Substrate Reaction Research Articles

On the Horsley’s test for morphine

In the Horsley test for morphine, to a hot solution of morphine acetate silver nitrate solution is added. Metallic silver is separated and the filtrate is coloured blood-red by nitric acid. In this communication the reactivity of both reagent and substrate was checked and commented. The first reaction is nucleophilic attack of nitrate anion to the carbonyl group of the ester, forming acetyl nitrate and a phenoxide ion. The electrodotic property of the last ion originates a secondary carbanion at C-2. This unstable intermediate cedes an electron to an Ag+ forming metallic silver and a free radical in the morphine molecule which is stabilised by coupling with another similar species, forming 2,2’-bimorphine.

Improving the Long-term Enantioselectivity of a Silicon-Carbon Bond-Forming Enzyme.

Enantioselectivity is a key advantage of enzymatic catalysis. Understanding the most important factors influencing enantioselectivity necessitates thorough investigation for each specific enzyme. In this study, we explore various approaches to optimize reaction conditions for organosilicon production using an immobilized Cytochrome C recently tailored via directed evolution. Over extended reactions, this enzyme experiences a loss of enantioselectivity. Mass spectrometry (MS) revealed covalent modifications on the enzyme, but mutating the respective amino acids did not restore enantioselectivity. Nuclear magnetic resonance (NMR), along with a detailed comparison of the influence of reaction components such as cosolvents and reducing agents, indicated significant conformational changes in the presence of the diazo ester substrate. Additionally, we identified sodium ascorbate as a suitable and milder reducing agent compared to the previously used sodium dithionite, ensuring anaerobic conditions for silicon-carbon bond formation. Ultimately, maintaining a high enzyme-to-substrate ratio in the reaction was found to be crucial for achieving high enantiomeric purity of the organosilicon product over four days in sequential, repetitive batch reactions, thus improving the previously established reaction system. The methods and findings presented here are particularly valuable for addressing enantioselectivity issues in other enzymes that operate with diazo compounds as the substrates in carbene-transfer reactions.

Synergistically Enhanced Co-Adsorption of Reactant and Hydroxyl on Platinum-Modified Copper Oxide for High-Performance HMF Oxidation.

Electrochemical oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) provides an environmentally friendly route for producing the sustainable polymer monomer 2,5-furandicarboxylic acid (FDCA). Thus, precisely adjusting the synergistic adsorption among key reactive species, such as HMF and OHads, on the carefully designed catalyst surface is essential for achieving satisfactory catalytic performance for HMF oxidation to FDCA as it is closely related to the adsorption strength and configuration of the reaction substrates. This kind of regulation will ultimately facilitate the improvement of HMF oxidation performance. In this work, Pt nanoparticles modified CuO nanowires (denoted as Pt/CuO@CF) are constructed for the selective electrooxidation of HMF to FDCA under alkaline conditions. The well-designed Pt/CuO@CF demonstrates highly impressive catalytic performance across a range of HMF concentrations, ranging from the commonly used concentrations to higher levels typically not explored (10, 25, 50, 75, and 100mm) with high FEFDCA (all above 95%) and outstanding long-term stability (15 cycles). In situ experimental characterizations confirm that the designed heterogeneous interface between Pt and CuO enhances the enrichment of HMF and OHads species on the catalyst surface. Theoretical calculations reveal the anchored Pt nanoparticles reduce the adsorption barrier for HMF and OHads, thereby promoting the highly selective oxidation of HMF to FDCA.

Diels-Alder Cycloaddition of Cyclopentadiene to C60 and Si60 and Their Endohedral Li+ Counterparts.

