Anion-Binding Behavior of Hybrid Calixpyrroles

Abstract

Hybrid calixpyrrole systems are calixpyrrole-like macrocycles that are based on more than one type of small molecule building block. Structurally, these "mixed-breed" macrocycles differ from calixpyrroles in that some pyrrolic units in the latter are replaced by other hetereocyclic units such as furan, thiophene, bipyrrole, and bithiophene. Although several such systems have been reported in recent years, only a few have been studied as possible anion receptors. In this paper, the results of detailed anion binding studies involving several prototypic systems are reported. Taken in concert, these results highlight the fact that some hybrid systems, including compounds 2-5, display anion affinities that are considerably weaker than those of the parent system 1. On the other hand, they also show that compounds 6-8 are good receptors for "Y-shaped" anions, such as carboxylates, and that they bind these species with high affinity. These findings are strongly supported by solid-state structural studies, which reveal an interesting "cross binding mode" for the binding of carboxylate anions by the bis-thiophene, bis-pyrrole system 7.

Bisamides Derived from Azulene‐1,3‐ and ‐5,7‐dicarboxylic Acids as New Building Blocks for Anion Receptors

“…Such differences in geometry can lead to dramatic changes in selectivity and binding affinity, as has been shown for hybrid systems containing different building blocks. [8,9] …”

“…[6] However, our knowledge of structure/affinity relationships is still limited [7] and there are many examples of how small changes in ligand constitution can drastically alter the binding properties. [8,9] For this reason, it is important to have a large pool of structural subunits-building blocks-that can help in fine-tuning the host-guest interactions.…”

Anion binding to a tetracopper resorcinarene-based complex

“…These include the calix [4]arene that has cationic ammonium groups for binding (13) and a calix [4]arene with amidourea groups that is a colorimetric anion receptor (14). Along with these are calix [4]pyrroles with etheric handles which show a strong affinity for chloride (15,16), a zinc cyclen calix [4]arene that binds anions (17) and a resorcinarene compound that binds anions through C -H interactions (18).…”

Computational Study on the Conformational Characteristics of Calix[4]pyrrole Derivatives

“…Calix [4]pyrrole (1), porphyrinogen-like macrocycle, has been drawn much attention due to its significant anion recognition properties. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] Although the first synthesis of 1 was initially reported in 1886, 3 the guest binding properties had not been extensively investigated until late 1990's. 4,5 Calix [4]pyrrole adopts four major conformations as in the case of calix [4]arene.…”