Crystallographic Studies Research Articles

Constructing Co4(SO4)4 Clusters within Metal-Organic Frameworks for Efficient Oxygen Electrocatalysis.

Multinuclear metal clusters are ideal candidates to catalyze small molecule activation reactions involving the transfer of multiple electrons. However, synthesizing active metal clusters is a big challenge. Herein, on constructing an unparalleled Co4(SO4)4 cluster within porphyrin-based metal-organic frameworks (MOFs) and the electrocatalytic features of such Co4(SO4)4 clusters for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is reported. The reaction of CoII sulfate and metal complexes of tetrakis(4-pyridyl)porphyrin under solvothermal conditions afforded Co4-M-MOFs (M═Co, Cu, and Zn). Crystallographic studies revealed that these Co4-M-MOFs have the same framework structure, having the Co4(SO4)4 clusters connected by metalloporphyrin units through Co─Npyridyl bonds. In the Co4(SO4)4 cluster, the four CoII ions are chemically and symmetrically equivalent and are each coordinated with four sulfate O atoms to give a distorted cube-like structure. Electrocatalytic studies showed that these Co4-M-MOFs are all active for electrocatalytic OER and ORR. Importantly, by regulating the activity of the metalloporphyrin units, it is confirmed that the Co4(SO4)4 cluster is active for oxygen electrocatalysis. With the use of Co porphyrins as connecting units, Co4-Co-MOF displays the highest electrocatalytic activity in this series of MOFs by showing a 10mAcm-2 OER current density at 357mV overpotential and an ORR half-wave potential at 0.83V versus reversible hydrogen electrode (RHE). Theoretical studies revealed the synergistic effect of two proximal Co atoms in the Co4(SO4)4 cluster in OER by facilitating the formation of O─O bonds. This work is of fundamental significance to present the construction of Co4(SO4)4 clusters in framework structures for oxygen electrocatalysis and to demonstrate the cooperation between two proximal Co atoms in such clusters during the O─O bond formation process.

Binary and Halide-free Catalyst Systems Based on Al/Ga/In Aminopyridylbisphenolate Complexes for the Cycloaddition of Epoxides and CO2.

Group 13 complexes bearing an aminopyridylbisphenol ligand have been prepared [ML-X; L = ligand, M = Al (X = Cl and Br), Ga (X = Cl, Br, and I), or In (X = Cl)]. The structures of the complexes containing the chloride ligand (ML-Cl; M = Al, Ga, and In) have been directly compared through an X-ray crystallography study, with differences in the monomeric or dimeric nature of their structures observed. All of the complexes obtained have been studied as potential catalysts for the synthesis of cyclic carbonates from epoxides and CO2. It has been found that the indium complex, as part of a traditional binary catalyst system (catalyst + tetra-butylammonium halide cocatalyst), displays the highest catalytic activity and is active under rather mild reaction conditions (balloon pressure of CO2). Meanwhile, it has been found that the GaL-I complex is a competent single-component catalyst (no need for addition of a cocatalyst) at more elevated reaction temperatures and pressures. A full substrate scope has been performed with both developed catalyst systems to demonstrate their applicability. In addition to the experimental results, a density functional theory study was performed on both catalyst systems. These results explain both why the indium catalyst is the most active under binary catalyst system conditions and how the gallium catalyst with an iodide (GaL-I) is able to act as a single-component catalyst in contrast to the indium-based complex.

Characterization of the Structural Requirements for the NADase Activity of Bacterial Toll/IL-1R domains in a Course-based Undergraduate Research Experience.

