Interaction of imidazoline- and imidazolidine-based nitroxides with chloroplasts

In this work, we investigated the interaction of a number of novel pH-sensitive spin probes (imidazoline- and imidazolidine-based nitroxides) with isolated chloroplasts. The light-induced changes in the electron paramagnetic resonance signals of these radicals are determined by several factors: ΔpH-driven accumulation of nitroxides inside the thylakoids, consumption (or evolution) of oxygen by chloroplasts, and irreversible loss of spin probe paramagnetism. A comparative study of these radicals characterized by different pKa allowed us to conclude that these spin probes can be used as pH indicators for monitoring the intrathylakoid pH- and light-induced changes in oxygen concentration in chloroplast suspension.