title: Ion-mediated electron transfer in a supramolecular donor-acceptor ensemble.
abstract: Ion binding often mediates electron transfer in biological systems as a cofactor strategy, either as a promoter or as an inhibitor. However, it has rarely, if ever, been exploited for that purpose in synthetic host-guest assemblies. We report here that strong binding of specific anions (chloride, bromide, and methylsulfate but not tetrafluoroborate or hexafluorophosphate) to a tetrathiafulvalene calix[4]pyrrole (TTF-C4P) donor enforces a host conformation that favors electron transfer to a bisimidazolium quinone (BIQ2+) guest acceptor. In contrast, the addition of a tetraethylammonium cation, which binds more effectively than the BIQ2+ guest in the TTF-C4P cavity, leads to back electron transfer, restoring the initial oxidation states of the donor and acceptor pair. The products of these processes were characterized via spectroscopy and x-ray crystallography.
authors.affiliation: Department of Chemistry and Biochemistry, University Station-A5300, University of Texas, Austin, TX 78712-0165, USA.
authors.forename: Jung Su
authors.initials: JS
authors.lastname: Park
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Karnas
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: Ping
authors.initials: P
authors.lastname: Chen
authors.forename: Karl M
authors.initials: KM
authors.lastname: Kadish
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Bielawski
authors.forename: Todd W
authors.initials: TW
authors.lastname: Hudnall
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Lynch
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Sessler
mesh_terms: D000838:Anions / Q000737:chemistry*; D001965:Bromides / Q000737:chemistry; D047250:Calixarenes / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D004583:Electrons; D007093:Imidazoles / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011809:Quinones / Q000737:chemistry*; D013463:Sulfuric Acid Esters / Q000737:chemistry
chemical_list: D000838:Anions; D001965:Bromides; D002412:Cations; D002712:Chlorides; D007093:Imidazoles; D011809:Quinones; D013463:Sulfuric Acid Esters; C552241:bisimidazolium quinone; C526949:tetrathiafulvalene calix(4)pyrrole; D047250:Calixarenes; C033522:methyl sulfate