Structural Transition Research Articles

Nanofibrous Chitin Clusters Constructed via Controllable Crystalline Structure Transition for 3D Functional Materials

AbstractIntensively studied polymeric particle production technologies often rely on the combination of polymer self‐assembly and particle processing techniques. Herein, an elegant crystallization transition‐mediated strategy is proposed to confine molecular self‐assembly within a limited range, avoiding the need for extra particle processing steps. This approach enables the production of the regenerated nanofibrous chitin clusters woven with the helical nanofibers. By dissolving the β‐chitin in an aqueous NaOH solution and adjusting the degree of deacetylation (DD value) to 28.0–41.4%, the chitin chains self‐assembly pathway is facilitated to undergo a crystalline transition from α‐chitin to hydrated chitosan. This transition diminishes the chitin chains self‐assembly tendency and confines the self‐assembly to the submicro‐ and micrometer scales. The morphological parameters of these chitin clusters, including cluster size, nanofiber tentacle density, diameter, and helical pitch, can be tuned by adjusting the DD value. These nanofibrous chitin clusters are successfully employed as building blocks to create 3D structural materials for thermal insulation and functional food applications, demonstrating their potential in constructing advanced materials. It is anticipated that the crystalline structure transition‐mediated concept can be applied to other polymeric particle fabrication, opening up a new avenue for designing advanced particles for various applications.

Local-structure insight into the improved superconducting properties of Pb-substituted La(O, F)BiS2: a photoelectron holography study

Pb-substituted La(O, F)BiS2 (Pb-LaOFBiS2) exhibits improved superconducting properties and a resistivity anomaly around 100 K that is attributed to a structural transition. We have performed temperature(T)-dependent photoelectron holography (PEH) to study dopant incorporation sites and the local structure change across the anomaly. The PEH study of Pb-LaOFBiS2 provided evidence for the dominant incorporation sites of Pb and F: Pb atoms are incorporated into the Bi sites and F atoms are incorporated into the O site. No remarkable difference in the local structures around Pb and Bi atoms was observed. Across the temperature of the resistivity anomaly (T*), photoelectron holograms of Bi 4f changed. Comparisons of holograms with those of non-substituted LaOFBiS2 sample, as well as simulated holograms, suggested that (1), above T*, the tetragonal structure of Pb-LaOFBiS2 is different from the tetragonal structure of LaOFBiS2 and (2), below T*, the tetragonal structure still remains in Pb-LaOFBiS2. We discuss a possible origin of the difference in the structure above T* and the implication of the result below T*, which are necessary ingredients to understand the physical properties of Pb-LaOFBiS2.

Stress-Driven Grain Boundary Structural Transition in Diamond by Machine Learning Potential.

Understanding the structural dynamics of carbon grain boundaries, particularly in diamond, is essential for advancing next-generation device applications. Carbon's diverse allotropes, driven by its versatile chemical bonding, hold immense potential, yet analyzing these boundaries is challenging due to the limitations of experimental techniques and the computational demands of ab initio molecular dynamics simulations. In this study, a machine learning-based molecular dynamics potential, rigorously trained on ab initio data, that accurately predicts structural transitions in incoherent twin boundaries within diamond is introduced. This potential reveals the atomic-scale mechanisms driving these transitions and identifies an 80% reduction in interfacial thermal conductance during the grain boundary transition. These findings provide deep insights into the complex behavior of diamond grain boundaries, uncovering a novel mechanism that regulates thermal properties and paving the way for enhanced thermal management in diamond-based technologies.

