Noncovalent forces such as hydrogen bonding, electrostatics, and hydrophobic effects are ubiquitous in natural systems. Biomolecules combine many of these intrinsically weak interactions to effectively carry out a wide variety of biological processes like protein folding and substrate recognition. Inspired by nature, chemists have been able to use these forces to design new synthetic systems that are able to recognize a variety of targets. Foldamers are one class of molecules that has been developed for this purpose. Their well-characterized structural features make them ideal candidates for the development of new receptors.

Molecular recognition using foldamers can be classified into two main categories. The first one is foldamer recognition of small guests such as ions and small molecules. In general, these types of foldamers are designed to adopt circular or helical conformations that project functionality in a convergent manner to form cavity-like moieties where small molecules can bind. Binding of this type of foldamers to the guest molecules can be described as endo-recognition (Fig. 7.1a). Foldamers that form helices and tubular structures have been reviewed elsewhere [1] and we will focus here only on those that have been used as receptors. The second category is foldamer recognition of biomacromolecules such as proteins and DNA. In this type of recognition, the target is usually larger than the receptor molecule. The foldamer is often designed to project functionality in an ordered fashion that will complement the surface of the desired target. This is a case of exo-recognition (Fig. 7.1b).

In this chapter, we will focus on foldamers that recognize and bind to small molecules and biomacromolecules. We will also discuss foldamers designed to recognize crystal surfaces in an attempt to mimic biomineralization processes. For the purpose of this chapter, we will include only those foldamers for which there is evidence of a well-organized structure prior to binding.

Fig. 7.1 (a) Endo-recognition of a guest molecule (dark gray) by a foldamer host (light gray); (b) Exo-recognition of a host (dark gray) by a foldamer guest (light gray).

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