Small Net Charge Research Articles

Device modeling of oxide–semiconductor channel antiferroelectric FETs using half-loop hysteresis for memory operation

In this work, the memory characteristics of oxide–semiconductor (OS) channel antiferroelectric FETs (AFeFETs) are investigated by developing a compact model of AFeFETs. The model consists of an analytic junctionless FeFET model and a newly developed AFe Preisach model. The AFe Preisach model can reproduce arbitrary minor loop measurement results. The key feature of AFeFETs is using the half-loop hysteresis of AFe in contrast to the full hysteresis of Fe. Only a small net charge is required and minority carrier generation is not necessary for erase operation, which is preferable for a typical OS channel. Based on the developed model, we systematically vary the device parameters of the OS channel and AFe gate insulator, analyze the memory window using operation point analysis, and show the potential of OS channel AFeFETs for memory applications.

Influence of the span 80/Gelatin B combination on the formulation and stabilization of Argan oil-in-water emulsions

The present study aims to evaluate the effect of the combination of a linear protein: Gelatin type B and an oil-soluble emulsifier Span 80 (sorbitan monooleate) in the stabilization of argan oil-in-water emulsions. For this purpose, the emulsifiying properties of Gelatin itself with Argan oil as lipid phase were investigated first, by preparing oil-in-water (O/W) emulsions containing 10 wt%. Argan oil and varying Gelatin concentrations (0.5-2 % w/w), we have also formulated Argan O/W emulsions by span 80 alone at levels ranging from 1 to 6 wt%. Subsequentely, we explored the influence of the simultaneous application of the Span 80 and the gelatine on the stability properties and on the droplets size of Argan O/W emulsions, using different mixtures of the two emulsifiers. We compared the stability properties (flocculation, creaming, and phase separation) of argan O/W emulsions prepared with type B gelatine as the only emulsifier with those of emulsions prepared with span 80 and mixture of gelatin/Span. For stable emulsions, our analysis was completed with measurement of droplets size and Zeta Potential. Finally, all of the experimental results and the storage time showed that the emulsions prepared by 10 wt% argan oil and 2 (w/w) % Gelatin+ 3 wt% Span 80 were the most stable with optimum conditions for minimal creaming, small droplets size (size <1µm) and high net droplet charge (absolute value of ZP > 23). The presence of span 80 in coexistence with gelatin, even in small quantitiees, has a profound influence on the stability of the argan O/W emulsions.

Combinational effects of acid and salt addition on colloidal, interfacial, and emulsifying properties of purified soybean oil bodies

Soybean oil-storing organelles called oil bodies/oleosomes (OBs) are a potential eco-friendly plant-based emulsifier, whereas combinational effects of acid and salt addition on emulsifying properties of OBs were still unclear. This study aimed at investigating colloidal, interfacial, and emulsifying properties of OBs in the presence of acetic acid and NaCl. The purified OBs isolated from soybean seeds were dispersed into 10 mM acetate or phosphate buffer solutions at pH 4.0–7.0 with different NaCl concentrations between 0 and 100 mM. Without added NaCl, the purified OBs were finely dispersed at pH 4.0 and 4.5 by electrostatic repulsion, whereas they aggregated at pH 5.0 and 5.5 probably due to small net charge. The NaCl addition caused screening of the electrostatic interaction between OBs and induced salting-in of OBs. Interfacial tension and interfacial viscoelasticity analyses showed that strongly-charged OBs tended to more slowly sparsely adsorb onto oil-water interface to form less elastic adsorbed layer; this tendency might result from electrostatic adsorption energy barrier between the adsorbed- and non-adsorbed OBs. The OB-stabilized emulsions slightly coalesced under at pH 4.0 and 4.5 without added NaCl probably due to a relatively small amount of the surface protein load. Under all the other tested pH (4.0–7.0) and NaCl (0–100 mM) conditions, the OB-stabilized emulsions were stable against coalescence because of the improved surface load. These results suggest that OBs can be widely applicable for various food emulsions as a potential eco-friendly emulsifier with the appropriate formulation of acid and salt.

