Indirect detection of nitrogen-14 in solids via protons by nuclear magnetic resonance spectroscopy

This Communication describes the indirect detection of N-14 nuclei (spin I = 1) in solids by nuclear magnetic resonance (NMR) spectroscopy. The two-dimensional correlation method used here is closely related to the heteronuclear multiple quantum correlation (HMQC) experiment introduced in 1979 to study molecules in liquids, which has recently been used to study solids spinning at the magic angle. The difference is that the coherence transfer from neighboring H-1 nuclei to N-14 is achieved via a combination of J couplings and residual dipolar splittings (RDS). Projections of the two-dimensional correlation spectra onto the N-14 dimension yield powder patterns which reflect the N-14 quadrupolar interaction. In contrast to the indirect detection of N-14 via 13 C nuclei that was recently demonstrated [Gan, J. Am. Chem. Soc. 128 (2006) 6040; Cavadini et. al., J. Am. Chem. Soc., 128 (2006) 7706], this approach may benefit from enhanced sensitivity, and does not require isotopic enrichment in C-13, although the H-1 line-widths may have to be reduced upon selective deuteration. (c) 2006 Elsevier Inc. All rights reserved.