Electron Spin Resonance Studies Research Articles

EPR Study of KO2 as a Source of Superoxide and •BMPO-OH/OOH Radical That Cleaves Plasmid DNA and Detects Radical Interaction with H2S and Se-Derivatives.

Superoxide radical anion (O2•−) and its derivatives regulate numerous physiological and pathological processes, which are extensively studied. The aim of our work was to utilize KO2 as a source of O2•− and the electron paramagnetic resonance (EPR) spin trapping 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO) technique for the preparation of •BMPO-OOH and/or •BMPO-OH radicals in water solution without DMSO. The method distinguishes the interactions of various compounds with •BMPO-OOH and/or •BMPO-OH radicals over time. Here, we show that the addition of a buffered BMPO-HCl mixture to powdered KO2 formed relatively stable •BMPO-OOH and •BMPO-OH radicals and H2O2, where the •BMPO-OOH/OH ratio depended on the pH. At a final pH of ~6.5–8.0, the concentration of •BMPO-OOH radicals was ≥20 times higher than that of •BMPO-OH, whereas at pH 9.0–10.0, the •BMPO-OH radicals prevailed. The •BMPO-OOH/OH radicals effectively cleaved the plasmid DNA. H2S decreased the concentration of •BMPO-OOH/OH radicals, whereas the selenium derivatives 1-methyl-4-(3-(phenylselanyl) propyl) piperazine and 1-methyl-4-(4-(phenylselanyl) butyl) piperazine increased the proportion of •BMPO-OH over the •BMPO-OOH radicals. In conclusion, the presented approach of using KO2 as a source of O2•−/H2O2 and EPR spin trap BMPO for the preparation of •BMPO-OOH/OH radicals in a physiological solution could be useful to study the biological effects of radicals and their interactions with compounds.

Electron spin resonance studies of (La0.6Ln0.4)0.67Ca0.33MnO3 (Ln = La, Pr, Nd and Sm) nanoparticles at different temperatures

In this work, (La0.6Ln0.4)0.67Ca0.33MnO3 (Ln = La, Pr, Nd and Sm) nanoparticles (NPs) synthesized by sol-gel process were investigated by electron spin resonance (ESR) in the temperature range 100–330 K. At the high temperature the ESR signals of La0.67Ca0.33MnO3 (LCMO) NPs only consist of a single peak with Landé g factor of 2.0. This signal is contributed from the paramagnetic (PM) Mn ions in the LCMO NPs. With decreasing the temperature the PM resonance line is split into two resonance lines, one is ferromagnetic (FM) resonance line shifting towards low field while the other is antiferromagnetic (AFM) resonance line moving to a high field. The resonance peak-to-peak spectra linewidth, increases monotonically with decreasing the temperature owing to the strong double exchange interactions below the Curie temperature (T C). Resonance field is almost temperature independent in the PM phase whereas it drops fast at temperature below T C. Consequently, the Landé g factor in the PM region is very close to 2.0 whereas in the range of 2.17–2.47 under FM state due to the strong FM interactions. For the Pr (Nd)-doped LCMO NPs below T C, their g values are in the range of 2.04–2.18 due to the substantial reduction of the FM interactions caused by the Pr (Nd)-doping at La-site. The g values of the Sm-doped LCMO NPs exhibit a slight fluctuation around 1.88 (but smaller than 2.0) within the measured temperature due to the existence of weak magnetic interactions under the PM states.

Magneto-optical properties of Cr3+ in β-Ga2O3

β-Ga2O3 is a wide bandgap semiconductor that is attractive for various applications, including power electronics and transparent conductive electrodes. Its properties can be strongly affected by transition metal impurities commonly present during the growth such as Cr. In this Letter, we determine the electronic structure of Cr3+ by performing a correlative study of magneto-photoluminescence (magneto-PL) and electron paramagnetic resonance. We unambiguously prove that the so-called R1 and R2 PL lines at around 1.79 eV originate from an internal transition between the first excited state (2E) and the 4A2 ground state of Cr3+. The center is concluded to have monoclinic local symmetry and exhibits a large zero-field splitting (∼147 μeV) of the ground state, which can be directly measured from the fine structure of the R1 transition. Furthermore, g-values of the first excited state are accurately determined as ga = 1.7, gb = 1.5, and gc* = 2.1. Our results advance our understanding of the electronic structure of Cr in β-Ga2O3 and provide a spectroscopic signature of this common residual impurity.

