High-resolution Solid-state NMR Research Articles

High-Resolution 17O Solid-State NMR as a Unique Probe for Investigating Oxalate Binding Modes in Materials: The Case Study of Calcium Oxalate Biominerals.

Oxalate ligands are found in many classes of materials, including energy storage materials and biominerals. Determining their local environments at the atomic scale is thus paramount to establishing the structure and properties of numerous phases. Here, we show that high-resolution 17O solid-state NMR is a valuable asset for investigating the structure of crystalline oxalate systems. First, an efficient 17O-enrichment procedure of oxalate ligands is demonstrated using mechanochemistry. Then, 17O-enriched oxalates were used for the synthesis of the biologically relevant calcium oxalate monohydrate (COM) phase, enabling the analysis of its structure and heat-induced phase transitions by high-resolution 17O NMR. Studies of the low-temperature COM form (LT-COM), using magnetic fields from 9.4 to 35.2 T, as well as 13C-17O MQ/D-RINEPT and 17O{1H} MQ/REDOR experiments, enabled the 8 inequivalent oxygen sites of the oxalates to be resolved, and tentatively assigned. The structural changes upon heat treatment of COM were also followed by high-resolution 17O NMR, providing new insight into the structures of the high-temperature form (HT-COM) and anhydrous calcium oxalate α-phase (α-COA), including the presence of structural disorder in the latter case. Overall, this work highlights the ease associated with 17O-enrichment of oxalate oxygens, and how it enables high-resolution solid-state NMR, for "NMR crystallography" investigations.

New insights into aging in LiNiO2 cathodes from high resolution paramagnetic NMR spectroscopy.

Bulk degradation processes are examined in the LiNiO2 cathode using high resolution solid-state NMR, combined with magnetometry and X-ray diffraction. Capacity decay is correlated with bulk heterogeneity, whereby multiple structural domains coexist in the charged state, and the Li content and electrochemical activity of these domains is unraveled for the first time.

Distinguishing Different Hydrogen-Bonded Helices in Proteins by Efficient 1H-Detected Three-Dimensional Solid-State NMR.

Helical structures in proteins include not only α-helices but also 310 and π helices. These secondary structures differ in the registry of the C═O···H-N hydrogen bonds, which are i to i + 4 for α-helices, i to i + 3 for 310 helices, and i to i + 5 for π-helices. The standard NMR observable of protein secondary structures are chemical shifts, which are, however, insensitive to the precise type of helices. Here, we introduce a three-dimensional (3D) 1H-detected experiment that measures and assigns CO-HN cross-peaks to distinguish the different types of hydrogen-bonded helices. This hCOhNH experiment combines efficient cross-polarization from CO to HN with 13C, 15N, and 1H chemical shift correlation to detect the relative proximities of the COi-Hi+jN spin pairs. We demonstrate this experiment on the membrane-bound transmembrane domain of the SARS-CoV-2 envelope (E) protein (ETM). We show that the C-terminal five residues of ETM form a 310-helix, whereas the rest of the transmembrane domain have COi-Hi+4N hydrogen bonds that are characteristic of α-helices. This result confirms the recent high-resolution solid-state NMR structure of the open state of ETM, which was solved in the absence of explicit hydrogen-bonding restraints. This C-terminal 310 helix may facilitate proton and calcium conduction across the hydrophobic gate of the channel. This hCOhNH experiment is generally applicable and can be used to distinguish not only different types of helices but also different types of β-strands and other hydrogen-bonded conformations in proteins.

Amyloid fibril formation kinetics of low-pH denatured bovine PI3K-SH3 monitored by three different NMR techniques.

