TEMPO Moiety Research Articles

Harmonizing Energies: The Interplay Between a Nonplanar SalEn-Type Molecule and a TEMPO Moiety in a New Hybrid Energy-Storing Redox-Conducting Polymer.

Redox-conducting polymers based on SalEn-type complexes have attracted considerable attention due to their potential applications in electrochemical devices. However, their charge transfer mechanisms, physical and electrochemical properties remain unclear, hindering their rational design and optimization. This study aims to establish the influence of monomer geometry on the polymer's properties by investigating the properties of novel nonplanar SalEn-type complexes, poly[N,N'-bis(salicylidene)propylene-2-(hydroxy)diaminonickel(II)], and its analog with 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO)-substituted bridge (MTS). To elucidate the charge transfer mechanism, operando UV-Vis spectroelectrochemical analysis, electrochemical impedance spectroscopy, and electron paramagnetic resonance are employed. Introducing TEMPO into the bridge moiety enhanced the specific capacity of the poly(MTS) material to 95mA h g-1, attributed to TEMPO's and conductive backbone's charge storage capabilities. Replacement of the ethylenediimino-bridge with a 1,3-propylenediimino- bridge induced significant changes in the complex geometry and material's morphology, electrochemical, and spectral properties. At nearly the same potential, polaron and bipolaron particles emerged, suggesting intriguing features at the overlap point of the electroactivity potentials ranges of polaron-bipolaron and TEMPO, such as a disruption in the connection between TEMPO and the conjugation chain or intramolecular charge transfer. These results offer valuable insights for optimizing strategies to create organic materials with tailored properties for use in catalysis and battery applications.

Bis(2,2,6,6-tetramethyl-1-(λ1-oxidaneyl)piperidin-4-yl) 3,3′-((2-hydroxyethyl)azanediyl)dipropionate

TEMPO-containing conductive polymers are used in organic electronics due to their electrochemical properties. One of significant limitations in developing such materials is the structural modification by several TEMPO moieties. Here, we report a synthesis of the first-generation dendrimer containing two TEMPO fragments, bis(2,2,6,6-tetramethyl-1-(λ1-oxidaneyl)piperidin-4-yl) 3,3′-((2-hydroxyethyl)azanediyl)dipropionate, that can be implemented into a conductive polymer structure. The resulting product was characterized using 1H and 13C nuclear magnetic resonance spectroscopy (NMR) and high-resolution mass spectroscopy (HRMS).

Electrochemical alcohol oxidation using a TEMPO nitroxide polymer as a homogeneous and surface‐confined catalyst

AbstractPolymers containing TEMPO moieties are effective catalysts for the electrochemical oxidation of alcohols. Such polymers, almost exclusively, are non‐commercial and are prepared using multi‐step synthetic procedures. Here we show that a commercially available TEMPO bearing polymer, Polyamine Immobilised Piperidinyl Oxyl (PIPO), is an effective homogeneous and surface‐confined polymeric catalyst for electrochemical alcohol oxidation at carbonaceous electrodes. We probe electrolytic conditions for effective and stable electrocatalytic alcohol oxidation showing that dichloromethane (DCM), containing tetrabutylammonium perchlorate (TBAP) and N‐methyl imidazole (NMI), is a suitable medium for homogeneous catalysis whilst carbonate buffer (pH 9.5) is better suited when PIPO is adsorbed at the electrode surface. These findings demonstrate the viability of PIPO as an effective and accessible catalyst for electrochemical alcohol oxidations.

Expression of concern: Valence tautomeric interconversion of bis-dioxolene cobalt complex with imino-pyridine functionalized by TEMPO moiety in solid solutions with isostructural nickel analogue: phase transitions and monocrystal destruction.

Expression of concern for 'Valence tautomeric interconversion of bis-dioxolene cobalt complex with imino-pyridine functionalized by TEMPO moiety in solid solutions with isostructural nickel analogue: phase transitions and monocrystal destruction' by Michael P. Bubnov et al., Dalton Trans., 2024, 53, 9151-9160, https://doi.org/10.1039/D4DT00453A.

