Chemistry and Photochemistry of Pyruvic Acid Adsorbed on Oxide Surfaces.
The surface chemistry and photochemistry of gas phase pyruvic acid (CH3COCOOH) on two oxides, Al2O3 and TiO2, have been investigated using transmission Fourier Transform Infrared (FTIR) Spectroscopy and mass spectrometry. At 298K, the carboxylic acid group within pyruvic acid is found to react with surface hydroxyl groups (M OH, where M=Al or Ti) to yield pyruvate as a predominant adsorbed organic species. Upon broadband UV irradiation, 280 nm, there is a loss of adsorbed pyruvate with the concomitant formation of new products. The photochemical loss of pyruvate is higher on TiO2 than Al2O3 indicating that photochemistry is enhanced on the surface of a semiconductor oxide, TiO2, compared to an insulator oxide, Al2O3. Analysis of products extracted from the surface with mass spectrometry shows the formation of several new compounds. This includes zymonic acid, which is found to be present under both dark and light conditions, and other higher molar mass oligomeric species such as parapyruvic acid, acetolactic acid, and 2,4 dihydroxy 2 methyl 5 oxohexanoic acid (DMOHA) that form only under irradiation. Although this study shows that there are some parallels between aqueous phase photochemistry of pyruvic acid and the photochemistry of adsorbed pyruvic acid in terms of the products that form, there are also distinct differences with several other new photoproducts observed on these oxide surfaces including lactic acid dimers and trimers as well as a significant amount of even larger oligomeric species not seen in the aqueous phase. Because of the role of pyruvic acid, the simplest of the alpha keto acids, in the atmosphere and in metabolic pathways, these results have implications to the chemistry that occurs in both indoor and outdoor environments and during prebiotic Earth conditions. Overall, this study provides insights into the surface chemistry and photochemistry of pyruvic acid on different oxides (Al2O3 and TiO2)
The journal of physical chemistry. A