Shielding tensors amino groups

P-O- H-O-C and P-O- H-O-P hydrogen bond distance in l (left) and dl (right) forms of O-phosphorylated amino acids. (B) 31P chemical shielding tensor orientation in O-phosphorylated amino acids showing three orthogonal projections of the phosphate group hydrogen bond in tyrosine. Taken from Ref. [36],... 

There are different parameters that can provide insights into the hydrogen bond interaction in the solid state. Solid state 13C-NMR studies of protonated and deprotonated carboxylates in amino acids have shown that the values of the principal elements of the nuclear shielding tensor change significantly with the protonation state of the carboxylic groups [54—59]. The orientation of the three CSA tensors for the COOH and COO" groups in a peptide is depicted in Fig. 3.2.21. 

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