3 research outputs found
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><sub>a</sub> 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
CCSDÂ(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