Nitroxides as antioxidants

Low molecular weight nitroxides are nonimmunogenic, cell-permeable, nontoxic stable radicals that readily partition among various cellular compartments. As paramagnetic species, detectable by electron paramagnetic resonance (EPR), nitroxides report on subtle changes in their chemical environment. Consequently, they have been predominantly used as biophysical markers to probe cellular metabolism, intracellular pH, oxygen level, molecular mobility of proteins and lipids, and membrane structure. Additionally, nitroxides are proposed as contrast agents for nuclear magnetic resonance (NMR) imaging. Nitroxides can be classified into two types based on electrochemical behavior in cyclic voltametric experiments: (1) the oxazolidine derivatives exhibit irreversible redox behavior in the regions of positive and negative potentials (2) the piperidine and proxyl derivatives form a redox couple with their oxidized intermediate and exhibit a reversible behavior in the regions of positive potential. This chapter describes the procedures adopted for applying and assaying the antioxidative activity of nitroxides.