Search Results (213)

MgCr₂O₄ nanospinel samples were synthesized using a modified Pechini method, followed by controlled calcination. The resulting materials were evaluated in terms of crystal structure, particle morphology, and optical and electronic properties. Their oxidative activity towards the degradation of organic dyes was investigated via photocatalysis, Fenton-like, and photon-Fenton-like processes. Various analytical techniques were employed to characterize the samples, including X-ray diffraction (XRD) with Rietveld refinements, infrared (IR) spectroscopy, UV–Vis spectroscopy, colorimetry, and transmission and high-resolution transmission electron microscopy (TEM/HRTEM). Structural characterization revealed that MgCr₂O₄ crystallized after calcination at 600 °C, and Rietveld refinements confirmed cubic Fd-3m symmetry. IR spectra confirmed the short-range order through the presence of vibrational modes assigned to CrO₆^2- octahedra. UV–Vis spectroscopy indicated mixed Cr valences (Cr³+/Cr⁶+) for samples calcined at temperatures below 900 °C, with Cr⁶+ eliminated at higher temperatures, confirmed by electron paramagnetic resonance (EPR) spectroscopy. This suggests that an oxidation reaction occurred due to oxygen vacancies in the lattice. Optical bandgap (Eg) increased with temperature. Samples calcined at low temperatures were dark green and became more saturated at temperatures above 900 °C, suggesting photoresponse to visible light, as indicated by the Eg values. The oxidative activity of the nanospinels in degrading the dyes methylene blue (MB) and rhodamine B (RhB) under visible light depended on the nature of the dye, the catalyst concentration, and the use of H₂O₂ in the process to improve the formation of hydroxyl radicals (•OH), as confirmed by photohydroxylation of terephthalic acid (TA). The highest degradation rate was observed in the photo-Fenton-like process, with 96% and 97% degradation of RhB and MB dyes in 60 min, reaching a kinetic rate constant (${\mathit{K}}_{app}$) of 0.055 min⁻¹ and 0.051 min⁻¹, respectively. This study highlights the importance of controlling various parameters to promote the formation of reactive oxygen species (ROS) required for oxidative degradation by nanospinels. Full article

The NiO/Al₂O₃-CaO, CuO/Al₂O₃-CaO and CoO/Al₂O₃-CaO catalytic systems were investigated for the decomposition of ozone. Each of the three different Al₂O₃-CaO carriers was obtained after treatment of the initial precursor at 1100 °C for 2, 4 and 6 h, respectively, to examine the effect of annealing on support calcination. AAS, XRD, XPS, EPR, SEM and BET were applied for sample characterization. The carrier comprises a mixture of corundum α-Al₂O₃, θ-Al₂O₃ and Ca₃Al₂O₃. The XRD spectra of the active phases of the catalysts show the existence of Co₃O₄, NiO, Ni₂O₃ and CuO. The SEM micrographs reveal spherical particles for the NiO/Al₂O₃–CaO sample. In contrast, the CoO/Al₂O₃–CaO sample exhibits a morphology composed of wool-like fibers and perpendicularly oriented plate-like structures. The CuO/Al₂O₃–CaO sample consists not only of fibrous structures but also of distinct, separated aggregates. The obtained catalysts have highly developed specific surface areas. Their catalytic activity depends on the calcination conditions of the support, and the best results are observed after 2h treatment for all of the investigated samples due to the smaller crystallite size and higher specific surface area. The activity of the investigated catalysts for the ozone decomposition reaction follows the order NiO/Al₂O₃-CaO > CoO/Al₂O₃-CaO > CuO/Al₂O₃-CaO. Full article

