Bond Formation Research Articles

Relationship between the interfacial properties of lactoferrin-(−)-epigallocatechin-3-gallate covalent complex and the macroscopic properties of emulsions

This study explored the relationship between the interfacial behavior of lactoferrin-(−)-epigallocatechin-3-gallate covalent complex (LF-EGCG) and the stability of high internal phase Pickering emulsions (HIPPEs). The formation of covalent bond between lactoferrin and polyphenol was verified by the increase in molecular weight. In LF-EGCG group, the surface hydrophobicity, interfacial pressure, and adsorption rate were decreased, while the molecular flexibility, interfacial film viscoelasticity, and interfacial protein content were increased. Meanwhile, LF-EGCG HIPPE possessed reduced droplet size, increased ζ-potential and stability. Rheology showed the viscoelasticity, structural recovery and gel strength of LF-EGCG HIPPE were improved, giving HIPPE inks better 3D printing integrity and clarity. Moreover, the free fatty acids (FFA) release of LF-EGCG HIPPE (62.6%) was higher than that of the oil group (50.1%). Therefore, covalent treatment effectively improved the interfacial properties of protein particles and the stability of HIPPEs. The macroscopic properties of HIPPEs were positively regulated by the interfacial properties of protein particles. The result suggested that the stability of emulsions can be improved by regulating the interfacial properties of particles.

Smart zwitterionic coatings with precise pH-responsive antibacterial functions for bone implants to combat bacterial infections.

Hydrophilic antifouling coatings based on zwitterionic polymers have been widely applied for the surface modification of bone implants to combat biofilm formation and reduce the likelihood of implant-related infections. However, their long-term effectiveness is significantly limited by the lack of effective and precise antibacterial activity. Here, a pH-responsive smart zwitterionic antibacterial coating (PSB/GS coating) was designed and robustly fabricated onto titanium-base bone implants by using a facile two-step method. First, dopamine (DA) and a poly(sulfobetaine methacrylate-co-dopamine methacrylamide) (PSBDA) copolymer were deposited on implants via mussel-inspired surface chemistry, resulting in a hydrophilic base coating with abundant catechol residues. Next, an amino-rich antibiotic, gentamicin sulfate (GS), was covalently linked to the coating through the formation of acid-sensitive Schiff base bonds between the amine groups of GS and the catechol residues present in both the zwitterionic polymer and the DA component. During the initial implantation period, the hydrophilic zwitterionic polymers demonstrated the desired anti-fouling properties that could effectively reduce protein and bacterial adhesion by over 90%. With time, the bacterial proliferation led to a decrease in the microenvironment pH value, resulting in the hydrolysis of the acid-sensitive Schiff base bonds, thereby releasing GS on demand and effectively enhancing the anti-biofilm properties of coatings. Benefiting from this synergistic antifouling and smart antibacterial activities, the PSB/GS coating exerted an excellent anti-infective activity in both in vivo preoperative and postoperative infection rat models. This proposed facile yet effective coating strategy is expected to provide a promising solution to combat bone implant-related infections.

Thiolated nanoclays as a potential mucoadhesive material: Optimization by design of experiments and multivariate regression

An integrated strategy based on design of experiments (DoE) and multivariate regression was carried out to produce an optimized surface functionalized nanoclay (Mt–SH) with potential mucoadhesive properties. A mercaptosilane was grafted in montmorillonite in order to immobilize thiol groups (–SH) on the clay. The functionalization was confirmed by IR, TGA, XRF and XRD analyses. Five variables involved in the synthesis were optimized in order to maximize two responses: mass of functionalized nanoclay and amount of thiol groups attached in the clay surface. This optimization was performed by a two–step DoE strategy using Plackett–Burman and Box–Behnken designs. The five variables and two responses were simultaneously calibrated in a single ANOVA–validated PLS regression model. Analyzing scores, loading and surface response plots, the main processing variables, interactions and quadratic terms were found achieving the optimal processing conditions for the synthesis. The quadratic model (R2 > 0.8589) predicted an optimized functionalized nanoclay of mass 3.29 ± 0.13 g of Mt–SH with 19.65 ± 0.78 μmol –SH per g Mt–SH (P < 0.05). The optimized Mt–SH was evaluated by in vitro and in situ mucoadhesion assays with porcine mucin and fresh intestinal mucus by using rheometry. The complex viscosity showed an increase of ∼54-fold higher compared to the unmodified Mt, and ∼12.8-fold increase in the elastic modulus, which indicates a more resistance to elastic deformation probably due to an increase in cross-linking points between Mt–SH and mucus. The formation of disulfide bonds between thiol groups from Mt–SH and glycoproteins in the mucin could be a reasonably explanation which shows a correlation respect other thiolated materials which show the same mucoadhesion properties. These results could project this functionalized silicate material as a potential mucoadhesive prospect for pharmaceutical applications.

