Bond Of Substrate Research Articles

Visible-Light-Induced α-Arylation of Ketones with (Hetero)aryl Halides.

An enamine-mediated photoredox catalyzed C(sp2)-C(sp3) cross-coupling of dual radical precursors for the arylation of ketone is presented in this Letter. These reactions led to the formation of an enamine by using pyrrolidine to functionalize the C(sp3)-H bond in ketone substrates, which could be smoothly converted to α-arylated ketones with inert aryl bromides and even aryl chlorides in moderate to good yields under mild reaction conditions. The photocatalytically induced C(sp2)-C(sp3) cross-coupling between unactivated noncyclic ketones and aryl halides was achieved, and multiple carbonyl α-arylated backbones containing various natural products and drug molecules were successfully constructed.

Ligand Noninnocence in β-Diketiminate and β-Diketimine Copper Complexes.

Metal-ligand cooperative systems have a long precedent in catalysis, with the classification depending on the site of substrate bond cleavage and formation and on redox state changes. Recently, our group reported the participation of a β-diketiminate ligand in chemical bonding to heterocumulenes such as CO2 and CS2 by tricopper complexes, leading to cooperative catalysis. Herein, we report the reactivity of these copper clusters, [Cu3EL]- (E = S, Se; L = tris(β-diketiminate) cyclophane ligand), toward other electrophiles, viz. alkyl halides and Brønsted acids. We identified a family of ligand-functionalized complexes, Cu3EL (R) (R = primary alkyls), and a series of disubstituted products, Cu3EL (R)2, through single-crystal X-ray diffraction, mass spectrometry, and infrared and UV-visible spectroscopy. As part of mechanistic studies on these alkylation reactions, we evaluated the acid-base reactivity of these complexes and the influence of the backbone substitution on the reduction potential. Implications of these findings for ligand noninnocence and the relevance of the metal core as a cofactor for the ligand's reactivity are discussed.

Site-selective peptide bond hydrolysis and ligation in water by short peptide-based assemblies

The evolution of complex chemical inventory from Darwin's nutrient-rich warm pond necessitated rudimentary yet efficient catalytic folds. Short peptides and their self-organized microstructures, ranging from spherical colloids to amyloidogenic aggregates might have played a crucial role in the emergence of contemporary catalytic entities. However, the question of how short peptide fragments had functions akin to contemporary complex enzymes to catalyze cleavage and formation of highly stable peptide bonds that constitute the backbone of all proteins remains an unresolved yet fundamentally important question in terms of the origins of enzymes. We report short-peptide-based spherical assemblies that demonstrated residue-specific cleavage and formation of peptide bonds of diverse peptide-based substrates under aqueous environment. Despite the short sequence length, the assemblies utilized the synergistic collaboration of four residues which included the catalytic triad of extant serine proteases with a nonproteinogenic amino acid (quinone moiety), to facilitate proteolysis, ligation, and a three-step (hydrolysis-ligation-hydrolysis) cascade. Such short-peptide-based catalytic assemblies argue for their candidacy as the earliest protein folds and open up avenues for biotechnological applications.

Bonded Interface Enabled Durable Solid‐state Lithium Metal Batteries with Ultra‐low Interfacial Resistance of 0.25 Ω cm2

AbstractThe solid‐state batteries (SSBs) with Li anode present one of the most promising energy storage systems due to their enhanced energy density and safety. However, interfacial problems between Li anode and solid‐state electrolyte hinder the advancement of SSBs. Among them, insufficient solid‐solid interfacial contact is the main issue, which causes large resistance and hinders Li+ diffusion, leading to current distribution unevenness and lithium dendrites growth. To meet these challenges, a silver/carbon interlayer composed of ultrafine Ag nanoparticles (≈5 nm) grown on COOH‐CNTs (nano‐Ag@COOH‐CNTs) is constructed. In which, nano‐Ag is designed to guide homogeneous Li deposition, while CNTs substrate bonds with Li6.5La3Zr1.5Ta0.5O12 (LLZTO) electrolyte by reactions between ─COOH groups and LLZTO alkaline surface, thus transforming loose physical solid‐solid contact to chemical bonding contact. In addition, nano‐Ag is immobilized by CNTs, avoiding the migration of Li+ implanted nano‐Ag during cycling. Therefore, nano‐Ag@COOH‐CNTs interlayer can boost Li+ transport at LLZTO/Li interface and inhibit Li dendrites, achieving an ultra‐low interfacial resistance of 0.25 Ω cm2, a high critical current density of 1.7 mA cm−2 and a long cycling over 2155 h at 0.5 mA cm−2. The modified SSBs with LiNi0.83Co0.12Mn0.05O2 cathode cycles stably over 500 cycles. Moreover, high‐loading SSBs operate stably for 85 cycles.