Both silicon and carbon are elements located in group 14 on the periodic table. Despite some similarities between these two elements, differences in reactivity are important, and whereas carbon is a central element in all known forms of life, silicon is barely found in biological systems. Here, we investigate the Diels-Alder cycloaddition reaction of cyclopentadiene (CP) and cyclopentasildiene (CPSi) with fullerenes C60, Li+@C60, Si60, and Li+@Si60 using density functional theory methods. The results reveal distinct kinetic and thermodynamic trends that govern the reactivity and selectivity. For C60, the [6,6] pathway is kinetically and thermodynamically favored, whereas for Si60, the [5,6] pathway is preferred thermodynamically but not kinetically. The introduction of lithium cations increases the reactivity of both C60 and Si60. Energy decomposition analysis (EDA) unveils the importance of the components of the interaction energy between CPSi and the corresponding fullerenes. The findings provide insights into the interplay of electronic structure, substrate reactivity, and fullerene electrophilicity in cycloaddition reactions.

Rational Design of Nanozymes for Engineered Cascade Catalytic Cancer Therapy.

Nanozymes have shown significant potential in cancer catalytic therapy by strategically catalyzing tumor-associated substances and metabolites into toxic reactive oxygen species (ROS) in situ, thereby inducing oxidative stress and promoting cancer cell death. However, within the complex tumor microenvironment (TME), the rational design of nanozymes and factors like activity, reaction substrates, and the TME itself significantly influence the efficiency of ROS generation. To address these limitations, recent research has focused on exploring the factors that affect activity and developing nanozyme-based cascade catalytic systems, which can trigger two or more cascade catalytic processes within tumors, thereby producing more therapeutic substances and achieving efficient and stable cancer therapy with minimal side effects. This area has shown remarkable progress. This Perspective provides a comprehensive overview of nanozymes, covering their classification and fundamentals. The regulation of nanozyme activity and efficient strategies of rational design are discussed in detail. Furthermore, representative paradigms for the successful construction of cascade catalytic systems for cancer treatment are summarized with a focus on revealing the underlying catalytic mechanisms. Finally, we address the current challenges and future prospects for the development of nanozyme-based cascade catalytic systems in biomedical applications.

Electrochemical Oxidative Carbonylation/Coupling Reaction Using Anode to Oxidize the Trasition‐Metal‐Catalyst and Substrate

We reported an electrochemical oxidative carbonylation of N‐phenylpyridin‐2‐amine derivatives under mild condtions without an external oxidant. Our approach demonstrated a novel electrochemical oxidative carbonylation reaction mode in which the simultaneous reaction of catalyst and substrate with the anode has been developed. Furthermore, an electrochemical C‐H activation for the synthesis of cyclized pyridinium ion has also been realized. Mechanistic investigations suggested that the process involved a “PdII/PdIII/PdI/PdII” catalytic cycle, and H2 was generated at the cathode.

Construction, characterization and application of rutin loaded zein - Carboxymethyl starch sodium nanoparticles.

In this paper, zein-carboxymethyl starch (CMS) nanoparticles were prepared by antisolvent precipitation method to improve the stability of rutin (RT). The encapsulation efficiency, loading capacity, oxidation resistance, structural properties were evaluated. The results showed that electrostatic, hydrogen bond and hydrophobic interaction were the main driving forces for the formation of nanoparticles. The size and PDI of all prepared zein -RT-CMS nanoparticles were <190 nm and 0.3, respectively, and the zeta-potential was about -25 mV. When zein /RT/CMS was 1:0.02:3, the maximum encapsulation rate of nanoparticles reached 86.2 %. The constructed stabilized RT significantly improved the antioxidant activity of free RT, and the antioxidant activity of RT was up to 88 %. In addition, a high temperature and low humidity simulation system with asparagine/glucose as the reaction substrate was established to study the inhibitory effect of zein- RT- CMS carrier on the production of acrylamide. The results showed that the zein-CMS carrier could improve the thermal stability of RT and inhibit the formation rate of acrylamide in thermal processing. When zein /RT/CMS was 1:0.02:3, the inhibition rate of acrylamide could reach 33.51 %, thus reducing acrylamide formation in thermal processing.

