Single-pulse NMR Research Articles

Soluble Electrolyte-Coordinated Sulfide Species Revealed in Al–S Batteries by Nuclear Magnetic Resonance Spectroscopy

Rechargeable aluminum–sulfur (Al–S) batteries have recently garnered significant interest to the low cost, earth abundance, safety, and high theoretical capacity of the electrode materials. However, Al–S batteries exhibit many challenges that plague other metal–sulfur battery systems, including significant capacity fade of the sulfur electrode due to the formation of electrolyte-soluble reaction intermediates. Here, Al–S cells using chloroaluminate-containing ionic liquid electrolytes were investigated up from the molecular level using multidimensional solid-state 27Al MAS NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical measurements. Solid-state 27Al single-pulse NMR measurements acquired on cycled sulfur electrodes containing electrolyte-soaked separator revealed multiple discharge products, which were distinguished into liquid- and solid-phase products based on 27Al chemical exchange and nutation NMR experiments. During discharge, electrolyte-soluble sulfide species form that coordinate with the AlCl4– chloroaluminate anions, resulting in (SxAlCl4)y− electrolyte complexes. These electrolyte-coordinated sulfide species persist upon charge, resulting in the loss of active mass that explains the significant capacity fade observed upon galvanostatic cycling. XPS, XRD, and solid-state 27Al NMR measurements reveal that solid amorphous Al2S3 forms reversibly upon discharge. The results highlight the technological importance of understanding how electrolyte-soluble sulfide species coordinate with the complex electroactive species used in multivalent metal–sulfur batteries, which can affect their reversibility and electrochemical properties.

Real-Time NMR Recording of Fermentation and Lipid Metabolism Processes in Live Microalgae Cells.

Non‐invasive and real‐time recording of processes in living cells has been limited to detection of small cellular components such as soluble proteins and metabolites. Here we report a multiphase NMR approach using magic‐angle spinning NMR to synchronously follow microbial processes of fermentation, lipid metabolism and structural dynamic changes in live microalgae cells. Chlamydomonas reinhardtii green algae were highly concentrated, introducing dark fermentation and anoxia conditions. Single‐pulse NMR experiments were applied to obtain temperature‐dependent kinetic profiles of the formed fermentation products. Through dynamics‐based spectral editing NMR, simultaneous conversion of galactolipids into TAG and free fatty acids was observed and rapid loss of rigid lipid structures. This suggests that lipolysis under dark and anoxia conditions finally results in the breakdown of cell and organelle membranes, which could be beneficial for recovery of intracellular microbial useful products.

Investigation of the single-pulse NMR echo origin in cobalt using additional magnetic video-pulses

Investigation of the single-pulse NMR echo origin in cobalt using additional magnetic video-pulses

NMR Spectroscopic Windows on the Systemic Effects of SARS-CoV-2 Infection on Plasma Lipoproteins and Metabolites in Relation to Circulating Cytokines.

To investigate the systemic metabolic effects of SARS-CoV-2 infection, we analyzed 1H NMR spectroscopic data on human blood plasma and co-modeled with multiple plasma cytokines and chemokines (measured in parallel). Thus, 600 MHz 1H solvent-suppressed single-pulse, spin-echo, and 2D J-resolved spectra were collected on plasma recorded from SARS-CoV-2 rRT-PCR-positive patients (n = 15, with multiple sampling timepoints) and age-matched healthy controls (n = 34, confirmed rRT-PCR negative), together with patients with COVID-19/influenza-like clinical symptoms who tested SARS-CoV-2 negative (n = 35). We compared the single-pulse NMR spectral data with in vitro diagnostic research (IVDr) information on quantitative lipoprotein profiles (112 parameters) extracted from the raw 1D NMR data. All NMR methods gave highly significant discrimination of SARS-CoV-2 positive patients from controls and SARS-CoV-2 negative patients with individual NMR methods, giving different diagnostic information windows on disease-induced phenoconversion. Longitudinal trajectory analysis in selected patients indicated that metabolic recovery was incomplete in individuals without detectable virus in the recovery phase. We observed four plasma cytokine clusters that expressed complex differential statistical relationships with multiple lipoproteins and metabolites. These included the following: cluster 1, comprising MIP-1β, SDF-1α, IL-22, and IL-1α, which correlated with multiple increased LDL and VLDL subfractions; cluster 2, including IL-10 and IL-17A, which was only weakly linked to the lipoprotein profile; cluster 3, which included IL-8 and MCP-1 and were inversely correlated with multiple lipoproteins. IL-18, IL-6, and IFN-γ together with IP-10 and RANTES exhibited strong positive correlations with LDL1–4 subfractions and negative correlations with multiple HDL subfractions. Collectively, these data show a distinct pattern indicative of a multilevel cellular immune response to SARS CoV-2 infection interacting with the plasma lipoproteome giving a strong and characteristic immunometabolic phenotype of the disease. We observed that some patients in the respiratory recovery phase and testing virus-free were still metabolically highly abnormal, which indicates a new role for these technologies in assessing full systemic recovery.

