Passage Of Ions Research Articles

Modelling H2S induced catalyst contamination in polymer electrolyte fuel cells: performance degradation and regeneration with ozone

ABSTRACT Under steady-state isothermal conditions, a numerical simulation has been conducted to predict the performance of a Polymer Electrolyte Fuel Cell in the presence of 100 ppm of H2S along anode stream. The simulated polarisation curves are in good agreement with the experimental results. The simulated results are presented as distribution contours, illustrating liquid water activity, membrane water content, reaction heat, and current density. The contours were captured at a voltage of 0.65 V and are illustrated in the cathode catalyst layer interface. The simulated results indicate that the H2S contaminants block active catalyst sites, hindering ion passage and preventing the Oxygen Reduction Reaction and leads to membrane dehydration. Additionally, the reaction rate slows down due to catalyst poisoning affecting proton conductivity, membrane water content, and current density distribution. A theoretical investigation using DFT was conducted to understand the atomic-level interaction of the PGM catalyst with H2S contaminant, assessing the poisoning effect and reaction mechanisms involved in catalyst degradation. Pt-Sads gets strongly adsorbed on the Pt catalyst layer by a value of −6.05 eV resulting in performance degradation. Furthermore, the DFT analysis of the O3 cleaning of the contaminated catalyst reveals that SO2 is most likely released during the process

Extreme Heating of Minor Ions in Imbalanced Solar-wind Turbulence

Abstract Minor ions in the solar corona are heated to extreme temperatures, far in excess of those of the electrons and protons that comprise the bulk of the plasma. These highly nonthermal distributions make minor ions sensitive probes of the collisionless processes that heat the corona and power the solar wind. The recent discovery of the “helicity barrier” offers a mechanism in which imbalanced Alfvénic turbulence in low-β plasmas preferentially heats protons over electrons, generating high-frequency, proton-cyclotron-resonant fluctuations. We use the hybrid-kinetic particle-in-cell code Pegasus++ to drive imbalanced Alfvénic turbulence in a 3D low-β plasma with additional passive ion species, He2+ and O5+. A helicity barrier naturally develops, followed by clear phase-space signatures of oblique proton-cyclotron-wave heating and Landau-resonant heating from the imbalanced Alfvénic fluctuations. The former results in characteristically arced ion velocity distribution functions, whose non-bi-Maxwellian features are shown by linear ALPS calculations to be critical to the heating process. Additional features include a steep transition-range electromagnetic spectrum, proton-cyclotron waves propagating in the direction of the imbalance, significantly enhanced proton-to-electron heating ratios, ion temperatures that are considerably more perpendicular with respect to magnetic field, and extreme heating of heavier species in a manner consistent with mass scalings inferred from spacecraft measurements. None of these features are realized in an otherwise equivalent simulation of balanced turbulence. If seen simultaneously in the fast solar wind, these signatures of the helicity barrier would testify to the necessity of incorporating turbulence imbalance in a complete theory for the evolution of the solar wind.

The effect of environmental factors on transepithelial potential in a model Amazonian teleost, the tambaqui (Colossoma macropomum): Implications for sodium balance in harsh environments.

The tambaqui (Colossoma macropomum, G. Cuvier 1818) thrives both in the ion-poor waters of the Amazon and in commercial aquaculture. In both, environmental conditions can be harsh due to low ion levels, occasional high salt challenges (in aquaculture), low pH, extreme PO2 levels (hypoxia and hyperoxia), high PCO2 levels (hypercapnia), high ammonia levels (in aquaculture), and high and low temperatures. Ion transport across the gill is affected by active transport processes, passive diffusive permeability, ion concentrations (the chemical gradient), and transepithelial potential (TEP, the electrical gradient). The latter is a very important indicator of ionoregulatory status but is rarely measured. Using normoxic, normocapnic, ion-poor, low-dissolved organic carbon (DOC) well water (27°C, pH 7.0) as the acclimation and reference condition, we first confirmed that the strongly negative TEP (-22.3 mV inside relative to the external water) is a simple diffusion potential. We then evaluated the effects on TEP of more complex waters from the Rio Negro (strong hyperpolarization) and Rio Solimões (no significant change). Additionally, we have quantified significant effects of acute, realistic changes in environmental conditions-low pH (depolarization), hypercapnia (depolarization), hypoxia (depolarization), hyperoxia (hyperpolarization), elevated NaCl concentrations (depolarization), and elevated NH4Cl concentrations (depolarization). The TEP responses help explain many of the changes in net Na+ flux rates reported in the literature. We have also shown marked effects of temperature on TEP and unidirectional Na+ flux rates (hyperpolarization and decreased fluxes at 21°C, depolarization and increased fluxes at 33°C) with no changes in net Na+ flux rates. Calculations based on the Nernst equation demonstrate the importance of the TEP changes in maintaining net Na+ balance.

