Electrostatic Interaction Forces Research Articles

Electrical double layer interactions between soil colloidal particles: Polarization of water molecule and counterion

The electrical double layer (EDL) interactions strongly affect aggregation and dispersion of soil colloidal particles. In this research a modified model taking the polarization of water molecule and counterion into account was proposed based on nonlinear Poisson-Boltzmann theory to describe electrostatic interaction. The polarizations of both the counterion and the water molecule can increase the interaction between ion/water and soil particle surface, and then decrease the surface potential. Particle surface potential also depends on the surface separation when the EDL overlaps. The midpoint potential between colloidal particles decreases with increase of ion polarization but increases in the presence of water polarization through the change of the double layer thickness. Both the electrostatic repulsive pressure between soil particles and its force range increase markedly in the presence of the polarization of water molecules, but decrease with increase of counterion polarization. The water molecule polarization, rather than the counterion polarization, contributes more to EDL interactions. The counterion polarization is the origin of Hofmeister effects of the EDL interactions, which is affected by water polarization. The theoretical predicted force curve between clay particles by the modified model was verified by the experimental determination of surface force. In addition, the hydration force, fitted to a double exponential decay function, can be estimated by subtraction of the electrostatic interaction force based on DLVO theory from that based on the present model.

Effective removal of organic pollutants by adsorption onto chitosan supported graphene oxide-hydroxyapatite composite: A novel reusable adsorbent

A hetero-structured adsorbent with outstanding adsorption performance has acquired an increased attention due to their excellent behaviour in environmental applications. Tailoring of graphene oxide and hydroxyapatite with suitable biopolymeric adsorbents would enhance the porosity, stability, specific surface area and shows high sorption performance. Herein, chitosan reinforced graphene oxide-hydroxyapatite (CS@GO-Hap) matrix was fabricated efficiently in the atmosphere of nitrogen by co-precipitation technique. Here, chitosan acted as a host in the preparation and provided the surface for a composite generation. The batch mode method was applied to investigate the adsorption performance of CS@GO-Hap composite, showed an adsorption efficiency of 43.06, 41.32 and 40.03 mg/g for the removal of the toxic Congo Red (CR), Acid Red 1 (AR1) and Reactive Red 2 (RR2) dyes from water, respectively. The composite showed enhanced adsorption at the pH of 2 and the removal efficiency of CS@GO-Hap composite decreased with increase in pH. The adsorption kinetic and isotherm fitted well with pseudo-second-order and the Freundlich model, respectively. The thermodynamic study of the adsorption of dyes showed that the process was spontaneous. The regeneration experiments emphasized that the desorption was ideal, and exhibited more than 65% regeneration ability with 0.1 M NaOH solution. The mechanism of dyes adsorption on CS@GO-Hap composite involved the electrostatic force interaction, surface complexation, hydrogen bondings and π−π stacking interactions. The findings of the study revealed the exceptional behaviour of CS@GO-Hap composite in removing the azo dyes from aqueous solutions and the great significance of the composite in the future application in water/wastewater treatment process.

Combined toxicity of microplastics and cadmium on the zebrafish embryos (Danio rerio)

The effects of microplastics (MPs) on organisms have drawn a worldwide attention in the recent years. In this study, zebrafish embryos were employed to assess the combined effects of MPs and cadmium (Cd) on the aquatic organisms. Lethal and sublethal effects were recorded at 8, 24, 32, 48 and 96 hpe (hour post exposure, hpe). The exposure under a series concentration of MPs and/or an environmental level Cd has the negative impacts on survival and heart rate (HR). And there was a positive correlation between MPs concentration and lethal and sublethal toxicity under combined exposure. The physiological parameters showed that the mixture of two stressors had the antagonistic toxicity under low concentration of MPs (0.05, 0.1 mg/L) while the synergistic sublethal toxicity under high levels of MPs (1, 5, 10 mg/L) on zebrafish embryos. Both the scanning electron micrographs (SEM) and fluorescence microscope photos suggested an electrostatic interaction and weak physical forces generated between MPs and chorion membrane. It is inferred that the 10 μm MPs could induce the protective effect of chorion membrane and cause complex toxicities with Cd. But when it involved with other pollutants, the toxic effects and mechanism are still waiting to be figured out.