TLRs initiate innate immune signaling pathways via Toll/IL-1R (TIR) domains on their cytoplasmic tails. Various bacterial species also express TIR domain-containing proteins that contribute to bacterial evasion of the innate immune system. Bacterial TIR domains, along with the mammalian sterile α and TIR motif-containing protein 1 and TIRs from plants, also have been found to exhibit NADase activity. Initial X-ray crystallographic studies of the bacterial TIR from Acinetobacter baumannii provided insight into bacterial TIR structure but were unsuccessful in cocrystallization with the NAD+ ligand, leading to further questions about the TIR NAD binding site. In this study, we designed a Course-Based Undergraduate Research Experience (CURE) involving 16-20 students per year to identify amino acids crucial for NADase activity of A. baumannii TIR domain protein and the TIR from Escherichia coli (TIR domain-containing protein C). Students used structural data to identify amino acids that they hypothesized would play a role in TIR NADase activity, and created plasmids to express mutated TIRs through site-directed mutagenesis. Mutant TIRs were expressed, purified, and tested for NADase activity. The results from these studies provide evidence for a conformational change upon NAD binding, as was predicted by recent cryogenic electron microscopy and hydrogen-deuterium exchange mass spectrometry studies. Along with corroborating recent characterization of TIR NADases that could contribute to drug development for diseases associated with dysregulated TIR activity, this work also highlights the value of CURE-based projects for inclusion of a diverse group of students in authentic research experiences.

Mapping protein conformational landscapes from crystallographic drug fragment screens.

Proteins are dynamic macromolecules. Knowledge of a protein's thermally accessible conformations is critical to determining important transitions and designing therapeutics. Accessible conformations are highly constrained by a protein's structure such that concerted structural changes due to external perturbations likely track intrinsic conformational transitions. These transitions can be thought of as paths through a conformational landscape. Crystallographic drug fragment screens are high-throughput perturbation experiments, in which thousands of crystals of a drug target are soaked with small-molecule drug precursors (fragments) and examined for fragment binding, mapping potential drug binding sites on the target protein. Here, we describe an open-source Python package, COLAV (COnformational LAndscape Visualization), to infer conformational landscapes from such large-scale crystallographic perturbation studies. We apply COLAV to drug fragment screens of two medically important systems: protein tyrosine phosphatase 1B (PTP-1B), which regulates insulin signaling, and the SARS CoV-2 Main Protease (MPro). With enough fragment-bound structures, we find that such drug screens also enable detailed mapping of proteins' conformational landscapes.

Oleanane-type triterpenoids from Sabia limoniacea and their anti-inflammatory activities

Eighteen new oleanane-type triterpenoids were isolated from the stems of Sabia limoniacea, including sabialimon A (1), a triterpenoid with an unprecedented 6/6/6/7/7 pentacyclic skeleton and seventeen undescribed triterpenoids, sabialimons B−R (2 − 18), along with six previously described analogs (19 − 24). Their structures were fully elucidated via extensive spectroscopic analysis including 1D and 2D NMR, high-resolution electrospray ionization mass spectrometry (HRESIMS), experimental electronic circular dichroism measurements and X-ray crystallographic studies. Compound 1 is the first triterpenoid that possesses a rare ring system (6/6/6/7/7) with an oxygen-bearing bridge between C-17 and C-18 and a hemiketal form at C-17, which is generated a larger ring by the degradation of C-28 and D/E-ring expansion. Biological evaluation revealed that sabialimon I (9), sabialimon K (11), sabialimon P (16) and 11,13(18)-oleanadien-28-hydroxymethyl 3-one (20) exhibited significantly inhibitory activities against nitric oxide (NO) release with IC50 values of 29.65, 23.41, 18.12 and 26.64 μM, respectively, as compared with the positive control (dexamethasone, IC50 value: 40.35 μM). Furthermore, sabialimon P markedly decreased the secretion of TNF-α, iNOS, IL-6 and NF-κB and inhibited the expression of COX–2 and NF-κB/p65 in LPS-induced RAW264.7 cells in a dose-dependent manner.

Very Strong Hydrogen Bond in Nitrophthalic Cocrystals.