Hyperbranched TEMPO-based polymers as catholytes for redox flow battery applications.

Application of redox-active polymers (RAPs) in redox flow batteries (RFBs) can potentially reduce the stack cost through substitution of costly ion-exchange membranes by cheap size-exclusion membranes. However, intermolecular interactions of polymer molecules, i.e., entanglements, particularly in concentrated solutions, result in relatively high electrolyte viscosities. Furthermore, the large size and limited mobility of polymers lead to slow diffusion and more sluggish heterogeneous electron transfer rates compared to quickly diffusing small molecules. Although a number of RAPs with varying electrolyte viscosities have been reported in the literature, the relation between the RAP structure and the hydrodynamic properties has not been thoroughly investigated. Herein, hyperbranched 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO)-based polymers intended for application as low-viscosity catholytes for RFBs are presented and the influence of the structure and the molar mass distribution on the hydrodynamic properties is investigated. A new synthesis approach for TEMPO-based polymers is established based on step-growth polymerization of a TEMPO-containing monomer using an aza-Michael addition followed by a postpolymerization modification to improve solubility in aqueous solutions. The compact structure of hyperbranched polymers was demonstrated using size-exclusion chromatography (SEC) with viscometric detection and the optimum molar mass was found based on the results of viscometric and crossover investigations. The resulting RAP revealed a viscosity of around 21 mPas at a concentration corresponding to around 1 M TEMPO-containing units, according to the calculated mass of the repeating unit, showing potential for high capacity polymer-based catholytes for RFBs. Nevertheless, possible partial deactivation of TEMPO units lowered the active TEMPO concentration of the hyperbranched RAPs. A faster diffusion and higher charge transfer rate were observed for the hyperbranched polymer compared to the previously reported linear polymers. However, in RFB tests, a poor performance was observed, which is attributed to the side reactions of the oxidized TEMPO moieties. Finally, pathways for overcoming the main remaining challenges, i.e., high loss of material during dialysis as an indication of being prone to crossover, the partial deactivation of TEMPO moieties, and the subsequent side reactions under battery conditions, are suggested.

Valence tautomeric interconversion of bis-dioxolene cobalt complex with imino-pyridine functionalized by TEMPO moiety in solid solutions with isostructural nickel analogue: phase transitions and monocrystal destruction.

Valence tautomeric complexes (VT) are promising systems for creating molecular devices. From this viewpoint, valence tautomeric complexes with a hysteresis loop on the magnetic curve are of special interest as potential memory elements. The hysteresis loop is a consequence of retarded structural rearrangements which investigation is an actual problem. Recently, we have described a new VT transition taking place in a bis-dioxolene cobalt complex with imino-pyridine having a TEMPO substituent (A. A. Zolotukhin, et al., Inorg. Chem., 2017, 56, 14751-14754). Valence tautomeric transformation occurs with a hysteresis loop and is accompanied by a phase transition. The phase transition taking place during cooling is accompanied by crystal destruction. This fact makes it impossible to monitor the structural changes responsible for the hysteresis loop. The current research attempts to resolve this problem. A nickel compound of the same composition (TEMPO-imino-pyridine)Ni(3,6-DBSQ)2 was synthesized and characterized. It was established to be isostructural with the cobalt complex. It was used as an inert matrix for the dilution of the VT cobalt complex. The number of solid solutions with Co/Ni ratios of 1 : 1, 1 : 2, 1 : 4, and 1 : 8 was obtained. Variable temperature magnetic susceptibility measurements show that VT transformation with a hysteresis loop takes place in all solid solutions. The hysteresis loop is shifted to low temperatures primarily due to the shifting of its low-temperature boundary with dilution. The hysteresis width does not change significantly with dilution. DSC detected that transformations are accompanied by phase transitions at different temperatures at cooling and heating. The phase transition at the first cooling occurs at slightly lower temperatures compared with subsequent cycles. These temperatures correspond to the transition temperatures detected from the magnetic curves. The phase transition during the first cooling is accompanied by crystal destruction. Physical destruction takes place in the crystals of all solid solutions. X-ray diffraction powder patterns confirm that phase transition is accompanied by considerable reorganization of the crystal structure typical for the first order transitions. The unit cell volume of solid solutions is larger than that of pure complexes. Especially calculated crystal invariom indicated that the "lattice energy" in a solid solution is the lowest compared with that in "pure" nickel and cobalt complexes.

