Strong Electron Paramagnetic Resonance Signal Research Articles

Spin Trapping of Nitric Oxide by Hemoglobin and Ferrous Diethyldithiocarbamate in Model Tumors Differing in Vascularization.

Animal tumors serve as reasonable models for human cancers. Both human and animal tumors often reveal triplet EPR signals of nitrosylhemoglobin (HbNO) as an effect of nitric oxide formation in tumor tissue, where NO is complexed by Hb. In search of factors determining the appearance of nitrosylhemoglobin (HbNO) in solid tumors, we compared the intensities of electron paramagnetic resonance (EPR) signals of various iron-nitrosyl complexes detectable in tumor tissues, in the presence and absence of excess exogenous iron(II) and diethyldithiocarbamate (DETC). Three types of murine tumors, namely, L5178Y lymphoma, amelanotic Cloudman S91 melanoma, and Ehrlich carcinoma (EC) growing in DBA/2 or Swiss mice, were used. The results were analyzed in the context of vascularization determined histochemically using antibodies to CD31. Strong HbNO EPR signals were found in melanoma, i.e., in the tumor with a vast amount of a hemorrhagic necrosis core. Strong Fe(DETC)2NO signals could be induced in poorly vascularized EC. In L5178Y, there was a correlation between both types of signals, and in addition, Fe(RS)2(NO)2 signals of non-heme iron-nitrosyl complexes could be detected. We postulate that HbNO EPR signals appear during active destruction of well-vascularized tumor tissue due to hemorrhagic necrosis. The presence of iron-nitrosyl complexes in tumor tissue is biologically meaningful and defines the evolution of complicated tumor-host interactions.

Efficient Electronic Modulation of g-C 3 N 4 Photocatalyst by Implanting Atomically Dispersed Ag 1 -N 3 for Extremely High Hydrogen Evolution Rates

Efficient Electronic Modulation of g-C ₃ N ₄ Photocatalyst by Implanting Atomically Dispersed Ag ₁ -N ₃ for Extremely High Hydrogen Evolution Rates

Diradicals or Zwitterions: The Chemical States of m -Benzoquinone and Structural Variation after Storage of Li Ions

Diradicals or Zwitterions: The Chemical States of <i>m</i> -Benzoquinone and Structural Variation after Storage of Li Ions

Determination of the crystal field levels in TmV2Al20

Analysis of inelastic neutron scattering data recorded for the rare earth intermetallic compound TmV2Al20 yields a cubic crystal field Hamiltonian with parameters x = −0.63(1) and W = +0.43(1) K (Lea, Leask & Wolf notation). This result is supported by a strong electron paramagnetic resonance signal that is consistent with magnetic splitting of the first excited (Γ5(1)) state. Using this crystal field Hamiltonian, single crystal magnetisation and specific heat data are then interpreted in terms of a model that involves partial Al flux substitution of an approximately 10% depleted Tm “cage” site.

Reactive sputtered ZnO thin films: Influence of the O2/Ar flow ratio on the oxygen vacancies and paramagnetic active sites

Zinc oxide thin films were prepared under oxygen-deficient and oxygen-rich conditions by changing the oxygen to argon ratio (O2/Ar) during the reactive sputtering deposition at room temperature. The effects of increasing the partial pressure of oxygen in the sputtering gas from 20 to 70% O2/Ar on the thin film composition, crystallinity and defects that can act as active sites for gas reactions were studied using X-rays diffraction, X-rays photoelectron spectroscopy (XPS), Raman scattering and electron paramagnetic resonance (EPR). All the films exhibited a textured (0002) wurtzite phase and a crystallite size that increases as the partial pressure of oxygen in the sputtering gas increases. The XPS analysis showed that the number of oxygen vacancies decreases as the oxygen percent in the sputtering gas increases. The Raman spectra of the samples contained a band related to a hydroxide, OH, bond in addition to the vibrational modes associated with the wurtzite structure. A strong EPR signal, consistent with the OH acting as a paramagnetic center, was detected in all the films. An additional, but very weak EPR peak, was observed in the film grown at 20% O2/Ar, which was assigned to singly ionized oxygen vacancies located in the crystallite lattice. These paramagnetic centers are highly reactive because of their unpaired electrons and their formation will have important effects on the physical and chemical properties of the thin films.

