Different Concentrations Of Cations Research Articles

Comparative study on effects of pH, electrolytes, and humic acid on the stability of acetic and polyacrylic acid coated magnetite nanoparticles

The poor colloidal stability of magnetite nanoparticles (MNPs) limits their mobility and application, so various organic coatings (OCs) were applied to MNPs. Here, a comparative study on the colloidal stability of MNPs coated with acetic (HAc) and polyacrylic acids (PAA) was conducted under varied pH (5.0–9.0) in the presence of different concentrations of cations and anions, as well as humic acid (HA). Comparing the effects of various cations and anions, the stability of both HAc/PAA-MNPs followed the order: Na+ > Ca2+and PO43− > SO42− > Cl−, which could be explained by their adsorption behaviors onto HAc/PAA-MNPs and the resulting surface charge changes. Under all conditions even with more anion adsorption onto HAc-MNPs (0.14–22.56 mg/g) than onto PAA-MNPs (0.04–18.34 mg/g), PAA-MNPs were more negatively charged than HAc-MNPs, as PAA has a lower pHIEP (2.6 ± 0.1) than that of HAc (3.7 ± 0.1). Neither the HAc nor PAA coatings were displaced by phosphate even at considerably high phosphate concentration. Compared with HAc-MNPs, the stability of PAA-MNPs was greatly improved under all studied conditions, which could be due to both stronger electrostatic and additional steric repulsion forces among PAA-MNPs. Besides, under all conditions, Derjaguin-Landau-Verwey-Overbeek (DLVO) explained well the aggregation kinetic of HAc-MNPs; while extended DLVO (EDLVO) successfully predict that of PAA-MNPs, indicating steric forces among PAA-MNPs. The aggregation of HAc/PAA-MNPs was all inhibited in varied electrolyte solutions by HA (2 mg C/L) addition. This study suggested that carboxyl coatings with higher molecular weights and pKa values could stabilize MNPs better due to stronger electrostatic and additional steric repulsion. However, in the presence of HA, these two forces were mainly controlled by adsorbed HA instead of the organic pre-coatings on MNPs.

Mammea A/AA (MA) potency as ratiometric absorbance based molecular probe: Cations detection and quantification ability

MA is a phenyl coumarin extracted from the bark of the stem of Mammea Africana. This compound exhibits two absorption peaks in the region between 300 and 550 nm, whose relative wavelength positions, their absolute absorbances and the ratio of their absorbances depend on the molecular environment. In this work, this property was exploited for the first time to detect and quantify metal ions in aqueous solution. Alkali (Mg2+, Na+, Ca2+, K+), transition (Zn2+, Fe2+, Co2+, Cu2+) and heavy (Hg2+, Pb2+, Sn2+) metal ions were considered. We found that the MA spectroscopic response depends on the nature and class of the cations in solution, indicating a binding interaction. Our method applied to the detection and quantification of cations in different mineral waters, allowed us to obtain the concentrations of different cations with good accuracy. A theoretical calculation using DFT methods provided the geometrical structures of the organometallic complexes, which revealed that the metal ions are chelated by MA at the carbonyl site of the coumarin moiety. In addition, calculation of electronic transitions by TDDFT as well as analysis of MOs showed that the photophysics of complexes involving MA and a metal cation is governed by intra-ligand, ligand-to-metal and metal-to-ligand electron transfer.

Effects of Ion Characteristics on the Leaching of Weathered Crust Elution-Deposited Rare Earth Ore.

To reveal the ion-exchange mechanism in the leaching process of weathered crust elution-deposited rare earth ores with different leaching agents, the effects of a variety of cations and anions at different concentrations on the leaching process were investigated, including Al3+, Fe3+, Ca2+, Mg2+, Na+, K+, and Cl−, , and . Meanwhile, the relationships between different concentrations of cations and anions and leaching efficiency were investigated, as was the relationship between different concentrations of cations and anions and zeta potential. The effect of different ions on the swelling of clay minerals during leaching process was also investigated. The results shown that was the most affected electrolyte cation in terms of rare earth leaching efficiency during the leaching process of weathered crust elution-deposited rare earth ore among three different cationic valence states, and the leaching efficiency was 86.93% at the optimal leaching concentration. The influence of the three anions on the leaching efficiency of rare earth was , and the leaching efficiency of rare earth were 83.21, 81.52, and 80.12% at the optimal leaching concentration, respectively. The had the greatest effect on the zeta potential of weathered crust elution-deposited rare earth ore, and the zeta potential was −18.1 mV at the optimal leaching concentration. Additionally, the order of the effect of three anions on zeta potential was . Combined with the effect on the rare earth leaching process, anions and cations were considered separately, and and Cl− were selected; the relationship between the rare earth leaching efficiency and zeta potential conforms to the follow equations: :Y = −0.48X2 – 13.51X – 1.58, R2 = 0.98133 and Cl−:Y= −1.22X2 – 17.64X + 23.29, R2 = 0.99010. It was also found in the swelling experiment of the weathered crust elution-deposited rare earth ore that the swelling ratio of clay minerals was the lowest when the cation and anion were and Cl− and the swelling ratios were 1.874 and 2.015%, respectively.

