Raman Microspectroscopy of LiDNA Fibres

The conformation of low-salt LiDNA in fibrous form has been studied by Raman microspectroscopy. The recorded spectrum of a fibre soaked in ethanol is very similar to that of a fibre at low relative humidity. From x-ray experiments it is known that in the latter case the DNA adopts the C conformation. Therefore, it can be concluded that this is also the case in a low-salt LiDNA fibre soaked in ethanol. Further, it has been observed that the DNA conformation did not change when the excess ethanol was allowed to evaporate. The C form is also found when the fibre is in contact with ethanol vapour only. These results are in agreement with x-ray studies. However, our experiments with a LiDNA fibre in tert-butanol are not in agreement with x-ray results. Only when the tert-butanol is absolutely free from water is a state intermediate between the B and C forms found.