Mechanism of Na+ Insertion in Alkali Vanadates and Its Influence on Battery Performance

Sodium‐ion batteries may become an alternative to the widespread lithium‐ion technology due to cost and kinetic advantages provided that cyclability is improved. For this purpose, the interplay between electrochemical and structural processes is key and is demonstrated in this work for Na_2.46V₆O₁₆ (NVO) and Li_2.55V₆O₁₆ employing operando synchrotron X‐ray diffraction. When NVO is cycled between 4.0 and 1.6 V, Na‐ions reversibly occupy two crystallographic sites, which results in remarkable cyclability. Upon discharge to 1.0 V, however, Na‐ions occupy also interstitial sites, inducing irreversible structural change with some loss of crystallinity concomitant with a decrease in capacity. Capacity fading increases with the ionic radius of the alkali ions (K⁺ > Na⁺ > Li⁺), suggesting that smaller ions stabilize the structure. This correlation of structural variation and electrochemical performance suggests a route toward improving cycling stability of a sodium‐ion battery. Its essence is a minor Li⁺‐retention in the A_2+xV₆O₁₆ structure. Even though the majority of Li‐ions are replaced by the abundant Na⁺, the residual Li‐ions (≈10%) are sufficient to stabilize the layered structure, diminishing the irreversible structural damage. These results pave the way for further exploitation of the role of small ions in lattice stabilization that increases cycling performance.     

Low‐Cost Hollow Mesoporous Polymer Spheres and All‐Solid‐State Lithium,Sodium Batteries

A practical, low‐cost synthesis of hollow mesoporous organic polymer (HMOP) spheres is reported. The electrochemical properties of Li⁺/Na⁺‐electrolyte membranes with these spheres substituting for oxide filler particles in poly(ethylene oxide) (PEO)‐filler composite are explored. The electrolyte membranes are mechanically robust, thermally stable to over 250 °C, and block dendrites from a metallic‐lithium/sodium anode. The Li⁺/Na⁺ transfer impedance across the lithium/sodium–electrolyte interface is initially acceptable at 65 °C and scavenging of impurities by the porous‐spheres filler lowers this impedance relative to that with Al₂O₃. All‐solid‐state Li/LiFePO₄ and Na/NaTi₂(PO4)₃ cells give stable discharge capacity of ≈130 and 80 mAh g^?1, respectively, at 0.5 C and 65 °C for 100 cycles.     

Workshop 7: 2

Glutamine, the preferred precursor for neurotransmitter glutamate, is likely to be the principal substrate for the neuronal System A transporter SAT1 in vivo. By measuring currents associated with SAT1 expression in Xenopus oocytes, we found that SAT1 mediates transport of small, neutral, aliphatic amino acids including glutamine, alanine and the System A‐specific analogue 2‐(methylamino) isobutyrate, each with K_0.5 of 0.3–0.5 mm . Amino acid transport is driven by the Na⁺ electrochemical gradient. Kinetic data indicates that Na⁺/cotransport comprises the ordered binding first of Na⁺ (a voltage‐dependent step), then alanine, then simultaneous translocation. Li⁺ (but not H⁺) can substitute for Na⁺ but results in reduced V_max. In the absence of amino acid, SAT1 mediates a cation leak with selectivity Na⁺, Li⁺, H⁺, K⁺. The temperature‐dependence of the leak current (E_a = 17 ± 3 kcal/mol) is consistent with carrier‐mediated Na⁺ uniport activity (cf 13 ± 2 kcal/mol for Na⁺/alanine cotransport) but the leak does not saturate at physiological [Na⁺], suggesting channel activity. Despite a Na⁺ Hill coefficient of 1, we obtained Na⁺/amino acid coupling coefficients greater than 1 from simultaneous measurement of charge and [³H]alanine or [³H]glutamine uptake. Interpretation of these data is model‐dependent and consistent with either (1) an all‐carrier model in which Na⁺/amino acid cotransport is thermodynamically coupled 2 : 1, cotransport is preferred over Na⁺ uniport, and in which there is little cooperativity between Na⁺ binding events, or (2) 1 : 1 coupling in parallel with an always‐on Na⁺ channel activity. In either scenario, the presence of SAT1 at the plasma membrane and resultant Na⁺ fluxes will place a significant energy burden on the cell.     

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.     

