Sodium Coordination Research Articles

Synthesis, crystal structures and properties of three sodium coordination polymers based on bridging polyoxometalate ligands

The syntheses, crystal structures, spectral characterization, electrochemical, photoredox properties and biological studies of three sodium coordination polymers viz. (ImH)4[(µ2-HMo7O24)Na(H2O)8]∙7H2O 1 (Im = Imidazole), [(TEAH)Na5(H2O)12(µ5-Mo7O24)] 2 (TEA=triethanolamine) and [Na2(PyrH)2(µ2-Mo8O26)(H2O)7]∙8H2O 3 (Pyr = pyrazole) are reported. The unique Na atom in 1 exhibits ten coordination unlike hexa coordination observed in 2 and 3. The µ2-bridging heptamolybdate (or octamolybdate) anion in 1 (or 3) links the sodium cations into an infinite chain resulting in a one-dimensional coordination polymer. In 2, the heptamolybdate anion exhibits an unprecedented µ5-nonadentate binding resulting in a three- dimensional (3D) structure. Compounds 1–3 exhibit characteristic Raman bands. Solar irradiation of 2 results in photodimerization, which is further supported by electrochemical studies. Compounds 1–3 exhibit antibacterial activity, with 3 being the most effective against S. Pyogenes, followed by P. aeruginosa, S.typhi and S. aureus. Compound 3 exhibits excellent antidiabetic and anti-inflammatory properties. A comparative study of the binding modes of several heptamolybdates and octamolybdates based compounds is presented.

Solvent-free CO2 cycloaddition by one- and two-dimensional sodium coordination polymers based on hydrazonic ligands

We successfully synthesized and characterized four new coordination polymers of sodium: sodium 4-hydroxy-3-{[2-(pyridine-4-carbonyl)hydrazinylidene]methyl}benzene-1-sulfonate (NaL4-Py), sodium 3-[(2-benzoylhydrazinylidene)methyl]-4-hydroxybenzene-1-sulfonate (NaLPh), sodium 3-[(2-acetylhydrazinylidene)methyl]-4-hydroxybenzene-1-sulfonate (NaLMe), and sodium 3-[(2-carbamoylhydrazinylidene)methyl]-4-hydroxybenzene-1-sulfonate (NaLNH2). These polymers were synthesized through a 1:1 condensation reaction of hydrazide derivatives with sodium salicylaldehyde-5-sulfonate monohydrate (NaSalSO3) and were thoroughly characterized using various analytical techniques. The compounds NaLMe and NaLPh, crystallized in the P 1‾ and P21/n space groups, respectively, forming one-dimensional polymers. On the other hand, NaLNH2 and NaL4-Py crystallized in the Cmca and P 1‾ space groups, respectively, forming two-dimensional coordination polymers. The coordination environment of the sodium cation differed among the compounds, with the imine nitrogen atom interfering in NaL4-Py and NaLPh. The sulfonate group exhibited various coordination modes, resulting in the different dimensionalities of the polymers. Compounds NaL4-Py and NaLPh acted as heterogeneous Lewis acid catalysts for the solvent-free cycloaddition reaction of epichlorohydrine and CO2 into valued cyclic carbonate. High selective conversion (68 %) of epichlorohydrin to cyclic carbonate was obtained at mild conditions, 60 °C and 1 bar CO2, after 24 h of reaction.

Ion Dynamics at the Intermediate Charging State of the Sodium Vanadium Fluorophosphate Cathode.

