Water proton magnetisation lifetimes in the Earth's magnetic field to follow free-radical formation in real time

Real-time imaging of free-radical formation by experimental methods is important in physical chemistry, biochemistry and radiobiology. Here we show for the first time that the formation of free-radicals during the time course of a chemical reaction can be imaged by monitoring the Earth’s field magnetic resonance of water protons in an open-coil spectrometer. The relaxation rate constants of water magnetisation are enhanced as reactions leading to hydroxyl radicals and subsequent oxygen formation proceed on timescales of tens of minutes. In our work the reaction of iodide-catalysed H2O2 decay was followed by Earth’s field relaxation measurements in real time. The relaxivity of the reaction product and that of several other paramagnetic compounds was measured in water. Spin-trap molecules were used to capture ∙OH radical species, thus altering the reaction rate in proportion to the formation of paramagnetic compounds. Thereby, a new experimental method opening the way for magnetic resonance imaging of reactive oxygen species in the Earth’s magnetic field is proposed, following the formation of intermediate and stable radical species in water.