Optimal control theory enables homonuclear decoupling without Bloch–Siegert shifts in NMR spectroscopy

Abstract

The Bloch–Siegert shift is a phenomenon in NMR spectroscopy and atomic physics in which the observed resonance frequency is changed by the presence of an off-resonance applied field. In NMR, it occurs especially in the context of homonuclear decoupling. Here we develop a practical method for homonuclear decoupling that avoids inducing Bloch–Siegert shifts. This approach enables accurate observation of the resonance frequencies of decoupled nuclear spins. We apply this method to increase the resolution of the HNCA experiment. We also observe a doubling in sensitivity for a 30 kDa protein. We demonstrate the use of band-selective Cβ decoupling to produce amino acid-specific line shapes, which are valuable for assigning resonances to the protein sequence. Finally, we assign the backbone of a 30 kDa protein, Human Carbonic Anhydrase II, using only HNCA experiments acquired with band-selective decoupling schemes, and instrument time of one week.

Nearest-neighbor NMR spectroscopy: categorizing spectral peaks by their adjacent nuclei

“…The pulse shape was designed using recently developed homonuclear decoupling techniques from optimal control theory 37 , which permit selective decoupling of closely spaced bands of frequencies without causing any undesirable offresonance effects, such as Bloch-Siegert shifts 38 . The pulse is applied in the middle of the 13 C indirect encoding period.…”

“…An initial state of ρ(0) = I z and a desired final state of λ(T) = −I z was set for these spins. Inversion of the passive spins is sufficient for decoupling 37 . To ensure the pulse achieves proper chemical shift encoding in the nearby methyl region, we sampled 130 spins from ω ∈ [8.5, 27.5] ppm and alternated the initial state ρ(0) between I x and I y .…”

“…The simultaneous optimization of inversion and encoding behavior ensures that decoupling does not cause any off-resonance effects on the methyl spins. The optimized pulse shape was generated using the toggling frame implementation [37][38][39] of the GRAPE (gradient ascent pulse engineering) algorithm [40][41][42][43][44] . The optimization was seeded with a random pulse shape.…”

Controlling the isomerization dynamics of iodide acetonitrile dimer complex by optimally designed electromagnetic field: A wave packet based approach

“…Having control over a chemical event has been an important topic of contemporary research . Both theoreticians and experimentalists are involved in developing methodologies which can have control over chemical phenomena . One of the common ways to get selective control is by the use of electromagnetic radiation.…”

NMR Resolution Enhancement and Homonuclear Decoupling Using Non-Uniform Weighted Sampling

“…Such couplings give rise to a cosine modulation, cos(πJt), in the free-induction decay (FID), which leads to broadening or a resolved multiplet structure. As for molecular weight, a variety of approaches have been developed to address this problem: isotopic labelling schemes that eliminate adjacent 13 C nuclei 4,7,8 ; band selective decoupling (although this is only effective for a subset of residues) 9 ; virtual decoupling by computational deconvolution 10 ; and constant time evolution, which while effective entails a substantial reduction in sensitivity 11 .…”