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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.

In this paper, we present the IRMPD spectra of three ionic complexes between guanine (G) and silver (Ag+): [GAg-H2O]+, [GAgG]+ produced in the electrospray ionization source of the mass spectrometer, and [GAg]+ produced by collision induced dissociation of the [GAgG]+ complex. On the basis of the comparison of theoretically calculated IR spectra, we show that there are two isomers of each complex containing two different keto-amino (KA) tautomers of G (GKA(1,9) and GKA(1,7)). The observed isomers are the most stable structures in aqueous solution, and their experimentally estimated relative populations are in better agreement with the calculated relative populations in solution than in the gas phase, both at 298 K. We concluded that these observations suggest that GKA(1,9) and GKA(1,7) coexist in solution according to previous theoretical reports (Colominas, C.; et al. J. Am. Chem. Soc. 1996, 118, 6811). We were unable to find any evidence of the presence of the GEA(9), GKA(3,7), GKA(3,9), or GKA(7,9), whose relative stabilities in solution are strongly dependent on the theoretical method used to account for the solvent effect (Hanus, M.; et al. J. Am. Chem. Soc. 2003, 125, 7678).

The present study reports the first structural characterization of protonated cyameluric acid ([CA + H]+) in the gas phase, which paves the way for prospective bottom-up research on the condensed-phase chemistry of CA in the protonated form. A number of [CA + H]+ keto-enol isomers can a priori be produced as a result of protonation at available N and O positions of precursor neutral CA tautomers, yet ab initio computations predict different reduced [CA + H]+ isomer populations dominating the solution and gas phases that are involved in the ion generation process (i.e., electrospray ionization). Infrared multiple photon dissociation spectra were recorded in the 990-1900 and 3300-3650 cm-1 regions and compared with theoretical [B3LYP/6-311++G(d,p)] IR absorption spectra of several [CA + H]+ isomers, providing a satisfactory agreement for the most stable monohydroxy form in the gas phase, [1358a]+, yet the contribution of its nearly isoenergetic OH rotamer, [1358b]+, cannot be neglected. This is indicative of the occurrence of [CA + H]+ isomer interconversion reactions, assisted by protic solvent molecules, during their transfer into the gas phase. The results suggest that available O positions on neutral CA are energetically favored protonation sites in the gas phase.

The Katsuki-Sharpless epoxidation reaction is one of the most recognized chiral catalytic reactions, allowing for chiral epoxides to be used as starting materials for a series of synthetic pathways. The complete understanding of this reaction mechanism depends on the identification and description of species formed from Ti(IV) alkoxides and alkyl tartrates precatalysts. Despite previous reports on the nature of a bimetallic catalyst based on IR spectroscopy and NMR analysis, some debate remains. Therefore, we carried out mass spectrometry analysis by direct extraction of the ions from the reaction media by ESI(-)-FT-ICR and evaluated the observed ions by CID and IRMPD experiments. These techniques allowed us to detect carboxylates that correlate to the species in the reaction media and to confirm the actual presence of the titanium-tartrate complexes in solution. Our IRMPD results suggest the carboxylate dimer as an asymmetric species with two tartrates coordinated to a single Ti atom, while the other Ti center is coordinated by labile alkoxydes that could be easily exchanged by the organic peroxide and the substrate, allowing the epoxidation reaction to take place.

Cisplatin (cis-diamminedichloroplatinum(II), cis-[PtCl2(NH3)2]), widely used drug in cancer treatment, has been allowed to react with simple molecular targets (L) mimicking biological functional groups. The selected molecules (L = acetamide, dimethylacetamide, urea and thiourea) react by ligand exchange leading to cis-[PtCl(NH3)2(L)]+ complexes that have been assayed by ESI-MS, IRMPD spectroscopy and computations in order to characterize their structure and platination site. Formal five-coordinate complexes are also delivered by ESI, [(PtCl(NH3)2(H2O)(L)]+, notably absent only when L is thiourea. IRMPD spectroscopy combined with computational analysis has revealed non-covalent adducts of the reactant aqua complex with an external ligand L corresponding to {cis-[PtCl(NH3)2(H2O)]+ · L}, reminiscent of the Eigen-Wilkins encounter complex invoked in the ligand displacement path in solution. The complex, successfully isolated in the gas phase, undergoes ligand exchange yielding cis-[PtCl(NH3)2(L)]+ + H2O when activated by multiple IR photons, testifying at the same time both structure and reactivity.

