Electron Paramagnetic Resonance Signal Research Articles

Solvent Controlled Generation of Spin Active Polarons in Two-Dimensional Material under UV Light Irradiation.

Polarons belong to a class of extensively studied quasiparticles that have found applications spanning diverse fields, including charge transport, colossal magnetoresistance, thermoelectricity, (multi)ferroism, optoelectronics, and photovoltaics. It is notable, though, that their interaction with the local environment has been overlooked so far. We report an unexpected phenomenon of the solvent-induced generation of polaronic spin active states in a two-dimensional (2D) material fluorographene under UV light. Furthermore, we present compelling evidence of the solvent-specific nature of this phenomenon. The generation of spin-active states is robust in acetone, moderate in benzene, and absent in cyclohexane. Continuous wave X-band electron paramagnetic resonance (EPR) spectroscopy experiments revealed a massive increase in the EPR signal for fluorographene dispersed in acetone under UV-light irradiation, while the system did not show any significant signal under dark conditions and without the solvent. The patterns appeared due to the generation of transient magnetic photoexcited states of polaronic character, which encompassed the net 1/2 spin moment detectable by EPR. Advanced ab initio calculations disclosed that polarons are plausibly formed at radical sites in fluorographene which interact strongly with acetone molecules in their vicinity. Additionally, we present a comprehensive scenario for multiplication of polaronic spin active species, highlighting the pivotal role of the photoinduced charge transfer from the solvent to the electrophilic radical centers in fluorographene. We believe that the solvent-tunable polaron formation with the use of UV light and an easily accessible 2D nanomaterial opens up a wide range of future applications, ranging from molecular sensing to magneto-optical devices.

Electron paramagnetic resonance and luminescence spectroscopy of transition metal ion impurities and X-ray-induced radicals in brushite

Calcium phosphates hold paramount importance as the constituents of hard tissue of living organisms. Among them, brushite (CaHPO4·2H2O), also known as dicalcium phosphate dihydrate (DCPD), is a common precursor in phosphate synthesis and is becoming increasingly appealing as a biomaterial for bone regeneration applications. This study presents a comparative analysis of structural, morphological, thermal, and spectroscopic properties of synthetic brushite prepared by the wet precipitation method with several brushite products available from commercial vendors. Electron paramagnetic resonance (EPR) spectroscopy revealed that Mn2+ and Fe3+ ions are common trace impurities in commercial products. Following exposure to X-rays, EPR signals of several phosphorous-related radicals emerge. The annealing of the irradiated samples gives rise to broad thermally stimulated luminescence (TSL) signals in the 40-120 °C range, which correlates with the annealing kinetics of the radicals. The stability of radiation-induced EPR and TSL signals is limited by the phase transformation temperature from brushite to monetite (CaHPO4). The results of this study provide novel insights into the formation and stability of phosphorous-related radicals and demonstrate how minuscule amounts of impurity ions can strongly influence the spectroscopic properties of brushite.

Sulfite activation by non-thermal plasma coupled with Fe2+ for ibuprofen degradation: In-depth insight into activation energy barrier and mechanism

This paper underscores the pivotal role of Fe2+ in influencing the degradation of ibuprofen (IBP) within non-thermal plasma (NTP) activated sulfite (S) system. At 200 μM Fe2+ dosage, the rate of IBP degradation can attain 94.8 %. In contrast to the absence of Fe2+, there was a 43.1 % increase in the rate of IBP degradation. The quenching experiment indicates that SO4·− and ·OH constitute the principal species in the system. This phenomenon predominantly stems from the Fenton-like reaction, expediting the conversion of H2O2 to ·OH. Additionally, the activation of sulfite by the Fe2+ and NTP promotes a concurrent increase in SO4·−. The introduction of Fe2+ results in the detection of a substantial quantity of ·OH and SO4·− in the system, validated through direct detection and electron spin resonance (ESR) signals. According to the density functional theory (DFT), the energy barrier of NTP/Fe2+ activation sulfite is lower than that of NTP system activation. By comparing the specific degradation pathways of NTP/S/Fe2+ and NTP/S systems, it can be concluded that the degradation of pollutants in NTP/S/Fe2+ system mainly depends on the action of active free radicals (·OH and SO4·−), while that in NTP/S system is mainly due to non-free radicals.

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.

Gamma Irradiation Effect on Polymeric Chains of Epoxy Adhesive.

