2.B.13 The Tetrapyrrolic Macrocyclic Anion Antiporter, Anion/Cation Symporter (TPMC) Family
Meso-octamethyloctafluorocalixpyrrole, a simple tetrapyrrolic macrocycle, and other pyrroles function as chloride/nitrate and chloride/bicarbonate antiporters for lipid bilayer transmembrane anion transport (Gale et al. 2010). They are examples of synthetic macrocyclic pyrrole-based systems capable of transmembrane anion transport (Gale 2011). A variety of such compounds can transport different ions such as nitrate, bicarbonate and chloride, and anion transport is influenced by the presence of cations (Adriaenssens et al. 2013). These versatile molecules function as receptors, transporters and molecular switches (Kim and Sessler 2015). Due to their anion transport capacities, they can induce appoptosis in animal cells (Ko et al. 2014).
Calixpyrrole macrocycles exhibit versatility in the development of transmembrane ion transporters. These cyclic compounds are capable of binding both anions and large, polarizable cations through the pyrrolic N–H groups and the aromatic cup, respectively (Gale et al. 2017). Meso-octamethylcalixpyrrole promotes CsCl transmembrane co-transport (symport). Fluorination of the pyrrole rings enhances the acidity of the NH hydrogen bond donor groups, leading to stronger NH-Cl- interactions and dramatically changing the transmembrane transport activity of the molecule. For example, compound 2 is an efficient anion exchanger, promoting nitrate/chloride and bicarbonate/chloride exchange (Gale et al. 2017). Compound 2 is capable of chloride uniport in the absence of caesium cations. Strapped calixpyrroles 3–6, bearing triazole groups that enhance the chloride binding affinity enhanced chloride/nitrate exchange. An oligoether-strapped calixpyrrole 7 formed stable 1:1 ion-pair complexes with LiCl and NaCl and functioned both as a chloride/nitrate exchanger as well as an M+/Cl- co-transporter.
This family is related to the family with TC# 2.B.19.
The generalized reactions catalyzed by tetrapyrrolic compounds are:
Anion-1 (in) + Anion-2 (out) → Anion-1 (out) + Anion-2 (in)
Anion (in) + Cation (in) → Anion (out) + Cation (out)