title: Principles of spin-echo modulation by J-couplings in magic-angle-spinning solid-state NMR.
abstract: In magic-angle-spinning solid-state NMR, the homonuclear J-couplings between pairs of spin-1/2 nuclei may be determined by studying the modulation of the spin echo induced by a pi-pulse, as a function of the echo duration. We present the theory of J-induced spin-echo modulation in magic-angle-spinning solids, and derive a set of modulation regimes which apply under different experimental conditions. In most cases, the dominant spin-echo modulation frequency is exactly equal to the J-coupling. Somewhat surprisingly, the chemical shift anisotropies and dipole-dipole couplings tend to stabilise--rather than abscure--the J-modulation. The theoretical conclusions are supported by numerical simulations and experimental results obtained for three representative samples containing 13C spin pairs.
authors.affiliation: Chemistry Department, Southampton University, SO17 1BJ, UK.
authors.forename: Luminita
authors.initials: L
authors.lastname: Duma
authors.forename: Wai Cheu
authors.initials: WC
authors.lastname: Lai
authors.forename: Marina
authors.initials: M
authors.lastname: Carravetta
authors.forename: Lyndon
authors.initials: L
authors.lastname: Emsley
authors.forename: Steven P
authors.initials: SP
authors.lastname: Brown
authors.forename: Malcolm H
authors.initials: MH
authors.lastname: Levitt
mesh_terms: D016880:Anisotropy; D002247:Carbon Isotopes; D003198:Computer Simulation; D005650:Fumarates / Q000737:chemistry; D005998:Glycine / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D015394:Molecular Structure; D009587:Nitrogen Isotopes; D011789:Quantum Theory; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D013113:Spin Labels
chemical_list: D002247:Carbon Isotopes; D005650:Fumarates; D009587:Nitrogen Isotopes; D000644:Quaternary Ammonium Compounds; D013113:Spin Labels; D005998:Glycine