B-DNA's B-II conformer substate population increases with decreasing wateractivity. 2. A Fourier transform infrared spectroscopic study of nonoriented d(CGCGAATTCGCG)(2)

Nonoriented hydrated films of the sodium salt of the d(CGCGAATTCGCG)(2) dod ecamer, with Gamma (water molecules per nucleotide) = 20, 14, 8, and 6, wer e investigated by Fourier transform infrared spectroscopy. Curve resolution of the spectral region containing the symmetric stretching vibration of th e ionic phosphate at two temperatures allows estimation of B-DNA's B-I/B-II conformer substate population ratio, The B-I/B-II population ratio decreas es at 290 K with decreasing water activity from 1.4 for Gamma = 20 to 1.2, 1.0, and 0.72 for Gamma = 14, 8, and 6. Increasing B-II population with dec reasing water activity is attributed to differences in hydration as the dri ving force for the B-I --> B-II transition. An enhanced B-II population cou ld be significant for the interaction of proteins with B-DNA in chromatin. We surmize that the B-II substate could be an intermediate in the transitio n of canonical B- to A-DNA.