On the thermodynamic characterization of membrane gating particles by their Boltzmann distribution

The characterizations of gating particles of ionic channels in nerve membranes by their equivalent valencies and their electric dipole moment changes are compared. The gating particle is represented as a system of electric charges in fixed positions in an external electric field and the potential energy of such a system is calculated in the approximation of a constant electric field. The proper expression of the Boltzmann distribution of the gating particles is presented. It is shown that the dipole moment of transition of the gating particle is the only proper thermodynamic (macroscopic) characteristics of the gating particles based on the available experimental information and does not depend on any microscopic assumption as the equivalent valency does.     

Response of Nonspherical Biological Particles to Alternating Electric Fields

The stable orientation evoked by an alternating electric field is discussed for biological particles of arbitrary shapes and compositions. Ellipsoidal particles with and without shells are treated as special cases. It is shown that as the frequency of the electric field changes there may be sudden jumps in the stable direction as well as gradual changes.     

Electric polarization of polyelectrolyte and colloid media: dielectric versus electro-optic approach

The theories of dielectric dispersion and of electric birefringence as a representative of electro-optic methods are considered and it is shown that they both depend in a similar way simply on the real part of the complex electric polarizability of the macromolecules or the particles. The latter also contains the permanent dipole moment. Experimental data on dielectric dispersion, electric birefringence and electric light scattering of strongly elongated, rod-like poly(tetrafluoroethylene) particles are compared and an attempt is made to extend the dielectric dispersion curve to lower frequencies using electric birefringence and electric light scattering data. Further, the experimental data on dielectric dispersion, electric light scattering, electro-orientation and dipolophoresis for the more complicated Escherichia coli particles are compared. Again, the possibility to extend the 10 kHz-100 MHz dielectric dispersion curve down below 1 Hz by using electric light scattering data is examined. The good matching of the dielectric dispersion and electric light scattering frequency curves found in the overlapping frequency range (10 kHz-5 MHz) essentially enhances the chance that dielectric dispersion below 1 MHz is related to alpha dispersion and not to electrode polarization. Thus it is not only possible to obtain additional information on the mechanism of polarization at lower-frequency dielectric dispersion, but also to extend our knowledge about the effective dielectric properties of biological complex fluids to frequencies essentially below 1 MHz. This could be important for the understanding of the effect of low-frequency electromagnetic fields on living matter.     

Electro-optic evidence for the control of the structure of bacteriophage f1 by a minor coat protein

The structures of the filamentous bacteriophage f1 and its gene 3 amber mutant R4 have been compared using electric birefringence, electric dichroism, and ultrasonic vibration. The electro-optic experiments showed that the phage particles can be oriented in an electric field. The birefringence and dichroism as a function of field strength are not the same for the A-protein mutant and for the wild-type particle. Studies using ultrasonic vibration to fragment the bacteriophage show that the stabilities of the f1 and R4 particles differ.     

Analysis of the differential cross sections for bremsstrahlung during collisions between two charged particles in a uniform electric field

Under the nonrelativistic Born approximation, differential cross sections are derived for elastic collisions between two point charged particles in an external constant uniform electric field and for bremsstrahlung during these collisions.An analysis of the cross sections obtained shows that, due to the interference of the wave functions of two colliding particles during their reflection from the potential barrier of an external electric field, the differential cross sections for elastic collisions and for unpolarized bremsstrahlung (i) are both oscillatory in character and (ii), instead of being linearly proportional to one another (as in the case without an externale electric field), are related in a more complicated manner.     

Electrical Sizing of Particles in Suspensions: I. Theory

The processes involved during the passage of a suspended particle through a small cylindrical orifice across which exists an electric field are considered in detail. Expressions are derived for the resulting change in current in terms of the ratios of particle to orifice volume and particle to suspending fluid resistivity, and particle shape. Graphs are presented of the electric field and of the fluid velocity as functions of position within the orifice, and of the shape factor of spheroids as a function of their axial ratio and orientation in the electric field. The effects of the electric and hydrodynamic fields on the orientation of nonspherical particles and on the deformation of nonrigid spheres is treated, and the migration of particles towards the orifice axis is discussed. Oscillograms of current pulses produced by rigid, nonconducting spheres in various orifices are shown and compared with the theoretical predictions.     

