A protein cage acts as a mould for growing coordination polymers with precise control over the size of the resulting particles.
Coordination polymers and metal–organic frameworks form a class of materials with an ever-expanding list of applications. Their use for the controlled encapsulation and release of drugs, for example, is one area in which the ability to produce particles of uniform size is of great importance.
Now, Trevor Douglas and co-workers from Montana State University have used1 a protein cage as a template to grow particles of an iron-phenanthroline-based coordination polymer. The key to the assembly of the coordination polymer is to link together — inside the protein cage — several units of an already formed iron(II) complex using a copper-catalysed Huisgen cycloaddition between alkynes and azides. The interior of the protein cage has 24 cysteine residues, each of which is functionalized with an alkyne. These are then coupled to the azide groups attached to the phenanthroline ligands of the iron complex.
Alternately adding a trialkyne and more of the iron complex to the protein cage results in the formation of a branched coordination polymer within the protein cage. In the absence of the protein cage, similar reactions lead to uncontrolled polymerization and precipitation of the coordination polymer.
References
Lucon, J. et al. A click chemistry based coordination polymer inside small heat shock protein. Chem. Commun. 10.1039/b920868b (2009).
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Davey, S. Tiny template. Nature Chem (2009). https://doi.org/10.1038/nchem.502
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DOI: https://doi.org/10.1038/nchem.502
