PATTERNS OF MUONIUM ADDITION TO IMIDAZOLES - A MODEL OF RADIATION-PRODUCED HYDROGEN-ATOM REACTIVITY WITH KEY BIOLOGICAL SUBUNITS

From a study of imidazole derivatives using transverse-field muon spin rotation (TE-mu SR) spectroscopy, it is found that muonium adducts ar e formed preferentially at the 2- and 5-position, the latter predomina ting;It is further concluded that muonium is the true precursor of the se radicals, and so this approach is valid for the study of organic mo lecules, of biological relevance, in which muonium acts as a radioacti ve hydrogen atom probe (tracer) of reactions involving free II-atoms, such as are produced during the radiolysis of aqueous (intracellular) media. In experiments where the imidazole was present simultaneously w ith acetone, competitive addition was found, so that Me(2)C-OMu radica ls were formed: evidence is presented for a specific interaction (Mu . .. N) between the radical muon and the imidazole ('pyridine-type') nit rogen atom, the strength of which varies according to the nature of su bstituents in the imidazole moiety. Muonium adducts of a simpler sub-u nit (the C=N functional group) are also studied.