Ion Trapping Mechanism Research Articles

Translocation versus ion trapping in the root uptake of 2,4-dichlorophenol by wheat seedlings.

Understanding of the plant uptake of ionizable organic compounds is critical to the evaluation of crop contamination, plant protection, and phytoremediation. This study investigated the time-dependent uptake of 2,4-dichlorophenol (DCP) by intact wheat seedling roots and subsequent translocation to shoots at pH 5.0 and 8.0. Sorption of DCP by cut roots and shoots at these two pHs was conducted to provide the uptake limits and the Donnan charge. For comparison, sorption was also conducted for 1,3-dichlorobenzene (DCB), a nonionizable compound having a structure similar to that of DCP. The DCB sorption isotherms were linear and independent of pH, yielding a consistent log Klip of 3.56 with both roots and shoots, reflective of the essential dominant role of lipids in plant partition uptake. Whereas the DCP sorption also showed a linear isotherm at pH 5.0 with log Klip = 2.88, the sorption at pH 8.0 was nonlinear with a concave downward shape, especially at low concentrations. With live wheat seedlings, the DCB uptake by roots and the DCB translocation to shoots rapidly approached a steady state, showing no obvious pH effect. On the DCP uptake by live plants, there was a rapid attainment of a steady state in roots at pH 5.0 coupled with a retarded transport to shoots due presumably to the polarity of DCP. At pH 8.0, the root uptake of DCP was comparatively slower and the translocation to shoots was completely inhibited due presumably to DCP ionization. At high pH, DCP was supposedly accumulated in an ionized form in root cells via an ion-trapping mechanism.

New molecular understanding of hydrated ion trapping mechanism during thermally-driven desalination by pervaporation using GO membrane

The graphene oxide (GO)-based membranes have shown effective salt separation from the brine solution. Although several experimental works have been done to study the salt rejection in the thermal-driven desalination system, the behavior of ions inside the GO nanochannels during the pervaporation process remains mostly unelucidated. Moreover, the previous theoretical studies on the driving force for ion transport within the GO membrane only focused on pressure, voltage, or concentration gradient. Here, we investigated the transport of water molecules and hydrated cations through the GO membrane in a temperature-assisted system by using dispersion-corrected density functional theory (DFT) calculations at PBE/Grimme with the ions under extreme confinement, reactive molecular dynamics (MD) simulations as well as validated by experimental methods. The water permeation increases with temperature, while the transport of cations remains minimal, which was not observed in other non-thermal desalination approaches. We have shown that high temperature eases the binding between the hydrated divalent cations and the oxygen functional groups on the GO nanosheets by reducing the hydration shell. Furthermore, the cross-linked cations inside the GO nanochannel create an accessible corridor for water molecules and block other cations such as Na+. Our simulation results provide a new mechanism of ion transport in the GO membranes by the thermal-driven process, which can be tailored by using other cations with higher charge density and high temperature to speed up the process.

Prevention of crystalline silica-induced inflammation by the anti-malarial hydroxychloroquine

Objectives: Inhalation of crystalline silica (cSiO2) remains a significant occupational hazard and may lead to the development of silicosis. When cSiO2 particles are phagocytized by alveolar macrophages, they cause disruption of the lysosomal membrane which results in cell death. There are currently no pharmaceutical treatments directed at this mechanism of disease; however, many existing pharmaceuticals, such as hydroxychloroquine (HCQ), become sequestered in the lysosome through an ion-trapping mechanism. The objective of this research was to determine whether HCQ can prevent cSiO2-induced toxicity by blocking LMP in alveolar macrophages.Materials and methods: This study assessed the ability of in vitro treatment with HCQ to block toxicity and lysosomal membrane permeability in cSiO2-exposed mouse bone-marrow derived macrophages. Additionally, C57Bl/6 mice were treated with HCQ by oral gavage before cSiO2 exposure, and the ability of HCQ to prevent lung injury and inflammation was assessed.Results: In vitro studies demonstrated that HCQ attenuated activation of the NLRP3 inflammasome and blocked LMP. Mice treated with HCQ in vivo showed a modest trend towards decreased cSiO2-induced toxicity. Ex vivo culture of alveolar macrophages collected from cSiO2-treated mice showed significantly less NLRP3 inflammasome activation after in vivo exposure to HCQ.Conclusions: Our findings suggest that hydroxychloroquine blocks LMP and can significantly decrease cSiO2-induced toxicity in vitro. HCQ may be a promising treatment for prevention of cSiO2-induced lung damage.