The study of materials for space exploration is one of the most interesting targets of international space agencies. An essential tool for realizing light junctions is epoxy adhesive (EA), which provides an elastic and robust material with a complex mesh of polymeric chains and crosslinks. In this work, a study of the structural and chemical modification of a commercial two-part flexible EA (3M™ Scotch-Weld™ EC-2216 B/A Gray), induced by 60Co gamma radiation, is presented. Combining different spectroscopic techniques, such as the spectroscopic Fourier transform infrared spectroscopy (FTIR), the THz time-domain spectroscopy (TDS), and the electron paramagnetic resonance (EPR), a characterization of the EA response in different regions of the electromagnetic spectrum is performed, providing valuable information about the structural and chemical properties of the polymers before and after irradiation. A simultaneous dissociation of polymeric chain and crosslinking formation is observed.The polymer is not subject to structural modification at an absorbed dose of 10 kGy, in which only transient free radicals are observed. Differently, between 100 and 500 kGy, a gradual chemical degradation of the samples is observed together with a broad and long-living EPR signal appearance. This study also provides a microscopic characterization of the material useful for the mechanism evaluation of system degradation.

Stability of Iodine Species Trapped in Titanium-Based MOFs: MIL-125 and MIL-125_NH2.

Two titanium-based MOFs MIL-125 and MIL-125_NH2 are synthesized and characterized using high-temperature powder X-ray diffraction (PXRD), thermogravimetric analysis(TGA), N2 sorption, Fourier transformed infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet-visible spectroscopy (UV-Vis), and electron paramagnetic resonance (EPR). Stable up to 300°C, both compounds exhibited similar specific surface areas (SSA) values (1207 and 1099m2g-1 for MIL-125 and MIL-125_NH2, respectively). EPR signals of Ti3+ are observed in both, whith MIL-125_NH2 also showing ─NH2 ●+ signatures. Both MOFs efficiently adsorbed iodine in continuous gas flow over five days, with MIL-125 trapping 1.9g.g-1 and MIL-125_NH2 trapping 1.6g.g-1. MIL-125_NH2 exhibited faster adsorption kinetics due to its smaller band gap (2.5 against 3.6eV). In situ Raman spectroscopy conducted during iodine adsorption revealed signal evolution from "free" I2 to "perturbed" I2, and I3 -. TGA and in situ Raman desorption experiments showed that ─NH2 groups improved the stabilization of I3 - due to an electrostatic interaction with NH2 ●+BDC radicals. The Albery model indicated longer lifetimes for iodine desorption in I2@MIL-125_NH2, attributed to a rate-limiting step due to stronger interaction between the anionic iodine species and the ─NH2 ●+ radicals. This study underscores how MOFs with efficient charge separation and hole-stabilizer functional groups enhance iodine stability at higher temperatures.

ESR and optical investigation of tetragonal PbTiO3 nanoparticles embedded in lithium tetraborate glass matrix

Glass-nanocomposites (GNCs) samples of composition [(100−x) Li2B4O7–xPbTiO3] with x = 5, 10, 15 and 20 mol% were prepared by melt quenching method. The two phases of the GNCs samples, a glassy phase and PbTiO3 nanoparticles/clusters phase, can be seen in the energy dispersive X-ray spectra and scanning electron microscopic micrographs. Fourier transformation infrared spectra of the GNCs samples exhibited bands due to triangular with NBO’s and tetrahedral borate groups. Additionally, the Ti4+ ions exist in both TiO4 and TiO6 structural units while the Ti3+ ions exist in TiO6 structural units. The electron spin resonance (ESR) spectra of the GNCs samples exhibit two ESR signals, broad and narrow, corresponding to the Ti3+ (3d1) ions in both tetragonal deformed octahedral and in the other structural configuration, respectively. The optical transmission spectra of the GNCs samples exhibited three transmission bands, 3Γ5 → 2Γ3, 2B2g → 2B1g and 2B2g → 2A1g transitions, in the visible region. The variation in optical band gap (Eopt) with increasing PbTiO3 content were due to the conversion between BO3 with NBOs and BO4 units as well as the reduction of Ti4+ to Ti3+ ions in the GNCs matrix. These results demonstrate that the present GNCs may be used for practical applications such as optical devices.

