Generation of Naphthoquinone Radical Anions by Electrospray Ionization: Solution, Gas-Phase, and Computational Chemistry Studies

Abstract

Radical anions are present in several chemical processes, and understanding the reactivity of these species may be described by their thermodynamic properties. Over the last years, the formation of radical ions in the gas phase has been an important issue concerning electrospray ionization mass spectrometry studies. In this work, we report on the generation of radical anions of quinonoid compounds (Q) by electrospray ionization mass spectrometry. The balance between radical anion formation and the deprotonated molecule is also analyzed by influence of the experimental parameters (gas-phase acidity, electron affinity, and reduction potential) and solvent system employed. The gas-phase parameters for formation of radical species and deprotonated species were achieved on the basis of computational thermochemistry. The solution effects on the formation of radical anion (Q(•-)) and dianion (Q(2-)) were evaluated on the basis of cyclic voltammetry analysis and the reduction potentials compared with calculated electron affinities. The occurrence of unexpected ions [Q+15](-) was described as being a reaction between the solvent system and the radical anion, Q(•-). The gas-phase chemistry of the electrosprayed radical anions was obtained by collisional-induced dissociation and compared to the relative energy calculations. These results are important for understanding the formation and reactivity of radical anions and to establish their correlation with the reducing properties by electrospray ionization analyses.

Characterization of Vanadyl and Nickel Porphyrins Enriched from Heavy Residues by Positive-Ion Electrospray Ionization FT-ICR Mass Spectrometry

“…The classes of organic compounds include polycyclic aromatic hydrocarbons (PAH) [29] , polyenes [30][31][32] , organometallics (e.g. metallocenes and metalloporphyrins) [33][34][35][36][37] , quinines [38] , and fullerenes [39] . Van Berkel et al [33,34] were the first to systematically investigate the electrospray ionization of model metalloporphyrins, and observed the molecular ions.…”

Gas‐phase fragmentation reactions of protonated benzofuran‐ and dihydrobenzofuran‐type neolignans investigated by accurate‐mass electrospray ionization tandem mass spectrometry

“…All molecules were optimized with the B3LYP/6‐31G(d) model by using Gaussian 03 suite programs . The B3LYP method was chosen to calculate the selected parameters, which provided accurate measurements at minimum computational cost . Vibrational frequencies indicated that all structures were minima in the potential energy surface.…”

Electronic structure and gas‐phase chemistry of protonated α‐ and β‐quinonoid compounds: a mass spectrometry and computational study

“…ESI in combination with MS/MS analysis can be used to elucidate the gas‐phase chemistry of several classes of natural compounds . The number of studies on quinones has increased, because these compounds have interesting electrochemical behavior in the ESI source . The protonated and deprotonated species of 1,4‐naphthoquinone can occur during ESI analysis, and the radical anion has also been detected .…”

“…The number of studies on quinones has increased, because these compounds have interesting electrochemical behavior in the ESI source . The protonated and deprotonated species of 1,4‐naphthoquinone can occur during ESI analysis, and the radical anion has also been detected . Several papers have described the gas‐phase reactivity of quinonoid compounds by combining ESI studies with computational chemistry .…”

“…The protonated and deprotonated species of 1,4‐naphthoquinone can occur during ESI analysis, and the radical anion has also been detected . Several papers have described the gas‐phase reactivity of quinonoid compounds by combining ESI studies with computational chemistry . However, dissociation of the protonated 1,4‐naphthoquinone ( 1 ) and 1,2‐naphthoquinone ( 2 ) has not been investigated (Fig.…”