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96 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I06-Nanoscience	Magnetisation configuration in arrays of permalloy rectangles and its impact on magnetisation reversal P. J. Newton , N. B. Devlin , S. M. Masur , M. Ghidini , D. Backes , F. Maccherozzi , A A Pacheco-Pumaleque , M A González Esqueche , C. H. W. Barnes Materials Research Express 8 DOI: 10.1088/2053-1591/ac2442 Diamond Proposal Number(s): [24373] Open Access Show Abstract ▼ Abstract: The remanent domain structures of composite element magnetic barcodes have been imaged using photo-emission electron microscopy with contrast from x-ray magnetic circular dichroism (XMCD-PEEM) and analysed with reference to the results of micromagnetic simulations. The magnetisation configuration at the end of wide strips is found to be perpendicular to the majority magnetisation direction. This transitions to an incomplete rotation for nominal strip widths below 300 nm and is found to affect the mechanics of magnetisation reversal for nominal strip widths below 200 nm, owing to a difference in magnetisation orientation when an external magnetic field is applied that is just smaller than the magnetic coercivity of the structures and a corresponding change in reversal dynamics. This change in domain structure as strip width decreases is consistent with both the influence of shape anisotropy and with measurements of magnetic hysteresis. The magnetisation reversal characteristics of composite element structures are found to be dependent on the relative magnetisation configurations of neighbouring strips, which in turn are found to vary stochastically upon the application and removal of a magnetic field along the easy axis of the structure. It is found that the application of a canted field is necessary to ensure sharp, consistent magnetisation reversal of bits when writing a binary code. These results confirm that either improved lithography of narrower strips or non-rectangular elements would be necessary to further increase the number of individually programmable bits in a barcode.	Sep 2021
Theoretical Physics	Determination of spin chirality using x-ray magnetic circular dichroism Gerrit Van Der Laan Physical Review B 104 DOI: 10.1103/PhysRevB.104.094414 Open Access Show Abstract ▼ Abstract: A threefold symmetric kagome lattice that has negative spin chirality can give a nonzero x-ray magnetic circular dichroism (XMCD) signal, despite the total spin moment amounting to zero. In order to explain this, I present here a rule for the rotational symmetry invariance of the XMCD signal. A necessary condition is the existence of an anisotropic XMCD signal for the local magnetic atom, which can arise from a spin anisotropy either in the ground state or the final state. The angular dependence of the XMCD as a function of the beam direction has an unusual behavior. The maximum dichroism is not aligned along the spin direction, but depends on the relative orientation of the spin with respect to the atomic orientation. Therefore, different geometries can result in the same angular dependence, and the spin direction can only be determined if the atomic orientation is known. The consequences for the x-ray magneto-optical sum rules are given. The integrated XMCD signals are proportional to the anisotropy in the orbital moment and the magnetic dipole term, where the isotropic spin moment drops out.	Sep 2021
B23-Circular Dichroism	Communication breakdown: Dissecting the COM interfaces between the subunits of nonribosomal peptide synthetases Christopher D. Fage , Simone Kosol , Matthew Jenner , Carl Öster , Angelo Gallo , Milda Kaniusaite , Roman Steinbach , Michael Staniforth , Vasilios G. Stavros , Mohamed A. Marahiel , Max J. Cryle , Józef R. Lewandowski Acs Catalysis DOI: 10.1021/acscatal.1c02113 Diamond Proposal Number(s): [16655] Open Access Show Abstract ▼ Abstract: Nonribosomal peptides are a structurally diverse and bioactive class of natural products constructed by multidomain enzymatic assembly lines known as nonribosomal peptide synthetases (NRPSs). While the core catalytic domains and even entire protein subunits of NRPSs have been structurally elucidated, little biophysical work has been reported on the docking domains that promote interactions—and thus transfer of biosynthetic intermediates—between subunits. In the