Electron Spin Resonance Signal Intensity Research Articles

An electron paramagnetic resonance time-course study of oxidative stress in the plasma of electronic cigarette exposed rats.

The long-term consequences of electronic cigarette (Ecig) use in humans are not yet known, but it is known that Ecig aerosols contain many toxic compounds of concern. We have recently shown that Ecig exposure impairs middle cerebral artery (MCA) endothelial function and that it takes 3days for MCA reactivity to return to normal. However, the sources contributing to impairment of the endothelium were not investigated. We hypothesized that the increased levels of oxidative stress markers in the blood are correlated with impaired MCA reactivity. We used electron paramagnetic resonance (EPR) spectroscopy to examine plasma from 4-month-old male Sprague-Dawley rats that were exposed to either air (n=5) or 1h Ecig exposure, after which blood samples were collected at varying times after exposure (i.e., 1-4, 24, 48 and 72h postexposure, n=4 or 5 in each time group). The EPR analyses were performed using the redox-sensitive hydroxylamine spin probe 1-hydroxy-3-carboxymethyl-2,2,5,5-tetramethyl-pyrrolidine (CMH) to measure the level of reactive oxidant species in the plasma samples. We found that EPR signal intensity from the CM• radical was significantly increased in plasma at 1-4, 24 and 48h (P<0.05, respectively) and returned to control (air) levels by 72h. When evaluating the EPR results with MCA reactivity, we found a significant negative correlation (Pearson's P=0.0027). These data indicate that impaired cerebrovascular reactivity resulting from vaping is associated with the oxidative stress level (measured by EPR from plasma) and indicate that a single 1h vaping session can negatively influence vascular health for up to 3 days after vaping. HIGHLIGHTS: What is the central question of this study? Does the time course of oxidative stress triggered by electronic cigarette exposure follow the cerebral vascular dysfunction? What is the main finding and its importance? Electron paramagnetic resonance analysis shows that the oxidative stress induced after a single 1h exposure to electronic cigarette aerosol takes ≤72h to return to normal, which mirrors the time course for vascular dysfunction in the middle cerebral artery that we have reported previously.

Distribution of Radiation-Induced Defects in Quartz at the ACKIO Uranium Prospect, Athabasca Basin, Saskatchewan: Tracing Uranium-Bearing Fluids

Abstract Quartz grains from the ACKIO uranium prospect, located near the eastern margin of the Athabasca Basin, Saskatchewan, have been investigated using powder X-band electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of quartz separates from samples systematically collected from the Athabasca Supergroup sandstones and the underlying metamorphosed basement reveal a suite of silicon-vacancy hole centers, which were formed by the bombardment of alpha particles emitted from the radioactive decay of uranium, thorium, and their unstable progeny. The differences in EPR signal intensities of these hole centers indicate that quartz grains received different accumulative doses of alpha particle irradiation in different locations within the ACKIO prospect. For example, quartz extracted from a mineralized sample has the highest EPR signal intensity due to the presence of disseminated uraninite. For quartz sampled at distance from uranium mineralization, the elevated intensities of the silicon-vacancy hole centers most likely indicate a temporary source of radiation, such as ancient uranium-bearing fluids. The median EPR intensities of quartz from the basement rocks at ACKIO are an order of magnitude higher than those of its counterpart from the Athabasca sandstones. Also, the EPR intensities of quartz along the sandstone–basement contact at ACKIO differ by more than two orders of magnitude, suggesting limited migration of uranium-bearing fluids along this contact in the study area. Instead, anomalously high EPR intensities in quartz close to the sandstone–basement contact and elsewhere are restricted to fault gouges and brecciated areas, suggesting that they are the structural pathways for channelized migration of ancient uranium-bearing fluids. A three-dimensional distribution model of the EPR signal intensities has been constructed to define conduits for the migration of ancient uranium-bearing fluids at ACKIO and suggest favorable targets for further exploration. These findings demonstrate the power of EPR spectroscopy in delineating pathways of uranium-bearing fluids and predicting potential mineralization targets.

