Anion Conductance Research Articles

Structural basis and molecular mechanisms of Cl- transmembrane transport in cardiomyocytes

The intracellular concentration of chlorine anions ([Cl-]i), the equilibrium potential for chlorine anions (ECl) and transmembrane chloride currents (ICl) are the factors that significantly influence the electrophysiological properties of excitable tissue, including the myocardium. Several types of chloride (anion) conductance have been identified in the heart. In recent years, a number of transmembrane proteins demonstrating chloride conductance have been identified (CFTR, ClC, TMEM16, LRRC8), and the expression of these macromolecules in cardiac tissue has been confirmed. Accumulated data allow for establishing a molecular substrate for some chloride anion currents (ICl,PKA, ICl,ir, ICl,vol, ICl,swell, ICl,Ca, Ito2) detected in the heart. Furthermore, the molecular mechanisms regulating [Cl-]i and ECl through chloride cotransporters (KCC, NKCC1) and chloride-bicarbonate exchangers have been established. The variety of structures determining chloride transmembrane conductivity and the complexity of molecular mechanisms regulating chloride homeostasis underlie the complex effects of activation of chloride transporters in the pacemaker, conduction system and working myocardium of the heart. This review discusses the structural, biophysical properties and molecular regulation of chloride transporter protein complexes identified in the myocardium. The review also covers the mechanisms by which chloride transmembrane transport influences the bioelectrical activity of cardiomyocytes.

Alkaline Earth Bismuth Fluorides as Fluoride-Ion Battery Electrolytes.

Fluoride-ion batteries have several potential advantages over lithium-ion batteries. Materials development is still needed, however, to realize electrolytes with sufficiently high anion conductivity and compatibility with anode and cathode layers. Fluoride compounds are difficult to synthesize directly as single crystals but can be realized from oxide film precursors via topotactic chemistry techniques. Here, we create crystalline alkaline earth bismuth fluoride films BaBiF5 and SrBiF5 through oxide molecular beam epitaxy and topotactic fluorination. We characterize their ionic conductivities and demonstrate their potential as electrolytes. Finally, we realize epitaxial synthesis of BaBiF5 on BaF2 substrates, providing a route to thin film fluoride-ion battery devices.

Regulating Li+ transport behavior by cross-scale synergistic rectification strategy for dendrite-free and high area capacity polymeric all-solid-state lithium batteries

The inability to effectively inhibit the lithium (Li) dendrite growth is identified as the real culprit hindering the practical application of polyethylene oxide (PEO)-based electrolytes. Herein, a novel PEO composite electrolyte with ion rectifier is developed based on the cross-scale synergistic rectification strategy. At the micro-scale, the array structure of the ion rectifier suppresses the growth of PEO crystals and their distribution in the non-ionic conduction direction through space confinement, alleviating ion-migration crosstalk and enabling polymer chain rectification. Furthermore, the matrix contains abundant copper ions and oxygen-containing groups that inhibit anion conduction and accelerate Li+ migration at the nanoscale, respectively, to achieve ion flow rectification. Implementing this strategy results in a uniform, fast, and stable Li+ migration/diffusion behavior from the electrolyte to anode interface. The critical current density of the PEO electrolyte is increased to 2.5 mA cm−2, indicating a significant improvement in dendrite growth inhibition. Impressively, the composite electrolytes exhibit long-term stability (>4000 h at 0.2 mA cm−2) and ultra-high current-density tolerance (>200 h at 1 mA cm−2). Moreover, the composite electrolytes enable stable cycling of high-area-capacity (3.11 mAh cm−2, 20 mg cm−2) LiFePO4/Li pouch cells, highlighting the importance of this strategy for the practical application of PEO electrolytes.

Cl--dependent amplification of excitatory synaptic potentials at distal dendrites revealed by voltage imaging.