Na super ionic conductor (NASICON)-type polyanionic vanadium fluorophosphate Na3V2O2(PO4)2F (NVOPF) is a promising cathode material for high-energy sodium-ion batteries. The dynamic diffusion and exchange of sodium ions in the lattice of NVOPF are crucial for its electrochemical performance. However, standard characterizations are mostly focused on the as-synthesized material without cycling, which is different from the actual battery operation conditions. In this work, we investigated the hopping processes of sodium in NVOPF at the intermediate charging state with 23Na solid-state nuclear magnetic resonance (ssNMR) and density functional theory (DFT) calculations. Our experimental characterizations revealed six distinct sodium coordination sites in the intermediate structure and determined the exchange rates among these sites at variable temperatures. The theoretical calculations showed that these dynamic processes correspond to different ion transport pathways in the crystalline lattice. Our combined experimental and theoretical study uncovered the underlying mechanisms of the ion transport in cycled NVOPF and these understandings may help the optimization of cathode materials for sodium-ion batteries.

Effect of compression temperature on the structure and properties of hot compressed sodium borosilicate glasses from molecular dynamics simulations

Applying pressure during glass formation or annealing is an effective method to modify the properties of oxide glasses. The effect of compression temperature on the structure and properties of a sodium borosilicate glass has been investigated using molecular dynamics simulations. The connection between macroscopic properties (density and elastic moduli) and microscopic structures (short- and medium-range order) was investigated. Young’s modulus increased with the compression temperature and then reached a plateau at temperatures close to the glass transition temperature. The modulus increase was found to correlate linearly with glass density change. Correlations with structural changes, such as fraction of four-fold coordinated boron, oxygen triclusters, sodium ion coordination number and the Na–O and Na–Na distances were studied. The results suggest that the pressure-induced transformation from three-fold to four-fold coordinated boron was achieved through the formation of oxygen triclusters, which is different from the commonly observed mechanism involving nonbridging oxygen during the boron coordination change. In addition, the linear correlation between sodium coordination number and glass density suggests that change of sodium ion local environment and redistribution of sodium ions also play an important role in the property behaviour during pressure quenching of the glasses.

Structural subtleties and catalytic activity of sodium aminophenolate complexes in polylactide degradation: towards sustainable waste management solutions.

This study explores the intricate coordination chemistry of sodium aminophenolate species and their significant role in the depolymerization of polylactide (PLA), offering novel insights into catalytic degradation processes. By examining sodium coordination entities, including dimers and larger aggregates such as tetramers, we reveal how structural modifications, particularly the manipulation of steric hindrances, influence the formation and stability of these complexes. The dimers, characterized by a unique four-center core (Na-O-Na-O), serve as a foundational motif, which is further elaborated to obtain complexes with varied coordination environments through strategic ligand design. Our research delves into the lability of the amino arm in these complexes, a critical factor that facilitates the coordination of PLA to the sodium center, thereby initiating the depolymerization process. Moreover, DFT studies have been pivotal in identifying the most energetically favorable structures for catalysis, highlighting a distinct preference for an eight-membered ring motif stabilized by intramolecular hydrogen bonds. This motif not only enhances the catalyst's efficiency but also introduces a novel structural paradigm for sodium-based catalysis in PLA degradation. Experimental validation of the theoretical models was achieved through NMR spectroscopy, which confirmed the formation of the active catalyst forms and monitored the progress of PLA degradation. The study presents a comprehensive analysis of the influence of ligand structure on the catalytic activity, underscoring the importance of the eight-membered ring motif. Furthermore, we demonstrate how varying the steric bulk of substituents on the amino arm affects the catalyst's performance, with benzyl-substituted ligands exhibiting superior activity. Our findings offer a profound understanding of the structural factors governing the catalytic efficiency of sodium aminophenolate complexes in PLA degradation. This research not only advances the field of coordination chemistry but also presents a promising avenue for the development of efficient and environmentally friendly catalysts for polymer degradation.

