Oxidation Potential Research Articles

Electrochemical DNA hybridization signal amplification system using methylene blue and ascorbic acid

This study presents a method for real-time monitoring of heterogeneous DNA hybridization using chronoamperometry (CA). The electrochemical assay is based on methylene blue (MB)-labeled ssDNA target (tMB) hybridization with a complementary ssDNA capture probe (p) chemisorbed to a gold electrode through the Au-S linkage. Real-time monitoring of nucleic acid binding is enabled by introducing ascorbic acid (AA) during CA measurements at oxidative potential. After hybridization, the newly formed MB-labeled double stranded DNA (ptMB) oxidized AA and, as a result, shuttled the electrons directly to the electrode. AA-ptMB electrocatalytic cycle allows amplifying the signal from hybridized MB-labeled DNA through oxidation of AA. The process consists three particular processes: hybridization of tMB to the surface probe, reaction between AA and ptMB, and (c) the electron transfer from ptMB to the electrode. We have demonstrated that system is limited by the AA-ptMB redox reaction (bimolecular constant, k = 8 ± 0.1 M–1 s–1). AA-ptMB cycle is sequence-specific, thus fully developed current saturation curves can be used to calculate hybridization parameters and evaluate binding kinetics under various conditions. In addition, evaluating the initial hybridization rate allows quantifying the concentration of labeled ssDNA (tMB) in several minutes. This study provides the first report of a simple electrocatalytic cycle between MB-labeled DNA and a reducer AA for monitoring DNA hybridization in real time.

Elucidating the potential of bimetallic mixed metal oxide (FeO/NiO) in fusion with pristine and N- and S-doped graphene oxide for biomedical applications

Antimicrobial resistance is attributed to acquiring new mechanisms by microbes to combat antimicrobial agents, highlighting the necessity to discover new antimicrobial agents to protect human health. Graphene and its derivatives have shown antimicrobial potential due to their physical and chemical distinctive features. Potent antibacterial properties were observed by decorating the surface of graphene and its derivatives with inorganic nanoparticles, such as metal and metal oxide. In an attempt to reliably overcome antimicrobial resistance, the multifunctional nanocomposites, including FeO/NiO, FeO/NiO/GO, FeO/NiO/N-GO, and FeO/NiO/S-GO, were synthesized using a wet chemical method. Accordingly, the structural analysis was performed using X-ray diffraction (XRD), infrared spectroscopy (IR), energy dispersive X-ray (EDX), ultraviolet-visible spectroscopy (UV–vis), and scanning electron microscopy (SEM). For antibacterial potential, the synthesized nanocomposites were tested against non-resistant and resistant strains of bacteria. Notably, moderate antibacterial potential was found for FeO/NiO/N-GO nanocomposite with a MIC value of 12.5 μg/mL, compared to the MIC of pure Ciprofloxacin, a positive control, with a value of 1.25 μg/mL. Toward antifungal potential, the synthesized nanocomposites were assessed against various spores of fungal strains. In this regard, the synthesized nanocomposites were demonstrated as potent antifungal agents. Among the synthesized nanocomposites, FeO/NiO and FeO/NiO/S-GO exhibited the highest ZOI against Aspergillus flavus. Additionally, the activity of these nanocomposites was evaluated by means of total reducing power (TRP), total antioxidant capacity (TAC), and free radical scavenging. Further, the antioxidant, brine shrimp lethality, and hemolytic potential of the synthesized nanocomposites were evaluated to compare their effectiveness. According to brine shrimp lethality, all synthesized nanocomposites were sufficiently active, with a calculated median lethal concentration (LC50) showing ≥ 50 % mortality. The obtained results provide a promising base for the incorporation of nanocomposites in pharmaceutical and biomedical products.