Evolutionary origins of synchronization for integrating information in neurons.

The evolution of brain-expressed genes is notably slower than that of genes expressed in other tissues, a phenomenon likely due to high-level functional constraints. One such constraint might be the integration of information by neuron assemblies, enhancing environmental adaptability. This study explores the physiological mechanisms of information integration in neurons through three types of synchronization: chemical, electromagnetic, and quantum. Chemical synchronization involves the diffuse release of neurotransmitters like dopamine and acetylcholine, causing transmission delays of several milliseconds. Electromagnetic synchronization encompasses action potentials, electrical gap junctions, and ephaptic coupling. Electrical gap junctions enable rapid synchronization within cortical GABAergic networks, while ephaptic coupling allows structures like axon bundles to synchronize through extracellular electromagnetic fields, surpassing the speed of chemical processes. Quantum synchronization is hypothesized to involve ion coherence during ion channel passage and the entanglement of photons within the myelin sheath. Unlike the finite-time synchronization seen in chemical and electromagnetic processes, quantum entanglement provides instantaneous non-local coherence states. Neurons might have evolved from slower chemical diffusion to rapid temporal synchronization, with ion passage through gap junctions within cortical GABAergic networks potentially facilitating both fast gamma band synchronization and quantum coherence. This mini-review compiles literature on these three synchronization types, offering new insights into the physiological mechanisms that address the binding problem in neuron assemblies.

PH-induced conformational changes in the selectivity filter of a potassium channel lead to alterations in its selectivity and permeation properties.

The Selectivity Filter (SF) in tetrameric K+ channels, has a highly conserved sequence, TVGYG, at the extracellular entry to the channel pore region. There, the backbone carbonyl oxygens from the SF residues, create a stack of K+ binding sites where dehydrated K+ binds to induce a conductive conformation of the SF. This increases intersubunit interactions and confers a higher stability to the channel against thermal denaturation. Indeed, the fit of dehydrated K+ to its binding sites is fundamental to define K+ selectivity, an important feature of these channels. Nonetheless, the SF conformation can be modified by different effector molecules. Such conformational plasticity opposes selectivity, as the SF departs from the "induced-fit" conformation required for K+ recognition. Here we studied the KirBac1.1 channel, a prokaryotic analog of inwardly rectifying K+ channels, confronted to permeant (K+) and non-permeant (Na+) cations. This channel is pH-dependent and transits from the open state at neutral pH to the closed state at acidic pH. KirBac1.1 has the orthodox TVGYG sequence at the SF and thus, its behavior should resemble that of K+-selective channels. However, we found that when at neutral pH, KirBac1.1 is only partly K+ selective and permeates this ion causing the characteristic "induced-fit" phenomenon in the SF conformation. However, it also conducts Na+ with a mechanism of ion passage reminiscent of Na+ channels, i.e., through a wide-open pore, without increasing intersubunit interactions within the tetrameric channel. Conversely, when at acidic pH, the channel completely loses selectivity and conducts both K+ and Na+ similarly, increasing intersubunit interactions through an apparent "induced-fit"-like mechanism for the two ions. These observations underline that KirBac1.1 SF is able to adopt different conformations leading to changes in selectivity and in the mechanism of ion passage.

Quantum features of the transport through ion channels in the soft knock-on model

Ion channels are protein structures that facilitate the selective passage of ions across the membrane cells of living organisms. They are known for their high conductance and high selectivity. The precise mechanism between these two seemingly contradicting features is not yet firmly established. One possible candidate is the quantum coherence. In this work we study the quantum model of the soft knock-on conduction using the Lindblad equation taking into account the non-hermiticity of the model. We show that the model exhibits a regime in which high conductance coexists with high coherence. Our findings second the role of quantum effects in the transport properties of the ion channels.

