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Gas-phase interactions between Ba2+ and deprotonated cytosine (C(−H)) were studied in [C(−H)Ba]+ and [C(−H)BaC]+ complexes by IRMPD spectroscopy coupled to tandem mass-spectrometry in combination with DFT calculations. For the [C(−H)BaC]+ complex only one [C(−H)KAN1O−Ba-Canti]+ isomer was found, although the presence of another structure cannot be excluded. This isomer features a central tetracoordinated Ba2+ that simultaneously interacts with keto-amino [C(−H)]− deprotonated on N1 and neutral keto-amino C. Both moieties are in different planes as a consequence of an additional NH…O=C hydrogen bond between C and [C(−H)]−. A sequential IRMPD dynamics is observed in this complex. For the [C(−H)Ba]+ complex produced by electrospray ionization two isomers ([C(−H)KAN1OBa]+ and [C(−H)KAN3OBa]+) were identified, in which Ba2+ interacts simultaneously with the C=O group and the N1 or N3 atom of the keto-amino [C(−H)]−, respectively. A comparison with the related [C(−H)Pb]+ complex (J. Y. Salpin et al., Chem. Phys. Chem. 2014, 15, 2959–2971) is also presented. Fil: Cruz Ortiz, Andres Felipe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Taccone, Martín Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Maitre, Philippe. Universite de Paris XI. Laboratoire de Chimie Physique; Francia Fil: Rossa, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Pino, Gustavo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

Lanthanide triflates are effective Lewis acid catalysts in reactions involving carbonyl compounds due to their high oxophilicity and water stability. Despite the growing interest, the identity of the catalytic species formed in lanthanide catalysed reactions is still unknown. We have therefore used mass spectrometry and ion spectroscopy to intercept and characterize the intermediates in a reaction catalysed by ytterbium and dysprosium triflates. We were able to identify a number of lanthanide intermediates formed in a simple condensation reaction between a C-acid and an aldehyde. Results show correlation between the reactivity of lanthanide complexes and their charge state and suggest that the triply charged complexes play a key role in lanthanide catalysed reactions. Spectroscopic data of the gaseous ions accompanied by theoretical calculations reveal that the difference between catalytic efficiencies of ytterbium and dysprosium ions can be explained by their different electrophilicity.

A heteroditopic ligand associated with a calix[6]arene scaffold bearing a tris(imidazole) coordinating site at its small rim and an amine/pyridine ligand at its large rim has been prepared, and its regioselective coordination to ZnII at the small rim and FeII in the amine/pyridine ligand has been achieved. The heterodinuclear complex obtained displays an overall cone conformation capped by the tris(imidazole)ZnII moiety and bears a non-heme FeII complex at its base. Each of the metal centers exhibits one labile position, allowing the coordination inside the cavity of a guest alkylamine at ZnII and the generation of reaction intermediates (FeIII (OOH) and FeIV O) at the large rim. A dependence between the chain length of the encapsulated alkylamine and the distribution of FeIII (OOH) intermediates and FeIII (OMe) is observed. In addition, it is shown that the generation of the FeIV O intermediate is enhanced by addition of the alkylamine guest. Hence, this supramolecular system gathers the three levels of reactivity control encountered in oxidoreductases: i) control of the FeII redox properties through its first coordination sphere, allowing us to generate high valent reactive species; ii) control of guest binding through a hydrophobic funnel that drives its alkyl chain next to the reactive iron complex, thus mimicking the binding pocket of natural systems; iii) guest-modulated reactivity of the FeII center towards oxidants.

The formation and investigation of sulfur-based cysteine radicals cationized by a group 1A metal ion or Ag+ in the gas phase are reported. Gas-phase ion-molecule reactions (IMR) and infrared multiple-photon dissociation (IRMPD) spectroscopy revealed that the Li+ , Na+ , and K+ adducts of the cysteine radical remain S-based radicals as initially formed. Theoretical calculations for the three alkali metal ions found that the lowest-energy isomers are Cα -based radicals, but they are not observed experimentally owing to the barriers associated with the hydrogen-atom transfer. A mechanism for the S-to-Cα radical rearrangement in the metal ion complexes was proposed, and the relative energies of the associated energy barriers were found to be Li+ >Na+ >K+ at all levels of theory. Relative to the B3LYP functional, other levels of calculation gave significantly higher barriers (by 35-40 kJ mol-1 at MP2 and 44-47 kJ mol-1 at the CCSD level) using the same basis set. Unlike the alkali metal adducts, the cysteine radical/Ag+ complex rearranged from the S-based radical to an unreactive species as indicated by IMRs and IRMPD spectroscopy. This is consistent with the Ag+ /cysteine radical complex having a lower S-to-Cα radical conversion barrier, as predicted by the MP2 and CCSD levels of theory.

