Pulsed Nuclear Magnetic Resonance Spectroscopy Research Articles

Tracking nitrite's deviation from Stokes-Einstein predictions with pulsed field gradient 15N NMR spectroscopy.

Predicting the behavior of oxyanions in radioactive waste stored at the Department of Energy legacy nuclear sites requires the development of novel analytical methods. This work demonstrates 15N pulsed field gradient nuclear magnetic resonance spectroscopy to quantify the diffusivity of nitrite. Experimental results, supported by molecular dynamics simulations, indicate that the diffusivity of free hydrated nitrite exceeds that of free hydrated sodium despite the greater hydrodynamic radius of nitrite. Investigations are underway to understand how the compositional and dynamical heterogeneities of the ion networks at high concentrations affect rheological and transport properties.

High-performance anion exchange membrane water electrolysis by polysulfone grafted with tetramethyl ammonium functionalities

‘Green’ hydrogen production using anion exchange membrane (AEM) water electrolysis is one of the most promising approaches to address the severe energy crisis facing human society. However, to enable commercially viable hydrogen generation, huge improvement in the AEM technology is imperative, including membrane stability, higher operating temperature, ion conductivity, power performance, and cost reduction. Herein, a novel anion conductive membrane for water electrolysis is synthesized using low-cost and eco-friendly polysulfone as the base polymer, while chemical grafting of quaternary ammonium functionalities has been exploited to confer anion conductive properties. The physicochemical features, the mechanical properties, and the electrochemical performance were widely investigated by a combination of various techniques including DMA, pulsed field gradient nuclear magnetic resonance spectroscopy, electrochemical impedance spectroscopy, and linear sweep voltammetry in an electrolysis cell. The quaternary-ammonium-modified polysulfone (qPSU) membrane exhibited impressive hydrolytic and mechanical stabilities as a result of a nanophase segregation between hydrophilic/hydrophobic domains in such electrolytes. The latter feature enables the formation of wide percolating ion clusters in the qPSU AEM, which form a highly interconnected pathway for efficient hydroxide conduction. Water electrolysis single cells equipped with this membrane reached the remarkable current density of 4.2 A/cm2 at 2.2 V and 90 °C.

A High-Entropy Multicationic Substituted Lithium Argyrodite Superionic Solid Electrolyte

Bulk-type solid-state batteries (SSBs) constitute a promising next-generation technology for electrochemical energy storage. However, in order for SSBs to become competitive with mature battery technologies, (electro)chemically stable, superionic solid electrolytes are much needed. Multicomponent or high-entropy lithium argyrodites have recently attracted attention for their favorable material characteristics. In the present work, we report on increasing the configurational entropy of the Li6+aP1–xMxS5I solid electrolyte system and examine how this affects the structure-conductivity/stability relationships. Using electrochemical impedance spectroscopy and 7Li pulsed field gradient nuclear magnetic resonance (NMR) spectroscopy, multicationic substitution is demonstrated to result in a very low activation energy for Li diffusion of ∼0.2 eV and a high room-temperature ionic conductivity of ∼13 mS cm–1 (for Li6.5[P0.25Si0.25Ge0.25Sb0.25]S5I). The transport properties are rationalized from a structural perspective by means of complementary neutron powder diffraction and magic-angle spinning NMR spectroscopy measurements. The Li6.5[P0.25Si0.25Ge0.25Sb0.25]S5I solid electrolyte was also tested in high-loading SSB cells with a Ni-rich layered oxide cathode and found by X-ray photoelectron spectroscopy to suffer from interfacial side reactions during cycling. Overall, the results of this study indicate that optimization of conductivity is equally important to optimization of stability, and compositionally complex lithium argyrodites represent a new playground for a rational design of (potentially advanced) superionic solid electrolytes.

