Electron Spin Resonance Determination Research Articles

Facile fabrication of magnetically recyclable Fe3O4/BiVO4/CuS heterojunction photocatalyst for boosting simultaneous Cr(VI) reduction and methylene blue degradation under visible light

It is a challenging problem that develops a low-cost, efficient and sustainable technology in order to remove heavy metals and organic contaminants in the practical wastewater. Herein, a novel recyclable Fe3O4/BiVO4/CuS (FBCu) heterojunction photocatalyst was facilely fabricated by a method, coating CuS nanoparticles on the surface of Fe3O4 and BiVO4 simultaneously. FBCu composite not only has the ability to degrade Cr(VI) or methylene blue (MB) alone under visible light irradiation, but also exhibits higher photocatalytic ability in simultaneously removing Cr(VI) and MB mixed pollutants. The superior photocatalytic performance of FBCu is related to the formation of p-n heterojunction, which extends the spectral response and facilitates the efficiency of charge carriers separation and utilization. Moreover, FBCu exhibits satisfactory properties of reusability and stability after five cycling experiments in the Cr(VI)-MB coexistence system. Furthermore, the detailed mechanism for simultaneous removal of mixed pollutants was proposed and verified by DRS results, photoelectrochemical analysis, scavenger experiments and electron spin resonance determination. This work provides a recyclable photocatalyst with eco-friendliness and multifunctional applications in water pollution.

Ultrasound assisted Fenton-like degradation of dyes using copper doped graphitic carbon nitride.

A novel copper doped graphitic carbon nitride (Cu-C3N4) was successfully synthesized and used as an effective Fenton-like catalyst. Cu-C3N4 was characterized by scanning electron microscopy, surface area analyzer, Fourier transform infrared spectroscopy, X-ray diffractometer, and X-ray photoelectron spectroscopy. Effect of process parameters including catalyst dosage, hydrogen peroxide (H2O2) concentration, solution pH, and initial methylene blue (MB) concentration was investigated to evaluate catalytic performance. The pseudo first-order kinetic model was used to describe the catalytic process. The enhancement of MB degradation is observed assisted by ultrasound. MB degradation of 96% is obtained within 30 min in Cu-C3N4/H2O2/ultrasound system, and the corresponding rate constant is 0.099 min-1. Effective MB degradation is obtained over a broad pH range (3.3-9.9). The catalytic mechanism is examined by ultraviolet-visible spectra, quenching test, and electron spin resonance determination. The dominant mechanism of MB degradation is ascribed to the ultrasonic H2O2 activation by Cu-C3N4 for hydroxyl radical generation. Cu-C3N4 has good reusability and is effective to degrade rhodamine B and acid orange 7. This work not only contributes to the field of wastewater treatment, but also provides insights into the synthesis of Fenton-like catalysts. The results manifest that Cu-C3N4 is a promising Fenton-like catalyst for dye degradation in the field of environmental pollution remediation.

Photocatalytic Cr(VI) sequestration and photo‐Fenton bisphenol A decomposition over white light responsive PANI/MIL‐88A(Fe)

Polyaniline (PANI)/MIL‐88A(Fe) (Px@M88) composites were constructed through a simple one‐pot hydrothermal method. The photocatalytic and photo‐Fenton activities of Px@M88 composites toward reduction of Cr(VI) and degradation organic pollutants were explored by white light irradiation. PANI, as a conductive polymer, can improve MIL‐88A(Fe)’s conductivity and the efficiency of photogenerated e−–h+ pair separation. In the presence of H2O2, a photo‐Fenton reaction occured to boost the degradation efficiency of organic pollutants like bisphenol A. In addition, P9@M88 showed excellent recycling and stability in cycling experiments. Finally, a possible reaction mechanism for photocatalytic degradation was proposed and verified by X‐ray photoelectron spectroscopy and electron spin resonance determination and electrochemical characterizations.