Mining and characterization of new enzymes based on Phi29 DNA polymerase

In recent years, the bacteriophage Φ29 (Phi29) DNA polymerase has garnered increasing attention due to its high-fidelity amplification capacity at constant temperatures. To advance the industrial application of this type of isothermal polymerases, this study mined and characterized new enzymes from the microbial metagenome based on the known Phi29 DNA polymerase sequence. The results revealed that a new enzyme, Php29 DNA polymerase, was identified in the microbial metagenome with plants as the hosts. This enzyme exhibited higher strand displacement activity, with a 59.5% similarity to bacteriophage Φ29. Experimental validation demonstrated that the enzyme had 3'→5' exonuclease activity, and its amplification products can serve as substrates for further catalytic reactions. The discovery and validation of Php29 DNA polymerase gives insights into the future industrial application of isothermal polymerases.

Pneumatic conveying inkjet bioprinting for the processing of living cells

Inkjet printing techniques are often used for bioprinting purposes because of their excellent printing characteristics, such as high cell viability and low apoptotic rate, contactlessmodus operandi, commercial availability, and low cost. However, they face some disadvantages, such as the use of bioinks of low viscosity, cell damage due to shear stress caused by drop ejection and jetting velocity, as well as a narrow range of available bioinks that still challenge the inkjet printing technology. New technological solutions are required to overcome these obstacles. Pneumatic conveying printing, a new type of inkjet-based printing technique, was applied for the bioprinting of both acellular and cellular fibrin-hydrogel droplets. Drops of a bioink containing 6 × 106HEK293H cells ml-1were supplied from a sterile nozzle connected to a syringe pump and deposited on a gas stream on a fibrinogen-coated glass slide, here referred to as biopaper. Fibrinogen film is the substrate of the polymerization reaction with thrombin and Ca2+present in the bioink. The pneumatic conveying printing technique operates on a mechanism by which drop ejection and deposition in a stream of gas occurs. The percentage of unprinted and printed dead HEK293H cells was 5 ± 2% and 7 ± 4%, respectively. Thus, compared to normal handling, pneumatic conveying printing causes only little damage to the cells. The velocity of the drop approaching the biopaper surface is below 0.2 m s-1and does not cause any damage to the cells. The cell viability of printed cells was 93%, being an excellent value for inkjet printing technology. The HEK293H cells exhibited approximately a 24 h lag time of proliferation that was preceded by intense migration and aggregation. Control experiments proved that the cell migration and lag time were associated with the chemical nature of the fibrin hydrogel and not with cell stress.

A Versatile Self‐Templating Approach for Constructing Ternary Halide Perovskite Heterojunctions to Achieve Concurrent Enhancement in Photocatalytic CO2 Reduction Activity and Stability

AbstractMetal halide perovskite (MHP)‐based photocatalysts encounter significant stability challenges in water‐containing systems, posing a major obstacle to their application in artificial photosynthesis. Herein, an innovative and universal strategy is present to create MHP‐based ternary heterojunctions based on a self‐templating method. A series of composite catalysts featuring sandwich hollow structures are constructed, with MHPs such as CsPbBr3, Cs3Bi2I9, Cs3Sb2Br9, and Cs2AgBiBr6 serving as the intermediate layers. The unique sandwich structure effectively shields MHPs from direct water contact, allowing MHP‐based photocatalysts to exhibit exceptional stability in water‐containing photocatalytic environments for durations exceeding 200 h. Furthermore, the hollow design ensures complete contact between the reaction substrates with both the oxidation and reduction functional areas. Compared to single perovskite materials, MHP‐based ternary heterojunction photocatalysts exhibit stronger oxidation capability and improved charge separation efficiency, leading to a substantial enhancement in photocatalytic CO2 reduction performance. Notably, the ternary heterojunction with CsPbBr3 as the intermediate layer achieves an electron consumption rate of up to 1824 µmol g−1 h−1 for CO2 reduction, which is far superior to other reported MHP‐based catalysts under similar conditions. This study provides a potent strategy for simultaneously enhancing the stability and activity of MHP‐based photocatalysts, paving the way for their potential applications in artificial photosynthesis.

