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  Infrared Spectroscopy of Phenylalanine Ag(I) and Zn(II) Complexes in the Gas Phase

Polfer, N. C., Oomens, J., Moore, D. T., Helden, G. v., Meijer, G., & Dunbar, R. C. (2006). Infrared Spectroscopy of Phenylalanine Ag(I) and Zn(II) Complexes in the Gas Phase. Journal of the American Chemical Society, 128(2), 517-525. doi:10.1021/ja0549291.

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Polfer, Nick C., Author
Oomens, Jos, Author
Moore, David T., Author
Helden, Gert von1, Author           
Meijer, Gerard1, Author           
Dunbar, Robert C., Author
1Molecular Physics, Fritz Haber Institute, Max Planck Society, ou_634545              


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 Abstract: Infrared multiple-photon dissociation (IR-MPD) spectroscopy has been applied to singly-charged complexes involving the transition metals Ag⁺ and Zn²⁺ with the aromatic amino acid phenylalanine. These studies are complemented by DFT calculations. For [Phe+Ag]⁺ the calculations favor a tridentate charge solvation N/O/ring structure. The experimental spectrum strongly supports this as the predominant binding geometry and, in particular, rules out a significant presence of the salt-bridge conformation. Zn²⁺ forms a deprotonated dimer complex with Phe, [Zn+Phe₂-H]⁺, in which the +2 oxidation state serves as a useful biomimetic model for zinc protein sites. A number of low-energy conformations were located, of which the lowest-energy conformer predicted by the calculations involves a Phe ligand deprotonated on the carboxylic acid, while the other Phe ligand is in the tridentate charge solvation conformation. The calculated IR spectrum of this conformer gives a close fit to the experimental spectrum, strongly supporting this as the predominant binding geometry. This most stable calculated complex is characterized by N/ O/ring metal chelation with a tetrahedral-type coordination core of Zn²⁺ to N and O of both ligands. Another similar tightly chelated structure shows a square-planar-type coordination core, but this structure is computed to be less stable and gives a less satisfactory match to the experimental spectrum. This preference for the tetrahedral geometry of the Lewis-basic atomic ligands parallels the common Zn(II) coordination geometry in proteins. The number of clearly identifiable peaks resolved in the IR-MPD spectra as well as the much-improved matches between the observed spectra and the DFT-calculated spectra of the most stable geometries compared to previous studies are noteworthy for systems of this size and complexity. These results demonstrate that IR spectroscopy of transition metal-amino acid complexes in combination with DFT calculations is a very powerful structural tool, readily applicable to biomimetic systems that model, for example, the reaction centers of proteins in the solvent-free environment. In addition, we present a novel ion-capturing method for Fourier transform ion cyclotron resonance mass spectrometry which removes the necessity of a buffer gas pulse, while allowing ion trapping at moderate voltages with apparently reduced collisional excitation of the ions.


Language(s): eng - English
 Dates: 2006
 Publication Status: Issued
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: eDoc: 241689
DOI: 10.1021/ja0549291
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Title: Journal of the American Chemical Society
  Alternative Title : J. Am. Chem. Soc.
Source Genre: Journal
Publ. Info: -
Pages: - Volume / Issue: 128 (2) Sequence Number: - Start / End Page: 517 - 525 Identifier: -