Polymeric sodium salts and monomeric lanthanide coordination compounds with diphenyl-N-trichloroacetylamidophosphate: synthesis and characterization

The two new sodium coordination polymers [NaL]n (1Na) and [NaL·2.5H2O]n (2Na) on the base of carbacylamidophosphate type ligand diphenyl-N-trichloroacetylamidophosphate (HL, CCl3C(O)N(H)P(O)[OC6H5]2) and the two series of new lanthanide tris- and anionic tetrakis-complexes of general formulas [Ln(L)3phen] (1Ln; Ln3+ = La, Nd, Eu, Tb; phen = 1,10-phenanthroline), PPh4[Ln(L)4] (2Ln; Ln3+ = La, Nd, Eu, Tb) are reported. The obtained compounds' structural, spectroscopic, and thermal properties are discussed in detail based on X-ray diffraction data with shapes of polyhedra analysis, IR, 1H NMR, absorption and luminescence spectroscopy, and thermal gravimetric analysis.

Tumor Microenvironment Mediated Spermidine-Metal-Immunopeptide Nanocomplex for Boosting Ferroptotic Immunotherapy of Lymphoma.

Immunotherapy as an alternative treatment strategy for B-cell lymphoma is undesirable because of tumor heterogeneity and immune surveillance. Spermidine (SPM), as a regulator of the tumor microenvironment (TME), can facilitate the release of damage-associated molecular patterns (DAMPs) from cancer cells, promote immune recognition, and thus alleviate immune surveillance in the TME. Hence, in this work, self-assembled spermidine-based metal-immunopeptide nanocomplexes (APP-Fe NCs; APP is anti-programmed death ligand-1 peptide) with pH-responsive release kinetics were prepared via the flash nanocomplexation (FNC) technique based on the noncovalent interaction between APP-SPM-dextran (DEX) and sodium tripolyphosphate (TPP) and coordination between Fe3+ and TPP. An in vitro study suggested that APP-Fe NCs effectively induce strong oxidative stress and mitochondrial dysfunction and subsequently lead to ferroptosis in cells by interfering with homeostasis in lymphoma cells. Further investigation on lymphoma mice models demonstrated that APP-Fe NCs effectively inhibited the growth and liver metastasis of lymphomas. Mechanistically, by triggering ferroptosis in tumor tissues, these spermidine-containing APP-Fe NCs efficiently facilitated the release of DAMPs and ultimately reshaped TME to enhance immunotherapy efficacy in lymphoma. Combined with its good histocompatibility and facile preparation technique, this pH-responsive APP-Fe NCs with regulation on TME may hold potential for cascade amplification on the combinative immunotherapy of lymphoma in the clinic.

Structural insights into thrombolytic activity of destabilase from medicinal leech

Destabilase from the medical leech Hirudo medicinalis belongs to the family of i-type lysozymes. It has two different enzymatic activities: microbial cell walls destruction (muramidase activity), and dissolution of the stabilized fibrin (isopeptidase activity). Both activities are known to be inhibited by sodium chloride at near physiological concentrations, but the structural basis remains unknown. Here we present two crystal structures of destabilase, including a 1.1 Å-resolution structure in complex with sodium ion. Our structures reveal the location of sodium ion between Glu34/Asp46 residues, which were previously recognized as a glycosidase active site. While sodium coordination with these amino acids may explain inhibition of the muramidase activity, its influence on previously suggested Ser49/Lys58 isopeptidase activity dyad is unclear. We revise the Ser49/Lys58 hypothesis and compare sequences of i-type lysozymes with confirmed destabilase activity. We suggest that the general base for the isopeptidase activity is His112 rather than Lys58. pKa calculations of these amino acids, assessed through the 1 μs molecular dynamics simulation, confirm the hypothesis. Our findings highlight the ambiguity of destabilase catalytic residues identification and build foundations for further research of structure–activity relationship of isopeptidase activity as well as structure-based protein design for potential anticoagulant drug development.

