title: Cooperative AND ion-pair recognition by heteroditopic calix[4]diquinone receptors.
abstract: A new family of heteroditopic calix[4]diquinone receptors capable of the cooperative recognition of ion-pair species through a contact binding mechanism has been developed. The receptors bind contact ion pairs cooperatively, with an unprecedented AND recognition phenomenon being observed to operate in certain cases, in which receptors display no affinity for either of the individual "free" cation or anion, but bind the cation and anion ion-pair strongly. X-ray crystallographic, solution-state, and computational methods rationalize the observed recognition behavior of the receptors. It is shown that the contact ion-pair interaction occurs through a pi-stacking-mediated folding of the receptors such that the anion and cation binding sites are arranged in close proximity, while in the solid state an unusual ion-mediated receptor dimerization is observed. Molecular dynamics simulations are further used to explain the observed trends in the association constants of different ion-pair species and the mechanism of interaction.
authors.affiliation: Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QR, UK.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Lankshear
authors.forename: Ian M
authors.initials: IM
authors.lastname: Dudley
authors.forename: Kar-Man
authors.initials: KM
authors.lastname: Chan
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Cowley
authors.forename: Sérgio M
authors.initials: SM
authors.lastname: Santos
authors.forename: Vitor
authors.initials: V
authors.lastname: Felix
authors.forename: Paul D
authors.initials: PD
authors.lastname: Beer
mesh_terms: D047250:Calixarenes / Q000138:chemical synthesis* / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation; D011809:Quinones / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D011809:Quinones; C528544:calix(4)diquinone; D047250:Calixarenes