Structural Characterization Research Articles

Structural studies of the IFNλ4 receptor complex using cryoEM enabled by protein engineering

IFNλ4 has posed a conundrum in human immunology since its discovery in 2013, with its expression linked to complications with viral clearance. While genetic and cellular studies revealed the detrimental effects of IFNλ4 expression, extensive structural and functional characterization has been limited by the inability to express and purify the protein, complicating explanations of its paradoxical behavior. In this work, we report a method for robust production of IFNλ4. We then use yeast surface display to affinity-mature IL10Rβ and solve the 72 kilodalton structures of IFNλ4 (3.26 Å) and IFNλ3 (3.00 Å) in complex with their receptors IFNλR1 and IL10Rβ using cryogenic electron microscopy. Comparison of the structures highlights differences in receptor engagement and reveals a distinct 12-degree rotation in overall receptor geometry, providing a potential mechanistic explanation for differences in cell signaling, downstream gene induction, and antiviral activities. Further, we perform a structural analysis using molecular modeling and simulation to identify a unique region of IFNλ4 that, when replaced, enables secretion of the protein from cells. These findings provide a structural and functional understanding of the IFNλ4 protein and enable future comprehensive studies towards correcting IFNλ4 dysfunction in large populations of affected patients.

A rare case of a zero-field single-ion magnet in a cerium(III) pseudo-icosahedral complex.

The synthesis and structural characterisation of [Ln(Tp2-Fu)2]I (1-Ln; Ln = La, Ce, Pr, Nd) (Tp2-Fu = hydrotris(3-(2'-furyl)-pyrazol-1-yl)borate) have been reported as an isomorphous series adopting pseudo-icosahedral ligand field geometries. Continuous shape measurement (CShM) analyses on the crystal field environments of 1-Ln show the smallest values yet reported for complexes employing two hexadentate ligands (e.g. bis-scorpionate environments), with the smallest belonging to 1-La. Single-ion magnetism for 1-Ce, 1-Pr and 1-Nd was probed with ac magnetic susceptibility studies revealing slow magnetic relaxation for 1-Nd in applied magnetic fields and in zero-applied field for 1-Ce, which is a rare observation for Ce(III)-based single-ion magnets. The energy barrier to magnetic relaxation for 1-Ce was experimentally determined to be Ueff = 30(5) cm-1, which is comparable to that of other cerium-based single-molecule magnets in the literature, where these systems stablise the mJ = ±5/2 state and possess large energy gaps between the ground and first excited state that do not agree with the experimentally determined barrier.

Lipidic folding pathway of α-Synuclein via a toxic oligomer

Aggregation intermediates play a pivotal role in the assembly of amyloid fibrils, which are central to the pathogenesis of neurodegenerative diseases. The structures of filamentous intermediates and mature fibrils are now efficiently determined by single-particle cryo-electron microscopy. By contrast, smaller pre-fibrillar α-Synuclein (αS) oligomers, crucial for initiating amyloidogenesis, remain largely uncharacterized. We report an atomic-resolution structural characterization of a toxic pre-fibrillar aggregation intermediate (I1) on pathway to the formation of lipidic fibrils, which incorporate lipid molecules on protofilament surfaces during fibril growth on membranes. Super-resolution microscopy reveals a tetrameric state, providing insights into the early oligomeric assembly. Time resolved nuclear magnetic resonance (NMR) measurements uncover a structural reorganization essential for the transition of I1 to mature lipidic L2 fibrils. The reorganization involves the transformation of anti-parallel β-strands during the pre-fibrillar I1 state into a β-arc characteristic of amyloid fibrils. This structural reconfiguration occurs in a conserved structural kernel shared by a vast number of αS-fibril polymorphs including extracted fibrils from Parkinson’s and Lewy Body Dementia patients. Consistent with reports of anti-parallel β-strands being a defining feature of toxic αS pre-fibrillar intermediates, I1 impacts viability of neuroblasts and disrupts cell membranes, resulting in an increased calcium influx. Our results integrate the occurrence of anti-parallel β-strands as salient features of toxic oligomers with their significant role in the amyloid fibril assembly pathway. These structural insights have implications for the development of therapies and biomarkers.