Unlocking the potential of mixed-valence silver oxide for electrochemical valorization of 5-hydroxymethylfurfural into valuable products

The burgeoning interest in the electrocatalytic conversion of biomass-derived compounds, exemplified by 5-hydroxymethylfurfural (HMF), into economically valuable products underscores the significance of such studies. Within this context, the electrocatalytic oxidation of HMF into 2,5-diformylfuran (DFF) using the mixed-valence silver (I, III) oxide (AgO) as the catalyst is presented for the first time. A thorough investigation has been carried out to explore the complex factors influencing the electrochemical transformation of the HMF to DFF, involving applied potentials, reactant concentrations, and the significant implications of mass transfer phenomena. Under optimized conditions, DFF, one of the highest value-added intermediates, can be produced with selectivity as high as 54%. Additionally, a yield of 10.8 μmol cm−2 h−1 was obtained under mild basic condition. Another pivotal aspect of this work involves meticulously examining the reaction process, bolstered by a comprehensive analytical approach that integrates high-performance liquid chromatography (HPLC), and operando Raman spectroscopy. The amalgamation of operando Raman spectroscopy with advanced simulation techniques represents a novel endeavor, offering a groundbreaking pathway to unravel the complexities inherent in these compounds and contribute substantially to the understanding of HMF oxidation and its intermediates. By looking closely at the catalyst surface during the reaction, a valuable insight into the steps involved was developed, helping in proposing an in-depth reaction pathway.

The effects of photochemical aging and interactions with secondary organic aerosols on cellular toxicity of combustion particles

Fine particulate matter (PM2.5) is associated with numerous adverse health effects, including pulmonary and cardiovascular diseases and premature death. Significant contributors to ambient PM2.5 include combustion particles and secondary organic aerosols (SOA). Combustion particles enter the atmosphere and undergo an aging process that changes their shape and composition, but there is limited study on the health effects of combustion particle aging and interactions with SOA. This study aimed to understand how biological responses to combustion particles would be affected by atmospheric aging and interaction with anthropogenic SOA. Fresh combustion particles underwent photochemical aging in a potential aerosol mass (PAM) oxidation flow reactor and interacted with SOA produced by the oxidation of toluene vapor in the PAM reactor. Photochemical aging and SOA interactions lead to significant changes in the PAH content and oxidative potential of the particle. Photochemical aging and SOA interactions also affected the biological responses, such as the inflammatory response and CYP1A1 induction of the particles in monoculture and coculture cells. These findings highlight the significance of photochemical aging and SOA interactions on the composition and cellular responses of combustion particles.

Between and within-city variations of PM2.5 oxidative potential in five cities in Colombia

AbstractFine particulate matter (PM2.5) has been shown to cause oxidative stress, which has negative health consequences. The oxidative potential (OP) of PM2.5, a promising health exposure metric, was assessed in five Colombian cities using the synthetic respiratory tract lining fluid assay that tracks the depletions of glutathione and ascorbate. For this, a set of 91 integrated 2-week ambient PM2.5 samples were collected using Ultrasonic Personal Aerosol Samplers (UPAS) at background (5), traffic (37), industrial (12) and residential (37) sites. Across all site types, mean PM2.5 mass concentration was 20.20 ± 9.36 µg m− 3. The oxidative potential (OPAA for ascorbate and OPGSH for glutathione) varied widely across cities with an average of 2.67 ± 1.27 for AA and 2.93 ± 1.22 % depletion m− 3 for GSH. OP metrics among cities were not correlated with PM2.5 mass concentrations. Overall, industrial sites showed higher PM2.5 mass concentrations and OPAA. In contrast, OPGSH was not found to differ among industrial, traffic, or residential sites, but was lower for background sites. Our findings provide substantial evidence of variations in PM2.5 OP between cities and within the cities. Further research is needed to assess the association between OP and adverse health effects, as well as to attribute the sources that cause such variations.

Ene‐Reductase‐Catalysed Oxidation Reactions

Ene‐reductases from the Old Yellow Enzyme (OYE) family have been traditionally employed in the reduction of conjugated C=C double bonds. This study explores the underutilised oxidative potential of OYEs, demonstrating their capability to catalyse the enantioselective desaturation of carbonyl compounds. Utilising a deprotonated tyrosine residue as a catalytic base, we developed a method to enable OYE‐catalysed desaturation at ambient temperature and alkaline pH, without the need for high‐temperature conditions. Through screening of various OYE enzymes, we identified several candidates from different genera with enhanced desaturase activity across different substrates. This work broadens the scope of biocatalytic applications for OYEs, introducing a novel approach to the synthesis of chiral α,β‐unsaturated carbonyl compounds.

