Spinning 31P NMR Research Articles

Novel sol-gel route for expanding the glass forming region of tin phosphate glass for secondary battery electrode applications

In this paper, tin-phosphate amorphous glass and nano-crystallized ceramic materials were synthesized by sol-gel methods and heat treated at 400 °C with the composition of xSnO2− (100-x)P2O5 (xSnP: ‘x’ from 40 to 90 mol%). The electrical and thermal properties of tin-phosphate materials were investigated by electrical impedance spectroscopy (EIS) and thermogravimetry – differential thermal analysis – mass spectroscopy (TG–DTA–MS). Moreover, the local structure of xSnP was characterized by 119Sn-Mössbauer and magic angle spinning (MAS) 31P NMR spectroscopies. Homogeneous glasses were obtained for xSnP with ‘x’ from 50 to 80, while Sn(HPO4), SnO2, and Sn3(PO4)2 nanoparticles formed in 40SnP and 90SnP compositions, respectively. The nano-crystallized 40SnP and 90SnP samples showed large electrical conductivity (σ) of 2.02×10−5 and 1.04×10−4S cm−1 due to the conductive crystalline phases of SnP2O7 and defective SnO2, respectively. The lower σ of about 10−8S cm−1 were recorded for xSnP with ‘x’ from 50 to 80 owing to the decomposition of the 3D network built by phosphate tetrahedrons. 119Sn-Mössbauer spectra proved the growing number of SnIVO6 units, which do not contribute to the rise of electrical conductivity. On the other hand, larger σ values of 1.79×10−4 and 6.4×10−3S cm−1 were confirmed for 40SnP and 90SnP samples after heat treatment, resulting in partial reduction of SnIV to SnII and growing of the 3D network structure by PO43−. It is concluded that highly electrically conductive xSnP samples can be synthesized by the sol-gel method followed by slow heat treatment. In addition, the battery evaluation was performed of xSnP samples as cathode and anode in a sodium-ion battery. The highest initial capacity recorded for 90SnP nano-crystallized ceramic at 37.97 mAh g−1 under a current rate of 20 mA g−1 with capacity retention (%) of 48.15% after 100 cycles as a cathode material. The anode test showed that the 40SnP nano-crystallized ceramic has the largest initial capacity of 375 mAh g−1 and after heat treatment 50SnP glass significantly increased to 425 mAh g−1 compared with 186 mAh g−1 before heat treatment. Also, the heat treatment effect on the initial capacity of 90SnP nano-crystallized ceramic with observation largest value of 470 mAh g−1. These results open the way to maybe applying these glass and nano-crystallized ceramic materials in all-solid-state batteries.

Speciation of Phosphorus in Pet Foods by Solid-State 31P-MAS-NMR Spectroscopy.

Solid-state magic angle spinning 31P NMR spectroscopy is used to identify and quantify phosphorus-containing species in pet foods. The measurement is challenging due to the long spin-lattice relaxation times (T1s). Data acquisition times are shortened by acquiring data with a tip angle smaller than 90° and shortening the repetition time. However, the spin-lattice relaxation times (T1s) of the different 31P compounds are quite different, necessitating a separate measurement for each compound in the pet food. Knowledge of T1 is used to calculate the relative amount of 31P in the samples. Samples of known concentration are also measured, enabling the quantitative measurement of total phosphorus content.

Magic angle spinning 31P NMR spectroscopy reveals two essentially identical ionization states for the cardiolipin phosphates in phospholipid liposomes