Mechanisms by which Li+ stimulates the (Na++K+)-dependent ATPase

The addition of LiCl stimulated the (Na⁺+K⁺)-dependent ATPase activity of a rat brain enzyme preparation. Stimulation was greatest in high Na⁺/low K⁺ media and at low Mg. ATP concentrations. Apparent affinities for Li⁺ were estimated at the α-sites (moderate-affinity sites for K⁺ demonstrable in terms of activation of the associated K⁺-dependent phosphatase reaction), at the β-sites (high-affinity sites for K⁺ demonstrable in terms of activation of the overall ATPase reaction), and at the Na⁺ sites for activation. The relative efficacy of Li⁺ was estimated in terms of the apparent maximal velocity of the phosphatase and ATPase reactions when Li⁺ was substituted for K⁺, and also in terms of the relative effect of Li⁺ on the apparent K_M for Mg· ATP. With these data, and previously determined values for the apparent affinities of K⁺ and Na⁺ at these same sites, quantitative kinetic models for the stimulation were examined. A composite model is required in which Li⁺ stimulates by relieving inhibition due to K⁺ and Na⁺ (i) by competing with K⁺ for the α-sites on the enzyme through which K⁺ decreases the apparent affinity for Mg·ATP and (ii) by competing with Na⁺ at low-affinity inhibitory sites, which may represent the external sites at which Na⁺ is discharged by the membrane NA⁺/K⁺ pump that this enzyme represents. Both these sites of action for Li⁺ would thus lie, in vivo, on the cell exterior.     

Slurry‐Fabricable Li+‐Conductive Polymeric Binders for Practical All‐Solid‐State Lithium‐Ion Batteries Enabled by Solvate Ionic Liquids

For mass production of all‐solid‐state lithium‐ion batteries (ASLBs) employing highly Li⁺ conductive and mechanically sinterable sulfide solid electrolytes (SEs), the wet‐slurry process is imperative. Unfortunately, the poor chemical stability of sulfide SEs severely restrict available candidates for solvents and in turn polymeric binders. Moreover, the binders interrupt Li⁺‐ionic contacts at interfaces, resulting in the below par electrochemical performance. In this work, a new scalable slurry fabrication protocol for sheet‐type ASLB electrodes made of Li⁺‐conductive polymeric binders is reported. The use of intermediate‐polarity solvent (e.g., dibromomethane) for the slurry allows for accommodating Li₆PS₅Cl and solvate‐ionic‐liquid‐based polymeric binders (NBR‐Li(G3)TFSI, NBR: nitrile?butadiene rubber, G3: triethylene glycol dimethyl ether, LiTFSI: lithium bis(trifluoromethanesulfonyl)imide) together without suffering from undesirable side reactions or phase separation. The LiNi_0.6Co_0.2Mn_0.2O₂ and Li₄Ti₅O₁₂ electrodes employing NBR‐Li(G3)TFSI show high capacities of 174 and 160 mA h g^?1 at 30 °C, respectively, which are far superior to those using conventional NBR (144 and 76 mA h g^?1). Moreover, high areal capacity of 7.4 mA h cm^?2 is highlighted for the LiNi_0.7Co_0.15Mn_0.15O₂ electrodes with ultrahigh mass loading of 45 mg cm^?2. The facilitated Li⁺‐ionic contacts at interfaces paved by NBR‐Li(G3)TFSI are evidenced by the complementary analysis from electrochemical and ⁷Li nuclear magnetic resonance measurements.     

Transport of lithium and rectification by frog skin

The isolated frog skin, bathed with Li⁺-Ringer (Na⁺-free) on the outside and Na⁺-Ringer on the inside, can maintain a normal potential difference (PD) and short-circuit current (s.c.c.) for more than 6. h. The s.c.c. correspondended to the Li⁺ influx. The Na⁺ efflux was 4% of the s.c.c. 10⁻⁵ M ouabain depressed Li⁺ influx and s.c.c. 10¹⁰⁻⁵ M amiloride abolished the Li⁺ s.c.c., while 0.1 unit/ml oxytocin stimulated it. When the inside of the skin was bathed with Li⁺-Ringer, PD and s.c.c. fell to zero within 2 h. The oxygen consumption of skin slices bathed in Li⁺-Ringer was 29% lower than controls bathed in Na⁺-Ringer.When the isolated frog skin is bathed in Na₂SO₄-Ringer it shows electrical rectification which has been correlated with the active transport of Na⁺. In skins transporting Li⁺, rectification characteristics are similar to those of skins transporting Na⁺. When the inner face of the skin is bathed with Li⁺-Ringer, rectification, PD and s.c.c. decline in a parallel fashion.It is concluded that: (1) Li⁺ can be transported when Na⁺ is present at the inner face. (2) Amiloride, ouabain and oxytocin affect Li⁺ and Na⁺ transport in a similar manner. (3) Li⁺ transport, like Na⁺ transport, is associated with rectification. (4) Active transport of Na⁺ and Li⁺ seems to depend on two different but associated proceses; one taking place at the external barrier (where rectification occurs) as shown by the effect of amiloride; and the other of an inner site related to energy requirements and affected by ouabain and Li⁺. (5) The cation being transported is not necessarily activating the (Na⁺-K⁺-ATPase.     

