Images of the nitroxide probe, demonstrating its
fluorescence properties.
A new generation of nitroxide fluorescent probes have been developed by chemists from the Queensland University of Technology (QUT) node of the Centre that both help protect the material by capturing the damaging free radicals involved, as well as fluorescing to signal how much the polymer has degraded.
By scavenging the free radicals the probe hinders the cascading effects of free radical damage, with the fluorescence providing a vivid indication of onset and also the extent of free radical damage.
‘One of the strengths of this new probe’, says James Blinco a PhD student at QUT and Centre member, ‘ is that it is far more sensitive than other available techniques. These methods only begin to work when the free radical damage is already quite high. In the probes that we have made, they fluoresce as soon as free radicals have been trapped, which makes them much more useful for detecting free radical stress.’
Things as diverse as plastics, paints, modern materials and even human tissue are susceptible to free radical damage. Polypropylene, for example, is intrinsically susceptible to photo- and thermo-oxidative degradation, both of which are mediated by free-radical species. In order to create a durable polymer, stabilizers are heavily relied upon in the processing of polypropylene to scavenge the free radicals formed as the polymer degrades, which in turn retards oxidative polymer degradation. Although this process extends the performance of the material and its application lifetime, the polymer is still ultimately susceptible to free radical damage.
James Blinco, PhD student with the probe.
There are currently a number of techniques available to probe polymer degradation, however, none of them are able to trap free-radicals as the QUT compounds do.
‘As current techniques for observing free radical damage in polymer degradation were not sensitive in the earliest period of damage in a polymer, we were searching for alternative methods to observe polymer degradation,’ says Associate Professor Steve Bottle, Centre member at QUT. ‘Ultimately we found a way in which we could both stabilize the polymer as well as monitor its breakdown during the induction period.’
The latest fluorescent additives created by Associate Professor Bottle and his team at QUT stabilize the polymer through trapping the free radicals before they can do damage to the material. The starting state of the probe is a non-fluorescing material which can be soaked into a polymer. As the probe traps free radicals the fluorescence is switched on, thus creating a neat marker of free radical damage.
As the probe can easily be applied to a polymer either through an external application, or injected into the polymer during the manufacturing process, it shows great potential for various materials. Yet, the applications of the nitroxides probes go beyond material science into the realm of the biomedical as they are used for antioxidants as well as diagnostic purposes, such as in medical imaging.
‘What we have created here’, says Bottle, ‘is a sensitive tool which acts as both an inhibitor of damage as well as a marker of this damage. We have manipulated the structure of the compound so that it fluoresces under different wave-lengths thus creating a strong diagnostic tool for not only various materials, but also for biological systems.’
Editor's Note: Article first published in the summer 2007/08 edition of Radical News, the newsletter from the ARC Centre of Excellence for Free Radical Chemistry and Biotechnology. For permission to reproduce this article please contact the ARC Centre of Excellence for Free Radical Chemistry and Biotechnology.
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