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The structure of the a (4) ion from protonated YGGFL was studied in a quadrupole ion trap mass spectrometer by 'action' infrared spectroscopy in the 1000-2000 cm(-1) ('fingerprint') range using the CLIO Free Electron Laser. The potential energy surface (PES) of this ion was characterized by detailed molecular dynamics scans and density functional theory calculations exploring a large number of isomers and protonation sites. IR and theory indicate the a (4) ion population is primarily populated by the rearranged, linear structure proposed recently (Bythell et al., J. Am. Chem. Soc. 2010, 132, 14766). This structure contains an imine group at the N- terminus and an amide group -CO-NH(2) at the C-terminus. Our data also indicate that the originally proposed N-terminally protonated linear structure and macrocyclic structures (Polfer et al., J. Am. Chem. Soc. 2007, 129, 5887) are also present as minor populations. The clear differences between the present and previous IR spectra are discussed in detail. This mixture of gas-phase structures is also in agreement with the ion mobility spectrum published by Clemmer and co-workers recently (J. Phys. Chem. A 2008, 112, 1286). Additionally, the calculated cross-sections for the rearranged structures indicate these correspond to the most abundant (and previously unassigned) feature in Clemmer's work.

Model ferric heme nitrosyl complexes, [Fe(TPP)(NO)](+) and [Fe(TPFPP)(NO)](+), where TPP is the dianion of 5,10,15,20-tetrakis-phenyl-porphyrin and TPFPP is the dianion of 5,10,15,20-tetrakis-pentafluorophenyl-porphyrin, have been obtained as isolated species by the gas phase reaction of NO with [Fe(III)(TPP)](+) and [Fe(III) (TPFPP)](+) ions delivered in the gas phase by electrospray ionization, respectively. The so-formed nitrosyl complexes have been characterized by vibrational spectroscopy also exploiting (15)N-isotope substitution in the NO ligand. The characteristic NO stretching frequency is observed at 1825 and 1859 cm(-1) for [Fe(III)(TPP)(NO)](+) and [Fe(III)(TPFPP)(NO)](+) ions, respectively, providing reference values for genuine five-coordinate Fe(III)(NO) porphyrin complexes differing only for the presence of either phenyl or pentafluorophenyl substituents on the meso positions of the porphyrin ligand. The vibrational assignment is aided by hybrid density functional theory (DFT) calculations of geometry and electronic structure and frequency analysis which clearly support a singlet spin electronic state for both [Fe(TPP)(NO)](+) and [Fe(TPFPP)(NO)](+) complexes. Both TD-DFT and CASSCF calculations suggest that the singlet ground state is best described as Fe(II)(NO(+)) and that the open-shell AFC bonding scheme contribute for a high-energy excited state. The kinetics of the NO addition reaction in the gas phase are faster for [Fe(III)(TPFPP)](+) ions by a relatively small factor, though highly reliable because of a direct comparative evaluation. The study was aimed at gaining vibrational and reactivity data on five-coordinate Fe(III)(NO) porphyrin complexes, typically transient species in solution, ultimately to provide insights into the nature of the Fe(NO) interaction in heme proteins.

The species formally obtained from the protonation of sulfuric acid is examined as a naked ion in the gas phase, and its IR spectral features are reported. The major fundamental vibrational bands have been acquired in both the 700−1700 and the 3400−3800 cm−1 spectral ranges using state of the art equipment at the CLIO facility, namely, FT-ICR mass spectrometry coupled to the tunable IR beam of either a free electron laser or a tabletop optical parametric oscillator/amplifier (OPO/OPA) laser source. In this way, the structural features of the sampled ion could be ascertained and found to conform to the most stable isomer on the [H3,S,O4]+ potential energy surface. The experimental IR multiple photon dissociation (IRMPD) spectrum is in fact consistent with the IR spectrum calculated for the trihydroxyoxosulfonium cation OS(OH)3+, providing a conclusive structural probe.

Cationic zirconocene complexes are active species in Ziegler-Natta catalysis for olefin polymerization. Their structure and metal-ligand bond strength strongly influence their activity. In the present work, the infrared multiphoton dissociation (IRMPD) spectrum of mass selected Zr(C(5)H(5))(2)(OH)(CH(3)CN)(+) cations was obtained in the 300-1500 cm(-1) fingerprint range by coupling a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer equipped with an electrospray ionization (ESI) source and the infrared free electron laser (IR-FEL) at the Centre Laser Infrarouge d'Orsay (CLIO). The experimental efforts are complemented by quantum chemical calculations at the MP2 and B3LYP levels using the 6-311G* basis set. Vibrational assignments of transitions observed in the IRMPD spectra to modes of the Zr-O-H, C(5)H(5), and CH(3)CN moieties are based on comparison to calculated linear absorption spectra. Both the experimental data and the calculations provide unprecedented information about structure, metal-ligand bonding, charge distribution, and binding energy of the complex.

