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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Advancing the Performance of Lithium-Rich Oxides in Cooperation with Inherent Complexities: Engineering Domain Structure

The nanodomain structure of lithium- and manganese-rich, composite cathode materials has been systematically altered through synthesis conditions while keeping larger-scale morphological differences to a minimum. Clear changes in electrochemical performance across the samples studied are observed, especially with respect to the anomalous impedance at low states-of-charge. Atomic-scale modeling, coupled to electrochemical measurements and physical characterization, reveals the local consequences of the high-voltage activation charge process as a function of specific domain structures. Furthermore, the results explain the influence of different postactivation structures on the insertion of Li-ions and the associated impedance during discharge. This work adds to our series of studies on lithium- and manganese-rich oxides, demonstrating that the inherent performance of LMRs can be greatly enhanced through rational, highly controlled synthetic strategies based on an understanding of synthesis–structure–property relationships across length scales.

25 ENERGY STORAGE↗
DOE OSTI2026

Structural Propensities in Cs2MBiX6 (M=Na, Ag; X=Cl, Br) Bismuth Halide Double Perovskites

A previously unreported low-temperature phase transition in the bismuth halide double perovskite Cs2AgBiCl6 is reported, thereby establishing trends in the structural ground state across Cs2NaBiCl6, Cs2AgBiCl6, and Cs2AgBiBr6. Using the combined toolkit of variable-temperature synchrotron X-ray and neutron powder diffraction, Raman spectroscopy, and density-functional theory–based electronic structure modeling, we demonstrate a cubic Fm¯3m → tetragonal I4/m transition upon cooling with distinct onset temperatures. Neutron powder diffraction refinements permit the unambiguously assignment of the low-temperature phase of Cs2NaBiCl6 to I4/m, correcting prior reports of an I4/mmm ground state. Cs2AgBiCl6 is also found to transforms to a structure crystallizing in the I4/m space group at low temperatures. Temperaturedependent Raman data and density-functional theory-based modeling capture the softening and freezing of out-of-phase octahedral-tilt modes and quantify relative instabilities. Solid-state nuclear magnetic resonance spectroscopy at room temperature completes the characterization and helps underpin the subtle differences in covalency across the compounds. Trends in the phase transition temperature Ts and tilt magnitudes emerge from coupled effects of halide identity, M(I)–site bonding character, and a mismatch between interatomic distances. These results establish the structure– dynamics–bonding framework for tuning tilt-driven instabilities in halide double perovskites.

Tian, Haowen↗
DOE OSTI2025

Carbonation of Alkaline Earth Metal Hydroxides: Structure across Nano- to Mesoscales

The conversion of gaseous CO 2 into a solid constitution through mineralization is an active area of carbon capture, and alkaline earth metal hydroxides (M(OH) 2 , M = Ca 2+ , Mg 2+ ) are frontrunners in this area. As model systems, nanolime samples are excellent templates for the study of this reaction. Here, we have examined these under ambient pressure conditions with controlled humidity and CO 2 . Utilizing a broad range of analytical methods, we first established the purity and structures of the selected materials. We then examined the structural changes due to carbonation, using infrared spectroscopy, X-ray scattering, and neutron scattering. The resulting structural changes are resolved from nanoscale to mesoscale and from early-stage to late-stage carbonation. Ca(OH) 2 and Mg(OH) 2 are found to behave quite differently. As expected from prior work, the carbonation of Ca(OH) 2 is kinetically favored. Further, our structure studies suggest this is due to a facile reaction at the fractal interface of the particles. From early- to late-stage carbonation, there is a consistent increase in the fractal roughness. This is in contrast to Mg(OH) 2 where the same surface evolves into a smooth conformal coating. For this material the major reacting component is at the mesoscale, suggesting globular particle growth or evolving macro-porosity. Because neutron scattering is sensitive to hydrogen content, we expected a significant change as M(OH) 2 evolves to MCO 3 . Such a change is found for Ca(OH) 2 but not for Mg(OH) 2 , providing evidence for the formation of hydrated carbonates for the later material. The formation of a conformal layer along with water-rich carbonate formation is an impediment to the use of Mg(OH) 2 for carbon capture. For energy-efficient carbon capture, it would be desirable to enhance carbonation rates for Mg(OH) 2 , and one possible route would be the use of anhydrous fluids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

