Alkaline Aqueous Solution Research Articles

Ultrapotassic plutons as a source of uranium of vein-type U-deposits (Moldanubian Zone, Bohemian Massif): insights from SIMS uraninite U–Pb dating and trace element geochemistry

AbstractThe Bohemian Massif hosts significant hydrothermal U-deposits associated with shear zones in the high-grade metamorphic basement. But there is a lack of evidence of a genetic link between mineralization and U-fertile igneous rocks. This contribution provides constraints on the major U source of the vein-type U-deposits, the timing of ore formation and the metallogenetic model. The anomalous trace element signatures of the low-temperature hydrothermal deposits (high Zr, Y, Nb, Ti, ∑REE) and their close spatial relation with ultrapotassic rocks of the durbachite series point to a HFSE and REE enriched source rock. The durbachites have high U content (13.4–21.5 ppm) mainly stored in magmatic uraninite and other refractory minerals (e.g., thorite, zircon, allanite) that became metamict over a time interval sufficient to release U from their crystal structure, as suggested by the time gap between emplacement of the durbachites (EMP uraninite U–Pb age ~ 338 Ma) and hydrothermal activity (SIMS uranium ore U–Pb age ~ 270 Ma). Airborne radiometric data show highly variable Th/U ratios (1.5–6.0), likely reflecting a combination between (1) crystallization of magmatic uraninite, (2) hydrothermal alteration, and (3) leaching and mobilization of U along NW–SE-trending fault zones, manifested by elevated Th/U values in the radiometric map. The presence of rare magmatic uraninite in durbachites suggests almost complete uraninite dissolution; EMP imaging coupled with LA-ICP-MS analyses of refractory accessory phases revealed extensive mobilization of U together with HFSE and REE, providing direct evidence for metal leaching via fluid-driven alteration of radiation-damaged U-rich minerals. The large-scale HFSE and REE mobilization, demonstrated by the unusual trace element signatures of the U-deposits, was likely caused by low-temperature (270–300 °C), highly alkaline aqueous solutions containing F-, P-, and K-dominated complexing ligands. The first SIMS U–Pb age of 270.8 ± 7.5 Ma obtained so far for U-mineralization from the Bohemian Massif revealed a main Permian U mineralizing event, related to crustal extension, exhumation of the crystalline basement, and basin formation, as recorded by U–Pb apatite dates (280–290 Ma) and AFT thermal history models of the durbachites. The Permo-Carboniferous sedimentary cover probably represented a source of oxidized basinal brines infiltrating the basement-hosted durbachite plutons and triggering massive metal leaching. The interaction between basin-derived brines and durbachites resulted in significant modification of the chemical composition of the hydrothermal system (K and F release during biotite chloritization, P liberation through monazite alteration), leading to the formation of ore-bearing fluids responsible for the metallogenesis of the basement-hosted unconformity-related U-deposits in shear zones in the Bohemian Massif.

Electrochemical detection of 4(5)-methylimidazole in aqueous solutions

4(5)-methylimidazole (4-MeI) is a potential carcinogen widely used in food colours. EU regulations specify a maximum allowable concentration of 200 ppm for 4-MeI in caramel colours. This study reports an electrochemical determination technique for 4-MeI in caramel colours for the first time. The effect of pH and interference from air were studied to optimize the detection conditions on a glassy carbon electrode in aqueous alkaline solutions using square wave voltammetry (SWV) technique. The concentration of 4-MeI was quantitatively measured down to 10 μM (~0.8 ppm). Traditional methods such as HPLC, GC, spectrometry and immunoassays involve either expensive instrumentation and reagents or time consuming preparation and detection processes. This study demonstrates the possibility of rapid and simple electrochemical determination of (4-MeI) in food colours with minimum workup using a portable potentiostat.

Photocatalytic Hydrogen Production with A Molecular Cobalt Complex in Alkaline Aqueous Solutions.

