“Double-WURST” Decoupling for15N- and13C-Double-Labeled Proteins in a High Magnetic Field

A “Double-WURST” decoupling sequence is constructed for simultaneously decoupling the¹³CO and¹³C_αregions in¹⁵N/¹³C-double-labeled proteins. It uses frequency-shifted WURST decoupling combined with standard WURST decoupling. The power can be reduced by two-thirds compared to conventional WURST decoupling, which decouples the entire¹³C region including the unneeded region between¹³CO and¹³C_α. Well-decoupled spectra are acquired using the Double-WURST decoupling sequence with a test¹⁵N/¹³C-double-labeled peptide sample and 8 and 19.6 kDa¹⁵N/¹³C-double-labeled proteins. It has also been shown that adiabatic decoupling, WURST, for example, has already reached its highest decoupling indexn(=2) defined in a relation of decouple range Δfversus RF pulse strengthf_1rms, i.e., Δf= λ(f_1rms)ⁿ, where λ is a constant. Forngreater than 2, the energy conservation law would be violated, and therefore is not possible.