P-31 and C-13 chemical shielding tensors in the phosphoenolpyruvate moietyfrom rotary resonance recoupling C-13 and P-31 MAS and single crystal P-31NMR

A P-31 and C-13 NMR study of powder and single crystal samples of two phosp hoenolpyruvate (PEP) compounds, the tris-ammonium salt monohydrate (NH4)(3) (PEP). H2O (1), and the mono-ammonium-salt (NH4)(H2PEP) (2) is presented. T he P-31 chemical shielding tensors in 1 are measured by P-31 single crystal NMR on four minuscule samples and assigned without ambiguity by exploiting the orientation-dependent P-31-P-31 dipolar splittings of the resonance li nes. The orientation of the P-31 chemical shielding tensor is discussed in terms of the C-2v- and C-3-type distortions of the phosphate PO4-coordinati on sphere. From C-13 MAS NMR experiments with 31P rotary resonance recoupli ng on polycrystalline powder samples the orientations of the P-31 chemical shielding tensors in 1 and 2 are obtained, for 1 in very good agreement wit h the P-31 single crystal NMR results. Only some of the orientational param eters of the three C-13 chemical shielding tensors in the PEP moiety of 1 c ould be derived from C-13 MAS NMR experiments with P-31 rotary resonance re coupling.