Radial electric field and rotation of the ensemble of plasma particles in tokamak

The velocity of macroscopic rotation of an ensemble of charged particles in a tokamak in the presence of an electric field has been calculated in a collisionless approximation. It is shown that the velocity of toroidal rotation does not reduce to a local velocity of electric drift and has opposite directions on the inner and outer sides of the torus. This result is supplemented by an analysis of the trajectories of motion of individual particles in the ensemble, which shows that the passing and trapped particles of the ensemble acquire in the electric field, on the average, different toroidal velocities. For the trapped particles, this velocity is equal to that of electric drift in the poloidal magnetic field, while the velocity of passing particles is significantly different. It is shown that, although the electric-field-induced shift of the boundaries between trapped and passing particles in the phase space depends on the particle mass and charge and is, in the general case, asymmetric, this does not lead to current generation.     

Experimental and Simulation Studies of Electro-rheology

Abstract

Electro-rheological fluids are colloidal dispersions that, under the influence of an applied electric field, can show a spectacular increase in yield stress and viscosity. Despite many technological roles for fluids with a viscosity that can be controlled electrically, progress at making them commercially viable products has been slow, partly due to a lack of understanding of this phenomenon at the microscopic level. In this report, simulation and experimental data are combined to provide insights into the microscopic origins of this effect. The simulations produce electric field-induced “strings” of particles that span the electrodes, in agreement with the experimental observation, and are responsible for the major enhancements in the viscosity. The field also causes a strong distortion in the first coordination shell of colloidal particles. The combination of shear and electric field produces a long-range microstructure that is periodically forming and decaying, caused by the competing effects of electric field and shear rate. Comparison with experiment reveals that the Electro-rheological effect is driven by the applied field-induced Stokesian diffusion of the solid particles and relies little on the accompanying Brownian motion.     

Energy of electrons emitted as a result of separation of surfaces

Experiments indicating acceleration of charged particles as a result of separation of solid surfaces are analyzed. As a possible mechanism of such acceleration, generation of surface charge on the separated surfaces of a cleaved ionic crystal is considered. The maximum electric field generated due to the charging of the separated surfaces and the energy of electrons accelerated in such a field are estimated. It is shown that, for the maximum attainable electric field, conditions are created for the generation of runaway electrons that, even at atmospheric pressure, electrons are accelerated to high energies, not experiencing collisions with gas particles.     

Electron cyclotron resonance plasma heating in the CERA-RX facility under a randomly pulsating electric field

The results of the numerical simulation of the electron cyclotron resonance (ECR) heating of plasma particles in the CERA-RX facility under a randomly pulsating electric field (the collective effects taken into account) are presented. Under these conditions, the electron energy spectrum was found to be depleted to the low energy region due to an increase in the number of particles in the high energy region. The obtained effect depends on the polarity of the pulsating electric field.     

Formation of ordered structures in systems of charged thin cylindrical grains

Conditions for the formation of various orientational and spatial configurations of charged cylindrical particles in an external electric field are investigated both analytically and numerically. Analytical expressions allowing one to determine the tilt angle of cylinders relative to the symmetry axis/plane of the electric trap are proposed. A new algorithm for numerical modeling of the dynamics of interacting nonspherical particles is developed. Conditions for correct modeling of uniformly charged cylinders by means of “bipoles” consisting of two coupled point charges of the same sign are determined. The studies have been performed in a wide range of parameters close to those typical of laboratory experiments with dusty plasmas.     

