Pure Shift NMR Spectroscopy

Abstract

Pure shift NMR spectroscopy, or broadband homonuclear decoupled NMR spectroscopy, produces NMR spectra that contain only chemical shift information. In a pure shift NMR spectrum the effects of J-coupling are hidden so that all multiplets are collapsed to singlets. Pure shift methods can deliver a significant improvement in resolution of NMR signals and greatly reduce signal overlap. Pure shift NMR can be achieved using direct or indirect acquisition; for direct acquisition, real-time-or interferogram-based FID collection can be used. The range of pure shift methods includes those that refocus the effects of J-coupling (BIRD, Zangger-Sterk, band selective decoupling, and anti z-COSY); manipulate the evolution of chemical shift within a constant time delay to keep the J-evolution in an indirect acquisition constant; or extract a 1-D spectrum from a 2-D J dataset. The methods and their mechanisms in weakly coupled systems are described using the product operator formalism. Examples are provided for a range of applications.

Improving the performance of J‐modulated ADEQUATE experiments through homonuclear decoupling and non‐uniform sampling

“…As with the pulse sequence originally described by Köver and coworkers, a scaling factor, K, is built into the pulse sequence to upscale the size of the homonuclear 13 C– 13 C coupling constants being measured. Modifications inherent to the recently reported 1,1‐HD‐ADEQUATE and 1,n‐HD‐ADEQUATE experiments have also been incorporated, including an initial Testing for Adjacent Nuclei with a Gyration Operator (TANGO) cluster to efficiently dephase any residual 1 H– 13 C magnetizerion and a BIRD‐based ‘chunked’ data acquisition to achieve homodecoupling along the F 2 dimension …”

“…As an example, NUS methods have thus been applied to facilitate better measurement of scalar and dipolar coupling constants . The development of broadband homodecoupled or pure shift NMR methods that collapse proton–proton couplings, thereby enhancing both resolution and sensitivity, has also been developed and is the subject of several recent reviews . Recently, we have communicated the development of homodecoupled analogs of the 1,1‐ADEQUATE and 1,n‐ADEQUATE experiments that, in a manner analogous to pure shift HSQC, can improve the sensitivity of these otherwise relatively low sensitivity but extremely useful experiments that can provide an alternative means of probing challenging structures when more sensitive methods, e.g.…”

Pure shift 1H NMR: what is next?

“…[9] An extensive review of all these methods can be found in Refs. [1,2] In order to decouple one set of spins (active spins) from all their neighbours (passive spins), they have to be selected and manipulated independently of other spins. The first method that was published based on this idea was proposed in 1982 by Garbow et al, where active and passive spins are differently manipulated by using a bilinear rotation decoupling (BIRD) element ( Fig.…”

Structure elucidation of uniformly 13C labeled small molecule natural products

“…Recently developed pure shift analogs of the HSQC experiment have served to further increase resolution and sensitivity. [10–12] In addition to 1 H and 13 C chemical shifts, HSQC spectra provide a wealth of structurally relevant information. In fact, there are successful examples of using just 1 H and multiplicityedited 1 H– 13 C HSQC data for automated structure verification purposes.…”