Structural Units Research Articles

Decrypting the skeletal toxicity of vertebrates caused by environmental pollutants from an evolutionary perspective: From fish to mammals.

The rapid development of modern society has led to an increasing severity in the generation of new pollutants and the significant emission of old pollutants, exerting considerable pressure on the ecological environment and posing a serious threat to both biological survival and human health. The skeletal system, as a vital supportive structure and functional unit in organisms, is pivotal in maintaining body shape, safeguarding internal organs, storing minerals, and facilitating blood cell production. Although previous studies have uncovered the toxic effects of pollutants on vertebrate skeletal systems, there is a lack of comprehensive literature reviews in this field. Hence, this paper systematically summarizes the toxic effects and mechanisms of environmental pollutants on the skeletons of vertebrates based on the evolutionary context from fish to mammals. Our findings reveal that current research mainly focuses on fish and mammals, and the identified impact mechanisms mainly involve the regulation of bone signaling pathways, oxidative stress response, endocrine system disorders, and immune system dysfunction. This study aims to provide a comprehensive and systematic understanding of research on skeletal toxicity, while also promoting further research and development in related fields.

Photoredox Catalyzed Synthesis of gem-Difluoroalkenes and Monofluorinated Cyclooctenes via 1,5-HAT Process.

gem-Difluoroalkenes and monofluorinated cycloalkenes have emerged as basic structural units in a variety of bioactive molecules and natural products. Thus, developing straightforward and efficient methods for synthesizing fluorinated alkene compounds is of considerable significance. Herein, we disclose a visible-light-induced defluorination of 2-trifluoromethyl-1-alkene via a 1,5-HAT process using N-alkoxyphtalimides as both radical precursor and potential nucleophile. The mild and stepwise reaction leads to a variety of structurally diverse gem-difluoroalkenes and monofluorinated cyclooctenes with high efficiency, respectively.

MXene@c-MWCNT Adhesive Silica Nanofiber Membranes Enhancing Electromagnetic Interference Shielding and Thermal Insulation Performance in Extreme Environments

HighlightsThe SiO2 nanofiber membranes and MXene@c-MWCNT6:4 as one unit layer (SMC1) were bonded together with 5 wt% PVA solution.When the structural unit is increased to three layers, the resulting SMC3 has an average electromagnetic interference SET of 55.4 dB and a low thermal conductivity of 0.062 W m−1 K−1.SMCx exhibit stable electromagnetic interference shielding and excellent thermal insulation even in extreme heat and cold environment.

Enhancing dye-sensitized solar cell performance: Optimizing Cu2ZnSnS4/ZnCo2O4 nanocomposites as efficient and cost-effective counter electrodes

This study investigates the utilization of Cu2ZnSnS4/ZnCo2O4 (CZTS/ZCO) nanocomposites prepared through hydrothermal and combustion methods as counter electrodes in Dye-Sensitized Solar Cells (DSSCs). Different ratios of Cu2ZnSnS4 and ZnCo2O4 were explored, and comprehensive analyses were conducted using X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), High-Resolution TEM (HRTEM), Brunauer–Emmett–Teller (BET) surface area analysis, Raman Spectroscopy, Electrochemical Impedance Spectroscopy (EIS), cyclic voltammetry (CV), Tafel analysis, Field Emission Scanning Electron Microscopy (FESEM), and Incident Photon-to-Electron Conversion Efficiency (IPCE), alongside long-term stability assessments. The CZTS:ZCO ratio of 2:1 exhibited the highest efficiency, reaching 8.81 %, with an open-circuit voltage of 729 mV, short-circuit current of 17.80 mAcm−2, and a fill factor of 67.9 %. This surpasses the efficiency of the reference Pt cell (8.42 %), which had an open-circuit voltage of 735 mV, short-circuit current of 17.16 mAcm−2, and a fill factor of 66.8 %. The average crystallite sizes for the main peaks of CZTS and ZCO samples were estimated to be 19.8 and 16.7 nm, respectively. The crystallite size can significantly affect the charge transfer and conductivity in the counter electrode during electrochemical processes; the presence of nanocrystals with these sizes can notably enhance the electrochemical properties and conductivity of the synthesized samples. Raman analysis results indicate that no additional phases or secondary phases such as ZnS and CuSnS3 have formed in the kesterite CZTS structure, and the crystal has formed as a single phase. Additionally, the F2g modes in the Raman spectrum of ZCO indicate tetrahedral units in the spinel ZCO structure, and the A1g modes represent octahedral structures in this phase, indicating the formation of suitable ZCO phase. The superior performance of the CZTS/ZCO nanocomposite can be attributed to its enhanced crystalline structure, superior charge transport characteristics, and improved electrocatalytic behaviours.

