A new conformation-specific infrared band of A-DNA in films.

A band at 1185 cm-1 occurs in the infrared spectra of nucleic acids in their A-type conformation which has been reproduced in the literature, too. The absorbance of this band is proportional to the fraction of the A form of DNA samples containing a mixture of different forms. The 1185 cm-1 band has been assigned tentatively to a vibration of the sugar-phosphate backbone with a fairly high contribution from the sugar moiety. Drastic dehydration of the DNA films is accompanied by a continuous intensity decrease of the 1185 cm-1 band indicating a collapse of the A form.