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The enzyme activity of catechol oxidase (CO) give rise to enzymatic browning, leading to undesirable changes in fruits and vegetables. The aim of this work is to investigate the inhibitory effect of five essential oils (EOs) on CO from date fruits (Phoenix dactylifera). Catechol oxidase has been purified from date fruit through three-phase partitioning (TPP). Essential oils were extracts from Artemisia herba-alba, Artemisia campestris, Thymus vulgaris, Origanum vulgare, and Salvia Rosmarinus, and were tested against CO. The composition of these five essential oils was then identified using GC-MS. Major constituents identified were camphor (20.91%) and davanone D (19%) for A. herba alba, capillene (47.79%) for A. compestris, thymol (33.75%) and linalool (30.44%) for T. vulgaris, carvacrol (68.60%) for O. vulgare, and camphor (33.89%) for S. Rosmarinus. The EO from A. campestris was the most potent inhibitor of enzyme (IC50 = 3.44±0.09 mg/mL) while the weakest effect was observed for EO of O. vulgare (IC50 = 10.24±0.29 mg/mL). Different mechanism of inhibition was obtained. Hence, a competitive inhibition for both EOs of A. herba-alba and T. vulgaris, uncompetitive behavior for A. campestris, noncompetitive mechanism for S. rosmarinus and O. vulgare were observed. The docking molecular of those major constituents was investigated using crystal structure of CO from Ipomoea batatas (1BT1). The best-docked compound was davanone D (-5.55 kcal/mol) while camphor show weaker docking scores (3.79 kcal/mol). Thus, the results from our work could be important and offer an approach of control enzymatic browning using essential oils. [ABSTRACT FROM AUTHOR]

Given the widespread and diverse effects of transition metal ions such as copper and zinc in multiple biological processes, this research endeavor addresses herein the microwave‐aided synthesis of two novel tetradentate ONNO (L1) and tridentate NNO (L2) donor Schiff base ligands derived from 4,5‐dimethyl‐1,2‐phenylenediamine and 4‐bromo‐2‐hydroxybenzaldehyde in a 1:2 ratio and from 4,5‐dimethyl‐1,2‐phenylenediamine and 5‐methoxy‐2‐hydroxybenzaldehyde in a 1:1 ratio, with their respective zinc, ZnL1(1) and ZnL2(3), and copper, CuL1(2) and CuL2(4), Schiff base metal complexes, which are comprehensively characterized utilizing physiochemical and analytical techniques, along with geometry optimization using the DFT approach. Spectrophotometric analyses have been used to assess the biomimetic activity in the conversion of 3,5‐DTBC to 3,5‐DTBQ with turnover numbers 53.4 and 78 h−1 in methanol for 2 and 4, whereas the zinc complexes are found to be ineffective. With CT‐DNA, possible modes of interaction with the synthesized complexes have been explored using absorption spectroscopy, where the associated binding constants ranged between 1.541 × 105 and 2.186 × 105 M−1. EtBr‐bound DNA was used in the fluorescence quenching experiments with Stern–Volmer constant (Ksv) values in the range 4.084 × 104 and 3.402 × 104 M−1, showing a stronger association with CT‐DNA. The compounds' ability to inhibit bacterial strains was also examined in vitro, as well as their ability to reduce inflammation, through the protein denaturation method and the DPPH assay for antioxidant activity have been performed. Furthermore, molecular docking simulations have been carried out to obtain a deeper comprehension of the molecular‐level interactions with CT‐DNA and cyclooxygenase‐2 (COX‐2). [ABSTRACT FROM AUTHOR]

Several novel quinazoline derivatives bearing phenolic hydroxyl moiety (2–7) have been produced with good yields and screened for biological activities. All the title compounds were characterized using spectroscopic techniques such as 1H NMR, 13C NMR, FTIR, and HRMS. Then, the anti-browning effects of synthesized quinazoline derivatives were investigated in vitro. The IC50 values for molecules 2–7 were calculated as 0.085, 1.145, 0.106, 6.86, 0.52, 7.07 µM, respectively. Ki constants, which are inhibitory-enzyme binding constants, were calculated by using Lineweaver–Burk graphs as 0.16 ± 0.0620, 0.906 ± 0.3029, 0.055 ± 0.0171, 9.363 ± 2.5809, 0.773 ± 0.3204, 7.863 ± 1.9107 µM, respectively. In computer-aided analysis, to gain insights electrochemical properties, synthesized compounds were analysed theoretically by density functional theory. Molecular docking studies and MD simulations were performed to identify possible inhibitor-enzyme binding interactions. According to obtained results, all the compounds formed hydrogen bonds with Asn 112 and Asn 414, and showed π-cation interaction with Phe2 70, gatekeeper residue in target protein. Supporting the nm level inhibition, MD simulations indicate that protein-inhibitor complex maintain the stability and have high number of hydrogen bond formation during the simulation. [ABSTRACT FROM AUTHOR]

