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Results for “Membrane Structure”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Structural insights on ligand recognition at the human leukotriene B4 receptor 1

The leukotriene B4 receptor 1 (BLT1) regulates the recruitment and chemotaxis of different cell types and plays a role in the pathophysiology of infectious, allergic, metabolic, and tumorigenic human diseases. Here we present a crystal structure of human BLT1 (hBLT1) in complex with a selective antagonist MK-D-046, developed for the treatment of type 2 diabetes and other inflammatory conditions. Comprehensive analysis of the structure and structure-activity relationship data, reinforced by site-directed mutagenesis and docking studies, reveals molecular determinants of ligand binding and selectivity toward different BLT receptor subtypes and across species. The structure helps to identify a putative membrane-buried ligand access channel as well as potential receptor binding modes of endogenous agonists. These structural insights of hBLT1 enrich our understanding of its ligand recognition and open up future avenues in structure-based drug design.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Leveraging microfluidic dielectrophoresis to distinguish compositional variations of lipopolysaccharide in E. coli

Lipopolysaccharide (LPS) is the unique feature that composes the outer leaflet of the Gram-negative bacterial cell envelope. Variations in LPS structures affect a number of physiological processes, including outer membrane permeability, antimicrobial resistance, recognition by the host immune system, biofilm formation, and interbacterial competition. Rapid characterization of LPS properties is crucial for studying the relationship between these LPS structural changes and bacterial physiology. However, current assessments of LPS structures require LPS extraction and purification followed by cumbersome proteomic analysis. This paper demonstrates one of the first high-throughput and non-invasive strategies to directly distinguish Escherichia coli with different LPS structures. Using a combination of three-dimensional insulator-based dielectrophoresis (3DiDEP) and cell tracking in a linear electrokinetics assay, we elucidate the effect of structural changes in E. coli LPS oligosaccharides on electrokinetic mobility and polarizability. We show that our platform is sufficiently sensitive to detect LPS structural variations at the molecular level. To correlate electrokinetic properties of LPS with the outer membrane permeability, we further examined effects of LPS structural variations on bacterial susceptibility to colistin, an antibiotic known to disrupt the outer membrane by targeting LPS. Our results suggest that microfluidic electrokinetic platforms employing 3DiDEP can be a useful tool for isolating and selecting bacteria based on their LPS glycoforms. Future iterations of these platforms could be leveraged for rapid profiling of pathogens based on their surface LPS structural identity.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Mapping structural and dynamic divergence across the MBOAT family

Membrane-bound O-acyltransferases (MBOATs) are membrane-embedded enzymes that catalyze acyl chain transfer to a diverse group of substrates, including lipids, small molecules, and proteins. MBOATs share a conserved structural core, despite wide-ranging functional specificity across both prokaryotes and eukaryotes. The structural basis of catalytic specificity, regulation and interactions with the surrounding environment remain uncertain. Here, we combine comparative molecular dynamics (MD) simulations with bioinformatics to assess molecular and interactional divergence across the family. In simulations, MBOATs differentially distort the bilayer depending on their substrate type. Additionally, we identify lipid binding sites surrounding reactant gates in the surrounding membrane. Complementary bioinformatic analyses reveal a conserved role for re-entrant loop-2 in MBOAT fold stabilization and a key hydrogen bond bridging DGAT1 dimerization. Finally, we predict differences in MBOAT solvation and water gating properties. These data are pertinent to the design of MBOAT-specific inhibitors that encompass dynamic information within cellular mimetic environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Insights into the Water Transport Mechanism in Polymeric Membranes from Neutron Scattering

Polymeric membranes are ubiquitous in transport applications including gas separation, water desalination, solid-state batteries, and fuel cells. The transport mechanism in certain classes of membranes is well understood. It is generally believed that polymeric membranes used in gas separation follow the solution-diffusion model. However, the transport mechanism in other membranes such as the ones used in water desalination is less clear as both the solution-diffusion and hydrodynamic models have been proposed. In this contribution, we study the structure as well as the water and polymer dynamics of several polymeric membranes using small-angle and quasi-elastic neutron scattering. We demonstrate that on the scale of a few nanometers, water appears to diffuse through a desalination membrane at a rate comparable to bulk water, while water diffuses at a rate that is a factor of 2 slower in an anion-exchange membrane. These results illustrate the importance of studying both the structure and dynamics of membrane materials and have important implications in understanding the transport mechanisms that differentiate the different types of polymeric membranes.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Size‐Induced Ferroelectricity in Antiferroelectric Oxide Membranes