Bonding Heterogeneity and Nanoprecipitation on Substituting the Anionic Framework in Mg3Sb2 for p‐Type Zintl Thermoelectrics

Designing zintl compounds with complex crystal structures and large unit cells containing heavy elements may inherit bonding heterogeneity‐induced lattice anharmonicity, leading to intrinsically low thermal conductivity. In this work, alloying‐induced bonding heterogeneity in the extensively explored α‐Mg3(Sb, Bi)2 phase due to local atomic ordering, site preferences, and prevailing heterogenous interfaces is evaluated in the p‐type Mg3(Sb1−2xBixSnx)2‐based polyanionic nanocomposites for different alloying concentrations. The inherent susceptibility for partial phase transition (trigonal → monoclinic) is observed upon alloying, which is driven by alterations in bonding patterns, localized distortion, and secondary phase formation. At low alloying content (x ≤ 0.05), a trigonal (Sb, Sn) phase is observed, while for higher alloying content (x ≥ 0.1), a cubic Mg2Sn nanophase emerges. A synergistic reduction in thermal conductivity and enhanced power factor maximize the zT ≈ 0.25(±0.05) at 673 K in the optimized p‐type Mg3(Sb0.9Bi0.025Sn0.025)2 nanocomposites. The study highlights bonding heterogeneity‐induced structural transitions as an inherent challenge, where the dominant role of anionic sites becomes pivotal for determining/deriving favorable structural and functional properties in Mg3(Sb, Bi)2‐based zintl compounds.

Beryllium-Based ABX3-Type Organic-Inorganic Hybrid Halide Ferroelastic.

Organic-inorganic hybrid ferroelastic materials attract great interest in multiple application scenarios, including data storage, shape memory, actuators, mechanical switches, etc. Despite hybrid molecular ferroelastics being the subject of extensive studies due to their remarkable structural and compositional versatility, hybrid metal halide ferroelastics composed of group IIA metal elements have rarely been reported up to now. Herein, a beryllium (Be)-based hybrid halide ABX3-type ferroelastic, CBA-BeF3 (CBA = cyclobutylamine), has been reported for the first time. CBA-BeF3 demonstrates an order-disorder structural phase transition at 356 K, accompanied by a distinct change in symmetry that belongs to the paraelastic-ferroelastic transition with an Aizu notation of mmmF2/m. The observation of ferroelastic domain evolution and stress-strain hysteresis phenomena indicates the ferroelastic nature of CBA-BeF3. This work showcases a brand-new family of hybrid halide ferroelastics and is of great inspiration to explore more group IIA metal-based ferroelastic materials.

The differential impacts of equivalent gating-charge mutations in voltage-gated sodium channels.

Voltage-gated sodium (Nav) channels are pivotal for cellular signaling, and mutations in Nav channels can lead to excitability disorders in cardiac, muscular, and neural tissues. A major cluster of pathological mutations localizes in the voltage-sensing domains (VSDs), resulting in either gain-of-function, loss-of-function effects, or both. However, the mechanism behind this functional diversity of mutations at equivalent positions remains elusive. Through hotspot analysis, we identified three gating charges (R1, R2, and R3) as major mutational hotspots in VSDs. The same amino acid substitutions at equivalent gating-charge positions in VSDI and VSDII of the cardiac sodium channel Nav1.5 show differential gating property impacts in electrophysiology measurements. We conducted molecular dynamics (MD) simulations on wild-type channels and six mutants to elucidate the structural basis of their differential impacts. Our 120-µs MD simulations with applied external electric fields captured VSD state transitions and revealed the differential structural dynamics between equivalent R-to-Q mutants. Notably, we observed transient leaky conformations in some mutants during structural transitions, offering a detailed structural explanation for gating-pore currents. Our salt-bridge network analysis uncovered VSD-specific and state-dependent interactions among gating charges, countercharges, and lipids. This detailed analysis revealed how mutations disrupt critical electrostatic interactions, thereby altering VSD permeability and modulating gating properties. By demonstrating the crucial importance of considering the specific structural context of each mutation, our study advances our understanding of structure-function relationships in Nav channels. Our work establishes a robust framework for future investigations into the molecular basis of ion channel-related disorders.