The thermodynamic favorability of an alkaline solution for the oxidation of water suggests the need for developing hydrogen evolution reaction (HER) catalysts that can function in basic aqueous solutions so that both of the half reactions in overall water splitting can occur in mutually compatible solutions. Although photocatalytic HERs have been reported mostly in acidic solutions and a few at basic pHs in mixed organic aqueous solutions, visible-light driven HER catalyzed by molecular metal complexes in purely alkaline aqueous solutions remains largely unexplored. Here, we report a new cobalt complex with a tetrapyridylamine ligand that catalyzes photolytic HER with turnover number up to 218 000 in purely aqueous solutions at pH 9.0. Density functional theory (DFT) calculations suggested a modified electron transfer (E)-proton transfer (C)-electron transfer (E)-proton transfer (C) (mod-ECEC) pathway for hydrogen production from the protonation of CoII-H species. The remarkable catalytic activity resulting from subtle structural changes of the ligand scaffold highlights the importance of studying structure-function relationships in molecular catalyst design. Our present work significantly advances the development of a molecular metal catalyst for visible-light driven HER in more challenging alkaline aqueous solutions that holds substantial promise in solar-driven water-splitting systems.

Dissolution dynamics of poly(4-hydroxystyrene) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions investigated by quartz crystal microbalance (QCM) method

Abstract The molecular size of alkaline cation has been reported to affect the dissolution of resist film in alkaline aqueous solution. However, the details are still unclear. In this study, the dissolution dynamics of poly(4-hydroxystyrene) (PHS) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions was investigated to clarify the effects of small alkaline cations on the dissolution dynamics of typical backbone polymer for chemically amplified resists by a quartz crystal microbalance (QCM) method. The temporal changes in the frequency and impedance of QCM substrates during development were measured. The maximum impedance reachable during development significantly exceeded that of the developer saturated with PHS unlike the case of tetramethylammonium and tetraethylammonium cations. This means that the PHS matrix near surface was swollen by decreasing the size of alkaline cation. By either increasing or decreasing the size of alkaline cation from tetramethylammonium and tetraethylammonium cations, the transient swelling layer became thick.

Effect of the phase composition of AK12M2 and AK12pch silumins on the corrosion and electrochemical behaviour in weakly alkaline aqueous solution. Part 2. Electrochemical and corrosion testing of silumins under various external conditions in weakly alkaline aqueous solution

Effect of the phase composition of AK12M2 and AK12pch silumins on the corrosion and electrochemical behaviour in weakly alkaline aqueous solution. Part 2. Electrochemical and corrosion testing of silumins under various external conditions in weakly alkaline aqueous solution

B-site disorder driven Griffiths-like phase and electrochemical behavior in Y2NiCrO6 double perovskite

In this investigation, nanoparticles of B-site disordered Y2NiCrO6 (YNCO) double perovskite were synthesized by the facile sol–gel method to evaluate their magnetic and electrochemical properties. Their crystallographic structure is monoclinic and the average size of the particles is 79±16 nm. XPS analysis indicated a mixed oxidation states of B-site transition metals Ni2+/Ni3+ and Cr2+/Cr3+. The mixed valence states of Ni and Cr, along with the mixed magnetic phases of YNCO, constitute a signature of the B-site disorder. This antisite disorder contributed to the observation of a Griffiths-like phase arising from ferromagnetic short-range interactions above the magnetic transition up to the Griffiths temperature, T G = 137 K. The synthesized YNCO double perovskite demonstrated a promising behavior as an electrode material for electrochemical supercapacitors. In a three-electrode system, it displayed a specific capacitance of 270 F g−1 at a current density of 0.5 A g−1. In a symmetric two-electrode system, YNCO exhibited a specific capacitance of 180 F g−1 at 0.5 A g−1, alongside an energy density of 6.25 Wh kg−1 at 250 W kg−1 power density. In both cases, we employed a mild 0.5 M neutral aqueous Na2SO4 solution as the electrolyte, in contrast to the typically employed corrosive and concentrated alkaline aqueous solution. The fascinating magnetic and charge storage properties of the B-site disordered YNCO double perovskite indicate its potential for use in spintronic devices and as efficient electrodes in symmetric hybrid supercapacitors.