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; Lasso peptides are natural products characterized by a mechanically interlocked topology. The conformation of lasso peptides has been probed in the gas phase using ion mobility–mass spectrometry (IM–MS) which showed differences in the lasso and their unthreaded branched-cyclic topoisomers depending on the ion charge states. To further characterize the evolution of gas phase conformations as a function of the charge state and to assess associated changes in the hydrogen bond network, infrared multiple photon dissociation (IRMPD) action spectroscopy was carried out on two representative lasso peptides, microcin J25 (MccJ25) and capistruin, and their branched-cyclic topoisomers. For the branched-cyclic topoisomers, spectroscopic evidence of a disruption of neutral hydrogen bonds were found when comparing the 3+ and 4+ charge states. In contrast, for the lasso peptides, the IRMPD spectra were found to be similar for the two charge states, suggesting very little difference in gas phase conformations upon addition of a proton. The IRMPD data were thus found consistent and complementary to IM–MS, confirming the stable and compact structure of lasso peptides in the gas phase.

Protonated furan (C4H5O+, furanH+) and protonated pyrrole (C4H6N+, pyrroleH+) are generated by chemical ionization of the respective parent molecules in the cell of an FT-ICR mass spectrometer using CH5+/C2H5+ as protonating agents. The protonation site is investigated by resonant infrared multiphoton dissociation (IRMPD) spectroscopy in the 900–1700 cm−1 fingerprint range employing the free electron laser (FEL) at the Centre Laser Infrarouge Orsay (CLIO). Comparison with quantum chemical calculations at the B3LYP/6-311G(2df, 2pd) level of theory demonstrates unambiguously that only the Cα protonated isomers are observed, which correspond to the global minima on the potential energy surfaces of both protonated heterocyclic molecules. Spectroscopic features corresponding to protonation at the Cβ atom or at the heteroatom are not detected. The IRMPD spectra correspond to the first spectroscopic identification of both protonated heterocyclic molecules in the gas phase. During the course of the experiments, the IRMPD spectrum of the furan radical cation (C4H4O+, furan+) has been detected as well. Comparison of the IR spectra of the neutral molecules with the IRMPD spectra of the radical cation and the protonated species reveals the effects of both ionization and protonation on the structural properties of these fundamental heterocyclic molecules.

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.

International audience; The local structure of phosphorylated residues in peptides and proteins may have a decisive role on their functional properties. Recent IRMPD experiments have started to provide spectroscopic signatures of such structural details; however, a proper modeling of these signatures beyond the harmonic approximation, taking into account temperature and entropic effects, is still lacking. In order to bridge this gap, DFT-based Car-Parrinello molecular dynamics simulations have been carried out for the first time on a phosphorylated amino acid, gaseous deprotonated phosphoserine. It is found that all vibrational signatures are successfully reproduced, and new deconvolution techniques enable the assignment of the vibrational spectrum directly from the dynamics results and the comparison of vibrational modes at several temperatures. The lowest energy structure is found to involve a strong hydrogen bond between the deprotonated phosphate and the acid with relatively small free energy barriers to proton transfer; however, we find that proton shuttling between the two sites does not occur frequently. Anharmonicities turn out to be important to reproduce the frequencies and shapes of several experimental bands. Comparison of room temperature and 13 K, effectively harmonic dynamics, allows insight to be obtained into vibrational anharmonicities. In particular, a significant blue-shift and broadening of the C=O stretching frequency from 13 to 300 K can be ascribed to intrinsic anharmonicity rather than to anharmonic coupling to other modes. On the other hand, significant couplings are found for the stretching motions of the hydrogen bonded P-O bond and of the free P-OH bond, mainly with modes within the phosphate group.

The gas-phase structures of cytosine–Ag+ [CAg]+ and cytosine–Ag+–H2O [CAg–H2O]+ complexes have been studied by mass-selected infrared multiphoton dissociation (IRMPD) spectroscopy in the 900–1800 cm−1 spectral region using the Free Electron Laser facility in Orsay (CLIO). The IRMPD experimental spectra have been compared with the calculated IR absorption spectra of the different low-lying isomers (computed at the DFT level using the B3LYP functional and the 6-311G++(d,p) basis set for C, H, N and O atoms and the Stuttgart effective core potential for Ag). For the [CAg]+ complex, only one isomer with cytosine in the keto-amino (KA) tautomeric form and Ag+ interacting simultaneously with the C(2)[double bond, length as m-dash]O(7) group and N(3) of cytosine was observed. However, the mono-hydration of the complex in the gas phase leads to the stabilization of a two quasi-isoenergetic structure of the [CAg–H2O]+ complex, in which Ag+ interacts with the O atom of the water molecule and with the N(3) or C(2)[double bond, length as m-dash]O(7) group of cytosine. The relative populations of the two isomers determined from the IRMPD kinetics plot are in good agreement with the calculated values. Comparison of these results with those of protonated cytosine [CH]+ and its mono-hydrated complex [CH–H2O]+ shows some interesting differences between H+ and Ag+. In particular, while a single water molecule catalyzes the isomerization reaction in the case of [CH–H2O]+, it is found that in the case of [CAg–H2O]+ the addition of water leads to the stabilization of two isomers separated by small energy barrier (0.05 eV). Fil: Berdakin, Matias. 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: Steinmetz, Vincent. Université Paris Sud; Francia Fil: Maitre, Philippe. Université Paris Sud; Francia 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

