DIRECT OBSERVATION OF ASYMMETRIC H-1 N-14 TRIPLETS AND APPLICATIONS OF ASYMMETRIC DIPOLE-DIPOLE SPLITTINGS TO STRUCTURE DETERMINATION BY SOLID-STATE NMR-SPECTROSCOPY/
R. Mcnamara et al., DIRECT OBSERVATION OF ASYMMETRIC H-1 N-14 TRIPLETS AND APPLICATIONS OF ASYMMETRIC DIPOLE-DIPOLE SPLITTINGS TO STRUCTURE DETERMINATION BY SOLID-STATE NMR-SPECTROSCOPY/, Journal of the American Chemical Society, 117(29), 1995, pp. 7805-7811
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.