Multistep Reaction Research Articles

Improving the Sensitivity of a Multiplexed Digital Immunoassay Based on Extremely High Bead Analysis Efficiency.

The development of a detection methodology with high sensitivity, stability, and user-friendliness for quantification of proteins at subfemtogram levels is essential for clinical applications such as early screening, disease diagnosis, and monitoring disease progression. A traditional micropartition-based digital enzyme-linked immunosorbent assay (dELISA) results in significant bead loss due to intricate partitioning based on Poisson distribution, multistep reaction operations, nonglobal signal recognition, and reading modes, which have not yet achieved the ultimate detection sensitivity. This study introduces an ultrasensitive multiplexed digital immunoassay with extremely high bead analysis efficiency (HiBeA) through integrating the bead transfer strategy in multistep immunoreaction processing and flow cytometry detection mode. Typically, a bead analysis ratio over 95% was achieved, ensuring high sensitivity, efficiency, and stability of the established HiBeA using as few as only 5,000 beads. As a proof of concept, HiBeA was utilized for the multiplexed detection of IL-10 and IL-6, achieving detection limits of 5.9 and 8.8 fg/mL, respectively. This signifies a 3- to 4-fold enhancement in detection sensitivity under the same reaction time while using only 1% of the assay bead number compared to the commercial single-molecule array (SiMoA) system. HiBeA presents ultrasensitivity, robust detection stability based on tailored, multistep operation of immune-reaction, and the ability to perform multiplexed detection, thereby offering substantial prospects for the advancement of ultrasensitive clinical diagnostics.

Breaking linear scaling relationships in oxygen evolution via dynamic structural regulation of active sites

The universal linear scaling relationships between the adsorption energies of reactive intermediates limit the performance of catalysts in multi-step catalytic reactions. Here, we show how these scaling relationships can be circumvented in electrochemical oxygen evolution reaction by dynamic structural regulation of active sites. We construct a model Ni-Fe2 molecular catalyst via in situ electrochemical activation, which is able to deliver a notable intrinsic oxygen evolution reaction activity. Theoretical calculations and electrokinetic studies reveal that the dynamic evolution of Ni-adsorbate coordination driven by intramolecular proton transfer can effectively alter the electronic structure of the adjacent Fe active centre during the catalytic cycle. This dynamic dual-site cooperation simultaneously lowers the free energy change associated with O–H bond cleavage and O–O bond formation, thereby disrupting the inherent scaling relationship in oxygen evolution reaction. The present study not only advances the development of molecular water oxidation catalysts, but also provides an unconventional paradigm for breaking the linear scaling relationships in multi-intermediates involved catalysis.

Bimetallic active sites with tailored d-bands boost multistep sulfur redox reactions for enhanced lithium-sulfur battery performance

Bimetallic active sites with tailored d-bands boost multistep sulfur redox reactions for enhanced lithium-sulfur battery performance

Triazole Drives Hole Localization and Superoxide Radical Formation for Enhancive Photocatalytic Cascade Isomerization/C─C Bond Scission of Biomass to Lactic Acid.

Chemocatalytic synthesis of lactic acid (LA) from biomass sugars involves heat-absorbing multistep cascade reactions mediated by different active sites, often encountering unsatisfactory selectivity. Here, a hole-localized carbon nitride-based photocatalyst (C-CNN) is constructed by covalent binding of heptazine and triazole skeleton via C─N bonds and further conjugated interaction with activated carbon, achieving the complete conversion of various biomass sugars to LA (up to 98.6% selectivity) at room temperature for 2h. The introduced triazole electron donor in C-CNN can not only enhance the adsorption of sugar for the enhanced aldose-to-ketose isomerization over the localized hole (Lewis acid) on the triazole skeleton, but also modulate the valence band oxidation to circumvent the formation of •OH but only •O2 ‒ for selective C3‒C4 cleavage of ketose, thus realizing the exclusive synthesis of LA. Moreover, near-infrared light absorption endowed by activated carbon can supply sufficient interface photothermal effect for ambient LA production. Life cycle assessment shows that the photocatalytic system has good prospects for industrialization in terms of both energy and environment. This work offers novel insights into the multidirectional utilization of solar energy for the value-added conversion of biomass through rational modulation of photothermal active sites.

