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Electro‐optic scattering studies on deoxyribonucleic acid
Author(s) -
Jennings B. R.,
Plummer H.
Publication year - 1970
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1970.360091106
Subject(s) - dipole , electric field , chemistry , rotational diffusion , birefringence , intensity (physics) , dielectric , relaxation (psychology) , anisotropy , molecular physics , scattering , moment (physics) , electric dipole moment , nuclear magnetic resonance , stiffness , optics , molecule , physics , classical mechanics , thermodynamics , optoelectronics , psychology , social psychology , organic chemistry , quantum mechanics
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 (Δ 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 Δ I was observed, from which a rotary diffusion constant ( D ) of 1200 s −1 was determined. Interpreting the electric field data in terms of the classical dipolar orientation theory led to values of 2.4 × 10 −25 cm (7.4 × 10 −14 esu) and 4.3 × 10 −25 cm (13 × 10 −14 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 Kratky‐Porod “stiffness” parameter of x = 24 for the wormlike coil model. Although curved, the molecules appeared to orientate in low‐intensity 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.