Dependence of the internal relaxation time for DNA on salt type as inferred by quasielastic light scattering

Abstract

AbstractQuasielastic light scattering methods were used to study calf thymus DNA in solutions of LiCl, NaCl, NH4Ac, and NH4Cl. Plots of the reciprocal relaxation time (1/τ) vs sin2(θ/2), where θ is the scattering angle, exhibit two linear regions, in accordance with theories for semiflexible polymers based on the t → 0 approximation. In these theories the slope of the linear region at low angles is associated with the translational diffusion coefficient (Dt), whereas the slope of the linear region at high angles is associated with the segmental diffusion coefficient (Ds = kT/ƒs). The midpoint of the “transition” between these two linear regions is associated with the mean displacement between segments (b). Data presented here indicate that the Rouse‐Zimm parameters b and ƒs are significantly different for DNA in 0.4M NH4Cl relative to the other salts at comparable ionic strengths. It is suggested that this difference reflects local solvent structure and that both b and Ds are sensitive to the local water structure.