Introduction: Misfolding of amyloidogenic proteins is a molecular hallmark of neurodegenerative diseases in humans. A detailed understanding of the underlying molecular mechanisms is mandatory for developing innovative therapeutic approaches. The bovine PI3K-SH3 domain has been a model system for aggregation and fibril formation. Methods: We monitored the fibril formation kinetics of low pH-denatured recombinantly expressed [U-13C, 15N] labeled bovine PI3K-SH3 by a combination of solution NMR, high-resolution magic angle spinning (HR-MAS) NMR and solid-state NMR spectra. Solution NMR offers the highest sensitivity and, therefore, allows for the recording of two-dimensional NMR spectra with residue-specific resolution for individual time points of the time series. However, it can only follow the decay of the aggregating monomeric species. In solution NMR, aggregation occurs under quiescent experimental conditions. Solid-state NMR has lower sensitivity and allows only for the recording of one-dimensional spectra during the time series. Conversely, solid-state NMR is the only technique to detect disappearing monomers and aggregated species in the same sample by alternatingly recoding scalar coupling and dipolar coupling (CP)-based spectra. HR-MAS NMR is used here as a hybrid method bridging solution and solid-state NMR. In solid-state NMR and HR-MAS NMR the sample is agitated due to magic angle spinning. Results: Good agreement of the decay rate constants of monomeric SH3, measured by the three different NMR methods, is observed. Moderate MAS up to 8kHz seems to influence the aggregation kinetics of seeded fibril formation only slightly. Therefore, under sufficient seeding (1% seeds used here), quiescent conditions (solution NMR), and agitated conditions deliver similar results, arguing against primary nucleation induced by MAS as a major contributor. Using solid-state NMR, we find that the amount of disappeared monomer corresponds approximately to the amount of aggregated species under the applied experimental conditions (250µM PI3K-SH3, pH 2.5, 298K, 1% seeds) and within the experimental error range. Data can be fitted by simple mono-exponential conversion kinetics, with lifetimes τ in the 14-38h range. Atomic force microscopy confirms that fibrils substantially grew in length during the aggregation experiment. This argues for fibril elongation as the dominant growth mechanism in fibril mass (followed by the CP-based solid-state NMR signal). Conclusion: We suggest a combined approach employing both solution NMR and solid-state NMR, back-to-back, on two aliquots of the same sample under seeding conditions as an additional approach to follow monomer depletion and growth of fibril mass simultaneously. Atomic force microscopy images confirm fibril elongation as a major contributor to the increase in fibril mass.

Tapping into the native Pseudomonas bacterial biofilm structure by high-resolution multidimensional solid-state NMR

We present a multidimensional magic-angle spinning (MAS) solid-state NMR (ssNMR) study to characterize native Pseudomonas fluorescens colony biofilms at natural abundance without isotope-labelling. By using a high-resolution INEPT-based 2D 1H–13C ssNMR spectrum and thorough peak deconvolution at the 1D ssNMR spectra, approximately 80/134 (in 1D/2D) distinct biofilm chemical sites were identified. We compared CP and INEPT 13C ssNMR spectra to differentiate signals originating from the mobile and rigid fractions of the biofilm, and qualitatively determined dynamical changes by comparing CP buildup behaviors. Protein and polysaccharide signals were differentiated and identified by utilizing FapC protein signals as a template, a biofilm forming functional amyloid from Pseudomonas. We identified several biofilm polysaccharide species such as glucose, mannan, galactose, heptose, rhamnan, fucose and N-acylated mannuronic acid by using 1H and 13C chemical shifts obtained from the 2D spectrum. To our knowledge, this study marks the first high-resolution multidimensional ssNMR characterization of a native bacterial biofilm. Our experimental pipeline can be readily applied to other in vitro biofilm model systems and natural biofilms and holds the promise of making a substantial impact on biofilm research, fostering new ideas and breakthroughs to aid in the development of strategic approaches to combat infections caused by biofilm-forming bacteria.

