Covalent Reaction Research Articles

Non-Invasive Ultra-Sensitive Detection of Breast Cancer Biomarker using Cerium Nanoparticle Functionalized Graphene Oxide enabled Impedimetric Aptasensor

Epidermal growth factor receptor (EGFR) is a transmembrane protein and a key biomarker implicated in the pathogenesis of breast cancer. Early and precise detection of EGFR is crucial for effective diagnosis, prognosis, and therapeutic intervention. However, conventional EGFR detection techniques, such as biopsy and immunohistochemistry, are often invasive, time-consuming, and limited in sensitivity, highlighting the demand for non-invasive, highly sensitive detection methods. In this study, we fabricated a cerium oxide (CeO₂) and graphene oxide (GO) nanocomposite-based aptasensor for the non-invasive detection of EGFR using electrochemical impedance spectroscopy (EIS). The CeO₂-GO nanocomposite was synthesized via the sol-gel method and characterized through UV-Vis spectroscopy, FTIR, TEM, and XRD, confirming the crystalline structure of hexagonal CeO₂ nanoparticles on amorphous GO sheets. The nanocomposite was functionalized with aptamers specific to EGFR using covalent coupling reactions. The EIS analysis of the fabricated aptasensor (GCE/CeO₂-GO/EGFR-Apt/BSA) demonstrated a wide linear detection range from 10 fg mL-1 to 100 ng mL-1, with an ultralow detection limit of 1.87 fg mL-1 in PBS, 3.16 fg mL-1 in serum, 5.31 fg mL-1 in sweat, and 6.14 fg mL-1 in saliva samples. These results highlight the aptasensor’s high sensitivity, specificity, and potential for real-time, non-invasive EGFR monitoring in clinical samples such as serum, sweat, and saliva. This approach would facilitate early detection of cancer and personalized diagnostics in point-of-care settings.

Advanced Vitrimer with Spiropyran Beads: A Multi-Responsive, Shape Memory, Self-Healing, and Reprocessable Smart Material.

Thermosetting materials have limitations in terms of reshaping and recycling due to their irreversible bond structures, leading to significant plastic waste issues. Recently, epoxy vitrimers based on dynamic covalent bond exchange have been introduced as promising alternatives to traditional thermosets. Particularly, they demonstrate significant potential applications in the field of multi-responsive materials. In this research, a self-healable and mechano-responsive vitrimer (EB-V) is successfully prepared, incorporating epoxide spiropyran beads (ESP beads) derived from citric acid and epoxy derivatives. To enable self-reporting of cracks through color changes, ESP beads are covalently bonded to the vitrimer via an epoxy-carboxylic acid reaction. The photochromic properties of EB-V are demonstrated by color and fluorescence changes, and its tensile strength increased from 2.0 to 6.8MPa compared to the control sample. Dynamic mechanical analysis confirmed the covalent exchange reaction of the vitrimer, revealing its reconfigurable behavior and stress relaxation at elevated temperatures. Furthermore, EB-V exhibited exceptional properties, including self-healing and reprocessability. As a smart material, it holds great promise for a wide range of applications, such as sensors, actuators, 4D printing, and industrial safety diagnostics.

Multiple covalent modification enables nylon fiber biosensor with robust scrub-resistant and signal-capture ability for multiscenario health monitoring and security warning

Nylon fibers have great potentials in smart textiles due to excellent wear resistance, resilience, and chemical stability, whereas poor combination between fibers and conductive materials causes discontinuous signal capture. In this work, nylon fibers/di-aldehyde cellulose nanocrystals/polypyrrole (NFACP) biosensors with robust scrub-resistant and signal-capture ability were fabricated by interfacial multiple covalent reactions. The best NFACP0.2 biosensor exhibited high conductivity (354 S/m), robust mechanical strength and stretching-releasing dynamic durability. Especially, its textile sensors still possessed high sensitivity and excellent sensing performance after repeated washing and friction. Moreover, NFACP0.2 biosensor was designed into various multifunctional health monitoring and security warning systems for “stress reducing exercise” enthusiasts, high-altitude activities, and deep-sea exploration, demonstating great potentials of conductive nylon fiber biosensor in flexible electronics.

