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Hydrogen Induced Disproportionation of Samarium Cobalt Intermetallics Enabling Promoted Hydrogen Evolution Reaction Activity and Durability in Alkaline Media
Get PDFTransition metal nanoparticles hold great promise as electrocatalysts for alkaline hydrogen evolution reaction HER , however, addressing the simultaneous challenges of ensuring sufficient active sites, promoting favorable water dissociation, and optimizing binding energy toward hydrogen intermediates remains a formidable task. To overcome these hurdles, a novel gaseous hydrogen engineering strategy is proposed by in situ embedding cobalt nanoparticles within a samarium hydride matrix Co SmH2 via hydrogen induced disproportionation of SmCo5 particles for efficient alkaline HER. The as designed Co SmH2 delivered an overpotential as low as 252 mV at 100 mA cm amp; 8722;2, surpassing the performance of pristine Co by 100 mV. Notably, this catalyst lasts remarkably long maintaining a durability at amp; 8776;500 mA cm amp; 8722;2 for 120 h. A combination of in situ Raman spectroscopy, in situ X ray absorption spectroscopy, density functional theory calculation and post HER characterizations unambiguously unveiled that the surface SmH2 transforms into samarium hydr oxide during electrocatalysis. This transformation not only inhibits the aggregation of the ultrafine cobalt nanoparticles but also significantly enhances the water dissociation and optimizes the binding energy of active cobalt species toward hydrogen intermediate, resulting in concurrent improvement of kinetics, thermodynamics, and stability of the HER proces
Modulation of the FKBP51 structure by protein engineering and isolation of conformation locking antibodies and affibodies
No full textProteins are biomolecules with an intrinsic flexibility that enables them to carry out their functions by interacting with other proteins, substrates, cells, and many other molecules. The structural flexibility of a protein influences ligand protein binding, and for some therapeutic targets, this feature can limit the access to its binding site. This presents a constraint for the development of novel molecules to inhibit or activate a target protein. The FK506 binding protein 51 FKBP51 is a member of the immunophilin family, and it is linked to several psychiatric and stress related disorders, among many other reported diseases. Various members of the FKBP family possess an FK1 domain with a highly conserved active site or orthosteric site . This is not only specific for FKBPs, but it is common to find largely conserved orthosteric sites across protein families. Due to small differences in the amino acid sequence of FKBP51 compared to other members of its family, this protein exhibits higher flexibility than other FKBPs, which translates into a higher number of possible conformers. One of these reported conformers forms a transient binding pocket that can potentially accommodate FKBP51 selective ligands without interacting with other members of this pro tein family. This doctoral thesis focuses on the development of research tools to shift the conformational ensemble of FKBP51 from the native low energy state closed conformation to a conformer with a sta bilized transient binding pocket that can bind conformation specific ligands. The first part of this work focuses on a protein engineering and screening strategy that was used to successfully identify FKBP51 variants with a favored open conformation of a transient binding pocket. To that end, the amino acids of the FKBP51 FK1 domain were systematically modified by random and Site Saturation Mutagenesis SSM to spot FKBP51 muteins that change the distribution of the protein to an open conformation, favoring the binding of two reported conformation specific ligands. Firstly, random mutagenesis was used to mutate the FK1 domain encoding gene of FKBP51. With this genetic material, a Yeast Surface Display YSD library presenting a pool of mutagenesis variants was created and screened via high throughput Fluorescence Activated Cell Sorting FACS . From this first library, a specific region of the protein that destabilizes the FKBP51 binding pocket was identified. Subsequently, an SSM of the identified region spanning glycine 64 to serine 69 was applied, and a second YSD library was created and screened via FACS ..