Chromium-based metal-organic framework embedded with cobalt phthalocyanine for the sensitively impedimetric cytosensing of colorectal cancer (CT26) cells and cell imaging

In this study, we have prepared the series of nanohybrids of Cr-based metal-organic framework (Cr-MOF) and cobalt phthalocyanine (CoPc) nanoparticles (denoted as Cr-MOF@CoPc) and investigated them as novel platforms of electrochemical cytosensors for determining colorectal cancer (CT26) cells. The developed Cr-MOF@CoPc nanohybrids were composed of irregularly small nanoparticles, mixed metal valence states of Cr2+/Cr3+/Cr5+ and Co2+/Co3+, rich functional groups of C–O and COO and strong fluorescence performance, as well as high specific area and large pore volume. These intrinsic features of Cr-MOF@CoPc nanohybrids endowed them with strong immobilization ability toward aptamer strands via π- π* stacking, electrostatic interaction, and van der Waals force, excellent electrochemical property, strong fluorescence intensity, and good biocompatibility. Compared with cytosensors based on the sole metal MOFs (Cr-MOF and CoPc) and other reported bulk MOF-based sensors, the constructed Cr-MOF@CoPc-based cytosensor exhibited low detection limit toward CT26 cells, for which the sensing performance was modulated by changing the dosage of CoPc nanoparticles. Electrochemical impedance spectroscopy and differential pulse voltammetry results showed extremely low detection limits of 36 and 8 cells mL−1, respectively, within the concentration range of the CT26 cell suspension (50–1 × 107 cells mL−1), along with high selectivity, excellent stability, and acceptable reproducibility. Thus, the prepared cytosensor can be extensively applied for the analysis of other kinds of cancer cells when anchored their corresponding aptamer strands, providing great potential applications in the biosensor and biomedical fields.

Electrostatic Interaction of Two Conducting Spheroids

Finite-element method is used to calculate the force of electrostatic interaction of two conducting spheroidal objects with specified surface charges in the absence of external field.

MotP Subunit is Critical for Ion Selectivity and Evolution of a K+-Coupled Flagellar Motor.

The bacterial flagellar motor is a sophisticated nanomachine embedded in the cell envelope. The flagellar motor is driven by an electrochemical gradient of cations such as H+, Na+, and K+ through ion channels in stator complexes embedded in the cell membrane. The flagellum is believed to rotate as a result of electrostatic interaction forces between the stator and the rotor. In bacteria of the genus Bacillus and related species, the single transmembrane segment of MotB-type subunit protein (MotB and MotS) is critical for the selection of the H+ and Na+ coupling ions. Here, we constructed and characterized several hybrid stators combined with single Na+-coupled and dual Na+- and K+-coupled stator subunits, and we report that the MotP subunit is critical for the selection of K+. This result suggested that the K+ selectivity of the MotP/MotS complexes evolved from the single Na+-coupled stator MotP/MotS complexes. This finding will promote the understanding of the evolution of flagellar motors and the molecular mechanisms of coupling ion selectivity.

Antiproliferative activity and human serum albumin binding propensity of [SnMe2Cl2(bu2bpy)]: multi-spectroscopic analysis, atomic force microscopy, and computational studies

