Properties of cerium-zirconium mixed oxides partially substituted by neodymium: Comparison with Zr-Ce-Pr-O ternary oxides

CeO₂ doped with praseodymium, neodymium and/or zirconium atoms were prepared by coprecipitation and by the sol-gel method. Structural properties were investigated by in situ XRD and Raman spectroscopy while oxygen storage capacity (OSC) was measured by transient CO oxidation. All the compounds, except pure Nd₂O₃, have a fluorite-type structure as well as a Raman band at 560 cm⁻¹ characteristic of the oxygen vacancies involving non-stoichiometric oxides. The lattice parameter under hydrogen, being dependent on the temperature, revealed two reduction mechanisms: one at a low temperature at the surface and another at a high temperature in the bulk. Ce-Nd binary oxides show a strong tendency towards crystallite aggregation, which reduces accessibility to gases and OSC properties. Zirconium improves the thermal resistance to sintering of both Ce-Nd and Ce-Pr oxides. The Zr-Ce-Pr-O followed by Zr-Ce-Nd-O compounds displaying high oxygen mobility at a low temperature, appear to be very promising for practical applications such as OSC materials.     

Interpretation of toroidal current and loop voltage temporal evolution during RF-current drive experiment on the T-7 tokamak

A simple analytical model is developed and solved to describe time evolution of the loop voltage and toroidal current when RF and inductive current drive take place simultaneously. A relation for the real value of the RF driven current has been obtained under these conditions. Comparison with experimental data from T-7 tokamak allows to estimate the role of the skin effect during RF current drive.The authors would like to thank A. Ya. Kislov for the basic data on the T-7 tokamak transformer. They are also indebted to V. V. Parail and G.V. Pereverzev for many clarifying discussions.     

Efficiency of decomposition procedures for the determination of some elements in soils by atomic spectroscopic methods

Nine decomposition procedures for soil samples, such as via acid mixtures and fusion in open systems and microwave and autoclave dissolution (in closed systems under elevated temperature and pressure) were assessed using certified soil reference materials. The determination of various elements in solutions was performed by FAAS and ICP-OES and the results were compared with certified values and with direct current arc OES analysis. Received: 3 March 1997 / Revised: 30 May 1997 / Accepted: 3 June 1997     

Novel estradiol derivatives labeled with Ru,W, and Co complexes. Influence on hormone-receptor affinity of several organometallic groups at the 17 alpha position

In order to elucidate the extent to which recognition of the estrogen receptor is influenced by addition of an organometallic substituent at the 17 alpha position, modification of 17 beta-estradiol at this position was carried out by using the organometallic groups -C identical to C(eta 5-C5H4)RuCp, CH2-(eta 5-C5H4)RuCp, -C identical to C-(eta 5-C5H4)-W(CO)3(Me), -(C identical to CCHO)Co2(CO)6, and -(C identical to CCH2OH)Co2(CO)6. The relative binding affinity (RBA) values for estradiol receptor alpha showed that recognition was good (RBA between 20 and 13.5%) when the organometallic moiety was attached at the end of a rigid alkyne spacer. However, the affinity of the modified hormone for the receptor was severely reduced (RBA = 1%) for a substituent such as -CH2-(eta 5-C5H4)RuCP, in which the spacer is reduced to a single flexible sp3 carbon atom, allowing the organometallic moiety greater freedom of movement around the attachment point. The RBA values found were in agreement with results obtained from a molecular-modeling study in which 5, an organometallic hormone with a rigid spacer, or 7, a molecule with a flexible spacer, was inserted into the cavity of the recently characterized Ligand-Binding Domain of estrogen receptor alpha.     

Single-phase and gram-scale routes toward nearly monodisperse Au and other noble metal nanocrystals

Single-phase approaches are introduced for the synthesis of nearly monodisperse Au and other noble metal nanocrystals. The new approaches possess all the advantages of the popular Brust method. With weak ligands or surfactants for the metal ions, the control of the size and size distribution of the nanocrystals in synthesis in the size range between 1 and 15 nm was achieved via maintaining balanced nucleation and growth by tuning the activities of the metal precursors and reducing reagents. Because only weak ligands are employed in the new synthetic schemes, surface modification and functionalization of the resulting nanocrystals can be readily carried out.     