Diethyl carbonate and dimethyl carbonate are prototype examples of eco-friendly solvents used in lithium-ion batteries. Nevertheless, their degradation products affect both the battery performance and its safety. Therefore, it is of paramount importance to understand the reaction mechanisms involved in the ageing processes. Among those, redox processes are likely to play a critical role. Here we show that radiolysis is an ideal tool to generate the electrolytes degradation products. The major gases detected after irradiation (H2, CH4, C2H6, CO and CO2) are identified and quantified. Moreover, the chemical compounds formed in the liquid phase are characterized by different mass spectrometry techniques. Reaction mechanisms are then proposed. The detected products are consistent with those of the cycling of Li-based cells. This demonstrates that radiolysis is a versatile and very helpful tool to better understand the phenomena occurring in lithium-ion batteries., The degradation of organic solvents used in lithium-ion batteries reduces battery performance. Here, the authors present a radiolysis technique which is not only more efficient than conventional thermally activated ageing methods, but also allows mechanistic analysis of the degradation process.

Differential Ion Mobility Spectrometry (DIMS) provides orthogonal separation to mass spectrometry, and DIMS combined with the high sensitivity of a quadrupole ion-trap is shown to be useful for the separation and identification of saccharides. A comprehensive analysis of the separation of anomers (α- and β-methylated glucose) and epimers (α-methylated glucose and mannose) ionized with Li(+), Na(+), and K(+) is performed. DIMS separation is found to be better for saccharides cationized with the two latter species. The corresponding resolving power for the two glucose anomers with Na(+) is found to be very close to the corresponding drift-tube IMS value. The lithiated complexes are investigated further using a combination of infrared spectroscopy integrated to ion-trap mass spectrometry and quantum chemical calculations. Together with DIMS, consistent results are obtained. It is found that two competing structural motifs might be at play, depending on the subtle balance between the maximization of the coordination of the metal cation and the intrinsic conformational energetics of the saccharide, which is for a large part driven by hydrogen bonding. The comparison of simulated and observed spectra clearly shows that a band at ∼3400 cm(-1) is specific to a structural motif found in the lithiated glucose complexes, which could explain the trends observed in the DIMS spectra of the saccharide complexes. It is shown that DIMS-MS/MS using wavelength specific IR activation would provide a new orthogonal dimension to mass spectrometry.

Gaseous [C7H7O]+ ions have been formed by protonation of benzaldehyde or tropone (2,4,6-cycloheptatrienone) in the cell of an FT-ICR mass spectrometer using C2H5(+) as a Brønsted acid. The so-formed species have been assayed by infrared multiphoton dissociation (IRMPD) using the free electron laser (FEL) at the CLIO (Centre Laser Infrarouge Orsay) facility. The IRMPD features are quite distinct for ions from the two different precursors, pointing to two different isomers. A number of potential structures for [C7H7O]+ ions have been optimized at the B3LYP/6-31+G(d,p) level of theory, and their relative energies and IR spectra are reported. On this basis, the IRMPD spectra of [C7H7O]+ ions are found to display features characteristic of O-protonated species, with no evidence of any further skeletal rearrangements. The so-formed ions are thus hydroxy-substituted benzylium and tropylium ions, respectively, representative members of the benzylium/tropylium ion family. The IRMPD assay using the FEL laser light has allowed their unambiguous discrimination where other mass spectrometric techniques have yielded a less conclusive answer.

The protonated leucine methyl ester structure was probed using mid-infrared multiphoton dissociation (IRMPD) spectroscopy performed at CLIO, the Orsay Free Electron Laser facility. A first experimental spectrum was obtained with a Fourier-transform ion-cyclotron-resonance mass spectrometer with ions generated through a MALDI process. A second spectrum was recorded with ions generated using ElectroSpray Ionisation and trapped in a Paul ion-trap. These two experimental spectra are analyzed and compared with infrared absorption spectra derived from hybrid density functional theory calculations. The two IRMPD spectra are in excellent agreement, although the one recorded with the Paul ion-trap presents a better resolution with an fwhm of the IRMPD bands of 20–25 cm −1 . Comparison with the calculated IR absorption spectra clearly shows that only the lowest energy isomer is formed under both experimental conditions. The CO stretch, together with two vibrational modes of the ammonium group were the three infrared signatures identified in the photon energy range explored here.

