X-ray magnetic circular dichroism measurements using an X-ray phase retarder on the BM25 A-SpLine beamline at the ESRF

6 páginas, 8 figuras.Circularly polarized X-rays produced by a diamond X-ray phase retarder of thickness 0.5 mm in the Laue transmission configuration have been used for recording X-ray magnetic circular dichroism (XMCD) on the bending-magnet beamline BM25A (SpLine) at the ESRF. Field reversal and helicity reversal techniques have been used to carry out the measurements. The performance of the experimental set-up has been demonstrated by recording XMCD in the energy range from 7 to 11 keV.This work was partially supported by a Spanish CICYTMAT2008- 06542-C04 grant. MALM and RB acknowledge the Ministerio de Ciencia e Innovación of Spain for their Postdoctoral and PhD grants, respectively. We also acknowledge the Spanish Ministerio de Ciencia e Innovación and Consejo Superior de Investigaciones Científicas for financial support.Peer reviewe

Polymorphic transformation from body-centered to face-centered cubic vanadium metal during mechanosynthesis of nanostructured vanadium nitride determined by extended x-ray absorption fine structure spectroscopy

The pathway for vanadium nitride VN formation obtained by milling treatment has been traced out. At the initial stages of the process, the reactant, vanadium metal, showing body-centered cubic bcc structure, becomes highly distorted. Simultaneously, the formation of a small nucleus of the product, VN, takes place. X-ray absorption spectroscopy XAS has allowed the quantification of the distortion degree as well as the detection of the VN nucleus in the early stages of their formation, while other standard structural characterization techniques are unable to detect such phenomena. For increasing milling times, apart from the expected increase in the size of the VN nucleus, a polymorphic transformation from bcc to fcc vanadium metal has been recorded. This phase might play a key role in the overall synthesis process and could be a reaction intermediate in other solid state processes involving V metal. The sensitivity of XAS to noncrystalline domains and to highly distorted environments, as well as the use of high resolution x-ray diffraction, has provided the relevant information to understand the whole reaction process.European Synchrotron Radiation Facility (ESRF)-ME-737SpLine CRG (beamline BM25 at the ESRF)-25- 01-657Ministerio de Educación y Ciencias de España-BQU2002-04364-C02-01 y BQU2002- 04364-C02-

Nanostructured Au(111)/Oxide epitaxial heterostructures with tailoring plasmonic response by a one-step strategy

In this work, we present a strategy for developing epitaxial incommensurate nanostructured Au/oxide heterostructures with tunable plasmonic response. Previously, high-quality single-phase and single-oriented alfa-Fe2O3(0001) thin films were achieved, which have been used as a template for noble-metal epitaxial deposition. The complex systems have been grown by pulsed laser deposition on two different types of oxide substrates: alfa-Al2O3(0001) and SrTiO3(111). A one-step procedure has been achieved tailoring the isolated character and the morphological features of Au nanostructures through the substrate temperature during Au growth, without altering the structural characteristics of the hematite layer that is identified as a single iron oxide phase. The epitaxial character and the lattice coupling of Au/oxide bilayers are mediated through the sort of oxide substrate. Single-oriented Au(111) islands are disposed with a rotation of 30° between their crystallographic axes and those of alfa-Fe2O3(0001). The Au(111) and SrTiO3(111) lattices are collinear, while a rotation of 30° happens with respect to the alfa-Al2O3(0001) lattice. The crystallographic domain size and crystalline order of the hematite structure and the Au nanostructured layer are dependent on the substrate type and the Au growth temperature, respectively. Besides, the functional character of the complex systems has been tested. The localized surface plasmons related to Au nanostructures are excited and controlled through the fabrication parameters, tuning the optical resonance with the degree of Au nanostructuring.This work was supported by the Ministerio Español de Ciencia, Innovación y Universidades (MCIU), and the Consejo Superior de Investigaciones Cientificas (CSIC) through the project PIE-2010 6 OE 013. J.L.-S. and E.E. acknowledge the FPI fellowship and the Torres Quevedo contract (ref: PTQ-14-07289). The ESRF, MCIU, and CSIC are acknowledged for the provision of synchrotron radiation facilities. The authors thank Dr M.A. García for the useful discussion about the plasmonic results and Carlos Beltrán for technical support during the experiments at the BM25 beamline at The ESRF

Improving the co and ch4 gas sensor response at room temperature of alpha-fe2o3(0001) epitaxial thin films grown on srtio3(111) incorporating au(111) islands