Investigation of the structural and electrical conductivity properties in pure and cation exchanged rectorite

Clay minerals, as biofriendly and low-cost materials, are highly essential for the modern industrial applications including the production of clean energy, its storage and conversion. Here, the capabilities of pure and cation exchanged rectorite, a regularly interstratified phyllosilicate from Beatrix Mine (South Africa) were explored and discussed. A comprehensive characterization was performed by means of high resolution solid-state NMR, electrochemical impedance spectroscopy and powder X-ray diffraction. 23Na MAS and 3QMAS NMR spectroscopy was used to characterize accessibility of interlayer space in rectorite for exchangeable cations. Three Na sites attributed to easily exchangeable Na+ on the surface or in large pores, Na+ in dehydrated micaceous interlayers and Na+ in hydrated smectite interlayers were identified. Differences in hydration states in smectitic interlayers depending on the type of intercalation were detected using 1H MAS NMR. A higher amount of hydrating water molecules in pure and Mg-exchanged rectorites was attributed to the higher hydration energy of Ca2+ and Mg2+. The temperature dependences of electrical conductivity in this work were best described using the empirical Vogel-Tammann-Fulcher equation with the temperature-dependent effective activation energy parameter. Significantly stronger change of activation energy in Mg2+ exchanged rectorite in the temperature range of 10 °C to 50 °C as compared to pure rectorite and its Na+, Li+ and NH4+ modifications was related to an extensive H-bond network in the interlayers, which facilitated an effective proton transfer responsible for electric conductivity. The obtained resutls suggested a greater potential for the use of Mg-exchanged rectorite as ionic conductor at enhanced temperatures.

One-Shot Resin 3D-Printed Stators for Low-Cost Fabrication of Magic-Angle Spinning NMR Probeheads.

Additive manufacturing such as three-dimensional (3D)-printing has revolutionized the fast and low-cost fabrication of otherwise expensive NMR parts. High-resolution solid-state NMR spectroscopy demands rotating the sample at a specific angle (54.74°) inside a pneumatic turbine, which must be designed to achieve stable and high spinning speeds without mechanical friction. Moreover, instability of the sample rotation often leads to crashes, resulting in costly repairs. Producing these intricate parts requires traditional machining, which is time-consuming, costly, and relies on specialized labor. Herein, we show that 3D-printing can be used to fabricate the sample holder housing (stator) in one shot, while the radiofrequency (RF) solenoid was constructed using conventional materials available in electronics stores. The 3D-printed stator, equipped with a homemade RF coil, showed remarkable spinning stability, yielding high-quality NMR data. At a cost below 5 €, the 3D-printed stator represents a cost reduction of over 99% compared to repaired commercial stators, illustrating the potential of 3D-printing for mass-producing affordable magic-angle spinning stators.

In Situ Multinuclear Magic-Angle Spinning NMR: Monitoring Crystallization of Molecular Sieve AlPO4-11 in Real Time.

Molecular sieves are crystalline three-dimensional frameworks with well-defined channels and cavities. They have been widely used in industry for many applications such as gas separation/purification, ion exchange, and catalysis. Obviously, understanding the formation mechanisms is fundamentally important. High-resolution solid-state NMR spectroscopy is a powerful method for the study of molecular sieves. However, due to technical challenges, the vast majority of the high-resolution solid-state NMR studies on molecular sieve crystallization are ex situ. In the present work, using a new commercially available NMR rotor that can withhold high pressure and high temperature, we examined the formation of molecular sieve AlPO4-11 under dry gel conversion conditions by in situ multinuclear (1H, 27Al, 31P, and 13C) magic-angle spinning (MAS) solid-state NMR. In situ high-resolution NMR spectra obtained as a function of heating time provide much insights underlying the crystallization mechanism of AlPO4-11. Specifically, in situ 27Al and 31P MAS NMR along with 1H → 31P cross-polarization (CP) MAS NMR were used to monitor the evolution of the local environments of framework Al and P, in situ 1H → 13C CP MAS NMR to follow the behavior of the organic structure directing agent, and in situ 1H MAS NMR to unveil the effect of water content on crystallization kinetics. The in situ MAS NMR results lead to a better understanding of the formation of AlPO4-11.

