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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]

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]

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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• 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

In this work, we are interested in finding new catalysts for catecholase, whose principle is based on the oxidation reaction of catechol to o-quinone. In this context, we have studied a series of seven quinoline-based compounds. The present work indicates that the complexes formed between seven selected quinoline compounds and the copper salts viz. Cu(OAc)2, CuSO4, Cu(NO3)2, and CuCl2 elicit catalytic activities for the oxidation of catechol to o-quinone. The complexes formed with the Cu(OAc)2 salt show a much higher catalytic activity than the others, whereas the Cu(NO3)2 and CuCl2 salts formed complexes with low catalytic activity. This study also shows that the oxidation rate depends on two factors, namely the chemical structure of the ligands and the nature of the ions coordinated with the copper.

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 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.)

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]

The ubiquitous type-3 copper enzyme polyphenol oxidase (PPO) has found itself the subject of profound inhibitor research due to its role in fruit and vegetable browning and mammalian pigmentation. The enzyme itself has also been applied in the fields of bioremediation, biocatalysis and biosensing. However, the nature of PPO substrate specificity has remained elusive despite years of study. Numerous theories have been proposed to account for the difference in tyrosinase and catechol oxidase activity. The "blocker residue" theory suggests that bulky residues near the active site cover CuA, preventing monophenol coordination. The "second shell" theory suggests that residues distant (∼8 Å) from the active site, guide and position substrates within the active site based on their properties e.g., hydrophobic, electrostatic. It is also hypothesized that binding specificity is related to oxidation mechanisms of the catalytic cycle, conferred by coordination of a conserved water molecule by other conserved residues. In this review, we highlight recent developments in the structural and mechanistic studies of PPOs and consolidate key concepts in our understanding toward the substrate specificity of PPOs. [ABSTRACT FROM AUTHOR]

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]

[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]

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.

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.

In this study, a comprehensive approach to advance the inhibitory effect of Hibiscus sabdariffa extract on apple polyphenol oxidase (PPO) was performed. PPO was extracted, purified, and characterized for optimal activity, whereas response surface methodology generated a quadratic polynomial model to fit the experimental results for hibiscus extraction. The optimum conditions allowed to predict a maximum recovery of anthocyanins (256.11 mg delphinidin-3-O-glucoside/g), with a validated value of 272.87 mg delphinidin-3-O-glucoside/g dry weight (DW). The chromatographic methods highlighted the presence of gallic acid (36,812.90 µg/g DW extract), myricetin (141,933.84 µg/g DW extract), caffeic acid (101,394.07 µg/g DW extract), sinapic acid (1157.46 µg/g DW extract), kaempferol (2136.76 µg/g DW extract), and delphinidin 3-O-β-d-glucoside (226,367.08 µg/g DW extract). The inactivation of PPO followed a first-order kinetic model. A temperature-mediated flexible fit between PPO and anthocyanins was suggested, whereas the molecular docking tests indicated that PPO is a good receptor for cafestol, gallic acid, and catechin, involving hydrophobic and hydrogen bond interactions. PRACTICAL APPLICATION: It is well known that enzymatic browning is one of the most important challenges in the industrial minimal processing of selected fruit and vegetable products. Novel inhibitors for polyphenol oxidase are proposed in this study by using an anthocyanin-enriched extract from Hibiscus sabdariffa L. Based on our results, combining the chemical effect of phytochemicals from hibiscus extract with different functional groups with minimal heating could be an interesting approach for the development of a new strategy to inhibit apple polyphenol oxidase., (© 2023 Institute of Food Technologists.)

