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Maleic anhydride is often used as a modifier to improve the thermal performance of the material due to its unique structure and properties. However, in order to meet higher demands, it is often imperative to have better heat resistance and thermal stability. Currently, the traditional method is physically blend inorganic nanoparticles to further improve thermal performance. Unfortunately, inorganic nanoparticles have a fatal problem in that they are not uniformly dispersed in the system, which severely limits their application. Here, we used organic–inorganic molecule, MAPOSS (methyl methacrylate‐based cage oligomeric silsesquioxane), to chemically modify the copolymer. And considering the unique structure of MAPOSS, we used two monomers with different polarities to study its influence on the thermal properties of the copolymerization system (MMA‐MAH‐MAPOSS and ST‐MAH‐MAPOSS), and discussed the interaction mechanism, respectively. As a result, MAPOSS introduced can not only be evenly distributed in the polymerization system via chemical bonding and physical interactions but also effectively improve the thermal stability and high‐temperature resistance of the polymers. Thereinto, the Tg of MMA‐MAH copolymer is increased to above 130°C, and the carbon residue rate is up to 7.3%. The carbon residue rate is increased to 15.6% without affecting the Tg of the ST‐MAH copolymer. [ABSTRACT FROM AUTHOR]

Flexible electronics ushers in a revolution to the electronics industry in the 21st century. Ideally, all components of a flexible electronic device including the functional component shall comply with the deformation to ensure the structural and functional integrity, imposing a pressing need for developing room‐temperature strain‐tolerant semiconductors. To this end, there is a long‐standing material dilemma: inorganic semiconductors are typically brittle at room temperature except for size‐induced flexibility; by contrast, organic semiconductors are intrinsically soft and flexible but the electrical performance is poor. This is why the discovery of bulk plasticity in Ag2S at room temperature and ZnS in darkness is groundbreaking in solving this long‐standing material dilemma between the mechanical deformability and the electrical performance. The present review summarizes the background knowledge and latest advances in the emerging field of plastic inorganic semiconductors. At the outset, we argue that the plasticity of inorganic semiconductors is vital to strain tolerance of electronic devices, which has not been adequately emphasized. The mechanisms of plasticity are illustrated from the perspective of chemical bonding and dislocations. Plastic inorganic materials, for example, ionic crystals (insulators), ZnS in darkness, and Ag2S, are discussed in detail in terms of their prominent mechanical properties and potential applications. We conclude the article with several key scientific and technological questions to address in the future study. [ABSTRACT FROM AUTHOR]

The crystal structure of new isostructural compounds MgCo2Ga5 and MgNi2Ga5 has been investigated using single-crystal X-ray diffraction. Both compounds represent a new type of structure: orthorhombic, space group Pnnm, oP16, with the following lattice parameters: a = 6.2700(2) Å, b = 6.6946(2) Å, c = 6.0789(2) Å (for MgCo2Ga5) and a = 6.2693(3) Å, b = 6.6968 Å, c = 6.0794 Å (for MgNi2Ga5). The MgCo2Ga5 and MgNi2Ga5 are closely related to the tetragonal structure of CoGa3 which crystallizes in the ht-IrIn3 type. The orthorhombic structures of MgCo2Ga5 and MgNi2Ga5 are derived from CoGa3 via a translationengleiche symmetry reduction of index 2. The symmetry reduction from P42/mnm to Pnnm causes that the 4c site splits into two sites 2c and 2d. The gallium atoms together with cobalt or nickel form 3D-nets with channels, in which magnesium atoms are inserted. The formation of these polyatomic nets is confirmed by distribution of electron localization function (ELF) and charges of atoms. [ABSTRACT FROM AUTHOR]

In this paper we elaborate and evaluate the Roby-Gould bond index method (RGBI) for classifying and interpreting the nature of chemical bonds [Gould et al., Theor. Chem. Acc., 2008, 119, 275]. We emphasize that the RGBI method defines atoms as subspaces of a Hilbert space, represented as projection operators, and in accord with basic mathematical requirements concerning the assignment of probabilities to such subspaces. The definition of the bond indices between such atoms follows from simple set theoretical ideas concerning the sharing of, and differences between, atomic electron populations; and from the geometric properties associated with these subspaces—properties which are closely aligned with older chemical notions, which are reviewed. We also introduce the Araki angle percentage ionicity of a bond, which is easily read off from a compact two-dimensional representation of the chemical bond, which we call the bond dial diagram. Additionally we explore the theory with defining atoms by the occupied natural atomic spinorbitals (NAOs) of Reed and coworkers, instead of the atomic natural orbitals (ANOs) previously used. Bond indices from these ANO- and NAO-based atoms are applied to a dataset of 353 molecules, including 27 first row molecules, 280 organic molecules, and 46 semiochemical molecules, comprising 33 A–H bonds, where A are first and second row elements, 1779 C–X, 3415 H–X bonds (X = C, N, O, S), and a few more other types of bonds. The bond indices from the ANO-based atoms are much more in accord with chemists' expectations as compared to those obtained from NAO-based atoms provided that the excited triplet state defines the ANOs for group 2 atoms.

