Quinone Formation Research Articles

Catechol-derived Mannich bases: radical regulatory properties, cytotoxicity and interaction with biomolecules

Free radicals are ubiquitous in biological systems, being responsible for pathogenesis of degenerative diseases and participating in vitally important biochemical processes, which are mediated by radical regulatory agents. The effects of the aliphatic amine substituents in the catechol-derived Mannich bases on their antioxidant and pro-oxidant activity were investigated. It has been found that the presence of catechol moiety in the structure of Mannich bases allows them to act as Cu(II) reductants, efficient Fe(II) chelators and potent DPPH radical scavengers. It has been found that the plausible mechanism of the DPPH radical scavenging proceeds via quinone formation, followed by their interaction with ethanol via the Michael addition reaction. In the neutrophil respiratory burst assay, several compounds have demonstrated a weak antioxidant activity at the micromolar level (0.1–10 µM), whereas at the millimolar level (0.1 mМ) a strong pro-oxidant effect has been observed. Additionally, at the highest used concentrations a pronounced cytotoxicity against dermal fibroblasts DF-2 and an immunosuppressive effect against T-lymphocytes have been observed for all the synthesized compounds. It has been demonstrated that the oxidation of catechols in the presence of low-molecular thiols results in the formation of covalent adducts, which provides an insight into their cytotoxicity and detoxification pathways.

Synthesis of Palladium Nanomaterials Using Plant Leaf Extract and their Enhanced Photocatalytic Activities against Organic Dyes

Aims and Objectives: This study aimed to carry out the green synthesis of palladium nanoparticles (Pd NPs) using the aqueous leaves extract of Eclipta alba. The appearance of a characteristic surface plasmon resonance peak at 410 nm confirmed the synthesis of Pd NPs. Method: The average particle sizes of 13 nm were observed by using the leaf concentrations of 10 mL with a certain amount of PdCl2 (0.001 M) at 25 ̊ C. The Pd NPs, as synthesized under the optimized conditions (10 mL extract + 60 ̊ C + 0.001 M PdCl2), were spherical in shape, small in size, and uniformly distributed, as depicted by HR-TEM images. Results: FTIR, XRD, DLS, and zeta potential further confirmed the formation of Pd NPs. The Pd NPs synthesized at optimized conditions exhibited strong catalytic activity in dye Eosin yellow, Rose Bengal, Tartrazine, and Ponceau S degradation by discoloration of dyes in 3 hrs. The removal of all dyes by the Pd NPs was optimized by varying specific operating parameters, such as initial dye concentration, solution pH, irradiation time, and temperature. Conclusion: This high activity of Pd NPs may be due to their small size, high dispersion, and surface- capping phytochemicals. result: Bio-fabrication of metallic Pd NPs using different plant extracts compared to other reducing agents is more scalable, rapid, and cost-effective for generating bulk nanoparticles. The phytochemical principles, such as phytoconstituents, reduce the PdCl2 to Pd NPs and are implicated in the capping and stability of the nanoparticles. Hence, the leaves of Eclipta alba have different polyols and are well known. Apart from this, hydroxyl groups in phenolic compounds may participate in the bio-reduction of PdCl2. Such compounds can chelate metal ions to form their quinones form, which is an intermediate palladium complex. Then, stabilization of the intermediate form and reduction of Pd2+ to Pd0 occurred due to free electrons or nascent hydrogen produced during the bio-reduction reaction. Finally, Pd-NPs were prepared due to the collision of neighboring Pd0 atoms. These significant conjugations exist in the keto-enol system within the quinone form of the compound.

Mechanisms of the initial stage of non-enzymatic oxidation of wine: A mini review.

Non-enzymatic oxidation is a primary factor affecting wine quality during bottling or aging. Although red and white wines exhibit distinct responses to oxidation over time, the fundamental mechanisms driving this transformation remain remarkably uniform. Non-enzymatic oxidation of wine commences with the intricate interplay between polyphenols and oxygen, orchestrating a delicate redox dance with iron and copper. Notably, copper emerges as an accelerant in this process. To safeguard wine integrity, sulfur dioxide (SO2) is routinely introduced to counteract the pernicious effects of oxidation by neutralizing hydrogen peroxide and quinone. In this comprehensive review, the initial stages of non-enzymatic wine oxidation are examined. The pivotal roles played by polyphenols, oxygen, iron, copper, and SO2 in this complex oxidative process are systematically explored. Additionally, the effect of quinone formation on wine characteristics and the intricate dynamics governing oxygen availability are elucidated. The potential synergistic or additive effects of iron and copper are probed, and the precise balance between SO2 and oxygen is scrutinized. This review summarizes the mechanisms involved in the initial stages of non-enzymatic oxidation of wine and anticipates the potential for further research.

