Pseudogap and precursor superconductivity in underdoped cuprate high temperature superconductors: A far-infrared ellipsometry study

With the technique of infrared ellipsometry we performed a detailed study of the temperature- and doping dependence of the c-axis response of a series of YBa₂Cu₃O_7−δ single crystals. In particular, we explored the anomalous electronic properties at temperatures above the macroscopic superconducting transition temperature, T _c, whose conflicting explanations range from a precursor superconducting state to electronic correlations that compete with superconductivity. We show that the c-axis spectra provide evidence that both kinds of correlations are present and that their contributions can be disentangled based on an analysis with a so-called multilayer-model. We find that the onset temperature, T ^*, and the energy scale, Δ_PG, of the competing pseudogap increase rapidly towards the underdoped side whereas they vanish on the overdoped side. In addition, we provide evidence that in a strongly underdoped sample the precursor superconducting correlations develop below an onset temperature, T ^ons, that is considerably lower than T ^* but still much higher than T _c.     

A Critical Review of the Electrocatalysis Reported at C60 Modified Electrodes

Electrodes modified with C₆₀ have been reported to be electrocatalytic for a range of analytical targets. In this review we critically overview the recent explosion of interest in C₆₀ modified electrodes.     

Density functional theory calculations of pentabromidooxomolybdate(V) anion with 2,2′-bipyridinium cation: Comparison between the calculated geometry and the crystal structure determination at 293 and 90 K

Mo^V ion complex in the [MoOBr₅]²⁻ anion is crystallized with 2,2′-bipyridinium dication. Mo^V is in a distorted octahedral environment at both 293 and 90 K, and is displaced from the plane of the four bromido ligands, with the Mo–Br_trans to the oxo ligand being significantly longer than the other equatorial bromido ligands. Extensive hydrogen bonding of the types (C,N)–H···(Br,O) and offset face-to-face interactions leading to a supramolecular crystal lattice that engineers the entrapment of [MoOBr₅]²⁻ anion. This is further stabilized by the Br···Br intermolecular interactions that hold the anionic network. The anisotropic cell contraction results in significant changes in nonbonding contacts. DFT calculations at the B3LYP level of theory using the pseudo potentials of “LANL2DZ” and “LANL2TZ (Mo)/6-31G*(C, N, Br, H)”, Slater Type Orbital (STO) and 3-21G basis sets were carried out. DFT calculations results from different basis sets were compared, and results show that the optimized calculated geometry is relatively consistent with the X-ray data and hence the observed structure for the complex is indeed possible. HOMO and LUMO orbitals and the energy gag were also determined.     

Dimorphamides A – C,New Polyphenolic Amides from Atriplex dimorphostagia

Dimorphamides A–C ( 1 – 3 , resp.), three new polyphenolic amides, have been isolated from the BuOH‐soluble fraction of the whole plant of Atriplex dimorphostagia, along with two known compounds, thymidine and N‐[(E)‐feruloyl]tyramine. Their structures have been determined on the basis of spectral studies.     

Physiochemical properties and novel biological applications of Callistemon viminalis‐mediated α‐Cr2O3 nanoparticles

We report an eco‐friendly synthesis of α‐Cr₂O₃ nanoparticles (NPs) using Callistemon viminalis (Bottle Brush) flower extracts as an efficient reducing and capping agent. NPs of sizes 15 nm and 17 nm were synthesized by annealing them at 400°C and 500°C, respectively, which were characterized by X‐ray diffraction, UV–Vis, Fourier transform‐infrared, high‐resolution‐transmission electron microscopy/scanning electron microscopy, SAED, energy‐dispersive X‐ray spectroscopy and SQUID. Microplate‐based assay was used for examining antibacterial potential against 12 pathogenic bacterial strains, and their minimum inhibitory concentrations were calculated. MTT cytotoxic assay was accomplished on Leishmania tropica amastigotes and promastigotes, which revealed IC₅₀ values of 44 μg/ml and 10.56 μg/ml, respectively. An IC₅₀ value of 46.32 μg/ml was obtained for HepG2 cancer cells. Enzyme inhibition studies indicated good acetylcholinesterase, moderate butyrylcholinesterase and low alpha‐glucosidase inhibition. Hemolytic assay indicated hemocompatibility at low concentration. In addition, good DPPH radical scavenging and moderate reducing power and total antioxidant potential was revealed by α‐Cr₂O₃ NPs.     

A New Method for the Oxybromination of Aromatic Compounds with Copper(II)bromide and Potassium Dichromate

Abstract

A new and mild method for oxybromination of aromatic compounds with CuBr ₂ and K ₂ Cr ₂ O ₇ in HOAC is reported.     

Deposition of crystalline copper films from tetranuclear copper (II) complexes without application of reducing atmosphere

Crystalline copper films were deposited by aerosol‐assisted chemical vapor deposition (AACVD) in the absence of hydrogen from two newly synthesized complexes [Cu(deae)(TFA)]₄·1.25THF ( 1 ) and [Cu₄(OAc)₆(bdmap)₂(H₂O)₂]·4H₂O ( 2 ) [deae = N, N‐diethylaminoethanolate, TFA = trifloroacetate, OAc = acetate and bdmap = 1,3‐bis(dimethylamino)‐2‐propanolato]. These precursors were prepared in high yield using mixed ligands and crystallized in tetragonal and triclinic crystal systems with space groups 14₁/a and P ? 1. Complexes 1 and 2 thermally decomposed at 290 and 250 °C, respectively, to yield copper films which were characterized by SEM/EDX for their morphology and composition and PXRD for their crystallinity and phase. These films have smooth morphologies with particle sizes within the range of 0.3–0.6 µm and may find applications in fabrication of ultralarge‐scale integrated circuits. Copyright © 2010 John Wiley & Sons, Ltd.