13C chemical shielding tensor orientations in a phosphoenolpyruvate moiety from 13C rotational-resonance MAS NMR lineshapes

Abstract: The absolute orientations of the three 13C chemical shielding tensors in the phosphoenolpyruvate (PEP) moiety in a PEP-model compound with known crystal structure are reported. The study uses a fully 13C-enriched polycrystalline sample of triammonium phosphoenolpyruvate monohydrate, (NH4)3(PEP)⋅H2O, and 13C MAS NMR experiments fulfilling various different 13C rotational-resonance conditions. The absolute 13C chemical shielding tensor orientations are derived by iterative fitting, employing numerically exact simulations, of various rotational-resonance 13C MAS NMR lineshapes of the three-13C-spin system in fully 13C-enriched (NH4)3(PEP)⋅H2O. The implications of the results of this study for future, biochemically oriented solid-state NMR studies on the PEP moiety are outlined. [Copyright &y& Elsevier]