Insights into the Storage Mechanism of Layered VS2 Cathode in Alkali Metal‐Ion Batteries

VS₂ is one of the attractive layered cathodes for alkali metal‐ion batteries. However, the understanding of the detailed reaction processes and energy storage mechanism is still inadequate. Herein, the Li⁺/Na⁺/K⁺ insertion/extraction mechanisms of VS₂ cathode are elucidated on the basis of experimental analyses and theoretical simulations. It is found that the insertion/extraction behavior of Li⁺ is partially irreversible, while the insertion/extraction behavior of Na⁺/K⁺ is completely reversible. The detailed intermediates and final products (Li_0.33VS₂, LiVS₂, Na_0.5VS₂, NaVS₂, K_0.6VS₂, K_zVS₂, z > 0.6) during the discharging/charging processes are identified, indicating that VS₂ undergoes different phase transitions and solid–solution reactions in different battery systems, which have a great influence on the battery performance. Moreover, the diffusion of Na⁺ in VS₂ cathode is demonstrated to be much slower than that of Li⁺ and K⁺. Such mechanistic research provides a reference for in‐depth understanding of energy storage in layered transition metal sulfides/selenides.     

Effects of monovalent cations on phosphate accumulation and storage of the ectomycorrhizal fungus Suillus bovinus

Comparative in vivo ³¹P-NMR studies of the fungus Suillus bovinus (L.: Fr.) O. Kuntze in pure culture have produced interesting new data. To investigate the response of phosphate metabolism to a change in external monovalent cations, samples were exposed to a Hoagland solution containing different monovalent cations Li⁺, Na⁺, K⁺, or Rb⁺ at 10 mM concentration. A method of nutrient cycling during analysis where the cation was changed and the phosphate kept constant allowed us to determine the kinetics of phosphate accumulation, storage and incorporation into polyphosphate following exposure to the range of test cations. Different external monovalent cations had different effects upon changes in the content of both phosphate and polyphosphate. Treatment with Li⁺, Na⁺, or Rb⁺ resulted in a change in phosphate accumulation to 60, 73, and 107% and in content of the intracellular mobile polyphosphate (polyP) to 119, 112, and 94%, respectively, compared with the control taken as 100%. The effect of each cation is related to its position in the periodic table. Reversing this process, i.e., exchanging with K⁺, returned phosphate metabolism to normal. Although, the increase in depolarization of the cell membrane should affect the internal pH, fungal metabolism using energy requiring mechanisms appeared necessary to maintain the intracellular pH. Thus, increasing contents of mobile polyP were the consequence of an increasing energy demand. On the other hand, the increasing depolarization of the cell membrane following the sequence Rb⁺ < K⁺ < Na⁺ < Li⁺ inhibited the net P_i accumulation. Furthermore, it is postulated that the P_i accumulation was also regulated by the intracellular content in polyP.     

Lithium transport by fibroblastic mouse cells: Characterization and stimulation by serum and growth factors in quiescent cultures

