Reversal Potential Research Articles

Spatial Confinement of Li Metal in Hollow Microcapsule Hosts Enabled by Heteroatom-Driven Inward Growth

In recent years, the demand for advanced batteries with high energy densities has increased significantly, along with the growing demand for electric vehicles. Li metal has garnered considerable research attention as a promising anode material because of its high theoretical specific capacity (3860 mAh g−1) and low electrochemical equilibrium potential (−3.040 V vs. standard hydrogen electrode). However, Li metal batteries still have several hurdles in their practical application because Li metal anodes experience infinite volume expansion, which induces continuous rupture and formation of solid-electrolyte interphase (SEI) layers. This leads to electrolyte consumption and corrosion of Li metal, resulting in a low Coulombic efficiency and poor cycling performance. In addition, the uncontrollable dendrite growth of Li metal may cause early battery failure and safety issues. To address these problems, extensive research efforts have been made, including artificial SEI layers, optimized electrolyte formula, and rational design of three-dimensional (3D) host materials.Among the various 3D host materials under development, carbon-based materials with hollow structures have been investigated extensively because of their attractive features. The enlarged void space (cavity) of the hollow hosts can accommodate a significant amount of Li deposits, while inhibiting volume changes during plating–stripping cycles. In addition, hollow carbon possesses much lower density than metal-based materials, thereby increasing the specific capacity and energy density. However, the lithiophobic nature of carbon combined with its high resistance to Li+ transport through nanopores on the walls significantly hinders the formation of Li deposits inside the cavity. Li may nucleate on the outer surface of the carbon particles in a nonuniform manner, thereby causing the growth of Li dendrites and electrochemically inactive Li deposits.In this study, we synthesize metal-organic framework-derived carbon microcapsules with heteroatom clusters (Zn and Ag) on the capsule walls and demonstrate that Ag-assisted nucleation of Li metal alters the outward-to-inward growth in the microcapsule host. The cavity inside the microcapsule host, which was generated by etching with tannic acid, provides large void spaces for Li metal storage. Atomic Ag clusters decorated by a galvanic displacement reaction serve as preferential nucleation sites with a reduced energy barrier and promote the inward growth of Li metal in the cavity, while suppressing nonuniform Li plating on the outer surface. Through combined electrochemical, microstructural, and simulation studies, we verify the beneficial role of Ag-assisted Li nucleation in facilitating inward growth inside the cavity of the microcapsule host, resulting in enhanced electrochemical performance. This study provides new insights into the design of reversible host materials for practical Li-metal batteries.

On the Viability of Carbon Dioxide in-Situ Resource Utilization (ISRU) to Produce Chemical Feedstocks on Mars

The vision of a sustained human presence in space and extraterrestrial bodies necessitates an ever-larger share of life sustaining materials to be produced by in-situ resource utilization (ISRU). In this context, on Mars, NASA envisions the transformation of Martian atmospheric carbon dioxide into potential feed stocks through a process of climate enhancing resource utilization (with the technology being applicable for CO2 utilization on Earth as well) [1]. Amongst the potential raw materials present on Mars, the presence of stable brines in the liquid phase [2] (due to dissolved perchlorate salts suppressing the freezing point of water to < 213K) along with the availability [3] of 95 vol.% atmospheric CO2, can enable the development of a CO2-H2O electrolyzer to produce CO2 reduction products and O2. In this work, we examine the viability of such an electrolyzer system operating at or near Martian ambient conditions by developing thermodynamic and electrochemical polarization models of this system for various CO2 reduction products. Given the extreme operating conditions, the models were first applied to existing experimental data from an operational water electrolyzer under simulated Martian conditions to evaluate fit [2]. For the proposed CO2-H2O electrolyzer, the Nernst potential for various reactions, the anode/cathode catalysts, their corresponding overpotentials and separator conductivity were calculated or parameterized from experiments in the literature. This was integrated into the polarization model to predict the performance of these electrolyzers under Martian conditions and for various desired products. The polarization curves were calculated for the following possible reaction products; CO (# of e- = 2), HCHO (# of e- = 4), CH3OH (# of e- = 6), CH4 (# of e- = 8), C2H4 and C2H5OH (# of e- = 12) under both Earth and Mars conditions. CH4 and C2H5OH were found to be thermodynamically favored products as compared to other(s) across the range of operational temperatures from 230 K to 298 K. CO, HCHO and C2H4 can serve as potential feed stocks for downstream processing into other useful chemicals on Mars and strategies are discussed for their selective production.REFERENCES[1]. NASA, small business innovation research (SBIR) & small business technology transfer (STTR) program, 2022 phase I solicitation[2].Gayen, P., Sankarasubramanian, S., & Ramani, V. K., Fuel and oxygen harvesting from Martian regolithic brine. Proceedings of the National Academy of Sciences, 117(50), 31685, (2020).[3].Meyen, Forrest E., et al. "Thermodynamic model of Mars oxygen ISRU experiment (MOXIE)." Acta Astronautica 129, 82 (2016). Figure 1. Calculated electromotive force of the production of various CO2 reduction products. Figure 1