Protonation at the formyl oxygen atom of benzaldehydes leading to the formation of carboxonium ions yields two distinct isomers, depending on the relative orientation of the proton either cis or trans with respect to the hydrogen atom on the adjacent carbon. In this context, the IR multiple photon dissociation (IRMPD) spectra of protonated ortho, meta, and para-hydroxybenzaldehydes (OH-BZH+ ), delivered into the gas phase by electrospray ionization of hydro-alcoholic solutions, are reported in the 3200-3700 cm-1 spectral range. This range is characteristic of O-H stretching modes and thus able to differentiate cis and trans carboxonium isomers. Comparison between IRMPD spectra and DFT calculations at the B3LYP/6-311++G(2df2p) level suggests that for both p-OH-BZH+ and m-OH-BZH+ only cis conformers are present in the ion population analyzed. For o-OH-BZH+ , IRMPD spectroscopy points to a mixture comprising one trans and more than one cis conformers. The energy barrier for cis-trans isomerization calculated for each OH-BZH+ isomer is a measure of the degree of π-electron delocalization. Furthermore, IRMPD spectra of p-OH-BZH+ , m-OH-BZH+ and protonated phenol (this last used as reference) were recorded also in the fingerprint range. Both the observed C-O and O-H stretching vibrations appear to be a measure of π-electron delocalization in the ions.

The structures of three proton-bound dimers (Met2H+, MetTrpH+, and Trp2H+) are investigated in the gas phase with infrared multiple photon disassociation (IRMPD) spectroscopy in combination with quantum chemical calculations. Their IRMPD spectra in the range of 600–1850 cm–1 are obtained experimentally using an FT-ICR mass spectrometer and the CLIO free electron laser as an IR light source. The most abundant conformers are elucidated by comparing the IRMPD spectra with harmonic frequencies obtained at the B3LYP-GD3BJ/6-311++G** level of theory. Discrepancies between the experimental and theoretical data in the region of 1500–1700 cm–1 are attributed to the anharmonicity of the amino bending modes. We confirm the result of a previous IRMPD study that the structure of gas-phase Trp2H+ is charge-solvated but find that there are more stable structures than originally reported (Feng, R.; Yin, H.; Kong, X. Rapid Commun. Mass Spectrom.2016, 30, 24–28). In addition, gas-phase Met2H+ and MetTrpH+ have been revealed to have charge-solvated structures. For all three dimers, the most stable conformer is found to be of type A. The spectrum of Met2H+, however, cannot be explained without some abundance of type B charge-solvated conformers as well as salt-bridged structures.

International audience; Protonated intermediates are postulated to be involved in the rate determining step of many sugar reactions. This paper presents a study of protonated sugar species, isolated in the gas phase, using a combination of infrared multiple photon dissociation (IRMPD) spectroscopy, classical ab initio molecular dynamics (AIMD) and quantum mechanical vibrational self-consistent field (VSCF) calculations. It provides a likely identification of the reactive intermediate oxocarbenium ion structure in a D-galactosyl system as well as the saccharide pyrolysis product anhydrogalactose (that suggests oxocarbenium ion stabilization), along with the spectrum of the protonated parent species: methyl D-galactopyranoside-H +. Its vibrational fingerprint indicates intramolecular proton sharing. Classical AIMD simulations for galactosyl oxocarbenium ions, conducted in the temperature range ~300-350 K (using B3LYP potentials on-the-fly) reveal efficient transitions on the picosecond timescale. Multiple conformers are likely to exist under the experimental conditions and along with static VSCF calculations, they have facilitated the identification of the individual structural motifs of the galactosyl oxocarbenium ion and protonated anhydrogalactose ion conformers that contribute to the observed experimental spectra. These results demonstrate the power of experimental IRMPD spectroscopy combined with dynamics simulations and with computational spectroscopy at the anharmonic level to unravel conformer structures of protonated saccharides, and to provide information on their lifetimes.