Serum enhances the rate of Li⁺ entry and exit in quiescent cultures of mouse fibroblasts by 2- to 3-fold. Tertiary cultures of whole mouse embryos as well as established fibroblast lines (3T3, 3T6) show the increase in Li⁺ permeability when serum is added to cultures whose growth has been arrested by serum deprivation. Growing cells are only slightly more permeable to Li⁺ in the presence of serum. Purified compounds which initiate DNA synthesis also rapidly increase Li⁺ entry; mitogenic levels of thrombin and the combination of epidermal growth factor, insulin, and bovine serum albumin were the most effective ones tested. The effect of serum on Li⁺ uptake occurs within a few minutes, is not affected by inhibitors of macromolecular synthesis, and appears mainly to increase the Vmax of entry. Inhibitors of energy production partially reduce Li⁺ entry but do not block the activation by serum. One portion of Li⁺ uptake (?40%), which is inhibited by ouabain, phloretin, or Na⁺ deprivation, is mediated by the Na⁺/K⁺ pump in the plasma membrane. A second mechanism of Li⁺ entry which is blocked by Na⁺ or amiloride appears to be a Na⁺ specific “porter.” The activity of both components is stimulated by serum. The increased activity of the putative Na⁺ porter would increase Na⁺ availability to the Na⁺ pump and may account for its enhancement by serum, which was also noted previously (Rozengurt and Heppel, '75).     

The Na+/H+ Exchanger Present in Trout Erythrocyte Membranes is Not Responsible for the Amiloride-insensitive Na+/Li+ Exchange Activity

The protein responsible for the Na⁺/Li⁺ exchange activity across the erythrocyte membrane has not been cloned or isolated. It has been suggested that a Na⁺/H⁺ exchanger could be responsible for the Na⁺/Li⁺ exchange activity across the erythrocyte membrane. Previously, we reported that in the trout erythrocyte, the Li⁺/H⁺ exchange activity (mediated by the Na⁺/H⁺ exchanger βNHE) and the Na⁺/Li⁺ exchange activity respond differently to cAMP, DMA (dimethyl-amiloride) and O₂. We concluded that the DMA insensitive Na⁺/Li⁺ exchange activity originates from a different protein. To further examine these findings, we measured Li⁺ efflux in fibroblasts expressing the βNHE as the only Na⁺/H⁺ exchanger. Moreover, the internal pH of these cells was monitored with a fluorescent probe. Our findings indicate that acidification of fibroblasts expressing the Na⁺/H⁺ exchanger βNHE, induces a Na⁺ stimulated Li⁺ efflux activity in trout erythrocytes. This exchange activity, however, is DMA sensitive and therefore differs from the DMA insensitive Na⁺/Li⁺ exchange activity. In these fibroblasts no significant DMA insensitive Na⁺/Li⁺ exchange activity was found. These results support the hypothesis that the trout erythrocyte Na⁺/Li⁺ exchange activity is not mediated by the Na⁺/H⁺ exchanger (βNHE) present in these membranes. Received: 6 December 1996/Revised: 11 August 1997     

An Ion‐Exchange Promoted Phase Transition in a Li‐Excess Layered Cathode Material for High‐Performance Lithium Ion Batteries

A new approach to intentionally induce phase transition of Li‐excess layered cathode materials for high‐performance lithium ion batteries is reported. In high contrast to the limited layered‐to‐spinel phase transformation that occurred during in situ electrochemical cycles, a Li‐excess layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ is completely converted to a Li₄Mn₅O₁₂‐type spinel product via ex situ ion‐exchanges and a post‐annealing process. Such a layered‐to‐spinel phase conversion is examined using in situ X‐ray diffraction and in situ high‐resolution transmission electron microscopy. It is found that generation of sufficient lithium ion vacancies within the Li‐excess layered oxide plays a critical role for realizing a complete phase transition. The newly formed spinel material exhibits initial discharge capacities of 313.6, 267.2, 204.0, and 126.3 mAh g^?1 when cycled at 0.1, 0.5, 1, and 5 C (1 C = 250 mA g^?1), respectively, and can retain a specific capacity of 197.5 mAh g^?1 at 1 C after 100 electrochemical cycles, demonstrating remarkably improved rate capability and cycling stability in comparison with the original Li‐excess layered cathode materials. This work sheds light on fundamental understanding of phase transitions within Li‐excess layered oxides. It also provides a novel route for tailoring electrochemical performance of Li‐excess layered cathode materials for high‐capacity lithium ion batteries.     

