Search

Glutathione is a biologically abundant and redox active tripeptide that serves to protect cells from oxidative stress and rid the body of toxic heavy metals. The present study examines the coordination complexes of glutathione (GSH) with metals that are central to redox processes in biology, Zn, Cu, and Fe, using infrared multiple photon dissociation (IRMPD) action spectroscopy with a free electron laser. For all three metals, a complex between the metal dication and deprotonated GSH was formed, M(GSHH)+. The experimental IRMPD spectra were compared to scaled harmonic vibrational spectra calculated at the MP2/6-311+G(d,p) level of theory after thorough exploration of conformational space using a simulated annealing protocol. Interestingly, spectra calculated at the B3LYP or oB97XD level do not match experiment as well. These findings offer the first gas-phase spectroscopic evidence for how the biologically relevant metal ions coordinate with glutathione. There are spectral features that are common to all three metals, however, noting the differences in the strengths of the common features between the three metals enables an assessment of the preference or specificity that each individual metal has for a given coordination site. Additionally, all three metals form structures where the deprotonated thiol of the cysteine side chain coordinates with the metal center, which is consistent with the involvement of the thiol site in biologically relevant redox chemistry. Introduction Glutathione (L-g-glutamyl-L-cysteinylglycine, GSH) is a biologically abundant tripeptide. [ABSTRACT FROM AUTHOR]

The SmO+ bond energy has been measured by monitoring the threshold for photodissociation of the cryogenically cooled ion. The action spectrum features a very sharp onset, indicating a bond energy of 5.596 ± 0.004 eV. This value, when combined with the literature value of the samarium ionization energy, indicates that the chemi-ionization reaction of atomic Sm with atomic oxygen is endothermic by 0.048 ± 0.004 eV, which has important implications on the reactivity of Sm atoms released into the upper atmosphere. The SmO+ ion was prepared by electrospray ionization followed by collisional breakup of two different precursors and characterized by the vibrational spectrum of the He-tagged ion. The UV photodissociation threshold is similar for the 10 K bare ion and the He tagged ion, which rules out the possible role of metastable electronically excited states. Reanalysis and remeasurement of previous reaction kinetics experiments that are dependent on D0(SmO+) are included, bringing all experimental results in accord. [ABSTRACT FROM AUTHOR]

The solution kinetics of a proton-coupled electron transfer reaction involving two-electron oxidation of a Ru compound with concomitant transfer of two protons to a quinone derivative have been interpreted to indicate the formation of a long-lived intermediate between the reactants. We characterize the ionic reactants, products, and an entrance channel reaction complex in the gas phase using high-resolution mass spectrometry augmented by cryogenic ion IR photodissociation spectroscopy. Collisional activation of this trapped entrance channel complex does not drive the reaction to products but rather yields dissociation back to reactants. Electronic structure calculations indicate that there are four low-lying isomeric forms of the non-covalently bound complex. Comparison of their predicted vibrational spectra with the observed band pattern indicates that the C=O groups of the ortho-quinone attach to protons on two different –NH2 groups of the reactant scaffold, exhibiting strong O–H–N contact motifs. Since collisional activation does not lead to the products observed in the liquid phase, these results indicate that the reaction most likely proceeds through reorientation of the H-atom donor ligand about the metal center. [ABSTRACT FROM AUTHOR]

While the strong axial U＝O bonds confer high stability and inertness to UO22+, it has been shown that the axial oxo ligands can be eliminated or replaced in the gas-phase using collision-induced dissociation (CID) reactions. We report here tandem mass spectrometry experiments initiated with a gas-phase complex that includes UO22+ coordinated by a 2,6-difluorobenzoate ligand. After decarboxylation to form a difluorophenide coordinated uranyl ion, [UO2(C6F2H3)]+, CID causes elimination of CO, and then CO and C2H2 in sequential dissociation steps, to leave a reactive uranium fluoride ion, [UF2(C2H)]+. Reaction of [UF2(C2H)]+ with CH3OH creates [UF2(OCH3)]+, [UF(OCH3)2]+ and [UF(OCH3)2(CH3OH)]+. Cleavage of C–O bonds within these species results in the elimination of methyl cation (CH3+). Subsequent CID steps convert [UF(OCH3)2]+ to [UO2(F)]+ and similarly, [U(OCH3)3]+ to [UO2(OCH3)]+. Our experiments show removal of both uranyl oxo ligands in "top-down" CID reactions and replacement in "bottom-up" ion–molecule and dissociation steps. [ABSTRACT FROM AUTHOR]

We recently reported a detailed investigation of the collision-induced dissociation (CID) of [UO2(NO3)3]- and [UO2(NO3)2(O2)]- in a linear ion trap mass spectrometer (J. Mass Spectrom. DOI:10.1002/jms.4705). Here, we describe the CID of [UO2(NO3) (O2)]- which is created directly by ESI, or indirectly by simple elimination of O2 from [UO2(NO3)(O2)2]-. cid of [UO2(NO3)(O2)]- creates product ions as at m/z 332 and m/z 318. The former may be formed directly by elimination of O2, while the latter required decomposition of a nitrate ligand and elimination of NO2. DFT calculations identify a pathway by which both product ions can be generated, which involves initial isomerization of [UO2(NO3)(O2)]- to create [UO2(O)(NO2)(O2)]-, from which elimination of NO2 or O2 will leave [UO2(O)(O2)]- or [UO2(O)(NO2)]-, respectively. For the latter product ion, the composition assignment of [UO2(O)(NO2)]- rather than [UO2(NO3)]- is supported by ion-molecule reaction behavior, and in particular, the fact that spontaneous addition of O2, which is predicted to be the dominant reaction pathway for [UO2(NO3)]- is not observed. Instead, the species reacts with H2O, which is predicted to be the favored pathway for [UO2(O)(NO2)]-. This result in particular demonstrates the utility of ion-molecule reactions to assist the determination of ion composition. As in our earlier study, we find that ions such as [UO2(O) (NO2)]- and [UO2(O)(O2)]- form H2O adducts, and calculations suggest these species spontaneously rearrange to create dihydroxides. [ABSTRACT FROM AUTHOR]

