KMo5O13 and KNb1.76Sb3.24O13

The title compounds, potassium pentamolybdenum oxide, KMo₅O₁₃, and potassium niobate antimonate or potassium niobium antimony oxide (1/1.76/3.24), KNb_1.76Sb_3.24O₁₃, were synthesized by solid‐state reactions and are isomorphous in space group Cmcm. The structure of the Mo complex has three unique Mo atoms and consists of MoO₆ octahedra sharing edges to form Mo₂O₆ pairs and Mo₃O₉ triplets, which, in turn, form layers by sharing corners. These layers are linked together in the [100] direction, yielding a three‐dimensional network similar to that of KSb₅O₁₃. This framework delimits interconnected tunnels, running approximately along the [110] and [10] directions, in which K⁺ ions are located. In the isomorphous KNb_1.76Sb_3.24O₁₃ structure, one of the Mo sites in KMo₅O₁₃ is replaced by Sb and the other two Mo sites have been replaced by Nb/Sb.     

Highly Efficient and Practical Syntheses of Lavendamycin Methyl Ester and Related Novel Quinolindiones

The novel 7-(N-formyl-, 7-(N-acetyl-, and 7-(N-isobutyrylamino)-2-methylquinoline-5,8-diones were synthesized in excellent overall yields in three steps via the nitration of the commercially available 8-hydroxy-2-methylquinoline followed by a reduction-acylation step and then oxidation. Acid hydrolysis of 7-(N-acetylamino)-2-methylquinoline-5,8-dione (14a) afforded the novel 7-aminoquinoline-5,8-dione 7 in excellent yields. Due to our efficient preparation of dione 14a, we now report a short and practical method for the total synthesis of the potent antitumor agent lavendamycin methyl ester (1b) with an excellent overall yield.     

Electrochemical behaviour of an indium electrode in concentrated KOH solutions at different temperatures

Summary The electrochemical behaviour of pure indium in KOH solutions (1–4M) was studied at different temperatures (25–70°C) by potentiostatic techniques. Two anodic peaks corresponding to the formation of In(OH)₃ and In₂O₃ were observed. The heights of the two peaks increased with the increase of alkali concentration. An increase of temperature increased the peak currents and shifted their corresponding potentials to more negative values. The variation of the peak currents and peak potentials with scan rate suggested that the anodic dissolution of indium was a diffusion controlled process. In cyclic voltammetry, the reverse scan consistently showed one peak which was attributed to the reduction of anodic oxidation products into indium. X-ray diffraction analysis confirmed the presence of In(OH)₃ at the first anodic peak, In(OH)₃ and In₂O₃ at the second anodic peak and In₂O₃ in the permanent passive region.

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Zum elektrochemischen Verhalten einer Indium-Elektrode in konzentrierter Kalilauge bei verschiedenen Temperaturen

Zusammenfassung Es wurde das Verhalten von reinem Indium in 1 – 4M KOH-Lösungen bei Temperaturen zwischen 25 und 70°C mittels potentiostatischer Methoden untersucht. Zwei anodische Peaks, entsprechend der Bildung von In(OH)₃ und In₂O₃, traten auf. Die Höhe der beiden Peaks wurde mit zunehmender Alkalikonzentration gesteigert. Eine Temperaturerhöhung verstärkte die Peakströme und verschob die entsprechenden Potentiale zu negativeren Werten. Die Abhängigkeit der Peakströme und Peakpotentiale von der Scangeschwindigkeit legte den Schluß nahe, daß die anodische Lösung von Indium in einem diffusionskontrollierten Prozeß stattfindet. Bei der cyclischen Voltammetrie zeigte der reverse Scan einheitlich einen Peak, der der Reduktion der anodischen Oxidationsprodukte zu Indium zugeschrieben wurde. Röntgendiffraktionsanalyse bestätigte die Präsenz von In(OH)₃ beim ersten anodischen Peak, In(OH)₃ beim zweiten Peak und In₂O₃ im permanent passiven Bereich.

     

New conductivity detection response equation for anions eluted with fully and partially ionised eluents in non-suppressed ion chromatography

A response equation for conductivity detection in ion chromatography has been derived. This equation is applicable to non-suppressed ion chromatography using both fully ionised and partially ionised eluents. A prime assumption of this equation is that when partially ionised eluents are used (such as benzoic acid), both the ionised and neutral components of the eluent species contribute to the detector response of anionic analytes. Experimental evidence is provided to support this assumption in that pH changes accompanying the elution of an analyte have been measured. These pH changes are proportional to the concentration of analyte injected onto the column, in accordance with predictions from the response equation. Furthermore, it is shown that protonated eluents (such as benzoic acid) give more sensitive detection than equivalent ionised eluents (such as potassium benzoate) and the signal enhancement achieved using a protonated eluent species is in accordance with theory.     

Prediction of retention times for anions in linear gradient elution ion chromatography with hydroxide eluents using artificial neural networks

The feasibility of using an artificial neural network (ANN) to predict the retention times of anions when eluted from a Dionex AS11 column with linear hydroxide gradients of varying slope was investigated. The purpose of this study was to determine whether an ANN could be used as the basis of a computer-assisted optimisation method for the selection of optimal gradient conditions for anion separations. Using an ANN with a (1, 10, 19) architecture and a training set comprising retention data obtained with three gradient slopes (1.67, 2.50 and 4.00 mM/min) between starting and finishing conditions of 0.5 and 40.0 mM hydroxide, respectively, retention times for 19 analyte anions were predicted for four different gradient slopes. Predicted and experimental retention times for 133 data points agreed to within 0.08 min and percentage normalised differences between the predicted and experimental data averaged 0.29% with a standard deviation of 0.29%. ANNs appear to be a rapid and accurate method for predicting retention times in ion chromatography using linear hydroxide gradients.     