Oxygen Doping Cooperated with Co-N-Fe Dual-Catalytic Sites: Synergistic Mechanism for Catalytic Water Purification within Nanoconfined Membrane.

Atom-site catalysts, especially for graphitic carbon nitride-based catalysts, represents one of the most promising candidates in catalysis membrane for water decontamination. However, unravelling the intricate relationships between synthesis-structure-properties remains a great challenge. This study addressed the impacts of coordination environment and structure units of metal central sites based on Mantel test, correlation analysis and evolution of metal central sites. An optimized unconventional oxygen doping cooperated with Co-N-Fe dual-sites (OCN Co/Fe) exhibited synergistic mechanism for efficient peroxymonosulfate activation, which benefited from a significant increase in charge density at the active sites and the regulation in the natural population of orbitals, leading to selective generation of SO4 •-. Building upon these findings, the OCN-Co/Fe/PVDF composite membrane demonstrated a 33 min-1 ciprofloxacin (CIP) rejection efficiency and maintained over 96% CIP removal efficiency (over 24h) with an average permeance of 130.95 L m-2 h-1. Our work offers a fundamental guide for elucidating the definitive origin of catalytic performance in advance oxidation process (AOPs) to facilitate the rational design of separation catalysis membrane with improved performance and enhanced stability. This article is protected by copyright. All rights reserved.

Dual-functional pentamode metamaterial with water-like and topological transmission properties

In this paper, a water-like pentamode metamaterial (PM) with a single metallic material is designed and the topological edge-state transmission properties of elastic waves in the PM are thoroughly investigated. Numerical results indicate that by introducing structural perturbation into PM, the Dirac point degeneracy at K-point can be opened and topological band inversion can be generated. Topological edge states are also obtained by organizing PM structural units, which are robust to defects such as bending and cavities. In addition, it also has the mimics water in acoustic properties over a wide frequency range, i.e. it exhibits transparency when surrounded by water. Therefore, it will have both good transmission efficiency and acoustic stealth performance when used as an underwater waveguide. The dual-functional PM proposed in this study provides theoretical guidance for designing underwater stealth acoustic waveguides.

A Fluorine‐Effect‐Enabled Photocatalytic 4‐Exo‐Trig Cyclization Cascade to Access Fluoroalkylated Cyclobutanes

Cyclobutanes are popular structural units in bioactive compounds and versatile intermediates in synthetic chemistry, but their synthesis is challenging owing to high ring strain. In this study, a novel method for highly regio‐ and diastereoselective synthesis of fluoroalkylcyclobutanes bearing vicinal quaternary and tertiary stereocenters is realized by a photocatalytic 4‐exo‐trig cyclization cascade of thioalkynes or trifluoromethylalkenes. Density functional theory calculations reveal that a unique fluorine effect, arising from hyperconjugative π→σ*C‐F interactions, accounts for the regio‐reversed radical addition at the sterically hindered alkene carbon, which facilitates an unprecedented 4‐exo‐trig ring closure. This chemistry enables the direct and controllable construction of medicinally valuable quaternary‐carbon‐containing cyclobutanes from readily available raw materials, nicely complementing the existing methods.

