Investigation of potential-sensitive fluorescent dyes for application in nitrate sensitive polymer membranes

The applicability of various potential-sensitive dyes (PSD) for optical sensing of anions is reported. Specifically, nitrate-responsive polymer membranes have been developed which are composed of a plasticized polymer, an anion exchange catalyst, and a fluorescent dye. On exposure to nitrate, the fluorescence intensity of such membranes increases, while the wavelengths of the excitation and emission maxima remain virtually unchanged. The membranes typically are 2–4 μm thick and exhibit highest sensitivity to nitrate in the 2 to 200 mgl^–1 range. Signal changes on exposure to 100 mmol/l nitrate can be as high as +300%. The detection limit is 0.2 mgl^–1. The cationic PSD octadecyl acridine organe was tested in combination with a tin-organic and an indium-organic anion carrier rather than with tridodecylmethylammonium chloride, but both carriers were found to display no improved selectivity. Received: 2 December 1995 / Revised: 28 March 1996 / Accepted: 5 April 1996     

A simple cobalt catalyst system for the efficient and regioselective cyclotrimerisation of alkynes

The intermolecular cyclotrimerisation of terminal and internal alkynes can be catalysed by simple cobalt complexes such as a CoBr2(diimine) under mild reaction conditions when treated with zinc and zinc iodide with high regioselectivity in excellent yields.     

Furancarbonsäuren aus Rinderharn

Furancarboxylic Acids in Cattle Urine The urine of cattle contains large amounts of furancarboxylic acids. The same acids were isolated from rats after feeding with methyl esters of the so-called F-acids. Since the F-acids were not detected in cattle-food, they must be produced somewhere in the body of cattle.     

On the use of local basis sets for localized molecular orbitals

Two procedures are discussed for the direct variational optimization of localized molecular orbitals which are expanded in local subsets of the molecular basis set. It is shown that a Newton-Raphson approach is more efficient than an iterative diagonalization scheme. The effect of the basis-set truncation on the quality ofab-initio SCF results is investigated for Be, Li₂, HF, H₂O, NH₃, CH₄ and C₂H₆.     

High-temperature elemental analysis and pyrolysis techniques for stable isotope analysis

A universal method for pyrolysis and elemental analysis, suitable for the online determination of deuterium, carbon, nitrogen and oxygen isotopes for organic and inorganic substances, is presented. The samples are pyrolytically decomposed in a high-temperature pyrolysis (HTP) system, at a temperature exceeding 1400 degrees C, in the presence of reactive carbon. The method is suitable for the analysis of stable isotope ratios from hydrogen, carbon, nitrogen and oxygen. The instrumentation and experimental procedure are simple and cost-effective. The reproducibility of the delta values for D/H is better than 3 per thousand, and for (18)O, (13)C (organic) and (15)N (inorganic) it is approximately 0.2 per thousand. The HTP system is suitable for solid and liquid samples and can use an autosampler for the samples. Results are presented for the isotopic composition of international reference materials and selected laboratory reference materials, which demonstrate the precision and accuracy of the method. Possible problems in the measurement of nitrates and their solutions are particularly discussed. The analyses of oxygen isotopes in selected geological samples (carbonates, silicate, biotite) are demonstrated.     

2D-NMR: Part VI. 2D-INADEQUATE spectral analysis and crystal structure of tricyclo[7.3.1.02,7]tridecane

2-Hydroxy-13-oxo-tricyclo[7.3.1.0^2,7]tridecane derivatives can be obtained by reaction of cyclohexanone with alcohols under alkaline conditions. The unambiguous assignment of all signals of the¹H-NMR- and¹³C-NMR-spectrum is possible by 2D-¹H-¹³C-shift correlation and 2D-INADEQUATE. Compound1 crystallizes in space group P2₁/n witha=8.518 (1),b=14.789 (2),c=19.321 (2) Å, =94.91 (1)°,Z=8,D _c =1.22 Mg cm^–3. The structure refined toR=0.100 andR _w =0.097 for 1719 observed reflections. Two independent molecules form centrosymmetric hydrogen-bonded dimers.Part V:Haslinger E.,Kalchhau-ser H.,Robien W.,Steindl H., Monatsh. Chem.115, 597 (1984).     

Synthesis and Characterization of Methylzinc Tri(tert‐butyl)silylphosphanide as well as Related Sodium and Potassium Phosphanylzincates

The reaction of dimethylzinc and tri(tert‐butyl)silylphosphane in toluene yielded dimeric methylzinc tri(tert‐butyl)silylphosphanide ( 1 ) which crystallized tetrameric. Compound 1 was deprotonated with sodium in DME and the solvent‐separated dimeric ion pair [(dme)₃Na]⁺ [(dme)Na(MeZn)₂(μ‐PSitBu₃)₂]^? ( 2 ) was isolated. The reaction of 1 in THF with two equivalents of potassium and one equivalent of tri(tert‐butyl)silylphosphane gave dimeric [{tBu₃Si(H)P}{(thf)₂K}₂(MeZn)(PSitBu₃)]₂ ( 3 ). Both of these phosphanylzincates contain Zn₂P₂ cycles with Zn‐P bond lengths of approximately 237 pm, whereas in 1 larger Zn‐P bond lengths of 248.5 pm were found due to the larger coordination numbers of the phosphorus and zinc atoms.     

Large‐scale extrusion processing and characterization of hybrid nylon‐6/SiO2 nanocomposites

Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide‐6 (PA‐6) is achieved using a twin‐screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6 kg h^?1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA‐6 showed higher amounts of γ‐phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E‐modulus increased from 2.7 to 3.9 GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E′ and E″) increased and tan δ decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd.