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991.
Crassous A Bernard R Fusil S Bouzehouane K Le Bourdais D Enouz-Vedrenne S Briatico J Bibes M Barthélémy A Villegas JE 《Physical review letters》2011,107(24):247002
Using heterostructures that combine a large-polarization ferroelectric (BiFeO3) and a high-temperature superconductor (YBa2Cu3O(7-δ)), we demonstrate the modulation of the superconducting condensate at the nanoscale via ferroelectric field effects. Through this mechanism, a nanoscale pattern of normal regions that mimics the ferroelectric domain structure can be created in the superconductor. This yields an energy landscape for magnetic flux quanta and, in turn, couples the local ferroelectric polarization to the local magnetic induction. We show that this form of magnetoelectric coupling, together with the possibility to reversibly design the ferroelectric domain structure, allows the electrostatic manipulation of magnetic flux quanta. 相似文献
992.
Ultrasonically enhanced extraction of bioactive principles from Quillaja Saponaria Molina 总被引:3,自引:0,他引:3
Gaete-Garretón L Vargas-Hernández Y Cares-Pacheco MG Sainz J Alarcón J 《Ultrasonics》2011,51(5):581-585
A study of ultrasonic enhancement in the extraction of bioactive principles from Quillaja Saponaria Molina (Quillay) is presented. The effects influencing the extraction process were studied through a two-level factorial design. The effects considered in the experimental design were: granulometry, extraction time, acoustic Power, raw matter/solvent ratio (concentration) and acoustic impedance.It was found that for aqueous extraction the main factors affecting the ultrasonically-assisted process were: granulometry, raw matter/solvent ratio and extraction time. The extraction ratio was increased by Ultrasonics effect and a reduction in extraction time was verified without any influence in the product quality. In addition the process can be carried out at lower temperatures than the conventional method.As the process developed uses chips from the branches of trees, and not only the bark, this research contributes to make the saponin exploitation process a sustainable industry. 相似文献
993.
Valero E Tambalo S Marzola P Ortega-Muñoz M López-Jaramillo FJ Santoyo-González F de Dios López J Delgado JJ Calvino JJ Cuesta R Domínguez-Vera JM Gálvez N 《Journal of the American Chemical Society》2011,133(13):4889-4895
A new approach for the preparation of carbohydrate-coated magnetic nanoparticles is reported. In a first step, we show that the pH-driven assembly-disassembly natural process that occurs in apoferritin protein is effective for the encapsulation of maghemite nanoparticles of different sizes: 4 and 6 nm. In a second step, we demonstrate that the presence of functional amine groups in the outer shell of apoferritin allows functionalization with two carbohydrates, N-acetyl-D-glucosamine and d-mannose. High-resolution electron microscopy (HREM), high angle annular dark field scanning electron microscopy (HAADF-STEM), electron energy loss spectroscopy (EELS), X-ray diffraction (XRD), and SQUID technique have been used to characterize the magnetic samples, termed herein Apomaghemites. The in vivo magnetic resonance imaging (MRI) studies showed the efficiency in contrasting images for these samples; that is, the r(2) NMR relaxivities are comparable with Endorem (a commercial superparamagnetic MRI contrast agent). The r(2) relaxivity values as well as the pre-contrast and post-contrast T(2)*-weighted images suggested that our systems could be used as perspective superparamagnetic contrast agents for magnetic resonance imaging (MRI). The carbohydrate-functionalized Apomaghemite nanoparticles retained their recognition abilities, as demonstrated by the strong affinity with their corresponding carbohydrate-binding lectins. 相似文献
994.
Gonzalez J Anglada JM Buszek RJ Francisco JS 《Journal of the American Chemical Society》2011,133(10):3345-3353
The effect of a single water molecule on the OH + HOCl reaction has been investigated. The naked reaction, the reaction without water, has two elementary reaction paths, depending on how the hydroxyl radical approaches the HOCl molecule. In both cases, the reaction begins with the formation of prereactive hydrogen bond complexes before the abstraction of the hydrogen by the hydroxyl radical. When water is added, the products of the reaction do not change, and the reaction becomes quite complex yielding six different reaction paths. Interestingly, a geometrical rearrangement occurs in the prereactive hydrogen bonded region, which prepares the HOCl moiety to react with the hydroxyl radical. The rate constant for the reaction without water is computed to be 2.2 × 10(-13) cm(3) molecule(-1) s(-1) at room temperature, which is in good agreement with experimental values. The reaction between ClOH···H(2)O and OH is estimated to be slower than the naked reaction by 4-5 orders of magnitude. Although, the reaction between ClOH and the H(2)O···HO complex is also predicted to be slower, it is up to 2.2 times faster than the naked reaction at altitudes below 6 km. Another intriguing finding of this work is an interesting three-body interchange reaction that can occur, that is HOCl + HO···H(2)O → HOCl···H(2)O + OH. 相似文献
995.
J. P. Urquijo Herley Casanova Javier Garces Alvaro L. Morales 《Hyperfine Interactions》2011,203(1-3):85-91
This study refers to the effect of sodium polyacrylate concentration (1 to 5 mass %) and pH (10 to 12) on the synthesis of magnetic nanoparticles (magnetite?Cmaghemite) and their characterization by Mössbauer spectroscopy. The magnetic particles were obtained by coprecipitation method using iron chloride (II) and iron chloride (III) as precursor reagents and sodium polyacrylate as stabilizing agent. All samples showed Mössbauer broad resonance lines in typical doublet and sextets patterns of magnetite or maghemite with corresponding wide particle size distributions. The stability of magnetic particles was carried out by measuring particle sizes with dynamic light scattering (DLS). The z-average values for magnetic particles were in the range 24 to 590 nm and no significant change in size was observed on aging by leaving this material in air for 20 days. X-ray diffraction patterns showed characteristic peaks of the spinel structure and have an increase in their broadening as the pH decreases, effect that is dominated by the decrease in crystallite sizes. The nanoparticles showed to be magnetic at pH 12 and at room temperature. 相似文献
996.
