This paper reports an attempt to structurally characterize isolated ligand-protected gold nanoclusters by means of gas-phase InfraRed Multiple Photon Dissociation (IRMPD) spectroscopy compared to quantum chemistry Density Functional Theory (DFT) calculations. The mass-selected kilodalton nanocluster complexes consist of ten or eleven gold atoms that are bound to glutathione or phosphine ligands and are produced by ElectroSpray Ionization (ESI) in the form of multiply charged anions or cations. This study allows us to build some methodology benchmarks for species that are large for IRMPD experiments and that are used for biochemistry applications. These gas-phase results on isolated ions are compared to condensed phase data from Fourier-Transform InfraRed (FTIR) spectroscopy and to theoretical IR spectra that are calculated with two different functional/basis sets, namely B3LYP/6-31G* and M06L/LanL2DZ, at the scaled static harmonic level. Although theoretical calculations are able to reproduce well the experimental IR spectra, the size of such species and the presence of many possible interactions between ligands make difficult a precise assignment among the many possible molecular arrangements.

This project aims to develop an original approach to investigate the damage at the molecular level on biomolecules from the indirect irradiation effects. We will construct a new device to put biomolecules in the gas phase, based on the soft laser desorption from microdroplets directly into vacuum, and this source will be coupled with an irradiation platform.

Metal-ligand cluster ions are structurally characterized by means of gas-phase infrared multiple photon dissociation spectroscopy. The mass-selected complexes consist of one or two metal cations M3+ (M = Al, Fe, or Ru) and two to five anionic bidentate acetylacetonate ligands. Experimental IR spectra are compared with different density functional theory calculations, namely, PBE/TZVP, B3LYP/6-31G(*), and M06/6-31+G(**). Frequency analysis was also performed at different levels, namely, scaled static harmonic and unscaled static anharmonic, or with ab initio molecular dynamics simulations at the PBE/TZVP level. All methods lead to simulated spectra that fit rather well with experimental data, and the spectral red shifts of several main bands, in the 1200 cm(-1)-1800 cm(-1) range, are sensitive to the strength of the metal-ligand interaction and to the spin state of the ion. Due to the rigidity of those complexes, first principles molecular dynamics calculations provide spectra similar to that produced by static calculations that are already able to catch the main spectral signatures using harmonic calculations at the B3LYP/6-31G(*) level.

Synopsis Many studies are devoted to functionalized metallic nanoparticles, for many applications: in Physics, due to their localized surface plasmon resonances; in Chemistry, due to their specific catalytic properties that depend on their surface nature; in Biology, due to their optical or magnetic properties coupled to their potential for targeting and vectorization of bioactive molecules within living cells. In this last domain, gold and silver nanoparticles are especially of interest and, for the control of their biological effects, it is very important to have a fine knowledge of the structural properties and the chemical stabilities of their functional ligands.

We report the UV and IR photofragmentation spectroscopies of protonated synephrine in a cryogenically cooled Paul trap. Single (UV or IR) and double (UV-UV and IR-UV) resonance spectroscopies have been performed and compared to quantum chemistry calculations, allowing the assignment of the lowest-energy conformer with two rotamers depending on the orientation of the phenol hydroxyl (OH) group. The IR-UV hole burning spectrum exhibits the four expected vibrational modes in the 3 μm region, i.e., the phenol OH, Cβ-OH, and two NH2+ stretches. The striking difference is that, among these modes, only the free phenol OH mode is active through IRPD. The protonated amino group acts as a proton donor in the internal hydrogen bond and displays large frequency shifts upon isomerization expected during the multiphoton absorption process, leading to the so-called IRMPD transparency. More interestingly, while the Cβ-OH is a proton acceptor group with moderate frequency shift for the different conformations, this mode is still inactive through IRPD.

Various hydroxypyridine derivatives are endogenous or synthetic photosensitizers which could contribute to solar radiation damage. The study of their excited states could lead to a better understanding of their action mechanisms. We present here the ultraviolet (UV) spectra of the protonated 2-, 3- and 4-hydroxypyridine. These spectra were obtained with an experimental device coupling an electrospray ion source with a cold quadrupole ion trap and a time of flight mass spectrometer. They display well resolved vibrational structures, with a clear influence of the position of the OH group. These results are interpreted with excited states calculations at the coupled cluster CC2 level.