Date Leaves-Derived Submicron/Nano Carbon-Modified Glassy Carbon Electrode for Highly Sensitive and Simultaneous Detection of 1-Naphthol and 2-Naphthol

This study introduces a novel approach for synthesizing biomass derived carbon from date leaves waste, employing a straightforward combination of pyrolysis and ball milling processes. This process yields active carbon in submicron and nanometer sizes, characterized by detailed surface, structural, and compositional analyses, confirming suitability of the materials for electrochemical applications. Utilizing this synthesized carbon, we have developed a modified glassy carbon electrode (DLSNC/GCE) for the highly-sensitive and simultaneous detection of phenolic contaminants, specifically 1-naphthol (1-NP) and 2-naphthol (2-NP), which are crucial for environmental monitoring. The study describes two innovative fabrication methods for electrochemical sensors. The first method controls the direct oxidation of 1-NP and 2-NP, while the second method exploits redox peaks associated with quinone formation from dihydroxy naphthalene, revealing superior analytical performance for the simultaneous detection of the analytes. The electrochemical sensor demonstrated exceptional sensitivity and selectivity towards 1-NP and 2-NP. This revolution emphasizes the potential of using date leaves-derived carbon materials in constructing low-cost, efficient electrochemical sensors for environmental monitoring and electrochemical applications.

Discovery of a Gut Bacterial Metabolic Pathway that Drives α-Synuclein Aggregation.

Parkinson's disease (PD) etiology is associated with aggregation and accumulation of α-synuclein (α-syn) proteins in midbrain dopaminergic neurons. Emerging evidence suggests that in certain subtypes of PD, α-syn aggregates originate in the gut and subsequently spread to the brain. However, mechanisms that instigate α-syn aggregation in the gut have remained elusive. In the brain, the aggregation of α-syn is induced by oxidized dopamine. Such a mechanism has not been explored in the context of the gastrointestinal tract, a niche harboring 46% of the body's dopamine reservoirs. Here, we report that Enterobacteriaceae, a bacterial family prevalent in human gut microbiotas, induce α-syn aggregation. More specifically, our in vitro data indicate that respiration of nitrate by Escherichia coli K-12, which results in production of nitrite that mediates oxidation of Fe2+ to Fe3+, creates an oxidizing redox potential. These oxidizing conditions enabled the formation of dopamine-derived quinones and α-syn aggregates. Exposing nitrite, but not nitrate, to enteroendocrine STC-1 cells induced aggregation of α-syn that is natively expressed in these cells, which line the intestinal tract. Taken together, our findings indicate that bacterial nitrate reduction may be critical for initiating intestinal α-syn aggregation.

Polymerizable rotaxane of cucurbituril protecting dopamine based adhesive hydrogels

The catechol moiety found within mussel proteins plays a pivotal role in enhancing their adhesive properties. Nonetheless, catechol compounds, such as dopamine (DOP) derivatives, are susceptible to oxidation, leading to the formation of quinone. This oxidation process poses a significant challenge in the development of DOP-based hydrogels, hampering their adhesion capabilities and hindering polymerization. To protect DOP moieties from oxidation, DOP and N-(3-aminopropyl)methacrylamide (AMA) moieties were grafted onto the side groups of biocompatible poly(glutamic acid) (PGA). Subsequently, the DOP unit, serving as a second guest, would be captured by a polymerizable rotaxane of cucurbituril (CB[n]), in which the host molecule CB[8] complexed with the first guest, polymerizable methyl viologen (MV), forming a protective function and dynamic cross-linking. Upon exposure to light curing, a composite network emerged through the synergy of covalent cross-linking and supramolecular host-guest complexation of DOP with CB[8]. The generated complexation between DOP and CB[8] could protect the DOP moieties, resulting in photocured hydrogels with exceptional adhesive strength and remarkable tensile capabilities. Moreover, 3D printing technology was used to create various models with these DOP-based hydrogels, demonstrating their promising applications in future.

