Organic Free Radicals Research Articles

The synergistic effect of peracetic acid and nitrogen doped biochar prepared at pyrolysis temperature of 1000°C on tetracycline degradation: Performance and mechanism

N doped biochar NBC1000 was prepared at a pyrolysis temperature of 1000 ℃. 33.57 % of the total C coexisted with N in heterocycles, and over 90 % of N existed in the form of graphite N and pyridine N, indicating that replacing C in aromatic rings is the main way of N doping. Up to 60.2 % of graphite N in the total N reflected a high degree of graphitization. N doping lead to a decrease in O content (from 17.82 % to 11.13 %) and O-containing groups (carbonyl and carboxyl), causing PFR to transition from an oxygen-adjacent C centred type (g=2.0034) to C centred type (g=2.0021) and the latter has stronger catalytic ability. The above characteristics driven by high temperature and nitrogen doping are the reasons why NBC1000 has high electron transfer ability and thus induces the formation of ∙O2−. The NBC1000/peracetic acid (PAA) system can degraded tetracycline (TC), tetracycline hydrochloride (TCH), and methyl orange (MO) completely and the presence of anions like Cl−，SO42− and NO3− did not affect the degradation of TC. TC has been degraded in the NBC1000/PAA system through the mixed pathways of free radical and non radical dominated by ∙O2− and 1O2. In terms of the formation mechanism of ∙O2−, the transfer of electrons to dissolved oxygen through the electron shuttle action of NBC1000 is considered the key pathway. However, the organic anion (RO−) formed by the dissociation of PAA under weak alkalinity is the effective electron donor that promoted the substantial formation of ∙O2−. In addition，RO− provide electrons to the biochar while also forming organic free radicals RO∙. That's why optimal TC degradation was exhibited under weakly alkaline conditions. Besides, three possible pathways for TC degradation are proposed.

Free radical mechanisms of ammonium sulfate as intensively used industrial materials on suppressing organic pollutants

Organic free radicals are critical intermediates for the generation and inhibition of organic pollutants during industrial processes. Clarifying the free radical mechanism of pollutant inhibition is significant for their efficient control. Ammonium sulfate is intensively used in industrial materials to suppress organic pollutants. In this study, organic free radical intermediate species in metal-catalyzed reactions inhibited by ammonium sulfate were identified using continuous-wave electron paramagnetic resonance (EPR) spectroscopy, providing direct evidence for the free radical mechanisms of organic pollutants inhibition. The transverse (T2) and longitudinal (T1) relaxation time variations catalyzed by different metal catalysts in the presence of ammonium sulfate were compared using pulsed-wave EPR. Consequently, after the addition of ammonium sulfate, the observed increase in T2 suggests that ammonium sulfate leads to radical concentration reduction. A decrease in the T1 relaxation time suggests the enhanced interaction between organic radicals and metals, which is an obstacle to subsequent radical reactions. Therefore, ammonium sulfate dominantly changed the free radical intermediates species, concentrations, and their reactivity, and then inhibited the organic pollutants formations. The inhibition mechanisms of ammonium sulfate on metal-catalyzed pollutants were then proposed combining EPR analysis, X-ray characterization, and high-resolution mass spectrometry screening. As a result, (1) occupying the active sites of metal catalysis and (2) inhibiting free radical intermediates are the two main intrinsic inhibition mechanisms of ammonium sulfate. The findings provide new perspectives on the efficient inhibition of organic pollutants in industrial processes involving various metal catalysts.

Insight into the inhibition mechanisms of Ca-, N-, S-containing compounds on persistent organic pollutant formation from the thermal reaction of anthracene on copper chloride

