High-resolution 31P NMR Research Articles

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.

Phospholipids in Motion: High-Resolution 31P NMR Field Cycling Studies.

Diverse phospholipid motions are key to membrane function but can be quite difficult to untangle and quantify. High-resolution field cycling 31P NMR spin-lattice relaxometry, where the sample is excited at high field, shuttled in the magnet bore for low-field relaxation, then shuttled back to high field for readout of the residual magnetization, provides data on phospholipid dynamics and structure. This information is encoded in the field dependence of the 31P spin-lattice relaxation rate (R1). In the field range from 11.74 down to 0.003 T, three dipolar nuclear magnetic relaxation dispersions (NMRDs) and one due to 31P chemical shift anisotropy contribute to R1 of phospholipids. Extraction of correlation times and maximum relaxation amplitudes for these NMRDs provides (1) lateral diffusion constants for different phospholipids in the same bilayer, (2) estimates of how additives alter the motion of the phospholipid about its long axis, and (3) an average 31P-1H angle with respect to the bilayer normal, which reveals that polar headgroup motion is not restricted on a microsecond timescale. Relative motions within a phospholipid are also provided by comparing 31P NMRD profiles for specifically deuterated molecules as well as 13C and 1H field dependence profiles to that of 31P. Although this work has dealt exclusively with phospholipids in small unilamellar vesicles, these same NMRDs can be measured for phospholipids in micelles and nanodisks, making this technique useful for monitoring lipid behavior in a variety of structures and assessing how additives alter specific lipid motions.

Enzyme-Substrate-Cofactor Dynamical Networks Revealed by High-Resolution Field Cycling Relaxometry.

The remarkable power and specificity of enzyme catalysis rely on the dynamic alignment of the enzyme, substrates, and cofactors, yet the role of dynamics has usually been approached from the perspective of the protein. We have been using an underappreciated NMR technique, subtesla high-resolution field cycling 31P NMR relaxometry, to investigate the dynamics of the enzyme-bound substrates and cofactor on guanosine-5'-monophosphate reductase (GMPR). GMPR forms two dead end, yet catalytically competent, complexes that mimic distinct steps in the catalytic cycle: E·IMP·NADP+ undergoes a partial hydride transfer reaction, while E·GMP·NADP+ undergoes a partial deamination reaction. A different cofactor conformation is required for each partial reaction. Here we report the effects of mutations designed to perturb cofactor conformation and ammonia binding with the goal of identifying the structural features that contribute to the distinct dynamic signatures of the hydride transfer and deamination complexes. These experiments suggest that Asp129 is a central cog in a dynamic network required for both hydride transfer and deamination. In contrast, Lys77 modulates the conformation and mobility of substrates and cofactors in a reaction-specific manner. Thr105 and Tyr318 are part of a deamination-specific dynamic network that includes the 2'-OH of GMP. These residues have comparatively little effect on the dynamic properties of the hydride transfer complex. These results further illustrate the potential of high-resolution field cycling NMR relaxometry for the investigation of ligand dynamics. In addition, exchange experiments indicate that NH3/NH4+ has a high affinity for the deamination complex but a low affinity for the hydride transfer complex, suggesting that the movement of ammonia may gate the cofactor conformational change. Collectively, these experiments reinforce the view that the enzyme, substrates, and cofactor are linked in intricate, reaction-specific, dynamic networks and demonstrate that distal portions of the substrates and cofactors are critical features in these networks.

Synthesis, Characterization, and Stability of Americium Phosphate, AmPO4.

AmPO4 was prepared by a solid-state reaction method, and its crystal structure at room temperature was solved by powder X-ray diffraction combined with Rietveld refinement. The purity of the monazite-like phase was confirmed by spectroscopic (high-resolution solid-state 31P NMR and Raman) and microscopic (SEM-EDX and TEM) techniques. The thermal and self-irradiation stability have been studied. The compound is stable under argon and air atmosphere at least up to 1773 K. It remains crystalline under self-irradiation for circa two months, with a crystallographic volume swelling of ∼1.5%, and then is amorphizing over a year. However, microcrystals are present in the amorphous material even after a two year period of time. All these characteristics are discussed in relation to the potential application of AmPO4 as a stable form of Am in radioisotope power sources for space exploration and of behavior of the monazites under irradiation.