Effects of cationic concentration on controlling the interlayer spacings for highly effective ion rejection via graphene oxide membranes.

The effect of cationic concentration on controlling the interlayer spacings of graphene oxide (GO) membranes is systemically studied. It was found that a higher concentration leads to narrower interlayer spacings, and thus, ions in salt solutions were effectively rejected. This provides a new avenue for ion separation using graphene-based membranes.

Enhanced performance triboelectric nanogenerators based on solid polymer electrolytes with different concentrations of cations

Triboelectric nanogenerators (TENGs), as a promising energy harvesting technology, have attracted considerable attention and various approaches have been developed to improve their output performance. An innovative strategy was proposed recently by using solid polymer electrolyte (SPE) with asymmetric pairing ions as the friction layer, showing excellent potential to achieve high-performance TENGs. However, it is far from clear what are the effects of SPE on TENG performance as only one electrolyte, CaCl2, was used for the investigation. Herein, PTFE/PVA-MClx TENGs based on SPEs with different types of electrolytes, including LiCl, ZnCl2, CaCl2, FeCl3, and AlCl3, were fabricated and their performances were investigated. All the devices demonstrated superior output performance than that of the control PTFE/PVA TENG. Specifically, the PTFE/PVA-LiCl TENG exhibited remarkably enhanced triboelectric performance with an output voltage of ~1345 V, a short-circuit current density of ~260 mA m−2 and a maximum power density of ~83 W m−2, four times higher than that of the control PTFE/PVA TENG. Detailed investigations revealed that in combination with improved triboelectric property, the enhanced interaction of SPEs with opposite triboelectric layers further significantly boost the triboelectric outputs. This work presents a new method to increase the interaction between triboelectric layers to effectively improve the outputs of TENGs, and to facilitate the development of high performance TENGs.

Electrolyte effects in a model of proton discharge on charged electrodes

Abstract We report results on the influence of NaCl electrolyte dissolved in water on proton discharge reactions from aqueous solution to charged platinum electrodes. We have extended a recently developed combined proton transfer/proton discharge model on the basis of empirical valence bond theory to include NaCl solutions with several different concentrations of cations and anions, both stoichiometric (1:1) compositions and non-stoichiometric ones with an excess of cations. The latter solutions partially screen the electrostatic potential from the surface charge of the negatively charged electrode. 500–1000 trajectories of a discharging proton were integrated by molecular dynamics simulations until discharge occurred, or for at most 1.5 ns. The results show a strong dependence on ionic strength, but only a weak dependence on the screening behavior, when comparing stoichiometric and non-stoichiometric solutions. Overall, the Na + cations exert a more dominant effect on the discharge reaction, which we argue is likely due to the very rigid arrangements of the cations on the negatively polarized electrode surface. Thus, our model predicts, for the given and very high negative surface charge densities, the fastest discharge reaction for pure water, but obviously cannot take into account the fact that such high charge densities are even more out of reach experimentally than for higher electrolyte concentrations.

Geographical characterisation of honeys according to their mineral content and antioxidant activity using a chemometric approach

SummaryIn this article, discrimination models are presented, relating the origin of honey samples to several variables, being the concentrations of different cations and anions in the honey samples measured by ion chromatography, and parameters that measure/reflect the antioxidant activity of the honey samples. The unsupervised method, principal component analysis, and supervised discrimination methods, such as linear and quadratic discriminant analysis, and classification and regression trees (CART), were applied to evaluate the existence of data patterns and the relationship between geographical origin and the measured parameters. The model with the best predictive ability (%CCRTEST = 66.67%), the best overall % specificity (80%) and the best overall % sensitivity (67%) was found to be CART. It was proven that the mineral content and parameters analysed can provide enough information for the geographical characterisation and discrimination of honey.

