Photochemistry of the pyruvate anion produces CO2, CO, CH3\u2013, CH3, and a low energy electron

Connor J Clarke,Jan R R Verlet,Jemma A Gibbard,Basile F E Curchod,Lewis Hutton

doi:10.1038/s41467-022-28582-4

Abstract

The photochemistry of pyruvic acid has attracted much scientific interest because it is believed to play critical roles in atmospheric chemistry. However, under most atmospherically relevant conditions, pyruvic acid deprotonates to form its conjugate base, the photochemistry of which is essentially unknown. Here, we present a detailed study of the photochemistry of the isolated pyruvate anion and uncover that it is extremely rich. Using photoelectron imaging and computational chemistry, we show that photoexcitation by UVA light leads to the formation of CO2, CO, and CH3−. The observation of the unusual methide anion formation and its subsequent decomposition into methyl radical and a free electron may hold important consequences for atmospheric chemistry. From a mechanistic perspective, the initial decarboxylation of pyruvate necessarily differs from that in pyruvic acid, due to the missing proton in the anion.

Highlights

The photochemistry of pyruvic acid has attracted much scientific interest because it is believed to play critical roles in atmospheric chemistry
Pyruvic acid and its conjugate base, the pyruvate anion, CH3COCOO− (Fig. 1), are pervasive throughout nature. Both are present within seawater, fogs, aerosols, clouds, and the atmosphere[1,2], having biogenic and anthropogenic origins[3,4,5,6]. Their presence in atmospheric aerosols has attracted particular attention due to the rich photochemistry of pyruvic acid, which differs between the gas- and solution phase and at their dividing interface[7,8,9], and because pyruvic acid serves as a representative α-dicarbonyl in atmospheric models[10]
The decarboxylation process is facilitated by an intramolecular proton transfer in the S1 excited state, with additional possible involvement of triplet states depending on the environment[11,15]

Summary

Introduction

The photochemistry of pyruvic acid has attracted much scientific interest because it is believed to play critical roles in atmospheric chemistry. The broad photoelectron peak in the 3.8 ≤ hν ≤ 4.3 eV spectra, which red-shifts with decreasing hv, can be attributed to direct electron detachment of the pyruvate anion, forming the neutral D0 ground state.

Results

Conclusion