Selective Sensing of Anions with Calix[4]pyrroles Strapped with Chromogenic Dipyrrolylquinoxalines

Abstract

New calix [4]pyrroles bearing dipyrrolylquinoxaline as strapping elements have been synthesized and characterized by spectroscopic means. The binding behavior of these receptors at 25 °C was investigated first by proton NMR spectroscopy in CD 3 CN/DMSO-d 6 (9:1 v./v.), as well as by UVvis spectroscopy and isothermal titration calorimetry (ITC) in CH 3 CN/DMSO (97:3 v./v.). The receptors displayed a selective colorimetric response when exposed to the fluoride, dihydrogen phosphate, and acetate anions (studied in the form of the corresponding tetrabutylammonium salts) and an enhanced affinity as compared to a comparable calix [4]pyrrole system lacking the dipyrrolylquinoxaline-containing strap. KeywordsStrapped-calix [4]pyrrole; anion sensing; dipyrrolylquinoxaline; colorimetric sensor Motivated in part by an increasing appreciation of the importance of anions in the environment and biology, considerable continues to be devoted to the design and synthesis of anion receptors possessing high affinity and selectivity. 1,2 A variety of systems that are capable of recognizing anions are now known, and most general classes have been discussed at some length in a variety of recent reviews. 3,4 Much of our own work of late has focused on a set of modified calix [4] pyrrole-based receptors known as strapped-or capped-calix [4]pyrroles. These modified calix [4]pyrrole derivatives generally display affinities and selectivities towards anions that are significantly enhanced relative to simple calix[4]pyrroles. They thus offer the attractive possibility of tuning the anion recognition properties of this well-studied class of receptors. 5-9 However, to be useful in certain applications, the augmented affinity of the strapped calix[4]pyrroles would need to be coupled with a "read out" element that would allow the anion binding event to be followed easily. Within the context of this general goal, we are particularly interested in developing strapped calix [4]pyrrole-based receptors that are capable of producing a colorimetric response upon anion recognition. In this paper, we wish to report the design, synthesis, and anion binding properties of calix [4]pyrroles that contain dipyrrolylquinoxalines as a part of the strap as shown in Scheme 1. These systems, which produce an easy-to-see visual response in the presence of certain anions, offer a further potential advantage in that they possess additional pyrrole subunits on the strap that are expected to interact with the chhlee@kangwon.ac.kr. quinoxaline chromophore via a variety of second order interactions, including through conjugation and anion-pi effects. NIH Public AccessThe synthesis of receptor 4 starts with ketone 1, a species that was prepared by the reaction of oxalyl chloride with two equivalents of 2-(3-oxobutyl)pyrrole. 11 Once in hand, 1 was reacted with 1,2-diamino-4-nitro-benzene in the presence of acid to afford bisketone 2 in 24% yield. 10 Treatment of this latter intermediate with neat pyrrole in the presence of trifluoroacetic acid afforded the bis-dipy...

Artificial Receptors for the Recognition of Phosphorylated Molecules

“…802 Significant changes in the absorption spectrum were observed upon the addition of various anions as their TBA salts in a solution of 97:3 CH 3 CN:DMSO. Binding affinities increased with decreasing anion size (fluoride > chloride > bromide > acetate > dihydrogenphosphate.…”

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.…”

Substituent effects on anion sensing of salicylidene Schiff base derivatives: Tuning sensitivity and selectivity

“…Most of these sensors are developed based on hydrogen bonding interaction [12][13][14], deprotonation [15][16][17] or chemical reaction [18][19][20]. However, many anion sensors are not able to differentiate F À , AcO À and H 2 PO 4 À because of their similar basicity and surface charge density [21,22]. Among various anions, F À is attracting a great deal of interest because of the importance of this anion in dental health and its possible toxicity when administered in high doses [23,24].…”