Metal-organic frameworks with different oxidation states of metal nodes and aminoterephthalic acid ligand for degradation of Rhodamine B under solar light

Metal-organic frameworks (MOFs) have been investigated recently as effective visible light photocatalysts. In this report, we synthesized nickel, iron, and titanium-based MOFs with different oxidation states of metal ions and aminoterephthalic acid ligand for photocatalytic degradation of Rhodamine B (RhB) dye under solar light irradiation. The photoluminescence analysis revealed that the Fe-MOF could suppress the recombination of photoinduced charges and effectively degrade the dye. The photocatalytic experiment demonstrated that the Fe-MOF exhibited higher degradation efficiency of dye (90 %) compared to the Ni-MOF (9 %) and Ti-MOF (50 %) at pH 7 in 90 min. In addition, the effects of catalyst amount, dye concentration, and solution pH on dye degradation were investigated. The photodegradation of dye using Fe-MOF was well-fitted to the first-order kinetics with an R2 value of 0.9987. Furthermore, reactive oxygen species test and electron paramagnetic resonance study revealed that the superoxide anion radicals were mainly responsible for the dye degradation. Cyclic test analysis indicates that there was no substantial decrease in the degradation efficiency of dye after four consecutive cycles.

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

Molecular organic fluorophores are currently used in organic light-emitting diodes, though non-emissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular charge-transfer excitonic states and associated small singlet-triplet energy separations; triplets can then be converted to emissive singlet excitons resulting in efficient delayed fluorescence. However, the mechanistic details of the spin interconversion have not yet been fully resolved. We report transient electron spin resonance studies that allow direct probing of the spin conversion in a series of delayed fluorescence fluorophores with varying energy gaps between local excitation and charge-transfer triplet states. The observation of distinct triplet signals, unusual in transient electron spin resonance, suggests that multiple triplet states mediate the photophysics for efficient light emission in delayed fluorescence emitters. We reveal that as the energy separation between local excitation and charge-transfer triplet states decreases, spin interconversion changes from a direct, singlet-triplet mechanism to an indirect mechanism involving intermediate states.

Effect of yttrium substitution in Fe-doped ZnO nanoparticles: An EPR study

In this work, we investigated the effect of Y3+ inclusion in ZnO nanoparticles doped with Fe3+ synthesized by the sol gel method. Transmission Electron Microscopy (TEM) images showed agglomerated nanostructures with different shapes and average particle size distributions ranging from 6 nm to 44 nm in diameter. Electron Paramagnetic Resonance (EPR) studies of the Zn0.98−yY0.02FeyO (y=0.00, 0.02, 0.03 and 0.04) were carried out using X band (9.7 GHz) at room temperature. For undoped ZnO and doped with Y3+, complex line shapes were observed as a result of oxygen vacancies (VO+1). In addition, the Y3+ inclusion provokes an enhancement of the linewidth and the resonance field due to intrinsic defects in the hexagonal structure. This observation is compatible with a shortest relaxation time by reason of the particle size reduction and an extra antiferromagnetic local field as a result of the Y3+ presence. For co-doped ZnO samples, the EPR spectra confirms the presence of Fe3+ and Y3+ at the core Zn sites, altering the lattice strain of the ZnO structure. This result was monitored by the zero-field splitting (ZFS) parameters of the spin Hamiltonian, corroborating a reduction in the Fe - Fe interaction. The presence of Y ions was also confirmed in interstitial sites, resulting in a small g-shift from 4.2 to 4.0 associated with modifications of the rhombic component, E, of the Spin–Hamiltonian. This study contributes to the understanding of structural defects caused by the Y and Fe inclusion in the Wurtzite crystal structure of ZnO, a material with potential applications in spintronic devices.