Recent applications of coinage metal nanoparticles passivated with salicylaldehyde and salicylaldehyde-based Schiff bases.

Salicylaldehyde (SD) and its derivatives are effective precursors for generating coinage metal (gold, silver, and copper) nanoparticles (NPs). These NPs have a variety of potential environmental applications, such as in water purification and sensing, and those arising from their antibacterial activity. The use of SD and its derivatives for synthesizing coinage NPs is attractive due to several factors. First, SD is a relatively inexpensive and readily available starting material. Second, the synthetic procedures are typically simple and can be carried out under mild conditions. Finally, the resulting NPs can be tailored to have specific properties, such as size, shape, and surface functionality, by varying the reaction conditions. In an alkaline solution, the phenolate form of SD was converted to its quinone form, while ionic coinage metal salts were converted to zero-valent nanoparticles. The capping in situ produced quinone of coinage metal nanoparticles generated metal-enhanced fluorescence under suitable experimental conditions. The formation of iminic bonds during the formation of Schiff bases altered the properties (especially metal-enhanced fluorescence) and applications.

Theoretical Study on the Multiple Free Radical Scavenging Reactions of Pyranoanthocyanins.

The free radical trapping capacities of multiple pyranoanthocyanins in wine storage and ageing were theoretically explored by density functional theory (DFT) methods. Intramolecular hydrogen bonds were detected in all pyranoanthocyanins, and the planarity of the compounds worsened with an increasing dielectric constant in the environment. Solvents significantly influenced the reaction enthalpies; thus, the preferred thermodynamic mechanisms of the free radical scavenging reactions were modified in different phases. This study incorporates hydrogen atom transfer (HAT), proton loss (PL), electron transfer (ET) reactions, and demethylation (De) of methoxy group mechanisms. The three pyranoanthocyanins have the capacity to capture n1+1 free radicals, where n1 represents the number of methoxy groups. In the gas phase, they prefer employing the n1-De-HAT mechanism on the guaiacyl moiety of the B ring, resulting in the formation of a stable quinone or a quinone radical to scavenge free radicals. In the benzene phase, pyranoanthocyanins trap free radicals via a PL-n1-De-HAT mechanism. In the water phase, the targeted pyranoanthocyanins may dissociate in the form of carboxylate and tend to utilize the n2-PL-n1-De-ET mechanism, where n2 and n1 represent the number of phenolic groups and methoxy groups, respectively, facilitating multiple H+/e- reactions.

The content of phenols and activity of polyphenol oxidase in the hametophyte of dominant mosses in forest ecosystems of the Ukrainian Roztochia

Bryophytes are indicators of the state of forest ecosystems. Dominant species of forest mosses are sensitive to the influence of abiotic factors and demonstrate adaptive reactions different from vascular plants, which are decisive for the prediction of changes in the natural environment. We have analyzed the changes in the content of water-soluble phenols and the activity of polyphenol oxidase n the hametophyte of dominant epigean forest mosses depending on changes in the intensity of insolation, the water and temperature regime of soils and air in experimental localities of forest ecosystems of the Ukrainian Roztochia. The highest content of water-soluble phenolic compounds was found in the resistant mosses Polytrichum formosum and Atrichum undulatum on the territory of protected beech forest under conditions of low light intensity and sufficient humidity of local vegetation. The maximum indicators of the content of phenolic compounds were found in A. undulatum (199.5±9.8 μg/g of dry matter mass), and the lowest – in Plagiomnium affine (54.7±2.6 μg/g of dry matter mass) that is sensitive to changes in the ecological conditions of local vegetation in all studied areas. A significant decrease in the content of phenolic compounds in areas of disturbed ecosystems may indicate the active participation of phenols in the adaptation of mosses to the effects of high light intensity, elevated temperatures and moisture deficit. The highest indicators of polyphenol oxidase activity were determined in P. affine (120.4±6.1 relative units/g of dry matter mass*s) and P. formosum (41.8±2.1 relative units/g of dry matter mass*s) from local vegetation under unfavorable conditions on the territory of stationary recreation. A direct correlation between the content of phenolic compounds and the activity of polyphenol oxidase was not established. The higher activity of this enzyme under conditions of high light intensity than in shaded local plants may indicate a relationship between polyphenol oxidase and photosynthesis. An increase in the activity of polyphenol oxidase contributes to the significant formation of quinones, which, accumulating in cell walls, reduce the processes of lipid peroxidation, regulate their permeability and ensure better moisture storage in the moss turfs.

