Exchange Nuclear Magnetic Resonance Spectroscopy Research Articles

Li-Ion Dynamics in Li2S:LiI Composites – on the Effect of Solid-Solution Formation on Overall Li+ Transport

The enormous interest in developing powerful all-solid-state Li-ion batteries led to a boost in electrolyte research. Some Li-ion conductors have Ag-bearing analogs; the fast Ag+ ion conductor, Ag3SI, could be one of such materials. So far, no clear evidence is available that the Li-counterpart, Li3SI, does exist. Here, we treated an equimolar mixture of Li2S and LiI in high-energy ball mills and followed structural changes via X-ray diffraction (XRD) and magic-angle spinning (MAS) 6,7Li nuclear magnetic resonance (NMR) measurements. Differences in local structures as sensed by MAS NMR will be discussed for annealed and non-annealed samples, that is, powder samples directly obtained after finishing the ball-milling procedure. For nanocrystalline, non-annealed Li2S:LiI, the MAS NMR response is characterized by a broad distribution of NMR lines showing chemical shifts between that of pure Li2S and LiI, hence pointing to the formation of solid-solution like regions.Ion dynamics on different length scales was probed with variable-temperature, potentiostatic conductivity spectroscopy as well as solid-state NMR spin-lattice relaxation (SLR) measurements. Defect-rich nanocrystalline Li2S:LiI has to be characterized by an overall conductivity that is 2 orders of magnitude higher as compared to that of the microcrystalline, annealed reference sample. SLR NMR experiments supports this result and reveal lower activation energies for both the fast local hopping ion dynamics and long-range ion diffusivity in the sample directly obtained after ball milling. Finally, mixing-time dependent 6Li 2D exchange NMR spectroscopy reveals even (very) slow Li+ exchange between the Li2S-rich and LiI-rich regions in the nanocrystalline sample. Off-diagonal intensities are especially seen for mixing times longer than 80 ms.

An integrated solid-state lithium-oxygen battery with highly stable anionic covalent organic frameworks electrolyte

<h2>Summary</h2> Rechargeable solid-state lithium-oxygen (Li-O₂) batteries are considered promising candidates for next-generation energy storage systems. However, the development of solid-state Li-O₂ batteries has been limited by the lack of solid-state electrolytes (SSEs) with high ionic conductivities and high stability toward air/metal Li. To address this challenge, we report the three-dimensional covalent organic framework (3D COF) CD-COF-Li with a prominent Li-ion conductivity of 2.7 × 10⁻³ S cm⁻¹ as the SSE for Li-O₂ batteries. The ion transport in the porous COFs is clarified through two-dimensional exchange nuclear magnetic resonance spectroscopy (2D-EXSY NMR), which provides a method at the forefront for understanding Li-ion transport in the molecular channel. Solid-state Li-O₂ batteries with CD-COF-Li deliver a high specific capacity (9,340 mAh g⁻¹) and a record cycling life (100 cycles). These findings pave the way for the application of COFs as superior Li-ion conductors in other next-generation solid-state energy storage systems.

Dynamics of base pairs with low stability in RNA by solid-state nuclear magnetic resonance exchange spectroscopy

Base pairs are fundamental building blocks of RNA. The base pairs of low stability are often critical in RNA functions. Here, we develop a solid-state NMR-based water-RNA exchange spectroscopy (WaterREXSY) to characterize RNA in solid. The approach uses different chemical exchange rates between iminos and waterto evaluate base pair stability; the less stable ones would exchange more frequently, leading to stronger cross-peaks on WaterREXSY. Applied to the riboA71-adenine complex (the 71nt-aptamer domain of add adenine riboswitch from Vibrio vulnificus), the U47⋅U51 base pair, which is critical in ligand binding, was found to be less stable than other base pairs. The imino-water exchange rates of U47 at different temperatures are about 500-800 s-1, indeed indicative of low stability. This implies a highly complex and plastic triad involving U47⋅U51 and that the opening of the U47⋅U51 base pair may be the early stage of ligand release.

NMR and Theoretical Study of In-Pore Diffusivity of Ionic Liquid-Solvent Mixtures.

