Electrodynamic Characteristics of Solid Solutions Pb(Fe1 – xScx)2/3W1/3O3 in a Broad Spectral Range

Physics of the Solid State - The methods of broadband dielectric spectroscopy are used to study the effect of substitution of Fe3+ by Sc3+ in Pb(Fe1 – xScx)2/3W1/3O3 solid...     

Quantification of the binding constant of copper(II) to the amyloid-beta peptide

The amyloid beta (A beta) peptide of Alzheimer's disease binds copper(II), and the peptide-bound metal may be a source of reactive oxygen species and neurotoxicity. To circumvent peptide aggregation and reduce redox activity, there is growing interest in using metal chelates as drug therapeutics for AD, whose design requires accurate data on the affinity of A beta peptides for copper(II). Reports on Cu2+ binding to A beta range from approximately 10(5) to approximately 10(9); these values' being obtained for different peptide lengths (1-16, 1-28, 1-40, 1-42) at varying pH. Herein, we report that Cu2+'s binding to A beta(1-40) at 37 degrees C occurs in a 1:1 stoichiometry with a pH-dependent binding constant: 1.1 (+/-0.2) x 10 (9) M (-1) and 2.4 (+/-0.2) x 10 (9) M(-1) at pH 7.2 and 7.4, respectively. Under identical conditions, A beta(1-16) reveals a comparable binding constant, confirming that this portion of the peptide is the binding region. Several previously reported values can be reconciled with the current measurement by careful consideration of thermodynamics associated with the presence of competing ligands used to solubilize copper.     

Chlorobiphenyl (PCB) composition of extracts of subsurface soil, superficial dust and air from a contaminated landfill

Samples of 3 matrices (air, superficial dust and subsurface soil) from an aged PCB-containing landfill were extracted and the extracts refined for bioassay. Acetone:hexane extraction was modestly selected for non-planar compounds. Coplanar PCBs and PCDFs were enriched about 2-fold in the subsequent benzene:methylene chloride extracts of the soil. Extract refinement with Florisil slurry and alumina column chromatography did not appreciably change the composition of the extracts. CB 28 (2,4,4′-triCB) dominated in all extracts. The congener composition of soil and air were surprisingly similar, being enriched in tri- and tetraCBs while dust retained higher proportions of congeners with 4 and 5 chlorines. It is postulated that anaerobic dechlorination in the moist subsurface soil depleted the higher chlorinated congeners; more volatile congeners escaped into the atmosphere while moderately chlorinated congeners were trapped in the superficial dust and debris. The refined extracts represent distinct compositions of environmental PCB mixtures suitable for bioassay. Received: 21 November 1995 / Revised: 9 April 1996 / Accepted: 14 April 1996     

Dual reactivity of N-heterocyclic carbenes towards copper(II) salts

Complexes of N-heterocyclic carbenes (NHCs) with copper(II) halogenides are unstable. Upon formation, these complexes decompose to give haloamidinium salts. Contrastingly, O-substituted copper(II) NHC complexes are fairly stable. A series of new five-, six- and seven-membered ring NHC complexes of Cu(OAc)(2) have been synthesised and characterised in the solid state.     

X-ray diffraction study of ceramic samples of SrCu1/3Nb1/3O3

Ceramic samples of SrCu_1/3Nb_2/3O₃, obtained either by slow cooling or by quenching from 1200°C, were studied by X-ray diffraction using the Rietveld method. The slow-cooled SrCu_1/3Nb_2/3O₃ samples contain one phase with a perovskite structure (R _B = 4.14%, tetragonal crystal symmetry, space group P4/mmm, Z = 1, a = 3.935 ?, c = 4.124 ?), its diffraction peaks being considerably broadened. The samples quenched from 1200°C contain two SrCu_1/3Nb_2/3O₃ forms with a perovskite structure: one of them is oxygen deficient (R _B = 3.37%, tetragonal crystal symmetry, space group P4/mmm, Z = 1, a = 3.9687 ?, c = 4.0718 ?), and the other has no oxygen deficiency (R _B = 3.20%, tetragonal crystal symmetry, space group P4/mmm, Z = 1, a = 3.95307 ?, c = 4.08935 ?).     

New high-temperature superconductor Bi4Sr4CaCu3O14+x . Crystal structure and defectiveness of cationic sublattice

Crystal structure of a new high-temperature superconductor Bi₄Sr₄CaCu₃O_14+x is determined (AgK_α, a=5.411(2), b=5.417(3), c=27.75(1) Å, space group Pbmm, R=8.80%, R_w=11.92%, 248 F(hkl)). The structure has two types of copper-oxygen layers with diverse coordination of oxygen to Cu. The separate BiO layers of the (BiO)₂ double layer differ in structure. Percolation methods are used to relate superconductive properties of the new superconductor to defectiveness of its cationic sublattice.