A Novel Natural Siderophore Antibiotic Conjugate Reveals a Chemical Approach to Macromolecule Coupling.

Inspired by natural sideromycins, the conjugation of antibiotics to siderophores is an attractive strategy to facilitate "Trojan horse" delivery of antibiotics into bacteria. Genome analysis of a soil bacterium, Dactylosporangium fulvum, found a "hybrid" biosynthetic gene cluster responsible for the production of both an antibiotic, pyridomycin, and a novel chlorocatechol-containing siderophore named chlorodactyloferrin. While both of these natural products were synthesized independently, analysis of the culture supernatant also identified a conjugate of both molecules. We then found that the addition of ferric iron to purified chlorodactyloferrin and pyridomycin instigated their conjugation, leading to the formation of a covalent bond between the siderophore-catechol and the pyridomycin-pyridine groups. Using model reactants, this iron-based reaction was found to proceed through a Michael-type addition reaction, where ferric iron oxidizes the siderophore-catechol group into its quinone form, which is then attacked by the antibiotic pyridyl-nitrogen to form the catechol-pyridinium linkage. These findings prompted us to explore if other "cargo" molecules could be attached to chlorodactyloferrin in a similar manner, and this was indeed confirmed with a pyridine-substituted TAMRA fluorophore as well as with pyridine-substituted penicillin, rifampicin, and norfloxacin antibiotic analogues. The resultant biomimetic conjugates were demonstrated to effectively enter a number of bacteria, with TAMRA-chlorodactyloferrin conjugates causing fluorescent labeling of the bacteria, and with penicillin and rifampicin conjugates eliciting antibiotic activity. These findings open up new opportunities for the design and facile synthesis of a novel class of biomimetic siderophore conjugates with antibiotic activity.

Gelatin Carbon Dots Interaction with Nitrosyl Ruthenium Complex: Fluorescence Quenching and Chemiluminescence Mechanisms.

Carbon dots (CDs) exhibit luminescence, biocompatibility, and higher water solubility. This material has been developed for biological applications, specifically in bioimaging. In this work, the gelatin carbon dots (CDg) was obtained from commercial gelatin using a hydrothermal method in domestic microwave, and the suppression fluorescent mechanism were enhanced by the addition of the [RuII(bdq)(NO)(tpy)]3+ (Rubdq-NO+) complex ion. After purification through a dialysis bag, the resulting CDs (CDg) exhibit fluorescent emission at 400nm and maintained fluorescence stability in an aqueous solution (pH = 7) for 30days under 5 ◦C. Fluorescence quenching studies revealed an electrostatic interaction between the negative charge from CDg (δ = - 20mV) and the positively charged nitrosyl (NO+) ligand of the ruthenium complex (Rubdq-NO+), resulting in quenching of the CDg fluorescence due to the inner filter effects (IFE). The chemiluminescence reaction of CDg and Rubdq-NO-CDg in presence of norepinephrine (NOR) were evaluated. NOR in PBS are liable to undergo spontaneous oxidation to quinone form (NOR-quinone). CDg are believed interact with NOR-quinone and an electron transfer occur obtained CDg+ accompanied to green emission fluorescence (520nm). While for Rubdq-NO-CDg in presence of NOR, the green emission occurs accompanied by NO0 release using DAF-2 probe.

Bridging population pharmacokinetic and semimechanistic absorption modeling of APX3330.

APX3330 ((2E)-2-[(4,5-dimethoxy-2-methyl-3,6-dioxo-1,4-cyclohexadien-1-yl)methylene]-undecanoic acid), a selective inhibitor of APE1/Ref-1, has been investigated in treatment of hepatitis, cancer, diabetic retinopathy, and macular edema. APX3330 is administered orally as a quinone but is rapidly converted to the hydroquinone form. This study describes the pharmacokinetics of APX3330 and explores effect of food on absorption. Total plasma quinone concentrations of APX3330 were obtained following oral administration from studies in healthy Japanese male subjects (single dose-escalation; multiple-dose; food-effect) and patients with cancer patients. Nonlinear mixed effects modeling was performed using Monolix to estimate pharmacokinetic parameters and assess covariate effects. To further evaluate the effect of food on absorption, a semi-physiologic pharmacokinetic model was developed in Gastroplus to delineate effects of food on dissolution and absorption. A two-compartment, first order absorption model with lag time best described plasma concentration-time profiles from 49 healthy Japanese males. Weight was positively correlated with apparent clearance (CL/F) and volume. Administration with food led to an 80% higher lag time. CL/F was 41% higher in the cancer population. The semi-physiologic model indicates a switch from dissolution-rate control of absorption in the fasted-state to gastric emptying rate determining absorption rate in the fed-state. Oral clearance of APX3330 is higher in patients with cancer than healthy Japanese males, possibly due to reduced serum albumin in patients with cancer. Delayed APX3330 absorption with food may be related to higher conversion to the more soluble but less permeable hydroquinone form in the gastrointestinal tract. Future work should address pharmacokinetic differences between APX3330 quinone and hydroquinone forms.