(Digital Presentation) Experimental Results on the Determination of the Billiter Potential

The experimental effects at the Billiter potential are measured in narrow intervals of the equilibrium potentials (A, B). The Billiter potential + 0.475 V SHE [1-3] is confirmed by the following experimental results [4,5,7- 9]. The change in the direction of the current between a dropping mercury and a mercury bottom in solutions of redox systems Fe(CN)6 3 - - Fe(CN)6 4 - and quinone-hydroquinone at a given potential E equil . = + 475 V SHE has been established with exactness ± 1-2 mV [4, 5]. This result was confirmed in [6]. At E equil. > +0.475 V SHE, the current flows from a mercury bottom to dropping electrode and at E equil. < +0.475 V SHE - in the opposite direction. Electrocapillary curves have been found by drop-weight method in these solutions in narrow range E equil. ~+0.4 ÷+0.55 V SHE with a maximum at E equil. ~ + 0.475 V SHE [4].A self-recording galvanometer was used to record the reversal of the current between a mercury bottom and a dropping electrode in solutions of redox systems [7-9]. In a solution of quinone-hydroquinone redox system, a recorded positive current decreases exactly to zero at E = + 228 mV SCE (+ 475 mV SHE), and then a negative current increases with continuous dropping of mercury. E equil. changes by itself since an adsorbed quinone on mercury drops are removed from solution onto mercury bottom (A).The current reversal at E ~+ 0.22 ÷ + 0.23 V SCE (~+0.475 V SHE) has been recorded by a recorder between a mercury bottom and a dropping electrode in acidified Hg2(NO3)2 solutions with the addition of complexing agents (triethanolamine, sodium ethylenediaminetetraacetate, thiocarbamide, others) [7-9].The electrocapillary curves (ECC) have been measured by weight-drop method in these solutions (B; with sodium ethylenediaminetetraacetate). After passing the electrocapillary maximum for reversible Hg2 2+/ Hg electrode at E ~ + 0.22 ÷ + 0.23 V SCE, we have obtained an ascending branch of ECC of an ideally polarizable electrode at E equil. < ~+0.190 ÷ +0.210 V SCE. A registered second current reversal at these E equil. corresponds to the transition from a small descending branch of ECC of Hg2 2+/Hg electrode to an ascending branch of ECC of an ideally polarizable electrode. The electrocapillary maximum was also obtained using diluted acidified solutions of Hg2(NO3)2.An increase in a polarization resistance and a change in polarization capacitance have been detected when impedance measuring with reversible electrodes at Ee ~ +0.475 V SHE. These effects were also measured on mercury drops in the diluted 10-10 N solution of Hg2(NO3)2 + 0.1÷ 0.001 N KNO3 The increase in polarization resistance was explained by the achievement of chemical equilibrium of half-reactions at Ee quil. ~ +0.475 V SHE [6,7,16].Measurements by the immersion method with redox systems and solid electrodes of the second kind confirm the reversal of the current at E ~+ 475 V SHE. Submersible small solid electrodes must be absolutely clean and dry [5]. This method is under development.According to [8 - 10], Billiter potential corresponds to some electrode with zero chemical activity (transitional from metals to non-metals with the intermediate electron work function 5.19 eV). The same zero activity is obtained at chemical equilibrium of half-reactions when the sum of changes of chemical potentials of electrons and ions Δμion + Δμelectron = 0, and potential drops in double - electric layers are compensated. The components Δμion= 0 and Δμelectron≠ 0 correspond to potentials of zero charge Ep. z.c. For mercury, the electron work function is 4.52 eV and Δμelectron = 4.52 eV - 5.19 eV = - 0.67 eV. In order Δμion + Δμelectron = 0, Δμion should be equal + 0.67 eV. Indeed, if E p.z.c. = - 0.193 V SHE for mercury is changed by + 0.67 V we obtain the chemical equilibrium of half-reactions at ~ +0.475 V SHE. REFERENCES J.Billitzer, Methods for Determination of the Absolute Potentials, Trans. Amer. Electrochem. Soc., 1930,57, 351.The Encyclopedia of Electrochemistry, C.A. Hampel (ed.), (Reinhold,New York, NY) (1964).H.J.Oel, H Strelow,Z. Electrochem, 1954,58,665.A.I.Chernomorskii, Soviet Electrochemistry, 1981, 17, 874.A.I.Chernomorskii, Russian Journal of Physical Chemistry,1981, 55, p.206.Ya.I.Tur’yan, Redox Reactions and Potentials in Analytical Chemistry, Khimiya, Moscow, 1989.A.I. Chernomorskii,N.S.Polizan, Reports of Academy of Sciences of the Uzbekistan,1990, 6, 35.A.I.Chernomorskii, Thernodynamics of Electrodes, FAN, Tashkent, 1993.A.I.Chernomorskii, The Intermediate Electron Bond and Half-reactions, Scientific Resources, New York, 1999.A.I. Chernomorskii, Journal of The Electrochemical Society, 2021, 168,116514. Figure 1