Magnesium hydroxide, seawater and olive mill wastewater to reduce swelling potential and plasticity of bentonite soil

The improvement in physical properties of expansive soils after addition of non-conventional additives is studied. The tested agents were magnesium hydroxide, seawater and olive mill wastewater. The use of these materials, which can be obtained from natural sources or as by-products derived from industrial processes, can lead to greater sustainability of the construction process. In the case of olive mill wastewater, its management is still an issue in many regions where production of olive oil is a main economic activity. The untreated soil used was a sample of pure bentonite. To evaluate the effects of the additives, the physical properties of the soil such as compaction, consistency, bearing capacity and swelling pressure were studied. The mineral compositions of the treated soils were evaluated by XRD tests. Test results showed that the non-conventional additives tested reduced the plasticity and the swelling potential of the soil. Indeed the tested agents proved to be very effective to produce reductions in the swelling pressure of 60–87% in comparison with the original swelling pressure of the untreated bentonite. X-ray diffraction tests proved that magnesium hydroxide, seawater and olive mill wastewater promoted mineral changes within bentonite, especially smectite to illite conversion. This conversion is due to the alterations promoted by the additives on conditions such as pH and concentration of different cations (magnesium, calcium, potassium, etc.) The mineral modifications occurred are behind the sharp reductions in swelling pressure and plasticity of bentonite.

Divalent Cations in Tears, and Their Influence on Tear Film Stability in Humans and Rabbits

Reduced tear film stability is reported to contribute to dry eye. Rabbits are known to have a more stable tear film than humans. Thus, we sought to examine the tears of rabbits and humans for metal cations, and to test how they influence tear film stability. Tears were collected from 10 healthy humans and 6 rabbits. Tear osmolality was measured by vapor pressure osmometer, and metals analyzed using inductively coupled plasma (ICP) mass spectrometry or ICP atomic emission spectroscopy. The influence of divalent cations on tears was analyzed by measuring surface tension using the Langmuir trough in vitro, using different concentrations of cations in the subphase, and grading the tear break-up in rabbits in vivo after instillation of chelating agents. Rabbit tears had a higher osmolality compared to humans. Major metals did not differ between species; however, rabbits had higher levels of Mg(2+) (1.13 vs. 0.39 mM) and Ca(2+) (0.75 vs. 0.36 mM). In rabbit tears in vitro, diminishing divalent cations resulted in a decrease in the maximum surface pressure from 37 to 30 mN/m. In vivo, an increase in the amount of tear film that was broken-up was found. In contrast, when changing divalent cation concentrations in human tears, the maximum surface pressure remained at 26 mN/m. The normal osmolality of rabbit tears is significantly higher than that in humans. While divalent cations had little influence on human tears, they appear to have an important role in maintaining tear film stability in rabbits.

The effect of different valency cations on DMFC performance

An in situ study of the effects of Na +, Mg 2+ and Cr 3+ on direct methanol fuel cell (DMFC) performance is reported. The result showed that dramatic decrease of the cell voltage was mainly ascribed to the increase of the cathode overpotential. Meanwhile, the different contamination effects by introducing Na +, Mg 2+ and Cr 3+ to the anode and the cathode were compared. When the same molar concentration of different cations was added to the anode feed, the contamination effect on the cell performance followed the order of Na + > Mg 2+ > Cr 3+. Owing to the fast transfer speed and the low affinity to the sulfonic acid groups in the ionomer phase, the low-valent cations may cause much more proton losses than the high-valent cations in the cathode catalyst layer (CCL) within the same time. So the low-valent cations led to the higher cathode overpotential than the high-valent cations. When the same molar concentration of cations was directly added to the CCL, the contamination effects on the cell voltage showed an opposite trend which is Na + < Mg 2+ < Cr 3+. This is presumably because a high-valent cation can exchange more protons than a low-valent cation in the CCL.

