The13C and15N chemical shift tensors of L-[l-13C]alanyl-L-[15N]alanine have been determined from the dipole-coupled powder patterns and verified with the decoupled spectra. The principal values of the13C tensor are σ11= -115.5, σ22= -42.3, and 0–33= 33.5 ppm, and the polar angles relating the13C-15N bond to the chemical shift tensor are β = 90° and a = -39.5°. Although the13C powder pattern widths of Ala Ala and AcGlyAlaNH2differ by only 2%, the anisotropy and asymmetry parameters differ by 10 and 25%, respectively. The principal values for the15N chemical shift tensor are σ11= 65.3,σ22= 78.1, and σ33= 215.5 ppm, and the orientation of the13C-15N bond to the σ33axis is 106°. AlaAla and AcGlyAlaNH2show a striking difference in asymmetry parameters (0.06 vs. 0.16) and anisotropy (144 vs. 165).
ASJC Scopus subject areas
- Colloid and Surface Chemistry