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Incorporation of Europium in Topological Insulator Epitaxial Films
No full textIn the field of topological materials, the interaction between band topology and magnetism remains a current frontier for the advancement of new topological states and spintronic functionalities. Doping with rare-earth elements with large magnetic moments is a current approach to exploit the phenomenology of such interaction. However, dopant solubility into the main matrix plays a major role. In this sense, the present work is focused on elucidating how Eu incorporates into Bi2Te3 lattice as a function of doping. This work reports a systematic investigation of the structural and electronic properties of bismuth telluride epitaxial layers doped with Eu. Bi2Te3 films were grown by molecular beam epitaxy on (111) BaF2 substrates with nominal Eu doping ranging from 0% up to 9%. X-ray diffraction analysis and scanning transmission electron microscopy reveal that Eu atoms enter substitutionally on Bi sites up to 4% of Eu doping. In contrast, the 9% Eu-doped sample contains epitaxially oriented nanoclusters of EuTe. X-ray photoelectron and absorption spectroscopies show that Eu atoms enter the Bi2Te3 crystal matrix in the divalent Eu2+ state for all Eu concentrations. Angle-resolved photoemission experiments indicate that the topological surface state is preserved in the presence of the local magnetic moments introduced by the Eu impurities
Structure of a robust bacterial protein cage and its application as a versatile biocatalytic platform through enzyme encapsulation
No full textUsing a newly discovered encapsulin from Mycolicibacterium hassiacum, several biocatalysts were packaged in this robust protein cage. The encapsulin was found to be easy to produce as recombinant protein. Elucidation of its crystal structure revealed that it is a spherical protein cage of 60 protomers (diameter of 23 nm) with narrow pores. By developing an effective coexpression and isolation procedure, the effect of packaging a variety of biocatalysts could be evaluated. It was shown that encapsulation results in a significantly higher stability of the biocatalysts. Most of the targeted cofactor-containing biocatalysts remained active in the encapsulin. Due to the restricted diameters of the encapsulin pores (5–9 Å), the protein cage protects the encapsulated enzymes from bulky compounds. The work shows that encapsulins may be valuable tools to tune the properties of biocatalysts such as stability and substrate specificity
The Non-Fibrillating N-Terminal of α-Synuclein Binds and Co-Fibrillates with Heparin
No full textThe intrinsically disordered protein α-synuclein (aSN) is, in its fibrillated state, the main component of Lewy bodies—hallmarks of Parkinson’s disease. Additional Lewy body components include glycosaminoglycans, including heparan sulfate proteoglycans. In humans, heparan sulfate has, in an age-dependent manner, shown increased levels of sulfation. Heparin, a highly sulfated glycosaminoglycan, is a relevant mimic for mature heparan sulfate and has been shown to influence aSN fibrillation. Here, we decompose the underlying properties of the interaction between heparin and aSN and the effect of heparin on fibrillation. Via the isolation of the first 61 residues of aSN, which lacked intrinsic fibrillation propensity, fibrillation could be induced by heparin, and access to the initial steps in fibrillation was possible. Here, structural changes with shifts from disorder via type I β-turns to β-sheets were revealed, correlating with an increase in the aSN1–61/heparin molar ratio. Fluorescence microscopy revealed that heparin and aSN1–61 co-exist in the final fibrils. We conclude that heparin can induce the fibrillation of aSN1–61, through binding to the N-terminal with an affinity that is higher in the truncated form of aSN. It does so by specifically modulating the structure of aSN via the formation of type I β-turn structures likely critical for triggering aSN fibrillation
Impact of water degumming and enzymatic degumming on gum mesostructure formation in crude soybean oil
No full textPhospholipid gum mesostructures formed in crude soybean oil after water degumming (WD) and enzymatic degumming (ED) were studied at a range of phospholipid and water concentrations. For ED, phospholipase C (PLC), phospholipase A2 (PLA2) and a mixture of phospholipases Purifine 3G (3G) were used. Both WD and ED resulted in lamellar liquid-crystalline phases, however, of different topology. The dependence of the bilayer spacings (as observed by SANS and SAXS) on the ratio between amount of water and amphiphilic lipids differed for WD and PLA2 ED vs PLC and 3G ED. This difference was also observed for dynamics at molecular scale as observed by time-domain (TD) NMR and attributed to partial incorporation of diglycerides and free fatty acids into gum bilayers after PLC and 3G ED. Feasibility of using TD-NMR relaxometry for quantification of the gum phase and estimation of degumming efficiency was demonstrated
