Slice selective absorption-mode J-resolved NMR spectroscopy

Abstract

Limited chemical shift dispersion and broad multiplet patterns limit resolution in 1H NMR spectra. J-Resolved spectroscopy overcomes this problem to a great extent. However, the phase-twist line shape in J-Resolved spectroscopy allows only the magnitude mode of the experiment to be practical, which degrades resolution. Recently, various pure shift or broadband homonuclear decoupling approaches have been integrated with J-Resolved spectroscopy to eliminate the broad dispersive contribution. In the present work, we demonstrate a broadband 1H–1H J-Resolved spectrum with a greatly reduced dispersive contribution using the concept of slice selection. We show that slice selective excitation, t1 encoding, storage, and detection of the in-phase absorptive signals can be executed, while a gradient-based suppression of the dispersive antiphase signals can be performed during the storage period. In more than two spin systems, a small part of the doubly antiphase absorptive signal may also contribute to the spectrum in addition to the inphase absorptive signals. The overall effect is a reduced multiplet pattern similar to a regular J-Resolved case as the passive spins remain unflipped due to slice selective pulses. However, the effect is broadband for a fraction of the spins when all slices are considered analogous to Zangger-Sterk (ZS) broadband homo-decoupling. Further, the fresh magnetization from neighboring slices can be accessed in different scans by frequency shifting of the slice selective pulses without a recycle delay-an elegant aspect of the ZS pulse element. This allows faster signal averaging, improving sensitivity which depends on the T1 relaxation time of the signals. This method displays sensitivity up to 4–20 percent of the regular J-RES 1H signals.