Lithium ion trapping mechanism of SiO2 in LiCoO2 based memristors

Pt/LiCoO2/SiO2/Si stacks with different SiO2 thicknesses are fabricated and the influence of SiO2 on memristive behavior is investigated. It is demonstrated that SiO2 can serve as Li ion trapping layer benefiting device retention, and the thickness of SiO2 must be controlled to avoid large SET voltage and state instability. Simulation model based on Nernst potential and diffusion potential is postulated for electromotive force in LiCoO2 based memristors. The simulation results show that SiO2 trapping layer decreases the total electromotive field of device and thereby prevents Li ions from migrating back to LiCoO2. This model shows a good agreement with experimental data and reveals the Li ion trapping mechanism of SiO2 in LiCoO2 based memristors.

A toxicokinetic study of specifically acting and reactive organic chemicals for the prediction of internal effect concentrations in Scenedesmus vacuolatus.

The toxic potency of chemicals is determined by using the internal effect concentration by accounting for differences in toxicokinetic processes and mechanisms of toxic action. The present study examines toxicokinetics of specifically acting and reactive chemicals in the green algae Scenedesmus vacuolatus by using an indirect method. Concentration depletion in the exposure medium was measured for chemicals of lower (log KOW < 3: isoproturon, metazachlor, paraquat) and moderate (log KOW 4-5: irgarol, triclosan, N-phenyl-2-naphthylamine) hydrophobicity at 7 to 8 time points over 240 min or 360 min. Uptake and overall elimination rates were estimated by fitting a toxicokinetic model to the observed concentration depletions. The equilibrium of exposure concentrations was reached within minutes to hours or was even not observed within the exposure time. The kinetics of bioconcentration cannot be explained by the chemical's hydrophobicity only, but influential factors such as ionization of chemicals, the ion trapping mechanism, or the potential susceptibility for biotransformation are discussed. Internal effect concentrations associated with 50% inhibition of S. vacuolatus reproduction were predicted by linking the bioconcentration kinetics to the effect concentrations and ranged from 0.0480 mmol/kg wet weight to 7.61 mmol/kg wet weight for specifically acting and reactive chemicals. Knowing the time-course of the internal effect concentration may promote an understanding of toxicity processes such as delayed toxicity, carry-over toxicity, or mixture toxicity in future studies.

Ion-trapping properties of SCRIT

We have developed a novel internal target formation technique, SCRIT (Self-Confining Radioactive-isotope Ion Target) with the aim to achieve electron scattering off unstable nuclei. This technique is based on the ion trapping phenomenon in an electron storage ring. To establish the applicability of SCRIT as a target formation technique, we studied in detail its ion-trapping properties. We focused particularly on the spatial distribution of the trapped target ions and their behavior in time evolution. Over 90% of injected ions were trapped in SCRIT, and the overlap efficiency between the trapped target ion cloud and the electron beam was about 10%. From time evolution measurements and computer simulations, we found that variations in trapping lifetime depending on electron beam instability, space charge effect, and q/A values are crucial to understanding the ion-trapping mechanism of SCRIT.