Biosynthesis of Ester-Bond Containing Quinolone Alkaloids with (3R,4S) Stereoconfiguration.

Asperalins represent a novel class of viridicatin natural products with potent inhibitory activities against fish pathogens. In this study, we elucidated the biosynthesis of asperalins in the Aspergillus oryzae NSAR1 heterologous host and identified the FAD-dependent monooxygenase AplB stereoselectively hydroxylates viridicatin to yield a unique 3R,4S configuration. The monomodular NRPS AplJ catalyzes a rare intramolecular ester bond formation reaction using dihydroquinoline as a nucleophile. Subsequent modifications by cytochrome P450 AplF, chlorinase AplN, and prenyltransferase AplE tailor the anthranilic acid portion, leading to the formation of asperalins. Additionally, we explored the potential of AplB for the hydroxylation of viridicatin analogs, demonstrating its relaxed substrate specificity. This finding suggests that AplB could be developed as a biocatalyst for the synthesis of viridicatin derivatives.

Transition-Metal-Free Sulfoximidation of Sulfonylhydrazones for the Synthesis of N-Sulfanylidenehydrazonamides.

Herein, we report a transition-metal-free C-H bond sulfoximidation protocol of sulfonyl hydrazones with hypervalent iodine(III) reagents. A library of novel N-sulfaneylidenehydrazonamides was constructed via chemoselective C-N bond formation reactions at aldehyde C-H bonds of sulfonyl hydrazones in the presence of a base. The reaction demonstrated broad substrate group diversity under exceedingly mild reaction conditions, and excellent yields were achieved at room temperature.

Electrochemical synthesis of heterocyclic compounds via carbon–heteroatom bond formation: direct and indirect electrolysis

Abstract Electrochemical organic synthesis has attracted attention as an environmentally friendly method for constructing heterocyclic compounds via carbon–heteroatom bond formation. Herein, we describe the representative examples of electrochemical reactions to produce heterocycles and discuss them according to whether they involve direct or indirect electrolysis.

Electrochemistry-Enabled C-Heteroatom Bond Formation of Alkyl Germanes.

Because of their robustness and orthogonal reactivity features, alkyl germanes bear significant potential as functional handles for the construction of C(sp3)-rich scaffolds, especially in the context of modular synthetic approaches. However, to date, only radical-based reactivity has been accessible from these functional handles, which limits the types of possible decorations. Here, we describe the first general C(sp3)-heteroatom bond formation of alkyl germanes (-GeEt3) by leveraging electrochemistry to unlock polar reactivity. This approach allowed us to couple C(sp3)-GeEt3 with a variety of nucleophiles to construct ethers, esters, amines, amides, sulfonamides, sulfides, as well as C-P, C-F, and C-C bonds. The compatibility of the electrochemical approach with a modular synthetic strategy of a C1 motif was also showcased, involving the sequential functionalization of Cl, Bpin, and ultimately GeEt3 via electrochemistry.

Promoting Proton Donation through Hydrogen Bond Breaking on Carbon Nitride for Enhanced H2O2 Photosynthesis.

