Determination of molecular geometry by high-order multiple-quantum evolution in solid-state NMR,

M. Edén, A. Brinkmann, H. Luthman, L. Eriksson, and M. H. Levitt,
J. Magn. Reson. 144, 266-279, (2000).
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The principles of molecular geometry determination by high-​quantum heteronuclear local field spectroscopy in solid-​state NMR are discussed. The extreme multiple-​quantum coherences in a cluster of nuclear spins are allowed to evolve in the presence of heteronuclear through-​space couplings to two spins of a different type. The multiple-​quantum dephasing curve is dependent of the homonuclear spin-​spin couplings used and may be described in terms of geometric parameters. The triple-​quantum version of the experiment is demonstrated by determining the psi torsion angle in a [15N2,13C3]-labelled sample of the peptide ala-ala-gly. Two regions of torsion angle space fit the experimental data, one in the neighborhood of -152°, and one in the neighborhood of +161°. The latter determination is in excellent agreement with the X-ray estimate of +160.5°.