The effect of hydrostatic pressure on g-tensor and hyperfine coupling constants of nitroxide radical characterized by ab initio calculations

We present a computational study characterizing the effect of hydrostatic pressure on magnetic spin parameters, which enter the analysis of the electron paramagnetic resonance (EPR) spectra. Site-directed spin labeling (SDSL) in combination with EPR spectroscopy is a powerful tool for investigating the structures and dynamics of biological molecules. In studies using SDSL-based EPR spectroscopy, it is essential to know the spin parameters, such as the g-factor and the hyperfine constants, precisely. However, the experimental characterization of these spin parameters under extreme conditions is often challenging. We report quantum-chemistry calculations of g-tensors and hyperfine coupling tensors (A-tensors) for the nitroxide radical spin label in the pressure range of 0-15 GPa. The hydrostatic pressure causes structural changes, which, in turn, result in the linear changes of the g- and A-tensors. The observed linear dependence of the g- and A-tensors suggests that these quantities can serve as reporters of a local pressure in complex environments. The corresponding simulated EPR spectra at the 9 GHz and 230 GHz reveal that the changes of EPR spectrum are more pronounced in the former. Our results indicate that the computational approach can address the challenge of determining magnetic spin parameters under extreme conditions, such as under high hydrostatic pressure.