Universality of the Sodium Ion Binding Mechanism in Class A G‐Protein‐Coupled Receptors

The allosteric modulation of G‐protein‐coupled receptors (GPCRs) by sodium ions has received significant attention as crystal structures of several receptors show Na⁺ ions bound to the inactive conformations at the conserved Asp^2.50. To date, structures from 24 families of GPCRs have been determined, though mechanistic insights into Na⁺ binding to the allosteric site are limited. We performed hundreds‐of‐microsecond long simulations of 18 GPCRs and elucidated their Na⁺ binding mechanism. In class A GPCRs, the Na⁺ ion binds to the conserved residue 2.50 whereas in class B receptors, it binds at 3.43b, 6.53b, and 7.49b. Using Markov state models, we obtained the free energy profiles and kinetics of Na⁺ binding to the allosteric site, which reveal a conserved mechanism of Na⁺ binding for GPCRs and show the residues that act as major barriers for ion diffusion. Furthermore, we also show that the Na⁺ ion can bind to GPCRs from the intracellular side when the allosteric site is inaccessible from the extracellular side.     

The effect of sodium cation concentration on the electrochemical reduction of copper(I) thiosulfate complexes

The electrochemical behavior of copper(I) thiosulfate complexes from aqueous solutions containing different amounts of sodium perchlorate NaClO₄ is studied by the methods of hydrodynamic voltammetry and potentiometry with a Na⁺-selective electrode. The electrochemical reaction orders p with respect to Na⁺ cations are determined from the dependences of exchange currents and direct reaction currents at fixed potential on the equilibrium concentration of Na⁺ cations. The reaction order p is close to 1 in the Na⁺ concentration range of 0.06–0.12 M and drops to zero for $c_{Na^ + } $ > 0.12 M. The ion pair (IP) {Na[Cu(S₂O₃)₂]}_2? the formation of which precedes the electron transfer reaction is the electrochemically active species for the reduction of copper(I) thiosulfate complexes. The stability constant of IP is determined (K = 27.0 ± 2.4) as well as the rate constants of IP formation and decomposition.     

Calix[4]pyrrole‐Based Heteroditopic Ion‐Pair Receptor That Displays Anion‐Modulated,Cation‐Binding Behavior

A new ditopic ion‐pair receptor 1 was designed, synthesized, and characterized. Detailed binding studies served to confirm that this receptor binds fluoride and chloride ions (studied as their tetraalkylammonium salts) and forms stable 1:1 complexes in CDCl₃. Treatment of the halide‐ion complexes of 1 with Group I and II metal ions (Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, and Ca²⁺; studied as their perchlorate salts in CD₃CN) revealed unique interactions that were found to depend on both the choice of the added cation and the precomplexed anion. In the case of the fluoride complex [ 1? F]^? (preformed as the tetrabutylammonium (TBA⁺) complex), little evidence of interaction with the K⁺ ion was seen. In contrast, when this same complex (i.e., [ 1? F]^? as the TBA⁺ salt) was treated with the Li⁺ or Na⁺ ions, complete decomplexation of the receptor‐bound fluoride ion was observed. In sharp contrast to what was seen with Li⁺, Na⁺, and K⁺, treating complex [ 1? F]^? with the Cs⁺ ion gave rise to a stable, receptor‐bound ion‐pair complex [Cs ?1? F] that contains the Cs⁺ ion complexed within the cup‐like cavity of the calix[4]pyrrole, which in turn was stabilized in its cone conformation. Different complexation behavior was observed in the case of the chloride complex [ 1? Cl]^?. In this case, no appreciable interaction was observed with Na⁺ or K⁺. In addition, treating [ 1? Cl]^? with Li⁺ produces a tightly hydrated dimeric ion‐pair complex [ 1? LiCl(H₂O)]₂ in which two Li⁺ ions are bound to the crown moiety of the two receptors. In analogy to what was seen in the case of [ 1? F]^?, exposure of [ 1? Cl]^? to the Cs⁺ ion gives rise to an ion‐pair complex [Cs ?1? Cl] in which the cation is bound within the cup of the calix[4]pyrrole. Different complexation modes were also observed when the binding of the fluoride ion was studied by using the tetramethylammonium and tetraethylammonium salts.     

