Changes In Ionic Environment Research Articles

Rheological and dielectric behavior of sodium carboxymethyl cellulose (NaCMC)/Ca2+ and esterified NaCMC/Ca2+ hydrogels: Correlating microstructure and dynamics with properties

Polyelectrolyte-based conductive hydrogels are being extensively explored for applications in energy storage and as electrode materials for batteries. We synthesized ionically crosslinked sodium carboxymethyl cellulose (NaCMC), esterified NaCMC, and Ca2+ doped esterified NaCMC hydrogels. This work aims to understand the effect of Ca2+ ions on the NaCMC and esterified NaCMC. FTIR, SEM, Rheology and EIS studies were performed to understand the structure and dynamics of hydrogels. Results confirmed that Ca2+ ions have an important role in determining the rheological and dielectric response of hydrogels. Power law behavior was observed in their rheological response with exponent (n) of 0.81 for G′ and 0.76 for G″ of ionically crosslinked NaCMC, 5.38 for G′ and 4.70 for G″ of esterified NaCMC, whereas, negative exponents −1.44 for G′ and −1.10 for G″ of Ca2+ ion doped esterified NaCMC. Ionically crosslinked NaCMC hydrogels have relaxation times (τ) in the range of 8.9 × 10−5 s–2.8 × 10−5 s may be due to the formation of temporary dipoles by electrostatic bridge formations with dc conductivity of (0.1 S/cm–5 S/cm), whereas, esterified NaCMC showed relaxation times (10−3 s–8.9 × 10−5 s) with increasing ester crosslinks and dc conductivity of (0.05 S/cm–0.8 S/cm). Interestingly, Ca2+ ion doped esterified hydrogels showed multiple dielectric relaxations on Ca2+ ion addition with different relaxation times may be due to change in ionic environment. The understanding obtained from this work may be useful for designing tuneable hydrogels with optimum electrical and mechanical properties.

An Ultrasensitive Silicon Photonic Ion Sensor Enabled by 2D Plasmonic Molybdenum Oxide.

Silicon photonics has demonstrated great potential in ultrasensitive biochemical sensing. However, it is challenging for such sensors to detect small ions which are also of great importance in many biochemical processes. A silicon photonic ion sensor enabled by an ionic dopant-driven plasmonic material is introduced here. The sensor consists of a microring resonator (MRR) coupled with a 2D restacked layer of near-infrared plasmonic molybdenum oxide. When the 2D plasmonic layer interacts with ions from the environment, a strong change in the refractive index results in a shift in the MRR resonance wavelength and simultaneously the alteration of plasmonic absorption leads to the modulation of MRR transmission power, hence generating dual sensing outputs which is unique to other optical ion sensors. Proof-of-concept via a pH sensing model is demonstrated, showing up to 7 orders improvement in sensitivity per unit area across the range from 1 to 13 compared to those of other optical pH sensors. This platform offers the unique potential for ultrasensitive and robust measurement of changes in ionic environment, generating new modalities for on-chip chemical sensors in the micro/nanoscale.

Structure of an H1-Bound 6-Nucleosome Array Reveals an Untwisted Two-Start Chromatin Fiber Conformation

Chromatin adopts a diversity of regular and irregular fiber structures invitro and invivo. However, how an array of nucleosomes folds into and switches between different fiber conformations is poorly understood. We report the 9.7Å resolution crystal structure of a 6-nucleosome array bound to linker histone H1 determined under ionic conditions that favor incomplete chromatin condensation. The structure reveals a flat two-start helix with uniform nucleosomal stacking interfaces and a nucleosome packing density that is only half that of a twisted 30-nm fiber. Hydroxyl radical footprinting indicates that H1 binds the array in an on-dyad configuration resembling that observed for mononucleosomes. Biophysical, cryo-EM, and crosslinking data validate the crystal structure and reveal that a minor change in ionic environment shifts the conformational landscape to a more compact, twisted form. These findings provide insights into the structural plasticity of chromatin and suggest a possible assembly pathway for a 30-nm fiber.

From octopus to dendrite-Semiflexible polyelectrolyte brush condensates in trivalent counterion solution.

