Dielectric properties of poly-L-glutamic acid in salt-free aqueous solutions

The electric permittivity of poly-L-glutamic acid (PGA) in salt-free aqueous solutions was measured in the frequency range 2.5 kHz – 100 MHz at different concentrations and degrees of ionization. Two samples of different molecular weight were investigated. The experimental results could under most circumstances be described by a superposition of two dispersion curves of the Cole-Cole type. The low-frequency dielectric parameters were strongly molecular weight dependent, the high-frequency ones not. Strong concentration effects were observed resulting in increasing specific dielectric increments and relaxation times with decreasing concentration. Using the theory proposed by Van der Touw and Mandel to interpret the experimental results these concentration effects could be ascribed to the influence of the polyion interactions on the average dimensions and the rigidity of the polyelectrolyte chains. The change in the total dielectric increment and low-frequency relaxation time with degree of ionization correctly reflects the helix-coil transition of PGA occurring in ths region α = 0.3–0.5. The effect of counterion size and charge on the dielectric behaviour was also found to be consistent with the theoretical model.     

Dielectric properties of polyelectrolytes. I. A study on tetra-n-butyl ammonium polyacrylate

Dielectric constant and loss of aqueous solutions of tetra-n-butyl ammonium polyacrylate ((Bu)₄NPA) were measured in the frequency range from 300 Hz to 6 MHz as compared with sodium and other salts at various conditions. Our results show that there are two dispersions observed in the low-frequency range (LFD, several ten kHz to MHz), respectively, both of which are roughly expressed as the Cole-Cole dispersion formula with Cole parameters about 0.3. The large values of dielectric increment, its nonlinear concentration dependence, and other features suggest that both dispersions are explained by relaxations of two different ionic processes. For HFD, experimental results were qualitatively similar to those have been reported and compared with theories of the Maxwell-Wagner-type effect. On the other hand, LFD may be attributable to the polarization of loosely bound counterions. A model available for LFD was presented on the basis of counterion fluctuation.     

Effect of counterion concentration on the dielectric behavior of a polypeptidic chain in the helix–coil transition

On the basis of the two-state model of a polyelectrolyte solution, the ion concentration in the polymer domain has been calculated by using the spherical Poisson–Boltzmann equation. The ion accumulation in the neighboring of the polyion influences, on different time scales, various electrical properties of the solution, in particular the low-frequency electrical conductivity and the high-frequency dielectric dispersion. These predictions have been compared with recent dielectric measurements on poly (L -glutamic acid) aqueous solutions during the conformational transition from the α-helix to random coil, and a satisfactory agreement has been found. This finding suggests that counterion distribution plays a different role in determining the electrical properties of charged polymer solutions, causing a electrophoretic contribution of the polymer domain to the electrical conductivity and influencing the high-frequency dielectric dispersion. © 1993 John Wiley & Sons, Inc.     

Dielectric properties of spherical macroion suspensions. I. Study on monodisperse polystyrene latex

Dielectric properties of polystyrene latex suspended in aqueous media are investigated with special attention to the effect of volume fraction of the latex and salt concentration. The experimental data show the existence of two dispersions, one in the low-frequency range from 10(3) to 10(5) Hz. and the other in the high-frequcncy range from 10(5) to 10(7) Hz. In the salt-free system. both dispersions are of the Debye type and their relaxation limes arc insensitive to the volume fraction. Addition of H2SO4 to the suspension enlarges the magnitude of the low-frequency dispersion and reduces that of the high-frequency dispersion. whereas it does not affect the relaxation times. In the mixture of two species of counterions, e.g. H+ and Na(+), the low-frequency dispersion deviates from the Debye type. while the high-frequency dispersion docs not. From these facts, the high- and low-frequency dispersions are thought to be due to the radial and tangential components of the displacement current at the surface of the latex. The latter process is consistent with the Schwarz theory of the dielectric dispersion of colloidal suspensions.     