Preparation of attapulgite nanoparticles modified polypropylene adsorption membrane and its application in small molecular pollutant adsorption

In this study, a novel surface covalent reaction method was used to modify attapulgite nanoparticles on the surface of polypropylene adsorption membrane to adsorb various small molecular pollutants for the first time. The surface covalent reaction method has the advantage of step control. Therefore, the uniformity and stability of attapulgite nanoparticles can be ensured, and then could effectively improve the adsorption performance of polypropylene adsorption membrane. On the other hand, compared with various materials modified on the surface of polypropylene adsorption membrane currently, attapulgite nanoparticles has the characteristics of low cost and environmental friendliness, which is more conducive to the large-scale practical application. The polypropylene adsorption membrane modified with attapulgite nanoparticles was characterized by field emission scanning electron microscopy, fourier transform infrared spectrometer and X-ray diffractograph, and it was confirmed that the attapulgite nanoparticles was successfully modified on the surface of the polypropylene adsorption membrane. The experimental results showed that the adsorption capacities of polypropylene adsorption membrane modified with attapulgite nanoparticles could reach 11.53 mg/g, 8.7 mg/g and 5.78 mg/g for cyromazine, malachite green and dagenan respectively within 10 s. In the case of the above three analytes, the minimum detected concentration could reach 0.02 mg/mL, and the relative standard deviation was about 10 %. At the same time, the adsorption performance of polypropylene adsorption membrane modified with attapulgite nanoparticles did not decrease significantly after 50 cycles. A standard recovery of 76.8 % − 89.5 % and a relative standard deviation of 7.2 % − 15.2 % were obtained by using the polypropylene adsorption membrane modified with attapulgite nanoparticles to adsorb cyromazine in cucumber skin samples, indicating that the polypropylene adsorption membrane modified with attapulgite nanoparticles has the ability to treat complex samples.

Prominent Neuroprotective Potential of Indole-2-N-methylpropargylamine: High Affinity and Irreversible Inhibition Efficiency towards Monoamine Oxidase B Revealed by Computational Scaffold Analysis

Background: Monoamine oxidases (MAO) are flavoenzymes that metabolize a range of brain neurotransmitters, whose dysregulation is closely associated with the development of various neurological disorders. This is why MAOs have been the central target in pharmacological interventions for neurodegeneration for more than 60 years. Still, existing drugs only address symptoms and not the cause of the disease, which underlines the need to develop more efficient inhibitors without adverse effects. Methods: Our drug design strategy relied on docking 25 organic scaffolds to MAO-B, which were extracted from the ChEMBL20 database with the highest cumulative counts of unique member compounds and bioactivity assays. The most promising candidates were substituted with the inactivating propargylamine group, while further affinity adjustment was made by its N-methylation. A total of 46 propargylamines were submitted to the docking and molecular dynamics simulations, while the best binders underwent mechanistic DFT analysis that confirmed the hydride abstraction mechanism of the covalent inhibition reaction. Results: We identified indole-2-propargylamine 4fH and indole-2-N-methylpropargylamine 4fMe as superior MAO-B binders over the clinical drugs rasagiline and selegiline. DFT calculations highlighted 4fMe as more potent over selegiline, evident in a reduced kinetic requirement (ΔΔG‡ = −2.5 kcal mol−1) and an improved reaction exergonicity (ΔΔGR = −4.3 kcal mol−1), together with its higher binding affinity, consistently determined by docking (ΔΔGBIND = −0.1 kcal mol−1) and MM-PBSA analysis (ΔΔGBIND = −1.5 kcal mol−1). Conclusions: Our findings strongly advocate 4fMe as an excellent drug candidate, whose synthesis and biological evaluation are highly recommended. Also, our results reveal the structural determinants that influenced the affinity and inhibition rates that should cooperate when designing further MAO inhibitors, which are of utmost significance and urgency with the increasing prevalence of brain diseases.

