Charge Selectivity Research Articles

Fast assessment of structural models of ion channels based on their predicted current-voltage characteristics.

Computational prediction of protein structures is a difficult task, which involves fast and accurate evaluation of candidate model structures. We propose to enhance single-model quality assessment with a functionality evaluation phase for proteins whose quantitative functional characteristics are known. In particular, this idea can be applied to evaluation of structural models of ion channels, whose main function - conducting ions - can be quantitatively measured with the patch-clamp technique providing the current-voltage characteristics. The study was performed on a set of KcsA channel models obtained from complete and incomplete contact maps. A fast continuous electrodiffusion model was used for calculating the current-voltage characteristics of structural models. We found that the computed charge selectivity and total current were sensitive to structural and electrostatic quality of models. In practical terms, we show that evaluating predicted conductance values is an appropriate method to eliminate models with an occluded pore or with multiple erroneously created pores. Moreover, filtering models on the basis of their predicted charge selectivity results in a substantial enrichment of the candidate set in highly accurate models. Tests on three other ion channels indicate that, in addition to being a proof of the concept, our function-oriented single-model quality assessment method can be directly applied to evaluation of structural models of some classes of protein channels. Finally, our work raises an important question whether a computational validation of functionality should be included in the evaluation process of structural models, whenever possible.

Determinants of Cx43 Channel Gating and Permeation: The Amino Terminus

Separate connexin domains partake in proposed gating mechanisms of gap junction channels. The amino-terminus (NT) domains, which contribute to voltage sensing, may line the channel’s cytoplasmic-facing funnel surface, stabilize the channel’s overall structure through interactions with the transmembrane domains and each other, and integrate to form a compound particle to gate the channel closed. Interactions of the carboxyl-terminus (CT) and cytoplasmic loop (CL) domains underlie voltage- and low pH-triggered channel closure. To elucidate potential cooperation of these gating mechanisms, we replaced the Cx43NT with the Cx37NT (chimera Cx43∗NT37), leaving the remainder of the Cx43 sequence, including the CT and CL, unchanged. Compared to wild-type Cx43 (Cx43WT), Cx43∗NT37 junctions exhibited several functional alterations: extreme resistance to halothane- and acidification-induced uncoupling, absence of voltage-dependent fast inactivation, longer channel open times, larger unitary channel conductances, low junctional dye permeability/permselectivity, and an overall cation selectivity more typical of Cx37WT than Cx43WT junctions. Together, these results suggest a cohesive model of channel function wherein: 1) channel conductance and size selectivity are largely determined by pore diameter, whereas charge selectivity results from the NT domains, and 2) transition between fully open and (multiple) closed states involves global changes in structure of the pore-forming domains transduced by interactions of the pore-forming domains with either the NT, CT, or both, with the NT domains forming the gate of the completely closed channel.

Electrically charged selectivity of poly-para-xylylene deposition.

The bottom-up patterning approach provides intrinsic advantages associated with unlimited resolution but is limited by the materials available for selection. A general and simple approach towards the selective deposition of poly-para-xylylenes is introduced in this communication. The chemical vapour deposition (CVD) of poly-para-xylylenes is inhibited on the high-energy surfaces of electrically charged conducting substrates. This technology provides an approach to selectively deposit poly-para-xylylenes irrespective of the substituted functionality and to pattern these polymer thin films from the bottom up.

