A coarse‐grained MARTINI‐like force field for DNA unzipping in nanopores

In nanopore force spectroscopy (NFS) a charged polymer is threaded through a channel of molecular dimensions. When an electric field is applied across the insulating membrane, the ionic current through the nanopore reports on polymer translocation, unzipping, dissociation, and so forth. We present a new model that can be applied in molecular dynamics simulations of NFS. Although simplified, it does reproduce experimental trends and all‐atom simulations. The scaled conductivities in bulk solution are consistent with experimental results for NaCl for a wide range of electrolyte concentrations and temperatures. The dependence of the ionic current through a nanopore on the applied voltage is symmetric and, in the voltage range used in experiments (up to 2 V), linear and in good agreement with experimental data. The thermal stability and geometry of DNA is well represented. The model was applied to simulations of DNA hairpin unzipping in nanopores. The results are in good agreement with all‐atom simulations: the scaled translocation times and unzipping sequence are similar. © 2015 Wiley Periodicals, Inc.     

Synthesis and electric field actuation of an ionic liquid polymer

Polymerizable ionic liquids and their actuation in an electric field are a combination of material and properties with unique potential to display structural and fluid dynamics above that found in small molecule ionic liquids. In an effort to blend ionic liquid nature with actuation response, we have synthesized a new ionic liquid ammonium sulfonate monomer and polymer. The liquid temperature ranges of both the monomer and polymer ionic liquid systems are quite large extending from their respective glass transitions (Tg) of -57 and -49 degrees C to decomposition at approximately 200 degrees C. Particularly remarkable is the small Tg increment that accompanies the transformation from monomer to polymer. The electrowetting behavior of the polymer and of the monomer presents an interesting contrast. This communication will encompass the polymerization, characterization, and actuation of these new ionic liquids.     

Swelling Behavior of Semi‐Interpenetrating Polymer Network Hydrogels Based on Chitosan and Poly(acryl amide)

Semi‐interpenetrating polymer networks (semi‐IPNs) composed of chitosan and polyacrylamide (PAAm) hydrogels have been prepared, and the effect of changing pH, temperature, ionic concentration, and applied electric fields on the swelling of the hydrogels was investigated. The swelling kinetics increased rapidly, reaching equilibrium within 60 min. The semi‐IPN hydrogels exhibited a relatively high swelling ratios of 385%–569% at T=25°C. The swelling ratio increased with decreasing pH below pH=7 due to the dissociation of ionic bonds. The swelling ratio of the semi‐IPN hydrogels was pH, ionic concentration, temperature, and electric field dependent. Differential scanning calorimetry (DSC) was used to determine the volume of free water in the semi‐IPN hydrogels, which was found to increase with increasing PAAm content.     

Side‐chain functionalized liquid‐crystalline polymers and blends. IX.* Phase behavior and structure of comb‐shaped liquid‐crystalline ionomers containing calcium ions

Liquid‐crystalline (LC) ionomers containing 2–15 mol % calcium ions were synthesized by the exchange reaction between the nematic LC copolymer, bearing oxycyanobiphenyl mesogenic groups, and the carboxyl groups of acrylic acid, with calcium acetate. The incorporation of 2–3 mol % Ca ions in the LC copolymer leads to some rise in the clearing point and glass‐transition temperature. A further increase in the concentration of metal ions (>5 mol %) is accompanied by induction of the smectic A phase where clearing point and glass‐transition temperatures keep constant values. Phase behavior of the LC ionomers may be understood on the basis of a structural model that considers the dual role of calcium ions in a polymer matrix. Metal ions act as points of noncovalent electrostatic binding of the polymer chains and are capable of forming larger ionic associates (multiplets). The comparison of the phase behavior of sodium and calcium containing LC ionomers shows that the formation of ionic links may lead to the growth of structure defects suppressing a positive influence of charged groups on the mesophase clearing temperature. The orientation behavior of the LC ionomers in the magnetic field was studied. It was shown that the incorporation of calcium ions (3 mol %) in the LC copolymer matrix leads to the growth of orientation order parameter S of the nematic phase. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3953–3959, 2001     

