Gradient BIRDR: A method to select uncoupled magnetization

The gradient-BIRD-method is an effective way to select C-13-bound protons. By changing the phase of the proton pi-pulse, the same sequence can be used to select protons attached to C-12 atoms, i.e,, for filtering out the C-13 -bound protons. These filters, consisting of single or double gradient-BIRD , clusters (BIRD inversion for remote protons) have considerable filtering bandwidth. Because of the efficient suppression of the coupled magnetizatio n, we implemented the gradient-BIRD, filter in HMBC to replace the conventi onal low-pass filter. (C) 1999 Academic Press.