C–H/O interactions of aromatic CH donors within proteins: a crystallographic study

C–H/O interactions of aromatic C–H donors within proteins have been studied by analyzing the data in the Protein Data Bank (PDB). The C–H/O interactions were studied between aromatic donors; phenylalanine, tyrosine, and tryptophan and the acceptors; alcohol, backbone amide, and side-chain amide groups. The analysis of the C–H–O angle indicates that protein C–H donors do not show a preference for linear contacts. Although there is no tendency for linear C–H/O interactions, there are only around 3% of bifurcated C–H/O interactions. Furthermore, the analyses of the C–H/O interactions indicate an influence of simultaneous classical hydrogen bonds, especially for the tyrosine systems. The calculated electrostatic potential maps for model systems can explain the results of the crystallographic analysis. These results can be important for recognizing the C–H/O interaction of aromatic rings in the crystal structures of proteic systems.