Monitoring off-resonance signals with SHARPER NMR – the MR-SHARPER experiment

We demonstrate an extension to the SHARPER (Sensitive Homogenous and Refocussed Peaks in Real Time) NMR experiment which allows more than one signal to be monitored simultaneously, while still giving ultra-sharp, homo- and hetero-decoupled NMR signals. This is especially valuable in situations where magnetic field inhomogeneity would normally make NMR a problematic tool, for example when gas evolution is occurring during reaction monitoring. The originally reported SHARPER experiment only works for a single, on-resonance NMR signal, but here we demonstrate the Multiple Resonance SHARPER approach can be developed, which in principle can acquire multiple on-/off-resonance signals simultaneously while retaining the desirable properties of the parent sequence. In practice, the case of two resonances, e.g. those of a reactant and a product, will most of the time be considered for MR-SHARPER, as illustrated here.