Novel donor-acceptor-donor type electrochromic polymers based on 1,3-indandione modified triphenylamine derivatives as new acceptor units

Two donor (D)-acceptor (A)-donor (D) type of conjugated monomers, ITPA and ICTPA, consisted of 1H-indene-1,3(2H)-dione (IN)- or 2-(3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile (INCN)-substituted triphenylamine as the acceptor unit, were synthesized by Stille coupling reaction and Knovenagel condensation reaction, and their corresponding polymers (PITPA and PICTPA) were prepared by electrochemical polymerization. Both ITPA and ICTPA hade low initial oxidation potential of 0.70 V and 0.76 V, respectively, which was conducive to achieve high-quality polymer films. In comparison with FTPA which was not substituted by IN unit, ITPA and ICTPA exhibited the distinct red-shifted and dual absorption bands due to the stronger electron-withdrawing ability of IN and INIC units. Moreover, the electrochromic results demonstrated that PITPA possessed much higher optical contrast of 41 %, higher coloration efficiency (CE) of 445.5 cm2 C−1 at 1100 nm with extremely fast response time as low as 0.3 s, and a promising optical memory behavior compared with its counterpart without IN unit. These results suggested that the introduction of IN unit into triphenylamine could improve the electrochromic performance of the conjugated polymers and also provide a new strategy to develop novel and high-performance electrocheomic polymers.

The AUREX cell: a versatile operando electrochemical cell for studying catalytic materials using X-ray diffraction, total scattering and X-ray absorption spectroscopy under working conditions.

Understanding the structure-property relationship in electrocatalysts under working conditions is crucial for the rational design of novel and improved catalytic materials. This paper presents the Aarhus University reactor for electrochemical studies using X-rays (AUREX) operando electrocatalytic flow cell, designed as an easy-to-use versatile setup with a minimal background contribution and a uniform flow field to limit concentration polarization and handle gas formation. The cell has been employed to measure operando total scattering, diffraction and absorption spectroscopy as well as simultaneous combinations thereof on a commercial silver electrocatalyst for proof of concept. This combination of operando techniques allows for monitoring of the short-, medium- and long-range structure under working conditions, including an applied potential, liquid electrolyte and local reaction environment. The structural transformations of the Ag electrocatalyst are monitored with non-negative matrix factorization, linear combination analysis, the Pearson correlation coefficient matrix, and refinements in both real and reciprocal space. Upon application of an oxidative potential in an Ar-saturated aqueous 0.1 M KHCO3/K2CO3 electrolyte, the face-centered cubic (f.c.c.) Ag gradually transforms first to a trigonal Ag2CO3 phase, followed by the formation of a monoclinic Ag2CO3 phase. A reducing potential immediately reverts the structure to the Ag (f.c.c.) phase. Following the electrochemical-reaction-induced phase transitions is of fundamental interest and necessary for understanding and improving the stability of electrocatalysts, and the operando cell proves a versatile setup for probing this. In addition, it is demonstrated that, when studying electrochemical reactions, a high energy or short exposure time is needed to circumvent beam-induced effects.

Synthesis and application of biomass-based graphene oxide using microwave-assisted pyrolysis method

Graphene and related materials have excellent potential to revolutionise many emerging fields, but the large quantity synthesis using environmentally sustainable methods is still challenging. This work studies the synthesis of graphene oxide from food waste biochar with negatively charged properties, which is initially produced using microwave pyrolysis. The synthesised graphene oxide achieved 64.53 % carbon content, 345.79 m2/g surface area, 0.074 cm3/g micropore volume, large reactive surface area, and ribbon/banded organisation. The performance of carbon-based material is evaluated in the fabrication of a modified screen-printed carbon electrode (SPCE) for selective dopamine (DA) detection in the coexistence of ascorbic acid (AA) and uric acid (UA). The electrostatic interactions between the negatively charged biochar-based graphene oxide (BBGO) on the surface SPCE and opposite-charged dopamine assisted the oxidation potential with interfering species by electrostatic repulsion of AA and UA. This manuscript substantiates the resource recovery from organic materials and sustainable graphene oxide synthesis, underscoring their application in detecting positively charged species.