Cover Feature: In-Cage Interactions in the Clathrate Superconductor Sr8Si46 (Chem. Eur. J. 4/2020) Keywords: chemical bonding; clathrate; high-pressure synthesis; silicon; strontium Chemical bonding, clathrate, high-pressure synthesis, silicon, strontium. [Extracted from the article]

The main descriptors of chemical bonding such as bond order (BO) and electron density at the bond critical point, ρc, are customarily used to understand the crystal and electronic structure of materials, as well as to predict their reactivity and stability. They can be obtained in the framework of crystal chemistry and quantum chemistry approaches, which are mostly applied as alternatives to each other. This paper verifies the convergence of the two approaches by analyzing a plethora of quantum chemistry data available in the literature. The exponential correlation between the electron descriptors [BOij and ρc(ij)] and the length of chemical bonds, Rij, which is basic in crystal chemistry, was confirmed for 72 atom pairs, regardless of the nature of their interactions (ionic/covalent, metal–metal, etc.). The difference between the BOij (Rij) correlations obtained in this work and those accepted in crystal chemistry for the same atomic pairs does not exceed the dispersion of quantum chemistry data, confirming the qualitative validity of the BO conservation principle. Various examples are presented to show that knowledge of the exponential parameters ensures a surprisingly simple determination of two basic electron descriptors in any complex compound with known interatomic distances. In particular, the BO analysis for 20 Re6-cluster complexes illustrates the BO conservation for systems with delocalized electrons. Despite the significant transfer of electron density from the Re–Re to the Re–ligand bonds, the total number of Re valence electrons used in bonding remains close to the formal value of seven electrons.

We present an update on recently developed methodology and functionality in the computer program Local Orbital Basis Suite Toward Electronic‐Structure Reconstruction (LOBSTER) for chemical‐bonding analysis in periodic systems. LOBSTER is based on an analytic projection from projector‐augmented wave (PAW) density‐functional theory (DFT) computations (Maintz et al., J. Comput. Chem.2013, 34, 2557), reconstructing chemical information in terms of local, auxiliary atomic orbitals and thereby opening the output of PAW‐based DFT codes to chemical interpretation. We demonstrate how LOBSTER has been improved by taking into account time‐reversal symmetry, thereby speeding up the DFT and LOBSTER calculations by a factor of 2. Over the recent years, the functionalities have also been continually expanded, including accurate projected densities of states (DOSs), crystal orbital Hamilton population (COHP) analysis, atomic and orbital charges, gross populations, and the recently introduced k‐dependent COHP. The software is offered free‐of‐charge for non‐commercial research. [ABSTRACT FROM AUTHOR]

The study aims to understand the carbonization mechanism when an ns NIR transparent fiber laser beam irradiation of polycarbonate (PC) instead of irradiation using a UV laser beam or ultrashort pulsed laser beam. It reveals that PC can be decomposed with an ns transparent 1064 nm laser beam. The laser fluence threshold under which to cause ablation in PC was not a constant value. The threshold decreased as the scanning pulse number increased. The threshold fluence was above 2.9 J/cm2 at irradiation with 10 pulses. The threshold fluence was above 11.6 mJ/cm2 at irradiation with 2 pulses. The optical transmittance of PC was decreased under laser irradiation. The optical transmittance was reduced by 50% and 90% at laser fluence of 2.9 J/cm2 and 11.6 J/cm2, respectively, at irradiation with 15 pulses. In addition, x-ray photoelectron spectroscopy measurements show that the C/O ratio was reduced 20.8% and 33.2%, respectively. The water contact angle was reduced due to the carbon loss at the PC surface. Inside marking of PC produced a darker contrast than surface marking due to that the carbon was lost at the surface, in contrary, carbonate concentration remained when marking inside the bulk of PC. [ABSTRACT FROM AUTHOR]

In many cases, idealized crystal structure models cannot rationalize the actual properties of intermetallic compounds. For a realistic approach in materials research, microstructures and defects need to be taken into account. In case of clathrate compounds, particularly the intrinsic framework vacancies (denoted as Zintl defects) demand consideration. Consequently, clathrate research produces evidence that modern‐day structure chemistry involves the utilization of advanced X‐ray diffraction methods combined with elaborated bulk phase analyses, the investigation of phase relations, and the study of mutual interrelations in the triangle chemical bonding–structure–properties. Herein, we review some fundamental contributions to the specific defect chemistry of intermetallic clathrates. [ABSTRACT FROM AUTHOR]

Lithium sulfur batteries (LSBs) are promising next-generation rechargeable batteries due to the high gravimetric energy, low cost, abundance, nontoxicity, and high sustainability of sulfur. However, the dissolution of high-order polysulfide in electrolytes and low Coulombic efficiency of Li anode require excess electrolytes and Li metal, which significantly reduce the energy density of LSBs. Quasi-solid-state LSBs, where sulfur is encapsulated in the micropores of carbon matrix and sealed by solid electrolyte interphase, can operate under lean electrolyte conditions, but a low sulfur loading in carbon matrix (<40 wt %) and low sulfur unitization (<70%) still limit the energy density in a cell level. Here, we significantly increase the sulfur loading in carbon to 60 wt % and sulfur utilization to ~87% by dispersing sulfur in an oxygen-rich dense carbon host at a molecular level through strong chemical interactions of C-S and O-S. In an all-fluorinated organic lean electrolyte, the C/S cathode experiences a solid-state lithiation/delithiation reaction after the formation of solid electrolyte interphase in the first deep lithiation, completely avoiding the shuttle reaction. The chemically stabilized C/S composite retains a high reversible capacity of 541 mAh·g-1 (based on the total weight of the C/S composite) for 200 cycles under lean electrolyte conditions, corresponding to a high energy density of 974 Wh·kg-1. The superior electrochemical performance of the chemical bonding-stabilized C/S composite renders it a promising cathode material for highenergy and long-cycle-life LSBs. [ABSTRACT FROM AUTHOR]

Samarium hexaboride is an anomaly, having many exotic and seemingly mutually incompatible properties. It was proposed to be a mixed‐valent semiconductor, and later a topological Kondo insulator, and yet has a Fermi surface despite being an insulator. We propose a new and unified understanding of SmB6 centered on the hitherto unrecognized dynamical bonding effect: the coexistence of two Sm−B bonding modes within SmB6, corresponding to different oxidation states of the Sm. The mixed valency arises in SmB6 from thermal population of these distinct minima enabled by motion of B. Our model simultaneously explains the thermal valence fluctuations, appearance of magnetic Fermi surface, excess entropy at low temperatures, pressure‐induced phase transitions, and related features in Raman spectra and their unexpected dependence on temperature and boron isotope. [ABSTRACT FROM AUTHOR]