Thermal stability of the electron spin resonance signal of modern continental barite

The electron spin resonance (ESR) method has been successfully applied to dating hydrothermal barite; however, there have been few studies of modern continental barite, such as that generated by fault movement or in sedimentary deposits. To better understand the geological processes involved in the formation of continental barite, its thermal characteristics and age firstly need to be defined. In this study, one fault barite sample and two sedimentary barite samples were obtained from continental sites in China for ESR signal thermal stability experiments. Microwave-power experiments indicate that 0.5 mW produces the maximum ESR signal intensity and the highest signal-to-noise ratio. Stepwise-heating results reveal that ESR signal intensities remain stable below 100 °C then show an increasing trend that peaks at ∼180 °C, following which they decrease rapidly between 180 and 320 °C and disappear at ∼380 °C. Isothermal heating results show that ESR signal intensities remain stable within a temperature range of 100–200 °C but show a decreasing trend for temperatures of 240–320 °C. These results indicate that the thermal decay of the ESR signal intensity for the three studied continental barites follows second-order decay kinetics. The thermal lifetimes calculated for the three samples are 6.3 × 108, 7.5 × 107, and 8.7 × 106 a, respectively. Thus, barite ESR dating can be used to date related geological events since early Pleistocene.

A pilot study of mitochondrial response to an in vivo prosthetic joint Staphylococcus aureus infection model.

Prosthetic joint infections (PJI) are associated with orthopaedic morbidity and mortality. Mitochondria, the "cell's powerhouses,"are thought to play crucial roles in infection response and in increased risk of sepsis mortality. No current research discusses PJI's effect on mitochondrial function and a lack of understanding of immune-infection interactions potentially hinders patient care. The purpose of this pilot study was to evaluate the impact of simulated PJI on local tissue mitochondrial function. Using an established prosthetic implant-associated in vivo model, tissues were harvested from the surgical limb of a methicillin-sensitive Staphylococcus aureus implant-associated infection group (n = 6) and compared to a noninfected group (n = 6) at postoperative day (POD) 21. Using mitochondrial coupling assays, oxygen consumption rate and extracellular acidification rate were assessed in each group. Electron flow through mitochondrial complexes reflected group activity. Electron Paramagnetic Resonance (EPR) spectrometry measured the oxidizing potential of serum samples from infected versus noninfected groups. On POD21, colony-forming units per gram of tissue showed 5 × 109 in the infected group and 101 in the noninfected group (p < 0.0001). Maximal respiration and oxygen consumption due to adenosine triphosphate synthesis were significantly lower in isolated mitochondria from infected limbs (p = 0.04). Both groups had similar complex I, III, IV, and V activity (p > 0.1). Infected group EPR signal intensity reflecting reactive oxygen species levels was 1.31 ± 0.30 compared to 1.16 ± 0.28 (p = 0.73) in the noninfected group. This study highlights PJI's role in mammalian cell mitochondrial dysfunction and oxidative tissue damage, which can help develop interventions to combat PJI.

Paramagnetic radiation-induced radicals in calcium pyrophosphate polymorphs

Calcium pyrophosphate (Ca2P2O7) is a promising material for biomedical and optical applications; however, relatively little is documented on the radiation-induced point defects of the material. This study reports on the formation, identity, and properties of X-ray-induced radicals in γ-, β-, and α-polymorphs of Ca2P2O7. Complementary thermally stimulated luminescence (TSL), electron paramagnetic resonance (EPR), and solid-state nuclear magnetic resonance (NMR) spectroscopy techniques were combined to reveal the effects of ionising radiation on each polymorph. The high temperature polymorphs β-, and α-Ca2P2O7 exhibited diminishing variety and intensity of EPR signals, whereas the opposite trend was observed in the TSL response. TSL glow curves consisted of multiple peaks in the temperature range of 20–350 °C, with maximum emission intensity located at approximately 600 nm. Multiple electronic spin 1/2 paramagnetic centres were identified on the basis of spin-Hamiltonian parameters determined from EPR spectra simulations. Annealing kinetics of the individual paramagnetic centres were determined to provide an interpretation of the complex nature of TSL glow curves. A decrease of the 31P spin-lattice relaxation T1 times after irradiation was detected for all Ca2P2O7 polymorphs. The results highlight the importance of structure, morphology, and synthesis conditions on the formation of charge traps in Ca2P2O7 and expand the knowledge base on the variety of radiation-induced radicals in phosphate materials.