In this study, the multi-spectroscopic methods (UV-vis, fluorometric, circular dichroism), atomic force microscopy (AFM), cyclic voltammetry, molecular docking, and predictor online software (SwissADME-AdmetSAR) were used to investigate the interaction of complex [SnMe2Cl2(bu2bpy)] with human serum albumin (HSA). The calculated binding constant by UV-vis spectroscopy was about 104 M−1. Also, the polarity around the Trp-214 residue and the hydrophobicity were changed. The complex has a strong ability to quench the intrinsic fluorescence of HSA through static quenching procedure. The electrostatic force and hydrophobic interactions are dominant in the binding process based on the results of thermodynamic parameters (ΔH0 < 0 and ΔS0 > 0). The results of competitive binding measurements exhibited that the Sn(IV) complex bound to site II of HSA. Synchronous fluorescence, AFM, circular dichroism spectroscopy and molecular docking simulation results indicated that the binding of Sn(IV) complex to HSA induces the conformational changes of HSA. The in silico ADMET studies reveal that [SnMe2Cl2(bu2bpy)] and its ligand possess great biological potential. The results from cyclic voltammetry experiments also confirm interaction between HSA and Sn(IV) complex. Based on the non-radiative energy transfer theory of Forster, the binding distance between the complex (acceptor) and HSA (donor) was obtained (r = 1.77 nm). Furthermore, there was a good agreement between theoretical (molecular docking method) and experimental results. Finally, elucidation of the mechanism of anticancer activity revealed that Sn(IV) complex possesses potential cytotoxicity against MCF-7 breast cancer cells and is able to induce significant levels of apoptosis at concentrations below IC50 value.

Sorption Behavior and Mechanisms of Organic Contaminants to Nano and Microplastics.

Nano and microplastics (NPs/MPs) have received widespread attention in recent years. Because of their large specific surface area and hydrophobicity, NPs/MPs can adsorb various organic contaminants. This article gives a brief review of the sorption behavior of organic contaminants to NPs/MPs, summarizes the possible sorption mechanisms, and analyzes the influencing factors in the environment on the sorption behavior and mechanisms of NPs/MPs. The main mechanisms of sorption of organic contaminants to NPs/MPs are partitioning, surface sorption (hydrogen bonding, π–π interaction, electrostatic interaction, and van der Waals force), and pore filling. The sorption behavior of organic contaminants to NPs/MPs is not only affected by the properties of the NPs/MPs and the organic contaminants, but also by the solution chemistry, such as the pH, ionic strength, and dissolved organic matter.

A highly sensitive fluorescence sensor based on lucigenin/chitosan/SiO2 composite nanoparticles for microRNA detection using magnetic separation.

In this paper, a convenient reverse-phase microemulsion method for the synthesis of SiO2 nanoparticles (NPs) by simply introducing the chitosan and fluorescent dye of lucigenin during the formation reaction of SiO2 NPs was proposed. Addition of chitosan can make the SiO2 NPs porous, and increases lucigenin molecule incorporation into chitosan/SiO2 NPs nanopores based on electrostatic interaction and supermolecular forces. Therefore, fluorescence quantum yield of the lucigenin/chitosan/SiO2 composite nanoparticles was increased by introduction of chitosan and compared with lucigenin/SiO2 NPs without chitosan. Because the number of negative charges carried when using single-stranded DNA (ssDNA) was different from that of double-stranded DNA (dsDNA), the numbers of lucigenin/chitosan/SiO2 composite nanoparticles with positive charge adsorbed using ssDNA or dsDNA were different. Consequently, fluorescence intensity caused using ssDNA or dsDNA/miRNA was clearly discriminative. With increase in target DNA/miRNA concentration, the difference in fluorescence intensity also increased, resulting in a good linear relationship between fluorescence intensity sensitizing value and target miRNA concentrations. Therefore, a new fluorescence analysis method for direct detection of let-7a in human gastric cancer cell samples without enzyme, label free and no immobilization was established using lucigenin/chitosan/SiO2 composite nanoparticles as a DNA hybrid indicator. The proposed method had high sensitivity and selectivity, low cost and the detection limit was 10 fM (S/N = 3).

