Accordion BIRD-HMBC experiments: Improved one-bond correlation suppression in accordion heteronuclear multiple-bond correlation-type experiments

摘要

Modifications of the BIRD-HMBC experiment, in which the accordion principle and a constant time period have been introduced, are presented. With the simple accordion BIRD-HMBC, the use of a BIRDr,X element in the middle of the variable long-range couplings evolution period efficiently eliminates unwanted (1)J(CH) signals and samples a broad range of long-range heteronuclear couplings. While the accordion BIRD-HMBC experiment shows reduced F-1 modulation, superior suppression of unwanted (1)J(CH) signals and sensitivity comparable to the ACCORD-HMBC, the addition of another constant time period suppresses F-1 modulation due to H-1-H-1 coupling, while preserving the excellent suppression of unwanted (1)J(CH) signals. The constant-time (CT) accordion BIRD-HMBC experiment combines sensitivity similar to the CIGAR-HMBC and superior suppression of unwanted (1)J(CH) signals. Results of identically optimized ACCORD-HMBC, accordion BIRD-HMBC, CT accordion BIRD-HMBC and CIGAR-HMBC experiments performed on a sample of strychnine are compared and discussed. Copyright (c) 2006 John Wiley & Sons, Ltd.