Relaxation filtered hyperfine spectroscopy (REFINE).

ABSTRACT

A simple and general applicable method to separate spectrally overlapping hyperfine spectra of two paramagnetic compounds is presented. Overlapping spectral contributions from different paramagnetic species are a common situation in electron paramagnetic resonance (EPR) spectroscopy, resulting in complicate EPR spectra of metal enzymes, organic radicals or in the field of material sciences. On the other hand, the longitudinal relaxation times T1 of these species contributing to the overall EPR signal can vary by several orders of magnitude, depending on the paramagnetic component under study. These differences can be used to selectively study individual species by using an inversion-recovery preparation sequence as a filter. Here, we demonstrate the possibility to separate hyperfine spectra of two spectrally overlapping paramagnetic species by combining an inversion-recovery based relaxation filter together with ESEEM or ENDOR hyperfine spectroscopy (REFINE). The feasibility of the presented method is demonstrated on model compounds and the necessary requirements are discussed.