Intermediate Structure Research Articles

Right Atrial Function Role in Tricuspid Regurgitation-Related Systemic Venous Congestion

Tricuspid regurgitation (TR) is a frequent valvular pathology and when significant, may cause systemic venous congestion (SC). The right atrium (RA) is an intermediate structure between the tricuspid valve and the venous system and its role in SC is not yet defined. A total of 116 patients with a measurable TR effective regurgitant orifice area (EROA) and regurgitant volume (RVol) were selected from 2020 to 2022. SC was estimated by echocardiography using inferior vena cava diameter and estimated right atrial pressure (eRAP) and by clinical congestive features. TR grade was mild in 23 patients (20%), moderate in 53 patients (46%), and severe in 40 patients (34%). There was a significant decrease in RA function measured by strain with increasing TR severity (p<0.001). There was a marked difference in RA strain between the groups with eRAP >10 and ≤10mmHg (25±11% vs 11±7%, p<0.0001). Variables independently associated with inferior vena cava diameter were RA strain (β -0.532, p<0.001), RA volume indexed (β 0.249, p=0.002), RVol (β 0.229, p=0.005) and EROA (β 0.185, p=0.016), and independently associated with eRAP >10mmHg were EROA (odds ratio [OR] 1.024, 95% confidence interval [CI] 1.002 to 1.046), RVol (OR 1.039, 95% CI 1.007 to 1.072) and RA strain (OR 0.863, 95% CI 0.794 to 0.940). The addition of RA strain to models containing EROA or RVol significantly improved the power of the model. RA strain was independently associated with the presence of 3 or more congestive features. In conclusion, echocardiographic and clinical signs of SC are frequent in higher degrees of TR, and RA function seems to play a key role in modulating the downstream effect of TR.

Metal doping fabricated heterobimetallic nickel-zinc composites and its performance-enhancing sensitivity towards nitrogen dioxide

Monitoring and detecting poisonous nitrogen dioxide (NO2) is greatly challenged by ambiguous knowledge about the sensing mechanism and structures of sensitive materials and reaction intermediates. In particular, synthetic strategies like doping and coupling, although do improve gas-sensing activity, have made the structural identification rather difficult. In the work, we have comprehensively examined nickel-doped zinc oxide (marked as ZON) and its material-coupled composites (ZON/Y) for sensing NO2 by density functional theory. The material (Y) varies from graphitic carbon nitride (CN), graphene (Gr) to cellulose (Cel). It is revealed that the metal doping greatly promotes the NO2 adsorption over the material coupling. This well reproduces the experimental findings that the Ni-doped ZnO has much faster response time than ZnO, ZnO/g-C3N4 and ZnO/graphene. Of all the studied SMs, ZON/CN exhibits superior NO2 gas-sensing performance. Along the reaction pathway, it gives NO2 adsorption free energy of − 0.860 eV, followed by the mildest uphill process of catching the second NO2 (0.320 eV) and the modest downhill process of forming nitrate (−0.680 eV). The large adsorption energy of the initial step is attributed to the fabricated heterobimetallic Ni-Zn sensing active sites. The better sensitivity of ZON/CN is further evidenced by analyses of structures and interfacial bondings.

Comprehensive survey of VUV induced dissociative photoionization of aniline: Role of H migration assisted isomerization

A complete dissociation progression of aniline under VUV irradiation over the entire relevant internal energy range and inclusive of all decay channels is presented. The onset energy and breakdown curve was found to be instrumental in selecting relevant pathways out of multiple possibilities predicted by computation for all significant decay channels. The relevance of the ring contraction in the formation of the intermediate five-member ring structure and its consequences for the important channels such as HNC, H and HNCH losses are highlighted. In addition, a potential route for the formation of previously unexplored and astronomically important fragments HNCH and HCCN has been found. It could be deduced that aniline differs from its bicyclic nitrogenated counterpart, naphthalamine, as ring contraction in aniline is found to be favourable over ring expansion. Moreover, the role of H migration-assisted isomerization is highlighted in the context of the formation of astronomically important species.

