Uncovering a Multispecies Radical Network in UV-Irradiated Pyruvic Acid.

Area of Science:

• Photochemistry
• Radical chemistry
• Spectroscopy

Background:

• Alpha-keto acids are known radical precursors under UV irradiation.
• Current electron paramagnetic resonance (EPR) evidence simplifies their radical behavior to a single ketyl species.
• This simplification may obscure their full photochemical and radical behavior.

Purpose of the Study:

• To investigate the complex radical species formed from alpha-keto acids upon UV irradiation.
• To resolve the simplification of single ketyl species assignment in EPR studies.
• To provide a more comprehensive understanding of UV-induced radical chemistry in alpha-keto acids.

Main Methods:

• Utilized isotope labeling combined with 9.5 GHz EPR spectroscopy.
• Monitored irradiation-time-resolved radical buildup and temperature-dependent decay.
• Employed high-frequency EPR (94 GHz) and DFT-guided simulations for spectral deconvolution.

Main Results:

• Identified at least four distinct radical species originating from pyruvic acid.
• Characterized the dominant monomeric ketyl radical.
• Also identified a methyl radical, a carboxylate radical anion, and a dimeric ketyl species.

Conclusions:

• Alpha-keto acids exhibit multispecies radical chemistry under UV irradiation.
• This complex radical behavior needs consideration when interpreting solid-state EPR or dDNP data.
• The findings are relevant for understanding atmospheric chemistry processes involving alpha-keto acids.