VDAC Solvation Free Energy Calculation by a Nonuniform Size Modified Poisson-Boltzmann Ion Channel Model.

Voltage-dependent anion channel (VDAC) is the primary conduit for regulated passage of ions and metabolites into and out of a mitochondrion. Calculating the solvation free energy for VDAC is crucial for understanding its stability, function, and interactions within the cellular environment. In this article, numerical schemes for computing the total solvation free energy for VDAC-comprising electrostatic, ideal gas, and excess free energies plus the nonpolar energy-are developed based on a nonuniform size modified Poisson-Boltzmann ion channel (nuSMPBIC) finite element solver along with tetrahedral meshes for VDAC proteins. The current mesh generation package is also updated to improve mesh quality and accelerate mesh generation. A VDAC Solvation Free Energy Calculation (VSFEC) package is then created by integrating these schemes with the updated mesh package, the nuSMPBIC finite element package, the PDB2PQR package, and the OPM database, as well as one uniform SMPBIC finite element package and one Poisson-Boltzmann ion channel (PBIC) finite element package. With the VSFEC package, many numerical experiments are made using six VDAC proteins, eight ionic solutions containing up to four ionic species, including ATP4- and Ca2+, two reference states, different boundary values, and different permittivity constants. The test results underscore the importance of considering nonuniform ionic size effects to explore the varying patterns of the total solvation free energy, and demonstrate the high performance of the VSFEC package for VDAC solvation free energy calculation.

Double-Walled Carbon Nanotubes Enable Breakdown of the Trade-off between Ion Selectivity and Water Permeability.

Although evidence has been presented for desalination potentials in single-walled carbon nanotubes (SWCNTs), it is still very challenging to overcome the trade-off between ion selectivity and water permeability by simply tuning the carbon nanotube (CNT) size. In this work, we prove that double-walled carbon nanotubes (DWCNTs) can make it. Employing a series of molecular dynamics simulations, we find a striking phenomenon that tuning the combination architecture of DWCNTs can significantly improve the desalination performance, with the salt rejection rate even reaching 100% in some cases while maintaining high levels of water flux. Specifically, under a certain outer CNT (20,20), with the increase in inner CNT radius, the salt rejection rate reaches a maximum for the CNT (9,9), attributed to the small size of the inner CNT and the space between the two CNT walls that significantly impedes the ion passage; however, it still allows the passage of massive water. Furthermore, as the pressure difference increases, the water flux greatly increases, while the salt rejection rate only slightly decreases for the CNTs (8,8) and (9,9), effectively addressing the trade-off between ion selectivity and water permeability. As a result, optimizing the architecture of DWCNTs should be an effective strategy for designing an efficient desalination membrane, which is still a challenge for SWCNTs.

Separation of Gold(I) from cyanide-containing wastewater by functional polymer inclusion membrane containing guanidinium ionic liquid

The effective recovery of dicyanoaurate from metallurgical wastewater has both economic and environmental implications, but achieving this goal remains challenging. This research introduces an innovative polymer inclusion membrane (PIM) based on guanidinium ionic liquids, specifically designed to efficiently and selectively separate gold(I) from aurocyanide-laden wastewater. Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis were employed for the comprehensive characterization of the PIM. Through optimization of the transport properties, an impressive initial gold(I) flux of 2.32 × 10−11 mol cm−2 s−1 was achieved, corresponding to a permeability of 9.16 × 10−4 cm s−1. Spectral characterization and theoretical simulation indicated the occurrence of an anion exchange process between thiocyanate, SCN−, of the ionic liquid N,N,N’,N’-tetramethyl-N“,N”-dioctyl-guanidinium thiocyanate ([diOTMG+∙SCN-]) and dicyanoaurate, Au(CN)2−, in the feed phase. A gold(I) transport model and a kinetic permeation model were proposed, and important transport parameters were calculated to clarify the transport mechanism of gold(I) through the membrane. Significantly, even when operating in actual wastewater, the PIM system was able to efficiently transfer gold(I) from the feed phase to the receiving phase within 20 h while blocking the passage of other metal ions through the membrane, demonstrating its impressive selective separation capabilities. This environmentally friendly PIM system based on guanidinium salt ionic liquids provides a new avenue for efficiently extracting gold(I) from dicyanoaurate wastewater, contributing to sustainable resource use and effective environmental protection.

