Computational estimates of the gas-phase acidities of dihydroxybenzoic acid radical cations and their corresponding neutral species

The gas-phase acidities (GAs) of the radical cations of all six isomers of dihydroxybenzoic acid (x,y-DHB), which are prototypical matrices used in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry have been calculated using density functional theory (DFT). The GAs vary from 815.3 kJ/mol for the most acidic species (3,4-DHB) to 862.7 kJ/mol for the least acidic one (2,5-DHB). The reported GAs of the x, y-DHB radical cations are in excellent agreement with previous experimental measurements. The results indicate that deprotonation, in all six radical cations, takes place on the phenol sites. In addition, the GAs of the six neutral DHB isomers have been similarly calculated. (C) 2003 Elsevier B.V. All rights reserved.