Counterion polarization

Three processes by which counterion polarizations of DNA and polypeptides can relax have been discussed in the literature (19, 20), with different conclusions as to the parts they play in determining the observed low frequency behavior. The three are ... 

For a particle diameter of about 1 fim, x 2 x l(F cm-, and g a 0.2, a Asg of ca. 3SOOO is obtained at room temperature. The dispersion occurs in the low-frequency range of 1—10 kHz, in quantitative agreement with the relaxation time given by (46). There can be little doubt that the still more remarkable low-frequency dielectric dispersion of biological cells and tissue is also due to such counterion-polarization effects. 

According to the fluctuation-dissipation theorem [1], the electrical polarizability of polyelectrolytes is related to the fluctuations of the dipole moment generated in the counterion atmosphere around the polyions in the absence of an applied electric field [2-4], Here we calculate the fluctuations by computer simulation to determine anisotropy of the electrical polarizability Aa of model DNA fragments in salt-free aqueous solutions [5-7]. The Metropolis Monte Carlo (MC) Brownian dynamics method [8-12] is applied to calculate counterion distributions, electric potentials, and fluctuations of counterion polarization. 

IV. COUNTERION DISTRIBUTIONS, ELECTRIC POTENTIALS, AND FLUCTUATIONS OF COUNTERION POLARIZATION... 

The polarization of ionic atmosphere around a polyelectrolyte molecule has been experimentally studied by dielectric and electro-optical techniques in a wide concentration range. In a solution with no added salt, the polyions have an extended conformation and may entangle with each other. This complicates the interpretation of the counterion polarization, since it has been theoretically analyzed for solutions with no interactions between the... 

Field strength dependence of the LF effect shows better the molecular weight dependence of the LF effect amplitude. The first power dependence of this effect on the field strength (Figure 14) means that a saturated ionic induced dipole moment, resulting from the tightly bound counterion polarization, can explain the permanent-like moment behavior of stabilized suspensions in weak fields. 

Experimentally, the molecular weight independence of the HF effect (in polyelectrolyte solutions) has been confirmed many times. Van der Touw and Mandel [64,65] attributed the HF dispersion to polarization of bound counterions along a part of the polyelectrolyte molecule. They introduced a model in which the polyelectrolyte is considered as a nonlinear sequence of rodlike subunits and the counterion polarization along the subunit is supposed to be responsible for the amplitude and the critical frequency of HF relaxation. Both quantities would essentially be independent of the molecular weight of the polyion. In solutions, where interactions between macromolecules are taken into account, the length of the above-mentioned subunit is related to the correlation distance between the macromolecular chains [25,26,92], Counterion polarization perpendicular to the polyion axis is pro-... 

An orientation assumed to originate solely from the condensed counterion polarization is theoretically predicted to be almost independent of the ionic strength [96]. Upon an increase of the ionic strength, however, the experiments show a decrease of orientation in most investigations. In the ion atmosphere treatment of Rau and Chamey [97], an additional polarization of noncondensed solvent ions is shown to appear on the addition of salt. Strong dependence of this polarization on the ionic strength is predicted. The results... 

Ookubo N, Hirai Y, Ito K, Hayakawa R. Anisotropic counterion polarization and their dynamics in aqueous polyelectrolytes as studied by frequency-do-main electric birefringence relaxation spectroscopy. Macromolecules 1989 22 1359-1366. 

Given the eomplexity of the chemical composition of the microemulsions, there are several sources of the dielectric polarization in the system. The contributions are expected to be related to the various processes connected with interfacial polarization, counterion polarization, and the motions of the anionic head groups of the siufactant molecules at the interface with the water phase (39, 96, 97,112, 113). The contribution in polarization can also be related to various components of the system containing dipole groups, such as bound and free water (114). 

As an additional remark, the decrease in the number of counterions near the polyion in the presence of high electric fields will also decrease the counterion polarization and thus the magnitude of the induced dipole moment. This, in turn, will change the reaction moment of chemical transformations involving induced dipoles. In any case, macromolecular complexes in which polyelectrolytic subunits are associated decrease in stability with increasing electric fields. 

Thus, in general, the induced dipole moment will reach a saturation value m. As pictured in Figure 2, a restricted charge displacement may be accompanied by an orientational charge of the dipole axis. The electric field dependence of the total moment may be described in terms of coth functions as in the case of the counterion polarization in linear polyelectrolytes. See also Yoshioka et... 

A counterion polarization mechanism has been proposed to explain the electric induction of conformational changes in polyelectrolyte complexes such as the (U A U) triple helix. In accordance with this idea, the external electric field shifts the ionic atmosphere of the (U A U) complex and thereby induces a dipole moment. At the negative pole of the induced macrodipole, the screening by the ion cloud of the negative phosphate residues is reduced. This, in turn, causes repulsion between the ends of the polyanions and leads finally to the unwinding of the triple helix. It later came to our attention that a polarization mechanism had already been proposed for strand separation of DNA by Poliak and Rein. " ... 

All interfaces give rise to Maxwell—Wagner and counterion polarization effects as described in Section 3.5. 

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