Transmembrane Ion Transport Research Articles

Multi-Omics Reveal the Improvements of Nutrient Digestion, Absorption, and Metabolism and Intestinal Function via GABA Supplementation in Weanling Piglets

The nonprotein amino acid γ-aminobutyric acid (GABA) can enhance intestinal function in piglets; however, the mechanisms involved are not yet fully understood. To explore the effects of GABA and its underlying mechanisms, weanling piglets were randomly assigned to three groups, receiving either a basal diet or a basal diet supplemented with GABA (80 mg/kg or 120 mg/kg). The results demonstrated that dietary GABA improved growth performance and reduced diarrhea incidence (p < 0.05). Additionally, GABA supplementation decreased the serum and intestinal levels of pro-inflammatory cytokines (p < 0.05), and improved intestinal morphology. Multi-omics analyses were employed to explore the alterations caused by GABA supplementation and elucidate the related mechanisms. Microbiota profiling revealed improved beta-diversity and changes in the composition of ileal bacteria and fungi. Amino acid metabolism, lipid metabolism, and digestive processes were primarily enriched in the GABA group according to metabolomics analysis. A transcriptome analysis showed significant enrichment in ion transmembrane transport and nutrition absorption and digestion pathways in the ileum. Furthermore, increased lipase and trypsin activity, along with the elevated expression of tight junction proteins confirmed the beneficial effects of GABA on intestinal nutrient metabolism and barrier function. In conclusion, dietary 80 mg/kg GABA supplementation improved nutrient digestion and absorption and intestinal function in weanling piglets.

Poly(bis(1‐methylpiperazin‐1‐ium‐amide) Nanofilm Composite Membrane with Nanochannel‑Enabled Microporous Structure and Enhanced Steric Hindrance for Magnesium/Lithium Separation

AbstractEfficient lithium/magnesium (Li+/Mg2+) separation attainment is fundamental to the extraction of lithium from brine by nanofiltration membrane separation process, which is essential for resource recovery and a circular water economy. However, for poly(piperazine‐amide) nanofilm composite membranes, the higher electronegativity affects the Mg2+ rejection and consequently Li+/Mg2+ separation performance. Manipulating the positive charge density and pore size regulation of the nanofiltration membranes are determinative of the Li+/Mg2+ separation performance improvement. Here, a new monomer 1,1′‐(hexane‐1,6‐diyl)bis(1‐methylpiperazin‐1‐ium) bromide containing bis‐quaternary ammonium cations is employed as a molecular building block to fabricate polyamide nanofilms via interfacial polymerization. The dual quaternary ammoniums and the rod‐shaped conformation of the monomer confer enhanced electropositivity, steric hindrance, loosely packed microporous network structure (pore diameter∼0.8–1.35 nm), and high free volume. The resultant membrane exhibits high water permeance of 28.34 L m−2 h−1 bar−1 with good Li+/Mg2+ selectivity of up to 76.9. In addition, the membrane also exhibits chlorine stability performance owing to the lack of the chlorine sensitive −NH groups in the formed tertiary amide structures. Computational insights on the structural properties, nanofilm formation, and transmembrane water and ion transport behaviors are provided. This study offers insightful theoretical and technological concepts to design and construct membrane materials for energy‐efficient separations.

Transcriptome analysis of Ochratoxin a (OTA) producing Aspergillus westerdijkiae fc-1 under varying osmotic pressure

ABSTRACT Ochratoxin A (OTA) is a toxic secondary metabolite produced by the Aspergillus species which can contaminate various food products. This study analysed the transcriptome of the Aspergillus westerdijkiae fc-1 strain under NaCl concentrations of 0, 20, and 100 g/L using RNA-Seq technology to examine gene transcriptional changes linked to osmotic stress and OTA production. Significant changes were observed in metabolic-pathways associated with carbohydrates, cellular communication, and hydrolase activity under 20 g/L NaCl. The HOG1 gene, associated with osmotic pressure regulation was down-regulated by 78.06%. In contrast, OTA biosynthesis genes otaA, otaB, and otaC were up-regulated by 3.26 fold, 1.99 fold, and 2.06 fold, respectively. Conversely, the otaD gene was down-regulated by 43.50%. At 100 g/L NaCl, pathways related to ion transport, peptide metabolism, ribosomal function, and transmembrane transporter protein activities were significantly up-regulated. The HOG1 gene was up-regulated by 28.32% and OTA biosynthesis genes otaA, otaB, otaC, and otaD showed up-regulation of 27.06%, 36.80%, 19.59%, and 5.72 fold, respectively. The study highlights the role of metabolic pathways in osmotic stress regulation and the correlations between HOG1 expression and OTA biosynthesis genes, providing insights for developing strategies to prevent OTA contamination in food.

