Iron TAML activators of peroxides ate functional catalase-peroxidase mimics. Switching from hydrogen peroxide (H2O2) to dioxygen (O-2) as the primary oxidant was achieved by using a system of reverse-micelles of Aerosol OT (AOT) in n-octane. Hydrophilic TAML, activators are localized, in the aqueous microreactors of reverse micelles where water is present in much lower abundance than in bulk water. n-Octane Serves as:a proximate reservoir supplying O-2 to result in partial oxidation of Fe-III to Fe-IV-Containing species, mostly the (FeFeIV)-Fe-III (major) and (FeFeIV)-Fe-IV (minor) dimers which coexist with the Fe-III TAML,monomeric species. The speciation depends on the pH and. the degree of hydration w(0), viz, the amount of water in the reverse micelles., The previously unknown Fe-III-Fe-IV dimer has been characterized by UV-vis, EPR, and Mossbauer spectroscopies. Reactive electron donors such as NADH, pinacyanol chloride; and hydroquinone undergo the TAML-catalyzed oxidation by O-2. The oxidation of NADH, studied in most detail, is much faster at the lowest degree of hydration w(0) (in "drier micelles") and is accelerated' by light through NADH photochemistry. Dyes that are more resistant to oxidation than pinacyanol chloride (Orange II, Safranine O) ate not oxidized in the reverse micellar media. Despite the limitation of low reactivity, the new systems highlight an encouraging step in replacing TAML peroxidase-like chemistry with more attractive dioxygen-activation chemistry: