Reaction Cycle Research Articles

Enzymatic Synthesis of Bioactive Structured DHA Phospholipids via Stable Immobilized Phospholipase-Catalyzed Esterification in a Solvent-Free Medium

The enzymatic esterification of docosahexaenoic acid (DHA) with glycerophosphocholine (GPC) was investigated to produce bioactive structured DHA phospholipids with DHA esterified at the sn-2 position, which may contribute to the prevention of neurodegenerative diseases such as Alzheimer’s. This reaction is complex due to the low solubility of GPC in anhydrous organic media and the limited stability of enzymes under such conditions. The immobilized phospholipase Quara® LowP (QlowP-C18) proved to be the most effective catalyst, achieving a 58% yield of di-substituted DHA phospholipids (Di-DHA-PC) in just 48 h under optimal conditions (solvent-free media at 60 °C) with 95% purity. Advanced immobilization and post-immobilization techniques significantly improved the stability of QlowP-C18, increasing its longevity threefold and enabling reuse for up to five reaction cycles at 40 °C. The total production reached 120.4 mg of highly pure DHA-di-substituted phospholipid. These findings highlight the effectiveness of stable immobilized enzymes in solvent-free systems and underscore their potential for the efficient and sustainable production of highly pure Di-DHA-PC, which could be used as a functional or nutraceutical ingredient for the prevention of neurodegenerative diseases.

Establishment and Application of a Rapid Detection Method of Cyprinid Herpesvirus 2 (CyHV-2) in Aquacultural Waters by Using a Novel One-Pot RAA-CRISPR/Cas12a Combined With Fe-Iron Flocculation Technology.

Cyprinid herpesvirus 2 (CyHV-2) poses a substantial global threat to goldfish (Carassius auratus) and crucian carp (Carassius carassius). Despite the development of several sensitive molecular diagnostic techniques, there is an ongoing demand for alternative visualisation platforms to streamline the workflow, enhance safety profiles, and improve accessibility for end-users. In this study, we have integrated recombinase-aided amplification (RAA) technology with the CRISPR/Cas12a system to establish a rapid diagnostic system for CyHV-2, termed one-pot RAA-CRISPR/Cas12a. This method enables the results of detection within 60 min. The RAA-CRISPR/Cas12a platform is capable of detecting as few as 10 copies of CyHV-2 per reaction cycle without exhibiting cross-reactivity with other pathogens. The positive detection rate in clinical samples exceeds that of conventional PCR approaches, underscoring its high precision. Furthermore, the method could be used in conjunction with iron flocculation for the concentration and detection of viruses within aquaculture settings. This approach minimises the dissection of aquatic organisms, thereby maximising animal welfare and bolstering detection efficiency. Collectively, our findings validate the RAA-CRISPR/Cas12a method as a robust, specific, confirmatory, user-friendly and promising approach for on-site diagnosis of CyHV-2.

Recycling the recyclers: strategies for the immobilisation of a PET-degrading cutinase.

Enzymatic degradation of polyethylene terephthalate (PET) represents a sustainable approach to reducing plastic waste and protecting fossil resources. The cost efficiency of enzymatic PET degradation processes could be substantially improved by reusing the enzymes. However, conventional immobilisation strategies, such as binding to porous carriers, are challenging as the immobilised enzyme can only interact with the macromolecular solid PET substrate to a limited extent, thus reducing the degradation efficiency. To mitigate this challenge, this work compared different immobilisation strategies of the PET-degrading cutinase ICCGDAQI. Immobilisation approaches included enzyme fixation via linkers to carriers, the synthesis of cross-linked enzyme aggregates with different porosities, and immobilisation on stimulus-responsive polymers. The highest degradation efficiencies were obtained with the pH-responsive material Kollicoat®, where 80% of the initial enzyme activity could be recovered after immobilisation. Degradation of textile PET fibres by the cutinase-Kollicoat® immobilisate was investigated in batch reactions on a 1 L-scale. In three consecutive reaction cycles, the product yield of the released terephthalic acid exceeded 97% in less than 14h. Even in the fifth cycle, 78% of the maximum yield was achieved in the same reaction time. An advantage of this process is the efficient pH-dependent recovery of the immobilisate after the reaction, which integrates seamlessly into the terephthalic acid recovery by lowering the pH after hydrolysis. This integration therefore not only simplifies the downstream processing, but also provides a cost-effective and resource-efficient solution for both enzyme reuse and product separation after PET degradation, making it a promising approach for industrial application.

