Showing papers on "Conductance published in 1988"

Discrete Ba2+ block as a probe of ion occupancy and pore structure in the high-conductance Ca2+ -activated K+ channel.

Abstract: In this study, high-conductance Ca2+-activated K+ channels from rat skeletal muscle were incorporated into planar phospholipid bilayers, and discrete blockade of single channels by Ba2+ was studied. With 150 mM K+ held constant in the internal solution, increasing external K+ over the range 100-1,000 mM raises the rate of Ba2+ dissociation. This "enhancement effect," which operates at K+ concentrations 3-4 orders of magnitude higher than those required for the "lockin" effect described previously, depends on applied voltage, saturates with K+ concentration, and is not observed with Na+. The voltage dependence of the Ba2+ off-rate varies with external K+ in a way suggesting that K+, entering the channel from the external side, forces Ba2+ dissociation to the internal solution. With K+ held fixed in the external solution, the Ba2+ off-rate decreases as internal K+ is raised over the range 0-50 mM. This "lock-in" effect is similar to that seen on the external side (Neyton and Miller, 1988), except that the internal lock-in site is of lower affinity and shows only a fivefold preference for K+ over Na+. All the results taken together argue strongly that this channel's conduction pathway contains four sites of very high affinity for K+, all of which may be simultaneously occupied under normal conducting conditions. According to this view, the mutual destabilization resulting from this high ionic occupancy leads to the unusually high conductance of this K+-specific channel.

GABAA-receptor function in hippocampal cells is maintained by phosphorylation factors

Abstract: Gamma aminobutyric acid (GABA) mediates fast synaptic inhibition in the central nervous system by activating the chloride-permeable GABAA channel. The GABAA conductance progressively diminishes with time when the intracellular contents of hippocampal neurons are perfused with a minimal intracellular medium. This "run down" of the GABA-activated conductance can be prevented by the inclusion of magnesium adenosine triphosphate and calcium buffer in the intracellular medium. The amount of chloride conductance that can be activated by GABA is determined by competition between a calcium-dependent process that reduces the conductance and a phosphorylation process that maintains the conductance.

A model for electrical resonance and frequency tuning in saccular hair cells of the bull-frog, Rana catesbeiana.

Abstract: 1. Electrical resonance in solitary hair cells was examined under several experimental conditions using the tight-seal recording technique in the whole-cell current-clamp mode. 2. Resonance was characterized by the frequency and quality factor of oscillations in membrane potential evoked by depolarizing current pulses. Oscillation frequency increased with depolarization, from about 90 Hz at the resting potential to a limiting value of about 250 Hz. The quality factor of the oscillations was a bell-shaped function of membrane potential that reached a maximum of up to 12.6 at a potential slightly positive to the resting potential. 3. Pharmacological experiments were performed to assess which of three ionic currents participate in electrical resonance. Reduction of the voltage-gated Ca2+ current (ICa) and the Ca2+-activated K+ current (IK(Ca)) by lowering the extracellular Ca2+ concentration, or reduction of IK(Ca) with tetraethylammonium ion (TEA) degraded the resonance. In contrast, blockade of the transient K+ current (IA) with 4-aminopyridine (4-AP) had no significant effect. 4. To test the sufficiency of the Ca2+ and the Ca2+-activated K+ currents to account for resonance, we developed a model using mathematical descriptions of the two currents derived in the preceding paper (Hudspeth & Lewis, 1988), with additional terms for leakage conductance and membrane capacitance. The model correctly predicts the oscillatory responses to applied current pulses, including the non-linear dependences of oscillation frequency and quality factor on membrane potential. 5. Simulations of current-clamp experiments in the presence of a reduced extracellular Ca2+ concentration or of TEA were generated respectively by decreasing the model's values for the maximal Ca2+ or Ca2+-activated K+ conductances. The model's predictions of membrane-potential oscillations under these conditions agree qualitatively with experimental results, providing further support for the model as a description of the resonance mechanism. 6. To identify the factors most important in determining the hair cell's resonance properties, we systematically altered the values of selected parameters in the model. Frequency was most profoundly influenced by increasing the magnitude and activation rate of the Ca2+-activated K+ conductance, whereas the quality factor was most sensitive to increases in the level of the Ca2+ conductance. 7. By including a term describing activation of the hair cell's mechanically sensitive transduction conductance, we used the model to predict a tuning curve for responses to mechanical inputs of various frequencies.(ABSTRACT TRUNCATED AT 400 WORDS)

