Hydrogen-bonded structure and C-13 NMR chemical shift tensor of amino acid residue carbonyl carbons of peptides and polypeptides in the crystalline state .1.

C-13 chemical shift tensor components (delta(11) delta(22) and delta(33)) Of glycine (Gly), L-valine (Val), L-leucine (Leu), and L-asparagine (Asp) residue carbonyl carbons (C = O) of peptides and polypeptides covering a wide range of hydrogen-bond lengths (R(N-O)) in the crystalline state have been measured by slow magic-angle-spinning solid-state C-13 NMR. From these experiments, it is found that delta(22), which lies approximately along the amide C = O bond, moves linearly downfield with a decrease in R(N-O) and the slope and intercept of the variation of delta(22) against R(N-O) depend on the amino acid residue. Using this relationship, the R(N-O) values for polypeptides were determined by observation of the 822 Of the guest Gly residue incorporated into host polypeptides. delta(11), and delta(33) are found to be insensitive to the change in R(N-O) and amino acid residues. Moreover, it is found that the sum of delta(11) and delta(33) is almost constant (337.5 +/- 3.5 ppm) and is independent of the amino acid residue. The quantum-chemical calculation on the C-13 shielding constant for a peptide model compound was carried out by the finite perturbation theory within the INDO framework. This calculation acceptably explains the experimental results.