β Scribed by B. R. Jennings; H. Plummer
No coin nor oath required. For personal study only.
Measurements have been made of the intensity of light scattered from aqueous solutions of calf thymus DNA with and without the application of electric fields. For fields approaching 150 V/cm and frequencies below 2.5 KHz, changes (Ξ__I__) of up to 10% in the residual scattered intensity were observed. In agreement with previous dielectric and electric birefringence measurements, a low frequency dispersion of Ξ__I__ was observed, from which a rotary diffusion constant (D) of 1200 s^β1^ was determined. Interpreting the electric field data in terms of the classical dipolar orientation theory led to values of 2.4 Γ 10^β25^ cm (7.4 Γ 10^β14^ esu) and 4.3 Γ 10^β25^ cm (13 Γ 10^β14^ esu) for the permanent dipole moment and the anisotropy of the electric polarisabilities respectively. Furthermore the permanent dipole moment was along the major molecular axis and the particles orientated in the field as rigid entities. The zero field data indicated a molecular shape which was not rodlike but corresponded to the KratkyβPorod βstiffnessβ parameter of x = 24 for the wormlike coil model. Although curved, the molecules appeared to orientate in lowβintensity electric fields as rigid, but not rodlike molecules. The implications of this on recent discrepancies in D determined by two or more dynamic relaxation methods is briefly discussed.
π SIMILAR VOLUMES
It is rather difficult for me to have anticipated everything that Doctor Doty was going to talk about; and, not having had tlic pleasure of attending any of the Oak Ridge Syniposia, I have no precedence on whicli to base my activities iii the role of a discussant. I will t r y to arrange rriy remark