In this work, the functional character of complex -Fe2O3(0001)/SrTiO3(111) and Au(111) islands/ -Fe2O3(0001)/SrTiO3(111) heterostructures has been proven as gas sensors at room temperature. Epitaxial Au islands and -Fe2O3 thin film are grown by pulsed laser deposition on SrTiO3(111) substrates. Intrinsic parameters such as the composition, particle size and epitaxial character are investigated for their influence on the gas sensing response. Both Au and -Fe2O3 layer show an island-type growth with an average particle size of 40 and 62 nm, respectively. The epitaxial and incommensurate growth is evidenced, confirming a rotation of 30 between the in-plane crystallographic axes of -Fe2O3(0001) structure and those of SrTiO3(111) substrate and between the in-plane crystallographic axes of Au(111) and those of -Fe2O3(0001) structure. -Fe2O3 is the only phase of iron oxide identified before and after its functionalization with Au nanoparticles. In addition, its structural characteristics are also preserved after Au deposition, with minor changes at short-range order. Conductance measurements of Au(111)/ -Fe2O3(0001)/SrTiO3(111) system show that the incorporation of epitaxial Au islands on top of the -Fe2O3(0001) layer induces an enhancement of the gas-sensing activity of around 25% under CO and 35% under CH4 gas exposure, in comparison to a bare -Fe2O3(0001) layer grown on SrTiO3(111) substrates. In addition, the response of the heterostructures to CO gas exposure is around 5–10% higher than to CH4 gas in each case.This work has been supported by the Ministerio Español de Ciencia e Innovación (MICINN) and the Consejo Superior de Investigaciones Cientificas (CSIC) through the projects PIE-2010-OE-013- 200014, PIE 2021-60-E-030 and RTI2018-095303-A-C52. The ESRF, MICINN and CSIC are acknowledged for the provision of synchrotron radiation facilities. A.S. acknowledges financial support from Comunidad de Madrid for an “Atracción de Talento Investigador” Contract (2017-t2/IND5395)

Interlayer-Confined Cu(II) Complex as an Efficient and Long-Lasting Catalyst for Oxidation of H2S on Montmorillonite

Removal of highly toxic H2S for pollution control and operational safety is a pressing need. For this purpose, a montmorillonite intercalated with Cu(II)-phenanthroline complex [Cu[(Phen)(H2O)2]2+ (Mt-CuPhen) was prepared to capture gaseous H2S under mild conditions. This hybrid material was simple to obtain and demonstrated an outstanding ability to entrap H2S at room temperature, retaining high efficiency for a very long time (up to 36.8 g of S/100 g Mt-CuPhen after 3 months of exposure). Sorbent and H2S uptake were investigated by elemental analysis, X-ray powder diffraction measurements, diffuse reflectance (DR) UV–Vis and infrared spectroscopy, thermal analysis and evolved gas mass spectrometry, scanning electron microscopy equipped with energy-dispersive X-ray spectrometer, and X-ray absorption spectroscopy. The H2S capture was studied over time and a mechanism of action was proposed. The entrapping involves a catalytic mechanism in which [Cu[(Phen)(H2O)2]2+ acts as catalyst for H2S oxidation to S0 by atmospheric oxygen. The low cost and the long-lasting performance for H2S removal render Mt-CuPhen an extremely appealing trap for H2S removal and a promising material for many technological applications

Design, Synthesis, Characterization, and Evaluation of the Anti-HT-29 Colorectal Cell Line Activity of Novel 8-Oxyquinolinate-Platinum(II)-Loaded Nanostructured Lipid Carriers Targeted with Riboflavin

Colorectal cancer is occasionally called colon or rectal cancer, depending on where cancer begins to form, and is the second leading cause of cancer death among both men and women. The platinum-based [PtCl(8-O-quinolinate)(dmso)] (8-QO-Pt) compound has demonstrated encouraging anticancer activity. Three different systems of 8-QO-Pt-encapsulated nanostructured lipid carriers (NLCs) with riboflavin (RFV) were investigated. NLCs of myristyl myristate were synthesized by ultrasonication in the presence of RFV. RFV-decorated nanoparticles displayed a spherical shape and a narrow size dispersion in the range of 144–175 nm mean particle diameter. The 8-QO-Pt-loaded formulations of NLC/RFV with more than 70% encapsulation efficiency showed sustained in vitro release for 24 h. Cytotoxicity, cell uptake, and apoptosis were evaluated in the HT-29 human colorectal adenocarcinoma cell line. The results revealed that 8-QO-Pt-loaded formulations of NLC/RFV showed higher cytotoxicity than the free 8-QO-Pt compound at 5.0 µM. All three systems exhibited different levels of cellular internalization. Moreover, the hemotoxicity assay showed the safety profile of the formulations (less than 3.7%). Taken together, RFV-targeted NLC systems for drug delivery have been investigated for the first time in our study and the results are promising for the future of chemotherapy in colon cancer treatmen

Correlation between surface reconstruction and polytypism in InAs nanowire selective area epitaxy

Themechanism of widely observed intermixing of wurtzite and zinc-blende crystal structures in InAs nanowire (NW) grown by selective area epitaxy (SAE) is studied. We demonstrate that the crystal structure in InAs NW grown by SAE can be controlled using basic growth parameters, and wurtzitelike InAs NWs are achieved.We link the polytypic InAs NWs SAE to the reconstruction of the growth front (111)B surface. Surface reconstruction study of InAs (111) substrate and the following homoepitaxy experiment suggest that (111) planar defect nucleation is related to the (1 × 1) reconstruction of InAs (111)B surface. In order to reveal it more clearly, a model is presented to correlate growth temperature and arsenic partial pressure with InAs NW crystal structure. This model considers the transition between (1 × 1) and (2 × 2) surface reconstructions in the frame of adatom atoms adsorption/desorption, and the polytypism is thus linked to reconstruction quantitatively. The experimental data fit well with the model, which highly suggests that surface reconstruction plays an important role in the polytypism phenomenon in InAs NWs SAE.https://doi.org/10.1103/PhysRevMaterials.1.074603Peer Reviewe