Promoting effect of interfacial hole accumulation on photoelectrochemical water oxidation in BiVO4 and Mo-doped BiVO4

Hole transfer at the semiconductor-electrolyte interface is a key elementary process in (photo)electrochemical (PEC) water oxidation. However, up to now, a detailed understanding of the hole transfer and the influence of surface hole density on PEC water oxidation kinetics is lacking. In this work, we propose a model for the first time in which the surface accumulated hole density in BiVO4 and Mo-doped BiVO4 samples during water oxidation can be acquired via employing illumination-dependent Mott-Schottky measurements. Based on this model, some results are demonstrated as below: (1) Although the surface hole density increases when increasing light intensity and applied potential, the hole transfer rate remains linearly proportional to surface hole density on a log-log scale. (2) Both water oxidation on BiVO4 and Mo-doped BiVO4 follow first-order reaction kinetics at low surface hole densities, which is in good agreement with literature. (3) We find that water oxidation active sites in both BiVO4 and Mo-doped BiVO4 are very likely to be Bi5+, which are produced by photoexcited or/and electro-induced surface holes, rather than VOx species or Mo6+ due to their insufficient redox potential for water oxidation. (4) Introduction of Mo doping brings about higher OER activity of BiVO4, as it suppresses the recombination rate of surface holes and increases formation of Bi5+. This surface hole model offers a general approach for the quantification of surface hole density in the field of semiconductor photoelectrocatalysis.

Photo- and Electrocatalytic Hydrogen Evolution by Heteroleptic Dirhodium(II,II) Complexes: Role of the Bridging and Diimine Ligands.

A series of heteroleptic Rh2(II,II) complexes, cis-[Rh2(μ-DPhF)2(μ-bncn)2]2+ (1; bncn = benzo[c]cinnoline), cis-[Rh2(μ-DPhF)(μ-OAc)(μ-bncn)2]2+ (2), and cis-[Rh2(μ-OAc)2(μ-bncn)2]2+ (3), is presented, and the excited state and redox properties of each complex was characterized for the photo- and electrocatalytic production of H2. The oxidation potentials shift anodically from 1 to 3, consistent with a highest occupied molecular orbital (HOMO) with significant metal-ligand mixing, Rh2(δ*)/DPhF(π/nb). In contrast, modest differences in the first two bncn-localized reversible reduction potentials were observed in 1 - 3. The lowest energy metal/ligand-to-ligand charge transfer (1ML-LCT) transition, Rh2(δ*)/DPhF(π/nb) → bncn(π*), shifts from 633 nm in 1 to 553 nm in 2, and the metal-to-ligand charge transfer (1MLCT) Rh2(π*) → bncn(π*) absorption in 3 appears at 462 nm in CH3CN. Although the 3ML-LCT excited state of 2 is shorter lived than that of 1, 2.7 ns as compared to 19 ns, respectively, photocatalytic hydrogen generation is observed for the former upon 595 nm irradiation in the presence of 0.1 M TsOH (p-tolylsulfonic acid) and 0.1 M BNAH (1-benzyl-1,4-dihydronicotinamide). The temperature dependence of the 3ML-LCT lifetimes of 1 and 2 shows the presence of a thermally accessible deactivating state. In addition, the singly reduced intermediate, [2]-, is photoactive and able to generate hydrogen in the presence of TsOH. Importantly, the electrocatalytic currents generated by equimolar concentrations of 1 - 3 in CH3CN are nearly identical, consistent with a mechanism of catalysis that is localized on the bncn ligand and does not require a Rh-H hydride intermediate. This finding can be used to develop earth-abundant first-row transition metal complexes for photo- and electrocatalytic H2 production.