Despite having a lower energy density than common batteries, electric double-layer capacitors (EDLCs) offer several advantages for high-power applications, including high power density, quick charge and discharge time, and long cycle life. Room-temperature ionic liquids (RTILs) have been intensely studied as promising electrolytes for applications in ELDCs because of their wide potential window, low volatility, as well as thermal and chemical stability. The main deficiency of neat RTILs in such applications is the sluggish diffusivity, which restricts the EDLCs' power density. To alleviate the slow diffusivity, RTILs can be used in a mixture with organic solvents. In this study, we applied two-dimensional exchange nuclear magnetic resonance spectroscopy (2D EXSY NMR) and molecular dynamics (MD) simulations to investigate the diffusivity of anions of an RTIL, namely, 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (BMIM+-TFSI-), dissolved in five different organic solvents, in the micropores of activated carbon. We determined that the relative concentrations of ions in solutions in the micropores were higher than those in the bulk solutions and were also solvent-dependent. The ion diffusivities in the pores were found to be almost 2 orders of magnitude slower than in the bulk solutions, with methanol showing the largest relative disparity. These results suggested that the interactions of solvents with the activated carbon are critical not only to the power density of EDLCs but also to the energy density. The comparisons of ion diffusivities between the experiments and the MD simulations suggest the need to consider also the surface functionalities of activated carbon for the simulation of ion diffusion in the micropores of activated carbon.

Direct observation of reversible bond homolysis by 2D EXSY NMR.

Bond homolysis is one of the most fundamental bond cleavage mechanisms. Thus, understanding of bond homolysis influences the development of a wide range of chemistry. Photolytic bond homolysis and its reverse process have been observed directly using time-resolved spectroscopy. However, direct observation of reversible bond homolysis remains elusive. Here, we report the direct observation of reversible Co–Co bond homolysis using two-dimensional nuclear magnetic resonance exchange spectroscopy (2D EXSY NMR). The characterization of species involved in this homolysis is firmly supported by diffusion ordered NMR spectroscopy (DOSY NMR). The unambiguous characterization of the Co–Co bond homolysis process enabled us to study ligand steric and electronic factors that influence the strength of the Co–Co bond. Understanding of these factors will contribute to rational design of multimetallic complexes with desired physical properties or catalytic activity.

Interactions of IDPs with Membranes Using Dark-State Exchange NMR Spectroscopy.

Membrane interactions of proteins play a role in essential cellular processes in both physiological and disease states. The structural flexibility of intrinsically disordered proteins (IDPs) allows for interactions with multiple partners, including membranes. However, determining conformational states of IDPs when interacting with membranes can be challenging. Here we describe the use of nuclear magnetic resonance (NMR), including dark-state exchange saturation transfer (DEST), to probe IDP-membrane interactions in order to determine whether there is an interaction, which residues participate, and the extent/nature of the interaction between the protein and the membrane. Using α-synuclein and tau as typical examples, we provide protocols for how the membrane interactions of IDPs can be probed, including details of how the samples should be prepared and guidelines on how to interpret the results.

A lithium argyrodite Li6PS5Cl0.5Br0.5 electrolyte with improved bulk and interfacial conductivity

The increased safety associated with all-solid-state batteries using inorganic ceramic electrolytes make it a promising technology, with potential to replace current commercial battery systems. The key challenges to realize this technology are the development of new solid electrolytes with high ionic conductivity and optimization of the ionic transport pathways across the multiple phases of the battery. In this study an optimal composition of the argyrodite i.e. Li6PS5Cl0.5Br0.5 is synthesized via the mechanical milling method. This material possesses a higher bulk ionic conductivity and reduced activation energy than the single halogen doped argyrodites i.e. Li6PS5X (X = Cl and Br), assessed by temperature-dependent impedance spectroscopy and Nuclear Magnetic Resonance (NMR) relaxometry. A combined X-ray and neutron diffraction analysis reveals an influence of the composition and distribution of halogen atoms on the Li-ion conductivity. All-solid-state batteries fabricated using Li2S as cathode show a high reversible capacity of 820 mAh g−1 for up to 30 cycles. In addition, the Li-ion diffusion across the interface between the Li2S cathode and Li6PS5Cl0.5Br0.5 electrolyte is probed by exchange NMR spectroscopy. It reveals that Li-ion diffusion across this interface was the main factor limiting the performance of Li6PS5Cl0.5Br0.5 in the battery, despite its high bulk ionic conductivity.

