DIRECT OBSERVATION OF ASYMMETRIC H-1 N-14 TRIPLETS AND APPLICATIONS OF ASYMMETRIC DIPOLE-DIPOLE SPLITTINGS TO STRUCTURE DETERMINATION BY SOLID-STATE NMR-SPECTROSCOPY/

High-resolution solid-state NMR spectra of H-1 nuclei directly bonded to N-14 nuclei can be extracted from two-dimensional H-1/N-14 heteronu clear correlation spectra of single crystal samples. The H-1 resonance s are asymmetric triplets, since the heteronuclear dipole-dipole inter action between a spin one-half H-1 and a spin one N-14 is influenced b y the large N-14 quadrupole coupling constant and can be observed in b oth N-14 fundamental (Delta m = 1) and N-14 overtone (Delta m = 2) spe ctra. N-14 fundamental spectra have two resonances for each magnetical ly distinct N-14 nucleus, each of which is a doublet in the heteronucl ear correlation spectra; the asymmetric H-1 triplets can be reconstruc ted from the doublets of both resonances. N-14 overtone spectra are si mpler, since they have a single asymmetric H-1 triplet associated with a single N-14 resonance for each magnetically distinct N-14 nucleus. H-1 chemical shift frequencies, the splittings from H-1/N-14 heteronuc lear dipole-dipole couplings, N-14 quadrupole splittings, and N-14 sec ond-order shifts can all be measured with both fundamental and overton e H-1/N-14 heteronuclear correlation spectra. In addition, the H-1 and N-14 resonance frequencies for the bonded hydrogen and nitrogen nucle i are correlated in these spectra. The spectral parameters from asymme tric H-1/N-14 triplets are demonstrated to offer substantial advantage s over those of the corresponding symmetric N-14/H-1 doublets for dete rmining structures of peptides by solid-state NMR spectroscopy, even t hough both sets of parameters arise from the same dipole-dipole intera ctions.