Pyridine Diphosphonate Ligand for Stabilization of Tetravalent Uranium and Neptunium in Aqueous Medium under Aerobic Conditions.

Though uranium is usually present in its +6 oxidation state (as uranyl ion) in aqueous solutions, its conversion to oxidation states such as +4 or +5 is a challenging task. Electrochemical reduction and axial oxo activation are the preferred methods to get stable unusual oxidation states of uranium in an aqueous medium. In previous studies, dicarboxylic acid has been used to stabilize UO2+ in aqueous alkaline solutions. In the present work, a diphosphonate ligand was chosen due to its higher complexing ability compared to that of the carboxylate ligands. Neptunium complexation studies with 2,6-pyridinediphosphonic acid (PyPOH) indicated the formation of different species at different pH values and the complexation facilitates disproportionation of NpO2+ to Np4+ and NpO22+ at pH 2. Hexavalent actinides form insoluble complexes in aqueous media at pH = 2, as confirmed by UO22+ complexation studies. The in situ complexation-driven precipitation resulted in conversion to pure Np4+ in aqueous media as the Np4+-PyPOH complex. A strong complexing ability of the PyPOH ligand toward the Np4+ ion is also seen for the stabilization of the electrochemically generated U4+ in aqueous medium under aerobic conditions. The U4+-PyPOH complex was found to be stable for 3 months. Raman, UV-vis, fluorescence, and cyclic voltametric studies along with density functional theory (DFT) calculations were done to get structural insights into the PyPOH complexes of actinides in different oxidation states.

Lignin‐Alkali Metal Ion Self‐Catalytic System Initiated Rapid Polymerization of Hydrogel Electrolyte with High Strength and Anti‐Freezing Ability

AbstractHydrogel electrolyte is not resistant to freezing and has weak mechanical properties, and its fabrication is time‐consuming and energy‐consuming, limiting its application. Here, a simple, universal, and fast gelation based on dealkaline lignin (DL) ‐alkali metal ions is developed. The complex formed by catechol and alkali metal ions promotes the equilibrium of redox reactions. The produced SO4−·, OH· and singlet oxygen (1O2) radicals are responsible for the rapid polymerization of vinyl monomers. Alkali metal ions play a dual role in the rapid polymerization and frost resistance of hydrogel electrolytes. By modulating the mass ratio of DL and metal ion concentration, the preferred hydrogel electrolyte can be fabricated in an alkaline aqueous solution for 4 min at room temperature and possesses excellent anti‐freezing performance (0.51 mS cm−1 at −40 °C) and strong mechanical properties (tensile stress: 0.4 MPa, strain: 1125%). The hydrogel electrolyte‐assembled supercapacitor exhibits high stability at low temperatures. The specific capacitance retention is 89.7 % and 88.7 % after 5000 charge/discharge cycles at 25 and −20 °C, respectively. The lignin‐alkali metal ions self‐catalytic system completely different from the reported lignin‐oxidizing metal ion system will open up a new way for the fabrication of anti‐freezing ionic conductors and energy storage devices.

Degradation Characteristics of Glass Fiber Reinforced Plastics Using Unsaturated Polyester as Matrix in Weak Alkaline Aqueous Solution

Degradation Characteristics of Glass Fiber Reinforced Plastics Using Unsaturated Polyester as Matrix in Weak Alkaline Aqueous Solution

Effect of the phase composition of AK12M2 and AK12pch silumins on the corrosion and electrochemical behaviour in weakly alkaline aqueous solution. Part 1. Thermodynamic calculation of the phase composition of silumins

Effect of the phase composition of AK12M2 and AK12pch silumins on the corrosion and electrochemical behaviour in weakly alkaline aqueous solution. Part 1. Thermodynamic calculation of the phase composition of silumins

Molecular Modeling Study of Bis-sulfonamide Derivatives Synthesis Targeting Aromatase Enzyme as Anticancer