Superoxide Radicals in Uranyl Peroxide Solids: Lasting Signatures Identified by Electron Paramagnetic Resonance Spectroscopy

AbstractU(VI) peroxide phases (studtite and meta‐studtite) are found throughout the nuclear fuel cycle and exist as corrosion products in high radiation fields. Peroxides are part of a family of reactive oxygen species (ROS) that include hydroperoxyl and superoxide species and are produced during alpha radiolysis of water. While U(VI) peroxides have been thoroughly investigated, the incorporation and stability of ROS species within studtite have not been validated. In the current study, electron paramagnetic resonance (EPR) spectroscopy was used to identify the presence of free radicals within a series of U(VI) peroxide samples containing depleted, highly enriched, and natural uranium. Density functional theory calculations indicated that the predicted EPR signals matched well with a superoxide (O2−⋅) species incorporated into the studtite structure, confirming the presence of ROS in the material. Further analysis of samples that were synthesized between 1945 and 2023 indicated that there is a correlation between the radical signal and the product of specific activity multiplied by age of the sample.

Superoxide Radicals in Uranyl Peroxide Solids: Lasting Signatures Identified by Electron Paramagnetic Resonance Spectroscopy.

U(VI) peroxide phases (studtite and meta-studtite) are found throughout the nuclear fuel cycle and exist as corrosion products in high radiation fields. Peroxides are part of a family of reactive oxygen species (ROS) that include hydroperoxyl and superoxide species and are produced during alpha radiolysis of water. While U(VI) peroxides have been thoroughly investigated, the incorporation and stability of ROS species within studtite have not been validated. In the current study, electron paramagnetic resonance (EPR) spectroscopy was used to identify the presence of free radicals within a series of U(VI) peroxide samples containing depleted, highly enriched, and natural uranium. Density functional theory calculations indicated that the predicted EPR signals matched well with a superoxide (O2 -⋅) species incorporated into the studtite structure, confirming the presence of ROS in the material. Further analysis of samples that were synthesized between 1945 and 2023 indicated that there is a correlation between the radical signal and the product of specific activity multiplied by age of the sample.

Radiation-Induced Defects in Uranyl Trinitrate Solids.

Actinides are inherently radioactive; thus, ionizing radiation is emitted by these elements can have profound effects on its surrounding chemical environment through the formation of free radical species. While previous work has noted that the presence of free radicals in the system impacts the redox state of the actinides, there is little atomistic understanding of how these metal cations interact with free radicals. Herein, we explore the effects of radiation (UV and γ) on three U(VI) trinitrate complexes, M[UO2(NO3)3] (where M = K+, Rb+, Cs+), and their respective nitrate salts in the solid state via electron paramagnetic resonance (EPR) and Raman spectroscopy paired with Density Functional Theory (DFT) methods. We find that the alkali salts form nitrate radicals under UV and γ irradiation, but also note the presence of additional degradation products. M[UO2(NO3)3] solids also form nitrate radicals and additional DFT calculations indicate the species corresponds to a change from the bidentate bound nitrate anion into a monodentate NO3• radical. Computational studies also highlight the need to include the second sphere coordination environment around the [UO2(NO3)3]0,1 species to gain agreement between the experimental and predicted EPR signatures.

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.

Electron paramagnetic resonance as a tool to determine the sodium charge storage mechanism of hard carbon

Hard carbon is a promising negative electrode material for rechargeable sodium-ion batteries due to the ready availability of their precursors and high reversible charge storage. The reaction mechanisms that drive the sodiation properties in hard carbons and subsequent electrochemical performance are strictly linked to the characteristic slope and plateau regions observed in the voltage profile of these materials. This work shows that electron paramagnetic resonance (EPR) spectroscopy is a powerful and fast diagnostic tool to predict the extent of the charge stored in the slope and plateau regions during galvanostatic tests in hard carbon materials. EPR lineshape simulation and temperature-dependent measurements help to separate the nature of the spins in mechanochemically modified hard carbon materials synthesised at different temperatures. This proves relationships between structure modification and electrochemical signatures in the galvanostatic curves to obtain information on their sodium storage mechanism. Furthermore, through ex situ EPR studies we study the evolution of these EPR signals at different states of charge to further elucidate the storage mechanisms in these carbons. Finally, we discuss the interrelationship between EPR spectroscopy data of the hard carbon samples studied and their corresponding charging storage mechanism.