Dual Pathways of Photorelease Carbon Monoxide via Photosensitization for Tumor Treatment.

Carbon monoxide (CO) gas therapy, as an emerging therapeutic strategy, is promising in tumor treatment. However, the development of a red or near-infrared light-driven efficient CO release strategy is still challenging due to the limited physicochemical characteristics of the photoactivated carbon monoxide-releasing molecules (photoCORMs). Here, we discovered a novel photorelease CO mechanism that involved dual pathways of CO release via photosensitization. Specifically, the photosensitizer Chlorin e6 (Ce6) sensitized oxygen to produce singlet oxygen (1O2) and oxidized photoCORM Mn2(CO)10 to release CO in an air-saturated solvent under red light (655 nm, 50 mW/cm2) irradiation. Furthermore, Ce6 and Mn2(CO)10 could undergo multistep photochemical reactions to release CO, as well as the degradation of the photosensitizer Ce6 in an oxygen-depleted solution. As a proof of concept, we demonstrated the feasibility and tumor inhibition of this CO release strategy both in vitro and in vivo. These results provide a robust platform for the development of new approaches to CO-mediated modulation of signaling pathways and further facilitate the practical use of gas therapeutic methods in tumor therapy in vivo.

Building Localized NADP(H) Recycling Circuits to Advance Enzyme Cascadetronics.

The catalytic action of enzymes of a cascade trapped within a mesoporous electrode material is simultaneously energized, controlled and observed through the efficient, reversible electrochemical NAD(P)(H) recycling catalyzed by one of the enzymes. In their nanoconfined state, nicotinamide cofactors are tightly channeled current carriers, mediating multi-step reactions in either direction (oxidation or reduction) with a rapid response time. By incorporating a hydrogen‑borrowing enzyme pair, the internal action of which opposes the external voltage bias driving oxidation or reduction, a reduction process can be performed under overall oxidizing conditions, and vice versa. The power of the method to control and resolve complex metabolic pathways is demonstrated using a non-linear, three-enzyme cascade extended by incorporating a fourth enzyme, urease. The latter generates in situ ammonia, which is enzymatically consumed in a reductive process, but the immediate current response to each addition of urea is observed, unusually, by applying an oxidizing potential. A practical consequence is that enzyme-catalyzed electrochemical reduction reactions requiring anaerobic conditions (to avoid O2 interference) can readily be studied under ambient aerobic conditions. The results illustrate how a complex enzyme cascade confined within a porous electrode and connected to an electrical power source manifests characteristics associated with electronic circuits.

COFcap2, a recyclable tandem catalysis reactor for nitrogen fixation and conversion to chiral amines

Two or more catalysts conducting multistep reactions in the same reactor, concurrent tandem catalysis, could enable (bio)pharmaceutical and fine chemical manufacturing to become much more sustainable. Herein we report that co-immobilization of metal nanoparticles and a biocatalytic system within a synthetic covalent organic framework capsule, COFcap-2, functions like an artificial cell in that, whereas the catalysts are trapped within 300-400 nm cavities, substrates/products can ingress/egress through ca. 2 nm windows. The COFcap-2 reactor is first coated onto an electrode surface and then used to prepare eleven homochiral amines using dinitrogen as a feedstock. The amines, including drug product intermediates and active pharmaceutical ingredient, are prepared in >99% enantiomeric excess under ambient conditions in water. Importantly, the COFcap-2 system is recycled 15 times with retention of performance, addressing the relative instability and poor recyclability of enzymes that has hindered their broad implementation for energy-efficient, low waste production of chemicals and (bio)pharmaceuticals.

Direct Synthesis of Unprotected C-Glycosides via Photoredox Activation of Glycosyl Ester.