In nature, catechol oxidase catalyzes the oxidation of o‐diphenol to o‐quinone to produce a series of highly important polyphenolic natural products. Although mimicking the functionality of natural enzyme using a nanozyme was found to be beneficial, attaining a high specificity is challenging. Herein, we have explored the thickness‐dependent oxidase activity and specificity of Cu‐metal‐organic framework (MOF) nanosheets. The unique synthetic method offers control over the thickness of the Cu‐MOF nanosheets. The ultrathin (4 nm) Cu‐MOF (Cu‐UMOF) nanosheets as an oxidase nanozyme exhibit high specificity for catechol oxidation without having any peroxidase activity. Interestingly, the thicker (20–30 nm) Cu‐MOF nanosheets showed poor catechol oxidase and peroxidase activity. The binuclear Cu‐center, coordinative, and electronic unsaturation tuned electronic structure in Cu‐UMOF, resulting in higher specificity for catechol oxidation than thicker Cu‐MOF. [ABSTRACT FROM AUTHOR]

The motivation to find functional models of different metalloenzymes comes from their potential to develop better catalysts inspired by nature. Generally, metalloenzymes can activate aerial dioxygen due to the metal ions in it. Amongst the numerous metalloenzymes, catechol oxidase, and phenoxazinone synthase are the two most discussed metalloenzymes that are of interest to the research community for their ability to oxidize small organic substrates in an eco-friendly way. In this research work, Aegle marmelos (L.) Corrêa (a plant Indigenous to India) ash has been prepared as per the method mentioned in the Ayurvedic Pharmacopoeia of India (API). The ash's mineral composition has been evaluated using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The ability of Aegle marmelos (L.) Corrêa ash to mimic the function of catechol oxidase, and phenoxazinone synthase-like metalloenzymes have been explored. The results of this study confirm that Aegle marmelos (L.) Corrêa ash can as a catalyst for promoting the aerobic oxidation of the organic substrates 3,5-di-tert-butylcatechol (3,5-DTBC) and o-aminophenol (OAPH) to their corresponding chromophores, which are the functions of catechol oxidase and phenoxazinone synthase metalloenzymes respectively. The average values of Vmax and KM-like kinetic parameters for catechol oxidase mimicking activity of ash are (3.4826 ​± ​0.0896) x 10−5 ​M ​S−1 and (512.9146 ​± ​13.7268) x 10−5 ​M, respectively. Similarly, the average values of Vmax and KM-like kinetic parameters for phenoxazinone synthase mimicking activity of ash are (1.8871 ​± ​0.0461) x 10−5 ​M ​S−1 and (1823.0084 ​± ​25.3384) x 10−5 ​M, respectively.

The trend of modelling native enzymes is increasing day by day with the motive of mechanistic elucidation of enzyme-catalyzed reactions and the efficiency of catalysts. Most of the metalloenzymes are capable to activate molecular oxygen due to the presence of metal ions. Among these, copper-based metalloenzyme catechol oxidase has an attractive feature of its oxidizing ability to generate ortho-quinones from catechol. Moreover, the conversion of catechol to ortho-quinones is an important tool for the determination of hormonally active catecholamines such as adrenaline, noradrenaline, and dopa. Nevertheless, the use of native enzymes is highly expensive and the employment of biomimetic models can be the best alternative. This review summarizes some of the widely used modelling methods and their successful applications. Additionally, we also briefly elucidated the structure–activity relationship, kinetic studies of the catalytic oxidation of the substrate, and different external factors influencing the catalytic cycle such as pH, temperature, etc. [ABSTRACT FROM AUTHOR]

Tyrosinase is the most predominant member of the coupled binuclear copper (CBC) protein family. The recent trapping and spectroscopic definition of the elusive catalytic ternary intermediate (enzyme/O2/monophenol) of tyrosinase dictates a monooxygenation mechanism that revises previous proposals and involves cleavage of the μ‐η2:η2‐peroxide dicopper(II) O–O bond to accept the phenolic proton, followed by monophenolate coordination to copper concomitant with aromatic hydroxylation by the non‐protonated μ‐oxo. Here, we compare and contrast previously proposed and current mechanistic models for monophenol monooxygenation of tyrosinase. Next, we discuss how these recent insights provide new opportunities towards uncovering structure–function relationships in CBC enzymes, as well as understanding fundamental principles for O2 activation and reactivity by bioinorganic active sites. [ABSTRACT FROM AUTHOR]