The Modulated Crystal Structure of K 2 V 3 O 8

Weak lattice distortions can tune exchange pathways and magnetic interactions in square-lattice quantum magnets. K 2 V 3 O 8 is a mixed valence (V 4+ /V 5+ ) fresnoite oxide that exhibits strong spin–lattice coupling at low temperature. Here, we combine single-crystal neutron diffraction (90 K) and laboratory X-ray diffraction (50 K) to solve the low-temperature structure as an orthorhombic (3 + 1)D incommensurately modulated phase in superspace group Cmm2(β,0,1/2)0s0 [No. 196]. What initially appeared as two independent modulation vectors, q 1 = 0.3132(6)[$110$] + 1/2c* and q 2 = 0.3132(6)[$1\bar{10}$] + 1/2c*, are more naturally described as a single one-dimensional modulation wave q = 0.626(1)a* + 1/2c* in a C-centered orthorhombic lattice, related to the parent tetragonal cell by the transformation a + b, −a + b, c. Refinement with a 4-fold rotational twin inherited from the P4bm parent structure solves oxygen-dominated framework distortions and K + displacements. A de Wolff section (t = 0.40) enables a symmetry-mode decomposition, identifying three dominant mm2 (C 2v ) modes: GM3 for framework tilt, A5 for interlayer shear, and Z5 for c-axis breathing. The mode-resolved structure provides a unified, symmetry-based explanation for reported low-temperature Raman and IR anomalies and clarifies the structural origin of the spin–lattice coupling in the S = 1/2 two-dimensional quantum spin compound.

K2V3O8↗
DOE OSTI2024

Capturing Coupled Structural and Electronic Motions During Excited-State Intramolecular Proton Transfer via Computational Multiedge Resonant Inelastic X-ray Scattering

Proton-transfer processes build the foundation of many chemical processes. In Excited State Intramolecular Proton Transfer (ESIPT) processes the proton transfer process is impulsively started through light. Here, in this study, we explore the changes in coupled atomic and electronic motions during and following ESIPT through computational time-resolved Resonant Inelastic X-ray Scattering (trRIXS). Excited-state Ab Initio Molecular Dynamics (AIMD) simulations combined with Time-Dependent Density Functional Theory (TDDFT) calculations were performed for 10-hydroxybenzo[h]quinoline to obtain trRIXS signatures. RIXS at both the nitrogen and oxygen K-edges were computed to resolve the dynamics electronic structure from both the proton donor and acceptor perspective. The results show how RIXS can reveal the local electronic structure, the coupling between different electronic states and how electronic structure and coupling change during the proton transfer process. Additionally, we observe a strong correlation between spectral changes and structural changes during ESIPT.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Imaging Three-Dimensional Molecular Structure and Dynamics with Multiparticle Covariance and Cumulant Coulomb Explosion Analysis

Coulomb explosion imaging (CEI) provides a direct means of imaging molecular geometry by correlating fragment ion momenta following the fragmentation of a molecular polycation. Here, we demonstrate the use of three-body covariance and four-body cumulant analysis to extract three-dimensional (3D) structural information from the X-ray-induced Coulomb explosion of tert-butyl iodide (C4H9I). Site-selective ionization at the iodine 4d edge with intense femtosecond soft X-ray pulses from an X-ray free-electron laser (XFEL) enables rapid charge buildup and molecular breakup. By correlating ionic fragments in the molecular frame, we isolate complete dissociation channels and reveal subtle structural changes, such as umbrella-type motion of the branched alkyl chain, during the ionization process. Comparison with point-charge simulations of the Coulomb explosion shows close agreement, validating the approach. Furthermore, these results establish covariance/cumulant mapping as a powerful strategy for imaging complex three-dimensional molecular structures and point the way toward time-resolved CEI using both XFEL and tabletop sources for capturing ultrafast structural dynamics.

