Bridge Bonds Research Articles

Prediction of a Cyclic Hydrogenated Boron Molecule as a Promising Building Block for Borophane.

We have extensively searched for a cyclic hydrogenated boron molecule that has a three-center two-electron bond at the center. Using first-principles calculations, we discovered a stable molecule of 2:4:6:8:-2H-1,5:1,5-μH-B8H10 and propose its existence. This molecule can be regarded as a building block for sheets of topological hydrogen boride (borophane), which was recently theoretically proposed and experimentally discovered. The electronic structure of the cyclic hydrogenated boron molecule is discussed in comparison with that of cyclic hydrogenated carbon molecules.

LCST/UCST transition of acrylate copolymer with cosolvency behaviors in alcohol aqueous solutions

Though the mechanism of temperature-induced lower critical solution temperature (LCST) in water is clear for the classic homopolymer poly(N-isopropylacrylamide) (PNIPAM), the LCST of other homopolymer or copolymer remains to be understood. In this work, a novel random copolymer poly(2-hydroxyethyl-co-methyl acrylate) (P(HEA-co-MA)) was prepared. The LCST of the copolymer P(HEA-co-MA) can vary from 11 °C to 65 °C by adjusting flexibly the ratio of the two monomers, showing a broad tunable range. The experimental results showed that the balance of hydrogen bond bridge formed by P(HEA-co-MA) in water and the hydrophobic interaction between polymers can cause the LCST transition of P(HEA-co-MA). An interesting observation is that the sharp phase transition (cosolvency) of P(HEA-co-MA) exists when a rather small amount of alcohol or water is added in polymer solutions at constant temperatures. Moreover, it was found that the increase of LCST is correlated with the increase of alcohol concentration in the water-rich regime, but the decrease of upper critical solution temperature (UCST) is related to the increase of water concentration in the alcohol-rich regime. This work shed light on the understanding of cosolvency by studying the solution behavior of copolymer P(HEA-co-MA) in mixed solvents, which can be of interest for the design of stimuli-responsive polymer materials by variation in solvent composition.

Monomer morphology selection rules for an accurate design of bulk heterojunction: An updated theoretical account

Theoretical simulation of film morphology with bulk heterojunction (BHJ) has become a technological breakthrough point for material and performance development in recent years. Stemming from the precision of calculation and the boom of materials, the unified process for predicting the relevant properties of BHJ through monomers needs to be further updated. This study analyzed the sensibilities of environmental changes (monomers, the acceptors of D/A and A/A in morphology) on structures and properties from fullerene to non-fullerene materials. The results showed that it is inaccurate to predict morphology only by optimizing the monomer through employing a unified process. Due to material specificity, excessive environmental sensitivity could lead to prediction errors. In different environments, the properties of C60 with rigid structure vary greatly. The stability of fused ring electron acceptors (FREAs) is determined by the type and number of bridge bonds (single and ethylenic bonds) in main backbones, where a small number and strong conjugation are favorable. As a result, flexible ITIC is insensitive to the environment, which could be performed using a unified process. This may be the main reason for their excellent properties. This work puts forward higher requirements for the accuracy of a theoretical calculation process, and also provides an updated theoretical account for an accurate design of bulk heterojunction.

Reduction of Nitric Oxide to Nitrous Oxide in Flavodiiron Proteins: Catalytic Mechanism and Plausible Intermediates

