Optical Rotatory Dispersion and Conformation of Polyadenylic and Polyuridylic Acids.

The application of optical rot,atory dispersion to nucleic acids and polynucleotides is fairly recent (l-6). Doty et cd. (2) made a comprehensive study of the optical rotatory dispersion of deoxyribonucleic acid, ribonucleic acid, and complexes of some homopolynucleotides; their results strongly suggested a close relationship between the optical rotations and the secondary structure of nucleic acids. A systematic study by Ts’o and his co-workers (4-7) for the optical rotatory dispersion of polyand mononucleotides in both aqueous and organic solvents also revealed the important contributions to optical rotatory dispersion of the secondary structures and base interactions of polynucleotides. Almost all these investigations, however, were made in the visible region of the spectra because of the instrument limitation. Since the rotatory properties in the visible region are directly influenced by the Cotton effects in the absorption bands, the extension of the optical rotatory dispersion measurements toward the ultraviolet region is therefore expected to provide more information than those in the visible region alone. Some such results on DNA, RNA, and mononucleotides have already been reported elsewhere (8,Q). In this report we present the optical rotatory dispersion (between 190 and 600 rnp) of polyadenylic acid, polyuridylic acid, and their complexes, with solvents of different pH values and different temperatures. The use of synthetic polynucleotides as model systems we believe will help us understand the more complicated natural nucleic acids, which contain a multiplicity of bases and base sequences. Our results not only corroborate data in the corresponding absorption spectra, but also contain considerable detail not evident there, thus establishing optical rotatory dispersion as a useful tool in the study of the microstructure of nucleic acids.