Imaging↗
DOE OSTI2026

Task Sharing of Proton Incorporation in Vertically Aligned Nanocomposite Triple Conductors: Growth, Structure, and Surface Exchange Kinetics

As protonic ceramic electrolysis cells emerge for efficient H 2 production, there is a need to develop air electrode materials enabling fast, durable steam splitting and proton incorporation. Single-phase triple conductors may fail to satisfy the myriad performance/stability requirements, and their critical charge-carriers (holes, oxygen vacancies, and protons) are in competition, limiting their concentrations. Instead, we propose task-sharing, vertically aligned nanocomposites (VANs), comprising a proton conductor (BaZr 0.9 Y 0.1 O 3-δ ) and a redox-active mixed ionic electronic conductor (Ce 0.9 Pr 0.1 O 2-δ ), that may enable rapid proton surface exchange at the solid–gas interface and transport along the solid–solid heterointerfaces. We grew VANs by pulsed laser deposition and investigated the interplay between their processing conditions, structure, and proton and oxygen surface exchange kinetics. We varied the substrate temperature, laser repetition rate, laser fluence, and processing oxygen pressure. The crystallinity and phases were characterized by grazing-incidence X-ray diffraction, and the strain and structural order as a function of depth were evaluated by angle-dependent synchrotron X-ray pair distribution function analysis. To evaluate the potential for interdiffusion, the formation energies of substitutional defects were simulated with density functional theory. Corresponding structural analysis and elemental mapping were performed by scanning/transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy-loss spectroscopy, indicating distinct nanoscale compositional regions with a hierarchical structure embedded in individual VANs columns and minimal interdiffusion across a bilayer film. Proton and oxygen surface exchange coefficients (k H , k O ) and polarization resistances were evaluated by electrical and optical relaxations and impedance spectroscopy of VAN-incorporated protonic ceramic electrochemical cells, respectively, at 400–500 °C, demonstrating values comparable to some of the best-known triple and mixed conductors.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Structural Gating Enhances Long-Distance Light-Driven Interfacial Electron Transfer

Structural gating provides a molecular means to transfer electrons preferentially in one desired vectorial direction, a behavior needed for applications in artificial photosynthesis. At the interfaces utilized herein, visible-light absorption by a transition metal complex opens a “structural gate” by planarization of otherwise rotating phenyl rings in p-phenylene ethynylene (PE) bridge units. Planarization provides a conjugated pathway for electron flow toward a conductive oxide surface. Interfacial electron transfer to the oxide restores rotation and closes the gate to the unwanted recombination reaction. This structural gating results in nearly quantitative long-distance (>20 Å) interfacial electron transfer that occurs ~1000 times faster than transfer in the opposite direction. A comparative kinetic study of these complexes with those that contain ionic bridge units, without gating function, as a function of the applied potential and hence –ΔG° provided a physical basis for the structural gating. A small distance-dependent reorganization energy with weak electronic coupling underlies the success of this gate that enables efficient long-distance electron transfer and slow recombination.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Mechanical Toughening of Two-Dimensional Covalent Organic Frameworks Enabled by Graphene-Based Sandwich-Structured Nanocomposites

Low resistance to fracture in two-dimensional covalent organic frameworks (2D COFs) limits their practical applications, especially in mechanically demanding fields, such as flexible electronics and sensing devices. We address this critical limitation by fabricating a sandwich-structured nanocomposite consisting of graphene layers sandwiched between 2D COF layers (2D COFs/graphene/2D COFs) via chemical vapor deposition. Here, our sandwich-structured nanocomposites exhibit a remarkable improvement in modulus E, fracture toughness K IC , and critical energy release rate G C compared to pure 2D COFs. This enhancement is likely due to the graphene layers as the backbone of the sandwich structure effectively carrying and redistributing mechanical stress within the nanocomposite. Our findings demonstrate that a sandwich structure can improve the mechanical robustness of a 2D COF so that it can preserve the functionality and mechanical integrity for applications in stretchable electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Precise Modulation of CO 2 Sorption in Ti 8 Ce 2 –Oxo Clusters: Elucidating Lewis Acidity of the Ce Metal Sites and Structural Flexibility

