Substrate Reaction Research Articles

Ni/Al multilayer reactions on nanostructured silicon substrates

Fast energy release, which is a fundamental property of reactive multilayer systems, can be used in a wide field of applications. For most applications, a self-propagating reaction and adhesion between the multilayers and substrate are necessary. In this work, a distinct approach for achieving self-propagating reactions and adhesion between deposited Ni/Al reactive multilayers and silicon substrate is demonstrated. The silicon surface consists of random structures, referred to as silicon grass, which were created by deep reactive ion etching. Using the etching process, structure units of heights between 8 and 13 µm and density between 0.5 and 3.5 structures per µm2 were formed. Ni and Al layers were alternatingly deposited in the stoichiometric ratio of 1:1 using sputtering, to achieve a total thickness of 5 µm. The analysis of the reaction and phase transformation was done with high-speed camera, high-speed pyrometer, and X-ray diffractometer. Cross-sectional analysis showed that the multilayers grew only on top of the silicon grass in the form of inversed cones, which enabled adhesion between the silicon grass and the reacted multilayers. A self-propagating reaction on silicon grass was achieved, due to the thermally isolating air pockets present around these multilayer cones. The velocity and temperature of the reaction varied according to the structure morphology. The reaction parameters decreased with increasing height and decreasing density of the structures. To analyze the exact influence of the morphology, further investigations are needed.

Metal‐, Oxidant‐, and Additive‐Free Sulfenylation of Imidazo[1,2‐a]pyridines Using Sulfenamides and an I2 Catalyst

AbstractA novel sulfenylation reagent (sulfenamide) was applied to establish a simple and efficient process to convert C−H bond in imidazo[1,2‐a]pyridine to C−S bond. This process only requires sulfenamides as the sulfenylation reagent and I2 as an inexpensive and readily available catalyst, without using metal catalysts, oxidants, additives, or even light radiation. The proposed reaction features excellent reactivity, substrate compatibility, and regioselectivity.

Gas sensing performance of Tungsten doped V2O5 nanorod thin-films deposited by hot filament CVD combined with DC sputtering

High-quality polycrystalline tungsten doped vanadium pentoxide thin-films were prepared using Hot Filament Chemical Vapor Deposition technique (HFCVD) combined with sputtering by changing target to substrate distance and reaction duration. Scanning electron microscopy and X-ray diffraction revealed that the morphologies and crystalline structures of the films are depending on the deposition parameters such as target to substrate distance and deposition time. Raman spectroscopy is also used to analyse the oxidation states of the vanadium-based films. The deposited nanorod thin-film was exposed to ammonia and ethanol gases to test their gas sensing performance. It exhibits a sensing response of 1.8 and 1.65 at a concentration of 200 ppm ammonia and ethanol and has a recovery time of 44 and 31 s, respectively.

Visible‐Light‐Promoted Aliphatic C−H Chlorination and Bromination Using Haloform as the Halogen Donor and Azidobenziodoxole as the Mediator

AbstractAn azidobenziodoxole (BIN3)‐mediated tunable radical reaction system for selective chlorination and bromination of tertiary and secondary C(sp3)−H bonds of alkyl substrates using haloform as the halogen donor was developed. Reactions of various substrates with BIN3 under visible light irradiation without any photo or metal catalysts gave C−H chlorinated or brominated products. These reactions are selective, and compatible with many functional groups. Mechanistic studies suggest that haloform serves as the halogen atom donor and HN3 generated in situ from the reaction of BIN3 and water relays the radical chain reaction as the hydrogen atom donor. HN3 reacts with CHX2⋅ to form CH2X2 and N3⋅, which propagates a radical chain by abstracting a hydrogen atom of the alkane substrate.

Photochemical radical benzylic bromination with Br2: Computational modeling of the mechanism and microkinetic

Halogenation of organic compounds is an important functionalization process for further chemical transformation and the benzylic hydrogen is reactive towards the photochemically generated Br atom. This work reports the free energy profile of the several steps of the reaction of the Br atom with toluene leading to benzyl bromide, (dibromomethyl)benzene, and (tribromomethyl)benzene using reliable theoretical B2GP-PLYP method. A detailed microkinetic analysis of the reaction rate and product distribution was also performed. Our analysis points out that polar solvent increases the reaction rate in relation to apolar one. Substitution on the aromatic ring cannot be explained by the electrophilic mechanism in an apolar medium. The reactivity of different benzylic substrates was evaluated, and we have found that the cyano electron-withdrawing group in the aromatic ring retards the reaction, while the ortho-methoxy group, and oxygen and nitrogen atoms bonded to the benzylic carbon, enhance the reaction rate.