S-TiO2/UiO-66-NH2 composite for boosted photocatalytic Cr(VI) reduction and bisphenol A degradation under LED visible light

Series sulfur-doped TiO2/amine-functionalized zirconium metal organic frameworks (S-TiO2/UiO-66-NH2) composites (U1Tx) were facilely fabricated from the as-prepared S-TiO2 and UiO-66-NH2 via ball-milling method. The photocatalytic activities of U1Tx toward Cr(VI) reduction and bisphenol A (BPA) degradation were tested under low-power LED visible light. The results demonstrated that U1T3 exhibited better photocatalytic performances than the pristine S-TiO2 and UiO-66-NH2 due to the improved separation and migration of electrons and holes. Furthermore, the influence factors like pH values and foreign ions on the photocatalytic performances of U1Tx were also investigated. The Box-Behnken design methodology was utilized to further clarify that the inorganic foreign anions and dissolved organic matters could exert significant effects on photocatalytic Cr(VI) reduction performance. As well, the possible pathway of BPA degradation was depicted. After four runs of Cr(VI) removal, it was found that U1T3 exhibited preferable reusability and water stability. The probable reaction mechanism was proposed and verified by active species capture experiments, electron spin resonance determination and electrochemical analyses.

PSL, TL 및 ESR 분석에 의한 감마선 조사 한약재의 검지 특성

The detection characteristics of gamma-irradiated (0~10.0 kGy) medicinal herbs (Platycodon grandiflorum, Acanthopanax chiisanensis) were investigated by photostimulated luminescence (PSL), thermoluminescence (TL), and electron spin resonance (ESR). The results of the PSL, a first screening method in comparison with the TL, showed photon counts greater than 5,000 counts/60 s (positive) in the irradiated samples, while the non-irradiated samples yielded photon counts less than 700 counts/60 s (negative). The TL was also applied for the detection method of irradiated medicinal herbs and showed that the non-irradiated sample revealed a glow curve with a low intensity, while the irradiated samples showed a higher intensity. These results were normalized by re-irradiating the mineral grains with a irradiation dose of 1.0 kGy, and a second glow curve was recorded. The ratio of the intensity of the first glow curve (TL1) to that after the normalization dose (TL2) was determined and compared with the recommended threshold values. TL ratio (TL1/TL2) was below 0.007 for the non-irradiated sample and higher than 0.1 for all irradiated samples (above 1.0 kGy). ESR spectroscopy revealed specific signals (6.065 mT) derived from free radicals in cellulose containing irradiated medicinal herbs. The P. grandiflorum showed clearer signals than A. chiisanensis. From the results of our studies, the PSL, TL, and ESR determinations were found to be suitable for the detection of irradiated medicinal herbs such as P. grandiflorum and A. chiisanensis.

Relevance of Sunscreen Application Method, Visible Light and Sunlight Intensity to Free‐radical Protection: A Study of ex vivo Human Skin

With the continued rise in skin cancers worldwide there is a need for effective skin protection against sunlight damage. It was shown previously that sunscreens, which claimed UVA protection (SPF 20+), provided limited protection against UV-induced ascorbate radicals in human skin. Here the results of an electron spin resonance (ESR) investigation to irradiate ex vivo human skin with solar-simulated light are reported. The ascorbate radical signal in the majority of skin samples was directly proportional to the irradiance over relevant sunlight intensities (0.9-2.9 mW cm(-2)). Radical production (substratum-corneum) by UV (wavelengths < 400 nm) and visible components (> 400 nm) was approximately 67% and 33% respectively. Ascorbate radicals were in steady state concentration at low irradiance (approximately 1 mW cm(-2) equivalent to UK sunlight), but at higher irradiance (approximately 3 mW cm(-2)) decreased with time, suggesting ascorbate depletion. Radical protection by a four star-rated sunscreen (with UVA protection) was optimal when applied as a thin film (40-60% at 2 mg cm(-2)) but less so when rubbed into the skin (37% at 4 mg cm(-2) and no significant protection at 2 mg cm(-2)), possibly due to cream filling crevices, which reduced film thickness. This study validates ESR determinations of the ascorbate radical for quantitative protection measurements. Visible light contribution to radical production, and loss of protection when sunscreen is rubbed into skin, has implications for sunscreen design and use for the prevention of free-radical damage.

