IRMPD Spectroscopy of Bare Monodeprotonated Genistein, an Antioxidant Flavonoid

Abstract

Genistein is a naturally occurring polyphenol belonging to the family of flavonoids with estrogenic properties and proven antioxidant, anti-inflammatory, and hormonal effects. Genistein and its derivatives are involved in radical scavenging activity by way of mechanisms based on sequential proton-loss electron transfer. In view of this role, a detailed structural characterization of its bare deprotonated form, [geni-H] − , generated by electrospray ionization, has been performed by tandem mass spectrometry and infrared multiple photon dissociation (IRMPD) spectroscopy in the 800–1800 cm –1 spectral range. Quantum chemical calculations at the B3LYP/6-311+G(d,p) level of theory were carried out to determine geometries, thermochemical data, and anharmonic vibrational properties of low-lying isomers, enabling to interpret the experimental spectrum. Evidence is gathered that the conjugate base of genistein exists as a single isomeric form, which is deprotonated at the most acidic site (7-OH) and benefits from a strong intramolecular H-bond interaction between 5-OH and the adjacent carbonyl oxygen in the most stable arrangement.

Protonated Forms of Naringenin and Naringenin Chalcone: Proteiform Bioactive Species Elucidated by IRMPD Spectroscopy, IMS, CID-MS, and Computational Approaches

“…Comparison of the calculated spectra with the experimental one of [Nar + H] + , reported in Figures 3 and S11 In general, for all conformers considered, the 180°rotation of C4′−OH has little influence on relative energies, yielding species with similar free energy as observed for neutral naringenin. 20 Furthermore, in agreement with similar findings in an IRMPD study on deprotonated genistein 68 and with an IR study on neutral naringenin, 69 the calculated IR spectra for each pair of such conformers are completely superimposable as can be noted in the calculated spectra IR collected in the Supporting Information (Figures S10−S12).…”

Hydrogen-Deuterium-Exchange-Based Mass Distribution Shifts in High-Resolution Cyclic Ion Mobility Separations

“…As their deprotonated ions, the pair of isomers has only two exchangeable hydrogens (Figure ). Notably, these two compounds also have known deprotonation sites from previous work, allowing for confident identification of the H/D exchange sites. − These two isomers were resolved after 3 m of cIMS-MS separation (Figure , left). When subjected to our HDX-induced mass-distribution-based shift analysis, it was found that despite only having two labile hydrogens exchanged for deuteriums, their t Rel.…”

“…80,81 Interestingly, as compared to our previous work, we observed orthogonality between these HDX-induced mass-distributionbased shifts and the arrival time order of the isomers, themselves. We attribute this orthogonality to be based on how the mass distribution of each molecule changes upon deuteration, where upon doubling the mass of an atom from H to 2 H, its contribution to the center of mass and moment of inertia is increased as compared other atom mass changes (e.g., 35 Cl to 37 Cl or 79 Br to 81 Br). Lastly, we demonstrated inverse isotopologue shifts for 4-iodoaniline, which we attribute to the change in mass distribution, and specifically center of mass contributions, between the d0 and d3 isotopologues.…”