Alba Espargar Salom Llabrs Sven J. Saupe Carles Curutchet F. Javier Luque Raimon Sabat 《Angewandte Chemie (International ed. in English)》2020,59(21):8104-8107
Amyloids are characterized by their capacity to bind Congo red (CR), one of the most used amyloid‐specific dyes. The structural features of CR binding were unknown for years, mainly because of the lack of amyloid structures solved at high resolution. In the last few years, solid‐state NMR spectroscopy enabled the determination of the structural features of amyloids, such as the HET‐s prion forming domain (HET‐s PFD), which also has recently been used to determine the amyloid–CR interface at atomic resolution. Herein, we combine spectroscopic data with molecular docking, molecular dynamics, and excitonic quantum/molecular mechanics calculations to examine and rationalize CR binding to amyloids. In contrast to a previous assumption on the binding mode, our results suggest that CR binding to the HET‐s PFD involves a cooperative process entailing the formation of a complex with 1:1 stoichiometry. This provides a molecular basis to explain the bathochromic shift in the maximal absorbance wavelength when CR is bound to amyloids. 相似文献
997.
Antonia Kagkoura Javier Hernandez‐Ferrer Ana M. Benito Wolfgang K. Maser Nikos Tagmatarchis 《化学:亚洲杂志》2020,15(15):2350-2356
A facile strategy for the controllable growth of CdS nanoparticles at the periphery of MoS2 en route the preparation of electron donor‐acceptor nanoensembles is developed. Precisely, the carboxylic group of α‐lipoic acid, as addend of the modified MoS2 obtained upon 1,2‐dithiolane functionalization, was employed as anchor site for the in situ preparation and immobilization of the CdS nanoparticles in an one‐pot two‐step process. The newly prepared MoS2/CdS hybrid material was characterized by complementary spectroscopic, thermal and microscopy imaging means. Absorption spectroscopy was employed to register the formation of MoS2/CdS, by observing a broad shoulder centered at 420 nm due to CdS nanoparticles, while the excitonic bands of MoS2 were also evident. Moreover, based on the efficient quenching of the characteristic fluorescence emission of CdS at 725 nm by the presence of MoS2, strong electronic interactions at the excited state between the two species within the ensemble were identified. Photoelectrochemical assays of MoS2/CdS thin‐film electrodes revealed a prompt, steady and reproducible anodic photoresponse during repeated on‐off cycles of illumination. A significant zero‐current photopotential of ?540 mV and an anodic photocurrent of 1 μA were observed, underlining improved charge‐separation and electron transport from CdS to MoS2. The superior performance of the charge‐transfer processes in MoS2/CdS is of direct interest for the fabrication of photoelectrochemical and optoelectronic devices. 相似文献
998.
Frontispiece: Multiple Stable Conformations Account for Reversible Concentration‐Dependent Oligomerization and Autoinhibition of a Metamorphic Metallopeptidase
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999.
Cover Picture: From the Lindlar Catalyst to Supported Ligand‐Modified Palladium Nanoparticles: Selectivity Patterns and Accessibility Constraints in the Continuous‐Flow Three‐Phase Hydrogenation of Acetylenic Compounds (Chem. Eur. J. 20/2014)
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1000.
Ring Opening and Bidentate Coordination of Amidinate Germylenes and Silylenes on Carbonyl Dicobalt Complexes: The Importance of a Slight Difference in Ligand Volume
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Prof. Javier A. Cabeza Dr. Pablo García‐Álvarez Dr. Enrique Pérez‐Carreño Diego Polo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(28):8654-8663
The reactions of [Co2(CO)8] with one equiv of the benzamidinate (R2bzam) group‐14 tetrylenes [M(R2bzam)(HMDS)] (HMDS=N(SiMe3)2; 1 : M=Ge, R=iPr; 2 : M=Si, R=tBu; 3 : M=Ge, R=tBu) at 20 °C led to the monosubstituted complexes [Co2{κ1M?M(R2bzam)(HMDS)}(CO)7] ( 4 : M=Ge, R=iPr; 5 : M=Si, R=tBu; 6 : M=Ge, R=tBu), which contain a terminal κ1M–tetrylene ligand. Whereas the Co2Si and Co2Ge tert‐butyl derivatives 5 and 6 are stable at 20 °C, the Co2Ge isopropyl derivative 4 evolved to the ligand‐bridged derivative [Co2{μ‐κ2Ge,N‐Ge(iPr2bzam)(HMDS)}(μ‐CO)(CO)5] ( 7 ), in which the Ge atom spans the Co?Co bond and one arm of the amidinate fragment is attached to a Co atom. The mechanism of this reaction has been modeled with the help of DFT calculations, which have also demonstrated that the transformation of amidinate‐tetrylene ligands on the dicobalt framework is negligibly influenced by the nature of the group‐14 metal atom (Si or Ge) but is strongly dependent upon the volume of the amidinate N?R groups. The disubstituted derivatives [Co2{κ1M?M(R2bzam)(HMDS)}2(CO)6] ( 8 : M=Ge, R=iPr; 9 : M=Si, R=tBu; 10 : M=Ge, R=tBu), which contain two terminal κ1M–tetrylene ligands, have been prepared by treating [Co2(CO)8] with two equiv of 1 – 3 at 20 °C. The IR spectra of 8 – 10 have shown that the basicity of germylenes 1 and 3 is very high (comparable to that of trialkylphosphanes and 1,3‐diarylimidazol‐2‐ylidenes), whereas that of silylene 2 is even higher. 相似文献