Complexes of 18-crown-6 ether (18C6) with four protonated amino acids (AAs) are examined using infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light generated by the infrared free electron laser at the Centre Laser Infrarouge d'Orsay (CLIO). The AAs examined in this work include glycine (Gly) and the three basic AAs: histidine (His), lysine (Lys), and arginine (Arg). To identify the (AA)H+(18C6) conformations present in the experimental studies, the measured IRMPD spectra are compared to spectra calculated at the B3LYP/6-311+G(d,p) level of theory. Relative energies of various conformers and isomers are provided by single point energy calculations carried out at the B3LYP, B3P86, M06, and MP2(full) levels using the 6-311+G(2p,2d) basis set. The comparisons between the IRMPD and theoretical IR spectra indicate that 18C6 binds to Gly and His via the protonated backbone amino group, whereas protonated Lys prefers binding via the protonated side-chain amino group. Results for Arg are less definitive with strong evidence for binding to the protonated guanidino side chain (the calculated ground conformer at most levels of theory), but contributions from backbone binding to a zwitterionic structure are likely.

An l-proline based catalyst with a charged phenyl-pyridium substituent (1) was used to analyze intermediates of an organocatalyzed aldol reaction by infrared multi-photon dissociation (IRMPD) mass spectrometry after transfer into the gas phase via electrospray ionization (ESI). IRMPD spectra were interpreted with the aid of density functional theory (DFT) computations. A structurally restricted enamine species was used as a reference molecule for the calculated vibrational frequencies. A close correlation between theory and experiment was found for the energetically most favoured oxazolidinone structures.

International audience; Metabolomics strongly relies on liquid chromatography hyphenated to tandem mass spectrometry (LC-MS/MS) for the separation and identification of metabolites. Retention times and fragmentation mass spectra are used as identification parameters. A complementary approach is proposed here based on alternative approaches for both the separation and identification, and is illustrated in the case of isomeric forms of aminobutyric acids (C4H9NO2). Differential mobility spectrometry (DMS), a very efficient method for the separation of isomers of small molecules, is coupled with high resolution tandem mass spectrometry Fourier transform ion cyclotron resonance (FT-ICR). Identification of the DMS peaks associated with the various isomers is based on isomer-specific infrared multiple photon dissociation (IRMPD) in the mid-infrared range. Two operation modes of the DMS-MS/MS(IRMPD) are used. Structural identification of the various isomers is first achieved based on the comparison of IRMPD spectra of DMS- and mass-selected ions with IR absorption spectra of candidate structures derived from quantum chemical calculations. For this purpose, the DMS device is used in selective mode. Alternatively, when the DMS is using in scanning mode, identification can also be achieved based on specific depletion of DMS peaks at selected IR wavelength. These two operation modes for identification of isomers are illustrated in conjunction with the use of modifier-assisted DMS separation.

Curcumin (Cur) is a natural polyphenol with a wide spectrum of biological activities and appealing therapeutic potential. Herein, it has been delivered by electrospray ionization as gaseous protonated species, [Cur + H]+, and as a Cu(ii) complex, [Cu(Cur - H)]+, a promising antioxidant and radical scavenger. The gas phase structures were assayed by infrared multiple photon dissociation (IRMPD) spectroscopy in both the fingerprint (800-2000 cm-1) and hydrogen stretching (3100-3750 cm-1) ranges. Comparison between the experimental features and linear IR spectra of the lowest energy structures computed at the B3LYP/6-311+G(d,p) level reveals that bare [Cu(Cur - H)]+ exists in a fully planar and symmetric arrangement, where the metal interacts with the two oxygens of the syn-enolate functionality of deprotonated Cur and both OCH3 groups are engaged in H-bonding with the ortho OH. The effect of protonation on the energetic and geometric determinants of Cur has been explored as well, revealing that bare [Cur + H]+ may exist as a mixture of two close-lying isomers associated with the most stable binding motifs. The additional proton is bound to either the diketo or the keto-enol configuration of Cur, in a bent or nearly planar arrangement, respectively.

