Solid-state 23Na, 139La, 27Al and 29Si nuclear magnetic resonance spectroscopic investigations of cation location and migration in zeolites LaNaY

²³Na Magic-angle spinning (MAS), double rotation (DOR) and two-dimensional nutation nuclear magnetic resonance (NMR) and static ¹³⁹La NMR spectroscopy were applied to study the location and migration of sodium and lanthanum cations in faujasites. Generally, ²³Na MAS NMR spectroscopy of as-exchanged and hydrated zeolites LaNaY was used for the quantitative determination of non-localized Na⁺ in the large cavities at a ²³Na NMR shift of −9 ppm and of sodium cations observed at −13 ppm. The latter originate from Na⁺ ions located on position SII in the large cavities, on position SI in the hexagonal prisms and on positions SII′ and/or SI′ in the sodalite cages. The ²³Na MAS NMR signal at about −13 ppm was found to be caused by two coonents. The component that is characterized by a quadrupolar interaction causing a field-dependent shift and a signal at v₁ = 2v_rf in the two-dimensional quadrupolar nutation spectra is attributed to Na⁺ enclosed in the sodalite cages. The ²³Na MAS NMR spectra of dehydrated lanthanum-exchanged faujasites are characterized by a low-field Gaussian line of Na⁺ located on SI positions in the hexagonal prisms and a high-field quadrupole pattern of Na⁺ located on positions SII and SI′. The migration of lanthanum cations from the large cavities to position SI′ in the sodalite cages was monitored by ¹³⁹La NMR spectroscopy and verified by a theoretical estimation of the electric field gradient. The lanthanum migration was found to be coupled with a strain of SiOT and AlOT angles observed by ²⁹Si and ²⁷Al MAS NMR high-field shifts, respectively.     

Solid-state Na and C NMR characterization of Na3C60

Two separate samples of Na₃C₆₀ were prepared by direct reaction of C₆₀ with sodium metal vapor, and subjected to different annealing times of 10 days and 16 days. Solid-state ¹³C and ²³Na NMR, along with elemental analysis, powder X-ray diffraction (XRD) and Raman spectroscopy, were used to characterize both samples. The Raman spectra of both materials have a single peak at 1447 cm⁻¹ which correspond to the A_g peak of C₆₀³⁻, consistent with the stoichiometry of Na_xC₆₀ with x=3. The powder XRD patterns are also virtually identical for both samples. However, solid-state ²³Na and ¹³C NMR spectra of the two samples are significantly different, suggesting a relationship between annealing times and the final structure of the alkali fulleride. Variable-temperature ²³Na magic-angle spinning (MAS) NMR experiments reveal the existence of two or three distinct sodium species and reversible temperature-dependent diffusion of sodium ions between octahedral and tetrahedral interstitial sites. ¹³C MAS NMR experiments are used to identify resonances corresponding to free C₆₀ and fulleride species, implying that the samples are segregated-phase materials composed of C₆₀ and non-stoichiometric Na₃C₆₀. Variable-temperature ¹³C MAS NMR experiments reveal temperature-dependent motion of the fullerides.     

Distribution and mobility of phosphates and sodium ions in cheese by solid‐state 31P and double‐quantum filtered 23Na NMR spectroscopy

The feasibility of solid‐state magic angle spinning (MAS) ³¹P nuclear magnetic resonance (NMR) spectroscopy and ²³Na NMR spectroscopy to investigate both phosphates and Na⁺ ions distribution in semi‐hard cheeses in a non‐destructive way was studied. Two semi‐hard cheeses of known composition were made with two different salt contents. ³¹P Single‐pulse excitation and cross‐polarization MAS experiments allowed, for the first time, the identification and quantification of soluble and insoluble phosphates in the cheeses. The presence of a relatively ‘mobile’ fraction of colloidal phosphates was evidenced. The detection by ²³Na single‐quantum NMR experiments of all the sodium ions in the cheeses was validated. The presence of a fraction of ‘bound’ sodium ions was evidenced by ²³Na double‐quantum filtered NMR experiments. We demonstrated that NMR is a suitable tool to investigate both phosphates and Na⁺ ions distributions in cheeses. The impact of the sodium content on the various phosphorus forms distribution was discussed and results demonstrated that NMR would be an important tool for the cheese industry for the processes controls. Copyright © 2010 John Wiley & Sons, Ltd.     