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The ethylene epoxidation is a challenging catalytic process, and development of active and selective catalyst requires profound understanding of its chemical behaviour under reaction conditions. The systematic study on intermetallic compounds in the Ca–Ag system under ethylene epoxidation conditions clearly shows that the character of the oxidation processes on the surface originates from the atomic interactions in the pristine compound. The Ag-rich compounds Ca2Ag7 and CaAg2 undergo oxidation towards fcc Ag and a complex Ca-based support, whereas equiatomic CaAg and the Ca-rich compounds Ca5Ag3 and Ca3Ag in bulk remain stable under harsh ethylene epoxidation conditions. For the latter presence of water vapour in the gas stream leads to noticeable corrosion. Combining the experimental results with the chemical bonding analysis and first-principles calculations, the relationships among the chemical nature of the compounds, their reactivity and catalytic performance towards epoxidation of ethylene are investigated. [ABSTRACT FROM AUTHOR]

Structural and electronic properties, Fermi surface topology, and chemical bonding features in layered 1111-oxyarsenides LaRhAsO and LaIrAsO are studied and compared using ab initio simulations. The nonmagnetic metal LaIrAsO is found to be weakly sensitive to both electronic and hole doping. However, the Rh-containing phase is predicted to exhibit weak band magnetism and can turn into a nonmagnetic state by hole doping. Therefore, the LaRhAsO oxyarsenide can be considered as a possible "electronic" analogue of the LaFeAsO compound, the basic phase of layered FeAs superconductors. [ABSTRACT FROM AUTHOR]

After a compact history of the PT, from Döbereiner's triads to the theoretical predictions up to element 172, a number of particular issues is discussed: Why may Z = 172 be a limit for stable electron shells? What are the expected stability limits of the nuclear isotopes? When are formally empty atomic orbitals used in molecular electronic structures? What is 'Secondary Periodicity'? When do the elements (Ir, Pt, Au), at the end of a bond, simulate (N, O, I), respectively? Some new suggestions for alternative PTs are commented upon. As a local connection, Johan Gadolin's 1794 analysis of the Ytterby mineral is mentioned. [ABSTRACT FROM AUTHOR]

The properties of the materials are intimately related to the nature of the chemical bond. Research to explain the peculiarities of superionic materials by focusing on the bonding character of the materials is presented. In particular, a brief review of some fundamental aspects of superionic conductors is given based on the talk presented at "Solid State Chemistry 2018, Pardubice" in addition to some new results related to the subject. Specifically, the topics on bond fluctuation model of ionic conductors, the role of medium range structure in the ionic conductivity, bonding aspects of non-Arrhenius ionic conductivity and elastic properties of ionic conductors are discussed. Key concepts that are gained from these studies is stressed, such as the importance of the coexistence of different types of bonding, and the role of medium range structure in glasses for efficient ionic transport in solids. These concepts could help the development of new materials. [ABSTRACT FROM AUTHOR]

This article reports the theoretical and experimental study of nonresonant mechanisms (CHEM) of surface‐enhanced Raman spectroscopy (SERS) of pyridine (Py). An improvement in the Raman dispersion intensity of Py is determined after the chemical absorption on CuO nanoparticles synthesized in NaCl. The density functional theory predicts the formation of new electronic states as result of the chemical bond (CB) established between the Py molecule and the (CuO)n clusters. This study is focused on the study of the most intense vibrational modes of Py before and after chemical adsorption. The CHEM by CB mechanisms is found as responsible for the SERS effect in Py. [ABSTRACT FROM AUTHOR]

Identifying the phase evolution and revealing the chemical bonds of hydrated cements accurately is crucial to regulate the performance of cementitious materials. In this paper, a coupled Raman/BSE-EDS analysis was proposed to determine the chemical bonds of tricalcium silicate hydrates and the interface transition zone (ITZ) between inner C-S-H and anhydrates. The results show that the Raman/BSE-EDS method can accurately identify the chemical bonds of inner C-S-H and inner ITZ regions, which confirms the mixed structure of inner C-S-H and nano calcium hydroxide (CH). The inner ITZ shows a lattice change region with a thickness of 700–1000 nm, which can be attributed to the pre-disassembly process of C3S crystal. The successful application of coupled Raman/BSE-EDS provides new insight into the hydration process and multi-structure features of traditional cementitious materials.

X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) are applied to investigate the properties of fine-grained concentrates on artisanal, small-scale gold mining samples from the Kubi Gold Project of the Asante Gold Corporation near Dunwka-on-Offin in the Central Region of Ghana. Both techniques show that the Au-containing residual sediments are dominated by the host elements Fe, Ag, Al, N, O, Si, Hg, and Ti that either form alloys with gold or with inherent elements in the sediments. For comparison, a bulk nugget sample mainly consisting of Au forms an electrum, i.e., a solid solution with Ag. Untreated (impure) sediments, fine-grained Au concentrate, coarse-grained Au concentrate, and processed ore (Au bulk/nugget) samples were found to contain clusters of O, C, N, and Ag, with Au concentrations significantly lower than that of the related elements. This finding can be attributed to primary geochemical dispersion, which evolved from the crystallization of magma and hydrothermal liquids as well as the migration of metasomatic elements and the rapid rate of chemical weathering of lateralization in secondary processes. The results indicate that Si and Ag are strongly concomitant with Au because of their eutectic characteristics, while N, C, and O follow alongside because of their affinity to Si. These non-noble elements thus act as pathfinders for Au ores in the exploration area. This paper further discusses relationships between gold and sediments of auriferous lodes as key to determining indicator minerals of gold in mining sites.