Hypervalent Iodine Mediated Synthesis of 2‐Aminobenzazoles and 2‐Aminobenzothiazoles

AbstractThe hypervalent iodine mediated, silica gel promoted synthesis of 2‐aminobenzazoles and 2‐aminobenzothiazole derivatives under metal‐free mild conditions within short time (30 min) has been developed. Under this process, PhI(COOCF3)2 (PIFA) or PhI(COOCH3)2 (PIDA) acts as an oxidant and radical initiator direct activated the ortho‐C−H bond of substrate, silica gel as weakly lewis acid effectively increased the reactivity of the reaction system. This method is compatible with various of arylurea and arylthiourea substrates, which is green, efficient, simple to operate and suitable for practical application.

Construction Methods and Lessons Learned for a Non-Proprietary Ultra-High Performance Concrete Overlay

The work presented in this paper includes the construction methods and lessons learned from the placement of a non-proprietary ultra-high performance concrete (UHPC) overlay through the rehabilitation of a concrete bridge deck located in Socorro, New Mexico, USA. The selected bridge is a multi-cell, box girder bridge with four spans and a total length of 91.4 m and a width of 16.5 m with two traffic lanes. Rehabilitation of the bridge involved removing the top surface of the existing deck (deteriorated concrete), installing a high-performance deck (HPD) leveling course, and placing a 25 mm UHPC overlay. Sensors were installed in the bridge superstructure (multi-cell box girders, HPD, and overlay) for long-term monitoring. Overlay assessment included physical testing to evaluate the condition of the overlay–substrate bond by chain dragging and direct tension pull-off testing. Conclusions and lessons learned from this investigation serve as a fundamental list of best practices and recommendations for field construction of a non-proprietary UHPC overlay. Recommendations for preparatory tasks including material selection, substrate surface preparation, placement preparation, handling of materials, and UHPC mixing are provided. The recommendations also list best practices concerning the placement of the overlay, curing procedures, and quality assurance testing. Lastly, suggestions are presented for contracts pertaining to UHPC overlay projects.

Terminal C(sp3)-H borylation through intermolecular radical sampling.

Hydrogen atom transfer (HAT) processes can overcome the strong bond dissociation energies (BDEs) of inert C(sp3)-H bonds and thereby convert feedstock alkanes into value-added fine chemicals. Nevertheless, the high reactivity of HAT reagents, coupled with the small differences among various C(sp3)-H bond strengths, renders site-selective transformations of straight-chain alkanes a great challenge. Here, we present a photocatalytic intermolecular radical sampling process for the iron-catalyzed borylation of terminal C(sp3)-H bonds in substrates with small steric hindrance, including unbranched alkanes. Mechanistic investigations have revealed that the reaction proceeds through a reversible HAT process, followed by a selective borylation of carbon radicals. A boron-sulfoxide complex may contribute to the high terminal regioselectivity observed.

Synergy of oxygen vacancy and Mn-substitution on SrTiO3 perovskites supported copper nanocatalysts for enhanced cyclohexylbenzene oxidation

Aiming at the main challenge of poor atomic economy for selective oxidation of hydrocarbons, synergistic catalysis on heterogenous catalysts has been focused on precisely regulating oxidation of specific chemical bonds in organic substrates. Here, a series of copper nanocatalysts loaded on Mn-substituted SrTiO3 perovskite-type oxides with varying Mn/Ti ratios for cyclohexylbenzene (CHB) oxidation to form cyclohexylbenzene-1-hydroperoxide (CHBHP) were successfully synthesized by coprecipitation method assisted by a micro-liquid-film reactor. It was found that the introduction of manganese created numerous oxygen vacancies in nanocatalysts, promoting the activation of oxygen molecules. Moreover, both copper and manganese ions enhanced the activated adsorption of CHB substrate. In particular, as-constructed Cu-based nanocatalyst with a substitution of 15% Mn into Ti sites showed superior catalytic oxidation efficiency with a ∼30% yield of CHBHP product, which is at the highest level compared with previously reported heterogenous catalysts, mainly attributable to the favorable synergy between copper, manganese, and oxygen vacancies. This work sheds light on the importance of multi-active site synergistic catalysis in advanced alkane oxidation processes.