Passive electrical properties of the membrane and cytoplasm of cultured rat basophil leukemia cells. I. Dielectric behavior of cell suspensions in 0.01-500 MHz and its simulation with a single-shell model

Frequency dependence of relative permittivity (dielectric constant) and conductivity, or the 'dielectric dispersion', of cultured cells (RBL-1 line) in suspension was measured using a fast impedance analyzer system capable of scanning 92 frequency points over a 10 kHz-500 MHz range within 80 s. Examination of the resulting dispersion curves of an improved reliability revealed that the dispersions consisted of at least two separate components. The low-frequency component (dispersion 1) had a permittivity increment (delta epsilon) of 10(3)-10(4) and a characteristic frequency (fc) at several hundred kHz; for the high-frequency component (dispersion 2), delta epsilon was smaller by a factor of 10(2) and fc = 10-30 MHz. Increments delta epsilon for both components increased with the volume fraction of cell suspension, while fc did not change appreciably as long as the conductivity of suspending medium was fixed. By fitting a model for shelled spheres (the 'single-shell' model) to the data of dispersion 1, the dielectric capacity of the plasma membrane phase (Cm) was estimated to be approx. 1.4 microF/cm2 for the cells in an isotonic medium. However, simulation by this particular shell model failed to reproduce the entire dispersion profile leaving a sizable discrepancy between theory and experiment especially at frequencies above 1 MHz where dispersion 2 took place. This discrepancy could not be filled up even by taking into consideration either the effect of cell size distribution actually determined or that of possible heterogeneity in the intracellular conductivity. The present data strongly indicate the need for a more penetrating model that effectively accounts for the behavior of dispersion 2.     

Light scattering of aqueous solutions of DNA, poly(acrylic acid), and tobacco mosaic virus under alternating electric field

Two new techniques, amplitude modulation (AM) and frequency modulation (FM) of an electric field, are developed for the light-scattering study of polymer solutions under ac electric fields. The AM technique makes it possible to observe accurately the frequency dependence of the intensity changes of scattered light due to the electric field. The FM one allows us to obtain directly the frequency derivative of the intensity change. The techniques are applied to DNA, poly(acrylic acid), and tobacco mosaic virus in the frequency range from 10 Hz to 100 kHz. A low-frequency relaxation is found for both DNA and poly(acrylic acid). The obsersved relaxation time of DNA agrees with that in the dielectric relaxation of DNA, which has been attributed to the rotation of the molecule with a quasipermanent dipole. In the case of poly(acrylic acid), the relaxation strength increases with increasing degree of neutralization. TMV at a concentration of 0.1% exhibits a negative relaxation at low frequencies, which indicates the rotation of TMV aggregate with a permanent dipole along its minor axis.     

Effect of ions on counterion fluctuation in low-molecular weight DNA dielectric dispersions

The dielectric permittivity of aqueous solutions of low-molecular weight DNA (Mr = 3.2 X 10(5) ) in the presence of MgCl2 and AgNO3 has been measured in the frequency range from 5 kHz to 30 MHz, at a temperature of 25 degrees C. The DNA concentration was 3.5 X 10(-4) M in terms of phosphate and the salt concentration was varied from 1 X 10(-5) to 2 X 10(-4) M. The dielectric results have been analyzed in terms of two contiguous dielectric dispersions, and characteristic parameters have been discussed on the basis of polyelectrolyte theories which deal with counterion fluctuation. Some molecular parameters of the DNA molecule in electrolyte solutions are estimated.     

High-frequency dielectric study of side-chain dynamics in poly(lysine) aqueous solutions

The high-frequency dielectric properties of poly(lysine) of different chirality in aqueous solutions have been measured in the frequency range from 1 MHz to 1.8 GHz. The dielectric spectra show the existence of relatively small dielectric dispersions at around 100 MHz that have been attributed to internal motion in the polymer chain, due to side-chain polar groups. Our results indicate that the local structure of the chain and its possibility to undergo a conformational transition induced by pH does not modify the main feature of the side-chain dynamics, the dielectric strength being largely proportional to the concentration of charged groups. A similar behavior has been found in poly(alpha-glutamate) and in poly(gamma-glutamate) aqueous solutions, where the dielectric parameters appear to be related to the change in the charge density on the main chain, rather than to the accompanying conformational helix-coil transition.     

Dielectric relaxation measurements of 12 kbp plasmid DNA

The dielectric properties of 12 kbp plasmid DNA have been measured as a function of temperature in the range 5 degrees C to 40 degrees C. Time domain reflectometry was used to obtain dielectric data over the frequency range from 200 kHz to 3 GHz. Values of the frequency dependent polarisability per DNA macromolecule have been determined from the measurements. Possible mechanisms that could account for the dielectric dispersion are also discussed, in particular the counterion fluctuation model of Manning-Mandel-Oosawa.     