Early adopters of electric vehicles in Germany unveiled

The socioeconomic characteristics of early adopters of electric vehicles (EVs) differ from those of buyers of conventional vehicles, as do their attitudes towards new technologies, their mobility, and their awareness of ecological issues. They are found to have a higher average income, a higher level of education and more cars at their disposal per household. However, most of the existing studies are based on small samples, or used stated preference surveys which attempted to describe potential purchasers of EVs. Furthermore, when it comes to the kind of EV, most of the studies analyse the adoption of battery electric vehicles (BEVs) only, with just a few looking at the adoption of plug-in hybrid electric vehicles (PHEVs). An analysis of representative data collected from more than 3,000 owners of BEVs and PHEVs in Germany partially confirms the findings mentioned, but finds that aspects such as socioeconomic characteristics and their attitudes vary greatly among EV users. First the paper gives an overview of the socioeconomics of EV drivers in Germany, and key facts about their driving and charging behaviour. Subsequently, the main factors motivating people to buy an EV are identified and analysed for owners of BEVs and PHEVs. This is complemented by an analysis of general attitudes of EV owners towards factors such as the image of EVs, environmental awareness and mode choice. To conclude, the willingness to pay for technologies such as fast-charging, inductive charging and battery size selection is analysed.

Charge selectivity in polymer:Fullerene-based organic solar cells with a chemically linked polyethylenimine interlayer

The power conversion efficiency of solar cells can be optimized via an efficient charge collection by electrodes. In this study, a simple linear polyethylenimine (LPEI), which is an insulating polymer, was adopted as the cathode interfacial layer of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)-based bulk-heterojunction organic solar cells (OSCs) with a non-inverted configuration. All photovoltaic parameters of the OSCs were significantly enhanced by depositing LPEI onto the oxygen plasma-treated P3HT:PCBM active layers. The causes of performance enhancement in OSCs were studied. Results revealed that the microstructure and morphology of the P3HT:PCBM layer were almost unaffected by the oxygen plasma treatment and the subsequent LPEI deposition. The X-ray photoelectron spectra of the specimens demonstrated that with the aid of oxygen plasma treatment, the linked LPEI molecules formed a well-aligned dipole layer on top of the P3HT:PCBM layer through the bonding of nitrogen (N) with oxygen (O). The results from quantum chemical calculations showed that the LPEI molecule with an N–O bond had a larger dipole moment at an appropriate direction than that without an N–O bond. By contrast, the LPEI molecules can form a dipole layer with a random orientation in the absence of N–O bonds. The conductive atomic force microscopy images of the specimens showed that the well-aligned dipole layer could facilitate electron transfer and could block hole transfer from the P3HT:PCBM to the cathodes. The well-aligned and augmented interface dipoles improved the charge selectivity at the cathodes and the photovoltaic performance of the devices.

Influence of Electron Extracting Interface Layers in Organic Bulk‐Heterojunction Solar Cells

The influence of different electron extracting interlayers such as calcium (Ca), zirconium acetylacetonate (ZrAcac), and a polyfluorene derivative (PFN) in combination with an aluminum (Al) cathode is investigated on the performance of bulk‐heterojuntion solar cells. Two different photoactive systems, P3HT:PC61BM and PDPP:PC71BM, are selected for this study. The electroabsorption measurements have been carried out for obtaining the built‐in voltage (Vbi) and transfer matrix simulations for the determination of parasitic absorption. The solar cell performance is influenced by different parameters such as diode turn‐on voltage, leakage currents, built‐in voltages, and parasitic absorption. The small diode turn‐on voltage and high parasitic absorption in Ca contact devices limit the open circuit voltage and short circuit current, respectively. Likewise, high leakage currents using ZrAcac contact limit the fill factor in P3HT:PC61BM solar cell devices. However, the PFN‐based devices with small parasitic absorption, smaller leakage currents, and a relatively high Vbi show maximum performance with both material systems. This work highlights the importance of choosing the suitable interlayers in device optimization and clearly demonstrates that not only the low work function of an electron extracting interlayer but also its optical properties and charge selectivity significantly influence the final solar cell performance.

Prototyping of beam position monitor for medium energy beam transport section of RAON heavy ion accelerator

A heavy ion accelerator, RAON is going to be built by Rare Isotope Science Project in Korea. Its target is to accelerate various stable ions such as uranium, proton, and xenon from electron cyclotron resonance ion source and some rare isotopes from isotope separation on-line. The beam shaping, charge selection, and modulation should be applied to the ions from these ion sources because RAON adopts a superconducting linear accelerator structure for beam acceleration. For such treatment, low energy beam transport, radio frequency quadrupole, and medium energy beam transport (MEBT) will be installed in injector part of RAON accelerator. Recently, development of a prototype of stripline beam position monitor (BPM) to measure the position of ion beams in MEBT section is under way. In this presentation, design of stripline, electromagnetic (EM) simulation results, and RF measurement test results obtained from the prototyped BPM will be described.

