title: Intimate interactions with carbonyl groups: dipole-dipole or n→π*?
abstract: Amide carbonyl groups in proteins can engage in C═O···C═O and C-X···C═O interactions, where X is a halogen. The putative involvement of four poles suggests that these interactions are primarily dipolar. Our survey of crystal structures with a C-X···C═O contact that is short (i.e., within the sum of the X and C van der Waals radii) revealed no preferred C-X···C═O dihedral angle. Moreover, we found that structures with a short X(-)···C═O contact display the signatures of an n→π* interaction. We conclude that intimate interactions with carbonyl groups do not require a dipole.
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
authors.forename: Kimberli J
authors.initials: KJ
authors.lastname: Kamer
authors.forename: Amit
authors.initials: A
authors.lastname: Choudhary
authors.forename: Ronald T
authors.initials: RT
authors.lastname: Raines
mesh_terms: D000577:Amides / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006219:Halogens / Q000737:chemistry*; D006846:Hydrocarbons, Halogenated / Q000737:chemistry*; D008958:Models, Molecular; D050050:Protein Carbonylation; D011506:Proteins / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D000577:Amides; D006219:Halogens; D006846:Hydrocarbons, Halogenated; D011506:Proteins