Axon Initial Segment GABA Inhibits Action Potential Generation throughout Periadolescent Development.

Neurons are remarkably polarized structures: dendrites spread and branch to receive synaptic inputs while a single axon extends and transmits action potentials (APs) to downstream targets. Neuronal polarity is maintained by the axon initial segment (AIS), a region between the soma and axon proper that is also the site of action potential (AP) generation. This polarization between dendrites and axons extends to inhibitory neurotransmission. In adulthood, the neurotransmitter GABA hyperpolarizes dendrites but instead depolarizes axons. These differences in function collide at the AIS. Multiple studies have shown that GABAergic signaling in this region can share properties of either the mature axon or mature dendrite, and that these properties evolve over a protracted period encompassing periadolescent development. Here, we explored how developmental changes in GABAergic signaling affect AP initiation. We show that GABA at the axon initial segment inhibits action potential initiation in layer (L)2/3 pyramidal neurons in prefrontal cortex from mice of either sex across GABA reversal potentials observed in periadolescence. These actions occur largely through current shunts generated by GABAA receptors and changes in voltage-gated channel properties that affected the number of channels that could be recruited for AP electrogenesis. These results suggest that GABAergic neurons targeting the axon initial segment provide an inhibitory "veto" across the range of GABA polarity observed in normal adolescent development, regardless of GABAergic synapse reversal potential.Significance Statement GABA receptors are a major class of neurotransmitter receptors in the brain. Typically, GABA receptors inhibit neurons by allowing influx of negatively charged chloride ions into the cell. However, there are cases where local chloride concentrations promote chloride efflux through GABA receptors. Such conditions exist early in development in neocortical pyramidal cell axon initial segments (AISs), where action potentials (APs) initiate. Here, we examined how chloride efflux in early development interacts with mechanisms that support action potential initiation. We find that this efflux, despite moving membrane potential closer to action potential threshold, is nevertheless inhibitory. Thus, GABA at the axon initial segment is likely to be inhibitory for action potential initiation independent of whether chloride flows out or into neurons via these receptors.

Linear transformations of the Butler–Volmer equation

The conventional ways of determining the kinetic parameters (exchange or corrosion current and Tafel slopes) of the Butler–Volmer (BV) equation have serious drawbacks. In this paper linear transformations of the BV equation are proposed, based on the observation that the BV equation is a solution of a second-order, linear, homogeneous differential equation. The proposed method offers a very simple multilinear calculation method which can be applied in narrower or wider polarization ranges around the equilibrium or corrosion potential. The performance of a linearized form was tested on simulated and measured data series.

Controlled synthesis of Mo and Ni codoped Co2P as environmentally friendly catalyst for urea, freshwater and seawater oxidation

