FELIX papers of the Williams group

Papers of the Williams group (Berkeley) showing the results of several FELIX measurement campaigns:

Coordination of Trivalent Metal Cations to Peptides: Results from IRMPD Spectroscopy and Theory

James S. Prell, Tawnya G. Flick, Jos Oomens, Giel Berden, and Evan R. Williams

Abstract: Structures of trivalent lanthanide metal cations La3+, Ho3+, and Eu3+ with deprotonated Alan (n = 2-5) or Leu-enk (Tyr-Gly-Gly-Phe-Leu) are investigated with infrared multiple photon dissociation (IRMPD) spectroscopy between 900 and 1850 cm-1 and theory. In all of these complexes, a salt bridge is formed in which the metal cation coordinates to the carboxylate group of the peptide, resulting in a limited conformational space and many sharp IRMPD spectral bands. The IRMPD spectra clearly indicate that all carbonyl groups solvate the metal cation in each of the Alan complexes. Due to strong vibrational coupling between the carbonyl groups, a sharp, high-energy amide I band due to in-phase stretching of all of the amide carbonyl groups bound to the metal cation is observed that is separated by 50 cm-1 from a strong, lower-energy amide I band. This extent of carbonyl coupling, which is sometimes observed in condensed-phase peptide and protein IR spectroscopy, has not been reported in IRMPD spectroscopy studies of other cationized peptide complexes. Intense bands due to carbonyl groups not associated with the metal cation are observed for Leu-enk complexes, indicating that a side chain group, such as the Tyr or Phe aromatic ring, prevents complete carbonyl coordination of the metal cation. Substitution of smaller lanthanide cations for La3+ in these peptide complexes results only in minor structural changes consistent with the change in metal cation size. These are the first IRMPD spectra reported for lanthanide metal cationized peptides, and comparison to previously reported protonated and alkali metal or alkaline earth metal cationized peptide complexes reveals many trends consistent with the higher charge state of the lanthanide cations. © 2010 American Chemical Society.
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Reference: Journal of Physical Chemistry A 114 (2010) 854-860.

Isomer Population Analysis of Gaseous Ions From Infrared Multiple Photon Dissociation Kinetics.

James S. Prell, Terrence M. Chang, Jeffrey A. Biles, Giel Berden, Jos Oomens, and Evan R. Williams

Infrared multiple photon dissociation (IRMPD) kinetics measured with tunable laser radiation from a free electron laser (FEL) are used to probe the relative populations of and interconversions between energetically competitive isomers of gas-phase ions at 298 K. On-resonance IRMPD kinetics of monoisomeric benzoate anion and anilinium (protonated aniline) are measured to determine the extent of overlap of the laser beam with the precursor ion population (93%). IRMPD kinetics indicating different photodissociation behavior for different isomers obtained at isomer-specific resonances are used to determine relative populations of salt bridge and charge-solvated isomers for ArgGly·Na+, Ser·Cs+, and Arg·Na+. These values and Gibbs free energy differences obtained from them for thermal precursor populations are compared to values reported using other, less direct population probes. Rapid interconversion of two charge-solvated isomers occurs for ArgGly·Li+, precluding population analysis for this ion. ArgGly·Na+, ArgGly·Li+, and Arg·Na+ exhibit IRMPD induction periods lasting many seconds for some isomers at the laser photon energies and power used, indicating that IRMPD relative spectral intensities are time-dependent for these ions and that the relative band intensities in IRMPD spectra measured with short irradiation times may not provide meaningful information about relative isomer populations. These results constitute the first direct probe of ion isomer populations using IRMPD kinetics obtained with a FEL and illustrate a number of caveats in interpreting IRMPD spectra measured with just a single irradiation time. These results also indicate that more complete overlap of the laser beam with the ions will be highly advantageous in future instrument designs for IRMPD kinetics and spectroscopy experiments. © 2011 American Chemical Society.
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Journal of Physical Chemistry A 115 (2011) 2745-2751.

