IRMPD signature of protonated pantothenic acid, an ubiquitous nutrient

Highlights: • Pantothenic acid, an essential nutrient, is examined as isolated molecule. • IRMPD spectroscopy is used as structural probe. • A comprehensive computational survey of isomers and conformers is presented. • The favored protonation site is established. • Conformational motifs include multiple hydrogen bonding interactions. Intrinsic properties of pantothenic acid, an essential nutraceutical, are examined. The effect of protonation on the energetic and geometric features of pantothenic acid, generated as gaseous protonated species, are investigated by infrared multiple photon dissociation (IRMPD) spectroscopy over an extended frequency range (800–2000 cm⁻¹ and 2800–3700 cm⁻¹). DFT calculations are exploited to identify the possible structures and predict the absorption spectra at the B3LYP/6-311++G(d,p) level. Two amide-protonated structures, characterized by the most stable binding motifs, account well for the experimental spectrum, thus revealing structurally diagnostic features of potential benefit for the development of highly sensitive and selective nutrient screening.