Strategies for synthesizing human milk lacto-N-fucopentaoses oligosaccharides

Lacto-N-fucopentaoses (LNFPs) of type I to V are representative components of human milk oligosaccharides (HMOs) and have garnered increasing attention due to their multi-functional activities. These activities include regulating intestinal flora, resisting pathogen adhesion, and promoting the development and repair of the nervous system. Due to the limited resource of HMOs, artificial synthesis of HMOs can provide an alternative pathway to circumvent this limitation. Currently, LNFPs can be produced using various methods, including biosynthesis, chemical synthesis, and enzymatic synthesis. Currently, emphasis is placed on the last two methods. Chemical synthesis-based methods typically involve strict reaction conditions, cumbersome steps, and low yields. On the other hand, enzymatic synthesis offers several advantages, including mild reaction conditions, high yield, and good selectivity. However, only a few reports have focused on in vivo fermentation as a means to produce LNFPs, despite its cost advantage. In vivo fermentation presents an opportunity to supply the key substrates for fucosyl transfer reactions, namely LNnT and GDP-Fuc, along with the required biosynthesis enzymes. Further exploration of this approach is warranted.This paper aims to review the synthesis methods of LNFPs, their functional activities, and emerging trends in their development. By evaluating the different synthesis approaches, this review seeks to contribute to the advancement of LNFPs production and utilization.

Organocatalyst‐Controlled Divergent Asymmetric Aza‐Friedel‐Crafts Reactions of Indol‐3‐ones with 1‐ and 2‐Naphthols

AbstractIndol‐3‐ones are readily available reaction substrates, but their utility in asymmetric reactions is underdeveloped. Herein, we describe the organocatalytic asymmetric aza‐Friedel‐Crafts‐type reaction of indol‐3‐ones with 1‐ and 2‐naphthols. By using spirocyclic chiral phosphoric acids and quinine‐incorporated squaramides as the organocatalysts, two classes of structurally distinct chiral compounds, namely 2‐(hydroxylnaphthyl)‐indolin‐3‐ones and tetrahydrofuroindoles, are formed respectively. These quaternary centre‐containing indoline derivatives may find use in the synthesis of biologically active molecules.

An artificial multienzyme cascade for the whole-cell synthesis of rare ketoses from glycerol.

In our previous study, we constructed a one-pot multi-enzyme system for rare ketoses synthesis based on L-rhamnulose-1-phosphate aldolase (RhaD) from accessible glycerol in vitro. To eliminate tedious purification of enzymes, a facile Escherichia coli whole-cell cascade platform was established in this study. To enhance the conversion rate, the reaction conditions, substrate concentrations and expressions of related enzymes were extensively optimized. The biosynthetic route for the cascade synthesis of rare ketoses in whole cells was successfully constructed and three rare ketoses including D-allulose, D-sorbose and L-fructose were produced using glycerol and D/L-glyceraldehyde (GA). Under optimized conditions, the conversion rates of rare ketoses were 85.0% and 93.0% using D-GA and L-GA as the receptor, respectively. Furthermore, alditol oxidase (AldO) was introduced to the whole-cell system to generate D-GA from glycerol, and the total production yield of D-sorbose and D-allulose was 8.2gl-1 only from the sole carbon source glycerol. This study demonstrates a feasible and cost-efficient method for rare sugars synthesis and can also be applied to the green synthesis of other value-added chemicals from glycerol.

