Ferricyanide Reduction Research Articles

Comparative analysis of antioxidant and antibacterial activities of leaf and zest essential oils from "Citrus limon”

This work is part of the study of the antibacterial and antioxidant activity of Algerian aromatic and medicinal plants. We conducted a study on a plant widely used by the local population, Citrus limon, an aromatic plant from the Ghardaïa region. Essential oils were extracted from Citrus limon (zest and leaves) using hydrodistillation, yielding 1.12% for the zest and 0.71% for the leaves. The essential oils were analyzed using GC/MS, identifying 35 constituents in the leaf oils, with 19.41% L-Limonene and 15.02% Nerol acetate, and 25 constituents in the zest oils, with 45.62% L-Limonene, 9.40 Beta-Pinene and 8.3% 3-Carene as major compounds. The antioxidant activity of the essential oils was evaluated using three methods. The first method was the DPPH free radical scavenging test, where the zest showed an IC50 of 135.678 mg/mL, higher than that of the leaf essential oil (IC50 of 34.238 mg/mL). The second method, potassium ferricyanide reduction (FRAP), showed that the essential oils of the leaves had an antioxidant activity of EC50 = 63.3773 mg/mL, and the zest showed EC50 = 200.875 mg/mL. The third method, ammonium phosphomolybdate, based on molybdate reduction (TAC), gave antioxidant activities for the leaves and zest, respectively, of EC50 = 1.5722 mg/mL and EC50 = 1.9604 mg/mL. The antibacterial activity was tested against six reference bacterial strains, with Klebsiella pneumoniae being the most sensitive to both essential oils, showing inhibition zones of 48 mm for the leaf oil and 40 mm for the zest oil. According to the obtained results, the essential oils appear to exhibit excellent antioxidant and antibacterial activity.

Iron Nanostructure Primes Arbuscular Mycorrhizal Fungi Symbiosis Tightly Connecting Maize Leaf Photosynthesis via a Nanofilm Effect.

It is crucial to clarify how the iron nanostructure activates plant growth, particularly in combination with arbuscular mycorrhizal fungi (AMF). We first identified 1.0 g·kg-1 of nanoscale zerovalent iron (nZVI) as appropriate dosage to maximize maize growth by 12.7-19.7% in non-AMF and 18.9-26.4% in AMF, respectively. Yet, excessive nZVI at 2.0 g·kg-1 exerted inhibitory effects while FeSO4 showed slight effects (p > 0.05). Under an appropriate dose, a nano core-shell structure was formed and the transfer and diffusion of electrons between PS II and PS I were facilitated, significantly promoting the reduction of ferricyanide and NADP (p < 0.05). SEM images showed that excessive nZVI particles can form stacked layers on the surface of roots and hyphae, inhibiting water and nutrient uptake. TEM observations showed that excessive nanoparticles can penetrate into root cortical cells, disrupt cellular homeostasis, and substantially elevate Fe content in roots (p < 0.05). This exacerbated membrane lipid peroxidation and osmotic regulation, accordingly restricting photosynthetic capacity and AMF colonization. Yet, appropriate nZVI can be adhered to a mycelium surface, forming a uniform nanofilm structure. The strength of the mycelium network was evidently enhanced, under an increased root colonization rate and an extramatrical hyphal length (p < 0.05). Enhanced mycorrhizal infection was tightly associated with higher gas exchange and Rubisco and Rubisco enzyme activities. This enabled more photosynthetic carbon to input into AMF symbiont. There existed a positive feedback loop connecting downward transfer of photosynthate and upward transport of water/nutrients. FeSO4 only slightly affected mycorrhizal development. Thus, it was the Fe nanostructure but not its inorganic salt state that primed AMF symbionts for better growth.

Unraveling the Electron Transfer in Cupriavidus necator – Insights Into Mediator Reduction Mechanics

AbstractCupriavidus necator, despite lacking direct electron transfer capabilities, demonstrates efficient reduction of various redox mediators in oxygen‐free cultivation within bioelectrochemical systems. This study investigates the reduction site of ferricyanide through inhibition and expression rate analysis of oxygen and nitrate respiration chain complexes, comparing aerobic cultivation conditions with fructose as carbon and electron donor to autotrophic (CO2/H2/O2) and anodic cultivation conditions (fructose/anode). Azide inhibition identified cytochrome c oxidase as the primary complex facilitating electron transfer to ferricyanide, with a secondary role proposed for nitrite reductase NirS, demonstrating a 3.9±1.1‐fold higher expression when exposed to anodic conditions. The 2.9±0.6‐fold increase in the expression of the natural porin OmpA under anodic conditions implies its potential involvement in ferricyanide uptake. Additionally, chemically permeabilizing cell membranes with cetyltrimethylammonium bromide doubles ferricyanide reduction rates without an anode present, offering insights for optimizing redox mediation in C. necator based bioelectrochemical systems. This study opens up new possibilities for the targeted optimization of mediated electron transfer in C. necator and other organisms.

