Abstract
Gas-phase molecular properties of volatile organic compounds (VOCs) play an important role in the selection of gas-phase reagent ions for chemical ionization mass spectrometry (CI-MS). We apply hybrid density functional theory (DFT) to compute proton affinity (PA), ionization energy (IE), and global reactivity parameters for VOCs, which are widely regarded as the primary
sources of taints and off-flavors in wine. Atomic polar tensor (APT) charges and total energies at the stationary point for neutral and protonated molecules are also computed. PA and IE values determine the CI-MS mode of reactions, either proton transfer or electron transfer from the reagent gas ions to VOCs.
Global reactivity parameters, such as chemical potential (µ), chemical hardness (η), softness (σ), and electrophilic nature (ω) as obtained from frontier molecular orbitals, are considered useful in rationalizing the chemical reactivity patterns of the molecules. A benchmark calculation of indole molecule with MP2, B3LYP, and M06-2X DFT methods at thermodynamically and kinetically stable protonation sites further supports the applied DFT method. Since
limited data are available on computed parameters, the reported values would support CI-MS quantification of trace-level VOCs not only in wine but also in various food products.
Supplementary materials
Title
Supporting Material
Description
Data on the total energy at the stationary point of the
neutral and protonated complex together with the net atomic charge, bond length change post protonation are collected as supplementary material for all species occurring in this study.
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