Synthetic C-glycosides play a crucial role in molecular biology and medicine. With the surge of interest in C-glycosides and the demand to provide efforts with sufficient feedstock, it is highly significant to pursue novel methodologies to access C-glycosides in a concise and efficient manner. Here, we disclose an attractive strategy that diverges itself from conventional multistep reaction sequences involving the manipulations of protecting groups. Widely available native sugars first react with 1,4-dihydropyridine acids via a site-selective Mitsunobu reaction, converting them into bench-stable radical precursors. Under visible-light-enabled photoredox catalysis conditions, the resulting glycosyl radicals undergo C-C bond formation reactions, yielding a variety of C-glycosides with excellent stereoselectivity. Our method demonstrates good tolerance to a wide range of functional groups and has been successfully applied in the post-transformation of drug molecules and the preparation of C-glycosyl amino acids.

Fully Exposed Ru Clusters for the Efficient Multi-Step Toluene Hydrogenation Reaction.

Liquid organic hydrogen carriers (LOHCs) are attractive platform molecules that play an important role in hydrogen energy storage and utilization. The multi-step hydrogenation of toluene (TOL) to methylcyclohexane (MCH) has been widely studied in the LOCHs systems, due to their relatively low toxicity and reasonable hydrogen storage capacity. Noble metal catalysts such as Ru has exhibited good performance in multi-step hydrogenation reactions, while the application is still hindered by their high cost and low specific activity. Therefore, the primary challenge lies in the development of noble metal catalysts with both robust activity and efficient atomic utilization. In this study, a series of Ru species ranging from single atoms, fully exposed clusters to nanoparticles were fabricated to investigate their structural evolution in the TOL multi-step hydrogenation reaction. The fully exposed and atomically dispersed Ru clusters, composed of an average of 3 Ru atoms, exhibit superior catalytic performance and recycle ability in TOL multi-step hydrogenation. Moreover, it delivers a high turnover frequency of 9850.3 h-1 under the relatively mild reaction (100 °C, 1.5 MPa), compared with those of single atoms and nanoparticles, and shows a notable advantage over catalysts reported in previous studies. From density functional theory (DFT) calculations, the overall barrier of the TOL multi-step hydrogenation reaction over the fully exposed Ru clusters is significantly lower than that of single atoms and nanoparticles, resulting in its higher activity. The present work provides an efficient strategy to regulate the reaction pathway of multi-step complicated catalytic reactions by designing fully exposed metal cluster catalysts.

Overcoming Energy-Scaling Barriers: Efficient Ammonia Electrosynthesis on High-Entropy Alloy Catalysts.

Electrochemically converting nitrate (NO3 -) to value-added ammonia (NH3) is a complex process involving an eight-electron transfer and numerous intermediates, presenting a significant challenge for optimization. A multi-elemental synergy strategy to regulate the local electronic structure at the atomic level is proposed, creating a broad adsorption energy landscape in high-entropy alloy (HEA) catalysts. This approach enables optimal adsorption and desorption of various intermediates, effectively overcoming energy-scaling limitations for efficient NH3 electrosynthesis. The HEA catalyst achieved a high Faradaic efficiency of 94.5±4.3% and a yield rate of 10.2±0.5mg h-1 mgcat -1. It also demonstrated remarkable stability over 250 h in an integrated three-chamber device, coupling electrocatalysis with an ammonia recovery unit for continuous NH3 collection. This work elucidates the catalytic mechanisms of multi-functional HEA systems and offers new perspectives for optimizing multi-step reactions by circumventing adsorption-energy scaling limitations.

Efficient amine-assisted CO2 hydrogenation to methanol co-catalyzed by metallic and oxidized sites within ruthenium clusters

Amine-assisted two-step CO2 hydrogenation is an efficient route for methanol production. To maximize the overall catalytic performance, both the N-formylation of amine with CO2 (i.e., first step) and the subsequent amide hydrogenation (i.e., second step) are required to be optimized. Herein, a class of Al2O3-supported Ru catalysts, featuring multiple activated Ru species (i.e., metallic and oxidized Ru), are rationally fabricated. Density functional theory calculations suggest that metallic Ru forms are preferred for N-formylation step, whereas oxidized Ru species demonstrate enhanced amide hydrogenation activity. Thus, the optimal catalyst, containing unique Ru clusters with coexisting metallic and oxidized Ru species, efficiently synergize the conversion of CO2 into methanol with exceptional selectivity (>95%) in a one-pot two-step process. This work not only presents an advanced catalyst for CO2-based methanol production but also highlights the strategic design of catalysts with multiple active species for optimizing the catalytic performances of multistep reactions in the future.