Hibiscus sabdariffa L. Flower Distilled Water Extract Antibacterial Activity towards Streptococcus mutans: An in vitro Study

Dental and oral health is an essential factor that must be considered because it affects general body health. Streptococcus mutans is known to be a cause of dental plaque formation. Dental plaque is a biofilm formed by microorganisms from solid substrate bonds exopolymer matrix. Fixed orthodontic treatment in its use impacts changes in the environment and composition of the oral flora, as well as increases the amount of plaque accumulation that causes damage to hard tissue and periodontal tissue. The aim of this study is to investigate the minimum concentration of compounds in Hibiscus Sabdariffa L. extract in inhibiting metabolic activity and killing S. mutans in vitro. Methods: This study was an in vitro, the experimental study with post-test only control group design. First, H. Sabdariffa L. flower extraction was carried out with the help of distilled water, and then serial dilution was carried out to obtain various concentrations of H. Sabdariffa L. flower extract. Several S. mutans cultures were then exposed to various concentrations of H. Sabdariffa L. flower, and then a colony count was performed in each culture to identify Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC). It was found that S. mutans had 0% growth at a concentration between 25% and 100%, and S. mutans had a growth of 7.1% / 92.9% growth inhibition of S. mutans at a concentration of 12.5%. MBC of roselle flower extract against S. mutans is 25% and MIC of roselle flower extract against S. mutans is 12.5%.

Electroreductive Ring-Opening Carboxylation of 1,3-Oxazolidin-2-ones with CO2 for Accessing β-Amino Acids.

Electrocarboxylation of the C(sp3)-O bond in 1,3-oxazolidin-2-ones with CO2 to achieve β-amino acids is developed. The C-O bond in substrates can be selectively cleaved via the single electron transfer on the surface of a cathode or through a CO2• - intermediate under additive-free conditions. A great diversity of β-amino acids can be obtained in a moderate to excellent yield and readily converted to various biologically active compounds.

Anderson-type polyoxometalate-based metal-organic framework as an efficient heterogeneous catalyst for selective oxidation of benzylic C-H bonds.

Oxidative transformation of benzylic C-H bonds into functional carbonyl groups under mild conditions represents an efficient method for the synthesis of aromatic carboxylic acids and ketones. Here we report a high-efficiency catalyst system constructed from an Anderson-type polyoxometalate-based metal-Organic framework (POMOF-1) and N-hydroxyphthalimide (NHPI) for selective oxidation of methylarenes and alkylarenes under 1 atm O2 atmosphere. POMOF-1 exerted a synergistic effect originating from the well-aligned Anderson {CrMo6} clusters and Cu centers within the framework, and this entailed good cooperation with NHPI to catalyze the selective oxidation. Accordingly, the reactions exhibit good tolerance and chemical selectivity for a wide range of substrates bearing diverse substituent groups, and the corresponding carboxylic acids and ketones were harvested in good yields under mild conditions. Mechanism study reveals that POMOF-1 worked synergistically with NPHI to activate the benzylic C-H bonds of substrates, which are sequentially oxidized by oxygen and HOO˙ to give rise to the products. This work may pave a way to design high-efficiency catalysts by integration of polyoxometalate-based materials with NPHI for challenging C-H activation.

Investigation of laser wire bonding for the fabrication of tensegrity structures

Tensegrity structures are structures in which elements stabilize each other by bearing compressive or tensile loads. They have a high potential for lightweight design. As structures with tensile loads, wires can be used that are connected to other structures using a laser bonding process. Investigations of bonding a mild steel wire with a diameter of 1 mm onto a flat substrate have been conducted using a coaxial deposition welding head. The influence of the parameters focus position, laser power, wire feed rate and bonding processing time has been investigated regarding the bonding quality. A process window for a stable process and a sufficient bond of wire and substrate was determined. The laser intensity and stickout length have a significant influence on the bonding. High intensities and stickout lengths lead to wire burn back and no bond with the substrate while wire backup occurred at low intensities and stickout lengths.

A frontier-orbital view of the initial steps of lytic polysaccharide monooxygenase reactions.