We studied the photoionization of 2-pyridone and its tautomer, 2-hydroxypyridine by means of VUV synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer. The photoionization efficiency (PIE) spectrum is composed of steps. The state energies of the [2-pyridone](+) cation in the X[combining tilde] ground and A excited electronic states, as well as of the [2-hydroxypyridine](+) cation in the electronic ground state, are determined. The slow photoelectron spectra (SPES) are dominated by the 0(0)(0) transitions to the corresponding electronic states together with several weaker bands corresponding to the population of the pure or combination vibrational bands of the cations. These vibrationally-resolved spectra compare very well with state-of-the-art calculations. Close to the ionization thresholds, the photoionization of these molecules is found to be mainly dominated by a direct process whereas the indirect route (autoionization) may contribute at higher energies.

The gas-phase conformation of the intact (parent) unprotected RGD(-) peptide anion has been investigated using a combination of anion photoelectron spectroscopy and quantum chemistry calculations of its low-energy stable structures. The experimentally observed RGD(-) species correspond to a conformation in which the guanidinium group is protonated, the C-terminus is neutral, the aspartic acid carboxyl is deprotonated, and the anion's excess electron orbital is localized on the protonated guanidinium. This structure is reminiscent of the RGD loop, which is the peptide motif recognized by trans-membrane integrins. The parent RGD(-) radical anion was generated using a unique infrared desorption-photoemission-helium jet ion source, whose ability to produce radical anions of peptides may also have analytical mass spectrometric implications.

The paper presents IR spectroscopic data and theoretical frequency calculations, in the C–H and N–H stretch region, on jet-cooled formamide molecules and dimers. By using dipole-bound or quadrupole-bound anion formation, one is able to monitor IR absorption in the neutral beam on mass-selected species. For isolated formamide, resonant IR excitation leads to autodetachment of the excess electron in the dipole-bound anion. For the formamide dimer, the IR spectrum is characteristic from the cyclic dimer, with two neighbouring bonded N–H stretches and a complex spectrum with several lines and a broad absorption band in the C–H region absorption, as for the cyclic formic acid dimer. In this double H-bond configuration, IR absorption cannot lead to vibrational predissociation but it probably produces hot neutral dimers with large-amplitude intermolecular motions that reinforce autodetachment of the nascent weakly bound anions. Thus, the present original IR spectroscopic technique, which allows for rigorous mass-selection of the neutrals, seems to be relevant for any polar neutral species.

We report gas-phase experimental and theoretical results on the configurations of weakly-bound neutral polar complexes without chromophores: the water dimer and the formamide-water complex. Experimental data are obtained by combining infrared (IR) absorption spectroscopy, in the 2800-3800 cm(-1) domain, with the Rydberg electron transfer (RET) technique leading to dipole-bound anion (DBA) formation. In the absence of IR excitation, RET to neutral complexes with a given total dipole moment, and thus a given molecular structure, leads to DBAs which are observed without any possible fragmentation. In the presence of the IR laser, prior to ionisation, resonant IR absorption of intramolecular vibrations of the parent neutral complexes can either induce the breaking of the weak intermolecular bonds (vibrational predissociation of the neutral) or the fast departure of the excess electron after RET (autodetachment of the DBA). Anion signal depletion, monitored at the parent mass, is then a signature of resonant IR absorption from mass- and structure-selected neutral complexes. The validity of the present experimental method and of different types of quantum chemistry calculations is discussed by comparison between calculated harmonic or anharmonic frequencies, the present experimental gas-phase IR spectra, and previous experimental data on these two test-case hydrogen-bonded complexes.

A study of the reduction of nitric oxide (NO) by gas mixtures simulating gases obtained by biomass pyrolysis, in simulated conditions of a reburning zone, has been performed in a fused silica jet-stirred reactor at 1 atm. The temperatures ranged from 1100 to 1400 K, the initial mole fraction of NO was 1000 ppm and that of the reburn-fuel (mixture of CO and H2; mixture of methane, ethylene, and acetylene; and mixture of CO, H2, methane, ethylene, and acetylene) was varied. The equivalence ratio was varied from 0.5 to 2.5, corresponding to an excess air of 2 to 0.4. It was shown that the reduction of NO varies as the temperature and that for a given temperature, a maximum reduction of NO occurs, in slightly fuel-rich conditions. Overall, the present results show the same trends as observed in previous studies involving simple hydrocarbons or natural gas as reburn fuel. A detailed chemical kinetic modeling of the present experiments was performed using an updated and improved kinetic scheme. A reasonable agr...