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]

Graphical abstract In quest of copper complexes having [CuN 3 O] cores, [Cu(phen)(L –Val)(H 2 O)]NO 3 (1) and [Cu(bpy)(L –Val)]ClO 4 (2) complexes have been synthesized and structurally characterized (phen = 1,10–phenanthroline; bpy = 2,2′–bipyridine). 1 possesses a distorted square-pyramidal, whereas 2 has a distorted square-planar coordination geometry. Structural features of both 1 and 2 reveal the formation of supramolecular networks via inter- and intra-molecular hydrogen bonding interactions. The mechanism of ligand substitution of 1 and 2 by thiourea (TU) is a biphasic process in which an initial fast and dissociative reaction is followed by a slower and associative one. It is concluded from the activation parameters that the difference in structure does not affect the mechanism. Complexes 1 and 2 have also been evaluated as functional models for the catechol oxidase enzyme and phenoxazinone synthese and they are promising candidates as functional mimics for catechol oxidase and phenoxazinone synthase. Highlights • Biomemicking of copper enzymes using mixed NO-ligands. • Effect of the structure on the biomimetic activity. • Stabilization of supramolecular networks via inter- and intra-molecular hydrogen bonding interactions in both complexes. Abstract In quest of copper complexes having [CuN 3 O] cores, [Cu(phen)(l –Val)(H 2 O)]NO 3 (1) and [Cu(bpy)(l –Val)]ClO 4 (2) complexes have been synthesized and structurally characterized (phen = 1,10–phenanthroline; bpy = 2,2′–bipyridine). Complex 1 possesses a distorted square-pyramidal, whereas 2 has a distorted square-planar coordination geometry. Structures of 1 and 2 have supramolecular networks formed via inter- and intra-molecular hydrogen bonding interactions. The kinetics and mechanism of ligand substitution of 1 and 2 by thiourea (TU) were studied in detail and showed a biphasic process in which an initial fast reaction is followed by a slower one. The activation parameters for the fast reaction: Δ H # = 68 ± 4 and 73 ± 5 kJ mol−1, Δ S # = 43 ± 10 and 54 ± 9 J K−1 mol−1 for 1 and 2 , respectively, supports a dissociative substitution mechanism. Whereas for the slow reaction: Δ H # = 33 ± 6 and 43 ± 3 kJ mol−1, Δ S # = −77 ± 10 and −56 ± 9 J K−1 mol−1 for 1 and 2 , respectively, support an associative substitution mechanism. It is concluded from the activation parameters that the difference in structure does not affect the mechanism. Complexes 1 and 2 have also been evaluated as functional models for the catechol oxidase enzyme and phenoxazinone synthase. The model complexes 1 and 2 show catecholase activity of K cat = 10.9 × 103 and 11.4 × 103 h−1 and phenoxazinone synthase activity of K cat = 2.1 × 103 and 4.3 × 103 h−1, respectively. Compared to the enzyme itself (K cat = 8.3 h−1), the model complexes 1 and 2 are promising candidates as functional mimics for catechol oxidase and phenoxazinone synthase. [ABSTRACT FROM AUTHOR]

Rational ligand design approaches allowed {Cu2(μ-OH/OMe)} cores to be accommodated within μ-phenoxido bis(tetradentate) and μ-phenoxido bis(tridentate) ligands having thioether donors. The complexes [Cu2(μ-H2L1)(μ-OH)](ClO4)2·2H2O (1), [Cu2(μ-L2)(μ-OH)(OH2)](ClO4)2 (2a) and [Cu2(μ-L2)(μ-OCH3)(OH2)](ClO4)2 (2b) were obtained from an N2O3S2 donor set bearing the H3L1 ligand (2,6-bis-[{2-(2-hydroxyethylthio)ethylimino}methyl]-4-methylphenol) and N2OS2 donor set containing the HL2 ligand (4-methyl-2,6-bis-[{2-(methylthio)phenylimino}methyl]phenol) without showing double phenoxido bridging or any type of preformed inter-fragment aggregation. Previously, we showed that H3L (2,6-bis[((2-(2-hydroxyethoxy)ethyl)imino)methyl]-4-methylphenol), the ether analogue of H3L1, in the presence of carboxylate anions, was responsible for the self-aggregation of preformed {Cu2} fragments and gave two types of [Cu4] complexes comprising [Cu4O] and [Cu4(OH)2] cores (T. S. Mahapatra, A. Bauzá, D. Dutta, S. Mishra, A. Frontera and D. Ray, ChemistrySelect, 2016, 1, 64–74). The molecular structures of 1, 2a and 2b were determined via single crystal X-ray diffraction and solution studies, which indicated the presence of [Cu2] species. This was further confirmed via UV-vis spectroscopy and HRMS analysis. The synthesized complexes were screened for their potential as catalysts for the catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH2). A change in the mechanism of catalytic oxidation was observed with a change in the ligand backbone. All three complexes also showed DNA binding properties, which were further substantiated via molecular docking studies. Their DNA binding affinities were quantitatively ascertained using their intrinsic binding constant, Kb, values which were found to be 4.2 × 104, 5.6 × 104 and 4.8 × 104 M−1, respectively. Furthermore, the complexes displayed efficient DNA cleavage behaviour with pBR322 and the oxidative path was established in presence of ROS, singlet oxygen, 1O2, and the superoxide anion, O2·−. [ABSTRACT FROM AUTHOR]