Dynamics of optical excitations in a Fe/MgO(001) heterostructure from time-dependent density functional theory

In the framework of real-time time-dependent density functional theory (RT-TDDFT) we unravel the layer-resolved dynamics of the electronic structure of a (Fe)$_1$/(MgO)$_3$(001) multilayer system after an optical excitation with a frequency below the band gap of bulk MgO. Substantial transient changes to the electronic structure, which persist after the duration of the pulse, are mainly observed for in-plane polarized electric fields, corresponding to a laser pulse arriving perpendicular to the interface. While the strongest charge redistribution takes place in the Fe layer, a time-dependent change in the occupation numbers is visible in all layers, mediated by the presence of interface states. The time evolution of the layer-resolved time-dependent occupation numbers indicates a strong orbital dependence with the depletion from in-plane orbitals (e. g., $d_{x^2-y^2}$ of Fe) and accumulation in out-of-plane orbitals ($d_{3z^2-r^2}$ of Fe and $p_z$ of apical oxygen). We also observe a small net charge transfer away from oxygen towards the Mg sites even for MgO layers which are not directly in contact with the metallic Fe.

Ligand Effect on Bonding in Gold(III) Carbonyl Complexes.

We quantitatively assess the Dewar-Chatt-Duncanson (DCD) components of the Au(III)-CO bond and the charge density polarization at the CO, in a series of neutral, cationic, and dicationic bis- and monocyclometalated gold(III) complexes via charge-displacement (CD) analysis. A striking feature concerns the very small net electron charge flux from CO to the metal fragment which is unexpectedly stable toward both the charge of the complex and the oxidation state of gold (I, III). All systems exhibit a similar trend for the σ charge rearrangement in the region of the carbonyl bond, where, by contrast, the π back-donation trend variation is large, which is strictly correlated to the change in CO bond distance and the shift in CO stretching frequencies, in close analogy with the gold(I) carbonyl complexes. In the whole series of gold(III) compounds, a large Au(III) ← CO σ donation is measured (from 0.19 to 0.31 electrons), as well as a significant Au(III) → CO π back-donation (from -0.09 to -0.22 electrons), which however is not generally able to completely balance the polarization of the CO π electrons in the direction from oxygen to carbon (C ← O) induced by the presence of the metal fragment [LAu(III)]0/+1/+2. Surprisingly, all the gold(III) complexes in the series are characterized by a very small anisotropy in the Au(III) → CO in-plane and out-of-plane π back-donation components, in sharp contrast with the marked anisotropy found before for the experimentally characterized [(C^N^C)Au(III)CO]+ complex. A first attempt to figure out a rationale on the bonding/reactivity relationship for Au(III)-CO is made by performing a comparative study with an isostructural [(N^N^C)Pt(II)CO]+ complex in a model water-gas shift (WGS) reaction.

Label-Free and Highly Sensitive Detection of Buckwheat 16kD Allergenic Protein with Field Effect Transistor (FET) Sensor and Immunochromatography Strip

