Characterization of the Order/Disorder Transition of Poly‐1‐Methyl Adenylic Acid in Neutral Solution by Raman Difference Spectroscopy

A detailed analysis of the hypo‐ and hyper‐chromic intensity changes as well as the changes in frequency and band shape in the Raman spectra of poly(m 1 A) upon melting has been made using a newly developed Raman difference technique. An interpretation of these changes allows us to suggest a structure for the double‐helix of this polymer in neutral solution which resembles that of poly(A) in acid pH. In the helix the backbone geometry is shown to be similar to the C 3 endo or A genus and the existence of a hydrogen bond is inferred from the asymmetric band shape of 1100 cm −1 PO − 2 stretching vibration wich is not found either in self‐stacked poly(A) at neutral pH. It is expected that the application of the Raman difference technique will result in a detailed description of conformational features of these important macromolecules which cannot be drawn from the resuits of other optical methods.