Resonance attachment of low energy (0–15 eV) electrons to imide-containing molecules, phthalimide (PTI) and pyromellitic diimide (PMDI), was investigated in the gas-phase by means of Electron Transmission Spectroscopy (ETS) and Dissociative Electron Attachment Spectroscopy (DEAS). Among a variety of low intensity negatively charged fragments formed by DEA, in both compounds the dominant species was found to be a long-lived (μs) parent molecular anion formed at zero energy. In addition, in PMDI long-lived molecular anions were also observed at 0.85 and 2.0 eV. The experimentally evaluated detachment times from the molecular anions as a function of incident electron energy are modeled with a simple computational approach based on the RRKM theory. The occurrence of radiationless transitions to the ground anion state, followed by internal vibrational relaxation, is believed to be a plausible mechanism to explain the exceptionally long lifetime of the PMDI molecular anions formed above zero energy.

The gas-phase empty-level structures and formation of anion states via resonance attachment of low-energy electrons to the flavonoids naringenin (III), quercetin (IV) and myricetin (V) and the smaller reference molecules chromone (I) and flavone (II) are investigated experimentally for the first time. Dissociative electron attachment spectroscopy (DEAS) is used to measure the fragment anion currents generated through dissociative decay channels of the molecular anions of compounds I–V, detected with a mass filter as a function of the incident electron energy in the 0–14 eV energy range. Due to the insufficient volatility of flavonoids III–V, the energies of vertical electron attachment associated with temporary occupation of the lower-lying virtual orbitals are measured with electron transmission spectroscopy (ETS) only in the smaller reference molecules I and II. The experimental findings are interpreted with the support of appropriate density functional theory calculations with the B3LYP functional. The experimental vertical electron attachment energies measured in the ET spectra of I and II are compared with the orbital energies of the neutral molecules scaled using an empirically calibrated linear equation. The vertical and adiabatic electron affinities are evaluated at the B3LYP/6-31+G(d) level as the anion/neutral total energy difference. The latter theoretical method is also used for evaluation of the most stable conformers of the neutral molecules, O–H bond dissociation energies and thermodynamic energy thresholds for production of the anion fragments observed in the DEA spectra. A possible role played by loss of an H₂ molecule from the parent molecular anion in vivo in the mitochondrial respiratory chain is briefly discussed.

Low-energy (0–12 eV) electron attachment to molecules of a typical matrix substance used for matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS), namely α-cyano-4-hydroxicynnamic acid, has been investigated in the gas phase at different temperatures ranging from 140°C to 260°C by means of electron capture negative-ion mass spectrometry (ECNI MS). The yield of negative ions, formed by electron capture, was measured as a function of incident electron energy for four different temperatures. The long-lived parent molecular anion, [M]⁻ ( m/z 189), was observed in the negative-ion mass spectra of the substance under investigation. Its autodetachment lifetime was estimated to be approximately 600 μs. It was found that at 140°C the main decay channel of the long-lived temporary molecular anion of α-cyano-4-hydroxicynnamic acid is a formation of the [M – COOH]⁻ fragment negative ion ( m/z 144) with an intensity of 37.2% in percentage terms in respect of the total anion current. There are also [M – H]⁻, [M – CO₂]⁻ and [CN]⁻ fragments in the spectra with intensities of about 7.7%, 21.6% and 3.1% at 140°C. It was shown that the escape of the CO₂ molecule from the parent molecular anion is a slow process. It takes [M]⁻ about 10μs to decay on carbon dioxide molecules and [M – CO₂]⁻ fragment anions. Increasing the temperature of the target molecule alters the negative-ion mass spectra of α-cyano-4-hydroxicynnamic acid significantly. A possible role for the findings in typical MALDI MS experiments is discussed.

Small molecular species present in mitochondria as, e.g. quinones and oxygen, can capture cellular electrons thus behaving as electron carriers or reactive species, supporting the fundamental process of respiration, and providing protection from pathogens. When xenobiotics penetrate living cells, their delicate redox balance can be altered by capture of cellular electrons to form temporary negative ions. The latter can give rise to the formation of reactive species via dissociative electron attachment (DEA), as observed under gas-phase or electrochemical conditions. DEA to isolated biorelevant molecules studied in vacuo with the support of in silico methods can serve as a model to predict the behaviour of these species in vivo under conditions of electron ‘leakage’ in the lipid-protein-cytosol media or in enzymatic active centres. The present review summarises the results of studies on the correlation between the biological activity of various classes of compounds and fragment species formed by DEA. The following classes of compounds are included into the present review: chlorinated organic pollutants, brominated ethers, captafol and 2,6-dichloroisonicotinic acid, atrazine and bromoxynil, non-steroidal anti-inflammatory drugs, natural polyphenolic compounds, anthralin, salicylic acid and related compounds, ascorbic acid, melatonin, tryptophan, indole and related compounds and some organic peroxides. Formation of temporary molecular anions and their decay are characterised using electron transmission spectroscopy (ETS) and DEA spectroscopy. Quantum-chemical calculations support the identification of the dissociation products. Cellular electron attachment to unnatural electron acceptors is likely to be the first step of cascade processes which constitute the molecular mechanisms of electron-driven biological processes. The fragment species detected with DEA are of importance for understanding the metabolism of xenobiotics, including side effects produced by drugs.