Four inhibitors (CaO, CaS, CH4N2S, and (NH4)2SO4) were employed to inhibit the formation of multiple unintentional persistent organic pollutants (POPs) and environmentally persistent free radicals (EPFRs) using anthracene as a precursor, with CuCl2 serving as both a transition metal catalyst and chlorine source. The inhibition mechanisms were elucidated in terms of chlorine immobilization, catalyst deactivation, and free radical regulation. The inhibition efficiency of the four inhibitors on polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polychlorinated naphthalenes (PCNs) ranged from 64.7 % to 98.4 %, with the corresponding inhibition rates on toxic equivalency quantity ranging from 86.3 % to 99.7 %. The distribution of homologs shifted towards less chlorinated species, indicating effective suppression of chlorination. Calcium- and nitrogen-containing compounds consumed chlorine sources by forming CaCl2, CaClOH, and NH4Cl, while sulfur-containing compounds deactivated catalysts by forming CuSO4. EPFRs derived from anthracene were identified as carbon-centered anthracene-type and anthraquinone-type radicals. Positive correlations were observed between POPs and EPFRs concentrations, suggesting the pivotal role of organic free radicals as intermediates in POPs formation. Anthraquinones derived from anthracene underwent decomposition, recombination and chlorination, leading to the formation of PCDD/Fs and PCBs. The addition of inhibitors reduced EPFRs concentrations by 74.2–95.1 %. Sulfur- and nitrogen-containing inhibitors generated radicals that attacked POPs precursors and intermediates, forming heteroatomic compounds and inhibiting POPs formation. These findings enhanced the understanding of the source control mechanisms of POPs and provided theoretical and technical support for the synergistic inhibition of POPs and EPFRs in industrial thermal processes.

Environmentally persistent free radicals and other paramagnetic species in wildland-urban interface fire ashes

Wildland-urban interface (WUI) fires consume fuels, such as vegetation and structural materials, leaving behind ash composed primarily of pyrogenic carbon and metal oxides. However, there is currently limited understanding of the role of WUI fire ash from different sources as a source of paramagnetic species such as environmentally persistent free radicals (EPFRs) and transition metals in the environment. Electron paramagnetic resonance (EPR) was used to detect and quantify paramagnetic species, including organic persistent free radicals and transition metal spins, in fifty-three fire ash and soil samples collected following the North Complex Fire and the Sonoma-Lake-Napa Unit (LNU) Lightning Complex Fire, California, 2020. High concentrations of organic EPFRs (e.g., 1.4 × 1014 to 1.9 × 1017 spins g−1) were detected in the studied WUI fire ash along with other paramagnetic species such as iron and manganese oxides, as well as Fe3+ and Mn2+ ions. The mean concentrations of EPFRs in various ash types decreased following the order: vegetation ash (1.1 × 1017 ± 1.1 × 1017 spins g−1) > structural ash (1.6 × 1016 ± 3.7 × 1016 spins g−1) > vehicle ash (6.4 × 1015 ± 8.6 × 1015 spins g−1) > soil (3.2 × 1015 ± 3.7 × 1015 spins g−1). The mean concentrations of EPFRs decreased with increased combustion completeness indicated by ash color; black (1.1 × 1017 ± 1.1 × 1017 spins g−1) > white (2.5 × 1016 ± 4.4 × 1016 spins g−1) > gray (1.8 × 1016 ± 2.4 × 1016 spins g−1). In contrast, the relative amounts of reduced Mn2+ ions increased with increased combustion completeness. Thus, WUI fire ash is an important global source of EPFRs and reduced metal species (e.g., Mn2+). Further research is needed to underpin the formation, transformation, and environmental and human health impacts of these paramagnetic species in light of the projected increased frequency, size, and severity of WUI fires.

Dynamic stereomutation of vinylcyclopropanes with metalloradicals

The ever increasing demands for greater sustainability and lower energy usage in chemical processes call for fundamentally new approaches and reactivity principles. In this context, the pronounced prevalence of odd-oxidation states in less precious metals bears untapped potential for fundamentally distinct reactivity modes via metalloradical catalysis1–3. Contrary to the well-established reactivity paradigm that organic free radicals, upon addition to a vinylcyclopropane, lead to rapid ring opening under strain release—a transformation that serves widely as a mechanistic probe (radical clock)4 for the intermediacy of radicals5—we herein show that a metal-based radical, that is, a Ni(I) metalloradical, triggers reversible cis/trans isomerization instead of opening. The isomerization proceeds under chiral inversion and, depending on the substitution pattern, occurs at room temperature in less than 5 min, requiring solely the addition of the non-precious catalyst. Our combined computational and experimental mechanistic studies support metalloradical catalysis as origin of this profound reactivity, rationalize the observed stereoinversion and reveal key reactivity features of the process, including its reversibility. These insights enabled the iterative thermodynamic enrichment of enantiopure cis/trans mixtures towards a single diastereomer through multiple Ni(I) catalysis rounds and also extensions to divinylcyclopropanes, which constitute strategic motifs in natural product- and total syntheses6. While the trans-isomer usually requires heating at approximately 200 °C to trigger thermal isomerization under racemization to cis-divinylcyclopropane, which then undergoes facile Cope-type rearrangement, the analogous contra-thermodynamic process is herein shown to proceed under Ni(I) metalloradical catalysis under mild conditions without any loss of stereochemical integrity, enabling a mild and stereochemically pure access to seven-membered rings, fused ring systems and spirocycles.