Graphical abstract Critical role of carboxylate bridging was examined for carboxylate coordination assisted aggregation in [Cu 4 (µ 4 –O)(µ–L1) 2 (µ 1,3 –O 2 CCH 3) 4 ]·H 2 O (2a) and [Cu 4 (µ 4 –O)(µ–L1) 2 (µ 1,3 –O 2 CC 2 H 5) 4 ]·H 2 O (2b) avoiding ligand imine arm hydrolysis. Highlights • New ligand HL1 has been examined for synthesis of CuII coordination aggregates. • Use of carboxylates give rise to µ 4 –oxido bridged [Cu 4 ] complexes 2a and 2b. • Partial ligand arm hydrolysis observed in absence of any carboxylates. • The Cu 2 based building blocks present in MeOH solution showed catecholase activity. • DNA binding ability of the synthesized complexes was checked. Abstract The dinuclear copper(II) complex [Cu 2 (µ–L2NH) 2 (OH 2) 2 ](ClO 4) 4 (1) was obtained following one imine side arm hydrolysis of HL1 (2,6-bis-[{3-(diethylamino)propylimino}methyl]-4-methylphenol). Introduction of carboxylates inhibited the hydrolysis and resulted in two tetranuclear copper(II) complexes [Cu 4 (µ 4 –O)(µ–L1) 2 (µ 1,3 –O 2 CCH 3) 4 ]·H 2 O (2a) and [Cu 4 (µ 4 –O)(µ–L1) 2 (µ 1,3 –O 2 CC 2 H 5) 4 ]·H 2 O (2b). Use of perchlorate and carboxylate salts of copper(II) for the reactions under study with HL1 has directed these reactions. Perchlorate anions in presence of H 2 O molecules, as hydrolytic nucleophiles, triggered imine arm hydrolysis and bridging carboxylate anions allowed transformation of copper(II) bound H 2 O molecule to μ 4 -oxido central nucleating group via hydroxido-bridge. The complexes were obtained from simultaneous chelation and bridging by the hydrolyzed and as used ligand anions L2NH− and HL1− respectively. These complexes have been characterized in the solid state by X-ray crystallography and FT-IR spectroscopy. Solution phase stability of Cu 2 -based fragments was studied by UV–vis absorption spectroscopy. Solution properties have been examined for substrate binding in catechol oxidase activity and binding affinity for biomacromolecules like DNA and Human Serum Albumin. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Mononuclear copper(II) complexes as functional models for catechol oxidase enzymes. • X-ray crystal structures of 2 and 5 confirms the trigonal bipyramidal geometry. • Rate of the reaction in micellar media is higher than those in aqueous solution. • Ligand stereoelectronic factors of the metal complexes determine the catecholase-like activity. Abstract A series of mononuclear copper(II) complexes of the type [Cu(L)Cl 2 ] 1 – 6 , where L is a tridentate 3 N ligand such as N -methyl- N ′-(pyrid-2-ylmethyl)ethylenediamine (L1), N -ethyl- N ′-(pyrid-2-ylmethyl)ethylenediamine (L2), N -phenyl- N ′-(pyrid-2-ylmethyl)ethylenediamine (L3), N,N -dimethyl- N ′-(pyrid-2-ylmethyl)ethylenediamine (L4), N,N -diethyl- N ′-(pyrid-2-ylmethyl)-ethylenediamine (L5) and N -methyl- N ′-(pyridin-2-ylmethyl)benzene-1,2-diamine (L6), has been isolated and studied as functional models for catechol oxidase enzymes in different aqueous micellar media. The X-ray crystal structures of 2 and 5 contain a CuN 3 Cl 2 chromophore with a trigonal bipyramidal based coordination geometry. Interestingly, all the complexes form cationic [Cu(L)(DBC)(H 