The13C chemical shift tensors have been determined for the glycine carbonyl carbon in a homologous series of peptides of the general form N-acetyl[l-13C]glycyl-X-amide, where X was [15N]glycine, dl-[15n] <-tyrosine, l-[15n] <phenylalanine and DL-[15N]alanine. The principal values and molecular orientations of the tensors were extracted from15N dipole-coupled13C powder spectra. The shift tensor of a powdered sample of [l-I3C]glycyl[15N]glycine•HClsH2O was determined by the same method and was found to agree to within 1 ppm in principal values and 2° in orientation with the previous single crystal measurements of R. E. Stark et. al. (J. Magn. Reson. 1983, 55, 266). The shift tensors of the five peptides were found to be significantly different in both principal values and molecular orientation. However, the isotropic chemical shifts of the end-protected peptides in D2O were nearly identical. From these data it is concluded that lattice environment has a significant effect on the chemical shift tensors of peptide carbonyl carbons. An approach to approximating carbonyl13C chemical shift tensors of peptides in proteins with use of the isotropic chemical shift in the molecule of interest is proposed. In addition, the utility of the powder pattern technique for accurately determining the chemical shift tensors of peptide carbonyl carbons is demonstrated.
ASJC Scopus subject areas
- Colloid and Surface Chemistry