TEMPO Radical Research Articles

π-Self-Assembly of a Coronene on Carbon Nanomaterial-Modified Electrode and Its Symmetrical Redox and H2O2 Electrocatalytic Reduction Functionalities.

The structure–electroactivity relationship of graphene has been studied using coronene (Cor), polyaromatic hydrocarbon (PAH), and a subunit of graphene as a model system by chemically modified electrode approach. In general, graphene and PAH do not show any redox activity in their native form. Herein, we report a simple electrochemical approach for the conversion of electro-inactive coronene to a highly redox-active molecule (Cor-Redox; E°′ = 0.235 ± 0.005 V vs Ag/AgCl) after being adsorbed on graphitic carbon nanomaterial and preconditioned at an applied potential, 1.2 V vs Ag/AgCl, wherein, the water molecule oxidizes to dioxygen via hydroxyl radical (•OH) intermediate, in acidic solution (pH 2 KCl–HCl). When the same coronene electrochemical experiment was carried out on an unmodified glassy carbon electrode, there was no sign of faradic signal, revealing the unique electrochemical behavior of the coronene molecule on graphitic nanomaterial. The Cor-Redox peak is found to be highly symmetrical (peak-to-peak potential separation of ∼0 V tested by cyclic voltammetry (CV)) and surface-confined (ΓCor-Redox = 10.1 × 10–9 mol cm–2) and has proton-coupled electron-transfer (∂E°′/∂pH = −56 mV pH–1) character. Initially, it was speculated that Cor is converted to a hydroxy group-functionalized Cor molecule (dihydroxy benzene derivative) on the graphitic surface and showed the electrochemical redox activity. However, physicochemical characterization studies including Raman, IR, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), redox-site selective oxidation probe, cysteine (for dihydroxy benzene), radical scavenger ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl, TEMPO), and scanning electrochemical microscopy (SECM) using ferricyanide redox couple have revealed that coronene cationic radical species like electroactive molecule is formed on graphitic material upon the electrochemical oxidation reaction at a high anodic potential. It has been proposed that •OH generated as an intermediate species from the water oxidation reaction is involved in the coronene cationic radical species. Studies on coronene electrochemical reaction at various carbon nanomaterials like multiwalled carbon, single-walled carbon, graphite, graphene oxide, and carbon nanofiber revealed that graphitic structure (without any oxygen functional groups) and its π–π bonding are key factors for the success of the electrochemical reaction. The coronene molecular redox peak showed an unusual electrocatalytic reduction of hydrogen peroxide similar to the peroxidase enzyme-biocatalyzed reduction reaction in physiological solution.

Preparation and Characterization of Carrot Nanofiber and their Reinforced Nanocomposite Films

In this study, the cellulose nanofiber (CNF) was prepared using carrot slag discarded from industrial carrot juice. The FTIR results of the carrot fiber show that the impurities such as lignin have been removed after alkali and acid neutralization treatment. In addition, it was confirmed that the carrot nanofiber was successfully prepared by the 2,2,6,6-tetramethylpiperidine (TEMPO) radical oxidation method. Subsequently, the obtained nanofiber was surface modified by styrene suspension polymerization and silane coupling agent, respectively. The results of water contact angle analysis show that the hydrophobicity of the modified nanofibers was improved. Moreover, a set of nanocomposite films were prepared by incorporating carrot nanofiber into sodium alginate (SA) and polystyrene (PS), respectively by using solution casting method. The obtained results showed that the TEMPO radical oxidized nanofiber containing film had the best transmittance in SA nanocomposite series. On the other hand, styrene suspension polymerization modified nanofiber containing one exhibited the best transparency in PS nanocomposite series.

To be a radical or not to be one? The fate of the stable nitroxide radical TEMPO [(2,2,6,6-Tetramethylpiperidin-1-yl)oxyl] undergoing plasma polymerization into thin-film coatings.