Photo‐stabilization mechanisms of High‐Density Polyethylene (HDPE) by a commercial few‐layer graphene

AbstractThis work studied few‐layer graphene (FLG) dominant action mechanisms as a photo‐stabilizer. High‐density polyethylene (HDPE) containing 0–0.5 wt% FLG were exposed to UVA radiation in a QUV chamber, according to ASTM G154 for different exposure times, ranging from 0 to 672 h. The chemical, rheological, and mechanical properties were tracked using attenuated total reflection‐Fourier transform infrared (ATR‐FTIR), rheological measurements, and tensile tests. The experimental results showed that the addition of only 0.25 wt% FLG fully stabilized 1‐ to 3‐mm thick HDPE for an exposure time of 672 h. Electron paramagnetic resonance (EPR) test was performed on the UV‐exposed mixture of hydrogen peroxide (H2O2) and the FLG aqueous suspensions (0, 0.2, 1, and 5 mg/mL), to study the FLG performance and mechanisms as a photo‐stabilizer. The results showed that FLG effectively decreased the characteristic EPR signal intensity due to both UV absorption/reflection and free radical scavenging. Fifty‐seven percent of the reduction was found to be due to UV absorption/reflection and 43% due to free radical scavenging. It is demonstrated that UV absorption/reflection and free radical scavenging are the dominant ones among the three FLG photo‐stabilizing mechanisms (UV absorption/reflection, free radical scavenging, and physical barrier to oxygen).Highlights FLG showed potential as a photo‐stabilizer for HDPE. Addition of 0.25 wt% FLG fully stabilized HDPE for 672 h of UVA exposure. FLG demonstrated UV absorption/reflection and free radical scavenging effects.

Low temperature Overhauser effect in silicon doped with As75 in strong magnetic fields

Peculiarities of the Overhauser effect for arsenic atoms in silicon in a strong magnetic field at low temperatures are considered. Dynamic equations describing the change in the electron paramagnetic resonance (EPR) signal at times exceeding the spin relaxation time have been obtained and solved. Under these conditions, the EPR signal intensity dependence on the pumping time is governed by the rate of the nuclear polarization. It is shown that the degree of nuclear polarization can reach significant value even for relatively weak pumping, and the times of establishment of nonequilibrium nuclear polarization differ significantly from the cross-relaxation time.

Thermal annealing of neutron irradiation generated paramagnetic defects in transparent Al2O3 ceramics

It is fundamentally important to understand, control, and predict the effect of irradiation on the structure and optical properties of functional materials. In this work, the thermal stability of fast-neutron induced point defects has been investigated in polycrystalline transparent alumina ceramics. The results of a combined study of electron paramagnetic resonance (EPR) and photoluminescence spectroscopy are presented in this paper. The EPR signals related to different trapped-hole centers as well as electron-type F+ centers have been observed after neutron irradiation. Rapid decay of the total EPR signal intensity occurs after annealing in 600–750 K temperature range. The selective luminescence bands related to the F- and F2-type centers are detected under irradiated corundum ceramics photoexcitation within relevant defect absorption bands (i.e. intracenter excitation/emission).

Identification of radiation processing of different plant foods of Pakistan origin using the rapid technique of Electron Spin Resonance (ESR) spectrometry

Electron Spin Resonance (ESR) spectrometry is a potential technique for detection of irradiated foods like plant foods, which contain cellulosic materials as well as low molecular weight sugars and like the meat and fish, which contain bones. This study is focused on identification of irradiated foods such as tree nuts (pine nuts and walnuts), beans and pulses (red grams, white beans, pinto beans and green peas), and food containing low molecular weight sugars (pan masala and dried dates). The food samples were obtained from Pakistan and exposed to different permissible doses of radiation using electron beam linear accelerator. The control and irradiated samples were kept at room temperature in the laboratory for the record of ESR spectra. For post-irradiation stabilities the food samples were analysed at different intervals of time (15, 90 and 300 days). The controlled samples in case of cellulosic foods showed ESR signal at g0 = 2.004 and irradiated samples were shown with triplet signal indicative of the presence of radiation-induced cellulose radicals. Similarly, in case of Pan Masala and dried dates, a straight signal at zero level was observed for un-irradiated samples and a complex ESR signal was appeared for irradiated samples. The observed radiation-induced signals were dose-dependent and showed an increasing trend with an increase in radiation dose. The comparison of intensities of ESR signals was also carried out along with the study of post-irradiation stabilities of the ESR signals and method proved to be valid for differentiation of controlled and irradiated samples of food.

