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

Response of a Permanently Charged Polyelectrolyte Brush to External Ions: The Aspects of Structure and Dynamics

Structure and dynamics inside permanently charged polyelectrolyte brushes, sodium polystyrene sulfonate brushes, during their response to the introduction of external ions (NaCl) are investigated by neutron reflectivity and dielectric spectroscopy. Neutron reflectivity measurements show that the segmental density of the inner part of the brushes decreases and that of the outer part increases when the salt level is tuned from the salt-free condition to a moderate level (<10^-2 M)-the brushes swell further compared with the salt-free condition. This is attributed to the breakup of the multiplets formed by dipole-dipole pairs, and by this process, the previously constrained chain segments by the multiplets are released. Dielectric spectroscopy discovers a giant dipole by the charge separation of the adsorbed counterions and the PSS^- chains, induced by electric field. The dynamics of the induced giant dipole is accelerated with the increase of external salt, as a result of the charge regularization by elevated salt level. At high-enough salt level, the screening effect reduces the electrostatic repulsion between the neighboring chains and makes the brushes shrink.

Barrier-induced dielectric counterion relaxation at super-low frequencies in salt-free polyelectrolyte solutions

Based on the thermally activated diffusion of counterions over the barrier of the electrostatic binding potential, we construct a scaling theory for the slow dielectric response in dilute and semi-dilute polyelectrolyte solutions. The theory is based on an analytic evaluation of the mean-escape time of a single counterion from the surface of a polyelectrolyte chain and uses a variational expression for the electrostatic potential of a charged cylinder including counterion condensation. This mean-escape time shows a range of characteristic power-law dependencies on the polyelectrolyte length and the polyelectrolyte monomer concentration. The existence of this novel dielectric mode at super-low frequencies reflects the wide spectrum of experimental findings for the super-low-frequency dielectric relaxation mode and thereby helps to reconcile conflicting interpretations of experimental data in terms of conventional scaling laws. We also devise a scaling theory for the counterion condensation of finite-length polyelectrolyte chains at finite concentration, which allows us to include polyelectrolyte charge renormalization in dilute as well as semi-dilute solutions in a unified theoretical framework.

Dielectric behavior of polyelectrolytes II. The cylinder

The dipolar correlation function for a system of coupterions diffusing on the surface of a polyelectrolyte cylinder is computed. The influence of screened coulombic repulsions on the dielectric increment is determined. Dissociation and reassociation of the counterions to the cylinder is treated microscopically and the coupled bulk diffusion is solved in the presence of the Poisson-Boltzmann potential. It is found that the correlation function contains a small, fast decaying, molecular weight independent part arising from diffusion around the cylinder and a large, slowly decaying, molecular weight dependent part arising from diffusion along the cylinder axis. The dissociation-reassociation kinetics can play a large, possible dominant, role in determining the relaxation rates.

Liposome-induced DNA compaction and reentrant condensation investigated by dielectric relaxation spectroscopy and dynamic light scattering techniques

Interaction of DNA with oppositely charged objects, such as multivalent ions, cationic surfactants, cationic liposomes, basic proteins, and alcohols, up to nano- or mesoscopic particles, gives rise to a very interesting and fascinating phenomenology, where the shape, size, and stability of the resulting aggregates depend on a delicate balance between different driving forces, mainly of electrostatic origin. We have studied the cationic liposome-DNA complexes during the whole complexation process, below, close to, and above the isoelectric condition, where the number of cationic lipids equals the number of phosphate groups on the DNA chain. We took advantage of the combined use of dynamic light scattering, laser Doppler electrophoretic mobility, and radio-wave dielectric relaxation measurements in order to characterize both the structural parameters (hydrodynamic radius) and the electrical parameters (charge and counterion concentration) of the resulting structures. These structures are fundamentally of two types, clusters of liposomes stuck together by DNA chains (cluster phase in low-density colloidal suspension) and coexisting DNA coils and DNA globules, according to the procedure through which interactions occur (liposomes in excess DNA solution or DNA in excess liposome suspension).

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 eta 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.