Preparation process and mechanical properties of laser cladding gradient molybdenum coating on copper alloy

Different types of Mo coatings were prepared on the surface of a copper alloy via laser cladding technology in this study to address the problem of low hardness of copper alloy current-carrying friction subsets. Meanwhile, the problems of high reflectivity of copper alloy materials to infrared laser light and mutual insolubility of Cu and Mo were solved by introducing an intermediate layer structure, and the coating process was optimized to obtain a coating with excellent formation. The microstructure, hardness, and interfacial shear bond strength of coatings were tested. Results showed that the Mo coating prepared using a plasma-spheroidized powder had a lower dilution rate and finer and tighter grain growth compared with the Mo coating prepared by crushing agglomerated powder. The coating phase mainly consisted of Mo, Ni3Mo, MoO2, and Cu0.81Ni0.19. The unfused particles present in the plasma-spheroidized powder coating acted as a second hard reinforcing phase, which could significantly increase the hardness of the coating. Three kinds of coatings exhibited strong bond strength, and coatings prepared from different powders fractured in diverse ways. In sum, the plasma-spheroidized Mo coating prepared using the three-way powder feeding method not only had good formation but also possessed the most excellent mechanical properties.

Structural Anisotropy-Driven Atomic Mechanisms of Phase Transformations in the Pt-Sn System.

Using in situ atomic-resolution scanning transmission electron microscopy, atomic movements and rearrangements associated with diffusive solid to solid phase transformations in the Pt-Sn system are captured to reveal details of the underlying atomistic mechanisms that drive these transformations. In the PtSn4 to PtSn2 phase transformation, a periodic superlattice substructure and a unique intermediate structure precede the nucleation and growth of the PtSn2 phase. At the atomic level, all stages of the transformation are templated by the anisotropic crystal structure of the parent PtSn4 phase. In the case of the PtSn2 to Pt2Sn3 transformation, the anisotropy in the structure of product Pt2Sn3 dictates the path of transformation. Analysis of atomic configurations at the transformation front elucidates the diffusion pathways and lattice distortions required for these phase transformations. Comparison of multiple Pt-Sn phase transformations reveals the structural parameters governing solid to solid phase transformations in this technologically interesting intermetallic system.

Spin Order Transfer from a Parahydrogen Molecule to a Cyanide Ion in the Iridium Complex under the SABRE Conditions

A possibility of generating a high degree of spin polarization of 13C and 15N nuclei in the cyanide ion, which forms the coordination bond with the metal ion, using parahydrogen is demonstrated for the first time for the new iridium carbene complex as an example. The spin–spin interaction constants in the synthesized complex and the structure of the hydride intermediate are determined by an analysis of the 13С NMR spectra detected using broadband and selective heteronuclear decoupling. The cyanide ion is shown to coordinate to the metal ion by the carbon atom in one of two equatorial positions, and two pyridine molecules are arranged in the axial and equatorial positions. The signal amplification factors for 13С and 15N nuclei of the cyanide anion (5665 and –49 555, respectively) are estimated by NMR spectroscopy of the polarized substrate using the SABRE method from an ultralow magnetic field of 0.5 μT. This amplification corresponds to 15.5% polarization of nitrogen nuclei achieved within several seconds at room temperature.

Simplified Equations to Find the Relationship Between Soil and Structure Displacements for Rectangular Single Column and Footing on Dry Voidless Cohesionless Soil Due to Vertical Loads

Usually, structural designers are assuming the soil as rigid object when they design small to intermediate structures, or assuming the settlement of soil to be always within the acceptable range. However, the engineering practice shows that high percentage of cracks and failures in structures are related to soil settlement reasons, non-uniform soil settlement for example. Geotechnical engineers developed many methods to calculate the settlement of soil, but the majority of these methods are geotechnical engineering oriented, and standard structural engineer may struggle using them. Therefore, because of the importance of finding the approximate soil settlement in many cas-es during the design process or during the implementation of the structure, this study gives simple equations that can predict the soil settlement with acceptable accuracy, by creating a relationship between the soil settlement and the displacement of the structure. The targeted equation will allow us to find the soil settlement from knowing the approximate displacement of the structure. Such an equation gives a conceptual value to be used in 3D analysis of structures using computer programs like SAP2000 and ETABS. The targeted structure in this study is a simple one rectangular column and footing structure

Scanning tunneling microscopy under chemical reaction at solid–liquid and solid–gas interfaces

The task of bridging the pressure gap between ideal ultrahigh vacuum conditions and more realistic reaction conditions involving gas and liquid phases is crucial in surface and interfacial chemistry. Scanning tunneling microscopy (STM) has played a key role in addressing this challenge by enabling atomic-scale probing of the interface. STM enabled us to study surface structure, electronic structure, atomic manipulation, dynamics of molecules and atoms, and chemical properties of the surface at the atomic scale. Over the past four decades, the field of STM has undergone explosive growth. This review article focuses on recent advances in operando STM, specifically in the study of solid–liquid and solid–gas interfaces. It highlights the latest works in ambient-pressure STM, which has enabled the observation of atomic features under various gas and reaction conditions. This information sheds light on the surface mobility of adsorbates and atomic structures of reaction intermediates. The review also addresses research on electrochemical STM, which investigates the evolution of surface morphology under electrochemical processes and provides insights into atomic-scale reaction mechanisms. Finally, the article outlines future challenges and perspectives for operando STM techniques.