Mechanistic Insights into the Copper‐Catalyzed Cross‐Dehydrogenative Allylic Alkynylation Reaction

AbstractAllylic functionalization reactions are an important tool for constructing many organic compounds, as they allow for the insertion of the versatile allyl group. Numerous catalytic processes have been developed, primarily utilizing noble metals such as palladium and pre‐functionalized substrates. Conversely, the copper‐catalyzed oxidative C−H derivatization route, whether thermal or photocatalyzed, remains relatively underdeveloped. This is mostly due to the lack of a general concept and corresponding mechanistic understanding. Here we present a comprehensive analysis of the mechanism of this transformation. We utilized a range of spectroscopic techniques, including UV‐Vis, NMR, and EPR, single crystal x‐ray diffraction, as well as cyclovoltammetry, and DFT calculations. We propose that there are no free organic radicals involved in this cross‐dehydrogenative coupling, and that the reaction pathway is analogous to the well‐known Karash‐Sosnovsky reaction.

Coupling organic free-radical molecules to lumped-element superconducting resonators

A promising route toward the realization of a molecular spin quantum processor relies on coupling magnetic molecules to individual photons confined within superconducting resonators. As a simple approximation to such a hybrid scheme, here we explore the conditions that determine the collective coupling of DPPH organic free radicals to lumped-element LC superconducting resonators. In these chips, multiple resonators are coupled to a single readout line. This enables designing the relevant resonator properties, such as resonance frequency, cavity volume, and impedance while keeping a perfect transmission for the device. Here, we exploit these design possibilities to achieve a coherent spin-photon coupling regime. Besides, we study how this coupling depends on the relative orientation of the external dc magnetic field concerning the photon magnetic field and the spins locations concerning the chip surface.

Radicals as Chiral Catalysts for Asymmetric Radical Cyclization Reactions

AbstractDue to the innate highly reactive properties and short life‐time, organic free radicals can often serve as promoters or intermediates to engage in various radical transformations, which are often otherwise difficult to access by ionic pathway‐based mechanisms. With the evolvement of radical chemistry, chiral radical catalyzed‐transformations have recently emerged as an attractive and robust platform for synthesis of chiral molecules of interest. Herein, we highlight several creative and strategic advances in chiral radical catalyst design, cyclization reaction achievements, and future challenges. Key ScientistsIn the 1980s, some pioneering studies by Feldman and Oshima revealed that the thiyl radical could catalyze cyclization of vinylcyclopropane with alkenes, providing access to racemic cyclopentanes. In 1996, Brian P. Roberts reported an interesting enantioselective hydrosilylation of prochiral alkenes by using thioglucose‐derived chiral thiyl radical catalysts. Since then, chiral radical catalysis has become an emerging and promising catalytic strategy in organic synthesis. However, this field has not been extensively explored further until the Maruoka group in 2014 achieved the asymmetric C—C bond formation by employing a newly designed indanol core‐based chiral thiyl radical catalyst. In this protocol, an enantioselective radical cyclization of vinylcyclopropanes with electron‐rich alkenes was developed. In 2020, Chen and Xiao disclosed a nitrogen radical‐catalyzed version of this reaction. Later, this strategy was further expanded to metalloradical catalyzed asymmetric radical cascade cyclization reactions by Zhang in 2021. Later on, Wang, Fu and Zhang et al. described a novel class of boryl radical‐catalyzed asymmetric radical cycloisomerization reactions, further showcasing enormous synthetic potential of chiral radical catalysis. This Emerging Topic has focused on asymmetric radical cyclization reactions involving diverse chiral radical catalysts.