Overview of High-Performance Timing and Position-Sensitive MCP Detectors Utilizing Secondary Electron Emission for Mass Measurements of Exotic Nuclei at Nuclear Physics Facilities.

Timing and/or position-sensitive MCP detectors, which detect secondary electrons (SEs) emitted from a conversion foil during ion passage, are widely utilized in nuclear physics and nuclear astrophysics experiments. This review covers high-performance timing and/or position-sensitive MCP detectors that use SE emission for mass measurements of exotic nuclei at nuclear physics facilities, along with their applications in new measurement schemes. The design, principles, performance, and applications of these detectors with different arrangements of electromagnetic fields are summarized. To achieve high precision and accuracy in mass measurements of exotic nuclei using time-of-flight (TOF) and/or position (imaging) measurement methods, such as high-resolution beam-line magnetic-rigidity time-of-flight (Bρ-TOF) and in-ring isochronous mass spectrometry (IMS), foil-MCP detectors with high position and timing resolution have been introduced and simulated. Beyond TOF mass measurements, these new detector systems are also described for use in heavy ion beam trajectory monitoring and momentum measurements for both beam-line and in-ring applications. Additionally, the use of position-sensitive timing foil-MCP detectors for Penning trap mass spectrometers and multi-reflection time-of-flight (MR-TOF) mass spectrometers is proposed and discussed to improve efficiency and enhance precision.

Ultrathin cyclodextrin-based nanofiltration membrane with tunable microporosity for antibiotic desalination

Nanofiltration (NF) membranes play a crucial role in ion separation and antibiotic purification due to their energy efficiency and environment-friendliness. However, conventional polymeric membranes are susceptible to the “trade-off” between permeability and selectivity due to the lack of intrinsically rigid micropores. Herein, the amino-cyclodextrins (amino-CDs) with different cavity sizes were synthesized and employed as the building block to construct 15-nm-thick nanofilms. The rational incorporation of macrocycles with well-defined and tunable cavity into nanofilm enabled a significant enhancement of water permeance and a precise manipulation of molecular weight cut-off of the membranes. Thanks to the significant difference of inherent energy barrier for passage of ions through CD cavity, the CD-incorporated membranes achieved a high Cl−/SO42− selectivity of 87. In addition, the CD-regulated membranes showed an excellent antibiotic desalination performance, out-performing the state-of-the-art membranes for antibiotic purification. This work provides a gateway to the development of nanofiltration membranes with precise molecular sieving for antibiotic desalination.

Ion-exchange induced multiple effects to promote uranium uptake from nonmarine water by micromotors

As the fundamental resource in nuclear energy, uranium is a sword of two sides, due to its radioactive character that could cause severe impact to the environment and living creatures once released by accident. However, limited by the passive ion transport, the currently available uranium adsorbents still suffer from low adsorption kinetics and capacity. Here, we report a self-driven modular micro-reactor composed of magnetizable ion-exchange resin and adsorbents that can be used to dynamically remove uranium from nonmarine waters. Because of the long-range pH gradient and phoretic flow established by the recyclable ion-exchange resin, the micro-reactor shows a fast uranium adsorption rate and reaches a uranium extraction capacity of 629.3 mg g−1 within 10 min in 30 ppm uranium solution, as well as good recyclability in repeated use. Numerical simulation result confirms that the phoretic flow and electric field accelerate uranium transport to the adsorbent. Our work provides a new solution for the removal of radioactive uranium with high efficiency.

In Situ Built ZnS/MXene Heterostructure by a Mild Method for Inhibiting Polysulfide Shuttle in Li-S Batteries.