Understanding the Ligand Influence in the Multistep Reaction of Diazoalkanes with Palladium Complexes Leading to Carbene-Aryl Coupling.

The reaction of diphosphino aryl complexes [Pd(C6F5)(L-L)(NCMe)](BF4) (L-L = dppe, dppp, dppb) with diazoalkanes N2CHR (R = -CH=CHPh, Ph) leads to η3-allyl or η3-benzyl palladium derivatives that are the organometallic products resulting from carbene-aryl coupling. The experimental trend shows that the reaction is favored for dppe > dppp > dppb. It involves several consecutive steps, i.e., diazoalkane coordination, nitrogen extrusion to give a Pd-carbene, and migratory insertion, which are experimentally inseparable, but they can be studied with the help of DFT calculations. The bulkiness and bite angle of the ligand exert a large influence in the relative rate of the steps involved in the reaction, and we have found that carbene formation by N2 extrusion is the step with the largest barrier for dppe. In contrast, the coordination of the diazoalkane is the most energy-demanding step for the larger dppp and dppb diphosphines. Thus, ligand substitution controls the rate, an important elemental step rarely considered in mechanistic studies of carbene cross coupling reactions. Since diazoalkanes are the most common carbene precursors, either directly or generated from hydrazones, the choice of ligand can be very important to facilitate the entrance of the carbene precursor in the catalytic cycle.

Precisely designing asymmetrical selenium-based dual-atom sites for efficient oxygen reduction

Owing to their synergistic interactions, dual-atom catalysts (DACs) with well-defined active sites are attracting increasing attention. However, more experimental research and theoretical investigations are needed to further construct explicit dual-atom sites and understand the synergy that facilitates multistep catalytic reactions. Herein, we precisely design a series of asymmetric selenium-based dual-atom catalysts that comprise heteronuclear SeN2–MN2 (M = Fe, Mn, Co, Ni, Cu, Mo, etc.) active sites for the efficient oxygen reduction reaction (ORR). Spectroscopic characterisation and theoretical calculations revealed that heteronuclear selenium atoms can efficiently polarise the charge distribution of other metal atoms through short-range regulation. In addition, compared with the Se or Fe single-atom sites, the SeFe dual-atom sites facilitate a reduction in the conversion energy barrier from *O to *OH via the coadsorption of *O intermediates. Among these designed selenium-based dual-atom catalysts, selenium-iron dual-atom catalysts achieves superior alkaline ORR performance, with a half-wave potential of 0.926 V vs. a reversible hydrogen electrode. In addition, the SeN2–FeN2-based Zn–air battery has a high specific capacity (764.8 mAh g−1) and a maximum power density (287.2 mW cm−2). This work may provide a good perspective for designing heteronuclear DACs to improve ORR efficiency.

Efficient synthesis of highly substituted benzoselenazole derivatives through the one-pot, multi-step Ullmann coupling reaction

Efficient synthesis of highly substituted benzoselenazole derivatives through the one-pot, multi-step Ullmann coupling reaction

General access to furan-substituted gem-difluoroalkenes enabled by PFTB-promoted cross-coupling of ene-yne-ketones and difluorocarbene.

Replacement of a carbonyl group with fluorinated bioisostere (e.g., CF2[double bond, length as m-dash]C) has been adopted as a key tactical strategy in drug design and development, which typically improves potency and modulates lipophilicity while maintaining biological activity. Consequently, new gem-difluoroalkenation reactions have undoubtedly accelerated this shift, and conceptually innovative practices would be of great benefit to medicinal chemists. Here we describe an expeditous protocol for the direct assembly of furan-substituted gem-difluoroalkenes via PFTB-promoted cross-coupling of ene-yne-ketones and difluorocarbene. In this multi-step tandem reaction process, the furan ring and the gem-difluorovinyl group are constructed simultaneously in an efficient manner. These products can serve as bioisosteres of the α-carbonyl furan core, which is an important scaffold present in natural products and drug candidates. The broad generality and practicality of this method for late-stage modification of bioactive molecules, gram-scale synthesis and versatile derivatisation of products has been described. Biological activity evaluation showed that the gem-difluoroalkene skeleton exhibited dramatic antitumor activity.