Proton polarizability of poly(L-tyrosine)–hydrogen phosphate hydrogen bonds as a function of alkali cations

We studied films of poly(L -tyrosine) with hydrogen phosphate (residue/phosphate, 1:1) by ir spectroscopy. The influences of the alkali cations (Li⁺, Na⁺, K⁺) and of the degree of hydration were clarified. If Li⁺ ions are present, the OH ?^?OP hydrogen bonds formed in the dried films between the tyrosine OH groups and hydrogen phosphate are asymmetrical. The formation of hydrogen phosphate–hydrogen phosphate hydrogen bonds is prevented by the presence of the Li⁺ ions. With an increase in the degree of hydration, the tyrosine–phosphate bonds are not broken but become slightly stronger. Completely different behaviour is found if K⁺ ions are present. In dry films, the OH ?^?OP ? O^? ?HOP hydrogen bonds formed between tyrosine and hydrogen phosphate show large proton polarizability. The tyrosine proton has a noticeable residence time at the acceptor O atom of the phosphate. The difference in the behaviour of the system with K⁺ ions when compared to the system with Li⁺ ions can be explained, since the hydrogen acceptor O atom of phosphate ions is more negatively charged due to the weaker influence of the K⁺ ions. Furthermore, POH ?^?OP hydrogen bonds between hydrogen phosphate molecules are formed. With an increase in the degree of hydration, the tyrosine–hydrogen phosphate hydrogen bonds are broken, all tyrosine protons are found at the tyrosine residues, and the -PO₃^? groupings are in a symmetrical environment, indicating that the K⁺ ions are removed from these groupings. If the degree of hydration increases further, hydrogen-bonded systems such as hydrogen phosphate–water–hydrogen phosphate are formed that show large proton polarizability due to collective proton motion. When Na⁺ ions are present, the OH ?^?OP ? O^? ?HOP hydrogen bonds formed in dry films still show proton polarizability, but the residence time of the tyrosine proton at the phosphate is very short.     

Li/Na exchange and Li active transport in human lymphoid cells U937 cultured in lithium media

Lithium transport across the cell membrane is interesting in the light of general cell physiology and because of its alteration during numerous human diseases. The mechanism of Li⁺ transfer has been studied mainly in erythrocytes with a slow kinetics of ion exchange and therefore under the unbalanced ion distribution. Proliferating cultured cells with a rapid ion exchange have not been used practically in study of Li⁺ transport. In the present paper, the kinetics of Li⁺ uptake and exit, as well as its balanced distribution across the plasma membrane of U937 cells, were studied at minimal external Li⁺ concentrations and after the whole replacement of external Na⁺ for Li⁺. It is found that a balanced Li⁺ distribution attained at a high rate similar to that for Na⁺ and Cl^? and that Li⁺/Na⁺ discrimination under balanced ion distribution at 1–10 mM external Li⁺ stays on 3 and drops to 1 following Na, K-ATPase pump blocking by ouabain. About 80% of the total Li⁺ flux across the plasma membrane under the balanced Li⁺ distribution at 5 mM external Li⁺ accounts for the equivalent Li⁺/Li⁺ exchange. The majority of the Li⁺ flux into the cell down the electrochemical gradient is a flux through channels and its small part may account for the NC and NKCC cotransport influxes. The downhill Li⁺ influxes are balanced by the uphill Li⁺ efflux involved in Li⁺/Na⁺ exchange. The Na⁺ flux involved in the countertransport with the Li⁺ accounts for about 0.5% of the total Na⁺ flux across the plasma membrane. The study of Li⁺ transport is an important approach to understanding the mechanism of the equivalent Li⁺/Li⁺/Na⁺/Na⁺ exchange, because no blockers of this mode of ion transfer are known and it cannot be revealed by electrophysiological methods. Cells cultured in the medium where Na⁺ is replaced for Li⁺ are recommended as an object for studying cells without the Na,K-ATPase pump and with very low intracellular Na⁺ and K⁺ concentration.     

Intersubunit bridging by Na+ ions as a rationale for the unusual stability of the c-rings of Na+-translocating F1F0 ATP synthases

The oligomeric c-rings of Na⁺-translocating F₁F₀ ATP synthases exhibit unusual stability, resisting even boiling in SDS. Here, we show that the molecular basis for this remarkable property is intersubunit crossbridging by Na⁺ or Li⁺ ions. The heat stability of c₁₁ was dependent on the presence of Na⁺ or Li⁺ ions. For equal stability, 10 times higher Li⁺ than Na⁺ concentrations were required, reflecting the 10 times lower binding affinity for Li⁺ than for Na⁺. In a recent structural model of c₁₁, the Na⁺ or Li⁺ binding ligands are located on neighboring c-subunits, which thus become crossbridged by the binding of either alkali ion with a concomitant increase in the stability of the ring. Site-directed mutagenesis strengthens the essential role of glutamate 65 in the crossbridging of the subunits and also corroborates the proposed stabilizing effect of an ion bridge including aspartate 2.     

