title: Hydrogen bonding to pi-systems of indole and 1-methylindole: is there any OH...phenyl bond?
abstract: The weak hydrogen-bonded complexes between proton donors and the pi-cloud of indole and 1-methylindole (MI) are investigated theoretically by three different methods: DFT/B3LYP, MPW1B95, and MP2. This study addresses the question as to whether the 1:1 complex can only form between the proton and the pi-cloud of the pyrrole part of indole or if there also exists a 1:1 complex between the proton and the pi-cloud of the phenyl ring. For the water-indole system, the more elaborate MP2 and MPW1B95 methods yield only one minimum with a hydrogen bond to the pyrrole part and weak secondary interactions to the phenyl ring, in agreement with a recent criticism by Van Mourik (Chem. Phys. 2004, 304, 317-319) that the B3LYP functional is unable to account for the dispersion interaction. However, for the 1:1 complexes between MI and 2-propanol, all three methods indicate that both the five-membered and the six-membered rings of the indole chromophore can form pi-complexes. For the MI-trifluoroethanol (TFE) system, it is shown that the ethanol conformation is specific for the interaction site: for the complex to the five-membered ring, TFE is in the cis-gauche conformation, while for the complex to the six-membered ring site, it is in the trans conformation. These results are discussed as a function of local interactions in the systems.
authors.affiliation: Department of Chemistry, University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
authors.forename: Ru Bo
authors.initials: RB
authors.lastname: Zhang
authors.forename: Ken R F
authors.initials: KR
authors.lastname: Somers
authors.forename: Eugene S
authors.initials: ES
authors.lastname: Kryachko
authors.forename: Minh Tho
authors.initials: MT
authors.lastname: Nguyen
authors.forename: Thérèse
authors.initials: T
authors.lastname: Zeegers-Huyskens
authors.forename: Arnout
authors.initials: A
authors.lastname: Ceulemans