**Acknowledgement**

The authors thank Anneken Grün and André Karbach, Kaiserslautern, for their help in the syntheses as well as Dr. Lars Kästner, University of the Saarland, Homburg, for assistance with confocal laser microscopy and Yvonne Schmitt, Kaiserslautern, with fluorescence spectroscopy.

### **5. References**


by laser excitation at 488 nm.

**4. Conclusions** 

**Author details** 

Wolfgang E. Trommer

**Acknowledgement** 

spectroscopy.

**5. References** 

*Soc.* 110, 1915-1917

*Department of Chemistry, TU Kaiserslautern, Germany* 

important radicals. *Org. Biomol. Chem.* 1, 2585-2589

measurements with **3** a Nikon Eclipse E 600 confocal microscope equipped with a Hamamatsu ORCA-ER camera was employed. After 20 minutes of incubation with 1 µM spin trap and 0.5 % DMSO the cells were washed three times with RPMI medium and the coverslip was mounted on a chamber and put under the microscope. Imaging was achieved

To determine the half-life of fluorescence, a representative cell was defined as region of interest (ROI) and the evolution of average intensity of the ROI was investigated in the

At the moment, the *p*-nitrostilbene-*tert*-butyl-nitrone (**1**) seems to be best suited for investigations of ROS formation in mitochondria. Unfortunately, the cytotoxicity of the coumaryl derivative (**2**) limits it application potential. The third molecule, 4-pyrrolidine-1,8 naphthylimido-methylphenyl-*tert*-butyl-nitrone (**3**) still requires further detailed evaluation. If confirmed that it distributes fairly evenly throughout the cell it would nicely complement data from **1**. With respect to the bioreduction leading to fluorescence recovery and timedependent changes in fluorescence, although reproducible, we still have to make sure that

presence and absence of various inhibitors of components of mitochondrial proteins.

this was not due to an experimental artifact employing different instrumentation.

Stefan Hauck, Yvonne Lorat, Fabian Leinisch, Christian Kopp, Jessica Abrossinow and

The authors thank Anneken Grün and André Karbach, Kaiserslautern, for their help in the syntheses as well as Dr. Lars Kästner, University of the Saarland, Homburg, for assistance with confocal laser microscopy and Yvonne Schmitt, Kaiserslautern, with fluorescence

Berliner, L.J. (1991). Applications of *in vivo* EPR. In: *EPR Imaging and in vivo EPR.* Eaton, G.R., Eaton, S.S. & Ohno, Keiichi, eds. pp. 291-310. CRC Press, Boca Raton, FL, USA Blough, N.V. & Simpson, D.J. (1988). Chemically mediated fluorescence yield switching in nitroxide-fluorophore adducts: optical sensors of radical/redox reactions. *J. Amer. Chem.* 

Bottle, S.E., Hanson, G.R. & Micallef, A.S. (2003). Application of the new EPR spin trap 1,1,3 trimethylisoindole N-oxide (TMINO) in trapping OH· and related biologically