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Browning, caused by enzymatic activity and storage conditions, affects cabbage during cold storage and is crucial for customer acceptance. This study investigated the effect of cardboard packaging containing low concentrations of nano-orange oil (ONE) at 0.006% in palm wood waste powder for anti-browning and extending the shelf life of cabbage. The incorporation of ONE into palm wood powder (PWP) using different methods (soaking, vapor, vapor with ultrasonic device, and control) was examined before using the active PWP to develop cardboard cabbage packaging. The reuse of the active cabbage box packaging was also investigated for up to three reuses. The results showed that a greater anti-browning effect was achieved with cardboard packaging made from active PWP with orange oil vapor and an ultrasonic device compared to other adsorption methods, with significantly higher inhibition of the key browning enzyme activities of polyphenol oxidase (PPO) and peroxidase (POD). Additionally, antioxidant activity and bioactive compounds were improved, maintaining the bright green color of cabbage after 21 days of storage. The shelf life of cabbage stored in active cardboard was extended to at least 21 days compared to 5 days for the control. The active cabbage box with PWP and ONE vapor with an ultrasonic device showed potential for reuse at least two times. Limonene was found on the surface of stored cabbage and may be a key factor in antimicrobial activity, helping to control microbial growth on the cabbage surface within standard limits during long-term storage. This finding provides valuable guidance for reducing cabbage waste during transportation and storage from farm to market. PRACTICAL APPLICATION: This research offers new insights into active cardboard packaging made from palm wood powder with a low concentration of orange oil vapor to prevent browning and microbial growth in storage boxes. The optimal method for producing this packaging uses nano-orange oil vapor at 0.006% with an ultrasonic device, which could be feasible for large-scale production. The packaging effectively reduced PPO and POD enzyme activity, delaying browning and extending cabbage shelf life by at least threefold compared to the control, while maintaining color and freshness. This cost-effective method promotes the sustainable use of agricultural waste in the fresh vegetable industry, as it can be reused at least twice, benefiting farmers and reducing cabbage waste., (© 2024 Institute of Food Technologists.)

• Four new Schiff base metal complexes in 1:1 and 1:2 ratios are synthesized from tri dentate NNO donor ligand. • DFT approach is employed for theoretical computations. • The Cu(II) complex showed better catechol oxidase activity as well as higher binding propensity with CT-DNA. • The Cu(II) complex has significant anti-oxidant activity and the Co(II) complex has superior anti-inflammatory activity. The present work focuses on the microwave-assisted synthesis, characterization and biological applications of a novel tridentate NNO donor Schiff base ligand derived from the condensation of 4-(Diethylamino)salicylaldehyde and 4,5-Dimethyl - 1 , 2-phenylenediamine, along with its transition metal complexes of Cu(II) and Co(II) in 1:1 and 1:2 ratios each respectively. A theoretical basis for comprehending the electronic framework and characteristics of the complexes has been studied through the use of a computational approach. Further, the distorted octahedral geometry of the Schiff base metal complexes is confirmed by using analytical methods such as elemental analysis, molar conductance, ESI-MS, UV–Vis, FTIR, TGA and NMR spectra, which confirmed that NNO donor site of the ligand is coordinated with the metal ions. The complexes have been screened for their potential application as a catalyst for the catalytic conversion of 3,5-di‑tert‑butyl‑catechol (3,5-DTBC) to 3,5-di‑tert-butylquinone (3,5-DTBQ) and the turnover numbers (K cat) have been found in the range 36.46–43.05 h−1 in methanol. Absorption spectroscopic technique has been employed to examine the possible modalities of interactions with the synthesized complexes using CT-DNA and the related binding constants exhibited in the range 2.58 × 104 M−1 to 1.98 × 105 M−1 thus depicting appreciable binding affinity. To evaluate the bioactivities, in-vitro assays for anti-oxidant and anti-inflammatory activity have also been implemented. The Cu(II) complex (CuL) has significant anti-oxidant activity and the Co(II) complex (CoL) has superior anti-inflammatory activity compared to all other complexes with IC 50 values of 238.78 µM and 140.25 µM respectively. To better understand the molecular-level interactions and identify probable binding energies of inhibitors, molecular docking simulations have been performed. [Display omitted] [ABSTRACT FROM AUTHOR]

A typical symptom of postharvest chilling injury (PCI) in pineapple fruit (Ananas comosus (L.) Merr.) is internal browning (IB) near the fruit core. Since vascular bundles (VBs) are localized to this region, it was hypothesized that the VBs might be the site of IB. To test this, the anatomy and histochemistry of VBs during chilling stress in four pineapple cultivars with different levels of sensitivity to PCI were examined. Fruit were stored at 10°C for up to three weeks to stimulate translucency symptoms (TS; the initiation of IB). After three weeks of chilling exposure, the cultivars 'MD2' showed 0%, 'Pattavia' and 'Savee' showed 10-16%, and 'Trad Sri Thong' showed 100% TS and IB symptom. Scanning electron microscopy and in situ histochemical staining techniques that detect enzymes and substrates commonly associated with IB initiation were used in parallel. The TS of pineapple fruit coincided with the collapse of the phloem tissue. The VBs in the tissue where IB was initiated (i.e., the flesh adjacent to the core or F/C) had the highest activity of polyphenol oxidase, hydrogen peroxide, and phenolic compounds. The IB-resistant 'MD2' genotype had fewer VBs, but a greater proportion of sclerenchyma fibers (P

Within the framework of the present study, a polydentate ligand with S and N donor sites along with its CuII‐based chelates were prepared and characterized. Elemental and thermal analyses, μeff and ΛM measurements as well as spectroscopy techniques including FT‐IR, electronic spectra, and EPR are the characterization tools. Computational chemistry calculations were applied to confirm the geometrical assignments of the penta and hexa coordinated perchlorato and chloro derivatives, respectively. Octahedral and trigonal bipyramidal stereochemistries were assigned for these copper(II) chelates. Powder X‐ray spectroscopy data were processed by Expo 2014 computer program for the structural illustration of one of the existing octahedral metal complexes. Biomimicking of copper(II) containing proteins phenoxazinone synthase and catechol oxidase was studied and the obtained results demonstrated promising oxidase‐like activity of the present CuII‐base complexes. Kinetic measurements were also performed to identify the potential catalytic pathways of the studied oxidation processes. The type of the counter‐anion included in the complexes significantly controls the structural features and the catalytic properties. [ABSTRACT FROM AUTHOR]

