Optical Properties of CsDNA Films as a Function of Hydration

Abstract

The refractive indices of wet-spun films of CsDNA have been measured for light polarized parallel and perpendicular to the helical axis as a function of relative humidity (RH). These data have been combined with previously published data (Biopolymers 30 (1990) 877-887) for the volume per base pair and water content as a function of RH in order to extract the optical polarizabilities. This work was motivated by the study of Weidlich et al. (Biopolymers 26 (1987) 439-453) who reported a approximately 35% increase at the A-to-B transition in the parallel and perpendicular polarizabilities of NaDNA. In contrast, a much smaller increase in the polarizabilities of CsDNA is found near the A-to-B transition: approximately 12% for the perpendicular direction and < or = 4% for the parallel direction.

Orientational order and evolution of the properties of biomolecules in anisotropic media

“…The expression for b in Eqs. (2) indicates that the condition = [8,9] cor responds to the quantity b( ) = 1 -r 0 = b H > 0 and values L ⊥ (b H ) = < L ⊥k and Δf( ) > 0. Now , Eq.…”

“…where the correction σ to anisotropy Δf has the form (9) For the discussed objects, the quantities σ > 0 are not small and are significant for determining SΔγ values from Eq. (8).…”

“…The use of the tensor f V = ( + 2)/3 [8,9] with Δf V = σ V = 0 in Eqs. The values L j = 1/3 [10,11] correspond to A = 0, = ( )/3, Δf* = Q( -1)/3, and…”

“…For statistically uniaxial macromolecules with the longitudinal axis l, the tensor γ is characterized by the longitudinal (γ l ) and transverse (γ t ) components or by the mean value = (γ l + 2γ t )/3 and anisotropy Δγ = γ l -γ t . For bio molecules in anisotropic media, and Δγ were deter mined using the quantity [8,9] (1) for (where = (ε || + 2ε ⊥ )/3), isotropic tensor f V = ( + 2)/3 [8,9], or components L j = 1/3 [10,11]. These models predetermine and Δγ values and are responsible for unphysical consequences from spectral data [5].…”