Stabilization effect and interaction mechanism of mannoprotein on anthocyanins in mulberry juice

This study aimed to investigate the problem of color instability in mulberry juice, examine the effect of mannoprotein (MP) dosage on improving the stability of anthocyanins in mulberry juice, and explore the molecular binding mechanism between them. As the mass ratio of anthocyanins to MP of 1.07 × 10−3: 1–1.65 × 10−3: 1, the retention rates of anthocyanins in mulberry juice and simulated system were significantly improved in the photostability experiment, with the highest increase of 128.89 % and 24.11 %, respectively. In the thermal stability experiment, it increased by 7.96 % and 18.49 %, respectively. The synergistic effect of combining MP with anthocyanins has been demonstrated to greatly enhance their antioxidant capacity, as measured by ABTS, FRAP, and potassium ferricyanide reduction method. Furthermore, MP stabilized more anthocyanins to reach the intestine in simulated in vitro digestion. MP and cyanidin-3-glucoside (C3G) interacted with each other through hydrogen bonding and hydrophobic interactions. Specific amino acid residues involved of MP in binding process were identified as threonine (THR), isoleucine (ILE) and arginine (ARG). The identification of the effective mass concentration ratio range and binding sites of MP and anthocyanins provided valuable insights for the application of MP in mulberry juice.

Optimization of Flavonoid Extraction from Abelmoschus manihot Flowers Using Ultrasonic Techniques: Predictive Modeling through Response Surface Methodology and Deep Neural Network and Biological Activity Assessment.

Understanding the optimal extraction methods for flavonoids from Abelmoschus manihot flowers (AMF) is crucial for unlocking their potential benefits. This study aimed to optimize the efficiency of flavonoid extraction from AMF. After comparing extraction methods, the ultrasonic cell crusher demonstrated superior performance over conventional techniques. Four key factors-solid-to-liquid ratio (1:10 to 1:50 g·mL-1), ethanol concentration (55% to 95%), ultrasonic time (10 to 50 min), and ultrasonic power (5% to 25% of 900 W)-were investigated and normalized using the entropy weight method. This led to a comprehensive evaluation (CE). Optimization of extraction conditions for the ultrasonic cell crusher was achieved through response surface methodology and a deep neural network model, resulting in optimal parameters: ethanol volume fraction of 66%, solid-to-liquid ratio of 1:21 g/mL, extraction efficiency of 9%, and extraction duration of 35 min, yielding a CE value of 23.14 (RSD < 1%). Additionally, the inhibitory effects of the optimized extracts against Streptococcus mutans (S. mutans) were assessed. The results revealed that AMF extract (AMFE) exhibits inhibitory effects on S. mutans, with concomitant inhibition of sucrase and lactate dehydrogenase (LDH). The MIC of AMFE against planktonic S. mutans is 3 mg/mL, with an MBC of 6 mg/mL. Within the concentration range of 1/8 MIC to 2 MIC of AMFE, the activities of sucrase and LDH decreased by 318.934 U/mg prot and 61.844 U/mg prot, respectively. The antioxidant activity of AMFE was assessed using the potassium ferricyanide reduction and phosphomolybdenum methods. Additionally, the effect of AMFE on DPPH, ABTS, and ·OH free radical scavenging abilities was determined. The concentrations at which AMFE exhibited over 90% scavenging rate for ABTS and DPPH free radicals were found to be 0.125 mg/mL and 2 mg/mL, respectively.