A multi edge study investigating Co oxidation states of pristine LiNixMnyCo1 x yO2 cathode materials by high energy resolution X ray spectrometry
No full textThe investigation of Co oxidation states in pristine LiNixMnyCo1 amp; 8722;x amp; 8722;yO2 NMC cathodes NMC111, NMC622, NMC811 has been a subject of ongoing debate, with conflicting findings in the literature. In this study, we present a novel and comprehensive approach to address and clarify this issue using a variety of high energy resolution X ray spectroscopy techniques. To shed light on the Co oxidation states in NMC cathodes, we employed independent measurements including X ray absorption spectrometry in both soft and hard X ray ranges, as well as resonant X ray emission spectrometry in the soft X ray range. The investigation centered on the transition metal TM K and L edges, providing a thorough exploration of the electronic structure transitions. The study identified minor shifts in Co oxidation states, and theoretical calculations quantified the ratio of Co atoms undergoing oxidation state changes, which were approximately 2.05 NMC111 to NMC622 and 3.75 NMC111 to NMC811 . Independent measurements that targeted electronic structure transitions using K edge and L edge absorption and emission spectrometry were strategically combined to enhance the reliability of the results. The diverse methodological approach aimed to contribute to a comprehensive understanding of Co oxidation states in NMC cathodes. This study highlights the importance of combining complementary techniques to address intricate scientific debates effectivel
X ray reflective coatings made of Pt, Al2O3 Pt, and Al2O3 Ni Pt produced by atomic layer deposition
No full textThe X ray reflectance of Pt based coatings deposited by atomic layer deposition ALD has been measured in support of assessing the feasibility of using this deposition method for the production of X ray mirror coatings that can achieve high X ray reflectance without causing unacceptably large degradation of mirror figure as a result of coating stress driven substrate deformation. Specifically, reflectance measurements of single layer Pt, Al2O3 Pt bilayer, and Al2O3 Ni Pt trilayer coatings grown by ALD on flat Si substrates were made using synchrotron radiation at X ray energies in the range from 0.35 to 10 keV, revealing that the reflectance of the bilayers and trilayers is superior to that of single layer sputtered Ir below 3.5 keV. Single layer Pt and Al2O3 Pt bilayer coatings produced using thermal ALD were also deposited onto both the front and back surfaces of thin, figured, sub arcsecond quality Xray telescope mirror segments made of polished, single crystal Si, without discernible degradation of surface figure. These results, along with the successful implementation of batch coating of two such mirrors simultaneously with high reflectance coatings grown by thermal ALD, demonstrate the viability of employing stress balanced, doublesided ALD coatings to mitigate substrate deformation resulting from film stress in high reflectance coatings. This approach may thus enable the mass production of high performance, sub arcsecond X ray telescope mirrors. c 2024 Optica Publishing Group. All rights, including for text and data mining TDM , Artificial Intelligence AI training, and similar technologies, are reserve
Advancing photoemission orbital tomography towards a metrological method for absolute electron density reconstruction
No full textCharacterization of thermoregulatory mechanisms in kinases involved in splicing control
No full textAlternative splicing of pre mRNAs can regulate the expression and function of proteins. As such it is a major tool of eukaryotes to adapt their proteome and thus the whole organism to external and internal changes of circumstances. In mammals body temperature cycles result in oscillating alternative splicing driven by rhythmic phosphorylation of SR proteins. Recently, it has been shown that this is facilitated by temperature dependent activity of Cdc2 like kinases CLKs . Temperature sensitivity is conserved across evolution and the active temperature range of the kinases is adapted to the body temperature or growth temperature of the corresponding organism. While it has been shown that the temperature dependence of CLK activity is mediated by conformational changes in the activation segment, the mechanisms by which the active temperature range of the kinases is adapted to the organisms body temperature remained elusive. Here we show multiple structural features fine tuning the active temperature range of CLK homologues. We characterized a CLK homologue, CmLIK, and its substrate phosphorylation from the ancient thermophilic red alga C. merolae and could show that kinase activity at high temperatures is mediated by activation segment stabilization via a salt bridge in the P 1 loop. In contrast to other CLK homologues auto phosphorylation of CmLIK shows markedly different patterns than substrate