Investigating radical pair reaction dynamics of B12 coenzymes 2: Time-resolved electron paramagnetic resonance spectroscopy

Abstract

The chemistry of B₁₂ coenzymes is highly sensitive to the nature of their upper axial ligand and can be further tuned by their environment. Methylcobalamin, for example, generates RPs photochemically but undergoes non-radical biochemistry when bound to its dependent enzymes. Owing to the transient nature of the reaction intermediates, it remains a challenge to investigate how their environment controls reactivity. Here, we describe how to use time-resolved electron paramagnetic spectroscopy to directly monitor the generation and evolution of transient radicals that result from the photolysis of a B₁₂ coenzyme. This method produces evolving, spin-polarized spectra that are rich in mechanistic detail.

Keywords: Geminate pairs; Magnetic resonance; Methyl radical; Methylcobalamin; Photolysis; Radical pairs; Spin chemistry; Spin-polarized spectra; f-pairs.