Theoretical Kinetic Model Research Articles

Carbon-13 Hyperpolarization of α-Ketocarboxylates with Parahydrogen in Reversible Exchange.

Signal Amplification by Reversible Exchange (SABRE) is a relatively simple and fast hyperpolarization technique that has been used to hyperpolarize the α-ketocarboxylate pyruvate, a central metabolite and the leading hyperpolarized MRI contrast agent. In this work, we show that SABRE can readily be extended to hyperpolarize 13C nuclei at natural abundance on many other α-ketocarboxylates. Hyperpolarization is observed and optimized on pyruvate (P13C=17%) and 2-oxobutyrate (P13C=25%) with alkyl chains in the R-group, oxaloacetate (P13C=11%) and alpha-ketoglutarate (P13C=13%) with carboxylate moieties in the R group, and phenylpyruvate (P13C=2%) and phenylglyoxylate (P13C=2%) with phenyl rings in the R-group. New catalytically active SABRE binding motifs of the substrates to the hyperpolarization transfer catalyst-particularly for oxaloacetate-are observed. We experimentally explore the connection between temperature and exchange rates for all of these SABRE systems and develop a theoretical kinetic model, which is used to fit the hyperpolarization build-up and decay during SABRE activity.

Production of microalgae in wastewater and brackish waters: kinetic, lipid content, bioremediation and cost analysis studies

ABSTRACT The cultivation of microalgae in domestic wastewater offers a sustainable solution for the treatment of effluents, while at the same time producing biomass rich in lipids, potentially usable in the production of biofuels. Furthermore, reuse contributes to the treatment of wastewater, transforming a byproduct into a valuable source of nutrients for the production of microalgae biomass. This study involves the production of microalgae in open cultivation, using domestic effluents as a source of nutrients in brackish environments, to study the potential for biodiesel production. Intracellular lipids were between 17 and 20%. As for the bioremediation capacity, the results showed removal levels greater than 95% of nutrients, as well as bacterial and pollutant load reduction. The growth kinetics and the prediction of theoretical kinetic models through the use of computational tools show significant differences, due to the lack of control of process parameters in open cultivations. Based on the literature review and market research, a cost analysis for large-scale production in open crops was made, comparing with closed crops and finding lower costs in the implementation, maintenance and production of biodiesel in the production open.

Kinetics of indium separation and recovery from In–Sn alloys in ITO waste target products via vacuum evaporation

The environmentally friendly recycling of ITO waste material to regenerate indium resources is crucial for sustainability. The hydrogen reduction process, particularly the green and low-carbon technique of vacuum distillation, is crucial in the production of In–Sn alloys. However, a thorough examination of the mechanics underlying its evaporation throughout this process has yet to be performed. These mechanics are investigated in the present study for 92In–8Sn alloys under specific conditions, including temperatures between 1173 and 1373 K, pressure of 5 Pa, and crucible depth of 25 mm. The relationship between temperature and the rate of volatilization is mathematically represented as ω = e(a+b∙T). Furthermore, the equation ω = A2 + (A1-A2)/(1 + e(h-h0)/dh) was used to predict the dependency of the volatilization rate on crucible depth, ranging from 25 to 65 mm at 1323 K and 5 Pa. The mass transfer coefficients for the alloy at different temperatures were calculated, and a theoretical kinetic model for evaporation behavior indicated that vapor-phase mass transfer is the limiting step in the process of vacuum distillation of this alloy. This study presents a theoretical basis for the retrieval of In from the In–Sn alloy using vacuum distillation.