Photoconductivity of Hf-based binary metal oxide systems

To explore the possibility of bandgap engineering in binary systems of oxide insulators we studied photoconductivity of nanometer-thin Hf oxide layers containing different concentrations of cations of different sorts (Si, Al, Sr, or Ce) deposited on (100)Si. The lowest bandgap of the Hf:Al oxide is close to the value 6–6.2 eV of elemental amorphous Al2O3 and insensitive to the Al content for concentrations of Al exceeding 36%. This result suggests that the Al oxide subnetwork with the largest bandgap preserves this energy width while development of a narrower gap of HfO2 is prevented possibly by dilution of the second cation subnetwork. When Ce is admixed to HfO2 an intermediate bandgap value (between the CeO2 and HfO2 bandgap widths) of 5.3+0.1 eV is observed for all concentrations of Ce, suggesting that the electronic structure of both elemental oxide subnetworks which form the binary metal oxide system, is affected. In Hf:Si oxide samples photoconductivity thresholds of 5.6–5.9 eV corresponding to the bandgap of HfO2 are observed for all studied Si concentrations, suggesting phase separation to occur. The photoconductivity of SrHfO3 exhibits two thresholds at 4.4 and 5.7 eV, which are close to the bandgaps of elemental SrO and HfO2, respectively, indicating, again, phase separation. Through this work we have illustrated photoconductivity as a feasible method to trace phase separation in nanometer-thin layers of binary systems of metal oxides.

Investigation of Interaction of Fluoroquinolones with Aluminum, Iron and Magnesium ions Using Capillary Zone Eletrophoresis

The present study describes the application of capillary zone electrophoresis (CZE) to investigate interactions between ciprofloxacin, enrofloxacin, lomefloxacin, levofloxacin, ofloxacin, norfloxacin and sparfloxacin—antimicrobial drugs called fluoroqinolones, and polyvalent metal ions (Mg2+, Fe3+ and Al3+), commonly used in daily medicine practice as components of multi-mineral and antacida drugs. It was observed that polyvalent metal ions exhibit strong interactions with these drugs. The strength of these interactions depends on the metal ion, the molecular structure of the fluoroquinolone, and the pH which is very important for the investigations of complex formations. Two different pH values, 3.25 and 8.02, were utilized in this study. Addition of fluoroquinolone to background electrolyte and injection of samples consisting of different concentrations of cations allowed to observe changes in peak area depending on the concentration of the metal ion. A mathematical model for quantitative evaluation of the complex formation constant K was used. Our investigation shows new possibilities of quantitative characterization of the interactions between fluoroquinolones and metal ions using CZE. Such investigations were not described so far in the literature.

Temporal variation in the surface‐water chemistry of a blanket bog on Dartmoor, southwest England: analysis of 5 years' data

SummaryBlanket‐bog peats, mapped as the Winter Hill and Crowdy associations by the Soil Survey of England and Wales, are an oceanic manifestation of the ombrotrophic ‘raised‐bog’ (Hochmoor) peats that cover large tracts in the boreal zone of the northern hemisphere. This paper examines monthly analyses from 1992 to 1997 of major ions and other variables from an upland blanket bog in southwest England in relation to seasonality, rainfall, and the chemical composition of rainwater. Average ionic composition of surface water (and peat) integrates variable atmospheric solute inputs over the years. The dominant ions in the surface water, Na+ and Cl–, showed only weak seasonality, but divalent cations a stronger seasonal pattern with a summer maximum. Mean pH ranged from c. 4.4 in February to c. 4.2 in August. Changes in concentration of different cations were closely interlinked by cation exchange. The anion deficit, accounted for by anionic groups on the dissolved organic matter, was strongly seasonal with a summer maximum, as was optical absorbance at 320 nm. Nitrate and NH4+ were both at much smaller concentrations than in rain. Nitrate exceeded 1 μmol l−1 only during cold periods in winter, mainly following drought in the summer of 1995; NH4+ reached a few μmol l−1 only in summer. There was evidence of net retention of S by the peat in wet sites and during wet periods, and of net release of SO42– (and acidity) under dry conditions. The 1995 summer drought and ensuing dry year in 1996 had marked and persistent effects on pH, apparent ion deficit (DEF), SO42–, the divalent cations and Fe.