Electrical Properties of Phospholipid Vesicles

The capacitance of the membrane of phospholipid vesicles and the electrical properties of the vesicle interior have been determined. To this end the electrical properties of phospholipid vesicles have been investigated over a frequency range extending from 1 kHz to 100 MHz. The dielectric behavior is characterized by two dispersions, one placed between 1 kHz and 1 MHz and the other between 1 and 100 MHz. The relaxational behavior at low frequencies is explained by counterion movement tangential to the vesicle surface and a reasonable value for the fixed charge of the vesicles is calculated from the dispersion magnitude. The relaxation at high frequencies is of the Maxwell-Wagner type and appears caused by the phospholipid bilayer bounding the interior phase of the vesicles. It is consistent with the existence of a closed bilayer with a capacitance of about 2 μF/cm² and an internal phase similar to the vesicle suspending medium. There is no indication of other than normally structured water inside the small vesicles.     

Dielectric increment and dielectric dispersion of solutions containing simple charged linear macromolecules. II. Experimental results with synthetic polyelectrolytes

The electric permittivity of aqueous solutions of different synthetic polyelectrolytes have been measured as a function of frequency in the range 5 kHz up to 100 MHz in the absence of added salt. Solutions of polymethacrylic acid and polyacrylic acid of different degrees of polymerization, both partially neutralized with NaOH, were investigated as well as solutions of Na-polystyrenesulphonate at different concentrations.For all systems a dispersion profile with two separated dispersion regions was obtained with a molecular weight dependent value of the static electric permittivity. The low frequency dispersion region was found to be characterized by a molecular weight dependent mean relaxation time while for the high frequency dispersion region both the mean relaxation time and the dielectric increment are molecular weight independent. It is shown that the reciprocal values of the specific increments and of the relaxation times depend linearly on the macromolecular concentration. Extrapolation of the corresponding quantities to infinite dilution was found to be possible. A comparison of these extrapolated values with calculated ones according to the previously derived theory also applicable to flexible macromolecules establishes that this theory describes satisfactorily the dielectric behaviour of the systems investigated.The conclusion is reached that the high frequency dispersion and relaxation can be attributed to fluctuations in the distribution of bound counterions along limited parts of the macromolecule. The relaxation time of the low frequency dispersion region seems to be essentially determined by the rotation of the complete molecule and the static electric permittivity can he explained in terms of fluctuations in the counterion density extending over the whole macromolecule.     

Dielectric behavior of DNA in water–organic co-solvent mixtures

The radiowave dielectric dispersions of DNA in different water–organic co-solvent mixtures have been measured in the frequency range from 100 kHz to 100 MHz, where the polarization mechanism is generally attributed to the confinement of counterions within some specific lengths, either along tangential or perpendicular to the polyion chain. The dielectric dispersions have been analyzed on the basis of two partially different dielectric models, a continuum counterion fluctuation model proposed by Mandel and a discrete charged site model, proposed by Minakata. The influence of the quality of the solvent on the dielectric parameters has been investigated in water–methanol and water–glycerol mixtures at different composition, by varying the permittivity ?_m and the viscosity η of the solvent phase. The analysis of the dielectric spectra in solvents where electrostatic and hydrodynamic interactions vary with the solvent composition suggests that both the two models are able, in principle, to account for the observed high-frequency dielectric behavior. However, while some certain assumptions are necessary about the polyion structure within the Mandel model, no structural prerequisite is needed within the Minakata model, where the polarization mechanism invoked considers a radial counterion exchange with the outer medium, which is largely independent of the local polyion conformation.     

Passive electrical properties of the membrane and cytoplasm of cultured rat basophil leukemia cells. II. Effects of osmotic perturbation

The effects of osmotic perturbation on the dielectric behavior of cultured rat basophilic leukemia (RBL-1) cells were examined. Cells exposed to osmolalities (pi) of 145-650 mosmolal showed dielectric dispersions of the following characteristics: Permittivity increment delta epsilon(= epsilon l - epsilon h where epsilon l and epsilon h refer to the low- and high-frequency limit values) for a fixed volume concentration increased with pi; gross permittivity behavior was apparently of a typical Cole-Cole type; however, frequency dependence of conductivity was undulant and could be simulated by a superposition of two separate Cole-Cole type dispersions; separation of these subdispersions along the frequency axis was an increasing function of pi, and so was conductivity increment in the high-frequency region. As examined by light microscopy, the cells were spherical in spite of imposed anisotonic stresses and behaved as osmometers at 200-410 mosmolal. When normalized by dividing by number (not volume) concentration, delta epsilon remained relatively constant irrespective of pi. Apparent membrane capacities (Cm), analyzed by applying a single-shell model, increased systematically from a hypotonic value of approx. 1 microF/cm2 up to 5 microF/cm2 at 650 mosmolal. This increase was interpreted as due to increased cellular 'surface/volume' ratios that were confirmed by scanning electron microscopy. Cole-Cole's beta parameter, which culminated around 0.9 for isotonic cells and declined to approx. 0.8 for anisotonic cells, did not parallel the broadening of cell volume distribution but appeared to reflect changes in the intracellular conductivity caused by the anisotonic challenge. The results indicate that the dispersion method can probe changes in surface morphology as well as subcellular organelles' constitution of living cells.     