A theoretical calculation and kinetic modeling analysis of H-abstraction from 1-octene for subsequent isomerization and [formula omitted]-dissociation

As a main component of alkenes, 1-octene is the key important intermediate in the process of oxidation or pyrolysis of n-decane or higher alkanes. In this work, quantum chemistry calculations of the 1-octene combustion and pyrolysis were illustrated for the potential energy surface, including the H-abstraction reactions and subsequent isomerization and β-dissociation reactions. The primary β-dissociation reactions after the H-abstraction reaction involving H atoms and CH3/NH2/NO2 radicals are detailed description with kinetic calculation. The rate constants of the primary pyrolysis reaction of 1-octene from 300 to 2000K were determined with the RRKM theory combined with CTST. The results indicated the H-abstraction reactions adhere to the Evans-Polanyi principle within the calculation uncertainty 1 kcal/mol. The 3-site exhibited the highest competitiveness in the 1-octene H-abstraction process and dominated, whereas the 1-site is lack of competitiveness due to overcome higher energy barriers (2–4 kcal/mol). The five-membered or six-membered ring in the H atom transfer process served as the most favorable structure for the isomerization reaction of 1-octenyl because of the lowest transition state energy. The dissociation channel for converting 1-octenyl to various octadienes and H atoms consumed the least 1-octenyl in the dissociation process. Following temperatures exceeding 570K, INT6 exhibits a preeminent 1-octenyl consumption ratio, attributed to the synergy between the enthalpy and entropy effects. The modified kinetic data of 1-octene H-abstraction reactions by four radicals and the subsequent isomerization and β-dissociation was expanded from 300 to 2000K, 0.01–100 atm. The modified model shows the better experimental prediction capabilities.

Generalised analytical method unravels framework-dependent kinetics of adsorption-induced structural transition in flexible metal–organic frameworks

Flexible metal–organic frameworks (MOFs) exhibiting adsorption-induced structural transition can revolutionise adsorption separation processes, including CO2 separation, which has become increasingly important in recent years. However, the kinetics of this structural transition remains poorly understood despite being crucial to process design. Here, the CO2-induced gate opening of ELM-11 ([Cu(BF4)2(4,4’-bipyridine)2]n) is investigated by time-resolved in situ X-ray powder diffraction, and a theoretical kinetic model of this process is developed to gain atomistic insight into the transition dynamics. The thus-developed model consists of the differential pressure from the gate opening (indicating the ease of structural transition) and reaction model terms (indicating the transition propagation within the crystal). The reaction model of ELM-11 is an autocatalytic reaction with two pathways for CO2 penetration of the framework. Moreover, gas adsorption analyses of two other flexible MOFs with different flexibilities indicate that the kinetics of the adsorption-induced structural transition is highly dependent on framework structure.

Kinetics of indium and indium–tin soldering materials in vacuum volatilization

Vacuum volatilization is a clean and efficient method for metal purification, alloy separation, and comprehensive recovery of secondary resources. The evaporation kinetics of In and In–Sn alloys were investigated to better understand the evaporation mechanism during the vacuum volatilization of In. The evaporation rates of the In and In–Sn alloys at 1173–1373 K and 5 Pa increased significantly with increasing temperature in accordance with the equation ω = e(a+b∙T). The evaporation rates at 1323 K and 5 Pa decreased with increasing crucible depth in accordance with the equation ω = a2+(a1-a2)/(1+e(h-b)/c). For In and In–Sn, the total mass-transfer coefficients of In were obtained at different temperatures and crucible depths. A theoretical kinetic model of In was established and limiting links were obtained vacuum volatilization of In and In–Sn.

Metal Binding of Alzheimer's Amyloid-β and Its Effect on Peptide Self-Assembly.