Doubly bridged biscalix[4]arene for homotropic and heterotropic allosteric effects on ion recognition

A novel host, which shows homotropic and heterotropic allostery for Na⁺ and Ag⁺ recognition, is constructed by utilizing a biscalix[4]arene skeleton bearing bipyridine and ester moieties. The host binds two Na⁺ ions, but the second binding to Na⁺ is considerably suppressed by the first Na⁺ ion bound in the other binding site.     

Ion solvation in water clusters

We describe here molecular dynamics computer simulations performed to study the solvation of ions (Cl^? and Na⁺) in water clusters. Our simulations show that the calculated structure and dynamics of the clusters is very sensitive to the potential model which is used to describe the interactions. From the comparison with thermodynamic data and data from the photoelectron spectra we conclude that in Cl^?(H₂O)_n (n≤20) clusters the ion is located on the surface of the cluster.     

Vacancy‐Controlled Na+ Superion Conduction in Na11Sn2PS12

Highly conductive solid electrolytes are crucial to the development of efficient all‐solid‐state batteries. Meanwhile, the ion conductivities of lithium solid electrolytes match those of liquid electrolytes used in commercial Li⁺ ion batteries. However, concerns about the future availability and the price of lithium made Na⁺ ion conductors come into the spotlight in recent years. Here we present the superionic conductor Na₁₁Sn₂PS₁₂, which possesses a room temperature Na⁺ conductivity close to 4 mS cm^?1, thus the highest value known to date for sulfide‐based solids. Structure determination based on synchrotron X‐ray powder diffraction data proves the existence of Na⁺ vacancies. As confirmed by bond valence site energy calculations, the vacancies interconnect ion migration pathways in a 3D manner, hence enabling high Na⁺ conductivity. The results indicate that sodium electrolytes are about to equal the performance of their lithium counterparts.     

Atomistic Characterisation of Li+ Mobility and Conductivity in Li7−xPS6−xIx Argyrodites from Molecular Dynamics Simulations,Solid‐State NMR,and Impedance Spectroscopy

The atomistic mechanisms of Li⁺ ion mobility/conductivity in Li_7?xPS_6?xI_x argyrodites are explored from both experimental and theoretical viewpoints. Ionic conductivity in the title compound is associated with a solid–solid phase transition, which was characterised by low‐temperature differential scanning calorimetry, ⁷Li and ¹²⁷I NMR investigations, impedance measurements and molecular dynamics simulations. The NMR signals of both isotopes are dominated by anisotropic interactions at low temperatures. A significant narrowing of the NMR signal indicates a motional averaging of the anisotropic interactions above 177±2 K. The activation energy to ionic conductivity was assessed from both impedance spectroscopy and molecular dynamics simulations. The latter revealed that a series of interstitial sites become accessible to the Li⁺ ions, whilst the remaining ions stay at their respective sites in the argyrodite lattice. The interstitial positions each correspond to the centres of tetrahedra of S/I atoms, and differ only in terms of their common corners, edges, or faces with adjacent PS₄ tetrahedra. From connectivity analyses and free‐energy rankings, a specific tetrahedron is identified as the key restriction to ionic conductivity, and is clearly differentiated from local mobility, which follows a different mechanism with much lower activation energy. Interpolation of the lattice parameters as derived from X‐ray diffraction experiments indicates a homogeneity range for Li_7?xPS_6?xI_x with 0.97≤x≤1.00. Within this range, molecular dynamics simulations predict Li⁺ conductivity at ambient conditions to vary considerably.     