The flavin dependent nonheme diiron proteins comprise a family of enzymes, which can act as scavengers for both molecular oxygen and nitric oxide. The reduction of nitric oxide to nitrous oxide and water in flavodiiron proteins (FDPs) has been studied both experimentally and computationally, but the reaction mechanism is far from well understood. From experiments, it is known that two NO molecules can bind to the reduced active site, forming an observable diferrous dinitrosyl complex. A main question has been whether nitrous oxide can be formed directly from the diferrous dinitrosyl complex or if further reduction and/or protonation is needed to make this step feasible. Experiments have shown that nitrous oxide can be formed in a deflavinated form of the enzyme, indicating that further reduction is not needed. In the present study, hybrid density functional theory calculations are performed on a cluster model of the Thermotoga maritima FDP active site. We show that nitric oxide can be reduced to nitrous oxide and water using a direct coupling mechanism, i.e., without further additions to the reduced active site. The diferrous dinitrosyl complex can form an unstable N–N bridging hyponitrite intermediate, which can rotate into an N–O bond bridging hyponitrite with a low barrier. From this intermediate, the N–O bond cleavage leading to release of nitrous oxide is energetically feasible. An energy profile for the entire catalytic cycle of such a direct coupling mechanism is presented, and it is shown that the suggested mechanism agrees with data on FDP variants. Finally, an energy profile for the entire process starting with the fully reduced enzyme turning over four NO equivalents is constructed. This energy profile suggests explanations to experimentally observed states, such as the dihydroxyl form of the fully oxidized diferric state, and the difference with respect to returning to the original oxidized state after NO reduction between the flavinated and the deflavinated form of the enzyme.

Uptake of BF Dye from the Aqueous Phase by CaO-g-C3N4 Nanosorbent: Construction, Descriptions, and Recyclability

Removing organic dyes from contaminated wastewater resulting from industrial effluents with a cost-effective approach addresses a major global challenge. The adsorption technique onto carbon-based materials and metal oxide is one of the most effective dye removal procedures. The current work aimed to evaluate the application of calcium oxide-doped carbon nitride nanostructures (CaO-g-C3N4) to eliminate basic fuchsine dyes (BF) from wastewater. CaO-g-C3N4 nanosorbent were obtained via ultrasonication and characterized by scanning electron microscopy, X-ray diffraction, TEM, and BET. The TEM analysis reveals 2D nanosheet-like nanoparticle architectures with a high specific surface area (37.31 m2/g) for the as-fabricated CaO-g-C3N4 nanosorbent. The adsorption results demonstrated that the variation of the dye concentration impacted the elimination of BF by CaO-C3N4 while no effect of pH on the removal of BF was observed. Freundlich isotherm and Pseudo-First-order adsorption kinetics models best fitted BF adsorption onto CaO-g-C3N4. The highest adsorption capacity of CaO-g-C3N4 for BF was determined to be 813 mg. g−1. The adsorption mechanism of BF is related to the π-π stacking bridging and hydrogen bond, as demonstrated by the FTIR study. CaO-g-C3N4 nanostructures may be easily recovered from solution and were effectively employed for BF elimination in at least four continuous cycles. The fabricated CaO-g-C3N4 adsorbent display excellent BF adsorption capacity and can be used as a potential sorbent in wastewater purification.

Identification and Anti-Hyperuricemic Activity of Xanthine Oxidase Inhibitory Peptides from Pacific White Shrimp and Swimming Crab Based on Molecular Docking Screening

The xanthine oxidase (XO) inhibitory peptides from pacific white shrimp or swimming crab were identified by molecular docking, and the anti-hyperuricemic activity of the peptides was confirmed in hyperuricemic cells. In our study, 17 novel XO inhibitory peptides were purified from pacific white shrimp or swimming crab, and Ala-Glu-Ala-Gln-Met-Trp-Arg (AEAQMWR, 891.01 Da, IC50 = 8.85 ± 0.05 mM) exhibited the greatest XO inhibitory activity in vitro. Molecular docking results indicated that attractive charge, salt bridge, and hydrogen bond showed a crucial effect on the interactions of XO inhibitory peptides with the pivotal residues of Arg880, Glu802, and Glu1261. In addition, XO inhibitory peptides alleviated hyperuricemia by inhibiting inflammation and preventing increased uric acid transporter expression levels in hyperuricemia cells. Overall, these results further confirmed that screening of XO inhibitory peptides rapidly via molecular docking was feasible.

