31P Magic-angle Spinning NMR Spectra Research Articles

Identification of phosphorus sites in amorphous LiPON thin film by observing internuclear proximities

Amorphous lithium phosphorus oxynitrides (LiPON), prepared by reactive magnetron sputtering, have become the electrolytes of choice for all-solid-state thin film microbatteries since its discovery in early 1990s. Nevertheless, there is still a lack of understanding of their atomic-level structure and its influence on ionic conductivity. Solid-state NMR spectroscopy represents a promising technique to determine the atomic-level structure of LiPON glasses but is challenging owing to its low sensitivity in the case of thin film materials. Recently, 31P solid-state NMR spectra of LiPON thin films were acquired under magic-angle spinning (MAS) conditions and assigned with the help of density functional theory (DFT) calculations of NMR parameters. However, the identification of the different P local environments in these materials is still a challenge owing to their amorphous structure and the lack of resolution of the 31P MAS NMR spectra. We show herein how the NMR observation of internuclear proximities helps to establish the nature of P sites in LiPON thin films. The 31P-14N proximities are probed by a transfer of population in double resonance (TRAPDOR) experiment, whereas 31P-31P proximities are observed using one-dimensional (1D) 31P double-quantum (DQ)-filtered and two-dimensional (2D) 31P homonuclear correlation spectra as well as dipolar dephasing experiments using DQ-DRENAR (DQ-based dipolar-recoupling effects nuclear alignment reduction) technique. The obtained NMR data further support the recently proposed assignment of 31P NMR signals of LiPON thin films. With the help of this assignment, the simulation of the quantitative 1D 31P NMR spectrum indicates that PO43- orthophosphate anions prevail in LiPON thin films and N atoms are mainly incorporated in [O3PNPO3]5− dimeric anions. PO3N4− isolated tetrahedra and [O3POPO3]4− anions are also present but in smaller amounts.

Lithium conduction and the role of alkaline earth cations in Li2S–P2S5–MS (M = Ca, Sr, Ba) glasses

There has been considerable interest in lithium-sulfide glasses with high lithium ion conductivities because of their potential applications in solid-state electrolytes. Here, new sulfide glasses containing alkaline earth cations, Li2S–P2S5–MS (M = Ca, Sr, Ba), were synthesized by melt quenching. Furthermore, the glass-forming regions in these glasses were identified.Three samples containing equimolar alkaline earth cations (60Li2S–30P2S5–10MS) were selected and their Li+ conductivities were measured. Lower Li+ conductivities were observed in 60Li2S–30P2S5–10MS than in Li2S–P2S5. The local structures of P and Li were characterized by 31P and 6Li solid-state magic angle spinning (MAS) NMR to determine the cause for the observed decrease in the Li+ conductivities and understand the role of alkaline earth cations in the Li2S–P2S5 glasses. A higher-field shift of the PS43− was observed in the 31P MAS NMR spectra of the glasses containing alkaline earth cations, which was attributed to the formation of bridging structures between PS43− units by alkaline earth cations. Moreover, more than half of the Li had low mobility, which is consistent with the conductivity. These results highlight the presence of an effective conduction path around the PS43− in contrast to P2S74− and P2S64−.

Structure of P2O5–SiO2 Pure Network Former Glasses Studied by Solid State NMR Spectroscopy

The structure of binary (SiO2)100-x–(P2O5)x glasses has been investigated by Raman scattering, 29Si and 31P magic angle spinning (MAS) as well as static 31P NMR spectroscopy. 29Si chemical shift trends reflect the successive replacement of Si–O–Si by Si–O–P linkages as the compositional parameter x is increased. While 31P MAS NMR does not resolve separate phosphate species, the static 31P NMR lineshapes were successfully simulated by considering the effect of uncorrelated distribution functions of the chemical shift tensor components upon the line shape. On the basis of these simulations, which were also found to be consistent with the experimental 31P MAS NMR spectra, two distinct sites can be resolved: a dominant site characterized by an axially symmetric chemical shift tensor, assigned to P(3) units, and (only in the case of the x = 25 and 30 glasses) a Gaussian component reflecting phosphate species interacting with five- and six-coordinated silicon species. For 0 ≤ x < 25, the decrease in average coo...

Novel Cu(I)-selective chelators based on a bis(phosphorothioyl)amide scaffold.