Specific membrane lipid composition is crucial for optimized structural and functional organization of biological membranes. Cardiolipin is a unique phospholipid and important component of the inner mitochondrial membrane. It is involved in energy metabolism, inner mitochondrial membrane transport, regulation of multiple metabolic reactions and apoptotic cell death. The physico-chemical properties of cardiolipin have been studied extensively but despite all these efforts there is still lingering controversy regarding the ionization of the two phosphate groups of cardiolipin. Results obtained in the 1990s and early 2000s suggested that cardiolipin has two disparate pKa values where one of the protons was proposed to be stabilized by an intramolecular hydrogen bond. This has led to extensive speculations on the roles of these two putative ionization states of cardiolipin in mitochondria. More recently the notion of two pKa values has been challenged and rejected by several groups. These studies relied on external measurements of proton adsorption or electrophoretic mobility of membranes but did not take into account the low pH phase behavior and chemical stability of cardiolipin. Here we used 31P NMR to show that in the physiologically relevant membrane phospholipid environment, cardiolipin carries two negative charges at physiological pH. We additionally demonstrate the pH dependent phase behavior and chemical stability of cardiolipin containing membranes.

The effect of pH on the structure and phosphate mobility of casein micelles in aqueous solution

The mobility of phosphate groups in aqueous solutions of casein micelles and sodium caseinate from bovine milk was determined with magic angle spinning (MAS) 31P NMR as a function of the pH between pH 4 and pH 8. The chemical shifts and the relative amplitudes of the signals from mobile inorganic phosphate (orthophosphate) and mobile organic phosphate (phosphorylated serines) as well as that of immobile phosphate (colloidal calcium phosphate, and immobile phosphorylated serines) were determined. Sodium caseinate contained very little orthophosphate and all phosphates were mobile over the whole pH range. In micellar casein solutions most of the phosphate was immobile at pH > 6.0, but the fraction of mobile organic and inorganic phosphate increased sharply between pH 5.5 and pH 4.5, showing the disintegration of the CCP nanoclusters. Protonation of the phosphates with decreasing pH was determined from the chemical shift and was related to their mobility. The signal of mobile organic phosphate was different for micellar casein solutions and sodium caseinate demonstrating the influence of calcium phosphate in the former. The microscopic structure of protein solutions was investigated with confocal laser scanning microscopy. Large protein clusters were observed below pH 5.2 with a density that increased with decreasing pH down to pH 3.9. The mobility of either organic or inorganic phosphate at pH 6.8 was not significantly different after the pH had been reduced to 4.8 and subsequently increased to 6.8, but the microstructure was strongly influenced by the pH-cycling.

Cluster harvesting in the WBr6-P system.

A combined thermal scanning-X-ray diffraction (XRD) approach was performed for the WBr(6)-P system to detect and analyze phases in this system, including metal-rich phases generated with increasing amounts of elemental (red) phosphorus under partial PBr(3) release. Phases were characterized by powder XRD. A black crystalline powder of W(4)(PBr)Br(10) was obtained after reduction of WBr(6) with elemental phosphorus at 450 °C. The crystal structure of the new compound was found to be isotypic with the structure of W(4)(PCl)Cl(10) on the basis of powder XRD data. The structure of W(4)(PBr)Br(10) is represented by a cyclobutadiene-like tetranuclear tungsten cluster interconnected into a layered (W(4)(μ(4)-PBr)Br(6)(i))Br(8)/(2)(a-a) arrangement via outer bromide ligands. The μ(4)-capping bromophosphinidene ligand was verified by solid-state magic-angle spinning (31)P NMR spectroscopy.

Monomer and Dimer of Mono‐titanium(IV)‐Containing α‐Keggin Polyoxometalates: Synthesis, Molecular Structures, and pH‐Dependent Monomer–Dimer Interconversion in Solution

AbstractPowder and crystalline samples of the monomer (Et2NH2)5[α‐PW11TiO40]·2H2O (EtN‐1) and a crystalline sample of the μ‐oxo dimer (Et2NH2)8[(α‐PW11TiO39)2O]·6H2O (EtN‐2) of mono‐titanium(IV)‐containing α‐Keggin polyoxometalates (POMs) were prepared and characterized by elemental analysis, thermogravimetry/differential thermal analysis (TG/DTA), FTIR, single‐crystal X‐ray crystallography, and solid‐state cross‐polarization magic angle spinning (CPMAS) 31P NMR and solution (31P and 183W) NMR spectroscopy. The molecular structure of the dimeric polyoxoanion with a μ‐oxo group in 2 was determined for the first time. The monomer–dimer equilibrium in solution was clarified by pH‐varied 31P NMR spectroscopy.