Infrared multiple photon dissociation spectra for the chloride ion solvated by either water, methanol or ethanol have been recorded using an FTICR spectrometer coupled to a free-electron laser, and are presented here along with assignments to the observed bands. The assignments made to the Cl(-)/H(2)O, Cl(-)(CH(3)OH), and Cl(-)(CH(3)CH(2)OH) spectra are based on comparison with the neutral H(2)O, CH(3)OH, and CH(3)CH(2)OH spectra, respectively. This work confirms that a band observed around 1400 cm(-1) in the Cl(-)(H(2)O) spectrum is not due to the Ar tag in Ar predissociation spectra. The carrier of this band is, most likely, the first overtone of the OHCl bend. Based on the position of the overtone in the IRMPD spectrum, 1375 cm(-1), the fundamental must occur very close to 700 cm(-1) and observation of this band should aid theoretical treatments of the spectrum of this complex. B3LYP/6-311++G(2df,2pd) calculations are shown to reproduce the IRMPD spectra of all three solvated chloride species. They also predict that attaching one or two Ar atoms to the Cl(-)(H(2)O) complex results in a shift of no more than a few wavenumbers in the fundamental bands for the bare complex, in agreement with previous experiment. For both alcohol-Cl(-) complexes, the S(N)2 "backside attack" isomers are not observed and Cl(-) is predicted theoretically, and confirmed experimentally, to be bound to the hydroxyl hydrogen. For Cl(-)(CH(3)CH(2)OH), the trans and gauche conformers are similar in energy, with the gauche conformer predicted to be thermodynamically favoured. The experimental infrared spectrum agrees well with that predicted for the gauche conformer but a mixture of gauche and anti conformers cannot be ruled out based on the experimental spectra nor on the computed thermochemistry.

Protonated fluorobenzene ions (C6H6F+) are produced by chemical ionization of C6H5F in the cell of a FT-ICR mass spectrometer using either CH5+ or C2H5+. The resulting protonation sites are probed by IR multiphoton dissociation (IRMPD) spectroscopy in the 600-1700 cm-1 fingerprint range employing the free electron laser at CLIO (Centre Laser Infrarouge Orsay). Comparison with quantum chemical calculations reveals that the IRMPD spectra are consistent with protonation in para and/or ortho position, which are the thermodynamically favored protonation sites. The lack of observation of protonation at the F substituent, when CH5+ is used as protonating agent, is attributed to the low-pressure conditions in the ICR cell where the ions are produced. Comparison of the C6H6F+ spectrum with IR spectra of C6H5F and C6H7+ reveals the effects of both protonation and H F substitution on the structural properties of these fundamental aromatic molecules.

Using Fourier transform ion cyclotron resonance mass-spectrometry (FT-ICR-MS) in combination with infrared multiphoton dissociation (IRMPD) spectroscopy, at the free electron laser (FEL) facility CLIO in Orsay (France), we obtain the IR spectra, in the 900–1900 cm −1 range, of two model protonated dipeptides: N -acetyl-alanine (AcNH-Ala) and alanyl-histidine (Ala-His). By comparison with simulated spectra, calculated at the B3LYP/6-31++G ** level for many low-lying possible conformers of these two species, we are able to assign the position of the protonation site, on the acetyl oxygen for AcNH-Ala and on the side-chain imidazole nitrogen for Ala-His, and to obtain some more information on the low-lying equilibrium structures of these two species in the gas phase.

The infrared spectroscopy of gaseous ions Fe(CH3OCH3)2+ and Fe(CH3OCH2CH2OCH3)n+ (n=1–2) has been studied in the 800–2000 cm−1 energy range using the coupling of the free electron laser CLIO and an FTICR mass spectrometer, and compared to spectra calculated by ab initio quantum chemistry. The match between experimental and theoretical infrared spectra appears to be very good, the experimental spectra corresponding to the most stable structure predicted by the calculations. Characteristic absorption bands of functional groups have been evidenced, allowing this coupling to be a very powerful tool for structure elucidation in the gas phase.

International audience; The vibrational spectra of the gaseous sodium complexes of glycine (Gly-Na+) and proline (Pro-Na+) have been recorded in the spectral range 1150-2000 cm-1. The complexes were formed by matrix-assisted laser desorption-ionisation, introduced in the cell of a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer, and their infrared absorption spectra were recorded using photons of variable energy emitted by a free electron laser. Photon absorption was probed by the diminished intensity of the parent ion, due to its infrared induced dissociation into bare sodium cation and the free amino acid, and the appearance of Na+. The observed absorption bands are assigned using ab initio computations of the IR spectra of the lowest energy isomers in each case. They provide the first experimental evidence that the salt bridge isomer is formed in the case of Pro-Na+. In contrast, charge solvation by chelation of Na+ between nitrogen and the carbonyl oxygen seems to be most favorable for Gly-Na+, but a mixture of isomers cannot be ruled out in this case.