A Fluorine-Effect-Enabled Photocatalytic 4-Exo-Trig Cyclization Cascade to Access Fluoroalkylated Cyclobutanes.

Cyclobutanes are popular structural units in bioactive compounds and versatile intermediates in synthetic chemistry, but their synthesis is challenging owing to high ring strain. In this study, a novel method for highly regio- and diastereoselective synthesis of fluoroalkylcyclobutanes bearing vicinal quaternary and tertiary stereocenters is realized by a photocatalytic 4-exo-trig cyclization cascade of thioalkynes or trifluoromethylalkenes. Density functional theory calculations reveal that a unique fluorine effect, arising from hyperconjugative π→σ*C-F interactions, accounts for the regio-reversed radical addition at the sterically hindered alkene carbon, which facilitates an unprecedented 4-exo-trig ring closure. This chemistry enables the direct and controllable construction of medicinally valuable quaternary-carbon-containing cyclobutanes from readily available raw materials, nicely complementing the existing methods.

Luminescent Dansyl-Calix[5]arene for the Recognition of Biogenic Amines

Abstract: A luminescent calix[5]arene with a covalently linked dansyl chromophore substituent has been successfully used, both in solution and in the gas phase (ESI-MS), for the recognition of biogenic amines that contain linear alkylammonium structural unit. Binding constant values, determined by fluorescence spectroscopy, revealed a greater affinity for cadaverine, spermidine, and L-lysine, in which the terminal ammonium group allows for additional stabilizing interactions with the dansyl moiety. objective: the recognition of selected biogenic amines both in solution and in the gas phase (ESI-MS), and determining the relative binding constant values by fluorescence spectroscopy

Linear, Planar, Orbicular, and Macrocyclic Multinuclear Zinc (Meth)acrylate Complexes.

Zinc carboxylate complexes are widely utilized as artificial models of metalloenzymes and as secondary building units of PCPs/MOFs. However, the relationship between the structure of the monodentate carboxylato ligand and the molecular arrangement of multinuclear zinc carboxylate complexes is not fully understood because of the coordination flexibility of the Zn ion and carboxylato ligands. Herein, we report the structural analysis of a series of complexes derived from zinc (meth)acrylate which has a linear infinite chain structure. The molecular structure of μ4-oxido-bridged tetranuclear complexes [Zn4(μ4-O)(OCOR)6] revealed a distorted Zn4O core. Crystallization of zinc acrylate under aqueous conditions afforded a μ3-hydroxido-containing pentanuclear complex [Zn5(μ3-OH)2(OCOR)8] as the repeating unit of an infinite sheet-like structure in the solid state. It was also obtained by the hydrolysis of the μ4-oxido-bridged tetranuclear complex. In sharp contrast, the methacrylate analog retained the methacrylato ligands under aqueous crystallization conditions to form a macrocyclic dodecanuclear complex with methacrylato as the sole ligand.

Mechanically programmable substrate enable highly stretchable solar cell arrays for self-powered electronic skin

Development of stretchable solar cells to accommodate large strain without sacrificing the power conversion efficiency is challenging. This study presents a novel approach to manufacture highly stretchable solar cell arrays, which can be integrated into wearable medical devices to operate under challenging environments. Overcoming the limitations of rigid metal wires, liquid metal wires are employed to connect single crystal silicon solar cells, ensuring both high conversion efficiency and exceptional stretchability (up to 100%). The manufacturing process introduces embedding electrospinning films into elastic silicone substrates to create a tight bond between rigid solar cells and stretchable substrates with programmable strain capabilities. Notably, a stretchable interconnect wire is efficiently fabricated using the semi-liquid metal template printing technique and demonstrates remarkable conductivity (up to 6 × 106 S/m). Individual structural unit of solar cell presents an impressive tensile rate of 200%, and endures up to 5000 cycles of tensile testing. The overall solar cell array exhibits outstanding adaptability to extensive bending and twisting, with a mere 0.1% short-circuit current reduction in its maximum stretched state. The stretchable photovoltaic device is successfully employed in creating self-powered electronic skin for continuous real-time monitoring of parameters, showcasing its valuable potential in wearable medical electronic devices and comprehensive sports health monitoring.