Lytic polysaccharide monooxygenases (LPMOs) are copper enzymes that oxidatively cleave the strong C-H bonds in recalcitrant polysaccharide substrates, thereby playing a crucial role in biomass degradation. Recently, LPMOs have also been shown to be important for several pathogens. It is well established that the Cu(II) resting state of LPMOs is inactive, and the electronic structure of the active site needs to be altered to transform the enzyme into an active form. Whether this transformation occurs due to substrate binding or due to a unique priming reduction has remained speculative. Starting from four different crystal structures of the LPMO LsAA9A with well-defined oxidation states, we use a frontier molecular orbital approach to elucidate the initial steps of the LPMO reaction. We give an explanation for the requirement of the unique priming reduction and analyse electronic structure changes upon substrate binding. We further investigate how the presence of the substrate could facilitate an electron transfer from the copper active site to an H2O2 co-substrate. Our findings could help to control experimental LPMO reactions.

A silylboronate-mediated strategy for cross-coupling of alkyl fluorides with aryl alkanes: mechanistic insights and scope expansion.

The construction of C(sp3)-C(sp3) bonds is pivotal in organic synthesis; however, traditional methods involving alkyl halides are often limited by substrate tolerance and bond dissociation energies, particularly with alkyl fluorides. Herein, we report a silylboronate-mediated cross-coupling strategy that circumvents these challenges, enabling the efficient formation of C(sp3)-C(sp3) bonds between alkyl fluorides and aryl alkanes under mild conditions. Various alkyl fluorides have also been effectively utilized, demonstrating the versatility and broad applicability of this approach. The use of diglyme is critical for this transformation which encapsulates potassium cations and enhances the reaction efficiency. Conventional alkyl halides, including chlorides, bromides, and iodides, are also suitable for this transformation. Density functional theory (DFT) calculations were conducted on the silylboronate-mediated coupling reactions for the first time. Interestingly, while experimental results suggest a radical mechanism, DFT calculations indicate a preference for an ionic pathway.

Addition of alcohols to 4-methylene-1,3-dioxolanes

The addition of alcohols to 2-methylene-1,4-dioxaspiro[4.5]decane under the conditions of CF3CO2H catalysis occurs with the selective formation of the corresponding alkoxy derivatives. The conditions that ensure the preparative isolation of target compounds in 63-94% yields are determined, and the relative activity of alcohols in the addition reaction at the exocyclic double bond of substrates is determined.

Structural Insight into Polymerase Mechanism via a Chiral Center Generated with a Single Selenium Atom.

DNA synthesis catalyzed by DNA polymerase is essential for all life forms, and phosphodiester bond formation with phosphorus center inversion is a key step in this process. Herein, by using a single-selenium-atom-modified dNTP probe, we report a novel strategy to visualize the reaction stereochemistry and catalysis. We capture the before- and after-reaction states and provide explicit evidence of the center inversion and in-line attacking SN2 mechanism of DNA polymerization, while solving the diastereomer absolute configurations. Further, our kinetic and thermodynamic studies demonstrate that in the presence of Mg2+ ions (or Mn2+), the binding affinity (Km) and reaction selectivity (kcat/Km) of dGTPαSe-Rp were 51.1-fold (or 19.5-fold) stronger and 21.8-fold (or 11.3-fold) higher than those of dGTPαSe-Sp, respectively, indicating that the diastereomeric Se-Sp atom was quite disruptive of the binding and catalysis. Our findings reveal that the third metal ion is much more critical than the other two metal ions in both substrate recognition and bond formation, providing insights into how to better design the polymerase inhibitors and discover the therapeutics.

Enantioselectivity in the enzymatic dehydration of malate and tartrate: Mirror image specificities of structurally similar dehydratases.

Malate (2-hydroxysuccinic acid) and tartrate (2,3-dihydroxysuccinic acid) are chiral substrates; the former existing in two enantiomeric forms (R and S) while the latter exists as three stereoisomers (R,R; S,S; and R,S). Dehydration by stereospecific hydrogen abstraction and antielimination of the hydroxyl group yield the achiral products fumarate and oxaloacetate, respectively. Class-I fumarate hydratase (FH) and L-tartrate dehydratase (L-TTD) are two highly conserved enzymes belonging to the iron-sulfur cluster hydrolyase family of enzymes that catalyze reactions on specific stereoisomers of malate and tartrate. FH from Methanocaldococcus jannaschii accepts only (S)-malate and (S,S)-tartrate as substrates while the structurally similar L-TTD from Escherichia coli accepts only (R)-malate and (R,R)-tartrate as substrates. Phylogenetic analysis reveals a common evolutionary origin of L-TTDs and two-subunit archaeal FHs suggesting a divergence during evolution that may have led to the switch in substrate stereospecificity preference. Due to the high conservation of their sequences, a molecular basis for switch in stereospecificity is not evident from analysis of crystal structures of FH and predicted structure of L-TTD. The switch in enantiomer preference may be rationalized by invoking conformational plasticity of the amino acids interacting with the substrate, together with substrate reorientation and conformer selection about the C2C3 bond of the dicarboxylic acid substrates. Although classical models of enzyme-substrate binding are insufficient to explain such a phenomenon, the enantiomer superposition model suggests that a minor reorientation in the active site residues could lead to the switch in substrate stereospecificity.

