Interaction of Magnesium Ions with Semiquinone Radicals of Tiron, an Indicator of Reactive Oxygen Species

It has been shown using experimental (electron paramagnetic resonance) and quantum chemical (density functional theory) research methods that the previously observed changes in the electron paramagnetic resonance spectrum of the semiquinone Tiron radical in seawater are due to its interaction with Mg²⁺ ions. The formation of a complex between Mg²⁺ and the Tiron radical is due to the electrostatic attraction of ions carrying large charges of the opposite sign (+2 and –3), on the one hand, and the ability of Mg²⁺ ions to bind effectively to bidentate oxygen-containing ligands, on the other hand. The formation of tight contact ion pairs leads to a redistribution of the electron and spin density in the Tiron radical, which can be judged by the observed changes in the electron paramagnetic resonance spectrum of this radical.