Machine Learning Enables Accurate Prediction of Quinone Formation during Drug Metabolism.

Metabolism helps in the elimination of drugs from the human body by making them more hydrophilic. Sometimes, drugs can be bioactivated to highly reactive metabolites or intermediates during metabolism. These reactive metabolites are often responsible for the toxicities associated with the drugs. Identification of reactive metabolites of drug candidates can be very helpful in the initial stages of drug discovery. Quinones are soft electrophiles that are generated as reactive intermediates during metabolism. Quinones make up more than 40% of the reactive metabolites. In this work, a reliable data set of 510 molecules was used to develop machine learning and deep learning-based predictive models to predict the formation of quinone-type metabolites. For representing molecules, two-dimensional (2D) descriptors, PubChem fingerprints, electro-topological state (E-state) fingerprints, and metabolic reactivity-based descriptors were used. Developed models were compared to the existing Xenosite web server using the untouched test set of 102 molecules. The best model achieved an accuracy of 86.27%, while the Xenosite server could achieve an accuracy of only 52.94% on the test set. Descriptor analysis revealed that the presence of greater numbers of polar moieties in a molecule can prevent the formation of quinone-type metabolites. In addition, the presence of a nitrogen atom in an aromatic ring and the presence of metabolophores V51, V52, and V53 (SMARTCyp descriptors) decrease the probability of quinone formation. Finally, a tool based on the best machine learning models was developed, which is accessible at http://14.139.57.41/quinonepred/.

Anthracene boronic acid functionalized activated screen-printed carbon electrode: A strategy for direct phosphate voltammetric detection

Phosphates (Pi) in water can be beneficial for aquatic plants and animals as they serve as a nutrient source. However, excess amounts of Pi in water can lead to eutrophication, a process that leads to excessive plant growth and oxygen depletion and, thus affects the aquatic ecosystem. Pi can also contribute to the formation of harmful algal blooms, which can produce toxins that are harmful to both humans and animals. Therefore, maintaining Pi amount within the safe range is important and through the aid of analytical tools the concentration level can be managed. Electrochemical sensors are versatile and powerful tools for environmental monitoring. We herein report a direct voltammetric sensing of Pi using a screen-printed carbon electrode functionalized with anthracene boronic acid (SPCE/ANBA). The complexation of ANBA with Pi through specific BA-Pi binding leads to the quinone formation that has been utilized for Pi detection in an electrochemical system for the first time. Under optimized conditions, the SPCE/ANBA modified electrode exhibited a wide linear range between 10 µM and 100 mM with high selectivity and sensitivity and a detection limit of 3.2 µM (S/N = 3). Finally, the SPCE/ANBA modified electrode was successfully tested with an environmental water sample (tap and lake) by using standard addition method. It was found that the system has satisfactory real sample results.

Metal‐Enhanced Fluorescence due to Salicylaldehyde‐Silver Nanoparticle Interactions for Fe3+ Sensing

AbstractSilver nanoparticles were synthesized using alkaline salicylaldehyde (SL) in the presence of silver nitrate. SL was oxidized to quinone form, while silver(I) was converted to silver (0). The solution was highly fluorescent, (quantum yield 7 %, λex 290 nm, λmax 424 nm), where silver (0) exhibited metal‐enhanced fluorescence and quinone acted as the fluorophore. The fluorescence was selectively quenched with the addition of Fe3+. No other metal shows such drastic fluorescence quenching. Thus, silver‐enhanced fluorescence is used to detect iron selectively and sensitively (limit of detection 2×10−9 M, linear detection ranges from 10−4 M to 8×10−9 M). The detection of iron was also done at various water of natural sources (drinking water tap water, rainwater, and Ganga River water). The iron concentration was quite similar to atomic absorption spectroscopy. The enhancement of fluorescence of the sliver atom is attributed to enhanced photonic mode density, related to the lightning rod effect. The quenching of silver‐enhanced fluorescence was attributed to the destruction of the capping agent due to SL‐iron complexation. The variation of distance between the fluorophore and metalized surface was anticipated for the alteration of fluorescence with and without the Fe3+ion.

