Nitrogen-15 chemical shift tensors and conformation of poly(β-benzyl L-aspartate) in the solid state by NMR

The relationship between the N-15 isotropic chemical shift (delta(iso)) or N-15 chemical shift tensor components (delta(11), delta(22), and delta(33)) and the main-chain conformation-such as the right-handed alpha-helix (alpha(R)-helix), left-handed alpha-helix (alpha(L)-helix), left-handed omega-helix (omega(L)-helix), and antiparallel beta-sheet (beta-sheet) forms of N-15-labeled poly(beta-benzyl L-aspartate) [Asp*(OBzl)](n) in the solid state-was studied using solid-state N-15 NMR methods. We have found that the delta(iso) and delta(22) of Asp*(OBzl) residue were significantly displaced depending upon conformation: delta(iso) (alpha(L)-helix, 98.9; alpha(L)-helix, 96.8; omega(L)-helix, 96.3; beta-sheet, 100.0 ppm) and delta(22) (alpha(R)-helix, 52.8; alpha(L)-helix, 48.3; omega(L)-helix, 47.4; beta-sheet, 56.4 ppm). Thus, it became apparent that the delta(iso) and delta(22) are very useful barometers for the conformational analysis, especially for the determination of the helical sense of [Asp*(OBzl)](n) in the conformational analysis, especially for the determination of the helical sense of [Asp*(OBzl)](n) in the solid state.