Reactions between glycolic acid and Cu+ in the gas phase.: An experimental and theoretical study

The gas-phase reactions between glycolic acid and Cu+ have been investigated by means of mass spectrometry techniques. The mass-analyzed ion kinetic energy (MIKE) spectrum reveals that the adduct ions [HOCH2-COOH-Cu+] decompose spontaneously by losing CH2O2, CO, and H2O. A minor fragmentation corresponding to the loss of H-2 is also observed. The structures and bonding characteristics of the different complexes involved in the glycolic acid-Cu+ potential energy surface (PES) have been theoretically studied by density functional theory (DFT) calculations carried out at the B3LYP/6-311+G(2df,2p)//B3LYP/6-31G* level. The attachment of Cu+ to glycolic acid gives rise to two energetically degenerated structures: a chelated form in which Cu+ interacts with the carbonyl oxygen and the hydroxyl oxygen atoms and another one in which the attachment of Cu+ takes place exclusively at the carbonyl oxygen atom. The estimated glycolic acid-Cu+ binding energy is 222 kJ/mol. Different mechanisms for the spontaneous fragmentations observed experimentally are proposed. The main conclusion is that the loss of 46 u should correspond dominantly to the loss of formic acid and in a lower proportion to the loss of CO + H2O.