A Study on Macrocyclic Polymers and Their Synthesis |
The term supra-molecular chemistry, which was coined byJean-Marie Lehn, means “Chemistry beyond the molecule”. While individualmolecules consist of atoms joined by covalent bond, supra-molecular chemistrymakes use of intermolecular interaction like hydrogen bonds, π-stacking andelectrostatic forces bringing molecules together to form larger species.Hydrogen bonding enables compounds containing electronegative functional groupsto interact with protons to form extended arrays. Molecules with aromatic ringscan stack together by virtue of π-π interactions. Electrostatic interactionsinclude ion-ion, ion-dipole and dipole-dipole interactions, where positivelyand negatively charged species associate. As supra-molecular chemistry focuseson how molecules interact with one another, there is emphasis oncomplementarity and pre-organization. Complementarity is the matching of a hostmolecule to the electronic and geometric needs of a guest. One can designsupra-molecular complexes that can behaves as molecular machines, such asshuttles, switches, and sensors. Within the field of supra-molecular chemistryLehn6 distinguished between ‘supra-molecule’ and ‘molecular assemblies’.Supra-molecules as were considered to be oligomers composed of a few componentsassembled via specific intermolecular associations whereas in molecularassemblies, large numbers of components assemble spontaneously into a structurethat has reasonably well defined microscopic organization and displayscharacteristics typical of macromolecules, e. g., fibre formation, glass andmelting transitions, chain entanglement and high property/ weight ratios7. Itis because they exhibit these typical properties that extended –chain molecularassemblies are frequently referred to as ‘supra-molecular polymers’.