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, [C6 H8 O6 ]H+ were generated by electrospray ionization of a 10 3 M H2 O/CH3 OH (1 1) AA solution. In order to structurally characterize the gaseous [C6 H8 O6 ]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 DSp 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 (c) 2016 John Wiley Sons, Ltd.
Journal of mass spectrometry JMS