Upgrade of Weak σ-hole Bond Donors via Cr(CO)3 Complexation.

Molecular recognition mediated by s-hole interactions is enhanced as the electrostatic potential at the σ-hole becomes increasingly positive. Traditional methods to strengthen σ-hole donor ability of atoms such as halogens often involve covalent modifications, such as, introducing electron-withdrawing substituents (neutral or positively charged) or electrochemical oxidation. Metal coordination, a relatively underexplored approach, offers a promising alternative. In this study, η6-coordination of Cr(CO)3 to haloarenes, a neutral system, is demonstrated to significantly increase the electrophilic character of halogen bond donors, enabling weak donors such as chloroanisole to form short and directional Cl···O halogen bonds. Structural characterization using single-crystal X-ray diffraction and computational analysis of a series of η6-Cr(CO)3-coordinated haloarenes provides evidence for this enhancement. Furthermore, the effect is shown to extend to other heteroatomic substituents on the coordinated arene, e.g., other halogen atoms as well as elements of groups 16, 15, and 14 of the periodic table, broadening the scope of this approach.

In Vitro Cholesterol-Lowering Bioactivity, Synthetic Pathway, and Structural Characterization of Exopolysaccharide Synthesized by Schleiferilactobacillus harbinensis Z171.

A strain identified as Schleiferilactobacillus harbinensis was isolated from Chinese sauerkraut, and its exopolysaccharide (EPS) exhibited excellent in vitro cholesterol-lowering bioactivity. Besides, the whole genome of this strain and the structure characteristics of the purified EPS were investigated in this study. S. harbinensis Z171 presented a strong EPS production capacity, with five nucleotide sugar biosynthesis pathways regulated by an EPS synthesis gene cluster. Structural characterization revealed that the purified fraction F-EPS1A was a neutral polysaccharide with a molecular weight of 6.4 × 104 Da. The structure of F-EPS1A contained a backbone that comprised blocks of four 1,2-linked and three 1,3-linked alpha mannose units. Some 1,2-linked alpha mannose residues were branched at C6 with side chains formed by single alpha mannose or a disaccharide consisting of 1,6-linked alpha mannose residues. The structural characteristics endowed F-EPS1A with a high level of cholesterol-lowering bioactivity. In addition, whole genome analysis indicated that S. harbinensis Z171 possessed a strong EPS production capacity. These findings suggested that the EPS produced by S. harbinensis Z171 could be applied as a potential cholesterol-lowering prebiotic agent or supplement in functional food.

Structure Characterization and Antioxidant Activity of a Novel Polysaccharide from Bacillus natto Fermented Millet Bran

To improve the high-value application of millet bran, a water-soluble polysaccharide was extracted from fermented millet bran (FMBP) by using Bacillus natto fermentation. A neutral polysaccharide, FMBP-1, was separated and purified from FMBP using an anion exchange column. Its structure and antioxidant activity in vitro were characterized and determined. The molecular weight of FMBP-1 was 1.154 × 104 Da, and its molecular weight distribution was relatively uniform. The monosaccharide composition, FT-IR, methylation, and NMR results indicated that FMBP-1 was only composed of glucose and was an α-(1→4)-D-glucan that branched at O-6 with a terminal 1-linked α-D-Glcp as a side chain. In addition, the antioxidant assays indicated that FMBP-1 possessed certain capacities for scavenging free radicals and reducing power, and this was in a concentration-dependent manner. This research will provide fundamental data regarding the structure–activity relationship of millet bran polysaccharides and provide a theoretical foundation for the high-value utilization of millet bran within the food and pharmaceutical industries.

Characterization for the Similarity Assessment Between the Proposed Biosimilar SB17 and Ustekinumab Reference Product Using State-of-the-Art Analytical Methods.