First example of coupling a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FTICR-MS) with an infrared Free Electron Laser (FEL) is presented. This experimental setup is ideally suited for the direct structural characterization of reactive polyatomic ions. Ultrasensitive measurements of the infrared vibrational spectrum of ionic reactive intermediate selectively prepared is allowed by the association of the high peak power of the FEL, its wide tunability, and the flexibility of FTICR-MS, where several mass selections and ion-molecule reactions can be combined. These possibilities are demonstrated in the case of Fe + complexes where two photofragmentation pathways compete. The resulting infrared spectrum is in excellent agreement, both with respect to the position and to the relative intensities of the infrared transitions, with predicted by ab initio electronic structure calculations. r 2003 Elsevier Science B.V. All rights reserved.

Analysis of the evolution of the binding energy to a late first-row transition metal cation M+ shows that the third ligand is significantly less strongly bound than the two first. The present study suggests that a new type of cluster-assisted reactions could be induced by the metal center when it is tri-coordinated. Cu+ complexes have been chosen as models for the quantum chemical calculations (density functional and post-Hartree–Fock ab initio). First, an emphasis is made on the analysis of the evolution of the binding energy as the coordination number n varies from 1 to 4 in Cu+(H2O)n and Cu+(CO)n. The evolution of the electronic repulsion between the σ donating orbitals of the ligands and the 3d orbitals is discussed in details. Second, we consider the successive substitution reactions of CO by H2O ligand from Cu+(CO)n (n=1–4). Our calculations suggest that rather than the simple substitution reaction of CO by ROR′ (R, R′=H, alkyl), formation of an acid or ester could occur in the coordination sphere of the metal. Whereas kinetics is likely to be unfavorable in the case of Cu+, such condensation reaction of ROR′ and CO could be observed with late first-row transition metal cations such as Fe+.

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.

International audience; Guanine radical cations are formed upon oxidation of DNA. Deoxyguanosine (dG) is used as a model, and the gas-phase infrared (IR) spectroscopic signature and gas-phase unimolecular and bimolecular chemistry of its radical cation, dG˙+, A, which is formed via direct electrospray ionisation (ESI/MS) of a methanolic solution of Cu(NO3)2 and dG, are examined. Quantum chemistry calculations have been carried out on 28 isomers and comparisons between their calculated IR spectra and the experimentally-measured spectra suggest that A exists as the ground-state keto tautomer. Collision-induced dissociation (CID) of A proceeds via cleavage of the glycosidic bond, while its ion–molecule reactions with amine bases occur via a number of pathways including hydrogen-atom abstraction, proton transfer and adduct formation. A hidden channel, involving isomerisation of the radical cation via adduct formation, is revealed through the use of two stages of CID, with the final stage of CID showing the loss of CH2O as a major fragmentation pathway from the reformed radical cation, dG˙+. Quantum chemistry calculations on the unimolecular and bimolecular reactivity are also consistent with A being present as a ground-state keto tautomer.

Characterization of ε-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 ε-N-acetyllysine containing model octapeptides (KAc YAGFLVG and YAKAc GFLVG) has been examined in detail. Collision-induced dissociation (CID) mass spectra of bn (n = 4-7) fragments of ε-N-acetylated lysine containing peptides are compared with those of N-terminal acetylated and doubly acetylated (both ε-N and N-terminal) peptides, as well as acetyl-free peptides. Both direct and nondirect fragments are observed for acetyl-free and singly acetylated (ε-N or N-terminal) peptides. In the case of ε-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 ε-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 ε-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.

The study of metal ion–DNA interaction aiming to understand the stabilization of artificial base pairing and a number of noncanonical motifs is of current interest, due to their potential exploitation in developing new technological devices and expanding the genetic code. A successful strategy has been the synthesis of metal-mediated base pairs, in which a coordinative bond to a central metal cation replaces a H-bond in a natural pair. In this work, we characterized, for the first time, the gas phase structure of the cytosine···Ag+···cytosine (C–Ag+–C) complex by means of InfraRed-MultiPhoton-Dissociation (IR-MPD) spectroscopy and theoretical calculation. The IR-spectrum was confidently assigned to one structure with the Ag+ acting as a bridge between the heteronitrogen atoms in each cytosine (both in the keto-amino form). This structure is biologically relevant since it mimics the structure of the hemiprotonated C–H+–C dimer responsible for the stabilization of the i-motif structure in DNA, with the replacement of the NH···N bond by a stronger N···Ag+···N bond. Moreover, since the structure of the C–Ag+–C complex is planar, it allows an optimum intercalation between pairs of the two antiparallel strand duplex in the DNA i-motif structure. Fil: Berdakin, Matias. 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: Steinmetz, Vicent. Universite Paris Sud; Francia Fil: Maitre, Philippe. Universite Paris Sud; Francia 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

Using quantum chemical calculations and infrared multiphoton dissociation (IRMPD) spectroscopy in the fingerprint and X-H stretching regions, we demonstrate here that the all-Ala b 6 fragment ion features a macrocyclic structure with C2 symmetry. For this structure, the ionizing proton is equally shared by the Ala(1) and Ala(4) amide oxygens in a Zundel-type symmetric (X…H+…X) H-bond.