Sodium requirement and metabolism in nitrogen-fixing cyanobacteria

Sodium affects the metabolism of eukaryotes and prokaryotes in several ways. This review collates information on the effects of Na⁺ on the metabolism of cyanobacteria with emphasis on the N₂,fixing filamentous species. Na⁺ is required for nitrogenase activity inAnabaena torulosa, Anabaena L-31 andPlectonema boryanum. The features of this requirement have been mainly studied inAnabaena torulosa. The need for Na⁺ is specific and cannot be replaced by K⁺, Li⁺, Ca 2 + or Mg²⁺. Processes crucial for expression of nitrogenase such as molybdenum uptake, protection of the enzyme from oxygen inactivation and conformational activation of the enzyme are not affected by Na⁺. Mo-Fe protein and Fe protein, the two components of nitrogenase are synthesized in the absence of Na⁺ but the enzyme complex is catalytically inactive. Photoevolution of O₂ and CO₂ fixation, which are severely inhibited in the absence of Na⁺, are quickly restored by glutamine or glutamate indicating that Na⁺ deprivation affects photosynthesis indirectly due to deficiency in the products of N₂ fixation. Na⁺ deprivation decreases phosphate uptake, nucleoside phosphate pool and nitrogenase activity. These effects are reversed by the addition of Na⁺ suggesting that a limitation of available ATP caused by reduced phosphate uptake results in loss of nitrogenase activity during Na⁺ starvation. Na⁺ influx inAnabaena torulosa andAnabaena L-31 is unaffected by low K⁺ concentration, is carrier mediated, follows Michaelis-Menten kinetics and is modulated mainly by membrane potential. Treatments which cause membrane depolarisation and hyperpolarisation inhibit and enhance Na⁺ influx respectively. These cyanobacteria exhibit rapid active efflux of Na⁺, in a manner different from the Na⁺/H⁺ antiporter mechanism found inAnacystis nidulans. Na⁺ requirement in nitrogen metabolism including nitrate assimilation, synthesis of amino acids and proteins, in respiration and oxidative phosphorylation, in transport of sugars and amino acids, cellular distribution of absorbed sodium, physiological basis of salt tolerance and prospects of reclamation of saline soils by cyanobacteria are the other aspects discussed in this review.     

Glucose-6-phosphate dehydrogenase-dependent hydrogen peroxide production is involved in the regulation of plasma membrane H+-ATPase and Na+/H+ antiporter protein in salt-stressed callus from Carex moorcroftii

Glucose‐6‐phosphate dehydrogenase (G6PDH) is important for the activation of plant resistance to environmental stresses, and ion homeostasis is the physiological foundation for living cells. In this study, we investigated G6PDH roles in modulating ion homeostasis under salt stress in Carex moorcroftii callus. G6PDH activity increased to its maximum in 100 mM NaCl treatment and decreased with further increased NaCl concentrations. K⁺/Na⁺ ratio in 100 mM NaCl treatment did not exhibit significant difference compared with the control; however, in 300 mM NaCl treatment, it decreased. Low‐concentration NaCl (100 mM) stimulated plasma membrane (PM) H⁺‐ATPase and NADPH oxidase activities as well as Na⁺/H⁺ antiporter protein expression, whereas high‐concentration NaCl (300 mM) decreased their activity and expression. When G6PDH activity and expression were reduced by glycerol treatments, PM H⁺‐ATPase and NADPH oxidase activities, Na⁺/H⁺ antiporter protein level and K⁺/Na⁺ ratio dramatically decreased. Simultaneously, NaCl‐induced hydrogen peroxide (H₂O₂) accumulation was abolished. Exogenous application of H₂O₂ increased G6PDH, PM H⁺‐ATPase and NADPH oxidase activities, Na⁺/H⁺ antiporter protein expression and K⁺/Na⁺ ratio in the control and glycerol treatments. Diphenylene iodonium (DPI), the NADPH oxidase inhibitor, which counteracted NaCl‐induced H₂O₂ accumulation, decreased G6PDH, PM H⁺‐ATPase and NADPH oxidase activities, Na⁺/H⁺ antiporter protein level and K⁺/Na⁺ ratio. Western blot result showed that G6PDH expression was stimulated by NaCl and H₂O₂, and blocked by DPI. Taken together, G6PDH is involved in H₂O₂ accumulation under salt stress. H₂O₂, as a signal, upregulated PM H⁺‐ATPase activity and Na⁺/H⁺ antiporter protein level, which subsequently resulted in the enhanced K⁺/Na⁺ ratio. G6PDH played a central role in the process.     