NO Reactions Inside Crystals

AbstractReactions of chemisorbed reagents inside the crystalline molecular solid state are rare but offer unexploited methods for selective solvent‐free chemical synthesis. Here we show that the greenhouse gas precursor, nitric oxide (NO) is chemisorbed by crystals of the hexafluorophosphate salts of complexes containing dicobalt sites. On NO sorption a cascade of reactions results in the in‐crystal synthesis of nitrite and other gaseous NOx. Recrystallization enabled structural elucidation of the mixed valent {[(bpbp)Co2(μ‐(η1‐O : η1‐N)‐ONO)]2(bdc)}4+ (bpbp=2,6‐bis(N,N‐bis(2‐pyridylmethyl)aminomethyl)‐4‐tert‐butylphenolato, bdc=1,4‐benzenedicarboxylato) cation. Overlapping signals in the solid‐state EPR spectra confirm the CoIICoIII oxidation state and the presence of NO2 trapped inside the unrecrystallised solid products (br. g=4, triplet g=2 (340 mT), A(N)=73 MHz), despite three cycles of vacuum and N2 flushing. Consistently, νN−O bands appear in the Raman and IR spectra that are due to the coordinated nitrate and the trapped NO2 that were synthesized in‐crystal. The latter is expelled by heating the solid to 160 °C or by recrystallization. Dimetallic cooperativity is proposed for the NO transformations in these rare examples of selective, chemisorptive substrate reactions in the solid‐state.

On the O2 "Surfactant" Effect during Ag/SiO2 Magnetron Sputtering Deposition: The Point of View of In Situ and Real-Time Measurements.

The use of gaseous species has been proposed in the literature to counteract the three-dimensional growth tendency of noble metals on dielectric substrates and favor an earlier percolation without compromising electrical properties. This "surfactant" effect is rationalized herein in the case of O2 presence during magnetron sputtering deposition of Ag films on SiO2. In situ and real-time techniques (X-ray photoemission, film resistivity, UV-visible optical spectroscopy) and ex situ characterizations (X-ray diffraction and transmission electron microscopy) were combined to scrutinize the impact of O2 addition in the gas flow (%O2), revealing three regimes of evolution of film resistivity, morphology, structure, and chemical composition. At low oxygen flow conditions (%O2 < 4), the observed drastic decrease of the percolation threshold is assigned to a combination of (i) a change in nanoparticle density, wetting, and crystallographic texture and (ii) a delayed coalescence effect. The driving force is ascribed to the presence of specific adsorbed oxygen moieties, the nature of which starts evolving at intermediate oxygen flow conditions (10 ≤ %O2 < 20). At high oxygen flow (20 ≤ %O2 < 40), the found detrimental impact on film resistivity is assigned to an actual oxidation in the form of a Ag2O-like poorly crystallized compound. For all %O2, a composition gradient is observed across the film thickness, with a more metallic Ag at the substrate interface. A correlation between percolation and the nature of the detected O moieties is observed. In parallel to an oxygen spillover mechanism, this gradient can be explained by the competition between different surface processes occurring before percolation, namely, aggregation, metal oxidation, and substrate reactivity. Such findings pave the way to a rational use of O2 as a modifier for Ag growth.

Versatile Product Detection via Coupled Assays for Ultrahigh-Throughput Screening of Carbohydrate-Active Enzymes in Microfluidic Droplets.

Enzyme discovery and directed evolution are the two major contemporary approaches for the improvement of industrial processes by biocatalysis in various fields. Customization of catalysts for improvement of single enzyme reactions or de novo reaction development is often complex and tedious. The success of screening campaigns relies on the fraction of sequence space that can be sampled, whether for evolving a particular enzyme or screening metagenomes. Ultrahigh-throughput screening (uHTS) based on in vitro compartmentalization in water-in-oil emulsion of picoliter droplets generated in microfluidic systems allows screening rates >1 kHz (or >107 per day). Screening for carbohydrate-active enzymes (CAZymes) catalyzing biotechnologically valuable reactions in this format presents an additional challenge because the released carbohydrates are difficult to monitor in high throughput. Activated substrates with large optically active hydrophobic leaving groups provide a generic optical readout, but the molecular recognition properties of sugars will be altered by the incorporation of such fluoro- or chromophores and their typically higher reactivity, as leaving groups with lowered pKa values compared to native substrates make the observation of promiscuous reactions more likely. To overcome these issues, we designed microdroplet assays in which optically inactive carbohydrate products are made visible by specific cascades: the primary reaction of an unlabeled substrate leads to an optical signal downstream. Successfully implementing such assays at the picoliter droplet scale allowed us to detect glucose, xylose, glucuronic acid, and arabinose as final products of complex oligosaccharide degradation by glycoside hydrolases by absorbance measurements. Enabling the use of uHTS for screening CAZyme reactions that have been thus far elusive will chart a route toward faster and easier development of specific and efficient biocatalysts for biovalorization, directing enzyme discovery by challenging catalysts for reaction with natural rather than model substrates.