Unraveling the role of peanut protein in baijiu-peanut pairing flavor complexity: A focus on ethanol-induced denaturation

Food processing, cooking, and consumption introduce various factors that affect food flavor, distinguishing it from its objective composition. This study focuses on liquor-accompanying food pairing, investigating the interaction between baijiu aroma compounds and peanut proteins, and the effect of ethanol on it. Peanut globulins significantly inhibited the release of baijiu aroma compounds through hydrogen bonding (2.63–3.23 Å), hydrophobic interactions, and covalent reactions (−2.85 to −5.64 kcal/mol), resulting in flavor modification. In the presence of ethanol, peanut globulins adopt a more compact and aggregated structure, reducing their affinity for binding aroma compounds. Surprisingly, this structural change promotes a salting-out effect, significantly promoting the release of aldehydes, phenols, and aromatic compounds, enhancing the grassy, floral, and sweet aroma of baijiu. This finding improves the understanding of alcohol pairing and proposes a novel strategy for enhancing the overall flavor profile of baijiu by modifying accompanying food choices.

Mutualistic Synthesis from Orthogonal Dynamic Covalent Reactions

AbstractMutualisms are interactions that benefit all species involved. It has been widely investigated in neighbouring subjects, such as biology, ecology, sociology, and economics. However, such a reciprocal relationship in synthetic chemical systems has rarely been studied. Here, we demonstrate a mutualistic synthesis where byproducts from two orthogonal chemical reactions aid each other′s production. Disulfide exchange and hydrazone exchange were chosen to generate two dynamic combinatorial libraries. A minor tetrameric macrocycle from the active disulfide library was quantitatively amplified in the presence of the hydrazone library. This incorporation also turned on the previously inert hydrazone reaction, producing a linear species that formed a “handcuffs” catenane with the disulfide tetramer. These findings not only lend robust support to the hypothesis of “RNA‐peptide coevolution” for the origin of life but also broaden the scope of synthetic chemistry, highlighting the untapped potential of minor products from different reactions. Additionally, the co‐self‐assembly of these mutualistic entities to form supramolecular structures opens new avenues for future development of composite nanosystems with synergistic properties.

Protein-phenolic interactions and reactions: Discrepancies, challenges, and opportunities.

Although noncovalent interactions and covalent reactions between phenolic compounds and proteins have been investigated across diverse scientific disciplines, a comprehensive understanding and identification of their products remain elusive. This review will initially outline the chemical framework and, subsequently, delve into unresolved or debated chemical and functional food-related implications, as well as forthcoming challenges in this topic. The primary objective is to elucidate the multiple aspects of protein-phenolic interactions and reactions, along with the underlying overwhelming dynamics and possibilities of follow-up reactions and potential crosslinking between proteins and phenolic compounds. The resulting products are challenging to identify and characterize analytically, as interactions and reactions occur concurrently, mutually influencing each other. Moreover, they are being modulated by various conditions such as the reaction parameters and, obviously, the chemical structure. Additionally, this review delineates the resulting discrepancies and challenges of properties and attributes such as color, taste, foaming, emulsion and gel formation, as well as effects on protein digestibility and allergenicity. Ultimately, this review is an opinion paper of a group of experts, dealing with these challenges for quite a while and aiming at equipping researchers with a critical and systematic approach to address current research gaps concerning protein-phenolic interactions and reactions.

