A method for enhancing the sensitivity of N-15 spectra of nonspinning solid
s through H-1 indirect detection is introduced. By sampling the H-1 signals
in the windows of a pulsed spin-lock sequence, high-sensitivity H-1 spectr
a can be obtained in two-dimensional(2D) spectra whose indirect dimension y
ields the N-15 chemical shift pattern. By sacrificing the H-1 chemical shif
t information, sensitivity gains of 1.8 to 2.5 for the N-15 spectra were ac
hieved experimentally. A similar sensitivity enhancement was also obtained
for 2D N-15-H-1 dipolar and N-15 chemical shift correlation spectroscopy, b
y means of a 3D H-1/N-15-H-1/N-15 correlation experiment. We demonstrate th
is technique, termed PRINS for proton indirectly detected nitrogen static N
MR, on a crystalline model compound with long H-1 T-1 rho and on a 25-kDa p
rotein with short H-1 T-1 rho. This H-1 indirect detection approach should
be useful for enhancing the sensitivity of N-15 NMR of oriented membrane pe
ptides. It can also be used to facilitate the empirical optimization of N-1
5-detected experiments where the inherent sensitivity of the sample is low.
(C) 2001 Academic Press.