Copper(II) Complexes of Sulfonated Salan Ligands: Thermodynamic and Spectroscopic Features and Applications for Catalysis of the Henry Reaction.

Copper(II) complexes formed with sulfonated salan ligands (HSS) have been synthesized, and their coordination chemistry has been characterized using pH-potentiometry and spectroscopic methods [UV-vis, electron paramagnetic resonance (EPR), and electron-electron double resonance (ELDOR)-detected NMR (EDNMR)] in aqueous solution. Several bridging moieties between the two salicylamine functions were introduced, e.g., ethyl (HSS), propyl (PrHSS), butyl (BuHSS), cyclohexyl (cis-CyHSS, trans-CyHSS), and diphenyl (dPhHSS). All of the investigated ligands feature excellent copper(II) binding ability via the formation of a (O-,N,N,O-) chelate system. The results indicated that the cyclohexyl moiety significantly enhances the stability of the copper(II) complexes. EPR studies revealed that the arrangement of the coordinated donor atoms is more symmetrical around the copper(II) center and similar for HSS, BuHSS, CyHSS, and dPhHSS, respectively, and a higher rhombicity of the g tensor was detected for PrHSS. The copper(II) complexes of the sulfosalan ligands were isolated in solid form also and showed moderate catalytic activity in the Henry (nitroaldol) reaction of aldehydes and nitromethane. The best yield for nitroaldol production was obtained for copper(II) complexes of PrHSS and BuHSS, although their metal binding ability is moderate compared to that of the cyclohexyl counterparts. However, these complexes possess larger spin density on the nitrogen nuclei than that for the other cases, which alters their catalytic activity.

Cobalt sulfide-reduced graphene oxide: An efficient catalyst for the degradation of rhodamine B and pentachlorophenol using peroxymonosulfate

In this study, cobalt sulfide-reduced graphene oxide (CoS-rGO) nanocomposite was prepared by a solvothermal route and its structure, morphology and composition were assessed using various techniques, including transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The catalytic performance of CoS-rGO was evaluated for activation of peroxymonosulfate (PMS) for the elimination of rhodamine B (RhB) and pentachlorophenol (PCP) in water. The effects of various operating parameters on the degradation efficiency were systematically studied. Under optimized operating conditions, the CoS-rGO/PMS system achieved fast (less than 10 min) elimination of RhB and PCP at room temperature, as evidenced by high-performance liquid chromatographic (HPLC) analysis. Electron Paramagnetic Resonance (EPR) studies along with scavenging experiments revealed that sulfate radicals (SO4•−) were the primary players in the catalytic process. Interestingly, the CoS-rGO catalyst was stable after 8 cycles without obvious activity loss. The results reported in the present study hold promise for potential application of CoS-rGO for PMS activation for the elimination of various organic pollutants.

Morphological, magnetic and EPR studies of ZnO nanostructures doped and co-doped with Ni and Sr

Herein, were analyzed the effects of Sr and Ni addition on the morphological, electronic and magnetic properties of ZnO nanoparticles synthesized by the sol gel route. Morphological analysis showed agglomerated particles with nonuniform shapes (polyhedral, hexagonal and spherical) and the average size distributions were calculated counting more than 100 nanoparticles (sizes between 43 and 75 nm). For pure ZnO sample, the selected area electron diffraction (SAED) showed bright and concentric discontinuous diffraction rings, while the co-doped samples, presented patterns well-organized concentric circular rings, typical of reflection of regularly arranged atoms. The electron paramagnetic resonance (EPR) was employed to analyze the intrinsic defects due to the dopant inclusion. In addition, the EPR spectra were simulated using the spin quantum number (S = 1) for Ni2+ to understand the experimental results. Ni ions were used as a local probe in the comparative study by EPR, capturing subtle modifications in the zero-field interactions due to induced strain in the lattice. Microscopically the changes observed, through the EPR study, result from the reduction of the axial distortion of the ligand field and increasing in the distortion perpendicular to the principal axis. Magnetic study showed a typical significant diamagnetism at 300 K, while a paramagnetic contribution was more evident at 4 K. The work contributes to clarify the complex magnetic response in ZnO nanoparticles doped and co-doped with Sr and Ni.

