Dimeric Complexes of Tryptophan with M2+ Metal Ions

TitleDimeric Complexes of Tryptophan with M2+ Metal Ions
Publication TypeJournal Article
Year of Publication2009
AuthorsR.C Dunbar, J.D Steill, N.C Polfer, J. Oomens
JournalJournal of Physical Chemistry A
Volume113
Number5
Pagination845-851
Date PublishedFeb
Type of ArticleArticle
ISBN Number1089-5639
Accession NumberISI:000262902500009
KeywordsAB-INITIO, AMINO-ACIDS, BINDING-ENERGIES, CONFORMERS, dissociation, GAS-PHASE, GRAMICIDIN, INFRARED ACTION SPECTROSCOPY, SPECTROSCOPY, THEORETICAL DFT, ZWITTERION STABILITY
Abstract

IRMPD spectroscopy using the FELIX free electron laser and a Fourier transform ICR mass spectrometer was used to characterize the structures of electrosprayed dimer complexes M(2+)Trp(2) of tryptophan with a series of eight doubly charged metal ions, including alkaline earths Ca, Sr, and Ba, and transition metals Zn, Cd, Mn, Co, and Ni. With the support of DFT thermochemical calculations, at least three different structural motifs were distinguished spectroscopically, depending critically on the nature of the metal ion. The spectral signatures of a ligand in the charge-solvated (CS) configuration, namely peaks near 1730 and 1150 cm(-1), were prominent in all the spectra, and it was clear that all the dimer complexes contain at least one CS ligand. The spectra indicated that the second ligand is zwitterionic (ZW) for all complexes except the Ni case, with the second ligand having an extended binding geometry with smaller metals but showing some admixture of a compact chelated geometry with larger alkaline earths. It was concluded that these dimer complexes have a mixed configuration of ligands, denoted CS/ZW. The Ni(2+)Trp(2) complex is exceptional, with the spectroscopy and the thermochemical calculation both indicating a CS/CS configuration of ligands. This geometry appears to correlate with the exceptionally small size and high binding strength of the Ni2+ cation. The complex CdClTrp(1+) was also obtained and gave a clear spectrum showing a CS ligand configuration. The presence of a CS ligand in all the dimeric complexes of the 2+ metals is an interesting contrast with the monomer complex Ba(2+)Trp, in which the ligand is ZW.

URL<Go to ISI>://000262902500009
Division

GUTHz

Department

Molecular Dynamics

PID

28f45bcd88775f746d561e79bc9e68b2

Alternate TitleJ. Phys. Chem. A

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