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The structure of peptide fragmentswas studied using “action”IR spectroscopy. We report on room temperature IR spectra of b4fragments of protonated GGGGG, AAAAA, and YGGFL in the X–H(X = C, N, O) stretching region. Experiments were performed with atandem mass spectrometer combined with a table top tunable laser,and the multiple photon absorption process was assisted using an auxiliaryhigh-power CO2laser. These experiments provided well-resolvedspectra with relatively narrow peaks in the X–H (X = C, N,O) stretching region for the b4fragments of protonatedGGGGG, AAAAA, and YGGFL. The 3200–3700 cm–1range of the first two of these spectra are rather similar, andthe corresponding peaks can be assigned on the basis of the classicalb ion structure that has a linear backbone terminated by the oxazolonering at the C-terminus and ionizing proton residing on the oxazolonering nitrogen. The spectrum of the b4of YGGFL, on theother hand, is different from the two others and is characterizedby a band observed near 3238 cm–1. Similar bandpositions have recently been reported for one of the four isomersof the b4of YGGFL studied using double resonance IR/UVtechnique. As proposed in this study, the IR spectrum of this ionat room temperature can also be assigned to a linear N-terminal amineprotonated oxazolone structure. However, an alternative assignmentcould be proposed because our room temperature IR spectrum of theb4of YGGFL nicely matches with the predicted IR absorptionspectrum of a macrocyclic structure. Because not all experimentalIR features are unambiguously assigned on the basis of the availableliterature structures, further theoretical studies will be requiredto fully exploit the benefits offered by IR spectroscopy in the X–H(X = C, N, O) stretching region. [ABSTRACT FROM AUTHOR]

A potentially tetradentate ligand was synthesized by the addition of α-Li-picoline to the 2,6-bis(diphenylphosphine sulfide)-3,5-diphenylphosphinine (SPS) ligand. The corresponding Pd complex (3) was obtained by the reaction with [(COD)PdCl2]. An air-stable cationic Pd(II) complex (4) was obtained after abstraction of Cl−with silver salt. The role of the additional binding site in the stabilization of the cationic complex was explored using NMR spectroscopic and tandem ESI-MS studies combined with DFT calculations. Additionally the picoline moiety was used to tune the electronic properties of the cationic complex 7to modify the activity in the Lewis acid-catalyzed allylation of aldehydes. [ABSTRACT FROM AUTHOR]

Tautomerism of the nucleobase uracil is characterized in the gas phase through IR photodissociation spectroscopy of singly hydrated protonated uracil created with tandem mass spectrometric methods in a commercially available Fourier transform ion cyclotron resonance mass spectrometer. Protonated uracil ions generated by electrospray ionization are re-solvated in a low-pressure collision cell filled with a mixture of water vapor seeded in argon. Their structure is investigated by IR photodissociation spectroscopy in the NH and OH stretching region (2500−3800 cm−1) with a tabletop IR laser source and in the 1000−2000 cm−1range with a free-electron laser. In both regions the IR photodissociation spectrum exhibits well-resolved spectral signatures that point to the presence of two different types of structure for monohydrated protonated uracil, which result from the two lowest-energy tautomers of uracil. Ab initio calculations confirm that no water-catalyzed tautomerization occurs during the re-solvation process, indicating that the two protonated forms of uracil directly originate from the electrospray process. [ABSTRACT FROM AUTHOR]

The performance of infrared (IR) spectroscopy of gas-phase ions in a commercially available 7 T Fourier transform ion cyclotron resonance mass spectrometer has been characterized. A -allyl−palladium reactive intermediate, (-allyl)Pd(P(C6H5)3)2, involved in the catalytic allylation of amine is studied. A solution of this transition metal complex is electrosprayed, and the IR multiple photon dissociation (IRMPD) spectrum of the mass-selected ions is recorded in two spectral ranges. The fingerprint spectrum (650−1550 cm-1) is recorded using the Orsay free-electron laser, and the dependence of the IRMPD efficiency on laser power and irradiation time is characterized. The DFT-calculated IR absorption spectrum of the (-allyl)Pd(P(C6H5)3)2complex shows good agreement with the experimental spectrum. The -interaction between the palladium and the allyl moiety is reflected by the assignment of the IRMPD bands, and the observed allylic CH2wagging modes appear to form a sensitive probe for the -interaction strength in metal−-allyl complexes. This spectral assignment is further supported by the analysis of the different IRMPD photofragmentation patterns observed at different photon energies, which are found to result from wavelength-specific photofragmentations. Nine peaks are well-resolved in the experimental spectrum, for which the bandwidth (fwhm) is on the order of 15 cm-1. Resonances with a calculated IR intensity of 5 km/mol or larger are shown to be amenable for IRMPD, indicating an excellent sensitivity of our new experimental setup. Finally, the IR spectrum has also been recorded in the CH stretching region (2950−3150 cm-1) using a tabletop IR optical parametric oscillator/amplifier (OPO/OPA) laser source. [ABSTRACT FROM AUTHOR]

Gaseous C7H7Oions have been formed by protonation of benzaldehyde or tropone (2,4,6-cycloheptatrienone) in the cell of an FT-ICR mass spectrometer using C2H5as 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 C7H7Oions have been optimized at the B3LYP/6-31G(d,p) level of theory, and their relative energies and IR spectra are reported. On this basis, the IRMPD spectra of C7H7Oions 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. [ABSTRACT FROM AUTHOR]