The thermodynamic equilibrium potential of urea electrolysis (0.37 V) is lower than that of conventional water electrolysis (1.23 V). In this paper, the urea oxidation reaction performance of Ni-Co2P was regulated and enhanced by doping with different quantity of Mo. The growth characteristics of Mo doping Ni-Co2P were characterized and analyzed to reveal the electrochemical properties of the target catalysts, and finally the electrochemical performance tests were carried out. The experimental results show that MoNi-Co2P-0.12 electrode exhibits superior catalytic activity and durability at an iR compensation of 90. What is noteworthy is that at a current density of 10 mA cm−2, the MoNi-Co2P-0.12 catalyst showed an ultra-low voltage of 1.244 V with a small Tafel slope (79.52 mV dec−1) and stable catalysis for over 12 h, which is one of the best catalytic activities reported to date. Experimental results show that the increased activity of the MoNi-Co2P-0.12 catalyst is attributable to synergic catalytic effect of Mo and Co, electron regulation and exposure of more active sites. Density functional theory (DFT) calculations demonstrate the doping of Mo can increase the urea adsorption energy of the MoNi-Co2P material compared with the Ni-Co2P material, and is also conducive to the improvement of the conductivity of the MoNi-Co2P material. This work provides new research into the use of cheap transition metal catalysts as an alternative to precious metal catalysts for urea electrolysis.

Menthol excites dural afferent neurons by inhibiting leak K+ conductance in rats

Menthol—a natural organic compound—is widely used for relieving various pain conditions including migraine. However, a high dose of menthol reportedly decreases pain thresholds and enhances pain responses. Accordingly, in the present study, we addressed the effect of menthol on the excitability of acutely isolated dural afferent neurons, which were identified with a fluorescent dye, using the whole-cell patch-clamp technique. Under a voltage-clamped condition, menthol altered the holding current levels in a concentration-dependent manner. The menthol-induced current (IMenthol) remained unaffected by the addition of selective transient receptor potential melastatin 8 antagonists. Moreover, the reversal potential of IMenthol was similar to the equilibrium potential of K+. IMenthol was accompanied by an increase in input resistance, thereby suggesting that menthol decreases the leak K+ conductance. Under a current-clamped condition, menthol caused depolarization of the membrane potential and decreased the threshold for the generation of action potential. While the IMenthol was substantially inhibited by 10 μM XE-991, a selective KV7 blocker, the M-current mediated by KV7 was not detected in the nociceptive neurons tested in the present study. Moreover, IMenthol decreased under acidic extracellular pH conditions or in the presence of 3 μM A-1899, a selective K2P3.1 and K2P9.1 blocker. The present results suggest that menthol inhibits leak K+ channels, possibly acid-sensitive two-pore domain K+ channels, thereby increasing the excitability of nociceptive sensory neurons. The resultant increase in neuron excitability may partially be responsible for the pronociceptive effect mediated by high menthol doses.

Functional Characterization of the A414G Loss-of-Function Mutation in HCN4 Associated with Sinus Bradycardia

Patients carrying the heterozygous A414G mutation in the HCN4 gene, which encodes the HCN4 protein, demonstrate moderate to severe bradycardia of the heart. Tetramers of HCN4 subunits compose the ion channels in the sinus node that carry the hyperpolarization-activated ‘funny’ current (If), also named the ‘pacemaker current’. If plays an essential modulating role in sinus node pacemaker activity. To assess the mechanism by which the A414G mutation results in sinus bradycardia, we first performed voltage clamp measurements on wild-type (WT) and heterozygous mutant HCN4 channels expressed in Chinese hamster ovary (CHO) cells. These experiments were performed at physiological temperature using the amphotericin-perforated patch-clamp technique. Next, we applied the experimentally observed mutation-induced changes in the HCN4 current of the CHO cells to If of the single human sinus node cell model developed by Fabbri and coworkers. The half-maximal activation voltage V1/2 of the heterozygous mutant HCN4 current was 19.9 mV more negative than that of the WT HCN4 current (p &lt; 0.001). In addition, the voltage dependence of the heterozygous mutant HCN4 current (de)activation time constant showed a −11.9 mV shift (p &lt; 0.001) compared to the WT HCN4 current. The fully-activated current density, the slope factor of the activation curve, and the reversal potential were not significantly affected by the heterozygous A414G mutation. In the human sinus node computer model, the cycle length was substantially increased, almost entirely due to the shift in the voltage dependence of steady-state activation, and this increase was more prominent under vagal tone. The introduction of a passive atrial load into the model sinus node cell further reduced the beating rate, demonstrating that the bradycardia of the sinus node was even more pronounced by interactions between the sinus node and atria. In conclusion, the experimentally identified A414G-induced changes in If can explain the clinically observed sinus bradycardia in patients carrying the A414G HCN4 gene mutation.