The processing of synaptic signals in somatodendritic compartments determines neuronal computation. Although the amplification of excitatory signals by local voltage-dependent cation channels has been extensively studied, their spatiotemporal dynamics in elaborate dendritic branches remain obscure owing to technical limitations. Using fluorescent voltage imaging throughout dendritic arborizations in hippocampal pyramidal neurons, we demonstrate a unique chloride ion (Cl-)-dependent remote computation mechanism in the distal branches. Excitatory postsynaptic potentials triggered by local laser photolysis of caged glutamate spread along dendrites, with gradual amplification toward the distal end while attenuation toward the soma. Tour de force subcellular patch-clamp recordings from thin branches complemented by biophysical model simulations revealed that the asymmetric augmentation of excitation relies on tetrodotoxin-resistant sodium ion (Na+) channels and Cl- conductance accompanied by a more hyperpolarized dendritic resting potential. Together, this study reveals the cooperative voltage-dependent actions of cation and anion conductance for dendritic supralinear computation, which can locally decode the spatiotemporal context of synaptic inputs.

Anion-Exchange Membrane Oxygen Separator.

Anion-exchange membranes (AEMs), known for enabling the high conductivity of hydroxide anions through dense polymeric structures, are pivotal components in fuel cells, electrolyzers, and other important electrochemical systems. This paper unveils an unprecedented utilization of AEMs in an electrochemical oxygen separation process, a new technology able to generate enriched oxygen from an O2/N2 mixture using a small voltage input. We demonstrate a first-of-its-kind AEM-based electrochemical device that operates under mild conditions, is free of liquid electrolytes or sweep gases, and produces oxygen of over 96% purity. Additionally, we develop and apply a one-dimensional time-dependent and isothermal model, which accurately captures the unique operational dynamics of our device, demonstrates good agreement with the experimental data, and allows us to explore the device's potential capabilities. This novel technology has far-reaching applications in many industrial processes, medical oxygen therapy, and other diverse fields while reducing operational complexity and environmental impact, thereby paving the way for sustainable on-site oxygen generation.

Microwave Synthesis of New Co-Polypyrrole-Polyketone Anion Exchange Membranes

Polyketones can be easily converted in a series of new polymeric anion exchange membranes (AEMs) with a stable polypyrrole-polyketone backbone structure from which the ion exchange side-groups stem [1-3]. Here we present our findings on the functionalization with two different cycloaliphatic primary amines of a commercial and inexpensive terpolymer polyketone (PK) through the Paal-Knorr chemistry. We also studied the possibility to drastically reduce the reaction time by investigating alternative and greener heating sources such as microwave heating. The molecular structure, thermal and conductive properties of the membranes were studied in order to shed light on and compare the effect of the different heating methods on the materials behavior [4], and to lead the way to their further optimization for the possible application in electrochemical devices. The obtained membranes showed a promising anion conductivity in the hydroxide form, up to 10mScm-1, and an exceptional thermal stability, about 250°C.[1] G.Nawn, K.Vezzù, G.Cavinato, G.Pace, F.Bertasi, G.Pagot, E.Negro, V. Di Noto, Adv. Funct. Mater. 2018, 1706522[2] N.Ataollahi, F.Girardi, E.Cappelletto, K.Vezzù, V.Di Noto, P.Scardi, E.Callone, R.Di Maggio. Journal of Applied Polymer Science. 2017, 134, 45485.[3] A.R.Alvi, K.Vezzù, , G.Pagot, P.Sgarbossa, G.Pace, V.Di Noto, Macromolecular Chemistry & Physics. 2022, 223, 2100409.[4] S.Bonizzoni, D.Stucchi, T.Caielli, E.Sediva, M.Mauri, P.Mustarelli, ChemElectroChem. 2023, e202201077. Figure 1

All‐Aromatic Polymer‐Based Anion Conductive Ionomers with Different Ion Exchange Capacities for Water Electrolysis

Anion exchange membrane water electrolysis (AEMWE) is vital for efficient, environmentally friendly, and cost‐effective hydrogen production. Herein, fluorene‐based polymers containing alkyl ammonium groups with different ion exchange capacities (IECs) for use in anion exchange membranes (AEMs) and anion exchange ionomers (AEIs) are investigated. Among the AEMs tested, the AEM with an IEC of 2.2 meq g−1 shows the highest anion conductivity because of its efficient water uptake characteristics. The anode catalyst layers utilize AEIs and iridium oxide catalyst particles. It is essential to select AEIs with appropriate IEC and suitable solvents for high‐performance anodes in water electrolyzers. Morphological and physical property evaluations reveal that moderate hydrophilicity and suppression of water swelling of AEIs improve water electrolysis performance. The optimized catalyst layer achieves better water electrolysis performance (2.64 V, 1.8 A cm−2 at 30 °C) than the conventional catalyst layer (3.83 V, 1.8 A cm−2 at 30 °C). Although the water electrolysis performance in this study falls short of the final targets, further research on anion conductive polymers and catalyst layers, based on this study's findings, is expected to promote practical applications of AEMWEs.

