Irreversible Oxidation Research Articles

Simultaneous Electrochemical Determination of Sildenafil Citrate and Tadalafil using a Multi Walled Carbon Nanotubes Modified Glassy Carbon Electrode by Adsorptive Stripping Linear Sweep Voltammetry

An adsorptive stripping linear sweep voltammetric method was developed for the simultaneous determination of sildenafil citrate and tadalafil. The voltammetric working electrode was a glassy carbon electrode modified with carboxylic multi‐walled carbon nanotubes. The sensitivity of the developed voltammetric method was significantly increased by this modification. Both analytes spontaneously adsorbed on the modified electrode surface due to their adsorption affinities. The irreversible oxidation signals of both analytes were used as the analytical signals. The electrochemical behaviour of sildenafil citrate and tadalafil was assessed0.99

Developing a sensitive electrochemical platform constructed with nanoparticles of dysprosium supported on graphene nanoplatelets for the determination of yohimbine

Yohimbine, an α2-adrenoceptor antagonist, is used in the treatment of erectile dysfunction. However, it has various side effects such as tachycardia, arrhythmias, hypertension, dizziness, and poisoning. Some of its side effects are also manifested as anxiety, headaches and increased urinary output. Considering the consumption of yohimbine with dietary supplements and its side effects on the human system, the development of a novel, simple and sensitive method for the determination of yohimbine is significant. For this purpose, an electrochemical method was developed on a glassy carbon electrode (GCE) modified with dysprosium oxide (Dy2O3) and graphene nanoplatelets (GRNP). The electrochemical platform (GCE/GRNP@Dy2O3) possessed high electro-active surface area and lower value of charge transfer resistance (Rct). Yohimbine undergoes irreversible oxidation through a diffusion-controlled process. The observation of improved voltammetric behavior and enhanced peak response for yohimbine at GCE/GRNP@Dy2O3 could be attributed to the high synergistic effect between Dy2O3 and GRNP in addition to the increased surface area and electrocatalytic activity. The expected sensing mechanism of GCE/GRNP@Dy2O3 towards yohimbine might be attributed to the surface oxygen vacancies of Dy2O3 which are available on the surface of the nanocomposite. The oxygen atoms can interact with the functional groups of yohimbine and facilitate the oxidation of yohimbine. The peak response and concentration were found to be correlated over a range of 8.0 × 10−9–7.8 × 10−7 M. The GCE/GRNP@Dy2O3 system exhibited a detection limit (LOD) of 5.7 × 10−9 M for yohimbine. Average recovery values of 98.0 %–104.9 % with lower RSD values in yohimbine supplements and 101.0 %–103.0 % in artificial urine confirmed that GCE/GRNP@Dy2O3 provides reliable results for the determination of yohimbine.

Environmentally friendly screen-printed electrodes for the selective detection of 4-bromo-2,5-dimethoxyphenethylamine (2C-B) in forensic analysis.

In response to the growing need for sustainable analytical methods, this study explores the repurposing of screen-printed electrodes (SPEs) that would otherwise be discarded. This involves recoating the working electrode surface with a graphite (Gr) and chitosan (CTS) dispersion, creating a reusable SPE (SPE-Gr/CTS). Demonstrating its utility, SPE-Gr/CTS was employed for the detection of 4-bromo-2,5-dimethoxyphenethylamine (2C-B), a phenylethylamine commonly used for recreational proposes. Identifying 2C-B in fluid oral and seized samples is of great interest for forensic and toxicological applications. The 2C-B detection using SPE-Gr/CTS was optimized in Britton-Robinson buffer solution (0.1 mol L-1) at pH 2.0, employing square-wave adsorptive stripping voltammetry. The electrochemical behavior of 2C-B on SPE-Gr/CTS exhibited one irreversible oxidation and a reversible redox process. The proposed method presented a dynamic linear range for 2C-B determination (0.05 to 7.5 μmol L-1) with a low LOD (0.015 μmol L-1). Moreover, the stability of 2C-B electrochemical responses on SPE-Gr/CTS was confirmed using the same or different electrodes (N = 3), with a relative standard deviation of less than 5.0%. Interference studies with seventeen other illicit drugs and adulterants demonstrated that the proposed method is selective for 2C-B detection even in the presence of these substances. Real seized and oral fluid samples containing 2C-B were analyzed using this method, and the results were confirmed by LC-MS. The proposed device demonstrates to be an environmentally friendly and selective sensor for 2C-B detection in forensic analysis, offering a rapid and straightforward screening method for seized and biological samples. In addition, a portable and sensitive determination of 2C-B in forensic samples is presented with minimal sample consumption (50 μL).