Abstract Despite extensive studies on size effects in ferroelectrics, how structures and properties evolve in antiferroelectrics with reduced dimensions still remains elusive. Given the enormous potential of utilizing antiferroelectrics for high‐energy‐density storage applications, understanding their size effects will provide key information for optimizing device performances at small scales. Here, the fundamental intrinsic size dependence of antiferroelectricity in lead‐free NaNbO 3 membranes is investigated. Via a wide range of experimental and theoretical approaches, an intriguing antiferroelectric‐to‐ferroelectric transition upon reducing membrane thickness is probed. This size effect leads to a ferroelectric single‐phase below 40 nm, as well as a mixed‐phase state with ferroelectric and antiferroelectric orders coexisting above this critical thickness. Furthermore, it is shown that the antiferroelectric and ferroelectric orders are electrically switchable. First‐principle calculations further reveal that the observed transition is driven by the structural distortion arising from the membrane surface. This work provides direct experimental evidence for intrinsic size‐driven scaling in antiferroelectrics and demonstrates enormous potential of utilizing size effects to drive emergent properties in environmentally benign lead‐free oxides with the membrane platform.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Heterogeneous Integration of Freestanding Bilayer Oxide Membrane for Multiferroicity

Transition metal oxides exhibit a plethora of electrical and magnetic properties described by their order parameters. In particular, ferroic orderings offer access to a rich spectrum of fundamental physics phenomena, in addition to a range of technological applications. The heterogeneous integration of ferroelectric and ferromagnetic materials is a fruitful way to design multiferroic oxides. The realization of freestanding heterogeneous membranes of multiferroic oxides is highly desirable. In this study, epitaxial BaTiO 3 /La 0.7 Sr 0.3 MnO 3 freestanding bilayer membranes are fabricated using pulsed laser epitaxy. The membrane displays ferroelectricity and ferromagnetism above room temperature accompanying the finite magnetoelectric coupling constant. Further, this study reveals that a freestanding heterostructure can be used to manipulate the structural and emergent properties of the membrane. In the absence of the strain caused by the substrate, the change in orbital occupancy of the magnetic layer leads to the reorientation of the magnetic easy-axis, that is, perpendicular magnetic anisotropy. These results of designing multiferroic oxide membranes open new avenues to integrate such flexible membranes for electronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ionization behavior of nanoporous polyamide membranes

Escalating global water scarcity necessitates high-performance desalination membranes, for which fundamental understanding of structure–property–performance relationships is required. In this study, we comprehensively assess the ionization behavior of nanoporous polyamide selective layers in state-of-the-art nanofiltration (NF) membranes. In these films, residual carboxylic acids and amines influence permeability and selectivity by imparting hydrophilicity and ionizable moieties that can exclude coions. We utilize layered interfacial polymerization to prepare physically and chemically similar selective layers of controlled thickness. Additionally, we then demonstrate location-dependent ionization of carboxyl groups in NF polyamide films. Specifically, only surface carboxyl groups ionize under neutral pH, whereas interior carboxyl ionization requires pH >9. Conversely, amine ionization behaves invariably across the film. First-principles simulations reveal that the low permittivity of nanoconfined water drives the anomalous carboxyl ionization behavior. Furthermore, we report that interior carboxyl ionization could improve the water–salt permselectivity of NF membranes over fourfold, suggesting that interior charge density could be an important tool to enhance the selectivity of polyamide membranes. Our findings highlight the influence of nanoconfinement on membrane transport properties and provide enhanced fundamental understanding of ionization that could enable novel membrane design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Cryo-EM analysis of S. aureus TarL, a polymerase in wall teichoic acid biogenesis central to virulence and antibiotic resistance

Wall teichoic acid (WTA), a covalent adduct of Gram-positive bacterial cell wall peptidoglycan, contributes directly to virulence and antibiotic resistance in pathogenic species. Polymerization of the Staphylococcus aureus WTA ribitol-phosphate chain is catalyzed by TarL, a member of the largely uncharacterized TagF-like family of membrane-associated enzymes. We report the cryo–electron microscopy structure of TarL, showing a tetramer that forms an extensive membrane-binding platform of monotopic helices. TarL is composed of an amino-terminal immunoglobulin-like domain and a carboxyl-terminal glycosyltransferase-B domain for ribitol-phosphate polymerization. The active site of the latter is complexed to donor substrate cytidine diphosphate–ribitol, providing mechanistic insights into the catalyzed phosphotransfer reaction. Furthermore, the active site is surrounded by electropositive residues that serve to retain the lipid-linked acceptor for polymerization. Our data advance general insight into the architecture and membrane association of the still poorly characterized monotopic membrane protein class and present molecular details of ribitol-phosphate polymerization that may aid in the design of new antimicrobials.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Composition and in situ structure of the Methanospirillum hungatei cell envelope and surface layer

