Radio frequency assisted homonuclear recoupling - A Floquet description of homonuclear recoupling via surrounding heteronuclei in fully protonated to fully deuterated systems

We present a Floquet theory approach for the analysis of homonuclear recoupling assisted by radio frequency (RF) irradiation of surrounding heteronuclear spins. This description covers a broad range of systems from fully protonated to deuterated proteins, focusing in detail on recoupling via protons and deuterons separately as well as simultaneously by the double nucleus enhanced recoupling (DONER) scheme. The theoretical description, supported by numerical simulations and compared to experimental results from a partially deuterated model compound, indicates that in perdeuterated systems setting the RF amplitude equal to the magic angle spinning (MAS) frequency is not necessarily optimal for recoupling via ¹H and/or ²H nuclei and modified recoupling conditions are identified.