Alkali metal ion selectivity of the hemocyanin channel

Summary The selectivity of the hemocyanin channel was measured for alkali metal ions and ammonium. Permeability ratios relative to K⁺ measured from biionic potentials were: NH ₄ ⁺ (1.52)>Rb⁺ (1.05)>K⁺ (1.0)>Cs⁺ (0.89)>Na⁺ (0.81)>Li⁺ (0.35). Single-channel ion conductance was a saturating function of ion concentration regardless of the cation present in the bathing medium. Maximal conductances were 270, 267, 215, 176, 170 and 37 ps for K⁺, Rb⁺, NH ₄ ⁺ , Cs⁺, Na⁺ and Li⁺, respectively. Current-voltage curves for the different monovalent cations were measured and described using a threebarrier model previously used to explain the voltage dependence of the instantaneous channel conductance (Cecchi, Alvarez & Latorre, 1981). In this way, binding and peak energies were estimated for the different ions. Considering the energy peaks as transition states between the ion and the channel, it is concluded that they follow Eisenman's selectivity sequences XI (cis peak, i.e., Li⁺>Na⁺>K⁺>Rb⁺>Cs⁺; highest field strength), VII (central peak) and II (trans peak). The cis side was that to which hemocyanin was added and was electrically ground. The binding energies, on the other hand, follow Eisenman's series XI for strong electric field sites. Binding of NH ₄ ⁺ to the cis-well suggests that the orientation of the ligands in the site is tetrahedric.     

Structural Changes in Li2MnO3 Cathode Material for Li‐Ion Batteries

Structural changes in Li₂MnO₃ cathode material for rechargeable Li‐ion batteries are investigated during the first and 33^rd cycles. It is found that both the participation of oxygen anions in redox processes and Li⁺‐H⁺ exchange play an important role in the electrochemistry of Li₂MnO₃. During activation, oxygen removal from the material along with Li gives rise to the formation of a layered MnO₂‐type structure, while the presence of protons in the interslab region, as a result of electrolyte oxidation and Li⁺‐H⁺ exchange, alters the stacking sequence of oxygen layers. Li re‐insertion by exchanging already present protons reverts the stacking sequence of oxygen layers. The re‐lithiated structure closely resembles the parent Li₂MnO₃, except that it contains less Li and O. Mn⁴⁺ ions remain electrochemically inactive at all times. Irreversible oxygen release occurs only during activation of the material in the first cycle. During subsequent cycles, electrochemical processes seem to involve unusual redox processes of oxygen anions of active material along with the repetitive, irreversible oxidation of electrolyte species. The deteriorating electrochemical performance of Li₂MnO₃ upon cycling is attributed to the structural degradation caused by repetitive shearing of oxygen layers.     

Energy distribution and ion selectivity of the bacterial potassium channel

The ion selectivity of the bacterial potassium channel K_CSA is explained upon comparing the energy characteristics of the interaction of cations (Li⁺, Na⁺, K⁺) with atoms of the selectivity filter of the protein pore. Quantum-chemical calculations reveal a deeper potential well for potassium ions, which accounts for preferred K⁺ permeation. It is shown that the conventional methods with AMBER, CHARMM, OPLS force fields in standard parametrization as well as partial re-parametrization give incorrect estimates of ion energy distribution in the channel.     

Possible existence of ion pairs at the mouths of ion channels

An electrostatic calculation suggests that when an ion is bound near the mouth of a channel penetrating a low-dielectric membrane, a counter ion may form an ion pair with this ion. The tendency towards ion-pair formation is remarkably enhanced at channel mouths by forces (image forces) arising from the charges induced on the boundaries between different dielectrics. The binding constant for the formation of ion-pairs of monovalent ions is estimated under the assumption that local interactions between the counter ion and the channel wall are negligibly small. It is of the order of 1–10 molal^?1 or more for the binding of a Cl^? (F^?) counter ion to an $\text{Na}{}^{\mathrm{+}}$ ($\text{Li}{}^{\mathrm{+}}$) ion if appropriate conditions are fulfilled. The binding constant depends on the position of the binding site, the dimensions and geometries of the channel and channel mouth, and the state of ion loading of the channel, as well as the ionic species. The present results also indicate that when cation (anion) channels have anionic (cationic) groups as integrant parts of their channel walls, interactions between these charged groups and permeant ions are markedly enhanced by the image forces.     

