A Contactless Impedance Probe for Simple and Rapid Determination of the Ratio of Liquids with Different Permittivities in Binary Mixtures

Simple contactless cells with planar or tubular electrodes have been designed for measurement of the permittivity of solutions. The cells, connected to an integrated circuit of astable multivibrator, respond primarily to the capacitance component of the cell impedance, the multivibrator frequency depends in a defined manner on the solution permittivity and is readily used as the analytical signal in determinations of the ratios of components in binary liquid mixtures; water solution of methanol, ethanol and dioxane have been tested. The response of the cell with planar electrodes satisfies well the simple theoretical model and both the cells provide results with a sufficient sensitivity, a low LOD value (units of %vol) and a good precision (around 1%rel). The cell simplicity, small dimensions, long‐term stability and the possibility of powering them from a battery make them suitable for hand‐held meters. As an example of application in practice, the content of ethanol was determined in the car fuel petrol.     

On Estimating the Asymptotic Variance of Stationary Point Processes

We investigate a class of kernel estimators $\widehat{\sigma}^2_n$ of the asymptotic variance σ ² of a d-dimensional stationary point process $\Psi = \sum_{i\ge 1}\delta_{X_i}$ which can be observed in a cubic sampling window $W_n = [-n,n]^d\,$ . σ ² is defined by the asymptotic relation $Var(\Psi(W_n)) \sim \sigma^2 \,(2n)^d$ (as n →? ∞) and its existence is guaranteed whenever the corresponding reduced covariance measure $\gamma^{(2)}_{red}(\cdot)$ has finite total variation. Depending on the rate of decay (polynomially or exponentially) of the total variation of $\gamma^{(2)}_{red}(\cdot)$ outside of an expanding ball centered at the origin, we determine optimal bandwidths b _n (up to a constant) minimizing the mean squared error of $\widehat{\sigma}^2_n$ . The case when $\gamma^{(2)}_{red}(\cdot)$ has bounded support is of particular interest. Further we suggest an isotropised estimator $\widetilde{\sigma}^2_n$ suitable for motion-invariant point processes and compare its properties with $\widehat{\sigma}^2_n$ . Our theoretical results are illustrated and supported by a simulation study which compares the (relative) mean squared errors of $\widehat{\sigma}^2_n$ for planar Poisson, Poisson cluster, and hard-core point processes and for various values of n b _n .     

New Potential Biocatalysts by Laccase Immobilization in PVA Cryogel Type Carrier

Laccases are enzymes belonging to the Oxidoreductases class. These enzymes may be good biocatalysts for different processes, at laboratory and industrial levels. A successful use at industrial scale demands a higher stability of the enzyme. As an easy way to obtain longer life biocatalysts, the immobilization process is recommended. Thus, the paper presents different ways of obtaining new biocatalysts by a laccase covalent immobilization on a macroporous carrier based on poly(vinyl alcohol) cryogel. Different procedures of covalent immobilization are described, the newly obtained biocatalysts being characterized. According to the experimental data, the stability of the immobilized enzyme increased and the pH profile changed, compared with those of the free enzyme.     

Column switching in zone electrophoresis on a chip

This feasibility study deals with column switching in zone electrophoresis (ZE) separations on a column coupling (CC) chip. The column switching implemented into the ZE separations an on-chip sample clean up applicable for both the multicomponent and high salinity samples. In addition, complemented by different separation mechanisms in the coupled columns (channels), it provided benefits of two-dimensional separations. Properly timed column switching gave column-to-column transfers of the analytes, characterized by 99-102% recoveries, delivered to the second separation stage on the chip the analyte containing fractions contaminated only with minimum amounts of the matrix constituents. A diffusion driven transport of the matrix constituents to the second channel of the chip (due to direct contacts of the electrolyte solutions in the bifurcation region), representing 0.1-0.2% of the loaded sample constituents, was found to accompany the sample clean up performed on the CC chip. This source of potential disturbances to the separation in the second channel, however, is not detectable in a majority of practical situations. With respect to a 900 nl volume of the sample channel on the CC chip, the electric field and isotachophoresis (ITP) stackings were employed to minimize the injection dispersion in the separations and concentrate the analytes. Here, the column switching, removing a major part of the stacker from the separation system, provided a tool effective in a control of the destacking of analytes. Highly reproducible ZE separations as attained in this work also for the chip-to-chip and equipment-to-equipment frames can be ascribed, at least in part, to suppressions of electroosmotic and hydrodynamic flows of the solutions in which the separations were performed.     

