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

A 31P and 13C NMR study of powder and single crystal samples of two phosphoenolpyruvate (PEP) compounds, the tris-ammonium salt monohydrate (NH4)3 (PEP).H2O (1), and the mono-ammonium-salt (NH4)(H2PEP) (2) is presented. The 31P chemical shielding tensors in 1 are measured by 31P single crystal NMR on four minuscule samples and assigned without ambiguity by exploiting the orientationdependent 31P-31P dipolar splittings of the resonance lines. The orientation of the 31P chemical shielding tensor is discussed in terms of the C2x - and C3x-type distortions of the phosphate PO4-coordination sphere. From 13C MAS NMR experiments with 31P rotary resonance recoupling on polycrystalline powder samples the orientations of the 31P chemical shielding tensors in 1 and 2 are obtained, for 1 in very good agreement with the 31P single crystal NMR results. Only some of the orientational parameters of the three 13C chemical shielding tensors in the PEP moiety of 1 could be derived from 13C MAS NMR experiments with 31P rotary resonance recoupling.