Conformational flexibility of human ribokinase captured in seven crystal structures.

d-ribose is a critical sugar substrate involved in the biosynthesis of nucleotides, amino acids, and cofactors, with its phosphorylation to ribose-5-phosphate by ribokinase (RK) constituting the initial step in its metabolism. RK is conserved across all domains of life, and its activity is significantly enhanced by monovalent metal (M+) ions, particularly K+, although the precise mechanism of this activation remains unclear. In this study, we present several crystal structures of human RK in both unliganded and substrate-bound states, offering detailed insights into its substrate binding process, reaction mechanism, and conformational changes throughout the catalytic cycle. Notably, bound ATP exhibited significant conformational flexibility in its triphosphate moiety, a feature shared with other RK homologues, suggesting that achieving a catalytically productive triphosphate configuration plays a key role in regulating enzyme activity. We also identified a unique conformational change in the M+ ion binding loop of human RK, specifically the flipping of the Gly306-Thr307 peptide plane, likely influenced by the ionic radius of the bound ion. These findings provide new insights into the RK reaction mechanism and its activation by M+ ions, paving the way for future investigations into the allosteric regulation of human RK and related sugar kinase enzymes.

Synthesis of chiral alcohol (S)-CHBE by co-immobilization of double enzymes based on organic-inorganic hybrid nanoflower.

The chiral alcohols (S)-4-chloro-3-hydroxy-butyric acid ethyl ester ((S)-CHBE) is a critical intermediate in the synthesis of various active pharmaceutical ingredients. This study presents the first investigation of the efficient production of (S)-CHBE using organic-inorganic hybrid nanoflowers (GDH-CR@HNFs) for the co-immobilization of glucose dehydrogenase (BsGDH) and carbonyl reductase (BsCR). By optimizing immobilization conditions, we significantly enhanced the catalytic activity and immobilization efficiency of the hybrid nanoflowers. The GDH-CR@HNFs exhibited superior catalytic performance compared to the free dual enzyme system, demonstrating a higher affinity for the substrate COBE (47-fold lower Km value), increased maximum reaction rate (Vmax), and improved catalytic efficiency (Kcat/Km). Additionally, the GDH-CR@HNFs displayed enhanced temperature adaptability, pH stability, and storage stability. The GDH-CR@HNFs retained over 60% of their initial catalytic activity after 8cycles of reuse. The hydrophobic nature of the substrate COBE can lead to substrate inhibition of the free enzyme. However, GDH-CR@HNFs exhibited excellent substrate tolerance, maintaining a high conversion rate (65%) even at a substrate concentration of 200mM, significantly outperforming the free enzyme system (13.8% conversion rate). The hybrid nanoflower co-immobilization strategy offers a novel approach to addressing substrate and product inhibition issues in enzyme-catalyzed reactions, paving the way for the industrial production scale of (S)-CHBE.

Understanding Substrate Binding and Reactivity of Stearoyl-CoA Desaturase (SCD1) through Classical and Multiscale Molecular Dynamics Simulations

Understanding Substrate Binding and Reactivity of Stearoyl-CoA Desaturase (SCD1) through Classical and Multiscale Molecular Dynamics Simulations

Theoretical study of the in situ formation of H2O2 by lytic polysaccharide monooxygenases: the reaction mechanism depends on the type of reductant.