present study, we closely examine the COM domains that mediate COMmunication between donor epimerization (E) and acceptor condensation (C) domains found at the termini of NRPS subunits. Through a combination of X-ray crystallography, circular dichroism spectroscopy, solution- and solid-state NMR spectroscopy, and molecular dynamics (MD) simulations, we provide direct evidence for an intrinsically disordered donor COM region that folds into a dynamic helical motif upon binding to a suitable acceptor. Furthermore, our NMR titration and carbene footprinting experiments illuminate the residues involved at the COM interaction interface, and our MD simulations demonstrate folding consistent with experimental data. Although our results lend credence to the previously proposed helix-hand mode of interaction, they also underscore the importance of viewing COM interfaces as dynamic ensembles rather than single rigid structures and suggest that engineering experiments should account for the interactions which transiently guide folding in addition to those which stabilize the final complex. Through activity assays and affinity measurements, we further substantiate the role of the donor COM region in binding the acceptor C domain and implicate this short motif as readily transposable for noncognate domain crosstalk. Finally, our bioinformatics analyses show that COM domains are widespread in natural product pathways and function at interfaces beyond the canonical type described above, setting a high priority for thorough characterization of these docking domains. Our findings lay the groundwork for future attempts to rationally engineer NRPS domain–domain interactions with the ultimate goal of generating bioactive molecules.	Aug 2021
I10-Beamline for Advanced Dichroism	Ferromagnetism in ultrathin surface-free La0.7Sr0.3MnO3 layers in electrostatically defined heterostructures A. Galdi , N. Coppola , C. Sacco , L. Maritato , P. Bencok , P. Steadman , P. Orgiani , C. Aruta Physical Review Materials 5 DOI: 10.1103/PhysRevMaterials.5.084409 Diamond Proposal Number(s): [14915] Show Abstract ▼ Abstract: Electrostatically defined perovskite oxide heterostructures, in which carriers are confined by the modulation of the A-site ion charge, offer new possibilities of tuning the magnetic properties of manganite oxides. We investigate the preferential orientation of ferromagnetic and antiferromagnetic moments in ultrathin La 0.7 Sr 0.3 MnO 3 layers embedded in antiferromagnetic Sr MnO 3 as they undergo a metal-to-insulator transition with decreasing thickness. Our results evince the role of orbital occupation, metallicity, and competition of different magnetic phases, in absence of spurious effects occurring in thin films as a result of symmetry breaking at La 0.7 Sr 0.3 MnO 3 interfaces and of incorporation of oxygen vacancies.	Aug 2021
I10-Beamline for Advanced Dichroism	Tuning 2D magnetism in Fe3+XGeTe2 films by element doping Shanshan Liu , Zihan Li , Ke Yang , Enze Zhang , Awadhesh Narayan , Xiaoqian Zhang , Jiayi Zhu , Wenqing Liu , Zhiming Liao , Masaki Kudo , Takaaki Toriyama , Yunkun Yang , Qiang Li , Linfeng Ai , Ce Huang , Jiabao Sun , Xiaojiao Guo , Wenzhong Bao , Qingsong Deng , Yanhui Chen , Lifeng Yin , Jian Shen , Xiaodong Han , Syo Matsumura , Jin Zou , Yongbing Xu , Xiaodong Xu , Hua Wu , Faxian Xiu National Science Review DOI: 10.1093/nsr/nwab117 Diamond Proposal Number(s): [20748] Open Access Show Abstract ▼ Abstract: Two-dimensional (2D) ferromagnetic materials have been discovered with tunable magnetism and orbital-driven nodal-line features. Controlling the 2D magnetism in exfoliated nanoflakes via electric/magnetic fields enables the boosted Curie temperature (TC) or phase transitions. One of the challenges, however, is the realization of high TC 2D magnets that are tunable, robust and suitable for large scale fabrication. Here, we report molecular-beam epitaxy growth of wafer-scale Fe3+XGeTe2 films with TC above-room-temperature. By controlling the Fe composition in Fe3+XGeTe2, a continuously-modulated TC in a broad range of 185–320 K has been achieved. This widely tunable TC is attributed to the doped interlayer Fe that provide a 40% enhancement around the optimal composition X = 2. We further fabricated magnetic tunneling junction device arrays that exhibit clear tunneling signals. Our results show an effective and reliable approach, i.e. element doping, to produce robust and tunable ferromagnetism beyond room temperature in a large-scale 2D Fe3+XGeTe2 fashion.	Jul 2021