A field effect transistor (FET) sensor detects the change in charge generated by binding of a specific target molecule to the sensor. This simple mechanism allows label-free rapid detection. However, the sensitivity of detection depends on the net charge of the targeted molecule. Buckwheat 2S albumin (BWp16), which is one of the major allergens of buckwheat, constitutes an analyte of buckwheat in food, but its small net charge limits its sensitivity to a FET sensor. We show here that pretreatment of BWp16 with sodium dodecyl sulfate (SDS) increases the net charge of this analyte and increases sensitivity to 1 ng/ml of BWp16 using a FET sensor. Our results suggest a FET sensor is applicable to food safety management. We also developed an immunochromatography assay strip for convenient and rapid detection of BWp16 to a lower limit of 5 ng/ml. Food Allergen Labeling Regulations in Japan require mandatory labeling of seven allergens in foods at 10 µg/g or more, including buckwheat proteins. Allergenic contamination of food is usually monitored using enzyme-linked-immunosorbent-assay (ELISA), which requires multiple handling steps, an enzyme-labeled secondary antibody, and optical equipment for quantification. In contrast, a FET sensor and an immunochromatography assay strip are potential assay tools without those drawbacks due to their direct sensing mechanism. In this study, we propose a FET sensor and an immunochromatography assay strip be devised for detection of buckwheat protein. Here we attempt to improve the sensitivity of a FET sensor for buckwheat protein BWp16 by increasing the net charge of its molecules. BWp16 was determined specifically using a FET sensor. The response of the FET sensor was improved markedly by pretreatment of recombinant BWp16 (rBWp16) with SDS. The response of the FET sensor was correlated positively with the concentration of rBWp16 down to a detection limit below1 ng/ml. The charge number of BWp16 calculated from its molecular weight (15,106 Da) and isoelectric point (pH 5.25) was small (−3.67/molecule) at the sensing condition of pH 7.4 used with the FET sensor. After the pretreatment with SDS, BWp16 was covered with enough negative charge to increase sensitivity to approximately 10 ng of buckwheat proteins/g of food material. We devised an immunochromatography assay strip and tested the strip on 40 food samples. The assay strip gave a lower limit of detection below 5ng/ml of BWp16. SDS pretreatment of BWp16 protein from buckwheat increased its sensitivity to detection with a FET sensor nearly 1000-fold. This simple charge-amplification technique can increase the sensitivity of a FET sensor to a targeted protein that would ordinarily carry a small net charge. Both a FET sensor and an immunochromatography assay strip achieved highly sensitive and specific detection of buckwheat protein.

Electrophoresis of Janus particles: A molecular dynamics simulation study

In this work, we use molecular dynamics and lattice-Boltzmann simulations to study the properties of charged Janus particles in an electric field. We show that for a relatively small net charge and a thick electrostatic diffuse layer, mobilities of Janus particles and uniformly charged colloids of the same net charge are identical. However, for higher charges and thinner diffuse layers, the Janus particles always show lower electrophoretic mobility. We also demonstrate that the Janus particles align with the electric field and the angular deviation from the field's direction is related to their dipole moment. We show that the latter is affected by the thickness of electrostatic diffuse layer and strongly correlates with the electrophoretic mobility.

Electrostatic Repulsion Governs TDP-43 C-terminal Domain Aggregation.

Electrostatic Repulsion Governs TDP-43 C-terminal Domain Aggregation.

Charge on luminous bodies resembling natural ball lightning produced via electrical arcs through lump silicon.

A phenomenon resembling natural ball lightning can be produced via electrical arcing through silicon. We use lump silicon instead of silicon wafers to achieve higher production rates and larger, longer-lived luminous balls than previously reported. The luminous balls consist of a silicon core surrounded by a porous network of loosely bound silicon dioxide nanoparticles. We find that the balls carry a small net charge on the order of 10(-12) C and propose that the nanoparticles are electrostatically bound to the core due to this charge.

Weak self-interactions of globular proteins studied by small-angle X-ray scattering and structure-based modeling.

We investigate protein-protein interactions in solution by small-angle X-ray scattering (SAXS) and theoretical modeling. The structure factor for solutions of bovine pancreatic trypsin inhibitor (BPTI), myoglobin (Mb), and intestinal fatty acid-binding protein (IFABP) is determined from SAXS measurements at multiple concentrations, from Monte Carlo simulations with a coarse-grained structure-based interaction model, and from analytic approximate solutions of two idealized colloidal interaction models without adjustable parameters. By combining these approaches, we find that the structure factor is essentially determined by hard-core and screened electrostatic interactions. Other soft short-ranged interactions (van der Waals and solvation-related) are either individually insignificant or tend to cancel out. The structure factor is also not significantly affected by charge fluctuations. For Mb and IFABP, with a small net charge and relatively symmetric charge distribution, the structure factor is well described by a hard-sphere model. For BPTI, with a larger net charge, screened electrostatic repulsion is also important, but the asymmetry of the charge distribution reduces the repulsion from that predicted by a charged hard-sphere model with the same net charge. Such charge asymmetry may also amplify the effect of shape asymmetry on the protein-protein potential of mean force.