Effects of Anions on the Zwitterion Stability of Glu, His and Arg Investigated by IRMPD Spectroscopy and Theory

Jeremy T. O'Brien, James S. Prell, Giel Berden, Jos Oomens and Evan R. Williams

Abstract: Interactions of halide anions (Cl–, Br–, and I–) with glutamic acid (Glu), histidine (His), and arginine (Arg) and their effects on stabilizing the zwitterionic form of these amino acids were investigated using infrared multiple photon dissociation (IRMPD) spectroscopy between 850–1900 cm-1 and hybrid density functional theory. The IRMPD spectra of Glu•X–and His•X–each have a diagnostic carbonyl stretching band at 1750 cm-1 from a carboxylic acid group, indicating that the nonzwitterionic form of these amino acids is most stable. In contrast, a broad band at 1625 cm-1 for Arg•X–, consisting of the antisymmetric stretch of a carboxylate group and hydrogen bonded NH bends, clearly shows that Arg is zwitterionic in these complexes. There are many similarities between these spectra and those of cationized amino acids, which aid in spectral interpretation. Cl–and Cs+ are of comparable size, and attachment of either ion to these amino acids has little effect on the frequencies of these diagnostic carbonyl stretches. The coordination of cations to these amino acids is different from that of anions, resulting in a favorable alignment of the dipole moment of the carbonyl group with the electric field of ions of either polarity, which causes a redshift in this band, i.e., a Stark effect. There is a slight redshift (10 cm-1) in the carbonyl stretch band at 1750 cm-1 for Glu•X–and His•X–with decreasing anion size, consistent with both a Stark effect and with greater carboxylate character for the carboxylic acid group in complexes with the less acidic halide ions. The anion size has little effect on the structures and relative zwitterion stabilities for most of these complexes, which can be attributed to the large size of the halide anions investigated compared to that of the alkali metal cations where size effects are more pronounced. The spectra calculated for the lowest-energy structures are generally consistent with the experimental spectra, although no single structure accounts for the many distinct bands in the IRMPD spectra of His•X– © 2010 Elsevier.
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Reference: International Journal of Mass Spectrometry 297 (2010) 116-123.

The Ionic Hydrogen/Deuterium Bonds between Diammoniumalkane Dications and Halide Anions.

Maria Demireva, Jos Oomens, Giel Berden, Evan R. Williams

Abstract: Halide-anion binding to 1,12-dodecanediammonium, tetramethyl-1,12-dodecanediammmonium, and tetramethyl-1,7-heptanediammonium has been investigated with infrared multiple-photon dissociation (IRMPD) spectroscopy in the 1000–2250 cm-1 spectral region and with theory. Both charged ammonium groups in these diammonium compounds interact with the halide anion resulting in an ionic hydrogen bond (IHB) stretching frequency outside of the spectral frequency range that can be measured with the free-electron laser (FEL). This frequency is shifted into the spectral range upon exchanging all of the labile hydrogen atoms with deuterium atoms, thus making measurement of the ionic deuterium bond (IDB) stretching frequency possible. The IDB stretching frequency shifts to higher values with increasing halide-anion size, methylation of the ammonium groups, and alkane chain length, consistent with the halide-anion–deuterium bond strength decreasing with decreasing gas-phase basicity of the halide anion and the increasing gas-phase basicity of the ammonium groups. The IDB stretching frequency also depends on the alkane chain length owing to constraints on the angle of the bonds between the halide anion and the two ammonium groups. There are additional bands in the IDB stretching feature in the IRMPD spectra, which are attributed to Fermi resonances and arise from coupling with overtone or combination bands that can be identified from theory and depend on the halide-anion identity and alkane chain length. © 2013 WILEY-VCH.
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Reference: ChemPlusChem 78 (2013) 995-1004.

Halide anion binding to Gly3, Ala3 and Leu3.
T.M. Chang, G. Berden, J. Oomens, and E.R. Williams
International Journal of Mass Spectrometry xx (2014) xx-xx. (online first)
© 2014 Elsevier. International Journal of Mass Spectrometry (2014)