Friedel-Crafts Reactions with N-Heterocyclic Alcohols.

N-Heterocyclic alcohols are shown to be excellent substrates for superacid-promoted Friedel-Crafts reactions. The N-heterocyclic alcohols ionize to produce reactive, dicationic intermediates which provide good to excellent yields of arylation products.

Quantitative probing of reactive oxygen species and their selective degradation on contaminants in peroxymonosulfate-based process enhanced by picolinic acid

The processes of Fe(III) activated peroxymonosulfate (PMS) in degrading contaminants have been extensively studied. Herein, a biodegradable chelating agent, picolinic acid (PICA), was introduced to the PMS/Fe(III) process to improve the reaction efficiency. The emphases of this study were placed on the quantification of steady-state concentrations of reactive oxygen species (ROS). Experiments presented that five types of ROS, including Fe(IV), SO4•−, HO•, 1O2 and O2•− coexisted in this system. Four typical probe compounds were used to quantify the steady-state concentration of ROS under different variables. The steady-state concentration of Fe(IV) ([Fe(IV)]ss) was 3–5 orders of magnitude higher than that of other ROS, followed by 1O2 and SO4•−, whereas HO• had the lowest concentration. The reaction between PMS and PICA was first explored in our study and results showed that 1O2 and O2•− would form in this reaction. Owing to the hybrid oxidation by multiple ROS, this system showed high oxidation capacity, and could effectively degrade a variety of pollutants. The contributions of ROS to the alleviation of pollutants varied depending on their concentrations and specific reactivity of substrates. Generally, organic contaminants with phenol structures were prone to react with Fe(IV). Overall, this study compared the steady-state concentrations of different ROS and revealed the intrinsic ROS formation mechanisms.

Gold nanohole arrays with ring-shaped silver nanoparticles for highly efficient plasmon-enhanced fluorescence

To enhance the interaction between electromagnetic fields and reduce photoluminescence (PL) lifetime in plasmon-enhanced fluorescence, this study presents a novel approach involving the fabrication of gold (Au) nanohole arrays (ANA) decorated with ring-shaped silver nanoparticles (AgNPs) on a silicon-dioxide (SiO2)/silver (Ag) substrate. The surface plasmon resonance coupling in terms of the PL reactions of ANA substrates with and without ring-shaped AgNPs is investigated via experiments and numerical simulations. The remarkable enhancement of PL intensity of the proposed substrate is attributed to increased absorption, which enables the tuning of surface-enhanced electromagnetic fields. Specifically, the Raman signal of rhodamine 6G (R6G) dye and the PL intensity of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) molecules are significantly enhanced 3.7 and 2.2 times, respectively, compared to those of the bare ANA substrate. Meanwhile, the PL lifetime is reduced by 46.15%. These results confirm that ANAs decorated with ring-shaped AgNPs can significantly improve plasmon-enhanced fluorescence. The findings presented herein demonstrate the potential to revolutionize biosensing, imaging, and photonics.

Nanostructured Pine-Like Platinum on Self-Supported Substrates for Robust Hydrogen Evolution Reaction

Nanostructured Pine-Like Platinum on Self-Supported Substrates for Robust Hydrogen Evolution Reaction

Dual Nickel/Photoredox‐Catalyzed Synthesis of N‐formyl N,N’‐Diaryl Ethylenediamines via Multiple C−N/C−C Coupling of Nitroarenes with Trimethylamine

AbstractN,N’‐Diaryl ethylenediamines are common feedstocks in organic synthesis and important structural motifs in medicinal chemistry. Whereas the C−N formation reactions based on anilines and aryl halides are the most direct methods to access N,N’‐diaryl ethylenediamines, the photocatalytic synthetic version remains undeveloped. Herein we describe the dual nickel/photoredox‐catalyzed amination reaction using nitroarenes and trimethylamine as reaction substrates. This cascade transformation hinges on the multiple C−N and C−C coupling events based on the nitrogen radical and α‐aminomethyl radical derived from nitroarene and trimethylamine, respectively. A variety of N‐formyl N,N’‐diaryl ethylenediamines can be obtained under the reaction protocol. Subsequent hydrolysis offers the N,N’‐diaryl ethylenediamines for further derivatizations.

