Ion Perturbation Research Articles

Twist pz Orbital and Spin Moment of the Wavy-Graphene/L10-FePd Moiré Interface

A crystallographically heterogeneous moiré interface of hexagonal graphene (Gr) and a tetragonal L10-FePd alloy is bonded via van der Waals (vdW) forces. Robust interfacial perpendicular magnetic anisotropy was discovered at the L10-FePd side of the Gr/L10-FePd heterogeneous interface (H. Naganuma et al. ACS Nano, 2022, 16, 4139). This study focuses on the Gr side of the Gr/L10-FePd interface. X-ray absorption spectroscopy measurements of Gr from two different angles demonstrated that in addition to the π* orbital peak being observed at a glance incident angle (θΑ = 30°), it was also observed at a nominal incident (NI) angle (θΑ = 90°). The appearance of the π* peak at NI is attributed to the wavy Gr and strong bonding of the chemisorption-type vdW force. The densities of states of px, py, and pz from first-principles calculations indicate another reason for the π* peak at NI. The pz orbital of C twists into the x–y plane owing to its chemical bond with Fe or perturbation of the Fe ion to the C orbital. This twisted pz orbital appears near the Fermi level. Thus, the π* peak at NI can be interpreted to appear owing to three reasons: (i) the wavy Gr, (ii) the twisted pz orbital near the Fermi level, and (iii) the chemisorption-type vdW force. The X-ray magnetic circular dichroism of the C K-edge and first-principles calculations revealed that wavy Gr has a spin magnetic moment of 0.018 μB/C atoms but no orbital magnetic moment.

Fast dual-mode switchable smart window based on the dual-frequency liquid crystal electrohydrodynamic instability

In the past decade, liquid crystals for use in switchable smart windows have become a research hotspot. Dual-frequency liquid crystals (DFLCs), in particular, are now widely studied and applied in fast-response liquid crystal devices. In this work, we determine that a DFLC scatters light when a voltage frequency close to its crossover frequency is applied. The principle behind this phenomenon is then investigated. The experimental results show that the scattering of light is a dynamic process that is caused by ion perturbation. Based on the results of this investigation, a double-layer liquid crystal (LC) shutter is prepared. It is shown that the fabricated device can be quickly switched between transparent, dark, and scattering states solely by changing the voltage frequency; this ability also has a useful application in connection to privacy-protecting smart windows. The DFLC is combined with dynamic scattering to accelerate the response time of the scattering.

The Structure of Water Bonded to Phosphate Groups at the Electrified Zwitterionic Phospholipid Membranes/Aqueous Interface

AbstractGaining insight into the water structure at the electrified phospholipid membranes/aqueous interface is vital and essential for elucidating the mechanism of many biochemical reactions, but still remains a formidable challenge. Herein, based on the superiority of surface enhanced infrared absorption (SEIRA) spectroscopy combined with electrochemistry in interfacial analysis, the evolution of local water structure at the zwitterionic phospholipid membranes/aqueous interface with an external electric field is revealed by means of ion perturbation. The strongly hydrogen‐bonded water directly bonded to the phosphate groups (PO2−) has a strong mechanical strength to resist potential perturbations, and that portion of water greatly affects the electrostatic properties of the phospholipid membranes. This study innovates the basic understanding of electric double layer (EDL) at the membranes/aqueous interface.

The Structure of Water Bonded to Phosphate Groups at the Electrified Zwitterionic Phospholipid Membranes/Aqueous Interface.

Gaining insight into the water structure at the electrified phospholipid membranes/aqueous interface is vital and essential for elucidating the mechanism of many biochemical reactions, but still remains a formidable challenge. Herein, based on the superiority of surface enhanced infrared absorption (SEIRA) spectroscopy combined with electrochemistry in interfacial analysis, the evolution of local water structure at the zwitterionic phospholipid membranes/aqueous interface with an external electric field is revealed by means of ion perturbation. The strongly hydrogen-bonded water directly bonded to the phosphate groups (PO2- ) has a strong mechanical strength to resist potential perturbations, and that portion of water greatly affects the electrostatic properties of the phospholipid membranes. This study innovates the basic understanding of electric double layer (EDL) at the membranes/aqueous interface.

K(+) regulates Ca(2+) to drive inflammasome signaling: dynamic visualization of ion flux in live cells.