We investigate the gas-phase structures and fragmentation chemistry of deprotonated carbohydrate anions using combined tandem mass spectrometry, infrared spectroscopy, regioselective labelling, and theory. Our model system is deprotonated, [lactose-H]-. We computationally characterize the rate-determining barriers to glycosidic bond (C1-Z1 reactions) and cross-ring cleavages, and compare these predictions to our tandem mass spectrometric and infrared spectroscopy data. The glycosidic bond cleavage product data support complex mixtures of anion structures in both the C1 and Z1 anion populations. The specific nature of these distributions is predicted to be directly affected by the nature of the anomeric configuration of the precursor anion and the distribution of energies imparted. i.e., Z1 anions produced from the β-glucose anomeric form have a differing distribution of product ion structures than do those from the α-glucose anomeric form. The most readily formed Z1 anions ([1,4-anhydroglucose-H]- structures) are produced from the β-glucose anomers, and do not ring-open and isomerize as the hemiacetal group is no longer present. In contrast the [3,4-anhydroglucose-H]-, Z1 anion structures, which are most readily produced from α-glucose forms, can ring-open through very low barriers (25 kJ mol-1) to form energetically and entropically favorable aldehyde isomers assigned with a carbonyl stretch at ∼1640 cm-1. Barriers to interconversion of the pyranose [β-galactose-H]-, C1 anions to ring-open forms were larger, but still modest (≥51 kJ mol-1) consistent with evidence of the presence of both forms in the infrared spectrum. For the cross-ring cleavage 0,2A2 anions, ring-opening at the glucose hemiacetal of [lactose-H]- is rate-limiting (180 (α-),197 kJ mol-1 (β-anomers)). This finding offers an explanation for the low abundance of these product anions in our tandem mass spectra.

Tacrolimus (TAC) is an efficient immunosuppressant used in organ transplantation procedures. There is an intrinsic correlation between TAC and Ca2+ because of the dependence of its action mechanism on calcium and calcineurin, and the role of ion coordination on TAC identification and quantitation. To depict the Ca2+ binding sites in TAC, this work carried out gas-phase vibrational infrared multiple photon dissociation spectroscopy of [Ca(TAC)]2+ and of three other TAC mimetic molecules (probes 1-3). Density functional theory (DFT) and Monte Carlo (MC) simulations were also used to support the experimental data assignment, and natural bond orbital (NBO) analysis was carried out to depict the coordination sphere. PM3 and B3LYP/6-31G(d) levels of theory displayed similar trends during the MC simulations, suggesting that PM3 is a viable alternative to more expensive DFT calculations, at least during the conformational analysis step. Infrared spectroscopy of the [Ca(probe X)1]2+ and [Ca(probe X)3]2+ ( X = 1-3) complexes allowed for a useful guide for building guess geometries and for the band assignment of the [Ca(TAC)]2+ complex. Nevertheless, the MC approach was particularly useful for exploring the potential energy surface. The lowest energy conformation for [Ca(TAC)]2+ was found by MC simulations and is 32.92 kJ mol-1 lower in energy than the one found by comparing the results obtained for Ca2+ coordination in probes, despite the calculated spectra being virtually identical. Both approaches are good ways to depict the coordination sites, and these results suggest that using small molecules as models is a reliable approach to depict the geometry or coordination sites of extensive ions, yielding a robust correlation between experimental and theoretical spectra. Furthermore, MC survey produced a lower energy conformation with a good match to the experimental results. Both methods depict the Ca2+ coordination sphere as a hexacoordinated environment where the main coordination centers are carbonyl groups.