Promotion of plasmalogen biosynthesis reverse lipid changes in a Barth Syndrome cell model

In Barth syndrome (BTHS) mutations in tafazzin leads to changes in both the quantities and the molecular species of cardiolipin (CL), which are the hallmarks of BTHS. Contrary to the well-established alterations in CL associated with BTHS; recently a marked decrease in the plasmalogen levels in Barth specimens has been identified. To restore the plasmalogen levels, the present study reports the effect of promotion of plasmalogen biosynthesis on the lipidome of lymphoblasts derived from Barth patients as well as on cell viability, mitochondria biogenesis, and mitochondrial membrane potential. High resolution 31P NMR phospholipidomic analysis showed an increase in the levels of plasmenylethanolamine (the major plasmalogen in lymphoblasts), which reached values comparable to the control and a compensatory decrease in the levels of its diacyl-PE counterpart. Importantly, 31P NMR showed a significant increase in the levels of CL, while not altering the levels of monolysocardiolipin. Mass spectrometry measurements showed that the promotion of plasmalogen biosynthesis did not change the molecular species profile of targeted phospholipids. In addition, promotion of plasmalogen biosynthesis did not impact on cellular viability, although it significantly decrease mitochondria copy number and restored mitochondrial membrane potential. Overall, the results showed the efficacy of the promotion of plasmalogen biosynthesis on increasing the CL levels in a BTHS cell model and highlight the potential beneficial effect of a diet supplemented with plasmalogen precursors to BTHS patients.

Dynamic Characteristics of Guanosine-5'-monophosphate Reductase Complexes Revealed by High-Resolution 31P Field-Cycling NMR Relaxometry.

The ability of enzymes to modulate the dynamics of bound substrates and cofactors is a critical feature of catalysis, but the role of dynamics has largely been approached from the perspective of the protein. Here, we use an underappreciated NMR technique, subtesla high-resolution field-cycling 31P NMR relaxometry, to interrogate the dynamics of enzyme bound substrates and cofactors in guanosine-5'-monophosphate reductase (GMPR). These experiments reveal distinct binding modes and dynamic profiles associated with the 31P nuclei in the Michaelis complexes for the deamination and hydride transfer steps of the catalytic cycle. Importantly, the substrate is constrained and the cofactor is more dynamic in the deamination complex E·GMP·NADP+, whereas the substrate is more dynamic and the cofactor is constrained in the hydride transfer complex E·IMP·NADP+. The presence of D2O perturbed the relaxation of the 31P nuclei in E·IMP·NADP+ but not in E·GMP·NADP+, providing further evidence of distinct binding modes with different dynamic properties. dIMP and dGMP are poor substrates, and the dynamics of the cofactor complexes of dGMP/dIMP are disregulated relative to GMP/IMP. The substrate 2'-OH interacts with Asp219, and mutation of Asp219 to Ala decreases the value of Vmax by a factor of 30. Counterintuitively, loss of Asp219 makes both substrates and cofactors less dynamic. These observations suggest that the interactions between the substrate 2'-OH and Asp219 coordinate the dynamic properties of the Michaelis complexes, and these dynamics are important for progression through the catalytic cycle.

Determination of 31P Chemical Shift Tensor from Microcrystalline Powder by Using a Magnetically Oriented Microcrystal Array

The 31P chemical shift tensor for phenylphosphonic acid (PPA) was determined by using a magnetically oriented microcrystal array (MOMA)—a single-crystal-like composite in which microcrystals are aligned three-dimensionally in a polymer matrix—prepared from a microcrystalline powder of PPA. High-resolution 31P NMR spectra were obtained for a PPA-MOMA without magic angle spinning (MAS), from which the chemical shift anisotropy (CSA) was determined. The single-crystal rotation method was applied to the MOMA to determine the principal axes of the 31P chemical shift tensor with respect to the crystallographic axes. The present results demonstrate that the MOMA method can provide a powerful means of determining all of the information on 31P CSA from a microcrystalline powder without MAS.