Influence of the Molecular Weight and the Presence of Calcium Ions on the Molecular Interaction of Hyaluronan and DPPC
No full textHyaluronan is an essential physiological bio macromolecule with different functions. One prominent area is the synovial fluid which exhibits remarkable lubrication properties. However, the synovial fluid is a multi-component system where different macromolecules interact in a synergetic fashion. Within this study we focus on the interaction of hyaluronan and phospholipids, which are thought to play a key role for lubrication. We investigate how the interactions and the association structures formed by hyaluronan (HA) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) are influenced by the molecular weight of the bio polymer and the ionic composition of the solution. We combine techniques allowing us to investigate the phase behavior of lipids (differential scanning calorimetry, zeta potential and electrophoretic mobility) with structural investigation (dynamic light scattering, small angle scattering) and theoretical simulations (molecular dynamics). The interaction of hyaluronan and phospholipids depends on the molecular weight, where hyaluronan with lower molecular weight has the strongest interaction. Furthermore, the interaction is increased by the presence of calcium ions. Our simulations show that calcium ions are located close to the carboxylate groups of HA and, by this, reduce the number of formed hydrogen bonds between HA and DPPC. The observed change in the DPPC phase behavior can be attributed to a local charge inversion by calcium ions binding to the carboxylate groups as the binding distribution of hyaluronan and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine is not changed
Harmonic Analysis in d-dimensional Superconformal Field Theory
No full textSuperconformal blocks and crossing symmetry equations are among central ingredients in any superconformal field theory. We review the approach to these objects rooted in harmonic analysis on the superconformal group that was put forward in \cite{Buric:2019rms,Buric:2020buk}. After lifting conformal four-point functions to functions on the superconformal group, we explain how to obtain compact expressions for crossing constraints and Casimir equations. The later allow to write superconformal blocks as finite sums of spinning bosonic blocks. This paper is a review, prepared as a contribution to a conference in honour of Vitaly Tarasov and Alexander Varchenko
Structural peculiarities of lysozyme – PLURONIC complexes at the aqueous-air and liquid-liquid interfaces and in the bulk of aqueous solution
No full textInteraction between proteins and synthetic polymers that represent a perspective potential in drug delivery or/and already used in medicine plays a key role in biological functioning of both molecules along with a system as a whole. In present study association between hen egg white lysozyme and Pluronic triblock-copolymers (L121, P123 and F127) in the bulk of the solution as well as at the aqueous-air and liquid-liquid interfaces was analyzed by means of spectroscopic and radiochemical assay. In protein-Pluronic complexes lysozyme keeps the secondary structure (CD and SAXS data results), while fluorescence and UV-analysis indicates changes in the local surrounding of fluorophoric amino acid residues. Radiochemical assay in combination with molecular docking reveals the formation of the complexes, in which proline residues turned to the interface between water and hydrophobic medium
Structure and Function of a guarded Arabidopsis Immune Signaling Ubiquitin Ligase
No full textThe Arabidopsis thaliana E3 ubiquitin ligase SAUL1 (SENESCENCE-ASSOCIATED E3 UBIQUITIN LIGASE 1), which acts as a positive regulator during pattern-triggered immunity (PTI), is characterized by two intriguing hallmarks.