Decisive Influence of Environment on Aromatic/Aromatic Interaction Geometries. Comparison of Aromatic/Aromatic Interactions in Crystal Structures of Small Molecules and in Protein Structures

Geometries of aromatic/aromatic interactions in crystal structures of small molecules from the Cambridge Structural Database (CSD) (benzene/benzene, toluene/toluene, and p -phenol/ p -phenol interactions) and in protein structures from the Protein Data Bank (PDB) (Phe/Phe and Tyr/Tyr interactions) were studied and compared. The data show a larger influence of crystal packing/surrounding, more than the influence of substituents, on geometries of aromatic/aromatic interactions. While the interactions in crystal structures from the CSD show preference for parallel stacking interactions at the large offsets, in proteins from the PDB, they show preference for T-shaped geometries with small offsets.