Structure, Location, and Spatial Proximities of Hydroxyls on γ-Alumina Crystallites by High-Resolution Solid-State NMR and DFT Modeling: Why Edges Hold the Key

The atomic-scale characterization of surface active sites on γ-alumina still represents a great challenge for numerous catalytic applications. Here, we combine advanced density functional theory (DFT) calculations with one- and two-dimensional proton solid-state NMR experiments to identify the exact location and the spatial proximity of hydroxyl groups on γ-alumina crystallites. Our approach relies on revisited models for the (100), (111), basal (110)b, and lateral (110)l facets of γ-alumina, as well as for the edges at their intersections. Notably, we show that the ≃0 ppm AlTd-μ1-OH protons are predominantly located on edges, where these are free from the H-bond network. The proximities among the AlTd-μ1-OH as well as with μ2-OH groups are revealed by 1H–1H dipolar correlation experiments and analyzed in the light of the DFT calculations, which identify their location on the basal (110)b facet and on the (110)b/(100) and (110)b/(110)l edges. Using chlorine atoms to probe the presence of hydroxyls, we show that the chlorination occurs selectively by exchanging μ1-OH located on edges and on lateral (110)l facets. By contrast, the basal (110)b and lateral (111) facets are not probed by Cl. This exchange explains the disappearance of the ≃0 ppm peak and of the correlations involving AlTd-μ1-OH species. Moreover, after chlorination, a deshielding of the AlTd is observed on high-resolution 27Al NMR spectra. More subtle effects are visible on the proton correlation spectra, which are attributed to the disruption of the H-bond network in the course of chlorination.

On the applicability of cosine-modulated pulses for high-resolution solid-state NMR of quadrupolar nuclei with spin > 3/2

In MQMAS-based high-resolution solid-state NMR experiments of half-integer spin quadrupolar nuclei, the high radiofrequency (RF) field requirement for the MQ excitation and conversion steps with two hard-pulses is often a sensitivity limiting factor in many practical applications. Recently, the use of two cosine-modulated (cos) low-power (lp) pulses, lasting one-rotor period each, was successfully introduced for efficient MQ excitation and conversion of spin-3/2 nuclei with a reduced RF amplitude. In this study, we extend our previous investigations of spin-3/2 nuclei to systems with higher spin values and discuss the applicability of coslp-MQ excitation and conversion in MQMAS and MQ-HETCOR experiments under slow and fast spinning conditions. For the numerical simulations and experiments we used a moderate magnetic field of 14.1 T. Two spin-5/2 nuclei (85Rb and 27Al) are mainly employed with a large variety of CQ values, but we show that the practical set up is also available for higher spin values, such as spin-9/2 with 93Nb in Cs4Nb11O30. We demonstrate for nuclei with spin value larger than 3/2 a preferential use of coslp-MQ acquisition for low-gamma nuclei and/or large CQ values with a much reduced RF-field with respect to that of hard-pulses used with conventional methods.

Determining Local Magnetic Susceptibility Tensors in Paramagnetic Lanthanide Crystalline Powders from Solid-State NMR Chemical Shift Anisotropies

Exploring magnetic properties at the molecular level is a challenge that has been met by developing many experimental and theoretical solutions, such as polarized neutron diffraction (PND), muon-spin rotation (μ-SR), electron paramagnetic resonance (EPR), SQUID-based magnetometry measurements, and advanced modeling on open-shell systems and relativistic calculations. These methods are powerful tools that shed light on the local magnetic response in specifically designed magnetic materials such as contrast agents, for MRI, molecular magnets, magnetic tags for biological NMR, etc. All of these methods have their advantages and disadvantages. In order to complement the possibilities offered by these methods, we propose a new tool that implements a new approach combining simulation and fitting for high-resolution solid-state NMR spectra of lanthanide-based paramagnetic species. This method relies on a rigorous acquisition thanks to short high-power adiabatic pulses (SHAP) of high-resolution solid-state NMR isotropic and anisotropic data on a powdered magnetic material. It is also based on an efficient modeling of this data thanks to a semiempirical model based on a parametrization of the local magnetism and the crystal structure provided by diffraction methods. The efficiency of the calculation relies on a thorough simplification of the electron-nucleus interactions (point-dipole interaction, no Fermi contact) which is validated by experimental analysis. By taking advantage of the efficient calculation possibilities offered by our method, we can compare a great number of simulated spectra to experimental data and find the best-matching local magnetic susceptibility tensor. This method was applied to a series of isostructural lanthanide oxalates which are used as a benchmark system for many analytical methods. We present the results of thorough solid-state NMR and extensive modeling of the hyperfine interaction (including up to 400 paramagnetic centers) that yield local magnetic susceptibility tensor measurements that are self-consistent as well as consistent with bulk susceptibility measurements.

