[Franklin and Gosling]

Date:
1952-1953
Reference:
PP/CRI/H/1/42/7
Catalogue details

Licence: In copyright

Credit: [Franklin and Gosling]. Source: Wellcome Collection.

    1/11
    m ROUGH DRAFT 1. A NOTE ON MOLECULAR CONFIGURATION XN SODIUM THYMONUCI¿.ATE Rosalind E. Franklin and R. G. Gosling 17/3/53. Sodium thymonucleate fibres givo two distinct types of X-ray diagram. The first, corresponding to a crystalline form obtained at about 75# relative humidity, has been des- ÍM' ( ) • V 4-, )^A cribed in detail elsewhere • . At high^humidities a new structure, showing a lower degree of order appears, and persists over a wide range of ambient humidity and water content. The water content of the fibres, which are crys talline at lower humidities, may vary from 8bout 50# to several hundred per cent, of the dry weight in'this structure. Other fibres which do not give crystalline structure at all, show this less ordered structure at much lower humidities. The diagram of this structure, which we have called structure B, shows in striking manner the features characteristic of i / V ( ) kH helical structures . Although this cannot be taken ss proof that the structure is helical, other considerations make the existence of a helical structure highly probable. J Structure B is derived from the crystalline structure A when the sodium thymonucleate (NaDNA) fibres take up quantities of water in excess of about 40# of their weight. The change Í3 accompanied by an increase of about 30# in the length of the fibre, and by a substantial re-arrangement of the molecule. J It therefore seems reasonable to assume that in structure B the structural units of NaDNA (molecules or groups of molecules) are relatively free from the influence of neighbouring groups, each unit being shielded by a sheath of water. Each unit is therefore free to take up its least-energy configuration Independently of its neighbours and, in view of the nature of the long-chain molecules involved, it is highly likely that the