Ionic liquid plasticizers comprising solvating cations for lithium metal polymer batteries

Ternary solid polymer electrolytes (TSPEs) with ionic liquids (ILs) including alkyl-based ammonium cations and low coordinating anions suffer from the lack of Li+ ion coordination by the ILs compared to the immobile polymer backbone, in terms of Li+ ion transport. Thus, solvating ionic liquids (SILs) with an oligo(ethylene oxide) side chain attached onto the cation were prepared to improve the interaction between Li+ and the IL and accelerate Li+ transport in TSPEs. A variety of methods, such as pulsed field gradient nuclear magnetic resonance spectroscopy, Li metal plating/stripping and measurements of Sand's times were used to show that Li+ ion transference numbers increase with the oligo(ethylene oxide) side chain length in SIL-based TSPEs, which results in faster Li+ ion transport and translates into much slower lithium depletion at a given current, thereby delaying the onset of fast dendrite growth of lithium metal.

Fast Water-Assisted Lithium Ion Conduction in Restacked Lithium Tin Sulfide Nanosheets

While two-dimensional (2D) materials may preserve some intrinsic properties of the corresponding layered bulk material, new characteristics arise from their pronounced anisotropy or confinement effects. Recently, exceptionally high ionic conductivities were discovered in 2D materials such as graphene oxide and vermiculite. Here, we report on the water-assisted fast conduction of lithium ions in restacked lithium tin sulfide nanosheets. Li0.8Sn0.8S2 exfoliates spontaneously in water and can be restacked into homogeneous films in which the lithium content is decreased, and a partial substitution of sulfur with hydroxyl groups takes place. Using a recursive supercell refinement approach in reciprocal space along with real-space pair distribution function analysis, we describe restacked lithium tin sulfide as a partially turbostratically disordered material composed of lithium-containing and lithium-depleted layers. In humid air, the material takes up multiple layers of water that coordinate lithium ions in the space between the layers, increasing the stacking distance and screening the interaction between lithium ions and the anionic layers. This results in a 1000-fold increase in ionic conductivity up to 47 mS cm–1 at high humidities. Orientation-dependent impedance spectroscopy suggests a facile in-plane conduction and a hindered out-of-plane conduction. Pulsed field gradient nuclear magnetic resonance spectroscopy reveals a fast, simultaneous diffusion of a majority and a minority species for both 7Li and 1H, suggesting water-assisted lithium diffusion to be at play. This study enlarges the family of nanosheet-based ionic conductors and helps to rationalize the transport mechanism of lithium ions enabled by hydration in a nanoconfined 2D space.

Propylene carbonate-nitrile solvent blends for thermally stable gel polymer lithium ion battery electrolytes

Gel polymer electrolytes (GPEs) based on poly (vinylidene difluoride-co-hexafluoropropylene) (PVdF-HFP) containing propylene carbonate (PC), isobutyronitrile (IBN) and trimethyl acetonitrile (TMAN) solvent blend electrolytes were developed to enhance high temperature electrochemical performance and to improve safety of LiNi3/5Mn1/5Co1/5O2 (NMC622)‖graphite lithium ion battery (LIB) cells. These liquid electrolytes (LE) consist of lithium bis(trifluoro-methane)sulfonimide (LiTFSI) as conducting lithium salt and PC/nitrile (1:1, v/v) solvent blends. Ethylene sulfite (ES) and vinylene carbonate (VC) were used as solid electrolyte interphase (SEI) forming additives and contributing to an excellent cycling stability of electrolytes comprising nitrile solvents in NMC622‖graphite cells. Electrochemical impedance spectroscopy (EIS), pulsed field gradient nuclear magnetic resonance spectroscopy (PFG NMR) and relative permittivity determination reveal remarkable ion conducting properties of IBN and TMAN solvents. Since their electrolytes are incompatible with lithium metal electrodes, their electrochemical stability window (ESW) was determined using lithiated lithium titanate (Li7Ti5O12) (LTO) as counter and reference electrodes and the obtained values were confirmed by quantum mechanical computation. Differential scanning calorimetry (DSC) and accelerating rate calorimetry (ARC) confirmed significantly improved safety of IBN and TMAN containing electrolytes. Therefore, PVdF-HFP-based GPEs containing PC/nitrile solvent blends are a promising alternative to SOTA electrolyte for battery cycling at elevated temperature (60 °C) in NMC622‖graphite cells.

