Abstract
Abstract Solid-state 2H NMR spectra were measured as a function of relative humidity for nonoriented DNA films and oriented DNA fibers deuterated at C8 carbons of the purine bases. The line-shape analyses of the quadrupole echo spectra from oriented DNA fibers demonstrated that the purine base planes of the A form of DNA were tilted by about 70° relative to the helix axis, and that base planes of the B form varied significantly, although they were, on average, perpendicular to the helix axis. These results were generally consistent with the X-ray fiber diffraction studies and the single crystal structures of oligonucleotides. Analyses of 2H relaxation times, T1 and T2, showed at 79% RH that the orientation of the base planes fluctuated about an axis normal to the helix axis with a correlation time, τc=3.6×10−8 s and amplitude of 8.5°. The correlation time of the base plane fluctuation was 1.5×10−8 s and the amplitude was 13.5° at 92% RH. In addition, at 92% RH, but not at 79% RH, the base planes reoriented slowly, τc ≈10−6 s, about the helix axis, through an rms angle of ca. 30°.
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