High-resolution 1H/17O NMR correlation under fast magic-angle spinning: revisiting cross-polarization for quadrupolar nuclei

An efficient experiment for 1H/17O heteronuclear correlation is presented combining forward-and-back cross-polarization and low-power cosine multiple-quantum magic-angle spinning methods. Double cross-polarization (DCP) is compared with the heteronuclear multiple-quantum correlation (HMQC) method. Both experiments are applicable in instances of enhanced proton polarization such as with dynamic nuclear polarization. Under fast magic-angle spinning, cross-polarization becomes a viable method for polarization transfer and provides an order of magnitude enhancement over HMQC. In particular, it is observed that faster sample spinning opens up regions of rf fields optimal for spin-locking and cross-polarization with much less T2 signal loss. The incorporation of multiple-quantum magic-angle spinning enables high 17O isotropic resolution via proton detection.