Chemistry. 2021 Jun 17. doi: 10.1002/chem.202101515. Online ahead of print.
ABSTRACT
We investigated the photoionization and fragmentation of isolated metal protoporphyrin IX cations (MPPIX with M = Fe, Co, Zn) by means of VUV action spectroscopy in the energy range of 8.5-35 eV. Experiments were carried out in the gas phase by interfacing an electrospray ionization tandem mass spectrometer with a synchrotron beamline. The mass spectra and partial ion yields show that photoexcitation of the precursor ions predominantly leads to • CH 2 COOH radical side-chain losses of the macrocycle with additional methyl radical ( • CH 3 ) side-chain losses. Ionization, in contrast, leads to the formation of the intact ionized precursor and various doubly charged fragments which are mostly due to side-chain cleavages. Although statistical fragmentation dominates, we found evidence for non-statistical processes such as new fragments involving e.g. single and double H 2 O losses, indicating that different relaxation mechanisms are at play upon photoionization compared to photoexcitation. The measured ionization energies were 9.6 ± 0.2 eV, 9.4 ± 0.2 eV and 9.6 ± 0.2 eV for FePPIX + , CoPPIX + and ZnPPIX + , respectively.
PMID:34137472 | DOI:10.1002/chem.202101515