The diethyl dithiophosphate complex of tetraphenylantimony(V) and its solvated form, [Sb(C6H5)4{S2P(OC2H5)2}] · 1/2 C6H6: Synthesis, crystal structure, and 13C, 31P CP/MAS NMR study. an example of monodentate coordination of dithio ligands

The O,O′-diethyl dithiophosphate complex of tetraphenylantimony(V) [Sb(C6H5)4{S2P(OC2H5)2}] (I) and its benzene-solvated form I · 1/2C6H6 (II) were synthesized and studied by high-resolution solid-state 13C and 31P NMR (MAS NMR). The diethyl dithiophosphate (Dtph) groups in I and II were quantitatively characterized by the 31P chemical shift anisotropy (δaniso), the asymmetry parameter (η), and the principal values of chemical shift tensors (δxx, δyy, δzz). The calculation of the anisotropy parameters included construction of χ2 statistic diagrams from full 31P MAS NMR spectra. In both complexes, the Dtph groups were found to have mainly axially symmetric 31P chemical shift tensors (for δzz < δxx ≈ δyy) with similar anisotropy parameters (δaniso and η), which is due to their identical S-monodentate function. According to X-ray diffraction data, II has a trigonal bipyramidal (TBP) molecular structure with Smonodentate coordination of Dtph in the TBP axial position and outer-sphere position of the benzene molecule. The desorption of the outer-sphere benzene solvent molecules from structure II, which was noted in MAS NMR experiment, passes through the formation of three intermediate solvated forms with benzene content n < 1/2.

Surface Modification of Boron Nitride Nanoparticles by Decylphosphonic Acid Characterized by Solid-state NMR

Abstract We have attempted to modify the surface of boron nitride (BN) nanoparticles by decylphosphonic acid and have characterized the surface layer of BN nanoparticles by means of high-resolution solid-state 31P NMR. The surface of BN nanoparticles was successfully modified, and the 31P NMR spectra showed two types of bonding states for the organic modifier. They are tentatively assigned to P–B and P–N bonding states from consideration of the residual line broadening due to interaction with quadrupole nuclei.

High Resolution Field Cycling for Analysis of Lipid Dynamics in Membranes

Phospholipid dynamics often play a role in binding of peripheral membrane proteins. Whether there are discrete phospholipid binding sites on the proteins is often difficult to assess unless binding is quite tight. Yet for many proteins that bind reversibly to membranes, weaker interactions with specific phospholipids can have important functional consequences. For example, phosphatidylinositol‐specific phospholipase C (PI‐PLC) enzymes can be activated by nonsubstrate phospholipids with the extent of activation tuned by the lipid composition. Activity of the Bacillus thuringiensis PI‐PLC is significantly enhanced by a small amount of phosphatidylcholine (PC) in the target membrane. Whether (and where) there is a discrete site for an activator PC molecule or whether lipid mixtures alter bilayer properties is hard to distinguish. High resolution 31P and 13C NMR relaxation studies from 0.005 to 11.7 T can be used to explore interactions of such a peripheral membrane protein with mixed phospholipid vesicles as well as with small molecules. If spin‐labeled proteins are used, estimates of site‐off rates and phospholipid binding site location can be made. With this novel approach for PI‐PLC, we see that (i) discrete complexes for each type of phospholipid on the enzyme with lifetimes around a microsecond must exist; (ii) the discrete site for a substrate analog is spatially different from that for activator PC; and (iii) modeling coupled with the NMR results suggests a PC site, near a series of tyrosine residues, that would aid in anchoring the protein to membranes. The high resolution field cycling method illustrated here may be extended to a wide range of proteins that reversibly bind to membranes to explore differential interactions with phospholipid components as well as other intermolecular interactions.