Investigating the structure-property correlation in porous materials is a fundamental and consistent focus in various scientific domains, especially within sorption research. Metal oxide clusters with capping ligands, characterized by intrinsic cavities formed through specific solid-state packing, demonstrate significant potential as versatile platforms for sorption investigations due to their precisely tunable atomic structures and inherent long-range order. This study presents a series of Ti 8 Ce 2 -oxo clusters with subtle variations in coordinated linkers and explores their sorption behavior. Notably, Ti 8 Ce 2 -BA (BA denotes benzoic acid) manifests a distinctive two-step profile during CO 2 adsorption, accompanied by a hysteresis loop. This observation marks a new instance within the metal oxide cluster field. Of intrigue, the presence of unsaturated Ce(IV) sites was found to be correlated with the stepped sorption property. Moreover, the introduction of an electrophilic fluorine atom, positioned ortho or para to the benzoic acid, facilitated precise control over gate pressure and stepped sorption quantities. Advanced in-situ techniques systematically unraveled the underlying mechanism behind this unique sorption behavior. The findings elucidate that robust Lewis base-acid interactions are established between CO 2 molecules and Ce ions, consequently altering the conformation of coordinated linkers. Conversely, the F atoms primarily contribute to gate pressure variation by influencing the Lewis acidity of the Ce sites. This research advances the understanding in fabricating metal-oxo clusters with structural flexibility and provides profound insights into their host-guest interaction motifs. Furthermore, these insights hold substantial promise across diverse fields and offer valuable guidance for future adsorbent designs grounded in fundamental theories of structure-property relationships.

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

Electrochemically Determined and Structurally Justified Thermochemistry of H atom Transfer on Ti-Oxo Nodes of the Colloidal Metal–Organic Framework Ti-MIL-125

Titanium dioxide (TiO 2 ) has long been employed as (photo)electrodes for reactions relevant to energy storage and renewable energy synthesis. Proton-coupled electron transfer (PCET) reactions with equimolar amounts of protons and electrons at the TiO 2 surface or within the bulk structure lie at the center of these reactions. Because a proton and an electron are thermochemically equivalent to an H-atom, these reactions are essentially H-atom transfer reactions. Thermodynamics of H-atom transfer has a complex dependence on the synthetic protocol and chemical history of the electrode, the reaction medium, and many others; together, these complications preclude the understanding of the H-atom transfer thermochemistry with atomic-level structural knowledge. Herein, we report our success in employing open-circuit potential (E OCP ) measurements to quantitatively determine the H-atom transfer thermochemistry at structurally well-defined Ti-oxo clusters within a colloidally stabilized metal–organic framework (MOFs), Ti-MIL-125. The free energy to transfer H-atom, Ti 3+ O–H bond dissociation free energy (BDFE), was measured to be 68(2) kcal mol -1 . To the best of our understanding, this is the first report on using E OCP measurements to quantify thermochemistry on any MOFs. The proton topology, the structural change upon the redox reaction, and BDFE values were further quantitatively corroborated using computational simulations. Furthermore, comparisons of the E OCP -derived BDFEs of Ti-MIL-125 to similar parameters in the literature suggest that E OCP should be the preferred method for quantitatively accurate BDFE calculations. Here, the reported success in employing E OCP for nanosized Ti- MIL-125 should lay the ground for thermochemical measurements of other colloidal systems, which are otherwise challenging. Implications of these measurements on Ti-MIL-125 as an H-atom acceptor in chemical reactions and comparisons with other MOFs/metal oxides are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Structural and Electronic Tuning of Luminescent Zn II Complexes Based on an o -Terphenyl Ligand Motif

