A NOVEL COMPOSITE 90-DEGREES PULSE SEQUENCE WHICH PROVIDES DISTORTIONLESS NMR-SPECTRA AND SUPPRESSES WITHOUT DESTROYING THE WATER MAGNETIZATION

A novel 90 degrees composite pulse sequence which allows one to record 1D and 2D NMR spectra without disturbing the water magnetization is d escribed. A home-written program was used to optimize the pulse angles for which the pulse sequence response fitted best the desired excitat ion profile, producing a neat and distortionless spectrum with a broad null excitation at the carrier frequency. The resulting pulse sequenc e was first evaluated using the simulation program ''PENCIL'' and then tested on two protein samples. A 3.5 degrees phase shift of the last pulse was required to cancel correctly the water signal. The pulse sch eme was appended to a NOESY pulse sequence. Inspection of the water cr oss section revealed interactions between water and some protons of dr osomycine, a small insect antifungal protein. (C) 1998 Academic Press.