title: Anion binding modes in meso-substituted hexapyrrolic calix[4]pyrrole isomers.
abstract: We report on the synthesis of a new receptor for anions, meso-substituted hexapyrrolic calix[4]pyrrole 1. The calix[4]pyrrole's core features two additional pyrrole side-arms suspended above or below the calix[4]pyrrole core. This hexapyrrolic calix[4]pyrrole 1 is formed as cis- and trans-configurational isomers, the structures of which have been determined by single crystal X-ray diffraction. The anion binding experiments revealed interesting difference in the binding mode: The cis-1 isomer binds anions in a mixed binding mode featuring a combination of hydrogen bonding and anion-π interactions resulting in an unexpected strong binding. On the other hand, the trans-1 isomer displays only hydrogen bonding and lower affinity for anions. This is unexpected as one would assume both isomers to display the same binding modes. Overall, the titrations of 1 using UV spectrophotometry and NMR titrations by anions reveal that cis-isomer 1 displays higher affinity (10(5)-10(6) M(-1)) and cross-reactivity for anions, while the trans-isomer 1 shows a more selective response to anions. Such differences in binding mode in configurational isomers are so far unexplored and a feature deserving further study.
authors.affiliation: Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University , Bowling Green, Ohio 43403, United States.
authors.forename: Kai-Chi
authors.initials: KC
authors.lastname: Chang
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Minami
authors.forename: Petr
authors.initials: P
authors.lastname: Koutnik
authors.forename: Pavel Y
authors.initials: PY
authors.lastname: Savechenkov
authors.forename: Yuanli
authors.initials: Y
authors.lastname: Liu
authors.forename: Pavel
authors.initials: P
authors.lastname: Anzenbacher
mesh_terms: D000838:Anions / Q000737:chemistry; D001665:Binding Sites; D047250:Calixarenes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000838:Anions; D011166:Porphyrins; C469811:calix(4)pyrrole; D047250:Calixarenes