Yellow-transmissive blue electrochromic polymers based on triphenylamine and ProDOT derivatives

Electrochromic polymer with yellow hue is few relative to those with other two primary colors due to its optical absorption at short wavelength of ≈ 450 nm. Triphenylamine (TPA) and its derivatives (TPAs) as chromogenic groups are frequently used to construct neutral yellow electrochromic polymers, however, those polymers based on TPAs usually exhibit low transmittance at oxidation state due to the residual absorption at short wavelength. Here, three neutral yellow electrochromic polymers (PBBE-1, PBBE-2 and PBBE-3) with different content ratios of ProDOT-10, TPA-4 and benzene were synthesized by Suzuki coupling reaction. With ProDOT-10 content in polymeric chain increasing, the oxidation potentials of polymers decrease gradually. Due to the twisted molecular structure, the absorption peaks of polymers almost remain unchanged when ProDOT-10 content in polymer reaches critical value, which provide an effective method for preparing neutral yellow electrochromic polymers. During oxidation process, PBBE-1 turns to black; PBBE-2 turns to dark blue; PBBE-3 turns to light grey, further to light blue. Through optimizing TBA-4/ProDOT-10 ratio, the electrochromic properties of polymers have been improved, such as optical contrast, response time and coloration efficiency. Especially, PBBE-3 possesses 40 % optical contrast at 435 nm, which is higher than reported TPAs based polymers at short wavelengths.

Strain tunable electronic, optical, and photovoltaic properties of monolayer β2-SrX2Y4 (X = Al, Ga, In, Y = S, Se)

In recent years, the experimentally synthesized two-dimensional material MoSi2N4, known for its excellent mechanical strength and environmental stability, has attracted significant attention as a representative of the MA2Z4 family. However, people's understanding of some MA2Z4 materials is still limited. In this study, we systematically investigated the properties of monolayer β2-SrX2Y4 (X=Al, Ga, In; Y=S, Se) with a seven-layer atomic configuration using first-principles calculations, focusing on their response to external strain engineering. Our results demonstrate that monolayer β2-SrX2Y4 exhibits characteristics of a direct bandgap semiconductor, and the majority of these materials retain these characteristics under applied strain. However, an unexpected transition from a direct bandgap to an indirect bandgap was observed in monolayer β2-SrAl2S4 under strain. Moreover, as strain changes from compressive to tensile, the imaginary part peak of the dielectric function for most β2-SrX2Y4 materials shifted towards lower energies (redshifted). Notably, in their pristine structures, only β2-SrAl2S4 and β2-SrAl2Se4 can facilitate water splitting by crossing the oxidation and reduction potentials of water. By applying strain, we successfully enabled β2-SrGa2S4 and β2-SrIn2S4 to possess the capability to drive water oxidation–reduction reactions. Furthermore, we calculated the second-order elastic constants and analyzed the Grüneisen parameter and thermal expansion coefficient based on the fitted energy density and strain relationships. This study highlights the potential applications of β2-SrX2Y4 in photocatalysis and optoelectronic devices and provides valuable insights for implementing biaxial strain in two-dimensional materials.

Application of composite persulfate oxidation to remediate weathered lubricating oil-contaminated soils: Batch and pilot-scale studies

In this study, two novel composite persulfate (PS) oxidants [base pulverized NaOH composite persulfate (BPS) and metal (iron and manganese) composite persulfate (MPS)] were developed. The feasibility, mechanisms, and optimal conditions for remediating weathered lubricating oil (WLO)-contaminated soils using composite PS oxidants were evaluated. BPS was prepared by blending PS and NaOH powders (molar ratio = 1:0.3), while MPS was prepared by mixing PS, FeCl2, and KMnO4 at a molar ratio of 1:0.3:0.05 for PS:Fe:Mn. The oxidation of rhodamine B (RhB) dye using BPS and MPS followed second-order kinetics. MPS process was more effective in organic oxidation, likely due to its electron transfer mechanism. The generation of •SO4- in the BPS process required activation by •OH, potentially leading to more efficient and stable •SO4- generation and subsequent organic chemical oxidation. Radical analyses revealed that •SO4- was present in the pH range of 3–12, with the strongest •OH signal at pH 7–9. Employing hybrid BPS and MPS for WLO-contaminated soil remediation could achieve optimal TPH removal efficiency due to the combined generation of •OH (high reactivity) and •SO4- (stable characteristics). The addition of BPS helped neutralize acidified soils and maintained a higher soil pH (around 6.1). The multi-stage oxidation using the hybrid composite PS oxidants (MPS + BPS) at a 1:1 ratio (w/w) achieved 84 % TPH removal (initial TPH = 7721 mg/kg) after three oxidation stages (5 % w/w oxidant dosage). The composite oxidation process offers a more reactive oxidation potential with an extended oxidant life without causing a substantial pH drop.

