The orientation and dissociation field effect of DNA in solution

Abstract

INTRODUCTIONA high electric field may affect the electrolyte conductivity of a polyelectrolyte solution with very long stretched polyions in two different ways. An increase of the conductivity because of increased dissociation is generally observed at high field strengths (dissociation field effe~t).l-~ On the other hand, there is an effect of the field on the mean mobility of the charge carriers which may be noticeable even a t moderate field strengths. Due to polarization of the inner ionic atmosphere of the polyions, electric dipoles are induced on these particles, causing an orientation of their long axes in direction of the field. As a consequence of anisotropy of the nonspherical particles, anisotropy of the conductivity is produced in the solution (orientation field effect) .6 This effect has been established experimentally with dilute solutions of highly polymerized polyph~sphates.~*~J In this case, particularly large electric dipole moments are created on the long stretched polyions. The experimental results are in good agreement with theoretical conclusions.6JThe magnitude of the orientation field effect decreases rapidly with decreasing length of the polyions. For this reason all attempts so far to measure the effect for other polyelectrolytes with smaller polyions had failed because of experimental difficulties. By means of a somewhat improved experimental set-up it has been possible now to detect the effect in the case of certain samples of desoxyribonucleic acid (DNA). This substance is of particular interest, since its polyions in the helical form8 are supposed to be fairly rigid, having only a slight flexibility,9J0 in contrast to the polyphosphate ions which are more or less coiled, depending on concentration. This different structure should result in a different concentration dependence of the orientation field effect of polyphosphate and DNA. Thus the measurements with DXA provide an important test of previous discussions on the nature of the orientation field effect. Measurements of the dissociation field effect of DNA have also been performed and discussed.

Linear Dichroism of Biological Chromophores

“…The mechanism of DNA orientation is still not well understood. Evidence from dielectric dispersion studies (292,293) and high field denaturation of DNA (294) suggests that the induced dipole moment originates primarily from the migration of ions along the molecular surface. Field reversal experiments (81,286) show that the orientation arises from a field-induced dipole, and transient electric birefringence experiments seem to show that in the absence of a large counterion density the induced dipole moment decreases precipitously (295).…”

Orientation effects on the electrophoretic mobility of rod-shaped molecules in free solution

“…The orientation of rod-shaped charged polyelectrolytes under the influence of an electric field has been measured by a number of techniques including electrical birefringence (1-6), electrical conductivity (7,8), and transient electric dichroism (9).…”

Biochemical Analysis

“…A recent paper considered the effect of an electric field on the electrolyte conductivity in solution (158). Studies on DNA showed that field effects w-ere observable and conformed to theory.…”