Low Work-function Poly(3,4-ethylenedioxylenethiophene): Poly(styrene sulfonate) as Electron-transport Layer for High-efficient and Stable Polymer Solar Cells.

Low-work-function poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) modified with polyethylenimine (PEIE) was used as an electron transport layer (ETL) for polymer solar cells (PSCs). A thin layer of PEIE film was spin-coated onto the surface on the PEDOT:PSS films, thus substantially changing their charge selectivity from supporting hole transport to supporting electron transport. It was also found that the PEDOT:PSS/PEIE ETL exhibited higher interfacial contact, a more favorable active morphology, and improved charge mobility. By virtue of these beneficial properties, inverted PSCs based on low-bandgap semiconducting photoactive layers achieved a notably improved power conversion efficiency (PCE) of 7.94%, superior even to the corresponding performance of devices with only a ZnO layer. Surpassing our expectations, compared with the extreme degradation of device stability observed when pure PEDOT:PSS is used, PEIE-modified PEDOT:PSS can considerably suppress device degradation because of the hydrophobic and alkaline nature of PEIE, which not only reduces the hygroscopicity of the PEDOT:PSS but also neutralizes the acidic PEDOT:PSS and thus prevents the corrosion of the ITO cathode. These results demonstrate the potential of PEIE-modified PEDOT:PSS for use as an efficient ETL in commercial printed electronic devices.

Molecular basis of claudin-17 anion selectivity.

Claudin-17 is a paracellular channel-forming tight junction protein. Unlike the cation channels claudin-2 and -15, claudin-17 forms a distinct anion-selective channel. Aim of this study was to determine the molecular basis of channel formation and charge selectivity of this protein. To achieve this, residues located in the extracellular loops (ECL) 1 and 2 of claudin-17 were substituted, preferably those whose charges differed in claudin-17 and in claudin-2 or -15. The respective mutants were stably expressed in MDCK C7 cells and their ability to form charge-selective channels was analyzed by measuring ion permeabilities and transepithelial electrical resistance. The functional data were combined with homology modeling of the claudin-17 protomer using the structure of claudin-15 as template. In ECL1, K65, R31, E48, and E44 were found to be stronger involved in Cldn17 channel function than the clustered R45, R56, R59, and R61. For K65, not only charge but also stereochemical properties were crucial for formation of the anion-selective channel. In ECL2, both Y149 and H154 were found to contribute to constitution of the anion channel in a distinct manner. In conclusion, we provide insight into the molecular mechanism of the formation of charge- and size-selective paracellular ion channels. In detail, we propose a hydrophilic furrow in the claudin-17 protomer spanning from a gap between the ends of TM2 and TM3 along R31, E48, and Y67 to a gap between K65 and S68 lining the anion channel.

High-Performance, Air-Stable, Low-Temperature Processed Semitransparent Perovskite Solar Cells Enabled by Atomic Layer Deposition

We demonstrate high-performance, air-stable, low-temperature processed (≤100 °C) semitransparent (ST) perovskite solar cells (PSCs) by the applications of atomic layer deposition (ALD) technology to deposit ZnO and Al2O3 films as cathode buffer layer (CBL) and encapsulation layer, respectively. The application of ALD ZnO film as CBL in PSCs delivers several remarkable features, including fine-tunability of the work function of the electrode, low deposition temperature (80 °C), high charge selectivity, good electron-transporting ability (filed-effect mobility = 16.1 cm2 V–1 s–1), and excellent film coverage. With these desired interfacial properties, the device with opaque Ag electrode delivers high power conversion efficiency (PCE) up to 16.5%, greatly outperforming the device with state-of-the-art CBL ZnO nanoparticles film (10.8%). For ST PSCs employing Ag nanowires as transparent top electrode, a remarkable PCE of 10.8% with a corresponding average visible transmittance (AVT) of 25.5% is demonstrated, ...