Solid State Phase Transitions in Poly(ethylene oxide) Crystals Induced by Designed Chain Defects

We have used Cu(I)-catalyzed azide–alkyne cycloaddition to synthesize a new series of poly(ethylene oxide)s having in the center of their chains two 1,2,3-triazole (TR) rings separated by (CH2)n spacers with 2 ≤ n ≤ 4 (PEO11-TR-(CH2)n-TR-PEO11). The degree of crystallinity obtained by temperature-dependent WAXS measurements indicates that only one out of the two PEO11 chains of the three polymers forms a 72 helix upon cooling to −10 °C and crystallizes into a monoclinic unit cell known from PEO homopolymer. A solid-state phase transition occurs for all samples during heating below their melting temperature. Solid-state 13C MAS cross-polarization and single-pulse NMR spectroscopy indicate the complete incorporation of the chain defects into the PEO crystals (PEO-TR phase) during this transition. The 2D WAXS pattern of an oriented PEO11-TR-(CH2)2-TR-PEO11 sample generates a structural model where the crystal lattice of the initial PEO phase becomes highly distorted during the solid-state phase transition du...

29Si{27Al}, 27Al{29Si} and 27Al{1H} double-resonance NMR spectroscopy study of cementitious sodium aluminosilicate gels (geopolymers) and gel-zeolite composites.

The influence of starting materials and synthesis route on the properties and the structure of cementitious sodium aluminosilicate gels is not fully understood, partly due their amorphous nature and the fact that they often contain residual reactants, which can make the results of single-pulse NMR spectroscopy applied to these materials difficult to interpret or ambiguous. To overcome some of these limitations, 29Si{27Al} TRAPDOR NMR as well as 27Al{29Si} and 27Al{1H} REDOR NMR spectroscopy were applied to materials synthesized by the one-part alkali-activation route from three different amorphous silica starting materials, including rice husk ash. The latter led to formation of a fully amorphous sodium aluminosilicate gel (geopolymer), while the materials produced from the other silicas contained amorphous phase and crystalline zeolites. Application of the double-resonance NMR methods allowed to identify hydrous alumina gel domains in the rice husk ash-based material as well as significantly differing amounts of residual silica in the three cured materials. Four-coordinated Al existed not only in the aluminosilicate gel framework but also in a water-rich chemical environment with only a small amount of Si in proximity, likely in the alumina gel or possibly present as extra-framework Al in the aluminosilicate gel. The results demonstrate how the employment of different silica starting materials determines the phase assemblage of one-part alkali-activated materials, which in turn influences their engineering properties such as the resistance against chemically/biologically aggressive media.

Complex F,Cl Apatite Solid Solution Investigated Using Multinuclear Solid-State NMR Methods

A series of synthetic F,Cl apatites with low hydroxyl content was investigated using 31P, 19F, and 35Cl solid-state magic angle spinning (MAS) NMR spectroscopic methods. 31P single-pulse (SP) NMR spectra show that for each composition the phosphate 31P chemical shift depends on occupancy of the nearest anion site for each composition. Overall the average chemical shift deviates from linear across the F/Cl series. For intermediate compositions 19F SP NMR spectra reveal complex, broadened spectral profiles that are not correlated to composition. 19F{35Cl} TRAPDOR results indicate that the spectral profiles do not reflect occupancy of F and Cl in adjacent column anion sites. We propose that the complex 19F lineshapes are principally due to broad distributions of 19F–Ca distances arising from displacement of F along the anion channel. Approximate fluorine atomic positions are estimated based on 19F chemical shifts of alkaline earth fluoride salts, and the results are in good accord with those proposed for int...

Cumulative Single-Pulse NMR Echoes in Cobalt

<p class="1Body">In this work the cumulative single-pulse echo effect in cobalt was studied when a train of single-pulse echoes generated by a repeating single RF pulse sequence, exhibits growth rather than damping. The phenomenon is observed below some threshold value of radio-frequency pulse power when the nonresonant mechanism of single-pulse echo excitation in cobalt becomes effective.<strong></strong></p>

On the Role of the Hyperfine Field Anisotropy in the Formation of a Single-Pulse NMR Spin Echo in Cobalt

In this work, we show that the single-pulse echo in cobalt is formed by the exciting radio-frequency pulse edges distortion mechanism due to mainly hyperfine field anisotropy beginning with a certain value of radio-frequency pulse power. Before this threshold radio-frequency power, the single-pulse echo is formed by nonresonant mechanism as in lithium ferrite.

Non-linear signal detection improvement by radiation damping in single-pulse NMR spectra.

When NMR lines overlap and at least one of them is affected by radiation damping, the resonance line shapes of all lines are no longer Lorentzian. We report the appearance of narrow signal distortions, which resemble hole-burnt spectra. This new experimental phenomenon facilitates the detection of tiny signals hidden below the main resonance. Theoretical analysis based on modified Maxwell–Bloch equations shows that the presence of strong transverse magnetization creates a feedback through the coil, which influences the magnetization of all spins with overlapping resonance lines. In the time domain this leads to cross-precession terms between magnetization densities, which ultimately cause non-linear behavior. Numerical simulations corroborate this interpretation.

