title: Anion binding studies of fluorinated expanded calixpyrroles.
abstract: The anion binding properties of fluorinated calix[n]pyrroles (n = 4-6) in aprotic solvents (acetonitrile and DMSO) and modified reaction conditions allowing for the synthesis and isolation of the hitherto missing dodecafluorocalix[6]pyrrole from the condensation of 3,4-difluoro-1H-pyrrole and acetone are described. In acetonitrile solution containing 2% water, the association constants for the 1:1 binding interaction between octafluorocalix[4]pyrrole and chloride anion obtained with isothermal titration calorimetry (ITC) and (1)H NMR titration methods were found to match reasonably well. As compared to its nonfluorinated congener, octafluorocalix[4]pyrrole was found to display enhanced binding affinities for several representative anions in pure acetonitrile as judged from ITC analyses. Similar analyses of the fluorinated calix[n]pyrroles revealed an increase in the relative affinity for bromide over chloride with increasing macrocycle size, as manifest in a decrease in the binding ratio K(a(Cl))/K(a(Br)). Anion binding studies in the solid state, involving single-crystal X-ray diffraction analyses of the chloride and acetate anion complexes of octafluorocalix[4]pyrrole and decafluorocalix[5]pyrrole, respectively, confirmed the expected hydrogen bond interactions between the pyrrolic NH protons and the bound anions.
authors: Department of Chemistry and Biochemistry, 1 University Station-A5300, The University of Texas at Austin, Austin, TX 78712-0165, USA. sessler@mail.utexas.edu
authors: Jonathan L
authors: JL
authors: Sessler
authors: Won-Seob
authors: WS
authors: Cho
authors: Dustin E
authors: DE
authors: Gross
authors: James A
authors: JA
authors: Shriver
authors: Vincent M
authors: VM
authors: Lynch
authors: Manuel
authors: M
authors: Marquez