Silver oxide doped iron oxide/alginate nanocomposite coated cotton cloth for selective catalytic reduction of potassium ferricyanide

Silver oxide doped iron oxide (Ag2O–Fe2O3) nanocatalyst was prepared and coated on cotton cloth (CC) as well as wrapped in sodium alginate (Alg) hydrogel. Ag2O–Fe2O3 coated CC (Ag2O–Fe2O3/CC) and Ag2O–Fe2O3 wrapped Alg (Ag2O–Fe2O3/Alg) were utilized as catalysts in reduction reaction of 4-nitrophenol (4-NP), congo red (CR), methylene blue (MB) and potassium ferricyanide (K3[Fe(CN)6]). Ag2O–Fe2O3/CC and Ag2O–Fe2O3/Alg were found to be effective and selective catalyst for the reaction of K3[Fe(CN)6]. Further amount of catalyst, K3[Fe(CN)6] quantity, amount of NaBH4, stability of catalyst and recyclability were optimized for the reaction of K3[Fe(CN)6] reduction. Ag2O–Fe2O3/Alg and Ag2O–Fe2O3/CC were appeared to be the stable catalysts by maintaining high activity during recyclability tests showing highest reaction rate constants (kapp) of 0.3472 and 0.5629 min−1, correspondingly. However, Ag2O–Fe2O3/CC can be easily recovered as compared to Ag2O–Fe2O3/Alg by simply removing from the reaction which is the main advantage of Ag2O–Fe2O3/CC. Moreover, Ag2O–Fe2O3/Alg and Ag2O–Fe2O3/CC were also examined in real samples and found useful for K3[Fe(CN)6] reduction involving real samples. The Ag2O–Fe2O3/CC nanocatalyst is a cost and time saving material for economical reduction of K3[Fe(CN)6] and environmental safety.

Determination of Antioxidant Activity of The Leaves of Hawthorn (Crataegus Monogyna)

This study was carried out to make decision the antioxidant activity of the leaves of hawthorn (Crataegus monogyna), which is a natural source of antioxidants. For this purpose, the leaves of hawthorn were collected and dried, and an ethanol extract was prepared. Total antioxidant activity (with respect to the ferric thiocyanate method), ion reduction capacity of Cu2+ (copper method), and Fe3+ (potassium ferricyanide reduction method) were determined on the prepared ethanol extracts. Additionally, scavenging activity of DPPH (1,1-diphenyl-2-picrylhydrazyl) and determination of the total phenolic-flavonoid compound content were carry out. The extracts obtained from Hawthorn (Crataegus monogyna) leaves were found to inhibit lipid peroxidation (of linoleic acid emulsion) by 40.9%. This inhibition occurred at a concentration of 10 µg/mL of the extracts. At the similar concentration, BHT exhibited 68.3% inhibition, while trolox exhibited 29.9% inhibition. Hawthorn (Crataegus monogyna), which was found to have a higher total phenolic content than trolox, exhibited significant DPPH scavenging and metal reduction activities. During the investigation of the antioxidant activity of the ethanol extract obtained from Crataegus monogyna, α-tocopherol, its water-soluble analogue trolox and BHT (butylated hydroxytoluene) were utilized as reference antioxidant compounds.

Electrocatalytic aptasensor for bacterial detection exploiting ferricyanide reduction by methylene blue on mixed PEG/aptamer monolayers

Pathogen-triggered infections are the most severe global threat to human health, and to provide their timely treatment and prevention, robust methods for rapid and reliable identification of pathogenic microorganisms are required. Here, we have developed a fast and inexpensive electrocatalytic aptamer assay enabling specific and ultrasensitive detection of E. coli. E. coli, a biomarker of environmental contamination and infections, was captured on the mixed aptamer/thiolated PEG self-assembled monolayers formed on electrochemically pre-treated gold screen-printed electrodes (SPE). Signals from aptamer - E. coli binding were amplified by electrocatalytic reduction of ferricyanide mediated by methylene blue (MB) adsorbed on bacterial and aptamer surfaces. PEG operated as an antifouling agent and inhibited direct (not MB-mediated) discharge of ferricyanide. The assay allowed from 10 to 1000 CFU mL−1E. coli detection in 30 min, with no interference from B. subtilis, in buffer and artificial urine samples. This electrocatalytic approach is fast, specific, sensitive, and can be used directly in in-field and point-of-care applications for analysis of bacteria in human environment.

