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.     

Dielectric behavior of DNA solution at radio and microwave frequencies (at 20 degrees C).

The dielectric constant and conductivity of calf thymus DNA were investigated at frequencies between 0.1 MHz and 70 GHz. This work is to investigate the dielectric properties of DNA in low gigahertz region and also to study whether the dielectric behavior of the water is affected by the presence of highly charged DNA. The results of these measurements indicate the presence of two anomalous dispersions, the one between 1 MHz and 1 GHz and the second one above 1 GHZ. The dispersion at low frequencies is likely to arise from polar groups in the DNA molecule. The relaxation behavior of unbound water in DNA solution is only slightly affected by the presence of DNA at concentrations below 1%.     

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 properties of developing rabbit brain at 37 degrees C

The dielectric properties of developing rabbit brain were measured at 37 degrees C between 10 MHz and 18 GHz using time domain and frequency domain systems. The results show a variation with age of the dielectric properties of brain. An analysis of the data suggests that the water dispersion in the brain of newly born animals can be represented by a Debye equation. This dispersion increases in complexity with age, and there is evidence of a smaller additional relaxation process centered around 1 GHz. It is concluded that the principal contribution to this subsidiary dispersion region arises from water of hydration.     

Electric permittivity and dielectric dispersion of low-molecular weight DNA at low ionic strength.

The dielectric properties of sonicated calf-thymus DNA (MW approximately 3 X 10(5) g mol-1) have been investigated in a frequency range between a few kHz and 100 MHz. Two samples, sonicated in a different way were used after proper characterization including light-scattering, viscometry and contour length distribution by electron microscopy. Dielectric measurements were performed at several concentrations between 10(-4) and 3 X 10(-3) monomol 1-1 and 22 degrees C. Under all circumstances two separated dispersion regions were observed, the corresponding specific increments of which decreased with increasing concentration. The same was observed with the mean relaxation time of the high frequency dispersion. Both the frequency and concentration dependence was largely analogous to what is observed with other polyelectrolytes. Values of the dielectric parameters extrapolated to infinite dilution could also be interpreted in the same manner as for more simple, charged macromolecules and no specific effects had to be taken into account.     

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.     

Dielectric behavior of wild-type yeast and vacuole-deficient mutant over a frequency range of 10 kHz to 10 GHz.

Dielectric behavior of Saccharomyces cerevisiae wild-type and vacuole-deficient mutant cells has been studied over a frequency range of 10 kHz to 10 GHz. Both types of cells harvested at the early stationary growth phase showed dielectric dispersion that was phenomenologically formulated by a sum of three separate dispersion terms: beta 1-dispersion (main dispersion) and beta 2-dispersion (additional dispersion) and gamma-dispersion due to orientation of water molecules. The beta 1-dispersion centered at a few MHz, which has been extensively studied so far, is due to interfacial polarization (or the Maxwell-Wagner effect) related to the plasma membrane. The beta 2-dispersion for the vacuole-deficient mutant centered at approximately 50 MHz was explained by taking the cell wall into account, whereas, for the wild-type cells, the beta 2-dispersion around a few tens MHz involved the contributions from the vacuole and cell wall.     

Microwave dielectric measurements of erythrocyte suspensions.

Complex dielectric constants of human erythrocyte suspensions over a frequency range from 45 MHz to 26.5 GHz and a temperature range from 5 to 40 degrees C have been determined with the open-ended coaxial probe technique using an automated vector network analyzer (HP 8510). The spectra show two separate major dispersions (beta and gamma) and a much smaller dispersion between them. The two major dispersions are analyzed with a dispersion equation containing two Cole-Cole functions by means of a complex nonlinear least squares technique. The parameters of the equation at different temperatures have been determined. The low frequency behavior of the spectra suggests that the dielectric constant of the cell membrane increases when the temperature is above 35 degrees C. The real part of the dielectric constant at approximately 3.4 GHz remains almost constant when the temperature changes. The dispersion shifts with temperature in the manner of a thermally activated process, and the thermal activation enthalpies for the beta- and gamma-dispersions are 9.87 +/- 0.42 kcal/mol and 4.80 +/- 0.06 kcal/mol, respectively.     

The dipolar origin of protein relaxation

1. A set of parameters is proposed to check the interpretation of the dielectric behaviour of protein solutions as a rigid-dipole relaxation of prolate ellipsoids of revolution in the frequency range between 20 kHz and 10 MHz. Besides the delta(b)-function of Scheraga, another analogous function (delta(a)) is presented to establish size and shape of globular proteins. A study of the influence of solvent viscosity on the dielectric dispersion also gives strong evidence in favour of rigid-dipole relaxation. 2. Measurements of the dielectric dispersion of monomer solutions of bovine serum albumin and transferrin are reported. Monomers of bovine serum albumin were obtained by fractionation on Sephadex G-150. Low-conductivity solutions of both proteins are obtained by passage through an ion-exchange resin. 3. Computer analysis of the experimental dispersion curves by use of a two-term Debye dispersion gives valuable information about transferrin and leads to an axial ratio 4.5 for a prolate ellipsoid of revolution. The dielectric increment of bovine serum albumin is very low and no conclusive results have yet been obtained.     

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.     