International audience; The chemical difference between DNA and RNA nucleosides is their 2′-hydrogen versus 2′-hydroxyl substituents. Modification of the ribosyl moiety at the 2′-position and 2′-O-methylation in particular, is common among natural post-transcriptional modifications of RNA. 2′-Modification may alter the electronic properties and hydrogen-bonding characteristics of the nucleoside and thus may lead to enhanced stabilization or malfunction. The structures and relative glycosidic bond stabilities of the protonated forms of the 2′-O-methylated purine nucleosides, 2′-O-methyladenosine (Adom) and 2′-O-methylguanosine (Guom), were examined using two complementary tandem mass spectrometry approaches, infrared multiple photon dissociation action spectroscopy and energy-resolved collision-induced dissociation. Theoretical calculations were also performed to predict the structures and relative stabilities of stable low-energy conformations of the protonated forms of the 2′-O-methylated purine nucleosides and their infrared spectra in the gas phase. Low-energy conformations highly parallel to those found for the protonated forms of the canonical DNA and RNA purine nucleosides are also found for the protonated 2′-O-methylated purine nucleosides. Importantly, the preferred site of protonation, nucleobase orientation, and sugar puckering are preserved among the DNA, RNA, and 2′-O-methylated variants of the protonated purine nucleosides. The 2′-substituent does however influence hydrogen-bond stabilization as the 2′-O-methyl and 2′-hydroxyl substituents enable a hydrogen-bonding interaction between the 2′- and 3′-substituents, whereas a 2′-hydrogen atom does not. Further, 2′-O-methylation reduces the number of stable low-energy hydrogen-bonded conformations possible and importantly inverts the preferred polarity of this interaction versus that of the RNA analogues. Trends in the CID50% values extracted from survival yield analyses of the 2′-O-methylated and canonical DNA and RNA forms of the protonated purine nucleosides are employed to elucidate their relative glycosidic bond stabilities. The glycosidic bond stability of Adom is found to exceed that of its DNA and RNA analogues. The glycosidic bond stability of Guom is also found to exceed that of its DNA analogue; however, this modification weakens this bond relative to its RNA counterpart. The glycosidic bond stability of the protonated purine nucleosides appears to be correlated with the hydrogen-bond stabilization of the sugar moiety.

The ion corresponding to protonated sulfurous acid, H3SO3(+), has been successfully delivered into the gas phase by electrospray ionization of the solution of a suitable precursor and an in-source fragmentation process. The neutral acid is a highly elusive molecule. However, its gas-phase basicity has been ascertained by means of a kinetic study of proton-transfer reactivity. The structure of the H3SO3(+) sampled ion has been probed by IRMPD spectroscopy in two complementary IR frequency ranges in conjunction with density functional theory calculations and found to conform to a trihydroxosulfonium ion. The characteristic IR signatures may aid in deciphering the presence of this species in extraterrestrial atmospheres.

The structure and the dynamics of the isomerization of an ions, which are observed upon low-energy collision induced dissociation of protonated peptides in tandem mass spectrometry (MS/MS), are investigated using a combination of gas phase infrared spectroscopy and theory. IR spectra in the fingerprint region are discussed, but a particular emphasis is given to the NH stretching region which turns out to be highly structurally diagnostic. Overall, theory and infrared spectroscopy provide compelling evidence that an ions undergo cyclisation and/or rearrangement reactions. In the cases of the a2 and a3 ions of oligoglycine, the analysis of the NH stretching region is fully consistent with our previous conclusions based on the IR fingerprint spectra. In the case of the a4 ions of oligoglycine, a band observed near 3550 cm−1 provides a clear-cut signature of the permuted imine–amide structure, thus allowing for a better structural assignment. The dynamics of the rearrangement chemistry of the imine–amide structure is discussed in details, and a critical discussion on the influence of the experimental CID conditions is proposed in the case of the YG a2 ion.

