Decarboxylation of Carnitine and α-Cyano-4-Hydroxycinnamic Acid under Particle Bombardment

Protonated carnitine and α-cyano-4-hydroxycinnamic acid were formed by laser photon irradiation, by MeV-ion bombardment and by electrospray. The spontaneous fragmentations of protonated molecules formed upon particle bombardment are compared with the decompositions induced by low- and high-energy collisions of molecules protonated by electrospray. The determination of fragmentation mechanisms was achieved using labelled compounds and by means of ab initio calculations. The most prominent fragmentation of protonated molecules formed under particle bombardment is an unexpected loss of carbon dioxide. More classical processes dominate the decomposition induced by collisions of electrosprayed species: loss of trimethylamine and 4-hydroxybutyrolactone from protonated carnitine, loss of water from protonated cinnamic acid but no loss of CO₂. Decarboxylation occurring before or concomitant with protonation is proposed to interpret these results.