Sensitivity-enhanced static 15N NMR of solids by 1H indirect detection

A method for enhancing the sensitivity of N-15 spectra of nonspinning solids 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 spectra can be obtained in two-dimensional(2D) spectra whose indirect dimension yields the N-15 chemical shift pattern. By sacrificing the H-1 chemical shift information, sensitivity gains of 1.8 to 2.5 for the N-15 spectra were achieved experimentally. A similar sensitivity enhancement was also obtained for 2D N-15-H-1 dipolar and N-15 chemical shift correlation spectroscopy, by means of a 3D H-1/N-15-H-1/N-15 correlation experiment. We demonstrate this technique, termed PRINS for proton indirectly detected nitrogen static NMR, on a crystalline model compound with long H-1 T-1 rho and on a 25-kDa protein 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 peptides. It can also be used to facilitate the empirical optimization of N-15-detected experiments where the inherent sensitivity of the sample is low. (C) 2001 Academic Press.