AbstractExposure of bacterial cells to selected azaarenes causes respiratory inhibition, membrane damage, decreased cellular ATP synthesis, and decreased cell viability. The purpose of this work was to examine the chemical mechanisms of acute toxicity of azaarenes and provide a preliminary model of azaarene cellular effects. Results of bioassays andin vitrospectrochemical and electrochemical experiments suggest that azaarenes alter membranes and electron transfer (ET) molecular assemblies primarily through noncovalent interactions not involving organic or oxy free radicals. The data suggest that membranes and membrane‐linked systems are altered via azaarene‐mediated chelation of divalent cations (Ca and Mg) found in the lipopolysaccharide matrix of the bacterial outer membrane. This gives rise to altered structure/function of periplasmic and inner membrane systems, and may contribute to changes in ET. Electrochemical analyses indicate that azaarenes also change the redox chemistry of flavin centers and seem to increase the ease with which ET processes occur between biochemical electron donors (NADH) and tetrazolium acceptors (iodonitrotetrazoli