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Guided ion beam tandem mass spectrometry (GIBMS) was used to measure the kinetic energy dependent product ion cross sections for reactions of the lanthanide metal praseodymium cation (Pr+) with O2, CO2, and CO and reactions of PrO+ with CO, O2, and Xe. PrO+ is formed through barrierless exothermic processes when the atomic metal cation reacts with O2 and CO2, whereas all other reactions are observed to be endothermic. Analyses of the kinetic energy dependences of these cross sections yield 0 K bond dissociation energies (BDEs) for PrO+, PrC+, PrCO+, and PrO2+. The 0 K BDE for PrO+ is determined to be 7.62 ± 0.09 eV from the weighted average of five independent thresholds. This value is combined with the well-established ionization energy (IE) of Pr to indicate an exothermicity of the chemi-ionization reaction, Pr + O → PrO+ + e−, of 2.15 ± 0.09 eV. Additionally, BDEs of Pr+–C, OPr+–O, and Pr+–CO are determined to be 2.97 ± 0.10. 2.47 ± 0.11, and 0.31 ± 0.07 eV. Theoretical Pr+–O, Pr+–C, OPr+–O, and Pr+–CO BDEs are calculated for comparison with experimental values. The Pr+–O BDE is underestimated at the B3LYP and PBE0 level of theory but better agreement is obtained using the coupled-cluster with single, double, and perturbative triple excitations, CCSD(T), level. Density functional theory approaches yield better agreement for the BDEs of Pr+–C, OPr+–O, and Pr+–CO.

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Methionine (Met) cationized with Zn2+, forming Zn (Met-H)+(ACN) where ACN = acetonitrile, Zn (Met-H)+, and ZnCl+(Met), as well as Cd2+, forming CdCl+(Met), were examined by infrared multiple photon dissociation (IRMPD) action spectroscopy using light generated from the FELIX free electron laser. A series of low-energy conformers for each complex was found using quantum-chemical calculations in order to identify the structures formed experimentally. For all four complexes, spectral comparison indicated that the main binding motif observed is a charge solvated, tridentate structure where the metal center binds to the backbone amino group nitrogen, backbone carbonyl oxygen (where the carboxylic acid is deprotonated in two of the Zn2+ complexes), and side-chain sulfur. For all species, the predicted ground structures reproduce the experimental spectra well, although low-lying conformers characterized by similar binding motifs may also contribute in each system. The current work provides valuable information regarding the binding interaction between Met and biologically relevant metals. Further, the comparison between the current work and previous analyses involving alkali metal cationized Met as well as cysteine (the other sulfur containing amino acid) cationized with Zn2+ and Cd2+ allows for the elucidation of important metal dependent trends associated with physiologically important metal-sulfur binding.