UV-C irradiation enables digital zirconia colouring. This study investigates the atomic mechanism driving this defect-induced optical change. The band gap was calculated from the absorption spectra with the Tauc plot. The absorption spectra were measured using UV–visible spectroscopy. The surface composition was evaluated through X-ray photoelectron spectroscopy (XPS). The location of the oxygen vacancy was tested through electron paramagnetic resonance (EPR). The computer calculation using Density Functional Theory was conducted and the density of states (DOSs) were calculated. The band gap reduced rapidly from the baseline group (3.184 eV) to the 30 min irradiated group (3.097 eV). The XPS results showed that the electron density around O1s reduced and the electron density around Zr 3d increased. The EPR signal (g = 2.0037) increases progressively as the UV-C irradiation time is prolonged from 15 min to 24 h, indicating the accumulation of paramagnetic defect centres. The DOSs suggested the emergence of defect-associated states and band-edge tailing in oxygen deficient models, consistent with the experimentally observed reduction in the Tauc-derived optical band gap. This study confirmed the mechanism by which UV-C-induced oxygen vacancies modify the colour of 3Y-TZP. Full article

We report an electron paramagnetic resonance (EPR) study of radiation-induced defects in Ba₃(PO₄)₂, aiming to understand their role in radio-photoluminescence (RPL). Ba₃(PO₄)₂ is a promising host for rare-earth dopants in optical and dosimetric applications. We compare the effects of ultraviolet (UV) and X-ray irradiation on the electron trapping by Eu³⁺, as well as the formation of intrinsic defects by radiation in Eu-doped and undoped samples. Both irradiation types generate Eu²⁺ centers with axial symmetry at one specific Ba lattice site, as confirmed by Q-band EPR. Additional EPR signals near $g\approx 2$ reveal radiation-induced centers unrelated to Eu dopants. Detailed analysis of X- and Q-band spectra identifies an H⁰ center and two electron-trapping defects, one tentatively assigned to an oxygen vacancy (F-type center). These findings pave the way for understanding the complex defect landscape governing charge trapping and stability in Ba₃(PO₄)₂. Full article

Low-voltage instrumentation and control (I&C) cables in nuclear power plants are continuously exposed to gamma (γ) radiation within containment areas, leading to cumulative degradation of their polymer insulation over decades of operation. Since conventional mechanical aging assessments are destructive, this study establishes a non-destructive diagnostic framework using high-frequency dielectric spectroscopy. Cable samples with ethylene propylene rubber (EPR) insulation and chlorosulfonated polyethylene (CSPE) jackets were subjected to controlled γ-irradiation at doses up to 1200 kGy. The broadband dielectric response was analyzed along with derived novel diagnostic parameters from capacitance and loss tangent spectra and a machine learning AI algorithm. The results show a strong, material-dependent relationship between radiation dose and dielectric indicators. For EPR insulation, the central capacitance (CC) and (C × F × LF) exhibit high positive sensitivity for Black and White EPR materials, respectively, whereas for CSPE jackets, the central frequency (CF) shows a pronounced monotonic decrease with the radiation exposure. These findings enable a straightforward, transparent interpretation of dielectric data and implement a new, accurate method of irradiated cables diagnosis. Full article

Sodium-pumping NADH: ubiquinone oxidoreductase (Na⁺-NQR) is an important component of the aerobic respiratory chain of Vibrio cholerae. It oxidizes NADH, reduces ubiquinone, and uses the free energy of this redox reaction to move sodium across the cell membrane. The enzyme is a membrane complex of six subunits, two 2Fe−2S centers, and four flavins. Both the oxidized and reduced forms of Na⁺-NQR exhibit EPR signals due to flavin semiquinone radicals. It has been shown that in the oxidized form of the enzyme, the radical is a neutral flavin, while in the NADH-reduced form, the radical is an anionic flavin. Electron Spin Echo Envelope Modulation Spectroscopy (ESEEM) was used to probe the presence of the magnetic nucleus ²³Na in the immediate vicinity of the paramagnetic centers. The contribution of the ²³Na nucleus was observed only in the ESEEM spectra of the anionic flavin semiquinone previously assigned to FMN_NqrB. Analysis shows that the Na⁺ ion is within ~3–4 Å of the flavin radical. This distance is consistent with two models: (i) complexation of the Na⁺ ion with the carbonyl group of CO4; or alternatively, (ii) a “cation-π interaction,” between Na⁺ and the electron-rich π-system of the flavin aromatic rings. Full article