Self-compacting micro concrete in structural strengthening: application as a bond bridge

RESUMO O objetivo deste trabalho foi avaliar a eficiência de um microconcreto para reforços estruturais, como ponte de aderência entre concreto velho e concreto novo. Foi avaliada a substituição da areia por um fíler, subproduto de britagem, a partir de um traço de referência. Os ligantes utilizados foram cimento Portland (85%) e sílica ativa (15%). A relação água/ligante e proporção entre cimento e sílica ativa foram obtidas de forma experimental, maximizando-se a utilização do aditivo superplastificante e obtendo-se condições aceitáveis de autoadensabilidade das misturas. Foram avaliadas as propriedades no estado fresco e endurecido, aderência do microconcreto em dois substratos e como ponte de aderência, simulando uma situação de reforço estrutural. Obtiveram-se boas propriedades de autoadensabilidade do MC, com aumento de 26% no espalhamento e 5% no tempo de escoamento do MC com 15% de substituição em relação ao MC de referência. Para 15% de substituição, observou-se aumento de 18% no módulo de elasticidade e redução de quase 9% na absorção total de água. Também se obtiveram bons resultados de aderência em substrato de concreto, demonstrados pela ruptura coesiva observada no ensaio de aderência. Em situação de reparo estrutural, o material mostrou-se satisfatório como ponte de aderência entre concretos.

Recent advances of stimuli-responsive viologen-based nanocomposites

The unique electron-deficient viologen-based compounds are the terminally substituted 4,4′-bipyridine with excellent photoelectric response features to be applied in the preparation of stimuli-responsive materials.

Tetrahomo corona[4]arene-based spirophanes: synthesis, structure, and properties.

In contrast to a plethora of macrocyclic and cage compounds, spirophanes have remained largely unexplored. We report herein the construction, structure and properties of unprecedented tetrahomo corona[4]arene-based ditopic and tritopic macrocycles of spiro structures. Synthesis was conveniently achieved by means of an efficient SNAr reaction from simple and commercially available starting materials. Racemic samples were resolved into enantiopure chiral tetrahomo i-corona[4]arenes, spirophanes and bispirophanes which show interesting chiroptical properties. The acquired electron-deficient macrocyclic compounds were found to adopt unique conformational structures and to form distinct complexes with TTF in the solid state. Our study provides a new opportunity to develop multitopic macrocycles of different topologies which have potential applications in supramolecular chemistry.

Soybean oleosome-based oleogelsviapolymer-bridging based structuring. Mechanical properties at large deformations

Oleosomes have emerged in the last decade as a multipurpose oil-in-water emulsion suitable for engineering new lipids materials. The need to increase alternative and sustainable methods to modulate the rheological properties of emulsions has been the leading research interest in the oleogelation field. Soybean oleosomes are evaluated as building blocks for creating oleogels in combination with sodium alginate or ι-carrageenan as the structuring elements. Polymer bridging provides a route to produce compact soft, malleable gels by exploiting attractive electrostatic interactions between negatively charged polysaccharides and oleosome surfaces. We investigated the viscoelastic properties of concentrated polymer bridged gels by oscillatory rheological measurements. The rheological characteristics are governed predominantly by the type of polysaccharide and by the ratio between polysaccharide and oleosome content. One yielding step at low strains indicates the breaking of polysaccharide bridging bonds and was visible in all samples. A two-step yielding process, where the second step corresponds to the cage-breaking process, was present at polysaccharide/oleosome ratios where optimum bridging occurs for alginate and carrageenan, 0.005 g/g, 0.01 g/g, respectively. Nonetheless, the bumps corresponding to the second yielding point were more prominent in alginate gels than in carrageenan gels due to the greater bridging ability of alginate. Identifying these rheological hallmarks could provide new ideas towards the improved design of plant-based fatty food products,e.g., cream cheeses and vegan sausages surrogates.