P2X7 purinergic receptor engagement with extracellular ATP induces transmembrane potassium and calcium flux resulting in assembly of the NLRP3 inflammasome in LPS-primed macrophages. The role of potassium and calcium in inflammasome regulation is not well understood, largely due to limitations in existing methods for interrogating potassium in real time. The use of KS6, a novel sensor for selective and sensitive dynamic visualization of intracellular potassium flux in live cells, multiplexed with the intracellular calcium sensor Fluo-4, revealed a coordinated relationship between potassium and calcium. Interestingly, the mitochondrial potassium pool was mobilized in a P2X7 signaling, and ATP dose-dependent manner, suggesting a role for mitochondrial sensing of cytosolic ion perturbation. Through treatment with extracellular potassium we found that potassium efflux was necessary to permit sustained calcium entry, but not transient calcium flux from intracellular stores. Further, intracellular calcium chelation with BAPTA-AM indicated that P2X7-induced potassium depletion was independent of calcium mobilization. This evidence suggests that both potassium efflux and calcium influx are necessary for mitochondrial reactive oxygen generation upstream of NLRP3 inflammasome assembly and pyroptotic cell death. We propose a model wherein potassium efflux is necessary for calcium influx, resulting in mitochondrial reactive oxygen generation to trigger the NLRP3 inflammasome.

Coulometric calcium pump for thin layer sample titrations.

A selective electrochemical calcium pump based on a fast diffusive calcium ionophore-based membrane is reported. An initially nonpolarized ionophore-based membrane allows one to establish a net calcium flux by applying a potential step function (i.e., 250 mV for 30 s). The resulting calcium flux is released into a microliter scale thin layer reservoir, and the resulting ion perturbation is monitored by either a potentiometric or a coulometric readout. This chemical perturbation in the thin layer thus acts as a titration agent that is precisely controlled by coulometry. A linear correlation between released and detected calcium is confirmed by the two different readout modes. Having demonstrated the efficiency of the calcium pump in background electrolyte solutions, a complexometric titration with known concentrations of EDTA in the thin layer sample was performed. With the potentiometric readout, titrations in the range of 0.25-0.75 mM gave a precision of 3%, whereas the coulometric readout gave a range of 0.02-0.12 mM and a precision of 2%. Improved precision is expected by better control of the thin layer geometry by microfabrication. The significance of this work is that the coupling of a selective calcium pump with a thin layer element can give rise to rapid and complete sample concentration changes and result in a promising platform for titrations either on the laboratory bench or for in situ measurements in environmental or diagnostic settings.

Characterization of seasonal and longitudinal variability of EEJ in the Indian region

AbstractThis paper presents the seasonal and longitudinal variability of the equatorial electrojet (EEJ) based on geomagnetic variation data from two electrojet stations in the northern Indian Ocean at a longitudinal separation of ~15°: i.e., at 77°E and at 93°E. One complete year of data is used (i.e., from November 2011 to October 2012) at the two longitudes and compared with the climatological model of the equatorial electrojet (EEJM‐2.0). The results of our analysis show that (i) the monthly averaged hourly values of EEJ strength at 77°E and 93°E are overall in agreement with global characteristics of EEJ with significant departures over the year of study, (ii) the monthly average hourly daytime values at Campbell Bay and Vencode show poor correlation (r < 0.7) for 5 out of 10 months, (iii) comparison of observed EEJ strength at respective longitudes and the current densities derived from EEJM‐2.0 show overall agreement with significant differences for monthly mean hourly daytime values at respective longitudes, and (iv) day‐to‐day variability in noontime EEJ amplitudes between the two longitudes is >10 nT, >20 nT for 30% of quiet days, sorted by planetary index (Kp) <1 and <2. This variability is reflected in monthly average values (V) mechanisms for persistent differences in EEJ on day‐to‐day basis are sought from perturbation of westward ion drifts by neutral winds caused by the upward propagation of gravity waves from troposphere/stratosphere into the mesosphere. These mechanisms have been identified theoretically and experimentally. The four‐wave structure of ionospheric current densities obtained by EEJM‐2.0 and other contemporary models closely resembles atmospheric tidal signatures and has a common origin. The magnitude and persistence of these differences, at short spatial scales (15°), are significant observation. These effects are reflected in the monthly and seasonal signatures of EEJ and contribute to the contemporary models.