Conventional and high-field pulsed EPR experimental studies on Bazhenov oil formation under the influence of 50 Hz electromagnetic field

Heavy and extra-heavy oil are generating considerable interest in terms of replacing light oil role in the next few years. Nowadays, various enhanced oil recovery (EOR) methods are under development for an effective exploration and oil refining of unconventional oil sources. Electrical methods are among the most commonly discussed types of EOR techniques. Despite this interest, no one as far as we know has studied the effectiveness and mechanisms of electromagnetic (EM) heating influence on heavy oil conversion. It is common knowledge that heavy oils often contain stable paramagnetic centers, which potentially can serve as at least signaling species to follow the EOR upgrading degree. For the first time, to the best of our knowledge, pulsed and high-frequency (high-field, with 3.4 T detection magnetic field) electron paramagnetic resonance (EPR) techniques were exploited to investigate the EM heating influence on Bazhenov formation heavy oil by subjecting it to 50 Hz (0.75 T) electromagnetic field in laboratory conditions. The obtained samples were analyzed by a set of physico-chemical methods including SARA analysis (S: Saturates, A: Aromatics, R: Resins, A: Asphaltenes), gas chromatography–mass spectrometry (GCMS) in addition to pulsed and conventional (cw) EPR spectroscopy. SARA analysis has shown an increase in the content of asphaltenes from 1.2 ± 0.3 wt% in the initial oil to 1.4 ± 0.4, 1.4 ± 0.3, 1.3 ± 0.2, 1.3 ± 0.5 wt% in the samples obtained at 10, 20, 30 and 40 min respectively. Interestingly, this content has drastically dropped to 0.2 ± 0.05 and 0.3 ± 0.02 wt% in the samples obtained at 50 and 60 min of EM heating. Analogically for resins content change which has firstly increased from 1.5 ± 0.5 wt% in the initial oil to 1.9 ± 0.5, 2.6 ± 0.6, 3.0 ± 0.2, 3.0 ± 0.6 wt% in the samples obtained at 10, 20, 30 and 40 min respectively. Then this content has decreased to 0.5 ± 0.05 and 1.0 ± 0.04 wt% in the samples obtained at 50 and 60 min of EM heating. The content of saturated and aromatic compounds has been found to reach 99.3 ± 0.6 wt% in the sample obtained at 50 min comparing to 97.3 ± 1.1 wt% in the initial oil. Moreover, the GCMS data have showed a significant increase in the content of normal alkanes, which resulted from the processes of oil high molecular compounds fractions conversion as a consequence of alkyl substituents elimination. Our data points towards the idea that the investigated oil sample EPR signal intensity and their spectroscopic characteristics do not change with the EM heating either in the X- or W-band frequencies. g|| and g⊥ were found equal to 2.0024 and 2.0015 respectively at 3357 and 3358 mT for the initial sample and the obtained sample after 60 min of EM heating. Similar results (g||=2.0004 and g⊥=1.9991) were obtained for these samples at 3360 and 3362 mT. The findings of this study can help for better understanding of the mechanisms ruling the impact of electromagnetic heating on enhancing oil recovery.

Photoinduced Electron Transfer in Multicomponent Truxene-Quinoxaline Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) can respond to light in a number of interesting ways. Photochromism is observed when a structural change to the framework is induced by the absorption of light, which results in a color change. In this work, we show that introducing quinoxaline ligands to MUF-7 and MUF-77 (MUF = Massey University Framework) produces photochromic MOFs that change color from yellow to red upon the absorption of 405 nm light. This photochromism is observed only when the quinoxaline units are incorporated into the framework and not for the standalone ligands in the solid state. Electron paramagnetic resonance (EPR) spectroscopy shows that organic radicals form upon irradiation of the MOFs. The EPR signal intensities and longevity depend on the precise structural details of the ligand and framework. The photogenerated radicals are stable for long periods in the dark but can be switched back to the diamagnetic state by exposure to visible light. Single-crystal X-ray diffraction analysis reveals bond length changes upon irradiation that are consistent with electron transfer. The multicomponent nature of these frameworks allows the photochromism to emerge by allowing through-space electron transfer, precisely positioning the framework building blocks, and tolerating functional group modifications to the ligands.