Thermodynamics of aqueous association and ionization reactions at high temperatures and pressures

Abstract: Electrochemical and electrical conductance cells have been widely used at ORNL over the years to quantitatively determine equilibrium constants and their salt effects to 300°C (EMF) and 800°C (conductance) at the saturation pressure of water (EMF) and to 4000 bars (conductance). The most precise results to 300°C for a large number of weak acids and bases show very similar thermodynamic behavior, which will be discussed. Results for the ionization constants of water, NH3(aq), HCl(aq), and NaCl(aq), which extend well into the supercritical region, have been fitted in terms of a model with dependence on density and temperature. The entropy change is found to be the driving force for ion-association reactions and this tendency increases (as it must) with increasing temperature at a given pressure. Also, the variation of all thermodynamic properties is greatly reduced at high fixed densities. Considerable variation occurs at low densities. From this analysis, the dependence of the reaction thermodynamics on the P-V-T properties of the solvent is shown, and the implication of large changes in hydration for solutes in the vicinity of the critical temperature will be discussed. Finally, the change in the molar compressibility coefficient for all reactions in water is shown to be the same and dependent only on the compressibility of the solvent.

Recent Developments in Contact Conductance Heat Transfer

Abstract: The characteristics of thermal contact conductance are increasingly important in a wide range of technologies. As a consequence, the number of experimental and theoretical investigations of contact conductance has increased. This paper reviews and categorizes recent developments in contact conductance heat transfer. Among the topics included are the theoretical/analytical/numerical studies of contact conductance for conforming surfaces and other surface geometries; the thermal conductance in such technological areas as advanced or modern materials, microelectronics, and biomedicine; and selected topics including thermal rectification, gas conductance, cylindrical contacts, periodic and sliding contacts, and conductance measurements. The paper concludes with recommendations for emerging and continuing areas of investigation.

Single-channel events and gating behavior of the cardiac gap junction channel

Abstract: The activity of gap junction channels between pairs of neonatal rat heart cells in culture was studied under control conditions and during uncoupling procedures by using dual whole-cell voltage clamp techniques. Under control conditions gap junctional conductance ranged from 0.05 to 35 nS. In cell pairs exhibiting low gap junctional conductance (less than 500 pS), single-channel events with a unitary conductance of 53 +/- 2 pS (5 experiments; 186 events) were apparent. Event duration and open-time probability were estimated to be 0.95 sec and 0.17, respectively. When the junctional conductance in well-coupled cell pairs (with initial junctional conductance, greater than 5 nS) was reduced by cytoplasmic acidification or application of heptanol, single-channel events could be visualized. Compared to low-conductance controls, unitary channel conductance was unaltered (for acidification the conductance was 58 +/- 3 pS in 11 experiments with 253 events; for heptanol the conductance was 61 +/- 1 pS in 2 experiments with 171 events), while the probability of channels being open was decreased. The constancy of unitary channel conductance under control conditions and during uncoupling procedures suggests that opening and closing of the gap junction channel are all-or-none processes during which no stable subconductance states are formed.

Inward rectification of resting and opiate-activated potassium currents in rat locus coeruleus neurons

Abstract: Intracellular recordings were made from rat locus coeruleus neurons in vitro, and membrane currents were measured at potentials from -50 to -130 mV. In the absence of any applied agonists, the slope conductance of the cells increased 3-fold when the cell was hyperpolarized from -60 to -120 mV. This conductance increase was complete within 5 msec of the onset of a hyperpolarizing command and was subsequently independent of time for several seconds. The conductance increase was blocked by cesium chloride (1-2 mM), rubidium chloride (1-2 mM), or barium chloride (1-100 microM). The membrane potential range over which the conductance increased was centered at the potassium equilibrium potential (EK; extracellular potassium concentration, 2.5-10.5 mM): the current/voltage (I/V) relation of the cell could be well described by supposing that there were 2 potassium conductances, one voltage independent (G1) and the other (inward rectifier, Gir) activated according to the expression Gir = Gir,max/(1 + exp[(V - EK)/k]), where k ranged from 15 mV in 2.5 mM potassium to 6 mV in 10.5 mM potassium. The additional membrane potassium conductance that developed when agonists at mu-opioid and alpha 2-adrenoceptors were applied also became larger with membrane hyperpolarization, and this voltage dependence was also reduced or blocked by rubidium, cesium, and barium; in the presence of these agonists the current also reached its final value within 5 msec. However, the conductance increased by the agonists (Gag) was not well expressed by simply increasing the values of G1 and Gir,max. It was best described by a potassium conductance that increased according to Gag,max/(1 + exp[(V - Vm)/k]), where Vm (the potential at which the conductance was half-maximum) was close to the resting potential of the cell.(ABSTRACT TRUNCATED AT 400 WORDS)

Conductance of an array of elastic scatterers: A scattering-matrix approach.

