The project is focused on identifying unknown chemical reactions responsible for atmospheric oxidation processes and understanding how they may lead to particle growth. This species plays a key role in oxidative stress -a serious state of imbalance in biological systems considered to be involved in the development of cancer, neurodegenerative illnesses and a number of other health and life threatening conditions. The project may benefit different publics: from chemists interested on fundamental properties of molecules and reactivity, to scientists working on atmospheric chemistry and biochemistry. Both the Madrid and Oslo groups have well established research programs in related fields. The leader of the Oslo group is head of the physical chemistry group and a core member of the Centre of Theoretical and Computational Chemistry. The expertise of the leader of the Madrid group encompasses the experimental and computational study of the bonding situations and reaction mechanisms of organic and organimetallic compounds. The collaboration of both groups will provide more accurate parameters for use in large-scale climate models.
Summary of project results
The Project aims at a deeper understanding of the reactivity of superoxide anion. This anion is one of the most relevant reactive oxygen species both at the atmospheric level (with implication in climate changes) and in biological systems (where it may cause alterations in cellular macromolecules). Despite that, very little is known on elementary chemical reactions involving O2·∙– in both chemical and biological environments. During the first year, partners completed all the required experiments and quantum chemical calculations to explore nucleophilic substitution reactions involving alkyl halides and O2·∙– and also partially hydrated O2·∙–. Thus, the effect of solvation of superoxide anion by water molecules on its nucleophilicity has been investigated in detail by means of a combination of mass-spectrometry experiments and quantum chemical calculations including direct dynamics trajectory calculations. To this end, the reaction rates of the bimolecular nucleophilic substitution (SN2) reactions of O2·∙– (H2O)n clusters (n= 0 to 5) and CH3Cl and CH3Br were studied in detail. It was experimentally found that the corresponding reaction rates decrease when the number of water molecules in the cluster increases. In nice agreement with these experimental findings, our Density Functional Theory calculations clearly indicate that the attachment of water molecules to superoxide anion is translated into a much higher SN2 activation barriers, i.e. from a practically barrierless process for the reaction between O2·∙– and CH3Cl to barrier heights in the range of 6-13 kJ/mol for O2·∙–(H2O) or even higher values for O2·∙–(H2O)2. These results confirm the role of O2·∙– as a possible organic halide scavenger when solvated by only a few water molecules. This role is severely hampered by greater solvations. During the second year, partners focused on the reactivity of O2·∙– and O2H– with NO. They were able to gain more insight into the differences of reactivity of these reactive oxygen species. Results have been reported in two international publications: “Nucleophilic Substitution in Reactions between Partially Hydrated Superoxide Anions and Alkyl Halides” M. J. Ryding, A. Debnárová, I. Fernández, E. Uggerud, J. Org. Chem. 2015, 80, 6133-6142. And “Oxidation of NO by small oxygen species H02 and Ox – the role of negative charge, electronic spin and water solvatin”, M. HJ. Ryding, I. Fernández, E. Uggerud, Phys, Chem. Phys 2016, 18, 9528.
Summary of bilateral results
The obtained results contributed to gain more insight into the chemistry of oxygen reactive species. In addition, they have wider effects in the sense that partners have had to adapt their computational methodologies to this specific topic. Within this new insight in their hands, partners have started to apply the new methods to related systems Partners anticipate a significant impact of the published results (in terms of the quality of the journals and cites received) because they are focused on aspects which are of interest not only to the wide audience of researchers working on the atmospheric processes, but also to those interested in the reactivity and bonding situation of molecules from a more fundamental point of view. The current project will serve as starting point for a more ambitious research plan, i.e. the computational/experimental characterization of important atmospheric processes which strongly affect Earth’s climate and consequently, human well-being. For these reasons, partners do believe that the impact of the Oslo/Madrid collaboration will be quite remarkable. This project has consolidated the relationship between the awarded researchers. Besides the current project, different related and non-related projects have been envisioned (some of them have already been started). The new projects will ensure the cooperation in the near future