Showing papers on "Ion published in 1977"

Reconstruction of the action potential of ventricular myocardial fibres

Abstract: 1. A mathematical model of membrane action potentials of mammalian ventricular myocardial fibres is described. The reconstruction model is based as closely as possible on ionic currents which have been measured by the voltage-clamp method.2. Four individual components of ionic current were formulated mathematically in terms of Hodgkin-Huxley type equations. The model incorporates two voltage- and time-dependent inward currents, the excitatory inward sodium current, i(Na), and a secondary or slow inward current, i(s), primarily carried by calcium ions. A time-independent outward potassium current, i(K1), exhibiting inward-going rectification, and a voltage- and time-dependent outward current, i(x1), primarily carried by potassium ions, are further elements of the model.3. The i(Na) is primarily responsible for the rapid upstroke of the action potential, while the other current components determine the configuration of the plateau of the action potential and the re-polarization phase. The relative importance of inactivation of i(s) and of activation of i(x1) for termination of the plateau is evaluated by the model.4. Experimental phenomena like slow recovery of the sodium system from inactivation, frequency dependence of the action potential duration, all-or-nothing re-polarization, membrane oscillations are adequately described by the model.5. Possible inadequacies and shortcomings of the model are discussed.

Dielectric dispersion and dielectric friction in electrolyte solutions. II

Abstract: Presented herein is a thorough investigation of the consequences of coupling ion migration to dielectric relaxation in the solvent. A self‐consistent continuum model is developed from both local (stress tensor) and global (dissipation function) considerations. The friction coefficient of a moving ion is computed in terms of the dimensionless coupling parameter where e is the ion charge, η is the solvent viscosity, e0 and e∞ are the low and high frequency dielectric constants of the solvent, respectively, τD is the Debye dielectric relaxation time of the pure solvent, and R is the ionic radius. For small ions the computed frictional drag is practically independent of ion radius, provided some degree of hydrodynamic slip is allowed at the ion surface. The effect of ion migration on the dielectric relaxation time of the solution is analyzed in detail. It is shown that the Debye–Falkenhagen effect should lead to an increase in the observed relaxation time, while the kinetic ion–solvent coupling introduces one...

Physical chemistry of glass surfaces

Abstract: Six typical problem areas requiring improved understanding of glass surfaces are identified. Results obtained from several surface-analysis instruments show that five types of surfaces are characteristic of a silicate glass at any time in its history. The type of surface is dependent on the environmental history of the glass and may be defined in terms of surface compositional profiles. Several important glass surface topics of current interest are discussed. These include: corrosion mechanisms; mixed-alkali effect; surface passivation with solution ions; protective film formation; the role of CaO, R 2 O/SiO 2 and Al 2 O 3 in glass corrosion; glass surface area to solution volume ratio; relevance of autoclave procedures in durability tests; and bioglass-bone bonding mechanisms.

A global thermospheric model based on mass spectrometer and incoherent scatter data MSIS, 2. Composition

Abstract: Measurements of O, He, and Ar from neutral gas mass spectrometers on four satellites (Ogo 6, San Marco 3, Aeros A, and AEC-C) and inferred oxygen and hydrogen densities from an ion mass spectrometer on AE-C have been combined with a neutral temperature and nitrogen density model to produce a global model of thermospheric composition in terms of inferred variations at 120 km. The data set covers the time period from mid-1969 to mid-1975. The MSIS (mass spectrometer and incoherent scatter data) model is compared with the Ogo 6 model (Hedin et al., 1974). Ar variations at 120 km tend to be in phase with temperature variations and inverse to the He, O, and H variations.

Ionic conductivity in Li3N single crystals

Abstract: Lithium ionic conductivity of Czochralski‐grown Li3N single crystals using electrochemical transport measurements is reported. The highest Li ionic conductivity was found perpendicular to the hexagonal c axis, the anisotropy decreasing from two to one decade between 20 and 200 °C. Ambient Li ionic conductivity parallel to the Li2N planes of the layer structure was found to be σ=10−3 Ω−1 cm−1 with an activation energy of 0.25 eV. These values are comparable with the best data reported for Li β‐alumina single crystals.