Inhibition kinetics of human serum butyrylcholinesterase by Cd 2+, Zn 2+ and Al 3+: comparison of the effects of metal ions on cholinesterases

Butyrylcholinesterase (BChE, EC 3.1.1.8) has been purified about 6600-fold from human serum with a procedure including ammonium sulfate fractionation (55–70%) with acid step at pH 4.5 and procainamide–Sepharose 4B affinity chromatography. The purified enzyme exhibited negative cooperativity with respect to butyrylthiocholine (BTCh) binding at pH 7.5. K S was found to be 0.128±0.012 mM. Inhibition kinetics of the enzyme by Cd 2+, Zn 2+ and Al 3+ were studied in detail. The 1/ v vs 1/[BTCh] plots in the absence (control plot) and in the presence of different concentrations of cations intersected above 1/[BTCh]-axis. The data were analyzed by means of a nonlinear curve fitting program. The results demonstrated that all of the three cations are the linear mixed-type inhibitors of BChE. Ca 2+ and Mg 2+ had no effect on the enzyme activity in the experimental conditions. But when the enzyme was inhibited by 0.5 mM Cd 2+ or Zn 2+, Ca 2+ and Mg 2+ partially reactivated the inhibited allosteric form of BChE. Results were compared with data obtained from brain BChE purified from sheep.

The synergistic inhibition effect and thermodynamic properties of 2-mercaptobenzimidazol and some selected cations as a mixed inhibitor for pickling of mild steel in acid solution

The effect of some selected metal cations, viz., Na +, Al 3+ and Zn 2+ on the corrosion of mild steel in 1 M sulphuric acid solution containing a thiol called 2-mercaptobenzimidazol, has been studied by potentiodynamic polarization technique, over the temperature range 30 to 50 °C. The efficiency of mixed inhibitor was tested for different concentrations of cations ranged from 10 −6 to 10 −3 M. It was found that the presence of metal cations together with the thiol in the corrosive medium increases the inhibition efficiency at all the concentrations and temperatures studied. The decrease in corrosion current was associated with the positive shift in the corrosion potential, in the presence of investigated cations. This denotes that inhibition was found to be predominantly anodic and following the Langmiur adsorption isotherm over the wide concentration range of metal cations. The activation energy and thermodynamic parameters were calculated at different temperatures.

Direct electrochemistry of the enzyme, methylamine dehydrogenase, from bacterium W3A1

The electrochemical response of methylamine dehydrogenase from bacterium W3A1 at edge-plane-oriented pyrolytic graphite (epg) and modified gold electrodes has been investigated. Quasi-reversible electron transfer has been observed. Variations in concentration of different cations and anions gave rise to both promotion and inhibition of the direct response. A catalytic response of the enzyme in the presence of methylamine has been observed at both an epg electrode and a 2,2'-dithiodiglycolic-acid-modified gold electrode surface, and the effects of various cations and anions on the catalytic peak current have been investigated. The spectroelectrochemical results obtained at an optically transparent thin-layer electrode, modified with 2,2'-dithiodiglycolic acid, are also reported. In the presence of 1,1'-dimethylferrocene-3-(1-ethanol-2-amine) (14.8 microM), the results reveal a midpoint potential of -148 mV for methylamine dehydrogenase from bacterium W3A1. This is in very close agreement to the value obtained in the cyclic voltammetric investigations of -140 mV.

Der Einfluß monovalenter Kationen auf die Nitratreduktion von Spinacia oleracea L.

Summary Experiments were carried out to determine the influence of different univalent cations on the activity of nitrate reductase from spinach in vitro and in vivo. Nitrate reductase activity was maximal at pH 7.75 and 28°C. Under these conditions the alkali ions Li+, Na+, K+ and Rb+ had no different effect on the activity of the enzyme in vitro. In further investigations it could be shown that monovalent cations had clearly different effects on the activity of nitrate reductase in vivo. In order to get better results of the cations plant material of a low salt status was used. Compared to the control K+ induced, after a lag phase of 3 h, a remarkable increase in the rates of nitrate reduction. Rb+ had a stimulating effect, too, but was less effective. Na+ and Li+ were without effect. These differences are not attributable to different concentrations of cations within the cell. For example, under the conditions used for estimating the activity of the enzyme (50 mM K+, or Na+ respectively), the rate of uptake into the leaf tissue was similar for K+ and Na+. The investigations show that the inductive formation of nitrate reductase caused by nitrate depends on the presence of certain cations, i.e. under natural conditions there is a strict requirement for K+.