Spectral, thermal, structural and DFT studies of new luminescent heterobimetallic MOF of lead and sodium based on diglycolic acid ligand having unusual coordination environment for photodegradation and antibacterial applications

Single crystals of a new bimetallic MOF of diglycolic acid ligand with different metals such as sodium and lead have been synthesized via the gel-diffusion method. The Single crystal X-ray diffraction studies revealed that an unusual coordination environment arises due to the mutual coordination of both sodium and lead metals. The grown crystals was further characterized by FTIR, PXRD, TG-DTG, BET, and Photoluminescence studies. DFT studies of the bimetallic MOF implies a high electrophilicity index (5.3148 eV) that predicts high biomolecular binding capacity of the molecule. The complex under study has a hardness value of 1.7645 eV, indicating that the material is hard. The simulated PXRD is in good agreement with the experimental PXRD pattern which confirms the structural integrity of crystals within the bulk. The antibacterial activity as well as the degradation property of the material towards methylene blue was also studied in detail. The photocatalytic degradation and biological studies suggest that the grown crystals are found to be an effective material for the degradation of organic pollutant methylene blue and can be used for antimicrobial applications.

Flexibility and Regularity of the Hydration Structures of Ions by an Example of Na+: Nonempirical Insight

The stationary nonempirical simulations of [Na(H2O)n]+ clusters with n in the range of 28-51 carried out at the density functional level with a hybrid B3LYP functional and the Born-Oppenheimer molecular dynamics modeling of the size-selected clusters reveal the interrelated structural and energetic peculiarities of the sodium ion hydration structures. Surface, bulk, and transient structures are distinguished by different locations of the sodium nucleus (close to either the spatial center of the structure or one of its side faces) and a consistently changing coordination number (which typically equals five or six). The differences and correlations between the stationary and averaged dynamically changing configurations are quantified. The ⟨rNaO⟩, mean Na-O distances for the first-shell water molecules, are found to depend both on the spatial character of the structure and the local coordination of sodium. The ⟨rNaO⟩ values are compared to different experimental estimates, and the virtual discrepancy of the latter is explained based on the results of cluster simulations. Different coordination neighborhoods of the sodium ion are predicted depending on its local fraction in actual specimens.

Co-Crystallization Kinetics of 2:1 Benzoic Acid–Sodium Benzoate Co-Crystal: The Effect of Templating Molecules in a Solution

The addition of dissolved templating molecules in crystallization will create “supramolecular assemblies” within the solution, serving as “anchor points” for the solute molecules to nucleate and grow. In this work, nucleation and crystal growth kinetics of 2:1 benzoic acid (HBz)–sodium benzoate (NaBz) co-crystallization with or without templates in a solution were analyzed by monitoring the concentration of the mother liquor during cooling crystallization. The results showed that the addition of the dissolved 2:1 or 1:1 HBz–NaBz co-crystals as templating molecules could reduce the critical free energy barrier of 2:1 HBz–NaBz co-crystal during its nucleation, but did not significantly affect the order of crystal growth rate. On the other hand, the critical free energy barrier of the nucleation process was increased if dissolved NaBz was used as a templating molecule, while a significant rise in the order of crystal growth rate occurred. The crystal habit obtained from the NaBz-templated system was needle-like, suggesting that sodium–sodium coordination chains of NaBz supramolecular assemblies in the solution phase were responsible for creating elongated crystals. Conversely, a large prismatic crystal habit found in non-templated and 2:1 and 1:1 HBz–NaBz co-crystal-templated systems implied that those templating molecules formed sparsely interconnected supramolecular assemblies in the solution phase.

Solid state structure of sodium β-1-thiophenyl glucuronate identifies 5-coordinate sodium with three independent glucoronates

Glucuronic acid is a key component of the glycosaminoglycans (GAGs) Chrondroitin Sulfate (CS), Heparin/Heparan sulfate (HS) and Hyaluronic Acid (HA), as well an important metabolite derivative. In biological systems the carboxylate of uronic acids in GAGs is involved in important H-binding interactions, and the role of metal coordination, such as sodiated systems, has indications associated with a number of biological effects, and physiological GAG-related processes. In synthetic approaches to GAG fragments, thioglycoside intermediates, or derivatives from these, are commonly employed. Of the reported examples of sodium coordination in carbohydrates, 6-coordinate systems are usually observed often with water ligands involved, Herein we report an unexpected 5-coordinate sodiated GlcA crystal structure of the parent GlcA, but as a thioglycoside derivative, whose crystal coordination differs from previous examples, with no involvement of water as a ligand and containing a distorted trigonal bypramidal sodium with each GlcA having five of 6 oxygens sodium-coordinated.

