Decarboxylation of carnitine and alpha-cyano-4-hydroxycinnamic acid under particle bombardment

Protonated carnitine and alpha -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 bom bardment are compared with the decompositions induced by low- and high-ener gy collisions of molecules protonated by electrospray, The determination of fragmentation mechanisms was achieved using labelled compounds and by mean s of ab initio calculations. The most prominent fragmentation of protonated molecules formed under particle bombardment is an unexpected loss of carbo n dioxide. More classical processes dominate the decomposition induced by c ollisions of electrosprayed species: loss of trimethylamine and 4-hydroxybu tyrolactone from protonated carnitine, loss of water from protonated cinnam ic acid but no loss of CO2. Decarboxylation occurring before or concomitant with protonation is proposed to interpret these results.