Dielectric theory and properties of DNA in solution

Manipulation of coacervate droplets with an electric field

Many biopolymers are highly charged, and as in the case of many polymer mixtures, they tend to phase separate as a natural consequence of chain connectivity and an associated relatively low entropy of polymer mixing. Recently, it has become appreciated that the phase-separated structures formed by such polyelectrolyte blends, called "complex coacervates," underlie numerous biological structures and processes essential to living systems, and there has been intense interest in understanding the unique physical features of this type of phase-separation process. In the present work, we are particularly concerned with the field responsiveness of stabilized coacervate droplets formed after the phase separation of polyelectrolyte blend solution and then exposed to deionized water, making the droplet interfacial layer acquire a viscoelastic character that strongly stabilizes it against coalescence. We show that we can precisely control the positions of individual droplets and arrays of them with relatively low-voltage electric fields (on the order of 10 V/cm) and that the imposition of an oscillatory field gives rise to chain formation with coarsening of these chains into long fibers. Such a phase-separation-like process is generally observed in electrorheological fluids of solid colloidal particles subjected to much larger field strengths. The key to these coacervates' electrorheological properties is the altered interfacial viscoelastic properties when the droplets are introduced into deionized water and the associated high polarizability of the droplets, similar to the properties of many living cells. Since many different molecular payloads can be incorporated into these stable droplets, we anticipate many applications.

Ionic mobility in DNA films studied by dielectric spectroscopy

Double-helix DNA molecules can be found under different conformational structures driven by ionic and hydration surroundings. Usually, only the B-form of DNA, which is the only form stable in aqueous solution, can be studied by dielectric measurements. Here, the dielectric responses of DNA molecules in the A- and B-form, oriented co-linearly within fibres assembled in a film have been analyzed. The dielectric dispersion, permittivity and dissipation factor, have been measured as a function of frequency, strength voltage, time, temperature and nature of the counter-ions. Besides a high electrode polarization component, two relaxation peaks have been observed and fitted by two Cole-Cole relaxation terms. In the frequency range that we investigated (0.1 Hz to 5 ·10(6) Hz) the dielectric properties are dominated by the mobility and diffusivity of the counter-ions and their interactions with the DNA molecules, which can therefore be characterized for the A- and B-forms of DNA.

Dielectric behavior of aqueous solutions of plasmid DNA at microwave frequencies

The relative permittivity and dielectric loss of aqueous solutions of plasmid (pUC8.c1 and pUC8.c2) DNA have been measured at 20 degrees C over the frequency range 100 MHz-10 GHz. The solutions had a concentration of 0.1% DNA, and were studied both in the relaxed and the supercoiled form. The dielectric measurements were made using a variety of techniques including frequency domain and time domain methods of operation. No evidence of any resonance absorption, nor of any other kind of enhanced absorption, was observed.

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%.

The role of the ionic environment in the orientation of nucleic acids in electric fields

The relationship between polyelectrolyte theories based on linear charge density models and the electric-field induced orientation of the polyelectrolytes, poly(A), poly(C) and DNA is examined by varying their ionic environment with respect to ionic strength and acidity. The degree of counterion condensation on the polyelectrolytes predicted by the theories of Manning and Record is shown to be related linearly to the orientation as measured by their dichroism in the field. Micro-structural differences between poly(A) and poly(C) account for the differences in their dependence on the pH of the medium which affects the counterion condensation and thus the polarization in the orienting electric fields. The results consequently support recent treatments of linear polyelectrolytes having a high charge density which model them as smoothly charged linear polyions, but indicate that these models are insufficient to account for some of the effects of microstructural variations.

Microwave dielectric relaxation in muscle. A second look

The dielectric permittivity and conductivity of muscle fibers from the giant barnacle, Balanus nubilus, have been measured at 1, 25, and 37 degrees C, between 10 MHz and 17 GHz. The dominant microwave dielectric relaxation process in these fibers is due to dipolar relaxation of the tissue water, which shows a characteristic relaxation frequency equal to that of pure water, ranging from 9 GHz (1 degree C) to 25 GHz (37 degree C). The total permittivity decrease, epsilon 0 -- epsilon infinity, due to this process accounts for approximately 95% of the water content of the tissue; thus, the major fraction of tissue water is dielectrically identical to the pure fluid on a picosecond time scale. A second dielectric process contributes significantly to the tissue dielectric properties between 0.1 and 1--5 GHz, and arises in part form Maxwell-Wagner effects due to the electrolyte content of the tissue, and in part from dielectric relaxation of the tissue proteins themselves.

Complex admittance of Na+ conduction in squid axon

The complex admittance, Y(p), of squid axon was measured (4--1000 Hz) during step voltage clamp to obtain linear data on Na+ conduction. Y(p) is used as a spectroscopic tool to identify Na+ and K+ conduction, which dominate Y(p) at low frequencies and can be separated from each other and from the static capacitance. Na+ conduction is readily distinguishable from K+ conduction in that it produces a steady-state negative conductance. The admittance of the Na+ system can show an anomalous resonance or an antiresonance depending on whether the net shunt conductance is negative or positive. Use of the Na+ negative conductance to neutralize leakage yields a measurement of dielectric capacitance at low frequency. A 90 degrees phase angle suggests that the capacitance is ideal.

Resonance induced alterations of intracellular biophysical properties

A treatment of cancer by the application of external electromagnetic energy at a resonant frequency capable of the generation of heat intracellularly to induce selective thermal death of cancer cells is described. This process also allows for the detection of cancer cells by the use of differential resonant frequencies including nuclear magnetic resonance and electron spin resonance techniques. This process permits the selective treatment of cancer cells by the compartmentalized alteration of biophysical properties in the cancer cells and the detection of cancer cells by determination of their biophysical properties. The process comprises an ability to determine the respective resonant frequencies of cancer cells and normal cells at a cellular level. An external alternating electromagnetic field is then applied at the resonant frequency of the cancer cells which differs from the resonant frequency of the normal cells. The cancer cells absorb significant energy at this resonant frequency whereas the normal cells absorb minimal energy at this frequency. Generating the heat intracellularly instead of extracellularly results in the cell's membrane, which is an effective thermal barrier, enhancing the process by keeping the heat within the cell instead of outside of the cell. This process is enhanced by the nuclear differences between cancer cells and normal cells and by the energy changes characteristic of structural and conformational changes in the deoxyribonucleic acid and the histones of the nucleus including their interrelationship. This process promises great efficacy in the diagnosis and the treatment of neoplastic and also perhaps of artherosclerotic diseases.