Observation of an ionospheric acceleration mechanism producing energetic (keV) ions primarily normal to the geomagnetic field direction

Abstract: O/sup +/ ions with energies of approximately 1 keV have been observed flowing upward out of the ionosphere with a pitch angle distribution having a minimum along the magnetic field direction and maxima in about 130/sup 0/--140/sup 0/ range. The measurements were obtained with an energetic ion mass spectrometer experiment on the satellite 1976-65B at an altitude of about 7600 km in the northern dayside polar cusp. The data are interpreted as resulting from a mechanism which accelerates ambient ionospheric ions in a direction perpendicular to the geomagnetic field.

Separation of sodium and calcium currents in the somatic membrane of mollusc neurones. With an Appendix by Yu A. Shakhovalov

Abstract: 1. Characteristics of the transmembrane ionic currents under controlled changes in ionic composition of extra- and intracellular medium were studied in isolated neurones from the ganglia of molluscs, Helix pomatia, Limnea stagnalis and Planorbis corneus. The neurones were investigated by a new technique which allows for dialysis of their interior and for clamping of the potential at the surface membrane without using micro-electrodes. 2. Replacement of K ions by Tris inside the neurones eliminated the outward K current so that the actual time course of the inward current could be measured. The latter was separated into two additive components, one of which was carried by Na ions and the other one by Ca ions. 3. Both inward currents were unaltered by tetrodotoxin (TTX); however, Ca current could be separately blocked by externally applied Cd ions (Kd = 7·2 × 10−5 M) and by the use of fluoride as an intracellular anion. 4. No reversal of Na inward current could be achieved in neurones dialysed with Na-free solution, indicating the absence of outward current carrying ions through the corresponding channels. With 5 m M-Na inside the cell, the equilibrium potential was close to the value predicted by the Nernst equilibrium. 5. A non-specific outward current could be detected in K-free cells at membrane potentials exceeding 20-40 mV. Its time course was proportional to 1 — exp (—t/τns). Cd ions depressed this current. The presence of the non-specific outward current made an exact measurement of the equilibrium potential for the Ca inward current impossible. 6. The kinetics of Na inward currents could be described by m3h and those of the Ca current by m2h law. The corresponding values for Vm = 0 are: τm(Na) = 1·1 ± 0·5 msec, τm(Ca) = 2·4 ± 1·0 msec, τh(Na) = 7·9 ± 2·0 msec. The inactivation of Ca current included two first-order kinetic processes with τh1 = 50 ± 10 msec and τh = 320 ± 30 msec. 7. The data presented are considered to be a proof of the existence of separate systems of Na and Ca ion-conducting channels in the nerve cell membrane.

A study of the ion selectivity and the kinetic properties of the calcium dependent slow inward current in mammalian cardiac muscle.

Abstract: 1. A voltage-clamp method combining a single surcose gap and two intracellular micro-electrodes was used to measure membrane currents in ventricullar myocardial fibres. 2. The adequacy of the voltage-clamp method is demonstrated by comparing the total current, It, across the gap with the voltage difference, delta V, between the two intracellular micro-electrodes, i.e. another independent way of measuring membrane currents. With both current measurements the slow inward current, Is, shows the same voltage- and time-dependences. 3. The sensitivity of the slow inward current to variation in external Ca and Na concentrations was investigated systematically. The reversal potential of the slow inward current was sensitive to variation of both ion species. 4. From the reversal potential measurements relative permeabilities of the conductance channels of the slow inward current were estimated as PCa/PNa approximately 1/0-01 and PCa/PK approximately 1/0-01 by means of the constant field equation. 5. The activation and inactivation kinetics of the slow inward current were explored in detail and related to the plateau of the action potential.

Correlation between d-band occupancy and crystal structure in the rare earths

Abstract: The rare-earth crystal structure sequence ${\mathrm{hcp}}^{\ensuremath{\rightarrow}}$ Sm-${\mathrm{type}}^{\ensuremath{\rightarrow}}$ double-${\mathrm{hcp}}^{\ensuremath{\rightarrow}}$ fcc observed for decreasing atomic number and increasing pressure is quantitatively correlated with the $d$-band occupancy through the $d$-band energy contribution to the total energy. Self-consistent calculations show that the number of $d$ electrons is very sensitive to the relative size of the ion core. The theory thus accounts for La's anomalous double-hcp structure and the apparent deviations from the electron-per-atom rules exhibited by certain rare-earth Laves phases.