A valence-bond curve-crossing model is proposed to account for the shape of the energy profile of the hydrogen exchange in HCN and isovalent molecules HXY. The adiabatic energy profile associated to the 1,2-hydrogen shift as a function of the bending angle might display one, two or three minima. We propose that these energy profiles can be modeled as the avoided-crossing of three diabatic curves. Ab initio valence-bond calculations performed on HCN/CNH support this model suggesting that the preference for the bent HXY structures versus the linear ones essentially correlates with the 2 Σ – 2 Π splitting of the XY moiety.

We present both theoretical and experimental photodissociation results on the products of the methane dehydrogenation by W+ in the gas phase. We show that the reaction may lead to two isomers: whereas only the methylidenetungsten WCH2+ had been proposed, we show that the hydridomethylidynetungsten HWCH+ can also be formed. Both density functional and highly correlated ab initio quantum chemical calculations have been performed using a relativistic core potential for W+. Spin–orbit couplings have been evaluated semiempirically. We found the HWCH+ and the WCH2+ isomers to be nearly degenerate, the latter structure exhibiting a strong agostic distortion. Photodissociation of the mass selected [W,C,2H]+ product of the reaction has been carried out in a Fourier transform ion cyclotron resonance mass spectrometer. The H+WCH+ channel has been observed as the major photofragmentation channel and a photodissociation threshold of 2.5±0.1 eV has been derived. This low-energy value is in good agreement with the therm...

The structure and energies of neutral Mg(NH3)nclusters have been investigated by experiment and theory, the ionization energy (IE) thresholds of these clusters being the probe of the differential solvation. Experimentally, the IE’s of the magnesium atoms solvated by ammonia have been investigated by tunable laser ionization of clusters prepared in a simple pick-up source. IE’s of clusters Mg(NH3)n have been measured for n=1 up to 37. The solvation of the magnesium ion is more efficient than that of the closed shell neutral Mg atom, resulting in a steep decrease of the ionization energy of ammonia clusters of increasing sizes (1.3 eV for n=1, 2.2 eV for n=2, and 2.9 eV for n=3). The stepwise decrease becomes smaller for higher order clusters (n>20) but the asymptotic value does not appear to be reached even at n=37, suggesting a still developing electrostatic stabilization of the ion clusters at these sizes. Quantum chemical calculations have been performed which reveal the unique features of the solvation...

The electronic ground state and the three first excited states of AgNH 3 have been investigated theoretically. At the ab initio CASPT2 level, there is a quasi-degeneracy of the C 3 v minima of the 2 A 1 and 2 E excited states ( D e =1.38 and 1.40 eV, respectively). While the 2 E state displays a clear Ag(5p π )+NH 3 character, the nature of the 2 A 1 is more subtle, with both charge transfer and Rydberg characters. Semi-empirical introduction of the spin–orbit coupling enables the interpretation of a few features of the intricated R2PI spectrum.

Ab initio CASPT2 calculations show that the Ag(NH3)2 cluster displays two isomers (surface and interior), both in its ground and first excited states. In the ground state the surface structure is slightly preferred, whereas in the three first (quasidegenerate) excited states the interior structure is strongly preferred, like in the ionic cluster. This feature explains the fall of the ion signal observed (on the ns scale) in the R2PI spectrum: the signal vanishes as the excited cluster passes the isomerisation barrier. Comparison with the Na(NH3)2 system is made.

The 24 valence isomers of diphosphinine, P2(C−H)4, have been investigated at an electron-correlated ab initio level and by density functional theory. In analogy with benzene, the three planar forms exhibit full aromaticity and are the most stable isomers on the potential surface. The next isomers, by order of stabilities, are the diphosphabenzvalenes, the Dewar diphosphabenzenes, the prismanes, and the diphosphabicyclopropenyls. They are distinctly less stable than the planar isomers, and their relative energies range from 23 all the way to 93 kcal/mol above the absolute minimum. Among the planar isomers, the most stable one is the (ortho) 1,2-diphosphabenzene, in apparent contradiction with the fact that this species has not been synthesized yet. Some lines of thought to resolve this apparent dilemma are proposed, and the relative reactivities of planar isomers are discussed in terms of their different diradical character. Strain energies are calculated for the nonplanar isomers and compared to those of ...