Nicotinamide adenine dinucleotide (NAD) is found in all living cells where the oxidized (NAD+) and reduced (NADH) forms play important roles in many enzymatic reactions. However, little is known about NAD+ and NADH conformational changes and kinetics as a function of the cell environment. In the present work, an analytical workflow is utilized to study NAD+ and NADH dynamics as a function of the organic content in solution using fluorescence lifetime spectroscopy and in the gas-phase using trapped ion mobility spectrometry coupled to mass spectrometry (TIMS-MS) and infrared multiple photon dissociation (IRMPD) spectroscopy. NAD solution time decay studies showed a two-component distribution, assigned to changes from a “close” to “open” conformation with the increase of the organic content. NAD gas-phase studies using nESI-TIMS-MS displayed two ion mobility bands for NAD+ protonated and sodiated species, while four and two ion mobility bands were observed for NADH protonated and sodiated species, respectively. Changes in the mobility profiles were observed for NADH as a function of the starting solution conditions and the time after desolvation, while NAD+ profiles showed no dependence. IRMPD spectroscopy of NAD+ and NADH protonated species in the 800–1800 and 3200–3700 cm−1 spectral regions showed common and signature bands between the NAD forms. Candidate structures were proposed for NAD+ and NADH kinetically trapped intermediates of the protonated and sodiated species, based on their collision cross sections and IR profiles. Results showed that NAD+ and NADH species exist in open, stack, and closed conformations and that the driving force for conformational dynamics is hydrogen bonding of the N–H–O and O–H–O forms with ribose rings.

Gas phase protonated guanine-cytosine (CGH+) pair was generated using an electrospray ionization source from solutions at two different pH (5.8 and 3.2). Consistent evidence from MS/MS fragmentation patterns and differential ion mobility spectra (DIMS) point toward the presence of two isomers of the CGH+ pair, whose relative populations depend strongly on the pH of the solution. Gas phase infrared multiphoton dissociation (IRMPD) spectroscopy in the 900-1900 cm-1 spectral range further confirms that the Watson-Crick isomer is preferentially produced (91%) at pH = 5.8, while the Hoogsteen isomer predominates (66%) at pH = 3.2). These fingerprint signatures are expected to be useful for the development of new analytical methodologies and to trigger isomer selective photochemical studies of protonated DNA base pairs. 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: 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: Berthias, Francis. Université Paris Sud; Francia 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: 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

The radical cation of cytosine (Cyt.+ ) is generated by dissociative oxidation from a ternary CuII complex in the gas phase. The radical cation is characterized by infrared multiple photon dissociation (IRMPD) spectroscopy in the fingerprint region, UV/Vis photodissociation (UVPD) spectroscopy, ion-molecule reactions, and theoretical calculations (density functional theory and ab initio). The experimental IRMPD spectrum features diagnostic bands for two enol-amino and two keto-amino tautomers of Cyt.+ that are calculated to be among the lowest energy isomers, in agreement with a previous study. Although the UVPD action spectrum can also be matched to a combination of the four lowest energy tautomers, the presence of a nonclassical distonic radical cation cannot be ruled out. Its formation is, however, unlikely due to the high energy of this isomer and the respective ternary CuII complex. Gas-phase ion-molecule reactions showed that Cyt.+ undergoes hydrogen-atom abstraction from 1-propanethiol, radical recombination reactions with nitric oxide, and electron transfer from dimethyl disulfide.

The bare, five-coordinate iron(II) heme nitrosyl complex [Fe(II)hemeH(NO)]+, namely, an iron(II) complex of the dianion of protoporphyrin IX holding a proton on one vinyl group, has been obtained i...