Singlet oxygen generation from phosphatidylcholine hydroperoxide in the presence of copper

This study pursued whether singlet oxygen ( 1O 2) is generated from phosphatidylcholine hydroperoxide (PCOOH), the oxidized modification product of a major constituent of biomembranes and serum lipoproteins. The 1O 2 formation was detected, by utilizing the oxidation of 2,2,6,6-tetramethyl-4-piperidone (TMPD) by 1O 2 to yield 2,2,6,6-tetramethyl-4-piperidone-1-oxyl (TEMPONE), which generates electron spin resonance (ESR) signals. The TEMPONE signal was detected in human plasma with addition of PCOOH by ESR determination after introducing copper(II). The TEMPONE formation was proportional to the amounts of PCOOH added according to moles of active oxygen. The TEMPONE signal intensity was weakened significantly in the presence of β-carotene and histidine in a concentration-dependent manner, but was not at all decreased by mannitol, Mn-superoxide dismutase and catalase. In addition, HPLC-chemiluminescence analysis demonstrated that incubation with the PCOOH/Cu(II) combination oxidized cholesterol, a relatively oxidation-resistant component, to the cholesterol hydroperoxide. These results reveal that 1O 2 is generated from PCOOH in contact with copper(II). In conclusion, this in-vitro study provides directly the 1O 2 formation in living organisms following the advancement of peroxidation of constitutive lipids.

DEVELOPMENT OF HIGH-PERFORMANCE HEAVY OIL HYDROCRACK1NG CATALYSTS: CHARACTERIZATION OF ATMOSPHERIC RESIDUE FEED

ABSTRACT The characterization results of the atmospheric residue obtained from Saudi Arabian Light crude oil show the complex nature and composition of this material. The distillation results showed that about 50 percent of Arab Light crude is the atmospheric residue. The elemental analysis of the residue showed that high amount of carbon, sulfur and nitrogen is present along with heavy metals such as nickel and vanadium. The determination of hydrocarbon types by HPLC exhibited that 12% polars and 27% aromatics are present along with 6% asphaltenes. Nuclear magnetic resonance study conducted on the residue and its fraction provides a detailed composition in terms of aliphatic and aromatic nature of the residue and its fractions. The results showed that the residue contains 21% aromatic and 79% aliphatic carbon. The aliphatic carbon is present in saturates and as side chains of aromatic and polar molecules whereas the aromatic carbons are those in the ring structure. Asphaltenes separated from the residue were characterized for their different properties to understand its complexity. The use of electron spin resonance spectroscopy provides determination of the free radicals present in the residue. Asphaltenes were analyzed using the state-of-the-art high temperature high pressure electron spin resonance (ESR) technique in the temperature range 20 to 625 °C and at 30 and 50 bar hydrogen pressure. The ESR determination at 30 bar shows that me pressure was not enough to prevent the boiling of the asphaltene and thus a decrease in the spin concentration was observed beyond 350 °C temperature. The data at 50 bar pressure showed the adequacy of this pressure for ESR measurement. The PMRTA analysis of asphaltene showed a decrease in residual hydrogen with increasing temperature.

Effect of methanol intoxication on free‐radical induced protein oxidation

Oxygen free radicals are generated during methanol-induced liver injury, as was shown for ethanol. The effect of methanol intoxication (6 g kg−1 body wt.) on protein modification in the liver of rats was investigated. Electron spin resonance determination indicated an increase in the free radical signal 6 and 12 h after intoxication. After 7 days of treatment, the contents of malondialdehyde and carbonyl groups in proteins were significantly increased. The level of amino groups and sulphydryl groups and the amount of tryptophan in proteins were decreased, whereas the amount of bi-tyrosine was increased significantly. Changes in protein structure resulted both from free radical action and formaldehyde generation during methanol intoxication. Copyright © 2000 John Wiley & Sons, Ltd.