Synthesis and investigations on correlation between EPR and optical properties of Fe doped Li2SiO3

Iron doped lithium metasilicate sample was synthesized using a combustion technique and characterized by XRD (X ray diffraction), SEM (scanning electron microscopy), FTIR (Fourier transform infrared spectroscopy), optical, and EPR (electron paramagnetic resonance) analyses. The phase purity of the combustion synthesized products was confirmed by XRD analysis. SEM data suggested the formation of a porous compound by virtue of the entrapment of the gases that evolved during the sample synthesis. FTIR data confirmed the formation of SiO bonds in the system. Optical data confirmed the existence of both divalent and trivalent iron in the system. Characteristic absorption bands in the region 215–270 nm and 535–620 nm were observed due to the presence of Fe3+ in Oh and Td geometry respectively. On the other hand, the presence of bands at 967 and 1442 nm suggested the stabilisation of Fe2+ also in both Oh and Td geometries, respectively. The divalent iron being a non-Kramer ion, could not be observed by EPR. However, strong temperature-dependent EPR signals were observed in the sample owing to Fe3+. By analyzing the EPR data, super-paramagnetic type of behaviour was observed in the system. Furthermore, the relaxation times along with other EPR spectroscopic parameters were estimated for the system.

The Overlooked Occurrence of Environmentally Persistent Free Radicals in an Area with Low-Rank Coal Burning, Xuanwei, China.

The mining and burning of low-rank coal in Xuanwei, China have attracted a great deal of research attention because of the generated polyaromatic hydrocarbons (PAHs) and the high incidence of lung cancer in this region. Given the abundant transition metals in the allitic soil, we hypothesized that environmentally persistent free radicals (EPFRs) are formed in this region and the potential risk had not been addressed. Strong electron paramagnetic resonance (EPR) signals of 3.20 × 1017 - 3.10 × 1019 spins/g were detected in environmental samples, including chimney soot, coal, soil and total suspended particles (TSP). These EPR signals did not significantly change after 18-months storage and had g-values in the range of 2.0039-2.0046, suggesting typical organic free radicals. Similar strong EPR signals were observed in PAH (anthracene and pyrene as model compounds) degradation on simulated soil particles and lasted over one month even when the applied PAHs were 100% degraded. Based on g-value and bond width, we propose that EPR signals detected in TSP and soot originated from both coal combustion and PAH photodegradation. Further research is thus urgently required to investigate EPFR generation, exposure and risk in Xuanwei to better understand the cause of high lung cancer incidence.

Polystyrenesulfonate Dispersed Dopamine with Unexpected Stable Semiquinone Radical and Electrochemical Behavior: A Potential Alternative to PEDOT:PSS

Inspired by the p-doped PEDOT:PSS, a traditional anode modifier, we proposed to prepare polydopamine:polystyrenesulfonate (PDA:PSS) via the self-polymerization of dopamine in aqueous PSS initially. However, DA and its semiquinone radical were dispersed by PSS to form DA:PSS successfully. Interestingly, a strong electron spin resonance signal was detected in DA:PSS, suggesting the stable semiquinone radical was formed. More importantly, water-soluble DA:PSS exhibited stable and quasi-reversible electrochemical oxidation behavior, and excellent film-formation capability. Consequently, as an indium tin oxide (ITO) anode modifier, solution processed DA:PSS film showed hole injection property in organic light emitting diodes. Our results open a new avenue for the design of semiconductor and organic electronic application inspired by the electron transfer of phenol derivatives such as DA. Phenol-based organic electronic material has showed potential and it should be taken into consideration in the future.