Development of Nonclassical Photoprecursors for Rh2 Nitrenes.

Characterization of reactive intermediates in C-H functionalization is challenging due to the fleeting lifetimes of these species. Synthetic photochemistry provides a strategy to generate post-turnover-limiting-step intermediates in catalysis under cryogenic conditions that enable characterization. We have a long-standing interest in the structure and reactivity of Rh2 nitrene intermediates, which are implicated as transient intermediates in Rh2-catalyzed C-H amination. Previously, we demonstrated that Rh2 complexes bearing organic azide ligands can serve as solid-state and in crystallo photoprecursors in the synthesis of transient Rh2 nitrenoids. Complementary solution-phase experiments have not been available due to the weak binding of most organic azides to Rh2 complexes. Furthermore, the volatility of the N2 that is evolved during in crystallo nitrene synthesis from these precursors has prevented the in crystallo observation of C-H functionalization from lattice-confined nitrenes. Motivated by these challenges, here we describe the synthesis and photochemistry of nonclassical nitrene precursors based on sulfilimine ligands. Sulfilimines bind to Rh2 carboxylate complexes more tightly than the corresponding azides, which has enabled the full solid-state and solution-phase characterization of these new complexes. The higher binding affinity of sulfilimine ligands as compared with organic azides has enabled both solution-phase and solid-state nitrene photochemistry. Cryogenic photochemical studies of Rh2 sulfilimine complexes confined within polystyrene thin films demonstrate that sulfilimine photochemistry can be accomplished at low temperature but that C-H amination is rapid at temperatures compatible with N═S photoactivation. The potential of these structures to serve as platforms for multistep in crystallo cascades is discussed.

Efficient removal of perfluorinated compounds with the polyamide nanofiltration membrane and membrane fouling resistance analysis

Abstract Perfluorinated compounds (PFCs) are significant pollutants known for their high toxicity and resistance to natural degradation, posing a severe threat to both the global environment and human health. In this study, a polyamide (PA) membrane with an intermediate layer structure of MXene-TiO2 (referred to as MXT-NFM) was utilized for the removal of PFCs. Experimental results confirm that MXT-NFM exhibited remarkable capacity in intercepting PFCs, accompanied by the high water flux. To gain insights into the mechanisms governing membrane fouling induced by PFCs, inorganic ions, and organics, a series of fouling tests were conducted using MXT-NFM under diverse conditions. Additionally, the XDLVO theory was employed to provide a theoretical perspective on the interactions occurring during the fouling process. The findings suggest that the MXene-TiO2 intermediate layer contributed to the exceptional hydrophilicity and rough surface properties, enabling multiple functionalities. These include alleviating membrane pore plugging, improving the physical configuration of the PA layer, and effectively mitigating fouling phenomena in coexisting systems during practical applications. Moreover, the particle size of pollutant colloids and the acid–base interaction were identified as decisive factors influencing the development of membrane fouling.

Systemic approach in the study of the properties and pressure-induced structural transformations in TaN: First-principles molecular dynamics simulations

First-principles molecular dynamics simulations were used to investigate pressure- and temperature-induced phase transitions in different TaN polymorphs. The driving forces and intermediate structures were established for the CoSn-like TaN (ε phase) to WC-type TaN (θ phase) and ε to NaCl type-TaN (δ phase) structural transformations that were observed in experiments and for the θ to hP4-194, θ to cP2-221, δ to cP2-221 and δ to tP4-129 phase transitions that were predicted in this investigation. Other possible TaN polytypes were systematically investigated and five new prospective phases were found: oP8-25, oP12-25, hP8-194, tP8-105 and tI8-109. All new structures are thermodynamically, dynamically and mechanically stable, and their formation energy is only slightly higher than that of the θ phase (by 0.014–0.032 eV/atom). The relative stability, electronic structure, chemical bonding, vibrational spectra, elastic moduli and their spatial anisotropy, Vickers hardness, fracture toughness, Debye temperature and optical properties (real and imaginary parts of the dielectric function, reflectivity spectrum) of the tantalum mononitrides mentioned above were systematically calculated and discussed. The oP12-25, tP8-105 and tI8-109 novel phases exhibit the Vickers hardness (33.1–34.2 GPa), fracture toughness (5.52–5.59 MPa m1/2) and Debye temperatures (609.7–616.1 K) that are higher compared to those of the known TaN structures. The TaN polytypes with the strong Ta-N bonds with minimal fraction of ionicity were found to possess the best mechanical properties. Further experimental investigations are highly desirable to confirm the results presented in this paper.