Au Modified F-TiO2 for Efficient Photocatalytic Synthesis of Hydrogen Peroxide.

In this work, Au-modified F-TiO2 is developed as a simple and efficient photocatalyst for H2O2 production under ultraviolet light. The Au/F-TiO2 photocatalyst avoids the necessity of adding fluoride into the reaction medium for enhancing H2O2 synthesis, as in a pure TiO2 reaction system. The F− modification inhibits the H2O2 decomposition through the formation of the ≡Ti–F complex. Au is an active cocatalyst for photocatalytic H2O2 production. We compared the activity of TiO2 with F− modification and without F− modification in the presence of Au, and found that the H2O2 production rate over Au/F-TiO2 reaches four times that of Au/TiO2. In situ electron spin resonance studies have shown that H2O2 is produced by stepwise single-electron oxygen reduction on the Au/F-TiO2 photocatalyst.

Antibacterial and In Vivo Studies of a Green, One-Pot Preparation of Copper/Zinc Oxide Nanoparticle-Coated Bandages.

Simultaneous water and ethanol-based synthesis and coating of copper and zinc oxide (CuO/ZnO) nanoparticles (NPs) on bandages was carried out by ultrasound irradiation. High resolution-transmission electron microscopy demonstrated the effects of the solvent on the particle size and shape of metal oxide NPs. An antibacterial activity study of metal-oxide-coated bandages was carried out against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). CuO NP-coated bandages made from both water and ethanol demonstrated complete killing of S. aureus and E. coli bacteria within 30 min., whereas ZnO NP-coated bandages demonstrated five-log reductions in viability for both kinds of bacteria after 60 min of interaction. Further, the antibacterial mechanism of CuO/ZnO NP-coated bandages is proposed here based on electron spin resonance studies. Nanotoxicology investigations were conducted via in vivo examinations of the effect of the metal-oxide bandages on frog embryos (teratogenesis assay—Xenopus). The results show that water-based coatings resulted in lesser impacts on embryo development than the ethanol-based ones. These bandages should therefore be considered safer than the ethanol-based ones. The comparison between the toxicity of the metal oxide NPs prepared in water and ethanol is of great importance, because water will replace ethanol for bulk scale synthesis of metal oxide NPs in commercial companies to avoid further ignition problems. The novelty and importance of this manuscript is avoiding the ethanol in the typical water:ethanol mixture as the solvent for the preparation of metal oxide NPs. Ethanol is ignitable, and commercial companies are trying the evade its use. This is especially important these days, as the face mask produced by sonochemistry (SONOMASK) is being sold all over the world by SONOVIA, and it is coated with ZnO.

Activation of peroxydisulfate by carbon nanotube for the degradation of 2,4-dichlorophenol: Contributions of surface-bound radicals and direct electron transfer

Carbon materials have been used to activate peroxydisulfate (PDS) for the degradation of organic pollutants. The mechanism involved, especially whether radicals are formed in these processes, is still under debate. In this research, multi-walled carbon nanotube (MWCNT) was employed to activate PDS for the removal of 2,4-dichlorophenol (2,4-DCP). The effects of solution pH, PDS concentration, 2,4-DCP concentration, and MWCNT loading on the degradation of 2,4-DCP were investigated. The mechanism was explored via radical scavenging experiments, electron paramagnetic resonance (EPR) and MWCNT surface characterization. The results showed that the rate of 2,4-DCP degradation increased with the increasing solution pH, PDS concentration and MWCNT loading. The presence of OH and SO4− signals in EPR studies, no inhibitory effect in radical scavenging experiments, and the chlorination of MWCNT observed by X-ray photoelectron spectroscopy (XPS) suggested that surface reactions involving both surface-bound radicals and direct electron transfer were responsible for 2,4-DCP degradation. Reusability tests showed that the surface sites responsible for surface-bound radical formation were poisoned after PDS activation, while those responsible for direct electron transfer remained active after five cycles. This research provided the first in-depth insights for the dual roles of MWCNT in the PDS activation process.