Titanocene(III) mediated radical cyclization of α-bromo carbonyl compounds: synthesis of tri-substituted tetrahydrofurans

A novel and efficient methodology has been developed for the construction of synthetically important tri-substituted tetrahydrofuran derivatives from bromo-alkenes and bromo-alkynes by radical cyclization reactions using the radical initiator Cp₂TiCl, generated in situ from commercially available titanocene dichloride and Zn dust in tetrahydrofuran under argon.     

Comparison of zirconia- and silica-based reversed stationary phases for separation of enkephalins

In this study, the separation of biologically active peptides on two zirconia-based phases, polybutadiene (PBD)-ZrO2 and polystyrene (PS)-ZrO2, and a silica-based phase C18 was compared. Basic differences in interactions on both types of phases led to quite different selectivity. The retention characteristics were investigated in detail using a variety of organic modifiers, buffers, and temperatures. These parameters affected retention, separation efficiency, resolution and symmetry of peaks. Separation systems consisting of Discovery PBD-Zr column and mobile phase composed of a mixture of acetonitrile and phosphate buffer, pH 2.0 (45:55, v/v) at 70 degrees C and Discovery PS-Zr with acetonitrile and phosphate buffer, pH 3.5 in the same (v/v) ratio at 40 degrees C were suitable for a good resolution of enkephalin related peptides. Mobile phase composed of acetonitrile and phosphate buffer, pH 5.0 (22:78, v/v) was appropriate for separation of enkephalins on Supelcosil C18 stationary phase.     

Radical promoted Wagner-Meerwein-type rearrangement of epoxides in camphoric systems using a Ti(III) radical source

[Chemical reaction: see text] A radical based Wagner-Meerwein-type rearrangement has been observed in camphoric systems. The radical was generated from the epoxide using Cp2TiCl as the radical source. The radical initiator Cp2TiCl was prepared in situ from commercially available Cp2TiCl2 and Zn dust in THF under argon.     

High-performance liquid chromatographic separation and dual competitive binding assay of corrinoids in biological material

Corrinoids were extracted with hot ethanol from human plasma and faeces and separated by high-performance liquid chromatography. The corrinoids (cobalamin and cobalamin analogues) were quantified in the eluted fractions by a dual radioisotope assay using as binders intrinsic factor and haptocorrin to detect cobalamin and total corrinoids, respectively. Recoveries ranged from 37.7 +/- 5.1% for hydroxycobalamin to 75.0 +/- 9.1% for cyanocobalamin. In plasma, the main forms of cobalamin were the coenzymes methylcobalamin and 5'-deoxyadenosylcobalamin (32.1 +/- 13.4 and 28.4 +/- 12.3%, respectively, of total corrinoids). The cobalamin analogue fraction of plasma was eluted with a retention time close to that of cobinamide and of deoxyadenosylcobalamin. In the faeces, most of the corrinoids separated were detected better by the haptocorrin assay than by the intrinsic factor assay. One corrinoid peak was eluted with the same retention time as cobinamide. This peak was detected by haptocorrin assay but not by intrinsic factor assay. It could therefore correspond to cobinamide.     

Estimation scheme for level-dependent uncertainty of analytical result: application for determination of 1-hydroxypyrene in urine

The estimation scheme of uncertainty of determination of 1-hydroxypyrene (1-OHP) in urine was developed analysing the main stages of the analytical procedure: (1) preparation of 1-OHP standards, (2) creation of the calibration curve for the high performance liquid chromatography (HPLC) analysis method with the evaluation of recovery, (3) measuring procedure of aliquot of urine, (4) adjusting the pH of aliquot and hydrolysis with enzyme, (5) solid phase extraction, (6) concentration of the extract, (7) injection of the extract to chromatograph and analysing by the HPLC method, (8) calculation of 1-OHP mass from the calibration curve, (9) calculation of 1-OHP concentration in urine. The evaluation of the uncertainty is based on quantification of individual components. Combined uncertainty was calculated using the law of propagation of uncertainties according to the EURACHEM/CITAC guidelines. Level dependence of the uncertainty arises from the calibration curve. The limits of detection and quantification were found to be equal to 0.03 and 0.1 ng/mL, respectively. The calculated expanded level-dependent uncertainty covers 47–27–25% within the concentration range 0.03–0.1–0.4 ng/mL with the materials and equipment used. These parameters could easily be recalculated according to the proposed scheme if there are some changes in the analysis procedure.