Chlorination mechanism of benzene series in aqueous system under the combined action of Cl- and multiple free radicals

In this study, non-targeted analysis revealed that the Fe2+/perodisulfate/Cl- system degraded aniline (AN) and nitrobenzene (NB), yielding 7 types and 4 types of aromatic chlorides, respectively. In order to explore their chlorination mechanism and the influence of different functional groups, various reactions (radical adduct formation (RAF), hydrogen atom abstraction (HAA) and single electron transfer (SET)) of benzene series with various functional group with sulfate radical (SO4·-), hydroxyl radical (·OH), chlorine radical (·Cl) and dichloride anion radicals (Cl2·-) were explored by Gibbs free energy (ΔG), and the subsequent reactions of SET and HAA products (organic free radical) were innovatively explored by ΔG. This study revealed that the reaction between benzene compounds containing electron-donating groups and ·Cl was dominated by HAA rather than RAF; the reaction between benzene compounds containing electron-withdrawing groups and ·Cl was dominated by RAF. Aromatic compounds containing electron-donating groups can undergo SET reaction and generate aromatic chlorides in the presence of O2 and Cl-. Combined with the product analysis, it was found that the HAA reaction of aromatic compounds will lead to the obvious formation of biphenyl compounds and aromatic chlorides in the presence of Cl-. Compared with the conditions of RAF of ·Cl and chlorination of SET products, the chlorination reaction between HAA products and Cl- is ubiquitous, which is more likely to be the key to the formation of aromatic chlorides in mixed systems. This study provides a theoretical basis for further study on the formation risk of chlorinated products in advanced oxidation process.

Boryl Radical as a Catalyst in Enabling Intra- and Intermolecular Cascade Radical Cyclization Reactions: Construction of Polycyclic Molecules.

Cascade radical cyclization constitutes an atom- and step-economic route for rapid assembly of polycyclic molecular skeletons. Although an array of redox-active metal catalysts has recently shown robust applications in enabling various catalytic cascade radical processes, the use of free organic radical as the catalyst, which is capable of triggering strategically distinct cascades, has rarely been developed. Here, we disclosed that the benzimidazolium-based N-heterocyclic carbene (NHC)-boryl radical is capable of catalyzing cascade cyclization reactions in both intra- and intermolecular pathways, assembling [5,5] fused bicyclic and [6,6,6] fused tricyclic molecules, respectively. The catalytic reactions start with the chemo- and regioselective addition of the boryl radical catalyst to a tethered alkene or alkyne moiety, followed by either an intramolecular formal [3+2] or an intermolecular [2+2+2] cycloaddition process to construct bicyclo[3.3.0]octane or tetrahydrophenanthridine skeletons, respectively. Eventually, a β-elimination occurs to release the boryl radical catalyst, completing a catalytic cycle. High to excellent diastereoselectivity is achieved in both catalytic reactions under substrate control.

Boryl Radical as a Catalyst in Enabling Intra‐ and Intermolecular Cascade Radical Cyclization Reactions: Construction of Polycyclic Molecules

AbstractCascade radical cyclization constitutes an atom‐ and step‐economic route for rapid assembly of polycyclic molecular skeletons. Although an array of redox‐active metal catalysts has recently shown robust applications in enabling various catalytic cascade radical processes, the use of free organic radical as the catalyst, which is capable of triggering strategically distinct cascades, has rarely been developed. Here, we disclosed that the benzimidazolium‐based N‐heterocyclic carbene (NHC)‐boryl radical is capable of catalyzing cascade cyclization reactions in both intra‐ and intermolecular pathways, assembling [5,5] fused bicyclic and [6,6,6] fused tricyclic molecules, respectively. The catalytic reactions start with the chemo‐ and regioselective addition of the boryl radical catalyst to a tethered alkene or alkyne moiety, followed by either an intramolecular formal [3+2] or an intermolecular [2+2+2] cycloaddition process to construct bicyclo[3.3.0]octane or tetrahydrophenanthridine skeletons, respectively. Eventually, a β‐elimination occurs to release the boryl radical catalyst, completing a catalytic cycle. High to excellent diastereoselectivity is achieved in both catalytic reactions under substrate control.