phosphorylation. Furthermore, we identified an H bond network from a residue in the P 1 loop of a CLK homologue from A. thaliana, AtAFC3, that stabilizes the activation segment and also mediates kinase activity at higher temperatures. We could show that AFCs play a role in heat responsive hypocotyl elongation in A. thaliana upstream of PIF4, the major regulator of thermomorphogenesis. Our results demonstrate stabilization of the P 1 loop of the activation segment as a common mechanism mediating CLK homologue activity at high temperatures. With the characterization of CmLIK we found a model system to study an ancient CLK homologue with activity at high temperatures. Our findings lay the foundation for exploration of genetic engineering of crop plant AFCs to facilitate kinase activity at higher temperatures and adapting their thermomorphogenesis accordingly. This could lead to a partial solution of the problems crop plant growth faces due to global warmin
Magnetic properties of the spiral spin liquid and surrounding phases in the square lattice XY model
Get PDFSpiral spin liquids possess a subextensively degenerate ground state manifold, represented by a continuum of energy minima in reciprocal space. Since a small change of the spiral state wave vector requires a global change of the spin configuration in real space, it is a priori unclear how such systems can fluctuate within the degenerate ground state manifold. Only recently it was proposed that momentum vortices are responsible for the liquidity of the spiral phase and that these systems are closely related to an emergent rank 2 U 1 gauge theory H. Yan et al. [Phys. Rev. Res. 4, 023175 2022 ]. As a consequence of this gauge structure, fourfold pinch point singularities were found in a generalized spin correlator. In this paper, we use classical Monte Carlo and molecular dynamics calculations to embed the previously studied spiral spin liquid into a broader phase diagram of the square lattice XY model. We find a multitude of unusual phases and phase transitions surrounding the spiral spin liquid such as an effective four state Potts transition into a collinear double striped phase resulting from the spontaneous breaking of two coupled amp; 8484;2 symmetries. Since this phase is stabilized by entropic effects selecting the momenta away from the spiral manifold, it undergoes a second phase transition at low temperatures into a nematic spiral phase which only breaks one amp; 8484;2 symmetry. We also observe a region of parameters where the phase transition into the spiral spin liquid does not break any symmetries and where the critical exponents do not match those of standard universality classes. We study the importance of momentum vortices in driving this phase transition and discuss the possibility of a Kosterlitz Thouless transition of momentum vortices. Finally, we explore the regime where the rank 2 U 1 gauge theory is valid by investigating the fourfold pinch point singularities across the phase diagra
Investigation of Quantum Spin Systems with Auxiliary Particles
No full textThis thesis presents advances in the description of quantum magnets, primarily through the development of a new method called the pseudo Majorana functional renormalization group PMFRG . The PMFRG is capable of accurately describing strongly interacting quantum magnets in challenging scenarios where most other methods fail. Fundamental to the formalism of the PMFRG is a resummation of Feynman diagrams, which allows direct treatment of the many body problem in the ther modynamic limit of infinitely many particles. While exact resummation schemes are impossible, the PMFRG uses the framework of the renormalization group to perform a numerical summation of several classes of diagrams to infinite order. Notable examples of such diagrams are associated with common phenomena such as magnetic order, as well as more exotic quantum spin liquids, which are phases described by emergent gauge theories and fractionalization. To exploit this advan tage, spin operators for which diagrammatic techniques are limited are mapped to auxiliary Majorana fermions. This mapping proves to be advantageous compared to the more commonly used complex fermions. After establishing its formalism, the PMFRG is applied to paradigmatic problems in the field of frustrated mag netism at finite temperature. The numerical results obtained with the PMFRG are shown to be quantitatively accurate, typically providing errors of less than 10 compared to exact solutions. In particular, the PMFRG remains applicable to more general scenarios of frustrated three dimensional magnets where exact so lutions are unavailable, and where most other methods are infeasible. In addition, this thesis investigates emergent higher rank gauge theories with immobile quasiparticle excitations known as fractons. The physics of several pinch point features associated with these gauge theories is then analyzed. Using the PMFRG, it is found that these phases are very fragile under the inclusion of quan tum fluctuations. Finally, a new fracton spin model is constructed that exhibits an exactly soluble point with a spin liquid phase. The stability of this phase is then verified by numerically exact quantum Monte Carlo simulations of the spin model compared to the analytical solution of the emergent rank 2 lattice gauge theory, making it the first two body spin model with an emergent fracton quantum spin liquid. The following chapters therefore present substantial progress in two important areas numerical solutions of the quantum many body problem and the study of emergent gauge theories in spin system