29Si- und 23Na-Festkörper-MAS-NMR-Untersuchungen an Modifikationen des Na2Si2O5

²⁹Si and ²³Na Solid State MAS NMR Investigations of Modifications of the Sodium Phyllosilicate Na₂Si₂O₅ . The results of ²⁹Si- and ²³Na-MAS NMR investigations on four modifications of the synthetic Na₂Si₂O₅ demonstrate that the α-, β- and δ-modifications are characterized unequivocally by the parameters of the corresponding NMR spectra. The studies on γ-Na₂Si₂O₅ show that this sample contains a large amount of secondary compounds. For α- und β-Na₂Si₂O₅ the the structural details of the silicate sheets are reflected by the ²⁹Si MAS NMR spectra while from the ²³Na MAS NMR spectra conclusions about the coordination number of the sodium atoms can be derived. The ²⁹Si MAS NMR investigations on δ-Na₂Si₂O₅ indicate that the silicate sheet of this modification consist of identical SiO₄-tetrahydra the parameter of which differ from those of α- and β-Na₂Si₂O₅. The ²³Na MAS NMR studies show that in the interlayer space of δ-Na₂Si₂O₅ two nonidentical sodium atoms exists. The NMR results give rise to the suggestion that one of the sodium is surrounded by five and the other one by six oxygen atoms.     

Investigation of cation environment and framework changes in silicotitanate exchange materials using solid-state Na, Si, and Cs MAS NMR

Crystalline silicotitanate (CST), HNa₃Ti₄Si₂O₁₄·4H₂O and the Nb-substituted CST (Nb-CST), HNa₂Ti₃NbSi₂O₁₄·4H₂O, are highly selective Cs⁺ sorbents, which makes them attractive materials for the selective removal of radioactive species from nuclear waste solutions. The structural basis for the improved Cs⁺ selectivity in the niobium analogs was investigated through a series of solid-state magic angle spinning (MAS) NMR experiments. Changes in the local environment of the Na⁺ and Cs⁺ cations in both CST and Nb-CST materials as a function of weight percent cesium exchange were investigated using ²³Na and ¹³³Cs MAS NMR. Framework changes induced by Cs⁺ loading and hydration state were investigated with ²⁹Si MAS NMR. Multiple Cs⁺ environments were observed in the CST and Nb-CST material. The relative population of these different Cs⁺ environments varies with the extent of Cs⁺ loading. Marked changes in the framework Si environment were noted with the initial incorporation of Cs⁺, however with increased Cs⁺ loading the impact to the Si environment becomes less pronounced. The Cs⁺ environment and Si framework structure were influenced by the Nb-substitution and were greatly affected by the amount of water present in the materials. The increased Cs⁺ selectivity of the Nb-CST materials arises from both the chemistry and geometry of the tunnels and pores.     

Contribution of Na counterions to H-AOT&Na-AOT-based W/O microemulsion formation using aqueous NaOH solutions as estimated by pyranine absorbance

The objective of this study is to estimate the contribution of Na⁺ as a counterion in the formation of H-AOT&Na-AOT-based W/O microemulsions using aqueous NaOH solution by pyranine absorbance measurements. A mixture of an aqueous NaOH solution containing pyranine/H-AOT&Na-AOT/isooctane was emulsified by changing the mixing ratio of Na-AOT (X_Na-AOT = 0–1) and the mole fraction of NaOH (X_NaOH = [NaOH]/the AOT⁻ concentration in the water pool = 0–1). The phase behavior of the emulsified mixture was evaluated from the absorbance of pyranine at the isosbestic point and by visual observations. W/O microelumsions are formed at the mid-range of X_Na-AOT, whereas the emulsified mixture separates into two phases at lower X_Na-AOT and higher X_Na-AOT. The two phase boundaries shift toward lower X_Na-AOT as with increasing X_NaOH. The phase behavior depends on the degree of screening of electrostatic repulsions between the polar headgroups of AOT⁻ by the Na⁺ counterion. Interestingly, nano-sized W/O microemulsions are formed without phase separation using a highly concentrated NaOH aqueous solution when the Na-AOT mixing ratio is appropriately adjusted. The phase behavior was plotted as X_NaOH versus X_Na-AOT, and the correlation equations for the two phase boundaries were obtained by fitting the points. The contribution of the Na⁺ counterion from NaOH to W/O microemulsion formation was estimated by the correlation equations. The absorbance of pyranine and the size of W/O microemulsions, as measured by DLS, were plotted as a function of X_Na⁺=(x[Na⁺   from   NaOH]+[Na⁺   from   Na-AOT])/[AOT⁻], in which x is the ratio contributed by NaOH. The absorbance and size correlates well with X_Na⁺, indicating that X_Na⁺ is a meaningful parameter for quantitatively estimating phase behavior and size variation.     