This work presents the studies of a very strong hydrogen bond (VSHB) in biologically active phthalic acids. Research on VSHB comes topical due to its participation in many biological processes. The studies cover the modelling of intermolecular interactions and phthalic acids with 2,4,6-collidine and N,N-dimethyl-4-pyridinamine complexes with aim to obtain a VSHB. The four synthesized complexes were studied by experimental X-ray, IR, and Raman methods, as well as theoretical Car-Parrinello Molecular Dynamics (CP-MD) and Density Functional Theory (DFT) simulations. By variation of the steric repulsion and basicity of the complex' components, a very short intramolecular hydrogen bond was achieved. The potential energy curves calculated by the DFT method were characterized by a low barrier (0.7 and 0.9 kcal/mol) on proton transfer in the OHN intermolecular hydrogen bond for 3-nitrophthalic acid with either 2,4,6-collidine or N,N-dimethyl-4-pyridinamine cocrystals. Moreover, the CP-MD simulations exposed very strong bridging proton dynamics in the intermolecular hydrogen bonds. The accomplished crystallographic and spectroscopic studies indicate that the OHO intramolecular hydrogen bond in 4-nitrophthalic cocrystals is VSHB. The influence of a strong steric effect on the geometry of the studied cocrystals and the stretching vibration bands of the carboxyl and carboxylate groups was elaborated.

Supramolecular Binding of Phosphonate Dianions by Nanojars and Nanojar Clamshells.

Despite the widespread use of phosphonates (RPO32-) in various agricultural, industrial, and household applications and the ensuing eutrophication of polluted water bodies, the capture of phosphonate ions by molecular receptors has been scarcely studied. Herein, we describe a novel approach to phosphonate binding using chemically and thermally robust supramolecular coordination assemblies of the formula [RPO3⊂{cis-CuII(μ-OH)(μ-pz)}n]2- (Cun; n = 27-31; pz = pyrazolate ion, C3H3N2-; R = aliphatic or aromatic group). The neutral receptors, termed nanojars, strongly bind phosphonate anions by a multitude of hydrogen bonds within their highly hydrophilic cavities. These nanojars can be synthesized either directly from their constituents or by depolymerization of [trans-CuII(μ-OH)(μ-pz)]∞ induced by phosphonate anions. Electrospray-ionization mass spectrometry, UV-vis and variable-temperature, paramagnetic 1H and 31P NMR spectroscopy, single-crystal X-ray diffraction, along with chemical stability studies toward NH3 and Ba2+ ions, and thermal stability studies in solution are employed to explore the binding of various phosphonate ions by nanojars. Crystallographic studies of 12 different nanojars offer unprecedented structural characterization of host-guest complexes with doubly charged RPO32- ions and reveal a new motif in nanojar chemistry, nanojar clamshells, which consist of phosphonate anion-bridged pairs of nanojars and double the phosphonate-binding capacity of nanojars.

Influence of aluminium in wetting characteristics of Zn-Al alloy

In this article, the effect of aluminium in Zn-5 wt%Al alloy is studied after heat treatment at 375 ⁰C focusing particularly on its effect at grain boundaries or grain boundary junctions. The understanding of such behaviour is crucial for microstructural controlling during alloy processing, ensuring better alloy performance for various applications. Using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), the microstructural and crystallographic study of the alloy was carried out. The SEM results of the annealed sample show a lenticular-shaped wetting layer corresponding to the lower energy of the grain boundary. It was observed that Zn is distributed throughout the sample, while the concentration of Al is increased at the grain boundaries as evidenced by the elemental spectra. XRD result confirms that no new phases are formed thereby confirming the formation of an Al-rich solid solution at the grain boundary. The absence of new phases indicates that aluminium in the alloy tends to lower grain boundary energy by occupying grain boundary positions, rather than forming a new compound, thereby reaching thermodynamic equilibrium. This study is important for developing advanced engineering materials with solid-state lubrication capabilities, for diverse industrial applications.

Harnessing the Reactivity of ortho-Alkynylaldehydes: Silver Triflate Catalyzed Regioselective Synthesis of Phosphonylated Fluorescent Molecules

AbstractAn efficient approach for the facile synthesis of phosphonylated 1,3-dihydrofuro[3,4-b]quinolines and dihydrofuro[3,4-b]pyridines is developed. Reaction proceeds by the formation of new C–P and C–O bonds affording Z-selective phosphonylated products at room temperature. Diphenylphosphine oxides and dialkyl phosphites are explicitly incorporated into the carbonyl carbon of o-alkynylaldehydes in good to excellent yields. The reaction exhibits mild conditions, broad substrate scope, and the formation of three new bonds in the presence of a silver catalyst. The mechanistic studies revealed that the reaction proceeded via an ionic pathway in a 5-exo-dig manner to give Z-selective products, which was validated by X-ray crystallographic studies. Photophysical studies of selected compounds revealed the emission maxima in the range of 455 nm.

