Mesomorphism and the effect of an electric field on the conductivity of the mesophases of lithium, sodium, and potassium 4-(trifluoromethyl)-3,6-dioxaperfluorooctanesulfonates

Mesophases were established for the first time in sodium and potassium 4-(trifluoromethyl)-3,6-dioxaperfluorooctanesulfonates (R_ofSO₃ ⁻) and in their binary systems Na,K/R_ofSO₃(I) and Na/NO₃,R_ofSO₃(II). An increase in the temperature range of the mesophase was detected in system (I). The application of an electric field increases the conductivity of the mesophase. For the isotropic Na,K/R_ofSO₃ melts an anomalous conductivity isotherm was obtained for the first time. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 4, pp. 234–238, July–August, 1997.     

Variable temperature 1H, 23Na,and 29Si MAS NMR studies on sodium silicate hydrates of composition Na2O · SiO2 · nH2O (n = 9, 6, 5): Local structure in crystals,melts, supercooled melts,and glasses

The local structure in crystals, melts, supercooled melts, and glasses of sodium silicate hydrates of composition Na₂O · SiO₂ · nH₂O (n = 9, 6, 5) is studied by variable temperature ¹H, ²³Na, and ²⁹Si MAS NMR spectroscopy. Detailed in situ investigations on the melting process of the crystalline materials reveal the importance of H₂O motion in the melting mechanism. Depending on the local coordination, crystallographically distinct Na sites show different behaviour during the melting process. Upon melting, the monomer silicate anions present in the crystalline hydrates undergo condensation reactions to oligomeric silicate anions. No recrystallization but glass formation occurs at low temperature if the melts were heated initially about 10 K above the melting point. In the glasses also oligomeric silicate anions are present with a preference for cyclotrimer species. In situ MAS NMR investigations and electric conductivity measurements of the melts, supercooled melts, and glasses suggest the distinction of three temperature ranges characterized by different local structure and dynamics of the sodium cations, water and silicate anions. These ranges comprise a glass and glass transition range A at low temperatures, an aggregation region B at intermediate temperatures, and a solution or electrolyte region C at high temperatures. In region B aggregation of sodium water complexes to hydrated polycation clusters is suggested, the dynamic behaviour of which is clearly different to that of the silicate anions, indicating that no long-lived contact ion pairs between sodium cations and silicate anions are formed.     

Effect of the size of the aliphatic chain on the NMR spectra and the electrical conductivity of melts of alkali metal alkanoates in alkanoic acids

The dependence of NMR spectra of ⁷Li, ²³Na, ¹³³Cs and of the conductivity of melts of lithium, sodium, and cesium alkanoates in melts of alkanoic acids on the length of the aliphatic chain of the anion has been studied. As the anion size increases, chemical shifts of ²³Na and ¹³³Cs nuclei toward weak fields and ⁷Li nuclei toward strong fields are observed. The nature of the chemical shifts of alkali metal nuclei and of the electricity transport characteristic in the studied systems is discussed in connection with the nature of cation-anion interactions and the size and degree of free rotation of the anion.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 1, pp. 81–87, January–February, 1993.     

Chromonic liquid crystals formed by CI Acid Red 266 and related structures

Chromonic liquid crystals are currently receiving increased attention because they have applications in a wide range of products. In this study, we have compared the chromonic mesophase behaviour of four azo dyes with similar chemical structures. Our objective is to determine if there is an obvious link between mesophase formation and dye chemical structure. Orange G does not form mesophases over the concentration range examined (saturated solution > ~20–30 wt%). The other three compounds all form nematic (N) and hexagonal (H) mesophases, but over very different concentration ranges. X-ray diffraction shows that the ordered Edicol Sunset Yellow (ESY) aggregates present in the mesophases have a single molecule cross section, while those of CI Acid Red have a cross section equivalent to six to eight molecules, probably organised in a ‘water-filled pipes’ structure. NMR quadrupole splittings of ²H₂O demonstrate that water binding to the aggregates is similar to that found for surfactant lyotropic mesophases. The sodium (²³Na) quadrupole splittings for Orange II and CI Acid Red are similar to the values found for surfactant hexagonal phases, suggesting that most sodium ions are ‘bound’ to the aggregates. This is unlike the behaviour of ESY where only one of the two sodium ions is bound.     

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.     

Stability constant of the sodium complex with 18-crown-6 in the mixed water-ionic liquid solvent

The stability constant of the Na⁺ complex with dibenzo-18-crown-6, [Na(DB18C6)]⁺, was measured by the ²³Na NMR method in the mixed water-ionic liquid solvent at 23°C. N-Butyl-4-methylpyridinium tetrafluoroborate (BMPTB) was used as room temperature ionic liquid. It was found that for the solvent containing 0.8 mol fraction of water and 0.2 mol fraction of BMPTB, the value log K = 0.77 ± 0.05. The addition of BMPTB to water was found to increase the solubility of the crown ether but to decrease the sodium nitrate solubility.     