Unsupervised Machine Learning‐Derived Anion‐Exchange Membrane Polymers Map: A Guideline for Polymers Exploration and Design

AbstractAlthough anion‐exchange membranes (AEMs) are commonly used in fuel cells and water electrolyzers, their widespread commercialization is hindered by problems such as low anion conductivity and durability. Moreover, the development of high‐performance AEMs remains complex and time consuming. Here, we address these challenges by proposing an innovative approach for the efficient design and screening of AEM polymers using unsupervised machine learning. Our model, which combines principal component analysis with uniform manifold approximation and projection, generates an intuitive map that clusters AEM polymers based on structural similarities without any predefined knowledge regarding anion conductivity or other experimentally derived variables. As a powerful navigation tool, this map provides insights into promising main‐chain structures, such as poly(arylene alkylene)s with consistently high conductivity and polyolefins with exceptional performance depending on the substituent. Furthermore, assisted by key molecular descriptors, inverse analysis with this model allows targeted design and property prediction before synthesis, which will significantly accelerate the discovery of novel AEM polymers. This work represents a paradigm shift not only in AEM research but also generally in materials research, moving from black‐box predictions toward interpretable guidelines that foster collaboration between researchers and machine learning for efficient and informed material development.

Glutamate transporters are involved in direct inhibitory synaptic transmission in the vertebrate retina.

In the central nervous system of vertebrates, glutamate serves as the primary excitatory neurotransmitter. However, in the retina, glutamate released from photoreceptors causes hyperpolarization in post-synaptic ON-bipolar cells through a glutamate-gated chloride current, which seems paradoxical. Our research reveals that this current is modulated by two excitatory glutamate transporters, EAAT5b and EAAT7. In the zebrafish retina, these transporters are located at the dendritic tips of ON-bipolar cells and interact with all four types of cone photoreceptors. The absence of these transporters leads to a decrease in ON-bipolar cell responses, with eaat5b mutants being less severely affected than eaat5b/eaat7 double mutants, which also exhibit altered response kinetics. Biophysical investigations establish that EAAT7 is an active glutamate transporter with a predominant anion conductance. Our study is the first to demonstrate the direct involvement of post-synaptic glutamate transporters in inhibitory direct synaptic transmission at a central nervous system synapse.

Molecular mechanism of anion permeation through aquaporin 6

Aquaporins (AQPs) are recognized as transmembrane water channels that facilitate selective water permeation through their monomeric pores. Among the AQP family, AQP6 has an intriguing characteristic as an anion channel, which is allosterically controlled by pH conditions and is eliminated by a single amino acid mutation. However, the molecular mechanism of anion permeation through AQP6 remains unclear. Using molecular dynamics simulations in the presence of a transmembrane voltage utilizing an ion concentration gradient, we show that chloride ions permeate through the pore corresponding to the central axis of the AQP6 homotetramer. Under low pH conditions, a subtle opening of the hydrophobic selectivity filter (SF), located near the extracellular part of the central pore, becomes wetted and enables anion permeation. Our simulations also indicate that a single mutation (N63G) in human AQP6, located at the central pore, significantly reduces anion conduction, consistent with experimental data. Moreover, we demonstrate that the pH-sensing mechanism in which the protonation of H184 and H189 under low pH conditions allosterically triggers the gating of the SF region. These results suggest a unique pH-dependent allosteric anion permeation mechanism in AQP6 and could clarify the role of the central pore in some of the AQP tetramers.