Toward a Reversible Calcium‐Sulfur Battery with a Lithium‐Ion Mediation Approach

Calcium represents a promising anode for the development of high‐energy‐density, low‐cost batteries. However, a lack of suitable electrolytes has restricted the development of rechargeable batteries with a Ca anode. Furthermore, to achieve a high energy density system, sulfur would be an ideal cathode to couple with the Ca anode. Unfortunately, a reversible calcium‐sulfur (Ca‐S) battery has not yet been reported. Herein, a basic study of a reversible nonaqueous room‐temperature Ca‐S battery is presented. The reversibility of the Ca‐S chemistry and high utilization of the sulfur cathode are enabled by employing a Li⁺‐ion‐mediated calcium‐based electrolyte. Mechanistic insights pursued by spectroscopic, electrochemical, microscopic, and theoretical simulation (density functional theory) investigations imply that the Li⁺‐ions in the Ca‐electrolyte stimulate the reactivation of polysulfide/sulfide species. The coordination of lithium to sulfur reduces the formation of sturdy Ca‐S ionic bonds, thus boosting the reversibility of the Ca‐S chemistry. In addition, the presence of Li⁺‐ions facilitates the ionic charge transfer both in the electrolyte and across the solid electrolyte interphase layer, consequently reducing the interfacial and bulk impedance of Ca‐S batteries. As a result, both the utilization of active sulfur in the cathode and the discharge voltage of Ca‐S batteries are significantly improved.     

An Anion‐Tuned Solid Electrolyte Interphase with Fast Ion Transfer Kinetics for Stable Lithium Anodes

The spatial distribution and transport characteristics of lithium ions (Li⁺) in the electrochemical interface region of a lithium anode in a lithium ion battery directly determine Li⁺ deposition behavior. The regulation of the Li⁺ solvation sheath on the solid electrolyte interphase (SEI) by electrolyte chemistry is key but challenging. Here, 1 m lithium trifluoroacetate (LiTFA) is induced to the electrolyte to regulate the Li⁺ solvation sheath, which significantly suppresses Li dendrite formation and enables a high Coulombic efficiency of 98.8% over 500 cycles. With its strong coordination between the carbonyl groups (C?O) and Li⁺, TFA^? modulates the environment of the Li⁺ solvation sheath and facilitates fast desolvation kinetics. In addition, due to relatively smaller lowest unoccupied molecular orbital energy than solvents, TFA^? has a preferential reduction to produce a stable SEI with uniform distribution of LiF and Li₂O. Such stable SEI effectively reduces the energy barrier for Li⁺ diffusion, contributing to low nucleation overpotential, fast ion transfer kinetics, and uniform Li⁺ deposition with high cycling stability. This work provides an alternative insight into the design of interface chemistry in terms of regulating anions in the Li⁺ solvation sheath. It is anticipated that this anion‐tuned strategy will pave the way to construct stable SEIs for other battery systems.     

A fluorescent aptasensor for potassium ion detection-based triple-helix molecular switch

Here, a biosensor based on a quadruplex-forming aptamer for the determination of potassium ion (K⁺) is presented. The aptamer was used as a molecular recognition element; it was adjacent to two arm fragments and a dual-labeled oligonucleotide serving as a signal transduction probe (STP) that is complementary of the arm fragment sequence. In the presence of K⁺, the aptamer was displaced from the STP, which was accompanied by decreased signal. The quenching percentage of fluorescence intensity was proportional to the concentration of K⁺ in the range of 0.05 to 1.4 mM. A detection limit of 0.014 mM was achieved. Furthermore, other metal ions, such as Na⁺, Li⁺, NH₄⁺, Mg²⁺, and Ca²⁺, caused no notable interference on the detection of K⁺.     

Properties of ion channels in the protoplasts of the Mediterranean seagrass Posidonia oceanica

Posidonia oceanica (L) Delile, a seagrass endemic of the Mediterranean sea, provides food and shelter to marine organisms. As environment contamination and variation in physico‐chemical parameters may compromise the survival of the few Posidonia genotypes living in the Mediterranean, comprehending the molecular mechanisms controlling Posidonia growth and development is increasingly important. In the present study the properties of ion channels in P. oceanica plasma membranes studied by the patch‐clamp technique in protoplasts obtained from the young non‐photosynthetic leaves were investigated. In protoplasts that were presumably originated from sheath cells surrounding the vascular bundles of the leaves, an outward‐rectifying time‐dependent channel with a single channel conductance of 58 ± 2 pS which did not inactivate, was selective for potassium and impermeable to monovalent cations such as Na⁺, Li⁺ and Cs⁺ was identified. In the same protoplasts, an inward‐rectifying channel that has a time‐dependent component with single channel conductance of the order of 10 pS, a marked selectivity for potassium and no permeation to sodium was also identified, as was a third type of channel that did not display any ionic selectivity and was reversibly inhibited by tetraethylammonium and lanthanum. A comparison of Posidonia channel characteristics with channels identified in terrestrial plants and other halophytic plants is included.     