ATRP with ppb Concentrations of Photocatalysts.

In atom transfer radical polymerization (ATRP), dormant alkyl halides are intermittently activated to form growing radicals in the presence of a CuI/L/X-CuII/L (activator/deactivator) catalytic system. Recently developed very active copper complexes could decrease the catalyst concentration to ppm level. However, unavoidable radical termination results in irreversible oxidation of the activator to the deactivator species, leading to limited monomer conversions. Therefore, successful ATRP at a low catalyst loading requires continuous regeneration of the activators. Such a regenerative ATRP can be performed with various reducing agents under milder reaction conditions and with catalyst concentrations diminished in comparison to conventional ATRP. Photoinduced ATRP (PhotoATRP) is one of the most efficient methods of activator regeneration. It initially employed UV irradiation to reduce the air-stable excited X-CuII/L deactivators to the activators in the presence of sacrificial electron donors. Photocatalysts (PCs) can be excited after absorbing light at longer wavelengths and, due to their favorable redox potentials, can reduce X-CuII/L to CuI/L. Herein, we present the application of three commercially available xanthene dyes as ATRP PCs: rose bengal (RB), rhodamine B (RD), and rhodamine 6G (RD-6G). Even at very low Cu catalyst concentrations (50 ppm), they successfully controlled PhotoATRP. Well-defined polymers with preserved livingness were prepared under green LED irradiation, with subppm concentrations ([PC] ≥ 10 ppb) of RB and RD-6G or 5 ppm of RD. Interestingly, these PCs efficiently controlled ATRP at wavelengths longer than their absorption maxima but required higher loadings. Polymerizations proceeded with high initiation efficiencies, yielding polymers with narrow molecular weight distributions and high chain-end fidelity. UV-vis, fluorescence, and laser flash photolysis studies helped to elucidate the mechanism of the processes involved in the dual-catalytic systems, comprising parts per million of Cu complexes and parts per billion of PCs.

Air stability of monolayer WSi2N4 in dark and bright conditions

Two-dimensional materials with chemical formula MA2Z4 are a promising class of materials for optoelectronic applications. To exploit their potential, their stability with respect to air pollution has to be analyzed under different conditions. In a first-principle study based on density functional theory, we investigate the adsorption of three common environmental gas molecules (O2, H2O, and CO2) on monolayer WSi2N4, an established representative of the MA2Z4 family. The computed adsorption energies, charge transfer, and projected density of states of the polluted monolayer indicate a relatively weak interaction between substrate and molecules resulting in an ultrashort recovery time of the order of nanoseconds. O2 and water introduce localized states in the upper valence region but do not alter the semiconducting nature of WSi2N4 nor its band-gap size apart from a minor variation of a few tens of meV. Exploring the same scenario in the presence of photogenerated electrons and holes, we do not notice any substantial difference except for O2 chemisorption when negative charge carriers are in the system. In this case, monolayer WSi2N4 exhibits signs of irreversible oxidation, testified by an adsorption energy of -5.5 eV leading to an infinitely long recovery time, a rearrangement of the outermost atomic layer bonding with the pollutant, and n-doping of the system. Our results indicate stability of WSi2N4 against H2O and CO2 in both dark and bright conditions, suggesting the potential of this material in nanodevice applications.