Transcriptome and metabolome analyses reveal the regulatory role of MdPYL9 in drought resistance in apple

BackgroundThe mechanisms by which the apple MdPYL9 gene mediates the response to drought stress remain unclear. Here, transcriptome and metabolome analyses of apple plants under drought were used to investigate the mechanisms by which MdPYL9 regulates the response to drought stress in apple. MdPYL9-overexpressed transgenic and non-transgenic apple histoculture seedlings were rooted, transplanted, and subjected to drought treatments to clarify the mechanisms underlying the responses of apples to drought stress through phenotypic observations, physiological and biochemical index measurements, and transcriptomic and metabolomic analyses.ResultsUnder drought stress treatment, transgenic plants were less affected by drought stress than non-transgenic plants. Decreases in the net photosynthetic rate, stomatal conductance, and transpiration rate of transgenic apple plants were less pronounced in transgenic plants than in non-transgenic plants, and increases in the intercellular CO2 concentration were less pronounced in transgenic plants than in non-transgenic plants. The relative electrical conductivity and content of malondialdehyde, superoxide anion, and hydrogen peroxide were significantly lower in transgenic plants than in non-transgenic plants, and the chlorophyll content and activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) were significantly higher in transgenic plants than in non-transgenic plants. The number of differentially expressed genes (DEGs) involved in the response to drought stress was lower in transgenic plants than in non-transgenic plants, and the most significant and highly annotated DEGs in the transgenic plants were involved in the flavonoid biosynthesis pathway, and the most significant and highly annotated DEGs in control plants were involved in the phytohormone signal transduction pathway. The number of differentially accumulated metabolites involved in the response to drought stress was lower in transgenic plants than in non-transgenic plants, and up-regulated metabolites were significantly enriched in apigenin-7-O-glucoside in transgenic plants and in abscisic acid in non-transgenic plants. In the flavonoid biosynthetic pathway, the expression of genes encoding chalcone synthase (CHS) and chalcone isomerase (CHI) was more significantly down-regulated in non-transgenic plants than in transgenic plants, and the expression of the gene encoding 4-coumarate-CoA ligase (4CL) was more significantly up-regulated in transgenic plants than in non-transgenic plants, which resulted in the significant up-regulation of apigenin-7-O-glucoside in transgenic plants.ConclusionsThe above results indicated that the over-expression of MdPYL9 increased the drought resistance of plants under drought stress by attenuating the down-regulation of the expression of genes encoding CHS and CHI and enhancing the up-regulated expression of the gene encoding 4CL, which enhanced the content of apigenin-7-O-glucoside.

CsSHMT3 gene enhances the growth and development in cucumber seedlings under salt stress.

Salt stress is one of the major factors limiting plant growth and productivity. Many studies have shown that serine hydroxymethyltransferase (SHMT) gene play an important role in growth, development and stress response in plants. However, to date, there have been few studies on whether SHMT3 can enhance salt tolerance in plants. Therefore, the effects of overexpression or silencing of CsSHMT3 gene on cucumber seedling growth under salt stress were investigated in this study. The results showed that overexpression of CsSHMT3 gene in cucumber seedlings resulted in a significant increase in chlorophyll content, photosynthetic rate and proline (Pro) content, and antioxidant enzyme activity under salt stress condition; whereas the content of malondialdehyde (MDA), superoxide anion (H2O2), hydrogen peroxide (O2·-) and relative conductivity were significantly decreased when CsSHMT3 gene was overexpressed. However, the content of chlorophyll and Pro, photosynthetic rate, and antioxidant enzyme activity of the silenced CsSHMT3 gene lines under salt stress were significantly reduced, while MDA, H2O2, O2·- content and relative conductivity showed higher level in the silenced CsSHMT3 gene lines. It was further found that the expression of stress-related genes SOD, CAT, SOS1, SOS2, NHX, and HKT was significantly up-regulated by overexpressing CsSHMT3 gene in cucumber seedlings; while stress-related gene expression showed significant decrease in silenced CsSHMT3 gene seedlings under salt stress. This suggests that overexpression of CsSHMT3 gene increased the salt tolerance of cucumber seedlings, while silencing of CsSHMT3 gene decreased the salt tolerance. In conclusion, CsSHMT3 gene might positively regulate salt stress tolerance in cucumber and be involved in regulating antioxidant activity, osmotic adjustment, and photosynthesis under salt stress. KEY MESSAGE: CsSHMT3 gene may positively regulate the expression of osmotic system, photosynthesis, antioxidant system and stress-related genes in cucumber.