An Electrostatic/Hydrogen Bond Switch as the Basis for the Specific Interaction of Phosphatidic Acid with Proteins

Phosphatidic acid (PA) is a minor but important phospholipid that, through specific interactions with proteins, plays a central role in several key cellular processes. The simple yet unique structure of PA, carrying just a phosphomonoester head group, suggests an important role for interactions with the positively charged essential residues in these proteins. We analyzed by solid-state magic angle spinning 31P NMR and molecular dynamics simulations the interaction of low concentrations of PA in model membranes with positively charged side chains of membrane-interacting peptides. Surprisingly, lysine and arginine residues increase the charge of PA, predominantly by forming hydrogen bonds with the phosphate of PA, thereby stabilizing the protein-lipid interaction. Our results demonstrate that this electrostatic/hydrogen bond switch turns the phosphate of PA into an effective and preferred docking site for lysine and arginine residues. In combination with the special packing properties of PA, PA may well be nature's preferred membrane lipid for interfacial insertion of positively charged membrane protein domains.

Distinguishing Individual Lipid Headgroup Mobility and Phase Transitions in Raft-Forming Lipid Mixtures with 31P MAS NMR

A model membrane system composed of egg sphingomyelin (SM), 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC), and cholesterol was studied with static and magic angle spinning 31P NMR spectroscopy. This model membrane system is of significant biological relevance since it is known to form lipid rafts. 31P NMR under magic angle spinning conditions resolves the SM and DOPC headgroup resonances allowing for extraction of the 31P NMR parameters for the individual lipid components. The isotropic chemical shift, chemical shift anisotropy, and asymmetry parameter can be extracted from the spinning side band manifold of the individual components that form liquid-ordered and liquid-disordered domains. The magnitude of the 31P chemical shift anisotropy and the line width is used to determine headgroup mobility and monitor the gel-to-gel and gel-to-liquid crystalline phase transitions of SM as a function of temperature in these mixtures. Spin-spin relaxation measurements are in agreement with the line width results, reflecting mobility differences and some heterogeneities. It will be shown that the presence of DOPC and/or cholesterol greatly impacts the headgroup mobility of SM both above and below the liquid crystalline phase transition temperature, whereas DOPC displays only minor variations in these lipid mixtures.

Luminescent Polyoxotungstoeuropate Anion‐Pillared Layered Double Hydroxides.

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Sodium X-type faujasite zeolite decomposition of dimethyl methylphosphonate (DMMP) to methylphosphonate: Nucleophilic zeolite reactions I

Dimethyl methylphosphonate (DMMP), used extensively as a nerve agent simulant, strongly adsorbs in X-type faujasite zeolite and undergoes nucleophilic substitution by the supercage oxygens. Solid state magic angle spinning (MAS) 31P and cross polarization (CP) MAS 13C NMR studies of the zeolite were performed after adsorption of DMMP into it. Methylphosphonate ions and possibly a framework methyl species are formed at low levels of water. The greater reactivity of NaX than the reactivity of NaY toward VX (phosphonothioic acid, methyl-, S-[2-[bis(1-methylethyl)amino]ethyl] O-ethyl ester) and one of its simulants [G.W. Wagner, P.W. Bartram, Langmuir 15 (1999) 8113], may be attributable to the smaller Si:Al ratio of NaX. Consequently, the NaX framework oxygen atoms are more nucelophilic and supercage Na ions are present to attract the methylphosphonate ion leaving groups.