Characterization of e-N-acetylated lysine containing peptides, one of the most prominent post-translational modifications of proteins, is an important goal for tandem mass spectrometry experiments. A systematic study for the fragmentation reactions of b ions derived from e-N-acetyllysine containing model octapeptides (KAcYAGFLVG and YAKAcGFLVG) has been examined in detail. Collision-induced dissociation (CID) mass spectra of bn (n = 4–7) fragments of e-N-acetylated lysine containing peptides are compared with those of N-terminal acetylated and doubly acetylated (both e-N and N-terminal) peptides, as well as acetyl-free peptides. Both direct and nondirect fragments are observed for acetyl-free and singly acetylated (e-N or N-terminal) peptides. In the case of e-N-acetylated lysine containing peptides, however, specific fragment ions (m/z 309, 456, 569 and 668) are observed in CID mass spectra of bn (n = 4–7) ions. The CID mass spectra of these four ions are shown to be identical to those of selected protonated C-terminal amidated peptides. On this basis, a new type of rearrangement chemistry is proposed to account for the formation of these fragment ions, which are specific for e-N-acetylated lysine containing peptides. Consistent with the observation of nondirect fragments, it is proposed that the b ions undergo head-to-tail macrocyclization followed by ring opening. The proposed reaction pathway assumes that bn (n = 4–7) of e-N-acetylated lysine containing peptides has a tendency to place the KAc residue at the C-terminal position after macrocyclization/reopening mechanism. Then, following the loss of CO, it is proposed that the marker ions are the result of the loss of an acetyllysine imine as a neutral fragment. Copyright © 2014 John Wiley & Sons, Ltd.

International audience; Gas-phase infrared spectra of deprotonated phosphorylated amino acids ([pAA-H](-))-phosphoserine ([pSer-H](-)), phosphothreonine ([pThr-H](-)), and phosphotyrosine ([pTyr-H](-))-and of the dihydrogen phosphate anion H(2)PO(4)(-) have been recorded in the mid-IR region (650-2000 cm(-1)) under tandem mass spectrometry conditions. The experimental setup involved a Paul ion trap equipped with an electrospray ionization source coupled with a tunable free electron laser (FEL). Spectral assignment of the observed IRMPD bands and identification of the vibrational signatures of the phosphorylation have been performed by comparison with DFT calculations. The H(2)PO(4)(-) anion has been used as a simple model of a free deprotonated phosphate group, helping the identification of the IR signatures of phosphorylation. Our results show that deprotonation occurs on the phosphate group for the three amino acids. A comparison between the deprotonated and protonated phosphorylated amino acids is reported for the most important vibrational features.

International audience; The gas-phase structures of protonated uracil, thymine, and cytosine are probed by using mid-infrared multiple-photon dissociation (IRMPD) spectroscopy performed at the Free Electron Laser facility of the Centre Laser Infrarouge dOrsay (CLIO), France. Experimental infrared (IR) spectra are recorded for ions that were generated by electrospray ionization, isolated, and then irradiated in a quadrupole ion trap; the results are compared to the calculated infrared absorption spectra of the different low-lying isomers (computed at the B3LYP/6-31++G(d,p) level). For each protonated base, the global energy minimum corresponds to an enolic tautomer, whose infrared absorption spectrum matched very well with the experimental IRMPD spectrum, with the exception of a very weak IRMPD signal observed at about 1800 cm-1 in the case of the three protonated bases. This signal is likely to be the signature of the second-energy-lying oxo tautomer. We thus conclude that within our experimental conditions, two tautomeric ions are formed which coexist in the quadrupole ion trap.

Coordination complexes of the magnesium nitrate cation with water [MgNO(3)(H(2)O)(n)](+) up to n=7 are investigated by experiment and theory. The fragmentation patterns of [MgNO(3)(H(2)O)(n)](+) clusters generated via electrospray ionization indicate a considerable change in stability between n=3 and 4. Further, ion-molecule reactions of mass-selected [MgNO(3)(H(2)O)(n)](+) cations with D(2)O reveal the occurrence of consecutive replacement of water ligands by heavy water, and in this respect the complexes with n=4 and 5 are somewhat more reactive than their smaller homologs with n=1-3 as well as the larger clusters with n=6 and 7. For the latter two ions, the theory suggests the existence of isomers, such as complexes with monodentate nitrato ligands as well as solvent-separated ion pairs with a common solvation shell. The reactions observed and the ion thermochemistry are discussed in the context of ab initio calculations, which also reveal the structures of the various hydrated cation complexes.

The systems Fe(H2O)n+/COH2O and Fe(CO)n+/COH2O (n = 1 and 2) were investigated in a triple cell Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Using mixtures of CO with a very small amount of water, the ligand exchange equilibrium was reached, allowing experimental determination of the relevant equilibrium constants and free energies of reaction. Quantum chemical calculations at the B3LYP level of theory on the reactant and product species allowed us to determine the entropic terms and to derive the relative bond energies of CO and H2O in the mono- and bis-ligated complexes. For n = 1, H2O is more strongly bound to Fe+ than CO by 4.1 ± 1.6 kJ·mol−1 at 298 K. For n = 2, at the same temperature, H2O is more strongly bound than CO to (H2O)Fe+ by 7.6 ± 1.6 kJ·mol−1, and to (CO)Fe+ by more than 20.1 kJ·mol−1. Copyright © 2003 John Wiley & Sons, Ltd.

Definitely different: the path towards sorting out a long-standing dichotomy in carbocation chemistry is disclosed by infrared multiple photon dissociation spectroscopy of tropylium and benzylium isomers of C(8)H(9)(+) ions.

Gas phase mid-infrared spectroscopy of molecular ions can nowadays be performed with high performance mass spectrometers coupled to free electron lasers (FEL). The wide and continuous tunability of highly intense FELs in the mid-infrared region can be exploited for performing infrared multiple photon dissociation (IRMPD) spectroscopy of molecular ions. This review will focus on gas phase IRMPD spectroscopic investigations aiming at probing the structure and the reactivity of transition metal complexes. The performance of infrared spectroscopy for characterizing the coordination mode of polydentate ligands and the spin state of the metal will be illustrated. Infrared spectroscopy has also been exploited to probe the reactivity of metal complexes, and a special attention will be given to the infrared spectroscopy of reactive intermediates.