Hemolysis of human erythrocytes by transient electric field

Abstract: Exposure of human erythrocytes, under isotonic conditions, to a high voltage pulse of a few kV/cm leads to total hemolysis of the red cells. Experiments described herein demonstrate that the hemolysis is due to the effect of electric field. Neither the effect of current nor the extent of the rapid Joule-heating to the suspending medium shows a direct correlation with the observed hemolysis. Voltage pulsation of the erythrocyte suspension can induce a transmembrane potential across the cell membrane and, at a critical point, it either opens up or creates pores in the red cells. In isotonic saline the pores are small. They allow passage of potassium and sodium ions but not sucrose and hemoglobin molecules. The pores are larger in low ionic conditions and permit permeation of sucrose molecules, but under no circumstances can hemoglobin leak out as the direct result of the voltage pulse. Kinetic measurements indicate that the hemolysis of the red cells follows a stepwise mechanism: leakage of ions leads to an osmotic imbalance which in turn causes a colloidal hemolysis of the red cells. Other effects of the voltage pulsation are also discussed.

Theoretical study of inner-shell alignment of atoms in electron impact ionisation: angular distribution and polarisation of X-rays and Auger electrons

Abstract: The alignment of ions with an inner-shell vacancy resulting from ionisation by a fast charged particle is considered. The alignment has been calculated in the Born approximation using the Herman-Skillman model. The angular distribution and polarisation of characteristic X-radiation and Auger electrons from decay of aligned ions are discussed. It is shown that the theoretical anisotropy of the angular distribution is sensitive to the wavefunctions used. The results of calculations using the Herman-Skillman wavefunctions are in much better agreement with experiment than the previous calculations involving the hydrogen-like functions.

Carbon-14: Direct Detection at Natural Concentrations

Abstract: The14C atoms naturally present in a piece of 19th-century wood have been detected directly by means of a tandem Van de Graaff accelerator used as a high-energy mass spectrometer. The14C ions were easily resolved from interfering ions with the use of a ΔE-E detector telescope (this telescope consists of a pair of detectors; one of them measures the specific ionization, ΔE, and the sum of the signals from both detectors gives the total energy for each ion, ET). The technique offers a number of practical advantages.

Models of interstellar clouds. I. The Zeta Ophiuchi cloud

Abstract: Techniques for constructing detailed models of diffuse interstellar clouds are described. The models are designed to reproduce the observational data on the abundance and rotational excitation of H/sub 2/, the abundances of other molecules and of atomic ions, and the fine-structure populations of carbon. Results are presented for the zeta Ophiuchi cloud. A model with two components accounts adequately for all the available observational data. The temperature and total density are respectively 110 K and 500 cm/sup -3/ in the outer region and 22 K and 2500 cm/sup -3/ in the inner core. The measured abundance of CH can be reproduced by postulating a rate coefficient of 5 x 10/sup -16/ cm/sup 3/ s/sup -1/ at 22 K for the radiative association reaction C/sup +/+H/sub 2/..-->..CH/sub 2//sup +/+hv. The measured abundances of HD and OH can be reproduced by an ionization rate of 1.6 x 10/sup -17/ s/sup -1/ and a rate coefficient of 5 x 10/sup -10/ cm/sup 3/s/sup -1/ for the reaction O/sup +/+H..-->..O+H/sup +/. The abundances of CO and CN are reproduced by using plausible estimates of their photo-dissociation rates, but the chemical scheme seriously underestimates the abundance of CH/sup +/. The concentrations of other simple moleculesmore » are predicted. The molecule C/sub 2/ may be detectable. The known heating sources appear adequate to maintain the inferred temperatures.« less

Intrinsic acidities of substituted phenols and benzoic acids determined by gas-phase proton-transfer equilibriums