Go in and Go out — Change in Local Structure and Diffusivity in Monoclinic Li3+X V2(PO4)3 upon Li Insertion and Extraction

The use of Li-ion batteries in our daily life has become vital and is going to increase further as the demand for portable energy storage systems will continue to rise in the future. Considering advanced anode and cathode materials a fundamental understanding is needed to visualize the electrochemical processes, local changes in structure and diffusivity upon insertion and extraction of Li ions. Monoclinic α-Li3+x V2(PO4)3 (LVP), crystallizing with the space group P21 /n, serves as a very attractive model compound to study these changes. As a chameleon-like electrode material it can be used as both the anode and cathode active material [1]. The Li ions in LVP (x = 0) are equally distributed over 3 crystal sites, which are clearly resolved in high-resolution 7Li magic angle spinning (MAS) nuclear magnetic resonance (NMR). As has been shown earlier by the Goward group [2], 1D and 2D exchange NMR spectroscopy is an excellent tool to identify site-specific ion mobilities and to identify the electrochemically active Li positions. Less attention has, however, been paid to LVP with x > 0. Although the topic has been addressed earlier [2,3], a complete picture about the correlation of local magnetic structures with macroscopic phase transitions is still missing. Here, we used 7Li MAS NMR, combined with both X-ray and neutron diffraction to throw some light on the changes LVP undergoes during Li uptake and release (− 2 < x < 2). As an example, Li insertion causes a drastic change of the original 7Li NMR spectrum of LVP. For Li3.5V2(PO4) the spectrum recorded at ambient bearing gas temperature consists of at least 4 distinct NMR signals being sharper than those of the starting materials with x = 0. Further increase of x to values larger than 1 reveals a second change leading a quite complex NMR signal with many overlapping lines. For Li3.5V2(PO4) and Li4.0V2(PO4) 2D 6Li MAS NMR will help us to understand the elementary hopping processes in the vanadium phosphate. Financial support by the Austrian Federal Ministry for Science, Research and Economy as well as the Christian-Doppler Forschungsgesellschaft is highly appreciated. [1] W.-F. Mao, H.-Q. Tang, Z.-Y. Tang, J. Yan, and Q. Xu, ECS Electrochem. Lett., 2 (7), A69-A71, (2013). [2] L. S. Cahill, R. P. Chapman, J. F. Britten, and G. R. Goward, J. Phys. Chem. B, 110, 7171-7177, (2006). [3] C. Liu, R. Massé, X. Nan, G. Cao, Energy Storage Mater., 4, 15-58, (2016). [4] S.-C. Yin, P. S. Strobel, H. Grondey, L. F. Nazar, Chem. Mater., 16, 1456-1465, (2004).

Discovery and characterization of a sulfoquinovose mutarotase using kinetic analysis at equilibrium by exchange spectroscopy.

Bacterial sulfoglycolytic pathways catabolize sulfoquinovose (SQ), or glycosides thereof, to generate a three-carbon metabolite for primary cellular metabolism and a three-carbon sulfonate that is expelled from the cell. Sulfoglycolytic operons encoding an Embden–Meyerhof–Parnas-like or Entner–Doudoroff (ED)-like pathway harbor an uncharacterized gene (yihR in Escherichia coli; PpSQ1_00415 in Pseudomonas putida) that is up-regulated in the presence of SQ, has been annotated as an aldose-1-epimerase and which may encode an SQ mutarotase. Our sequence analyses and structural modeling confirmed that these proteins possess mutarotase-like active sites with conserved catalytic residues. We overexpressed the homolog from the sulfo-ED operon of Herbaspirillum seropedicaea (HsSQM) and used it to demonstrate SQ mutarotase activity for the first time. This was accomplished using nuclear magnetic resonance exchange spectroscopy, a method that allows the chemical exchange of magnetization between the two SQ anomers at equilibrium. HsSQM also catalyzed the mutarotation of various aldohexoses with an equatorial 2-hydroxy group, including d-galactose, d-glucose, d-glucose-6-phosphate (Glc-6-P), and d-glucuronic acid, but not d-mannose. HsSQM displayed only 5-fold selectivity in terms of efficiency (kcat/KM) for SQ versus the glycolysis intermediate Glc-6-P; however, its proficiency [kuncat/(kcat/KM)] for SQ was 17 000-fold better than for Glc-6-P, revealing that HsSQM preferentially stabilizes the SQ transition state.