ConspectusMetal ions have been identified as key factors modulating the aggregation of amyloid-β peptide (Aβ) implicated in Alzheimer's disease (AD). The presence of elevated levels of metal ions in the amyloid plaques in AD patients supports the notion that the dysfunction of metal homeostasis is connected to the development of AD pathology. Here, recent findings from high- and low-resolution biophysical techniques are put into perspective, providing detailed insights into the molecular structures and dynamics of metal-bound Aβ complexes and the effect of metal ions on the Aβ aggregation process. In particular, the development of theoretical kinetic models deducing different microscopic nucleation events from the macroscopic aggregation behavior has enabled deciphering of the effect of metal ions on specific nucleation processes. In addition to these macroscopic measurements of bulk aggregation to quantify microscopic rates, recent NMR studies have revealed details about the structures and dynamics of metal-Aβ complexes, thereby linking structural events to bulk aggregation. Interestingly, transition-metal ions, such as copper, zinc, and silver ions, form a compact complex with the N-terminal part of monomeric Aβ, respectively, where the metal-bound "folded" state is in dynamic equilibrium with an "unfolded" state. The rates and thermodynamic features of these exchange dynamics have been determined by using NMR relaxation dispersion experiments. Additionally, the application of specifically tailored paramagnetic NMR experiments on the Cu(II)-Aβ complex has been fruitful in obtaining structural constraints within the blind sphere of conventional NMR experiments. This enables the determination of molecular structures of the "folded" Cu(II)-coordinated N-terminal region of Aβ. Furthermore, the discussed transition-metal ions modulate Aβ self-assembly in a concentration-dependent manner, where low metal ion concentrations inhibit Aβ fibril formation, while at high metal ion concentrations other processes occur, resulting in amorphous aggregate formation. Remarkably, the metal-Aβ interaction predominately reduces one specific nucleation step, the fibril-end elongation, whereas primary and surface-catalyzed secondary nucleation mechanisms are less affected. Specific inhibition of fibril-end elongation theoretically predicts an enhanced generation of Aβ oligomers, which is an interesting contribution to understanding metal-Aβ-associated neurotoxic effects. Taken together, the metal binding process creates a metal-bound Aβ complex, which is seemingly inert to aggregation. This process hence efficiently reduces the aggregation-prone peptide pool, which on the macroscopic level is reflected as slower aggregation kinetics. Thus, the specific binding of metals to the Aβ monomer can be linked to the macroscopic inhibitory effect on Aβ bulk aggregation, providing a molecular understanding of the Aβ aggregation mechanism in the presence of metal ions, where the metal ion can be seen as a minimalist agent against Aβ self-assembly. These insights can help to target Aβ aggregation in vivo, where metal ions are key factors modulating the Aβ self-assembly and Aβ-associated neurotoxicity.

Do film reactions affect ozone gas–liquid fast-moderate reaction kinetics in the proximity of gas–water interface?

Kinetics of the ozonation of water contaminants is usually based on mol balance equations applied in the water bulk. In these models, direct and free radical reactions are considered, neglecting the contribution of reactions developed in the proximity of the gas–water interface. In this work, a theoretical kinetic model of the ozonation involving direct and free radical reactions in the film and water bulk is carried out. The model is based on film and penetration absorption theories. Time concentration profiles are assessed by coupling the non-stationary penetration theory with bulk mass balances. Studied variables are chosen according to their influence on the numbers of Hatta and instantaneous reaction factor. These parameters are equilibrium ozone and compound concentrations, direct rate constant, and mass transfer coefficient. The effect of pH and hydrogen peroxide are studied. Calculated results reveal that direct reaction contribution in the film has a significant importance, especially in fast-moderate kinetic regimes of ozone absorption. Absence of film free radical reactions leads to compound removal rates slightly lower than the complete mechanism (fast regimes develop). Formation of hydrogen peroxide and its reaction with ozone leads to the formation of free radicals.

