No abstract

A new two-dimensional NMR carbon−proton chemical shift correlation experiment, the MAS-J-HMQC experiment, is proposed for natural abundance rotating solids. The magnetization transfer used to obtain the correlations is based on scalar heteronuclear J couplings. The 2D map provides through-bond chemical shift correlations between directly bonded proton−carbon pairs in a way similar to that in corresponding high-resolution liquid-state experiments. The transfer through J coupling is shown to be efficient and more selective than those based on heteronuclear dipolar couplings. The experiment, which works at high MAS spinning frequencies, yields the unambiguous assignment of the proton resonances. The experiment is demonstrated on several organic compounds.

A refocused INEPT through-bond coherence transfer technique is demonstrated for NMR of rigid organic solids and is shown to provide a valuable building block for the development of NMR correlation experiments in biological solids. The use of efficient proton homonuclear dipolar decoupling in combination with a direct spectral optimization procedure provides minimization of the transverse dephasing of coherences and leads to very efficient through-bond (1)H-(13)C INEPT transfer for crystalline organic compounds. Application of this technique to 2D heteronuclear correlation spectroscopy leads to up to a factor of 3 increase in sensitivity for a carbon-13 enriched sample in comparison to standard through-bond experiments and provides excellent selectivity for one-bond transfer. The method is demonstrated on a microcrystalline sample of the protein Crh (2 x 10.4 kDa).