SB17 is being developed as a biosimilar to ustekinumab reference product (RP), a human monoclonal antibody (IgG1 kappa immunoglobulin) that binds to the common p40 subunit of cytokines interleukin (IL)-23 and IL-12. Binding to this subunit prevents interaction with their receptor, resulting in modulation in the immune system responses that play a key role in inflammatory disease. The objective of this study was to demonstrate structural, physicochemical, and biological similarity between ustekinumab RP and SB17 using various state-of-the-art analytical methods. Comprehensive analytical characterization was conducted by the quality range and side-by-side comparison approach for SB17 versus the European Union (EU) and US ustekinumab RP using various analytical methods. Comparisons included purity, product-related impurity, charge heterogeneity, primary structure, posttranslational modification, higher-order structure, quantity, Fab-related biological activities (potency and binding activity), and Fc-related biological activities. On the basis of the analytical similarity assessment, the structural, physicochemical, and biological characterization results demonstrated that SB17 is comparable to the ustekinumab RP. In the structural aspects, it was confirmed that there is no clinically meaningful difference between posttranslational modification profiles and higher-order structures of SB17 compared with the ustekinumab RP. Product-related impurities in the form of aggregates were also confirmed to be similar. SB17 has lower acidic and basic variants compared with ustekinumab RP, owing to the difference in the producing cell line. Ustekinumab RP is expressed in an Sp2/0 cell line, whereas SB17 is expressed in CHO cell line. However, the difference between SB17 and ustekinumab RP in the charge variants is not considered to be clinically meaningful, since equivalent biological activity was observed. In the case of mechanism of action (MoA)-related biological activities, SB17 is highly similar to the EU and US ustekinumab RP with respect to overall critical and noncritical quality attributes analyzed. Moreover, similarity or lack of activity in Fc-related biological activities was also confirmed. On the basis of these results, SB17 is expected to have comparable safety and efficacy as compared with ustekinumab RP. In summary, the overall analytical characterization and similarity assessment results show that SB17 is comparable to the EU and US ustekinumab RP in terms of structural, physicochemical, biophysical, and biological attributes.

Nanoscale Structure and Interfacial Electrochemical Reactivity of Moiré-Engineered Atomic Layers.

ConspectusThe electronic properties of atomically thin van der Waals (vdW) materials can be precisely manipulated by vertically stacking them with a controlled offset (for example, a rotational offset─i.e., twist─between the layers, or a small difference in lattice constant) to generate moiré superlattices. In recent years, the application of this "twistronics" concept to interfacial electrochemistry has unveiled unique pathways for tailoring the electrochemical reactivity. This Account provides an overview of our work that leveraged a suite of structural characterization methods, such as interferometric four-dimensional scanning transmission electron microscopy, dark-field transmission electron microscopy, and scanning tunneling microscopy, along with nanoscale electrochemical measurement techniques, namely, scanning electrochemical cell microscopy (SECCM), to uncover and dissect the profound impact of electrode electronic structure, controlled by interlayer twist, on interfacial electron transfer kinetics. At the heart of our findings is the discovery that moiré engineering enables the isolation of thermodynamically unfavorable stacking configurations, or topological defects, that substantially increase the standard electron transfer rate constant at the solid-liquid interface beyond what has been measured on conventional, nontwisted two-dimensional (2D) materials. This enhancement in interfacial reactivity can be attributed to the localization of a high density of electronic states within these particular sites in the superlattice, a similar effect to that which occurs upon incorporation of physical defects or vacancies in an electrode material but instead using an atomically pristine surface with a highly tunable structure. Throughout our studies, understanding the nuances of the relationship between the preimposed moiré twist angle and the observed electron transfer kinetics has heavily relied on the interrogation of additional factors such as spontaneous superlattice reconstruction and three-dimensional localization of electronic states, illustrating the importance of combining electrochemical measurements with both nanoscale structural probes and theoretical modeling for designing and optimizing moiré-engineered electrodes. The insight afforded by our efforts in this space continues to deepen our understanding of the fundamental mechanisms governing electron transfer at electrochemical interfaces at large and also points to the revolutionary prospect of twistronics for advancing electrochemical technologies. While our electrochemical studies have, so far, focused largely on graphene-based moiré materials, we also offer a perspective on the promise of transition metal dichalcogenide (TMD)-based moirés as candidates for highly versatile (photo)electrode surfaces. Accordingly, we provide a discussion of our studies on the structural relaxation observed in moiré superlattices of TMDs, and we summarize our work combining SECCM with field-effect electrostatic gating of TMDs to deconvolute the influences of material conductivity and intrinsic electron transfer kinetics from the overall electrochemical response of a semiconducting 2D material. Overall, this body of work establishes a distinctive foundation for the design of a wide range of materials with tailored properties that can provide crucial insights into interfacial charge transfer chemistry─potentially serving as platforms for sensing, energy conversion, and electrocatalysis─in addition to the emergent exotic correlated electron physics that originally ignited intense interest in moiré twistronics.

