetic acid. In contrast to the reaction with ruthenium clusters, Os₃(CO)₁₂ and H₂Os₃(CO)₁₀ also give the adduct Os₃(CO)₁₀(CH₃COOH) (I). The structure of I has been fully elucidated by X-ray diffraction. Crystals of I are monoclinic, space group P2₁/m, with unit cell parameters a 7.858(6), b 12.542(8), c 9.867(6) Å, β 109.92(2)°, Z = 2. In I an edge of the triangular cluster of osmium atoms is doubly bridged by a hydride and an acetate ligand. Ten terminal carbonyl groups are bonded to the metal atoms.     

Color Displays with Gel-Glass Dispersed Liquid Crystals

Liquid crystal microdroplets trapped into silica gel-glasses by sol-gel processes may be used for display applications. Gel-glass dispersed liquid crystals (GDLC) are switched between opaque and transparent states by applying external AC-voltage signals; no polarizers are required. The feasibility of applying these materials to colored displays has been explored. A comparative study of different dyes for GDLC color displays, which were either embedded in the sol-gel matrix or dissolved in the liquid crystal microdroplets is presented.     

Extraction of Pb(II), Cd(II), and Hg(II) from aqueous solution by nitrogen and thiol functionality grafted to silica gel measured by calorimetry

The reaction of ethylene sulfide with 3-aminopropyltrimethoxysilane gave a new silylating agent, which was anchored onto a silica surface via the sol–gel procedure. This surface displayed a chelating moiety containing nitrogen and two sulfur basic centers potentially capable of extracting cations from aqueous solutions. The process of metal extraction was followed by a batch method, and fitted to a modified Langmuir equation. The maximum adsorption capacities found were: 2.06 ± 0.01, 3.72 ± 0.02, and 5.14 ± 0.02 mmol g⁻¹ for Pb(II), Cd(II), and Hg(II), respectively. The enthalpies of bending are: −1.16 ± 0.04, −3.60 ± 0.10, and −8.94 ± 0.03 kJ mol⁻¹ for Cd(II), Pb(II), and Hg(II), respectively. The Gibbs free energies of binding agree with the spontaneity of the proposed reactions between cations and basic centers.     

The chemistry and the stereochemistry of poly(n-alkyliminoalanes) : III. The crystal and molecular structure of the adduct (HalN-i-Pr)6AlH3

The crystal and molecular structure of the adduct (HAlN-i-Pr)₆AlH₃ has been determined from single-crystal and three dimensional X-ray diffraction data collected by counter methods. The cage-type molecular structure consists of two six-membered rings, (AlN)₃, joined together by four adjacent transverse AlN bonds; the loss of two of these bonds allows the complexation of one alane molecule, with five-coordination of the aluminum (trigonal bipyramidal geometry), through two AlN bonds and two AlHAl bridge bonds. The AlN bond lengths range from 1.873 to 1.959 Å; the average AlH bond length is 1.50(1) Å for the four-coordinated aluminum atoms; the average distance of the two apical hydrogens from the five-coordinated aluminum atom is 1.92(5) Å. Colourless prismatic crystals of the compound have the following crystal data: triclinic space group P$\text{1}$; a = 17.13(2); b = 10.78(2); c = 10.20(2) Å; α = 124.3(4), β = 92.0(4), γ = 92.1(5); Z = 2; calculated density 1.157 g/cm³. The structure has been refined by block-matrix, least-squares methods using 4358 independent reflections to a standard unweighted R factor of 4.9%.     

Reaction of thiete 1,1-dioxide with α-chlorobenzalphenylhydrazine and methyl phenylhydrazonochloroacetate

Thiete 1,1-dioxide reacts with 2 moles of α-chlorobenzalphenylhydrazine and methyl phenylhydrazonochloroacetate in the presence of triethylamine leading to the pyrazole derivatives 6 and 7 whose structure and mechanism of formation are discussed.     

Flow analysis-vapor phase generation-Fourier transform infrared (FA-VPG-FTIR) spectrometric determination of nitrite

In this work, the coupling between flow analysis (FA)–vapor phase generation (VPG) and Fourier transform infrared spectrometry (FTIR) has been proposed as a novel and alternative strategy for the determination of nitrite. The analyte was transformed into the gaseous nitric oxide (NO) by on-line reaction with potassium iodide (KI) or ascorbic acid in acidic medium. The gaseous NO generated was transported by means of a N₂ gas carrier stream inside the IR gas cell and the corresponding FTIR spectrum was acquired in a continuous mode. The absorbance at 1876 cm⁻¹, corrected by a baseline established between 1879 and 1872 cm⁻¹ at a nominal resolution of 2 cm⁻¹, was selected as a measurement criterion. The effect of different spectroscopic and flow analysis experimental parameters, such as nominal resolution, number of scans, reducing agent and its concentration, acidic medium, reagents and sample flow rates, and the carrier gas flow rate on the analytical signal, and then in the figures of merit were initially evaluated by using a standard short path length (10 cm) IR gas cell. The optimization of the system was carried out by the univariate method. The main aims of this study were: (i) to investigate the on-line generation of gaseous nitric oxide in a continuous flow system, and (ii) the use of Fourier transform infrared spectrometry as an alternative and selective detector for the determination of nitrite. The proposed method was initially tested and applied for the determination of nitrite in samples with very high concentration of nitrite, such as frankfurters.     

Heterogeneous catalysts for cyclic carbonate synthesis from carbon dioxide and epoxides

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