Most studies indicate the important role of estrogen in the mechanism of occurrence and development of breast cancer. The importance of our research is the synthesis of bis-sulfonamide compounds that inhibit the aromatase enzyme, which is the main enzyme in the biosynthesis of estrogen. Molecular modeling of studied compounds was carried out by Molegro Virtual Docker (MVD) targeting aromatase enzyme and binding energy calculated to select the most encouraging compound. The highest binding energy among the studied compounds was -118.52 kcal/mol (compound A5) comparing with the aromatase substrate androstenedione -132.51 kcal/mol and the aromatase inhibitor letrozole -136.52 kcal/mol. Several of these compounds were synthesized in a simple way with good yields by reacting sulfonyl chloride derivatives with amino derivatives in an alkaline aqueous solution, or in a pyridine solution. The physicochemical characteristics and identification of synthesized compounds were determined by various analytical methods such as Mass spectrometry, Infrared spectroscopy and Nuclear Magnetic Resonance.

Ultrasonic treatment duration: A nuanced parameter in synthesis affecting structural properties and ORR performance of KOH-activated carbon

In this study, we investigate the effects of the duration of ultrasonic treatment during the impregnation process of a carbon precursor with an aqueous alkaline solution on the structural and electrochemical properties of KOH-activated carbon materials. Our findings using polyacrylonitrile (PAN)-derived carbon materials reveal that extended ultrasonic treatment leads to a more consistent distribution of the activating agent, promoting more uniform surface activation. This leads to notable shifts in the material's structure and surface chemistry, thereby influencing its functionality as an electrode material in supercapacitors and its electrocatalytic activity in the oxygen reduction reaction (ORR). Our results indicate a 6 % difference in the specific surface area and an 8 wt% rise in oxygen content when comparing samples without ultrasonic treatment to those treated for 10 min. Moreover, the specific capacitance increases from 133.9 to 163.5 F g−1, and the ORR activity ascends from 1.88 to 2.23 mA cm−2. This research highlights the potential of ultrasonic treatment duration as a variable to fine-tune the structure and properties of porous carbon materials, emphasizing its scientific and technological significance in the production of stable porous carbon materials.

Hydrogen and deuterium adsorptions and their equilibrium isotope effect on tungsten in alkaline solutions

The equilibrium isotope effect (EIE) of hydrogen isotopes (H and D) on the W electrode in alkaline aqueous (H2O) and heavy water (D2O) solutions was empirically studied based on the relevant electrochemical adsorption isotherms, which were determined using the phase-shift method and electrochemical impedance spectra. For a fractional surface coverage range of 0.2 < θ < 0.8, the potential differences (ΔE) for hydrogen isotope adsorptions on the W electrode were 70 mV, which were much lower than those on the Ni, Ti, Pd, and Rh electrodes. Furthermore, the value of EIE on the W electrode was 13.4, significantly higher than that on the Ti and most Pt-group metal (Pt, Ir, Pt–Ir alloy, and Rh) electrodes. The W electrode can therefore be considered as a potential electrocatalyst for optimizing the hydrogen and deuterium evolution reactions (HER and DER) and EIE of hydrogen isotopes, particularly in water electrolysis and the hydrogen isotope effect.

Elucidation of Degradation Behavior of Nitrazepam, a Benzodiazepine Drug, under Basic Conditions: Study on Degradability of Drugs in Stomach (IV).

This study investigates the stability of nitrazepam (NZP), a benzodiazepine drug, under basic conditions, since alkaline putrefactive amines and ammonia are produced once bodies are left to decompose for a long period postmortem after a murder involving NZP or an accidental overdose of NZP. The degradation of NZP in an aqueous alkaline solution was investigated by LC/photodiode array detector (PDA) where the NZP degradation product was isolated and purified by solid-phase extraction using Oasis® MCX, and its chemical structure was determined by LC/time-of-flight (TOF)-MS, NMR spectroscopy, and single-crystal X-ray crystallography. The results revealed that NZP was immediately degraded under basic conditions with 2-amino-5-nitrobenzophenone being an intermediate which further degraded to provide 2-hydroxy-5-nitrobenzophenone as the final degradation product. These results are expected to be useful in clinical chemistry and forensic science, such as the detection of drugs during postmortem examination and suspected addiction.

