Orchestrated approaches using pure shift NMR: Extraction of spectral parameters, ultra-high resolution, and sensitivity enhancement.

Abstract

The limited chemical shift range of protons and pairwise interaction among all the abundant nuclear spins of a molecule makes 1 H spectrum too complicated. As a consequence, the straightforward analysis and the accurate extraction of their interaction strengths from the 1 H spectrum of a complex spin system are formidably difficult or often impossible. This problem persists in the determination of scalar couplings be it between two abundant homonuclear spins or between 1 H and an abundant heteronuclear spin (viz., 19 F and 31 P). Such problems are encountered in many situations where the determination of homonuclear and heteronuclear couplings is challenging. The several pure shift based one-dimensional and two-dimensional NMR strategies recently developed in our laboratory for the straightforward extraction of homonuclear and heteronuclear interaction parameters in diverse situations are discussed. Initially, the unique application of pure shift technique that paves the way for easy and straightforward extraction of magnitudes of heteronuclear couplings, namely, n JHX (where X stands for 19 F, 31 P, etc.), is discussed. Subsequently, several pure shift edited one-dimensional and two-dimensional NMR strategies that are developed for the direct extraction of homonuclear and heteronuclear couplings and for achieving ultra-high-resolved 1 H spectra with complete eradication of zero frequency peaks and the evolution of unwanted couplings. The enhancement in the sensitivity has also been achieved in the slice-selective pure shift experiments by the rapid acquisition of proton spectrum where the polarization from the adjacent protons is transferred to the selectively excited proton.