Oxidation of sulfur, hydrogen, and iron by metabolically versatile Hydrogenovibrio from deep sea hydrothermal vents.

Chemolithoautotrophic Hydrogenovibrio are ubiquitous and abundant at hydrothermal vents. They can oxidize sulfur, hydrogen or iron, but none are known to use all three energy sources. This ability though would be advantageous in vents hallmarked by highly dynamic environmental conditions. We isolated three Hydrogenovibrio strains from vents along the Indian Ridge, which grow on all three electron donors. We present transcriptomic data from strains grown on iron, hydrogen or thiosulfate with respective oxidation and autotrophic CO2 fixation rates, RubisCO activity, SEM, and EDX. Maximum estimates of one strain's oxidation potential were 10, 24, and 952mmol for iron, hydrogen and thiosulfate oxidation and 0.3, 1, and 84mmol CO2 fixation, respectively, per vent per hour indicating their relevance for element cycling in-situ. Several genes were up- or downregulated depending on the inorganic electron donor provided. Although no known genes of iron-oxidation were detected, upregulated transcripts suggested iron-acquisition and so far unknown iron-oxidation-pathways.

Facile and innovation synthesis of Zn-Mn-Co-LDH/polypyrrole and its application in investigating ethanol oxidation in an alkaline medium

Overvoltage and low current are observed for ethanol electrooxidation on the surface of many unmodified electrodes. Therefore, it is desirable to use a suitable catalyst for ethanol electrooxidation to increase the current. This research introduces a new sensor to catalyze ethanol oxidation in an alkaline environment. This new Zn-Mn-Co LDH/PolyPyrrole/GCE nanocomposite sensor exhibits high catalytic activity for ethanol electrooxidation. It changes the oxidation potential of ethanol to a less positive potential. To identify this proposed sensor, X-ray diffraction (XRD), Brauner Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy, field emission scanning electron microscopy (FESEM), thermal analysis (TGA), high-resolution transmission electron microscopy (HR-TEM) and cyclic voltammetry techniques were used. Ethanol electrooxidation was investigated by cyclic voltammetry technique. The effects of scan rate and ethanol concentration on the ethanol oxidation peak have been investigated. The proposed sensor showed long-term stability. This prepared nanocomposite can be used as an anode catalyst for ethanol fuel cells.

Exploring the defect formation and ionic migration in A2Zr2O7 (A = La, Ce, Nd, and Gd) Pyrochlore solid-state electrolytes

This study investigated the potential of A2Zr2O7 pyrochlore phase oxides (A = La, Ce, Nd, and Gd) as solid oxide fuel cell (SOFC) electrolyte materials. A2Zr2O7 ceramics were synthesized using the sol-gel process, and their disordered pyrochlore structure was confirmed by X-ray Diffraction and Rietveld refinement. Field Emission Scanning Electron Microscopy (FE-SEM) was used to examine the morphology of the materials, while X-Ray Photoelectron Spectroscopy (XPS) confirmed a high oxygen ion concentration. UV–Vis Diffuse Reflectance Spectroscopy (DRS) and density of states calculations consistently showed similar bandgap patterns in all zirconate pyrochlore. Density Functional Theory (DFT) simulations provided insights into the electronic structure and migration pathways. A two-probe conductivity study confirmed the relation between the ionic conductivity and ordering degree of pyrochlore. At 750 °C, LZO, CZO, and GZO exhibited ionic conductivity values of 5.44 × 10−3 S/cm, 3.00 × 10−3 S/cm, and 2.01 × 10−3 S/cm respectively, while NZO demonstrated a conductivity of 1.27 × 10−2 S/cm at 700 °C, which is higher than that of the other samples. This study favours the use of the sol-gel route for processing zirconate pyrochlore materials, highlighting its ability to achieve high densities at lower temperatures and exhibit enhanced ionic conductivity. A2Zr2O7 has emerged as a promising oxide-ion conducting solid electrolyte for intermediate temperature SOFC applications within the 600–750 °C temperature range.