Bis(dialkyl/aryl-phosphorothioyl)amide (BPA) derivatives are versatile ligands known by their high metal-ion affinity and selectivity. Here, we synthesized related chelators based on bis(1,3,2-dithia/dioxaphospholane-2-sulfide)amide (BTPA/BOPA) scaffolds targeting the chelation of soft metal ions. Crystal structures of BTPA compounds 6 (N(-)R3NH(+)) and 8 (NEt) revealed a gauche geometry, while BOPA compound 7 (N(-)R3NH(+)) exhibited an anti-geometry. Solid-state (31)P magic-angle spinning NMR spectra of BTPA 6-Hg(II) and 6-Zn(II) complexes imply a square planar or tetrahedral geometry of the former and a distorted tetrahedral geometry of the latter, while both BTPA 6-Ni(II) and BOPA 7-Ni(II) complexes possibly form a polymeric structure. In Cu(I)-H2O2 system (Fenton reaction conditions) BTPA compounds 6, 8, and 10 (NCH2Ph) were identified as most potent antioxidants (IC50 32, 56, and 29 μM, respectively), whereas BOPA analogues 7, 9 (NEt), and 11 (NCH2Ph) were found to be poor antioxidants. In Fe(II)-H2O2 system, IC50 values for both BTPA and BOPA compounds exceeded 500 μM indicating high selectivity to Cu(I) versus the borderline Fe(II)-ion. Neither BTPA nor BOPA derivatives showed radical scavenging properties in H2O2 photolysis, implying that inhibition of the Cu(I)-induced Fenton reaction by both BTPA and BOPA analogues occurred predominantly through Cu(I)-chelation. In addition, NMR-monitored Cu(I)- and Zn(II)-titration of BTPA compounds 8 and 10 showed their high selectivity to a soft metal ion, Cu(I), as compared to a borderline metal ion, Zn(II). In summary, lipophilic BTPA analogues are promising highly selective Cu(I) ion chelators.

Supramolecular copper halide networks using the coordinative flexibility of the cyclo-P 2S 3 middle deck in (C 5Me 5) 2Mo 2P 2S 3: Phosphorus versus sulfur coordination

Reaction of solutions of [ Cp 2 ∗ Mo 2P 2S 3] ( 1; Cp ∗ = η 5-C 5Me 5) in CH 2Cl 2 with solutions of CuHal (Hal = Cl, Br, I) in CH 3CN gave after slow diffusion the novel coordination polymers [ Cp 2 ∗ Mo 2P 2S 3(CuCl) 4] ( 2), [ Cp 2 ∗ Mo 2P 2S 3(CuBr) 3] ( 3) and [ Cp 2 ∗ Mo 2P 2S 3(CuI) 3] ( 4). The products were characterized by elemental analysis, 31P magic angle spinning (MAS) NMR spectroscopy and single-crystal X-ray crystallography. The solid-state structures of 2 and 3 are composed of two-dimensional polymeric networks, whereas that of 4 contains parallel stacks of one-dimensional ribbons. In all cases the planar cyclo-P 2S 3 middle deck of the organometallic building block 1 provides one or two P atoms of the PS dumbbells along with the singly bridging sulfur atom as coordination sites for the various copper halide subunits. The assignment of P atoms follows from the correlation of 31P MAS NMR spectra with X-ray crystallographic data. In all compounds the distribution of main group atoms in the cyclo-P 2S 3 middle deck is different from that previously found in the starting material 1.

High-resolution 2H MAS NMR applied to deuterium analogs of hydrido η 2-dihydrogen complexes

2H solid-state, variable temperature magic angle spinning (MAS) NMR spectra of precipitated samples of the deutero dideuterium complexes Ru(D) 2(η 2-D 2) 2(PCy 3) 2 and RuD(η 2-D 2)I(PCy 3) 2 [Cy=cyclohexyl] are presented. They show that even at moderate MAS speed, high resolution is achieved at 7 and 14 T allowing 2H chemical shifts and quadrupole couplings to be obtained and assigned to different solid and gaseous 2H species. These two parameters allow identifying chemically different hydrogen species in the material. The analysis of these parameters in this study reveals the presence of three different species in the sample, namely the complexes RuD(η 2-D 2)I(PCy 3) 2 and RuD(η 2-D 2) 2I(PCy 3) 2, and highly mobile HD/D 2. These assignments are supported by 2H T 1 relaxation times and 31P MAS NMR spectra. Moreover, variable temperature MAS NMR spectra reveal temperature-dependent line-shape changes, which are clear indications of intramolecular hydrogen exchange of the deutero and the dideuterium ligands and which give an estimate for the activation energy of this process.