Chronic heat stress upregulates pyruvate metabolic process and gluconeogenesis but downregulates immune responses in Sahiwal cattle.

Climate change and growing population and their strain on animal production are the impending challenges that the developing countries, like India, need to tackle in the coming days. This study aimed to detect and analyze the uncharacterized variation in the gene expression patterns with the change of condition, from thermoneutral to chronic hot-humid, in the Sahiwal cattle, one of the best breeds of milk-producing cattle in India, known for being heat-tolerant. Using RNA-Seq analysis on peripheral blood mononuclear cells (PBMCs), 4021 differentially expressed mRNAs (2772 upregulated, 1249 downregulated) and 1303 differentially expressed long non-coding RNAs (769 upregulated, 534 downregulated) were identified, with the thresholds of false discovery rate < 0.05 and|log2(fold change)| > 2. Significantly (p-adjusted < 0.05) overrepresented Gene Ontology (GO) terms, Kyoto Encyclopedia of Genes and Genomes (KEGG), and Reactome pathways were analyzed, revealing upregulation of processes like pyruvate metabolic process, gluconeogenesis, ion transmembrane transport, neuropeptide signaling pathway, and animal organ development, with genes like SHH, GRK1, CHRM3, CAMK2A, and HSPB7 were upregulated, while translation and immune responses, with genes like RPS3, EEF1A1, TNF, BoLA-DRB3, and UBB were downregulated. Analysis of cis-mRNAs of DE-lncRNAs showed presence of both up- and down-regulated cis-mRNAs for both up- and down-regulated lncRNAs indicating existence of positive and negative regulation of mRNA expression by lncRNAs. Managemental nudges that decrease metabolic heat generation, like betaine and chromium supplementation, and increase heat dissipation, like microenvironment cooling, should be utilized. This study highlights the role of pyruvate metabolism and gluconeogenesis in coping up with heat stress and offers an improved understanding of the heat stress response of Sahiwal cattle along with the genes and pathways responsible for it.

Metabolic Pathophysiology of Cortical Spreading Depression: A Review.

Cortical spreading depression (CSD) is an electrophysiologic pathological state in which a wave of depolarization in the cerebral cortex is followed by the suppression of spontaneous neuronal activity. This transient spread of neuronal depolarization on the surface of the cortex is the hallmark of CSD. Numerous investigations have demonstrated that transmembrane ion transport, astrocytic ion clearing and fatigue, glucose metabolism, the presence of certain genetic markers, point mutations, and the expression of the enzyme responsible for the production of various arachidonic acid derivatives that participate in the inflammatory response, namely, cyclooxygenase (COX), all influence CSD. Here, we explore the associations between CSD occurrence in the cortex and various factors, including how CSD is related to migraines, how the glucose state affects CSD, the effect of TBI and its relationship with CSD and glucose metabolism, how different markers can be measured to determine the severity of CSD, and possible connections to oligemia, orexin, and leptin.