Separation of lanthanides erbium and ytterbium on indium electrodes by modulated potential selective extraction in molten salts and a thermodynamic and kinetic analysis of the process

The main purpose of this paper is to study the extraction and separation of key fragment elements based on the electrolytic refining process of spent fuel dry reprocessing. Firstly, the electrochemical mechanisms of Er(III) and Yb(III) in LiCl-KCl molten salts were investigated on W and In film electrodes with applied cyclic voltammetry (CV), square wave voltammetry (SWV) and open circuit potential (OCP) at 773 K. The results indicated that the reduction behaviour of In(III) and Yb(III) ions were a two-step transfer process and Er(III) ions was a one-step transfer process. Then, the kinetic parameters in electrochemical processes were calculated on an In electrode with different temperatures. The OCP approach was used to determine the equilibrium potential of Er(III)/Er(0) in the temperature range of 773 K∼848 K, and thermodynamic parameters of the In3Er alloy were provided. Based on electrochemical behaviour results, the electrochemical extraction of Er(III) and Yb(III) from LiCl-KCl-ErCl3 molten salts and LiCl-KCl-YbCl3 molten salts at liquid In electrodes was performed by constant potential and constant current electrolysis, respectively. The electrolysis products were determined by X-ray diffraction (XRD), scanning electron microscopy and energy dispersive spectrometry (SEM-EDS), the primary intermetallic compounds generated in the alloys were In3Er and In3Yb. The average extraction rates for Er(III) and Yb(III) were 94.70% and 96.54%, respectively, according to inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis. Er(III) and Yb(III) were selectively extracted and separated from LiCl-KCl-ErCl3-YbCl3 molten salts by potentiostatic control on the basis of the previously studied Lns (Er and Yb) extraction on In electrodes. The separation rate of Er(III) and Yb(III) by electrochemical selective deposition was 94.21%.

Hydrogen egress from palladium surfaces: A microelectrode-based investigation

Atomic hydrogen could participate in multiple electrochemical reactions during egress from Palladium (Pd) into aqueous environments. Possible reactions include hydrogen recombination to form H2, the oxygen reduction reaction (ORR) and “hydrogen ionisation” to form H+. Here, bulk measurements and microelectrode-based methods were used to mechanistically investigate such reactions occurring during hydrogen egress from Pd. Significant ORR was detected on hydrogen-charged Pd (Pd-H) surfaces, when using a Platinum (Pt) microelectrode (ME) in the redox competition mode. However, minor hydrogen recombination was also detected while using the Pt ME in the sample generation-tip collection (SG-TC) mode. Hydrogen ionisation is observed to occur when Pd (H) is anodically polarised. These reactions can all be linked to the highly negative equilibrium potential of the atomic H/H+ redox couple. Atomic hydrogen being a strong reducing agent thus tends to efficiently reduce various oxidants in solution resulting in different products, under varying conditions.

Deciphering Reversible Homogeneous Catalysis of the Electrochemical H2 Evolution and Oxidation: Role of Proton Relays and Local Concentration Effects**

AbstractNickel bisdiphosphine complexes bearing pendant amines form a unique series of catalysts (so‐called DuBois’ catalysts) capable of bidirectional/reversible electrocatalytic oxidation and production of dihydrogen. This unique behaviour is directly linked to the presence of proton relays installed close to the metal center. We report here for the arginine derivative [Ni(P2CyN2Arg)2]6+ on a mechanistic model and its kinetic treatment that may apply to all DuBois’ catalysts and show that it allows for a good fit of experimental data measured at different pH values, catalyst concentrations and partial hydrogen pressures. The bidirectionality of catalysis results from balanced equilibria related to hydrogen uptake/evolution on one side and (metal)‐hydride installation/capture on the other side, both controlled by concentration effects resulting from the presence of proton relays and connected by two square schemes corresponding to proton‐coupled electron transfer processes. We show that the catalytic bias is controlled by the kinetic of the H2 uptake/evolution step. Reversibility does not require that the energy landscape be flat, with redox transitions occurring at potentials up to 250 mV away for the equilibrium potential, although such large deviations from a flat energy landscape can negatively impacts the rate of catalysis when coupled with slow interfacial electron transfer kinetics.

Deciphering Reversible Homogeneous Catalysis of the Electrochemical H2 Evolution and Oxidation: Role of Proton Relays and Local Concentration Effects.