The structure of peptide fragments was studied using “action” IR spectroscopy. We report on room temperature IR spectra of b4 fragments of protonated GGGGG, AAAAA, and YGGFL in the X−H (X = C, N, O) stretching region. Experiments were performed with a tandem mass spectrometer combined with a table top tunable laser, and the multiple photon absorption process was assisted using an auxiliary high-power CO2 laser. These experiments provided well-resolved spectra with relatively narrow peaks in the X−H (X = C, N, O) stretching region for the b4 fragments of protonated GGGGG, AAAAA, and YGGFL. The 3200−3700 cm−1 range of the first two of these spectra are rather similar, and the corresponding peaks can be assigned on the basis of the classical b ion structure that has a linear backbone terminated by the oxazolone ring at the C-terminus and ionizing proton residing on the oxazolone ring nitrogen. The spectrum of the b4 of YGGFL, on the other hand, is different from the two others and is characterized by a band observed near 3238 cm−1 . Similar band positions have recently been reported for one of the four isomers of the b4 of YGGFL studied using double resonance IR/UV technique. As proposed in this study, the IR spectrum of this ion at room temperature can also be assigned to a linear N-terminal amine protonated oxazolone structure. However, an alternative assignment could be proposed because our room temperature IR spectrum of the b4 of YGGFL nicely matches with the predicted IR absorption spectrum of a macrocyclic structure. Because not all experimental IR features are unambiguously assigned on the basis of the available literature structures, further theoretical studies will be required to fully exploit the benefits offered by IR spectroscopy in the X−H (X = C, N, O) stretching region. Fil: Durand, Sylvère. Universite Paris Sud; Francia Fil: Rossa, Maximiliano. Universite Paris Sud; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Hernández, Oscar. Universite Paris Sud; Francia Fil: Paizs, Béla. Bangor University; Reino Unido Fil: Maître, Philippe. Universite Paris Sud; Francia

Cisplatin and transplatin (cis- and trans-[PtCl2(NH3)2]) have been allowed to react with methionine (Met) in water solution in a study aimed to characterize the monofunctional complex primarily formed. The thioether function of methionine is known to have a very high affinity for square planar platinum(II) and sulfur-containing biomolecules have been proposed as a cisplatin drug reservoir on the way to platination at DNA. Both cisplatin and transplatin yield [PtCl(NH3)2Met]+ complexes, delivered by electrospray ionization in the gas phase and sampled as isolated species using tools based on mass spectrometry. The collision induced dissociation spectra of both cis-[PtCl(NH3)2Met]+ and trans-[PtCl(NH3)2Met]+ are quite similar and also the transport properties assayed by ion mobility mass spectrometry do not allow any appreciable discrimination. However, the vibrational spectra obtained by IR multiple photon absorption (IRMPD) spectroscopy show distinct features. Their analysis, supported by quantum chemical calculations, has revealed that while cisplatin attack is mainly directed to the sulfur atom of Met, transplatin shows a more balanced partition between sulfur and nitrogen binding. Among the vibrational signatures characterizing cis-[PtCl(NH3)2Met]+ and trans-[PtCl(NH3)2Met]+ complexes, the asymmetric NH2 stretching of the α-amino group of the amino acid at ca. 3440 cm−1 is peculiar and diagnostic of S-platination. IRMPD kinetics evaluated at this frequency support the prevailing S-attack by cisplatin while approximately a 1 : 2 ratio of S- versus N-coordination is observed by transplatin, to be possibly related to the trans effect at the platinum center.

International audience; The deleterious cellular effects of ionizing radiation are well-known, but the mechanisms causing DNA damage are poorly understood. The accepted molecular events involve initial oxidation and deprotonation at guanine sites, triggering hydrogen atom abstraction reactions from the sugar moieties, causing DNA strand breaks. Probing the chemistry of the initially formed radical cation has been challenging. Here, we generate, spectroscopically characterize, and examine the reactivity of the Watson–Crick nucleobase pair radical cation in the gas phase. We observe rich chemistry, including proton transfer between the bases and propagation of the radical site in deoxyguanosine from the base to the sugar, thus rupturing the sugar. This first example of a gas-phase model system providing molecular-level details on the chemistry of an ionized DNA base pair paves the way toward a more complete understanding of molecular processes induced by radiation. It also highlights the role of radical propagation in chemistry, biology, and nanotechnology.