Luminescent Polyoxotungstoeuropate Anion‐Pillared Layered Double Hydroxides

AbstractNovel luminescent polyoxometalate anion‐pillared layered double hydroxides (LDHs) were prepared by aqueous ion exchange of a Zn–Al LDH precursor in nitrate form with the europium‐containing polyoxotungstate anions [EuW10O36]9–, [Eu(BW11O39)(H2O)3]6– and [Eu(PW11O39)2]11–. The host–guest interaction has a strong influence on the nature of the final intercalated species, as evidenced by elemental analysis, powder X‐ray diffraction (XRD), infra‐red (IR) and Raman spectroscopy, solid state magic‐angle spinning (MAS) 11B and 31P NMR spectroscopy, and photoluminescence spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

What Makes the Bioactive Lipids Phosphatidic Acid and Lysophosphatidic Acid So Special?

Phosphatidic acid and lysophosphatidic acid are minor but important anionic bioactive lipids involved in a number of key cellular processes, yet these molecules have a simple phosphate headgroup. To find out what is so special about these lipids, we determined the ionization behavior of phosphatidic acid (PA) and lysophosphatidic acid (LPA) in extended (flat) mixed lipid bilayers using magic angle spinning 31P NMR. Our data show two surprising results. First, despite identical phosphomonoester headgroups, LPA carries more negative charge than PA when present in a phosphatidylcholine bilayer. Dehydroxy-LPA [1-oleoyl-3-(phosphoryl)propanediol] behaves in a manner identical to that of PA, indicating that the difference in negative charge between LPA and PA is caused by the hydroxyl on the glycerol backbone of LPA and its interaction with the phosphomonoester headgroup. Second, deprotonation of phosphatidic acid and lysophosphatidic acid was found to be strongly stimulated by the inclusion of phosphatidylethanolamine in the bilayer, indicating that lipid headgroup charge depends on local lipid composition and will vary between the different subcellular locations of (L)PA. Our findings can be understood in terms of a hydrogen bond formed within the phosphomonoester headgroup of (L)PA and its destabilization by competing intra- or intermolecular hydrogen bonds. We propose that this hydrogen bonding property of (L)PA is involved in the various cellular functions of these lipids.

Magnitudes and Orientations of 31P Chemical Shielding Tensors in Pt(II)−Phosphine Complexes and Other Four-Fold Coordinated Phosphorus Sites

31P MAS and double-quantum filtered 31P MAS NMR experiments at and near the n = 0 rotational resonance condition, as well as off-magic angle spinning 31P NMR experiments on two polycrystalline samples of Pt(II)-phosphine thiolate complexes are reported. Numerical simulations yield complete descriptions of the two 31P spin pairs. 195Pt MAS NMR spectra are straightforward to obtain but sensitively reflect only some parameters of the 195Pt(31P)2 three-spin system. Based on the 31P NMR results obtained and in conjunction with a large body of literature data and irrespective of the chemical nature of the specimen, a unified picture of the dominating motif of 31P chemical shielding tensor orientations of phosphorus sites with 4-fold coordination is identified as a local (pseudo)plane rather than the directions of P element bond directions.

The ion exchange properties and equilibrium constants of Li+, Na+ and K+ on zirconium phosphate highly dispersed on a cellulose acetate fibers surface

Highly dispersed zirconium phosphate was prepared by reacting celullose acetate/ZrO2 (ZrO2 = 11 wt%, 1.0 mmol g-1 of zirconium atom per gram of the material) with phosphoric acid. High power decoupling magic angle spinning (HPDEC-MAS) 31P NMR and X-ray photoelectron spectroscopy data indicated that HPO4(2-) is the species present on the membrane surface. The specific concentration of acidic centers, determined by ammonia gas adsorption, is 0.60 mmol g-1. The ion exchange capacities for Li+, Na+ and K+ ions were determined from ion exchange isotherms at 298 K and showed the following values (in mmol g-1): Li+= 0.05, Na+= 0.38 and K+= 0.57. Due to the strong cooperative effect, the H+/Na+ and H+/K+ ion exchange is of non ideal nature. These ion exchange equilibria were treated with the use of models of fixed tridentate centers, which consider the surface of the sorbent as polyfunctional sorption centers. Both the observed ion exchange capacities with respect to the alkaline metal ions and the equilibrium constants are discussed by taking into consideration the sequence of the ionic hydration radii for Li+, Na+ and K+. The matrix affinity for the ions decreases with increasing the cations hydration radii from K+ to Li+. The high values of the separation factors S Na+/Li+ and S K+/Li+ (up to several hundreds) support the application of this material for the quantitative separation of Na+ and K+ from Li+ from a mixture containing these three ions.

