from first principles PP-I-1

PP-IV-7Effect of Medium on Hemin Oxidative Destruction by Hydrogen PeroxideGradova M.A., Lobanov A.V.1 Semenovov Institute of Chemical Physics RAS, Moscow, Russiam.a.gradova@gmail.comCatalytic activity of hemin (FeIII-protoporphyrin IX, FePP) and its derivatives in hydrogenperoxide decomposition is often used in biomimetic catalase model systems. However, incontrast to heme holoenzymes, isolated hemin undergoes oxidative destruction in presence ofhydrogen peroxide, leading to the formation of ferric species. In neutral or alkaline mediumthis process results in the formation of colloidal aggregates of ferric oxyhydroxides, whichpossess a large specific area, high sorption capacity and hence catalytic activity, particularlyin hydrogen peroxide decomposition. In contrast to Fe-porphyrins, which show a relativelyweak photoactivity as compared with d 0 -d 10 Me-porphyrins, the rate of H 2 O 2 decompositionon ferric colloids increases significantly under irradiation due to their semiconductingproperties. Thus there is a catalyst transformation during the reaction in vitro whichsignificantly changes the shape of the kinetic curve.The rate of both hemin oxidative destruction and H 2 O 2 catalytic decomposition was shown todepend on the aggregation state of the pigment in solution [1]. The present study comparesthe rates of both processes in a medium with varying acidity and in micellar solutions ofdifferent surfactants in order to reveal the nature of intramolecular interactions, which governthe aggregation processes and influence the catalytic activity of FePP. The most effectivehydrogen peroxide decomposition associated with rapid hemin destruction was obtained inalkaline solutions, corresponding to a dimeric state of the pigment with an absorptionmaximum at 386 nm. In acidic medium the rate of both processes is extremely slow,indicating the presence of oligomer aggregates with a narrow absorption band at 366-372 nm.The stability and catalytic activity of the monomeric form of FePP, expected to bepredominant in micellar solutions and obtained in aqueous solutions near pH7 with anabsorption maximum in the range of 392-402 nm, strongly depends on the surface charge ofthe surfactant micelles. Further studies should reveal the mechanism of FePP stabilization,resulting in a significant increase in catalytic activity of the protein-associated cofactor.References:[1] A.V. Lobanov, S.M.Vasiliev, G.G. Komissarov. Macroheterocycles 2(3) (2009), 1-3.291