Preparation of Fine Spherical Particles of Precursors for Yttrium Barium Cuprate Superconductors via thermal decomposition of triethylene glycol solution

A new synthesis route of fine spherical precursor powders for YBaCuO superconducters via thermal decomposition of triethylene complexes has been developed. YBa₂Cu₃O_7–δ and YBa₂Cu₃O₈ ceramics with sharp superconducting transitions can be obtained in one step from the 1 μm grained precursor powder.     

Protein abundance quantification in embryonic stem cells using incomplete metabolic labelling with 15N amino acids,matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry,and analysis of relative isotopologue abundances of peptides

An isotope dilution method for protein quantification is presented in the context of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) and mass fingerprinting experiments, revealing an unappreciated high reproducibility and accuracy of relative peak intensity measurements. Labelled proteins were generated by growing cells in a medium containing (15)N-enriched amino acids, and were mixed with proteins of natural isotopic composition from control cells in ratios of approximately 0:1, 1:7, 1:2, 2:1, 7:1, and 1:0 (labelled/unlabelled). Mixtures were separated by two-dimensional gel electrophoresis and analysed by MALDI-TOFMS using typical experimental conditions. A linear relationship is demonstrated between the relative isotopologue abundances (RIA values) for particular peaks in the isotopic distribution of tryptic peptide fragments of the proteins, and the mole fractions of labelled proteins in the mixture. Analysis of RIA values (ARIA quantification) for peptides of six typical silver-stained protein spots for the various mixtures could reproduce the experimentally contrived ratios with approximate errors between 4% (2:1 mixture) and about 18% (1:7 mixture). A consideration of error and its propagation is discussed. ARIA does not require complete separation of the isotope patterns of labelled and unlabelled peptides, and is therefore advantageous in combination with all kinds of labelling experiments in biological systems, because it is compatible with minimal metabolic incorporation of labelling reagent. Simulations indicate that the minimum required (15)N enrichment of the total amino acid pool sufficient for ARIA is less than 4%. In an accompanying paper in this issue, we apply ARIA to proteins differentially labelled with isotope-coded alkylation reagents.     

Konzentrierung von spurenelementen durch extraktion mit aliphatischen monokarbonsäuren

Factors affecting the separation of iron(III) by solvent-extraction with n-caprylic acid have been investigated. The extraction of iron(III) is diminished more in the presence of sulphate than of chloride, owing to the formation of complexes, while with aluminium salts, when compared with sodium salts, a salting-out effect predominates. Thermodynamic analysis of the change in distribution coefficient as a function of various concentration parameters has shown that the iron(III) is extracted as a trinuclear complex: the extractability is therefore better for larger amounts of iron, and less satisfactory for trace amounts. When sodium caprylate is used instead of the acid to avoid large pH changes when macro-amounts of iron are to be extracted, a substoichiometric amount must be added, otherwise all the metal ions will be extracted by a simple ion-exchange mechanism. Evidence is also presented for the formation of mixed complexes of iron with copper and with nickel: the degree of separation for these pairs of metals is therefore much less than would be predicted from the behaviour of the individual ions. Chromium(III) also forms a mixed complex with iron, but as its formation is kinetically inhibited, investigations under equilibrium conditions are difficult to realize. However, if the extractions are carried out quickly, with only short contact times, the separation of iron from chromium is hardly affected.     

XPS depth profiling investigations on La2Zr2O7 layers prepared by chemical solution deposition

La₂Zr₂O₇ (LZO) layers have been recently investigated as potential buffer layers for superconducting YBa₂Cu₃O_7–x coated conductors deposited on Ni tapes. Chemical solution deposition was used for LZO layer preparation. X-ray photoelectron spectroscopy (XPS) depth profiling is demonstrated to be an important method for layer characterization in addition to X-ray diffraction techniques. XPS measurements revealed layers that are homogeneous in depth, very smooth, and have no significant impurities. A slight difference to the nominal La:Zr stoichimetry is discussed in combination with structural defects that are suspected from spectral changes during ion sputtering.     