The stable nitroxide radical TEMPO [(2,2,6,6-Tetramethylpiperidin-1-yl)oxyl] has a multitude of applications in fields ranging from energy storage to biomedical applications and many more. However, to date, the processes of incorporating nitroxide radicals into thin-film coatings are laborious and not cost-effective, which hinders their wider use in many applications. In contrast, the authors have recently demonstrated the facile method of plasma polymerization of TEMPO into thin-film coatings that retain the stable nitroxide radicals. In this work, we are using three types of mass spectroscopic methods (plasma-mass spectrometry, time of flight secondary ion mass spectrometry, and high-performance liquid chromatography-mass spectrometry) and electron spin resonance to track the fate of the TEMPO molecule from monomer flask through the plasma and inside the resulting coatings. The results of this study demonstrate that TEMPO is a versatile monomer that can be used across different plasma reactors and reliably retain the stable nitroxide radical in the resulting thin-film coatings if certain process conditions are observed, namely, higher process pressures and lower powers.

An alternative strategy to detect bacterial contamination in milk and water: a newly designed electrochemical biosensor

The detection of acyl homoserine lactones (AHLs) can render their use as biomarkers and it may provide a chance to fight against food contamination and bacterial pathogens. For this purpose, in this study, an electrochemical biosensor was designed for the detection of AHLs to prevent harmful bacterial activities. The electrochemical biosensor was constructed by coating of zinc phthalocyanine bearing stabile TEMPO radical groups (TEMPO-ZnPc) on a glassy carbon electrode (GCE) and it was utilized for AHL detection. GCE/TEMPO–ZnPc electrode acted as amperometric biosensor for 3-oxo-C12-HSL, C10-HSL, C8-HSL, C6-HSL, and C4-HSL molecules, the sensor electrode only selectively sensed 3-oxo-C12-HSL molecule among the tested AHL molecules. The sensing measurements showed that 3-oxo-C12-HSL produced by Pseudomonas aeruginosa was detected between 2.32 × 10–6 and 39.9 × 10–6 mol dm−3 concentrations with 1.8 × 10–6 mol dm−3 limit of detection (LOD) in water. Additionally, the electrochemical biosensor was successfully applied for the detection of AHLs in milk samples. The sensing results indicated that GCE/TEMPO–ZnPc electrode can be used as rapid, sensitive, and selective biosensor for the detection of foodborne pathogens.

Photo-Oxidation Coupled Kabachnik–Fields and Bigenelli Reactions for Direct Conversion of Benzyl alcohols to α-Aminophosphonates and Dihydropyrimidones

A tandem one-pot solvent free approach for the direct conversion of benzyl alcohols to α-amino phosphonates and dihydropyrimidones is reported. The method relies on a metal free photo-oxidation of benzyl alcohols to benzaldehydes under UV irradiation using ammonium perchlorate followed by Kabachnik–Fields and Biginelli reactions. The reaction conditions are moderate and metal free with good substrate scope. The control experiments were performed to investigate the role of the ammonium perchlorate and molecular oxygen as oxidants. The quenching experiments in the presence of TEMPO and other radical quenchers suggest radical based mechanism.

Chemoselective Catalytic α-Oxidation of Carboxylic Acids: Iron/Alkali Metal Cooperative Redox Active Catalysis.

We developed a chemoselective catalytic activation of carboxylic acid for a 1e- radical process. α-Oxidation of a variety of carboxylic acids, which preferentially undergo undesired decarboxylation under radical conditions, proceeded efficiently under the optimized conditions. Chemoselective enolization of carboxylic acid was also achieved even in the presence of more acidic carbonyls. Extensive mechanistic studies revealed that the cooperative actions of iron species and alkali metal ions derived from 4 Å molecular sieves substantially facilitated the enolization. For the first time, catalytic enolization of unprotected carboxylic acid was achieved without external addition of stoichiometric amounts of Brønsted base. The formed redox-active heterobimetallic enediolate efficiently coupled with free radical TEMPO, providing synthetically useful α-hydroxy and keto acid derivatives.

Electrochemical Oxidation of Organic Molecules at Lower Overpotential: Accessing Broader Functional Group Compatibility with Electron-Proton Transfer Mediators.