Adsorption of monoclonal IgG on polystyrene microspheres

In this paper the adsorption of a monoclonal antibody IgG-1 isotype against HBsAg onto positively and negatively charged polystyrene beads has been studied. To determine the role played by electrostatic forces in the adsorption process different pH values were used. It was confirmed that the affinity of adsorption isotherms depends on the electrostatic interaction between protein and polymer surface. The maximum adsorption amount is located around the i.e.p. of the dissolved protein, and decreases markedly as pH moves away. Thus, the major driving force for adsorption of monoclonal antibodies on polystyrene beads comes from the hydrophobic interaction between the antibody molecules and the adsorbent surface. Desorption of preadsorbed IgG molecules by increasing ionic strength has shown that the positively charged polystyrene is also more hydrophobic in character than the negatively charged one. Finally, electrokinetic experiments have determined that the electric double layer (e.d.l.) of monoclonal antibody changes as the consequence of adsorbing on charged polymer surfaces.     

The electro‐optical properties of ‘charged’ PDLCs

The application of high intensity electric fields to polymer dispersed liquid crystal (PDLC) films can induce changes in their electro‐optical properties and morphology. In particular, a quasilinear electro‐optical response to an external electric field can be achieved if an internal built‐in d.c. field is induced. In this work, we show how the liquid crystal/polymer weight ratio influences the electro‐optical response of ‘charged’ PDLCs, i.e. of PDLC films after the application of a high intensity electric field. We observed that a quasilinear electro‐optical response can be achieved in a well determined range of composition. Larger liquid crystal concentrations are unable to maintain the built‐in field, while PDLCs with lower liquid crystal loadings do not allow the onset of a built‐in d.c. field.     

Ionic conductivity of pure water in charged porous matrix

It is commonly recognized that the ionic conductivity of pure water is very poor because of very low ionic concentrations. However, this work indicates that pure water in charged porous matrixes can be moderately conductive because of the ions in the electric double layer established at the solid/water interfaces. The ionic conductivity of pure water in a charged matrix changes with the electrode potential of the matrix and is influenced by the structural parameters. Both experimental measurements and theoretical calculations reveal that ionic conductivity may reach the order of 10(-3) S cm(-1) in commonly accessible potential region in a porous matrix made of gold nanoparticles. These results would help to understand and optimize the electrode processes in electrochemical devices without deliberately added electrolytes, such as polymer electrolyte membrane fuel cells.     

Electric Double‐Layer Capacitor Based on an Ionic Clathrate Hydrate

Herein, we suggest a new approach to an electric double‐layer capacitor (EDLC) that is based on a proton‐conducting ionic clathrate hydrate (ICH). The ice‐like structures of clathrate hydrates, which are comprised of host water molecules and guest ions, make them suitable for applications in EDLC electrolytes, owing to their high proton conductivities and thermal stabilities. The carbon materials in the ICH Me₄NOH ? 5 H₂O show a high specific capacitance, reversible charge–discharge behavior, and a long cycle life. The ionic‐hydrate complex provides the following advantages in comparison with conventional aqueous and polymer electrolytes: 1) The ICH does not cause leakage problems under normal EDLC operating conditions. 2) The hydrate material can be utilized itself, without requiring any pre‐treatments or activation for proton conduction, thus shortening the preparation procedure of the EDLC. 3) The crystallization of the ICH makes it possible to tailor practical EDLC dimensions because of its fluidity as a liquid hydrate. 4) The hydrate solid electrolyte exhibits more‐favorable electrochemical stability than aqueous and polymer electrolytes. Therefore, ICH materials are expected to find practical applications in versatile energy devices that incorporate electrochemical systems.     