Static SIMS analysis of carbonate on basic alkali‐bearing surfaces

Carbonate is a somewhat enigmatic anion in static secondary ion mass spectrometry (SIMS) because abundant ions containing intact CO₃^2? are not detected when analyzing alkaline‐earth carbonate minerals common to the geochemical environment. In contrast, carbonate can be observed as an adduct ion when it is bound with alkali cations. In this study, carbonate was detected as the adduct Na₂CO₃·Na⁺ in the spectra of sodium carbonate, bicarbonate, hydroxide, oxalate, formate and nitrite and to a lesser extent nitrate. The appearance of the adduct Na₂CO₃·Na⁺ on hydroxide, oxalate, formate and nitrite surfaces was interpreted in terms of these basic surfaces fixing CO₂ from the ambient atmosphere. The low abundance of Na₂CO₃·Na⁺ in the static SIMS spectrum of sodium nitrate, compared with a significantly higher abundance in salts having stronger conjugate bases, suggested that the basicity of the conjugate anions correlated with aggressive CO₂ fixation; however, the appearance of Na₂CO₃·Na⁺ could not be explained simply in terms of solution basicity constants. The oxide molecular ion Na₂O⁺ and adducts NaOH·Na⁺ and Na₂O·Na⁺ also constituted part of the carbonate spectral signature, and were observed in spectra from all the salts studied. In addition to the carbonate and oxide ions, a low‐abundance oxalate ion series was observed that had the general formula Na_2?xH_xC₂O₄·Na⁺, where 0 < x < 2. Oxalate adsorption from the laboratory atmosphere was demonstrated but the oxalate ion series also was likely to be formed from reductive coupling occurring during the static SIMS bombardment event. The remarkable spectral similarity observed when comparing the sodium salts indicated that their surfaces shared common chemical speciation and that the chemistry of the surfaces was very different from the bulk of the particle. Copyright © 2003 John Wiley & Sons, Ltd.     

Femtosecond time-resolved molecular multiphoton ionization and fragmentation of Na2: experiment and quantum mechanical calculations

We present a comparison between experimental and theoretical results for pump/probe multiphoton ionizing transitions of the sodium dimer, initiated by femtosecond laser pulses. It is shown that the motion of vibrational wave packets in two electronic states is probed simultaneously and their dynamics is reflected in the total Na ₂ ⁺ ion signal which is recorded as a function of the time delay between pump and probe pulse. The time dependent quantum calculations demonstrate that two ionization pathways leading to the same final states of the molecular ion exist: one gives an oscillating contribution to the ion signal, the other yields a constant background. From additional measurements of the Na⁺-transient photofragmentation spectrum it is deduced that another ionization process leading to different final ionic states exists. The process includes the excitation of a doubly excited bound Rydberg state. This conclusion is supported by the theoretical simulation.     

Single Crystalline Na0.7MnO2 Nanoplates as Cathode Materials for Sodium‐Ion Batteries with Enhanced Performance

Single crystalline rhombus‐shaped Na_0.7MnO₂ nanoplates have been synthesized by a hydrothermal method. TEM and HRTEM analyses revealed that the Na_0.7MnO₂ single crystals predominantly exposed their (100) crystal plane, which is active for Na⁺‐ion insertion and extraction. When applied as cathode materials for sodium‐ion batteries, Na_0.7MnO₂ nanoplates exhibited a high reversible capacity of 163 mA h g^?1, a satisfactory cyclability, and a high rate performance. The enhanced electrochemical performance could be ascribed to the predominantly exposed active (100) facet, which could facilitate fast Na⁺‐ion insertion/extraction during the discharge and charge process.     

Complex formation of O-carboxymethylcalix[4]resorcinolarene with alkaline metal and ammonium ions

Complex formation of 3,5,10,12,17,19,24,26-octa(carboxymethoxy)-1,8,15,22-tetraundecylcalix[4]arene (H₈X) with Li⁺, Na⁺, K⁺, and NH₄ ⁺ ions was studied by ¹H NMR spectroscopy and pH-metry in water—DMSO solutions. Binding of one cation occurs during the stepped deprotonation of four carboxymethyl groups in H₈X. The K⁺ ion was found to be bound more efficiently than Li⁺ and Na⁺. The further deprotonation to the penta- and hexaanion leads to the coordination with two cations. The most stable binuclear complex is formed with the Li⁺ ion.     

