Search Results (29)

This study presents a theoretical investigation into the voltammetric behavior of bipolar interfacial nanopores due to the effect of potential scan rate (1–1000 V/s). Finite element method (FEM) is utilized to explore the current–voltage (I–V) properties of bipolar interfacial nanopores at different bulk salt concentrations. The results demonstrate a strong impact of the scan rate on the I–V response of bipolar interfacial nanopores, particularly at relatively low concentrations. Hysteresis loops are observed in bipolar interfacial nanopores under specific scan rates and potential ranges and divided by a cross-point potential that remains unaffected by the scan rate employed. This indicates that the current in bipolar interfacial nanopores is not just reliant on the bias potential that is imposed but also on the previous conditions within the nanopore, exhibiting history-dependent or memory effects. This scan-rate-dependent current–voltage response is found to be significantly influenced by the length of the nanopore (membrane thickness). Thicker membranes exhibit a more pronounced scan-rate-dependent phenomenon, as the mass transfer of ionic species is slower relative to the potential scan rate. Additionally, unlike conventional bipolar nanopores, the ion current passing through bipolar interfacial nanopores is minimally affected by the membrane thickness, making it easier to detect. Full article

This review presents current knowledge related to the voltage-dependent anion channel-1 (VDAC1) as a multi-functional mitochondrial protein that acts in regulating both cell life and death. The location of VDAC1 at the outer mitochondrial membrane (OMM) allows control of metabolic cross-talk between the mitochondria and the rest of the cell, and also enables its interaction with proteins that are involved in metabolic, cell death, and survival pathways. VDAC1′s interactions with over 150 proteins can mediate and regulate the integration of mitochondrial functions with cellular activities. To target these protein–protein interactions, VDAC1-derived peptides have been developed. This review focuses specifically on cell-penetrating VDAC1-based peptides that were developed and used as a “decoy” to compete with VDAC1 for its VDAC1-interacting proteins. These peptides interfere with VDAC1 interactions, for example, with metabolism-associated proteins such as hexokinase (HK), or with anti-apoptotic proteins such as Bcl-2 and Bcl-xL. These and other VDAC1-interacting proteins are highly expressed in many cancers. The VDAC1-based peptides in cells in culture selectively affect cancerous, but not non-cancerous cells, inducing cell death in a variety of cancers, regardless of the cancer origin or genetics. They inhibit cell energy production, eliminate cancer stem cells, and act very rapidly and at low micro-molar concentrations. The activity of these peptides has been validated in several mouse cancer models of glioblastoma, lung, and breast cancers. Their anti-cancer activity involves a multi-pronged attack targeting the hallmarks of cancer. They were also found to be effective in treating non-alcoholic fatty liver disease and diabetes mellitus. Thus, VDAC1-based peptides, by targeting VDAC1-interacting proteins, offer an affordable and innovative new conceptual therapeutic paradigm that can potentially overcome heterogeneity, chemoresistance, and invasive metastatic formation. Full article

In this study, a 3D model of a proton exchange membrane fuel cell (PEMFC) with crossed channels and an ultra-thin membrane is developed to investigate the feasibility of self-humidification; experiments utilizing a PEMFC stack with identical configurations are conducted to validate the simulation results and further investigate the effects of various operating conditions (OCs) on self-humidification. The results indicate that the crossed flow channel leads to enhanced uniformity of water distribution, resulting in improved cell performance under low/no humidification conditions. External humidifiers for the anode can be removed since the performance difference is negligible (≤3%) between RHa = 0% and 100%. Self-humidification can be achieved in the stack at 90 °C or below with an appropriate back pressure among 100–200 kPa. As the current density increases, there is a gradual convergence and crossing of the voltage at low RH with that at high RH, and the crossover points are observed at 60–80 °C with suitable pressure when successful self-humidification is achieved. Below the current density of the point, the stack’s performance is inferior at lower RH due to membrane unsaturation, and conversely, the performance is inferior at higher RH due to flooding; this current density decreases with higher pressure and lower temperature. Full article

