reported a similar degradation profile of hemin + : the two -CH2COOH groups were the first groups to be eliminated, depending on their similar energies of removal, estimated to be 2.4 and 2.9 eV. However, even though this removal was followed by the loss of -CH3, and finally the -CH=CH2, these groups remained intact with the main tetrapyrrole ring in our experiments. Moreover, the fragmentation of hemin + and heme was thoroughly studied theoretically by using DFT, with comparison to the experimental data .