EPR Spectroscopy as a Tool to Characterize the Maturity Degree of Humic Acids.

The major indicator of soil fertility and productivity are humic acids (HAs) arising from decomposition of organic matter. The structure and properties of HAs depend, among others climate factors, on soil and anthropogenic factors, i.e., methods of soil management. The purpose of the research undertaken in this paper is to study humic acids resulting from the decomposition of crop residues of wheat (Triticum aestivum L.) and plant material of thuja (Thuja plicata D.Don.ex. Lamb) using electron paramagnetic resonance (EPR) spectroscopy. In the present paper, we report EPR studies carried out on two types of HAs extracted from forest soil and incubated samples of plant material (mixture of wheat straw and roots), both without soil and mixed with soil. EPR signals obtained from these samples were subjected to numerical analysis, which showed that the EPR spectra of each sample could be deconvoluted into Lorentzian and Gaussian components. It can be shown that the origin of HAs has a significant impact on the parameters of their EPR spectra. The parameters of EPR spectra of humic acids depend strongly on their origin. The HA samples isolated from forest soils are characterized by higher spin concentration and lower peak-to-peak width of EPR spectra in comparison to those of HAs incubated from plant material.

Vanadyl doped Li-zinc borate glasses: Optical and ESR study

Glasses with the composition xV2O5-(15-x) Li2O-70B2O3-15ZnO, for x varies from 0 to 4 mol. %, were synthesized using standard quenching technique. The amorphous nature for selected samples (x= 0, 1 and 4 mol. %) was ensured from X-ray diffraction (XRD) measurements. The samples were found to compose mainly from BO3 and BO4 basic structural units as inferred from Fourier transform infrared (FTIR) data. The number of BO4 (BO3) structural units was found to decrease (increase) with increasing the number of NBOs. These structural modifications within the glass network are responsible for the here observed composition dependence optical energy gap (Eotp) and Urbach band tail (ΔE). The electron spin resonance (ESR) results revealed a tetragonal compression for VO2+ ions present in octahedral coordination, with distinct optical transitions in the visible spectral regime.

Electron paramagnetic resonance study of the paramagnetic centers in gamma-irradiated oxalic acid dihydrate single crystal

The Electron Paramagnetic Resonance (EPR) spectra of the radicals produced by γ-irradiation of a single crystal of oxalic acid dihydrate (C2H6O6) have been reported. The EPR spectra of gamma-irradiated single crystals of oxalic acid dihydrate have been studied for different orientations of crystals in a magnetic field. As a result of studies carried out along three axes, it has been determined that there are two biradicals. The EPR spectra have been investigated at temperatures between 125 and 450 K. The spectra have been found to be temperature independent. The g values of the radiation damage centers observed in oxalic acid dihydrate acid single crystal and the hyperfine structure constants of the free electron with nearby protons have been obtained from the single crystal EPR analysis.