Influence of Resins on the Structure and Dynamics of SBR Compounds: A Solid-State NMR Study

The tackifying effect of resins used in the tire industry highly depends on the compatibility and interaction strength with the rubber matrix. Here, uncured and cured styrene/butadiene rubber compounds, either in the presence or absence of a hydrocarbon aromatic tackifying resin, were studied by means of high-resolution and time-domain solid-state NMR (SSNMR) techniques to investigate resin/polymer interactions and the effect of the resin on the dynamics of polymer chains. 13C direct excitation and cross-polarization spectra, combined with low-field measurements of 1H T1 and analysis of 1H on-resonance free-induction decay, provided information on the dynamic heterogeneity of the samples and the degree of mixing between the resin and the rubber matrix. Moreover, 1H T1 and T1ρ relaxation times at variable temperatures were used to investigate the effect of resin on both segmental dynamics activated at the glass transition and collective polymer dynamics. SSNMR findings were discussed in relation to crosslink density and Tg data. The obtained results show that the resin is intimately mixed with the polymer, while maintaining its rigid character. A slowdown of segmental dynamics, related to an increase in Tg, was found as a consequence of resin addition, while no effect was evidenced on fragility and collective polymer dynamics.

Characterization of peptide O⋯HN hydrogen bonds via1H-detected 15N/17O solid-state NMR spectroscopy.

High sensitivity and resolution solid-state NMR methods are reported, that straightforwardly select hydrogen-bonded 15N-17O pairs from amongst all other nitrogen and oxygen sites in peptides, to aid protein secondary and tertiary structure determination. Significantly improved sensitivity is obtained with indirect 1H detection under fast MAS and stronger relayed dipole couplings.

Lithium isotope tracing in silicon-based electrodes using solid-state MAS NMR: a powerful comprehensive tool for the characterization of lithium batteries.

The introduction of lithiated components with different 7Li/6Li isotopic ratios, also called isotopic tracing, can give access to better understanding of lithium transport and lithiation processes in lithium-ion batteries. In this work, we propose a simple methodology based on high-resolution solid-state NMR for the determination of the 7Li/6Li ratio in silicon electrodes following different strategies of isotopic tracing. The 6Li and 7Li MAS NMR experiments allow obtaining resolved spectra whose spectral components can be assigned to different moieties of the materials. In order to measure the ratio of the 6Li/7Li NMR integrals, a silicon electrode with a natural 7Li/6Li isotope abundance was used as a reference. This calibration can then be used to determine the 7Li/6Li ratio of any similar samples. This method was applied to study the phenomena occurring at the interface between a silicon electrode and a labeled electrolyte, which is an essential step for isotopic tracing experiments in systems after the formation of the solid electrolyte interphase (SEI). Beyond the isotopic exchanges between the SEI and the electrolyte already observed in the literature, our results show that isotopic exchanges also involve Li-Si alloys in the electrode bulk. Within a 52-hour contact, the electrolyte labeling disappeared: isotopic concentrations of the electrolyte and electrode become practically homogenized. However, at the electrode level, different silicides are characterized by rather different isotopic enrichment. In the present work, ToF SIMS and liquid state NMR were also used to cross-check and discuss the solid-state NMR method we have proposed.