The atypical cation-conduction and gating properties of ELIC underscore the marked functional versatility of the pentameric ligand-gated ion-channel fold.

The superfamily of pentameric ligand-gated ion channels (pLGICs) is unique among ionotropic receptors in that the same overall structure has evolved to generate multiple members with different combinations of agonist specificities and permeant-ion charge selectivities. However, aside from these differences, pLGICs have been typically regarded as having several invariant functional properties. These include pore blockade by extracellular quaternary-ammonium cations in the micromolar-to-millimolar concentration range (in the case of the cation-selective members), and a gain-of-function phenotype, which manifests as a slower deactivation time course, as a result of mutations that reduce the hydrophobicity of the transmembrane pore lining. Here, we tested this notion on three distantly related cation-selective members of the pLGIC superfamily: the mouse muscle nicotinic acetylcholine receptor (nAChR), and the bacterial GLIC and ELIC channels. Remarkably, we found that, whereas low millimolar concentrations of TMA(+) and TEA(+) block the nAChR and GLIC, neither of these two quaternary-ammonium cations blocks ELIC at such concentrations; instead, both carry measurable inward currents when present as the only cations on the extracellular side. Also, we found that, whereas lidocaine binding speeds up the current-decay time courses of the nAChR and GLIC in the presence of saturating concentrations of agonists, the binding of lidocaine to ELIC slows this time course down. Furthermore, whereas mutations that reduce the hydrophobicity of the side chains at position 9' of the M2 α-helices greatly slowed the deactivation time course of the nAChR and GLIC, these mutations had little effect--or even sped up deactivation--when engineered in ELIC. Our data indicate that caution should be exercised when generalizing results obtained with ELIC to the rest of the pLGICs, but more intriguingly, they hint at the possibility that ELIC is a representative of a novel branch of the superfamily with markedly divergent pore properties despite a well-conserved three-dimensional architecture.

Charge, size, and cellular selectivity for multiwall carbon nanotubes by maize and soybean.

Maize (Zea mays) and soybean (Glycine max) were used as model food-chain plants to explore vegetative uptake of differently charged multiwall carbon nanotubes (MWCNTs). Three types of MWCNTs, including neutral pristine MWCNT (p-MWCNT), positively charged MWCNT-NH2, and negatively charged MWCNT-COOH, were directly taken-up and translocated from hydroponic solution to roots, stems, and leaves of maize and soybean plants at the MWCNT concentrations ranging from 10.0 to 50.0 mg/L during 18-day exposures. MWCNTs accumulated in the xylem and phloem cells and within specific intracellular sites like the cytoplasm, cell wall, cell membrane, chloroplast, and mitochondria, which was observed by transmission electron microscopy. MWCNTs stimulated the growth of maize and inhibited the growth of soybean at the exposed doses. The cumulative transpiration of water in maize exposed to 50 mg/L of MWCNT-COOHs was almost twice as much as that in the maize control. Dry biomass of maize exposed to MWCNTs was greater than that of maize control. In addition, the uptake and translocation of these MWCNTs clearly exhibited cellular, charge, and size selectivity in maize and soybean, which could be important properties for nanotransporters. This is the first report of cellular, charge, and size selectivity on the uptake by whole food plants for three differently charged MWCNTs.