Polycarboxylic acids as network modifiers for water durability improvement of inorganic–organic hybrid tin-silico-phosphate low-melting glasses

We investigated the water durability of the inorganic–organic hybrid tin-silico-phosphate glasses Me 2SiO–SnO–P 2O 5 (Me designs the organic methyl group) doped with organic acids (salicylic acid (SA), tartaric acid (TA), citric acid (CA) and butane tetracarboxylic acid (BTCA)) containing one or more of carboxylic groups per molecule. The structure, thermal properties and durability of the final glasses obtained via a non-aqueous acid–base reaction were discussed owing to the nature and the concentration of the acid added. 29Si magic angle spinning (MAS) NMR and 31P MAS NMR spectra, respectively, showed clearly a modification of the network in the host glass matrix of the Me 2SiO–SnO–P 2O 5 system. The polycondensation enhancement to form –P–O–Si–O–P– linkages (PSP) and the increase of the Q 2 unit (two bridging oxygens per phosphorus atom) over the Q 3 unit (three bridging oxygens per phosphorus atom) as a function of the acid in the order SA<TA<CA<BTCA, suggest the formation of a chain-like structure which contrasts with the high cross-linkage in the Me 2SiO–SnO–P 2O 5 matrix. In addition, this structural change is accompanied by a decrease of the coefficient of thermal expansion and an increase of the water durability of the glasses with the acids containing a large number of carboxylic groups per molecule. The presence of carboxylic groups of the acid acting as network modifier may retard the movement of water molecules through the glasses due to the steric hindrance strengthening the PSP connections in a chain-like structure.

The Cytoplasmic Domains of Phospholamban and Phospholemman Associate with Phospholipid Membrane Surfaces

Phospholamban (PLB) and phospholemman (PLM, also called FXYD1) are small transmembrane proteins that interact with P-type ATPases and regulate ion transport in cardiac cells and other tissues. This work has investigated the hypothesis that the cytoplasmic domains of PLB and PLM, when not interacting with their regulatory targets, are stabilized through associations with the surface of the phospholipid membrane. Peptides representing the 35 C-terminal cytoplasmic residues of PLM (PLM(37-72)), the 23 N-terminal cytoplasmic residues of PLB (PLB(1-23)), and the same sequence phosphorylated at Ser-16 (P-PLB(1-23)) were synthesized to examine their interactions with model membranes composed of zwitterionic phosphatidylcholine (PC) lipids alone or in admixture with anionic phosphatidylglycerol (PG) lipids. Wide-line 2H NMR spectra of PC/PG membranes, with PC deuterated in the choline moiety, indicated that all three peptides interacted with the membrane surface and perturbed the orientation of the choline headgroups. Fluorescence and 31P magic-angle spinning (MAS) NMR measurements indicated that PLB(1-23) and P-PLB(1-23) had a higher affinity for PC/PG membranes, which carry an overall negative surface charge, than for PC membranes, which have no net surface charge. The 31P MAS NMR spectra of the PC/PG membranes in the presence of PLM(37-72), PLB(1-23), and P-PLB(1-23) indicated that all three peptides induced clustering of the lipids into PC-enriched and PG-enriched regions. These findings support the theory that the cytoplasmic domains of PLB and PLM are stabilized by interacting with lipid headgroups at the membrane surface, and it is speculated that such interactions may modulate the functional properties of biological membranes.

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.

States and Dynamic Behavior of Protons and Water Molecules in H3PW12O40 Pseudoliquid Phase Analyzed by Solid-State MAS NMR

The states and dynamic behavior of acidic protons and water molecules in solid H3PW12O40·nH2O (0 < n < 6), which would be closely related to its pseudoliquid phase catalysis, were quantitatively elucidated by the comprehensive application of 31P, 1H, and 17O magic-angle spinning (MAS) NMR. 1H and 17O MAS NMR were sensitive to the local environment in the pseudoliquid phase (e.g., hydrogen bonding), and 31P MAS NMR was effective especially to quantify the states of the protons. At 173 K, several peaks appeared in the 31P MAS NMR spectra that were reasonably assigned to phosphorus atoms in polyanions (PW12O403-) having different numbers of acidic proton(s) directly attached to them. Hence, the acidic protons reside either directly on the polyanions as “isolated acidic protons” or as H3O+ or H5O2+, and the amounts of these species were determined as a function of water content. The relative intensity of the 31P MAS NMR peaks obeyed binomial distribution for all the range of 0 < n < 6, which shows that the isolated acidic protons and protonated water molecules (H3O+ and H5O2+) are distributed uniformly (i.e., randomly) in the solid. The distribution of these species was well explained by the random removal of water from the solid bulk. At 298 K, the 31P MAS NMR peaks coalesced, revealing that the isolated acidic protons, which are the origin of the strong acidity in the pseudoliquid phase, migrate between the neighboring polyanions much faster than catalytic reactions. This is the first quantitative observation of the protons in hydrated heteropolyacids by spectroscopic methods.