Cover Picture: Mutualistic Synthesis from Orthogonal Dynamic Covalent Reactions (Angew. Chem. Int. Ed. 44/2024)

Cover Picture: Mutualistic Synthesis from Orthogonal Dynamic Covalent Reactions (Angew. Chem. Int. Ed. 44/2024)

Titelbild: Mutualistic Synthesis from Orthogonal Dynamic Covalent Reactions (Angew. Chem. 44/2024)

Titelbild: Mutualistic Synthesis from Orthogonal Dynamic Covalent Reactions (Angew. Chem. 44/2024)

From the TOP: Formation, recognition and resolution of topoisomerase DNA protein crosslinks

Since the report of “DNA untwisting” activity in 1972, ∼50 years of research has revealed seven topoisomerases in humans (TOP1, TOP1mt, TOP2α, TOP2β, TOP3α, TOP3β and Spo11). These conserved regulators of DNA topology catalyze controlled breakage to the DNA backbone to relieve the torsional stress that accumulates during essential DNA transactions including DNA replication, transcription, and DNA repair. Each topoisomerase-catalyzed reaction involves the formation of a topoisomerase cleavage complex (TOPcc), a covalent protein-DNA reaction intermediate formed between the DNA phosphodiester backbone and a topoisomerase catalytic tyrosine residue. A variety of perturbations to topoisomerase reaction cycles can trigger failure of the enzyme to re-ligate the broken DNA strand(s), thereby generating topoisomerase DNA-protein crosslinks (TOP-DPC). TOP-DPCs pose unique threats to genomic integrity. These complex lesions are comprised of structurally diverse protein components covalently linked to genomic DNA, which are bulky DNA adducts that can directly impact progression of the transcription and DNA replication apparatus. A variety of genome maintenance pathways have evolved to recognize and resolve TOP-DPCs. Eukaryotic cells harbor tyrosyl DNA phosphodiesterases (TDPs) that directly reverse 3′-phosphotyrosyl (TDP1) and 5′-phoshotyrosyl (TDP2) protein-DNA linkages. The broad specificity Mre11-Rad50-Nbs1 and APE2 nucleases are also critical for mitigating topoisomerase-generated DNA damage. These DNA-protein crosslink metabolizing enzymes are further enabled by proteolytic degradation, with the proteasome, Spartan, GCNA, Ddi2, and FAM111A proteases implicated thus far. Strategies to target, unfold, and degrade the protein component of TOP-DPCs have evolved as well. Here we survey mechanisms for addressing Topoisomerase 1 (TOP1) and Topoisomerase 2 (TOP2) DPCs, highlighting systems for which molecular structure information has illuminated function of these critical DNA damage response pathways.

Synthesis of Adhesive Polyrotaxanes Through Sequential Self-Assembly via Supramolecular Interactions and Dynamic Covalent Interactions.

Self-assembly is an effective approach to construct complicated structures. Polyrotaxanes (PRs) as one of the typical polymer types with complex structure, own interlocked structures and dynamic components, in which it results in unique characteristics and functions. Currently, the synthesis of which involves covalent reactions to hinder the development of polyrotaxanes. Herein, we employed supramolecular interactions as well as dynamic covalent bonds to synthesize PRs by sequential self-assembly. First, we prepared M1 possessing two diamine structures and M2 of a bisammonium salt with two dibenzylammonium (DBA) units modified by two stoppers at its ends, then M1 and M2 self-assembled into supramolecular polymers stemming from hydrogen bonding of [N+-H ⋅ ⋅ ⋅ O] under high concentrations. After adding 2,6-pyridinedicarboxaldehyde (M3), the imine bond formation enabled the generation of macrocycles, transforming supramolecular polymers into PRs. Besides, the solution of polyrotaxanes was applied as the adhesive for diverse hard and soft materials. This strategy provides an important approach for synthesizing PRs, accelerating the advances of mechanically interlocked polymers.