Na+(Li+)/Branched-chain amino acid cotransport inPseudomonas aeruginosa

Summary A transport system for branched-chain amino acids (designated as LIV-II system) inPseudomonas aeruginosa requires Na⁺ for its operation. Coupling cation for this system was identified by measuring cation movement during substrate entry using cation-selective electrodes. Uptakes of Na⁺ and Li^– were induced by the imposition of an inwardly-directed concentration gradient of leucine, isoleucine, or valine. No uptake of H^– was found, however, under the same conditions. In addition, effects of Na⁺ and Li⁺ on the kinetic property of the system were examined. At chloride salt concentration of 2.5mm, values of apparentK _m andV _max for leucine uptake were larger in the presence of Na⁺ than Li⁺. These results indicate that the LIV-II transport system is a Na⁺(Li⁺)/substrate cotransport system, although effects of Na⁺ and Li⁺ on kinetics of the system are different.     

Presence of a Na+/H+ antiporter in Methanobacterium thermoautotrophicum and its role in Na+ dependent methanogenesis

Methane formation from H₂/CO₂ by methanogenic bacteria is dependent on Na⁺ ions. In this communication it is shown with Methanobacterium thermoautotrophicum that a Na⁺/H⁺ antiporter plays a role in methane formation from H₂ and CO₂ and in the regulation of the ΔpH. This is based on the following findings:

1. Li⁺ ions, an alternative substrate of Na⁺/H⁺ antiporters, could replace Na⁺ in stimulating methanogenesis from H₂ and CO₂.
2. Harmaline, amiloride, and NH ₄ ⁺ , which are inhibitors of Na⁺/H⁺ antiporters, inhibited methanogenesis; inhibition was competitive to Na⁺ or Li⁺.
3. Addition of Na⁺ or Li⁺ rather than of other cations to cell suspensions resulted in an acidification of the suspension medium. The rate and extent of acidification was affected by those inhibitors, which inhibited methanogenesis competitively to Na⁺ or Li.
4. During methane formation from H₂ and CO₂ the generation of a ΔpH (inside alkaline) was dependent on the presence of Na⁺ or Li⁺. However, methanogenesis was also dependent on Na⁺ or Li⁺ under conditions where ΔpH was zero.
5. ATP synthesis driven by an electrogenic potassium efflux was significantly enhanced in the presence of Na⁺ or Li⁺. Na⁺ or Li⁺ were shown to prevent acidification of the cytoplasm under these conditions.

     

Highly Reversible Na Storage in Na3V2(PO4)3 by Optimizing Nanostructure and Rational Surface Engineering

Sodium‐ion batteries (NIBs) have attracted more and more attention as economic alternatives for lithium‐ion batteries (LIBs). Sodium super ionic conductor (NASICON) structure materials, known for high conductivity and chemical diffusion coefficient of Na⁺ (≈10^?14 cm² s^?1), are promising electrode materials for NIBs. However, NASICON structure materials often suffer from low electrical conductivity (<10^?4 S cm^?1), which hinders their electrochemical performance. Here high performance sodium storage performance in Na₃V₂(PO₄)₃ (NVP) is realized by optimizing nanostructure and rational surface engineering. A N, B codoped carbon coated three‐dimensional (3D) flower‐like Na₃V₂(PO₄)₃ composite (NVP@C‐BN) is designed to enable fast ions/electrons transport, high‐surface controlled energy storage, long‐term structural integrity, and high‐rate cycling. The conductive 3D interconnected porous structure of NVP@C‐BN greatly releases mechanical stress from Na⁺ extraction/insertion. In addition, extrinsic defects and active sites introduced by the codoping heteroatoms (N, B) both enhance Na⁺ and e^? diffusion. The NVP@C‐BN displays excellent electrochemical performance as the cathode, delivering reversible capacity of 70% theoretical capacity at 100 C after 2000 cycles. When used as anode, the NVP@C‐BN also shows super long cycle life (38 mA h g^?1 at 20 C after 5000 cycles). The design provides a novel approach to open up possibilities for designing high‐power NIBs.