Changes in structure and dynamics elicited by agonist ligand binding at the extracellular side of G protein coupled receptors (GPCRs) must be relayed to the cytoplasmic G protein binding side of the ...receptors. To decipher the role of water-mediated hydrogen-bond networks in this relay mechanism, we have developed graph-based algorithms and analysis methodologies applicable to datasets of static structures of distinct GPCRs. For a reference dataset of static structures of bovine rhodopsin solved at the same resolution, we show that graph analyses capture the internal protein-water hydrogen-bond network. The extended analyses of static structures of rhodopsins and opioid receptors suggest a relay mechanism whereby inactive receptors have in place much of the internal core hydrogen-bond network required for long-distance relay of structural change, with extensive local H-bond clusters observed in structures solved at high resolution and with internal water molecules.
The intramolecular “inverse” frustrated Lewis pairs (FLPs) of general formula 1‐BR2‐2‐(Me2N)2C=N‐C6H4 (3–6) BR2=BMes2 (3), BC12H8, (4), BBN (5), BBNO (6) were synthesized and structurally ...characterized by multinuclear NMR spectroscopy and X‐ray analysis. These novel types of pre‐organized FLPs, featuring strongly basic guanidino units rigidly linked to weakly Lewis acidic boryl moieties via an ortho‐phenylene linker, are capable of activating H−H, C−H, N−H, O−H, Si−H, B−H and C=O bonds. 4 and 5 deprotonated terminal alkynes and acetylene to form the zwitterionic borates 1‐(RC≡C‐BR2)‐2‐(Me2N)2C=NH‐C6H4 (R=Ph, H) and reacted with ammonia, BnNH2 and pyrrolidine, to generate the FLP adducts 1‐(R2HN→BR2)‐2‐(Me2N)2C=NH‐C6H4, where the N‐H functionality is activated by intramolecular H‐bond interactions. In addition, 5 was found to rapidly add across the double bond of H2CO, PhCHO and PhNCO to form cyclic zwitterionic guanidinium borates in excellent yields. Likewise, 5 is capable of cleaving H2, HBPin and PhSiH3 to form various amino boranes. Collectively, the results demonstrate that these new types of intramolecular FLPs featuring weakly Lewis acidic boryl and strongly basic guanidino moieties are as potent as conventional intramolecular FLPs with strongly Lewis acidic units in activating small molecules.
Novel intramolecular “inverse” frustrated Lewis pairs have been prepared and their ability to activate small molecules investigated.
The palladium‐catalyzed coupling of amines with aryl halides or aryl alcohol derivatives, commonly dubbed Buchwald–Hartwig amination, has matured from a synthetic laboratory procedure to a technique ...that is widely used in natural product synthesis as well as in other fields of academic interest. Furthermore, due to the versatility and reliability of this reaction, researchers in industrial environments have included this methodology in their toolbox as a standard procedure for the synthesis of amine derivatives. Therefore, it is not surprising that first industrial processes up to ton‐scale have been performed using this cross‐coupling reaction. The authors who are involved in the application of this reaction to industrial processes on this scale give an overview of the recent developments in this field of chemistry, also including fundamental principles, with a special focus on the industrial approach and issues to be considered relevant in scaling‐up this transition metal‐catalyzed chemistry. This review differs from the already existing excellent academic reviews by focusing on the practical problems arising during implementing the methodology in an industrial environment as well as giving practical hints to this end.
In this work, we select four types of substitute cations, Ti4+, Al3+, Mg2+ and Zn2+, to compare their influence on LiNi0.8Co0.1Mn0.1O2. After modification, the average lengths of NiO bonds are ...elongated with the turn of the Ti, Al, Mg, pristine and Zn-substituted, namely the bond energies are diminished with this sequence, according to their roughly inverse square relation. This tendency is also obeyed by oxygen defects, which induces the NiLi exchanging and surface decomposition, and then exert the effect on electrochemical behavior of Ni-rich cathodes. Among the investigated samples, the Ti-modified sample, which possesses the highest NiO bond energy, presents the best cyclic stability and rate capability, retaining 93.8% in the 200th cycle and 155.1 mAh g−1 under 5C, which is ∼12% higher than the pristine sample. Our approaches illustrate the importance of NiO network and provide a novel thought to further improve these promising cathodes.
We explore whether government ownership affects the cost of debt using a sample of fully and partially privatized companies. On average across firms, a one-percentage-point decrease in government ...ownership is associated with an increase in the credit spread, used as a proxy for the cost of debt, by three-quarters of a basis point. However, fully privatized companies exhibit lower credit spreads than partially privatized firms, indicating the cost of a lengthy privatization process. Empirical evidence suggests that these findings result from decreasing government guarantees, firm performance improvements, ownership uncertainty, and bondholder-shareholder conflicts.
A rigorous definition of intrinsic bond strength based on the partitioning of a molecule into real‐space fragments is presented. Using the domains provided by the quantum theory of atoms‐in‐molecules ...(QTAIM) together with the interacting quantum atoms (IQA) energetic decomposition, we show how an in situ bond strength, matching all the requirements of an intrinsic bond energy, can be defined between each pair of fragments. Total atomization or fragmentation energies are shown to be equal to the sum of these in situ bond energies (ISBEs) if the energies of the fragments are measured with respect to their in‐the‐molecule state. These energies usually lie above the ground state of the isolated fragments by quantities identified with the standard fragment relaxation or deformation energies, which are also provided by the protocol. Deformation energies bridge dissociation energies with ISBEs, and can be dissected by using well‐known tools of real‐space theories of chemical bonding. Similarly, ISBEs can be partitioned into ionic and covalent contributions, and this feature adds to the chemical appeal of the procedure. All the energetic quantities examined are observable and amenable, in principle, to experimental determination. Several systems, exemplifying the role of each energetic term presented herein, are used to show the power of the approach.
