Determination of thorium isotopes in gas lantern mantles by alpha-spectrometry

A procedure for the determination of the three main isotopes of thorium in gas lantern mantles by alpha-spectrometry has been developed. The samples examined were dissolved in concentrated nitric acid and thorium was precipitated as hydroxide. Thorium was then dissolved in hydrochloric acid to be extracted into a TOPO solution, back-extracted with sulfuric acid, electrodeposited onto a steel disc and finally counted alpha-spectrometrically. The radiochemical recovery for thorium was 94% with a counting efficiency of 37%.     

Complete 1H and 13C NMR assignments of aurasperone A and fonsecinone A, two bis-naphthopyrones produced by Aspergillus aculeatus

Complete assignments of 1H and 13C NMR chemical shifts of the polyketides aurasperone A and fonsecinone A were made by means of nuclear Overhauser enhancement and heteronuclear NMR correlation experiments. These compounds were isolated for the first time from Aspergillus aculeatus, an endophytic fungus obtained from leaves of Melia azedarach(Meliaceae).     

Secondary ion mass spectrometric investigation of Au-based composites.

The electrodeposition of thick gold layers plays an important role both in traditional and high-tech productions, such as jewelry and microelectronics, respectively. In this work a secondary ion mass spectrometric study will be presented on Au co-deposits with (sub-)micrometric ceramic powders, in order to harden gold. Mass spectra are used to identify the components deposited, providing evidence of the additives and/or eventual contaminants introduced during electrolysis. Furthermore, analysis of ion depth profiles and the intensity distribution of ionic species along the film were studied.     

Non-oxo vanadium(IV) alkoxide chemistry: solid state structures, aggregation equilibria and thermochromic behaviour in solution

The reversible thermochromic behaviour of homoleptic [{V(OR)(4)}(n)] complexes in solution [R = Pr(i) (product I), Bu(s) (B(s)), Nep (N) and Cy (C)] is accounted for the existence of an aggregation equilibrium involving dimeric and monomeric species in which vanadium(iv) is respectively five- and four-coordinate. Bulky R groups such as Bu(t) and Pe(t) (tert-pentoxide) prevent aggregation and therefore give rise to exclusively mononuclear compounds (B(t) and P(t), respectively) that are not thermochromic. The complexes and their temperature-dependent interconversion were characterised by single crystal X-ray diffractometry, magnetic susceptibility measurements and electronic, FTIR and EPR spectroscopies in a wide temperature range. Equilibrium constants and enthalpy and entropy changes for the dimerization reactions have been determined and compared with literature data.     

Trypanocidal activity of oxoaporphine and pyrimidine-β-carboline alkaloids from the branches of Annona foetida Mart. (Annonaceae)

Phytochemical investigation of the branches of Annona foetida Mart. led to isolation from the CH(2)Cl(2) extract of four alkaloids: Atherospermidine (1), described for the first time in this species, liriodenine (2), O-methylmoschatoline (3), and annomontine (4). Their chemical structures were established on the basis of spectroscopic data from IR, MS, NMR (1D and 2D), and comparison with the literature. Compounds 2-4 showed potent trypanocidal effect when evaluated against epimastigote and trypomastigote forms of Trypanosoma cruzi.     

Full NMR analysis of annomontine, methoxy- annomontine and N-hydroxyannomontine pyrimidine-beta-carboline alkaloids

Using modern NMR techniques, including 1H--13C and 1H--15N heteronuclear correlation experiments, the complete and unambiguous 1H, 13C, and 15N NMR chemical shift assignments of annomontine, methoxyannomontine, and N-hydroxyannomontine pyrimidine-beta-carboline alkaloids were performed. All 1H--1H scalar coupling constants and signal multiplicities were determined, and all nOe observations were also included.     

Secondary ion mass spectrometric investigation on ruthenium oxide systems: a comparison between poly- and nanocrystalline deposits

The influence of different RuO(2) crystallite sizes was investigated by secondary ion mass spectrometry (SIMS) on the oxide deposited on various support materials (Ni, Ti, Al(2)O(3), oxidized Si(100)). In order to examine the effect of an oxidic environment on the film structure, RuO(2) 20%-TiO(2) 80% at. mixed oxide was deposited on Ti. The polycrystalline coatings were prepared by heating the Ru (and Ti)-containing solution dropped on the supports.1 RuO(2) nanocrystalline coatings were grown by chemical vapor deposition (CVD) from Ru(COD)(eta(3)-allyl)(2).2 The identification of mixed oxide clusters showed the higher reactivity of Ni and Al(2)O(3) over the other substrates. Diffusion and migration characteristics were observed to be influenced by the nature of the support. The results are complementary to those of a previous SIMS investigation.3 Copyright 2000 John Wiley & Sons, Ltd.     

Glucose sensors based on enzyme immobilization onto biocompatible membranes obtained by radiation-induced polymerization

Amperometric glucose biosensors based on glucose oxidase immobilized onto poly(2-hydroxyethylmethacrylate) membranes obtained by γ radiation-induced polymerization were constructed. In a threeelectrode configuration, smooth or platinized platinum electrodes with different shapes were used, in order to detect the amount of hydrogen peroxide produced in the glucose oxidation. A saturated calomel electrode and a platinum foil were used as a reference and counterelectrode, respectively. The biocompatible obtained sensors were characterized as regards the temperature effect, the response, and lifetime. The determination of glucose in standard solutions was carried out, and linear calibration curves were obtained. Depending on the electrode configuration, the sensor had a response time of 1–4 min, and the measuring range extended from 5 × 10^?5 to 4 × 10^?3M.     

Determination of thorium isotopes in bastnaesite ores

A procedure for the determination of alpha-emitting thorium isotopes in bastnaesite ores has been developed. The refractory sample was completely decomposed by potassium fluoride fusion in a platinum crucible followed by transposition to a pyrosulfate fusion. The pyrosulfate cake was dissolved in HCl and the resulting precipitate dissolved in DTPA solution; thorium was coprecipitated as hydroxide using cerium present in bastnaesite as natural carrier. Thorium was then extracted into a TOPO solution, separated by using Dowex 1-X8 for anionic exchange, electrodeposited and finally analyzed by alpha-spectrometry. Thorium was also determined spectrophotometrically using Arsenazo as a colorimetric reagent. The thorium yield of the above discussed chemical procedure is more than 85%.