Crystal structures of bacterial peptidoglycan amidase AmpD and an unprecedented activation mechanism

9 pags, 5 figs, 2 tabsAmpD is a cytoplasmic peptidoglycan (PG) amidase involved in bacterial cell-wall recycling and in induction of β-lactamase, a key enzyme of β-lactam antibiotic resistance. AmpD belongs to the amidase-2 family that includes zinc-dependent amidases and the peptidoglycan-recognition proteins (PGRPs), highly conserved pattern-recognition molecules of the immune system. Crystal structures of Citrobacter freundii AmpD were solved in this study for the apoenzyme, for the holoenzyme at two different pH values, and for the complex with the reaction products, providing insights into the PG recognition and the catalytic process. These structures are significantly different compared with the previously reported NMR structure for the same protein. TheNMRstructure does not possess an accessible active site and shows the protein in what is proposed herein as an inactive "closed" conformation. The transition of the protein from this inactive conformation to the active "open" conformation, as seen in the x-ray structures, was studied by targeted molecular dynamics simulations, which revealed large conformational rearrangements (as much as 17 Å ) in four specific regions representing one-third of the entire protein. It is proposed that the large conformational change that would take the inactive NMR structure to the active x-ray structure represents an unprecedented mechanism for activation of AmpD. Analysis is presented to argue that this activation mechanism might be representative of a regulatory process for other intracellular members of the bacterial amidase-2 family of enzymes. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.This work was supported, in whole or in part, by the National Institutes of Health. This work was also supported by grants from the Spanish Ministry of Science and Technology (BFU2008-01711), EU-CP223111 (CARE-PNEUMO, European Union), and the COMBACT program (S-BIO-0260/2006). We acknowledge the Spanish Ministerio de Ciencia e Innovación (PI201060E013) and Consejo Superior de Investigaciones Científicas for financial support and for provision of synchrotron radiation facilitie

Formation of titanium monoxide (001) single-crystalline thin film induced by ion bombardment of titanium dioxide (110)

© 2015 Macmillan Publishers Limited. All rights reserved. A plethora of technological applications justify why titanium dioxide is probably the most studied oxide, and an optimal exploitation of its properties quite frequently requires a controlled modification of the surface. Low-energy ion bombardment is one of the most extended techniques for this purpose and has been recently used in titanium oxides, among other applications, to favour resistive switching mechanisms or to form transparent conductive layers. Surfaces modified in this way are frequently described as reduced and defective, with a high density of oxygen vacancies. Here we show, at variance with this view, that high ion doses on rutile titanium dioxide (110) induce its transformation into a nanometric and single-crystalline titanium monoxide (001) thin film with rocksalt structure. The discovery of this ability may pave the way to new technical applications of ion bombardment not previously reported, which can be used to fabricate heterostructures and interfaces.Peer Reviewe

A combined micro-Raman, X-ray absorption and magnetic study to follow the glycerol-assisted growth of epsilon-iron oxide sol-gel coatings

[EN] Epsilon iron oxide (ε-FeO) coatings on Si(100) substrates are obtained by an easy one-pot sol-gel recipe assisted by glycerol in an acid medium. Glycerol, given its small dimensions, enables the formation of ε-FeO nanoparticles with a size of a few nanometers and the highest purity is reached in coatings after a densification treatment at 960 °C. The structural and compositional evolution up to 1200 °C is studied by confocal Raman microscopy and X-ray absorption spectroscopy techniques, correlating the existing magnetic properties. We report a novel characterization method, which allows monitoring the evolution of the precursor micelles as well as the intermediate and final phases formed. Furthermore, the inherent industrial technology transfer of the sol-gel process is also demonstrated with the ε-FeO polymorph, impelling its application in the coatings form.This work has been supported by the Ministerio de Ciencia e Innovación (MCINN, Spain) through the projects PIE: 2021-60-E-030, PIE: 2010-6-OE-013, PID2019-104717RB-I00 (2020–2022), MAT2017-86540-C4-1-R, RTI2018-095856-B-C21 (2019–2021), RTI2018-097895-B-C43 and RTI2018-095303-A-C52. The authors are grateful to The ESRF (France), MCINN and Consejo Superior de Investigaciones Científicas (CSIC, Spain) for the provision of synchrotron radiation facilities and to the BM25-SpLine Staff for their valuable help. A.S.and A.M.-N acknowledge financial support from Comunidad de Madrid (Spain) for an “Atracción de Talento Investigador” Contract 2017-t2/IND5395 and 2018-T1/IND-10360, respectivel