Long-Term Stability of Ferri-/Ferrocyanide as an Electroactive Component for Redox Flow Battery Applications: On the Origin of Apparent Capacity Fade

We assess the suitability of potassium ferri-/ferrocyanide as an electroactive species for long-term utilization in aqueous organic redox flow batteries. A series of electrochemical and chemical characterization experiments was performed to distinguish between structural decomposition and apparent capacity fade of ferri-/ferrocyanide solutions used in the capacity-limiting side of a flow battery. Our results indicate that, in contrast with previous reports, no structural decomposition of ferri-/ferrocyanide occurs at tested pH values as high as 14 in the dark or in diffuse indoor light. Instead, an apparent capacity fade takes place due to a chemical reduction of ferricyanide to ferrocyanide, via chemical oxygen evolution reaction. We find that this parasitic process can be further exacerbated by carbon electrodes, with apparent capacity fade rates at pH 14 increasing with an increased ratio of carbon electrode surface area to ferricyanide in solution. Based on these results, we report a set of operating conditions that enables the long-duration cycling of alkaline ferri-/ferrocyanide electrolytes and demonstrate how apparent capacity fade rates can be engineered by the initial system setup. If protected from direct exposure to light, the structural stability of ferri-/ferrocyanide anions allows for their practical deployment as electroactive species in long duration energy storage applications.

Black Gold-Based “Antenna–Reactor” To Activate Non-Plasmonic Nickel: Photocatalytic Hydrodechlorination and Hydrogenation Reactions

Activation of organic chlorides is a challenging reaction due to their chemical inertness, while hydrogenation of alkene and alkynes faces poor selectivity. In this work, we have demonstrated the use of nickel-loaded black gold (black Au–Ni) that absorbs broadband light from visible to near-infrared of the sunlight due to plasmonic coupling between Au NPs, for photocatalytic hydrodechlorination and propene and acetylene hydrogenation reactions. Hot carriers, the polarizing electric field, and the photothermal effect generated in these catalysts enabled photocatalytic bond activation of these two challenging reactions using visible light at lower temperatures and atmospheric pressure. The black Au–Ni catalyst showed a multifold increase in its activity as compared to black Au. The plasmon-assisted reaction mechanism of hydrodechlorination was supported by intensity-dependent catalysis, kinetic isotope effect (KIE), competitive C–Cl bond activation with one-electron ferricyanide reduction, finite-difference time-domain (FDTD) simulations, and quantum chemical studies. Cluster model-based density functional theory studies show that the reactions have substantial barriers, which were bypassed via an excited state accessed through plasmonic excitations. FDTD studies indicate substantial enhancement of the electric field at the hotspots, iron reduction competed for hot carriers when run in conjunction with C–Cl bond activation, KIE was marginally higher in light as compared to the dark, and the catalyst showed power-dependent activity. These observations indicated the hot carrier involvement in the hydrodechlorination reactions in addition to the photothermal effect.

In Situ Prussian Blue-Electrocatalyst Formation on Intrinsic Iron-Containing Pristine-MWCNT as a Template and Its EQCM and SECM Interrogations and Batch Injection Analysis of Hydrogen Peroxide

Herein, we report in-situ electrochemical derivatization of the intrinsic iron species in a pristine-multiwalled carbon nanotube (MWCNT) as Prussian blue (PB) modified MWCNT hybrid (MWCNT@PB) using a dilute solution of ferricyanide as a derivatization agent in pH 2 HCl-KCl solution. The PB hybrid system showed a defined redox peak at an apparent standard electrode potential, Eo’ = 0.18 V vs Ag/AgCl with an excess surface value, 1.71 × 10−10 mol cm−2. A discreet EQCM study on the electrochemical preparation of MWCNT@PB using MWCNT and ferricyanide precursors reveal the specific stripping of iron species and uptake of iron species, potassium and ferricyanide ions upon the electrochemical preparation condition. In-situ imaging of MWCNT@PB was carried out using SECM with ferricyanide as a redox mediator under a feedback-current mode. It has been identified that a mixed-potential based electrochemical reaction involving oxidative stripping of iron to iron ion species (step-1) coupled with reduction of ferricyanide to ferrocyanide (step-2) followed by a chemical interaction between the iron ion and ferricyanide (step-3) have occurred for the overall formation of MWCNT@PB hybrid. Electrocatalytic and electroanalytical performance of the MWCNT@PB hybrid towards H2O2 reduction and sensing were demonstrated by performing cyclic voltammetric, amperometric i-t and batch injection analysis.

