The effect of stereochemistry on the oxidation of organic molecules adsorbed on aerosol particles has been revealed in a model system.
Organic molecules are released into the atmosphere from both natural and man-made sources. The oxidation of such species adsorbed onto aerosol particles is of interest because these processes can have an impact on the chemical composition of the atmosphere and the propensity of aerosols to promote cloud formation. A specific example of this is the ozonolysis of carbon–carbon double bonds, which are widespread in biosurfactants and terpenes found in the atmosphere, but there have been few studies on the effect of their stereochemistry1.
Now, Franz Geiger and colleagues at Northwestern University in Illinois have shown that the propensity of a chiral alkene adsorbed on an aerosol particle to undergo ozonolysis may depend on its orientation on the surface and hence its stereochemistry. The differences in chemical accessibility would then lead to the enrichment of one stereoisomer of the product over the other.
As a model for atmospheric aerosol particles, the researchers prepared silicate substrates functionalized with diastereomeric alkenes. Kinetic studies of the ozonolysis reaction showed that the diastereomer with the alkene group oriented towards the gas phase reacts twice as fast as the one oriented away from it. This finding could lead to the use of chiral organic molecules as 'markers' to distinguish between anthropogenic and biogenic sources of certain organic carbon emissions.
References
Stokes, G. Y. et al. Atmospheric heterogeneous stereochemistry. J. Am. Chem. Soc. 10.1021/ja904206t (2009).
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Croft, L. Stereochemistry in the sky. Nature Chem (2009). https://doi.org/10.1038/nchem.409
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DOI: https://doi.org/10.1038/nchem.409