Inner strength. A rigorous definition of intrinsic bond strength based on the partitioning of a molecule into real‐space fragments, amenable to experimental determination, is presented (see figure).
•Bi2S3@NC nanospheres were fabricated via a simple in-situ polymerization coating and sulfidation-in-nanosphere strategy.•The strong Bi-C covalent bond can enhance the electrochemical kinetics, and ...maintain the structural stability during cycling process.•The Bi2S3@NC nanospheres demonstrated long-life cycle performance and superior rate capability.
Bi2S3 is investigated as promising anode materials for lithium-ion batteries (LIBs) due to its high theoretical capacity. However, the poor rate performance and fast capacity decay induced by the huge volume change during the lithiation/delithiation process, which seriously hinder the practical application in LIBs. Herein, Bi2S3@N-doped carbon (Bi2S3@NC) nanospheres with strong Bi-C covalent bond are constructed and application in LIBs, which exhibit outstanding rate performance and excellent long-term cycling stability. The high conductivity of N-doped carbon layer and strong Bi-C covalent bond can significantly enhance the electrochemical kinetics, as well as maintain the structural stability during cycling process. Benefiting from these advantages, the Bi2S3@NC nanospheres provide excellent rate performance (412 mA h g−1 at 5.0 A g−1), and outstanding long-term cycling stability (a high reversible capacity of 510 mA h g−1 is achieved after 1000 cycles at 1.0 A g−1). Furthermore, the assembled Bi2S3@NC//LiFePO4@C full cell delivers high capacity of 341 mA h g−1 at 0.2 A g−1, and outstanding cycle performance (206 mA h g−1 after 200 cycles), demonstrating great potential for practical application in high performance LIBs.
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•The bond behavior between RAC and deformed steel bars after FTCs was investigated.•The bond stress distribution for RAC after FTCs was discussed.•A bond stress-slip model for RAC after FTCs was ...proposed and verified.
In cold regions, freeze-thaw damage can deteriorate the structural performance of reinforced concrete structures. This paper investigated the bond behavior between recycled aggregate concrete (RAC) and deformed steel bars after freeze-thaw cycles (FTCs). Sixty-three specimens for pull-out tests were prepared with three different recycled coarse aggregate replacement ratios (0%, 30% and 50%) and seven different FTCs (0, 50, 100, 150, 200, 250 and 300). Additionally, nine made-to-measure pull-out specimens with built-in strain gauges were tested to tentatively study the bond stress distribution along the interface between the steel bars and the RAC after the FTCs. The results show that as the FTCs increased, the bond strength decreased and became increasingly significant as the RCA replacement ratios increased, while the bond slip was relatively stable as the FTCs increased and exhibited a similar increasing trend for all the mixtures at the higher number of FTCs. The bond stress focused on local areas and formed local stress concentrations when the pull-out force was close to the peak value. Finally, a two-segment bond stress-slip model to describe the bond behavior between RAC with RCA replacement ratios less than 50% and deformed steel bars after FTCs was proposed, showing a good correlation with the test results.
Proximal noncovalent forces are commonplace in natural systems and understanding the consequences of their juxtaposition is critical. This paper experimentally quantifies for the first time a ...Hydrogen Bond‐Enhanced Halogen Bond (HBeXB) without the complexities of protein structure or preorganization. An HBeXB is a halogen bond that has been strengthened when the halogen donor simultaneously accepts a hydrogen bond. Our theoretical studies suggest that electron‐rich halogen bond donors are strengthened most by an adjacent hydrogen bond. Furthermore, stronger hydrogen bond donors enhance the halogen bond the most. X‐ray crystal structures of halide complexes (X−=Br−, I−) reveal that HBeXBs produce shorter halogen bonds than non‐hydrogen bond analogues. 19F NMR titrations with chloride highlight that the HBeXB analogue exhibits stronger binding. Together, these results form the foundation for future studies concerning hydrogen bonds and halogen bonds in close proximity.
The amount that a hydrogen bond to an iodine donor strengthens the resulting halogen bond is quantified for the first time. The results point out that the halogen bond is most influenced by stronger hydrogen‐bond donors and more electron‐rich halogens.
Polyoxometalates (POMs) have conducive properties such as controlled Brønsted and Lewis acidity, high thermal stability, nontoxic nature, tunable solubility, and less corrosiveness. POMs have been ...extensively applied in catalytic organic reactions and have an exciting prospect for industrial applications. This review summarized recent progress in the application of POMs as acid catalysts for various organic reactions including CC bond formation, CN bond formation, CO bond formation, heterocyclic synthesis reactions, cyanosilylation and hydrolysis reactions. Various POMs catalysts including heteropoly acids (HPAs) and cationic functionalized HPAs with Brønsted acidity, HPAs supported on non-precious metal support with Brønsted acidity (or both Brønsted and Lewis acidity), transition metal substituted POMs with Lewis acidity were applied in above reactions. This review attempts to provide up-to-date information about POMs acid-catalyzed organic reactions and propose future prospects.
This review summarized recent progress in the POMs acid-catalyzed organic reactions including the CC bond formation, CN bond formation, CO bond formation, heterocyclic synthesis, cyanosilylation and hydrolysis reactions. Display omitted
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