Electronic structure and energy transitions in oxides and fluorides doped by octahedrally surrounded Cr3+ ions

Electronic structure and energy transitions in oxides and fluorides doped by octahedrally surrounded Cr3+ ions

Structural phase transitions in Ni/Ag/Ti and Ni/Cu/Ti tri-layered thin films

Structural phase transitions in Ni/Ag/Ti and Ni/Cu/Ti tri-layered thin films

Seasonal variation of microbial community and diversity in the Taiwan Strait sediments.

Seasonal variation of microbial community and diversity in the Taiwan Strait sediments.

High-Pressure Computational Analysis of CsCdF₃: Structural Stability, Electronic Transitions, and Thermodynamic Properties

High-Pressure Computational Analysis of CsCdF₃: Structural Stability, Electronic Transitions, and Thermodynamic Properties

First-principles study of the electronic, vibrational, thermodynamic properties and phase stability of orthorhombic KClO4 under pressure

First-principles study of the electronic, vibrational, thermodynamic properties and phase stability of orthorhombic KClO4 under pressure

Polarization rotation in a ferroelectric BaTiO3 film through low-energy He-implantation

Domain engineering in ferroelectric thin films is crucial for next-generation microelectronic and photonic technologies. Here, a method is demonstrated to precisely control domain configurations in BaTiO3 thin films through low-energy He ion implantation. The approach transforms a mixed ferroelectric domain state with significant in-plane polarization into a uniform out-of-plane tetragonal phase by selectively modifying the strain state in the film’s top region. This structural transition significantly improves domain homogeneity and reduces polarization imprint, leading to symmetric ferroelectric switching characteristics. The demonstrated ability to manipulate ferroelectric domains post-growth enables tailored functional properties without compromising the coherently strained bottom interface. The method’s compatibility with semiconductor processing and ability to selectively modify specific regions make it particularly promising for practical implementation in integrated devices. This work establishes a versatile approach for strain-mediated domain engineering that could be extended to a wide range of ferroelectric systems, providing new opportunities for memory, sensing, and photonic applications where precise control of polarization states is essential.

Structural characterization of codon 129 polymorphism in prion peptide segments (PrP127-132) using the Markov State Models.

Structural characterization of codon 129 polymorphism in prion peptide segments (PrP127-132) using the Markov State Models.

Unraveling the molecular grammar and the structural transitions underlying the fibrillation of a viral fibrillogenic domain.

Hendra virus (HeV) is a biosafety level 4 human pathogen belonging to the Henipavirus genus within the Paramyxoviridae family. In HeV, the phosphoprotein-encoding gene also drives the synthesis of the V and W proteins that are two major players in the host innate immune response evasion. These three proteins share a common intrinsically disordered N-terminal domain (NTD) and have distinct C-terminal domains. We recently reported the ability of a short region (i.e., PNT3), located within the shared NTD, to form fibrils. We subsequently identified a PNT3 motif (EYYY) critically involved in fibrillation and deciphered the contribution of each tyrosine to the process. Herein, we combined mutational studies with various biochemical and biophysical approaches to further investigate the molecular mechanisms underlying PNT3 fibrillation. The results show that (i) lysine residues play a critical role in driving fibrillation, (ii) hydrophobic residues affect the nucleation step, and (iii) charge distribution strongly affects the fibrillation propensities. Vibrational Raman spectroscopy data further validated the role of lysine residues in promoting fibrillation and enabled documenting the formation of cross-β amyloid structures. Altogether, these results illuminate the molecular mechanisms involved in fibril formation and pave the way towards the rational design of inhibitors.

Coupling Subunit-Specific States to Allosteric Regulation in Homodimeric Cyclooxygenase-2.