We describe the formal algorithm and numerical applications of a novel convex quadratic programming (QP) strategy for performing the variational minimization that underlies natural resonance theory (NRT). The QP algorithm vastly improves the numerical efficiency, thoroughness, and accuracy of variational NRT description, which now allows uniform treatment of all reference structures at the high level of detail previously reserved only for leading "reference" structures, with little or no user guidance. We illustrate overall QPNRT search strategy, program I/O, and numerical results for a specific application to adenine, and we summarize more extended results for a data set of 338 species from throughout the organic, bioorganic, and inorganic domain. The improved QP‐based implementation of NRT is a principal feature of the newly released NBO 7.0 program version. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The chemistry of d-block metal-metal multiple bonds has been extensively investigated in the past 5 decades. However, the synthesis and characterization of species with f-block metal-metal multiple bonds are significantly more challenging and such species remain extremely rare. Here, we report the identification of a uranium-rhodium triple bond in a heterometallic cluster, which was synthesized under routine conditions. The uranium-rhodium triple-bond length of 2.31 Å in this cluster is only 3% longer than the sum of the covalent triple-bond radii of uranium and rhodium (2.24 Å). Computational studies reveal that the nature of this uranium- rhodium triple bond is 1 covalent bond with 2 rhodium-touranium dative bonds. This heterometallic cluster represents a species with f-block metal-metal triple bond structurally authenticated by X-ray diffraction. These studies not only demonstrate the authenticity of the uranium-metal triple bond, but also provide a possibility for the synthesis of other f-block metal-metal multiple bonds. We expect that this work may further our understanding of the bonding between uranium and transition metals, which may help to design new d-f heterometallic catalysts with uranium-metal bonds for small-molecule activation and to promote the utilization of abundant depleted uranium resources. [ABSTRACT FROM AUTHOR]

REMo2B5 (RE = Ce, Pr, Nd) and CeW2B5 have been synthesized by arc melting with further annealing at 1300 °C. CeMo2B5 crystallizes in a new structure type with space group Pnma, a = 11.0298(2) Å, b = 3.12080(5) Å, c = 9.9594(2) Å, Z = 4. Its structural arrangement reveals puckered [B6]‐hexagonal rings, trigonal‐prismatic‐ and empty pyramidal‐tetrahedral‐slabs. The structure can be related to the derivatives of AlB2 and CrB prototypes. The boron atoms form a two‐dimensional network of corrugated ribbons, each composed of four edge‐linked [B6] rings infinitely extending along the b‐axis. CeMo2B5 is a Pauli paramagnet. Electrical transport measurements together with the calculated density of states at the Fermi level of 3.81 states eV–1 f.u.–1 indicate CeMo2B5 to be a typical metallic system. Electronic structure calculations reveal significant hybridization of Ce 4f5d states with Mo 4d states. The chemical bonding scenario is dominated by chains of [Ce2Mo2] clusters with multi‐center bonds. These clusters are connected via metallic Mo–Mo bonds. This metal‐framework, in turn, is stabilized by bonding interactions with the boron ribbons to which it donates electrons. [ABSTRACT FROM AUTHOR]

HIV-1 Gag is a large multidomain poly-protein with flexible unstructured linkers connecting its globular subdomains. It is compact when in solution but assumes an extended conformation when assembled within the immature HIV-1 virion. Here, we use molecular dynamics (MD) simulations to quantitatively characterize the intra-domain interactions of HIV-1 Gag. We find that the matrix (MA) domain and the C-terminal subdomain CActd of the CA capsid domain can form a bound state. The bound state, which is held together primarily by interactions between complementary charged and polar residues, stabilizes the compact state of HIV-1 Gag. We calculate the depth of the attractive free energy potential between the MA/ CActd sites and find it to be about three times larger than the dimerization interaction between the CActd domains. Sequence analysis shows high conservation within the newly-found intra-Gag MA/CActd binding site, as well as its spatial proximity to other well known elements of Gag –such as CActd’s SP1 helix region, its inositol hexaphosphate (IP6) binding site and major homology region (MHR), as well as the MA trimerization site. Our results point to a high, but yet undetermined, functional significance of the intra-Gag binding site. Recent biophysical experiments that address the binding specificity of Gag are interpreted in the context of the MA/CActd bound state, suggesting an important role in selective packaging of genomic RNA by Gag. [ABSTRACT FROM AUTHOR]

RNA-protein interaction plays important roles in post-transcriptional regulation. Recent advancements in cross-linking and immunoprecipitation followed by sequencing (CLIP-seq) technologies make it possible to detect the binding peaks of a given RNA binding protein (RBP) at transcriptome scale. However, it is still challenging to predict the functional consequences of RBP binding peaks. In this study, we propose the Protein-RNA Association Strength (PRAS), which integrates the intensities and positions of the binding peaks of RBPs for functional mRNA targets prediction. We illustrate the superiority of PRAS over existing approaches on predicting the functional targets of two related but divergent CELF (CUGBP, ELAV-like factor) RBPs in mouse brain and muscle. We also demonstrate the potential of PRAS for wide adoption by applying it to the enhanced CLIP-seq (eCLIP) datasets of 37 RNA decay related RBPs in two human cell lines. PRAS can be utilized to investigate any RBPs with available CLIP-seq peaks. PRAS is freely available at . [ABSTRACT FROM AUTHOR]

