BLOCH-SIEGERT SHIFT COMPENSATED AND CYCLIC IRRADIATION SIDE-BAND ELIMINATED, DOUBLE-ADIABATIC HOMONUCLEAR DECOUPLING FOR C-13-DOUBLE-LABELED AND N-15-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-1 5-double-labeled proteins, together with a compensating decoupling app lied on the opposite side of the C-13(alpha) resonance frequency. In a quite broad range, the double-adiabatic decoupling eliminates efficie ntly the cyclic sidebands caused by direct irradiation of the adiabati c decoupling and reduces significantly the Bloch-Siegert shift. The re maining Bloch-Siegert shift, which is almost a linear function of offs et, can be removed by a dilated evolution time. The decoupling sequenc e 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.