The effect of salt content on the structure of iota‐carrageenan systems: 23Na DQF NMR and rheological studies

²³Na NMR spectroscopy has been used to study the effects of Na⁺ ion concentrations on the structure of 1% (w/w) iota‐carrageenan systems, a natural gelling polysaccharide used as a thickener in the food industry. Rheological and ²³Na T₁ relaxation time measurements revealed that gel formation correlates with decreases in ion mobility over the range of 0–3% (w/w) sodium content. ²³Na single‐quantum (SQ) and double‐quantum‐filtered (DQF) NMR experiments performed on these systems provided evidence for a ‘bound’ sodium ion fraction in a specifically ordered environment. These results have allowed us to propose a model for the carrageenan gelation mechanism in the presence of Na⁺ ions. Copyright © 2009 John Wiley & Sons, Ltd.     

Zur Kenntnis des Natrium-tetrahydroxoaluminat-chlorids Na2[Al(OH)4]Cl

On the Sodium Tetrahydroxoaluminate Chloride Na₂[Al(OH)₄]Cl The hitherto unknown compound Na₂[Al(OH)₄]Cl was prepared by crystallisation from a NaCl containing sodium aluminate solution. According to the X-ray single crystal investigation (tetragonal, space group P4/nmm, a = 7.541 Å, c = 5.059 Å, Z = 2) the compound represents the first example of a crystalline hydroxoaluminate with monomeric [Al(OH)₄]^? anions. Cl^? shows a quadratic anti prismatic coordination to 4 Na⁺ and over hydrogen bonds to 4 O^2? while Na⁺ is octahedrally coordinated by 4 O^2? and 2 Cl^? (axial). The results of the crystal structure analysis are confirmed by ²⁷Al and ²³Na MAS NMR investigations. Na₂[Al(OH)₄]Cl decomposes at about 200°C without intermediates under formation of β-NaAlO₂ and NaCl.     

Fast Sodium‐Ion Conductivity in Supertetrahedral Phosphidosilicates

Fast sodium‐ion conductors are key components of Na‐based all‐solid‐state batteries which hold promise for large‐scale storage of electrical power. We report the synthesis, crystal‐structure determination, and Na⁺‐ion conductivities of six new Na‐ion conductors, the phosphidosilicates Na₁₉Si₁₃P₂₅, Na₂₃Si₁₉P₃₃, Na₂₃Si₂₈P₄₅, Na₂₃Si₃₇P₅₇, LT‐NaSi₂P₃ and HT‐NaSi₂P₃, based entirely on earth‐abundant elements. They have SiP₄ tetrahedra assembled interpenetrating networks of T3 to T5 supertetrahedral clusters and can be hierarchically assigned to sphalerite‐ or diamond‐type structures. ²³Na solid‐state NMR spectra and geometrical pathway analysis show Na⁺‐ion mobility between the supertetrahedral cluster networks. Electrochemical impedance spectroscopy shows Na⁺‐ion conductivities up to σ (Na⁺)=4×10^?4 S cm^?1. The conductivities increase with the size of the supertetrahedral clusters through dilution of Na⁺‐ions as the charge density of the anionic networks decreases.     