Here, the structural and photophysical properties of five chiral Zn complexes incorporating a carbazolate (Cz) donor that is electronically decoupled from a pyridyl acceptor by an ortho -connection to a bridging phenylene group are presented. The bidentate ligand in the unsubstituted bis-ligated parent complex was methylated at key positions to constrain the torsional freedom of the donor/acceptor moieties, resulting in three structurally modified bis-ligated derivatives, all exhibiting energy gaps between the singlet and triplet excited states (ΔE ST ) between 22 and 27 meV. Methylation improves the photoluminescence quantum yield (up to 30% in solution), while the low ΔE ST of these complexes allows for dual-emission properties in all of the bis-ligated derivatives. Structural modification of the Cz/pyridyl ligand was also investigated by linking the unsubstituted bidentate ligand to generate a tetradentate, tetrapodal ligand. The solution-state structure of the tetradentate ligand is similar in its free and ligated forms, featuring a binding site reminiscent of enzymes and metal-sequestering ligands. The resulting tetradentate complex [Zn(N 2 R 2 )] shows enhanced through-bond conjugation, increasing the ΔE ST to 89 meV, thereby eliminating the dual-emission characteristics of the bis-ligated complexes. Furthermore, this complex shows a 50-fold improvement in hydrolytic stability in organic solution relative to the parent complex. These compounds and their analyses are intended to enrich the understanding of compounds exhibiting through-space charge transfer and guide the search for earth-abundant metal complexes for applications in photosensitization and luminescence.

aromatic compounds↗
DOE OSTI2026

Structural Heterogeneity in Medium-Entropy AgMnSbPbTe 4 for Glassy Thermal Transport and High Thermoelectric Performance

Medium-entropy semiconductors represent a unique category of entropy-engineered materials. They possess a considerable level of randomness in atomic mixing, although this is not sufficient to conclusively achieve single-phase structure stabilization, in contrast to high-entropy materials. This introduces strong competition between the formation of different phases, which can potentially lead to structural heterogeneity. Here, in this work, we uncover endotaxial nanoprecipitates in the microscopically identified homogeneous medium-entropy semiconductor AgMnSbPbTe 4 . These nanoprecipitates initially crystallize in a cubic phase $(Fm\bar{3}m)$ within kinetically stabilized AgMnSbPbTe 4 , subsequently evolving into a thermodynamically stable monoclinic phase $(P2_1/c)$ during thermal annealing while maintaining an endotaxial relationship with the matrix lattice. This nanophase segregation and the resultant lattice mismatch at interfaces introduce strain fluctuations up to 5% at intervals of 20 nm across the entire microstructure. Within the matrix phase, atomic displacement of up to 23 pm was observed. This structural heterogeneity results in glass-like thermal transport behavior, achieving an ultralow lattice thermal conductivity κ L = 0.312 Wm –1 K –1 at 800 K, which is in accordance with the amorphous limit predicted by the Cahill model. The synergy of band convergence effect and well-maintained carrier mobility leads to a maximum ZT of 1.72 at 800 K and an average ZT avg of 1.02 over the temperature range of 300–825 K. This study highlights that the underexplored structural heterogeneity in medium-entropy semiconductors can potentially yield beneficial phenomena, such as the phonon-glass electron-crystal transport behavior in this case, which holds promise for advancing thermoelectric applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Surface Hydroxyls of Imogolite Nanotubes Drive Distinct Structures and Mobility Differentiation of Nanoconfined Water