Unravelling the role of a green rejuvenator agent in contrasting the aging effect on bitumen: A dynamics rheology, nuclear magnetic relaxometry and self-diffusion study

This paper evaluated the potentialities of a green and biocompatible rejuvenator agent (HR) in conferring an appreciable resistance against the effects caused by artificial aging on a given bitumen. Both neat and aged bitumens were analyzed and compared to analogous samples modified with HR. Control samples containing a vegetable oil as softening agent were also tested for comparison. The tested samples were subjected to a second aging cycle. Structural differences between the samples were carried out through an inverse Laplace transform of the NMR spin-echo decay (T2) and self-diffusion measurements by pulsed gradient spin echo nuclear magnetic resonance (PGSE-NMR) spectroscopy. In addition, dynamic rheological analyses were conducted to determine the dependence of the gel-sol transition temperature on both the type of additive and ageing process. The present study clearly highlighted the fact that artificial ageing, realized here by the rolling thin film oven test (RTFOT) and the pressure ageing vessel (PAV) test, induced important structural modifications. The analysis of relaxation times and self-diffusion coefficients indicated that ageing promoted the formation of molecular populations characterized by a shift of the distribution toward higher molecular weights compared to unaged bitumen. Diffusion data showed also an Arrhenius-like temperature dependence. A correlation between all the data was attempted to understand the role of the investigated additives. The eco-friendly biocompatible rejuvenator helped not only to restore the structure of the aged bitumen, but even slowed down the processes of a second aging (aiming at the first aged sample).

Obtaining Hydrodynamic Radii of Intrinsically Disordered Protein Ensembles by Pulsed Field Gradient NMR Measurements.

In the disordered state, a protein exhibits a high degree of structural freedom, in both space and time. For an ensemble of disordered or unfolded proteins, this means that the ensemble comprises a high diversity of structures, ranging from compact collapsed states to fully extended polypeptide chains. In addition, each chain is highly dynamic and undergoes conformational changes and local dynamics on both fast and slow timescales. The size properties of disordered proteins are thus best described as ensemble averages. A straightforward measure of the size is the hydrodynamic radius, RH, of the ensemble. Since the disordered state is conformationally fluid, the observed RH does not refer to a particular shape or fold. Instead, it should be interpreted as a measure for the average compaction of the structural ensemble. In addition to characterizing the disordered ensemble itself, RH can be used to, with good precision, monitor changes in the ensemble size properties upon functional interactions of the disordered protein, e.g., dimerization, ligand binding, and folding pathways. Here, we present a step-by-step protocol for diffusion measurements using pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy. We describe how to calibrate the magnetic field gradient and offer different schemes for sample preparation. Finally, we describe how to obtain RH directly from the diffusion coefficient as well as from using an internal standard as a reference.

Paclitaxel/β-Cyclodextrin interactions, a perspective from pulsed NMR spectroscopy experiments

Cyclodextrins are cyclic cone shaped oligosaccharides. A guest molecule can be incorporated into the hydrophobic inner of the cyclodextrin to form non-covalent complexes. The formation of these complexes in general, increases the solubility, stability, dissolution rate, and bioavailability of drugs with poor water solubility. Different techniques were applied to gain insights about the interaction between paclitaxel and randomly methylated-β-cyclodextrin during the formation of an inclusion complex. Results from infrared spectroscopy, differential scanning calorimetry, nuclear magnetic resonance and scanning electron microscopy were compared. The fast and economical pulsed nuclear magnetic resonance spectroscopy allows to explain that mol paclitaxel:mol RAMEβ-CD 1:20 was the best ratio to obtain inclusion complexes. In addition, the preferred aromatic ring for the inclusion is that in the position 3’ of the side chain of paclitaxel molecule.

Single platform spin-spin nuclear relaxation time (1H NMR) based technique for assessing dissolution and agglomeration of CuO nanoparticles