Deciphering the potassium storage phase conversion mechanism of phosphorus by combined solid-state NMR spectroscopy and density functional theory calculations

Phosphorus is the potential anode material for emerging potassium-ion batteries (PIBs) owing to the highest specific capacity and relatively low operation plateau. However, the reversible delivered capacities of phosphorus-based anodes, in reality, are far from the theoretical capacity corresponding to the formation of K3P alloy. And, their underlying potassium storage mechanisms remain poorly understood. To address this issue, for the first time, we perform high-resolution solid-state 31P NMR combined with XRD measurements, and density functional theory calculations to yield a systemic quantitative understanding of (de)potassiation reaction mechanism of phosphorus anode. We explicitly reveal a previously unknown asymmetrical nanocrystalline-to-amorphous transition process via rP ↔ (K3P11, K3P7, beta-K4P6) ↔ (alpha-K4P6) ↔ (K1−xP, KP, K4−xP3, K1+xP) ↔ (amorphous K4P3, amorphous K3P) that are proceed along with the electrochemical potassiation/depotassiation processes. Additionally, the corresponding K-P alloys intermediates, such as the amorphous phases of K4P3, K3P, and the nonstoichiometric phases of “K1−xP”, “K1+xP”, “K4−xP3” are experimentally detected, which indicating various complicated K-P alloy species are coexisted and evolved with the sluggish electrochemical reaction kinetics, resulting in lower capacity of phosphorus-based anodes. Our findings offer some insights into the specific multi-phase evolution mechanism of alloying anodes that may be generally involved in conversion-type electrode materials for PIBs.

Structure and Molecular Dynamics in Metal-Containing Polyamide 6 Microparticles

Polymer microparticles are used in additive manufacturing, separation and purification devices, biocatalysis, or for the recognition of biomolecules. This study reports on the effect of metal fillers on the structure and molecular dynamics of polyamide 6 (PA6) microparticles (MPs) containing up to 19 wt.% of Al, Cu, or Mg. These hybrid MPs are synthesized via reactive microencapsulation by anionic ring-opening polymerization in solution, in the presence of the metal filler. 13C high-resolution solid-state NMR (ssNMR) spectroscopy is employed as the primary characterization method using magic angle spinning (MAS) and cross-polarization (CP)/MAS. Depending on the metal filler, the ssNMR crystallinity index of the MP varies between 39–50%, as determined by deconvolution of the 13C MAS and CP/MAS spectra. These values correlate very well with the crystallinity derived from thermal or X-ray diffraction data. The molecular dynamics study on PA6 and Cu-containing MP shows similar mobility of carbon nuclei in the kHz, but not in the MHz frequency ranges. The paramagnetic Al and Mg have an observable effect on the relaxation; however, conclusions regarding the PA6 carbon motions cannot be unequivocally made. These results are useful in the preparation of hybrid microparticles with customized structures and magneto-electrical properties.

Heat Treatment-Induced Conductivity Enhancement in Sulfide-Based Solid Electrolytes: What is the Role of the Thio-LISICON II Phase and of Other Nanoscale Phases?

