Peroxone chemistry: Formation of H2O3 and ring-(HO2)(HO3) from O3/H2O2

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National Academy of Sciences

RESUMO

The recent observation [Wentworth, P., Jones, L. H., Wentworth, A. D., Zhu, X. Y., Larsen, N. A., Wilson, I. A., Xu, X., Goddard, W. A., Janda, K. D., Eschenmoser, A. & Lerner, R. A. (2001) Science 293, 1806–1811] that antibodies form H2O2 from 1O2 plus H2O was explained in terms of the formation of the H2O3 species that in the antibody reacts with a second H2O3 to form H2O2. There have been few reports of the chemistry for forming H2O3, but recently Engdahl and Nelander [Engdahl, A. & Nelander, B. (2002) Science 295, 482–483] reported that photolysis of the ozone–hydrogen peroxide complex in argon matrices leads to significant concentrations of H2O3. We report here the chemical mechanism for this process, determined by using first-principles quantum mechanics. We show that in an argon matrix it is favorable (3.5 kcal/mol barrier) for H2O2 and O3 to form a [(HO2)(HO3)] hydrogen-bonded complex [head-to-tail seven-membered ring (7r)]. In this complex, the barrier for forming H2O3 plus 3O2 is only 4.8 kcal/mol, which should be observable by means of thermal processes (not yet reported). Irradiation of the [(HO2)(HO3)-7r] complex should break the HO–OO bond of the HO3 moiety, eliminating 3O2 and leading to [(HO2)(HO)]. This [(HO2)(HO)] confined in the matrix cage is expected to rearrange to also form H2O3 (observed experimentally). We show that these two processes can be distinguished isotopically. These results (including the predicted vibrational frequencies) suggest strategies for synthesizing H2O3 and characterizing its chemistry. We suggest that the [(HO2)(HO3)-7r] complex and H2O3 are involved in biological, atmospheric, and environmental oxidative processes.

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