Unveiling the degradation mechanism of cathodic MoS2/C electrocatalysts for PEMWE applications

Molybdenum dichalcogenides (MoS2) are promising non-noble alternatives to replace platinum (Pt) for Hydrogen Evolution Reaction (HER) electrocatalysis in Proton Exchange Membrane Water Electrolyzers (PEMWE). The knowledge acquired on this class of catalyst for hydrodesulfurization (HDS) reactions has enabled significant advances in designing active MoS2 for HER. However, the stability of MoS2 in the dynamic operating conditions of a PEMWE coupled to renewable energy sources is often overlooked in the literature and is the focus of the present work. Herein, using nano slabs of 2H MoS2 supported on high surface area carbon, we dynamically monitored Mo dissolution trends both under HER conditions and at more anodic potentials to mimic start-ups and shut-downs of a PEMWE device. We report minimal Mo dissolution under HER conditions but it continuously increased with higher electrode potentials. In particular, Mo dissolution peaked during the irreversible oxidation from Mo(IV) to Mo(VI) starting at E = 0.7 VRHE which in turn fully annihilates HER activity. Since no change in Mo and S surface composition was observed, the decline in HER activity was attributed to the continuous exfoliation of the 2D MoS2 stacked layers induced by oxidation/dissolution of Mo. Additionally, our findings indicate that Mo cations can redeposit onto the cathode catalytic layer, forming a Mo blue film primarily composed of Mo(VI) species. This redeposition hampers HER performance by blocking catalytic sites and diminishing the catalyst's overall efficiency. These insights demonstrate the need to avoid excursions above E = 0.6 VRHE for the safe use of MoS2 cathode catalyst in PEMWE.

Synthesis and electropolymerization of a selenophene based chemiluminescent monomer and its use in blood detection

A new selenophene based trimeric chemiluminescent compound, namely 5,7-di(selenophen-2-yl)-2,3-dihydrothieno[3,4-d]pyridazine-1,4-dione (S2T-Lum), was synthesized in two steps via electron donor-acceptor-donor approach. Its chemiluminescent reaction with hydrogen peroxide was investigated in an alkaline solution in the presence of various catalysts such as different metal ions, hemin and blood samples and the results were compared with its thiophene analogue (T2T-Lum) and luminol. It was found that S2T-Lum was very sensitive to copper(II) and iron(III) ions, and blood samples. Also, it can be easily concluded that S2T-Lum as a new member of luminol type compounds is a potential candidate for the detection of blood findings in forensic science. Furthermore, S2T-Lum has an irreversible oxidation peak at 1.28 V vs Ag/AgCl, which is responsible from its electropolymerization. S2T-Lum was successfully polymerized electrochemically via potentiodynamic electrolysis without cleavage of its chemiluminescent active appendage. To the best of our knowledge, its corresponding polymer PS2T-Lum film is the first member of selenophene based luminol type electroactive polymers.

CHARACTERIZATION AND ELECTROCHEMICAL BEHAVIOUR OF BORON DOPED DIAMOND IN DETECTING AMODIAQUINE

Amodiaquine (AQ) is an essential medicine in treating malaria. Yet, the threat of drug resistance and toxicity necessitates accurate measurement of AQ in the human body. This research determines the amodiaquine (AQ) detection performance of boron-doped diamond (BDD) working electrodes. The study utilizes different pulse velocity (DPV) methods to analyze the AQ reaction behavior of BDD. The research demonstrates the reaction mechanism: Two electrons are transferred, and irreversible oxidation reactions occur. The sensor limit of detection (LOD) is measured to determine the performance of working electrodes for AQ detection. The LOD is calculated between 0.0645 µM and 0.3 µM, and changes in analytical concentrations relative to maximum current are calculated. The LOD of the BDD electrode is 1.5×10–8 M, lower than previous research on AQ sensors, showing the effectivity of the BDD electrode as an AQ sensor.

