Reduction Peak Potential Research Articles

Synthesis, Structural, Electrochemical, and DFT Studies of Highly Substituted Nonplanar Ni(II) Porphyrins and Their Intensity-Dependent Third-Order Nonlinear Optical Properties.

We designed and successfully synthesized highly substituted electron-deficient nonplanar Ni(II) porphyrins and their derivatives (1-7) in moderate to good yields. These derivatives were comprehensively characterized by various spectroscopic techniques and single-crystal X-ray diffraction (SCXRD) analysis. SCXRD analysis confirmed the structures of compounds 2, 4, and 7, adopting saddle-shape geometry. These nonplanar porphyrins demonstrated significant bathochromic shifts in their absorption spectra compared to parent NiTPP, attributed to the influence of bulky β-substituents and/or peripheral fusion. π-Extended porphyrins 6 and 7 displayed panchromatic absorption spectra extending into the NIR region. Porphyrins 6 and 7 demonstrated a profound anodic shift (∼400 mV) in their first reduction peak potentials compared to precursor NiTPP(NO2)Br6. The experimental absorption spectral pattern matches the simulated absorption spectra obtained from TD-DFT studies. The femtosecond laser intensity-dependent third-order nonlinear optical studies revealed that NiDFP(VCN)2Br6 (6) and NiDFP(VCN)2(PE)6 (7) displayed giant optical nonlinearities compared to the other porphyrins. Among all, NiDFP(VCN)2Br6 (6) possessed the highest two-photon absorption coefficient (β) and cross-section (σTPA) values in the range of 22-33 × 10-10 m/W and 3.77-6.95 × 106 GM, respectively. These findings suggest that the investigated nonplanar π-extended porphyrins are promising candidates for future optoelectronic applications.

Hydrothermal synthesis of iron titanate hexagonal nanoplates for electrochemical detection of nitrofurazone.

Anelectrochemical sensoris established using an iron titanate (FeTiO3) modified glassy carbon electrode (GCE) to detect nitrofurazone. Various microscopic and spectroscopic analysis was performed to reveal the properties of the prepared FeTiO3 hexagonal nanoplates. The FeTiO3/GCE presents enhanced electrochemical response to nitrofurazone at the peak reduction potential of - 0.471V with a larger peak current than the bare GCE due to high electrical conductivity, enhanced specific surface area, and abundant active sites. The superior nitrofurazone detection performance includes the low limit of detection of 0.002μM and the sensitivity of 0.551 µA µM-1cm-2 in the linear concentration range of 0.01-162.2μM. The reproducibility and selectivity studies of the FeTiO3/GCE show excellent results with a relative standard deviation of < 5%. The practicability of FeTiO3/GCE is confirmed by monitoring nitrofurazone in actual samples. This work demonstrates that perovskite-type FeTiO3 has great potential in real-world sample analysis, and provides a new way to develop high-performance electrochemical sensors.

Improving the electrochemical characteristics and performance of a neutral all-iron flow battery by using the iron reduction bacteria

At present, the all-iron redox flow batteries (RFBs) have greater application potential due to high accessibility of electrolytes compared to traditional RFBs. Meanwhile, although electroactive bacteria can accelerate the electrons transfer, their potential to improve the performance of RFBs has been overlooked. Previously, we had confirmed that ferrous-oxidizing bacteria (FeOB) could enhance the performance of an all-iron RFB, therefore we conducted several batch experiments and chronopotentiometry experiments by using the ferric-reducing bacteria (FeRB) or mixed culture (FeOB and FeRB) to demonstrate whether they have the same or stronger effects on Fe3+-DTPA/Na4[Fe(CN)6] RFB. The results showed that the experimental reactors could achieve higher charging current density and initial cathodic potential during constant voltage charging process. The electrochemical impedance spectroscopy data and cyclic voltammetry curves demonstrated that the polarization impedance increased slower and reduction peak potential of experimental groups also emerged a positive shift compared to CK. According to chronopotentiometry experiments results, the microbes could function at maximum 0.3 M, 12 mA/cm2, and also improved the charging specific capacity. Combined the SEM pictures and microbial composition analysis, the main functional electroactive FeRB were Alcaligenes, Corynebacterium and Bacillus, which indicated to have important potential in improving the performance of RFBs.

