Dynamics Of Sodium Ions Research Articles

Gelation of Na-alginate aqueous solution: A study of sodium ion dynamics via NMR relaxometry

Sodium alginate (SA) hydrogels have a wide range of applications including tissue engineering, drug delivery and formulations for preventing gastric reflux. The dynamics of sodium ions during the gelation process of SA solution is critical for clarification of the gelation procedure. In this work, nuclear magnetic resonance (NMR) relaxometry and pulsed-field-gradient (PFG) NMR diffusometry were used to investigate the dynamics of the sodium ions during the gelation of SA alginate. We find that sodium ions are in two different states with the addition of divalent calcium ions, corresponding to Ca2+ crosslinked and un-crosslinked regions in the hydrogels. The sodium ions within the un-crosslinked regions are those released from the alginate chains without Ca2+ crosslinking. The relative content of sodium ions within the Ca2+ crosslinked regions decreased with the increase in the content of calcium ions in the system. The relaxation time T2 of sodium ions within the Ca2+ crosslinked and un-crosslinked regions shift to shorter and longer relaxation time with the increase in concentration of calcium ion, which indicates the closer package of SA chains and the larger space for the diffusion of free sodium ions. This work clarifies the dynamics of 23Na+ in a calcium alginate gel at the equilibrium state.

Structure and Sodium Ion Dynamics in Sodium Strontium Silicate Investigated by Multinuclear Solid-State NMR

The high oxide ion conductivity of the proposed sodium strontium silicate ion conductors Sr0.55Na0.45SiO2.775 (>10–2 S·cm–1 at 525 °C) and its unusual alkali metal substitution strategy have been extensively questioned in the literature. Here, we present a comprehensive understanding of the structure of this material using a combination of XRD and multinuclear 17O, 23Na, and 29Si solid-state NMR spectroscopy data and a detailed investigation of the Na ion dynamics by high temperature 23Na NMR line shape analysis and relaxation rates measurements. Both 23Na and 29Si NMR spectra demonstrate the absence of Na doping in strontium silicate SrSiO3 and the presence of an amorphous phase identified as Na2O·2SiO2 glass as the Na-containing product. Devitrification at 800 °C yields crystallization of the Na2O·2SiO2 glass into the known crystalline α-Na2Si2O5 phase which was positively identified by its XRD pattern and the extensive and clear 17O, 23Na, and 29Si NMR fingerprints. High temperature 23Na NMR reveals that the Na ions are mobile in the Na2O·2SiO2 amorphous component below its glass transition temperature (∼450 °C). In contrast, 23Na NMR data obtained on the crystalline α-Na2Si2O5 shows limited Na dynamics below ∼650 °C, and this result explains the large discrepancy in the conductivity observed in the literature which strongly depends on the thermal history of the Sr0.55Na0.45SiO2.775 material. These insights demonstrate that the high conductivity observed in Sr0.55Na0.45SiO2.775 is due to Na conduction in the Na2O·2SiO2 glass, and this motivates the quest for the discovery of low temperature fast ion conductors in noncrystalline solids.

Research data supporting K.K. Inglis et al., "Structure and Sodium Ion Dynamics in Sodium Strontium Silicate Investigated by Multinuclear Solid-State NMR", Chemistry of Materials, DOI:10.1021/acs.chemmater.6b00941

This includes all the FIDs and processed NMR data published in the paper “Structure and Sodium Ion Dynamics in Sodium Strontium Silicate Investigated by Multinuclear Solid-State NMR” Blanc Chemistry of Materials 2016 00941v. All the NMR data were acquired and processed with Topspin 3.2. Please see the paper for more details. The file Na_dopedSrSiO3_NMR_23Na29Si17Odata contains all 29Si, 17O and 23Na NMR data (except 23Na variable temperature NMR data) and the content is described here: File 1 Sr0.55Na0.45SiO2.775 29Si MAS (Fig 2) File 2 devitrified Sr0.55Na0.45SiO2.775 29Si MAS (Fig 2) File 3 Sr0.55Na0.45SiO2.775 23Na MAS at 20 T (Fig 3) File 4 Sr0.55Na0.45SiO2.775 23Na MAS at 9.4 T (Fig 3) File 5 devitrified Sr0.55Na0.45SiO2.775 23Na MAS at 20 T (Fig 3) File 6 devitrified Sr0.55Na0.45SiO2.775 23Na MAS at 9.4 T (Fig 3) File 7 devitrified 17O enriched Sr0.55Na0.45SiO2.775 17O MAS at 20 T (Fig S1) File 8 devitrified 17O enriched Sr0.55Na0.45SiO2.775 17O MAS at 9.4 T (Fig S1) File 9 Sr0.55Na0.45SiO2.775 after quenching from 934 °C 29Si MAS (Fig S4) File 10 devitrified Sr0.55Na0.45SiO2.775 after quenching from 934 °C 29Si MAS (Fig S4) The file Na_dopedSrSiO3_NMR_23NaVT_dynamics gives all the 23Na NMR variable temperature data used to produce Figures 4-7, S3 and S5.