Photocatalytic H2O2 production has attracted much attention as an alternative way to the industrial anthraquinone oxidation process but is limited by the weak interaction between the catalysts and reactants as well as inefficient proton transfer. Herein, we report on a hydrogen-bond-broken strategy in carbon nitride for the enhancement of H2O2 photosynthesis without any sacrificial agent. The H2O2 photosynthesis is promoted by the hydrogen bond formation between the exposed N atoms on hydrogen-bond-broken carbon nitride and H2O molecules, which enhances proton-coupled electron transfer and therefore the photocatalytic activity. The exposed N atoms serve as proton buffering sites for the proton transfer from H2O molecules to carbon nitride. The H2O2 photosynthesis is also enhanced through the enhanced adsorption and reduction of O2 gas toward H2O2 on hydrogen-bond-broken carbon nitride because of the formation of nitrogen vacancies (NVs) and cyano groups after the intralayer hydrogen bond breaking on carbon nitride. A high light-to-chemical conversion efficiency (LCCE) value of 3.85% is achieved. O2 and H2O molecules are found to undergo a one-step two-electron reduction pathway by photogenerated hot electrons and a four-electron oxidation process to produce O2 gas, respectively. Density functional theory (DFT) calculations validate the O2 adsorption and reaction pathways. This study elucidates the significance of the hydrogen bond formation between the catalyst and reactants, which greatly increases the proton tunneling dynamics.

Arsinothricin Biosynthesis Involving a Radical SAM Enzyme for Noncanonical SAM Cleavage and C-As Bond Formation.

Arsinothricin is a potent antibiotic secreted by soil bacteria. The biosynthesis of arsinothricin was proposed to involve a C-As bond formation between trivalent As and the 3-amino-3-carboxypropyl (ACP) group of S-adenosyl-l-methionine (SAM), which is catalyzed by the protein ArsL. However, ArsL has not been characterized in detail. Interestingly, ArsL contains a CxxxCxxC motif and thus belongs to the radical SAM enzyme superfamily, the members of which cleave SAM and generate a 5'-deoxyadenosyl radical. Here, we found that ArsL cleaves the Cγ,Met-S bond of SAM and generates an ACP radical that resembles Dph2, a noncanonical radical SAM enzyme involved in diphthamid biosynthesis. As Dph2 does not contain the CxxxCxxC motif, ArsL is a unique radical SAM enzyme that contains this motif but generates a noncanonical ACP radical. Together with the methyltransferase ArsM, we successfully reconstituted arsinothricin biosynthesis in vitro. ArsL has a conserved RCCLKC motif in the C-terminal sequence and belongs to the RCCLKC-tail radical SAM protein subfamily. By truncation and mutagenesis, we showed that this motif plays an important role in binding to the substrate arsenite and is highly important for its activity. Our results suggested that ArsL has a canonical radical SAM enzyme motif but catalyzes a noncanonical radical SAM reaction, implying that more noncanonical radical SAM chemistry may exist within the radical SAM enzyme superfamily.

C(sp3)-N Bond Formation via Deoxygenative Amination of Alcohols

C(sp3)-N Bond Formation via Deoxygenative Amination of Alcohols

Effects of quenching rate on the plasma gas-phase synthesis of graphene: Insight from the experiments and ReaxFF studies

This investigation analysed the effects of quenching rate on the plasma gas-phase synthesis of graphene. The quenching rate was modulated by the flowrate/type of radial gas whish was injected in the plasma downstream. The experimental results showed that the plasma pyrolysis of acetylene produced spherical carbon nanoparticles. The content graphene flakes in the products increased with the quenching effect, and the layer number of graphene decreased accordingly. Further characterisation confirmed that a high quenching rate increased the crystallinity of the product, reduced the amorphous carbon content, and resulted in better oxidation resistance. The graphene formation pathway was carried out by the molecular dynamics simulations (ReaxFF), focusing on the effect of the quenching rate on graphene growth. As the quenching rate increased, the decrease in the time for surface reactions lowered the generation of five- and seven-membered rings, reducing the possibility of edge growth bending. Besides, an increased quenching rate rapidly lowered the growth temperature and thus retarded the C–H bond breakage at the edges of the carbon clusters. The C–H bonds terminated C–C bond formation at the edges of the carbon clusters, preventing edge growth bending of the carbon clusters, and thus contributing to the growth of lamellar structure. These results suggested that increasing the quenching rate is an effective method for regulating the plasma gas-phase synthesis of graphene.

C‐C Bond Formation by Dual Pyrrolidine and Nickel Catalysis: Allylation of Ketones by Allylic Alcohols.

