Conformational study of solid polypeptides by H-1 combined rotation and multiple pulse spectroscopy NMR

The relation between the H-1 chemical shift and the conformation of linear homopolypeptides and cyclic dipeptides in the solid state has been studied utilizing the H-1 combined rotation and multiple pulse spectroscopy (CRAMPS) NMR method. It was found that the H-1 chemical shift of the H-alpha signal of homopolypeptides depends on the secondary structure such as alpha-helix or beta-sheet form, whereas those of the side-chain proton signals (H-beta, H-gamma, H-delta, etc.) are almost independent of the secondary structure. The H-1 chemical shifts of the H-alpha signal of homopolypeptides having the alpha-helix and the beta-sheet forms were 3.9-4.0 ppm and 5.1-5.5 ppm, respectively. Accordingly, the H-1 chemical shift of the H-alpha is very useful for conformational analysis of polypeptides in the solid stare. Furthermore, it is shown that the H-1 chemical shift of the H-alpha and the NH signals of cyclic dipeptides are sensitive to the ring conformation and the hydrogen bond length in the solid state.