31P Resonance Research Articles

NMR and Mössbauer characterization of tin(II)–tin(IV)–sodium phosphate glasses

xSnO–(100−x)NaPO3 glasses were prepared under argon atmosphere for 0⩽x⩽40. Wet chemical analyses and Mössbauer spectroscopy indicate the presence of Sn(II) and Sn(IV) in the glasses, with a majority of Sn(II). 119Sn NMR and Mössbauer spectra show that the local environment of Sn(II) are characteristic of SnO in network forming sites. The 119Sn NMR spectrum of an oxidized glass shows that Sn(IV) are located in sites similar to SnP2O7. 31P MAS–NMR spectra show that the sodium metaphosphate chains are depolymerized by SnO, and that dissociation into the phosphate melt is complete. The 31P resonances were assigned to middle-chain group charge compensated by Na+(Q2(Na)), chain-end group charge compensated by Sn2+(Q1(Sn(II))) and Na+(Q1(Na)). The 31P MAS–NMR spectrum of the oxidized glass enabled to measure the chemical shift of (Q1(Sn(IV))), and the double-quantum filtered 31P MAS–NMR spectrum showed that Sn(IV) sites are inserted in the phosphate glass network.

Probing Structure and Dynamics in Poly[2,2‘-(m-phenylene)-5,5‘-bibenzimidazole] Fuel Cells with Magic-Angle Spinning NMR

H2/air fuel cell polymer electrolyte membranes, consisting of poly[2,2‘-(m-phenylene)-5,5‘-bibenzimidazole] (PBI) doped with phosphoric acid, have been studied by 1H and 31P magic-angle spinning (MAS) NMR to investigate the polymer−acid interaction and the unresolved question of the nature of the proton conductivity. The 1H and 31P resonances have been fully assigned, giving a complete picture of the species present and allowing a study of the local motion of these species by nuclear relaxation. These results have been compared to conductivity measurements, enabling conclusions to be drawn with regard to the molecular motion causing proton conductivity.

In Situ High-Pressure NMR Studies of Co2(CO)6[P(p-CF3C6H4)3]2 in Supercritical Carbon Dioxide: Ligand Substitution, Hydrogenation, and Hydroformylation Reactions

The dimeric cobalt complex Co2(CO)6[P(p-CF3C6H4)3]2 (1) reacts reversibly with hydrogen to produce HCo(CO)3[P(p-CF3C6H4)3] (4). The carbonyl and the phosphine ligands of both 1 and 4 are very labile. Compound 1 reacts with CO to give Co2(CO)7[P(p-CF3C6H4)3] (2), and compound 4 reacts with CO and P(p-CF3C6H4)3 (L) to give HCo(CO)4 (5) and HCo(CO)2[P(p-CF3C6H4)3]2 (6), respectively. The 31P NMR studies show that, in the presence of 1, the line width of the 31P resonance of L is temperature dependent, and at constant temperature, its broadening is proportional to the square root of the concentration of 1. This broadening is attributed to its exchange reaction with the mononuclear cobalt radical (CO)3LCo• (3), which is generated by the homolysis of 1. Compound 1 catalyzes the hydroformylation of olefins in supercritical carbon dioxide. In contrast to the unsubstituted Co2(CO)8, the phosphine-modified catalyst system is stable under low CO pressures and the hydroformylation reactions can be carried out at low pressures. In situ monitoring of 31P and 59Co NMR spectra of the solution shows that the phosphine-containing hydrido cobalt complexes 4 and 6 are the only hydrido cobalt complexes present in detectable concentrations in 1-catalyzed hydroformylation reactions; nevertheless, the possibility that the observed activity for 1 comes primarily from the more active HCo(CO)4, present in concentrations below detectable limits, has not been rigorously excluded.

Effect of bulky lesions on DNA: solution structure of a DNA duplex containing a cholesterol adduct.

The three-dimensional solution structure of two DNA decamers of sequence d(CCACXGGAAC)-(GTTCCGGTGG) with a modified nucleotide containing a cholesterol derivative (X) in its C1 '(chol)alpha or C1 '(chol)beta diastereoisomer form has been determined by using NMR and restrained molecular dynamics. This DNA derivative is recognized with high efficiency by the UvrB protein, which is part of the bacterial nucleotide excision repair, and the alpha anomer is repaired more efficiently than the beta one. The structures of the two decamers have been determined from accurate distance constraints obtained from a complete relaxation matrix analysis of the NOE intensities and torsion angle constraints derived from J-coupling constants. The structures have been refined with molecular dynamics methods, including explicit solvent and applying the particle mesh Ewald method to properly evaluate the long range electrostatic interactions. These calculations converge to well defined structures whose conformation is intermediate between the A- and B-DNA families as judged by the root mean square deviation but with sugar puckerings and groove shapes corresponding to a distorted B-conformation. Both duplex adducts exhibit intercalation of the cholesterol group from the major groove of the helix and displacement of the guanine base opposite the modified nucleotide. Based on these structures and molecular dynamics calculations, we propose a tentative model for the recognition of damaged DNA substrates by the UvrB protein.

