A RAMAN-STUDY OF THE TIME VARIABILITY FOR THE A-TO-B TRANSITION IN WET-SPUN FILMS OF CALF-THYMUS DNA

The time evolution of the A-to-B transition has been monitored by Rama n spectroscopy and found to vary significantly for different samples. Though all samples were prepared in the identical fashion, some sample s completed the transition on the time scale of several hours while ot her samples took days. The shortest time required for the A conformati on to disappear was about 2 hours, as determined by the disappearance of the A-form Raman band at 807 cm(-1). For these fastest transforming samples, the B-form Raman band at 835 cm(-1) was clearly evident afte r about 5 hours. These data are consistent with the hypothesis that th e A conformation of DNA is stabilized by intermolecular interactions.