Heteronuclear decoupling interference during symmetry-based homonuclear recoupling in solid-state NMR

Abstract

We examine the influence of continuous-wave heteronuclear decoupling on symmetry-based double-quantum homonuclear dipolar recoupling, using experimental measurements, numerical simulations, and average Hamiltonian theory. There are two distinct regimes in which the heteronuclear interference effects are minimized. The first regime utilizes a moderate homonuclear recoupling field and a strong heteronuclear decoupling field; the second regime utilizes a strong homonuclear recoupling field and a weak or absent heteronuclear decoupling field. The second regime is experimentally accessible at moderate or high magic-angle-spinning frequencies and is particularly relevant for many realistic applications of solid-state NMR recoupling experiments to organic or biological materials.

Double-Quantum 13C Nuclear Magnetic Resonance of Bathorhodopsin, the First Photointermediate in Mammalian Vision

“…Four 13 C 2 -labeled rhodopsin isotopomers were studied, namely, [9,[10][11][12][13] C 2 ], [11,[12][13] C 2 ], [12, C 2 ], and [14, C 2 ]-retinylidene rhodopsin. Since the reconstituted samples are optically dense, the light penetration was improved by grinding frozen rhodopsin samples in liquid nitrogen to form particles of diameter ∼200 µm which were then mixed with ∼100 µm diameter glass beads.…”

“…All procedures were performed in dim red light to avoid premature isomerization. 13 C NMR spectra of the labeled chromophores were recorded using the double-quantum filtered pulse sequence reported in ref 12. Symmetry-based double-quantum recoupling using pulse sequences with the symmetry R20 2 9 , combined with phase-cycling to remove signals that do not pass through double-quantum coherence, achieves a clean suppression of the natural 13 C background signals from the protein and the lipid.…”

“…Figure 2. Double-quantum filtered 13 C NMR spectra of (a) [9,[10][11][12][13] C2], (b) [11,[12][13] C2], (c) [12, C2], (d) [14, C2] rhodopsin before (above) and after (below) 10 h of illumination with 420 ( 5 nm light. All spectra are the Fourier transforms of ∼12 000 NMR signals acquired at a temperature <120 K with magic-angle spinning at 7.00 ( 0.05 kHz.…”

Solid‐state NMR for the analysis of high‐affinity ligand/receptor interactions

“…These reduce sample warming and facilitate the efficient decoupling of protons as a greater mismatch between the low-g and proton rf amplitudes is possible (103). With the advent of optimized sequences and higher spinning frequencies, alternative solutions to these issues have been found with the development of experiments that do not require proton decoupling during the homonuclear recoupling periods of the sequence (104). These have found application to the study of ligand/receptor interactions (105).…”

A large geometric distortion in the first photointermediate of rhodopsin, determined by double-quantum solid-state NMR

“…The double-quantum excitation and reconversion intervals (s exc and s rec , respectively) were both set equal to 380 ls to maximize the double-quantum efficiency. No radiofrequency field was applied on the 1 H channel during the R20 2 9 recoupling sequence since the high-power 13 C rf field (70 kHz in the present case) achieved sufficient heteronuclear decoupling (Marin-Montesinos et al 2005). A SPINAL-64 (Fung et al 2000) decoupling sequence was applied on the 1 H channel during detection of the 13 C free induction decay.…”