With high specific surface area, excellent polysulfide conversion activity, and fast electron/ion transfer at the interface, MXene-derived heterostructures can be employed as catalysts for lithium-sulfur (Li-S) batteries to accelerate sulfur redox kinetics and suppress shuttle effect. However, the preparation of MXene-derived heterostructures often requires high-temperature reactions, which can easily lead to the oxidation of MXene and sacrifice the electrical conductivity. Herein, a catalytic two-dimensional heterostructure (ZnS/MXene) was successfully synthesized via a mild method. The MXene skeleton retains the original nanosheet structure without oxidation. The in situ-grown ZnS nanospheres prevent the restacking of MXene nanosheets, which not only increases the active sites, but also guarantees channels for the fast passage of lithium ions. The interfacial built-in electric field further promotes electron/ion migration, thereby expediting the polysulfide conversion and suppressing the shuttle effect. Consequently, the batteries using ZnS/MXene modified separators exhibit a high initial discharge capacity of 1230 mAh g-1 at 0.1 C and a low decaying rate of 0.082 % per cycle after 500 cycles at 0.5 C. This work offers a reference for the fabrication of MXene-based heterostructure in Li-S batteries.

Quantification of hemolysis rates from pulsed field ablation

Abstract Introduction Pulsed electric fields induce hemolysis of red blood cells as a dose-dependent effect of the electric field. Voltage pulsations induce a transmembrane potential across the cell membrane and either open up or create pores in the red cells. In isotonic conditions, the pores allow passage of potassium and sodium ions but not sucrose or hemoglobin, and leakage of ions leads to an osmotic imbalance which in turn causes a colloidal hemolysis of the red cells. Objective To quantify hemolysis rates during pulsed field ablation (PFA). Methods We created a computational model of PFA to determine the total volume of blood hemolyzed from each pulse during catheter ablation using pulsed field energy. The percentage hemolysis was calculated as a function of electric field intensity utilizing existing published experimental data. A single electrode delivering a single pulse of 100 microseconds duration was modeled at voltages of 1 kV, 1.5 kV, and 2 kV. Results The total volume of hemolyzed blood per pulse increased with increasing applied voltage (Figure). For 2 electrodes in direct tissue contact, the electrode surface exposed to the blood pool generated 19 microliters of hemolyzed red blood cells with a single pulse of a 2 kV field strength. In the case of a single pulse train consisting of 50 pulses, using a catheter configuration with 20 electrodes, an estimate of total volume per pulse train is approximately 9.5 mL of hemolyzed blood. In the case of electrodes not in direct contact with endocardial tissue, and exposed to the blood pool, up to double this volume could be anticipated per pulse train. Hemolyzed volume can be reduced with better tissue contact (reducing exposure to blood), or potentially with the use of irrigation to dilute the local red blood cell concentration. Increased tonicity of the irrigant fluid may also reduce the osmotic pressure increases that result in hemolysis. Conclusions Typical voltages utilized in pulsed field ablation can cause significant hemolysis, which is exacerbated by inadequate tissue contact. A greater number of electrodes and number of pulses delivered increases the risk, whereas better tissue contact, and the use of irrigation, may reduce it.

Prediction of conformational states in a coronavirus channel using Alphafold-2 and DeepMSA2: Strengths and limitations

The envelope (E) protein is present in all coronavirus genera. This protein can form pentameric oligomers with ion channel activity which have been proposed as a possible therapeutic target. However, high resolution structures of E channels are limited to those of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), responsible for the recent COVID-19 pandemic. In the present work, we used Alphafold-2 (AF2), in ColabFold without templates, to predict the transmembrane domain (TMD) structure of six E-channels representative of genera alpha-, beta- and gamma-coronaviruses in the Coronaviridae family. High-confidence models were produced in all cases when combining multiple sequence alignments (MSAs) obtained from DeepMSA2. Overall, AF2 predicted at least two possible orientations of the α-helices in E-TMD channels: one where a conserved polar residue (Asn-15 in the SARS sequence) is oriented towards the center of the channel, ‘polar-in’, and one where this residue is in an interhelical orientation ‘polar-inter’. For the SARS models, the comparison with the two experimental models ‘closed’ (PDB: 7K3G) and ‘open’ (PDB: 8SUZ) is described, and suggests a ∼60˚ α-helix rotation mechanism involving either the full TMD or only its N-terminal half, to allow the passage of ions. While the results obtained are not identical to the two high resolution models available, they suggest various conformational states with striking similarities to those models. We believe these results can be further optimized by means of MSA subsampling, and guide future high resolution structural studies in these and other viral channels.