TARGETING RESIDUAL CANCER FROM THE INVASIVE MARGIN OF GLIOBLASTOMA USING COMPUTATIONAL TOOLKITS

Abstract AIMS Infiltrative margin GBM, as a proxy for residual disease post-surgery, can be identified by 5-aminolevulininc acid (5ALA) to facilitate the discovery of uniquely expressed or upregulated molecular pathways. Complementary bioinformatics approaches offer reproducible ways to enable interoperability of heterogenous data sources towards identification of therapeutic targets associated with GBM infiltration. METHOD RNA-seq primary tumour data was first categorised as: 5ALA+ (infiltrative margin) vs tumour core and 5ALA+ vs 5ALA- (reactive brain). Two levels of filtration (genes with adjusted p-value &amp;lt;0.05; degree of fold change with log2&amp;gt;1.5) were applied to genes, creating two separate gene lists. Cross-referencing gene lists identified transcripts upregulated in both 5ALA+ vs core and 5ALA+ vs 5ALA-. This candidate gene list was inputted into STRING to generate an uncurated protein-protein interaction (PPI) network, which returned a significant PPI enrichment p-value to confirm network connectivity, and next inputted into Metascape to elucidate biological processes associated with tumour infiltration. RESULTS Of 141 upregulated 5ALA+ genes TCP10L3, HELT, MGAM, ALOX5 and FOXI1 exhibited the greatest fold change. The most prevalent 5ALA+ biological processes were primitive streak formation, disaccharide metabolic process and sodium ion transmembrane transport. LOC157273, LINC00200, LINC00656, LOC285626 and LINC01568 were identified as long non-coding RNAs (lncRNA) most abundant in the infiltrative margin of GBM relative to tumour core and reactive brain. Regulatory associations between candidate 5ALA+ lncRNA and genes, and in silico drug repurposing via molecular docking, are being investigated. CONCLUSION The plasticity of GBM warrants analysis of the GBM infiltrative margin via computational toolkits to enhance understanding of upregulated molecular pathways, functionally associated with an invasive phenotype.

Macroscale connectome topographical structure reveals the biomechanisms of brain dysfunction in Alzheimer's disease.

The intricate spatial configurations of brain networks offer essential insights into understanding the specific patterns of brain abnormalities and the underlying biological mechanisms associated with Alzheimer's disease (AD), normal aging, and other neurodegenerative disorders. This study investigated alterations in the topographical structure of the brain related to aging and neurodegenerative diseases by analyzing brain gradients derived from structural MRI data across multiple cohorts (n = 7323). The analysis identified distinct gradient patterns in AD, aging, and other neurodegenerative conditions. Gene enrichment analysis indicated that inorganic ion transmembrane transport was the most significant term in normal aging, while chemical synaptic transmission is a common enrichment term across various neurodegenerative diseases. Moreover, the findings show that each disorder exhibits unique dysfunctional neurophysiological characteristics. These insights are pivotal for elucidating the distinct biological mechanisms underlying AD, thereby enhancing our understanding of its unique clinical phenotypes in contrast to normal aging and other neurodegenerative disorders.

Unveiling mitochondria as central components driving cognitive decline in alzheimer's disease through cross-transcriptomic analysis of hippocampus and entorhinal cortex microarray datasets

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by symptoms such as memory loss and impaired learning. This study conducted a cross-transcriptomic analysis of AD using existing microarray datasets from the hippocampus (HC) and entorhinal cortex (EC), comparing them with age-matched non-AD controls. Both of these brain regions are critical for learning and memory processing and are vulnerable areas that exhibit abnormalities in early AD. The cross-transcriptomic analysis identified 564 significantly differentially expressed genes in HC and 479 in EC. Among these, 151 genes were significantly differentially expressed in both tissues, with functions related to synaptic vesicle clustering, synaptic vesicle exocytosis/endocytosis, mitochondrial ATP synthesis, hydrogen ion transmembrane transport, and structural constituent of cytoskeleton, suggesting a potential association between cognitive decline in AD, synaptic vesicle dynamics, dysregulation of cytoskeleton organization, and mitochondrial dysfunction. Further gene ontology analysis specific to the HC revealed the gene ontology enrichment in aerobic respiration, synaptic vesicle cycle, and oxidative phosphorylation. The enrichment analysis in CA1 of HC revealed differentiation in gene expression related to mitochondrial membrane functions involved in bioenergetics, mitochondrial electron transport, and biological processes associated with microtubule-based process, while analysis in the EC region showed enrichment in synaptic vesicle dynamics which is associated with neurotransmitter release and the regulation of postsynaptic membrane potential and synaptic transmission of GABAergic and glutamatergic synapse. Protein-protein interaction analysis highlighted central hub proteins predominantly expressed in mitochondria, involved in regulation of oxidative stress and ATP synthesis. These hub proteins interact not only within the mitochondria but also with proteins in the vesicular membrane and neuronal cytoskeleton, indicating a central role of mitochondria. This finding underscores the association between clinical symptoms and mitochondrial dysregulation of synaptic vesicle dynamics, cytoskeleton organization, and mitochondrial processes in both the HC and EC of AD. Therefore, targeting these dysregulated pathways could provide promising therapeutic targets aimed at cognitive decline and memory impairment in early AD stages.