Microstructural study with enhanced dielectric and magnetic properties of Cu1-xCdxFe2O4 nanoparticles prepared at low-temperature green-synthesized technique

The green elaboration tool has taken much consideration due to its consistent and economical ways of producing pure and regular dispersed NPs. The preparation tool is a simple, environmentally friendly, and cost-effective method that does not use toxic chemicals. Therefore, the biological mechanisms themselves act as a reducing agent that prevents, on the surface of nanoparticles, the adsorption of chemical agents. Therefore, we focus in this work on the bio-synthesizes and the characterization (crystallographic, magnetic, transport, and dielectric study) of Cu1-xCdxFe2O4(x = 0.0, 0.3 and x = 0.5) spinel ferrites. X-ray diffraction, transmission electron microscopy (TEM), and photoelectron spectroscopy (XRD and XPS) have been employed to study crystallographic characteristics and chemical bond formation. Surface parameters analysis was conducted using BET isotherms and validated the decreases in specific surface area in the substitution sample. The electrical investigation proves the semiconductor behavior, and the thermal activation are dominated by the small polaron hopping mechanism in the nano-ferrites Cu1-xCdxFe2O4. In addition, the prepared NPS exhibits low dielectric losses. Using the ZFC-FC and M(H) measurement techniques, important modifications in the magnetic behaviors have been detected in the elaborated nanoparticles. Accordingly, the substitution of Cu1-xCdxFe2O4 leads to transitions from ferromagnetic to superparamagnetic behaviors, the increase of the magnetic saturation, and decreased magnetic anisotropy has been shown in Cu0·7Cd0·3Fe2O4 spinel structure.

Synthesis, structural, spectroscopic and theoretical insights into a new malononitrile derivative: A candidate for nonlinear optical applications

Functionalized alkylidene malononitriles play a crucial role as donor-acceptor molecules, exhibiting notable nonlinear optical (NLO) properties. Allylidene malononitriles, an analogue of alkylidene malononitriles, have not been explored before for their optical properties. The present work deals with the synthesis of (Z)-2-(3-(4-bromophenyl)-3-chloroallylidene) malononitrile using Knoevenagel condensation reaction of Z-3-(4-bromophenyl)-3-chloroacrylaldehyde and malononitrile. Structure of the compound was elucidated by single-crystal X-ray crystallography and related spectroscopic studies like FT-IR, NMR (1H, 13C), and UV–Vis spectroscopy, which were further supported with computational studies using Density Functional Theory (DFT) approach. The photoluminescence spectra showed that the compound exhibited an emission peak at 425 nm with an excitation wavelength of 352 nm. The single crystal study reveals that the compound belongs to a monoclinic system with space group P21/c. The thermal characteristics of the compound was analysed using TGA-DTA/DSC. Investigation of the third-order nonlinear susceptibility was done by femtosecond Z-scan technique and demonstrated the potential of phenyl-substituted allylidene malononitriles for its nonlinear optical applications. The observed positive lensing and strong reverse saturable absorption (RSA) at both visible (532 nm) and Near IR (800 nm) regions make this compound a promising candidate for optoelectronic applications.

Crystallographic fragment-binding studies of the Mycobacterium tuberculosis trifunctional enzyme suggest binding pockets for the tails of the acyl-CoA substrates at its active sites and a potential substrate-channeling path between them.

