On the interconnection between products formed by dissociative electron attachment to gas-phase abscisic acid and its microbial (but not plants) metabolic pathways

Abstract

Low-energy (0–14 eV) electron-driven processes in a racemic mixture of the chiral abscisic acid (ABA) molecules are studied using dissociative electron attachment (DEA) spectroscopy under gas-phase conditions. DFT calculations are employed to understand the electronic structure of the ABA molecule to assign the experimental findings. The lowest two normally empty π* molecular orbitals of ABA are predicted to lie in a bound region, whereas the vertical electron attachment energy to occupy the π3* LUMO+2 orbital is estimated to be 1.33 eV. The long-lived (90 μs) parent molecular negative ions are formed by thermal electron attachment via vibrational Feshbach resonance. The adiabatic electron affinity of the ABA molecule is experimentally estimated to be about 0.9 eV. With very few exceptions, the fragmentation of ABA by resonance electron attachment occurs at thermal electron energy, the dominant decay being associated with the formation of the 4-oxoisophorone negative ion (m/z = 152) and the isomeric form of the sorbic acid molecule as a neutral counterpart. The structure of ABA microbial metabolites coincides with that of the DEA products with m/z = 152, 204, and 220 and of the neutral species generated as a counterpart of the m/z = 111 negative ions. The likely relation of these findings to electron-triggered biological processes is briefly discussed in the framework of electron donation to ABA from the microbial nanowires.