Spectroelectrochemical studies of TDMQ20: A potential drug against Alzheimer’s disease

Alzheimer’s Disease (AD), reported for the first time in 1906, is a common disease that remains incurable to this day. In the past, a family of treatments using Cu(II) chelators failed during clinical trials, evidencing the importance of pre-clinical studies. In this work, we performed electrochemical characterisation of TDMQ20, a new potential drug against AD, using electrochemistry and spectroelectrochemistry. On the basis of voltammetry, we determined that TDMQ20 undergoes a two-step irreversible oxidation process and a one-step irreversible reduction process. Both oxidation and reduction reactions are pH-sensitive. Bidimensional UV–Vis spectroelectrochemistry (UV–Vis-SEC) allowed us to confirm that oxidation of TDMQ20 can occur both on the aliphatic chain and on the aromatic ring. The results expand the knowledge of the TDMQ20 redox activity in the human body which is important from the point of view of the toxicity of the proposed therapy.

Origin of enhanced electrochemical performance in lithium-rich cathode materials via the fast ion conductor Li2O-B2O3-LiBr

Lithium-rich cathode materials have garnered significant attention in the energy sector due to their high specific capacity. However, severe capacity degradation impedes their large-scale application. The employment of fast ion conductors for coating has shown potential in improving their electrochemical performance, yet the structural and chemical mechanisms underlying this improvement remain unclear. In this study, we systematically analyze, through first-principles calculations, the mechanism by which Li2O-B2O3-LiBr (Hereafter referred to as LBB) coating enhances the electrochemical performance of the lithium-rich layered cathode material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 (Hereafter referred to as OLO). Our calculations reveal that the LBB coating introduces a more negative valence charge (average −0.14 e) around the oxygen atoms surrounding transition metals, thereby strengthening metal-oxygen interactions. This interaction mitigates irreversible oxygen oxidation caused by anionic redox reactions under high voltages, reducing irreversible structural changes during battery operation. Furthermore, while the migration barrier for Li+ in OLO is 0.61 eV, the LBB coating acts as a rapid conduit during the Li+ deintercalation process, reducing the migration barrier to 0.32 eV and slightly lowering the internal migration barrier within OLO to 0.43 eV. Calculations of binding energies to electrolyte byproducts HF before and after coating (at −7.421 and −3.253 eV, respectively) demonstrate that the LBB coating effectively resists HF corrosion. Subsequent electrochemical performance studies corroborated these findings. The OLO cathode with a 2% LBB coating exhibited a discharge capacity of 157.12 mAh g−1 after 100 cycles, with a capacity retention rate of 80.38%, whereas the uncoated OLO displayed only 141.67 mAh g−1 and a 72.45% capacity retention. At a 2 C rate, with the 2 wt% LBB-coated sample maintaining a discharge capacity of 140.22 mAh g−1 compared to only 107.02 mAh g−1 for the uncoated OLO.

Facile fabrication of bismuth oxide anchored graphene oxide for the effective electrochemical sensing of diuron

BackgroundDiuron (DU), a weed controller widely used in the agricultural industry, prolonged conception of this agrochemical residue contaminated with environmental water bodies and soil sources could cause an acute impact on the human health system. This work utilized the electrochemical determination technique due to their rapid detection, outstanding sensitivity, and economical purpose. MethodsThe electrochemical behavior of DU at the γ-Bi2O3 microplates interconnected with sheet-like graphene oxide (GO) as a surface-modified electrode was scrutinized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The surface-modified γ-Bi2O3/GO/GCE elucidates superior electrocatalytic performance towards the irreversible oxidation response of diuron than the other surface-modified electrode in the phosphate buffer solution of 0.1 M. Significant findingsThe γ-Bi2O3/GO/GCE electrode displayed an extensive detection range of 0.1–631 µM with a 0.751 µM lower detection limit furthermore, noticeable 0.0280 µA µM-1 cm-2 sensitivity for diuron determination. In addition, the DPV experiment exposed that the γ-Bi2O3/GO/GCE electrode achieves stupendous selectivity, durability, and acceptable feasibility of the real-time samples.

Improving Hybrid Tin Halide Films of Lead-Free Perovskite Solar Cells with a Volatile Additive of Dipropyl Sulfide.