Derivative potentiometric stripping analysis with a thin film of mercury on a glassy carbon electrode

Derivative potentiometric stripping analysis is based on the pre-concentration of metal analytes in a thin film of mercury on a glassy carbon electrode and subsequent measurement of the electrode potential subject to controlled transport of oxidant to the electrode surface. The mechanism for the stripping process with respect to oxidant concentration, electrode rotation rate and instrument parameters is discussed, together with analytical results and applications.     

Potentiometric stripping analysis for lead in urine

Potentiometric stripping analysis is based on the preconcentration of analytes by means of potentiostatic reduction and amalgamation at a thin-film mercury electrode. After preconcentration, the potentiostatic circuitry is disconnected and the amalgamated metals are oxidized either by mercury(II) ions or by dissolved oxygen. Lead can be determined in acidified urine samples by potentiometric stripping analysis after the addition of Triton X-100. In deaerated samples the detection limit is 1 μg l^?1, and in non-deaerated samples 12 μg l^t-1, the preconcentration time being 16 min.     

Electrochemical deposition of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> for thermoelectric microdevices

The electrolyses of solutions of bismuth oxide and tellurium oxide in nitric acid with molar ratios of Bi:Te=3:3–4:3 lead to cathodic deposits of films of bismuth telluride (Bi₂Te₃), an n-type semiconductor. Current densities of 2–5 mA/cm² were applied. Voltammetric investigations showed that Bi₂Te₃ deposition occurred at potentials more negative than −0.125 V (Ag/AgCl, 3 M KCl). The deposit was identified as bismuth telluride (γ-phase) by X-ray analysis. Hall-effect measurements verified the n-type semiconducting behaviour. The films can be deposited in microstructures for thermoelectric microdevices like thermoelectric batteries or thermoelectric sensors.     

Flow potentiometric stripping analysis for mercury(II)

The optimum experimental conditions, with respect to sample and stripping solution composition, in computerised flow potentiometric stripping analysis for mercury(II) with a gold working electrode are described. When pre-electrolysis -was done in a sample to which ammonia and iodide had been added and stripping was done in an acidified bromide solution containing chromium(VI), a detection limit of 2 nM (0.4 μg kg^-1) was obtained after 90 s of pre-electrolysis, the dynamic range being almost three decades. Copper(II) interfered when present in a 1000-fold excess and silver(I) when present in a 5-fold excess over mercury(II).     

Syntheses of Phencyclone Analogues. Applications for NMR Studies of Hindered Rotations and Magnetic Anisotropy in Crowded Diels–Alder Adducts

Undergraduate organic chemistry special laboratory projects based upon the synthesis of phencyclone, 1 (a potent Diels-Alder diene), and the preparation of a series of highly hindered Diels-Alder adducts of the phencyclone, were described earlier. Details of the synthesis of an analogue of 1 are presented here as an extension of these projects. The analogue, 3,6-dibromophencyclone, 2, and adducts from a wide range of dienophiles, can be prepared by undergraduate organic chemistry students. These adducts (from 1 or 2) are eminently suitable for student characterization by NMR to examine aspects of hindered rotation, magnetic anisotropy, and dynamic NMR spectroscopy, using modern one- and two-dimensional multinuclear methods with a medium-field instrument (7 T), to observe ¹H, ¹³C, and ¹⁹F. Use of 2 effectively doubles the range of potential target compounds for students. The Diels-Alder adducts (and their precursors) have been studied by molecular modeling methods. This present paper describes the reaction of 2 with 4, the dienophile N-(4-dimethylamino-3,5-dinitrophenyl)maleimide (Tuppys maleimide), to form the adduct 5. Compound 5 has been well-characterized by 1D and 2D ¹H and ¹³C NMR, and is illustrative of the wide range of adducts that can be made from 2 by students. The structure of 5, as determined by geometry optimization at the semiempirical (AM-1) level, is included here.