A solid-state 31P NMR study of 1:1 silver–triphenylphosphine complexes — Interpretation of 1J(107,109Ag,31P) values,

High-resolution solid-state 31P NMR spectroscopy was used to investigate a series of 1:1 silver–triphenylphosphine complexes, [Ph3PAgX]n, where X is a monovalent anion and n = 1, 2, 3, 4, or ∞. The 31P CP MAS NMR spectra reveal the number of distinct phosphorus sites in these complexes as well as the |1J(109Ag,31P)| values, which range from 401 ± 10 Hz (X = N3–) to 869 ± 10 Hz (X = SO3CF3–). The data obtained here and in earlier investigations indicate that |1J(109Ag,31P)| values for silver–tertiary phosphine complexes decrease as Ag–P bond lengths increase. This experimental conclusion is supported by DFT calculations, which also indicate that the Fermi-contact mechanism is the only important spin–spin coupling mechanism for 1J(109Ag,31P) in these complexes. In addition, the crystal structure of a silver–triphenylphosphine trifluoroacetate tetramer was determined using X-ray crystallography, and the structure of a silver–triphenylphosphine chloride tetramer was reinvestigated.

31P NMR spectroscopy of phospholipid metabolites in postmortem schizophrenic brain

Evidence has been accumulating that schizophrenia involves abnormalities in the composition and metabolism of cell membrane phospholipids (PLs) in the brain. In vivo 31P MRS has been used to measure the metabolic precursors and degradation products of PL metabolism in schizophrenia. Because in vivo line widths are substantially broader than in solution, only the broad phosphomonoester (PME) and phosphodiester bands, or partly resolved resonances of individual metabolites, are typically measured in vivo in the 31P spectrum. In addition to poor resolution, the relatively low signal-to-noise ratio (SNR) makes precise quantitation difficult. An alternative with substantially better resolution and precision for quantitation is high-resolution NMR spectroscopy of extracts of samples from postmortem brain. Here we determine absolute concentrations of the individual PL metabolites phosphocholine (pc), phosphoethanolamine (pe), glycerophosphocholine (gpc), and glycerophosphoethanolamine in aqueous extracts of tissue from frontal, temporal, and occipital cortex of postmortem brain for schizophrenics, controls, and patients with other mental illnesses (psychiatric controls [PC]) using high-resolution 31P NMR spectroscopy. For the complete groups, which included both males and females, there were no statistically significant differences for schizophrenics vs. controls for any of the four PL metabolites in any of the three brain regions. Trends (0.05 < P < 0.10) were noted for increased gpc in schizophrenia in all three regions. PC differed from both controls and schizophrenics in several measures. When only males were considered, gpc was significantly (P < 0.05) elevated in all three brain regions in schizophrenia.

Structure and NMR assignment in calcined and as-synthesized forms of AlPO-14: a combined study by first-principles calculations and high-resolution 27Al–31P MAS NMR correlation

The high-resolution 27Al and 31P NMR spectra of two as-synthesized forms of the microporous aluminophosphate AlPO-14 and the corresponding calcined-dehydrated form were assigned using both "first-principles" calculations of NMR parameters (GIPAW, as implemented in NMR-CASTEP) and a 27Al-31P heteronuclear correlation NMR experiment (MQ-J-HETCOR) that exploits 27Al multiple-quantum coherences and J couplings to identify Al-O-P linkages. NMR parameters calculated from published AlPO-14 crystal structures, which are derived from powder X-ray diffraction (XRD) data, are in poor agreement with experiment and it was necessary to optimize the structure geometry using energy minimization before satisfactory agreement was obtained. Comparison of simulated powder XRD patterns from the experimental and the energy-minimized structures shows that the changes in relative atomic positions in the optimized structure are relatively small and yield only minor adjustments in the Bragg peak intensities. These results indicate that a combination of NMR spectroscopy and first-principles calculation of NMR parameters may soon be considered a generally useful step in the refinement of the structures of microporous materials derived from powder diffraction data.