Electrochemical organic oxidation reactions are highly appealing because protons are often effective terminal electron acceptors, thereby avoiding undesirable stoichiometric oxidants. These reactions are often plagued by high overpotentials, however, that greatly limit their utility. Single-electron transfer (SET) from organic molecules generates high-energy radical-cations. Formation of such intermediates often requires electrode potentials far above the thermodynamic potentials of the reaction and frequently causes decomposition and/or side reactions of ancillary functional groups. In this Account, we show how electrocatalytic electron-proton transfer mediators (EPTMs) address this challenge. EPTMs bypass the formation of radical-cation intermediates by supporting mechanisms that operate at electrode potentials much lower (≥1 V) than those of analogous direct electrolysis reactions.The stable aminoxyl radical TEMPO (2,2,6,6-tetramethylpiperidine N-oxyl) is an effective mediator for electrochemical alcohol oxidation, and we have employed such processes for applications ranging from pharmaceutical synthesis to biomass conversion. A complementary electrochemical alcohol oxidation method employs a cooperative Cu/TEMPO mediator system that operates at 0.5 V lower electrode potential than the TEMPO-only mediated process. This difference, which arises from a different catalytic mechanism, rationalizes the broad functional group tolerance of Cu/TEMPO-based aerobic alcohol oxidation catalysts.Aminoxyl mediators address long-standing challenges in the "Shono oxidation," an important method for α-C-H oxidation of tertiary amides and carbamates. Shono oxidations are initiated by a high-potential SET step that limits their utility. Aminoxyl-mediated Shono-type oxidations have been developed that operate at much lower potentials and tolerate diverse functional groups. Analogous reactivity underlies α-C-H cyanation of secondary cyclic amines, a new method that enables efficient diversification of piperidine-based pharmaceutical building blocks and preparation of non-natural amino acids.Electrochemical oxidations of benzylic C-H bonds are commonly initiated by SET to generate arene radical cations, but such methods are again plagued by large overpotentials. Mediated electrolysis methods that promote hydrogen-atom-transfer (HAT) from benzylic C-H bonds to Fe-oxo species and phthalimide N-oxyl (PINO) support C-H oxygenation, iodination, and oxidative-coupling reactions. A complementary method merges photochemistry with electrochemistry to achieve amidation of C(sp3)-H bonds. This unique process operates at much lower overpotentials compatible with diverse functional groups.These results have broad implications for organic electrochemistry, highlighting the importance of "overpotential" considerations and the prospects for expanding synthetic utility by using mediators to bypass high-energy outer-sphere electron-transfer mechanisms. Principles demonstrated here for oxidation are equally relevant to electrochemical reductions.

Heme-FeIII Superoxide, Peroxide and Hydroperoxide Thermodynamic Relationships: FeIII-O2•- Complex H-Atom Abstraction Reactivity.

Establishing redox and thermodynamic relationships between metal-ion-bound O2 and its reduced (and protonated) derivatives is critically important for a full understanding of (bio)chemical processes involving dioxygen processing. Here, a ferric heme peroxide complex, [(F8)FeIII-(O22-)]- (P) (F8 = tetrakis(2,6-difluorophenyl)porphyrinate), and a superoxide complex, [(F8)FeIII-(O2•-)] (S), are shown to be redox interconvertible. Using Cr(η-C6H6)2, an equilibrium state where S and P are present is established in tetrahydrofuran (THF) at -80 °C, allowing determination of the reduction potential of S as -1.17 V vs Fc+/0. P could be protonated with 2,6-lutidinium triflate, yielding the low-spin ferric hydroperoxide species, [(F8)FeIII-(OOH)] (HP). Partial conversion of HP back to P using a derivatized phosphazene base gave a P/HP equilibrium mixture, leading to the determination of pKa = 28.8 for HP (THF, -80 °C). With the measured reduction potential and pKa, the O-H bond dissociation free energy (BDFE) of hydroperoxide species HP was calculated to be 73.5 kcal/mol, employing the thermodynamic square scheme and Bordwell relationship. This calculated O-H BDFE of HP, in fact, lines up with an experimental demonstration of the oxidizing ability of S via hydrogen atom transfer (HAT) from TEMPO-H (2,2,6,6-tetramethylpiperdine-N-hydroxide, BDFE = 66.5 kcal/mol in THF), forming the hydroperoxide species HP and TEMPO radical. Kinetic studies carried out with TEMPO-H(D) reveal second-order behavior, kH = 0.5, kD = 0.08 M-1 s-1 (THF, -80 °C); thus, the hydrogen/deuterium kinetic isotope effect (KIE) = 6, consistent with H-atom abstraction by S being the rate-determining step. This appears to be the first case where experimentally derived thermodynamics lead to a ferric heme hydroperoxide OO-H BDFE determination, that FeIII-OOH species being formed via HAT reactivity of the partner ferric heme superoxide complex.