Insights into Omicron's Low Fusogenicity through In Silico Molecular Studies on Spike-Furin Interactions.

The Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant and its subvariants have a unique set of mutations. Two of those mutations (N679 K and P681 H) reside close to the S1 /S2 furin cleavage site (FCS; 685-686). When these mutations reside together, they exert less-efficient membrane fusion than wild type and most other variants of concern such as the Delta variant. Here, we in silico targeted these mutations to find out which of the amino acids and interactions change plays the key role in fusion. To comprehend the epistatic effect of N679 K and P681 H mutations on the spike protein, we in silico constructed three types of spike protein sequences by changing the respective amino acids on 679 and 681 positions (P681 H, N679 K, K679 N-H681 P variants). We then analyzed the binding affinity of furin and spike (Furin-Wild, Furin-Omicron, Furin-P681 H, Furin-N679 K, and Furin-K679 N/H681 P) complexes. Omicron and P681 H variants showed a similar higher binding energy trend compared to the wild type and N679 K. The variation in hydrogen, hydrophobic, and salt bridge bonds between spike protein and furin provided an explanation for the observed low fusogenicity of Omicron. The fate of the epistasis in furin binding and possible cleavage depends on the efficient interaction between FCS in spike and furin catalytic triad, and in addition, the loss of the hydrogen bond between Arg 681 (spike) and Asn 295 (furin) along with inhibitor-like ineffective higher affinity plays an important role in the enzymatic activity.

States of silicon nanoclusters containing carbon impurities

The structural and electronic states of defective complexes in the Si29 cluster with the participation of carbon and hydrogen atoms were determined by the method of non-conventional strong binding (MNSB) in combination with the method of molecular dynamics. It is shown that carbon atoms in silicon clusters form a bridge bond with two silicon atoms and localized in a hexagonal position at the center of the cell, forming a defect of the Si29 : Ci type. The introduction of hydrogen into a silicon cluster results in the formation of a defective Ci-H-Si complex and a decrease of binding energy of the Si29 : Ci defect. Based on the calculations, it was found that presence of leads to carbon gives shallow levels in the band gap of nano-silicon, and the defective carbon-hydrogen complex in a hydrogenated cluster, depending on the charge state of the defective complex. Moreover this exhibits both deep and shallow levels. Keywords: MD and MNSB methods, silicon nano-clusters, hydrogenated cluster, structural defects, ab initio methods, carbon and hydrogen atoms, spatial structure, shallow and deep levels.

Состояния кремниевых нано-кластеров, содержащих примеси углерода

Abstract The structural and electronic states of defective complexes in the Si29 cluster with the participation of carbon and hydrogen atoms were determined by the method of non-conventional strong binding (MNSB) in combination with the method of molecular dynamics. It is shown that carbon atoms in silicon clusters form a bridge bond with two silicon atoms and localized in a hexagonal position at the center of the cell, forming a defect of the Si29:Ci type. The introduction of hydrogen into a silicon cluster results in the formation of a defective Ci-H-Si complex and a decrease of binding energy of the Si29:Ci defect. Based on the calculations, it was found that presence of leads to carbon gives shallow levels in the band gap of nano-silicon, and the defective carbon-hydrogen complex in a hydrogenated cluster, depending on the charge state of the defective complex. Moreover this exhibits both deep and shallow levels.

Atomically resolved study of initial stages of hydrogen etching and adsorption on GaAs(110)

The initial stages of hydrogen adsorption on GaAs(110) surfaces at room temperature are investigated by atomically resolved scanning tunneling microscopy and spectroscopy. Two effects are found to occur simultaneously: On the one hand a surface phase separation occurs, creating $1\ifmmode\times\else\texttimes\fi{}1$ reconstructed fully hydrogen-covered areas while leaving the surface in between completely hydrogen free. In the fully hydrogen-covered areas, hydrogen bonds equally to As- and Ga-derived dangling bonds, unbuckling and passivating the surface. On the other hand, hydrogen-induced point defects are formed with increasing density. The dominating defects consist of As vacancy--hydrogen defect complexes, formed by preferential hydrogen etching of As. Using a defect-molecule model the Ga-H bridge bonds and double-occupied Ga dangling bonds are suggested to be at the origin of the observed surface Fermi level pinning 0.25 to 0.3 eV above the valence band edge, identical within error margins for $p$- and $n$-doped GaAs(110).