Sodium quantitation in soft drinks: A rapid methodology by qNMR

High sodium dietary intake has a positive association with an increase in blood pressure and can be correlated with risk factors of disease. Considering that the World Health Organization recommends a sodium intake lower than 2 g day^-1 for adults, the hidden sodium content in processed foods is an important factor that compromises the assessment of a healthy diet. Accordingly, the present paper aimed to quantitate the sodium content of conventional soft drinks and their diet versions using nuclear magnetic resonance spectroscopy as a quantitative analytical technique (²³Na qNMR). The results show one free sodium signal (Na⁺) displayed as a singlet at 0 ppm in the ²³Na NMR spectrum, making its quantitation highly specific. This signal alone was used to directly determine the concentration of sodium in soft drinks. Flame photometry analysis was used to validate the method, and an excellent linearity was found in qNMR analysis (r = 0.9994) in comparison with flame photometry (r = 0.9958). In addition, a good correlation was found between sodium concentrations obtained by ²³Na NMR and flame photometry in the evaluated commercial soft drinks. Since the intensity of the resonance line is directly proportional to the number of nuclei (spins), the concentration of sodium in soft drinks can be determined via this straightforward method without the need for external calibration. The experimental acquisitions are fast (approximately 15 min), allowing the analysis of several samples in a short period of time. This is a novel alternative for sodium quantitation using an efficient NMR methodology.     

The 3d states of23Na and7Li: determination of unresolved hyperfine splittings and radiative lifetimes

The electronic transitions from the ground state to the 3d states have been studied for²³Na and⁷Li atoms by two-photon Doppler-free laser spectroscopy. The positions of the resonances are used to determine the unresolved hyperfine structure of the 3d states from which the magnetic-dipole hyperfine interaction constantsA are derived. The results for theA factors are:A(3d ² D _3/2;²³Na)=+527(25) kHz;A(3d ² D _5/2;²³Na)=+108.5(2.4) kHz;A(3d ² D _3/2;⁷Li)=+843(41) kHz;A(3d ² D _5/2;⁷Li)=+343.6(1.0) kHz. For the fine structure intervals fs of the 3d doublets we obtain: fs(3d Na)=-1 494 444(44) kHz and fs(3d Li)=+1 083 936(60) kHz. The linewidths of the resonances are evaluated with respect to the natural lifetimes of the 3d states. For Na the result is τ(3d Na)=19.27(23) ns.     

Determination of sodium and phosphorus in organophosphorus compounds by fast-neutron activation

A method is described for the determination of sodium and phosphorus using the NG-160 neutron generator and an automated pneumatic transport device. The reactions²³Na (n, p)²³Ne and³¹P(n, α)²⁸ Al are utilized for the determination of sodium and phosphorus, respectively. For the determination of sodium, hermetically sealed vials are indispensable. The time required for one determination is 6 to 8 min. A rapid method for the determination of macro-amounts of sodium against a phosphorus background is also described, leading to the general conclusion that isotopes with γ-quantum energies close to 0.51 MeV can be determined against a background of positron radiation sources in a well-type crystal.     

Coordination-cluster model for analyzing interactions in Na-O-H melts

A procedure for calculating the thermodynamic activity coefficients of oxygen and hydrogen in dilute Na-O-H system melts over the temperature range 300–600°C was suggested. The thermodynamic activity coefficients of hydrogen in liquid sodium calculated by the coordination-cluster model equations were used to determine the equilibrium hydrogen pressure over melts. The calculation results were compared with the experimental partial hydrogen pressures over the Na(excess)-Na₂O-NaH system at x _O = x _H. The calculated values were in qualitative agreement with the experimental data.     

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.     

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.     

On the concentration dependence of the nature of polyelectrolyte solutions as detected by 23Na relaxation

Dependence of ²³Na nuclear magnetic relaxation on concentration and degree of polymerization is reported for solutions of Na polystyrenesulfonate. In the concentration range 10^?1 ? c 10^?1 eq/e, ²³Na relaxation is far outside the extreme-narrowing limit and relaxation rates depend on the degree of polymerization. These phenomena seem to disappear outside this range.     

Measurement of the radionuclide 24Na produced by neutron exposure to the body

Three workers were exposed to neutrons at a criticality accident at a uranium conversion test plant. The (n,g) reaction with body sodium (²³Na) gave rise to ²⁴Na, which emits 1,369 keV and 2,754 keV gamma-rays. One of the workers was measured with a whole-body counter to estimate the specific activity of ²⁴Na [i.e., ²⁴Na (Bq)/²³Na (g)] in the body. The estimated specific activity (9,510 Bq^.g^-1) was converted to neutron dose, using a dose coefficient (0.066 mGy per specific activity). The method was useful for the retrospective estimation of neutron doses. This revised version was published online in July 2006 with corrections to the Cover Date.     