Sodium ion dynamics in a sulfonate based ionomer system studied by 23Na solid-state nuclear magnetic resonance and impedance spectroscopy

A poly(2-acrylamido-2-methyl-1-propane-sulphonate) (PAMPS) ionomer containing both sodium and quaternary ammonium cations functionalised with an ether group, has been characterised in terms of its thermal properties, ionic conductivity and sodium ion dynamics. The ether oxygen was incorporated to reduce the Na+ association with the anionic sulfonate groups tethered to the polymer backbone, thereby promoting ion dissociation and ultimately enhancing the ionic conductivity. This functionalised ammonium cation led to a significant reduction in the ionomer Tg compared to an analogue system without an ether group, resulting in an increase in ionic conductivity of approximately four orders of magnitude. The sodium ion dynamics were probed by 23Na solid-state NMR, which allowed the signals from the dissociated (mobile) and bound Na+ cations to be distinguished. This demonstrates the utility of 23Na solid-state NMR as a probe of sodium dynamics in ionomer systems.

Diffusion of water and sodium counter-ions in nanopores of aβ-lactoglobulin crystal: a molecular dynamics study

The dynamics of water and sodium counter-ions(Na+)in a C2221 orthorhombic β-lactoglobulin crystal is investigated by means of 5 ns molecular dynamics simulations. Theeffect of the fluctuation of the protein atoms on the motion of water and sodium ions isstudied by comparing simulations in a rigid and in a flexible lattice. The electrostaticinteractions of sodium ions with the positively charged LYS residues inside the crystalchannels significantly influence the ionic motion. According to our results, water moleculesclose to the protein surface undergo an anomalous diffusive motion. On the other hand, themotion of water molecules further away from the protein surface is normal diffusive.Protein fluctuations affect the diffusion constant of water, which increases from0.646 ± 0.108 to0.887 ± 0.41 nm2 ns−1, when protein fluctuations are taken into account. The pore size (0.63–1.05 nm) and thewater diffusivities are in good agreement with previous experimental results. The dynamicsof sodium ions is disordered. LYS residues inside the pore are the main obstacles to themotion of sodium ions. However, the simulation time is still too short for providing aprecise description of anomalous diffusion of sodium ions. The results are not only ofinterest for studying ion and water transport through biological nanopores, butmay also elucidate water–protein and ion–protein interactions in protein crystals.

Enhancement of Na+ Diffusion in a Bicontinuous Cubic Phase by the Ionophore Monensin

Pulsed field gradient spin-echo NMR diffusion and relaxation measurements were used to investigate how the Na+ ionophore monensin affected the dynamics of sodium ions in a Myverol 18-99/saline bicontinuous Ia3d cubic phase (BCP). The monensin Na+ binding number was estimated from 23Na line widths to be between 3 and 6. The dependence of the apparent Na+ diffusion coefficient on the concentration of monensin revealed monensin-induced Na+ transport. At high monensin concentrations, the enhancement of D(Na+) was offset by Na+-monensin binding. The greatest enhancement was measured at short diffusion times (delta < or = 5 ms), which we explain in terms of the bicontinuous topology of the cubic phase and a combination of tortuosity and bilayer permeability effects. We also propose numerical simulations which would enable the separation of the two effects. To our knowledge, this is the first study of ionophore-mediated cation diffusion in a bicontinuous cubic phase. The approach could be used to study the dynamics of hydrophilic species in the aqueous channels of BCPs and similar structures, as well as to measure the ion-transporting efficiency of ionophores.

A quantitative model of the planetary Na&amp;lt;sup&amp;gt;+&amp;lt;/sup&amp;gt; contribution to Mercury’s magnetosphere