Dielectric scaling in polyelectrolyte solutions with different solvent quality in the dilute concentration regime

In this note, we present a set of radiowave dielectric spectroscopy measurements of two dilute, differently-charged polyelectrolyte solutions, under different solvent conditions. We have found that both the dielectric strength, Delta epsilon, and the relaxation time, tau(ion), of the dielectric relaxation process associated with the counterion polarization along a length scale of the order of the correlation length obey the scaling laws with the polyion concentration, according to the Ito model. This is verified with good accuracy independently of the quality of the solvent, which has been varied from poor to good solvent conditions. This finding supports evidence to the fact that, in dilute solutions, the counterion polarization is independent of the polyion concentration, in spite of what occurs at the semi-dilute concentrations.

A study of the dielectric properties of E. coli ribosomal RNA and proteins in solution

The permittivity of ribosomal proteins and ribosomal RNA (rRNA) in solution was measured in the range 100 kHz to 1 GHz at four different temperatures (5, 15, 25 and 35 degrees C). The experimental dielectric relaxation was analysed by the Cole-Cole equation and, from the best-fit parameters, the average values of the dipole moment and molecular radius of the proteins were obtained. The activation enthalpy was calculated from an Arrhenius plot of the relaxation time. The energy involved in the dielectric polarization of free proteins has a magnitude of about one hydrogen bond. The data on RNA were analysed according to the Mandel model. This analysis allowed the calculation of the "subunit b" as defined by Mandel. This parameter is dependent on the temperature and therefore the relaxation time does not follow the Arrhenius law. Our data thus show that, in solution, the rRNA structure is thermally rather unstable and highly flexible.

Polarization of counterions in polyelectrolytes

A theory of the polarization of counterions bound to a polyion, such as a DNA, in low and high electric field strengths is developed using statistical mechanics of inhomogeneous systems. For low fields, one finds that the polarizability p is (Zq)2rho0betaL3/(12[l + Lrho0sigma(L, b, xi, Z, I, rho0)]), where sigma = integral1 0(lambda' - lambda0) ¿dc(lambda - lambda')/dlambda¿lambda = lambda0 dlambda']), Z and L are the valence and the length of the polyion, respectively, q is the proton charge, beta = 1/kBT, T is the temperature, kB is the Boltzmann constant, I is the ionic strength, lambda = x/L and lambda0 = x0/L are scaled distances, x0 is a reference point such that the inhomogeneous counterion density at x0 is equal to rho0--the uniform density in the absence of an electric field E--and c(x) is the direct correlation function of the homogeneous counterion-polyion phase, which includes attractive and repulsive interactions. If Lsigma(L, ...) is much less than one, then the polarizability is proportional to L3. If the term Lsigma(L, ...) is much larger than one, the polarizability scales as L2. The induced dipole moment saturates and its value is the same as that of Mandel-Manning theories. The onset of the saturation, however, depends critically on the direct correlation function and hence polyelectrolyte effects. In the formalism, the polarization of the counterions is the equilibrium response to an electric field provided E is less than Esaturated. A dynamical scheme that incorporates the fact that in high fields the bound counterions conduct is discussed.

Temperature dependence of DNA dielectric dispersion at radiofrequency

We have studied the dielectric behavior of DNA aqueous solutions at various ionic strengths and in the presence of the specific DNA ligand ethidium bromide, in the frequency range 1 MHz-1 GHz, at different temperatures ranging from 5 to 40 degrees C. The activation enthalpies of the dielectric relaxations studied were obtained by Arrhenius plots of In(tau T)-1 vs. T-1. The results are consistent with a counterion fluctuation model as previously developed by Mandel and colleagues.

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.

Conversion of B DNA between solution and fiber conformations

At low salt and high DNA concentration, rodlike DNA molecules form specific aggregates containing about seven parallel DNA molecules packed in a bundle. Bundle formation can be reversed by addition of small amounts of EDTA, and formation of the specific aggregates can be induced at higher salt concentration by addition of trivalent ions. In contrast to monomeric DNA, the aggregated species has the optical anisotropy expected for the B form as observed in fibers.

Dielectric behavior of linear polyelectrolytes

The dipolar correlation function for a system of counterions diffusing on the surface of a polyelectrolyte cylinder is computed. Repulsive coulombic interactions between the counterions are taken into account. Lateral dissociation and reassociation to the cylinder is treated microscopically. Numerical calculations needed to obtain quantitative results for the long time behavior are presented. The model dependence on its parameters is interpreted with special emphasis on parameter values typical of DNA.