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

Abstract

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 H(2)O(2) from (1)O(2) plus H(2)O was explained in terms of the formation of the H(2)O(3) species that in the antibody reacts with a second H(2)O(3) to form H(2)O(2). There have been few reports of the chemistry for forming H(2)O(3), 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 H(2)O(3). 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 H(2)O(2) and O(3) to form a [(HO(2))(HO(3))] hydrogen-bonded complex [head-to-tail seven-membered ring (7r)]. In this complex, the barrier for forming H(2)O(3) plus (3)O(2) is only 4.8 kcal/mol, which should be observable by means of thermal processes (not yet reported). Irradiation of the [(HO(2))(HO(3))-7r] complex should break the HO-OO bond of the HO(3) moiety, eliminating (3)O(2) and leading to [(HO(2))(HO)]. This [(HO(2))(HO)] confined in the matrix cage is expected to rearrange to also form H(2)O(3) (observed experimentally). We show that these two processes can be distinguished isotopically. These results (including the predicted vibrational frequencies) suggest strategies for synthesizing H(2)O(3) and characterizing its chemistry. We suggest that the [(HO(2))(HO(3))-7r] complex and H(2)O(3) are involved in biological, atmospheric, and environmental oxidative processes.