The Mycobacterium tuberculosis trifunctional enzyme (MtTFE) is an α2β2 tetrameric enzyme in which the α-chain harbors the 2E-enoyl-CoA hydratase (ECH) and 3S-hydroxyacyl-CoA dehydrogenase (HAD) active sites, and the β-chain provides the 3-ketoacyl-CoA thiolase (KAT) active site. Linear, medium-chain and long-chain 2E-enoyl-CoA molecules are the preferred substrates of MtTFE. Previous crystallographic binding and modeling studies identified binding sites for the acyl-CoA substrates at the three active sites, as well as the NAD binding pocket at the HAD active site. These studies also identified three additional CoA binding sites on the surface of MtTFE that are different from the active sites. It has been proposed that one of these additional sites could be of functional relevance for the substrate channeling (by surface crawling) of reaction intermediates between the three active sites. Here, 226 fragments were screened in a crystallographic fragment-binding study of MtTFE crystals, resulting in the structures of 16 MtTFE-fragment complexes. Analysis of the 121 fragment-binding events shows that the ECH active site is the `binding hotspot' for the tested fragments, with 41 binding events. The mode of binding of the fragments bound at the active sites provides additional insight into how the long-chain acyl moiety of the substrates can be accommodated at their proposed binding pockets. In addition, the 20 fragment-binding events between the active sites identify potential transient binding sites of reaction intermediates relevant to the possible channeling of substrates between these active sites. These results provide a basis for further studies to understand the functional relevance of thelatter binding sites and to identify substrates for which channeling is crucial.

Solvothermal Synthesized Heterostructured Bi2S3–TiO2 Nanoparticles as Highly Selective Fluorescence Probe for Nitrobenzene

This study describes a facile one-pot solvothermal method for the synthesis of heterostructured (HS) Bi2S3–TiO2 (BT) nanoparticles (NPs) and utilizes its potential for sensing the nitrobenzene (NB) as a fluorescent probe. The characterization of as-synthesized BT NPs endorses the mixed morphology with an average particle size of 14[Formula: see text]nm and the crystallography study depicted the orthorhombic Bi2S3 and tetragonal anatase TiO2 phases. The selectivity and sensitivity of BT NPs toward NB were examined by comparing the fluorescence quenching with a few other selected organic aromatic compounds. The appreciable quenching efficiency of 97% was achieved with NB. The visual response of the BT/NB mixture was noticed under UV light ([Formula: see text][Formula: see text]nm). The quenching parameters of the BT/NB system have been evaluated by modifying Stern–Volmer and double logarithmic equations. The results attribute the prevalence of dynamic quenching within the concentration range (0.4[Formula: see text]mM to 5[Formula: see text]mM) and beyond 5[Formula: see text]mM, both static and dynamic quenching coexist. Further, thermodynamic studies of the BT/NB system indicate the spontaneous hydrophobic interaction. Moreover, a reliable outcome has been demonstrated in the sensing application of BT NPs in real water samples.

A classic antibiotic reimagined: Rationally designed bacitracin variants exhibit potent activity against vancomycin-resistant pathogens

Bacitracin is a macrocyclic peptide antibiotic that is widely used as a topical treatment for infections caused by gram-positive bacteria. Mechanistically, bacitracin targets bacteria by specifically binding to the phospholipid undecaprenyl pyrophosphate (C55PP), which plays a key role in the bacterial lipid II cycle. Recent crystallographic studies have shown that when bound to C55PP, bacitracin adopts a highly ordered amphipathic conformation. In doing so, all hydrophobic side chains align on one face of the bacitracin-C55PP complex, presumably interacting with the bacterial cell membrane. These insights led us to undertake structure-activity investigations into the individual contribution of the nonpolar amino acids found in bacitracin. To achieve this we designed, synthesized, and evaluated a series of bacitracin analogues, a number of which were found to exhibit significantly enhanced antibacterial activity against clinically relevant, drug-resistant pathogens. As for the natural product, these next-generation bacitracins were found to form stable complexes with C55PP. The structure-activity insights thus obtained serve to inform the design of C55PP-targeting antibiotics, a key and underexploited antibacterial strategy.

Biophysical and structural analyses of the interaction between the SHANK1 PDZ domain and an internal SLiM.