Alkylation of Aniline with Benzyl Alcohol by Using Ni/O‐Clay: Kinetic Studies

AbstractThis study investigates the alkylation of aniline using benzyl alcohol over a Ni (30)/O‐clay catalyst, focusing on optimizing reaction conditions and understanding the reaction kinetics. The catalyst demonstrated 70% conversion of aniline with 75% selectivity toward benzylideneaniline (BDA) at 343 K in a 6‐hour reaction time. Catalyst characterization was performed using BET, NH3‐TPD, XRD, and FE‐SEM techniques, revealing a mesoporous structure with strong and medium acidic sites that enhance catalytic activity. Key parameters influencing the reaction, including temperature, molar ratio, catalyst loading, oxidants, and solvents, were systematically investigated. The Weisz‐Prater criterion confirmed the absence of mass transfer resistance, and kinetic studies validated the Langmuir‐Hinshelwood‐Hougen‐Watson (LHHW) mechanism. The activation energy was calculated and found to be 37 kcal/mol. The Ni (30)/O‐clay catalyst exhibited excellent reusability, maintaining activity and selectivity up to four reaction cycles. This work highlights the potential of Ni‐organoclay catalyst for green, cost‐effective synthesis of alkylated aniline derivatives, paving the way for sustainable and efficient industrial processes. The results emphasize the importance of heterogeneous catalysts in enhancing selectivity and minimizing by‐products in environmentally friendly chemical transformations.

Fluted pumpkin waste potential as a green solid bioalkaline catalyst for neem seed oil biodiesel synthesis

Developing green routes for biodiesel synthesis is essential for sustaining environmental benignity. Thus, this present study investigated the development of a solid catalyst using fluted pumpkin (Telfairia occidentalis) pod husk as a bio-based raw material via high-temperature furnace heating, ranging from 300 – 1000 oC. The catalyst properties were investigated by conducting surface functional group, surface crystallinity, surface area, and pore distribution analyses. The efficacy of the synthesized catalyst was investigated using 28 randomized experiments carried out on transesterification of esterified neem oil, which established 12:1, 3.5 wt.%, and 60 min as optimal conditions for methanol/neem oil ratio, catalyst dosage, and reaction time, respectively, with a maximum neem seed oil methyl esters (NSOME) yield of 96.71% through response surface methodology. The statistical assessment of the developed model gave a correlation coefficient (R) of 0.9907 and a coefficient determination of 0.9816 (R2). The physicochemical properties of the NSOME agree with American and European standard limits, making it suitable for transportation and energy purposes. The catalyst could be deployed for three reaction cycles with high turnover frequencies. Hence, fluted pumpkin waste and neem oil are suitable as a green route for biodiesel synthesis.

Turning waste into wealth: Enzyme-activated DNA sensor based on reactant recycle for spatially selective imaging microRNA toward target cells.