Evaluation of Turner relaxed state as a model of long-lived ion-trapping structures in plasma focus and Z-pinches

Relatively long-lived spheroidal structures coincident with the neutron emission phase have been observed in frozen deuterium fiber Z-pinch and some plasma focus devices. Existence of energetic ion-trapping mechanism in plasma focus has also been inferred from experimental data. It has been conjectured that these are related phenomena. This paper applies Turner’s theory [L. Turner, IEEE Trans. Plasma Sci. 14, 849 (1986)] of relaxation of a Hall magnetofluid to construct a model of these structures and ion-trapping mechanism. Turner's solution modified for a finite-length plasma is used to obtain expressions for the magnetic field, velocity, and equilibrium pressure fields and is shown to represent an entity which is simultaneously a fluid vortex, a force-free magnetic field, a confined finite-pressure plasma, a charged object, and a trapped energetic ion beam. Characteristic features expected from diagnostic experiments are evaluated and shown to resemble experimental observations.

Niemann-Pick C1 Functions Independently of Niemann-Pick C2 in the Initial Stage of Retrograde Transport of Membrane-impermeable Lysosomal Cargo

The rare neurodegenerative disease Niemann-Pick Type C (NPC) results from mutations in either NPC1 or NPC2, which are membrane-bound and soluble lysosomal proteins, respectively. Previous studies have shown that mutations in either protein result in biochemically indistinguishable phenotypes, most notably the hyper-accumulation of cholesterol and other cargo in lysosomes. We comparatively evaluated the kinetics of [(3)H]dextran release from lysosomes of wild type, NPC1, NPC2, and NPC1/NPC2 pseudo-double mutant cells and found significant differences between all cell types examined. Specifically, NPC1 or NPC2 mutant fibroblasts treated with NPC1 or NPC2 siRNA (to create NPC1/NPC2 pseudo-double mutants) secreted dextran less efficiently than did either NPC1 or NPC2 single mutant cell lines, suggesting that the two proteins may work independently of one another in the egress of membrane-impermeable lysosomal cargo. To investigate the basis for these differences, we examined the role of NPC1 and NPC2 in the retrograde fusion of lysosomes with late endosomes to create so-called hybrid organelles, which is believed to be the initial step in the egress of cargo from lysosomes. We show here that cells with mutated NPC1 have significantly reduced rates of late endosome/lysosome fusion relative to wild type cells, whereas cells with mutations in NPC2 have rates that are similar to those observed in wild type cells. Instead of being involved in hybrid organelle formation, we show that NPC2 is required for efficient membrane fission events from nascent hybrid organelles, which is thought to be required for the reformation of lysosomes and the release of lysosomal cargo-containing membrane vesicles. Collectively, these results suggest that NPC1 and NPC2 can function independently of one another in the egress of certain membrane-impermeable lysosomal cargo.

Transition from Spark Discharge to Constricted Glow Discharge in Atmospheric Air by Capacitor Coupled Discharge

The transition from a spark discharge to a constricted glowdischarge in atmospheric air was studied with a capacitor coupledpin-to-water plasma reactor. The reason of the transition isconsidered to be of various factors, namely the change of the airgap due to the polarization of water molecules by the electricfield, the feedback effect of the capacitors, and the ion trappingmechanism. The effects of the frequency of the power supply,inter-electrode gap, and coupled capacitance on the dischargetransition were also investigated.

How Far Can a Molecule of Weak Acid Travel in the Apoplast or Xylem?

The plant hormones auxin, abscisic acid (ABA), and the gibberellins (GAs) are all weak acids subject to the ion-trapping mechanism that tends to remove them from the extracellular space and concentrate them in the cytoplasm of plant cells. If a molecule of one of these compounds enters the

Possibility of atmospheric pressure glow discharge in air

The atmospheric pressure discharge in an air gap between two dielectric barrier electrodes has been studied experimentally and the development of an electron avalanche in such an air gap was simulated numerically. The results show that, while it is possible to obtain glow discharge in an air gap not longer than 2 mm, the streamer discharge could only be obtained in an air gap longer than 5 mm if no methods could be used to lower the electric field when discharging. The "iontrapping mechanism", which was said to be responsible for the atmospheric pressure glow discharge, was not verified in the experiments.

Fluorescence properties and staining behavior of monodansylpentane, a structural homologue of the lysosomotropic agent monodansylcadaverine.