A new series of MnII and FeIII chelates containing pyridine and phenolate‐based ligands was synthesized by treating the metal salt in ethanol with the Schiff‐bases, which were formed in situ. Analytical (C, H, N, and M), thermal analysis (thermogravimetric analysis & differential thermogravimetric), and spectroscopic techniques (IR, UV–Vis, ESR) in addition to molar conductance and magnetic measurements were employed to characterize the prepared metal chelates. Mono‐nuclear metal complexes, with N5 donor containing pentadentate Schiff‐base ligands were obtained. In addition, two dibridged homobinuclear iron(III) complexes with N4O donors containing phenolate‐based ligand were successfully isolated. Six‐coordinate complex species in an octahedral environment is proposed for both MnII and FeIII metal complexes. The density function theory study was used to optimize the geometrical shapes of three of the existing metal complexes and to identify some global reactivity descriptors. In addition, spectral data of PXRD with Expo 2014's structural solution software were utilized in the structural illustration of a representative MnII and FeIII complexes. Aerobic catalytic oxidation of 4‐tert‐butylcatechol (4‐TBCH2) and o‐aminophenol under catalytic conditions was studied by using the present manganese(II) and iron(III) complexes. The synthesized MnII and FeIII chelates exhibited a promising catalytic activity and probable catalytic sequences have been discussed. [ABSTRACT FROM AUTHOR]

Abstract Background Many fungi boost the deconstruction of lignocellulosic plant biomass via oxidation using lytic polysaccharide monooxygenases (LPMOs). The application of LPMOs is expected to contribute to ecologically friendly conversion of biomass into fuels and chemicals. Moreover, applications of LPMO-modified cellulose-based products may be envisaged within the food or material industry. Results Here, we show an up to 75-fold improvement in LPMO-driven cellulose degradation using polyphenol oxidase-activated lignin building blocks. This concerted enzymatic process involves the initial conversion of monophenols into diphenols by the polyphenol oxidase MtPPO7 from Myceliophthora thermophila C1 and the subsequent oxidation of cellulose by MtLPMO9B. Interestingly, MtPPO7 shows preference towards lignin-derived methoxylated monophenols. Sequence analysis of genomes of 336 Ascomycota and 208 Basidiomycota reveals a high correlation between MtPPO7 and AA9 LPMO genes. Conclusions The activity towards methoxylated phenolic compounds distinguishes MtPPO7 from well-known PPOs, such as tyrosinases, and ensures that MtPPO7 is an excellent redox partner of LPMOs. The correlation between MtPPO7 and AA9 LPMO genes is indicative for the importance of the coupled action of different monooxygenases in the concerted degradation of lignocellulosic biomass. These results will contribute to a better understanding in both lignin deconstruction and enzymatic lignocellulose oxidation and potentially improve the exploration of eco-friendly routes for biomass utilization in a circular economy.

