Abstract
Abstract Electric birefringence (EB) and electric linear dichroism (ED) of a sonicated DNA (Mw=1.24×105) sample were studied in solutions containing various additives at 7 °C. Signals of EB at 535 nm and of ED at 260 nm were measured in the electric field range 0–ca. 19 kV/cm. Both signals obeyed the Kerr law at low field strengths (E<ca. 5 kV/cm) and showed a saturating trend at high fields. The mean relaxation time, <τ>EB, obtained from the decay of EB, was field-strength dependent, indicating the effect of the polydispersity of sDNA. The field strength dependence of steady-state EB signals was nearly identical with that of ED signals. These results were analyzed with the “classical” orientation functions derived for mono- and polydisperse systems. The optical anisotropy factor (g3–g1) of sDNA was ca. −2.0×10−2, while the average angle between the orientation axis of sDNA and the transition moment of the base pair was ca. 70° at 260 nm. The electric moment of sDNA was influenced by ionic strength, counterions, and other additives. The weight-average length lw of sDNA decreased in this order: 0.2 mM NaCl**>9-aminoacridinium chloride (P⁄D=10)>1.0 mM NaCl>0.33 mM MgCl2> 20 vol% glycerol. Values of lw/base pair were 2.8−2.7 Å in the glycerol and 3.6−3.4 Å in the 1.0 mM NaCl.
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