Improved performance accordion heteronuclear multiple-bond correlation spectroscopy - IMPEACH-MBC

A modification of the recently reported ACCORD-HMBC long-range heteronuclea r shift correlation experiment is described. The new experiment, IMPEACH-MB C (improved performance accordion heteronuclear multiple-bond correlation), introduces a new pulse sequence element, a constant time variable delay. T he incorporation of the constant time variable delay into the IMPEACH-MBC s equence suppresses H-1-H-1 coupling modulation inherent to the utilization of the accordion principle to sample a broad range of potential long-range heteronuclear couplings. H-1-H-1 coupling modulation, which introduces an F -1 modulation or a "skew" of responses in the second frequency domain of th e ACCORD-HMBC experiment, is suppressed in the IMPEACH-MBC experiment. Resu lts of identically optimized IMPEACH-MBC and ACCORD-HMBC experiments perfor med on a sample of strychnine are compared. (C) 1999 Academic Press.