Biochemical and morphological characteristics of arterial actomyosin

An active preparation of natural actomyosin was extracted from eanine arteries in solutions of low ionic strength containing ATP. In this solution, arterial actomyosin appeared by electron microscopy to dissociate into thick filaments corresponding to myosin and thin filaments corresponding to F-actin. In a high ionic strength solution without ATP, electronmicrographs of arterial actomyosin showed an “arrow-head” filamentous structure which also has been described for skeletal actomyosin (myosin B). The actomyosin preparation also had many of the biochemical characteristics reported for skeletal actomyosin including the ability to hydrolyze ATP, undergo superprecipitation (contraction), and respond to the changes in the concentration of free Ca 2+. The concentration of ATP had a noticeable effect on the superprecipitation (contraction) and clearing (relaxation) of arterial actomyosin with relatively low concentrations promoting superprecipitation and high concentrations promoting clearing. Varying concentrations of Na + and K + also influenced the superprecipitation with the partial replacement of K + by equimolar concentrations of Na + resulting in an enhanced superprecipitation of arterial actomyosin. The present study could provide an explanation for the manner in which changes in intracellular concentrations of different cations and ATP alter the contractile function of the arteries.

The significance of ionic concentrations in the internal media of animals.

Summary1. The electrical and ionic gradients across a cell membrane depend on its permeability properties, on the concentration and net valency of the organic constituents of the cytoplasm and on the critical energy barrier to the extrusion of sodium. Such considerations do not, however, explain the small extent to which the concentration of potassium varies in myoplasm which may, instead, be related to the effects of potassium on particular enzymes.2. The fact that the apparent optimum level of potassium cannot usually be maintained in animals in which the extracellular level of sodium is below about 140 mM may explain why so many non‐marine animals have internal media of about that concentration, for more concentrated body fluids would require more work for their regulation.3. In axoplasm, the concentration of potassium is more nearly proportional to the concentration of sodium in the internal medium and this may partly explain the general correlation between the extracellular levels of sodium and potassium.4. The relation between pH and temperature in poikilothermic vertebrates is such as to suggest that the prime function of acid‐base regulation is to control the ionization of imidazole groups.5. High tensions of carbon dioxide cannot be maintained in water‐breathing animals because of the high solubility of this gas in water as compared with oxygen. Bicarbonate levels are correspondingly low to give a suitable pH. Higher tensions are possible in air‐breathing animals, and also necessary if water and heat are to be conserved, but an uncertain upper limit is set by the need for oxygen. The associated higher levels of bicarbonate confer the advantage of better buffering.6. Calcium and bicarbonate levels are not obviously limited by the solubility of calcium carbonate and a more general limitation on the composition of body fluids seems to arise from the low solubilities of calcium phosphates.7. The pattern of ionic balance in vertebrate plasma, reflected in a nearly constant value to the molar ratio ([Ca] + 5 × 10‐‐4)/([K] +0.034 [Na]), may be explained in terms of the maintenance of a constant electrical gradient across certain areas of cell membrane, between the inner and outer double layers.8. The patterns of cation balance in the haemolymphs of molluscs, crustacea and insects are also reviewed, with emphasis on the correlations existing between the concentrations of different cations. An attempt is made to relate the correlations in the mollusca to the concentrations of cations at the surfaces of cells.

Possible screening of surface charges on crayfish axons by polyvalent metal ions.

1. The effect of different polyvalent metal ions in the external solution upon the threshold membrane potential for spike initiation in crayfish axons has been studied by means of intracellular micro-electrodes. The metal ions tested included six divalent cations (Ca(2+), Mg(2+), Sr(2+), Ba(2+), Co(2+), and Ni(2+)) and three trivalent cations (La(3+), Y(3+) and Eu(3+)).2. Identical extracellular concentrations of different cations with the same valence had essentially the same effect on threshold membrane potential. However, a very low concentration of trivalent cations (about 225 muM) was found to be equivalent to a much higher divalent cation concentration (13.5 mM) as measured by their effects on threshold potential.3. Upon a tenfold increase in concentration, the threshold potential for spike initiation was shifted in a positive direction by 30.6 mV with divalent cations and by 20.8 mV with trivalent cations.4. It is shown that a hypothesis involving screening of negative charges at the axonal membrane surface, based on Gouy-Chapman theory, predicts these various experimental results rather closely.5. It is concluded that a high negative charge density, sufficient to render a screening mechanism possible, exists at the surface of crayfish axons in the region of the sodium ;gates'.6. The density of surface charges is calculated to be approximately 1e(-)/43 A(2). This calculation is discussed in connexion with the possible molecular identity of the sodium ;gates' in crayfish axons and other excitable systems.