Interplay between counterion-mediated interaction and stiffness inherent to polymer chain can bring substantial complexity to the morphology and dynamics of polyelectrolyte brush condensates. Trivalent counterions induce collapse of flexible polyelectrolyte brushes, over a certain range of grafting density, into octopus-like surface micelles; however, if individual chains are rigid enough, the ion-mediated local nematic ordering assembles the brush chains into fractal-like dendritic condensates whose relaxation dynamics is significantly slower than that in the surface micelles. Notably, the trivalent ions condensed in the dendritic condensates are highly mobile displaying quasi-one-dimensional diffusion in parallel along the dendritic branches. Our findings in this study are potentially of great significance to understanding the response of cellular organization such as chromosomes and charged polysaccharides on membranes to the change in ionic environment.

Insight of electrolyte-free voltammetry at microelectrodes

Electrode reactions without deliberately adding supporting electrolyte are complicated with electric migrations associated with redox reactions, formation of double layers and ion–ion interactions relevant to electrode reactions. The complications can be realized quantitatively through voltammetry at various sized microelectrodes, partly because of negligibly small solution resistance effects and partly because of steady-state voltammograms, which can be analyzed theoretically without capacitive time-dependent current. The present review deals with (i) techniques of fabrication of many sized microelectrodes, (ii) conditions of keeping low electrolyte concentrations, (iii) ionic contribution of forming double layers, (iv) participation in counter ions for electrode reactions and (v) change in ionic environment by redox reactions.

Time-Resolved Small-Angle X-ray Scattering Reveals Millisecond Transitions of a DNA Origami Switch.

Self-assembled DNA structures enable creation of specific shapes at the nanometer-micrometer scale with molecular resolution. The construction of functional DNA assemblies will likely require dynamic structures that can undergo controllable conformational changes. DNA devices based on shape complementary stacking interactions have been demonstrated to undergo reversible conformational changes triggered by changes in ionic environment or temperature. An experimentally unexplored aspect is how quickly conformational transitions of large synthetic DNA origami structures can actually occur. Here, we use time-resolved small-angle X-ray scattering to monitor large-scale conformational transitions of a two-state DNA origami switch in free solution. We show that the DNA device switches from its open to its closed conformation upon addition of MgCl2 in milliseconds, which is close to the theoretical diffusive speed limit. In contrast, measurements of the dimerization of DNA origami bricks reveal much slower and concentration-dependent assembly kinetics. DNA brick dimerization occurs on a time scale of minutes to hours suggesting that the kinetics depend on local concentration and molecular alignment.

Studying homogeneity and zeta potential of membranes using electroacoustics

Abstract The goal of this paper is to show that electroacoustic spectroscopy can be used as a viable means for characterizing membranes. A novel set-up was designed for performing these experiments with a standard electroacoustic zeta potential probe typically used for measuring ζ-potential in concentrated dispersions. Calculation of zeta (ζ) potential from the measured signal was performed with a newly derived electroacoustic theory that takes into account overlap of double layers in the membrane pores (nano-filtration membrane NF 270 manufactured by Dow Chemicals). Several titrations were performed: two salt titrations with potassium chloride and copper sulfate, and pH titration in several solutions of KCl. In all these experiments, changes in ionic environment caused changes in the ζ-potential within the pores of the membrane, as was measured by changes in electroacoustic current. In all cases the results were consistent with theoretical expectations based on prior research and knowledge of ion effects on ζ-potential. Lastly, differences in electroacoustic signal from one area of the membrane to the next (all of the same material) shed some light into the homogeneity of the membrane itself.

The effects of changes in ionic environment and modification of adrenergic function on the vascular responses to sympathomimetic amines.

Abstract The responses to each of four sympathomimetic amines: noradrenaline 200 ng, octopamine 50 μg, metaraminol 20 μg and tyramine 100 μg were studied in the perfused rat mesentery preparation. Perfusion with Ca2+- and Mg2+-free solutions potentiated the responses to all four amines compared with control responses obtained during normal Krebs perfusion. Under perfusion conditions using either normal or Ca2+- and Mg2+-free Krebs solution, nialamide and reserpine retained their characteristic effects on the responses to each amine. Cocaine and desipramine abolished the responses to tyramine but potentiated those to noradrenaline and metaraminol under all perfusion conditions. The responses to each of the amines were only antagonized by ouabain when Ca2+ ions were present in the perfusion solution. It is concluded that perfusion with Ca2+- and Mg2+-free solution interferes with the normal uptake mechanisms occurring in the adrenergic neuron.