Dielectric behaviour of frozen DNA in solution

In this article, measurements are reported on ice and frozen DNA solutions between 100 Hz–10 MHz. Pure ice is shown to exhibit single relaxation behaviour, which confirms previous work taken over a more restricted frequency range. The frozen DNA solution displays double‐dispersion behaviour. One dispersion centred around 3 kHz is due to a defect mechanism while the other, centred around 2 MHz, may be attributed to counterion flow through the water immediately adjacent to the DNA molecule. Bioelectromagnetics 20:40–45, 1999. © 1999 Wiley‐Liss, Inc.     

Dielectric studies of electrolytic poly(α-amino acid)s in aqueous solutions

The dependence of the dielectric constant and dielectric loss of aqueous solutions of poly-ε, N-succinyl-L -lysine on its degree of polymerization, degree of neutralization, concentration of the polymer, and counterion type was studied in a frequency range from 300 Hz to 5 MHz. Regardless of the conformation, a low-frequency dispersion in a frequency range lower than 10 kHz and a high-frequency dispersion in a range higher than 100 kHz were found. The large value of the dielectric increment, its nonlinear dependence on concentration, its remarkable dependence on counterion type, and its dependence on the degree of polymerization suggest that the low-frequency dispersion is mainly due to the polarization of loosely bound counterions. These data were found for both the helical and coiled forms. The rotational motion of the electric dipole on the molecule could not have been primarily responsible for these results. On the other hand, the high-frequency dispersions may be attributable to the Maxwell–Wagner-type effect. The results were compared with the dispersions of poly(L -glutamic acid), poly(L -lysine), and their salts reported previously.     

Electric behaviour of natural and demineralized bones. Dielectric properties up to 1 GHz

In this paper we have measured the dielectric spectrum of water-saturated bones in native and demineralized states up to 1 GHz in the time domain. A novel method of analysis of the time domain spectroscopy data has been used. The results show a dielectric dispersion centered around 400 MHz for native samples and around 200 MHz for demineralized ones. The proposed mechanism for this dispersion is the movement of polar side chains, which is in agreement with what happens in hydrated collagen fibres.     

Microwave absorption in oligomers of ethylene glycol

The dielectric properties of biologically and pharmaceutically important low-molecular weight ethylene glycols H(-OCH2CH2-)n -OH (n = 1,2,4,6) were investigated to clarify the effect of chain length on the dielectric properties. The measurement of dielectric constant and dielectric loss was carried out over the frequency range 200 MHz to 20 GHz at temperatures of 25 degrees C to 55 degrees C. It is found that in these molecules microwave dielectric losses are significant. The dispersion behaviour of these molecules can be represented by Cole-Cole equation. The dielectric properties of these homologous ethylene glycols are discussed in terms of the effects of chain length and intermolecular hydrogen bonds regarding the molecular conformations. These wide frequency range dielectric data have also been discussed in view of the suitable selection of the oligomer of ethylene glycol for cosmetic preparations and other pharmaceutical applications with the intention of protection of the skin from weak microwave radiations present in the surrounding environment. These systematic microwave dielectric data with frequency and temperature variation are not available and are provided in this paper.     

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 properties of mouse lymphocytes and erythrocytes

In order to study the effect of the nucleus on dielectric behavior of the whole cell, permittivity (dielectric constant) and conductivity of mouse lymphocytes and erythrocytes were measured over a frequency range from 0.1 to 250 MHz. Erythrocytes (spherocytes) showed a single dielectric dispersion, which was explained by a single-shell model that is a conducting sphere covered with a thin insulating shell. On the other hand, lymphocytes showed a broad dielectric dispersion curve which was composed of two subdispersions. The high-frequency subdispersion, which was not found for erythrocytes, was assigned to the Maxwell-Wagner dispersion of the nucleus occupying about 65% of the total cell volume. Analysis of the lymphocyte dispersion was carried out by a double-shell model, in which a shelled sphere, i.e., nucleus, is incorporated into the single-shell model. The following electrical parameters were consequently estimated; the capacitance of the plasma membrane, 0.86 microF.cm-2; the conductivity of the cytoplasm, 3.2 mS.cm-1; the capacitance and conductance of the nuclear envelope are, respectively, 0.62 microF.cm-2 and 15 S.cm-2, and the permittivity and conductivity of the nucleoplasm are 52 and 13.5 mS.cm-1.     

Dielectric relaxation spectroscopy on dimyristoylphosphatidylcholine-packaged gramicidin A

The complex permittivities of aqueous suspensions of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and of DMPC packaged gramicidin A' (DMPC-GA) have been determined over the frequency range of 1 MHz to 1 GHz and the temperature range of 0-60 degrees C. A dielectric relaxation/loss has been observed at about 66 MHz for the DMPC suspension (30 degrees C) and at about 57 MHz for the DMPC-GA suspension (30 degrees C). This dielectric relaxation/loss has been attributed to the rotational mobility of the zwitterionic group of DMPC. The temperature dependence (from 60 degrees C to 0 degrees C) of this dispersion/absorption process of the DMPC suspension indicates a sharp reduction of the dielectric relaxation at about 20 degrees C. This dielectric change is related to the conversions of shape and structure of bilayer aggregates. This sharp reduction of the dielectric relaxation disappears or broadens when GA is incorporated into the DMPC aqueous suspension. The interpretation of these results is that the GA addition into the DMPC aqueous suspension induces a small decrease of the rotational mobility of the zwitterionic group above the lipid phase transition, and a small increase of the rotational mobility of the zwitterionic group below the lipid phase transition.     

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.