PURIFICATION OF HYDROCARBON NATURAL GASES FROM HYDROGEN SULFIDE IN A TUBULAR TURBULENT APPARATUS

Purification of gases and petroleum products from sulfur compounds has always been one of the main problems of oil and gas processing and gas transportation. In recent decades, this problem has become even more urgent due to the tightening of requirements for the quality of petroleum products and the transition to high requirements for combustible natural gas supplied and transported through main gas pipelines. To ensure standardized indicators for hydrogen sulfide in gas, purification of this component is required. Traditionally, desulphurization of light hydrocarbon raw materials is reduced to removing hydrogen sulfide with amine solutions and removing mercaptans with aqueous-alkaline solutions using absorption equipment. To purify natural petroleum gas from hydrogen sulfide, it seems promising to use direct-flow vortex devices with small dimensions to create the required interfacial surface, as well as low hydraulic resistance. Based on the high rate of reaction of hydrogen sulfide with a hydrogen sulfide absorbent based on formaldehyde, research has been carried out to develop a technology for purifying associated petroleum gas using a tubular turbulent apparatus. By creating a high specific contact surface between the gas phases and the hydrogen sulfide absorber using the proposed technology, high efficiency in purifying associated gas from hydrogen sulfide was achieved under field conditions. Purified associated petroleum gas with a hydrogen sulfide content of 0.003 g/m3 complied with the STO Gazprom standard 089-2010 and the Technical Regulations of the Eurasian Economic Union 046/2018.

Ultra-stable and long-lived multi-color room temperature phosphorescent carbon dot and silica composites for data encryption and anti-counterfeiting

Carbon dot (CD)-based room temperature phosphorescence (RTP) materials have garnered fundamental attention due to their unique and irreplaceable advantages. However, developing CD-based materials with stable multi-color RTP emission is also desired. Herein, we present a rational design of carbon dots and SiO2 composite (CD@ Silica) fabrication, which demonstrates excellent stability in its RTP, showcases multi-color emission, and experiences thermal enhancement. Multi-color afterglow emission is achieved in CD/fluorescence dyes@ Silica composite systems due to the high efficiency of the Förster resonant energy transfer (FRET) processes between CDs and fluorescence dyes. The covalent interactions between CDs and silica shells protect the triplet state, and the structure significantly promotes the multi-color RTP emission realized in some challenging environments (such as in acid or alkaline aqueous solution). Utilizing the stable phosphorescence emission, we successfully implement the concepts of multi-level information encryption and fingerprint anti-counterfeiting through CD@ Silica composites.

Biomass-derived Co, N and P co-doped 3D porous carbon as an effective electrocatalyst for oxygen reduction reaction

Fuel cells are an important and promising energy system which has attracted lots of attention. The research on non precious metal catalysts is extremely important for the development of fuel cells. In this work, we fabricated metal organic hybrids (MOH) from chitosan, phytic acid, and CoCl2 through a simple chemical method, and further obtained the Co, N, and P co-doped 3D porous carbon material, with the Co atoms exhibiting good monodispersity on the surface. Due to the size effect brought by the single atom doping of Co and the influence of N and P doping on the microenvironment of the active center, the obtained Co-NPC-6 M exhibits excellent catalytic performance for ORR in the alkaline aqueous electrolyte solution.

