The formation of negative ions of some diterpene alkaloid molecules having conjugated πС=С and πС=О bonds in their structure by resonance electron capture has been studied. The mass spectra of these compounds are due to electron capture onto the lowest unoccupied molecular orbital (LUMO), which is π*-С=С or π*-С=О in nature. It has been found that the partial conversion of the test compound molecules into the enol form is possible on transferring into a gas phase; for this purpose, the appearance potentials of the ions (M–H)– and (M–OCH3)– have been compared with the calculated thermodynamic thresholds of their appearance in the keto and enol forms.

According to available experimental data, the formation of long-lived (∼10−5 s) negative molecular ions (NMIs) due to resonant electron capture (REC) by polyatomic molecules is observed experimentally with the proviso that their electron affinity (EA) is on the order of several tenths of electronvolt or above. Such compounds are characterized by large NMI formation cross sections. High ability to effectively capture thermal electrons correlates with their ability to capture free radicals, in particular, to act as inhibitors of radical polymerization [1]. It is likely that these compounds will exhibit antioxidant activity as well. It is therefore of interest to use the REC technique for studying antioxidant compounds, of which the bioflavonoid quercetin (QU) (1) (Fig. 1) and its derivatives are prominent representatives [2, 3].

Processes resulting in the formation of negative ions by molecules of some diterpene alkaloids via resonance electron capture have been studied. The mass spectra of these compounds have a small number of lines represented largely by intense peaks in the thermal electron energy region and are due to electron capture onto the lower unoccupied molecular orbital, which is π*-C=O or π*-Ph-C=O in character.