Determination of the N–H Bond Lengths for Simple Peptides in the Solid State by Natural Abundance 15N Two-Dimensional Separated Local Dipolar Field (2D-SLDF) NMR Spectroscopy

Publisher Website
Google Scholar
Abstract
The N–H bond lengths of simple petides were determined under the condition of high-resolution spectroscopy by analyzing the dipolar side-band patterns obtained from samples of natural abundance, as recorded by 15N two-dimensional (2D) separated local dipolar field (SLDF) NMR spectroscopy combined with cross-polarization and magic-angle spinning (CP-MAS) techniques. It was found that the dipolar side-band pattern obtained from the one-dimensional (1D) cross section taken from the 2D spectrum can be conveniently used to distinguish the 15N signal of the N–H group from that of the N–C group, whose peak positions are very close to each other. Further, spectral simulations of the 15N dipolar patterns of the peptides were performed in order to determine the N–H bond lengths of the amino acid residues of natural abundance at the C-terminus. These values were determined to be 1.07, 1.12, and 1.09 Å for Ala–Gly, Gly–Pro–Ala, and Ala–Pro–Gly, respectively, with an accuracy of 0.01—0.02 Å. The obvious difference in the bond lengths between the last two compounds suggests that the degree of interchain packing, as estimated from the N–H bond lengths, significantly differs between Gly–Pro–Ala and Ala–Pro–Gly. This finding is consistent with the previous data regarding the presence or absence of ring-puckering motion at the Pro residue, as examined by the 13C spin-lattice relaxation times in the laboratory frame.