title: Heteronuclear double-quantum MAS NMR spectroscopy in dipolar solids.
abstract: A new pulse sequence for high-resolution solid-state heteronuclear double-quantum MAS NMR spectroscopy of dipolar-coupled spin-12 nuclei is introduced. It is based on the five-pulse sequence known from solution-state NMR, which is here applied synchronously to both spin species. The heteronuclear double-quantum (HeDQ) spinning-sideband patterns produced by this experiment are shown to be sensitive to the heteronuclear distance, as well as the relative orientations of the chemical-shift and dipolar tensors. In particular, it is shown that the HeDQ patterns exhibit an enhanced sensitivity to the chemical shielding tensors as compared with the single-quantum spinning-sideband patterns. The detection of HeDQ patterns via the I and S spins is discussed. The isolated (13)C-(1)H spin pair in deuterated ammonium formate with (13)C in natural abundance was chosen as a model system, and the perturbing influence of dipolar couplings to surrounding protons on the (13)C-(1)H DQ coherence is discussed. The pulse sequence can also be used as a heteronuclear double-quantum filter, hence providing information about heteronuclear couplings, and thus allowing the differentiation of quaternary and CH(n) bonded carbons. The elucidation of (13)C-(1)H dipolar proximities is presented for a sample of bisphenol A polycarbonate with (13)C in natural abundance, recorded with a broadband version of the synchronized five-pulse sequence.
authors.affiliation: Max-Planck-Institut für Polymerforschung, Mainz, D-55021, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Saalwächter
authors.forename: R
authors.initials: R
authors.lastname: Graf
authors.forename: D E
authors.initials: DE
authors.lastname: Demco
authors.forename: H W
authors.initials: HW
authors.lastname: Spiess
mesh_terms: D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D000644:Quaternary Ammonium Compounds / Q000737:chemistry
chemical_list: D000644:Quaternary Ammonium Compounds