M2Ga6Te10 (M: Li,Na): Two New Non‐metallic Filled β‐Manganese Phases – X‐ray and NMR Studies

Two new non‐metallic filled β‐manganese phases M₂Ga₆Te₁₀ (M: Li, Na) are obtained as black, homogeneous, microcristalline samples as well as single crystals by direct reaction of the elements. According to the single crystal structure determinations both compounds crystallize in space group R32 (No. 155, Z = 2) with the lattice constants: a = 1436.9(2), c = 1759.0(4) pm (T = 180 K, Li₂Ga₆Te₁₀) and a = 1458(1) pm, c = 1776.1(4) pm (T = 290 K, Na₂Ga₆Te₁₀). Their structures are characterized by tetrahedral close packings of Te^2–, corresponding to the arrangement of Mn atoms in β‐Mn. While Ga³⁺ ions are distributed in an ordered way over 12% of the tetrahedral holes, the M⁺ ions occupy all distorted octahedral (“metaprismatic”) holes. As the Li⁺ ions are too small they occupy off‐center positions inside the metaprisms. Positions with the strongest off‐centering can only be refined on the basis of a split model. MAS‐NMR measurements, including multiple quantum NMR, allowed the two different crystallographic M⁺ sites to be distinguished unambigously by separate ⁷Li and ²³Na signals, respectively. The assignment of the NMR signals was supported by measurements of samples in which Li⁺ was partly substituted by larger cations (Sn²⁺, Pb²⁺).     

Studies of lithium and sodium complexation by silicon podand solvents

The complex formation of lithium and sodium ions with silicon podand solvents: phenyl-tris(1,4-dioxapentyl) silane (PhSi23) and ethyl-tris(1,4-dioxapentyl) silane (EtSi23) has been studied by FTIR, ¹H-, ¹³C-, ⁷Li- and ²³Na NMR. The far FTIR spectra show that the Li⁺ cations fluctuate very fast whereas Na⁺ cations are still localised between the oxygen atoms of the oxaalkyl chains. The ⁷Li NMR spectra prove that one Li⁺ cation can be coordinated not only by one but also two silicon podand molecules. The concentration dependence of the molar conductivity of LiClO₄ in the podand solvents indicates charge transfer between ion clusters.     

NMR study of 23Na complexing by polyethers,siloxanes and polyamides

Complexation of Na⁺-ion with polyethers and polyamides is studied by using ²³Na NMR spectroscopy. The variation of the linewidth and the position of the ²³Na NMR signal give evidence for the interaction of oxygen atoms of poly(ethylene oxide) in acetonitrile and those of siloxanes in T.H.F. with the solvated ion. In addition chemical shift data are given for perturbation of the Na⁺ solvation shell by interaction of the ion with substituted amides and polyamides in T.H.F.     

Cold NaOH/urea aqueous dissolved cellulose for benzylation: Synthesis and characterization

Cold NaOH/urea aqueous dissolved cellulose was studied for the synthesis of benzyl cellulose by etherification with benzyl chloride. By varying the molar ratios of benzyl chloride to OH groups in cellulose (1.5–4.0) and reaction temperatures (65–70 °C), benzyl cellulose with a degree of substitutions (DS) in the range of 0.29–0.54 was successfully prepared under such mild conditions. The incorporation of benzyl groups into cellulose was evidenced by multiple spectroscopies, including FT IR, ¹H NMR, ¹³C NMR, CP/MAS ¹³C NMR and XRD. In addition, the thermal stability and surface morphology of the benzyl cellulose was also investigated with regard to the degree of substitution. The results indicated that the benzyl cellulose product with a low DS (0.51) in the present study reached the same solubility in many organic solvents as compared to those prepared in heterogeneous media. After benzylation, the sample decomposed at a lower temperature with a wider temperature range, which indicated that the thermal stability of benzyl cellulose was lower than that of the native cellulose. In addition, benzylation resulted in a pronounced reduction in crystallinity as well as a fundamental alteration of morphology of the native cellulose.     