Photoinduced Dehydrogenative Borylation via Dihydrogen Bond Bridged Electron Donor and Acceptor Complexes.

Air-stable amine- and phosphine-boranes are discovered as donors to integrate with pyridinium acceptor for generating photoactive electron-donor-acceptor (EDA) complexes. Experimental results and DFT calculations suggest a dihydrogen bond bridging the donor and acceptor. Irradiating the EDA complex enables an intra-complex single electron transfer to give a boron-centered radical for dehydrogenative borylation with no need of external photosensitizer and radical initiator. The deprotonation of Wheland-like radical intermediate rather than its generation is believed to determine the good ortho-selectivity based on DFT calculations. A variety of α-borylated pyridine derivatives have been readily synthesized with good functional group tolerance.

Theoretical Investigation of Geometries and Bonding of Indium Hydrides in the In2Hx and In3Hy (x = 0-4,6; y = 0-5) Series.

Boron hydrides have been an object of intensive theoretical and experimental investigation for many decades due to their unusual and somewhat unique bonding patterns. Despite boron being a neighboring element to carbon, boron hydrides almost always form non-classical structures with multi-center bonds. However, we expect indium to form its interesting molecules with non-classical patterns, though such molecules still need to be extensively studied theoretically. In this work, we investigated indium hydrides of In2Hx (x = 0-4,6) and In3Hy (y = 0-5) series via DFT and ab initio quantum chemistry methods, performing a global minimum search, chemical bonding analysis, and studies of their thermodynamical stability. We found that the bonding pattern of indium hydrides differs from the classical structures composed of 1c-2e lone pairs and 2c-2e bonds and the bonding pattern of earlier investigated boron hydrides of the BnHn+2 series. The studied stoichiometries are characterized by multi-center bonds, aromaticity, and the tendency for indium to preserve the 1c-2e lone pair.

Metallocene-based covalent metal-organic porous polymers and their derivatives

Metal-organic porous materials (MOPMs), represented by the famous metal–organic frameworks (MOFs), have attracted extensive attention in recent years. While MOFs are unstable in nature, they are constructed by coordination bond with low bond energies (<30 kJ/mol). This work proposed a series of metallocene-based covalent metal–organic porous polymers (CMOPPs). The obtained materials show the incredible ability with resistance to air, water, as well as even to high concentration of HCl or NaOH. Additionally, the metallocene-based CMOPPs possess a specific surface area (SSA) value as high as 716.3 m2g−1, abundant micropores, high heterogeneous catalysis and redox activity. The pyrolyzed derivatives at high temperatures consist of Fe3C/C and Fe/C nanostructures, and possess characteristic ferromagnetism. Generally, constructing of stable MOPMs is realized by strong covalent bond bridging. This work opens a new world of MOPMs which have a great potential to apply in catalysis, electrochemistry, adsorption, separation, gas storage, and so on.