Sodium and lithium one-dimensional coordination polymers with 1H-indazole-3-carboxylic acid: Crystal structures, vibrational spectra and DFT calculations

Sodium(I) and lithium(I) one-dimensional coordination polymers, [Na(IND3CAH)(IND3CAH2)]n (1) and [Li(IND3CAH)(H2O)]n (2), with 1H-indazole-3-carboxylic acid (IND3CAH2) have been synthesized and investigated by a single crystal X-ray diffraction and vibrational spectroscopy. In compound 1, both the O-deprotonated (IND3CAH−) and neutral (IND3CAH2) forms of the acid act as the tridentate ligands and are bound with Na+ via two oxygen atoms and the 1H-indazole nitrogen atom forming polymeric chains. Each Na+ ion is six-coordinate in a distorted octahedral geometry (NaO4N2). In compound 2, the Li+ ion is five-coordinate (LiO4N) and the coordination sphere is intermediate between square-pyramid and trigonal-bipyramid. The deprotonated IND3CAH− ion acts as the bidentate ligand coordinated to Li+ ion via one carboxylate oxygen atom and the 1H-indazole nitrogen atom. In contrast to 1, the carboxylate group exhibits the monoatomic bridging mode. In addition, the oxygen atom of the water molecule also links two adjacent Li+ ions. The bridging ligands lead to the formation of polymeric ribbons of edge-sharing O4N distorted pyramids. Intermolecular NH⋯O and OH⋯O hydrogen bonds have a distinctive effect on crystal packing of the title compounds. The IR and Raman spectra of 1 and 2 in the solid state confirm the results from X-ray analysis. Vibrational spectra of the ligand IND3CAH2 and its deuterated derivative (IND3CAD2) have been measured and assigned based on DFT calculations.

The Effects of Alkaline Earth Metals on the Structure of Sodium Borosilicate Glasses: <sup>11</sup>B and <sup>29</sup>Si NMR Study

The effect of substitution of alkaline earth metals for sodium on the structure of alkali borosilicate glasses had been studied using the solid-state 11B and 29Si NMR spectroscopy. NMR spectra enable to evaluate the relative mole fractions of different silicon and boron structural units in studied samples. The obtained results demonstrate that alkaline earth metals increase the polymerization degree of the silicon structural units at the expense of de-polymerization of the boron units. The reason for these changes is preferential coordination of sodium and alkaline earth metals to the boron units, that increases strongly for the studied alkaline earth metals.

Sodium Coordination and Protonation of Poly(ethoxy phosphate) Chains in the Gas Phase Probed by Ion Mobility-Mass Spectrometry.

The two-dimensional shape information yielded by ion mobility-mass spectrometry (IM-MS), usually reported as collision cross section (CCS), is often correlated to the underlying three-dimensional structures of the ions through computational chemistry. Here, we used theoretical approaches based on molecular mechanics (MM), molecular dynamics (MD), and density functional theory (DFT) to elucidate the structures of sodiated poly(ethoxy phosphate) polymer ions at different degrees of polymerization (DP) for three different charge states (1+, 2+, and 3+) by comparing computational results to experimentally obtained CCS values. From the calculated structures, we extract several key interaction distances which merge in clusters for all screened charge states and DPs, independent of the three-dimensional structures and the polymer ion structural rearrangements. These distances were also used to extract the minimum coordination numbers in poly(ethoxy phosphate) and to describe the preferred coordination geometries. When sodiated and protonated polymer ions are compared, the experimental CCS evolutions differ at small DP values and merge at higher DPs. We investigated in more depth this difference for two selected species, namely, [PEtP5 + 2Na+]2+ and [PEtP5 + 2H+]2+. For the protonated ions, we explored the different protonation sites to extract three-dimensional structure candidates and rationalize the CCS behaviors.