Archaea share genomic similarities with Eukarya and cellular architectural similarities with Bacteria, though archaeal and bacterial surface layers (S-layers) differ. Using cellular cryo–electron tomography, we visualized the S-layer lattice surroundingMethanospirillum hungatei, a methanogenic archaeon. Though more compact than known structures,M. hungatei’s S-layer is a flexible hexagonal lattice of dome-shaped tiles, uniformly spaced from both the overlying cell sheath and the underlying cell membrane. Subtomogram averaging resolved the S-layer hexamer tile at 6.4-angstrom resolution. By fitting an AlphaFold model into hexamer tiles in flat and curved conformations, we uncover intra- and intertile interactions that contribute to the S-layer’s cylindrical and flexible architecture, along with a spacer extension for cell membrane attachment.M. hungateicell’s end plug structure, likely composed of S-layer isoforms, further highlights the uniqueness of this archaeal cell. These structural features offer advantages for methane release and reflect divergent evolutionary adaptations to environmental pressures during early microbial emergence.

Science & Technology - Other Topics↗
DOE OSTI2024

Modification of ZIF‐8 Membranes for Gas Separation Using X‐ray Radiation

Abstract We report an X‐ray radiation‐induced modification of the structure and gas permeation behavior of ZIF‐8 membranes. With 300 min irradiation time, CO 2 permeance decreases by only 9 %, while N 2 and CH 4 permeances reduce by 75 and 65 %, respectively, leading to 3.7‐ and 2.6‐fold enhancements in ideal selectivity for CO 2 /N 2 and CO 2 /CH 4 .

Lee, Dennis T.↗
DOE OSTI2023

Large-scale physically accurate modelling of real proton exchange membrane fuel cell with deep learning

Proton exchange membrane fuel cells, consuming hydrogen and oxygen to generate clean electricity and water, suffer acute liquid water challenges. Accurate liquid water modelling is inherently challenging due to the multi-phase, multi-component, reactive dynamics within multi-scale, multi-layered porous media. In addition, currently inadequate imaging and modelling capabilities are limiting simulations to small areas (<1 mm 2 ) or simplified architectures. Herein, an advancement in water modelling is achieved using X-ray micro-computed tomography, deep learned super-resolution, multi-label segmentation, and direct multi-phase simulation. The resulting image is the most resolved domain (16 mm 2 with 700 nm voxel resolution) and the largest direct multi-phase flow simulation of a fuel cell. This generalisable approach unveils multi-scale water clustering and transport mechanisms over large dry and flooded areas in the gas diffusion layer and flow fields, paving the way for next generation proton exchange membrane fuel cells with optimised structures and wettabilities.

25 ENERGY STORAGE↗
DOE OSTI2020

The plant endoplasmic reticulum: an organized chaos of tubules and sheets with multiple functions

The endoplasmic reticulum is a fascinating organelle at the core of the secretory pathway. It is responsible for the synthesis of one third of the cellular proteome and, in plant cells, it produces receptors and transporters of hormones as well as the proteins responsible for the biosynthesis of critical components of a cellulosic cell wall. The endoplasmic reticulum structure resembles a spider-web network of interconnected tubules and cisternae that pervades the cell. The study of the dynamics and interaction of this organelles with other cellular structures such as the plasma membrane, the Golgi apparatus and the cytoskeleton, have been permitted by the implementation of fluorescent protein and advanced confocal imaging. In this review,we report on the findings that contributed towards the understanding of the endoplasmic reticulum morphology and function with the aid of fluorescent proteins, focusing on the contributions provided by pioneering work from the lab of the late Professor Chris Hawes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Analysis of plant ABCB organic acid transporters (Final Report)

Functional Analysis and Genetic Manipulation of Plant ABCB Organic Ion Transporters- The project explores how ABC transporters export hydrophobic aromatics, identifies structural characteristics that regulate lateral positioning, and uses nanodisc technology to create platforms for structural studies of ABC plasma membrane transport proteins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Self-assembly of cocontinuous nanostructured copolymer templates with compositional and architectural dispersity. Final Report