Sulfide-based solid Li+ electrolytes are one of the most promising electrolyte classes for solid-state battery applications. These solid electrolytes are typically prepared by means of high-energy ball milling, often followed by a heat treatment step for enhancing the Li+ ion conductivity. In many cases, heat treatment-induced conductivity enhancements have been attributed to the formation of a superionic thio-LISICON II phase. However, the chemical composition and structure of this phase as well as the origin of the conductivity enhancement are still under debate. Here, we have carried out a comprehensive study on the thiophosphate-based electrolyte system (1 – x) Li3PS4 + x LiI with x = 0–0.5. By combining electrochemical impedance spectroscopy, X-ray diffraction, and Raman spectroscopy as well as 7Li NMR line-shape analysis and high-resolution multidimensional 31P solid-state NMR measurements, we show that the widely used concept of a thio-LISICON II phase governing the ionic conductivity of heat-treated samples cannot explain the experimental observations. Double-quantum constant-time 31P NMR proves that P2S64– units are embedded in the amorphous phase of the ball-milled pristine samples. Upon heat treatment, the amorphous phase with the embedded P2S64– units is transformed into different nanoscale crystalline phases, a thio-LISICON II phase, a β-Li3PS4 phase, and a Li4PS4I-related phase. A structural model of the thio-LISICON II phase needs to explain the coupling pattern from two-dimensional double-quantum NMR presented here, showing two phosphorus environments with an approximate ratio of 2:1. Furthermore, our results indicate that in heat-treated samples, a highly disordered nanoscale Li4PS4I-related phase exists with an ionic conductivity even exceeding that of the thio-LISICON II phase.

Narrowing down the conformational space with solid-state NMR in crystal structure prediction of linezolid cocrystals

Many solids crystallize as microcrystalline powders, thus precluding the application of single crystal X-Ray diffraction in structural elucidation. In such cases, a joint use of high-resolution solid-state NMR and crystal structure prediction (CSP) calculations can be successful. However, for molecules showing significant conformational freedom, the CSP-NMR protocol can meet serious obstacles, including ambiguities in NMR signal assignment and too wide conformational search space to be covered by computational methods in reasonable time. Here, we demonstrate a possible way of avoiding these obstacles and making as much use of the two methods as possible in difficult circumstances. In a simple case, our experiments led to crystal structure elucidation of a cocrystal of linezolid (LIN), a wide-range antibiotic, with 2,3-dihydroxybenzoic acid, while a significantly more challenging case of a cocrystal of LIN with 2,4-dihydroxybenzoic acid led to the identification of the most probable conformations of LIN inside the crystal. Having four rotatable bonds, some of which can assume many discreet values, LIN molecule poses a challenge in establishing its conformation in a solid phase. In our work, a set of 27 conformations were used in CSP calculations to yield model crystal structures to be examined against experimental solid-state NMR data, leading to a reliable identification of the most probable molecular arrangements.

Understanding the conformational changes in the influenza B M2 ion channel at various protonation states

The characterization of influenza (A/B M2) ion channels is very important as they are potential binding sites for the drugs. We report the all-atom molecular dynamics study of the influenza B M2 ion channel in the presence of explicit solvent and lipid bilayers using the high resolution solid-state NMR structures. The importance of the various protonation states of histidine in the activation of the ion channel is discussed. The conformational changes at the closed and the open structures clearly show that the increase in tilt angle is necessary for the activation of the ion channel. Additionally, the free energy surfaces of the eight systems show the importance of the protonation state of the histidine residues in the activation of the influenza B M2 ion channel. The protonation of the histidine residues increases the tilt angle and the intra-helix distance which is evident from the superimposition of the structures corresponding to the maxima and the minima in the free energy landscape. The findings imply differences in the singly protonated and double protonated conformational states of BM2 ion channel and provide insights to help further studies of these ion channels as the drug targets for the influenza virus.

Ion and Molecular Transport in Solid Electrolytes Studied by NMR.

NMR is the method of choice for molecular and ionic structures and dynamics investigations. The present review is devoted to solvation and mobilities in solid electrolytes, such as ion-exchange membranes and composite materials, based on cesium acid sulfates and phosphates. The applications of high-resolution NMR, solid-state NMR, NMR relaxation, and pulsed field gradient 1H, 7Li, 13C, 19F, 23Na, 31P, and 133Cs NMR techniques are discussed. The main attention is paid to the transport channel morphology, ionic hydration, charge group and mobile ion interaction, and translation ions and solvent mobilities in different spatial scales. Self-diffusion coefficients of protons and Li+, Na+, and Cs+ cations are compared with the ionic conductivity data. The microscopic ionic transfer mechanism is discussed.