We have recently shown that monodansylcadaverine labels autophagic vacuoles. Analysis of the mechanism underlying the labeling revealed that monodansylcadaverine acts as a lysosomotropic agent, being concentrated into acidic compartments by an ion-trapping mechanism, and as a solvent polarity probe, increasing its relative fluorescence intensity by interacting with membrane lipids that are highly concentrated in the autophagic vacuoles. In this study, we synthesized three structurally related derivatives of monodansylcadaverine, replacing the primary amino group of monodansylcadaverine with a neutral (dansylamylamine; MDH), a polar (dansylaminopentanol; MDOH), or an acidic group (dansylaminovaleric acid; MDA), to replace the lysosomotropic character of the marker. Whereas MDH showed a specific staining of autophagic vacuoles, the polar and acidic derivatives did not show any staining. We further demonstrate that the MDH staining of autophagic vacuoles is independent on the acidic pH and thus on an ion-trapping mechanism, but it still shows the same preferences for autophagic membrane lipids as monodansylcadaverine. We propose that MDH can specifically interact with lamellar bodies of the autophagic type as a solvent polarity probe. Therefore, dansylated aminopentane can be used as a specific marker for autophagic vacuoles in vivo and in fixed cells.(J Histochem Cytochem 49:177-185, 2001)

Transport, cytoplasmic accumulation and mechanism of action of the toxin eutypine in Vitis vinifera cells

The mechanism of the toxic action of eutypine, 4-hydroxy-3-(3-methyl-3-butene-l-ynyl) benzaldehyde, a toxin produced by the fungus Eutypa lata , the agent of dying arm disease of the grapevine, was investigated with cell suspension cultures of Vitis vinifera cv. Gamay and l4 C-labelled eutypine. The study of the chemical characteristics of eutypine revealed that the toxin is a weak acid (pKa = 6.2), which also has a lipophilic character (water/octanol partition coefficient of 86). Eutypine was rapidly taken up by the cells and accumulated against a concentration gradient. Uptake showed no saturation at high eutypine concentration, and neither structural analogues of eutypine nor protein modifying reagents had an inhibitory effect on eutypine uptake. These data suggest a mechanism of passive diffusion for eutypine uptake. The eutypine accumulation observed in cells can be pardy explained by an ion trapping mechanism related to the ionization state of the toxin. It has been demonstrated that some eutypine molecules insert into cellular lipids, i.e. cell membranes. Such partition of eutypine in the cells might play a major role in the expression of its toxicity. Eutypine seems to affect the functioning of mitochondria by an uncoupling effect or by inhibiting succinate dehydrogenase activity. These results suggest that eutypine has the same properties as the uncoupling agents that act as mobile proton carriers. The reduction of the energetic charge following eutypine action could explain the symptoms observed in diseased plants.

PH-Dependent sorption, bioconcentration and algal toxicity of sulfonylurea herbicides

Uptake and toxicity of four sulfonylurea herbicides (metsulfuron-methyl, chlorsulfuron, triasulfuron and tribenuron-methyl) to the freshwater microalga Chlorella fusca have been investigated under different pH regimes. Toxicity parameters were inhibition of (a) cell volume growth and (b) reproduction of synchronized cell populations, cultivated under photoautotrophic conditions. At pH 6.5, EC 50 values ranged from 3.2 (metsulfuron-methyl) to 0.3 μmol/l (tribenuron-methyl) for the inhibition of cell volume growth, and from 2.2 to 0.2 μmol/l for the inhibition of cell reproduction. By lowering the pH of the growth medium to 5.0, the toxicity of chlorsulfuron was enhanced 25-fold, as indicated by an EC 50 value of 44.0 nmol/l for the inhibition of reproduction. The bioconcentration of the four sulfonylureas in Chlorella did not exceed a factor of 9 at pH 6.0, but was significantly increased at pH 5.0, with a maximum value of 53 for chlorsulfuron. These results suggest that the sulfonylureas penetrate the algal cell membranes primarily in their undissociated form and accumulate by an ion trapping mechanism.