Valence‐shell electron‐pair repulsion (VSEPR) theory constitutes one of the pillars of theoretical predictive chemistry. It was proposed even before the advent of the concept of "spin", and it is still a very useful tool in chemistry. In this article we propose an extension of VSEPR theory to understand the core structure and predict core polarization in the main‐group elements. We show from first principles (Electron Localization Function analysis) how the inner‐ and outer‐core shells are organized. In particular, electrons in these regions are structured following the shape of the dual polyhedron of the valence shell (3rd period) or the equivalent polyhedron (4th and 5th periods). We interpret these results in terms of "hard" and "soft" core character. All the studied systems follow this trend, providing a framework for predicting electron distribution in the core. We also show that lone pairs behave as "standard ligands" in terms of core polarization. The predictive character of the model was tested by proposing the core polarization in different systems not included in the original set (such as XeF4 and [Fe(CN)6]3−) and checking the hypothesis by means of a posteriori calculations. From the experimental point of view, the extension of VSEPR to the core region has consequences for current crystallography research. In particular, it explains the core polarization revealed by high resolution X‐ray experiments. [ABSTRACT FROM AUTHOR]

Photodynamic therapy (PDT) uses photosensitisers such as protoporphyrin IX (PpIX) to target tumours via the release of toxic singlet oxygen when irradiated. The effectivity of the treatment is limited by the innate properties of the photosensitizers; they typically exhibit inefficient accumulation in target tissue and high dark toxicity. Carbon dots (CDs) are biocompatible fluorescent nanoparticles which can improve PpIX cellular uptake and solubility. In this work, we present conjugates synthesised by host-guest encapsulation (PpIX@CD) and amide cross-linking (PpIX-CD). Characterization demonstrated conjugates have a loading efficiency of 34–48% and similar singlet oxygen production to PpIX. PpIX-containing CDs showed a 2.2 to 3.7-fold decrease in dark toxicity. PpIX-CD and PpIX@CD showed equivalent light-induced toxicity to PpIX in concentrations >1 μg/ml, leading to a 3.2 to 4.1-fold increase in photo-toxicity index (PI). The less soluble fraction of cross-linked conjugates (PpIX-CD)p did not show significant difference from PpIX. Confocal light scanning microscopy demonstrated rapid intracellular uptake and accumulation of conjugates. Our results demonstrate the variations between cross-linking strategies in CD-based conjugates, highlighting their potential as carriers in drug delivery and bioimaging applications. [ABSTRACT FROM AUTHOR]

All-ceramic restoration has become a popular technology for dental restoration; however, the relative bond strength between the ceramic and resin limits its further application. Long-term high bond strength, especially after thermal cycling, is of great importance for effective restoration. The effect of physical and/or chemical surface treatments on bonding durability is seldom reported. To overcome this problem, we investigate the bond strength between lithium disilicate ceramics (LDC) and two kinds of resin cements before and after thermal cycling for a variety of surface treatments including hydrofluoric acid, two kinds of silane and a combined effect. The shear bond strength in every group is characterized by universal mechanical testing machine averaged by sixteen-time measurements. The results show that when treated with HF and a mixed silane, the LDC surface shows maximum bonding strengths of 27.1 MPa and 23.3 MPa with two different resin cements after 5000 thermal cycling, respectively, indicating an excellent ability to resist the damage induced by cyclic expansion and contraction. This long-term high bond strength is attributed to the combined effect of micromechanical interlocking (physical bonding) and the formation of Si-O-Si and -C-C- at the interface (chemical bonding). This result offers great potential for enhancing bond strength for all-ceramic restoration by optimizing the surface treatment. [ABSTRACT FROM AUTHOR]

Abstraction of iodide from [(η5‐C5iPr5)2UI] (1) produced the cationic uranium(III) metallocene [(η5‐C5iPr5)2U]+ (2) as a salt of [B(C6F5)4]−. The structure of 2 consists of unsymmetrically bonded cyclopentadienyl ligands and a bending angle of 167.82° at uranium. Analysis of the bonding in 2 showed that the uranium 5f orbitals are strongly split and mixed with the ligand orbitals, thus leading to non‐negligible covalent contributions to the bonding. Investigation of the dynamic magnetic properties of 2 revealed that the 5f covalency leads to partially quenched anisotropy and fast magnetic relaxation in zero applied magnetic field. Application of a magnetic field leads to dominant relaxation by a Raman process. [ABSTRACT FROM AUTHOR]

Recently, silicone rubber (VMQ) was extensively used in household articles and medical devices. To develop a kind of safe and long‐term antimicrobial VMQ was of great significance. In this work, a kind of vinyl‐contained polyhexamethylene guanidine hydrochloride (VPHMG) was synthesized and used as antimicrobial additive for VMQ. With the increasing of VPHMG addition, the mechanical properties and antimicrobial properties of VMQ‐VPHMG were significantly improved. In particular, the antimicrobial rates against Escherichia coli and Staphylococcus aureus were higher than 99.99% as for 4 wt% of VPHMG addition. Moreover, the surface concentration of VPHMG as well as the antimicrobial rates revealed almost unchanged after being extracted by water and methanol. All the results indicated the vinyl‐contained VPHMG vulcanization and therefore provided the permanent antimicrobial performance for VMQ. [ABSTRACT FROM AUTHOR]

Antibodies are important for immunity and exist in several classes (IgM, IgD, IgA, IgG, IgE). They are composed of symmetric dimeric molecules with two antigen binding regions (Fab) and a constant part (Fc), usually depicted as Y-shaped molecules. Rheumatoid factors found in patients with rheumatoid arthritis are autoantibodies binding to IgG and paradoxically appear to circulate in blood alongside with their antigen (IgG) without reacting with it. Here, it is shown that rheumatoid factors do not react with native IgG in solution, and that their epitopes only become accessible upon certain physico-chemical treatments (e.g. heat treatment at 57 °C), by physical adsorption on a hydrophobic surface or by antigen binding. Moreover, chemical cross-linking in combination with mass spectrometry showed that the native state of IgG is a compact (closed) form and that the Fab parts of IgG shield the Fc region and thereby control access of rheumatoid factors and presumably also some effector functions. It can be inferred that antibody binding to pathogen surfaces induces a conformational change, which exposes the Fc part with its effector sites and rheumatoid factor epitopes. This has strong implications for understanding antibody structure and physiology and necessitates a conceptual reformulation of IgG models. [ABSTRACT FROM AUTHOR]