A Morphological Study of Poly[bis(trifluoroethoxy)phosphazene] Using High Resolution Solid-State 1H, 19F, 31P and 13C NMR Spectroscopy

High-resolution 19F, 1H, 31P and 13C solid-state NMR methods were assessed to ascertain their suitability for studying the morphological behavior in the crystalline domain of phosphazene polymers with partially fluorinated side-chains. Poly[bis(trifluoroethoxy)phosphazene] (PBFP) was used as a sample system. Fast magic angle spinning (MAS), along with simultaneous 19F and 1H decoupling using the xy-16 sequence, were employed, as this has proven to greatly improve resolution in 13C spectra of perfluorinated materials. Information obtained from Discrimination Induced by Variable Amplitude Minipulses (DIVAM) nutation experiments and cross-polarization (CP) methods aided the deconvolution analysis used to identify all components in the 1H, 19F and 13C signals. DIVAM nutation experiments were also used to discriminate between signals from the amorphous and crystalline domain. The crystallinity in the solvent-cast PBFP was determined to be approximately 70%, which was seen to increase to approximately 80% in the heat-treated material, for all nuclei studied. A preliminary assignment was made for the crystalline signals in the 1H and 13C spectra to the α-, β- and γ-phases. Therefore, high-resolution 13C and 1H methods are valuable tools for morphological investigations into this class of polymer.

Heterometallic manganese/zinc-phytate complex as a model compound for metal storage in wheat grains

Myo-inositol-1,2,3,4,5,6-hexakisphosphate, also known as phytate, is a natural metal chelate present in cereals, an important feedstock worldwide. This article reports the characterization of three metal storage model complexes: the homometallic Mn(II) myo-inositol-1,2,3,4,5,6-hexakisphosphate (IP6), the heterometallic Zn(II), Mn(II) analogue Na 4MnZn 4(C 6H 6O 24P 6) · (NO 3) 2 · 8H 2O (MnZn 4IP6) and the homometallic Zn(II) metal complex Na 3Zn 5(C 6H 6O 24P 6)OH · 9H 2O (Zn 5IP6). The techniques of high-resolution 23Na, 13C and 31P NMR, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) were applied in this study. The complexation of Zn(II) and Mn(II) by phosphate groups of IP6 is demonstrated by NMR and XPS results. 13C NMR results show a conformation for IP6 consisting of five equatorial phosphate groups to one axial group showing only one chemical environment for Zn and two for Mn, when characterized by XPS and EPR, in both Mn complexes. These results support, for the first time, a probable supramacromolecular structure for phytate complexes of transition metals. Based on the similarity between the EPR spectra of wheat seeds and that of the MnZn 4IP6 compound, the manganese storage centers in wheat grains can be assigned to similar heterometallic phytate complexes.

The phosphatidylcholine/lysophosphatidylcholine ratio in human plasma is an indicator of the severity of rheumatoid arthritis: Investigations by 31P NMR and MALDI-TOF MS

Objectives: Lipid second messengers, e.g. lysophosphatidylcholines (LPC) are involved in the pathogenesis of inflammatory diseases, for instance, rheumatoid arthritis (RA). Unfortunately, the analysis of LPC in complex mixtures as present in body fluids is still challenging. Design and methods: Matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) was applied for phospholipid (PL) analysis of organic extracts of synovial fluids from patients with RA as well as the corresponding plasma. These data were compared with results obtained by high resolution 31P NMR spectroscopy. Results: Synovial fluids may be replaced by plasma since the analysis of both body fluids gives very similar results. Patients undergoing treatment with TNF-α inhibitors (ADALIMUMAB (HUMIRA®)) were examined in order to investigate whether the clinically-significant attenuation of disease activity is accompanied by changes of the PL composition of plasma. It will be shown that especially the PC/LPC ratios of plasma represent a reliable measure of inflammation and increase upon therapy. Conclusions: Since plasma samples are readily available, our approach might be useful to draw conclusions before puncture of the affected joints is necessary and the PC/LPC ratio detected in plasma may serve as an indicator of RA in early stages.