Effects of the translational and rotational degrees of freedom on the hydration of simple solutes.

Molecular dynamics simulations with separate thermostats for rotational and translational motion were used to study the effect of these degrees of freedom on the structure of water around model solutes. To describe water molecules we used the SPC/E model. The simplest solute studied here, the hydrophobe, was represented as a Lennard-Jones particle. Since direct interaction between the hydrophobe and water molecules has no angular dependence the influence of the increase of the rotational temperature on the solvation of a hydrophobe is only indirect. In the next step the central solute was assumed to be charged with either a positive or a negative charge to mimic an ion in water. Hence, depending on the charge of the ion, the neighboring water molecules assumed different angular distributions. The principal conclusions of this work are: (i) an increase of the translational temperature always decreases the height of the first peak in the solute-water radial distribution function; (ii) an increase of the rotational temperature yields an increase in the first peak in the solute-water radial distribution function for hydrophobes and cations; (iii) in contrast to this, the solvation peak decreases around ions with sufficiently large negative charge; and (iv) an increase of the rotational temperature affects cations in an opposite way to anions. For this reason complex molecules with a small net charge may not be very sensitive to variation of the rotational temperature.

The Influence of Charge Distribution on Self-Association and Viscosity Behavior of Monoclonal Antibody Solutions

The present work investigates the influence of electrostatic surface potential distribution of monoclonal antibodies (MAbs) on intermolecular interactions and viscosity. Electrostatic models suggest MAb-1 has a less uniform surface charge distribution than MAb-2. The patches of positive and negative potential on MAb-1 are predicted to favor intermolecular attraction, even in the presence of a small net positive charge. Consistent with this expectation, MAb-1 exhibits a negative second virial coefficient (B₂₂), an increase in static structure factor, S((q→0)), and a decrease in hydrodynamic interaction parameter, H((q→0)), with increase in MAb-1 concentration. Conversely, MAb-2 did not show such heterogeneous charge distribution as MAb-1 and hence favors intermolecular repulsion (positive B₂₂), lower static structure factor, S((q→0)), and repulsion induced increase in momentum transfer, H((q→0)), to result in lower viscosity of MAb-2. Charge swap mutants of MAb-1, M-5 and M-7, showed a decrease in charge asymmetry and concomitantly a loss in self-associating behavior and lower viscosity than MAb-1. However, replacement of charge residues in the sequence of MAb-2, M-10, did not invoke charge distribution to the same extent as MAb-1 and hence exhibited a similar viscosity and self-association profile as MAb-2.

Charge Transfer between Water Molecules As the Possible Origin of the Observed Charging at the Surface of Pure Water

Classical molecular dynamics simulations point to an anisotropy of water–water hydrogen bonding at the water surface. Approaching from the gas phase, a region of primarily dangling hydrogens is followed by dangling oxygens before the isotropic bulk region. Using ab initio calculations, we translate this hydrogen bonding anisotropy to charge transfer between water molecules, which we analyze with respect to both instantaneous and averaged positions of the water surface. Similarly to the oil/water interface, we show that there is a region of small net negative charge extending 0.2 to 0.6 nm from the Gibbs dividing surface in the aqueous phase. Using a simple continuum model, we translate this charge profile to a zeta potential, which acquires for realistic positions of the shear surface the same negative sign as that observed experimentally, albeit of a smaller absolute value.

Graphene and graphene nanoribbons on InAs(110) and Au/InAs(110) surfaces: Anab initiostudy

We have performed an ab initio investigation of graphene adsorption on clean and Au-covered InAs(110) surfaces. Total energy results reveal that the graphene sheet is weakly attached to such surfaces, with adsorption energy of approximately 25 meV/(C atom). Graphene nanoribbons, on the other hand, are more strongly adsorbed, with adsorption energy of approximately 45 meV/(C atom). Based upon our electronic band structure calculations, we find that there are small net charge transfers between the graphene sheet or ribbon and the clean or Au-covered InAs(110) surface. There is an electronic charge displacement in the graphene-surface interface region, giving rise to an electric dipole moment along the surface normal. Scanning tunneling microscopy simulations lend support to the recently proposed ``transparency'' effect of the graphene sheet adsorbed on the clean InAs(110) surface [He et al., Nano Lett. 10, 3446 (2010)] and suggest that the effect is maintained for adsorption on the metallic Au/InAs(110) surface.