Synthesis and properties of crown ether isocyanide silver(I) derivatives: X-ray structure of a self-assembled 22-membered diargentacycle

The crown ether isocyanide CNR (R = benzo-15-crown-5) reacts with silver(I) salts in the appropriate molar ratio to give [Ag(CNR)_n]X (n = 1, 2; X = CF₃SO₃, BF₄). X-ray diffraction studies of [Ag(CF₃SO₃)(CNR)] show the molecules associated in a dinuclear manner with an antiparallel orientation. The silver centers are tetracoordinated to the isocyanide and to three oxygens, one from the triflate anion and two from the second crown ether in the dimer. The molecular structure displays five cycles: the two 15-crown ether rings, two five-membered argentacycles and a 22-membered diargentacycle. The crown ether in these complexes is able to detect alkaline cations from M(CF₃SO₃) (M = Li, Na, K) by NMR in d₆-acetone solutions, and to distinguish Li⁺-Na⁺ from K⁺.     

Experimental search for combined AC and DC magnetic field effects on ion channels

The hypothesis that specific combinations of DC and low frequency AC magnetic fields at so-called cyclotron-resonance conditions could affect the transport of ions through ion channels, or alter the kinetics of ion channels (opening and closing rates), has been tested. As a model system, the ion channels formed by gramicidin A incorporated in lipid bilayer membranes were studied. No significant changes in channel conductance, average lifetime, or formation rate as a function of applied fields could be detected over a wide range of frequencies and field strengths. Experiments were carried out to measure the time-resolved single-channel events and the average conductances of many-channel events in the presence of K⁺ and H⁺ ions. The channel blocking effect of Ca⁺⁺ was also studied. © 1993 Wiley-Liss. Inc.     

A study of Li+-selective permeation through lipid bilayer membranes mediated by a new ionophore (AS701)

The neutral, noncyclic, imide and ether containing ionophore AS701, has been developed as Li⁺-selective molecule, to be used potentially as an aid in the Li⁺-therapy of manic-depressive illness. The present report is a characterization of this molecule in neutral lipid bilayer membranes. This ionophore was found to the bilayers Li⁺-selective, acting as a selective carrier of monovalent cations. In addition, this molecule was found to be capable of acting as a selective carrier of monovalent anions. For both types of ions, the rate-limitting step in the process of permeation was found to be the diffusion of the carrier-ion complex through the membrane. The membrane-permeating species were found to be 2 : 1 carrier-ion complexes, carrying either a monovalent cation or a monovalent anion. The selectivity sequences among the ions studied being: Li⁺(1) > ClO₄^?(0.7) > Na⁺(0.07) > K⁺(0.016) > Rb⁺(0.0095) > Cs⁺(0.0083) > Cl^?(0.001). Mg²⁺ and SO₄^2? were found to be impermeant (under present experimental conditions). This sequence shows that the AS701 molecule has low selectivity for ions present in biological media, among those studied (i.e. Na⁺, K⁺, Mg²⁺, Cl^2? and SO₄^2?). This indicates that these ions will not interfere in the Li⁺ permeability induced by this carrier in vivo, and that the carrier will not interfere in the normal transport processes of these ions.     

Ion Conduction through C-Type Inactivated Shaker Channels

C-type inactivation of Shaker potassium channels involves entry into a state (or states) in which the inactivated channels appear nonconducting in physiological solutions. However, when Shaker channels, from which fast N-type inactivation has been removed by NH₂-terminal deletions, are expressed in Xenopus oocytes and evaluated in inside-out patches, complete removal of K⁺ ions from the internal solution exposes conduction of Na⁺ and Li⁺ in C-type inactivated conformational states. The present paper uses this observation to investigate the properties of ion conduction through C-type inactivated channel states, and demonstrates that both activation and deactivation can occur in C-type states, although with slower than normal kinetics. Channels in the C-type states appear “inactivated” (i.e., nonconducting) in physiological solutions due to the summation of two separate effects: first, internal K⁺ ions prevent Na⁺ ions from permeating through the channel; second, C-type inactivation greatly reduces the permeability of K⁺ relative to the permeability of Na⁺, thus altering the ion selectivity of the channel.     