Investigations of structure and transport in lithium and silver borophosphate glasses

Glasses in the system xLi 2O·(1− x)[0.5B 2O 3·0.5P 2O 5] and xAg 2O·(1− x)[0.5B 2O 3·0.5P 2O 5] have been prepared from melt quenching method. Glasses have been characterized for their densities, molar volumes, glass transition temperatures and heat capacities. Structural studies have been done using infrared and high resolution magic angle spinning nuclear magnetic resonance (HR MAS NMR) of 31P, 11B and 7Li nuclei. Boron is present only in tetrahedral coordination except in Li 2O-rich glasses. Transport properties have been investigated over a wide range of frequency and temperature. Silver containing glasses are found to possess higher conductivities and lower barriers than lithium containing glasses. A structural model has been proposed in which pure B 2O 3–P 2O 5 compositions are assumed to be constituted of BPO 4 units and modification occurs selectively on the phosphate moiety. Tetrahedral boron units are thus expected to be retained in the glass structure.

Solid State NMR Connectivity Studies in Dipolarly Coupled Inorganic Networks: Site Assignments in the Solid Electrolyte Material (CuI)8P12

Abstract The local structure of the fast solid ion conductor Cu2P3I2 = (CuI)8P12 is investigated using one- and two-dimensional 31P and 65Cu magic-angle spinning NMR techniques. Peak assignments are proposed on the basis of anisotropic and isotropic spin-spin interactions recovered via radio frequency driven dipolar recoupling (RFDR) and total through bond correlation spectroscopy (TOBSY) methods. Especially the previously proposed R306 14 pulse symmetry (R-TOBSY), which exploits scalar spin-spin interactions for coherence transfer, offers outstanding spectral selectivity with respect to 1 J coupling. Using sufficiently short mixing times it is thus possible to correlate selectively those 31P spins that are directly bonded, thereby providing detailed insights into phosphorus-phosphorus connectivities in the network. The final assignment of the nine resolved 31P resonances to the twelve crystallographically distinct phosphorus sites suggests a significant relationship between 31P chemical shifts and the detailed pyramidal P(P1/3)3 bonding geometry.

Naturally-occurring Modification Restricts the Anticodon Domain Conformational Space of tRNAPhe

Post-transcriptional modifications contribute chemistry and structure to RNAs. Modifications of tRNA at nucleoside 37, 3′-adjacent to the anticodon, are particularly interesting because they facilitate codon recognition and negate translational frame-shifting. To assess if the functional contribution of a position 37-modified nucleoside defines a specific structure or restricts conformational flexibility, structures of the yeast tRNAPhe anticodon stem and loop (ASLPhe) with naturally occurring modified nucleosides differing only at position 37, ASLPhe-(Cm32,Gm34,m5C40), and ASLPhe-(Cm32,Gm34,m1G37,m5C40), were determined by NMR spectroscopy and restrained molecular dynamics. The ASL structures had similarly resolved stems (RMSD∼0.6Å) of five canonical base-pairs in standard A-form RNA. The “NOE walk” was evident on the 5′ and 3′ sides of the stems of both RNAs, and extended to the adjacent loop nucleosides. The NOESY cross-peaks involving U33 H2′ and characteristic of tRNA's anticodon domain U-turn were present but weak, whereas those involving the U33 H1′ proton were absent from the spectra of both ASLs. However, ASLPhe-(Cm32,Gm34,m1G37,m5C40) exhibited the downfield shifted 31P resonance of U33pGm34 indicative of U-turns; ASLPhe-(Cm32,Gm34,m5C40) did not. An unusual “backwards” NOE between Gm34 and A35 (Gm34/H8 to A35/H1′) was observed in both molecules. The RNAs exhibited a protonated A+38 resulting in the final structures having C32·A+38 intra-loop base-pairs, with that of ASLPhe-(Cm32,Gm34,m1G37,m5C40) being especially well defined. A single family of low-energy structures of ASLPhe-(Cm32,Gm34, m1G37,m5C40) (loop RMSD 0.98Å) exhibited a significantly restricted conformational space for the anticodon loop in comparison to that of ASLPhe-(Cm32,Gm34,m5C40) (loop RMSD 2.58Å). In addition, the ASLPhe-(Cm32,Gm34,m1G37,m5C40) average structure had a greater degree of similarity to that of the yeast tRNAPhe crystal structure. A comparison of the resulting structures indicates that modification of position 37 affects the accuracy of decoding and the maintenance of the mRNA reading frame by restricting anticodon loop conformational space.