Effect of a Gas Discharge on the Ignition in the Hydrogen-Oxygen System

A kinetic model is constructed for ignition initiated by nonequilibrium gas-discharge plasma in the hydrogen-oxygen system. The model takes into account the effect of the electric field on the dissociation of molecules and on the buildup of active radicals, excited species, and charged species (electrons and positively and negatively charged ions). It is demonstrated by mathematical modeling that the induction period depends strongly on the reduced strength of the electric field (electron temperature). Four reduced kinetic networks are considered, and various components and reactions are shown to exert an effect on the nonthermal initiation of ignition in the H₂-O₂ system by low-temperature plasma.     

Plasma Parameters around a Chain-Like Structure of Dust Particles in an External Electric Field

The formation of a 1D chain-like structure of dust particles in a low-temperature argon plasma was studied. A new numerical model for calculation of the self-consistent spatial distribution of plasma parameters around a chain of dust particles was presented. The model described the motion of positively charged ions in the electric potential of several negatively charged dust particles, taking into account the action of an external electric field. The main advantage of the model was that the charges of the dust particles and the interparticle distances were determined self-consistently. As a result of numerical simulations, the dependencies of the spatial distributions of the plasma parameters (the densities of electrons and ions and the self-consistent electric potential) near the dust particles chain on the strength of the external electric field, an external force acted on the last particle, and the mean free path of the ions was determined. The obtained results made it possible to describe the process of the formation of chain-like structures of dust particles in discharge plasma.     

High Electric Field Strengths in Micellar Electrokinetic Capillary Electrophoresis with Ionic Liquids as Modifiers

Abstract

In this study, a method for the separation and determination of basic analytes in aqueous capillary electrophoresis (CE) was developed based on high electric field strengths and ionic liquids (ILs). The resulting electric field strengths ranged from 500 to 1000 V/cm. Trishydroxymethylaminomethane (Tris) and sodium cholate (SC) were used as main electrolytes. The ionic liquids 1‐ethyl‐3‐methylimidazoium tetrafluoroborate (1E‐3MI‐TFB) and 1‐butyl‐3‐methylimidazoium tetrafluoroborate (1B‐3MI‐TFB) were used as modifiers to improve the separation efficiency and selectivity. It was shown that increasing the applied electric field strengths not only caused short analysis time, but also did not induce excessive Joule heating in the capillary when ionic liquids were used as modifiers. The susceptibility to high electric field of separation efficiency in capillary electrophoresis, with the effect of ionic liquids, was subsequently discussed, and the developed method was used to analyze three model analytes in Sinacalia tangutica. The accurate results illustrated that high electric field strength with the ionic liquids was feasible in CE.     

Deviation from Ohm's law in electric field assisted capillary liquid chromatography

Earlier studies of electric field assisted LC (EF-LC) have shown that the effect on charged analytes of the application of an electric field over a capillary LC column is relatively small. Charged analytes can only be affected by the electric field while present in the mobile phase, which makes the effective time for influence of the electric field t(0) independent of retention time. Because the charged analytes only can be affected for a short time the electric field strength ought to be high in order to increase the impact of the electric field on the separation. We have, however, found that only a relatively low electric field strength can be used in EF-LC when pressure is used as main driving force. The useful field strength was limited by a dramatic increase in the current. This increase in current was found to origin from an increased concentration of buffer ions that have an electrophoretic mobility towards the pumped flow.     

Ionic space charge phenomena during SIMS analysis of ceramic materials

Summary Despite recent progress in instrument design the surface analysis of poorly conducting materials by modern techniques operating with either primary and/or secondary charged particles always leads to an accumulation of electric charges on the bombarded surface. In materials with an appreciable ionic conductivity the resultant electric field will induce the migration of mobile species and will therefore modify elemental concentration profiles. As an illustration of this problem we present a phenomenological study of an ionic model material which contains only one mobile species (e.g. sodium or hydrogen in oxide glasses at room temperature). A simultaneous numerical solution of the diffusion equation and of Poisson's equation permits to calculate the electric field and the ionic charge carrier concentration profiles in the near surface region of the material as a function of time. Although material ablation by sputtering is not yet taken into account, this approach gives useful insights into what happens in the near surface region of an ionic conductor on analysing it by SIMS or related techniques which also produce shallow charged layers on the surface of the target. On the other hand, the results are also applicable to plasma based treatments of glass surfaces currently applied in PVD coating processes.Presented at the 7th Working Conference on Applied Surface Analysis at Jülich (Germany), June 22–25, 1992 [Other lectures and posters in Fresenius' J Anal Chem (1993): 346:1–3]     