(i) On the one hand, SAUL1 is guarded by two heteromeric nucleotide-binding leucine-rich repeat protein (NLR) complexes. These initiate an inducible effector-triggered immunity (ETI) in the saul1 1 mutant. Although ETI is known now for more than 15 years its early regulations and the demarcation from PTI are still not fully understood. Therefore, the saul1 1 phenotype was used to investigate gene regulations during ETI by transcriptomics. These analyses revealed that observed gene regulations were highly similar to other autoimmune mutants and saul1 1 is therefore an ideal model to study ETI. By accessing global changes an early interplay of multiple plant hormones, like salicylic acid, jasmonic acid, ethylene and abscisic acid, was identified, which is likely to initiate the onset of ETI. In addition, repression of brassinosteroid (BR) signaling may be a potential reason of the autoimmune-related growth arrest in saul1 1. Before, BR signaling, as well as synthesis of camalexin and JA signaling have been associated exclusively with PTI. In conclusion, it was possible to show that ETI and PTI are not as distinct as originally thought. In addition, 19 very early differentially expressed genes were identified during the first two hours of the onset of the saul1 1 phenotype. Five of them were analyzed concerning their potential driving role during ETI and two transcription factors, ERF2 (Ethylene Response Factor 2) and ZAT7 (Zinc Finger of Arabidopsis thaliana 7), were identified that pose ideal candidates being initial regulators of ETI.(ii) On the other hand, SAUL1 is characterized by its plasma membrane localization and its domain structure which differ from other plant U-box type E3 ligases (PUBs). Structural experiments allowed to determine for the first time the structure of a PUB. This revealed that SAUL1 is most likely present as a U box-mediated con¬centration-dependent oligomer, which is mostly present as a dimer and tetramer. Therefore, SAUL1 activity may be controlled by oligomerization rendering the U box inaccessible in a multimeric state. Analyzing the domain organization, it was possible to identify a positively charged stretch next to the C terminus that is likely to bind to negatively charged phospholipids. Therefore, and due to the predicted flexibility of the C-terminal armadillo repeats, SAUL1 may bind to multi-vesicular bodies (MVBs) and to the plasma membrane at the same time. This could result in the observed patches at the plasma membrane, originating from MVB tethering, which would be regulated by oligomerization as well. In addition, the low-resolution structure of the SAUL1 binding partner BON1, a plant copine, was as well determined. Although no direct interaction between SAUL1 and BON1 could be observed, the performed experiments may suggest that Ca2+ ions may mediate a SAUL1-BON1 interaction.In conclusion, this thesis provides new insights into regulations during ETI, the structural organization of SAUL1, the concentration-dependent oligomerization of SAUL1, its membrane binding capacities and the interaction between SAUL1 and BON1
Development of photochemical and electrochemical cells for operando X-ray absorption spectroscopy during photocatalytic and electrocatalytic reactions
No full textPhotochemical and electrochemical reactions are highly relevant processes for (i) transforming chemicals (e.g. photoreduction of isopropanol to acetone, electrochemical hydrogenation of benzaldehyde to benzyl alcohol, etc.), and (ii) sustainable energy production (e.g. photoreduction of CO to methanol, electrocatalytic H evolution reaction). It is therefore of importance to monitor the structural changes and to understand the properties of active sites under photocatalytic and electrocatalytic reaction conditions. Operando X-ray absorption spectroscopy (XAS) provides the means to investigate the nature of active sites under realistic reaction conditions. In this contribution, we describe the successful development of photochemical and electrochemical cells for operando XAS measurements during photocatalytic and electrocatalytic reactions. We have used the operando photochemical cell to monitor the formation of Pt nanoparticles on graphitic carbon nitride nanosheets (g-CN-ns) via photodeposition under visible light illumination and observed the formation of highly dispersed Pt nanoparticles with an estimated size of ∼2.5 nm and >60% dispersion. We have also tested this cell to follow the oxidation state of Pt in Pt/TiO and Pt/g-CN-ns during H evolution reaction (HER). We observed that Pt predominantly existed as metallic (reduced) Pt species under HER conditions, and that PtO species were partially reduced from Pt to Pt upon illumination with UV or visible light. The rates of H evolution obtained in the photochemical cell (12.1 mmol g h on Pt/TiO and 1.01 mmol g h on Pt/g-CN-ns) were comparable to that obtained in a standard top-irradiated photoreactor (16.6 mmol g h on Pt/TiO and 1.76 mmol g h on Pt/g-CN-ns). The operando electrochemical cell was successfully tested to monitor the changes in the structure and oxidation state of Pd in Pd/C electrocatalyst during electrocatalytic hydrogenation (ECH) of benzaldehyde. It was demonstrated that Pd in Pd/C was present in a partially reduced state (∼80% Pd0 and ∼20% PdII) and Pd nanoparticles did not degrade upon the application of an external potential under ECH reaction conditions