Amplified imaging of microRNA (miRNA) in cancer cells is essential for understanding of the underlying pathological process. Synthetic catalytic DNA circuits represent pivotal tools for miRNA imaging. However, most existing catalytic DNA circuits can not achieve the reactant recycling operation in cells and in vivo. Additionally, specificity miRNA imaging in tumor site also is a challenge. Herein, inspired by "turning waste into wealth", we report a DNA sensor for imaging of miRNA in target cells based on apurinic/apyrimidinic endonuclease 1 (APE1)-activated reactant recycling catalytic DNA circuit. The sensing function of the DNA sensor is suppressed firstly through engineering an apurinic/apyrimidinic (AP) site. In the presence of APE1, the AP site undergoes hydrolysis, thereby activating sensing activity and triggering the strand displacement reaction (SDR) under miRNA assistance. In this catalytic DNA circuit, the next reaction cycle can be initiated when the duplex strand waste products are reverted into active components, which allows it to be performed continuously just consuming fuel DNA without depleting the reactant. Noteworthy, the liposome plays important role in overcome biological barriers for nucleic acid delivery. The amplified miRNA imaging strategy is carried out in vivo by this DNA sensor with reducing off-tumor signal under assistance with APE1, and enhances tumor-to-normal tissue contrast compared with traditional catalytic DNA circuit. Firstly, APE1-activated reactant recycling catalytic DNA circuit is developed. Secondly, miRNA image in cell and in animal is achieved with high spatial selectivity. Thirdly, the signal-to-background ratio for imaging is improved in vitro and in vivo. Lastly, our strategy provides an automatic yet versatile approach for the development of more efficient and selective DNA circuits capable of differentiating miRNA in cancer cells from those in normal cells, promising to be valuable in cancer diagnosis.

A Novel Reusable Polymer Supported Palladium Catalyst for HeckReaction

With the rapid development of “green” chemistry; researchers are highly interested towards more sustainable approaches and prefer to choose eco-friendly synthetic routes and materials. This paper deals with the development of a novel reusable heterogeneous palladium catalyst for Heck reaction. The catalyst (mPAN-Pd) was developed by a simple procedure via synthetic modification of polyacrylonitrile (PAN) with monoethanolamine (MEA) followed by complexation with palladium chloride (PdCl2). After detailed characteristic studies, the catalytic efficiency of mPAN-Pd in Heck coupling reaction was systematically evaluated and optimised the reaction condition through a set of experiments. This heterogeneous catalytic system was found be applicable over a series of aryl halides and terminal alkenes leading to corresponding coupling products in good yields. Furthermore, this catalyst offers easy recyclability by simple filtration and reused for at least 5 cycles of Heck reaction without losing much of its activity.

Forced Dynamic Operation of Propylene Selective Oxidation to Acrolein on Bismuth-Molybdate Structured Catalysts

Forced dynamic operation (FDO) of selective oxidation of propylene to acrolein is evaluated on a structured alumina foam coated with a mixed metal oxide catalyst (bismuth molybdate-based). Reactor experiments examine feed composition modulation as a strategy to increase the yield of acrolein. At lower temperatures, separating the oxidant (O2) and reductant (C3H6) enhances propylene conversion and acrolein selectivity. Variation in the reaction-regeneration switching amplitude and frequency gives a 40% higher cycle-averaged acrolein yield compared to steady-state operation (SSO) for the same overall feed composition. The results suggest that FDO maintains a higher concentration of selective oxygen species during the propylene feed, while pre-oxidation of the catalyst maximizes the amount of selective oxygen species, leading to increased acrolein yield at the beginning of the reaction cycle. Experiments at lower temperature for both commercial promoted and in-house, unpromoted catalysts reveal both catalysts are most active and selective at their highest oxidation states.

Loop engineering of enzymes to control their immobilization and ultimately fabricate more efficient heterogeneous biocatalysts.

