Mass–Energy Profiles Obtained by Quantum Chemical Computing Applied in Mass Spectrometry: A Case Study with Identification of a Group of Acetalized Monosaccharide Isomers

Accurate modeling of small molecules substantially reduces the logistical effort and time consumption to discover and then obtain chemicals with various applications. Molecular stereochemistry is fundamentally involved in the intermolecular interactions that give rise to biological activity. Establishing the configuration of the asymmetric carbon in diastereomers can be decisive in drug design. In the presented analytical technique, on the basis of quantitative structure–fragmentation relationship (QSFR), mass–energy profiles obtained by electron ionization mass spectrometry (EI-MS) for analytes are used, along with some profiles for candidate structures calculated by quantum chemical (QC) methods. Our paper establishes the analytical conditions that lead to the best matching scores of such profiles corresponding to the actual structures for some isomers of acetalized monosaccharides. The optimization was achieved by group validation of five analytes, using four independent variables: the QC method, the descriptor of calculated energy, the impact energy of electrons, and the descriptor of experimental energy. The true structures were obtained using experimental profiles obtained at low electronic impact energies, and profiles were calculated using the DFT (B3LYP/6-31G) and RM1 QC methods. The double quantification of the ionic mass and the energy that generates it, for only a few primary ions of the mass spectrum, even allows the differentiation of acetalized diastereomers.