A modified CRISIS‐HSQC for band‐selective IMPRESS

CRISIS (Compensation of Refocusing Inefficiency with Synchronized Inversion Sweep) is a powerful technique for obtaining multiplicity-edited HSQC spectra without compromising sensitivity. However, the stringent requirement for the duration of the CRISIS waveforms makes them unsuitable for other functions, such as band selection or IMPRESS (IMProved REsolution using Symmetrically Shifted pulses). We report here a modified CRISIS-gHSQC pulse sequence employing time-reversed 13C pi/2 EBURP-2 pulses. This IC-bs-gHSQC (IMPRESS-CRISIS-bs-gHSQC) sequence was found to be equally useful for acquiring multiplicity-edited, band-selective spectra individually or in tandem with IMPRESS. Remarkably, the latter provides multiple spectra in significantly less time and is the preferred approach when several crowded regions need to be assigned unambiguously. The use of adiabatic sweeps and the CRISIS pulses enable IC-bs-gHSQC to give better sensitivity than the original IMPRESS sequence for band-selective spectra.