Symmetry-based recoupling of 17 O– 1 H spin pairs in magic-angle spinning NMR Jacco D. van Beek a,1 , Ray Dupree b , Malcolm H. Levitt a, * a School of Chemistry, Southampton University, Highfield, Southampton, SO17 1BJ, UK b Department of Physics, University of Warwick, Coventry, CV4 7AL, UK Received 17 September 2005; revised 31 October 2005 Abstract We have performed magic-angle-spinning solid-state NMR experiments in which protons are recoupled to oxygen-17 nuclei by apply- ing a symmetry-based recoupling sequence at the proton Larmor frequency. Two-dimensional quadrupole-dipole correlation spectra are produced, in which the second-order quadrupolar shift of the oxygen-17 central transition is correlated with the recoupled heteronuclear dipole–dipole interaction. These spectra are sensitive to the relative orientation of the electric field gradient at the site of the oxygen-17 nucleus and the O–H internuclear vector. We also demonstrate experiments in which polarization is transferred from protons to oxygen- 17, and show that oxygen-17 signals may be selected according to the protonation state of the oxygen site. We discuss the small observed value of the heteronuclear dipolar splitting in the central-transition oxygen-17 spectra. Ó 2005 Elsevier Inc. All rights reserved. Keywords: Solid-state NMR; Quadrupolar nuclei; Oxygen-17; Correlation spectroscopy; Symmetry-based recoupling; MAS; Brucite 1. Introduction 17 O solid-state NMR of isotopically enriched materials is an important method for studying a wide range of sub- stances, including zeolites [1–3], glasses [4], battery materi- als [5], and membrane-bound peptides [6]. The NMR of 1 H– 17 O pairs is of particular interest for the study of acidic sites and hydrogen-bonded systems [3,7,8] since the 17 O quadrupole interaction and chemical shift tensors are sen- sitive to local structural perturbations [9]. Furthermore, the magnitude of the 1 H– 17 O dipole–dipole coupling, and its relative orientation with respect to the chemical shift and quadrupole coupling tensors of the 17 O nucleus [10] provide additional information. The 1 H– 17 O dipole–dipole coupling constant has a mag- nitude of around 15 kHz in a directly bonded hydroxyl moiety. Although this a considerable interaction, it is diffi- cult to observe, since 17 O nuclei in hydroxyl sites experience a large electric field gradient, leading to a second-order quadrupolar broadening of the 17 O central transition by several kHz at typical magnetic fields. Furthermore, in many samples, strong 1 H– 1 H interactions create additional complications. Nevertheless, the 1 H– 17 O dipolar coupling has been resolved in static samples by performing Hart- mann–Hahn cross-polarization from 1 H to 17 O, while spin-locking the 1 H nuclei by off-resonance irradiation sat- isfying the Lee-Goldburg condition, in order to reduce the effect of the 1 H– 1 H couplings [10]. Two-dimensional spec- troscopy was used to correlate the second-order quadrupo- lar shift of the 17 O central transition with the 1 H– 17 O dipolar coupling, allowing determination of the relative orientation of the 1 H– 17 O dipolar coupling and 17 O quad- rupolar interaction tensors [10]. In this paper, such two-di- mensional spectra are termed quadrupole-dipole (QD) correlation spectra. It would be desirable to perform QD correlation exper- iments under magic-angle-spinning (MAS) conditions, 1090-7807/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jmr.2005.11.003 * Corresponding author. Fax: +44 23 8059 3781. E-mail address: mhl@soton.ac.uk (M.H. Levitt). 1 Present Address: Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland. www.elsevier.com/locate/jmr Journal of Magnetic Resonance 179 (2006) 39–49 ARTICLE IN PRESS