title: Competition between hydrogen and halogen bonding in halogenated 1-methyluracil: Water systems.
abstract: The competition between hydrogen- and halogen-bonding interactions in complexes of 5-halogenated 1-methyluracil (XmU; X = F, Cl, Br, I, or At) with one or two water molecules in the binding region between C5-X and C4=O4 is investigated with M06-2X/6-31+G(d). In the singly-hydrated systems, the water molecule forms a hydrogen bond with C4=O4 for all halogens, whereas structures with a halogen bond between the water oxygen and C5-X exist only for X = Br, I, and At. Structures with two waters forming a bridge between C4=O and C5-X (through hydrogen- and halogen-bonding interactions) exist for all halogens except F. The absence of a halogen-bonded structure in singly-hydrated ClmU is therefore attributed to the competing hydrogen-bonding interaction with C4=O4. The halogen-bond angle in the doubly-hydrated structures (150-160°) is far from the expected linearity of halogen bonds, indicating that significantly non-linear halogen bonds may exist in complex environments with competing interactions.
authors.affiliation: EaStCHEM School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, KY16 9ST, United Kingdom.
authors.forename: Simon W L
authors.initials: SW
authors.lastname: Hogan
authors.affiliation: EaStCHEM School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, KY16 9ST, United Kingdom.
authors.forename: Tanja
authors.initials: T
authors.lastname: van Mourik
keywords: M06-2X; density functional theory; halogen bond; hydrogen bond; methyluracil