Abstract: Gas-phase proton-transfer equilibria: A I H + A2= A I + A2H, involving some 50 benzoic acids and phenols and various other standard acids with known acidities were measured with a pulsed electron beam high ion source pressure mass spectrometer. The equilibrium constants K were used to obtain the free energy changes and establish the relative and absolute gas-phase acidities of the benzoic acids and phenols. The gas-phase acidities of the substituted benzoic acids and phenols are compared with the corresponding aqueous acidities. The reasons for the very different attenuation of the substituent effects in water and Me2SO are examined. Ortho effects in the gas phase and specific hydrogen bonding effects are also discussed. The electron affinities of some phenolic radicals are determined from known bond dissociation energies and the gas-phase acidities. Linear free energy relationships have had a profound impact on the development of physical organic chemistry. Thus the classification of substituent effects on chemical reactions done in connection with Hammett type plots led to many of the now widely used concepts of bonding and electronic effects.] The ability of phenols and benzoic acids to ionize as Brqnsted acids in the experimentally easily accessible pH range made them the natural choice as references for free energy relationships.2 The vast majority of reaction types, including the reference reactions that have been successfully correlated by linear free energy relationship plots, are processes occurring in solution. Since ionic solvation is an integral and dominant part of the energetics of these reactions, interpretations of free energy correlations purely in terms of electronic arguments involving the reactants but not the solvent has been a perennial area of concern. One pertinent example is the finding that in most cases the differences in free energy of ionization of substituted phenols and benzoic acids are due to a change of ent r ~ p y . ' ~ Yet, i f solvation effects are not taken into account, electronic effects of the substituents should show up in the enthalpy and not in the entropy change. T o separate solvent effects from the intrinsic molecular effects of the substituents one needs to know the free energy and enthalpy change for the same process occurring in the dilute gas phase. Fortunately such data have recently become available from studies of gas-phase ion molecule reac t iok8 Information on the intrinsic acidities and basicities is obtained from studies of the gas-phase proton-transfer reactions A I H + A2= A I + A2H (1) In earlier work9*Io nly the sign of the free energy change could be obtained from the obsefved occurrence or nonoccurrence of the reaction in the forward direction. Many important results on gas-phase acidity orders were obtained with this technique.' ' I 3 More recently, the study of ion equilibriaI4 was extended to proton-transfer reactions in ICR mass spectrome t e r ~ , ' ~ high-pressure pulsed ion sources,16 and flowing afterglow apparatus.I7 The resulting determinations of K , AGO, and A H o have provided already many significant data. It is interesting to note that recentlyt* results from a b initio MO methods using relatively simple STO-3G basis sets have predicted energy changes (AE2) for the positive ion protontransfer reactions (eq 2) which are in very good agreement with gas-phase ion equlibria data ( A H * ) . Thus an important independent contribution for these reactions can be expected from theoretical calculations. On the other hand the negative ion systems (eq 1) are electron crowded systems in which electron repulsion and electron correlation are much more important. These systems require much more accurate calculations, larger basis sets, and electron correlation corrections. Therefore, unfortunately, numerous and good theoretical calculations of AE2 cannot be expected in the near A brief reportI9 on the gas-phase acidities of the monosubstituted benzoic acids was presented earlier from this laboratory. The present publication presents more extensive documentation of these early results and combines them with newly obtained results for the substituted phenols20 in a more comprehensive treatment of substituent effects on the acidity of benzoic acids and phenols. Experimental Section The acidity data obtained in this work were measured using a pulsed electron beam high-pressure mass spectrometer, which has been described previously.2' Briefly, a typical experiment is carried out as follows. A concentrated methanol solution containing a known molar ratio of the two acids of interest is prepared by dissolving accurately weighed amounts of the acids into methanol. This solution is injected with a syringe through a septum into a 5-L bulb containing I a tm of the buffer gas methane. NF3 (50 cm3) at I a tm are also injected into the bulb. The bulb and inlet system to the ion source are maintained at 150-200 "C to ensure complete vaporization of the rather involatile benzoic acids and phenols. Typically the bulb contains 1 atm of methane, 3 Torr each of the acids of interest, and I O Torr of NF3. After allowing sufficient time for mixing, this gaseous mixture is passed in slow flow through the ion source. The flow out of the bulb is controlled by means of an all metal valve. The gas mixture flows through I O mm i.d. tubing in and out of the ion source and then passes via a flow control capillary into a pump. The pressure in the flow system and ion source is maintained at some constant value in the 2-5 Torr range. Viscous flow results under these conditions. Therefore no fractionation of the minor components (Le., the acids) should occur and the partial pressure ratios of the acids in the ion source should be identical with those in the storage bulb. A confirmation of the expected lack of fractionation could be obtained by observing that the measured equilibrium constant K I changed by only 5% after 85% of the gas had flowed out of the 5-L storage bulb. The ratio of the neutral acids in the bulb was varied by a factor from 2 to 5 in separate experiments where new methanol solutions were prepared and injected. The equilibrium constants were found to be independent of the concentration ratios used. Ionization of the sample is accomplished by a short (-10 p s ) pulse of 2000-eV electrons, which creates some I O 7 ions and electrons. The N F3 undergoes dissociative electron attachment to produce F-. The fluoride ion rapidly abstracts protons from the benzoic acids and Journal of the American Chemical Society / 99:7 / March 30, I977 D ow nl oa de d by T A R B IA T M O D A R R E S U N IV o n A ug us t 1 9, 2 00 9 Pu bl is he d on M ar ch 1 , 1 97 7 on h ttp :// pu bs .a cs .o rg | do i: 10 .1 02 1/ ja 00 44 9a 03 2