Assignment of 23Na MAS NMR signals of ammonium- and lanthanum-exchanged sodium Y zeolites

Two distinct ²³Na MAS NMR lines in spectra of hydrated Na,NH₄-Y zeolites at about −9 and −13 ppm (referenced to crystalline NaCl) were assigned to sodium lattice cations located in the large cavities (SIII) and inside the truncated octahedra (SI′ or SII′). This assignment was supported by the appearance of these two signals in spectra of air-dried and heat-treated La,Na-Y zeolites (obtained by conventional or contact-induced solid-state ion exchange), the more so as the intensity ratios corresponded to the cation distribution known to arise after the distinctly different pretreatments. It is concluded that slowly tumbling sodium cations are located in SIII whereas Na cations in truncated octahedra show stronger quadrupole interactions. A ²³Na signal at −5.5 ppm sometimes observed in spectra of La,Na-Y zeolites was tentatively assigned to sodium cations located in the hexagonal prisms (SI).     

Sodium‐ and Potassium‐Hydrate Melts Containing Asymmetric Imide Anions for High‐Voltage Aqueous Batteries

Aqueous Na‐ or K‐ion batteries could virtually eliminate the safety and cost concerns raised from Li‐ion batteries, but their widespread applications have generally suffered from narrow electrochemical potential window (ca. 1.23 V) of aqueous electrolytes that leads to low energy density. Herein, by exploring optimized eutectic systems of Na and K salts with asymmetric imide anions, we discovered, for the first time, room‐temperature hydrate melts for Na and K systems, which are the second and third alkali metal hydrate melts reported since the first discovery of Li hydrate melt by our group in 2016. The newly discovered Na‐ and K‐ hydrate melts could significantly extend the potential window up to 2.7 and 2.5 V (at Pt electrode), respectively, owing to the merit that almost all water molecules participate in the Na⁺ or K⁺ hydration shells. As a proof‐of‐concept, a prototype Na₃V₂(PO₄)₂F₃|NaTi₂(PO₄)₃ aqueous Na‐ion full‐cell with the Na‐hydrate‐melt electrolyte delivers an average discharge voltage of 1.75 V, that is among the highest value ever reported for all aqueous Na‐ion batteries.     

Kinetics of the yttrium fluoride electroreduction in chloride melts

To establish the effect of the nature of supporting electrolytes KCl; K, Na/Cl; K, Na, Cs/Cl; and K, Na, Ba/Cl on the electrochemical deposition of yttrium from melts, the electroreduction of yttrium fluoride in the said melts is studied by a linear voltammetry method. The discharge of ions Y³⁺ in all the melts occurs via one stage. The diffusion coefficients, activation energy, product of transfer coefficients and the number of electrons n , diffusion layer thickness, diffusion constant, and rate constant of charge transfer are determined.Translated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 48–53.Original Russian Text Copyright © 2005 by N. Gasviani, Dzhaparidze, Kipiani, S. Gasviani, Abazadze.     

Synthesis of silica particles with lamellar and wormhole-like bi-modal mesopores using anionic surfactant as the template

Silica particles with lamellar and wormhole-like bi-modal mesopores have been synthesized using anionic surfactant (N-lauroylsarcosine sodium) as the template. The particles with diameters of 300―500 nm possess bi-modal mesopores with pore sizes of 3 nm and 12 nm, which were ascribed to the disordered wormhole-like mesophase and lamellar mesophase, respectively. The BET surface area of the particles was 536 m2/g and the pore volume was 0.83 cm3/g. The lamellar mesophase and cylindrical mesophase were formed...     

NMR spectroscopy of bismuth fluoride glasses with alkali cations

Results of the ⁷Li, ¹⁹F, and ²³Na NMR studies of ionic mobility in bismuth fluoride glasses in the systems BiF₃-LiF and BiF₃-MF-ZrF₄ (M = Li, Na, K, Cs) are summarized. Analysis of the ⁷Li, ¹⁹F, and ²³Na NMR spectra made it possible to reveal changes in the nature of ion motions in the fluoride, lithium and sodium sublattices of glasses upon temperature variation and to determine their types. The temperature ranges were found where main types of ion motions in the tested glasses are represented by diffusion of lithium ions, reorientations of fluorine-containing groups constituting the glass network, and diffusion of fluorine ions. The role of alkali cations in the formation of ionic mobility in bismuth fluorozirconate glasses is considered.