Structural basis of ubiquitin recognition and rational design of novel covalent inhibitors targeting Cdu1 from Chlamydia Trachomatis
No full textThe WHO designated neglected disease pathogen Chlamydia trachomatis CT is a gram negative bacterium responsible for the most frequently diagnosed sexually transmitted infection worldwide. CT infections can lead to infertility, blindness and reactive arthritis, among others. CT acts as an infectious agent by its ability to evade the immune response of its host, which includes the impairment of the NF amp; 954;B mediated inflammatory response and the Mcl1 pro apoptotic pathway through its deubiquitylating, deneddylating and transacetylating enzyme ChlaDUB1 Cdu1 . Expression of Cdu1 is also connected to host cell Golgi apparatus fragmentation, a key process in CT infections. Cdu1 may this be an attractive drug target for the treatment of CT infections. However, a lead molecule for the development of novel potent inhibitors has been unknown so far. Sequence alignments and phylogenetic searches allocate Cdu1 in the CE clan of cysteine proteases. The adenovirus protease adenain also belongs to this clan and shares a high degree of structural similarity with Cdu1. Taking advantage of topological similarities between the active sites of Cdu1 and adenain, a target hopping approach on a focused set of adenain inhibitors, developed at Novartis, has been pursued. The thereby identified cyano pyrimidines represent the first active site directed covalent reversible inhibitors for Cdu1. High resolution crystal structures of Cdu1 in complex with the covalently bound cyano pyrimidines as well as with its substrate ubiquitin have been elucidated. The structural data of this thesis, combined with enzymatic assays and covalent docking studies, provide valuable insights into Cdu1s activity, substrate recognition, active site pocket flexibility and potential hotspots for ligand interaction. Structure informed drug design permitted the optimization of this cyano pyrimidine based scaffold towards HJR108, the first molecule of its kind specifically designed to disrupt the function of Cdu1. The structures of potentially more potent and selective Cdu1 inhibitors are herein proposed. This thesis provides important insights towards our understanding of the structural basis of ubiquitin recognition by Cdu1, and the basis to design highly specific Cdu1 covalent inhibitor
Energy Storage in Derivatized Norbornadiene Quadricyclane as Molecular Solar Thermal System Investigated by XPS
No full textThe indispensable transition to renewable energy sources goes hand in hand with appropriate energy storage solutions. Molecular solar thermal MOST systems combine the utilization of solar power with the direct storage of the gained energy in a chemical manner. Upon irradiation, an energy lean compound is converted into its energy rich photoisomer, whereby the release of the stored energy can be catalytically triggered on demand. The molecule pair norbornadiene NBD and quadricyclane QC appears promising for MOST based applications. By suitable derivatization of its molecular framework, the conversion and storage properties are optimized. In particular, the overlap of the absorption profile of NBD with the solar spectrum defines the overall efficiency and requires novel molecular design. Not only the photoconversion yield from NBD to QC is essential for the general applicability, but also the back reaction from QC to NBD must occur in a controlled and efficient way. In this thesis, several 2,3 disubstituted NBD derivatives and their corresponding QC isomers were surveyed on model catalyst surfaces Pt, Ni, Au by synchrotron radiation based X ray photoelectron spectroscopy XPS . Specifically, the derivatization included cyano moieties, phenyl ester substitution, and ester substituted oxa NBD QC of various size. Investigations on the adsorption at low temperatures and subsequent temperature programmed experiments allowed for information on the respective systems on the molecular level, which enabled the deduction of thermally induced surface reactions. The focus was set on the conditions and the extent of the energy releasing cycloreversion reactions of the QC derivatives, by which the feasibility of the different molecule and catalyst combinations was assesse