Aluminum phosphate dispersed on a cellulose acetate fiber surface: Preparation, characterization and application for Li, Na and K separation

Cellulose acetate fibers with supported highly dispersed aluminum phosphate were prepared by reacting aluminum-containing cellulose acetate (Al₂O₃=3.5 wt.%; 1.1 mmol g⁻¹ aluminum atom per gram of the material) with phosphoric acid. Solid-state NMR spectra (CPMAS ³¹P NMR) data indicated that HPO₄²⁻ is the species present on the fiber surface. The specific concentration of acidic centers, determined by ammonia gas adsorption, is 0.50 mmol g⁻¹. The ion exchange capacities for Li⁺, Na⁺ and K⁺ ions were determined from ion exchange isotherms at 298 K and showed the following values (in mmol g⁻¹): Li⁺=0.03, Na⁺=0.44 and K⁺=0.50. The H⁺/Li⁺ exchange corresponds to the model of the ideal ion exchange with a small value of the corresponding equilibrium constant K=1.1×10⁻². Due to the strong cooperative effect, the H⁺/Na⁺ and H⁺/K⁺ ion exchange is non-ideal. These ion exchange equilibria were treated with the use of models of fixed bi- or tridentate centers, which consider the surface of the sorbent as an assemblage of polyfunctional sorption centers. Both the observed ion exchange capacities with respect to the alkaline metal ions and the equilibrium constants were discussed by taking into consideration the sequence of the ionic hydration radii for Li⁺, Na⁺ and K⁺. The matrix affinity order for the ions decreases as the hydration radii of the cations increase, i.e. Li⁺>Na⁺>K⁺. The high values of the separation factors S_Na⁺/Li⁺ and S_K⁺/Li⁺ (up to several hundred) provide quantitative separation of Na⁺ and K⁺ from Li⁺ from a mixture containing these three ions.     

Transport of amino acids through liquid membranes III. The alkaline ion role

This paper discusses the alkaline ion (Na⁺) role in the uphill transport of amino acids through a bulk liquid membrane. The aqueous phases (source phase - S and receiving phase - R) are made up of equimolar concentrations of amino acid (4.38 mM p-aminobenzoic acid (PABA)) and alkaline ion (75 mM Na⁺). A chloroform solution containing 5 mM dibenzo-18-crown-6 (DB18C6) represents the bulk liquid membrane (M). The data obtained show that at the S-M interphase, the amino acid is coupled with the carrier via the H₃N⁺ group rather than being transported to the R-M interphase, where Na⁺ substitutes the amino acid. If Na⁺ is absent, the amino acid is transported to the opposite direction. These results support the hypothesis that the presence of Na⁺ ion in the aqueous phases assures the ‘biological’ direction of aminobenzoic acids transport through membranes.     

WQD-1沸石离子交换性能的研究

测定了W_QD-1沸石在一价碱金属离子混合溶液中的分配系数、饱和交换量和在25℃时，NH⁺₄/K⁺、NH⁺₄/Na⁺交换等温线。得出该沸石一价离子选择性序列为：Cs⁺>Rb⁺>K⁺>Na⁺>Li⁺, Na⁺/K⁺交换自由焓变ΔG(T,P)=-6.745 KJ/mol。     

Zum Ionenaustausch einwertiger Kationen an synthetischen Natriumpolysilicaten mit Schichtstruktur

Ion Exchange of Monovalent Cations in Synthetic Sodium Polysilicates with Layer Structure Cation-exchange equilibria of synthetic sodium polysilicates Ilerit (Na₂O · 8.3SiO₂ 8.9 H₂O) and Magadiite (Na₂O · 13 SiO₂ · 6.8 H₂O) with H⁺, Li⁺ and K⁺ Ions were investigated with respect to their selectivity behaviour. The range of ion selectivity is: H⁺ > Na⁺ > Li⁺ > K⁺. Thermodynamic data ΔG, ΔH, and ΔS were determined by means of the integral thermodynamic equilibria constants K_th of the ion-exchange reactions.     