NMR Studies of Phosphorus Chalcogenide—Copper Iodide Coordination Compounds.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Solid state NMR and X-ray diffraction study of three forms of the aluminophosphate AlPO 4-ZON

As-synthesized, calcined and calcined-rehydrated AlPO 4- ZON materials have been studied using powder XRD and multinuclear solid state NMR techniques. A new assignment for the four 31P signals of the as-synthesized sample is presented. A Rietveld refinement on synchrotron data allows to elucidate the structure of the calcined material. Although the space group (Pbca) and the framework topology are similar to those of the previously studied as-synthesized and calcined-rehydrated materials, all four Al sites now exhibit a fourfold coordination. This is in agreement with the result of an 27Al 5QMAS NMR experiment. Furthermore, the bond distances deduced from this structural refinement, combined with a 31P homonuclear correlation experiment, allow assignment of the 31P resonances. Only a partial assignment of the 27Al signals could be achieved for the rehydrated material.

Spectroscopic Analyses of the Interaction Between Hammerhead Ribozymes and Metal Ions

AbstractFor Abstract see ChemInform Abstract in Full Text.

Characterization of the Room-Temperature Structure of SnP2O7 by 31P Through-Space and Through-Bond NMR Correlation Spectroscopy

The room-temperature structure of SnP2O7 has been investigated using various one- and two-dimensional (1- and 2D) magic-angle spinning (MAS) NMR experiments. We show that 31P homonuclear through-bond and through-space correlation NMR spectroscopies allow us to discriminate between the 12 possible space group symmetries of the structure. In particular, the 31P 2D refocused INADEQUATE experiment allows us to resolve an impressive number of distinct 31P resonances, showing that the asymmetric unit contains at least 49 different P2O7 groups with two inequivalent P sites. The results suggest that the symmetry of the SnP2O7 room-temperature structure is monoclinic with space group P21 or Pc.

2-Thia-1,3,5-triaza-7-phosphaadamantane 2,2-Dioxide (PASO2). Comparative Structural and Reactivity Investigation with the Water-Soluble Phosphine Ligand 1,3,5-triaza-7-phosphaadamantane (PTA)

The derivative 2-thia-1,3,5-triaza-phosphaadamantane 2,2-dioxide (PASO2) has been characterized by spectroscopy and by X-ray crystallography. Unlike its PTA (1,3,5-triaza-7-phosphaadamantane) analogue, replacement of a −CH2− unit in PTA with −SO2− renders PASO2 largely insoluble in water at ambient temperature (<0.70 g/L vs 236 g/L for PTA). This latter property makes it of no use as a water-solubilizing ligand for organometallic complexes. Interestingly, alkylation of PASO2 with methyl iodide occurs quantitatively at the phosphorus center to afford the iodide salt. This derivative has also been characterized by X-ray crystallography and 1H/31P NMR spectroscopy, where the 31P resonance was observed to be shifted downfield relative to PASO2 (−39.2 vs −115.9 ppm). Although PTA has long been thought to react with methyl iodide to provide exclusively a monoalkylated product at one of the nitrogen centers, a close examination of this process via 31P NMR spectroscopy has shown monomethylation to take place at b...

Spectroscopic analyses of the interaction between hammerhead ribozymes and metal ions

Biologically active RNA molecules utilize metal ions to fold into specific conformations or to form a catalytic center. Hammerhead ribozymes also contain a metal ion-binding motif in their conserved core region. This motif and bound metal ions have recently been focused on from the viewpoint of whether the metal ions are a catalytic metal or a structural metal. We studied the interaction between metal ions and an RNA oligomer, r(GGACGAGUCC), which mimics the metal ion-binding motif of hammerhead ribozymes, using NMR spectroscopy in solution. Using 15N-labeled RNA oligomers, the chemical shift of N7 of the G7 residue [N7(G7)] in the metal ion-binding motif was specifically perturbed upon the addition of Cd(II). It was also found that the 31P resonance of the phosphate of the A9 residue showed the largest perturbation of all the 31P resonances during titration. These data indicate that divalent cations can bind to the metal ion-binding motif in solution, and that the binding sites for cations are N7(G7) and the phosphate of A9. More importantly, the metal ion-binding motif is an independent functional module that can capture divalent cations without the assistance of other conserved residues in hammerhead ribozymes.