A novel sensor array was developed based on the enzyme/nanozyme hybridization for the identification of tea polyphenols (TPs) and Chinese teas. The enzyme/nanozyme with polyphenol oxidase activity can catalyze the reaction between TPs and 4-aminoantipyrine (4-AAP) to produce differences in color, and the sensor array was thus constructed to accurately identify TPs mixed in different species, concentrations, or ratios. In addition, a machine learning based dual output model was further used to effectively predict the classes and concentrations of unknown samples. Therefore, the qualitative and quantitative detection of TPs can be realized continuously and quickly. Furthermore, the sensor array combining the machine learning based dual output model was also utilized for the identification of Chinese teas. The method can distinguish the six teas series in China, and then precisely differentiate the more specific tea varieties. This study provides an efficient and facile strategy for the identification of teas and tea products., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Green tea is popular among consumers because of its high nutritional value and unique flavor. There is often a strong correlation among the type of tea, its quality level and the price. Therefore, the rapid identification of tea types and the judgment of tea quality grades are particularly important. In this work, a novel sensor array based on nanozyme with polyphenol oxidase (PPO) activity is proposed for the identification of tea polyphenols (TPs) and Chinese green tea. The absorption spectra changes of the nanozyme and its substrate in the presence of different TPs were first investigated. The feature spectra were scientifically selected using genetic algorithm (GA), and then a sensor array with 15 sensing units (5 wavelengths × 3 time) was constructed. Combined with the support vector machine (SVM) discriminative model, the discriminative rate of this sensor array was 100% for different concentrations of typical TPs in Chinese green tea with a detection limit of 5 μM. In addition, the identification of different concentrations of the same tea polyphenols and mixed tea polyphenols have also been achieved. Based on the above study, we further developed a facile and efficient new method for the category differentiation and adulteration identification of green tea, and the accuracy of this array was 96.88% and 100% for eight types of green teas and different adulteration ratios of Biluochun, respectively. This work has significance for the rapid discrimination of green tea brands and adulteration., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Mannose-binding lectin plays an essential role in bacteria or virus-triggered immune response in mammals. Previous proteomic data revealed that in Eriocheir sinensis, the mannose-binding protein was differentially expressed after Spiroplasma eriocheiris infection. However, the function of mannose-binding protein against pathogen infection in invertebrates is poorly understood. In this study, a crab mannose-binding protein (EsMBP) was characterized and enhanced the host resistance to S. eriocheiris infection. The application of recombinant C-type carbohydrate recognition domain (CTLD) of EsMBP led to increased crab survival and decreased S. eriocheiris load in hemocytes. Meanwhile, the overexpression of CTLD of EsMBP in Raw264.7 cells inhibited S. eriocheiris intracellular replication. In contrast, depletion of EsMBP by RNA interference or antibody neutralization attenuated phenoloxidase activity and hemocyte phagocytosis, rendering host more susceptible to S. eriocheiris infection. Furthermore, miR-381-5p in hemocytes suppressed EsMBP expression and negatively regulated phenoloxidase activity to exacerbate S. eriocheiris invasion of hemocytes. Taken together, our findings revealed that crab mannose-binding protein was involved in host defense against S. eriocheiris infection and targeted by miR-381-5p, providing further insights into the control of S. eriocheiris spread in crabs., Competing Interests: Declaration of competing interest The authors declare that there are no competing financial interests., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Enzymatic browning poses a significant challenge that limits in vitro propagation and genetic transformation of plant tissues. This research focuses on investigating how adding antioxidant substances can suppress browning, leading to improved efficiency in transforming plant tissues using Agrobacterium and subsequent plant regeneration from rough lemon (Citrus × jambhiri). When epicotyl segments of rough lemon were exposed to Agrobacterium, they displayed excessive browning and tissue decay. This was notably different from the 'Hamlin' explants, which did not exhibit the same issue. The regeneration process failed completely in rough lemon explants, and they accumulated high levels of total phenolic compounds (TPC) and polyphenol oxidase (PPO), which contribute to browning. To overcome these challenges, several antioxidant and osmoprotectant compounds, including lipoic acid, melatonin, glycine betaine, and proline were added to the tissue culture medium to reduce the oxidation of phenolic compounds and mitigate browning. Treating epicotyl segments with 100 or 200 μM melatonin led to a significant reduction in browning and phenolic compound accumulation. This resulted in enhanced shoot regeneration, increased transformation efficiency, and reduced tissue decay. Importantly, melatonin supplementation effectively lowered the levels of TPC and PPO in the cultured explants. Molecular and physiological analyses also confirmed the successful overexpression of the CcNHX1 transcription factor, which plays a key role in imparting tolerance to salinity stress. This study emphasizes the noteworthy impact of supplementing antioxidants in achieving successful genetic transformation and plant regeneration in rough lemon. These findings provide valuable insights for developing strategies to address enzymatic browning and enhance the effectiveness of plant tissue culture and genetic engineering methods with potential applications across diverse plant species., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Mahmoud et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Polyphenol oxidases (PPOs) comprise tyrosinases (TYRs) and catechol oxidases (COs), which catalyse the initial reactions in the biosynthesis of melanin. TYRs hydroxylate monophenolic (monophenolase activity) and oxidize diphenolic (diphenolase activity) substrates, whereas COs react only with diphenols. In order to elucidate the biochemical basis for the different reactions in PPOs, cDNA from walnut leaves was synthesized, the target gene encoding the latent walnut tyrosinase (jrPPO1) was cloned, and the enzyme was heterologously expressed in Escherichia coli. Mutations targeting the two activity controller residues (Asn240 and Leu244) as well as the gatekeeper residue (Phe260) were designed to impair monophenolase activity of jrPPO1. For the first time, monophenolase activity of jrPPO1 towards L-tyrosine was blocked in two double mutants (Asn240Lys/Leu244Arg and Asn240Thr/Leu244Arg) while its diphenolase activity was partially preserved, thereby converting jrPPO1 into a CO. Kinetic data show that recombinant jrPPO1 resembles the natural enzyme, and spectrophotometric investigations proved that the copper content remains unaffected by the mutations. The results presented herein provide experimental evidence that a precisely tuned interplay between the amino acids located around the active center controls the substrate specificity and therewith the mono- versus diphenolase activity in the type-III copper enzyme jrPPO1. [ABSTRACT FROM AUTHOR]

A template Schiff condensation of 2,6‐pyridine dicarbaldehyde or 2,6‐diformyl‐4‐ bromophenol and 1,3–diamino‐2‐hydroxy propane or 3,4‐diaminotoluene in the presence of copper(II) salts (CuX2) (X = Cl, Br, CH3COO, or ClO4) affords different types of copper(II) complexes. Depending on the employed molar ratio of the dicarbonyl compounds and diamines, different types of copper(II) complexes formed during the template condensation reaction. Structural formulation of the complexes was confirmed by elemental analysis (C, H, N, and M), physical measurements such as thermal analysis (TAG & DTG), molar conductivity, and magnetic moments in addition to spectral studies (UV–Vis, IR, and ESR). Homobinuclear in a four‐coordinate square planar and five‐coordinate square pyramidal and trigonal bipyramidal in monomeric structures are proposed. A mononuclear hexa‐coordinate in an octahedral geometry is suggested as well. Oxidase biomimetic catalytic activity of these newly synthesized copper(II) complexes was examined toward the aerobic oxidation of 4‐tert‐butylcatechol (4‐TBCH2) and o‐aminophenol under catalytic conditions. Both catalytic and kinetic investigations demonstrate promising oxidase catalytic activity and based on the kinetic results, probable mechanistic catalytic implications are discussed. Geometrical structures of representative copper(II) complexes were determined by optimizing their bond lengths, bond angles, dihedral angles, and the structural index (τ). [ABSTRACT FROM AUTHOR]