Correlation between Copper(II)-Lactate Complexes in Aqueous Alkaline Solutions and Copper(I) Oxide (Cu2O) Electrodeposited

Cuprous oxide (Cu2O) is a p-type semiconductor well-investigated as materials for photovoltaics and photoelectrodes due to its low cost. There is a number of reports on the Cu2O electrodeposition from aqueous alkaline electrolytes containing copper(II) salt and lactate ions as complex formers. Cu2O electrodeposition behaviors and several properties of resulting Cu2O are known to depend on the electrolyte pH, but mention of the reasons for this is limited. Recently, we have succeeded in identifying two different copper(II)-lactate complexes (1 and 2 in Table I) formed in the alkaline region depending on pH [1], and their formation constants determined made it possible to discuss the electrodeposition in terms of cathodic overpotential, or driving force, for the deposition. In addition, we found that the complexing took at least 1 day to reach equilibrium [2], suggesting that aging is mandatory after the preparation of electrolytes for reproducible electrodeposition. In this study, we prepared a set of thermodynamically well stabilized copper(II)-lactate electrolytes containing 0.4 M Cu(CH3COO)2·H2O and 3.0 M lactic acid, and compared the Cu2O electrodeposition at several different pH but unified overpotential from the CuII/Cu2O redox equilibrium at each pH. The effects of the pH-dependent complexes on the crystallographic orientation and electrical properties of Cu2O were rigorously investigated.Table I summarizes the relationship between the two complexes, deposition current density, and the properties of resulting Cu2O layers. In concert with the change of the complex, distinct differences in the properties were found bordering about pH 9.5. Since Cu2O shows p-type properties with intrinsic Cu+ defects, the conductivity of Cu2O depends on the amount of introduced Cu+ defects, the origin of p-type carriers. If the reduction of the complexes occur exactly according to the stoichiometry:2Cu(H–1L)L– (1) + H2O + 2e = Cu2O + 4L– 2Cu(H–1L)2 2– (2) + 3H2O + 2e = Cu2O + 4L– + 2OH– then, there should be no Cu+ defects. In practice, however, the defects often occur in Cu2O, because O2– ions can be incorporated into the lattice through an acid-base reaction like OH– = O2– + H+, independently of the reduction reactions. The amount of Cu+ defects is thus influenced by how readily the reduction of the complexes occur. The lower carrier density of Cu2O deposited at lower pH can be due to the ease in reduction of lower symmetric complex 1 dominant in the electrolytes, because complex with lower symmetry is generally more favorable to be reduced than that with higher one (2 in this case). The formation of Cu+ defects can also indebted to OH– activity near the cathode. At lower pH, the independent incorporation of O2– is restricted due to lower OH– activities, while high pH electrolytes with higher OH– activities provide an environment conducive to Cu+ defects. As a result, Cu2O layers with few Cu+ defects, low carrier density, and high resistivity is deposited from the electrolytes with complex 1. Owing to the low carrier density, the deposition becomes limited by carrier diffusion showing a low deposition current density.Although the deposited Cu2O crystals were randomly oriented at the early stage of electrodeposition irrespective of the pH, the deposits from lower and higher pH electrolytes became to have 〈100〉 and 〈111〉 orientations, respectively, as the electrodeposition proceed. Regarding the cubic Cu2O crystal, {100} planes have a higher surface energy than {111} planes. Therefore, under low current density (at lower pH), that is slow crystal growth with thermodynamic equilibrium control, Cu2O crystals with stable {111} facets are advantageous to appear. In contrast, at high current densities (at higher pH), the conditions favoring the appearance of {111} facets weaken and crystals with {100} facets appear. In such a growth mode, crystals whose preferential growth direction are not perpendicular to the planar substrate (cathode) were eliminated as the growth proceeds, because the directions interfere each other. As a result, the surface of thick Cu2O layers obtained from lower pH electrolytes is composed of square pyramidal grains with the vertex pointing perpendicular to the substrate; here, the faces of the pyramids correspond to four {111} facets. In contrast, the surface those obtained at higher pH is composed of triangular pyramidal grains with {100} facets.Consequently, it is considered that the two different complexes directly affect the difference in carrier density and conductivity of electrodeposited Cu2O, and the deposition current density changes depending on these electrical properties. Then, the current density determines the crystallographic orientation of resulting Cu2O.[1] T. Chen, et al., J. Electrochem. Soc., 166, D761 (2019); [2] T. Chen, et al., J. Electrochem. Soc., 165, D444 (2018). Figure 1

