13C n.m.r. study of the structure and the metal ion binding sites of neuropeptides composed of L‐Asp and L‐Glu

13C NMR spectral data are presented for a variety of possible neuropeptides composed of L-Asp, Ac-L-Asp, and L-Glu which contain alpha and beta peptide linkages. The data for the various compounds are compared to the data presented for Ac-Asp-Glu, a known neuropeptide, in order to gain structural information about the related compounds. Indications are that for compounds 1 and 5, the cis peptide bond configuration exists due to the interaction of zwitterionic species. This interaction appears to be eliminated when the beta peptide bonds are formed, as in the case of compounds 3 and 7. Spin-lattice relaxation times were used to confirm the structures. Electron-nuclear relaxation rates are also used to elucidate the metal ion binding sites of these species.