To overcome the safety hazard of the liquid electrolytes used in traditional lithium batteries, solid electrolytes have drawn more attention because of their advantages such as non-volatility, easy processing, good mechanical properties, and stability. In this paper, sodium alginate (SA) nanofiber membranes were used as the backbone of PEO-based solid electrolytes. SA nanofiber membranes were prepared by electrospinning with assistance from PEO and cross-linked with calcium ions to construct a nanofiber network skeleton, which provided a guarantee for the stability of the subsequent electrolyte preparation process. The effects of spinning conditions and crosslinking time on the structure and performances of the nanofiber membranes were investigated. Meanwhile, the relationship between the skeleton of nanofiber membranes cross-linked with calcium ions and ion conductivity was investigated. The optimal parameters of the electrospinning process including concentration, voltage, distance, and SA content were discussed, and the fiber diameter and its distribution were analyzed. Furthermore, Fourier transform infrared (FTIR) spectrometer, thermal gravimetric analyzer analysis (TGA), X-ray diffraction (XRD), and energy dispersive spectrometer (EDS) maps were used to characterize the nanofiber membranes and electrolytes. The results showed that the thermal performance of cross-linked nanofiber membranes improved and the crystallinity of the PEO matrix decreased. The ion conductivity of the electrolytes was characterized by electrochemical impedance spectroscopy (EIS) testing, and the results showed that the assembled lithium symmetric battery had a good ion conductivity of 6.82 × 10⁻⁵ S/cm at 30 °C. Full article

Carboxymethyl cellulose (CMC)/polyvinyl alcohol (PVA) composite nanofiber membranes were prepared by electrostatic spinning, using CMC and PVA as raw materials and glutaraldehyde as a cross-linking agent. The structure, morphology, thermal stability, and filtration performance of CMC/PVA nanofiber membranes were characterized by advanced instrumental analysis methods such as scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, ultraviolet analysis, and energy spectrum analysis. The results show that the average fiber diameter decreases from 381 nm to 183 nm when the spinning voltage is 23 KV and the jet speed is 2 µL/min. The obtained fiber has the smallest particle size and the most uniform distribution. Infrared spectroscopy analysis confirms that the adsorption behavior of nanofiber membranes on Cu²⁺ and Cr⁶⁺ is chemical adsorption. The retention rates of CMC/PVA nanofiber membranes for Cu²⁺ and Cr⁶⁺ reached 97.2% and 98.8%, respectively. The adsorption capacities of Cu²⁺ and Cr⁶⁺ were 26.34 and 28.93 mg·g⁻¹, respectively. The adsorption of heavy metal ions by nanofiber membranes can be explained by the pseudo-second-order kinetic mechanism of the chemisorption process and the Langmuir isotherm model. Full article

Prolonged hyperglycemia related to diabetes and its complications leads to multiple cellular disorders, the central one being the dysfunction of mitochondria. Voltage-dependent anion channels (VDAC) of the outer mitochondrial membrane control the metabolic, ionic, and energy cross-talk between mitochondria and the rest of the cell and serve as the master regulators of mitochondrial functions. Here, we have investigated the effect of pharmacological suppression of VDAC1 by the newly developed inhibitor of its oligomerization, VBIT-4, in the primary culture of mouse lung endotheliocytes and downregulated expression of VDAC1 in human skin fibroblasts on the progression of mitochondrial dysfunction upon hyperglycemic stress. The cells were grown in high-glucose media (30 mM) for 36 h. In response to hyperglycemia, the mRNA level of VDAC1 increased in endotheliocytes and decreased in human skin fibroblasts. Hyperglycemia induced overproduction of mitochondrial ROS, an increase in the susceptibility of the organelles to mitochondrial permeability transition (MPT) pore opening and a drop in mitochondrial membrane potential, which was accompanied by a decrease in cell viability in both cultures. Treatment of endotheliocytes with 5 µM VBIT-4 abolished the hyperglycemia-induced increase in susceptibility to spontaneous opening of the MPT pore and ROS generation in mitochondria. Silencing of VDAC1 expression in human skin fibroblasts exposed to high glucose led to a less pronounced manifestation of all the signs of damage to mitochondria. Our data identify a mitochondria-related response to pharmacological and genetic suppression of VDAC activity in vascular cells in hyperglycemia and suggest the potential therapeutic value of targeting these channels for the treatment of diabetic vasculopathies. Full article

