In a in The Journal of Chemical Physics (special edition: The Physical Chemistry of Solar Fuels Catalysis), Lauren M. Pellows et al. use electron paramagnetic (EPR) spectroscopy to characterize photocatalytic E-state intermediates in the catalytic cycle of MoFe protein of the nitrogenase enzyme. Illuminating CdS quantum dot - MoFe protein biohybrids at 233 K, revealed that all the EPR active E-state intermediates in the catalytic cycle can be trapped and characterized. Simulations of the EPR data allowed for quantification of the different E-state intermediate populations, along with mapping of these populations onto the Lowe–Thorneley kinetic scheme.