Lytic polysaccharide monooxygenases (LPMOs) are a unique group of monocopper enzymes that exhibit remarkable ability to catalyze the oxidative cleavage of recalcitrant carbohydrate substrates, such as cellulose and chitin, by utilizing O2 or H2O2 as the oxygen source. One of the key challenges in understanding the catalytic mechanism of LPMOs lies in deciphering how they activate dioxygen using diverse reductants. To shed light on this intricate process, we conducted in-depth investigations using quantum mechanical/molecular mechanical (QM/MM) metadynamics simulations, molecular dynamics (MD) simulations, and density functional theory (DFT) calculations. Specifically, our study focuses on elucidating the in situ formation mechanism of H2O2 by LPMOs in the presence of cellobiose dehydrogenase (CDH), a proposed natural reductant of LPMOs. Our findings reveal a proton-coupled electron transfer (PCET) process in generating the Cu(ii)-hydroperoxide intermediate from the Cu(ii)-superoxide intermediate. Subsequently, a direct proton transfer to the proximal oxygen of Cu(ii)-hydroperoxide results in the formation of H2O2 and LPMO-Cu(ii). Notably, this mechanism significantly differs from the LPMO/ascorbate system, where two hydrogen atom transfer reactions are responsible for generating H2O2 and LPMO-Cu(i). Based on our simulations, we propose a catalytic mechanism of LPMO in the presence of CDH and the polysaccharide substrate, which involves competitive binding of the substrate and CDH to the reduced LPMOs. While the CDH-bound LPMOs can activate dioxygen to generate H2O2, the substrate-bound LPMOs can employ the H2O2 generated from the LPMO/CDH system to perform the peroxygenase reactions of the polysaccharide substrate. Our work not only provides valuable insights into the reductant-dependent mechanisms of O2 activation in LPMOs but also holds implications for understanding the functions of these enzymes in their natural environment.

Direct Knitting of Pincer Palladium Complexes into Hyper-Crosslinked Polymers for Superior Catalytic Performance in Suzuki-Miyaura Reactions.

Using a direct knitting strategy, we successfully prepared a novel heterogeneous catalyst consisting of pyridine-bridged bis(imidazolium-2-ylidene) palladium complexes (CNC-Pd) embedded in a knitted network polymer. The resulting catalysts (HCP-CNC-Pd-d) exhibited high specific surface areas of 982 m2 g-1 with microporous and mesoporous structures. The large surface area enhances contact between the substrate and the catalytic center, while the strong chelation between CNC and the metal ion ensures the catalyst's durability. The HCP-CNC-Pd-d catalysts exhibited superior performance, achieving an impressive 99 % yield in the Suzuki coupling reaction between bromobenzene and phenylboronic acid. The catalyst also demonstrated good performance across a range of substrates in the Suzuki-Miyaura coupling reactions. Furthermore, the catalyst could be recycled for over 10 cycles without any significant loss in activity and selectivity. This highly cost-effective and convenient approach provides valuable insights into the design and application of heterogeneous catalysts in various fields.

Structure and catalytic activity of the SAM-utilizing ribozyme SAMURI.

Ribozymes that catalyze site-specific RNA modification have recently gained increasing interest for their ability to mimic methyltransferase enzymes and for their application to install molecular tags. Recently, we reported SAMURI as a site-specific alkyltransferase ribozyme using S-adenosylmethionine (SAM) or a stabilized analog to transfer a methyl or propargyl group to N3 of an adenosine. Here, we report the crystal structures of SAMURI in the postcatalytic state. The structures reveal a three-helix junction with the catalytic core folded into four stacked layers, harboring the cofactor and the modified nucleotide. Detailed structure-activity analyses explain the cofactor scope and the structural basis for site selectivity. A structural comparison of SAMURI with SAM riboswitches sheds light on how the synthetic ribozyme overcomes the strategies of natural riboswitches to avoid self-methylation. Our results suggest that SAM and its analogs may serve as substrates for various RNA-catalyzed reactions, for which the corresponding ribozymes remain to be identified.

Amide-Directed Highly Enantioselective Hydrogenation of Diverse Acyclic Multisubstituted Alkenes Under Mild Conditions.