Brain edema in acute liver failure: mechanisms and concepts

Brain edema and associated increase in intracranial pressure continue to be lethal complications of acute liver failure (ALF). Abundant evidence suggests that the edema in ALF is largely cytotoxic brought about by swelling of astrocytes. Elevated blood and brain ammonia levels have been strongly implicated in the development of the brain edema. Additionally, inflammation and sepsis have been shown to contribute to the astrocyte swelling/brain edema in the setting of ALF. We posit that ammonia initiates a number of signaling events, including oxidative/nitrative stress (ONS), the mitochondrial permeability transition (mPT), activation of the transcription factor (NF-κB) and signaling kinases, all of which have been shown to contribute to the mechanism of astrocyte swelling. All of these factors also impact ion-transporters, including Na(+), K(+), Cl(-) cotransporter and the sulfonylurea receptor 1, as well as the water channel protein aquaporin-4 resulting in a perturbation of cellular ion and water homeostasis, ultimately resulting in astrocyte swelling/brain edema. All of these events are also potentiated by inflammation. This article reviews contemporary knowledge regarding mechanisms of astrocyte swelling/brain edema formation which hopefully will facilitate the identification of therapeutic targets capable of mitigating the brain edema associated with ALF.

Redox Modulation of Magnetic Slow Relaxation in a 4f-Based Single-Molecule Magnet with a 4d Carbon-Rich Ligand

A ruthenium carbon-rich-based ligand that brings redox reversibility to a dysprosium-based single-molecule magnet is reported. Long-distance perturbation of the 4f ion is achieved upon oxidation, resulting in an overall enhancement of the magnetic slow relaxation.

Ion interactions with non-polar and amphiphilic solutes in water

Despite its extensive use in, for example, the concentration and crystallization of proteins, the salting out phenomenon remains poorly understood, with many--sometimes contradictory--explanations found in the literature. Following our earlier work using isotope substitution neutron scattering on an aqueous tertiary butyl alcohol (TBA) with added NaCl that examined in detail the molecular-level interactions in the system, and suggested that attempts to understand salting out through ion perturbation of the non-polar hydration shell may not be appropriate, we report here on two further sets of high resolution structural experiments that detail the structural interactions between ion, solvent and amphiphile in a wider range of relevant systems. First, a set of X-ray absorption spectroscopy experiments probed the effects on the hydrophobic hydration shell of Kr of adding a range of different salts (specifically Na2SO4, NaClO4, NaCl, NaNO3 and Mg(ClO4)2). The bottom line from these experiments is that the hydration shell is essentially unaffected by the added ions, underlining further the stability of the shell to such perturbations. The second set of experiments was a further isotope substitution neutron scattering study of the molecular-level solution structures of aqueous TBA, this time for a range of different added ions (CsF, NaBr, and NaCl at three concentrations), for which we have in addition extracted equilibrium constants to quantify the relative strengths of the various interactions. From this second set of results, we can conclude again that the solvent structure is essentially unperturbed by both the various ions and the amphiphile, and also identify a number of ion-specific effects. Comparing our results with those obtained from simulations that are not constrained by the experimental data underlines how sensitive structural conclusions are to the assumed potential functions, and that drawing conclusions from simulations not constrained to fit experimental data can lead to seriously erroneous conclusions.

Dynamics of Formamide Ionic Solutions Investigated by Ultrafast Optical Kerr Effect

Molecular dynamics of formamide solutions of alkali metal halide salts were investigated using the time-resolved ultrafast optical Kerr effect (OKE) to observe the effects of ion solvation on the dynamics of a nonaqueous high-permittivity H-bonding solvent. The picosecond orientational and ultrafast intermolecular dynamics of liquid formamide as a function of concentration of NaI and KI are compared with the temperature effect on the pure solvent. The effect of a range of other salts at fixed concentration is also recorded. Transient OKE and corresponding low-frequency (THz) Raman spectra of the solutions revealed differences in the solvent dynamics caused by ion solvation. Increasing concentrations of NaI and KI have the effect of slowing down the diffusive reorientation and reducing the librational frequencies of formamide, with cation-related effects observed on the THz Raman spectrum. These effects are discussed in terms of an ion perturbation of the H-bonding structure in the solution. This approach provides a valuable means of investigating the dynamics, structure, and interactions in complex, interacting systems.

Predicting Bound Ions on the Protein Surface

Biological macromolecules exist in the complex environment of the cell, constantly interacting with other molecules and ions. Some of the ions may bind directly to proteins affecting their structure and thus altering their function. Though the X-ray crystallography remains to be one of the most popular methods of proteins structure determination, typically the positions of bound ions are not routinely revealed. Here we report a development of an approach, based on numerical solutions of the Poisson-Boltzmann equation (PBE) as implemented in DelPhi, which predicts the positions of surface bound ions taking into account geometrical considerations as well. The method is tested against existing experimental data of proteins with different types of ions on the surface and it is shown that it the electrostatic potential is the dominant factor for ion binding not involving chemical interactions. We further outline the importance of such an approach with respect to relaxing the limits of Poisson-Boltzmann formalism in describing the perturbation of ion's concentration in the space regions with large local electrostatic potential. The work is supported by NIH, NIGMS, grant number 1R01GM093937-01.