Deciphering the high overpotential of the oxygen reduction reaction via comprehensively elucidating the open circuit potential

The reduction peak potential of Pt-based catalysts during cathodic scans emerges as a novel indicator for predicting ORR performance, proposing a strategy to enhance the OCP and reduce the overpotential by kinetically inhibiting Pt oxidation.

Electrochemical Reduction of Ytterbium in Non-Aqueous Solvents - Towards Production of Pure Medical Lutetium-177

In recent years targeted radionuclide therapy has become a topic of great interest as a growing number of cancers can potentially be treated with radionuclides like lutetium-177 and samarium-153. To facilitate this growth and meet the demand, preparation and purification of lutetium-177 is increasing in importance. In the most common production route, enriched ytterbium-176 targets are irradiated and the produced lutetium-177 is separated from the ytterbium target material. This challenging separation is commonly performed using ion exchange resins, a method limited in scalability as the chemical similarity between ytterbium and lutetium results in poor separation at higher concentrations.An alternative method to aid the separation of lutetium from ytterbium is the electrochemical reduction of ytterbium as a change in oxidation states changes chemical properties significantly. Ytterbium has an accessible divalent state, whereas lutetium has not. However, the very negative value of the Yb(III)/Yb(II) standard reduction potential (E0= -1.04 V vs. SHE) does pose some challenges as it becomes a necessity to work in non-aqueous solvents with a very low water content. Similar research has already been performed in our group, looking into the separation of samarium-153 from europium-154, reducing europium in nitrate media, followed by a separation over TEVA resin. In this study, we investigated the reduction of ytterbium in ethylene glycol, dimethyl sulfoxide, tetrahydrofuran and N,N-dimethyl formamide by cyclic voltammetry, linear sweep voltammetry and electronic impedance spectroscopy. The influence of multiple variables such as moisture content on the reduction kinetics and stability of Yb(II) was determined and a Koutecky-Levich analysis was performed. Our results demonstrate that the reduction of ytterbium in non-aqueous solvents is feasible but attempts to perform bulk electrolysis were not successful yet. Ethylene glycol, dimethyl sulfoxide and N,N-dimethyl formamide demonstrate favorable conditions and in each solvents clear reduction and oxidation peaks were observed. It was found that the solvents do affect the peak separation, reduction potential and sensitivity to passivation. Figure 1

Revisiting Open Circuit Corrosion of Cr in Unpurified Molten FLiNaK Salts with a Multi-Modal Approach

