Structure and fragmentation of glycine, alanine, serine and cysteine radical cations. A theoretical study

The structure of glycine, alanine, serine and cysteine radical cations, as well as their Cα-R fragmentations have been studied at the B3LYP/6-31++G(d,p) level of theory. For all systems the loss of COOH is found to be the most favourable process. However, when R1 size increases, fragmentations that lead to R1 or R1+ start become competitive. The energy of a Cα-R fragmentation can be related to the ionization potential of the two generated fragments, in such a way that the preferred process is the one that leaves the positive charge in the fragment with a lower ionization potential.