B23-Circular Dichroism	Modelling the adsorption of proteins to nanoparticles at the solid-liquid interface Mikhail Soloviev , Giuliano Siligardi , Danilo Roccatano , Enrico Ferrari Journal Of Colloid And Interface Science 162 DOI: 10.1016/j.jcis.2021.07.072 Diamond Proposal Number(s): [27024] Show Abstract ▼ Abstract: Hypothesis: We developed a geometrical model to determine the theoretical maximum number of proteins that can pack as a monolayer surrounding a spherical nanoparticle. We applied our new model to study the adsorption of receptor binding domain (RBD) of the SARS-CoV-2 spike protein to silica nanoparticles. Due to its abundance and extensive use in manufacturing, silica represents a reservoir where the virus can accumulate. It is therefore important to study the adsorption and the persistence of viral components on inanimate surfaces. Experiments: We used previously published datasets of nanoparticle-adsorbed proteins to validate the new model. We then used integrated experimental methods and Molecular Dynamics (MD) simulations to characterise binding of the RBD to silica nanoparticles and the effect of such binding on RBD structure. Findings: The new model showed excellent fit with existing datasets and, combined to new RBD-silica nanoparticles binding data, revealed a surface occupancy of 32% with respect to the maximum RBD packing theoretically achievable. Up to 25% of RBD’s secondary structures undergo conformational changes as a consequence of adsorption onto silica nanoparticles. Our findings will help developing a better understanding of the principles governing interaction of proteins with surfaces and can contribute to control the spread of SARS-CoV-2 through contaminated objects.	Jul 2021
B23-Circular Dichroism	Interaction of a short peptide with G-quadruplex-forming sequences: An SRCD and CD study Claudia Honisch , Eugenio Ragazzi , Rohanah Hussain , John Brazier , Giuliano Siligardi , Paolo Ruzza Pharmaceutics 13 DOI: 10.3390/pharmaceutics13081104 Diamond Proposal Number(s): [21245] Open Access Show Abstract ▼ Abstract: G-quadruplex (G4) forming DNA sequences were recently found to play a crucial role in the regulation of genomic processes such as replication, transcription and translation, also related to serious diseases. Therefore, systems capable of controlling DNA and RNA G-quadruplex structures would be useful for the modulation of various cellular events. In particular, peptides represent good candidates for targeting G-quadruplex structures, since they are easily tailored to enhance their functionality. In this work, we analyzed, by circular dichroism and synchrotron radiation circular dichroism spectroscopies, the interaction of a 25-residue peptide deriving from RHAU helicases (Rhau25) with three G-quadruplex-forming oligonucleotide sequences, in both sodium- and potassium-containing buffers, the most relevant monovalent cations in physiological conditions. The peptide displayed greater affinity for the G4 sequences adopting a parallel structure. However, it showed the ability to also interact with antiparallel or hybrid G-quadruplex structures, inducing a conformation conversion to the parallel structure. The stability of the oligonucleotide structure alone or in presence of the Rhau25 peptide was studied by temperature melting and UV denaturation experiments, and the data showed that the interaction with the peptide stabilized the conformation of oligonucleotide sequences when subjected to stress conditions.	Jul 2021
B23-Circular Dichroism	Free radicals and ROS induce protein denaturation by UV photostability assay Paolo Ruzza , Claudia Honisch , Rohanah Hussain , Giuliano Siligardi International Journal Of Molecular Sciences 22 DOI: 10.3390/ijms22126512 Diamond Proposal Number(s): [13661, 14857, 15931, 16643, 17413] Open Access Show Abstract ▼ Abstract: Oxidative stress, photo-oxidation, and photosensitizers are activated by UV irradiation and are affecting the photo-stability of proteins. Understanding the mechanisms that govern protein photo-stability is essential for its control enabling enhancement or reduction. Currently, two major mechanisms for protein denaturation induced by UV irradiation are available: one