Eliminating Non-Corner-Sharing Octahedral for Efficient and Stable Perovskite Solar Cells.

The metal halide (BX6)4- octahedron, where B represents a metal cation and X represents a halide anion, is regarded as the fundamental structural and functional unit of metal halide perovskites. However, the influence of the way the (BX6)4- octahedra connect to each other has on the structural stability and optoelectronic properties of metal halide perovskite is still unclear. Here, the octahedral connectivity, including corner-, edge-, and face-sharing, of various CsxFA1-xPbI3 (0≤x≤0.3) perovskite films is tuned and reliably characterized through compositional and additive engineering, and with ultralow-dose transmission electron microscopy. It is found that the overall solar cell device performance, the charge carrier lifetime, the open-circuit voltage, and the current density-voltage hysteresis are all improved when the films consist of corner-sharing octahedra, and non-corner sharing phases are suppressed, even in films with the same chemical composition. Additionally, it is found that the structural, optoelectronic, and device performance stabilities are similarly enhanced when non-corner-sharing connectivities are suppressed. This approach, combining macroscopic device tests and microscopic material characterization, provides a powerful tool enabling a thorough understanding of the impact of octahedral connectivity on device performance, and opens a new parameter space for designing high-performance photovoltaic metal halide perovskite devices.

Improved Mechanical Performance in FDM Cellular Frame Structures through Partial Incorporation of Faces

The utilization of lattice-type cellular architectures has seen a significant increase, owing to their predictable shape and the ability to fabricate templated porous materials through low-cost 3D-printing methods. Frames based on atomic lattice structures such as face-centered cubic (FCC), body-centered cubic (BCC), or simple cubic (SC) have been utilized. In FDM, the mechanical performance has been impeded by stress concentration at the nodes and melt-solidification interfaces arising from layer-by-layer deposition. Adding plates to the frames has resulted in improvements with a concurrent increase in weight and hot-pocket-induced dimensional impact in the closed cells formed. In this paper, we explore compressive performance from the partial addition of plates to the frames of a SC-BCC lattice. Compression testing of both single unit cells and 4 × 4 × 4 lattices in all three axial directions is conducted to examine stress transfer to the nearest neighbor and assess scale-up stress transfer. Our findings reveal that hybrid lattice structure unit cells exhibit significantly improved modulus in the range of 125% to 393%, specific modulus in the range of 13% to 120%, and energy absorption in the range of 17% to 395% over the open lattice. The scaled-up lattice modulus increased by 8% to 400%, specific modulus by 2% to 107%, and energy absorption by 37% to 553% over the lattice frame. Parameters that emerged as key to improved lightweighting.

Structural Properties of Amorphous Vanadium Pentoxide Under Compression

Structural properties of amorphous vanadium pentoxide (V2O­5) under compression investigated by molecular dynamics simulation. The simulated amorphous V2O5 is composed of basic structural units of type VO5, VO6 at low-pressure and VO6, VO7 at high-pressure. These basic structural units connected by vertex-, edge- and face- shared links to form a structural network. The random distribution of atom and void clusters leading to a high degree of disorder in the V2O5 structure. Under compression, the fraction of average vertex-, edge- and face- shared links increased strongly. The number of VCs and VTs also increases as the large voids are divided into smaller voids. Our results also elucidated the decreasing of cross-section and increasing of length in VTs are main causes for increasing ion conductivity of the amorphous V2O5.

Chainsaw: protein domain segmentation with fully convolutional neural networks.