Reticulocyte lipoxygenase changes the passive electrical properties of bovine heart submitochondrial particles

Purified reticulocyte lipoxygenase oxygenates the polyunsaturated phospholipids of sonified submitochondrial particles from bovine heart as measured by a burst of oxygen uptake. Over the frequency range of 0.5 to 100 MHz, the complex impedance of the submitochondrial particles as a function of the frequency before and after lipoxygenase attack was measured. From these data, the membrane capacity, the conductivity of the membrane and the conductivity inside the particles were calculated. Lipoxygenase action causes a 4-fold increase in the membrane capacity and a 2-fold increase in the membrane conductivity. Using the method of deformation of electric pulses, kinetic measurements were performed. In parallel to the changes of the passive electric properties, a partial inhibition of NADH oxidase and succinate oxidase was caused by the lipoxygenase attack. Oxygen uptake, changes of the passive electric properties and the inhibition of respiratory enzymes were prevented by lipoxygenase inhibitors. Owing to the high oxygen consumption produced by the lipoxygenase reaction, anaerobiosis was reached within the first 30 s in the closed chamber. Therefore, it must be concluded that the changes in passive electric properties and the inhibition of the respiratory enzymes are due to secondary anaerobic processes such as the hydroperoxidase reaction catalyzed by the lipoxygenase or a slow redistribution of peroxidized membrane lipids. The results are discussed in relation to the breakdown of mitochondria during the maturation process of red cells.     

Quasistatic simulation of microwave discharges in a spherically symmetric electrode system in nitrogen

Results are presented from one-dimensional quasistatic simulations of steady microwave discharges in a spherically symmetric electrode system in nitrogen at pressures of 1–8 Torr. The computational model includes the equation for calculating the electric field strength in the quasistatic approximation, Poisson’s equation, the balance equations describing the kinetics of charged and neutral plasma particles, and the time-independent homogeneous Boltzmann equation for electrons. The processes involving vibrationally excited particles are taken into account by the familiar analytic expression for the vibrational distribution of molecules in the diffusion approximation. It is shown that, because of the electric field nonuniformity, the physical properties (in particular, the plasma ion composition) are different in different discharge regions.     

The ac field patterns about living cells

The presence of the small ac electric fields produced by living cells is shown by the gentle dielectrophoretic force on tiny dielectric particles. The beauty of the field patterns is made evident as the cell and particles settle in a hanging drop. Patterns characteristic of repulsion and of attraction, as well as of a dipolar and quadripolar nature, are observable.     

The ac field patterns about living cells

The presence of the small ac electric fields produced by living cells is shown by the gentle dielectrophoretic force on tiny dielectric particles. The beauty of the field patterns is made evident as the cell and particles settle in a hanging drop. Patterns characteristic of repulsion and of attraction, as well as of a dipolar and quadripolar nature, are observable.     

An insulator-based (electrodeless) dielectrophoretic concentrator for microbes in water

Dielectrophoresis (DEP), the motion of a particle caused by an applied electric field gradient, can concentrate microorganisms non-destructively. In insulator-based dielectrophoresis (iDEP) insulating microstructures produce non-uniform electric fields to drive DEP in microsystems. This article describes the performance of an iDEP device in removing and concentrating bacterial cells, spores and viruses while operated with a DC applied electric field and pressure gradient. Such a device can selectively trap particles when dielectrophoresis overcomes electrokinesis or advection. The dielectrophoretic trapping behavior of labeled microorganisms in a glass-etched iDEP device was observed over a wide range of DC applied electric fields. When fields higher than a particle-specific threshold are applied, particles are reversibly trapped in the device. Experiments with Bacillus subtilis spores and the Tobacco Mosaic Virus (TMV) exhibited higher trapping thresholds than those of bacterial cells. The iDEP device was characterized in terms of concentration factor and removal efficiency. Under the experimental conditions used in this study with an initial dilution of 1 x 105 cells/ml, concentration factors of the order of 3000x and removal efficiencies approaching 100% were observed with Escherichia coli cells. These results are the first characterization of an iDEP device for the concentration and removal of microbes in water.     