Corrosion and mitigation of environmental degradation of structural materials in high-temperature Gen IV molten salt reactors, are critical issues. However, any corrosion studies have historically been forensic post-test examinations and materials development has occurred mainly by trial and error until recently. Meanwhile, a fundamental understanding can only be achieved by recognizing how the corrosion system of model materials in molten fluoride salts evolves as a function of time. A number of in-situ spectroscopy techniques to identify corrosion product compositions in molten salts have been suggested in recent years. Raman, high-temperature UV-Vis absorption spectroscopy, and X-ray absorption spectroscopy are a few of them [1,2]. These techniques' major limitations include the fact that they are mainly qualitative, and complex hardware requiring a beam focusing inside the glove box is needed. At the same time, electrochemical techniques have been presented which can provide the information on behavior of both metal and its corrosion product in the continuously evolving corrosion system in molten salts. However, use of single isolated methods renders it difficult to obtain mechanistic information on instantaneous, time-dependent processes and phenomena during corrosion. These are needs gaps opportunities. In this work we present a detailed electrochemical analysis of the corrosion of polycrystalline chromium at 600°C in FLiNaK over 50 h including an electrochemical analysis of in-situ near-instantaneous corrosion rates corroborated with other methods.A variety of corroborating methods including (1) in-situ electrochemical diagnostic techniques, (2) static immersion exposure with gravimetric and SEM analysis, (3) electrochemical impedance spectroscopy, (4) XRD, (5) ICP-OES, was utilized to study the corrosion behavior in unpurified FLiNaK at 600°C. The focus was to evaluate the viability of using an external non-reactive electrode to measure the concentration of corrosion products via redox process analysis in order to determine the corrosion rate during the process of OCP corrosion of Cr in FLiNaK. This work reports the possibility of using of electrochemical techniques such as CV for the instantaneous determination of Cr corrosion rates when Cr is exposed to a 600oC FLiNaK salts for 50 h. It was found that the concentration of dissolved corrosion products, in the more likely possible forms of CrF3 - and CrF6 3- , might be calculated by established analytical approaches to CV analysis such as Berzins-Delahay (soluble/insoluble) and Randles-Ševcik equations (soluble/soluble). The calculated values showed the definite concentration of Cr(II)/Cr(III) corrosion products at the distance of the external electrode (due to the static corrosion conditions). These finding supported by XRD and ICP-OES. A semi-infinite diffusion model was employed in this study to adjust the calculated concentrations assuming a stagnant solution and diffusion based one-dimensional concentration diffusion profile in order to calculated the Cr(III) concentration at a fixed position in the Cr(III) concentration gradient. It was shown that the semi-infinite diffusion model helps correctly describe this profile between 10 and 50 h, based on the geometry of the working electrode and corrosion cell. Based on these results the OCP corrosion rate was interpreted to switch over 50 h from initially charge transfer control Cr(II) oxidation at early times with likely HF and Cr(III) reduction, followed by mass transport control regulated by a salt film and then possible stifling due to depletion of HF and Cr(III) solubility limits.The results of half-cell redox potentials and peak currents pertaining to oxidation/reduction of Cr corrosion products were correlated to the concentrations of particular Cr species and compared with the results of mass loss experiment and ex-situ ICP-OES of post-exposed FLiNaK. The mass loss of the Cr(II)/Cr(III) metal that was approximated by spatially integrating the concentration profiles at a selected time, and the result of Cr mass loss separately obtained from gravimetric measurements showed a reasonable agreement. Furthermore, the rate of accumulation of Cr ions in the residual FLiNaK salt after 50 h of exposure determined by ICP-OES, correlated with the electrochemical CV and EIS analysis. In addition to this, the oxidation and reduction peak potentials pertaining to Cr/CrF3 - and CrF3 -/CrF6 3- redox reactions (measured on Pt wire) were compared with the OCP (measured on Cr) to provide insights on the predominant anodic and cathodic reactions. Acknowledgments This research was supported as part of the fundamental understanding of transport under reactor extremes (FUTURE), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Utilization of the Malvern-Panalytical Empyrean diffractometer was supported by Nanoscale Materials Characterization Facility with National Science Foundation under award CHE-2102156. References Y. Liu et al., (2020) Corrosion Science. 169 108636. https://doi.org/10.1016/j.corsci.2020.108636.S. Fayfar, et al., (2022). https://doi.org/10.26434/chemrxiv-2022-3nspm.

Alumina nanoparticles modified electrode for sensitive detection of tinidazole in drug and urine samples

We provide a simple, robust, and novel method based on a stable dispersion of α-alumina (Al2O3) nanoparticles to modified glassy carbon electrode (GCE) for the quantitative detection of the tinidazole (TIN) drug, a derivative of the nitroimidazole moiety. Because of the adverse effects due to the consumption of large quantities, we need an analytical tool for quantitative detection. A well-defined reduction peak potential for TIN was observed at − 0.65 V vs. Ag/AgCl with enhanced catalytic peak at Chit@alumina modified GCE at neutral pH (0.1 M PBS). Under the experimental conditions, the fabricated electrode shows a broad linear response to concentrations of TIN in the ranges of 6.0 × 10−9 M to 36 × 10−6 M with correlation coefficient of 0.9974. The lowest detection limit was identified as 16 nM, and the current sensitivity was measured to be 12.16 μA∙ nM−1∙cm−2. Furthermore, the synthesized voltammetic sensor has adequate recovery ranges, remarkable anti-interference performance against biomarkers and other electroactive molecules, and also exhibits good storage stability and repeatability. The developed sensor's application studies were successfully used to detect TIN in biological specimens and drug tabulations.