InfraRed Multiple Photon Dissociation (IRMPD) spectroscopy was used to assay the structural features of the fragment ions resulting from the elimination of H3PO4 in the Collision-Induced Dissociation (CID) of protonated serine. The results are interpreted with the aid of density functional theory calculations. Experiment and theory point to an aziridine-ring structure, implying participation of the vicinal amino group in the formation of this species. This finding constitutes a benchmark for investigating the same process in the CID of phosphorylated peptides.

Formation of Ti+(H2)n clusters (n=1–6) has been studied by both temperature-dependent equilibrium measurements and density functional theory (DFT). The successive binding energies (BDEs) were measured to be 7.5±0.5, 9.7±0.6, 9.3±0.7, 8.5±0.4, 8.2±0.4, and 8.7±0.4 kcal/mol for n=1–6, respectively. The relatively low value of the n=1 BDE is due to a curve crossing from the Ti+[a4F(sd2)] ground state to the Ti+[b4F(d3)] first excited asymptote with the addition of the first ligand. The first BDE is 10 kcal/mol when measured with respect to the excited state asymptote. This series of almost constant BDEs is unlike any other M+(H2)n series. The present DFT calculations show these relatively constant BDE values for the Ti+(H2)n clusters are due to an electronic occupation which allows the Ti+ ion to interact equally with up to six H2 ligands. Bond lengths, geometries, and vibrational frequencies from the DFT calculations are reported here for all clusters. The influence of basis set size and computational metho...

The electronic structure and geometry of (n = 1−6) have been studied at the B3LYP and ab initio levels. We find that the ground state of W(CO)+ is linear with a sextet spin state, that a linear sextet and a bent quartet are nearly degenerate for and that doublet states are unambiguously the ground states of to Successive (CO)n-1W+−CO binding energies have been computed to be larger than any of those previously determined for other transition metals. We compare our results with available experimental data. Electron transfers are very important: (i) σ donation from the CO's to the metal is found to be more favorable when involving 5d rather than 6p leading to a preference for the bent rather than linear structures for (n = 2−4); (ii) π back-donation plays a crucial role in shaping these molecules. These effects provide the driving force for the spin changes as the number of ligands increases. Spin lowering is associated with an increasing number of doubly rather than singly occupied 5dπ metal orbitals, whi...

Oxidative damage to DNA yields guanine radical cations. Their gas-phase IR spectroscopic signature and acidity have been modelled by the radical cation of 9-methylguanine. Comparisons with quantum chemistry calculations suggest that radical cation formation produces the ground-state keto tautomer, which has an N-H acidity enhanced by ~470 kJ mol(-1).

The dissociations of a series of HnX−H bonds (HnX = H3C, H2N, HO, F) are investigated by means of an ab initio valence bond method, in order to probe the existence and the mechanism of the weakening effect that a lone pair on the X atom might exert on the adjacent bonds. One manifestation of the lone pair bond weakening effect is a break in the curve displaying the variations of the HnX−H bond energy (De) as a function of the X electronegativity (χ(X)). The weakening effect is found to exist and to be significant, gradually increasing in the series (HnX = H2N to F). It is shown to correspond to a stabilization of the dissociated products, due to an electronic reorganization of the HnX fragment that gradually undergoes a rehybridization throughout the dissociation. By this mechanism, the lone pair(s) acquire more s character, to the detriment of the orbital involved in the breaking bond, thus increasing the average s character in the valence state of the X atom. In contrast, when no lone pairs are present ...

The C - C bond formation activated under negative electrospray ionization of an acetonitrile solution of 1,3,5-trinitrobenzene is reported. The solvent function is to provide a source of cyanide ion, a highly problematic reagent, which is found to attack the electron-deficient aromatic ring to form a covalently bound anionic complex (Meisenheimer complex). The structure of the complex is elucidated by means of collision induced dissociation mass spectrometry and IR multiple photon dissociation spectroscopy in the 'fingerprint' region.

The intracellular signal transductor cAMP, generated as a protonated species ([cAMP + H]+) in an electrospray ionization source, has been assayed by infrared multiple photon dissociation (IRMPD) spectroscopy. IRMPD spectra have been recorded both in the 800–1800 cm−1 mid-IR range and in the N–H and O–H stretching region, between 3200 and 3700 cm−1. Extensive quantum chemical calculations have been performed at both B3LYP and MP2 levels of theory using the 6-311+G(2df,2p) basis set. At both levels of theory, the N7 protonated structures are predicted to be much higher in energy than the N1 and N3 protonated ones. Overall, the experimental spectrum is in very good agreement with the calculated IR spectra of the two lowest energy structures corresponding to protonation on either the N1 or the N3 adenine site. For both structures a syn conformation about the glycosidic bond is predicted at either level of theory. The NH stretching region appears to be the most structurally informative in terms of orientation about the glycosidic bond. It also suggests that the energetics derived at the MP2/6-311+G-(2df,2p) level are more reliable.