Alanine aminotransferase assay biosensor platform using silicon nanowire field effect transistors

Frequent monitoring of serum alanine aminotransferase (ALT) activity is essential to prevent drug-induced liver injury (DILI). Current ALT assays are restricted to centralized clinical laboratories, making frequent patient monitoring logistically difficult. To address this, we demonstrated the capability of commercial foundry manufactured silicon nanowire field effect transistor (SiNW-FET) biosensors in a form factor that enables frequent near-patient monitoring. Here, we designed an ALT assay, by coupling the ALT-catalyzed production of pyruvate to the reduction of ferricyanide, enabling both spectrophotometric and electrical measurement of ALT activity. The two methods yield comparable ALT activity detection across a dynamic range wide enough to monitor patients at risk for DILI. This study demonstrates kinetic activity measurement of an endogenous enzyme using uncoupled SiNW-FETs, and commercial manufacturing of SiNW-FET sensor arrays for use in a portable biosensor platform.

Proton-translocating NADH:ubiquinone oxidoreductase of Paracoccus denitrificans plasma membranes catalyzes FMN-independent reverse electron transfer to hexaammineruthenium (III)

NADH-OH, the specific inhibitor of NADH-binding site of the mammalian complex I, is shown to completely block FMN-dependent reactions of P. denitrificans enzyme in plasma membrane vesicles: NADH oxidation (in a competitive manner with Ki of 1 nM) as well as reduction of pyridine nucleotides, ferricyanide and oxygen in the reverse electron transfer. In contrast to these activities, the reverse electron transfer to hexaammineruthenium (III) catalyzed by plasma membrane vesicles is insensitive to NADH-OH. To explain these results, we hypothesize the existence of a non-FMN redox group of P. denitrificans complex I that is capable of reducing hexaammineruthenium (III), which is corroborated by the complex kinetics of NADH: hexaammineruthenium (III)-reductase activity, catalyzed by this enzyme. A new assay procedure for measuring succinate-driven reverse electron transfer catalyzed by P. denitrificans complex I to hexaammineruthenium (III) is proposed.

SnLa2O5 wrapped carboxymethyl cellulose mixed calcium alginate nanocomposite beads for efficient reduction of pollutants

In this project, lanthanum oxide doped tin oxide (SnLa2O5) nanomaterial was prepared and characterized morphologically and physiochemically by different techniques. The catalytic performance of SnLa2O5 was assessed toward catalytic reduction of 4-nitrophenol (4-NP), methyl orange (MO), congo red (CR), methylene blue (MB) and potassium ferricyanide (K3[Fe(CN)6]). SnLa2O5 was found to be efficient for K3[Fe(CN)6] in the presence of NaBH4, which reduced in only 8.0 min. SnLa2O5 was further wrapped in carboxymethyl cellulose mixed calcium alginate (CMC-Alg) hydrogel beads because the powder catalyst cannot be simply recovered from reaction media to recycle and use again. SnLa2O5 wrapped CMC-Alg (SnLa2O5/CMC-Alg) was assessed for detail analysis of K3[Fe(CN)6] reduction. The effect of NaBH4, K3[Fe(CN)6] concentration and amount of catalyst was optimized using SnLa2O5/CMC-Alg. The amount of catalyst has positive impact on catalytic reduction of K3[Fe(CN)6]. The kinetic study revealed that K3[Fe(CN)6] reduction by SnLa2O5 and SnLa2O5/CMC-Alg was fast, which completed in 8.0 and 4.0 min with rate constant of 0.4283 min−1 and 0.7461 min−1, respectively. These findings indicated that the developed SnLa2O5/CMC-Alg is best and proficient nanocatalyst for K3[Fe(CN)6] reduction. The efficiency along with cost-effective and simple treatment route of the developed nanocatalyst have prospect to compete and replace the reputable commercial catalysts.