Heterogeneous solvent-metal-free aerobic oxidation of alcohol under ambient conditions catalyzed by TEMPO-functionalized porous poly(ionic liquid)s.

Heterogeneous solvent-metal-free aerobic oxidation of alcohols under ambient conditions is interesting but remains a significant challenge. Herein, a series of porous TEMPO-functionalized poly(ionic liquid)s (TEMPO-PILs) featuring a pure polycationic framework were successfully developed through the free radical polymerization of the ionic liquid 3-(2-chloroacetic acid-2,2,6,6-tetramethyl-1-oxo-4-piperidyl)-1-vinylimidazolium chloride and bis-vinylimidazolium bromide salt. Characterizations revealed that the obtained TEMPO-PILs possessed a high TEMPO density, abundant bromide ions, and a tunable porous structure, which enabled them to serve as solvent-free heterogeneous organocatalysts for the metal-free aerobic oxidation of benzyl alcohol under ambient conditions, exhibiting high catalytic activity and stable recyclability. A high yield of 99% coupled with a turnover frequency (TOF) of 13.3 h-1 was obtainable, which is higher than most of the reported TEMPO-based heterogeneous catalysts, even superior to homogeneous TEMPO-functionalized ionic liquids. Furthermore, a broad range of alcohols were effectively converted into their corresponding ketones and aldehydes. A possible reaction mechanism is proposed for understanding the catalytic oxidation behavior, indicative of the synergistic effect of TEMPO moieties and bromide ions.

Room Temperature Electron Spin Coherence in Photogenerated Molecular Spin Qubit Candidates.

One of the main challenges in the emerging field of molecular spintronics is the identification of new spin qubit materials for quantum information applications. In this regard, recent work has shown that photoexcited chromophore-radical systems are promising candidates to expand our repertoire of suitable candidate molecules. Here, we investigate a series of three chromophore-radical compounds composed of a perylene diimide (PDI) chromophore and a stable 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) radical by transient electron paramagnetic resonance (EPR) techniques. We explore the influence of isotope labeling of the TEMPO moiety on the EPR spectra and electron spin coherence times of the molecular quartet states generated upon photoexcitation and illustrate that (i) a coherent manipulation of the spin state is possible in these systems even at room temperature and that (ii) a spin coherence time of 0.7 μs can be achieved under these conditions. This demonstration of electron spin coherence at ambient temperatures paves the way for practical applications of such systems in functional molecular devices.

Additive-Free Organic Radical Batteries Prepared through Electrochemical Polymerization of TEMPO-Decorated Terthiophene

Batteries based on organic active materials offer a promising alternative to traditional metal-based systems due to environmental issues as well as high possible charging and discharging rates. However, the established organic materials suffer from a very low intrinsic electrical conductivity, requiring the addition of conductive materials. Herein, we present an approach to overcome this problem through the application of a conductive polythiophene decorated with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) units through electrochemical polymerization of suitable monomers directly onto the battery electrode. We demonstrate that a terthiophene linked to one TEMPO moiety not only allows successful electropolymerization but also the construction of additive-free organic batteries. Based on electrochemical investigations in combination with quantum chemical simulations, we can evaluate the underlying redox processes at the molecular level. Cell tests demonstrate the principle functionality of the system with rate capabilities of up to 20% capacity retention at 50C and a good long-term stability with a capacity loss of only 0.03% per cycle.