Solid–solid and solid–liquid conversion of sodium and silver nano coordination polymers

Solid-state conversion of a three-dimensional sodium coordination polymer [Na(μ6-HTar)]n (1), (H2Tar = (+)‐tartaric acid), synthesized by a sonochemical procedure, to a two-dimensional silver coordination polymer [Ag(μ3-HTar)(H2O)]n (2) has been observed upon mechanochemical cation exchange reaction of 1 with AgNO3. The conversion of 2 to 1 via solid-state reaction has also been investigated. These samples were characterized by IR spectroscopy, X‐ray powder diffraction (XRD), thermo gravimetric and differential thermal analyses (TG-DTA), Energy-dispersive X-ray spectroscopy (EDAX) and Scanning Electron Microscopy (SEM). It was observed that the conversion of compound 1 to compound 2 is irreversible. In addition it was confirmed that [Ag(μ3-HTar)(H2O)]n (2) converted to [Ag2(HTar)]n (3) during solid–liquid reaction in water.

Ionic radii of hydrated sodium cation from QTAIM.

The sodium cation is ubiquitous in aqueous chemistry and biological systems. Yet, in spite of numerous studies, the (average) distance between the sodium cation and its water ligands, and the corresponding ionic radii, are still controversial. Recent experimental values in solution are notably smaller than those from previous X-ray studies and ab initio molecular dynamics. Here we adopt a "bottom-up" approach of obtaining these distances from quantum chemistry calculations [full MP2 with the 6-31++G(d,p) and cc-pVTZ basis-sets] of gas-phase Na+(H2O)n clusters, as a function of the sodium coordination number (CN = 2-6). The bulk limit is obtained by the polarizable continuum model, which acts to increase the interatomic distances at small CN, but has a diminishing effect as the CN increases. This extends the CN dependence of the sodium-water distances from crystal structures (CN = 4-12) to lower CN values, revealing a switch between two power laws, having a small exponent at small CNs and a larger one at large CNs. We utilize Bader's theory of atoms in molecules to bisect the Na+-O distances into Na+ and water radii. Contrary to common wisdom, the water radius is not constant, decreasing even more than that of Na+ as the CN decreases. We also find that the electron density at the bond critical point increases exponentially as the sodium radius decreases.

Coordination polymers from dithiolato complexes and alkali metal cations: How a crystallizing and coordinating solvent influences the dimensionality

This article describes the influence of different solvents on the versatility of coordination-networks, formed from alkali metal coordination complex and transition metal bis(dithiolato) complex [M(btdt)2]1− (M = Cu(III) and Au(III); btdt = 2,1,3-benzenethiadiazole-5,6-dithiolate) in compounds 1–7: {[Na(CH3OH)4][Cu(btdt)2]}n (1), {[Na(THF)4][Cu(btdt)2]}n (2), {[Na(CH3COCH3)2][Cu(btdt)2]}n (3), {[Na(DMF)2][Cu(btdt)2]}n (4), {[Na(CH3CN)2][Cu(btdt)2]}n (5) {[Na(THF)2][Na(THF)(OH2)] [Au2(btdt)4]}n (6) and {[Na(CH3COCH3)2][Au(btdt)2]}n (7). The coordination polymers 1–5, based on copper(III)-bis(dithiolene) complex [CuIII(btdt)2]1−, are synthesized by the recrystallization of a dark-brown coloured precipitated precursor (P1) having a black appearance from the different solvents. The precursor P1 was obtained by the reaction of one mole equivalent of CuCl2·2H2O with two mole equivalents of H2btdt in MeOH, treated with an excess amount of NaOH in an open air atmosphere. For the preparation of compounds 6 and 7, AuCl3·2H2O was treated with H2btdt in MeOH containing NaOH to obtain precipitated precursor P2, which was recrystallized from THF and acetone to produce single crystals of 6 and 7 respectively. In the crystal structures of coordination polymers 1–7, where sodium coordination complex is a cationic component, the dimensionality of the networks of the resulting coordination polymers has greatly been influenced by the nature of hybridization of central carbon atom of the sodium-coordinated solvent, which happens to be the recrystallizing solvent. In order to investigate the influence of the counter cation on the structural diversity and dimensionality, we have compared the supramolecular chemistry of these sodium metal based coordination polymers 1–7 with that of our previously reported potassium-based coordination polymers {[K(CH3COCH3)3][Cu(btdt)2]}n and {[K(CH3CN)2][Cu(btdt)2]}n. All these compounds have been characterized unambiguously by single crystal X-ray crystallography and routine spectroscopy (IR, UV-visible and NMR). Interestingly, copper compounds 1 and 3–5 exhibit two quasi-reversible reduction responses at −0.13 V and −1.10 V vs Ag/AgCl respectively in DMF solutions.