Anodization and Plasma Electrolytic Oxidation Treatments of AZ91D Mg Alloy in Alkaline Aqueous Solutions

Mg alloys, such as AZ91 (Mg-9mass%Al-1mass%Zn), are lightweight materials with excellent mechanical properties. The applications of Mg alloys in automobiles could significantly contribute to reducing carbon dioxide emissions. Mg alloys are fully recyclable and abundantly available, which increases their desirability in light of rising environmental consciousness. However, the low corrosion resistance of Mg alloys is one of the major limitations to further applications.In Mg alloys, corrosion behavior is known to be related to the microstructure. During the real-time in situ observation of the corrosion process under galvanostatic polarization, filiform corrosion proceeded along the outside of the β phase (in lamellar α + β microstructure and along the α-mother phase 1. Furthermore, the β phase exhibited a higher potential in the OCPs of each phase and a small area with the boundary in 0.1 M NaCl at pH 8.0 2. Thus, the surface films of β phases was thought to suppress the corrosion of Mg alloys. Mg alloys can be treated by anodic oxidation or plasma electrolytic oxidation to obtain excellent corrosion resistance. The latter is similar to anodic oxidation but applies a higher voltage, which causes a discharge on the electrode surface and the resulting plasma modifies the oxide film significantly.In this study, anodic oxidation and plasma electrolytic oxidation were performed on AZ91D Mg alloy in alkaline solutions such as sodium phosphate. This study aims to compare the two methods in the same solution and to produce an Al-rich surface film with excellent corrosion resistance.In anodic oxidation, the size of the electrode area was approximately 1 cm2. The surface of the specimen was coated with epoxy resin, followed by paraffin. The reference electrode was Ag / AgCl (3.33 M KCl). The experiments were performed at 25 ℃. The scan rate of potentiodynamic polarization was set at 23 mV min-1. The starting potential was set at 20 mV lower than the open-circuit potential. The anodic oxidation treatments were terminated at 0 V, 3 V, and 5 V. Plasma electrolytic oxidation was performed with a liquid volume of 500 mL. The sample was mounted on a resin holder. The electrode surface was approximately 50 mm2. A Pt plate was used as the counter electrode. The sample and the counter electrode were fixed at a distance of 0.5 cm. A plasma-generating power supply was used. The solution was cooled down to 20 ℃ while the voltage was applied. The frequency and the pulse interval were adjusted. The voltage and type of solution were changed to produce the film. Z. Shao, M. Nishimoto, I. Muto, and Y. Sugawara, Corrosion Science, 192, 109834 (2021).Z. Shao, M. Nishimoto, I. Muto, and Y. Sugawara, Journal of Magnesium and Alloys, 11, 137-153 (2023).

Noncatalytic Reductive Deiodination of Thyroid Hormones. Electrochemistry and Quantum Chemical Calculations

AbstractNoncatalytic processes may occur spontaneously leading often to undesired products. Electrochemical measurements provide data for thermodynamic calculations. Cyclic voltammetry of thyroxine (T4) and 3,3’,5‐triiodothyronine (T3) in N,N‐dimethylformamide (DMF) and alkaline aqueous solutions of pH 10–14 on glassy carbon electrodes yielded the values of redox potentials for the reduction leading to deiodination of those thyroid hormones under noncatalytic conditions. The first step of T4 deiodination occurs in DMF at −1.93 V vs. Fc+/Fc and for T3 at −1.95 V, which was confirmed by quantum‐chemical calculations at DFT and DLPNO‐CCSD(T) levels. In alkaline aqueous solutions, owing to poor solubility of these compounds, it was possible to determine only approximate values equal to −1.6 to −1.7 V vs. Ag/AgCl for the first step of deiodination. The reduction potentials do not depend on pH under these conditions. As shown by calculations, further steps exhibit very close reduction potentials. The radicals formed as products of concerted dissociative electron transfer to T4 and T3 are relatively kinetically stable which leads to side reactions initiated by radicals in uncatalyzed deiodination processes.