Spidroin N-terminal Domain Promotes a pH-dependent Association of Silk Proteins during Self-assembly

Spider silks are spun from concentrated solutions of spidroin proteins. The appropriate timing of spidroin assembly into organized fibers must be highly regulated to avoid premature fiber formation. Chemical and physical signals presented to the silk proteins as they pass from the ampulle and through the tapered duct include changes in ionic environment and pH as well as the introduction of shear forces. Here, we show that the N-terminal domain of spidroins from the major ampullate gland (MaSp-NTDs) for both Nephila and Latrodectus spiders associate noncovalently as homodimers. The MaSp-NTDs are highly pH-responsive and undergo a structural transition in the physiological pH range of the spider duct. Tryptophan fluorescence of the MaSp-NTDs reveals a change in conformation when pH is decreased, and the pH at which the transition occurs is determined by the amount and type of salt present. Size exclusion chromatography and pulldown assays both indicate that the lower pH conformation is associated with a significantly increased MaSp-NTD homodimer stability. By transducing the duct pH signal into specific protein-protein interactions, this conserved spidroin domain likely contributes significantly to the silk-spinning process. Based on these results, we propose a model of spider silk assembly dynamics as mediated through the MaSp-NTD.

Nanoconfinement-Enhanced Conformational Response of Single DNA Molecules to Changes in Ionic Environment

We show that the ionic environment plays a critical role in determining the configurational properties of DNA confined in silica nanochannels. The extension of DNA in the nanochannels increases as the ionic strength is reduced, almost tripling over two decades in ionic strength for channels around 100 x 100 nm in dimension. Surprisingly, we find that the variation of the persistence length alone with ionic strength is not enough to explain our results. The effect is due mainly to increasing self-avoidance created by the reduced screening of electrostatic interactions at low ionic strength. To quantify the increase in self-avoidance, we introduce a new parameter into the de Gennes theory: an effective DNA width that gives the increase in the excluded volume due to electrostatic repulsion.

Inhibitory transmission, activity-dependent ionic changes and neuronal network oscillations

Oscillatory network activity arises from interactions between synaptic and intrinsic membrane properties of neurons. In this review, we summarize general mechanisms of synchronous neuronal oscillations. In addition, we focus on recent experimental and computational studies which suggest that activity-dependent changes of ionic environment can affect both the synaptic and intrinsic neuronal properties and influence the network behavior. GABA(A) receptor (GABA(A)R)-mediated signaling, that is based on Cl(-) and HCO(3)(-) permeability, is thought to be important for the oscillogenesis and synchronization in cortical networks. A remarkable feature of GABAergic synapses is that prolonged GABA(A)R activation may lead to switching from a hyperpolarizing to a depolarizing response. This is partly due to a positive shift of the GABA(A) R reversal potential (E(GABA)) that is generated by GABA-induced Cl(-) accumulation in neurons. Recent studies suggest that activity-dependent E(GABA) changes may have important implications for the mechanisms of gamma oscillations and seizure-like discharges. Thus, a better understanding of the impact of intracellular Cl(-) dynamics on network behavior may provide insights into the mechanisms of physiological and pathological brain rhythms. Combination of experiments and simulations is a promising approach for elucidating which properties of the time-varying ionic environment can shape the dynamics of a given circuit.

Estimation of Membrane Potential by Flow Cytometry

In most living cells, differences between interior and exterior concentrations of ions (e.g., Na(+), K(+), Cl(-)) generate an electrical potential across the cytoplasmic membrane. Membrane potential, like other cellular parameters, may change early in the course of surface receptor-mediated cell activation processes related to the development, differentiated function, and pathology of a large number of cell types. Changes in ionic environment may play a role in transmembrane signaling in response to cell surface ligand-receptor interactions. Thus, it is frequently of scientific interest to estimate membrane potential in individual cells. This unit provides methods for accomplishing this goal by flow or static cytometry using any of a number of cationic or anionic lipophilic fluorescent probes known as distributional dyes. The first of the two protocols is able to estimate the membrane potential of eukaryotic or bacterial cells. The second is more accurate, but can only be used with bacteria.

