Ionization and Photofragmentation of Isolated Metalloporphyrin Cations Investigated by VUV Action Spectroscopy*.

ABSTRACT: We investigated the photoionization and fragmentation of isolated metal protoporphyrin IX cations (MPPIX⁺ with M=Fe, Co, Zn) by means of vacuum-ultraviolet (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 ^. CH₂ COOH radical side-chain losses of the macrocycle with additional methyl radical (^. CH₃ ) 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 for example single and double H₂ 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.

SUBMITTER: Schubert K 

PROVIDER: S-EPMC8457234 | biostudies-literature | 2021 Aug

REPOSITORIES: biostudies-literature