title: Observation of the Second-Order Quadrupolar Interaction as a Dominating NMR Relaxation Mechanism in Liquids: The Ultraslow Regime of Motion.
abstract: We report variable-temperature (VT) (17)O NMR spectra of [5-(17)O]-d-glucose in an aqueous solution and in glycerol at 14.1 and 21.1 T. The VT (17)O NMR data cover a wide range of motion for which the molecular rotational correlation time (τc) of glucose changes more than 5 orders of magnitude. The observed line width of the (17)O NMR signal for [5-(17)O]-d-glucose displays a maximum at ω0τc ≈ 1 and a minimum at ω0τc ≈ 150, where ω0 is the angular Larmor frequency of (17)O. Under the ultraslow motion condition (i.e., ω0τc > 150), the line width of the observed (17)O NMR signal increases drastically with τc, suggesting that the second-order quadrupolar interaction becomes the predominant relaxation mechanism. While this relaxation mechanism has long been predicted by theory, the current study reports the first experimental observation of such a phenomenon. The implications of this new relaxation mechanism on the spectral resolution limit in liquid-state NMR spectroscopy for half-integer spins are discussed.
authors.affiliation: Department of Chemistry, Queen's University , Kingston, Ontario K7L 3N6, Canada.
authors.forename: Jiahui
authors.initials: J
authors.lastname: Shen
authors.affiliation: Department of Chemistry, Queen's University , Kingston, Ontario K7L 3N6, Canada.|Department of Chemistry, University of Ottawa , Ottawa, Ontario K1N 6N5 Canada.
authors.forename: Victor
authors.initials: V
authors.lastname: Terskikh
authors.affiliation: Department of Chemistry, Queen's University , Kingston, Ontario K7L 3N6, Canada.
authors.forename: Gang
authors.initials: G
authors.lastname: Wu