Complete kinetic and photochemical characterization of the multi-step photochromic reaction of donor-acceptor Stenhouse adducts.

Donor-acceptor Stenhouse adducts (DASA) are negative photochromic compounds exhibiting a multi-step photoisomerization mechanism. Previous studies have described a first photoactivated step, followed by a thermally controlled one. This study emphasizes the key role of the intermediate species, using high-rate acquisition photokinetic absorption spectroscopy. We have investigated the multi-step processes at different temperatures and irradiation power values. For the first time, we have combined our experimental setup with a three-species photokinetic model to determine the kinetic constants and quantum yields of each step of a DASA compound. Finally, we have identified the key role of the intermediate species, showing that double irradiation experiments allow the tuning of the photochromic reaction.

Accuracy of kinetic parameters in multiple methods for separating multi-step thermal degradation reactions of biomass into single-step reactions

Accuracy of kinetic parameters in multiple methods for separating multi-step thermal degradation reactions of biomass into single-step reactions

‘It just feels like it's gonna be so very long?’ Exploring the resources used by university students in noticing, navigating, and resolving issues during math-intensive problem solving in chemistry

Problem solving is a complex endeavour that requires students to understand concepts and procedures, as well as knowing when and how to apply them effectively. This study is part of a broader research project examining how university students engage with math-intensive problem solving in chemistry. Here, we focus specifically on the cognitive resources students use to notice, navigate, and resolve potential obstacles. We observed student pairs as they worked collaboratively on a task in chemical kinetics that involved deriving a rate law for a multi-step reaction. Through qualitative analysis of their discussions, we identified three categories of resources: implicit models, episodic memories, and standard procedures. Our findings suggest that implicit models and episodic memories play a key role in helping students navigate uncertainty by shaping their expectations, pointing to a connection between these resources and situational knowledge—a type of knowledge that is critical in enhancing students’ strategic flexibility and refining their intuitions. Overall, this work aims to provide insight into the role of intuitive reasoning in problem solving, emphasising the importance of integrating conceptual, procedural, and situational knowledge. It also opens up opportunities to help students foster expert-like problem-solving skills through directed learning activities that actively engage them in using and reflecting on these knowledge types and how these connect to their own intuitions.

Multienzyme Cascade Catalyzed Skeleton Rearrangement in a Caged Polyketide Biosynthesis.

Rearrangement of the skeleton is crucial for improving the structural complexity and diversity of type II polyketide natural products. In this study, we investigated the rearrangement process from a planar aromatic tetracyclic intermediate to the caged lactones, which is managed by five oxidoreductases. We chemically synthesized the proposed linear tetracyclic substrate, validated the transformation process through in vivo and in vitro experiments, and elucidated the enzyme-catalyzed mechanism using isotope labeling. Significantly, a short-chain dehydrogenase TjhD5 was discovered to play a multifunctional role for multistep reactions.

Improved Methods for the Synthesis of B10H14 and N-Heterocycle-Coordinated B9H13 (N-Het·B9H13).

Improved methods for the synthesis of B10H14 and a series of N-heterocycle-coordinated B9H13 complexes (N-Het·B9H13) have been developed with readily obtained KB11H14 as the starting material. Oxidation of KB11H14 could provide B10H14 in over 90% yield. Then, the N-Het·B9H13 complexes were prepared from the as-synthesized B10H14 through in situ multistep reactions by reacting with NaH, N-heterocycles, and dilute hydrochloric acid. Among these N-Het·B9H13 complexes, 4-(triphenylvinyl)pyridine-coordinated B9H13 (1k) exhibits a significant aggregation-induced emission (AIE) effect in a THF/H2O mixed solution, and 8-aminoisoquinoline-coordinated B9H13 (2p) exhibits a positive solvatochromism phenomenon. These improved methods provide new approaches to synthesizing B10H14 and N-Het·B9H13 complexes with potential applications in luminescent materials.