Determination of the Backbone Structure of Nucleic Acids and Nucleic Acid Oligomers by Laser Raman Scattering

Raman spectra of fibers of DNA that have been prepared in the A, B, and C forms are presented and compared with Raman spectra of DNA and RNA in dilute solution. It is shown that the phosphate vibrations in the region 750-850 cm(-1) are very sensitive to the specific conformation of the phosphate group in the backbone chain and are virtually independent of all ohter factors. Thus, a very simple method for the determination of the specific conformation of the backbone chain of nucleic acids, at least so far as the sugar-phosphate chain is concerned, appears available. The method is applied to short oligomers and dimers of ribonucleosides. It is found that at low temperatures, at pH 7, the phosphate group goes into the geometry of the A conformation when the stacking forces between the bases are sufficiently strong.