Achromatic and isochronous lattice design of P2DT bending section in RAON accelerator

In RAON heavy ion accelerator, generally, the In-flight Fragmentation (IF) and Isotope Separation On-Line (ISOL) systems are employed in order to produce various isotope beams. Out of the isotope beams, the beams generated by the ISOL system are transported from the low energy linac SCL3 to the high energy driver linac SCL2. The post-accelerator to the driver linac transport (P2DT) section that consists of the charge stripper section, the 180° bending section, and the SCL2 matching section is placed between the SCL3 and the SCL2. In this P2DT section, however, the transverse and longitudinal emittance growth can aggravate the beam acceptance of the SCL2. Besides, the growth at the P2DT 180° bending section is considered a significant issue because of the unexpected achromatic effect. Therefore an achromatic and isochronous lattice design should be devised to prevent the transverse and longitudinal emittance from increasing while the multi-charge beams flow through the bending section. This study reports an improved design for the achromatic and isochronous lattice up to the second-order. After satisfying the first-order achromatic and isochronous condition by adjusting the field strength of quadrupoles with this design, the simple and efficient method will be utilized with the aim of getting the minimum number of sextupoles. The research on the collimator for the charge selection at the bending section will be also represented by using the designed lattice.

ChemInform Abstract: Functional Membranes via Nanoparticle Self‐Assembly

AbstractReview: [98 refs.

Reduced glomerular size selectivity in late streptozotocin-induced diabetes in rats: application of a distributed two-pore model.

Microalbuminuria is an early manifestation of diabetic nephropathy. Potential contributors to this condition are reduced glomerular filtration barrier (GFB) size- and charge selectivity, and impaired tubular reabsorption of filtered proteins. However, it was recently reported that no significant alterations in charge selectivity of the GFB occur in early experimental diabetic nephropathy. We here aimed at investigating the functional changes in the GFB in long-term type-1 diabetes in rats, applying a novel distributed two-pore model. We examined glomerular permeability in 15 male Wistar rats with at least 3 months of streptozotocin (STZ)-induced diabetes (blood glucose ∼20 mmol/L) and in age-matched control rats. The changes in glomerular permeability were assessed by determining the glomerular sieving coefficients (θ) for FITC-Ficoll (molecular radius 20–90 Å) using size exclusion HPLC. The values of θ for FITC-Ficoll of radius >50 Å were significantly increased in STZ-diabetic rats compared to age-matched controls (θ for 50–69 Å = 0.001 vs. 0.0002, and θ for 70–90 Å = 0.0007 vs. 0.00006, P < 0.001), while θ for FITC-Ficoll <50 Å tended to be lower in diabetic rats than in controls (θ for 36–49 Å = 0.013 vs. 0.016, ns). According to the distributed two-pore model, there was primarily an increase in macromolecular transport through large pores in the glomerular filter of diabetic rats associated with a loss of small-pore area. Deterioration in the glomerular size selectivity due to an increase in the number and size-spread of large pores, with no changes in the permeability of the small-pore system, represent the major functional changes observed after 3 months of induced experimental diabetes.

Crosstalk in glomerular injury and repair.

The glomerulus is a unique structure required for filtration of blood, while retaining plasma proteins based on size and charge selectivity. Distinct cell types form the structural unit that creates the filtration barrier. Structurally, fenestrated endothelial cells line the capillary loops and lie in close contact with mesangial cells. Podocytes are connected by specialized intercellular junctions known as slit diaphragms and separated from the endothelial compartment by the glomerular basement membrane. In order for this highly specialized structure to function, cross-communication between these cells must occur. Although classical studies have established key roles for vascular endothelial and platelet-derived growth factors in glomerular cross-communication, novel paracrine signaling pathways within the glomerulus have recently been identified. In addition, unique cellular pathways of established signaling cascades have been identified that are important for maintaining glomerular barrier function in health and disease. Here, we will review our current understanding of the processes of cross-communication between the unique cellular constituents forming the glomerular filtration unit. We will highlight recent findings of cellular crosstalk via signaling pathways that regulate glomerular barrier function in pathophysiological conditions.