Dynamic light scattering of native silk fibroin solution extracted from different parts of the middle division of the silk gland of the Bombyx mori silkworm.

Dynamic light scattering (DLS) measurements were performed on aqueous solutions of native silk fibroin extracted from three parts, the posterior (MP), the middle (MM), and the anterior parts (MA), of the middle division (M) of the silk gland of the Bombyx mori silkworm to study the dynamics and aggregation properties of silk fibroin. In the MP part, fibroin molecules are present as aggregates (or clusters) being composed of several large protein complexes or elementary unit (EU), which are further associated to make a large assembly connected via divalent metallic ions. In the MM part, such clusters of EU take more compact structure, and finally in the MA part, clusters disappear, but EUs are more or less aligned to keep the assembly, and the EU takes the conformation of wormlike cylinder capped with hemispheres at both ends. The overall conformational change in solution structure was interpreted as being due to the change in ionic environment in the solution. DLS study was also performed on regenerated silk fibroin solutions, which revealed that fibroin is present as a single molecule dominantly and their association behavior seems completely different from that of native samples and does not depend on types and concentration of added metallic ions.

The effects of calcium blocker on the changes of ionic environment in liver cells stressed by experimental endotoxemia

The far-infrared spectra of bicyclo(3.1.0.)hexane, 3-oxabicyclo(3.1.0.)hexane, and 3,6-dioxabicyclo(3.1.0.)hexane exhibit series of Q branches in the frequency range 250–125 cm−1, like those observed for 6-oxabicyclo(3.1.0.)hexane (cyclopentene oxide) by Carreira and Lord (J. Chem. Phys. 51, 2735 (1969)). The Q branches are interpreted as single quantum jumps of a one-dimensional ring-puckering vibration governed by a potential function of the form V(cm−1) = A(Z4 + BZ2 + CZ3), where Z is a reduced ring-puckering coordinate.The potential parameters for bicyclo(3.1.0.)hexane are A, 24.31 cm−1; B, 26.67; C, 9.63; for 3-oxabicyclo(3.1.0.)hexane, 27.77 cm−1, 20.63, 7.84; and for 3,6-dioxabicyclo(3.1.0.)hexane, 25.25 cm−1, 17.23, 7.33. They were determined by an iterative least-squares fit to the observed four, seven, and nine Q branches, respectively. These potential functions all have only a single minimum, implying a single stable conformation. The dipole moment, μrms, for 3,6-dioxabicyclo(3.1.0.)hexane in benzene solution was determined to be 2.50 D, clearly indicating that the stable conformation is the boat form. The boat conformation had been determined to be the stable form for cyclopentene oxide from a microwave study by Lafferty (J. Mol. Spectrosc. 36, 84 (1970)). There is no direct evidence for the preferred conformation of the remaining two molecules but consideration of torsional interactions about the 1–2 and 4–5 bonds as well as the similarity of the spectra and potential functions for these molecules suggests that the boat conformation is the stable form of all of these molecules.

Correlations between changes in membrane capacitance induced by changes in ionic environment and the conductance of channels incorporated into bilayer lipid membranes

The action of metal polycations and pH on ionic channels produced in bilayer lipid membranes (BLM) by three different toxins was studied by measuring membrane capacitance and channel conductance. Here, we show that critical concentrations of Cd2+, La3+ or Tb3+ induce complex changes in membrane capacitance. The time course of capacitance changes is similar to the time course of channel blocking by these ions at low concentration. No changes in BLM capacitance or conductance were observed in the range of pH 5.8-9.0. A pH shift from 7.4 to 3-4 or 11-12 induced large changes in BLM capacitance and channel conductance. For all studied channel-forming proteins, the initial capacitance increase preceded the conductance decrease caused by addition of polycations or by a change in pH. A close relationship between membrane lipid packing and ion channel protein is suggested.

