Measurement of 13C–1H dipolar couplings in solids by using ultra-fast magic-angle spinning NMR spectroscopy with symmetry-based sequences

Abstract

We show that (13)C-(1)H dipolar couplings in fully protonated organic solids can be measured by applying a Symmetry-based Resonance-Echo DOuble-Resonance (S-REDOR) experiment at ultra-fast Magic-Angle Spinning (MAS). The (13)C-(1)H dipolar couplings are recovered by using the R12 recoupling scheme, while the interference of (1)H-(1)H dipolar couplings are suppressed by the symmetry properties of this sequence and the use of high MAS frequency (65 kHz). The R12 method is especially advantageous for large (13)C-(1)H dipolar interactions, since the dipolar recoupling time can be incremented by steps as short as one rotor period. This allows a fine sampling for the rising part of the dipolar dephasing curve. We demonstrate experimentally that one-bond (13)C-(1)H dipolar coupling in the order of 22 kHz can be accurately determined. Furthermore, the proposed method allows a rapid evaluation of the dipolar coupling by fitting the S-REDOR dipolar dephasing curve with an analytical expression.

Resolution and measurement of heteronuclear dipolar couplings of a noncrystalline protein immobilized in a biological supramolecular assembly by proton-detected MAS solid-state NMR spectroscopy

“…Nonetheless, measurements of heteronuclear dipolar couplings from single sites in biological solids remains challenging, since not only are all homonuclear but also all heteronuclear dipolar interactions are averaged out by the fast magic angle spinning [9]. R-symmetry based approaches have been shown to recouple heteronuclear dipolar couplings under MAS frequencies of 40 kHz [10] and 65 kHz [11]. Recently, a family of simple two-dimensional pulse sequences, based on cross-polarization (CP) with variable contact times and direct 13 C or 15 N detection have been applied successfully to the measurement of 1 H- 13 C and 1 H- 15 N dipolar couplings on single amino acids and tripeptides under 60 kHz MAS [12].…”

Studying dynamics by magic-angle spinning solid-state NMR spectroscopy: Principles and applications to biomolecules

“…They all consist of a rotor-synchronized pulse sequence that counteracts the MAS averaging. The most commonly used approaches are cross-polarization (CP) buildup measurements [164,165], Lee-Goldburg CP [111,166], phase-inverted CP [167,168], DIPSHIFT experiments [169,170], R-sequences [153,158,171,172], homonuclear SPC5 [173], T-MREV [174], or variants of REDOR [147] and TEDOR recoupling [106,175]. Systematic errors of dipolar-coupling measurements often are a challenge, and may arise from: (i) Experimental imperfections of the pulse sequence, in particular RF-field inhomogeneities or missetting of the applied RF-field amplitude.…”

Analysis of local molecular motions of aromatic sidechains in proteins by 2D and 3D fast MAS NMR spectroscopy and quantum mechanical calculations

“…Hence, a number of techniques have been developed during recent years to reintroduce those interactions and a large variety of pulse schemes have been published. [11][12][13][14][15] Recoupling of anisotropic spin interactions is achieved by application of pulse sequences that are often based on symmetry rules introduced by Levitt. 16 These sequences are called CN n n and RN n n , where the symbols N, n, and n are small symmetry integer numbers that depend on the rotation properties of the spin angular moment during the rotor-synchronized train of radio frequency (RF) pulses.…”