We recently reported a detailed investigation of the collision-induced dissociation (CID) of [UO2(NO3)3]- and [UO2(NO3)2(O2)]- in a linear ion trap mass spectrometer (J. Mass Spectrom. DOI:10.1002/jms.4705). Here, we describe the CID of [UO2(NO3) (O2)]- which is created directly by ESI, or indirectly by simple elimination of O2 from [UO2(NO3)(O2)2]-. cid of [UO2(NO3)(O2)]- creates product ions as at m/z 332 and m/z 318. The former may be formed directly by elimination of O2, while the latter required decomposition of a nitrate ligand and elimination of NO2. DFT calculations identify a pathway by which both product ions can be generated, which involves initial isomerization of [UO2(NO3)(O2)]- to create [UO2(O)(NO2)(O2)]-, from which elimination of NO2 or O2 will leave [UO2(O)(O2)]- or [UO2(O)(NO2)]-, respectively. For the latter product ion, the composition assignment of [UO2(O)(NO2)]- rather than [UO2(NO3)]- is supported by ion-molecule reaction behavior, and in particular, the fact that spontaneous addition of O2, which is predicted to be the dominant reaction pathway for [UO2(NO3)]- is not observed. Instead, the species reacts with H2O, which is predicted to be the favored pathway for [UO2(O)(NO2)]-. This result in particular demonstrates the utility of ion-molecule reactions to assist the determination of ion composition. As in our earlier study, we find that ions such as [UO2(O) (NO2)]- and [UO2(O)(O2)]- form H2O adducts, and calculations suggest these species spontaneously rearrange to create dihydroxides. [ABSTRACT FROM AUTHOR]

Electrospray ionization (ESI) can produce a wide range of gas-phase uranyl (UO2 2+) complexes for tandem mass spectrometry studies of intrinsic structure and reactivity. We describe here the formation and collision-induced dissociation (CID) of [UO2(NO3)3]- and [UO2(NO3)2(O2)]-. Multiple-stage CID experiments reveal that the complexes dissociate in reactions that involve elimination of O2, NO2, or NO3, and subsequent reactions of interesting uranyl-oxo product ions with (neutral) H2O and/or O2 were investigated. Density functional theory (DFT) calculations reproduce experimental results and show that dissociation of nitrate ligands, with ejection of neutral NO2, is favored for both [UO2(NO3)3]- and [UO2(NO3)2(O2)]-. DFT calculations also suggest that H2O adducts to products such as [UO2(O)(NO3)]- spontaneously rearrange to create dihydroxides and that addition of O2 is favored over addition of H2O to formally U(V) species. [ABSTRACT FROM AUTHOR]

Electrospray ionization (ESI) can produce a wide range of gas-phase uranyl (UO2 2+) complexes for tandem mass spectrometry studies of intrinsic structure and reactivity. We describe here the formation and collision-induced dissociation (CID) of [UO2(NO3)3]- and [UO2(NO3)2(O2)]-. Multiple-stage CID experiments reveal that the complexes dissociate in reactions that involve elimination of O2, NO2, or NO3, and subsequent reactions of interesting uranyl-oxo product ions with (neutral) H2O and/or O2 were investigated. Density functional theory (DFT) calculations reproduce experimental results and show that dissociation of nitrate ligands, with ejection of neutral NO2, is favored for both [UO2(NO3)3]- and [UO2(NO3)2(O2)]-. DFT calculations also suggest that H2O adducts to products such as [UO2(O)(NO3)]- spontaneously rearrange to create dihydroxides and that addition of O2 is favored over addition of H2O to formally U(V) species. [ABSTRACT FROM AUTHOR]

The reduction of carbon dioxide to oxalate has been studied by experimental Collisionally Induced Dissociation (CID) and vibrational characterization of the alkali metal oxalates, supplemented by theoretical electronic structure calculations. The critical step in the reductive process is the coordination of CO2 to an alkali metal anion, forming a metal carbonite MCO2− able to subsequently receive a second CO2 molecule. While the energetic demand for these reactions is generally low, we find that the degree of activation of CO2 in terms of charge transfer and transition state energies is the highest for lithium and systematically decreases down the group (M = Li–Cs). This is correlated to the strength of the binding interaction between the alkali metal and CO2, which can be related to the structure of the oxalate moiety within the product metal complexes evolving from a planar to a staggered conformer with increasing atomic number of the interacting metal. Similar structural changes are observed for crystalline alkali metal oxalates, although the C2O42− moiety is in general more planar in these, a fact that is attributed to the increased number of interacting alkali metal cations compared to the gas-phase ions. [ABSTRACT FROM AUTHOR]