Identifying the plateau sodium storage behavior of hard carbon through the spin state

Hard carbon has emerged as a promising anode material for rechargeable sodium-ion batteries, owing to its abundant precursor sources and remarkable reversible charge storage capacity. The key to achieving an extended sodium storage capacity lies in the plateau capacity largely associated with the closed-pore structure, yet a comprehensive understanding in this area remains incomplete. In our study, we utilized electron paramagnetic resonance (EPR) spectra to discern the spin state of unpaired electrons within hard carbon materials, enabling the identification of sodium storage plateau regions. Hard carbon anodes with plateau capacity predominantly exhibit delocalized spins, evident in the EPR spectrum by limited spin density and a linewidth exceeding 100 G. These spins originate from the extended aromatic structure within small-sized but curved nano-graphite and the closed-pore walls, which are crucial for plateau capacity. Conversely, hard carbon anodes exclusively possessing slope capacity are characterized by localized spins, presenting a typical narrow and intense Lorentzian EPR signal. These localized spins arise from the edge defects of the nano-graphite structure, serving as favourable sites for sodium adsorption. Our development of a methodology to discern hard carbon plateau capacity behavior based on EPR spectra presents a facile and rapid approach for advancing high-performance hard carbon materials.

Estimating the initial absorbed dose of radiation in dried figs using EPR spectroscopy

Dried figs were studied by Electron Paramagnetic Resonance (EPR) spectroscopy for identification of radiation treatment and dosage assessment. Gamma-irradiated samples show a multicomponent "sugar-like" EPR spectrum with line width of 6–8 mT, centered at g = 2.004. The investigation of the influence of the instrumental parameters microwave power and modulation amplitude on the EPR signal show saturation effect at microwave power above 2 mW and over modulation at modulation amplitude above 0.4 mT. Determination of the stability of radiation induced signals shows, that identification of previous radiation treatment is possible for a long time period after irradiation even more than one year. Dose-response curves of gamma-irradiated samples exhibits a linear response up to about 4 kGy and the saturation of the EPR signal at higher doses. A Single Aliquot Additive dosing method used to estimate the initial absorbed dose in irradiated dried fig flesh shows initial dose 0.25 kGy for the sample irradiated by 5 kGy and 3.7 kGy for those irradiated using 10 kGy. Taking into account the signal decay after 150 days of storage, the dose defined as initial should be 4.65 kGy for the 5 kGy irradiated sample and 8 kGy for that irradiated using 10 kGy.

Coordination complexes of reduced organic dye isoviolanthrone with transition metals and lanthanides [Mn(II), Dy(III), Gd(III), Nd(III)

The reduction of a vat dye isoviolanthrone to the dianion state in the presence of metal-containing compounds yields binuclear coordination complexes. Two manganese(II) acetylacetonate units coordinate to isoviolanthrone2− (L) in {(K+)cryptand}2{[MnII(acac)2]2⋅L}2– (1) with an average Mn–O bond length of 2.022(2) Å. Dysprosium(III)- or gadolinium(III)-2,2,6,6-tetramethyl-3,5-heptanedionate (TMHD) units form {(K+)cryptand}2{[MIII(TMHD)3]2⋅L}2− (M = DyIII for 2 and GdIII for 3) with the length of the M−O bonds of 2.193(3) and 2.254(4) Å, respectively. Tris(cyclopentadienyl)neodymium(III) forms {(Cs+)cryptand}2{[Cp3NdIII]2⋅L}2–⋅C6H4Cl2 (4) with the Nd–O bonds of 2.264(2) and 2.308(2) Å length. The formation of isoviolanthrone2− is supported by their optical spectra, disappearance of the bands of the CO vibrations in the IR-spectra as well as elongation of the CO bonds in 1–4. High-spin (S = 5/2) MnII atoms in 1 have exchange interaction of J = − 0.122 cm−1 at g = 1.98. Lanthanides have weaker coupling through isoviolanthrone2− in 2 and 3 with J = − 0.029 and D = − 0.004 cm−1 for DyIII and J = 0.0019 cm−1 for GdIII. Complex 4 with two Cp3NdIII species demonstrates the χMT value of 2.33 emu⋅K/mol at 300 K, and this value is lower than the theoretically calculated value of 3.39 emu⋅K/mol. The decrease of χMT is observed in the whole 300–1.9 K range providing negative Weiss temperatures of –32 K. That is explained by magnetic behavior of Cp3NdIII similar to pristine Cp3NdIII. Complexes comprising MnII, GdIII, and NdIII show electron paramagnetic resonance (EPR) signals. Zero-field splitting (ZFS) is observed from MnII and GdIII allowing the estimation of zero-field splitting parameter D as − 0.047 and E close to 0 cm−1 for 1 and − 0.033 and − 0.020 cm−1 for 3. Complex 4 with NdIII manifests an asymmetric two-component EPR signal without ZFS. Weak antiferromagnetic couplings are explained by diamagnetism of isoviolanthrone2− and rather long distances between the metal centers of 15.47–16.25 Å. This study shows that the dianions of organic dyes are promising bidentate ligands for preparation of coordination complexes with d- and f-block metal ions.