Competitive binding exchange between alkali metal ions (K+, Rb+, and Cs+) and Na+ ions bound to the dimeric quadruplex [d(G4T4G4)]2: a 23Na and 1H NMR study

A comparative study of the competitive cation exchange between the alkali metal ions K⁺, Rb⁺, and Cs⁺ and the Na⁺ ions bound to the dimeric quadruplex [d(G₄T₄G₄)]₂ was performed in aqueous solution by a combined use of the ²³Na and ¹H NMR spectroscopy. The titration data confirm the different binding affinities of these ions for the G‐quadruplex and, in particular, major differences in the behavior of Cs⁺ as compared to the other ions were found. Accordingly, Cs⁺ competes with Na⁺ only for the binding sites at the quadruplex surface (primarily phosphate groups), while K⁺ and Rb⁺ are also able to replace sodium ions located inside the quadruplex. Furthermore, the ¹H NMR results relative to the CsCl titration evidence a close approach of Cs⁺ ions to the phosphate groups in the narrow groove of [d(G₄T₄G₄)]₂. Based on a three‐site exchange model, the ²³Na NMR relaxation data lead to an estimate of the relative binding affinity of Cs⁺ versus Na⁺ for the quadruplex surface of 0.5 at 298 K. Comparing this value to those reported in the literature for the surface of the G‐quadruplex formed by 5′‐guanosinemonophosphate and for the surface of double‐helical DNA suggests that topology factors may have an important influence on the cation affinity for the phosphate groups on DNA. Copyright © 2009 John Wiley & Sons, Ltd.     

Na5Br(OH)4: Darstellung und Kristallstruktur einer Verbindung im System NaOH/NaBr

Na₅Br(OH)₄: Synthesis and Structure of a Compound in the System NaOH/NaBr The pseudobinary system NaOH/NaBr is investigated by X-ray methods. The structure of the compound Na₅Br(OH)₄ was solved by single crystal data: Na₅Br(OH)₄: Pnma, Z = 8, a = 11.846(2) Å, b = 18.782(4) Å, c = 6.431(1) Å, Z(F_o) = 1 202 with (F_o)² ≥ 3σ(F_o)², Z(parameter) = 100, R/R_w = 0.030/0.035 The compound crystallizes in a new type of structure. Pairs of octahedra around O by 5 Na and 1 H to [Na₅(OH)]₂ are orientated in such a way to one another that two ions OH^? form a parallelogram hinting to unusual bent hydrogen bridge bonding.     

Characterization of poly(vinylidene fluoride)/Na+‐MMT composites: An investigation into the β‐crystalline nucleation effect of Na+‐MMT

Poly(vinylidene fluoride)(PVDF)/Na⁺‐MMT composites have been successfully prepared utilizing sodium montmorillonite (Na⁺‐MMT) via N,N‐dimethylformamide (DMF) solution mixing. The dispersion of Na⁺‐MMT layers in composites were investigated by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The effect of adding Na⁺‐MMT on crystallization behavior of PVDF was specifically studied. The β‐crystalline nucleation effect of Na⁺‐MMT was investigated and confirmed by differential scanning calorimetry (DSC), XRD, and Fourier transform infrared (FTIR) results. The interaction between PVDF and the surface of Na⁺‐MMT layers in DMF solution was confirmed by UV‐Vis absorbency. The effect of adding Na⁺‐MMT on rheological and electrical properties of PVDF/Na⁺‐MMT composites were also determined. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 903–911, 2009     

Vinyl polymerization. 403. Polymerization of vinyl monomer initiated with sodium poly-p-vinylphenolate

The polymerization of vinyl monomer initiated by poly-p-vinylphenol (PVPh) in NaOH aqueous solution was carried out at 85°C with shaking. Methyl methacrylate (MMA) was polymerized, whereas styrene and acrylonitrile were not. PVPh, which is dissociated into phenolate form (PVPh^?Na⁺) in NaOH aqueous solution, was effective for the polymerization. The effects of the amounts of MMA, PVPh, NaOH, and H₂O on the conversion of MMA were studied. The rate of polymerization of MMA increased with an increase in the molecular weight of PVPh-Na. The overall activation energy was estimated as 54 kJ mol^?1. The polymerization proceeded through a radical mechanism. The addition of tetra-n-butylammonium bromide increased the rate of polymerization.     

