Asynchronous through-bond homonuclear isotropic mixing: application to carbonā??carbon transfer in perdeuterated proteins under MAS
Abstract
Multiple-bond carbonā??carbon homonuclear mixing is a hurdle in extensively deuterated proteins and under fast MAS due to the absence of an effective proton dipolar-coupling network. Such conditions are now commonly employed in solid-state NMR spectroscopy. Here, we introduce an isotropic homonuclear 13Cā??13C through-bond mixing sequence, MOCCA, for the solid state. Even though applied under MAS, this scheme performs without rotor synchronization and thus does not pose the usual hurdles in terms of power dissipation for fast spinning. We compare its performance with existing homonuclear 13Cā??13C mixing schemes using a perdeuterated and partially proton-backexchanged protein. Based on the analysis of side chain carbonā??carbon correlations, we show that particularly MOCCA with standard 180-degree pulses and delays leading to non-rotor-synchronized spacing performs exceptionally well. This method provides high magnetization transfer efficiency for multiple-bond transfer in the aliphatic region compared with other tested mixing sequences. In addition, we show that this sequence can also be tailor-made for recoupling within a selected spectral region using band-selective pulses.
Source: Journal of Biomolecular NMR