Variation of molecular structures affecting tar yield: A comprehensive analysis on coal ranks and depositional environments

Coal with a tar yield ≥ 7 %, which is measured in the Gray-King assay, is called tar-rich coal in China. However, the comprehensive impact of coal ranks and depositional environments on tar yield is still unclear. Here, the coal petrology, molecular structure, and depositional environment of the samples were thoroughly investigated to clarify the influence of the coal rank and depositional environment on the tar-rich coal. The difference in the tar yield is attributed to the molecular structure. Concerning Fourier transform infrared (FTIR) spectroscopy, the high tar production resulted from the existence of relatively long aliphatic side chains and high aliphatic hydrogen content. For the 13C nuclear magnetic resonance analysis, the structure of the aliphatic carbon also played a crucial role in tar formation. Among these, the various unstable structural parameters (falH/fas, (fas + fap)/fa', fas/fa', falH/fal*) and weak bonds could improve the tar yield. Furthermore, the molecular structures were also controlled by the coal rank. More specifically, the CH2/CH3 in FTIR and the falH, falH/fa*, fas/fa’ in 13C NMR had similar patterns with coal rank, which was close to the pattern between the coal rank and the tar yield. This effect also indicated that the tar yield was mainly influenced by bridge bonds, aliphatic side chains, and branched aromatic carbon. Between similar coal ranks, the molecular structure differences originated from the depositional environment. For the coal facies, the tissue preservation index (TPI) and vegetation index (VI) were negatively correlated with CH2/CH3, Hal/H, and “A factor”. In contrast, they were positively correlated with the oxidation degree (Io2). The gelification index (GI) was also positively correlated with CH2/CH3 and Hal/H. Consequently, the coal-forming environment with a relatively high degree of decomposition, low woody tissue content, and high gelification can form key molecular structures easier, which is beneficial for the tar yield.

Effect of Nature of Substituents on Coordination Properties of Mono- and Disubstituted Derivatives of Boron Cluster Anions [BnHn]2– (n = 10, 12) and Carboranes with exo-Polyhedral B–X Bonds (X = N, O, S, Hal)

This review systematizes data on the coordination ability of mono- and disubstituted derivatives of boron cluster anions and carboranes in complexation with transition metals. Boron clusters anions [BnHn]2–, monocarborane anions [CBnHn–1]–, and dicarboranes [C2BnHn–2] (with non-functionalized carbon atoms) (n = 10, 12) containing the B–X exo-polyhedral bonds (X = N, O, S, Hal) are discussed. Synthesis and structural features of complexes known to date are described. The effect of complexing metal and substituent attached to the boron cage on the composition and structures of the final complexes is analyzed. It has been established that substituted derivatives of boron cluster anions and carboranes can act as both ligands and counterions. A complexing agent can coordinate substituted derivatives of the boron cluster anions due to three-center two-electron 3c2e MHB bonds, by the substituent functional groups, or a mixed type of coordination can be realized, through the BH groups of the boron cage and the substituent. As for B-substituted carboranes, complexes with coordinated substituents or salts with non-coordinated carborane derivatives have been isolated; compounds with MHB bonding are not characteristic of carboranes.

Dramatic Size‐dependence of Rhn+ Clusters in Reacting with Small Hydrocarbons: Rh3+ Cluster Catalysis for Dehydrogenation

AbstractWe report a joint experimental and theoretical study of the gas‐phase reactions between rhodium clusters Rhn+ (n=1–24) and small hydrocarbons. It is found that most Rhn+ clusters react with CH4 to form absorption products Rhn(CH4)1,2+ but Rh3+ reacts to form carbide indicative of complete dehydrogenation; Rh2+ reacts with CH4 to form partial dehydrogenation products Rh2CH2+ and Rh2C2H6+. The distinctive reactivity of Rh3+ is also found for the reactions with C2H2, C2H4 and C2H6, where the complete dehydrogenation product Rh3C2+ is also formed. Analysis of reaction kinetics demonstrates that the cooperation of three Rh atoms plays a key role in the dehydrogenation reaction. Notably, Rh3+ bears a large HOMO‐LUMO gap and reasonable stablity, and the roughly equal contribution of electrostatic and orbital interactions provide advantages to form two symmetric Rh−H−C hydrogen bridge bonds which promote the synergic cluster catalysis for hydrogen atom transfer and C−H bond dissociation. The efficient dehydrogenation mediated by an Rh3+ cluster opens a window to design new catalysts for C−H activation.