Identification of pivotal genes and pathways in Chorea-acanthocytosis using comprehensive bioinformatic analysis.

Chorea-acanthocytosis (ChAc), an autosomal recessive disorder, is associated with cognitive and behavioral abnormalities. Previous studies were focused around exploring the functional annotation of VPS13A gene in ChAc, whereas the genetic labyrinth underlying this disease and plausible drug targets were underexplored. In the present study, we have identified the pivotal genes and molecular pathways implicated in ChAc using comprehensive bioinformatics analysis. In our analysis we found 27 distinct genes in Homo sapiens linked to ChAc, out of which 15 were selected as candidate genes for enrichment analysis based on their Gene Ontology (GO) annotations and involvement in relevant molecular pathways. By constructing a Protein-Protein Interaction (PPI) network consisting of 26 nodes and 62 edges, we identified two gene modules. Subsequently, using the MCODE algorithm, we identified 6 hub genes-ATN1, JPH3, TBP, VPS13A, DMD, and HTT-as core candidates. These hub genes are primarily associated with processes such as neuron development and differentiation, the CAMKK-AMPK signaling cascade, ion transmembrane transport systems, and protein localization. Furthermore, using drug gene databank we identified 23 FDA-approved drugs that possess the propensity to target 3 out of the 6 identified hub genes. We believe that our findings could open promising avenues for potential therapeutic interventions in ChAc.

Light-Powered Propeller-like Transporter for Boosted Transmembrane Ion Transport.

Membrane-active molecular machines represent a recently emerging, yet important line of expansion in the field of artificial transmembrane transporters. Their hitherto demonstrated limited types (molecular swing, ion fishers, shuttlers, rotors, etc.) certainly call for new inspiring developments. Here, we report a very first motorized ion-transporting carrier-type transporter, i.e., a modularly tunable, light-powered propeller-like transporter derived from Feringa's molecular motor for consistently boosting transmembrane ion transport under continuous UV light irradiation. Based on the EC50 values, the molecular propeller-mediated ion transport activities under UV light irradiation for 300 s are 2.31, 1.74, 2.29, 2.80, and 2.92 times those values obtained without irradiation for Li+, Na+, K+, Rb+, and Cs+ ions, respectively, with EC50 value as low as 0.71 mol % for K+ ion under light irradiation.

Mechanisms by Which Exogenous Substances Enhance Plant Salt Tolerance through the Modulation of Ion Membrane Transport and Reactive Oxygen Species Metabolism.

Soil salinization is one of the major abiotic stresses affecting plant growth and development. Plant salt tolerance is controlled by complex metabolic pathways. Exploring effective methods and mechanisms to improve crop salt tolerance has been a key aspect of research on the utilization of saline soil. Exogenous substances, such as plant hormones and signal transduction substances, can regulate ion transmembrane transport and eliminate reactive oxygen species (ROS) to reduce salt stress damage by activating various metabolic processes. In this review, we summarize the mechanisms by which exogenous substances regulate ion transmembrane transport and ROS metabolism to improve plant salt tolerance. The molecular and physiological relationships among exogenous substances in maintaining the ion balance and enhancing ROS clearance are examined, and trends and research directions for the application of exogenous substances for improving plant salt tolerance are proposed.

Regulation of Cell Membrane Potential through Supramolecular System for Activating Calcium Ion Channels.

The regulation of the cell membrane potential plays a crucial role in governing the transmembrane transport of various ions and cellular life processes. However, in situ and on-demand modulation of cell membrane potential for ion channel regulation is challenging. Herein, we have constructed a supramolecular assembly system based on water-soluble cationic oligo(phenylenevinylene) (OPV) and cucurbit[7]uril (CB[7]). The controllable disassembly of OPV/4CB[7] combined with the subsequent click reaction provides a step-by-step adjustable surface positive potential. These processes can be employed in situ on the plasma membrane to modulate the membrane potential on-demand for precisely controlling the activation of the transient receptor potential vanilloid 1 (TRPV1) ion channel and up-regulating exogenous calcium-responsive gene expression. Compared with typical optogenetics, electrogenetics, and mechanogenetics, our strategy provides a perspective supramolecular genetics toolbox for the regulation of membrane potential and downstream intracellular gene regulation events.