Cx43 hemichannels (HCs) and Panx1 channels are two genetically distant protein families. Despite the lack of sequence homology, Cx43 and Panx1 channels have been the subject of debate due to their overlapping expression and the fact that both channels present similarities in terms of their membrane topology and electrical properties. Using the mimetic peptides Gap19 and ¹⁰Panx1, this study aimed to investigate the cross-effects of these peptides on Cx43 HCs and Panx1 channels. The single-channel current activity from stably expressing HeLa-Cx43 and C6-Panx1 cells was recorded using patch-clamp experiments in whole-cell voltage-clamp mode, demonstrating 214 pS and 68 pS average unitary conductances for the respective channels. Gap19 was applied intracellularly while ¹⁰Panx1 was applied extracellularly at different concentrations (100, 200 and 500 μM) and the average nominal open probability (NP_o) was determined for each testing condition. A concentration of 100 µM Gap19 more than halved the NP_o of Cx43 HCs, while 200 µM ¹⁰Panx1 was necessary to obtain a half-maximal NP_o reduction in the Panx1 channels. Gap19 started to significantly inhibit the Panx1 channels at 500 µM, reducing the NP_o by 26% while reducing the NP_o of the Cx43 HCs by 84%. In contrast ¹⁰Panx1 significantly reduced the NP_o of the Cx43 HCs by 37% at 100 µM and by 83% at 200 µM, a concentration that caused the half-maximal inhibition of the Panx1 channels. These results demonstrate that ¹⁰Panx1 inhibits Cx43 HCs over the 100–500 µM concentration range while 500 µM intracellular Gap19 is necessary to observe some inhibition of Panx1 channels. Full article

Ion channels are the second largest class of drug targets after G protein-coupled receptors. In addition to well-recognized ones like voltage-gated Na/K/Ca channels in the heart and neurons, novel ion channels are continuously discovered in both excitable and non-excitable cells and demonstrated to play important roles in many physiological processes and diseases such as developmental disorders, neurodegenerative diseases, and cancer. However, in the field of ion channel discovery, there are an unignorable number of published studies that are unsolid and misleading. Despite being the gold standard of a functional assay for ion channels, electrophysiological recordings are often accompanied by electrical noise, leak conductance, and background currents of the membrane system. These unwanted signals, if not treated properly, lead to the mischaracterization of proteins with seemingly unusual ion-conducting properties. In the recent ten years, the technical revolution of cryo-electron microscopy (cryo-EM) has greatly advanced our understanding of the structures and gating mechanisms of various ion channels and also raised concerns about the pore-forming ability of some previously identified channel proteins. In this review, we summarize cryo-EM findings on ion channels with molecular identities recognized or disputed in recent ten years and discuss current knowledge of proposed channel proteins awaiting cryo-EM analyses. We also present a classification of ion channels according to their architectures and evolutionary relationships and discuss the possibility and strategy of identifying more ion channels by analyzing structures of transmembrane proteins of unknown function. We propose that cross-validation by electrophysiological and structural analyses should be essentially required for determining molecular identities of novel ion channels. Full article

Diseases spread by mosquitoes lead to the death of 700,000 people each year. The main way to reduce transmission is vector control by biting prevention with chemicals. However, the most commonly used insecticides lose efficacy due to the growing resistance. Voltage-gated sodium channels (VGSCs), membrane proteins responsible for the depolarizing phase of an action potential, are targeted by a broad range of neurotoxins, including pyrethroids and sodium channel blocker insecticides (SCBIs). Reduced sensitivity of the target protein due to the point mutations threatened malaria control with pyrethroids. Although SCBIs—indoxacarb (a pre-insecticide bioactivated to DCJW in insects) and metaflumizone—are used in agriculture only, they emerge as promising candidates in mosquito control. Therefore, a thorough understanding of molecular mechanisms of SCBIs action is urgently needed to break the resistance and stop disease transmission. In this study, by performing an extensive combination of equilibrium and enhanced sampling molecular dynamics simulations (3.2 μs in total), we found the DIII-DIV fenestration to be the most probable entry route of DCJW to the central cavity of mosquito VGSC. Our study revealed that F1852 is crucial in limiting SCBI access to their binding site. Our results explain the role of the F1852T mutation found in resistant insects and the increased toxicity of DCJW compared to its bulkier parent compound, indoxacarb. We also delineated residues that contribute to both SCBIs and non-ester pyrethroid etofenprox binding and thus could be involved in the target site cross-resistance. Full article