Experimental Study on the Effects of L(+)-Ascorbic Acid Treatment to the ESR Signals of Human Fingernails

The effects of L(+)-ascorbic acid (AA) (an antioxidant commonly known as vitamin C) on the electron spin resonance (ESR) signals from fingernails were examined in relation to X-ray and UV irradiation. The ESR signal intensity, stability, and sensitivity to radiation were measured under different storage conditions. The experimental results indicated that the behavior of the increase in the ESR intensity of the AA samples varied depending on the storage and location conditions, showing sensitivity to light and signal instability at room temperature. It was found that the AA treatment caused a large increase in the peak-to-peak intensities with continuous signal growth with storage time, which may provide an enhancement to the radiation-dependent signal in fingernails. It was also suggested that the use of AA for pre-treatment could sufficiently remove the disturbing signals induced by heat or UV light exposure, which is expected to improve the reliability of radiation dosimetry using fingernails. Further studies with different antioxidant conditions are needed to better characterize the complex changes of the ESR signals from fingernails.

Synthesis, Electron Spin Resonance and Photoluminescence properties of Sm3+ ion doped Zn-Mn nanoferrites synthesized by glycol-thermal method

Nanocrystalline Zn0.5Mn0.5SmxFe2-xO4 (0 ≤ x ≤ 0.05) with average crystallite sizes varying between 12 and 17 nm were synthesized by the glycol-thermal process. X-ray diffraction (XRD) analysis confirmed a single-phase cubic spinel structure in all the compounds. Substituting a smaller Fe3+ ion with a larger rare-earth (RE) Sm3+ ion has affected the distribution of metal ions on tetrahedral (A) and octahedral (B) sites. In this work, a comprehensive study has been carried out on nanocrystalline particles of RE Sm3+ ion doped into Zn-Mn ferrite to estimate intrinsic strain through Williamson-Hall (W–H) analysis. The results were compared with those obtained from the Debye Scherrer equation. Tensile microstrain within the nanocrystals were detected from W-H plots for x = 0, 0.01,0.02 and 0,05 samples, while compressive microstrain was observed for x = 0.02 and 0.05 samples. A scanning electron microscope (SEM) has been used to study the morphology of nanoparticles and it revealed spherical-shaped nanoparticles. Energy dispersive X-rays (EDX) confirmed the phase purity and the elemental composition with no impurity elements were observed. Crystallite sizes affect electron spin resonance (ESR) signal intensity and the line width. The g-values fluctuated ranging from 2.31 to 2.51 due to fluctuating crystallite sizes. Photoluminescence (PL) displayed a blue-violet emission with maxima centred at 418 nm and 438 nm under the excitation wavelength of 320 nm. The electron spin resonance and photoluminescence results show that the Sm doped Zn-Mn ferrites are promising candidates for applications in blue LEDs.

An EPR study of gamma irradiated mixed materials based on sucrose for dosimetric purposes

Since the recent past it was known that sucrose showed some good results as dosimeter using Electron Paramagnetic Resonance (EPR) technique. However there is still considerable interest in improving its accuracy and precision as well as in developing new systems with improved characteristics. In view of this fact, materials consisting of mixture at two different ratios (70:30 and 50:50%) between sucrose and ascorbic acid, sucrose and cysteine and sucrose and diphenylamine were studied by EPR spectroscopy. The obtained new materials were irradiated by γ-rays having doses varying from 0.5 up to 20 kGy. Before irradiation no EPR spectra were recorded. After irradiation complex EPR spectra with dominants of the sucrose spectrum in them were observed. The influence of the instrumental settings on the EPR signal intensity was reported. It was found out that the dose response of sucrose has linear dependence up to 20 kGy. The dose response of the new materials is compared with those in case of sucrose. The results showed that the addition of ascorbic acid, cysteine and diphenylamine to sucrose were leading to decrease in its sensitivity, but the EPR dose response remains unchanged. It was supposed that the decrease in the sensitivity was probably due to the antiradical activity of the added substances. To check this assumption the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity (FRSA) of the used substances was studied. It was concluded that these mixed materials can be used for dosimetric purposes, however they have lower sensitivity compared to sucrose.