Electric permittivity of alfalfa mosaic virus in aqueous solutions

The electric permittivity of alfalfa virus particles in buffer solutions of three different concentrations at pH 7 was studied between 10 kHz and 100 MHz. The experimental results could be described with one single dispersion curve of the Cole-Cole type characterized by a concentration independent specific dielectric increment and mean relaxation time. The results were interpreted semi-quantitatively in terms of counterions–atmosphere polarizability, neglecting counterion repulsion.     

Dielectric properties of aqueous solutions of sonicated DNA above 40 MHz

The dielectric properties of sonicated calf-thymus DNA sodium salt in aqueous solutions have been studied in the frequency range from 40 MHz to 2 GHz by time domain spectroscopy (TDS). A dielectric dispersion not previously reported was found, which has a characteristic frequency of about 150 MHz. All of the dielectric parameters are insensitive to the size of DNA fragments and to helix-to-coil transitions. The study of this dispersion as a function of DNA concentration and temperature allows us to conclude that it may be due to counterion fluctuation on short sections, probably in a direction transverse to the macromolecular axis.     

On the electric polarization of DNA

Dielectric dispersion of DNA was studied in the frequency range 100 Hz–100 kHz at four different temperatures (6–30°C). The dielectric increment ε₀–ε_∞ increased with the rise of temperature. The relaxation time, on the other hand, decreased. Both the increase in dielectric increment and the decrease in relaxation time could not be explained on the basis of the counterion polarization theory. Dipole moment was estimated from Kirkwood theory. It was found to decrease systematically with temperature. Even at 0°C there was a dipole moment of 10⁴D.     

Dielectric analysis of Escherichia coli suspensions in the light of the theory of interfacial polarization.

Dielectric measurements of Escherichia coli suspensions were carried out over a frequency range from 10 kHz to 100 MHz, and marked dielectric dispersions having characteristic frequency of approximately 1 MHz were observed. On the basis of the cell model that a spheroid is covered with two confocal shells, a dielectric theory was developed to determine accurately four electrical parameters for E. coli cells such as the conductivity of the cell wall, the dielectric constant of the cell membrane, and the dielectric constant and the conductivity of the protoplasm. The observed data were analyzed by means of the procedure based on the dielectric theory to yield a set of plausible electrical parameters for the cells. By taking account of the size distribution of the cells and a dielectric relaxation of the protoplasm, the observed dispersion curves were successfully reconstituted by the present theory.     

Dielectric study of low-molecular weight mannan triacetate in chloroform

The permittivity ϵ′ and dielectric loss ϵ′' of low-molecular weight mannan triacetate in chloroform in the frequency range 1 kHz to 10 MHz at 20°C are reported. Deviations from a rod-like configuration are suggested to account for the observed behaviour of the dielectric relaxation time as a function of the degree of polymerization.     

Hydrodynamic behavior and molecular conformation of poly(L-lysine HBr) in carbonate buffer solution

In carbonate buffer at pH 10.5, a transparent solution of poly(L -lysine HBr) was obtained up to fairly high concentration of 3 g/dl at room temperature. The hydrodynamic behavior of the solution has been studied by sedimentation analyses and viscosity measurements. A dimer form for high concentrations and a monomer form for low concentrations were inferred. The dimer and monomer forms were assigned to a β-structure and α-helix, respectively, based on the CD and optical rotary dispersion spectra. Using CD spectroscopy, a reversible transition between α-helix and β-structure was observed as a function of either poly(L -lysine HBr) concentration or temperature. An aggregated form which was assigned to the antiparallel pleated sheet appeared at 50°C on the basis of its ir spectrum.