Dispersion Forces and the Molecular Origin of Internal Friction in Protein.

Internal friction in macromolecules is one of the curious phenomena that control conformational changes and reaction rates. It is held here that dispersion interactions and London-van der Waals forces between nonbonded atoms are major contributors to internal friction. To demonstrate this, the flipping motion of aromatic rings of F10 and Y97 amino acid residues of cytochrome c has been studied in glycerol/water mixtures by cross relaxation-suppressed exchange nuclear magnetic resonance spectroscopy. The ring-flip rate is highly overdamped by glycerol, but this is not due to the effect of protein-solvent interactions on the Brownian dynamics of the protein, because glycerol cannot penetrate into the protein to slow the internal collective motions. Sound velocity in the protein under matching solvent conditions shows that glycerol exerts its effect by rather smothering the protein interior to produce reduced molecular compressibility and root-mean-square volume fluctuation (δVRMS), implying an increased number of dispersion interactions of nonbonded atoms. Hence, δVRMS can be used as a proxy for internal friction. By using the ansatz that internal friction is related to nonbonded interactions by the equation f(n) = f0 + f1n + f2n(2) + ..., where the variable n is the extent of nonbonded interactions with fi coefficients, the barrier to aromatic ring rotation is found to be flat. Also interesting is the appearance of a turnover region in the δVRMS dependence of the ring-flip rate, suggesting anomalous internal diffusion. We conclude that cohesive forces among nonbonded atoms are major contributors to the molecular origin of internal friction.

Dynamic heterogeneities in glass-forming systems

We discuss the manifestation of dynamic heterogeneities in binary glass formers made of components with strongly different glass transition temperatures as revealed by 2H and 31P nuclear magnetic resonance spectroscopy (NMR) techniques such as line-shape, spin-lattice relaxation, and 2D exchange NMR. Polymer–plasticizer and non-polymeric mixtures are considered. Together with results from dielectric spectroscopy as well as from dynamic light scattering the component dynamics is probed separately. While the high-Tg component shows relaxation features similar to that of neat glass formers, the majority of the low-Tg component displays significantly faster dynamics and shows pronounced dynamic heterogeneities, i.e., an extremely broad distribution of correlation times G(ln τ), which may lead to quasi-logarithmic correlation functions and which are reflected in a characteristic NMR phenomenology. Consequently, two glass transition temperatures with non-trivial concentration dependences are identified. The dynamic heterogeneities are transient in nature as proven by 2D exchange NMR. Thus, below the upper Tg liquid-like (isotropic) reorientation as well as exchange within the distribution G(ln τ) is observed in an essentially rigid matrix formed by the high-Tg component. Yet, we find indications that a small fraction of the low-Tg component follows the dynamics of the high-Tg component. The results are compared with those collected for glass formers subjected to confining geometries. In both cases, the NMR features are very similar suggesting that also in binary glass formers (intrinsic) confinement effects may control the dynamics.

Insights into Li+ Migration Pathways in α-Li3VF6: A First-Principles Investigation

Magnetic, structural, and defect properties of lithium vanadium hexafluoride (α-Li3VF6) are investigated theoretically with periodic quantum chemical methods. It is found that the ferromagnetic phase is more stable than the antiferromagnetic phase. The crystal structure contains three inequivalent Li sites (Li(1), Li(2), and Li(3)), where Li(1) occupies the middle position of the triplet Li(2)-Li(1)-Li(3). The calculated Li vacancy formation energies show that vacancy formation is preferred for the Li(1) and Li(3) sites compared to the Li(2) position. The Li exchange processes between Li(1) ↔ Li(3), Li(1) ↔ Li(2), and Li(2) ↔ Li(3) are studied by calculating the Li(+) migration between these sites using the climbing-image nudged elastic band approach. It is observed that Li exchange in α-Li3VF6 may take place in the following order: Li(1) ↔ Li(3) > (Li(1) ↔ Li(2) > Li(2) ↔ Li(3). This is in agreement with recently published results obtained from 1D and 2D (6)Li exchange nuclear magnetic resonance spectroscopy.