Constitutive sodium permeability in a C. elegans two-pore domain potassium channel

Two-pore domain potassium (K2P) channels play a central role in modulating cellular excitability and neuronal function. The unique structure of the selectivity filter in K2P and other potassium channels determines their ability to allow the selective passage of potassium ions across cell membranes. The nematode C. elegans has one of the largest K2P families, with 47 subunit-coding genes. This remarkable expansion has been accompanied by the evolution of atypical selectivity filter sequences that diverge from the canonical TxGYG motif. Whether and how this sequence variation may impact the function of K2P channels has not been investigated so far. Here, we show that the UNC-58 K2P channel is constitutively permeable to sodium ions and that a cysteine residue in its selectivity filter is responsible for this atypical behavior. Indeed, by performing in vivo electrophysiological recordings and Ca2+ imaging experiments, we demonstrate that UNC-58 has a depolarizing effect in muscles and sensory neurons. Consistently, unc-58 gain-of-function mutants are hypercontracted, unlike the relaxed phenotype observed in hyperactive mutants of many neuromuscular K2P channels. Finally, by combining molecular dynamics simulations with functional studies in Xenopus laevis oocytes, we show that the atypical cysteine residue plays a key role in the unconventional sodium permeability of UNC-58. As predicting the consequences of selectivity filter sequence variations in silico remains a major challenge, our study illustrates how functional experiments are essential to determine the contribution of such unusual potassium channels to the electrical profile of excitable cells.

Challenges in using 0.45 µm filters to assess potentially bioavailable trace elements in the dissolved fraction of river and peat bog waters of the Boreal Zone

Passing through a 0.45 µm filter can significantly alter the concentrations of dissolved trace elements (TEs) in organic-rich waters of the Boreal Zone. However, little evidence has been provided about the impacts of filtration on the size distribution of dissolved TEs. This limitation hinders our comprehension of how filtration affects the assessment of the potentially bioavailable forms of dissolved TEs (i.e. ions and small molecules). Using AF4-UV-ICP-MS, this study systematically investigates such artefacts and their influence on the concentrations of dissolved, primarily ionic, and colloid-associated TEs in river waters and peat bog waters of the Boreal Zone. In river waters (circumneutral pH), membrane filtration had a significant impact on TEs that are associated with inorganic colloids such as Al, Mn, Fe, As, the rare earth elements, Pb, and Th. Approximately 20–80 % of primarily ionic TEs (< 0.5 kDa) and 100 % of large inorganic (ca. 40–300 nm) TEs were excluded from the filtrates under clogged conditions. In contrast, little impact of filtration was observed for bog waters (pH 4). Similarly, cartridge filtration of river waters also led to a decrease in concentrations and size distributions of dissolved TEs. However, cartridge filtration demonstrated a higher efficiency in allowing the passage of ions and excluding colloids than membrane filtration. On average, the ratio of the dissolved concentrations between a cartridge and a membrane filtrate was 1.0 ± 0.2. For primarily ionic species, the average ratio was 1.4 ± 0.4, while for colloidal species, it was 0.4 ± 0.1. Therefore, despite having similar dissolved concentrations, filtration methods with the same nominal pore size can yield different concentrations of bioavailable forms of TEs. These findings may be important for studies of the environmental relevance of dissolved TEs in surface waters of the Boreal Zone, and organic-rich waters elsewhere.

Utilization of substrate specific membrane channels in liposome based biosensors: A nitrite biosensor with NirC nitrite channels

A liposome-based nitrite biosensor was prepared by encapsulating the nitrite reductase NirB enzyme and embedding the nitrite-specific NirC channels in the liposome structure. The proteoliposomes were coated on the glassy carbon electrode modified with the multi-walled carbon nanotube/chitosan matrix. The absence of channels in the liposome structure inhibits the generation of typical reduction peaks upon the addition of nitrite suggesting that ion channels are necessary for the passage of charged ions into the liposome. The response of the NirB and NirC incorporated liposome-based biosensor (CBLip/MWCNTs/CHIT/GC electrode) to the nitrite is shown to be fast and reproducible. The electrode shows a linear response between 1–500 µM nitrite concentrations. The sensitivity of the CBLip/MWCNTs/CHIT/GC electrode was 707 mA.M−1.cm−2, lower than that of the unentrapped NirB-loaded electrode (1131 mA.M−1.cm−2). While the electrode prepared with the unentrapped enzyme lost its activity in 30 days,entrapment of the enzyme in the liposome preserved the electrode activity by 55 %. The electrodes showed unexpected oxidation responses against high concentrations of sulfate and formate, theincorporation of NirC channels contributed to increasing the specificity of the electrode towards nitrite in the presence of these ions. The use of substrate-specific membrane channels in liposome-based biosensors was achieved for the first time in the present study.