Characterizing the removal of Pb2+ and Zn2+ from an acidic smelting wastewater using electrocatalytic internal Fe0/C micro-electrolysis

The discharge of acid non-ferrous metal smelting wastewater has received unprecedented attention with increasing threat to ecosystems and human health. A combined process of electrocatalytic internal Fe0/C micro-electrolysis (ECIME) fluidized bed was developed at lab scale (2.0L) to investigate the co-removal performance, optimization conditions and reaction characteristics differences of Pb2+ and Zn2+ from acid smelting wastewater. The results of cyclic voltammogram (CV) and XPS reveal that Pb2+ and Zn2+ can be electrodeposited on the carbon microelectrodes surface in ECIME system, and the positive shift degree of the reductive peak potentials under cathodic polarized is positively correlated with the voltage intensity. Metal ions reaction flow direction of ECIME system and SEM, EDS, XPS characterizations indicated that the removal of Pb2+ and Zn2+ were mainly attribute to electroreduction deposition and in-situ iron polymer hydroxyl flocculation, and including four reaction processes of electroreduction on surface of external electrode, iron-carbon particles microelectrode, self-flocculation and secondary flocculation. But the removal of Pb2+ and Zn2+ show different dominant reaction path, Pb2+ removal mainly depended on the electroreduction deposition (64.11%), whereas Zn2+ dominated by iron-based flocculation (62.93%). Response surface optimization based on the average efficiency indicated that the co-removal of Pb2+ and Zn2+ mainly depended on polarization voltage, reaction time, initial pH and electrolyte concentration with optimal conditions of 11.0 V, 58.65 min, 5.0, and 0.08 mol/L, and its optimal average removal efficiency reached 98.52% (initial concentration 100 mg/L), and the residual concentrations were 0.081 mg/L and 1.890 mg/L, respectively. These findings provide insights and theoretical for developing electrochemical platform to realize heavy metal wastewater zero discharge.

A new deep clustering method with application to customer selection for demand response program

Demand response (DR) is regarded as a promising solution to the problem of renewable energy integration, while it remains one of the key barriers for DR to target the right customers, i.e. the customers with high potential in peak reduction. Exploring the electricity consumption behaviors of customers can help DR program practitioners evaluate customers’ peak reduction potential. Clustering has been the most common approach to describe customers’ consumption behaviors in the literature. However, the existing clustering methods suffer from either unscalability or poor performance when handling a large number of daily load curves. To overcome these issues, a new deep learning-based clustering method is proposed in this paper, which integrates both intra-cluster compactness and inter-cluster separation into the objective function of clustering for consideration. Based on the clustering results, a new customer selection framework is developed to identify the potential good candidates for DR programs, which takes the stability of consumption behaviors and the characteristics at peak hours into account. Case studies on a London dataset demonstrate the superiority of the proposed clustering method over classical K-means and two state-of-the-art deep clustering methods in terms of clustering validity indexes. Furthermore, the simulations performed on an actual price-based pilot show that the customers selected by the proposed customer selection framework contribute to 59 % of total peak reduction with only accounting for 23 % of population.

Heterostructure of amorphous nickel boride anchored 2D-layered cobalt selenide nanosheets as a disposable strip sensor for detection of toxic pollutant 5-nitroquinoline in aquatic samples

