An Experimental and Theoretical Study of the 13C and 31P Chemical Shielding Tensors in Solid O-Phosphorylated Amino Acids

A series of l and dl forms of O-phosphorylated amino acids (serine, threonine, tyrosine) have been studied by using solid-state multinuclear NMR spectroscopy and ab initio calculations. Principal elements of the 13C and 31P chemical shielding tensors have been measured and discussed in relation to zwitterionic structures and intermolecular contacts. DFT calculations have been compared with experimental data showing their ability to reproduce experimentally obtained tensor values in this challenging class of compounds. The changes of orientation of 31P chemical shielding tensor with respect to the molecular frame in the presence of hydrogen bonds have been revealed and discussed on the ground of theoretical calculations. The measurements of internuclear P···P distances, based on Zeeman magnetization exchange betwen 31P spins with differing chemical shielding tensor orientations, were exploited for a clear distinction between enantiomers and racemates.