Structure and mechanical properties of superabsorbent poly(acrylamide)-montmorillonite composite hydrogels

The structure of superabsorbent poly(acrylamide)-clay-based composite (SAPC) was studied by means of XRD, SEM, NMR, FTIR, TGA and DSC. The study showed that the acrylamide was intercalated in the lamina of clay in bimolecular layers. The hydrogels exhibited typical viscoelastic properties. The composite showed a strong response to changes in ionic environment (pH) and electric field strength, as well as chemomechanical properties.

Modulation of melphalan uptake in murine L5178Y lymphoblasts in vitro by changes in ionic environment

The alkylating agent melphalan is actively transported in mammalian cells by two amino acid transport carriers: the sodium-dependent carrier with substrate preference for alanine-serine-cysteine (system ASC), and a sodium-independent carrier with preference for leucine (system L). The effect of altering the ionic environment of murine L5178Y lymphoblasts was investigated in order to determine not only the direct effects of hydrogen and calcium ions on these transport systems, but also the indirect effects of agents or modulators known to alter intracellular calcium. Melphalan transport followed a bell-shaped distribution curve over a pH range from 3 to 9 with a pH optimum of 4.3 and 4.6 for transport by systems ASC and L, respectively. Those agents that could cause a decrease in cytosolic calcium such as the calcium channel blockers verapamil, diltiazem and nitrendipine, the calcium chelator (ethyleneglycol-bis-(β-aminoethylether) N, N, N′, N′-tetraacetic acid (EGTA) and reduction of pH were found to augment melphalan uptake, whereas conditions that would elevate intracellular calcium such as the calcium ionophore A23187, the calcium channel agonist (−) Bay K 8644, elevation of extracellular calcium and the calcium pump inhibitor trifluoperazine were all found to decrease melphalan uptake. These findings suggest that modification of ionic environment directly or indirectly by agents known to alter intracellular calcium can modulate melphalan uptake

O-120 - Effects of changes in ionic environment on the actions of periarterial nerve stimulation(PNS), phenylephrine(PHE) and serotonin(5-HT) in the perfused mesenteric artery of SHR and WKY

O-120 - Effects of changes in ionic environment on the actions of periarterial nerve stimulation(PNS), phenylephrine(PHE) and serotonin(5-HT) in the perfused mesenteric artery of SHR and WKY

On the mechanisms underlying cardiac standstill: Factors determining success or failure of escape pacemakers in the heart

The mechanisms underlying cardiac standstill in health and disease are considered. Ventricular standstill results from failure of impulse formation or transmission in the ventricles. In the healthy heart, idioventricular automaticity is not brought into play and instead is suppressed by the sinus node by virtue of its faster rate (overdrive suppression). However, should the sinus node activity be suppressed or atrioventricular (AV) conduction blocked, overdrive suppression no longer persists. For this reason, the ventricular pacemakers activate the ventricles at a slow rate and under the regulatory activity of the sympathetic system. In the diseased heart, the idioventricular pacemakers or the regulatory mechanism can be altered structurally or functionally. This can be the result of the disease, compensatory mechanisms or therapeutic interventions. Disease may affect the idioventricular pacemakers directly or indirectly through anoxia, a change in ionic environment or an alteration of sympathetic innervation. Compensatory mechanisms may affect reflex actions, blood supply or heart rate. Drug administration may alter autonomic balance, block the action of neuromediators on their receptors or modify diastolic depolarization or its ability to attain the threshold. Because of these different direct and indirect actions, a sudden cessation of sinus node activity or sudden AV block may result in the diseased heart in a prolonged and even fatal cardiac standstill, especially if the tolerance to ischemia of other organs (notably the brain) is decreased.

An ultrastructural approach to the adaptive role of the cell wall in the intertidal algaFucus virsoides

The ultrastructure of the cell wall and the distribution of alginate, cellulose and fucoidans were studied in the intertidal algaFucus virsoides. Microanalysis and precipitation with KPA revealed a cation localization in the wall, mainly corresponding with sulphated polysaccharide distribution. Thus, the adaptive resistance to changes in ionic environment seems to take place through a cation binding to the cell wall polysaccharides, principally at the thallus surface, employing an avoidance mechanism.