Structural basis of the T4 bacteriophage primosome assembly and primer synthesis

The T4 bacteriophage gp41 helicase and gp61 primase assemble into a primosome to couple DNA unwinding with RNA primer synthesis for DNA replication. How the primosome is assembled and how the primer length is defined are unclear. Here we report a series of cryo-EM structures of T4 primosome assembly intermediates. We show that gp41 alone is an open spiral, and ssDNA binding triggers a large-scale scissor-like conformational change that drives the ring closure and activates the helicase. Helicase activation exposes a cryptic hydrophobic surface to recruit the gp61 primase. The primase binds the helicase in a bipartite mode in which the N-terminal Zn-binding domain and the C-terminal RNA polymerase domain each contain a helicase-interacting motif that bind to separate gp41 N-terminal hairpin dimers, leading to the assembly of one primase on the helicase hexamer. Our study reveals the T4 primosome assembly process and sheds light on the RNA primer synthesis mechanism.

Internal adjustment and digital transformation of intermediate inputs: Economic performance and environmental effects

With the increasing importance of supply chain security and the vigorous development of the digital economy, the trend of internal adjustment and digital transformation of intermediate input has become more obvious. Therefore, the impact this dual structural adjustment of intermediate input will have on the economy and environment is an interesting and practical topic. Therefore, this article proposes a new decomposition framework for intermediate input and total output, and constructs a production model that considers intermediate inputs and digital transformation. Based on the WIOT, socioeconomic accounts, and environmental accounts of the WIOD from 2000 to 2014, the panel regression model is used to analyze the economic benefits and environmental impacts brought by the internal adjustment of intermediate inputs and digital transformation.The results show that the internal adjustment of intermediate inputs and digital transformation can promote the improvement of total output by influencing multiple aspects of the economy and environment. The internal adjustment of nondigital intermediate inputs promotes the expansion of export scale and reduces the carbon intensity of added value. The digital transformation of intermediate input and internal adjustment of intermediate input strengthen the direct technical connection between domestic and foreign markets and increase the value-added share of the domestic market. However, the adjustment of intermediate input structure may also bring negative economic environmental effects. This article enriches the research on the adjustment of intermediate input structure from the dual perspectives of internalization and digitization, taking into account economic performance and environmental effects. Based on the research results, we put forward some ideas to promote high-quality development from the perspective of adjusting the structure of intermediate investment, such as countries (or regions) should actively promote the development and implementation of digital technology.

Optical, surface, and structural studies of InN thin films grown on sapphire by molecular beam epitaxy

A series of indium nitride (InN) thin films have been grown on sapphire substrates by molecular beam epitaxy (MBE) technology under different growth conditions of temperature and plasma power. Their structural, surface, and optical properties are studied by a variety of techniques of scanning electron microscopy, Hall effect, x-ray diffraction, photoluminescence (PL), Raman scattering, x-ray photoelectron spectroscopy (XPS), synchrotron radiation x-ray absorption near edge structure (XANES), and so on. The lower carrier concentration in InN can be obtained with a higher MBE growth temperature and a lower plasma power. As the plasma power increases, the PL peak energy is observed to shift toward the higher energy side and the Raman E2 (high) and A1 (LO) modes are shifted to the lower frequency. The residual compressive strain in epitaxial InN is relaxed. The lower plasma power and the higher growth temperature are preferred for the MBE growth of high-quality InN films. The influencing factors on the InN PL peak and band gap Eg have been revealed. It is evidenced that the InN PL peak and Eg can be shifted from high down to ∼0.65 eV with the carrier concentration down to low E19 cm−3 and the plasma power down to ∼80 W. Both the XPS and N K-edge XANES revealed the antisite defect of N on the In site, NIn. The XANES In L-edge measurements on the In L3-edge of InN films with various carrier concentrations has indicated the fourfold InN intermediate crystal structures. These obtained results are significant and useful to deepen the understanding and promote further investigation in InN and III-N materials.

