Introduction to supramolecular chemistry

Supramolecular chemistry is concerned with the organization of molecules in biological media, in materials and in all other molecular assemblies involving so-called "weak" or non-covalent bonds. Supramolecular chemistry is a vast field of investigation that has seen considerable growth since the 1987 Nobel Prize was awarded to three pioneering chemists, D. J. Cram, J.-M. Lehn and C. Pedersen, whose work highlighted what is now known as "host-guest" chemistry. It's worth noting that the thematic evolution of this field has led to the development of even more complex systems with varied functionalities (mechanical, electro-optical, etc.), including the molecular machines honored in 2016 by the Nobel Prize in Chemistry awarded jointly to J.-P. Sauvage, J. F. Stoddart and B. L. Feringa.

It was probably the phenomena of molecular recognition, often identified with "host-guest" chemistry, that contributed to the rise of supramolecular chemistry. In 1967, Pedersen showed for the first time that alkali metal salts could be solubilized in apolar organic solvents in the presence of a host molecule (a crown ether). These associations between two distinct entities to form a "host-guest complex" will not be limited to the recognition of metal cations. The recognition of neutral or charged molecules, metal cations, anions or even a fragment of a biological macromolecule, such as peptides or oligosaccharides, is based on concepts of complementarity and pre-organization, where steric and electronic affinities ensure the stability and selectivity of intermolecular associations. Major applications involve the transport, storage or transformation of molecular entities of interest. These often complex systems have opened the way to understanding the host-substrate interactions that underpin key processes in living systems, such as neuronal information transfer and drug-receptor interactions. They have also enabled the development of new catalytic processes, and the design of assemblies ranging from the nanometric (liposomes, micelles, liquid crystals) to the macroscopic (supramolecular polymers, crystal crystals, etc.), to name but a few examples.

The content of this first article refers mainly to organic chemistry concepts that were de facto linked to the emergence of supramolecular chemistry as defined by J.-M. Lehn. First, we present the non-covalent intermolecular interactions that form the basis of these reversible self-associating systems. In the next two sections, we present synthetic molecular receptors, highlighting the variety and complexity of covalent and self-assembled receptors. The final section deals with the phenomenon of molecular recognition and some of its applications, with a particular focus on supramolecular catalysis.