The identification of reactive radical species using quenching and electron paramagnetic resonance (EPR) tests has attracted extensive attention, but some mistakes or misinterpretations are often ...present in recent literature. This review aims to clarify the corresponding issues through surveying literature, including the uncertainty about the identity of radicals in the bulk solution or adsorbed on the catalyst surface in quenching tests, selection of proper scavengers, data explanation for incomplete inhibition, the inconsistent results between quenching and EPR tests (e.g., SO4•− is predominant in quenching test while the signal of •OH predominates in EPR test), and the incorrect identification of EPR signals (e.g., SO4•− is identified by indiscernible or incorrect signals). In addition, this review outlines the transformation of radicals for better tracing the origin of radicals. It is anticipated that this review can help in avoiding mistakes while investigating catalytic oxidative mechanism with quenching and EPR tests.
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•The determination methods for detecting reactive radical species are summarized.•The uncertainty about the identity of radicals in quenching tests is proposed.•The misinterpretations over the radical identification in EPR tests are reviewed.•The transformation and interconversion of radicals are concluded.
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•An approach to predict the optimal Hubbard Ueff value used in DFT+U is proposed.•Optimize the Ueff for Li2MnO3 by comparing these calculated Fermi-contact shifts.•Finding optimal ...Ueff helps calculate SS-NMR parameters and material properties.
The isotropic chemical shifts can be calculated by hybrid functionals, which costs lots of computational resources. To save time, DFT+U could be employed to calculate the isotropic chemical shifts. However, the calculated properties are very sensitive to the Hubbard correction value Ueff. Here the double Fermi-contact-shift verification approach with DFT+U method is proposed with much higher computational efficiency, that is, concurrently calculate the Fermi-contact shifts on two nuclei (6Li and 17O) to predict the optimal Ueff. The optimal Ueff is also helpful to the quadrupolar coupling constant CQ, g-factor, band structure and density of states.
Cancer causes the second-highest rate of death world-wide. A major shortcoming inherent in most of anticancer drugs is their lack of tumor selectivity. Nanodrugs for cancer therapy administered ...intravenously escape renal clearance, are unable to penetrate through tight endothelial junctions of normal blood vessels and remain at a high level in plasma. Over time, the concentration of nanodrugs builds up in tumors due to the EPR effect, reaching several times higher than that of plasma due to the lack of lymphatic drainage. This review will address in detail the progress and prospects of tumor-targeting via EPR effect for cancer therapy.
In this study, a new perovskite Sr9Y2W4O24:Mn4+ is presented and its photoluminescence properties are examined in conjunction with electron paramagnetic resonance (EPR) analysis for comparison. ...Sol-gel synthesis resulted in a series of samples, that were characterized in detail using X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FT-IR), diffuse reflectance spectrum (DRS), photoluminescence spectra (PL) and EPR. XRD patterns are consistent with standard data, affirming the tetragonal crystal arrangement of the synthesized samples. The band gap estimation based on DRS indicated a value of 5 eV. PL emission analysis identified a far-red emission peak (2Eg→4A2) at 677 nm, confirms the presence of Mn in the 4+ ionic state in the inorganic matrix. Crystal field analysis also demonstrated the presence of Mn4+ in a strong crystal field environment. Additionally, EPR analysis revealed distinct features of the observed broad line with a width of approximately 400 G and a six-line spectrum with g ∼1.98 characteristic of the Mn4+ doped Sr9Y2W4O24 perovskite. The prevailing evidence strongly suggests the likelihood of Mn4+ dopant ions occupying W6+ sites within the perovskite lattice. The EPR experimental data also confirmed the simulation data indicating the presence of Mn4+ ions in a given inorganic matrix. This investigation provides a comprehensive insight into the structural and spectroscopic properties of Mn4+ doped Sr9Y2W4O24 perovskites, confirming their potential as advanced lighting technologies to facilitate enhanced agricultural practices and plant cultivation.
Non‐thermal atmospheric pressure plasma has attracted considerable attention in recent years due to its potential for biomedical applications. Determining the mechanism of the formation of reactive ...species in liquid treated with plasma is thus of paramount importance for both fundamental and applied research. In this work, the origin of reactive species in plasma‐treated aqueous solutions was investigated by using spin‐trapping, hydrogen and oxygen isotopic labelling and electron paramagnetic resonance (EPR) spectroscopy. The species originating from molecules in the liquid phase and those introduced with the feed gas were differentiated by EPR and 1H NMR analysis of liquid samples. The effects of water vapour and oxygen admixtures in the feed gas were investigated. All the reactive species detected in the liquid samples were shown to be formed largely in the plasma gas phase. It is suggested that hydrogen peroxide (determined by UV/Vis analysis) is formed primarily in the plasma tube, whereas the radical species ⋅OOH, ⋅OH and ⋅H are proposed to originate from the region between the plasma nozzle and the liquid sample.
Cool plasma! The source of reactive oxygen species induced by non‐thermal plasma in water has been investigated by UV, EPR and 1H NMR spectroscopy and MS in conjunction with the use of isotopically labelled water. The main regions in which species are formed are identified (see picture). An understanding of the fundamental properties of plasma is of paramount importance in applied biomedical plasma research.