Modulation of the conformation, fibrillation, and fibril morphologies of human brain α-, β-, and γ-synuclein proteins by the disaccharide chemical chaperone trehalose

Human α-, β-, and γ-synuclein (syn) are natively unfolded proteins present in the brain. Deposition of aggregated α-syn in Lewy bodies is associated with Parkinson's disease (PD) and γ-syn is known to be involved in both neurodegeneration and breast cancer. At physiological pH, while α-syn has the highest propensity for fibrillation followed by γ-syn, β-syn does not form any fibrils. Fibril formation in these proteins could be modulated by protein structure stabilizing osmolytes such as trehalose which has an exceptional stabilizing effect for globular proteins. We present a comprehensive study of the effect of trehalose on the conformation, aggregation, and fibril morphology of α-, β-, and γ-syn proteins. Rather than stabilizing the intrinsically disordered state of the synucleins, trehalose accelerates the rate of fibril formation by forming aggregation-competent partially folded intermediate structures. Fibril morphologies are also strongly dependent on the concentration of trehalose with ≤ 0.4M favoring the formation of mature fibrils in α-, and γ-syn with no effect on the fibrillation of β-syn. At ≥ 0.8M, trehalose promotes the formation of smaller aggregates that are more cytotoxic. Live cell imaging of preformed aggregates of a labeled A90C α-syn shows their rapid internalization into neural cells which could be useful in reducing the load of aggregated species of α-syn. The findings throw light on the differential effect of trehalose on the conformation and aggregation of disordered synuclein proteins with respect to globular proteins and could help in understanding the effect of osmolytes on intrinsically disordered proteins under cellular stress conditions.

A transient intermediate RNA structure underlies the regulatory function of the E. coli thiB TPP translational riboswitch.

Riboswitches are cis-regulatory RNA elements that regulate gene expression in response to ligand binding through the coordinated action of a ligand-binding aptamer domain (AD) and a downstream expression platform (EP). Previous studies of transcriptional riboswitches have uncovered diverse examples that utilize structural intermediates that compete with the AD and EP folds to mediate the switching mechanism on the timescale of transcription. Here we investigate whether similar intermediates are important for riboswitches that control translation by studying the Escherichia coli thiB thiamin pyrophosphate (TPP) riboswitch. Using cellular gene expression assays, we first confirmed that the riboswitch acts at the level of translational regulation. Deletion mutagenesis showed the importance of the AD-EP linker sequence for riboswitch function. Sequence complementarity between the linker region and the AD P1 stem suggested the possibility of an intermediate nascent RNA structure called the antisequestering stem that could mediate the thiB switching mechanism. Experimentally informed secondary structure models of the thiB folding pathway generated from chemical probing of nascent thiB structures in stalled transcription elongation complexes confirmed the presence of the antisequestering stem, and showed it may form cotranscriptionally. Additional mutational analysis showed that mutations to the antisequestering stem break or bias thiB function according to whether the antisequestering stem or P1 is favored. This work provides an important example of intermediate structures that compete with AD and EP folds to implement riboswitch mechanisms.

Tuning of structural/functional feature of carbon fibers: New insights into the stabilization of polyacrylonitrile

The transformation mechanisms from linear polyacrylonitrile (PAN) to ladder structure during stabilization is still controversial. Here, the thermal stabilization mechanism of PAN in nitrogen and air are investigated by variable temperature infrared spectrometry (VTIR), Solid-state (ss) NMR spectroscopy and the density functional theory (DFT). Our results show that the stabilization process of PAN under air is initiated via oxidation reaction, followed by the cyclization and dehydrogenation reaction. Furthermore, during the stabilization of PAN in nitrogen, a new intermediate structure with longer conjugation than the final isolated pyridine ring structure is proposed. Subsequently, we optimized the atmosphere of stabilization process according to the evolution of molecular structure. Consequently, compared with the traditional approach of heat treatment in air, pretreating the precursor fibers in nitrogen at a relative low temperature are shown to improve the char yield by 14.6%, and increase the thermal conductivity by 663%.

MicroED structure of a protoglobin reactive carbene intermediate

MicroED structure of a protoglobin reactive carbene intermediate

High-resolution crystal structures of transient intermediates in the phytochrome photocycle

High-resolution crystal structures of transient intermediates in the phytochrome photocycle

Principles of human pre-60S biogenesis.

During the early stages of human large ribosomal subunit (60S) biogenesis, an ensemble of assembly factors establishes and fine-tunes the essential RNA functional centers of pre-60S particles by an unknown mechanism. Here, we report a series of cryo-electron microscopy structures of human nucleolar and nuclear pre-60S assembly intermediates at resolutions of 2.5 to 3.2 angstroms. These structures show how protein interaction hubs tether assembly factor complexes to nucleolar particles and how guanosine triphosphatases and adenosine triphosphatase couple irreversible nucleotide hydrolysis steps to the installation of functional centers. Nuclear stages highlight how a conserved RNA-processing complex, the rixosome, couples large-scale RNA conformational changes with pre-ribosomal RNA processing by the RNA degradation machinery. Our ensemble of human pre-60S particles provides a rich foundation with which to elucidate the molecular principles of ribosome formation.