title: Ion-regulated allosteric binding of fullerenes (C60 and C70) by tetrathiafulvalene-calix[4]pyrroles.
abstract: The effect of ionic species on the binding of fullerenes (C60 and C70) by tetrathiafulvalene-calix[4]pyrrole (TTF-C4P) receptors and the nature of the resulting supramolecular complexes (TTF-C4P + fullerene + halide anion + tetraalkylammonium cation) was studied in the solid state through single crystal X-ray diffraction methods and in dichloromethane solution by means of continuous variation plots and UV-vis spectroscopic titrations. These analyses revealed a 1:1 stoichiometry between the anion-bound TTF-C4Ps and the complexed fullerenes. The latter guests are bound within the bowl-like cup of the C4P in a ball-and-socket binding mode. The interactions between the TTF-C4P receptors and the fullerene guests are highly influenced by both the nature of halide anions and their counter tetraalkylammonium cations. Three halides (F(-), Cl(-), and Br(-)) were studied. All three potentiate the binding of the two test fullerenes by inducing a conformational change from the 1,3-alternate to the cone conformer of the TTF-C4Ps, thus acting as positive heterotropic allosteric effectors. For a particular halide anion, the choice of tetraalkylammonium salts serves to modulate the strength of the TTF-C4P-fullerene host-guest binding interactions and, in conjunction with variations in the halide anion, can be exploited to alter the inherent selectivity of the host for a given fullerene. Differences in binding are reflected in the excited state optical properties. Overall, the present four-component system provides an illustration of how host-guest binding events involving appropriately designed artificial receptors can be fine-tuned via the addition of simple ionic species as allosteric modulators.
authors: Department of Chemistry, The University of Texas at Austin , 105 East 24th Street-Stop A5300, Austin, Texas 78712-1224, United States.
authors: Christina M
authors: CM
authors: Davis
authors: Jong Min
authors: JM
authors: Lim
authors: Karina R
authors: KR
authors: Larsen
authors: Dong Sub
authors: DS
authors: Kim
authors: Young Mo
authors: YM
authors: Sung
authors: Dani M
authors: DM
authors: Lyons
authors: Vincent M
authors: VM
authors: Lynch
authors: Kent A
authors: KA
authors: Nielsen
authors: Jan O
authors: JO
authors: Jeppesen
authors: Dongho
authors: D
authors: Kim
authors: Jung Su
authors: JS
authors: Park
authors: Jonathan L
authors: JL
authors: Sessler
mesh_terms: D000494:Allosteric Regulation; D000495:Allosteric Site; D000838:Anions / Q000737:chemistry; D047250:Calixarenes / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D018360:Crystallography, X-Ray; D037741:Fullerenes / Q000737:chemistry*; D006846:Hydrocarbons, Halogenated / Q000737:chemistry; D008752:Methylene Chloride / Q000737:chemistry; D008958:Models, Molecular; D000644:Quaternary Ammonium Compounds / Q000737:chemistry
chemical_list: D000838:Anions; D002412:Cations; D037741:Fullerenes; D006846:Hydrocarbons, Halogenated; D000644:Quaternary Ammonium Compounds; C526949:tetrathiafulvalene calix(4)pyrrole; C069836:fullerene C70; D047250:Calixarenes; D008752:Methylene Chloride; C069837:fullerene C60