Identification of NV Centers in Synthetic Fluorescent Nanodiamonds and Control of Defectiveness of Crystallites Using Electron Paramagnetic Resonance

A 100 nm synthetic diamond particle with a large (&gt; 4 ppm) amount of nitrogen vacancy (NV) centers has been studied. The latter exhibit lines associated with forbidden Delta m_s = 2 and allowed Delta m_s = 1 transitions in the electron paramagnetic resonance (EPR) spectra of the ground state of the NV(-) center. The luminescence intensity of particles in the range 550-800 nm increases with an increase in the irradiation dose of 5 MeV electrons and correlates with the integrated intensity of the peak EPR line with a g-factor g = 4.27. This value is used to estimate the concentration of NV(-) centers and to select diamond powders with the highest fluorescence intensity. The dependence of the EPR signal intensity of the Delta m_s = 2 transition of the NV(-) center on the microwave power that increases before decaying rather well characterizes the crystal quality of the local environment of the centers under study in these particles. The intensity of the x, y Delta m_s = 1 transition (at ~ 281.2 mT, 9.444 GHz) turns out to be sensitive to changes in particle size in the submicron range and the appearance of near-surface defects obtained during mechanical processing. Keywords: luminescence, nitrogen vacancy centers, synthetic diamond, nanocrystals, electron paramagnetic resonance.

Идентификация NV-центров в синтетических флуоресцентных наноалмазах и контроль дефектности кристаллитов методом электронного парамагнитного резонанса

A 100 nm synthetic diamond particle with a large (&gt; 4 ppm) amount of nitrogen vacancy (NV) centers has been studied. The latter exhibit lines associated with forbidden Delta m_s = 2 and allowed Delta m_s = 1 transitions in the electron paramagnetic resonance (EPR) spectra of the ground state of the NV(-) center. The luminescence intensity of particles in the range 550-800 nm increases with an increase in the irradiation dose of 5 MeV electrons and correlates with the integrated intensity of the EPR line with a g-factor g = 4.27.This value is used to estimate the concentration of NV(-) centers and to select diamond powders with the highest fluorescence intensity. The dependence of the EPR signal intensity of the Delta m_s = 2 transition of the NV(-) center on the microwave power has the form of a curve with saturation and subsequent decay, and rather well characterizes the crystal quality of the local environment of the centers under study in these particles. The intensity of the x,y Delta m_s = 1 transition (at ~281.2 mT, 9.444 GHz) turns out to be more sensitive to changes in particle size in the submicron range and the appearance of near-surface defects obtained during mechanical processing.

Identification of NV Centers in Synthetic Fluorescent Nanodiamonds and Control of Defectiveness of Crystallites Using Electron Paramagnetic Resonance

A 100 nm synthetic diamond particle with a large (&gt; 4 ppm) amount of nitrogen vacancy (NV) centers has been studied. The latter exhibit lines associated with forbidden Delta m_s = 2 and allowed Delta m_s = 1 transitions in the electron paramagnetic resonance (EPR) spectra of the ground state of the NV(-) center. The luminescence intensity of particles in the range 550-800 nm increases with an increase in the irradiation dose of 5 MeV electrons and correlates with the integrated intensity of the EPR line with a g-factor g = 4.27. This value is used to estimate the concentration of NV(-) centers and to select diamond powders with the highest fluorescence intensity. The dependence of the EPR signal intensity of the Delta m_s = 2 transition of the NV(-) center on the microwave power has the form of a curve with saturation and subsequent decay, and rather well characterizes the crystal quality of the local environment of the centers under study in these particles. The intensity of the x, y Delta m_s = 1 transition (at ~ 281.2 mT, 9.444 GHz) turns out to be more sensitive to changes in particle size in the submicron range and the appearance of near-surface defects obtained during mechanical processing. Keywords: luminescence, nitrogen vacancy centers, synthetic diamond, nanocrystals, electron paramagnetic resonance.

Relationship between tectonism and desertification inferred from provenance and lithofacies changes in the Cenozoic terrestrial sequence of the southwestern Tarim Basin

