Macromolecular cages

[1] Metal Organic Polyhedra (MOPs) comprise a specific type of self-assembled macromolecular cage that is formed through unique coordination and is typically chemically and thermally stable.

The discrete self-assembly of metal ions and organic scaffolds to form MOPs into highly symmetrical architectures, is a modular process and has various applications.

Specific examples of this are ferritin, capsid, and the tobacco mosaic virus, which are formed by the self-assembly of protein subunits into a polyhedral symmetry.

In order for the cage to work effectively and have biomedical relevance, it has to be chemically stable, biocompatible, and needs to operate mechanistically in aqueous media.

Macromolecular cages in general can be used for a variety of applications (e.g. nanoencapsulation, biosensing, drug delivery, regulation of nanoparticle synthesis, and catalysis).

The macromolecular cages made from non-linear polymers are designed to have molecular recognition, respond to external stimuli and self-assemble into higher order structures.

[citation needed] C60 has versatile applications due to its macromolecular cage structure; for example, it can be used for water purification, catalysis, bio-pharmaceuticals, serve as a carrier of radionuclides for MRI, and drug delivery.

One synthetic method uses ring opening and multiple click chemistry in the first step to form trefoil and quatrefoil-shaped polymers, which can then be topologically converted into cages using hydrogenolysis.

[4] Another synthetic strategy employs intramolecular ring-opening metathesis oligomerization of a star polymer and this reaction method is catalyzed by diluted Grubb's third generation catalyst.

The first reported case of the formation of non-native VLP constructs into a capsid-like structure utilized a functionalized gold core for nucleation.

In one case, a 3D macromolecular cage with icosahedral symmetry (resembling viral capsids) was formed based on the synthetic strategy in 2D origami.

Endohedral fullerene
MOP synthesis
The RNA exosome is a biomolecular cage that has nuclease activity which catalyzes the breakdown of RNA molecules. Shown above is the whole RNA exosome with a helical protein framework and a central chamber where RNA degradation takes place.
Depicted is the tobacco mosaic virus protein coat; virus protein coats known as capsids are examples of macromolecular cages in nature. The protein shell encapsulates a hollow chamber which contains the viral genomic information.
Ferritin is a hollow sphere that has an outer diameter close to 12 nm and an inner diameter of 7-8 nm. The inner chamber of ferritin uptakes or binds iron in its ferrous state and stores iron in its ferric or trivalent state.