Direct observation of the active sites in methane dehydroaromatization by NMR

Direct observation of the active sites in methane dehydroaromatization by NMR

Revealing two important tryptophan residues with completely different roles in a dye-decolorizing peroxidase from Irpex lacteus F17

BackgroundDye-decolorizing peroxidases (DyPs) represent a novel family of heme peroxidases that use H2O2 as the final electron acceptor to catalyze the oxidation of various organic compounds. A DyP from Irpex lacteus F17 (Il-DyP4, corresponding to GenBank MG209114), obtained by heterologous expression, exhibits a high catalytic efficiency for phenolic compounds and a strong decolorizing ability toward various synthetic dyes. However, the enzyme structure and the catalytic residues involved in substrate oxidation remain poorly understood.ResultsHere, we obtained a high-resolution structure (2.0 Å, PDB: 7D8M) of Il‑DyP4 with α-helices, anti-parallel β-sheets and one ferric heme cofactor sandwiched between two domains. The crystal structure of Il‑DyP4 revealed two heme access channels leading from the enzyme molecular surface to its heme region, and also showed four conserved amino acid residues forming the pocket for the conversion of hydrogen peroxide into the water molecule. In addition, we found that Trp264 and Trp380, were two important residues with different roles in Il‑DyP4, by using site-directed mutagenesis and an electron paramagnetic resonance (EPR) study. Trp264 is a noncatalytic residue that mainly is used for maintaining the normal spatial conformation of the heme region and the high-spin state of heme Fe3+ of Il‑DyP4, while Trp380 serves as the surface-exposed radical-forming residue that is closely related to the oxidation of substrates including not only bulky dyes, but also simple phenols.ConclusionsThis study is important for better understanding the catalytic properties of fungal DyPs and their structure–function relationships.

Light-Induced Electron Paramagnetic Resonance Study of Charge Transport in Fullerene and Nonfullerene PBDB-T-Based Solar Cells

Light-Induced Electron Paramagnetic Resonance Study of Charge Transport in Fullerene and Nonfullerene PBDB-T-Based Solar Cells

Luminescence and electron spin resonance studies of narrow-band UVB emitting Gd3+ doped Y2SiO5 nanophosphors synthesized by sol-gel method

Y2SiO5 nanophosphors doped with various Gd3+ ion concentrations were synthesized by citrate-based sol-gel method and investigated through X-ray diffraction (XRD), FTIR, electron spin resonance (ESR) and optical studies. XRD revealed the characteristic peaks of the planes corresponding to a monoclinic phase of a P21/c space group. The XRD analysis using Scherrer's formula showed that the Y2SiO5 crystallites were sized 22 nm. The FTIR spectral analysis of the characteristic vibrational bands of the Y2SiO5 matrix revealed an intense absorption band at 1039 cm−1. The ESR studies revealed the presence of Gd3+ ions in the octahedral locations of the Y2SiO5 matrix. The photoluminescence (PL) excitation spectra disclosed a prominent band at 273 nm, which was selected for excitation of Gd3+:Y2SiO5 nanophosphors. An ultraviolet luminescence emission band was detected at 313 nm due to the 6P7/2→8S7/2 transition under 273 nm excitation.

Photocatalytic Degradation of Ethiofencarb by a Visible Light-Driven SnIn4S8 Photocatalyst.

This work reports the preparation and detailed characterization of stannum indium sulfide (SnIn4S8) semiconductor photocatalyst for degradation of ethiofencarb (toxic insecticide) under visible-light irradiation. The as-prepared SnIn4S8 showed catalytic efficiency of 98% in 24 h under optimal operating conditions (pH = 3, catalyst dosage of 0.5 g L−1). The photodegradation reaction followed pseudo-first-order kinetics. The major intermediates have been identified using gas chromatography/mass spectrometry. •O2− and •OH radicals appeared to be the primary active species in the degradation process as revealed by scavenger and electronic spin resonance studies, while photogenerated holes had a secondary role in this process. A plausible mechanism involving two routes was proposed for ethiofencarb degradation by SnIn4S8 after identifying the major intermediate species: oxidative cleavage of the CH2-S and the amide bonds of the carbamate moiety. Lastly, SnIn4S8 was found to be efficient, stable, and reusable in treating real water samples in three successive photodegradation experiments. This study demonstrates the prospect of SnIn4S8 photocatalysis in treatment of natural and contaminated water from extremely toxic organic carbamates as ethiofencarb.