Enzyme immobilization is indispensable for enhancing enzyme performance in various industrial applications. Typically, enzymes require specific spatial arrangements for optimal functionality, underscoring the importance of correct orientation. Despite well-known N- or C-terminus tailoring techniques, alternatives for achieving orientation control are limited. Here, we propose a novel approach that tailors the enzyme surface with engineered His-rich loops. To that aim, we first solve the X-ray crystal structure of a hexameric alcohol dehydrogenase from Thermus thermophilus HB27 (TtHBDH) (PDB: 9FBD). Guided by this 3D structure, we engineer the enzyme surface with a new loop enriched with six His residues to control enzyme orientation. Molecular dynamics simulations reveal that the engineered loop's imidazole rings have greater solvent accessibility than those in native His residues, allowing for more efficient enzyme immobilization on certain metal chelate-functionalized carriers. Using carriers functionalized with iron (III)-catechol, the apparent Vmax of the immobilized loop variant doubles the immobilized His-tagged one, and vice versa when both variants are immobilized on carriers functionalized with copper (II)-imidodiacetic acid. His-tagged and loop-engineered TtHBDH show high operational stability reaching 100% bioconversion after 10 reaction cycles, yet the loop variant is faster than the His-tagged one.

Dual recycling signal amplification strategy based on autocatalytic entropy-driven circuit and DNAzyme for colorimetric detection of platelet-derived growth factor-BB.

Platelet-derived growth factor-BB (PDGF-BB), an important protein biomarker, is closely associated with tumorigenesis. Therefore, it is important to develop a simple and sensitive method to detect PDGF-BB. Herein, we developed a dual recycling signal amplification strategy for colorimetric and sensitive detection of PDGF-BB using a PDGF-BB specific aptamer. In the presence of PDGF-BB, the first entropy-driven circuit (EDC) reaction cycle was triggered for colorimetric signal amplification. Meanwhile, a catalytic Mg2+-dependent DNAzyme was formed on one side of the EDC product, which could cleave its substrate and generate numerous "mimic trigger" DNA products. Then, an autocatalytic EDC (AEDC) reaction was triggered by the "mimic trigger" DNA, and the signal amplification efficiency of this colorimetric assay was significantly improved. This AEDC- and DNAzyme-based colorimetric assay showed a good linear range from 5.0 to 100 nM for PDGF-BB and the limit of detection was calculated to be 2.2 nM. In addition, PDGF-BB has been quantitatively detected in human serum samples. This colorimetric assay can be easily extended to detect different protein biomarkers by using other recognition elements (aptamers) and shows great potential for clinical diagnosis and prognosis.

Immobilisation of zero-valent silver-decorated jujube activated carbon (Ag0/JAC) on polyester fabric for catalytic reduction of 4-nitrophenol

ABSTRACT Heterogeneous catalytic technology is highly effective for pollutant degradation, but achieving recyclability remains a critical challenge. In this study, a recyclable Ag/AC photocatalyst coating was developed on polyester fabric using a dip-coating method, where polyester fabric served as a support due to its adaptability, durability, handling ease and enhanced pollutant adsorption. This research focuses on the immobilisation in-situ of Ag nanoparticles on jujube kernel activated carbon (JAC) modified polyester fabric (Ag/JAC@PEF) for the reduction n of 4-Nitrophenol (4-NP). The process involves coating the fabrics (PEF) with jujube kernel activated carbon through sonication. The produced Ag, JAC@PET, and Ag/JAC@PEF have been characterised utilising various physicochemical methods, such as X-ray diffraction (XRD), Fourier Transformed Infra-Red (FTIR), trans mission electron microscopy (TEM), scanning electron microscopy (SEM), and Thermogravimetric analysis (TGA), Raman spectroscopy, and N2 adsorption – desorption isotherms. Catalytic tests revealed that the coated fabrics exhibited excellent catalytic performance for the reduction of 4-NP. All coated fabrics successfully facilitated the reduction of 4-NP using NaBH4 as the reducing agent. Among them, the 10%Ag/5%JAC@PET sample, with a 6 cm2 surface area, exhibited the highest catalytic efficiency, achieving a reduction rate constant of 1.2457 min− 1 and nearly 98% removal within 60 minutes. This high performance is attributed to the favourable combination and close contact between Ag0 and AC in the catalyst, as well as the porous structure of the polyester fabric, which facilitated pollutant adsorption while providing recovery potential. Additionally, the Ag/JAC@PEF catalyst exhibited exceptional stability over several reaction cycles using a 6 cm2 surface area and 10% silver nanoparticles. This study highlights the potential of polyester fabric-based coatings for practical applications in catalyst recovery.

