Impurity-induced local magnetism and density of states in the superconducting state of YBa2Cu3O7

17O NMR is used to probe the local influence of nonmagnetic Zn and magnetic Ni impurities in the superconducting state of optimally doped high TC YBa2Cu3O7. Zn and Ni induce a staggered paramagnetic polarization, similar to that evidenced above TC, with a typical extension xi=3 cell units for Zn and xi>or=3 for Ni. In addition, Zn is observed to induce a local density of states near the Fermi energy in its neighborhood, which also decays over about 3 cell units. Its magnitude decreases sharply with increasing temperature. This allows direct comparison with the STM observations done in BiSCCO.     

Controlling the biological effects of spermine using a synthetic receptor

Polyamines play an important role in biology, yet their exact function in many processes is poorly understood. Artificial host molecules capable of sequestering polyamines could be useful tools for studying their cellular function. However, designing synthetic receptors with affinities sufficient to compete with biological polyamine receptors remains a huge challenge. Binding affinities of synthetic hosts are typically separated by a gap of several orders of magnitude from those of biomolecules. We now report that a dynamic combinatorial selection approach can deliver a synthetic receptor that bridges this gap. The selected receptor binds spermine with a dissociation constant of 22 nM, sufficient to remove it from its natural host DNA and reverse some of the biological effects of spermine on the nucleic acid. In low concentrations, spermine induces the formation of left-handed DNA, but upon addition of our receptor, the DNA reverts back to its right-handed form. NMR studies and computer simulations suggest that the spermine complex has the form of a pseudo-rotaxane. The spermine receptor is a promising lead for the development of therapeutics or molecular probes for elucidating spermine's role in cell biology.     

Observation of heteronuclear overhauser effects confirms the 15N-1H dipolar relaxation mechanism in a crystalline protein

The observation of proton to nitrogen-15 heteronuclear Overhauser effects in the microcrystalline protein Crh is used to confirm that the principal mechanism of relaxation of amide nitrogens is due to the fluctuation of the N-H dipolar couplings caused by N-H bond dynamics. Our observations reveal the central role of water as the main source of proton magnetization, and we provide an analysis of the different pathways that could lead to the observed results.     

Pressure-induced chemical decomposition and structural changes of boric acid

A combined synchrotron X-ray diffraction, Raman scattering, and infrared spectroscopy study of the pressure-induced changes in H(3)BO(3) to 10 GPa revealed a new high-pressure phase transition between 1 and 2 GPa followed by chemical decomposition into cubic HBO(2), ice-VI, and ice- VII at approximately 2GPa. The layered triclinic structure of H(3)BO(3) exhibits a highly anisotropic compression with maximum compression along the c direction, accompanied by a strong reduction of the interlayer spacing. The large volume variation and structural changes accompanying the decomposition suggest high activation energy. This yields a slow reaction kinetics at room temperature and a phase composition that is highly dependent on the specific pressure-time path followed by the sample. The combined results have been used to propose a mechanism for pressure-induced dehydration of H(3)BO(3) that implies a proton disorder in the system.     

Raman and infrared spectra of doped La8+xSr2−y(SiO4)6O2+δ compounds compared to the ab initio‐obtained spectroscopic characteristics of fully stoichiometric La8Sr2(SiO4)6O2

Vibrational spectroscopy data were used to gain insight into the possible locations of extra oxygen ions introduced into La_8+xSr_2−y(SiO₄)₆O_2+δ compounds to raise their ionic conductivity. Perturbations observed in the Raman and infrared spectra of these compounds with increasing δ were explained by using the ab initio calculation results for the fully stoichiometric (x = y = δ = 0) lattice. This allowed the inference that the extra oxygen ions are incorporated into La O tunnel‐like fragments inherent in the studied structures. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrochromic properties of nanocrystalline WO3 thin films grown on flexible substrates by plasma-assisted evaporation technique

Thin films of Tungsten trioxide (WO₃) were deposited on ITO-coated flexible Kapton substrates by plasma-assisted activated reactive evaporation (ARE) technique. The influence of growth and microstructure on optoelectrochromic properties of WO₃ thin films was studied. The nanocrystalline WO₃ films grown at substrate temperature of 250°C were composed of vertically elongated cone-shaped grains of size 65 nm with relative density of 0.71. These WO₃ films demonstrated higher optical transmittance of 85% in the visible region with estimated optical band gap of 3.39 eV and exhibited better optical modulation of 66% and coloration efficiency of 52.8 cm²/C at the wavelength of 550 nm.     

Synthesis of functional phosphines with ortho‐substituted aryl groups: 2‐RC6H4PH2 and 2‐RC6H4P(SiMe3)2 (R = 2‐i‐Pr‐ or 2‐t‐Bu‐)

The synthesis and characterization of 2‐i‐PrC₆H₄PCl₂ ( 3 ), 2‐t‐BuC₆H₄PCl₂ ( 4 ), 2‐i‐PrC₆H₄PH₂ ( 5 ), 2‐t‐BuC₆H₄PH₂ ( 6 ), 2‐i‐PrC₆H₄P(SiMe₃)₂ ( 7 ), and 2‐t‐BuC₆H₄P(SiMe₃)₂ ( 8 ) are described. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:265–270, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20606     

Upper limits of auditory rotational motion perception

Three experiments are reported, which investigated the auditory velocity thresholds beyond which listeners are no longer able to perceptually resolve a smooth circular trajectory. These thresholds were measured for band-limited noises, white noise, and harmonic sounds (HS), and in different acoustical environments. Experiments 1 and 2 were conducted in an acoustically dry laboratory. Observed thresholds varied as a function of stimulus type and spectral content. Thresholds for band-limited noises were unaffected by center frequency and equal to that of white noise. For HS, however, thresholds decreased as the fundamental frequency of the stimulus increased. The third experiment was a replication of the second in a reverberant concert hall, which produced qualitatively similar results except that thresholds were significantly higher than in the acoustically dry laboratory.     

Micro-spectrometry in the visible range with full-field optical coherence tomography for single absorbing layers

A time-domain full-field OCT adapted to the visible range and with an original configuration using an interferometric objective, that minimizes mechanical vibrations and some settings and that performs imaging without moving the sample, is presented. This setup achieves micrometer scale imaging, 1.5 μm in the axial direction and 1.2 μm in the lateral one. The principle of micro-spectrometry from OCT data by Fourier transform is described and the influence of some key data processing parameters is simulated and discussed. The experimental spectra reconstruction from tomographic data is validated by comparison with transmittance spectra. Imaging and spectra of dyes at a micrometer scale are obtained from the same data volume.     

Synthesis and electrochemical studies of LiMn1−xCuXO4 cathode material

LiMn_1.8Cu_0.2O₄ was investigated in order to improve the electrochemical properties of LiMn₂O₄. We report the synthesis and characterization of materials prepared by solid-state reaction. The structural properties evaluated by the X-ray diffraction and vibrational spectroscopy show that a single phase was formed. Conductivity of LiMn_1.8Cu_0.2O₄ cathode is found to be 8×10⁻⁶ S/cm at 25 °C. The cyclic voltammetry data shows the reversibility of the electrode material. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.