Open-cell Titration of Seawater for Alkalinity Measurements by Colorimetry Using Bromophenol Blue Combined with a Non-linear Least-squares Method

The open-cell titration of seawater was studied for alkalinity measurements by colorimetry. 1) The colorimetric pH of free hydrogen ion concentration, pH(F(ind)), was calculated from the ratio of the absorbances at 436 and 590 nm (R = (590nm)A/(436nm)A), along with the molar absorption coefficient ratios (e(1), e(2) and e(3)/e(2)) and a tentative acid dissociation constant value (pK(a(2))). 2) The perturbation of hydrogen ion was evaluated from the change in titration mass (Deltam). The total hydrogen ion concentration at m + Deltam, pH(T(at m+Deltam)), was calculated using pH(F(ind)) for a mass m and constants for sulfate (S(T)) and fluoride (F(T)). 3) The alkalinity (A(T)) was computed from the titrant mass (m + Deltam) and the corresponding pH(T(at m+Deltam)) through a non-linear least-squares approach using the pK(a(2)) value as a variable parameter. Seawater sample at 2000 m depth from the West Pacific was analyzed. The resulting A(T) (2420.92 +/- 3.35 micromol kg(-1)) was in good agreement with the A(T) measured by potentiometric electric force (2420.46 +/- 1.54 micromol kg(-1)). The resulting pK(a(2)) was 3.7037, in close proximity to that reported by King et al. (pK(a(2)) = 3.695).

Electrostatic instabilities in circularly polarized microwave produced magnetized plasmas

The growth rate of electrostatic instabilities of electron oscillation and low-frequency (LF) ion oscillation are investigated for a plasma produced by a circularly polarized microwave field during the breakdown process. The plasma is magnetized by an external homogenous static magnetic field on the direction of microwave field propagation. Numerical calculations show that the electron and ion perturbations are unstable in such an anisotropic plasma. Electron perturbations have the maximum growth rate across the magnetic field. In addition, ion perturbation growth rate is minimum on this direction. The LF ion oscillation is excited by Cherenkov emission mechanism due to the nonequilibrium form of the electron velocity distribution function. Electron oscillation growth rate decreases by increasing the external magnetic field, while the LF ion oscillation increases smoothly and reaches a maximum when the electron oscillation is stopped.

Anesthetic potency and the perturbation of positive ion or proton acceptor sites in the nerve membrane

Anesthetic potency and the perturbation of positive ion or proton acceptor sites in the nerve membrane

Impact of geo‐engineering on the ion composition of the stratosphere

A remedy called “geo‐engineering solution” has been recently proposed by some scientists to handle the global warming problem through injection of sulfates high aloft into the stratosphere. However, this idea may have some other side impacts. We have investigated the perturbation caused by geo‐engineering solution on the stratospheric charged species using a coupled neutral‐ion photochemical model. Model calculations indicate additional production of sulfuric acid immediately after the injection which further leads to increased abundance of heavy negative ion family by several orders of magnitude over the ambient. After 2 months, most of the H2SO4 vapor condensed to H2SO4 aerosols and the density of charged aerosol increases several folds and the effect spread further in the tropics. The perturbation in ionic species spread globally after about 1 year but became weaker in magnitude. The ion perturbation has implications on the electrical properties of the atmospheric medium.

Efficiency improvements for ion chamber calculations in high energy photon beams

This article presents the implementation of several variance reduction techniques that dramatically improve the simulation efficiency of ion chamber dose and perturbation factor calculations. The cavity user code for the EGSnrc Monte Carlo code system is extended by photon cross-section enhancement (XCSE), an intermediate phase-space storage (IPSS) technique, and a correlated sampling (CS) scheme. XCSE increases the density of photon interaction sites inside and in the vicinity of the chamber and results-in combination with a Russian Roulette game for electrons that cannot reach the cavity volume-in an increased efficiency of up to a factor of 350 for calculating dose in a Farmer type chamber placed at 10 cm depth in a water phantom. In combination with the IPSS and CS techniques, the efficiency for the calculation of the central electrode perturbation factor Pcel can be increased by up to three orders of magnitude for a single chamber location and by nearly four orders of magnitude when considering the Pcel variation with depth or with distance from the central axis in a large field photon beam. The intermediate storage of the phase-space properties of particles entering a volume that contains many possible chamber locations leads to efficiency improvements by a factor larger than 500 when computing a profile of chamber doses in the field of a linear accelerator photon beam. All techniques are combined in a new EGSnrc user code egs_chamber. Optimum settings for the variance reduction parameters are investigated and are reported for a Farmer type ion chamber. A few example calculations illustrating the capabilities of the egs_chamber code are presented.