An experimental and theoretical kinetic modeling study of the thermal decomposition of methyl-2-methyl butanoate behind shock waves

In order to investigate the combustion chemistry of a branched ester namely Methyl-2-methylbutanoate (M2MB), thermal decomposition of M2MB diluted in Argon was carried out behind reflected shock waves in the temperature range 959 -1392 K using a single pulse shock tube (SPST). The post shock mixtures were analyzed quantitatively as well as qualitatively using gas chromatography (GC) and gas chromatography coupled with mass spectrometry (GC–MS). Methane (CH4), Ethane (C2H6), Ethylene (C2H4), Methanol (CH3OH), Propene (C3H6) and Methyl acrylate (C4H6O2) were the major products observed during thermal decomposition. The various oxygenated compounds were found as minor products. The first order rate constant observed for the decomposition of M2MB is kexpt(959–1392 K) = (2.13 ± 0.457) × 109 exp [(19200 ± 561)/T] s−1 The temperature dependent kinetics of the CC and CO homolytic bond cleavages as well as of the H-migration for the unimolecular decomposition reactions were calculated using RRKM/ME over the temperature range of 959–1392 K. A reaction scheme involving 42 species and 61 elementary reactions, was proposed to simulate the reactant and product concentration over the studied temperature range. A comparison study of decomposition kinetics of branched chain ester and long chain ester is discussed in this work. The concentration profiles for reactant and all the products observed from simulations and experimental results were observed to be in very good agreement.

Acidity reduction using ionic liquids: Extraction, kinetic, and theoretical study

Naphthenic acids (NAs) are toxic compounds naturally present in most petroleum sources with a highly variable concentration depending on their origin.Their occurrence in crude oil can produce severe corrosion problems and catalyst deactivation in oil refineries, consequently impacting their economic value and productivity. Thus, extracting and recovering the NA from crude oil is necessary. In this work, the extraction capacity of two ionic liquids (ILs) of different nature has been studied: 1-ethyl-3-methylimidazolium acetate, [EMIm][OAc], and trihexyltetradecylphosphonium dicyanamide, [P14,6,6,6][CCN2]. In addition, kinetic data were obtained for [P14,6,6,6][CCN2], and a theoretical kinetic model was developed to adjust the experimental data. Two extraction mechanisms have been analyzed using molecular dynamics computational simulations and quantum mechanical calculations. Molecular dynamic results show that a cluster of IL is first formed in each extraction process, and NA molecules are deposited on its surface. Different outcomes are obtained for diffusion coefficient values and radial distribution function. Furthermore, the quantum chemistry calculations show that a proton transfer is thermodynamically favorable in the case of [EMIm][OAc], thus extraction mechanism occurs through a neutralization reaction, whereas for [P14,6,6,6][CCN2], it is not, pointing to a physical extraction.

The reactions of 2-furfuryl alcohol with hydrogen atom: A theoretical calculation and kinetic modeling analysis

The rate constants for H-initiated reactions of 2-furfuryl alcohol (2FFOH) were calculated for the first time by a high-level quantum chemical method combined with the Rice–Ramsperger–Kassel–Marcus (RRKM) theory/Master equation method. A detailed potential energy surface was constructed by the CCSD(T)/CBS//M06–2X/def2-TZVP method, involving H-abstraction, initial H-addition, adduct-subsequent pathways and interconnected conversion pathways. The H-addition reaction on the β-carbon and δ-carbon sites to form bimolecular products 2-methylene-2,3-dihydrofuran plus OH and 2-methylene-2,5-dihydrofuran plus OH were found to be the major product channels at high temperatures. No significant pressure dependence is observed for the total rate constants of 2FFOH + H. However, the overall kinetics behavior does not reflect the site characteristics, i.e., the site-specific rate constants for each reaction channel show different temperature and pressure dependences. The total rate constants via the H-addition mechanism are higher by factors of 3.3–10 than those via H-abstraction channels under all studied conditions. The present updated kinetic model obtained by applying these new calculated rate constants can better predict 2FFOH decomposition, especially at 30 Torr, and it can also lead to good predictions of the speciation profiles (e.g., vinyl ketene) during 2FFOH pyrolysis. The data calculated in the present work can provide valuable information for the development of combustion models of furan-based biofuels.

