Analysis of plutonium in biological and environmental materials

A procedure for separation of plutonium from some biological and environmental materials has been tested in model and real conditions. The procedure involves a commonly used way of conversion of plutonium to oxidation state (IV) in nitric acid medium and sorption of Pu(IV) on a strongly basic anion exchanger from hydrochloric acid medium thus eliminating interference of²²⁸Th with the²³⁸Pu analysis.     

Combined cysteine and homocysteine quantitation in plasma by trap and release membrane introduction mass spectrometry

Recently, a new and efficient method for total homocysteine (tHcy) quantitation in plasma using trap and release membrane introduction mass spectrometry (T&R-MIMS) with a versatile removable direct introduction membrane probe (DIMP) was described [R. Haddad, M. A. Mendes, N. F. Hoehr and M. N. Eberlin, Analyst, 2001, 126, 1212]. Herein we report on the use of the DIMP-T&R-MIMS technique for total cysteine (tCys) quantitation; hence combined tCys and tHcy quantitation in plasma or serum can be achieved. The method employs Cys and Hcy derivatization with ethyl chloroformate (after disulfide bond reduction with dithiothreitol and protein precipitation with trichloroacetic acid), preconcentration in a capillary silicone membrane, and their thermal desorption to the gas phase inside the ion source region of a mass spectrometer, at a point exactly between the two ionization filaments. Thermal desorption uses the uniform heat radiation provided by the two ionization filaments. The analytes are then ionized by electron ionization and both Cys and Hcy are quantitated by mass spectrometry using selected ion monitoring. For tCys quantitation, good linearity and reproducibility was observed for concentrations ranging from 5 to 350 microM, recovery was near 95%, and the limit of detection (LOD) was of 2 microM. This LOD is well below the mean Cys concentration in plasma, and serum samples from a large group of healthy people showed a mean tCys concentration of 132 +/- 45 microM.     

Modellbetrachtungen zum Verständnis unerwarteter Eigenschaften der metalloiden Clusterverbindung [Ga84(N(SiMe3)2)20][Li6Br2(THF)20]·2Toluol

Towards the Understanding of the Unexpected Properties of the Metalloid Cluster Compound [Ga₈₄(N(SiMe₃)₂)₂₀][Li₆Br₂(THF)₂₀]·2Toluol In several short communications we have recently reported on the electrical and superconducting properties of the crystalline title compound 1 which contains anionic Ga₈₄R₂₀‐moieties. Here we present a collection of these results, complemented and interpreted by using DFT‐calculations on model clusters (Ga₈₄(NH₂)₂₀^?). These calculations allow a) a first insight into the dynamics of the Ga₈₄‐moieties (e.g. a rotation of the central Ga₂‐dumbbell) and thus an explanation of the temperature‐dependent Ga‐NMR‐spectra described recently, and b) estimations on the lattice energy of 1 and its resulting unexpected energetic stabilization compared to metallic gallium. A possible contribution of the cations in the electrical conduction mechanism of 1 can also be made feasible with model calculations. The basis for all the results presented is to be found in the “perfect” arrangement of nanoscopic Ga₈₄‐clusters in the crystal. This theoretically predicted condition for superconductivity in a “chain” of identical metal cluster molecules is a requirement which can hardly be realized by means of physical fabrication methods. Therefore, on the one hand the results presented here make for some disillusionment in the field of nanoscience, but on the other hand, especially in the field of synthetic chemistry, they present rewarding challenges for fundamental work in the future.     

Strain fields at contacts between small particles

Stress fields between interacting small particles ( approximately 100 nm) have been investigated by transmission electron microscopy. The background for these TEM observations is discussed in terms of adhesion stress fields (due to surface forces), the action of an applied point force, possibly magnetic, and dislocations or misfit strains due to an unfavorable matching of crystal lattices at the grain boundary. A further explanation might be sought along the line "squeezed-in oxide" which can be visualized as a coherent particle or a dislocation loop. Accompanying theoretical calculations have been performed and compared with the experimental results.     

Fabrication of superhydrophobic surfaces from binary colloidal assembly

In this work, superhydrophobic surfaces were derived from binary colloidal assemblies. CaCO(3)-loaded hydrogel spheres and silica or polystyrene ones were consecutively dip-coated on silicon wafers. The former assemblies were recruited as templates for the latter self-assembly. Due to the hydrophilicity difference between silicon wafers and CaCO(3)-loaded hydrogel spheres, the region selective localization of silica or polystyrene spheres leads to irregular binary structures with a hierarchical roughness. The subsequent modification with low surface energy molecules yields a superhydrophobic surface. The heating treatment may largely enhance the mechanical stability of the resulting binary structures, which allows regeneration of the surface superhydrophobicity, providing a good durability in practice.     