Contactless conductivity detection of synthetic polymers in non-aqueous size-exclusion electrokinetic chromatography

A capacitively coupled contactless conductivity detection (CCD) system has been applied for the detection of neutral synthetic polymers in capillary size-exclusion electrokinetic chromatography (SEEC). Polystyrene standards, that were used as a model compounds, were separated on a capillary column packed with porous 10 microm silica particles with an electrokinetically driven mobile phase, and detected by CCD and UV detection simultaneously. Mass-calibration curves for polystyrene were constructed. Satisfactory results were obtained for the linearity, the run-to-run repeatability (<0.2% for the relative retention and <4% for the peak area) and the robustness of the detector. One of the major issues in this preliminary study was to investigate the origin of the peaks observed for the polystyrene standards. The effect of the molar mass of the polystyrenes on the sensitivity was small. Therefore, the signals obtained could not be explained as the result of an increased viscosity and a decreased solution conductivity of the solute zone. An alternative hypothesis is suggested, and recommendations for further research are given.     

Investigations on the behaviour of acidic, basic and neutral compounds in capillary electrochromatography on a mixed-mode stationary phase

This work describes the separation of acidic, basic and neutral organic compounds as well as inorganic anions in a single run by capillary electrochromatography employing a stationary phase which exhibits both strong anion-exchange and reversed-phase chromatographic characteristics. The positive surface charge of this stationary phase provided a substantial anodic electroosmotic flow. The analytes were separated by a mixed-mode mechanism which comprised chromatographic interactions (hydrophobic interactions, ion-exchange) as well as electrophoretic migration. The influence of ion-exchange and hydrophobic interactions on the retention/migration of the analytes could be manipulated by varying the concentration of a competing ion and/or the amount of organic modifier present in the background electrolyte. Additionally the effects of pH changes on both the chromatographic interactions as well as the electrophoretic migration of the analytes were investigated.     

Advances in ion chromatography: speciation of μ 1−1 levels of metallo-cyanides using ion-interaction chromatography

Fe(CN)^4?₆, Cu(CN)^3?₄, Co(CN)^3?₆, Fe(CN)^3?₆, Ni(CN)^2?₄ and Cr(CN)^3?₆ are determined by ion-interaction chromatography using a C₁₈ column and methanol-tetrahydrofuran-10 mM phosphate buffer (pH 7.9) (25 + 1 + 74, v/v/v) containing 5 mM tetrabutylammonium hydroxide as mobile phase, with spectrophotometric detection at 214 nm. Detection limits are in the range 0.01–0.5 mg 1^?1. In an alternative approach, an automated on-line sample preconcentration technique is used wherein a 2-ml volume of sample containing metallo-cyanides is loaded onto a C₁₈ precolumn which has been equilibrated with the above mobile phase. The bound solutes are then eluted from the precolumn to a C₁₈ analytical column where they are separated using the same mobile phase as employed to equilibrate the precolumn. Detection limits are in the rate 0.08–1.58 μg 1^?1 and calibration graphs are linear up to 200 μg 1^?1. The preconcentration step is shown to give quantitative recoveries for all species except Fe(CN)^4?₆ and (CN)^3?₄. The iron(II) complex does not bind quantitatively to the precolumn, and extensive studies with the copper complex suggested that low recoveries were due to dissociation and ligand-exchange reactions occurring during the chromatographic separation process. Negative interference effects were observed for Cl^? and SO^2?₄ when present at a level of 250 mg 1^1?, and UV-absorbing anions such as Br^?, SCN^?, NO^?₂ and NO^?₃ caused positive interference when present at concentrations as low as 1 mg 1^?1. The negative interferences could be reduced by diluting the sample and the positive interferences could be eliminated by incorporating an additional step in the preconcentration process, in which UV-absorbing anions bound to the precolumn after sample loading were eluted selectively using an eluent consisting of 10 mM NaCl in phosphate buffer (pH 6.7).     

Modelling,optimisation and control of selectivity in the separation of aromatic bases by electrokinetic chromatography using a neutral cyclodextrin as a pseudostationary phase

A simple mathematical model describing the separation of a series of aromatic bases by electrokinetic chromatography using beta-cyclodextrin (beta-CD) as a pseudostationary phase is described. The model takes into account changes in electrolyte pH and the different formation constants between the neutral and charged forms of the analytes with the CD. Constants in the model were obtained within the two-dimensional experimental space defined by pH and [beta-CD] with nonlinear regression using only five experimental points. These constants agreed with expected trends in analyte-CD interactions and predicted much higher formation constants for the neutral analyte-CD complex than for the charged analyte-CD complex. Correlation between predicted and observed mobilities using additional 20 points within the experimental space gave r(2) = 0.995. Optimisation of the pH and [beta-CD] was performed using both the normalised resolution product and minimum resolution product criteria and provided two optimum separations which exhibited different selectivities. Differences between predicted and observed migration times at these optima were less than 2.5 and 5% for the normalised resolution product and the minimum resolution criteria, respectively. In both cases the correct migration order was predicted. The model was also applied successfully to the optimisation of conditions for the separation of a specific mixture of analytes or for conditions under which particular analytes migrated in a desired order.