The zwitterion ligand L1 has been synthesized and characterized by single-crystal X-ray diffraction, and spectroscopic techniques (1H, 13C NMR, FT-IR, ESI-MS, and UV–Vis). The crystal structure shows that L1 molecules are planar and are connected via intermolecular N-H----O and intramolecular N-H----O interactions. The NMR analysis shows the presence of two mesomeric forms of L1: zwitterion and ketone-imidazolidine. The kinetic study of in situ complexes is followed by UV–vis spectroscopy and revealed a binuclear structure built from square base pyramidal geometry and octahedral one. In situ complexes obtained from L1 with different copper (II) salts are studied for their catecholase activities using 3,5-di- tert -butylcatechol. The obtained 3,5-di -tert -butylquinone was characterized by single-crystal X-ray diffraction,. The results show that the catalytic activity depends on the nature of the metal salt anion. From Michaelis-Menten model, we have evaluated the dissociation constant and the bond constant which are in good agreement with those of literature. The structure-activity relationship show that the high rate of catalytic oxidation depends on the presence of copper ion in the complex. Image 1 • Synthesis of zwitterionic imidazole derivative. • Crystal form of ligand L1. • Catecholase activity studies by in situ copper complexes. [ABSTRACT FROM AUTHOR]

The napthyl/pyridine-pyrazole-derived complexes, [Mn(L1)Cl2] (1), [Co(L1)Cl2] (2), [Cu(µ-Cl)(Cl)(L)]2 (3), [Cu2(L)2(N3)3(µ2-N3)] (4), and [Co(L2)Cl2] (5) (where L1 = bis-(3,5-dimethyl-pyrazol-1-ylmethyl)-napthalen-1-ylmethyl-amine (L1), L = 5-methyl-pyrazol-1-ylmethyl) -napthalen-1-ylmethyl-amine (L) and L2 = 2-[2-(3,5-dimethyl-pyrazol-1-yl)-1-methyl-ethyl]-pyridine), exhibited phenoxazinone synthase activity in methanol in the range 5–54 h−1. Binuclear copper(II) derivatives 3 and 4 show better catalytic activities than manganese(II) and cobalt(II) derivatives. The kinetic studies reveal that phenoxazinone chromophore is produced via a complex-substrate intermediate. Further, 3 and 4 show catecholase activity in methanol in the presence of oxygen. All the complexes showed potent antimicrobial activity against the tested strains of bacteria and fungi. Complex 1 was synthesized for the first time by mixing L1 and MnCl2 (1:1) and characterized by single-crystal X-ray crystallography, cyclic voltammetry, density functional theory, and thermogravimetry analysis. The present study suggests that napthyl/pyridyl-anchored pyrazole metal complexes are interesting scaffolds for the development of novel model compounds for biochemical reaction and efficient antimicrobial agents. [ABSTRACT FROM AUTHOR]

Ternary copper(II) complexes with the molecular formulae of [CuIILL′]X or [CuIILL′X]; L = l -Valinate; L′ = α, ά-bipyridyl or 1,10 - phenanthroline and X is Cl¯, Br¯, NO 3 ¯, AcO¯, ½SO 4 2− or ClO 4 ¯ were synthesized. Elemental and thermal analysis in addition to electrochemical (molar conductance and cyclic voltammetry), magnetic moment measurements as well spectral (FT-IR, UV–Vis and ESR) techniques were used to characterize the complexes. The spectroscopic results suggested square pyramidal and square planar geometries for the five- and four-coordinate complexes respectively. Powder X-ray diffraction spectral data along with the structure solution program Expo 2014 has been used for structural elucidation of the sulfato complexes 1 and 5. Stopped follow technique was employed to study the substitution of the nonelectrolytic coordinately counter anion ligand by using thiourea (TU) as a function of nucleophile and a biphasic process is proposed. An initial fast reaction is followed by a slower one and the initial one was found to be counter ion dependent. Bio-mimicking the multicopper oxidase enzyme such as catechol oxidase and phenoxazinone synthase is a further goal of the present study. Catalytic examinations displayed that the present complexes are promising candidates as functional mimic of the examined enzymes and the probable mechanistic catalytic sequences are discussed. Image 1 • Synthesis and characterization of ternary copper(II) complexes containing L -Valinate and α, ά-Bipyridyl or 1,10-phenanthroline •Ligand substitution and oxidase biomimetic catalytic activity studies •Structure of representative complexes was confirmed by powder XRD diffraction along with computational studies. [ABSTRACT FROM AUTHOR]