Self-consistent field model for condensed matter

Abstract: A model for condensed matter is described in which the ions surrounding a particular atom are replaced by a positive charge distribution which is constant outside of a sphere containing the atom and zero inside. The orbital functions, both bound and free, are obtained as solutions of the Dirac equation and are used to self-consistently determine the potential function. In order to obtain the desired equation-of-state data from the calculations, three different and somewhat arbitrary prescriptions are used to separate quantities pertaining to the atom from those of the electron gas in which it is imbedded. Results are shown for 14 elements, including the $5d$ transition metals, in the neighborhood of normal solid density. Equation-of-state data for nickel, copper, and zinc are also given and are compared with experiment.

Ionic adsorption on variable charge mineral surfaces theoretical charge development and titration curves

Abstract: A completely general theory is presented which can be used to describe both anion and cation adsorption on amphoteric oxide surfaces. It takes account of the fact that both the surfaces and adsorbing species are charged and that the surfaces change their charge when ionic adsorption takes place. The theory is applicable to both specific and non-specifically adsorbed ions. It is shown to account for the pH dependent charge curves of goethite, silica and two tropical soils.

Heating tokamaks via the ion-cyclotron and ion-ion hybrid resonances

Abstract: The ion-ion hybrid resonance can occur at high plasma densities in tokamaks and thereby absorb energy from the fast magnetosonic mode which would otherwise propagate freely. Ion-cyclotron resonance regions, although they occur in the low-density peripheral plasma, can nonetheless cause sufficient absorption to compete with fundamental cyclotron resonance damping by ions. For the ion-ion hybrid resonance it is shown that: (1) the energy absorption occurs via a sequence of mode conversions. (2) A poloidal field component normal to the ion-ion hybrid mode conversion surface strongly influences the mode conversion process, so that roughly equal electron and ion heating occurs in the present proton-deuterium experiments, while solely electron heating is predicted to prevail in deuterium-tritium reactors. (3) The ion-ion hybrid resonance suppresses toroidal eigenmodes. (4) Wave absorption in minority fundamental ion-cyclotron heating experiments will be dominated by ion-ion hybrid mode conversion absorption for minority concentrations exceeding roughly 1%.

An O18 Study of Field‐Assisted Pore Formation in Compact Anodic Oxide Films on Aluminum

Abstract: The mechanism of field‐assisted pore formation in 15% wt aqueous solutions was studied by O18 tracing techniques. Compact base layers were first formed in an O18 labeled solution and further oxidized in a nonlabeled solution, leading to field‐assisted pore formation. The O18 content and depth distribution was measured in these duplex films. It was found that the initial number of O18 atoms per square centimeter is conserved to within 2% and that the major part of the oxygen of the initial base layer is located on the top of the duplex film with the same O18 isotopic concentration. This observation shows clearly that the pore formation does not take place through a simple oxide dissolution process whether chemical or field assisted. Pore formation consists of some kind of oxide decomposition involving only cation transfer into the solution. The values of the cationic and anionic currents are calculated. Possible mechanisms for ion movement are discussed.

A neutron diffraction study of hydration effects in aqueous solutions

Abstract: The nature of ionic hydration for the cations in NiCl2 solution and the anions in NaCl solution has been investigated by neutron diffraction experiments on samples which have been isotropically enriched. Well defined hydration numbers are found for both the Ni2+ ion and Cl- ion.