Whilst catalytic ketone allylation using palladium(0) is well–precedented, nickel(0)‐catalysed equivalents of such reactions remain scarce. We report here the first nickel‐catalysed allylation of ketones which uses an easily handled and inexpensive bench‐stable Ni(II) pre‐catalyst. This method avoids generation of stoichiometric by‐products via the use of readily available allyl alcohols, rather than the esters or related derivatives which are often used in such transformations. Under the optimised conditions, 25 monoallylated ketones were obtained in 16% to 98% yield and with high selectivity for the linear (E)–isomers.

A General Nucleation Model for Semiconductor Nanocrystals.

We introduce a nonclassical model for nanocrystal nucleation in solution which centers on the dynamic interplay of chemical bond breakage and formation coupled with the desolvation of precursor molecules, which we term the molecular chemistry (MC) model. Departing from classical theory, our model employs the bond count as the key variable rather than particle size, thereby redefining the role of supersaturation and its role in determining the so-called critical nucleus size. We apply the model to CdSe nanocrystal formation in nonpolar solvents and showcase its efficacy in predicting solvent dynamics, precursor characteristics, crystal phase, stoichiometry, "magic number" behavior, and transition states. While the coupled-cluster method is used to determine the bond energy, we show that it is possible to derive reaction pathways by reducing the calculations to algebraic approximations for the nucleation energy. This singular set of bond energy parameters allows nanocrystal nucleation and growth to be conceptualized as a straightforward chemical reaction.

Late-Stage C(sp2)-C(sp3) Diversification via Nickel Oxidative Addition Complexes.

Herein, we describe nickel oxidative addition complexes (Ni-OACs) of drug-like molecules as a platform to rapidly generate lead candidates with enhanced C(sp3) fraction. The potential of Ni-OACs to access new chemical space has been assessed not only in C(sp2)-C(sp3) couplings but also in additional bond formations without recourse to specialized ligands and with improved generality when compared to Ni-catalyzed reactions. The development of an automated diversification process further illustrates the robustness of Ni-OACs, thus offering a new gateway to expedite the design-make-test-analyze (DMTA) cycle in drug discovery.

Additive-Assisted Forming High-Quality Thin Films of Sn-Oxo Cluster for Nanopatterning.

Recently, metal-oxo clusters (MOCs) have attracted significant interest in fabricating nanoscale patterns in semiconductors via lithography. However, many MOCs are highly crystalline, making it difficult for them to form films and hindering subsequent nanopatterning processes. In this study, we developed a novel and simple method to enhance the film-forming ability of aromatic tetranuclear Sn-oxo clusters by adding additives. Theoretical calculations and Fourier-transform infrared (FTIR) analysis revealed the formation of intermolecular hydrogen bonds between the Sn-oxo clusters and additives, which induced a crystal-gel phase transition at -20 °C, thereby inhibiting the easy crystallization of the Sn-oxo clusters. High-quality and uniform thin films with surface roughness below 0.3 nm were prepared via spin coating. The obtained thin films exhibited good lithographic performance under deep ultraviolet (DUV), electron beam, and extreme-ultraviolet irradiation without a photo acid generator/photoinitiator, and 13- and 21 nm-wide line patterns were obtained on the films via electron-beam and extreme-ultraviolet lithographies. This study will pave the way for the further investigation of novel MOCs for advanced lithography and other thin-film applications.

Optimization the Potential of Solution Process Fluorine Passivated Zinc Oxide Electron Transport Layer for Stable InP-Quantum Dot Light Emitting Diodes

The pervasive use of zinc oxide (ZnO) as an electron transport layer in quantum dot (QD) electroluminescent devices is constrained due to its chemical instability with the QD layer and the formation of interface quenching sites. The effect of fluorine passivation of sol-gel processed ZnO in QD light-emitting devices (QLEDs) is investigated in depth. An examination of the interaction between the ZnO surface and fluorine species revealed that the passivation of oxygen vacancies and the formation of stable hydrogen bonds with hydroxyl groups on ZnO surface have a significant influence on the stability and efficiency of the device. Such exceptional functions of fluorine have been found to effectively capture defects at the interface between ZnO and the emissive layer, therefore mitigating the interface quenching sites. The initial fluorination device demonstrated a significant improvement in external quantum efficiency (EQE) from 5.72 % to 20.07 %, and half of the device lifetime (LT50 at an initial luminance of 1500 cd/m2) was 286 hours. Further passivating the remaining active oxygen on the ZnO surface can extend the stability of the device to 542 hours with an EQE of 15.2 %, which is among the longest lifetime reported so far for green InP-QLEDs. Our report offers the possibility of utilizing straightforward and highly effective fluorination by spin-coating technique to attain long-lasting InP-QLED devices with remarkable performance.

