Solid-State NMR Dipolar and Chemical Shift Anisotropy Recoupling Techniques for Structural and Dynamical Studies in Biological Systems

Abstract

With the development of NMR methodology and technology during the past decades, solid-state NMR (ssNMR) has become a particularly important tool for investigating structure and dynamics at atomic scale in biological systems, where the recoupling techniques play pivotal roles in modern high-resolution MAS NMR. In this review, following a brief introduction on the basic theory of recoupling in ssNMR, we highlight the recent advances in dipolar and chemical shift anisotropy recoupling methods, as well as their applications in structural determination and dynamical characterization at multiple time scales (i.e., fast-, intermediate-, and slow-motion). The performances of these prevalent recoupling techniques are compared and discussed in multiple aspects, together with the representative applications in biomolecules. Given the recent emerging advances in NMR technology, new challenges for recoupling methodology development and potential opportunities for biological systems are also discussed.

Ultrafast Magic Angle Spinning Solid-State NMR Spectroscopy: Advances in Methodology and Applications

“…As shown in Figure 29c, 1 H/ 14 N OT CW RESPDOR gives a much stronger correlation than 1 H/ 14 N D-HMQC despite a 17-fold shorter experimental time. While a similar frequency sweep was demonstrated to observe wide 27 Al spectra using TARPDOR and REAPDOR approaches, 378 a frequency swept RESPDOR experiment successfully observed a very wide 195 Pt spinning sideband manifold within minutes to a few hours. 379…”

“…It is conclusive that the resolution enhancement by introducing an additional heteronuclear (i.e., 13 C, 14 N, 15 N, 27 Al, 31 P, etc.) chemical shift dimension into RN-symmetry recoupling experiments could improve the accuracy of proton CSA measurement, especially for more complex systems.…”

“…99,322,333,335,345,347 The mostly used methods for proton-detected experiments under fast-MAS are D-HMQC and D-RINEPT, and the pulse sequences are shown in Figure 23a,b; in these experiments, the recoupling pulse sequences (like R 3 , SR4, and PMRR) with RF field strength set at 2v R can be applied in the recoupling periods. Recently, Venkatesh et al have systematically compared the proton-detected D-HMQC and D-RINEPT experiments at fast-MAS frequencies for various quadrupolar nuclei, including 35 Cl, 71 Ga, 27 Al, and 17 O, by applying the SR4 symmetry sequence on protons during the recoupling periods; as an example, proton-detected 2D 1 H{ 71 Ga} D-HMQC and D-RINEPT correlation spectra of Ga(acac) 3 at 50 kHz MAS are shown in Figure 23c,d. 333 It was demonstrated that proton detection can provide a substantial gain in sensitivity and enables high efficiency on the data acquisition; in fact, the total experimental time to obtain a 2D heteronuclear correlation spectrum utilizing proton detection is similar to that required for the acquisition of a 1D spin−echo spectrum of quadrupolar nuclei.…”

“…The introduction of MAS to suppress anisotropic line-broadening interactions, such as CSA and dipolar couplings, to obtain “solution-like” high-resolution spectra of solids has created numerous avenues to investigate a variety of solid-state systems. The development of recoupling techniques to measure CSA, dipolar couplings, and quadrupolar couplings, efficient decoupling pulse sequences, dynamic nuclear polarization (DNP) instrumentation and methods, use of paramagnetic relaxation effect (PRE), and the employment of multidimensional approaches have dramatically enhanced the power of MAS NMR spectroscopy. − In fact, the “no need to dissolve a system in a solvent” for MAS NMR has enabled atomic-resolution studies of some of the most challenging systems for the first time. Such systems include polycrystalline, amorphous, frozen, and fibril solids.…”

Advances in the characterization of inorganic solids using NMR correlation experiments

“…The sensitivity of these heteronuclear correlation experiments has notably been improved using indirect detection via protons at high MAS frequencies 32 . Several reviews about homo-and hetero-nuclear recoupling sequences, mainly for spin-1/2 nuclei, have been published [33][34][35][36][37][38][39][40][41] . Through-bond correlation experiments, primarily for spin-1/2 isotopes in organic solids, 42,43 as well as correlation experiments for quadrupolar nuclei [44][45][46][47][48] have also been surveyed.…”