B3LYP DFT molecular orbital approach, an efficient method to evaluate the thermochemical properties of MALDI matrices

The thermochemical properties of seven UV-MALDI matrices and two IR-MALDI matrices were evaluated by means of ab initio molecular orbital calculations using the B3LYP functional density approach with 6-31+G(d,p) and 6-311+G(2d,2p) basis sets. These thermochemical properties include ionization energy, proton and electron affinities of neutral molecules and proton affinity of deprotonated molecules. The choosen UV-MALDI matrices are: 2,5-dihydroxybenzoic acid (2,5DHB), nicotinic acid (NA) and 2-aminonicotinic acid (2ANA), picolinic acid (PA) and 3-hydroxypicolinic acid (3HPA), 2-aminobenzoic acid (2ABA) and 4-nitroaniline (4NiAn) while the studied IR-MALDI matrices are urea (U) and glycerol (G). The proton affinities of neutral and deprotonated molecules are in very good agreement with the available experimental values (the differences between experimental and calculated values are smaller than the precision on the experimental measurements); the calculated ionization energies are close to the experimental values of adiabatic electronic transitions; the calculated electron affinities are new and cannot be compared with corresponding experimental values since they are not available. (Int J Mass Spectrom 217 (2002) 231-244) (C) 2002 Elsevier Science B.V. All rights reserved.