Synopsis
The bands within the range of 800-850 cm-' of Raman spedra of polynucleotides sensitive to the change in conformation of sugar-phosphate backbone are analyzed theoretically. The bands are interpreted as the appearance of a quasi-local deoxyribose vibrational mode whose frequency is dependent on the ring puckering. The localization region of the vibrational mode is pointed out. The theory eatablishes a relationship between the observed spectral intensity and the population of deoxyribose conformational states described in the framework of the pseudorotation concept.
The approach developed allowed one to describe the band shapes and their temperature behavior, and to determine the pseudorotation potential of deoxyribose in the helix %form of A . T containing polynucleotidea. Using the analysis o f --spectra of DNA fibers in water-ethanol mixture the deoxyribose flexibility during the B-A transition is investigated in terms of the population of conformers and effective potential. It is shown that N-and S-type deoxyribcse conformers are populated in the DNA %form (those of the S-type are preferable), whereas N-type conformers are primarily populated in the DNA x-form.