Bipyrrole-Strapped Calix[4]pyrroles: Strong Anion Receptors That Extract the Sulfate Anion

Abstract

Cage-type calix[4]pyrroles 2 and 3 bearing two additional pyrrole groups on the strap have been synthesized. Compared with the parent calix[4]pyrrole (1), they were found to exhibit remarkably enhanced affinities for anions, including the sulfate anion (TBA(+) salts), in organic media (CD2Cl2). This increase is ascribed to participation of the bipyrrole units in anion binding. Receptors 2 and 3 extract the hydrophilic sulfate anion (as the methyltrialkyl(C(8-10))ammonium (A336(+)) salt) from aqueous media into a chloroform phase with significantly improved efficiency (>10-fold relative to calix[4]pyrrole 1). These two receptors also solubilize into chloroform the otherwise insoluble sulfate salt, (TMA)2SO4 (tetramethylammonium sulfate).

Tuning the Electrochemistry of Free‐Base Porphyrins in Acidic Nonaqueous Media: Influence of Solvent, Supporting Electrolyte, and Ring Substituents

“…Anions are known to bind to the central protons of expanded free-base porphyrins and related macrocyclesi nt heir neutral form, [40][41][42][43][44][45][46][47] and one of our interests in the present study was to investigate how changes in the supporting electrolyte anion would affect both the measured reduction potentials and the stabilityo ft he porphyrin products formed in the first and/or second reduction on the electrochemical and spectroelectrochemical timescale. Examples of the electrochemical data are given in Figures S3 and S4, which illustrate cyclic voltammograms of H 2 TPP in the four solvents containing TBAX, where X = Cl À ,Br À ,I À ,and ClO 4 À .…”

Extraction and transport of sulfate using macrocyclic squaramide receptors

“…11 While a number of receptors for selective sulfate recognition have recently been reported, [13][14][15][16][17][18][19][20][21][22][23][24][25] there are relatively few examples of suitable receptors that overcome the Hofmeister bias to allow LLE of sulfate. [26][27][28][29][30][31][32][33] Sessler and co-workers have successfully employed calix[n]pyrroles to extract sulfate into organic media in the presence of methyltrialkylammonium ions. [26][27][28] Wu and co-workers have demonstrated that a tripodal hexaurea receptor is capable of extraction of sulfate ions into chloroform solution in the presence of TBACl and that the sulfate can be back-extracted with aqueous barium chloride to regenerate the receptor as a chloride complex.…”

Recent Advancements in Calix[4]pyrrole‐Based Anion‐Receptor Chemistry

“…Such high fluoride anion selectivity can be attributed to the presence of the bulky calix [4]arene cap, which possesses phenyl spacers that are less flexible and thus increase the rigidity of the calix [4]pyrrole core. [57] Copyright (2014) American Chemical Society. 1 H NMR titration in CDCl 3 has also revealed that receptor 9 binds fluoride anions in its monohydrated form.…”