Structure characterization and mechanism of angiotensin I-converting enzyme (ACE) inhibitory peptides modified by plastein reaction derived from tiger nut (Cyperus esculentus)

The development of peptides derived from plants, which have potential anti-angiotensin converting enzyme (ACE) activity and other bioactivities, are of scientific interest. ACE inhibitory peptide (CLPP, the ACE inhibitory rate is 76.52 ± 1.07%) was obtained by hydrolysis of tiger nut (Cyperus esculentus) protein with alkaline protease. The plastein product (PCLPP, the ACE inhibitory rate is 85 ± 2.33%) was prepared by modifying CLPP with a plastein reaction. The results of SEM, IR, and XRD show that the structure of PCLPP is different from that of CLPP. The results of differential scanning calorimetry, fluorescence, and free amino analysis showed that the reaction was carried out by aggregation and condensation. These results suggest that the plastein reaction may be an effective method to increase the variety of bioactive peptides.

Synthesis, structural characterization, and luminescence properties of zinc(II) coordination polymers containing bis(4-pyridyl)benzylamine

Synthesis, structural characterization, and luminescence properties of zinc(II) coordination polymers containing bis(4-pyridyl)benzylamine

Targeting protein-ligand neosurfaces with a generalizable deep learning tool.

Molecular recognition events between proteins drive biological processes in living systems1. However, higher levels of mechanistic regulation have emerged, in which protein-protein interactions are conditioned to small molecules2-5. Despite recent advances, computational tools for the design of new chemically induced protein interactions have remained a challenging task for the field6,7. Here we present a computational strategy for the design of proteins that target neosurfaces, that is, surfaces arising from protein-ligand complexes. To develop this strategy, we leveraged a geometric deep learning approach based on learned molecular surface representations8,9 and experimentally validated binders against three drug-bound protein complexes: Bcl2-venetoclax, DB3-progesterone and PDF1-actinonin. All binders demonstrated high affinities and accurate specificities, as assessed by mutational and structural characterization. Remarkably, surface fingerprints previously trained only on proteins could be applied to neosurfaces induced by interactions with small molecules, providing a powerful demonstration of generalizability that is uncommon in other deep learning approaches. We anticipate that such designed chemically induced protein interactions will have the potential to expand the sensing repertoire and the assembly of new synthetic pathways in engineered cells for innovative drug-controlled cell-based therapies10.

In-situ characterization of temperature-dependent domain structure and permittivity of KTN crystals with applied field

In-situ characterization of temperature-dependent domain structure and permittivity of KTN crystals with applied field

Exploring the Pollinator Community: Diversity and Abundance of Flower-Visiting Insects on Cowpea in Bilone, Obala, Cameroon