Ultrasensitive Electrochemical Sensor for Catecholamine Detection Using Stable Covalent pH Sensitive Thin Films

Electrochemical detection of catecholamine neurotransmitters has been widely studied and possess lots of potential for the onsite analysis. Electrochemical sensors, however, have limitations that are due to strong interfering species that exist in the same sample matrix as the analyte of interest. In addition, the stability of the fabricated electrochemical sensor is important for reusability and reproducibility. Our research group activities have focused on fabricating stable thin films of electrocatalysts (phthalocyanines) and their graphene conjugates using covalent coupling reactions and electrografting method. The formed thin films exhibited excellent stability, electroanalytical and electrocatalytic properties. The flexible structural modification of phthalocyanines allowed for the incorporation of pH sensitive functional group and different metal ions for electrocatalysis. The use of pH sensitive electrocatalysts is a step away from using insulating and negatively charged polymers for screening interferents. The evaluation of modified electrodes were conducted in the negative and positively charged redox systems, such as [Fe(CN)6]3-/4- and [Ru(NH3)6]2+/3+. Excellent electrocatalytic properties were obtained and the electrodes could detect the neurotransmitters selectively and screen-off ascorbic acid, uric acid using the solution pH.

Mutualistic Synthesis from Orthogonal Dynamic Covalent Reactions.

Mutualisms are interactions that benefit all species involved. It has been widely investigated in neighbouring subjects, such as biology, ecology, sociology, and economics. However, such a reciprocal relationship in synthetic chemical systems has rarely been studied. Here, we demonstrate a mutualistic synthesis where byproducts from two orthogonal chemical reactions aid each other's production. Disulfide exchange and hydrazone exchange were chosen to generate two dynamic combinatorial libraries. A minor tetrameric macrocycle from the active disulfide library was quantitatively amplified in the presence of the hydrazone library. This incorporation also turned on the previously inert hydrazone reaction, producing a linear species that formed a "handcuffs" catenane with the disulfide tetramer. These findings not only lend robust support to the hypothesis of "RNA-peptide coevolution" for the origin of life but also broaden the scope of synthetic chemistry, highlighting the untapped potential of minor products from different reactions. Additionally, the co-self-assembly of these mutualistic entities to form supramolecular structures opens new avenues for future development of composite nanosystems with synergistic properties.

Fluoromethylketone-Fragment Conjugates Designed as Covalent Modifiers of EcDsbA are Atypical Substrates.

Disulfide bond protein A (DsbA) is an oxidoreductase enzyme that catalyzes the formation of disulfide bonds in Gram-negative bacteria. In Escherichia coli, DsbA (EcDsbA) is essential for bacterial virulence, thus inhibitors have the potential to act as antivirulence agents. A fragment-based screen was conducted against EcDsbA and herein we describe the development of a series of compounds based on a phenylthiophene hit identified from the screen. A novel thiol reactive and "clickable" ethynylfluoromethylketone was designed for reaction with azide-functionalized fragments to enable rapid and versatile attachment to a range of fragments. The resulting fluoromethylketone conjugates showed selectivity for reaction with the active site thiol of EcDsbA, however unexpectedly, turnover of the covalent adduct was observed. A mechanism for this turnover was investigated and proposed which may have wider ramifications for covalent reactions with dithiol-disulfide oxidoreducatases.

A portable and versatile fluorescent platform for high-throughput screening of toxic phosgene, diethyl chlorophosphate and volatile acyl chlorides

Highly toxic phosgene, diethyl chlorophosphate (DCP) and volatile acyl chlorides endanger our life and public security. To achieve facile sensing and discrimination of multiple target analytes, herein, we presented a single fluorescent probe (BDP-CHD) for high-throughput screening of phosgene, DCP and volatile acyl chlorides. The probe underwent a covalent cascade reaction with phosgene to form boron dipyrromethene (BODIPY) with bright green fluorescence. By contrast, DCP, diphosgene and acyl chlorides can covalently assembled with the probe, giving rise to strong blue fluorescence. The probe has demonstrated high-throughput detection capability, high sensitivity, fast response (within 3 s) and parts per trillion (ppt) level detection limit. Furthermore, a portable platform based on BDP-CHD was constructed, which has achieved high-throughput discrimination of 16 analytes through linear discriminant analysis (LDA). Moreover, a smartphone adaptable RGB recognition pattern was established for the quantitative detection of multi-analytes. Therefore, this portable fluorescence sensing platform can serve as a versatile tool for rapid and high-throughput detection of toxic phosgene, DCP and volatile acyl chlorides. The proposed “one for more” strategy simplifies multi-target discrimination procedures and holds great promise for various sensing applications.