Lead-free perovskite solar cells with hybrid tin halides (Sn-PVKs) as harvesters have attracted attention with respect to eliminating the contamination of conventional hybrid lead halides. However, Sn-PVK films usually have inferior performance due to rapid crystallization and uncontrollable morphology. Moreover, Sn2+ ions suffer from irreversible oxidation that results in self-doping and device instability. Additive engineering is a key strategy for improving the quality of Sn-PVK films, but solid residues of additives could degrade the transport-recombination process. In this work, dipropyl sulfide (DPS) was introduced as a volatile additive into the precursor solution, and no residue exists in the Sn-PVK films after thermal annealing. The coordinating ability of DPS molecules stabilized Sn2+ ions to form the intermediate complex, which retards the crystallization and oxidation of Sn-PVK films. Consequently, the power conversion efficiencies of devices increase from 11.0% to 12.9% with less recombination and a lower leakage current, and the stability of the devices is improved simultaneously.

Preventive conservation of paper-based relics with visible light high-transmittance ultraviolet blocking film based on carbon dots

Paper-based relics is an important carrier for recording and preserving information, however, it faces irreversible UV-induced damage, including photocleavage, oxidation, acidification and discoloration, which seriously affects its value and lifespan. Carbon dots (CDs) possess excellent UV absorption and good chemical stability, making them suitable for UV protection. Herein, we propose a high-security and efficient method utilizing CDs films (CDFs) for preventive protection of paper against UV damage. The CDFs with high tunable UV absorbance and minimal absorbance in the visible light range, effectively shield paper from UV radiation while preserving its visual appeal. Moreover, the UV transmittance of the film can be fine-tuned to the content of CDs and can be easily removed from the paper without residue. Artificial accelerated UV aging experiments demonstrate the deceleration of acidification, oxidation, and photocleavage in the protected bamboo paper and Xuan paper. This research paces a new direction for the protection of paper and paper-based relics and artworks with emerging carbon materials, offering customizable protection effects tailored to specific preservation and exhibition requirements. This research pioneers a novel approach to preventive protection of paper and paper-based relics using emerging carbon dots materials, offering tailored protection for diverse preservation needs.

Enhanced Dynamic Operational Stability of Ni-Based Electrodes for Alkaline Water Electrolysis

Due to the accelerating paradigm shift toward renewable energy, water electrolysis systems have been evaluated for their ability to act as long-term renewable energy stores, wherein the energy is stored in the form of hydrogen gas. However, when renewable energy sources are employed, the power provided is intermittent, so developing highly active and durable electrode materials that function under these conditions is necessary. In particular, the irregular power supply accelerates severe degradation of the Ni-based electrodes due to irreversible surface oxidation, structural defects or collapse of the layered structure. Herein, we designed and fabricated Ni-based binary electrodes for alkaline water electrolyzers (Ni-Al & Ni-P electrodes for HER, Ni-Fe LDH electrodes for OER), and evaluated their electrochemical performance under dynamic operating conditions. Importantly, no significant OER & HER performance degradation was observed after the lab-scale dynamic operation tests, and no structural deformation or metal ion dissolution was found to occur. We further demonstrated the stability under the dynamic using advanced analysis and simulation techniques (XAS, in-situ ICP-MS, DFT calculations)

Deciphering the Role of p-Type ZnCo2O4 Semiconductor Nanoflakes for Selective Enhancement of Voltammetric Responses Toward Redox Species System: Interfacial Electron-Transfer Kinetics and Adsorption Capacity

In this study, we describe experimental efforts to decipher the role of ZnCo2O4 nanoflakes (ZCO-NFs) for selective enhancement of voltammetric responses of screen-printed electrode (SPE) toward redox species system. The ZCO-NFs sample was characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and UV–vis spectroscopy. The electrochemical characterization of bare SPE and modified SPE electrodes was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Mott−Schottky analysis. A series of redox systems including paracetamol (PA), dopamine (DA), chloramphenicol (CAP), furazolidone (FZD), p-nitrophenol (p-NP), carbaryl (CBR), ofloxacin (OXF), and erythromycin (ERY) were selected to investigate for (i) reversible redox process, (ii) irreversible electrochemical oxidation process, and (iii) irreversible electrochemical reduction process on both bare-SPE and ZCO-NFs/SPE electrodes. The obtained results showed that ZCO-NFs possess the selective enhancement of electrochemical response for redox systems with an increase of 24%–90% for PAR, DA, FZD, CAP, and CBR and a decrease of 13%–49% for p-NP, ERY, and OFX. The different electrochemical response of redox species at nanostructured semiconductor electrodes is attributed to the contribution of both the adsorption capacity of redox species and the interfacial electron transfer process between electrode and redox species. An insight into the interfacial electron transfer kinetics and its contribution to the enhancement of electrochemical response on p-type semiconductor electrode is helpful in designing high-performance sensing platforms based on spinel oxide nanostructures.