Nickel bisdiphosphine complexes bearing pendant amines form a unique series of catalysts (so-called DuBois' catalysts) capable of bidirectional/reversible electrocatalytic oxidation and production of dihydrogen. This unique behaviour is directly linked to the presence of proton relays installed close to the metal center. We report here for the arginine derivative [Ni(P2 Cy N2 Arg )2 ]6+ on a mechanistic model and its kinetic treatment that may apply to all DuBois' catalysts and show that it allows for a good fit of experimental data measured at different pH values, catalyst concentrations and partial hydrogen pressures. The bidirectionality of catalysis results from balanced equilibria related to hydrogen uptake/evolution on one side and (metal)-hydride installation/capture on the other side, both controlled by concentration effects resulting from the presence of proton relays and connected by two square schemes corresponding to proton-coupled electron transfer processes. We show that the catalytic bias is controlled by the kinetic of the H2 uptake/evolution step. Reversibility does not require that the energy landscape be flat, with redox transitions occurring at potentials up to 250 mV away for the equilibrium potential, although such large deviations from a flat energy landscape can negatively impacts the rate of catalysis when coupled with slow interfacial electron transfer kinetics.

Probing electrophysiological activity of amphiphilic Dynorphin A in planar neutral membranes reveals both ion channel-like activity and neuropeptide translocation

Dynorphin A (DynA) is an endogenous neuropeptide that besides acting as a ligand of the κ-opioid receptor, presents some non-opioid pathophysiological properties associated to its ability to induce cell permeability similarly to cell-penetrating peptides (CPPs). Here, we use electrophysiology experiments to show that amphiphilic DynA generates aqueous pores in neutral membranes similar to those reported previously in charged membranes, but we also find other events thermodynamically incompatible with voltage-driven ion channel activity (i.e. non-zero currents with no applied voltage in symmetric salt conditions, reversal potentials that exceed the theoretical limit for a given salt concentration gradient). By comparison with current traces generated by other amphiphilic molecule known to spontaneously cross membranes, we hypothesize that DynA could directly translocate across neutral bilayers, a feature never observed in charged membranes following the same electrophysiological protocol. Our findings suggest that DynA interaction with the cellular membrane is modulated by the lipid charge distribution, enabling either passive ionic transport via membrane remodeling and pore formation or by peptide direct internalization independent of cellular transduction pathways.

Effects of F- on the electrochemical properties and electrodeposition nucleation mechanism of Ce(III) in LiCl-KCl melts

The purpose of this work is to systematically investigate the effect of F− on the electrochemical properties and electrodeposition nucleation of Ce(III) in LiCl-KCl molten salt. Electrochemically reversible, three-electron transfer and diffusion-controlled Ce(III)/Ce redox reactions were still observed by using Cyclic voltammetry (CV), Square wave voltammetry (SWV), and Chronopotentiometry (CP) methods in the LiCl-KCl molten salt containing F−. With the addition of F−, a negative shift in peak and equilibrium potentials were observed, indicating that F− could interact with Ce(III) via the coordination competition with Cl−. Also, F− ions were found to decrease both the diffusion coefficient and exchange current density j0 of Ce(III). In addition, the thermodynamic data of Ce(III)/Ce at multiple F− concentrations were calculated theoretically, which showed that Ce(III) preferred to form [CeCl5F]3−complexes in chlorine molten salts. Finally, the effect of F− on the electrodeposition nucleation mechanism of Ce(III) at tungsten electrodes was studied. The results showed that the nucleation and growth mechanism shifted from instantaneous nucleation to between instantaneous and progressive nucleation with the addition of F−. The current research paves a new way for changing the nucleation mode of electrodeposition, which provides a new direction to retrieve the uranium dendrites during the electrorefining of spent nuclear fuel.

Resting membrane state as an interplay of electrogenic transporters with various pumps.

In this study, a new idea that electrogenic transporters determine cell resting state is presented. The previous assumption was that pumps, especially the sodium one, determine it. The latter meets difficulties, because it violates the law of conservation of energy; also a significant deficit of pump activity is reported. The amount of energy carried by a single ATP molecule reflects the potential of the inner mitochondrial membrane, which is about -200 mV. If pumps enforce a resting membrane potential that is more than twice smaller, then the majority of energy stored in ATP would be dissipated by each pump turning. However, this problem could be solved if control is transferred from pumps to something else, e.g., electrogenic transporters. Then pumps would transfer the energy to the ionic gradient without losses, while the cell surface membrane potential would be associated with the reversal potential of some electrogenic transporters. A minimal scheme of this type would include a sodium-calcium exchanger as well as sodium and calcium pumps. However, note that calcium channels and pumps are positioned along both intracellular organelles and the surface membrane. Therefore, the above-mentioned scheme would involve them as well as possible intercellular communications. Such schemes where various kinds of pumps are assumed to work in parallel may explain, to a great extent, the slow turning rate of the individual members. Interaction of pumps and transporters positioned at distant biological membranes with various forms of energy transfer between them may thus result in hypoxic/reperfusion injury, different kinds of muscle fatigue, and nerve-glia interactions.

