Calix[4]pyrroles: versatile molecular containers with ion transport, recognition, and molecular switching functions

Abstract

Over the last two decades, calix[4]pyrroles have attracted considerable attention as molecular containers. Used in this capacity, they have been exploited as strong and selective receptors and as extractants for both anions and ion pairs. More recently, calix[4]pyrroles have found application as carriers, systems capable of transporting ions and ion pairs across lipophilic membranes. The use of calix[4]pyrroles as building blocks for the preparation of stimulus-responsive material has also been demonstrated. In this latter context, as well as others, the conformational switching, from 1,3-alternate to cone upon anion binding has been exploited to control both structure and substrate binding. In this Review, we describe recent results involving the use of calix[4]pyrrole systems for ion transport. Also summarised is work devoted to the formation of higher order supramolecular aggregates and studies of their response to external stimuli. Taken together, these examples serve to highlight new uses of calix[4]pyrroles as molecular containers.

[C–H⋯anion] interactions mediate the templation and anion binding properties of topologically non-trivial metal–organic structures in aqueous solutions

“…The phosphate binding protein of Escherichia coli binds phosphate selectively with a K D of 0.7 μM 9–12. Recent achievements involving the recognition of anions in water by synthetic receptors include the sensitive detection of pollutants,13–18 the transportation of ions across membranes, and the sensing of biologically relevant anions in vivo 19–25. Gale and co-workers have published comprehensive reviews of these applications and other recent highlights in the field 26–28…”

Approach to modulate the sensing range of molecular transducers

“…Trifluoroacetic acid and DMSO-d6 were also purchased from Sigma-Aldrich. 1 H NMR spectra were recorded on Bruker arx 400 MHz spectrometer. UV-vis spectra were recorded in 1 cm quartz cuvette on Varian Cary 500 spectrophotometer.…”

“…The interaction/binding can be classified into two major categories, specific [1][2][3][4][5] and non specific [6][7][8][9][10][11][12]. Non specific binding based sensors take advantage of differential binding interactions of a set of non specific receptors to impart desired specificity.…”

SPECTROSCOPIC STUDY OF EFFECTS OF TETRAALKYLAMMONIUM CATIONS ON F−-SENSING PROPERTIES OF CALIX[4]PYRROLE BORADIAZAINDACENE DYE

“…1 Since then, calix [4]pyrrole-based receptors have attracted an increasing attention to modulate the anion-binding affinity and selectivity of the parent calix [4]pyrrole. [2][3][4][5][6] In general, calix [4]pyrrole derivatives are prepared to sense halide anions through hydrogen bonds 7,8 or the ion-pairing effect. 9,10 In an anion-sensing process, tetrabutylammonium (TBA + ) cation salts are readily utilized, yet the effects of various tetraalkylammonium cations have been largely ignored.…”