2 O)]+ adduct species in which DBC2− acts as a monodentate ligand, and the adduct species interacts strongly with anionic SDS micelles. The rates of the oxygenase reaction follow the trend SDS > TX-100 ∼ water > CTAB, revealing that the rate of the reaction in micellar media are higher than those in aqueous solution and that the nature of biomimetic microenvironments of the micellized copper(II) catalyst and also the ligand stereoelectronic factors like donor atom basicity and steric bulk of ligand N -alkyl substituents, determine the catecholase-like activity. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A ditopic bis(pyrazolyl)methane-based ligand has been prepared. • A μ 4 -oxido-bridged tetranuclear Cu(II) complex has been obtained. • The complex has been characterized by single crystal X-ray diffraction. • The catecholase activity of the complex was investigated. Abstract A new tetranuclear copper(II) complex, {But-C 6 H 2 (O)[CH = N-CH 2 -CH(pz) 2 ] 2 } 2 Cu 4 (μ 4 -O)(OAc) 4 (L 2 Cu 4 (μ 4 -O)(OAc) 4 , pz = pyrazolyl ring) has been prepared from the condensation reaction of 4- tert -butyl-2,6-diformylphenol with two equivalents of bis(pyrazolyl)ethanamine moieties in the presence of two equivalents of copper(II) acetate. The complex has been characterized by X-ray diffraction studies in solid state, as well as by UV–Vis, IR, and ESI spectroscopies. The structure of this inverse coordination complex consists of a central oxygen ion surrounded by four copper(II) cations residing in the corners of a distorted tetrahedron; the remaining coordination sites of the Cu2+ ions are filled by imine donors and acetate counter-ions, leaving the bis(pyrazolyl)methane donor groups uncoordinated to the copper(II) centers. In contrast to the solid-state structure, this compound was found to be dinuclear in solution, LCu 2 (OAc) 2 (OH). The complex catalyzes the oxidation of 3,5-di- tert -butylcatechol (DTBC) and 4- tert -butylcatechol (TBC) to their corresponding quinones. The catalytic mechanism was investigated using DTBC as a substrate, and it was found that the oxidation reaction occurs via two different pathways, one involving molecular oxygen and the other hydrogen peroxide as oxidants. [ABSTRACT FROM AUTHOR]

Copper(II) complexes of five peptide ligands containing at least three histidine residues have been tested as catalysts in catechol oxidation and superoxide dismutation. All systems exhibit considerable catechol oxidase-like activity, and the Michaelis-Menten enzyme kinetic model is applicable in all cases. Beside the Michaelis-Menten parameters, the effects of pH, catalyst and dioxygen concentration on the reaction rates are also reported. Considering the rather different sequences, the observed oxidase activity seems to be a general behavior of copper(II) complexes with multihistidine peptides. Interestingly, in all cases {Nim/2Nim,2N−} coordinated complexes are the pre-active species, the bound amide nitrogens were proposed to be an acid/base site for facilitating substrate binding. The studied copper(II)-peptide complexes are also able to effectively dismutate superoxide radical in the neutral pH range. [ABSTRACT FROM AUTHOR]