The development of disposable electrode-based sensors is of great importance for the electrochemical monitoring of toxic pollutants in wastewater systems, which are often present and mutually inhibiting during sample detection. In this work, a distinctive approach was taken to use an electrochemical heterostructure sensor with chemically reduced nickel boride (Ni3B) nanoparticles anchored in two-dimensional (2D) layered cobalt selenide (CoSe) nanosheets. The prepared hybrid structure (2D CoSe/Ni3B) enables large active sites and a strong synergistic effect between nanostructures to improve the electrocatalytic activity in the detection of water pollutant 5-nitroquinoline (5-NQ) with a disposable screen-printed carbon electrode (SPCE). The 2D CoSe/Ni3B/SPCE exhibits a reduction peak potential of −0.63 V for 5-NQ, with an increased reduction peak current compared to that of other electrodes. The fabricated disposable strip electrode is suitable for the electrochemical testing of pollutants. The proposed hybrid 2D CoSe/Ni3B/SPCE disposable sensor showed a wide linear range of 0.2–378 μM and a low detection limit of 0.042 μM for 5-NQ. The developed 2D CoSe/Ni3B hybrid nanostructure-based disposable sensor efficiently detects 5-NQ in hazardous water contaminants by voltammetric analysis and showed acceptable recoveries. Based on the results, it is believed that the proposed work provides a clear idea for the fabrication of transition metal-based metal boride and selenide heterostructures with excellent catalytic activity for the electrochemical detection of various pollutants in real-time monitoring.

An input-output-based Bayesian neural network method for analyzing carbon reduction potential: A case study of Guangdong province

Economic development, population growth, industrialization and urbanization have led to large increases in anthropogenic carbon emission that has caused a variety of negative impacts on climate change and eco-environment systems. This study develops an input-output-based Bayesian neural network (IO-BNN) method for simulating the carbon emission of various economic sectors and generating the desired schemes of emission reduction. IO-BNN is applied to Guangdong province to identify its carbon emission path, carbon peak, and carbon reduction potential over a long-term planning horizon (2021–2050), in which multiple scenarios are designed to examine the effects of different environmental policies on economic and energy activities. Major findings are: (i) the key sectors and factors affecting Guangdong's carbon emission and economic development are equipment (Equ), construction (Con), transport and storage (Tra), other service (Oth), per capita energy consumption (CEC), and primary energy consumption (EC); (ii) under different environmental policies, Guangdong's carbon emission would reach the peak during 2025–2035 and then continuously decrease during 2036–2050; (iii) Guangdong's carbon emission would peak in 2025 under the optimal scenario, associated with adjustment of industrial structure (i.e. part of secondary industry would be shifted to tertiary industry) as well as reduction of primary energy consumption.

Proton-Conductive and Electrochemical-Sensitive Sensing Behavior of a New Mn(II) Chain Coordination Polymer

In this work, a novel Mn(II) chain coordination polymer (Mn-CP), {[Mn(iip)(2bbpum)0.5(H2O)3]·2H2O}n [H2iip = 5-iodoisophthalic acid, 2bbpum = N,N′-bis(2-pyridinemethyl)oxamide] was synthesized under ambient conditions. Mn-CP further assembles into a 3D supramolecular architecture through hydrogen bonds, halogen bonds, and ππ stacking interactions. The composite Mn-CP/nafion membrane has low activation energy for proton transfer, which results in its temperature-insensitive proton conductivity. The cyclic voltammetry demonstrates that the Mn-CP electrode (Mn-CP/GCE) shows quite different redox properties in 0.1 M H2SO4 and 0.1 M PBS aqueous solutions. The Mn-CP/GCE exhibits a couple of irreversible redox peaks with an oxidation peak potential suitable for the nitrite oxidation in 0.1 M H2SO4. Quite differently, in the PBS aqueous buffer solution, the Mn-CP electrode has a couple of irreversible redox peaks. The reduction peak potential is appropriate for the H2O2 reduction. So, the Mn-CP/GCE can be used not only in the electrocatalytic oxidation of NO2– but also in the electrocatalytic reduction of H2O2. The amperometric response reveals that the Mn-CP/GCE exhibits high-selective and extremely sensitive oxidation sensing of NO2– and reduction sensing of H2O2. The exponential detection range is 0.01–20 mM for NO2– and 0.01–10.5 mM for H2O2. The linear detection range for both H2O2 and NO2– is 0.01–0.10 mM. The detection limit is 1.865 μM for NO2– and 8.57 μM for H2O2. The Mn-CP/GCE exhibits high electrochemical stability and fine reproducibility. Moreover, the strategy can be translated to a portable screen-printed electrode (SPE). The Mn-CP/SPE shows more sensitive sensing to NO2– and H2O2 than Mn-CP/GCE. Moreover, it can detect NO2– and H2O2 efficiently in the real-world samples. So, Mn-CP may be a potential dual nonenzymatic electrochemical sensory material for NO2–via oxidation sensing and H2O2via reduction sensing.

