High-resolution localized spatiotemporal encoding correlated spectra under inhomogeneous magnetic fields via asymmetrical gradient encoding/decoding

A Single-Scan Inhomogeneity-Tolerant NMR Method for High-Resolution Two-Dimensional J-Resolved Spectroscopy

OBJECTIVE

A robust and general single-scan NMR method, SGEN-J, is proposed for real-time recording high-resolution two-dimensional (2D) homonuclear J-resolved spectra under inhomogeneous magnetic fields.

METHODS

This proposed NMR method is designed based on the combination of a selective gradient encoding module to encode chemical shifts with spatial positions, and a J-modulation decoding module to reveal encoded structural information. Multi-band SGEN-J is further implemented to effectively enhance spectral sensitivity with a sustained tolerance of field inhomogeneity.

RESULTS

The SGEN-J provides an effective way to rapidly recover chemical shifts, J coupling constants, and multiplet patterns under inhomogeneous magnetic fields. Experiments on various chemical solutions were performed to demonstrate the feasibility and effectiveness of SGEN-J. Experiments on pig marrow tissues were performed to further investigate the applicability of SGEN-J to biological samples with intrinsic susceptibility variations.

CONCLUSION

Based on intrinsic advantages, SGEN-J serves as a helpful complement to existing 2D J-resolved methodologies in molecular structure elucidation and biomedical study, and offer bright perspectives for real-time analyzing in vivo biological systems and monitoring in situ chemical reactions.

High-resolution NMR spectroscopy in inhomogeneous fields

High-resolution NMR spectroscopy, providing information on chemical shifts, J coupling constants, multiplet patterns, and relative peak areas, is a mainstream tool for analysis of molecular structures, conformations, compositions, and dynamics. Generally, a homogeneous magnetic field is a prerequisite for obtaining high-resolution NMR information. Magnetic field inhomogeneity, whether from non-ideal experimental conditions or from intrinsic magnetic susceptibility discontinuities in samples, represents a hurdle for applications of high-resolution NMR. Numerous techniques have been proposed for measuring high-resolution NMR spectra free from the influence of inhomogeneous magnetic fields. Besides developments and improvements in NMR instrumentation, various types of experimental approaches have been established for recovering NMR information in inhomogeneous magnetic fields. Three main types are systematically described in this review. In addition, other high-resolution NMR approaches or data processing methods are also briefly described. All high-resolution NMR approaches covered in this review have individual advantages and disadvantages in practical applications, and no one technique is applicable to all practical circumstances. Hence, they are complementary for high-resolution NMR applications in inhomogeneous fields. The underlying mechanisms of these approaches are presented, together with analyses of their applicability and efficiency.