The fluoride and chloride complexes with 1,3,5-trinitrobenzene (TNB–F− and TNB–Cl−) are obtained as gaseous species by electrospray ionization and are assayed by IR multiple photon dissociation spectroscopy along with quantum chemical calculations. The stable structure is quite different for the two complexes. A strongly covalent σ-complex (Meisenheimer complex) holding fluorine on a tetrahedral carbon at a formerly unsubstituted ring position is the stable form of TNB–F− while a σ-complex with fluorine bound to a nitro-substituted carbon is 78 kJ/mol higher in energy. The TNB–Cl− complex presents an off-center binding of chlorine placed above a CH group of a scantily perturbed TNB unit. This structure conforms to a weak σ-binding motif. The observed vibrational features support two diverse binding motifs and previous findings about TNB–I− and TNB–Br− show the transition to occur between the fluoride and chloride adducts while both I− and Br− complexes are consistent with a weak σ-binding motif. Implication of these results is expected in the design of halide ion transporters.

In a recent study, we reported experimental determinations of bond dissociation energies and entropies for V + (H 2 ) n ( n = 1 to 6) and suggested that a spin change from quintet to triplet occurs upon addition of the sixth H 2 ligand. A very recent theoretical paper by Niu et al. disputes this and concludes that the experimental results are consistent with purely quintet clusters (J. Niu, B.K. Rao, S.N. Khanna and P. Jena, Chem. Phys. Letters 230 (1994) 299). In this Comment, we restate our reasons for the proposed spin charge and argue that important aspects of the results of Niu et al. are incorrect.

The geometries and H2 binding energies have been determined for Co(H2)n (sup +), for n = 1-6. The binding energies are in good agreement with experiment. The shape of the clusters is used to explain the pairwise decrease in the binding energies. The bonding in CoH2 (sup +) and Co(H2)2 (sup +) is very similar and is enhanced by sd (sigma) hybridization. The next two H2 molecules add to the side of Co(H2)2 (sup +). These two additional H2 molecules cannot benefit from sd (sigma) hybridization and are less strongly bound. The addition of the fifth and sixth H2 molecules eliminates sd (sigma) hybridization as a mechanism for reducing Co-H2 repulsion. This coupled with the smaller Co to H2 (sigma *) donation results in another decrease in the binding energies.

The H-bonded network rearrangements in the S(0), S(1) and D(0) states of the neutral and cationic p-CreOH(H(2)O)(NH(3)) complexes were studied experimentally by means of (1 + 1)/(1 + 1') REMPI (Resonantly Enhanced MultiPhoton Ionization) and time resolved LIF (Laser Induced Fluorescence) spectroscopies combined with DFT (Density Functional Theory) calculations at the B3LYP/6-311G++(d,p) level. A comparison of the rearrangement process of the H-bonded network in the three states is given. Two cyclic H-bonded isomers were found on the S(0) potential energy surface and the results indicate that the rearrangement in this state is unlikely at the temperature of the supersonic expansion due to the presence of a high-energy barrier (7503 cm(-1)). On the other hand, the re-determination of the S(1) excited state lifetimes confirms that neither the H-bonded rearrangement nor the excited state hydrogen transfer (ESHT) reaction takes place in the S(1) state at the excitation energies of this work. Thus, it is concluded that the absorption of the second photon to reach the D(0) state takes place from the S(1) state of the cyclic-(OH-OH(2)-NH(3)) isomer. A preferential evaporation of H(2)O upon vertical ionization of the cyclic-(OH-OH(2)-NH(3)) isomer is observed which is consistent with a statistical redistribution of the internal energy. Nevertheless, our theoretical calculations suggest that initial excitation of the H-bonded network rearrangement modes may also play a role to leave the H(2)O molecule as a terminal moiety in a chain-(OH-NH(3)-OH(2))(+) isomer. The reaction pathway for the solvent rearrangement involves a double proton transfer process with a very low energy barrier (575 cm(-1)) that is overcome at the vertical ionization energy of the complex.

International audience; Transition metal-ion complexation is essential to the function and structural stability of many proteins. We studied silver complexation with the octarepeat motif ProHisGlyGlyGlyTrpGlyGln of the prion protein, which shows competitive sites for metal chelation including amide, indole and imidazole groups. This octapeptide is known as a favourable transition metal binding site in prion protein. We used ion mobility spectrometry (IMS), infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory calculations (DFT) to identify the binding motifs of a silver cation on HisGlyGlyGlyTrp peptide as well as on peptide subsequences. Ultra-violet photodissociation (UVPD) and collision induced dissociation mass spectrometry together with the time-dependent density functional method was then exploited to study the influence of binding sites on optical properties and on the ground and excited states reactivity of the peptide. We show that the metal cation is bound to the p-system of the indole group and a nitrogen atom of the imidazole group and that charge transfers from the indole group to the silver cation occur in excited electronic states.