Is "Water in Salt" Electrolytes the Ultimate Solution? Achieving High Stability of Organic Anodes in Diluted Electrolyte Solutions Via a Wise Anions Selection.

The introduction of the water-in-salt (WIS) electrolytes concept to prevent water splitting and widen the electrochemical stability window, has spurred extensive research efforts toward development of improved aqueous batteries. The successful implementation of these electrolyte solutions in many electrochemical systems shifts the focus from diluted to WIS electrolyte solutions. Considering the high costs and the tendency of these nearly saturated solutions to crystallize, this trend can be carefully re-evaluated. Herein we show that the stability of organic electrodes comprising the active material perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), is strongly influenced by the solvation character of the anions rather than the concentration of the electrolyte solution. Even though the charging process of PTCDA involves solely insertion of cations (i.e., principal counter-ions), surprisingly, the dominant factor influencing its electrochemical performance, including long-term electrode stability, is the type of the co-ions (i.e., electrolytic anions). Using systematic electrochemical analysis combined with theoretical simulations, we show that the selection of kosmotropic anions results in fast fading of the PTCDA anodes, while a selection of chaotropic anions leads to excellent stability, even at electrolytes concentrations as low as 0.2 M. These findings provide a new conceptual approach for designing advanced electrolyte solutions for aqueous batteries.

Non-Globular Organic Ionic Plastic Crystal Containing a Crown-Ether Moiety - Tuning Its Behaviour Using Sodium Salts.

Organic ionic plastic crystals (OIPCs) are a class of soft materials showing positional order while still allowing orientational freedom. Due to their motional freedom in the solid state, they possess plasticity, non-flammability and high ionic conductivity. OIPC behavior is typically exhibited by 'simple' globular molecules allowing molecular rotation, whereas the interactions that govern the formation of OIPC phases in complex non-globular molecules are less understood. To better understand these interactions, a new family of non-globular OIPCs containing a 15-crown-5 ether moiety was synthetized and characterized. The 15C5BA molecule prepared does not exhibit the sought-after behavior because of its non-globular nature and strong intermolecular H-bonds that restrict orientational motion. However, the OIPC behavior was successfully obtained through complexation of the crown-ether moiety with sodium salts containing chaotropic anions. Those anions weaken the interactions between the molecules, allowing rotational freedom and tuning of the thermal and morphological properties of the OIPC.

Antifreezing Hydrogel Electrolyte with Ternary Hydrogen Bonding for High-Performance Zinc-Ion Batteries.

The new-generation flexible aqueous zinc-ion batteries require enhanced mechanical properties and ionic conductivities at low temperature for practical applications. This fundamentally means that it is desired that the hydrogel electrolyte possesses antifreezing merits to resist flexibility loss and performance decrease at subzero temperatures. Herein, a highly flexible polysaccharide hydrogel is realized in situ and is regulated in zinc-ion batteries through the Hofmeister effect with low-concentration Zn(ClO4 )2 salts to satisfy the abovementioned requirements. The chaotropic ClO4 - anions, water, and polymer chains can form ternary and weak hydrogen bonding (HB), which enables the polymer chains to have improved mechanical properties, breaks the HB of water to remarkably decrease the electrolyte freezing point, and reduces the amounts of free water for effective side reactions and dendrite inhibition. Consequently, even at -30 °C, the Zn(ClO4 )2 in situ optimized hydrogel electrolyte features a high ionic conductivity of 7.8 mS cm-1 and excellent flexibility, which enables a Zn/polyaniline (PANI) battery with a reversible capacity of 70 mA h g-1 under 5 A g-1 for 2500 cycles, and renderd the flexible full battery with excellent cycling performances under different bending angles. This work provides a new pathway for designing high-performance antifreezing flexible batteries via the Hofmeister effect.

Chaotropic salts impact in HPLC approaches for simultaneous analysis of hydrophilic and lipophilic drugs.

Simultaneous determination of drugs with different physicochemical properties necessitates thorough research and careful selection of high-performance liquid chromatography conditions. In the present study, various concepts of high-performance liquid chromatography method development for this aim have been discussed. Moreover, the work was motivated by the advantages of utilizing different chaotropic anions as a new promising approach to overcome the limitations of ion-pairing agents commonly used for this purpose. Based on log P values, atorvastatin (log P = 6.36) and lisinopril (log P = -1.22) were chosen as representative examples for lipophilic and hydrophilic drugs, respectively. Several simple, economic, fast, and reliable high-performance liquid chromatography methods were developed for their simultaneous analysis and are presented in a comparative manner, highlighting their advantages and limitations. Peak elution profile showed satisfying retentions and resolution about 3. Photo-diode array calculations were exploited for identifying the molecules by their ultra-violet spectra and peak purity, calculated and presented as rectangular-shaped ratio grams. The linearity check showed excellent results and satisfactory system suitability parameters of both peaks. This confirms the investigation results and conclusions for the influence of the chaotropic salts on N-containing molecules, by increasing their retentivities, and improving peak shapes, even on different quality columns without end-capping and base-deactivating of separation matrixes.

Structure-Activity Relationships for the Affinity of Chaotropic Polyoxometalate Anions towards Proteins.