Aims: Investigations in cowpea fields allowed the characterization of the community structure of flower-visiting insects. Study Design: Seeds were sown in 15 plots (6x5.5 m each). Place and Duration of Study: Campus of Obala Higher Institute of Agriculture and Management (OHIAM), Bilone agroecological farm (Obala-Cameroon), from May to June 2016 and 2017. Methodology: Insects were identified in-situ or captured and stored in papillotes (Lepidoptera adults) or labelled vials containing 70° ethanol (other insects). Abundances allowed the determination of 11 alpha diversity indices. Beta diversity was tested using Bray-Curtis dissimilarity index and the correlation between species occurrences. Results: A total of 929 specimens belonged to five orders, 10 families, 13 species were recorded. Hymenoptera was the most family-rich and abundant (four families, 94.3% of the collection) followed by Diptera and Lepidoptera (two families each). Neuroptera and Orthoptera (one family each). Apidae was the most species-rich and abundant (three species; 72.9%), then Formicidae (one, 10.1%), Megachilidae (two; 9.8%). Apis mellifera (Apidae) was the most abundant (35.5%), then Xylocopa olivacea (Apidae) (22.3%), Amegilla calens (Apidae) (15.1%), Myrmicaria opaciventris (Formicidae) (10.1%), and Megachile (Chalicodoma) cincta (Megachilidae) (8.2%). The afrotropical useful predator Ascalaphus africanus (Ascalapidae) and the phytophagous pest Pteropera carnapi (Acrididae) were recorded. Exotic myasigenic species Calliphora vicina (Calliphoridae) and Musca domestica (Muscidae) were recorded. Acrididae, Nymphalidae and Pieridae cumulatively represented 3.1% pest species in the collection. Assemblages showed low species richness, high species diversity, and highly even community. Numbers of simply abundant species were close to that co-dominants. A negative correlation was noted between Acraea acerata (Nymphalidae) and Apis mellifera adansonii (Apidae), Ap. mellifera and Calliphora vicina (Calliphoridae), Ap. mellifera and Synagris conuta (Vespidae). Several positive correlations were recorded. Conclusion: In Bilone, results highlighted the importance of flower-visiting insects for the cowpea pollination and crop yield. Species were moderately abundant and assemblages functioned on the base of niche partitioning nomocenosis (log-linear model) of more or less disturbed environments with strong competition between pioneer species for the available resources.

Altering Lipid A Precursor Ion Types in the Gas Phase for In-Depth Structural Elucidation via Tandem Mass Spectrometry.

Lipid A, a well-known saccharolipid, acts as the inner lipid-glycan anchor of lipopolysaccharides in Gram-negative bacterial cell membranes and functions as an endotoxin. Its structure is composed of two glucosamines with β(1 → 6) linkages and various fatty acyl and phosphate groups. The lipid A structure can be used for the identification of bacterial species, but its complexity poses significant structural characterization challenges. In this work, we present a comprehensive strategy combining condensed-phase sample preparation, electrospray ionization, and gas-phase ion/ion reactions with tandem mass spectrometry for detailed lipid A structural elucidation. We use proton transfer reactions, charge-inversion reactions, and sequential ion/ion reactions for magnesium transfer to generate targeted lipid A ions. The strategy, established with a synthetic monophosphoryl lipid A (MPLA) and known MPLA and diphosphorylated lipid A (DPLA) from Escherichia coli F583, demonstrated that [MPLA - 2H]2-, [MPLA - H]-, and [MPLA - H + Mg]+ precursor ions offer complementary information for MPLA, while [DPLA - H]-, [DPLA + H]+, and [DPLA - H + Mg]+ precursor ions provide analogous information for DPLA analysis. We validated the strategy using known lipid A species and also successfully applied this strategy to profile unknown MPLA and DPLA in the same E. coli strain.

Multiple myeloma-associated non-crystalline proximal tubulopathy and crystalline cast nephropathy: Biochemical and structural features of disease-causing monoclonal kappa light chains.

Various tubular diseases in patients with multiple myeloma (MM) are caused by monoclonal immunoglobulin light chains (LCs). However, the physicochemical characteristics of the disease-causing LCs contributing to the onset of MM-associated tubular diseases remain unclear. We herein report a rare case of MM-associated combined tubulopathies: non-crystalline light chain proximal tubulopathy (LCPT) and crystalline light chain cast nephropathy (LCCN). The patient's urinary κ-LC (Bence-Jones proteins, BJP-κ PT-CN) was detected through immunofixation. Renal biopsy revealed cytoplasmic vacuoles in swollen proximal tubular cells and distal tubular casts. Immunohistochemistry showed proximal tubular reabsorption granules and distal tubular casts positively stained with an anti-κ-LC antibody. Electron microscopy identified vacuolation and an increased number of lysosomes in proximal tubular epithelial cells without crystalline structures. Distal tubular casts comprised numerous crystals with both rod-shaped and needle-like configurations and tube-shaped materials. To elucidate the molecular mechanisms underlying tubular toxicity, we performed the following physicochemical analyses of BJP-κ PT-CN: N-terminal amino acid sequencing, cDNA cloning, size-exclusion chromatography, thermal shift assays, and X-ray crystallography. The variable segment of BJP-κ PT-CN was derived from the IGKV1-39 gene. The characteristic features of BJP-κ PT-CN were a positively charged surface patch, concentration-dependent monomer-dimer equilibrium, and the R61G mutation. This is the first biochemical and structural characterization of disease-causing BJPs in MM-associated LCPT and crystalline LCCN. The results obtained suggest that these characteristic features enhance protein binding to negatively charged sites on brush-border membranes in proximal tubules and promote the formation of organized casts in distal tubular lumens.

