The15N chemical shift tensors of a homologous series of peptides of the form N-acetyl[l-13C]glycyl[15N]-X-amide (X = glycine, alanine, and tyrosine) and the unprotected dipeptide [l-13C]glycyl[15N]glycine hydrochloride have been determined from13C dipole-coupled15N powder patterns. It was found that the shift tensor principal values differ greatly while their molecular orientation does not. The common shift tensor orientation places σ22perpendicular to the peptide plane, and σ33at a 99° angle with respect to the C-N bond. The orientations of σ11 and σ22were previously unknown for15N chemical shift tensors of amides. Comparison of magic angle spinning (MAS) spectra with solution spectra shows significantly different solid and solution isotropic chemical shifts for several of the peptides studied, demonstrating that at least part of the variation in principal values is due to lattice effects. This conclusion is borne out by the MAS spectrum of N-acetyl[l-13C]glycl-[15N]phenylalaninamide, which shows at least three peaks corresponding to different lattice environments.
ASJC Scopus subject areas
- Colloid and Surface Chemistry