Meaningful and Effective? Considering Victims’ Interests Through Participation at the International Criminal Court

This article explores the role of victims in the criminal proceedings of the International Criminal Court and the extent to which their interests have impacted upon the ICC judges’ decision making in light of human rights law and victimological theorisation. The article begins by first outlining how victims’ interests can be considered in international criminal proceedings, before contrasting this role with the purpose of international criminal justice. The second part of the article examines victim participation within the ICC and how this has affected judicial decision making to assess its effectiveness. The contest between the rights of victims and the role of Prosecutor in determining the selection of charges and perpetrators is also examined in an effort to add to the current debate on victim participation at the ICC. The author finds that at the ICC, despite innovative victim provisions, victims’ interests have little impact on outcomes of the Court. The author argues that in order to ensure the Court is more responsive to victims understanding of justice it should give greater weight to their interests, which in turn is likely to improve their satisfaction with the ICC, as well as public confidence and legitimacy of the work of the Court.

Equilibrium electroconvective instability.

Since its prediction 15 years ago, hydrodynamic instability in concentration polarization at a charge-selective interface has been attributed to nonequilibrium electro-osmosis related to the extended space charge which develops at the limiting current. This attribution had a double basis. On the one hand, it has been recognized that neither equilibrium electro-osmosis nor bulk electroconvection can yield instability for a perfectly charge-selective solid. On the other hand, it has been shown that nonequilibrium electro-osmosis can. The first theoretical studies in which electro-osmotic instability was predicted and analyzed employed the assumption of perfect charge selectivity for the sake of simplicity and so did the subsequent studies of various time-dependent and nonlinear features of electro-osmotic instability. In this Letter, we show that relaxing the assumption of perfect charge selectivity (tantamount to fixing the electrochemical potential of counterions in the solid) allows for the equilibrium electroconvective instability. In addition, we suggest a simple experimental test for determining the true, either equilibrium or nonequilibrium, origin of instability in concentration polarization.

Service charge and capacity selection of an inland river port with location-dependent shipping cost and service congestion

The inland waterway transportation has attracted a lot of attention worldwide in the last fifteen years. This paper studies the location, service charge and capacity decision of an inland river port to maximize its revenue or profit. The cargo shippers are assumed to be uniformly distributed along the inland river and can be shipped to the junction port via pure road transportation service or transshipment service with the inland river port. The natural heterogeneity of the river’ navigational condition is modeled by a location-dependent waterway transportation cost and the service congestion on the port is captured by the M/M/1 queueing model. We analytically investigate the properties of the optimal solutions for various decision problems associated with the inland river port. The effects of the natural heterogeneity and port service congestion of those optimal solutions are investigated. Those theoretical results are carefully examined in the case study of the Yangtze River.

Free Energy Simulations of Ion Translocation through Voltage-Gated Proton Channel Hv1

The human voltage-gated proton channel (hHV1) is a transmembrane protein that is responsible for the selective permeation of protons across cell membranes in nasal mucosa, sperm, and white blood cells. hHV1 is a four-helix bundle (S1-S4) with anionic Asp112 on S1 forming a salt bridge with cationic Arg residues on helix S4 in the narrow region of the pore [Kulleperuma et al., J. Gen. Physiol. 141, 445-465 (2013)]. Mutation of Asp112 to Val abrogates channel properties. Unexpectedly, replacing Asp112 by a smaller neutral residue such as Ser turns HV1 into an anion selective channel that conducts Cl-, as does the double mutant D112V-V116S [Musset et al., Nature 480, 273-277 (2012); Morgan et al., J. Gen. Physiol. 142, 625-640 (2013)]. Although HV1 and its mutants exhibit drastic differences in ion permeation, the molecular basis of proton selectivity in WT and anion selectivity in mutants remains unexplained.As the first step towards elucidating the charge selectivity of HV1, we perform molecular dynamics simulations with umbrella sampling to compute the free energy profile for the translocation of Na+ and Cl- ions through the pore of a homology model of HV1 and its mutants. The calculations are repeated in conformational states of the channel differing in the extent of hydration of the pore and in the relative arrangements of pore residues. Results show how ion solvation and electrostatic interactions with charged side chains in the pore lumen modulate the energetics of ion permeation in HV1 and suggest a structural basis for charge selectivity.