NMR studies of phosphorus chalcogenide–copper iodide coordination compounds

The local structures of the new phosphorus chalcogenide – copper iodide coordination compounds (CuI)P4Se4, (CuI)2P8Se3, (CuI)3P4Se4, and (CuI)3P4S4 are investigated using comprehensive 63Cu, 65Cu, and 31P magic angle spinning NMR techniques. Peak assignments are proposed on the basis of homo- and heteronuclear indirect spin–spin interactions, available from lineshape analysis and/or two-dimensional correlation spectroscopy. In particular, the 31P-63,65Cu scalar coupling constants have been extracted from detailed lineshape simulations of the 31P resonances associated with the Cu-bonded P atoms. In addition, the RNνn pulse symmetry concept of Levitt and coworkers has been utilized for total through-bond correlation spectroscopy (TOBSY) of directly-bonded phosphorus species. The resonance assignments obtained facilitate a discussion of the 31P and 63,65Cu NMR Hamiltonian parameters in terms of the detailed local atomic environments. Analysis of the limited data set available for this group of closely related compounds offers the following conclusions: (1) bonding of a special phosphorus site in a given P4Xn (X = S, Se) molecule to Cu+ ions shifts the corresponding 31P NMR signal upfield by about 50 ppm relative to the uncomplexed molecule, (2) the magnitude of the corresponding scalar 31P-63,65Cu spin–spin coupling constant tends to decrease with increasing Cu–P distance, and (3) the 63,65Cu nuclear electric quadrupolar coupling constants appear to be weakly correlated with the shear strain parameter specifying the degree of local distortion present in the four-coordinated [CuI2P2] and [CuI3P] environments. Overall, the results illustrate the power and potential of advanced solid state NMR methodology to provide useful structural information in this class of materials.

Metabolite diffusion in giant muscle fibers of the spiny lobster Panulirus argus.

The time- and orientation-dependence of metabolite diffusion in giant muscle fibers of the lobster Panulirus argus was examined using (31)P- and (1)H-pulsed-field gradient nuclear magnetic resonance. The (31)P resonance for arginine phosphate and the (1)H resonances for betaine, arginine/arginine phosphate and -CH(2)/-CH groups were suitable for measurement of the apparent diffusion coefficient, D. Diffusion was measured axially, D(//), and radially, D( perpendicular ), in fibers over diffusion times of 20 to 300 ms. Diffusion was strongly anisotropic, and D(//) was higher than D( perpendicular ) at all times. Radial diffusion decreased with time until a steady-state value was reached at a diffusion time of approximately 100 ms. Changes in D( perpendicular ) occurred over a time scale that was consistent with previous measurements from fish and mammalian muscle, indicating that diffusion is hindered by the same types of barriers in these diverse muscle types. The time dependence indicated that the sarcoplasmic reticulum is the principal intracellular structure that inhibits mobility in an orientation-dependent manner in skeletal muscle. The abdominal muscles in P. argus are used for anaerobic, burst contractions during an escape maneuver. The fact that these muscle fibers have diameters that may exceed hundreds of microns in diameter, and nearly all of the mitochondria are localized near the sarcolemmal membrane, suggests that barriers that hinder radial diffusion of ATP equivalents may ultimately limit the rate of post-contractile recovery.

Synthesis and characterization of MAPO-11 molecular sieves

In this work MAPO-11 molecular sieve was prepared with several degrees of magnesium substitution. The syntheses were carried by using phosphoric acid, pseudo-boehmite and magnesium acetate as sources of structural elements and diisopropylamine as the structure-directing agent. The samples were characterized by powder X-ray diffraction, thermogravimetry, infrared spectroscopy, solid-state nuclear magnetic resonance, scanning electron microscopy and elemental analysis. The X-ray diffractograms indicate that the AEL structure is obtained free of contaminating phases up to a magnesium molar ratio of 0.3 in the reaction mixture. Higher levels of magnesium cause the formation of other phases. Thermogravimetry, MAS nuclear magnetic resonance of 31P and infrared spectroscopy confirm the magnesium isomorphous substitution for aluminum up to this magnesium content in the reaction mixture.