Deposition of Aβ aggregates in the form of amyloid fibrils is a pathological hallmark of Alzheimer's disease. Understanding the structure and dynamics of Aβ fibrils is important for delineating the ...mechanism of Aβ aggregation and developing effective therapeutic strategies. Here we used site-directed spin labeling and EPR spectroscopy to study the Aβ40 fibril structure and dynamics. We obtained the EPR spectra of 40 spin-labeled Aβ40 fibril samples, with spin labeling coverage of the entire Aβ40 sequence. Analysis of the spin exchange interaction and spin label mobility using spectral simulations suggest that the strength of spin exchange interaction is primarily determined by static disorder in the Aβ40 fibrils. EPR data suggest that the entire Aβ40 sequence except residue D1 is highly ordered and the two hydrophobic regions at residues 17–20 and 31–36 show the lowest static disorder. Dynamic disorder is relatively constant across all reside positions, with residues 22 and 23 having the highest dynamic disorder. Comparison of the EPR data for Aβ40 and Aβ42 fibrils shows overall more ordered packing interactions in Aβ40 fibrils. Another noteworthy difference is the C-terminal residue, which has high static disorder in Aβ42 fibrils, but is ordered in Aβ40 fibrils. The higher static disorder in Aβ42 fibrils may lead to increased fragmentation, monomer dissociation, and structural defects, which may contribute to increased aggregation through secondary nucleation.
•We obtained EPR data of 40 Aβ40 fibril samples, covering all residue positions.•EPR data show relatively constant dynamic disorder across Aβ40 sequence.•Residues 22 and 23 have the highest dynamic disorder.•Static disorder shows high sequence-dependent variability.•Aβ42, with a disordered C-terminus, has higher static disorder than Aβ40 fibrils.
Nitrate is a pervasive aquatic contaminant of global environmental concern. In nature, the most effective nitrate reduction reaction (NRR) is catalyzed by nitrate reductase enzymes at neutral pH, ...using a highly‐conserved Mo center ligated mainly by oxo and thiolate groups. Mo‐based NRR catalysts mostly function in organic solvents with a low water stability. Recently, an oxo‐containing molybdenum sulfide nanoparticle that serves as an NRR catalyst at neutral pH was first reported. Herein, in a nanoparticle‐catalyzed NRR system a pentavalent MoV(=O)S4 species, an enzyme mimetic, served as an active intermediate for the NRR. Potentiometric titration analysis revealed that a redox synergy among MoV−S, S radicals, and MoV(=O)S4 likely play a key role in stabilizing MoV(=O)S4, showing the importance of secondary interactions in facilitating NRR. The first identification and characterization of an oxo‐ and thiolate‐ligated Mo intermediates pave the way to the molecular design of efficient enzyme mimetic NRR catalysts in aqueous solution.
In neutral: The nitrate reduction reaction (NRR) is essential for water remediation. In an artificial NRR catalyst, an enzyme mimetic intermediate has been identified for the first time in the activation of the NRR at neutral pH. The newly identified intermediate is stable in neutral water, and the secondary electronic interactions were found to play a key role.
Heat-triggered drug release from temperature-sensitive nanocarriers upon the application of mild hyperthermia is a promising approach to achieve site-specific delivery of drugs. The combination of ...mild hyperthermia (41-42 °C) and temperature-sensitive liposomes (TSL) that undergo lipid phase-transition and drug release has been studied extensively and has shown promising therapeutic outcome in a variety of animal tumor models as well as initial indications of success in humans. Sensitization of liposomes to mild hyperthermia by means of exploiting the thermal behavior of temperature-sensitive polymers (TSP) provides novel opportunities. Recently, TSP-modified liposomes (TSPL) have shown potential for enhancing tumor-directed drug delivery, either by triggered drug release or by triggered cell interactions in response to heat. In this review, we describe different classes of TSPL, and analyze and discuss the mechanisms and kinetics of content release from TSPL in response to local heating. In addition, the impact of lipid composition, polymer and copolymer characteristics, serum components and PEGylation on the mechanism of content release and TSPL performance is addressed. This is done from the perspective of rationally designing TSPL, with the overall goal of conceiving efficient strategies to increase the efficacy of TSPL plus hyperthermia to improve the outcome of targeted anticancer therapy.
Abstract
Fibrous nanosilica (KCC‐1) oxynitrides are promising solid‐base catalysts. Paradoxically, when their nitrogen content increases, their catalytic activity decreases. This counterintuitive ...observation is explained here for the first time using
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N‐solid‐state NMR spectroscopy enhanced by dynamic nuclear polarization.
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•Photolysis of oxime ester compound was studied by time-resolved and pulsed EPR.•Spin polarized Iminyl and benzoyloxy radicals were initially generated.•Decarboxylation rate of ...benzoyloxy in various solvents were measured by pulsed EPR.•Dehydrogenated solvent radicals were observed after the photolysis.•Addition rate of dehydrogenated cyclohexane radical with olefins were determined.
To generate spin-polarized free radicals, the photolysis of 1,2-octane-dione, 1-4-(phenylthio)-2-(o-benzoyloxime) (OXE01) was investigated using time-resolved electron paramagnetic resonance (TR-EPR) and pulsed EPR. This photolysis proceeds through α-cleavage of the N-O bond of OXE01 to yield iminyl and benzoyloxy radicals, the latter of which is converted to a phenyl radical by decarboxylation. The phenyl radical promptly abstracts hydrogen atoms from the surrounding solvent molecules to produce a solvent dehydrogenated radical (solvent radical). The spin polarization created in the initial OXE01 triplet excited state was preserved during these series of reactions, which enhanced EPR sensitivity. This enabled us to observe the TR-EPR spectra of the intermediate free radicals, except phenyl. The decarboxylation rate of the benzoyloxy radical was measured in various solvents by probing the free induction decay signal of the product solvent radicals using pulsed EPR. This new method for preparing free radicals with spin-polarization was applied to determine the addition reaction rate constants of the cyclohexyl radical, a solvent radical, to olefins using pulsed EPR monitoring of the electron spin echo signals of the radical.
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