Circular dichroism of flow‐oriented nucleic acids. II. Comparison between observed and calculated spectra

The ultraviolet circular dichroism (CD) of oriented DNA and RNA molecules is calculated by an extension of Johnson and Tinoco's theory [(1969) Biopolymers 7, 727–749] for unoriented molecules. The calculations are carried out for molecular models of A‐DNA, B‐DNA, planar B‐DNA, C‐DNA, and RNA‐11‐α. The calculated curves are compared to measured spectra [(1975) J. Mol. Biol. 92, 449–466] Chung and Holzwarth, for oriented solutions of DNA in buffer, DNA in 6 M LiCl or in ethylene glycol, and double‐stranded viral RNA. The calculation, which considers only base–base interactions, predicts that the CD of B‐DNA, measured with light propagating parallel to the helix axis, should be large and semiconservative, whereas the CD for light propagating perpendicular to the helix axis should be nonconservative. These predictions agree qualitatively with the experimental observations for DNA in buffer; agreement improves if one assumes the bases to be exactly perpendicular to the helix axis. For the other geometries, agreement is less satisfactory, but qualitative agreement with experiment is obtained and the signs of the specific CD spectra are in accord with observations.