Novel tetracycline hybrids: synthesis, characterization, docking studies and in-vitro evaluation of antibacterial activity

BackgroundThe biggest menace in the world today is the infection caused by pathogenic bacteria in humans, where majority of the available antibiotics fail to provide therapeutic results due to resistance. The discovery of new molecules is the need of the hour and several research groups worldwide are contributing to fight this scare. This work highlights our efforts towards discovering novel tetracycline hybrids that could serve as potent agents against several pathogenic bacterial strains causing infections. In total, ten compounds were synthesized which were chemically conjugates of Minocycline, an age-old tetracycline, and naturally occurring aldehydes and ketones available from the plant sources. Structural characterization of these compounds was done using Mass and 1HNMR. Molecular docking was carried out in order to predict the binding affinity of these compounds to various bacterial enzymes and known protein targets and to establish the structure–activity relationships. Molecular dynamic simulation studies and in silico pharmacokinetic and toxicity prediction studies were done to determine in silico pharmacokinetics and toxicity of compounds. In-vitro antibacterial activities were done using standard protocols against gram positive bacteria like Enterococcus faecalis, Staphylococcus aureus and gram-negative bacteria like Klebsiella pneumoniae, Pseudomonas aeruginosa and Escherichia coli.ResultsPromising results were obtained viz. compound 1,2 and 10 were found to be more potent against Staphylococcus aureus, compound 1 against Enterococcus faecalis, compound 2 and 3 against Escherichia coli, compound 7 and 8 against Pseudomonas aeruginosa and compound 7 against Klebsiella pneumoniae when compared with minocycline as standard compound.ConclusionAll the synthesized compounds were screened for their anti-bacterial activity against gram positive and gram negative microorganisms. Amongst the ten synthesized minocycline hybrids, four minocycline hybrids exhibited potent antibacterial activity as compared to minocycline. These hybrids can serve as a promising lead compound for antibiotic drug discovery.

Molecule-Based Proton-Electron Mixed Conductor with the Highest Ambipolar Conductivity.

Proton-electron mixed conductors (PEMCs) are an essential component for potential applications in hydrogen separation and energy conversion devices. However, the exploration of PEMCs with excellent mixed conduction, which is quantified by the ambipolar conductivity, σamb = σeσH/(σe + σH) (σe: electronic conductivity; σH: proton conductivity), is still a great challenge, largely due to the lack of structural characterization of both conducting mechanisms. In this study, we prepared a molecule-based proton-electron mixed-conducting cation radical salt, (ET)4[Pt2(pop)2(Hpop)2]·PhCN (ET: bis(ethylenedithio)tetrathiafulvalene, pop2-: P2H2O52-), by electrocrystallization. The salt shows metallic electronic conduction, which arises from the (ET)2•+ layers, with a high σe value (1-2 S cm-1 at room temperature). The metallic state was corroborated by magnetic susceptibility measurement and band structure calculation. The salt also shows superprotonic conduction (σH = 2.1 × 10-2 S cm-1 at room temperature under dried conditions), which relies on the one-dimensional (1D) hydrogen-bonding network of protonated paddlewheel-type Pt-dimer complex anions, [Pt2(pop)2(Hpop)2]2-. Crystallographic and computational studies revealed the presence of infinite intra- and intermolecular O-H···O hydrogen bonds, which show a double-well-like potential energy curve with a negligible energy barrier in the 1D chain, facilitating Grotthuss-type proton hopping via Lewis basic sites. Among the structurally defined PEMCs, the present salt displays the highest room temperature σamb value of 2.1 × 10-2 S cm-1 even under dried conditions. The σamb value has the same order as those of reported perovskites-type metal oxides at high temperatures and achieves a level that is beneficial for the practical applications.