The homodimeric cyclooxygenase enzymes (COX-1 and COX-2) oxygenate arachidonic acid (AA) to generate prostaglandins. COX-2 behaves as a conformational heterodimer in solution comprised of allosteric (Eallo) and catalytic (Ecat) subunits that function cooperatively. We previously utilized 19F-nuclear magnetic resonance spectroscopy (19F-NMR) to show that the cyclooxygenase active site entrances in a COX-2 homodimer construct exhibited composite tightened and relaxed states that are dependent upon the type of ligand bound. A third state, hypothesized to represent the alteration of a loop comprised of residues 120-129, was also detected in the presence of ligands that allosterically potentiate activity. We report here studies that couple the use of 19F-NMR with COX-2 heterodimer constructs to characterize states arising in the individual subunits. Glycine and proline substitutions at Ser-121 were introduced to examine how these mutations alter the 120-129 loop. In the presence of AA, the subunits exhibited asymmetry, with tightened and relaxed states observed in Eallo and Ecat, respectively. Allosteric ligand binding resulted in a shift to equivalent symmetrical states, with tightened states observed in the presence of the allosteric inhibitor flurbiprofen and relaxed states observed in the presence of the allosteric potentiator palmitic acid. The S121P substitution results in a shift to equivalent relaxed states, as well as an alteration of the 120-129 loop in the absence of bound ligand. We put forth a model linking the observed differential states arising from allosteric ligand binding with structural transitions across the dimer interface that govern the regulation of cyclooxygenase activity.

Four‐Center Two‐Electron Bond in 3,6‐Di(tert‐butyl)naphthalene‐1,8‐diyl Bis(tert‐butyl Nitroxide)

Three polymorphs of the title compound were found, showing a head‐to‐tail (N–O)2 four‐membered ring. The aand b phases underwent a reversible structural phase transition across ca. 140 K, while the g phase was independent. The interatomic O…N distances are 79‐81% of the sum of the van der Waals radii, consistent with the diamagnetic properties observed in the magnetic and ESR studies for the a phase. A thermally accessible zero‐field splitting pattern was recorded in solid‐state ESR, and applying a singlet‐triplet (ST) model afforded 2Jobs/kB = –1.87(8)×103 K (H = –2JS1•S2). The SQUID results showed 2Jobs/kB = –2.159(5)×103 K. Thanks to the introduction of two tert‐butyl groups on the naphthalene core, the generation of triplet species is reversible below 430 K. The residual electron density map from the crystallographic data and the QTAIM analysis indicate a four‐center two‐electron s‐bond nature in (N–O)2. Two DFT‐optimized structures were given, featuring 2Jcald/kB = –8864 K as a covalent model and –974 K as a biradical model. Thus, we can propose a mechanism involving two‐step equilibria; a chemical equilibrium between the covalent and biradical forms and a subsequent spin equilibrium between the S and T states in a biradical.

Strain‐Induced, Thermally Tunable Light‐Heavy Hole Emission of Perovskite Nanocrystal‐Based Heterostructure

AbstractUnderstanding the role of strain in the electronic structure and emission of encapsulated perovskite nanocrystals (PNCs) is critical for their light‐emitting application. Herein, photoluminescence (PL) and the structure of Type‐I CsPbBr3@PbBrOH are explored by a combination of temperature‐dependent optical spectroscopy with x‐ray diffraction analysis. The results reveal that the anisotropic lattice mismatch of embedded CsPbBr3 NC with the PbBrOH matrix induces an asymmetric strain. The asymmetric strain increases significantly at low temperatures due to the different thermal response of CsPbBr3 and PbBrOH, where the former undergoes a structural transition between two different orthorhombic phases, while the latter is only subjected to a continuous thermal shrinkage. The asymmetric strain lifts the light hole‐heavy hole (LH‐HH) degeneracy of CsPbBr3, which introduces novel radiative recombination pathways and gives rise to PL spectral splitting. This study unveils the asymmetric strain‐triggered PL spectral splitting and thermal tuning of the emission in PNC‐based heterostructure, which not only provides an in‐depth understanding of the fundamental properties of perovskite but also opens a gate for developing perovskite‐based multi‐color light sources.

