Anion-binding Macrocycles

Evgeny A. Katayev, Patricia J. Melfi, and Jonathan L. Sessler 

Modem Supramolecular Chemistry Strategies for Macrocycle Synthesis. Edited by Francois Diederich, Peter J. Stang, and Rik R. Tykwinski Copyright 2008 WILEY-VCH Veriag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31826-1 

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Employing the same calix[4]quinone receptor, Beer et al. have constructed a strap from an anion-binding macrocycle terminated with the [Ru(bpy)2+] and /ac-[ReCl(CO)3bpy] reporter sites [399], The emission quantum yields and lifetimes of 69 and 70 are significantly diminished with respect to their unoxidized calix[4]arene congeners 71 and 72 (69 t = 30 ns, 4>e = 1 x 10-3 vs. 71 ... 

Dipolar electrostatic interactions have also been manipulated for the purposes of anion binding. Macrocyclic receptor 10 was shown to be capable of binding halide anions through interactions with the positive ends of the S = O and P = O dipoles (54). Evidence was also provided for the simultaneous binding of primary alkyl ammonium cations (to the oxygen atoms) and halide anions (to the dipoles). This topic of simultaneous cation and anion recognition is of considerable current interest. Further examples will be encountered during this chapter. 

Application of Cation and Anion Binding Properties of Macrocyclic Polyamines... 

Recently considerable attention has been directed at anion binding ligands. Macrobicyclic 27 29) and macrotricyclic amines 30,31) were topologically designed to host anions such as spherical Cl-, linear Nf 32). These anion substrates are incorporated into macrocyclic cavities lined with appropriate anion-binding sites capable of forming hydrogen bonds like those of protonated amines (see /, below). 

Chemical transformations at the macroeyclic chromophorc of expanded porphyrins are still not known. The complexation behavior of expanded porphyrins is very different from that of nonexpanded porphinoid macrocycles. The coordination hole of the expanded porphyrins is often too big for the complexation of a single metal ion, so in fact two metal ions can be chelated. With some expanded porphyrins, anion binding is observable, a striking difference to the nonexpanded porphyrins. The complexation behavior and the host-guest chemistry of expanded porphyrins is a rapidly growing field of research. The work in this field has been reviewed. Ie f... 

In addition to phosphate and halide anion binding, carboxylate chelation by sapphyrin macrocycles has been the subject of recent investigation. To date, two crystal structures have been solved. A 2 1 complex formed between diprotonated sapphyrin 3 and trifluoroacetic acid shows that the oxyanions are chelated above and below the sapphyrin plane (Figure 10). ° Greater complexity of organi-... 

An X-ray crystal structure determination of the bis(thf) adduct of this macrocycle revealed an approximately planar ring of dimensions ca. 12 x 7 A with the thf guests each chelated by two Hg atoms. No structural results relating to the anion-binding properties of these macrocycles have yet been reported. ... 

Expanded porphyrins display anion binding in solution and in the solid, a new facet of the chemistry of porphyrin-related macrocycles [3.18]. 

Fitting the macrocyclic polyamine 38 with a side chain bearing a 9-aminoacridine group yields a coreceptor capable of both anion binding, via the polyammonium subunit, and stacking interaction via the intercalating dye. It interacts with both the triphosphate and the adenine groups of ATP and provides in addition a catalytic site for its hydrolysis (see structure 82 and Section 5.2) [4.27]. 

Multiple recognition and catalysis in ATP hydrolysis with increased ATP/ADP selectivity has been achieved with a multifunctional anion receptor containing a macrocyclic polyamine as anion binding site, an acridine group as stacking site and a catalytic site for hydrolysis (structure 82) [4.27]. Phosphoryl transfer is accelerated by other types of hydrogen-bonding receptors [5.24a]. 

The range and versatility of amide anion binding hosts is very extensive. Macrocyclic amides have also been reported, such as 4.42 which forms a remarkable sandwich compound with sulfate in the solid state. Sulfate binding is enhanced by protonation of the tertiary amine groups and the host is thus a hybrid between amide and ammonium binding sites. The triethylbenzene scaffold has been used to prepare... 

Work by K Travis Holman and Jerry Atwood at the University of Missouri, USA has resulted in a tricationic host 4.66 based on the macrocycle cyclotriveratrylele (CTV, Section 7.7), which exhibits a deep anion binding pocket surrounded by three metal centres. A guest PF6 anion fits neatly into the cavity, stabilised by C—H F interactions, which may be differentiated from symmetry-related, noninteracting protons on the other side of the metallated aryl ring by H NMR spectroscopy. The X-ray crystal structure of this material is shown in Figure 4.26. 

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