Archimedean cuboctahedron: Structure

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  • Published: Jul 15, 2015
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Archimedean cuboctahedron: Structure

Archimedes

Nuclear magnetic resonance spectroscopy reveals the details of the construction of an Archimedean cuboctahedron constructed from X-shaped organic building blocks linked together through metal ions.

 

 

Multidimensional mass spectrometry, involving ion mobility separation and tandem mass spectrometry and nuclear magnetic resonance spectroscopy reveals the details of the construction of an Archimedean cuboctahedron constructed from X-shaped organic building blocks linked together through metal ions.

Ting-Zheng Xie, Kai Guo, Zaihong Guo, Mingjun Huang, Xiaocun Lu, Jing-Yi Li, Charles Moorefield, Stephen Cheng, Chrys Wesdemiotis and George Newkome of the Department of Polymer Science, at The University of Akron, in Ohio, Yu-Sheng Chen of ChemMatCARS, at The University of Chicago, Argonne, Illinois, Wen-Yang Gao and Lukasz Wojtas of the University of South Florida, Tampa, Mary Jane Saunders of Florida Atlantic University, Boca Raton, USA, Guo-Hong Ning of The University of Tokyo, Japan, and Sheng-Yun Liao of Tianjin University of Technology, China, explain that simply by changing the concentration or using different counterions, the team can reversibly split their cuboctahedron into two octahedral. This they refer to as an interesting new type of fusion-fission switching process.

Solid reaction

 

Archimedean polyhedra are a group of symmetrical solids with regular polygons for faces and equal angles at the vertices, like a classic football with its 12 pentagons and 20 hexagons, the same polyhedron with which chemists are familiar as buckminsterfullerene, [60]fullerene. These solid bodies are also found in nature as the rigid shells, or capsids, of many different viruses, as well as certain cellular transport vesicles. Usually, the biological solids are formed by recognition and self-assembly processes of the individual protein building blocks. Moreover, chemists have for many years turned to these processes to construct complex supramolecular and other entities of their own as well as large molecular cages held together by coordination bonds.

Now, Wesdemiotis, Newkome and their international collaborators have made one such polyhedron, by approaching the cuboctahedron with a retrosynthetic analysis approach. The product is just 6 nanometres across and has a surface composed of eight triangles and six squares. In order to construct this object, the team began with an X-shaped, organic building block, which, laid over the surface of a hypothetical cuboctahedron, would provide the correct angles between the edges, 60 and 90 degrees. The team used twelve of these tailored X-shaped terpyridine ligands and 24 metal ions (zinc or cadmium) as the ligand is able to bind metal ions to hold everything together.

Prescribed monomers

 

The team used various spectroscopic techniques - one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry - model calculations, and single-crystal analyses with synchrotron X-ray diffraction to confirm the structure of their metallo-cuboctahedron. Intriguingly, they could even make out the shape of individual molecules using electron microscopy. One novel observation they made with this structure is that it can divide in two reversibly depending on the solution concentration. Since this process changes the mass, mass spectrometry provides the ideal means to monitor it; the orthogonal dimension of ion mobility separation further confirms the presence of a single species in the monomeric and dimeric states as well as the size expected for the cuboctahedron based on the simulations. "These chemical phenomena are reminiscent of biological fission and fusion processes," the researchers say in Angewandte Chemie. The team suggests that this new process could allow them to make a new series of nanoscale building blocks for use in materials science and host-guest chemistry. A zinc-based, cuboctahedron, for instance, might be useful as a drug-delivery agent. The cubooctahedron also resembles protein complexes, such as clatherin, COP I, and COP II, which are involved in cellular vesicle formation and so might find utility in biomedical sciences too.

"This synthetic method gives access to large multicomponent architectures that mimic biological molecules using easily synthesized Archimedean-prescribed monomers, thus adding a new series of nanoscale building blocks ," the team concludes.

"As for the next step in this research, I am sure that George Newkome in whose group the Archimedean cuboctahedron was designed and synthesized, will examine many useful applications of such materials, for example, molecular encapsulation and transport," Wesdemiotis told SpectroscopyNOW. Wesdemiotis who is the mass spectrometrist in the team and so adds that,  "The next step is to advance methods that achieve complete characterization inside the mass spectrometer, through top-down multidimensional techniques that combine separation, fragmentation (or other analytically discriminating reaction), and mass analysis.  Such methodologies would be useful for systems that cannot be purified or fractionated by traditional chromatography methods, as is true for many organometallic assemblies and polymer-biomolecule conjugates."

 

Related Links

Angew Chem Int Edn 2015, online: "Precise Molecular Fission and Fusion: Quantitative Self-Assembly and Chemistry of a Metallo-Cuboctahedron"

 

Article by David Bradley

 

 

 

 

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

 

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