Differential expression of ion channel coding genes in the endometrium of women experiencing recurrent implantation failures

Our study probed the differences in ion channel gene expression in the endometrium of women with Recurrent Implantation Failure (RIF) compared to fertile women. We analyzed the relative expression of genes coding for T-type Ca2+, ENaC, CFTR, and KCNQ1 channels in endometrial samples from 20 RIF-affected and 10 control women, aged 22–35, via microarray analysis and quantitative real-time PCR. Additionally, we examined DNA methylation in the regulatory region of KCNQ1 using ChIP real-time PCR. The bioinformatics component of our research included Gene Ontology analysis, protein–protein interaction networks, and signaling pathway mapping to identify key biological processes and pathways implicated in RIF. This led to the discovery of significant alterations in the expression of ion channel genes in RIF women’s endometrium, most notably an overexpression of CFTR and reduced expression of SCNN1A, SCNN1B, SCNN1G, CACNA1H, and KCNQ1. A higher DNA methylation level of KCNQ1’s regulatory region was also observed in RIF patients. Gene-set enrichment analysis highlighted a significant presence of genes involved with ion transport and membrane potential regulation, particularly in sodium and calcium channel complexes, which are vital for cation movement across cell membranes. Genes were also enriched in broader ion channel and transmembrane transporter complexes, underscoring their potential extensive role in cellular ion homeostasis and signaling. These findings suggest a potential involvement of ion channels in the pathology of implantation failure, offering new insights into the mechanisms behind RIF and possible therapeutic targets.

G-quadruplex-Based Artificial Transmembrane Channels Induce Cancer Cell Apoptosis by Perturbing Potassium Ion Homeostasis.

Transmembrane ion transport modality has received a widespread attention due to its apoptotic activation toward anticancer cell activities. In this study, G-quadruplex-based potassium-specific transmembrane channels have been developed to facilitate the intracellular K+ efflux, which perturbs the cellular ion homeostasis thereby inducing cancer cell apoptosis. Cholesterol-tag, a lipophilic anchor moiety, serves as a rudiment for the G-quadruplex immobilization onto the membrane, while G-quadruplex channel structure as a transport module permits ion binding and migration along the channels. A c-Myc sequence tagged with two-cholesterol is designed as a representative lipophilic G-quadruplex, which forms intramolecular parallel G-quadruplex with three stacks of G-quartets (Ch2-Para3). Fluorescence transport assay demonstrates Ch2-Para3 a high transport activity (EC50 = 10.9 × 10-6 m) and an ion selectivity (K+/Na+ selectivity ratio of 84). Ch2-Para3 mediated K+ efflux in cancer cells is revealed to purge cancer cells through K+ efflux-mediated cell apoptosis, which is confirmed by monitoring the changes in membrane potential of mitochondria, leakage of cytochrome c, reactive oxygen species yield, as well as activation of a family of caspases. The lipophilic G-quadruplex exhibits obvious antitumor activity in vivo without systemic toxicity. This study provides a functional scheme aimed at generating DNA-based selective artificial membrane channels for the purpose of regulating cellular processes and inducing cell apoptosis, which shows a great promising for anticancer therapy in the future.

Whole-genome resequencing identifies candidate genes associated with heat adaptation in chickens

The wide distribution and diverse varieties of chickens make them important models for studying genetic adaptation. The aim of this study was to identify genes that alter heat adaptation in commercial chicken breeds by comparing genetic differences between tropical and cold-resistant chickens. We analyzed whole-genome resequencing data of 186 chickens across various regions in Asia, including the following breeds: Bian chickens (B), Dagu chickens (DG), Beijing-You chickens (BY), and Gallus gallus jabouillei from China; Gallus gallus murghi from India; Vietnam native chickens (VN); Thailand native chickens (TN) and Gallus gallus spadiceus from Thailand; and Indonesia native chickens (IN), Gallus gallus gallus, and Gallus gallus bankiva from Indonesia. In total, 5,454,765 SNPs were identified for further analyses. Population genetic structure analysis revealed that each local chicken breed had undergone independent evolution. Additionally, when K = 5, B, BY, and DG chickens shared a common ancestor and exhibited high levels of inbreeding, suggesting that northern cold-resistant chickens are likely the result of artificial selection. In contrast, the runs of homozygosity (ROH) and the ROH-based genomic inbreeding coefficient (FROH) results for IN, TN, and VN chickens showed low levels of inbreeding. Low population differentiation index values indicated low differentiation levels, suggesting low genetic diversity in tropical chickens, implying increased vulnerability to environmental changes, decreased adaptability, and disease resistance. Whole-genome selection sweep analysis revealed 69 candidate genes, including LGR4, G6PC, and NBR1, between tropical and cold-resistant chickens. The genes were further subjected to GO and KEGG enrichment analyses, revealing that most of the genes were primarily enriched in biological synthesis processes, metabolic processes, central nervous system development, ion transmembrane transport, and the Wnt signaling pathway. Our study identified heat adaptation genes and their functions in chickens that primarily affect chickens in high-temperature environments through metabolic pathways. These heat-resistance genes provide a theoretical basis for improving the heat-adaptation capacity of commercial chicken breeds.