Straightforward detection of the secondary ionisation of the phosphate group and pK determinations by high-resolution solid-state 31P NMR

The suitability of high-resolution solid-state 31P NMR for a straightforward determination of the protonation state of phosphate groups as well as of their pK2 values extracted from solid state mono : dianionic ratios has been demonstrated.

High-Resolution 31P Field Cycling NMR as a Probe of Phospholipid Dynamics

We have used high-resolution field-cycling 31P NMR spectroscopy to measure spin-lattice relaxation rates (R1 = 1/T1) of multicomponent phospholipid vesicle and micelle samples over a large field range, from 0.1 to 11.7 T. The shape of the curve for R1 as a function of field and a model-free analysis were used to extract tauc, a correlation time for each type of phospholipid molecule in the bilayer that is likely to reflect rotation of the molecule about the axis perpendicular to the membrane surface; Sc2, a chemical shift anisotropy (CSA) order parameter; and tauhf, a time constant reflecting faster internal motion. This 31P technique was also used to monitor association of a peripheral membrane protein, Bacillus thuringiensis phosphatidylinositol-specific phospholipase C, with both phosphatidylcholine and phosphatidylmethanol bilayers. Differences in phospholipid dynamics induced by the protein shed light on how zwitterionic phosphatidylcholine, and not the anionic phosphatidylmethanol, activates the enzyme toward its substrate.

Conformational analysis of 1,3,6,2-dioxazaphosphocanes and 1,3,6,2-dioxazasilocanes

The steric structure of 1,3,6,2-dioxazaphosphocanes and 1,3,6,2-dioxazasilocanes in solution was established by high-resolution 1H, 13C, and 31P NMR spectroscopy and PM3 calculations. It is shown that the preferred conformation of the eight-membered heterocycle is chair-chair (crown).

Physiological and morphological evidences for the presence acidocalcisomes in Trypanosoma evansi: single cell fluorescence and 31P NMR studies.

A new Ca(2+) intracellular store, the acidocalcisome, has been reported in trypanosomatids. It has been characterized physiologically as a Ca(2+) store sensitive to nigericin. The Ca(2+)/H(+)-ATPase is the system responsible for Ca(2+) accumulation, which depends on a pH gradient formed by ATP- and PPi-dependent proton pumps. In this work we present physiological and morphological evidences for the presence of acidocalcisomes in Trypanosoma evansi. The parasites were purified and loaded with the fluorescent dye Fura 2-AM in order to detect the intracellular changes of Ca(2+) levels in individual cells. The simultaneous incubation of T. evansi cells with ionomycin and nigericin led to large release of Ca(2+) (ca. 200 nM) from intracellular stores, which was not observed with either agent alone. On the other hand, no enhancement of the nigericin-induced Ca(2+) release was observed in the presence of oligomycin. Additionally, the pretreatment with bafilomycin decreases the nigericin-induced Ca(2+) release. These results confirm the presence of an intracellular non-mitochondrial acidic Ca(2+) storage compartment. These results suggest that H(+)-ATPase is involved in the process of Ca(2+) accumulation into the acidocalcisomes. Furthermore, the cells loaded with acridine orange exhibited abundant fluorescent vacuoles, which were sensitive to nigericin or bafilomycin A(1). Electronic transmission microscopy observations demonstrated the presence of electron dense particles in the parasites. High levels of inorganic pyrophosphate and triphosphate were detected in perchloric acid extracts of T. evansi by high resolution 31P NMR. Taken together, these results present the first evidence for the presence of acidocalcisomes in T. evansi.