PEG–PLGA nanoparticles for encapsulating ciprofloxacin

Antibiotic medications have been found to hinder the success of regenerative endodontic treatment due to the rapid degradation of the drug, and the acidic nature of ciprofloxacin (CIP) can be harmful to stem cells of the apical papilla (SCAPs), the cells responsible for regeneration. In this study, a nanocarrier system was used for controlled drug release for longer drug activity and less cytotoxicity to the cells. CIP was loaded in poly (ethylene glycol) methyl ether-block-poly (lactide-co-glycolide) (PEG–PLGA) nanoparticles (NPs) with an ion-pairing agent. The NPs demonstrated a monodispersed spherical morphology with a mean diameter of 120.7 ± 0.43 nm. The encapsulation efficiency of the CIP-loaded PEG–PLGA NPs was 63.26 ± 9.24%, and the loading content was 7.75 ± 1.13%. Sustained CIP release was achieved over 168 h and confirmed with theoretical kinetic models. Enhanced NP bactericidal activity was observed against Enterococcus faecalis. Additionally, CIP-loaded PEG–PLGA NPs had a low cytotoxic effect on SCAPs. These results suggest the use of a nanocarrier system to prolong the antibiotic activity, provide a sterile environment, and prevent reinfection by the bacteria remaining in the root canal during regenerative endodontic treatment.

Protein-Peptide Turnover Profiling reveals the order of PTM addition and removal during protein maturation

Post-translational modifications (PTMs) regulate various aspects of protein function, including degradation. Mass spectrometric methods relying on pulsed metabolic labeling are popular to quantify turnover rates on a proteome-wide scale. Such data have traditionally been interpreted in the context of protein proteolytic stability. Here, we combine theoretical kinetic modeling with experimental pulsed stable isotope labeling of amino acids in cell culture (pSILAC) for the study of protein phosphorylation. We demonstrate that metabolic labeling combined with PTM-specific enrichment does not measure effects of PTMs on protein stability. Rather, it reveals the relative order of PTM addition and removal along a protein’s lifetime—a fundamentally different metric. This is due to interconversion of the measured proteoform species. Using this framework, we identify temporal phosphorylation sites on cell cycle-specific factors and protein complex assembly intermediates. Our results thus allow tying PTMs to the age of the modified proteins.

Impact of different factor VIII inhibitor kinetic profiles on the inhibitor titer quantification using the modified Nijmegen–Bethesda assay

BackgroundCoagulation factor VIII (FVIII) inhibitor titer quantification is vital for optimizing care in people with hemophilia A. ObjectivesThis study analyzed the impact of the different kinetic profiles of four FVIII monoclonal antibodies on inhibitor titer quantification using the modified Nijmegen–Bethesda assay. MethodsConcentration‐related and time‐related profiles of FVIII antibodies (4A4, BO2C11, 2‐54, ESH‐8) were evaluated in vitro. FVIII residual activity was measured using a one‐stage clotting assay and chromogenic substrate assay. Profiles of the FVIII antibodies were compared with the theoretical kinetic model: the ideal log (residual activity)‐linear (inhibitor concentration) relationship. Different theoretical kinetic model–dependent and –independent criteria to calculate FVIII inhibitor titer were compared. ResultsFactor VIII monoclonal antibodies had different concentration‐related and time‐related profiles, ideal for comparative analysis using the modified Nijmegen–Bethesda assay. The kinetic profile of 4A4 was similar to the theoretical kinetic model, while BO2C11 showed a steeper curve, and 2‐54 and ESH‐8 a flatter curve, than the model. In the modified Nijmegen–Bethesda assay, conversion of measured FVIII residual activities for different inhibitor dilutions into FVIII inhibitor titer is based on the theoretical kinetic model. Therefore, titer calculations for FVIII inhibitors that deviate from the model are prone to underestimation or overestimation. Calculating a theoretical dilution at 50% FVIII residual activity by sigmoidal regression reflecting different kinetic inhibition profiles can provide a more accurate titer result. ConclusionKinetic profiles of FVIII antibodies can deviate from the theoretical kinetic model in the modified Nijmegen–Bethesda assay, leading to differences in FVIII inhibitor titer quantification.