The effect of NO and SO2 on the oxidation of a CO-H-2 mixture was studied in a jet-stirred reactor at atmospheric pressure and for various equivalence ratios (0.1, 1, and 2) and initial concentrations of NO and SO2 (0-5000 ppm). The experiments were performed at fixed residence time and variable temperature ranging from 800 to 1400 K. Additional experiments were conducted in a laminar flow reactor on the effect of SO2 on CO-H-2 oxidation in the same temperature range for stoichiometric and reducing conditions. It was demonstrated that in fuel-lean conditions, the addition of NO increases the oxidation of the CO-H-2 mixture below 1000 K and has no significant effect at higher temperatures, whereas the addition of SO2 has a small inhibiting effect. Under stoichiometric and fuel-rich conditions, both NO and SO2 inhibit the oxidation of the CO-H-2 mixture. The results show that a CO-H-2 mixture has a limited NO reduction potential in the investigated temperature range and rule out a significant conversion of HNO to NH through reactions like HNO + CO double left right arrow NH + CO2 or HNO + H-2 double left right arrow NH + H2O. The chain terminating effect of SO2 under stoichiometric and reducing conditions was found to be much more pronounced than previously reported under How reactor conditions and the present results support a high rate constant for the H + SO2 + M double left right arrow HOSO + M reaction. The reactor experiments were used to validate a comprehensive kinetic reaction mechanism also used to simulate the reduction of NO by natural gas blends and pure C-1 to C-4 hydrocarbons. (C) 2003 Wiley Periodicals, Inc.

We report experimental (Rydberg electron transfer) and theoretical results on dipole-bound anions of urea, deuterated urea, 1,1- and 1,3-dimethylureas and tetramethylurea. For the 1,1-dimethylurea and tetramethylurea molecules, which possess only one low-lying energy conformer, the experimental excess electron energies are found to be in good agreement with neutral structure quantum chemistry calculations and semi-empirical model calculations of the corresponding dipole-bound anions. For 1,3-dimethylurea two low-lying energy conformers (trans–trans and cis–trans) should contribute to the dipole-bound anion formation behaviour but cannot fully account for it. The large-amplitude motion, associated with the anti/syn conformations of urea molecules, has been studied by performing experiments on the deuterated species and by calculating the potential energy surfaces, for both the neutral and the dipole-bound anion, along the corresponding coordinate. Even if this low-frequency mode is very likely to be involved in the anomalous anion formation behaviour, a full understanding of this process could only come from a dynamic theory, beyond the Born–Oppenheimer approximation, of both the electron and the large-amplitude nuclear motions which possess similar characteristic frequencies.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The reduction of nitric oxide (NO) by a mixture of methane, ethylene and acetylene with and without addition of SO2 has been studied in a fused silica jet-stirred reactor operating at 1atm in simulated conditions of the reburning zone. The temperatures were ranging from 800 to 1400K. In these experiments, the initial mole fractions of NO and SO2 were 0 or 1000ppm, that of methane, ethylene and acetylene were, respectively, 2400, 1200 and 600ppm. The equivalence ratio has been varied from 0.5 to 2.5. It was demonstrated that the reduction of NO varies as the temperature and that for a given temperature, a maximum NO reduction occurs slightly above stoichiometric conditions. The addition of SO2 inhibited the process of reduction of NO under the present conditions. The present results generally follow those obtained in previous studies involving simple hydrocarbons or natural gas as reburn fuel. A detailed chemical kinetic modeling of the present experiments was performed using an updated and improved kinetic scheme (1006 reversible reactions and 145 species). An overall reasonable agreement between the present data and the modeling was obtained. Also, the proposed kinetic mechanism can be successfully used to model the reduction of NO by ethane, ethylene, a natural gas blend (methane–ethane 10:1). The kinetic modeling indicates that the reduction of NO proceeds via the following sequence of reactions: HCCO+NO=HCNO+CO; HCCO+NO=HCN+CO2; HCN+O=NCO+H; HCN+O=NH+CO; HCN+H=CN+H2; HCNO+H=HCN+OH; CN+O2=NCO+O; NCO+H=NH+CO; NCO+NO=N2O+CO; NCO+NO=CO2+N2; NH+NO=N2O+H; NH+NO=N2+OH. The inhibition of this process by SO2 is explained by the sequence of reactions H+SO2+M=HOSO+M and HOSO+H=SO2+H2 that acts as a termination process: H+H+M=H2+M.