The PDZ (Postsynaptic density protein-95[PSD-95]/Discs-large) domain, prevalent as a recognition module, has attracted significant attention given its ability to specifically recognize ligands with consensus motifs (also termed PDZ binding motifs [PBMs]). PBMs typically bear a C-terminal carboxylate as a recognition handle and have been extensively characterized, whilst internal ligands are less well known. Here we characterize a short linear motif (SLiM) - EESTSFQGP - as an internal PBM based on its strong binding affinity towards the SHANK1 PDZ domain (SHANK1656-762 hereafter referred to as SHANK1). Using the acetylated analogue Ac-EESTSFQGP-CONH2 as a competitor for the interaction of SHANK1 with FAM-Ahx-EESTSFQGP-CONH2 or a typical fluorophore-labelled C-terminal PBM - GKAP - FITC-Ahx-EAQTRL-COOH - the internal SLiM was demonstrated to show comparable low-micromolar IC50 by competition fluorescent anisotropy. To gain further insight into the internal ligand interaction at the molecular level, we obtained the X-ray co-crystal structure of the Ac-EESTSFQGP-CONH2/SHANK1 complex and compared this to the Ac-EAQTRL-COOH/SHANK1 complex. The crystallographic studies reveal that the SHANK1 backbones for the two interactions overlap significantly. The main structural differences were shown to result from the flexible loops which reorganize to accommodate the two PBMs with distinct lengths and terminal groups. In addition, the two C-terminal residues Gly and Pro in Ac-EESTSFQGP-CONH2 were shown not to participate in interaction with the target protein, implying further truncation and structural modification using peptidomimetic approaches on this sequence may be feasible. Taken together, the SLiM Ac-EESTSFQGP-CONH2 holds potential as an internal ligand for targeting SHANK1.

Intriguing steroid glycosides for cancer therapy by suppressing the DNA damage response and mTOR/S6K signaling pathways

Two rare 8-hydroxysteroid glycosides (6–7), and their downstream metabolites (1–5) with an unprecedented 6/6/5/5/5-pentacyclic scaffold, together with seven known analogues (8–14) were isolated from the twigs and leaves of Strophanthus divaricatus. Their structures were fully assigned by analysis of the spectroscopic and ECD data, NMR calculations, X-ray crystallographic study, and chemical methods. In addition, the inhibitory effects of 1–14 on liver and lung cancer cell lines were evaluated, and preliminary structure–activity relationship was discussed. Data-independent acquisition (DIA)-based quantitative proteomic analysis and biological verification of H1299 cells suggested that this family of compounds may play an anticancer role by suppressing both DNA damage response (DDR) and mTOR/S6K signaling pathways.

D4-Symmetric Dirhodium Tetrakis(binaphthylphosphate) Catalysts for Enantioselective Functionalization of Unactivated C-H Bonds.

Dirhodium tetrakis(2,2'-binaphthylphosphate) catalysts were successfully developed for asymmetric C-H functionalization with trichloroethyl aryldiazoacetates as the carbene precursors. The 2,2'-binaphthylphosphate (BNP) ligands were modified by introduction of aryl and/or chloro functionality at the 4,4',6,6' positions. As the BNP ligands are C2-symmetric, the resulting dirhodium tetrakis(2,2'-binaphthylphosphate) complexes were expected to be D4-symmetric, but X-ray crystallographic and computational studies revealed this is not always the case because of internal T-shaped CH-π and aryl-aryl interactions between the ligands. The optimum catalyst is Rh2(S-megaBNP)4, with 3,5-di(tert-butyl)phenyl substituents at the 4,4' positions and chloro substituents at the 6,6' positions. This catalyst adopts a D4-symmetric arrangement and is ideally suited for site-selective C-H functionalization at unactivated tertiary sites with high levels of enantioselectivity, outperforming the best dirhodium tetracarboxylate catalyst developed for this reaction. The standard reactions were conducted with a catalyst loading of 1 mol % but lower catalyst loadings can be used if desired, as illustrated in the C-H functionalization of cyclohexane in 91% ee with 0.0025 mol % catalyst loading (29,400 turnover numbers). These studies further illustrate the effectiveness of donor/acceptor carbenes in site-selective intermolecular C-H functionalization and expand the toolbox of catalysts available for catalyst-controlled C-H functionalization.