Thermal cracking of the large molecular alcohols in shale oil by experimental study and kinetic modeling

There is an important influence of alcohols in shale oil on its thermochemical properties. In this work, the fractions and species of the alcohols in shale oil from retorting oil shale were studied experimentally. The alcohols exist mainly in the form of linear carbon chains with different lengths, as well as different sites of hydroxyls. Then, 7-tetradecanol and pentadecanol were selected for further exploring the pyrolysis mechanisms through theoretical calculation and kinetic modeling, due to their abundance and representativeness in alcohols of shale oil. Density functional theory (DFT) method was utilized to reveal the difficulty of the thermal cracking of these two alcohols. The results indicated that the dissociation energies of C-C bonds are lower than those of C-H bonds, the reaction of eliminating water has a low activation energy. The Mulliken charges imply that there is a large electrostatic attraction between the O atom and its attached C atom in 7-tetradecanol, but an electrostatic repulsion between them in pentadecanol, which is thought to have an effect on the elimination of water. Finally, the detailed pyrolysis kinetic mechanisms of these two alcohols were written in a systematic manner by the GRI-Mech3.0 mechanism. A large number of the kinetic parameters were computed by the group-additivity method, which are consistent with the thermochemical data calculated by DFT. In summary, this research provides a theoretical basis for development of the kinetic mechanisms of large molecular alcohols and the accurate surrogate shale oil model.

Optical absorption investigations for efficient crystal violet dye removal from wastewater via carbon nanotubes:Montmorillonite-based nanocomposite.

The current study reports a facile method to fabricate functionalized multi-walled carbon nanotubes and montmorillonite clay mineral-based nanocomposite matrix and its detailed characterization using spectroscopic and morphological techniques. The nanocomposites have been studied for their potential applications in the treatment of contaminated water using batch adsorption studies. The investigations conducted using optical absorption spectroscopic measurements for the adsorption process indicate that the nanocomposite matrix can effectively remove almost 98% of the dye from aqueous solution. The nanocomposites have showed fast and strong adsorption behaviour for the dye with the maximum adsorption capacity (qm ) of ~467.3mg g-1 in 25 min. The experimental data at equilibrium were also correlated with the theoretical adsorption isotherm and kinetic models. The results demonstrate that the experimental data fits well to the Freundlich adsorption isotherm model and conforms to second-order kinetics. Furthermore, the nanocomposite exhibits good recyclability without any marked decrease in the adsorption performance even after five adsorption cycles of usage which indicates its potential application as reusable adsorbent for the efficient removal of hazardous dyes from contaminated water.

Thermal decomposition of isopentanol: A theoretical calculation and kinetic modeling analysis

Isopentanol (3-methyl-1-butanol, 3M1B) is a prospective bioderived fuel with advantages over ethanol that make it a suitable substitute for gasoline. Although there have been studies on the combustion properties of 3M1B, reaction kinetics for its thermal decomposition is scarce. This study explores the reaction pathways for the thermal decomposition of 3M1B through theoretical calculations. Six reactions with tight transition states, and nine bond dissociation reactions (i.e., barrierless reactions) were considered. For reactions with tight transition states, the CCSD(T)/CBS//M06–2X-D3(0)/def2-TZVP method was used, and the MRCISD(+Q)/CBS//CASPT2/cc-pVDZ method was adopted for the bond dissociation reactions. The conventional transition state theory (CTST), including multi-structural torsional anharmonicity (MS-T) correction, addressed those reactions with tight transition states. The MS-T method thoroughly examined the co-effect of the multiple structures and torsional anharmonicity. Direct bond-breaking reactions were studied using the variational transition state theory (VTST). Subsequently, system-specific quantum Rice-Ramsperger-Kassel (SS-QRRK) theory and Rice-Ramsperger-Kassel-Marcus/Master Equation (RRKM/ME) were employed to obtain the rate constants for reactions with tight transition states and direct bond-breaking reactions at different temperatures and pressures (T/P) regimes (T = 298–2400 K, P = 0.01–100 atm), respectively. The results showed that water elimination and C-C bond dissociation play a significant role for 3M1B unimolecular decomposition, other molecular elimination and bond dissociation channels can be ignored. Combining the reaction pathways and the corresponding pressure dependent rate constants into the kinetic model resulted in good predictions of the speciation profiles during 3M1B pyrolysis. These data are valuable for the development of the combustion models of 3M1B.

