Fractal-like patterns in DNA films, B form at 0% relative humidity, and antiheteronomous DNA: an IR study

This report details the observation of (a) the intact double helix of DNA at 0% relative humidity in poly(dA).poly(dT) and poly(dA-dT).poly(dA-dT) films, (b) the fractal-like growth of DNA crystals in films of poly(dA).poly(dT), and (c) poly(dA).poly(dT) with adenines in the B form and thymines in the A form. Observation (a) is based on the behavior of the middle ir signature of double-helical base stacking, the 1714 cm-1 peak, at low water activity. This observation is modeled as a trapping of water in the polycrystalline part of these films. We interpret the glycosidic region of the middle ir spectra of the polycrystalline films of poly(dA).poly(dT) at 0% relative humidity to indicate that at least part of the adenine strand in is the B conformation and the thymine strand is in the A form, whereas previous assignments of poly(dA).poly(dT) films at 75% relative humidity indicated the opposite strand conformation assignment [E. Taillandier et al. (1987) Biochemistry, Vol. 26 p. 3361].