325 research outputs found

    Structural, electronic, vibrational and dielectric properties of LaBGeO5_5 from first principles

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    Structural, electronic, vibrational and dielectric properties of LaBGeO5_5 with the stillwellite structure are determined based on \textit{ab initio} density functional theory. The theoretically relaxed structure is found to agree well with the existing experimental data with a deviation of less than 0.2%0.2\%. Both the density of states and the electronic band structure are calculated, showing five distinct groups of valence bands. Furthermore, the Born effective charge, the dielectric permittivity tensors, and the vibrational frequencies at the center of the Brillouin zone are all obtained. Compared to existing model calculations, the vibrational frequencies are found in much better agreement with the published experimental infrared and Raman data, with absolute and relative rms values of 6.04 cm1^{-1}, and 1.81%1.81\%, respectively. Consequently, numerical values for both the parallel and perpendicular components of the permittivity tensor are established as 3.55 and 3.71 (10.34 and 12.28), respectively, for the high-(low-)frequency limit

    Pore formation of phospholipid membranes by the action of two hemolytic arachnid peptides of different size

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    AbstractPin2 and Oxki1 are cationic amphipathic peptides that permeate lipid membranes through formation of pores. Their mechanism of binding to phosphocholine (PC) membranes differs. Spin-probe experiments showed that both Pin2 and Oxki1 penetrate the lipid membrane of small unilamellar vesicles (SUVs). Moreover, the leakage of calcein and dextrans from PC vesicles showed that Pin2 agrees with the accumulation of peptides on lipid membranes and form pores of different size. On the other hand, Oxki1 did not act strictly cooperatively and form pores of limited size

    Raman scattering from phonons and magnons in RFe3)BO3)4

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    Inelastic light scattering spectra of several members of the RFe3(BO3)4 family reveal a cascade of phase transitions as a function of temperature, starting with a structural, weakly first order, phase transition followed by two magnetic phase transitions. Those consist of the ordering of the Fe-spin sublattice revealed by all the compound, and a subsequent spin-reorientational transition for GdFe3(BO3)4. The Raman data evidence a strong coupling between the lattice and magnetic degrees of freedom in these borates. The Fe-sublattice ordering leads to a strong suppression of the low energy magnetic scattering, and a multiple peaked two-magnon scattering continuum is observed. Evidence for short-range correlations is found in the `paramagnetic' phase by the observation of a broad magnetic continuum in the Raman data, which persists up to surprisingly high temperatures.Comment: 17 pages, 13 figure

    Cerium(III) dihydroxidohexa­oxidotetra­borate chloride

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    The crystal structure of the title compound, Ce[B4O6(OH)2]Cl, is built from polyborate sheets parallel to the (001) plane. These sheets stack along the [001] direction and are linked by Ce atoms exhibiting an CeO8Cl2 coordination sphere. O—H⋯O and O—H⋯Cl hydrogen bonds additionally stabilize the structural set-up. The polyborate sheet is made up of zigzag borate chains running along the [10] direction. These zigzag chains are inter­connected by shared O-vertices, resulting in a two-dimensional layer with nine-membered rings. All B and O atoms (except for the terminal OH atoms) lie in the nearly planar sheets of polyborates, leading to their isotropic atomic displacement parameters being significantly smaller than usual. This may be attributed to the fact that the atomic displacement parameters correlate not only with their atomic masses but with their coordination environments also

    Острофазовый белок лактоферрин и ингибиторы протеиназ крови больных с Q-образующим инфарктом миокарда, осложненным острой сердечной недостаточностью

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    153 patients with Q-wave noncomplicated and complicated myocardial infraction have been examined. Blood serum was studied for acute-phase proteins (alfa-2-macroglobulin (MG), alfa-1-antitrypsin (ATr), and lactoferrin (LF)) in 97 patients ((57.9 ± 1.06) years old). Blood was sampled at the 1st, 7th, and 14th days after myocardial infraction. The decrease of MG in acute phase was observed in patients with cardiogenic shock. Increased concentrations of LF and unchanged MG level at the 1—7 days were observed at pulmonary edema.Обследованы 153 пациента с Q-образующим неосложненным и осложненным инфарктом миокарда (ИМ). Сыворотка крови на содержание белков острой фазы альфа-2-макроглобулина (МГ), альфа-1-антитрипсина (АТр) и лактоферрина (ЛФ) исследована у 97 пациентов (средний возраст (57,9 ± 1,06) года). Забор крови осуществлялся на 1, 7 и 14-е сут развития ИМ. Установлено, что снижение МГ в острой фазе наблюдается у больных с кардиогенным шоком. Повышенные концентрации ЛФ и неизменные МГ на 1—7-е сут выявлены при отеке легких

    X-ray and Electron Diffraction Study of MgO

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    Phospholipid dependent mechanism of smp24, an α-helical antimicrobial peptide from scorpion venom

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    Determining the mechanism of action of antimicrobial peptides (AMPs) is critical if they are to be developed into the clinical setting. In recent years high resolution techniques such as atomic force microscopy (AFM) have increasingly been utilised to determine AMP mechanism of action on planar lipid bilayers and live bacteria. Here we present the biophysical characterisation of a prototypical AMP from the venom of the North African scorpion Scorpio maurus palmatus termed Smp24. Smp24 is an amphipathic helical peptide containing 24 residues with a charge of + 3 and exhibits both antimicrobial and cytotoxic activity and we aim to elucidate the mechanism of action of this peptide on both membrane systems. Using AFM, quartz crystal microbalance-dissipation (QCM-D) and liposomal leakage assays the effect of Smp24 on prototypical synthetic prokaryotic (DOPG:DOPC) and eukaryotic (DOPE:DOPC) membranes has been determined. Our data points to a toroidal pore mechanism against the prokaryotic like membrane whilst the formation of hexagonal phase non-lamellar phase structures is seen in eukaryotic like membrane. Also, phase segregation is observed against the eukaryotic membrane and this study provides direct evidence of the same peptide having multiple mechanisms of action depending on the membrane lipid composition

    Stable amorphous georgeite as a precursor to a high-activity catalyst .

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    Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable—and hence little known and largely ignored1—georgeite. The first three of these minerals are widely used as catalyst precursors2, 3, 4 for the industrially important methanol-synthesis and low-temperature water–gas shift (LTS) reactions5, 6, 7, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase2, 3, 8, 9, 10 is usually zincian malachite. This is prepared by a co-precipitation method that involves the transient formation of georgeite11; with few exceptions12 it uses sodium carbonate as the carbonate source, but this also introduces sodium ions—a potential catalyst poison. Here we show that supercritical antisolvent (SAS) precipitation using carbon dioxide (refs 13, 14), a process that exploits the high diffusion rates and solvation power of supercritical carbon dioxide to rapidly expand and supersaturate solutions, can be used to prepare copper/zinc hydroxycarbonate precursors with low sodium content. These include stable georgeite, which we find to be a precursor to highly active methanol-synthesis and superior LTS catalysts. Our findings highlight the value of advanced synthesis methods in accessing unusual mineral phases, and show that there is room for exploring improvements to established industrial catalysts
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