Direct hydroxylation of benzene to phenol using hydrogen peroxide is a cornerstone of sustainable green chemistry. This paper presents the results of a stability study of an iron-containing mordenite catalyst in the liquid-phase hydroxylation of benzene to phenol with a 30% aqueous hydrogen peroxide solution. The study utilizes a combination of catalytic activity measurements, dynamic light scattering (DLS), and electron paramagnetic resonance (EPR) spectra. The system is initially shown to exhibit high phenol selectivity; however, over time, DLS measurements indicate aggregation of the catalyst particles with an increase in the average particle diameter from 1.8 to 2.6 μm and the formation of byproducts–dihydroxybenzenes. Iron is present predominantly as magnetite nanoparticles (Fe₃O₄) ~10 nm in diameter, stabilized on the outer surface of mordenite, with minor leaching (<10%) due to the formation of iron ion complexes with ascorbic acid as a result of the latter’s interaction with magnetite particles. Using a thermodynamic approach based on the Ulich formalism (first and second approximations), it is shown that the reaction of benzene hydroxylation H₂O₂ in the liquid phase is thermodynamically quite favorable (ΔG° = −(289–292) kJ·mol⁻¹ in the range of 293–343 K, K = 1044–1052). It is shown that ascorbic acid acts as a redox mediator (reducing Fe³⁺ to Fe²⁺) and a regulator of the catalytic medium activity. The stability of the catalytic system is examined in terms of the Lyapunov criterion: it is shown that the total Gibbs free energy (including the surface contribution) can be considered as a Lyapunov functional describing the evolution of the system toward a steady state. Ultrasonic (US) treatment of the catalytic system is shown to redisperse aggregated particles and restore its activity. It is established that the catalytic activity is due to nanosized Fe₃O₄ particles, which react with H₂O₂ to form hydroxyl radicals responsible for the selective hydroxylation of benzene to phenol. Full article

Triarylmethyl radicals (TAMs) have recently emerged as highly effective polarizing agents in dynamic nuclear polarization (DNP) under viscous conditions, enabling substantial hyperpolarization via the solid-effect (SE) DNP mechanism even at room temperature. A comparable, though less pronounced, enhancement was observed for BDPA radicals embedded in phosphocholine-based lipid bilayers. Given the increasing interest in elucidating the structure and dynamics of biopolymers and their high-molecular-weight assemblies—such as cell membranes—this study focuses on the design, synthesis, and characterization of paramagnetic agents tailored for DNP-based structural biology. To this end, we synthesized a series of TAM derivatives functionalized with lipophilic substituents and characterized their magnetic resonance properties, including isotropic hyperfine interaction (HFI) constants on carbon nuclei and electron spin relaxation times (T₁ and T_m) at low temperatures (80 K). Echo-detected EPR spectra and electron spin echo envelope modulations (ESEEM) were recorded for novel TAM incorporated into liposomes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). These low-temperature measurements revealed that the radicals are localized either at the liposome surface or within the lipid bilayer, ensuring optimal accessibility to water molecules. Crucially, the presence of a single cholesterol moiety provides strong noncovalent anchoring within the hydrophobic core of the bilayer. Guided by these findings, we identify an amphiphilic TAM bearing a single cholesterol group and polar carboxyl functionalities as a highly promising candidate for DNP applications in membrane biology, combining efficient polarization transfer, bilayer integration, and aqueous accessibility. Full article

We have investigated the structural, morphological, magnetic, and up-conversion luminescence properties of the Yb³⁺/Er³⁺-doped LiGdF₄ nanocrystals precipitated in the silica glassy matrix. Morphological analysis showed uniform distribution of LiGdF₄ nanocrystals (tens of nm in size), embedded in silica glass matrix. FTIR spectroscopy analysis showed trifluoracetates thermolysis with silica lattice formation and structural analysis by XRD is consistent with the LiGdF₄ crystallization process, most likely through an autocatalytic reaction. The stress and crystalline lattice distortion are assigned to the doping and glass matrix environment where the growth process occurs. The EPR spectra associated with the Gd³⁺ ions have shown a well-defined spectrum in the xerogel, associated with the trifluoroacetate ligand environment. In the LiGdF₄ nanocrystals, the broad and unresolved spectrum is due to an envelope of unresolved anisotropic fine structure and a high dipole–dipole interaction between the Gd³⁺/Yb³⁺/Er³⁺ paramagnetic ions. Under 980 nm laser light pumping, we observed the characteristic “blue”, “green” and “red” up-conversion luminescences of the Er³⁺ ions through Yb → Er energy transfer process, that imply three and two-photon process; near UV up-conversion luminescence of Gd³⁺ is observed at about 280–300 nm where Yb → Er and Er → Gd energy transfer is involved. The UC luminescence properties can be improved up to two times by additional Yttrium co-doping due to the induced crystal field distortion. Full article