Abstract: In the past, the conductance of disordered systems has been extensively studied with use of the Anderson tight-binding Hamiltonian. In this paper we use a different model, which views the semiconductor as regions of free propagation with occasional elastic scattering by a random array of scatterers. Each impurity is characterized by a scattering matrix which can, in principle, be derived for any arbitrary scattering potential. The randomness is introduced through the impurity location. The overall scattering matrix of the device is calculated by combining (using the appropriate law of composition) the scattering matrices of successive sections. The conductance is then evaluated with use of the multichannel Landauer formula. One advantage of this approach is that the quantum conductance can be compared with the semiclassical conductance, which is determined by combining the probability scattering matrices obtained by replacing each element of the (amplitude) scattering matrices by its squared magnitude. This comparison allows us to see clearly the effects of quantum interference. Numerical examples illustrating the onset of weak and strong localization, as well as conductance fluctuations, are presented. Even for samples shorter than the electron elastic mean free path, the size of the conductance fluctuations is close to the universal value if the two-probe conductance formula is used, though it is much larger when the four-probe formula is used.

Field-effect analysis for the determination of gap-state density and Fermi-level temperature dependence in polycrystalline silicon

Abstract: The field-effect conductance has been used in two distinct ways to determine the gap-state density in polycrystalline silicon. The relationship between the surface potential and the gate voltage, which determines the gap-state density, has been deduced according to the incremental method, already proposed by Suzuki et al., and a new method. The new method is based on the temperature dependence of the derivative of the field-effect conductance with respect to the gate voltage. The results from the two methods are in good agreement and show a rapidly increasing gap-state density in the upper half of the gap. The temperature analysis of the field-effect conductance indicates that the position of the Fermi level is temperature dependent. The contribution to this dependence from the statistical shift has been determined.

Potassium conductance of the squid giant axon. Single-channel studies.

Abstract: The patch-clamp technique was implemented in the cut-open squid giant axon and used to record single K channels. We present evidence for the existence of three distinct types of channel activities. In patches that contained three to eight channels, ensemble fluctuation analysis was performed to obtain an estimate of 17.4 pS for the single-channel conductance. Averaged currents obtained from these multichannel patches had a time course of activation similar to that of macroscopic K currents recorded from perfused squid giant axons. In patches where single events could be recorded, it was possible to find channels with conductances of 10, 20, and 40 pS. The channel most frequently encountered was the 20-pS channel; for a pulse to 50 mV, this channel had a probability of being open of 0.9. In other single-channel patches, a channel with a conductance of 40 pS was present. The activity of this channel varied from patch to patch. In some patches, it showed a very low probability of being open (0.16 for a pulse to 50 mV) and had a pronounced lag in its activation time course. In other patches, the 40-pS channel had a much higher probability of being open (0.75 at a holding potential of 50 mV). The 40-pS channel was found to be quite selective for K over Na. In some experiments, the cut-open axon was exposed to a solution containing no K for several minutes. A channel with a conductance of 10 pS was more frequently observed after this treatment. Our study shows that the macroscopic K conductance is a composite of several K channel types, but the relative contribution of each type is not yet clear. The time course of activation of the 20-pS channel and the ability to render it refractory to activation only by holding the membrane potential at a positive potential for several seconds makes it likely that it is the predominant channel contributing to the delayed rectifier conductance.

Numerical study of transport properties in continuum percolation

Abstract: The authors present numerical simulations of AC conductance for a random resistor-capacitor network. The conductance obeys a probability density function p(g) varies as g- alpha (0( alpha (1). They use a highly efficient propagation algorithm to calculate the effective conductance of a long strip of a lattice. At low frequencies, they find that for the concentration p of conducting bonds less than the percolation threshold pc, the imaginary part of conductance is proportional to frequency Im(geff) approximately= omega and the real part of conductance shows an anomalous frequency dependence Re(geff) approximately= omega 2- alpha . The results of simulations in such a continuum system are in agreement with the predictions of the effective medium and the Maxwell-Garnett approximation. They also calculate the non-universal DC conductivity exponents in continuum percolation; the results are consistent with earlier theoretical predictions and numerical calculations.