Fc domain mediated self-association of an IgG1 monoclonal antibody under a low ionic strength condition

Recently, we reported that IgG1 monoclonal antibody A (MAb A) underwent liquid-liquid phase separation and separated into light and heavy phases under a low ionic strength condition. The liquid-liquid phase separation was induced due to self-association of MAb A in the heavy phase when the initial concentration of MAb A was between the two critical concentrations [Nishi et al., Pharm. Res., 27, 1348-1360 (2010)]. Here, we determined the interaction site of MAb A by using proteolytic Fab and Fc fragments of MAb A. The mean hydrodynamic diameter of the Fc fragment increased in a low ionic strength buffer, and furthermore the SPR measurement detected interactions of the Fc fragment with both whole MAb A and the Fc fragment, whereas the Fab fragment interacted with neither whole MAb A nor the Fc fragment. No binding was detected under an isotonic ionic strength condition. Zeta potential of MAb A was significant positive below pH 5.5 and negative above pH 6.5. Between pH 5.5 and 6.5 where the phase separation is significantly induced, MAb A had only a small positive or negative net charge. The isothermal titration calorimetry dilution method revealed that dissociation of MAb A accompanied endothermic heat changes, suggesting that intermolecular interactions among MAb A molecules were attributed to the enthalpically driven process. These results suggest that liquid-liquid phase separation of MAb A is mediated by a weak electrostatic intermolecular interaction among MAb A molecules mainly at Fc portions.

Off-equatorial orbits in strong gravitational fields near compact objects—II: halo motion around magnetic compact stars and magnetized black holes

Off-equatorial circular orbits with constant latitudes (halo orbits) of electrically charged particles exist near compact objects. In the previous paper, we discussed this kind of motion and demonstrated the existence of minima of the two-dimensional effective potential which correspond to the stable halo orbits. Here, we relax previous assumptions of the pseudo-Newtonian approach for the gravitational field of the central body and study properties of the halo orbits in detail. Within the general relativistic approach, we carry out our calculations in two cases. Firstly, we examine the case of a rotating magnetic compact star. Assuming that the magnetic field axis and the rotation axis are aligned with each other, we study the orientation of motion along the stable halo orbits. In the poloidal plane, we also discuss shapes of the related effective potential halo lobes where the general off-equatorial motion can be bound. Then we focus on the halo orbits near a Kerr black hole immersed in an asymptotically uniform magnetic field of external origin. We demonstrate that, in both the cases considered, the lobes exhibit two different regimes, namely one where completely disjoint lobes occur symmetrically above and below the equatorial plane, and another where the lobes are joined across the plane. A possible application of the model concerns the structure of putative circumpulsar discs consisting of dust particles. We suggest that the particles can acquire a small (but non-zero) net electric charge, and this drives them to form the halo lobes.

Air ion concentrations in various urban outdoor environments

Atmospheric ions are produced by many natural and anthropogenic sources and their concentrations vary widely between different environments. There is very little information on their concentrations in different types of urban environments, how they compare across these environments and their dominant sources. In this study, we measured airborne concentrations of small ions, particles and net particle charge at 32 different outdoor sites in and around a major city in Australia and identified the main ion sources. Sites were classified into seven groups as follows: park, woodland, city centre, residential, freeway, power lines and power substation. Generally, parks were situated away from ion sources and represented the urban background value of about 270 ions cm −3. Median concentrations at all other groups were significantly higher than in the parks. We show that motor vehicles and power transmission systems are two major ion sources in urban areas. Power lines and substations constituted strong unipolar sources, while motor vehicle exhaust constituted strong bipolar sources. The small ion concentration in urban residential areas was about 960 cm −3. At sites where ion sources were co-located with particle sources, ion concentrations were inhibited due to the ion-particle attachment process. These results improved our understanding on air ion distribution and its interaction with particles in the urban outdoor environment.