Gas phase charged aggregates of bis(2-ethylhexyl)sulfosuccinate (AOT) and divalent metal ions: first evidence of AOT solvated aggregates

Assembling and chelating properties of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) towards divalent metal ions have been investigated in the gas phase by electrospray ionization mass spectrometry. A variety of positively charged monometallated and mixed metal aggregates are formed. Interestingly, several ions contain solvent (MeOH, H(2)O) molecules and constitute the most abundant AOT cationic aggregates not containing sodium. These species are the first example of solvated AOT-metal ion aggregates in the gas phase. By increasing the surfactant aggregation number, the abundance of solvated species becomes lower than that of unsolvated ones. Decompositions of ionic species have been studied by tandem mass spectrometry, and their stability has been determined through energy resolved mass spectrometry. In contrast with positively charged AOT-alkaline metal ion aggregates, whose decompositions are dominated by the loss of individual surfactant molecules, AOTNa-divalent ion aggregates mainly dissociate through the cleavage of the AOT H(2)C-O bond followed by further intramolecular fragmentations. This finding, that is consistent with an enhanced chelation of divalent ions with AOT(-) head groups, has been taken as an indication that such aggregates are characterized by a reverse micelle-like organization with a ionic core formed by the metal cations interacting with the negatively charged surfactant polar heads, whereas the surfactant alkyl chains point outside.     

Synthesis of imidazolium‐functionalized ionic polyurethane and formation of CdTe quantum dot–polyurethane nanocomposites

A series of positively charged imidazolium‐functionalized ionic polyurethanes (IPUs) were prepared in one‐step polymerization process by polymerization of presynthesized short‐chain imidazolium‐based ionic diol, polyethylene glycols with different molecular weights as long‐chain diols, and toluylene‐2,4‐diisocyanate. The structures of IPUs are confirmed by ¹H NMR analysis, and the thermogravimetric analysis measurement indicates that the IPUs have high degradation temperature. Fluorescent nanocrystal–polymer composites CdTe–IPU can be prepared conveniently, by the electrostatic interaction between positively charged IPUs and the negatively charged aqueous CdTe quantum dots (QDs). UV–vis absorption and photoluminescence spectra indicate the photochemical stability and strong fluorescent emission of CdTe–IPU composites. The quantum yields (QYs) of the composites are high and basically restore the QYs of the pure QDs. In addition, the transmission electron microscopy photographs show that the QDs in composites are uniform (about 3 nm in diameter) and monodisperse. The obtained nanocomposites are powder or elastomers with good film building. The casted CdTe–IPU films are transparent under visible light, and the colors of the composites and their films are vivid under a UV lamp. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Ionic Circuits Based on Polyelectrolyte Diodes on a Microchip

Green means go : A polyelectrolyte diode on a microchip exhibits well‐defined nonlinear rectifying behavior. This system visualizes the dynamic distribution of ions in a charged polymer phase under an electric field on a real‐time basis using fluorescence images (see picture). Multiple polyelectrolyte diodes are integrated on a microchip to produce a variety of logic gates based on ionic circuits.

     

Ionic Covalent Organic Frameworks: Design of a Charged Interface Aligned on 1D Channel Walls and Its Unusual Electrostatic Functions

Covalent organic frameworks (COFs) have emerged as a tailor‐made platform for designing layered two‐dimensional polymers. However, most of them are obtained as neutral porous materials. Here, we report the construction of ionic crystalline porous COFs with positively charged walls that enable the creation of well aligned yet spatially confined ionic interface. The unconventional reversed AA‐stacking mode alternately orientates the cationic centers to both sides of the walls; the ionic interface endows COFs with unusual electrostatic functions. Because all of the walls are decorated with electric dipoles, the uptake of CO₂ is enhanced by three fold compared to the neutral analog. By virtue of sufficient open space between cations, the ionic interface exhibits exceptional accessibility, efficiency, and selectivity in ion exchange to trap anionic pollutants. These findings suggest that construction of the ionic interface of COFs offers a new way to structural and functional designs.     

