Electrostatic Surface Properties Research Articles

Electrostatic Changes in Lycopersicon esculentum Root Plasma Membrane Resulting from Salt Stress

Salinity-induced alterations in tomato (Lypersicon esculentum Mill. cv Heinz 1350) root plasma membrane properties were studied and characterized using a membrane vesicle system. Equivalent rates of MgATP-dependent H(+)-transport activity were measured by quinacrine fluorescence (DeltapH) in plasma membrane vesicles isolated from control or salt-stressed (75 millimolar salt) tomato roots. However, when bis-[3-phenyl-5-oxoisoxazol-4-yl] pentamethine was used to measure MgATP-dependent membrane potential (DeltaPsi) formation, salt-stressed vesicles displayed a 50% greater initial quench rate and a 30% greater steady state quench than control vesicles. This differential probe response suggested a difference in surface properties between control and salt-stressed membranes. Fluorescence titration of vesicles with the surface potential probe, 8-anilino-1-napthalenesulphonic acid (ANS) provided dissociation constants (K(d)) of 120 and 76 micromolar for dye binding to control and salt-stressed vesicles, respectively. Membrane surface potentials (Psi(o)) of-26.0 and -13.7 millivolts were calculated for control and salt-stressed membrane vesicles from the measured K(d) values and the calculated intrinsic affinity constant, K(i). The concentration of cations and anions at the surface of control and salt-stressed membranes was estimated using Psi(o) values and the Boltzmann equation. The observed difference in membrane surface electrostatic properties was consistent with the measured differences in K(+)-stimulated kinetics of ATPase activity between control and salt-stressed vesicles and by the differential ability of Cl(-) ions to stimulate H(+)-transport activity. Salinity-induced changes in plasma membrane electrostatic properties may influence ion transport across the plasma membrane.

Modification of polyvinyl chloride surface electrostatic properties by an ion beam

When polyvinyl chloride (PVC) is irradiated by an ion beam, at medium doses of 150 keV Ar + ions, the surface electrostatic properties of this polymer are dramatically changed. The triboelectrostatic charge can be decreased from 1.24 to 0.02 nC cm −2 or less and the electrostatic potential decreases from 800–1000 to 0–50 V. The charge time constant decreases from a few hours to less than 1 s and the surface resistivity drops by four orders of magnitude. New anti-static materials may be produced.

Comparison of the properties of plasmalemma vesicles purified from wheat roots by phase partitioning and by discontinuous sucrose gradient centrifugation

Plasmalemma vesicles were purified from 7‐day‐old wheat (Triticum aestivum L. cv. Drabant) roots by a) discontinuous sucrose gradient (SG), b) aqueous polymer two‐phase partitioning (PP) and c) SG followed by PP (SG + PP). SG‐purified plasmalemma preparations were 2‐3 fold more contaminated with mitochondria (cytochrome c oxidase, EC 1.9.3.1) when compared to PP and (SG + PP)‐purified plasmalemma. The electrostatic surface properties, as measured by 9‐aminoacridine fluorescence, were similar in PP and (SG + PP)‐purified plasmalemma and different from SG‐purified. The latency of the MG‐ATPase measured with Triton X‐100 was 51, 81 and 82% for SG‐, PP‐ and (SG + PP)‐purified plasmalemma vesicles, respectively. The higher latency of the ATPase (and lower specific activity in the absence of Triton X‐100) in PP‐purified and (SG + PP)‐purified preparations was not due to an effect of PEG, since exposure of SG‐purified preparations to PEG either in the wash medium or in the ATPase assay medium did not change ATPase activity. It is concluded that SG‐purified plasmalemma vesicles are more contaminated than PP‐purified preparations and that the former are likely to be leaky. They are, therefore, less suitable for use in studies of transport across the plasmalemma.

Activated Charcoal Reborn

In the JanuaryArchives, Curtis et al 1 , described their study of the efficacy of ipecac alone v activated charcoal plus a cathartic v the three together in the treatment of a simulated aspirin tablet overdose. They accounted for 70% of the ingested aspirin dose in the urine of patients following a standard ipecac regimen, compared with 56% in patients receiving activated charcoal. Their results provided another piece of impressive evidence for the efficacy of activated charcoal in treating the overdose patient. The fine, black, fluffy powder of activated charcoal used as an antidote since the 19th century results from the destructive distillation of organic materials, usually wood pulp. Following activation with steam or strong acid, activated charcoal's surface area (1,000 sq m/mL) and electrostatic properties favor binding with most poisons. CLINICAL EXPERIENCE Linden et al 2 reported on the use of repeated doses of activated charcoal in treating 11

Electrostatic surface properties of plasmalemma vesicles from oat and wheat roots. Ion binding and screening investigated by 9-aminoacridine fluorescence

Right-side-out and sealed plasmalemma vesicles were isolated from roots of spring wheat (Triticum aestivum L. cv. Drabant) and oat (Avena sativa L. cv. Brighton) by two-phase partition in a medium containing sucrose (0.25 mol l(-1)). Oat root plasmalemma vesicles were discovered to contain a strongly fluorescent compound with an emission maximum at 418 nm. The surface potential of the membranes was monitored by 9-aminoacridine fluorescence and the effect of protein concentration, mannitol versus sucrose, absence of osmoticum, concentrations of salt, and titrations with chelators investigated. It is concluded that i) protein concentrations of less than 50 μg ml(-1) for oat and 100 μg ml(-1) for wheat plasmalemma vesicles should be used to avoid serious problems with non-linearity of response of 9-aminoacridine fluorescence, ii) mannitol can be used instead of sucrose as the osmoticum, iii) the vesicles were ruptured in the absence of osmoticum allowing us to monitor both sides of the membranes, iv) plasmalemma vesicles from oat roots are more negative than vesicles from wheat roots, and v) oat and wheat root plasmalemma vesicles are isolated with about the same amounts of bound Ca(2+) and Mg(2+). These bound divalent cations may not, however, reflect the in-vivo conditions since the tissues were homogenised in the presence of ethylenediaminetetraacetic acid.

A perturbation-variational theory for molecular fluid interphases in the presence of an electric field

The perturbation-variational theory of Tarazona and Navascues is extended to analyse the effect of the presence of an electric field in the interphase. Molecular orientation in the interphase of polar fluids is found at first order. Different electrostatic surface properties have been analysed, including the surface polarizability and surface susceptibility. Numerical results for carbon monoxide are presented.

6.2 In Situ Measurements of Dust

In this colloquium, my colleagues and I have reported on data from both the lunar surface and from interplanetary space. I am going to comment briefly amd individually on each of these disciplines insofar as they pertain to cosmic dust, but first I would preface those comments with a personal philosophy for each of the two stated disciplines. The two philosophies, you will find, are directly opposite. Concerning the lunar surface, one must recognize that it is a relatively unexplored area for in situ measurements. Accordingly, one must be sufficiently flexible and open-minded to include and consider all available experimental evidence and data until a somewhat consistent model of the lunar surface is derived. Further, and in a similar vein, one’s thinking must not be limited to what little we already know about the lunar surface nor to what is known about the Earth’s surface and terrestrial particles -- assuming that lunar particles are similar to Earth particles. Our lunar experimen shows strong evidence for the electrostatic transport of fines, and yet it is difficult to accommodate that phenomenon on the lunar surface in view of associated parameters that have been derived for the lunar surface, and in terms of what we know about the electrostatic surface properties of terrestrial particulates. But the electrostatic surface properties have been determined in the laboratory on terrestrial particles which are known to have vastly different properties from lunar fines. Thus, it becomes importhat to compile and consider all available data during this early exploration.