Structure−Property Correlations in Lithium Phosphate Glasses: New Insights from 31P ↔ 7Li Double-Resonance NMR

The macroscopic properties of binary alkali phosphate glasses are characterized by the presence of unexpected minima in the glass transition temperatures at alkali concentrations near 20−25 mol %. In the present study, the structural origin of this behavior is explored on the basis of multinuclear single- and double-resonance NMR experiments. 31P magic-angle spinning NMR spectra track the successive network depolymerization caused by Li2O addition, while 6Li chemical shifts indicate a lithium coordination number of four to five. The monotonic evolution of these spectra with increasing alkali content reveals that the nonlinear macroscopic behavior does not reflect any abrupt structural changes at the local level. In contrast, 31P{7Li} rotational echo double-resonance spectroscopy indicates substantial restructuring on longer distance scales, relating to the spatial arrangement of the lithium ions with respect to the phosphorus sites in the network. The data suggest that the average number of lithium atoms ...

Determining the Structure of Trimethylphosphine Bound to the Brønsted Acid Site in Zeolite HY: Double-Resonance NMR and ab Initio Studies

Solid-state NMR methods and ab initio calculations have been employed to investigate the structure of the trimethylphosphine (TMP)−Brønsted acid site complex in zeolite HY. 27Al/31P and 27Al/1H rotational echo double-resonance NMR experiments performed at −150 °C were utilized to measure Al−P and Al−HB distances for the acid site−TMP complex of 3.95 (±0.05) and 2.8−3.1 Å, respectively, where HB is the Brønsted acid site proton. A more accurate measurement of the Al−HB distance was not possible since models that assume the presence of isolated Al−H spin pairs are not valid in this case. A P−HB distance of 1.40 (±0.02) Å was obtained by fitting the spinning sidebands in the 1H magic angle spinning (MAS) NMR spectrum. These internuclear distances are within the range of the Al−P, Al−HB, and P−HB distances obtained from ab initio calculations for the ion pair (IP) TMPH+−zeolite complex that is formed by transferring a Brønsted acid proton to TMP. In contrast to the 31P MAS NMR spectra, which indicated that the only stable species was TMPH+, ab initio calculations on small cluster models predicted that the neutral complex should be more stable than the IP complex. However, use of a larger zeolite fragment in the calculations enhanced the relative stability of the IP structure.

Multinuclear MAS NMR study on the microporous aluminophosphates AlPO4-41 and SAPO-41

Medium pore aluminophosphate molecular sieves SAPO-41 and AlPO4-41 and their manganese containing derivatives have been synthesized hydrothermally using di-n-propylamine as an organic template. 13C, 27Al and 31P magic-angle spinning (MAS) NMRspectroscopy have been used to study the structural changes occurring upon isomorphous substitution of silicon into the alumino-phosphate framework. These changes are most pronounced in the 31P MAS NMR spectra. While SAPO-41 and MnAPSO-41 show only a single resonance at -30.5 ppm, AlPO4-41 and MnAPO-41 exhibit multiple line 31P NMR spectra. After calcination of the latter samples only a single resonance at -31.5 ppm is observed. The different lines can be assigned to defect sites (e.g. P-OH) and the crystallographically inequivalent T-atoms present in the AFO structure on the basis of 1H–31P cross-polarization experiments.

Structural study of phosphate groups in layered metal phosphates by high-resolution solid-state31P NMR spectroscopy

In studies of a series of crystals of layered metal phosphate compounds by magic angle spinning (MAS) NMR spectroscopy, it has been found that there is a distinct correlation between the 31 P isotropic chemical shift value and the type of phosphate group. The isotropic 31 P chemical shifts of (H 2 PO 4 ) - , (HPO 4 ) 2- and (PO 4 ) 3- groups appear around δ -10, -20 and -30, respectively. These assignments were made unambiguously by measuring the 31 P MAS NMR spectra with and without 1 H high-power decoupling together with the cross-polarization transfer technique between 1 H and 31 P nuclei (CP MAS spectra).