Voltammetric Ion Sensing with Ionophore-Based Ion-Selective Electrodes Containing Internal Aqueous Solution, Improving Lifetime of Sensors.

The possibility of voltammetric ion sensing is demonstrated, for the first time, for ion-selective electrodes (ISEs) containing an internal aqueous solution. ISEs selective to calcium, lithium and potassium ions are used as model systems. The internal solution of the ISEs contains a chloride salt of the respective cation and a ferrocenemethanol or ferrocyanide/ferricyanide redox couple. A platinum wire is used as the internal reference electrode. It is shown, theoretically and experimentally, that the dependence of oxidation and reduction peak potentials on the sample composition obeys the Nernst law, while the peak currents virtually do not depend on the sample composition. Thus, the electrode behavior is similar to that reported by Bakker's group for solid contact ISEs with ultra-thin membranes (200-300 nm). It is shown that the use of classical ISEs with relatively thick membranes (100-300 µm) and internal aqueous solution allows for the sensor lifetime of about one month. It is also shown that use of a suitable background electrolyte allows for improvement of the detection limits in voltammetric measurements with ISEs.

Demand response modeling in a day-ahead wholesale electricity market in Japan, considering the impact of customer risk aversion and dynamic price elasticity of demand

This study aims to develop a mathematical modeling approach to maximize the welfare of the price-responsive customers (CUs) in a wholesale electricity market in Tokyo, Japan. The contributions made by this paper in the quest to determine the role of CUs in a demand response market are twofold. First, the aversion of the CUs to the risk of choosing the Demand Response Programs (DPRs) is taken into account by considering their expected utility from consuming electricity. The proposed model is founded on the customer theory in microeconomics, using the concept of the expected utility function to model the behavior of the risk-averse CUs in response to different DPRs. Second, it introduces an hourly-based model for the short-term price elasticity of demand, considering the day-ahead price mechanism defined in the Japan Electric Power Exchange (JEPX) market. The estimated price elasticities are used in a price elasticity matrix of demand (PEMD) to precisely reflect the different response strategies, including flexible, in-flexible forward-shifting, backward shifting, and optimizing responses. An accurate day-ahead hourly load forecasting is performed, using the Seasonal Autoregressive Integrated Moving Average (SARIMA) model, which is trained on four years of data provided by the Tokyo Electric Power Company (TEPCO), with a mean absolute percentage error (MAPE) of 0.94%. The developed model is used to analyze the CUs’ behaviors with different response strategies in the JEPX market in Tokyo. By applying the Time-of-Use (TOU) and Real-Time-Pricing (RTP) programs, the results reveal a peak reduction potential of 10.7% and 7.3%, respectively, for the flexible CUs. Applying the RTP program to the curtailable loads can achieve a 7.7% reduction in daily peak demand and a 1.6% reduction in daily electricity consumption.

Redox Data of Tris(polypyridine)manganese(II) Complexes

Very little cyclic voltammetry data for tris(polypyridine)manganese(II) complexes, [MnII(N^N)3]2+, where N^N is bipyridine (bpy), phenanthroline (phen) or substituted bpy or phen ligands, respectively; are available in the literature. Cyclic voltammograms were found for tris(4,7-diphenyl-1,10-phenanthroline)manganese(II) perchlorate only. In addition to our recently published related research article, the data presented here provides cyclic voltammograms and corresponding voltage-current data obtained during electrochemical oxidation and the reduction of four [MnII(N^N)3]2+ complexes, using different scan rates and analyte concentrations. The results show increased concentration and scan rates resulting in higher Mn(II/III) peak oxidation potentials and increased peak current-voltage separations of the irreversible Mn(II/III) redox event. The average peak oxidation and peak reduction potentials of the Mn(II/III) redox events stayed constant within 0.01 V. Similarly, the average of the peak oxidation and reduction potentials of the ligand-based reduction events of [MnII(N^N)3]2+ were constant within 0.01 V.