The influence of the composition of chaotropic polyoxometalate (POM) anions on their affinity to biological systems was studied by means of atomistic molecular dynamics (MD) simulations. The variations in the affinity to hen egg-white lysozyme (HEWL) were analyzed along two series of POMs whereby the charge or the size and shape of the metal cluster are modified systematically. Our simulations revealed a quadratic relationship between the charge of the POM and its affinity to HEWL as a consequence of the parabolic growth of POM⋅⋅⋅water interaction with the charge. As the charge increases, POMs become less chaotropic (more kosmotropic) increasing the number and the strength of POM-water hydrogen bonds and structuring the solvation shell around the POM. This atomistic description explains the proportionally larger desolvation energies and less protein affinity for highly charged POMs, and consequently, the preference for moderate charge densities (q/M=0.33). Also, our simulations suggest that POM⋅⋅⋅protein interactions are size-specific. The cationic pockets of HEWL protein show a preference for Keggin-like structures, which display the optimal dimensions (≈1 nm). Finally, we developed a quantitative multidimensional model for protein affinity with predictive ability (r2 =0.97; q2 =0.88) using two molecular descriptors that account for the charge density (charge per metal atom ratio; q/M) and the size and shape (shape weighted-volume; VS ).

Theoretical Considerations and the Microelectrophoresis Experiment on the Influence of Selected Chaotropic Anions on Phosphatidylcholine Membrane Surface Charge Density.

Influence of sodium salts of selected chaotropic anions from the Hofmeister series (NaCl, NaBr, NaNO3, NaI) on the surface charge density of phosphatidylcholine membranes was studied. Small unilamellar lipid vesicles were used as a model system in the investigations. The theoretical and experimental approach to the interactions between inorganic anions and phosphatidylcholine membranes is presented. Experimental membrane surface charge densities data were determined as a function of pH of the aqueous electrolytes using microelectrophoresis method. The quantitative description of the interactions between zwitterionic phosphatidylcholine membrane and monovalent anions is presented. The equilibria constants of the binding of solution ions onto phospholipid surface were calculated. Knowledge of these parameters was essential to determine the theoretical membrane surface charge density values. The theoretical data were compared to the experimental ones in order to verify the mathematical model. Both approaches indicate that the anion-phosphatidylcholine membrane interaction increases with the size of the anion. The adsorption of chaotropic anions to membranes was found to follow the Hofmeister series I- > NO3- > Br- > Cl-.

Effects of lyotropic anions on thermodynamic stability and dynamics of horse cytochrome c.

This paper evaluates the effect of various lyotropic anions (chloride, sulfate, perchlorate, iodide, nitrate, bromide) on the thermodynamic stability and dynamics of native cytochrome c (Cyt c) at pH 7.0. The results of equilibrium and kinetic studies revealed that: (i) at low to intermediate concentrations (≤ 0.5 M), both chaotropic and kosmotropic anions restrict the dynamics of native protein, (ii) at relatively higher concentrations (≥ 1.0 M), the denaturing effect of chaotropic anions dominates, which increases the level of structural-fluctuations responsible to unfold the protein according to Hofmeister series (perchlorate > iodide > nitrate > bromide), and (iii) the lyotropic anions affect the thermal and global stability of Cyt c according to Hofmeister series. The m-value was determined from ΔΔG vs [Cosolute] plot and was found to be positive for sulfate and negative for other anions consistent with effect of lyotopic anions on protein stability according to Hofmeister series.

A structural model for facultative anion channels in an oligomeric membrane protein: the yeast TRK (K(+)) system.

TRK transporters, a class of proteins which generally carry out the bulk of K(+) accumulation in plants, fungi, and bacteria, mediate ion currents driven by the large membrane voltages (-150 to -250 mV) common to non-animal cells. Bacterial TRK proteins resemble K(+) channels in their primary sequence, crystallize as membrane dimers having intramolecular K(+)-channel-like folding, and complex with a cytoplasmic collar formed of four RCK domains (Nature 471:336, 2011; Ibid 496:324, 2013). Fungal TRK proteins appear simpler in form than the bacterial members, but do possess two special features: a large built-in regulatory domain, and a highly conserved pair of transmembrane helices (TM7 and TM8, ahead of the C-terminus), which were postulated to facilitate intramembranal oligomerization (Biophys. J. 77:789, 1999; FEMS Yeast Res. 9:278, 2009). A surprising associated functional process in the fungal proteins which have been explored (Saccharomyces, Candida, and Neurospora) is facilitation of channel-like chloride efflux. That process is suppressed by osmoprotective agents, appears to involve hydrophobic gating, and strongly resembles conduction by Cys-loop ligand-gated anion channels. And it leads to a rather general hypothesis: that the thermodynamic tendency for hydrophobic or amphipathic transmembrane helices to self-organize into oligomers can create novel ionic pathways through biological membranes: fundamental hydrophobic nanopores, pathways of low selectivity governed by the chaotropic behavior of individual ionic species and under the strong influence of membrane voltage.

Chaotropic Anions Strongly Stabilize Short, N-Capped Uncharged Peptide Helicies: A New Look at the Perchlorate Effect.

Regiospecific binding of perchlorate ions to the N-terminus of short-chained template-substituted polyalanine sequences in water dramatically increases helicity.