Reactions of alkynes with C-S bond formation: recent developments.

Alkynes are important in organic synthesis. This review mainly focuses on recent advances (2013-2023) on alkynes with C-S bond formation, based on more than 30 types of sulfur reagents. The reactions of alkynes with various sulfur-containing compounds including RSSR (disulfides), RSH (thiols), S8 (elemental sulphur), alkynyl thioethers, RSCN, AgSCF3, K2S, Na2S, dithiane, RSCl, NFSI, RNCS, EtOCS2K, thiocarbamate, RSONH2, thiourea, sulfoxide, RSO2N3, CS2, RSO2NH2, RSO2NHNH2, RSO2Cl, RSO2Oar, RSO2SR', DABCO·(SO2)2, Na2S2O5, K2S2O5, RSO2H, RSO2Na and related compounds are discussed. Diverse mechanisms such as radical, electrophilic/nucleophilic addition, rearrangement, C-C bond cleavage, and CuAAC are discussed. The content is organized by substrates and reactivity patterns. We hope it will help in future research in this area.

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.

Benzisoselenazoles as Selenophenolate Anion Surrogates for the Formation of Carbon-Selenium Bonds via the Selena-Kemp Reaction.

The in situ base-promoted generation of unstable selenophenolate anions from 1,2-benzisoselenazoles via a variant of the Kemp elimination has been developed. 2-Cyano-substituted selenophenolate anions obtained by this methodology were engaged in nucleophilic substitution, aromatic nucleophilic substitution, and Pd-catalyzed cross-coupling reactions to give functionalized arylalkyl and diaryl selenides in moderate to excellent yields.

Tailoring molecular structure and electromechanical properties of polydimethylsiloxane elastomer for enhanced energy conversion efficiency

AbstractThe molecular structure of dielectric elastomers dictates their mechanical, electrical, and properties to react under external stimuli, influencing their suitability for applications such as actuators, sensors, and energy harvesting devices. The molecular structure of polymers can be tailored by incorporating plasticizers and particulate fillers to achieve multifunctional properties. However, achieving a balance between flexibility and maintaining mechanical strength due to incorporation of fillers induced phase separation and compromised intermolecular interactions remains challenging. In the present work, polydimethylsiloxane (PDMS) composites are synthesized using plasticizer and particulate fillers, polyethylene glycol (H‐(OCH2CH2)nOH) and titanium diboride (TiB2) respectively in various concentrations using shear mixing and doctor blade casting technique. Molecular structure of synthesized PDMS composite is confirmed by observing peaks of Raman spectra sift, which exhibits robust CO bonds dominating for both fillers. Chain entanglement due to filler incorporation significantly affects the crosslink density of PDMS composite, it increases with the concentration of plasticizer and possesses inverse relation for particulate. Furthermore, interdependence of the filler types and concentration are found on the mechanical as well as electrical properties. The specific deformation energy exhibits a significant increase of 118.9% when comparing particulate to the plasticizer at concentration of 8 wt.%. Although plasticizer increases the actuation strain and energy conversion efficiency but decreases the electrical breakdown voltage in comparison to particulate. By systematically varying fillers concentration, subtle changes in multifunctional properties are achieved. Overall, this investigation provides a framework for tailoring dielectric elastomer composites with desired electromechanical characteristics through the amalgamation of filler types and crosslinking densities, all intricately tied to the molecular architecture for electromechanical sensors.Highlights Filler incorporation changes DE molecular structure and materials properties. Formation of additional bonds and micro‐capacitors in DE enhances capacitance. Actuation strain in DE depends on filler type and concentration. Energy conversion efficiency varies with the concentration of filler.