Two- and three-dimensional H-1/C-13 PISEMA experiments and their application to backbone and side chain sites of amino acids and peptides

Two-dimensional H-1/C-13 polarization inversion spin exchange at the magic angle experiments were applied to single crystal samples of amino acids to demonstrate their potential utility on oriented samples of peptides and pro teins. High resolution is achieved and structural information obtained on b ackbone and side chain sites from these spectra. A triple-resonance experim ent that correlates the H-1-C-13(alpha) dipolar coupling frequency with the chemical shift frequencies of the alpha-carbon, as well as the directly bo nded amide N-15 site, is also demonstrated. In this experiment the large H- 1-C-13(alpha) heteronuclear dipolar interaction provides an independent fre quency dimension that significantly improves the resolution among overlappi ng C-13 resonances of oriented polypeptides, while simultaneously providing measurements of the C-13(alpha) chemical shift,H-1-C-13 dipolar coupling, and N-15 chemical shift frequencies and angular restraints for backbone str ucture determination. (C) 1999 Academic Press.