The aggregation behaviors of organic radicals in polar fluorinated arenes

AbstractPolar fluorinated arenes can promote organic free radical reactions, which have attracted scientists’ interest in recent years. However, it is still unknown how these solvents interact weakly with organic radical molecules to influence their reactivity. In this study, we investigated how organic free radicals aggregate in five polar fluorocarbon solvents, and demonstrated that different substituents can influence their aggregation behaviors. In these solvents, small organic radicals with simple substituents maintain a homogeneous solution; however, radicals with substituents that form intermolecular hydrogen bonds or with long‐chain aliphatic hydrocarbons tend to aggregate in them, whereas substituents of long‐chain aliphatic hydrocarbons tend to promote aggregation better. The critical aggregation concentrations of these aggregates are measured by concentration‐dependent UV–visible spectroscopy. Their topological morphologies are all spherical based on TEM. The compactness and rotational motivation speed of radical molecules within these aggregates are determined by EPR spectroscopy. The particle sizes of these aggregates are determined by analyzing their cyclic voltammograms. Most excitingly, electrochemical experiments reveal that the aggregation behaviors of free radical molecules with intermolecular hydrogen bonds can significantly increase their catalytic rate for electro‐oxidizing benzyl alcohol in such a solvent. The results of this study indicate that in polar fluorinated arenes organic radical molecules’ aggregation behaviors are related to their structures. This may provide guidelines for regulating organic radical reactivity in these solvents in the future.

Synthesis of novel p-aminophenyl derivates of DPPH free radical

2,2-Diphenyl-1-picrylhydrazyl (DPPH) is an intensely coloured organic stable free radical with paramagnetic and redox properties. In this work we present three new derivatives of DPPH, in which an amino substituent was designed for one of the p-phenyl position. The synthetic details and the structural characterizations of the compounds are shown.

Activation of peroxymonosulfate with natural pyrite-biochar composite for sulfamethoxazole degradation in soil: Organic matter effects and free radical conversion

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) represent an effective method for the remediation of antibiotic-contaminated soils. In this study, a natural pyrite-biochar composite material (FBCx) was developed, demonstrating superior activation performance and achieving a 76% removal rate of SMX from soil within 120 min. There existed different degradation mechanisms for SMX in aqueous and soil solutions, respectively. The production of 1O2 and inherent active species produced by soil slurry played an important role in the degradation process. The combination of electron paramagnetic resonance (EPR) and free radical probe experiments confirmed the presence of free radical transformation processes in soil. Wherein, the·OH and SO4·− generated in soil slurry did not directly involve in the degradation process, but rather preferentially reacted with soil organic matter (SOM) to form alkyl-like radicals (R·), thereby maintaining a high concentration of reactive species in the system. Furthermore, germination and growth promotion of mung bean seeds observed in the toxicity test indicated the environmental compatibility of this remediation method. This study revealed the influence mechanism of SOM in the remediation process of contaminated soil comprehensively, which possessed enormous potential for application in practical environments.

ENDOR Spectroscopy Reveals the "Free" 5'-Deoxyadenosyl Radical in a Radical SAM Enzyme Active Site Actually is Chaperoned by Close Interaction with the Methionine-Bound [4Fe-4S]2+ Cluster.