Design and Construct Cyclic Carbonate Functionalized Chitosan‐Based Hydrogel Enabling Photodecarboxylase Immobilization with Enhanced Stability and Reusability

AbstractFatty acid photodecarboxylase (FAP) plays a crucial role in the green production of biofuel and other valuable biochemicals. However, the reusability of immobilized FAP has been limited due to inadequate durability. Here, a porous, translucent chitosan hydrogel sphere carrier functionalized with cyclic carbonate group to enhance the reusability of immobilized FAP is presented. Based on the arrangement of basic amino acid residues on the surface of FAP, bis(cyclic carbonate) containing a flexible chain from CO2 is designed and synthesized. This compound is used to modify porous hydrogels obtained via a template‐etching process. FAP is then covalently immobilized within the hydrogel framework through a reaction with the remaining cyclic carbonate groups, as evidenced by quartz crystal microbalance analysis. The modified porous hydrogel carrier, PH3‐BC‐II, significantly improves the activity of FAP, achieving a maximum conversion of 70.0%, with the enzyme loading of 125.3 mg g−1 (dry carrier). Furthermore, PH3‐BC‐II retains >50% of its initial activity after eight consecutive reaction cycles (total runtime of 24 h) at high fatty acid substrate concentrations. This study provides an effective strategy for constructing stable immobilized (photo)enzymes from sustainable materials.

Insights into the flexibility of the domain-linking loop in actinobacterial coproheme decarboxylase through structures and molecular dynamics simulations.

Prokaryotic heme biosynthesis in Gram-positive bacteria follows the coproporphyrin-dependent heme biosynthesis pathway. The last step in this pathway is catalyzed by the enzyme coproheme decarboxylase, which oxidatively transforms two propionate groups into vinyl groups yielding heme b. The catalytic reaction cycle of coproheme decarboxylases exhibits four different states: the apo-form, the substrate (coproheme)-bound form, a transient three-propionate intermediate form (monovinyl, monopropionate deuteroheme; MMD), and the product (heme b)-bound form. In this study, we used cryogenic electron microscopy single-particle reconstruction (cryo-EM SPR) to characterize structurally the apo and heme b-bound forms of actinobacterial coproheme decarboxylase from Corynebacterium diphtheriae. The flexible loop that connects the N-terminal and the C-terminal ferredoxin domains of coproheme decarboxylases plays an important role in interactions between the enzyme and porphyrin molecule. To understand the role of this flexible loop, we performed molecular dynamics simulations on the apo and heme b coproheme decarboxylase from Corynebacterium diphtheriae. Our results are discussed in the context of the published structural information on coproheme-bound and MMD-bound coproheme decarboxylase and with respect to the reaction mechanism. Having structural information of all four enzymatically relevant states helps in understanding structural restraints with a functional impact.

Ruthenium‐Zeolite Catalyzed Dehydrative N‐Benzylation of Amides for the Construction of Macrolactams Under Continuous Flow

AbstractContinuous‐flow synthesis of acyclic amides and macrolactams has been demonstrated successfully via N‐benzylation of amides using a highly reusable heterogeneous Ru‐Zeolite as a catalyst, which gives only water as the byproduct. N‐Benzylation of acyclic amides furnished 30 N‐benzylated amides whereas intramolecular N‐benzylation with alcohols was well tolerated with 15 examples of macrolactams bearing 11‐ to 15‐membered rings. Notably, the scalability of this flow process has been demonstrated from milligrams to gram scale using the Ru‐Zeolite heterogeneous catalyst. Moreover, the reusability of the catalyst is exemplified by the 16 reaction cycles carried out with one time‐packed heterogeneous catalyst in the reactor bed.