Li3N as a Cathode Additive for High‐Energy‐Density Lithium‐Ion Batteries

The formation of a solid‐electrolyte interphase on the anode surface of an Li‐ion battery using an organic liquid electrolyte robs Li⁺ irreversibly form the cathode on the initial charge if the cells are fabricated in the discharged state. In order to increase the cathode capacity, the use of Li₃N as a sacrificial source of Li⁺ on the initial charge has been evaluated chemically and electrochemically as an additive to an LiCoO₂ cathode. Li₃N is shown to be chemically stable in a dry atmosphere as small particles with fresh surfaces and can increase the reversible capacities of a full cell without compromising the rate capability of the cells.     

The cardiac ryanodine receptor: Looking for anomalies in permeation properties

Anomalies in the permeation properties of the cardiac RyR channel reconstituted into bilayer lipid membranes were investigated systematically. We tested the presence of the anomalous mole fraction effect (AMFE) for the ion conductance and the reversal potential with varying mole fractions of two permeant ions, while the total ion concentration was lower, as in previous studies, to avoid the masking effect of the channel pore saturation with ions. Mixtures of Ba²⁺ with other divalents (Ca²⁺, Sr²⁺), of Ca²⁺ with monovalents (Li⁺, Cs⁺), and of Na⁺ with other monovalents (Cs⁺, Li⁺) were used. We revealed a clear anomaly only for the ion conductance measured in the Na⁺-Cs⁺ and Ca²⁺-Li⁺ mixtures as computed by a Poisson-Nernst-Planck/density functional theory (PNP/DFT) model. Furthermore, we found a significant minimum in the concentration dependence of the reversal potential determined under Li⁺/Ca²⁺ bi-ionic conditions. Our study led to new observations that may have important implications for understanding the mechanisms involved in ion handling in the RyR channel pore; furthermore our results could be useful for further validation of ion permeation models developed for the RyR channel.     

Ion behavior in the selectivity filter of HCN1 channels

Hyperpolarization-activated cyclic-nucleotide gated channels (HCNs) are responsible for the generation of pacemaker currents (I_f or I_h) in cardiac and neuronal cells. Despite the overall structural similarity to voltage-gated potassium (Kv) channels, HCNs show much lower selectivity for K⁺ over Na⁺ ions. This increased permeability to Na⁺ is critical to their role in membrane depolarization. HCNs can also select between Na⁺ and Li⁺ ions. Here, we investigate the unique ion selectivity properties of HCNs using molecular-dynamics simulations. Our simulations suggest that the HCN1 pore is flexible and dilated compared with Kv channels with only one stable ion binding site within the selectivity filter. We also observe that ion coordination and hydration differ within the HCN1 selectivity filter compared with those in Kv and cyclic-nucleotide gated channels. Additionally, the C358T mutation further stabilizes the symmetry of the binding site and provides a more fit space for ion coordination, particularly for Li⁺.     

Molecular basis of ion permeability in a voltage‐gated sodium channel

Voltage‐gated sodium channels are essential for electrical signalling across cell membranes. They exhibit strong selectivities for sodium ions over other cations, enabling the finely tuned cascade of events associated with action potentials. This paper describes the ion permeability characteristics and the crystal structure of a prokaryotic sodium channel, showing for the first time the detailed locations of sodium ions in the selectivity filter of a sodium channel. Electrostatic calculations based on the structure are consistent with the relative cation permeability ratios (Na⁺ ≈ Li⁺ ≫ K⁺, Ca²⁺, Mg²⁺) measured for these channels. In an E178D selectivity filter mutant constructed to have altered ion selectivities, the sodium ion binding site nearest the extracellular side is missing. Unlike potassium ions in potassium channels, the sodium ions in these channels appear to be hydrated and are associated with side chains of the selectivity filter residues, rather than polypeptide backbones.     