Thermoluminescence (TL) and electron paramagnetic resonance (EPR) of dumortierite sensitized by heat treatments

The present study presents the effect of heat treatment on TL and EPR of dumortierite. It was found that applying a heat treatment at 1200 °C for 1h, followed by slow cooling to room temperature, is optimal for improving its TL sensitivity. The glow curves of the sensitized dumortierite sample show TL emission bands centered at 350, 475, and 580 nm. The kinetic parameters of the TL peaks were obtained using the Tm-Tstop and deconvolution methods. In addition, sensitized dumortierite exhibits a linear response with γ-radiation dose and low fading in its TL response. Studies using the technique of EPR were carried out to investigate the defect center EPR signals observed after γ-irradiation. A single defect center with an axially symmetric g-tensor was observed with principal values g∥ = 2.0009 and g⊥ = 2.0017. The center was attributed to an F+ center and appears to correlate with the TL peak at 200 °C.

EPR studies of ferredoxin in spinach and cyanobacterial thylakoids related to photosystem I-driven NADP+ reduction.

Photosynthetic light-dependent reactions occur in thylakoid membranes where embedded proteins capture light energy and convert it to chemical energy in the form of ATP and NADPH for use in carbon fixation. One of these integral membrane proteins is Photosystem I (PSI). PSI catalyzes light-driven transmembrane electron transfer from plastocyanin (Pc) to oxidized ferredoxin (Fd). Electrons from reduced Fd are used by the enzyme ferredoxin-NADP+ reductase (FNR) for the reduction of NADP+ to NADPH. Fd and Pc are both small soluble proteins whereas the larger FNR enzyme is associated with the membrane. To investigate electron shuttling between these diffusible and embedded proteins, thylakoid photoreduction of NADP+ was studied. As isolated, both spinach and cyanobacterial thylakoids generate NADPH upon illumination without extraneous addition of Fd. These findings indicate that isolated thylakoids either (i) retain a "pool" of Fd which diffuses between PSI and membrane bound FNR or (ii) that a fraction of PSI is associated with Fd, with the membrane environment facilitating PSI-Fd-FNR interactions which enable multiple turnovers of the complex with a single Fd. To explore the functional association of Fd with PSI in thylakoids, electron paramagnetic resonance (EPR) spectroscopic methodologies were developed to distinguish the signals for the reduced Fe-S clusters of PSI and Fd. Temperature-dependent EPR studies show that the EPR signals of the terminal [4Fe-4S] cluster of PSI can be distinguished from the [2Fe-2S] cluster of Fd at > 30K. At 50K, the cw X-band EPR spectra of cyanobacterial and spinach thylakoids reduced with dithionite exhibit EPR signals of a [2Fe-2S] cluster with g-values gx = 2.05, gy = 1.96, and gz = 1.89, confirming that Fd is present in thylakoid preparations capable of NADP+ photoreduction. Quantitation of the EPR signals of P700+ and dithionite reduced Fd reveal that Fd is present at a ratio of ~ 1 Fd per PSI monomer in both spinach and cyanobacterial thylakoids. Light-driven electron transfer from PSI to Fd in thylakoids confirms Fd is functionally associated (< 0.4 Fd/PSI) with the acceptor end of PSI in isolated cyanobacterial thylakoids. These EPR experiments provide a benchmark for future spectroscopic characterization of Fd interactions involved in multistep relay of electrons following PSI charge separation in the context of photosynthetic thylakoid microenvironments.

4f/5d Hybridization Induced Single-Electron Delocalization in an Azide-Bridged Dicerium Complex.