Ultrathin Free-Standing Porous Aromatic Framework Membranes for Efficient Anion Transport.

Porous aromatic frameworks (PAFs) show promising potential in anionic conduction due to their high stability and customizable functionality. However, the insolubility of most PAFs presents a significant challenge in their processing into membranes and subsequent applications. In this study, continuous PAF membranes with adjustable thickness were successfully created using liquid-solid interfacial polymerization. The rigid backbone and the stable C-C coupling endow PAF membrane with superior chemical and dimensional stabilities over most conventional polymer membranes. Different quaternary ammonium functionalities were anchored to the backbone through flexible alkyl chains with tunable length. The optimal PAF membrane exhibited an OH- conductivity of 356.6 mS ⋅ cm-1 at 80 °C and 98 % relative humidity. Additionally, the PAF membrane exhibited outstanding alkaline stability, retaining 95 % of its OH- conductivity after 1000 hours in 1 M NaOH. To the best of our knowledge, this is the first application of PAF materials in anion exchange membranes, achieving the highest OH- conductivity and exceptional chemical/dimensional stability. This work provides the possibility for the potential of PAF materials in anionic conductive membranes.

Ultrathin Free‐Standing Porous Aromatic Framework Membranes for Efficient Anion Transport

AbstractPorous aromatic frameworks (PAFs) show promising potential in anionic conduction due to their high stability and customizable functionality. However, the insolubility of most PAFs presents a significant challenge in their processing into membranes and subsequent applications. In this study, continuous PAF membranes with adjustable thickness were successfully created using liquid‐solid interfacial polymerization. The rigid backbone and the stable C−C coupling endow PAF membrane with superior chemical and dimensional stabilities over most conventional polymer membranes. Different quaternary ammonium functionalities were anchored to the backbone through flexible alkyl chains with tunable length. The optimal PAF membrane exhibited an OH− conductivity of 356.6 mS ⋅ cm−1 at 80 °C and 98 % relative humidity. Additionally, the PAF membrane exhibited outstanding alkaline stability, retaining 95 % of its OH− conductivity after 1000 hours in 1 M NaOH. To the best of our knowledge, this is the first application of PAF materials in anion exchange membranes, achieving the highest OH− conductivity and exceptional chemical/dimensional stability. This work provides the possibility for the potential of PAF materials in anionic conductive membranes.

High-strength anion-exchange fuel cell membranes based on imidazole-functionalized poly-ether-ether-ketone materials

Poly-ether-ether-ketone (PEEK), an organic polymer material with good thermal stability and tensile strength, has been regarded as an ideal material for anion-exchange membrane (AEM). Metal-organic framework materials (MOFs) possess excellent chemical stability and mechanical properties. In this work, MOF-801 was impregnated with ionic liquid and the obtained IL@MOF-801 was introduced into imidazole-functionalized PEEK to obtain IL@MOF/Im-PEEK composite anion exchange membranes. The addition of IL@MOF-801 not only increases the ion transport channels but also forms hydrogen bonding network with the imidazole groups on PEEK, which is beneficial for improving ion transport properties and mechanical strength. The anion-exchange membrane consisting of 4% IL@MOF-801/Im-PEEK achieved an anionic conductivity of 116.8 mS/cm at 80 °C and 100% RH and excellent mechanical properties with a tensile strength of up to 208.7 MPa.

CFTR expression in human salivary gland acinar cells.