This study proposes a single platform tool to capture aggregation and dissolution behaviour of copper oxide nanoparticles in acellular conditions using spin-spin nuclear relaxation time data. The spin-spin nuclear relaxation time gathered from pulsed 1H Nuclear magnetic resonance (NMR) spectroscopy can be mathematically translated to the wetted surface area of nanoparticles. The effect of suspension media (artificial lung fluid, algal growth media, and 1 mM NaNO3) and CuO nanoparticle concentrations (500 mg/L, 250 mg/L, and 100 mg/L) on dissolution, hydrodynamic size, and wetted surface area were determined for seven days. The data obtained through 1H NMR spectroscopy was compared with conventional techniques used for measuring dissolution (atomic absorption spectroscopy) and agglomeration (Centrifugal particle sedimentation, Dynamic light scattering). Dissolution experiments showed CuO nanoparticles to have a range of dissolution from 6% to 90%, based on the nature of media. Hydrodynamic size measurements captured the increment in the size of nanoparticles (73% increase) due to aggregation, and reduction in the size of the nanoparticles (88% decline) due to dissolution. Similarly, the temporal variation in the spin-spin nuclear relaxation time of the nanoparticles ranging from 0.25% to 72% detected dissolution and agglomeration of nanoparticles in three different media conditions. The temporal variation in the wetted surface area with respect to concentration and suspension media ranged from 2 m2/g to 380 m2/g. We have determined experimentally the complex interplay between size reduction-wetted surface area-dissolution of nanoparticles and how it evolves over 7 days period for CuO nanoparticles.

Diffusion coefficient of lithium ions in garnet-type Li6.5La3Zr1.5Ta0.5O12 single crystal probed by 7Li pulsed field gradient-NMR spectroscopy

Diffusion coefficient of lithium ions in Li6.5La3Zr1.5Ta0.5O12 (LLZTO) single crystal is measured using 7Li pulsed field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy in the temperature range from 298 K to 353 K. The Li diffusion coefficient in LLZTO is evaluated to be 1.9 × 10−13 m2 s−1 at 298 K with the activation energy of 0.43 eV. The ionic conductivity of LLZTO single crystal is measured by impedance spectroscopy, which gives 7 × 10−4 S cm−1 at 298 K with the activation energy of 0.43 eV. The diffusion coefficient obtained by PFG-NMR is lesser than the diffusion coefficient calculated from ionic conductivity using Nernst-Einstein relation. The small discrepancy gives the Haven ratio of 0.4, which suggests a correlated migration of the lithium ions in the tetrahedral and octahedral sites in LLZTO. To compare the present result with previous reports, the diffusion time (Δ) dependence is carefully checked in PFG-NMR not only for the single crystal but also the crushed powdered samples, which revealed no significant dependence in the single crystal but small dependence in the crushed samples which may be due to the restricted diffusion in the powder grains.

Variability of seed oil content, fatty acid composition, and nervonic acid content in <em>Acer truncatum</em>, native to 14 regions of China

The seed oil of 138 accessions of 14 Acer truncatum (Aceraceae family) populations native to China were analyzed by pulsed nuclear magnetic resonance spectroscopy and gas chromatography-flame ionization detection. The oil content ranged from 17.81% to 36.56% (mean: 28.57%), which mainly consisted of 14 types of fatty acids. Palmitic (4.69%), stearic (2.30%), oleic (25.19%), linoleic (32.97%), linolenic (2.76%), cis-11-eicosenoic (7.90%), erucic (16.49%), and nervonic (5.76%) fatty acids accounted for 98% of total fat. The nervonic acid content ranged from 3.90% to 7.85% among the accessions. Significant variations in oil content and predominating fatty acids were observed among populations. Hierarchical cluster analysis and principal component analysis detected obvious geographical variation trends among A. truncatum populations which correlate with environmental variations (especially altitude, temperature, and precipitation) and supported the grouping of the populations into three groups according to geographic locations.

Ion Transport Properties and Ionicity of 1,3-Dimethyl-1,2,3-Triazolium Salts with Fluorinated Anions.

1,2,3-Triazolium salts are an important class of materials with a plethora of sophisticated applications. A series of three novel 1,3-dimethyl-1,2,3-triazolium salts with fluorine, containing anions of various size, is synthesized by methylation of 1,2,3-triazole. Their ion conductivity is measured by impedance spectroscopy, and the corresponding ionicities are determined by diffusion coefficients obtained from 1H and 19F pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy data, revealing that the anion strongly influences their ion conductive properties. Since the molar ion conductivities and ionicities of the 1,3-dimethyl-1,2,3-triazolium salts are enhanced in comparison to other 1,2,3-triazolium salts with longer alkyl substituents, they are promising candidates for applications as electrolytes in electrochemical devices.