Possible Role of Caspase-3 Inhibition in Cadmium-Induced Blockage of Apoptosis

Cadmium (Cd) and chromium (Cr) are human carcinogens. Cr(VI) is taken up into cells and reduced by cellular reductants to the potential DNA damaging species Cr(V), (IV), and (III). Reactive oxygen species and carbon-based radicals may also be produced during Cr reduction. We previously found that Cd blocks Cr-induced apoptosis, which could allow a larger proportion of genetically damaged cells to escape and become transformed. This study helped define the mechanisms of Cd-induced suppression of apoptosis. Chinese hamster ovary (CHO K1-BH4) cells were treated with either Cd (5–20 μM), Cr(VI) (350 μM), or Cd (5–20 μM) plus Cr(VI) (350 μM) for 3 h and then cultured in metal-free media for an additional 48 h at which time DNA was extracted or nuclei were examined to determine apoptosis. Cd markedly reduced Cr-induced DNA fragmentation and reduced the number of Cr-induced apoptotic cell nuclei to control levels. Additional study investigated the biokinetics and cellular metabolism of Cr. Cd did not alter the cellular Cr accumulation and there were no differences in the levels of reduced glutathione, a compound possibly important in Cr reduction and reflective of the cellular reducing environment. The antiapoptotic effect of Cd was not due to diminished cellular reduction of Cr(VI) as assessed by electron–spin resonance determination of the levels of Cr(V). Thus, Cd suppression of Cr-induced apoptosis is not based on altered Cr toxicokinetics or metabolism. In addition to Cr, Cd also inhibited apoptosis induced by hygromycin B and actinomycin D. Cd was a very effective inhibitor of caspase-3 activity, a central mediator of apoptosis, with nontoxic levels of Cd resulting in up to ∼60% inhibition. These results indicate that Cd may have a generalized inhibitory effect on apoptosis, possibly by inhibiting caspase-3. Inhibition of apoptosis by Cd may allow a greater portion of genetically damaged cells to survive, or give selective growth advantages, and has implications as a potential nongenotoxic mechanism of Cd carcinogenesis.

Effect of methanol intoxication on free-radical induced protein oxidation.

Oxygen free radicals are generated during methanol-induced liver injury, as was shown for ethanol. The effect of methanol intoxication (6 g kg(-1) body wt.) on protein modification in the liver of rats was investigated. Electron spin resonance determination indicated an increase in the free radical signal 6 and 12 h after intoxication. After 7 days of treatment, the contents of malondialdehyde and carbonyl groups in proteins were significantly increased. The level of amino groups and sulphydryl groups and the amount of tryptophan in proteins were decreased, whereas the amount of bi-tyrosine was increased significantly. Changes in protein structure resulted both from free radical action and formaldehyde generation during methanol intoxication.

Relationship among antioxidant activity, vasodilation capacity, and phenolic content of red wines.

The relationship among antioxidant activity, based on the electron-spin resonance determination of the reduction of Fremy's radical, vasodilation activity, and phenolic content was investigated in 16 red wines. The wines were selected to provide a range of origins, grape varieties, and vinification methods. Sensitive and selective HPLC methods were used for the analysis of the major phenolics in red wine: free and conjugated myricetin, quercetin, kaempferol, and isorhamnetin; (+)-catechin, (-)-epicatechin, gallic acid, p-coumaric acid, caffeic acid, caftaric acid, trans-resveratrol, cis-resveratrol, and trans-resveratrol glucoside. Total anthocyanins were measured using a colorimetric assay. The total phenolic content of the wines was determined according to the Folin-Ciocalteu colorimetric assay and also by the cumulative measurements obtained by HPLC. The 16 wines exhibited a wide range in the values of all parameters investigated. However, the total phenol contents, measured both by HPLC and colorimetrically, correlated very strongly with the antioxidant activity and vasodilation activity. In addition, the antioxidant activity was associated with gallic acid, total resveratrol, and total catechin. In contrast, only the total anthocyanins were correlated with vasodilation activity. The results demonstrate that the different phenolic profiles of wines can produce varying antioxidant and vasodilatant activities, which opens up the possibility that some red wines may provide enhanced health benefits for the consumer.