Radiation-induced defects in strontium carbonate rod for EPR dosimetry applications

The radiation-induced defects in strontium carbonate (SrCO3) rod dosimeter in the dose range of 2.5Gy–25 kGy was investigated using electron paramagnetic resonance (EPR) technique. The EPR spectra of γ-irradiated strontium carbonate (SC) rods exhibit a strong EPR signal with the spectroscopic splitting g-factor 2.008 and a weak signal at g-factor 2.003. This signal increases with increasing irradiation dose. The dose-response function has a good linearity in the low dose range of 2.5–500Gy and slight sub-linearity in the high dose range of 0.5–25 kGy. The dosimeter is nearly humidity independent in the level of 33–77% relative humidity during irradiation. The temperature coefficient of the dose-response function is 0.22% per °C in the temperature range of 20–40°C. The rod dosimeter exhibits a maximum deviation from water equivalency by 7% in the energy range of 0.3–5MeV. The overall uncertainty of dose determination using SC dosimeter is 5.2% and 4.54% (2σ) for low and high dose range, respectively.

Applications of EPR Spectrometer in Environmental Samples

Electron paramagnetic resonance (EPR) spectrometer was widely applied to physics, chemistry and biomedicine. This research provided possible electron and valence information of environmental samples interaction through high sensitivity. The EPR signals of transition metals and organic radicals were distinguished well. Three kinds of carbon nanotubes (CNTs) (MW50, MW30 and MWG) had strong EPR signals. Addition of transition metals may be a suitable way to decrease environmentally persistent free radicals (EPFRs). The potential risks of EPFRs in BC and the reactive free electron in transition metals must be addressed to ensure their safe and scientific absorption application.

Adsorption of a Carboxylic Acid-Functionalized Aminoxyl Radical onto SiO2

Silicon wafers both without and with silicon(IV) oxide surface coverage were covered with benzene solutions of stable organic radical 3-(N-tert-butyl-N-aminoxyl)benzoic acid (mNBA). X-ray photoelectron spectroscopy supported the presence of the radical on both surface-cleaned (oxide-reduced) and oxide-covered surfaces. Optical waveguide spectroscopy showed that the radical retained its structure while adsorbed to the surface of the wafers, without noticeable decomposition. AFM and MFM imaging showed that the radical formed blocky particles with a change in rms roughness from 0.3 nm premodification to 1.7 nm postmodification on the surface-cleaned silicon. Similar experiments using oxide-coated silicon showed that the radical adsorbed to form much smoother layers, with a small change in rms roughness from 0.2 to 0.3 nm. Contact angle measurements of water on the premodified and postmodified samples showed a large, hydrophobic change in the silicon oxide surface but only a modest change in the surface-cleaned silicon surface. Samples of mNBA adsorbed onto silica gel showed strong electron-spin resonance signals from the aminoxyl spin, even years after production. The results demonstrate the prospects for treating and coating oxide-covered silicon wafers and silicon oxide-coated particles with a paramagnetically active organic substrate, without major chemical modification of the pretreatment surface; the resulting organic spin sites can be stable for years.

Physicochemical and adsorption properties of hypercross‐linked polystyrene with ultimate cross‐linking density

The paper describes unexpected properties of hypercross-linked polystyrenes with ultimate cross-linking degrees of 300, 400, and 500%, where three, four, or five methylene links, respectively, could bind each polystyrene phenyl ring to its spacious neighbors. The polymers exhibit a strong electron spin resonance signal, unusual spectra in IR, UV, and visible ranges, and they are not typical dielectrics. The nonfunctionalized hypercross-linked polymers absorb significant amounts of inorganic acids, salts, and bases due to interactions of protons or other cations with electron-donating fragments of the aromatic network with the high extent of mutual connectivity and also due to dispersion interactions of anions with the polymer matrix.

Defects characterization of Dy-doped BaTiO3 ceramics via electron paramagnetic resonance