Innovative ion exchange membranes have become commercially available in recent years. However, information about their structural and transport characteristics is often extremely insufficient. To address this issue, homogeneous anion exchange membranes with the trade names ASE, CJMA-3 and CJMA-6 have been investigated in Na_xH_(3−x)PO₄ solutions with pH 4.4 ± 0.1, 6.6 and 10.0 ± 0.2, as well as NaCl solutions with pH 5.5 ± 0.1. Using IR spectroscopy and processing the concentration dependences of the electrical conductivity of these membranes in NaCl solutions, it was shown that ASE has a highly cross-linked aromatic matrix and mainly contains quaternary ammonium groups. Other membranes have a less cross-linked aliphatic matrix based on polyvinylidene fluoride (CJMA-3) or polyolefin (CJMA-6) and contain quaternary amines (CJMA-3) or a mixture of strongly basic (quaternary) and weakly basic (secondary) amines (CJMA-6). As expected, in dilute solutions of NaCl, the conductivity of membranes increases with an increase in their ion-exchange capacity: CJMA-6 < CJMA-3 << ASE. Weakly basic amines appear to form bound species with proton-containing phosphoric acid anions. This phenomenon causes a decrease in the electrical conductivity of CJMA-6 membranes compared to other studied membranes in phosphate-containing solutions. In addition, the formation of the neutral and negatively charged bound species suppresses the generation of protons by the “acid dissociation” mechanism. Moreover, when the membrane is operated in overlimiting current modes and/or in alkaline solutions, a bipolar junction is formed at the CJMA- 6/depleted solution interface. The CJMA-6 current-voltage curve becomes similar to the well-known curves for bipolar membranes, and water splitting intensifies in underlimiting and overlimiting modes. As a result, energy consumption for electrodialysis recovery of phosphates from aqueous solutions almost doubles when using the CJMA-6 membrane compared to the CJMA-3 membrane. Full article

Energy storage systems have aroused public interest because of the blooming development of intermittent renewable energy sources. Vanadium redox flow batteries (VRFBs) are the typical candidates owing to their flexible operation and good cycle durability. However, due to the usage of perfluorinated separator membranes, VRFBs suffer from both high cost and serious vanadium ions cross penetration. Herein, we fabricate a series of low-budget and high-performance blend membranes from polyvinylpyrrolidone (PVP) and cardo-poly(etherketone) (PEKC) for VFRB. A PEKC network gives the membrane excellent mechanical rigidity, while PVP endows the blend membranes with superior sulfonic acid uptake owing to the present N-heterocycle and carbonyl group in PVP, resulting in low area resistance. Meanwhile, blend membranes also display low vanadium ion permeability resulting from the electrostatic repulsion effect of protonated PVP polymer chains towards vanadium ions. Consequently, the 50%PVP-PEKC membrane has a high ionic selectivity of 1.03 × 10⁶ S min cm⁻³, while that of Nafion 115 is nearly 17 times lower (6.03 × 10⁴ S min cm⁻³). The VRFB equipped with 50%PVP-PEKC membrane has high coulombic efficiencies (99.3–99.7%), voltage efficiencies (84.6–67.0%) and energy efficiencies (83.9–66.8%) at current densities of 80–180 mA cm⁻², and possesses excellent cycle constancy, indicating that low-cost x%PVP-PEKC blend membranes have a great application potentiality for VRFBs. Full article

Graphene, in spite of exceptional physio-chemical properties, still faces great limitations in its use and industrial scale-up as highly selective membranes (enhanced ratio of proton conductivity to fuel cross-over) in liquid alcohol fuel cells (LAFCs), due to complexity and high cost of prevailing production methods. To resolve these issues, a facile, low-cost and eco-friendly approach of liquid phase exfoliation (bath sonication) of graphite to obtain graphene and spray depositing the prepared graphene flakes, above anode catalyst layer (near the membrane in the membrane electrode assembly (MEA)) as barrier layer at different weight percentages relative to the base membrane Nafion 115 was utilized in this work. The 5 wt.% nano-graphene layer raises 1 M methanol/oxygen fuel cell power density by 38% to 91 mW·cm⁻², compared to standard membrane electrode assembly (MEA) performance of 63 mW·cm⁻², owing to less methanol crossover with mild decrease in proton conductivity, showing negligible voltage decays over 20 h of operation at 50 mA·cm⁻². Overall, this work opens three prominent favorable prospects: exploring the usage of nano-materials prepared by liquid phase exfoliation approach, their effective usage in ion-transport membrane region of MEA and enhancing fuel cell power performance. Full article