Synthesis and characterization of nanoapatites organofunctionalized with aminotriphosphonate agents

Organofunctionalized apatite nanoparticles were prepared using a one step process involving dissolution/precipitation of natural phosphate rock and covalent grafting of nitrilotris(methylene)triphosphonate (NTP). The synthesized materials were characterized by Brunauer–Emmett–Teller (BET) surface measurement, thermogravimetry, inductively coupled plasma emission spectroscopy (ICP–ES), elemental analysis, multinuclear solid state cross-polarization/magic angle spinning (CP/MAS) and single-pulse NMR spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDXA). After grafting BET measurements yielded particle specific surface areas ranging from 88 to 193m2g−1 depending on the grafted phosphonate. The results show that the surfaces of the nanoapatite particles can be covered with functional groups bound through a variable number of R–P–O–Ca bonds to render them organoapatites.

Solid‐state NMR spectra of paramagnetic silica‐based materials: observation of 29Si and 27Al nuclei in the first coordination spheres of manganese ions

Some silica-based solids, prepared by the sol/gel method in the presence of high Mn2+ concentrations, have been characterized by the 29Si, 27Al MAS NMR spectra and 29Si T1 measurements. The single-pulse 29Si and 27Al MAS NMR spectra have shown broad spinning sideband patterns that are interpreted in terms of anisotropic bulky magnetic susceptibility (BMS) and dipole-field effects. In the absence of paramagnetic isotropic shifts, the 29Si and 27Al nuclei observed in the single-pulse NMR spectra have been assigned to nuclei remote from paramagnetic centers. It has been demonstrated that the 29Si and 27Al nuclei, which are in the vicinity of the manganese ions, can be detected by the Hahn-echo MAS NMR experiments at different carrier frequencies.

Fundamental mechanisms of single-pulse NMR echo formation

A theoretical investigation of the formation of the so-called single pulse NMR echo has been undertaken in the presence of both Larmor and Rabi frequency inhomogeneities. It is found that this echo phenomenon, together with weaker, equally spaced secondary echoes, evolves from multiple-pulse excitation under certain constraints with respect to interpulse time intervals compared with longitudinal and transverse relaxation times. These transient coherences arise from a complex superposition of oscillatory free induction decays, which extend further into the time domain because of cumulative dephasing within each pulse in a multiple-pulse sequence. The effect is present for large Larmor inhomogeneity in isolation, but is stronger in the simultaneous presence of both frequency inhomogeneities, characteristic of ferromagnets. Predictions of this model analysis are confirmed through experiment via conventional, zero-field, pulsed NMR on binary $^{51}\mathrm{VFe}$ and pure elementary (enriched) $^{57}\mathrm{FeFe}$ ferromagnets.

A 23Na NMR study of hydrous layered silicates

Sodium-23 single-pulse NMR spectra have been obtained for the layered sodium polysilicate hydrates, makatite, kanemite, octosilicate, magadiite and kenyaite. The kanemite spectra were severely distorted by second-order effects from strong quadrupolar interactions. However, the regular behaviour of the linewidth with frequency allowed the isotropic chemical shift and quadrupole interaction constant for the single peak to be deduced. The spectra of octosilicate, magadiite and kenyaite contain either one or two peaks. Powder X-ray diffraction indicates that the spectra with two lines correspond to samples contaminated by sodium chloride, which is a result of relevance to the conclusions of two previous authors. A 1H,23Na heteronuclear shift correlation spectrum for magadiite shows that strongly hydrogen-bonded protons are responsible for the single magadiite 23Na cross-polarisation signal. The presence of these hydrogen-bonded protons, and the detection of a single sodium site, indicate that there are significant differences between the interlayer conformations of kanemite, octosilicate, magadiite and kenyaite and the known structure of makatite, which has no hydrogen-bonded protons and two sodium sites. The 23Na isotropic chemical shifts of kanemite, octosilicate, magadiite and kenyaite indicate that the relevant sodium species have coordination numbers of five or six; both arrangements are known to occur with makatite. The estimated quadrupole interaction constants infer that the value is five for kanemite and six for octosilicate, magadiite and kenyaite.

Development of a High-speed NMR Technique for Sensing Maturity of Avocados

This study demonstrates the feasibility of using an NMR technique for high-speed on-line sensing of maturity of avocados. Results of our previous studies indicate that it is possible to use high-speed, single-pulse NMR techniques to evaluate quality of fruits and vegetables. The single-pulse free induction decay (FID) spectrum measurement technique was used successfully to evaluate maturity of avocados and sugar content of fresh prunes, and was found to have desired features for high-speed sensing of fruit quality. In this study we successfully used a specially designed conveyor belt to acquire FID spectra of avocados while they were moving at speeds up to 250 mm/s. The oil/water resonance peak ratio, obtained from the spectrum, correlates very well (r2 = 0.98) with the dry weight of the fruit.