Synthetic Receptors for Anions

A detailed study of these complexes showed that a significant part of their binding affinity derived from hydrophobic interactions between the two peptide rings that did not directly involve the anion [127]. The authors propose that such intrareceptor interactions may well be the key to the development of more efficient synthetic receptors [3, 7]. Since prediction of these interactions may be problematic, DCC represents an attractive method for developing these structurally complex molecules. 

---

Anion recognition synthetic receptors for anions and their application in sensors Snowden, T. S. Anslyn, E. V. Curr. Opin. Chem. Biol. 1999, 3, 740-746. 

While the above-mentioned non-covalent interactions (hydrogen bonds, charge-charge) have been widely used in the design of efficient and selective synthetic receptors for anions either alone or combined, the use of attrac-... 

The last paragraph of a chapter like this one asks the writer to predict if the non-covalent interaction of anions with jt-system will be as important and useful as the nowadays well-established cation-n interaction. We are cautious in answering this question affirmatively, but we have to confess that we are currently working in the construction of synthetic receptors for anions that do incorporate electron deficient ir-aromatic systems. We hope that our designs will be valuable for the experimental evaluation of the anion-JT interaction in solution and we will report shortly our findings. Once the strength of the anion-jt interaction in solution is determined, it will be easier to evaluate its possible use in the construction of selective receptors for anions making use of the directionality properties that we have discussed in the chapter. 

Hosts 23, 24 and 28 are ditopic and contain two electron rich receptor sites they are therefore suitable hosts for bis-cations or two mono-cations. The development of synthetic receptors for anionic species has been rather slower than the development of synthetic receptors for cations and cryptand species of this type are rather rare, although some interesting examples have been reported. For ditopic hosts, electron deficient receptor sites can be incorporated to give the new cryptand species shown diagrammatically in Scheme 3 in which the ellipses represent electron rich (for example diaza-crown ether) receptor sites and the rectangles represent electron deficient receptor sites. This scheme also indicates possible guest species below each class of ditopic host and clearly the mixed system 29 is of particular interest because it can potentially complex both components of a guest salt. 

Kubik et al. have used DCC for the optimization of a synthetic receptor for anions. Kubik had previously designed the cyclic peptide 54 which binds to anions in aqueous solvents [125] (Figure 3.13). Based on the observation that 54 forms a... 

As already mentioned, in contrast to the cobaltocenium moiety, the ferrocene derivatives represent neutral redox-active receptors for anions. As we are losing coulombic interactions, the complexation is mediated solely via hydrogen bonding. Consequently, the corresponding association constants can be evaluated only in HB non-competitive solvents and they are usually much lower when compared with those of cobaltocenium derivatives. This apparent disadvantage is compensated by the much higher synthetic potential of ferrocene (commercial availability of many derivatives, much easier synthetic handling) and the excellent electrochemical properties of this compound. 

Membranes and Molecular Assemblies The Synkinetic Approach 6 Calixarenes Revisited 7 Self-assembly in Supramolecular Systems 8 Anion Receptor Chemistry 9 Boronic Acids in Saccharide Recognition 10 Calixarenes An Introduction, 2nd Edition 11 Polymeric and Self Assembled Hydrogels From Fundamental Understanding to Applications 12 Molecular Logic-based Computation 13 Supramolecular Systems in Biomedical Fields 14 Synthetic Receptors for Biomolecules Design Principles and Applications... 

While interesting neutral alternatives to the unsaturated expanded porphyrin derivatives, calix[n] pyrroles (n = 4, 5, 6, 8) are relatively limited in their scope for anion binding because of the constraints of the cavity size. Nevertheless pyrroles linked by an sp3 hybridised carbon atom are of considerable interest because of their resemblance to the anti-cancer agents the prodigiosins (Section 4.2.4), moreover pyrrole anion-receptor chemistry is synthetically versatile and hence a range of acyclic pyrroles and hybrid amidopyrroles such as 4.50-4.52 have been developed, particularly by the groups of... 

The bicyclic guanidinium tetramer 43 was first reported as a possible binder for helical oligonucleotides. Initial studies with 43 and sulfate anions showed that the tetramer formed double-helical dimers around sulfate counterions [69]. Despite the initial proposal of using this receptor for membrane transport of oligonucleotides, all subsequent work on 43 has been conducted on helical peptides. For example, the binding of 43 with several synthetic peptides caused an increase in the helicity and helical stability of the peptides in 10% water/methanol [70]. The peptide containing four Asp derivatives showed the... 

---