Vitamin C: an experimental and theoretical study on the gas‐phase structure and ion energetics of protonated ascorbic acid |
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| Authors: | Andreina Ricci Federico Pepi Paola Cimino Anna Troiani Stefania Garzoli Chiara Salvitti Brunella Di Rienzo Vincenzo Barone |
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| Affiliation: | 1. Department of Mathematics and Physics, Second University of Naples, Caserta, Italy;2. Department of Chemistry and Drug Technologies, ‘Sapienza’ University of Rome, Rome, Italy;3. Department of Pharmaceutical Science, University of Salerno, Fisciano (Sa), Italy;4. Scuola Normale Superiore, Pisa, Italy |
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| Abstract: | In order to investigate the gas‐phase mechanisms of the acid catalyzed degradation of ascorbic acid (AA) to furan, we undertook a mass spectrometric (ESI/TQ/MS) and theoretical investigation at the B3LYP/6‐31 + G(d,p) level of theory. The gaseous reactant species, the protonated AA, C6H8O6]H+, were generated by electrospray ionization of a 10?3 M H2O/CH3OH (1 : 1) AA solution. In order to structurally characterize the gaseous C6H8O6]H+ ionic reactants, we estimated the proton affinity and the gas‐phase basicity of AA by the extended Cooks's kinetic method and by computational methods at the B3LYP/6‐31 + G(d,p) level of theory. As expected, computational results identify the carbonyl oxygen atom (O2) of AA as the preferred protonation site. From the experimental proton affinity of 875.0 ± 12 kJ mol?1 and protonation entropy ΔSp 108.9 ± 2 J mol?1 K?1, a gas‐phase basicity value of AA of 842.5 ± 12 kJ mol?1 at 298 K was obtained, which is in agreement with the value issuing from quantum mechanical computations. Copyright © 2016 John Wiley & Sons, Ltd. |
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| Keywords: | protonated ascorbic acid mass spectrometry kinetic method gas‐phase basicity of ascorbic acid quantum mechanical calculation |
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