Zirconium Phosphate Dispersed on a Cellulose Fiber Surface: Preparation, Characterization, and Selective Adsorption of Li+, Na+, and K+ from Aqueous Solution

Highly dispersed zirconium phosphate was prepared by reacting Cel/ZrO2 (ZrO2=6.7 wt%; 0.56 mmol g−1 of zirconium atom per gram of the material) with phosphoric acid. High power decoupling magic angle spinning (HPDEC-MAS)31P NMR and X-ray photoelectron spectroscopy data indicated that HPO2−4 is the species present on the fiber surface. The X-ray diffraction patterns showed that zirconium hydrogen phosphate particles were amorphous and had an ion-exchange capacity, determined by ammonia gas adsorption, of 0.30 mmol g−1. The ion-exchange capacities for Li+, Na+, and K+ ions were determined from ion-exchange isotherms at 298 K and showed the following values (in mmol g−1): Li+=0.01, Na+=0.23, and K+=0.30. The higher affinity of the surface hydrogen phosphate particles for Na+ and K+ is due to its lamelar structure which permits easier diffusion of these two ions whose hydrated radii are smaller than that of Li+.

Polyamine-nucleic acid interactions and the effects on structure in oriented DNA fibers.

Fibrous oriented calf thymus DNA containing the natural polyamines spermidine (Spd) and putrescine (Put), and the degradation polyamines cadaverine (Cad) and 1,3-diaminopropane (DAP), have been investigated at different water contents using nuclear magnetic resonance (NMR) methods, fiber X-ray diffraction and gravimetric measurements. When judged by X-ray only the DAP and Spd samples seem to undergo a B-A-form transition at reduced water activity. Solid-state two-dimensional rotor-synchronized magic angle spinning (2D-syncMAS) 31P-NMR, however, shows the A-form to be present also in the Put sample, and it appears that the separation between the amine units of diamines is correlated with the amount of A-form present. In addition, the solid-state NMR data show the polyamine-bound DNA samples to have a significant deviation from the ordinary B-form DNA structure, displaying similar amounts of BI and BII nucleotide conformations. The low water content of the samples suggest that the polyamines themselves act as hydrators of DNA. Water 2H-NMR results are in agreement with this observation. The quadrupolar splittings of the polyamine 2H signals for samples at low water content indicate some preferential spatial orientations of the polyamines in the ordered DNA environment. The polyamines show relatively fast macroscopic diffusion as detected by NMR self-diffusion measurements.

Structural Analysis of the Protein/Lipid Complexes Associated with Pore Formation by the Bacterial Toxin Pneumolysin

Pneumolysin, a major virulence factor of the human pathogen Streptococcus pneumoniae, is a soluble protein that disrupts cholesterol-containing membranes of cells by forming ring-shaped oligomers. Magic angle spinning and wideline static (31)P NMR have been used in combination with freeze-fracture electron microscopy to investigate the effect of pneumolysin on fully hydrated model membranes containing cholesterol and phosphatidylcholine and dicetyl phosphate (10:10:1 molar ratio). NMR spectra show that the interaction of pneumolysin with cholesterol-containing liposomes results in the formation of a nonbilayer phospholipid phase and vesicle aggregation. The amount of the nonbilayer phase increases with increasing protein concentration. Freeze-fracture electron microscopy indicates the coexistence of aggregated vesicles and free ring-shaped structures in the presence of pneumolysin. On the basis of their size and analysis of the NMR spectra it is concluded that the rings are pneumolysin oligomers (containing 30-50 monomers) complexed with lipid (each with 840-1400 lipids). The lifetime of the phospholipid in either bilayer-associated complexes or free pneumolysin-lipid complexes is > 15 ms. It is further concluded that the effect of pneumolysin on lipid membranes is a complex combination of pore formation within the bilayer, extraction of lipid into free oligomeric complexes, aggregation and fusion of liposomes, and the destabilization of membranes leading to formation of small vesicles.