High Lithium Transference Number Electrolytes Containing Tetratriflylpropene's Lithium Salt.

Electrolytes with a high lithium transference number linked with high ionic conductivity are urgently needed for high power battery operation. In this work, we present newly synthesized lithium tetra(trifluoromethanesulfonyl)propene as a salt-in-glyme-based "salt-in-solvent" electrolyte. We employ impedance spectroscopy in symmetric Li/electrolyte/Li cells and pulsed field gradient nuclear magnetic resonance spectroscopy to investigate the lithium conduction mechanism. We find predominant lithium conductivity with very high lithium transference numbers (∼70% from the polarization experiments) and three times higher ionic conductivity compared to well-known lithium triflate in diglyme electrolyte. This is a consequence of the reduced mobilities of large anions linked with improved ionic dissociation.

Correlation between Ionic Liquid Cytotoxicity and Liposome-Ionic Liquid Interactions.

This study aims at extending the understanding of the toxicity mechanism of ionic liquids (ILs) using various analytical methods and cytotoxicity assays. The cytotoxicity of eight ILs and one zwitterionic compound was determined using mammalian and bacterial cells. The time dependency of the IL toxicity was assessed using human corneal epithelial cells. Hemolysis was performed using human red blood cells and the results were compared with destabilization data of synthetic liposomes upon addition of ILs. The effect of the ILs on the size and zeta potential of liposomes revealed information on changes in the lipid bilayer. Differential scanning calorimetry was used to study the penetration of the ILs into the lipid bilayer. Pulsed field gradient nuclear magnetic resonance spectroscopy was used to determine whether the ILs occurred as unimers, micelles, or if they were bound to liposomes. The results show that the investigated ILs can be divided into three groups based on the cytotoxicity mechanism: cell wall disrupting ILs, ILs exerting toxicity through both cell wall penetration and metabolic alteration, and ILs affecting solely on cell metabolism.

Solidification of the Blends of Fully Hydrogenated Coconut Oil and Non-hydrogenated Coconut Oil

Coconut oil is one of the generally used edible fats in food industries. To modify its texture, coconut oil is frequently treated by full-hydrogenation. Since full-hydrogenation results in extremely hard fat; therefore, blending with more soft material is a good option to reach the required texture. The aim of the present study was to establish the solidification characters of the blends containing both fully hydrogenated and non-hydrogenated coconut oils. Investigations were carried out by means of pulsed nuclear magnetic resonance spectroscopy (pNMR) and differential scanning calorimetry (DSC). Solidification phenomenon was interpreted by the Avrami model. Based on the results, parameters of the Avrami model were calculated. The results proved that these two fats are completely miscible and the equilibrium SFC value of their blends modified in accordance to the blending ratios and temperature gradient. DSC measurements did not show any significant difference in crystallization curves of the samples. Our results may be utilized in food technology, especially when production of fat containing foods needs cooling, for example in the manufacturing of margarine, shortenings, and confectionary fats.

Impact of Micellar Surfactant on Supersaturation and Insight into Solubilization Mechanisms in Supersaturated Solutions of Atazanavir.

The goals of this study were to determine: 1) the impact of surfactants on the "amorphous solubility"; 2) the thermodynamic supersaturation in the presence of surfactant micelles; 3) the mechanism of solute solubilization by surfactant micelles in supersaturated solutions. The crystalline and amorphous solubility of atazanavir was determined in the presence of varying concentrations of micellar sodium dodecyl sulfate (SDS). Flux measurements, using a side-by-side diffusion cell, were employed to determine the free and micellar-bound drug concentrations. The solubilization mechanism as a function of atazanavir concentration was probed using fluorescence spectroscopy. Pulsed gradient spin-echo proton nuclear magnetic resonance (PGSE-NMR) spectroscopy was used to determine the change in micelle size with a change in drug concentration. Changes in the micelle/water partition coefficient, K m/w , as a function of atazanavir concentration led to erroneous estimates of the supersaturation when using concentration ratios. In contrast, determining the free drug concentration using flux measurements enabled improved determination of the thermodynamic supersaturation in the presence of micelles. Fluorescence spectroscopic studies suggested that K m/w changed based on the location of atazanavir solubilization which in turn changed with concentration. Thus, at a concentration equivalent to the crystalline solubility, atazanavir is solubilized by adsorption at the micelle corona, whereas in highly supersaturated solutions it is also solubilized in the micellar core. This difference in solubilization mechanism can lead to a breakdown in the prediction of amorphous solubility in the presence of SDS as well as challenges with determining supersaturation. PGSE-NMR suggested that the size of the SDS micelle is not impacted at the crystalline solubility of the drug but increases when the drug concentration reaches the amorphous solubility, in agreement with the proposed changes in solubilization mechanism. Micellar solubilization of atazanavir is complex, with the solubilization mechanism changing with differences in the degree of (super)saturation. This can result in erroneous predictions of the amorphous solubility and thermodynamic supersaturation in the presence of solubilizing additives. This in turn hinders understanding of the driving force for phase transformations and membrane transport, which is essential to better understand supersaturating dosage forms.