Abstract The point defects and the structural and dielectric properties of Dy-doped BaTiO 3 ceramics prepared at 1400 °C were investigated. The solubility of Dy in the self-compensation mode was determined to be x = 0.07 for (Ba 1− x Dy x )(Ti 1− x Dy x )O 3 , and no EPR signals associated with the Dy 3+ Kramers ion or the Ba and Ti vacancies were detected using the electron paramagnetic resonance (EPR) technique. As x increases, the dielectric behavior changed from a first-order phase transition to a diffuse phase transition to a Y7R dielectric-temperature stability. A strong EPR signal at g = 1.974, which is rare among rare-earth-doped BaTiO 3 ceramics appeared unexpectedly in the single-phase (Ba 1− x Dy x )Ti 1− x /4 O 3 ceramics with deliberately designed Ti vacancies. This signal was attributed to ionized Ba vacancy defects. A preference for the self-compensation mode of Dy 3+ ions is responsible for the appearance of Ba vacancies. The real formula of the nominal (Ba 1− x Dy x )Ti 1− x /4 O 3 is expressed as (Ba 1− x Dy 3 x /4 )(Ti 1− x /4 Dy x /4 )O 3 . In addition, the defect chemistry is discussed.

Influence of Free Radicals Signal from Dental Resins on the Radio-Induced Signal in Teeth in EPR Retrospective Dosimetry

In case of radiological accident, retrospective dosimetry is needed to reconstruct the absorbed dose of overexposed individuals not wearing personal dosimeters at the onset of the incident. In such a situation, emergency mass triage will be required. In this context, it has been shown that Electron Paramagnetic Resonance (EPR) spectroscopy would be a rapid and sensitive method, on the field deployable system, allowing dose evaluation of a great number of people in a short time period. This methodology uses tooth enamel as a natural dosimeter. Ionising radiations create stable free radicals in the enamel, in a dose dependent manner, which can be detected by EPR directly in the mouth with an appropriate resonator. Teeth are often subject to restorations, currently made of synthetic dimethacrylate-based photopolymerizable composites. It is known that some dental composites give an EPR signal which is likely to interfere with the dosimetric signal from the enamel. So far, no information was available about the occurrence of this signal in the various composites available on the market, the magnitude of the signal compared to the dosimetric signal, nor its evolution with time. In this study, we conducted a systematic characterization of the signal (intensity, kinetics, interference with dosimetric signal) on 19 most widely used composites for tooth restoration, and on 14 experimental resins made with the most characteristic monomers found in commercial composites. Although a strong EPR signal was observed in every material, a rapid decay of the signal was noted. Six months after the polymerization, the signal was negligible in most composites compared to a 3 Gy dosimetric signal in a tooth. In some cases, a stable atypical signal was observed, which was still interfering with the dosimetric signal.

The yellow color center and trapped electrons in beryl

The yellow color of beryl has been related to charge-transfer between Fe 3+ ions substituting for octahedral Al 3+ ions in the crystal and the surrounding oxygen ions. This assumption is contradicted by results from Electron Paramagnetic Resonance (EPR) measurements. A strong EPR signal from octahedral Fe 3+ ions can be found in beryl of all colors and in colorless beryl. An EPR signal unique to yellow beryl comes from Fe 3+ ions at a tetrahedral site. I propose that the yellow color of beryl comes from charge-transfer of tetrahedral Fe 3+ ions. A simple model involving electrons trapped in the crystal structure explains the creation and the decay of the yellow color. The absence of trapped electrons in dark red beryl can explain the high temperature stability of its color. There is no evidence that iron ions are located in the channels of the beryl structure, which has often been assumed.

Novel Solid State Nitric Oxide Sensor Using Siloxane-Poly(Oxypropylene) (PPO)

In this paper, a novel solid state Nitric Oxide (NO) sensor made of a spin trap (iron(II)-diethyldithiocarbamate complex, FeDETC) encapsulated in a siloxane-poly(oxypropylene) (PPO) matrix was developed. Nitric oxide (NO), a free radical molecule, has numerous roles in various physiological functions, such as the regulation of blood pressure, immune response to bacterial infection, and nervous systems. Siloxane-polyether hybrid materials, for example siloxane-poly(oxypropylene) (PPO), are easy to prepare, transparent and flexible. The combination of all these characteristics in a unique material allows it to be used in several scientific and technological areas, including human health. NO radical is trapped in FeDETC, which allows its detection by electron paramagnetic resonance (EPR). FeDETC was added while PPO was a sol, which was then left in air for gelation. The novel sensor was dived directly into a solution of NO, when the NO-FeDETC complex was formed. Our results show that the novel sensor responds to NO, with similar sensitivity as previously published sensors. PPO sensors present a strong EPR signal and a high stability, keeping its signal for 45 days. We have studied ways to accelerate the NO release from the sensor, in order to study its potential as a drug delivery system. We observed an acceleration in NO release by using a modulated magnetic field of 40 G at 100 kHz; as well as by UV irradiation. Thermal induced NO release was also tested by heating NO-FeDETC PPO up to 50°C, with good results.