Enzyme-inspired dry-powder polymeric catalyst for green and fast pharmaceutical manufacturing processes

Catalysis in pharma manufacturing processes is typically homogeneous, expensive and with hard catalyst recovery/regeneration. Herein an enzyme-inspired dry-powder molecularly imprinted polymeric (MIP) system was designed for fast, selective oxidation of a cholesterol derivative and easy catalyst regeneration. The strategy involved the synthesis of a template-monomer (T:M) complex followed by the crosslinked polymerization in supercritical carbon dioxide (scCO2). A 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-MIP catalyst is obtained after the template cleavage from the matrix, and the oxidation of the NH groups turns available TEMPO moieties within the MIP. The oxidation of benzyl alcohol, 5α-cholestan-3β-ol and cholic acid was fast, in high yield and with selective oxidation capacity.

Amphi-Active Superoxide-Solvating Charge Redox Mediator for Highly Stable Lithium-Oxygen Batteries.

A multifunctional electrolyte additive for lithium oxygen batteries (LOBs) was designed to have (1) a redox-active moiety to mediate decomposition of lithium peroxide (Li2O2 as the final discharge product) during charging and (2) a solvent moiety to solvate and stabilize lithium superoxide (LiO2 as the intermediate discharge product) in electrolyte during discharging. 4-Acetamido-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidin-1-yl)oxyl) or AAT was employed as the additive working for both charge and discharge processes (amphi-active). The redox-active moiety was rooted in TEMPO, while the acetamido (AA) functional group inherited the high donor number (DN) of N,N-dimethylacetamide (DMAc). Integrating two functional moieties (TEMPO and AA) into a single molecule resulted in the bifunctionality of AAT (1) facilitating Li2O2 decomposition by the TEMPO moiety and (2) encouraging the solvent mechanism of Li2O2 formation by the high-DN AA moiety. Significantly improved LOB performances were achieved by the superoxide-solvating charge redox mediator, which were not obtained by a simple cocktail of TEMPO and DMAc.

Synthesis of the pentasaccharide repeating unit corresponding to the capsular polysaccharide of Escherichia coli O20:K83:H26

A concise synthetic strategy has been developed for the synthesis of the pentasaccharide repeating unit of the capsular polysaccharide of Escherichia coli (E. coli) strain applying block [2 + 3] stereoselective glycosylation. A functionalized disaccharide thioglycoside donor prepared using “armed-disarmed” glycosylation concept, was coupled with suitably protected trisaccharide glycosyl acceptor in the presence of a combination of N-iodosuccinimide (NIS) and perchloric acid supported over silica (HClO4–SiO2) to give the target pentasaccharide derivative in 65% yield. A late-stage regioselective oxidation of the primary hydroxyl group using a combination of TEMPO and Bis(acetoxy)iodobenzene (BAIB) furnished d-galacturonic acid moiety in the functionalized pentasaccharide derivative.

TEMPO-Functionalized Carbon Nanotubes for Solid-Contact Ion-Selective Electrodes with Largely Improved Potential Reproducibility and Stability.

