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1.
de Souza JM Freire PT Bordallo HN Argyriou DN 《The journal of physical chemistry. B》2007,111(19):5034-5039
A first study of possible changes instigated by deuteration in amino acids was carried out using neutron diffraction, inelastic neutron scattering, and Raman scattering in l-alanine, C2H4(NH2)COOH. Careful analysis of the structural parameters shows that deuteration of l-alanine engenders significant geometric changes as a function of temperature, which can be directly related to the observation of new lattice vibration modes in the Raman spectra. The combination of the experimental data suggests that C2D4(ND2)COOD undergoes a structural phase transition (or a structural rearrangement) at about 170 K. Considering that this particular amino acid is a hydrogen-bonded system with short hydrogen bonds (O...H approximately 1.8 A), we evoke the Ubbelohde effect to conclude that substitution of hydrogen for deuterium gives rise to changes in the hydrogen-bonding interactions. The structural differences suggest distinct relative stabilities for the hydrogenous and deuterated l-alanine. 相似文献
2.
R. O. Gonalves P. T. C. Freire H. N. Bordallo J. A. Lima F. E. A. Melo J. Mendes Filho D. N. Argyriou R. J. C. Lima 《Journal of Raman spectroscopy : JRS》2009,40(8):958-963
Raman spectra of deuterated L ‐alanine have been obtained at high‐pressure conditions. A phase transition at ∼1.5 GPa associated with the splitting of some internal modes and increase of the wavenumber of the external modes was observed. Similarly to the hydrogenated L ‐alanine crystal, this first transition was related to a symmetry change. Moreover, further modifications of the Raman spectra were observed at 4.4 GPa, which may be associated to conformational changes of the molecule. To give further support to such a hypothesis, neutron powder diffraction measurements were performed. Information about the cell parameter at atmospheric pressure gave valuable information about the N D distances, shedding light on the behavior of the torsional vibration of ND3+. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
3.
A. Maljuk V. Tsurkan V. Zestrea O. Zaharko A. Cervellino A. Loidl D.N. Argyriou 《Journal of Crystal Growth》2009,311(16):3997-4000
We report the first successful floating-zone growth of high-quality CoAl2O4 single crystals with volume up to 1 cm3 free from inclusions and sub-grains. The neutron rocking curves of the CoAl2O4 crystal have the width of about 0.30 degree proving the excellent quality of the grown samples. X-ray synchrotron experiments show that crystals have spinel structure with the lattice constant a0=8.09853(1) Å. Magnetization measurements give the effective magnetic moment μeff=4.63 μB per Co+2 ion in a good agreement with previous measurements on ceramic samples. 相似文献
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N. Jalarvo N. Aliouane H. N. Bordallo C. J. Milne J. R. Veira D. N. Argyriou 《The European physical journal. Special topics》2007,141(1):69-72
Quasielastic neutron scattering (QENS) has been used to
investigate the dynamical behaviour of H2O in the
superconductor Na0.28CoO2 .yH2O. The
measurements were obtained at room temperature for a molar
concentration of water, y = 1.3. From the analysis of the
Q-dependence of the EISF and the line-width we found that the water
dynamics can be well described by rotational motion that likely
correspond to re-orientation of the H2O molecule. We were also
able to define a rotational correlation time of τ= 1.85 ps. 相似文献
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7.
Jalarvo N Bordallo HN Aliouane N Adams MA Pieper J Argyriou DN 《The journal of physical chemistry. B》2008,112(3):703-709
Incoherent inelastic neutron scattering experiments were performed on Na0.7CoO2 and Na0.28CoO2.1.3H2O in order to understand how the dynamics of the hydrogen-bond network of water is modified in the triangular crystalline lattice NaxCoO2.yH2O. Using quasi-elastic neutron scattering (QENS), we were able to differentiate between two types of proton dynamics: a fast process (due to water strongly bound into the sodium cobalt oxyhydrate structure during the hydration process) and a slow process (likely attributable to a collective motion). High-resolution QENS experiments, carried out on Na0.28CoO2.1.3H2O, show that, at temperatures above 310 K, the water dynamics can be well-described by a random jump diffusion model characterized by a diffusion constant equal to 0.9 x 10(-9)m2/s, which is significantly lower than the rate of diffusion for bulk water. Furthermore, our results indicate that, at room temperature, the sodium ions have no influence on the rotational dynamics of the "fast" water molecules. 相似文献
8.
Prokhnenko O Feyerherm R Dudzik E Landsgesell S Aliouane N Chapon LC Argyriou DN 《Physical review letters》2007,98(5):057206
Neutron powder diffraction and single crystal x-ray resonant magnetic scattering measurements suggest that Dy plays an active role in enhancing the ferroelectric polarization in multiferroic DyMnO3 above T(Dy)(N)=6.5 K. We observe the evolution of an incommensurate ordering of Dy moments with the same periodicity as the Mn spiral ordering. It closely tracks the evolution of the ferroelectric polarization. Below T(Dy)(N), where Dy spins order commensurately, the polarization decreases to values similar for those of TbMnO3. The higher P(s) found just above T(Dy)(N) arises from the contribution of Dy spins so as to effectively increase the amplitude of the Mn spin spiral. 相似文献
9.
Hydrogen in N-methylacetamide: positions and dynamics of the hydrogen atoms using neutron scattering
Bordallo HN Argyriou DN Barthès M Kalceff W Rols S Herwig KW Fehr C Juranyi F Seydel T 《The journal of physical chemistry. B》2007,111(27):7725-7734
This work reports neutron diffraction and incoherent neutron scattering experiments on N-methylacetamide (NMA), which can be considered the model building block for the peptide linkage of polypeptides and proteins. Using the neutron data, we have been able to associate the onset of a striking negative thermal expansion (NTE) along the a-axis with a dynamical transition around 230 K, consistent with our calorimetric experiments. Observation of the NTE raises the question of possible proton transfer in NMA, which, from our data alone, still cannot be settled. We can only speculate that intermolecular repulsive forces increase as the O...H distance decreases upon cooling, and that around 230 K the lattice relaxes without observation of an actual proton transfer. However, the existence of a nonharmonic potential, reflected by the behavior of the phonon vibrations together with the observation of NTE, could be justified by the "vibrational" polaron theory in which a dynamic localization of the vibrational energy is created by coupling an internal molecular mode to a lattice phonon. More generally, this work shows that neutron powder diffraction techniques can be very powerful for investigating structural deformations in small peptide systems. 相似文献
10.
Prokhnenko O Feyerherm R Mostovoy M Aliouane N Dudzik E Wolter AU Maljuk A Argyriou DN 《Physical review letters》2007,99(17):177206
We report on diffraction measurements on multiferroic TbMnO(3) which demonstrate that the Tb- and Mn-magnetic orders are coupled below the ferroelectric transition T(FE) = 28 K. For T相似文献