text: One of the first examples of encapsulating a structure at the molecular level was demonstrated by Donald Cram and coworkers; they were able to isolate highly unstable, antiaromatic cyclobutadiene at room temperature by encapsulating it within a hemicarcerand. Isolation of cyclobutadiene allowed chemists to experimentally confirm one of the most fundamental predictions of the rules of aromaticity.
  In another example the cage consists of a gallium tetrahedral cluster compound stabilized by 6 bidentate catechol amide ligands residing at the tetrahedron edges. The guest is a 16 electron and thus very reactive ruthenium metallocene (an organometallic catalyst) with a cyclopentadienyl ligand (red) and a 1,3,7-octatriene ligand (blue). The total charge for this anion is 11 and the counterions are  5 tetramethyl ammonium cations and 6 potassium cations. The ruthenium compound decomposes in water within minutes but encapsulated it survives in water for weeks.
  Large metalla-assemblies, known as metallaprisms, contain a conformationally flexible cavity that allows them to host a variety of guest molecules.  These assemblies have shown promise as agents of drug delivery to cancer cells.
  An application of encapsulation is controlling reactivity, spectroscopy, and structure. For instance, excited state reactivity of free 1-phenyl-3-tolyl-2-proponanone (abbreviated A-CO-B) yields products A-A, B-B, and AB, which result from decarbonylation followed by random recombination of radicals A• and B•. Whereas, the same substrate upon encapsulation reacts to yield the controlled recombination product A-B, and rearranged products (isomers of A-CO-B).
  Other applications:
  * the encapsulation of filaments of a self-assembling bi-copper complex in polymer nanowires.