The key role of CFTR in secretory epithelia has been extensively documented. Additionally, CFTR plays a significant role in ion absorption in exocrine glands, including salivary and sweat glands. Most of the knowledge about CFTR expression comes from animal models such as the mouse or the rat, but there is limited information about CFTR expression in human tissues. In the present study, we assessed the expression of CFTR in human submandibular and parotid glands. Consistent with findings in rodent salivary glands, our immunolocalization studies show that CFTR is expressed in duct cells. However, CFTR expression in human salivary glands differs from that in rodents, as immunolocalization and single-cell RNA sequencing analysis from a previous study performed in the human parotid gland revealed the presence of CFTR protein and transcripts within a distinct cell cluster. Based on cell marker expression, this cluster corresponds to acinar cells. To obtain functional evidence supporting CFTR expression, we isolated human parotid acinar cells through collagenase digestion. Acinar cells displayed an anion conductance that was activated in response to cAMP-increasing agents and was effectively blocked by CFTRInh172, a known CFTR blocker. This study provides novel evidence of CFTR expression within acinar cells of human salivary glands. This finding challenges the established model positioning CFTR exclusively in duct cells from exocrine glands.NEW & NOTEWORTHY This study addresses the uncertainty about the impact of CFTR on human salivary gland function. We found CFTR transcripts in a subset of duct cells known as ionocytes, as well as in acinar cells. Isolated human parotid acinar cells exhibited Cl- conductance consistent with CFTR activity. This marks the first documented evidence of functional CFTR expression in human salivary gland acinar cells.

Effect of B-site cationic substitution on the structural, spectroscopic, and conductivity behaviour of Ho2(Hf1-xZrx)2O7 (x=0 and 1)

Ideally, a solid electrolyte which is a central component of SOFC should exhibit high anionic or cationic ionic conductivity at the proposed operating temperatures. In most cases, the performance is compromised when operating above 1000 °C due to poor mechanical, thermal and chemical stability of selected functional and non-functional materials. In this context, pyrochlores are one of the potential candidates due to their high conductivity, flexibility to accommodate large cations, and high mechanical, thermal and chemical stability. In this study, we report the synthesis of nano-powders of Ho2Hf2O7 (HH) and Ho2Zr2O7 (HZ) pyrochlore ceramics by eco-friendly alginate mediated ion-exchange process also known as Leeds Alginate Process (LAP) and provide further insight into the structure - conductivity relationship of HH and HZ compounds by EXAFS studies. Both the compositions were sintered at temperatures, ranging from 1100 °C-1500 °C at 2 h dwell time to achieve the desired high-density ceramic with stable pyrochlore structure. X-ray diffraction and Extended X-ray absorption fine structural (EXAFS) analysis showed superlattice reflections and complex coordination geometry of these oxides. The coordination number and disorder factor in the case of HZ were found to be more stable than the HH sample, as evident from the EXAFS. Impedance spectroscopy and dc-conductivity analysis showed a better charge transport behavior in HZ ceramics than in HH making HZ as a preferred solid electrolyte for SOFC. The conductivity of Ho2Zr2O7 is comparable with the best-known fluorite oxide-ion conductor such as Sc2O3-stabilized ZrO2 at 500 °C.

A poly(binaphthyl-co-terphenyl quinuclidinium) anion exchange membrane with excellent alkaline stability and anion conductivity

Poly(aryl quinuclidinium) AEMs with improved anion conductivity and dimensional stability were prepared by introducing twisted structural units.

Изменение состава твердых нестехиометрических соединений методом ионного переноса

The paper presents results of measuring electron and ion transfer numbers of titanium hydride, carbide and nitride. It is shown that these compounds had mixed electron-ionic (anionic) conductivity. The dependences of the ion transfer number on the non-metal content in titanium carbide and nitride were obtained, and the change of the non-metal content under the influence of an electric field was studied. The non-metal atoms in non-stoichiometric titanium carbide and nitride were located in the octahedral voids of the titanium cubic lattice, forming a non-metal sublattice. Non-stoichiometric titanium hydride had a fluorite-type cubic crystal lattice, and the hydrogen atoms were located in the tetrahedral voids of the cubic titanium lattice. In titanium boride, ionic conductivity appeared near compounds of stoichiometric composition. It is shown that the formation of interstitial phases corresponded to the Hegg criterion. Due to the existence of vacancies in the non-metal sublattice, ion transfer was possible under the influence of an electric field, resulting in a chemical composition change of non-stoichiometric compounds. Analysis of the physicochemical properties of non-stoichiometric transition metal compounds was carried out as an opportunity to detect the ionic conductivity of carbides, nitrides and oxides.

Enhanced OH− conductivity from 3D alkaline graphene oxide electrolytes for anion exchange membrane fuel cells

Herein, we have engineered graphene oxide through pH change and freeze drying to get three-dimensional alkaline graphene oxide, and the resulting solid electrolyte exhibited efficient anion conductivity behavior.