Antioxidant Activity Measured by Fluorescence Investigation of Antioxidant and Probe Structure as well as their Mobility and Position
- This doctoral thesis is concerned with determining antioxidant mobility by fluorescence, especially in lipid membranes. It expands on previously determined data regarding antioxidant diffusion by employing different lipids, synthetic antioxidants, and varying pH. The probes used are derivatives of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), which are known for their exceptionally long lifetimes in aerated aqueous media (325 ns in H2O under air). Their n,π* singlet-excited state is efficiently quenched by an aborted hydrogen abstraction mechanism, which makes them ideally suited to probe antioxidant diffusion.
During the course of my Ph. D. thesis I was able to expand the toolbox of available DBO derivatives with a very reactive one, Fluorazophore-R, and a more acid-stable lipophilic derivative, Fluorazophore-LE.
I was also able to determine the mutual lateral diffusion coefficient of a synthetic vitamin E derivative with single-photon counting measurements. This N-tocopherol displays higher mutual lateral diffusion coefficients than α-tocopherol (5.4 × 10–7 cm–1 s–1 vs. 3.73 × 10–7 cm–1 s–1 at 40°C, respectively) with a very similar activation energy of 43 ± 6 kJ/mol (compared to 47±5 kJ/mol, which is indicative of a higher antioxidant potency.
Expanding on previous experiments I was also able to probe the differing behavior of α-tocopherol at the phase transition threshold of liposomes composed of a high melting fully saturated lipid, DPPC. Above the phase transition temperature, mutual lateral diffusion coefficients of 10–7 cm2 s–1 were found, similar to the ones in POPC, while above the pre-transition temperature the coefficients were 10–8 cm2 s–1. This confirms the high accuracy of our measurement principle.
Furthermore, the first steps have been taken in investigating the pH dependence of the synthetic antioxidant L-ascorbyl-6-palmitate, which is only a decent lipophilic antioxidant in low pH environments.
Additionally, I have worked on a third party funded research project for a company analyzing urine and blood samples, the results of which I am not at liberty to discuss.
