High-resolution spectroscopy of cluster ions.

Vibrational spectroscopy measurements are described for mass-selected metal cation-molecular complexes using the technique of infrared resonance-enhanced photodissociation (REPD) spectroscopy. We discuss the mechanism of the REPD process in the infrared and how multiphoton techniques or rare gas tagging can be employed to facilitate dissociation processes in strongly bound complexes. Spectra are reported for Fe+(CO2)n complexes that demonstrate the formation of coordination spheres around the metal cation and for Mg+(CO2)n complexes, where the interaction with theory makes it possible to obtain structures for small clusters. Both of these studies investigate the asymmetric stretch region of CO2. Ni+(C2H2)n complexes are studied in the C-H stretch region, demonstrating evidence for intracluster cyclization reactions. Finally, experiments are described for metal ion-benzene (M = V, Al) complexes excited in the benzene ring distortions and C-H bending region. These experiments confirm the ~ -bonded configura...

Infrared spectroscopy to probe structure and dynamics in metal ion-molecule complexes

A Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer has been installed at a free electron laser (FEL) facility to obtain infrared absorption spectra of gas phase ions by infrared multiple photon dissociation (IRMPD). The FEL provides continuously tunable infrared radiation over a broad range of the infrared spectrum, and the FT-ICR mass spectrometer, utilizing a 4.7Tesla superconducting magnet, permits facile formation, isolation, trapping, and high-mass resolution detection of a wide range of ion classes. A description of the instrumentation and experimental parameters for these experiments is presented along with preliminary IRMPD spectra of the singly-charged chromium-bound dimer of diethyl ether (Cr(C4H10O)2+) and the fluorene molecular ion (C13H10+). Also presented is a brief comparison of the fluorene cation spectrum obtained by the FT-ICR-FEL with an earlier spectrum recorded using a quadrupole ion trap (QIT).

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Free electron laser-Fourier transform ion cyclotron resonance mass spectrometry facility for obtaining infrared multiphoton dissociation spectra of gaseous ions

Determining the structure and dynamics of large biologically relevant molecules is one of the key challenges facing biology. Although X-ray crystallography (XRD) and nuclear magnetic resonance (NMR) yield accurate structural information, they are of limited use when sample quantities are low. Mass spectrometry (MS) on the other hand has been very successful in analyzing biological molecules down to atto-mole quantities and has hence begun to challenge XRD and NMR as the key technology in the life sciences. This trend has been further assisted by the development of MS techniques that yield structural information on biomolecules. Of these techniques, collision-induced dissociation (CID) and hydrogen/deuterium exchange (HDX) are among the most popular. Despite advances in applying these techniques, little direct experimental evidence had been available until recently to verify their proposed underlying reaction mechanisms. The possibility to record infrared spectra of mass-selected molecular ions has opened up a novel avenue in the structural characterization of ions and their reaction products. On account of its high pulse energies and wide wavelength tunability, the free electron laser for infrared experiments (FELIX) at FOM Rijnhuizen has been shown to be ideally suited to study trapped molecular ions with infrared photo-dissociation spectroscopy. In this paper, we review recent experiments in our laboratory on the infrared spectroscopic characterization of reaction products from CID and HDX, thereby corroborating some of the reaction mechanisms that have been proposed. In particular, it is shown that CID gives rise to linear fragment ion structures which have been proposed for some time, but also yields fully cyclical ring structures. These latter structures present a possible challenge for using tandem MS in the sequencing of peptides/proteins, as they can lead to a scrambling of the amino acid sequence information. In gas-phase HDX of an amino acid it is shown that the structure can be changed from a charge solvated to a zwitterionic structure, thereby demonstrating that HDX can be an invasive technique, in fact changing the structure of the analyte. These results emphasize that more fundamental work is required in order to understand the underlying mechanisms in two of the most important structural techniques in MS.

https://polfer.chem.ufl.edu/Publications/pdf_files/21.pdf

Reaction products in mass spectrometry elucidated with infrared spectroscopy.

Vibrational predissociation spectroscopy of the H2-tagged mono- and dicarboxylate anions of dodecanedioic acid

OH stretching vibrations of hydrogen-bonded cluster ions of phenol (PhOH), [PhOH−(H2O)n]+ (n = 1−4), (PhOH)2+, and (PhOH−methanol)+ have been observed with infrared photodissociation spectroscopy in combination with an ion-trapping technique. Cluster ions were efficiently generated by ionization of phenol followed by a jet expansion and were mass-selectively stored by the radio frequency ion trap method, which allows us to observe infrared multiphoton dissociation yield spectra of size-selected cluster ions. For [PhOH−(H2O)n]+, the OH stretching vibrations of the water moieties strongly suggested that the n ≥ 3 cluster ions exhibit the proton-transferred form, [PhO−H3O+(H2O)n-1], while the n = 1 and 2 ions are of the nontransferred form, [PhOH+−(H2O)n]. As for (PhOH)2+, the infrared spectra indicate that the dimer ion is characterized as the open form, in which the phenol ion acts as a proton donor and the neutral phenol as an acceptor through their single hydrogen bond. The similar open form is also foun...

Characterization of the Hydrogen-Bonded Cluster Ions [Phenol−(H2O)n]+ (n = 1−4), (Phenol)2+, and (Phenol−Methanol)+ As Studied by Trapped Ion Infrared Multiphoton Dissociation Spectroscopy of Their OH Stretching Vibrations

Takahiro Sawamura

Papers

Characterization of the Hydrogen-Bonded Cluster Ions [Phenol−(H2O)n]+ (n = 1−4), (Phenol)2+, and (Phenol−Methanol)+ As Studied by Trapped Ion Infrared Multiphoton Dissociation Spectroscopy of Their OH Stretching Vibrations

Infrared dissociation spectroscopy of the OH stretching vibration of phenol—rare gas van der Waals cluster ions