generated by the local heating of water molecules bound to the proteins and the other by the formation of reactive free radicals. To discriminate which is the likely or dominant mechanism we have studied the effects of thermal and UV denaturation of aqueous protein solutions with and without DHR-123 as fluorogenic probe using circular dichroism (CD), synchrotron radiation circular dichroism (SRCD), and fluorescence spectroscopies. The results indicated that the mechanism of protein denaturation induced by VUV and far-UV irradiation were mediated by the formation of reactive free radicals (FR) and reactive oxygen species (ROS). The development at Diamond B23 beamline for SRCD of a novel protein UV photo-stability assay based on consecutive repeated CD measurements in the far-UV (180–250 nm) region has been successfully used to assess and characterize the photo-stability of protein formulations and ligand binding interactions, in particular for ligand molecules devoid of significant UV absorption.	Jun 2021
B21-High Throughput SAXS B23-Circular Dichroism	An artificial membrane binding protein-polymer surfactant nanocomplex facilitates stem cell adhesion to the cartilage extracellular matrix Rosalia Cuahtecontzi-Delint , Graham J. Day , William J. P. Macalester , Wael Kafienah , Wenjin Xiao , Adam W. Perriman Biomaterials 5 DOI: 10.1016/j.biomaterials.2021.120996 Diamond Proposal Number(s): [21035] Show Abstract ▼ Abstract: One of the major challenges within the emerging field of injectable stem cell therapies for articular cartilage (AC) repair is the retention of sufficient viable cell numbers at the site of injury. Even when delivered via intra-articular injection, the number of stem cells retained at the target is often low and declines rapidly over time. To address this challenge, an artificial plasma membrane binding nanocomplex was rationally designed to provide human mesenchymal stem cells (hMSCs) with increased adhesion to articular cartilage tissue. The nanocomplex comprises the extracellular matrix (ECM) binding peptide of a placenta growth factor-2 (PlGF-2) fused to a supercharged green fluorescent protein (scGFP), which was electrostatically conjugated to anionic polymer surfactant chains to yield [S−]scGFP_PlGF2. The [S−]scGFP_PlGF2 nanocomplex spontaneously inserts into the plasma membrane of hMSCs, is not cytotoxic, and does not inhibit differentiation. The nanocomplex-modified hMSCs showed a significant increase in affinity for immobilised collagen II, a key ECM protein of cartilage, in both static and dynamic cell adhesion assays. Moreover, the cells adhered strongly to bovine ex vivo articular cartilage explants resulting in high cell numbers. These findings suggest that the re-engineering of hMSC membranes with [S−]scGFP_PlGF2 could improve the efficacy of injectable stem cell-based therapies for the treatment of damaged articular cartilage.	Jun 2021
I10-Beamline for Advanced Dichroism	Study of spin pumping through α‐Sn thin films Łukasz Gladczuk , Leszek Gladczuk , Piotr Dluzewski , Gerrit Van Der Laan , Thorsten Hesjedal Physica Status Solidi (rrl) – Rapid Research Letters 100 DOI: 10.1002/pssr.202100137 Diamond Proposal Number(s): [15211, 16099] Open Access Show Abstract ▼ Abstract: Elemental tin in the α‐phase is an intriguing member of the family of topological quantum materials. In thin films, with decreasing thickness, α‐Sn transforms from a 3D topological Dirac semimetal (TDS) to a 2D topological insulator (TI). Getting access to and making use of its topological surface states is challenging and requires interfacing to a magnetically ordered material. Herein, the successful epitaxial growth of α‐Sn thin films on Co, forming the core of a spin‐valve structure, is reported. Time‐ and element‐selective ferromagnetic resonance experiments are conducted to investigate the presence of spin pumping through the spin‐valve structure. A rigorous statistical analysis of the experimental data using a model based on the Landau–Lifshitz–Gilbert–Slonczewski equation is applied. A strong exchange coupling contribution is found, however no unambiguous proof for spin pumping. Nevertheless, the incorporation of α‐Sn into a spin valve remains a promising approach given its simplicity as an elemental TI and its room‐temperature application potential.	May 2021

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