Crystalline defects such as oxygen vacancies have been studied little by electron paramagnetic resonance (EPR) spectroscopy for silicate-based luminescent materials. In this study, lutetium oxyorthosilicate powders were prepared by the sol–gel method, using TEOS (silicon source) and rare earth salts as precursors. The cross-linking agent, Glymo, contributed silicon atoms to the precursor solution in all systems. The addition of Glymo to Lu₂SiO₅, Lu₂SiO₅:Eu and Lu₂SiO₅:Eu/Yb influenced the morphology and chemical structure of the powders, leading to Lu₂Si₂O₇ formation. The crystalline defects in the lutetium silicate systems were investigated by EPR spectroscopy, and several defects related to oxygen were identified, as well as impurities from the precursors. Photoluminescence emission spectra revealed Eu³⁺ transitions between ⁵D₀ → ⁷F₀, ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ under 258 nm excitation, in addition to oxygen vacancy emissions between 500 and 550 nm. Oxygen vacancies were identified and confirmed by correlating EPR and photoluminescence studies. Full article

One of the cytochrome b₅₆₁ family members in C. elegans, named Cecytb-2, was investigated. Purified recombinant Cecytb-2 showed typical visible absorption spectra, EPR signals, and redox midpoint potentials, very similar to those of human Dcytb, which is responsible for intestinal iron acquisition by its ferric reductase activity. Fast kinetic experiments using pulse radiolysis and stopped-flow techniques showed that Cecytb-2 donates electrons to monodehydroascorbate radicals with a much lower reactivity than other cytochrome b₅₆₁ members, but it can accept electrons from ascorbate (AsA) as rapidly as other members. DEPC treatment of Cecytb-2 caused significant inhibition of electron acceptance from AsA and lowered the midpoint potential of heme b_L. MS/MS MASCOT analyses verified that N-carbethoxylations of conserved Lys98 and heme b_L axial His101 residues on the cytosolic side were major causes of the inhibition. Reconstituted Cecytb-2 in sealed vesicle membranes, in which AsA was entrapped, showed significant transmembrane ferric reductase activity. In situ hybridization analysis revealed that Cecytb-2 mRNA was distributed in intestinal cells. Immunohistochemical analysis indicated that Cecytb-2 resided in intestinal lumens. Knockdown of the Cecytb-2 gene expression in N2 worms indicated a significant suppression of growth under ferrous ion-deficient conditions. Thus, the ferric reductase activity conferred by Cecytb-2 seems to participate in iron acquisition and is very important for normal growth in low-ferrous conditions, confirming that Cecytb-2 is a genuine Dcytb homolog in C. elegans. Full article

Background/objectives: Interactions of infusions of Ginkgo biloba, ginseng, Yerba Mate, and green tea, with free radicals, were examined. The aim of these studies was to determine quenching of free radicals by the extracts from the selected plant raw materials that are useful in the treatment of Alzheimer’s disease. Methods: The interactions were tested by an X-band (9.3 GHz) EPR spectroscopy and UV-Vis spectrophotometry. The model DPPH free radicals were used. The magnitude and changes with time of EPR and UV-Vis spectra of DPPH by the tested extracts were measured. Results: EPR and UV-Vis lines of DPPH free radicals decrease with increasing time of interactions of the extracts with DPPH, and after reaching the minimum value, it does not change with time. Ginseng infusion quenched free radicals the least. Ginkgo biloba extract quenches free radicals a little stronger than ginseng extract. Taking into account the tested extracts, Ginkgo biloba and ginseng extracts interact with free radicals less effectively compared to extracts of Yerba mate and green tea. Ginkgo biloba and ginseng extracts quench free radicals weaker than Yerba Mate and green tea extracts. Conclusions: Yerba Mate extract definitely had the strongest antioxidant properties. This extract quenches free radicals most effectively, what can be useful in the case of Alzheimer’s disease. Given its strong antioxidant properties, green tea extract can also be particularly recommended in the case of Alzheimer’s disease. Full article

