Anions, synthetic receptors

Polymer supports have been used in order to covalently graft enzymes and receptors in order to perform biological tests (ELISA assays). Recently, polystjrone derived resins have been used to covalently link cationic and anionic synthetic receptor molecules. A particularly nice example of a polystyrene-grafted phosphate binding synthetic receptor is shown in Figure 13.4. 

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. 

The increasing interest in anionic recognition has focused attention towards synthetic receptors possessing positively charged moieties which could induce non-covalent... 

Secondary amides are versatile and highly accessible hydrogen bond donors that have been used in numerous synthetic receptors, hi the biological arena, there are many examples of proteins that employ amide NH- anion interactions to bind negatively charged guests [5-9]. The first example of a synthetic amide containing receptor, pubUshed in 1986 by Pascal and co-workers, was a crytpand-like tris-amide that was shown to interact with fluoride in DMSO-de [10]. 

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. 

Kqrwords Anionic templates - Molecularly imprinted polymers - Self-assembly Biomimicry - Synthetic receptors... 

MIPS, as an extremely versatile class of potent synthetic receptors, where the benefits for anion recognitions are beginning to emerge. 

In this article, we will describe different approaches to the design of fluorescence sensors for anions that exploit distinctive mechanism-based concepts. In most case, synthetic receptors are used for anion binding and induce specific responses from the appended fluorophores, leading to selective and sensitive sensing. 

ABSTRACT. In this review the concept of immobilizing electrophilic centers in synthetic receptors is described. The design of neutral metallomacrocycles and metalloclefts with an immobilized electrophilic center (U02 etc.), combined with hydrogen bonding moieties, 7t-7c-stacking, etc. proved to a useful approach for complexation of polar neutral molecules and of anions. By systematic variation of the structures a high degree of specificity has been obtained. 

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. 

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