Permeability control in electro‐sensitive microcapsules with immobilized ferroelectric liquid crystalline segments

Nylon‐polystyrene microcapsules with immobilized ferroelectric liquid crystalline segments were prepared, and permeability control of an encapsulated core material was investigated under an external electric field. A ferroelectric liquid crystal monomer possessing both mesogenicity and chirality responded effectively to the external electrical field. Permeation of the material (oxprenolol) contained in the inner aqueous core of the microcapsules was enhanced under a weak electric field (2 V). Furthermore, the permeability of oxprenolol did not depend on the external electric field in the absence of the ferroelectric liquid crystal segments. To clarify the controlled‐release mechanism of the core material, the light transmittance of the polymer membranes was quantitatively evaluated under an external electric field using a handmade polarized light transmittance apparatus. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1749–1757, 2008     

Novel polymer electrolytes prepared by copolymerization of ionic liquid monomers

Ionic liquid monomer couples were prepared by the neutralization of 1‐vinylimidazole with vinylsulfonic acid or 3‐sulfopropyl acrylate. These ionic liquid monomer couples were viscous liquid at room temperature and showed low glass transition temperature (Tg) at ?83 °C and ?73 °C, respectively. These monomer couples were copolymerized to prepare ion conductive polymer matrix. Thus prepared ionic liquid copolymers had no carrier ions, and they showed very low ionic conductivity of below 10^?9 S cm^?1. Equimolar amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to imidazolium salt unit was then added to generate carrier ions in the ionic liquid copolymers. Poly(vinylimidazolium‐co‐vinylsulfonate) containing equimolar LiTFSI showed the ionic conductivity of 4 × 10^?8 S cm^?1 at 30 °C. Advanced copolymer, poly(vinylimidazolium‐co‐3‐sulfopropyl acrylate) which has flexible spacer between the anionic charge and polymer main chain, showed the ionic conductivity of about 10^?6 S cm^?1 at 30 °C, which is 100 times higher than that of copolymer without spacer. Even an excess amount of LiTFSI was added, the ionic conductivity of the copolymer kept this conductivity. This tendency is completely different from the typical polyether systems. Copyright © 2002 John Wiley & Sons, Ltd.     

Microstructure and viscoelasticity of electrorheological suspensions with hybrid core‐shell microspheres

A novel type of electrorheological (ER) fluids with hybrid microspheres as dispersed phases was prepared and their rheological properties in dynamic and oscillatory modes in the presence of electric field were studied. Hybrid microspheres are new types of inorganic‐organic composites consisting of inorganic hollow cores covered with a thin layer of conjugated polymer poly (3‐octylthiophene)—P₃OT, followed by a polyurethane electrolyte shell of defined thicknesses and controlled (electronic and ionic) conductivities. It has been found that the rate of ER response for the applied electric field of the order of few kV/mm, as well as the recovery time after high shear loads of the novel ER fluids, was significantly improved in comparison to the typical solid electrolyte‐based materials. It has been shown that upon the application of an electric field the suspensions of hybrid microspheres form a gel‐like network structure at low strain region with reasonable rigidity characterized by the domination of G′ moduli over G″ and broad linear viscoelastic range. It was shown that at electric fields as high as 3 kV/mm, the investigated ER materials exhibited predominantly elastic behavior and were able to endure strains up to 3% without significant deformation of the material microstructure. Moreover, the novel ER materials exhibited much faster microstructure recovery after high shear loads in comparison to ER fluids comprising core‐shell composites without poly (3‐octylthiophene) interlayer, which makes them more suitable for the applications requiring immediate response to an external electric field.