Hyaluronic Acid/Chondroitin Sulfate-Based Dynamic Thiol-Aldehyde Addition Hydrogel: An Injectable, Self-Healing, On-Demand Dissolution Wound Dressing.

Frequent removal and reapplication of wound dressings can cause mechanical disruption to the healing process and significant physical discomfort for patients. In response to this challenge, a dynamic covalent hydrogel has been developed to advance wound care strategies. This system comprises aldehyde functionalized chondroitin sulfate (CS-CHO) and thiolated hyaluronic acid (HA-SH), with the distinct ability to form in situ via thiol-aldehyde addition and dissolve on-demand via the thiol-hemithioacetal exchange reaction. Although rarely reported, the dynamic covalent reaction of thiol-aldehyde addition holds great promise for the preparation of dynamic hydrogels due to its rapid reaction kinetics and easy reversible dissociation. The thiol-aldehyde addition chemistry provides the hydrogel system with highly desirable characteristics of rapid gelation (within seconds), self-healing, and on-demand dissolution (within 30 min). The mechanical and dissolution properties of the hydrogel can be easily tuned by utilizing CS-CHO materials of different aldehyde functional group contents. The chemical structure, rheology, self-healing, swelling profile, degradation rate, and cell biocompatibility of the hydrogels are characterized. The hydrogel possesses excellent biocompatibility and proves to be significant in promoting cell proliferation in vitro when compared to a commercial hydrogel (HyStem® Cell Culture Scaffold Kit). This study introduces the simple fabrication of a new dynamic hydrogel system that can serve as an ideal platform for biomedical applications, particularly in wound care treatments as an on-demand dissolvable wound dressing.

Electronic Effect Driven Specific and Sensitive Recognition toward GHB.

Precise detection of a trace substance that intrinsically possesses weak chemical activity and less-distinctive spatial structure is of great significance, but full of challenges, as it could not be effectively recognized via either an active covalent reaction process or multiple noncovalent interactions toward its simple structure. Here, the electronic-effect-driven recognition strategy was proposed to visually sense an illicit drug, γ-hydroxybutyric acid (GHB), which was treated as an analyte model due to its inherent simple structure. In particular, a sensing system composed of two probes substituted by the nitro (-NO2) and the hydrogen (-H), was constructed with the characteristic yellow coloring and blue fluorescence, as well as high sensitivity (0.586 ng/mL), fast response (0.2 s), and specific recognition, even in the presence of 22 interferents. In addition, a portable eyeshadow box-like sensing chip was fabricated and proven to be reliable and feasible in sensing GHB disguised in liquors for self-protection in a covert manner. Hence, this work developed an electronic-effect-driven modulation strategy of the recognition interaction between the probe and the analyte and, thus, would open up a new thought for detecting the analyte with weak activity and a simple structure, as well as propel the relevant application in real scenarios.

Porous Crystalline Organic Cages Made by Design

AbstractShape‐persistent organic cages are an intriguing class of molecular porous materials. Through hierarchical molecular design, size and shape of the intrinsic molecular voids are controlled by dynamic covalent chemistry, while pore structure and topology are governed by noncovalent alignment in the solid state. However, the predictable and reliable crystallization of organic cages is still challenging since long‐range superstructures are solely based on weak and rather unidirectional supramolecular interactions. In this tutorial review, we provide a general classification of porous solid‐state materials and discuss specific design principles regarding the dynamic covalent reactions, the small‐molecule building blocks and solid‐state engineering. Furthermore, we introduce the most important analytical techniques for porous materials with a special focus on organic cages.

Optimized Functionalization of Graphene Oxide for Enhanced Mechanical Properties in Epoxy Resin Composites

Optimized Functionalization of Graphene Oxide for Enhanced Mechanical Properties in Epoxy Resin Composites