Abstract Nanoconfined fluids, particularly water, govern subsurface geochemistry, yet the molecular-level mechanisms by which mineral surfaces dictate confined water structure and mobility remain poorly resolved. Here, we combine solution- and solid-state proton (1H) NMR spectroscopy, NMR relaxometry, modulated-gradient spin–echo (MGSE) NMR diffusometry, infrared spectroscopy, and molecular dynamics simulations to demonstrate that surface hydroxyls drive the structural and dynamic differentiation of water in imogolite nanotubes. In saturated suspensions, we observe the coexistence of distinct water 1H environments, each exhibiting significantly reduced mobility, which we attribute to strong interactions with the imogolite surfaces. As more mobile water is removed, long-range water diffusivity in the fibrous solid samples slows to 1.6 × 10–10 m2·s–1 while local fluctuations increase to 3.4 × 10–8 m2·s–1, indicating a significant increase in molecular restriction through surface interactions. Together, our experiments reveal three coexisting populations with varied structures and mobilities, all distinct from liquid bulk water. We resolve a persistent solid-like interfacial layer strongly bound to surface hydroxyls, characterized by an unusually short T2 (<1 ms), and a very close effective 1H–1H distance of ∼1.55 Å between water and the inner-surface silanol group. An inner-core population occupying the inner cavity exhibits an intermediate dynamic regime with restricted axial diffusion, while outer-surface water associated with aluminum hydroxyls retains relatively higher mobility. These results experimentally substantiate a hierarchy of water populations in imogolite and show how surface chemistry dictates the structures and dynamics of confined water.

Fleming, Xander B. [Earth and Environmental Scienc↗
DOE OSTI2024

Liquid Structure of Iron and Iron–Nitrogen–Carbon Alloys Within the Cores of Small Terrestrial Bodies

Abstract Nitrogen has been proposed to be stored within planetary cores, but its effects on the structure and density of molten Fe–alloys have not been explored experimentally. Using energy‐dispersive X‐ray diffraction, we determined the structure of Fe–N(–C) liquids at core conditions (1–7 GPa and 1700–1900°C) within a Paris‐Edinburgh press. Variation of N up to 7 wt.% and C up to 1.5 wt.% results in near‐linear changes in Fe–Fe atom distances and structure factor with increasing light element content. We did not observe a significant pressure‐driven structural transition in Fe–N(–C) liquids. We model the expansion of the Fe–Fe bonds using a modified Birch‐Murnaghan equation of state. With this model, we demonstrate that N or C contamination could lead to an overestimation of the Fe–Fe distances of pure Fe. We observe that the incorporation of 1 wt.% N or C into Fe results in a change in Fe–Fe distances that is twice as significant as the effect of 1 GPa. By approximating the change in volume, we infer that N and C incorporated in liquid iron could contribute to the density deficit observed in the cores of terrestrial bodies.

Pease, Allison [Department of Earth and Environmen↗
DOE OSTI2025

Crystallographic Texture, Structure, and Stress Transmission in Nugget Sandstone Examined With X‐Ray Tomography and Diffraction Microscopy

Subsurface processes in sandstones are controlled by porosity, permeability, and deformation mechanisms, all of which are controlled by a complex interplay of crystallographic rock texture, structure, and micromechanics. Texture, structure, and micromechanics have historically been studied using optical and electron microscopy of thin-sections. Here, we employed a new combination of in situ X-ray tomography and ray diffraction microscopy to study crystallographic texture, structure, and grain stresses in 3D. We examined these features in a sample of Nugget sandstone, a sandstone constituting hydrocarbon reservoirs across the American West. Our aims are threefold. First, we demonstrate the utility of X-ray diffraction microscopy probes for revealing texture, structure, and stress transmission in 3D. Second, we apply these techniques to Nugget sandstone and discuss findings in the context of prior work. Third, we study grain stress tensor evolution during mechanical compression to examine whether their heterogeneity and orientation evolution reflect that of inter-particle forces in granular materials. Our results show: (a) larger grains featured higher intra-granular misorientations, possibly from an increased prevalence of cements; (b) pores closed parallel to the loading direction and opened normal to loading; (c) grain stresses featured heterogeneity and orientations similar to inter-particle forces in non-cohesive granular materials; (d) grains featured compressive stresses in the loading direction and tensile stresses orthogonal to the loading direction, the latter resisting sample dilation and grain separation. Our work demonstrates the first known application of multi-modal X-ray tomography and diffraction microscopy to sandstone, providing new 3D insight into the nature of quartz cement and stress evolution.