FTIR-Based Metabolomics for Characterization of Antioxidant Activity of Different Parts of Sesbania grandiflora Plant

Sesbania grandiflora, one of the flowering plants with great potential as a source of natural antioxidants because it contains chemicals such as tannin, phenolics, and flavonoids. However, there has been no extensive investigation on the antioxidant activity of isolated from different parts of this plant. This study aims to investigate the correlation between antioxidant activity and secondary metabolites extracted from three different parts (leaves, stem barks, and roots) of S. grandiflora plant using Fourier-transform infrared spectroscopy (FTIR) based metabolomics approach. The FTIR is a very useful technique for identifying the functional groups present in the mixtures, while antioxidant assay provides the base to select the part of the plant as the most potential source of antioxidant. The antioxidant properties were determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS), and potassium ferricyanide reduction method. The multivariate data - analyses using Principal Component Analysis (PCA) and Partial Least Square (PLS) were conducted to compare the distribution of metabolites extracted from different parts of the S. grandiflora plant investigated. The PLS was performed to evaluate the relationship between the components of the extracts obtained from different parts of the plant and their antioxidant activities. The results exhibited that antioxidant activities of the extract of the stem barks, and roots are higher than that of the extract of the leaves. Also, the PLS model indicated that the functional group absorption data were significantly correlated with the IC50 values of antioxidant activity. Subsequently, based on the results of PLS ​​analysis displayed that C=C, C=O, and along with C-O functional groups are proposed as the main contributors to the antioxidant activity of the extracts tested. The extracts of different parts were grouped using PCA analysis with a total of principal components (PC) of 94%.

Preparation of Cu‐W Nanoflakes and their Catalytic Performance for the Hydrogenation of 4‐Nitrophenol

Abstract4‐Nitrophenol (4‐NP) is one of the most common organic pollutants in industrial waste waters due to its solubility and toxicity. The catalytic degradation of 4‐NP to 4‐aminophenol (4‐AP) is an economical and sustainable process, which transfers waste and toxicity to profitable materials. Fabricating metal nanoparticle based efficient heterogeneous catalysts is crucial to treating these kinds of pollutants. Here in, Cu−W nanoflakes (Cu−W NFs) with thin sheet like structure were prepared by a simple one‐pot method by using polyoxometalate as precursor. The Cu−W NFs served in hydrogenation of 4‐NP reaction as catalyst, achieved high conversion with rate constant (k) of 2.584×10−2 s−1. Notably, the sustainable catalyst Cu−W NFs exhibit no significant degradation of catalytic activity over 16 cycles, manifested good durability and high conversion (&gt;91 %). Also, the reduction of potassium ferricyanide can also be catalyzed by Cu−W NFs with high efficiency. This work provided a concise approach for fabricating highly effective catalyst and was expected to be a potential universal method to obtain sustainable competitive catalyst for utility in treating pollution.

Quantifying transport and electrocatalytic reaction processes in a gastight rotating cylinder electrode reactor via integration of Computational Fluid Dynamics modeling and experiments

Understanding the complexity of the multiple processes of mass, momentum, charge, and heat transport, and how these affect reaction kinetics at the electrode/electrolyte interface is one of the major challenges in the field of energy and catalysis. The rapid and rational scale-up of electrocatalytic systems to industrial scales require a detailed understanding of nonlinear transport-reaction processes, accessible only through the building of multi-physics models that capture with high fidelity the complexity of real-world devices. The gastight rotating cylinder electrode (RCE) reactor is a promising lab-scale tool that can decouple transport from intrinsic kinetics to generate data for first-principle models useful in the design of industrial, electrochemical reactors. Computational Fluid Dynamics (CFD) studies have previously been used to investigate the bulk flow in RCE reactors for simple corrosion and electroplating processes. However, the quantification of changes in local concentration within the viscous layer where catalysis takes place requires capturing the correct flow conditions inside the hydrodynamic boundary layer near the surface of the electrode. This requires simulations with spatial resolution in the nm and μm scale and temporal resolutions between ms and s scales that are similar to the timescales for reactions on the electrode surface. In this study, experimental electrocatalysis is combined with CFD modeling to elucidate and parameterize the hydrodynamics in a gastight RCE reactor. CFD simulations of the electrochemical ferricyanide reduction reaction under mass transport limited conditions are used to evaluate the validity of the CFD model parameters by comparing calculated dimensionless mass transport descriptors to dimensionless correlations obtained experimentally. Justifications for assumptions and details of the simulation methods used in this study are presented to provide a detailed understanding of the effect that each model parameter has on the ability to accurately simulate electrocatalysis in RCE systems. The simulation methodology reported here is a first step towards the development of multi-scale models for the study of transport dependent electrocatalytic processes, such as the electrochemical transformation of CO2 to fuels and chemicals.