Conductance technique in MOSFETs: Study of interface trap properties in the depletion and weak inversion regimes

Abstract: A new and accurate approach to a.c. conductance measurements on MOSFETs is presented. It is shown that the conductance technique can be used to study interface trap properties in most of the silicon band-gap by direct measurement on a single MOSFET. The equivalent circuit is analyzed and the influence of the channel length on the inversion layer response is discussed in detail. It is shown that the channel time constant is mainly determined by the channel length. For small channel lengths L

cGMP-dependent channel protein from photoreceptor membranes: single-channel activity of the purified and reconstituted protein

Abstract: The cGMP-dependent channel protein has been purified from bovine rod photoreceptor membranes and incorporated into planar lipid membranes. At low divalent cation concentrations, cGMP stimulated single-channel current fluctuations. The probability Po of the channel being open strongly depended on the cGMP concentration (EC50 = 31 microM; Hill coefficient, n = 2.3); whereas the single-channel conductance (lambda = 26 pS) was independent of the agonist concentration. The agonist-stimulated increase in the probability of an open channel was largely due to shorter closed times and, to a lesser extent, due to the channel staying open for a longer time. The current-voltage relationship of the single open channel deviated from ohmic behavior, and the open probability decreased at more negative membrane potentials. The rectification of the macroscopic cGMP-induced current in artificial bilayers that contained many channel copies can be accounted for by the voltage dependence of channel gating together with the nonlinearity of the current-voltage curve of an open channel. Current fluctuations exhibited a variety of sublevels, indicating that the channel may exist in more than one conductive state.

Incorporation in lipid bilayers of a large conductance cationic channel from mitochondrial membranes.

Abstract: Membranes from subcellular fractions of adrenal medulla were incorporated in phospholipid bilayers formed at the tip of microelectrodes. Current fluctuations recorded in the presence of a transmembrane potential revealed the existence of a voltage-dependent channel of large conductance. This channel is characterized by fast kinetics and four conductance levels separated by jumps of 100, 220 and 220 pS in 150 mM NaCl. It is permeant to Na+,K+, tetraethylammonium, Cl- and acetate and has some cation selectivity. Exposure to trypsin or pronase abolished the voltage-dependence. Upon subcellular fractionation, the activity was found to be associated with mitochondria. A similar activity was observed in mitochondrial fractions from other organs. By its kinetics, its selectivity and its potential-dependence, this channel differs from the voltage-dependent anion channel of outer mitochondrial membranes.

Three kinetically distinct potassium channels in mouse neuroblastoma cells.

Abstract: 1. Mouse neuroblastoma cells were utilized to examine the electrical properties of single K+ channels which might underlie multiple components of outward current in vertebrate neurones. The conductance, kinetics of activation, inactivation, and pharmacology of three types of channels were compared. 2. Two types of voltage-dependent channels, primarily permeable to K+, were identified which did not require the presence of internal Ca2+. The first had gating kinetics best classified as a delayed rectifier. The conductance of the open channel was 35 pS (22 degrees C) in solutions having symmetrical 125 mM-K+ concentrations. 3. The second type of channel had a conductance of 14 pS under identical conditions. The gating kinetics of this type of channel were distinct from those of the delayed rectifier. The mean first latency, and lifetime of the open state at any voltage, were longer. The maximum probability of an open channel was smaller, so that this parameter appeared less sensitive to the membrane potential. The rate of inactivation of the channel was slower. Further, at the more negative membrane potentials tested, the level of steady-state inactivation was less for this type of channel. 4. The delayed rectifier channel was more sensitive to the blocking action of 4-aminopyridine than the channel with low conductance. 5. A Ca2+ -activated, voltage-dependent K+ channel, having a conductance of 140 pS, was also identified. The maximum probability of an open channel increased, and the voltage for half-maximal activation shifted to a more negative potential as the internal Ca2+ was increased. 6. The time course of inactivation of K+ currents recorded from the whole cell declined in two phases, probably due to the presence of the two types of voltage-dependent K+ channels.

Electronic transport in small strongly localized structures

Abstract: We review some recent results on the low-temperature transport properties (T < 4K) of very small silicon metal-oxide field-effect transistors in the insulating regime of conduction. Our devices are lithographically patterned to have widths as small as 0.05 µm and lengths as short as 0.06 µm. These small transistors exhibit new and unexpected sample-specific fluctuation behavior in the gate voltage, temperature, and magnetic field dependence of the conductance. We discuss both resonant tunneling and Mott variable-range hopping, the two main transport mechanisms in these devices at low temperature.