Enzyme Surface Residues Direct Encapsulation into Metal–Organic Frameworks for Performance Regulation

AbstractHerein, we highlight the role of nitrogen‐enriched surface groups on proteins in directing topological transformations of metal–organic frameworks (MOFs). Using a modified‐protein‐directed MOFs template synthesis (mDTS) strategy, we demonstrate that these surface modifications on cytochrome c (Cyt c) selectively induce the formation of leaf‐like zeolitic imidazolate frameworks (ZIF‐L). This approach not only enables a structural transition from ZIF‐8 to a more open ZIF‐L framework but also substantially enhances the catalytic activity and loading of Cyt c beyond traditional immobilization methods. Adjusting the concentration of the surface modifier allows for precise tuning of the Cyt c activity, allowing optimal enzyme function at specific modifier levels. Furthermore, our results reveal that surface modifications of a variety of proteins can facilitate the formation of ZIF‐L, emphasizing the broad applicability of the mDTS method. This approach offers significant promise for developing highly efficient protein‐MOF composites, offering transformative potential for industrial catalysis and biotechnological applications.

Effect of Halide Tuning on the Structural, Dielectric, and Optical Properties of Two-Dimensional 2-Chloroethylammonium Lead Halides.

Layered hybrid organic-inorganic lead halides have gained a lot of attention for optoelectronic applications. A notable subset within this category is perovskites comprising halogenated amines since they may exhibit reduced band gap or polar order. We synthesized three compounds comprising 2-chloroethylammonium (CEA+) cations, with the chemical formula CEA2PbX4 (X = Cl, Br, I). X-ray diffraction studies show that at room temperature (RT), CEA2PbBr4 and CEA2PbI4 crystallize in Pbnm symmetry, with ordered CEA+ cations. CEA2PbBr4 and CEA2PbI4 undergo one structural phase transition (PT) into a disordered Pmnm phase near 315 and 360 K, respectively. CEA2PbCl4 shows a different packing of CEA+ with the organic chains oriented perpendicularly to the perovskite layers. It undergoes two PTs at 332 and 203 K from the high-temperature (HT) disordered I4/mmm phase to the partially ordered intermediate Pbnm phase and completely ordered low-temperature (LT) phase of the unknown space group. All compounds emit photoluminescence (PL): orange, yellow-green, and yellow for CEA2PbI4, CEA2PbCl4, and CEA2PbBr4, respectively, and bromide exhibits a very high quantum efficiency of 48%. Overall, our findings show that halide engineering strongly modulates hydrogen and halogen bonding strength, affecting the structural arrangement of building units, molecular dynamics, and thus optoelectronic properties.

The conserved HIV-1 spacer peptide 2 triggers matrix lattice maturation.

The virus particles of human immunodeficiency virus type 1 (HIV-1) are released in an immature, non-infectious form. Proteolytic cleavage of the main structural polyprotein Gag into functional domains induces rearrangement into mature, infectious virions. In immature virus particles, the Gag membrane-binding domain, MA, forms a hexameric protein lattice that undergoes structural transition, following cleavage, into a distinct, mature MA lattice1. The mechanism of MA lattice maturation is unknown. Here we show that released spacer peptide 2 (SP2), a conserved peptide of unknown function situated about 300 residues downstream of MA, binds MA to induce structural maturation. By high-resolution in-virus structure determination of MA, we show that MA does not bind lipid into a side pocket as previously thought1, but instead binds SP2 as an integral part of the protein-protein interfaces that stabilize the mature lattice. Analysis of Gag cleavage site mutants showed that SP2 release is required for MA maturation, and we demonstrate that SP2 is sufficient to induce maturation of purified MA on lipid monolayers in vitro. SP2-triggered MA maturation correlated with faster fusion of virus with target cells. Our results reveal a new, unexpected interaction between two HIV-1 components, provide a high-resolution structure of mature MA, establish the trigger of MA structural maturation and assign function to the SP2 peptide.