Patterns of muonium addition to imidazoles: a model of radiation-produced hydrogen-atom reactivity with key biological subunits

Abstract

From a study of imidazole derivatives using transverse-field muon spin rotation (TF-µSR) spectroscopy, it is found that muonium adducts are formed preferentially at the 2- and 5-position, the latter predominating. It is further concluded that muonium is the true precursor of these radicals, and so this approach is valid for the study of organic molecules, of biological relevance, in which muonium acts as a radioactive hydrogen atom probe (tracer) of reactions involving free H-atoms, such as are produced during the radiolysis of aqueous (intracellular) media.

In experiments where the imidazole was present simultaneously with acetone, competitive addition was found, so that Me₂Ċ–OMu radicals were formed: evidence is presented for a specific interaction (Mu ⋯ N) between the radical muon and the imidazole (‘pyridine-type’) nitrogen atom, the strength of which varies according to the nature of substituents in the imidazole moiety.

Muonium adducts of a simpler sub-unit (the CN functional group) are also studied.