Modification of K+ conductance of heart cell membrane by BRL 34915.

Abstract: 1. The effect of the K+ channel agonist BRL 34915 on membrane conductance was investigated in isolated guinea-pig cardiac myocytes. 2. BRL 34915 reduced the duration of the transmembrane action potential and slightly increased the membrane resting potential in a concentration-dependent manner. 3. BRL 34915 removed the rectification in the steady-state current-voltage relationship. At membrane potentials more negative than the K+ equilibrium potential, membrane conductance was reduced. In the presence of 10−4 mol/l BRL 34915, the current-voltage relationship was linear, i.e. of an ohmic type. 4. The BRL 34915-mediated change in membrane conductance was susceptible to the K+ channel blockers BaCl2 and tetrahydroaminoacridine. 5. In conclusion, BRL 34915 modifies K+ conductance in the cardiac cell membrane. The precise nature of the K+ conductance change remains to be elucidated.

Surface charge near the cardiac inward-rectifier channel measured from single-channel conductance.

Abstract: The conductance of a channel to permeable ions depends on the number of ions near the mouth of the pore. Surface charge controls the local concentration, and impermeable cations can modify this charge. Correlating channel conductance with the concentration of impermeable cations therefore determines the local charge near the open pore. This paper presents data from cell-attached patches on embryonic chick ventricle cells, and it uses the conductance of inward-rectifier channels in the patch (in 100mm K, with various concentrations of Na, Ca, Ba, and Mg) to estimate the local surface potential. The results indicate the presence of ionized residues near the mouth of the channel. Using the Boltzmann equation and the Gouy-Chapman relation, the surface potential due to these residues (in 100K/33Na/0Ca/0Ba/0Mg) is −40 mV, and the charge density is −0.25e/nm2.

Whole-cell potassium currents in single early distal tubule cells.

Abstract: The apical membrane potassium conductance of amphibian early distal tubules is sensitive to changes in the intracellular pH, with cellular acidification causing a decreased conductance. With the whole-cell patch-clamp technique, we have measured the total potassium conductance of single isolated early distal tubule cells of the frog. With symmetrical potassium gluconate solutions, the whole-cell current was found to be strongly rectifying, with an inward conductance of 12.9 nS (at intracellular pH between 7.6 and 8.0) and an outward conductance of 1.0 nS. The inward current was almost totally inhibited by the addition of 10 mM Ba2+ to the bath solution. The use of pipette solutions with pH between 7.0 and 8.0 showed a positive correlation between intracellular pH and conductance. In contrast, acidification of the extracellular solution caused no significant change in conductance.

Voltage dependence of the basolateral membrane conductance in the Amphiuma collecting tubule.

Abstract: The basolateral potassium conductance of cells of most epithelial cells plays an important role in the transcellular sodium transport inasmuch as the large negative equilibrium potential of potassium across this membrane contributes to the electrical driving force for Na+ across the apical membrane. In the present study, we have attempted to establish, theI-V curve of the basolateral membrane of theAmphiuma collecting tubule, a membrane shown to be K+ selective. TransepithelialI-V curves were obtained in short, isolated perfused collecting tubule segments. The “shunt” conductance was determined using amiloride to block the apical membrane Na+ conductance. In symmetrical solutions, the “shunt”I-V curve was linear (conductance: 2.2±0.3 mS·cm−2). Transcellular current was calculated by subtracting the “shunt” current from the transepithelial current in the absence of amiloride. Using intracellular microelectrodes, it was then possible to measure the basolateral membrane potential simultaneously with the transcellular current. The basolateral conductance was found to be voltage dependent, being activated by hyperpolarization: conductance values at −30 and −80 mV were 3.6±1.0 and 6.6±1.0 mS·cm−2, respectively. BasolateralI-V curves were thus clearly different from that predicted by the “constant field” model. These results indicate that the K+-selective basolateral conductance of an amphibian collecting tubule shows inward (“anomalous”) rectification. Considering the electrogenic nature basolateral Na−K-pump, this may account for coupling between pump-generated potential and basolateral K+ conductance.

Gating properties of channels formed by Colicin Ia in planar lipid bilayer membranes.

