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.     

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.     

Engineering the structure and magnetic properties of crystalline solids via the metal-directed self-assembly of a versatile molecular building unit

We report the supramolecular chemistry of several metal complexes of N-(4-pyridyl)benzamide (NPBA) with the general formula [Ma(NPBA)2AbSc], where M = Co2+, Ni2+, Zn2+, Mn2+, Cu2+, Ag+; A = NO3-, OAc-; S = MeOH, H2O; a = 0, 1, 2; b = 0, 1, 2, 4; and c = 0, 2. NPBA contains structural features that can engage in three modes of intermolecular interactions: (1) metal-ligand coordination, (2) hydrogen bonding, and (3) pi-pi stacking. NPBA forms one-dimensional (1-D) chains governed by hydrogen bonding, but when reacted with metal ions, it generates a wide variety of supramolecular scaffolds that control the arrangement of periodic nanostructures and form 1- (2-4), 2- (5), or 3-D (6-10) solid-state networks of hydrogen bonding and pi-pi stacking interactions in the crystal. Isostructural 7-9 exhibit a 2-D hydrogen bonding network that promotes topotaxial growth of single crystals of their isostructural family and generates crystal composites with two (11) and three (12) different components. Furthermore, 7-9 can also form crystalline solid solutions (M,M')(NPBA)2(NO3)2(MeOH)2 (M, M' = Co2+, Ni2+, or Zn2+, 13-16), where mixtures of Co2+, Ni2+, and Zn2+ share the same crystal lattice in different proportions to allow the formation of materials with modulated magnetic moments. Finally, we report the effects that multidimensional noncovalent networks exert on the magnetic moments between 2 and 300 K of 1-D (4), 2-D (5), and 3-D (7, 8, 10, and 13-16) paramagnetic networks.     

Ultrasound-assisted method for determination of chemical oxygen demand

A method for determination chemical oxygen demand (COD) assisted by use of ultrasound has been successfully evaluated for the first time. The method uses instrumentation simpler and cheaper and, in some instances, safer than that used by previous methods for the same purpose. The new device used for sonication is an all-glass cylindrical sonotrode that can be introduced directly into the reaction mixture. Use of this device enables more efficient interaction between sample and ultrasonic energy. The optimized experimental conditions are high ultrasonic power (55% amplitude, 0.9-second pulses each second), high sulfuric acid concentration (>60%), and a sonication time of 2 min. Under these conditions the method has limitations similar to those of the official COD method with regard to the type of organic compound. It works adequately with easily oxidized organic matter (potassium hydrogen phthalate and dextrose) and other organic compounds difficult to oxidize by conventional methods (e.g. phenol and acetic acid) but the COD values obtained with volatile compounds and difficult organic matter are poor. Chloride is tolerated up to a concentration of 7000 mg L(-1) without any masking agent. Gasification of the sample is recommended to improve results; use of air and argon resulted in no significant differences - bubbling with air during sonication resulted in COD values for certified materials and real wastewater samples statistically identical with the certified COD values and those obtained by the classic (open reflux) method. The use of ultrasound energy for COD determination thus seems to be an interesting and promising alternative to conventional oxidation methods used for the same purpose.     

Selective hydrogenation of phenylacetylene on Pd/Al2O3: Effect of the addition of Pt and particle size

Phenylacetylene hydrogenation on Pd, Pt and Pd–Pt/Al₂O₃ catalysts has been studied. In all catalysts activity was found not to depend on particle size. However, selectivity to styrene was found to depend on Pd/Al₂O₃ catalysts. Carbon deposition in both metal and support explains such a behavior. Nevertheless, in small Pd particles a longer residence time of styrene may control the selectivity.     

Sequential injection system with higher dimensional electrochemical sensor signals Part 2. Potentiometric e-tongue for the determination of alkaline ions

An intelligent, automatic system based on an array of non-specific-response chemical sensors was developed. As a great amount of information is required for its correct modelling, we propose a system generating it itself. The sequential injection analysis (SIA) technique was chosen as it enables the processes of training, calibration, validation and operation to be automated simply. Detection was carried out using an array of potentiometric sensors based on PVC membranes of different selectivity. The diluted standard solutions needed for system learning and response modelling are automatically prepared from more concentrated standards. The electrodes used were characterised with respect to one and two analytes, by means of high-dimensionality calibrations, and the response surface of each was represented; this characterisation enabled an interference study of great practical utility. The combined response was modelled by means of artificial neural networks (ANNs), and thus it was possible to obtain an automated electronic tongue based on SIA. In order to identify the ANN which provided the best model of the electrode responses, some of the network's parameters were optimised and its usefulness in determining NH₄⁺, K⁺ and Na⁺ ions in synthetic samples was then tested. Finally, it was used to determine these ions in commercial fertilisers, the obtained results being compared with reference methods.     

Molecular intercalates

The paper deals with the relations between host lattices and guest molecules. Several types of interaction of the guest molecules and the host material are explained and some conclusions are made about the arrangement of various guest molecules in the van der Waals' gap.