Electrochemical Characterization of TEMPO Radical in Ionic Liquids

Electrochemical Characterization of TEMPO Radical in Ionic Liquids

It takes two for chronic wounds to heal: dispersing bacterial biofilm and modulating inflammation with dual action plasma coatings.

Chronic wounds are affecting increasingly larger portions of the general population and their treatment has essentially remained unchanged for the past century. This lack of progress is due to the complex problem that chronic wounds are simultaneously infected and inflamed. Both aspects need to be addressed together to achieve a better healing outcome. Hence, we hereby demonstrate that the stable nitroxide radical (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) can be plasma polymerized into smooth coatings (TEMPOpp), as seen via atomic force microscopy, X-ray photoelectron spectroscopy and ellipsometry. Upon contact with water, these coatings leach nitroxides into aqueous supernatant, as measured via EPR. We then exploited the known cell-signalling qualities of TEMPO to change the cellular behaviour of bacteria and human cells that come into contact with the surfaces. Specifically, the TEMPOpp coatings not only suppressed biofilm formation of the opportunistic bacterium Staphylococcus epidermidis but also dispersed already formed biofilm in a dose-dependent manner; a crucial aspect in treating chronic wounds that contain bacterial biofilm. Thus the coatings' microbiological efficacy correlated with their thickness and the thickest coating was the most efficient. Furthermore, this dose-dependent effect was mirrored in significant cytokine reduction of activated THP-1 macrophages for the four cytokines TNF-α, IL-1β, IL-6 and IP-10. At the same time, the THP-1 cells retained their ability to adhere and colonize the surfaces, as verified via SEM imaging. Thus, summarily, we have exploited the unique qualities of plasma polymerized TEMPO coatings in targeting both infection and inflammation simultaneously; demonstrating a novel alternative to how chronic wounds could be treated in the future.

Radical dendrimers: Synthesis, anti-tumor activity and enhanced cytoprotective performance of TEMPO free radical functionalized polyurethane dendrimers

Polyurethane dendrimers up to fourth generation, functionalized with stable 4-hydroxy-2, 2, 6, 6-tetramethylpiperidin-1-yloxyl (4-hydroxy TEMPO), were prepared via a single-step urethane interchange reaction and their structures were confirmed by NMR, FT-IR, MALDI-TOF MS and SEC-MALLS techniques. The terminal TEMPO radicals of the dendrimers exhibited a triplet with nitrogen hyperfine splitting constant of 14.4 G, at g = 2.0026 in the EPR spectrum and their paramagnetic nature were confirmed by vibrating sample magnetometer. The MTT assay results revealed that the G4 dendrimer had significant anti-tumor activity in A549 lung adenocarcinoma cells and this dendrimer was found not induced any cell death in normal L132 lung cells. Further, antioxidant effect of G4 dendrimer was evaluated in normal L132 lung cells; the in-vitro studies include cell morphological studies, measurement of total intracellular reactive oxygen species (ROS) using H2DCF dye and analysis of SOD, CAT, GSH and GPx. This study demonstrated the efficacy of the dendrimers through decrease in free radicals and confirmed their enhanced cytoprotective performance over N-acetyl cysteine standard used.

BIOMIMETIC APPROACHES TO STUDY OF PROPERTIES OF MEDICINAL SUBSTANCES

The review is devoted to an assessment of the current level of use of biomimetic approaches to the study of the properties of known drugs and the development of new drugs. In this review, we consider the main biological functions of superoxide dismutase, namely the catalytic decomposition of toxic superoxide anion of oxygen to the molecular form of oxygen and protection against induced apoptosis. The biomimetic enzymes-Mn- and TEMPO-containing equivalents of superoxide dismutase SOD with antitumor and antioxidant activity were discussed more detail. The relationship between the properties and activity of SOD mimetics with their structure among them the nature of the anion and ligands, the coordination number, the geometry of the presence of conjugated bonds, and other parameters of the molecules. The study of the properties of Mn-SOD mimetics makes it possible to develop a new class of drugs successfully tested by in vivo and in vitro experiments and which are at the stages of clinical trials. Stable TEMPO radicals containing compounds are able to perform SOD functions, exhibiting antioxidant activity in relation not only to superoxide-anion, but also to peroxynitrile, and moreover to act as a spin label. The biomimetic membrane systems (monolayers, planar lipid bilayers, liposomes and other nano-sized objects) are discussed too for studying properties in in vitro experiments and for delivering potent and medicinal substances. The biomimetic approach combination allows to create the new promising drugs, including those based on SOD mimetics, and to develop the synthetic analogues of biologically active substances and methods of their delivery. The advantages of such dosage forms are lower toxicity of the preparations, lack of immunogenicity and a decrease in the dose of potent drugs.