Electric birefringence study of the purple membrane of Halobacterium halobium

An electric birefringence study was carried out on aqueous suspensions of the purple membrane of Halobacterium halobium. In addition to the characterization of both native and modified membrane samples, the dependence of electric birefringence on pH and ionic strength was also investigated. The results indicate that purple membrane shows electric birefringence at a field strength as low as 200 V/cm. The permanent dipole moment and polarizability ranged from 20,500 debyes and 1.01 × 10^?14 cm³ for a purple membrane concentration of 0.40 mg/mL to 41,000 debyes and 2.05 × 10^?14 cm³ for a concentration of 0.80 mg/mL. It was also found that removal of the retinyl group of bacteriorhodopsin substantially decreases but does not eliminate the electric birefringence of the membrane. The solubilization of the membrane by Triton X-100, however, completely abolishes the electric birefringence. These experiments indicate that there is an interaction between adjacent bacteriorhodopsin molecules within the purple membrane via the retinyl chromophore moiety that builds up the permanent dipole moment. They also suggest that there are two types of response when purple membrane suspensions are placed in an electric field. One is an alignment of the disk-shaped particles with the field. The other is a stacking of the particles following their alignment by the electric field, which is promoted by the induced dipole moment.     

Theory of single-file noise.

A general theoretical approach to the analysis of electric fluctuations generated by the so-called single-file diffusion through narrow channels is presented. The formalism is a slight extension of an approach to electric fluctuations in discrete transport systems with negligible interactions between the particles recently developed by one of the authors. In the single-file transport mechanism interactions between the particles must be taken into account. Three main results of principal interest are: (a) the electric fluctuations around stationary states (at equilibrium and non-equilibrium) are determined by the time-dependent solutions of the macroscopic single-file transport equations, (b) as a direct consquence of the interactions between the ions in the single-file transport the macroscopic time-dependent current and the autocorrelation function of the microscopic current fluctuations can exhibit damped oscillatory behavior, and the current noise spectrum can show peaking, (c) the number of binding sites for the ions within the pores seems to have a strong influence on the oscillatory behavior: with increasing number of binding sites the damping of the oscillations decreases and the peaking of the spectrum becomes stronger.     

Theory of single-file noise

A general theoretical approach to the analysis of electric fluctuations generated by the so-called single-file diffusion through narrow channels is presented. The formalism is a slight extension of an approach to electric fluctuations in discrete transport systems with negligible interactions between the particles recently developed by one of the authors. In the single-file transport mechanism interactions between the particles must be taken into account. Three main results of principal interest are: (a) the electric fluctuations around stationary states (at equilibrium and non-equilibrium) are determined by the time-dependent solutions of the macroscopic single-file transport equations, (b) as a direct consequence of the interactions between the ions in the single-file transport the macroscopic time-dependent current and the autocorrelation function of the microscopic current fluctuations can exhibit damped oscillatory behavior, and the current noise spectrum can show peaking, (c) the number of binding sites for the ions within the pores seems to have a strong influence on the oscillatory behavior: with increasing number of binding sites the damping of the oscillations decreases and the peaking of the spectrum becomes stronger.     

Electric field generated by axial longitudinal vibration modes of microtubule

Microtubules are electrically polar structures fulfilling prerequisites for generation of oscillatory electric field in the kHz to GHz region. Energy supply for excitation of elasto-electrical vibrations in microtubules may be provided from GTP-hydrolysis; motor protein–microtubule interactions; and energy efflux from mitochondria. We calculated electric field generated by axial longitudinal vibration modes of microtubules for random, and coherent excitation. In case of coherent excitation of vibrations, the electric field intensity is highest at the end of microtubule. The dielectrophoretic force exerted by electric field on the surrounding molecules will influence the kinetics of microtubule polymerization via change in the probability of the transport of charge and mass particles. The electric field generated by vibrations of electrically polar cellular structures is expected to play an important role in biological self-organization.