Structure-Guided Design of Potent Coronavirus Inhibitors with a 2-Pyrrolidone Scaffold: Biochemical, Crystallographic, and Virological Studies.

Zoonotic coronaviruses are known to produce severe infections in humans and have been the cause of significant morbidity and mortality worldwide. SARS-CoV-2 was the largest and latest contributor of fatal cases, even though MERS-CoV has the highest case-fatality ratio among zoonotic coronaviruses. These infections pose a high risk to public health worldwide warranting efforts for the expeditious discovery of antivirals. Hence, we hereby describe a novel series of inhibitors of coronavirus 3CLpro embodying an N-substituted 2-pyrrolidone scaffold envisaged to exploit favorable interactions with the S3-S4 subsites and connected to an invariant Leu-Gln P2-P1 recognition element. Several inhibitors showed nanomolar antiviral activity in enzyme and cell-based assays, with no significant cytotoxicity. High-resolution crystal structures of inhibitors bound to the 3CLpro were determined to probe and identify the molecular determinants associated with binding, to inform the structure-guided optimization of the inhibitors, and to confirm the mechanism of action of the inhibitors.

Crystallographic study on microstructure evolution and mechanical properties of coarse grained heat affected zone of a 500 MPa grade wind power steel

The effect of different welding heat inputs on the microstructure and mechanical properties of the simulated coarse grained heat affected zone (CGHAZ) of high-strength wind power steel with yield strength of 500 MPa has been investigated using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Charpy impact tests have demonstrated that there exists an optimum heat input of ∼20 kJ/cm that allows optimum impact toughness to be obtained for the CGHAZ. It was shown that this is related to the refined bainitic structure and the highest density of high-angle grain boundaries (HAGBs) with misorientation angle of more than 45°. In crystallographic visualization studies, it was shown that the weakest variant selection occurs for the bainite transformation in the optimal heat input, leading to the highest density of HAGBs with each Closed-packet group containing two or three Bain groups and showing a staggered arrangement structure. The contribution that can effectively deflect and prevent crack propagation during impact experiments has to come from the block boundary. However, it was also found that the center segregation induced by C and Mn reduces the low-temperature impact toughness of the core sample before and after simulated welding, and affects the fluctuations of impact toughness and fatigue performance of simulated CGHAZ. Mn segregation can have a genetic effect on the welding heat affected zone, inducing a lower temperature martensitic transformation, which in turn leads to a decrease in low-temperature toughness and fatigue crack arrest performance.

Structural and Spectroscopic Analysis of Reddish-Orange Emitting (Y1−x)2WO6:xEu3+ (0 ≤ x ≤ 0.11) Nanophosphors for Anti-Counterfeiting Application

Exploring luminescent materials that meet the necessary specifications for anti-counterfeiting applications has been the focus of extensive research. In this study, we delve into a double perovskite-structured material, (Y1−x)2WO6:xEu3+ (0 ≤ x ≤ 0.11), synthesized via a chemical combustion method. The crystallographic studies using the X-ray diffraction pattern confirm the crystallization of the nanophosphors into the monoclinic phase with a P2/c space group. The Raman and Fourier transform infrared spectroscopy studies provide insights into the nature of chemical bonding within the material. UV visible spectra are analysed to determine the optical energy gap. Notably, the photoluminescence emission spectra of the Eu3+ incorporated phosphors exhibit a distinct emission peak at 609 nm, corresponding to the 5D0 → 7F2 electric dipole transition of the Eu3+ ions. The optimal photoluminescence intensity is observed for the x = 0.07 nanophosphor, with estimated chroma coordinates of (0.500, 0.316), placing it in the reddish-orange region of the chromaticity diagram. The incorporation of Eu3+ enhances magnetization, attributed to the presence of Eu3+ ions in the 7F2 state. The luminance stability is a critical factor for long-term performance, the x = 0.07 phosphor was analysed under rigorous physical and chemical testing and is found to be stable, making it a favourable candidate as a luminescence pigment for anti-counterfeiting applications.