Immobilized angiotensin II type I receptor: A powerful method of high throughput screening for antihypertensive compound identification through binding interaction analysis

The enormous growth in drug discovery paradigm has necessitated continuous exploration of new methods for drug-protein interaction analysis. To enhance the role of these methodologies in designing rational drugs, this work extended an immobilized angiotensin II type I receptor (AT1R) based affinity chromatography in antihypertensive compound identification. We fused haloalkane dehalogenase at C-terminus of AT1R and expressed the fusion receptor in E. coli. The expressed receptor was covalently immobilized onto 8.0 μm microspheres by mixing the cell lysate with 6-chlorocaproic acid-modified amino polystyrene microspheres. The immobilized AT1R was utilized for thermodynamic and kinetic interaction analysis between the receptor and four specific ligands. Following confirmation of these interactions by molecular docking, we identified puerarin and rosmarinic acid by determining their binding to the receptor. Azilsartan, candesartan, valsartan and olmesartan displayed two kinds of binding sites to AT1R by injection amount-dependent method. By molecular docking, we recognize the driving forces of the interaction as electrostatic interaction, hydrogen bonds and van der Waals force. The dissociation rate constants (kd) of azilsartan, candesartan, valsartan and olmesartan to AT1R were 0.01138 ± 0.003, 0.05142 ± 0.003, 0.07547 ± 0.004 and 0.01310 ± 0.005 min−1 by peak profiling assay. Comparing with these parameters, puerarin and rosmarinic acid presented lower affinity (KA: 0.12 × 104 and 1.5 × 104/M) and slower kinetics (kd: 0.6864 ± 0.03 and 0.3005 ± 0.01 min−1) to the receptor. These results, taking together, indicated that the immobilized AT1R has the capacity to probe antihypertensive compounds.

Functionalized carbon fibers assembly with Al/Bi2O3: A new strategy for high-reliability ignition

Carbon fiber is used to construct an energy conversion component with the purpose of high reliability, safety and potential application in micro size. The carbon fiber oxidant (CFO) is endowed as the carrier for the assembly of CFO/Al/Bi2O3 while long-range electrostatic force and covalent interactions are analyzed as the main force. The self-assembly can function with a voltage as low as 15.34 V and can detonate RDX successfully without using primary explosives and traditional bridge film unit. The ignition mechanism is deduced that carbon fibers have a transient high conductivity when the voltage is charged. The one-dimensional structure and micro-size make the puncture easily and reliably. Moreover, the integration of Al/Bi2O3 enhanced its initiation power and reliability. The research broadens the understanding of carbon fiber as one-dimensional material, and more applications are expected in this new field by considering the variety of carbon fiber size, different sorts of reactive materials and so on.

Analytical estimates of the pull-in voltage for carbon nanotubes considering tip-charge concentration and intermolecular forces

Two-side accurate analytical estimates of the pull-in parameters of a carbon nanotube switch clamped at one end under electrostatic actuation are provided by considering the proper expressions of the electrostatic force and van der Waals interactions for a carbon nanotube, as well as the contribution of the charge concentration at the free end. According to the Euler–Bernoulli beam theory, the problem is governed by a fourth-order nonlinear boundary value problem. Two-side estimates on the centreline deflection are derived. Then, very accurate lower and upper bounds to the pull-in voltage and deflection are obtained as function of the geometrical and material parameters. The analytical predictions are found to agree remarkably well with the numerical results provided by the shooting method, thus validating the proposed approach. Finally, a simple closed-form relation is proposed for the minimum feasible gap and maximum realizable length for a freestanding CNT cantilever.

Antibacterial activity of polypyrrole-based nanocomposites: a mini-review

Abstract The development of polypyrrole-based nanocomposites as alternative antibacterial agents represents a promising strategy to be applied against the prevailing multi-resistant bacteria. Herein, it is reported the most recent development of antibacterial materials based on the combination of polypyrrole and different fillers (metal nanoparticles, carbon nanotubes, and polysaccharides) and strategies to improve their action (such as light and electrical stimulus). The synergistic interaction of electrostatic forces provided by charged polypyrrole combined with the permeation of nanoparticles through the cell wall favors the leakage of cytoplasmic components and reinforces the antibacterial activity of the resulting material, observed in all-organic composites of polypyrrole and chitosan that reached superior performance against Escherichia coli (108 CFU) or metal-polymer composites (polypyrrole-palladium) with an outstanding performance against different types of bacteria. The development of binary and ternary composites is explored to potentialize the antibacterial synergy of components.

О силе электростатического взаимодействия между двумя проводящими сфероидами

Application of finite element method for calculation of electrostatic interaction force of two conducting bodies of spheroidal shape with preset charges on their surfaces in zero external field is considered.