Identification and Characterization of Gamma‐Irradiated Dried Lentinus edodes Using ESR, SEM, and FTIR Analyses

A detailed electron spin resonance (ESR) analysis for different parts of gamma-irradiated (0 to 50 kGy) dried mushroom (Lentinus edodes) was conducted to identify radiation-induced signals. All studied mushroom parts except gills produced strong dose-dependent radiation-induced ESR signals particularly at about g = 2.0076, 20005, and 1.9911 demonstrating the generation of crystalline sugar radicals following irradiation. The intensity of these signals was highest in cap skin samples, followed by the cap core, stem skin, whole mushroom powder, and stem core samples, respectively. ESR-based identification was easily possible at 2 kGy or more using mushroom cap skin or cap core as samples. The radiation-induced ESR signals were found sensitive to thermal treatment showing the limitation of ESR-based detection in case of heat-processed samples. Scanning electron microscopy (SEM) showed micro-structural damage upon irradiation resulting decreased percentage of rehydration; however, no major alteration was observed through the Fourier transform infrared (FTIR) spectra. Irradiation changed the structural morphology; however, the main functional groups were stable against radiation treatment. Food irradiation can confirm hygienic quality and prolong the product shelf life. However, due to lack of international consensus, effective identification methods and detailed quality characterization are required for the general use of this technology.

A Novel Electron Paramagnetic Resonance Phenomenon in a Barium Stronium Titanate Ceramic

The electron paramagnetic resonance (EPR) technique was employed to investigate the point defects in barium strontium titanate ceramics. All samples showed a strong EPR signal with g = 2.000, which was indexed as intrinsic Ti-vacancy defects. In (Ba0.85Sr0.15)TiO3ceramic, which showed a tetragonal symmetry and consisted of the crystallites with average size of ~ 220 nm, a novel EPR powder spectrum was observed - the g-factor of theg= 2.000 signal evolved into ag-tensor, and the two weak signals withg3= ~ 2.6 andg1= ~ 1.6 gradually shifted toward the g2 = 2.000 signal and approached to each other with increasing temperature.

Electron paramagnetic resonance studies on Mn doped GaSb

We report on the X-band (∼9.43 GHz) electron paramagnetic resonance (EPR) investigations carried out on polycrystalline Ga1−xMnxSb (x=0.02). A strong EPR signal with an effective g factor (geff) close to 2.00 was observed, suggesting that the ionic state of Mn which replaces Ga ion in the lattice, is Mn2+ attributable to ΔM=1 transition of the ionized Mn acceptor A−, Mn(3d5). The apparent absence of EPR signal, typical for neutral Mn acceptor at g=2.7 suggests either no such centers are present or the signal broadens beyond detection limit. The temperature dependent EPR studies combined with dc magnetization data suggest the possible coexistence of antiferromagnetic and ferromagnetic phases at very low temperatures.

Identification of Substitutional Nitrogen and Surface Paramagnetic Centers in Nanodiamond of Dynamic Synthesis by Electron Paramagnetic Resonance

Production of nanodiamond particles containing substitutional nitrogen is important for a wide variety of advanced applications. In the current work nanodiamond particles synthesized from a mixture of graphite and hexogen were analyzed to determine the presence of substitutional nitrogen using pulsed electron paramagnetic resonance (EPR) spectroscopy. Nitrogen paramagnetic centers in the amount of 1.2 ppm have been identified. The spin relaxation characteristics for both nitrogen and surface defects are also reported. A new approach for efficient depletion of the strong nonnitrogen EPR signal in nanodiamond material by immersing nanodiamond particles into ice matrix is suggested. This approach allows an essential decrease of the spin relaxation time of the dominant non-nitrogen defects, while preserving the substitutional nitrogen spin relaxation time.