Phase diagrams of systems with cationic α-helical membrane-spanning model peptides and dioleoylphosphatidylcholine

Ternary phase diagrams have been constructed of systems with dioleoylphosphatidylcholine (DOPC) and water, and two α-helical membrane-spanning model peptides, KKLAKK16[KK(LA) 6KK] and KKLAKK20[KK(LA) 8KK]. It was found that these peptides induced non-lamellar liquid crystalline phases. The amount of peptide needed for this phase transition depended on the water content and the temperature; and for KKLAKK16, a smaller amount of peptide was needed to induce non-lamellar phases than for KKLAKK20. Both peptides were found to induce an isotropic phase, and KKLAKK16 also induced a reversed hexagonal phase. Both peptides may also reside in a lamellar (L α) phase. When magic angle spinning (MAS) 31P NMR experiments were performed on samples containing the L α phase and an isotropic phase, four different isotropic chemical shifts were observed. The isotropic chemical shifts could be assigned to the phases, using spinning sidebands to calculate the chemical shift anisotropy (CSA) corresponding to each isotropic shift. MAS 13C NMR also indicated a difference in the aggregational state of the peptides between the L α and isotropic phases. The phase diagrams were compared to the phase diagram of a similar model peptide, AWW(LA) 5WWA in systems with DOPC and water. It was concluded that the phase behaviour was influenced by both electrostatic interactions between the peptides and the lipid headgroups, and the difference between the hydrophobic length of the peptide and the hydrophobic thickness of the lipid bilayer.

Vibrational and solid state (CP/MAS) 31P NMR spectroscopic studies of bis(trimethylphosphine)gold(I) halides

The 1:2 AuX/PMe3 (X=Cl,Br,I) complexes have been prepared and studied by infrared, Raman and solid-state cross polarisation magic angle spinning (CP MAS) 31P NMR spectroscopy. The new complex bis(trimethylphosphine)iodogold(I) [AuI(PMe3)2] was prepared by the reaction of [AuI(PMe3)] with PMe3 in dimethylformamide solution. A new method for the preparation of the corresponding bromide complex [AuBr(PMe3)2], from [NBu4][AuBr2] and PMe3, is described. The IR, Raman and CP MAS 31P NMR spectra of the X=Cl, Br compounds are essentially identical, whereas those for X=I show differences that are suggestive of relatively minor differences in the crystal structure relative to the X=Cl, Br compounds. The latter compounds exist as the ionic species [Au(PMe3)2]+X−, and the X=I complex is also essentially ionic, but with a possible weak Au⋯I interaction; this conclusion is supported by the 197Au Mössbauer spectrum of this compound. The solid-state CP MAS 31P NMR spectra of the chloride and bromide complexes consist of doublets due to the presence of 1J(197Au–31P) coupling. This study is the first in which such coupling is observed for the P–Au–P coordination environment. The 1J(197Au–31P) coupling constants are estimated from the doublet splittings.

Static and magic angle spinning 31P NMR spectroscopy of two natural plasma membranes

Static and magic angle spinning 31P NMR spectroscopy was used for the first time in natural plasma membranes from erythrocytes and skeletal muscle to study phospholipid arrangement and composition. Typical static powder-like spectra were obtained showing that phospholipids were in a bilayer arrangement. Magic angle spinning narrowed spectra into two components. The first one corresponded to phosphatidylcholine and the second one to the other phospholipids with intensities in agreement with the known phospholipid composition. These findings show that NMR data previously acquired using model membranes can be transposed to studies on phospholipids in their natural environment.