Enantioselective hydrogenation of tetrasubstituted alkenes to form 1,2-contiguous stereocenters is a particularly appealing but highly challenging transformation in asymmetric catalysis. Despite the notable progress achieved in enantioselective hydrogenation over the past decades, enantioselective hydrogenation of all-carbon tetrasubstituted alkenes containing multiple alkyl groups remains an unsolved challenge. Here, we report a rhodium-catalyzed highly diastereo- and enantioselective hydrogenation of diverse acyclic multisubstituted alkenes under mild conditions. The coordination assistance of the amide group to the metal center generates a highly active catalyst that effectively overcomes the low reactivity of substrates and precisely controls the stereoselectivity. The generality of this catalyst system is exemplified by its efficacy across at least three types of alkenes including β,γ-unsaturated amides, α,β-unsaturated amides, and enamides.

The Effect of Accessibility of Insoluble Substrate on the Overall Kinetics of Enzymatic Degradation

ABSTRACTThe enzymatic reaction kinetics on cellulose and other solid substrates is limited by the access of the enzyme to the reactive substrate sites. We introduce a general model in which the reaction rate is determined by the active surface area, and the resulting kinetics consequently reflects the evolving relationship between the exposed substrate surface and the remaining substrate volume. Two factors influencing the overall surface‐to‐volume ratio are considered: the shape of the substrate particles, characterized by a single numerical parameter related to its dimensionality, and the distribution of the particle sizes. The model is formulated in a form of simple analytical equations, enabling fast and efficient application to experimental data, and facilitating its incorporation into more detailed and complex models. The application of the introduced formalism exploring its potential to account for the observed reaction rate is demonstrated on two examples: the derivation of particle size distribution from experimentally determined reaction kinetics, and the prediction of reaction slowdown from experimental particle size distribution.

Knoevenagel-IMHDA and -IMSDA sequences for the synthesis of chiral condensed O,N-, S,N- and N-heterocycles.

Domino Knoevenagel-cyclization reactions of styrene substrates, containing an N-(ortho-formyl)aryl subunit, were carried out with N-substituted 2-cyanoacetamides to prepare tetrahydro-4H-pyrano[3,4-c]quinolone and hexahydrobenzo[j]phenanthridine derivatives by competing IMHDA and IMSDA cyclization, respectively. The diastereoselective IMHDA step with α,β-unsaturated amide, thioamide, ester and ketone subunits as a heterodiene produced condensed chiral tetrahydropyran or thiopyran derivatives, which in the case of Meldrum's acid were reacted further with amine nucleophiles in a multistep domino sequence. In order to simplify the benzene-condensed tricyclic core of the targets and get access to hexahydro-1H-pyrano[3,4-c]pyridine derivatives, a truncated substrate was reacted with cyclic and acyclic active methylene reagents in diastereoselective Knoevenagel-IMHDA reactions to prepare novel condensed heterocyclic scaffolds. The chemo-, regio- and diastereoselectivity of the cyclization step were investigated and structural elucidation was aided by single crystal X-ray analysis.

A review on conversions of Furfural: Gateway for numerous applications

Due to highly functionalized molecular structure, furfural has made a huge impact in renewable platforms. As there is a big need of producing renewable sources, this review reveals several attempts made by researchers distributed in every nook and corner of the world to produce furfural-based derivatives. As furfurals are converted to various forms, they reflect many applications both with respect to economy and environment friendly approach. In this review, a summarized detail of various reactions of furfural substrates are provided which includes Diels-Alder reactions, Oxidations, Hydrogenations, Hydrogenolysis, Conversions to C6 Carboxylic acids, Furfuryl amines, Cyclopentenones and other useful compounds. These compounds and their applications in various fields are mentioned systematically. The chemical as well as biocatalytic conversions are explained in detail which will help to know the future challenges and hurdles when design and optimization of furfural derivatives are concerned.