Abstract
Hydrogen peroxide is a key substance in the appearance of life and maintenance of the life-supporting conditions on the Earth. Electron transfer processes between H2O2 and various reducers are of major interest for the environment, natural life, technology, etc. An overview of structure, proprieties and main reactions of hydrogen peroxide in model and real systems is presented. The authors try to find the answers to the following questions: why this substance has the unique and specific dual reduction-oxidation properties, what is the connection between its structure and reactions, what role it plays in the catalytic reduction processes occurring in the natural environment and technological systems, accompanied by the formation of intermediate compounds, active radicals, complete and partial charge transfer complexes, etc. The thermodynamic possibility of the synchronous two-electron transfer during the inner sphere reaction with the involvement of metal ion complexes capable of changing the valence by two units is discussed. The role of the partial charge transfer structures which combine the properties of the initial reagents and the expected reaction products is demonstrated. Such complexes can be decomposed both reversibly and irreversibly. In case when the single-electron transfer is thermodynamically preferable, the main oxidizing particle is OH-radical, capable to interact non-selectively with almost all the water-soluble organic substances. Special attention is paid to the photo initiation of peroxidase transformation processes. The results of our multi-annual research of these issues are reported.
Highlights
This brief review covers a comprehensive material obtained during the long-term research, outlining a new vision on the role of hydrogen peroxide in natural waters and water-containing objects
The main task of this paper is to demonstrate that hydrogen peroxide is not an occasional "intermediate station" on the halfway of oxygen four-electron reduction to water
In the presence of transition metals, it is usually 42-50 kJ/mol instead of 126 kJ/mol expected for thermal decay. It was shown [19] that intermediate reactions in the process of hydrogen peroxide decomposition are expedient from the energetic point of view with transition species HOand H2O2 → Me (HO2) [20]
Summary
This brief review covers a comprehensive material obtained during the long-term research, outlining a new vision on the role of hydrogen peroxide in natural waters and water-containing objects. The main task of this paper is to demonstrate that hydrogen peroxide is not an occasional "intermediate station" on the halfway of oxygen four-electron reduction to water. About 2.3 bln years ago, after a ‘Great Oxidation Event’, it has passed through the two states – reducing and oxidizing [9] Perhaps it looks strange, but the very first organisms were living due to the oxygenic photosynthesis. To understand a whole picture, it is important, that counteraction between the opposite flows of oxidizers and reductants always give rise to hydrogen peroxide occurrence, that is the key halfway point between water and oxygen. The carriers of oxidative equivalents, which are substances with lack of electrons on low energy molecular orbitals, are capable to join electrons These species include metal ions, oxygen, hydrogen peroxide, free radicals, etc. An important point for the model system is that its active center contains manganese dimer complex [14]
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