Novel pathways linked to the expression of temperament in Merino sheep: a genome-wide association study

Animal temperament refers to the inherent behavioural and emotional characteristics of an animal, influencing how it interacts with its environment. The selection of sheep for temperament can change the temperament traits of the selected line and improve the welfare and production (reproduction, growth, immunity) of those animals. To understand the genetics that underly variation in temperament in sheep, and how selection on temperament can affect other production traits, a genome-wide association study was carried out. Merino sheep from lines selected for traits of calm and nervous temperament, and a commercial population, on which the temperament traits had never been assessed, were used. Blood samples from the three populations were genotyped using an Illumina GGP Ovine 50 K Genotyping BeadChip. The calm and nervous populations in the selected lines presented as distinct genetic populations, and 2 729 of the 45 761 single nucleotide polymorphisms (SNPs) had significantly different proportions between the two lines. Of those 2 729 SNPs, 2 084 were also associated with temperament traits in the commercial population. A genomic annotation identified 81 candidate genes for temperament, nearly half of which are associated with disorders of social behaviour in humans. Five of those 81 candidate genes are related to production traits in sheep. Two genes were associated with personality disorders in humans and with production traits in sheep. We identified significant enrichment in genes involved in nervous system processes such as the regulation of systemic arterial blood pressure, ventricular myocyte action, multicellular organismal signalling, ion transmembrane transport, and calcium ion binding, suggesting that temperament is underpinned by variation in multiple biological systems. Our results contribute to understanding of the genetic basis of animal temperament which could be applied to the genetic evaluation of temperament in sheep and other farm animals.

Exploration on the potential efficacy and mechanism of methyl salicylate glycosides in the treatment of schizophrenia based on bioinformatics, molecular docking and dynamics simulation

The etiological and therapeutic complexities of schizophrenia (SCZ) persist, prompting exploration of anti-inflammatory therapy as a potential treatment approach. Methyl salicylate glycosides (MSGs), possessing a structural parent nucleus akin to aspirin, are being investigated for their therapeutic potential in schizophrenia. Utilizing bioinformation mining, network pharmacology, molecular docking and dynamics simulation, the potential value and mechanism of MSGs (including MSTG-A, MSTG-B, and Gaultherin) in the treatment of SCZ, as well as the underlying pathogenesis of the disorder, were examined. 581 differentially expressed genes related to SCZ were identified in patients and healthy individuals, with 349 up-regulated genes and 232 down-regulated genes. 29 core targets were characterized by protein-protein interaction (PPI) network, with the top 10 core targets being BDNF, VEGFA, PVALB, KCNA1, GRIN2A, ATP2B2, KCNA2, APOE, PPARGC1A and SCN1A. The pathogenesis of SCZ primarily involves cAMP signaling, neurodegenerative diseases and other pathways, as well as regulation of ion transmembrane transport. Molecular docking analysis revealed that the three candidates exhibited binding activity with certain targets with binding affinities ranging from −4.7 to −109.2 kcal/mol. MSTG-A, MSTG-B and Gaultherin show promise for use in the treatment of SCZ, potentially through their ability to modulate the expression of multiple genes involved in synaptic structure and function, ion transport, energy metabolism. Molecular dynamics simulation revealed good binding abilities between MSTG-A, MSTG-B, Gaultherin and ATP2B2. It suggests new avenues for further investigation in this area.