MOF-818 nanozyme-based colorimetric and electrochemical dual-mode smartphone sensing platform for in situ detection of H2O2 and H2S released from living cells

Hydrogen peroxide (H2O2) and hydrogen sulfide (H2S) play a key role in many cellular signaling pathways. The efficient and accurate in situ detection of H2O2 and H2S released from living cells has attracted extensive research interests. Herein, we presented a portable colorimetric and electrochemical dual-mode sensor for detection of cellular secreted H2O2 and H2S based on MOF-818 nanozyme. MOF-818 containing trinuclear copper centers not only possesses excellent peroxidase-like activity under 37 °C and acidic conditions, but also exhibits outstanding electrocatalytic reduction activity to H2O2 (reduction peak potential at −0.08 V vs Ag/AgCl). Meanwhile, the copper sites of MOF-818 can be coordinated with sulfide, reducing the catalytic activity of MOF-818. As a result, the colorimetric and electrochemical sensing of H2O2 and H2S were established based on “signal-on” and “signal-off” strategies, respectively. Additionally, the combination of a smartphone and a miniature electrochemical analyzer enables dual-mode colorimetric and electrochemical sensing platform for in situ detection of H2O2 and H2S released from live cells. This portable dual-mode sensor based on MOF nanozyme not only opens a new path for point-of-care testing, but also has potential applications in the field of cell biology and clinical diagnosis.

Molecular Structures and Redox Properties of Homoleptic Aluminum(III) Complexes with Azobisphenolate (azp) Ligands

To elucidate the oxidation behavior of the 2,2′-azobisphenolate (azp) ligand, a series of homoleptic 1:2 AlIII complexes of four azp derivatives (L1) with 5,5′-dichloro-, 5,5′-dimethyl-, 5,5′-di-t-butyl-, 3,3′,5,5′-tetramethyl-substituents and of one imino derivative (L2) were synthesized and obtained as TPP[Al(L)2]·solvent (TPP = tetraphenylphosphonium ion). The X-ray crystal structure analyses showed that the two ONO-tridentate ligands were meridionally coordinated to a central AlIII ion in an almost perpendicular manner to give a homoleptic octahedral coordination structure in all the AlIII complexes. The proton nuclear magnetic resonance spectra suggested that all the AlIII complexes retained the homoleptic coordination structure in solution. From the cyclic voltammetry measurements in dichloromethane solutions, all the AlIII complexes with the azp ligands showed two partially reversible oxidation waves, and an additional reversible or partially reversible reduction wave. The substitution effects on the first oxidation and reduction peak potentials were revealed in the AlIII complexes with the azp ligands. On the other hand, the imino complex showed a partially reversible oxidation wave accompanying a film deposition. The density functional theory (DFT) calculations indicated that the molecular orbital (MO) coefficients of the frontier MOs in the AlIII complexes were present on the ligands and were absent on the AlIII ion. These results confirmed that the azp ligands are susceptible to oxidation and can give a relatively stable oxidation species depending upon substituent effects.

Unbiased Photoelectrode Interfaces for Solar Coupling of Lignin Oxidation with Biocatalytic C═C Bond Hydrogenation.

The pulp and paper manufacturers generate approximately 50 million metric tons of lignin per annum, most of which has been abandoned or incinerated because of lignin's recalcitrant nature. Here, we report bias-free photoelectrochemical (PEC) oxidation of lignin coupled with asymmetric hydrogenation of C═C bonds. The PEC platform consists of a hematite (α-Fe2O3) photoanode and a silicon photovoltaic-wired mesoporous indium tin oxide (Si/mesoITO) photocathode. We substantiate a new function of photoelectroactivated α-Fe2O3 to extract electrons from lignin. The extracted electrons are transferred to the Si/mesoITO photocathode for regenerating synthetic nicotinamide cofactor analogues (mNADHs). We demonstrate that the reduction kinetics of mNAD+s depend on their reduction peak potentials. The regenerated mNADHs activate ene-reductases from the old yellow enzyme (OYE) family, which catalyze enantioselective reduction of α,β-unsaturated hydrocarbons. This lignin-fueled biocatalytic PEC system exhibits an excellent OYE's turnover frequency and total turnover number for photobiocatalytic trans-hydrogenation through cofactor regeneration. This work presents the first example of PEC regeneration of mNADHs and opens up a sustainable route for bias-free chemical synthesis using renewable lignin waste as an electron feedstock.

