As Franklin was wrestling with the structural implications of her x-ray data on DNA, Randall contributed this note on a possibly
useful method for looking at the problem.
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1951-11-28 (November 28, 1951)
Randall, J. T.
Original Repository: Churchill Archives Centre. The Papers of Rosalind Franklin
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One well-known type of optical rotation (e.g. quartz) arises from a helical arrangement of atoms in the crystal. I suppose
it is technically too difficult to observe this in nucleic acid fibers, although it should be quite feasible in sheets. In
fact it has already been observed in gelatin films by Robinson and Bott (Nature, 168, 325, 1951). An interesting point is
that specific rotation in many substances is very high near an absorption band. Thus the optical rotation of a film of nucleic
acid could be observed photographically (this is a standard technique) near [lambda]2500 where the nucleotides absorb and
the effect of moisture content and stress could also be studied. (The law is very similar to that of the Sellmeier dispersion
The method has possibilities in solution as a means of correlation with light-scattering work. I doubt if it is theoretically
possible to correlate the rotation with helical structure only since it can arise from asymmetric carbon atoms, but it might
be a very useful method in showing changes of configuration arising from changes of pH etc.