A Hybrid Mg2+/Li+ Battery Based on Interlayer‐Expanded MoS2/Graphene Cathode

The hybrid Mg²⁺/Li⁺ battery (MLIB) is a very promising energy storage technology that combines the advantage of the Li and Mg electrochemistry. However, previous research has shown that the battery performance is limited due to the strong dependence on the Li content in the dual Mg²⁺/Li⁺ electrolyte. This limitation can be circumvented by significantly improving the diffusion kinetics of Mg²⁺ in the electrode, so that both Li⁺ and Mg²⁺ ions can be utilized as charge carriers. Herein, a free‐standing interlayer expanded MoS₂/graphene composite (E‐MG) is demonstrated as a cathode for MLIB. The key advantage of this cathode is to enable the efficient intercalation of both Mg²⁺ and Li⁺. The E‐MG electrode displays a reversible capacity of ≈300 mA h g^?1 at 20 mA g^?1 in an MLIB cell, corresponding to a specific energy density up to ≈316.9 W h kg^?1, which is comparable to that of the state‐of‐the‐art Li‐ion batteries (LIBs) and has no dendrite formation. The composite electrode is stable against cycling with a coulombic efficiency close to 100% at 500 mA g^?1. This new electrode design represents a significant step forward for building a safe and high‐density electrochemical energy storage system.     

Toward the Sustainable Lithium Metal Batteries with a New Electrolyte Solvation Chemistry

Herein, a new solvation strategy enabled by Mg(NO₃)₂ is introduced, which can be dissolved directly as Mg²⁺ and NO₃^? ions in the electrolyte to change the Li⁺ ion solvation structure and greatly increase interfacial stability in Li‐metal batteries (LMBs). This is the first report of introducing Mg(NO₃)₂ additives in an ester‐based electrolyte composed of ternary salts and binary ester solvents to stabilize LMBs. In particular, it is found that NO₃^? efficiently forms a stable solid electrolyte interphase through an electrochemical reduction reaction, along with the other multiple anion components in the electrolyte. The interaction between Li⁺ and NO₃^? and coordination between Mg²⁺ and the solvent molecules greatly decreases the number of solvent molecules surrounding the Li⁺, which leads to facile Li⁺ desolvation during plating. In addition, Mg²⁺ ions are reduced to Mg via a spontaneous chemical reaction on the Li metal surface and subsequently form a lithiophilic Li–Mg alloy, suppressing lithium dendritic growth. The unique solvation chemistry of Mg(NO₃)₂ enables long cycling stability and high efficiency of the Li‐metal anode and ensures an unprecedented lifespan for a practical pouch‐type LMB with high‐voltage Ni‐rich NCMA73 cathode even under constrained conditions.     

Monovalent ion and calcium ion fluxes in sarcoplasmic reticulum

Summary The ion permeability of sarcoplasmic reticulum vesicles from skeletal and heart muscle has been characterized by radioisotope flux, osmotic and membrane potential measurements, and by incorporating vesicles into planar phospholipid bilayers. The sarcoplasmic reticulum membrane is uniquely permeable to various biologically relevant monovalent ions. At least two and possibly three separate passive permeation systems for monovalent ions have been identified: 1) a K⁺, Na⁺ channel, 2) an anion channel, and 3) a H⁺ (OH^–) permeable pathway which may or may not be synonymous with the anion channel. A possible physiological function of these monovalent ion permeation systems is to permit rapid movement of K⁺, Na⁺, H⁺ and Cl across the membrane to counter electrogenic Ca²⁺ fluxes during Ca²⁺ release and uptake by sacroplasmic reticulum.     

Exploiting Lithium–Ether Co‐Intercalation in Graphite for High‐Power Lithium‐Ion Batteries

The intercalation of lithium ions into graphite electrode is the key underlying mechanism of modern lithium‐ion batteries. However, co‐intercalation of lithium‐ions and solvent into graphite is considered undesirable because it can trigger the exfoliation of graphene layers and destroy the graphite crystal, resulting in poor cycle life. Here, it is demonstrated that the [lithium–solvent]⁺ intercalation does not necessarily cause exfoliation of the graphite electrode and can be remarkably reversible with appropriate solvent selection. First‐principles calculations suggest that the chemical compatibility of the graphite host and [lithium–solvent]⁺ complex ion strongly affects the reversibility of the co‐intercalation, and comparative experiments confirm this phenomenon. Moreover, it is revealed that [lithium–ether]⁺ co‐intercalation of natural graphite electrode enables much higher power capability than normal lithium intercalation, without the risk of lithium metal plating, with retention of ≈87% of the theoretical capacity at current density of 1 A g^?1. This unusual high rate capability of the co‐intercalation is attributed to the (i) absence of the desolvation step, (ii) negligible formation of the solid–electrolyte interphase on graphite surface, and (iii) fast charge‐transfer kinetics. This work constitutes the first step toward the utilization of fast and reversible [lithium–solvent]⁺ complex ion intercalation chemistry in graphite for rechargeable battery technology.