Enhanced electrochemical oxidation and machine learning-assisted sensing of tetrabromobisphenol A using activated carbon facilitated CoWO4 heterostructures

The escalating levels of environmental pollution, particularly from commercially used products, highlight the imperative of efficient sensor technologies to facilitate timely and effective remediation strategies. Herein, a simple method is proposed to enhance the electrochemical performance of CoWO4 structures by coupling them with activated carbon (AC) for direct tetrabromobisphenol A (TBPA) oxidation. The systematic comparison shows that incorporation of AC with CoWO4 not only improves the overall effective surface area (ESA) of the catalyst by 1.8-fold but also improves the cyclic voltammetry (CV) based irreversible oxidation current by 2.0-fold owing to improved conductivity and surface characteristics. Differential pulse voltammetry (DPV) based optimization of the sensory characteristics confirmed robust electrocatalytic TBPA oxidation within a 0.1 to 1.0 µM concentration range, achieving a 0.024 µM detection limit within PBS (0.1 M) (pH 5.0). Moreover, density functional theory (DFT) analysis confirms the non-covalent interaction favorability between TBPA and CoWO4 surface, validating TBPA’s easy adsorption onto the catalytic surface and, thus, facilitated electron mobility between the molecule and the catalyst during the surface oxidation process. The DPV sensing interpreted using machine learning (ML) algorithms confirmed the detection accuracy of the developed sensor. Among the adopted models, artificial neural networks (ANN) achieved the highest R2 score (0.9659) and the lowest values across Mean Squared Error (MSE), Mean Absolute Error (MAE), and Root Mean Squared Error (RMSE) error matrices confirming its suitability in deciphering DPV correlations.Integrating ANN with DPV based electrocatalytic oxidation sensing underscores machine learning’s potential in analyzing complex electrochemical signatures, thus advancing intelligent sensing for precise environmental monitoring.

Defect‐Driven Oxidation Enabled V2CTx MXene with Ultralong‐Cycling and High‐Rate Capability in Aqueous K+ Storage

AbstractOwing to the adverse influences of irreversible oxidation, the development of MXene‐based materials, especially those with satisfactory performance and longevity for aqueous energy storage, continues to suffer severe challenges. Herein, the strategy of targeted passivation‐supported defect‐lock‐oxygen is conceived, whereby engineered the V2CTx material for controllable partial oxidation with enhanced regioselectivity. When the material works, inside the intrinsic defects, the outward diffusion of oxidation is confined by the Lewis bases around the defects, which allows for the controllable progress of oxidation. The defect‐locked oxygen oxidizes the exposed carbon, thus forming sufficient amorphous carbons for enhancing the capacitive‐type adsorption of K‐ions. Then the oxidized defects enabled the fast kinetics via the cross‐layer transport of K‐ions. Benefiting from the strategy, the electrode assembly V2CTx‐RTIL (V2CTx equipped with room temperature ionic liquid) exhibits high capacity, good rate capability, and ultra‐longevity compared with those of the MXene materials so far reported. This work presents the first strategy of targeted passivation‐supported defect‐lock‐oxygen for high‐rate capability and super long‐cycling aqueous K+ storage and hopefully would provide the inspiration for the future design of novel electrodes.