Molecular exchange of n-hexane in zeolite sieves studied by diffusion–diffusion and T1-diffusion nuclear magnetic resonance exchange spectroscopy

Molecular exchange properties and diffusion of n-hexane embedded in a bimodal pore structure with characteristic length scales in the order of nano and micrometres, respectively, formed by packing of zeolite particles, are studied. Two-dimensional (2D) nuclear magnetic resonance (NMR) diffusion correlation experiments together with relaxation–diffusion correlation experiments are performed at low magnetic field using a single-sided NMR scanner. The exchange time covers a range from 10−3 to 10−1 s. The molecular exchange properties are modulated by transport inside the zeolite particles. Different exchange regimes are observed for molecules starting from different positions inside the porous sample. The influence of the spin–lattice relaxation properties of the fluid molecules inside the zeolite particles on the signal intensity is also studied. A Monte Carlo simulation of the exchange process is performed and is used to support the analysis of the experimental data.

Studying base pair open–close kinetics of tRNA Leu by TROSY-based proton exchange NMR spectroscopy

The millisecond conformational flexibility is functionally important for nucleic acids and can be studied through probing the base pair open–close kinetics by proton exchange nuclear magnetic resonance (NMR) spectroscopy. Here, the traditional imino proton exchange NMR experiments were modified with transverse relaxation optimized spectroscopy and were applied to accurately measure imino proton exchange rates of all base pairs in Escherichia coli tRNA Leu (CAG), and their dependence on magnesium ion concentration. Finally, we correlated millisecond conformational flexibility with aminoacylation of tRNA Leu and proposed that the flexibility of the acceptor stem and the core region might contribute to aminoacylation of tRNA Leu.

On the use of 2D correlation and exchange NMR spectroscopy in organic porous materials

Two-dimensional (2D) nuclear magnetic resonance (NMR) methods for the investigation of correlation and exchange have been introduced in recent years and have been applied to a range of different systems. Here, we report on the use of 2D NMR diffusion-diffusion correlation spectroscopy for the investigation of diffusion anisotropy in cellular plant tissues and of diffusion-diffusion exchange spectroscopy for the study of the diffusive exchange of dextran in a dispersion of polyelectrolyte multilayer hollow capsules. Furthermore, diffusion-relaxation correlation spectroscopy was applied to both systems.

Laser-Induced Luminescence Study of Samarium(III) Thiodiglycolate Complexes

studies of hydration structure for lanthanides. The fact that many f-element salts which have relatively large lattice energies are fairly soluble in water is a reflection of the strength of the interactions between the metal cations and water molecules. In turn, this strong hydration competes with complexation by ligand as the process of complexation involves the displacement of one or more water molecules by a ligand. The techniques for studying the size and/or structure of the hydration sphere can be classified as direct or indirect methods. The direct methods include X-ray and neutron diffraction, extended X-ray absorption fine structure (EXAFS), nuclear magnetic resonance (NMR) relaxation measurements, luminescence decay. The indirect methods involve compressibility, NMR exchange and adsorption spectroscopy measurements. 15 The luminescence of trivalent lanthanides has presently extensively attracted in a variety of complexes in solution with much attention. This includes the determination of the local structures in crystalline materials, glasses, and solutions. The luminescence intensity and lifetime of trivalent lanthanide (Ln) and actinide (An) ions has been used to gain information on the composition and structure of the first coordination sphere of these ions in solution in materials ranging from inorganic compounds to systems of biological interest. 16 The luminescence lifetime of Ln and An is related to N H2O (the number of H2O molecules in the primary coordination sphere of the metal ion) due to the energy transfer from the excited state of the metal ion to the O-H vibration of the coordinated water molecules. A correlation between the luminescence decay constant kobs (the reciprocal of the excited state lifetime) and the NH2O of trivalent lanthanide (Ln) and actinide (An) ions has therefore been investigated to establish a method for determining the NH2O from measurements of the luminescence lifetime. 17 The calibration relations were derived on the basis of the linear correlation of the luminescence decay constant kobs vs. volume percentage of H2O in D2O-H2O solutions and the inner-sphere hydration number N H2O in