Maternal hyperhomocysteinemia increases seizures susceptibility of neonatal rats

AimsNeonatal seizures are severe pathologies which may result in long-term neurological consequences. High plasma concentrations of homocysteine – hyperhomocysteinemia (hHCy) - are associated with epilepsy. In the present study, we evaluated susceptibility to seizure of neonatal rats with prenatal hHCy. Main methodsPrenatal hHCy was induced by feeding females with a high-methionine diet. Experiments were performed on pups during the first three postnatal weeks. Flurothyl-induced epileptic behavior was assessed according to Racine's scale. Epileptiform activity in the hippocampus was recorded using electrophysiological methods. The balance of excitation/inhibition, functional GABAergic inhibition and GABA reversal potential in hippocampal neurons were analyzed. Key findingsRats with hHCy developed more severe stages of behavioral patterns during flurothyl-induced epilepsy with shorter latency. Electrophysiological recordings demonstrated higher background neuronal activity in rats with hHCy. Seizure-like events triggered by flurothyl (in vivo) or 4-aminopyridine (in vitro) showed shorter latency, higher power and amplitude. An increased glutamate/GABA synaptic ratio was shown in the pyramidal neurons of rats with hHCy and more slices demonstrated excitation by isoguvacine, a selective GABA(A) receptor agonist, during the first and second postnatal weeks. The GABA driving force and the reversal potential of GABA(A) currents were more positive during the second postnatal week for hHCy rats. SignificanceThe higher susceptibility to seizures in rats with prenatal hHCy due to a shift in the balance of excitation/inhibition toward excitation may underlie the clinical evidence about the association of hHCy with an increased risk of epilepsy.

Unveiling the antibacterial potential and antibiotic-resistance breaker activity of Syzygium jambos (Myrtaceae) towards critical-class priority pathogen Klebsiella isolates

Background: Klebsiella has developed multiple-drug resistance (MDR) to a wide range of medicines, including carbapenems and third generation cephalosporins which are often regarded as the most effective drugs against MDR bacteria. The present study examined the anti-klebsiella, modes of action, and antibiotic-resistance reversal potential of Syzygium jambos (Myrtaceae) leaf (SJL) and bark (SJB) methanol extracts towards a panel of sixteen MDR K. pneumoniae and K. oxytoca strains and clinical isolates. Methods: The anti-klebsiella potential of SJL and SJB was assessed by determining the minimal inhibitory (MIC) and minimal bactericidal concentrations (MBC) using broth microdilution. Extracts were tested alone, in combination with an efflux pump inhibitor (PaβN), and in association with conventional antibiotics at their sub-inhibitory concentrations. Effects of SJL were also evaluated on bacterial kinetic growth, H+-ATPase-mediated pump, and cell membrane integrity, using standards. Results: SJL and SJB were shown to have anti-klebsiella action, with MICs ranging from 64 to 2048 g/mL. SJL was found to be more effective, acting on all tested pathogens with 100 ≤ MIC ≤ 2048 µg/mL, indicating considerable to moderate activity and generating bactericidal effects on more than half of the MDR Klebsiella strains investigated. SJL also produced a remarkably active effect (MIC ≤ 100 µg/mL), with MIC of 64 µg/mL against K. pneumoniae KP26. In the presence of PaβN, SJL and SJB activity rose significantly, demonstrating the involvement of active efflux machinery as MDR mechanisms. SJL displayed significant MDR reversal potential, as evidenced by an enhanced efficacy of conventional antibiotics, when in association. The activity of doxycycline and levofloxacin was improved on 100% of studied MDR pathogens. Interestingly, SJL also significantly enhanced the efficacy of the last resort drugs cefixime (cephalosporin) and imipenem (carbapenems) at more than 75% at MIC/2. Exposure of K. pneumoniae KP63 to SJL at 0.5×MIC, MIC, and 2×MIC for 20 h produced a concentration-dependent trend toward greater bacterial killing, extending the latent phase. In addition, SJL showed pronounced inhibition of the H+-ATPase-mediated pump and mildly disrupted the cytoplasmic membrane. Conclusion: This work provides a solid experimental foundation for considering S. jambos leaf extract as a viable treatment option for MDR Klebsiella-related illnesses. Keywords: Antibiotic-resistance modifying agents; efflux pump inhibitor; food plants; Klebsiella infections; multidrug resistance; Syzygium jambos.