Photoelectron spectroscopy of isolated multiply negatively charged oligonucleotides

Ultraviolet photoelectron spectroscopy in an ion beam was used to investigate the electronic properties of isolated DNA oligonucleotides [dA(5)-4H](4-) and [dT(5)-4H](4-), carrying four excess negative charges. We find the fourth adiabatic electron affinity to be slightly negative for [dA(5)-4H](4-), while it is positive for [dT(5)-4H](4-). This implies a significant influence of the base composition on energetics, which is in turn relevant for analytic applications and also for charge transport properties.     

Biologically active compounds through catalysis: efficient synthesis of N-(heteroarylcarbonyl)-N'-(arylalkyl)piperazines

A practical route for the synthesis of new biologically active 5-HT(2 A) receptor antagonists has been developed. In only three catalytic steps, this class of central nervous system (CNS) active compounds can be synthesized efficiently with high diversity. As the initial step, an anti-Markovnikov addition of amines to styrenes provides an easy route to N-(arylalkyl)piperazines, which constitute the core structure of the active molecules. Here, base-catalyzed hydroamination reactions of styrenes with benzylated piperazine proceeded in high yield even at room temperature. After catalytic debenzylation, the free amines were successfully carbonylated with different aromatic and heteroaromatic halides and carbon monoxide to yield the desired compounds in good to excellent yields. The two key reactions, base-catalyzed hydroamination of styrenes and palladium-catalyzed aminocarbonylation of haloarenes/heterocycles, showed tolerance towards various functional groups, thereby demonstrating the potential to synthesize a wide variety of new derivatives of this promising class of pharmaceuticals.     

A validated gas chromatographic method for the evaluation of enzymatic enantioselectivity in kinetic resolution applications

An enantioselective gas chromatography (GC) method has been developed and validated for determination of the enantiomers of citronellol in kinetic resolution experiments. S-(-)-beta-Citronellol is a precursor of rose oxide. After solid-phase extraction (SPE) with ethyl acetate, the enantiomers of R-(+)-beta-citronellol and S-(-)-beta-citronellol and their corresponding acetate- and butyrate esters were separated through enantioselective GC respectively. The method was validated and found to be reproducible, specific, accurate, and precise. Analyte recoveries and detection limits were also determined. The applicability of this method was shown in a kinetic resolution experiment using lipase A of Bacillus subtilis.     

Übergangsmetall-methylen-komplexe: LVI. Organoruthenium-komplexe mit offenkettigen und carbocyclischen alkyliden-brücken: Synthese,konstitution, isomerie,protonierung und thermolytischer abbau

The eighteen new μ-alkylidene ruthenium complexes 5a–r and 5t are very easily and cleanly obtained along the diazoalkane or the hydrazone routes that involve treatment of the dinuclear, metal-metal doubly bonded precursor compound [(η⁵-C₅H₅)Ru(μ-NO)]₂ (3) either with the diazoalkanes oxidizing agent (e.g., MnO₂), with the respective hydrazones. Similarly, sulfur dioxide adds cleanly to the RuRu double bond of 3, thus giving the complex (μ-SO₂)[(η⁵-C₅H₅)Ru(NO)]₂ (5s). Regardless of the nature of the carbene bridge ligands, the dimetallacyclopropanes exhibit, in contrast to their iron analogues, exclusively terminal nitrosyl ligands. cis/trans-Isomerism with predominating amounts of the trans-isomers is observed for the derivatives that display unsymmetrically substituted carbene bridges.Treatment of the μ-methylene- and μ-ethylidene complexes (μ-CH₂)[(η⁵-C₅H₅)Ru(NO)]₂ (5a) and (μ-CHCH₃)[(η⁵-C tetrafluoroboric acid or trifluoromethanesulfonic acid in diethyl ether yields, at ambient temperature, quantitatively the ionic complexes 6a,b and 7a,b, respectively, which were shown by ¹H NMR spectroscopy to contain metal-metal bridging hydrogen functionalities. The reaction of hydrogen bromide with 5a under the same conditions gives the neutral bromo(methyl) complex 6d. This latter compound results from the isolable ionic intermediate of composition [(μ-CH₂)(μ-H){(η⁵C₅H₅)Ru(NO)}₂]⁺Br^? (6c), which reaction stems from the nucleophilicity of the halide ion present in 6c.     

Die Kristallstruktur des Natriumorthogermanats,Na4GeO4

The crystal structure of the title compound has been determined from single crystal X-ray diffraction data and refined toR=0.125. The unit cell is triclinic, space group P, (No. 2),a=5.688(1),b=5.701(1),c=8.583(1) Å, =81.32(1), =71.50(1), =67.95(1)° andZ=2. The structure consists of isolated [GeO₄] tetrahedra linked together by four- and five-coordinate sodium atoms. Na₄GeO₄ is isostructural with Na₄CoO₄ (which has been described to be non-centrosymmetric and for which a centrosymmetric model is presented), K₄GeO₄, K₄SnO₄ and K₄PbO₄.