Peptide bond interatomic distances

Figure 2-5 Dimensions of the peptide linkage. Interatomic distances in nm, including the hydrogen bond length to an adjacent peptide linkage, are indicated. The atoms enclosed by the dotted lines all lie approximately in a plane. However, as indicated in the lower drawing, the nitrogen atom tends to retain some pyramidal character.

Figure 3-4. Dimensions of a fully extended polypeptide chain. The four atoms of the peptide bond (colored blue) are coplanar. The unshaded atoms are the a-carbon atom, the a-hydrogen atom, and the a-R group of the particular amino acid. Free rotation can occur about the bonds that connect the a-carbon with the a-nitrogen and with the a-carbonyl carbon (blue arrows). The extended polypeptide chain is thus a semirigid structure with two-thirds of the atoms of the backbone held in a fixed planar relationship one to another. The distance between adjacent a-carbon atoms is 0.36 nm (3.6 A). The interatomic distances and bond angles, which are not equivalent, are also shown. (Redrawn and reproduced, with permission, from Pauling L, Corey LP, Branson PIR The structure of proteins Two hydrogen-bonded helical configurations of the polypeptide chain. Proc Natl Acad Sci U S A 1951 37 205.)...

Highly accurate interatomic distances (ultimately 0.05 A) may be obtained from REDOR experiments [49], which are therefore an attractive tool for studies of hydrogen bonding. This technique has been used recently to characterise ex-helix structures in polypeptides by measuring 13C=0---H-15N hydrogen bond lengths [50]. The intrachain 13C- 15N interatomic distances, measured for a number of different samples, were found to be 4.5 0.1 A. This finding was used as evidence for the a-helix structure, which is consistent with the conformation dependent displacements of 13C chemical shifts of the Ca, Cp and carbonyl carbons of the peptide unit [51]. 

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