Redox-crippled MitoQ potently inhibits breast cancer and glioma cell proliferation: A negative control for verifying the antioxidant mechanism of MitoQ in cancer and other oxidative pathologies

Mitochondria-targeted coenzyme Q10 (Mito-ubiquinone, Mito-quinone mesylate, or MitoQ) was shown to be an effective antimetastatic drug in patients with triple-negative breast cancer. MitoQ, sold as a nutritional supplement, prevents breast cancer recurrence. It potently inhibited tumor growth and tumor cell proliferation in preclinical xenograft models and in vitro breast cancer cells. The proposed mechanism of action involves the inhibition of reactive oxygen species by MitoQ via a redox-cycling mechanism between the oxidized form, MitoQ, and the fully reduced form, MitoQH2 (also called Mito-ubiquinol). To fully corroborate this antioxidant mechanism, we substituted the hydroquinone group (-OH) with the methoxy group (-OCH3). Unlike MitoQ, the modified form, dimethoxy MitoQ (DM-MitoQ), lacks redox-cycling between the quinone and hydroquinone forms. DM-MitoQ was not converted to MitoQ in MDA-MB-231 cells. We tested the antiproliferative effects of both MitoQ and DM-MitoQ in human breast cancer (MDA-MB-231), brain-homing cancer (MDA-MB-231BR), and glioma (U87MG) cells. Surprisingly, DM-MitoQ was slightly more potent than MitoQ (IC50 = 0.26 μM versus 0.38 μM) at inhibiting proliferation of these cells. Both MitoQ and DM-MitoQ potently inhibited mitochondrial complex I-dependent oxygen consumption (IC50 = 0.52 μM and 0.17 μM, respectively). This study also suggests that DM-MitoQ, which is a more hydrophobic analog of MitoQ (logP: 10.1 and 8.7) devoid of antioxidant function and reactive oxygen species scavenging ability, can inhibit cancer cell proliferation. We conclude that inhibition of mitochondrial oxidative phosphorylation by MitoQ is responsible for inhibition of breast cancer and glioma proliferation and metastasis. Blunting the antioxidant effect using the redox-crippled DM-MitoQ can serve as a useful negative control in corroborating the involvement of free radical-mediated processes (e.g., ferroptosis, protein oxidation/nitration) using MitoQ in other oxidative pathologies.

The ferryl generation by fenton reaction driven by catechol

The Fenton and Fenton-like reactions are based on the decomposition of hydrogen peroxide catalyzed by Fe(II), primarily producing highly oxidizing hydroxyl radicals (HO∙). While HO∙ is the main oxidizing species in these reactions, Fe(IV) (FeO2+) generation has been reported as one of the primary oxidants. FeO2+ has a longer lifetime than HO∙ and can remove two electrons from a substrate, making it a critical oxidant that may be more efficient than HO∙. It is widely accepted that the preferential generation of HO∙ or FeO2+ in the Fenton reaction depends on factors such as pH and Fe: H2O2 ratio. Reaction mechanisms have been proposed to generate FeO2+, which mainly depend on the radicals generated in the coordination sphere and the HO∙ radicals that diffuse out of the coordination sphere and react with Fe(III). As a result, some mechanisms are dependent on prior HO∙ radical production. Catechol-type ligands can induce and amplify the Fenton reaction by increasing the generation of oxidizing species. Previous studies have focused on the generation of HO∙ radicals in these systems, whereas this study investigates the generation of FeO2+ (using xylidine as a selective substrate). The findings revealed that FeO2+ production is increased compared to the classical Fenton reaction and that FeO2+ generation is mainly due to the reactivity of Fe(III) with HO∙ from outside the coordination sphere. It is proposed that the inhibition of FeO2+ generation via HO∙ generated from inside the coordination sphere is caused by the preferential reaction of HO∙ with semiquinone in the coordination sphere, favoring the formation of quinone and Fe(III) and inhibiting the generation of FeO2+ through this pathway.

