Mass spectrometric and theoretical studies on dissociation of the SS bond in the allicin: Homolytic cleavage vs heterolytic cleavage

On the basis of the tandem mass spectrometry (ESI-MS/MS) technique and DFT calculations, an experimental and theoretical investigation has been conducted into the gas-phase dissociation of the S1S1′ bond in the allicin as well as that of the SC (S1C2, S1′C2′) bond. Meanwhile, the influence of protonation, alkali metal ion and electron transfer on the dissociation of the S1S1′ bond has been taken into account. ESI-MS/MS experiments and DFT calculations show that in the neutral allicin, [allicin + Li]+ and [allicin + Na]+, the S1S1′ bond favors homolytic cleavage, while in the allicin radical cation and protonated allicin, the S1S1′ bond prefers heterolytic cleavage. In addition, alkali metal ions can strengthen the S1S1′ bond in the allicin, while protonation or the loss of an electron will weaken the S1S1′ bond.