Structural characterization of nitro-substituted phenoxyiminato nickel complexes; inter-molecular π–π interactions in the solid states and effect of the electron drawing groups on catalytic activity

Three phenoxyiminato nickel complexes [(L)Ni(PPh 3)(Ph)] have been prepared by the introduction of the electron drawing nitro substitutes on ortho or para-position of phenoxy and characterized by X-ray crystallography. Experimental and theory calculation suggested that the ortho and para nitro groups may be equally responsible for the small net charge on the central metal atoms because the interplanar angles between o-nitro planes and aromatic rings (28.7–37.3°) are much higher than those between p-nitro planes and aromatic rings (8.2–13.8°). In the solid states of these nickel complexes there exist the short inter-molecular π–π stacking interactions with the distances of 3.5828 Å ( ortho-nitro), 3.5844 Å ( para-nitro), and 3.0929 Å ( ortho- and para-nitro) between two neighboring nitro-phenyl moieties.

Selective Degradation of Proteins by Laser Irradiation onto Gold Nanoparticles in Solution

Lysozyme and bovine serum albumin (BSA) were selectively degraded in their mixed solution containing gold nanoparticles by an appropriate pH selection of the solution under irradiation of a laser with 532 nm corresponding to the plasma oscillation of the nanoparticles. Lysozyme and BSA were selectively degraded at a pH of 7.0–11.0 and ∼4.0, respectively. The mechanism of the selective degradation is as follows: Lysozyme molecules are considered to aggregate selectively on the gold nanoparticle in a pH range of 7.0–11.0, because they have a sufficiently small net charge of an opposite sign to the ζ-potential of the gold nanoparticle. In this pH range, the lysozyme molecules aggregating on the gold nanoparticle are degraded selectively under the laser irradiation, because the gold nanoparticle creates a high temperature region (chemical species in this region is suffered from degradation) in its close vicinity by the laser irradiation as shown in our previous studies. The same discussion is true to the selective degradation of BSA at a pH of ∼4.0.

Trans-Channel Interactions in Batrachotoxin-Modified Skeletal Muscle Sodium Channels: Voltage-Dependent Block by Cytoplasmic Amines, and the Influence of μ-Conotoxin GIIIA Derivatives and Permeant Ions

External μ-conotoxins and internal amine blockers inhibit each other's block of voltage-gated sodium channels. We explore the basis of this interaction by measuring the shifts in voltage-dependence of channel inhibition by internal amines induced by two μ-conotoxin derivatives with different charge distributions and net charges. Charge changes on the toxin were made at residue 13, which is thought to penetrate most deeply into the channel, making it likely to have the strongest individual interaction with an internal charged ligand. When an R13Q or R13E molecule was bound to the channel, the voltage dependence of diethylammonium (DEA)-block shifted toward more depolarized potentials (23 mV for R13Q, and 16 mV for R13E). An electrostatic model of the repulsion between DEA and the toxin simulated these data, with a distance between residue 13 of the μ-conotoxin and the DEA-binding site of ∼15 Å. Surprisingly, for tetrapropylammonium, the shifts were only 9 mV for R13Q, and 7 mV for R13E. The smaller shifts associated with R13E, the toxin with a smaller net charge, are generally consistent with an electrostatic interaction. However, the smaller shifts observed for tetrapropylammonium than for DEA suggest that other factors must be involved. Two observations indicate that the coupling of permeant ion occupancy of the channel to blocker binding may contribute to the overall amine-toxin interaction: 1), R13Q binding decreases the apparent affinity of sodium for the conducting pore by ∼4-fold; and 2), increasing external [Na +] decreases block by DEA at constant voltage. Thus, even though a number of studies suggest that sodium channels are occupied by no more than one ion most of the time, measurable coupling occurs between permeant ions and toxin or amine blockers. Such interactions likely determine, in part, the strength of trans-channel, amine-conotoxin interactions.