Enhancement of the electrical and thermal conductivity of epoxy-based composite films through the construction of the multi-scale conductive bridge structure

Electrically conductive adhesive films (ECAFs), a novel electrically and thermally adhesive material, have been widely used in the large-area bonding of microelectronics packaging. However, it is still a challenge to optimize the silver micro-flakes (Ag-MFs) dispersion, and build a more effective electrically and thermally conductive network. In this study, we improved the dispersion of Ag-MFs in epoxy matrix through the intermolecular hydrogen bonding, and proposed a new multi-scale conductive bridge structure. Specifically, poly (3,4-ethylenedioxythiophene)/poly (styrene sulfonate) (PEDOT/PSS or P/P for short) can form the intermolecular hydrogen bonding with Ag-MFs based on the sulfonic groups of PSS chain and the carboxyl group located on the surface of Ag-MFs, resulting in improving dispersion of Ag-MFs. Besides, PEDOT can occur conformation change from benzoid conformation to quinone conformation and form PEDOT conductive crystalline nanofibril, and then multi-scale conductive bridge structure with Ag-MFs were constructed. Moreover, the initial viscosity of epoxy-based composite is maintained within 106 mPa s, which means Ag-MFs is uniformly dispersed after the addition of P/P. Scanning electron microscopy (SEM) and oscillating viscoelastic measurement were used to demonstrate the improved dispersion of Ag-MFs after the addition of P/P. In addition, atomic force microscope (AFM) and Raman spectroscopy were used to verify the conformation change of PEDOT. Compared with ECAF without P/P, the electrical and thermal conductivity of ECAF with 6 wt% P/P was enhanced by 73.1% and 166.3%, respectively. Meanwhile, scattering parameter (S-parameter) measurements demonstrated that ECAF with 6 wt% P/P had excellent radio-frequency behavior at 2–4 GHz, indicating high-performance in the microelectronics packaging industry.

Oxidative Stress and Neuroinflammation in Parkinson's Disease: The Role of Dopamine Oxidation Products.

Parkinson's disease (PD) is a chronic neurodegenerative condition affecting more than 1% of people over 65 years old. It is characterized by the preferential degeneration of nigrostriatal dopaminergic neurons, which is responsible for the motor symptoms of PD patients. The pathogenesis of this multifactorial disorder is still elusive, hampering the discovery of therapeutic strategies able to suppress the disease's progression. While redox alterations, mitochondrial dysfunctions, and neuroinflammation are clearly involved in PD pathology, how these processes lead to the preferential degeneration of dopaminergic neurons is still an unanswered question. In this context, the presence of dopamine itself within this neuronal population could represent a crucial determinant. In the present review, an attempt is made to link the aforementioned pathways to the oxidation chemistry of dopamine, leading to the formation of free radical species, reactive quinones and toxic metabolites, and sustaining a pathological vicious cycle.

Computational Studies of Rubber Ozonation Explain the Effectiveness of 6PPD as an Antidegradant and the Mechanism of Its Quinone Formation.

The discovery that the commercial rubber antidegradant 6PPD reacts with ozone (O3) to produce a highly toxic quinone (6PPDQ) spurred a significant research effort into nontoxic alternatives. This work has been hampered by lack of a detailed understanding of the mechanism of protection that 6PPD affords rubber compounds against ozone. Herein, we report high-level density functional theory studies into early steps of rubber and PPD (p-phenylenediamine) ozonation, identifying key steps that contribute to the antiozonant activity of PPDs. In this, we establish that our density functional theory approach can achieve chemical accuracy for many ozonation reactions, which are notoriously difficult to model. Using adiabatic energy decomposition analysis, we examine and dispel the notion that one-electron charge transfer initiates ozonation in these systems, as is sometimes argued. Instead, we find direct interaction between O3 and the PPD aromatic ring is kinetically accessible and that this motif is more significant than interactions with PPD nitrogens. The former pathway results in a hydroxylated PPD intermediate, which reacts further with O3 to afford 6PPD hydroquinone and, ultimately, 6PPDQ. This mechanism directly links the toxicity of 6PPDQ to the antiozonant function of 6PPD. These results have significant implications for development of alternative antiozonants, which are discussed.