Vitamin C: an experimental and theoretical study on the gas-phase structure and ion energetics of protonated ascorbic acid.
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 10-3M 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-1and protonation entropy ΔSp108.9 ± 2 J mol-1K-1, a gas-phase basicity value of AA of 842.5 ± 12 kJ mol-1at 298 K was obtained, which is in agreement with the value issuing from quantum mechanical computations. Copyright © 2016 John Wiley & Sons, Ltd.
Department of Mathematics and Physics, Second University of Naples, Viale Lincoln,5, 81100, Caserta, Italy.
Andreina
A
Ricci
Department of Chemistry and Drug Technologies, 'Sapienza' University of Rome, P.le A. Moro 5, 00185, Rome, Italy.
Federico
F
Pepi
Department of Pharmaceutical Science, University of Salerno, Via Giovanni Paolo II, 84084, Fisciano (Sa), Italy.
Paola
P
Cimino
Department of Chemistry and Drug Technologies, 'Sapienza' University of Rome, P.le A. Moro 5, 00185, Rome, Italy.
Anna
A
Troiani
Department of Chemistry and Drug Technologies, 'Sapienza' University of Rome, P.le A. Moro 5, 00185, Rome, Italy.
Stefania
S
Garzoli
Department of Chemistry and Drug Technologies, 'Sapienza' University of Rome, P.le A. Moro 5, 00185, Rome, Italy.
Chiara
C
Salvitti
Department of Mathematics and Physics, Second University of Naples, Viale Lincoln,5, 81100, Caserta, Italy.
Brunella
B
Di Rienzo
Scuola Normale Superiore, Piazza Cavalieri 7, I-56126, Pisa, Italy.
Vincenzo
V
Barone
D001205:Ascorbic Acid / Q000032:analysis* / Q000737:chemistry*; D005740:Gases / Q000032:analysis / Q000737:chemistry; D007477:Ions / Q000032:analysis / Q000737:chemistry; D007700:Kinetics; D013058:Mass Spectrometry; D008958:Models, Molecular
D005740:Gases; D007477:Ions; D001205:Ascorbic Acid
gas-phase basicity of ascorbic acid; kinetic method; mass spectrometry; protonated ascorbic acid; quantum mechanical calculation