''Double-WURST'' decoupling for N-15- and C-13-double-labeled proteins in a high magnetic field

A ''Double-WURST'' decoupling sequence is constructed for simultaneously decoupling the (CO)-C-13 and C-13(alpha) regions in N-15/C-13-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 entire C-13 region including the unneeded region between (CO)-C-13 and C-13(alpha). Well-decoupled spectra are acquired using the Double-WURST decoupling sequence with a test N-15/C-13-double-labeled peptide sample and 8 and 19.6 kDa N-15/C-13-double-labeled proteins. It has also been shown that adiabatic decoupling, WURST, for example, has already reached it highest decoupling index n (=2) defined in a relation of decouple range Delta f versus RF pulse strength f(1rms), i.e., Delta f = lambda(f(1rms))(n), where lambda is a constant. For n greater than 2, the energy conservation law would be violated, and therefore is not possible. (C) 1996 Academic Press, Inc.