Atmospheric Oxidation of Peroxyacetic Acid

The full reactive atmospheric oxidation profile of peroxyacetic acid under high NO conditions was examined using electronic structure calculations at various levels of theory. The three pathways resulting from the reaction of peroxyacetic acid with the hydroxyl radical were (1) addition of OH to the central carbon, (2) abstraction of the acidic hydrogen, and (3) abstraction of the methyl hydrogen. These pathways were followed to terminal product steps, the major products being acetic acid for pathway 1 and formaldehyde for pathways 2 and 3

Carboxylic Acid Catalyzed Hydration of Acetaldehyde

Electronic structure calculations of the pertinent stationary points on the potential energy surface show that carboxylic acids can act effectively as catalysts in the hydration of acetaldehyde. Barriers to this catalyzed process correlate strongly with the p<i>K</i>_a of the acid, providing the potential to provide the predictive capacity of the effectiveness of carboxylic acid catalysts. Transition states for the acid-catalyzed systems take the form of pseudo-six-membered rings through the linear nature of their hydrogen bonds, which accounts for their relative stability compared to the more strained direct and water-catalyzed systems. When considered as a stepwise reaction of a dimerization followed by reaction/complexation, it is likely that collisional stabilization of the prereactive complex is more likely than reaction in the free gas phase, although the catalyzed hydration does retain the potential to proceed on water surfaces or in droplets. Lastly, it is observed that postreactive diol–acid complexes are significantly stable (∼12–17 kcal/mol) relative to isolated products, suggesting the possibility of long-lived hygroscopic species that could act as a seed molecule for condensation of secondary organic aerosols

Thermodynamics and Kinetics for the Free Radical Oxygen Protein Oxidation Pathway in a Model for β‑Structured Peptides

Oxidative stress plays a role in many biological phenomena, but involved mechanisms and individual reactions are not well understood. Correlated electronic structure calculations with the MP2, MP4, and CCSD­(T) methods detail thermodynamic and kinetic information for the free radical oxygen protein oxidation pathway studied in a trialanine model system. The pathway includes aerobic, anaerobic and termination reactions. The course of the oxidation process depends on local conditions and availability of specific reactive oxygen species (ROS). A chemical mechanism is proposed for how oxidative stress promotes β-structure formation in the amyloid diseases. The work can be used to aid experimentalists as they explore individual reactions and mechanisms involving oxygen free radicals and oxidative stress in β-structured proteins