Solid-contact ion-selective electrodes (SCISEs) can overcome essential limitations of their counterparts based on liquid contacts. However, attaining a highly reproducible and predictable E0, especially between different fabrication batches, turned out to be difficult even with the most established solid-contact materials, i.e., conducting polymers and large-surface-area conducting materials (e.g., carbon nanotubes), that otherwise possess excellent potential stability. An appropriate batch-to-batch E0 reproducibility of SCISEs besides aiding the rapid quality control of the electrode manufacturing process is at the core of their “calibration-free” application, which is perhaps the last major challenge for their routine use as single-use “disposable” or wearable potentiometric sensors. Therefore, here, we propose a new class of solid-contact material based on the covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with a chemically stable redox molecule, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). This material combines the advantages of (i) the large double-layer capacitance of MWCNT layers, (ii) the adjustable redox couple ratio provided by the TEMPO moiety, (iii) the covalent confinement of the redox couple, and (iv) the hydrophobicity of the components to achieve the potential reproducibility and stability for demanding applications. The TEMPO-MWCNT-based SC potassium ion-selective electrodes (K+-SCISEs) showed excellent analytical performance and potential stability with no sign of an aqueous layer formation beneath the ion-selective membrane nor sensitivity toward O2, CO2, and light. A major convenience of the fabrication procedure is the E0 adjustment of the K+-SCISEs by the polarization of the TEMPO-MWCNT suspension prior to its use as solid contact. While most E0 reproducibility studies are limited to a single fabrication batch of SCISEs, the use of prepolarized TEMPO-MWCNT resulted also in an outstanding batch-to-batch potential reproducibility. We were also able to overcome the hydration-related potential drifts for the use of SCISEs without prior conditioning and to feature application for accurate K+ measurements in undiluted blood serum.

Liquid Crystal Nanoparticle Conjugates for Scavenging Reactive Oxygen Species in Live Cells.

The elevated intracellular production of or extracellular exposure to reactive oxygen species (ROS) causes oxidative stress to cells, resulting in deleterious irreversible biomolecular reactions (e.g., lipid peroxidation) and disease progression. The use of low-molecular weight antioxidants, such as 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), as ROS scavengers fails to achieve the desired efficacy because of their poor or uncontrolled cellular uptake and off-target effects, such as dysfunction of essential redox homeostasis. In this study, we fabricated a liquid crystal nanoparticle (LCNP) conjugate system with the fluorescent dye perylene (PY) loaded in the interior and poly (ethylene glycol) (PEG) decorated on the surface along with multiple molecules of TEMPO (PY-LCNP-PEG/TEMPO). PY-LCNP-PEG/TEMPO exhibit enhanced cellular uptake, and efficient ROS-scavenging activity in live cells. On average, the 120 nm diameter PY-LCNPs were conjugated with >1800 molecules of TEMPO moieties on their surface. PY-LCNP-PEG/TEMPO showed significantly greater reduction in ROS activity and lipid peroxidation compared to free TEMPO when the cells were challenged with ROS generating agents, such as hydrogen peroxide (H2O2). We suggest that this is due to the increased local concentration of TEMPO molecules on the surface of the PY-LCNP-PEG/TEMPO NPs, which efficiently bind to the plasma membrane and enter cells. Overall, these results demonstrate the enhanced capability of TEMPO-conjugated LCNPs to protect live cells from oxidative stress by effectively scavenging ROS and reducing lipid peroxidation.

Symmetric CEST-active lanthanide complexes for redox monitoring.

Two symmetric ligands harbouring two TEMPO radicals and two functionalized acetamide arms (R = OMe (L1), CF3 (L2)) were prepared and chelated to lanthanide ions (EuIII, YbIII for both L1 and L2, DyIII for L1). Luminescence measurements on the europium complexes support the coordination of a single water molecule. The TEMPO arms are magnetically interacting in L1 (and its complexes) but not in L2. The TEMPO moieties can be reversibly oxidized into an oxoammonium (0.33-0.36 V vs. Fc+/Fc) or reduced into a hydroxylamine (ill-defined redox wave, reduction by ascorbate), which are both diamagnetic. The europium complexes [Eu(L1)]3+ and [Eu(L2)]3+ in their hydroxylamine form exhibit a temperature dependent CEST effect, which is maximal at 25 °C (30%) and 37 °C (12%), respectively. The CEST activity is dramatically reduced in the corresponding nitroxide forms due to the paramagnetism of the ligand. The europium complexes show no cytotoxicity against M21 cell lines over long incubation times (72 h) at high concentration (40 μM).

