Planetary nano: Orbital system

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  • Published: Sep 15, 2014
  • Author: David Bradley
  • Channels: NMR Knowledge Base
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Inner space

Planet–Satellite Nanostructures Made To Order by RAFT Star Polymers Credit: Rossner Vana/Angewandte/Wiley

German researchers have produced nanoparticles surrounded by a group of smaller nanoparticles in what might whimsically be described as a system resembling a tiny planet with orbiting satellites. Nuclear magnetic resonance spectroscopy and other techniques reveal the details.

Physical chemists Christian Rossner and Philipp Vana of the University Goettingen, Germany, explain in Angewandte Chemie how investigation and application of complex nanostructures requires chemists to find ways to create hierarchical arrangements of distinct domains on a small scale. They have now turned to polymers generated using a RAFT, reversible addition–fragmentation chain transfer, polymerization. They have started with a star-shaped polymer and decorated it with trithiocarbonate groups on the outer periphery. These entities can then subsequently be attached to a gold surface, which provides a stable support so that a larger gold nanoparticle can be connected to smaller, "orbiting" nanoparticle satellites.

The team explains that, "By adjusting the molecular weight of the polymeric linker, nanostructures with tailored planet–satellite distances, as evidenced by transmission electron microscopy, are obtained. This strategy offers a straightforward way to prepare gold nanoparticle scaffolds with multiple reactive functionalities at defined distances from the central core." Being able to control the distance between the satellites would be critical to fine-tuning energy levels of the system and thus its electrical, optical and other physical properties.

Getting the measure of nano objects

Such a precise and controllable nanoscopic architecture might be useful in sensor technology or even as a nanoscopic measuring device for determining the size of nanoscopic biological objects visually. Such structures might also be able to trap and transport chemical payloads, such as pharmaceuticals to specific target sites in the body, such as cancer cells.

The RAFT technique is key to the team's success allowing them to synthesise precisely defined polymers with a specific degree of polymerization. This allows them to make batches of very uniform polymers of a given chain length, something that is generally not possible with conventional polymerization methods where a broad range of chain length and branching is commonplace if complex conditions are not precisely controlled. The RAFT technique is also amenable to the synthesis of comb-like and star-shaped polymers that require much more sophisticated synthetic schemes otherwise.

Four-point plan

The researchers demonstrated that treating gold nanoparticles with their four-pointed star polymers saw attachment via three of the points, or rays, while the fourth was left available for potential binding to the smaller, satellite gold nanoparticles. They used NMR spectroscopy to verify the star polymer structure early in the process. The team adds that they can also attach dangling polymer chains to the satellite nanoparticles to which a variety of reactive chemical groups might also be attached for additional functionality.

Fundamentally, Rossner and Vana explain that their modular procedure for preparing multifunctional nanoparticle scaffolds with chemical functionality exposed at set distances from a central core could allow sophisticated, yet precisely controlled structures to be generated for a wide range of applications. The variety of trithiocarbonate reactions available in itself offers many possibilities for the construction of diverse structures.

Related Links

Angew Chem Int Edn, 2014, online: "Planet–Satellite Nanostructures Made To Order by RAFT Star Polymers"

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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