Gallium-, Indium-Mangan- und Thallium-Rhenium-Carbonylverbindungen

Gallium-, Indium-Manganese-, and Thallium-Rhenium Carbonyl Compounds Compounds of type Na{Cl_4?nM[Mn(CO)₅]_n} (M ? Ga, In; n = 1, 2, 3) were prepared by reaction of the Lewis acids MCl₃ and NaMn(CO)₅. Instead of the sodium salts were obtained the compounds (C₃H₇CO₂)₂InMn(CO)₄L (Indium atom with the coordination number 5) from Indium(III) butyrate with two carboxylate groups bonded as chelate ligands and NaMn(CO)₄L [L ? CO, P(C₆H₅)₃] in the molar ratio 1:1. By reacting TlCl with NaRe(CO)₅ i.r. spectroscopic measurements of the solution pointed out the intermediate product TlRe(CO)₅, which was unstable against a disproportionation reaction into Tl and Tl[Re(CO)₅]₃. The last named compound delivered as a thermal decomposition product Re₂(CO)₈[μ-TlRe(CO)₅]₂. I.r. bands of the new compounds were assigned.     

Enzyme and microbial sensors for phosphate, phenols, pesticides and peroxides

Biosensors employing a biocatalyst on a different level of integration have been developed for monitoring environmental pollution. These probes range from laboratory specimen to commercial detectors applied to analyzers. Recent developments on amperometric enzyme and microbial biosensors are presented here. A monoenzymatic bulk-type carbon electrode is described for biosensing organic hydroperoxides in aqueous solutions; peroxidase is immobilized within the electrode body and the direct electron transfer between electrode and enzyme is measured. Both, reversible and irreversible inhibitors of acetylcholinesterase have been quantified by using a kinetically controlled acetylcholine enzyme sequence electrode. The inhibitory effect of pesticides such as butoxycarboxime, dimethoate, and trichlorfon could be quantified within 6 min in molar concentrations. Different multi-enzyme electrodes have been developed for the determination of inorganic phosphate. These sensors represent examples of sequentially acting enzymes in combination with enzymatic analyte recycling. Using this type of amplification nanomolar concentrations can be measured.     

Carbon-carbon and carbon-nitrogen coupling reactions catalyzed by palladium nanoparticles derived from a palladium substituted Keggin-type polyoxometalate

Palladium 15-20 nm particles stabilized by a Keggin-type polyoxometalate were prepared by reduction of K(5)PPdW(11)O(39) with H(2). The nanoparticles were shown to be effective catalysts for Suzuki-, Heck-, and Stille-type carbon-carbon coupling and carbon-nitrogen coupling reactions of bromoarenes in aqueous media. Chloroarenes were also reactive in reaction media without solvent. [reaction: see text]     

Über die Aufnahme von Blei und Wismut durch Glasoberflächen

Zusammenfassung Versuche über die Adsorption von Radioblei an Glas zeigen, daß aus wäßrigen Lösungen aufgenommene Bleiionen in zwei verschiedenen Zuständen am Glas vorliegen — einem lockeren Adsorptions-Zustand, der auf Ionenaustauschadsorption beruht, und einer festen, vorwiegend homöopolaren Bindung an das Glasnetzwerk. Weitere Versuche gaben Aufschluss über den Mechanismus der Aufnahme in die beiden Zustände. Die Messung der Adsorption und Desorption von Radioblei ist zur Untersuchung von Glasoberflächen geeignet: So ist es — wie durch Versuche an Natronglas und Quarzglas gezeigt wird —möglich, charakteristische Unterschiede zwischen den Oberflächen verschiedener Gläser festzustellen. Weiters erhält man für Glasproben gleicher Zusammensetzung Einblick in die chemische und thermische Vorgeschichte der Oberflächen. Schließlich liefert die Ablösung von Radioblei von Gläsern unter gewissen Bedingungen Aussagen über den Angriff von Lösungen auf das Glas. Auch Wismut kann an Glasoberflächen sehr fest gebunden werden.Herrn Prof. Dr.L. Ebert in Verehrung zum 60. Geburtstag gewidmet.     

A novel MCR of isocyanates, aldehydes, and dienophiles

[reaction: see text] A novel one-pot procedure for the three-component coupling reaction of isocyanates, aldehydes, and dienophiles (IAD reaction) has been developed. Condensation of isocyanates and aldehydes and subsequent Diels-Alder reactions with electron-deficient dienophiles furnishes endo-selective amino-substituted cyclohexenes in good yield.     

Interpretation of contact angle measurements on two different fluoropolymers for the determination of solid surface tension

Contact angle measurements with a large number of liquids on the semi-fluorinated acryl polymer EGC-1700 films are reported. The surface tension was determined to be gammasv=13.84 mJ/m2 from contact angles of octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane (DMCPS). Inertness of these two liquids makes them ideal for determination of surface tension of low-energy fluoropolymers. On the other hand, contact angles of many other liquids deviated somewhat from a smooth contact angle pattern that represents the EGC-1700 surface tension. It is argued that noninertness of the molecules of these liquids gives rise to specific interactions with the polymer film, causing the deviations. Furthermore, contact angles of a series of n-alkanes (n-hexane to n-hexadecane) showed systematic deviations from this curve, similar to the trend observed for n-alkanes/Teflon AF 1600 systems studied earlier. Adsorption of vapor of short-chain liquids onto the polymer film caused their contact angles to fall above the gammasv=13.84 mJ/m2 curve, and a parallel alignment of molecules of the long-chain n-alkanes in the vicinity of the solid was the explanation for the deviation of their contact angles below it. It is found that vapor adsorption effect is more significant in the case of Teflon AF 1600, while the alignment of liquid molecules close to the surface is more pronounced for EGC-1700.     

Validation of the extended simultaneous kinetics and ringdown model by measurements of the reaction NH2 + NO

The determination of rate constants for fast chemical reactions from nonexponential cavity ringdown profiles requires a consideration of the interfering laser bandwidth effect that arises if the line width of the ringdown probe laser exceeds the absorption line width of the detected species. The deconvolution of the kinetics and the bandwidth effect can be accomplished with the extended simultaneous kinetics and ringdown (eSKaR) model presented by Guo et al. (Guo, et al. Phys. Chem. Chem. Phys. 2003, 5, 4622). We present a detailed validation of this eSKaR model by a corresponding investigation of the well-known rate constant for the reaction NH2 + NO. Line profiles of the pulsed ringdown probe laser and the NH2 absorption line were determined from forward modeling of experimental ringdown profiles and verified by narrow-bandwidth laser absorption measurements. In addition, the rate constant for the title reaction was evaluated using the eSKaR model and also by means of a conventional pump-probe approach with variable time delays between the photolysis (pump) and ringdown (probe) laser pulses. The resulting room temperature rate constant for the NH2 + NO reaction, k1= (8.5 +/- 1.0) x 10(12) cm(3) mol(-1) s(-1), and the room temperature pressure broadening coefficient of NH2, = 2.27 GHz/bar, measured on the A2A1<-- X2B1 transition at wavelengths around lambda = 597 nm, were found to be in excellent agreement with the available literature data.