Bismuth Pyridine Dipyrrolide Complexes: a Transient Bi(II) Species Which Ring Opens Cyclic Ethers.

A family of group 15 MIII pyridine dipyrrolide complexes has been prepared and fully characterized; the reduction of these complexes was investigated with traditional strong metal reductants, which led either to over-reduction in the case of Mg and Zn or to ligand redistribution and "ate" complex formation when KC8 was used. However, by utilizing organosilanes as soluble reductants, the ring opening and two electron reduction of thf solvent was observed with concomitant formation of Bi-C and Si-O bonds; this is an example of a main group complex that is capable of ring opening a cyclic ether in the absence of additional metal reducing agents. The proposed BiII intermediate in this mechanism could be trapped using the stable organic radical TEMPO.

Nitroxide-Grafted Nanometric Metal Oxides for the Catalytic Oxidation of Sugar

A new series of ([2,2,6,6-tetramethylpiperidin-1-yl]oxy) (TEMPO) catalysts supported on nanometric metal oxides (TiO2, AlO2, CeO2) and their efficiency for sugar oxidation are herein described. The preparation of such hybrid catalysts was carried out by modification of a metal oxide surface with a monolayer of phosphonic linker bearing a TEMPO radical. All prepared catalysts were carefully characterized by diffuse reflectance Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and transmission electron microscopy. The efficiency of these new hybrid TEMPO supported materials for sugar oxidation was evaluated on methyl α-d-glucoside, as a model carbohydrate. The three hybrid catalysts showed high selectivity, activity, and stability, suggesting a promising potential for rapidly obtaining acid sugar derivatives.

Rabi oscillations as a tool to detect strong coupling of paramagnetic center with the nuclear spin bath

We show that strong coupling with the nuclear spin ensemble leaves an imprint on the nutation dynamics of the electron spin in the form of forced oscillations. The frequency of these oscillations equals Larmor precession frequency of the nuclear spins. This effect is evidenced by our experimental data on Rabi oscillations of paramagnetic nitroxyl radical TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl) dispersed in glassy and crystalline ethanol. The data are interpreted in terms of a simple model that represents an impact of the proton spin bath as random local field with certain probability distribution. The electron spin coherence times of TEMPO in ethanol obtained by means of Hahn spin echo and Carr-Purcell-Meiboom-Gill sequences are compared with the calculations based on a spin diffusion model.

Structure-morphology impact upon segmental dynamics and diffusion in the biodegradable ultrafine fibers of polyhydroxybutyrate-polylactide blends

An innovative remedies’ implementation with a focus on the transition from custom macro- to nano-scaled therapeutic polymer vehicles relies upon the appropriate design of novel drug-polymer compositions, their functionalization at molecular and nano-scale levels, and addressed diffusion-kinetic processes that control drug distribution at any given time in both a proper polymer implant and surrounding biological media. In the framework of this paradigm, ultrathin fibers formed by blending poly(3-R-hydroxybutyrate) [PHB] with poly (l-lactic acid) [PLA] and loaded with modeling drug (dipyridamole [DPD]) were fabricated by solution electrospinning. PHB/PLA ratio and DPD content affected considerably the geometric shape, crystallinity of a single filament. As follows from the optical microscopy and SEM data, in the absence of the drug or at its low concentration (<3 wt.%), the PHB/PLA fibers appear as ellipsoid-like fragments alternating with cylindrical ones. At the higher content of the drug (3–5%), the abnormal ellipsoid-like structures disappear and all the fibers have cylindrical geometry. By the DSC technique it was shown that PHB/PLA ratio influenced on the crystallinity of fibers and modulated the general course of DSC thermograms. The ESR spectra of the TEMPO radical preliminary embedded into fiber volume represent a superposition of two elementary spectra belonging to the radical populations with different correlation times τ1 and τ2 that reflects heterogeneity of the PHB and PLA intercrystalline amorphous regions with slow and fast segmental dynamics respectively. The combination of structure-morphology characteristics of the ultrathin fibers determines the polymer dynamics and drug diffusivity as well as the corresponding profiles of drug release. A coherent model of drug release from the PHB fibrillar and ellipsoidal mats was advanced.