The modern-day Tarim Basin is covered almost entirely by the Taklimakan sand desert and is one of the most arid regions in the world. Unraveling the aridification history of the desert is important for understanding global climate changes during the Cenozoic, yet the timing and mechanisms driving its formation remain controversial. One of the leading hypotheses is that the uplift of the Pamir, located to the west of the Tarim Basin, blocked the intrusion of moist air and induced the aridification in the Tarim Basin. In this study, we explore the linkage between the uplift of the Pamir and the desertification in the Tarim Basin from the late Eocene to the middle Miocene in the Aertashi section, which is located at the southwestern edge of the Tarim Basin and offers the longest sedimentary record with a reliable age model. Provenance changes in fluvial deposits along the Aertashi section were examined using electron spin resonance (ESR) signal intensity and crystallinity index (CI) of quartz in the sand fraction of fluvial sandstones and clast counting based on the identification of clast types by thin section observation to identify timings of tectonic events in the Pamir, from which clastic materials were supplied to the Aertashi section by rivers. Our results suggest that major provenance changes in the drainage of the paleo-Yarkand river delivering clasts to the Aertashi section occurred at ca. 27, 20, and 15 Ma. These timings are mostly consistent with those observed in previous provenance studies in the Aertashi section and probably reflect tectonic events in the Pamir. On the other hand, according to the previous studies, the first occurrence of sand dune deposits indicates that the Tarim Basin was relatively arid after ca. 34 Ma. Hence, our result does not support the hypothesis that the initial aridification in the Tarim Basin was triggered by the uplift of the Pamir and the resultant blocking of moisture supply from the Paratethys Sea, although the subsequent intensification of tectonic events at ca. 27 Ma in the Pamir might have caused aridification indicated by the initiation of loess deposition.

Identifying the chloroperoxyl radical in acidified sodium chlorite solution.

The present study identified the active radical species in acidic sodium chlorite and investigated the feasibility of quantifying these species with the diethylphenylenediamine (DPD) method. Electron spin resonance (ESR) spectroscopy was used to identify the active species generated in solutions containing sodium chlorite (NaClO2). The ESR signal was directly observed in an acidified sodium chlorite (ASC) aqueous solution at room temperature. This ESR signal was very long-lived, indicating that the radical was thermodynamically stable. The ESR parameters of this signal did not coincide with previously reported values of the chlorine radical (Cl●) or chlorine dioxide radical (O = Cl●-O and O = Cl-O●). We refer to this signal as being from the chloroperoxyl radical (Cl-O-O●). Quantum chemical calculations revealed that the optimal structure of the chloroperoxyl radical is much more thermodynamically stable than that of the chlorine dioxide radical. The UV-visible spectrum of the chloroperoxyl radical showed maximum absorbance at 354 nm. This absorbance had a linear relationship with the chloroperoxyl radical ESR signal intensity. Quantifying the free chlorine concentration by the DPD method also revealed a linear relationship with the maximum absorbance at 354 nm, which in turn showed a linear relationship with the chloroperoxyl radical ESR signal intensity. These linear relationships suggest that the DPD method can quantify chloroperoxyl radicals, which this study considers to be the active species in ASC aqueous solution.

Gamma radiation effects on quartz Al and Ti center electron spin resonance signal intensity: Implications for quartz provenance discrimination

Abstract Quartz is one of the most common rock-forming minerals and crystallizes over a wide range of temperature and pressure conditions. This diversity of quartz crystallization environments is reflected by trace-element compositional variations, which can be used to distinguish between different source sediments. Trace elements that are incorporated into the quartz lattice form corresponding paramagnetic centers (impurity centers, such as Al and Ti centers), which can be detected using the electron spin resonance (ESR) method. However, whether the quartz impurity center ESR signal intensity (quartz ESR-SI) can be used for quartz sediment provenance tracing remains uncertain. In the present study, five present-day (modern) fluvial sediments from the Songhua, Yellow, Yangtze, Huai, and Pearl rivers in China and eight ancient fluvial sand lenses from the Yichang Gravel Layer (YGL) located in the middle Yangtze River were sampled for major- and trace-element determinations by ICP-OES and ICP-MS for the purpose of provenance discrimination. A total of 1404 ESR spectra were also collected to evaluate the effect of γ-ray dose (varying from 50 to 50 000 Gy) on quartz ESR-SI to establish the relationship between quartz element contents and quartz ESR-SIs and thereby to assess the potential utility of quartz ESR-SI for sediment provenance analysis. Results indicate that: (1) quartz collected from the different studied locations can be distinguished by element contents; (2) the quartz Al center ESR-SI increases with increasing γ-ray dose from 50 to 50 000 Gy; (3) the quartz Ti center ESR-SI increases within a γ-ray dose of 10 000 Gy and decreases beyond 10 000 Gy; (4) quartz Al and Ti center ESR-SIs are closely related to the contents of Al and Ti in quartz; and (5) a plot of quartz Ti center ESR-SI vs. Al center ESR-SI using data for a γ-ray dose range of 4000–7000 Gy is the best indicator of fluvial sediment provenance using the ESR method.