Process mediated by gold nanoparticles encapsulated in polymeric gels evidenced by EPR spectroscopy

Gold (Au0) nanoparticles (AuNPs) have been investigated for decades as selective catalysts for a series of reactions including alcohol oxidation, alkene hydrogenation and nucleophilic addition to C-C multiple bonds. In this study, the reduction/oxidation processes mediated by AuNPs embedded within a polymeric hydrogel have been tested. In particular, we monitored two processes: i) the reduction of 4-nitrophenol and ii) the reduction of a TEMPO moiety covalently linked to a fluorescent moiety, in the presence of AuNPs/hydrogel. The hybrid AuNPs/hydrogel material was obtained by reduction of a gold salt within the cross-linked poly(ethylene glycol)/β-cyclodextrin gel following a procedure previously reported. We found that this material is suitable for cyclic reduction of 4-nitrophenol as the material is not structurally modified after the reduction process. The electron paramagnetic resonance (EPR) signal of the TEMPO moiety decreases in the first instance, due to reduction by AuNPs, and slightly increases in time, proving the oxidizing property of AuNPs embedded in hydrogel.

Novel neuroprotection using antioxidant nanoparticles in a mouse model of head trauma.

Free radicals and reactive oxygen species are related to deteriorating pathological conditions after head trauma because of their secondary effects. 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) scavenges free radicals; however, this molecule is also toxic. Here, we have evaluated the neuroprotective effect of antioxidant nanoparticles, which consisted of a novel core-shell type nanoparticle containing 4-amino-TEMPO, that is, redox-active nitroxide radical-containing nanoparticles (RNPs). Institute of Cancer Research mice were subjected to a head-impact procedure, randomly divided into four groups and intravenously (3 mg/kg) administered phosphate-buffered saline, TEMPO, micelle (a self-assembling block copolymer micelle without a TEMPO moiety), or RNP through the tail vein immediately thereafter and intraperitoneally at days 1, 3, and 5 after traumatic brain injury (TBI). The RNP distribution was detected by rhodamine labeling. Cognitive behavior was assessed using the neurological severity score and a rotarod test at days 1, 3, and 7 following TBI, and contusion volume was measured at day 7 after TBI. Free radical-scavenging capacity was analyzed by electron paramagnetic resonance on day 1 after TBI, and immunostaining was used to observe mobilization of microglia (Iba-1) and rescued neuronal cells (NeuN). Redox-active nitroxide radical-containing nanoparticle was detected in the microvessels around the injured area in the brain. Cognitive behavior assessment was significantly better, and contusion volume was significantly smaller in the RNP group compared with the other groups. Superoxide anion scavenging capacity was significantly higher in the RNP group, and neuronal loss was significantly suppressed around the injured area at day 7 after TBI. Furthermore, in the RNP group, neurodegenerative microglia production was suppressed at days 3 and 7 after TBI, whereas neuroprotective microglia production was higher at day 7 after TBI. The RNP administration after TBI improved cognitive behavior and reduced contusion volume by improving reactive oxygen species scavenging capacity. Therefore, RNP may have a neuroprotective effect after TBI. Therapeutic test.

Accurate Determination of Membrane Penetration of Proteins Using Fluorescence Quenching and Molecular Dynamics Simulations