Mechanisms of Herbicide Absorption Across Plant Membranes and Accumulation in Plant Cells

In most cases, a herbicide must traverse the cell wall, the plasma membrane, and organellar membranes of a plant cell to reach its site of action where accumulation causes phytotoxicity. The physicochemical characteristics of the herbicide molecule including lipophilicity and acidity, the plant cell membranes, and the electrochemical potential in the plant cell control herbicide absorption and accumulation. Most herbicides move across plant membranes via nonfacilitated diffusion because the membrane's lipid bilayer is permeable to neutral, lipophilic xenobiotics. Passive absorption of lipophilic, ionic herbicides or weak acids can be mediated by an ion-trapping mechanism where the less lipophilic, anionic form accumulates in alkaline compartments of the plant cell. A model that includes the pH and electrical gradients across plant cell membranes better predicts accumulation concentrations in plant cells of weak acid herbicides compared to a model that uses pH only. Herbicides also may accumulate in plant cells by conversion to nonphytotoxic metabolites, binding to cellular constituents, or partitioning into lipids. Evidence exists for herbicide transport across cell membranes via carrier-mediated processes where herbicide accumulation is energy dependent; absorption is saturable and slowed by metabolic inhibitors and compounds of similar structure.

Uptake and Accumulation of the Herbicide Bentazon by Cultured Plant Cells

Cellular absorption of the herbicide bentazon, a weak acid with pK(a) 3.45, was investigated using suspension-cultured cells of velvetleaf (Abutilon theophrasti Medic.). Bentazon accumulated rapidly to concentrations approximately four times that of the external medium. Bentazon accumulation against a concentration gradient was not due to its conversion to metabolites, partitioning into lipids, or binding onto cellular constituents. Bentazon uptake was related linearly to the external bentazon concentration, implying that movement of the herbicide into cells was not carrier-mediated. Bentazon was able to diffuse freely and extensively out of the cells, indicating that bentazon can readily diffuse across cell membranes. Potassium cyanide and carbonyl cyanide m-chlorophenyl hydrazone inhibited bentazon accumulation as did nitrogen gas when bubbled through the uptake medium. Absorption was pH-dependent with the greatest amount of bentazon accumulating at acidic external pH. Calculations indicated that conversion of uncharged bentazon to bentazon anion in the cytoplasm accounts for cellular accumulation of bentazon. These results provide evidence that bentazon is absorbed across membranes via simple diffusion and that bentazon accumulates in plant cells via an energy-dependent, ion-trapping mechanism which results in bentazon accumulation in the cytoplasm.

Transport of Xenobiotics in Higher Plants I. Structural Prerequisites for Translocation in the Phloem

Summary The correlation between the mobility of xenobiotics in the phloem and their chemical structure was investigated using the following substances: phloem-mobile 2,4-D, xylem-mobile 2,4-dichloro-anisole derived from the elimination of the carboxyl group, xylem-mobile defenuron and atrazine, and their ambimobile derivatives N-(p-carboxyphenyl)-N′-methylurea, phenylureidoacetic acid and 2-chloro-4,6-bis-( β -alanino)-l,3,5-triazine. Mobility was characterized quantitatively by the translocation rates and the translocation quotient Q tr . The Q tr was determined by the Sinapis test exhibiting the ratio of mobility in phloem following leaf application and mobility in xylem following root application. Analysis of exudates from detached Yucca inflorescence stalks revealed the presence of phloem- and ambimobile compounds without any metabolic conversions in the phloem sap exclusively. The partition coefficients of substances mobile in the phloem were higher at p H 8 than at p H 5. The corresponding coefficients of xylem-mobile chemicals were of the same value. These results suggest that xenobiotics enter the sieve element-companion cell complex by diffusion. Phloem- and ambimobile compounds are accumulated by an ion trapping mechanism causing their retention in the sieve tube and preventing a complete escape along the path. Consequently, acidic compounds with pK a lower than 7 are expected to be phloem- or ambimobile.