Nitrogen-15 chemical shift anisotropy and H-1-N-15 dipolar coupling tensors associated with the phenylalanine residue in the solid state

Nitrogen-15 chemical shift anisotropy (CSA) and H-1-N-15 dipolar coupling t ensors associated with the Phe-16 residue of the magainin2 peptide are repo rted in this Letter. The experimental results predict that the magnitudes o f the N-15 CSA tensor are sigma(11N) = 55 +/- 2, sigma(22N) = 80 +/- 2 and sigma(33N) = 220 +/- 2 ppm. The results also suggest that the least shielde d element, sigma(33N), is in the peptide plane making an angle of 22 +/- 3 degrees with the N-H bond vector whereas sigma(11N) and sigma(22N) are 45 /- 15 degrees away from the peptide plane and the normal to the peptide pla ne, respectively. The magnitudes of the principal elements of the N-15 CSA tensors associated with N-15-Phe-16 and N-15-Gly-18 sites of the magainin2 peptide are significantly different while the orientation of the tensors in the molecular frame is the same. (C) 1999 Elsevier Science B.V. All rights reserved.