Molecular Receptors — Design Principles

Molecular receptors are defined as organic structures held by covalent bonds, that are able to bind selectively ionic or molecular substrates (or both) by means of various intermolecular interactions, leading to an assembly of two or more species, a supermolecule. 

The design of molecular receptors amounts to expressing in an organic molecule the principles of molecular recognition. 

Receptor chemistry, the chemistry of artificial receptor molecules, represents a generalized coordination chemistry, not limited to transition-metal ions but extending to all types of substrates cationic, anionic, or neutral species of organic, inorganic, or biological nature [1.13]. 

The ideas of molecular recognition and of receptor chemistry have been penetrating chemistry more and more over the last twenty years, namely in view of their bio-organic implications, but more generally for their significance in intermolecular chemistry and in chemical selectivity. 

In addition to maximizing contact area, inclusion also leads to more or less complete solvent exclusion from the receptor site, thus minimizing the number of solvent molecules to be displaced by the substrate on binding. 

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Brown K T and Murakami M 1964 A new receptor potential of the monkey retina with no detectable latency Nature 201 626-8 Hong F T 1989 Relevance of light-induced charge displacements in molecular electronics design principles at the supramoleuclar level J. Mol. Electron. 5 163-85... 

The self-assembling principle has begun to be exploited by chemists in the design of synthetic molecular receptors. Hunter and co-workers [61] describe the use of metalloporphyrin coordination chemistry to build up the self-association of a very stable cyclic porphyrin dimer 45 which recognizes derivatives of terephthalic acid (46, 47) through hydrogen-bonding interactions (Scheme 15). 

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... 

Figure 9. (a) Schematic representation of the five-module format of a photoactive triad which is switchable only by the simultaneous presence of a pair of ions. This design involves the multiple application of the ideas in Figure 1. The four distinct situations are shown. Note that the presence of each guest ion in its selective receptor only suppresses that particular electron transfer path. The mutually exclusive selectivity of each receptor is symbolized by the different hole sizes. All electron transfer activity ceases when both guest ions have been received by the appropriate receptors. The case is an AND logic gate at the molecular scale. While this uses only two ionic inputs, the principle established here should be extensible to accommodate three inputs or more, (b) An example illustrating the principles of part (a) from an extension of the aminomethyl aromatic family. The case shown applies to the situation (iv) in part (a) where both receptors are occupied. It is only then that luminescence is switched "on". Protons and sodium ions are the relevant ionic inputs.

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