Enhanced Stability of Lactobacillus paracasei Aspartate Ammonia-Lyase via Electrospinning for Enzyme Immobilization

This study investigates the immobilization of Lactobacillus paracasei AAL (LpAAL) protein onto polyvinyl alcohol/nylon 6/chitosan nanofiber membranes using dextran polyaldehyde as a biodegradable cross-linker. Immobilization enhanced the enzyme’s stability, shifting its optimal reaction conditions from 40 °C to 45 °C and pH from 8.0 to 8.5. While immobilization slightly reduced its catalytic efficiency, it significantly improved enzyme stability and reusability. The immobilized enzyme retained 85% of its initial activity after 7 days of storage at room temperature, compared to 55% for the free enzyme. Reusability tests demonstrated that immobilized LpAAL protein maintained approximately 50% of its activity after six consecutive reaction cycles, highlighting its robustness over repeated use. These results underscore the advantages of nanofiber-based immobilization in enhancing enzyme stability and utility for industrial applications, offering a practical approach to overcoming the limitations associated with free enzyme systems.

Transient Allosteric Regulation of Catalysis by Effector Switching in a Pt2L4 Cage.

The complexity of allosteric enzymatic regulation continues to inspire synthetic chemists seeking to emulate interconnected biological systems. In this work, a Pt2L4cage capable of catalyzing the cyclization reaction of an alkynoic tosyl amide is orthogonally coupled to a diacid-catalyzed carbodiimide-hydration cycle. This new Pt-catalyzed cyclization reaction is demonstrated to exhibit electronic regulation by inclusion of different guest effectors. The orthogonal diacid-catalyzed carbodiimide hydration cycle produces transiently diverse guests that influence the rate of the Pt-catalyzed cyclization reaction to different extents. Further complexity can be introduced to the system through displacing the transiently-formed, weakly bound anhydride guest with the stronger binding fumaronitrile, affecting the catalytic rate to a larger extent for the duration of the orthogonal reaction cycle. The modulation of a Pt-catalyzed cyclization reaction can thus be regulated transiently over the course of the reaction-either up- or down-regulating the turnover frequency (TOF)-via coupling with a temporally controllable orthogonal process. This study demonstrates that principles of allosteric enzymatic regulation can also be applied to simple artificial systems.

Transient Allosteric Regulation of Catalysis by Effector Switching in a Pt2L4 Cage

The complexity of allosteric enzymatic regulation continues to inspire synthetic chemists seeking to emulate interconnected biological systems. In this work, a Pt2L4 cage capable of catalyzing the cyclization reaction of an alkynoic tosyl amide is orthogonally coupled to a diacid‐catalyzed carbodiimide‐hydration cycle. This new Pt‐catalyzed cyclization reaction is demonstrated to exhibit electronic regulation by inclusion of different guest effectors. The orthogonal diacid‐catalyzed carbodiimide hydration cycle produces transiently diverse guests that influence the rate of the Pt‐catalyzed cyclization reaction to different extents. Further complexity can be introduced to the system through displacing the transiently‐formed, weakly bound anhydride guest with the stronger binding fumaronitrile, affecting the catalytic rate to a larger extent for the duration of the orthogonal reaction cycle. The modulation of a Pt‐catalyzed cyclization reaction can thus be regulated transiently over the course of the reaction—either up‐ or down‐regulating the turnover frequency (TOF)—via coupling with a temporally controllable orthogonal process. This study demonstrates that principles of allosteric enzymatic regulation can also be applied to simple artificial systems.

Computational Investigation of the Role of Metal Center Identity in Cytochrome P450 Enzyme Model Reactivity.

