CHARACTERIZATION OF N-15 CHEMICAL-SHIFT AND H-1-N-15 DIPOLAR COUPLINGINTERACTIONS IN A PEPTIDE-BOND OF UNIAXIALLY ORIENTED AND POLYCRYSTALLINE SAMPLES BY ONE-DIMENSIONAL DIPOLAR CHEMICAL-SHIFT SOLID-STATE NMR-SPECTROSCOPY

The magnitudes and orientations of the principal elements of the N-15 chemical shift and H-1-N-15 dipolar coupling interaction tensors perta ining to the glycine residue in N-15-acetyl glycine (NAG) and [N-15-Gl y]collagen were determined by the analysis of one-dimensional dipolar chemical shift powder patterns. A one-dimensional H-1-N-15 dipolar N-1 5 chemical shift spectrum was obtained on a [N-15-Gly]collagen fiber s ample with the fiber axis oriented parallel to the external magnetic f ield. The dipolar chemical shift spectrum enabled the orientation of t he peptide plane to be determined relative to the direction of the app lied magnetic field or the triple-helix axis of the collagen fiber. Th e magnitudes of the principal elements of the tensors and their orient ations in the molecular frame for these two sites are quite different. The magnitudes of the chemical shift tensors are 42.3, 67, and 223.4 ppm for [N-15-Gly]collagen and 37, 82.8, and 220.4 ppm for NAG. The an gle CON) between the least shielded N-15 chemical shift tensor element , sigma(33N), and the N-H bond is 24.5 degrees for [N-15-Gly]collagen and 25.5 degrees (or 154.5 degrees) for NAG. The angle (alpha(N)) betw een the most shielded N-15 chemical shift tensor element, sigma(11N), and the projection of the N-H bond on the (sigma(11N)-sigma(22N) plane is 145 degrees for [N-15-Gly]collagen and 25 degrees (or 155 degrees, 205 degrees, or 335 degrees) for NAG. Because of the identical dipola r chemical shift powder patterns for four different alpha(N) values (3 5 degrees, 145 degrees, 215 degrees, and 325 degrees) the correct valu e of the alpha(N) angle was determined as 145 degrees using the dipola r chemical shift spectrum of the oriented [N-15-Gly]collagen sample.