Polynucleotides II : The X-ray diffraction patterns of solutions of the randomly coiled and helical forms of polyriboadenylic acid

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It has been possible to obtain wide-angle X-ray diffraction photographs of dilute solutions of the acid form of polyriboadenylic acid in the form of sharp powder diagrams. The spacings so measured indicate a marked degree of similarity between the structure of the polymer in solution and in the solid state as a fibre. Consequently, the fibre can be identified with the acid form of the polymer. These observations are considered in terms of the two proposed models of the helical form of polyriboadenylic acid. It is concluded that they are only compatible with the model which has hydrogen bonds between the adenine groups of opposite chains as major cohesive forces for chain interaction. The ability of dilute solutions of acid-stable polyriboadenylic acid (helical form) to give sharp diffraction patterns is taken as evidence that individual molecules behave as microcrystals.