S-nitrosation of cysteine plays an important role in storage and transport of NO, a key signaling molecule in vivo . An approach to detect this modification in the bare, charged amino acid is presented, based on IR multiple photon dissociation (IRMPD) spectroscopy. Protonated and deprotonated S-nitrosocysteine ions, [SNOCys+H] + and [SNOCys−H] − , have been obtained by electrospray ionization and assayed for IR activity in either the 1000–1900 cm −1 or the 3000–3600 cm −1 wavenumber range. The so-obtained IRMPD spectra display characteristic features ascribed to the presence of the S-nitrosation motif, which are missing in the corresponding IRMPD spectra of the native cysteine ions, [Cys+H] + and [Cys−H] − . In particular, the NO stretching mode is unambiguously identified by the red shift observed for the 15 N-labelled species. The interpretation of the IRMPD spectra is supported by density functional theory calculations of the optimized geometries, relative energies and IR spectra of [SNOCys+H] + and [SNOCys−H] − . Both sampled ions comprise a thermally averaged population of conformers contributing to the experimental IRMPD spectra. This notion is supported by the agreement between the calculated IR absorption spectra of the several conformers, and the recorded IRMPD spectrum. The gathered evidence points to a characteristic NO stretching mode that emerges as a pronounced feature at 1460–1490 cm −1 in the IRMPD spectrum of [SNOCys−H] − , namely in a region where [Cys−H] − displays no IRMPD activity. Conversely, the NO stretching vibration of [SNOCys+H] + is enclosed in a wide absorption including the C O stretching mode at 1780 cm −1 . The [SNOCys−H] − negative ions are thus a promising benchmark in a search for S-nitrosation features using IRMPD spectroscopy.

International audience; Cross-coupling reactions can be efficiently catalyzed using palladium complexes. The formation of low-coordinated, highly reactive Pd(0), which is believed to be the catalytic species, is critical. The mechanism of the reduction of a stable and readily available allyl Pd(II) complex into Pd(0) by a combination of K2CO3 and PhB(OH)2 has been studied. We report on the characterization of the associated reactive solution using a combination of density functional theory and experimental methods. First, the stoichiometric reaction of an (allyl)(phosphine)palladium(II) complex with K2CO3 was first investigated using trandem mass spectrometry. A palladium-carbonate complex could be characterized in the electrospray mass spectrum of the reactive solution. Gas-phase infrared spectra of mass-selected complexes have been recorded, giving further information on the coordination mode (κ1) of the carbonate ligand. This structural information derived from spectroscopy is critical because the relative energy of the two κ1- and κ2-carbonate isomers is difficult to determine theoretically, presumably because of the charge transfers at play between the carbonate and the palladium. Second, the product of the stoichiometric addition of PhB(OH)2 to this carbonate complex was investigated. Both 31P and 1H NMR data provide compelling evidence for the formation of the desired 14-electron Pd(0) complex.

The first IR spectrum of a perfluorinated carbanion has been obtained in the gas phase by IRMPD spectroscopy. Quantum chemical calculations at the MP2/cc-pVTZ level were performed yielding the optimized geometries and IR spectra for a covalently bound C 2 F 5 − species and for conceivable loosely bound F − (C 2 F 4 ) complexes. Both the computational results and the IR characterization point to a covalent structure for the assayed species in agreement with the reactivity pattern displayed with selected neutrals.

IRMPD spectroscopy in the ‘fingerprint’ and X H (X = C, N, O) stretching regions was used to probe the structures of the YG a 2 ions generated from protonated YGGFL and doubly protonated YGGFLR. Our experiments indicate a mixture of cyclic and rearranged ‘imine–amide’ structures. The cyclic isomer is generated from the initially formed protonated imine terminated linear structure by head-to-tail cyclization. Proton transfer between the secondary amine of the ring and the amide nitrogen followed by ring opening leads to the rearranged ‘imine–amide’ isomer. Quantum chemical calculations demonstrate that this proton transfer is catalyzed by the tyrosine side chain ring for the YG a 2 ion. Isomer specific IRMPD bands observed in the two spectral regions clearly show the presence of the cyclic and rearranged ‘imine–amide’ isomers, the latter being characterized by an IR signature at ∼3545 cm −1 associated with the C-terminal amide NH 2 asymmetric stretch.

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

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.

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+.

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.

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