An ancient enzyme family responsible for the catabolism of the prebiotic chemical cyanuric acid (1,3,5-triazine-2,4,6-triol) was recently discovered and is undergoing proliferation in the modern world due to industrial synthesis and dissemination of 1,3,5-triazine compounds. Cyanuric acid has a highly stabilized ring system such that bacteria require a unique enzyme with a novel fold and subtle active site construction to open the ring. Each cyanuric acid hydrolase monomer consists of three isostructural domains that coordinate and activate the three-fold symmetric substrate cyanuric acid for ring opening. We have now solved a series of X-ray structures of an engineered, thermostable cyanuric acid ring-opening enzyme at 1.51 ~ 2.25 Å resolution, including various complexes with the substrate, a tight-binding inhibitor, or an analog of the reaction intermediate. These structures reveal asymmetric interactions between the enzyme and bound ligands, a metal ion binding coupled to conformational changes and substrate binding important for enzyme stability, and distinct roles of the isostructural domains of the enzyme. The multiple conformations of the enzyme observed across a series of structures and corroborating biochemical data suggest importance of the structural dynamics in facilitating the substrate entry and the ring-opening reaction, catalyzed by a conserved Ser-Lys dyad. [ABSTRACT FROM AUTHOR]

Using the DFT methods, we computationally predict the stability of cage compounds E4nRn (E = B, C; R = H, F; n = 4, 8, 12, 24) based on Platonic bodies and Archimedean polyhedrons in which all vertices are replaced by tetrahedral E4R fragments. Cage compounds B60R12 and C60 with pyramidal units B5R or C5 are also examined and it is shown that only boron compounds are stable. The nature of chemical bonding in the discussed compounds is analyzed using the AdNDP and NBO methods. The hydrocarbons have classical 2c-2e C-C σ-bonds, while the boron compounds are formed by the polyhedral units with the delocalized multicenter bonds which connected three and more boron atoms. The new example of spherical aromaticity according to the 2(N+1)2 rule in the case of B16F4 with multicenter 16c-2e bonds are revealed. Stable compound B60H12 contains 12 5c-2e B-B bonds. [ABSTRACT FROM AUTHOR]

Mutations that confer herbicide resistance are a primary concern for herbicide-based chemical control of invasive plants and are often under-characterized structurally and functionally. As the outcome of selection pressure, resistance mutations usually result from repeated long-term applications of herbicides with the same mode of action and are discovered through extensive field trials. Here we used acetohydroxyacid synthase (AHAS) of Kochia scoparia (KsAHAS) as an example to demonstrate that, given the sequence of a target protein, the impact of genetic mutations on ligand binding could be evaluated and resistance mutations could be identified using a biophysics-based computational approach. Briefly, the 3D structures of wild-type (WT) and mutated KsAHAS-herbicide complexes were constructed by homology modeling, docking and molecular dynamics simulation. The resistance profile of two AHAS-inhibiting herbicides, tribenuron methyl and thifensulfuron methyl, was obtained by estimating their binding affinity with 29 KsAHAS (1 WT and 28 mutated) using 6 molecular mechanical (MM) and 18 hybrid quantum mechanical/molecular mechanical (QM/MM) methods in combination with three structure sampling strategies. By comparing predicted resistance with experimentally determined resistance in the 29 biotypes of K. scoparia field populations, we identified the best method (i.e., MM-PBSA with single structure) out of all tested methods for the herbicide-KsAHAS system, which exhibited the highest accuracy (up to 100%) in discerning mutations conferring resistance or susceptibility to the two AHAS inhibitors. Our results suggest that the in silico approach has the potential to be widely adopted for assessing mutation-endowed herbicide resistance on a case-by-case basis. [ABSTRACT FROM AUTHOR]

Mendeleev's proposal of the periodic table was the final step in what happened to be a long series of attempts by leading chemists of the day to devise a "modern" system for the chemical elements and their compounds following on from Dalton's notion of atoms in the early nineteenth century. While most of the early systems (including, finally, Mendeleev's) were based on an ordering of the known elements by atomic weight, the (then) new concept of "valency" introduced by Frankland, Kekulé and others in the 1850s inspired many of the significant contributions (inter alia by Lothar Meyer) in the final decade before 1869. This chapter will begin with a summary of some key developments of chemical concepts during the first half of the nineteenth century and will emphasize the key role played by the Congress at Karlsruhe in 1860 and the way it shaped the development towards a periodic table of the chemical elements. We will then briefly recapitulate the role that "valency" played in the evolution towards a periodic table of the elements and how it has impacted the development of chemistry subsequently. The principal value of the valence concept is its role as an ordering principle for the elements, their compounds and their chemical structures. As chemists expanded the number of elements and their numerous compounds, it has become apparent that it also has significant limitations, and since its origins were based on a very limited view of chemical bonding and no structural information, it has had to adapt significantly during the last 150 years. Modern concepts generalizing structure formation and bonding capabilities of molecular fragments are generally based on qualitative frontier orbital models, which are guided by increasingly accurate quantum mechanical calculations. The difficulties encountered in the establishment of relationships between concepts of chemical bonding and quantum chemical modelling of the chemical bond are illustrated for metal-metal bond polarity in oligonuclear complexes at the end of the chapter. [ABSTRACT FROM AUTHOR]

The main production process parameters of ultra-low-density fiberboard (UDF) were selected by use of response surface methodology, and then the properties of UDF were improved by adding a coupling agent. Microstructures and chemical bonding in UDF were analyzed by scanning electron microscopy and infrared spectroscopy. The results showed that the desirable process parameters for UDF production were the amount of urea-formaldehyde resin adhesive (18%), the hot pressing temperature (170 °C), the hot pressing time (200 s), and the amount of KH560 coupling agent added (1%). The main physical and mechanical properties of UDF obtained included internal bond strength (0.59 MPa), modulus of rupture (19.8 MPa), and 24h thickness swelling (10.0%). These properties exceeded the requirements of ISO 16895 (2016). [ABSTRACT FROM AUTHOR]