Both reentrant loops of the sodium-coupled glutamate transporters contain molecular determinants of cation selectivity

In the brain, glutamate transporters terminate excitatory neurotransmission by removing this neurotransmitter from the synapse via cotransport with three sodium ions into the surrounding cells. Structural studies have identified the binding sites of the three sodium ions in glutamate transporters. The residue side-chains directly interact with the sodium ions at the Na1 and Na3 sites and are fully conserved from archaeal to eukaryotic glutamate transporters. The Na2 site is formed by three main-chain oxygens on the extracellular reentrant hairpin loop HP2 and one on transmembrane helix 7. A glycine residue on HP2 is located closely to the three main-chain oxygens in all glutamate transporters, except for the astroglial transporter GLT-1, which has a serine residue at that position. Unlike for WT GLT-1, substitution of the serine residue to glycine enables sustained glutamate transport also when sodium is replaced by lithium. Here, using functional and simulation studies, we studied the role of this serine/glycine switch on cation selectivity of substrate transport. Our results indicate that the side-chain oxygen of the serine residues can form a hydrogen bond with a main-chain oxygen on transmembrane helix 7. This leads to an expansion of the Na2 site such that water can participate in sodium coordination at Na2. Furthermore, we found other molecular determinants of cation selectivity on the nearby HP1 loop. We conclude that subtle changes in the composition of the two reentrant hairpin loops determine the cation specificity of acidic amino acid transport by glutamate transporters.

Insights into the Structure and Transport of the Lithium, Sodium, Magnesium, and Zinc Bis(trifluoromethansulfonyl)imide Salts in Ionic Liquids

Details of the lithium (Li+), sodium (Na+), magnesium (Mg2+), and zinc (Zn2+) cation coordination and electrolyte transport properties are examined using molecular dynamics (MD) simulations for the N-butyl-N-methylpyrrolidinium bis(trifluoromethansulfonyl)imide (pyr14TFSI) ionic liquid (IL) doped with LiTFSI, NaTFSI, Mg(TFSI)2, and Zn(TFSI)2 salts. MD simulations are performed as a function of temperature using a polarizable force field (APPLE&P) that yields the Li+, Na+, Mg2+, and Zn2+ cation binding energies to the TFSI– anions in excellent agreement with quantum chemistry results. At 333 K, 4.7–4.8 TFSI– oxygen atoms from approximately three TFSI– anions coordinate Li+ and Na+, while Zn2+ and Mg2+ cations are instead coordinated by approximately six TFSI– oxygen atoms. Significant Na+ coordination with the fluorine atoms of the TFSI– anions is observed, unlike for Li+, Mg2+ and Zn2+. The cation–TFSI– binding motifs and the propensity of the salts to form large aggregates are temperature dependent with ...