Calix[4]pyrrole as a Chloride Anion Receptor:  Solvent and Countercation Effects

Abstract

The interaction of calixpyrrole with several chloride salts has been studied in the solid state by X-ray crystallography as well as in solution by isothermal titration calorimetry (ITC) and (1)H NMR spectroscopic titrations. The titration results in dimethylsulfoxide, acetonitrile, nitromethane, 1,2-dichloroethane, and dichloromethane, carried out using various chloride salts, specifically tetraethylammonium (TEA), tetrapropylammonium (TPA), tetrabutylammonium (TBA), tetraethylphosphonium (TEP), tetrabutylphosphonium (TBP), and tetraphenylphosphonium (TPhP), showed no dependence on method of measurement. The resulting affinity constants (K(a)), on the other hand, were found to be highly dependent on the choice of solvent with K(a)'s ranging from 10(2)-10(5) M(-1) being recorded in the test solvents used for this study. In dichloromethane, a strong dependence on the countercation was also seen, with the K(a)'s for the interaction with chloride ranging from 10(2)-10(4) M(-1). In the case of TPA, TBA, and TBP, the ITC data could not be fit to a 1:1 binding profile.

Carboxylate Anion Diminishes Chloride Transport through a Synthetic, Self‐Assembled Transmembrane Pore

“…[22,23] We have used it to characterize the SAT molecules and the Cl -complexes that are the subject of this paper. (6) in CH 3 CN/2-PrOH (1:1 v/v) was sprayed, only two peaks with ion abundances greater than 20% were observed in the mass range 600 to 2400. The base peak was observed at m/z 1245.6 and corresponds to [6-H] -.…”

“…Six of these compounds (1)(2)(3)(4)(5)(6) all have the basic structure ∼(Gly) 3 -Pro-(Xxx) 3 ∼. A seventh (7), discussed below, is a fluorescent analogue of 5.…”

“…The final two peptides, 5 and 6, have the sequence (Gly) 3 -Pro-Gly-Gly-Glx in which Glx is benzylated Glu in 5, Glu in 6, and in 7 Glx is Glu that has been esterified by 1-pyrenemethanol. All eight heptapeptides (1)(2)(3)(4)(5)(6)(7)(8), have the (C 18 H 37 ) 2 NCOCH 2 OCH 2 CO∼ group at the N terminus of the peptide.…”

“…[3,4,5] In many cases, the ability of these receptor molecules to complex anions has been characterized by X-ray crystallography. Solution complexation of various anions has also been studied for cyclic [6] and acyclic receptors. [7] Our particular interest has been in designing molecules that can form pores in phospholipid bilayers and not only complex anions, but transport them across a membrane.…”

Screening Solvent Effects in Anion Recognition

“…The situation becomes even more difficult when charges are involved, as the solubility of the components of the system may vary wildly between different solvents, while counterion effects, conformational flexibility and preferential solvation can further complicate any attempted analysis. Accordingly, investigations of anion recognition in which more than a handful of solvents have been examined are rare, [5][6][7] and an empirical scale describing the binding abilities of anions was only very recently established. 8 The limited understanding of the relative importance of potential energetic contributors to anion recognition undoubtedly impedes the design of new synthetic receptors that could be exploited in industrially important separations, sensing, medicine, membrane transport, templated synthesis, catalysis and beyond.…”