Magnetic resonance techniques are powerful, nondestructive, non-invasive tools with broad applications in radiation dosimetry. Electron paramagnetic resonance (EPR) enables direct quantification of dose-dependent radiation-induced paramagnetic defects, while nuclear magnetic resonance (NMR) reflects the influence of such defects through changes in line width and nuclear spin relaxation. To date, these methods have typically been applied independently. Their combined use to probe radiation damage in the same material offers new opportunities for comprehensive characterization and preferred dosimetry techniques. In this work, we apply both EPR and NMR to investigate radiation damage in lithium carbonate (Li₂CO₃). A detailed EPR analysis of γ-irradiated samples shows that the concentration of paramagnetic defects increases with dose, following two distinct linear regimes: 10–100 Gy and 100–1000 Gy. A gradual decay of the EPR signal was observed over 40 days, even under cold storage. In contrast, ⁷Li NMR spectra and spin–lattice relaxation times in Li₂CO₃ exhibit negligible sensitivity to radiation doses up to 1000 Gy, while ¹H NMR results remain inconclusive. Possible mechanisms underlying these contrasting behaviors are discussed. Full article

Free radicals in G-361 human melanoma malignum control cells and the cells cultured with simvastatin were examined by EPR spectroscopy. The proliferation of the cells was determined. The aim of this work was to examine the influence of simvastatin used at different concentrations in the G-361 cell culture on its free radicals. The concentrations of simvastatin—0.1 μM, 1 μM, 3 μM, and 5 μM—were tested. EPR spectra of free radicals were measured by an X-band (9.3 GHz) spectrometer. Amplitudes, integral intensities, linewidths, and g factors were determined. Melanin biopolymers are the main source of o-semiquinone free radicals in G-361 human melanoma malignum cells, for which the EPR lines show characteristic g values of 2.0046–2.0059, but also, free radicals occurring in other cellular structures may contribute to these signals. The amount of free radicals decreases after interactions of simvastatin with the G-361 cells, and this effect depends on the concentration of simvastatin. The highest amounts of free radicals exist in G-361 cells cultured with simvastatin at concentrations of 3 μM and 5 μM. The relatively lower amounts of free radicals occur in G-361 cells cultured with simvastatin at concentrations of 0.1 μM and 1 μM. The fast spin–lattice relaxation processes exist in the control G-361 cells and in the cells cultured with simvastatin, regardless of simvastatin concentration. Full article

Copper is an essential micronutrient for plants, but excessive levels can induce toxicity and impair physiological functions. This study evaluates the toxic effects of copper sulfate (CuSO₄) on the germination of common wheat (Triticum aestivum), with emphasis on the gas emission dynamics and oxidative stress biomarkers. Seeds were germinated in agar and exposed to CuSO₄ at concentrations of 1 µM, 100 µM, 1 mM, and 10 mM; distilled water served as the control. Ethylene and ammonia emissions were quantified using CO₂ laser photoacoustic spectroscopy, while electron paramagnetic resonance (EPR) spectroscopy was employed to detect free radicals and Cu²⁺ complexes. Exposure to Cu concentrations ≥ 1 mM significantly inhibited germination and biomass accumulation. Enhanced ethylene and ammonia emissions, particularly at 10 mM, indicated stress-related metabolic responses. The EPR spectra confirmed the presence of semiquinone radicals and Cu²⁺ complexes under higher Cu levels. These results demonstrate that photoacoustic and EPR techniques are effective tools for the early detection of metal-induced phytotoxicity and offer a non-invasive approach to environmental toxicity screening and plant stress assessment. Full article