1/2H and 13C hyperfine coupling constants to 5'-deoxyadenosyl (5'-dAdo•) radical trapped within the active site of the radical S-adenosyl-l-methionine (SAM) enzyme, pyruvate formate lyase-activating enzyme (PFL-AE), both in the absence of substrate and the presence of a reactive peptide-model of the PFL substrate, are completely characteristic of a classical organic free radical whose unpaired electron is localized in the 2pπ orbital of the sp2 C5'-carbon (J. Am. Chem. Soc. 2019, 141, 12139-12146). However, prior electron-nuclear double resonance (ENDOR) measurements had indicated that this 5'-dAdo• free radical is never truly "free": tight van der Waals contact with its target partners and active-site residues guide it in carrying out the exquisitely precise, regioselective reactions that are hallmarks of RS enzymes. Here, our understanding of how the active site chaperones 5'-dAdo• is extended through the finding that this apparently unexceptional organic free radical has an anomalous g-tensor and exhibits significant 57Fe, 13C, 15N, and 2H hyperfine couplings to the adjacent, isotopically labeled, methionine-bound [4Fe-4S]2+ cluster cogenerated with 5'-dAdo• during homolytic cleavage of cluster-bound SAM. The origin of the 57Fe couplings through nonbonded radical-cluster contact is illuminated by a formal exchange-coupling model and broken symmetry-density functional theory computations. Incorporation of ENDOR-derived distances from C5'(dAdo•) to labeled-methionine as structural constraints yields a model for active-site positioning of 5'-dAdo• with a short, nonbonded C5'-Fe distance (∼3 Å). This distance involves substantial motion of 5'-dAdo• toward the unique Fe of the [4Fe-4S]2+ cluster upon S-C(5') bond-cleavage, plausibly an initial step toward formation of the Fe-C5' bond of the organometallic complex, Ω, the central intermediate in catalysis by radical-SAM enzymes.

Tannin Industry Waste-Derived Porous Carbon: An Effective Adsorbent from Black Wattle Bark for Organic Pollutant Removal

In Brazil, a significant part of the biomass is unused, contributing to environmental pollution. The tannin industry commonly extracts tannins from the bark of Acacia mearnsii or black wattle, leaving a significant residue of 70% (w w−1). This study investigates the conversion of black wattle bark into a porous carbonaceous material to efficiently remove organic pollutants. Using ZnCl2 as a chemical activation reagent, the experiments varied the impregnation time, carbonization rates, and temperatures. Additional experiments aimed to increase the specific surface area (SSA). X-ray diffraction (XRD) analysis showed the formation and removal of ZnO, which increased porosity. Scanning electron microscopy (SEM) showed an irregular morphology with pores. Fourier-transform infrared (FTIR) spectroscopy indicated characteristic bands, and electron paramagnetic resonance (EPR) detected organic free radicals. The SSAs exceeded 1000 m2 g−1, averaging 1360 m2 g−1, with a maximum of 1525 m2 g−1. Micropores (1.4 nm) were consistent. The structure of the material and the high SSA suggest a potential for efficient removal of aromatic impurities by π–π interactions. This approach addresses the issue of biomass waste, provides a solution for environmental remediation, and represents a transformative strategy for biomass utilization.

Association between Vitamin A and cancer: A review

Vitamin A is a fat-soluble micronutrient vital for the immune system, cellular differentiation, epithelial barrier function, and eyesight; they also play a significant function as a potent antioxidant regulating oxidative stress and the onset of cancer. There are two ways to get it through food: Provitamin A (beta-carotenoid) and preformed Vitamin A (retinol and retinyl ester). Uncontrolled cell proliferation and the development of metastatic features are characteristics of cancer initiated by agents such as aflatoxin, tobacco smoke’s carcinogenic compounds, and solar ultraviolet radiation. Vitamin A, an antioxidant vitamin, is hypothesized to exert chemo-preventive effects and reduce the risk of cancer by preventing tissue damage through the capture of organic free radicals, an end-product of numerous metabolic processes. This review is performed to investigate the association between Vitamin A and cancer. From March 2017 to March 2022, relevant articles were searched through PubMed, Science Direct, and Google Scholar databases. All the studies involving Vitamin A and cancer were included in this review. Intake of Vitamin A was significantly inversely associated with improved cancer prognosis. The present review demonstrates that there is an inverse association between Vitamin A and cancer treatment.

Unusual reactivity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) with Fe3+ controlled by competing reactions.