Protein domains are fundamental units of protein structure and play a pivotal role in understanding folding, function, evolution, and design. The advent of accurate structure prediction techniques has resulted in an influx of new structural data, making the partitioning of these structures into domains essential for inferring evolutionary relationships and functional classification. This paper presents Chainsaw, a supervised learning approach to domain parsing that achieves accuracy that surpasses current state-of-the-art methods. Chainsaw uses a fully convolutional neural network which is trained to predict the probability that each pair of residues is in the same domain. Domain predictions are then derived from these pairwise predictions using an algorithm that searches for the most likely assignment of residues to domains given the set of pairwise co-membership probabilities. Chainsaw matches CATH domain annotations in 78% of protein domains versus 72% for the next closest method. When predicting on AlphaFold models, expert human evaluators were twice as likely to prefer Chainsaw's predictions versus the next best method. github.com/JudeWells/chainsaw.

Cation Distribution and Anion Transport in the La3Ga5-xGe1+xO14+0.5x Langasite Structure.

Exploration of compositional disorder using conventional diffraction-based techniques is challenging for systems containing isoelectronic ions possessing similar coherent neutron scattering lengths. Here, we show that a multinuclear solid-state Nuclear Magnetic Resonance (NMR) approach provides compelling insight into the Ga3+/Ge4+ cation distribution and oxygen anion transport in a family of solid electrolytes with langasite structure and La3Ga5-xGe1+xO14+0.5x composition. Ultrahigh field 71Ga Magic Angle Spinning (MAS) NMR experiments acquired at 35.2 T offer striking resolution enhancement, thereby enabling clear detection of Ga sites in different coordination environments. Three-connected GaO4, four-connected GaO4 and GaO6 polyhedra are probed for the parent La3Ga5GeO14 structure, while one additional spectral feature corresponding to the key (Ga,Ge)2O8 structural unit which forms to accommodate the interstitial oxide ions is detected for the Ge4+-doped La3Ga3.5Ge2.5O14.75 phase. The complex spectral line shapes observed in the MAS NMR spectra are reproduced very accurately by the NMR parameters computed for a symmetry-adapted configurational ensemble that comprehensively models site disorder. This approach further reveals a Ga3+/Ge4+ distribution across all Ga/Ge sites that is controlled by a kinetically governed cation diffusion process. Variable temperature 17O MAS NMR experiments up to 700 °C importantly indicate that the presence of interstitial oxide ions triggers chemical exchange between all oxygen sites, thereby enabling atomic-scale understanding of the anion diffusion mechanism underpinning the transport properties of these materials.

Wideband terahertz absorber based on the coupling of the double ellipse de-overlapping and I-shaped structure

In this letter, a wideband terahertz absorber based on a double ellipse de-overlapping and an I-shaped structure is presented. Its structure unit is a typical metal-medium-metal structure, the top metal is composed of a double ellipse de-overlapping and the central layer of an I-shaped structure, and the bottom layer is also a double ellipse de-overlapping. Broadband absorption is achieved by adjusting the structural parameters of the unit, equivalent circuit model is used to evaluate the resonant frequencies of different absorption peaks. The operation frequencies of the absorber can be extended from 5.5 THz to about 1.2 THz. The operation bandwidth of terahertz waves decreases from close to 2 THz to about 0.5 THz by adjusting the structural parameters of the unit. The device demonstrates excellent broadband absorption ability at various incidence angles, exhibiting strong angular stability. The wideband terahertz absorber can be used in terahertz communication, terahertz imaging, terahertz sensing, and other fields.

Mechanistic Basis of the Cu(OAc)2 Catalyzed Azide-Ynamine (3 + 2) Cycloaddition Reaction.