Complexation thermodynamics of some alkali-metal cations with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane in Acetonitrile

The interaction of 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (Kryptofix5) with alkali-metal cations (Li⁺, Na⁺, K⁺) in aprotic medium (acetonitrile) has been investigated. Conductance measurements demonstrated that 1:1 metal cation:ligand stoichiometries are found with these cations in this solvent. ⁷Li and ²³Na NMR experiments were carried out by titration of the metal cation solutions with Kryptofix5 solution in CD₃CN + CH₃CN at 298 K. Thermodynamic parameters of complexation for this ligand and alkali-metal cations in acetonitrile at 278–308 K were derived from titration conductometry. The highest stability is found for sodium complex. The complexation sequence, based on the value of log K at 278–308 K was found to be Na⁺ > K⁺ > Li⁺.     

Induction and Acceleration of Bonelike Apatite Formation on Tantalum Oxide Gel in Simulated Body Fluid

Untreated tantalum metal forms bonelike apatite layer on its surface in a simulated body fluid (SBF) after a long period. The apatite formation on the tantalum metal is significantly accelerated, when the metal was previously subjected to NaOH and heat treatments to form an amorphous sodium tantalate on its surface. The fast formation of the apatite on the NaOH- and heat-treated tantalum metal was explained as follows. The sodium tantalate on the surface of the metal releases the Na⁺ ion via exchange with H₃O⁺ ion in SBF to form a lot of Ta-OH groups on its surface. Thus formed Ta-OH groups induce the apatite nucleation and the released Na⁺ ion accelerates the apatite nucleation by increasing ionic activity product of the apatite in SBF due to increase in OH^– ion concentration. In the present study, in order to confirm this explanation, apatite formations on sodium tantalate gels with different Na/Ta atomic ratios, which were prepared by a sol-gel method were investigated. It was found that even Na₂O-free tantalum oxide gel forms the apatite on its surface in SBF. This proves that the Ta-OH groups abundant on the gel can induce the apatite nucleation. The apatite-forming ability of the gels increased with increasing Na/Ta atomic ratios of the gels. The sodium-containing tantalum oxide gels released the Na⁺ ion, the amount of which increased with increasing Na/Ta atomic ratios of the gels. The released Na⁺ ion gave an increase in pH of SBF. These results prove that the apatite nucleation induced by the Ta-OH groups is accelerated with the released Na⁺ ion by increasing ionic activity product of the apatite in SBF.     

Interaction between Na+ and polymer in aqueous solution of sodium salts of poly(2-hydroxyethyl methacrylate-co-methacrylic acid) studied by 23Na-NMR

The interaction between Na⁺ and polymer was studied by ²³Na-NMR for the aqueous solution of P(HEMA-co-MAANa), sodium salt of poly(2-hydroxyethyl methacrylate-co-methacrylic acid), as a function of the polymer concentration, charge density of the polymer chain, and temperature. The NMR line width of ²³Na-NMR in 1% (w/v) aqueous solution of the P(HEMA-co-MAANa) narrowed with increasing temperature due to the rapid exchange of Na⁺ between free and polymer-bound states with a rate of exchange exceeding the quadrupolar relaxation rate in the latter state. At high concentrations of the polymer above 1.0% (w/v) at 298 K, the ²³Na-NMR relaxation fits for a single Lorentzian due to the rapid exchange between two Na⁺ states. However, it follows a biexponential decay of magnetization in dilute solutions of polymer. The biexponential decay character of relaxation increased with the increase of the fraction of the MAANa monomer unit on the polymer chain. This feature of ²³Na-NMR relaxation was used to deduce the correlation time (τ_c), the degree of binding (p_B), and the quadrupole coupling constants (X) of the polymer-bound counterion. The χ and τ_c values show that the mobilities of the polymer chain are correlated with the motion of Na⁺ in aqueous solution of the polymer and there is a small degree of the specific binding between COO^? and Na⁺. No evidence in support of the intramolecular conformational change by the charge density variation in P(HEMA-co-MAANa) was obtained. © 1993 John Wiley & Sons, Inc.