Development, structure characterization and stability of food grade selenium nanoparticles stabilized by tilapia polypeptides

A novel method was used to prepare selenium nanoparticles (SeNPs) in this paper. SeNPs were prepared by direct reducing the sodium selenite (Na2SeO3) using tilapia polypeptides (TP). Meanwhile, TP acted as a stabilizing agent for the SeNPs. It was found that TP-SeNPs was reduced from Na2SeO3 to element selenium then aggregated to a certain size to form a red SeNPs core, which was encapsulated by the polypeptides. We found that the formation of TP-SeNPs may induce selenium binding at the expense of the anti-parallel structure in the β-sheet structure of protein. The main bonding forces of TP-SeNPs were electrostatic interaction and hydrophobic interaction forces. It was found that the TP-SeNPs solution was relatively stable in neutral and alkaline environment. Under the condition of pH = 8, the TP-SeNPs solution showed better storage stability.

ANALYSIS OF ELECTROSTATIC PROPERTIES OF POLYSTYRENE FOAM FILTRATION MEDIA

The relevance of research. The analysis of the aqueous suspension filtration initial stage through clean polystyrene foam filtration media carried out. Such feature of its work as hydro-sorting is considered. The degree of imbalance and interaction with other electrostatic systems in aqueous suspension determines the layer of potential-forming ions, which is formed around the core of the system. It determines system’s sign and most of the electrical double layer charge. It is usually determined using a physical quantity such as electrostatic or ζ-potential. The aim of this work is to determine the electrostatic properties of polystyrene foam granules and the degree of influence on the process of retaining various nature colloidal particles on their surface when filtering an aqueous suspension through them.&#x0D; Research results. The relationship between the sizes of polystyrene foam granules and the concentrations of electrostatic charge on their surface analyzed. Using the Poison-Boltzmann theory, a relationship between an electrostatic charge and an electric double layer of polystyrene foam granules in aqueous suspension showed. The importance of the ζ-potential researching for controlling of colloidal suspensions filtering process substantiated. The electrostatic properties of different morphology colloids studied. Analysis of research data confirms the hypothesis of a very close connection between the various morphologies colloids ζ-potential magnitude and their electric double layer interaction force with electric double layer of polystyrene foam granules in an aqueous suspension. This means that the polystyrene foam filter “charging” time is closely connected to the values of colloids ζ-potential in the filtered aqueous suspension.&#x0D; Conclusions. The initial filtration stage through clean polystyrene foam media is significantly different from the main stage of filtration due to the electrostatic interaction forces predominance. The time difference of the colloidal crusts complete formation completion on polystyrene foam granules of different diameters is so insignificant that it can be neglected and this time is considered the same for polystyrene foam granules of different diameters. Regardless of the origin nature, the retention intensity of the colloids by polystyrene foam filtration media granules and, consequently, the polystyrene filter “charging” time is directly depends on their z-potential value.&#x0D;

Application of a Cellular Automaton Method to Model the Structure Formation in Soils Under Saturated Conditions: A Mechanistic Approach

Soil functions are closely related to the structure of soil microaggregates. Yet, the mechanisms controlling the establishment of soil structure are diverse and partly unknown. Hence, the understanding of soil processes and functions requires the connection of the concepts on the formation and consolidation of soil structural elements across scales that are hard to observe experimentally. At the bottom level, the dynamics of microaggregate development and restructuring build the basis for transport phenomena at the continuum scale. By modeling the interactions of specific minerals and/or organic matter, we aim to identify the mechanisms that control the evolution of structure and establishment of stationary aggregate properties. We present a mechanistic framework based on a cellular automaton model to simulate the interplay between the prototypic building units of soil microaggregates quartz, goethite, and illite subject to attractive and repulsive electrostatic interaction forces. The resulting structures are quantified by morphological measures. We investigated shielding effects due to charge neutralisation and the aggregate growth rate in response to the net system charge. We found that the fraction as well as the size of the interacting oppositely charged constituents control the size, shape, and amount of occurring aggregates. Furthermore, the concentration in terms of the liquid solid ratio has been shown to increase the aggregation rate. We further adopt the model for an assessment of the temporal evolution of aggregate formation due to successive formation of particle dimers at early stages in comparison to higher order aggregates at later stages. With that we show the effect of composition, charge, size ratio, time and concentration on microaggregate formation by the application of a mechanistic model which also provides predictions for soil aggregation behaviour in case an observation is inhibited by experimental limitations.