Abstract. We examine the circulation of heavy ions of planetary origin within Mercury’s magnetosphere. Using single particle trajectory calculations, we focus on the dynamics of sodium ions, one of the main species that are ejected from the planet’s surface. The numerical simulations reveal a significant population in the near-Mercury environment in the nightside sector, with energetic (several keV) Na + densities that reach several tenths cm-3 at planetary perihelion. At aphelion, a lesser (by about one order of magnitude) density contribution is obtained, due to weaker photon flux and solar wind flux. The numerical simulations also display several features of interest that follow from the small spatial scales of Mercury’s magnetosphere. First, in contrast to the situation prevailing at Earth, ions in the magnetospheric lobes are found to be relatively energetic (a few hundreds of eV), despite the low-energy character of the exospheric source. This results from enhanced centrifugal acceleration during E × B transport over the polar cap. Second, the large Larmor radii in the mid-tail result in the loss of most Na + into the dusk flank at radial distances greater than a few planetary radii. Because gyroradii are comparable to, or larger than, the magnetic field variation length scale, the Na + motion is also found to be non-adiabatic throughout most of Mercury’s equatorial magnetosphere, leading to chaotic scattering into the loss cone or meandering (Speiser-type) motion in the near-tail. As a direct consequence, a localized region of energetic Na + precipitation develops at the planet’s surface. In this region which extends over a wide range of longitudes at mid-latitudes ( ~ 30°–40°), one may expect additional sputtering of planetary material.Key words. Magnetospheric physics (planetary magnetospheres) – Space plasma physics (charged particle motion and acceleration; numerical simulation studies)

Sodium ion dynamics in the nonstoichiometric layer-type oxide Na 0.67Ni 0.33Ti 0.67O 2 studied by 23Na NMR

Sodium ion dynamics in the nonstoichiometric layer-type oxide Na 0.67Ni 0.33Ti 0.67O 2 powder was studied by 23Na NMR techniques. Even though 23Na is a quadrupole nucleus, the spectra are dominantly governed by magnetic susceptibility anisotropy of paramagnetism rather than quadrupole interaction. The static resonance line becomes narrower at higher temperature manifesting motional narrowing. The line shape is not axially symmetric below 270 K but becomes symmetric at higher temperature. This indicates that the Na + motion is faster than 10 −8 s and isotropic in two-dimension above 270 K resulting in averaging out the anisotropy in the ab-planes. Two different prismatically coordinated Na sites of the sample are reported by XRD but the fast and isotropic Na motion in the ab-planes averages out the locational difference in the NMR spectra. At lower temperature, the Na + motion slows down and becomes anisotropic in the ab-planes enough to see the anisotropy in the plane.

Dynamics of sodium ions in NaClO4 complexed in poly(propylene-oxide): A 23Na nuclear magnetic resonance study

Amorphous poly(propylene oxide), PPO (molecular weights, 425 and ∼106), complexed with NaClO4 salt has ionic conductivities as high as 10−5 S/cm at room temperature. In an attempt to directly study the dynamics of the Na+ ions, (I=3/2) nuclear magnetic resonance (NMR) spin-lattice relaxation times, T1, and spin–spin relaxation times, T2, at a resonance frequency of 77.0 MHz have been measured over the temperature range from 150 to 390 K. A range of salt compositions [(PPO)nNaClO4; n=8–30] have been investigated. In addition, the glass transition temperature for each sample is reported. The recovery of equilibrium magnetization following a π/2 pulse is biexponential as expected for a spin I=3/2 system in the viscous liquid region. Below Tg a better fit to the magnetization recovery curve can be obtained if Kohlrausch–Williams–Watts (KWW) functions are used in place of the exponential functions. At low temperature the molecular motion has slowed to the point where a common spin temperature is not achieved by ionic diffusion. Two T2 values are observed over a limited temperature region near the T1 minimum. In the remaining low temperature region only the T2 associated with the central transition could be determined because the large 23Na quadrupole coupling constant made detection of the satellite transitions impossible. There is no evidence from the NMR relaxation time data for two Na+ populations. The experimental spin-lattice relaxation times can be analyzed to determine the correlation time for the ionic motion as a function of reciprocal temperature. The correlation time data display a distinct change in behavior at Tg which is interpreted as an indication of a crossover between two ionic transport mechanisms. Plots of T1 as a function of Tg/T indicate that dynamics for T&amp;gt;Tg are largely determined by the flexibility of the polymer host (the α process) whereas a different process dominates for T&amp;gt;Tg (presumably the β process). A comparison of correlation times derived from NMR relaxation times and ionic conductivities show a marked difference especially in the region of Tg. The conductivity decreases rapidly while the sodium ion motion continues with a correlation time ∼10−6 s through the glass transition.

NMR studies of 23Na+ in frozen bovine serum albumin solution

An NMR investigation of the dynamics of sodium ions in the residual non-freezing water in bovine serum albumin solutions cooled to below freezing points is described. Measurements of signal intensities and transverse relaxation times indicated that all of the sodium is concentrated into the non-freezing water and that correlation times are of the same order as those in water at protein interfaces. It is concluded that non-freezing water, therefore, is likely to be a medium in which chemical reactions can readily take place.