The optical activity of nucleic acids and their aggregates.

Abstract

This review includes experimental and theoretical work on absorption and scattering of light by chiral macromolecules. All molecules absorb light, but only chiral (handed) molecules show a preferential absorption for right or left circularly polarized light. This phenomenon of circular dichroism (CD) has been very useful in characterizing any chiral aggre­ gate of chromophores-including proteins, nucleic acids, and their complexes. We discuss theoretical methods that relate the absorption and circular dichroism of a polymer or aggregate to the optical proper­ ties of its constituent parts. The experimental data reviewed is limited essentially to nucleic acids, for lack of space. Two new experimental methods that are particularly useful for mac­ romolecules or for systems that scatter a significant fraction of the incident light are fluorescence-detected circular dichroism and circular intensity differential scattered light. Fluorescence-detected circular di­ chroism (FDCD), as the name implies, used the intensity of the fluores­ cence emitted to monitor the intensity of the light absorbed (167). This method provides two main advantages: (a) The spectrum of a complex system containing many chromophores, but only a few fluorophores is greatly simplified, and (b) scattering artifacts, which plague circular dichroism studies using transmitted light measurements, are partly avoided by use of fluorescence detection. The theory (159, 160) and