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Smoking - A glowing issue

The Centre’s new generation of nitroxide fluorescent probes are set to re-enforce the dangers of smoking cigarettes. Visual demonstrations using these probes will show the presence of free radicals in cigarette smoke and when combined with discussions about free radicals will provide a powerful message to students.

In their quest to gain the additional electron they require for stability, free radicals are highly reactive molecules and as a consequence are often damaging to our bodies and the materials we use. External environmental factors such as pollution, sunlight and cigarette smoke can initiate the production of free radicals.

In our bodies free radicals interact with molecules in cells. This can result in oxidative damage to proteins, membranes and DNA, causing disease.

Materials such as plastics and other modern polymers degrade due to free radical processes, which in the presence of oxygen accelerate the breaking of chemical bonds in the polymer. Therefore to prolong the lifetime of polymers, stabilisers are generally added during production to mop up free radicals that are formed as the material starts to degrade.

Stable free radical compounds called nitroxides are potent scavengers of polymer radicals. As a result, the plastics industry commonly utilise nitroxides and their precursors as additives to plastic products. Although the presence of stabilisers extends the performance and lifetime of the material, the polymer remains susceptible to free radical degradation. It therefore becomes important to monitor the extent of free radical damage in order to determine the lifetime of materials. Previously, detection mechanisms were not sensitive enough to identify the initial changes that ultimately lead to the material’s failure.

To address this issue, Dr Kathryn Fairfull-Smith and others in Associate Professor Steve Bottle’s laboratory at the QUT node of the Centre, have developed new free radical stabilisers based on nitroxides that not only scavenge free radicals but glow (fluoresce) when they encounter them. The fluorescent property of these nitroxide- containing additives allows visualisation of free radical damage to polymers.

The additives possess a highly fluorescent component called a fluorophore linked to the nitroxide. The fluorophore used in the new polymer additive is also used in glow sticks. Fluorescence occurs when a molecule that has absorbed energy at a specific wavelength re-emits this energy at a different wavelength as it relaxes back to its ground state.

“Our novel polymer additive can act as a sensor or a switch because the nitroxide effectively short-circuits the fluorescence that should arise from the fluorophore”, reveals Fairfull-Smith. “As the polymer starts to degrade, free radicals are formed which are captured by the nitroxide portion of the additive. The short-circuiting effect of the nitroxide is then removed and the fluorophore starts to glow at sites in the material where free radicals are present and hence able to do damage,” adds Fairfull-Smith.

Despite being designed and tested for use in plastics, these additives have widespread applications - from monitoring the stability of roof coatings, paints and glues to locating free radicals in human and animal cells.

One application being investigated currently by Ms Branka Miljevic from the International Laboratory for Air Quality and Health at QUT is in the detection of air-borne radicals in pollution, including cigarette smoke and engine exhaust fumes.

“Here at the International Laboratory for Air Quality and Health, we are interested in assessing the toxicological impact of particles coming from different indoor and outdoor pollutant sources, like cigarette smoke, office printers, vehicle exhaust and wood smoke. Nitroxide fluorescent probes allow us to do that on quantitative level”, says Miljevic.

To investigate radicals in cigarette smoke, mainstream cigarette smoke was bubbled through a flask containing nitroxide-fluorophore additive in solution. The cigarette smoke was generated using a specially adapted smoking machine. With each puff of smoke, the fluorescent intensity of the solution increased. This indicated that as expected there are free radicals in cigarette smoke, but also that the nitroxide additive is able to detect their presence.

More importantly, the Centre recognises that this research has wider application as a powerful visual demonstration of the presence of free radicals in cigarette smoke, and intends to provide the resources to run such demonstrations for students in good health programs around Australia.

For more information about the International Laboratory for Air Quality and Health go to: www.ilaqh.qut.edu.au