Hydrogen production from ZnCl2 salt: Application of chlor-alkali method

This experimental study investigates the efficiency of hydrogen production from an aqueous ZnCl2 solution using an electrochemical method within a chlor-alkali reactor. A laboratory-scale reactor with separate anode and cathode compartments was constructed for this purpose. The compartments are separated by a Nafion 212 membrane, which prevents the mixing of the anolyte and catholyte solutions while allowing the passage of positive ions (Zn+). Each compartment is equipped with five carbon rod electrodes. The anode chamber is fed with an aqueous ZnCl2 solution, while the cathode chamber is supplied with pure water. The experiments were conducted with a constant electrolyte transfer rate of 0.3g/s into the reactor, at three different cell voltages (5.0, 7.5, and 10.0V) and two different cell temperatures (20 °C and 45 °C). Due to the small reactor dimensions and the dilution effect caused by adding pure water to the cathode compartment which decreases electrolyte density and adversely affects the current a noticeable reduction in hydrogen gas production was observed. Furthermore, the ZnCl2 electrolyte mass flow rate did not significantly impact the current or the generation of hydrogen and chlorine gases. Consequently, no changes were made to the mass flow rate of pure water or the electrolyte. The presence of active chlorine gas was found to cause the erosion of the carbon rod electrodes in the anode chamber. As a result, the amount of chlorine gas produced in the anode chamber is significantly lower than the hydrogen gas produced in the cathode chamber. At a cell temperature of 20 °C, a mass flow rate of 0.3 g/s, and a cell voltage of 5 V with ZnCl2 aqueous solution, the minimum hydrogen production rate is 0.625 mL/min. In contrast, at a cell temperature of 45 °C, a mass flow rate of 0.3 g/s, and a cell voltage of 10 V, the maximum hydrogen production rate is 4.97 mL/min.

322 Nutrient transport across gastrointestinal tissues using Ussing chambers

Abstract One of the principal roles of the gut is the absorption of nutrients to meet animal needs. While in vivo measures such as total tract digestibility indicate the totality of the nutrients that disappear, these methods provide no information on the digestion, site, flux, and mechanism of nutrient absorption. Nutrient absorption is a complex set of transport pathways including passive diffusion, facilitated transport, ion exchange, active transport, and secondary active transport that is driven by electrochemical gradients. To tease apart the complexities of nutrient transport at different sites along the gastrointestinal tract, Ussing chambers have been a useful tool. Two ex vivo chambers, filled with oxygenated physiological buffer, and separated by epithelial tissue allow for the detection of nutrient flux, transepithelial currents, and/or membrane permeability. Historically, detection of the nutrient of interest was achieved using radio-labelled or fluorescent tracers. Beyond detecting flux (uptake, efflux, net flux), Ussing chambers can also tease apart the complex network of transport pathways that govern nutrient absorption. Isolating specific transport pathways can be broad spectrum inhibitors, and alterations to the physiological buffers to target transport pathways of interest. Altering the electrical gradient using a voltage clamp for instance, can be used to neutralize, inhibit, or promote, the electrical gradient; such alterations can be especially useful for charged nutrients. Inhibitors, meanwhile, inhibit the activity of entire families of proteins, useful for when the role of specific protein transporters is of interest. Alterations to buffer composition, such as bicarbonate-free buffer solutions or the inclusion and exclusion of compounds with similar size and charge, can isolate transport solely dependent on that solute or provide knowledge on the solutes that may share a common transport mechanism. Together, these modulations allow for a powerful tool to study the presence or absence of nutrient transport and has been crucial in establishing absorption kinetics of ionic nutrients (e.g., Na+, Cl-), small organic nutrients (e.g., short chain fatty acids, glucose), and macromolecules (e.g., immunoglobulins). Done in conjunction with other techniques, Ussing chambers can offer strong insight to improve our understanding of nutrient absorption and epithelial physiology of the gut. This presentation will discuss the methods key to successful use of Ussing chambers, alongside with their limitations and ways to augment data generated by Ussing chambers.