Red-Shifted and Enhanced Photoluminescence Emissions from Hydrogen-Bonded Multicomponent Nontraditional Luminogens.

Nontraditional luminogens (NTLs) without large π-conjugated aromatic structures have attracted a great deal of attention in recent years. Developing NTLs with red-shifted and enhanced emissions remains a great challenge. In this work, we developed a NTL composed of three components, i.e., polymaleic acid (PMA), arginine (Arg), and polyacrylamide (PAM), and investigated its photoluminescent behavior and mechanism. Compared with the single components and binary components, the PMA/Arg/PAM solid exhibited two red-shifted emission peaks at 510 and 562 nm and higher quantum yields. Structural characterizations demonstrated that hydrogen bonds formed between the nonconventional chromophores in PMA and Arg lead to more extended through-space conjugation and rigidified conformations, which is the fundamental reason for the red-shifted emission and higher quantum yield of the PMA/Arg/PAM solid. In addition, theoretical calculations proved that excited-state proton transfer occurs between the carboxyl groups of PMA and amino groups of Arg via photoexcitation, resulting in dual emissions in the PMA/Arg/PAM solid. This work provides a deeper understanding of the photoluminescence mechanism of NTLs based on multiple hydrogen bonds and is helpful in guiding the design of NTLs with red-shifted and enhanced emissions.

Single-layer MoSeN – a synthetic Janus two-dimensional transition-metal compound grown by plasma-assisted molecular beam epitaxy

Abstract Two-dimensional (2D) nanomaterials hold immense application potentials such as in high-performance nano-electronics, and asymmetric 2D structures with inherent electric dipoles will extend the application promises. Yet synthesizing asymmetric 2D structures remains challenging. Herein, we report the first synthesis of single-layer (SL) hexagonal (H-) phase polar Janus MoSeN via nitrogen-plasma-assisted molecular beam epitaxy. This is a significant achievement given the incommensurate valence between Mo, Se, and N, and the inherent strain from the Janus architecture. Using an array of compositional and structural characterization methods, we establish the atomic configurations of the synthesized MoSeN SL, confirming that they are 2D Janus transition-metal chalcogen-nitrides rather than alloys. By employing density functional theory calculations and transport measurements, we explore the structural feasibility and offer insights into its electronic properties, demonstrating its metallic behavior with ohmic contact characteristics. Piezoresponse force microscopy measurements reveal vertical piezoelectricity and ferroelectric potentials from the Janus MoSeN SL. Therefore, it exhibits great potential for applications in, e.g. piezoelectric and ferroelectric devices, sensing technologies, and optoelectronic devices. This work not only addresses existing challenges in 2D nanomaterial research but also opens new avenues for the development of advanced functional materials.

Structure–Antioxidant Activity Relationship of Polysaccharides Isolated by Microwave/Ultrasonic-Assisted Extraction from Pleurotus ferulae

To investigate the structure–antioxidant activity relationship, Pleurotus ferulae polysaccharides were extracted using ultrasonic (U-PFPS) and microwave/ultrasonic-assisted methods (MU-PFPS). Compared to U-PFPS with a molecular weight of 1.566 × 103 kDa, MU-PFPS exhibited a lower molecular weight of 89.26 kDa. In addition, unlike U-PFPS, which is primarily composed of glucose (Glu:Man:Gal = 91.1:3.5:5.4), MU-PFPS has a more balanced composition of Glu:Man:Gal in the ratio of 39.4:27.8:32.8 and contains more branched chains. Furthermore, antioxidant analysis revealed that high concentration (at concentrations above 600 μg/mL) MU-PFPS demonstrated stronger protective effects against oxidative damage in RAW264.7 cells than U-PFPS did. Collectively, these data suggest that lower molecular weight and higher branching degree of polysaccharides at appropriate concentrations may correlate with enhanced antioxidant enzyme activities. Our work provides a method for isolating polysaccharides with higher antioxidant activity and offers insights into the structure–activity relationship of polysaccharides, laying the foundation for future applications in polysaccharide modification and structural characterization.