Inter- and intra-molecular contributions of neighboring dipolar pairs to the precise determination of interatomic distances in a simple [13C, 15N]-peptide by 13C, 15N-REDOR NMR spectroscopy

Both 13C- and 15N-REDOR experiments were performed to determine the 13C-15N interatomic distance in [ 1-13C]N-acetyl-Pro-[15N]Gly-Phe crystal and to evaluate the inter- or intra-molecular dipolar contributions leading to its errors. The interatomic distance was determined to be 3.43 Å after removing the intermolecular contribution to the echo dephasing arising from the intermolecular dipolar interaction with labeled nuclei of the neighboring molecule. This contribution was estimated by extrapolation to infinite dilution of the labeled sample in unlabeled peptide. The theoretical formalism was developed for the nucleus coupled with two heteronuclei. The conformation of this peptide turned out to be β-turn type II on the basis of the abovementioned interatomic distance.