Low field electric birefringence study of monovalent cation-DNA interactions |
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Authors: | C. Marion B. Roux J.C. Bernengo M. Hanss |
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Affiliation: | Laboratorie de Chimie Biologique, Université Claude Bernard, Lyon 1, 43, boulevard du 11 Novembre 1918, 69622 Villeurbanne, France |
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Abstract: | The effects of monovalent cations on DNA have been studied using static and dynamic electric birefringence. Kerr's law is obeyed in a limited E range (<30 Vcm?1) and the steady state birefringence values are close for the different cations. The birefringence kinetics have been analysed in terms of three relaxation times. On a semilogarithmice plot of Δn(t), the tail of the curve is linear over a wide range of time for Na+, K+, NH4+ and Li+. Only for Cs+ solution is no linear part found and a much longer relaxation time is determined. This only contributes a small part of the total birefringence. With Cs+ this contribution is more field-dependent than for the other cations and we observe a larger molecular flexibility. On the other hand, with Li+ a greater stiffness of the DNA molecule appears. The electrical polarizabilities anisotropies decrease in the order: Cs+ >NH+4 >K+ >Na+ >Li+. There are no significant differences in the optical anisotropy factors. |
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