Probing the Binding States of GDP to Cdc42 Using Urea Interaction

The inactive state of the small G Protein Cdc42, the Cdc42 · GDP · Mg2+ ternary complex, was investigated using fluorescence, Mn2+ substituted electron paramagnetic resonance, and 31P nuclear magnetic resonance spectroscopy at various urea concentrations. The urea interaction with the protein was used to probe the binding state of GDP · Mg2+ to Cdc42. Two binding states of the Cdc42 · GDP · Mg2+ ternary complex with different binding stability were observed. The two binding states were characterized by two sets of 31P resonance of GDP phosphate groups, namely Pα and Pβ, Pα′, and Pβ′. The high populated binding state I (Pα and Pβ) was more stable and less sensitive to the urea interaction. Yet the population of binding state II (Pα′ and Pβ′) was lower, and the binding of GDP · Mg2+ to Cdc42 in this state was more sensitive to the urea interaction. The release of GDP · Mg2+ from the ternary complex in binding state II was faster than in state I.

Synthesis, Crystal Structure, and Solid State NMR Spectroscopy of (C10N4H28)[Zn6(HPO4)2(PO4)4]·2H2O, a New Zinc Phosphate with a Layer Structure

A new zinc phosphate, (C10N4H28)[Zn6(HPO4)2(PO4)4]·2H2O, with a layered architecture has been synthesized, for the first time, in the presence of 1,4-bis(3-aminopropyl)piperazine as the structure-directing agent. The structure comprises a network of ZnO4 and phosphate tetrahedra forming macroanionic layers with eight-membered apertures. Charge compensation is achieved by the quadruply protonated amine occupying interlamellar space and interacts with the inorganic layers via hydrogen bonding. The title compound is related to several other zinc phosphates in framework stoichiometry or crystal structure. Crystal data: (C10N4H28)[Zn6(HPO4)2(PO4)4]·2H2O, triclinic, space group P1(No. 2), a=8.3343(9) Å, b=12.413(1) Å, c=17.363(2) Å, α=75.269(2)°, β=78.868(2)°, γ=76.270(2)°, V=1670.7(5) Å3, Z=2, R1=0.0584, wR2=0.153. Proton-decoupled 31P MAS NMR reveals six 31P resonances with nearly equal intensities, which is in good agreement with the six distinct crystallographic phosphorus sites in the framework as indicated from X-ray structural analysis. 1H→31P CP/MAS is used to obtain more details of the proximity between hydrogen and phosphorus atoms, and in combination with 2D RFDR NMR to assign the six phosphorus sites.

Structural Investigation by Multinuclear Solid State NMR and X-ray Diffraction of As-Synthesized, Dehydrated, and Calcined AlPO4-SOD

AlPO4-SOD, a microporous aluminophosphate, was synthesized in a quasi-nonaqueous medium using dimethylformamide as solvent and template. The as-synthesized, dehydrated, calcined materials and the corresponding rehydrated phases were investigated by various solid-state nuclear magnetic resonance (NMR) and powder X-ray diffraction techniques. Structural data from the NMR study are in a very good agreement with the as-synthesized AlPO4-SOD structure refined from powder synchrotron data. 31P homonuclear correlation and 31P/27Al 3QHETCOR experiments allowed the complete assignment of 31P and 27Al resonances to the corresponding crystallographic sites. 31P and 27Al NMR spectra are drastically modified after dehydration at 200 °C and calcination at 800 °C. A possible structural rearrangement of the template molecules is proposed that explains NMR and XRD data of the dehydrated material. The structure of the calcined material solved by powder XRD is in agreement with the NMR data.

The effect of phosphorus on the properties and structure of GeAsS glasses

Stoichiometric Ge-poor (<50% GeS 2) GeAsPS glasses, as well as GeAsPS glasses with a fixed Ge:As:P ratio of 5:1:1 and S contents ranging from 56% to 74%, were synthesized. The compositional dependence of the physical properties and nuclear magnetic resonance (NMR) spectra of the stoichiometric glasses indicates that tetrahedral SPS 3/2 groups constitute the dominant P species. On reducing the S content, the absorption edge of variable S GeAsPS glasses remains constant until S deficits of about 25% are attained. Raman spectra of stoichiometric and S-deficient glasses show bands attributed to As 2P 2S 8 and (As,P) 4S 3 species, respectively, whereas those of variable S glasses with S deficits ⩽15% show a high frequency band indicating the presence of tetrahedral SPS 3/2 groups. NMR spectra of glasses with S deficits of 7–15% are dominated by a 31P resonance at about 117 ppm that is assigned to trigonal PS 3/2 groups. NMR spectra of glasses with S deficits ⩾10% have a 31P resonance near −100 ppm, indicating that tetrahedral SPS 3/2 and trigonal PS 3/2 groups are replaced by species containing P–P and, ultimately, P–(Ge, As) bonds as the S content of these glasses decreases. Comparison of these results with those for GeAsS glasses demonstrates that P–P bonds form preferentially to metal–metal bonds containing either Ge or As, and that P tends to associate with As instead of Ge as next nearest neighbors.