Simulation study on dynamics of A- to B-form transition in aqueous DNA solution: Effect of alkali metal counterions

DNA and its conformational transition can be used to design nanometer-scale structures, nano-tweezers and nanomechanical devices. Experiments and molecular simulations have been used to study the concentration effect on the A-DNA→B-DNA conformational transition, but a systematical investigation on counterion effect on the dynamics of this transition has not been reported up to now. In present work, restrained and unrestrained molecular dynamics (MD) simulations have been performed to characterize the stability of DNA conformations and the dynamics of A-DNA→B-DNA transitions in aqueous solutions with different alkali metal counterions. The DNA duplex d(CGCGAATTCGCG)₂, coion Cl^? and counterions Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ as well as water molecule were considered using the PARM99 force field in the AMBER8 package. It was found that B-form DNA is more stable than A-form DNA in aqueous electrolyte solutions with different alkali metal counterions. Increasing KCl concentration in solution hinders the A-DNA→B-DNA transition and the transition times for different alkali metal counterions conform to neither the simple sequence related to naked ion size nor to hydrated diameter, but an apparently abnormal sequence of K⁺ < Rb⁺ < Cs⁺ < Na⁺ < Li⁺. This abnormal sequence can be well understood in terms of an electrostatic model based on the effective cation diameters and the modified mean-spherical approximation (MMSA). The present results provide valuable information for the design of DNA-based nanomaterials and nanodevices.     

Counterion binding by poly(styrenesulfonate)

Binding isotherms of poly(styrenesulfonate) with hydrogen and selected alkali ions have been determined by dialysis equilibrium and dye spectroscopy, employing Pb²⁺, Mg²⁺, and Ca²⁺ as the competing divalent ions. The observed degrees of counterion binding, Θ_z, defined as the number of bound counterfoils of valence z per poly ion site-group, agree quite well with those predicted by Manning's two variable theory. The binding preference follows the order Cs⁺ > Rb⁺ > K⁺ > Na⁺ > H⁺ >Li⁺, indicating that the binding process is of a territorial nature. Independently performed light scattering measurements show that a plot of the radius of gyration, >S _z>, against the actual polyion charge gives a sigmoidal curve. This result is taken to indicate that (1) a polyion is, in general, not completely neutralized in the Θ-state and that (2) a polyion may be not fully stretched when the polyion charge density is largest.     

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.     

Structural Elucidation of β‐Lactam Diastereoisomers through Ion Mobility Mass Spectrometry Studies and Theoretical Calculations

The ion mobility combined with mass spectrometry and theoretical calculations were used to characterize and separate six diastereoisomeric β‐lactams. The influence of traveling wave height and wave velocity, size of the alkali metal ion (Li⁺, Na⁺ and K⁺) and drift gases with varying masses and polarizabilities (N₂ and CO₂) on separation efficacy was additionally examined. The best separation of diastereoisomers of β‐lactams was observed for adducts with Na⁺ and Li⁺ ions, whereas other parameters had little impact on separation process. The isomeric β‐lactams were characterized by both experimental and theoretical collision cross sections. The theoretically calculated values of collision cross sections obtained from extensive molecular dynamics and density functional theory calculations for model structures agreed well with those established experimentally. The relationship between separation efficacy and the configuration at the carbon atoms C5 and C6 of β‐lactam ring was defined. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and physicochemical investigation of hexafluoro complexes of germanium with mixed alkali metal cations

Hexafluoro complexes of germanium with mixed alkali-metal cations having the composition formula MM'GeF₆, which crystallize in a rhombic syngony were synthesized. The unit cell parameters of the compounds have been determined. It was found that MM'GeF₆ are biaxial optical crystals, and their optical and refractometric constants are given. It was shown that the substitution of the Na⁺ cation in Na₂GeF₆ by K⁺, Rb⁺, Cs⁺ leads to a varied degree of distortion of the hexafluoro ion. It was found (NMR data) that a change in the dynamic state of the octahedral ions is due to a transition from a restrained rotation to an isotropic one.Institute of Chemistry of the Far-Eastern Scientific Center, Russian Academy of Sciences, 690022 Vladivostok. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2473–2482, November, 1992.