Abstract: Colicin Ia forms voltage-dependent channels when incorporated into planar lipid bilayers. A membrane containing many Colicin Ia channels shows a conductance which is turned on when high positive voltages (greater than +10 mV) are applied to the cis side (side to which the protein is added). The ionic current flowing through the membrane in response to a voltage step shows at first an exponential and then a linear rise with time. The relationship between the steady-state conductance, achieved immediately after the exponential portion, and voltage is S-shaped and is adequately fit by a Boltzmann distribution. The time constant (tau) of the exponential is also dependent on voltage, and the relation between these two parameters is asymmetric around Vo (voltage at which half of the channels are open). In both cases the steepness of the voltage dependence, a consequence of the number of effective gating particles (n) present in the channel, is greatly influenced by the pH of the bathing solutions. Thus, increasing the pH leads to a reduction in n, while acidic pH's have the opposite effects. This result is obtained either by changing the pH on both sides of the membrane or on only one side, be it cis or trans. On the other hand, changing pH on only one side by addition of an impermeant buffer fails to induce any change in n. At the single-channel level, pH had an effect both on the unitary conductance, doubling it in going from pH 4.5 to 8.2, as well as on the fraction of time the channels stay open, F(v). For a given voltage, F(v) is clearly diminished by increasing the pH. This titration of the voltage sensitivity leads to the conclusion that gating in the Colicin Ia molecule is accomplished by charged amino- acid residues present in the protein molecule. Our results also support the notion that these charged groups are inside the aqueous portion of the channel.

Photoresponsive crown ethers. Part 20. Reversible photocontrol of association–dissociation equilibria between azobis(benzo-18-crown-6) and diammonium cations

Abstract: The solution properties of complexes formed from azo(benzo-18-crown-6)(1) and polymethylene-α,ω-diammonio cations [H3N+(CH2)nNH3+(2)] have been evaluated through measurements of average molecular weights, viscosity, n.m.r. spectra, and electrical conductance. The trans compound (1) and (2; n= 6) forms a polymeric complex with Nav(average aggregation number)= 20 while trans-(1) and (2; n= 12) form a 1 : 1 pseudocyclic complex. The difference is related to the geometrical fitness of the two terminal ammonium cations to the two crown rings in trans-(1), i.e. when the distance between the two ammonium cations in (2) is shorter than that between the two crown rings in (1), they form a polymeric complex. When the two distances are comparable, they form the 1 : 1 pseudocyclic complex. The n.m.r. chemical shift of the methylene protons in the 1 : 1 trans-(1)–(2; n= 12) complex move to higher magnetic field by 0.10–0.58 p.p.m., findings which support the view that in the complex these methylene protons lie exactly on the azobenzene moiety of trans-(1). Photoisomerised cis-(1) shows different aggregation modes because of the change in the distance between the two crown rings: a 1 : 1 complex for cis-(1)+(2; n= 6) and a 2 : 2 complex for cis-(1)+(2; n= 12). The photoinduced depolymerisation from the polymeric complex to the low molecular weight 1 : 1 complex for (1)+(2; n= 6) has been detected by viscosity measurements: ηsp/C= 0.440 for trans-(1)+(2; n= 6) and 0.354 for cis-(1)(cis% 70–78%)+(2; n= 6). The photoresponsive change in the aggregation mode is accurately reflected by the change in the electrical conductance. The conductance for (1)+(2; n= 6) increases on u.v. irradiation and decreases on visible light irradiation. This photoresponsive wave can be reproduced many times by alternate irradiation with u.v. and visible light. The reverse photoresponsive wave is observed for (1)+(2; n= 12). The conductance changes were well correlated with the changes in the aggregate size of these complexes. This is a novel example of reversible interconversion of polymers and low molecular weight pseudomacrocycles and of the transmission of light energy to electrical conductance.

Transparent, Electrically Conductive Composites Derived from Polypyrrole and Poly[Vinyl Chloride) by Vapor-Phase Polymerization: Effect of Environment on Polymerization and Reaction Mechanism

Abstract: Transparent, electrically conductive composite films were obtained by vapor-phase polymerization of pyrrole into a poly(vinyl chloride) (PVC) matrix containing FeCl3. The effects of water and of organic solvents on the polymerization were investigated. It was found that the conductance of the films increases in the presence of both water vapor and of good solvents or swelling agents for PVC. The conductivity of the films rises with reaction time and so does the rate of increase with higher FeCl3 concentration. The production of HCl was monitored by two methods, the precipitation of AgCl in an aqueous solution of silver nitrate and the increase in conductance of an aliquot of distilled water which had been placed into the reaction chamber. On the basis of our experimental results, we propose a reaction mechanism that explains the observed increase of conductance with time. A universal kinetic formula has been derived which relates the increase of electrical conductance to other parameters characte...