New method of kinetic modeling for CO2 absorption into blended amine systems: A case of MEA/EAE/3DEA1P trisolvent blends

AbstractIn order to establish an accurate kinetic model for the aqueous amine blends, monoethanolamine (MEA), 2‐(ethylamino) ethanol (EAE), and 3‐(diethylamino)‐1‐propanol (3DEA1P) have been chosen as a typical CO2 absorption trisolvents. The reaction kinetics of aqueous amine blends with carbon dioxide have been investigated first combining experiments and molecular simulations. The stopped‐flow technology has been used to obtain the observed reaction rate constant of the overall reactions over the temperature range of 293 to 313 K and at different amine concentrations. A theoretical kinetic model, based on the first‐principles quantum‐mechanical simulations, has been put forward to interpret the reactions between CO2 and the aqueous trisolvent amine blends systems. The proposed model, based on the zwitterion mechanism and the base‐catalyzed mechanism, shows good prediction with an acceptable absolute average deviation (AAD) of 6.32%, and has been found to be satisfactory in determining the kinetics of the involved complicated reactions.

Bimetallic nickel/manganese phosphate-carbon nanofiber electrocatalyst for the oxidation of formaldehyde in alkaline medium.

The development of earth-abundant transition metal-based catalysts, supported by a conductive carbonaceous matrix, has received great attention in the field of conversion of formaldehyde derivatives into toxic-free species. Herein, we report a comprehensive investigation of bimetallic electrocatalyst activity towards the electrooxidation of formaldehyde. The bimetallic phosphate catalyst is prepared by co-precipitation of Ni and Mn phosphate precursors using a simple reflux approach. Then the bimetallic catalyst is produced by mixing the Ni/Mn with carbon fibres (CNFs). The structural properties and crystallinity of the catalyst were investigated by using several techniques, such as scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and Brunauer Emmett−Teller theory. The system performance was studied under potentiostatic conditions. Some theoretical thermodynamic and kinetic models were applied to assess the system performance. Accordingly, key electrochemical parameters, including surface coverage (Γ) of active species, charge transfer rate (ks), diffusion coefficient of the formaldehyde (D), and catalytic rate constant (kcat) were calculated at Γ = 1.690 × 10−4 mmol cm−2, ks = 1.0800 s−1, D = 1.185 × 10−3 cm2 s−1 and kcat = 1.08 × 105 cm3 mol−1 s−1. These findings demonstrate the intrinsic electrocatalytic activity of formaldehyde electrooxidation on nickel/manganese phosphate- CNFs in alkaline medium.

In situ electrochemical monitoring of ROS influence in the dynamics of ascorbic acid and polyphenolic compounds in apple fruits

In situ recording of the voltammetric profile of different apple (Malus domestica Borkh.) varieties (Golden, Granny Smith, Reineta, Red delicious, Fuji, and Braeburn) without and with ROS generation is reported. The voltammetric response associated to the oxidation of ascorbic acid (AA) and polyphenolic (PPs) components was recorded. The obtained voltammetric profiles were satisfactorily fitted to a theoretical kinetic model consisting of the competing, dual activation pathways of AA and PPs followed by a degradative step. The rate constants for these processes were calculated from voltammetric data revealing significant differences between varieties. The activation pathways as well as the influence of electrochemical ROS generation on it were variety-sensitive while the degradative step was almost variety insensitive and lightly sensitive to ROS generation.