Chiral Phosphoric Acid Catalyzed Asymmetric Hydrolysis of Biaryl Oxazepines for the Synthesis of Axially Chiral Biaryl Amino Phenol Derivatives

AbstractThe development of catalytic asymmetric reaction with water as the reactant is challenging due to the reactivity‐ and stereoselectivity‐control issues resulted from the low nucleophilicity and the small size of water. We disclose herein a chiral phosphoric acid (CPA) catalyzed atroposelective ring‐opening reaction of biaryl oxazepines with water. A series of biaryl oxazepines undergo the CPA catalyzed asymmetric hydrolysis in a highly enantioselective manner. The key for the success of this reaction is the use of a new SPINOL‐derived CPA catalyst and the high reactivity of biaryl oxazepine substrates towards water under acidic conditions. Density functional theory calculations suggest that the reaction proceeds via a dynamic kinetic resolution pathway and the CPA catalyzed addition of water to the imine group is both enantio‐ and rate‐determining.

Chiral Phosphoric Acid Catalyzed Asymmetric Hydrolysis of Biaryl Oxazepines for the Synthesis of Axially Chiral Biaryl Amino Phenol Derivatives.

The development of catalytic asymmetric reaction with water as the reactant is challenging due to the reactivity- and stereoselectivity-control issues resulted from the low nucleophilicity and the small size of water. We disclose herein a chiral phosphoric acid (CPA) catalyzed atroposelective ring-opening reaction of biaryl oxazepines with water. A series of biaryl oxazepines undergo the CPA catalyzed asymmetric hydrolysis in a highly enantioselective manner. The key for the success of this reaction is the use of a new SPINOL-derived CPA catalyst and the high reactivity of biaryl oxazepine substrates towards water under acidic conditions. Density functional theory calculations suggest that the reaction proceeds via a dynamic kinetic resolution pathway and the CPA catalyzed addition of water to the imine group is both enantio- and rate-determining.

Containment of sulfate in leachate as gypsum (CaSO4·2H2O) mineral formation in bio-cemented sand via enzyme-induced carbonate precipitation

Enzymatically induced carbonate precipitation (EICP) using urea hydrolysis is a well-known bio-cementation process that not only promotes the precipitation of calcium carbonate (CaCO3) but can provide excess calcium cations for further reaction depending on the substrate constituents and reaction stage. This study presents the EICP recipe to contain sulfate ions in landfill leachate sufficiently using remaining calcium cations and a series of tests were conducted to validate its ability to retain sulfates. The reaction rate for 1 M CaCl2 and 1.5 M urea was identified by controlling the purified urease content and the curing time of the EICP process. The results showed that 0.3 g/L of purified urease produced 46% CaCO3 and reduced sulfate ions by 77% after 3 days of curing. The shear stiffness in EICP-treated sand was enhanced 13 times by CaCO3 precipitation followed by 1.12 times increment due to subsequent precipitation of gypsum (CaSO4·2H2O) crystals implying sulfate containment. A cost-efficient EICP treatment using soybean crude urease instead of lab-grade purified urease exhibited lower sulfate removal efficiency (i.e., 18%) with only nominal formation of gypsum in the EICP-treated sand. The addition of gypsum powder was effective in increasing sulfate removal by 40% when soybean crude urease was used for EICP.

Electrochemically Mediated Fixation of CO2: Synthesis of Functionalized Oxazolidine‐2,4‐Diones by Three‐Component Reactions

AbstractCarbon dioxide is a harmful greenhouse gas, as well as a valuable resource. Here, a three‐component cyclization reaction was developed for the synthesis of oxazolidine‐2,4‐diones by immobilizing CO2 under the electrochemistry and copper catalyst. Propargyl amide was used as the reaction substrate to capture carbon dioxide to produce carboxyl anion, while selenide produced electrophilic receptor to activate the triple bond under electrochemical conditions. Then, intramolecular cyclization reaction was carried out to obtain the target product. Through this environmentally friendly strategy, a series of important oxazolidine‐2,4‐diones was synthesized.