Catechol oxidases (COs) and tyrosinases (TYRs) are both polyphenol oxidases (PPOs) that catalyze the oxidation of ortho‐diphenols to the corresponding quinones. By the official classification, only TYRs can also catalyze the hydroxylation of monophenols to ortho‐diphenols. Researchers have been trying to find the molecular reason for the mono‐/diphenolase specificity for decades. However, the hypotheses for the lack of monophenolase activity of plant COs are only based on crystal structures so far. To test these hypotheses, we performed site‐directed mutagenesis studies and phylogenetic analyses with dandelion PPOs offering high phylogenetic diversity, the results of which refute the structure‐based hypotheses. While plant PPOs of phylogenetic group 2 solely exhibit diphenolase activity, plant PPOs of phylogenetic group 1 unexpectedly also show monophenolase activity. This finding sheds new light upon the molecular basis for mono‐/diphenol substrate specificity and challenges the current practice of generally naming plant PPOs as COs. [ABSTRACT FROM AUTHOR]

Galactose Oxidase (GOase) and catechol oxidase (COase) are the metalloenzymes of copper having monomeric and dimeric sites of coordination, respectively. This paper summarizes the results of our studies on the structural, spectral and catalytic properties of new mononuclear copper (II) complexes [CuL(OAc)] (1), and [CuL 2 ] (2), (HL = 2,4‑dichloro‑6‑{[(2′‑dimethyl‑aminoethyl)methylamino]methyl}‑phenol) which can mimic the functionalities of the metalloenzymes GOase and COase. The structure of the compounds has been elucidated by X-ray crystallography and the mimicked Cu(II) catalysts were further characterized by EPR. These mimicked models were used for GOase and COase catalysis. The GOase catalytic results were identified by GC–MS and, analyzed by HPLC at room temperature. The conversion of benzyl alcohol to benzaldehyde were significant in presence of a strong base, Bu 4 NOMe in comparison to the neutral medium. Apart from that, despite of being monomeric in nature, both the homogeneous catalysts are very prone to participate in COase mimicking oxidation reaction. Nevertheless, during COase catalysis, complex 1 was found to convert 3,5‑ditertarybutyl catechol (3,5-DTBC) to 3,5‑ditertarybutyl quinone (3,5-DTBQ) having greater rate constant, k cat or turn over number (TON) value over complex 2. The generation of reactive intermediates during COase catalysis were accounted by electrospray ionization mass spectrometry (ESI-MS). Through mechanistic approach, we found that H 2 O 2 is the byproduct for both the GOase and COase catalysis, thus, confirming the generation of reactive oxygen species during catalysis. Notably, complex 1 having mono-ligand coordinating atmosphere has superior catalytic activity for both cases in comparison to complex 2 , that is having di-ligand environment. Representing the formation of active catalyst from [CuL(OAc)] (HL = 2,4‑dichloro‑6‑{[(2′‑dimethyl‑aminoethyl)methylamino]methyl}-phenol) during galactose oxidase (GOase) mimicking catalysis by utilizing 1 atm of O 2 as oxidant via superoxide generation process. Unlabelled Image • Syntheses of Mannich base Cu(II) complexes as metalloenzyme mimics • Galactose Oxidase (GOase) and catechol oxidase (COase) based catalysis • The generation of reactive oxygen species during catalysis • Reduction of aerial oxygen to form hydrogen peroxide • Mechanistic aspects of GOase and COase via electrospray ionization mass spectrometry [ABSTRACT FROM AUTHOR]

Abstract Catechol oxidase (PPO) was extracted and purified from Tadela (Phoenix dactylifera L.) date fruit, by a procedure that included (NH 4) 2 SO 4 precipitation followed by dialysis, Q-Sepharose bb ion-exchange chromatography and HPLC gel filtration chromatography. Some of its biochemical characteristics were studied. The purification rate and the yield were 80% and 20%, respectively. The Tadela date fruit catechol oxidase exhibited a molecular weight of 90 kDa using SDS-PAGE. The catechol oxidase showed only o ‑diphenolase and triphenolase activities while no monophenolase activity was detected. A better affinity was observed using catechol as substrate (Km = 35 mM) with thus, a higher Vmax/Km ratio (80 U/mM·mL). This enzyme is thermostable in the temperature range (30–60 °C) with optimum activity in acidic range of pH. Four inhibitors were used for the control of enzymatic browning, of which sodium metabisulfite was the most potent (IC 50 = 0, 11 mM). The values of K I and mechanism of inhibition were also determined. No significant change on enzyme activity was noticed in the presence of metal ion and detergents. Therefore, thermal inactivation was studied in the temperature range between 60 and 80 °C using catechol as substrate. Their kinetic (K, D, t 1/2 , Zt, Ea) and thermodynamic (ΔH, ΔG and ΔS) parameters were also estimated. Highlights • Catechol oxidase from Tadela date fruit was purified and characterized. • Sodium Metabisulfite, Sodium azide, l ‑cysteine and ascorbic acid were excellent PPO inhibitors. • The Tadela catechol oxidase is a thermostable enzyme and its thermal inactivation was described by a first order reaction. • The sensitivity of enzyme towards temperature is amplified in presence of inhibitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fluorescent nanozyme with catechol oxidase activity was studied. • The nanozyme combines functions of catechol recognition and signal output. • Catechol sensing based on the nanozyme without addition of other agent. • The method is facile and shows good selectivity. Nanozymes, an unusual category of nanomaterials possessing enzymatic properties, and have generated considerable interest regarding their application feasibilities on several important fronts. In the present work, an innovative sensing device for catechol was established ground on a fluorescent nanozyme (Cu-BDC-NH 2) that exhibited catechol oxidase activity. The fluorescent nanozyme combines both functions of catechol recognition and response signal output, and can realize the sensing of catechol without the addition of other chromogenic agents. In the existence of Cu-BDC-NH 2 , catechol can be oxidized efficiently to produce quinones or polymers with strong electron absorption capacity, which immediately results in efficient fluorescence quenching of Cu-BDC-NH 2. However, other common phenolic compounds, such as phenol, the other two diphenols (hydroquinone and resorcinol), phloroglucinol, and chlorophenol, do not result in efficient fluorescence quenching of Cu-BDC-NH 2. The method shows a nice linear relationship between catechol concentration prep the fluorescence intensity of Cu-BDC-NH 2 in the scope of 0–10 μM, with a detection limit of 0.997 μM. The detection of catechol in actual water samples has also achieved the satisfactory consequences, which provides a new strategy for the convenient and selective detection of catechol. [ABSTRACT FROM AUTHOR]