Contraction of striated muscle is triggered by a massive release of calcium from the sarcoplasmic reticulum (SR) into the cytoplasm. This intracellular calcium release is initiated by membrane depolarization, which is sensed by voltage-gated calcium channels Ca_V1.1 (in skeletal muscle) and Ca_V1.2 (in cardiac muscle) in the plasma membrane (PM), which in turn activate the calcium-releasing channel ryanodine receptor (RyR) embedded in the SR membrane. This cross-communication between channels in the PM and in the SR happens at specialized regions, the SR-PM junctions, where these two compartments come in close proximity. Junctophilin1 and Junctophilin2 are responsible for the formation and stabilization of SR-PM junctions in striated muscle and actively participate in the recruitment of the two essential players in intracellular calcium release, Ca_V and RyR. This short review focuses on the roles of junctophilins1 and 2 in the formation and organization of SR-PM junctions in skeletal and cardiac muscle and on the functional consequences of the absence or malfunction of these proteins in striated muscle in light of recently published data and recent advancements in protein structure prediction. Full article

Shrinkage is observed in many electrospun membranes. The stretched conformation of the macromolecular chains has been proposed as the possible cause. However, so far, our understanding of the fundamentals is still qualitative and cannot provide much help in the shrinkage control. In this paper, based on the crimped fibers after stimulus-induced shrinkage, a clear evidence of buckling, the gradient pre-strain field in the cross-section of the electrospun fibers, which is the result of a gradient solidification field and a tensile force in the fibers during electrospinning, is identified as the underlying mechanism for the stimulus-induced shrinkage. Subsequently, two buckling conditions are derived. Subsequently, a series of experiments are carried out to reveal the influence of four typical processing parameters (namely, the applied voltage, solution concentration, distance between electrodes, and rotation speed of collector), which are highly relevant to the formation of the gradient pre-strain field. It is concluded that there are some different ways to achieve the required shrinkage ratios in two in-plane directions (i.e., the rotational and transverse directions of the roller collector). Some of the combinations of these parameters are more effective at achieving high uniformity than others. Hence, it is possible to optimize the processing parameters to produce high-quality membranes with well-controlled shrinkage in both in-plane directions. Full article

Proton exchange membrane fuel cell (PEM-FC) aggregation pressure causes extensive strains in cell segments. The compression of each segment takes place through the cell modeling method. In addition, a very heterogeneous compressive load is produced because of the recurrent channel rib design of the dipole plates, so that while high strains are provided below the rib, the domain continues in its initial uncompressed case under the ducts approximate to it. This leads to significant spatial variations in thermal and electrical connections and contact resistances (both in rib–GDL and membrane–GDL interfaces). Variations in heat, charge, and mass transfer rates within the GDL can affect the performance of the fuel cell (FC) and its lifetime. In this paper, two scenarios are considered to verify the performance and lifetime of the PEM-FC using different innovative channel geometries. The first scenario is conducted by adopting a constant channel height (H = 1 mm) for all the differently shaped channels studied. In contrast, the second scenario is conducted by taking a constant channel cross-sectional area (A = 1 mm²) for all the studied channels. Therefore, a computational fluid dynamics model (CFD) for a PEM fuel cell is formed through the assembly of FC to simulate the pressure variations inside it. The simulation results showed that a triangular cross-section channel provided the uniformity of the pressure distribution, with lower deformations and lower mechanical stresses. The analysis helped gain insights into the physical mechanisms that lead to the FC’s durability and identify important parameters under different conditions. The model shows that it can assume the intracellular pressure configuration toward durability and appearance containing limited experimental data. The results also proved that the better cell voltage occurs in the case of the rectangular channel cross-section, and therefore, higher power from the FC, although its durability is much lower compared to the durability of the triangular channel. The results also showed that the rectangular channel cross-section gave higher cell voltages, and therefore, higher power (0.63 W) from the fuel cell, although its durability is much lower compared to the durability of the triangular channel. Therefore, the triangular channel gives better performance compared to other innovative channels. Full article