Cu-EDTA decomplexation by UV/peracetic acid oxidation and coupled Cu recovery by alkaline precipitation: Efficiency and mechanism

The high degree of complexation between metal ions and organic ligands presents a significant challenge to their removal via conventional chemical precipitation methods. Currently, oxidative decomplexation followed by alkali precipitation of Cu2+ represents an efficacious strategy for addressing Cu-ethylenediaminetetraacetic acid (Cu-EDTA). The efficacy of activated peracetic acid (PAA) processes in degrading contaminants has demonstrated excellent performance due to their higher oxidation potential. In this study, the UV/PAA process was initially employed for Cu-EDTA decomplexation, resulting in complete removal within 30 min. The 92.41 % released Cu2+ was successfully recovered by alkaline precipitation within 90 min. The mechanism of decomplexation is comprised of two principal stages. Firstly, the UV/PAA process gradually generates reactive oxygen species (ROS), including R-C•, •OH, and 1O2. These ROS facilitate the decomplexation of Cu-EDTA, resulting in the release of Cu2+. Additionally, Cu2+ can participate in the activated PAA, further promoting the production of ROS, which in turn enhances the removal of organic ligands. Furthermore, the transformation process of Cu-EDTA was subjected to analysis, along with the decomplexation products. Meanwhile, except for HCO3−, H2PO4−, and humic acid, which exerted a relatively minor impact on Cu2+ recovery, Cl− and NO3− demonstrated a negligible influence. Moreover, the reaction exhibits enhanced efficacy under acidic conditions and demonstrates robust performance in electroplating wastewater samples. In summary, this study provided a promising method for the decomplexation of Cu-EDTA efficiently and Cu recovery.

Molecular Properties of Branched Aliphatic α-Amino Acids in Water.

Four branched-chain aliphatic α-amino acids─α-alanine, valine, leucine, and isoleucine (1-4)─were investigated by quantum-chemical calculations in water as a solvent by two methods. The B3LYP variant of DFT calculations was used to obtain the electronic structure and molecular descriptors of these species in their canonical amino acid form as well as the related zwitterionic form in three oxidation states (cation, neutral molecule, and anion). A total of 24 species were subjected to full geometry optimization and complete vibration analysis. Quantities related to ionization or affinity processes were evaluated under adiabatic conditions. The calculated standard reaction Gibbs energy facilitates evaluation of the absolute oxidation and reduction potential. The absolute reduction potential correlates with the electrophilicity index, and the absolute oxidation potential correlates with the adiabatic ionization energy. This finding makes it possible to skip the tedious vibrational analysis and use electronic properties to estimate the redox potentials. The molecular descriptors were compared with the calculated properties of four linear amino acids (glycine, β-alanine, GABA, and DAVA). Parallel calculations using the DLPNO-CCSD(T) method gave analogous results for 24 species. The absolute oxidation potential was related to the antioxidant activity index, which showed only a moderate antioxidant activity of 1-4.

Coupled sulfur and nitrogen cycling at a catchment scale: insights from isotopic and molecular techniques

The biogeochemical cycles of nitrogen (N) and sulfur (S) play important roles in sustaining the Earth's ecosystem. However, their potential coupling process and underlying mechanisms in the nature remain unclear. Through joint applications of river water's isotopic compositions, isotope-pairing experiments, and molecular techniques, this study revealed the coupled N-S cycling processes at a catchment scale from both geochemical and biological perspectives. The river water's natural abundance isotopic compositions indicated that sulfide oxidation was an important source (67.0 ± 5.5 % in summer and 72.0 ± 5.5 % in winter) of riverine sulfate (SO42−). In addition, sulfide oxidation and NOx reduction (especially denitrification) were tightly coupled in summer but less significantly so in winter. However, the coupling of sulfide oxidation and dissimilatory nitrate reduction to ammonium (DNRA) could not be overlooked in winter. The 15N pairing experiments quantitatively showed that the high sulfide oxidation rates in summer (4.7 ± 2.3 mol/km2/h) were significantly associated with the denitrification. Metagenomics and qPCR analyses of the soils supported the isotopic interpretations, substantiating the metabolic potential and coexistence of bacterial denitrification, DNRA, and sulfide oxidation, which was more prevalent in summer. This study reveals comprehensive evidence that sulfide oxidation and NOx reduction are tightly coupled at the catchment scale, which provides a new perspective towards a better understanding of N-S cycling.