Generation of Nucleophilic Character in the Cys25/His159 Ion Pair of Papain Involves Trp177 but Not Asp158

Studies on papain (EC 3.4.22.2), the most thoroughly investigated member of the cysteine proteinase superfamily, have contributed substantially to our understanding of the roles of noncovalent interactions in enzyme active center chemistry. Previously, we reported evidence that the long-held view that catalytic competence develops synchronously with formation of the catalytic site (Cys25)-S-/(His159)-Im+H ion pair is incorrect and that conformational rearrangement is necessary for each of the partners to play its role in catalysis. A decrease in the level of mutual solvation of the partners of the noncatalytic "intimate" ion pair should release the nucleophilic character of (Cys25)-S- and allow association of (His159)-Im+H with the leaving group of a substrate to provide its general acid-catalyzed elimination. Hypotheses by which this could be achieved involve electrostatic modulation of the ion pair and perturbation of its hydrophobic shielding from solvent by Trp177. The potential electrostatic modulator closest to the catalytic site is Asp158, the mutation of which to Ala substantially decreases catalytic activity. Here we report an investigation of these hypotheses by a combination of computer modeling and stopped-flow pH-dependent kinetic studies using a new series of cationic aminoalkyl 2-pyridyl disulfide time-dependent inhibitors as reactivity probes. These probes 2-4 (n = 2-4), which exist as equilibrium mixtures of H3N+-[CH2]n-S-S-2-pyridyl+H and H3N+-[CH2]n-S-S-2-pyridyl which predominate in acidic and weakly alkaline media, respectively, were shown by modeling and kinetic analysis to bind with various degrees of effectiveness near Asp158 and in some cases also near Trp177. Kinetic analysis of the reactions of 2-4 and of the reaction of CH3-[CH2]2-S-S-2-pyridyl+H <==>CH3-[CH2]2-S-S-2-pyridyl 1 and normal mode calculations lead to the conclusion that Asp158 is not involved in the generation of nucleophilic character in the ion pair and demonstrates a key role for Trp177.

Effect of interface chloride ion perturbation on oscillatory electrodissolution

This paper investigated the effect of chloride ion perturbation on the electrodissolution behavior of carbon steel in 5.0 M H 3PO 4 solution. The results indicated that the oscillatory electrodissolution changes significantly when the electrode/electrolyte interface was disturbed by injecting small quality of chloride ion-containing solution. The mode of current oscillations changed from the mono-periodic to the nonperiodic behavior with higher frequencies but lower amplitudes. After a transient response disappeared, the permanent influence in the current oscillations was observed. Potential distributions on the surface of the electrode were monitored in situ by using scanning reference electrode technology during the electrodissolution process. The potential maps show clearly that localized corrosion was induced after the chloride perturbation. The enforced solution homogenization by bubbling nitrogen at the electrode/electrolyte interface after a few seconds of the chloride perturbation could not eliminate such influence, indicating that chloride ions may enter the passive film and resulted in degradation in chemical stability of the film because of permanent damage. Such a degradation of the passive film only appears when the transient concentration gradient of the chloride ions on the surface is sufficiently high. The long duration of impact on electrodissolution caused by chloride ion perturbation suggests that the passive film does not totally dissolve during the active period in each oscillatory cycle.

Ankle extensor proprioceptors contribute to the enhancement of the soleus EMG during the stance phase of human walking

A rapid plantar flexion perturbation applied to the ankle during the stance phase of the step cycle during human walking unloads the ankle extensors and produces a marked decline in the soleus EMG. This demonstrates that sensory activity contributes importantly to the enhancement of the ankle extensor muscle activation during human walking. On average, the EMG begins to decline approximately 52 ms after the perturbation. In contrast, a rapid dorsi flex ion perturbation produces a group Ia mediated short-latency stretch reflex burst with an onset latency of approximately 36 ms. The transmission of sensory traffic from the foot and ankle was suppressed in 10 subjects by an anaesthetic nerve block produced with local injections of lidocaine hydrochloride. The anaesthetic block had no effect on the stance phase soleus EMG, the latencies of the EMG responses, or the magnitude of the EMG decline following the plantar flexion perturbation. Therefore, it is more likely that proprioceptive afferents, rather than cutaneous afferents, contribute to the background soleus EMG during the late stance phase of the step cycle. The large difference in onset latencies between the short-latency reflex and unload responses suggests that the largest of the active group Ia afferents might not contribute strongly to the background soleus EMG, although it remains to be determined which of the proprioceptive pathways provide the more important contributions.