Bloch-Siegert shift compensated and cyclic irradiation sidebands eliminated, double-adiabatic homonuclear decoupling for 13C- and 15N-double-labeled proteins

A Gaussian-shaped, offset-independent adiabatic decoupling is adopted to decouple (CO)-C-13 from C-13(alpha) or vice versa for C-13- and N-15-double-labeled proteins, together with a compensating decoupling applied on the opposite side of the C-13(alpha) resonance frequency. In a quite broad range, the double-adiabatic decoupling eliminates efficiently the cyclic sidebands caused by direct irradiation of the adiabatic decoupling and reduces significantly the Bloch-Siegert shift. The remaining Bloch-Siegert shift, which is almost a linear function of offset, can be removed by a dilated evolution time. The decoupling sequence is also quite insensitive to the RF field intensity or inhomogeneity due to the reduced transverse components of RF field at C-13(alpha), leading to an efficient decoupling even under unfavorable conditions. (C) 1998 Academic Press.