Novel methods for identification and quantification of the mushroom nephrotoxin orellanine Thin-layer chromatography and electrophoresis screening of mushrooms with electron spin resonance determination of the toxin

Orellanine, (2,2′-bipyridine)3,3′,4,4′-tetrol-1,1′-dioxide, the toxin from several Cortinariaceæ species, induces an acute renal failure which can be very severe or even irreversible and fatal. It is therefore important to be able to quickly and simply identify orellanine in mushroom samples with classical methods, readily available in any laboratory, such as anti-poison centers. This article reports the results of three analytical methods: calssical TLC on cellulose plates in n-butanol-acetic acid-water and two original methods, electrophoresis on agarose gel and direct electron spin resonance (ESR) after enzymatic oxidation. They were applied to detect orellanine in 34 Cortinariaceæ and 4 other species of toadstools. Our three sets of results are convergent. TLC (detection limit: 15 ng with fluorescence densitometry), electrophoresis (25 ng) and even ESR (5 μg), are sensitive enough for our purpose, and a sophisticated method like HPLC (detection limit: 50 pg) is not required. As the ESR spectrum of the toxin semiquinone is highly specific, TLC or electrophoresis coupled with ESR are a convenient alternative to liquid chromatography coupled with mass spectrometry, with the same specificity, for a confirmation or with samples such as ours with high toxin contents. ESR unambiguously confirms the relatively high contents of orellanine, from 0.45% ( C. henrici) to 1.1–1.4% ( C. orellanus), found in five Cortinarius from the subgenus Leprocybe, section Orellani. The five species, though they are from different geographic origins, have a more or less that orellanine semiquinone can be easily detected by ESR directly in the fresh mushroom. The toxin is absent in the other mushrooms we tested, especially in D. cinnamomea and C. splendens, which have been claimed as toxic and suspected to contain orellanine.

Subcellular distribution of a nitroxide spin-labeled netropsin-acridine hybrid in living KB cells: Electron Spin Resonance study

NETGA is an hybrid derivative which possesses an intercalating heterocyclic nucleus related to amsacrine and a minor groove binding squeletton related to netropsin. Cellular uptake of this drug has been studied by Electron Spin Resonance (ESR) spectroscopy using a spin-label derivative of NETGA (SL-NETGA). ESR determination of the kinetics of the drug repartition between the cytoplasm and nucleus showed that NETGA accumulated very rapidly and predominantly in the nucleus. Analysis of the anisotropic ESR spectra recorded in the nuclear compartment are in agreement with a strong binding of the drug to the DNA besides confirmed by a maximum ΔTm of 12°C between the spin-label compound-DNA complex and the DNA alone.

Electron spin resonance determination of the redox state of iron and its relationship to radiation-induced defect centers in oxidized and reduced ZrF 4-based glasses

Electron spin resonance (ESR) studies have been carried out on a series of ZrF 4-based glasses comprising a fixed base glass composition of the ZBLAN type doped with 0, 10, and 100 ppm FeF 3, each melted under three atmospheres: Ar, Ar + O 2, and O 2. The object of this exercise was to develop a free-standing method of quantitative analysis for Fe 3+ in these materials. The accomplishment of this objective required the fabrication of an absolute spin concentration standard consisting of a ZBLAN glass doped with 100 ppm Mn 2+ and exploration of the issue of the ESR “oscillator strength” of Fe 3+ in glasses. Competitive electron and hole trapping by Fe 2+, Fe 3+, and five intrinsic color centers was investigated following γ-irradiation at room temperature and 100-keV X irradiation at 77 K and sequences of isochronal anneals to higher temperatures. The oscillator strength of Fe 3+ in ZBLAN glasses was deduced to be 0.9±0.1 by quantitative comparison of the changes in ESR signal strength of Fe 3+ with the corresponding changes in signal strength of the color centers, which on the basis of elementary considerations were assumed to have oscillator strengths of 1.0. The redox ratio R = [Fe 3+]/[Fe] total was then shown to be 0.63±0.18 in glasses melted under continuous O 2 atmosphere. The uncertainty in R is due principally to difficulties in establishing the proper baseline for numerical integration of the experimental first-derivative spectra; prospects for improving the precision of this measurement are discussed.