Mapping the Initial Stages of a Protective Pathway that Enhances Catalytic Turnover by a Lytic Polysaccharide Monooxygenase.

Oxygenase and peroxygenase enzymes generate intermediates at their active sites which bring about the controlled functionalization of inert C-H bonds in substrates, such as in the enzymatic conversion of methane to methanol. To be viable catalysts, however, these enzymes must also prevent oxidative damage to essential active site residues, which can occur during both coupled and uncoupled turnover. Herein, we use a combination of stopped-flow spectroscopy, targeted mutagenesis, TD-DFT calculations, high-energy resolution fluorescence detection X-ray absorption spectroscopy, and electron paramagnetic resonance spectroscopy to study two transient intermediates that together form a protective pathway built into the active sites of copper-dependent lytic polysaccharide monooxygenases (LPMOs). First, a transient high-valent species is generated at the copper histidine brace active site following treatment of the LPMO with either hydrogen peroxide or peroxyacids in the absence of substrate. This intermediate, which we propose to be a CuII-(histidyl radical), then reacts with a nearby tyrosine residue in an intersystem-crossing reaction to give a ferromagnetically coupled (S = 1) CuII-tyrosyl radical pair, thereby restoring the histidine brace active site to its resting state and allowing it to re-enter the catalytic cycle through reduction. This process gives the enzyme the capacity to minimize damage to the active site histidine residues "on the fly" to increase the total turnover number prior to enzyme deactivation, highlighting how oxidative enzymes are evolved to protect themselves from deleterious side reactions during uncoupled turnover.

Effect of magnetic field assisted thermal diffusion on microstructure and properties of titanium alloy laser cladding coating

Ti–Al composite coating was prepared on the surface of a titanium alloy by the laser cladding technology and coaxial powder feeding under argon protection. The cladding material was AlSi10Mg aluminum alloy powder. The intermediate sample was thermally diffused at high temperature for 6 h and then placed in a certain intensity of the alternating electromagnetic field until completely cooled. The alloy substrate and coating solidified under the action of the alternating electromagnetic field, and the surface coating of a high strength titanium alloy was obtained. The morphology and microstructure of the composite coating were analyzed by SEM, XRD, and energy dispersive spectroscopy (EDS), and the hardness of the coating was measured. The results showed that the high temperature thermal diffusion promoted the interatomic diffusion; repaired some defects, such as cracks and pores; and eliminated the elemental metals that did not participate in the reaction, and the surface hardness of the coating joint reached the maximum. The electromagnetic stirring makes the titanium alloy coating and substrate bond well, the joint is relatively straight, the number of cracks and pores is obviously reduced, and the comprehensive performance of the coating is improved.

NHC-catalyzed enantioselective access to β-cyano carboxylic esters via in situ substrate alternation and release

A carbene-catalyzed asymmetric access to chiral β-cyano carboxylic esters is disclosed. The reaction proceeds between β,β-disubstituted enals and aromatic thiols involving enantioselective protonation of enal β-carbon. Two main factors contribute to the success of this reaction. One involves in situ ultrafast addition of the aromatic thiol substrates to the carbon-carbon double bond of the enal substrate. This reaction converts almost all enal substrate to a Thiol-click Intermediate, significantly reducing aromatic thiol substrates concentration and suppressing the homo-coupling reaction of enals. Another factor is an in situ release of enal substrate from the Thiol-click Intermediate for the desired reaction to proceed effectively. The optically enriched β-cyano carboxylic esters from our method can be readily transformed to medicines that include γ-aminobutyric acids derivatives such as Rolipram. In addition to synthetic utilities, our control of reaction outcomes via in situ substrate modulation and release can likely inspire future reaction development.