ABSTRACT
We present here a bimodal Floquet theoretical and experimental investigation of the direction of sweep in the swept-frequency two pulse phase modulated (SW(f)-TPPM) scheme used for heteronuclear dipolar decoupling in solid-state NMR. The efficiency of the decoupling turns out to be independent of the sweep direction.
Subject(s)
Magnetic Resonance Spectroscopy/methods , Algorithms , Tyrosine/chemistryABSTRACT
Recently, a pulse scheme for heteronuclear spin decoupling in solid-state NMR, called swept-frequency two-pulse phase modulation (SW(f)-TPPM), was introduced which outperforms the standard TPPM and small phase incremental alteration (SPINAL) schemes. It has also been shown that the frequency-sweep profile can be varied to achieve optimal efficiency for crystalline and liquid-crystalline samples, respectively. Here we present a detailed comparison of the proton decoupling performance for SW(f)-TPPM sequences with tangential sweep profiles (SW(f) (tan)-TPPM) and linear sweep profiles (SW(f) (lin)-TPPM). Using the (13)CH(2) resonance of crystalline tyrosine as a model system, it is shown that linear profiles have a decoupling performance which is at least as good and in some instances slightly better than that obtained from tangential sweep profiles. While tangential sweep profiles require a tangent cut-off angle as an additional parameter, the lack of that parameter makes linear sweep profiles easier to implement and optimise.
Subject(s)
Nuclear Magnetic Resonance, Biomolecular/methods , Tyrosine/analysis , Carbon Isotopes , Protons , Reference Standards , Sensitivity and SpecificityABSTRACT
Nanocrystalline SnO2 samples of different grain sizes, prepared by inert gas condensation technique (IGCT) and chemical precipitation method and conforming to the tetragonal phase, have been studied by variable speed (3-10 kHz) 119Sn MAS NMR at 11.74 Tesla field. 119Sn solid-state NMR results show that the IGCT prepared samples have good crystallinity and phase purity compared to the samples prepared by the chemical method. The determination of 119Sn chemical shielding parameters (delta iso, delta delta and eta) from slow MAS spectra shows that the 119Sn isotropic chemical shift (delta iso) is strongly influenced at smaller grain sizes, attributable to the change in the O2- local symmetry for the surface 119Sn ions at smaller grain sizes. The observed line widths in MAS spectra are significantly larger than the life-time broadening due to spin-lattice (T1) and spin-spin (T2) relaxation. The 119Sn MAS NMR spectra are thus inhomogeneously broadened by a distribution of isotropic chemical shifts, the line broadening increasing with decrease in grain size.