Determination of the electron temperature in a supersonic jet of a gas-discharge source from current measurements by an insulated probe system

The aim of this work is to substantiate the possibility of using the classical procedure for determining the electron temperature for diagnosing a supersonic jet of a collisionless plasma of a diatomic gas using the current-voltage characteristic of an insulated probe system. The probe system consists of a cylindrical probe and a reference electrode composed of several cylinders, all placed transversely in the plasma flow. The ratio of the current-collecting surface area of the reference electrode to the area of the probe is arbitrary and can be significantly less than required by the theory of a single probe. Based on a previously constructed mathematical model of current collection, which includes the calculation of the equilibrium potential of the reference electrode as a function of the probe bias voltage, a procedure is developed for determining the electron temperature by measuring the probe currents in a jet of a gas-discharge source of a laboratory dissociated plasma. An approximation of the floating potential of the insulated probe system in a strongly nonequilibrium plasma of a gas-discharge source jet is found, which allows one to determine the boundaries of the transition region of the current-voltage characteristic using a priori information on the plasma parameters. A formula is obtained for extrapolating the ion probe current vs. bias potential relationship into the transition region of the current-voltage characteristic. Within the framework of the adopted mathematical model of charged plasma particle collection, a numerical analysis of the method error of the electron temperature determination procedure is performed. Quantitative characteristics of the effect of the insulated probe system geometry on the method error are obtained. A numerical simulation of the effect of the probe current measurement errors showed that, within the framework of the adopted model, the accuracy of determining the electron temperature using the insulated probe system is comparable with the accuracy of measurements with a single cylindrical probe. The results obtained may be used in the diagnostics of a laboratory plasma of a gas-discharge source.

CO2-Induced Ocean Acidification Alters the Burrowing Behavior of Manila Clam Ruditapes philippinarum by Reversing GABAA Receptor Function.

Biological burrowing behavior is an important driver shaping ecosystems that is being threatened by CO2-induced ocean acidification; however, the effects of ocean acidification on burrowing behavior and its neurological mechanism remain unclear. This study showed that elevated pCO2 significantly affected the burrowing behaviors of the Manila clam Ruditapes philippinarum, such as increased foot contraction, burrowing time, and intrabottom movement and decreased burrowing depth. Delving deeper into the mechanism, exposure to elevated pCO2 significantly decreased extracellular pH and increased [HCO3-]. Moreover, an indicator GABAA receptor, a neuroinhibitor for movement, was found to be closely associated with behavioral changes. In situ hybridization confirmed that the GABAA receptor was widely distributed in ganglia and foot muscles, and elevated pCO2 significantly increased the mRNA level and GABA concentration. However, the increase in GABAA receptor and its ligand did not suppress the foot movement, but rather sent "excitatory" signals for foot contraction. The destabilization of acid-base homeostasis was demonstrated to induce an increase in the reversal potential for GABAA receptor and an alteration in GABAA receptor function under elevated pCO2. This study revealed that elevated pCO2 affects the burrowing behavior of Manila clams by altering GABAA receptor function from inhibitory to excitatory.

Solid oxide cell electrolytes deposited by atmospheric suspension plasma spraying at high velocity and high temperature

AbstractMetal‐supported solid oxide cells with Yttria‐stabilized zirconia (YSZ) electrolytes fabricated by atmospheric plasma spraying are routinely found to have open‐circuit voltages (OCVs) below the Nernst potential due to gas crossover and combustion resulting from electrolyte defects. To improve splat bonding and reduce coating defects, YSZ electrolytes were fabricated here at &gt;800°C substrate temperatures and torch‐substrate relative velocities of 4 and 12 m/s by atmospheric suspension plasma spraying. Electrolyte microstructures appeared dense, with porosities estimated to be approximately 2.2–3.5 vol%. Minimal segmentation cracking was observed on samples fabricated at 12 m/s. The full cells that were electrochemically tested had permeabilities in the range of 4–6 × 10−19 m2, and the maximum recorded OCV was ∼26 mV below the Nernst potential for 750°C. Potential performance gains from YSZ deposition at substrate temperatures &gt;800°C may have been masked by poor substrate‐fuel electrode contact. Using electrochemical impedance spectroscopy, it was found that the ohmic and polarization resistances decreased and increased, respectively, over time. The calculated distribution of relaxation times of the tested cells, together with observations from the literature, were employed to identify possible cell degradation mechanisms observed during short‐term durability testing.