Measurement of indirect spin—spin coupling constants between crystallographically equivalent nuclei. Determination of 2J(31P, 31P) in solid Ag[P(m‐tolyl)3]2NO3

AbstractSolid‐state 31P magic angle spinning (MAS) NMR spectra of Ag[P(m‐tolyl)3]2NO3 were investigated as a function of the magic angle spinning frequency. Examination of the 31P MAS NMR spectra obtained at 4.70 and 9.40 T indicates that the two phosphorus nuclei have identical isotropic chemical shifts, that is, they are crystallo‐graphically equivalent, δ = 11.2 ppm. However, since the orientation of their respective chemical shift tensors is not coincident, the two phosphorus nuclei are magnetically non‐equivalent and exhibit spinning‐frequency dependent 31P NMR lineshapes. Analysis of the spinning‐frequency dependent 31P MAS NMR spectra at 4.70 and 9.40 T indicates that 2J(31P, 31P) = 140 Hz. This value was confirmed by 2D J‐resolved spectroscopy. The determination of an indirect spin‐spin coupling constant between two nuclei which constitute an ‘isolated’ spin pair with identical isotropic chemical shifts is not possible in conventional solution‐state NMR studies unless a third spin is introduced. The 31P MAS NMR spectra of Ag[P(m‐tolyl)3]2NO3 also exhibit resolvable splittings due to 109Ag and 107Ag; 1J(109Ag, 31P) = 517±5 Hz and 1J(107Ag, 31P) = 453 ± 5 Hz. In solution NMR studies these couplings are not always observed because of rapid metal‐ligand exchange.

Influence of heteronuclear dipolar interactions on magic angle spinning NMR spectra of solids containing isolated three-spin systems

Average Hamiltonian theory (AHT) is used to predict magic angle spinning (MAS) NMR spectra arising from isolated three-spin (I = 1/2) systems consisting of two crystallographically equivalent spins (A and A′) and a third heteronuclear spin (X). Under conditions of rapid sample spinning, the theory predicts the AA′ region of the MAS NMR spectra to consist of two equally intense peaks separated by the heteronuclear indirect spin-spin coupling constant J AX = J A′X, analogous to the situation in solution NMR studies. However, under slow spinning conditions the theory indicates a general eight-peak MAS spectrum for the AA′ region. Furthermore, it is shown that the two A-spin sub-spectra which arise from the two allowed spin states of X (m X = ±1/2) are different in that one is ‘squeezed’ while the other is ‘stretched’. Qualitatively, the heteronuclear dipolar interactions between the X spin and the crystallographically equivalent spins are responsible for the different A-spin sub-spectra associated with m X = +1/2 and m X = -1/2. In accord with theory, the 199Hg satellite peaks observed in 31P MAS NMR spectra of Hg(PPh3)2(NO3)2 (A, A′ = 31P; X = 199Hg) depend on the spin state of the 199Hg nucleus. In contrast, the heteronuclear dipolar interaction does not contribute to the linewidths observed in MAS NMR spectra of heteronuclear two-spin systems.

19F–31P J-Resolved MAS NMR Spectroscopy of an "Inorganic Adamantane"

The application is demonstrated of 19F-31P J-resolved spectroscopy to the mobile PF6- moiety present in KPF6. The 31P MAS NMR spectra of KPF6 recorded without 19F decoupling and with 19F multiple-pulse decoupling are shown. The resoln. in the multiple-pulse decoupled expts. was dependent upon the rotation frequency. This dependence is attributed to interplay between motional influences, cycle time of the multiple-pulse sequence, and suppression of the line-broadening effect of the 19F-19F interaction by magic-angle spinning (MAS) alone.

Spinning-rate-dependent line shape in 31P magic-angle spinning NMR spectra of inorganic phosphates

We have found that the line shape in 31P magic-angle spinning (MAS) NMR spectra is dependent on the spinning rate of the sample for pyrophosphates and metaphosphates such as Na 4P 2O 7, Na 4P 2O 7·10H 2O, Ag 4P 2O 7, and (KPO 3) n . The dependence can be explained by spectral spin diffusion of 31P spins through dipole-dipole interaction.

High-resolution solid-state 29Si and 31P NMR of silicon-phosphorous compounds containing six-coordinated silicon

29Si and 31P chemical-shift data for Si(HPO 4) 2·H 2O and SiP 2O 2 were obtained from magic angle spinning (MAS) NMR spectra. According to the 29Si chemical shifts, the silicon atoms are six-coordinated in both compounds. There are two non-equivalent silicon-oxygen octahedra in the structure of SiP 2O 2, but there is only one in Si(HPO 4) 2·H 2O. From 31P MAS NMR spectra it is possible to distinguish four different PO 4 tetrahedra in SiP 2O 7 and two in Si(HPO 4) 2·H 2O. Additional information on the symmetry of the PO 4 tetrahedra is obtained from broad line 31P NMR spectra.