Novel bis (crown ether)-based potassium sensor for biological applications

Based on structure-selectivity studies on bis-benzo-crown ether derivatives, 2,2-bis[3,4-(15-crown-5)-2-nitrophenylcarbamoxymethyl]tetradecane (BME-44) was designed and synthesized. The performance characteristics of this new, highly lipophilic ionophore of the group of bis-nitrobenzo-15-crown-5 derivatives with urethane linkage when used in liquid membrane electrodes are evaluated with special regard to the requirements of biological and clinical applications. Potentiometric steady-state and flow-through dynamic data are presented to prove the sensor capabilities for clinical and physiological potassium determinations.Dedicated to Professor W. Simon on the occasion of his 60th birthday     

Solid-state NMR spectroscopic methods in chemistry

Over the last decades, NMR spectroscopy has grown into an indispensable tool for chemical analysis, structure determination, and the study of dynamics in organic, inorganic, and biological systems. It is commonly used for a wide range of applications from the characterization of synthetic products to the study of molecular structures of systems such as catalysts, polymers, and proteins. Although most NMR experiments are performed on liquid-state samples, solid-state NMR is rapidly emerging as a powerful method for the study of solid samples and materials. This Review outlines some of the developments of solid-state NMR spectroscopy, including techniques such as cross-polarization, magic-angle spinning, multiple-pulse sequences, homo- and heteronuclear decoupling and recoupling techniques, multiple-quantum spectroscopy, and dynamic angle spinning, as well as their applications to structure determination. Modern solid-state NMR spectroscopic techniques not only produce spectra with a resolution close to that of liquid-state spectra, but also capitalize on anisotropic interactions, which are often unavailable for liquid samples. With this background, the future of solid-state NMR spectroscopy in chemistry appears to be promising, indeed.     

Chromogenic calix[4]arene as ionophore for potentiometric and optical sensors

Chromogenic calix[4]arene derivative was synthesized and tested as an ionophore for potentiometric and optical sensors. Distinct sodium selectivity was observed with this ionophore based, plasticized PVC membranes in potentiometric measurements suggesting their utility for biological applications. Optode membranes exhibited sodium sensitivity in the 5 x 10(-2) -10(-4)M concentration range. The optical sensitivity was improved by the use of an internal, lipophilic base (TDDA). The operation of the optical sensor is in accordance with the ion-exchange theory.     

Data for the gas-liquid chromatographic analysis of essential oils. Determination of the composition of the essential oil of Marjoram

Summary By identification of the essential oil component ‘cis-sabinene hydrate acetate’ of marjoram we demonstrate that the mass spectrum—furnish to the chemical composition and molecular configuration of compounds—can lead to incorrect qualitative identification if retention data are not taken into consideration. We studied also the temperature-dependence of the retention data of different compounds, and our measurements showed that because of the different temperature-dependence, a change in the temperature of the analysis results in a change in order of elution. The use of this phenomenon, originating from the change of the retention data, both increases the safety of qualitative identification and aids determination of the optimum measurement conditions in both isothermal and temperature-programmed modes of operation. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

Deposition precipitation for the preparation of carbon nanofiber supported nickel catalysts

Deposition precipitation of nickel hydroxide onto modified carbon nanofibers has been studied and compared to deposition onto silica. The carbon nanofiber support materials consisted of graphite-like material of the fishbone-type with a diameter of 20-50 nm and a specific surface area of 150 m2/g. Modification involved surface oxidation (CNF-O) optionally followed by partial reduction (CNF-OR) or thermal treatment (CNF-OT). Titration of the support materials showed the presence of 0.17 and 0.03 mmol/g carboxylic acid groups for CNF-O and CNF-OR, respectively. For the CNF-OT only basic groups were present. The deposition precipitation of 20 wt % nickel onto these supports has been studied by time dependent pH and nickel loading studies. With silica, nickel ion adsorption did not occur prior to nucleation of the nickel hydroxide phase at pH = 5.6. With CNF-O, nickel ion adsorption took place right from the start of the deposition process at pH = 3.5, and at pH = 5.6 already 4 wt % nickel was adsorbed. Nucleation of nickel hydroxide onto adsorbed nickel ion clusters proceeded subsequently. Characterization of the dried Ni/CNF-O samples with TEM and XRD showed well dispersed and thin (5 nm) platelets of nickel hydroxide adhering to the carbon nanofibers. After reduction at 773 K in hydrogen the Ni/CNF-O contained metallic nickel particles of 8 nm homogeneously distributed over the fibers. With CNF-OR and CNF-OT, precipitation of large platelets (> 500 nm) separate from the support took place. Clearly, the presence of carboxylic acid groups is essential to successfully deposit nickel hydroxide onto modified carbon nanofibers.     

Stereochemistry and 13C NMR investigation of 9-halotetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones

It was shown that the halogen atom occupies the quasi-axial position in the predominant conformer of the 9-halo derivatives of tetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones. When R³ = Me, the conformational equilibrium is determined by the latter substituent which is always quasi-axial. The effects of the methyl group and the halogen atoms on the ¹³C chemical shifts (SCS values) were used for the identification of cis and trans isomers. Interesting non additivity of substituent effects was found in derivatives bearing quasi-axial substituents at C-6 and C-9: and this was caused by the ring flattening.