Determination of the depth of membrane penetration provides important information for studies of membrane protein folding and protein-lipid interactions [1,2]. Here we use a combination of molecular dynamics (MD) simulations and depth-dependent fluorescence quenching to calibrate the methodology for extracting quantitative information on membrane penetration. The knowledge of the immersion depth of fluorescence quenchers (e.g., Doxyl or TEMPO spin probe attached to lipid acyl chains or headgroup) is critical for the determination of the transverse location of fluorescence probes attached to proteins and peptides. The question of bilayer penetration of TEMPO moiety, attached to lipid headgroup in TEMPO-PC, has recently came into prominence in two studies of interfacial solvation [3,4]. Here, we re-examine the arguments on TEMPO penetration using the cross-validation of MD simulations and depth-dependent fluorescence-quenching experiments, which confirms that TEMPO in TEMPO-PC penetrates below the level of phosphate groups. The proper analysis of fluorescence quenching requires the use of Tempo position below the level of phosphate groups; and failure to do so will result in substantial systematic errors in determining the penetration of the labeled site on a membrane protein [5]. Finally, we illustrate the application of this methodology by determining membrane penetration of site-selectively labeled mutants of diphtheria toxin translocation domain [6] and apoptotic inhibitor Bcl-xL [7]. [1] A. S. Ladokhin (2014) Biochim. Biophys. Acta 1838, 2289. [2] A. Kyrychenko et al. (2017) Reviews in Fluorescence 2016: Springer, 243-274. [3] C.-Y. Cheng et al. (2015) Biophys J 109, 330. [4] Y. Lee et al. (2016) Biophys J 111, 2481. [5] A. Kyrychenko et al. (2019) J Membr Biol 252, doi:10.1007/s00232-019-00094-1. [6] A. Kyrychenko et al. (2018) J Membr Biol 251, 379. [7] V. Vasquez-Montes et al. (2019) Biochim Biophys Acta 1867, 691.

The surface chemistry of a nanocellulose drug carrier unravelled by MAS-DNP.

Cellulose nanofibrils (CNF) are renewable bio-based materials with high specific area, which makes them ideal candidates for multiple emerging applications including for instance on-demand drug release. However, in-depth chemical and structural characterization of the CNF surface chemistry is still an open challenge, especially for low weight percentage of functionalization. This currently prevents the development of efficient, cost-effective and reproducible green synthetic routes and thus the widespread development of targeted and responsive drug-delivery CNF carriers. We show in this work how we use dynamic nuclear polarization (DNP) to overcome the sensitivity limitation of conventional solid-state NMR and gain insight into the surface chemistry of drug-functionalized TEMPO-oxidized cellulose nanofibrils. The DNP enhanced-NMR data can report unambiguously on the presence of trace amounts of TEMPO moieties and depolymerized cellulosic units in the starting material, as well as coupling agents on the CNFs surface (used in the heterogeneous reaction). This enables a precise estimation of the drug loading while differentiating adsorption from covalent bonding (∼1 wt% in our case) as opposed to other analytical techniques such as elemental analysis and conductometric titration that can neither detect the presence of coupling agents, nor differentiate unambiguously between adsorption and grafting. The approach, which does not rely on the use of 13C/15N enriched compounds, will be key to further develop efficient surface chemistry routes and has direct implication for the development of drug delivery applications both in terms of safety and dosage.

Incorporating electrospun nanofibers of TEMPO-grafted PVDF-HFP polymer matrix in viologen-based electrochromic devices

A novel polymer, denoted as TP-X, is synthesized by grafting 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) onto the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) backbone. TP-X was electrospun into a nanofibrous polymer matrix and introduced into viologen-based electrochromic devices (ECDs). Heptyl viologen (HV) was chosen as the electrochromic material and TEMPO was added as the stable redox couple in the ECDs in this study. The results show that the addition of TP-X nanofibers (TP-X NF) effectively reduced the aggregation of HV and the grafted TEMPO moieties provide the extended surface area for electron transfer. The reduction in viologen aggregation led to outstanding stability and the extended electron transfer surface area resulted in fast write-erase response for ECDs with TP-X NF polymer matrix. The optimized ECD containing the TP-10 NF showed fast write-erase response times of 2.3 and 1.5 s for bleaching and coloring at 605 nm, respectively. More importantly, the incorporation of TP-10 NF gave improved stability of the ECDs, which retained more than 83% of its initial transmittance change at 605 nm after 10,000 operation cycles, as compared to the conventional solution-type ECD (27.3%). This study provides a potential polymer matrix to be utilized in various electrochemical applications for pursuing decent performance and reliable stability.