Scaling exponent and dispersity of polymers in solution by diffusion NMR

Molecular mass distribution measurements by pulsed gradient spin echo nuclear magnetic resonance (PGSE NMR) spectroscopy currently require prior knowledge of scaling parameters to convert from polymer self-diffusion coefficient to molecular mass. Reversing the problem, we utilize the scaling relation as prior knowledge to uncover the scaling exponent from within the PGSE data. Thus, the scaling exponent—a measure of polymer conformation and solvent quality—and the dispersity (Mw/Mn) are obtainable from one simple PGSE experiment. The method utilizes constraints and parametric distribution models in a two-step fitting routine involving first the mass-weighted signal and second the number-weighted signal. The method is developed using lognormal and gamma distribution models and tested on experimental PGSE attenuation of the terminal methylene signal and on the sum of all methylene signals of polyethylene glycol in D2O. Scaling exponent and dispersity estimates agree with known values in the majority of instances, leading to the potential application of the method to polymers for which characterization is not possible with alternative techniques.

Effect of the degree of crosslinking on the interfacial layer structure of poly(vinyl chloride) dispersed with crosslinked poly(n-butyl methacrylate) particles

The interfacial layer structure of a model incompatible polymer blend system was analyzed using 1H pulse nuclear magnetic resonance (pulse NMR) spectroscopy. Non-crosslinked and crosslinked poly(n-butyl methacrylate) particles with a mean size of ca. 0.9 μm were prepared by seeded emulsion polymerization, and the degree of crosslinking was varied. The particles were powdered using a freeze-dry method and dispersed in poly(vinyl chloride) by melt blending. Dynamic mechanical analysis indicated that the non-crosslinked particles were completely compatible. In contrast, mutual diffusion of the polymer chains in the crosslinked particles was restricted within the particle/matrix interfacial layer. As a result, an incompatible phase structure in which the crosslinked particles were dispersed in the continuous phase was formed. Pulse NMR analysis indicated that the interfacial layer thickness was in the range of 17–98 nm. The thickness decreased with an increase in the degree of crosslinking in the particles. The interfacial layer thickness in the particles was approximately 10 times larger than that for the incompatible polymer pair. Tensile test results indicated that the elongation at break was dependent on the thickness of the interfacial layer. The yield stress was developed for the particles with high hardness that was independent of the interfacial thickness.

The diffusion and conduction of lithium in poly(ethylene oxide)-based sulfonate ionomers

Pulsed field gradient nuclear magnetic resonance spectroscopy and dielectric relaxation spectroscopy have been utilized to investigate lithium dynamics within poly(ethylene oxide) (PEO)-based lithium sulfonate ionomers of varying ion content. The ion content is set by the fraction of sulfonated phthalates and the molecular weight of the PEO spacer, both of which can be varied independently. The molecular level dynamics of the ionomers are dominated by either Vogel-Fulcher-Tammann or Arrhenius behavior depending on ion content, spacer length, temperature, and degree of ionic aggregation. In these ionomers the main determinants of the self-diffusion of lithium and the observed conductivities are the ion content and ionic states of the lithium ion, which are profoundly affected by the interactions of the lithium ions with the ether oxygens of the polymer. Since many lithium ions move by segmental polymer motion in the ion pair state, their diffusion is significantly larger than that estimated from conductivity using the Nernst-Einstein equation.