Alkali metal complexes of the Dipeptides PheAla and AlaPhe : IRMPD spectroscopy

TitleAlkali metal complexes of the Dipeptides PheAla and AlaPhe : IRMPD spectroscopy
Publication TypeJournal Article
Year of Publication2008
AuthorsN.C Polfer, J. Oomens, R.C Dunbar
JournalChem Phys Chem
Volume9
Number4
Pagination579-589
Date PublishedMar
Type of ArticleArticle
ISBN Number1439-4235
Accession NumberISI:000254461300011
Keywordsalkali metals, AROMATIC-AMINO-ACIDS, BINDING-SITES, CATION-PI INTERACTIONS, CATION/GLYCINE, COLLISION-INDUCED, density functional calculations, dissociation, GAS-PHASE, INFRARED-SPECTROSCOPY, INTERACTIONS, ION AFFINITIES, IR spectroscopy, mass, METHYL-ESTERS, peptides, spectrometry, THEORETICAL DISSECTION
Abstract

Complexes of PheAla and AlaPhe with alkali metal ions Na+ and K+ are generated by electroscopy ionization, isolated in the Fourier-transform ion cyclotron resonance (FT-ICR) ion trapping mass spectrometer, and investigated by infrared multiple-photon dissociation (IRMPD) using light from the FELIX free electron laser over the mid-infrared range from 500 to 1900 cm(-1). Insight into structural features of the complexes is gained by comparing the obtained spectra with predicted spectra and relative free energies obtained from DFT calculations for candidate conformers. Combining spectroscopic and energetic results establishes that the metal ion in always chelated by the amide carbonyl oxygen, whilst the C-terminal hydroxyl does not complex the metal ion and is in the endo conformation. It is also likely that the aromatic ring of Phe always chelates the metal ion in a cation-pi binding configuration. Along with the amide CO and ring chelation sites, a third Lewis-basic group almost certainly chelates the metal ion, giving a threefold chelation geometry. This third site may be either the C-terminal carbonyl oxygen, or the N-terminal amino nitrogen. From the spectroscopic and computational evidence, a slight preference is given to the carbonyl group, in an ROaNt chelation pattern, and either of these conformations, or a mixture of them, would be consistent with the present evidence. (R represents the pi ring site, O-o the amide oxygen, O-t the terminal carbonyl oxygen, and N-t the terminal nitrogen.) The spectroscopic findings are in better agreement with the MPW1PW91 DFT functional calculations of the thermochemistry compared with the B3LYP functional, which seems to underestimate the importance of the cation-pi interaction.

URL<Go to ISI>://000254461300011
Division

GUTHz

Department

Molecular Dynamics

PID

9569597aef8a4c8fae9858cd59d93fd7

Alternate TitleChemPhysChem

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