Dilanthanide complexes with one-electron delocalization are important targets for understanding the specific 4f/5d-bonding feature in lanthanide chemistry. Here, we report an isolable azide-bridged dicerium complex 3 [{(TrapenTMS)Ce}2(μ-N3)]• [Trapen = tris (2-aminobenzyl)amine; TMS = SiMe3], which is synthesized by the reaction of tripodal ligand-supported (TrapenTMS)CeIVCl complex 2 with NaN3. The structure and bonding nature of 3 are fully characterized by X-ray crystal diffraction analysis, electron paramagnetic resonance (EPR), magnetic measurement, cyclic voltammetry, X-ray absorption spectroscopy, and quantum-theoretical studies. Complex 3 presents a trans-bent central Ce-N3-Ce unit with a single electron of two mixed-valent Ce atoms. The unique low-temperature (2 K) anisotropic EPR signals [g = 1.135, 2.003, and 3.034] of 3 indicate that its spin density is distributed on the central Ce-N3-Ce unit with marked electron delocalization. Quantum chemical analyses show strong 4f/5d orbital mixing in the singly occupied molecular orbital of 3, which allows for the unpaired electron to extend throughout the cerium-azide-cerium unit via a multicentered one-electron (Ce-N3-Ce) interaction. This work extends the family of mixed-valent dilanthanide complexes and provides a paradigm for understanding the bonding motif of ligand-bridged dilanthanide complexes.

Date fruit melanin is primarily based on (−)-epicatechin proanthocyanidin oligomers

Plant-based melanin seems to be abundant, but it did not receive scientific attention despite its importance in plant biology and medicinal applications, e.g. photoprotection, radical scavenging, antimicrobial properties, etc. Date fruit melanin (DM) has complex, graphene-like, polymeric structure that needs characterization to understand its molecular properties and potential applications. This study provides the first investigation of the possible molecular composition of DM. High performance size-exclusion chromatography (HPSEC) suggested that DM contains oligomeric structures (569–3236 Da) and transmission electron microscopy (TEM) showed agglomeration of these structures in granules of low total porosity (10–1000 Å). Nuclear magnetic resonance (NMR) spectroscopy provided evidence for the presence of oligomeric proanthocyanidins and electron paramagnetic resonance (EPR) spectroscopy revealed a g-factor in the range 2.0034–2.005. Density functional theory (DFT) calculations suggested that the EPR signals can be associated with oligomeric proanthocyanidin structures having 4 and above molecular units of (−)-epicatechin. The discovery of edible melanin in date fruits and its characterization are expected to open a new area of research on its significance to nutritional and sensory characteristics of plant-based foods.

Towards liquid EPR dosimetry using nitroxides in aqueous solution.

Objective. Water-equivalent dosimeters are desirable for dosimetry in radiotherapy. The present work investigates basic characteristics of novel aqueous detector materials and presents a signal loss approach for electron paramagnetic resonance (EPR) dosimetry.Approach. The proposed principle is based on the radiation dose dependent annihilation of EPR active nitroxides (NO·) in aqueous solutions. Stable nitroxide radicals (3-Maleimido-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (MmP), 3-Carbamoyl-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (CmP)) in aqueous solutions containing dimethyl sulfoxide (DMSO) as an additive were filled in glass capillaries for irradiation and EPR readout. Radiation doses ranging from 1 to 64 Gy were applied with a clinical 6 MV flattening filter free photon beam. EPR readout was then performed with a X-band benchtop spectrometer. The dose response, temporal stability and reproducibility of the samples' EPR signal amplitudes as well as the influence of the nitroxide concentration between 10 and 160μM on the absolute signal loss were investigated using MmP. CmP was used to examine the dependence of the dose response on DMSO concentration between 0 and 10 vol%. An indirect effect model was fitted to the experimental data assuming irradiation induced radical reactions as the underlying mechanism.Main results. For an initial MmP concentration of 20μM, absolute EPR signal loss is linear up to a dose of 16 Gy with a yield G(-NO·) of approximately 0.4μmol J-1. Within five weeks upon sample irradiation to doses between 0 and 32 Gy relative EPR signal fluctuations were on average (126 readouts) below 1% (1σ). For c(MmP) ≥ 20μM, absolute signal loss is only weakly dependent on c(MmP), whereas it increases strongly with increasing c(DMSO) in the range 0-5 vol%. An indirect effect model is applicable to describe the reaction mechanism resulting in the observed dose response curve.Significance. Liquids consisting of nitroxides in aqueous solution and small amounts of DMSO (2 vol%) show promising basic characteristics for application as water-equivalent EPR dosimeter materials in radiotherapy. The EPR signal loss is based on an indirect effect mediated by diffusing radicals originating from the radiolysis of the water/DMSO mixture.