Mononuclear Fe enzymes such as heme-containing cytochrome P450 enzymes catalyze a variety of C-H activation reactions under ambient conditions, and they represent an attractive platform for engineering reactivity through changes to the native enzyme. Using density functional theory, we study both native Fe and non-native group 8 (Ru, Os) and group 9 (Ir) metal centers in an active site model of P450. We quantify how changing the metal changes spin state preferences throughout the catalytic cycle. Our calculations reveal an intermediate-spin ground state for all Fe intermediates while the heavier metals prefer low-spin ground states across most intermediates in the reaction cycle. We also study the rate-determining hydrogen atom transfer (HAT) step and the subsequent rebound step. We observe comparable HAT barriers for Fe and Ru, a much higher barrier for Os, and the lowest HAT barrier for Ir. Rebound steps are barrierless for all metals, and the rebound intermediate for Fe is most significantly stabilized. Examination of ground spin states of all intermediates in the reaction cycle reveals spin-allowed pathways for the group 8 metals and spin-forbidden energetics for the group 9 Ir with potential two-state reactivity. Our work highlights the differences between the group 8 metals and the group 9 Ir, and it suggests that engineered P450 enzymes with Ru in particular result in improved enzyme reactivity toward C-H hydroxylation.

Transition State Analogs of Human DNPH1 Reveal Two Electrophile Migration Mechanisms.

DNPH1 is responsible for eliminating the epigenetically modified nucleotide, 5-hydroxymethyl-2'-deoxyuridine 5'-monophosphate (hmdUMP), preventing formation of hmdUTP, a mutation-inducing nucleotide. Loss of DNPH1 activity sensitizes PARP inhibition-resistant BRCA-deficient cancers by causing incorporation of hmdUTP into DNA. Hydrolysis of hmdUMP by DNPH1 proceeds through a covalent intermediate between Glu104 and 2-deoxyribose 5-phosphate, followed by hydrolysis, a reaction cycle with two transition states. We describe synthesis and characterization of transition state mimics for both transition states of DNPH1. Both transition states prefer inhibitors with cationic charge at the anomeric center and provide a foundation for inhibitor design. Ground-state complexes show reaction coordinate nucleophiles poised 3.3-3.7 Å from the anomeric carbon while transition state analogs tighten the reaction coordinate to place the nucleophiles 2.7-2.8 Å from the anomeric carbon. Crystal structures of DNPH1 with transition state analogs reveal transition states where the electrophilic ribocation migrates between the leaving groups and attacking nucleophiles.

Two Novel Viologen/Polyoxometalate‐Based Compounds for the Efficient Photocatalytic Reduction of Cr (VI) Under Visible Light Irradiation

ABSTRACTDesigning efficient photocatalyst has attracted extensive attention for treating polluted wastewater containing Cr (VI). In this work, two viologen/polyoxometalate (POM)‐based compounds were synthesized, [Ni (mimb)2(H2O)4(β‐Mo8O26)]·4H2O (1) and [Zn (mimb)2(H2O)4(β‐Mo8O26)]·4H2O (2) (mimb = 1‐((3,5‐dimethylisoxazol‐4‐yl)methyl)‐[4,4′‐bipyridin]‐1‐ium), through a hydrothermal method and investigated their ability of photocatalytic reduction of Cr (VI). The structures of compounds 1–2 were characterized by single‐crystal X‐ray diffraction, revealing that both possess a zero‐dimensional (0D) structure and can form one‐dimensional (1D) chain structures through hydrogen bondings. Photocatalytic experiments demonstrate that compound 1 has superior photocatalytic performance compared to compound 2. Under optimal conditions (pH = 2, 15 mg catalysts, and 10 mg L−1 Cr (VI) concentration), compound 1 can completely reduce Cr (VI) within 20 min, while compound 2 requires 30 min. Compounds 1–2 also show good stability after photocatalytic reaction, and maintain high photocatalytic activity after five reaction cycles. Additionally, the photocatalytic reaction mechanism of compounds 1–2 was studied, and the free radical scavenging experiments show that its main active species are e−, h+, and ˙O2−. The nitroblue tetrazolium (NBT) experiments further confirm the crucial role of ˙O2− in the photocatalytic process. The good photocatalytic activity, stability, and recyclability of the viologen/POM‐based compounds suggest their potential application in the treatment of wastewater containing Cr (VI).