Strange effects of pulse shaping in water presaturation experiments

During the course of some water presaturation experiments with a shaped pul se envelope we observed inverted responses from certain signals flanking th e water response. This phenomenon did not occur when a rectangular presatur ation envelope was used. Apparently the leading and trailing edges of the s haped pulse act as adiabatic sweeps, causing the coupled magnetizations in question to be spin-locked. This gives rise to Hartmann-Hahn coherence tran sfer, and when the spin lock duration is equal to 1/(2J) the trajectories a re such as to carry these magnetization vectors to the -z axis, leading to inverted signals in the final spectrum. (C) 2000 Academic Press.