Using Rydberg Electron Transfer Spectroscopy, formation of dipole-bound anion complexes of formamide, N-methylformamide, N,N-dimethylformamide and N-methylacetamide with water has been studied. Each neutral complex can exist with several configurations and the lowest energy structures have been identified through comparison between Density Functional Theory calculations of the neutrals and measured electron binding energies of the observed weakly-bound anions.

By means of Rydberg electron-transfer spectroscopy (RETS), negative ion photoelectron spectroscopy (NIPES), and quantum chemistry calculations, we have studied electron attachment properties of a series of saturated disulfides: dimethyl disulfide, diethyl disulfide, and dipropyl disulfide. Both RETS and NIPES experiments show that the valence anions of these disulfides are stable. RETS further shows that these negative ions result from attachment of nonzero energy electrons (0.2 eV), in contrast to dimers and larger complexes. NIPES experiments provide vertical detachment energies for the three disulfide monomer anions along with their Franck-Condon profiles. Fitting these spectra, using model potentials for the S-S stretch coordinate, finds that the adiabatic electron affinities of these disulfides are positive but rather small, about 0.1 eV. These experimental data compare well with the results of ab initio calculations, performed-at the MP2 level with large basis sets.

The reduction of nitric oxide (NO) by C-1 to C-4 hydrocarbons, in simulated conditions of the reburning zone, has been studied at 1 atm in a jet-stirred reactor. The temperatures range was similar to 1000 to 1450 K, the equivalence ratio ranged from 0.7 to 2.5, the initial mole fractions of NO were 750-1000 ppm, and that of the reburn-fuel corresponded to 8800 ppm of carbon. A detailed chemical kinetic modeling of these experiments was performed using an updated and improved kinetic scheme. The modeling showed an overall reasonable agreement with the experimental results. According to this work, the reduction of NO by simple hydrocarbons mainly proceeds via reaction with ketenyl radical: Fuel --> C2H2 --> HCCO, CH; HCCO+NO --> HCNO + CO and HCN + CO2; HCNO+H --> HCN + OH; HCN + O --> NCO --> NH; NH + H -->N; N + NO --> N-2; NH + NO --> N2O followed by N2O+H --> N-2.

The reduction of nitric oxide (NO) by ethane in simulated reburning conditions has been studied in a fused silica jet-stirred reactor operating at 1 arm, in the temperature range 900-1400 K, in diluted conditions. In the present experiments, the initial mole fraction of NO was 1000 ppm, that of ethane was 4400 ppm. The equivalence ratio has been varied from 0.75 to 2. It was demonstrated that the reduction of NO varies as the temperature and that, for a given temperature, a maximum NO reduction occurs slightly above stoichiometric conditions. Then, optimal NO-reburning conditions can be achieved for particular combinations of equivalence ratio and temperature. The present results generally show the same trends as observed in previous studies using simple hydrocarbons or natural gas (NG) as reburn fuel. A detailed chemical kinetic modeling of the present experiments was performed using an updated and improved kinetic scheme (877 reversible reactions and 122 species). An overall reasonable agreement between the present data and the modeling was obtained although improvements of the model are still necessary. The proposed kinetic mechanism, already successfully used to model the reduction of NO by ethylene, acetylene and HCN, and the low temperature interactions between NO and simple alkanes in a JSR, was also validated through the modeling of the reduction of NO by a NG blend. According to this study, the main route to NO-reduction by ethane involves ketenyl radical. The model indicates that the reduction of NO proceeds through the reaction paths: HCCO + NO --> HCNO + CO followed by HCNO + H --> HCN + OH; HCN + O --> NCO --> HNCO --> NH2; NHi + NO --> N-2; NH + NO --> N2O; N2O + H O --> N-2.

The coupling between the dipole bound and valence electronic states of the nitromethane anion has been investigated via Rydberg electron transfer spectroscopy and field detachment spectroscopy of the bare and argon-solvated anions. The unique aspects of the nitromethane system are highlighted by comparing the solvation behavior of nitromethane anion with that of acetonitrile, a system in which the dipole bound state is well-isolated from the resonance arising from excess electron occupation of its high lying lowest unoccupied molecular orbital.