Forbidden ion transport through cation exchange membranes

Cation exchange membranes (CEMs) are widely used in many applications. The fixed anionic groups e.g., COO−, –SO3-, etc. in the polymer matrix ideally allows the passage only of oppositely charged cations, driven by a potential or a concentration gradient. Anions, charged negative, the same as the membrane matrix, cannot pass through the membrane due to electrostatic repulsion. Such “Donnan-forbidden” passage can, however, occur to some degree, if the electrical or concentration gradient is high enough to overcome the “Donnan barrier”. Except for salt uptake/transport in concentrated salt solutions, the factors that govern such Forbidden Ion Transport (FIT) have rarely been studied. In most applications of transmembrane ion transport, whether electrically driven as in electrodialysis, or concentration-driven, it is the transport of the counterion to the fixed charged groups, such as that of the proton through a CEM, that is usually of interest. Nevertheless, CEMs are also of interest in analytical chemistry, specifically in suppressed ion chromatography. As used in membrane suppressors, both transport of permitted ions and rejection of forbidden ions are important. If the latter is indeed governed by electrostatic factors, other things being equal, the primary governing factor should be the charge density of the membrane, tantamount to its ion exchange capacity (IEC). In fabricating microscale suppressors, we found useful to synthesize a new ion exchange polymer that can be easily molded to make tubular microconduits. Despite a high IEC of this material, FIT was also found to be surprisingly high. We measured several relevant properties for thirteen commercial and four custom-made membranes to discover that while FIT is indeed linearly related to 1/IEC for a significant number of these membranes, for very high water-content membranes, FIT may be overwhelmingly governed by the water content of the membrane. In addition, FIT through all CEMs differ greatly among strong acids, they may still be transported as the molecular acids and the extent is in the same order as the expected activity of the molecular acid in the CEM. These results are discussed with the perspective that even for strong acids, the transport does take place as un-ionized molecular acids.

Fine-tuning of membrane permeability by reversible photoisomerization of aryl-azo derivatives of thymol embedded in lipid nanoparticles

Responsiveness of liposomes to external stimuli, such as light, should allow a precise spatial and temporal control of release of therapeutic agents or ion transmembrane transport. Here, some aryl-azo derivatives of thymol are synthesized and embedded into liposomes from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine to obtain light-sensitive membranes whose photo-responsiveness, release behaviour, and permeability towards Cl- ions are investigated. The hybrid systems are in-depth characterized by dynamic light scattering, atomic force microscopy and Raman spectroscopy. In liposomal bilayer the selected guests undergo reversible photoinduced isomerization upon irradiation with UV and visible light, alternately. Non-irradiated hybrid liposomes retain entrapped 5(6)-carboxyfluorescein (CF), slowing its spontaneous leakage, whereas UV-irradiation promotes CF release, due to guest trans-to-cis isomerization. Photoisomerization also influences membrane permeability towards Cl- ions. Data processing, according to first-order kinetics, demonstrates that Cl- transmembrane transport is enhanced by switching the guest from trans to cis but restored by back-switching the guest from cis to trans upon illumination with blue light. Finally, the passage of Cl- ions across the bilayer can be fine-tuned by irradiation with light of longer λ and different light-exposure times. Fine-tuning the photo-induced structural response of the liposomal membrane upon isomerization is a promising step towards effective photo-dynamic therapy.

High-performance osmotic energy harvesting enabled by the synergism of space and surface charge in two-dimensional nanofluidic membranes

As promising prospects for renewable power harvesting, two-dimensional (2D) nanochannels for osmotic energy capture in a reverse electrodialysis arrangement have garnered significant attention. However, existing 2D nanochannel membranes have shown limited power generation capabilities due to challenges in balancing ion flux and selectivity. Here, we construct montmorillonite (MMT)/TEMPO-mediated oxidation cellulose nanofibers (TOCNFs) nanocomposite membranes for enhanced ion transmembrane transport. The intercalation of TOCNFs not only enlarges the interlayer distance, but also provides abundant space charge inside the nanochannels. Benefiting from the strong ion selectivity and high ion flux, the composite membrane achieves a remarkable power output of ∼16.57 W/m2 in the gradient of artificial seawater and river water, exceeding that of the state-of-the-art heterogeneous membrane-based osmotic energy conversion systems. Both experimental and theoretical findings confirm that the synergism of space and surface charge plays a crucial role in promoting osmotic energy conversion. This research contributes valuable insights into the optimization of 2D membranes for efficient clean energy harvesting purposes.