high energy diffraction microscopy↗
DOE OSTI2024

Structural mechanisms for binding and activation of a contact-quenched fluorophore by RhoBAST

The fluorescent light-up aptamer RhoBAST, which binds and activates the fluorophore–quencher conjugate tetramethylrhodamine-dinitroaniline with high affinity, super high brightness, remarkable photostability, and fast exchange kinetics, exhibits excellent performance in super-resolution RNA imaging. Here we determine the co-crystal structure of RhoBAST in complex with tetramethylrhodamine-dinitroaniline to elucidate the molecular basis for ligand binding and fluorescence activation. The structure exhibits an asymmetric “A”-like architecture for RhoBAST with a semi-open binding pocket harboring the xanthene of tetramethylrhodamine at the tip, while the dinitroaniline quencher stacks over the phenyl of tetramethylrhodamine instead of being fully released. Molecular dynamics simulations show highly heterogeneous conformational ensembles with the contact-but-unstacked fluorophore–quencher conformation for both free and bound tetramethylrhodamine-dinitroaniline being predominant. The simulations also show that, upon RNA binding, the fraction of xanthene-dinitroaniline stacked conformation significantly decreases in free tetramethylrhodamine-dinitroaniline. This highlights the importance of releasing dinitroaniline from xanthene tetramethylrhodamine to unquench the RhoBAST–tetramethylrhodamine-dinitroaniline complex. Using SAXS and ITC, we characterized the magnesium dependency of the folding and binding mode of RhoBAST in solution and indicated its strong structural robustness. The structures and binding modes of relevant fluorescent light-up aptamers are compared, providing mechanistic insights for rational design and optimization of this important fluorescent light-up aptamer-ligand system.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Extracting the femtometer structure of strange baryons using the vacuum polarization effect

Abstract One of the fundamental goals of particle physics is to gain a microscopic understanding of the strong interaction. Electromagnetic form factors quantify the structure of hadrons in terms of charge and magnetization distributions. While the nucleon structure has been investigated extensively, data on hyperons are still scarce. It has recently been demonstrated that electron-positron annihilations into hyperon-antihyperon pairs provide a powerful tool to investigate their inner structure. We present a method useful for hyperon-antihyperon pairs of different types which exploits the cross section enhancement due to the effect of vacuum polarization at theJ/ψresonance. Using the 10 billionJ/ψevents collected with the BESIII detector, this allows a precise determination of the hyperon structure function. The result is essentially a precise snapshot of the$$\bar{\Lambda }{\Sigma }^{0}\,(\Lambda {\bar{\Sigma }}^{0})$$ Λ ¯ Σ 0 ( Λ Σ ¯ 0 ) transition process, encoded in the transition form factor ratio and phase. Their values are measured to beR = 0.860 ± 0.029(stat.) ± 0.015(syst.),$$\Delta {\Phi }_{\bar{\Lambda }{\Sigma }^{0}}=(1.011\pm 0.094({{\rm{stat.}}})\pm 0.010({{\rm{syst.}}}))\,{{\rm{r}}}ad$$ Δ Φ Λ ¯ Σ 0 = ( 1.011 ± 0.094 ( stat. ) ± 0.010 ( syst. ) ) r a d and$$\Delta {\Phi }_{\Lambda {\bar{\Sigma }}^{0}}=(2.128\pm 0.094({{\rm{stat.}}})\pm 0.010({{\rm{syst.}}}))\,{{\rm{r}}}ad$$ Δ Φ Λ Σ ¯ 0 = ( 2.128 ± 0.094 ( stat. ) ± 0.010 ( syst. ) ) r a d . Furthermore, charge-parity (CP) breaking is investigated in this reaction and found to be consistent with CP symmetry.

Science & Technology - Other Topics↗