The Cu-catalyzed azide-alkyne cycloaddition (CuAAC) reaction is used as a ligation tool throughout chemical and biological sciences. Despite the pervasiveness of CuAAC, there is a need to develop more efficient methods to form 1,4-triazole ligated products with low loadings of Cu. In this paper, we disclose a mechanistic model for the ynamine-azide (3 + 2) cycloadditions catalyzed by copper(II) acetate. Using multinuclear nuclear magnetic resonance spectroscopy, electron paramagnetic resonance spectroscopy, and high-performance liquid chromatography analyses, a dual catalytic cycle is identified. First, the formation of a diyne species via Glaser-Hay coupling of a terminal ynamine forms a Cu(I) species competent to catalyze an ynamine-azide (3 + 2) cycloaddition. Second, the benzimidazole unit of the ynamine structure has multiple roles: assisting C-H activation, Cu coordination, and the formation of a postreaction resting state Cu complex after completion of the (3 + 2) cycloaddition. Finally, reactivation of the Cu resting state complex is shown by the addition of isotopically labeled ynamine and azide substrates to form a labeled 1,4-triazole product. This work provides a mechanistic basis for the use of mixed valency binuclear catalytic Cu species in conjunction with Cu-coordinating alkynes to afford superior reactivity in CuAAC reactions. Additionally, these data show how the CuAAC reaction kinetics can be modulated by changes to the alkyne substrate, which then has a predictable effect on the reaction mechanism.

Effects of liquefied gas temperature and negative pressure on the microstructural characteristics of oxide Mg2SiO4 using molecular dynamics simulation method

Our study focused on examining the behavior of oxide Mg2SiO4 under various liquefied gas temperatures, including 4.22 K (Helium), 77 K (Nitrogen), 83.88 K (Argon), 90 K (Oxygen), 194.3 K (Carbon), and 300 K (room temperature), while maintaining a pressure of 0 GPa. Additionally, we explored the effects of pressures ranging from 0 to −6 GPa at a temperature of 77 K using first principles molecular dynamics simulations. Our findings indicate significant variations in the system’s size, energy, and the lengths of Si-Si, Si-O, O-O, Si-Mg, Mg-O, and Mg-Mg bonds with decreasing temperature at 0 GPa and decreasing pressure at a temperature of 77 K. Moreover, substantial variations were observed in the average coordination number of bonds, the quantity of SiOx, MgOy structural units (where x = 4, 5 and y = 3, 4, 5, 6, 7), and bond angles of Si-O-Si, and Mg-O-Mg under negative pressure while remaining relatively constant across liquefied gas temperatures. Furthermore, we successfully established a linear relationship between temperature, pressure, and the total energy of the system. These insights into the behavior of oxide Mg2SiO4 serve as valuable groundwork for future experimental investigations, particularly in leveraging the material’s potential applications in advanced technological fields.

Anaerobic cyanides oxidation with bimetallic modulation of biological toxicity and activity for nitrite reduction

Cyanide is a typical toxic reducing agent prevailing in wastewater with a well-defined chemical mechanism, whereas its exploitation as an electron donor by microorganisms is currently understudied. Given that conventional denitrification requires additional electron donors, the cyanide and nitrogen can be eliminated simultaneously if the reducing HCN/CN− and its complexes are used as inorganic electron donors. Hence, this paper proposes anaerobic cyanides oxidation for nitrite reduction, whereby the biological toxicity and activity of cyanides are modulated by bimetallics. Performance tests illustrated that low toxicity equivalents of iron-copper composite cyanides provided higher denitrification loads with the release of cyanide ions and electrons from the complex structure by the bimetal. Both isotopic labeling and Density Functional Theory (DFT) demonstrated that CN−-N supplied electrons for nitrite reduction. The superposition of chemical processes reduces the biotoxicity and enhances the biological activity of cyanides in the CN−/Fe3+/Cu2+/NO2– coexistence system, including complex detoxification of CN− by Fe3+, CN− release by Cu2+ from [Fe(CN)6]3−, and NO release by nitrite substitution of −CN groups. Cyanide is the smallest structural unit of C/N-containing compounds and serves as a probe to extend the electron-donating principle of anaerobic cyanides oxidation to more electron-donor microbial utilization.