Synthesis and Structure of Copper Complexes of a N6O4 Macrocyclic Ligand and Catalytic Application in Alcohol Oxidation

Reactions between N6O4 macrocyclic 1,4,19,22,25,40-hexaaza-10,13,31,34-tetraoxa-6,14,27,35(1,4)-tetrabenzenacyclopentacontane (L) and several copper salts (viz. trifuoromethane and toluene sulfonates, nitrate, perchlorate, benzoate, and acetate) led to the formation of dinuclear compounds [Cu2(OSO2CF3)2(DMF)2L](SO3CF3)2 (1), [Cu2(p-OSO2C6H4Me)2L(DMF)2](SO3C6H4Me)2 (2), [Cu2(ONO2)2L(DMF)2](NO3)2 (3), [Cu2(OClO3)2(DMF)2L](ClO4)2 (4), [Cu2(OOCPh)2L(H2O)2](O2CPh)2 (5), and [Cu2(OOCMe)4L] (6), which were characterized by IR, elemental analysis and TG-DTA (thermogravimetric-differential thermal analysis), as well as by single-crystal X-ray diffraction, EPR (electron paramagnetic resonance) spectroscopy, and electrochemical techniques (cyclic voltammetry and controlled potential electrolysis). The molecular structures of compounds 1–6 reveal a considerable conformational flexibility of the ligand L, which allowed its readjustment for the formation of the metal compounds and confirmed the presence of dinuclear endo macrocyclic species. In every case, the L ligand coordinates to each copper cation via three nitrogen atoms, with the remaining coordination positions of the metal square pyramid environment being accomplished by neutral or anionic ligands. The macrocyclic cavities appear to be adequate for the enclosure of a neutral species as proved by compound 6 with 1,4-dioxane. The compounds, in combination with the TEMPO (2,2,6,6-tetramethyl-piperidinyloxyl) radical and in alkaline aqueous solution, act as efficient catalysts in the aerobic oxidation of different alcohols to the corresponding aldehydes (yields up to 99% and TON up 232) after 20 h at 70 °C. In addition, the microwave-assisted solvent-free peroxidative oxidation (by tert-butylhydroperoxide, TBHP) of 1-phenylethanol led to acetophenone yields up to 99% and TOF of 1.1 × 103 after 0.5 h, without any additive.

TEMPO-Modified Linear Polyethylenimine (LPEI) As Organic Radical Battery Electrode