Gas phase basicities and relative proton affinities of compounds between water and ammonia from pulsed ion cyclotron resonance thermal equilibriums measurements

Abstract: The pulsed ion cyclotron resonance method for precise determinations of proton transfer equilibrium constants has been applied to 46 carbon, nitrogen, oxygen, phosphorus, sulfur, arsenic, and selenium bases, with duplicating overlapping sequences, to obtain the relative proton affinities of water and ammonia. Where comparison is possible, the results are in generally good accord with those obtained by high-pressure mass spectroscopy. The results provide important new insights into the intrinsic effects of molecular structure on base strengths. Applications of these results to derive other gaseous ion thermochemical data are illustrated. In particular, methyl substituent effects on proton affinities have been extensively evaluated and interpretations are made of the comparisons with corresponding effects of homolytic bond dissociation energies of the conjugate acids of n-bases and with the hydride affinities of substituted methyl cations. Comparisons of the effects of n-alkyl substituents on the proton affinities of water and alcohols with carboxylic acids and their esters indicate that protonation is thermodynamically favored in the gas phase at the carbonyl oxygen of the latter. Large effects of polar electronegative substituents have been observed for various oxygen and nitrogen bases. An evaluation of entropy effects in gas phase proton transfer equilibria shows such effects to bemore » generally small for simple bases and approximately equal to entropy effects expected for changes in molecular rotational symmetry numbers. Finally, the present result provides the basis for evaluations of absolute proton affinities and of relative ion solvation energies.« less

Monte Carlo simulation of ion motion in drift tubes

Abstract: The motion of a swarm of ions in a uniform electric field is studied by simulating the motion of a single ion through many collisions with neutral atoms in order to obtain the drift velocity, average energy, and velocity distribution for the ions. For K+ ions in He at low field strengths, the results agree well with the solutions of the Boltzmann equation by Kumar and Robson; and for K+ in Ar at all field strengths, the computed mobilities demonstrate that the Viehland–Mason moment method can give useful results, especially if carried through to third order. The velocity distributions computed for O+ ions in He and Ar are used in the accompanying paper by Albritton et al. to analyze drift tube measurements of O+ reaction rates. Significant deviations from the Maxwell–Boltzmann form have been found and are seen to have important effects in that application. Velocity distributions have also been obtained for Li+ in He. The sensitivity of ionic mobilities to changes in the ion–atom interaction potential is examined with particular reference to K+ ions in Ar.

Scanning of sector mass spectrometers to observe the fragmentations of metastable ions

Abstract: Various methods of scanning the electric and the magnetic sectors of a double focusing mass spectrometer are critically discussed and assessed.

Characteristics of the chloride conductance in muscle fibers of the rat diaphragm.

Abstract: In muscle fibers from the rat diaphragm, 85% of the resting membrane ion conductance is attributable to Cl-. At 37 degree C and pH 7.0, GCl averages 2.11 mmho/cm2 while residual conductance largely due to K+ averages 0.34 mmho/cm2. The resting GCl exhibits a biphasic temperature dependence with a Q10 of 1.6 between 6 degree C and 25 degree C and a Q10 of nearly 1 between 25 degree C and 40 degree C. Decreasing external pH reversibly reduced GCl; the apparent pK for groups mediating this decrease is 5.5. Increasing pH up to 10.0 had no effect on GCl. Anion conductance sequence and permeability sequence were both determined to be Cl-greater than Br-greater than or equal to I-greater than CH3SO4-. Lowering the pH below 5.5 reduced the magnitude of the measured conductance to all anions but did not alter the conductance sequence. The permeability sequence was likewise unchanged at low pH. Experiments with varying molar ratios of Cl- and I- indicated a marked interaction between these ions in their transmembrane movement. Similar but less striking interaction was seen between Cl- and Br-. Current-voltage relationships for GCl measured at early time-points in the presence of Rb+ were linear, but showed marked rectification with longer hyperpolarizing pulses (greater than 50ms) due to a slow time-and voltage-dependent change in membrane conductance to Cl-. This nonlinear behavior appeared to depend on the concentration of Cl- present but cannot be attributed to tubular ion accumulation. Tubular disruption with glycerol lowers apparent GCl but not GK, suggesting that the transverse tubule (T-tubule) system is permeable to Cl- in this species. Quantitative estimates indicate that up to 80% of GCl may be associated with the T tubules.