Drosophila provides an inexpensive and quantitative platform for measuring whole animal drug response. A complementary approach is virtual screening, where chemical libraries can be efficiently screened against protein target(s). Here, we present a unique discovery platform integrating structure-based modeling with Drosophila biology and organic synthesis. We demonstrate this platform by developing chemicals targeting a Drosophila model of Medullary Thyroid Cancer (MTC) characterized by a transformation network activated by oncogenic dRetM955T. Structural models for kinases relevant to MTC were generated for virtual screening to identify unique preliminary hits that suppressed dRetM955T-induced transformation. We then combined features from our hits with those of known inhibitors to create a ‘hybrid’ molecule with improved suppression of dRetM955T transformation. Our platform provides a framework to efficiently explore novel kinase inhibitors outside of explored inhibitor chemical space that are effective in inhibiting cancer networks while minimizing whole body toxicity. [ABSTRACT FROM AUTHOR]

The forces that arise from the actin cortex play a crucial role in determining the membrane deformation. These include protrusive forces due to actin polymerization, pulling forces due to transient attachment of actin filaments to the membrane, retrograde flow powered by contraction of actomyosin network, and adhesion to the extracellular matrix. Here we present a theoretical model for membrane deformation resulting from the feedback between the membrane shape and the forces acting on the membrane. We model the membrane as a series of beads connected by springs and determine the final steady-state shape of the membrane arising from the interplay between pushing/pulling forces of the actin network and the resisting membrane tension. We specifically investigate the effect of the gel dynamics on the spatio-temporal deformation of the membrane until a stable lamellipodium is formed. We show that the retrograde flow and the cross-linking velocity play an essential role in the final elongation of the membrane. Interestingly, in the simulations where motor-induced contractility is switched off, reduced retrograde flow results in an increase in the rate and amplitude of membrane protrusion. These simulations are consistent with experimental observations that report an enhancement in protrusion efficiency as myosin II molecular motors are inhibited. [ABSTRACT FROM AUTHOR]

Recent experiments have reported an effect of weak radiofrequency magnetic fields in the MHz-range on the concentrations of reactive oxygen species (ROS) in living cells. Since the energy that could possibly be deposited by the radiation is orders of magnitude smaller than the energy of molecular thermal motion, it was suggested that the effect was caused by the interaction of RF magnetic fields with transient radical pairs within the cells, affecting the ROS formation rates through the radical pair mechanism. It is, however, at present not entirely clear how to predict RF magnetic field effects at certain field frequency and intensity in nanoscale biomolecular systems. We suggest a possible recipe for interpreting the radiofrequency effects in cells by presenting a general workflow for calculation of the reactive perturbations inside a cell as a function of RF magnetic field strength and frequency. To justify the workflow, we discuss the effects of radiofrequency magnetic fields on generic spin systems to particularly illustrate how the reactive radicals could be affected by specific parameters of the experiment. We finally argue that the suggested workflow can be used to predict effects of radiofrequency magnetic fields on radical pairs in biological cells, which is specially important for wireless recharging technologies where one has to know of any harmful effects that exposure to such radiation might cause. [ABSTRACT FROM AUTHOR]

A series of traction force microscopy experiments involving pairs of keratocytes migrating on compliant substrates were analyzed. We observed several instances where keratocytes that are about to collide turn before they touch. We term this phenomenon collision avoidance behavior and we propose that the turning is caused by the substrate mediated elastic interactions between the cells. A multipole analysis of the cell traction reveals that the left-right symmetry of the keratocyte traction pattern is broken during collision avoidance events. The analysis further shows that the cell migration direction reorients before the principal traction dipoles as the cells turn. Linear elasticity theory is used to derive the cell-cell interaction energy between pairs of keratocytes. The traction force applied by each cell is modeled as a two points (dipole) or three points (tripod) force model. We show that both models predict that cells that are about to collide in a head-on manner will turn before touching. The tripod model is further able to account for the quadrupole components of the traction force profile that we observed experimentally. Also, the tripod model proposes a mechanism that may explain why cells tend to scatter with a finite angle after a collision avoidance event. A relationship between the scattering angle and the traction force quadrupole moment is also established. Dynamical simulations of migrating model cells are further used to explain the emergence of other cell pair trajectories that we observed experimentally. [ABSTRACT FROM AUTHOR]

The effect of the gas mixture composition on the structure, chemical bond character and hardness of Si-B-C-N films was systematically studied. A series of Si-B-C-N films was deposited by reactive dc magnetron sputtering of the target composed of Si disc with B4C chips placed in the sputtering zone of disc. The films were deposited with nitrogen fractions 30-to-70% in Ar/N2 gas mixture and annealed in a vacuum at temperatures up to 1200°C. The films were characterized by X-ray diffraction, X-ray photo-electron spectroscopy, Fourier transform infrared spectroscopy, indentation tests. Addition of nitrogen in the gas mixture up to 60% led to an increase of hardness from 13.4 up to 17.8 GPa. With further increase in nitrogen content in gas mixture the film hardness decreased. The latter is caused by formation of the weak B-N bonds as well as C-C and C-C bonds that are characteristic of h-BN-like phase and graphite phase, respectively. [ABSTRACT FROM AUTHOR]

