Rationale: 2,4,6-Tris(4-formylphenyl)boroxine (TFPB) is a substituted boroxine containing a benzaldehyde molecule bonded to each boron atom. Boroxine cages are an emerging class of functional nanostructures used in host-guest chemistry, and benzaldehyde is a potential radiosensitizer. Reactions initiated by low-energy electrons with such complexes may dictate and bring new fundamental knowledge for biomedical and pharmaceutical applications.
Methods: The electron ionization properties of TFPB are investigated using a gas-phase electron-molecule crossed beam apparatus coupled with a reflectron time-of-flight mass spectrometer in an orthogonal geometry. Ionization and threshold energies are experimentally determined by mass spectra acquisition as a function of the electron energy.
Results: The abundance of the molecular precursor cation in the mass spectrum at 70 eV is significantly lower than that of the most abundant fragment C7 H5 O+ . Twenty-nine cationic fragments with relative intensities >2% are detected and identified. The appearance energies of six fragment cations are reported, and the experimental first ionization potential is found at eV. Moreover, eight double cations are identified. The present results are supported by quantum chemical calculations based on bound state techniques, electron ionization models and thermodynamic thresholds.
Conclusions: According to these results, the TPFB properties may combine the potential radiosensitizer effect of benzaldehyde with the stability of the boroxine ring.
© 2022 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.