On the mechanism of the unexpected facile formation of meso-diacetate products in enzymatic acetylation of alkanediols

The mechanism of the unexpected facile formation of meso-diacetate previously observed in the enzymatic resolution of dl/meso mixtures of 2,4-pentanediol and 2,5-hexanediol with Candida antarctica lipase B has been elucidated. It was found that the formation of meso-diacetate proceeds via different mechanisms for the two diols. Enzyme-catalyzed acylation of AcO-d(3) labeled (R)-monoacetates of meso-2,4-pentanediol and meso-2,5-hexanediol and analysis of the meso-diacetates obtained show that the former reaction proceeds via intramolecular acyl migration while the latter occurs via direct S-acylation of the alcohol. For the (R)-monoacetate of (R,S)-2,4-pentanediol the intramolecular acyl migration was fast and therefore direct S-acylation by the external acyl donor is suppressed. For the hexanediol monoacetate the rate ratio (pseudo E value) between (5R,2R)- and (5R,2S)-5-acetoxy-2-hexanol was experimentally determined to be k(R,R)/k(R,S) = 25, which is about 10-20 times lower than the E value for 2-pentanol and 2-octanol. In a preliminary experiment it was demonstrated that facile acyl migration in the 1,3-diol derivative can be utilized to prepare syn-1,3-diacetoxynonane (>90% syn) in high enantioselectivity (>99% ee) via a chemoenzymatic dynamic kinetic asymmetric transformation of a meso/dl mixture of 1,3-nonanediol.     

New Lignan,Benzofuran, and Sesquiterpene Derivatives from the Roots of Leontopodium alpinum and L. leontopodioides

Three new compounds, including a benzofuran, 1‐{(2R*,3S*)‐3‐(β‐D ‐glucopyranosyloxy)‐2,3‐dihydro‐2‐[1‐(hydroxymethyl)vinyl]‐1‐benzofuran‐5‐yl}ethanone ( 1 ), a lignan, [(2S,3R,4R)‐4‐(3,4‐dimethoxybenzyl)‐2‐(3,4‐dimethoxyphenyl)tetrahydrofuran‐3‐yl]methyl (2E)‐2‐methylbut‐2‐enoate ( 2 ), and a silphiperfolene‐type sesquiterpene, [(1S,2Z,3aS,5aS,6R,8aR)‐1,3a,4,5,5a,6,7,8‐octahydro‐1,3a,6‐trimethylcyclopenta[c]pentalen‐2‐yl]methyl acetate ( 3 ), together with the known coumarins obliquin ( 4 ) and its 5‐methoxy derivative 5 were isolated from the roots of Leontopodium alpinum. Another known coumarin derivative, 5‐hydroxyobliquin ( 6 ), was isolated from the roots of L. leontopodioides. The structures of these compounds were established by spectroscopic studies.     

New Triterpene Saponins from Herniaria glabra

Three new saponins 1–3 were isolated from Herniaria glabra by means of prep. HPLC and TLC. The structures were established mainly by a combination of 2D-NMR techniques (COSY, TOCSY, ROESY, HMQC, and HMBC) as O-α-L -rhamnopyranosyl-(1→4)-O-β-D -glucopyranosyl-(1-→6)-O-[β-D -glucopyranosyl-(1→2)]-β-D -glucopyranosyl medicagen-28-ate (herniaria saponin 4; 1 ), O-β-D -glucopyranosyl-(1→3)-O-α-L -rhamnopyranosyl-(1→2)-O-[β-(3R)-D -apiofuranosyl-(1→3)]-β-D -4-O-acetylfucopyranosyl 3-O-(β-D -glucuronopyranosyl)-16α-hydroxymedicagen-28-ate (herniaria saponin 5; 2 ), and O-α-L -rhamnopyranosyl-(1→4)-O-β-D -glucopyranosyl-(1→6)-O-[β-D -6-O-acetylglucopyra nosyl-(1→2)]-β-D -glucopyranosyl medicagen-28-ate (herniaria saponin 6; 3 ).     

The Role of the “Ligand Periphery” in the Coordination of Tripodal Triamidostannates(II) to Iridium: Simple Ligation vs. Cyclometallation

Reaction of the triamidostannates(II) MeSi{SiMe₂N(3,5‐xyl)}₃SnLi(OEt₂) ( 2a ) and MeSi{SiMe₂N(p‐tol)}₃SnLi(OEt₂) ( 2b ) with [IrCl(CO)(PPh₃)₂] gave the Ir^I‐Sn complex [MeSi{SiMe₂N(3,5‐xyl)}₃SnIr(PPh₃)₂(CO)] ( 3a ) for the former. In contrast, for the tolyl stannate CH‐activation occurred to give the Ir^III compound [MeSi{SiMe₂N(p‐tol)}₂{SiMe₂N(2‐C₆H₃‐4‐CH₃)}SnIr(H)(PPh₃)₂(CO)] ( 3b ). The latter is thus avoided by introduction of suitably placed substituents in the peripheral aryl groups of the triamidostannate ligand.