Cocontinuous nanostructured materials in which multiple domains of different materials simultaneously span three dimensional space offer opportunities to achieve combined properties not possible with a single homogeneous material. These architectures have importance in a broad range of energy-relevant technologies including batteries, supercapacitors, fuel cells, separation membranes, and catalysts. Achieving such structures in polymeric materials has been of long-standing interest in the field, due to both the inherently attractive properties of cocontinuous polymer morphologies as well as their ability to serve as templates for other functional nanostructured materials. Our work on this project has established that randomly-linked polymer architectures constructed from two immiscible polymer strands provide robust and highly tunable approaches to disordered cocontinuous nanostructures. In particular, we developed a detailed understanding of how the parameters (linker functionality and strand length, asymmetry, and dispersity) of randomly-linked networks controlled the breadth of the cocontinuous window over which both phases remain percolated. We further characterized how these nanostructures undergo orientation, while retaining cocontinuity, under mechanical deformation. We also compared their behavior to that of random multi-block polymers of linear architecture, which show similar propensity to form disordered nanostructures, albeit over narrower ranges of parameter space. Finally, we have explored the development of functional polymer nanostructures and composites based in part on the fundamental understanding obtained via this project.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A molecular mechanism for the generation of ligand-dependent differential outputs by the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that couples the binding of extracellular ligands, such as EGF and transforming growth factor-α (TGF-α), to the initiation of intracellular signaling pathways. EGFR binds to EGF and TGF-α with similar affinity, but generates different signals from these ligands. To address the mechanistic basis of this phenomenon, we have carried out cryo-EM analyses of human EGFR bound to EGF and TGF-α. We show that the extracellular module adopts an ensemble of dimeric conformations when bound to either EGF or TGF-α. The two extreme states of this ensemble represent distinct ligand-bound quaternary structures in which the membrane-proximal tips of the extracellular module are either juxtaposed or separated. EGF and TGF-α differ in their ability to maintain the conformation with the membrane-proximal tips of the extracellular module separated, and this conformation is stabilized preferentially by an oncogenic EGFR mutation. Close proximity of the transmembrane helices at the junction with the extracellular module has been associated previously with increased EGFR activity. Our results show how EGFR can couple the binding of different ligands to differential modulation of this proximity, thereby suggesting a molecular mechanism for the generation of ligand-sensitive differential outputs in this receptor family.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Gas permeable fluoropolymers and ionomers

Novel copolymers that are fluoropolymers including a first repeat unit that is fluorinated and cyclic and a second repeat unit from a trifluorovinyl methylene ether monomer having sulfur or sulfone functionality in the pendant group are disclosed. The copolymers have relatively high gas permeability as a result of a cyclic repeat unit in the copolymer backbone and ionomers from oxidation of the sulfur containing functionality are particularity useful in the cathode structure of a proton exchange membrane fuel cell.

Lousenberg, Robert Daniel↗
DOE OSTI2023

Reversible Switch in Charge Storage Enabled by Selective Ion Transport in Solid Electrolyte Interphase

Solid-electrolyte interphases (SEIs) in advanced rechargeable batteries ensure reversible electrode reactions at extreme potentials beyond the thermodynamic stability limits of electrolytes by insulating electrons while allowing working ions to transport. Such selective ion transport occurs naturally in biological cell membranes as a ubiquitous prerequisite of many life processes and a foundation of biodiversity. In addition, cell membranes can selectively open and close the ion channels in response to external stimuli (e.g., electrical, chemical, mechanical, thermal), giving rise to “gating” mechanisms that help manage intracellular reactions. We wondered whether the chemistry and structure of SEIs can mimic cell membranes, such that ion gating can be replicated. That is, can SEIs realize a reversible switching between two electrochemical behaviors, i.e., the ion intercalation chemistry of batteries and the ion adsorption of capacitors? Herein, we report such SEIs that result in thermally activated selective ion transport. The function of open/close gate switches is governed by the chemical and structural dynamics of SEIs under different thermal conditions, with precise behaviors as conducting and insulating interphases that enable battery and capacitive processes within a finite temperature window. Such an ion gating function is synergistically contributed by Arrhenius-activated ion transport and SEI dissolution/regrowth. Following the understanding of this new mechanism, we then develop an electrochemical method to heal the SEI layer in situ. As a result, the knowledge acquired in this work reveals the possibility of hitherto unknown biomimetic properties of SEIs, which will guide us to leverage such complexities to design better SEIs for future battery chemistries.

25 ENERGY STORAGE↗