Molecules and ions with a twelve or more membered ring are referred to as macrocycles. Crown ethers, calixarenes, porphyrins, and cyclodextrins are all classic examples. Macrocycles are a major and well-established branch of chemistry. The development of supramolecular macrocyclic chemistry, inspired by the lock and key idea, has aided the expansion of host-guest chemistry.
Supramolecular chemistry is a branch of chemistry concerned with "the chemistry of molecular assemblies and the intermolecular bond" and "organised entities resulting from the association of two or more chemical species held together by intermolecular forces." Noncovalent interactions between tiny molecules are used in supramolecular chemistry to self-assemble molecular structures. Hydrogen-bonding, hydrophobic, and electrostatic interactions, as well as template-directed self-assembly, are examples of these interactions. Supramolecular techniques can be used to make both dendrimers and supramolecular structures.