The fungal circadian clock photoreceptor Vivid (VVD) contains a photosensitive allosteric light, oxygen, voltage (LOV) domain that undergoes a large N-terminal conformational change. The mechanism by which a blue-light driven covalent bond formation leads to a global conformational change remains unclear, which hinders the further development of VVD as an optogenetic tool. We answered this question through a novel computational platform integrating Markov state models, machine learning methods, and newly developed community analysis algorithms. Applying this new integrative approach, we provided a quantitative evaluation of the contribution from the covalent bond to the protein global conformational change, and proposed an atomistic allosteric mechanism leading to the discovery of the unexpected importance of A’α/Aβ and previously overlooked Eα/Fα loops in the conformational change. This approach could be applicable to other allosteric proteins in general to provide interpretable atomistic representations of their otherwise elusive allosteric mechanisms. [ABSTRACT FROM AUTHOR]

Intermetallic compounds SrNi2Si and BaNi2Si were prepared by arc‐melting of stoichiometric mixture of the elements and subsequent annealing in welded niobium ampoules. Both compounds were investigated by X‐ray diffraction on powder as well as single crystal methods. The title compounds both crystallize in the BaNi2Ge structure type (space group Pmmn, Z = 2), a ternary ordered variant of TiCu3: a = 4.0296(9) Å, b = 6.5121(14) Å, c = 5.6839(21) Å, R1 = 0.040 for SrNi2Si and a = 4.0681(9) Å, b = 6.580(4) Å, c = 5.976(5) Å, R1 = 0.031 for BaNi2Si. The structure contains corrugated polyanionic [Ni2Si]2– layers, stacked according to the primitive sequence AA along the c axis. Six‐membered Ni rings adopt a boat conformation, silicon atoms are in the plane with nickel, and the alkaline earth cations sit between the layers. These two compounds extend the family AeNi2X (Ae = Ca, Sr, Ba; X = Si, Ge), where up to date CaNi2Si, SrNi2Ge, and BaNi2Ge are known. LMTO band structure calculations, including DOS, COHP, and ELF were performed to gain more insight into the electronic situation of SrNi2Si and BaNi2Si. [ABSTRACT FROM AUTHOR]

Comprehensive characterization of ligand-binding sites is invaluable to infer molecular functions of hypothetical proteins, trace evolutionary relationships between proteins, engineer enzymes to achieve a desired substrate specificity, and develop drugs with improved selectivity profiles. These research efforts pose significant challenges owing to the fact that similar pockets are commonly observed across different folds, leading to the high degree of promiscuity of ligand-protein interactions at the system-level. On that account, novel algorithms to accurately classify binding sites are needed. Deep learning is attracting a significant attention due to its successful applications in a wide range of disciplines. In this communication, we present DeepDrug3D, a new approach to characterize and classify binding pockets in proteins with deep learning. It employs a state-of-the-art convolutional neural network in which biomolecular structures are represented as voxels assigned interaction energy-based attributes. The current implementation of DeepDrug3D, trained to detect and classify nucleotide- and heme-binding sites, not only achieves a high accuracy of 95%, but also has the ability to generalize to unseen data as demonstrated for steroid-binding proteins and peptidase enzymes. Interestingly, the analysis of strongly discriminative regions of binding pockets reveals that this high classification accuracy arises from learning the patterns of specific molecular interactions, such as hydrogen bonds, aromatic and hydrophobic contacts. DeepDrug3D is available as an open-source program at with the accompanying TOUGH-C1 benchmarking dataset accessible from . [ABSTRACT FROM AUTHOR]

Dengue virus Type 2 (DENV-2) is predominant serotype causing major dengue epidemics. There are a number of studies carried out to find its effective antiviral, however to date, there is still no molecule either from peptide or small molecules released as a drug. The present study aims to identify small molecules inhibitor from National Cancer Institute database through virtual screening. One of the hits, D0713 (IC50 = 62 μM) bearing thioguanine scaffold was derivatised into 21 compounds and evaluated for DENV-2 NS2B/NS3 protease inhibitory activity. Compounds 18 and 21 demonstrated the most potent activity with IC50 of 0.38 μM and 16 μM, respectively. Molecular dynamics and MM/PBSA free energy of binding calculation were conducted to study the interaction mechanism of these compounds with the protease. The free energy of binding of 18 calculated by MM/PBSA is -16.10 kcal/mol compared to the known inhibitor, panduratin A (-11.27 kcal/mol), which corroborates well with the experimental observation. Results from molecular dynamics simulations also showed that both 18 and 21 bind in the active site and stabilised by the formation of hydrogen bonds with Asn174. [ABSTRACT FROM AUTHOR]

The last fifteen years have seen the emergence and overflow into the drug scene of “superpotent” N-benzylated phenethylamines belonging to the “NBOMe” series, accompanied by numerous research articles. Although N-benzyl substitution of 5-methoxytryptamine is known to increase its affinity and potency at 5-HT2 receptors associated with psychedelic activity, N-benzylated tryptamines have been studied much less than their phenethylamine analogs. To further our knowledge of the activity of N-benzyltryptamines, we have synthesized a family of tryptamine derivatives and, for comparison, a few 5-methoxytryptamine analogs with many different substitution patterns on the benzyl moiety, and subjected them to in vitro affinity and functional activity assays vs. the human 5-HT2 receptor subtypes. In the binding (radioligand displacement) studies some of these compounds exhibited only modest selectivity for either 5-HT2A or 5-HT2C receptors suggesting that a few of them, with affinities in the 10–100 nanomolar range for 5-HT2A receptors, might presumably be psychedelic. Unexpectedly, their functional (calcium mobilization) assays reflected very different trends. All of these compounds proved to be 5-HT2C receptor full agonists while most of them showed low efficacy at the 5-HT2A subtype. Furthermore, several showed moderate-to-strong preferences for activation of the 5-HT2C subtype at nanomolar concentrations. Thus, although some N-benzyltryptamines might be abuse-liable, others might represent new leads for the development of therapeutics for weight loss, erectile dysfunction, drug abuse, or schizophrenia. [ABSTRACT FROM AUTHOR]