2,2-Diphenyl-1-picrylhydrazyl (DPPH) is a stable organic free radical widely used in various fields as a model free radical. There is scarce information about the stability of this compound in the chemical environments in which it is used. Side reactions between DPPH and other species can alter the precision of experiments that use DPPH, such as the evaluation of antioxidant properties amongst others. Following recent investigations highlighting reactions between DPPH and metal cations or Lewis acids, a quantitative reaction between DPPH and Fe3+ in acetonitrile was studied in the present work. UV-Vis spectroscopy and electrochemistry were used to monitor the reaction. The results obtained indicate a fast and multistep reaction between Fe3+ and DPPH that can be simplified as a simple redox reaction with the formation of Fe2+ and DPPH+. The reaction mechanism proposed follows complex steps involving two competing phenomena: a disproportionation which accelerates the reaction and an oxidation process that slows it down through DPPH regeneration.

Synthesis and characterization of novel uranyl clusters supported by bis(pyrazolyl) methane ligands: biomimetic catalytic oxidation, BSA protein interaction and cytotoxicity studies.

Two novel uranyl complexes were synthesized using bis-pyrazolyl methane ligands. The complexes were characterized by several spectroscopic techniques, including UV-Vis, IR, NMR, mass spectrometry, fluorescence, electrochemical, and thermogravimetric analysis. The solid-state structure of the complex C1 was determined with the help of single-crystal X-ray diffraction studies. The complexes C1 and C2 efficiently catalyse the oxidation of 3,5-di-tert-butyl catechol and 2-aminophenol in the atmospheric air, imitating the catalytic activity of the catechol oxidase and phenoxazinone synthase enzymes. The kinetic parameters and the catalytic efficiency (K cat/K M) of the reactions were calculated. Formation of organic free radicals in the catalytic reactions was confirmed by EPR spectroscopy. The interaction of these complexes with the protein, bovine serum albumin, was investigated by using UV-Vis and fluorescence spectral analysis. The cytotoxicity of the complexes against MDAMB-231 and A549 cell lines was investigated, and IC50 values were determined.

Dynamic Nuclear Polarization from Lithium Metal, a New Method to Study Lithium Batteries

The massive development of portable electronics, electric vehicles, and the increased need for energy storage require higher battery energy density, improved efficiency, and safety. In this context, lithium metal is the ultimate high-energy-density battery anode material. However, its use as an anode material is limited due to the formation of lithium dendrites that could lead to low efficiency and potential safety issues. Therefore, understanding and controlling the formation of lithium dendrites is key to realise lithium metal batteries.Here we show a new approach combining Scanning Electron Microscopy (SEM) and Magic-Angle Spinning Dynamic Nuclear Polarization (MAS DNP) to study the interplay between lithium morphology and interface reactivity. We aim to understand how the Solid-Electrolyte-Interphase (SEI), formed at the surface of lithium metal, affects lithium morphology. 1,2. Whereas the morphology of lithium dendrites can easily be identified using SEM, information about the SEI is more challenging to access. Among the different techniques used to characterize battery material, Nuclear Magnetic Resonance (NMR), has emerged as a powerful method providing information about the chemical composition as well as dynamic properties of a given material, at the atomic scale. Yet, the main limitations of NMR are its low intrinsic sensitivity and lack of selectivity which highly complicate the study of thin interphase as the SEI. In the present work, we use MAS DNP to overcome the low sensitivity of NMR. MAS DNP is based on the transfer of the large electron spin polarization of unpaired electrons to the nuclear spins, leading to the enhancement of the NMR signal intensity. However, the addition of free organic radicals solution to the typical exogenous DNP may alter the nature of the SEI. Furthermore, exogenous DNP is not selective to the interfaces between the lithium metal and the SEI. In this respect, we use the recently developed Lithium metal DNP method which exploits lithium metal's conduction electrons to perform endogenous MAS DNP and achieve one order of magnitude hyperpolarization at room temperature3. In addition to the gain of sensitivity, this technique allows to selectively enhance the chemical species close to the lithium metal providing critical information about the chemical structure of the SEI. This approach, currently under development, provides a powerful tool in research to control and prevent the formation of lithium dendrites which typically result in rapid degradation and potential safety issues. Figure: A) Schematic representation of Lithium dendrites with SEM of lithium dendrites formed on a copper current collector. B) Schematic representation of SEI formed on lithium metal with 7Li MAS DNP spectra recorded with and without microwave irradiation on lithium dendrites