Infrared multiple photon dissociation spectroscopy of cationized methionine: effects of alkali-metal cation size on gas-phase conformation
| Autor: | Jeffrey D. Steill, P. B. Armentrout, Damon R. Carl, Theresa E. Cooper, Jos Oomens |
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| Rok vydání: | 2010 |
| Předmět: |
Cation binding
Photons Denticity Spectrophotometry Infrared Stereochemistry Chemistry Hydrogen bond General Physics and Astronomy Protonation Alkalies Dissociation (chemistry) Crystallography Methionine Metals Cations Side chain Infrared multiphoton dissociation Gases Physical and Theoretical Chemistry Conformational isomerism |
| Zdroj: | Physical chemistry chemical physics : PCCP. 12(14) |
| ISSN: | 1463-9084 |
| Popis: | The gas-phase structures of alkali-metal cation complexes of the amino acid methionine (Met) as well as protonated methionine are investigated using infrared multiple photon dissociation (IRMPD) spectroscopy utilizing light generated by a free electron laser. Spectra of Li(+)(Met) and Na(+)(Met) are similar and relatively simple, whereas the spectra of K(+)(Met), Rb(+)(Met), and Cs(+)(Met) include distinctive new bands. Measured IRMPD spectra are compared to spectra calculated at the B3LYP/6-311+G(d,p) level of theory to identify the conformations present in the experimental studies. For Li(+) and Na(+) complexes, the only conformation present is a charge-solvated, tridentate structure that binds the metal cation to the amine and carbonyl groups of the amino acid backbone and the sulfur atom of the side chain, [N,CO,S]. In addition to the [N,CO,S] conformer, bands corresponding to alkali-metal cation binding to a bidentate zwitterionic structure, [CO(2)(-)], are clearly present for the K(+), Rb(+), and Cs(+) complexes. Theoretical calculations of the lowest energy conformations of Rb(+) and Cs(+) complexes suggest that the experimental spectra could also include contributions from two additional charge-solvated structures, tridentate [COOH,S] and bidentate [COOH]. For H(+)(Met), the IRMPD action spectrum is reproduced by multiple low-energy [N,CO,S] conformers, in which the protonated amine group hydrogen bonds to the carbonyl oxygen atom and the sulfur atom of the amino acid side chain. These [N,CO,S] conformers only differ in their side-chain orientations. |
| Databáze: | OpenAIRE |
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