This application note describes the optimization of the 1H-15N CIGAR experiment for long-range nitrogen detection using VnmrJ 3 software. The software provides easy-to-use, interactive tools for setting up advanced experiments, allowing even novice users to obtain critical information about their research samples using the most advanced NMR experiments available.
The document explains that while standard HMBC experiments are optimized for a single coupling constant, steric crowding around nitrogen atoms can shift these constants across a broad range. The CIGAR (Constant Time Inverse-Detected Gradient Accordion Rescaled Heteronuclear Multiple-Bond Correlation) experiment addresses this by using an accordion-based constant evolution period to sample long-range coupling constants across a range of values, providing superior average signal intensity for 1H-15N data.
For typical survey spectra, values of 16 transients and 200 increments are recommended.
With typical parameters (16 transients, 200 increments), the experiment time is about 2.5 hours.
The CIGAR experiment setup described is supported by VnmrJ 3 software.