With increasing demand for electronic devices and electric vehicles, there is a need for good performance of electrochemical energy storage materials while considering cost, safety, and environmental impact [1][2]. Organic electrodes based on stable organic radicals such as (2,2,6,6,-tetramethylpiperidin-1-yl)oxy (TEMPO) are a promising alternative to conventional inorganic (i.e. metal, metalloid, and metal oxide) battery materials due to their highly reversible, stable electron transfer reaction. Organic radical electrodes have the potential to achieve high power density, low cost, and improved environmental sustainability compared to inorganic electrodes [2][1]. Despite these advantages, organic radical-based electrodes face problems including dissolution of the active material in common battery solvents (thus requiring radical immobilization on polymer supports) and low capacity due to poor electronic conductivity and/or low fractions of active radical material [2][3]. Previous work suggests the support polymer can affect the performance of organic radicals as electrocatalysts, mediators, or energy storage materials. Hickey et al. demonstrated enhanced electrocatalytic activity of TEMPO when immobilized on linear polyethyleneimine (LPEI), a cationic polymer with amine functionality [4] [5]. In this work we explore for the first time LPEI-TEMPO as a cathode material in sodium-ion and lithium-ion organic radical batteries. Figure 1a demonstrates the structure and stable electron transfer mechanism of LPEI-TEMPO. LPEI-TEMPO electrode is prepared by dissolving TEMPO-modified LPEI(prepared according to [3]) in 0.1 M HCl (10 mg/mL) with 2.5:1 wt% carboxylated carbon nanotubes, 2.5 M glutaraldehyde crosslinker (0.25 L in 80 L of solution) and polytetrafluoroethylene (PTFE) binder (5 wt%). This solution is deposited on Toray carbon paper (10L) and a steel current collector (20 L) for cyclic voltammetry and battery testing, respectively. Cyclic voltammetry measurements of LPEI-TEMPO (Figure 1b) confirm the reversible electron transfer of the TEMPO radical when immobilized on LPEI (electrolyte: 0.1 M TBAPF6 in acetonitrile; counter electrode: Pt; reference electrode: Ag/Ag+; scan rate: 100 mV/s). This work will present a detailed characterization of LPEI-TEMPO electrodes in sodium- and lithium-ion battery systems, including cyclic voltammetry, charge-discharge, rate capacity, and electrochemical impedance measurements. A preliminary sodium-ion half-cell charge-discharge test (Figure 1c) indicates a capacity of 30 mAh/g of LPEI-TEMPO (electrolyte: 1 M NaClO4 in 1:1 etheylene carbonate: tetrahydrofuran; Celgard 2340 separator; sodium metal anode). We will explore performance optimization of LPEI-TEMPO organic radical batteries, including a study of LPEI-TEMPO electrode-electrolyte interactions. [1] H. Nishide, S. Iwasa, Y. J. Pu, T. Suga, K. Nakahara, and M. Satoh, “Organic radical battery: Nitroxide polymers as a cathode-active material,” Electrochim. Acta, vol. 50, no. 2–3 SPEC. ISS., pp. 827–831, 2004. [2] D. R. Nevers, F. R. Brushett, and D. R. Wheeler, “Engineering radical polymer electrodes for electrochemical energy storage,” J. Power Sources, vol. 352, pp. 226–244, 2017. [3] M. Miroshnikov et al., “Power from nature: Designing green battery materials from electroactive quinone derivatives and organic polymers,” J. Mater. Chem. A, vol. 4, no. 32, pp. 12370–12386, 2016. [4] D. P. Hickey, R. D. Milton, D. Chen, M. S. Sigman, and S. D. Minteer, “TEMPO-Modified Linear Poly(ethylenimine) for Immobilization-Enhanced Electrocatalytic Oxidation of Alcohols,” ACS Catal., vol. 5, no. 9, pp. 5519–5524, Sep. 2015. [5] Q. Chen, C. Fang, Z. Shen, and M. Li, “Electrochemistry Communications Electrochemical synthesis of nitriles from aldehydes using TEMPO as a mediator,” Electrochem. commun., vol. 64, pp. 51–55, 2016. Figure 1

Conjugated Nitroxide Radical Polymers: Synthesis and Application in Flexible Energy Storage Devices

The synthesis and electrochemical behavior of nitroxide radical conjugated polymers (NCPs) have long been an intriguing topic in redox polymer-based energy storage. However, common (electro)chemical oxidation polymerization methods have proved difficult in the synthesis of well-defined NCPs, and many of these polymers have been difficult to process into thin films. In addition to these drawbacks and coupled with the complex charge-transfer and storage mechanisms, the use of NCPs as electrodes has been significantly limited. The aim of this work is to provide mechanistic insights into this complex charge-transfer and storage process using a new and well-defined NCP synthesized using an ultrafast cyclopolymerization with the Grubbs 3rd generation catalyst. The monomer, consisting of a 1,6-heptadiyne group and a TEMPO (i.e. 2,2,6,6-tetramethylpiperidine-1-oxy) radical, through the cyclopolymerization produced a well-defined NCP with a five-membered ring-containing polyene backbone. This polymer demonstrated excellent film formation properties, allowing the study of their thin-film electrochemical behavior. We found that the electrochemical oxidation of the conjugated backbone and its internal charge transfer to the nitroxide radicals were strongly affected by the applied potential window, current densities, and cycle numbers. Using these new insights, we successfully utilized our NCPs in a flexible energy storage device by fabricating high-performance NCP-coated carbon cloth-based flexible electrodes.

A novel profluorescent paramagnetic diaza-crown ether: synthesis, characterization and alkaline metal-ion complexation.

Starting from Kryptofix 22 two different branches were covalently attached through the nitrogen atoms, one containing a fluorescent moiety and the other the stable free radical TEMPO. The novel derivative exhibits fluorescence and paramagnetic properties, while the diaza-crown part ensures the affinity for alkaline metal-ions.