Direct electron spin resonance determination of dangling bond energies in rf sputtered hydrogenated amorphous silicon

The energy positions within the gap of the dangling bond levels are deduced from the variations in intensity of the equilibrium electron spin resonance signal as a function of Fermi level positions in undoped and doped rf sputtered hydrogenated amorphous silicon (a-Si:H). The measurements of optically induced spin signals are used to detect any changes in the dangling bond concentration induced by doping. The results place the singly occupied level at 0.05 eV below the middle of the gap, i.e., at 0.95 eV below the conduction band, in agreement with one of the two values proposed for glow discharge a-Si:H and give an effective correlation energy of +0.3 eV.

Doped poly(thiophene): Electron spin resonance determination of the magnetic susceptibility

E.S.R. studies of poly(thiophene) doped with AsF 5 and iodine are reported. At high AsF 5 concentration (∼ 24 mole % AsF 5), we find a temperature-independent Pauli spin susceptibility indicative of a metallic density of states. Measurements on iodine-doped samples in the intermediate regime (below 10 mole % I 3 −) indicate Curie spin concentration independent of the doping level, but significantly larger than in pristine poly(thiophene). The relaxation of these Curie spins is relatively fast (faster by several orders of magnitude with respect to that of pure poly(thiophene)) and temperature dependent. These features are discussed in terms of charge storage in polarons and bipolarons, and the possibility of formation of a finite density of electronic states in the gap.

ChemInform Abstract: ELECTRON SPIN RESONANCE DETERMINATION OF FORMATION CONSTANTS OF COPPER(II) DIPEPTIDE COMPLEXES

Chemischer InformationsdienstVolume 14, Issue 24 Article ChemInform Abstract: ELECTRON SPIN RESONANCE DETERMINATION OF FORMATION CONSTANTS OF COPPER(II) DIPEPTIDE COMPLEXES W. S. KITTL, W. S. KITTLSearch for more papers by this authorB. M. RODE, B. M. RODESearch for more papers by this author W. S. KITTL, W. S. KITTLSearch for more papers by this authorB. M. RODE, B. M. RODESearch for more papers by this author First published: June 14, 1983 https://doi.org/10.1002/chin.198324081AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume14, Issue24June 14, 1983 RelatedInformation

Application of stable radical-containing reagents to the ESR determination of metals

The emergence of complexing reagents whose molecules contain a stable free-radical group affords new opportunities to considerably expand the potential of electron spin resonance (ESR) as an analytical tool. These reagents make ESR determinations of practically every metal possible instead of only those possessing paramagnetic ions. Furthermore, the use of complexing reagents may improve the detection limits characteristic of direct ESR determinations.

Electron spin resonance determination of formation constants of copper(II) dipeptide complexes

Formation constants for complexes between copper(II) and a series of aliphatic dipeptides have been determined by e.s.r. spectroscopy. An iteration method for the evaluation of digitized e.s.r. spectra is introduced. The e.s.r. spectra and formation constants of all copper species obtained by this method are compared with the results of potentiometric titrations; thus the ambiguous formation of the complexes [CuL2H2] and [CuL2]2–(H2L =+H3N–CHR–CO–NH–CHR′–COO–; R,R′= alkyl) could be excluded. The existence of the dimer species [Cu2L2(OH)]– was confirmed. The influence of the side chains on the spectra of all complexes is discussed.