This work applies the Density Functional Theory (DFT) to study binuclear complexes of Mn2+ with the ligand 2-hydroxibenzilglycine and its substituted derivatives. The results showed the isomer 2 with multiplicity 11-ete as the most stable between all the structures and multiplicities obtained. Then, the most stable complex with the -OCH3, -Br, -Cl and -NO2 substituents were analyzed. Finally, the absolute hardness and the percentage of LUMO orbital participation for the substituted complexes were evaluated. Among them, the complexes with -NO2, -H, -Br groups were more likely to play the catalytic activity, respectively.

The polyphagous pest, Spodoptera littoralis (Boisduval), poses a significant global economic threat by gregariously feeding on over a hundred plant species, causing substantial agricultural losses. Addressing this challenge requires ongoing research to identify environmentally safe control agents. This study aimed to elucidate the insecticidal activity of the metabolite (ES2) from a promising endophytic actinobacterium strain, Streptomyces sp. ES2 EMCC2291. We assessed the activity of ES2 against the eggs and fourth-instar larvae of S. littoralis through spectrophotometric measurements of total soluble protein, α- and β-esterases, polyphenol oxidase (PPO), and catalase enzyme (CAT). The assessments were compared to commercial Biosad® 22.8% SC. Untargeted metabolomics using LC-QTOF-MS/MS identified 83 metabolic compounds as chemical constituents of ES2. The median lethal concentration (LC50) of ES2 (165 mg/mL) for treated Spodoptera littoralis eggs showed significant differences in polyphenol oxidase and catalase enzymatic activities, while the LC50 of ES2 (695 mg/mL) for treated S. littoralis fourth instar larvae showed lower significance in α- and β-esterase activities. Molecular docking of ES2 identified seven potent biocidal compounds, showing strong affinity to PPO and catalase CAT proteins in S. littoralis eggs while displaying limited binding to alpha and beta esterase proteins in the larvae. The results contribute to the understanding of ES2 as a promising alternative biopesticide, providing insights for future research and innovative applications in sustainable pest management strategies., (© 2024. The Author(s).)

The prophenoloxidase (PPO) activation and Toll antimicrobial peptide synthesis pathways are two critical immune responses in the insect immune system. The activation of these pathways is mediated by the cascade of serine proteases, which is negatively regulated by serpins. In this study, we identified a typical serpin, BmSerpin-4, in silkworms, whose expression was dramatically up-regulated in the fat body and hemocytes after bacterial infections. The pre-injection of recombinant BmSerpin-4 remarkably decreased the antibacterial activity of the hemolymph and the expression of the antimicrobial peptides (AMPs) gloverin-3 , cecropin-D , cecropin-E , and moricin in the fat body under Micrococcus luteus and Yersinia pseudotuberculosis serotype O: 3 ( YP III ) infection. Meanwhile, the inhibition of systemic melanization, PO activity, and PPO activation by BmSerpin-4 was also observed. Hemolymph proteinase 1 (HP1), serine protease 2 (SP2), HP6, and SP21 were predicted as the candidate target serine proteases for BmSerpin-4 through the analysis of residues adjacent to the scissile bond and comparisons of orthologous genes in Manduca sexta . This suggests that HP1, SP2, HP6, and SP21 might be essential in the activation of the serine protease cascade in both the Toll and PPO pathways in silkworms. Our study provided a comprehensive characterization of BmSerpin-4 and clues for the further dissection of silkworm PPO and Toll activation signaling.

DNA is self-assembled with Fmoc-amino acids and Cu 2+ to construct a supramolecular catechol oxidase-mimetic catalyst, which exhibits remarkable activity in catalyzing colorimetric reactions. This catalytic system is used for the detection of DNA hybridization with a high selectivity and a low detection limit.