Long-Term Stability of Ferri/Ferrocyanide As an Electroactive Component for Redox Flow Battery Applications: On the Origin of Apparent Capacity Fade

The attraction of aqueous organic redox flow batteries (AORFBs) lies in the potential for low mass-production cost and long lifetime of the organic molecules. To reach cell potentials >1.0 V, several AORFBs have employed the ferri/ferrocyanide redox couple as posolyte in alkaline conditions. Recent works have reported significant amounts of capacity fade of this redox couple at high pH, attributed either to chemical decomposition associated with cyanide ligand dissociation and irreversible hydroxylation of the iron complex [1,2], or due to cell unbalancing associated with electrochemical oxygen evolution reaction (OER) [3].We assess the chemical and electrochemical stability of ferri/ferrocyanide utilizing a volumetrically unbalanced, compositionally symmetric cell method [4]. A series of electrochemical and chemical characterization experiments was performed to distinguish between “real” capacity fade (redox-active is structurally damaged) and “apparent” capacity fade (redox-active remains structurally intact), when ferri/ferrocyanide electrolytes are used in the capacity-limiting side of a flow battery. Our results indicate that, in contrast with previous reports [1,2], no chemical decomposition of ferri/ferrocyanide occurs at tested pH values as high as 14 in the dark or in diffuse indoor light. Instead, an apparent capacity fade takes place due to an electroless reduction of ferricyanide to ferrocyanide, via electroless OER. We find that this parasitic process can be further enhanced by carbon electrodes, with apparent capacity fade rates at pH 14 increasing with an increased ratio of carbon electrode surface area to total amount of ferricyanide in solution. Based on these results, we report a set of operating conditions that enables the cycling of alkaline ferri/ferrocyanide electrolytes, and further demonstrate how apparent capacity fade rates can be engineered by the initial cell setup. If protected from direct exposure to light, the chemical stability of ferri/ferrocyanide anions allows for their practical deployment as electroactive species in long duration energy storage applications at alkaline pH values up to at least 14.

Protein-sized nanozymes «artificial peroxidase» based on template catalytic synthesis of Prussian Blue

We report on Prussian Blue based nanozymes, comparable in size with a natural enzyme peroxidase. Protein-sized nanoparticles have been synthesized in the course of reduction of ferric ion (Fe3+) and ferricyanide ([Fe(CN)6]3-) one-to-one mixture in reversed micelles (isooctane|AOT|water) used as templates. Aniline chosen as the best reductant for this aim has led to formation of composite (according to Raman spectroscopy) Prussian Blue – polyaniline nanoparticles. The protein-like size of the nanoparticles (∅ = 4 – 6 nm) has been confirmed by DLS and TEM imaging. Kinetic investigations of peroxidase-like activity in reversed micelles resulted in the catalytic rate constant belonging to the same size-dependence as regular bulk catalytically synthesized nanozymes (slope ≈ 2.6), allowing to denote the reported Prussian Blue nanoparticles synthesized in reversed micelles as nanozymes «artificial peroxidase». Hydrogen peroxide sensors made by dipping the suspension of the latter onto the electrode support, displayed two-fold higher sensitivity as compared to the Prussian Blue film-based ones. Protein-sized nanozymes «artificial peroxidase» would obviously provide an advantage over regular nanozymes in (bio)sensors and analytical kits.

Evaluation of a Direct Cellular Assay for NQO1 in the Presence of Phytochemicals

NAD(P)H:quinone oxidoreductase NQO1 is a phase ll enzyme that catalyzes the linked intracellular conversion of NADPH2 to NADP and duroquinone (DQ) to hydroduroquinone (DQH2) in cells. There are different methods to determine NQO1 activity. The classic NQO1 enzyme assay is the usual method for measuring NQO1 activity in cell lysates. We chose to determine the intact-cell activity to investigate the effect of the four compounds Quercetin (Q), Epigallocatechin-3-gallate, (EGCG), indole-3-carbinol (I3C), and Sulforaphane (SFN) in stimulating NQO1 activity. In brief, DQ-mediated reduction of the cell-membrane-imperative secondary electron acceptor, ferricyanide, was used to quantify intact-cell NQO1 activity. This approach involves adding quinone duroquinone to the cells and then measuring the appearance rate of the two-electron reduction product, durohydroquinone, by its ferricyanide reduction. In conclusion, I3C and SFN did not interfere with the enzymatic reaction. In contrast, Q and EGCG can interfere with the enzymatic reaction of NQO1 because Q and EGCG possess quinone structures, unlike I3C and SFN, which do not have the same shape.