Conformational Study of Solid Polypeptides by ¹H Combined Rotation and Multiple Pulse Spectroscopy NMR

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