Dynamic Exchange Properties of the Antiparallel BacteriochlorophyllcDimers

The dynamic exchange behavior of the (31R)-type bacteriochlorophyll (BChl) c dimer with an antiparallel piggy-back conformation has been investigated by two-dimensional nuclear magnetic resonance exchange spectroscopy (EXSY). The exchange rate between two BChl c molecules in the antiparallel dimer was evaluated from the integrated intensities of cross-peaks due to chemical exchange in the EXSY spectra, and its values were found to dramatically increase with the rise of solvent polarity. The temperature dependence of the exchange rates can be well expressed by the Arrhenius equation, the parameters of which show the correlation of the fast exchange rate with the stability of a transition state in the exchange process. Thermodynamic analysis was also applied to investigate the substituent effect on the exchange rate of the antiparallel dimer. The increase of the exchange rate upon addition of substituents at the peripheral 8-position was mainly attributed to the rise in frequency factor rather than activati...

129Xe nuclear magnetic resonance investigation of carbon black aggregate morphology

The morphology of three ‘normal’ ASTM carbon black reinforcement fillers (N110, N347, and N472) is investigated for the first time using one- and two-dimensional 129Xe nuclear magnetic resonance (NMR) spectroscopy. A wide range in 129Xe NMR chemical shift is observed among samples, and is attributed to variations in the physical nature of the unoccupied volume formed by the subunit particles of the aggregate. 129Xe NMR chemical shift and integrated intensity parameters are extracted from a single one-dimensional experiment, and interpreted in terms of aggregate void size, volume, and density. The rate of exchange of 129Xe atoms between different aggregates in a three component blend is approximated using two-dimensional exchange NMR spectroscopy, and found to occur on a timescale ∼6 ms≤ τ ex≤∼100 ms. No evidence of xenon exchange between samples N110 and N472 was observed on timescales less than 100 ms, an apparent consequence of the small aggregate void size in these samples. The 129Xe NMR chemical shift assignments for samples N110, N347, and N472 are shown to be not significantly shifted from their non-exchanging values.

Three-dimensional nuclear magnetic resonance exchange spectroscopy with rotary resonance in rotating solids: Application to tropolone dynamics

A three-dimensional nuclear magnetic resonance (NMR) experiment is described for the investigation of molecular rearrangements in the course of chemical exchange processes. The experiment relies on the two-dimensional correlation of the chemical shift tensors before and after exchange. The chemical shift tensors are retrieved under fast magic angle spinning by rotary resonance induced by a radio-frequency field whose magnitude matches the sample spinning frequency. The third dimension serves for the separation of the two-dimensional chemical shift patterns by the isotropic chemical shifts. The three-dimensional rotary-resonance C13-exchange experiment is demonstrated with an investigation of hydrogen-transfer and molecular diffusion processes in a sample of solid tropolone.

Investigation of molecular structure in solids by two-dimensional NMR exchange spectroscopy with magic angle spinning

An approach to the investigation of molecular structures in disordered solids, using two-dimensional (2D) nuclear magnetic resonance (NMR) exchange spectroscopy with magic angle spinning (MAS), is described. This approach permits the determination of the relative orientation of two isotopically labeled chemical groups within a molecule in an unoriented sample, thus placing strong constraints on the molecular conformation. Structural information is contained in the amplitudes of crosspeaks in rotor-synchronized 2D MAS exchange spectra that connect spinning sideband lines of the two labeled sites. The theory for calculating the amplitudes of spinning sideband crosspeaks in 2D MAS exchange spectra, in the limit of complete magnetization exchange between the labeled sites, is presented in detail. A new technique that enhances the sensitivity of 2D MAS exchange spectra to molecular structure, called orientationally weighted 2D MAS exchange spectroscopy, is introduced. Symmetry principles that underlie the construction of pulse sequences for orientationally weighted 2D MAS exchange spectroscopy are explained. Experimental demonstrations of the utility of 2D MAS exchange spectroscopy in structural investigations of peptide and protein backbone conformations are carried out on a model 13C-labeled tripeptide, L-alanylglycylglycine. The dihedral angles φ and ψ that characterize the peptide backbone conformation at Gly-2 are obtained accurately from the orientationally weighted and unweighted 2D 13C NMR exchange spectra.