Adsorption mechanism of As(III) on polytetrafluoroethylene particles of different size

Microplastics exhibit active environmental behavior and unique surface characteristics, and act as carriers for the migration of trivalent arsenic (As(III)) in the environment. Herein, the mechanism by which polytetrafluoroethylene (PTFE) microplastic particles adsorb As(III) is systematically determined. The larger the size of PTFE particles, the smaller the specific surface area, the higher the point of zero charge (PZC), and the more unfavorable adsorption of As(III); the highest adsorption amount can reach 1.05 mg g−1. The adsorption process can be divided into three stages by the intraparticle diffusion model: external mass transfer, intraparticle diffusion, and dynamic equilibrium, of which the external mass transfer stage is the adsorption rate-limiting stage. The Langmuir isotherm model better represented the equilibrium adsorption results. The adsorption of As(III) by PTFE was an exothermic process, and because the increase in temperature broke the hydrogen bond, the amount of adsorption was decreased, which was not conducive to spontaneous adsorption. In the pH range of 3–7, as the pH value increased, the amount of As(III) adsorbed by PTFE gradually decreased, which may be related to the change in PZC for PTFE and the protonation of As(III). The H on the surface hydroxyl group of the PTFE exhibited a very large positive potential (+82.37 kcal mol−1). Thus, it can attract the arsenic oxyanion, and As(III) was subsequently adsorbed on the surface of the PTFE through the hydrogen bond on the hydroxyl group. Electrostatic force and non-covalent interaction were the key mechanisms affecting the PTFE adsorption.

Modulating Nanoparticle Translocation by Surface Chemistry of Gold Nanopores

Abstract A simple and effective method for modulating nanoparticles (NPs) translocation through nanopore by tuning the surface change of chemically modified gold coated nanopore was developed. The gold-coated pore is simply prepared from a nanopipette and the partially insulated gold coating can be utilized to effectively concentrate NPs near the nanopore entrance. The surface modification of gold near the orifice effectively modulates the NP translocation behavior, mainly through electrostatic force and chemical interactions. This system can be extended to the detection of biological entities, such as virus and exosomes which have similar size of NPs.

Adsorption of low-concentration mercury in water by 3D cyclodextrin/graphene composites: Synergistic effect and enhancement mechanism

The efficient removal of mercury from aqueous media remains a severe challenge in ensuring environmental safety, especially for low-concentration mercury, which requires adsorbents with high mercury affinity. In this work, we reported a nanocomposite of β-cyclodextrin and three-dimensional graphene (3D CD@RGO) to enhance the adsorption affinity and capacity for mercury with low concentrations. Characterization of the nanocomposite revealed that cyclodextrin was well dispersed on the 3D graphene support structure to provide highly exposed hydroxyl groups. Adsorption experiments showed that CD@RGO exhibited different adsorption behaviors for mercury within different concentration ranges of 0.2–4.0 mg/L and 4.0–10.0 mg/L, and the adsorption affinity for the former range (KL = 10.05 L/mg) was 1.5 times higher than that for the latter range (KL = 6.69 L/mg). Moreover, CD@RGO had a high adsorption efficiency of 96.6% with a superb adsorption affinity (172.09 L/g) at Ce = 0.01 mg/L, which is 6.70 and 41.25 times higher than that of RGO and RCD (physical mixture of RGO and cyclodextrin), respectively, indicating a synergistic effect of CD@RGO for mercury adsorption. This enhancement can be attributed to the transformation of the adsorption mechanism from the outer-sphere force of electrostatic interaction in RGO to the inner-sphere surface complexation in CD@RGO.