Study of electrochemical behavior of two chemically similar acridines: Tacrine and 9-aminoacridine on hanging mercury drop electrode

ABSTRACT. The electrochemical behavior of two chemically related acridine compounds: tacrine (TAC) and 9-aminoacridine (9-AA) was investigated on a hanging mercury drop electrode (HDME). The electrochemical study was carried out by using Osteryoung square wave voltammetry (OSWV) and cyclic voltammetry (CV) techniques in the Britton-Robinson (B-R) buffer solution at pH = 2.0–12.0, KCl (0.1/0.2/0.3 M) and methanol (0.0-50%) mixture as supporting electrolyte. TAC showed maximum current at pH 7.5 while 9-AA at pH 10, KCl (0.3M), and 10% methanol. The study of electrochemical reduction of 9-AA and TAC on the HDME by using CV resulted in a quasi-reversibility, mainly diffusion-controlled reaction. The reaction involved 1e–/1H+ reduction at nitrogen atom in the case of the 9-AA while the second process involved the 2e–/2H+ reduction of the intra-cyclic azomethine group. The reduction peak potential of structurally related acridine compounds is influenced by the pH values and percentage of the organic solvent of the supporting electrolytes. Also, the study may provide insight into the electron transfer pathways of biological reactions of the acridines and their electrochemical behavior on the electrode.&#x0D; &#x0D; KEY WORDS: Tacrine, 9-Aminoacridine, Cyclic voltammetry, Osteryoung square wave voltammetry, Hanging mercury dropping electrode&#x0D; &#x0D; Bull. Chem. Soc. Ethiop. 2021, 35(3), 639-646.&#x0D; DOI: https://dx.doi.org/10.4314/bcse.v35i3.14

Cation effect on the electrochemical reduction of polyoxometalates in room temperature ionic liquids

Polyoxometalates (POMs) are compounds that undergo multiple successive one-electron redox transitions, making them convenient model reactants to study ion solvation effects. Room temperature ionic liquids (RTILs) are solvents made entirely of ions, and are expected to have interactions with the highly negatively charged POM reduction products. In this work, 12 RTILs with a range of different anions ([FSI]−=bis(fluorosulfonyl)imide, [TFSI]−=bis(trifluoromethylsulfonyl)imide, [BETI]−=bis(pentafluoroethylsulfonyl)imide, [BF4]−, [PF6]−) and cations (imidazolium, pyrrolidinium, sulfonium, ammonium, phosphonium) were employed as solvents to study the kinetics and thermodynamics of [S2W18O62]4− reduction, to shed light on solvation effects and ion-pairing effects caused by different RTIL structures. Up to six reversible reduction processes (producing highly negatively charged [S2W18O62]10−) were observed. For the RTILs that showed multiple processes, a clear trend in both the thermodynamics (inferred from the reduction peak potentials) and kinetics (inferred from the peak-to-peak separation) was observed, in the order: imidazolium &lt; sulfonium ≈ ammonium &lt; pyrrolidinium &lt; phosphonium, supporting strong interactions of the negatively charged POM reduction products with the cation. Two related POMs, [P2W18O62]6− and [PW12O40]3−, were also studied in the optimum RTIL found for [S2W18O62]4− ([C2mim][FSI]=1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide), revealing fast kinetics and asymmetric peaks for [PW12O40]3−. This work demonstrates the importance of understanding the solvation effects of RTIL ions for highly charged electrogenerated products, allowing tuning of the RTIL structure to achieve the optimum kinetics and thermodynamics for an electrochemical process.