Glycosylated flavonoid kaempferitrin: Electroanalytical detection and the proposal of an oxidation mechanism supported by quantum chemical calculations

In this work, the electrochemical behavior of the glycosylated flavonoid kaempferitrin was studied, and an electroanalytical methodology was developed for its determination in infusions of Bauhinia forficata using a boron-doped diamond electrode (BDD). The electrochemical behavior of the flavonoid was studied by cyclic voltammetry, and two irreversible oxidation peaks at 0.80 and 1.0 V vs Ag/AgCl were observed. The influence of the pH on the voltammograms was examined, and higher sensitivity was found at pH 7.0. The electrochemical process corresponding to peak 1 at 0.80 V is predominantly diffusion-controlled, as the study shows at varying scan rates. An analytical plot was obtained by square wave voltammetry at optimized experimental conditions (frequency = 100 s−1, amplitude = 90 mV, and step potential = 8 mV) in the concentration range from 3.4 μmol L−1 to 58 μmol L−1, with a linearity of 0.99. The limit of detection and limit of quantification values were 1.0 μmol L−1 and 3.4 μmol L−1, respectively. Three samples of Bauhinia forficata infusions (2 g of sample in 100 mL of water) were analyzed, and the KF values found were 5.0 × 10−4 mol L−1, 3.0 × 10−4 mol L−1, and 7.0 × 10−4 mol L−1, with recovery percentages of 98 %, 106 % and 94 %, respectively. Finally, experiments were performed with two other flavonoids (chrysin and apeginin) to compare and propose an electrochemical oxidation mechanism for kaempferitrin, which was supported by quantum chemical calculations.

Ytterbium-doping effect on the electrochemical and piezoelectric properties of poly(vinylidene fluoride) films

The optimal molar ratio of poly(vinylidene fluoride) (PVDF): dimethyl sulfoxide (DMSO) was investigated that promoted the β-phase formation, used during the PVDF film synthesis. The solution cast method was used for doping the PVDF films with ytterbium (III) nitrate salt hexahydrate. In general, Yb-doping in PVDF films improves thermal resistance, promotes β-phase formation, modifies the monomer conformation, reduces reversibility to electrochemical processes, and increases the d33 coefficient of piezoelectricity. The β-phase formation caused by Yb-doping alters the internal structures of the trans-gauche-trans-gauche’ (TGTG’) and all-trans (TTTT) chains inside the polymeric network. The coexistence between the trans-gauche and all-trans structures provides in both films the α-phase and β-phase coexistence. The presence of self-polarized CH2-CF2 dipoles, where the concentration of fluorine remains the same and the CH2 drastically increases after Yb3+ incorporation. The quasi-reversible shape shown in both voltammetry cyclic curves is related to irreversible oxidation and reduction reactions. Yb-PVDF exhibits specific pseudocapacitance values that are 30% higher than those of the PVDF films. Finally, the piezoelectric properties were improved with ytterbium incorporation.

Transpersulfidation or H2S Release? Understanding the Landscape of Persulfide Chemical Biology.

Persulfides (RSSH) are biologically important reactive sulfur species that are endogenously produced, protect key cysteine residues from irreversible oxidation, and are important intermediates during different enzymatic processes. Although persulfides are stronger nucleophiles than their thiol counterparts, persulfides can also act as electrophiles in their neutral, protonated form in specific environments. Moreover, persulfides are electrophilic at both sulfur atoms, and the reaction with a thiolate can lead to either H2S release with disulfide formation or alternatively result in transpersulfidation. Despite the broad acceptance of these reaction pathways, the specific properties that control whether persulfides react through the H2S-releasing or transpersulfidation pathway remain elusive. Herein, we use a combined computational and experimental approach to directly investigate the reactivity between persulfides and thiols to answer these questions. Using density functional theory (DFT) calculations, we demonstrate that increasing steric bulk or electron withdrawal near the persulfide can shunt persulfide reactivity through the transpersulfidation pathway. Building from these insights, we use a synthetic persulfide donor and an N-iodoacetyl l-tyrosine methyl ester (TME-IAM) trapping agent to experimentally monitor and measure transpersulfidation from a bulky penicillamine-based persulfide to a cysteine-based thiol, which, to the best of our knowledge, is the first direct observation of transpersulfidation between low-molecular-weight species. Taken together, these combined approaches highlight how the properties of persulfides are directly impacted by local environments, which has significant impacts in understanding the complex chemical biology of these reactive species.